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FeReLeCTtH TH PRYDE , ais 4h bas => ein agesaeue fan oa & py — = = aS 3 : : : : = SoS ESS SSIS 7 === =: ——— == = Sree ae ° = wna 3 P RS, wae PERE AON ah ae const eRe ae 5 at —PSToT st a fe Naren A es = > 2 ry WU AA neat 1 Bis ; : vats ‘ i i TENT axa ; “ bid es ; ELI LL fs rb +h eee SELHChUEE + tis; ve = =o 4) M ii hd je ha ies MaKe ae: a ah perpen ego Veet = - ; be : ‘ pees or : ao , = ~~ = ex < ry at Pa = ~ 4 i > conten 2 SS SSS SSSI SSS SS SSS SNe ee See Ss Pee PE eee es cs -sas> Rae Ne ee a ee : See Sa rTSsse: RET PSE Se = oS SSS Soon SSIS = : : : Sees a ewe = eee ee eee ee = eee re ede sear ale dey ae * a ey Stone ah ge ers sy Si Ee Se ise => — ‘ B} "y i ‘ us oe Cex Lik ery 4y bbe be pony = —-~ p> 4 Hh i 42h a ath PEST INST , he MY. HH in bi Dyes a <# =e + bey St Tetras > ai ee _ * a eis eee ee PEEESSTS TS TSS? Sees ee == oreo aves Me = - > ==z : ; ». po be cae aa ae a fe dv ht aC ee abates x e sa OSes a? u - cs yer vrs ag KAR Cgonsnveaedearyeena’ ay. gents ris G EIVOPeRsesd (iCeee deitss ——— a rs Dames - ae : Sn eer gepcaey nae ~ Pega . * “oo ™ = pane °. ~ . AS = Foams ee toe Staonal = 9 aa ve at ben ons :. = s a ae 2 i oe ~ come ne a me nee ne Speers on nae a ie SIs Se ee ee ) HN} a | 2 ‘ « i ‘ 5 a ? aon SEH * u ’ “ts - oy res ¥ i u l« ’ , yc hy . r ‘ ‘ 7 i ‘ 9 4 ‘ 4 ¢ . tt : ‘ . * e hy be, 4 ‘ rs ri ? * - « . , , f a . 4 2 * zr ’ ? A ‘ Pe hes f , . A) ‘ 4 f # 4 | ba + e ’ ‘va i 7 C ; yas i Geer bs fo on ea ' > eM ¢ mid ) ae bas THE MANUFACTURE OF PULP AND PAPER VOLUME III Pulp and Paper Manufacture IN FIVE VOLUMES An Official Work Prepared under the direction of the Joint Executive Committee of the Vocational Education Committees of the Pulp and Paper Industry of the United States and Canada Vout. I—Maruematics, How To Reap Drawings, Puysics. II—MecHanics AND HYDRAULICS, ELECTRICITY, CHEMISTRY. III—PREPARATION OF PULP. IV, V—MANUFACTURE OF- PAPER. THE MANUFACTURE OF PULP AND PAPER A TEXTBOOK OF MODERN PULP AND PAPER MILL PRACTICE Prepared Under the Direction of the Joint Executive - Committee on Vocational Education Representing the Pulp and Paper Industry of the United States and Canada VOLUME 1D PRoperRTIES oF PuLpweop; PeepsrRat-ow oF Woop;; MMaiyUFACTURE OF MECHANICAL, SULPHITE, SopA, AND SULPHATE PuLPs; TREAT- MENT OF PuLP; REFINING AND TESTING OF PULP; BLEACHING OF PULP Authors: H. N. Lee, A.M.; J. Newell Stephenson, M.S.; R. W. Hovey, B.Sc.; 8. Roy Turner, B.Sc.; Bjarne Johnsen, Dr. Ing.; Arthur Burgess Larchar; Karl M. Thorsen, Chem. Eng.; J. O. Mason; T. E. Kloss, B.8.; H. H. Hanson, §.B.; Max Cline; Albert H. Hooker, Jr., A.B.; D. 8. Davis, B.S.; and H. J. Buncke, C. E. Seconp EDITION SECOND IMPRESSION McGRAW-HILL BOOK COMPANY, Inc. NEW YORK: 370 SEVENTH AVENUE LONDON: 6 & 8 BOUVERIE ST.; E. C. 4 1927 Copyricuat, 1922, 1927, py THE Jornt ExecutTivE CoMMITTEE OF THE VOCATIONAL EpucATION COMMITTEES OF THE PULP AND Paper INDUSTRY. tC : ew ; beh ey ' : : Cte ‘ ei eo 0 y ae - . 2 ° Pa une : ie at Ie é C wo ( ‘ Sie torte Wants « «© c*Atn Rreurs: Reseaved,: «<< ¢ | : , pice € € < e,* of @¢.ce @ | coe @ <4e (i c C . INCLUDING THOSE OF TRANSLATION. « € « « ee ee ne eats err Maen! Tdi ae pr tet ee etec*ee € cee € es e 6 €G¢ fi S@¢e 8 @¢€ © « ‘ ee ¢ eco.< © PRINTED IN THD UNITED STATHS’ OF AMERICA QO 974 (wy hy a: PL 4 J 7, LN wr . 4. in te Vv ak | THE MAPLE PRESS YORK PA PREFACE TO SECOND EDITION The necessity for printing the fifth impression of this, the third, volume of The Manufacture of Pulp and Paper, has been made the occasion for bringing the text up to date. Since the original manuscript was prepared, some six years or so ago, there have been several important developments in the making of pulp, among which may be included bark presses, automatic grinders, continuous causticizers, pulp washing, and, in particu- lar, the recovery of fiber that was heretofore lost in mill effluents. Information concerning these and other developments is included in this new and revised edition. The section on bleaching has been entirely rewritten, under the co-authorship of H. H. Hanson and A. H. Hooker, Jr., the latter being an addition to the list of outstanding names of contributors to this textbook. The Joint Committee on Vocational Education takes this oceasion to thank all those who have so obligingly cooperated in the production of this textbook, and in the revision of this volume. J. N. STEPHENSON, Editor. GARDENVALE, P. Q. January, 1927. ee) Pag ass Vv PREFACE TO FIRST EDITION In numerous communities where night schools and extension classes have been started or planned, or where men wished to study privately, there has been difficulty in finding suitable textbooks. No books were available in English, which brought together the fundamental subjects of mathematics and element- ary science and the principles and practice of pulp and paper: manufacture. Books that treated of the processes employed in this industry were too technical, too general, out of date, or so descriptive of European machinery and practice as to be unsuit- able for use on this Continent. Furthermore, a textbook was required that would supply the need of the man who must study at home because he could not or would not attend classes. Successful men are constantly studying; and it is only by studying that they continue to be successful. There are many men, from acid maker and reel-boy to superintendent and mana- ger, who want to learn more about the industry that gives them a livelihood and by study to fit themselves for promotion and in- creased earning power. Pulp and paper makers want to under- stand the work they are doing—the how and why of all the various processes. Most operations in this industry are, to some degree, technical, being essentially either mechanical or chemical. It is necessary, therefore, that the person who aspires to under- stand these processes should obtain a knowledge of the under- lying laws of Nature through the study of the elementary sciences and mathematics, and be trained to reason clearly and logically. After considerable study of the situation by the Committee on Education for the Technical Section of the Canadian Pulp and Paper Association and the Committee on Vocational Educa-. tion for the Technical Association of the (U. 8.) Pulp and Paper Industry, a joint meeting of these committees was held in Buffalo Vil viii ' PREFACE TO FIRST EDITION in September, 1918, and a Joint Executive Committee was ap- pointed to proceed with plans for the preparation of the text, its publication, and the distribution of the books. ‘The scope of the work was defined at this meeting, when it was decided to provide for preliminary instruction in fundamental Mathematics and Elementary Science, as well as in the manufacturing operations involved in modern pulp and paper mill practice. The Joint Executive Committee then chose an Editor, Associate Editor, and Editorial Advisor, and directed the Editor to organize a staff of authors consisting of the best available men in their special lines, each to contribute a section dealing with his specialty. A general outline, with an estimated budget, was presented at the annual meetings in January and February, 1919, of the Canadian Pulp and Paper Association, the Technical Association of the Pulp and Paper Industry and the American Paper and Pulp Association. It received the unanimous approval . and hearty support of all, and the budget asked was raised by an appropriation of the Canadian Pulp and Paper Association and contributions from paper and pulp manufacturers and allied industries in the United States, through the efforts of the Technical Association of the Pulp and Paper Industry. To prepare and publish such a work is a large undertaking; its successful accomplishment is unique, as evidenced by these volumes, in that it represents the cooperative effort of the Pulp and Paper Industry of a whole Continent. The work is conveniently divided into sections and bound into volumes for reference purposes; it is also available in pamphlet form for the benefit of students who wish to master one part at a time, and for convenience in the class room. This latter arrangement makes it very easy to select special courses of study; for instance, the man who is specially interested, say, in the manufacture of pulp or in the coloring of paper or in any other special feature of the industry, can select and study the special pamphlets bearing on those subjects and need not study others not relating particularly to the subject in which he is interested, unless he so desires. ‘The scope of the work enables the man with but little education to study in the most efficient manner the preliminary subjects that are necessary to a thorough. understanding of the principles involved in the manu- facturing processes and operations; these subjects also afford an excellent review and reference textbook to others. The work PREFACE TO FIRST EDITION | ix is thus especially adapted to the class room, to home study, and for use as a reference book. It is expected that universities and other educational agencies will institute correspondence and class room instruction in Pulp and Paper Technology and Practice with the aid of these volumes. ‘The aim of the Committee is to bring an adequate opportunity for education in his vocation within the reach of every one in the industry. To have a vocational education means to be familiar with the past accomplishments of one’s trade and to be able to pass on present experience for the benefit of those who will follow. To obtain the best results, the text must be diligently studied; a few hours of earnest application each week will be well repaid through increased earning power and added interest in the daily work of the mill. To understand a process fully, as in making acid or sizing paper, is like having a light turned on when one has been working in the dark. As a help to the student, many practical examples for practice and study and review questions have been incorporated in the text; these should be conscientiously answered. This is the first volume published in English that deals solely and comprehensively with the manufacture of wood pulp. The attention here given to this subject is warranted by the essential place now held by this source of paper-making material. From a practically unknown factor fifty years ago, the making of paper is now a major industry, employing thousands of work- men, and converting much wood, otherwise worthless, into an important article of international commerce. The greatest advances in connection with the paper industry have been in the development of pulp manufacture. Even this volume is too small to tell the whole story, the study of which will fascinate and benefit anyone connected with this industry. A feature of this series of volumes is the wealth of illustrations, which are accompanied by detailed descriptions of typical apparatus. In order to bring out a basic principle, it has been necessary, in some cases, slightly to alter the maker’s drawing, and exact scales have not been adhered to. Since the textbook is in no sense a “machinery catalog,’ maker’s names have been mentioned only when they form a necessary descriptive item. Much of the apparatus illustrated and many of the processes = PREFACE TO FIRST EDITION described are covered by patents, and warning is hereby given that patent infringements are costly and troublesome. A valuable feature of this work, which distinguishes it from all others in this field, is that each Section was examined and criticised while in manuscript by several competent authorities; in fact, this textbook is really the work of more than one hundred men who are prominent in the pulp and paper industry. With- out their generous assistance, often at personal sacrifice, the work could not have been accomplished. Even as it stands, there are, no doubt, features that still could be improved. The Committee, therefore, welcomes helpful criticisms and sugges- tions that will assist in making future editions of still greater service to all who are interested in the pulp and paper industry. The Editor extends his sincere thanks to the Committee and others, who have been a constant support and a source of in- spiration and encouragement; he desires especially to mention Mr. George Carruthers, Chairman, and Mr. R. 8. Kellogg, Secretary, of the Joint Executive Committee; Mr. J. J. Clark, Associate Editor, Mr. T. J. Foster, Editorial Advisor, and Mr. John Erhardt of the McGraw-Hill Book Company, Inc. The Committee and the Editor have been generously assisted on every hand; busy men have written and reviewed manuscript, and equipment firms have contributed drawings of great value and have freely given helpful service and advice. Among these kind and generous friends of the enterprise are: Mr. M. J. Argy, Mr. O. Bache-Wiig, Mr. James Beveridge, Mr. J. Brooks Bever- idge, Mr. H. P. Carruth, Mr. Martin L. Griffin, Mr. H. R. Harrigan, Mr. Kenneth T. King, Mr. Maurice Neilson, Mr. Elis Olsson, Mr. J. S. Riddile, Mr. George K. Spence, Mr. Edwin Sutermeister, Mr. F. G. Wheeler, and Bird Machine Co., Cana- dian Ingersoll-Rand Co., Claflin Engineering Co., Dominion Engineering Works, E. I. Dupont de Nemours Co., General Electric Co., Harland Engineering Co., F. C. Huyck & Sons, Hydraulic Machinery Co., Improved Paper Machinery Co., E. D. Jones & Sons Co., A. D. Little, Inc., E. Lungwitz, National Aniline and Chemical Works, Paper Makers Chemical Co., Process Engineers, Pusey & Jones Co., Rice, Barton & Fales Wveashine and Iron Works, Ticonderoga Paper Co., Waterous Engine Works Co., Westinghouse Electric & Manufacturing Co., and many others, particularly the authors of the Shr PREFACE TO FIRST EDITION xl sections, who have devoted so much time and energy to the preparation of manuscript, often at personal sacrifice. | J. NEWELL STEPHENSON, Editor For THE Joint ExXEcuTIvVE COMMITTEE ON VOCATIONAL EDUCATION, GEORGE CARRUTHERS, Chairman, R. 8. Keuioge, Secretary, T. L. Crosstey, G. E. WILLIAMSON, C. P. WINstLow. Representing the Technical Sec- Representing the Technical As- tion of the Canadian Pulp and Paper sociation of the (U. 8.) Pulp and Association. Paper Industry. T. L. Crosstuy, Chairman, GeorGcE E. WILuiAMson, Chairman, GEORGE CARRUTHERS, Hvuau P. Baker, A. P. CosTIGANE, Henry J. Gum, Dan DavERIN, R. 8. KELLoGa, C, NELSON GAIN, Orro KRgEss, J. N. STEPHENSON. W. S. Lucey, C. P. WINSLOW. CONTENTS PREFACE TO SECOND EDITION . PREFACE TO First EDITION. SECTION 1 Properties of Pulpwood PART 1 IMPoRTANT FisER PropucinGc PLANTS OTHER THAN Woop. . SrRUCTURE AND GRowTH OF Woop... Some PuysicAL PROPERTIES OF Woop . BIBLIOGRAPHY... . . PART 2 ComposITION OF Woop. CoNnsTITUENTS OF Woop IN ayers Pcemmoccia BIBLIOGRAPHY . . . GLOSSARY . . ‘ EXAMINATION OU eTiONS : SECTION 2 Preparation of Pulpwood INTRODUCTION . : Tue Cut-Up MIL. Woop STORAGE AND On Tur Woop Room . EXAMINATION QUESTIONS . SECTION 3 Manufacture of Mechanical Pulp INTRODUCTION... . : GRINDERS AND cee f Tue Mecuanicat-Putp MILu. Mecuanicat-Pute Minti Layout . Mecuanicar-Putp Mitt OPERATION. GRINDING PROCESSES. ; GRINDER PRESSURE SYSTEMS . EXAMINATION QUESTIONS . SECTION 4 Manufacture of Sulphite eas History AND OUTLINE OF THE PROCESS . PREPARATION OF THE CooxING AcID Tur CooKING PROCESS. Puup, Actin, Raw MATERIALS, AND > Waste Liquor. EXAMINATION QUESTIONS. xiii 5-51 51-80 80-87 XIV CONTENTS SECTION 5 Manufacture of Soda Pulp Pace INTRODUCTORY 65 3 i Se ae oe ae ee 1-4 Tax Cooking LiguorkR 9.2 74 i tel 2 eS ee 5-25 Tue CookING PROCESS IN A Sant Mana, ER re WASHING PULP AND RECLAIMING CHEMICALS. ......... 4468 BIBLIOGRAPHY. .. . PP EX AMINATION Quustions. ae phe en ee re 81 SECTION 6 Manufacture of Sulphate Pulp ORIGIN AND OUTLINE of PROCESS 4° > vy fo. ae Sage ee | 1-5 Tap Liquor Room: . 4: 0s a Sn ee 5-18 THe DigesTER Room. ... . + ea vane obo 18-47 Ture DirruseR Room. ..... oo ET ce ge a eee 47-62 THES, HivAPORATORS 63 Ss te oe Co et Seo eae er 63-79 Toe FurRNAcE-RooMm. .. . vow NO Ee 79-98 APPENDIX TO SULPHATE Bae PP SO EXAMINATION QUESTIONS ..... . é- br eed el ee 123 SECTION 7 Treatment of Pulp CoARSE SCREENING. .... on ea Gay ee 1-20 FINE SCREENING. .. . ES Fea Oe eae 20-51 TREATMENT OF PULP AFTER soenneenie sae ue 51-87 HYDRAULIC PRESSING. ...°. 2) 40 4° > 9 87-96 Dryina MACHINES. 2.060606 eee we EXAMINATION QUESTIONS ...... 2 a) Pa SECTION 8 Refining and Testing of Pulp PARTE? INTRODUCTION TO REFINING OF PULP’) (°° > i eee 1-4 REFINERS 2.650. ee ee a 4-14 PAW i PHYSICAL? 1 8STR. 2.) os ee oe ol 0 ae 15-45 CHEMICAL TESTS. . 6. 0 6 6 4 et 46-52 EXAMINATION QUESTIONS ..... a5 Se eee 53 SECTION 9 Bleaching of Pulp BLEACHING POWDER . .-.0.0. 500... 5 ee 1-7 Liovrp:. CHLORINE ee. es . a gt a a 7-13 BLEACHING OPERATION AND Raper : oy ORS 14-33 ANALYSIS oF BLEACH AND Bieacn Liquor. | 7 (oe 33-41 MANUFACTURE OF GHLORIND ... .°. . 3°...) 41-51 EXAMINATION QUESTIONS ...... toe 4 53 Tastes I-TV. i°. 2 eee NON OO) a Oe 55-58 TRDEX) 3. 8.9 6 oe eee eee . , ov Se 59-76 ' Biber: SECTION ij PROPERTIES OF PULP WOOD (PART 1) BY H. N. LEE, A. M. STRUCTURAL, MICROSCOPICAL, AND PHYSICAL PROPERTIES OF WOOD IMPORTANT FIBER PRODUCING PLANTS OTHER THAN WOOD 1. Classification of Plants Used in Pulp and Paper Industry.— The fiber of many different kinds of plants can be made into pulp and paper. The principal factors that determine whether a plant shall or shall not be used in the manufacture of paper are: suitability of fiber; dependability of supply; cost of collection, transportation, and preparation; deterioration in storage. At the present time, wood is by far the plant most used; and the coniferous trees are utilized to a much greater extent than the trees of the hardwood, or broad-leaved, group; though for reasons of forest economy, it is necessary to make use of the latter also. In general, all plants utilized in pulp and paper - manufacture may be divided into six (6) classes, as shown in Table I, which has been arranged according to F, C. Clark, in Paper, Vol. X XIII, Feb. 20, 1919. 2. Use of Plants Other than Wood.—Cotton, linen, and bombax wool reach the pulp mill in the form of rags or waste from other manufactures. Jute, hemp sisal hemp, and manila hemp usually $1 PROPERTIES OF PULP WOOD §1 TABLE I CLASSIFICATION OF FIBERS USED IN PAPERMAKING (A) Ssed-hair fiber (B) Stem fiber (Bast family) (C) Leaf fiber (D) Fruit fiber (E) Wood fiber | Cotton (Gossypium) Bombax wool (Bombacacee) Flax (linen) Linum usitatissimum) Hemp (Cannabis sativa) Jute or Calcutta hemp (Corchorus capsularis & olitorius) Common nettle (Urtica dioica) Nettle fibers ; China grass (Boehmeria nivea) Ramie (Boehmeria tenacissima) | Indian corn (Zea mais) Sugar cane (Saccharum officinarum) Bamboo (Bambusa sp.) Sunn hemp (Crotalaria juncea) Manila hemp (Musa teztilis) Straw (from various cereals) Esparto (Lygeum spartum) New Zealand hemp (Phormium tenaz) Manila hemp (Musa tezxtilis) Sisal or Domingo hemp (Agave rigida) Aloe fiber (Fourcroya fetida) Pineapple leaf fiber (Ananas sativa) Vegetable wool from green cones of pine and fir Palm (Palme) Cocoanut fiber (Cocos nucifera) Larch, tamarack (Lariz) Fir (balsam and others) (Abies) Spruce (Picea) Cedar (Chamecyparis, Junt- Resinous : verus, Cupressus, Thuja) or : > ; Pine (Pinus) coniferous Hemlock (T7'suga) Cypress (T'axodium) Douglas fir (Pseudotsuga) etc. Birch (Betula) Beech (Fagus) Maple (Acer) Non-resinous | Poplar (Populus) or Chestnut (Castanea) broad-leaf | Gum (Nyssa) Basswood (Tilia) Tulip (Liriodendron) etc. §1 PROPERTIES OF WOOD 3 come from cordage or rough textile waste. Esparto is a grass that grows in Spain and Northern Africa; it is cut especially for pulp making. All the foregoing are discussed in detail the Sec- tion on Preparation of Rags and Other Fibers in Vol. IV. With the exception of wood and the plants just mentioned, the fibers of the other plants listed in Table I are used only to a very slight extent or are not used at all at the present time. Although some of these plants yield an inferior pulp, the main reason why they are not utilized to a greater extent is because they yield such a small percentage of pulp. | Fic. 1.—Cross Section of Part of Indian Corn Stem. X 20. (Prepared by the Forest Products Laboratories of Canada.) In this and similar plants, the only parts of value for paper pulp are the bast fibers B, which show as the darkest parts of the bundles F. The thin-walled parenchyma, or pith cells P, which make up the most of the stem, are of little or no value. 3. Structure of Stem of Indian Corn.—In Fig. 1' is shown a cross section of the stem of Indian corn, from which may be estimated the relative amount of useful fiber and useless or 1 Figs. 1-3, 5-8, 11-13, and 16-22, inclusive, are reproductions of very excellent photomicrographs prepared by the Forest Products Laboratories of Canada, to whom special thanks are extended; we particularly wish to thank Mr. J. D. Hale, of the Forest Products Laboratories of Canada. 4 PROPERTIES OF PULP WOOD §1 waste material; this figure may be used for the same purpose in connection with manila, New Zealand, and sisal hemps, bamboo, straw, sugar cane, palm, pineapple leaf, and similar plants. The only valuable parts of such plants are those that appear as dark spots in the illustration. These are called fibro-vascular bundles Ff, because they are made up of bundles of fibers, includ- ing chiefly the so-called bast-fibers B. ‘The space between the bundles is filled with short pith cells P. Whether it is the stem or the leaf of these plants that is used, there are always a very large number of short, thin-walled cells, which are practically valueless for the manufacture of paper pulp; this useless part fills up all the space between the bundles, and it can easily be seen that this makes up the greater part of the plant. 4, Reference Letters in Illustrations.—In all the figures used to illustrate Part 1 of this Section, the same reference letters always have the same meaning, as in the following list: List oF REFERENCE LETTERS USED IN MARKING ILLUSTRATIONS A, annual ring P, parenchyma B, bast fibers P, pith BP, bordered pit R, radial section C, cross section S, sapwood Cm, cambium Sm, summerwood CRC, central ray cell Sp, springwood D, resin duct or canal SP, simple pit F, fibro-vascular bundle _ T, tangential section H, heartwood Tr, tracheid K, bark V, vessel or pore L, middle lamella . W, wood M, medullary ray WF, wood fiber MRC, marginal ray cell 5. Structure of Stem of Clematis.—A cross section of the stem of clematis is shown in Fig. 2; this is typical of the general make- up of common plants that die at the end of each year. As can be seen, the fiber bundles are arranged in a single circle in the outer part of the stem. The part fitting like a cap over each bundle is the group of bast fibers, while the rest of the bundle includes short, more or less woody fibers. The hollow center of the stem is surrounded by pith cells, which, like those of Indian corn, are very short and thin. Here, again, only the bast fibers are useful for paper pulp, and the proportion of these is so small §1 PROPERTIES OF WOOD 5 Fig. 2.—Cross Section of Clematis Stem. X 20. (Prepared by the Forest Products Laboratories of Canada.) In this and similar plants, the only parts of value for paper pulp are the bast fibers B, which show as caps fitting on each fibro-vascular bundle F. The parenchyma (pith) cells P and the cells of the bundles, with the exception of the bast cells, are of little or no value. Fic. 3.—Cross Section of Stem of Flax Straw. X 20. (Prepared by the Forest Products Laboratories of Canada.) The bast fibers B, which form an almost complete ring just inside the periphery of the stem, are the fibers used in paper making. Inside this is the wide, woody part W of the stem, while the center is hollow. The wood is made up of very short fibers, and is of little or no value in pulp making. 6 PROPERTIES OF PULP WOOD Si as to make the plants of practically no value in the manufacture of pulp. 6. Structure of Stem of Flax.—Fig. 3 shows the appearance of the cross section of the stem of flax (Linum usitatissimum) ; it also illustrates in a general way the structure of hemp, jute, cotton (stalk), and other woody plants. In this class of plants, the individual bundles as seen in the clematis do not show, because they are so large that they have grown together. The whole central part is hollow; and, outside of this, these stem are made up of a wide zone of wood, which is practically the same as the wood of trees. But the fibers are very short, and they are of little or no value for pulp manufacture. The valuable part of such stems is in what is ordinarily called the bark, for it is here that the bast fibers occur, as shown at B. Since the bast fibers form so small a part of the stem, and since the rest is of no value, these plants are not used directly as pulp-making materials; but the fiber from them is obtained as waste from the cordage or textile industries. 7, Trees.—The trees are by far the most important of the plants used in the production of paper pulp. As shown in the classification, Table I, trees are divided into two main groups: the resinous, or coniferous, trees and the non-resinous, or broad-leaved, trees. After discussing wood in general, spruce _will be taken as an example of resinous woods and poplar as an example of non-resinous woods, and both types will be described in considerable detail. STRUCTURE AND GROWTH OF WOOD GENERAL DESCRIPTION OF WOOD 8. Wood Fibers.—Wood is not a solid, homogeneous sub- stance like steel or glass, but is made up of innumerable little hollow tubes, called fibers, which are usually closed at their ends. In any particular wood, the greater proportion of the fibers are very similar to one another, but there are some that are different; and in comparing one wood with another, very different kinds of fibers will be found. The fact that fibers differ not only in size and shape but also in actual structure and arrangement, is really the explanation of why one kind of wood $1 PROPERTIES OF WOOD 7 differs from another. In general, it may be said that the greater the difference in general appearance between two kinds of woods the greater will be the difference in the shape and arrangement of the individual elements of which the respective woods are composed. No two species of wood are exactly alike in structure; hence, it is possible to determine what kind or species any piece of wood is if one knows the structure of the various kinds. Tables II, III, IV, and V give the characteristics, by means of which, it is possible to distinguish the woods used in making paper pulp. Most of the fibers are arranged lengthwise, or along the grain, in a piece of wood (these would be in a vertical position in a standing tree trunk), and each fiber is firmly cemented to all the fibers adjacent to and surrounding it. A certain number of the fibers, or rather cells, of the wood lie in groups, which extend from the center of the tree outward; that is, they occupy the same position that would be occupied by anail that is driven from the surface to the center of the tree. In addition to the fibers placed vertically and the groups of cells lying horizontally in the standing tree, there are certain other cells, which occur in most woods, and which are often character- istic in shape or distribution of each different kind of wood; these will be described in detail in the case of some of the impor- tant pulp woods. 9. How a Tree Grows.—Before considering the minute structure of wood, a description will be given of how a tree erows. The actual growth takes place in the following manner. The roots absorb water, which contains a certain amount of mineral matter; this water, called the sap, is drawn up through the trunk of the tree, through the sapwood, which lies between the heartwood and the bark. The sap passes through the branches and, finally, to the green leaves. In the leaves, the sap is combined with carbon dioxide gas COs, which is taken into the leaves from the air, and the final product of the chemical reaction is sugar. This sugar is carried, in solution, down through the inner bark of the tree, and from thence into the wood, through what are called medullary rays M, (see Fig. 4). For explanation of reference letters, see Art. 4. For definition of terms, see Glossary, Art. 24. At the part of the tree where the bark is attached to the wood, there is a special layer of cells, called the cambium cells, Cm, which take up this sugar solution and grow and divide, making 8 PROPERTIES OF PULP WOOD $1 more and more cells. The new cells on the wood side gradually develop into wood fibers and the other types of woody cells, while those on the bark side form bark fibers; thus it is that a new layer ee i a 13 3 3 lJ fig OH p e Wy ey Wer j ae Mt i Fe YY ee \ Mtg wnt’ a\\\ \ARAEATA HAUTE, VAAL as oe \\\ x $ Leret AVY NNUNWANSiAN Se wee em Varn \\ ‘a NANA NAAN 1 FB, WTR TERR eas, \\\\ aN WER RRA L\\ = we. WS WAU) RRR I IWR SS i oe AY wa ee, \AAY 4) NN eth lV yee eh 4) Ay PY .\ CY aN 7 4 \\, ‘Wid Via OAABAA preventive Ne to tetas ‘a a TNS Ses as SS NN \ eee - A SNS N Ye aw). = Sasa ial ANY E) y | = \ \\ s AV AIS = Fic. 4.—Diagram of a Log of Wood, Cut to Show Cross, Radial, and Tangential Sections. C, cross section; R, radial section; 7, tangential section; S, sapwood; H, heartwood; A, annual ring; Sm, summerwood; Sp, springwood; M, medullary ray; P, pith: K, bark; Cm, cambium. of wood cells, or fibers, are added to the surface of the wood each year. Each year’s growth ring, or annual ring, A, is divided into two parts: that which is formed in the early part of the §1 PROPERTIES OF WOOD 4 growing season, which is composed of fibers with thin walls that enclose a comparatively large space Sp; and that which is formed during the later part of the growing season, which is made up of fibers having thicker walls that enclose a smaller space Sm. It is because of this difference between the two parts of the annual growth that the annual rings can be distinguished in wood, the early growth of each year being lighter in color, less dense, and softer than that formed later. Each year, one light, soft ring Sp, the so-called early wood or springwood, and one denser, harder ring Sm, the so-called late wood or summerwood, are added as long as the tree lives and grows. By counting the darker rings, one of which is formed each year, the age of the tree may be accurately determined. The annual rings vary greatly in width; those which are formed in seasons very favorable for tree growth may be one- half an inch or more wide, while those formed in seasons unfavor- able for tree growth may be less than one-fiftieth of an inch in width. In a tree grown in the forest, the annual rings of the first years of the tree’s growth are usually the widest and those of the last years the narrowest. In spruce, the rings average from one-eighth to one-sixteenth of an inch in width. 10. As the tree grows larger, the inner (central) part of the tree trunk H, called the heartwood, becomes more or less closed up. In many kinds of wood, the heartwood is darker in color than the part S outside of it, called the sapwood. It is only in the outer part, the sapwood, that water, or sap, can pass through the trunk in its journey from the reots to the leaves. In some woods, like spruce, balsam fir, and poplar, the heartwood and sapwood are, unless decayed, of the same color; but in most woods, like pine and oak, the heartwood is much darker in color than the sapwood. The heartwood and sapwood, even when different in color, are not different in structure; for the fibers formed during any growing season do not materially change in size or structure during later seasons. There is a slight change in the chemical nature of the wood, chiefly due to the resins, tannins, and other substances contained in the fibers, but there is very little change in the actual chemical composition of the cell walls. In many woods, small, foam-like growths also develop in the inner sapwood and heartwood, which fill up the open spaces in certain cells and thus prevent the passage of sap. PROPERTIES OF PULP WOOD $1 10 Fig. 5.—Photomicrograph of a Block of Spruce Wood. X. 20. (Prepared by the Forest Products Laboratories of Canada.) Fig. 6.—Photomicrograph of a Block of Balsam Fir Wood. X 20. — (Prepared by the Forest Products Laboratories of Canada.) PROPERTIES OF WOOD 11 Fig. 7.—Photomicrograph of a Block of Hemlock Wood. X 20. (Prepared by the Forest Products Laboratories of Canada.) | tr i UR | : | ae ii ql . ~u Fia. 8. Be ee ere ah of a Block of Jack Pine Wood. X 20. (Prepared by the Forest Products Laboratories of Canada.) 12 PROPERTIES OF PULP WOOD §1 THE MINUTE STRUCTURE OF SPRUCE WOOD 11. Coniferous, or Resinous, Woods.—As before stated, spruce will here be taken as an example of coniferous, or resinous, woods; its structure will now be examined minutely. Fig. 9 is a diagram of a small block of spruce wood, very much enlarged, showing a part of one annual ring. Yo Ree ° 2f{© (“J aay AO ——a Ss, © oy 1© ¢ we, ag ,, 2 ye De Ae a ey : ong fas [mE OMOMOY: ©® © © foe 3 off 2 Mo [© © O Lhe © © © f 0 oucou BP Fig. 9.—Diagram of a Small Block of Spruce Wood, Greatly Enlarged, Showing a Part of One Annual Ring. C, cross section; R, radial section; 7’, tangential section; D, resin duct; Sm, summerwood; Sp, springwood; Tr, tracheid; BP, bordered pit; ZL, middle lamella; M, medullary ray; CRC, central ray cell; MRC, marginal ray cell. As may be seen in the illustration, most of the fibers, or tracheids 7'r, as they are technically called, extend lengthwise in the wood; they are cemented to one another by a layer of sub- stance that is called the middle lamella L. This layer, the middle lamella, dissolves during the cooking process, and thus allows the fibers (tracheids) to separate. The larger, thin- §1 PROPERTIES OF WOOD : 13 walled tracheids are those of the springwood Sp, while the thick- walled tracheids are those of the summerwood Sm. The groups of cells M, which extend crosswise (outward from the center of the trunk), are the medullary ray cells, frequently called, simply, the ray cells. Each group is called a ray; and it may be noted that the cells MRC on the margins of the ray look different from those in the center CRC. This is because of the difference in the openings that occur in the cell walls, the openings in the cells of the margins showing a double circle, or bordered pit, while those of the central cells show only a single circle, or simple pit. The ray cells, because they are so short, are of little value for pulp; for- tunately, however, they form less than ten per cent of the total vol- ume of the wood, while the long fibers, or tracheids, which are of just the right dimensions for pulp, make up the remaining ninety per cent. 12. Resin Ducts.—Near the center of the top surface of the block, Fig. 9, which shows the cross section C of the wood, is an open space D, which is surrounded by cells that are smaller and thinner walled than the tracheids; this open space is a resin duct, or canal, and the cells surrounding it can form and secrete resin. An open space D may also be seen in the ray, near the center of the front face of the block; this is a resin duct in the ray. These open spaces, or resin ducts, extend lengthwise and cross wise throughout all the wood of spruce trees; it is from these ducts that the resin, or pitch, comes, which is so often seen on the ends of logs. A certain amount of resin also occurs in all the central cells of the rays; hence, some pitch is present in conifer- ous woods, like balsam fir, which do not have resin ducts in the wood. On the surfaces of some of the tracheids (fibers) may be seen double circles BP; these show the openings called bordered pits, which allow the sap to pass from one tracheid to another, in its journey from the roots to the leaves. 13. Cells of Coniferous Woods.—All the other coniferous woods are made up in a manner very similar to spruce. They, all, are composed mainly of long tracheids extending vertically, which make up the greater part of the wood, and rays that extend horizontally, which make up most of the remainder of the wood. ‘The pines differ from the spruces in having much larger resin ducts and in the size of the openings in the central ray cells, or the presence, in the hard pines, of toothed walls in the PROPERTIES OF PULP WOOD §1 14 a *“poulvis euy pus udAd AIA | BUON | pxBy AIOA euoN peyx1eyy AS¥oIs S[I0f puB SYOO] VovjINs YJoouIG | suON | pPsey “poy ouoN peyxIBUl “poyy 10po 1eps90 DIZSTIOZIOVAIVYO sSeFT | SUON | jos AOA | O1IYVUIOIY | POYIVUL JON Azequrtds 10 @S81800 JOU pooM | eUON | piBy “poy, anog peyreur Aro A Aszoquryds pue osIg0od pooM ]} 9U0N | PpilBy “poy nog peyreul Ara A auoN 3308 aT «| poyrew “poy soonids 19430 9} uvy} SssulI jenuuse Jepin = sey prey Ajjensn sonidg of AA | [Wg | ‘poul 03 4jog | Shoulsey | poyxIVUl “poy TTeus 4jJOS snoulsey | poyxIeul "poyy Teug | prey Ara | shoutseyY | poyxivur Ara A [eug | pavy AoA | SnoutsoyYy | poyxseur Alo A [eug | pavy AiaA | Snoutsoy | poxseur Ala A snoulser AIOA AT[BNsy | osIVT | prey AOA Aout peyreur A130 A oyIVUl es1eT] | prey 0} 4jJOoS Aoulg Apasntere pe os18'T 4JOS Aoulg pexivul JON Sor stale 138119} VIVGD 10430 | uy soy 4JOS 10 piv] 10poO pooMeuIUINg SOT}STIOJOVIVY @10UI 10 ,,T SS IO ,T Sse 10 ,,T Sso[ 10 ,,T 910UL 10 ,,T wu OF WT aioul 10 ,,% uG OF wl uv OF WG a G “UG 04 ai { MBI}S [Bq uMOoIg 443] uMOIq 0} MBI} balk te Shes | Ystppoy oy MBIYS B[Vq. MBI}S B[V MBIYS B[Bq MBIYS B[Vq MBIYS [Bq MBI}S BIBI MBI}S O[Vq MBI}S O[q poomdesg UFPIM poomdeg IO[OD pel esutviO uMOIg. SIP -pol 0} uMOIg Ystppey ystppey oyty A MBI}S OTB pei 9[¥@g q7eSsni TING qyoessni [ING MOT[9A 0} Poy uMOIQG 9SUBIO 0} YSIPpey uUMOIQ 9suUvIO Sesame oceans pehe c sat eni} Jay}O pus Wes[eg C- e ick Be 8 ee sonidg yov[q © a wd 0 Teale OCs sonidg pew a he © ie Sele ae eonidg out MA Ce sonidg Byig os 6hene € ees U19489 (A ‘Yoley aie a (Goiey) YoRViswuey, ae) & a) © 2 Pe @ die It sejsnog Be) ss 2 609 @ 615 Bee euld (JB9] -suOT) MOT[29 A UsIOyyNOG “-9ulg MOT[e A UIS4ISAM gg ag sulg sjodespo'y Sere oulg (pez) ABMION 0} YsIppey ie i “*autg yowr uMOIQ 99810 EG Palm a ae duIg iesng 0} AuIveIDg sould 944M JO 4jJog Ap poom4z1BeyT TEV +33 Co) (ol@) ‘no sod qysIO A poom Jo satoeds 10 puly ee (ofa poyeuU oy} G}IM Woes Sy) Il WIavi SGOOM (SNONISHA) SQOUFAINOD AO NOILVOIMILNAGI AHL aod §1 PROPERTIES OF WOOD 15 marginal ray cells. Fig. 10 is a diagram of cells of coniferous woods, in which (1) is a tracheid of springwood, (2) is a tracheid of summerwood, and the others are as follows: (3) cell from lining of resin duct; (4) wood parenchyma cell; (a) toothed mar- ginal ray cell of hard pine; (b) smooth marginal ray cell of soft pine; (c) central ray cell, showing piciform pitting; (d) central TABLE III FOR IDENTIFICATION OF CONIFEROUS WOODS (With use of the microscope) Characteristics Kind of wood Resin Ray Wood Spiral Ray cell canals tracheids | parenchyma a: pitting PIRCSE ETS cre. Gos. x. da. Large, Present Absent Absent | Very large or present large Bpruces (Picea)... 0004 6... Small Present (Absent) Absent | Piciform4 present ( =small) Larches (Lartz).........06. Small Present | (Terminal)? | Absent | Piciform! Douglas fir (Pseudotsuga)...| Present Present | (Terminal)? | Present | Piciform4 IpuCA DIES) wesashonie «enc. = 3 Traumatic! | Absent | (Terminal)? | Absent | Piciform only Hemlocks (T'suga)......... Traumatic! |} Present | (Terminal)? | Absent | Piciform4 only Cedars (Thuya Chamecy- DEE TR oe teas sisirans LE ER See eR. (edoosossru Jo asn yIIM) SGOOM SNONISHA-NON JO NOILVOMILNACI YOu A HIdvVL 22 PROPERTIES OF PULP WOOD §1 17. Cells of Non-Resinuous Woods.—lIn the block of poplar wood shown in Fig. 14, the rays are only one cell wide; but in most of the non-resinous woods used in the manufacture of pulp, the rays are made up of three or more rows of cells, placed [A Uf {ar (10) eae [PY G, ( ( =) @) o e/ Fia. 15.—Cells of Wood of Broad-Leaved Trees, Greatly Enlarged. (1), wood fiber from broad-leaved tree; (2), vessel, poplar, with large, clear openings at ends of segment; (3) vessel, birch, with scalariform openings at ends of segment; (4), vessel, beech, with clear or sclariform openings at ends of segments; (5) vessel, maple, with spiral thickenings; (6) vessel, chestnut, springwood; (7), vessel, chestnut, summerwood; (8), tracheid, chestnut, springwood; (9), wood parenchyma cells, which occur to a slight extent in most woods; (10) one medullary cell; M, openings in walls of vessels connecting with ray cells; BP, bordered pits in walls of vessels. side by side, which makes the medullary ray as a whole very much larger than it is in poplar. The shape and the distribution of the pits may be seen in Fig. 15. Here (1) is a fiber from a broad-leaved tree; the other numbers are as follows: (2) vessel, poplar, with large clear openings at ends of a segment; (3) vessel, birch, with scalariform openings at ends of segment; $1 PROPERTIES OF WOOD 23 (4) vessel, beech, with clear or scalariform openings at ends of segment; (5) vessel, maple, with spiral (helical) thickenings; (6) vessel, chestnut, springwood; (7) vessel, chestnut, summer- wood; (8) tracheid, chestnut, springwood, (9) wood paren- chyma cells, which occur to a slight extent in most non-resinous woods; (10) one medullary ray cell; M, openings in walls of pores where they adjoin ray cells; BP, bordered pits. In birch, Fig. 15 (3), the pits are extremely small and very crowded, while in chestnut, they are much larger and more scattered. The special groups of pits that appear as bands on the side walls of the vessels in Fig. 15, show the shape and arrange- ment of the pits leading from the pores into the ray cells, where the two come in contact in the wood. Comparing the pores of poplar with those of birch, for example, it will be found that where the ends of the segments join in poplar, Fig. 15 (2), there is a large, clear opening, while in birch, Fig. 15 (3), the opening is crossed by bars. Since these bars are similar in appearance to a ladder, they are called scalariform, which means ladder-like. The presence or absence of ‘these bars is a leading characteristic of the various woods, and from this feature alone, the kind of wood from which the pulp has been made can often be accurately determined. In most woods, the longest axis of the individual medullary rays is radial, as shown in poplar at M, Fig. 14. In some woods, however, as stated in Table V, the cells at the margins of the rays have their longest axis extending vertically. In certain woods, for example, maple and basswood, the pores have spiral (helical) thickenings on their inside surfaces, Fig. 15 (5); this latter characteristic is often obscured by the pits, but when seen, it is a sure indication of the kind of wood. 18. The Pores of Non-Resinous Woods.—In most of the non- resinous woods used in the manufacture of pulp, the pores are more or less evenly scattered throughout all the wood, and the wood, in this case, is called diffuse porous. Many of the hard woods, however, like chestnut, oak, elm, and hickory, show the pores in the springwood very large and crowded together, while the pores of the summerwood are much smaller and scat- tered, so that a distinct ring appears, which marks the springwood. These latter woods are called ring porous, to distinguish them from the diffuse porous woods. Compare Figs. 12 and 13. In some of the non-resinous woods, such as chestnut, the cells adjoining the pores, especially those in the springwood, are 24 PROPERTIES OF PULP WOOD i 4, mae és RO cart rath 5 Ot eS 3 Pouctt ns ac a eseeseresestonso taenainen -teetttnestamannansem scoters Ma ae (b) Spruce Fibers from Twentieth Annual Ring from Pith. X 20. X 20. Via. 16. (Prepared by the Forest Products Laboratories of Canada.) Notrr.—These fibers all came from same log. $1 PROPERTIES OF WOOD 25 Fic. 17.—Balsam Fir Fibers from Mature Wood. 20. (Prepared by the Forest Products Laboratories of Canada.) Fig. 18.—Hemlock Fibers from Mature Wood. x 20. (Prepared by the Forest Products Laboratories of Canada.) 26 PROPERTIES OF PULP WOOD $1 (a) Part of a tracheid (fiber) of jack pine showing type of pitting M in fiber wall where 1t adjoins a medullary ray; also bordered pits BP, which occur in the fiber wall where it adjoins another fiber. X 150. (b) Part of a tracheid (fiber) of balsam fir showing piciform pitting M in fiber wall where it adjoins a medullary ray.. X ; _ (c) Part of a tracheid (fiber) of Douglas fir showing piciform pitting M in fiber wall where it adjoins a medullary ray; also spiral thickenings S, which occur in the fiber wall. 150. Fic. 19. (Prepared by the Forest Products Laboratories of Canada.) Fic. 20.—Poplar Fibers from Mature Wood. X 20. (Prepared by the Forest Products Laboratories of Canada.) a a §1 PROPERTIES OF WOOD 27 Fig. 21.—Birch Fibers from Mature Wood. xX 20. (Prepared by the Forest Products Laboratories of Canada.) Fic. 22.—Chestnut Fibers from Mature Wood. X 20. (Prepared by the Forest Products Laboratories of Canada.) 28 PROPERTIES OF PULP WOOD §l larger, and have thin walls and bordered pits; these are called tracheids, since they are similar to the tracheids of the coniferous woods. See Fig. 15 (8). Parenchyma (pith) cells are irregularly scattered in the wood of many broad-leaved trees. See Fig. 15 (9). In the sapwood, these cells contain living protoplasm, and during the winter they are filled with starch or oil, which, together with similar substances stored in the ray cells, are used as food by the tree during the early growth in the spring. Wood of non-resinous, or broad-leaved, trees can always be easily distinguished from that of the coniferous trees by the fact that the former always have pores, or vessels, while the latter never contain them. LENGTH OF FIBERS 19. Variations in Length of Fibers.—In what follows, the term fiber is applied both to the wood fibers of the hardwoods and to the tracheids of the coniferous woods. As a general statement, it may be said that the average length of the fiber of hardwoods is a little more than one millimeter, or one twenty-fifth of an inch (see Figs. 20, 21, and 22), and the average length for the coniferous woods is three millimeters, or one-eighth of an inch (see Figs. 16, 17, 18,and19). In both cases, the fibers are, roughly, about one hundred times as long as they are wide. However, the fibers vary much in length in different parts of the same tree. Considering the end of cross-cut log, the wood may be divided into two parts: (1) the wood immediately adjoining the pith, where the fiber is always shorter than in, (2), the part adjoining the bark. In most coniferous trees, the fiber in the first annual ring, around the pith, averages less than one millimeter in length (see Fig. 16a, b, c). In each successive year from the pith, the fiber becomes longer, until about fifty years are covered. Beyond the fiftieth year from the pith, the average fiber changes but little. Again, the fiber length in any one tree varies a little according to its position eee the ground (see Fig. 23). The longest fiber is found in the wood at from ten to twenty feet from the ground, in most trees; above twenty feet or below ten feet, the fiber is found to be OrOreees shorter. The varia- tion in average fiber length at various heights from the ground ee a eS a a a ee 29 PROPERTIES OF WOOD $1 sos~p hq ‘mu y36ua) atqrt abvsaay sos~p hq ‘wu y26ua7 a1grt aanzou ansaap ZR S = =f Soae > : > § s ess S SPsss Soe Ege se = zs 2 = =~ = & p3ess 8 SI as ss s3 So gf phi ei i Ghost Lz = a & §8 gE ibd Sez Zl es | sysss i WN & ESS Sper a S sssyeeses ha 2 3S eX SS Bone te Ses es Sect fesse e MEY, Bs eo. Sess Q al 5 S88 Shoe vow omene| ggg 9.50 8 10.26 7 years 3 103 te ae 6 3.66 382 Z63mm. 8. Distance from ZN Average fibre length Fig. 23.—Longitudinal Diagram of Black Spruce Tree, Showing Average Fiber Length in Various Parts of Tree. 30 PROPERTIES OF PULP WOOD $1 has been found, in a white spruce tree about 100 years old, tobe as follows: 3 feet. from the pround ) 2.00 0.4.5 ae 2 b0 mm, 8 feet from the ground )i2.2.000 44. 6p =e 3.10 mm. 16 feet: from the ground .3.1.°4) +. 4) oe 3.50 mm. 24 feet from the ground: J...04..02 3 ae a 3.25 mm. 40 feet fromthe ground. ...c2s2... «2:4 see 3.00 mm. 56 feet from the ground .«..s. Sa... se - eee 2.60 mm. 72 feet from the ground: 7. 2) 3 eee. ee 2.40 mm. A similar variation occurs in trees of all species. In a horizontal direction, at any height from the ground, the variation in length of fiber in any tree may be illustrated by the following figures from white spruce, 106 years old, at three feet from the ground: 1st annual ring surrounding pith.............. 0.85 mm. 10th annual ring fron pith?> 3) =. 5) ae Pele oO ae 30th annual ring from pith ..2). 5 25.4). . > eee 2.25 mm. 50th annual*ting from pithe 2.) ae 3.10 mm. 86th annual ring from ‘pith. 9.22) ae 3.40 mm. 106th. annual ring from pith.) > 3.0 eee 3.80 mm. These figures give an idea of the variation in fiber length that may be expected in any tree. The following figures, taken from various sources, are general averages; they may serve to indicate the variation in average fiber length according to different species. Coniferous Woods White spruce (Picea canadensis).........+++++++++++: 3.10 Black spruce (Picea mariana)........---++++++++eeess 3.00 Sitka spruce (Picea sitchensis)..........+-++s++1+++ss 3.50 Engelmann Spruce (Picea engelmanni)...........-++-- 3.00 Balsam fir (Abies balsamea)...... 2.01... 24 6-9 a ees 3.00 Grand fir (Abies grandis).22 3... -). - ae ee i one cee aaa 3.20 White fir (Abies concolor). ....... 2. +53 4s 3.50 Douglas fir (Pseudotsuga tarifolia)........++-++.+5+++ 4.50 Hemlock (Tsuga canadensis). <0....... «2 Uae eee 2.90 Western Hemlock (T'suga heterophylla)...........+.++-+. 2.80 Tamarack (Laria laricina). 3.0... os 53 9 = 2.80 Western larch (Larix occidentalis)...........-+++++-+: 2570 Jack pine (Pinus divaricata)........ 00.052 00ers ees 3.50 Red: pine (Pinus resinosa)........0.. 0540. epee ea ees 3.20 Longleaf pine (Pinus palustris).........+..+000++000- 3.70 Loblolly pine (Pinus teda)...........--+-.+ 5s see S200 S- Shortleaf pine (Pinus echinata).........-.+++++0++05: 3.70 White pine (Pinus strobus)..........+22 +2 ese sees eees 3.30 $1 PROPERTIES OF WOOD 31 Coniferous Woods Lodgepole pine (Pinus murrayana)................... 3.20 Western yellow pine (Pinus ponderosa)............... 3.60 Bald cypress (T'axodiwm distichum)................... 3.30 Redwood (Sequoia sempervirens)..................... 5.50 Non-Resinous Woods White ash (Fraxinus americana)..................-.. 1.20 Aspen (poplar) Populus tremuloides)............,..... 1.15 Cottonwood (poplar) (Populus deltoides).............. 1.30 PME WOOO (1 LG OMETICANG). 0... 06 oc kc ce ee cee 115 Pee Deb pire (OetlG PODYTIHECTA)............00ccecuce. 1.20 Menowepiren (betula lilea)..... oe. ee ede ek cee bk 1650 BMY OO PUMICE) 60. 206. bel eco. 1-20 PesimutaGastaned dentata) 0... ac. ssc cu ee ce ctacar 1.00 Tulip tree (Liriodendron tulipifera)................... 1.80 Cucumber tree (Magnolia acuminata)................. 1.30 Paeasorinay yes syloalica).:..:.. 268s... bee cl ek 1.70 Red gum (liquidambar styraciflua)...2..2.0.... 00000. 1.60 aT PPS CINEPICONG) «oi. rss. soos meen efeescssceae. 1,50 PSMA CCIISUCCIUITULIN ogee lo cw ev ned ec es es 1.00 Sycamore (Platanus occidentalis).................... 1.70 SOME PHYSICAL PROPERTIES OF WOOD. 20. Variation in Specific Gravity.—Table VI gives some phys- ical properties of certain woods when green. It will be noticed that the data for specific gravity and weight per cubic foot are given in a slightly different manner from the usual way of report- ing these figures. By multiplying the weight per cubic foot by 1+ 2, wherein x is the amount of moisture in per cent, expressed decimally, (calculated on the oven-dry wood) in the wood at which the weight per cubic foot is desired, the weight per cubic foot at any desired moisture content can be obtained. Thus, to find shipping weight per cord of green wood, say white spruce, it is first necessary to determine or estimate the moisture content. Assuming it is 80% of oven-dry weight (= at X 100 = 44.4% of green weight), multiply 21.8 (the weight of a cubic foot from Table VI) by 1 + .80 = 1.80; the result is 21.8 X 1.80 = 39.2 lb. = the weight of one cubic foot of green white spruce. The rough wood will hardly run more than 90 cubic feet of solid wood to the cord; so the weight of a cord of green white spruce is 39.2 X 90 = 3528 pounds. Had the moisture 32 PROPERTIES OF PULP WOOD $1 content been 100% of the oven-dry wood, the cord would have weighed 21.8 X (1 + 1.00) X 90 = 3924 pounds. The specific gravity varies in a tree, decreasing, in general, from the butt to the top of the tree. The presence of rotholz (an abnormal formation of wood in localized sections, due to strain or climate) in coniferous wood increases the specific gravity. It should be remembered that wood is not a solid material, since the cells of which it is composed are hollow; hence, a block of wood is a combination of real substance and of air space. The wood substance itself has a specific gravity of approximately 1.54, but.an actual block of wood, as shown in Table VI, has a much lower specific gravity. In fact, the figures show that in ordinary pulp woods, more of their volume is made up of air space than of actual wood substance. 21. Moisture in Wood.—When green wood is allowed to become thoroughly air dry, it still contains a certain amount of aaa ako cee & Per cent Moisture 1) 10 20 30 40 50 60 70 80 90 100 Fer cent Relafive Humidity Fig. 24.—Curve Showing the Relation between Moisture in Wood and Moisture in Air Surrounding the Wood. moisture; but the amount (percentage) of this moisture varies, according to the amount of moisture (relative humidity) of the air surrounding the wood. Fig. 24 is a curve showing the percentage of moisture variation in wood corresponding to different relative humidities of the atmosphere surrounding it; the curve is based on average figures found for several different kinds of wood, at a temperature of about 70°F. | a $1 PROPERTIES OF WOOD 33 TABLE VI SOME PHYSICAL PROPERTIES OF CERTAIN WOODS, WHEN , GREEN! Meet or crear Load required to | Shrinkage in embed 0.444 inch | volume from volume and oven- Oiiwairht steel sphere to green to oven- ; E 4 its diameter3 dry condition Species : eons ai ft. | End | Side | Per cent of Gravity? Green Volume pounds Wiha h@nOUTUCE pris gies sh adie dass 0.35 21.8 300 280 13.0 Bist eS DEUCGIT als nak vo. :>|,. 0.38 PB 6 420 360 P13 ERGURO DEUCE Meera nia ches cit as ss 0.38 Ont 420 350 11.8 MT ka ODEUCE wae wig eile sce coe ee 0.34 21,2 430 370 tee Engelmann Spruce............... 0.31 19.3 250 240 10.4 LES Ean aie), Oys 7 Aa oe 0.34 alee 290 290 10.8 CATA SUIT ARE ot Oe Gate steles.s se 0.37 2a 420 360 10.6 VAIR LOR IIT Sr rert ents uieyacsie sus ook > 0.35 21.8 380 330 10.2 OSTA UTD as i ee 0.45 . 28.0 510 470 12.6 Eem)logk wie ieee Gacienicse8 guar 2 0.38 PN Fi 510 410 10.4 Western HemlOcke sc. .ecccussns ss ss 0.38 Diet. ¥ 540 430 Te UNSTaR Re. 3 8 ot Acs kate ee ee 0.49 30.5 400 380 13.6 NVCSLOLE MATCH Aeicet. ae Loa sievisle sy dist ons « 0.48 29.9 470 450 132 MD ACKP PING ei che well sues in Nae ane 0.39 24.3 380 370 10.4 Red Pine...... 7: et ede a re 0.43 26.8 360 340 11% Mon leaipmine mane: one sciclsd ssc > OR5o 34.3 550 590 1273 Woblollys Pines «wes: sdteiese sees.) 0.50 oleae 400 450 12.6 Shortiogt Meine ers cca ak s.508 108s wo5 « 0.50 Ble2 490 560 12.6 NMR oA GTS. PRES I re 0.36 22.4 300 300 eke TodgepolejPineso.. 02.565. .000. 0.38 2ons 320 330 Wah ti Westerney chow Eine .fa6 cas cele 0.38 2337 310 320 10.0 Baldueyvpness acre sees eke. se. | 0.41 25.6 470 380 10.7 IVVIaL GMA alIpieRetere ye sicle she dieses ss 0.52 32.4 1000 900 12%6 PAS TOH ME ODT Maelo ae 66 6 iSite ls aos,» 0.36 O20 4 270 320 ihe! REOUCOULWOOU sere face os aes siete ss 0.37 Dorm 380 340 eb al SHEA W OOO meres ciety 6 fete ces ee 0.33 20.6 280 250 15.8 IPA Cre DINO eck sah okies so seie sls 0.47 29.3 400 490 16.3 Wellaweisl Lehto ci. tele ie screws sis es 0.54 33.0 820 740 16.8 LEE ion oe 6 Moko S Ce eC aoe ae ene 0.54 33.6 950 820 16.2 SOS UL taeienrin teicas es easicG aue Hes) oe orc 0.40 25.0 530 420 LRG ON eeifs) MAA e ee aha Rie ee 0.37 Zoi 420 340 11.4 TOWGUI DERE! NEG ieeiectek lacs sb e-8 5 0.44 27.4 600 520 13.6 Bidck Cum .:, >a s> ) 648-70 eae rs mates Aspen (poplar)........... 0.34 ame 57.2519 26.83 Ae ee ? Not all from the same sample analyzed for cellulose and lignin. §1 CHEMICAL PROPERTIES OF WOOD 43 Schwalbe and Becker give the following table of the principal constituents of wood and some products of chemical treatment: Calculated on dry substance Pine, | Beech, | Birch, Bucs; Pinus | Fagus | Betula Poplsr, Picea | ‘] Tee b : Populus excelsa, my hd He bias tremula, o% tris, tica cosa, oO ‘ % % % ; ISA aot oae.8 Cth Sulack AE OE ee Ona 0.39 Alle, al 0.39 0.32 Cane RPNerrextractscs che Ga tic ccs css 0.78 1.92 0.31 O87 1.08 Fat, wax, (6) Aleohol extract.............:. 152 ese: 1.47 1.09 2.08 ANG resins (Cc) Sum Of (a) and-(6)............. 2.30 3.45 1.78 1.80 3.16 (d) Alcohol-benzene extract....... 2.34 Sr ee 1.20 1.68 2.87 Misti vlevaliieumer eres = of aes eke legacies cae 2.36 2.20 2.96 it Oh laf Pectin (according to von Fallenberg).......... ik BPs ith lal it eee 1.61 1.82 Acetic acid (Schorger’s method).............. 1.44 1.40 2.34 4.65 4.17 IDTOLOUNMEINE Ole Or tiaan eines. fos abc nd passe 0.69 0.80 1.05 0.74 0.63 PUriurohs..', ci... - ad GG ae ee 7.49 7.49 | 14.90 | 16.08 | 12.64 LE SILOS S ioieitielrdeaceicve eels ceva’ LTSSO"} 11027 224 786a|e 27207 23.75 Pet VI DentOSAM mien tele koe tele bocsle lle aie secs 3.00 Zale T02 0.84 0.72 Cellulose containing pentosan................ 63.95 | 60.54 | 67.09 | 64.16 | 62.89 Pentosnnumcellulose.. 704.6564. vs ec been 9.55 | 11.27 | 20.35 | 29.40 | 24.94 Cellulose corrected for pentosan.............. 57.84 | 54.25 | 53.46 | 45.30 | 47.11 Ug I EE REMC EMO Fase oe oon sc wo oon Sta eo sae 28.29 | 26.35 | 22.46 | 19.56 | 18.24 The cellulose content may vary by as much as 4 per cent in different parts of the same tree, and the resin content by 8 to 25 per cent of the amount present. Also, there is a greater proportion of cellulose in old trees than in young ones. The percentage of lignin is nearly constant throughout a tree. The variation in cellulose content is important, since, as this quantity decreases, there is a greater amount of impurities to be removed; hence, the yield of pulp must decrease. 28. How the Tree Grows.—It was shown in Art. 9 how trees grow, i.e., form wood substance. The first step is the combina- tion of water and carbon dioxide to form sugars. This sugar factory is principally in the leaves, where the green chlorophyl assists the reaction. It is generally believed that an inter- mediate product is formaldehyde CH,0, and that these molecules combine with one another, polymerize, as the chemists say, to form sugars, starches, gums, cellulose, lignin, etc., by different arrangements of this versatile substance. The intermediate products are mostly colloidal, and they form wood substance by absorption from the cambial sap (which carries them) by the cellulose already formed; that is, they may be said, for want of 44 PROPERTIES OF PULP WOOD §1 a better explanation, to stick to the surfaces of the cellulose cells or fibers. According to Abrams, plant growth proceeds by | the division of each cell in the cambium, giving two cells. The partition between the new cells is the middle lamella, adjacent to which, other walls are formed. With such a variety of sub- stances present, and in various stages of formation, it will be seen that the chemistry of wood is a very complex subject; in fact, new developments and discoveries make it necessary, quite frequently, completely to alter some of our conceptions. 29. Products of Destructive Distillation—When wood is subjected to destructive distillation, the principal products are charcoal, water, gases (mostly COs, but with some that are combustible), wood tar and tar oils, acetic acid, and methanol (wood or methyl, alcohol). All the methanol and much of the acetic acid, it is stated, comes from the lignin. That acetic and formic acid radicals are both present in wood, so that the acids are formed by mild hydrolysis, is shown as the result of treating wood with boiling water. Based on dry wood, there was found: Kinp oF Woop Acretic AcIp Formic Actp Spruce 1.17-1.53% 0.22% Pine 1.24—-140 0.205 Birch 3.15 0.175 The action of 10% sulphuric acid, at 110°C., produces acetic and formic acids; distillation with 12% hydrochloric acid pro- duces furfurol;! this is believed to originate with the pentosans. 30. Treatment of Wood for Pulp Making.—Stated briefly, the chemical processes of pulp manufacture produce, in solution, the soluble substances formed by the hydrolysis of the carbohy- drates and lignin; also, acids and their salts are formed by hydroly- sis and oxidation of wood substances, and are in part neutralized by lime and soda. Fats and resins are rendered soluble by alkaline treatment; they are only partially affected by the sulphite process, although residues are partly removed from the pulp by careful washing. The various constituents of wood will now be considered in the order of the relative amounts present; the action of the cooking treatment will be mentioned in this Section and the manufacturing operations will be discussed in greater detail in other parts of this volume. 1 See Glossary for definitions. §1 CHEMICAL PROPERTIES OF WOOD 45 CONSTITUENTS OF WOOD IN DETAIL CELLULOSE 31. Kinds of Cellulose.—As_ previously stated, the most important constituent of wood is cellulose. This substance forms the frame work of the tree; it also forms the interwoven fabric of the sheet of paper, when it has been separated from the other substances and reduced to individual fibers. The physical appearance of cellulose fibers, and some of the other properties also, varies in different trees; but the chemical characteristics, while approximately the same for cellulose from different sources, are not really constant. The chemical wood pulps obtained in the commercial processes are not absolutely identical with the so-called normal cellulose, which is represented by purified cotton, because wood pulps always contain a small percentage of the lower carbohydrates. But, with careful man- ipulation, it will undoubtedly be possible to isolate from any wood a cellulose that will be absolutely identical with the cotton cellulose. In the present state of the art, all fibers are cellulose to the papermaker. It is important to remember that cellulose pulps, on account of being somewhat affected by chemical treat- ment, are by no means identical. No doubt the future will see important developments, as a result of much needed chemical] study of this important and interesting substance; for the present, the matter can be presented only in the light that has been shed by painstaking investigation, and the mind should be kept alert and open to the further revelations that are sure to come. 32. Because of the association of cellulose with other substances present in plants, as fatty and waxy bodies, colloidal carbohy- drates, etc. (‘‘pectic’’ compounds), and lignin, the fibrous parts of grasses and reeds are known as adipo-celluloses, cuto-cellu- loses, and pecto-celluloses, while trees have ligno-celluloses. It has not been definitely proved, unfortunately, whether these substances are chemically connected or only physically associ- ated with cellulose ; this is an important point, since it is neces- sary to isolate the cellulose by chemical means in the manufacture of pulp by the sulphite, soda, and sulphate processes. 33. The Cellulose Molecule.—The structure of the cellulose molecule is still a matter of controversy, although from analysis, it can be expressed empirically as (CsH1005)n. In this formula, n is 46 PROPERTIES OF PULP WOOD $1 unknown; it is known to be very large, however, and has been given values that make the total molecular weight of the mole- cule between 5000 and 6000, or perhaps even greater. Note that the unit radical, Cs>5H00;, may be written 6CH,O —H.,0O; that is, it is equivalent to 6 molecules of formaldehyde minus 1 molecule of water. Since the molecule contains twice as many hydrogen as oxygen atoms (the same proportion as in water) and these are associated only with carbon, cellulose is called a carbohydrate, j.e., a hydrate of carbon. Based on its chemical behavior, several structural formulas for cellulose have been proposed, Irvine’s being perhaps the best: CH.OH CH————_O _cH_o—¢H—cHon—cHon— H bnoH O buou bu | du -0-—CH—CHOH_—-CHOH—CH—CH—CH,0H du.on Beet. However, Hibbert’s formula, CH,0OH cH_dH_o ha A~ es CHOH—CHOH—CH appears to satisfy the requirements of many reactions of cellulose. 34. a- and 6-Cellulose-—The outstanding characteristic of true cellulose is its resistance to the action of ordinary chemical agents, to atmospheric conditions, and to bacteria and fungi The inertness of the substance is the basis for its separation from the wood by pulp-making processes; and it is the reason why paper, well made, remains in perfect condition for centuries. There are, however, some enemies strong enough to break up or modify the cellulose molecule. The highly resistant cellulose of wood, referred to above as very similar to, if not identical with, the cotton cellulose, is known as a-cellulose. In addition to this, wood contains less resistant celluloses, which can be dissolved from wood by means of strong alkali. One part of this dissolved cellulose can be $1 CHEMICAL PROPERTIES OF WOOD 47 precipitated with acid and is called 6-cellulose; another part remains in solution and is called y-cellulose. Since the commer- cial processes for the isolation of cellulose are more severe than analytical methods, large amounts of the less resistant celluloses are removed in commercial processes. This accounts for the discrepancy between commercial yields and laboratory results of cellulose determinations, which may amount to 10%-20 %. 35. Action of Chemicals on Cellulose.—The chemicals used in the pulp mill are in dilute solution; they have but little effect on true cellulose. If, however, cellulose is treated with sodium hydrate, in 17%-18% solution, mercerization takes place (see Section 3, Vol. II); and, on washing out the sodium hydrate, the cellulose will be found to be hydrated, differing from the original cellulose in that it takes up more moisture and has also, generally, a higher absorbing power than cellulose. Hydrated cellulose resembles the original cellulose; they both have low reducing power, but hydrated cellulose is more easily hydrolyzed. A substance similar to this cellulose hydrate is formed by prolonged maceration in water, when hydrated or slow stock is formed in the paper-mill beater. The action of water at high temperatures is somewhat different, in that it tends to hydrolyze cellulose, breaking it down into carbohydrates of less molecular weight, such as gums and sugars. 36. The action of acids depends upon their strength. Strong sulphuric acid, as used in the manufacture of parchment papers, causes a hydration of the cellulose, similar to the reaction with strong alkali; further, the acid has a hydrolyzing effect on the cellulose, transforming it partly into so-called hydro-cellulose and, ultimately, into dextrose. Hydro-cellulose is also formed under the influence of weak acids; it does not have the fibrous structure of cellulose, and it has a strong reducing power. Strong nitric and sulphuric acids together form nitrates, ranging from celluloid to powerful explosives. Cellulose acetates are the basis of some photographic films, ete. 37. Strong oxidizing agents, as chlorates, hypochlorites at high temperatures, etc. convert the fibrous cellulose into the structureless oxycellulose, which is quite active chemically, but is useless to the papermaker. Cellulose and hydrated cellulose have little or no reducing power on Fehling’s solution (see Section on Refining and Testing 48 PROPERTIES OF PULP WOOD §1 of Pulp). Hydro-cellulose and its hydrates have distinct reduc- ing power. Oxycellulose and its hydrates have strong reducing power. 38. Cellulose is insoluble in ordinary solvents and regents. It is Soluble in 72% sulphuric acid, and also in ammoniacal copper compounds (as in the manufacture of Willisden goods), zine chlo- ride and hydrochloric acid (fiber vulcanizing process), and sodium hydrate and carbon disulphide (viscose process). Nitrocellulose, which is soluble in certain organic solvents, is basis of the Chardonnet silk process, explosives, ete. The fact that cellulose may be affected by both acids and alkalis is important to both the pulp maker and the paper maker. In the pulp mill, this action makes it necessary to exercise very careful control of the strength of acids and alkaline cooking liquors and of the temperature in the digester, since chemical action is greatly accelerated by heat. In the paper mill, ‘the cooking of rags is an alkaline treatment, and the bleaching of stock is an oxidizing action; either may attack the fiber, if the concentration or temperature of the cooking liquor is too high, or if acid or bleach residues remain in the stock, since at the temperature of drying, these may affect the quality of the paper. 39. Some Properties of Cellulose.—Cellulose is a colloid; that is, it gelatinizes by treatment with water and exposes a large surface in proportion to its weight. Thus it absorbs substances by what is, in effect, a form of solution, and it also adsorbs (holds on its surface) substances, because of its physical nature. The specific gravity of cellulose may be taken as 1.54; its specific heat is 0.366 (dry); its calorific value is 4223 Cal. (16,758 B. t. u.); its dielectric constant (dry) is 6.7 at 20°C. and 7.5 at 70°C. The dielectric density is about 500,000 volts per centimeter which accounts for the high insulating power of paper. In the presence of water, cellulose acts as an electrolyte. Certain filamentous fungi (thread-like molds) that are present in soils can dissolve cellulose, thus returning mature plant sub- stance to nature once more in the growth cycle. Some bacteria also dissolve cellulose. The by-products of such action are decomposed into carbon dioxide, methane, and hydrogen. — $1 CHEMICAL PROPERTIES OF WOOD 49 LIGNINS AND LIGNO-CELLULOSE 40. Molecular Formulas for Lignin.—Closely associated with cellulose, probably combined with it by a weak chemical connec- tion, is lignin, the combination being called ligno-cellulose. Since lignin and coniferyl alcohol have somewhat analogous reactions, Klason has considered lignin to be a condensation product of several molecules of this alcohol, with the formula C4oH 42011. But lignin is hardly a uniform compound, and recent researches by Klason appear to indicate at least two lignins in spruce—a-lignin Ceo2Ho207 and 6-lignin Ci9His0¢, the former representing about 63% and the latter 37% of the total lignin. Without prescribing the nature of the bond, Cross and Bevan suggest the following structural formula as satisfying best the reactions that lignin is known to give: CO O O OH ( Indefinitely vas Vas BANG Va connected to HC: CH—(CH::CO),—HC CH-CH-CH.CH agent ea ‘an HC O CH;0-HC CH-OCH; OH | £B-cellulose ew, . CH2 CO Any formula for lignin should make provision for the follow- ing constituent radicals: methoxyl, acetyl, hydroxyl, and perhaps arabinose. The hydroxyl may exist in two states of combination, as phenol or as aliphatic alcohol. Pyrocatechin, protocatechuic acid, and vanillin, have been obtained by the degradation of lignin. Klason has found coni- feryl alcohol, and Pictet and Gaulis isolated eugenol from the products of the vacuum distillation of lignin. All these com- pounds might be derived from a compound of the general formula given herewith, and present-day lignin formulas are, for the most part, based on the polymerization of such a body. Nuc—cZ_ocH, The two sources of raw material used in the investigation of lignin, are waste sulphite liquor, from which the ligno-sulphonic acids are precipitated, often as 6-naphthylamine salts; and the residues left after the digestion of wood with strong mineral acids. 50 PROPERTIES OF PULP WOOD $1 When one pauses to consider that the actual structural formula for water is even now a matter of controversy among chemists, it is easy to see that the structure of the lignin molecule is a difficult and complex problem of organic chemistry. 41. Formation of Lignin.—The formation of lignin takes place in young tracheids during growth. There is more lignin in wood of slow growth than in wood of quick growth. Since lignin and coniferyl alcohol have somewhat analogous reactions, some authorities assume that lignin is derived by condensation and oxidation of four molecules of this alcohol. é Lignified cell walls are disintegrated by some bacteria and some fungi, as Penecillium glaucum, Meruleus lacrimans, etc. Animals can digest a part of the lignin in woody plants. 42. Effect on Lignin of Chemicals and Cooking.—In the alkali cooking process, the lignin is oxidized or decomposed, forming alkali salts of lignin acids. These acids may be at least partly precipitated from the alkaline liquors by acids, and they differ from each other in their solubility in aleohol. The sulphite process is explained by the fact that sulphurous acid is added to the unsaturated carbon atoms of lignin, with the formation of ligno-sulphonic acids, which are present in the waste liquor as calcium salts. Two ligno-sulphonic acid compounds have been separated from the waste liquor. The similarity of this reaction to the addition of sulphurous acid to aldehydes and ketones suggests the presence of free carbonyl groups = C = O, which — OH can add H.SO; and form = SG. 43. Detection of Lignin.—The presence of lignin is shown by several distinct color reactions: aniline salts give a yellow color; ferric chloride gives green; iodine, in potassium iodide, gives dark brown; ferric chloride and potassium ferricyanide (1: 1) gives dark blue-black; phoroglucin + HCl gives ared colored compound, which is not decomposed by water. Another charac- teristic lignin reaction is the yellow color produced by chlorine gas, which changes into a purple on the addition of sodium sulphite. The chlorine forms with lignin a lignin chloride CioH1sCl4O9, which is soluble in sodium sulphite and in alkali. Along with this reaction, an oxidation of the lignin occurs. The Maule reaction is a treatment with potassium permanga- nate and hydrochloric acid; the washed material, on adding ammonia, gives vink to brown. §1 CHEMICAL PROPERTIES OF WOOD 51 The methoxyl content is also characteristic of lignin, and may be determined by distillation with hydriodic acid. OTHER CARBOHYDRATES 44, Soluble and Insoluble Carbohydrates.—Owing to the manner of formation, it is to be expected that wood will contain a variety of carbohydrates. Besides the highly inert cellulose, there are two general classes: those carbohydrates that are insoluble in water, but are soluble in dilute acids and alkalis; and those that are soluble in water. The first class comprises the hemi-celluloses. . The soluble carbohydrates are mostly sugars, such as mannose, arabinose, galactose, xylose, etc. Besides those present in raw wood, the cooking process forms sugars by hydrolysis of certain gums; as hexoses from hexosans (C.gHi003), and pentoses from pentosans (C;H;0,),, being unknown in each case. The hexoses include the fermentable sugars present in sulphite waste liquor; they may amount to 13.3% of the wood, of which 61%- 75% is fermentable. These sugars are destroyed by high tem- peratures at the end of the cooking, and the fermentable sugars go first. 45. The Hemi-Celluloses.—The hemi-celluloses are more easily hydrolyzed by dilute acids then the true celluloses, and are thus converted into the sugars found in the waste cooking liquors. ‘The principal hemi-celluloses in wood are pentosans, - frequently accompanied by hexosans, such as mannan and galactan. The most frequent pentosan is xylan, or wood gum, which gives xylose on hydrolysis, usually with small quantities of arabinose. Distillation with 12% hydrochloric acid gives methyl-furfurol, as well as furfurol, thus indicating that methyl pentosans are also present in wood. The amount of these substances varies between the hardwoods and the conifers, as a class, but is fairly constant for trees in each class. For example, pentosans in hardwoods are about 22%-26 % and in conifers 8%-9% of the dry wood; hexosans are about 3%-6% and 13%, respectively. According to cooking conditions, these gum-like carbohydrates are changed to sugars or saccharinic acids. In the sulphate 52 PROPERTIES OF PULP WOOD §1 process, methanol, methyl sulphide, and methyl mercaptan are also obtained. Fir is said to give more mercaptan than spruce. 46. Fats and Resins.—Fats and resins in pulpwoods are important, principally for the trouble they cause. In long leaf pine, there is enough resin to make its recovery attractive for commercial use, by treatment of the chips. Mills using this wood and some European mills, recover rosin from spent sulphate liquor. In other conifers, the amount of resin is small, and it varies with the species; there is practically none in hardwoods. The resins in pulpwoods are of slightly varying composition, but are practically the same as common rosin (colophony), the principal constituent of which is the anhydride of abietic acid. Turpentine also is frequently associated with rosin, and it can sometimes be recovered from pulpwood. Cymene, or spruce turpentine collects on the surface of the condensate when the relief gases from sulphite digesters are run through a cooling coil. It is an oily liquid, of pungent odor, which is better removed, since it tends to contaminate the pulp, if allowed to go back into the liquor with the recovered sulphur dioxide gas. 47. Much interest has been shown in this subject lately, and investigations have shown that the total extract of wood by organic solvents, instead of being all rosin, is about half fat. It has been further shown that the fat, in the presence of resins, is the principal cause of rosin troubles in the paper mill. If freshly cut wood is extracted with ether and then with alcohol, the ether will contain most of the fats, and it will be more fluid and sticky than the darker alcohol extract, which will contain the solid rosin acids. The fats can be removed from both these extracts by treatment with petrolic ether. The fats are largely combinations of glycerine, formed from Sugars present in the wood, and oleic and linoleic acids, probably formed from alde- hydes in the course of the sugar formation in the trees. 48. When wood is stored, changes take place in it, whereby the amounts of both the ether and alcohol extracts decrease. What is more important, these substances are changed by oxidation to harmless products. This is an argument for well-ventilated storage of wood, and for drying chips by hot air. . There is more fat and resin in pine than in spruce. Sieber gives: 7 CHEMICAL PROPERTIES OF WOOD $1 53 Seasoned wood Fresh wood . Fat (%) | Resin (%) Fat and Resin ( %) ote 0.50 0.48 2.54 ROME os ds eke 1243 | eect | 4.90 This investigator also found that only 4.2% of these substances was removed in cooking, while the cooking process removed 51.8% of the wood; and the bleaching process removed 15%; consequently, the percentage of fat and resin in pulp is higher than in wood, and the proportion of fat is also higher in pulp. Caustic soda will remove much of the resin, but it has a tendency to make the fibers yellow. In the paper mill, the resin particles seem to be coagulated by the insoluble fat; and since this is sticky (particularly so in summer), these lumps are caught on the Screens or are passed on to the machine. Here they may cause the paper to stick to the press rolls; or they may fill up the holes in the wire, or the pores of the felts. Mechanical pulp (groundwood) contains all the wood, except possibly a portion of the water-soluble substances, which may have been dissolved during driving or storing of the wood. The resin in paper made therefrom is less troublesome than resin that has been through the sulphite-pulp mill. Recent investigation on resins of Canadian woods gives results that may be summed up in the following table: RESINS IN CANADIAN PULPWOODS Per cent (based on oven-dry wood) ——— Ether Aleohol . (Soluble) eyasgey ee PACK EDIUCE .. 474...) 6. 0.3-0.4 0.3-0.4 0.6-0.8 DPRILEWSDTUCES, oc cr. ke 0.3-0.6 0.4-0.5 0.7-1.1 BORIMARE LT ee sks bss 0.6-0.8 0.8-1.2 1.4-2.0 BOPEATING! heii tiara. «ays 0 9c 0.9-1.5 0.5-0.8 1.42.3 The per cent of extract soluble in petrolic ether is higher for jack pine and balsam fir than for the spruces; the averages are: 54 PROPERTIES OF PULP WOOD $1 0.4—0.5 per cent for the spruces, 0.6—0.7 for balsam fir, and 0.8—1.2 for jack pine. 49. Waxes.—A wax-like substance that exists in the walls of wood cells is cutin. Suberin, a modification of cutin, impregnates the cellulose walls of cork cells (present in the bark of all trees), and it makes them and the bark quite impervious; it is a mixture of fats and glycerides of stearic and phelonic acids, together with cerin, or cork wax. The waxes cannot be oxidized or hydrolyzed. 50. Tannins.—Tannins are present in all woods, the bark con- taining the greater proportion of them. They also occur as solu- tions in the wood cells. A hot climate favors tannin formation. The bark of black spruce contains 7.2% tannins; Engelmann spruce, 12.6%-20.6%; Sitka spruce, up to 17.5%; Douglas fir, 7.2%; Eastern hemlock, 11%-13.1%; Western hemlock, 10%-— 14.4%; larch, 1.6%. Where wood is driven or stored in water, much of the tannin is extracted. Hardwoods as a rule contain much more tannin than conifers; birch bark has 10%; chestnut, about 15%; oak (smooth bark), 19%; quebracho, 50%. Tannins are also used as mordants in paper and textile mills and for inks. _Among other substances derived from bark, for medicinal or commercial use, are cascara, cinnamon, dyes, quinine, sassafras, etc. ‘These substances are useless to the paper maker, but they are interesting and often valuable as by-products. The bark of hemlock is the most important source of tannin from woods used in pulp making; oak bark is another important source, but oak is not a pulpwood. The bark is peeled off and sold by the cord; or, it is extracted with water and the extract is sold for its tannin content. The waste liquor from sulphite pulp, especially that derived from hemlock, contains considerable tannin material; this liquor, evaporated to 50% consistency, finds a ready market. Tannin value is dependent not only on the actual tannin present but also, somewhat, on non-tans, which impart certain qualities to leather. Chestnut wood is largely used in the Southern States for soda-pulp making, and the tannin is recovered by preliminary extraction of the chips. Chestnut wood is the principal source of tannin in the United States. 51. Miscellaneous Substances.—Among other substances present in pulpwoods are proteins (nitrogenous substances), coloring matters, turpentine, wood oils, and mineral matter. Turpentine can be recovered from the treatment of certain OO a a) ae Sl CHEMICAL PROPERTIES OF WOOD 55 pines; the other substances mentioned are too small in amount to require consideration by the pulp maker; they are practically all removed by the cooking process. EFFECTS OF PULP-MAKING PROCESS 52. All the Wood Not in the Pulp.—A brief statement will now be made regarding the effects of the pulp-making process on the various constituents of the wood, the purpose being merely to guide the student’s thought in the study of manufacturing processes. Reactions mentioned can only be stated as character- istic of classes of compounds. The student should be on the look out for new developments, and, where possible, should investigate these subjects on his own account. None of the substances in the bark need here be considered, since they are all removed with the bark in barking and cleaning the wood. Furthermore, some of the soluble materialsin the wood are partly dissolved by water during transportation and storage. Mechanical pulp (groundwood) contains all the wood except the bark and substances lost by solution. Some of the constitu- ents may change by oxidation during storage, and this change may continue, even after manufacture into paper. 53. Object of Chemical Treatment.—The object of the chem- ical processes is to remove all constituents of the wood, which would in any way diminish the value of the cellulose for making paper. Recent work has shown that the middle lamella is resolved, thus separating the individual cells. Either acid or alkaline liquor may be used for the cooking, and details of the processes are given in the later Sections. In so far as our present knowledge permits, the action of these liquors may be sum- marized as follows: 54. Results of the Processes.—Sugars are immediately dis- solved and may be destroyed under certain cooking conditions; sugar acids result from oxidation. Carbohydrates of higher molecular weight, as pentosans and hexosans, are hydrolyzed to aggregates of lower molecular weight, such as dextrins, which, in turn, and in company with other gums, are convertible into sugars, some of which are fermentable and are a source of ethyl alcohol. Acids, also, are formed from carbohydrates, due to the effect of oxidation. Acids, whether in the wood or produced during manufacture, 56 PROPERTIES OF PULP WOOD a, may dissolve as such, or they may form combinations with the bases present in the liquor; the resulting substance is usually soluble. Fats may be hydrolyzed to form acids, which, especially in the alkaline processes, readily form soaps (saponify). Resins are also saponified by alkalis; but, in the acid process, much of the fats and resins pass into the pulp. Substances of turpentine character distill off with the steam. Tannins, proteins, etc. either dissolve or are held in suspension after being released by the cooking. Lignin is changed to acids, which combine with the bases in the liquor. In the sulphite process, there is an addition of sulphurous acid to the lignin, as free carbonyl groups, =C = O, apparently without very extensive breaking down of the lignin. There is more drastic action in the alkaline processes, where, as. was shown in Art. 42, the lignin is resolved into at least two acids. The alkaline processes are applicable to more varieties of wood, than the sulphite process; and the drastic effect of the alkali in the soda process is modified by the development of the sulphate process, as will be shown in later Sections, where the action of the sodium hydrate in the former and of the sodium sulphide in the latter are fully explained. Some minor decompo- sition products are formed in both processes, due to the splitting off and conversion of side groups, as methoxyl—OCHs, etc. The removal of the lignin and gums leaves the cellulose practi- cally isolated. | The less resistant celluloses (8 and vy) are largely removed during cooking, due principally to the hydrolytic action of both types of cooking liquor. The extent to which cellulose itself is attacked depends on how drastic the cooking conditions are and, later on, upon the care exercised in the control of the bleaching operation. Bleached pulp may contain only 80%-90% a cellu- lose, showing that commercial pulps are uncertain mixtures. QUESTIONS (1) In what important chemical characteristics do (a) conifers differ from hardwoods? (6) spruces from pines? _ | (2) What is the most important part of wood to the paper maker? (3) Name a possible use for the sugar in wood. (4) With what substances is cellulose associated closely in trees and plants? ‘Name the compound celluloses so found. (5) Name three chemical agents that affect cellulose. ee $1 . BIBLIOGRAPHY —~=#57 BIBLIOGRAPHY Cellulose. Cross & Bevan: Longmans, London & New York, 1916. Paper Making. Cross & Bevan: Spon, London; Spon & Chamberlin, New York, 1920. Chemistry of Pulp and Paper Making. Sutermeister, E.: John Wiley & Sons, New York, 1921. Cellulose. Schwalbe, C.: Harz der Nadelholzer, Lieber, R.: Berlin, 1915. Kstimation of Cellulose in Wood. Johnson, B. & Hovey, R. W.: Pulp and Paper Magazine, 1918, p. 85. Waste Sulphite Liquor and its Conversion into Alcohol. Hagglund, E. (Trans. O. F. Bryant): Pulp and Paper Magazine, Dec. 6, 18, 20, 1920. Mannan Content of Gymnosperms. Schorger, A. W.: Journal Industrial and Engineering Chemistry, 1917, p. 748. Chemistry of Wood Decay. Rose, R. E. and Lisse, Martin Wm.: Journal Industrial and Engineer- ing Chemistry, 1917, p. 284. Chemistry of Wood. Schorger, A. W.: Jour. Ind. & Eng. Chem., 1917, p. 556. Chemistry and Structure of Plant Cells: Paper, Vol. 17 (1916) No. WW Guise ale) Chemical Composition of Spruce Lignin. Klason, P.: Pappers Tidning, 1917, p. 10. Determination of Lignin in Sulphite Pulp Wood, ete. Richter, E.: Pulp and Paper Magazine, 1914, p. 354. Notes on Oxycelluloses. Green, A. G.: J. S. C. I.,1 1904, p. 382. Also, Green, A. G. & Perkins, Pewee yams, 1., 1906, p. 652. Behavior of Wood and Cellulose in Presence of Sodium Hydroxide. Tauss, H.: J. 8. C. I., 1890, p. 883. Chemical Investigation of Wood Fiber. Grafe, W.: J. S. C. I., 1904, p. 1158. Pentosans of Lignified Fiber. Schulze and Tollins: J. S. C. I., 1892, p. 931. Furfural and Methyl Furfural Yielding Substances in Ligno-Cellulose. Fromherz, K.: J. 8. C. I.,-1907, p. 339. Wood Formation. Wislicenus & Kleinstuck: J. S. C. I., 1910, p. 268. Acetic and Formic Acids by Boiling Wood with Water. Bergstrom, H.: J. 8. C. I., ‘1913, p. 358. Action of Chlorine on Spruce Wood... | Heuser, E. & Sieber, R.: J. S. C. I., 1914, p. 71. Also, Z. Angew. Chemie., Vol. 26 (1913), No. 108, p. 801. 1Journal Society of Chemical Industry. References to this journal are principally to ab- stracts of articles in periodicals usually less accessible. 58 PROPERTIES OF PULP WOOD §1 Cellulose and Ligno-Cellulose. Cross, Go Fes Je 82CoL, 1914) p-11207; Chemistry of Sulphite Liquor. Kraus, H.: J. 8. C. I., 1906, p. 493. Constituents of Wood and their Economic Utilization. Konig, J. & Becker, E.: Z. Angew. Chemie., Vol. 32 (1919), p. 155. Chemical Constitution of Fir Wood Lignin. Klason, P.: Ark. Kemi. Min. o. Geol., Vol. 6, (1917) 21 pp. Chem. Zentralblatt, 1919, p. 92. Chemical Structure of Pine Wood Lignin. Klason, P.: Svensk Chemtidsskrift, 1917, pp. 5-16, 47-52. New Methods of Tannin Estimation. Lauffman, R.: J. 8. L. T, C., Dec., 1918. J. A. L. C. A., Vol. 14 (1919) p. 91. Destruction of Cellulose by Bacteria and Fungi. McBeth & Scales: U.S. Bureau of Plant Industry, Bul. 266. Behavior of Wood and Cellulose at High Temperatures in Presence of Water. Tauss,; Hos JS. Ca1., 1839; pi oie: Alcohol from Cellulose and Wood. Simonsen, E.: J. 8. C. I., 1898, p. 481. Conversion of Wood into Dextneca. Classen, A.: J. C. I., 1900, pp. 364, 1028. Mamlifachite of Tiextrose and Alcohol from Cellulose. Ekstrom, G.: J. 8. C. I., 1908, p. 32. Process of Converting Wood Cellulose. Ewen & Tomlinson: J. 8. C. I., 1904, p. 797. Hydrolysis of Cellulose and Ligno-Cellulose. Gallagher & Pearl: VIII International Congress Applied Chemistry, 1912. Cellulose, Abderhalden: Biochemisches Handlexicon, Band II, pp. 81-245. Chemical Constitution of Cotton Cellulose. Barthelmy, H.: Caoutchoue and Gutta Percha, Vol. 14 (1917), 9274- 80. New Cellulose Constants. Vieweg, W.: Pulp and Paper Magazine, Vol. 6 (1908), p. 237. Chemistry of Cellulose Cooking. Chambovet, A.: Paper, Jan. 26, 1921, (Trans.) from La Papeterie. Injurious Rosin in Sulphite Pulp. Johnsen, B.: Pulp and Paper Magazine, 1917, p. 577. Wood as a Raw Material in Paper Making. Johnsen, B.: Pulp and Paper Magazine, 1917, p. 333. Utilization of Waste Sulphite Liquor. Johnsen, B. & Hovey, R. W.: Forestry Branch (Canada) Bulletin No. 66. Effect of Chemical Reagents on the Microstructure of Wood. Abrams, A.: Jour. Ind. & Eng. Chem., Vol. 13 (1921), p. 786. $1 GLOSSARY 59 GLOSSARY Acetyl. The name of the radical CH;CO-—, considered to exist in com- bination in wood. Adipo-cellulose. A compound cellulose containing certain fatty sub- stances. : Alpha (a). Greek letter prefix used to denote the most resistant form of cellulose found in, or produced from, plants. Ammoniacal. Containing ammonia. Aniline. A basic substance recovered from coal tar. Its salts, as the sulphate and chloride, form a bright yellow color with lignin. Annual ring. The ring of wood added each year to the trunks and roots of trees. Arabinose. Asugar. Has a higher molecular weight than cane sugar. Bacteria. Minute living organisms that cause chemical action to take place in the tissues of plants and animals. Some are the cause of disease. Most of them are killed by chlorine. Bark. The rind or covering of the stems, branches, or roots of tree or plant. Beta (8). Greek letter prefix used to denote a less resistant form of cellulose. -cellulose is largely removed in making chemical pulp. Bisulphite. Name of the process, and of the liquor, by which sulphite pulp is produced. _ Bordered pit. An opening in the wall of certain fibers called tracheids, that appears to have a border or circle around it. Cambium. ‘The ring, or zone, of tender growing cells between the bark and the wood. Cell. One of the minute units, or elements, of various forms, of which plants are formed. Cerin. A wax-like substance found in the bark of certain trees. (de) Chardonnet process. Nitro-cellulose is dissolved in an organic sol- vent, extruded as a fine stream, and precipitated as a thread. Chlorophyl. The green coloring matter in leaves, which assists in the combination of water and carbon dioxide, to form substances from which wood substance is produced. Colloid. Resembling jelly or glue; uncrystalline. Starch is a typical colloid. Colophony. Rosin. Conifer. A tree of the pine family, so called from its bearing cones. Coniferous. Cone bearing; of, or pertaining to, the pine family. Coniferyl. An alcohol of high molecular weight. It is related to lignin and to vanillin, the active principle of the vanilla bean. It occurs in combination with glucose in the cambial sap of some conifers. Cross section. A section of a body at right angles to its length. Cutin. A wax-like substance found in plants in combination as cuto- cellulose. Deciduous. Not persistent, falling away, as the leaves of trees in the autumn. 60 PROPERTIES OF PULP WOOD $1 Dextrin (or deztrine). A carbohydrate with adhesive properties, formed by hydrolysis of starches, etc. It can be converted into dextrose. Dextrose. Glucose, or grape sugar CsH,.0,. It is important as a food stuff and as a source of alcohol. Dielectric. Resistant to passage of electricity. Diffuse porous. Said of wood whose pores are nearly uniform in size and more or less evenly distributed throughout both spring and summer wood. Epithelium. The somewhat modified parenchyma cells lining certain inter-cellular cavities, as the resin ducts. Fats. Compounds of glycerine and organic acids; these are glycerides. Fehling’s solution. A solution of copper sulphate, so prepared that the copper precipitated therefrom by reduction, is a measure of certain sub- stances in terms of dextrose. Fermentation. The process by which sugars are converted to alcohol. Fibro-vascular bundles. The strands that make up the framework of common herbaceous plants. . Filamentous. Thread-like (pertaining to fungi). Formic Acid. HCOOH, the first and strongest acid of the series of which it and acetic acid are most important. Formed by oxidation of methyl alcohol and formaldehyde, and by destructive distillation of wood. Formyl. The radical group HCO—. Furfurol (or furfural) (furfuraldehyde). A compound G,H,0-:CHO of which 4 carbon atoms and 1 oxygen atom form a ring, to which is attached the aldehyde group—CHO. It is a colorless, oily liquid of agreeable odor. Fusiform. Thick, but tapering toward each end. Fusiform ray is a medullary ray that is tapered at the ends. Galactan. A hexosan (CsH1205),, which on hydrolysis yields the sugar, galactose, which is fermentable. Gelatinous. Having the nature of jelly. Glyceride. See fats. Growth ring. Annual ring of growth; added to the trunk of a tree each year. , Gums. Carbohydrates that are sticky, like dextrin. Heartwood. The dead central portion of the trunk or of a large branch of a tree; often, but not always, darker colored than the outer sapwood. Hemi-cellulose. Non-fibrous carbohydrates that are comparatively resistant to hydrolysis. Hexosans. A sugar containing 6 carbon atoms in its radical, as galactan. Hydrated. A substance that has had a molecule of water added to its molecule. — : Hydrolysis. The splitting apart of a molecule in the presence of water, whereby the hydrogen unites with one part and the hydroxyl with the other. Lignin. The principal non-cellulose constituent of wood ; also called lignone. Ligno-cellulose. The combination of lignin and cellulose occurring in wood. It is broken down by hydrolysis and oxidation in isolating cellulose by the chemical processes. Linoleic acid. Occurs in combination with glycerine in linseed oil. It is this acid which enables varnish to absorb oxygen and form a hard film. © §1 GLOSSARY 61 Medullary ray. Plates of cellular tissue radiating from the pith to the bark. Mannose. A hexose sugar. Meruleus lacrimans. A fungus that destroys wood. Mercaptan. A mercaptan has the same formula as an aleohol when SH is substituted for the hydroxyl. Thus, ethyl mercaptan is C.H;SH and ethyl alcohol is C,H;0H. Mercaptans are ill-smelling substances formed in cooking wood by the sulphate process. Mercerization. ‘Treatment of cotton thread by sodium hydrate, whereby the thread becomes glossy. Methanol. Methyl, or wood, alcohol. Methoxy. The group CH;0-. Nitro-cellulose. A combination of cellulose and nitric acid. Mono-, di-, and tri- nitro-celluloses are formed. Non-porous. Said of wood whose fibers are all similar in size and shape, without pores or vessels. All coniferous woods are non-porous, while all broad-leaved trees have porous wood. Oleic acid. Occurs as the glyceride in olive oil; it causes rancidity. Oxycellulose. A structureless substance, formed by drastic action of oxidizing agents on cellulose. Parenchyma. Soft, more or less thin-walled, cellular tissue of plants, - usually containing living protoplasm in growing parts of the plants. Pectin. Insome plants, the principal non-cellulose constituent ; present as pecto-cellulose, corresponding to ligno-cellulose of wood. Penicillium glaucum. A mould that grows on moist wood. Pentosans. Carbohydrates of the general formula (CsHsO,4)n, which yield pentoses (sugars of the formula C;H,.0;) on hydrolysis. Phloroglucin. An organic compound that gives a reddish coloration with lignin. Piciform pits. Small pits in ray cells, as in spruce. Pit. An opening or depression in a cell wall or fiber. Pith. The softer, central part of a twig or stem. Pith flecks. Dark marks in wood due to cavities made by the larve of certain insects working in the cambium. Polymerize. To form a substance of higher molecular weight by the union of two or more molecules of the same substance. Pores. The large openings, or vessels, which occur in the wood of broad- leaved trees. Proteins. The constituents of plants and animals which contribute nitrogen to the food stuffs. Protoplasm. ‘The living matter of plant cells, similar to flesh in animals. Ray. Short for medullary ray. Ray cell. A cell of a medullary ray. Ray tracheid. A tracheid, i.e., a cell of bordered pits, found in the medullary rays of some coniferous woods. Resin. A substance found in trees, or prepared synthetically, which has the properties of rosin. Resin cell. A cell that secretes resin. Ring. The annual growth, or increment, of a tree. Ring-porous. Said of wood whose large pores, or vessels, are collected 62 PROPERTIES OF PULP WOOD $1 into a row or band in the spring growth of each annual ring; this is one of the distinguishing features of certain broad-leaved trees. Rosin (colophony). The hard substance left after the distillation of turpentine from the oily sap exuded by certain pines. Principally abietic acid. Used in sizing paper, making soap, ete. Rotholz. A darker colored, denser, and harder part of one or more annual rings which sometimes occurs in coniferous woods. Saccharine. Relating to sugar. Saccharinic acids are formed by oxida- tion of sugar. Sapwood. The living outer portion of the trunk or of-a large branch of a tree, lying between the heartwood and the bark; or, if no heartwood is present, all the wood of the trunk or branch of a tree. Scalariform. Having markings or structure suggestive of a ladder. Soda process. The process of making soda pulp; the principal chemical used in the cooking liquor is sodium hydrate, derived from sodium carbonate, or soda ash. Spirals. A term applied to the helical thickenings of the tracheids or vessels of certain woods. Springwood. The wood produced early in the growing season of each year, characterized by larger openings and with thinner walls in the tra- cheids, fibers, and vessels than the later growth (summerwood) of each annual ring. Starch. The name of a series of carbohydrates of the same general formula as cellulose (CsHioOs)n. Starches are non-fibrous and differ considerably, according to their source. Grains are principally starch. Stearic acid. The acid whose glyceride makes up many hard fats. Sugars. Carbohydrates of comparatively low molecular weights; they have a characteristic sweet taste. Suberin. A modification of cellulose, allied to cutin, contained in cork. Sulphate process. The process of making sulphate pulp; the principal chemical used is sodium sulphate. Sulphite process. The process of making sulphite pulp; the principal chemical used in the cooking liquor is calcium bisulphite. Tangential section. A longitudinal section of a body at right angles to one of its radii, as made by slicing off the outer part of the trunk of a tree. Tannins. Substances that have the property of hardening hides in the production of leather. Toothed. With teeth or short projections. Trachea. The pores or vessels as in the wood of broad-leaved trees. Tracheids. The long, narrow cells of which coniferous woods are largely composed, characterized by the presence of bordered pits. These cells, which are commonly called fibers, are the important part of wood used in papermaking, Transition. Change, as from springwood to summerwood. Transverse. Said of a wood section made at right angles to the axis of the trunk or stem; across the grain, or cross cut. Traumatic. Caused by wounding or bruising. Trunk, The main stem of a, tree. $1 GLOSSARY 63 Tylosis. A growth, frequently exhibiting repeated cell division, intruding within the cavity of a duct or vessel from a contiguous growing cell. Uniseriate. In one row or series. Veins. Threads of fibro-vascular tissue in a leaf or other part of a plant. Vessel. One of the segments of the tubes that extend vertically through- out the wood of the broad-leaved trees. Wood. The hard part of the stem of a plant lying between the pith and the bark. Wood elements. The cells, or units, making up the wood. Wood fibers. Long, slender cells, with thick walls and narrow cavities, which make up the body of the wood of broad-leaved trees; these are the important part of the wood used in papermaking. Wood parenchyma. Cells, or elements, of wood, containing living substance (in the sapwood), and extending end to end. They frequently contain starch or oil. Xylan. The pentosan from which the sugar xylose is derived by hydrolysis. PROPERTIES OF PULP WOOD EXAMINATION QUESTIONS (1) What determines the value of a plant as raw material for pulp making? (2) (a) How does the structure of other fiber-producing plants differ from that of wood? (b) Which give the highest yield of fiber? (3) Name some of the characteristics by which a specimen of wood may be identified (a) with the naked eye; (6) using a micro- scope. (4) (a) Of what elements or parts are coniferous woods composed? (6) How are the different elements arranged in the wood? (c) When wood is cooked, why do the fibers separate from one another? (5) How could you distinguish (a) a resinous from a non- resinous wood? (6) poplar from birch? (ce) spruce from fir? (6) What is the approximate average length (a) of coniferous fibers? (b) of fibers of broad-leaved trees? (c) Do fibers differ in length in the same log? (d) if so, how? (7) (a) Which is the stronger, wet wood or dry wood? (6) In general, which is the harder, a light wood or a heavy wood? (8) What are the meanings of the following terms: (a) annual ring? (b)cambium? (c) heartwood? (d) sapwood? (e) pore? (f) resin duct? (g) springwood? (h) summerwood? (2) vessel? (9) How does the amount of moisture in a piece of wood vary if the wood be taken from a place where the air is dry and placed where the air is moist? (10) Find the freight charge, at 17 cents per hundred pounds on a car containing 16 cords of white spruce, averaging 92 cu. ft. of solid wood and moisture content equal to 90% of the oven-dry weight. Ans. $103.65. §1 65 66 PROPERTIES OF PULP WOOD $1 (11) What are the important chemical constituents of pulp- woods? (12) Why is paper that was made centuries ago still in good condition? (13) What occurs when wood is cooked in a pulp mill? (14) What substances in wood are converted into sugars by hydrolysis? (15) Why is wood resin troublesome in the paper mill? SECTION 2 PREPARATION OF PULPWOOD By S. ROY TURNER, B.Sc. INTRODUCTION 1. Delivering Wood to Mill.—This Section deals with the handling and preparation of pulpwood from the time it reaches the mill until it is turned over as blocks, for the manufacture of mechanical pulp, or as chips, for the manufacture of chemical pulps. Wood may be delivered to the mill in any oné of the following ways: (a) Long logs, from 8 feet upwards in length, which have been cut in lumber camps and floated long distances to the mill. (b) Logs formed into rafts on the ocean, the large lakes, large rivers, etc. (c) ‘Farmers’ wood,” which is usually 4 ft. long and is either peeled or unbarked. This class of wood is cut by farmers, piled on a steep river bank (if cut near a mill) until high water comes, then pushed into the river, and floated to the mill. See (e) below. (d) Long unbarked logs, similar to class (a), piled about 9 feet high on flat cars and delivered at the mill siding, where the side braces are cut and the logs skidded (slid) into the mill pond or stored in piles in the mill yard, to be used as required. (e) Short wood, termed ‘car wood,’’ from 24 to 48 inches long, depending on the mill requirements, barked or unbarked, and delivered on cars at the mill siding. Farmers’ and settlers’ wood is usually delivered by them along a railway; it is then shipped by rail to the mill. (f) Wood, usually in 4-foot lengths, frequently barked by dealers and delivered to barges, schooners, or steamers. §2 1 2 PREPARATION OF PULPWOOD §2 2. Measurement of Pulpwood.—The solid volume in a stand- ard cord is assumed to be 95 cubic feet, although it actually may vary from 88 to 95 cubic feet, depending on the length and diam- eter of the wood, number of crooks, knots, etc., and whether it is rough or barked. Accordingly, the actual solid volume in a. cord may be from 66% to 74% of the volume of a standard cord of 128 cubic feet. When calculated from the board feet in timber, as estimated by the various log rules, a cord is generally assumed to be equivalent to 500 board feet. ee Green spruce weighs around 4,300 pounds per cord, while green balsam weighs around 4,500 pounds. Dry peeled wood weighs about 3,300-3,500 pounds. The moisture does not of course change the amount of fiber in the wood. The weight _ varies, however, with the sea- son in which the wood is cut, the length of time in storage, etc., since these factors change the moisture content, but do not, of course, change the amount of fiber in the wood. However, the weight and quality of the fiber are very seriously affected by fungi, Chie Grinleroom ond the fiber is often com- Mechénical Pulp pletely destroyed, leaving only a mass of punk. There Chip Grusher is a present day tendency to buy wood by weight of dry PIAGRAM OF Woop PREPARING OPERATIONS Log Fond, Cars, orlog Sforage Log Haul-up Slasher Block File Prum or Knife Barkers Block File Chip Screens Kepse Pemers fiber, and considerable pro- Boiler House : ‘ ‘ ‘ Chip. Bins gress is being made in this or ° ° ° ° Chemical Pulp direction. While this re- eee quires sampling and testing for moisture, it is far more sensible than the common practice of buying by volume, which may be made up of fiber, punk, or air. : When wood is bought in log lengths, the diameter and length are measured, and the contents in board feet (1 board foot is 1 ft. long, 1 ft. wide, and 1 in. thick and equals 7sth of a cubic foot) is found by means of tables computed for that purpose. Or the contents in board feet is found by one of the several “log rules;”’ this may be converted into cords by multiplying the number of §2 THE CUT-UP MILL 3 thousands of board feet so found by 2. Thus, if the result obtained is 17,250 feet (board feet), the number of cords of unbarked wood required to make this is 17.25 * 2 = 34.5 = 345 cords. In other words, a standard cord, 4’ x 4’ x 8’, is generally considered to be equivalent to 500 feet, board measure; as calculated for rough logs. 3. Diagram of Wood Preparing Operations.—The diagram, Fig. 1, shows very clearly the course of the wood from the log in the pond or storage to the grinder room or the chip bin. This diagram will be appreciated better after the reader has finished studying this section, and he will do well to study it then. THE CUT-UP MILL 4. General Arrangement.—The general arrangement of a cut-up mill usually includes a log haul-up, or jack ladder, a slasher, a system of conveyors (for conveying the cut logs, as wanted, and the refuse to the boiler room), and the driving element, which may be a motor, a steam St or a hydraulic turbine. Braie2: 5. In Fig. 2 is shown a very well laid out cut-up mill; it includes one parallel log haul-up, one five-saw slasher, two barking drums, two bark presses, and a system of conveyors to carry the blocks through the process. The logs are hauled from the river by means of a four-strand parallel log haul-up H, slashed into blocks (usually 2 ft. or 4 ft. long) on the 5-saw slasher S, and automatically discharged into conveyor 1, carried to conveyor 2, and thence to conveyor 3, 4 PREPARATION OF PULPWOOD §2 which distributes the blocks between the barking drums A and B. The blocks are discharged from the drums onto conveyor 4. A man is stationed at 5 to haul poorly barked blocks off conveyor 4 and on conveyor 2, which allows them to go through the drums again. The barked blocks continue along on conveyor 4 and are dumped on conveyor 6, to go direct to the wood room or storage pile. The bark that is discharged from the drums drops to a conveyor located beneath them and, in the ideal plant, is carried to the bark presses C and D, where a large proportion of the water is squeezed out of the bark, to fit it for use as fuel. After being pressed, the bark is discharged on conveyor 7, which takes it to the boiler house, where it is burned in a special furnace, provided with a large combustion space, called a Dutch oven. LOG HAUL-UPS 6. Parallel Log Haul-Ups.—The most economical method of hauling logs up from the river to the slasher is by means of a 1 as —— HiGs 34: parallel log haul-up, such as is shown in Fig. 3. The logs are driven end first into the boom (a pocket formed by floating logs, end touching end), in the direction indicated by the arrow, until — they bump on the boom stick 1, when they are moved sideways toward 2. At point 3, the boom is left open, and a man pulls §2 THE CUT-UP MILL 5 out to one side the logs that are too large to pass through the slasher and the logs that are better suited to being sawed into lumber. The pulpwood logs are fed to the haul-up; and when the logs have reached the inclined deck at 2, the wing links (see Fig. 6) of two or more submerged parallel, endless chains come up through the water and engage the logs. The chains convey the logs up the inclined deck 4 at a speed of about 70 to 80 ft. per min.; and when they reach the summit or driving end 5, the logs leave the chains, roll down the inclined plane 6 to table 7. Here they all have one end butted against a stop, to insure that the blocks are of uniform length after the logs pass through the slasher. The logs as they pass the log-haul are recorded as to marking, length, and diameter by one or more cullers, inspectors, or checkers. Thus a record is obtained of the amount of wood reaching the mill. Where there are several companies driving in the same river, and the driving is done by a logging association, the association generally provides one of the cullers. At the end of the season a settlement is then made for any logs belonging to another com- pany, based on the cullers’ tally-sheet. 7. The Chains.—As they travel up the deck of the log haul-up, the chains ride on steel wearing strips between hardwood guides until they reach the drive sprockets 5, Fig. 3; here they discharge the wood as previously described, pass through the deck, around the drive sprockets, and engage with the idler sprockets 8; they then slide down the steel-shod chain guides 9, around the flanged tail sprockets 10, and up the inclined plane again. These chains are made of short pieces of steel bars (links), riveted together, and have cast-steel lugs, or wing links, Fig. 6, that are 6, 8, or 10 inches high and spaced approximately 54 inches apart, center to center, the entire length of the chain. It is the duty of these wing links to engage the logs as the chains advance under them and approach the surface of the water. The wing links on each side of the chains emerge from the water at the same time, and the logs are carried up the deck in a hori- zontal position, at right angle to the direction of motion of the chains. The height of the wing links varies, on account of the average size (diameter) of the logs used in one mill being quite different from that used in another mill, and also on account of the different inclinations of the log haul-ups at different mills. 6 PREPARATION OF PULPWOOD §2 8. Raising and Lowering End of Haul-Up.—Fig. 3 also shows the hinged joint 11 of the inclined deck and the towers 12. A beam spans the towers; and when it is required to raise or lower the end of the log haul-up, to allow for variations in the elevation of the water or for repairs, chain blocks are slung on the beam for this purpose, and the tail sprockets are adjusted as desired. A cable then supports the adjusted end of the log haul-up, and the chain blocks ean be removed. This provision is necessary in winter weather. 9. Power Required for Haul-Up.—The angle of inclination of this class of haul-up (angle which plane makes with horizontal) is usually between 30° and 40°. The power required to operate the haul-up is easily found when the pull on the chains and the speed at which they travel is known. Thus, Let P = total pull of chains, in pounds : V = velocity of chains in feet per minute; W = total weight of chains and logs on the deck; & = coefficient of friction | : | f = factor of safety ¢@ = angle of inclination HP = horsepower Then, PVf Ht” 33000... ae The coefficient of friction may be usually taken as .3 and the factor of safety as 2. Then, for horizontal conveyors, ¢ =0, P = .3W, and ip: SW ee are ~~ 33000 —«55000 (2) For inclined conveyors, P = W(u cos ¢ + sin 9), and yp — WV(u cos ¢ + sin $) X2 WV(ucos ¢ + sin 9) oe 88000 If the reader is unfamiliar with the use of trigonometrical tables, he may use the following formula for P, which is the same as that given in Art. 156 of Mechanics and H ydraulics, §1, Vol. II, except that the minus sign has been changed to +, because the direction of motion is up the plane in this case. Here P = Bie §2 THE CUT-UP MILL 7 W =P, | = length of plane, and h = height of plane; then, P= ht uvP—B) Substituting this value of P in formula (1), .3 for u, and 2 for f, WV(h + 8/72 — h?) age 165001 4) The reason for changing the sign from — to + should be evi- dent. In the former case, it is desired to find the component of gravity acting parallel to the plane that pulls the body down the plane, and this is less by the amount of the friction; in the present case, the body is pulled wp the plane, and the component is increased by the amount of the friction. 10. Single-Strand Log Haul-Up.—By reason of the location of some cut-up mills relative to the boom from which the logs are drawn, another type of log haul-up is used; it is called a single- strand log haul-up and is shown in Fig. 4. Logs are hauled up, ae al Ss —— —— Fia. 4. end on, in a V-shaped, steel-lined trough 1 by means of flights (lugs) on a cable (see Fig. 20) or by spurs 2 on a single-strand conveyor chain 3, having a speed of about 250 ft. per min.; the logs are discharged at the top of theincline 4 onthedeck5. Here two quick-acting kicker arms, which are operated by steam or compressed-air cylinders below the floor and are controlled by an operator who commands a view of the whole sawing table, rise through the deck behind the log and roll it down the inclined plane and on the slasher chains; the kicker arms disappear through the deck, and the log is then butted, straightened, and 8 PREPARATION OF PULPWOOD §2 carried to the saws on slasher chains, as described in Art. 6. In some mills, the logs are discharged from the conveyor auto- matically, by gravity, without using the kicker arms. A log haul-up of this type is not as efficient as the parallel con- tinuous-chain type described in connection with Fig. 3; it is seldom seen, its use being entirely confined to mills in which logs cannot be brought up to the slasher parallel to one another or where logs are more than two feet in diameter. This type of haul-up is also used on swing-saw installations. See Art. 12. In British Columbia, where the logs often measure 6 ft. in diameter, they. must first be sawed in the same manner as for timber, and the timber conveyed to the slasher: here the single- strand conveyor is required. The log is first rolled upon a saw-mill carriage. . 11. European Practice.—In Europe, and in a few mills in America, the logs are bunched into slings before they leave the water; afterwards, they are hoisted out of the water and piled in long regular piles, about 12 ft. high, before being slashed, barked, and brought to the mill. Logs that have been regularly piled this way permit the free passage of air between the logs, and the wood contains considerably less moisture after being chipped than when wood is slashed, barked, and piled in ordinary storage piles. It is better practice to bark the wood before storing, however, since the wet wood is barked more easily; the barked wood dries better, and it is less subject to rot and to insect and mold attack. 12. Swing Saws.—When a mill is receiving only a small percentage of logs that are too long for the slasher to cut, it is advisable to install a swing-saw system, such as is shown in Fig. 5, to cut the logs into blocks of the required length. The logs are hauled from the mill pond by means of a single- strand log haul-up, as described in Art. 10 and shown in Fig. 4. As the log passes the summit of the incline, the chain is stopped, the log is rolled out of the trough and down the inclined deck 1 by - means of the kicker arms 2, which are operated by steam or air cylinders below the deck. These kicker arms are plungers or levers, and they push the log out of the conveyor to the log deck. When the log reaches the loader arms 3, it is held, and is only released when required to be rolled on the feed rolls 4. The feed rolls, which are operated by means of a lever and friction §2 THE CUT-UP MILL 9 pulley drive, carry the log against the log stop 5; the feed rolls are then stopped, the log stop is dropped by operating a foot pedal, and the revolving saw 6 is lowered by means of a lever and steam- or air-cylinder arrangement to the log, which is then cut to the correct length and dumped into the conveyor 7. The log ‘stop and saw are then raised, the feed rolls are revolved, and the log is carried against the log stop. These operations continue ly i yl iis _ =: F ’ SS . ‘ Fia. 5. until the log is completely cut up into blocks. The entire operat- ing mechanism is controlled by the sawyer, who stands on plat- form 8, from where he can oversee all operations. About 25 horsepower is sufficient to operate an arrangement of this kind. SLASHERS 13. Kind of Work Done by Slashers.—A slasher is a machine built as illustrated in Fig. 3; to cut logs into any predetermined length. The logs are picked up by endless feed-chains that run at 30-40 ft. per min., which form a cradle for holding the logs, and which carry them up an inclined plane and against 60-inch diameter circular saws that revolve at 750 r.p.m. The saws cut the logs into two or more pieces of the desired length. After the 10 PREPARATION OF PULPWOOD §2 pieces (blocks) are clear of the saws, they are automatically discharged into a conveyor that runs at right angles to the direc- tion of the slasher chains, and are conveyed to the barking drum or to the storage pile. , Slashers may be built on the concrete floor of a cut-up mill (also called the saw deck), the machinery being supported by steelwork in the floor; or they may be built, as is usually done, with the machinery supported on wooden bents, which are assem- bled on the floor of the cut-up mill and rigidly braced together. 14. Description of Slasher.—Referring to Fig. 3, assume that the logs are 12 ft. long and that they are to be cut into six equal lengths; there will, therefore, be required 12 feed chains, 2 chains for each block when cut to length. When the logs roll on the table 7, the ends are butted, and the 12 parallel continuous feed chains, coming through the table at 13, pick up one or more logs, convey them at a speed of about 30 ft. per min. up the sawing table 14 (which may be horizontal or slightly inclined), and carry them against the leading saw 15, which cuts the log into two pieces. After passing this saw, the width of the saw cut is increased to 14 in. by means of a spreader that is located directly behind the first saw, the object being to prevent cramping when passing through the following saws. At a distance of about 6 ft. from the center line of the first saw (leading saw), the two saws on the second arbors (shafts) 16 cut off the inside ends of the two pieces made by the leading saw 15. After passing through this second line of saws, the pieces are | carried through a third line of saws 17, the center line (axis) of whose arbor is located about 6 ft. from the axis of the second line of saws, and the outside pieces are cut in two; thus making 6 pieces (or blocks, as they are termed) from the original 12 ft. log, all of equal lengths. It is obvious that saws can be spaced, so as to cut blocks of other lengths. The blocks are now carried over the upper end of the slasher 20 and discharged on conveyor 18. These 12 continuous feed chains, like the haul-up chains, are constructed of steel bars, the ends of which are joined to one another by side links of the same length, similar to the construc- tion of a bicycle chain. On approximately 20-inch centers, _there are inserted, in place of the plain bar link, a special cradle casting, or spur, several types of which are shown in Fig. 6. Spurs of this character are also employed on the haul-up chains, $2 THE CUT-UP MILL 11 both on the parallel-chain and _ single-chain types of haul-up chains. The chains come through the table at 13, Fig. 3, are hauled up the chain troughs 19 to the drive sprockets 20; they pass around these sprockets and under the sawing table, where Sechior of Conveyor Chain wih Special Attachment Seciion of Conveyor Chain with Special Attachment 54'Centre lo Centre | 4" Seciion of Log Haul-upChan Lirection of Haul <—__ Section of Slasher Chair = —»> zm aaa amen Bee OPE EGO, —_ OLFASD |E4I Secron of ornveyor Cable wilh Flights Fig. 6. they engage with the idler sprockets 21; continuing on below the table, they come around the tail sprockets 22 and up through the table again at 13. The chains are driven by toothed drive sprockets 20 on shaft 23, which is geared to shaft 24. Shaft 24 12 PREPARATION OF PULPWOOD §2 is belt driven from shaft 25, which is driven from the second arbor shaft 16 by means of a belt and tightener 26. If, for any reason, it is desired to stop the travel of the load on the sawing table without stopping the saws, the tightener is raised by means of a rope running to the overhead beams and thence to a point near the operator, or by means of a lever attached to a bent of the slasher. Provision should always be made for stopping the travel of the chains on slashers at any time, as logs often get crossed on the sawing table, and time is saved only by stopping the travel of the logs. A log that is too large to be cut through by the saws occasionally gets on the slasher; in such case, the log is sawed part way through (as far as the saw will cut), the feed chains are stopped, and the remainder of the cut is chopped before the stick (log) enters the next saw. 15. Slasher Details—The arrangement of the saw arbors relative to the feed chains and other parts of the slasher is such that the saws may be removed in a few minutes of time, without removing the arbors from the bearings. Slashers are built for | all lengths of logs and to cut any length of blocks. The power required to operate a slasher successfully is 20 h.p. for each 60- inch saw; that is, a 5-saw slasher using 60-inch saws would require 20 X 5 = 100 h.p. This gives sufficient power to operate a log haul-up of not more than 4 chains, for a haul of not exceeding 75 feet. The drive for the slasher is usually from a basement, where a shaft is either direct-connected to a motor or is belt driven from a motor or a steam engine. The log haul-up is generally driven from the same drive shaft. A tightener is placed against the vertical belt 27, Fig. 3, which drives the countershaft 28, the latter being geared to the drive shaft 5. To stop the log haul-up, the tightener is released, and the belt slips on pulley 29. In mills where there is no basement, the drive for the log haul-up and slasher may be- arranged to come from overhead instead of from below. the floor. Where it is necessary to cut a short piece off the end of a log to remove rot, a bad end, or to cut to exact length, a trimmer saw is installed at one side of the slasher, usually ahead of the leading saw. Substantial safety guards should always be provided, in order to protect workmen from injury in case one of the rapidly revolv- ing saws burst or if, for any reason, a block should jump. Low §2 THE CUT-UP MILL 13 hanging screens in front of each saw, made of heavy wire are very satisfactory for this purpose. BARKING THE WOOD 16. Reason for Barking.—In order to make pulp of good qual- ity, it is necessary to remove the bark from the blocks; this opera- tion is sometimes called rossing. Another reason for removing the bark is that the bark has very little, if any, fiber value, and it consumes chemicals and steam in cooking, and takes up valu- able space, without yielding a return. Specks of bark make dirty pulp and paper, and it is easier to remove dirt from the wood than to remove it from pulp. Two principal types of appa- ratus are used; barking drums; knife barkers. However, wood is often barked by settlers and farmers with a draw-knife, and green poplar is peeled in the woods by splitting the bark with a long- handled chisel, called a spud, and pulling off the bark in long strips. BARKING DRUMS 17. Types of Barking Drums.—Generally speaking, there are two systems of barking wood in drums: the continuous system and the intermittent system. The continuous system is best adapted to present-day condi- tions, and is the one most used at the present time. In this system, the wood is fed automatically into one end of the barking drum, where it is tumbled about and automatically discharged at the other end. This system may again be divided into two classes : tumbling barrels, of which there are four types, and station- ary barkers. ‘The latter are not ‘‘drums,”’ strictly speaking, but will be described in this division. 18. Tumbling-Barrel Types.—Generally speaking, barking drums of this system all work on the same principles, although each of the four types has special features that are made use of in each particular drum, and which are described later. The blocks of wood are conveyed to the upper end of the drum (or drums) and are slid down an intake chute into the drum, in which they are tumbled against one another. This tumbling rubs off the bark, which passes out through narrow slots between the structural sections of which the drum is built, the blocks being 14 PREPARATION OF PULPWOOD §2 retained in the drum until they work their way out at the dis- charge end. 19. The disadvantages of this system are: (a) The ends of the blocks are more or less broomed; particles of dirt, some of which cannot be gotten rid of, are driven into the broomed ends; later, these particles appear in the paper, and are always a source of annoyance. (b) Blocks of wood may remain in the dvi for a considerable time and may finally be discharged badly slivered; this means a loss of wood. When blocks of wood not completely barked are discharged from the drum, they are returned to the intake end of the drum by means of a special return conveyor. The principal advantage of this system is that the bark is quickly and cheaply removed from the block without any great waste of wood, as is the case with the various types of knife barkers. 20. Aids in Removing Bark.—Some of the methods employed to aid in removal of bark from the blocks and in cleaning the wood are the following: (a2) Run the drum open, and use sprays at one or both Bias of the drum. : (6) Do the barking in a dry drum, but have a washing section running in a tank of water at the end of the dry drum, teal which all the wood is passed. (c) Revolve the drum and wood in a tank that is partly filled with water, using sweepers fastened to the outside of the drum, to keep the bark from accumulating in the bottom of the tank. 21. First Type of Barking Drum.—The first of the four types of the tumbling-barrel system of barking drums to be considered is illustrated in Fig. 7. This drum is built in three sections, A, B, and C, each 12 ft. in diameter by 15 ft. inlength. Each sec- tion has its own girth gear D, tires H, and 4 sets of supporting rollers F. The drum is constructed of heavy channel sections G, having the flanges turned out, thus giving a smooth interior, with the exception of the slots between the channels, which allow the bark to pass out. The channels are riveted to the heads H, the steel tires H, and the girth gear D, clearance being allowed between the three drum sections to avoid interference. The com- §2 THE CUT-UP MILL 15 plete drum may be set level or at a slight inclination, say 1 in. in 12 in., to help reduce end thrust. A retarding ring at the lower end of each section helps to hold the wood in that section for a longer time than would be the case if the ring were not there. An intake apron K, discharge apron L, and special nozzle spray- ers M are the remaining eine features of this type of drum. It is sometimes necessary to rivet a flat bar to the inside of one of the channel bars G in each section; this keeps the wood from sliding instead of tumbling. The AWE is driven by pulley S, through gear T and shaft U to gears V and D. Q y oD & ies ~) pool aria ITT TTT TTT po ty OyIy M > C ‘TF oe i " ae ET a fae sca fail | le Vi : es co mea P The blocks, which may come from the slasher, freight cars, block pile, or from the pond, fall from a conveyor to apron K, and thence into the drum. They are pushed forward by more blocks coming in, and they finally tumble out over the gate O, against the apron L, to the conveyor P. The bark falls into the trough below the drum and is carried away by the conveyor R. Blocks not cleanly barked are sorted out and sent back, as explained in Art. 5, and Fig. 2 The intake and Pridile sections of this drum run dry; only the discharge-end section is sprayed, to clean the wood. 22. Second Type of Barking Drums.—The second type of the tumbling-barrel system of barking drums is illustrated in Fig. 8. This drum is built in four ‘sections A, B, C, D; each section has its own tires HL, 4 sets of supporting rollers F', and each section is revolved separately by means of a girth sprocket G and chain H, which is driven from a line shaft K. The drum has a steel-plate shell, which gives a smooth interior, and slots are cut into the shell, to allow the bark to escape. The shells are riveted to the heads L, to the cast-steel tires E, and to the girth sprockets G, and the shells are all set level. The blocks are fed from conveyor 16 | PREPARATION OF PULPWOOD §2 M, down slide W, and the unbarked or imperfectly barked blocks are returned by conveyor N. The barking of the blocks is accomplished in the first three sections, which run dry, and the discharged bark is conveyed direct to the boiler house, by conveyor P, to be used as fuel. The blocks are tumbled from the third into the fourth section, which runs in a tank of water and is set slightly below the other sections; here the blocks are washed and discharged into a conveyor V. Any bark that is removed in the fourth section is run into the sewer. Wy 4 un IN BT IN Pa Hee idl Fia. 8. 23. Third Type of Barking Drums.—This type of the tumbling- barrel system of barking drums is illustrated in Fig. 9; and is a much used type. The drum is built in a single section (except drums longer than 30 ft.), and revolves in a tank of water. The blocks enter this drum in a manner similar to that previously described; they are tumbled about inside the drum until they are discharged over the dam sections 1 to conveyor 2. This drum is suspended in a semi-circular tank of water A, from an overhead structural framework, by means of 4 heavy steel chains K, which run on steel rings B (bolted between channel rings riveted to the exterior of the drum) and on traction wheels C’, which are supported on the overhead framework. Spring take-ups are provided for the traction wheels on one side, to equalize the load on the chains and absorb the shocks, and 4 special thrust rollers D take care of any side thrust of the drum. Like the drum shown in Fig. 8, this drum is revolved by means of a sprocket ring, bolted between channel rings that are riveted to the drum, and by a driving chain F, running on a sprocket iP OO a oe §2 THE CUT-UP MILL 14 which is driven by a motor M on the overhead framework. The drum is built of special U-shaped bars N, which run the full length of the drum and are assembled in such a manner as to give a corrugated interior surface, which tends to increase the barking action with less damage to the wood. The bark passes out through spaces between the U bars. Channel rings are riveted on the outside of the U bars, to make the drum keep its shape. Sweepers are bolted on the outside of the drum, which carry the bark from the bottom of the tank and discharge it into conveyor H. Incompletely barked wood is returned to the drum by conveyor _ E and chute S. 24. Fourth Type of Barking Drums.—This type of the tumbling-barrel system of barking drums is a combination of the drums shown in Figs. 7 and 9. The drum is built of special Ware pac Sie. Fre. 9, corrugated sections (bars), which are held in place to form a cir- cular cylindrical shape, with the bars running parallel to the axis, by means of cast-steel tires, a girth gear, and steel bands, all of which are riveted on the exterior of the drum. This drum runs in a semi-circular tank of water; it is supported by means of 4 sets of rollers, and is driven by a pinion and girth gear, which are located at the center of the drum. 25. Factors Affecting Capacity of Barking Drums.—Variations in the capacity of barking drums are due to the following: (a) The length of time that the wood has been in the water. (b) Whether the logs were driven in streams having rapids. (c) Whether the wood is allowed to stand in piles after being hauled from the water, or whether it is immediately barked. (d) Speed of drum and smoothness of interior. (e) Amount of wetting of wood and amount of wood in barker. Although the capacity of barking drums cannot be accurately determined, the following table will give a rough idea of what 18 PREPARATION OF PULPWOOD §2 may be expected under the conditions mentioned for the sizes of drums given: APPROXIMATE CAPACITY OF BARKING Drums. Corps PER Hoovr. Wood driven in quiet water Barking conditions Size of drums. Period in ; } : : : . Class of wood. 8’ x 30 10° <°30 12’ 45 water ON he Sea mere A ae Never! 2.5 5 10 River Ane sae 2 weeks 4.0 6 12 River 4 ee 2 months 5.0 9 15 Kiveri 4 months 7.0 12 20 REVex eek eee ee 6 months or more 9.0 16 20 .Wood driven in streams having rapids River... eee 2 months 7.5 16.0 27.0 Rivers... : sc... 2] 4enonths 12.0 20.0 32.0 River............| 6 months or more 20.0 Zoe 37.0 | 1 Wood that has never been in water requires about 3 hr. to bark; but only 3 hr. if it has been in water 6 mos. or longer. The number of cubic feet occupied by wood in drum or river divided by 160, gives drum capacity in cords quite closely. The treatment the wood gets in the water, the barking it gets in shooting rapids, etc., lessens the work for the barkers. To obtain the best results from any type of barking drum, namely, the greatest amount of clean wood with the least number of broomed ends, the drum should be run half full of wood. Wood barked in drums having smooth interiors will have less brooming on the ends of the blocks than when there is a pro- jection of some kind on the inside. 26. Power Required.—The amount of power required for any type of barking drum depends upon the amount of wood in the drum when the drum is started, and any motor that is installed should be large enough to take care of this starting torque. The motors listed in the following table are sufficiently large to operate drums of the sizes and speeds given. §2 THE CUT-UP MILL 19 Power ReEQuirED ror Barking Drums Size of barking drum .. Speed (r.p.m.) Power required 12’ X 45’ (3 sections)....... 6.0 150 h.p. 10’ X 30’ (1 section)....... (few 75 h.p. 8’ X 30’ (1 section)........ 9.0 50 h.p. FD In both of the above tables, the first dimension given in speci- fying the size of the drums is the diameter and the second dimen- sion is the length. STATIONARY BARKERS 27. Description of Stationary Barkers.—The latest type of barker to be developed is illustrated in Fig. 10. The logs are taken from the log haul-up, sorted into three sizes (large, medium, OO- Y LY), OO 1@ eee OY A xt BAIINHY tke AAO) vag ee 800), Vy sy "6s 102 O00, y rye WV [Bi (x¥ S795 EB ae lP-v< MS and small), and each size is continuously fed in the direction indicated by the arrow to a set of three pockets A, B,C. Revolv- ing at the bottom of each pocket are 4 double-ended cams D (for 16-foot logs), which are located in line on shafts EZ, which revolve at 15 r.p.m. The cams, which are approximately 6 ft. over all and have a 6-inch face, lift the logs and give them a 20 PREPARATION OF PULPWOOD §2 rolling motion in the pocket at a rate depending on how fast the logs are fed into the first pocket A. The well-barked logs, when discharged from the third pocket C, are conveyed either direct to the slasher, which, for chemical pulp, cuts them into 8-foot lengths, or they are conveyed to the storage yard, where they are piled and allowed to dry; all unbarked logs are returned by means of a conveyor to the first pocket to be re-barked. A water spray, playing on top of the wood in each pocket, keeps the bark wet and aids in its removal. The bark drops to the bottom of each pocket as it leaves the logs, and passes out of the drum through the slots F in which the cams work. Each barker is belt driven from a 175-horsepower motor, which connects to a pulley M on the main-line shaft; from this shaft, each cam shaft is driven at reduced speed by means of bevel and spur gears N and P. What may be called the center lines of the cams are set 60° apart, in order to give a more uniform torque on the motor. ; The maximum capacity of this barker has not been deter- mined, but the manufacturers claim it will bark 18 cords of wood per hour. 28. Advantages of Stationary Barkers.—The advantages claimed for this type of barker are: (a) A considerable reduction in the waste of wood over that barked, as formerly, on a knife barker. (b) A clean block, 8 ft. long, free from dirt specks or broomed ends; and when chipped, the chips will have fewer long slivers and sawdust than when shorter blocks are used. (c) A further saving is obtained by reason of slashing the log only once; this means that instead of great quantities of saw dust, which can be used only for fuel, the loss in saw dust is replaced with chips. Further, only one slasher saw is required. (d) The barked logs can be piled in the open air; this results in better chips and, consequently, better pulp. A possible disadvantage is the chance for splintering the outer layers of the wood through the rubbing action of the cams. INTERMITTENT BARKING DRUMS 29. Description and Operation.—The original barking drum of this type is shown in Fig. 11. The unbarked wood is stored in a hopper A, which is directly over the drum B; and when it is a §2 THE CUT-UP MILL 21 desired to fill the drum, the side door C of the drum is turned up and the door thrown open. The hopper doors are opened by the chain and gear H, to allow the wood to drop into the open drum, and they are closed when the amount of wood required to fill the drum has been taken out. The door of the drum is now bolted down, and the drum is revolved at the rate of 10 repim. While the drum is revolving, water is constantly flowing into the drum through the hollow journal at one end HK, and the bark (which has been separated from the wood inside the drum) goes WiGsel 1: out with the dirty water at the other end F through the hollow journal. After the wood has been in the drum a length of time sufficient to remove the bark, the drum is stopped, with the door side up, the door is unbolted, and the drum is turned 180° (half a revolution), so that the opening is down; the wood then falls through the open doorway and to the conveyor G below, where it is washed and carried away to the chippers. A drum of this type is particularly well adapted to barking blocks of wood or saw-mill slabs up to 8 ft. in length, these being neatly piled in the drum. On round pulpwood, it has a capacity of from 24 to 40 cords per 24 hours. About 30 h.p. is required to operate it when under full load. The body of the drum is approximately 9 ft. 6 in. diameter by 9 ft. in length; it is built of steel plates, bent and riveted to semi-steel heads, on which hollow journals are cast, which support the drum. Projecting angles inside the drum help to tumble the wood. 22 PREPARATION OF PULPWOOD §2 30. Other drums of this type are built of angle irons or channel irons, which are fastened to circular heads and bands; the bark falls through the openings between these. Water may be sprayed on the drum to wash off dirt and bark from the wood. When selecting barking equipment, it is important to consider these factors, in addition to the first cost of installation: kind of wood to be cleaned; loss of wood substances; capacity; operating cost; cost of maintenance. BARK PRESSES 31. Purpose of Pressing Bark.—That there may be as little waste as possible about the mill, the bark discharged from the barking drums that operate on wet wood, should be put through a bark press, to squeeze the water out of the bark; this will fit it for burning econornically in the boiler house, to which all wood refuse is conveyed (or trucked) and in which it is burned to generate steam. Wood waste requires that boilers be equipped with a large fire space, generally called a Dutch oven. The following figures show that the fuel derived from the bark from barking drums amounts to a considerable item in a year’s time: “One hundred cords of wood at a conservative estimate of 225 lb. per cord, will give 22,500 lb., or 114 tons, of dry bark. The pressing would cost 20 cents per ton of bark, or 2 to 24 cents per cord of wood. Bark containing 50% moisture has a net heating value of 3500 B.t.u. per pound of moist bark. One pound of bark is therefore equivalent to 0.27 lb. of coal that has a heating value of 13,500 B.t.u. per lb., assuming equal efficiency in the furnace. On this basis, a plant using 100 cords of wood per day would have 22% tons of moist bark, equivalent to 6.02 tons of coal, worth, say, $7 per ton. If efficiently burned, therefore, the bark would save the plant $42.14 per day. Bark containing — 80% moisture has a net heating value of 700 B.t.u. But 114 tons of dry bark would be represented by 56.75 tons that contained 80% moisture, and 1 ton would be equivalent to 0.053 tons of coal. In this case, the total coal equivalent for the day would be 3 tons. Reducing the moisture from 80% to 50% increases the daily coal equivalent by 3 tons, valued at $21. Deducting $2.50 per day to cover the cost of pressing, leaves a net saving of $0500 per year.’’! ‘From Technical Association Papers, Series VII, June, 1924. §2 THE CUT-UP MILL 23 In many cases, the bark is reasonably dry and does not need pressing; in other cases, the bark is burned wet, the heat derived from burning a part of it serving to dry the remaining part. Other wood waste, as chipper sawdust, is also an important factor. The pressed bark is conveyed with the mill refuse from the slasher, together, usually, with the refuse from the chip screens, to the Dutch oven, where it is burned without the addition of other fuel, though other wood waste may be mixed with it. Some Scandinavian mills dry their bark still further by waste heat in special dryers. (See Pulp and Paper Magazine, Inter- national No., 1925, page 143.) 32. Description of Bark Presses.—In the bark press, Fig. 12, bark is conveyed from the barking drums to the bark press and ee a ee ae ee I =a ap H 2 -+--- ES anv ] LN i I} LIA WH, ZI 1 | q 1 —& ZA i / spi l|[Al™ => a — a Oe 97 tT) Fie. 12. loaded on the endless chain 1, which carries the bark between the three presses. The pressed bark is discharged into a conveyor at the driving end of the bark press. The dryness will depend upon the dryness of the bark delivered to the press and upon other factors, as speed of operation. The chain on which the wet bark is deposited i is made up of flat sections of steel bars, which run at right angles to the direc- tions of the chains; they have a special section of chain, riveted to the ends of each bar. The bottom side of the flats comes in contact with the outside of the drums 2, while the bark on the top side of the flat is pressed by the disks 4. On each top shaft, there are 8 disks; each is bored large enough to allow any one disk to rise sufficiently high to permit a knot or other very hard sub- stance to pass through without causing all the disks on that shaft to rise a like distance. Thus only a small proportion of the bark passing through is affected by the entrance of some hard substance. As will be seen in the illustration, the pressure on the bark due to the weight of the larger disks, gradually increases as the bark travels along the chain toward the driving end. Handwheels on 24 PREPARATION OF PULPWOOD §2 the top of the structural steel framework permit the operator to raise the disk shafts. One press of the above type, equipped with a 15-h.p. motor is capable of pressing the bark from 400 cords of wood daily, as it comes from the barking drums. 33. Another press that works on somewhat the same principle is shown in Fig. 138. The wet bark is deposited on the endless chain at A, the bark is given one pressing, and is then discharged at H to a conveyor that carries it to the boiler house. The chain on which the bark is carried is somewhat similar to that described in the last article. sa 2G ee or The under side of the flats runs | y on the solid | | neem ES I steel roll B, the | ans. bark on the upper side being pressed by the weight of the disks F above. These disks, which are stacked one on top of the other, are bored large in the center and are guided in a vertical position by the guide rolls C. This arrangement allows a considerable weight to be placed on the bark to get rid of the water, and it still enables the disks to rise when very hard substances, such as knots, come along the chain. If it is desired to use a greater weight, the levers D are loaded, and a much greater pressure can be put on the bark by means of the roller Z. The chain of this bark press runs at 27 ft. per min., and the press is said to be capable of pressing to 60% dry the bape from barking drums that have a daily capacity of 400 cords. Piegs13; 34, A third type of bark press is shown in Fig. 14. Here the bark is deposited on apron A, made of heavy malleable-iron links, is spread out by a distributer, and is carried between the two presses, where a considerable amount of water is Squeezed out of the bark. After being squeezed, the bark is carried onward and dropped over the end on a conveyor, which trans- §2 WOOD STORAGE AND CONVEYING 25 ports it to the boiler house. The bottom drum B of each press runs in fixed journals, and is smooth and has a chilled surface; but the two top drums C, which revolve in sliding journals, are corrugated, the corrugations running parallel to the axis of the drum. Additional pressure can be secured and adjusted by ae Riera mae wes dh Fig. 14. LUA weights and levers B. Adjustable stops keep the upper rolls from touching the apron. A press 24 in. wide, with a 10-h.p. motor, will handle the bark from 25 cords of wood per hour. The disadvantage of this type of bark press is that if a knot or other hard substance get on the chain, the whole top roll will rise, and thus give a strip of unpressed bark across the entire face of the chains. With the disk type of press, the only bark not pressed is that part around the hard substance. That it may burn more freely, a small quantity of coal is usu- ally mixed with the bark coming from bark presses of this type. 34A. A 3-roll bark press on the principle of the sugar-mill rolls, with preliminary breaking rolls, has recently been developed. This press consists of two crushing and spreading rolls 1 and 2, Fig. 14a, and three pressing rolls 3, 4, and 5, all operating in conjunction with one another. As the rolls have adjustable journals, they can be so spaced as to pass large or small quantities of bark, as desired. The crusher rolls 1 and 2 have toothed and grooved surfaces, the teeth and grooves being staggered from the middle of the roll out, somewhat resembling the teeth in a herringbone gear, the purpose being to accomplish the following: (a) The teeth draw the bark into the rolls, and at the same time, through the pressure exerted, they crush’ the bark into smaller particles. (b) The lateral grooving on the crushing rolls permits the bark to spread sideways between the rolls, thus preparing an 254 PREPARATION OF PULPWOOD §2 even, continuous mass for pressing. (c) The crushing rolls exert a pressure up to approximately 1500 lb. per inch of width, and considerable water is removed at the nip. (d) The cutting of the rolls into teeth around the circumference, as well as the angle of the lateral grooves, permits the passage of water freely into the drain beneath the housing. | The bark is fed into the press at A, and after leaving the spread- ing and crushing rolls, it is conveyed into the pressing rolls by apron 6. These rolls are grooved around the circumference and also parallel to the axis,. forming rectangular-shaped teeth, which exert a biting effect on the bark and draw it into the press. Aan Fig. 14a. The top roll 3 exerts an’ approximate pressure on the bark at the nip of 1500 lb. per inch of width at three points of contact; namely, on the inside bottom roll 4, then on the turn-beam shoe 7, and, third, on the outside bottom roll 5. The grooving of the rolls, in conjunction with the grooving on the turn-beam shoe, permits the passage of water to the drain beneath the housing, and bark is then delivered to the conveyor going to the boiler house. The scraper plates 10 are cut to mesh accurately with the roll. The purpose of these plates is to keep the bark from following the roll and, at the same time, to permit the passage of water. Between the top and bottom rolls of the press is placed a rigid turn beam 9, on which is mounted a shoe 7, grooved on its face to mesh with the grooving of the bottom press roll and fitting closely to the roll. The turn-beam shoe is placed with its back edge 5 in. to 2 in. from the outside bottom press roll. The shoe : , §2 WOOD STORAGE AND CONVEYING 25b acts as a scraper for the inside bottom press roll, and with its clearance from the outside bottom press roll, allows the water that is squeezed from the bark to pass to the drain underneath. The application of pressure to the bark is accomplished by the weight of the rolls, plus additional pressure obtained through the screw and spring principle, resulting in a total pressure of approximately 60,000 Ib. per sq. in. on the rolls. The drive is of the positive gear, belt-driven motor type, all rolls being geared together, thus ensuring the same rate of travel for the bark throughout. The main drive and driven gears, as well as their pinions, are of cast iron; the roll gears are of cast steel. The press is built in three standard sizes, to meet the requirements of mills barking 400, 800, or 1200 cords of wood in 24 hours; the motors required are 25 h.p., 40 h.p., and 65 h.p., respectively. All presses are operated at 40 ft. per min. periph- eral speed of rolls or conveyor speed; at this speed, refuse bark will be delivered to the boilers as prepared fuel at approximately 62% moisture content. Fig. 14d. 34B. Another type of press has a perforated stock chamber, in which the bark is pressed by a plunger that is operated by a geared crank and flywheel. Fig. 14b shows the design very clearly. The feed hopper is shown at the center, and the resis- tance, against which the bark is pressed, at the right. WOOD STORAGE AND CONVEYING CONVEYORS STORAGE-PILE CONVEYORS 35. How Blocks Reach the Storage Pile-—When blocks are discharged from the slasher or from the barking drums (if they are first barked), they are usually transported to the storage pile 26 PREPARATION OF PULPWOOD §2 by means of an endless conveyor cable that has on it flights or buttons, which are equally spaced at such distances apart as to accommodate the length of the blocks. The blocks, cable, and flights run in a steel-shod conveyor trough, into which a small quantity of water is continuously run, to reduce the friction between the flights and the steel plates. It is customary to have a horizontal, or nearly horizontal, conveyor from the slasher or barking drum to the foot of the inclined conveyor, and the latter may be any one of the three popular types now to be described. 36. Trestle Type of Conveyor.—A block pile conveyor of the trestle type is shown in Fig. 15. An endless chain passes around a large gap wheel at A and up the inclined end of the conveyor. The blocks are dropped on the conveyor at D and are elevated to a height of 50 ft. or so by the conveyor. After reaching the high- est point, they are carried horizontally to the point where it is desired to discharge the blocks from the conveyor. When the cable reaches B, it then goes down the incline BC, around the tightener and gap wheels C, thence through a tunnel under the conveyor, and back again to the loading end. The trestle supports are approximately 125 ft. apart: At (a), Fig. 15, is shown one of the supporting frames, with block trough, side walk, and handrail. In Figs. 6 and 20 are shown typical troughs, sections of the sides of which can be removed for the purpose of dropping off the blocks. Several forms of lugs, as used on cables, are shown in Fig. 20, Art. 42. The discharging of the blocks is accomplished automatically by leaving the conveyor side open at the point where the blocks should be dropped. After a large number of blocks have been dropped the entire length of the conveyor, and the pile has reached the angle of repose for these blocks (the angle at which the blocks will no longer roll down), which is an angle of about : : | : ‘ ; §2 WOOD STORAGE AND CONVEYING 20 39° with the horizontal, portable sections of wooden chutes are laid on top of the pile. ‘These chutes cause less obstruction to the blocks than if they were discharged on the rough pile, and by this means, the blocks are distributed over a very large area. In the case of the conveyor here shown, the blocks were thus distributed to a distance of 225 ft. from the center line of the conveyor. The return cable runs in a tunnel, the bottom of which forms a return conveyor for bringing the wood back to the mill for use; the sides may be built permanent or by carefully piling wood to a height of 4 or 5 ft.; the top is made by laying pulpwood, which is removed to uncover the conveyor as the wood is used up. 37. Suspension Type of Conveyor.—The suspension type of storage-pile conveyor is shown in Fig. 16. The wood starts at A, Irie. 16. and is elevated and distributed in a manner similar to that already described. This conveyor, however, has an advantage in that in all the space between the piers H and F’, wood can be stored; moreover, while the area under the inclined section is being piled with wood, only the first cable requires to be oper- ated, which results in less power being used than with the con- veyor previously described. The horizontal distance between the supports may be as great as 600 ft. in conveyors of this type. 38. Standard Stacker.—In Fig. 17 is illustrated a standard stacker. The wood is transported by a horizontal conveyor to the stacker, and the blocks are then carried up the stacker by a chain or cable conveyor, similar to those described previ- 28 PREPARATION OF PULPWOOD §2 ously, to be dropped over the end B to the pile below. As the pile increases in height, portable chutes are used, operated as in previous cases, and the width of the pile is thereby extended. When it becomes impossible to discharge any more wood, that is, when the available working area is completely covered to the desired depth, the stacker is moved along a track that runs lengthways of the pile; in this manner, a great pile of wood can be stored at small expense. To keep the overhanging truss of the stacker from tipping over on the storage pile, the opposite end of Bigs id. | the stacker may be loaded with worn-out grinder stones or with concrete blocks. A track the full length of the storage pile, on which to run the stacker, is always necessary. . For a 70-foot stacker, it is advisible to use a 50-h.p. motor to operate it; for a 90-foot stacker, a 60-h.p. motor should be in- stalled; and for a 125-foot stacker, a 75-h.p. motor is necessary. CROSS CONVEYORS 39. Supplying Wood Room from Storage Pile——When the cut-up mill closes for the season, it is necessary to take wood from the storage pile to supply the mill requirements. Referring to the storage-pile conveyors shown in Figs. 15 and 16, the return tunnel at the end of the pile farthest from the mill is uncovered, and cross conveyors, which extend the entire width of the pile, transport the blocks to the open tunnel, which is further un- covered as the pile is drawn upon to supply mill requirements. The reason for starting at the end of the storage pile farthest §2 WOOD STORAGE AND CONVEYING 29 from the mill is, if the conveyor should get out of order, the blocks would then require to be hauled to the wood room, and the difference in the cost of hauling from the near and far ends of the storage pile amounts to a considerable item. It is also easier to begin piling new wood at the far end, while wood from the near end is being taken to the wood room. Referring to Fig. 16, a considerable saving in power is obtained by first using up the wood between the towers H and F; after which, the conveyor cable that operates in this section can be shut down. This procedure is often reversed, however, one important reason being that the oldest wood should be used first. A special case, too, is where the wood pile is between the pulp mill and the cut-up mill. A separate conveyor is then required, or the piling cable is reversed. 40. Portable Cross Conveyor.—To convey the blocks to the wood room (where a stacker is used), a portable cross conveyor is employed to deliver the blocks to a main conveyor, which is located back of the stacker. This main conveyor is also used to supply wood to the stacker during the time the storage is being built up. At such time, a side section of the main conveyor is removed, to allow the blocks to be dropped on the conveyor running up the inclined stacker. During winter, the moisture in the blocks freezes, causing the blocks to stick together, and in most mills, dynamite has frequently to be used to break down the pile, so the blocks can be carried in the portable cross conveyors. Although blasting is very dangerous, yet it is to be preferred to having men go on top of a pile, to break down the blocks, or to having men undermine a pile. Cross conveyors are also used to distribute wood on very large piles. A very good arrangement for keeping the portable cross conveyors supplied with blocks at the least risk of life is shown in Fig. 18. The cable A carrying anchor £, runs over pulley block F (attached to the conveyor frame), over pulley block H (near the foot of the pile), and is wound in either direction on the motor-driven drum K, which is preferably situated on a high bank. Otherwise, the cable should pass over a high pulley, in order to keep the anchor well up on the pile. The reversing motor is geared to two cable drums; it causes the heavy anchor H to be drawn back and forth across the working face of the storage pile and pulls down the wood from the top of the pile. With a device of this kind, dynamiting is unnecessary, and men 30 PREPARATION OF PULPWOOD §2 engaged in loading the conveyors seem to be laboring under much less strain than those working where dynamite is used. Fig. 18. 41. Pulpwood Reclaimer.—Another apparatus for dragging down wood from the storage pile is shown in Fig. 19. It consists of a carriage A running on track JT along the foot of the pile; it carries the motor M and bottom end of beam H. At the top of the beam are wheels W, which ride on light rails (laid on top of the pile), as the carriage moves along. A chain F, driven by a motor-driven sprocket N, at the foot of the beam, carries spurs which catch into the blocks on the down journey and drag them down the pile to the conveyor H. When a gully has been dug, the carriage is shifted a little. The beam always adjusts itself to the angle of repose of the pile. Except for the occasional necessity of using dynamite in the winter, no man runs the risk of climbing the pile; even then, the beam makes the ascent and descent much safer than usual. 42. Power Required to Operate Conveyors.—Conveyors may be either horizontal or inclined. For horizontal conveyors, the power required by a storage-pile conveyor depends upon weather conditions (wet, frosty, or dry), speed of conveyor, and condi- tions of the trough (wet or dry). A little water, fed at the top of an inclined, or the beginning of a horizontal, conveyor, makes very good lubrication for the sliding blocks and conveyor flights. Roughly, it requires a 50-h.p. motor to eonvey blocks at the rate of 40 per minute at a speed of 400 ft. per min. horizontally, or at 225 ft. per min. up an incline. The overload is sometimes as : . | . ‘ : §2 WOOD STORAGE AND CONVEYING 31 much as 50%. §3 THE MECHANICAL-PULP MILL 67 at 5. The pressure-water supply for the hydraulic cylinders of the grinder is shown connected at point 6. The volume of water required by pressure pumps is supplied from a pipe, which passes through the dam 7.. In order to strain out some of the grit and other foreign materials carried in suspension in the water, the water is passed through a wire sieve 8, usually of 60-mesh to the inch, before entering the pump-well below the screen. The strained water is then pumped to grinders by means of centrifugal pump 9. A pressure-reducing valve is located at 10, in the pipe line to the grinders. This valve reduces the pressure delivered by the <, LEGEND Jo -[20] | Low Fressure—"'— - Ly key To kefiners Fig. 40. centrifugal pump to the pressure required in the grinder cylinders. There is also a large enclosed tank 11, which is connected into the supply main for the grinders. The tank is filled about one- half with water and one-half with air; the air is compressed by the water pressure, and acts as a cushion on the grinder pressure- water supply-line, tending to maintain a constant pressure. Shower-water supply to the back of the grindstone is shown at 12; this, mixed with the pulp in grindstone pit 13, overflows into the stock sewer 14 beneath the grinders. In the stock sewer, sluicing or thinning water is added through pipe 15. The mixture of fiber then passes through slab rack or strainer 16 and into sliver screen 17, where the coarsest materials are scraped into sliver sewer 18, for disposal, and the fine materials pass through the screen and into the screened stock pit 36, from which they are pumped to the fine-screen distributing box 20 by means of centrifugal pump 19. The stock then passes into fine screen 21 68 MANUFACTURE OF MECHANICAL PULP §3 for further separation of the coarser fibers. Those fibers which do not pass through these screen plates are disposed of as tailings at 22, usually to a refiner. The mixture of fiber suspended in water, which passes through the screen plates, is suitable for manufacture into paper, and it flows into distributing box 23. This stock is then concentrated for storage or for commercial shipment in a thickener or wet machine shown at 24. The thickened stock passes out of the system at 25, carrying a small proportion of water with it. The water separated from the fibers contains from 15% to 20% of the original fiber content, and passes into a storage tank 27, through pipe connection 26. This tank, commonly called the white-water tank, is the source of supply for grinder showers 12 and for slush water pipe 15. It is very important that the supply of both shower and slush water be continuous while the grinders are in operation; to insure this an auxiliary fresh-water valve is usually provided at 28. The level of the water in the white- water tank 27 controls this valve, and it is so adjusted that it is closed whenever the tank is full of white water. The source of supply for the fresh water may be traced back to the strained- water pit beneath wire 8. The low-pressure fresh water is pumped by centrifugal pump 29 to valve 28, to auxiliary connec- tion 30, located in shower-water supply line, to supply water for floating pulpwood at 31, and to cooling water and hose con- nections on grinder bearings through reducing valve 32. It will be noted that at 30, provision has been made to use fresh water on grinder showers; this is usually done during the warm weather, to reduce temperatures in the system. Under these conditions, there is a surplus of water circulating in the system, and provision is usually made for reclaiming some of the stock, which would otherwise be wasted in the white water discharged from the system. The save-all 33 is used for straining the fiber out of this white water before passing to waste, as clarified white water, through outlet 34. The reclaimed stock, which is discharged at 35, is mixed with the fiber strained out at 25. . 87. Grinder Room and Wheel Pit.—Fig. 41 shows a cross sec- tion of a grinder room and wheel pit in a typical mechanical- pulp mill. The numbers up to 36 have the same significance as for Fig. 40. In addition to these common items, Fig. 41 shows: A, a horizontal, double-runner, low head, reaction hydraulic turbine, which supplies the power for driving the grindstones §3 Eee nes Y, THE MECHANICAL-PULP MILL Ml) oe 09 . ll 69 70 MANUFACTURE OF MECHANICAL PULP §3 connected to the turbine shaft at H. B,C are guide vanes; the water from wheel pit D passes through the guide vanes B and C, which direct the water against the turbine runners, located just inside the points marked B and C. The passing of the water through runners causes them to rotate and deliver power.to the grinder shaft at H. The circulation of water currents in the wheel pit is shown by solid arrows. D is the wheel pit, which, during operation of the turbine, is filled with water. J is a gate for the wheel pit; during operation this is open, but if the wheel pit is to be emptied, the gate is closed and water is drained out at V. F is the water level above the dam (forebay). G indicates iron racks, which are used to strain logs or other materials out of the water before it is allowed to pass through the turbines. JZ is a coupling, connecting the hydraulic turbine with the grinder shaft; K is the tailrace; and L is a draft tube. The water, after passing through turbine A, falls to the tailrace water level, through a cylindrical tube, the bottom of which is flared out and enlarged in area. The discharge of water to the tailrace from the turbine is shown by dotted arrows. M is a centrifugal pump, belt- connected to the grinder shaft. This is one of the types of pres- sure-water supply systems for the grinder hydraulic cylinders. N is a pipe gallery beneath grinder-room floor; it contains: (a) slush-water pipe (white water), 15; (b) shower-water pipe( white water or fresh water), 12; (c) grinder-pressure water pipe, 6; (d) return-water pipe d from grinder cylinders; (e) fresh-water pipe e for cooling bearings, etc. P is a crane, for handling grind- stones; & is an air pipe, for heating and ventilating; and T is an exhaust head, for allowing escape of moisture-laden air. Note.—The two grindstones nearest the turbine are shown with tops (casing) removed. | If the grinders were driven by electric motors, instead of being direct-connected to water turbines, the turbine A would have a generator at H, and the grinder shaft, in a pulp-mill at a distance from the power plant, would be connected to a motor. MECHANICAL-PULP MILL OPERATION 88. Establishing Grinder Conditions.—The details of the con- trolling factors to be taken into consideration for the manufacture of any particular quality of pulp are discussed 1 in Arts. 60-85, and they will not be repeated here. alll —_— = ————— §3 THE MECHANICAL-PULP MILL ral A natural condition that affects grinding operations is the variation in head that operates the hydraulic-power units and the available water storage. Fig. 42 shows sample curves for a typical pulp-mill turbine, operated at a constant speed of 240r.p.m. Curves Showing Horse Power Felveréd— Cubic heela 5ecopd Fassinglprougp lirbine, and Lificiepcy for Hydraulie lurbine peraling at £40 Kevolurions ver Mipuie. i ai ee . eee eel Afi AT fy he ln SS NBII eae NS Hei Es AS SNe a Ww S S / L) nae SS eee S NH YG or tS Cubic feel per Fecopd NS SeNEs BSN eis ERIS J Y ‘4 NG fepe ee me SS a EAG Sai aaa Fay. aes Ea Hie S ee Nig a, AS Fer lett £ Ss Per Cert Gale (pe7/7q Fig. 42. In ease it is necessary to conserve water, the turbines will be operated at their most efficient gate opening. By consulting the curves, it will be seen that the gate opening giving the maxi- mum efficiency at a head of 42.5 feet is 85%, when the power 72 MANUFACTURE OF MECHANICAL PULP §3 delivered is 1800 h.p. This gives the maximum power for a unit volume of water used under the standard speed of operation for the particular turbine installation tested. The quantity and quality of pulp made will be proportional to the total horsepower available and the degree of sharpness of the stone. In the spring- time, when there is a surplus of water, the turbines would be operated at the gate opening which would give the maximum horsepower output. Maintaining a constant speed of 240 r.p.m. at an operative head of 42.5 feet, the curves show that100% gate opening gives 2000 h.p. output, at an efficiency of 83%. It will be noted that the speed adopted for turbine operation was 240 r.p.m. This gives on a new 54-inch diameter grind- stone, a peripheral speed within the limits of good practice. (See Art. 80.) With the particular turbine used for driving the grinders, this speed is necessary; but in any case under investiga- tion, the curves shown in Fig. 38, for the relation of speed of operation, production factors, and quality of pulp, as shown by the Mullen (bursting strength) test on the paper, will give some indication as to what results may be expected. 89. Number of Grinders for Turbine Installation.—In order to - decide how many grinders may be driven by a turbine installa- tion, or to get an idea of the result of a proposed adjustment of speed and pressure, it is necessary to consider certain known factors and some that are known approximately, but which are subject to variations that are peculiar to the plant management, equipment, wood used, operating methods, ete. Suppose it is decided to make a news grade of pulp by means of three-pocket hand-fed grinders. The formula of Art. 77 gives h.p. = 0.000007933dN (uW)G, in which, h.p. = horsepower delivered at turbine shaft at the speed and gate opening selected (taken in this example as 1800 h.p.). d = diameter of grindstone in inches (here taken as 52 in.). N = revolutions per minute of grindstone (here taken as 240 r.p.m.). w = coefficient of friction between the wood and the stones (taken in this example as 0.16). W = total thrust of wood against grindstone for one grinder. With a 3-pocket grinder, having §3 THE MECHANICAL-PULP MILL 73 pockets 15 in. wide, the grinding surface per grinder, when pockets are 24 in. long, is 15 &K 24 xX 3 = 1080 sq. in. If the pressure per square inch of pocket area is 25 lb., the total thrust is We=11080' 25 = 27,000.lb. G = number of grindstones connected to the source of power; its value is to be found. Solving the above formula for G, and substituting the values here given, 1800 @ = 9,000007933 x52 x 240 x 16 x 27000 ~ * srinders. Evidently, four 3-pocket grinders (7.e., 4 grindstones) will be sufficient for this installation. The value, 4, for the number of grindstones, just found by means of this formula, is obviously a maximum figure, since it has been assumed that the total horsepower of the turbine was available. If the actual generated horsepower cannot be increased by further gate opening, the available power may be so reduced by such factors as character of wood, pocket binding, non-alinement of bearings, or if electrically driven, by loss of a certain amount of power in transmission, that it would become advisable to drive only three grinders from this turbine. Some mills bring their grinding capacity up more closely to the limit of available power by putting one or more four-pocket grinders on the line. Another way in which a small amount of excess power may be consumed, is to have on the line one grinder with a wider stone, say 32 in., to oie care of wood that is too long for the regular 27-in. stone. In the above equation, the total pressure against the grindstone is 27,000 lb.; hence, each hydraulic cylinder must supply a pres- sure (thrust) of 27000 + 3 = 9000 lb. If the grinder cylinders are 14 in. in diameter, the necessary water pressure for their supply is calculated thus: Let 7 = total of one cylinder (= 9000 lb.); d = effective diameter in inches of hydraulic cylinder, or 14 in. in this case; specific pressure of water supplied to hydraulic cylinder in pounds per square inch; P 9000 then, (804 X 147 Xp = 9000, or p = 7854 X 142 = 58.5 (Ib; per sq. in. It would be well to have the water pressure about 60 Ib. per sq. in. 74 MANUFACTURE OF MECHANICAL PULP §3 90. It will be noted that the coefficient of friction between the revolving stone and the pulpwood stick was taken as 0.16. This factor is subject to considerable variation, depending on the degree of sharpness of the stone, the grit of the stone, the amount of water used on the grinder shower, and the actual physical con- dition of the wood. When establishing grinding conditions in any particular mill, minor adjustments in pressure will be found neces- sary to provide for variations continually met with during oper- ation. 91. Starting Up the Pulp Mill.—It will be assumed that all pumps and equipment are at rest, and that all tanks and pits are in the usual condition when the pulp mill is started up. Since the mechanical-pulp making process is a continuous one, a regular sequence of operations is necessary to starting up the mill. The following outline is given, using Fig. 40 as a reference. 1. Open valve in pipe through dam 7, supplying fresh water to pump-well 8. 2. Start pumps 9 and 29; at the same time, Buen more air to tank 11, if necessary. 3. Valve 28 will then fill up tank 27, which will furnish supply of water at control valves at 12, 15, 16, 18. 4. Open valve 15, to fill up the stock sewers 14 and screen pits 36 with water. 5. Replace all dam boards for grinder pits at 13, and open shower pipes 12 on back of stone, so that grinder pit will fill up with water and flow over into stock sewer 14. 6. Start in operation screens 21, and deckers or wet machines 24. 7. Start screen 17, and open showers at 16 and 18. 8. Slowly open gates to hydraulic turbines to about 3% of the usual operating setting, making sure first that all the pressure feet on the grinders are delivering pressure against the stones. 9. Release pressure from some of the pockets, so that turbine starts revolving grinders; then put pressure on just enough pockets to keep stones in rotation while the turbine gates are opened to operating position. Supply a large amount of water on the stones, so they will not become heated. At the same time, the grind- stone pits should be kept full of water. 10. Start stock pump 19 and regulate its discharge #alve so that the volume pumped is just sufficient to carry away the §3 THE MECHANICAL-PULP MILL 75 mixture of fibers and water that passes through the sliver screen beneath 17. 11. Adjust flow through valve 15 until stock is of desired con- sistency for screening and pumping. 12. The system is now in continuous operation. The water used for conveying and classifying the fibers enters the stock sewers 14 and is pumped through the system to deckers 24, where the fibers are strained out, and the white water passes through pipe 26, white-water tank 27, and finally back to grinders. 92. Operating a Hand-fed Grinder.—One man usually oper- ates two hand-fed grinders. When there are more than two _WABRBBWWAAeseas’ _LRWABABAESVaBaae BAaBAaeasaeaseee NU SV, (i KS &) ZY &) 1) on): F e BAVAd RY a> (Oa) Wy DRESS cs N) BY Ly > a (Y Fig. 43. grinders connected to one source of power, the grinder operators must so arrange their pocket charging that there will be a mini- mum number of pockets off at the same time. The wood is piled by a helper in racks convenient to the reach of the operator. A general outline of the duties of a grinder operator is as follows: 1. He must sort out his wood and place it in the grinder pockets in such a way that there will be no pocket binding. Pocket binding causes a reduction in the pressure of the wood against the stone, due to some of it being transferred to sides of pockets by arch action. In Fig. 48, (a) and (b) show a good 76 MANUFACTURE OF MECHANICAL PULP §3 arrangement of wood in a pocket, (c) and (d) show a poor arrange- ment of wood in a pocket. 2. He must watch the motion of the tell-tale connected to each pressure foot, so he may be sure that there is no pocket binding or other source of interference with grinding. With inexperi- enced operators, the speed of the grindstones may become exces- sive, due to binding of wood in pockets. 3. He must regulate the temperature at which grinding takes place, by adjustment of the valve controlling the shower water on the back of the stone. As a guide to whether this is properly adjusted, he must watch the appearance of the pulp being dis- charged from the grinder pit. 4. He must keep an even flow of stock over the dam boards on the front of the pit. When this does not occur, it is necessary to clean out the grindstone pit with a fork-like tool provided for this purpose. 5. He must keep an accurate record of the number of racks of wood ground, unless the recording is otherwise provided. 93. Stone Dressing.—The stone dressing operation is the most important job in the mechanical-pulp mill. This operation is carried out by a man specially trained for this work, usually called a jiggerman, who follows the instructions of the grinder- room foreman. The object of the routine stone-dressing process is to maintain the stone production, taking into consideration the quality of wood ground, the grit, hardness or softness of the stone to be dressed, and the paper-making quality requirements of the stock to be made. To carry out this work satisfactorily, the foreman ~ must closely watch the variation in quality of wood, the freeness and general character of the final fiber mixture, the degree of sharpness of all the stones in the pulp mill, and the temperature at which the grinding is being done. It is here assumed that the other controlable variables remain practically constant. By inspection, the foreman notes the amount of stock over- flowing from the grindstone pit and checks the rate of production by feeling the rate of advance of the pressure foot as indicated by the telltale attached to the pressure foot of the grinder pocket. If the flow over the dam boards is small and the rate of cutting low, it is an indication that the stone needs sharpening or that some of the pockets are binding. If an examination shows the pockets are all free from binding, the fiber made is uneven, or too §3 THE MECHANICAL-PULP MILL ME fine and short, and the stone is warmer than the others, it is safe tosay that the stone requires sharpening. The decision to sharpen a particular stone is determined largely by comparison with the productive rates of the other stones and the freeness required in the finished stock. The grinder-room foreman may find, by an examination of stones, that the pulp is discharged from a grindstone pit in thick, bristly cakes. This is an indication that the stock is coarse and free. In many cases, the stock may have the correct consistency in passing out of the grinder pit and may appear to be satisfactory, but the rate of production may be found to be high, by examina- tion of the movement of the telltale. An examination of the stock in the blue glass test will show whether the uniformity, fiber coarseness, and length are satisfactory for the quality of _ pulp desired to be made. If the stock is found to be too coarse, or what amounts to a too free stock, the grinder-room foreman will “knock back” or dull the stone. In any given case, this process will be carried out in accord with the burring methods in use for the particular pulp made. The object is to dull the surface of the stone by the use of a finer-cut burr or brick, which is passed over the surface at a pressure decided upon by the grinder-room foreman, as proper to meet the particular conditions. 95. There may be large, fast grown wood in the grinder room during part of the day and small, slow grown wood in the grinders during the rest of the time. On the other hand, there may be a mixture of both woods in the grinder room at the same time. Whenever possible, it is desirable that two woods of such totally different qualities be ground on separately prepared stones; but if this is not practicable, the grinder-room foreman must adjust his stone surfaces in such a way that the quality of the final stock mixture is up to specifications, basing his action on all the infor- mation available. In some cases, as in the spring of the year, it may not be possi- ble to meet the requirements of stock quality with the combina- tion of natural conditions and a particular type of burr. The type of burr used must then be changed. When changing the burr on a grindstone surface, it is the usual practice to first “roll” the impression of the old burr from the face of the stone, using a fine cut burr, such as a 10-cut diamond. The fine burr is passed over the old surface a number of times, depending on the hardness 78 MANUFACTURE OF MECHANICAL PULP §3 of the stone; finally, the new burr impression placed on the stone’s surface, in the same manner as is generally used in stone sharpening. 96. The nature of the machines on which most mechanical pulp is used is such that the more uniform the quality of the stock supplied them the more efficiently they may be operated. It is therefore apparent that the grinder-room foreman must so arrange his stone sharpening that the interval between sharpenings is as constant as possible. Should a large number of stones be sharpened at one time, the physical properties of the stock would change (see Fig. 44) and cause operating trouble on — the paper machines. After sharpening a grindstone, the fiber mixture is usually made up of a combination of fine, re-ground fibers and of short, coarse fibers; the mixture gives a free stock and, consequently, a poor felting one. As the sharp irregular points on the stone’s surface are worn off, the fibers are drawn out and the stock slows up. These variations must be thoroughly understood, closely watched, and well managed by the grinder-room foreman. This is where the art in the manufacture of mechanical pulp comes strongly into play. 97. Importance of Freeness.—Reference has been made several times in Arts. 88-96 to the importance of the freeness of a mixture of mechanical-pulp fibers, and its indication of how the stock will act on a paper machine. Fig. 44 is a reproduction of a daily freeness-control chart used in a hand-fed mechanical-pulp mill, making a news grade of pulp. At the time the chart was com- piled, a mixture of black and white spruce containing less than 5% of balsam fir was being ground, 68 horsepower to the ton was being used, and there were 81 feet of stone width in operation, grinding 0.95 cord per foot per 24 hours. The intensity of pres- sure per square inch of pocket area averaged 27 lb., the average operating speed was 234 r.p.m., the grinding temperature was approximately 150°F., and the stones were dressed with a No. 10, 34-inch lead, spiral burr. Curve 1 shows the corrected variation in freeness of the stock leaving the sliver screens at 30-minute intervals for a period of 24 hours. This is the guide used by the grinder-room foreman in dressing the surfaces of his stones. ‘The desired uniform free- ness on the Green tester was 95. — ee §3 THE MECHANICAL-PULP MILL fa Curve 2 shows the variation in number of stones sharpened and dulled, and the time thus occupied. The stones sharpened are indicated by single vertical lines, placed above the base line at the point on the time scale where the stone was sharpened. When- ever a stone was dulled, it is indicated by a similar vertical line Freevess and While Waler Cops/slepcy Varlavion With STope Dharperi7g a RL ERA 100 1 er AN RY Wa Cy Pee wy BEEP PEEEEE Say OC ie oO. (Ae Fa Ce VORYIL a /0 ft OES Tirpe (tours Curve /. Tipe Varialiop ip Freepess with Sloct Leavig Sliver Fereeys. Curve 2. Variation ip Slopes Sharpeped and Pulled wil Tlie. Curve Variation i2 Consistency of Slust While Waler wiITP Tire. Fig. 44. below the base line. A close study of the relation of the time of burring to the freeness of the stock will show the regulation of the burring and dulling by the grinder-room foreman, in an attempt to maintain a uniform freeness of stock. In Art. 16 the deter- mination and expression of uniformity of groundwood pulp fibers were referred to. Information of this kind to supplement the 80 MANUFACTURE OF MECHANICAL PULP §3 freeness test would enable the grinder-room foreman to decide how far to go with his dulling and sharpening operations, in an attempt to maintain constant a factor, such as freeness, which does not completely determine the operating qualities of a stock. Curve 3 shows the variation in consistency of the. white-water used for thinning the stock discharged from the grinder pits. Since the fiber contained in this white water when mixed with the fresh ground pulp changes the drainage characteristics of the stock, a knowledge of this variation is necessary in the interpre- tation of the freeness of the finished stock. 98. Operating Control and Records.—The manufacturer of mechanical pulp endeavors to get the maximum amount of pulp GKINPER FOOM OPERATING FEF ORT (4) 68 Flicks Torack, 50ff wood fast grown, Qe pocket down hr. repacking Top gland. 70 Sicks Torack, wood stillgreen, slow grow, lor] 2 sticks of Jack Pine. /0 15, 3) roe Average vlerval of Tirge between sharpernipg-Fhes Tolals Te} Slush Waler 17) JSpower Water Cn as PIN OL Os | ime Cm Ol me foreqag Fia. 45. of suitable quality for paper manufacture from the minimum amount of wood and power, and with the least expenditure of effort and materials. In order intelligently to carry out this work, accurate quantitative information must be compiled of the opera- ting conditions from hour to hour and from day to day. This data must then be arranged in the form of records and charts, to furnish a guide for future operations. Fig. 45. gives a sample report for a mechanical-pulp mill. It is usually made out by the grinder-room foreman for his period on duty. It shows the details of his operations, and is used as a a elie he ee ea die ey ee ee §3 THE MECHANICAL-PULP MILL 81 guide for his operations and for the compilation of production statistics. Column (1). This space is marked stone number. It gives a record of the actual number of grindstones run. Here 11 refers to No. 1 line, No. 1 stone and 21 refers to No. 2 line, No. 1 stone (there are 3 stones on each line.) Column (2). Under this space, the grinder-room foreman enters the number of racks (here 3 cords) of wood ground by each stone; or, in the case of a grinderman operating two stones, the amount of wood ground by the two stones combined. This figure must be reported accurately, since it is the basis for the calcula- tion of the efficiency of conversion, as will be described later. Column (3). In this space, the number of grinder hours run are entered; opposite 11, in column 8, the 8 indicates that the grinder has been operated continuously for the full 8 hours of the tour or shift. Column (4). Incolumn 4, the lossin grinder-hours is indicated ; opposite line 12, it is indicated that one-third of a grinder-hour was lost; and in column 14, the cause of this is reported to be due to the re-packing of a cylinder gland. Column (5). This indicates the average pressure carried on the hydraulic cylinder. For any given grinder, this average should remain fairly constant, so long as the same quality of pulp is being made. Column (6). This refers to the amount that the gates on the hydraulic turbine are open. Knowing the operating head on the turbine and the speed of rotation of the grindstones, by referring to the turbine characteristics curves, Fig. 42, the horsepower delivered to the grinders may be calculated. Column (7). This gives the average revolutions per minute for the grinder. When the revolutions per minute of the grindstone and the diameter of the stone are known, the peripheral speed may be calculated. Column (8). This gives the average temperature of the stock in the grindstone pit, in degrees Fahrenheit. Columns (9), (10), (11), (12). These columns are used for reporting the particular burr used for dressing the stone’s surface and the time that the stone was sharpened. Column (13). In this column, the operating head of water for the hydraulic turbines is given. It is calculated as the difference in level of the water in tailrace and forebay. 82 MANUFACTURE OF MECHANICAL PULP §3 Column (14). In this column, general remarks relating to the operating conditions, quality and size of wood, etc. are indicated. Row (15). This row gives the totals of all the averages. Row (16). In row 16, under Nos, 1, 2, 3, 4, the number of turns of opening for each of the white-water ners supplying slush water to the stock sewers is indicated. These valves should all be calibrated, in order that they may be adjusted to supply the amount of water required for varying number of grinders in operation. The average pressure on the pipe line supplying white water is entered in the last column of row (16). Row (17). In the last column of row 17, the pressure in the shower-water pipe line is indicated. This acts as a guide for detecting any trouble, such as blocked pipes, and to make certain that a large enough supply is available at the grinder valves. Row (18). Under Nos. 1, 2, 3, 4, the valve openings of the stock and pressure-water pumps are indicated. 99. Determining Production——The amount of pulp made during the day is determined in different ways, depending upon the design of the pulp mill. The most accurate method, is to run the stock over wet machines (see Section on Treatment of Pulp), and then weigh and test for fiber content the pulp from the wet machines, or after it is pressed in hydraulic presses. When the amount of fiber of commercial quality is determined, the wood consumption is obtained from column (2) in the Grinder Room Operating Report, and the yield, or pounds of bone-dry fiber per barked cord, is calculated. The efficiency of conversion of wood into mechanical pulp (= F) is an important control figure. This is calculated by divid- ing the bone-dry weight of commercial quality of pulp per 100 cu. ft. of barked wood ground (= A) by the bone-dry weight per 100 cu. ft. of barked wood ground (= B); that is, A ea te For example, suppose there are 90 cu. ft. of solid, barked wood to the cord, and, as result of test, it is found that the wood ground contains 28.40% moisture and weighs 25.94 pounds per cu. ft. bone-dry. Suppose further that 100 cords of wood have been ground and 105.80 bone-dry tons of mechanical pulp have been made then wood ground = 100 X 90 = 9000 cu. ft. % §3 THE MECHANICAL-PULP MILL 83 Bone-dry weight of commercial quality of pulp per 100 cu. ft. of barked wood ground is NN = 2351.1 1b= A 100 Bone-dry weight per 100 cu. ft. barked wood is 100 X 25.94 = 2594 lb. = B Efficiency of conversion is Peer 2501.1 Ly ay 8 = “9594 ~*~ 100 = 90.64% This loss of about 9% of the wood is accounted for as screen- ings, or fibers unsuitable for paper making because of their size; white-water losses of very fine fiber, which passes from the cir- culating system with the surplus in white water passing to waste; water soluble constituents in the wood, which may easily go into solution, due to the finely divided state of the wood fibers and the high temperature of grinding. The horsepower per ton of pulp produced in 24 hours is equal to the rate of power delivered by turbines or motors divided by the bone-dry tons of pulp made in 24 hours. If, in the preceding example, an interpolation in the turbine characteristics curves showed that each of the four tur- bines used for driving the grinders was delivering on the average 1750 h.p., the total horsepower delivered would be 1750 X 4 = 7000 h.p. 7000 Then, -h.p. per ton = 105.80 7 65.22 h.p. per ton. QUESTIONS 1. Name the principal items of equipment in a mechanical-pulp mill. 2. Explain why either a decreased stream flow or a largely increased stream flow may result in a decrease in available power from hydraulic turbines. 3. What are the duties of a grinder room foreman? 4. What are the duties of a man operating a hand-fed grinder? 5. How is the time and degree of dressing a grindstone determined? GRINDING PROCESSES 100. Variation in Power for Same Quality and Quantity of Output.— When considering the grinding of mechanical pulp for different grades of paper, the reader is referred to Fig. 34(6) 84 MANUFACTURE OF MECHANICAL PULP §3 which shows that with a given horsepower input to the stone, for a given condition of speed and pressure, pulp of a wide variation in quality may be made. This is, of course, accompanied by a variation in tons of pulp made, sie is caused by the condition of the surface of the grindstone. In Arts. 28 and 29, the importance of the grit of the stone was pointed out. It is easy to understand that the more suitable is the grit in the stone for the quality of pulp to be made the less it is necessary to depend on the design of burr used. Without going into any more detail, the thought which the reader should get is that conditions vary in different pulp mills, depending upon just how the designer has made use of his natural conditions, and upon how the operation is carried out as compared with the original idea, as well as upon the policy of the management and the kind of pulp desired. An example that illustrates this point was given to the writer by one of the companies manufacturing burrs. In a mill making catalog-grade pulp, it was decided to try the same burr that was being used in another mill, with very good results, on the same grade of pulp. The burr in successful use was a No. 12 spiral, with a 2-inch lead. The same burr in the new mill gave a fine- fibered, slow stock; after some experimental work, it was found that a No. 7 spiral burr with the same lead gave the desired grade of pulp. In the new mill they used 30 lb. per sq. in. pressure on 14-inch cylinders, while in the old mill 60 lb. per sq. in. pressure on 14-inch cylinders was used, indicating twice as much. power to the grinder in the old mill. In the old mill, they had the advan- tage of the high intensity of pressure per square inch of pocket area, which, for a catalog-paper quality of pulp, required a fine spiral burr (No. 12 spiral, 2-inch lead). In the case of the new mill, their power conditions and pocket area, required the use of a lower pressure per square inch of pocket area; but to get the catalog-paper quality of stock, a coarser spiral bate was necessary. Assuming, then, that the anak made by both mills were the same, it is apparent that the mill using the lower pressure was paying more for power and labor attendance than was required by the other mill, to produce the stock quality required. 101. Newsprint Grade of Pulp.—The machines used for making newsprint paper vary in details of design and operation. If the speed of operation is high and the wire length (see Section on Paper Machines, Vol. IV) is short, a freer stock must often be §3 THE MECHANICAL-PULP MILL 85 made than for a machine operated at the same speed, but with a longer wire. The freeness of the stock made must also be varied with the proportion of sulphite used, the amount of beating and jordaning of the stock, the amount and kind of filler used, the temperature of the stock mixture, and the amount of fiber contained in the re-circulated water used for suspending the stock passing out on the wire. Variations in freeness of the stock, as delivered to the paper machine that is making newsprint, may be compensated for to a certain extent by varying the volume of water used for suspending the fibers; if the stock is made free in the grinder room, more suspending water must be used on the paper machine, to form the sheet on the wire; and if the stock is slow, less suspending water is required. For newsprint pulp manufacture, especially for machines oper- ated at over 600 feet a minute, it is almost essential to have a good quality of spruce wood. Small quantities of balsam fir, provided it is sound, are sometimes ground with spruce, without material effect on the quality of the pulp made. A power consumption of from 60 to 70 h.p. per ton will be required for newsprint quality of mechanical pulp. ‘80 /70 114. Constant-Pressure Centrifugal Pump, with Reducing Valve and Air Cushion.—Fig. 50 gives a diagrammatic layout of the system. It is the same one as included in Fig. 40. The centrifugal pump K in Fig. 50 operates at constant speed and maintains a delivery pressure somewhat in excess of what is required for the grinders. The reducing valve G is adjustable and controls the pressure in the grinder hydraulic cylinders. The water delivered to the grinders passes through pipe line J , into which is connected a tank I. .This tank is kept about two-thirds full of air under the same pressure as the water. The object of this tank is to equalize the pressure of the water in the system when a large number of pockets are thrown off at the same time. Water being practically incompressible, the result of a large volume demand on the centrifugal pump would be a pressure drop §3 THE MECHANICAL-PULP MILL 95 in the system. The air expanding in tank IJ under these con- ditions causes a delivery through open valve G of the water stored in tank. The gauge glass L is used to indicate the water level in the tank. This system has the advantage of being very flexible in use, prevents water hammer, and has a minimum of repair costs. It has the disadvantage of allowing speed variation, due to the constant-pressure water supply during pocket filling. Ceplrifugal Furgp ES Valvé Air CUusziog Fia. 50. 115. Special Grinder-Pressure Systems.—Considerable atten- tion has been given during the past two years to improvements in the pressure systems used for hand-fed grinder operation. For the hydraulic-turbine driven equipment, the object has been to find the most efficient speed of rotation for the operating head and gate opening on the turbine, and then to keep the prede- termined speed constant by varying the pressure in the hydraulic cylinders. In other words, the friction load on the turbine is maintained constant by varying the pressure in the hydraulic cylinder. Fig. 51 gives a general layout of a system of this type. Water is supplied to the suction side of centrifugal pump K, which operates at constant speed and delivers water at a pressure of 25-50 Ibs. per sq. in. above the average operating pressure in the grinder cylinder. The air tank F performs the same func- tion as in Fig. 50. The pressure-control valve at G varies the pressure in the grinder hydraulic-cylinders by throttling the _ high-pressure water that is delivered by the pump to the lower pressure at the discharge side H of the control valve G. The variation in the action of the control valve G is caused by the sprocket-and-chain drive, which connects shaft [ to control- 96 MANUFACTURE OF MECHANICAL PULP §3 valve drive shaft at J. If one pocket goes off (jams, or is opened for charging), the small speeding up of the grinders, due to load decrease, operates the control valve G, thus putting more pressure in the remaining cylinders and tending to maintain constant the total friction load of wood on grinders. Fig. 51. This system has many desirable features, and it is claimed that it saves as much as 15% of power and labor usually employed in the grinder department of mechanical-pulp mills. For motor-driven grinders, there are several systems in use, the object being to maintain a more uniform load on the driving motor. ‘The operation of these regulators is practically the same as the governor on magazine grinders, which has already been described. QUESTIONS 1, Mention some factors which cause a variation in the power consumed in the production of the same quality of pulp in different mills. 2. What grade of stone and condition of surface is satisfactory for the production of newsprint pulp? a _ ‘THE MECHANICAL-PULP MILL 97 ae What change in the method of dressing the stone might be made when producing pulp for wall board? or What quality of pulp is desired for the manufacture of manila paper? 5. (a) What is meant by brown pulp? (6) how is it produced? (c) what are its characteristics? AS For what grade of paper would you advocate the use of pulp manu- 1 dastired ey the Friedsam process? Why? * MANUFACTURE OF MECHANICAL PULP EXAMINATION QUESTIONS 1. What would you consider an ideal pulp stone? 2. What precaution must be taken in setting a stone with regard to the direction of the threads on the shaft? 3. What practical conditions largely determine the location of mechanical pulp mills? 4. Explain (a) what you mean by uniformity of pulp. (b) How it is tested? | 5. Describe a magazine grinder, and point out the differences between it and a hand-fed grinder. 6. Describe the different kinds of burrs, and mention the general effect of each on the character of the pulp produced. 7. How does the stone’s surface affect, (a) yield? (6) quality of pulp? (c) horsepower per ton? 8. (a) How does temperature of grinding affect the quality of the pulp? (6) How is the temperature controlled? 9. Explain what would happen if there should be a stoppage of water to the grinder cylinders, with regard (a) to the pulp production; (b) to the effect on the turbine and (c) to the effect on the grindstone. 10. Draw up a diagram showing the various stages of the manufacture of mechanical pulp. 11. What items should appear on the record sheet of a mechanical-pulp mill? 12. What conditions should be maintained for the manu- facture of pulp for cheap book paper? 13. What system of supplying high-pressure water to the grinder cylinders would you recommend for grinders direct- connected to hydraulic turbine? Explain your choice. 14. What main factors govern the power available for mechan- ical-pulp manufacture, where the grinders use water as a source of power? §3 99 SECTION 4 MANUFACTURE OF SULPHITE PULP By BsARNE JOHNSEN, Dr. Ina. HISTORY AND OUTLINE OF THE PROCESS HISTORY 1. Origin of the Process.—In 1866 and in 1867, the American Chemist, Benjamin Chew Tilghman, was granted English pat- ents on a process of cooking wood with a solution of sulphur dioxide SOz2 in water, with or without the addition of the bi- sulphite of an alkali, such as calcium bisulphite Ca(HSOs3)2 or magnesium bisulphite Mg(HSO3)o. The object of this process was to produce from wood a fibrous material suitable for the manufacture of paper, by removing from the wood the incrust- ing materials and recovering the pure fiber. These patents were the results of extensive experiments carried out by B. C. Tilghman and his brother, R. Tilghman, at the pulp and paper mills of W. W. Harding & Sons, in Manayunk, near Philadelphia. In his first attempts at cooking the wood with a solution of sulphur dioxide SO, in water at a high temperature and pressure, Tilghman obtained a pulp of dark color, which was very difficult to bleach. He discovered that the waste liquor from this cooking process. contained large quantities of sulphuric acid, and he attributed the poor color of the pulp to the action of this acid. He therefore added lime to the cooking acid, in order to neu- tralize the sulphuric acid formed during the cooking process, and the result was a pulp of light color and easy bleaching quality. _ 2. Paper makers who visited the mills at Manayunk at that time reported that experiments with the new process were made on a large scale and that a good grade of pulp was obtained. The §4 1 2 MANUFACTURE OF SULPHITE PULP §4 large-scale experiments were carried out in a horizontal cylinder, 50 feet long, with a diameter of 3 feet. This digester was made to rotate; it was lined with lead and was equipped with a worm of lead plate, which should act as a conveyor of the pulp during the rotation of the digester. The idea was to produce the pulp in a continuous process, the wood and liquor being forced through the digester, according to the counter-current principle. 3. It is obvious that enormous difficulties would be experienced with an experiment of this kind; and the reason why Tilghman was not able to make his process a commercial success must be attributed to the difficulties he had in preventing leakage, at the high pressure of 80 pounds, with this impractical equipment. Later on, he used a spherical digester, which proved to be more satisfactory. But, at that time, there was a drop in the price of soda, which made it possible to manufacture soda pulp at a low cost; and fearing the competition of the soda process under these circumstances, Tilghman decided to discontinue his experiments, after having spent several years and a fortune on the solution of the problem. 4. It is of historical interest to remember that Tilghman’s English patents included the cooking of wood with a solution of sulphurous acid and calcium bisulphite or other base. The patents also included recovery of the sulphur dioxide gases at the end of the cooking process, by absorbing them in water. It was also intended to utilize the waste liquor as a fertilizer or a binding material. Tilghman cooked spruce, hemlock, poplar, and willow, and his method of cooking was to boil ihe charge of wood and acid at 127°C. for 6 to 8 hours. 5. Making the Process a Commercial Success.—The Swedish chemist, C. D. Ekman, deserves the credit of having made the sulphite process a commercial success. Probably ignorant of the Tilghman patents, he had developed a process of cooking wood with a magnesium bisulphite solution Mg(HSO3)2, and started up the first sulphite mill in the world at Bergvik, Sweden, in 1874. This mill was equipped with six small rotating digesters, heated indirectly by means of a steam jacket and having a ca- pacity of about 800 pounds. The annual production of this mill was, In 1875, about 485 tons, and paper made from this sulphite §4 HISTORY AND OUTLINE OF THE PROCESS 3 pulp is still in existence. In 1876, Ekman published a pamphlet in Swedish, English, and German giving instructions for the use of this new product in the manufacture of paper. | At the same time the German chemist, A. Mitscherlich, was developing a sulphite process; but the experiments on a large scale were not entirely satisfactory in the first few years. It was not until 1880, that licensees of the process were able to produce commercially a pulp of good quality with Mitscherlich’s process, which really differed from the practical operation of the original Tilghman process only in that the wood was cooked at a low temperature and pressure and, therefore, more slowly. The heating of the wood and acid was done indirectly by means of steam-heated copper pipes, placed at the bottom of the digester. In Austria a sulphite process was developed by Eugen Ritter and Carl Kellner; it was operated secretly in their mills from about 1878, and was protected by an Austrian patent in 1882. Steam was admitted directly into the digester, and the time required for bringing the digester up to high temperature, and thereby the total cooking time, was considerably reduced. In America, the sulphite process was introduced by Charles 8. Wheelwright, who operated the Ekman process in the plant of the Richmond Paper Company, where he introduced many improve- ments in the manufacturing operations. Aug. Thilmany, who had bought the Mitscherlich patent for America and, in 1887, transferred the rights for United States and Canada to the International Fiber and Paper Company, directed the building of the first Mitscherlich mill in the United States for Geo. N. Fletcher and Albert Pack, in Alpena, Michi- gan. The Ritter-Kellner process was brought to this continent by Governor Russel and Charles Riordon, who built the first mill in Canada at Merritton, Ontario, in 1885. 6. Much credit is due to the pioneers in this industry and to the men who, during the comparatively short history of the sulphite process, have assisted in overcoming the technical difficulties of the early days and who, by the introduction of practical improvements in the processes, have made possible the development of the industry to its present importance. The production of the sulphite-pulp mills in the United States in 1925 was 1,400,000 tons, and in Canada, 843,000 tons. 4 MANUFACTURE OF SULPHITE PULP §4 OUTLINE OF THE PROCESS 7. Flow Sheets.—In diagram, Fig. 1, are show the flow sheets, which give the course of materials through the processes of con- version. Referring to (a), sulphur in the form of brimstone (S) or pyrites (FeS.) is burned in a sulphur burner or pyrites furnace, forming sulphur dioxide gas SOs. When using sulphur, the burning is completed in a combustion chamber; when pyrites are burned, a scrubber removes injurious dust. The gas is /low Seeks, Showy - Tower Syslery and Pirect Cooking Wilt: of-Ligee Systerp and lpdired Cooking Sufphur Jufohur Burger \CopbustigChapbe Sulphur Jufphur Burper\ \Copbustiglpagha or aha or or or ton or Fiyriles /oriles furpace Scrubber oe ites Furpace or Scrubber Ligesler tor [pdtrect Coofing ' Y Fil lo Screens | yy fry i phi etal, Fp to Sereegs| Blw Pit ae pon ae AC Nd) (a) 2) Course of Kew Malerial own Seta sk doneesos ” ” Gas 6900 le ee » ” Acid ” Oe ” Finished Marerial ” ” Fie. 1. cooled and passed into the bottom of the strong tower, and is mostly absorbed by combination with the limestone therein, in the presence of weak acid that trickles over the stones, forming strong acid. The weak gas escaping from the strong tower enters the weak tower, also charged with limestone, when it combines with the limestone and the shower of water, forming weak acid, which then passes to the strong tower. The strong acid goes to the reclaiming tower, to be fortified by suphur dioxide that is Cy Pie) oe ean a dle Re -- Sam paid, om 7 a F ~ - ~ §4 PREPARATION OF THE COOKING ACID so relieved from the digester during cooking. The relief gas is cooled before it enters the reclaiming tower, and the relief liquor is usually passed through a separator, which separates the gas from the liquor, the gas, and sometimes the liquor, being returned, after cooling, to the acid system. The fortified or cooking acid is then stored for use in the digester, into which the proper amount is fed along with the chips, and the cooking is done by introducing steam, which, in direct cooking—as here assumed—mixes directly with the digester charge. When the cooking is finished, excess pressure is relieved (relief handled as above), and the pulp, waste liquor, and gas are forced into -a blow pit. Steam and gas escape by a vent, waste liquor drains through the perforated false bottom, and the pulp is washed and pumped to the screens (as described in the Section on Treatment of Pulp). | Figure 1 (6) differs from (a) in that lime, instead of limestone, is used; this is treated with water in a slaking tank, to make milk of lime, which is used in an absorption tank or tower system to make strong acid, and which is fortified as above described, to make cooking acid. Chips and acid are charged into the di- gester; but in indirect cooking—assumed for this case—the steam does not mix with the charge; it enters a coil in the digester, which accounts for the condensate (condensed steam) noted in the diagram. Pulp, waste liquor, and gas are handled as described. Hither form of sulphur, either form of acid apparatus, and either form of digester may be combined, as desired. PREPARATION OF THE COOKING ACID 8. The preparation of the bisulphite liquor for the cooking process consists of (a) The burning of sulphur or pyrites; (6) the absorption of the resulting sulphur dioxide (SO) gas in a -milk-of-lime solution or in water in the presence of limestone; and (c) the strengthening of the acid with sulphur dioxide recovered from the cooking process. The raw materials used in this proc- ess are sulphur or pyrites and lime or limestone. 6 MANUFACTURE OF SULPHITE PULP §4 RAW MATERIALS SULPHUR 9. Occurrence and Properties.—Sulphur is a brittle, pale yellow solid. It melts at 113°C. to a mobile liquid of anamber color, but upon further heating it becomes thick; at about 200°C., it is so thick that it will not flow and has assumed a dark color; at 350°C., the sulphur again becomes fluid, but retains its dark color. Sulphur ignites at 248°C. and boils at 445°C., giving off dark brown vapors, which upon cooling, are condensed to a fine yellow powder called flowers of sulphur or sublimed sulphur. Brimstone, or roll sulphur, is formed by melting sulphur and casting it in sticks. There are other modifications of sulphur, which, however, are not of particular interest in acid making. The chemical symbol for sulphur is §, its atomic weight is 32.07, or roughly, 32; and one atom of sulphur will combine with two atoms of hydrogen or with one atom of a bivalent metal, forming so called sulphides. But the valence toward oxygen is variable. The most impor- tant of the oxygen combinations are sulphur dioxide SO2 and sulphur trioxide SO3, which form with water sulphurous acid H.SO; and sulphuric acid H,SO, respectively. Other combina- tions of sulphur, oxygen, and water are known as Thiosulphuric acid..... H28203 = (S202 + H,0) Dithioni¢c acid. 74. H.S20,4 = = (S205 + H.0) Trithionic acid......... HeS306 = (S305 + H2O) 10. The main sources of sulphur, as far as the sulphite pulp industry of the United States and Canada is concerned, are Louisiana and Texas, where it is found in free form about 600 feet and more below the surface. It is recovered in enormous quantities by melting with superheated water and pressing it to the surface by means of hot compressed air, and requires no further purification. Some sulphur is imported from Japan. 11. Sulphides.—Sulphur also occurs in nature in combination with metals as sulphides, such as iron sulphide, or pyrites, FeS2, which according to the formula contains 53.46 per cent sulphur and 46.54 per cent iron; but it is only seldom found in nature in this high purity. Usually, it occurs in mixture with sulphur compounds of other metals, such as copper, zinc, lead, etc., $4 PREPARATION OF THE COOKING ACID ff partly as sulphates and partly as sulphides, and the value of the ore for the sulphite pulp industry depends very much upon the quantity and nature of the accompanying metals. None of the other natural sulphides are so high in sulphur or part with it so easily as iron sulphide. Copper sulphide is detrimental, not only because it lowers the percentage of total sulphur in the ore but also because its greater fusibility makes it more difficult to regulate the temperature of roasting. Pyrites containing more than 8 per cent copper can be profitably employed only under very exceptional cirumstances. Lead sulphide also increases the fusibility and reduces the yield of sulphur in the roasting process, since it forms sulphate, which remains as such in the cinders. A good pyrite should be nearly free from lead, zinc, arsenic, antimony, and selenium. Regarding the last, it is well known that the presence of even very small quantities may cause serious trouble in the sulphite cooking process. The value of pyrites as compared with sulphur is of course determined by the price of recoverable sulphur at the mill, which again depends not only upon the location of the mill but also upon the chemical composition, as discussed above. LIMESTONE AND LIME 12. Limestone.—The appearance of a limestone depends upon the purity of the stone. In its purest form, the stone is white and crystalline, and it consists, practically, only of calcium car- bonate CaCO3, as, for instance, in marble. But the stone usually contains impurities, such as oxides of iron and aluminum and insoluble silica, which affect the appearance of the stone. This varies from the highly crystalline variety to the amorphous, porous stone, while the color may vary from white to yellow and grey. Also, the specific gravity varies, and is highest with the highly crystalline stone. The solubility of the limestone in sulphurous acid increases with the crystalline character and, of course, with the strength of the acid. Usually, the limestone contains magnesium carbonate MgCO;, and the properties of the stone vary according to the amount of magnesia. 13. Dolomite is a calcium-magnesium carbonate, normally containing 54.27% calcium carbonate and 45.73% magnesium 8 MANUFACTURE OF SULPHITE PULP §4 carbonate. But a stone containing one MgCO; to two CaCO; is also called dolomite. Limestone and dolomite are found in many places in ae: United States and Canada and in many different qualities. The variations in the composition of such stones are shown in the following table: Fess Insoluble CaCO; | MgCO; and Al,O matter Average Portneuf Co., Canada...... 95.80 1.30 | 0.60 1.25 Average Lake St. John, Canada..... 85.90 1.95 | 0.95 9.10 Marble Stone, UoS.4.42 eee 99 05) Pe ae 0.11 0:40 Bleachville, Ont., limestone ....... 07.63: hal aes 0.22 0.13 White Hock, Ohio.203, 2 cen ae 58.62 | 37.82 | 0.97 0.70 Portage duasfort..¢¢ 1 ee 55.76 | 48.40] 0.12 0.68 14. Lime.—Lime CaO is obtained by burning limestone, and the composition therefore depends upon the quality of the limestone. The reaction is Se Sie by the equation. CaCO; + heat =CaO + COs. While a low magnesia content, preferably not above 5 per cent, is considered the most suitable for the tower system, a high magnesia lime is preferred in the milk-of-lime systems. The composition of limes used in acid making is given in the follow- ing table: (1) (2) ess Perr CENT Per CrentT Per CENT Calcium,oxide, CaQ. sy cae canes 56.02 58.61 55.96 Magnesium oxide, MgO............ 40.10 40.25 37.98 Alumina and ferric oxide, Al,O3 and : Fe.0; gee RAN ESC a ca atte. (al We Eee) Woe: el SESS Ee aED 0-57 0.12 + 20 Sulphur trioxide, SOyat 20s tees 0.11 0.15 0.16 Ingolublevinstielg says Aion oe 0.94 0.07 1.51 Silica soluble in acid, SiOe.......... 0.47 0.15 1.81 Loss on ignition, H.O, COs, etc...... 1.43 0.51 1.00 §4 PREPARATION OF THE COOKING ACID 9 PREPARATION OF SULPHUR DIOXIDE 15. When sulphur or a sulphide burns, it combines with the oxygen of the air to form oxidation products of sulphur, mainly sulphur dioxide SO. The nature of the gas, the proportion of the sulphur dioxide to the other combinations of sulphur and oxygen, depends upon the prevailing conditions, such as the temperatures to which the gases are exposed and the proportion of sulphur gases to oxygen or air. In other words, the quality of the gas depends upon the construction and the operation of the sulphur burner or the pyrites furnace. SULPHUR BURNERS 16. Flat Burner.—The flat type of sulphur burners is essenti- ally a retort, to which the sulphur is fed intermittently through a door at the front. The retort itself is a one-piece iron casting, about 84 feet long and 33 feet wide; the cross section forms an arch with the highest inside dimension of 18 inches. The gases leave through an 8-inch pipe, which is usually bolted to the back of the furnace. To the open front of the furnace is bolted a second casting, which carries the door. The furnace rests on a brick foundation, and it is usually placed on rollers, to permit free expansion and contraction. The capacity of these burners is only about 5 pounds of sulphur per square foot of surface per hour, and they require, therefore, much floor space. Unless the flat burners are equipped with rakes to agitate the surface of the molten sulphur, they are inefficient, since the sulphur often contains a small quantity of oil, which during the process of burning forms a layer on the surface resembling asphalt, and this layer prevents the free contact of sulphur and air. The flat burners have now almost disappeared from the sul- phite mills, and modern plants are usually equipped with the more efficient rotary burner or the stationary vertical type. 17. Rotary Burner.—This consists (see Fig. 2) of cast-iron or steel cylinders A, to which are riveted the conical ends B. The burner rests on rollers K, which are revolved by means of gears, which give the horizontal cylinders a slow rotating motion of about 14 revolutions per minute. The burners are built in different sizes, depending upon the requirements of the mill, 10 MANUFACTURE OF SULPHITE PULP §4 two burners 4 feet diameter and 15 feet in length being sufficient for a 100-ton mill. | The front cone of the burner has a damper F, Fig. 2 (c), to regulate the admission of air; it is also equipped to receive the sulphur, either in solid form, by means of a worm from a hopper placed immediately in front of the burner, or in melted form, through a pipe C extending through the axis of the burner. In the latter case, the sulphur is often melted in a tank D, equipped Fira. 2. with steam coils, from which the molten sulphur flows to the various burners. But many mills have placed the melting tank just above each individual burner or over the combustion cham- ber, thus utilizing the heat from the burner and decreasing the steam consumption for this purpose considerably. When the burner revolves, the molten sulphur adheres to the side of the cylinder and is carried some way up the side before it drops back, thus increasing the surface of the sulphur mass exposed and giving efficient combustion. The rear cone is connected up to a short pipe line leading to the combustion chamber EH, which is a large steel chamber in which the gases from the burners are mixed thoroughly with air, in order to $4 PREPARATION OF THE COOKING ACID 11 secure complete combustion of any sulphur that may have been vaporized, but not entirely burned in the rotary. An auxiliary damper H between the rotary and the combustion chamber enables the operator to admit and regulate the extra air necessary for complete combustion. 18. It isa very easy matter to start up a rotary sulphur burner. If the sulphur is fed to the burner in solid form, the fire is started by throwing into the burner some rags soaked in oil, and then gradually feeding the sulphur. With liquid sulphur feeding, the sulphur in the melting tank must at first be heated to the melting point by admitting steam to the coils; at the same time, the sulphur in the pipe lines leading from the melting tank to the burner must be melted by applying a torch or a gas burner. In starting up, time may be gained by heating the burner itself with direct fire. | 19. Stationary Sulphur Burner.—The vertical, stationary burner known as the Vesuvius burner, Fig. 3, consists of an upright cylindrical steel shell, lined with fire brick, and equipped with four trays, one above the other. On the top is a large melting ket- tle A for sulphur, with a needle valve Bin the bottom. The valvecan be adjusted so as to admit a certain quantity of sulphur to the trays. The burner is started by building a fire on the top tray C, whereby the sulphur melts in the kettle; and by opening the needle valve a little, sulphur drops into the top tray C. When the top tray is full, the sulphur overflows into the next tray, from which it again overflows on the opposite side into the third tray. Each tray has a door and a damper D, to admit the required amount of air. The ashes collect at the bottom EH of the burner, while the gas leaving the top tray passes through the combustion chamber attached at F, and _ sufficient air for complete com- bustion is admitted at damper H. Regulation of draft is possible both by the opening of tray doors and by the damper K. This burner takes up very little space, requires no power and works automatically when once started. lpwel., ts 12 MANUFACTURE OF SULPHITE PULP §4 BURNING OF PYRITES 20. Reason for Burning Pyrites.—Owing to the compara- tively low sulphur prices and the simplicity of the process of sulphur burning, only very few sulphite mills on the American continent have used pyrites for the production of sulphur dioxide. But there are numerous deposits of pyrites in both the United States and in Canada; and with the modern types of furnaces, the roasting process is very simple and efficient. So it is actually only a question of the price of sulphur at the mill as com- pared with that of the pyrites ore, whether it would not be an economical advantage to replace the sulphur with pyrites. Of the many types of furnaces, the Herreshoff furnace and the Wedge furnace are most commonly in use in sulphuric acid plants in America and in Europe, as well as in European sulphite mills. 21. Herreshoff Furnace.—The Herreshoff furnace, Fig. 4, consists of a steel cylinder A lined with red brick B. It is divided by arches C, of fire brick, into several compartments, one on top of the other. The top of each of the arches forms a hearth upon which the ore is burnt. | Through the center of the furnace runs a hollow shaft D, which is driven by means of gears HE at the base, so as to make one revolution in two minutes. For each chamber, two hori- zontal arms F are attached to the central shaft, with lugs fitting into sockets on the shaft, and are held in place by their own weight. It is an easy matter to renew the arms during the operation of the furnace. The ore is fed automatically to the top chamber from a hopper K on the top of the furnace, and is distributed on the hearth. The rabbles (teeth) of one of the arms are set at such an angle that the ore is moved toward the center, while the position of the rabbles on the second arm causes the ore to turn over, whereby a large surface of the ore is exposed to the air. Arriving at the center of the top chamber, the ore drops through an opening into the chamber below, in which the rabbles slowly work the ore towards the outer edge of the hearth, where it drops into the chamber underneath; on the next, it is worked to the center, and so on, until the ore finally has passed through all chambers, and is discharged as cinder to the bottom shelf or chamber. ‘The air is admitted through openings around the bottom hearth, and passes through om 22 §4 PREPARATION OF THE COOKING ACID 13 all the chambers in the direction opposite to that of the ore. The quantity of air is so regulated as to secure the proper com- 9 \ | a Pp ‘s. ‘= @, So i v Ca — “ee beta emma x us Fs ‘ 4 : 2 ee aa (ZZ ean f ZAM AZZ ae Li cH Baw: Saige 4 223 ea a aw i= ; FECES zy rH Gy hee a LNW, ee NN : ULL IA TISSI TI. WI, VA <2 SES TA A) LRT ee rr kes TEER IO Gy JE Remain eoeeen yo Ao WLLL Li ‘(o—, jh ea = ne = a Am . W397. Wn -p Sj VZZZ) Vpn ieee ee : eee abl a = Aaa HA | — in 1 WILT : WY Vie —_—EEs il HN SSS A mire stan YG Nee $2 A ra} ~~ CGH bustion of the sulphur, so that the gas leaving the furnace from the top chamber at H carries the desired quantity of sulphur dioxide. The hollow central shaft and also the arms are cooled 14 MANUFACTURE OF SULPHITE PULP §4 with air. The small-size furnaces, of about 11 feet diameter, require 1 to 2 horsepower and will roast from 3 to 4 tons of pyrites in 24 hours. The larger size furnace, 16 feet in diameter, will roast about 9 tons in 24 hours. In the modern type of furnace, the individual rabbles can be replaced, and the cooling air to the shaft and arms can be regulated, so as to permit an effective control of the temperature within the furnace. 22. Wedge Furnace.—The Wedge furnace is very similar to the Herreshoff furnace in construction, but possesses certain characteristic features. The central shaft, which makes about 1 revolution in 4 minutes, has a diameter of 5 feet and is open at top and bottom, allowing air to circulate. It is sufficiently large and cool for a man to enter during the operation, for repair of the arms. The outside of the shaft, which is made of riveted steel plate, is protected by fire brick. The rabble arms are hollow and are equipped with pipes for air as well as water cooling. ‘The furnace has 7 horizontal hearths. The ore is automatically fed to the hopper and drops to the top shelf, where it is stirred by special rabbles and dried by the heat from the furnace. From this shaft, the dried ore drops to the center of the top hearth, and is slowly conveyed by the rabbles toward the periphery, as in the Herreshoff furnace. The cinder is discharged from the bottom hearth. The capacity of the furnace varies from 23 to 33 tons of ore in 24 hours. One furnace of the largest size would be sufficient for a 100-ton mill, assuming a sulphur content of 35 to 40 per cent of the ore and a sulphur content in the cinder of about 2 per cent. However, it is advisable to install two furnaces, to allow for repair shut-downs. Another type of furnace is similar to the rotary furnace de- scribed in the Sections on Soda Pulp and Sulphate Pulp. The pyrites, which must be thoroughly dry in any case, fall in a shower, as the furnace rotates, through the current of air passing through the furnace. 23. Starting a Pyrites Furnace.—The starting up of a pyrites furnace is more difficult than to start a sulphur burner and takes considerably more time, depending, of course, upon how long the furnace has been down. Before any ore is admitted, the furnace has to be brought to the required temperature for roasting, by maintaining a good fire in the furnace. When the desired temperature is reached, the pyrite, which has been dry- ee | §4 PREPARATION OF THE COOKING ACID 15 ing in the top chamber, is gradually fed to the furnace, and the air is regulated by means of the dampers, as well as by the gas pump or fan. BURNER GASES 24. Quantity of SO. Formed.—In the sulphite process, it is the object of the sulphur burning to form as much sulphur dioxide as possible, and to prevent the formation of other combinations of sulphur and oxygen. When, in the burning process, the sulphur unites with the oxygen of the air to form sulphur dioxide, according to the equation, mo O02 = SOs, one volume of oxygen forms an equal volume of sulphur dioxide. The volume of sulphur dioxide in the gas leaving the burner can therefore never be higher than the volume of oxygen present in the air supplied to the burner. Air contains about 21 per cent oxygen and 79 per cent nitrogen by volume, and the maximum SO2 content theoretically obtainable in the burner gases 1s therefore 21 per cent. But a gas of this strength is never ob- tained in practice; it varies usually between 14 and 18 per cent, depending upon the operation of the burner and the method of cooling the gases. The regulation of the air supply to the burner is the most important factor in this operation, since upon the air supply depends the extent to which the sulphur is oxidized and the extent to which the gases are diluted with excess air. If an insufficient quantity of air is admitted, sulphur will evaporate and condense in the coolers, in the form of sublimed sulphur, which will cause serious difficulties in clogging up the pipe lines; or it may partly reach the absorption system and seriously interfere with the cooking process. In either case, it means a direct loss in sulphur. 26. Combustion Chamber.—It is the principal object of the combustion chamber, Fig. 5, to assist in preventing sublimation, by completing the combustion of the sulphur. This is nothing but a large steel chamber, lined with brick that is backed with fire clay, located closely behind the burner, in which the gases are intimately mixed, and is equipped with dampers (H, Figs. 2 and 3) for admittance of air, if required. The combustion chamber has also one or more baffle plates or walls, to hold back 16 MANUFACTURE OF SULPHITE PULP $4 any dust particles and to assure effective mixing of the gases. In a great many mills, the value of the combustion chamber is not sufficiently recognized, and it is often built too small. In Cipder Copcrele oO NC IN EK BL KN lad Lt ‘ a BRR RNNN NS by WY ESS SSS NES ISR OASAASS PAI RK KK a eee Ps RSRSANESSSI RANIAAAINY RARASSRSNY SSSASSSSISY RSISSAAISSY 4 e i RASA RNSSASSASY KRSASASAASASS SSSI WARARATAN ISEASATASS) i RNESANSESSS] i AAAINAAINS V4 yA RSASSSBSSS A: PAST ZAZA SSV ZR ZS LAS POT TIRLWWV 77 ZENS ZEN ZZ NV ZN iGo: equation Fig. 5, the gases enter at LH, pass through the baffle wall by the holes W, and leave by outlet F. K and L are cleanouts. 27. Effect of Tempera- ture.—The temperature of the gas as it leaves the combus- tion chamber and enters the cast-iron pipe that connects it with the coolers is usually from 700° to 900°C. Itisim- portant to keep the tempera- ture at this point, in order to avoid the formation of any large amount of sulphur triox- ide gas SOz, which is always formed to some extent in the sulphur burning process. It is important to keep the SO; content of the gas as low as possible, since it combines with the calcium in the ab- sorption system, forming cal- cium sulphate CaSO,, which is an insoluble salt, and which represents a direct loss of sulphur. The presence of sul- phuric acid in the digester is also detrimental to the fiber in the cooking process. The formation of sulphur trioxide SO; according to the SO. + O = 803 depends in the first place upon the temperature. It is found that between 400° and 600°C., the maximum of SO; is produced; §4 PREPARATION OF THE COOKING ACID hg while at temperatures below 200°C. and around 900 to 1000°C., practically no SOs; is formed. It is therefore important to avoid the critical temperatures as much as possible; or, in other words, to keep the temperature in the combustion chamber high, and to cool the gases after leaving this chamber as quickly as possible. 28. Importance of Regulating Air Supply.—The rapidity with which the sulphur dioxide is oxidized to trioxide is also increased in the presence of much oxygen, and a large excess of air should therefore be carefully avoided. The correct amount of air required per pound of sulphur in order to produce a gas of a certain strength can easily be calcu- lated. In the following example, a strength of the burner gas of 16% is assumed, and it is assumed that there is no sublimation and no SO; formation. According to the formula, SOs = S09 | , 82 32 64 One molecule of oxygen Oz is used in the formation of one mole- cule of sulphur dioxide SOs, or a certain volume of oxygen gives an equal volume of SO2. On the other hand, one pound of sulphur combines with one pound of oxygen forming two pounds of sulphur dioxide. Or, one pound of sulphur reacts with one pound of oxygen, giving a volume of 11.75 cu. ft. at 20°C. and atmospheric pressure, producing a burner gas containing 11.75 cu. tt. of SOs. | Since the strength of the burner gas is assumed to be 16% 11.75 cu. ft. of oxygen required to produce this strength represents 16% of the total air admitted, assuming all the oxygen to be converted to sulphur dioxide. (In practice, a slight excess is required.) Therefore, volume of air = ao = 73.4 cu. ft The air and sulphur should be as dry as possible, since the pres- ence of moisture encourages the formation of sulphuric acid. GASES FROM PYRITES FURNACE 29. Amount of SO, Obtained from Pyrites——When sulphur dioxide is formed from pyrites, the following reaction takes place. 2FeS2 -+ 110 = Fe.03 + 4802 18 MANUFACTURE OF SULPHITE PULP §4 In this case, one portion of the oxygen is consumed in the oxida- tion of iron to iron oxide, and, from the equation, it is seen that, with pure pyrites, 3 volumes of oxygen are used in this oxidation for every 8 volumes of oxygen required in the formation of sulphur dioxide. In order to produce the same amount of sulphur dioxide, correspondingly more air is required in burning pyrites than when elementary sulphur is used, and the gases are accordingly more diluted with the extra nitrogen introduced. While the strongest gas theoretically obtainable in the burning. of sulphur is 21% (air contains about 21% of oxygen), the theoretically strongest gas with pyrite is 15.38% sulphur dioxide. In practical operation, a 12 to 14% gas may be obtained with modern equipment. The volume of air per pound of pyrite naturally depends very much upon the compo- sition of the ore, which also determines the consumption of oxygen. 30. Effect of Catalyzers on Amount of SO; Produced.—The quality of the gas leaving the furnace is also more variable than 50, 10 Ce er as Baa Sie ie \ y 250 300 400 500 600 700 800 2900 /o00T Fie. 6.—Effect of Temperature and Contact Substance upon the Formation of SOs (percentage of SO2 to SQs3). (a) No contact substance. (b) Contact with cinder from furnace (Fe2O3-CuO). (c) Contact with platinum. (d) Stability of SO3 in absence of contact substance (SOs decomposes at high tempera- ’ tures to SO2 + O). that from the sulphur burners, and it requires a special purifica- tion. The gas usually carries with it considerable quantities of mechanical impurities, which have to be removed in so-called dirt catchers or dust chambers, or by filtering, or by electrical precipi- $4 PREPARATION OF THE COOKING ACID 1g tation. The amount of SO; is also usually much higher, and it has to be removed in a special washing process; this is due to the fact that sulphur dioxide is more easily oxidized to sulphur trioxide in the presence of certain substances, as iron oxide. In the burning of sulphur, the only so-called catalyzer present is the metal of the burners and the piping; while in the pyrite process, the ore itself acts as a contact substance and accelerates the formation of SO;, even at the lower temperatures. The curves shown in Fig. 6 will give an idea of the action of such contact substances. 31. Removal of SO; from Gases.—The SQ; is usually removed in gas washers or scrubbers, which are nothing but chambers of lead, in which the gases meet with a fine spray of water. The SO; is easily absorbed; but only a small proportion of SO, is absorbed, due to the low solubility of this gas at high temperature. 32. Also, electrical precipitation according to the Cottrell process is used in some mills. Recently, it was suggested that the gas be filtered through sawdust. The SO; and sublimed sulphur are absorbed by the sawdust, and other oxidation prod- ucts, such as sulphur sesquioxide 8.03; and polythionic oxides (S20; and §;0;), are decomposed by the SO;, which is already absorbed by the filter, into SOs, which follows the gases, and into SO; and §, which are retained by the sawdust. This prevents the formation of these products in the cooking acid, where the SO; and, especially, the finely divided sulphur are extremely injurious in the subsequent cooking process. COOLERS 33. Types of Coolers.—It was already mentioned that a rapid cooling of the gas is very important in the production of a pure gas. At high temperature, the dry gas may be passed through cast-iron pipes; in some mills, these pipes are made rather long, allowing the gas to air-cool to some extent before it reaches the actual gas coolers. This is not good practice, since there is a danger of keeping the gas too long at the critical’ temperature for the formation of SO;. It is better to make the connection between the sulphur burners and gas coolers as short as possible and to make the cooling as rapid as possible. 20 MANUFACTURE OF SULPHITE PULP §4 34. There are several types of coolers in use. In many mills a au (1 4 4 4 g 4 Y 4 4 6 4 g y 4 g 4 4 6 4 4 6 4 g g 4 y g 4 y) 4 y g Y 4 4 4 4 4 4 4 g 4 5 4 ~ ale pond cooler is used, consisting of 6-inch lead pipes arranged parallel to one another and con- nected with flanges to lead head- | ers. The whole system being placed in a pond, the gas enters at one header and passes through the pipes, leaving at the oppo- site header, while the cooling water is running in the opposite direction, cooling the outside of the pipes. With good circula- tion of the water, a fairly good cooling is obtained; but it is obvious that with this method, the cooling water is not used to its fullest advantage, since the water nearest to the pipes will receive most of the heat. 35. A more efficient cooler is a combination of the submerged, horizontal-pond cooler and a ver- tical cooler consisting of vertical lead pipes connected at the top by U bends. The water is sprayed onto the pipes at the top, and flows down along the pipes, forming a thin film around the pipes. With this cooler, the gas may be cooled nearly to the temperature of the water. A cooling system of this type is shown at D in Fig. 13. 36. A still more efficient cooler is the patented cooler, Fig. 7, in which a great number of 1-inch lead pipes A are arranged vertically, and are connected to headers at top and bottom. The cooling water enters at C, at the top of the cooler, and leaves at §4 PREPARATION OF THE COOKING ACID 21 D, at the bottom of the cooler; the gas enters the bottom header at H, leaving through the top header at F. This cooler offers a larger cooling surface for the gas and uses much less water than those already mentioned. It may be considered a disadvantage of this cooler that the rather narrow pipes may be plugged, in case of much sublimation of sulphur. 37. In order to obtain an effective mixing, and consequent _ cooling of the gas, a new cooler has recently been developed. It Solsbilily of 5p, lerzperature Fia. 8. consists of corrugated lead plates, connected up to headers and _ forming chambers, through which the gases pass while the water flows on the outside. The corrugated sides effect an intimate mixing of the gases and afford a large cooling surface. The important point with a cooler is that it have sufficient capacity, both with regard to cooling surface and to diameter of the pipes. If the cooler is too small to permit the free passage of the gas, the result may be overheating in the burner, with sub- limation, and high vacuum on the line behind the cooler. 38. Main Object of Cooling Process.—While a rapid cooling of the gases is important in order to avoid the formation of large amounts of SO;3, the main object of the cooling process is to bring the temperature of the gas down to a point at which the 22 MANUFACTURE OF SULPHITE PULP $4 SO, is easily absorbed by the water. The solubility of the sul- phur dioxide in water is greatly dependent upon the temperature and also upon the pressure. This is shown in the preceding and following charts, Figs. 8 and 9. From these charts it is obvious that at low temperature and high pressure the same quantity of water will dissolve a larger amount of gas than at high temperature and low pressure. In Fig. 9, the pressures are given in millimeters of mercury and their Solubility of SQ; in Walter a? Various Fressures and Temperatures Yn lbs. Metcary 272 8/400 \ oe % AN ASS 23.2 3/200 % /93 — 1 + Volume of Waler CC. 5 6 7. 8 9 IG) H AZ IFA ee glo 50, by Volume Fia. 19. If the volume of water in the latter determination was 67.3 c.c., the percentage of total acid as SO2 was 14.0 (see table), and therefore the SO; content was 14.0 — 13.53 (previously found) A = 0.47%, or, based upon the total absorbed gas, os xX 100 = 3.36 % SOs. 72. Richter’s Method.— While this apparatus can be used for the determination of SOs, it is customary to determine the SO2 with the Orsat apparatus; and for an exact determination of SO. content, Richter’s method is recommended. According §4 PREPARATION OF THE COOKING ACID 47 to this method, the gas is passed, at a rate of 1000 ¢.c. in 20 to 25 minutes, first through a hard-glass sampling tube, surrounded with an iron jacket, and then through a tube 30 cm. long, which is filled with garnets and bits of porcelain and is cooled with ice. The gas is measured by the amount of water delivered by the siphon bottle that is used to induce its flow. After passing 2 to 5 liters of gas, the tube is washed out by drawing pure air through it, and, finally, is washed into a beaker, with water, to remove the SO; which has condensed on the beads. This is then determined gravimetrically by precipitation as BaSQu. 73. SO2 in Unabsorbed Gases.—It is advisable to test from time to time the gases leaving the top of the weak-acid tower, to make sure that no unabsorbed SO, is leaving thesystem. This is preferably done with Reich’s apparatus, as described above. Influence of SO:- and CaO- Content on Specific Gravity of Solutions meee set ere TPT Eee ia i eee eletette eee eee ih. a CO SSG i ea ae ee eee J OD ee ea j 0 Je soe Doe eae eee a ee ole) Tete LTT er to ee ea ae ee Annee . aR aa eee a ister eee relia eee | BRE HEEY -{EEH LUGS as SABRE waa Jon Eee Sea eee eas JE > Se Bea Rae eens JIE AS eee eP ate LS eS Ghee aise zath ASRS 4nG 224 NAGe eRe ae0P= «Seka ase Les ae athe eee eee 2 Bogs 2a tbeasgenein 7y eee TS RS / PME Noel Be rier oh ep ep e Des POL ete |e ot ele P ol aki Laan RS 0 / Zz 3 4 Y 6 7 Be Fig. 20. (a) Solution of SO2 in water (Scott) (6) Acid from tank system with 74% free SO2 (DB) (c) Acid from tower system with 62% free SO2 (Harpf) (d) Acid from tank system with 61% free SO» (Harpf) 74. Testing of Acid.—The acid maker is often provided with a hydrometer for a superficial test of the raw acid from the strong tower. This test may be useful in mills where there are no great variations in the raw acid; but it must be remembered that the density of the acid is influenced both by the total SO» content and by the percentage combined with the lime. The 48 MANUFACTURE OF SULPHITE PULP §4 preceding chart, Fig. 20, shows the variations in degrees Baumé with varying relation of free SO2 to total SO.; the table gives the Baumé reading for various strengths of acid, with almost con- stant relation between free and total SOx. | The actual composition of the raw acid as well as of the cooking acid is obtainable only from chemical tests. The methods in use are as follows; RELATION BETWEEN LIME AND BAUME RS 0 ROOM TEMPERATURE) Per cent SO. Relation | Relation ‘o Per total SO. | free SO, Bé. ; Total Free oe one bined lime total SO, | 3.9 2.59 1.84 0.75 0.66 3.9 tna g 4.0 2.63 Boy fre 0.86 0.75 5 wee 0.67 - 4.1 ya ei 1.86 0.89 0.78 3.0 0.68 4.2 2.56 1.76 0.80 0.70 3.6 0.69 4.3 2.91 1.88 1.03 0.90 3.2 0.65 4.4 3.10 2.02 1.08 0.95 3.8 0.65 4.5 2.98 1207 1:01 0.88 3.4 0.66 4.6 3.08 2.03 1.05 0.92 3.08 0.66 4.7 3.04 1.99 1,05 0.92 3.3 0.66 4.8 3.09 1.99 1.10 0.96 Ee 0.65 4.9 a:is 2.01 LotZ 0.98 3.2 0.64 5.0 oi26 2.07 1.20 1:06 Ps pea 0.63 5.2 3.03 2.27 1.26 £16 ove 0.64 bis 3.49 ba | 1s 1,12 8.1 0.63 5.4 4,62 2.29 jee LZ ae | 0.63 5.5 3.66 eS 1.29" Leis ae 0.65 Bes 3.83 2780 1.46 1.28 3.1 0.62 ey. 3.87 2.44 1.438 1.25 5 0.63 5.8 3278 2.34 1.44 1.26 3.0 9.62 6.0 3.94 2.48 1.51 1.32 3.0 0.62 | ToTaL SOe.—One cubic centimeter of the acid, measured with a pipette, is diluted with about 100 c.c. of distilled water, and is titrated with 7, iodine solution in the presence of starch solution. 10 The number of cubic centimeter of a iodine solution required multiplied by .3204 gives the total SOz2 in the liquor, expressed as a per cent. §4 PREPARATION OF THE COOKING ACID 49 Free SO..—A separate sample of the acid is titrated with i sodium hydrate solution, using phenolphthalein as indicator. If 1 c.c. of acid is used, the number of cubic centimeters of hydrate solution is multiplied by .3204, giving the percentage of free SOs. CoMBINED SO2.—Subtract the free SO, from the total SOs. Limse.—The value for combined SO: multiplied by .875 gives the per cent of lime, if a pure calcium stone or lime was used in the acid making. Calcium as well as magnesium may, of course, be determined directly and more accurately by the usual gravimetric methods. 75. Crandon Acid-Control System.—An instrument known as the Crandon acid-control system is constructed for auto- matic control of the free SO2 in the raw acid. This instrument works very satisfactorily in connection with the milk-of-lime sys- tem, and it is also used in some mills operating the tower sysnem The instrument based upon the relation between the conduc- tivity and the strength of acid. The principle involved is very simple, in that an alternating current of electricity is carried through the acid LZ by the use of electrodes, A and B, Fig. 21, the size and location of which are determined by making tests of the actual system under consideration, taking into account, of course, the speed at which the system is being operated, the strength of the acid that is being made, and also the percentage of lime that is being used. A solenoid C is set in series with the electrodes A and B, and operates the instrument in the following manner: A beam is suspended over the solenoid, and has, at either end, suitable pieces of metal (contactors) H and F that dip, as the beam tilts, into mercury cups G and H, which are directly connected to the motor M that operate the valve V, set in the milk-of-lime supply line. This beam has connected to it an armature K, which is drawn down by the solenoid when the acid is growing stronger; it continues to pull until such time as the acid is strong enough to pull the contactor H’, on the same end as the armature, into the mercury G, thus closing the starting switch of the motor, which would operate the valve toward an opening position, so as to admit more milk of lime; and when the liquor in the system has been sufficiently diluted, so that the current flowing through the liquor and solenoid is not sufficient to hold the armature beam 50 MANUFACTURE OF SULPHITE PULP §4 and contactor down on that side, the counter-balancing weight W, on the opposite end of the beam, will carry the contactor F on that end down, toward or into the mercury H, causing the motor to stop or to operate the valve toward a closing position. The instrument is regulated for a stronger or a weaker acid by moving the weight on the right-hand side of the beam to right or left according to the strength of acid desired. The sensitiveness 110-Volt Circus? of the instrument depends a great deal upon the voltage used in the solenoid. The installations vary in voltage from 123 to 110 volts, and, the windings on the solenoid vary, of course, according to the voltage that is being used. The circuit that comprises the electrodes and solenoid is entirely independent from the one that operates the motor; it is controlled by the Mercury switches at either end of the main beam. The motor itself is a fractional-horsepower reversing motor that runs at very high speed, around 2000 r.p.m. It is connected up $4 THE COOKING PROCESS 51 to the valve spindle on the milk-of-lime line by means of a speed reduction device, which consists of a worm-gear reduction and a set of spur gears. For complete control and record of the acid-making operations, indicating and recording instruments should be provided to give the temperature of the gas entering the absorption system, temperature of the water and acid, and volume of acid produced. THE COOKING PROCESS THEORY OF PROCESS 76. Composition of Wood.—The present-day routine of the cooking process is based more upon practical experience than upon actual knowledge of the chemical reactions that take place in the digester during the cooking. Our knowledge of the chemi- cal composition of the woods is still too limited to permit of an entirely satisfactory explanation of all the various reactions in the digester. But Klason’s investigations of the composition of one of the chief constituents of the wood, the so-called lignin, have resulted in a theory of the cooking process, by which it is possible to explain some of the most important reactions, and they form an excellent basis for future research. Before discussing Klason’s theory of cooking and the question of yield and quality of pulp, the composition of the wood must be briefly reviewed. It is generally recognized that all woods are composed of cellulose, lignin, sugars, and resins. But there is some difference _ of opinion with regard to the amount (proportion) of each of these constituents, and also as to their exact chemical constitution. Cellulose belongs to the group of organic compounds known as carbohydrates. Its chemical formula is expressed as (CgHi00s)n, n being unknown; its molecular weight is undoubtedly very high, and it is very resistant to the action of chemicals. It is on the basis of this resistance toward chemical reagents that the commer- cial processes for isolation of the cellulose fiber are based. Cellu- lose is, however, by no means absolutely resistant to hydrolysis and oxidation; and if the processes are not carefully controlled, the cellulose itself will break down chemically and physically, and will partly decompose into soluble products. This explains the variation in yield and in the quality of the fiber from different - cookings. 52 MANUFACTURE OF SULPHITE PULP $4 77. The sugars contained in the wood belong to the same large group of organic substances as cellulose; but they are of lower molecular weight, and they are less resistant to hydrolysis. They are either, like cellulose, hexoses, or are pentoses; some of them dissolve in boiling water, while others are hydrolyzed by the dilute acid in the cooking process, and still others resist even the cook- ing process, and remain with the cellulose in the sulphite pulp. 78. By resin, or pitch, is usually understood the substances that can be extracted from wood by means of organic solvents, such as ether, alcohol, benzol, ete. We may consider resin to be a mixture of fat and rosin in about equal proportions; it is gener- ally accepted that it is the fats which cause the pitch troubles in the pulp. These are only to a very limited extent dissolved in the cooking process. 79. The chemical composition of lignin is less known even than the composition of cellulose. It is hardly a uniform compound, being rather a mixture of two or more lignins of different consti- tution, but of similar reactions, typical for the lignin complex as a whole. ‘This lignin complex contains unsaturated groups, and it easily forms additional products; it is easily oxidized, and it contains so-called methoxy (CH3;0) groups. In this respect it resembles coniferyl alcohol, and Klason has shown that there is a great similarity between the lignin reactions and the reactions of coniferyl alcohol. Of particular interest is the behavior of these two compounds toward mineral acids. Both lignin and coniferyl alcohol restnafy when heated with a mineral acid; they form very dark, colored substances, and this undoubtedly explains why ~ Tilghman was unable to obtain a light-colored pulp when he attempted to cook wood with a sulphurous acid solution without the addition of any base; and it also explains the ‘‘burning”’ of the pulp, when insufficient calcium is present to neutralize the acids formed. Klason considers the lignin a condensation prod- uct of coniferyl alcohol; and the main reaction in the cooking process consists in the addition of bisulphite to the unsaturated groups of the lignin molecule, forming soluble calcium salts of lignin sulphonic acid. The addition of bisulphite to the lignin compound begins in _ the early stage of the cooking process, but does not result in the appearance of dissolved lignin compounds in the cooking §4 THE COOKING PROCESS 53 liquor until the higher temperatures are reached. This observa- tion, and also the fact that carbohydrates are dissolved in a fixed proportion to the amount of lignin dissolved, indicates that the lignin is present in the wood, not in a free form, but in combina- tion with carbohydrates. It must therefore be assumed, accord- ing to Hiagglund, that in the cooking process, an insoluble compound of carbohydrates and calcium salts of lignin sulphonic acid is formed, which, at the higher temperatures, is hydrolyzed, forming a soluble calcium salt of lignin sulphonic acid and dis- solved sugars. The speed with which this reaction takes place depends upon the temperature, the acid concentration, and the pressure, the temperature being by far the most important factor. According to Klason’s theory, the lignin complex binds four molecules of sulphur dioxide, two of which are permanently com- bined to ethylene groups (CH = CH), one. less permanently, and one molecule of SO:2 loosely combined with an active carbonyl group =CO. Since the SO is added to the lignin as bisulphite, it is natural that for each molecule of SOz, one-half molecule of calcium will be used; and it has been suggested as a control test during the process of cooking, to determine the amount of SO. present as bisulphite or ‘‘half-free” SO.. There should always be sufficient half-free SO, in the acid to completely dissolve the lignin of the wood. In other words, a sufficient amount of calcium must be present. 80. The average composition of bone-dry spruce wood, dis- regarding the fraction of a per cent of ash, is Oe a a 53.0% ONG G8 giana a er oa 14.0% UO Lhe 208 () 7 Bete re Mee. Sek irk) oo a. 0.7% EreteraADCoOsiNS 3. vi. os ia Sa don't 3.3% 100.0 On this basis, approximately 100 g. of SO. and 45 g.of CaO should be theoretically required per 1000 g. of bone-dry wood, for complete solution of the lignin. And these figures are very close to those obtained in commercial operation. If toward the end of the cooking process, the liquor should not contain suffi- cient sulphite to react with the ethylene groups (of the lignin), 54 MANUFACTURE OF SULPHITE PULP §4 some of the sulphite, which is loosely combined (to a carbonyl group), may combine permanently with ethylene groups; in which case, it would be possible to cook with less than the theo- retical requirement of bisulphite. It is accordingly important to have sufficient lime in the acid at the beginning of the cooking process. But even with an excess of calcium at the beginning of the cooking process, a great proportion of this calcium may disappear from the active cooking liquor, due to abnormal conditions existing in the digester. 81. Effects Produced by Cooking.—If a normal cooking acid is heated, a small quantity of sulphur trioxide is always formed; in the presence of suspended sulphur, this decomposition is more rapid, especially if the sulphur is in a very fine form in the acid .150 g. of very finely suspended sulphur (such as formed in the decomposition of thionic acids) or .250 g. of flowers of sulphur, per liter, would, according to Klason, during normal cooking time and at 135°C., decompose the cooking acid to such an extent that all calcium would be precipitated as gypsum. The effect of the presence of selenium in the cooking acid is 300 times as great as that of sulphur. Also, thiosulphuric acid (H28.03) and thionic (H2S20. and H.8;0¢) acids are formed when cooking acid is heated to the temperatures prevailing in the digester. The quantity of these acids increases slowly, the more slowly the more free SO2 there is present. At a later stage these acids are decomposed into sulphur trioxide, sulphur dioxide, and free sulphur, and the reaction is taking place fairly rapidly as long as calcium is present in the liquor as bisulphite. Finally, all the calcium will precipitate as gypsum. These are, of course, abnormal conditions, which must be guarded against; and one of the objections to the return of relief liquor to the acid system at the last stages of the cooking is based upon the danger of contaminating the fresh cooking acid with these foreign acids. In connection with this, the danger of poor circulation must also be mentioned, since this may result in local shortage of calcium at some points in the digester; and wherever the quantity of calcium is insufficient for the neutralization of the acids formed in the process, there is the danger of the acids resinifying the undissolved lignin, as mentioned above. The result is a dark coloring of the pulp or burning of the fiber. §4 THE COOKING PROCESS 55 82. Products of the Cooking Process.—The formation of the calcium salt of the lignin-sulphonic acid is the most important reaction in the cooking process; but other reactions are also taking place, of which not a great deal is known. It is known that formic acid and acetic acid are formed, and they can be identified in the waste liquor as well as in the relief gas. Also furfurol is formed, due to the action of acid upon the pentosans of the wood; it is found in the waste liquor, but mostly in the condensate of the relief gases. This latter is a heavy liquid, which often collects at the bottom of the acid tanks. Spruce turpentine, consisting largely of cymene, is also a by- product of the cooking process. It follows the relief gases; and if these are returned direct to the acid tanks, the turpentine, being lighter than the acid, will collect as a layer on the top of the acid, from where it may be removed by some skimming method. In other places, it is separated, together with the condensed strong SOz, from the relief gas after cooling, and is conducted to a separate tank, where it collects on the top and can be drawn off intermittently or continuously. It is considered very advantageous to remove this substance, which usually is obtained in largest quantities with fresh spruce wood, since an accumulation of the turpentine in the cooking acid is undesirable; partly, because it makes the cooking control difficult, and partly, because it has been made responsible for difficulties with pitch in the pulp. With the relief gas, methyl alcohol is also removed from the digester. Approximately 14 pounds of methyl alcohol is formed per ton of pulp during the cooking process, and about one-third of this escapes with the relief gas, the quantity varying with the method of relieving. The amount of oils in the relief gas, in- cluding spruce turpentine and furfurol, is, according to some investigators, about 2 to 3 pounds per ton of pulp, depending upon the nature of the wood. In the cooking process, the higher sugars of the wood are hydrolyzed into simple pentoses and hexoses, the latter forming the material for fermentation and production of ethyl alcohol . from the waste liquor. METHODS OF COOKING 83. Direct and Indirect Cooking Processes.—Reference was already made to the difference in the two cooking processes 56 MANUFACTURE OF SULPHITE PULP $4 known as the Ritter-Kellner process and the Mitscherlich process. The former, which is by far the most commonly used, is called the direct cooking process, because the digester charge is heated by direct steam; the steam condenses in the digester and thus constantly dilutes the acid, which should consequently be added in high concentration. It is possible with this method to bring the temperature up very quickly, and thereby shorten the cook- ing time to 8 hours or even less. The process is therefore also often referred to as the quick-cooking process. The Mitscherlich process is an indirect process, in which the digester charge is heated by means of steam-heated copper or lead coiis, placed inside the digester. The steam condenses in the coils, and no dilution of the acid takes place during the process of the cooking; consequently, the acid does not have to be so strong as in the direct cooking process. The indirect process is a slow-cooking process, the cooking time being from 20 to 30 hours or more. The maximum temperature during the cooking is from 125° to 135°C., while in the direct, quick-cooking process, the temperature is usually around 140° to 145°C. and may go up to 155° and 160°C. In other respects the two processes are identical, and the construction of the cooking vessels is practically the same, except for the modification required for the difference in method of heating. DIRECT, OR RITTER-KELLNER, PROCESS 84. Cooking Vessels.—One of the great difficulties in the development of the sulphite cooking process has been the con- struction of the cooking vessels and, especially, the development of a suitable lining, one that will resist the action of the sulphur dioxide solution and gas. Tilghman, as well as Ekman, used lead-lined digesters and indirect heating, and the lead lining was fairly satisfactory with the small Ekman digesters of about . 700 pounds capacity. With large digesters, however, the diffi- culties due to the difference in expansion of the lead lining and the steel shell proved very serious, epecially since lead does not, upon cooling, go back to its original size. The lining would form wrinkles, loosen from the shell, and ‘‘crawl’’ toward the lower part of the digester. $4 THE COOKING PROCESS 57 85. Lining Materials.—Another lining that was used in sev- eral mills was the Salomon-Briingger lining. It was observed that the heating coils in the Mitscherlich digesters, after a few cookings, became covered with a very resistant crust consisting of calcium deposits from the acid. The analysis of such deposits showed a calcium sulphate content of about 85 %, besides sulphites of calcium and copper, oxides of iron and aluminum, and silica. This experience was utilized by Salomon and Brine ger, in forming a similar protective coating on the inside of the digester shell. The digester itself was usually of the horizontal and rotating type with a double shell. The digester was filled with acid having a high calcium content; steam admitted to the shell, whereby the acid was heated, and the SO leaving the acid would cause the precipitation of monosulphite on the heated surface. The lining gradually increased in thickness, and was oxidized to sulphate in contact with the air. But while the acid-resisting quality of this lining was quite satisfactory at that time, the lining would at times break off; and with the strong acid employed on this continent, it was difficult to obtain a satisfactory crust. Bronze has been tried for small digesters; but, at the present time, acid-resisting bronze is only used for digester fittings, where an acid-resisting metal is required. The first brick linings were intended as a protection for the lead lining; but the lead lining is now omitted, and a modern digester lining consists of acid-resisting brick laid in an acid- resisting mortar. 86. The Digester.—The digester itself consists of a steel shell, constructed by riveting together steel plates, of about 14 inch thickness, by means of double butt straps. The tendency has been to increase the capacity of the digesters; and the usual size today is from 12 to 15 or 18 tons, while digesters as large as 30 tons capacity have been built. The following table shows various dimensions and capacities of the standard digester type for direct cooking. 58° MANUFACTURE OF SULPHITE PULP §4 CAPACITY OF STANDARD SULPHITE DIGESTERS WITH STAND- ARD LININGS EE EE eee Size of digester Thick- C it ise eT gee ees OF eT Contents ORE Gallons | Cords of : tes contents, Diameter, | Height, | lining, cubic feet of acid wood ; tons fiber feet feet inches 8 24 8 610 {33 3,000 2.48 8 30 8 840 1.75 SiRF 3.24 10 28 8 1,319 2.66 6,000 4.96 10 30 8 1.397 2.90 6,525 5.84 10 a7, 8 1,850 3.85 8, 663 7.16 10 40 8 2,024 4.50 9 450 7.81 11 30 8 1,672 3.48 7,330 6.47 11 37 8 2,896 4.60 10, 125 8.37 11 40 8 2,416 5.00 11,250 9.30 11 42 8 2,563 5.33 12,000 9.92 11 45 8 2,784 5.75 12,937 | 10.69 12 30 9 2,015 4.13 9 , 292 787 12 35 9 2,457 5.10 11,470 9.48 12 40 9 2,879 6.00 13,500 | 11-16 12 45 9 3,272 6.80 15,300 | 11.64 12 48 9 3,572 7.40 16,650 | 13.76 14 38 9 3,819 7.90 17,775 | 14.64 14 42 9 4,320 9.00 20,250 | 16.74 14 45 9 4,678 9.75 21, Oa4e ie 13 14 47 9 4,924 | 10.50 22,950 | 18.97 14 48 9 5,046 | 10.64 23,625 | 19.53 14 50 9 5,392 | 11.20 25,000 | 20.83 15 40 10 4,682 9.75 21,934 | 18.13 15 42 10 4,964 | 10.33 23,250 | 19.22 15 45 10 5,388 | 11.20 25,200 | 20.83 15 47 10 5,671 | 11.80 26,550 | 21.31 15 50 10 6,096 | 12.40 27,900 | 22.06 15 54 10 6,652 | 18.75 30,937 | 25.57 16 45 10 6,146 | 12.80 28,800 | 24.80 16 48 10 6,680 | 13.75 30,937 | 25.57 16 50 10 6,952 | 14.40 32,400 | 26.78 16 54 10 7,598 | 15.80 35,550 | 29.38 16 60 10 8,565 | 17.80 40,050 | 33.10 16 64 10 9,210 | 19.00 42,750 | 35.34 17 56 10 9,074 | 18.80 42,300 | 34.96 17 60 10 9,814 | 20.25 45,900 | 37.94 17 64 10 10,552 | 21.80 49,050 | 40.44 17 70 10 11,660 | 23.00 51,750 | 42.78 The figures in the above table are for average operation; they will neces- sarily vary, in respect to the last three columns, with local conditions. Digesters also vary from the dimensions given, but capacities can be approximated by comparing cubic contents. §4 THE COOKING PROCESS 87. Description of a Modern Digester.—A modern digester is seen in Fig. 22, which also shows a few details regarding the lining and the top and bottom fittings. With the present method of empty- ing the digester charge un- der pressure, the conical bottom is given an angle of about 70°, and it endsina flange, which carries the bottom bronze fitting, to which are connected flanges for the steam line, acid and # drain line, and _ blow-off valve. The steel shell is protec- ) ted by an acid-resisting brick lining; and all fit- tings projecting through the lining are made of acid- resistant bronze or of hard lead. Before the digester is lined, it is exposed to high temperature and pres- Sure several times, and the inside of the shell is thor- oughly cleaned by means of wire brushes, for the removal of oil and grease. It is then covered with a coat a, Fig. 22, 14 to 2 inches thick, consisting of cement and crushed quartz (1 part cement, 4 part fire clay and 3} part quartz), mixed with a 4°Be. solu- tion of silicate of soda and water. Against this (t—1—48) Ty 60 MANUFACTURE OF SULPHITE PULP $4 backing is laid two courses of brick, b and c, in a mixture of cement and quartz and silicate of soda. The inner course c must be of carefully selected, acid-resisting brick, with a resistant joint-stock consisting of 1 part litharge, 1 part cement, 2 part quartz and glycerine, with a small proportion of silicate — of soda. , The difficulties with the linings are often due to poor brick. The burning of the brick is an important feature, and it is therefore imperative that every brick be carefully inspected before it is placed in the digester. Special shapes are required for cones, corners, necks, etc. It is also customary to lay only a certain number of bricks in one shift, and to allow these to set before the work is continued. And it is likewise the practice to place the inside course of bricks first (In a mixture of litharge, cement, and glycerine, with a little silicate), and then press the outer course of bricks in place, between the inside course and the shell, in a cement grout. At times, only one course of brick is applied, which is then laid against a heavier backing of cement. Acid-resisting bronze ySsemmgg Sey ws oe 8 Fie. 23. Fie. 24. rings or sleeves prevent the acid from entering between the lining and the shell at the top and bottom flanges. The arrange- ment is shown at F in Fig. 22. For the protection of the cover, an acid-resisting bronze plate P is fastened to the bottom side of the cast-steel cover C. 88. The bronze casting T for the bottom of the digester is shown in Fig. 23. A typical blow-off valve V is shown in section in Fig. 24. This valve has a door through which the valve seat. can be inspected and the packing properly placed before each cooking. 3 §4 THE COOKING PROCESS 61 In Fig. 25 a typical Y valve as used for the steam line, is shown. : 89. The following composition has been recommended for a good acid-resisting bronze: RS aes 843-85 % Se ie a ays ans nas Ades: 4-103 fo) i act c Bn 4i_ 5 % Phosphorus not less than............ 0.05% Impurities not above 90. Thermometer wells W, Fig. 22, for indicating or recording thermometers, are placed either at the top or, better, one-third down the side, of the digester. They are made of bronze covered with lead. 91. The digester also carries fittings for connection with the acid and gas relief line L at the top of the digester. Usually, this is placed on the cover; but, in order to avoid the trouble of dis- connecting the relief line when the cover is removed after each cooking, this line is frequently connected up to the side of the digester neck. At any rate, the outlet should be covered with a good-sized strainer S, of acid-resisting bronze or, better, of hard lead, to keep chips and fiber from entering the relief line. These 62 MANUFACTURE OF SULPHITE PULP §4 strainers have a large number of 4” or 15” perforations, and may have the form of a ball or a cone. Ora perforated plate may be placed in the neck, resting upon a bronze ring projecting from the lining. 3 Steam, as a rule, is admitted only at the bottom fitting of the digester; but in a number of installations, several steam inlets are provided for on the conical bottom part. The steam line is equipped with a check valve, to keep the digester contents from entering the line, in case the pressure should fall in this main, and the regulation of the steam should be done from the charging floor. 92. Some mills have their digesters equipped with a side-relief line K, connected up to the side of the digester, approximately 6 feet from the top. By opening the side-relief valve at a certain stage in the cooking process, acid may be drawn off, whereby a gas space is created in the upper part of the digester; this allows “dry gas” to escape through the top relief line, which permits a better gas recovery and a better circulation in the digester. The opening for the side relief is, of course, also protected by a strainer. Furthermore, the digester is equipped with recording and indicat- ing pressure gauges and with a sampling cock H, for drawing samples of liquor during the process of cooking. 93. Thermometer Bulbs.—The thermometer-bulbs of both the indicating and the recording thermometers should be placed low . enough on the digester to insure that they will always be im- mersed in the cooking liquor; and since it is desirable to locate the recorder on the top of charging floor, where it may be con- veniently observed by the operator, it will be seen that a fairly long connecting tube must be used. It is therefore necessary to employ an actuating medium that will not be influenced by the changing temperatures of the atmosphere along the connecting tube. Experience has proved that a thermometer depending upon the vapor tension of a volatile liquid is best suited for this purpose. The bulb should be long enough to extend through the shell and lining and at least 6 inches into the digester; there- fore, the sensitive portion of the bulb should be not longer than the 6 inches that is exposed to the cooking liquor. The bulb must always be protected from the cooking liquor by a sleeve or nipple. 94. Temperature and Pressure Charts.—For recording gauges . and thermometers, a 12-inch chart is preferable to the smaller <) §4 THE COOKING PROCESS 63 ones, because of its larger graduations. Due to the importance of the temperature in the cooking process, it 1s imperative that the recorder register accurately; therefore, it should be eali- brated at very frequent intervals. This can be accomplished by immersing the sensitive portion of the bulb in an oil or water bath, and holding it at constant temperature for about fifteen minutes; the recorder should show the same temperature as an accurate indicating thermometer placed in the bath. The pres- sure gauges—both indicating and recording gauges should be provided—are also placed at a distance of about one-fourth to one-third from ‘the top of the digester, the recorder being located on the charging floor. QUESTIONS (1) What are the principal constituents of wood, and in what propor- tion (approximately) are they present? (2) Why is it necessary to have sufficient lime everywhere in the digester? (3) (a) What is the effect of selenium in the digester? (6) in the burning of the sulphur? > (4) (a) How is spruce turpentine collected? (6) why is it advanta- geous to collect it? (5) Why is bronze used for digester fittings? (6) Mention the advantages of using recording instruments in the digester house. 95. Pressure Regulator.—In Fig. 26 is shown a pressure regu- lator, by means of which, steam is automatically shut off when the maximum cooking pressure is reached. The regulator is connected to the digester pressure-gauge line by means of pipe A, which enters the regulator underneath the diaphragm B. As soon as the pressure in the digester exceeds a predetermined maximum pressure, which is regulated by weights, W, the dia- phragm forces the lever arm C upwards ; this opens the water valve D, which allows water to enter through EF and F into the cylinder G, forcing up the piston and weight H and causing K to fall, thus closing steam valve V on steam line. When the de- creased pressure allows weight W to fall, the valve D is reversed, and the water in G escapes through F and L. 96. Chip Bins.—These are constructed of wood or of concrete _ lined with wood, and are located above the digesters, so that the 64 MANUFACTURE OF SULPHITE PULP §4 chips can be fed into the digester by gravity. Cylindrical steel bins are also in use. In order to assure a rapid filling, a sharp angle should be provided for the inverted pyramid or cone that forms the bottom of the chip bin. When so constructed, the men do not have to enter the chip bin in order to assist in loosening the chips, which it is necessary to do, especially in cold weather and with very wet chips, when these freeze together and are difficult to move. To assist in loosening the chips at the Fig. 26. bottom of the bin, two or more steam pipes are connected up to the bin at this place. A chip bin usually has a capacity of at least two digester ‘charges. A large mill will often have a huge common bin that runs the full length of the digester house and with a spout for each digester. Entering a chip bin is dangerous; but if it be necessary, the men should be protected by safety ropes and a helper. ROUTINE OF THE COOKING PROCESS 97. Beginning of the Cooking Process.—When the blow-off valve and other lines have been closed, the digester is charged with chips, by opening the gate at the bottom of the chip bin and allowing the chips to run into the digester through a funnel, §4 THE COOKING PROCESS 65 until the digester is full of chips. The acid is then pumped in, either through the opening at the top, or through a bottom con- nection with the acid line. If the acid is added at the top, a copper extension pipe is connected to the acid line, which runs along the digesters at the charging floor. During the time of acid pumping, the digester opening should be covered with a hood, and escaping gas should be removed through a suction pipe. For the purpose of observing the height of the acid during the pumping, an open, vertical glass pipe is connected up to the digester at the test cock by means of rubber tubing. 98. When the acid is added at the top, there is always, with strong acids, considerable smell and loss of gas at the charging floor. It must also be assumed that much gas is absorbed by the chips, thus weakening the acid in its passage through the chips. Consequently, there will be weak acid at the bottom, where the strongest acid is desired on account of the material dilution that occurs at this point, and which is due to condensa- tion of steam in the cooking process. This is remedied by pump- ing the acid in at the bottom, which is the practice in many mills. A further advantage is thereby gained, in that chips and acid may be added simultaneously; this saves time, and the acid will unquestionably lift the chips from the narrow bottom and establish a volume of acid at this point, which should assist in a more even distribution of the heat; that is, it will create a better circulation in the digester. It is necessary, of course, to provide a satisfactory valve connection, to keep the acid from draining off when the digester is under pressure. Chips and acid having been added, the top cover is bolted on (using a gasket cut from a lap of pulp), the steam valve is opened, and the digester is gradually brought to the desired temperature and pressure. Once or twice, before the digester is brought up to full pressure, the top relief valve is opened and air is allowed to escape. 99. The points just mentioned are shown by the drops at A and B in the chart, Fig. 27, which shows the variations in pres- sure during the operation of a digester that is making easy- bleaching pulp. The corresponding temperature curve is shown in Fig. 28. These charts, together with Figs. 29 and 30, are about one-fourth the actual size, which is 114 inches in diameter. It is by following the line on the recording gauges 66 - MANUFACTURE OF SULPHITE PULP §4 and comparing the curve with a standard that has given good results under similar conditions that the cook (digester man) is able to duplicate results previously obtained. The curve also gives warning if things begin to go wrong. The pressure, consisting of the steam pressure (which is known. for each temperature) and the gas pressure (which depends upon the amount of gas present) increases very rapidly, and the maxi- \ 0 =: \2 \\ UT PS I KK Yypuirs A COU Wy, G LILY SEELEY Kiki RY My Uyintie. Yj Liu, HM AN Vy) Wy TH ANN \ My Mify Mii A \\ HI MI) Ly) Vy; - EZ Ay N \ We \ == x 1 mum pressure of 70 to 80 pounds is reached within 2 to 3 hours, depending upon the method of cooking. In order, therefore, to be able to increase the temperature, it is necessary to open the top relief valve, at B, Fig. 27. The mixture of strong acid and gas that leaves through this line at the beginning of the cooking process, is cooled and conducted to the reclaiming tower or to the acid storage tanks, according to routine of mill. A table giving pressures and the corresponding temperature will be found at the end of this volume. Figure 28 shows a temperature chart. ute Mere sl §4 THE COOKING PROCESS 67 100. Recovery of Sulphur Dioxide.—The practice of relieving is of course different in the different mills; it is a very important detail of the cooking operation and in the maintenance of a strong and uniform cooking acid. The recovery of sulphur dioxide from the cooking process was first practiced by V. Drewsen, who constructed the first separa- tor to separate the gas from the liquor in the latter stage of the SSS, WY SSNS SERS HOSS 5 oss e \\ SY S SxS SHER 2 ae se SS cM < Me a Ss L1% LTA Hs Ly AVILA \\\\ NY ANS ly | iN eo cooking process, when the liquor becomes contaminated with decomposition products. Some allow all the relief liquor up to a temperature of about 115°C. to run back to the reclaiming tower or tanks. Above this temperature, the liquor is taken through a separator, which is a large, cylindrical, steel vessel, with acid-resisting lining, about 15 feet in height by 5 feet in diameter. The liquor enters at the top through a lead pipe that extends into the separator; the separator is kept about one-third to one-half full. The pressure is here released, and most of the 68 MANUFACTURE OF SULPHITE PULP §4 SO: gas will consequently leave the liquor. The gas leaving the separator passes through a cooler and enters the reclaiming sys- tem, while the weak liquor (which is drawn off at the bottom and which always contains a small quantity of SO.) is either cooled and returned to the acid tower or it is discharged. As a rule, the weak liquor from the separator is not returned when the digester has reached a high temperature (for instance, 135°C.), as there is a danger of decomposition products, such as thionic acids and sulphur, being introduced into the fresh acid. Horizontal pond coolers, similar to those employed in acid making, are very often used for relief gas and liquor. But, in recent years, the so-called beehive cooler has been introduced in many mills as being particularly suitable, on account of few flanges, thus making it easy to keep the cooler tight; and it requires less water and less space than the pond coolers. The cooler consists of lead pipe, having a diameter of 3 to 4 inches, which is wound on a conical wooden form; the cooling water is applied in a shower at the top of the cone and flows over the pipes. Separate coolers are used for gas and for liquor, when the relief liquor is separated, which is usually done at the later stages of the cooking process. 101. When the digester temperature is about 125°C. or 130°C., the side-relief valve, if such is provided, is opened at C, Fig. 27, and the liquor allowed to drain off, ‘passing through the separator as described above. The liquor level in the digester is thereby lowered so much that no liquor, but only ‘dry gas,” leaves through the top-relief valve at D, Fig. 27 ; it is accordingly possible to relieve much gas during the last stages of the cooking process, and this assists in building up a strong acid in this re- claiming tower. It is also necessary to have a gas space in the digester at the end of the process, in order to be able to reduce the pressure quickly before blowing. The circulation is un- doubtedly also better, and the distribution of temperature is therefore more uniform, with the gas space created by side relief or by draining for a short period through the bottom valve, a practice which is also followed at times. 102. Relief Gas Strengthens Acid.—While the relieving of acid and gas is an important part of the cooking process itself, it is also very essential, for the manufacture of the cooking acid, that this operation be properly conducted. sla a §4 THE COOKING PROCESS 69 The reclaiming process, and the “building up” ofa strong acid, has become very important and typical for this continent, on account of the necessity of using a strong acid to cook the usually very wet wood in a comparatively short time. If the acid should become weak on account of too much weak relief liquor being returned to the acid, the relief liquor must pass through the separator, and only the gas may then be returned to the reclaim- I ] Nee - —=: ——F FF \ Mh Mh ) \ | My y ih & SNH Ww XS ES YY YY YY YY. / ; TS, ZUM ms “4 ing system, the liquor not being used. But even more necessary than a strong acid is a uniform acid; and in order to obtain uniform reclamation, the digesters must be properly spaced, that is to say, there should be a certain time between the steam- ing of each digester in the mill, of 1, 2, or 3 hours, depending upon number of digesters and cooking time. 103. No Standard Method of Cooking.—It is not possible to give any standard method of cooking; the process depends too much upon the nature of the wood, the composition of the acid, 70 MANUFACTURE OF SULPHITE PULP §4 the desired quality of pulp, and, especially, upon the instructions issued at each plant, which are based upon particular experience. With 10 or 11 hours cooking for easy-bleaching pulp, a tem- perature of 105° to 110°C. is usually reached after 4 hours, and this is gradually increased to 145° or 155°C., depending upon the wood and the acid. With shorter cooking time, the heating must be more rapid, and at times, a maximum temperature of LX ON , , 4, OO LO OK KR z SxS XY ot © 6 5 [TAD Sasa 6. CO-g, LTTE ELS 0 THT IF HELLELEEE ERROR Y HTH 30" I 160°C. is reached, while in the slower cooking, the temperature is raised more gradually, and the maximum temperature is kept below 140°C. Figs. 29 and 30 show pressure and tem- perature charts for cooking sulphite pulp, for news print, in 93 hours. The letters have the same significance as in Figs. 27 and 28. 104. Use of Superheated Steam.—Hither saturated or super- heated steam is used for heating the digester charge. The advantages of using superheated steam are less condensation dey SNM iy emp = §4 THE COOKING PROCESS 71 and dilution and more rapid heating; but a high superheat should be avoided, on account of the danger of overheating the pulp at the steam inlet. Furthermore, the rapid heating with highly superheated steam undoubtedly causes a local overheating of the acid, which results in the escape of free SO. and a local loss of lime, the latter being due to precipitation of monosulphite, the danger of which has been explained. 105. Steam Consumption.—The quantity of steam admitted to the digester at the various stages of the process varies con- siderably, not only in the different mills but also in the same mill, unless the steam is measured by steam-flow meters. An attempt has been made at standardizing the steam consumption, throughout the cooking process, by adopting standard curves for the steam flow; and on the basis of this, an instrument for auto- matic control of the cooking process has been developed and is in use in a few mills. 106. Completion of the Cooking.—During the process of cooking, samples are taken of the liquor; and in well conducted mills, certain standards for acid test at the various stages of the cook are maintained. When the cooking is almost completed as shown by the tests, the steam valve E, Fig. 22, is closed, and the pressure reduced at H, Fig. 27, by relieving at the top, until the pressure is about 40 or 50 pounds at F, Fig. 27; at which time, steam valves, as well as relief valves, are closed, the blow valve is opened, and the charge is blown into the blow pit, through a blow pipe of cast iron or bronze. Usually the instruc- tions are to blow the digester at a certain acid test; for instance, -25% to .3% SOs, if the liquor is passed through a cooler, or a test of the hot liquor of .05% to .07% SOs. This test is carried out as follows: Ten cubic centimeters of the liquor sample is diluted with about 100 c.c. distilled water; starch solution is added, and the sample is titrated with N/32 iodine solution until the color changes into blue. Each cubic centimeter of iodine solution used cor- responds to .01% SOz in the digester liquor. 107. Color Test.—If the progress and the endpoint of the cooking process be judged by the color of the liquor, a standard color scale can be made up of coffee solutions of various dilutions. The proportions of the coffee solution are as follows: Corrrr So.turion.—Eight ounces of best coffee beans; 2 ounces 72 MANUFACTURE OF SULPHITE PULP §4 of postum (cereal): and 2 ounces of chicory. Macerate thoroughly in a small quantity of cold water; add this mixture to 2 liters of distilled water; bring to boil over slow fire; and continue boiling from 30 to 45 minutes. Just before removing from boil, add the whole of an egg, partly beaten, and set solution aside to cool. Now filter through cheese cloth, and through double filter — paper, and then add 25 c.c. of formalin. Set this solution aside in amber bottle, as base color, and build color system by addition of distilled water, using the amounts indicated in the following table: .No. Parts color solution Parts water 1 1 10 2 1 9 3 1 8 4 1 7 5 1 6 6 1 5 7 1 4 8 1 3 9 1 2 10 1 1 These solutions are filled in a number of bottles and arranged to form a color scale. Behind these bottles should be a standard light source. Samples of digester liquor are filled in the same type of bottle and matched with the solutions of the color scale. Iodine solutions, and colored glass plates, are also used for color standards. OTHER CONTROL TESTS IN COOKING PROCESS 108. Strength of Liquor.—The percentage of total, combined, and free SO2 present in the cooking liquor at the various stages is determined as outlined in Art. 74. Toward the end of the cooking process, the value for free acid becomes higher than the value for total SO; this is due to the presence of organic acids formed in the process of cooking. But in mill practice, only the total SO: is usually determined. Klason has suggested the determination of (a) half free SOs, that is the SO that is combined as bisulphite; (b) free SOs; and §4 | THE COOKING PROCESS 73 (c) loosely combined SOs, that is SOs which reversibly combined with the lignin. In order to determine these three values, it is necessary to make three titrations as follows: (a) One cubic centimeter of the liquor is diluted to about 100 c.c. with distilled water, and is titrated with N/10 iodine solution. (b) One cubic centimeter of the liquor is diluted as above, and is titrated with N/10 sodium hydrate, using phenolphthalein as an indicator. ; (c) This second sample is then over-saturated with alkali and allowed to stand for afew minutes. The solution is then acidified and titrated with N/10 iodine solution. Assuming the first titration required a c.c. of N/10 iodine solution, the second titration required 6 c.c. of N/10 alkali solution, and the third titration required c c.c. of N/10 iodine solution, 32 (a +c — 2b) = per cent of half free SO. 32 (2b — c) = per cent of free SO» 32 (c — a) = per cent of loosely combined SO. The decrease of the half free SO2 and the increase of the loosely combined SO. shows the progress of the cooking process. At times the value for half free SO. may reach zero or even become negative. In such cases, the loosely combined SO: may leave its place in the lignin molecule and act as half free SO, combining with a different group of the lignin molecule, which results in a decrease of the amount of loosely combined SO, at the end of the process. . 109. Mitscherlich’s Ammonia Test.—The original ammonia test was meant to give an indication of the amount of lime present at the latter part of the cooking. The completion of the process was decided on the basis of the height and the appearance of the precipitate, and also on the color and smell of the liquor. The test was carried out in test tubes, about 8 inches long and graduated into 32 equal parts of the total capacity. Ammonia (1:1) is added in a volume, representing 1 of the 32 parts of the total of the tube, and the tube is made up with digester liquor, and shaken. After a few minutes, the height of the precipitate is observed. It was customary to consider the cooking finished when the height of the precipitate was about 3;d of the tube. 74 MANUFACTURE OF SULPHITE PULP $4 But this method is uncertain; and it is better to observe the point where the height of the precipitate no longer decreases, because at that point no more lignin is being dissolved. 110. The Blow Pit.—The blow pit is a large round tank built, similar to the acid tanks, of long leaf pine; or it is a square chamber of wood, or of concrete lined with wood, acid resistant brick, or tile. The capacity is about 2} times that of the digester. At a distance of about 1 foot from the solid bottom, the blow pit has a false bottom made of wood, 2 inches thick, with perforations. These openings are s inch on the top side and widen toward the bottom side to 3 inch, and the distance of the holes from each other is about 14 inches. In some mills, this false bottom may be made from perforated tile, and may be covered with cocoa matting. The perforated bottom is sup- ported by lumber, which, in turn, is so supported as to leave a space of at least an inch between it and the solid bottom, to permit the free flow of the liquor and water leaving the pulp. Under the false bottom is a drain pipe, with plug cock, through which the liquor can drain off quickly. The blow pit is also provided with doors on the sides and often, also, on the top, for washing; it has also an opening that is connected with a large pipe, through which the pulp is either pumped to the rifflers and screens or flushed into tanks. Inside the blow pit, and opposite to the blow pipe, is a so-called target, of bronze or iron, against which the digester contents are blown, with the object of opening up the pulp and breaking up the chip form. At the top of the pit is an opening, which is large enough to allow all steam and gas from the blow to be carried off through a wooden stack that runs alongside and to the top of the digester building. Due to the sudden release from the digester of a large volume of pulp and liquor under high pressure, and to condensation of steam in the blow pit, pressure as well as vacuum may occur in the blow pit, and this should be considered in the construction of the blow pit. . 111. Blowing and Washing.—Before blowing a digester, the blow pit is filled with water to about 1 foot above the false bot- tom, with the object of protecting this bottom as well as reducing fiber losses; it is often recommended to use warm water for this purpose. All openings are then carefully closed, and a water valve is opened on the line leading to the inside sprays, which are ae §4 THE COOKING PROCESS 75 located in the upper part of the blow pit. The blow-off valve on the digester is then opened a little at first, but later on, completely, and the pulp is blown into the pit, the blowing being assisted by opening the steam valve F, Fig. 22, in the bot- tom fitting 7 and opposite to the blow-off line. Steam and gases escape through the vent pipe at the top opening; and, unless provision is made for the condensation of the steam and the cooling and recovery of the SO. gas, both steam and gas will go into the atmosphere, which is the usual practice. If the digester does not blow clean, the pulp may be washed out with water from the top, but this requires a long time. It is better to close the blow valve, fill the bottom cone with water to a height sufficient to cover the pulp, and then introduce steam to loosen the pulp. The blow valve is finally opened and steam admitted through the steam valve. The liquor is now drained off into the sewer, if the mill is not equipped with a plant for the recovery of by-products. The doors are opened, and, as soon as the liquor has drained off, the washing begins. Warm water is preferable; both because cold water may precipitate some of the lignin substance on the fibers and give them a dark color, which would require bleach for its removal, and because warm water drains off faster and dissolves substances better. For the same reason, the washing should begin immediately, and the waste liquor should not be allowed to remain in contact with the pulp for a long time after blowing. At times, kerosene is added in the blow pit for elimination of troublesome pitch. The washing process may be carried out by filling the blow pit with water, after the liquor is drained off, and then permitting the water to drain off, repeating this operation several times. Or the drain water is allowed to run off continuously, the washing being continued by means of high-pressure hose streams through the various openings in the sides and top. The washing takes several hours, and lasts until the wash water shows no color from the liquor. A still better washing may be obtained with wash drums, working as pulp thickeners. INDIRECT COOKING PROCESS 112. The Mitscherlich (Indirect) Cooking Process.—This process is an indirect cooking process, and it requires a digester 76 MANUFACTURE OF SULPHITE PULP §4 which in construction is slightly different from the Ritter- Kellner digester. The digester is usually of the vertical type already described, but a horizontal digester may very often be used. In the lower part of the Mitscherlich digesters, the heating pipes are located. They are of hard lead or of copper, the former having the ad- vantage of less repairs and longer duration, while the latter have the advantage of a better heat transmission. The diame- ter of the pipes varies, being usually between 2% and 3% inches, and the total heating surface of the pipes may vary between .07 and .2 sq. ft. per cubic foot of digester capacity, depending upon such factors as the type of digester (vertical or horizontal), arrangement of coils, cooking time, and temperature of steam (pressure and superheat); .13 sq. ft. of heating surface per cubic feet of digester space may be considered a satisfactory ar- rangement for most conditions. The circulation in the digester with indirect heating is naturally not so good as with the direct heating; it is claimed that with the vertical Mitscherlich digester, the liquor circulates upward along the digester walls (since the heating coils are located around the circumference) and moves downward in the center, while in the Ritter-Kellner digester, the circulation is in the opposite direction. The temperature is more uniform in the horizontal digester, particularly in the rotating type that is used in some mills. Also, the mechanical disintegration of the chips due to the rota- tion of the cooking vessel, is considered an advantage for the latter type. | In Fig. 31 is shown a typical Mitscherlich digester of the stationary horizontal type, which is used in an American mill for slow cooking. The total length of this digester is 40 ft., and the inside diameter is 12 ft., the capacity being 4136 cubic feet. The heating coil consists of lead pipe with an outside diameter of z inches and an inside diameter of 4 inch and a total length of 312 feet, corresponding to a heating surface of 120 sq. ft. The pipes are located at the bottom of the digester, the steam entering and leaving the coils at A and B, respectively. The chips are blown into the digester through the two openings C; and C2 by means of a steam injector. Direct steam is then applied at D until it comes out at the diametrically opposite bottom cover Hz The four covers are tightened, and acid is pumped in at F until it reaches the required level, it being important that the acid cover THE COOKING PROCESS (i §4 ‘TE “OL eee PINEEAAS \\ > 242 iver ole UPahe- \ LPC SIAN i 525 foyay 78 MANUFACTURE OF SULPHITE PULP $4 the chips completely. It is also part of the object of the steam- ing process to make the chips heavy, in order to prevent them from floating on the acid. Another advantage of the steaming of the chips is the improved penetration, the theory being that when the cold acid is added, the steam in the chips condenses, creating a vacuum in the chips, which assists the penetration. When the cooking is completed, the pressure is reduced to 10 \ Ta ls Hyg ae Mi Ou LU LTH “ali “iy uf Lpupipife Ll) rh Lh % A OK? Xo y > S seta i ih i rf Ly, Ly ry LSS WN \\ NU : MN lb., by relieving through the relief line at D. The waste liquor is then blown into the sewer, and the digester is filled with water and again drained. After the bottom strainers at H, and EK, are removed, the digester is filled with water and the bottom covers tripped, allowing the stock to drop into the pits. (This method of emptying the digester is also used in European Ritter- Kellner mills.) Referring to Fig. 32, the temperature chart represents a typical slow cook with a digester of the above construction. The total Pea et a Sigh et es Se Tene eee Te §4 THE COOKING PROCESS 79 cooking time is in this case 38 hours, including 12 hours for direct steaming of the chips and 31 hours for washing and emptying. On the curve, the distance from A to B shows the time consumed in filling in the chips. From B to C’, the chips were steamed, and the acid was pumped in from C to D. The distance from D to EZ on the curve represents the time consumed in putting on covers and preparing for the heating. Steam is admitted to the coils at E; the relieving of gas is begun at it and is continued to G. The time from G to H is occupied with washing and emptying. The maximum temperature is 120°C. and the maximum pressure is 60 Ib.; but it is not unusual to allow the temperature to reach even 130°C., or slightly more, in the quicker Mitscherlich cooks, in which case, the increase of temperature in the beginning of the process must be more rapid. The typical Mitscherlich pulp is characterized by its strength and its beating qualities. 113. The Morterud Cooking Process.—This is also an indirect cooking process. But, while in the Mitscherlich process, the digester charge is heated by means of steam pipes placed in the interior of the cooking vessel, the liquor, in the Morterud pro- cess, is heated outside the digester in a separate heating ap- paratus, which consists of a cylindrical vessel, in which a battery of steam pipes is placed. This system is fully explained in the Section on Sulphate Pulp. The liquor is continuously leaving the bottom of the digester, which is equipped with a large strainer, to hold back the chips, and is forced by a pump through the heating apparatus to an inlet at the top of the digester. During this continuous and rapid circulation, the liquor is heated without being diluted. The idea, which combines some of the advantages of the direct and the indirect processes already mentioned, has been successfully employed in the alkaline cooking processes; but, up to the present time, it has not proved _ to be a success in the sulphite process, because of mechanical difficulties, which, no doubt, will be overcome. It is suggested, in connection with the use of this system of cooking, to transfuse a quantity of hot liquor from a digester that is near the blowing point to the digester just being filled, thus saving heat, time and some sulphur. 113A. Decker Process.—Several mills, using the direct cooking method, have recently installed the so-called decker system by which, in a series of digesters, all dry and wet relief from digesters, 80 MANUFACTURE OF SULPHITE PULP §4 which are already up to pressure, is injected into the digester that is just filled with chips and acid. The injection period is of the same duration as the spacing time, and, during this period, no direct steam is used from the steam line. The heat contained in the relief from the other digesters is sufficient to raise the tem- perature of the fresh digester charge to a point about 30°C. higher than the starting temperature, resulting in a saving of approximately 1000 pounds of steam per ton of pulp. The reclamation of relief gases, which is usually accomplished by cooling the gases and afterwards absorbing the gases in the raw acid, is, by this system, carried out in the digesters, and a comparatively weak acid is kept in the storage tanks. 113B. Monosulphite Process.—The use of sodium monosul- phite liquor in place of the usual calcium and magnesium bisul- phite liquors has, during the last few years, been advocated on the basis of higher yields and better quality of pulp, and the possibility of using species of woods that are not suitable for the present bisulphite processes. It is obvious that this process is capable of yielding a very strong pulp, suitable for various pur- poses; but the process of recovering the sodium base has appar- ently not been satisfactorily solved as yet, except in mills where a combination of this process with a modified soda process has been — found practicable. PULP, ACID, RAW MATERIALS, AND WASTE LIQUOR YIELD AND QUALITY OF PULP 114. Yield of Pulp.—It was mentioned that the resins in the wood are only to some extent dissolved in the cooking process. Resinous woods are therefore not suitable for the sulphite process, unless the resin is previously extracted, and only the less resinous woods, such as the spruces, balsam fir, and hemlock are com- monly used. Small quantities of white fir, tamarack, yellow pine, and poplar are also used in this process. The cellulose content of the wood varies considerably within the same species grown in different localities as well as with the different woods, spruce usually being higher in cellulose than balsam fir and hemlock. The yield of cellulose in the cooking process naturally depends upon the cellulose content of the wood; but it is also dependent upon the method of cooking, particu- eae ae te BRA Ni ee eg ee ee $4 THE COOKING PROCESS 81 larly the temperature and the circulation in the digester. It is generally found that wood contains from 50 to 55% of cellulose; but this cellulose is no doubt a mixture of various forms of cellulose and other hexosans and of pentosans. In the commer- cial processes, such high yields are practically never reached, on account of the fact that these carbohydrates, even celluloses, are attacked at high temperatures, being hydrolyzed into soluble sugars. ‘The more carefully the process is conducted thesmaller is the loss of fiber weight, due to destruction of these substances, and the higher is the yield of pulp. In quick cooking, such as is usually practiced in news mills, it is necessary to employ tem- peratures as high as 150° and even 160°C. ; but this is always at a cost of yield and quality. 115. The yield of good fiber is also dependent upon the amount of screenings, which again depends upon the circulation in the digester and the penetration. It is obvious that if the chips are not sufficiently penetrated by the acid at the temperature where the lignin is beginning to go into solution, or at about 105°C., the surface of the chips is cooked before the interior, or the sur- face is overcooked before the entire chip is softened. The result is a mixture of overcooked and undercooked fibers and a high percentage of Screenings. It is accordingly advisable to Secure a good penetration at low temperature. The penetration depends upon the size of the chips, and these should therefore be as uniform in size as possible. Furthermore, the moisture of the chips and the density of the wood are factors to be con- sidered. A moisture content of 25% to 35% is apparently the most satisfactory with the average wood, while with very dry chips the penetration is slower, due to the presence of air in the chips and to the dry condition of the cell wall. Steaming of the chips before the acid is introduced is intended to equalize the moisture of the chips and to improve the penetra- tion, as explained above. Experimentally, it has been found that an acid with a high free SO, content penetrates more rapidly than a weaker acid, and, also, that a high combined SO, causes a slow penetration. It is often attempted to improve the pene- tration, particularly with wet wood, by holding the temperatire of the digester at about 100°C. for an hour or two. There is a danger of losing the circulation by shutting off the steam at this point; but with several steam inlets through the walls of the 82 MANUFACTURE OF SULPHITE PULP §4 bottom digester cone, it is usually possible to obtain good circu- lation, even if the chips ‘settle.’ 116. The yield is often expressed in cords per ton, or pounds of pulp per cord, or per cubic foot of digester space. The first may vary between 1.7 and 2.2 cords per ton of pulp, and the last may be between 4 and 5 pounds per cubic foot, depending upon the factors mentioned already, but probably depending most upon the density of the wood. This is a factor which is not sufficiently appreciated, in spite of the fact that the amount of actual wood weight per cord, as well as the weight of chips per cubic foot of digester space, naturally varies considerably with the specific gravity (the density) of the wood. Expressed in these terms, a true figure of — the yield due to the cooking operation itself, is only obtainable when the actual weight of the wood per unit of volume is known. But this should be known also for the control of the cooking process, since it is customary to judge the progress of the cooking by means of titration tests or color tests of the liquor, to indicate to what extent the wood is dissolved. The amount of lignin in solution in the liquor at a certain point in the cooking, and therefore, also, the color of the liquor, depends largely, of course, upon the density of the wood or, what is the same thing, the proportion of wood to acid. Another factor besides the density of the wood that influences the amount of wood per cubic foot of digester space, is the method of charging the digesters with chips. If the chips are allowed to run into the digester from the chip bins at a rapid rate, the chips are packed very loosely. Some methods have, however, recently been developed, by which the chips are blown into the digester by air or by steam, resulting in a much better packing of the chips and an increased capacity of from 15 to 25 per cent. To what extent a denser packing of the chips will influence the circulation in the direct-cooking process and the blowing of the digester at the end of the cooking, has not been fully determined; but the value of increasing the amount of wood per digester charge is obvious when considering the increased capacity of the digester equipment and the higher concentration of the waste liquor. 117. Quality of Pulp.—The trade calls for a number of differ- ent grades of pulp, according to its intended use. An easy- \ % a5 * e _ % 4 i, x - Se eas Pee ee eae ee ee ee Pia aR $4 THE COOKING PROCESS 83 bleaching pulp can be produced either by quick cooking or by slow cooking. In both cases, it is desired to remove the lignin as completely as possible; but, in the former case, this can only be accomplished by going to a very high temperature and to “cook down”’ to a low acid test. As a rule, the pulps resulting from these cooks are mixtures of very easy-bleaching fibers with incom- pletely cooked fibers, and the attack on the fiber is apparent in its beating qualities. With a long cooking time it is possible to remove the lignin almost completely, without injury to the fiber, and the operator has it more nearly under his control to regulate the pliability and beating quality of the pulp. 118. The hydration of the fiber in the beating process is undoubtedly influenced by the presence of residual impurities from the wood, as well as by decomposition products of the cellulose. An overcooked, soft fiber will hydrate easily, but will very soon decrease in strength; while fiber that is not injured in the process of cooking, can be hydrated to a great extent before the strength drops down. This is the reason why Mitscherlich pulp is particularly suitable for grease-proof papers, which require maximum hydration. Uniformity of chips with regard to size, moisture content, and density, was mentioned as an important factor in penetration, and also of yield and quality. Even more important is uniformity with regard to wood species. On account of the chemical and physical difference between spruce, balsam fir, and hemlock, these woods should not be cooked together; and, wherever possible, the species should be sorted separately in the yard, and should be cooked separately. Decayed wood should also be avoided, because it gives a low yield per unit of volume, and a pulp of inferior strength and beat- ing quality. | 119. Dirt in pulp originates usually in the woodroom when the bark is incompletely removed; but the pulp may also contain uncooked particles, especially in the quick cooking, or pieces of knots, which are disintegrated into small pieces as the pulp is blown against the target in the blow pit. Dirt from this latter cause is greatly reduced by blowing at a low pressure, or by washing the pulp out of the digester, or, also, by constructing very long blow pits. The blowing of the digester at high pres- sure has undoubtedly also an unfavorable effect upon the fiber, 84 MANUFACTURE OF SULPHITE PULP §4 due to the sudden release of pressure, which, it is claimed, causes practically an explosion of the individual fibers. Dirt may also’ get in from accumulations in pipe lines, exposed tanks, ete. ACID, RAW MATERIALS, AND WASTE LIQUOR 120. The Best Acid.—The effect of a high percentage of free SOz in the cooking acid is to produce a more rapid cooking, which is probably due, largely, to a catalytic effect of the free acid. The advantage of a high free acid for penetration has already been mentioned. The percentage of combined SO, is known, as far as the mini- mum requirement for the cooking process is concerned. Experi- ence has shown that below .9% combined SOs, there is a proba- bility of obtaining a raw incompletely cooked pulp; between .9 and 1.1%, combined SO, is favorable for the production of easy- bleaching pulp; while with a high percentage of combined SO., the pulp becomes harder, unless the cooking time is materially increased, in which case, a very uniform pulp may be obtained. 121. Raw Materials Used per Ton.—Wood is the most important raw material in the sulphite process, and the quantity of wood used to produce a ton of air-dry pulp naturally varies considerably with its quality. From 1.7 to 2.2 cords of rough wood may be used per ton of pulp, depending upon the soundness of the wood, its density and chemical composition, and upon many factors in the manufacturing processes, as mentioned in the dis- cussion of yield, Arts. 114-116. It is also obvious that the wood consumption varies with the quality of the pulp, easy-bleaching pulp usually requiring more wood per ton than a very strong pulp, under average methods of manufacturing. There is still greater variation in the amount of sulphur per ton of pulp; because this depends a great deal upon the yield in the cooking process, and still more, upon the efficiency of the acid plant, especially of the recovery system. While it should be possible in commercial operation to produce pulp with 200 pounds of sulphur per ton continuously, the actual sulphur consumption in mill practice varies between 220 and 300 pounds per ton of pulp. The quantity of limestone or lime varies with the yield of pulp, and also with the composition of the acid, which may vary from .9% to 1.3% combined SOs, or more; and the excess lime in the liquor is not recovered. About 2300 U. 8. gallons of §4 _ THE COOKING PROCESS 85 acid are used per ton of pulp ; accordingly, from 260 to 370 pounds of limestone or from 150 to 210 pounds of lime may be consumed. 122. The steam consumption will, of course, also vary to some extent, but from 2.50 to 2.75 pounds of steam per pound of pulp, or 5000 to 5500 pounds per ton, is probably the consump- tion in most mills. The largest quantity of steam is consumed in heating the large volume of acid and the chips; and the total steam requirement per ton varies according to the temperature of the acid as it enters the digester, and, also, with the proportion of acid to wood. In order to save steam, itis therefore advantage- ous to fill the digester with as great a quantity of chips as possible; in Kurope, special mechanical devices have been designed to distribute and press the chips together in the digester. A considerable reduction in steam consumption is also effected by transfusion of liquor, as described above. The heat losses due to radiation from the digester can be reduced by effective insulation, the value of the insulation increasing with the decrease in thickness of the digester lining, since this in itself forms a good insulation. 123. The steam consumption with easy-bleaching pulp and strong pulp may be seen from the following figures, which are average figures for a number of direct cookings. iereatity Ol divester..................... 5785 cu. ft. Temperature of steam................... 230°-270°C, Pressure in steam line................... 90-100 lb., gauge as. sCStCi«ti<‘<“(C;C*C*:C;t:C*S 31,700 U.S. gallons Temperature of acid..... | Sr ee aan ae 26°C, Meemeoichips........................ 3175 cu. ft. Maximum digester temperature........... 140°C, Easy-BLEACHING STRONG maison cooking, hours................. 1518 — 113-18 Piao pulp, pounds.................. 27,500 29,260 Steam consumed, pounds............... 64,636 60,500 Pounds steam per pound OU eee ne 2.40 2.10 The distribution of the steam consumption throughout the cooking was, for easy-bleaching pulp, as follows: Cooking, up to 105°C., 44,785 pounds of steam; Cooking, from 105°C. to 140°C., 19,666 pounds ‘of steam.. In other words, 69.5% of the total steam consumption is used in heating the digester charge up to 105°C, 86 MANUFACTURE OF SULPHITE PULP $4 124. Utilization of Waste Liquor.—In the sulphite cooking process, the cellulose substance is separated in the form of pulp from the non-cellulose compounds of the wood, which go into solution and are discharged with the waste liquor. ‘These compounds represent more than 50% of the total weight of the wood, and they consist chiefly of reaction products of the lignin, sugars, and resins of the wood. On account of the many complicated reactions that take place during the cooking process, the chemical composition of the waste liquor is known only to a very limited extent. This is the main reason why it has not as yet been possible to recover and utilize properly the organic substances in the waste liquor; and the very few processes of utilization that have reached any commercial importance, are based upon the recovery of a mixture of many different com- pounds, rather than upon a separation of the various compounds and their refining, according to their chemical properties. One difficulty in the recovery of the waste products of the liquor is that they are present in a very dilute form, the solids represent- ing only 11 to 12% of the total liquor. In other words, for every ton of pulp, approximately 9 tons of liquor with 1.2 tons solid substances have to be handled; this means very large storage capacity. 125. If the liquor is evaporated to a high concentration, a product with adhesive properties is obtained, which may be used as a road binder, a binder for briquetting powdered mate- rials, or as a core binder in foundries. The concentrated liquor is also used as a tanning material. Evaporated to dryness, or to about 50% concentration, the substances may be utilized as a fuel, or they may be subjected to a distillation process. The solid substances may also be separated from the liquor by precipitation at high temperature and pressure, the recovered dry substance being used as fuel or in a distillation process. Other processes for the utilization of the waste liquor, as a paper sizing material, an adhesive, a tanning material, cattle food, and fertilizer have been suggested, and they are in use to some extent in other countries. The base of certain sulphur dyestuffs is also present in the waste liquor. 126. The processes of manufacturing ethyl alcohol from waste liquor have received much attention during recent years. The Pia be Bas. Aerie $4 THE COOKING PROCESS 87 higher sugars in the wood are hydrolysed, during the cooking process, into fermentable sugars. The free SO, is removed by heating and by neutralization, either after the liquor has been partly concentrated or in its original strength, or its effect may be counteracted by aeration. Yeast and yeast food are added, and the fermentation continued for 70 to 90 hours, after which time, the alcohol is distilled off. A yield of 95% alcohol amount- ing to about one per cent by volume of the original liquor is usually obtained. QUESTIONS (1) Give the operations performed in the digester room. (2) Referring to Question 1, what points are to be especially watched? (3) What becomes of the gas that goes off in the relief from a digester? (4) How is the quality of the pulp affected by the time of and temperature of cooking? (5) Mention the advantages and disadvantages of the use of superheated steam for cooking. (6) Describe a blow pit, and explain what takes place in it. (7) Mention some of the factors that influence the yield of pulp; explain how they act. (8) What precautions should be taken to obtain a high-quality pulp? (9) (a) What substances are contained in the waste sulphite liquor? (6) how can they be utilized? MANUFACTURE OF SULPHITE PULP EXAMINATION QUESTIONS (1) What materials are used in making sulphite pulp? (2) Name the principal features of the three types of sulphur burners. (3) Why is it necessary to have careful control of the tem- perature in the sulphur burner? | (4) How does the burning of pyrites differ from the burning of sulphur? | (5) Write the equations for all the reactions in the prepara- tion of cooking acid (a) by the milk-of-lime system, and (b) by the tower system. (6) What is the effect on the cooking acid of the recovery of sulphur dioxide? (7) Why is the presence of sulphur trioxide detrimental in burner gas? (8) Mention the reasons for the recovery of sulphur dioxide (9) What effect does cooking with sulphite have on the con- stituents of wood? (10) What happens to the bisulphite in the liquor during the progress of the cook? (11) Name the essential parts of a digester, and mention the function of each. (12) (a) How is a digester lined? (b) why is an acid-proof lining necessary? 7 (13) Explain the purpose and the operation of relieving the digester. (14) How does the cook know when to blow the digester? Explain one test. (15) Compare the Mitscherlich process with the Ritter- Kellner process as to equipment, time, and temperature ot cooking. 89 as SECTION 5 MANUFACTURE OF SODA PULP By Artuur Burcress LARCHAR WITH BIBLIOGRAPHY By Donaup E. Case INTRODUCTORY OBJECT OF THE PROCESS 1. The Fibrous and Non-Fibrous Parts of Wood.—Peeled or barked wood may be regarded as made up of two very different substances: one is fibrous, and it consists of short, thin, wood cells, or fibers; the other is non-fibrous. The two are closely combined in the wood, and in the so-called mechanical process of pulp making, no effort is made to separate them. Since the non-fibrous part is much more easily changed by the action of air, sunlight, and moisture than the fibrous part, this causes paper that is made from groundwood (mechanical) pulp to change color and to become brittle and worthless with the lapse of time. But, by boiling the wood in a solution of water and chemicals, the non-fibrous part may be changed and dissolved, which leaves the fibrous portion nearly pure. The aim of all chemical processes of pulp making is to separate the fibrous part of the wood, which is called cellulose, from the non-fibrous part by dissolving the latter in the solution above referred to. The separation is not complete; for some of the coloring matters in the non-fibrous part, which consists of lignin, resins, gums, sugars, coloring matter, etc., remain in the fibers, and some of the fiber is dissolved in the process. The most successful process is that which will perform the separation with the smallest loss of fiber. | The oldest chemical process for making pulp is called the soda process, so called because caustic soda NaOH is the chemical §5 1 2 MANUFACTURE OF SODA PULP §5 used; the product that results from this process is called soda pulp. In the United States, this process has developed prin- -cipally since 1880. The greater part of the soda pulp manu- factured on this continent is made in Maine, New York, and Pennsylvania; a little is made in the South and West, and a small amount is made in Canada. 2. Kinds of Wood Used for Making Soda Pulp.—The kinds of wood that have been found best suited to pulp making by the soda process are those from the broad-leaved trees, the majority of which shed their leaves in the winter and are called deciduous for this reason. First in order of importance and in ease of pulping, is aspen, usually known as poplar; white maple, birch, chestnut, balm of Gilead (or balsam poplar), gum, and basswood are also used. Wood from evergreen, cone-bearing trees, such as the pines, spruce and balsam fir, are being used to some extent. Soda pulp made from aspen or similar wood is put into papers when soft stock is desired; it enters into book, magazine, and writing papers, and it serves as a filler to complete the furnish made up largely of longer fibers. Owing to the shortness of the fibers in soda pulp, it does not make a strong paper; but papers in which it is used may be readily finished to a good surface. BRIEF OUTLINE OF THE SODA PROCESS 3. The Wood.—Peeled wood may be delivered to the mill from nearby points by teams or from distant points by railroad cars; in either case, it is cut or sawed into 4- or 5-foot lengths. Mills that are favorably situated may get their wood in log lengths direct from the forest, by floating or driving it down the stream; when this method is used, a cutting-up or slasher mill cuts the logs into 4- or 5-foot lengths. Broad-leaved woods other than poplar are not usually driven, owing to their liability to sink. A 50-mile drive is about the limit for distance. The wood (in 4- or 5-foot lengths) is conveyed by industrial cars or by carriers to a wood-preparing room, and is there cut into chips by chippers, the lengths of chips desired varying from 3 toginch. Thechipsare elevated to chip bins over the digesters, and they are run into the digesters by gravity. Wet chips do not flow readily, and a steam jet may be used to start them moving. Siar in aay i ae Tu Sedu” hee Le 7 $5 INTRODUCTORY 3 The preliminary operations are described in the Section on Preparation of Wood. 4. The Soda Process.—The caustic-soda, liquor goes into the digester with the chips, the digester head, or cover, is bolted on, and the contents is cooked by admitting steam into the digester. After the cooking is complete, the mixture of pulp and liquor that contains the dissolved part of the wood is discharged into a blow-pit, or cyclone, and from this into washing tanks or pans, where the pulp is drained and washed, to free it from the colored liquor (or the same result may be achieved by the use of con- tinuous rotary suction filters); the latter is boiled down in evap- orators, and is treated in the reclaiming department to recover the soda contained in it. The washed pulp is screened, thickened, and bleached > the bleached fiber is freed from chemicals in drainers or washers, and is run into a sheet on cylinder drying machines. The pulp is shipped to the paper mill in the form of rolls or bales. In case the pulp mill and the paper mill are close together, the drying machine is not always used, and the drained pulp is then furnished directly to the beaters from storage tanks. The black liquor from the washing tanks, after being thickened by boiling in multiple-effect evaporators, 1s charred in rotary furnaces to form black ash, which contains soda ash (sodium carbonate, NasCO;) to the extent of about $ths (80%) of its weight. This black ash, which is what is left when the black liquor is burned, is leached, and the soda ash thereby dissolved in water is pumped to the causticizing department, or liquor room, where new caustic liquor is made from it; or, it is charged, without further treatment, with lime into lime slaking pots or tanks as the first step in the preparation of caustic liquor. The diagram, or flow sheet, Fig. 1, shows the course through which the materials move in the different stages of the soda process; it should be carefully considered in connection with the statements in this and the preceding article. The manufacture of sulphate pulp has much in common with the making of soda pulp; because of this, and because of the slightly different treatment of the subject, it is recommended that the Section on Sulphate Pulp be also carefully studied by the student interested in the soda process. MANUFACTURE OF SODA PULP Lime Soda Ash Wood Muddy Liquor Chips Filler kress arSeiting Tank Clear Causitc. Dusl & Spliniers lo Boiler Furnace Chips Pie Black Liquor Blow Pir | Waler Black Liquer. Brown Pupp ThicK Black Liquor, Sludge lo Sewer Causiic Liquor Green (SodaAsh) Liquor Screens Bie Brown Pulp Waler Bleached Pufp ioade Leach Charcoal to rain Fia. 1. §5 §5 THE COOKING LIQUOR 5 THE COOKING LIQUOR PREPARING THE COOKING LIQUOR CHEMICALS USED 5. Soda Ash (and Electrolytic Caustic).—The chemicals used in the soda process to dissolve the non-fibrous part of the wood will now be discussed. Caustic soda, usually called caustic in the mills, is the chemical that enables the cooking liquor to act; it is called sodium hydrate (or sodium hydroxide) by chemists, and it has the molecular formula NaOH. In what follows, the word alkali will some- times be used instead of caustic or soda ash when referring to the chemicals used in the soda process. Two methods may be used to prepare caustic in the ahh mill: 6. By the first method, the caustic (NaOH) is prepared from another compound of sodium, which is called soda ash or sodium carbonate, and which has the molecular formula NasCOs. Soda ash is a heavy, white powder, and comes to the mill either in bulk carloads or in ‘burlap bags that hold a few hundred pounds each. Soda ash has been made for a long time from salt, the most abundant compound of sodium, and upon alarge scale, both in Europe and in the United States. Soda ash dissolves freely in water, and dissolved soda ash is what is being constantly made in the reclaiming department of the soda mill. It is clearly to be seen that if new caustic liquor is to be made from the dissolved soda ash that has been reclaimed on the premises, it can be done most cheaply at the mill; and that is where it is done—in the liquor room, or causticizing department, of the mill. Boiling soda-ash liquor with lime yields caustic soda; thus, Na2CO; + CaO + H.O = 2NaOH + CaCO; 7. By the second method, the electric current is used to make the caustic for the cooking liquor. Brine, made by dissolving salt (NaCl) in water, is acted on in suitable cells by the electric cur- rent, and caustic-soda liquor is one of the direct products of this process (see Section on Bleaching of Pulp). Many of the larger soda mills have electrolytic departments in which caustic is made. 6 MANUFACTURE OF SODA PULP §5 As will be seen later, not all of the soda ash that goes into the -iquor room to make caustic is returned to it as reclaimed ash after passing through the digesters and reclaiming department; some loss is bound to occur. To make good this loss, new soda ash or caustic that has been made electrolytically may be used. From the foregoing, it is clear that the reclaimed soda ash, which has already passed through the process, is the chief sub- stance employed in preparing caustic-soda cooking liquor; while fresh soda ash or caustic soda from the electrolytic plant or both, serve to replace the material lost in the process. 8. Lime.—Soda ash alone will not dissolve all the non-fibrous part of wood, although it has some dissolving and softening effect when wood is digested or cooked with it. Before it can be of use, it must undergo a chemical change, and this is brought about by boiling dissolved soda ash with slaked lime. Lime, therefore, is a very important material in the operation of a soda-pulp mill. This substance, which is so commonly used in preparing mortar and plaster in the building trades, is what is left when limestone (calcium carbonate, CaCOs;) is calcined, or burned, in a kiln or furnace; it is also called quicklime and caustic lime, and has the molecular formula CaO. Quicklime should not be left exposed to the air, since it then absorbs carbon dioxide from the air and reverts to the carbonate. Slaked lime, or calcium hydrate (also called calciwm hydroxide), Ca(OH)», results when lime and water are brought together, the reaction being expressed by the equation, CaO ~h H.O == Ca(OH)>, and considerable heat is given off during the reaction. It is best to use the purest lime for caustic-liquor making; any sand and clay-like impurities are likely to frit into small masses, which do not slake in the caustic liquor tanks and remain behind to clog the drains, when these are washed out. The presence of magnesia is a detriment; it is useless in causticizing, and it is generally believed that magnesia limes give trouble from slow settling. A well burned, but not over burned, lime is required in liquor making. Unburned stone or core is a nuisance; it is too heavy to wash away with the lime sludge, and it may be large enough and hard enough to cause breakage of the agitator arms. Different limestones give limes that act differently in settling. ; a et er SE ee ee a a er §5 THE COOKING LIQUOR 7 A pure, well burned lime, one that yields a rapid-settling sludge in the caustic tank, is the kind the liquor maker wants. 9. Water.—The third important material used in making caustic liquor is water; pulp cannot be made from dry materials. The quantity of water required for liquor making is not far from two gallons of water to one pound of soda ash used; this allows enough water to wash away the mud after drawing off the liquor, and to wash floors and drains. The water need not be filtered, since the liquor is cleared by the settling of the lime mud. It must, however, be free from light particles of carbon, as this often floats and makes trouble with the quality of the pulp. Much of the needed water comes into the causticizing depart- ment with the reclaimed soda ash. The hotter the water that is used in making the caustic the better, as it saves steam in the causticizing tank and speeds up the work in the liquor room. STORING AND CONVEYING COOKING LIQUORS 10. Tanks.—The boiling together of soda ash and slaked lime is carried on in tanks, which may also be used for settling the liquor, or other tanks may be used for this purpose.! Still other tanks are used as storage vessels for the clear, finished liquor, ready for the digesters. Although these tanks may be of various styles and shapes, the round, flat-bottomed, upright, open-topped tanks are most generally employed, and steel plate is the material universally used for the construction of caustic tanks. Carefully riveted and calked seams must be insisted on, in order to secure a tight job; and thick plate is required on the bottom, to withstand the grinding of the lime sludge upon it, when the liquor is stirred. 11. In order that the liquor and lime, as sludge, may be well mixed together, the tanks in which the boiling and mixing are done are equipped with agitators or stirrers. For vertical tanks, such as is shown in Fig. 2, these stirrers are secured to heavy cast-iron arms A, which are bolted to a steel shaft that stands plumb, in the center of the tank, with its lower end in a guide or step 7’; at the upper end is a bevel gear K, meshing with a pinion, driven by belt pulleys, as shown, the power required being transmitted from the main-line shafting. The stirring arms may *One system of liquor making employs a tall, vertical tower, which is essentially a tank. See Art. 17A. 8 MANUFACTURE OF SODA PULP §5 be flat, but are set diagonally to the bottom of the tank, and are made to turn in such a manner that the material will have a tendency to be lifted by the revolving of the agitator. Some tanks have agitators built like a screw propeller. Tanks have one or more connections on the side, near the bottom, for removing the clear liquor, and they have an opening O wae Zi arrangement permits clear liquor to be drawn from the tank with- out drawing the lime mud with it, the liquor passing down the ~ ei | coe ee /| a= JUN LSS ee & in the bottom for removal of the lime sludge. The clear liquor is drawn off through the pipe Po, hinged at J, which permits the E other end of the pipe to swing through an are of a circle, thus 4 raising or lowering F. As the level of the liquor falls, the upper ] end F of the pipe follows it, and it is kept by the chain in the same position relative to the upper surface of the liquor. This } $5 THE COOKING LIQUOR 9 pipe and out through O’. The agitator is, of course, stopped while the pipe is draining the liquor. 12. Caustic tanks similar to that illustrated in Fig. 2 may have baskets E of iron rods or perforated plates hung in them near the top. The lime is placed in these baskets, which thus keep any unburned core from getting into the tanks. The size of the tanks is likely to vary with the size of the mill, the space available, and the particular method of operating that is selected. 13. Pumps.—Liquids in the caustic-making department are moved by pumps from tank to tank, unless the tanks are so placed that the liquids can flow by gravity. These pumps are a very important feature of the mill; they must be working all the time or, at least, the greater part of the time; they must run fast enough to keep the mill running at full production ; they must not leak, for leaks mean loss of valuable material; and they must run without frequent renewals or repairs, because shutting down a pump for repairs often means a stoppage of the entire department. The centrifugal type of pump is the one best adapted to use in the liquor-making department. In this pump (described in the Section on General Mill Equipment, Vol. V), @ cast-iron impeller, or runner, is keyed to a shaft and revolves in a cast-iron Shell, or casing. The liquid is brought into the pump at the center of the runner, and the vanes of the whirling runner throw the liquid against the shell of the pump. A discharge opening on the rim of the shell guides the liquid into the discharge pipe. The centrifugal pumps may be belt driven from a main or counter shaft, or they may be direct connected to an engine or electric motor. Being heavy, simple, and made of cast iron, they stand hard usage and gritty liquids very well. Pumps should be set in a well-lighted, clean place, and they should have sufficient room around them to allow them to be easily inspected, packed, and repaired. 14. Piping.—Hither wrought-iron piping or the best grade of steel piping is used for the conveying of caustic liquor, and a great deal of trouble can be prevented by proper arrangement of the piping. While the size of the pipe used depends on the amount of liquid conveyed, it is better to have the piping larger than is necessary rather than too small; 4-inch piping is about right for most liquor-making work. 10 MANUFACTURE OF SODA PULP §5 All-iron, double-gate valves should be used on pipe lines, and the lines should be assembled with flanges. Long-turn elbows help in avoiding the fouling of pipe lines with lime mud and scale, and in many cases, putting in tees and plugs at points where there is an angle in the line will enable it to be cleaned out easily. In addition to being large enough, a pipe line must not leak and must not plug. 7 Every caustic-making tank has a pipe and valve for delivering each of the following ingredients to the tank; soda-ash liquor, weak caustic liquor, hot water and steam. There must also be provision made for admitting cold water under pressure to a hose and nozzle, if the lime mud is to be washed out. The basement of the caustic-tank room must be provided with a drain or sewer, to carry away the lime mud. LIQUOR-ROOM PRACTICE MAKING THE CAUSTIC LIQUOR 15. Three Systems for Making Liquor.—Three systems for making caustic liquor for soda-pulp cooking have been tried: The first system, and the one still in use in a large number of soda mills, may be called the batch system, because the liquor is made in certain quantities or batches. The operation is necessarily intermittent. | The second system, a continuous system, employs the caustic- making machinery in such a way that a constant, definite-sized stream of materials is entering at one place, a similar stream of finished caustic is running out at another place, and a current of sludge is flowing away at a third place. 3 The third system, or filtration system, is like the first, as regards the boiling of the liquor; but, instead of settling the lime sludge and draining off the clear liquor, the caustic liquor with the lime sludge in it, is pumped through filter presses, or continuous rotary filters, which allow the clear liquor to pass through, the lime sludge remaining behind, where it is washed free from caustic. 16. What Takes Place when Soda Ash and Lime are Boiled Together.—If a small lump of lime be dropped into a pail con- taining water, two things will be noticed; first, the lime begins to swell and crack and soon breaks down into a powder, which clouds < ee ae tee $5 THE COOKING LIQUOR 11 the liquid and covers the bottom of the pail; second, the water becomes warmer, and if sufficient lime be present, the water will actually boil. These two changes indicate that the lime is slaking. The chemical reaction between the lime and the water is expressed by the following equation: CaO + H20 = CaO.Hp, or Ca(OH). It has been proved by careful tests that water dissolves a small fraction of one per cent of its weight of lime. If, now, some of the clear liquid (from which the slaked lime has been settled) be put into a tumbler, and a little water, in which some washing soda has been dissolved, be poured into it, the liquid becomes cloudy at once, and the resulting precipitate gradually settles to the bottom of the tumbler as a white powder. This white powder is like the limestone from which the lime was made, except that it is a powder instead of solid rock. The clear liquid in the tumbler, to which the dissolved washing soda was added, is now found to contain caustic soda. The car- bon dioxide that was in the soda has changed places with the water in the slaked lime and chalk (calcium carbonate), and caustic soda, or sodium hydrate, is the result. This reaction, which is the cornerstone of liquor making, is expressed by the chemical equation, Ca(OH). —+ Na.CO; = CaCO; -} 2Na0QH This experiment, which may easily be performed by anyone, shows what takes place in the causticizing tanks when caustic liquoris made. Limeand dissolved soda ash are brought together; _ some of the lime dissolves, and chalk and caustic result from the reaction with soda ash, NaeCO3. More lime keeps dissolving, and the action, which is assisted by heat, goes on until nearly all the lime has become chalk, and most of the soda ash, 90% to 93%, is changed to caustic in mill practice. 17. The Continuous System.—Fig 3 shows diagrammatically a patented continuous system for making caustic soda. The lime and carbonate (soda-ash) liquor are running continually from the recovery system into one of three causticizing, or reaction, tanks and passing through the other two tanks. These reaction tanks fi, Re, Rs are fitted with agitators and steam coils. From the third reaction tank R;, the mixture of caustic liquor and lime mud 12 MANUFACTURE OF SODA PULP. 85 flows into one of three very large settling tanks S;, Se, S3. These settling tanks may be 24 feet or more across, and each has a very slow-moving agitator, which permits much settling and, at the same time, keeps the lime mud from becoming hard. The clear liquor from the top of the first settling tank S, overflows to the storage tank for digester liquor, while the thick mud in the bottom is pumped into the second settling tank Se, into which the weak caustic liquor from the top of the third tank S3 is flowing. The liquor from the top of the second tank is used to make up the proper volume in reaction tank A, for J = Sludge Y) fump | 3) 0 Sewer or Calcining Flant—" | Sludge Furp _,Strong Liquor to Sforage Fie. 8. slaking lime and diluting digester liquor when necessary. The mud from the second tank is pumped into the third tank, where water is being added. It will be perceived that the mud is traveling through the series of settling tanks in a direction oppo- site to the travel of the water, which is added at the third tank. This is the counter-current principle. The mud that is discharged from the third settling tank con- tains less than 1% of the soda that entered the first reaction tank. 17A. Another patented continuous causticizing and lime- recovery system is shown in elevation in Fig. 4. The lime is slaked in tank A, fitted with an agitator and charged by bucket elevator B. The slaked lime is pumped to one or both of the continuous causticizing towers. These consist each of preheater C for sodium carbonate liquor, and a reaction chamber D. The mixture of caustic soda and lime sludge is pumped to decanter E or F, in which is a slow-moving agitator. The clear caustic liquor is drawn off at the top, and is led to the liquor storage; et 85 THE COOKING LIQUOR 13 the muck, containing about 70% water, is pumped to a tank G, where it is stirred, and from which it is fed to rotary filters H. A vacuum pump K, with condensers and trap, maintains a vacuum of not less than 20 in. in the filters. The filter cake, containing about 30% water, is scraped off the filters, and is fed to the rotary kiln ZL. The carbonate of lime gradually dries as it passes through the kiln, and it eventually meets hot gases from the burning of producer gas, powdered coal, or oil. The reaction zone is the last 25 ft. of the furnace, where the carbonate is changed to quicklime; thus, CaCO; = CaO + CO,. The lime loss is said to be from 10% to 20%, and the soda loss in the liquor room, #% to 1%, which, however, is returned to the causticizer with the recovered lime. The gases from the kiln pass out through the stack M. FILTERS 18. The Filtration System.—In the filtration system, clear caustic liquor may be separated from lime mud by the use of filters, and settling may be avoided. Crude filters, in which the mixture of liquor and mud is run over a bed of sand, have been used, but mechanical filters are now employed. These may operate all the time, with a constant discharge of clear liquor and mud, the continuous filter, or they may be of the fill-and-dump type. 19. The Continuous Filter.—In the continuous type, Fig. 5, the filtering medium is a closely-woven wire cloth a, which is attached to the outside of a revolving drum b, which turns in an open tank c that contains the mixture to be filtered. The 14 MANUFACTURE OF SODA PULP $5 machine is so constructed that suction helps to deposit the sludge on the surface of the filter as the liquor flows through the wire cloth. One journal bearing is hollow; it carries a suction pipe and a compressed-air pipe, which end in a box that is divided into segments, one large and the other small. The inside end of pipes ¢ passes over these segments, and for the greater part of the time, suck out water from between the wooden drum and the wire covered with sludge. For a short part of each revolution, y TULL y y, Zn Uy) when passing the small segment, air is blown into the pipes e; this lifts the sludge from the wire and assists the scraper s in removing it. A shower ¢ also helps to remove the sludge. Wash- ing is effected by means of a spray of water from pipe d, which is outside of the drum and operates while the suction is on. An agitator in the bottom of the tank keeps the sludge in suspension. The drum is turned by means of the worm gear g. 20. The Fill-and-Dump Type.—The fill-and-dump type of filter has several parts: a shell, or chamber, to hold the mixture to be filtered; inlet and outlet connections; pipes, pumps, ete. Such a filter must be taken apart to dump the cakes, which are formed between corrugated plates covered with filter cloth. 21. The Leaf Type.—lIn the leaf type of filter, illustrated in Fig. 6, the liquor to be filtered is pumped into the shell. The Oe ar 5 : | gs THE COOKING LIQUOR 15 clear liquor passes through the cloth on the leaves, see view (d), while the mud builds up a cake on their surface. The frame is removed from the shell, or a portion of the shell is swung off on hinges, and the cake is removed by compressed air or by water. PLA Pate, IEW PUMP SIDE VIEW PRESS OPEN Cross-section through Gilter leaf and cake. Fig. 6. The pressure tank, or shell, E, is of steel; the front end is made open and is riveted to a heavy cast-iron circular flange, or ring, Ff. The ring is provided with heavy U bolts G1, which pass through lugs on ring F. The U bolts engage the radial locking arms of the head locker, which is described later, 16 MANUFACTURE OF SODA PULP §5 The front and rear ends of the filter carriage consist of support- ing plates for the filter leaves, fastened together with channel irons. The filter carriage is attached to, and has for its front end, the cast-iron head, which is mounted on wheels W, and trav- els on the outer track on top of the I beams J. The rear end is mounted on wheels W:2 and travels on rails K, see view (c), which are supported on brackets inside of the shell. The entire carriage telescopes into the press shell, the head closing the front end of the shell. This movement is accomplished by means of a chain drive, operated either by hand or by a compressed-air motor. The filter leaves are rectangular in shape, running longitu- dinally in the press shell, and are made of. specially rolled steel pipes L, see view (d), with a No. 12, 4-mesh, double-crimped, wire screen M solidly spot-welded to it. The forward corners of the leaves are connected to the head of the press. All filtrates are expelled here, through the head, and are discharged outside of the head into a trough or filtrate header N, see view (c). The leaves are, with the exception of the front and rear supporting lugs, entirely enclosed in extra-heavy, special-twill filter bags, which are made with the front end open, and are quickly drawn over the leaves, the open end being then sewed up by hand. The head-locking mechanism consists of radial lever arms P, see view (c), and the inner ends are pivoted to a movable collar fk, which is propelled along a central shaft by a toggle joint. The toggle joint is thrown in or out along the shaft by simply throwing a hand lever S in an arc of 180°. As the arms move inward, the outer ends engage in the U bolts, forcing the tongue or head into the groove on the ring and against the gasket, thus insuring a perfect air-tight and water-tight joint. If desired, a hand wheel, with a screw for propelling the locking mechanism, can be sub- stituted for the lever and toggle-joint device just described. The outlet V from each filter leaf passes through the head and ends in a special cock U, which empties into a launder or trough N. Immediately back of the cocks, the outer nipples are also connected by cross valves into a header or manifold. Both launder and header empty into a suitable box, placed alongside the press, and from whence the liquors are conveyed to their proper destination. 22. Operation of Filter—Filtration consists usually of a double operation, viz., cake building and cake washing. The GR se snare terres Hnigres §5 THE COOKING LIQUOR 17 cake retains a high percentage of valuable salts in soluble form, and these salts should be removed (recovered) as far as possible. To obtain good results in a pressure filter, the press must be filled rapidly, and it must be full of sludge and under constant pressure during filtration. A centrifugal pump is usually employed. To obtain a good wash, the cake building must be of even thickness over the entire filter area, and the filter leaves must be entirely submerged. This can be accomplished only by keep- ing the press shell full of sludge and under constant pressure (30 to 60 lb. per sq. in.) during filtration. Furthermore, to obtain a perfect wash, the cakes must be free from cracks, so the wash water may penetrate every square inch of the cake alike. To prevent cracking of the cake, the press must be quickly emptied of unfiltered sludge, which is sent back to the supply tank and is used in the next operation. The cakesare formed on the outside of the leaves; they must not be allowed to grow together. Referring to Fig. 6 (c), it is seen that the cake is built up, cover- ing the entire leaf, with the filter cloth on the inner side, and the harder part of the cake next the cloth and forming the foundation of the cake. Now since the sludge and the wash water enter the press through the same intake, both filtrate and wash water must travel the same course; namely, from the outer surface of the cake (which is the softer part and isin contact with the liquid), through the cake and the cloth, to the inside of the frame, and out of the press, as indicated by the arrows. Consequently, there is no cause for channels forming, since the wash water enters the softer part of the cake first, which is supported by the harder part, and this uniform cake gives an ideal wash, displacing practically all the liquor before wash water appears at the outlet. In case the cloths are mechanically clogged, i.e., clogged by dirt or mud, the press is closed and filled with water; the overflow valve is opened, and a steam hose is connected to the filtrate header on the head of the press. The outlet valve is now opened, and steam is allowed to enter the inside of the filter cloths, through the filtrate pipes. The steam will condense until the water is brought to a boil. The ascending steam causes the cloths to vibrate, and all the dirt is immediately removed and dropped to the bottom of the press shell. In case of chemical obstruction, such as lime incrustation, the operation is repeated as above, with the exception that the press 18 MANUFACTURE OF SODA PULP §5 is filled with a weak acid solution, which can be pumped into the press through the feed opening, and which, passing through the filter leaves, is carried out through the filtrate openings on the head and back to the storage tank that is used for this purpose. In this manner, the acid solution can be repeatedly passed through the press, as many times as desired, until the cloths are clean and open. In either case, the impurities removed from the cloths may be Hushed out through the excess valve and into the sewer. HANDLING TANKS 23. Mixing Lime and Carbonate Liquor.—The exact manner in which the lime and carbonate are brought together in tanks varies, different mill men having their own ideas regarding this. The carbonate liquor may be pumped in first and the lime thrown into it dry; or the lime may be slaked separately, and the milk of lime run into the liquor, which should be boiling hot. Again, the lime may be slaked in the basket that hangs in the tank. Or, both the carbonate liquor and the lime may be put into the tank at the same time, regardless of which is all in first. Again, a portion of the lime may be slaked in water in the boiling tank or run in from a separate slaking tank, and then the carbonate liquor started, the remainder of the lime being added with the rest of the liquor. Good settling of the sludge cannot be secured by slaking all the lime in water in the boiling tank, although good causticity may be obtained in this manner. ‘Titration (or the hydrometer, see Art. 27) will show the strength of the carbonate liquor, and it will indicate the amount of fresh soda ash required to make up for losses; this amount runs from 10% to 18% of the alkali sent to the digesters. 24, Boiling.—When the carbonate liquor (from the leaching of black ash) and the lime are all in the boiling tank, the contents should be nearly boiling, but the tank should not be full. One pound of lime in slaking generates 480 B.t.u., and the carbonate liquor should not be over 165° to 170°F., if the lime is slaked in the same tank; otherwise, the tank may boil over. It ought to be boiled strongly for 15 minutes or longer; then the diluting liquor, which may be second, third, or fourth wash liquor, is pumped in until the tank is nearly full, keeping the liquor — ee Nee f d 5 : z §5 THE COOKING LIQUOR tat boiling and stirring it all the time. At this point, the agitator is struck out, and a sample is taken out of the tank with a long- handled dipper, for the laboratory test. The original strength of the carbonate liquor in terms of car- bonate will be known. A second titration will now show how much carbonate remains and how much caustic soda is present. The carbonate converted (original minus final) divided by the original carbonate and multiplied by 100 is the percentage of conversion. If this shows that 90% or more of the soda ash has been changed into caustic, the tank is allowed to settle. If the change has not gone far enough, more lime may be added, and the stirring and boiling are renewed. Thorough mixing is the important thing, and this may often finish the tank without requiring extra lime. 25. Settling.—Good settling of the lime sludge is necessary: first, because lime in the liquor makes trouble in the cooking and in the bleaching of pulp; second, because any black dirt, or charcoal, or coke that may be in the sludge is likely to go to the digester with it, in which case, it will appear as specks in the fin- ished pulp. The quantity of liquor that can be made in the liquor room depends largely upon the time required for settling. 26. Pumping Off and Washing the Sludge.—Pumping may be begun as soon as the lime mud has settled enough to allow the siphon pipe (P., Fig. 2) to be lowered without clouding the clear liquor. The strong and second liquors are pumped off together, to make liquor having a strength of 16°-19°Tw. (say 11°-13° Be.) for the digesters. This allows changes to be made in the strength of the liquor to the digesters. The third liquor, about 3°-5°Tw. (say 2°-33°Be.), is pumped over, covering the mud from the strong liquor, and forming a new second liquor. The fourth liquor, about 1°Tw. (say 0.7°Be.) or less, is pumped over, covering the sludge from the second liquor and forming a new third liquor. The sludge from the third liquor is now made up with water, forming a new fourth liquor. ‘Stirring and settling are performed each time a sludge is made up with weak liquor. Three weak liquors, or washes, are usually all that can be taken off one tank; and if the settling and pumping are well done, this last liquor leaves the sludge with between 1% and 3% of the total soda ash put with it into the tank. 20 MANUFACTURE OF SODA PULP §5 27. Determining the Strength of Caustic Liquor.—For operat- ing purposes, the strength of the caustic liquors is determined by | the workman, who uses a hydrometer for this test. This instru- . ment measures the density of the liquid, and is made in many forms, one of which, the Baumé, was described in the Section on Physics, Vol. I. A similar hydrometer, but having a different scale, is called a Twaddell (abbreviated to Tw.) hydrometer, and its scale is called a Twaddell scale. This instrument can be used only for measuring the densities of liquids heavier than water. Both the Baumé and Twaddell scales are used in paper mills, but the author of this Section uses the Twaddell hydrome- ter in his mill, and the Twaddell scale has been employed exclu- sively throughout this Section. For the benefit of those readers who are accustomed to using the Baumé scale, the nearest practical Baumé equivalents are given in parenthesis, as in the last article. To convert exactly from one scale to the other, use may be made of the table at the end of this volume. Or, one of the following formulas may be used: Let J = number of degrees Twaddell B = number of degrees Baumé S = specific gravity of liquid 5T + 1000 5 =~ 1000 (1) 1457 ~ 200+ 7 (2) 200B weearia > (3) For example, to find the number of degrees Baumé correspond- ing. to 37°Tw., substitute in formula (2), and B = non ae = 22.64°Be., which is the same as the value given in the table at the end of this volume. If it were desired to know the specific gravity at 37°Tw., substitute in formula (1), and S = 5 X 37 + 1000 21-185 1000 ath 28. Getting Rid of the Lime Mud (Sludge).—In eoine mills, the final sludge is run directly into a river; in others, it must be used as filling material at some point around the mill premises. It is possible to dry and calcine this mud, thereby obtaining caustic lime from it. Revolving kilns, similar to those used in é| 3 | - 5 F =| §5 THE COOKING LIQUOR 21 clinkering cement, have been tried for this purpose, and the idea of reclaiming lime in this manner is becoming common. A Canadian mill has successfully used lime sludge for making calcium bisulphite cooking liquor in the sulphite process. 29. Storage of Digester Liquor.—Finished caustic liquor is stored in tanks; it is pumped from them to the digesters. Any lime mud that may have been accidentally pumped in from the boiling or settling tanks is allowed to settle out here. The amount of caustic in the tank at any given depth, meas- ured in inches, is calculated in the laboratory, and the volume is specified that contains the weight of caustic soda that is needed for one digester-full of chips. If electrolytic caustic be used to make up the losses, it may well be put in these storage tanks and thoroughly mixed with the rest of the liquor, by stirring with a current of air or by other means. The liquor-room foreman is responsible for the operations just described, and he must keep the mill supplied with clear cooking liquor of the right strength. THE COOKING LIQUOR 30. Amount of Liquor Required.—From 900-1100 gallons, depending on the amount of moisture in the chips, of caustic liquor having a density of 16°-19°Tw. (say 11°-13°Be.) is needed to cook a cord of wood. A mill making 100 tons of soda pulp per day will require from 140,000—180,000 gallons of liquor in 24 hours. Hach cord of wood (poplar) requires 800-950 pounds of total soda, expressed as sodium carbonate, but used principally as sodium hydrate; this contains 21%-25% actual sodium hydrate, NaOH, on the weight of dry wood. Not far from 80 tons of soda ash, of which 82%-90% is recovered from black ash, must go into the boiling tanks to make this liquor; 92% of this will be changed-to caustic, using for this purpose about 45 tons of lime. 31. Operation of Liquor Room.— When the liquor room is run on the batch system, it is operated about as follows: Suppose there are a dozen tanks for boiling and settling the liquor, and a half dozen other tanks for storage. At any time, there should be three tanks of the strongest liquor, testing 28°-30°Tw. (say 18°-19°Be.). One tank might be making up with a fresh charge of soda ash 22 MANUFACTURE OF SODA PULP §5 and lime. Two tanks will have second liquors, or first washes, in them, which would test about 8°Tw. (say. 54°Be.). Two tanks will be full of third liquor, or second wash, testing about 3°Tw. (say 2°Be.); and three tanks will contain fourth liquor, or third wash, testing 1°Tw. (say 0.7°Be.). One tank will be empty or washing out. The hydrometer strength of the strong - liquor and of the second liquor must be known, since these are to be pumped together, to make up the liquor for the digesters. To make a test, pour a little of the well-settled liquor into a testing tube made of iron pipe, with a flange on one end to serve as a base. Drop a Twaddell or Baumé hydrometer into this sample of liquor very carefully, and read the density on the scale. The temperature of the liquor must also be known, since the density decreases as the temperature increases. and the hydrom- eter will sink farther in hot liquor than in one of lower tempera- ture. It is therefore necessary to correct the hydrometer reading to some standard temperature (generally, either 60°F. or 15°C.), which is usually marked on the hydrometer. The safest way is to allow the liquor to cool to the temperature. marked on the hydrometer before inserting it in the liquor. 32. Suppose that the strong liquor, which has been settling the longest time, tests 28°T'w. and that the oldest second liquor tests 8°Tw. or SS QO N SS : Ned CZLZZLLL) | wh, Th L BS OR\ N ch N NEW LLM ENGL, EEN tes (o) th ei LLL LLL, ae \{/ "LLL Wy q / Z a 7 BS : N Ka Fig. 8. gasket 3, placed in a groove in the boss, into which fits a projection on the flange of the throat. The digester cover, or head, 4 is bolted to the throat piece by heavy bolts and nuts Be the bolts fit into slots in the rim of the cover and into similar slots in the flange of the throat casting. The bolt heads are made square, to keep the bolts from turning when the nuts are tight- ened up. This style of digester head is hinged to the throat cast- ing, and the bolts are removed when the head is to be raised. The joint between the head and throat is kept tight by a lead packing 3, which may be formed by pouring melted lead into the groove, or by caulking small lead pipe into it. A light chain block 6 swings the head on its hinges. The style of top shown in (6), Fig. 8, differs from that shown in (a), in that there is no hinge on the head, the head bolts being 30 MANUFACTURE OF SODA PULP §5 hinged to the throat piece by means of lugs and pins. The head is lifted off the throat piece by the hand-wheel and screw device 7, which runs along a rail 12 over the digester on small flanged wheels 8. A handier rig is shown in (c), Fig. 8. Here a single steel cast- ing 9 constitutes both throat piece and cover, and it is necessary to keep only one joint tight. This rig is handled in the same manner as in (6). The cover bolts 10 are jointed; one end screws into the boss on the digester, and the other end swings into the slot in the rim of the cover casting. 41. Horizontal digesters, which revolve slowly while the wood is cooking, have been used in a few soda mills. The following is a description, condensed from E. Sutermeister, of this type of digester. “Rotary riveted digesters in American practice are generally about 20-24 feet long and 7 feet in diameter; larger ones have been constructed, but have been very hard to keep tight, because the strains they set up as they rotate tend to start their seams. They are filled with chips through manholes in the sides; and, in order to get in as great a charge as possible, some form of tamping device is necessary. A steel cone, fixed (apex down) on the end of a shaft that is alternately lifted and dropped by an eccentric, gives excellent results in packing in the chips. Steam for heat- ing the charge generally enters the rotary through one of the two’ trunnions; the trunnion at the other end of the rotary is piped up, so air or steam can be relieved through it. After the cook is completed, the relief line is opened and the pressure reduced. The heads are then removed, and the charge is emptied into the wash pits below, by the simple expedient of revolving the rotary.” For an illustration of the horizontal rotary digester, see Sec- tion on Preparation of Rags and Other Fibers, Vol. IV. Double-shell digesters have been used for cooking wood by the soda process. The steam for heating the charge is contained in the space between the two shells. This type has not proved successful, by reason of leakage and waste of steam. 42. Ways of Heating and Circulating Contents of Digester.— There are several ways by which the chips and caustic-soda liquor may be heated in a soda digester. By the direct heating method, the steam may be led directly to the lower part of the digester; this causes the cooking to begin where the steam is admitted, and bigot in S50 §5 THE COOKING PROCESS IN A SODA MILL . 31 the boiling liquor rises through the mass in the digester, which sets up a circulation that finally brings the whole up to full cooking temperature. By the method of injector circulation, Fig. 7, the steam may be led through the shell of the digester and into a simple form of injector, K situated under the perforated bottom. A pipe leads from the top of the injector and up along the side of the digester. The pipe is supported by lugs to a point near the top of the diges- ter, where a curved deflecting plate or sprinkler, B is fastened in such a position as to spread over the chips the liquor that is dis- charged through the pipe. Several such injectors may be placed in a digester. In such an arrangement, the cooking begins at the top of the digester. Injector circulation gives good results in digesters of moderate height. An injector is simply a steam nozzle that discharges upward into a pipe that is open, at its lower end, to the liquor. The velocity of the steam keeps the liquor circulating, and it heats it at the same time. PUMP CIRCULATION 43. Distributing the Heat in a Digester.—The heat can be quickly distributed to all parts of the digester by using a pump for circulation, together with direct heating; such a system is illustrated in Fig. 9. Centrifugal pumps have been bolted to a flanged neck on the side of the lower part of the digester, below the false bottom; they may also be connected to the digester by means of piping. Reciprocating steam pumps may be used for the same purpose. The liquor that is drawn out by the pump is returned at the top of the digester. Any one or all three of these methods may, of course, be used on the same digester. In Fig. 9, steam is admitted through pipe D, valve V, and perforated coil K. £ is the relief connection, C is the cover, and the digester is charged through the throat B. The liquor drains through the perforated bottom N and flows to pump H, which feeds it through pipe 7, to be distributed over the chips. The charge is blown out through connection F, blow valve G, and blow pipe P. Mention may also be made of the coil method of heating, which has been tried in some mills; however, it had to be abandoned, 32 MANUFACTURE OF SODA PULP §5 because of mechanical difficulties. In this method, the steam was not allowed to enter the charge, but passed through coils of pipe, which were placed around the inside of the digester. Fig. 9. 44. Indirect Heating.—In the process using a system of indi- rect heating, illustrated in Fig. 10, a pump is used for the cir- culating, but the steam for heating is not blown directly into the digester D. Instead, the steam is led to a heater A outside of the digester; and the circulating liquor from the pump passes wt terra Ie ae ice Prine: me §5 THE COOKING PROCESS IN A SODA MILL _ 33 through this heater, which is so designed that the steam is on one side of and the liquor is on the other side of a series of tubes C. The condensed steam is fed back to the boilers or wash- water tanks by the condensate : pump G, instead of going into rt ~~ on _ a ae is $5 THE COOKING PROCESS IN A SODA MILL 43 agreed that ease of bleaching is improved by this addition. Offensive odors and corrosion of digesting equipment also result. Salt cake Na2SO., when added to the rotary incinerator, gives about the same result; the process then becomes virtually a sulphate process. A more recent suggestion is the use of mer- cury, but no mill results are available for determining the efficiency of this method. Cooking with a solution of sodium sulphite Na2SO; and caustic soda NaOH (the Keebra process) is being practiced in one or two mills. Information as to details is not available at this time. 61. Experimental Digesters.—The recal te obtained with small digesters are helpful in operating the larger digesters. But, it must be remembered that in the larger digesters, there is one important difference: the chips in the different sections of the digester do not all receive the same treatment. Thus, the top layer is cooked first with strong liquor that contains most of the caustic soda, and the pulp is then subjected to the action of a gradually weakening liquor for the remainder of the cook. The lower layers, on the contrary, while soaked with liquor of the original strength, receive their final cooking through the action of much weaker liquor, the caustic in which has been largely used up. [ach large digester, then, contains portions of pulp that have been cooked for different lengths of time at full temperature and that have been separated from the non-fibrous part of the wood by liquor of different composition. In the small, experimental digesters, the chips are all so near together that they all receive more nearly the same treatment. Since they are heated externally, there is no variation in the vol- ume and strength of the cooking liquor, due to condensation of steam. QUESTIONS (1) Describe briefly the principal types of digesters. (2) Why it is necessary to circulate digester liquor? how is it done? (3) Explain an indirect cooking system. (4) For what is the blow pit used? why is it sometimes a source of loss? (5) What metal is generally used in the soda mill? (6) Name some advantages in using recording gauges and thermometers. (7) Explain the effect of wetness of wood on the cooking of pulp. (8) What is meant by relieving a digester? why is it necessary 2 44 MANUFACTURE OF SODA PULP §5 WASHING PULP AND RECLAIMING CHEMICALS WASHING SODA PULP 82. Purpose of Washing.—The black mixture of pulp and of liquor, which contains the dissolved non-fibrous part of the wood, must be separated into clean pulp and black liquor as the next step in the soda process. The washing room or wash-tank room is that part of the mill where this separation is made. The man in charge of this department has three objects in mind: 1, to prepare clean brown pulp fast enough to keep the bleachers supplied; 2, to keep ahead of the digesters, 7. e., to have tanks ready when the digesters are ready to blow; 3, to have the black liquor in the strongest condition possible, 7.e., in such shape that there will be the least quantity of water and the greatest quantity of solid matter in it. The third object is necessary in order to reduce the work of the evaporators in their part of the reclaiming process and to reduce the amount of heat they consume in doing it. The brown pulp must be free from black liquor or it will not bleach properly. The pulp can be washed most quickly in shallow vessels, using only hot water, the hotter the better. But, in order to keep the black liquor strong, it is necessary to have the washing tanks, or pits, or pans, as they are variously called, of consider- able depth, and to begin the washing process with some weaker black liquor, which has drained from tanks filled previously. 83. Washing Tanks.—Washing tanks may be round, square, or oblong in shape, and they are usually built with open tops. Some of the most recently designed washing tanks are entirely covered, except for openings for filling, etc. They are made of steel plate, well riveted; a convenient size is one holding one digester of pulp. With tanks of this size, it is easier to keep separate the pulp received from different digesters. A false bottom of heavy steel plate A, Fig. 13, perforated with holes of about % inch diameter, closely spaced, and having a thin, finely perforated plate or wire net B resting on it, is supported 6 inches from the bottom by steel beams C, fastened to the bottom, and by an angle iron D, riveted around the inside of the tank. The perforated plate is bolted to the angle iron and to the flanges of the beam, and the joints in the thin, perforated plate are held §5 WASHING PULP AND RECLAIMING CHEMICALS 45 tight by means of iron straps. Below the false bottom, are the outlet P, for liquor to the liquor lines, and the outlet E, for waste water to the drain. There is also an opening F in the side of the tank, just above the false bottom, for washing out the brown pulp. 84, Piping in the Washing Room.—Wrought-iron piping is used in the washing room; this is neither rusted nor clogged up by black liquor. Each washing tank has a pipe G, Fig. 13, and valve H, for running on black liquor, and a pipe K, for running on warm water for washing. It is a good plan to have both these pipes connected to one pipe around the top of the tank, or across it, which should be perforated with small holes, for sprink- 46 MANUFACTURE OF SODA PULP §5 ling weak liquor or water over the top; or a distributor S may be used. A pipe having a high-pressure hose connection is provided to wash out the clean pulp from the tank. The black pulp from the blow pit is led into the washing tanks by means of a large, jointed pipe L, one end of which swings over a series of tanks and discharges into any one of them. 85. Pulp Canals or Sluices.— Washing tanks for soda pulp are supported on piers, and there should be room enough under them to permit a man to walk around easily and inspect the tanks for leaks. The pulp outlet from each tank connects to a canal or sluice, through which the brown pulp and water run to the next department. The floor of the washing room basement should be well drained; and it is well to have an arrangement for measuring and testing the volume of liquid that runs away from the washing room, in order to keep watch of the loss of alkali. The measuring is done by means of a weir, which was described in the Section on Mechanics and Hydraulics, Vol. I1. 86. Operation of the Washing Room.—The black pulp is taken down from the blow pit with the help of black liquor, which is pumped up for that purpose. In order that the first’ part of the blow may not pack too hard on the false bottom and thus make it difficult for the liquor to filter through it, the valve that controls the outflow of the strong liquor is not opened full until the tank is about one-third full. Care is also taken to keep the spout moving, so the pulp may not form a dense mass directly - under the discharge pipe, which might wash more slowly than the rest of the pulp in the tank. When the tank is full, the weak- liquor valve is opened, to let weak liquor flow on the top of the mass of pulp as fast as the black liquor is discharged at the bottom. This weak liquor shows from one-third to one-half the strength of the average of the strong black liquor that is being pumped to the evaporators. The time that the weak liquor is kept running on the pulp is gauged by the strength of the strong liquor flowing away from the tank. The accompanying diagram, Fig. 14, shows the rate at which the strength of the black liquor decreases at certain intervals of time. The curve, Fig. 14, shows the gradual variation in the density of wash liquors from a typical soda cook of poplar wood, as the ee RIN i sia i ee ices §5 WASHING PULP AND RECLAIMING CHEMICALS 47 Testing began after 10 minutes draining, and it will be noticed that the readings were taken with a Baumé hydrometer at 100°F. washing progresses. first half hour The density increased slightly during the then, for the next hour, it gradually fell off. At ) this time, washing with weak liquor stopped, and hot water was turned on for the rest of the washing period, during which time, the density fell off rapidly. The first stage, about to point A Washing with sly | aS) = 1S | om rlY! aw =\|= DENSITY of WASH LIQUORS from TYPICAL FOPLAR COOK panes Bimtemiep ue fo rece a yc ak ha ea ae bateqenpatanbaf-ap- i Saat ia Set Sale Se es Sf ek fa ek Da ne 8 tee ‘ a en 1 cy ' ea eae ant een pie eR pte eager et) a a Des ee ee eee ee ae ae | MEGGRER Ge Been JG aie eee ean is phon erie ee reap Says : ene aa fea mane Lieeli = ee Te feat ties ' ' badeap-pabafadadnd- deo -p-+-t- al ak ale ao dade-bet4 tae hd tot 1 ont ' ‘ 1 1 Ceo ee to tech eee ia ee Sikes eel= Se 7) 1 ' ee ore eee Eee iene foe ' ' ' ' feafatentadastente-t ‘i ates ac Soe iat eat ta et toe tr ne ee ery : 4 ' 1 at 1 1 yt 1 areal tas ae da a a wet Sara oe a f-+-40, ' or ' ' fata bad dab ota tte hat ogeabe dant dt ee Hiss) --L 4D ' We 1 - ee ee ee asl Tay Tena De ee a eee ee a ae eee i? li Hattie Ms arta abet od et Pet | ae poke se oS at as ae ey ‘a Se eat ' ' 1 1 ' 1 eats Oe esa ou Sh oO ae Sas cree ore Sa ace ba pebta-t ti iat tei aoe dae 1 ' heed ee L. 4. = SE Ay docks -4--- ayad~ =} -4--b-4- +24 rb t-+-7-4-4 eerie oat eat psa eee estan Spe ie gh tg 0 MN geen eg ae State ope =e te, ' 1 Pa pety etal 4--p-4--} -1- Goede Diane atop ge Pr ea ote cok er ft) at YO tet ' ' ener 1 iy a a f.-J-=1 Janpaqen bab ' os ‘ t ' ' ' wtint -4oet 4a agp tap dt ere ote pol ee mae Paes a oueoeSencuase fe See 1! 1 ' \- a-ha See eo: 4 t= “Se ey =o eager eet al “see 1 ' 1 ' ' T ah a ee ae ; a; fe ey BIRT pe VERE ities dee fd s ea dehy DS a Se tS eS eee ae +4 ' ‘ i oie 4 co daet rt banda tng ad -=t- i. a eee tee on ap ioe a Swe +3 tafateabad | ’ Cia ee 14 Tek ot es tedeob-}-3 arse) bh: r- AG GO a ee ee ins i 4 ' 4 4 ‘ prae-b=t—4 -beqe-p- ea--r-t —haates Ta Aan Se Sar ete Ve de et =a ! ' 1 ow ay Wea sl CURT ect ' oO nk n te a ae See eee t--j--t--L-J-— -4--1-5 = -1--|-- = = a et Hi ; 3 i. iz TOs evi 4 v ! in ANSe =F 3 +- 4 (i i oe Getty oat 18r- Ee Sia deopba dds Pate a Te nae a ae Se ee ee eee $2) 1-1 Hest roqe— -t-4- pr ored =p wn po tede-b- bata qaah atin -p at do-poe-s ' ee ee Se ‘ Ce ' 1 1 et aE iat Gr a ad St Sa OD bod fi ’ ' Nee ' 1 Ha cary a-ba fae nfo 4--h A Bet erat t ie eam oie rare pt tet ' 1 ES [@) r-t--\- cpp tach fpf obedient badach pape nab bat da 8 eC od 4 8 1 ’ rot eG og ‘ tes t-=4- Soa ines aie sap ae 1s od 56 OR, |e he 1o4 i n Hi uff ’ i ' 110 Spr ele : Jaw O ares = = A! pideer ie + 1 : ree ce Sho pafmins ' t ' t Puksdadia waren tar renet 7 tesa ‘ ' tek -Ler tc eae ry ae ee -t-4 ok er - rbd a a ES as gp eters eae ee or ee ere ee ee =- -+t3- ae ere ' a Saee: ee jm he tee da eb ee ee ntl wsaaectaeodns t ™N “O ie) Xe} Si -_- pu 4,00/ £2 pulled, pms Time— Hours & Minules Fig. 14. on the curve, shows the black liquor leaving the pulp as it is or displaced by the weak liquor; this liquor goes to the evaporat Say ) s a part of thi to point B, may be mixed with the black liquor, while the rest ) During the second stage, from A to C, the weak liquor wash is being displaced by hot water storage tank. After goes to the weak-liquor storage, for washing pulp, etc. point C, the effluent contains little of value and goes to the Points A, B, and C are not fixed, even for the same mill, ditch. For in- stance, if the weak-liquor storage is full, the effluent must be but must be varied slightly, according to conditions. discarded before point C is reached. Details of the cook represented by the curve are shown in the following tabulation 48 MANUFACTURE OF SODA PULP §5 Kindsof,, Wood j.aee teed hee ae os toe Gum and poplar Wood per dipestertasqasen: cous Gey 0c pe 3.7 cords Volume of cooking lgnot: +..44-5,.. har oe 3750 gal. Strength of cooking liquor................. 12 .5°Be. Time oftcookingt Sears 7a hie 8 hours Average:cooking: pressures); .y.10. /) eee 118 lb. per sq. in., gauge Xield!per-cord tank 2 eo 1150 pounds The outline of the curve will vary with tanks of different shapes and dimensions and also with changes in the method of cooking, 87. When this strong liquor reaches the lowest strength (1.036 sp. gr.,) permitted to go into the strong-liquor storage, the strong- liquor valve is shut and the weak-liquor valve at the bottom of the tank is opened. At the same time, the weak liquor is shut off from the top of the tank, and warm water is turned on. The tank is kept flooded with hot water, which gradually sinks through the pulp, taking the place of the liquor and washing the pulp as it goes down through it. | When the strength of the weak liquor becomes so low (drops from 1.036 to 1.005, average, 1.02 sp. gr.) that the soda in it is not worth the cost of boiling down the liquor, the drain valve is opened and the rest of the weak liquor is wasted. The strength of the discharge to the drain is 1.005 sp. gr. (1°Tw.) or less. The hot water, 90°-120°F., that is used for washing the pulp, is taken from the condensers of the evaporators, or from the outside liquor heater (Art. 44). The temperature of the weak liquor is usually 140°F. or higher. When the pulp is entirely clean, the wash-out valve is opened and the pressure water (35-50 Ib. per sq. in.) is turned on. The pulp and water flow through the pulp sluices into the next department, where it is to be screened and bleached. 88. It has been found that the manner in which the wood is cooked has a great effect upon the time required to wash it. Stock that washes easily and quickly is called free stock, while that which takes a longer time for this is called slow stock. Increasing the proportion of caustic soda to wood in the digester and prolonging the time the wood is cooking, tends to make stock slow, 7.e., it holds water and solutions longer. The reason is that cellulose hydrate, a gelatinous substance, begins to form on the fibers; the same phenomenon is observed in the case of greasy paper stock that has been beaten a long time. At the instant the pulp drops from the discharge pipe, it is of a §5 WASHING PULP AND RECLAIMING CHEMICALS 49 reddish-brown color, which turns to black almost instantly, the change of color being probably due to the action of air; but in the wash tank, the pulp is a great black, pudding-like, mass. Unless the pulp is under-cooked, there is now no appearance of the chip form. | If only fresh hot water were used in washing the pulp, it would be well and quickly washed, but the average strength of the black _ liquor would be low. This means that the evaporators must then boil more liquor and the fireman must burn more coal under the boilers, for each pound of soda recovered from the black liquor. Hence, washing with hot water only, will make the pulp cost more. Weak liquor is strengthened by passing it through the fresh pulp, thereby removing most of the black liquor adhering to the pulp. Cold water could be used instead of hot water, but the pulp would wash more slowly and would be harder to bleach. When cold water is put on black pulp, the washed pulp has a pink color; further, if cold water were used, there would be but little, if any, use for the hot water that comes from the evaporator condensers, and the heat in it would be wasted. 89. In the manufacture of sulphate pulp, the washing is done in closed vessels called diffusers (see Section on Sulphate Pulp), which are arranged in a series. The wash water enters the one first filled and passes through fresher charges until, finally, the now strong wash displaces the black liquor from the one last charged. 90. Analysis of Black Liquor.—The proportions of organic and inorganic constituents of the black liquor are indicated in the following analyses, which were made on an average sample of the liquor that first drained away from the stock. This liquor tested 127°Be. at 70°F., and 1 liter weighed 1097 grams. Grams Per cent | Per cent Black liquor per by on total | liter | weight | solids SU | 180.2 16.4 tne ee Es eS cs 917.3 83.6 LAN gl RS 19.5 1.8 10.8 moraraikealyas Na-O................. 49.9 4.5 21-8 Organic matter precipitated by H.SQ,. 2T20 2.5 15.1 na ee tt ee eS a SR eee ee lll ad 50 MANUFACTURE OF SODA PULP . §5 THE EVAPORATOR ROOM 91. Purpose of Reclaiming Department.—The purpose of the reclaiming department is to save the alkali in the black liquor, so that it may be used again, thus avoiding the necessity of using new alkali. While the black liquor contains other sub- stances of considerable value, practical methods of separating all of them have not yet been found, although experiments have been made with this in view. Some of the early soda mills wasted all the black liquor and had no reclaiming department whatever. As may be supposed, the first arrangements for reclaiming soda were not only crude but were also uneconomical. The black liquor contains part of the caustic soda and all of the soda ash that was contained in the caustic liquor pumped to the digesters; it also contains dissolved woody substances and a portion of the soda, the latter being in chemical combination with acid substances derived from the wood; it likewise contains a substance of the nature of sugar and contains coloring matters. The following is an analysis from a soda cook of poplar, based on total weight of solids dried at 100°C. (212°F.), according to Griffin: Per Cent Silica (SiOe). «ica. eae get ee tue ee O41 Oxides of iron and alumina (Fe2O3 and Al,O3)............ 0.02 Lime (CaQ) 00... 0 hisses tre nies § Rin te 0.05 Potash (K:0). oo. ok et ee es ee 0.69 Soda (Na2O)..... 0.05 0004. alge Poe ot Et 25.69 Carbon dioxide (CQs)....4....)... 44333 3.43 Acetic:acid (CiH Os) cas eee eee Wee 9.80 Organic matter extracted by naphtha.................... 1.56 Organic matter extracted by ether....................-. 7.14 Organic matter extracted by alcohol (abs.)...... SR re 28 . 26 Organic matter extracted by water...................... 17.02 Total alkali by titration of incinerated residue............ 44 25 92. Black liquor that drains away from the pulp through the false bottom of the washing tank is likely to have some pulp in it; hence, before sending it to the evaporators, it 1s necessary to remove this pulp. Various forms of filters have been used for this purpose. Burlap bagging has been used as a filtering mate- rial in tanks having false bottoms. Pulp fibers have a tendency to plug feed passages, valves, and tubes of the evaporator and to lodge on the heating surface; it should therefore be removed before entering the evaporators. . Revolving cylinders that are a a §5 WASHING PULP AND RECLAIMING CHEMICALS 51 covered with metal cloth have also been used as filters, and one type was shown in Fig. 3. ! The first step toward saving the alkali, after freeing the black liquor from particles of fiber, is to boil it down, or evaporate it, so there will be more solid matter and less water in a given amount of it. In the early forms of evaporators, the black liquor was boiled down by means of the direct flame from the black-ash furnace. 93. Multiple-Effect Evaporator.—Modern evaporators are all heated by steam; they are so constructed that a pound of steam admitted to them will have several times as great an effect in boiling (and, consequently, evaporating) the liquor as would be obtained by using the same steam in single kettles or cauldrons. Since the same steam is used in several different parts of the apparatus, in each of which the steam has an effect in inducing evaporation, the term multiple effect is given to this process of evaporation. All multiple-effect evaporators have certain distinct features and, also, many in common. The layout of a triple-effect evaporator (one having three effects) is shown in Fig. 15. To feed the liquor to the evaporator, a pump or gravity feed may be used, and some form of regulator is often employed. The evaporator bodies, or effects, see A, Fig. 15, are the parts of the system where the actual boiling takes place. These bodies contain tubes that have steam on one side and the black liquor on the other side. The steam may be inside the tubes and the liquor outside, or the liquor may be inside and the steam outside; and the liquor may be in thin films on the surface of the metal, or it may be in large masses surrounding the tubes, according to the make. Between the evaporator bodies, are separators, or catch alls, S for the purpose of separating any liquor that may be in the steam passing from one effect to the next. There must also be some means of creating a vacuum, such as a condenser X, with or without a vacuum pump. A tail pump W takes the liquor out of the evaporator. Evaporators are ae ee with the different bodies, or effects, either side by side as in Fig. 15, or arranged one above the other. In the latter case, the liquor is fed into the uppermost effect, and flows down into the lower ones. The hydrometer test of the black liquor, as it comes to the evaporators, may be about 14°-15°Tw. (say 93°-10°Be.), and 52 MANUFACTURE OF SODA PULP §5 the boiled down (evaporated) liquor may test over 70°Tw. (say 38°Be.), nearly four-fifths of the water in the liquor having Clee i ies A oe 4 [| RD aL ial I 1 TATA (mms 5 Ct fy ry aus is pe N fa meres 3 x O_ Pi Fe 1 spe ave ae a 7 vg 7 S 37 OC. ? 3 4 > g 7 e& 4 a Co) ch || | /r\ Fre. 15. a (ae been removed by evaporation. A part of this water condenses on the heating surface of the evaporator, and is returned with the §5 WASHING PULP AND RECLAIMING CHEMICALS 53 condensation from the first effect to the boilers; the remainder goes to the condenser, and is used to provide hot water for washing pulp. 94. Duties of the Evaporator Man.—The evaporator man regu- lates the feed and discharge, and also the steam pressure and vacuum in the several effects, with the object of making the out- going liquor of such strength that it will act well in the black-ash furnaces. He must also wash the machines regularly, since they cannot do good work without washing, and he must keep the pumps well packed and in good order. A great deal of the success in recovering alkali depends upon the evaporator man. 95. Evaporator Details.—In Fig. 16, is shown a section of one of the effects (an effect is also called a body or pan) of the layout illustrated in Fig. 15. Here A is the shell, in the bottom half of which is a nest of tubes B. The tubes do not occupy the entire sectional area of the shell (not counting the space between the tubes), but leave a segment on either side for liquor circulation. The pipes are all of the same length, and they connect the steam chest C with the space D, in which the condensation separates and leaves by the valve H. Steam enters at F, either fresh steam or vapor from a previous effect. Similar letters in Figs. 15 and 16 indicate the same detail in each. Black liquor enters at G at such a rate that the tubes B are covered. As the liquor heats, it rises through (or past) the tubes, gives up its vapor, and returns by the segment on either side of the tube nest. The liquid is heated by the latent heat in the steam that condenses in the tubes. The concentrated liquor collects in the bottom and passes through valve H to the next effect or to the rotary furnace room. K is a clean-out valve. Peep holes LZ enable the operator to watch the behavior of each unit, and the gauge M shows the pressure in the vapor space N; this pressure determines the temperature at which the liquid boils and, consequently, the pressure and temperature needed for the heating steam. P isan incandescent lamp. Since the vapor tends to carry away some drops of liquid, a separator, or baffle plate R, is placed below the vapor outlet S; the high vapor space greatly helps to diminish this trouble, which is called entrazn- ment. As shown in Fig. 15, the vapor goes to the next effect, and from the last effect, to the condenser X. The liquid-level gauge glass 7’, feed control valves V, condensation pumps U, the tail, 54 MANUFACTURE OF SODA PULP _ §5 magma, or heavy-liquor discharge pump W, condenser X, and vacuum pump Y, for the removal of insoluble and non-conden- sible gases from the condenser, are also shown. It will be per- ceived that the vapor pipes S increase in size as the evaporation progresses; this is because the volume of any gas increases as the pressure decreases. I SSS EE . SS e) tives va ete ow at NN eS Fig. 16. If exhaust steam is used in the first effect, its temperature will be about 225°F., and the general efficiency of the condenser and the cost of maintaining a good vacuum will ordinarily limit the temperature in the last effect to about 125°F. If a triple-effect evaporator is used, the vapor temperatures for effects 1, 2, and 3 will therefore be about 225°, 175°, and 125°, respectively. Since steam is used only in No. 1 and condenser water only in No. 3, the increase in efficiency over using three single-effect evaporators is obvious. This subject is discussed more fully in the Section on Sulphate Pulp. a ae ee eee ae, ——: §5 WASHING PULP AND RECLAIMING CHEMICALS 55 There are several makes of evaporators that have horizontal tubes, which are submerged in the liquid, and in which the steam condenses. 96. Film Evaporators.—The evaporator shown in Fig. 17 is commonly built in either three or four effects. Each effect has a feed head B and a discharge head C at the ends of a series of tubes. These heads are divided into a number of sections in such a manner that the tubes D form a series of manifolds or i CZZZZia Fre: 17. coils. The black liquor is fed into the first tube of a coil through a hole in the feed head B, and it escapes from the last tube of the coil through the discharge head C. The heating steam is confined in the shell #; it is introduced at Ff’, and the condensate is with- drawn at G. Live steam is used in the first effect, the second effect is heated by vapors from the first, and so on. The con- densation of the vapor here reduces the pressure on the liquid in the preceding effect, causing it to boil at a lower temperature, and therefore requiring less heat to evaporate it. The boiling of the liquor causes a great increase in volume, and this causes a rush of foamy liquor, which spreads a film of liquid on the sides of the tubes. For low pressures of steam (vapor), the temperature varies greatly for slight changes in pressure. Thus, the boiling point of water (temperature of steam) at 20 lb. per sq. in. pressure, absolute, is 228°F.; at 14.7 lb. (ordinary atmospheric pressure), it is 212°F.; at 10 lb., it is 193.2°F.; 5 Ib., it is 162.3°F.; at 2 Ib., 56 MANUFACTURE OF SODA PULP §5 it is 126.3°F.; at 1 lb., it is 101.8°F.; at 0.5 Ib., it is 82.0°F.; and at 0.1 lb., it is 43.1°F. An effect of common size has 22 coils of five tubeseach. A soda mill equipped with this type of evaporator ought to have at least one evaporator coil per ton of daily production. 96. The liquor escaping from the evaporator coils separates from the vapor in a large separating chamber H, Fig. 17, which is provided with baffles K. From this separating chamber, the vapor passes through pipe P to the shell of the next effect, where it acts as a heating agent. Any liquor carried by the vapor is separated from it in separator L and flows back to the chamber H. When the effects are placed one above the other, the liquor flows by gravity from one effect to the next. The density of the liquor gradually increases from 1.07 sp. gr. (14°Tw., say 93°Be.) to 1.325-1.350 (65°-70°Tw., say 35$°-373°Be.) for the finished, thick, black liquor, whichis discharged through the trap M, and is fed to the coils of the next effect or to the rotary furnace room. Fresh liquor enters at A. The vacuum pump creates a reduced pressure in the separation chamber and tubes of the final effect; the result is that the liquor boils at a much lower temperature, and the boiling can be effected by the vapor set free in the previous effect. Not being provided with a large dome, there is much chance for liquor to pull over. In the Section on Sulphate Pulp, a description is given of a disk evaporator that is sometimes used in soda-pulp mills. 97. According to Sutermeister, recent examinations of black liquor from poplar wood gave the following data: Grams dry Boiling points in degrees C. at the following Degrees Be. at ressures in inches of 1 matter per PB OE room temper- 100 grams : ature > : : : 10 in. 25 in. of liquor | 41 m. | 20 in. O in. eee ais L 7.8 124.5° | 114.3° 101° 90.5" a 58 Be 16 18.5 : 22 Aiek 128,.0° | 117.5° 104° 93.0°: 1, 62,0° 27 36.6 32 46.8 37 57.6 185.5" | 124.7° 112: 100.9° 69.0° 1 29.92 inches of mercury corresponds to standard atmospheric pressure, 14.7 lb. per inch, at 60°F. EN ee a ee ee ee vs. _—— Cl §5 WASHING PULP AND RECLAIMING CHEMICALS 57 98. Evaporator Troubles.—In the type of evaporator described in Fig. 17, the gaskets between the heads and the tube sheets give the most trouble, because of the small contact surfaces. The breaking of a gasket allows the liquor to short circuit, as it were, and thus cuts down the number of tubes that are working. When the gasket breaks on the final (last) effect, a thick, gummy liquor is likely to be formed in some of the tubes, which clogs the screen of the separating chamber. This result is due the presence of too little liquor in some of the tubes and too much liquor in some of the others. When thereis too little liquor pres- ent, it boils down too thick to flow freely. The tubes are sometimes coated on the liquor side with a scale of mineral matter; this is loosened by scraping, and is washed out when the machine is being overhauled; the tubes may become coated on the steam side also. The coating looks like carbon; it is caused by liquor getting into the steam or vapor. The little feed holes through which the liquor enters the coils, may plug up with scale, pulp, or packing; the gasket may give out; a tube may wear through; a tube may start leaking where it is expanded into the tube sheet; any one of the pumps may slow down or stop working altogether; holes may wear through the heads, because of the cutting action of the liquor passing through them; and there may be trouble with the valves, gauges, and piping. 99. Vertical-Tube Evaporators.—In other makes of evaporators, where the liquor is in the tubes, the machines are set vertically, and the vapor separates from the boiling liquid in the space above it. Inevery such case, the liquor flows from the first effect to the last one, where the vacuum is maintained by a condenser, which is generally assisted by a pump. Some evaporators require only a tail pump to remove the thick liquor. If a gravity feed is not provided, a feed pump is neces- sary. -Care must be taken that the packing of the pumps is in good order; otherwise, the loss through leaks may be considerable. An evaporator of the vertical-tube type is described in the Section on Sulphate Pulp. 58 MANUFACTURE OF SODA PULP §5 BURNING AND LEACHING BLACK ASH BURNING BLACK ASH 100. Changing Black Liquor to Black Ash.—The thick, black liquor that is pumped away from the last effect of the evaporator looks very much like molasses; it contains all the soda and all the intercellular substances dissolved from the wood, except what was wasted in the washing and evaporating departments. In order to use the soda over again, it is necessary to separate it from the non-fibrous part of the wood that it has helped to dissolve. To get back the soda, the mills now heat the liquor in a revolving, or rotary, furnace. The heat drives away the water that remains in the concentrated liquor, and then begins to char the woody material that remains. The latter finally begins to burn with a yellow flame until a considerable part of it is con- sumed; what is left is a red-hot cinder, known as black ash, which drops out of the discharge end of the furnace and is con- veyed to the leaching tanks. This cinder is essentially a mixture of carbon and sodium carbonate, because practically all the or- ganic compounds of sodium are converted to carbonate when heated in a current of air. There is some loss of sodium compounds in the flue gases and in the causticizing-room sludge; this is made up by the addition of extra soda ash in the causticizing tanks. The flow of liquor to the rotary is so regulated by the rotary runner (operator) that it is all converted to black ash; at full capacity this makes 15-20 tons of soda ash for each rotary furnace. 101. The Rotary Furnace.—The furnace in which the black ash is burned is a steel cylinder b, Fig. 18, adapted from Suter- meister. In many of the early furnaces, the length of the cylinder was 15-20 feet, but furnaces as long as 30 feet, have been used in modern practice; the diameter is from 9 to 10 feet, and the cylinder is lined with red brick. The furnace has heavy rings (tires) c riveted around it, which roll upon wheels d that have chilled cast-iron rims. A small engine m or other source of power is used to turn the furnace by means of gearing or a link belt. A large gear e is fastened to the shell in sections, and this meshes with a’ pinion that is connected to the source of power. In some cases, the chilled wheels transmit the motion to the fur- nace by friction. A cross section on line AB is shown in view (a). §5 WASHING PULP AND RECLAIMING CHEMICALS 59 RNS SEE LA OANTRN LAM AS LD EPS —S—- SRR SAD CRO a XC AE WR NOSSO? Ge eS eee 60 MANUFACTURE OF SODA PULP — §5 At the end of the furnace, where the flame enters and where the red-hot cinder drops out, a ring of sections (of cast iron) 2, called the lip, is bolted to the end of the shell in such a manner that the opening is somewhat smaller than the inside diameter of the furnace. This makes it possible to collect some of the burned and partly burned black ash in a considerable mass near the discharge end of the furnace, before it dumps into the car below or into whatever other means is provided for conveying the black ash to the dissolving tanks. The brick lining of the shell is thicker at the feed end than at the discharge end. This makes a slight slope, which causes the liquor and ash to move slowly toward the discharge end, as the furnace turns around. In front of the discharge end, is a firebox a, sometimes called a traverse furnace, carried on wheels that run on a track. The firebox has a fire-brick roof, and it has a nozzle that projects a little beyond the lip into the rotary. The firebox is, ordinarily, close to the furnace; but it may frequently be moved away from it, when it is necessary to chisel out the hard masses of black ash that often stick to its sides. Fuel is burned on the grates of the firebox, and the flames pass through the nozzle into the furnace The liquor is gradually dried, as it passes forward, and the woody matter in it finally starts burning. The hot gases pass out of the same end 7 of the rotary that the liquor feed pipe h enters. At this end of the rotary is an upright stationary flue 1, which has a ring of castings attached to it at the lower end, forming what is called the eye of the rotary. The gases pass through the eye on their way to the waste-heat boiler k, which is always con- nected to the rotary furnace. If desired, however, the gases may be sent directly to the stack. The waste-heat boiler may be vertical or horizontal, and it may have either a fire-brick setting or a steel-plate setting lined with fire brick. The hot gases from the rotary are useful in mine steam, although they are not so hot as the gases from an ordinary Holley furnace. The temperature varies greatly; it may range from 900° to 1600°F. The black Jiquor, which is running at the feed end of the rotary, grows gradually thicker as it moves forward toward the hotter end, where the flame from the firebox is coming in. A great deal of it adheres to the side of the furnace, which causes it to be carried upward as the furnace revolves, and it then rains §5 WASHING PULP AND RECLAIMING CHEMICALS 61 down through the flames. The wet interior surface of the rotary here exposes a large surface of the liquor to the action of the flames. 7 At the place where the liquor becomes too thick to flow, a ring of dried or baked liquor forms around the rotary, which must be cut or chiseled off about three times each day, in order that there may be a free discharge of black ash from the furnace. The large masses that are thus chiseled off may have to be broken up into smaller pieces with a sledge hammer. The rotary need not be stopped for this purpose, however. 102. Once a week, when the rotary is shut down, the ash on the inside is picked off with a pickaxe, and the furnace is cleaned down to the brick lining. The tubes of the waste-heat boiler are also scraped, and any deposit of fine black ash is cleaned out. The repairs necessary to make on rotary furnaces may be to the brick work of the firebox, the furnace lining, or to the waste- heat boiler setting, to the cast-iron work of the lip, the eye, and the firebox grates. The rails, the chilled-iron wheels, and the gearing also sometimes need renewal and repairs. 103. Furnace Troubles.—The following should be avoided and guarded against in operating the rotary furnace: weak liquor from the evaporators; cold furnace, due to poor firing; sliding of con- tents of furnace instead of the rolling movement that permits burn- ing most rapidly. For the black liquor to burn easily, it should have a specific gravity of between 1.325 and 1.350; see Art. 96. A stationary furnace into which black ash is sprayed, is being given a trial in one mill. All carbon in the liquor is burned and the alkali is fused. Much fuel saving is claimed for this system. See Wagner, Paper Trade Journal, Feb. 25, 1926, p. 179. LEACHING BLACK ASH 104. Object of Leaching.—The hot black ash is carried by a mechanical conveyor, or it may be washed out by a stream of water in a trough, into leaching tanks. Sometimes the dry ash is dumped into an empty tank and sometimes into a tank containing weak leached liquor. In either case, the next step is to separate the soda ash from the charcoal in the black ash. | As much as 80% of the weight of the black ash may be soda ash; the rest is charcoal and impurities. A part-of the dissolved intercellular substances in the black liquor has been changed into charcoal and the rest burned. The separation is a very simple matter; water dissolves soda ash, but will not dissolve charcoal. 62 MANUFACTURE OF SODA PULP aks The process of separating soda ash from the charcoal by means of water is called leaching. 105. Leaching Tanks.—The leaching tanks A, Fig. 19, are arranged with false bottoms B of perforated sheet steel. The black ash C rests on this bottom, and the water (with dissolved soda ash in it) passes through the perforations, leaving the char- coal behind. When the soda ash is all dissolved, the charcoal is discharged into the drain. It is advisable to have several leaching tanks working in Series, as shown diagrammatically in Fig. 19, which shows a Fig. 19. possible arrangement of four tanks, in which only the essentials are represented. The principle of operation is as follows: The charge that is nearly free from soda ash, say.tank II, is washed with fresh water from pipe EZ. The weak liquor from tank II goes through overflow D, from below the false bottom, to tank III, which has more soda ash. The liquor from tank III is stronger, and may then pass to tank IV containing the fresh charge of black ash, where it reaches its greatest strength and is ready for causticizing. The strong green liquor is delivered at kK. In the meantime, tank I is being dumped and filled with fresh black ash, when it, in turn, will be put in circuit as the last tank. When the liquor from this last tank weakens to a certain density, about 1.15 sp. gr. (30°Tw. or 19°Be.), it is turned into a tank of fresh black ash; the first tank is then dumped, and is ready for re-filling. ; en eee ee ee ee z : a §5 WASHING PULP AND RECLAIMING CHEMICALS 63 All these tanks are on the same level. The strong liquor flows by a pipe from the bottom of one tank to the top of the next, the liquor being forced upward by the weight of fresh water in the first tank. Wash-out valves are provided at F. A centrifugal pump is generally used to convey the strong carbonate (green) liquor to the causticizing room. Warm water should occasionally be run through the piping, to prevent the formation of a mineral deposit. | In one system of alkali recovery, leaching tanks are entirely omitted, the black ash being charged with lime into slaking tanks. The carbon passes through the causticizing apparatus with the sludge, and remains in it, or is burned if the calcium carbonate be calcined. 106. Composition of Black-Ash Residue.—Some thought has been given to devising some way of using this charcoal as fuel. It is doubtless a good fuel if dry; but it holds so much water that the mills have not yet found a way to dry it cheaply enough to make its use as a fuel economical. Among other uses that might be mentioned is its employment as a decolorizing carbon. The following is an analysis of the leached black-ash residue (carbon), which gives a good idea of its composition. The sample was first thoroughly dried and then exposed to the air. (TOOTS GTS Oe ea 6.06 % emer LDOUste, Nass... eo... ct ee ese lee 2.51 malemncarponace CaCOs oo... ob ead, 117 eM tIE, Witte et hls). ca Tiaale. Vales 0.37 erent eet arma RO ee) EE 29S ah sk Gn) ahs wre ony ne veel 0.34 Iron and alumina, Fe2,O; and Al,O3................... 0.26 Saas RNR eo Ta Fyn ay ae Facuss ds «od + ware ofa) ye 0.17 reGRMOUIDUALGAC AOU... . 2... cc ee cee et ee ne 0.07 Ma regue yacirercnce), Co... se es ea cee cle ek 89.05 © TU hou cent gee ee 100.00 % No use for this material that will even begin to take care of the amount manufactured has ever been developed. The most promising field seems to be its use as a fuel, since the heating value of the dried waste is 14,000 to 14,500 B.t.u. per pound. THE CHEMICAL LABORATORY 107. How the Laboratory Helps the Mill.—The chemical laboratory helps in the successful running of the soda mills in several ways: (a) By making an analysis of such crude materials as coal, 64 MANUFACTURE OF SODA PULP §5 lime, and salt. When this is done, and it is known that such analyses are made, the sellers of these materials are more’likely to supply the grade agreed upon. To the mill using 50,000 tons of coal a year, a difference of 1% in the ash that the coal contains will make a difference of 500 tons of ashes, which the mill pays for as coal and has to handle as ashes after the coal is burned. The grade of a coal cannot be determined by simply looking at it. Actual trial is the best test, and a chemical examination helps the mill manager to decide whether or not he desires to make such — trial; it also enables him to tell whether a large shipment is of the same grade as the trial lot. (b) By keeping control of the chemicals that are in liquid form, and controlling the quality of the finished product. 'The hy- drometer used by the men in the mill is not sufficient to keep this control, because there is no way of using this instrument that will enable one to tell what substances in the liquor make it of a cer- tain hydrometric strength. For instance, a liquid that has 83% of caustic soda, one that has 9% of soda ash, and one that — has 133% of salt will each show 20° on the Twaddell hydrometer and 13.2° on the Baumé hydrometer. There is no way, by the use of the hydrometer alone, that will enable one to determine whether a liquor is soda-ash liquor, caustic liquor, brine, or a mixture of these in any proportions. The chemist, however, has tests to ascertain this accurately, and he can specify the liquors for the digesters accordingly. Further, the amount of water in the pulp shipped to the customer must be known, if the weight of dry pulp, for which he pays, is to be invoiced to him correctly; and the color of the pulp must be kept so nearly to an established standard that it will be acceptable to the paper makers who use it. (c) By devising improvements in the method of handling materials, from which much saving of chemicals may result. By more careful chemical control of the cooking, bleach may be saved, and economy in the use of wood may be achieved. (d) When it is remembered that soda mills discharge as waste a large proportion of what enters as wood and all of the chalk calcium carbonate) that results from the causticizing process, it is easily seen that here is a broad field for the chemical laboratory. If these wastes are ever successfully converted into something of value, the laboratory will certainly have a large share in the work. §5 WASHING PULP AND RECLAIMING CHEMICALS 65 SOME SIMPLE TESTS 108. A few simple tests, which may be useful to those working in a soda mill, will here be described. The ability to make these tests will not make a man a chemist any more than being able to apply first aid in case of accident makesa manasurgeon. Never- theless, skill in making these tests will help a great deal in making things run smoothly about the mill. 109. Importance of Sampling.—It is first necessary to under- stand and remember that the sample to be tested must actually be like the large mass of material concerning which information is desired. Unless care be taken in selecting and preparing the sample, the result of the test will be worse than useless; because, in addition to getting incorrect proportions,a wrong idea will be formed regarding the material being tested. It is fully as impor- tant to do the sampling right as to perform the testing right. Thus, if one were testing a tank of caustic liquor that had not been well stirred, and which had a weaker liquor on the top than on the bottom (the heavier liquor, of course, falls to the bottom), and a sample were taken from the top only, all the work of testing and calculating the results would give a wrong amount for the liquor to be pumped to the digester. 110. Control of the Causticizing.—The test about to be de- scribed is one for determining what proportion of soda ash has been changed to caustic soda in the process of boiling with lime. When the liquor in the tank has been boiled and well stirred, it is certain that it is thoroughly mixed and that a sample taken from the tank with a long-handled dipper will fairly represent all the liquor in the tank. This sample is poured into a dipper having a short handle, and is allowed to rest for a few minutes, to allow the lime mud to settle. A few, say 10, cubic centimeters of clear liquor is then sucked up by means of a bulb in a certain form of glass tube called a pipette, which measures accurately. The liquor is allowed to run out of the pipette into a flask that has a capacity of 250 c.c. (about half a pint). A few drops of phenolphthalein are then dropped into the flask, and the color of the liquor instantly turns to a dark pink. The phenol- phthalein is called an indicator, and any liquid containing an alkali turns pink when this indicator is dropped into it. By means of a measuring tube called a burette, a weak (normal) solution of sulphuric acid is added, drop by drop, to the pink liquid in the flask, and the flask is given a rotary motion, to keep 66 MANUFACTURE OF SODA PULP §5 the liquid well stirred. In a short while, the pink color becomes fainter and fainter, until shortly a single drop of the acid destroys the pink color entirely, leaving the liquid colorless. As soon as this effect is secured, stop adding acid. The acid has thus far neutralized all the caustic soda (sodium hydrate) and half the carbonate in the liquor, as shown by the following equations: 2NaQ0H + H.SO, = NasSO,4 “fe H,0 (1) 2Na.CO; + H.SO, = 2NaHCO; + Na2SO, (2) The number of cubic centimeters of acid that has been used is read off on the burette, and a few drops of a solution of methyl orange is added to the solution in the flask. Methyl orange is another indicator, and it changes the solution from colorless to a light yellow. More of normal sulphuric acid solution is then run from the burette into the flask, being added drop by drop, with careful shaking. As soon as a single drop of the acid turns the yellow color to a light pink, cease adding acid. The total quantity of acid that has been used is read off from the scale of the burette, and a calculation is then made. The second addition of the acid has completed the neutralization of the sodium carbonate, as indicated by the equation, 2NaHCO; + H.SO, = Na2SO, — 2H.O —+ 2CO- (3) Hence, twice the difference between the first and second read- ings is the acid neutralized by (equivalent to) the carbonate not causticized, while the total acid consumed represents all the carbonate originally present. The total number of sodium atoms is the same, whether present as carbonate or as hydrate. The first reading of the burette is subtracted from the second, ’ the difference (which may be called the first difference) is multi- plied by 2, and the product is subtracted from the second reading; the latter remainder (which may be called the second difference) is divided by the second reading of the burette (which isthe total amount of normal acid solution used), and the quotient multi- plied by 100 is the per cent of the total soda ash that has been causticized, 7.e. changed to caustic soda. Thus, assume the readings to be as here given, the original acid reading in the burette being 0 (zero). Second burette reading (when yellow turns pink)....... Blin Cr, First burette reading (when pink becomes colorless)... . 25.9 ¢.c. First’ difference...) .4 2274 VEU) L.dueias as vg ree FF | » 7+ ele IN ee oe - aa 2 - ‘Da Cle ; = E . . 4 £ § WASHING PULP AND RECLAIMING CHEMICALS 67 Then, as directed in the last paragraph, 1.3 * 2 = 2.6 c.c. (= carbonate); 27.2 — 2.6 = 24.6 c.c. (= hydrate) = second difference; 24.6 + 27.2 = .904, and .904 x 100 = 90.4% = per cent of carbonate converted or causticized. To make the foregoing clear, let h = c.c. of acid required to neutralize the hydrate and c = c.c. of acid required to neutralize the carbonate. Suppose a c.c. of acid are required to neutralize all the hydrate and one-half the carbonate in the first reaction, and 6 c.c. of acid is used to neutralize all the hydrate and all the carbonate in the two reactions. Then, h+5=a (I) h+c=b (2) Multiplying (1) by 2, ; 2h +c = 2a (3) Subtracting (2) from (3), | h = 2a — 6 (4) 2a—b and 5 < 100 = per cent. of hydrate. (5) Subtracting (1) from (2) 5 =b-aore=20-a) 6) and o— xX 100 = per cent. of carbonate (7) In the particular case given, a = 25.9 e.c., b = 27.2 c.¢.} hence, substituting in (5), 2 X 25.9 — 27.2 Bli2 and substituting in (7), 2(27.2 — 25.9) alae 111. Testing Pulp for Moisture.—It is probable that no two mills use identically the same method for securing the samples to represent the pulp being tested. If the pulp be in rolls or bales the number of samples taken from each roll or bale may vary from one to ten. The size and shape of the sample may differ and the depth below the surface that the sample is taken may vary in different mills. Makers and users of pulp have cooper- ated in endeavoring to develope standard methods of sampling and analysis; the latest directions and methods are given in the Sections on Bleaching of Pulp and Refining and Testing of Pulp. xX 100 = 90.4% of hydrate; = 9.6% of carbonate. ° 68 MANUFACTURE OF SODA PULP §5 QUESTIONS (1) (2) Why must pulp be washed? (b) What are the principal constituents of black liquor? (2) What two advantages are gained by first washing the fresh pulp with weak liquor from the previous washing? (3) Why is black liquor evaporated? (4) For what purpose is the condenser attached to the multiple-effect evaporator? (5) Explain why a large amount of sodium carbonate is iouade in the black ash. (6) What becomes of the solution obtained by leaching the black ash? VOLUME OF BoTtrom Conr or Sopa AND SULPHITE DIGESTERS Broom asanwet a “ piceed | Not Vag OF ae foci Formula: Formula: Formula: Tv vw V = 907360" V = 50739 [HDD +4) + aH + h) | V = 3073004 D H V D H d h V v D H V (in.) | Cin.) | (cu. ft.) } (in.) | (in.) | (in.) | Cin.) (cu. ft.) | (cu. ft.) | (im.) | (in.) |(eu. ft.) 72 36 28.27 72 51 44 | 22 85.95 6.45 72 | 443 34.95 78 39 35.95 78 49 51 | 253 | 104.06 10.05 78 | 48 44.24 84 42 44.90 84 48 54 | 27 117.43 11.93 84 | 51} 55.45 90 45 55.22 90 45 61 | 303 | 135.22 17.19 90 | 554 68.11 96 48 67.02 96 44 64 | 32 149.56 19.86 96 | 593 82.72 102 51 80.39 | 102 46 72 | 36 188.09 28.27 | 102 | 63 99.30 108 54 95.43 | 108 45 74 | 37 202.02 30.70 | 108 | 63§ | 117.73 114 57 | 112.23 | 114 42 82 | 41 226.73 41.77 | 114 | 703 | 138.56 120 60 | 130.90 | 120 40 86 | 43 242.81 48.18 | 120 | 74 161.44 BIBLIOGRAPHY The following is a list of books and articles relating to the manufacture of Soda Pulp; for convenience, the books have been listed separately. In the list of articles, the names of several publications have been abbreviated as follows: J. 8S. C. I. means Journal Society of Chemical Industry; J. I. & E. C. means Journal Industrial and Engineering Chemistry; P. M. Mon. J. means Paper Makers’ Monthly Journal; P. T. Jour. means Paper Trade Journal; P. P. Mag. Can. means Pulp and Paper Magazine of Canada; W. P. T. Rev. means World’s Paper Trade Review; T. S. means Technical Section of the Paper Trade Journal. BOOKS Bersch, J.: Cellulose, Cellulose-produkte und Kautschuksurrogate; Berlin (1903). (English translation, ‘‘Cellulose, Cellulose Products, and Artifi- cial Rubber”? by Wm. T. Braunt. 336 pp. H.C. Baird and Co., Phila- delphia (1904). Beveridge, J.: The Paper Makers’ Pocket Book; pp87-90. D. Van Nos- trand Co., New York (1911). Butler, J. W., Paper Company; The Story of Paper Making; p88. J. W. Butler Company, Chicago (1901). Cross, C. F. and Bevan, E. J.: A Text-Book of Paper-Making; pp153-4, 327-60. E. & F. N. Spon, Ltd., London (1920). Cross, C. F., Bevan, E. J., and Sindall, R. W.: Woodpulp and Its Uses; 270 pp. D. Van Nostrand Co., New York (1911). Clapperton, G.: Practical Paper-Making; 2nd Edition, pp40 and 41; 178- 200. D. Van Nostrand Co., New York (1907). Davis, C. T.: The Manufacture of Paper; pp246-260. Henry Carey Baird & Co., Philadelphia (1886). Griffin, R. B. and Little, A. D.: The Chemistry of Paper-Making; pp161-179. H. Lockwood & Co., New York (1894). Hofman, Karl: Praktisches Handbuch der Papier Fabrikation, 2nd Edition, 2 vols., 1800 pp. Papier Zeitung, Berlin (1897). International Library of Technology; Vol. 20, Part 2; Manufacture of Paper; 58 pp. International Textbook Co., Scranton, Pa. (1902). Klemm, P.: Handbuch der Papierkunde; p122. Th. Grieben’s Verlag L. Fernau (1923). . Larchar, A. B.: Manufacture of Soda Pulp (Section 5 of The Manufacture of Pulp and Paper, Vol. II). McGraw-Hill Book Co., Inc., New York (1922). Leighton, M. O.: Preliminary Report on the Pollution of Lake Champlain; United States Department of Interior, Geological Survey, Water Supply and Irrigation Paper No. 121, 119 pp. Government Printing Office, Washington (1905). Schwalbe, C. G.: Die Chemie der Cellulose; Bibliographie, 2 Bde., Berlin (1910-1912). 69 70 MANUFACTURE OF SODA PULP 85 Sindall, R. W.: The Manufacture of Paper; D. Van Nostrand Co., New York (1908). Sindall, R. W.: Paper Technology (2nd Edition) ; Chas. Griffin & Cox London (1910). Stevens, H. P.: The Paper Mill Chemist (2nd Edition, pp161-167). Scott, Greenwood & Son, London (1919). Surface, H. E.: Effects of Varying Certain Cooking Conditions in Producing Soda Pulp from Aspen; U. S. Dept. of Agriculture, Bulletin No. 80. Government Printing Office, Washington (1914). Sutermeister, E.: Chemistry of Pulp and Paper Making; pp93-140. J. Wiley & Sons, Inc., New York (1920). Veitch, F. P., and Merrill, J. L.: Pulp and Paper from Waste Resinous Woods ; U. S. Dept. of Agriculture, Bulletin No. 159. Government Printing Office, Washington (1913). Watt, A.: The Art of Paper-Making, 6th Impression; pp55-63. In describ- ing the American Wood-Pulp (Soda) System the author still depends on an 1889 reference). Crosby Lockwood & Son, London (1921). Weeks, L. H.: A History of Paper Manufacturing in the United States, 1690-1916. The Lockwood Trade Journal Co.; New York (1916). Weigle, W. G., and Frothingham, E. H.: The Aspens—Their Growth and Management; U. S. Dept. of Agriculture, Forest Service, Bulletin No. 93, 35 pp. Government Printing Office, Washington (1911). Witham, G. S., Sr.: Modern Pulp and Paper Making; pp146-175. The Chemical Catalog Co., Inc., New York (1920). ARTICLES Achenbach, H. Working up Waste Liquors from Soda Cellulose Manufacture: Ger. Pat. 322,771 (Feb. 16, 1919). Aitken, J. E. Fractional Boiling of Esparto: Paper Maker and Brit. Paper Trade J., v. 62, pp487-91; P. P. Mag. Can., v. 19, pp1260-62; Paper, v. 29, No. 9, pp17-19, 40 (1921); Chem Abs., v. 16, p1149. Aiyar, S. S. . Distribution of Methoxyl in the Products of Cooking Jack Pine by the Soda Process: I. & E. C., v. 15. pp714-16 (July, 1923); Chem. Abs., v. 17, p2643; T. S., v. 77, p198. } Alford, H. C. Wood Pulp from Resinous Woods: U. S. Pat. 1,206,283 (Nov. 28, 1916). Anon. “Poplar Wood Pulp:’”? Wochenbl. ‘fiir Papierfab., v. 35, pp3941-2 (1904). Abstract of this article in J. S. C. I., v. 24, p148 (Feb. 15, 1905). Poplar as a Pulpwood in Italy. Swedish Translation of an Italian Letter: Svensk Pappers-Tidning, 12: te arg v. 22, pp225-6 (1909). Die Pappel (Populus canadensis) als Papierholz: Papier Fabrikant, v. 9, pp199-201 (1911). Poplar and the Paper Industry—L’Industria della Carta; Extract in, Paper, v. 5, No. 5, p13 (1911). —S Ts ee 2 —— ws ae be Cn oe as f Say nig EE ET, OR toate Tc Ee eo Ni) BIBLIOGRAPHY fp! Anon.—Continued. Experiments on the Bleaching of Soda Pulp: Papier Zeitung; Paper, v. 18, No. 24, p124 (Feb. 25, 1914). Technic of Soda Lye Manufacture: Paper, v. 16, No. 4, pp14 and 36 (Apr. 7, 1915). Black Liquor Distillation Products: Paper, v. 20, No. 6, pp18-19 (Apr. 18, 1917). By-products in Wood Pulp Manufacture: P. M. Mon. J., v. 50, p269 (1921). Brown Pulp: Papier-Fabr., v. 21, No. 36, pp412-15 (Sept. 9, 1923). Ford Uses Hardwood Scrap for Pulp: Paper, v. 32, No. 18, p8 (Aug. 22, 1923). Recovery of Caustic Soda from Esparto and Wood Pulp Boiling Liquors: P. M. Mon. J., v. 63, No. 6, pp213—15 (1925). New Soda Mill Will Have Novel Features: P. P. Mag. Can., v. 23, No. 28, p774 (July 9, 1925). Uses of Pulp from Bamboo: P. T. Jour., v. 81, No. 10, p48 (Sept. 3, 1925). Hardwood for Paper—Ford Company’s Achievement: The W. P. T Rev., v. 83, No. 19, p1576 (May 8, 1925). Arrhenius, S. The Physical Chemistry of Wood Cellulose Production: Chem. Ztg., v. 48, p402 (1924); Zellstoff u. Papier, v. 4, No. 8, pp182-84 (Aug., 1924); Medd. Vetenskapsakad, Nobelinst, v. 6, No. 10, 7pp. (1924); Translation in P. T. Jour., v. 82, No. 15, pp65-66 (Apr. 15, 1926); Tech. Assoc. Papers, v. 8, p138 (1925); Chem. Abs. v. 18, p3476. Austin, H. ~ “Scott”? Evaporators as Used in the Pulp Mill: P. T. Jour., v. 75, No. 11, pp65—-67 (Sept. 14, 1922). Bates, J. 8. ; Chemical Utilization of Southern Waste: Paper, v. 13, No. 23, pp19-21, 34 (Feb. 18, 1914); No. 24, pp108, 110, 112, 114, 116, 118, 120 (Feb 25, 1914); No. 26, pp19-21 (Mar. 11, 1914). Bradley, L., and McKeefe, E. P. Treatment of Black Liquor; Can. Pat. 245,831 (Jan. 3, 1925); Chem. Abs., v. 19, p1347. Bray, M. W., and Andrews, T. M. Chemistry of Pulps. A Comparison of the Chemical Changes of Jack Pine and Aspen Woods Cooked by the Soda Process: P. T. Jour., v. - 76, No. 19, pp49-51 (May 10, 1923); Paper Ind., v. 5, No. 4, pp626— 30 (July, 1923). Cellulophile. Theory of the Preparation and Recovery of Soda Liquors: Papeterie, v. 42, pp107-12, 151-6, 208-11 (1920); P. P. Mag. Can., v. 18, No. 40, pp1019, 1023 (Sept. 30, 1920): Chem. Abs., v. 14, p1754. Colas, L. J. B. A., Colas A. P. J., and L’Alfa Soc. Anon. Pour La Fabrikation Des Pates de Cellulose (Alkali Recovery from Black Liquor): British Pat. 218,385 (Apr. 4, 1923) U.S. Pat. 1,528,269 (May 19, 1925). 72 MANUFACTURE OF SODA PULP §5 Congdon, E. A. Manufacture of Chemical Fiber, The: School of Mines Quarterly, v 10, pp163-172 (1889). Cram, M. P. New Uses for Waste Soda Liquor: J. I. & E. C., v. 6, pp896-897 (Noy., 1914); Paper, v. 15, No. 11, p12 (Nov. 25, 1914). Darling, E. R. Rapid Analysis of Spent Caustic Liquors in Paper Mills: Chemist Analyst, No. 21 (1917); Paper, v. 21, No. 1, p15 (1917). De Cew, J. A. The Function of the Caustic Soda Process in the Production of Cellulose from Woods: J. 8. C. I., v. 26, pp561-3 (1907); Chem. Abs. v. 2, p319 (1908). Fay, H. Stock Density and Loss During Manufacture: Wochbl. Papierfabr., v. 56, No. 5, pp128-30 (Jan. 31, 1925); Discussion in No. 16, p489; No. 19, pp586-87 (Apr. 18, May 9, 1925); T. S., v. 81, p160; v. 82, p30. Fournier, R. Cocke of Plants for the pees of Paper Pulp: Cooking ‘under and without Pressure: Papier, v. 24, pp404-10 (1921); Chem. Abs., v. 15, p4050. Continuous Soda Process for the Preparation of Paper Pulp from Vegetable Materials: Papier, v. 25, pp67—-74, 109-18 (1922); Chem. Abs., v. 16, p1864. Continuous Digestion of Paper Pulp: Paper, v. 32, No. 5, pp5-6, 20 (May 23, 1923)—translation from Papier, v. 25, pp67—74, 109-18 (1922). Fuel Consumption in the Alkaline Cooking Process: Papeterie, v. 46, pp494-502 (June 10, 1924); Chem. Abs., v. 18, p2808; T. S., v. 79, p207. Fowler, R. A. Soda Pulp from Australian Hardwoods: Australian Forestry J. thily 15, 1921); Paper, v. 29, No. 8, pp24-25 (Oct. 26, 1921). Glamorgan Pipe and Founde Co. Continuous Causticizing in Soda and Sulphate Paper Mills: In their Bull. No. 5, Aug. 1923, 32 pp.; P. T. Jour., v. 77, No. 23, pp53-57 (Dec. 6, 1923). Continuous Recovery of Lime Sludges from Causticizing Operations: In their Bull. No. 4, Mar., 1923, 19 pp.; P. T. Jour., v. 77, No. 18, pp52-57 (Nov. 1, 1923); Chem. Abs., v. 18, p467. | Griffin, M. L. (| Report of the Committee on Soda Pulp Washing: Paper, v. 25, No. 4, pp132-38 (1919); Paper Maker, v. 59, p468 (Apr., 1920). Some Factors Influencing Yield and Strength of Pulp Cooked by the Soda Process: Paper, v. 30, No. 7, pp57-8 (1922); Paper Ind., v. 4, pp261-2; P. T. Jour., v. 74, No. 15, pp211-13; Tech. Assoc. Papers, v. 5, pp16-17 (1922); Chem. Abs. v. 16, p4059. Chemistry in the Soda Pulp Process: P. T. Jour., v. 80, No. 6; pp144—45 (Feb. 5, 1925); Paper Mill, v. 49, No. 6, pp74, 76 (Feb. 7, 1925); | §5 BIBLIOGRAPHY 73 Paper, v. 35, No. 17, pp62, 64 (Feb. 12, 1925); Paper Ind., v. 6, pp2159-60 (Mar.,.1925). Griffin, M. L., Chairman. Report of Committee on Soda Pulp: Paper, v. 19, No. 4, pp54, 56, 58, and 60 (Oct. 4, 1916). Griffin, M. L., Howell, W. H., Jr., and Spence, G. K. Causticizing Soda Liquors: Met. Chem. Eng., v. 17, pp599-603 (1917); Paper, v. 21, No. 4, ppd, 4, 6, 8, 10, 12 (Oct. 8, 1917). Haegglund, E. Decomposition of Spruce Wood with Alkali, etc.: Cellulosechemie, v. 5, pp81-87 (1924); Chem. Abs., v. 19, p1054. Chemistry of the Soda Process: Papier-Fabr., v. 23, p659 (1925); Pappers och. Travar for Finland, Nos. 13-14, 1925. Haegglund, E., and Grandell, G. Investigation of Black Liquor in the Manufacture of Soda Pulp and Its Behavior at High Temperatures: Acta. Acad. Aboensis Math. et Phys., v. 2, 17 pp. (1924); Chem. Zentr. 1925, I, pp1661-62; Chem. Abs., v. 19, pp3162-63. Hamm, C. 8. The Causes for the Deterioration of the Color of Soda Pulp from Ageing: P. T. Jour., v. 76, No. 16, pp47—48 (Apr. 19, 1923); Tech. Assoc., Papers, v. 6, pp40—41 (1923); T.S8., v. 77, p26. Harrop, J., and Forrest, H.O. — Causticization of Soda Ash: I. & E. C., v. 15, pp362-63 (Apr., 1923); emai. @7, p26. Haslam, R. T., and Ryan, W. P. Countercurrent Digestion of Wood: I. E. C., v. 16, pp144—6 (Feb., 1924). . Herzberg, W. Soda Pulp-Kraft Paper: Papier-Fabr., v. 23, No. 15, pp254—55 (Apr. 12, 1925); Wochbl. Papierfabr., v. 56, No. 18, pp390—91 (Mar. 28, 1925); T. S., v. 81, p137; Papier-Ztg., v. 50, No. 25, p1024 (Mar. 28, 1925). Heuser, E. The Rinman Process: Papier-Fabr., v. 21, pp325-30 (1923); Paper, v. 32, No. 24, pp3-6 (Oct. 3, 1923); W. P. T. Rev., v. 80, No. 10, pp822,824,826 (Sept. 7, 1923); T. S., v. 77, p198; Chem. Abs., v. 17, p3918. Hoffman, E. J. Chemical Investigations of Black Liquor: Paper, v. 23, No. 19, pp11-13 (1919); Chem. Abs., v. 18, p515. Howell, Jr., W. H. Special Equipment for Soda Mills: Paper, v. 25, No. 4, p30 (Oct. 1, 1919). Jacobs, C. B. . Carbon Catalyst: U. S. Pat. 1,462,752 (July 24, 1923). Jenke. Soda Pulp Manufacture According to Ungerer’s System in Stuppach: Hauptversammlung, Verein der Zellstoff u. Papier-Chem. Inc., 1924, pp177-80. 74 MANUFACTURE OF SODA PULP $5 Kessler, J. R., and Collins, G. N. Use of a Continuous Centrifugal in the Soda Pulp Mill: P. T. Jour., v. 74, No. 22, pp44—45 (1922). Klein, A. The Process of Manufacturing Chemical Wood Pulp: Proceedings, Verein der Zellstoff-und-Papier-Chemiker, Berlin, 1909. Also in, Papier Zeitung v. 34, pp227, 267; Chem. Abs. v. 3, p1341 (1909). Alkali Consumption in the Manufacture of Wood Pulp: Papier Ztg., v. 46, p4865 (1921). . Krenn, F. Purifying Soda Cellulose: Paper Industry, v. 5, No. 3, pp479-80 (June, 1923); Wochbl. Papierfabr., v. 54, pp698-99 (Mar. 10, 1923); T. S., v. 77, p132; Chem. Abs., v..17, p2642. Kress, O., and Wells, S. D. Improvements in Manufacture of Wood Pulp: Paper Trade J., p42, July 4, 1918. Lang, J. G. V. The Miintzing Woodpulp Digester: Paper, v. 15, No. 19, pp15-17 (1915). . Litchauer, Viktor. Die Amerikanische Aspenzellulose: Zentralblatt fir die Oster. ungar. Papierindustrie, v. 23, No. 26, pp822-5 (1905); Trans. in Paper, v. 23, No. 23, pp46—52 (1918). ° MacGregor, R. W. Evaporating Black Liquor: P. T. Jour., v. 81, No. 14, pp57-58 (1925); Paper Mill, v. 49, No. 40, pp10, 46 (1925); P. P. Mag. Can., v. 23, No. 438, pp1199-1200 (Oct. 22, 1925); Chem. Abs., v. 19, p3591. McKee, R. H., and Chilton, T. H. Causticizing in the Presence of Silicate: Paper, v. 30, No. 22, pp9-10. (1922); P. P. Mag. Can., v. 20, No. 33, pp693-94 (Aug. 17, 1922); P. M. Mon. J., v. 60, No. 11, pp419-20 (Nov. 20, 1922); Chem. Abs., v. 16, p3756. Mair, R., and Collins, G. N. Strength Testing of Soda Pulp: Tech. Assoc. Papers, v. 4, No. 1, pp6-7, 29 (1921). Miller, O. | Constitution of Soda Cellulose: Berichte, v. 41, pp 4297-4304; Chem. Abs., v. 3, p650 (1909). Miller-Moskan. The Reaction of Cellulose with Sodium Hydroxide: Berichte, v. 40, pp4903-5; Chem. Abs. v. 2, p1186 (1908). Moe, C. ; Operating a Soda or Sulphate Pulp Mill: Paper, v. 13, No. 24, pp156, 158, 160 (Feb. 25, 1914). Utilization of Lime Sludge (As a Corrective for Acid Soil and a Fertilizer It is Unequalled): P. T. Jour., v. 73, No. 21, pp44—46 (Nov. 24, 1921); Paper Ind., v. 3, No. 9, p1287 (Dec., 1921); Paper, v. 29, No. 12, ppl1—12 (Nov. 23, 1921); P. P. Mag. Can., v. 19, No. 47, p1192 (Nov. 24, 1921). 85 BIBLIOGRAPHY 75 Moore, H. K. Explosion Recovery Process for Black Liquor: Chem. Eng., v. 28, No. 1, pp8-16 (1920); Paper, v. 25, No. 24, pp1157-61; No. 25, pp1197—1201; No. 26, pp1241—46 (Feb. 18, 25, Mar. 3, 1920); Chem. Abs., v. 14, pp1438. Morrison, H. A. Continuous Filtration of Lime Mud in Manufacture of Caustic Soda: Paper Ind., v. 2, No. 11, pp1167—82 (Feb., 1921). Mount, J. E. The Causticizing System in the Soda Mill: P. T. Jour., v. 75, No. 17, pp61-63 (Oct. 26, 1922). Mount, W. D. Continuous Causticization for Paper Mills, with Provision for Unin- terrupted Recovery and Re-Use of the Lime Sludge: P. T. Jour., v. 75, No. 11, pp44 (Sept. 14, 1922); Paper Mill, v. 46, No. 36, p38 (Sept. 16, 1922); P. M. Mon. J., v. 60, No. 10, pp377—78 (Oct., 1922). Continuous Causticizing Plant of Penobscot Fiber Company, Great Works, Maine: P. P. Mag. Can., v. 22, pp407—-8 (Apr. 10, 1924); P. T. Jour., v. 78, No. 15, pp190—91 (Apr. 10, 1924); Tech. Assoc. Papers, v. 7, pp44—45 (1924); Paper Ind., v. 6, pp183, 185, 187, 189 (Apr., 1924); Paper, v. 33, No. 26, p144 (Apr. 17, 1924); Paper Mill, v. 48, No. 15, pp82, 84 (Apr. 12, 1924); T. S., v. 79, p171; Chem. Abs., v. 18, p1794. Nielsen, A. E. Indirect Cooking by Forced Circulation: Paper, v. 23, No. 10, pp11—15 (Nov. 13, 1918). Oman, E. Acid Vapors During Concentration of Black Liquor: Svensk Pappers Tid., v. 28, pp5—7, 32-33 (1925); Papier-Fabr., v. 23, No. 23, pp365— 69 (June 7, 1925); T.S., v. 82, p10; Chem. Abs., v. 19, p2564. Paine, Jr., A. G. Description of the Soda Process as Practiced at the Mills of the New York and Pennsylvania Company, 1908. In: Vol. IV (pp. 2628— 2633) of Pulp and Paper Investigation Hearings. United States House of Representatives, 60th Congress, 2nd Session, Doc. 1502. (Pub. by Government Printing Office, Washington, 1909). Payne, H. J. Chemical Engineering Methods in Soda Pulp Production: Chem. and Met. Eng., v. 30, pp817-22 (May 26, 1924); Chem. Abs., v. 18, p2427. Payne, J. H. Recovering Lime from Lime Sludge: Paper, v. 15, No. 9, pp15, 16, 38. Lime Recovery for Soda Pulp Mills: Paper, v. 17, No. 10, pp13—16 (Nov. 17, 1915). Raitt, W. Bamboo and Grasses for Paper Pulp: W. P. T. Rev., v. 84, pp562-68, 618-20 (1925). 76 MANUFACTURE OF SODA PULP §5 Rawling, F. G., and Staidl, J. A. 19M Chemical Studies on the Pulping of Aspen: Paper Ind., v. 7, p901 (Sept., 1925); P. T. Jour., v. 81, No. 8, pp49-51 (1925); Chem. Abs., v. 19, p3160. Reid, T. Anderson, Wood as a Papermaking Material: J. S. C. I., v. 5, pp273-276 (1886). Rinman,. E. L. New Soda Treatment of Wood Pulp: Summarized in Svensk Kemish Tidskrift; Papier-Fabr., J. S. C. I. (Feb. 29, 1912); Paper v. 7, No. 2, pp17 and 42 (Mar. 27, 1912). Rinman’s Black Liquor Recovery Process: U. S. Pat. 1,196,290 (Aug. 29, 1916); Paper, v. 19, No. 3, pp17, 18, and 32 (Sept. 27, 1916). Manufacture of Soda Cellulose, with Simultaneous Recovery of Chemi- cal Products from Waste Liquors: Svensk Pappers Tid., v. 24, p217 (1921); Chem. Abs., v. 16, -p827. The Rinman System for Working Cellulose and Chemical Products: Svensk Pappers Tid., v. 26, pp158-162 (1923); Chem. Abs., v. 17, p2rslyT. By ve7 (pte, Rinman Process for Cellulose Manufacture: Papier, v. 27, pp1029-33 (Sept., 1924); Paper, v. 35, p224 (Nov. 27, 1924). Samson, T. Indirect Cooking with External Circulation: Svensk Pappers Tid. No. 4 (Feb. 29, 1924); P. T. Jour., v. 79, No. 19, p55 (Nov. 6, 1924); f heve Pen gerald ghee (. : Sansone, R. Preparation of Soda Liquors for Cooking Wood: Papeterie, v. 45, pp890—94 (Sept. 25, Oct. 10, 1923). Various Types of Cookers Used (for alkaline cooking of rags and wood): Papeterie, v. 46, pp246-53, 342-46, 542-49 (1924); Paper, v. 34, pp557-59, 561-62 (1924); Chem. Abs., v. 18, p3271. Schroder, H. Apparatus for Soda Recovery in Soda Pulp Factories: Grimma. Chem. App., v. 1, pp161-8 (1914). Schwalbe C. G. The Cellulose Problem: Paper v. 2, No. 4, p9 (1911). Removal of Silicates from Spent Soda Liquor: Zellstoff u. Papier, v. 3, pp259-60 (Dec., 1923); T. S. v. 78, p262; Chem. Abs. v. 18, p1050. Schwalbe, C. G. and Robinoff, M. Action of Water and Alkali upon Cotton Cellulose: Zeitschrift fiir angew. Chemie, v. 24, pp256-58; Chem. Abs. v. 5, p1838 (1911). Sieber, R. Methods for Factory Control in Sulphate and Soda Mills: Papier- Fabr., v. 21, No. 7, pp89-94. (Feb. 18, 1923); Chem. Absgvi 17, p1714. Silcox, George W. Report on the Art of Printing and on Manufacture of Paper, with Appendix, 30 pp. In Vol. II, Reports of the Commissioners of the United States to the International Exhibition held at Vienna, 1873; eee yey an §5 BIBLIOGRAPHY | 77 United States Department of State. Government Printing Office, Washington, 1875. Spence, G. K. Uses of Lime in Pulp Manufacture: Paper, v. 30, No. 19, pp7-9; P. P. Mag. Can., v. 20, pp807-9. Use of Sulphur in Cooking Soda Pulp: Tech. Assoc. Papers, v. 3, pp14-16 (1920). Control of Causticizing Lime by Determining the Active (CaO) Con- tent: Paper Ind., v. 3, No. 8, pp1095-97 (Nov., 1921). Recovery and Its Control: P. T. Jour., v. 74, No. 7, pp50-52 (Feb. 16, 1922); Paper, v. 30, No. 7, pp92-3 (Apr. 19, 1922); Paper Mill, v. 45, No. 14, pp68, 70 (Apr. 15, 1922); Paper Ind., v. 4, No. 4, pp527, 529 (July, 1922); Chem. Abs., v. 16, p3391; Tech. Assoc. Papers, v. 5, No. 1, pp39-40 (1922). Evaporation of Spent Liquor in the Soda and Sulphate Pulp Processes: Paper, v.31, No. 26, pp120, 121, 128 (Apr. 18, 1923); Paper Ind., v. 5, No. 1, pp156, 159, 160 (Apr. 1923); Paper Mill, v. 47, No. 17, pp35, 40, 42 (Apr. 27, 1923); P. T. Jour, v. 76, No. 15, pp209, 211, 213 (Apr. 12, 1923); Tech. Assoc. Papers, v. 6, pp. 54—56 (June, 1923). Treatment of Spent Soda Liquor: Paper, v. 33, No. 10, pp7—10 (Dec. 27, 1923). Report of the Soda Pulp Committee: P. T. Jour., v. 78, No. 15, p189 (Apr. 10, 1924); Paper, v. 33, No. 26, p136 (Apr. 17, 1924); Paper Ind., v. 6, No. 1, p112 (Apr., 1924); Paper Mill, v..48, No. 15, p72h (Apr. 12, 1924); Tech. Assoc. Papers, v. 7, p83 (1924). Washing Brown Stock in Soda Pulp Mills for Bleachability: Paper Mill, v. 48, No. 22, pp16, 36 (May 31, 1924); Paper Ind., v. 6, pp1067, 1069 (1924). Report of Soda Pulp Committee: Paper Trade Jour., v. 80, No. 6, pl75 (Feb. 5, 1925); Paper, v. 35, No. 17, p66 (Feb. 12, 1925); Paper Ind., v. 6, No. 11, p1963 (Feb., 1925). Economy of Lime Reburning (in soda and sulphate manufacture): P. T. Jour., v. 80, No. 6, pp223-25; Paper Ind., v. 6, pp2157—59 (1925); P. P. Mag. Can., v. 23, No. 13, pp315-17 (Mar. 26, 1925); T.S., v. 81, p41; Chem. Abs., v. 19, p1495. Stevens, R. H. Making Paper from Pine Stumps: Paper, v. 34, pp901-3 (Sept. 4, 1924). Surface, H. E. The Production of Soda Pulp from Aspen: Paper, v. 15, No. 3, pp15-18 (Sept. 30, 1914); No. 7, pp17—20, 38 (Oct. 28, 1914); No. 8, pp20-21, 24 (Nov. 4, 1914). Sutermeister, E. The Soda Process for Cellulose Manufacture; The Consumption of Caustic Soda and Its Influence on Yield and Bleaching Properties (Presented at the Eighth International Congress of Applied Chemistry in New York, Sept. 11, 1912); Paper, v. 9, No. 2, pp15—16 (1912). Bleaching Soda and Sulphite Fibers: Paper, v. 14, No. 26, pp15-16 (Sept. 9, 1914). 78 MANUFACTURE OF SODA PULP $5 Sutermeister, E.—Continued. Soda-Pulp Manufacture: P. P. Mag. Can., v. 17, pp215-18, 243-6, 263-4, 289-92, 309-14, 327-30, 351-4, 375-8 (1919). Decay of Pulpwood and Its Effect on the Soda Process: Pik Mag: Can., v. 19, pp733-36 (1921). Losses in Making Soda Fiber: Paper Industry, v. 5, pp488-89 (1923); Paper Mill, v. 47, No. 22, pp38, 60 (1923); T. S., v. 77, p132; Chem. Abs., v. 17, p2642. Sutermeister, E., and Rafsky, H. R. Determining the Soda in ‘Black Liquor:” Paper, v. 8, No. 11, pp23- 25 (Aug. 28, 1912); J. I. & E. C,, v. 4, pp568-571 (Aug., 1912). Tauss, H. Verhaltem von Holz und Cellulose gegen erhéhte Temperature und erhéhten Druck bei Gegen-wart von Wasser: Dingl. polyt. J., v. 273, pp276-285 (1889). Abbreviated translation, ‘‘The Behavior of Wood and Cellulose at High Temperatures in Presence of Water,” in: J. S. C. L, v. 8, p913 (1889). Verhalten von Holz und Cellulose gegen erhéhte Temperature und erhéhten Druck bei Gegenwart von Natronlauge: Dingl, polyt. J., v. 276, pp411-28 (1890). Abbreviated translation, ‘‘The Behay- ior of Wood and Cellulose at High Temperatures and Pressures in Presence of Caustic Soda,” J. S. C. L., v. 9, p883 (1890). Thunholm, K. L. Evaporation of Waste Liquors from Cellulose Factories: Svensk Pappers Tid., No. 13, pp231-35, 1922; Papier Fabr., v. 20, No. 52, pp1774-79 (Dec. 31, 1922). Evaporation of Cellulose Waste Liquors: Svensk Pappers Tid., No. 25, pp345-46 (1922); Paper, v. 31, No. 26, pp149-50, 152, 154, 156 (Apr. 18, 1923); W. P. T. Rev., v. 80, p222 (July 20, 1923); Chem. Abs., v. 17, p2781; T. 8., v. 77, pp26, 131. Trostel, G. M. Extracting Soda Salts from Black Ash: Paper Ind., v. 2, No. 10, pp1563, 1565, 1567. Black Ash Bleaching: Paper, v. 26, No. 7, pp390, 392 (Apr. 21, 1920). Vidal, L. | Micrography of the Pulp of Sweet Gum: Mon. Papeterie Francaise, v. 56, pp204-5 (1925); Chem. Abs., v. 19, p2130. Vieweg, W. The Nature of Alkali-Cellulose: Papier Zeitung, v. 32, pp130-131, 174-175 (1907); Chem. Abs., v. 2, p1320 (1907). Action of Cold Caustic Soda on Cellulose: Berichte, v. 41, pp3269-75; Chem. Abs., v. 2, p3403 (1908). The Action of Cold Caustic Soda Solutions on Cellulose: Berichte, v. 40, pp3876-83; J. 8S. C. L, v. 26, p1157 (1907); Chem. Abs., v. 2, pl78 (1908). Waenting, P. New Methods for the Disintegration and Refining of Plant Fibers: Papier-Fabr., v. 21, p49 (Jan. 28, 1923); Wochbl. Papierfabr., v. 54, pp23-25 (Jan. 6, 1923). §5 BIBLIOGRAPHY | 79 Wallace, W. M. Recovering Soda from Waste Liquors: Brit. Pat. P217,468 Aug. 20, 1923; Chem. Abs., v. 19, p383. Walter, L. E., and Gunkel, L. Analysis of Lime Sludge from Causticizing Treatment in Pulp Manu- facture: Zellstoff u. Papier, v. 4, pp1-3 (Jan., 1924); T. S., v. 79, p26; Chem. Abs., v. 18, p1566. Walton, S. F. Carbon Pigment: U. 8. Pat. 1,552,973 (Sept. 8, 1925); Chem. Abs., v. 19, p3594. Wells, S. D. Some Experiments on the Conversion of Longleaf Pine to Paper and Pulp by the Soda and Sulphate Processes: J. I. & E. C., v. 5, pp906-7 (Nov., 1913). Experimental Work on Soda Cellulose; The Diminishing of Fuzz in Soda Pulp by Proper Cooking Conditions: Paper, v. 17, No., 4, pp14-15 (Oct. 6, 1915). Soda Pulp from Aspen Wood: The Effects of Moisture Introduced into the Digester in the Cooking of Soda Pulp: Mimeographed Report by the Forest Products Laboratory, Forest Service, U.S. Dept. of Agr. (Apr. 14, 1916); J. I. & E. C., v. 8, pp601-2 (July, 1916); Paper, v. 18, No. 17, pp13—-15 (July 5, 1916). Use of Spent Lyes in Soda Process: U. 8. Pat. 1,268,193; Paper, Aug. 21, 1918 (Index Folio 669). The Chemical Constitution of Soda and Sulphate Pulps from Coniferous Woods and Their Bleaching Qualities: J. I. & E. C., v. 13, No. 10, p936 (Oct., 1921), Chem. Abs., v. 15, p4049. American Pulpwoods: Paper, v. 32, No. 14, pp7-14; No. 15, pp6-8, 12, 16, 18 (July 25, Aug. 1, 1923); Paper Ind., v. 5, No. 4, pp642ff.; No. 5, 797ff.; No. 6,961ff. (July-Sept., 1923); P. P. Mag. Can., v. 21, No. 30, pp743-46; No. 31, pp771-74; No. 32, pp791-94; No. 33, pp819-21; No. 34, pp843—46 (July, Aug., 1923). Wells, S. D., Grabow, R. H., Staidl, J. A., and Bray, M. W. Chemistry of the Alkaline Woodpulp Processes I: Aspen, Loblolly Pine and Jack Pine by the Soda Process: Paper, v. 32, No. 9, pp5-14 (June 20, 1923); P. T. Jour., v. 76, No. 24, pp49-55 (June 14, 1923); Tech. Assoc. Papers, v. 6, pp42—48 (1923); T. S., v. 77, p132. Wells, S. D., Staidl, J. A., and Grabow, R. Use of Preliminary Impregnation in Cooking Wood by the Alkaline Processes: P. T. Jour., v. 80, No. 11, pp55-57 (1925); T. S., v. 81, p137; Chem. Abs., v. 19, p1774. Whitaker, M. C., and Bates, J. S. Chemical Utilization of Southern Pine Waste: J. I. & E. C., v. 6, pp289—-298 (Apr., 1914). White, A. H. Treating Waste Liquor from Soda Pulp Manufacture: U. S. Pat. 1,374,889 (Apr. 12, 1921). 80 MANUFACTURE OF SODA PULP §5 White, A. H., and Rue, J. D. Recovery Products of Black Liquor: Paper, v. 19, No. 23, pp56, 58, 60, 62, 64 (Feb. 14, 1917). Woodhead, R. Modified System of Cooking Pulp by the Alkaline Processes: Pal: Jour., v. 80, No. 14, pp91-93 (1925); T. S., v. 81, p160; Chem. Abs., v. 19, p1946. Ziegelmeyer, C. Soda Wood Pulp by Ungerer’s Process: Papier Ztg., v. 42, pp1855-56 (1918); J. 8. C. L, v. 37, p. 408A. MANUFACTURE OF SODA Palesle be EXAMINATION QUESTIONS (1) (a) State the principal difference between the mechanical process and the chemical processes of making pulp. (6) Which is the better for making high-class paper, and why? (2) (a) How is the cooking liquor prepared for the soda process? (b) is it acid or alkaline? (3) (a) Why does the recovery process fail to get all the soda used in the digester? (b) about what per cent is lost? (4) What are the characteristics of a good lime for a soda mill? (5) How would you remove the sludge from caustic liquor? (6) What do. you consider the best type of digester, and why? (7) What are the advantages and disadvantages in external systems of circulating digester liquor as compared with internal systems? (8) (a) How much steam is ordinarily required to cook a ton of soda pulp? (b) what becomes of the steam? _ (9) Name the principal factors that affect the operation of the digester. 7 (10) Mention some of the sources of trouble in running a digester. (11) As the washing of a tank of pulp progresses, at what density (specific gravity) is the black liquor turned from strong- liquor storage to weak-liquor storage, and when is it sent to the sewer? (12) (a) Why should hot water be used for washing pulp? (b) Why is it not feasible to use all fresh water? (13) Explain the advantages of a triple-effect evaporator as compared with three single effects. (14) How is black ash obtained, and what does it contain? (15) (a) Explain the leaching of black ash. (6) What sub- stances are found in the solution obtained? 81 SECTION 6 MANUFACTURE OF SULPHATE PULP By KARL M. THORSEN, Cuem. Ena. ORIGIN AND OUTLINE OF PROCESS 1, Object of Process.—The sulphate process for making wood pulp is a modification of the soda process; it was introduced in Danzig in 1884 by C. F. Dahl, with the intention of reducing the manufacturing cost by substituting sodium sulphate (salt cake) for the more expensive soda ash. The new industry was well received in Sweden, Norway, and Finland, where vast quantities of saw-mill refuse and the smaller sizes of wood, which had previously been used as cheap fuel or wasted, were utilized. The product is known as sulphate, or kraft, pulp. The word kraft is from the Swedish and means strength, a characteristic of this fiber. In America, the sulphate pulp industry is comparatively young. The first mill on the North American continent to manufacture this product was the mill of the Brompton Pulp & Paper Co. at East Angus, Quebec, which began making kraft pulp in 1907. In 1908, one mill was operated, with an estimated daily capacity of 25 tons; in 1918, there were 33 mills, with an estimated daily capacity of 1350 tons; in 1920, the estimated daily production in the United States and Canada was 2500 tons, which shows the constantly increasing popularity of the process. 2. Kind of Wood Used.—The woods employed for the manu- facture of sulphate pulp are almost exclusively coniferous, though nearly all species have been used with more or less success. The pulpwood used in 1918 for the purpose of manufacturing sulphate pulp is reported by the United States Department of Agriculture as follows: §6 } J 2 MANUFACTURE OF SULPHATE PULP $6 TABLE I Spruce: s v.cauls wont hea te Melis Cah a 37483 cords Hemlock. oi shee PG 3). co 37829 Balsam: fire ots ce, 6 34444 Jack pine..5 2.060005 th Dea 10547 Yellow pine. Vises. boca ee 90990 Tamera gla ig.. ein ar cewek.) Lee 44865 White pine<. si 8. £4. 08 8637 Slabs, and other mill waste... ......)...) eee 31754 TOCA. he bies s ikea s ons Soo Res ae 296549 cords Wood used in soda-pulp mills that employ some salt cake to replace a part of the alkali required is not included in the above table. 3. Size of Chips.—The size of the chips should be as nearly uniform as is possible, in order to obtain a uniform result in the digester. A small chip will naturally cook faster thana larger one. Consequently, when the small chip is cooked, it must either be exposed to the continued action of the cooking liquor (which will affect the fiber) or the charge (cook) must be blown before the big chips are thoroughly cooked. In either case, there is a loss of material, both wood and chemicals, and a decrease in the number of pounds of fiber obtained per cook. The careful sorting of chips is thus of great importance, although the actual size of the chips may be varied within certain limits, if only they are uniform in size. s-inch to 32-inch chip gives the best results, but a chip about 1 inch long seems to allow the liquor to act uniformly all through it. The figures in Table I show that only coniferous woods were used in the sulphate process. The rather severe treatment with alkali that is required in pulping resinous wood and the difficulty encountered in bleaching the fiber, have made coniferous woods less desirable for making soda pulp than the broad-leaved woods. — However, by adopting the sulphate process, the action of the alkali is less destructive, and the excellent qualities of the fiber of the coniferous woods are preserved. The yield of the wood, figured on the basis of bone-dry fiber from bone-dry wood, is considerably higher when the sulphate process is used (45%-— 48%) than when the wood is cooked with pure soda liquor (38%-40%). The figures just given for sulphate pulp have reference to kraft pulp. For easy bleaching pulp, consuming from 11%-13% bleach, a yield of 40%-42% can be maintained. $6 ORIGIN AND OUTLINE OF PROCESS 3 4. Character and Uses of Sulphate Fiber.—The fiber obtained by the sulphate process is remarkable for its strength and flexi- bility. The residues of resin that are sometimes found in the sulphite fiber are more completely destroyed by the alkaline treatment to which they are subjected in the sulphate process. Though the soda fiber is even purer than the sulphate fiber, the drastic action of the chemicals in the soda process robs the fiber of some of its strength. It is because of these properties that sulphate fiber has found use for making a paper that has great strength and durability; it is used, even, as a substitute for cotton, for making such washable fabrics as towels, aprons. mats, sacks, overalls, etc. Imitation leather for bags and also for shoes is made from sulphate fiber. An easy bleaching sul- phate fiber, though consuming a higher percentage of bleach, is often preferred to the soda fiber. The disadvantages of the process are the bad odors and the high cost of upkeep of the recovery room. The problem of making the smell less objectionable has yet to be solved. A shower, to wash the gases in the chimney, helps some; mixing the gases from the furnace with the combustion gases from the steam boilers before they go to the economizer, seems to be the most effective way, but it is expensive, since it lowers the tem- perature of the flue gases and increases their volume. | Notre.—tThe steam relieved from the digesters and from the diffusers when a digester charge is blown out, is best taken care of by a condenser or by leading the escaping steam underwater. 5. Outline of Process.—Sulphate pulp is obtained by treating chips of wood with a liquor, the active components of which are sodium hydrate NaOH, (commercially called caustic soda), and sodium sulphide, NaS. The pulping of the chips is per- formed in a closed steel tank, or digester, under steam pressure. When the wood is properly cooked, the charge is blown (emptied) into wash tanks—diffusers—where the fiber is washed clean from the liquor solution—the black liquor—which results from the cooking. This black liquor is concentrated in evaporators of various design, and is finally evaporated in a rotary furnace, from which it comes out as a black, semi-solid material, called the black ash. The black ash is burned in a furnace, where a brisk combustion is maintained, and the organic compounds of sodium are largely converted to sodium carbonate. The sodium salts used to 4 MANUFACTURE OF SULPHATE PULP $6 replace the losses of chemicals during the process are added here. The smelt (molten salts) escaping from the furnace is run down into a tank—dissolving tank—filled with weak wash from the liquor room to dissolve. When the resulting liquor—the green liquor—has reached a certain strength, it is brought into another tank, called the causticizer, or causticizing tank, where lime is added and the liquor is left to settle. The resulting clear liquor— the white liquor—is then drawn off, and is ready for the charging of another digester. X Ke) hg 40k i) 5 IS & ‘> 5 x |S Xy or 3s 2 ae "oy o> a < oo LF A sy. es oS. Y a CS We ) wor ene not? Y Digester Evaporators all Kinds) 1 3 o 4 white Liquor Fie. 1. The various steps of the process are clearly shown by the dia- gram, Fig. 1, which will be more clearly understood after the following pages have been studied. The diagram may be interpreted as follows: Beginning with space No. 1, the digester, the arrows show by the direction in — which they point whether the substance whose name is printed on an arrow is entering or leaving the apparatus indicated by $6 THE LIQUOR ROOM 5 numbers from 1 to 6. The order of the operations is the same as the order of the numbers, which is clockwise around the dia- gram. Starting with No. 1, the digester is charged with white liquor from causticizing tank No. 6; it is also charged with chips and steam. The discharge from the digester consists of relief gases, destination not given (eventually, the atmosphere), and black liquor, pulp, and steam to the diffuser, No. 2. Note that the diffuser is charged with black liquor from the digester, and that some black liquor enters the digester from the diffuser. Considering No. 2, the diffuser is charged, as just mentioned from the digester and also with water. It discharges steam and pulp and water, as hereinafter mentioned, and black liquor to the evaporators, No. 3. By proceeding in this manner, each step of the process will be made clear. The diagram shows every step and its order in the process. The different stepsand operations will now be described in detail, beginning with the liquor room. THE LIQUOR ROOM CAUSTICIZING 6. Reason for Causticizing.—Because of its composition, the green liquor from the dissolving tanks (see Fig. 1) is not ready for use for cooking pulp. The green liquor, a typical analysis of which is given in Table II, contains a considerable quantity of sodium carbonate NagCOs, which has practically no value as a resolvent of wood, 7.e., as a cooking agent. In order to convert this inactive sodium carbonate into active sodium hydrate NaOH, quicklime CaO is added to the green liquor in the liquor room, the sodium hydrate remains in solution, and a precipitate, or sludge, of calcium carbonate is formed. The sodium carbon- ate is said to be causticized, 7.e., made into caustic soda; thus, NazCO; + Ca(OH). = 2NaOH + CaCOs. The carbonate of lime, CaCOs, which is not soluble in water, is separated from the liquor by settling, sometimes by filtering, and the liquor thus obtained is the white (strong) liquor that is used in the digester for cooking the chips. 7. Causticizing Tanks.—The operations just described are. generally carried out in wrought-iron tanks, called causticizing 6 MANUFACTURE OF SULPHATE PULP $6 tanks, which may be of different shapes, but are always equipped with an agitator, and it is very important that this agitator pro- duces a thorough mixing. The utilization of the lime and the recovery of the alkali remaining in the sludge, are dependent on a thorough agitation. An agitator scraping well down at the bottom and on the sides and making about 14 r.p.m. will give satisfactory results. Tt VI HAIN si RB BEM AE Le = Fya.-2. In the case of a tank shaped like a vertical cylinder Fig. 2, the usual form of causticizing tank, there is danger of finally reaching a state in which the entire contents of the tank turn around like a solid body, the particles following the agitator without mixing with one another. This condition may be reme- died by attaching to the sides of the tank three or four angle- iron stationary arms B, which will retard the rotary movement $6 THE LIQUOR ROOM 7 of some parts of the liquor and produce a better mixing of the materials. Good agitation is obtained in a horizontal rectangular tank having a semi-cylindrical bottom. The upper half of the tank may have vertical sides in this case, or the entire tank may be cylindrical. The agitator is mounted on a horizontal shaft, and consists of scrapers, which lift the lime sludge near the surface of the liquor and then let it fall back through the liquor or wash water, thus giving the contents a thorough mixing. The packing glands, where the shaft penetrates the end of the tank constitute the weak point of this type of tank; they are liable to leak and must be watched carefully. This construction has been modified, and the tank improved, by making the agitator shaft shorter than the tank and driving it by a sprocket wheel on the shaft, which is chain-driven from a shaft situated above the tank. The tank is provided with swivel outlet, pipes for heating with steam, lime baskets, and a wash-out opening. 8. Settling and Washing the Sludge.—The lime is generally separated from the liquor by letting the lime sludge settle, and then drawing off the white liquor by means of a swivel pipe Byes 2. The separation is a case of one material falling through another. Here it is always a matter of lime in liquor, and the principal factor affecting the time required for a unit volume to settle is the dis- tance the lime sludge has to fall, 7.e., the height of the tank. The same volume of sludge will settle more quickly in a shallow tank of large diameter than in a deep and narrow tank of the same capacity. Whatever the type of tank used, it must be supplied with devices for admitting raw liquor, water, and steam. For the admission of steam, a perforated pipe, with the end closed, is to be preferred to an open pipe, and this pipe should go within a foot or less of the bottom of the tank. In the bottom of the tank is an outlet O, Fig. 2, for washing out the sludge. This outlet should be shut off with a disk or plug, seated in the outlet opening and flush with the bottom of the tank; in addition to this disk, it is advisable to have a plug cock or a gate valve on the outlet pipe, to make certain there is no leakage. If a plug cock only be used, there is a risk of getting the fitting between the tank and the cock plugged with sludge. The clear (white) liquor, which forms the upper part of the contents of the tank, is dis- charged through an outlet 0’, placed about one to two feet above Re > MANUFACTURE OF SULPHATE PULP 86 the bottom of the tank, where the swivel pipe P, which reaches well up to the top of the tank, connects to a swing joint J. By letting the pipe P, down as far as the lime has settled, the clear liquor is separated from the sludge. A float F, Fig. 2, is some- times attached to the free end of the pipe ; the float automatically keeps the open end of the pipe just below the upper surface of the liquor as it falls; but care must be taken that, as the pipe nears the bottom, it does not draw out sludge. The gear K drives the agitator, O is the outlet for the sludge; a fan pump delivers the white liquor to the storage tanks, in case these are not situated below the level of the causticizing tanks. Causticizing tanks are preferably equipped with lime baskets E, Fig. 2, which are made from iron bars, spaced about 1 inch apart. ‘The stones and unburned cores in-the lime are held in these baskets after the lime has dissolved, and are easily re- moved. ‘The sludge left in the tank is washed as described in ATE Ts | 9. Storage Tanks.—In addition to the causticizing tanks, the liquor room is equipped with storage tanks for strong and weak liquor. The storage tanks may be of any suitable shape, but should be fairly large, and should preferably be so placed that the liquor can run into them by gravity from the causticizing tanks above. The storage tanks should also be supplied with decanting pipes, similar to pipe P, in Fig. 2 to separate the white liquor from any sludge that may have entered from the causticizing tanks. 10. Adding the Lime.—The lime may be furnished to the tanks from a bucket traveling on a trolley-way above the tanks, or a tilting bucket on tracks, but it is often handled in barrows; in either case, the lime should be weighed. In some mills, it is customary to causticize all liquor in one tank, from which the liquor, sludge and all, is pumped into the settling tanks. The lime is then added in one tank only, which makes for better working conditions and a cleaner liquor room, when the tank is built in and the room is properly ventilated. It is to be noted that, with this arrangement, the time that is used for the trans- portation of the liquor from the causticizing tanks to the settling tanks is lost time, insofar as the continuity of the process is concerned; and if power is required to pump from onb set of tanks to the other, this power is wasted, since gravity might have been utilized. $6 THE LIQUOR ROOM | 9 11. The lime that is best suited to use in the liquor room for causticizing must, of course, contain a high percentage of CaO, and lime having less than 85 %-90% of CaO should not be considered; it must also contain but little magnesia, which impurity has a bad influence on the settling of the sludge; and the settling properties of the lime are of as much importance as the content of calcium oxide, CaO. The best method of determining the value of lime for the liquor room is to make actual causticizing experiments on a small scale, when a certain quantity of green liquor is analyzed for sodium carbonate Na.CO; and is treated with the quantity of lime that is theoretically necessary to obtain the desired result. An analysis of the white liquor! thus obtained will show how much of the oxide is consumed in causticizing the liquor and the completeness of conversion; and observations of the time of settling and the volume of settlings, will give valuable informa- tion concerning the adaptability of the lime for the liquor room. When deciding which of several grades of lime to purchase, the analysis of the lime should always be accompanied by actual causticizing tests and settling experiments. Lime that settles quickly, with a small volume of settlings, and at the same time is high in percentage of available CaO is what is wanted ; 60-65 pounds of such lime will causticize 100 pounds of NasCQOs. The quantity of lime used per ton of pulp varies between wide limits; it is usually about 500 pounds, depending upon the causticity, per cent of sulphide in liquor, and the quantity of alkali used for cooking. When lime is stored at the mill, the place of storage should be as dry and as air-tight as is possible. CAUSTICIZING OPERATIONS 12. Composition and Analysis of Green Liquor.—The composi- tion of the green liquor varies greatly, even the composition of the green liquor of successive batches varies. Its main com- ponents are sodium carbonate (NazCO;3) sodium sulphide (Na,S) sodium hydrate (NaOH) and sodium sulphate (Na2SOx) ; but there are also sodium sulphite, Na.SO3, sodium thiosulphate, NaS2O3, polysulphide of sodium, sodium silicate, sodium alumi- nate, and salt, NaCl. It is not essential that the liquor be * For analysis of white liquor, see Appendix, Art. 29. 10 MANUFACTURE OF SULPHATE PULP ~—=‘§&6 analyzed for all these components; in fact, for every-day analy- sis, it is sufficient to find the carbonate, sulphide, and hydrate of soda; and for the control of the smelter work, to determine the sulphate and sulphite, as will be shown later. Table II gives typical analyses of two different green liquors, the density of both being 20°Be. and the temperature 190°F. The losses of salt cake were 500 pounds per ton of pulp; the first strong wash was used with the strong liquor, and the succeeding washes were used in the dissolving tanks. TABLE II | Grams per |Pounds per| Grams _ per |Pounds per liter cu. ft. liter cu. ft. NaGOe. ule ia eee 138.35 8.637 153.17 9.562 Wat Eile sca ay eames 16.80 1.049 12.40 0.774 ING gS Scie cubes ems Mee TA he: 4.480 71.76 4.480 Naess. . isnot eee 16.11 1.006 |. 14.41 0.900 Note.—Grams per liter may be expressed as pounds per cubic foot by multiplying the numbers of grams per liter by .062428. 13. The component of greatest interest in the liquor room is the amount of sodium carbonate in the green liquor, since this determines the quantity of lime that is needed for the batch. By taking analyses from several charges of the green liquor and of the white liquor that results, it will soon be found what is the smallest quantity of lime that is needed to obtain the degree of causticity desired. In every-day practice, it will give just as much satisfaction, with less trouble, to fix this minimum quantity of lime to be used, and then let the liquor maker analyze the liquor, to ascertain whether its composition is what is wanted and if not, how much more lime must be added; the latter he can find out from a table that has been computed for this purpose. This method has some advantages in practice over having an analysis made of each tank of green liquor and finding from this analysis the total quantity of lime required. In the latter case, a control analysis of the ready white liquor may call fer an addi- tional quantity of lime, because of variations in the composition of the lime, and this additional quantity will often be a very substantial amount. On the other hand, if the minimum quan- tity of lime is added before an analysis is made, the error caused by the unsatisfactory composition of the relatively small quantity $6 THE LIQUOR ROOM 11 of extra lime will be of little importance, and no second analysis will be necessary. A chart or table, for determining the quantity of lime that must be added to the liquor in a causticizing tank of known volume, can readily be prepared by the mill chemist, for any causticity of the liquor, from the per cent of CaO in the lime and the cubic centimeters of standard acid neutralized by carbonate in the green liquor. (See Appendix to this Section.) 14. When a sulphate mill is first started, it is usual to prepare cooking liquor from soda ash, which is dissolved in water until a solution is obtained of 18°-20°Be. at 60°F. This liquor is then causticized with lime, and the caustic solution thus obtained is used for cooking. (The deficiency in total-liquor volume for the digester is covered with water in the first cook until some black liquor is obtained.) The first cooks will thus be soda cooks. When sufficient black liquor is obtained, the recovery room is started and as much salt cake is used as is advisable (not more than 500 pounds of salt cake per hour per firebox at good run). The liquor thus obtained will be sulphate white liquor proper. In a few cases only, the first white liquor is made to contain sodium sulphide, either by adding Na.S or by dissolving sulphur in the caustic soda solution. : 15. Effect of Concentration. When the green liquor is treated with lime, the following reaction, which is never complete, takes place: NasCO; + Ca(OH). = 2NaOH + CaCO; The completeness of this reaction depends to a certain extent upon the concentration of the solution of the sodium carbonate and the ratio of the amount of sodium carbonate to the calcium hydrate Ca(OH)2. While a weak solution of sodium carbonate, say one having a density of 7°Be. at 15°C., can be causticized as high as 99%, 7.e. 99% of carbonate is changed. to hydrate, it is impossible to reach a causticity of more than 95% with a solution of 19°Be. at 15°C. The reason for this is that with an increased concentration of sodium hydrate, the solubility of the calcium hydrate is decreased until, finally, there are not enough calcium ions in the solution to surpass the limit of the solubility of the calcium carbonate. 16. Effect of Sodium Carbonate.—The sodium carbonate in the white liquor is a dead load, having no value for the cooking process. In the cycle of operations, however, there are losses due 12 MANUFACTURE OF SULPHATE PULP $6 to the sodium carbonate that are proportional to its concentra- tion in the liquor. Thus, it is of great importance that the quan- tity of carbonate be kept as low as possible. By using a weak solution of liquor, a high degree of causticization can be main- tained, with small losses of lime; but the solution must be strong enough to contain the quantity of alkali that is necessary for the cook in the volume of liquor wanted for the digester. The alkali will have to be reclaimed, however, which requires that the water be evaporated, and this evaporation is expensive. The cost of the evaporation of the extra water used to obtain the higher degree of causticity must be balanced against the saving due to the decrease of content of sodium carbonate. However, another factor must be considered, which, in a mill having the usual equipment of settling tanks, eliminates the matter of high causticity altogether, and this is the volume of sludge that results from the charge. This sludge, which always contains a considerable proportion of the white liquor, has to be washed, in order to reclaim the valuable alkali. The resulting wash water finds use in filling up the dissolving tanks for a new batch, and its volume is thus limited. The final inevitable loss of alkali in the sludge thus depends upon the quantity of sodium salts that remain in the first strong sludge, and this, in turn, depends upon the strength of the liquor and the volume of precipitate of cal- cium carbonate. To work with a weaker solution, will make the quantity of lime necessary to obtain a particular causticity smaller, and will thus give a smaller volume of sludge in the weaker liquor; but at the same time, it will decrease the strength of the cooking liquor, increase the work for the evaporators, and lessen the capacity of the liquor room. A decrease of the lime alone, without changing the strength of the green liquor, will decrease the quantity of sodium hydrate; at the same time, it will increase the content of non-active sodium carbonate. With a fixed charge of sodium hydrate needed for the cooking, a larger quantity of chemicals will be called for, which may increase the losses in other departments so much as to offset the savings in the liquor room. In the average mill having standard equip- ment, the most satisfactory results are obtained when the green liquor is taken from the dissolving tanks testing 18°-20°Be., — hot, and a causticity of 75%-80% is maintained. 17. Washing the Sludge.—When the strong white liquor has settled and has been drawn off from the tank, there remains . | | §6 THE LIQUOR ROOM 13 in the tank a certain volume of sludge containing a considerable quantity of sodium components, which often amount to 25% or more of the original liquor. In order to reclaim the valuable substances in this sludge, it must be washed with water. As mentioned before, the volume of this wash water is limited to the volume of the dissolving tank, because it will have to be used to make another charge of liquor. The actual washing is often preceded by a preliminary wash with a small amount of water or with weak wash water, and the resulting liquor is sent with the strong liquor to the digester room. This procedure permits the use of more wash water and, in addition, increases the capacity of the tank room, since the tank space is relieved of liquor from the first wash. An additional quantity .of alkali is obtained from the same batch. This preliminary wash would, of course, require a little more time. Care should be taken that all washes are of as nearly the same size as is possible and that the maximum volume of water is used in each case, in order to recover the greatest amount of chemicals from the sludge. Samples of sludge should be taken at regular intervals and analyzed for the amount of soda being lost, and this loss should be reduced to a minimum. There may be occasions when it is advisable to do all washing with water; but this method, though it gives a quick wash, is not common. Another method is to use a series of washing tanks, thus: To the tank containing sludge most completely washed, add clear water and agitate. When this wash is settled, transport the clear liquor to a tank containing a sludge that has been washed one time less, proceeding in this manner until the entire number of washes has been obtained. Thus a tank that has never had any wash water in it is furnished with the clear liquor from a second (strongest) wash, and the sludge from this second wash is mixed with the liquor from the third wash; the sludge from the third wash is-‘mixed with clear water or with liquor from another weaker wash. This procedure is very slow, and it calls for a great capacity of tank room. It must be remembered that before a tank is ready for a new charge, the sludge has to settle through a distance equal to five times (if 4 washes are used) the height (depth) of the tank—once for strong liquor and four times for the four washes. It is further to be noted that the final volume of weak liquor obtained is not sufficient to fill the dissolving tanks for a new batch, because the sludge always retains some liquid. 14 MANUFACTURE OF SULPHATE PULP $6 18. If the size of the tank room permits, the best way to do the washing is to make the third and fourth wash with water, make each of them large enough to give half a tank of wash liquor, and then use this liquor for making up the first and second washes. If there is a separate storage tank, in which the last two washes can be mixed and from which wash can be drawn for the first or second wash whenever needed, there will be no delay on account of one tank waiting for another ; but, even if this should not be the case, there will not be many instances of delay, because there is always some of the liquor settled in the tanks containing the last washes, with which to make up another wash. Washing thus conducted will give very satisfactory results, and should reduce losses of chemicals in the liquor room to a quantity corresponding to 40-50 pounds of salt cake per ton of pulp. 19. Filter Presses.—Filter presses are employed to reclaim as much as possible of the valuable chemicals in the lime sludge. When a filter press is used, the process of washing the sludge is usually as follows: The causticizing tank is made up as usual and causticized, and the sludge is allowed to settle. The strong liquor is then drawn off to the white liquor storage. The wash from the filter press is run into the tank, and the agitator is started. The contents is allowed to settle, and the clear liquor is pumped to the dissolving tanks. The tank is then filled approximately half full with water; it is agitated, and the contents is dumped or is drawn off by gravity to the slurry tank. The slurry tank contains a rather heavy concentration of sludge, and from this tank, the sludge or slurry is pumped to the filter press for a time, to deposit a sufficiently thick cake. The pump is then connected to a hot-water tank, and the cake of sludge is washed with hot water in the press. When the filtrate tests O°Be., the cake of sludge is said to be sufficiently washed. The filter press is then opened and the press cake is discharged into cars or conveyors, the disposal of this depending on the use to which the plant desires to put it. In case a continuous filter is used, the deposit from washing and the removal of the cake go on without interruption. A brief description of one press of the first type will be given here; but it is to be noted that there is still room for its improve- ment and for adapting it to the work required of it. Fig. 3 shows a leaf type of filter press. Here the casing a, | : $6 THE LIQUOR ROOM 15 approximately cylindrical, is divided in halves by a horizontal plane passed through the axis. The two halves are connected by the ring 6 and are drawn tightly together by the bolts ¢ and eccentric shafts d. The filter leaves e are hung from the top of upper half of the case. These may consist of a ring of pipe f, perforated or slit around the inside and covered with a filter cloth g, which is prevented from collapsing by struts h that are braced by pins7. The distance between the leaves depends on the character of the material filtered. A dense, non-porous material requires leaves close together. HNN 7a \LLLLDLLLLL Y fA , ZA WH ry | |] | } | | Me, © % Me, In operation, the sludge enters at k, under pressure, and the liquid filters through cloths e, passes into frame pipe f, through nipple valve J, to discharge channel m. A sight glass is inserted at n, so that should the cloth brake, valves o can be closed and, filtration continued. Wash water may be introduced at p, and this may be followed by air, if desired, to dry the layer of sludge that has been deposited at r on the outside of the cloth. The cake may be washed out at s by forcing the water back into the filter leaves; or the bottom half of the case may be dropped, and the cake delivered to a truck or conveyor. Another type of leaf filter press has a nest of long rectangular leaves, which are introduced through the end of a long horizontal cylinder. The principle is the same as for the one described. A continuous filter is described and illustrated in the Section on Soda Pulp. 20. Care of Filter Press.—The principal trouble has been, and still is, to find a filter medium that will resist the severe action of the liquor. Insofar as the writer is aware, no filter has yet 16 MANUFACTURE OF SULPHATE PULP 86 been operated successfully on strong liquor; even after the strong liquor has been drawn off and the tank furnished with water before the sludge is taken on the filter, the action of the rather: weak liquor thus obtained necessitates a frequent changing of the cotton cloths that generally are used as filtering cover in the modern mechanical filters. It may be remarked, however, that a patented rubberized fabric holds considerable promise as a filter cover. The sludge, however, can be washed perfectly clean from soluble chemicals with a very small quantity of water. Wire cloth made from Monel metal has also been used as a cover | on filter leaves. The writer knows of one case in which a filter press thus equipped worked very successfully for a short period. A successful filter press would be ‘a welcome addition to the machinery of the sulphate mill; because it has great capacity, gives a perfectly clear liquor under all conditions, makes it possi- ble to get a high causticity, gives a large volume of strong liquor and scarcely any weak liquor, and produces a sludge that is practically free from soluble alkali. The quantity of steam used in causticizing the liquor is far less; in fact, the steam might be replaced entirely by prolonged agitation, and only a small vol- ume of hot water is required for the washing in the press. The tank room may then be just large enough to take the liquor in, aS space is required only for the causticizing tanks and filter presses. The washing is done in the filter, after the first strong liquor is settled and drawn off, 21. The Filter Box.—Another type of filter consists of a wide and shallow wooden box, which has a perforated sloping bottom and underneath that, a horizontal solid bottom. The perforated bottom is sometimes omitted. A drain pipe at the lower end of the sloping bottom serves as an outlet. The filter medium consists of a layer of gravel, on top of which is placed a layer of finer gravel or sand, and then a layer of sawdust, which is pro- tected by a grating or perforated plate. This filter is used for the sludge after the last wash, for the purpose of draining off as much of the wash water as is possible. The sludge that remains in the tank after the washing is finished, is agitated with a small quantity of water and dumped into the filter, where it is left to drain until the lime sludge shows cracks on the surface. The sludge then contains about 55% moisture ; and sludge that has been washed four times, twice with weak liquor and twice with water, will contain less than 2% sodium oxide in dry sludge. $6 THE LIQUOR ROOM 17 22. Disposal of Sludge.—In mills where it is not possible to dispose of the lime sludge in a river, it is often a serious problem how to get rid of the sludge. To reclaim the lime for use in the liquor room has not as yet become a general success, although at least one plant is recovering the lime by calcining (burning) the carbonate sludge—CaCO; = CaO + COs. It is necessary to add 15 % new lime to make up for losses and to counteract the accumulation of impurities. The impurities that come from the smelter lining ruin the lime for pulp making, and the settling properties of the lime are adversely affected by such impurities as aluminum and magnesium. When so treated, the lime sludge is drained on a sand filter, or taken from the filter press, and then shoveled into a conveyor, which feeds it into a rotary fur- nace of the type used in cement making,—similar to that shown in Fig. 23 at B, but about 100 feet long, and whichis heated with producer gas or powdered coal that is blown directly into the furnace. The regenerated quick lime has a brownish color, and comes out in balls varying from the size of a pea to that of one’s fist. The recovered product is not so good from sulphate-mill sludge as that recovered from a soda mill. However, a use has been found for the sludge in the manufac- ture of a special brick for building purposes. Another purpose for which lime sludge has been employed to good advantage, is as a fertilizer for soils that are deficient in lime. Certain precau- tions must be taken, however; and if transported considerable distances, the lime sludge must first be dried. Dry and pulver- ized lime sludge has also found a use in glass manufacturing. 23. In conclusion, it may be remarked that the liquor room is a very important part of the sulphate pulp mill; the work there should be carefully controlled and supervised, as so much depends upon this department being properly conducted. The next department of the plant, in order of operation, is the digester room, which will now be considered. QUESTIONS (1) Name the principal operations in a sulphate-pulp mill. (2) What alkaline process other than the sulphate process is used for cooking wood? how do the two processes compare as regards yield? (3) Mention the character and uses of sulphate fiber; why is it sometimes called kraft? 18 MANUFACTURE OF SULPHATE PULP §6 (4) What takes place in the liquor room? (5) Mention the qualities of a good lime; how much is required per ton of pulp? (6) What is meant by green liquor? Name its principal constituents. THE DIGESTER ROOM THE THEORY OF COOKING 24. Composition of Wood.—Wood is composed of cellulose fiber and lignin (also called ligno-cellulose), with varying amounts of other organic substances of more or less acid nature, and a very small percentage of inorganic substances. The ash (inorganic) content of spruce wood, for instance, is only 0.3%. The principal solid constituents of spruce, according to Klason, were given in the Section on Chemistry, but the table is here repeated, and it will be noted that approximately 50% of the | Cellulose... ui... oo 8 2. eee 53% : Lignin) ooo es ace Le en 29% Spruce { Other carbohydrates.................0+0-05. 13% | Resins, fats; ete:: ..,. . $5 Ae ee ee 4% Albuminates: 724.000). 6:4. a ee 1% dry weight of wood is cellulose. 25. Purpose of Cooking.—In any chemical process for manu- facturing wood pulp, the object of the digesting, or cooking, process is: Ist, in the case of easy bleaching pulp, to destroy the non-cellulose constituents of the wood (pentose, etc.) as completely as possible; 2d, in the case of kraft pulp, to cook the wood just enough to obtain a fiber that may be readily separated. Some loss of cellulose, however, cannot be avoided, and the purer the resulting fiber the greater is the loss. For pulping wood, either an acid treatment (as in the sulphite process) or an alkali treatment (as in the soda and the sulphate processes) is used. In the soda process, the cooking liquor is mainly composed of | sodium hydrate, while in the sulphate process, a mixture of so- dium hydrate and sodium sulphide is used as a solvent for the undesired wood substances. The action of the liquor on the wood and the chemical reactions that take place in the digester, are very much the same in the two processes, since, in both cases, $6 THE DIGESTER ROOM 19 the sodium hydrate chiefly governs the procedure; but the qualities of the resulting fiber are quite different. 26. Reactions in Digester.—According to our present knowl- edge, the nature of the reactions in the digester is an oxidation or hydrolysis (see Art. 27) of the lignin and carbohydrates. The resulting organic substances of an acid nature are later neutralized by the sodium hydrate, and the resulting salts are soluble either in water or in an excess of alkali. Fats and resinous substances are saponified, and are dissolved or carried in suspension in the liquor. The complicated molecule of lignin is partly hydrolyzed, which increases the possibilities of splitting up the lignin mole- cule into smaller molecules that are soluble in alkali. Wood alcohol, which is formed in considerable quantities during the cooking (26 pounds per ton of pulp according to Bergstrom and Fagerlind), is derived from the hydrolysis of the lignin. Klason’s research work indicated that the smallest quantity of active alkali (figured as NaOH) that will result in removal of all the non-cellulose matters in the wood is 20% of the dry weight of the wood; but he adds that this quantity will never suffice to carry through the perfect pulping of the wood, owing to the fact that a complete utilization of the alkali can never be obtained. His analyses show that about 40% of the alkali necessary to use in order to obtain an easy-bleaching pulp is left in the resulting black liquor as free hydrate or is so loosely engaged that it will combine with carbonic acid. From these results, he concludes that part of the alkali has to be used as a solvent for the organic sodium salts that are formed during the cooking. A further reaction of the alkali would lead to a precipitation on the fiber of the organic substances, which would form a protective covering. The fact that the alkali is thus engaged explains why the cellulose is not destroyed through the action of the excessive alkali. A solution of sodium hydrate, of 6°Be. will, according to Tauss, bring in solution 20.28% of cellulose that has been exposed to its action for three hours under a pressure of 150 Ib. per sq. in. These are conditions that are often actually reached at the end of a cook; but even a very much delayed discharging of the digester would not lead in actual mill practice to a loss of cellulose nearly as great as the figure quoted. The composition of the dry substances of the black liquor of 1.1166 sp. gr. in grams per liter from a soda cook is given by Klason as follows: 20 MANUFACTURE OF SULPHATE PULP §6 Na2SO, #96: 9s 8 Ae no) #il asl g)-8 etvelinn ei e'ee)o¥iin) ie \/ 31076 B “ele oft) atch es gin Ste nae 6.7 ag Na]... cases tis ealediiey oaecie ¢-ciecs Ale gb ponte ana 2.0¢g NazCOa. occas eh tage eipees bugs «sn ay se 2a 9.3¢ NaOH free or loosely engaged................ iS a 41.5¢g NaOH neutralized by the following acids: 27.2 ¢g. Formic and acetic acids........... 11.5 g. engaged 9.8 g. Lactic wetelpiet tee titans ee 49.0 g. engaged 10.9 g. Phenols, fats, and resinous acids.... 30.0 g. engaged 5 DRT eee ee ks oa eee 53.0 g. engaged e- NaOH neutralized by CO:.........., +24... . 0, 0 3.3¢g Total NaOt os i. i i ei ie ee 72.0 g. From repeated experiments, Klason learned that when the free alkali in the black liquor (found by determining the quantity of CO, the black liquor will absorb) exceeds 40% of the original quantity of active alkali, the result will be considerable losses of , Al. cellulose. In the analysis just given, there was sd x 100 72 = 59% of free alkali in the total NaOH. 27. Composition of Liquor in Sulphate Process.—The cooking liquor of the sulphate process differs from that of the soda process in its composition, in that the active alkali in the former is a mixture of sodium hydrate and sodium sulphide. It is acknowl- edged that sulphur dissolved in the soda liquor, even in small quantities, will improve the quality of the fiber to a certain extent and increase the yield. The fact that the presence of sulphur in the digester does improve the yield of the soda cook is credited to a reducing atmosphere that is created in the digester by the sodium sulphide. : Prof. Klason has also studied the reactions that take place in the sulphate digester, and he has found that the reactions are along very much the same lines as in the soda process. As in the soda cook, the solvent that acts on the wood in the sulphate process is sodium hydrate. The sodium sulphide in solution is partly hydrolyzed into sodium hydrate and sodium sulph-hydrate, thus NaS + H.0 = NaS + HOH@NaOH + NaSH The reaction represented by the foregoing equation is called a double decomposition, the metal of the salt changing places with the hydrogen of the water, both substances, the salt and the water, being decomposed. This reaction is reversible, and the direction is determined by the relative concentration of the sub- ae = 9 ——— ss i ee eee ee ee ee ee | ee oe $6 THE DIGESTER ROOM 21 stances on either side of the equation. A double decomposition in which water is one of the reacting compounds is termed hydrolysis, and the salt is said to be hydrolyzed. A sulph- hydrate is formed when § is substituted for O in the hydroxyl; thus, the formula for sodium hydrate is NaOH; substituting S for Oin the -hydroxyl OH, sodium sulph-hydrate, also called sodium hydrosulphide, NaSH isformed. (See Art.11, Appendix.) Referring again to the reactions in the sulphate process, the sodium sulphide as such is thought to have no influence whatever on the wood. As the hydrolysis proceeds and the sulphide becomes available as hydrate, the hydrate becomes active and combines with the acids that result from the decomposition of the lignin. The other member that results from the hydrolysis of the sulphide, the sulph-hydrate, can combine with the alcohols and phenols as well as the hydrate itself, and is better adapted to this purpose because of its weaker affinities. Thus the sodium sul- phide becomes available as active alkali only in the ratio that it is used up; and it is Klason’s opinion that the protective effects produced by the sulphide on the fiber are due to this property. How the sulphur is disposed of in the process, Klason shows by the following figures: RODE gsc b.b wigew elem cen ordlncn s 51.8% Engaged by volatile organic substances............ 15.0% Engaged as sodium sulphide...................... 15.8% Col yc SS O12 #250 aan 17.4% 100.0% The large quantity of sulphur not accounted for has very likely become oxidized to sulphate during the cooking. 28. Cause of Bad Odors.—The bad odors about a sulphate- pulp mill are due to the formation of methyl mercaptan CH3SH and, to a smaller extent, to methyl sulphide (CH3).8, both of which, as well as wood alcohol, are derived from the lignin through hydrolysis. A mercaptan is a compound that is derived from an alcohol by the substitution of S for O in the hydroxyl; thus, the formula for methyl] alcohol is CH;OH, and the formula for methyl mercaptan is CH;SH. In the presence of an excess of alkali, as when cooking easy-bleaching pulp, the odors are less perceptible, because the excess of alkali facilitates the formation of the less odorous methyl sulphide. The methyl mercaptan, 22 MANUFACTURE OF SULPHATE PULP $6 which in the presence of alkali is of a weak acid nature, gives with excess sodium hydrate, sodium mercaptide, CH,SN a, from which compound the methyl sulphide can be obtained in two Ways, as indicated by the following equations, in which R is some organic radical: CH;SNa + CH;OR = NaOR + (CH;).8 _ 2CH;3SNa = (CH3).8 + NaS 29. It is estimated that when cooking easy-bleaching pulp, there is formed about 220 grams of methyl mercaptan per metric ton (2204.6 lb.) of pulp, but that the quantity can be ten times as large when the amount of alkali used is not sufficient to dissolve all the lignin in the wood. Of course, the quantity of methyl mercaptan also depends upon the amount of sodium sulphide that is present in the liquor and upon the constitution of the lignin. Thus, under the same conditions, pine is said to give twice as much methyl mercaptan as spruce. | The organic substances found in the black liquor from sulphate liquor are also given by Klason & Segerfelt, and the analyses agree quite closely with those from the soda process, as shown by the following table: SULPHATE Process Sopa Process Lignin. jen vires hee ogc ee 542.9 Bon AG Acids of fats and phenols........ 24.7.f saree S Formicieid. 203.0 (aie meee ere 36.9 | 77 ACEtIO AGI is hc sateen Le ee 9 YG 9 eae Polos Laetic-acid AG. 4 Sc ee 303.4 grams 326 grams OPERATION OF DIGESTER ROOM 30. Treatment of Chips.—Chips from the wood room are treated under steam pressure with a certain quantity of active alkali, forming a part of a certain volume of liquor, containedina closed steel or wrought-iron tank, called a digester, where the liquor is by some means heated to a certain temperature. This treatment brings the non-cellulose materials in the wood into solution, and the cellulose fiber that makes up about 50% of the wood substance is freed. Close attention should be given to the definition of the follow- ing terms, which will be frequently used hereafter: a Fe es ie ‘ } : a 2 $6 THE DIGESTER ROOM 23 Active alkali: the sum of the sodium hydrate and sodium sulphide figured as NaOH, or as Na2O, according to the practice of the mill. Total active alkali: the number of pounds of active alkali used per charge. Total liquor: the volume of liquid used per charge. 31. The Digesters.—The digesters in the sulphate process are, as previously mentioned, made from steel or wrought-iron plates, either material giving equally good service. They are of different shapes and sizes, but the tendency is toward a larger unit. The large digester gives less work in the digester room; it is more economical in steam consumption than one of smaller size, be- cause it offers less surface per unit of volume, and thus lessens the losses of heat due to radiation. In spite of the steam economy that is derived from the use of a big digester, it is not advisable to let more than one-third of the output of a mill depend on one unit, if it can be avoided without going outside of standard equipment, for the reason that if it were necessary to shut down the digester, too much of the mill production would then be tied up. Digesters are either riveted or welded; the welded form is to be preferred, as it is often difficult to keep riveted digesters from leaking, which is generally due to inferior shop work. Since the cooking liquor has little corrosive action on the iron or steel, no lining is necessary, as is the case with digesters used in the sulphite process. 32. The outside of the digester should be carefully insulated with some non-heat-conducting material. It is estimated that digesters not so protected will lose by radiation approximately 3 B.t.u. per square foot per hour per degree Fahrenheit difference in temperature between inside and outside the shell of the digester (that is, under ordinary conditions, about .6 lb. of steam will be condensed to water, and the heat so liberated will be radiated), and that a cover of magnesia or asbestos will reduce these losses about 85%. To assure good service from the insulating covering, it should be put on in sections that can be easily removed, in case of leakage in the shell. The insulating covering should, in turn, be protected with some water-proof cloth—tarred jute will give good service—in order that the digester may be washed off and kept clean. 24 MANUFACTURE OF SULPHATE PULP $6 Figs. 4 and 6 show two forms of digester (described in detail later). Bis an opening for charging with chips and liquor, D is an inlet for steam, and Z is an outlet for relief of air, gas, and steam. At the bottom of the digester A is an opening F' for discharging the pulp. An asbestos-packed, extra-heavy, plug cock G, Fig. 6, is used to shut off the discharge pipe. To avoid putting the strain on the plug cock that would be caused by a lever, it should be operated by means of a worm gear and hand wheel. The plug cock has a long life and, if leaky, can easily be repacked, while a seated valve, unless furnished with an opening for washing out completely, will never give good service, pulp and chips are always liable to keep such a valve from shutting off tight. The same trouble is likely to affect the working of a gate valve, where the bonnet can get filled with pulp, the bonnet being the chamber into which the gate is drawn when the valve is opened. If a gate valve be used, its operation will be improved by having a black liquor or water line on the bonnet, to wash out, after each operation, the stock which accumulates there. There are two types of digesters—the vertical rotary digester and the vertical stationary digester. The horizontal rotary digester is very seldom used for making sulphate pulp, because of the trouble it gives in charging the cook. 33. Rotary Digesters.—The vertical rotary digester, A, Fig. 4, generally has a capacity of from 2 to 4.5 tons of kraft pulp, air-dry basis, per charge. Both ends are cone-shaped, the elements of the cone making an angle of 45° with the axis, thus making the total angle of the cone 90°. A cast-steel neck H is riveted or welded to the top end, to which a cover I is bolted with easily-removed, swing bolts K. The digester is charged through this opening. At the bottom of the digester, is an outlet F, about 6 in. in diameter, for the discharge of the pulp. The trunnions L, which support the digester and around which it revolves, rest in strong bearings M, supported on a rigid founda- tion N. The steam pipe D is continued up the inside of the digester, and is connected up with a perforated steam coil O, placed as high as possible and supported on the shell. The total area of the perforations in the coil should be equal to the area of the cross section of the pipe. It is important to protect all parts of the digester from the wearing effects of the rushing steam, which are considerable and may cause an accident; therefore, the perforations shavld be S © 1020304050: Fressure Diagram Rotary Digester Fia. 5. described. It will be observed that at the end of about 15 min- utes, the pressure has reached about 42 or 43 pounds; during this time the digester has completed 1} revolutions. The digester is then stopped and received for about 10 minutes and the pres- sure falls slightly to 40 pounds. The digester is then revolved — and the steaming is continued until a pressure of 80 pounds is reached, which takes 15 minutes more and makes the total elapsed time 40 minutes. The remaining steps are clearly indicated on the diagram. About 9000 lb. of steam is required to cook one ton of pulp. 37. Stationary Digesters.—The equipment of the stationary digester is very similar to that of the rotary digester, the chief ; | : $6 THE DIGESTER ROOM 29 difference being in the location of the various inlets and outlets. The ends of the station- ary digester are either both conical or the bot- tom is conical and the top is dish shaped or both ends are dish shaped. Fig. 6 shows a stationary digester hav- ing a conical bottom and with the top dish shaped. The objection to a dish-shaped bottom is that it gives more trouble in blowing than a conical bottom. The majority of the station- ary digesters used in the United States and Canada are smaller in diameter in proportion to the height than is the case with the rotary _ digesters.. 38. In addition to the manhole B, fitted with cover Cc, rip. 6, for charging the digester, there is an opening E at the top for relieving of gas and pressure. This opening, or outlet, should be placed as high as is possible, preferably in the neck of the di- gester, to avoid pulling over the liquor when the digester is relieved. A strainer prevents pulp from entering the relief line. In the early stage i. — Ge -— E \ A D a $6 MANUFACTURE OF SULPHATE PULP 30 MLL CLE L LL LTS ee 1 SSS XV SQ 7 =A\ coveweeeeren( ( fo $6 THE DIGESTER ROOM 31 of the cook, when the liquor in the digester is still rich in active alkali, and when most of the relieving occurs, the pull- ing over of a certain volume of the liquor might mean such big losses of alkali as to affect the quality of the pulp. Some digesters are so constructed that the relief valve is placed on the cover C of the top manhole. Although this arrangement is correct in principle, it gives trouble when taking the cover off. In the case that the relief pipe should plug up, a small live- steam connection should be provided on the relief line between the valve and the digester, to allow the obstruction to be blown back and clear the pipe. The steam is let into the digester through a coil K in the bottom. Another good way to arrange this coil is shown in Fig. 7. This method insures cooking of the chips in the cone and may help to maintain circulation, as it gives additional heat to the liquor in the center of the digester. The size of the perforations (7s-inch holes, in this case) and their number must be such that they will deliver up to the capacity of the steam pipe D, and the steam pipe should be large enough to supply a sufficient quantity of steam within the time allowed for steaming the digester. For a digester holding 1400 cubic feet, a 3-inch steam pipe is sufficiently large. The blow valve G, Fig. 6, is of the same type as for the rotary digester. The discharge (blow) line P is from 6 to 8 inches in diameter, according to the size of the digester. A 6-inch blow line will empty a 1400-cubic-foot digester, blown at an initial pressure of 80 pounds, in about 15 minutes. The operation of blowing the stationary digester can be made much simpler than blowing the rotary digester, since all the connections can be made permanent. 39. The digester is mounted on heavy cast-iron, steel, or con- concrete columns, and should be at a higher level than the floor, to make it easily accessible for operating the blow valve and for changing it. On the main steam line D, Fig. 6, going to the digester, should be a steam valve S. A check valve V should also be placed on each individual digester, to prevent liquor from going back to the steam boilers or to other digesters, in case the boiler pressure should drop below the pressure in the digester. If the steam pressure is much higher than the cooking pressure, a reducing valve ought to be placed in the main steam line to the digester 32 MANUFACTURE OF SULPHATE PULP §6 room; and if saturated steam (7.e., if the steam is not superheated) is used, there should also be a steam separator on the line, close to the digesters, to keep the steam as dry as possible. 40. A good arrangement is to have the digesters and a dummy connected to the same blow line. Check valves are put between the digesters and the main pipe, to keep stock from coming back into one digester pipe line when another is blown. Also, when stock is blown from a-digester to a diffuser, the solids or liquid matter in steam from the diffuser are trapped, first, in a receiver or steam separator and, second, in the dummy mentioned. When steam is relieved from a digester, solids and liquid matter are trapped in the dummy, and the steam goes from the dummy to a condenser or to the atmosphere. Stock and liquid caught in the dummy is blown back through the digester blow line into a diffuser, as may be necessary. 41. Operation of Stationary Digester.—The operation of the rotary digester was previously described in detail; the stationary digester is more easily operated and gives less work in the digester room. As soon as the digester is charged and the steam turned on, all the cook has to do is to observe his pressure gauge and take care that he relieve the digester without pulling out any liquor. Since the relief is the only means of obtaining circulation, the chances are that the cook will relieve more steam than is really essential to get uniform pulp. A steam-flow meter on the © digester-room steam line puts a means of control into the hands of the superintendent; at the same time, it serves as a guide for the digester man. The steam should be supplied to the digester fast enough to bring the charge to the cooking pressure and temperature within a time not to exceed one-third of the total time used for cooking. While coming up to cooking pressure, the relief valve E is operated as described in Art. 35. Thus, if the total cooking time is 4 hours (= 240 minutes), the cooking pressure should be reached in not more than 240 + 3 = 80 minutes. This applies to the cooking of kraft pulp. Sometimes, however, it will greatly improve the quality of the fiber if the time for steaming is prolonged. In case the wood is not uniform (for instance, wet and dry wood mixed), a longer time for reach- ing a pressure of 80 lb., below which pressure, no marked action of the liquor on the wood takes place, gives the mixed ships a better chance to be uniformly cooked. $6 THE DIGESTER ROOM 33 When the digester pressure is reached, the relief valve E, Fig. 6, is shut tight, provided good circulation has been maintained, and the steam valve S is left open just enough to keep up the digester pressure; that is, sufficient steam is admitted to make up for heat losses due to radiation. After the digester has been kept under pressure until the decomposition of the wood has reached nearly the point aimed for, near enough to finish the work by the time the digester is ready for blowing, the pressure is relieved down to H H ’ ' i ‘ Rt ee ee NE ee aaa ae a nn H eet ee A o SK ‘9) & & Q 2 3 © e & w Fressure Diagram Stationary higesler Fia. 8. blowing pressure, about 80 lb. per sq. in., and the digester is then emptied in the same manner as was the rotary digester. In case the digester does not blow clean, that is, if some pulp is left in the digester, the digester should be reblown. To do this, sufficient black liquor is run in to cover the stock that is left, the cover is bolted on, and the digester is steamed in the ordinary way, with the steam valve wide open, to give a good stirring effect. The pressure is brought up to 70-80 Ib., and the digester is discharged in the usual manner into the same diffuser as the previous part of the cook. To make sure the digester has blown empty, a light should be dropped in after each blow. Should it occur repeatedly that part of the charge is left in a digester, an improve- 34 MANUFACTURE OF SULPHATE PULP §6 ment may result if the digester is first relieved to 10-15 lb. below the blowing pressure, and then steam is turned on, with the steam valve wide open, until the blowing pressure is reached. Care must be taken that this pressure is not exceeded. The same stirring effect, though not so thorough, will be obtained if a steam puff be shot into the digester after the blow valve has been opened. For this purpose a steam inlet is sometimes provided well down in the cone, as at F’, Fig. 6. A pressure diagram for a stationary digester is given in Fig. 8. It is interesting to compare this with the diagram for the rotary digester given in Fig. 5. The pressure of the digester should be relieved as far down-as time will permit and without risking the possibility that the digester will not blow clean. In addition to the economy due to the heat that can be reclaimed, there will be less strain in the blow lines and on the diffuser bottoms. When easy-bleaching sulphate pulp is manufactured, the steaming should be done more slowly, which will produce better fiber. It is most important that the cooking of a digester charge be begun right, especially with stationary digesters; for, upon a correct start—correct charge, volume and strength of liquor, steam pressure, careful relieving, etc.—uniform cooking depends. 42. Storage for Chips.—The digester room is also equipped with a chip bin for storing the chips; but if not so equipped, conveying machinery of very large capacity is required. The chip bin should be placed above the digester, so the chips may fall into the digester by gravity and make the time of charging as short as possible. The chip bin should preferably have a capacity for a 14-hour run, that the wood room may be operated in day time only, with a margin of time in case something should go wrong with the chip conveyors or in the wood room. A separate chip bin on a lower elevation and equipped with its individual elevating machinery, can take the place of an exten- sive storage above the digesters and will, in case of digesters of large capacity, save the building of an expensive superstructure. In a mild climate, where it is not a question of protecting the machinery from cold weather, it might prove economical simply to put. up a light construction around the digesters and keep the main chip bin on the ground. $6 THE DIGESTER ROOM 35 43. White- and Black-Liquor Storage Tanks.—The digester room is also supplied with storage tanks for white and black liquor, though many mills prefer to have the black-liquor tanks in the evaporator building. These tanks are placed above the digester, and at a level high enough to permit the liquor to run into the digester by gravity in the time necessary to charge it with chips. The tanks should be large enough to hold all the liquor for one charge, which will have to be measured in these tanks; therefore, there is always a scale (graduated in inches or cubic feet) attached to the tanks. The white liquor for each charge should be tested chemically. (See Art. 12.) That the measuring may be as accurate as possible, the cross-sectional area of the tank should be a small as the height of the room permits, for a tank of required capacity. A mistake of an inch in depth in the case of a tank of large diameter, especially when the liquor is strong, means a rather large quantity of active alkali, and it might affect the quality of the cook. For example, for a tank 8 ft. in diameter, every inch of depth represents about 4.2 cu. ft., while in the case of a tank 6 ft. in diameter, every inch of depth represents only about 2.4 cu. ft. Besides, there is a certain saving of liquor when using a tank of smaller diameter, since the scale is more sensitive, and errors due to forced increases for the purpose of making the reading in even inches (instead of inches and fractions) when figuring the charging table, will mean less unessential liquor added. . The white liquor measuring tanks should have the outlet placed well above the bottom; this will provide a space for lime sludge, etc. to settle in, and only clear liquor will then go to the digesters. Through another outlet in the bottom, which is connected with the liquor room, the tank can be washed out without any loss of alkali. 44. Condensers.—In the case of stationary digesters, the need of a condenser to take care of the heat that is contained in the steam and gases relieved from the digester is much greater than when a rotary digester is used, because in the former all the agita- tion, the circulation of the liquor in the digester, is maintained by relieving off steam. The quantity of steam thus used to obtain circulation is considerable, even in the most favorable case, and it may easily become unnecessarily large, through carelessness on the part of the cook. In his endeavor to obtain a uniform cook (result of digestion), even a good man is liable to open his relief 36 MANUFACTURE OF SULPHATE PULP §6 valve too much. Not considering the economy involved in saving the steam relieved in the early stage of the cook, the heat that can be saved when relieving the pressure from 120 lb. down to 80 lb. corresponds to about 500,000 B.t.u. per ton of pulp, which is sufficient to raise the temperature of 500 gal. of water 125°. 45. Any surface condenser of ample capacity will answer the | purpose. A good type, one that has been used successfully, is shown in Fig. 9. Steam enters at A and leaves as water at B. C Cold water inlet Condensate Fia. 9. Cold water enters the jacket P at C and emerges hot at D. If preferred, a vertical box may be used instead of the water-jacket pipes P. The box is made any convenient height, but should be high enough to condense to water practically all the steam entering at A by the time it reaches B. When the digester is blown, a large quantity of steam is re- leased in a very short time, with a consequent and corresponding large loss of heat. A surface condenser able to take care of all this steam (condense it) must be of very large dimensions. A spray condenser is sometimes used for this purpose, but the condensate is likely to be contaminated with products derived eee Se ce etl oe Oe ee a Se ee eee ay, ee ee THE DIGESTER ROOM 37 $6 PeN BSRVSVey Fia. 10. 38 MANUFACTURE OF SULPHATE PULP §6 from the cooking of the wood. A diagrammatic view of a spray condenser is shown in Fig. 10, which gives an idea of how it is arranged. ‘The steam enters through the pipe A, which connects with the receiver, the lower end of this pipe being perforated, as indicated. As the steam discharges through the perforations, it meets the water spray from B and C and is condensed, falling to the bottom of the condenser, together with the excess water from the spray, as indicated at HE. The level of FH is controlled by the float F, the rising of which causes the link G to rise also and reduce the amount of water admitted to the condenser N. A vent pipe H keeps the pressure within the required limit. Pipe I connects to the sewer, and pipe J connects to the diffuser hot- water tank. The water is obtained boiling hot, and it is claimed that the bad odors of the water are not so strong that the water can not be used for washing purposes in the mill. 46. Testing Equipment.—A testing bench should be a part of the equipment of the digester room, so the cook can test the cooking liquor. A burette, some measuring flasks, and some pipettes are all the apparatus needed. A _burette that will automatically adjust itself to zero (0) when filled, is to be pre- ferred, because it eliminates the labor of adjusting or subtracting and lessens the chances for a mis-reading. The cook should also be furnished with a table showing how many inches of liquor are to be taken from the measuring tanks for the charge of active alkali that is wanted. This table makes it easy to change the charge of active alkali to correspond with changes in the wood and liquor. Such a table can be prepared by the chemist from a range of liquor analyses covering the possible range of the mill. 47. Indirect Heating of Cooking Liquor.—The advantages of indirect heating of the cooking liquor were appreciated very early in the development of the chemical pulp industry. This method of supplying heat for cooking does away with the diluting of the liquor, and the quantity of water that it is necessary to evaporate in order to reclaim the chemicals is less. For several years, the problem of indirect cooking was not much heard of; recently, however, it has again become acute, and at the present time, there are at least three different systems on the market, for indirect heating. As the general features of these systems are all about the same, only one system will be described here. Boon, ae * ’ ‘ Fe Te ee ee eS eT ee een =r §6 THE DIGESTER ROOM 39 48. In Fig. 11 is shown a heater A installed on a digester D. The heater contains the tubes C, through which passes the live steam that does the heating. The liquor in contact with the outside of the tubes is heated : by conduction, the heat of the 7 soar steam passing through the ———~ ~ % walls of the tubes. The lower end of each tube is pressed or screwed into a_ substantial tube sheet, while the upper end is closed and free, thus permitting unlimited expan- sion. A false, perforated bottom E in the digester strains the liquor from the chips. In operation, the digester is filled in the ordinary manner, ~ the chips and the _ liquor being run in simultaneously. When half the liquor charge is run in, the circulating pump F is started up. It is claimed that this procedure effects a better packing of the chips. As soon as the digester ———— is charged and the cover is on, the full pressure of steam is turned on through pipe H, and the condensate pump G, which discharges to the hot washing water storage, is started up. The cooking liquor flows from the bottom of the digester, through pipe S, the heater C, and passes on through pipe 7 to the top of the digester. The circulating pump F is able to handle the entire quantity of liquor in from 18 to 20 minutes; it requires a 5- to 74-h.p. motor to operate it. The condensate pump G, which can be run with a 10-h.p. motor, will take care of five digesters. nh er eewnnn = enn en = wn nn no == == -- is] | I =m ie ee i I he KA ai | U = = sn SS ae 40 MANUFACTURE OF SULPHATE PULP $6 The liquor is heated very rapidly. At 25 lb. per sq. in. pres- - ~ gure, the cold gas and air are relieved; after that, no further relieving is necessary. The maximum temperature of the diges- ter, 330°-345°F. (100-110 lb. per sq. in., gauge pressure), is reached within 12-14 hours, with heating steam at 150 Ib., gauge, without diluting the liquor, and without hurting the fiber through local overheating, which could hardly have been avoided when heating the digester that rapidly with direct steam. When the maximum cooking temperature is reached, the steam is shut off the heater, and the digester is then furnished with direct steam, as usual. The circulating pump is kept going for another 20-minute period, and the pump is then shut down. When the cook is ready to blow, the pressure is relieved in the ordinary manner, and the digester is then discharged. Among the advantages claimed are: saving of coal, which is partly due to the smaller amount of liquor to be evaporated; saving of salt cake and lime; production of a stronger fiber; and a saving of wood, on account of the better circulation obtained. The writer has experienced considerable trouble in discharging the digester, when operating this heating system; it was not possible to force the digester to empty its total contents, and some pulp would always be left at the bottom. To improve this condition, it was found necessary to discontinue the use of the heater and the circulating pump before the cooking temperature was reached, and to bring the pressure up to the last 15 lb. by means of direct live steam. QUESTIONS (1) How many heat units will be lost daily by radiation from a bare digester 8 ft. in diameter and 40 ft. (total) high, if the temperature inside is 300°F. and the temperature outside is 90°F.? Assume the bottom to be a cone, an element of which makes an angle of 45° with the horizontal, and that the top is flat. Ans. 15,515,000 B.t.u. (2) In the last example, if the coal used contain 13,000 B.t.u. per pound and the boiler plant delivers to the digester 50% of the heat energy of the coal, (a) how many pounds of coal are wasted per 24 hours through radiation - of heat? (b) what is the money loss, if coal is worth $7.00 per ton of 2000 pounds? (a) 2387 lb. Ans | (b) 8.935. $6 THE DIGESTER ROOM 41 (3) Compare the advantages and disadvantages of rotary and stationary digesters. (4) Why is good circulation necessary? (5) What is the reason for passing the relief gases through a condenser? FACTORS AFFECTING THE COOK 49. Effect of Sodium Sulphide and Sodium Hydrate.—Of the factors affecting the cook, the condition of the wood, the pressure of the steam and its corresponding temperature in the digester, the quantity of active alkali, the volume of total liquor, and the time the wood is exposed to the action of the liquor, are of the greatest importance. The relation between the sodium sulphide and the sodium hydrate, within certain limits, has but little influence on the quality of the fiber; but if the hydrate gets much in excess, 85% or more of the total active alkali, the fiber will be more like that obtained from a soda cook and the yield will be less, calculated on the basis of dry wood. On the other hand, an increase of sulphide to above 48%-50% will result in a slower action of the liquor. With all other conditions unchanged, an excessive quantity of sodium sulphide in proportion to the sodium hydrate, will result in an incomplete decomposition of the wood, and the fiber obtained will be raw and full of slivers. In order to complete the cooking within the appointed time, the charge of active alkali will have to be increased. The writer has observed this on several occasions when, on account of unsatisfactory lime, the causticity of the white liquor had to be lowered, which, in its turn, resulted in more sodium sulphide in relation to sodium hydrate. Whether an increase of pressure will help the conditions thus created by the excess sulphide, is doubtful; but, by making the cooking time longer, the result will be improved. According to various authorities, the best result from the cooking of sulphate pulp is obtained when 35%-40% of the active alkali of the white liquor consists of sodium sulphide. 50. Effect of Variation in Woods.—Variation in the condition of the woods will affect the cooking in several ways. Ifa mixture | of different kinds of woods is used, a change in the proportions of the several varieties will influence the result of the cooking; one kind of wood will give more fiber than another; one kind will call for a harder treatment with alkali than another. DeCew 42 MANUFACTURE OF SULPHATE PULP §6 gives the following figures for black spruce and hemlock; while they apply to mill results from soda mills, they are equally applicable to sulphate mills. Specific | Weight of Soda as | Soda | Yield (Ib.) in dry Gravity |cord (Ib.) | NazCOs oat fiber per cord Black spruce.....| 0.41 2250 900 40.0 1000 Hemlock als: 0.42 2300 950 41.3 970 If these two kinds of wood are used in a mixture, a change in the composition of this mixture will naturally change the result of the cook, and it will call for an adjustment of the charge of total active alkali. 51. Effect of Moisture in Chips.—Of greater influence than variation in woods is the variation in the amount of moisture in the chips. With increased moisture, the chips will weigh more and will pack better in the digester. Thus the digester will hold more wood, dry weight, and the total active alkali will have to be increased, to maintain the same quality of pulp. The harder packing of the wood in the digester will lessen the dead space between the chips, and the larger quantity of water in the chips decreases the quantity of water that can be absorbed by the chips; thus a charge of moist chips will call for a smaller total volume of liquor than a charge of dry chips. 52. Effect of Temperature and Pressure.—It was stated in the Section on Physics that saturated steam always has a definite temperature corresponding to a definite pressure. It is conven- ient to know what pressure corresponds to a particular tempera- ture; then, if the temperature at which the cooking is to be done is known, all that is necessary is to watch the steam gauge until the pressure gets to the point that corresponds to that tempera- ture. These values are usually obtained from steam tables, but if such a table is not at hand, the pressure may be calculated by . the following formula, which gives excellent results from 300° to 350°F. Let ¢ ie temperature in degrees F. absolute pressure (lb. per sq. in.) P = 431.53 — 3.4144¢ + .0073310 $6 THE DIGESTER ROOM 43 For example, suppose it is desired to know what pressure corresponds to a temperature of 320°F. Substituting 320 for ¢ in the formula, P = 431.53 — 3.4144 & 320 + .007331 X 320? 89.6 lb. per sq. in.; the gauge pressure is evidently p =P — 14.7 = 89.6 — 14.7 = 74.9, say 75 |b. per sq. in. 53. An increase in temverature, with other conditions in the digester unchanged, will have the tendency to make the yield of fiber smaller, the speed with which the liquor acts on the wood is increased, and, at the same time, the percentage of active alkali that is utilized within an equal period becomes larger. The following figures from a reliable source (Christiansen’s ‘‘ Natron- Zellstoff’’) show how the yield and the percentage consumption of the active alkali are affected by an increase from 320°F. to 350°F., with the same digester charge in both cases: | Yield of fiber = 48% Consumption of alkali used = 54% Yield of fiber 44.6% Consumption of alkali used = 76.3% 320°F. 350°F. Notse—tThe alkali utilized was here determined by titration and not, as in Klason’s figures, by saturation with carbonic acid. A low temperature is thus of great benefit to the yield. How- ever, it is not possible to work at a temperature much lower than 320° and obtain a free fiber. Below this temperature, even a great excess of alkali will not give well cooked pulp. At 320°F., an excessive charge of alkali is called for, to obtain a favorable result within a reasonable time, and an increased yield is not sufficient excuse for using so much active alkali that in the cycle of the process such great losses will be created. The most favorable conditions as to the utilization of the active alkali furnished to the digester, and the quality and yield of the fiber obtained from the cook, occur at a temperature of 330°-345°F. To maintain the highest possible capacity of the digester room, the maximum cooking temperature should be reached as early as possible. The steaming time for kraft pulp should not much exceed one-third the total cooking time, because the principal reactions that take place in the digester hardly start at a tem- perature lower than 300°F. (See Art. 41.) 44 MANUFACTURE OF SULPHATE PULP §6 54. Quantity of Active Alkali—The quantity of active alkali used for charging the digester is, perhaps, the factor that affects most seriously the results obtained from the cooking. If in- creased, it will, under otherwise similar conditions, change most radically the qualities of the fiber and will decrease the yield. The following illustration is from Christiansen’s ‘“Natron- Zellstoff:’’ two parallel cooks were run; in one the quantity of active alkali was 23.6%, calculated on the dry weight of wood, while in the other, this was changed to 30.6 %; the change caused a decrease of yield from 48.5% (on the basis of bone-dry fiber to bone-dry wood) to 33.6%. As previously mentioned, Art. 26, Klason found that 20% of active alkali (NaOH) is the smallest quantity actually engaged by the organic acids that are derived from the complete destruc- tion of all the non-cellulose constituents of the wood; and he pointed out that this quantity is insufficient in practice, and that under certain conditions, in order to obtain easy-bleaching pulp having satisfactory qualities, it will be necessary to use 30% to 33% of active alkali. 55. In the manufacture of kraft pulp, where a complete isolation of cellulose is not desired, it is possible to obtain an excellent product, and maintain a yield of about 50% fiber, with less than 20% alkali; but if the charge be made much smaller, it will then be necessary to adopt some means of mechanical treatment—kollergangs or refiners—in order to obtain a fiber that is suitable for the beaters. However, this mechanical treatment is very expensive; so much so, that it may offset the savings from the improved yield and the reduction in the losses of alkali. Nearly all manufacturers are trying to obtain a prod- uct that is ready for the beaters without applying any extra work, and, at the same time, to maintain the highest possible yield. The quantity of active alkali that is used varies, of course, from mill to mill, because of variations of other conditions. Satisfactory results are obtained when 20%-23% of active alkali is used, as compared with the dry weight of wood. 56. Total Liquor.—The volume of liquid used in the digester (the total liquor) should be kept as small as possible, to economize steam consumption. Too small a volume of liquid, however, must be avoided, as it will result in a lot of more or less burned or uncooked chips, which will be mixed with the perfectly digested $6 THE DIGESTER ROOM 45 fiber. This applies particularly to the stationary digester, whether directly or indirectly heated; but it is not so likely to occur in a rotary digester, where the tumbling assures a thorough mixing of chips and liquid. Again, with too small a total liquor charge, there will be a certain proportion of the chips that never come into contact with the liquor, at least, not in the early stage of the cook; but, at the same time, these chips will be exposed to the high temperature in the digester, which will cause a partial dry-distillation of the wood. Later on in the process, when the wood in the lower part of the digester is partly decom- posed and the volume of the resulting liquor (increased by the condensed steam) is sufficient to cover these chips also, the de- composition of the wood is retarded by the dry distillation of the wood and the low content of the alkali, as well as by the de- creased time for chemical action; as a consequence, these chips are not properly cooked when the time comes for blowing the digester. 57. Besides leading to inferior steam economy, too large a volume of total liquor, which a good cook (digester man) would never use, may also result in bad cooking, due to the fact that it is then very hard to relieve the pressure without pulling some liquor out of the digester through the relief line. At the begin- ning of the cook, when the relieving is so essential in. order to obtain good circulation, the active alkali in the digester is not utilized, and a loss of liquor will mean a corresponding loss of alkali that was intended for digesting the chips. The final result may be the same as though insufficient alkali had been furnished to the cook, and the fiber will have a general rough-looking ap- pearance, with hardly any chips properly cooked. Too small a volume of total liquor will result in an excess of uncooked chips, which means a waste of perfectly good wood. Since the conditions that will call for a change in the amount of total liquor result, principally, from changes in the amount of moisture in the chips, a control of this condition of the wood will assist in deciding how much liquid is necessary for the charge. Besides the quantity of active alkali that is essential for the cooking, the operation of the digester is also affected by the amount of moisture in the chips; and a close study of the relation of these factors—the total liquor and the ratio of the total active alkali to the moisture in the chips—will assist in determining how to charge the digester. 46 MANUFACTURE OF SULPHATE PULP $6 For a stationary digester, when cooking with direct steam, the necessary volume of the total liquor will vary between 45% and 50% of the digester volume, and it is rarely outside these figures. For a stationary digester, heated indirectly, where no condensa- tion takes place, the total liquor charge must be made greater, or from 55%-60%; with.a 60% charge, the liquor will usually show at the top of the digester. For a rotary digester, where it is necessary to cover only a little more than one-half the chips, 25%-30% of the digester volume is a safe charge of liquid. One method for determining whether the digester is having sufficient circulation, is to place a short piece of plank on the manhole, and sit on it. An experienced man can tell by the surge of liquor against the digester whether it is getting proper circula- tion. Also, an experienced sulphate man can tell whether diges- ters are getting proper circulation, even before entering the plant, because there is a typical odor present when digesters are not getting proper circulation. The odor is due to the chips being burned on top of the charge, which, in its turn, may depend on bad circulation, but is usually eS by too little liquid in 1 the digester. The total liquor should then be increased. 58. When to Blow.—The digester should be discharged as soon as the stage of digestion that is aimed for is reached, a point that can be learned only by experience with the wood and the digester, since a prolonged exposure of the fiber to the action of the liquor will cause a decrease in the yield and, at the same time, the quality of the pulp will suffer. This effect is not so marked in the manufacture of kraft pulp, where the charge of active alkali is hardly sufficient to cause any further action of the fiber; but, when cooking easy-bleaching pulp, where an excessive quantity of active alkali has to be used in order to obtain com- plete destruction of non-cellulose matter of wood, even a short delay in discharging the digester will cause great changes in the quality of the pulp and a considerable reduction in the yield. 59. The actual cooking time varies from mill to mill and with the size of the digesters; it is usually about 4 hours for kraft pulp, of which time, 14 hours is used for bringing the digester up to the desired temperature. For easy-bleaching pulp, the cooking time is longer, or about 5 hours, because the time for steaming the digester is then made longer, in order to get the chips properly soaked with the liquor before the temperature is ee a a a ee SS §6 THE DIFFUSER ROOM 47 reached at which the most important reactions take place. If perfect circulation be maintained and the chips be uniform as to size and moisture content, the time for steaming the digester might be decreased without any harmful consequences, thus increasing the capacity of the digester room. The same result can be obtained by increasing the charge of active alkali, in which case, the cook must be discharged just as soon as it is ready; a short delay then will mean bad economy. It is safe to say that, in the long run, it is not profitable to overload a digester room by fast cooking with too strong a liquor; and that the installation of additional digesters, to obtain a larger production, will pay for itself. QUESTIONS (1) (a) What is the best percentage of NaS in the cooking liquor? (b) What is the effect:-of an excess of NaS? (c) of NaOH? (2) State the best temperature for cooking sulphate pulp.. (3) What is the effect on the yield and quality of pulp of variations in the amount of active alkali used? am (4) Why should the volume of liquor be as low as possible? THE DIFFUSER ROOM 60. Purpose of Diffuser Room.—In the diffuser room, or wash room, the pulp discharged from the digester is freed from the liquid, the black liquor, that results from the cooking. This black liquor, which contains all the chemicals used for charging the digester (but in different form and proportions) and also the organic substances dissolved from the wood, has to be reclaimed as carefully as possible. To this end, the stock is first washed with water until it is perfectly clean. Before the chemicals in the liquor can be made useful again, they must be freed from all water that keeps them in solution and from the organic substances that are associated or combined with them. To ac- complish this regeneration of chemicals as economically as possible, it is the aim in the wash room to wash the stock clean with the least quantity of water, and, if possible, keep the con- centration of the resulting liquor so high that the heat gen- erated by burning the organic matters contained in it will be sufficient to evaporate all the water. That this result may be 48 MANUFACTURE OF SULPHATE PULP §6 accomplished, not only will the wash room have to be very well arranged and most carefully worked, but the machinery all through the mill will also have to be modern and up-to-date, 61. Reclaiming of Chemicals.—In the early days of the soda- pulp industry, the chemicals from the pulp contained in the wash water were all wasted, and no regeneration whatever was at- tempted. The economy in saving as much as possible of the chemicals was soon recognizéd, and the first step in that direction was to drain all the liquor from the digester that would flow off by gravity. This liquor was then regenerated in a rather crude way, and was used over again, as much as 70% of the chemicals being reclaimed. The pulp was freed from the rest of the chemicals through washing in the digester and also in the beaters, but the weak liquor that resulted from these latter operations was wasted. The great economy that resulted from this recovery, and also the laws that prohibited the washing of the chemicals into rivers and streams, induced experiments having as their aim still more complete recovery. Various forms of apparatus have been designed for the purpose, most of them similar to the present diffuser in their general principles, but differently ar- ranged, and at first, built only for a part of the digester charge. The first diffuser was constructed by Dahl, the originator of the sulphate process. At present, there is hardly any arrangement other than diffusers used for washing wood pulp manufactured by the sulphate process; and it is the exception when machinery of any other construction is used, though the washing is per- formed in open vats, in some cases. For washing straw pulp, which is very slimy in its structure and, because of this, very hard to wash clean, Lespermont introduced as early as 1873 an arrangement of a series of pulp thickeners, working according to the counter-current system. It is claimed that by adopting this method of washing, the straw cellulose can be washed very clean, with small losses of alkali and with comparatively little water. A somewhat similar system has recently been installed in a Canadian pulp mill; it is said to give good satisfaction. 62. Washing in Open Vats.—If the stock be washed in open vats, it is necessary to have an arrangement situated outside the wash room, by which the steam that is developed when dis- charging the digester is separated from the pulp and liquor. This is generally done by means of a cyclone arrangement, one is oc PO ee ee ee ee ee ——S ee $6 THE DIFFUSER ROOM 49 form of which is shown in Fig. 12. upper end of the cylindrical part A in a tangential direc- tion, as indicated in view (b). The solid and liquid materials are thus given a speedy rotary movement, which keeps them from being pulled out by the steam that escapes through the top. At the lower end, the cylindrical part A joins the cone-shaped part B that connects to a pipe C, through which the digester charge empties into a washing vat. The steam and other gases pass the baffle D and sleeve E and emerge at the throat Ff, Gis the pipe from the digester. 63. The wash tank is made of wrought iron, and is equipped with a false bottom, in most cases. Occasionally, there is a system of perforated pipes, placed right on the bottom and with the perforations turned downward, in order to save space in the tank. The purpose of the false bottom or perforated pipes is to obtain as large a drain- ing area as is possible, and, at the same time, retain the fiber in the vat dur- ing the washing period. Here the pulp is shot in at the iget, Fe The perforated bottom is very similar to the false bottom used in the diffuser, and will be described later. A perforated pipe is 50 MANUFACTURE OF SULPHATE PULP — -§6 placed in the top of the vat, through which the liquid used for washing is sprinkled over the stock. The bottom outlet of the vat is placed underneath the screen; it is so arranged that the liquor flowing from the tank can be directed either to the storage for black liquor for the recovery room or to a pump that dis- charges the liquor through the system of sprinklers on the top of the vats. A weak wash from one tank is used on a fresher charge in another. The vat is made large enough to hold one complete digester charge, and to allow a space for water of a depth of 12-18 inches. These open wash tanks, while still in use for soda pulp, have generally been replaced in sulphate mills by diffusers. 64. When the digester has emptied itself by blowing into the vat, the stock is leveled off and the drain valve is opened to the storage tanks. Before the stock is dry enough to permit cracks in the structure of the charge, through which water could escape to the bottom without properly serving its purpose for washing, weak liquor from another vat, where the strength of the liquor as determined by a hydrometer is considered too low to be sent to the recovery storage, is turned on through the top sprinkler pipes. This weak liquor wash is continued to a point where a further saving of the chemicals in the weak charge is considered to be uneconomical; the resulting liquor is then too weak to justify the cost of evaporation, and its cleansing effect is not satisfactory. The washing of the weak charge is then continued until it is considered clean, and the final resulting liquor is dis- charged into the sewer. The black liquor is collected in the recovery storage until the hydrometer shows density of about 5°Be. (hot), and the weak wash liquor is saved until its density is about 0°Be. (hot). 65. The washing of the charge, which up to now has been made with weak liquor, is continued with hot water, which is turned on through the sprinklers. The liquor that drains off through the bottom is admitted to the recovery storage until this tank tests weak (below 5°Be., hot), when it is turned on to another fresh charge. When the stock has been washed, clean water is let in under- neath the screen at the bottom, and the stock is flooded out through a manhole, placed on the side of the tank and opening into the stock chest. 86 THE DIFFUSER ROOM — 51 The open vat is a very slow working arrangement, and the volume of water used for washing is rather excessive. According to Sutermeister, Soda Pulp Manufacture, an actual time of 11—18 hours is needed to wash a layer of pulp that is 8-10 feet deep; of this time, 4-7 hours is required for collecting strong liquor and 5-6 hours for collecting weak liquor; the remainder of the total time is used for completing the wash. He gives the volume of strong liquor per ton of pulp as 1600-2100 gallons, and of the weak liquor as 1750-2220 gallons. 66. Description of Diffuser—The diffuser shown in Fig. 13 is an enclosed tank A made from steel or wrought-iron plates, either riveted or welded. As compared with the open vat, the height of the diffuser is greater than the diameter, the ratio usually being about 2to 1. The diffuser should be large enough to take care of an entire digester charge without getting so full that any considerable quantity of stock will blow out through the top, because of the velocity of the stock, when the digester is emptied. Good service in that respect is obtained from a diffuser that has about 10%-20% greater volume than the digester. At the top of the diffuser is an opening with a special fitting C, which affords an entrance B for the stock from the digester and an outlet G for the escaping steam and, sometimes, liquor and pulp carried with it. On the same fitting, there is usually a con- nection for wash water, etc., as indicated at D, and, occasionally, for asafety valve M. Immediately underneath the pipe through which the pulp is blown into the diffuser, a baffle plate is securely fastened; this plate is cone shaped, with the vertex upwards, and serves to spread the pulp, so the bottom of the diffuser will not be exposed to the shock of the inrushing charge; it serves also to distribute wash water. A false bottom consisting of screen F is placed as near as possible to the bottom of the diffuser. This false bottom must be of very strong construction, and its purpose is to make the draining area for the liquor as large as possible without letting any fiber through. The screen plate is usually #, inch thick, with ay inch perforations, spaced 3’; inch between centers. Underneath this top screen plate is a coarse wire screen, which keeps the top plate from contact with the heavy bottom plate and insures that the liquor will drain through all the holes of the top plate. The lower plate, which gives the false bottom its strength, 1s made from i-inch wrought iron, drilled with }3-inch holes, spaced 52 MANUFACTURE OF SULPHATE PULP $6 al iy) & le, . A | U/ ZZZZZZZZZZ u, To Storage 7] 86 THE DIFFUSER ROOM 53 1 inch between centers. All plates are made in sections, which can easily be taken out and replaced. The false bottom is supported on I beams, placed across the diffuser, and on an angle iron that is riveted to the shell and extends all around the wall. The empty space under the false bottom is partly filled with concrete, which serves as a support for the beams and also de- creases this space. If there is too much room under the screen, the space must be filled with liquor before the diffuser is blown into; otherwise, the false bottom will be subjected to a rather hard strain by the rapid flow of liquor through the screen at the start of the blowing; also, considerable fiber will find its way through the screen during this period of forced draining. When a concrete filling is put in, care must be taken to give a free passage for the liquor from every point of the bottom to the outlet H at the center. (Sometimes, the water from the last charge is left underneath the screen, to serve as a cushion for the bottom when the new charge is blown; this is bad practice, however, and will unnecessarily increase the volume of the water to be evaporated.) The screen bottom is generally level, though sometimes sloped toward the front of the diffuser. A sloping bottom not only lessens the capacity of the diffuser but it also prevents the diffuser from washing uniformly, since the layer of pulp will be thicker at one side than at the other. The purpose sought, that of making the stock wash out more easily, is not accom- plished either, because the water will run through the screen at the highest point and come up again at the front without bringing any pulp with it. An opening K of ample size and fitted with a heavy cast-steel frame is placed in the side of the diffuser, level with the false _ bottom, to which is bolted a cover that can easily be removed. When the stock is ready washed, this cover is taken off, and the stock is dumped into the stock chest 7, Fig. 14. To facilitate the operation of discharging the diffuser, a water inlet J, Fig. 13, is often placed opposite the dumping hole K, and about 12-18 inches above the screen. If the water entering at I be under good pressure, 40-50 Ib. per sq. in., and the stream be distributed by some means over the entire bottom, practically all the stock can be washed out with but little trouble, and the time for empty- ing the diffuser can be made very short. At the center, in the 54 MANUFACTURE OF SULPHATE PULP $6 bottom of the diffuser, is an outlet H for liquor and water, which may be conducted to storage tanks or to the sewer. 67. Battery of Diffusers.—The best and most common way of arranging a battery of diffusers is so to place them that their » ULL LLL “OCLs LLL LLL 0 SH (AA re [ be YY QE ELEVATION. Fia. 14. centers will lie on the circumference of a circle, as illustrated in Fig. 14. The discharge pipe A from the digesters C will have its outlet at the center of this circle, from which point, each $6 THE DIFFUSER ROOM 55 diffuser D can be reached by means of a swing pipe P. Joints S, are for pulp and S, for vapor and gases. The same effect may be obtained by placing the diffusers in a double row, as illustrated in Fig. 15, in which case, an extension L leads from each diffuser, to connect with the swinging arm P at the circumference of the circle. The former arrangement is to be preferred, because it is much easier to operate and is a neater looking arrangement. The latter is used only when the space available for the diffuser room does not permit the circular arrangement. While a diffuser is being filled, the steam and gases that are released are vented through pipe G, Figs. 14 and 15, to receiver R. Washed pulp is dumped through openings K to stock chest T, Fig. 14. Pipes for water, black liquor, and weak liquor are shown at W, Fig. 15. K is a dummy receiver that is used as a trap for pulp. Fig. 16 shows how the connections are made when a diffuser is blown into. The charge in digester C is blown through the pipe line A—A-—P into the diffuser D. The pressure in D is relieved 56 MANUFACTURE OF SULPHATE PULP §6 through the pipe line that carries the steam and the particles of liquor and pulp, brought away with the steam, into the receiver R. From here, the steam (which is now practically freed from solid or liquid particles) escapes through the vent pipe V, discharging into the atmosphere, into a dummy receiver K (Fig. 15), or to a condenser. The first receiver is made exactly the same as a diffuser and is handled in the same way; the second receiver, the 7 es, it RY — g yy | Tt ing i ia \ | 6 oN) ) Fig. 16. dummy, is made smaller, without any screen bottom, and is so connected that, when filled up, it can be discharged in the same manner as a digester. The pipes P and G are bound together rigidly and can swing around the joints S, and S,, making connection with diffuser D at joints 6 and g. The diffusers constituting the battery are placed respectively on the circle described when the pipe system P-G swings around the joints S,-S,; or, when as in Fig. 15, extension pipes L lead to this circle. 68. When the diffusers are arranged in a circle, a double swinging pipe system, like P-G, Fig. 16, is common. ‘This §6 THE DIFFUSER ROOM 57 arrangement makes it possible to use any one of the diffusers in the battery as a receiver. The diffuser used as a receiver in one blow is then used to blow into the next time a digester is dis- charged, without being washed in between. In this way, the arrangement of having one or two diffusers installed for the purpose of serving as receivers alone, is avoided. On the other hand, it is always necessary to have two diffusers empty before a cook can be blown and, in addition, the second diffuser will be idle from the time it has been used as a receiver until it is blown into. It also entails more work in the diffuser room, since there will be twice as many connections to make each time; sometimes Fra. 17. the swinging vent pipe is left connected with one diffuser until it is full, in the same manner as a receiver. In case separate receivers are used, there should always be two for each battery, if the diffuser room must work up to its capacity, in order that one can be washed and dumped while the other is filling up. If the diffuser is of ample size, one receiver should take care of at least ten cooks. If the receiver fills up too fast, it is advisable to reduce the blowing pressure on the digester. The liquor and water piping for a diffuser are arranged in practice in various ways. The piping for the wash water always gives the same result, whatever arrangement is used. The wash water is discharged into the diffuser at the top; and the same 58 MANUFACTURE OF SULPHATE PULP §6 arrangement is followed when high-pressure water is used for dumping the diffuser, unless a special inlet is provided, as shown at I in Fig. 13. It is not, however, immaterial how the liquor piping is arranged, and different arrangements appear to give quite different results. Fig. 17 shows three ways in which the liquor piping may be arranged. 69. In Case No. 1, the strong and weak liquor, as well as the drainage to the sewer, is taken out at the bottom of the diffuser. The strong liquor is piped to a special storage on a lower level than that of the diffuser bottom; the weak liquor is piped to ‘another tank, from which it is pumped on a fresh charge. With the outlet for the strong liquor at the bottom, no precaution is taken to keep any liquid in the diffuser, and the stock is liable to drain clear at the bottom. This might cause cracks in the pulp layer and give the water a chance to find its way through the pulp without doing the proper washing; in practice, such is found to be the case. In many instances, it proved to be nearly impossible to wash the diffuser clean, the stock around the periph- ery of the diffuser staying unwashed, even when the liquor going out at the bottom showed that hardly any chemical was left. The volume of weak liquor obtained was also very large, com- pared with that of the strong liquor; in fact, it was too large to be used for washing purposes, although the change from strong to weak liquor was made at a test as low as 4°-5°Be. Curve I in Fig. 18 illustrates a typical result, obtained when washing a 3-ton diffuser, with the outlet free at the bottom, pulp directly cooked in a stationary digester. 70. The second arrangement in Fig. 17 shows the other ex- treme, with the outlets for the strong liquor at the top of the diffuser, or even higher. In this case, the diffuser will always be standing full of liquid; the stock will be considerably diluted, and the water that rushes in at the top is likely to get mixed with the liquor at the top of the diffuser. If this happens, the effect of the washing will be somewhat similar to cleaning out a vessel, filled with some liquid, by taking out a certain volume of the soiling liquid and replacing it with water, continuing this operation until the liquid in the vessel is practically pure water. This result could be reached much faster, using far less water, by emptying the vessel completely and adding water in small amounts at a time, the vessel being emptied after each operation. Penegenat ee ee Te ee, re ee ee eT | eee $6 THE DIFFUSER ROOM 59 This latter illustration is an extreme case, of course, because the mixture of stock and liquid is rather thick and will not permit a perfect mixing; but it is true to some extent, as is shown by the rather slow drop of the test of the liquor at the end of the washing, when the pipe is thus arranged. This manner of piping the liquor is superior to the first arrangement; one advantage is that the operation valves are concentrated on one level, thus making it possible to discharge the strong diffuser-room liquor into tanks, from which it may be fed by gravity into the evaporators. 2 m_ — Duration of Washing,Hours. Washing Curves. Fig. 18. Curve II, Fig. 18, shows the result of washing by this arrange- ment in a 2.3-ton diffuser, pulp directly cooked in a rotary digester. 71. The ideal place for the drain pipe for the strong liquor is at such a height that the stock in the diffuser, when left to drain by itself, will be thick enough to prevent the liquor in the stock from mixing with the water or weak liquor that is run in from the top; at the same time, the pulp must neither pack so hard that it will offer too much resistance to the washing nor become dry enough to permit in its structure the formation of cracks and channels for the water. The height of the outlet from the bottom of the diffuser depends on the size of the diffuser as compared with its charge; but, as a rule, the best place is about the middle of the diffuser, as shown in III, Fig. 17. ; This last arrangement of the drain pipe makes it possible to blow into the diffuser, with the drain valve open, without expos- ing the bottom to too much strain and without getting the stock packed too hard at the bottom of the diffuser. The flow of 60 MANUFACTURE OF SULPHATE PULP 86 liquor from the diffuser during the blowing period is very rapid, and shortly after the diffuser is charged, all the liquor that will drain off by itself will be out. Curve III, Fig. 18, shows the result of washing a 2.6-ton diffuser, pulp directly cooked in a stationary digester, the piping being arranged as in III, Fig. 17. Note the relative time these three arrangements consume in delivering weak liquor below 8°Be. | 72. Operation of Diffusers——The usual manner of operating diffusers is to wash them in pairs; that is, when the liquor falls below a certain test, say 8°Be., instead of going to storage, it is passed from one diffuser to the top of the next one, and is there used as a primary wash as fast as itis obtained. In a battery of several diffusers, this is so managed that the first charge is blown in, say, No. 1 diffuser; the next charge is blown in No. 8 diffuser, proceeding in this manner until all the diffusers having odd numbers are filled. Then the following charge is emptied into No. 2 diffuser, the next into No. 4,andsoon. No. 1 and No. 2 diffusers (also No. 3 and No. 4, etc.) are operated in pairs, the ob- _ ject being that No. 1 diffuser shall be washed down to a test that is set as a minimum for the storage tanks by the time No. 2 is blown into. This will also be the case with No. 2 when a new charge is blowninto No.1. Assoon as No. 2 diffuser is charged and the self-draining liquor is run out, the weak liquor from No. 1 is turned on at the top of No. 2; No. 1 is then being washed with water, and this is continued until this diffuser is washed clean. By thus proceeding, the highest testing weak liquor will come in contact with the strong liquor in the fresh charge, and the dilution caused by the mixing of the two kinds of liquors, which will occur in spite of all precautions, will not be so high. As the test drops in No. 1 diffuser, the washing liquid used in No. 2 will gradually become weaker, until it is practically all water. 73. When the wash water is turned on, the diffuser becomes filled to the top, and the pressure due to the pump is then main- tained until the washing is finished. This pressure creates a more rapid flow through the stock, which keeps the stock from floating up, but, at the same time, causes it to pack harder in the diffuser and create a greater resistance to the flow of the water. An excessive pressure of the wash water might thus unduly delay | the washing. Since the call for water in the diffuser room varies considerably from time to time, it is very difficult to get a pump. $6 THE DIFFUSER ROOM 61 that will maintain the desired pressure under all conditions. To be able always to maintain the same pressure on the diffuser, it is advisable to conduct the excess water back to the tanks from which it is pumped, placing the return pipe on a level high enough to produce a natural head of water sufficient to create the desired pressure at the top of the diffuser. Favorable results of the washing, as regards time and the quantity of strong liquor, will be obtained with a water pressure of 18-20 lb. per sq. in. at the top of the diffuser, provided the outlet is placed midway of the height of the diffuser; with the overflow pipe higher up, the water pressure must be correspondingly increased. 74. As mentioned above, the resistance to the flow of water through the pulp increases toward the end of the washing. The weak liquor used for washing a fresh charge is thus obtained at a rate that is slower than the rate at which it will drain out of the next diffuser. Due to these conditions and also to the fact that No. 1 diffuser, for instance, might be weak ahead of time or not washed enough to be considered weak when No. 2 is blown into, the washing of the diffusers is often delayed considerably, when applying this system of washing in pairs. To increase the capacity of the diffuser room, the room is often equipped with special storage for weak liquor, from which weak liquor for wash- ing purpose is taken whenever wanted. There will then be no waiting; but the gradual drop in test of the liquor in the different layers of the stock in the diffuser will not be so marked as is the case when the washing is conducted in pairs. When this latter arrangement is used, the volume of weak liquor necessary for each charge is pumped into the diffuser, which is then left to drain for a while, to give the weak liquor time to settle well down and keep it from mixing with the wash water. 75. The water used for washing should preferably be hot, and sufficient hot water may be obtained by installing a condenser for the relief from the digesters. The use of hot water will increase the speed with which the stock is washed and thus give a larger capacity to the diffuser room. The use of hot water for washing means that the evaporators will have less work to do, since the liquor coming from the diffuser room will be warmer. Insulation on the liquor storage tanks will also help to keep the liquor hot for the evaporators. By having a small storage for black liquor, the heat losses due to radiation through the 62 MANUFACTURE OF SULPHATE PULP 86 tanks can be made smaller; but this will give a small margin on which to operate, and a large liquor storage is to be preferred. In order to economize heat, it is the practice in many mills to use only a small volume of hot water for washing. The hot water is then used as a continuation of the weak-liquor wash, and is usually supplied from a special tank, which is placed high enough to allow the water to flow in by gravity. After the hot water (of which only a volume corresponding to 2-3 feet of the diffuser height is used) has settled down in the stock, cold water is supplied from a pump, and the washing is completed with this. The hot water acts like a plunger, with higher washing efficiency, and prevents any lowering of the temperature of the black liquor. 76. Dumping a Diffuser—When the diffuser is washed clean, the manhole K, Figs. 13 and 14, at the bottom is opened up, high-pressure cold water is turned on at the top of the diffuser; and in case there is an inlet J, Fig. 13, at the bottom for water, this is also turned on. In this way, the principal part of the charge is dumped very quickly into the stock chest T, Fig. 14, which is situated underneath and between the diffusers. The stock that is left in the diffuser is washed out witha hose, using water under a pressure of about 50 lb. per sq. in. The entire operation of emptying the diffuser and putting on the door again should take less than 30 minutes. | The stock chest should be at least large enough to take care of one complete diffuser charge, with a consistency of stock in the chest not exceeding 2.5% bone-dry pulp. In case a fan pump is used to pump the stock, it is not advisable to figure on keeping the stock thicker than above mentioned, because trouble might then be experienced in getting the pump to throw. If a plunger pump be used, it will be possible to handle stock containing as much as 3.5% to 5% bone-dry pulp. QUESTIONS (1) Why is pulp washed? (2) Why is hot water preferred for washing pulp? (3) What is the first effluent called, and what does it contain? 2 Lif Fs 86 THE EVAPORATORS 63 - THE EVAPORATORS 77. Composition of Black Liquor.—The black liquor from the diffuser room contains practically all the chemicals that were used for the cooking and, in addition, the organic substances removed from the wood, see Art. 60, all of which are kept in solution in a considerable quantity of water. The composition of the black liquor varies for different localities and from time to time in the same locality, but the average composition at 15°Be. and 60°F. is 900 grams of water and 225 grams of solid matter, containing 60 grams Na.O, per liter of liquor; of the solids, about 50% is combustible, 1 lb. of solids having a heating value of about 6500 B.t.u. In order to regenerate the sodium com- pounds, it is necessary to remove the water and the organic matter; and it is the aim of the reclaiming process to generate sufficient heat to evaporate the water by burning the organic substances. The waste heat from the rotary furnace (described later) is, for this purpose, either utilized in a steam boiler and the steam thus generated used in multiple-effect evaporators, or else the furnace gases are led into a direct evaporator, where they come into immediate contact with the liquor to be evaporated. 78. Direct Evaporation.—The early installations for direct evaporation were very imperfect, and only a small proportion of the heat contained in the gases from the smelting furnace could be utilized. The liquor was held in a pan and the gases were passed over the surface of the liquor. The evaporation surface thus obtained was very limited. In order to increase the surface touched by the gases without using pans of very large dimensions, Dahl constructed a rather complicated and expensive steam- boiler arrangement, feeding the boiler with black liquor. This arrangement and others more or less intricate, never found general acceptance, because the problem of obtaining sufficient evaporation surface was solved by using disk evaporators. DISK EVAPORATORS 79. Description of a Disk Evaporator.—If correctly installed, the disk evaporator is easy to operate and its up-keep cost 1s low; at the same time, it is very efficient and the cost of installation is low. Fig. 19 shows two views of the rotor of one type of disk evaporator; view (0) is a section on the line XX, and shows 64 MANUFACTURE OF SULPHATE PULP LZ <7ZZA : N NE MO Vv | 4 /\ 4 | ee ee ees oo ee © que oo ees 6 en | in rm SS N V\ecemmameee | mame | (2S to Es ee ial ! TS Ly ___]| La ES A EN Cy 1 =\4 ——— Koss By SRB tesa SIE No =a iE | ES Fe) I | | 1 | a Ae ine LaREEENEEENS |p) Eras Vy fee SS | end ol (it i eee GD GNteewes | ES §6 $6 THE EVAPORATORS 65 the lower half. On a heavy steel shaft A are securely fastened 3 or 4 substantial cast-iron spiders B having 5 or 6 arms each. Between these spiders, the disk plates C are mounted and are supported by the rods D, which extend the entire length of the rotor. The disk plates are made from sheet iron that is from 3z—i inch thick; they are made in several sections, one of which is shown at (c), and each section takes in two or three sets of the rods D; the disk plates (rings) are separated from one another by spacers EZ that are made from pipe, and are 3 inches long. Since about one-sixth of the disk surface is at all times submerged in the liquor, at which time it does not come into contact with the hot gases, the surface touched by the gases (the effective evaporation surface), of 32 rings of a rotor, 8 ft. outside diameter, is about 1600 sq. ft. In some disk evaporators, every second section in the ring is omitted, in order to give the plates a spiral arrangement, which causes their surfaces to make an angle with the direction of the flue gases; this induces a slight sidewise motion in the gases, which has a tendency to make better contact between the gases and the liquor, and it also improves the reclaiming of the solid matters carried in the gases. This practice, however, practically halves the evaporation sur- face, and it necessitates an increased number of rotors. 80. The number of rotors for a disk-evaporator unit is deter- mined by the capacity of the smelter; they should provide an evaporation area large enough to cool the gases from the smelter to the desired temperature. Good results will be obtained with two disk rotors, of about 3200 sq. ft. of active evaporation sur- face, for a smelter unit having a capacity of 18-22 tons of pulp. If the smelter capacity is adequate to handle a production of 25-30 tons of pulp, a third rotor must be installed, in order properly to utilize the heat. Referring to Fig. 19, the gases pass between the plates in a direction at right angles to the shaft A. As shown in view (a), the bottom K and the roof R of the evaporator are shaped to conform to the rotor. 81. The rotors may be installed in a concrete pan, which should preferably be lined with sheet iron up to the level of the liquor, to prevent leakage through cracks in the cement work, which are hard to avoid. The bottom K of this pan is made dish-shaped, so as to afford a clearance between it and the rotors of not more than 2 inches, in order to make the volume of the liquor carried 66 MANUFACTURE OF SULPHATE PULP §6- in the machine as small as possible at any one time. The roof R is shaped similarly, in order to keep the gases in contact with the plates C. The raised part L of the bottom is made a little lower at its highest point than the liquor level, so the liquor may wash away any solid matter that falls on it. To permit all the liquor in the pan to drain through a single opening, in case it is necessary to entirely empty the pan, a canal that is level with the lowest part of the pan bottom and is about 8 inches wide is left on one side of the machine. The rotors are driven by heavy gearing G on the outside of the pan; they should be run fast enough to keep the liquor from getting dry and burning on the disk plates. If the speed of the rotor be too high, it will cause splashing and foaming of the liquor in the pan, which will make the machine less efficient and may cause loss of chemicals; 10-12 r.p.m. is the standard speed for rotors. The rotor that is closest to the incinerator, where the liquor is heaviest and the gases are hottest, might be driven a little faster than the others, so the liquor will not burn on the disk plates, and to make them last longer. 82. The liquor is fed to the back of the disk evaporator, behind the last rotor; its density should be high enough to provide enough black ash to generate sufficient heat (when burned in the furnace) for any further evaporation that may be necessary. Liquor testing 17°-19°Be. at 60°F. will usually be satisfactory in this respect. This density is easily attained in multiple-effect evaporators, described later. Should the liquor get weaker than is required to give good black ash, additional heat must be sup- plied by means of a wood or coal fire. If wood be used, it can be fired in smelters direct; this cannot be done with coal, since the impurities in the coal ashes will cause an inferior grade of smelt, which will result, later, in a white liquor that gives trouble in settling. Consequently, it is necessary to burn the coal on a special grate, where the ashes will not enter the smelter. Should the test of the black liquor be persistently less than 16°Be., it will not pay to make all the necessary evaporation in the disks; better economy is then effected by bringing the liquor up to the desired density in a multiple-effect, indirect evaporator (see Art. 89); too weak a liquor cannot be favorably handled in disk evaporators. The liquor then has to stay so long in the disk that the accumulated chemicals caught from the furnace gases makes the liquor gritty, and spoils it for making - §6 THE EVAPORATORS 67 black ash. It is for this same reason that the liquor pan for the disk rotor is made dish-shaped and the volume of the liquor is kept as small as possible. The liquor leaving the disk evaporator should test 26° — 32°Be. at the existing temperature, which corresponds to 32°-38°Be. at 60°F. The test to which it is necessary to bring the liquor will vary with the composition of the black liquor and with the length of the rotary furnace in which the evaporation is completed. 83. The outlet O, Fig. 19, for the black liquor is at the front end of the disk evaporator, either in the bottom or in the side. In either case, it should be so arranged that the level of the liquor cannot get lower than that at which the disk plate inserted in the liquor will be totally submerged. To carry a higher level of liquor in the disk evaporator is not advisable, since it will decrease the active area of the disks and will also make the quantity of liquor greater than necessary. In the bottom of the disk pan is another outlet M7, which makes it possible to empty the machine completely. Hot gases from the burning black ash in the rotary or smelting furnace enter the evaporator through the opening JN. 84. If the disk evaporator is placed high enough to permit the liquor to flow into the rotary furnace by gravity, it may not be necessary to screen the liquor; but if a pump is used to transfer the liquor from the evaporator to the furnace, it is advisable to have a screen box between the evaporator and the pump, for the purpose of catching the larger solids that are formed in the evaporator. A screen plate with 34-inch perforations will serve nicely for this. Whenever possible, the liquor should flow by gravity to the rotary from the disk evaporator. This saves the power required to drive the pump and the cost of its up keep. 85. When a body of air or gas is heated, it expands; its specific weight (density) decreases; the result is that the body of air (or gas) rises in the heavier air (or gas) surrounding it, just as a piece of light wood rises in water; the colder air (or gas) then flows in to take the place vacated by the lighter air (or gas); the current of cold air (or gas) thus created is called a draft. The - phenomenon just described is the cause of winds, chimney drafts, etc. When the draft is produced solely by the action of 68 MANUFACTURE OF SULPHATE PULP §6 heat, as in the above case, the draft is called a natural draft. If, however, the air is moved by mechanical means, as by an exhaust fan or a blowing fan, the draft that is created is called a mechanical draft. 3 When natural draft is employed to move the gases through the - evaporator, the utilization of heat generated by burning. the black ash is limited to raising the gases to a temperature sufficient to create a draft necessary to carry them away; and this tem- perature can be made lower by increasing the height of the stack. But, even with an exceedingly high stack, or if a fan be used to create the draft, it is not advisable to let the temperature of the gases escaping go below 200°-210°F., as there is then danger that the steam will condense to water on the last rotor instead of the water evaporating. If it be found necessary to let the gases leave the disk evaporator at a temperature higher than 250°— 275°F., it will probably be economical to use mechanical draft and increase the evaporation surface of the disk evaporator, so the temperature of the escaping gases will be about 210°F. 86. Another Type of Disk Evaporator.—In Fig. 23 is shown a disk evaporator A of a different type from that just described. Here the disk plates are placed at right angles to the direction of the flow of gases, the plates being so arranged that the gases are forced to take a tortuous zig-zag course through the machine. This produces more thorough agitation of the gases, and the contact between the gases and the liquid is more intimate; also, the solid particles that are carried by the gases (which are heavier and do not so easily change their direction as the gases) are more likely to get caught by the liquor on the disks. The great resistance offered by this evaporator to the movement of the gases necessitates the use of mechanical draft. It is claimed that the greater efficiency that is obtained by this arrangement is offset by the cost of operating the fan to produce the draft. 87. Use of Steam Boiler with High-Pressure Evaporator.— In the Scandanavian countries, the most modern sulphate mills have adopted a steam boiler to take care of the waste heat from the rotary furnace. The steam generated in the boiler is used in a high pressure evaporator for concentrating the liquor, and the vapors from the last effect of the evaporator are condensed in the cylinders of a drying machine. In this way, it 1s possible not only to evaporate all the water in the liquor but also to dry §6 THE EVAPORATORS 69 all the finished product without furnishing any fuel other than that found in the black liquor. Any type of steam boiler may be used for this purpose; but it must be so installed as to be easily cleaned, since a dust of chemicals accumulates rapidly and must be blown off the tubes frequently. The rating of the boiler is rather low and the first cost is heavy, but the economy resulting from the operation of this installation justifies the expense. American operators seem to favor the use of the heat in the gases from the rotary for evaporating liquor by passing them through a disk evaporator, which also reclaims as much as possible of the sublimed chemicals in the gases. If any heat is left, the gases may then be passed through an economizer, which is a device for heating water by means of hot gases before they enter the stack. 88. It is only in the most up-to-date mills, where every pre- caution has been taken to minimize the volume of black liquor obtained from the diffuser room, that it is possible to perform all the necessary evaporation with the heat that is obtained through burning the organic substances in the black liquor. Before passing the liquor to the disk evaporators, the excess water is usually removed in a multiple-effect, indirect evaporator. Steam is furnished in the first effect as a source of heat, but in the other effects, the vapors from a previous effect serve the same purpose; the vapors from the last effect are condensed, by some means, outside the machine. In order to utilize as much as possible of the heat supplied to the apparatus, and to maintain it at a large capacity, two or more effects of the apparatus work under vacuum, that is, the pressure is below that of the atmosphere. 89. Principle Governing Multiple-Effect Evaporators.—To analyze intelligently the work of this type of evaporator, certain physical laws applying to evaporation must be taken into account. The quantity of heat that is conducted from steam through a metal sheet to a boiling liquid is: (1) directly propor- tional to the area of the sheet; (2) directly proportional to the time; (3) directly proportional to the difference in temperature between the two sides of the sheet; (4) inversely proportional to the thickness of the sheet. (See Transmission of Heat in Section on Physics.) The only other factor that can affect the conduc- tion of heat is the material of which the sheet is made. Iron tubes are the only material used, but if steel should be employed, 70 MANUFACTURE OF SULPHATE PULP $6 the difference in heat conductivity between iron and steel is too small to be considered here. Variation in the thickness of a tube, within certain small limits, has also but slight influence on the capacity of the machine. | As pointed out in Physics, the temperature of the vapors over a boiling liquid that is contained in a closed vessel is always the same for the same liquid and the same pressure; also, if the temperature (or pressure) is increased, the pressure (or tempera- ture) is likewise increased. In other words, there is a definite temperature for every pressure, and a definite pressure for every temperature, for any particular liquid. The boiling point of black liquor is higher than that of pure water, and the difference increases as the density of the black liquor increases. Whatever the liquid, the temperature of boiling decreases as the pressure decreases. When steam (or other vapor) condenses, heat is given up (latent heat of vaporization) and becomes available as heat energy; it may be called the heat of condensation. In the case of an evaporator, the heat of condensation is transmitted through the walls of the tube containing the condensate (condensed steam) and is absorbed by the liquor that surrounds it. The temperature of the liquor is raised, and the object is to heat this liquor sufficiently to start it to boiling. Suppose a single-effect evaporator were used for this purpose, and suppose. further that the efficiency of the machine were 100%; then all the heat energy by the condensation of the steam would be absorbed by the liquor. A part of this heat raises the liquor to the temperature of boiling at the existing pressure (if the liquor is not already at that tem- perature), and the remainder supplies the heat necessary to convert the liquid into a vapor (the latent heat of vaporization). Ordinarily, the vapor escapes from the machine, and all the heat contained in it is thus lost. To save the heat in the vapor that escapes from this one effect, it is condensed in another effect, where it takes the place of live steam; and this may be repeated again and again, according to the number of effects. 90. A general layout, in elevation, of a quadruple-effect, vertical-tube evaporator is given in Fig. 20, and a vertical and a horizontal section of one of the effects or units is given in Fig. 21; the same reference letters are used for the corresponding parts in both illustrations. Each effect (unit) consists of a bottom chamber A, a tubular heating-unit chamber B, and a vapor- $6 THE EVAPORATORS 7a separation chamber C. Here the heating unit is a nest of tubes D (2 inches external diameter) for the up-flowing liquor, and a certain number of larger tubes D’ (4 inches external diameter), which act as down-flowing or circulating tubes. All these tubes are expanded into the upper and lower flat tube sheets #, and steam or other vapor is confined to the space around the tubes. The foam is kept just above the top tube sheet H. Since there . is a large area in a small tube in proportion to the volume of liquor it contains, the liquor in the small tubes boils first, and the vapor rises and escapes into the vapor chamber C, where it partly condenses, the condensate passing down the larger tubes D’. == ), hea] = —fLIN pet eet Ape) Sa saa Za \ LIEN IEO-«SOAN Tike Fig. 20. For foaming liquors, as in pulp mills, a high vapor space is essen- tial, to avoid entrainment of the liquor particles, which would be carried away in the steam; any such liquor leaving the space C in the steam is caught in the save-all S, Fig. 20, and is returned to the evaporator. The steam from the first effect Ff; passes through vapor pipe G, to the heating unit B of the second effect F2, entering at H; the steam generated in F’2 goes through G2 to the tube chamber of the third effect F3; etc. Live steam is fed into the first heating unit F, at H, while the steam from the last effect is condensed in some form of condenser K. A vacuum pump MM is usually required to remove gases that will not condense and which are mixed with the vapor (steam). These gases may also be removed from the steam space by connecting the air-relief cock N, Fig. 21, to the vacuum pump. The condensation from heating steam that occurs in the chamber B passes out through OQ, and is conducted to the drain or to the boiler, provided there is no vacuum in B; otherwise, this tailwater goes to the vacuum pump, M, Fig. 20. Unless fed by gravity from storage, a black-liquor feed pump P 72 MANUFACTURE OF SULPHATE PULP $6 ee | i ‘ ’ & supplies weak liquor to the first effect F; through pipe LZ, and valve V;. Pipes Le, L3, and La connect the other effects, and pipe L; takes the concentrated liquor to the storage tank for the disk evaporator. 91. Operation of a Quad- ruple-Effect Evaporator.—It is customary in pulp mills to sup- ply a quadruple-effect evaporator with steam at, say, 40 lb. per sq. in. for the first effect and to have a vacuum of 26 inches for the last effect. The temperature of steam at 40 lb., gauge, is 287°F. and at 26 in. vacuum, it is 127°F.; the temperature range is thus 287 — 127 = 160°F. To secure the best results, this range of temperature should be divided as equally as possible in each effect; that is, the differ- ence between the temperature outside the tubes in chamber B and the temperature inside the tubes should be, in this case, 160 + 4 = 40°F. Thus, the temperature outside the tubes in the first effect Fi is 287°F. and that inside the tubes should be 287 — 40 = 247°F.; these tem- peratures correspond to gauge pressures of 40 Ib. and 14 lb., re- spectively. In the second effect, F., the temperature outside the tubes will be the same as that inside the tubes of the first effect, or 247°F., and that inside the tubes should be 247 — 40 = 207°, which corresponds to a $6 THE EVAPORATORS 73 vacuum of 3in. In the third effect, ’; the temperature outside the tubes will be the same as that inside the tubes of the second effect, or 207°F., and that inside the tubes should be 207 — 40 = 167°F., which corresponds toa vacuum of about 184in. Inthe fourth (last) effect F4, the temperature outside the tubes is the same as that inside the tubes of the third effect, or 167°F., and that inside the tubes is 167 — 40 = 127°F., which corresponds to a vacuum of 26 in. Of course, were the initial pressure of the steam supplied to the first effect higher or lower than 40 lb. per sq. in. or the vacuum lower or higher than 26 in., the above working conditions would be varied accordingly. The object is to maintain a regular temperature difference throughout each effect, in order to obtain the proper amount of evaporation from each effect, as well as proper fuel economy. Under the conditions just mentioned, the liquor moves through a quadruple-effect evaporator as follows: The weak liquor is delivered to the first effect F, through inlet valve Vi, usually by a centrifugal pump. The progressive movement of the liquor from one effect to the next is effected by the difference in the boiling pressure in each machine, which makes it unnecessary to pump from one to the next. Thus, as mentioned above, the liquor inside the tubes of the first effect boils at a pressure of about 14 lb. gauge = about 14 + 15 = 29 lb. abs., and the liquor in the second effect boils at about 3 in. vacuum = about 13.5 lb. abs. Consequently, this difference in pressure, 29 — 13.5 = 15.5 lb. transmits the liquor from the first to the second effect, and it is transmitted from the second to the third and from the third to the fourth effects in a similar manner. The liquor becomes more concentrated as it leaves each effect; and when it leaves the last effect in its finally concentrated form, it is delivered to a storage tank, from which it is fed to the disk evaporators or to the rotary incinerators. The water condensed from steam in the first effect is con- ducted to the boiler supply or diffuser hot-water tank; from the second effect, directly or through the vacuum pump, to the drain; from third and fourth effects, also to the drain. The first condensate is pure water; the others are contaminated by liquids and gases derived from the wood. At the bottom and side of each effect is a manhole 7, to afford access to the tube sheet H, for cleaning and replacing tubes. 74 MANUFACTURE OF SULPHATE PULP $6 However, the rapid circulation of liquor makes cleaning hardly necessary, beyond an occasional boiling out with water, except under conditions which permit a hard scale to form (see Art. 94). 92. In Fig. 22, is shown a partial vertical section and partial elevation of an evaporator having horizontal tubes. In this + ¥ + +++ “tiGindencahin Outta t aeaee Concentraled Liquor lonext effect ELEVATION. ELEVATIONwih fron! PLATE removed. Fie. 22. apparatus, the steam is inside and the liquor is outside the tubes. The courses of the vapors and the liquor are essentially the same as for the vertical type shown in Figs. 20 and 21, and the letters are the same for corresponding parts in all three figures. 93. Above the liquor side, Fig. 20, of the first effect, is a vapor space C' that is directly connected to the steam space of the second $6 THE EVAPORATORS 75 effect; and if the connections between the two parts are sufti- ciently large, practically the same conditions as to temperature and pressure will prevail in both places. Hence, the condensa- tion of the vapors in the steam chamber of the second effect takes place at nearly the same temperature as does the evaporation of the liquor in the first effect, and the condensed water that leaves the second effect will be of the same temperature as the boiling liquor in the second effect. Provided there is no loss of heat in the vapors on their way between the two parts of the space, all the heat that is carried away in the vapors from the first effect will be absorbed by the liquor in the second effect. Since the heat given up by condensation is the principal part (propor- tion) of the heat of the steam furnished in the first effect, the result is that the quantity of water evaporated in a double- effect evaporator is nearly twice as great as that obtained from the same quantity of steam in a single-effect evaporator. Applying the same reasoning to a triple-effect. evaporator, the work done by the steam ought to be about 3 times that done in a single-effect evaporator, and the work done by the steam in a quadruple-effect evaporator ought to be nearly 4 times that done in a single-efiect evaporator; by work is here meant the amount of water evaporated. Results obtained from multiple-effect evaporators confirm this reasoning. According to Kirchner in “Das Papier,” 1 lb. of steam evaporated 0.95 lb. of water in a single-effect evaporator, and it evaporated 1.90 lb. and 2.85 lb. in double- and triple-effect machines, respectively. 94. High-Pressure Evaporators.—The capacity of an evapora- tor depends upon the temperature difference between the several effects, and the greater this difference the greater is the capacity of the machine. When the pressure in the tubes of the last effect is above that of the atmosphere, it is necessary to start with an initial temperature of the steam corresponding to a high pressure, in order that the machine may have great capacity and that its dimensions may not be too large. While this necessitates ‘very strong construction, which increases the first cost of the installation considerably, high-pressure evaporators have, never- theless, been favored in some mills, because it is then easy to take care of the heat contained in the vapors from the last effect. Delivered under a pressure of from 15-20 lb. per sq. in., these vapors are used on the dryers of a pulp or paper machine. Sev- eral mills equipped with this type of evaporator are able to dry 76 MANUFACTURE OF SULPHATE PULP §6 their total output of pulp up to 100% air-dry without furnishing any extra steam. High-pressure evaporation makes unnec- essary the cost of operating the machinery required to remove the condensate and to maintain the vacuum in the low-pressure evapo- rator. Considerable trouble, however, is experienced in operat- ing this type of evaporator on black liquor from the sulphate process. On account of the high temperature, especially in the first effect, a precipitation of the insoluble silicates of aluminum and calcium, which come from the smelter, takes place on the tubes. The scale that is thus formed is very hard to remove; in some instances, it has proved necessary to install a spare first effect, to give time for cleaning. 95. Advantages of Low-Pressure Evaporator.—As previously stated, the main source of heat for indirect evaporation is the latent heat given up when the steam condenses. This heat is nearly the same per pound of steam at whatever temperature (pressure) the steam condenses. By maintaining as high a vacuum as possible in the last effect, a big drop of temperature can be obtained within the machine and still make it possible to start in the first effect with a temperature of steam that corresponds to a rather low pressure (Art. 91). Thus the initial steam pressure for the evaporator system can be considerably less than ordinary boiler pressure. By employing a low-pressure vacuum evaporator, and reducing the steam from boiler pressure to the desired initial evaporator pressure in a steam-driven power generator (engine or turbine), it is thus possible to generate a considerable quantity of mechanical energy and still have heat for the evaporator. The power generator will then be operated very cheaply, since it takes only a little more fuel to raise the steam to ordinary boiler pressure, once it is steam, and there is use for low-pressure exhaust steam in the evaporator. Scale forming on the tubes of a low-pressure evaporator seldom occurs, because the temperature of the liquor is never high enough to precipitate the insoluble silicates. The first cost of a low- pressure system is less than that of a high-pressure system, as the construction can be made much lighter and, therefore, cheaper; but the cost of, and the expense of, operating the auxiliary pumps and condensers is considerable. Considerable mechanical work must be performed in maintain- ing the vacuum in, and removing the condensate from, the effects that work under vacuum. The weakest feature of the vacuum $6 THE EVAPORATORS 77 evaporator is the loss of heat in the vapors escaping from the last effect. Due to the low quality and low pressure of this steam, it, is very difficult to utilize the heat it contains; in ordinary practice, this steam is allowed to go to waste in a spray condenser or in a vacuum pump. In the end, a low-pressure system is more expensive than a high-pressure one. In spite of the greater expense involved in a low-pressure evaporator, this type is, as yet, the one preferred in the sulphate- pulp industry. In order to maintain the greatest possible capacity and secure the greatest economy in the operation of the system, the highest obtainable vacuum must be maintained on the liquor side of the last effect. 96. Pumps Required.—T'wo types of pumps are used to create the vacuum in the evaporator, and both are about equally satisfactory. In one type, the wet vacuum pump, the water that is needed to condense the vapors from the last effect and to cool the condensate to a temperature at which the best possible vac- uum is obtained, is taken in at the pump itself. In the other type, the dry vacuum pump, only the non-condensable gases are handled; the pump is supplementary to a condenser, usually a spray condenser, where the steam is condensed. The water is then removed from the condenser by a special pump, unless the condenser be, preferably, of the barometric type and is placed high enough (34 feet or more) to permit the water to run out of the condenser by gravity. 97. Operation of Indirect Evaporators.—Indirect evaporators are usually operated according to the direct-flow system, that is, the vapors and the liquor follow the same path through the machine. This method of operation makes it possible to let the liquor flow by itself from effect to effect, and it is necessary only to pump the liquor into the first effect and out of the last effect; the result of this is that the heaviest liquor, that having the highest boiling point, is heated by vapor of the lowest tempera- ture. However, the direct flow is much more convenient in operating the machine, and it is, for that reason, the way of running most favored. The counterflow system, where the weakest liquor is charged on the last effect and is brought by pumps from one effect to another opposite to the flow of the vapors, has never been suc- cessfully operated on black liquor, because of the foaming that 78 MANUFACTURE OF SULPHATE PULP $6 occurs when the weak liquor is let in under the high vacuum of the last effect. A more feasible method would be the mixed-flow system in which the weak liquor would be charged on the second effect; it would then flow through the following effects, and the rather heavy liquor in the last effect would be pumped into the steam~- heated first effect, where the evaporation would be completed to the desired consistency. In mills where all the evaporation is done in indirect evaporators before discharging to the rotary furnace, the liquor will have a very high consistency in the last effect at the temperature prevailing in it, and it will offer a heavy resistance to the escaping vapors. This condition will certainly be improved by having the final evaporation occur in the first effect, since the higher temperature therein will make the liquor thinner, although its concentration will be the same as before. 98. Types of Evaporators.—The different makes of evaporators may all be arranged into two principal types: horizontal-tube evaporators, and vertical-tube evaporators. In the horizontal-tube evaporator, the liquor may be outside and the steam inside the tubes, or the liquor may be inside and the steam outside the tubes. In the former, the length of the tubes has nothing to do with the height of the liquor layer; this makes it possible to get a comparatively large evaporation area and still keep the level of the liquor layer low. ‘This is an advantage, since a shallow liquor layer offers less resistance to the escaping steam bubbles. It is to be noted that the horizontal tubes are harder to clean from scale or deposits of pulp that may occur on the tubes. The vertical-tube evaporator usually holds a greater depth of liquor than the horizontal-tube type; consequently, the steam bubbles formed at the lower end of the tubes meet greater re- sistance when escaping. The liquor is here admitted to the inside of the tubes, and any deposits on the surface of the tubes are more easily removed. It is usually easier to re-tube a horizontal machine than a vertical one. The thin-film evaporators constitute still another type of indirect multiple-effect evaporator. By forcing a small stream of liquor into the hot tubes, it boils immediately, and the whole machine is filled with foam that passes rapidly through the tubes. Entrainment (carrying over) of liquid particles in the eT §6 THE FURNACE ROOM fy ‘steam, to which this type is particularly liable, is prevented by special catch-alls. The main feature of this type of evaporator, which may have either horizontal or vertical tubes, is the speed with which the machine can be started or shut down, the time for the liquor to go through the whole machine being only a few -minutes, and comparatively little liquor being present at any one instant. This type of evaporator will soon get dirty inside the tubes; but it is easily cleaned, and very quickly, by running water through them instead of liquor. An evaporator of this type is described in greater detail in the Section on Soda Pulp. QUESTIONS (1) Explain the principle of the disk evaporator. (2) What should be the concentration of the black liquor fed to the disk evaporator? (3) Why is evaporation necessary? (4) Trace the course of the black liquor, both as liquid and vapor, through a quadruple-effect evaporator. (5 What are the advantages of the high-pressure evaporator as com- pared with the low-pressure evaporator? (6) What is meant by entrainment, and how is it avoided? THE FURNACE ROOM THE ROTARY FURNACE 99. Outline of Process for Treating Black Liquor.—When the black liquor leaves the evaporators (whatever the type), it still contains a considerable quantity of water, the removal of which was originally a difficult and laborious task, because of the trouble offered to handling the tough, sticky mass that is formed by black liquor of high density. By adopting the rotary furnace B, Fig. 28, for this final evaporation, a better black ash is obtained and the labor cost is reduced considerably. The lumps of dry, or nearly dry, black liquor (black ash) that are delivered from the rotary furnace contain the main portion of the organic substances from the wood and the inorganic salts, more or less changed, from the white liquor. This black ash is mixed with the necessary quantity of salt cake, NasSOu, and is burned in the smelting furnace C, Fig. 23. The combus- 809 MANUFACTURE OF SULPHATE PULP 86 tion gases from the smelting furnace are led through the rotary Be where a part of their heat is used for the final evaporation. In the smelter, the combustible part of the black ash is burned out and the chemicals smelted (melted), the resulting smelt being let out continuously through the bottom. The carbon acts as a reducing agent, and the salt cake is mostly converted into sodium sulphide; thus, NaesO, -++- 2G Nas -+- 2CO,z The escaping smelt, which is now free from carbon and organic matter, is led over a spout into the dissolving tank M, from which the resulting solution, the green liquor, at a certain con- centration, is pumped to the causticizing tank in the liquor room. 100. The Rotary Furnace.—The rotary furnace B, Fig. 23, 1s formed of a riveted sheet-iron cylinder, or shell, of very strong construction. The cylinder is open at both ends; the opening in the front end of the rotary is 3 feet less in diameter than the diameter of the cylinder, and in the back end it is 4 feet less. The cylinder itself is made in various lengths and diameters, some manufacturers preferring a longer rotary, which makes it possible to secure a little greater evaporation in the rotary and deliver the gases somewhat cooler to the disk evaporator, if there be one. Rotarys up to 30 feet in length are used in sulphate mills for making black ash, though ordinarily the length is between 20 feet and 24 feet; the diameter is seldom less than 8 feet, 9 feet to 10 feet being the common size. 101. Description of Rotary Furnace.—Referring to Fig. 23, the inside of the rotary B is lined with brick, to protect the shell from the action of the hot, burning gases and from the chemicals, in case the ash should get on fire and smelt. The lining is generally 8 inches thick and is cylindrical, like the shell. It is advisable to make the entire lining of firebrick, or, at least, for one-half the length of the shell next to the smelting furnace, the temperature there being very high. On the outside of the rotary are attached two heavy steel tires T’, placed about one-fourth the length of the shell from either end. These tires rest on strong cast-steel truck wheels D, two for each tire. The wheels have flanges, the distance between the inside edges of which is about 14 inch greater than the width of the tires; they keep the rotary from sliding, but allow a little play, horizontally. In some cases, instead of flanged wheels, the Se ee eae ee ee ee ee $6 THE FURNACE ROOM 81 wheels are blank, and guide wheels are placed on either side of one of the tires. The rotary is caused to revolve by connecting two of the supporting wheels one on each tire, by a shaft, and then driving this shaft; the friction between the tires and the driving-supporting wheels causes the rotary to turn. Or, as shown in Fig. 23, a big gear # surrounds the rotary and is securely fastened to the shell; this gear should have plenty of air space, to avoid being heated excessively, and is made in sections, which can easily be removed. Gear H is driven by the pinion gear G. Red Brick Plane}: Red Bnich(LevationiZ Fia. 23. Of the two methods of driving the rotary, the first (which is not so common as the other) is the cheaper and is just as satisfactory. To reverse the motion of the rotary, which is desirable in the case of a double furnace (one made with two fire boxes), two loose pulleys and a fixed pulley between them are placed on the shaft of pinion G; two belts are used—one open and one crossed—both driven by the same pulley, which has a width of face equal to the combined width of all three pulleys on the shaft of pinion G. When the open belt is on the middle, or fixed, pulley, the rotary turns one way, and it turns in the opposite direction when the crossed belt is on the middle pulley. The same result can be obtained more cheaply and more conveniently, when an indi- vidual motor is used to drive the shaft instead of the pulleys and 82 MANUFACTURE OF SULPHATE PULP $6 belts, by reversing the direction of the motor. Since an acci- dental stoppage of the rotary and also of the disk evaporators might prove fatal to their durability, they are sometimes driven by a steam engine, to guard against such accidents. It is desirable that the rotary be placed high enough over the floor from which the smelting furnace is fired to give ample room for the discharged black ash. To avoid exposing the front sup- porting wheels to the hot ashes, their bearings should be protected by a retaining wall. 102. Although the purpose of the rotary furnace is to com- plete the evaporation of the black liquor, it fulfills another pur- pose of equal importance. Because of the manner of firing the black ash in the smelter, the gases that leave this furnace are rich in combustibles. When they leave the smelter, these gases are far above the ignition temperature, and the addition of air will make them burn with a long and hot flame. To operate most economically, the volume of air admitted to and mixed with these gases (secondary air) must be determined in the same manner as in every other case of combustion. The air could be supplied in the smelting furnace itself, above the burning ashes, in a manner similar to that in which secondary air is added in a Dutch oven; but, on account of the high temperature that is reached, this would have a tendency to shorten the life of the furnace and to increase the cost of upkeep. In the rotary fur- nace, there is always a cover of black liquor and ash to protect the lining; this lessens the danger for overheating the brickwork, and makes it more profitable to admit in front of the rotary the air needed to complete the combustion. Air leaks in at the front end of the rotary and also in the back end, but this is hard to avoid. The temperature of the gases leaving the rotary, especially if the furnace is very long, might not be high enough to permit further combustion (even if there are any combustibles left), for which reason, the air leaks at the back end should be kept at a minimum. At the front end, where the ashes are discharged, baffles should be so arranged as to allow the admis- sion of only just the volume of air that will give the final most advantageous results. Consequently, it is necessary not only to control the rate of combustion but also to check up the tempera- 1 A device is now on the market that very efficiently closes these sources of waste, and makes it possible to maintain a high per cent of CO: in the gases. ae a or $6 THE FURNACE ROOM 83 ture of the gases after they leave the apparatus, with a view to utilizing their heat. The average installation will probably show the best results when the flu2 gases show no carbon monoxide CO or hydrogen and contain 11%-14% carbon dioxide CO>. To obtain these results, it is essential that a certain definite draft be maintained in the back end of the rotary; a poor draft will most radically diminish the efficiency of the furnace installation, considering both heat economy and capacity. Too much draft will injuriously affect the output of the furnace unit, especially of the disk evaporator. A draft of 1 inch of water at the back end of the rotary, measured on the level of this furnace, will give best results, as a rule. 103. Density of Black Liquor.—The black liquor, which is fed into the rotary at the back and, preferably, through a jacketed and water-cooled pipe O, Fig. 23, should be of high enough density to make good black ash without requiring any extra fuel in the smelter. Ordinarily, black liquor in the kraft-pulp mill, testing 28°-32°Be., hot, corresponding to 31°-35°Be. at 60°F., will prove satisfactory; but, in case the black liquor carries a large amount of inorganic matter, the test must be carried higher. Poor black liquor will never give satisfactory results; and it not only necessitates extra fuel for the fire in the smelter, which is bad economy even under the best conditions, but it also causes the rotary to ring up (become coated) inside with black ash, which might finally make it impossible to make any progress whatever. The resulting black ash is also very poor,—light and dusty,—which makes it troublesome to burn in the smelting furnace; it also causes unduly large losses of chemicals, which are carried away with the gases and through the flues. The best black ash looks still a little moist, and it comes out in rather heavy lumps or porous masses, which burn well in the smelter. When burned, such black ash will give out 4000-5000 B.t.u. per pound. The speed at which the rotary revolves influences the appearance of the black ash; too fast a speed will usually produce a finer ash. For a 10-foot diameter rotary, one revolution every 50-60 seconds will be satisfactory. 104. Chemical Changes.—Certain changes in the constitution of the chemicals, which started in the disk evaporator (if there is one), occur in the rotary furnace. The carbon dioxide in the gases of combustion combines with the free sodium hydrate in the 84 MANUFACTURE OF SULPHATE PULP §6 black liquor, and also engages sodium combined with the weaker acids. The organic ingredients are melted, and a destructive distillation of them is partly started, the volatile carbohydrates that result taking fire immediately. Distillation should be avoided, in order to maintain a reducing atmosphere in the smelter. 105. Adding Salt Cake.—The salt cake Na2SO, that is used to make up the losses of chemicals during circulation, is mixed ordinarily with the black ash, or it can be added to the liquor before it is charged to the rotary. It would seem as though the latter practice possesses several advantages; and the perfect mixture that will be obtained in this manner ought to bring about a better reduction of the sulphate and, in addition, elimi- nate the losses of salt cake that are due to dusting. About 350 Ib. of salt cake per ton of pulp must be added to make up for losses in the process. The usual practice is to mix the salt cake with the black ash from the rotary while the ash is being shoveled into the smelter. By keeping daily records of the analyses and stocks of the liquor, it will be at once manifest whether the proper amount of salt cake (or niter cake) is being used. A certain fixed quantity of salt cake is fed per hour to each smelter as uniformly as possible, carefully mixed with the black ash; the weight of salt cake is then varied as may be deemed necessary, according to the quantity of liquor on hand. Any deficiency of the liquor stocks should rapidly be made up for by adding more salt cake than usually; an investigation should also be started, to determine the cause of the undue losses of chemicals. 106. Niter Cake.—It has recently been proposed to substitute niter cake for salt cake in replacing the losses of chemicals. Niter cake (sodium bisulphate) is a product in the manufacture of nitric acid, where Chili saltpeter, sodium nitrate NaNO; is treated with sulphuric acid H,SQu, to obtain nitric acid HNO3. In addition to the nitric acid, a product called niter cake is obtained, which has a formula closely corresponding to NaHSO,; NaNO; + H:SO, = NaHSO, + HNO;. The excess sulphuric acid can be driven off by heat and salt cake obtained, in accord- ance with equation (1), or it may be neutralized by sodium hydrate, in accordance with equation (2); thus, 2NaHSO, + heat = SO; + H.O + NaSO. . (1) NaHSO, + NaOH = NaSO, + H2O (2) -— Te ee a ee ee ee Be eg a ee ee ee ee ee a eS ee §6 THE FURNACE ROOM 85 The result of the two reactions is the same insofar as the alkali is concerned; but the first reaction gives sulphuric anhydride, which readily forms sulphuric acid, and the acid may damage machinery and vitiate the air. The acid may react with any sodium compound forming sulphate; thus NaCO; + H2SO. =Na.SO,+H20+CO.2. If such reaction occur with a sulphide, hydrogen sulphide, HS, a poisonous gas, is set free; thus, Naes -4- H.SO, = NaesO.+ Hes Niter cake should never be added to the smelt dissolving in the causticizing tanks. There have been at least two instances where men were killed when niter cake was used, presumably by hydrogen sulphide. 107. In the sulphate-pulp mills, where the losses of chemicals are low, the percentage of sulphides in the regenerated liquor will be correspondingly small, since a large portion of the sulphur is lost in the process and new sulphide can be formed only from the sulphate at hand in the smelting furnace. It is desirable to main- tain a high percentage of sulphide in the white liquor for several reasons: the product of the cooking will be of better quality, the yield of the wood will be larger, and the quantity of lime used per ton of pulp manufactured will be smaller, if the white liquor contain a larger proportion of sodium sulphide as compared with the sodium hydrate. By substituting niter cake for salt cake, the result will be the same as though nearly double the quantity of salt cake had been used, as concerns the possibilities of obtaining sulphide in the liquor; but, at the same time, the quantity of fresh sodium that is given to the liquor is Just suffi- cient to maintain the liquor stock. To make the use of niter cake possible, it is added to the black liquor as it enters the rotary or immediately before. The niter cake, which usually comes into the market in big blocks, is crushed in a stone crusher into rather small lumps; these are fed into the rotary, where a rapid reaction takes place, with the formation of carbon dioxide and also small quantities of hydrogen sulphide H.S. There is likewise some water formed in the reaction, which has to be allowed for by using a correspondingly higher concentration of the black liquor. The volume of gases formed is comparatively small, and it will scarcely affect the heat economy of the installation. This process is patented; it has not as yet been operated for any length of time, and it is 86 MANUFACTURE OF SULPHATE PULP §6 hard to say whether the results will be satisfactory. However, it appears to be feasible. The furnace room should be well ventilated, particularly, if niter cake is used. 108. Composition of Black Ash.—The black ash that is dis- charged from the rotary furnace contains the inorganic chemicals from the cooking, more or less changed in their constitution, and also the organic matter derived from the wood, but is practically free from water. The composition of the black ash is dependent on so many factors and varies so much with the conditions, that it is hard to give an average analysis; but good black ash should contain about 50% combustible matter. If not already mixed with the necessary quantity of salt cake, this is now added to the black ash, and the mixture is shoveled into the smelting furnace, the work of which is of great importance to the success of the process, and must be guided carefully to give proper results. It is not only a question of burning fuel to the greatest possible advantage but also to obtain a grade of smelt that fills the require- ments and to avoid the sublimation of chemicals through excessive heat. THE SMELTING FURNACE 109. Description of the Smelting Furnace.—In Fig. 24 is shown a combined partial front view and cross section, a vertical section, and a top view of a double smelting furnace. Partition a separates the two hearths F, F. Black ash from the rotary B is mixed with salt cake on the platform at P, and is shoveled into the furnace through the fire doors N. The gases pass into the common flue Q and through the throat Q’ to the rotary. The smelt—the fused mass of sodium carbonate and sulphide—flows out through spout K to the dissolving tank M. Air for combus- tion of the fuel and the carbon in the black ash is introduced through the nozzles H. The smelting furnace C, Figs. 23 and 24, is built of some refractory material, which must also resist the action of the smelting sodium salts. Soapstone is the material generally used for the lining of the bottom and side walls of the fireboxes, and also for arches and: flues. Chrome brick has also been used in building smelters; though a very expensive material, the better service given by it is said to justify the increased cost. TCL a ea No) THE FURNACE ROOM 87 110. Temperature of Furnace.—To ascertain the most econom- ical temperature at which to run a smelting furnace lined with soapstone, a series of laboratory tests was conducted. A full account of these tests appeared in Pulp and Paper Magazine, Vol. 19, of which the following is a summary: The fusion (melting) temperature of soapstone was found to be 1400°-1450°C. (2552°-2642°F'.). Legend Soap Sone YM Hn ked Brick ee Magnesia Brick MMM SAAT ANS SNA AW ANAS Z a < WU] es aa SSNS be ‘\ yi oe — =o = = = ae = =e = Sey = or =e ey = 4 = se = se tes as a a0 = es ean os mm = a ~ | (ea aN ae { NSS NS 4 ty Fie. 24. Action of fused sodium hydrate: After 15 minutes at 325°C. (617°F.), no evidence of any action could be noted; no action was noted until a temperature of 1250°C. (2282°F.) had been reached. With superheated sodium carbonate, slight action was noted after 15 minutes at 1200°C. (2192°F.), and considerable action was noted after after 15 minutes at 1250°C. (2282°F.). The lowest temperature at which the black ash could readily be reduced and fused was 900°C. (1652°). 88 MANUFACTURE OF SULPHATE PULP §6 Comparing these purely laboratory tests with practical tests made in an American sulphate mill, the lowest temperature mentioned in the laboratory tests (900°C. = 1652°F.), the lowest temperature at which black ash could be reduced, was found not to be practical in a mill; such a low temperature cannot exist, at least for any length of time. At the mill, the tests were undertaken to ascertain whether or not a furnace would operate satisfactorily at a temperature between 2000°F. and 2500°F., it being realized that if such a temperature could be maintained, soapstone would be saved and the life of the furnace would be greatly prolonged. The test was also made with a view to avoiding excessive temperatures; because this particular mill had trouble with the black ash melt- ing in the neck of the furnace, which obstructed the free passage of the gases. It was thought that by operating at a more uni- form and lower temperature, this trouble might be overcome. It has been found that the furnace will operate successfully at about 2000°F. Due to the black ash being hand fired, the temperature will vary greatly, according to the manner in which the firing is done. There are many factors, such as the depth of the furnace and other practical details, which must be taken into consideration. It is a fact, for instance, that the hottest place in the furnace, which might be called the ‘‘ melting pot,” changes its position quite frequently during firing; black ash will come down directly in front of the blow-pipes, altering the direction of the air a little, which immediately changes the position of the melting pot. The more evenly the furnace is fired the less is the excess heat required; it will be found that in most mills, about 2000°F. is a good temperature at which to operate the furnace. 111. Construction of Smelting Furnace.— Whatever the mate- rial used in the construction of the furnace, it is essential to have good, tight joints and to avoid the use of much mortar. The mortar is made from fire-clay; it should be so thin that when the stone to be laid is dipped into it, only a thin film of clay will stick to it, the stone being driven into place very solidly. The arches should not be built too flat; that is the part of the smelter which usually gives out first, and a flat arch is more liable to fall in when getting thin than a higher arch. The fire resistant lining is encased in brick work (usually, red brick), the purpose of which is to make the construction more solid and to tighten up nel ee tee ee ee ae ee | $6 THE FURNACE ROOM 89 eventual cracks in the lining. The whole construction is heavily reinforced, to keep it from opening up through uneven contrac- tion and expansion. The bottom of the firebox F, Fig. 24, is made to slope, to allow a speedy drainage of the smelt. It is of great importance that the smelt find its way out readily, in order to prevent re-oxidation of the sulphide and to avoid filling up the bottom of the firebox with smelt, which might block the air nozzles H. To keep the smelt from staying too long in the fire- box, the sectional area of the firebox should not be very large, and the smelting zone of the chemicals should be centralized close to the opening through which the smelt leaves the furnace. The smelting furnace is built either with one firebox (a single furnace) or with two fireboxes (a double furnace). The single furnace is easier to build and will cost less in up-keep; but the capacity of the machinery attached to the smelting furnace, the rotary furnace, and the disk evaporator, is not so well utilized as with a double furnace. The output of a single-furnace unit corresponds to about 18 tons of pulp at its best, while black ash sufficient for 30 tons or more of pulp may be burned in a double- furnace unit, if forced. It will be more economical however to run the furnace slower and be satisfied with an output corre- sponding to 22-25 tons of pulp per 24 hours, for a double furnace. 112. Air Nozzles.—The air to the smelting furnace is usually forced into the firebox through air nozzles H, Fig. 24. The air nozzles are preferably water-jacketed, the life of an uncooled pipe in the firebox being very short, and care should be taken to place the water outlet at the highest point of the nozzle, thus keeping it from getting air bound. The inlet water is carried to the lowest end of the nozzle by means of a pipe inside the jacket. The water admitted is usually cold, although, in some instances, it is pre-heated; the return water may with advantage be used for boiler feed water. The location of the nozzles, their number, and the pressure of the air supplied to them, depend on what capacity is expected of the firebox. When a small output of smelt is expected, the air nozzles should be placed rather steeply, on an angle of about 30°, in the front of the firebox, well drawn together toward the opening for the smelt, and should not be inserted too far into the smelter. In this manner, it will be possible to keep the nozzles and the spouthole open with but a low pressure of air (2 to 3 inches of 90 MANUFACTURE OF SULPHATE PULP ‘§6 water), the volume of air supplied being correspondingly small; two nozzles is then the usual number. When it is desired to maintain a large output of smelt, the air must be supplied under increased pressure. The smelting zone in the firebox must be larger; and in order to obtain this result and also to avoid blowing the flame and ashes out through the smelt outlet,—the spouthole,—the air nozzles must be set farther apart. 6.2. 108 MANUFACTURE OF SULPHATE PULP $6 The per cent of causticity (C) is the ratio of the sodium hydrate to the sum of the sodium hydrate and sodium carbonate, all expressed in terms of Na2O, and also expressed as a per cent. Omitting the sulphite, d = 0, and 6.2x 100a alesis io) 100 Sanus Substituting the values of « and z from equations (6) and (7), 2a — 6 7 Oey wremmyes t (5) 10. Analyzing White and Green Liquors.—The method just given for analyzing liquors calls for two different standard solutions, a normal (N/1) HCl solution, and a decinormal (N/10) iodine solution. It may, therefore, not be advisable to use this method in the mill, in the liquor room, or in the digester room. In the digester room especially, where a mistake may prove fatal to the success of the cook, it is better to employ a more direct method, in which only one reading of the burette is necessary. By this method, called the barium chloride method, the causticity of the liquor and its content of active alkali can be determined by using only one standard solution. 11. The Barium Chloride Method.—For the control of the liquor in the liquor room, a sample of the liquor is taken out after the minimum quantity of lime has been added, or, as some mills are operated ,when causticizing is thought to be complete. The analysis then proceeds as follows: I. Take 5 c.c. of the clear liquor and titrate it with N/1 HCl, using methyl orange as an indicator. The change in color from yellow to pink occurs when all the NaOH, all the Na.S, and all the NaeCQO; is neutralized. The reaction is expressed by the equation NaOH + NaS + NaeCO; + 5HCl Represent the amount of acid used by s e.e. II. Bring 25 c.c. of clear white liquor into a 250 c.c. measuring flask and mix with 50 c.c. of 10% barium chloride (BaCl, eryst.) solution; the mixture is then diluted to the mark, well mixed, and allowed to settle. The white precipitate thus obtained is barium carbonate BaCO3, and the sodium carbonate is thus eliminated, in accordance with the equation NazCOsz ~f- BaCl, = 2NaCl + BaCO3 $6 APPENDIX TO SULPHATE PULP 109 From the clear solution of the above mixture, 50 c.c. is carefully withdrawn, taking pains to avoid any of the precipitate. The sample thus obtained is titrated twice with N/1 HCl solution, first using phenolphthalein as an indicator, and then using methyl orange as an indicator. The first reaction ends when the original pink color of the phenolphthalein turns to colorless, and as a result of this reaction, which is expressed by the following equa- tion, NaOH + NaS + 2HCl = 2NaCl + NaHS + H:0 all the NaOH and half the Na.S is neutralized. Represent the amount of acid used by ¢ c.c. Continue the titration (using methyl orange as indicator) until the color turns from yellow to pink; this reaction neutralizes the sodium hydrosulphide (or sodium sulph-hydrate) NaHS, in accordance with the equation NaHS + HCl = NaCl + HS Represent the amount of acid used in this complete titration (both parts) by wu c.c. These results may be summarized thus: All NaOH + all Na.S + all NasCO; neutralized by s c.c. of HCl All NaOH + half (1/2) NaS neutralized by ¢ c.c. of HCl All NaOH -+ all NaS neutralized by wu c.c. of HCl From these results, are obtained the following formulas, which express the determinations of carbonate, hydrate, and sulphide: Naz00s, a Beatle, SN 9) (1) ‘MOH Seo eLemon| Nes 3 yx teefiaNes| © As before, representing the per cent of causticity by C, eee es x 100 (4) The student should compare this with determination of caus- ticity of carbonate liquors in section on Soda Pulp. The last formula gives the result that is of particular interest to the liquor maker. If the result as found is not satisfactory, the liquor maker should refer to a table (computed for the purpose) and ascertain how much more lime must be added to get the liquor to the proper causticity. The computation of this table 110 MANUFACTURE OF SULPHATE PULP $6 is a matter for the chemist, and the table will usually be different for each mill. In the digester room, where only the total active alkali is of interest, only the last part of the above analysis is made. Thus, 25 c.c. of the liquor is precipitated with 50 c.c. of 10% barium chloride solution and diluted to 250 c.c. in a measuring flask. Then 50 c.c. of the clear solution is withdrawn and titrated with N/1 HCl solution, using methyl orange as an indicator. The change of color from yellow to pink marks the end of the reaction, in accordance with the expression NaOH + Na.S + HCl-NaCl + H.S + HO which shows that all the NaOH and all the Na.S has been neutral- ized. The amount of acid used will be the same as in the total for II, above, 7.e., wu c.c. Representing the total active alkali by K, as before, [ = 6.2u g./l. as NasO| x) = 8u g./l. as NaOH } (5) Knowing the number of c.c. of acid used in making the fore- going analysis, a table (prepared for the purpose by the chemist) may be consulted for the purpose of determining directly how many inches to use out of the measuring tank. 12. From the results of analyses of white liquor carried out by this method, a table or chart can be prepared that will show the amount of liquor of any strength necessary for digester charge that requires a certain amount of alkali. : In the formula, 1 1 24 h= ax EX=XQ= 5 (1) Q = number of pounds of active alkali (given as NaOH) for a digester charge , A = area of measuring tank, in square feet; nz = number of c.c. of N/1 acid neutralized by the active alkali in the liquor by the barium chloride method; h = number of inches to be measured from the tank. : : 24 For any given size of tank, Tc acs constant, and pep (2) ns a $6 APPENDIX TO SULPHATE PULP 111 When preparing a table from this formula, ns is first kept constant and Q is varied (say at 50-lb. intervals) between the limits necessary to cover the digester sizes and cooking condi- tions. Then Q is kept constant, and values for ns are varied between proper (desired) limits. In this way, the value of h is obtained for any desired amount of active alkali and for any probable strength of white liquor. The actual weight of alkali must, of course, be determined for each digester, kind of wood, and quality of product. 13. Lime Sludge Analysis for Content of Sodium Salts.—The losses of chemicals in washing the lime sludge in the liquor room may be considerable; they are often times unduly large, because of poor settling qualities of the lime, or because proper care is not given to the washing by the man who operates the liquor room. Therefore, it is necessary to control the result of the washing - operations from time to time. It may also happen that chemicals are wasted, because of improper agitation of the sludge in the settling tank. If part of the sludge in the tank is never stirred up by the agitator, a sample of sludge taken as directed below may show only traces of alkali, while the losses are still quite large; this should receive special attention when the losses of chemicals in the sludge are investigated. When the sludge in a tank is fully washed, the amount of sludge is measured. The contents of the tank is then carefully agitated, and a good sized sample is taken out. If the settlings are very solid, it is advisable to mix in a little water before taking the volume of the sludge and the sample. The sample thus ob- tained is thoroughly stirred and, while still agitating, a test sample of 50 c.c. is withdrawn. The pipette used for this purpose must have an especially large discharge opening, to avoid having it plugged up with sludge. It is emptied into a porcelain dish, the inside is washed out with hot water, and 10 c.c. of a 10% solu- tion of ammonium carbonate, (NH.)2COs, is then added, after which, the sample is evaporated to dryness on a water bath. The ammonium salts are then driven off, by slightly heating the dish over a Bunsen burner, and the residue is washed out onto a filter, where the washing is continued until no coloration is shown with phenolphthalein. The filtrate is then titrated with N/10 sulphuric acid H.SO, solution, using methyl orange as an indicator. Note that 1 c.c. of acid corresponds to .004 g. of NaOH or to .0031 g. of Na2.O. 112 MANUFACTURE OF SULPHATE PULP §6 To find the total content of sodium salts in the sludge, the sample thus tested for alkali is slightly acidified with hydrochloric acid, and is then precipitated with BaCl, in a boiling solution. The precipitate of BaSO, is taken on a filter and carefully washed, after which, the filter is burned wet in a platinum crucible and heated to white heat to constant weight. The weight thus obtained, less the weight of the crucible, is multiplied by .609 (see Art. 3); the product is the total content of the sodium salts in the sample, expressed as NagSO,. Knowing the volume of the sludge in the tank, the size of the sample used for analysis, and the content of NaeSO, in the salt cake, the actual loss of chemicals in the sludge, figured as commercial salt cake, is readily estimated. 14. Black Liquor Analysis.—To determine the total content of the sodium salts in the black liquor, 10 ¢c.c. of liquor is diluted with water in a beaker and brought to boiling. A 50% solution of sulphuric acid is then added, drop by drop, until no further : precipitation takes place and the solution is slightly acid. The organic substances in the black liquor, which are precipitated by the acid, will form a ball-shaped mass in the boiling-hot solu- tion and are taken on a filter, where the precipitate is carefully washed with hot water. The filtrate, which contains the sodium salts (now all in the form of sodium sulphate) and the excess of sulphuric acid, is first evaporated to dryness on a water bath in - a platinum dish; then the remaining water and the sulphuric acid are driven off by cautiously heating the platinum dish to dull red heat. The sodium sulphate is then weighed immediately; or, the salt residue is dissolved in water that has been slightly acidified with hydrochloric acid, and is precipitated with BaCl. in hot solution, and the sodium sulphate is weighed as BaSOy,. The weight of NaeSO, (mol. wt. = 142) multiplied by .437 gives the content of sodium compounds in the sample as Na2O (mol. wt. = 62), since a = 437: The weight of BaSO, (mol. wt. = 233.5) multiplied by .609 is the sodium as NasSOu, since ss e as = .609. Or, the BaSO, multiplied by .266 gives the weight Bite is ; 62 of the sodium in the sample as Na2O, since 335 7 266.00 15. If the content of the sodium compounds in the black liquor at a certain specific gravity and temperature has once been determined and given either as Na2O or as Na2SOu,, the $6 APPENDIX TO SULPHATE PULP 113 concentration of sodium salts in black liquor of any density at the same temperature can be calculated by the formula a-99> in which Q = the content of sodium salts given as Na.O (some- times including Na2SO,) in grams per liter (g./1.) of the solution, the specific gravity of which is known and = d. Q, is the con- centration of sodium salts, expressed as the same compound in the desired solution, the specific gravity of which is represented by di. If it be desired to use American degrees Baumé instead of the specific gravity, 145 Pooh nie pasa ce) in which formula, Be. = number of degrees Baumé. 16. To determine the concentration of free caustic soda in the black liquor, a sample of 5 ¢.c. of liquor is mixed with 50 c.c. of 10% barium chloride solution (BaCl, cryst.) and is titrated with N/10 H.SOu,, using phenolphthalein as an indicator. The eolor of the solution is made brighter through the precipitation of barium sulphate, and the turn of color to red can easily be observed. ‘The number of c.c. of acid required for the reaction (= ne.c.) multiplied by .8 gives the content of free caustic soda in grams per liter (g./l.); thus, Grams NaOH per liter = 0.87 g./l. Because of the presence of sodium sulphide in the black liquor, the result obtained in the manner just described is not quite exact; but, since the concentration of sulphide in the black liquor at the end of the cooking process is generally low, the error can be neglected in practice. 17. For determining the total alkali content of the black liquor, 5 c.c. of the liquor is diluted to 50 c.c. in a measuring flask. To 5 c.c. of the solution thus obtained, add 10 c.c. of N/10 H25O4 solution and rapidly bring the mixture to boiling. The organic substances that are precipitated by the acid will form into a ball- shaped mass, and the solution containing them will be of a slightly yellow color. The excess of acid in this solution is determined by titration with N/10 barium hydrate Ba(OH)e solution, using phenolphthalein as an indicator. The amount of 114 MANUFACTURE OF SULPHATE PULP §6 this solution that is used to neutralize the acid is denoted by m c.c. Then | 8(10 — m) = total alkali as NaOH (1) 6.2110 — m) = total alkali as Na2O (2) All analyses here described should be made with solutions of as nearly the same temperature as is possible, so that the results obtained may be compared with each other directly, without reducing them to the same temperature. SUPPLEMENTARY TEST METHODS GREEN LIQUOR ANALYSIS Norr.—In mill practice, it is often desired to express the results obtained from burette readings as pounds of Na:O per cubic foot of liquor, to do this, in fact, directly from the burette readings. The following test methods may then be employed. It may be remarked that these methods are given here as a help to the mill chemist, and space does not permit of a discussion or explanations of the principles of chemistry involved. 18. Procedure.—A sample of the green liquor from the dis- solving tanks is passed through a filter; the clear filtrate is then analyzed as follows for: (a) NaOH + NaS + NasCO; + 4Na2SO3, expressed as Na.O. 2 c.c. of liquor is diluted with 50 c.c. of water, and is titrated with 0.5165N! hydrochloric acid, using methyl orange as an indicator. The number of c.c. of acid used, divided by 2, expresses the sum of the above mentioned components as Na2O in pounds per cubic foot. - ExxampLe.—10.45 c.c. of 0.5165N HCl + 2 = 5.23 lb. of NazO per cu. ft. (b) NaS, expressed as Na.O. 2 c.c. of the same liquor (clear filtrate) is brought undiluted into a porcelain dish, and is titrated with 0.5165N ammoniacal silver nitrate solution. The silver nitrate is added slowly, continuously stirring with a glass rod. When a new drop does not form any more black silver sulphide, the end point is reached. The num- ber of c.c. of 0.5165N solution consumed, divided by 2, gives the concentration of NaeS, expressed as Na2O, in pounds per cubic foot. 1'To obtain 0.5165N solution, take 1000 c.c. of N/1 solution and add 936 c.c. of distilled water. The total volume is then 1936 c.c., and 1936: 1000 =N/1: «N; from which, zN = 1000 + 1986 = 0.5165N. a a $6 APPENDIX TO SULPHATE PULP 115 Exampie.—3.78 c.c. of 0.5165N amm. silver nitrate + 2 = 1.89 lb. Na.S, expressed as Na.O, per cu. ft. (c) NaS + Na2S203 + NazSOs, expressed as Na2O. 30 c.c. of green liquor is diluted with 50 c.c. of water, acidified with acetic acid, and an excess of N/10 iodine solution is added. The excess of iodine over that required by the liquor is deter- mined by titration with N/10 sodium thiosulphate. When the solution is slightly yellow from iodine, a drop of starch is added, which colors the solution blue. The titration with thiosulphate ‘s then continued until the blue color disappears. Subtract the number of c.c. of thiosulphate used from the number of c.c. of iodine solution used, and divide the remainder by 10.33 or multiply it by 38;; the quotient (or product) expresses the total of the above components as Na2O, in pounds per cubic foot. EXAMPLE.— Used 31.00 ¢.c. N/10 iodine solution Used 10.32 c¢.c. N/10 thiosulphate Liquor consumed 20.68 c.c. N/10 solution Then, a = 20.68 X = = 2.00 lb. Na2O per cu. ft. (d) NaOH + Na.S, expressed as Na2O. 20 c.c. of green liquor is titrated with 50 c.c. of 15% barium chloride solution, which precipitates all but the hydrate and sulphide of sodium. This is then diluted to 250 c.c. and left to settle. 25 c.c. of the clear solution is withdrawn and titrated, using methyl orange as an indicator. The number of c.c. of 0.5165N acid consumed, divided by 2, gives the concentration of NaOH + NaS as NazO, in pounds per cubic foot. Exampie.—.40 c.c. of 0.5165N HCl + 2 = 2.70 lb. NaOH + Nas, expressed as Na2O, per cu. ft. of liquor. (ec) NazS + NaeS20s, expressed as NazO. 20 c.c. of green liquor is treated with 50 c.c. of 15% BaCl: solu- tion in a 250 c.c. measuring flask, and is made up to the mark; the contents, after being well shaken, are left to clear. Of the clear solution, 25 c.c. is withdrawn and mixed with 50 c.c. of water. After a slight excess of acetic acid has been added, the sample is titrated with N/10 iodine solution, added in excess. The excess of iodine is determined by re-titration with N/10 thiosulphate, using starch as an indicator. EXAMPLE.— Used 21.50 c.c. N/10 iodine solution Used 1.86 ¢.c. N/10 thiosulphate Consumed 19.64 c.c. N/10 iodine solution 116 MANUFACTURE OF SULPHATE PULP §6 19.64 Then, oa = 19.64 X = = 1.90 lb. Na2S + Na.S.0;, expressed as Na2O, per cu. ft. of liquor. (f) NaeSOu, expressed as Na.O. 10 c.c. of green liquor is diluted with 50 c.c. of water; the solution. is carefully acidified with a slight excess of hydrochloric acid, brought to boiling, and is precipitated with BaCl.. The precipi- tate is left on the water bath for a few hours, and is then filtered. When the precipitate is washed clear, filter, and all is brought. into a platinum crucible, burned, and heated, at white heat, to constant weight. The number of grams of barium sulphate (the precipitate obtained above) multiplied by 3.8 (3.799 more exactly) gives the number of pounds of Na2SO, per cubic foot; or, if multiplied by 1.66 (1.659 more exactly), it gives the number of pounds of Na2SO,, expressed as Na.O, per cubic foot. EXAMPLE.—0.. 2634 g. BaSO, X 3.8 = 1.00 Ib. Na,SO, per cu. ft.; or 0.2634 g. BaSO. X 1.66 = 0.44 lb. Na2SO., expressed as Na.O, per cu. ft. 19. Calculation of Results.—Using the results obtained in Art. 18, (1) NaeCO; = (a) — (d) — Ghee = 5.23 — 2.70 ms a = 2.48 Ib. per cu. ft. (2) NaOH = (d) — (6) = 2.70 — 1.89 = 0.81 lb. per cu. ft. (3) NaoS = (6) = 1.89 lb. per cu. ft. (4) NazSOs = (c) — (e) = 2.00 — 1.90 = 0.10 lb. per cu ft. (5) NaeS203 = (e) — (b) = 1.90 — 1.89 = 0.01 ]b. per cu. ft. (6) Na:SO, = (f) = 0.44 Ib. per cu. ft. SHORT METHOD FOR TESTING SULPHATE DIGESTER LIQUOR 20. Procedure.—The substances to be determined are the hydrate, sulphide, and carbonate of sodium in solution, expressed as pounds per cubic foot of Na,O. (A) NaOH + 4 NaS +4 NasCO;, expressed as Na,O. 1 c.c. of digester liquor is run into a cup, and 50 c.c. of water is added. This is titrated with 0.5165N HCl, using phenolphtha- lein as an indicator. The number of c.c. of acid used expresses $6 APPENDIX TO SULPHATE PULP © tia ly’ the amount of NaOH plus half the sulphide and half the carbonate. (B) 4 NasS + } NaeCOs;, expressed as Na2O. After the phenolphthalein end point is reached in (A), methyl] orange is added to the same sample, and the titration is finished with 0.5156N HCl. The additional number of c.c. of acid thus used represents the amount required to neutralize the remaining half of the sulphide and carbonate. (C) NasS, expressed as Na,O. 1 c.c. of digester liquor is run into a cup and, without addition of water, is titrated with 0.5165N ammoniacal silver nitrate solu- tion until no black precipitate of silver sulphide is formed. The titration is preferably done in ‘a porcelain dish, and the silver nitrate solution should be run in drop by drop, so the effect of one drop may be noted before another drop is added. 91. Calculation of Results.—Using the results obtained in Art. 20, | 5.15 c.c. = HCl burette reading at methyl-orange end point (B). 4.30 c.c. = HCl burette reading at phenolphthalein end point (A). 0.00 c.c. = HCl burette reading at start (A) 1.40 c.c. = AgNO; burette reading at end point (C) 0.00 c.c. = AgNO burette reading at start (C) (A) 4.30 c¢.c. = 4.30 lb. per cu. ft. of NaOH 14 NaS + 4NaeCQs. (B) 5.15 — 4.30 = 0.85 c.c. = 0.85 ie per cu. ft. of 1Na S + 4 Na2CO3; 0.85 X 2 = 1.70 ¢.c. = 1.70 lb. per cu. ft. of NaS + Na2CO;; and 1.70 — 1.40 = 0.30 c.c. = 0.30 Ib. per cu. ft. of NazCO; as Na2O. (C) 1.40 c.c. = 1.40 Ib. per cu. ft. of NazS as Na,0. 4.30 — 0.85 = 3.45 c.c. = 3.45 lb. per cu. ft. of NaOH as Na2O. QUICK METHOD FOR DETERMINATION OF WHITE LIQUOR 22. Procedure.—The following relates to ee determination of the sulphate cooking liquor. (A) For a total alkali, take 1 c.c. of white liquor and titrate with 0.5165 HCl, using methyl orange as an indicator, (B) Take 10 c.c. of white liquor, and place in a 250 c.c. flask; precipitate with 15% barium chloride solution, dilute to the 118 MANUFACTURE OF SULPHATE PULP $6 mark, shake well, and allow precipitate to settle. Withdraw 25 c.c. of the clear liquor and titrate, using phenolphthalein as an indicator for first end point; then continue titration, using methyl orange as an indicator. ExaMPues.—(A) 6.40 ¢.c. = NaOH + NaS + NazCOs. (B) 5.70 c.c. = end point with methyl orange for all NaOH + NaS; 4.60 c.c. = end point with phenolphthalein for NaOH + 3} Na.S. (5.70—4.60) X 2 =1.10 X 2 = 2.20cc. = 2.20]b. per cu. ft. of NaS as Na.O. 4.60 — 1.10 6.40 — 5.70 3.50 ¢.c = 3.50 lb. per cu. ft. of NaOH as Na,O. 0.70 c.c. = 0.70 lb. per cu. ft. of NazCO; as Na.O. I ll RECLAMATION OF BY-PRODUCTS 23. Three By-Products of the Sulphate Process.—In the proc- ess of regenerating the alkali that is contained in the black liquor, — 50% (more or less) of the dry weight of the wood that is carried in this liquor has to be removed, and the general practice, at - the present time, isto burn the organic substances. The immense amount of material at hand, and the means it supplies for the manufacturing of useful and valuable organic products, has, of course, been an’ inducement leading research chemists to seek a practical and more profitable method of recavery. Acetone, wood alcohol, light and heavy motor oils, and lubricants, may all be obtained through destructive distillation of the black liquor, but the methods so far suggested have not proved satisfactory. For this reason, only a few products that can easily be isolated are reclaimed, they are sulphate turpentine, wep wood alcohol, and hid rosin. 24. Turpentine.—The turpentine is already at hand in some wood as such, when the wood is charged into the digester. Dur- ing the early part of the cook, when the digester is relieved, to exhaust the air and maintain circulation, most of the turpentine is carried over in the escaping steam. Later in the process, when ° the cook is ready and the digester is relieved down to blowing pressure, the agitation caused by the rushing steam drives off another part of the turpentine. If thé relief gases are condensed and the condensate left to stand, the turpentine oil will separate from the water, and may be drawn off. The crude product thus obtained contains about 50% turpentine, and it must be purified by fractional distillation. A careful distillation, carried through $6 APPENDIX TO SULPHATE PULP 119 in a column apparatus, will result in a colorless and scentless product that compares very favorably with turpentine otherwise obtained. In some instances, it has been found necessary to wash the turpentine, after the distillation, with a weak solution of sulphuric acid, and follow this with a wash of sodium hydrate solution. It has also been found to be advantageous to add a little lead acetate solution before the final distillation, to remove the last traces of sulphur. In case of discoloration, the turpentine may be stored for some. time in glass containers exposed to sunlight. Among other products that may be isolated from the crude turpentine is methyl sulphide, which, according to Bergstrom, makes up about 30% of the total oil; this may become valuable, if it can be used as a solvent for nitro-cellulose in place of ether. The crude turpentine oil also contains a small percentage of wood alcohol and methyl] disulphide. : The actual quantity of crude turpentine oil obtained from the - condensate will naturally vary quite extensively with the kind of wood used; it will likewise vary with the manner of cooking and of relieving the digester. The lower the blowing pres- sure of the digester the larger will be the return of turpentine per charge, with the same wood. Apparatus especially designed for separating the turpentine from the condensed steam and for its distillation, may be purchased in the market. 25. Wood Alcohol.—Wood alcohol (methyl hydrate), which is not to be found as such in the wood, is a product that results from the hydrolysis of the higher carbohydrates. The quantity of wood alcohol actually formed in the digester during the cook is estimated to be about 25 pounds per ton of pulp, in the case of a straight soda cook. By the sulphate process, the quantity will not be so large, since a portion of the methyl compounds are engaged by the sulphur; from 7 to 9 pounds of wood alcohol may be expected per ton of pulp, the quantity formed in the digester being about twice this amount. The wood alcohol, like the turpentine, is to be found in the relief gases from the digester, and in the condensed fumes from evaporators also, particularly in the condensate from the second effect. The concentration of wood alcohol in both of these con- densates is very small, and the first operation is undertaken with a view to obtaining a solution having a higher percentage of alcohol. 120 MANUFACTURE OF SULPHATE PULP $6 The united condensate from the digester relief and from the second evaporator effect is continuously fed to the tower of the concentrating apparatus, over a perforated plate at the top in the lower compartment, which is filled with rock; it is then distributed over the whole section of the cylinder. Steam is introduced underneath the grate, and the rising steam meets the condensate as it runs down over the rocks, which afford a large evaporation area. As the vapors rise, they become richer and richer in their content of wood alcohol, which is more volatile than the water. The water flow through the coil in the top sec- tion is carefully adjusted, so as to obtain the highest possible concentration of alcohol in the vapors that leave the machine for the condenser; a temperature of between 170° and 180°F. will usually give the best results. The condensate from the condenser flows by gravity into a storage tank. The crude prod- uct obtained in this manner contains from 10% to 20% wood alcohol. When a sufficient quantity of the crude alcohol is at hand, redistillation is undertaken in an apparatus similar in construc- tion to the one previously described, but having a smaller capac- ity. It consists of a fairly large vessel, indirectly heated with a steam coil, in which the crude alcohol is charged. Above this vessel is placed a column filled with pebbles or small crushed stone. On top of the column is placed a cooler, and on top of that a condenser. When the vapors from the heating vessel strike the cooler in the top of the column, a part is condensed and runs back over the pebbles, where the condensate meets with fresh vapor from the bottom. The fraction with the lowest boiling point will thus accumulate at the top of the machine. The water in the cooler is regulated to maintain a temperature of 150°F. at the top of the column; in this manner, the vapor leaving the column will contain practically nothing but wood alcohol, which is condensed and collected in a tank. Wood alcohol obtained by this process has a concentration of about 98%; it is perfectly clear and is practically free from dis- coloration and scent; it contains but a trace of acetone, and is a far purer product than that obtained from the distillation of wood. | 26. Liquid Rosin.—When black liquor is left to stand for some time, a layer of soap is formed on top of the liquor; this soap has a yellow color, but turns black when exposed to the air. The soap $6 APPENDIX TO SULPHATE PULP 121 comes from the constituents of the wood that are of a resinous or fatty nature, and is formed through saponification of these constituents. The soaps that are the result of this hydrolysis are carried partly in solution and partly in suspension in the black liquor. The concentration of the solution of soap becomes less the higher the concentration of the other sodium salts. If the black liquor is left at rest,for some time, the part of the soap that is in suspension will float to the top, in very much the same way as cream comes to the top of milk. The concentration of the suspended soaps is higher in a more concentrated black liquor, and the separation of the soap from the liquor will be more complete accordingly; for this reason, the mills where this product is taken care of always carry a large stock of evaporated liquor. The storage tanks for this purpose are supplied with an overflow, an open spout at the top of the tank, through which the soap is run off into a special soap tank. Any black liquor that follows the soap into this tank is drawn off at the bottom. 27. The liquid rosin is obtained from the soap through pre- cipitation with an inorganic acid. If the soap be let into a boiling solution of hydrochloric acid, a dark brown oil is obtained, which is viscous at ordinary temperatures. The reaction takes place according to the formula NaR + HCl = HR + NaCl in which R represents some organic radical. The oil, which floats on top of the sodium chloride solution in a distinct layer, can easily be skimmed off. The acid value and iodine value of this oil or of the distillates that are obtained from the same through distillation in vacuo, indicate that the oil originates from the abietic and fatty acids in the wood. A gravel-like substance, which in time will separate from the oil and settle down to the bottom of the container, is derived from the lignins of the wood. According to Bergstrom, the sulphate liquid rosin consists of a mixture of fatty acids, principally palmitic acid and resin, with a small percentage of phytosterins. The composition of the liquid rosin, and the quantity obtained as well, varies greatly with different kinds of wood and with varying conditions of the same kind of wood. ‘Thus, the per- centage of the fatty acids will be considerably higher in liquid rosin obtained from wood cut in the summer time; and this will also be the case if only sap wood is used, as in mills utilizing 122 MANUFACTURE OF SULPHATE PULP §6 sawmill refuse. and C = 1.63; hence, by formula (4), _ 2800 X 100 X 1.63 ee er OKls A = 3803, say 380 lb. Ans. (b) Applying formula (1), B = 380 X .9 = 342 lb. Ans. In examples of this kind, it is useless to calculate results cor- rect to more than three significant figures. 5. The consistency of the stock in the storage tank varies con- siderably, depending upon the amount of water added to sluice it or pump it from the drainer. It is often between 2% and 4%, and the average practice possible under the conditions obtaining at each plant should be determined before designing the tank. The lower the consistency the larger the tank must be. Thus, if the consistency is 2%, each 100 lb. of air-dry fiber will occupy a space of approximately 80 cu. ft., since the weight of the stock will then be, using formula (5) of Art. 4, = - <. 100. = a x 100 = 5000 lb. Taking the weight of a cubic foot of the stock as 62.4 lb., the same as the weight of a cubic foot of water, which is close enough for all practical purposes, the number of cubic feet in 5000 lb. of stock is 5000 + 62.4 = 80 cu. ft., very nearly. It may here be remarked that it is advisable to keep the stock agitated while it is being stored in the tank, in order that it may be of practically uniform consistency throughout. This may be effected by using a paddle somewhat like that employed in an ice-cream freezer. MACHINES USED IN COARSE SCREENING 6. Necessity of Screening.—One of the leading processes em-- ployed in the treatment of pulp is the separation of the coarse fibers from the fine, or majority, fibers and the removal of dirt and foreign matter. This process separates the fibers into classes, according to size and length. The machine that accomplishes this separation is called a screen, and the process is called screen- ing. For the purpose of obtaining greater efficiency in screening, the reasons for which will be considered later, the pulp is first §7 COARSE SCREENING 5 passed through one or more sets of coarse screens and then, if desired, through a shallow tank called a riffer. It is important to appreciate at the outset that water plays an important part in all the processes, from the moment that pulps are made until they are incorporated into the finished products. Water acts as a conveyor for the fibers, holding them in suspen- sion as they are pumped from place to place while being sorted and treated. Finally, when no longer needed, the water is extracted in various ways. 7. The coarsest material in groundwood, consisting of thin slabs of unground wood and slivers of varying size, must be removed before any attempt is made to pump it, since this material will clog any type of pump. Accordingly, sufficient water is added to thin the mass, so it will flow freely. The con- sistency at this point is, approximately, from $% to 14%, but uniformity in consistency is not so important here as at all sub- sequent stages, since the machines for coarse screening present the largest passages through which the stock must pass. SCREENS FOR GROUNDWOOD 8. Slab Grating.——The machine shown in Fig. 1 is called a slab grating. The parts bearing numbers are designated as follows: 1, sprocket wheel for chain; 2, scraper; 3, chain; 4, bars; 5, stock canal; 6, platform. This machine is an elementary device for taking slabs and very coarse material from groundwood pulp before it is pumped. The stock runs in a canal in the direction indicated by the arrow. A grating of iron bars, set on edge and spaced about 1 inch apart, is placed in the path of the current of stock; this grating is inclined, as shown in (a). The coarse material that fails to pass between the bars is carried up the incline by the scrapers 2 on the chain 3, and are deposited on the platform 6, from which they are removed. The width of the scraper is such that it extends over all the bars. 9. Sliver Screens.—All sliver screens consist of a screening element, contain some device for the removal of slivers, and provide means for keeping the holes or slots in the screening element clear. The screening element is usually a perforated steel plate, having circular holes from { in. to 35 in. in diameter, and may be mounted on a stationary, rotating, or oscillating 6 TREATMENT OF PULP §7 frame. If the frame be stationary or oscillating, scrapers move over the surface of the plate and remove the slivers that are WS Wa Wi a (EWS (SS EZENS | 8=BNE/E ENS E/eNSB tvepage Uy Reeazza ez ho-b a - > VZA_VA ZA TA WZ key itiees ake deposited by the stock as it passes through the holes in the plate. If the frame and screen plate rotate, the screen is so constructed that it discharges the slivers at one end of the rotating drum to which the- screen is attached, and the flow of stock is always from the inside to outside. The slivers are freed from such fibers as cling to them by a shower of water, and are usually thrown away, while the larger slabs are returned to the grinders. The loss varies, depend- ing upon the size of the holes in the screen plate, and may be from 1% to 14%. The consistency of the stock going to this screen is © dependent upon the size of the per- forations in the screen; that is, if the perforations are large, the stock will naturally have a greater con- sistency than if they are small. Evidently, the size of the perfo- rations is a matter to be decided by the designer, who is largely gov- erned by the requirements of the subsequent processes. If only one set of sliver screens are to be used, the perforations should be rela- tively fine; but, if two sets are provided, the first set should have relatively large perforations, while those in the second set should be fine. The matter may be summed up thus: the larger the perforations in the screen beet ane sicker the stock may be, and the poorer the screening will be; conversely, the smaller the perforations the §7 COARSE SCREENING 7 thinner the stock must be, and the better will be the results ob- tained from screening. It is obvious that the size of the per- forations and the consistency of the stock affect the capacity (quantity production) of the screen. 10. Assume that the stock from the sliver screen has to be pumped to the screen room. If there is any considerable head to pump against, the quantity pumped is important. It would be possible to screen through a plate having #-inch or §-inch perforations at 14% consistency. Since 14% = .0125 = 45, it will require the pumping of 2000 + yo = 2000 X 80 = 160,000 lb. = 80 tons of liquid to secure 1 ton of air-dry pulp. Taking the weight of 1 gal. of stock as 84 = 4°," lb., the number of gallons pumped for each ton of air-dry pulp is 160,000 + 4°) = 160,000 * .12 = 19,200 gal. The stock passing through the screen would contain many slivers, which would clog the screen plate of the main screens, thus curtailing their capacity and detracting from the efficiency of screening. On the other hand, if the perforations were 3°5 inch to 3% inch in diameter, the con- sistency would be about 3% and the number of gallons of stock to be pumped for each ton of air-dry pulp would be, by formula (5) of Art. 4, ae x 100 + 4°22 = 48,000 gal. In the latter case, very few slivers would remain in the stock to affect ad- versely the main screens. Therefore, it may be found advisable to screen once at relatively high consistency, and then pump to a second set of screens, where the consistency is lowered by the addition of more white water, which is available at this point. The ultimate screening through holes at least as small as 3°5 inch in sliver screens, by whatever means accomplished, is very desirable, because it increases the capacity of all subsequent screens and improves the quality of screening. 11. Flat (Scraper) Type of Sliver Screen.—Fig. 2 shows an elementary type of sliver screen, which is used for groundwood only. The various numbered parts are designated as follows: 1, sprocket wheel for chain; 2, scraper; 3, chain; 4, screen plate; 5, shower pipe; 6, stock canal. The stock runs in canal 6 in the direction indicated by the _ arrow. A screen plate 4 is placed in the canal and inclined toward the path of the stock. As the stock passes through the screen plate, the coarse fibers are removed by the chain scraper, 8 TREATMENT OF PULP §7 as described in connection with Fig. 1. The screen plate usually consists of punched steel plates, the perforations being about 1 inch in diameter. The rejected slivers are cleaned by a shower of water from the pipe 5 before the scraper dumps them at the end of the plate, and the fibers thus washed off go into the accepted (screened) stock. Very little power is required to operate this screen; from 1 to 2 horsepower is sufficient. The screen just described would be considered by most manu- facturers as a crude sliver screen and inadequate for. proper screening, unless used in conjunction with some other type having finer perforations. It is obvious that a sliver screen is unnecessary for chemical PnP since there are no large slivers, as in groundwood. 12. Rotary Scraper Type of Sliver Screen.—A sliver screen for groundwood of the rotary scraper type is shown in Fig. 3. The numbers designate parts as follows: 1, scraper arm; 2, scraper; 3, screen plate (curved to an arc of a tirele)- 4, slab grating; 5,. tailings canal; 6, stock inlet; 7, shaft for scrapers; 8, shower to clean scrapers. The stock comes from the grinders through conduit 6 aad passes through the grating 4, which consists of flat iron bars on edge, and on which the slabs are deposited. The stock then passes into a spout, which delivers it into the open end of semi- circular screen plate 3, and falls by gravity through the per- forations in this plate into a tank beneath, from which it is usually pumped to the screen room. Scraper arms 1, mounted on a revolving shaft 7, carry scrapers 2, which are constantly passing over the surface of the screen plate, removing coarse slivers that are too large to pass through the perforations, and discharging them into canal 5, where they are washed by water showers 8. The washings gravitate to the tank below the screen, and the slivers are either collected for further treatment or are thrown away, according to individual mill practice. The scrapers 2 may either touch the plate or may be so adjusted as to clear the plate by a narrow margin, in order to prevent undue wear. This type of screen, equipped with plates having’ g-inch perfora- tions and with the minimum allowable spacing between them, has a capacity of about 3000 pounds of air-dry stock per square foot of screening surface in 24 hours, the consistency of the stock - being about .8%. The capacity of such a screen may be considerably increased COARSE SCREENING §7 : 2 MATTER va. HUTTE x °S “STW 10 TREATMENT OF PULP 87 by the addition of automatic shower pipes, mounted on scraper arms just behind the scraper and close to the screen plate. This device may be so designed as to direct a high-pressure shower : : : SONS R y N A . AN N A NA A A a nm am : N 8 KN A N § sL_N Ni ie Was rns oth _ DON Aw: ree Gey = Cs soo NEE J Fig.-4. against the perforated plate while the scraper arm to which it is attached is passing through the arc of the screen plate, and then automatically to stop the discharge during the rest of the revolution. The power required to drive a screen of this type, having a capacity of 100 tons per day, is small, from 2 to 3 horsepower approx- imately. A modification of this type of screen is also used to some extent. The gen- eral arrangement is the same; but the screen plate is mounted on a frame- work that revolves, and there are no scrapers. The slivers drop from the as- cending side of cylinder into a trough. 13. Sliver Screen, or Knotter (Rotating Screen Plate Type).—A sliver screen, or knotter, of the rotating screen plate type, which is suitable for both groundwood and chemical pulps, is shown in Fig. 4. The parts designated by the various numbers are: 1, case; 2, second part of runner; 3, first part of runner; 4, shower pipe; 5, end of case; 6, shaft; 7, trough to admit stock to be screened (outer part); 8, spout for accepted (screened) stock; 9, pulley; 10, radial plate; 11, spout —_— COARSE SCREENING 11 for rejected tailings; 12, spout from first part of runner to second part; 13, circumferential plate (perforated); 14, trough to admit stock to be screened (inner part); 15, pocket in first part of screen; 16, deflector from trough to first part of screen; 17, end plates (perforated). This machine consists of a rotating cylinder that is divided into two sections and is mounted on a steel shaft that runs in well-lubricated bearings, the whole being housed in a metal case 1. For all stock, mechanical and chemical (except sulphite stock), the machine is of iron and steel construction, including the screen plates. For sulphite pulp, the plates and framework are made of bronze, to resist corrosion by the acid liquor. The machine is a very simple and compact knotter. The stock enters spout 7 and its continuation 14, and flows into the inside of the revolving cylinder (drum), or runner, which is divided into two sections, numbered 2 and 3, as plainly shown in (a), a longitudinal section. Around the outside of both sections of this drum are secured the perforated screen plates 13. The stock must pass through the screen plates in order to reach the accepted stock discharge spout 8. The first section of the cylinder is divided into eight pockets 15 by radial plates 10. The stock enters these pockets as the cylinder revolves and the pockets come opposite the inlet spout 14. All the stock that is fine enough passes through the perforated plate 13 when a pocket is passing through the lower half of the revolution, and what is left is carried on the radial plates 10 up to a point where it will fall by gravity into a spout 12, which forms an inlet to the second section 2 of the revolving cylinder. This part of the cylinder is smaller in circumference than the first part, but it is covered with perforated screen plates of the same kind, and the perforations | are of the same size as those used on the first section. The stock is somewhat diluted by shower water from pipe 4, and has a second chance to pass through the screen plates, after flowing from section 3 to section 2. Note that the second section is conical; this causes the knots or slivers to pass out the larger end into spout 11 for removal to the refiners. The speed of the cylinder is from 25 to 30 r.p.m., and it requires but very little power to operate it; a 1 h.p. motor is ample. The machine is very simple in operation, and once the stock supply has been properly adjusted so that no good fiber is rejected, the knotter requires no attention beyond periodical 12 TREATMENT OF PULP 87 inspection and an occasional cleaning of parts of the screen plates. Its capacity varies with the consistency of the stock and the size of the screen plates. 14. The effect of the consistency of the stock on the capacity of a sliver screen can best be explained by describing an experi- ment carried out with a knotter (Fig. 4). The first section of plates had 75,840 holes of 3/8 in. diameter, and the second section had 34,048 holes of the same size. The stock had previously been freed from coarse material that would not pass through the 7/16 in. holes in the 1st sliver screen. The quantity of stock screened was measured by passing the effluent over a weir (de- scribed in Vol. 2, Section 1) in the box into which the screen Me Pe Oe is Yi atid a |_| CEE EEE EERE eee tis TT TT | 6¥adk drewoush 5treened| | | BERRA SERERARRSARERR ACR ea ONT | TT Ett tT eee ae eee tT ttt 2 fGen ee Ht A REERERREBSRAR Eek S-Cdasis#ehd bk eFAaR A ADA Se eae es eae CONT TOT TT Taor tT ist TT Teor TT TSsior TT 160. discharged. The consistency of the stock expressed in per cent of air-dry fiber, which was varied from .39% to .565%, was found by weighing representative samples, straining through Fourdrinier wire cloth having 60 meshes to the inch, drying the fiber in an oven, and calculating the weight as air-dry pulp. The object of the test was to determine the change in the number of tons of groundwood screened per hour as the consist- ency of the stock increased. The speed remained constant at 26 r.p.m. and the power practically constant at % h.p. The amount of stock fed to the screen was kept at such a rate that the rejected stock, or tailings, was practically free from good fibres. When the consistency was .39% the maximum quantity of stock the screen would pass, and still have clean tailings, was shown by the volume and consistency measurements to be 29.6 tons per 24 hours. This is represented by point 1 on Chart 1. §7 COARSE SCREENING 13 Less water was then mixed with the stock as fed, and a test showed that the consistency was .44% and the corresponding capacity of the screen was 38 tons per 24 hr., as represented by point 2 on the chart. Similarly, point 3 shows a consistency of .455% and a capacity of 40.2 tons; point 4 shows a consistency of about .49% and a capacity of about 42 tons; points 5, 6, and 7 show consistencies of .524%, .525%, and .568% and capacities of 32, 26.4, and 19.2 tons per 24 hr. A smooth curve is drawn through these points, not attempting to include those which are off the regular track. ‘This curve shows that the capacity of the screen goes up as the consistency increases, until a certain condi- tion is reached, and then rapidly falls off. It is evident that the best operation is obtained with a consistency of about .49%, when the capacity will be about 42 tons per 24 hr. If the con- sistency should fall to .42%, the screen could be expected to handle 35 tons. Very often the capacity of machines of this class may be materially increased without sacrificing efficiency, by adding wash water at that part of the screen where the stock has become so thick that further screening will not take place without thinning and agitation. SCREENS FOR CHEMICAL PULP 15. Chemical Pulp.—Chemical pulp as it comes’ from the storage tank contains certain fibers (uncooked chips and knots) that must be removed with as little agitation as possible before any attempt is made at fine screening. Such material is of inferior quality and color, and it becomes broken up into finer units if allowed to pass on to the subsequent processes, where its removal is much more difficult, if not entirely impossible. In theory, this separation of fibers is commonly accepted as correct practice; but many installations are inadequate, as designed, to give as thorough a separation as is desirable. The consistency of stock leaving the storage tanks is reduced from around 3% or 4% to about 2% or less by the addition of white water. White water is water that has been previously used to convey pulp through the system and has been extracted from the final product for further use; it is sometimes called re-water. The proper consistency should be determined for the particular type of knot screen that is to be used, as was previously pointed out in the case of groundwood. It is generally necessary 14 ! TREATMENT OF PULP §7 to use but one set of these screens, since it is possible to use screen plates having 3%s-inch round _ per- forations or 4¢-inch slots, which give very good results. While 31-inch perforations are much more common, they allow a considerable quantity of coarse shives to pass on to the fine screens. — Coarse screens having the screen plate secured to a rotating frame, of the same general design as that last described for groundwood and illustrated in Fig. 4, are in general use. Another screen of the same type, but of somewhat different con- struction, is described below. As supplied by the manufacturers, the screen is equipped with perforated plates throughout its entire length; but it has been found advantageous ; to alter this arrangement some- > what, in order to use finer perfo- rations and to increase the efficiency and capacity. The chips rejected by the knot- ters vary in quantity, depending upon the character and efficiency of the cooking process and the kind of wood used. The quantity so rejected may be as low as 1% or as high as 15% to 20%, in the case of a raw cook. 16. Worm Knotter for Chemical Pulp.— Two views of a worm knotter for screening chemical pulp are shown in Fig. 5. View (a) is partly an elevation and partly a longitudinal section; view (6) is partly an end view and partly a cross section. The various parts of the machine are designated by $7 COARSE SCREENING 15 numbers as follows: 1, stock inlet; 2, cylinder; 3, tailings outlet; 4, worm; 5, trunnion wheels; 6, accepted stock outlet; 7, pan for thinning stock; 8, inside shower; 9, outside shower; 10, screen plate; 11, trough to receive tailings; 12, sprocket. This knotter is a long cylinder made in sections, each of which is about 2 feet long. These skeleton sections (usually 4 or 5 in number) are all bolted together, and are secured at the ends to cast-iron heads, one of which is hollow and serves as an inlet 1. The hollow part of the head is cylindrical and acts as a trunnion or journal, rotating in a babbitted bearing and support- ing that end of the cylinder. The other end of the cylinder carries a track 13, which runs between two flanged trunnion wheels 5, which support that end of the cylinder. The cylinder is driven by a chain and sprocket wheel 12, the latter being keyed to the hollow inlet head 1. Perforated copper screen plates are held in position on the circumference of the cylinder by the framework, as shown in the cut. There are 4 plates, each about 23” x 253” to each 2-ft. section. Within the cylinder, and attached to the framework, is a worm 4 made of copper plate, which extends practically the entire length of the cylinder. The screen plates are kept clean by showers of water from pipe 9. The knotter shown in the cut is made up of 5 sec- tions but, instead of equipping the middle section with perforated plates as the manufacturers do, it was found advisable to sub- stitute unperforated copper plates at this point, as will be ex- plained later. In operation, the stock enters the knotter through the hollow head at 1 and immediately tends to run through the perforated plates. The consistency of the entering stock varies, depending upon mill conditions and upon the construction of the knotter; the larger the holes in the perforated plates the thicker the enter- ing stock may be. The maximum and minimum consistencies will be about .8% and .4%, respectively. Since chemical stock is “‘free,’”’ the water tends to leave the stock quickly. As a con- sequence, particularly if the perforations in the screen plates are fine (say about 3; in.), by the time the stock reaches the middle section 7, so much water has drained away that the stock at this point is too thick for screening. On this account, it has been found necessary to introduce white water here, to reduce the consistency of the stock to a point that will permit further screen- ing in the two remaining sections. It would be impossible to 16 TREATMENT OF PULP 87 thin the stock if perforated plates were used at the point of thin- ning; hence, unperforated plates are used to enclose the middle section. The knotter is set level, z.e., the axis of the cylinder is horizontal, and the worm pushes out at the front end any heavy material that will not go through the perforations. It is neces- sary to use a high-pressure shower to keep the screen plates clean, and the shower is directed against the outside of the cylin- der, driving back through the holes any material that is lodged in them. The framework, with the exception of the cast-iron inlet and outlet ends, is made entirely of bronze, and the bolts used for bolting the sections together are also of bronze. Since the cylinder revolves very slowly, approximately 20 r.p.m., the knot- ter requires but little power to operate it, 3 h.p. being usually allowed for each machine. : The capacity of this form of knotter varies, depending princi- pally upon the size of the perforations in the screen plates. Such a knotter, having 3-inch perforations, would have a capacity of (would screen) at least 50 tons sulphite, soda, or sulphate pulp per 24 hours. With 3%;-inch round holes or 3” by 3” slots, its - capacity when using the same class of stock would be about 30 tons per 24 hours. This machine is very simple of operation and requires very little attention for operation or repairs; the regula- tion of the stock supply is the only adjustment required. RIFFLING 17. Reasons for Riffling.—The word riffling is apparently a misnomer as applied to the treatment of fiber in the paper indus- try, since the flow of liquid containing the fiber to be treated by this operation must be slow and tranquil. Consequently, the operation is a settling process, not one of agitation, as would natu- rally be inferred from the meaning of the word as ordinarily used. The apparatus in which the process is conducted is called a riffer in this country, and a sandcatcher in Europe, the latter term being the more appropriate. The reasons for rifling, or settling, are as follows, considering mechanical and chemical pulp separately: ; 18. In the grinding of mechanical pulp, which operation is performed on sandstones, particles of the stones continually become loose and are carried along with the ground pulp, unless 87 COARSE SCREENING 17 the fibers are first passed over rifflers. The pieces of stone (sand) will pass along with the fibers and eventually find their way into the finished paper, causing small holes in the paper web when passing the calenders. Besides the sand resulting from the abrasion of the grindstone, mineral matters may be present that have become imbedded in the wood when driving in the river and which have not been removed in barking; also other impurities heavier than water may have found their way into the process, and can be removed only by settling (riffling). 19. In connection with chemical pulp, mineral matters adhering to or imbedded in the wood, as mentioned above when referring to mechanical pulp, may have found their way into the digester; consequently, after digesting, they are carried along with the fibers. Where digesters with mineral linings are used, a gradual process of abrasion sets in; these mineral particles are also carried along with the fibers, and the only way to extract them is by settling, i.e., by passing the stock over a properly proportioned riffler. Where especially fine chemical fibers are produced, the riffler is a further means for separating the fiber bundles, and it thus facilitates the screening process for certain types of screens. 20. Many systems do not include a riffler, as the amount of material taken out by the riffler is not considered sufficient to warrant the space and expenditure necessitated by it; this is particularly true of groundwood, sulphate pulp, and ‘‘news’’- grade sulphite systems. Where the knot screens have large perforations and allow con- siderable coarse material to pass through with the stock, it is often found, upon washing out the riffler, that a certain amount of this coarse material has been separated and collected along the bottom of the riffler ducts. This, however, is an expensive way of obtaining a result that ought to have been accomplished by the knotter. 21. The Riffling Process.—The riffling process consists in passing the liquid containing the fiber through a long trough having pockets in the bottom, in which the impurities settle. These pockets are usually formed by placing shallow dams or baffles at intervals along the trough. In order to secure the desired effect from this process, it is necessary to have a smooth (sluggish) flow, but care must be exercised that the flow is not so 2 18 TREATMENT OF PULP §7 slow that the fine fibers will settle. The speed of the flow and the consequent loss of fiber, depend on the depth of the liquid; for if the riffler is too deep, the velocity of flow next to the baffles will be considerably less than the average velocity of the stream, and fiber will settle out. It is therefore recommended that the maximum effective depth be limited to 24 inches, and the velocity at such depth should not be less than 40 ft. per min. By decreas- ing the depth, the velocity can also be decreased. These are not hard-and-fast figures, as most mill engineers have their own ideas about rifflers. The consistency of the stock in the riffler would preferably be the same as on the screens, the lower the amount of fiber for a given quantity of water the more effective is the riffling; but, in order to have an appreciable effect from riffling, the percentage of fiber must not be over .8% air dry for chemical pulp and 1% for groundwood. 22. A longitudinal section through a riffler is shown in Fig. 6. A is the compartment that receives the stock. JB is a baffle that = —S Sa ee eee — Soe | (| Z Z y) V 2 sia tye Y Y) = j Y SS A|LEQQ]Q]H}HHHAHHNsH WN) U (NI QS 55> Sj (( == = OY a= === = : LLL LL LEE ZL Fia. 6. can be raised and lowered, thus varying the depth of the opening C. By adjusting the baffle B to the proper height, a uniform distribution of the flowing stock is secured, and this produces as calm a flow as.is possible. The baffles D form the pockets for retaining the impurities that have settled out. The height of these baffles is from 4 in. to 8 in. E is a dam at the outlet, the height of which is adjustable, so that the working or effective depth F (which is the vertical depth from the top of the flowing stock to the line marking the tops of the baffles D) of the riffer can be regulated to produce the desired quantity to be passed over the riffler or to secure any other desired effect. After passing the dam Z, the stock flows into the channel G, whence it is generally passed to the screens. When putting the riffler in operation, it is essential that it be filled with water to Oa a oe eS. Se §7 COARSE SCREENING 19 the overflow height J of the dam; otherwise, good fiber will settle in the pockets formed by the baffles D. The depth of the riffler is about 18 in. and the width is from 6 ft. to 8 ft. When the height of the baffles is about 8 in., the distance between them should be about 8 in. or 9in. The depth H of the stock where it flows over the dam is always less than the effective depth F. It is important that rifflers be so constructed that they can be easily cleaned. Formulas for calculating quantity of flow may be found in the Section on Hydraulics, Vol. II. 23. Riffling Before and After Screening.—From the foregoing explanations, it will be clear that riffing should be done .before the fine-screening operations. When the cleanest possible pulp is desired, a felt lined riffler is sometimes used. The stock, at a consistency of from 2 of 1% to % of 1%, is passed through this riffler at a speed of about one foot per second, or even less, just before the last screening. A special grade of cotton felt having a long nap, is used to line the sides and bottom of the channel, and the baffle boards as well. To secure the best results, the depth of the stock over the tops of the baffle boards should be from 3 to 5 inches, about. The floor of the channel should be level, and suitable means should be provided for washing it out without interfering with mill operations, as frequent cleaning is necessary, at least once in 24 hours. So much space is required for this apparatus that its use is limited and decidedly questionable. 24. A variation of the felt riffler, as sometimes used in the paper mill, is secured by placing the felt-covered baffles horizontally and forcing the stock to rise in a back-and-forth direction, as indi- 20 TREATMENT OF PULP 87 cated in Fig. 7. The baffles are frames on which felt is tacked, and they are held in place by cleats. QUESTIONS AND EXAMPLES (1) Why is it necessary to provide storage for pulp? (2) What is meant by “consistency”? Find the consistency of the stock when the weight of the sample is 1320 grams and the bone-dry fiber in the sample weighs 13.068 grams? Ans. 1.1%. (3) Why is it necessary to screen pulp? (4) Make a table and a graphic chart showing the weight of air-dry pulp in a 15 ft. diameter tank according to depth. Take points at each foot of depth to 10 ft. and each per cent of consistency to 10%. (5) What is the mill name for water that has been removed from pulp by the screens? Mention some uses for it. (6) What difference in character would you expect in the material rejected by the coarse screens for groundwood and for sulphite? FINE SCREENING RESULTS SOUGHT IN FINE SCREENING 25. Purpose of Fine Screening.—Up to this point, the object of the screening process has been to prepare the main mass of fibers for the final screening. Assume, for example, that 4% of the stock in the form of very coarse fibers and shives has been removed by coarse screening. There then remains 96% of the original stock to deal with. Of this amount, probably all but 5% consists of fibers of the desired size and quality for the paper- making process. (These figures differ, of course, for different kinds of pulp, and are to be considered here only for purposes of illustration.) The purpose of fine screening, therefore, is to separate this main mass of fibers into two or more grades, accord- ing to the length and diameter of fiber required in each. The ideal apparatus is that which will effect this separation in the simplest and cheapest manner. 26. Grades of Pulp.—Different grades of paper require dif- ferent qualities of pulp. In order properly to design the details of the fine screening system, the maximum length and diameter of fibers allowable must be known or determined, because all fibers of this maximum size and smaller are intended to be segregated $7 FINE SCREENING 21 from the others by the fine screen. The exact dimensions of these limiting (maximum) fibers are seldom expressed in units of length (say decimals of an inch), as it would be almost impossible, commercially, to measure them. The proper standard reached by the pulp is determined by the experience of the paper or pulp maker, having regard for the use to which the pulp is to be put; and this zs controlled by the size and shape of the perforations or slots in the screen plates, by the force used in passing the fibers through them, and by the consistency of the stock. The standard here referred to does not cover all the physical properties of the pulp; it merely governs the maximum size of the fibers. 27. Features of a Fine Screen.—The essential parts of a fine screen are similar to those of the coarse screens; namely, a per- forated plate mounted on a frame, some apparatus for forcing the stock against the plate, and a housing or container for these parts. When stock is admitted to the screen, it comes into contact with the screen plates and tends to flow through the perforations. These small perforations (holes 3/5 inch in diameter or slots about z$o inch wide) offer greater resistance to the passage of the fibers than to the passage of the water in which they are suspended. Therefore, there is an immediate tendency for the fibers to collect around the holes and completely block them. To remedy this, an agitating action must be set up to prevent the separation and to allow the water to perform its only function— that of a conveyor. 28. Points to be Considered in Selecting a Screen.—A screen must perform a definite service; and certain conditions must be maintained, under which it is to be operated, if the desired results are to be obtained. In selecting the type of screen to be used, the main points to be considered are: (a) cleanliness of output; (6) cost of installation, upkeep, and repairs; (c) power required per unit of output; (d) space required; (e) capacity and efficiency of unit; (f) conditions necessary for proper operation. Each of these points will be considered in detail. (a) Cleanliness of Output.—This means comparative freedom from dirt specks, discolored fibers, etc. These are very often chargeable to the inefficiency of the preceding processes, and their origin should be determined before placing the blame on the type of screen used. (b) Cost of Installation, Upkeep, and Repairs.—The first cost of 22 TREATMENT OF PULP §7 a screen is very often given undue consideration by careless buyers. It is only by considering the system as a whole, taking into account the cost of operation and repairs, space and number of units required and efficiency of each, that an intelligent decision can be reached. Conditions vary at different mills, and each mill should be considered separately. Cost of operation and repairs covers the cost of labor, material, and power. (c) Power Required per Unit of Output.—This is usually ex- pressed in horsepower per ton of air-dry fiber screened in 24 hours. (d) Space Required per Unit.—Space required per ton of screened product per 24 hours is another important factor, since each square foot of floor surface represents a considerable expen- diture of capital. (e) Capacity and Efficiency of Unit.—It is evident from (d) that it is advisable to have the capacity (output) of each screen as large as practicable. The efficiency should be considered at the same time as the capacity and power. It might be possible to increase the capacity at the expense of efficiency of screening, and it is only after careful tests under standard conditions that the effective capacity of a screen may be determined. This is best illustrated by taking a concrete case: Suppose a centrifugal screen is capable of passing, under certain conditions of speed, size of screen-plate perforations, and consist- ency of stock, 15 tons of good stock out of 16 tons delivered to it; it extracts 1 ton of fiber of such quality that it is desirable to reject it, z.e., zsth of the stock going to the screen is rejected. Now suppose that by altering one or more of the conditions, the screen is capable (at an increased power consumption, perhaps) of screening 20 out of 22 tons delivered to it, but that the 2 tons rejected contain a considerable proportion of fibers that should not be rejected. The amount rejected is here # = 7th of the stock going to the screen, a considerably greater proportion than before. It is conceivable, however, that it might be advisable to operate under the latter conditions and re-screen the rejections, in order that practically all the good fibers of the standard desired may be extracted from the rejections, or tailings, as they are called. The two operations may be more efficient in respect to the final result than the single operation first considered. (f) Conditions Necessary for Proper Operation.—It is safe to assert that a large number of screens are being operated under conditions that do not allow of the most efficient capacity being 87 FINE SCREENING 23 realized, due to lack of knowledge of the requirements and in- ability to control conditions of operation. A careful test ought to be made, if the most efficient results are desired. 29. A Test of a Centrifugal Type of Screen.—A certain ground- wood screening system, installed in one of the larger mills of the country, was investigated to determine its efficient capacity per unit and the conditions under which it could be obtained and maintained. The system was considered good; it had been in operation for several years, when an increase in capacity became necessary. A study of the screen was made under the normal working conditions at the mill, with a view to ascertaining: (a) power consumption; (b) speed of rotation of agitator or impeller; (c) consistency of stock; (d) quantity and quality of stock accepted and rejected. It was found that the stock delivered to the screen contained so many slivers (which blocked the screen-plates) that no standard conditions or results could be obtained (7.e., it was impossible to secure uniformity in the quantity and quality of the output), because, after a few hours of operation, the screen rejected a large amount of stock that it ought to have accepted and that it» did accept when the screen plate was kept clean. This clogging of the screen plates had been known, but until the test figures were available, its full significance was not realized. This trouble was overcome to a certain extent by the cleaning of the screen plates; but to keep them clean and in proper screening condition, required so much extra labor and expense that it could not be afforded. The problem was resolved into eliminat- ing the objectionable slivers before the stock reached the fine screens, and it was solved by changing the screen plates in the coarse screens, by substituting plates having smaller perforations. It was also necessary to add more screen units, as the use of finer plates decreased the capacity of the coarse screens considerably. After these changes had been made, a second series of tests showed that the plates of the fine screen could be kept clean for a long period, with the result that there was a marked increase in efficiency and capacity. Thinking that the efficiency and capacity of the screen might be further increased, a change was made in the type of agitator or impeller used, on the theory that the stock was not being evenly distributed over the surface of the screen plates, and that the impeller was ‘‘churning”’ the stock without doing effective work, thereby consuming unnecessary 24 TREATMENT OF PULP 87 power. By varying the speed of rotation of the new impeller, and the consistency, the most efficient conditions were deter- mined for this particular screen system. With the same power consumption, it was found that the capacity was nearly doubled and that the quality of the screening had not suffered. 30. Influence of Consistency.—The beneficial results of ade- quate coarse screening and the effect produced by the use of the proper amount of force and distribution of stock by the impeller were considered in Art. 29; it now remains to show what effects may be produced by varying the consistency. The consistency of the stock at which any screen does its best work must be determined for that particular machine by actual test under operating conditions. If the stock be too thick, the percentage of rejections (tailings) will be too great, and they will contain fibers that ought to have been accepted. If, on the contrary, the stock be too thin, more power will be used to screen the same weight of fiber, and the capacity of the screen will be reduced. The extra water required to dilute the stock to this consistency will have to be handled during the subsequent stages of the process, with resulting increase in power used and decrease in capacity. A better idea of the results obtained under varying conditions may be obtained by reference to the consistency table given at the end of this section. This is a very convenient table, showing, as it does, the amount of water and air-dry fiber in different volumes of stock of varying consistency. Assuming that screening is being carried on at .35% when it might have been done at .50%, the difference in the number of gallons of water handled per ton of fiber at these two consistences is 20,518 gallons, found as follows: Referring to the above men- tioned table, the values in column II show the number of gallons of water required to dilute 1 ton of air-dry fiber to the consistency given in column I. According to the table, the number of gallons thus required when the consistency is .35 % is 68,154 gal., and when the consistency is .50%, the number of gallons required is 47,636; hence, 68154 — 47636 + 20518 gal. of water additional must be handled when the consistency is .35% than when it is .50%, an increase of 20518 + 47636 = .48+ =43%. ‘There will be nearly the same increase in power and a pate te reduction in the capacity of the screen. 31. Consistency Control.—In the majority of cases, the operator judges by sight whether the consistency is high or low, a a | ee ee ee ee ee ee ae . 87 FINE SCREENING 25 and increases or decreases water accordingly. It is possible to regulate automatically, within reasonable limits, by use of the apparatus described below, the consistency of stock coming from the storage tanks before screening. As previously stated, this stock may be 3% air dry, and means have been found for keeping stock of this consistency fairly uniform. Starting, then, with this regulated stock, if the quantity being used at any time while adding a continuous supply of the proper amount of water, can be determined, the mixture must be of a fairly uniform density (consistency). The problem thus reduces to finding some means of measuring the amount of stock of a certain density, which is to be continuously diluted by the requisite quantity of water to the consistency desired. The writer knows of no better method of controlling the consistency of stock as thin as .5% than by use of the mixing box shown in Fig. 8, to which the reader is now referred. Referring to Fig. 8, F’ is the feed pipe for the regulated stock; F” is the feed pipe for the water used to dilute the stock; S is the stock-measuring box; W is the water-measuring box; M is the mixing box, where the stock and water mingle; G’ and G”’ are gates, which can be raised and lowered to control the supply of stock and water admitted to mixing box M; 0’ and O” are outlet pipes for the excess stock and water, respectively; O is the outlet pipe from the mixing box M; A’ and A” are worm gears that are operated simultaneously by the wheel B; X and Y are the open- ings from the measuring boxes S and W, respectively, to the mixing box M. | The operation of the apparatus is as follows: More of the regu- lated stock than is required is pumped into the box S, filling the right-hand part to the top of the baffle plate P’, which it then overflows and the surplus runs out through the pipe 0’; the gate G’ is raised to such a height that just enough stock flows into the mixing box M to keep the overflow height in measuring box S at a constant height; in other words, it keeps the head h’ on the center of the opening X constant, and thus admits a constant supply of stock to the mixing box. The same effect is secured, and by the same means, in admitting water to the mixing box from the water-measuring box W, under a constant head his: The heights of the gates G’ and G” are so adjusted that the proper supply of stock and water is admitted to the mixing box to pro- ‘duce stock of the desired consistency. If the flow of stock and 26 TREATMENT OF PULP 87 water should vary, or if the overflow is greater than is desired, the gates G’ and G’” may be raised or lowered simultaneously, by turning wheel B, until they are situated at the proper height. 32. There may be variations in the method of applying the | principle just described, but more uniform results are achieved than can be obtained by the eye of the operator. The results of a typical consistency test for a centrifugal screen on groundwood are shown in Chart 4 (Art. 41); such charts illustrate very forci- bly the necessity of consistency control. From what has preceded, it is obvious that an increase in the consistency tends to lower the power consumption per ton of pulp fed in; but in securing this result, there is an increase in the proportion of tailings. As it may become necessary to screen the tailings again, there is evidently a point in the process where the saving in power is balanced by subsequent losses elsewhere; the consumption of power does not decrease, while the amount of tailings increases rapidly. 33. No. 2 and No. 3 Grades of Stock.—The chart referred to above shows that the tailings from the fine screens may amount to as much as 10%, in which case, it may be advisable to re- screen, removing such fibers as are not too coarse. The coarser fibers then left are diluted with water, usually white water, and by use of screen plates having larger perforations or slots, a second or third quality of stock is produced. This stock may be refined and reduced to the standard desired or it may be disposed of for special uses in different grades of paper. 34. General Difficulties.—Aside from those already discussed, the usual troubles attending screening operations are: broken screen plates, improperly fitted plates (allowing leaks of un- screened stock into the screened stock), difficulty of keeping plates clean (this applies more particularly to the screening of groundwood, and is more pronounced in certain types of screens), and the foaming of chemical pulp if the acid has not been properly removed in the blow pits. The remedy suggested for broken or improperly fitted plates is frequent periodical inspection of the stock accepted by each screen. Various methods of doing this are in use. One that is simple and effective consists in passing a pailful of screened stock through a piece of wire cloth of about 10 mesh; the majority of the finer particles readily pass through, leaving a film on the wire ’ 7 A 4 1 4 q a 2 §7 FINE SCREENING 27 cloth. If held before a strong light, slivers are quite easily distinguished. The cleaning of screen plates will be considered in connection with the description of the various types of screens. The foaming of stock is usually remedied by the addition of small amounts of some liquid, such as kerosene or anti-foam oil, which lowers the surface tension of the stock solution. In S\\, 3 The y Y DG att y Y Y Y wie Z g ig AWE WSyyy9 NY Z , vo ] DNA y in DIG AK Z Ui) WY gen G MZ Fok ANG aM hi V Sy VA Et Nd) WE = mB /\\l) () hs a a? Ay il lite —— agY BW Al QAS AG Dees) Mela g a iN) = ——- 7) ] a i) | % ! Bi sineDyy y A Bae oe oa 4 AO’ Ai rv ee LZ Y j aS A) ZS) yj} gs YY SSS SSS SSS} i MM —S KW these circumstances it is also advisable to use cold fresh water to dilute the stock and allow as much white water as possible to escape to the sewer, thereby removing the trace of acid that causes the trouble. TYPES OF FINE SCREENS 35. Diaphragm or Flat Screen.—A type of screen that is extensively used in the pulp and paper industry is the diaphragm screen, which is often called a flat screen, because all the plates lie in the same plane. This plane is either parallel to the floor 28 TREATMENT OF PULP §7. of the room (horizontal) or it may be inclined downward slightly, to aid the stock in flowing over the plates. The term diaphragm is applied to one of the most important parts of the screen, and from it, the machine takes its name of diaphragm screen. A screen of this type is shown in Fig. 9, (a) being a longitudinal section and (b) a cross section. The various parts designated by numbers are: 1, pulley; 2, shaft; 3, bearings for shaft; 4, adjust- ment nuts for diaphragm mechanism; 5, diaphragm plunger, or pitman; 6, screen frame; 7, wooden shoe; 8, grease box for cam; 9, clamp for shoe; 10, screen box; 11, flow box; 12, screen plate; 13, strips around edge to help secure screen plates; 14, wooden clamp for diaphragm (lower part); 15, wooden clamp for dia- phragm (upper part); 16, passage to flow box; 17, beam to carry bearings and grease boxes; 18, frame to which diaphragm is attached; 19, cross pieces of above frame; 20, cross pieces of screen box; 21, cross pieces of screen box (these support the screen plates); 22, diaphragm (rubber); 23, wooden connection between diaphragm board and plunger; 24, cam; 25, supporting arm for springs; 26, ball and socket joint; 27, arm bearing on shoe to make it follow cam; 28, adjusting springs; 29, spring to keep shoe on cam; 30, side strip to which end of screen plate is screwed; 31 and 32, fixed and movable parts of adjustable slide dam. 36. The diaphragm screen depends for its operation upon a combination of gravity flow and suction. The stock flows into one end of the screen box 10 and passes toward the other end over the screen plates 12. As the fibers pass over the screen plates, the accepted stock passes through the slots or perforations and runs into the space between the plates and the diaphragm 22, from whence it gravitates by the way of the passages 16 to the flow box 11, where the adjustable dam 31, 32 regulates the back pressure on stock under the screen plate and varies the effective head that induces the flow accordingly. Enough stock is admitted to the screen to keep the upper surface of the screen plates covered. Then the vibrating motion given to the dia- phragm 22 by the cam mechanism 5, 7, 24, which causes the diaphragm to rise and fall, creates a partial vacuum in the com- partment under the screen plates, thus causing a flow of stock through the slots or perforations. A greater volume of stock must be admitted to the screen than it can possibly accept (screen), because a fairly rapid flow must be maintained over the surface of the plates, which must be kept covered with a thin oe YS a ae ey : | : | FINE SCREENING q S=47q s ae 7 1 LMU LADY = = "oe Ss PT efi Ze ———— 184) wy AT = Oy) = (a) Li Se EZ 4 Fic. 9. 30 TREATMENT OF PULP §7 layer of stock to maintain the vacuum and insure proper opera- tion. For this reason, the rejections, or tailings, from a single screen of this type are very large and contain much good fiber. To cut down the final rejections to a reasonable amount, several screens are connected, end to end, each delivering the unscreened pulp to the next in succession. Such a battery of screens (usually 3 or 4 screens to a battery) is so arranged that by the addition of showers directed either against or with the current of stock across the plates, the fibers are prevented from settling, and good fibers are washed from shives and knots. Finally, the coarse fiber and tailings run out of the battery of screens at the opposite end to that from which the stock was admitted. The accepted stock is discharged, of course, from flow box 11. 37. The size of the screen box depends upon the size and number of screen plates to be used; that is, the box is wide enough to allow the screen plate to be placed lengthwise across it and is long enough to contain the combined width of all the screen plates it is desired to put init. A convenient height for the sides of the box is 2 feet above the level of the diaphragm. The joint at the level of the diaphragm, between the screen box and the diaphragm frame 18, is generally hinged on heavy hinges, which are placed on the side opposite from the flow box, thus permitting the upper part of the screen box to be tilted at regular intervals, when the plates and passages are thoroughly washed from beneath with a high-pressure stream of water, to prevent the formation of slime. For sulphite pulp, where the stock to be screened contains acid, the screen plates are made of bronze; but for groundwood, sulphate, and soda pulps, they are made of brass. A single plate — is about 34 feet long, 1 foot wide, and about 2 inch thick. The slots, which are wider at the bottom than at the top, are usually about 4 inches long and are arranged about 4 or 5 to the inch. The width (or caliper) of the slots varies with the kind and quality of the stock to be screened, and this dimension must be determined by each mill, according to the fiber it wishes to get. For first quality fiber, the width might range from .008 inch to .012 inch, for mechanical, sulphite, and soda pulps, and for screening the stock in the paper mill; for second quality fiber, widths from .011 inch to .015 inch, or even wider, are used. For sulphate pulps, wider slots are used than those just mentioned. The diaphragm 22 is a sheet of special rubber that is about ce a, ee 87 FINE SCREENING _ 31 1 inch thick; it is fastened to the screen frame with nails or SCrews. 38. The diaphragm screen is simple in operation. The shaft 2 of the agitating element is driven at about 125 to 175 r.p.m. Stock is admitted at a consistency dependent upon the work demanded of the screen by the general screening system; the finer the slots are in the plates the thinner (lower) the consistency must be. With the mechanism and screen plates in good repair, the only problem is to keep the screen plates clean. Scrapers, either hand or mechanical, are frequently used on diaphragm screens, especially those screens that are used on tailings. Screens of the inclined type (those with the screen plates inclined instead of horizontal) have a tendency to be self cleaning. A hand scraper is simply a piece of board about 6 in. by 18 in., with a long handle. The mechanical scraper consists of slats, which may be dragged over the surface of the screen in the direction of the flow of stock or may be pushed back and forth by oscillating arms. The one advantage of the diaphragm screen is the cleanliness of the output. The approximate amount of stock that can be screened per plate is from .275 to .4 tons in 24 hours, or more if the slots are large; the amount varies with the kind of fiber and other conditions. 39. The low capacity (output) for the size of the apparatus, involving as it does a large number of moving parts, results in a high cost per ton screened. Also, where economy of space is a factor, the diaphragm screen takes up a relatively large amount of room per unit of production. The power per ton screened varies, a 12-plate screen requiring about 3 h.p. The cost of operation of flat (diaphragm) screens is high as compared with centrifugal screens. No general authoritative information is obtainable as regards capacity at different consis- tencies, per cent of tailings (or rejected stock), and so forth, but the following figures are indicative of the cost of operation and repair as compared with centrifugal screens. The figures are taken from records kept at a mill where flat screens were replaced with centrifugal screens: Operating and repair cost per ton screened for flat screen was $1.12; for centrifugal screen, the cost was $0.21. The flat screen requires a large amount of attention while 32 TREATMENT OF PULP 87 running, to keep the slots in the screen plates clear and to adjust the flow of stock. It is necessary to open the screen box fre- quently, to clean inaccessible passages where slime tends to collect. The wooden construction and the large number of moving parts necessitate a large amount of repairs. Inspection of the screen while running should be (1) of the accepted stock, to determine the presence of coarse fibers, which indicates broken or ill-fitting screen plates, which should be searched for when their presence is suspected; (2) inspection of rejected stock, which may contain too much fine fiber, indicating clogged screen plates or the admission of too much stock to the screens; (3) for mechanical troubles. Methods of fastening screen plates vary; for security, screws at 5-inch or 6-inch intervals around the plate are used. A single bolt in the center of the joint between two plates not only gives security but also makes it easy to remove the plates; a number of patent fasteners are designed for the same purpose. 40. Horizontal Centrifugal Screens.—Figs. 10 and 11 show a longitudinal section and a cross section of two horizontal cen- trifugal screens. Both machines operate on the same principle, but their construction is different. 'The numbers listed herewith refer to parts of either machine: 1, outside casing; 2, pulp inlet; 3, distributors; 4, bearings; 5, shaft for runner or impeller; 6, impeller blade; 7, white-water shower inlet; 8, dome; 9, tailings outlet; 10, accepted stock outlet; 11, screen plate. Referring to Fig. 11 only, 12 is the plate cleaning shower, and 13 is a case enclosing gearing for rotating screen plates while cleaning. These screens are operated by the action of centrifugal force, which drives the stock against the encircling screen plates, through the perforations, to the outside. The principle is simple: when- ever a body is caused to revolve, it tends to move away from the center of rotation, and the faster the speed of rotation the greater is this tendency, 7.e., the greater is the centrifugal force. In the present case, there is no force acting on the stock tending to | force it toward the center, with the result that the stock is thrown radially outward, forced against the enclosing screen plates, and through the perforations. The stock enters through the inlet 2, Fig. 10 or 11, and is sepa- rated into several streams by the stationary distributors (com- partments) 3, from which it flows to the impeller blades 6; this insures a much better distribution of the stock, breaks it up as it FINE SCREENING 33 §7 N N N ; ; 4 N ; : : ‘Or iS YW ZX MSS a | NA SH Ws Leva eS ‘DLq ir SSSY SSL SA ASSIS st Vy r INNIS oa SR CRAIALELTLTY Fe SSS SS BZ Sods a SQ Sy YQ CAAA SSS g as LY, ZA rg SSS SSS SSS ES ES SY {a | eae aan nnn mene nee creme Soe ngaae 34 TREATMENT. OF PULP §7 were, than if it flowed in a single stream to the impeller blades. This matter of distribution is important, since it has a direct bearing on the capacity, horsepower consumed, and the efficiency of the screen. In Fig. 11, the stock enters from both sides of an | ' 1 rae 9} \ Pree a swt LLLLEZILE LILLE ip LLL LLL LLL LLL SSS AARAQ Ss . LIZIIIITI FED a, 77 00 fF HRS Hp RON V4 Ge xy, ff / () Hriey 11. the center through the orifices 3. Impellers, as well as distrib- utors and manner of introducing stock, vary in design, and these are the chief differences in this type of screen, as made by various manufacturers. The impeller, or agitator, consists of a shaft 87 FINE SCREENING 35 with blades set at regular intervals around it; it is generally made of cast iron for use with all classes of stock except sulphite, when bronze is advisable, to resist the acid. The impeller should rotate at a speed that has been predetermined to suit the condi- tions and the class of stock to be screened. The screen plates 11 are usually rolled copper sheets, perforated with holes varying from .05 in. to .07 in. or larger in diameter; a common size for eroundwood, sulphite, and soda pulps is zs in. (.0625 in.). For the screens here shown, the screen plates are secured to the frames, which are bolted to the screen body. In some designs, provision is made for the rotation of the screen plates at a slow speed, to facilitate cleaning them. | The accepted stock passes through the plates and falls by gravity through the space between the plates and the casing to opening 10, which is a discharge spout. The fibers that are too coarse to pass through the perforations in the screen plates are thrown off from the impeller by the short wings at the back of the machine shown in Fig. 10 or from the ends of the inclined blades of the machine in Fig. 11, and they find their way out of the tailings spout 9. The rear head of the machine shown in Fig. 10 is hollow, as indicated by 8, and one side of the chamber thus formed is perforated, thus providing a shower when water is forced into the chamber. In the case of the machine shown in Fig. 11, the water is introduced through the shower nozzles 7. This shower plays an important part in the operation of this type of screen. ‘The water 1s introduced at this point to wash the coarser fibers that have been forced to the end of the screen by the action of the impeller blades, thereby washing out some of the finer fibers from the coarser ones and increasing the screening efficiency. These screens are designed for continuous operation and require but little attention. The only running adjustments that are necessary are those for securing uniformity in the amount and consistency of the stock supplied. Inspection should be made of the accepted stock for coarse fibers, the presence of which indi- cates a broken or leaky screen plate. Likewise, inspection should be made of the rejected stock for fine fibers, the presence of which indicates that the consistency of the supply is too high, that too little shower water is used, or too large a quantity of stock is being admitted to the screen. This latter will also be indicated by increased power consumption. 36 TREATMENT OF PULP §7 41. The following graphic charts indicate capacities and power consumption with varying consistencies of stock for certain specific types of horizontal centrifugal screens under conditions as stated. Screens of the same design under different conditions and screens of different designs would have to be thoroughly tested, In order to determine their capacity and power consumption. These charts are inserted here to illustrate the necessity of exact knowledge of the governing factors; they are, ina general way only, applicable to all screens of this type. 50 8 BM ae Rs es EE CCE ee ee SECEC Cee “ PTC ee ers - 325 NES Ton in 8 Horsepower per Air Dry Ps} SER LASS ARRAS IER. ARR REAR AE SD WES Ss SRNR RS SALSA RRR ARDS AMARA RN ee Pa eet leet Le a ptt tt Pelldebk 7erAeobi tt ttt tT tt tt (e) {00 200 500° 400 500 Runner Speed R.P.M. The effect of varying factors is shown in Charts 2, 3, and 4. Chart No. 2 illustrates what happens to the power consumption and percentage of rejected stock (tailings) when the runner speed of the centrifugal screen handling growndwood stock is increased. The curves are based on the number of revolutions per minute for three differen tspeeds of the runner (impeller), the corresponding H.P. consumed for each ton of air-dry pulp fed to the machine, and the percentage of tailings. It will be seen that the power requirement increases rapidly and also that the percentage of tailings decreases, but less rapidly, as the speed increases. This may be easily explained, because it is evident that the higher the speed of rotation the greater must be the power required to drive the runner; also, as the speed of the runner §7 FINE SCREENING 37 increases, the centrifugal force throwing fibers through the screen will increase and the tailings will naturally be less on that account. Chart No. 3 shows the effect of increasing the runner speed on the horsepower consumed per ton of air-dry pulp fed to the machine, also the percentage of tailings when screening sulphite pulp. On both of these charts, the vertical figures at the left represent horsepower (h.p.) consumed and the figures at the right represent percentage of input that is discarded as tailings. The chart is read as follows: Assume that it is desired to find the horsepower (h.p.) consumed and the percentage of tailings in - groundwood pulp that is being screened with a runner speed of 300 r.p.m. The vertical line from the 300 figure at the bottom w 320 Qe Se Ee 8 ay Oe Be am eet fe ea a “in ae ister tel ra Sune Se oe sl iq\ SSD ae 28 aS RB ER ine So Poy g PCES Oe eS a Saas z eis =n 2 HH : Sole $ sl a" L] ® ti ime A Sone eee 2) 22°C CERO Me sae x Oo 1GOn e200 3500 400 Runner Speed R.F.M. crosses the power curve at a point which corresponds to 1.18 h.p. per ton of input and crosses the tailings curve at the 2% line. Similarly, for sulphite pulp, extend the horizontal to the left from the point where the vertical line at 300 revolutions crosses the power curve and find that the power consumed is .94; it crosses the tailings curve at 30%. Therefore, by increas- ing the speed to 400 revolutions, about 2% on the tailings 1s saved at an expenditure of .86 h.p. extra per ton of input. The sulphite tailings in the test from which these curves were obtained are high, because of the desire to obtain maximum cleanness in the accepted stock. By increasing the shower water in the ‘screen, more of these could have been washed through. Further- more, the plate perforations were finer than usual. In these tests, the consistency of the stock in each case was 5% air dry. The screen plates for groundwood had a total 38 TREATMENT OF PULP 87 area of 3360 sq. in., with 324,000 holes, each .0625 (3's) inch in diameter; while the plates for sulphite had the same area, but contained 358,000 holes, each .0550 inch in diameter. The groundwood screen took 30 horsepower while thaw for sulphite consumed 375 horsepower. Chart No. 4 is more complicated, and shows the mutual change ’ in the various factors of importance in screening. In this case, a centrifugal screen, with plates perforated with .065-inch holes, operated on sulphite pulp at a constant speed of 388 r.p.m. In this test, the consistency of the screened stock was changed from 18% to .88%. At the start we find the horsepower per ton is 3.3, and the tailings were 5.7% of the input, while the quantity +. lo srestasrratets os |_| BEEEEE Ne /0 30 Load 7ons Sake: per 24 Hours of stock fed was 18 tons per 24 hours. On increasing the con- sistency to .24%, the horsepower per ton dropped to 2.7, while tailings increased to only 6.2%. On further increasing the consistency, the horsepower gradually fell off to 1.6 at the end of the test, while the percentage of tailings had increased to 11.9%. The temporary drop in the tailings is not explained in the data, but may have been due to a thorough cleaning of the plates or even to a difference in temperature or in the character of stock from another digester. It will be noticed that the power consumption curve drops off less and less rapidly as the consistency of the stock isincreased. This indicates that the point is being approached at which a further increase in con- sistency will not cause a decrease in power consumed and that from there on, the power consumption will increase if the con- sistency be raised. 87 FINE SCREENING 39 This study of curves thus brings to light many important points in the operation of pulp mill machinery. 42. Vertical Type of Centrifugal Screens.—There are a few ZEL Lea 7. Br SST) MSG Nyy SII Ss rom UMM Dy, SV 4/7 . 5 Atos 16> 4 H H aD N as H HN N HN N HN NN HN N HN N x as Nez) aN S N N aN N N N N \ Ns SSS SN wal) ASSESS J : eS Y [oes Sa /. N : —— SILESESIOTTSSSESSEITEES LY emo Lp oe N SSS ——S Lo = LILIA L. SS: CH ith Ltt YZ CRRA AMVAVY ZZ, x Wht bttidhtetbithtd tts | sees . — ZZ. N S X SS Y SS J a PN ZZ screens on the market in which the axis of the shaft carrying the impeller is vertical instead of being horizontal, as in the case of the two machines described in Art. 40; these belong to what is called the vertical type of centrifugal screens. 40 TREATMENT OF PULP 87 A centrifugal screen of the vertical type is shown in Fig. 12. The pulp (stock) enters the screen through the inlet P and is discharged into the two chambers A and B. The stock overflows the two circular rims a and b and passes from the chambers A and B-to the upper and lower parts of the double runner, or distributor, D, which is rigidly connected to the shaft Y and turns with it, thus causing the stock to be thrown against the screen plate cylinder C by centrifugal force. The tailings, and what good fiber may not have passed through the screen plates, fall down on the table H, where they are diluted with water that enters the tailings runner F through pipe G and is thrown out through the nozzles H. In this diluted state, the tailings flow down on the wings of runner F, and they are thrown against the screen plates C for the second time. The washed tailings then fall to the bottom of bowl K, where they are washed by water from pipe L, and are finally discharged through the tailings outlet M. The accepted stock passes through the screen plates C into chamber N, drops to the bottom, and is discharged through the accepted stock outlet O. The screen-plate cylinder is made in four sections, which are held together by steel clamps. The screen plates rest on frames on leather cushions, which allow the necessary vibration. ‘The screen has hand holes, for inspection and cleaning. The inlet P is provided with a gate valve, for dilution of stock, if desired. 42A. Another type of horizontal centrifugal screen, one employing a different screening action, is being used for mechani- cal and chemical pulps. ie bial a Q 5 ad SS ; spe i {|| es ; Pst alte | a B mage a SS supecce PEE 3b eee cia Per epa pesaiatts tole lar be SES eS S COC ea eee Paleo ste & 20F eee on fesse aoe aT ae ls) 9 nO WO ae Sp eller [LI ie &° /2e3s3 4 § 6&6 l2 13 14 1§ 16 17 18 19 20 2l 22 Tons of Pulp Removed per24ffours The consistency of the stock supply, the speed of the cylinder, (and mesh of cylinder cover) are very important factors in determining the capacity; if the machine be operated properly, these are the only factors. Charts 5 and 6 indicate the capacity that may be expected from a decker having a cylinder 36 in. in diameter and 94 in. long when operating on groundwood, and show the effect of varying speed of mold and consistency of stock in the vat. No equivalent data concerning chemical pulps is available, but it is safe to expect a machine operating on chemical pulps to have a capacity that is three to four times as great as the chart shows for groundwood. Chart No. 5 shows the effect on the capacity of a decker, when the consistency of supply is altered at various speeds of the cylinder; and the curves on this chart also show what capacity may be expected from groundwood pulp, if the consistency of supply and speed of the cylinder are known. In this case the 56 TREATMENT OF PULP §7 cylinder was 94 in. long; so the capacity may readily be calculated in terms of tons per inch of cylinder width per day. As an example, assume that the supply has a consistency of 0.5%. Following this horizontal line, it is found that if the cylinder is rotating with a surface speed of 160 feet per minute, the capacity of the decker will be 7.6 tons per 24 hours; whereas at 207 feet per minute, the capacity will be 12.9 tons per 24 hours. On the other hand, if the consistency be increased to 0.7%, the capacity at 160 feet will be 10.7 tons per day. The slope of the curve therefore shows also that at the higher speeds an increase in consistency gives a correspondingly greater increase in capacity than at the lower speeds. el tT ere FEEEEE EEE HEE LT TT Aes TT tal ° J = baked | ( ped BNA a Ne Pere C\ BEGMERE S\N OSES | | | | fan} r\! Na EERee Lacy TN [3 NOL pa —d t, = bs po CCC aN CCS onmee, BERERaS et eb al SaeneeAG ce {{\ Sms me Sannn,- RAND DB | AY | | ol W Bis. igi Tons Of Pulp Removed per 24Hours Chart No. 6 shows the effect on the same machine of changing the distance of the stock level in the vat below the top of the cylinder. The wire speed in this case was kept constant at 207 feet per minute. With a consistency of 0.5% a 15-inch differ- ence in stock level gave a capacity of only 10.9 tons while the 9-inch level gave 12.8 tons, and the 3-inch level, 14.5 tons. In other words, the larger the area of the cylinder immersed in the stock the greater is the capacity of the machine. It is thus evident that a careful test should be made to determine the best operating conditions for each grade of stock. The consistency of stock delivered decreases as the level in the vat rises. In practice the level is maintained as high as possible to give the required consistency of discharge. 50. Pneumatic Thickener or Save-all.—Fig. 16 shows three views and one detail view of a pneumatic thickener, which is also a a eee as an Ne RE ee §7 TREATMENT OF PULP AFTER SCREENING 57 used as a save-all and as a water filter. A partial end view is shown at (a), a side view at (b), and a plan at (c). The numbers refer to the following details or parts: 1, air pump; 2, hand wheels “4 Je oa : Ren a \ wee TS dE 4 ee ' om a Mae, | . y es , a 4 ' | “a ¢ a H ail hb Soa OIE WOU AH ATT Usunza Fic. 16. for stock-inlet gate; 3, stock-inlet gate; 4, drive pulleys for cylinders; 5, cylinders; 6, doctor; 7, pressure, or blower, chamber; 8, vacuum, or suction, chamber; 9, pulp supply; 10 and 11, parts 58 TREATMENT OF PULP §7 of blower duct; 12, 13, 14, 15, parts of vacuum duct; 16, blower duct; 17, shower (water); 18, point where stock is blown off cylinder; 19, vat. As a decker, this machine is used to thicken chemical stocks. The cut shows two cylinders 5, which revolve in opposite direc- tions in a vat 19, the cylinders being covered with the usual wire cloth. The stock enters the vat over adjustable gates 3, which are operated by the hand wheels 2; the gates are nearly as wide as the cylinder is long, thereby effecting an even distribution of the stock without objectionable eddies. The fibers are deposited on the surface of the cylinders, as the result of the water passing through the wire-cloth covering. Instead of relying on a differ- ence of level between the stock on the outside and the water on the inside of the cylinder to force the water through the wire cloth, as in the machine shown in Fig. 15, a difference of air pressure is created for this purpose. Each cylinder is divided into radial sections (sectors) that run the full length of the cy- linder; see view (d), which shows an end view of the cylinder. The ends of each section are open, to provide an exit for the water that flows through the wire cloth into the pockets formed by the sections. As the cylinders revolve, the ends of each pocket pass by openings or ports in a duct in which a partial vacuum is maintained. The suction action thus induced in the pocket causes the water to flow through the wire cloth into the pocket, which it leaves by the ends. In this way, a film of stock is formed on the surface of the cylinder. As each section of the cylinder (pocket) reaches the top of its revolution, the ends again register with another opening or port in a duct in which air is maintained under pressure, and which lifts the sheet of pulp off the wire cloth, as shown at 18, view (d), whence it falls on the doctor 6 and then slides off into the tank or conveyor that is provided to receive it. A water shower 17 cleans the covering, and the operation of forming and discharging the sheet continues. On account of this alternating suction and blowing (which is due to the action of the air pump 1) and the length of time for the water to leave each pocket, the peripheral speed of the cylinder is much less than in other types of thickeners, a fair speed being 50 to 60 ft. per min. If the diameter of the cylinder is, say, 36 in., the number of revolutions per minute is thus about 5.3 to 6.4 r.p.m. The machines may be installed in single units or in batteries of ms §7 TREATMENT OF PULP AFTER SCREENING 59 two or more machines, bolted together, in which case, the arrange- ment of pressure and vacuum piping is varied accordingly. Different types of pressure and vacuum pumps are used, but the rotary type is the standard. The capacity of these machines is subject to the same general laws that govern the operation of eouch-roll deckers. When operating on sulphite stock, 3.5 tons per lineal foot per 24 hours is a fair estimate of the capacity of the pneumatic thickener. Chart No. 7, which is a record of actual tests, indicates the capacity at various consistencies of supply. The general effect of a change in consistency of the stock furnished to a pneumatic sulphite-pulp thickener may be judged from this chart. The Consislencies of Supply 12 1% 16 18 20 22 2% 26 28 50 52 34 Consistency of effluent-Air Ory Tons/o24Hours pulp was quick-cook sulphite, the cylinder was 74 inches wide, covered with 50-mesh wire, and traveled at a surface speed of 62 feet per minute. By changing the consistency from 0.2% to 0.6%, Chart 7, the capacity in tons of air-dry pulp for 24 hours is seen to have increased from 12 to 28 or, in terms of tons per foot of cylinder length, the corresponding capacities were 1.95 tons and 4.51 tons. The capacity at any intermediate consistency as, for instance, 0.4%, is found by extending the horizontal line at that figure until it strikes the curve and then following the perpendicular to the corresponding capacity figure which is here found to be 20 tons per 24 hours. Conversely, if it is desired to determine the consistency of supply that would give a capacity of 24 tons, follow the vertical line from 24 until it meets the curve, and then extend the horizontal to the con- sistency figure, which is found to be 0.5%. Many interesting points can be developed by the use of graphic charts. These machines require but very little labor to operate. The 60 _ TREATMENT OF PULP §7 cylinder facings need an occasional blowing out with the steam hose. One man can attend to practically any number of ma- chines required by an individual mill. The consistency of the stock delivered by the machine varies slightly with a varying consistency of supply, and may be altered somewhat by varying the amount of suction. Stock from 3% to 5% air dry is obtained from these machines. 51. The Water Extractor.—In Fig. 17, is shown a pulp thickener that differs materially from the couch-roll decker and pneumatic thickener previously described. The cut shows a plan (a) and an end view (b). The details or parts are numbered as follows: 1, cylinder; 2, paddles; 3, butterfly valve; 4, float; 5, vat; 6, shower; 7, thickened-pulp chamber; 8, agitator; 9, white- water box; 10, thickened-stock outlet; 11, nut on butterfly valve; 12, baffle. This machine operates under the same general principles as the decker described in connection with Fig. 15. The main differences are in the construction of the cylinder, absence of couch roll, and the way in which the thickened stock is delivered. In fact, it might perhaps be more appropriately called a water extractor, from the fact that as the pulp flows through the vat, the cylinder provides a means for the water to drain off, thereby leaving the remaining, or discharged, stock thicker. The cylinder consists of several spiders, mounted on a steel shaft. Around the circumference of these spiders, are bolted hard-wood slats 2, set at an angle, as shown in the cut. Over these is stretched a layer of heavy copper-wire cloth, about 31-inch mesh, which forms the support for the outer layer of fine mesh (30 to 50) wire cloth. A better support consists in winding around the slats a continuous copper wire, of about 14 gauge and about 4 inch center to center, upon which the usual 15-mesh and 30- mesh wire cloth covers are secured. The stock to be thickened enters by the butterfly valve 3. This valve is controlled by a float 4, which is set so as to keep the stock in the vat at a certain level. The cylinder revolves in the vat 5 in the direction indicated by the arrow, and the ends are sealed so the stock cannot run into the cylinder by way of the ends, which are connected with the white-water box 9. The water in the stock flows through the fine-mesh wire on the surface of the cylinder to the inside of the cylinder, and then flows out at the ends to the white-water box; this leaves the fiber on the 3 4 *. ; ‘! | TREATMENT OF PULP AFTER SCREENING 61 $7 (4) | — = fe mm a a ss i] ' ' 1 ' 1 1 4+ ------4- 62 TREATMENT OF PULP 87 surface of the cylinder, and it is carried along on the cylinder to the point where the shower 6 strikes it. The shower acts as a doctor, and it washes the thickened stock into thickened-pulp chamber 7. The baffle 12 divides the vat proper from the thickened-pulp chamber. The agitator 8 insures a thorough mixing of the stock, and it breaks up any fiber bunches or nodules. The pulp leaves by means of the discharge pipe 10. This machine is designed for continuous operation. The white water should be inspected to determine the amount of fiber in it, and an excess of good fiber indicates broken cylinder facings. This machine is also used as a slush machine for chemical pulps, water filter, and save-all. 51A. Continuous Vacuum Filters As Thickeners for Mechani- cal and Chemical Pulps.—On account of the fiber content of the water (rewater) leaving all the previously described types of apparatus for thickening pulps, some subsequent treatment of this rewater is necessary before any part of it should be discharged to the sewer. Attempts are being made to develop some appara- tus that will have a sufficiently high efficiency to make this second treatment unnecessary. In the dewatering of mechanical pulp, as much as 6 to 7 pounds of fiber per 1000 gallons may remain in the water discharged by the deckers. It is claimed that a continuous vacuum filter operating under proper conditions on the same grade of stock, will discharge water containing from ;'y of one pound to 14 pounds of stock per 1000 gallons of effluent. In thickening chemical pulps, the effluent is nearly free from fiber. These machines are built in sizes that ordinarily have such high capacity as to replace several of the previously described type of deckers. This type of machine does very satisfactory work; and it is merely a matter of a comparison of the cost of installation and operation of the two systems, to determine where such an installation is advisable. As these machines have not been used extensively in the pulp and paper industry, a study of the constructional details is advis- able, in order that they may be operated as economically as possible. 51B. Continuous Vacuum Filter.—The unit shown in Fig. 17A is the largest size pulp-type filter so far constructed, and consists essentially of eight filter disks 9 ft. diameter, and covered AR raid ae Wath P Raden pre Peanuts J ae aes A 4 _ A * ei ae Ma §7 TREATMENT OF PULP AFTER SCREENING — 63 with Fourdrinier wire or other suitable filter medium. The illus- tration ‘shows filtrate outlet and direct motor drive arrangement. These disks are assembled around a hollow cast-iron center shaft, which is mounted on a supporting frame and direct con- nected to a drive motor through a worm gear and speed reducer. A heavy sheet-steel tank, is supported from the same main frame that carries the center shaft and disks. When this tank is filled with stock or white water, the disks are submerged to a point well above their horizontal center line. The hollow center shaft terminates in a rotary plug valve, which is so constructed that Fie. 17 A; at all times its discharge port, or opening, connects only with the submerged portion of the filter disks. . % a Re: # ai §9 MANUFACTURE OF CHLORINE 43 through the pipe H. The sodium left behind combines with the hydroxyl of the water to form caustic soda. The chlorine, which is liberated at the cathode, passes out through the pipe G, and the caustic soda NaOH is discharged through the pipes F. The caustic formation occurs after the solution passes through the diaphragm, and the dia- phragm thus serves to keep the caustic soda and the chlorine apart. If they were allowed to mix, an immediate reaction would take place, and sodium hypochlorite, which is not desired in this cell, would be formed. The cathode chamber is formed by the perforated cathode on one side and the iron box K on the other, and the current flows through the latter to the cathode. The body of the cell is usually of con- crete; it is set up on a sup- port thatis a non-conductor of electricity, to prevent loss of current into the ground. The current en- ters on bus (conductor) M and leaves at N. Some of the original salt passes off with the caustic soda, but is recovered by evaporating the solution until the salt crystallizes; the salt is thus separated from the caustic soda, which is much more soluble and remains in solution. INSS SSSSSS MIMS SSS ESSSS4 SY WN SSSSS$ oon Oa wssss DS 4 Z j j j VY Y GY Y Z j Y j Y j j j 63. The Nelson Cell.—Another type of cell is shown in Fig. 14, known as the Nelson cell. A side view is shown, with a part broken out to show the interior construction of the cell. The ’ main body of the cell 7 is made of +-inch welded steel; but the upper part S is a slate gas dome, through which the graphite tt BLEACHING OF PULP | 89 anodes pass, and in which the chlorine gas collects. The per- forated steel cathode plate C is formed in the shape of a U, and encloses the sides and bottom of the anode compartment. The asbestos diaphragm D is shown as lying in close contact with the cathode, and is fastened at the top edges of the cathode. All joints are grouted in with cement, so that the anode and cathode chambers are separate, tight compartments, except for pipes that lead materials in and out. An automatic brine feed and level control is shown at A. B is the brine supply pipe; E the caustic outlet, and F the chlorine outlet. o.. 9 0 - 06. 36 2 Goma ong PN EA TAT A a a » Z ) Bw: eS e This cell is said to make chlorine gas of high purity, when so desired, because of the tightness of the compartments. This would be a desirable feature in making liquid chlorine; but for making bleach directly, the amount of dilution of chlorine by air isunimportant. Another feature of this cell is that steam may be admitted to the cathode chamber from time to time, to soften and open up the diaphragm pores, thus prolonging the life of the cell. | | 64. Other Cells.—There are several other types of diaphragm cells in use in America. The principle is the same in all, but they vary somewhat in construction. For example, the one shown in Fig. 15 is cylindrical, and has a central anode compart- ment # enclosed by a set of graphite anodes A. The diaphragm D, perforated cathode C, and cathode chamber B, surround the MANUFACTURE OF CHLORINE 89 graphite in turn. The reference letters indicate the same details y con- as in Fig. 13. A constant flow of brine is maintained b trolling the level in feed box P. In one make of cell, an oil is forced through the cathode chamber, to assist in carrying off the caustic liquor and to equalize the pressure of the anode liquor on the diaphragm. Fra. 15. Graphite is ordinarily used as the anode, and the current flows from it downwards, 65. Mercury Cells.—Another type of cell, one that does not through the brine solution, to a layer of mercury, which rests on have a diaphragm, is the mercury cell. 46 BLEACHING OF PULP $9 the bottom of the cell and which acts as the cathode. Sodium ions give up their electric charges more easily at a mercury cathode than the hydrogen ions do; hence, hydrogen is not formed when the cell is operating properly. As the sodium ions discharge, they form metallic sodium, which dissolves in the mercury and forms sodium amalgam (see Elements of Chemistry, Vol. II, under Amalgams). When the concentration of sodium in the mercury has reached the desired point, the mercury is replaced by fresh material. The removal of mercury may be continuous or it may be in the form of charges. Chlorine passes off at the anode in the usual way. The sodium is removed from the mercury by the action of water; the sodium amalgam is an alloy, not a chemical compound, and when it is brought into contact with water, the sodium immediately reacts with the water in the same manner as though it were free, caustic soda and hydrogen being formed and the mercury left free. Mercury cells differ principally in the method whereby the mercury cathode is replenished. 66. Description of Mercury Cell——A type of mercury cell that is extensively used is shown in Fig. 16. The cell consists of an enclosed box, which is supported by a hinge 14 at one end and by an eccentric roller 15 at the other end, thus providing for a tilting (up-and-down) movement of about 4 inch. The box is divided into three compartments, of which A and B at either end are anode chambers, while the larger middle compartment C is the cathode chamber. The anodes 1 and 4 are carbon plates, which are suspended from the top of the box. The principal cathode is a layer of mercury 2, which rests on the bottom of the box.. The partitions D and E do not extend completely to the bottom of the box, but dip into grooves that are filled with the mercury, aS shown, which thus entirely seals the middle com- partment from the other two. A secondary iron cathode 5 is suspended in thechamber C. With the cell in the position shown, the mercury is principally in chambers A and C. Brine is fed into A through pipe 8, and is decomposed by the current passing from anode 1 to the mercury below. The chlorine passes out through pipe 10, and the sodium is discharged at the mercury cathode, where it amalgamates with the mercury before it has an opportunity to react with the water. When a sufficient quantity of amalgam has been produced, the eccentric 15 revolves (about $9 MANUFACTURE OF CHLORINE 47 once per minute) and tilts the box, so that the amalgam that has been formed flows under partition D and into the cathode cham- ber C. Here it is decomposed by water, which is fed in through pipe 12. The sodium unites with the water to form hydrogen (which escapes at 11) and sodium hydrate (which is discharged at 13). The reactions that have been going on in chamber A are now repeated in chamber B, into which the mercury from the decomposed amalgam in C has passed by reason of the tilting of the box. The chlorine escapes at 9 and the brine enters at 7. The reaction in A now ceases until the next periodical tilting of the box, which will send the amalgam formed in B into chamber a ui ; E: ‘ a oe! Ciel ae ft ze int ‘| y 3 | | ae 4 OVW LLL DLL ry Eh ies 16. C and the mercury (which has been freed from the sodium in C) into A again. As will be noted, the electric circuit is divided; this insures that the iron cathode 5 and the mercury cathode 2 shall be charged alike, which prevents any formation of chlorine in chamber C, since this would contaminate the hydrogen, cause a waste of chlorine, and might cause an explosion. Dividing the current also prevents loss of mercury. As will be seen, the discharge of sodium from the amalgam in chamber C is a continu- ous process. ‘The source of direct current is represented at 16, and the drawing indicates that 10% of the current goes to the mercury cathode and 90% to the iron cathode. In another cell of the mercury type, a pump is used to transfer the mercury from the cathode chamber to the anode chamber. As before stated, the method of handling the mercury constitutes the principal difference in cells of this type. 67. Strength of Brine and Efficiency of Cells.—The brine used in electrolytic cells is a saturated solution of a good quality of 48 BLEACHING OF PULP §9 salt in water; this requires about 250 grams of salt per liter of water or about 16 pounds per cubic foot. The efficiency of a cell depends on the voltage and current taken for a given production of chlorine and caustic soda. The voltage depends on: (a) type of anode; (6) current density; (c) temperature; (d) distance between the electrodes; (e) concen- tration of brine. The last two of these may be left out of the discussion, because the distance between the electrodes is always made as small as possible by the manufacturer, and a saturated brine is always used. The two common anodes used in this country are graphite and carbon. Graphite is much more efficient, but is more expen- “sive. As the temperature rises, the resistance to electric current decreases until a point is reached where the high temperature makes the action of the cell chemicals on the parts of the cell too harsh. A satisfactory temperature at which to operate is 135°F. Increase in current density means increase in voltage. About 65 amperes per square foot of cathode surface is common practice. The theoretical voltage for a chlorine-caustic cell is 2.3 volts, but in actual practice it runs from 3.5 to 5.0 volts; 4 volts is very satisfactory in operation. The current efficiency is the ratio of the actual production of chlorine divided by the theoretical production for a given current. Losses in current efficiency are obtained chiefly by poor removal of the caustic at the cathode. If the caustic is not readily removed as it is formed, it will work back into the cell proper and react with chlorine. Hence, to get a high current efficiency, it is necessary to have as rapid a flow of brine through the cell as possible without so decreasing the amount of salt converted as to make evaporation of caustic and recovery of salt uneconomical. The cell should operate at 90% current efficiency. In ordinary practice, about 45% of the salt is actually converted to chlorine and caustic soda. The rest is sent through with the caustic and recovered. In figuring the efficiency of a cell, the product of amperes and volts should be considered, because power is what is bought. — . The theoretical production of chlorine per kilowatt-hour is .58 kilograms. In actual operation (90% efficiency and 4 volts), about 0.3 of a kilogram per kilowatt-hour should be obtained. This is equivalent to 1 kilogram per 3} kilowatt-hours or 4.5 horsepower-hours. §9 MANUFACTURE OF CHLORINE 49 68. Absorption of Chlorine.—The chlorine from the cells is passed into some form of apparatus in which the chlorine comes into intimate contact with milk of lime. The reaction that takes place is shown by the following equations: Ca(OH), + Cl, = CaOCl, + H.O, and peels = CaCl. +- Ca(OCl)e; or, 2Ca(OH). + 2Cle = CaCl, + Ca(OCl). + 2H.0. This reaction may take place in a tower, in which the chlorine gas passes upward and a spray of lime water is rained through the gas; or it may take place in what is known as a scrubber, in which the milk of lime is splashed through the gas current. Another plan is to pump the chlorine gas under a slight pressure into a tank of milk of lime, which is thoroughly stirred. In either case, the chlorine is brought into contact with a finely divided spray of milk of lime, in which there is always more lime than is required to absorb the ann The solution so formed is then allowed to settle, after which, the supernatant liquid is decanted and adjusted to the proper strength for use in the bleaching depart- ment. Some mills use the bleach liquor as weak as 15 grams of available chlorine per liter, while others prefer it as strong as 50 grams per liter. The sludge should be washed by stirring up with water, and again settled; this water will contain some bleach, and it is used to make milk of lime. 69. Hypochlorite Cells.—Another type of cell, the hypochlorite cell, is extensively used in bleaching cloth and, to some extent, in bleaching paper stocks. In this cell, the products of the reaction, chlorine and caustic soda, are allowed to combine immediately after formation in the cell, and a solution of sodium hypochlorite NaOCl is produced. In this cell, there is no diaphragm to separate the anode and cathode. The reaction is usually written 2NaOH + Cl, = NaOCl + NaCl + H,0}! It will be noticed that half of the salt is regenerated, and sodium hypochlorite bleach made in this way has the advantage 1 Recent investigations appear to show that the reaction is expressed by the following equation: 2Na0OH + Cl, = NaOCl, + H,0, the molecular formula Na,OCl, agreeing with that for calcium chloro- hypochlorite CaOCl., and suggesting a similar composition. 50 BLEACHING OF PULP §9 that no insoluble calcium salts can be formed. The disadvan- tages are high power (energy) consumption and high salt con- sumption. Secondary reactions that form chlorates take place very rapidly when the hypochlorite content in the cell liquor is still low, causing a waste of power (energy) and permitting only a fraction of the salt to be economically converted to the hypochlorites. LIQUID CHLORINE CONTAINERS. 70. Interstate Commerce Regulations.—The regulations of the Interstate Commerce Commission provide for the shipment of carload quantities (maximum, 30,000 lb.) of liquid chlorine in single-unit tank cars (A.R.A. Classification, Class V) and in multiple-unit cars carrying ton drums (I.C.C. Specifications, No. 27). Both types of cars are standard equipment with the principal chlorine manufacturers. | 71. Description of Class V Tank Car.—The single-unit tanks are made seamless, of #-inch steel plate, with no opening except the dome, and tested to 500 lb. pressure. The cover is a steel plate, stud-bolted to the opening, with a safety valve in the center, set to operate at 200 lb. per sq. in., together with four l-inch valves. The two valvesat angles to the length of the tank, discharge gas, and the other two connect with the discharge pipes, which extend inside to a sump at the bottom of the tank, and discharge liquid. ‘The entire valve assembly is covered with a cast-steel dome, which is provided with another cover plate. Each of the two liquid discharge pipes is equipped inside the tank with a monel-metal ball check valve, which closes auto- matically if either valve on the liquid pipes is sheared off in a wreck, or if the valves are opened suddenly. The tank is insulated with a 4-inch layer of cork board, enclosed in a 4-inch steel jacket. This insulation protects against interior pressure caused by a rise in temperature due to a fire, or to the weather. The tank is 28 ft. 6 in. long inside, and is 4 ft. 6 in. in diameter. The over-all length of the car is 32 ft. 9 in., with a maximum height of 10 ft. 10 in. The center of the valve varies from 9 ft. to 9 ft. 8 in. above the top of the rail; consequently, it is customary to use a copper tube, with an expansion bend, for the connection. -It is general practice to fill the cars with exactly 30,000 lb. (15 tons) of liquid chlorine. §9 MANUFACTURE OF CHLORINE 51 72. Description of One-ton Container.—The ton drums are made seamless, of 3-inch steel plate, fitted with two needle valves in one end, and tested to a pressure of 500 lb. per sq. in. The valves are connected to two inside pipes, which extend in opposite directions to the inside corners of the cylinders. When in a vertical line, one valve will discharge gas, and the other, liquid. Each drum is equipped with six safety plugs, three being screwed into each head, filled with a fusible metal that will melt at approx- imately 150°F. This will prevent rupture of the drum when it is exposed to fire. The ton drum is 80 in. long by 30 in. diameter, with a tare weight of 1300 lb., and holding 2000 lb., net, of liquid chlorine. These drums are shipped only in gondola cars or special multi- unit cars, holding 15 ton-drums, clamped in special cradles. x BLEACHING OF PULP EXAMINATION QUESTIONS (1) Write equations for (a) the reaction of chlorine with milk of lime and (6) of bleaching powder with water. Put the name of each substance under its molecular formula as it stands in the equations. - (2) What is meant by available chlorine? (3) Explain the principle of the electrolytic cell. (4) (a) What conditions favor the formation of calcium chloride? (b) Why is this formation to be avoided? (5) If you were building a mill, (a) which method of bleaching would you choose and wet (b) How would you obtain your bleach? (6) (a) Why should the man that cooks the pulp be interested in the way it bleaches? (b) What cooking conditions affect the bleaching operation? (7) (a) What is antichlor? (b) why is it used? (c) why is its use objectionable? ~ (8) (a) How is groundwood bleached? (b) Why is the color not permanent? (9) A sample of bleaching powder weighing 7.1 grams was dissolved in water, diluted to 1 liter, and 38 c¢.c. of standard sodium arsenite solution was oxidized by 50 c.c. of the bleach solution; (a) what was the percentage of chlorine in the bleach? (b) How many grams of chlorine per liter did the bleach contain? (a) 38%. Ans. (b) 2.7 g./1. (10) What dangers are to be avoided when making bleach and handling bleaching powder? (11) How is bleach tested? he E N F (12) If 50 c.c. of bleach solution require TD.o2c.C: of © — sodium thiosulphate, what is the strength in grams per ve of 35% bleaching powder? Ans. 6.3 g./1. 53 TABLE [| For Converting Decrees TWADDELL TO DEGREES BAUME ee Degrees Degrees Twaddell Baumé 1 Oy72 2 1.44 3 Zee. 4 2. 84 5 3.54 6 4.22 7 4.90 8 5.58 9 6. 24 10 6.90 11 7.56 12 8. 20 1s 8.85 14 9.49 15 TOS12 16 10. 74 17 11. 36 18 ip latsire 19 12.58 « 20 P18 Dl 13.78 22 14e8 7 23 14.96. 24 Tio 2a 16.11 Degrees | Degrees Degrees | Degrees Degrees | Degrees Twaddell| Baumé Twaddell| Baumé Twaddell} Baumé 26 16. 68 st 29.46 76 39.93 27 17. 25 52 29.92 77 40. 31 28 17.81 53 30. 37 78 40. 68 29 18. 36 54 30. 83 79 41. 06 30 18.91 55 31.28 80 41.43 OL 19.45 56 catt be 72 81 41.79 32 20. 00 57 32.16 82 42.16 33 20. 54 58 32. 60 83 42.53 34 21507 59 33.03 84 42.89 35 21.60 60 33.46 85 43.25 36 FAS. NBS 61 33. 89 86 43.60 37 22. 64 62 34, 31 87 43.96 38 Zoelo ; 63 34.73 88 44.31 39 23.66 64 35.15 89 44. 66 40 Bebo aly 65 30.07 90 45.00 41 24.67 66 35.98 91 AD, 30 42 2D aot 67 36. 39 92 45. 69 43 25. 66 68 36. 79 93 46. 03 44 26.15 69 Sis Ue) 94 46. 36 45 26. 63 70 3¢. 09 95 46.70 46 Pa fe Bal (Al 37.99 96 47.03 47 27.59 1 38. 38 97 47.36 48 28. 06 73 38.77 98 47.68 49 23208 74 39.16 99 48.01 50 29.00 75 39.55 100 48, 33 Specific Gravity at x°Tw. = 1 + .005x. For Convertinc Decrees Baumt to DEGREES TWADDELL For 7°Tw., sp. er. = 1 + .005 = 29.8 0.10 34.42 1.34 1072.0 1074.4 3004.0 29.6 0.20 52.60 11.44 1061.8 1082.5 1554.0 29.4 0.30 63.86 17.70 1055.6 1087.5 1063.0 29.2 0.39 UWPaowe 22.37 1051.0 1091.3 810.0 29.0 0.49 79.07 26.15 1047.2 1094.3 657.0 28.5 0.74 91.70 33.17 1040.3 1100.0 446.2 28.0 0.98 101.15 38.41 1035.0 1104.1 339.6 27 5 1.22 108.70 42.61 1030.8 1107.4 275.2 276.0 1.47 115.06 46.14 1027.2 1110.2 231.9 26.5 g Searan 120.55 49.19 1024.1 P11226 200.2 26.0 1.96 125.38 51.82 1021.4 Litany 176.7 25.5 BPH 129.75 54.31 1018.9 1116.5 158.1 25.0 2.45 133.77 56. 54 1016.6 1118.3 143.0 24.5 2.70 137.30 58.50 1014.7 1119.9 134.3 24.0 2.94 140. 64 60.36 1012.8 12133 120.8 23.0 3.43 146.78 63.77 1009.3 1123.9 104.5 22.0 3.92 152.16 66.76 1006.2 1126.2 92.3 C10 4.41 157.00 69.44 1003.4 1128.2 82.6 20.0 4.90 161.42 71.90 1000.8 1130.1 74.8 19.0 5.39 165.42 74.12 998.5 1131.8 68.5 18.0 5.88 169.14 76.19 996.4 1133.4 63.1 L740 6.37 172.63 78.13 994.3 1134.8 58.6 16.0 6.86 175.93 79.98 992.3 1136.1 54.6 15.0 1435 179.03 81.68 990.5 1137.4 Sie2 14.0 7.84 181.92 83.29 988.8 1138.6 49.03 13.0 8.32 184. 68 84.82 987.1 1139.7 45.55 12.0 8.82 187.31 86.28 985.5 1140.7 43.18 11.0 9.31 189.83 87.68 984.0 1141.7 41.05. 10.0 9.80 192.23 89.02 982.5 1142.6 39.13 9.0 10.28 194.52 90.29 981.2 1143.6 37.40 8.0 10.78 196.73 91.52 979.8 1144.6 35.79 7.0 ake O49 198.87 92.73 978.6 1145.4 34.33 6.0 11.76 200.94 93.86 977.4 1146.3 33.00 5.0 12.24 202.92 94.96 976.1 1147.0 31.76 4.0 12.74 204.85 96.03 974.8 1147.6 30.62 : 3.0 13.23 206.71 97.06 973.7 1148.4 29.55 < 2.0 13.72 208 . 52 98.07 972.6 1149.1 28.57 : 1.0 14.20 210.28 99.04 971.4 1149.7 27.66 0 14.69 212 100 970.4 1150.4 26.79 EO eee 56 a PROPERTIES OF SATURATED STREAM TABLE IV 2 FE af g : 3 =~ 4 © car 3S 5 5 © 1o) o4 o as 3 Cae =| a a ce 3.8 o o 3 “s “3 3.5 & EB 5 $5 we ae o — 3 oO a oo o a q e ea g o § 2 53.0 o oe a s o & ne Qs ad AB gq bee | Eg et os ES gs S28 g 3a af (= Phan ie Ee Cite H So cm 0 212 100 970.4 1150.4 26.79 14, 1 215.3 101.8 968. 2 1151.6 25.23 15. 2 218.5 103.6 966.2 1152.8 23.80 16. 3 221.5 105.3 964.3 1153.9 22.53 17 4 224.4 106.9 962.4 1154.9 21.40 18 5 227 .2 108.4 960.6 1155.9 20.38 19 6 229.8 109.8 958.8 1156.8 19.45 20 7 232.4 Viie3 959.2 1157.2 18.61 21 8 234.8 112.6 955.5 1158.6 17.85 22 9 237.1 113.9 954.0 1159.4 17.14 23. 10 239.4 115.2 952.5 1160.2 16.49 24 11 241.6 116.4 951.1 1161.0 15.89 25 12 243.7 117.6 949.6 1161.7 15.34 26 13 245.8 118.8 948.2 1162.4 14.82 27 14 247.8 119.9 946.8 1163.0 14.33 28 15 249.7 120.9 945.5 1163.7 13.88 29 16 251.6 122.0 944.2 1164.3 13.45 30 17 253.5 123.1 942.9 1164.9 13.05 31 18 255.3 124.1 941.6 1165.5 12.68 32 19 257.1 125.1 940.4 1166.1 12.33 33 20 258.8 126.0 939.3 1166.7 11.99 34 21 260.5 126.9 938.1 1167.2 11.67 35 22 262.1 127.8 936.9 1167.7 11.38 36 23 263.7 128.7 935.8 1168.2 11.09 37 24 265.3 129.6 934.8 1168.8 10.82 38 25 266.9 130.4 933.7 1169.3 10.57 39 26 268.3 131.3 932.5 1169.7 10.32 40 27 269.8 132.1 931.5 1170.2 10.09 41 28 271.3 132.9 930.5 1170.6 9.86 42 29 272.7 13007 929.5 riba ae 9.65 43 30 274.1 134.5 928.5 1171.5 9.45 44 31 275.4 135.2 927 .5 1171.9 9.26 45 32 276.8 135.9 926.6 1172.3 9.07 46 33 278.1 136.7 925.6 1172.7 8.89 47 34 279.4 137.4 924.7 1173.1 8.72 48 35 280.6 138.1 923.8 1173.5 8.56 49 36 281.9 138.8 922.9 1173.9 8.40 50. 37 283.1 139.5 922.0 1174.8 8.25 51 38 284.3 140.2 921.1 1174.6 8.10 52 39 285.5 140.8 920.2 1174.9 7.95 53 40 "7 141.5 919.4 1175.3 7.82 54 57 NNNNN ONNINNIN NANININISD NN SSN SSIS OSS TaBLE LV.—Continued PROPERTIES OF SATURATED STEAM qd owe i as ray ~~ 5 4 a & g ° 2 3 3 s) 5g § Se 3 a al t ‘8 2 ae 2. &* g § 28 % < Ss ae & & 3° 3 3B a au mH i a q £ a 3 0 ® vo 2° o'9 50 n & Qi, arg ADS yg a a) n & 8 ES R& SES s Bus Bs i= a= ir B ee, SS > aes 40 286.7 141.5 919.4 1178.3 7.82 54.7 42 289.0 142.8 917.6 1175.9 7.56 56.7 44 291.3 144.1 916.0 1176. 6 7.32 58.7 46 293.5 145.3 914.3 117772 7.09 60.7 48 295.6 146. 4 912.7 1177.8 6. 88 62.7 50 297.7 147.6 911.2 1178.4 6. 68 64.7 52 299.7 148.7 909.6 1178.9 6.50 66.7 54 301.7 149.8 908. 2 1179.5 6. 32 68.7 56 303. 6 150.8 906. 7 1180.0 6.14. 70.7. 58 305. 5 151.9 905. 3 1180.5 5.98 Te 2 60 307.3 152.9 903.9 1181.0 5.83 74.7 62 309.1 153.9 902.5 1181.5 5. 69 76.7 64 310.9 154.9 901.2 1182.0 5.56 78.7 66 312.6 155.8 899.8 1182. 4 5.43 80.7 68 314.4 156.8 898.5 1182.9 5.30 Bary, 70 316.0 157.7 897.2. 1183.3 5.18 84.7 72 317.7 158.7 895.9 1183.7 5.07 86.7 74 319.3 159.6 894.6 1184.1 4.96 88.7 76 320.9 160. 4 893.4 1184.5 4,86 90.7 78 322.4 161.3 892.2 1184.9 4.76 92.7 80 323.9 162. 1 891.0 1185.3 4.67 94.7 82 325.4 162.9 889.8 1185.7 4,57 96.7 84 326.9 163.8 888. 7 1186.1 4.48 98.7 86 328. 4 164.6 887.5 1186.4 4.40 100.7 88 329.8 165. 4 886. 4 1186.8 4, 32 102.7 90 331.2 166. 2 885.2 1187.1 4,24 104.7 92 332.5 166.9 884.3 1187.5 4.17 106.7 94 333.9 167.7 883. 2 1187.8 4.09 108.7 96 BOLDNes 168. 4 882.1 1188.1 4.02 llu. 7 98 336. 6 169. 2 881.1 1188.5 3.95 1127, 100 337.9 169.9 880.0 1188.8 3.89 114.7 102 339. 2 170.6 879.0 1189.1 3.83 116.7 104 340. 4 17138 878.0 1189.4 3.76 118.7 106 341.7 172.1 876.9 1189.7 3.71 120.7 108 343.0 172.8 875.8 1189.9 3. 65 122.7 110 344.2 173. 4 874.9 1190. 2 3.59 124.7 112 345.4 174.1 873.9 1190.5 3. 54 126.7 114 346. 6 174.7 873.0 1190.8 3.49 128.7 116 347.8 175.4 872.0 1191.1 3.43 130.7 118 348.9 176.1 871.0 1191.3 3.38 132-7 120 350. 1 176.7 870.1 - 1191.6 3. 34 134.7 58 INDEX Nore.—The paging begins with 1 in each Section, and each section has its number printed on the inside edge of the headline of each page. To find a reference, as *‘ Acidity, Testing pulp for, §8, p46,” glance through the volume until §8 is found, and then find page 46. A Absorption systems, Tank, §4, p23 Tower, §4, p29 for sulphur dioxide, §4, p23 Accumulator, §7, p91 a-cellulose, §1, p46 Acid, Best, for cooking, §4, p84 fortified or cooking, §4, p5 Regulating strength of, §4, p33 Strengthening the, §4, p68 Strong and weak (Def.), §4, p4 Acid bleaching, §9, p27 Acid from strong tower, Testing of, §4, p47 Acid making, Control of, §4, p38 Acid storage tanks, §4, p37 Acid-control system, Crandon, §4, p49 Acidity, Testing pulp for, §8, p46 Active alkali (Def.), §6, p23 Quantity of, §6, p44 Adipo-cellulose, §1, p45 Adsorb (Def.), §1, p48 Air nozzles in smelting furnace, §6, p89 Air supply, Pressure of, §6, p93 Regulating, in sulphur burning, §4, pl7 Air supply to smelter, §6, p91 Air-dry, Discussion of term, §7, p103 Air-dry fiber (Def.), §7, p3 weight (Def.), §8, p28 weight, Calculation of, §8, p28 Alcohol, Coniferyl, §1, p49 Ethyl, from waste liquor, §4, p86 Wood, as a by-product, §6, p119 Alcohols formed during cooking process, §4, p55 Alkali (= caustic), §5, p5 Alkali, active, Determination of, §6, p107 j Alkali, Active and total, §6, p23 Quantity of, §6, p44 Alkalinity, Testing pulp for, §8, p47 Ammonia test, Mitscherlich’s, §4, p73 Analysis (Def.), §6, p100 Barium chloride method of, §6, p108 Black liquor, §6, p112 Analysis of black liquor, §5, p49 of green liquor, §6, p103 Analysis green liquor, Alternative method of, §6, pll4 of slime sludge, §6, pl11 of liquors, §6, p103 of soda cook of poplar, §5, p50 of smelt, §6, p98 , of white and green liquor, §6, p108 Angle of repose (Def.), §2, p26 Annual ring, §1, p8& Annual rings, Width of, §1, p9 Antichlor, Use of, §9, p28 Arrangement of cut-up mill, §2, p3 Arsenite (sodium) solution, How to make, §9, p34 Arsenite solution, Standardizing N/10, §9, p34 Ash, Black, §5, p58 Composition of, §6, p86 Leaching, §5, p61 residue, Composition of, §5, p63 Ash, soda, Use of, in preparing caustic, §5, po Testing pulp for, §8, p41 Ashcroft tester, §8, p38 Auger, Use of, in sampling, §8, p20 Auger method, location of borings, §8, p19 of sampling pulp, §8, p19 Available chlorine (Def.), §9, p3 Determination of, §9, p37 Determination of, in bleaching powder, §9, p37 Determination of in bleach liquor, §9, p35 Penot method for, §9, p33 Available lime, §9, p34 Determination of, §9, p39 B Bale, Normal, §8, p17 Baled pulp, Sampling, §8, p19 Bales of pulp, Number sampled, §8, p22 Ball mill refiner, §8, p5 Barium chloride method of analysis, §6, p108 Bark, Aids in removal of, §2, pl4 Fuel value of §2, p22 60 INDEX Bark, Products from, §1, p35 Bark fibers, §1, p8 Bark of tree, §1, p34 : Bark press, Description of, §2, pp23-25 Moisture removed by, §2, p22 3-roll, §2, p25 Barkers, Knife, §2, p38 knife, Power to operate, §2, p39 Stationary, §2, p19 Stationary, Advantages of, §2, p20 Barking drum, First type of, §2, pl4 Fourth type of, §2, p17 Second type of, §2, p15 Third type of, §2, p16 Barking drums, §2, pp13-22 Capacity of, §2, p17 Continuous system, §2, p13 intermittent, Capacity of, §2, p22 intermittent, Description and opera- tion, §2, p20 Intermittent system, §2, p13 Power to operate, §2, p18 Tumbling-barrel types, §2, p13 Types of, §2, p13 Barking, wood, Reason for, §2, p13 Batch sytem for making caustic liquor (Def.), §5, p11 B-cellulose, §1, p46 Beaters, Bleaching in, §9, p16 Beater, Stone roll, §8, p9 Beehive cooler, §4, p68 Bellmer engine, §9, p18 Bibliography, §1, pp36, 57; §5, p69 Binder (of grindstone), §3, p15 Binder of grindstones, Composition of, §3, pl7 Bins, Chip, §2, p48; §4, p63 Black ash (Def.), §5, p58 Composition of, §6, p86 Leaching, §5, p61 Black ash from black liquor, §5, p58 Black ash residue, Composition of, §5, p63 Black liquor, Analysis of, §5, p49 Changing, to black ash, §5, p58 Composition of, §6, p63 Density of, §6, p83 Organic substances in, §6, p22 Process of treating, §6, p79 Use of organic matter in, §6, p97 Variation in strength of, §5, p46 what it contains, §5, p50 Black liquor analysis, §6, p112 Black liquor storage tanks, §6, p35 Bleach, Methods of testing, §9, p33 Bleach and bleach liquor, Analysis of, §9, p36 Bleach consumption, Determination of, §8 p41 liquor, Testing the, §9, p37 requirements of pulp, §9, pl4 dios Lag Bleach solutions, specific gravity table € for, §9, p38 i Bleached pulp, Washing, §9, p32 = Bleacher, Bellmer, §9, p18 Collins, §9, p22 Fletcher, §9, p19 Globe rotary, §9, p23 High-density, §9, p19 Semco, §9, p23 Bleaching, Acid, §9, p27 Bromine test for, §9, p15 Definition of, §9, pl Effect of, on chemical characteristics, §9, p26 Effect of, on strength of pulp, §9, p25 Factors of, §9, p24 Hypochlorous acid in, §9, p27 Shrinkage of pulp by, §9, p26 Two-stage, §9, p26 Use of permanganate No. in, §9, p15 Bleaching agents, §9, pl groundwood, §9, p3l in beaters, §9, p16 in tanks, §9, p17 manila, hemp, rope, and dutee §9, p29 old paper, §9, p30 operation, The, §9, p15 Bleaching powder, Analysis of, §9, p3 Chemical composition of, §9, p2 Determining available chlorine in, §9, p35 Handling, §9, p4 History of, §9, p2 Stability of, §9, p4 Suggestions for handling, §9, p5 To find weight of per liter in solution, §9, p36 | Bleaching pulp, Effect of cook on, §9, pl4 tags, §9, p30 ‘ soda pulp, §9, p29 sulphate pulp, §9, p29 sulphite pulp, §9, p28 Blocks (Def.), §2, p10 Blow pit (Def.), §5, p33 Description of, §4, p74 Blow tank (Def.), §5, p33 Blower, Positive pressure, §6, p91 Blowing digester, §4, p74; §6, p46 Blowing the digester, §5, p41 Blue-glass test for fibers, §8, p31 Board feet, Number of in cord, §2, p2 Number of in unbarked wood, §2, p3 j Boiler, steam, Use of with high-pressure oe evaporator, §6, p68 i Bone-dry fiber (Def.), §7, p3 Bone-dry weight, Per cent of, §8, p28 Boom (Def.), §2, p4 Bordered pits, §1, p13 Borings, Location of, in auger method, §8, pl9g INDEX 61 Borings for sampling, Location of, §8, p22 Box, Filter, §6, p16 Bridge trees (Def.), §3, p22 Brimstone, §4, p6 Brine, strength of, §9, p47 Broad-leaved (non-resinous) pl7 Broad-leaved woods, Tables for identify- ing, §1, pp20, 21 Bromine test for bleaching, §9, p15 Brown pulps, §3, p87 Burner gases, §4, p15 Burner, sulphur, Combustion chamber of, §4, p15 Flat type of, §4, p9 Rotary type of, §4, p9 Stationary, §4, pll Vesuvius, §4, pll Burr (Def.), §3, p47 Diamond-point, §8, p52 Pitch, cut, or number of, §3, p49 Sectional, §3, p86 Spiral, §3, p51 spiral, Lead of, §3, p52 Straight-cut, §3, p50 Thread, §3, p49 Burrs, Seasonal changes in coarseness of, §3, p64 Special, §3, p54 tests of different, §3, p55 Bush roll (Def.), §3, p47 By-products of sulphate process, §6, p118 C Calculation of air-dry weight, §8, p28 Cambium cells (Def.), §1, p7 Canals (ducts), §1, p13 Canals, Pulp, §5, p46 Capacity of screen (Def.), §7, p7 of sliver screen, Effect of consistency on, §7, p12 Car wood (Def.), §2, pl Carbohydrates, Soluble and insoluble, §1, pdl Catalyzers, Effect of, on amount of SOs produced, §4, p18 Caustic, Electrolytic process of preparing, §5, pd Caustic liquor, Amount required, §5, p21 Chemical reactions in making, §5, pl2 Continuous system in making, §5, pl2 Determining strength of, §5, p20 Three systems of making, §5, p10 Caustic liquor making, Filtration system of, §5, p13 Caustic soda (= caustic), Preparation of, §5, pd Determining percentage of soda ash changed to, §5, p65 woods, §l, Caustic tanks, §5, p7 Causticity, per cent of, Determination of, §6, p107 Causticizing, Control of, §5, p65 Causticizing and lime recovery system, New continuous, §5, p12 Causticizing tanks, §5, p11; §6, p5 Cell, Chlorine diaphragm, §9, p42 Cells, Efficiency of, §9, p47 Electrolytic, §9, p41 Hypochlorite, §9, p49 Mercury, §9, p45 Nelson, §9, p43 Cells of non-resinous woods, §1, p22 Cellulose (Def.), §5, p1 a-, B-, and y-, §1, p46 Action of acids and alkalis on, §1, p48 Action of certain fungi on, §1, p48 Action of chemicals on, §1, p47 Action of solvents and reagents on, §1, p48 Adipo-, cuto-, ligno-, pecto, §1, p45 Kinds of, §1, p45 Normal, §1, p45 Principal source of, §1, p41 resistent, Test for, §8, p51 Some properties of, §1, p48 Specific gravity of, §1, p48 Testing pulp for, §8, p47 Yield of, in pulp, §4, p80 Cellulose is a colloid, §1, p48 Cellulose molecule, Structure of, §1, p45 Cellulose nitrates and acetates, §1, p47 Centrifugal pump belted to grinder shaft, §3, p92 Centrifugal pump, Constant pressure, §3, p94 Centrifugal screens, Horizontal, §7, pp32, 40 Vertical, §7, p39 Centrifugal type of screen, Test of, §7, p23 Chains used in log haul-ups, §2, p5 Charging digester, §4, p64 Chart showing capacities for different con- sistencies, §7, p12 Charts, Cooking, §5, p39 Temperature and pressure (cooking), §4, p62 Charts showing capacities and power con- sumption of horizontal centrifugal screens with varying consistencies of stock and speeds of runner, §7, pp36—38 capacity of decker operating on groundwood, §7, pp55, 56, 59 Cheap book-paper grade of pulp, §3, p87 Chemical laboratory, Relation of to soda mill, §5, p63 Chemical processes, Object of, §5, pl Chemical pulp (Def.), §7, pl Impurities in, §7, p13 62 INDEX Chemical pulp, Screens for, §7, p13 Worm knotter for, §7, p14 Chemical treatment of wood, Object of, §1, pd5 Results of, §1, p55 Chemicals, Reclaiming of, §6, p48 Chemicals used in soda process, §5, p5 Chip bins, §2, p48; §4, p63 Chip conveyors, §2, p46 Chip crushers, Object of, §2, p44 Types of, §2, p45 Chip dryers, §2, p48 Chip screens, Capacity of, §2, p43 Power required for, §2, pp43, 44 Rotary type of, §2, p42 Shaker type of, §2, p43 Chippers, Capacity of, §2, p42 Description of, §2, p41 Necessity for, §2, p41 Chips, cooking, Factors affecting, §6, p41 Effect of moisture in, §6, p42 Size of, for sulphate pulp, §6, p2 Storage for, §6, p34 Treatment of (sulphate), §6, p22 Uniformity of, §4, p82 Weighing and sampling, §2, p47 Chloride chlorine (Def.), §9, p33 Determination of, §9, p39 Chlorine, Absorption of in electrolytic cells, §9, p49 Chlorine and lime, Heat reactions of, §9, p9 Chlorine, Available, §9, p3 Determination of, §9, p37 Determination of in bleaching pow- der, §9, p35 Penot method for, §9, p33 Chlorine, Constants for, §9, p11 Electrolytic, §9, p41 Chlorine, liquid, Absorption of in milk of lime, §9, p8 Containers for, §9, p50 History and use of, §9, p7 Chlorine, Safe use of, §9, p12 Total, §9, p34 Total, Determination of, §9, p39 Treatment of persons affected by, §9, pl3 Chlorine concentrations at various densities, Table for, §9, p38 Diaphragm cells, §9, p42 Factor, §9, p15 Cleaning wood, Methods of, §2, p37 Cleanliness of mechanical pulp, §3, p12 Clematis, Structure of stem of, §1, p4 Coffee solution, Proportions for, §4, p71 Cold grinding, §3, p63 Collins bleacher, §9, p22 Colloid, §1, p48 Color of mechanical pulp, §3, p11 Color test for cooking liquor, §4, p71 Combined SOz2 (Def.), §4, p33 How found, §4, p49 Combustion chamber of sulphur burner, §4, pls Comparison of milk-of-lime with tower system, §4, p34 Concentrating (Def.), §7, p51 Condenser, Spray, §6, p38 Surface, §6, p36 Condensers (for digesters), §6, p35 Coniferous woods, §1, p12 Characteristics of, §1, p15 Coniferous woods, Tables for identification .of, §1, pp14, 15 Coniferyl alcohol, §1, p49 Consistency control, §7, p24 of pulp (Def.), §7, p3 of stock, Influence of, §7, p24 Consistency, Effect of on capacity of sliver screen, §7, p12 Necessity for regulating, §7, p67, Consistency regulator, §7, p67 Constant-pressure centrifugal pump, §3, p94 Container-board grade of pulp, §3, p87 Continuous filter, §5, p13 process of manufacture, §7, p2 Continuous grinder, §3, p4la Continuous system for making caustic liquor (Def.), §5, p1l in making caustic liquor, §5, p12 of barking drums, §2, p13 Continuous vacuum filters as save-alls, §7, p83 as thickeners, §7, p62 Conveyor, cross, Portable, §2, p29 Portable sections of, §2, p32 Conveyor, Power required to operate, §2, p3l ; storage-pile, Suspension type of, §2, p27 Trestle type of, §2, p26 Conveyor, Temporary, §2, p32 Conveyor troughs, §2, p31 Conveyors, Chip, §2, p46 cross, Necessity for, §2, p28 Special-purpose, §2, p32 Uses and shapes of, §2, p31 Cooking, Best acid for, §4, p83 Effect of lignin on, §1, p50 of sodium sulphide and sodium hydrate on, §6, p41 of temperature and pressure on, 86, if a p42 Cooking, Effects produced by, §4, els Methods of, §4, p55 No standard method of, §4, p69 or fortified, acid, §4, p5 Steam consumption in, §4, pp/l, 845 Time required for, §4, p56 INDEX ) 63 Cooking charts, §4, pp66, 67, 69, 70, 78; §5, p39 Cooking chips, Factors affecting, §6, p41 Cooking liquor, Color test for, §4, p71 Importance of penetration of, §4, ps1 Indirect heating of, §6, p38 Testing for SOo, §4, p71 Cooking of wood, Substances removed by, §1, p53 Cooking process, Beginning of, §4, p64 Details of, §4, p64 End of, §4, p71 Danger of poor circulation during, §4, p54 Importance of lime in, §4, p54 Mitscherlich, §4, p75 Morterud, §4, p79 Products of, §4, p55 Theory of, §4, p51 Cooking processes, Direct and §4, p55 Cooking vessels, §4, p56 Cooking wood, Purpose of, §6, p18 Cooler, Beehive, §4, p68 Coolers, gas, Types of, §4, p19 Cooling gases, Main object of, §4, p21 Copper figure, Determination of, §8, p48 Copper sulphide, §4, p7 Cord, Relation of to cubic feet and board feet, §2, p2 Corn, Indian, Structure of stem of, §1, p3 Costs, Freight, §7, pp87—89 Couch roll (wet press), §7, p71 Counterflow system of vapor and liquor, §6, p77 Crandon acid-control system, §4, p49 Crazy chase (refiner), §8, p8 Cross conveyor, Portable, §2, p29 Portable sections of, §2, p32 Cross conveyors, Necessity for, §2, p28 Crushers, chip, Object of, §2, p44 Cu. F., Determination of, §8, p48 Cubic feet in cord, §2, p2 Cullers, Duties of, §2, p5 Cut of burr, §3, p49 Cutin, §1, p54 Cuto-cellulose, §1, p45 Cutter (for pulp sheets), §7, p100 Cut-up mill, General arrangement, §2, p3 indirect, dD Decay of pulpwood, §2, p35 Decker (Def.), §7, p52 Decker process, §4, p79 Deckering (Def.), §7, p51 ‘Delivering wood to mill, §2, pl Density of pulp (Def.), §7, p3 Determination (Def.), §6, p100 Quick, of white liquor, §6, p117 Determination of active alkali, §6, p107 of bleach consumption, §8, p46 of copper figure, or Cu. F., §8, p48 of per cent of causticity, §6, p107 of sodium carbonate, §6, p103 of sodium hydrate, §6, p103 of sodium sulphate, §6, p100 of sodium sulphide, §6, p101 of sodium sulphite, §6, plol De-watering (Def.), §7, p51 Dextrose, §1, p47 Diagram of wood preparing operations, §2, p3 Diamond-point burr, §3, p52 Diaphragm screen, §7, p27 Differential winder, §7, p84 Diffuse porous (Def.), §1, p23 Diffuser, Arrangement of piping, §6, p58 Description of, §6, p48 Dumping a, §6, p62 Use of, §6, p48 Diffuser room, Purpose of, §6, p47 Diffusers, Battery of, §6, p54 Operation of, §6, p60 Digester (Def.), §5, p25 Blowing, §6, p46 Blowing and washing, §4, p74 Blowing the, §5, p41 charging of, §4, p64 Distribution of heat in, §5, p31 Distribution of valves of, §5, p34 Double-shell, §5, p30 Filling the, §5, p37 Indirect heating in, §5, p32 Injector circulation in, §5, p31 Heating and circulating contents of, §5, p30 Horizontal, §5, p30 Materials required per charge of, §5, p3s modern, Construction of, §4, p59 Necessity for blowing clean, §5, p38 Operation of, §5, p36 Preparing for next cook, §5, p41 Prevention of heat waste in, §5, p33 Reactions in, §6, p19 Relieving the, §5, p40 Rotary, §6, p24 rotary, Operation of, §6, p26 Stationary, §6, p28 Stationary, Operation of, §6, p32 Steaming the, §5, p38 Use of black liquor in, §5, p42 Use of salt cake in, §5, p43 Use of sulphur in, §5, p42 vertical, Description of, §5, p27 Digester blow-off valves, §4, p60 Digester bottoms, §4, p60 Digester contents, Direct-heating method of circulating, §5, p30 Digester fittings, §4, p61 64 INDEX Digester house, Arrangement of, §5, p26 Digester-house details, §5, p33 Digester linings, §4, p57 Digester liquor, Storage of, §5, p21 Digester room, Operation of, §6, p22 Digester room equipment, Testing of, §6, p3s Digester (sulphate), (Def.), §6, p22 Digester troubles, §5, p42 Digesters, Arrangement of, §6, p32 Capacity of (table), §4, p58 Experimental, §5, p43 Gauges on, §5, p35 Riveted and welded, §5,; p26 soda, Table for volume of, §5, p68 Use of thermometers in, §5, p36 vertical and horizontal, Mitscherlich, §4, p76 Digesters used in sulphate process, §6, p23 Direct cooking process, §4, p56 Direct evaporation, . §6, p63 Direct-flow system of vapor and liquor, §6, p77 Direct-heating method of circulating di- gester contents, §5, p30 Dirt in pulp, §4, p83 Discontinuous process of manufacture, §7, p2 Disk evaporator, Arrangement of, §6, p67 Description of, §6, p63 Feeding liquor to, §6, p66 Number of rotors for, §6, p65 Disk type of refiner, §8, p6 Disk washers, §9, p32 Dissolving tank, §6, p91 Doctor blade (wet press), §7, p72 Dolomite, §4, p7 Double decomposition (Def.), §6, p20 _ Double-shell digester, §5, p30 Double-smelting furnace, §6, p86 Draft (Def.), §6, p67 Natural and mechanical, §6, p68 Dressing grindstone, §3, p76 Drum, barking, First, second, third, and fourth types, §2, pp14—17 Drums, Barking, §2, pp13—22 Capacity of, §2, p17 Power to operate, §2, p18 Drums, intermittent barking, Capacity of, §2, p22 Description and operation, §2, p20 Dry pulp, Baling of, §7, p105 Dry pulp in rolls, §7, p104 Dryers, Chip, §2, p48 (pulp), §7, pp98, 101 Drying machine, Cylinder type of, §7, p96 Drying machines, Purpose of, §7, p96 Drying pulp samples, §8, p27 Ducts, Resin, §1, p13 Dulling the grindstone, §3, p48 Dutch oven (Def.), §2, p22 Dynamiting a storage pile, §2, p29 Dynamiting storage pile, Device for avoid- ing, §2, p30 E Early wood, §1, p9 Economizer (Def.), §6, p69 Edge runner (refiner), §8, p8 Effects (Def.), §5, p51 Temperature and pressure in, §5, p54 Efficiency of cells, §9, p12 of converting wood into pulp, §3, p82 of turbine (for grinding), §3, p44 — Ekman’s sulphite process, §4, p2 Electrolytic cells, Strength of brine and efficiency of, §9, p47 Electrolytic chlorine, §9, p41 Enge process, §3, p89 European practice in handling logs, §2, p8& Evaporation, Direct, §6, p63 Evaporator, disk, Arrangement of, §6, p67 Description of, §6, p63 Feeding liquor to, §6, p66 Number of rotors for, §6, p65 Evaporator, Film, §5, p55 high-pressure, Use of steam boiler with, §6, p68 Horizontal-tube, §6, p74 Multiple-effect, §5, p51 multiple-effect, Principle governing, §6, p69 a quadruple-effect, Operation of, §6, p72 quadruple-effect vertical-tube, §6, p70 Triple-effect, §5, p51 Vertical-tube, §5, p57 Evaporator details, §5, p53 Evaporator man, Duties of, §5, p53 Evaporator troubles, §5, p57 Evaporators, High-pressure, §6, p75 _ indirect, Operation of, §6, p77 low-pressure, Advantages of, §6, p76 Pumps required for, §6, p77 Thin-film, §6, p78 Types of, §6, p78 Vertical tube, §6, pp70, 78 Work done by, §6, p75 Fan for supplying air to furnace, §6, p92 Farmer’s wood (Def.), §2, pl . a Fats in pulpwood, §1, p52 : Aa in wood, Trouble caused by, §4, p52 hy Fehling’s solution, §8, p49 a Feed chains, Continuous, §2, a oP Felt riffler, §7, p10 Felt (wet press), §7, p72 as Fiber (Def.), §1, pp6, 28 , Bone-dry and air-dry (Def.), §7, p3 sulphate, Character and uses of, §6, p3 — INDEX 65 Fiber, Testing with stereopticon or lantern, §8, p29 Fiber lengths, Diagram of, §1, p29 Table of, §1, p30 Fibers, Arrangement of, in wood §1, p7 Bark, §1, p8 Blue-glass, test for, §8, p31 Comparing for length and width, §8, p31 Majority (Def.), §7, p4 Variation in length of, §1, p8 Wood, §1, pp6, 8 Fibers used in papermaking, Table ro) p2 Fill-and-dump filter, §5, p14 Filling the digester, §5, p37 Film evaporator, §5, p55 Filter, Continuous, §5, p14 Filter, Continuous vacuum, §7, pp57, 62 as a save-all, §7, p72a Filter, Leaf type, §5, p14 Operation of, §5, p16 Filter box, §6, p16 Filter operations, Power required ba Ae p72c Recoveries from, §7, p72c Filter press, Care of, §6, p15 Filter presses, §6, p14 Filtration system for making caustic liquor (Def.), §5, p11 Fine screen, Features of, §7, p21 Fine screening, Purpose of, §7, p20 Finish of paper made from mechanical pulp, §3, p11 Fire in wood pile, Extinguishing, §2, p33 Flat screen, §7, p27 Flat type of sliver screen, §7, p7 Flax, Structure of stem of, §1, p6 Fletcher bleacher, §9, p19 Flowers of sulphur, §4, p6 Foaming of stock, §7, p27 Fortified, or cooking, acid, §4, p5 Fourdrinier pulp-drying machine, §7, p101 Free SO2, Determination of, §4, p73 Testing acid for, §4, p49 Free stock (Def.), §5, p48 Freeness (Def.), §8, p32 Freeness of pulp stock, §3, p7 of stock, Importance of, §3, p78 Freeness tester, §3, p7; §8, p34 Corrections for, §8, p35 Standard, §3, p9 Freight costs, Calculation of, §7, pp87-89 Table of, §7, p88 Friedsam process, §3, p89 Fungi, Action of, on cellulose, §1, p4s on lignin, §1, p50 Fungi that destroy wood, §2, p35 Furfurol, §1, p51 Furnace, Double-smelting, §6, p86 Fan for supplying air to, §6, p92 Furnace, pyrites, Starting up a, §4, p14 Rotary, §5, p58 Adding salt cake to, §6, p84 Chemical changes in, §6, p83 Description of, §6, p80 Furnace, smelting, Air nozzles in, §6, p89 Air supply to, §6, p91 Construction of, §6, p88 Description of, §6, p86 Operation of, §6, p93 spout, §6, p90 Furnace, Temperature of, §6, p87 Furnace room, Starting the, §6, p97 Furnace troubles, §5, p61 Furnaces for burning pyrites, §4, pp12-14 G y-cellulose, §1, p46 Gas and liquor, Reclaiming, §4, p35 Gas coolers, Types of, §4, p19 Gases, Burner, §4, p15 Main object of cooling, §4, p21 Temperature of before cooling, §4, p38 Gauges, Indicating and recording, §5, p35 Gauges on Digesters, §5, p35 Globe rotary bleacher, §9, p23 Glossary of terms used in Section 1, §1, p59 Grades of pulp, §7, p20 Green liquor, §6, p5 Alternative method of analyzing, §6, pll14 Amount of sodium carbonate in, §6, p10 Analysis of, §6, pp103, 108 Green liquor, Composition and analysis of, §6, p9 Concentration of sodium carbonate in, §6, pll Grinder, Continuous, §3, p41a Grinder, magazine, Description of, §3, p34 Operation of, §3, p35 Grinder, Operating a hand-fed, §3, p75 Three-pocket pulpwood, §3, p13 Grinder pockets, §3, p23 Grinder-pressure systems, §3, p89 Special, §3, p95 Grinder shaft, Centrifugal pump belted to, §3, p92 Grinders, Hand-fed, §3, p13 Bearings and foundations, §3, p21 Shafts and flanges for, §3, p19 Side casings for, §3, p22 Grinders, Horsepower to operate, §3, p57 hydraulic-cylinder, Automatic trip and timing device for, §3, p38 Hydraulic cylinders for, §3, p25 hydraulic-cylinder, Pressure water con- nections for, §3, p36 Magazine, §3, p33 Grindstones for, §3, p36 66 INDEX Grinders, Magazine, Output of, §3, p33 Shafts and flanges for, §3, p36 Sharpening device for, §3, p41 Grinders, Number of, for turbine installa- tion, §3, p72 Piping for hand-fed, §3, p30 Reversing valves for hydraulic cylinder, §3, p25 Size of wood for, §3, pp24, 33 Grinders with mechanical feed of wood, §3, p90 Grinding, Amount of water required for, §3, p30 Hot or cold, §3, p63 Power required for, §3, p42 Temperature of, §3, p63 Variation in power during, §3, p83 Grinding cooked and uncooked spruce, §3, pss Grinding operations, Conditions affecting, §3, p71 Grinding spruce, Experimental results, §3, p60 Grinding tests, §3, p55 Grindstone, Dulling or knocking back, §3, p48 Effect of variation in speed MY §3, p62 Preparing surface of, §3, p47 Pressure of wood against, §3, p57 Speed of, §3, p61 Variation in pressure between wood and, §3, p59 Grindstone dresser, p28 Mechanical-feed, §3, p27 Grindstone dressing, §3, p76 Grindstones, Artificial, §8, p18 Life of, §3, p19 Mechanical strength of, §3, p18 Origin of, §3, p14 Qualities of, §3, p15 Seasoning of, §3, p18 Selection of, §3, p45 Sharpening devices for, §3, p27 Sizes of, §3, p19 Soft or hard, §3, p15 Grindstones for Magazine grinders, §3, p36 Grit (of grindstone), §3, p15 Groundwood, Bleaching of, §9, p31 Groundwood pulp (Def.), §7, pl Description of process, §3, p3 History of, §3, pl Uses of, §3, p6 Wood used in, §3, p4 Growth ring, §1, p8 Gypsum precipitated in the cooking process, §4, p54 Hydraulic-feed, §3, 7 ; Half free SOe, Determination of, §4, p73 Hand-fed grinder, Operating, §3, p75 ’ Hydraulic press (downward-pressure type), Hand-fed grinders, §3, p13 Bearings and foundations, §3, p21 Piping. for, §3, p30 Shafts and flanges for, §3, p19 Side casings for, §3, p22 Size of wood for, §3, p24 Hand-operated stock for sharpening, §3, p27 Haul-up, log, Parallel, §2, p7 Single-strand, §2, p7 Haul-up, Power required for, §2, p6 Raising and lowering end of, §2, p6 Hazards in soda mill, §5, p25 Heartwood (Def.), §1, p9 Heat, Distribution of, in digester, §5, p31 Heat reactions of chlorine and lime, §9, p9 Heat waste, Prevention of, in digester, §5, p33 Hemi-celluloses, §1, p51 Hemp, Bleaching, §9, p29 Herreshoff furnace for burning pyrites, §4, p12 Hexosans, §1, p51 High-density bleachers, §9, p19 High-pressure evaporators, §6, p75 Horizontal centrifugal screen, Recent type of, §7, p40 Horizontal digester, §5, p30 Hot grinding, §3, p63 House, digester, Arrangement of, §5, p26 Hydration of pulp fiber, §4, p82 Hydraulic-accumulator pressure §3, p91 Hydraulic-cylinder grinders, Automatic trip . and timing device, §3, p38 Pressure water connections, §3, p36 Hydraulic cylinders for grinders, §3, p25 Hydraulic-feed grindstone dresser, §3, p28 system, ‘ §7, p91 (upward-pressure type), §7, p95 Hydraulic pressing, Advantages of, §7, p87 Hydraulic pressure system, Natural head, §3, p90 Hydro-cellulose, §1, p47 . Hydrochloric Acid, Tenth normal, §9, p40 — Hydrogen peroxide in bleaching, §9, p41 Hydrolysis (Def.), §6, p21 Hydrolyzed (Def.), §6, p21 zi” Hydrometer, Baumé and Twaddell scales — on, §5, p20 vf Twaddell, §5, p20 Hypochlorite cells, §9, p49 ’ Hypochlorous acid, Use of in bles 7 ; §9, p27 , I * D OMS z Indirect cooking process, §4, p56 Indirect heating in digester, §5, p32 Injector circulation in digester, §5, p31 INDEX 67 Intermittent barking drums, §2, p20 Intermittent process of manufacture, §7, p2 Intermittent system of barking drums, §2 p13 Iodide-starch paper, How to make, §9, p35 Iodine solution, Standardizing N/10, §9, p34 To make up N/10, §9, p34. Ions (Def.), §9, p41 Iron sulphide, §4, p6 , J Jordan type of refiner, §8, p10 Jute, Bleaching, §9, p29 K Knife barkers, §2, p38 Knocking back the grindstone, §3, p48 Knots (Def.), §8, pl Cause of, §8, p2 Knotter, Rotating screen plate type of, §7, plo Worm, for chemical pulp, §7, p14 Kollergang, Centrifugal, §8, pll Kollergang (refiner), §8, ps Kraft paper, Imitation, §3, p88 Kraft pulp (Def.), §6, pl L Laboratory, chemical, Relation of to soda mill, §5, p63 Lantern, Use of in testing fiber, §8, p29 Lap (Def.), §7, p70 Lapping (Def.), §7, p70 Late wood, §1, p9 Leaching (Def.), §5, p62 Leaching black ash, §5, p61 Leaching tanks, §5, p62 Lead of spiral burr, §3, p52 Lead sulphide, §4, p7 Leaf type filter, §5, p14 Lignin, §1, p49 . Action of fungi on, §1, p50 Amount of SO2 and CaO required for complete solution of, §4, p53 Detection of, §1, p50 Effect of, on chemicals and cooking, §1, p50 Formation of, §1, p50 Molecular formulas for, §1, p49 Lignin in wood, §4, p52 Ligno-cellulose, §1, p45 Lime, Adding to storage tanks, §6, p8& Lime, Available, §9, p34 Determination of, §9, p39 Lime, chemical, Specifications for, §9, p13 Importance of, in cooking process, §4, p54 Lime, Losses of, §5, p24 Per cent of in acid making, §4, p49 quantity of, To determine, §6, p9 slaked, Formation of, §5, p6 value of, To determine, §6, p9 Lime and carbonate liquor, Boiling of, §5, pls Mixing of, §5, pls Lime and chlorine, Heat reactions of, §9, p9 Lime (quicklime, caustic lime), Use of in soda process, §5, p6 Lime sludge, Analysis of, §6, pl11 Pumping off and washing, §5, p19 Settling of, §5, p19 Uses of, §5, p24 Lime sludge (mud), Disposition of, §5, p20 Limes, Composition of, §4, p8 Limestone, Characteristics of, §4, p7 Grade to use, §4, p33 Lining digesters, §4, p57 Liquid chlorine, Absorption of in milk of lime, §9, p8 Containers for, §9, 50 History and use of, 89, p7 Liquid rosin as a by-product, §6, p120 Liquor, analysis of green, Alternative method of, §6, p114 Black, analysis, §5, p49; §6, pl112 Liquor, black, Changing to black ash, §5, p58 Composition of, §6, p63 Density of, §6, ps3 Organic substances in, §6, p22 Process of treating, §6, p79 Use of organic matter in, §6, p97 Variation in strength of, §5, p46 What it contains, §5, p50 Liquor, caustic, Amount required, §5, p21 Determining strength of, §5, p20 Liquor, Composition of, in sulphate process, §6, p20 cooking, Color test for, §4, p71 Indirect heating of, §6, p38 Testing for SOze, §4, p71 Liquor, digester, Storage of, §5, p21 Green, §6, p5 Amount of sodium carbonate in, §6, p10 Analysis of, §6, p103 Composition and analysis of, §6, p9 Concentration of sodium carbonate in, §6, pll Liquor, Importance of penetration of, §4 ps1 lime and carbonate, Boiling of, §5, pls Mixing of, §5, p18 Liquor, Losses of, §5, p24 sulphate digester, Short method for testing, §6, p116 strength of, Determination of, §4, p72 68 INDEX | a Liquor, To measure, from tank, §5, p23 Total, §6, p23 Volume of, §6, p44 Liquor, waste, Substances reclaimed from, §4, p86 Utilization of, §4, p86 Liquor, weak and strong, Storage tanks for, §6, p8. White, or strong, §6, p5 Quick determination of, §6, p117 Liquor, white and black, storage tanks, §6, p35 white and green, Analysis of, §6, p108 Liquor and gas, Reclaiming, §4, p35 Liquor and pulp, Separating steam from, §6, p48 Liquor and vapor, Direct- and counter- flow system of, §6, p77 Mixed-flow system of, §6, p78 Liquor making, caustic, Continuous system, §5, p12 Filtration system, §5, p13 Liquor room, Operation of, §5, p21 Liquors, strength of mixture of, To calcu- late, §5, p23 Log haul-up, Chains used in, §2, pd Parallel, §2, p4 Single-strand, §2, p7 Logs, European practice in handling, §2, ps Loosely combined SO2, Determination of, §4, p73 Losses of soda liquor and lime, §5, p24 Lowering and raising end of haul-up, §2, p6 Low-pressure evaporator, §6, p76 Advantages of, M Magazine grinder, Description of, §3, p34 Operation of, §3, p35 Magazine grinders, §3, p33 ' Grindstones for, §3, p36 Output of, §3, p33 Shafts and flanges for, §3, p36 Sharpening device for, §3, p41 Size of wood for, §3, p33 Majority fibers (Def.), §7, p4 Manila, Bleaching, §9, p29 Manila-paper grade of pulp, §3, p87 Manufacturing processes, Continuous, dis- continuous or intermittent, §7, p2 Matrix (of grindstone), §3, p15 Measurement of pulpwood, §2, p2 Measuring liquor from tank, §5, p23 Mechanical draft (Def.), §6, p68 Mechanical-feed grindstone dresser, §3, p27 Mechanical pulp (Def.), §7, pl Description of process, §3, p3 Mechanical pulp, History of, §3, pl Physical properties of, §3, p6 Uses of, §3, p6 Wood used in, §3, p4 Mechanical-pulp mill, Grinder room and wheel pit, §3, p68 Starting up, §3, p74 Mechanical-pulp mill layout, §3, p66 Mechanical-pulp mill operation, §3, p70 Medullary rays (Def.), §1, pp7, 13 Mercaptan, (Def.), §6, p21 Mercaptide, Sodium, §6, p22 Mercerization, §1, p47 Mercury cells for generating chlorine, §9, p45 Methyl mercaptan, §6, p21 Methyl sulphide, §6, p21 Middle lamella, §1, p12 Milk of lime, Preparation of, §4, p23 Milk-of-lime reclaiming system, §4, p36 Milk-of-lime system, with Wedge pyrites furnace, §4, p27 Milk-of-lime system compared with tower system, §4, p34 Milk-of-lime systems, §4, p23 Mill, mechanical-pulp, Operation of, §3, p70 ; Starting up, §3, p74 Mill production, Determining, §3, p82 Mill reports and records, §3, p80 Mitscherlich cooking process, §4, p75 Mitscherlich towers, §4, p29 Mitscherlich vertical and horizontal digest- ers, §4, p76 Mitscherlich’s ammonia test, §4, p73 Mitscherlich’s sulphite process, §4, p3 Mixed-flow system of vapor and liquor, §6, p78 Mixing Box, Description of, §7, p25 Moisture determination, Importance of, §8, p15 Moisture in wood, §1, p32 Moisture removed by bark press, §2, p22 . Mono SOs: recorder, §4, p41 Monosulphite process, §4, p80 Morterud cooking process, §4, p79 Mud, lime, Disposing of, §5, p20 Mullen tester, §8, p38 Multiple-effect evaporator, §5, p51 Principle governing, §6, p69 Multi-press wet machine, §7, p64 N Natural draft (Def.), §6, p68 Nelson cell, §9, p43 a Newsprint grade of pulp, §3, p84 \: Niter cake, Use of, instead of salt cake, §6, p84 Nitrocellulose, §1, p48 Non-resinous (broad-leaved) pl7 k Ps woods, §1, — INDEX Non-resinous woods, Cells of, §1, p22 Tables for identifying, §1, pp20, 21 Normal bale (Def.), §8, p17 Normal cellulose, §1, p45 Number of burr, §3, p49 O Odors, bad, Cause of, §6, p21 Official tests, Conditions affecting, §8, p16 Old paper, Bleaching of, §9, p30 Orsat apparatus, §4, p40 Oxycellulose, §1, p47 Formation of, §8, p50 Oxycellulose test, §8, p48 P Paper, Bleaching old, §9, p30 Papermaking, fibers used in, Table Olesl, p2 Parallel log haul-up, §2, p4 Pecto-cellulose, §1, p45 Penetration of liquor, Importance of, §4, ps1 Penot method for available chlorine, §9, ate Pentosans, §1, p51 Percentage of SO2, To determine, §4, p40 ‘Perfect fibers, Separating waste products from, §8, p4 Permanganate No., Use of, in bleaching, §9, p15 Phenophthalein indicator, §9, p41 Physical properties of green wood, Table of, §1, p33 Pipes and valves used in caustic making, §5, plo Piping in washing room of soda-pulp mill, §5, p45 Pit, Blow, §5, p33 Grindstone, §3, pp29, 41 Pitch of burr, §3, p49 Pitch, or resin, §1, p13 Pitch or resin in wood, §4, p52 Pits, Bordered and simple, §1, p13 Plants used in pulp and paper industry, §1, pl Pneumatic thickener, or save-all, §7, p56 Pockets, Grinder, §3, p23 Poplar wood, Minute structure of, §1, p17 Pores (Def.), §1, p17 Porous, Diffuse and ring, §1, p23 Potassium chromate indicator, Potcher (Def.), §9, p16 _ Power, Variation in, during grinding, §3, ; ps3 Power available for grinding, §3, p43 _ Power required for chip screens, §2, pp43, ; 44 for grinding, §3, p42 §9, p41 69 Power required for knife barkers, §2, p39 for log haul-up, §2, p6 for slasher, §2, p12 for swing saws, §2, p9 in filter operations, §7, p72e to operate a stacker, §2, p28 to operate barking drums, §2, p18 to operate conveyors, §2, p3l Press, bark, Description of, §2, pp23-25 Moisture removed by, §2, p22 Press, filter, Care of, §6, p15 Leaf type of, §6, p14 Press, Hydraulic (downward-pressure type), §7, p91 (upward-pressure type), §7, p95 Pressed Pulp, §7, pl04 Presses, Bark, §2, p22 Pressing, hydraulic, p87 Pressure, Effect of on cooking, §6, p42 Pressure and Temperature charts (cook- Advantages of, §7, ing), §4, p62 Pressure and temperature of steam, §6, p43 Pressure of air supply, §6, p93 Pressure regulatcr for cooking, §4, p63 Pressure system, hydraulic, Natural head, §3, p90 Hydraulic-accumulator, §3, p91 Pressures in multiple-effect evaporators, §5, p54 Pulp, Accuracy of scales for wet weight of, §8, p18 Arranging and marking sheets for sampling, §8, p23 Auger method of sampling, §8, p19 Pulp, baled, Sampling, §8, p19 bleached, Washing, §9, p25 Pulp, Bleach requirements of, §9, p14 Bleaching soda, §9, p29 Bleaching sulphate, §9, p29 Bleaching sulphite, §9, p28 Care of wet samples of, §8, p26 Chemical (Def.), §7, pl Pulp, Chemical, §7, p13 Screens for, §7, p13 Worm knotter for, §7, p14 Pulp, Condition of, for testing, §8, p16 Consistency or density or (Def.), §7, p3 Constituents of wood contained in, §1, p55 Container-board, cheap book-paper, and manila-paper grades, §3, p87 Dirt in, §4, p83 dry, Baling, of, §7, p105 in rolls, §7, p104 Pulp, Effects of bleach on, §9, p15 Effects of cook on bleaching, §9, p14 Forms in which, is shipped, §8, p16 Grades of, §7, p20 70 Pulp, Handling (for shipment), §7, p103 Location of borings for sampling, §8, p22 mechanical, Cleanliness of, Color of, §3, pll Finish of paper made from, §3, pll Physical properties of, §3, p6 Resins in, §3, p12 Strength of, §3, 11 Testing uniformity of, §3, p10 Uniformity of, §3, p9 Uses of, §3, p6 Pulp, Mechanical or groundwood (Def.), §7, pl Description of process, §3, p3 History of, §3, pl Wood used in, §3, p4 Pulp, newsprint grade of, §3, p84 Number of bales sampled, §8, p22 Pressed, §7, p104 Quality of, §4, p82 sampling, Strip method of, §8, p18 Sampling rolled, §8, p22 ' Sampling very wet or frozen, §8, p21 shipping weight of, Determination of, §8, p17 Shrinkage of, by bleaching, §9, p26 Soda, §5, p2 Kinds of wood used for, §5, p2 Purpose of washing, §5, p44 Pulp, Storage of, before screening, §7, p2 strength of, Effect of bleaching on, §9, p25 Strength of, Proposed standard for testing, §8, p36a Sulphate, or kraft, §6, pl sulphite, Origin of process, §4, pl Pulp, Testing for acidity, §8, p46 for alkalinity, §8, p47 for ash, §8, p46 for cellulose, §8, p47 for color, §8, p44 ‘for freeness, §8, p34 for moisture, §5, p67 Pulp, testing for resin, §8, p46 ' ‘Testing unbeaten, for strength, §8, p42 Tests for, §8, p15 Time required in washing, §5, p48 Pulp, Uniformity of, §3, p10 Use of tintometer in testing color of, §8, p40 Wall-paper grade of, §3, p86 Washing bleached, §9, pp14, 32 Washing in open vats, §6, p48 Wedge method of sampling, §8, p23 wood, Action of bleach on, §9, p2 Yield of, §4, p80 Variation in, §4, p81 Pulp and liquor, Separating steam from, §6, p48 Pulp canals or sluices, §5, p46 §3, p12 INDEX Pulp dryers, §7, pp98, 101 Pulp-drying machine, Fourdrinier, §7, plol Pulp fiber, Hydration of, §4, p82 Pulp-making process, Effects of, §1, p55 Object of, §7, pl : Pulp mill, mechanical, Grinder room and wheel pit of, §3, p68 layout, §3, p66 Operation of, §3, p70 Starting up, §3, p74 Pulp samples, Drying, §8, p27 Weighing, §8, p27 Pulp sampling, Accuracy of wedge method of, §8, p25 Locating and cutting wedges, §8, p24 Modified wedge method, §8, p26 Pulp stock, liquid, Weight and volume of, §7, p107 Pulp testing, Sample can for, §8, p27 Pulp making, Treatment of wood for, §1, p44 Pulps, Brown, §3, p87 Pulpwood, Decay of, §2, p35 Fire protection in, §2, p33 Measurement of, §2, p2 Pulpwood grinder, Three-pocket, §3, p13 Pulpwood reclaimer, §2, p30 Pumps, Use of in caustic making, §5, p9 Pumps required for evaporators, §6, p77 Pyrites, §4, p6 Amount of SO2 obtained from, §4, p17 burning, Herreshoff furnace for, §4, p12 Wedge furnace for, §4, p14 Reason for burning, §4, pll Pyrites furnace, Starting up a, §4, pl4 Pyrometer, Recording, §4, p38 Q Quality of pulp, §4, p82 Quarry sap (Def.), §3, p18 Quick-cooking process, §4, p56 R Rags, Bleaching of, §9, p30 Raising and lowering end of haul-up, §2, p6 Raw materials, Amount used, §4, p84 Ray (cells), §1, p13 Rays, Medullary, §1, pp7, 13 Reaction tanks, §5, p12 Rechippers, §2, p46 Reclaimer, Pulpwood, §2, p30 Reclaiming department, Purpose of, §5, p50 Reclaiming gas and liquor, §4, p35 INDEX rf Reclaiming of chemicals, §6, p48 Reclaiming system, Milk-of-lime, §4, p36 Tower-acid, §4, p36 Recording wood reaching mill, §2, p5 Records and reports, Mill, §3, p80 Recovery of sulphur dioxide, §4, p35 Recovery tower, §4, p35 Reels (for pulp sheets), §7, p99 Refiner, Ball mill, §8, p5 Disk type of, §8, p6 Jordan type of, §8, p10 Selection of, §8, p13 Refiners, Types of, §8, p4 Refining by returning slivers to grinders, §8, p4 Refining process, Diagram of, §8, p3 Regulating air supply in sulphur burning, §4, p17 Regulating strength of acid, §4, p33 Regulator (consistency), §7, p67 Regulator, Pressure, for cooking, §4, p63 Reich’s apparatus, §4, p44 Rejections, or tailings (Def.), §7, p22 Relieving the digester, §5, p40 Reports and records, Mill, §3, p80 Repose, Angle of (Def.), §2, p26 Resin, or pitch, §1, p13 Testing pulp for, §8, p46 Resin ducts, §1, p13 Resin or pitch in wood, §4, p52 Resinous woods, §1, p12 Resins in Canadian woods, table of, §1, pd3 in mechanical pulp, §3, p12 in pulpwood, §1, p52 Resistent cellulose test, §8, p51 Re-water (Def.), §7, pp13, 51 Richter’s Method of determining SO;, §4, p47 Riffler, Description of, §7, pp18, 19 Felt, §7, p19 or sandcatcher (Def.), §7, p16 Riffling, (Def.), $7, p16 Riffling, Reasons for, §7, p16 Riffing before and after screening, §7, pl9g Riffling process, §7, p17 Ring, Annual or growth, §1, p8& Ring porous (Def.), §1, p23 Rings, width of annual, §1, p9 Roll sulphur, §4, p6 Rosin, Liquid, as a by-product, §6, p120 Rosin in pulpwood, §1, p52 Rotary digesters, §6, p24 Rotary furnace, §5, p58 Adding salt cake to, §6, p84 Chemical Changes in, §6, p83 Description of, §6, p80 Rotary type of sliver screen, §7, p8 Rotholz, §1, p32 Rotors for disk evaporator, §6, p65 Ss Salt cake, Use of in rotary furnace, §6, p84 Sample can for pulp testing, §8, p27 Samples, pulp, Drying, §8, p27 Weighing, §8, p27 Samples, wet, of pulp, Care of, §8, p26 Sampling, Importance of, §5, p65 Sampling and weighing chips, §2, p47 Sampling pulp, Accuracy of wedge method of, §8, p25 Arranging and marking sheets for, §8, p23 Auger method of, §8, p19 Locating and cutting wedges for, §8, p24 Location of borings for, §8, p22 Modified wedge method of, §8, p26 number of bales for, §8, p22 Strip method of, §8, p18 Wedge method of, §8, p23 Sampling rolled pulp, §8, p22 Sampling very wet or frozen pulp, §8, p21 Sap (Def.), §1, p7 Sapwood, §1, pp7, 9 Save-alls, Continuous vacuum filters as, §7, ps3 Elimination of white-water waste with, §7, p83 Felt type, §7, p80 Object of, §7, p78 Pneumatic, §7, p56 Sedimentation type of, §6, p81 Vacuum decker, §7, p65 Wire-cylinder type, §7, p79 Saw deck (Def.), §2, p10 Saws, Swing, $2, p& Scalariform (Def.), §1, p23 Scales, Accuracy of, for wet weight of pulp, §8, p18 Scraper type of sliver screen, §7, p7 Screen (Def.), §7, p4 Screen, Capacity of (Def.), §7, p7 Diaphragm, or flat, §7, p27 Effect of consistency on capacity of sliver, §7, p12 Screen (fine), Cleanliness of output; cost of installation, upkeep, and repairs; power required per unit of out- put; space required per unit; capacity and efficiency of unit; conditions necessary for , proper operation, §7, p21 Screen, fine, Features of a, §7, p21_ Selecting a, §7, p21 Screen, Inward flow, rotary type, §7, fine, p44 Recent type of horizontal centrifugal, §7, p40 72 INDEX Screen, Rotary type, slow speed, §7, p47 Screen, sliver, Quantity of stock pumped to, §7, p7 Rotary type of, §7, p8 Rotating screen plate type of, §7, plo Flat (scraper) type of, §7, p7 Screen, Tailings, §7, p42 Test of centrifugal type of, §7, p23 Screen operation, Control of, §7, p42 Screen plates, broken or improperly fitted, - Remedy for, §7, p27 Screening (Def.), §7, p4 Screening, fine, Purpose of, §7, p20 Machines used in coarse, §7, p4 Necessity of, §7, p4 Testing cleanness of, §8, p36 Screening operations, Difficulties attending, §7, p27 Screenings (Def.), §8, pl Difference between chemical pulp and groundwood, §8, p2 Influence of, on yield of pulp, §4, p80 Storing of, §8, pd Screens, chip, Rotary type of, §2, p42 Shaker type of, §2, p43 Screens, Horizontal centrifugal, §7, pp32, 40 Sliver, §7, p5 Vertical centrifugal, §7, p39 Screens for chemical pulp, §7, p13 Sectional burr (Def.), §3, p86 Sedimentation tester, §3, p8; §8, p33 Corrections for, §8, p35 Selenium, Effect of on cooking process §4, p54 Semco bleacher, §9, p23 Settling of lime sludge, §5, p19 Settling sludge, §6, p7 Sharpening devices for grindstones, §3, p27 Shipping weight of green wood, To find, §1, p3l of pulp, Determination of, §8, p17 Shive (Def.), §8, pl Shives, Cause of, §8, p2 Silver nitrate, Tenth normal, §9, p40 Simple pits, §1, p13. Single-strand log haul-up, §2, p7 Slab grating, §7, p5 Slaked lime, Formation of, §5, p6 Slasher, Power to operate, §2, p12 Slasher details, §2, p12 Slashers, Description of, §2, p10 Purpose of, §2, p9 Slitters (for pulp sheets), §7, p99 Sliver screen, Effect of consistency on capacity of, §7, p12 Sliver screen, Flat (scraper) type of, §7, p7 Rotary type of, §7, p8 Rotating screen plate type, §7, p10 Sliver screens, §7, p5 Sliver (Def.), §8, pl Slivers, Cause of, §8, p2 Slow stock (Def.), §5, p48; §7, p52 Slow-cooking process, §4, p56 Sludge (Def.), §6, pd Sludge, Disposal of, §6, p17 Lime, §5, p7 Analysis of, §6, p111 Disposing of, §5, p20 Pumping off and washing, §5, p19 Settling of, §5, p19 Uses of, §5, p24 Sludge, Settling and washing, §6, p7 Uses for, §6, p17 Washing the, §6, p12 Sluices, Pulp, §5, p46 Slushing (Def.), §7, p46 Smelt, Analysis of, §6, p97 Method of analyzing, §6, p98 Smelt soda, Analyzing, §6, p89 Smelting furnace, Air nozzles in, §6, p89 Air supply to, §6, p91 Construction of, §6, p88 Description of, §6, p86 Operation of, §6, p93 Smelting furnace spout, §6, p90 Smelting zone, Temperature of, §6, p95 SO2z, Amount obtained from pyrites, §4, p17 SO2, Combined, §4, p33 How is found, §4, p49 Effect of temperature on production of, §4, p16 free, Testing acid for, §4, p49 Half free, free, and loosely combined, Determination of, §4, p73 Quantity formed, §4, p15 Solubility of, §4, p22 Testing after cooling, §4, p39 Testing cooking liquor for, §4, p71 To determine percentage of, §4, p40 total, Testing acid for, §4, p48 in unabsorbed gases, §4, p47 SOz recorder, Mono, §4, p41 SO3, Determination of, §4, p44 Effect of catalyzers on amount pro- duced, §4, p18 Effect of temperature on production of, | §4, p16 Removal of, from gases, §4, p19 Richter’s method of. determining, §4, p47 SOz always formed when normal cooking acid is heated, §4, p54 Soda, caustic, Preparation of, §5, p5 Soda ash (= sodium carbonate), §5, p5 Soda ash, Determining percentage changed to caustic soda, §5, p65 Use of in preparing caustic, §5, pd Soda mill, Hazards in, §5, p25 INDEX 73 Soda process (Def.), §5, pl Chemicals used in, §5, p5 Outline of, §5, p3 Some simple tests in, §5, p65 Soda pulp (Def.), §5, p2 Bleaching, §9, p29 Kind of wood used for, §5, p2 Purpose of washing, §5, p44 Soda-pulp mill, Washing room of, §5, p44 Sodium amalgam, §9, p46 arsenite, Standardizing the, §9, p34 arsenite solution, How to make, §9, p34 bisulphite, Use of to bleach ground-wood pulp, §9, p31 carbonate, Determination of, §6, p103 Effect of, §6, p11 hydrate, Determination of, §6, p103 Effect of, on cooking, §6, p41 mercaptide, §6, p22 sulphate, Determination of, §6, p100 Sodium sulphide, Determination of, §6, p101 Effect of on cooking, §6, p41 sulphite, Determination of, §6, p101 thiosulphate solution, Standardizing of, §9, p36 Specific gravity of woods, Variation in, §1, p3l table for bleach solutions, §9, p38 » Spiral burr, §3, p51 Lead of, §3, p52 Splitters of wood blocks, §2, p40 Spout, Smelting furnace, §6, p90 Spray nozzles, Use of in fires, §2, p34 Springwood (Def.), §1, p9 Spruce wood, Minute structure of, §1, pl2 Stacker, Power to operate a, §2, p28 Standard, §2, p27 Standard conditions, Importance of, §3, p9 Standard freeness tester, §3, p9 Standard stacker, §2, p27 Starch-iodide indicator, §9, p41 Stationary barkers, §2, p19 Advantages of, §2, p20 Stationary digesters, §6, p28 Steam, Separating, from pulp and liquor, §6, p48 ; superheated, Use of in cooking, §4, p70 Steam consumption in cooking, §4, pp71, 85 Steaming the digester, §5, p38 Steropticon, Use of in testing fiber, §8, p29 Stock, Foaming of, §7, p27 Free or slow, §5, p48 Influence of consistency of, §7, p24 liquid pulp, Weight and volume of, §7, p107 Quantity of, pumped to sliver screen, §7, p7 Slow (Def.), §7, p52 Table of weights, volumes, etc., §7, p92 Stock, Thickening or concentrating, §7, p46 Stone roll beater, §8, p9 Storage of pulp before screening, §7, p2 Storage pile, dynamiting, Device for avoid- ing, §2, p30 Dynamiting a, §2, p29 How blocks reach the, §2, p25 Storage-pile conveyor, Suspension type of, §2, p27 Trestle type of, §2, p26 Storage tanks, Acid, §4, p37 Adding lime to, §6, p8 Reasons for, §7, p2 Storage tanks for weak and strong liquor, §6, p8 Straight-cut burr, §3, p50 Strength of liquor, Determination of, §4, p72 Strength of pulp, Proposed standard for testing, §8, p36a Strength of wood, Variation in, §1, p34 Strip method of sampling pulp, §8, pls Strong acid (Def.), §4, p4 Structure, minute, of poplar wood, §1, p17 of spruce wood, §1, p12 Structure of cellulose molecule, §1, p45 of stem of clematis, §1, p4 of stem of flax, §1, p6 of stem of Indian corn, §1, p3 Suberin, §1, p54 Sublimation, Test for, §4, p39 Sublimed sulphur, §4, p6 Sugars, Influence of, on yield of pulp, §4, p80 Sugars in wood, §4, p52 Sulphate digester liquor, Short method for testing, §6, p116 Sulphate fiber, Character and uses of, §6, ps Sulphate process, By-products of, §6, p118 Composition of liquor in, §6, p20 Kind of wood used in, §6, pl Object of, §6, pl Sulphate pulp (Def.), §6, p1 Bleaching of, §9, p29 Sulphite pulp, Bleaching, §9, p28 Sulph-hydrate (Def.), §6, p21 Sulphides, §4, p6 Sulphite process, Diagram of, §4, p4 Ekman’s, Mitschelich’s, Tilghman’s, §4, pp1-3 Origin of, §4, pl Outline of, §4, p4 Sulphur, Combinations of, with oxygen and water, §4, p6 : Effect of finely suspended, on cooking process, §4, p54 Flowers of, §4, p6 Occurrence and properties, §4, p6 Roll, §4, p6 Sublimed, §4, p6 74. INDEX Sulphur burner, Combustion chamber of, §4, p15 Flat type of, §4, p9 rotary type of, §4, p9 Stationary, §4, pll Vesuvius, §4, pll Sulphur dioxide, Absorption of, §4, p23 Effect of temperature on production of, §4, p16 How produced, §4, p9 Quantity formed, §4, p15 Recovery of, §4, pp35, 67 Solubility of, §4, p22 Use of, in bleaching, §9, p27 Sulphur trioxide, Effect of temperature on production of, §4, p16 Sulphuric acid, Effect of, on fiber, §4, p16 Sulphuric acid test (for pulp), §8, p42 Summerwood (Def.), §1, p9 Superheated steam, Use of, in cooking, §4, p70 Swing saws, §2, p8 Power to operate, §2, p9 System, Crandon acid-control, §4, p49 Milk-of-lime reclaiming, §4, p36 Tower-acid reclaiming, §4, p36 fi Table of weights, volumes, etc., of stock, §7, p92 white-water waste recoveries, §7, p86 Tailings, or rejections (Def.), §7, p22 Tailings screen, §7, p42 Tank, Blow, §5, p33 Dissolving, §6, p91 Leaching, §5, p62 Tank absorption systems, §4, p23 Tanks, Acid storage, §4, p37 Caustic, §5, p7 Causticizing, §6, p5 Reaction, §5, p12 Reasons for storage, §7, p2 Settling, §7, p72 Tanks, Storage, for weak and strong liquor, §6, ps8 White and black liquor, §6, p35 Tanks used in soda process, §5, p7 Tannin, Sources of, §1, p54 Tannins in wood, §1, p54 - Target (for blow pit), §4, p74 Temperature, Effect of, on cooking, §6, p42 Effect of, when burning sulphur, §4, pl6 Temperature and pressure charts (cooking), §4, p62 Temperature and pressure of steam, §6, p43 Temperature of furnace, §6, p87 of gases before cooling, §4, p38 of grinding, §3, p63 of smelting zone, §6, p95 Temperatures in multiple-effect evapo- rators, §5, p54 : Test, Blue-glass, for fibers, §8, p31 Oxycellulose, §8, p48 Unit weight, §8, p41 Test (for pulp), Sulphuric acid, §8, p47 Test for resistant cellulose, §8, p51 Tester, Freeness, §8, p34 Sedimentation, §8, p33 Standard freeness, §3, p9 Testers, Ashcroft and Mullen, §8, p41 Testing acid for free SOe, §4, p49 for total SO, §4, p48 from strong tower, §4, p47 Testing bleach, Methods of, §9, p33 Testing cleanness of screening, §8, p36 cooking liquor by color, §4, p71 ‘ cooking liquor for SOx, §4, p71 fiber with stereopticon or lantern, §8, p29 Testing pulp for acidity, §8, p46 for alkalinity, §8, p47 for ash, 8, p46 for cellulose, §8, p47 for color, §8, p44 for freeness, §8, p34 for resin, §8, p46 Testing strength of pulp, Proposed stand- - ard for, §8, p36c Testing SOe after cooling, §4, p39 unbeaten pulp for strength, §8, p42 Tests for pulp, §8, p15 Tests of pulp, official, Conditions affecting, §8, p16 Thermo-couple, §4, p38 Thermo-electric principle, §4, p38 Thermometer bulbs, §4, p62 Thermometers, Use of, in digesters, §5, p36 Thickener, or decker, §7, p52 Pneumatic, §7, p56 Thiosulphuric and thionic acids, when formed, §4, p54 Thread burr, (Def.), §3, p49 Tilghman’s experiments, §4, pl Tintometer, Use of, §8, p45 Total alkali (Def.), §6, p23 Total chlorine (Def.), §9, p34 Determination of, §9, p39 Total liquor (Def.), §6, p23 Volume of, §6, p44 Total SOe, Testing acid for, §4, p48 Tower, Recovery, §4, p35 Tower absorption systems, §4, p29 Tower-acid reclaiming system, §4, p36 Tower system, Two-, §4, p31 Tower system compared with milk-of-lime system, §4, p34 Towers, Mitscherlich, §4, p29 Tracheids, §1, p12 Tree, Bark of, §1, p34 INDEX 75 Tree grows, How, §1, p7 How (considered chemically), §1, p43 Triple-effect evaporator, Description of, §5, pol Troubles, Digester, §5, p42 Troughs, Conveyor, §2, p31 Tumbling barrel types of barking drums, §2, p13 Turbine installation, Number of grinders TOTO. te Turpentine as a by-product, §6, p118 Turpentine formed during cooking process, §4, p55 Turpentine in pulpwood, §1, p52 Twaddell hydrometer and scale, §5, p20 Two-stage bleaching, §9, p26 Two-tower system, §4, p3l U Uniformity of pulp, §3, p10 Unit weight test, §8, p38 v Vacuum decker save-alls, §7, p65 Vacuum filter, Continuous, §7, p57 Continuous, as a save-all, §7, p83 Continuous, as thickeners, §7, p62 Valves, Reversing, for hydraulic cylinder grinders, §3, p25 Valves and pipes used in caustic making, §5, plo Valves of digesters, §5, p34 Variation in pressure between wood and stone, §3, p59 Vat, open, Washing pulp in, §6, p48 Vertical digester, §5, p27 Vertical-tube evaporator, §5, p57 Vessels in plants (Def.), §1, p17 Vessels, Cooking, §4, p56 Vesuvius sulphur burner, §4, p11 Volume of liquid pulp stock, §7, p107 WwW Wall-paper grade of pulp, §3, p86 Washer (in bleaching), §9, p16 Washers, Disk, §9, p32 Vacuum rotary drum, §9, p32 Washing digester, §4, p75 pulp, Time required in, §5, p48 pulp in open vats, §6, p48 Washing room, Operation of, §5, p46 Piping in, §5, p45 of soda-pulp mill, §5, p44 Washing sludge, §6, pp7, 12 soda pulp, §5, p44 Washing tanks (pits or pans), §5, p44 Waste liquor, Substances obtained from, §4, p86 Waste liquor, Utilization of, §4, p86 Waste products, Separating, from perfect fibers, §8, p4 Water, Amount required for grinding, §3, p30 Effective head of, §3, p43 Importance of, §7, p5 Water, pressure, Sources of, §3, p90 Volume of, available for grinding, §3, p43 Water, White (Def.), §7, pp13, 51 extractor, §7, p60 for pressure system, §3, p90 required to extinguish fire in pile, §2, _ ped Water spray as protection from fire, §2, p34 Waxes in wood, §1, p54 Weak acid (Def.), §4, p4 Wedge furnace for burning pyrites, §4, p14 Wedge method of sampling pulp, §8, p23 Accuracy of, §8, p25 Modified, §8, p26 Weighing and sampling chips, §2, p47 Weighing pulp samples, §8, p27 Weight, air-dry, Calculation of, §8, p28 bone-dry, Per cent of, §8, p28 Weight of green wood, shipping, To find, §1, p3l of liquid pulp stock, §7, p107 of wood, §2, p2 Wet machine, Multi-press, §7, p74 Wet press, Description of, §7, p71 Wet presses (Def.), §7, p70 White liquor, Analysis of, §6, p108 Quick determination of, §6, p117 White-liquor storage tanks, §6, p35 White shiners, §8, p2 White (strong) liquor (Def.), §6, pd White water (Def.), §7, pp13, 51 White-water losses, Elimination of with save-alls, §7, p83 White-water waste recoveries, Table of, §7, ps6 Winder, Differential, §7, p100 Winders (for pulp sheets), §7, p99 Wood, Arrangement of fibers in, §1, p7 barking, Reason for, §2, p13 Car (Def.), §2, pl Changes in, during storage, §1, p52 Chief constituents of, §1, p41 chemical constituents of, Table of, §1, p43 Wood, chemical treatment of, Object of, §1, p55 Composition of, §4, p51; §6, p18 Wood, Constituents of, contained in pulp, §1, p55 cooking, Factors affecting, §6, p41 Decayed, to be avoided, §4, p82 Deliverying, to mill, §2, pl; §5, p2 76 INDEX Wood, Early and late, §1, p9 Farmer’s (Def.), §2, pl fats in, Trouble caused by, §4, p52 Fibrous and non-fibrous, §5, pl green, Table of physical properties of, §1, p33 To find shipping weight of, §1, p31 Lignin in, §4, p52 Measurement of, §2, p2 Methods of cleaning, §2, p37 Miscellaneous substances derived from, §1, p54 Moisture in, §1, p32 poplar, Minute structure of, §1, p17 Pressure of, against grindstone, §3, p57 Products of distillation of, §1, p44 pulp, Decay of, §2, p35 Fire protection in, §2, p33 Resins, fats, rosin, and turpentine in, §1, p52 Wood, Purpose of cooking, §6, p18 resin or pitch in, §4, p52 Results of chemical treatment of, §1, p55 size of, for hand-fed grinders, §3, p24 Size of, for magazine grinders, §3, p33 Splitting of, §2, p40 spruce, Average composition of, §4, p53 Minute structure of, §1, p12 Substances removed by cooking of, §1, p53 Sugars in, §4, p52 Supply of, for mechanical pulp, §3, p42 Treatment of, for pulpmaking, §1, p44 Variation in strength of, §1, p34 Waxes and tannins in, §1, p54 Weight of, §2, p2 Wood alcohol as a by-product, §6, p119 Wood and Stone, Variation in pressure between, §3, p59 Wood destroyed by fungi, §2, p35 fibers, §1, pp6, 8 losses, §3, p83 Wood preparing operations, Diagram of, §2, p3 Wood reach mill, Recording, §2, p5 Wood room, Operations in, §2, p36 Four ways of handling blocks in, §2, p37 Wood used in groundwood pulp, §3, p4 Woods, Broad-leaved or non-resinous, §1, pd7 broad-leaved (non-resinous), Tables for identifying, §1, pp20, 21 Canadian, Table of resins in, §1, p53 Coniferous (or resinous), §1, pl2 coniferous, Characteristics of, §1, pl5 Tables for identification of, §1, pp 14, 15 Woods, Effect of variation of in cooking, §6, p41 non-resinous, Cells of, §1, p22 Variation in specific gravity of, §1, pel Worm knotter for chemical pulp, §7, p14 xX Xylan and xylose, §1, p51 wie Yield of pulp, §4, p80 variation in, §4, p81 h 5 > gih a = 7 ce > a4 : 4a te ‘ Ps ? i y Pear i ~ re twee a (Ak +, + : ee { =, , : > ! ; Date Due : = rey ae —— ee fe - x ‘ _—_—_— | - \ < , 4 ipa inentlanietereseesiceasnf | epinainas peabetionesnn annie saieapecnncnae| nara etme ne SS ms Ce ne, | ea ee en eee | } - ————— —_——— ef tennessee —_e f Saint cnenpeietioe ee iteaa tag oe , 7 f F ati ee ci - ef a eee eee teres sas : ' siniacnenetedsh sis iacataenes ttt Cn | (poe ee ee ee \ ASO hee 8 Se en ernie esnips 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