URBANA ILLINOIS STATE GEOLOGICAL. SURVEY 3 3051 00005 6410 STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE STATE GEOLOGICAL SURVEY M. M. LEIGHTON, Chief REPORT OF INVESTIGATIONS — NO. 31 BRIQUETTING ILLINOIS COALS WITHOUT A BINDER BY COMPRESSION AND BY IMPACT A Progress Report of a Laboratory Investigation BY R. J. PIERSOL PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA. ILLINOIS 1933 STATE OP ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION John J. Hallihan, Director BOARD OP NATURAL RESOURCES AND CONSERVATION John J. Hallihan, Chairman Edson S. Bastin, Geology William A. Noyes, Chemistry John W. Alvord, Engineering William Tkelease, Biology Henry C. Cowles, Forestry Charles M. Thompson, Representing the President of the University of Illi- nois STATE GEOLOGICAL SURVEY DIVISION M. M. Leighton, Chief (2464—15468) Contents PAGE Chapter I 7 Summary 7 Introduction 8 Acknowledgements 9 Briquetting with and without a binder 9 Briquets by compression and carbonization 9 Possibility of preparing briquets without a binder 10 Nature of compaction without a binder 10 Compression and impact 10 Variables involved in the formation of briquets by compression and impact 10 Coals used in the investigation 12 Chapter II — Briquetting Illinois coals by compression without an artificial binder 13 Previous attempts to briquet bituminous coal by compression without an artificial binder 13 Raw fuel briquets without a binder 13 Fuel briquetting investigations by United States Geological Survey and United States Bureau of Mines 13 Briquetting investigations of Sweitoslawski, Roga, and Chorazy in Poland 13 Briquetting tests by Stansfield in Canada 14 Briquetting investigations by Levy in France 14 Briquets for subsequent carbonization 14 "Pure coal briquet" process by Sutcliffe and Evans in England .... 14 Briquetting tests by Parr, University of Illinois 15 Briquetting tests by Dobbelstein in Germany 15 Delkeskamp briquetting process in Germany 15 Hardy briquetting process in Belgium 15 Summary of earlier tests 15 Briquetting Illinois coal 16 Equipment used and procedure 16 Hydraulic press 17 Compaction die 17 Preparation of coal 17 Size 17 Moisture control 17 Method of heating coal 19 Temperature distribution 19 Range of variables 19 Preliminary tests 19 Further tests 20 Internal pressures developed in compressed coal 21 Briquetting by compression after preheating 23 Influence of time on character of the briquets 24 Effect of size of coal on quality of briquet 25 Incidental effects of compression 27 Effect of escape of fluid material 27 Case hardening effect 27 Effect of pressure on internal heat 27 Expansion of briquets 27 [3] PAGE Cross-sectional photomicrographs of compressed briquets 27 Conclusions 29 Chapter III — Briquetting Illinois coal by impact 30 Previous trial of impact method 30 Methods and equipment of present impact tests 30 Impact machine , 30 Briquetting dies 30 Methods of heating coal 31 Range of variation in conditions 33 Abrasion and friability tests 33 Application of information gained by compression to impact investiga- tions 35 Tests of impact process at room temperature 35 Initial tests 35 Tests on screened fractions of crushed coal 36 Effect of variations in weight of hammer and height of drop 36 Effect of multiple impact 36 Effect of various percentages of moisture 37 Conclusions 37 Tests of the impact m.ethod at elevated temperatures 38 Tests made with double impact 38 Effect of preheating the coal in the die 38 Effect of preheating the coal in an oven 38 Effect of moisture in coal preheated in the die 38 Effect of shape of die on quality of briquet from preheated coal 39 Effect of multiple impact upon quality of briquets from coal preheated in die 40 Tests with single impact 41 Coal preheated in the die 41 Coal preheated in an oven 41 Character of the briquets formed by impact 42 Description 42 Tests of hardness and toughness 43 Tumbling tests on Illinois coals 47 Conclusions drawn from results of impact tests 48 Chapter IV — Briquetting of representative Illinois coals by impact 49 Coals tested 49 Tests and results 50 Shattering tests of briquets made by double impact 50 Relative strength of briquets made by double and single impact 52 Conclusion 53 Chapter V — Future investigations 60 Determination of effect of varying quantities of mineral matter on briquets produced by the impact process 60 Determination of exact limits of controlling variables 60 Determination of physical and chemical causes of compaction 61 Studies of the effect of time and exposure upon the briquets 61 Burning characteristics of the briquet 61 Systematic tests of a variety of coals 61 Tests upon fine coals and coal dusts 61 Commercial tests of the impact process 62 Bibliography 63 [4] Illustrations FIGURE PAGE 1. Press for forming bricks by compression 17 2. Diagram of compaction die 18 3. Graph showing relation between minimum pressures and temperatures at which sufficient plasticity occurred to form briquets 21 4. Graph showing relation between temperature and magnitude of internal pressure 22 5. Graph showing loss of weight of coal in briquets made with and without preheating 23 6. Horizontal cross-section of a spherical briquet 26 7. Photomicrographs showing cross-section of a cylindrical briquet 28 8. Machine for forming briquets by impaction 31 9. Vertical cross-sections of the various shapes of briquets 32 10. Photographs of briquets of shape "B" (above), and "C" (below) 33 11. Graph showing results of tumbling tests on briquets formed by impaction as measured by percentage loss of weight 34 12. Cylindrical briquets formed by impaction. The rounded edges are due to abrasion during tumbling tests 42 13. Horizontal cross-section of impacted cylindrical briquet 44 14. Vertical cross-section of impacted cylindrical briquet 45 Tables PAGE 1. Source, size, and condition of coal used in briquetting tests 12 2. Effect of varying time at different conditions of temperature and pressure. . 25 3. Results obtained with dies of different shape by all tests under most favor- able conditions (made previous to final tests on uniformity of coals) .... 40 4. Results obtained in tumbling seven blocks of raw coal cut from natural benches 46 5. Chemical character of Franklin, Washington, and Will county coals in various stages of the briquets made from these coals, with the softening temperature of the ash 46 6. Strength of briquets made from various coals by double impact as deter- mined by dropping tests 51 7. Percentage loss of weight of double- and single-impact briquets during tumbling tests 51 8. Percentage loss of weight of briquets from various coals cleaned by 1.3 specific gravity separation 52 9. Systematic tests under favorable conditions of impact on a variety of Illi- nois coals 54 [5] Digitized by the Internet Archive in 2012 with funding from University of Illinois Urbana-Champaign http://archive.org/details/briquettingillin55731pier BRIQUETTING ILLINOIS COALS WITHOUT A BINDER BY COMPRESSION AND BY IMPACT A PROGRESS REPORT OF A LABORATORY INVESTIGATION By R. J. Piersol CHAPTER I Summary The briquetting of fine sizes of bituminous coal has long been regarded as a possible means of extending the market for this coal if it could be accom- plished without increasing the objectionable features of the coal and without adding greatly to its cost. Such fuel would probably find its best market among discriminating users of domestic coal seeking a moderate priced but clean fuel. The general excess of fine coal over the market demand has always been an important handicap of the bituminous coal mining industry, a condi- tion greatly accentuated by the recent rapid increase in mechanization. The preparation and marketing of satisfactory briquets would contribute to a correction of this condition. Numerous more or less successful attempts, on both laboratory and com- mercial scale, have been made to prepare briquets using various kinds of binders, which, however, not only add to the cost of the raw material but like- wise commonly increase the smokiness of the fuel. It appeared desirable therefore to investigate the possibility of preparing briquets from Illinois coal by some sort of compaction without the use of a binder. The present report presents the progress that has been made in such an exploratory investigation using continuous pressure in one set of tests and impaction in the other, these being the two most obvious means by which briquets might be made without a binder. Examination of the literature of briquetting and a brief series of tests described in the report indicated the probability that a satisfactory briquet could not readily be made by compression by the methods employed either previously as reported in the literature or by those used in the present series [7] 8 BRIQTJETTING ILLINOIS COALS WITHOUT BINDER of tests, the length of time required for the formation of each briquet being the most important obstacle to the success of the method. On the other hand tests of the impaction method gave promise of success ; this methods was, there- fore, more thoroughly investigated. The impaction tests consisted first of impaction with two blows upon coal preheated in the die and then upon coal preheated in an oven. The results indicated that the briquets of satisfactory quality with respect to hardness, friability, and general resistance to fracture and cleanliness can be made by the double-impact method when the coal is heated in the die, but less readily when the coal is preheated in an oven. On the other hand, tests using one blow upon preheated coal indicated that under certain definite conditions good briquets could be made from coal heated either in the die or in the oven by this single-impact process. Because of the great advantage of this process over any other that approached success it was selected as the most suitable to meet commercial conditions. The set of conditions recommended as of greatest promise of usefulness required 40 to 45 grams of coal crushed to pass a ^4 or %-inch screen, and an impact equivalent to the drop of a 500-pound weight 41/2 feet upon the coal preheated 10 minutes at 300° C. in an oven. 1 The possibility of making briquets by several variations of the impact method is demonstrated in the case of a fairly wide selection of Illinois coal but it is apparent that the process recommended produces most consistently the most satisfactory briquets as is indicated by the results of certain arbitrarily selected tumbling and shattering tests. It is planned to continue the investigation, particularly in regard to the effect of ash content of the coal upon the quality of the briquet, the effect of weathering upon the briquets, and in regard to their burning qualities. Tests will be extended likewise to include a larger group of coals and refuse dusts obtained at dedusting plants. It is believed that eventually it will be desirable for the coal industry to inaugurate pilot plant tests. Introduction An enlargement of the market for bituminous coal Avould probably result if clean, hard, low-ash and moderately priced briquets could be prepared from such coal. Since the fine sizes of coal are essential to the preparation of briquets, successful methods of manufacture would probably result in some relief to the pressure exerted upon the industry by the excess of fine coal pro- duced in the mining and cleaning processes. The essential requirements of a satisfactory coal briquet are moderate cost, resistance to breakage in handling and in weathering, and a relatively low ash content. Briquetting to be suc- 1 45 grams = 0.1 pound ; 300° C. = 572° P. INTRODUCTION 9 cessful should in general improve the quality of the fuel, increasing neither the smokiness nor the moisture content. The present investigation represents attempts, which under certain con- ditions were successful, to produce in the laboratory a satisfactory briquet that will represent an improvement over the raw fuel in the particulars noted above. Actual cost can be determined only by commercial scale production. It is planned to apply for patent to protect this process in the interest of the coal industry of Illinois. ACKNOWLEDGEMENTS Samples of coal for briquetting tests were furnished by various Illinois coal mining companies and members of the survey staff. The hydraulic press was used through the courtesy of Professor C. W. Parmelee, Head of Department of Ceramic Engineering, University of Illi- nois ; and the impact machine through the courtesy of Professor M. L. Enger, Head of Department of Theoretical and Applied Mechanics, University of Illinois. Assistance in the experimental tests was rendered by Mr. J. M. Nash, Physics Assistant, of the Survey. Mr. H. C. Roberts, Physics Assistant, of the Survey, prepared the photographs. Chemical analyses were carried out under the supervision of Dr. 0. W. Eees, Analytical Chemist of the Survey. Dr. G-. H. Cady, Senior Geologist, rendered valuable assistance in prepar- ing the manuscript, and Dr. M. M. Leighton, Chief, gave continued support to the investigation. BRIQUETTING WITH AND WITHOUT A BINDER It is particularly desirable to prepare briquets without the use of binders because binders add not only to the cost (an average of 72 cents per ton as compared to a total briquetting cost of $1.06 per ton (J/S) 2 but also to the smokiness of the original fuel. For these reasons and because it was believed possible to obtain compaction without the use of a binder, this investigation was limited to experiments in briquetting without a binder. BRIQUETS BY COMPRESSION AND CARBONIZATION The carbonization of briquets formed by compression without a binder has in some instances yielded a product representing an improvement over the original fuel. The cost of the process, however, is objectionable, particularly if satisfactory briquets can be made without carbonization. This process was therefore not considered as within the scope of the present investigations although the processes of compression employed in preparing briquets for carbonization are briefly described. 2 Figures in parentheses refer to articles listed in the bibliography at the end of the report. 10 BRIQUETTING ILLINOIS COALS WITHOUT BINDER POSSIBILITY OP PREPARING BRIQUETS WITHOUT A BINDER Nature of compaction without a binder. — The possibility that fine sizes of bituminous coal in small amounts might yield to certain conditions of pressure and temperature with proper time control to form a resistant solid mass is suggested by certain attributes of coal. Particularly significant is the plasticity of coal developed under pressure at comparatively low temperatures of about 300° C. Coal is one of the most susceptible of the rocks to earth pressures, the effect of which is to increase its hardness. Furthermore the "bituminous v components of coal, such as waxes and resins which are more or less plastic by nature, if not too greatly changed by the coalification process, might be ex- pected to yield to pressure and possibly to provide binding constituents. In view of these considerations, acknowledged to be more or less speculative, it did not seem unreasonable that conditions could be devised which would yield a firm briquet from at least some varieties of fine coal. Compression and impact. — With time as one of the factors in compaction it is evident that pressure of two kinds was possible — sustained pressure and suddenly applied pressure. This definitely provided two types of compaction, namely compression and impact. In the case of sustained pressure the time at which different pressures might be applied and the time during which the coal could be heated could be varied. In the case of impact only the time of heating and the amount of impact could be varied. A succession of impacts of the same or different amounts would of course be possible. Variables involved in the formation of briquets by compression and impact. — The physical conditions involved in the formation of briquets by compression and impact are particularly those represented by variations in time, pressure, and temperature, and the variations in the coal itself, such as size of grain, moisture content, ash content, and the nature and proportion of the banded ingredients — vitrain, clarain, durain, and fusain 3 — the amount of coal compressed, and the shape of the die. Variations in time are obviously limited by a practical consideration to not more than a few minutes for the formation of a single briquet. Pressure was limited by the capacity of the devices available to 70,000 pounds per square inch but economic considerations in industrial practice might require lower pressures. The range of temperatures of practical value are less than 350° C, since at higher temperatures the coal becomes excessively plastic and decom- poses with the evolution of troublesome gases and liquids. It was realized that different results might be obtained by applying the heat to the coal in the die during or before compression and in an oven before compression. 3 Vitrain is the coal composing the bright vitreous or glassy bands — called anthraxylon by Thiessen. Clarain is the coal composing the bright but not vitreous bands — called attrital coal by Thiessen. Durain is dull coal or "splint coal". It is uncommon in Illinois coals but thin layers of one inch or less are occasionally present particularly in coal No. 6. Fusain is "mineral charcoal" or "mother coal". INTRODUCTION 11 The size of the fine coal used in making the briquets might vary from powder of 100-mesh or smaller to two-inch coal, since this is the trade limit of fines. In these investigations, however, no tests were made on fines larger than 14 -inch mesh and most of the tests were made on fines of this size. The effect of variations in size of grain has not been thoroughly explored. The effect of variations in moisture content might be considerable since it is not improbable that moisture is responsible for part of the binding action. This effect of this variable was therefore explored to some extent. Undoubtedly variation in ash content is of great importance in the for- mation of briquets without a binder. However, as it seemed best to limit the present investigations to coals of average quality, no coals with excessive ash content were used. Eventually it is desirable to determine the permissible limits of ash content for the formation of satisfactory briquets. It should be realized, however, that ash is no more desirable in a briquet than in any kind of fuel and that clean coal is the essential raw material for the formation of a good briquet. Undoubtedly the different banded ingredients of the same coal will be affected differently by the briquetting process. Fusain particularly, since it is low in bituminous constituents and possesses little binding capacity, would be expected to yield a weak briquet or none at all under the same conditions under which clarain or vitrain would yield a strong briquet. Illinois coals contain only small amounts of durain. It is probable that fines in which fusain has concentrated will compact less readily than those in which there is little fusain. The quantity of coal used in the briquetting tests might be varied in- definitely. Since, however, most satisfactory combustion behavior is obtained with coal of nut size it seemed logical to consider that briquets within the range of nut sizes would prove most satisfactory. This gave a range between about two inches and three-eighths of an inch as the most favorable sizes for experimentation. Within this approximate range tests were made on briquets of several sizes, the largest 2^ inches in diameter and the smallest one-half inch in diameter, and on different weights of coal ranging from 2.5 to 250 grams. 12 BRIQUETTING ILLINOIS COALS WITHOUT BINDER COALS USED IN THE INVESTIGATION The coals used in the briquetting test came from different mines and seams and represent different sizes and quality of coal (Table 1). Table 1 — Source, size, and condition of coal received for briquetting tests County Seam Size 6 Various 5 +1M 6 +m 6 +IX 6 Vs 2 % 6 % 6 Vs 6 Vs 6 % 5 % 6 Vs 6 Vs 6 X 6 X 6 X 6 X 6 X 6 X 6 X 6 X 6 X 6 X 6 X Condition Sample Supplied by Washington (a)* Sangamon Jackson Franklin (c) . . . Macoupin (a) . . Will Franklin (b) . . . Franklin (a) . . . Williamson (a) . Perry (a) Saline Perry (b) Franklin (a) . . . St. Clair (a) . . . . Montgomery . . . Williamson (b) . Washington (b) . Perry (c) St. Clair (b) . . . Macoupin (b) . . Randolph Franklin (b) . . . Perry (b) Franklin Natural Natural. Xatural Natural Natural Natural Natural Natural Natural Natural Natural Natural Natural Floated on 1.3 gravity Floated on 1.3 gravity Floated on 1.3 gravity Floated on 1.3 gravity Floated on 1.3 gravity Floated on 1.3 gravity Floated on 1.3 gravity Floated on 1.3 gravity Floated on 1.3 gravity Floated on 1.3 gravity Floated on 1.3 gravity Column Car or tipple Car or tipple Car or tipple Car or tipple Car or tipple Car or tipple Car or tipple Car or tipple Car or tipple Car or tipple Car or tipple Car or tipple Face Face Face Face Face Face Face Face Car or tipple Car or tipple Car or tipple Survey. Company. Company. Company. Company. Company. Company. Company. Company. Company. Company. Company. Company. Survey. Survey. Survey. Survey. Survey. Survey. Survey. Survey. Company. Company. Company. * Letters in parentheses refer to different mines in the same county. The coal was in some instances used in the sizes supplied and in other cases was crushed to about 14-inch or less. CHAPTEK II— BRIQUETTING ILLINOIS COALS BY COMPRESSION WITHOUT AN ARTIFICIAL BINDER Previous Attempts to Briquet Bituminous Coal by Compression Without an Artificial Binder The following four attempts to briquet coal for raw fuel and five attempts to briquet coal for subsequent carbonization, in all cases without using a binder, have been described in the literature. RAW FUEL BRIQUETS WITHOUT A BINDER Fuel-briquetting investigations jointly by United States Geological Survey and United States Bureau of Mines (J/Sj.—Fvom 1904 to 1912, the Fuel Testing Plant of the United States Geological Survey at St. Louis investi- gated the physical and chemical properties of coal. Tests were made on the briquetting of coal, both with and without binder. Fine, moist coal at steam temperature was formed into 5-gram briquets in a hand press at a pressure of 4000 pounds per square inch. Holmes, who was in charge of the work, stated that "the results were unsatisfactory." Briquetting investigations of Sweitoslawslci, Roga, and Chorazy in War- saw, Poland (79). — In 1929, Sweitoslawski, Roga, and Chorazy used a hydraulic press to briquet both with and without binder 25-gram samples of coal under various conditions of time, temperature, and pressure. Without binder the time of heating the coal in the press ranged from 30 to 45 minutes. For eight non-coking coals, the optimum temperature range was from 400° to 420° C. At this temperature, the minimum pressure was 5700 pounds per square inch. Briquets made of non-coking coals showed high resistance to tumbling and shattering tests as compared to those made of coking coals. The best size assortment was found to be from less than 12-mesh to coal dust. They concluded that the properties of the finished briquets depend primarily upon the characteristics of the binder, but that when no binder is used, the properties of the finished briquets depend primarily upon the quality of the raw coal and upon the conditions under which the tests were conducted. [13] 14 BRIQUETTING ILLINOIS COALS WITHOUT BINDER Laboratory results indicated that briquets made without binder are stronger mechanically, ignite at low temperature, burn without crumbling, and produce less smoke than briquets made with binder. In 1930, the same investigators devised three methods for producing a stronger briquet from coking coals at a pressure range of from 2800 to 4300 pounds per square inch. In the first method the coal is heated to the tem- perature of incipient plasticity, thereby producing briquets having a granular structure ; in the second the coal is heated for the necessary length of time at the temperature of greatest plasticity in order to reduce the bituminous matter to the critical proportion; and in the third, the coal is heated at the upper temperature limit of plasticity in order to decrease the time of treatment. Their laboratory test showed that anthracite coals cannot be briquetted at any temperature without the use of binder, even at pressures up to 40,000 pounds per square inch. The strength of briquets of semi-bituminous coals was found to vary directly with their volatile content. All the briquets studied were made in a hydraulic press. This investigation remains in the laboratory stage. Briquetting tests by Stansfield of the Research Council of Alberta, Canada (73). — In 1931, Stansfield failed in attempts to form briquets with- out binder in a hand press at 400° C, rising coking coal and a mixture of coking coal and lignite. Briquetting investigations by Levy in Paris, France (57). — In 1932, Levy experimentally briquetted coal without artificial binder in a hydraulic press. The strongest briquets were made at a temperature range of from 430° to 450° C, the strength increasing up to the maximum attainable pressure of 20,000 pounds per square inch. A simultaneous application of heat and pres- sure for more than five minutes caused a decrease in the mechanical strength. The best assorted sizing of the coal particles was found to be from smaller than 25-mesh to larger than 400-mesh. The mechanical strength decreased as much as 40 per cent for briquets from coal smaller than 400-mesh and as much as 50 per cent for briquets from coal smaller than 8- and larger than 25-mesh. This investigation still remains on a laboratory scale. BEIQUETS FOR SUBSEQUENT CARBONIZATION "Pure Coal Briquet" Process by Sutcliffe and Evans in Leigh, England (78). — In 1910, Phillips and Phillips developed a laboratory process for pre- paring carbonized briquets which was later commercialized by Sutcliffe and Evans at the Leigh "Works of Messrs. Sutcliffe, Speakman and Company, under the name of "Pure Coal Briquets." Their process consists of briquetting without binder in a specially developed press a mixture of moist, pulverized coal with 20 per cent of pulverized coke breeze (added to prevent swelling BRIQUETTING BY COMPRESSION 15 at time of carbonization) at a pressure of 20,000 pounds per square inch. The resulting briquets are carbonized at temperatures from 600° to 1000° C. in order to give them mechanical strength. These carbonized briquets are said to contain 2 per cent volatile matter, to be easily ignited, to possess a structure similar to coal char, and to burn with a smokeless flame and high radiant heat. Briquetting tests by Parr at the University of Illinois (69). — In 1912, incidental to his work on low-temperature carbonization. Parr made a few tests on briquetting without binder a moist mixture of fine coal and coke breeze in a hand press with a maximum pressure of 1000 pounds per square inch. Upon subsequent carbonization the moisture was driven out causing the briquets to disintegrate. Briquetting tests by Dobbelstein in Essen, Germany (16). — In 1914, Dobbelstein made laboratory briquets from a mixture of fine coal and coke breeze at the plastic temperature of about 400° C, using pressures as high as 75,000 pounds per square inch. The briquets were subsequently carbonized. Delkeskamp Briquetting Process in Berlin, Germany (17). — In 1926, Delkeskamp formed briquets by mixing coal with a colloidal dispersion of coal in water. Tests showed that 6 to 20 per cent colloidal material was needed, depending on the type of coal, in order to briquet it at pressures of 2000 to 4000 pounds per square inch. The resulting briquets were carbonized at either high or low temperatures. Hardy Briquetting Process in Zandvoorde, Belgium (19). — In 1931, Hardy experimented with briquetting coal in a roll press at temperatures between 350° and 400° C. for subsequent carbonization. This process has not passed to a commercial stage. SUMMARY OF EARLIER TESTS These earlier tests achieved only moderate success in making briquets from bituminous coal without a binder. None of the attempts to make a raw fuel briquet reached the commercial stage, and although several processes for preparing briquets for carbonization passed into the commercial stage, the briquets previous to carbonization are weak and deteriorate rapidly. In all instances briquets for carbonization were compressed in a press, and were made from moist coal, or moist coal and coke breeze, the moisture acting as a temporary bond. Carbonization is necessary for permanent strength. In general, the tests were unsystematic in their exploration of the possibilities residing in variation in time, pressure, temperature, and various sizes of coal and briquets. 16 BRIQUETTING ILLINOIS COALS WITHOUT HINDER Briquetting Illinois Coals by Compression Without Binder The attempts made to briquet Illinois coals without a binder by com- pression were partially successful but the conditions under which compaction was possible were such as to make the method unsuitable for industrial usage. Certain facts revealed by the investigation of this process are significant with respect to the process of briquetting by impaction, described in Chapter III. Fig. 1. — Press used for forming briquets by compression. equipment used and procedure In the study of briquetting coal by compression in a hydraulic press, practically the same equipment and procedure was adopted as has been used by previous investigators (16, JfS, 57, 69, 73, 79.) BRIQTJETTING BY COMPRESSION 17 HYDEAULIC PEESS A 50,000-pound, hand operated, Eiehle hydralic press was used in com- pression experiments, the pressure being applied upon the bottom plate (Fig. 1). The pounds per square inch pressure applied to a briquet is de- termined by dividing the total pressure by the cross-sectional area of the briquet. COMPACTION DIE A spool-shaped steel die of the type shown in figure 2 was used to form briquets IV2 inches in diameter. The die is made of cold rolled steel, No. 2320 S. A. E., 3.5 per cent nickel. The auxiliary cylinder (A) forms the contacting member between the upper plate of the hydraulic press and the top plunger (B). The fine coal is compressed in the space (C) which is surrounded by the sleeve (D), the movable top plunger and the fixed bottom plunger (E) which rests on the lower plate of the hydraulic press. The plungers and inner sleeve are surrounded by an outer sleeve (F) with flanges (G). This spool is wound with heating coil (H), 20 feet of No. 19 resistance wire, which is covered with an asbestos jacket. The maximum temperature used was 425° C, although the die has an attainable temperature of 600° C. In the lower part of the outer sleeve there is an opening (I) within which a thermocouple may be inserted to measure the temperature of the die. The two plungers in contact with the coal have ends so formed as to give the desired shape to the briquet. All the dies constructed are 6 inches high, although sleeves and plungers of various sizes were used in the compression of coal briquets ranging from y 2 inch to V/ 2 inches in diameter. PBEPAEATION OF COAL Size. — The most desirable size of coal for briquetting was found to be smaller than 4-mesh. Coal less than y 2 inch in size was reduced to less than 4-mesh by putting it through rolls. Larger size coal was first put through a crusher which reduced it to approximately y 2 inch, and then through rolls. Moisture Control. — Samples were reduced to 2-pound lots and stored in glass jars when constancy of various specific percentages of moisture was required. For experiments at room moisture, the samples were air dried and then stored in paper sacks. In some instances, fine coal was submerged in water to alter experimental conditions. For percentages of moisture less than room moisture the coal was oven dried at 110° C. until it reached the desired value. 18 BRIQUETTING ILLINOIS COALS WITHOUT BINDER Fig. 2. — Diagram of Compaction Die. A Auxiliary cylinder B Top plunger C Briquet space D Inner sleeve E Bottom plunger F Outer sleeve G Flange H Heating coil I Thermocouple opening BRIQUETTING BY COMPRESSION 19 Method of heating coal. — In all instances the coal was heated in the com- paction die which had been previously heated to the desired temperature. In certain instances the briquet was formed by the immediate application of pressure, in others the coal was preheated in the die for definite lengths of time before the pressure was applied. The time of compression is the period during which the coal is subjected simultaneously to temperature and pressure. The temperature of the die was measured by inserting a chromel-alumel thermocouple into the hole in the base of the die so that the junction of the thermocouple was in contact with the bottom plunger. The die is of sufficient heat capacity to insure constancy of temperature. The thermocouple was calibrated against a standard thermocouple every two months during the investigation. Temperature distribution. — Experimental determination of the tempera- ture gradient of the coal within the die was accomplished as follows : The die was heated and maintained at a constant temperature of 300° C. The same amount of coal (45 grams) was inserted as was used in making a briquet and the bulb of a mercury thermometer was placed in the center of the coal, mak- ing it possible to measure the rate of temperature change at this position in the coal. At the end of 30 minutes the temperature at the center of the coal was the same as the temperature of the die. At the end of 45 minutes, the temperature of the coal increased to 330° C. and remained at this tempera- ture throughout the period of observation. RANGE OF VARIABLES In the investigation of briquetting by compression, unheated coal, coal heated in the die simultaneously to the application of pressure, and coal pre- heated in the die prior to the application of pressure, Avere used. Pressure was employed varying from 1,000 to 70,000 pounds per square inch, tempera- tures from to 370° C, and time from 3 to 60 minutes. The moisture con- tent of the coal before preheating was approximately 4 per cent with the exception of coal reduced to per cent moisture by heating at 110° C. for one hour. The dies used were two sizes, y 2 and iy 2 inches in diameter. PRELIMINARY TESTS Procedure and results. — The preliminary tests consisted of thirteen trials with Washington County No. 6 coal. Thirty-seven grams of coal containing 4 per cent moisture was used at temperatures varying from 25° to 380° C, with two trials at a pressure of 565 pounds per square inch, one trial at 1,700 pounds, and the remainder at 28,200 pounds, with a spherical die iy 2 inches in diameter. The time varied from 5 to 45 minutes. The result was four 20 BRIQUETTING ILLINOIS COALS WITHOUT BINDER poor briquets at 28,200 pounds pressure, at temperatures varying from 216° to 370° C, and time varying from 15 to 45 minutes. Mechanical difficulties or explosions attended the formation of two of these briquets. Extrusion ot mechanical difficulties also accompanied three unsuccessful trials. The preliminary tests, although they did not result in the formation of satisfactory briquets, at least indicated the nature of certain peculiar phenomena accompanying the tests, such as the explosive nature of the com- pacted coal, and the development of extreme plasticity. They also suggested lines of further investigation with respect to modification of the conditions originally imposed, such as the effect of preheating, variations in time up to one hour under various conditions of temperature and pressure, the effect of the size of the coal, and the effect of extrusion of fluid material. The pre- liminary tests likewise indicated the desirability of determining the relation- ship between temperature, pressure, and the development of plasticity and also the amount of internal pressure developed within the briquets. A second series of tests and experiments of an exploratory character was therefore carried out along the lines indicated. FURTHER TESTS Plasticity curve for coal. — Since it was apparent from the preliminary tests that coal under the conditions imposed developed plasticity and that if compaction took place it would probably be dependent upon this developed plasticity, a series of plasticity determinations as a basis for an incipient plasticity curve was desirable. By such a curve the lower limits of temperature and pressure at which briquets might be formed could be determined, pro- vided plasticity was the controlling factor and provided the coals used in the determination upon which the curve was based were of average character. Washington County coal obtained from a column which had been kept in cold storage for about 18 months was used. Since analyses of similar columns similarly stored showed little or no deterioration as a result of storage, it is believed that the coal was essentially equivalent to freshly mined coal. The plasticity tests were run in two sets — one with the li/o-inch die (37 and 42 grams) of which there were 48 trials, and one with the l/o-inch die (2.5 grams) consisting of 21 trials. For a series of specific pressures (at 1,000 pounds, 2,500 pounds, 5,000 pounds, and thence at 5,000 pound intervals to 30,000 pounds for the lV 2 -inch briquet, and at 2,000, 3,000. 4,000, 5,000, 10,000, 12,000, 25,000, 30,000. 35,000, 40,000. 45,000, 50,000, 60,000, and 70,000 pounds for the i^-inch briquet) briquets were made at varying temperatures from 0° C. to 350° C. for the l/Vmoh briquet, and from 160° C. to 360° C. for the li/ 2 -inch briquet. The trials resulted in 17 li/ 2 -inch briquets varying from good to poor, only one being good, and 13 medium or BEIQTJETTING BY COMPEESSION 21 poor i/o-inch briquets. Briquets were made more successfully in the small than in the large die, with which mechanical difficulties commonly developed ( 6 cases out of 48 ) . The criterion for the formation of a briquet was simply that it remained whole when pressed out of the die. In most instances, as noted above, the briquet was medium or poor in quality. By plotting on a temperature-pressure diagram (Fig. 3) the points at which briquets were formed, a fairly straight-line relationship is suggested, particularly by the points representing the l^-inch briquet. The graph suggests that at pressures of 60,000 to 70,000 pounds per square inch coal is plastic at low temperature u It D o ) O ( > • 5 INCH BRIQUET O 1.5 INCH BRIQUET o < • ^ < > < >^^ O IOOOO 20000 30000 40000 50000 PRESSURE (LBS. PER SQ. IN.) 60000 Fig. 3. — Graph showing relation between minimum pressures and tem- perature at which sufficient plasticity occurred to form briquets. and, on the other hand, that plasticity develops at atmospheric pressure at temperatures of about 360° C. The results for both sets of tests fall essentially on the same curve indicating that the pressure in pounds per square inch required for briquetting by compression is independent of both cross-sectional area and volume of the briquet in this range of sizes, which is 0.065 to 1.77 cubic inches, or a ratio of 1 to 27. The value of these tests lies in the fact that they demonstrate that large pressures are not necessary for compaction at temperatures above 300° C, provided the compaction can correctly be attributed to the development of plasticity, the thesis upon which the investigation proceeded. INTERNAL PRESSURES DEVELOPED IN COMPRESSED COAL In the preliminary and plasticity tests it was observed that high internal pressures, increasing with the temperatures, above 110° C. became evident in briquets when the external pressure was suddenly released. It appeared prob- 22 BRIQUETTING ILLINOIS COALS WITHOUT BINDER able that this sudden release of internal pressure, which was frequently of explosive violence, was responsible for failure of some of the briquets. It seemed desirable, therefore, to measure this internal pressure as a basis for determining the force necessary to overcome it. Eight tests were run on Washington County No. 6 coal. First an external pressure of 30,000 pounds per square inch was applied to 37 grams of coal in a li/^-inch spherical die, at temperatures varying from 125° to 370° C. The pressure was applied for 4 to 22 minutes, increasing with the temperature. The pressure was then suddenly reduced to between 500 and 1,000 pounds per square inch permitting internal pressure to be released without explosive violence. The hydraulic ram was set at a fixed position and the expansion of the briquet forced the oil to flow against the diaphram of the gauge, thereby registering the developed z™ 2000 40OO 6000 eooo 10000 PRESSURE (i-BS. PER SQ. IN.) 12000 Fig. 4. — Graph showing relation between temperature and magnitude of internal pressure. pressure ( Fig. 1 ) . The internal pressure then developed rose from 800 pounds per square inch for coal heated to 125° C. to 13,000 pounds for coal heated to 345° C. and to 370° C. An approximate straight-line relationship was found to exist between temperature and internal pressure (Fig. 4). It is apparent, therefore, that the formation of briquets by compression at tem- peratures of about 300° C. probably requires, in order to prevent disruption by explosion, confining pressure for at least a short period in the order of 10,000 pounds. It was found moreover that not only gases but also liquids were extruded as a result of the sudden development of internal pressures and further tests indicated that confining pressures not only prevented the extrusion of these materials but tended to produce a stronger briquet. The length of time that the confining pressure must be maintained increased with the temperature at which original compression was applied. BRIQUETTING BY COMPRESSION 23 Since the plunger which compressed the coal had a freedom of movement greater than the thermal expansion of the coal, it is believed that the pressure developed is due to some other cause, such as the evolved gases. BRIQUETTING BY COMPRESSION AFTER PREHEATING Preliminary tests and those on internal pressure and plasticity were almost entirely on coal heated in the die during compaction. It was realized that different conditions would probably exist if the coal were preheated before compression. Eight tests were accordingly run on preheated Washington County coal, using 42 grams of coal in a 1%-inch spherical die and one on 2.5 grams of coal in a %-inch spherical die. Six of the tests with the larger Ul o It o Z> t> -H; < uo}Siiiqs , B^ d CM ■ CM T-H T-H CM Tt< 00 CO C2 0C UlpfU'BJJ to to CD t>. CO CO lO CO c IILVV CO 3 : : T* r3 to -* ~t CO CM 31 uo^SinqsB y^ in © c isa CO -* Tt t- LO O I-- CTJ LO tnpfU'B.ij ^ to t~ LO 03 CC co co co co co CO T-H © o- 03 M 3 WAV OJ co T-H co CM CO uo^Sinqsra^ 110 cm' '3 t-h a> t-H t-H LO o- UipfUBJjI 00 >* CO CM CM r- 00 C3 c IHAV -* '. -* '■ CN 6 u : ^ : : C iO CO 1> "53 uojSuiqs'B^ ■* • ■* '■ '■ 5 j>> O ^ : : C "3 c C5 C t-H CO CM ■* o 5 TJatJ • 1 3 32 a _; M ■ Tfl ■■63 • a o O a =t3^^^-§ „ O g CO .3. cd >H td " a C a 3^ d S.SO ».S°n £ H-fi.9 O Wf o X- ■So o o > cm - o 3 co^^-^: CO •= CO 1-1 .2 <© O O c PQ P PC O Sh JO"" ^!h Jo .2S Bl5 . «t ~ 0) 0 lO lO T)H ^Tj(cO(NiHmiO'0'*(OtDCDtO (spnnod) jatauiBq jo ^qSia Al ooooooo o o o o o o o ooo oo o o ooooooo o o o o o o o ooo >o lO "O in in iO lO ia «5 lO lO m iQiOioio>OiOiOiOiOIN(N(N(N aip jo ad^qg OOOOOOO O OOOOOOOOOOOWPR (saqom) a;p jo ja^atcreiQ io io io o io io in io lOioioinioioioioioioioinin 1— i 1— 1 i-« i— ICINi- 1 i-H i— 1.— li— li— (i— t i-H i— I i— 1 i— li— ( i— ( i— li— I (,.) (sureiS) innotny OOOOOOO O OOOOOOOO10U5H5 10 10 TjH Tt< Tt< ^1 lO >0 ■* -* '*'^-ltlT^Tj<^t<^fl^-^l'^^COCO CM (M CP u 3 co "8 B -d a 3 O O 1 :::::: : : ::::::::::::: 3 o :::::: : : :::;::::::::: .Sioioicioioinio in 010 1010101010101010^^ ^C103 01010GO Oi 0©010101G1©0101010HMM 3 c3 *H Eh jaqmnu ;saj, OSOlOHCleoi lO tONOOOOH(NMtt(iOtONOO i—l i-H Ol CI CM C-l CM CM IM ^ OOOOOSS OOOOOOO 0§§§g§§§ gg§§gg§§ OOOO OOOOOOO OOOOOOO oooooooo oooooooo OOOO OOOOOOO OOOOOOO oooooooo oooooooo co co co co co co co co co co co cococococococo cocococococococo cocococococococo CO CO CO CO CM CM CM CM CM CM o iO >o to to to »o tO iO lO to »o »o tO to to to to to to to CM CM CM CM — I CM CO -* to CO NOOGOh CM CO "* id tO N 00 Ol O H N CO ■* t« -* -f ■* -t rt< •* -t< "* to to to to to to to lO lO tO (O CO © !C CO CD CO CO -O N N N coco tOto cococococococo cococococococo cocococococococo cocococococococo eg Z o 3j- 10 I s oj c CU CO rC -= S c ^ "0 o> 0) fe ° CO p- ., W m 1,32 o "S CO r~ O I a* I .a 1.2 *3 cS^co^ .CD ^ ctj S3B J £ g J.S •j'cie w O '2 ^ *£ -h 1*1.3 .S'ojtuo*' *t-| Ul CO j, ° C w 0) -'3 cu to +- 1 C M bo cti £ 03 . ! bo 'X S c 3 O . »& '-'o 5 3 k 5 ON 2,3 II « ^ £ ° S II 6 rt ta'S 2 " ^ to c . «•£,■** & 3 g mo a m * J P &S3 56 BRIQUETTING- ILLINOIS COALS WITHOUT BINDER c3 ft +3 K ■a s= o _: en 2 ■i 3 -i CM t~ OiCM -*" co" co^ 2pq (|) cjanbug §§§§§§§ OOOOOgg Ph pl, Ph Pl, ^ Pl, ooo (sa;nmtn) U9AO tn Sm^'Baqa.y; ooooooo ooooooo oooooo ooo (sa^nuiui) aip ni Snicjuaqajj ooooooo ooooooo oooooo ooo (4) '0 o'a-Hnwaduraj, ooooooo ooooooo oooooo ooo ooooooo ooooooo oooooo ooo co co co co co co co co co co co co co co co co co co co co cococo sjoBduii jo -oj^ CM CM !M CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM (M (^93j) doip jo ^qSiajj © CO tf ■* Tjl •"*! TjH CO CO -* ^ Tjf -^1 Tj< CO CO •* Tfl ^ •<# -# CO -*•*•*<■ o o O lO IC 1C IC lO lO w gr^t^t^t^t^-t^OcMCvicN 2 £> co jaqtunu cjsajL CO rt< lO CO t^ 00 C5 O >-H CM CO "tf io CD NOOCSOHCN CO^iO t^t^r^t^t^t^i^ oo oo oo oo oo oo oo ooooooooio oocrn CD CD CD CD CO CD CD CD CD CO CD CD CO CD CDCD CD CD CD CD COCOCO BRIQUETTING ILLINOIS COALS BY IMPACT 57 3 =1 o o - ■- QQ . o a ■ •o • 00 lO • GO i-i lO to © r-J oo| hP, §§£§§§!§ I §^§§§g§ §§§§§t^ **; oooooo ooooooooo ooooooo ooooooo ooo oooooo ooooooooo ooooooo ooooooo ooo oooooo ooooooooo ooooooo ooooooo ooo MrawMccm cococococoeocococi co co co co co co co co co co co co co co co co co CI Q i-O 'O '-O iO i.O »o iO iO »o c »o »o O »C tC »o ooo CI C iO lOLOlOlOlOiOiOlOlQ iO »C iO <0 i-O >0 >0 LO LO iO 'O iO i-O LO LOLOLO o (M CI CI t-- IS Is IS cococoooco^co'0606000006060606 >>oo GOooodcoooooSooooododooGOoo-^ P u P P. HSOOOlOH NM-*iOONOOfflO iH CI M -# IO <0 t» OOOOt- 1 CI CO -t< 10 CO t- 0)0000 OOOOOOOOi— 1 ^n ^h i-M r-< i-< i-H 1— 1 1— 1 1— 1 CI CI CI C I CI CM CM !M CO CO CO CO (^ t~ (^ t^ l^ l^ 1^ Is t~ 1-- t~ t- t- l~- I— Is t— t- IS l~ IS t^ t~ 1~- t-- Is b- l> O 3 A <& c CD 03 T3.P g 0) feiS c p ,8 rt c Z%u io C7 t< no 'E a ■Q c "£ S3 o«3 o a> OS 0) p 3 - CI - ft -H ^3 fl P 01 CO O 3, OS — FM P 3 cd tun 0) r 01 - -S r^ si 1 +- 1 ^3 to p co o> im ni C 3 +, c 0) 0) H . 3 ci H - ^ 0/ C~ ,£ - r O" s cc! "3 fa c P «>U OJ £1 - — 3 ucio P +- 1 ? -* 03M cS J3 : +-) ,-v^ ^ TS * -!- ■M- - 1 - 5 iski y 58 BRIQUETTTNG ILLINOIS COALS WITHOUT BINDER o O m ft § o„q to g (I) isnbug (S8|miiui) toao ui Smj'Gaqa.ig (sa^nuiui) 8ip ui Sm^aqaig (4) "0 o'a-mvBjaduigj, pH 00 co co ■•J ■* o o P* | OOO PhO§ PhOO|C 00000 000 00000 00000 00000 000 00000 o 00000 o 00000 CO CO CO - b- t~- r~ t- t-~ 1- t> BRIQUETTING ILLINOIS COALS BY IMPACT 59 CI o> o a — 6 O CO *± -Q >—* X. 3 bO o < ^t o4 co r^ id oJ r^ ■* -* • co 2 htoP MOCOHtO oo '- , CO lOrtKMMN rH 05 rH l(NH 1— I rH r- * i— I PhO l§oo§oo oo oo oo oooooooo oooo ooooooooo oo oo oo oooooooo oooo ooooooooo oo oo oo oooooooo oooo ooooooooo oo oo oo oooooooo oooo ooooooooo oo oo oo oooooooo oooo cocooicMcococococo coco coco coco cocococococococo cocococo CM H CM . NHNNHHHi lOiOiOiOiQi^'OiO'O >o io *o lO lO IO »C lO lOlCO lO ■*■*•*'•*' -^ •* tJH ■* tJ< CO r^i CO ■* CO **' CO ■*' CO CO rfi tJh -rji ■>* ■*•*'*'•<*< ooooooooo oo oo oo oooooooo oooo OOOOOOOOO i-OO "-OO lOO iO O O iO O O O O oooo lOioioioramioioio oj to oa io cm to M ifl o o io lo ifl lo lOLomio ooooooooo oo oo oo oooooooo oooo lOLOiOiOLOiOiOiOiO lOiO lO »0 lOiO IO li^ IO IO 1C IO "O IO ICIOIQIO o ti § §.s qO ft >>S § h.H o o io in r~ i^ t^ i^ t^ t^ t^ t~ t^ CO t~ IO io CO C2 m >o OH CD CO t- t^ t- I- t^ 1> 1> b- O 3,C w - ^ CD w , - tTn^ — CT3 = £ 3

*i - Si E-i a rH O X| 0) ■5b a D w Fi 10 a> ^ 1- IIS 01 c s M — , i-> cjO