jg . 'V: . International Correspondence Schools SCRANTON, PA. REG U.S. PAT. OFF INSTRUCTION PAPER with Examination Questions FIRST EDITION By-Product Coking 860 SCRANTON, PA. INTERNATIONAL TEXTBOOK COMPANY ADVICE TO THE STUDENT You learn only by thinking. Therefore, read your lesson slowly enough to think about what you read and try not to think of anything else. You cannot learn about a subject while thinking about other things. Think of the meaning of every word and every group of words. Sometimes you may need to read the text slowly several times m order to understand it and to remember the thought in it. This is what is meant by study Begin with the first line on page 1 and study every part of the lesson In its regular order. Do not skip anything. If you come to a part that you cannot understand after careful study, mark it in some way and come back to it a-fter you have studied parts beyond it. 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(o * 2 - ^ BY-PRODUCT COKING BY-PRODUCT COKING APPARATUS AND PRODUCTS RETORT COKE OVENS PRINCIPLES OF BY-PRODUCT COKING 1. Distillation. —When bituminous coal is placed in a vessel that has but one outlet and from which air is excluded, and the vessel is then subjected to external heat, the volatile portions of the coal will be driven off in the form of vapor. This process is known as the destructive distillation of coal, and the vessel in which the heating is accomplished is called a retort. If the vapor that is driven off is cooled, a por¬ tion of it will be condensed into liquids while the remainder will remain in the form of gas. The product remaining in the retort is termed retort-oven coke and has value both for domestic and metallurgical purposes. The liquids and gases that are distilled from the coal are known as by-products when the distillation is conducted primarily for the manufacture of coke even should they have a greater commercial value than the coke, and the process is called by-product coking. ■ The coke is the product generally sought and is the most valuable one, excepting where gas coals are heated in small retorts for the purpose of producing illu¬ minating gas, in which case the coke is a by-product. 2. Object of By-Product Coking.— When coking coal in ordinary beehive ovens, all the gases are consumed in COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ALL RIGHTS RESERVED §71 2 BY-PRODUCT COKING §71 the oven to generate heat for the coking process and there are consequently no products, other than coke, resulting from the operation. When it is understood that from each ton of coal having 28 per cent, of volatile matter there can be obtained approximately 10,000 cubic feet of illuminating and fuel gas, 5 pounds of ammonia gas, and 10 gallons of tar, worth altogether at least $1, and that 34,000,000 tons of coal are coked annually in the. United States alone, the enor¬ mous loss resulting from beehive-oven practice as compared with by-product coking can readily be seen. The manufacture of coke in by-product ovens is not a new industry, as ovens of this character were built and the tar and ammonia saved at Salzbach, Germany, as early as 1766; and in 1881, by-product coking was an established industry in that country. By-product ovens have replaced ovens of the beehive type almost entirely in Germany and other European countries. The reasons that they have not been more generally intro¬ duced in the United States are, that their first cost is at least $4,000 per oven as compared with $350 for a beehive oven, thus necessitating a much larger outlay to establish a coke plant; that it is necessary for them to be so situated that the waste gas can be marketed or utilized to advantage; that royalties are demanded by the owners of the patents in this country; and also that there has been an uncertainty in regard to the market for the by-products—tar and ammonia. 3. Coke Output From Retort Ovens. —In addition to the saving in by-products, retort ovens give an increased output in coke over the beehive oven. This is due to the fact that there is loss of fixed carbon in beehive ovens, owing to the burning of some of the coke during the process of coking, this loss being greater in coals low in volatile matter than in those higher in volatile matter. Also, in the retort process, a portion of the volatile hydrocarbons are said to be fixed—that is, decomposed—so that some of their car¬ bon is deposited on the coke produced from the fixed carbon of the coal, thus yielding from 1 to 2 per cent, more coke than §71 BY-PRODUCT COKING 3 would be expected from a calculation based on the amount of fixed carbon and ash in the coal. The by-product oven being constructed on the retort plan and keeping the coal from coming in contact with but little of the oxygen of the air, most of the fixed carbon in the coal is retained. 4. Coals Suited for By-Product Coke Ovens. Usually, coking coals low in volatile hydrocarbons produce a hard strong coke in by-product ovens, while those high in volatile matter produce coke that has a soft spongy struc¬ ture. Coals containing between 15 and 20 per cent, of vola¬ tile hydrocarbons can be coked without appreciable loss of fixed carbon in a by-product oven. The greater the percent¬ age of volatile matter in a coal, the greater will be the yield of gas, tar, and ammonia; but when there is over 28 per cent, of volatile matter in a coal, it does not usually give a first-class coke. Although the chemical analysis of a coking coal will indicate, to some degree, the chemical composition and probable quantity of coke, gas, and by-products that may be obtained from it, there are so many inconsistencies found in results, that these data can be determined with certainty only by actual test. It may be stated that a coal that will admit of coking in the beehive oven will offer no particular difficulty to treatment in the by-product oven; and it is claimed that some coals that will not coke in the beehive oven call be successfully coked ia the by-product oven. It is maintained by some that coking coals con¬ taining as high as 31 per cent, of volatile matter yield coke of a better structure when coked in by-product ovens than when coked in beehive ovens, owing to the increased depth of the charge and the increased weight on the lower part of the charge in the by-product ovens. This may be true in a measure for all the coal below 18 inches from the top, but since the upper 18 inches of the charge is also dense, it is probable that the slow dry heat has much to do with improving the structure of the coke. 5. Relative Costs of Beehive and By-Product Proc¬ esses. —Table I gives a comparison by a manufacturer of 4 BY-PRODUCT COKING §71 by-product ovens of the relative costs and results in making coke in beehive and by-product ovens, no account being taken of any royalties charged on the by-product ovens. TABLE I RELATIVE COST OF COKE MADE IN BEEHIVE AND IN BY-PRODUCT COKE OVENS S c V *0 C0 a 0 aS cfl c 0 ID'S 0 c c 0 0 bh (Sj ® 0. 5 ? o> p a c □ .2 S (U £ 75 Beehive . . $ 325 2.00 j 500 $162,500 66 $ 1.50 $.46 $.05 $2.01 By-product 4,000 4-25 235 940,000 7 i I.41 .70 •31 $1.41 I.OI These figures are made on the assumption of the following returns per ton of coal: 5 per cent, tar = 10 gallons at 2j cents ... $ .25 1 per cent, ammonia sulphate = 20 pounds at 2i cents.50 3,500 cubic feet of gas at 7.14 cents per 1,000 cubic feet.25 Total .$1.00 BY-PRODUCT COKING PLANTS 6. Location of By-Product Plants. —By-product plants are usually located near to where the coke is to be consumed, or where there is a market for the by-product gas, but railroad and water freights on coal and coke must be considered in settling on a location. Coal is a commodity easily handled, and can be shipped with but little loss. Coke, on the other hand, is bulkier, must be handled with more care and, besides, it deteriorates by exposure, particularly when shipped by §71 BY-PRODUCT COKING 5 water. The railroads recognize these facts and the freight rates for coal are usually enough below those for coke to equalize the two. The disposal of the gas is also a matter demanding careful consideration; and in the case of a plant to make blast-furnace coke, when proximity to a labor center is necessary, the market for the surplus gas makes a by-prod¬ uct oven plant adjoining the blast furnace a very attractive proposition. The recent developments in piping gas long distances under pressure have somewhat extended the limits of the problem, but in general the greatest advantage is gained by shortening the coke haul as much as possible. If domestic coke is to be the product, the need for locating near the market is equally apparent, particularly as the gas from this type of plant is especially adapted to city distribution. The disposal of the tar and ammonia is not so difficult a matter. The demand for tar is now quite extensive; and by means of tank cars the supply can be easily marketed from any desirable location for a by-product plant. Ammonia, in the form of strong crude liquor, is also easily shipped, but there is less likely to be as strong a local demand for it as for tar. In case ammonium sulphate is to be made, care must be taken to have a source of sulphuric acid supply assured. The other considerations, character of ground, proximity of water for boilers and condensation, freedom from floods and freshets, etc. are common to most industrial plants, and need not be further dealt with here. 7. General Arrangement of By-Product Coke-Oven Plant. —A general idea of the requirements of a by-product coke-oven plant may be had from Fig. 1, which is a view of the plant of the New England Gas and Coke Company at Everett, Massachusetts. This plant was designed to coke coal from Nova Scotia; and as there is a ready market for a large amount of illuminating gas in Boston and other near-by cities, especial attention has been paid in its design and operation to the production of gas for illuminating purposes. The coal for this plant is brought from Nova Scotia by steamship and is unloaded into a bin a. It is then raised up 6 Fin §71 BY-PRODUCT COKING 7 the inclines b in cars and dumped into the bins c , or else con¬ veyed over the bridge d to bins e. The coal is drawn into larries from these bins, carried to the ovens, and discharged into them, each bin supplying coal for two blocks of ovens. There is also a coal stock pile from which to draw in case of necessity. The traveling crane h transfers the coal from the stock pile to conveyers, which carry it to bins e for the second row of ovens; it is also conveyed across the bridge d to coal bins c for the first row of ovens. Retort ovens are long and narrow chambers from which the coal, when it is coked, may be pushed by a machine /, termed a coke pusher , into coke pans k , where it is quenched with water. The coke is next loaded into cars and shipped to consumers or else stored for the local trade. In this plant, there are eight blocks of ovens, each surmounted by a cantilever bridge / on which the larries run to and fro in carrying coal from the coal bins to the ovens. A battery of by-product ovens usually includes about fifty ovens, as this number can be easily charged from one coal bin. After the ovens are charged, all openings are sealed air¬ tight, except those on top that are connected by pipes with gas mains and through which the volatile part of the coal escapes when the walls of the ovens are heated with gas. The tar contained in the gas is removed in the condensing house m and the ammonia in the ammonia house n. The first gases given off by the coal are rich in illuminants, and are saved in the tank o; the balance of the gases are burned to heat the ovens and the products of combustion are drawn off and up the high chimneys p. The plant also includes a powerhouse r , and a small plant t for treating the tar, besides the numerous small buildings accessory to so extensive a plant. 8 BY-PRODUCT COKING §71 §71 BY-PRODUCT COKING 9 BY-PRODUCT COKE OVENS 8. Classification of By-Product Coke Ovens. —While there are a number of types of by-product coke ovens in use in Europe only two of these types have been adopted in the United States; these are the Otto-Hoifman, or vertical-flue, oven, and the Semet-Solvcty , or horizontal-flue, oven. These two types have been improved and adapted to meet con¬ ditions as they exist in America. Each by-product coke- oven plant of whatever type so far erected in the United States differs from the plants previously erected in a number of particulars that were supposed to be improvements. As many of these changes have not proved advantageous, they have been abandoned; therefore, only such particulars as are apparently satisfactory will be mentioned. OTTO-IIOFFMAN OVENS 9. German Otto-Hoffman Oven. —Fig. 2 is an illustra¬ tion of a block, or battery, of Otto-Hoffman by-product coke ovens in Germany. There are doors a at each end of the oven and when the coking operation is complete these doors are raised by a crab winch b mounted on wheels, so that it may be moved from oven to oven on tracks c. The doors are of cast iron and firebrick, and when raised the coke is pushed from the oven on to the yard, where it is quenched by streams of water as shown. After the coke has been removed from the retort, the doors are immediately lowered and luted with clay to make the retort air-tight. After the coke is quenched, it is loaded into barrows d and dumped into the railroad cars e. The gas coming off from the coal is conducted by the off¬ takes / to a central gas main that is raised quite high above the ovens in order that the gas flowing through it may be cooled by air and not absorb radiated heat from the ovens. 10. American Otto-Hoffman Oven. —Fig. 3 illustrates an Otto-Hoffman by-product oven plant at Johnstown, Penn¬ sylvania. The doors a in this case are raised by a block and §71 BY-PRODUCT COKING 11 fall attached to a gantry crane b and operated by hand or electric power. The latest innovation for quenching coke as it comes from the oven and then loading it into cars is shown at c. It consists of an iron box resting on a frame that is mounted on wheels, which run on a track as shown. The entire structure is so arranged that it may be moved at will from oven to oven by its own machinery. The coke is pushed directly from the oven into this quencher car, which is constructed with hollow cast-iron sides, thus forming a receptacle around the car into which water is pumped until it flows over the top of the inner wall on to the coke. The steam evolved acts as a dryer while the surplus steam passes out of the stacks d. This quencher car is used when it is desired to give the coke a silvery appearance similar to that shown by beehive coke that has been watered inside the oven. Except in appearance, there is probably no improve¬ ment in coke quenched in cars over that quenched in pans and on the yard. Probably, there is a saving in time of watering by the use of quencher cars. The quencher cars are supplied with doors that are opened as soon as the coke is cooled and the contents discharged into the railroad car e. The mechanism for moving the cooled coke from the quencher car consists of a heavy chain placed on the floor and extending through each door and outside underneath the floor. This, when moved by a motor, breaks up the coke and discharges it into the coke car e. The high stacks / carry off the waste gases from the ovens and assist the oven draft, which is usually aided by an exhaust fan placed at the end of an oven battery. The waste gases for heating the oven flues enter through the gas pipes g. 11. Otto-Hoffman Coke-Oven Section. —Fig. 4 shows a sectional elevation of a recent type of Otto-Hoffman oven. The coal for the ovens is dumped from the cars a into a track hopper b below the tracks, from which it is carried by elevators running inside the housing c to the top of the 12 §71 BY-PRODUCT COKING 13 bin d and there discharged. The coal is drawn from the bin d through gates and spouts e into the larry /. The larry in this case consists of five hoppers g, each having a spout to discharge the coal into the ovens. The whole is held by a framework mounted on a truck that moves on the rails h at each end of the ovens. The hoppers g are discharged through trunnel heads i in the top of the oven; and as the coal is thus distributed the entire length of the retorts j, little labor is required to level it. This leveling is frequently done by a rake k, which is moved back and forward by suit¬ able gears in connection with the coke pusher /. Two of the larry funnels discharge into pipes m through which the gas passes out of the oven and which connect with the gas mains o , o'. The object of the two gas mains is to keep the rich gas that comes off from the coal first from the poorer gas that comes off later. This might be done by a system of valves as readily from one main as from two, but there is an advantage in having two mains to these ovens, since the heat is applied alternately to one end and then to the other end of the retort. After the coal is coked, it is pushed out of the retort j by a pusher / that is operated by machinery located on the framework as shown. This frame runs on a track pp so that it can be placed opposite any oven. The coke is pushed into the quenching car q similar to that shown in Fig. 3. The water for quenching the coke flows through the ditch r from which it is drawn by the pump 5. While a piston pump is sometimes used for this purpose, it is cus¬ tomary to use a centrifugal pump as it will deliver a larger quantity of water under the small head, and because of its comparative simplicity in construction and light weight. The gas for heating the ovens comes from the gas tank through the pipes, as t or t’ , at one end of the oven, and enters the combustion chambers under the oven flues, where it mixes with the air from the air chambers u , which has been heated by passing through the checkerwork v. The burning gases then pass up vertical flues between the ovens into a horizontal flue running lengthwise of the oven, down other vertical flues at the other end of the oven into the chamber u' , then out 151—23 I3| 14 BY-PRODUCT COKING §71 through the checkerwork v '. After the current of gas has been passing in this direction for a certain time, until the air pass¬ ing through v has cooled the checkerwork, the direction of the current of burning gas is changed by means of suitable valves, as is fully explained later. The passage of the hot waste gases, after leaving the oven alternately through brick checkerwork v and v' on the way to the stack, heats the bricks and when the gas and air-currents are reversed the heat from the bricks is given up to the air before it meets the gas. This brickwork is called a regenerator , or some¬ times a hot-blast stove , and may be located in various places, sometimes at each side of the oven and sometimes directly under the center of the oven. The gas used for heating the oven is sometimes the last part of the gas given off in the process of coking and from which the by-products tar and ammonia have been removed, but often producer gas is used for this purpose. OTTO-HOFFMAN OVEN DETAILS 12. Retort.—Retort coke ovens are constructed so that the coal is not in direct contact with the flame that fur¬ nishes the heat for coking. The sides, walls, and bottoms of the retorts are built of firebrick or silica brick. The side walls are constructed of small bricks having a square section and bonded together so as to make a series of vertical flues. As it is necessary that the retorts should be gas-tight, the joints are made as true as possible and all the bricks are ground on carborundum wheels to a prescribed thickness. This method not only adds to the tightness of the wall, but is also much cheaper than the usual method of chipping and rubbing bricks by hand to give them smooth surfaces. The heat derived from the combustion of the gas in these flues is transmitted through the retort walls to the coal inside the retort and drives off the volatile matter, which is carried off in pipes to the by-product plant and there treated, as will be described in detail later. An Otto-Hoffman retort is shown in longitudinal section in Fig. 5, and Fig. 6 is a section alongside Fig. 5, through §71 BY-PRODUCT COKING 15 Fig. 5 Fig. 6 16 BY-PRODUCT COKING 71 the combustion chambers. The rectangular retort a is walled with silica firebrick on each side; the floor b that separates the retort chamber from the air chambers c and d is of fireclay tile, and the roof e above the retort, of fireclay bricks. The top of the retort has five trunnel heads / provided with suitable covers to make them air-tight. In some cases, the off-takes g are also used as trunnels through which the ovens are charged, as was explained in connection with Fig. 4; in other cases, they have no connection with the trunnel heads. The oven walls, front and back, are held together by tie- rods h that are passed through iron castings i and held in place by nuts j. These castings serve as buckstaves, and are sometimes made long enough above the ovens to carry a track on which the door-hoisting winch runs. The buck- staves also act as door slides and hold the brace bars and wedges employed to assist in making the door joints air-tight. 13. Size of Retort. —The retort has not been changed in shape in the several modifications of the Otto-Hoffman oven, but the dimensions have been varied as follows: width, from 15-8 inches to 22 inches; height, from 5 feet 6. inches to 6 feet 6 inches; and length, from 30 feet to 33 feet. The Camden, New Jersey, plant, which is one of the latest con¬ structions, has retorts 17 inches wide, 6 feet 6 inches high, and 33 feet long. The retorts are placed side by side, sepa¬ rated by a flue that makes them 2 feet lOi inches from center to center. They are charged with 5 tons of coal and produce, from this charge, about 3.75 tons of coke. A retort cannot be filled with coal, as a coking coal swells during coking and does not settle down again until most of the volatile matter has been expelled. 14. Air Chambers. — Directly beneath the floor of each oven are the two air chambers c, d connected by flues k , l with the regenerators m, m'. These air chambers deliver heated air, through the port holes o, o', to the combustion chambers n,n’, Fig. 6, situated parallel to, and on each side of, the air chambers. A partition p separates the air chambers from the air chamber d and also the combustion chamber ?i §71 BY-PRODUCT COKING 17 from the combustion chamber n'. If the air is admitted to the air chambers c at k , Fig. 5, it will pass through the port holes o into the combustion chamber n , Fig. 6, and thence up through the retort flues r and down through the flues r' to the combustion chamber n' before it can pass through the port holes o ', Fig. 5, into the air chamber d and to the outlet flue /.that conducts it to the regenerator in ', where it gives up its heat to the checkerwork. After the latter becomes heated to the proper temperature, the air-current is reversed and the regenerator m brought up to the required temperature. 15. Combustion Chambers.—The gas for heating the retorts is admitted through the nozzles q, q' to the combus¬ tion chambers n, Fig. 6, which are the counterparts of Fig. 7 the air chambers c , d , Fig. 5, and have similar partitions p to separate them. If the gas and the air for combustion are admitted to the combustion chamber n corresponding to the air chamber c , the products of combustion travel to the combustion chamber corresponding to d and so to the regenerator m 1 . Fig. 7 shows the combustion chambers n separated length¬ wise from the combustion chambers n' by the partition p , before the retort floors b, Fig. 5, are put on. The air cham¬ bers c, d are between the combustion chambers and are also separated by the partition p. 16. Vertical Flues in Retort Side Walls. —After the gases ignite in the combustion chamber, they pass upwards into a series of vertical flues r, r' as shown in the section, Fig. 6. These flues are between the side walls of two adjacent 1 ! §71 BY-PRODUCT COKING 19 retorts and terminate in a horizontal flue s. The combustion of the gas takes place alternately in the combustion cham¬ bers n, n' on opposite ends of the retorts. Assume that com¬ bustion is occurring in the chamber n , then the flames will pass up flues r into the horizontal flue s, and from the latter down the flues r 1 into the combustion chamber n' . From this chamber, the waste gases of combustion will pass through ports o' , Fig. 5, into air chamber d to flue / through regener¬ ator m' to flue u and thence to the stack. After the gas has burned until the bricks in the regenerator in' have become so hot that the waste gases escaping to the stack register 500° F., the gas and air are turned off from this end of the oven and turned into the other end. The current will now be reversed and the hot gases will flow in the opposite direction through the flues and out through flue k through the regenerator m and the flue t to the stack. 17. Retort Foundations. —The retorts are supported on massive foundations constructed of concrete and brick masonry. Fig. 8 shows the foundations up to the combustion- chamber floor for an oven similar in its arrangement to that shown in section in Figs. 5 and 6. The outer walls a are entirely concrete while the inner walls b are concrete below and brick masonry above. In order to prevent too much heat being transmitted through the floor of the combustion chambers to the masonry, a series of cooling flues c are introduced, which extend the length of the oven battery. Between the piers b and the foundation walls a , the flues s are constructed in which the regenerators are built. These flues are of fire-brick, as they conduct the hot gases that leave the oven at a temperature of 500° F. to the stack. Foundations of the kind illustrated are expensive and must be carefully constructed so that no settling will occur and crack the walls of the retorts. At each end of the battery, there are sometimes heavy end walls to resist expansion, but as these walls are not considered adequate to prevent dam¬ age to a battery of fifty ovens expansion spaces are left at several points in the length of a block of ovens. 20 BY-PRODUCT COKING 71 Another form of foundation is shown in Fig - . 4 in which the superstructure is supported on a steel framework, which, in turn, rests on two side piers and one central pier. 18. Regenerators. —The regenerators m, m', Figs. 5 and 6, and v, v', Fig. 4, are so called because the waste heat given off by the combustion of waste gases as they pass to the stack is partly absorbed by the checkerwork compo¬ sing the regenerators and is returned by the air passing through the flues to add to the heat of the gases when they - are burned in the combustion chamber of the oven. If, in Figs. 5 and 6*, air is admitted at t and allowed to pass through the regenerator m, the flue k , and air chamber c, into the combustion chamber n and flues r and the hot waste gases of combustion are allowed to pass down through /, n', d, l and the regenerator m' into the flue u, the waste gases will deliver up considerable of their heat to the first bricks they come in contact with, the heat decreasing in intensity toward the bottom of the regenerator. On the reversal of the air-current, so that air passes up through m' , /, d , n\ and r' and down through r, n, c,k,m, and t } the cool air will become heated in passing through m'\ and being hot before the combustion of the gases takes place will increase the heat of the gases resulting from the combustion. By reversing the air and gas currents every 30 minutes, the retort heat is kept fairly uniform and the regenerators become hotter and hotter as coking proceeds. To increase the tem¬ perature of the air before entering the regenerators, it is admitted through the arches v, w, and x, Figs. 6 and 7, in the substructure; and after passing the entire length of the oven block, is drawn back by a fan through the flues y and then forced by the fan into the flues t or u and the regenerator, and on to the combustion chambers. The air passing through the flues y cools the bottom of the retort floor and keeps it from get¬ ting too hot; and at the same time the air is preheated to 800° F., and then, by passing through the regenerator, to 1,500° F. Should this process continue without interruption, the ovens would become so hot that they would melt; but the §71 BY-PRODUCT COKING 21 temperature is regulated by the absorption of heat by the coal during coking and by radiation and cooling during the time the coke is being pushed from the oven and a new charge is being put in. Hence, the temperature in the oven probably does not exceed at any time 2,500° F. 19. Regulating the Heat. —The stack into which the waste gases finally escape is usually placed at the end of a block of ovens, though it may be at one side, as shown in Fig. 3. Fig. 9 is a plan showing the arrangement of piping at the stack end of a block of ovens for reversing the air and gas currents. A chamber a covered by a hood is connected with the flues t and u of the regenerators; a third flue b leads to the stack. The air for combustion is blown by a fan c through pipe d alternately to the right and left flues t and u , as the temperature demands, by shifting the valves e in 22 BY-PRODUCT COKING §71 the hood covering the chamber a. The gas for heating the ovens comes through the main / and is directed to the mains z , z\ one on each side of the block of ovens by the valve g. When the gas is going through the right-hand main z' to the combustion chamber n\ it is cut off from the left-hand main z leading to combustion chamber n , and vice versa. Assuming that combustion of gas is occurring in the chamber n\ the products of combustion will pass out through the left-hand flue /, and passing into the chamber a will be guided by the valve hood //, Fig. 10, into the stack flue b. As soon as the pyrometer, or heat-measuring instrument, located at k in flue b , Fig. 9, registers 500° F., an electric alarm bell indicates that the air and gas currents should be reversed. If the current is not reversed, the intake gener¬ ator will continually become cooler and the waste gases become hotter and hotter, thus causing a loss of heat through the stack. The attendant therefore throws the gas valve g and sends the gas through the left-hand gas main z to the combustion chambers n of the entire block of ovens. He also throws over the lever /, Fig. 10, which places the hood h in the position h' as indicated by the dotted lines and thus reverses the combustion air-current and the direction in which the waste gases travel to the stack flue b. This system produces a remarkably uniform heat in the ovens, which is a matter of importance, as irregular heating will §71 BY-PRODUCT COKING 23 retard coking operations in the cooler parts of the retorts and cause overheating in other parts. The supply of gas and air to each individual combustion chamber having once been determined, and the ports k and /, Fig. 5, regulated for the necessary supply of air to burn the gas coming through gas nozzles q and q', the two are never changed. 20. Economy of the Regenerator. —From an analysis of the gas used for heating the retorts of an oven, the value of the regenerating system may be calculated. An analysis of the Everett, Massachusetts, oven-heating gas is as follows: Per Cent. Marsh gas, CH< . 29.2 Hydrocarbons other than marsh gas .... 2.4 Hydrogen, H .50.5 Carbon monoxide, CO . 6.3 Carbon dioxide, C0 2 . 2.2 Oxygen, O . .3 Nitrogen, N . 9.1 Total.MO It was found that 1 cubic foot of this gas requires 4.54 cubic feet of air for complete combustion; hence, 5,000 cubic feet of gas requires 22,700 cubic feet of air. This air, at sea level, weighs 1,832 pounds with the mercury in the bar¬ ometer standing at 29.92 inches and the temperature 32° F. The specific heat of air for a constant pressure is .2374, therefore the amount of heat required for an increase of temperature of 1° F. is 1,832 X .2374 = 435 B. T. U., nearly. The air is preheated by the regenerators to 1,500° F., which is an increase of 1,468° F. over the temperature assumed for calculation. The heat recovered from the regenerators, therefore, amounts to 1,468 X 435 = 638,580 B. T. U. for each net ton of coal coked. According to analyses, the gas at this plant yields 567 B. T. U. per cubic foot, and this amount of heat is equivalent to a saving of 638,580 -f- 567 = 1,126 cubic feet of gas for each ton of coal coked. The saving in gas is not the only advan¬ tage derived from the system, for time is saved in the 24 BY-PRODUCT COKING §71 coking, as the heat from the regenerators hastens the distil¬ lation of a fresh charge of coal, where cold air would retard the operation for a time until the ovens had recovered their heat. 21. Control of the Oven Heat. —The combustion in the oven is observed through peep holes left for that pur¬ pose in the end of the oven walls between the buckstaves, and placed so that they command a view of the combus¬ tion chambers. If the gas pipe leading into the com¬ bustion chamber is clogged, this is easily detected here, as then the combustion chamber is not filled with gas. It is also advantageous to inspect the combustion chambers on the side on which the gas is not entering, as the amount of gas coming down through the vertical flues between the retorts can then be noted. A battery of ovens 'may be said to be burning properly when the waste gases descending into the regenerators show a slight mistiness, though not enough to obscure the view of the whole length of the combustion chamber. This indicates that the combustion is practically complete in the oven flues and passages and that the esca¬ ping gases are incombustible and, therefore, will give up only their waste heat to the checker brick, without any of the gas burning there and thus producing a temperature high enough to damage the reversing dampers and stack flue. An excess of gas in the flue leading to the regenera¬ tor indicates that the combustion in the oven flues is not complete enough to develop the full temperature about the retort where it is most desired, but that the highest heat will be reached in the regenerators, to their possible detri¬ ment and certainly to the disadvantage of the coking proc¬ ess. Such a condition indicates either too much gas pressure or not enough air. The air chamber on the air¬ heating side, which can be closely observed, as there is nothing to obscure the view, should show an even heat the whole of its length, without the alternate dark and light rings, which mark uneven heating. The gases issiiing from the smoke stack should show, at most, a white vapor due to §71 BY-PRODUCT COKING 25 condensed moisture. If any black smoke appears, it is a sign that the gas is not being properly burned. By referring to Fig. 6 and assuming that combustion is taking place in the combustion chamber n , the flame from the burning gas will decrease from the door to the parti¬ tion p . It will be evident that the flame in the other half of the oven will first pass down into the chamber n' through the flues nearest the partition p and decrease gradually to the door, thus the flues nearest the door will receive the smallest quantity of heat. This will make considerable dif¬ ference in the quality of coke at the door ends if the heat is not frequently reversed, so as to alternately heat the flues near the oven doors. This difference of heat is of small moment in the 33-foot oven, but precludes any possi¬ bility of increasing its length beyond that figure. UNDERFIRED BY-PRODUCT RETORT OVENS OTTO-HILGENSTOCK RETORT OVENS 22. In the Otto-Hoffman ovens thus far described, the gas enters and is ignited alternately at each end of the oven, With the vertical flues, it is difficult to distribute the heat uniformly by this method of firing; hence to economize in fuel and to heat both ends of the oven as nearly uniformly as possible through the entire coking operation, Messrs. Otto and Hilgenstock have devised a method of underfiring the ovens. The gas enters the combustion chamber from below and from several points instead of through a single opening at each end. The Otto-Hilgenstock oven shown in cross-section, Fig. 11, has come into prominence abroad, and although the coke oven entire has not been introduced in America, the principle of underfiring has been adopted in one instance at least. The section a at the right of the line A B, Fig. 11, is taken through the retort, and the sec¬ tion b at the left of the line A B is taken through the retort walls so as to show the flue construction. The combustion §71 BY-PRODUCT COKING 27 chambers c beneath the vertical flues are separated by parti¬ tions d in such a manner that a central chamber e is formed that has ports leading to the chambers / directly beneath the ovens. The vertical flues g and h are separated by a central partition i. The gas for heating the ovens is delivered to each oven by branch pipes j connected with the gas main k. Each branch pipe j has connected to it ten vertical pipes l of such a diameter that they will stand in the burner holes m with¬ out filling the latter. Each vertical pipe is supplied with a valve n to regulate the flow of gas through it. The air for combustion is admitted at the bottom of the holes m and passing upwards comes in contact with the gas issuing from the pipe l. This arrangement virtually forms a Bunsen burner, the flame from which rises up through the flues g. The gas, when burning, is drawn toward the partition i and, being baffled, passes down into the chamber e. Assu¬ ming that the flame of combustion is now extinct, the waste gases pass into /, then through the flue o into the waste-gas main p, and out to the stack. As there are no regenerators, the waste heat from the ovens cannot be utilized for pre¬ heating the air for combustion but may be utilized under steam boilers. The distribution of heat is said to be more uniform with this system than with end firing. The remainder of the oven does not differ much in arrangement and construction from the Otto-Hoffman oven. The method of charging by the larries q , of raising the oven doors by winches r, and the high off-take s with its gas main t have given place in the United States to more improved methods and appliances. SCHNIEWIND, OR UNITED-OTTO, BY-PRODUCT COKE OVEN 23. The improved heat distribution in the Otto-Hilgen- stock ovens induced Doctor Schniewind to combine the underfiring system with the regenerative system. He further simplified the oven construction by substituting a 28 BY-PRODUCT COKING §71 steel substructure for the masonry foundation. It was claimed by the opponents of the regenerative system of heating the air that the heat absorbed expanded the masonry and caused it and the retorts to crack. In order to avoid this, the regenerators are, in some instances, placed outside of the oven walls, and in the Schniewind type of oven the regenerators, although directly under the ovens, are separated from the oven substructure. 24. Fig. 12 (a) and (b) shows longitudinal sections of the Scliniewind oven and Fig. 12 (r) and ( d ) cross- sections through a series of ovens in a block taken on the lines A B and CD in (a) and (b) , respectively. The foun¬ dations a that support the substructure are of concrete; the posts b , girders c, and floorbeams d are of steel. The subfloor e is constructed of refractory material. Fig. 12 ( b) is a longitudinal section through a retort on the line CD of (d). If the air enters through the regener¬ ator /, it passes up through the flue g into the air chamber h situated directly under the retort o. The air now passes from h into the air chambers below and then through the holes i into the combustion chambers j shown in the section at the left in Fig. 12 (d ). Through the floor*?, Fig. 12 («), under the combustion chambers, there are ten gas pipes k, k' -—five connected to each gas main /, l ’. The flow of gas through each pipe k , k' is controlled by a separate valve, which admits of independent regulation. Above each com¬ bustion chamber, there are four vertical flues terminating at the top in a horizontal flue m through which the hot gases pass to the vertical flues on the left-hand side of the par¬ tition n. The course of the hot gases is then through the holes V into the chamber h', through a flue g', to the gen¬ erator f and thence to the stack. Fig. 12 (*:) is a cross-section through several ovens on the lines A B of ( a ) and (b) taken through the regenerator flues g , and the regenerators /. The flues h are under the retorts o , the hot air passing from h into the combustion chambers/, where it.meets the fuel gas entering through the 82417 §71 BY-PRODUCT COKING 29 pipes k , Fig. 12 {a). The flames rise up the vertical flues to the horizontal flue m, and travel across the oven to the other end of the retort and down the descending flues. Fig. 12 (d ) shows, at the left, a section on the line CD of Fig. 12 ( b) and at the right an elevation of the oven fronts. The section at the left is taken through the gas entrances and shows that the flame passes directly from the combustion chambers j up flues between two retorts as o, o , thus imparting heat to each. The elevation shows the doors q and the buckstaves r; the latter have grooves in which the doors slide when raised or lowered. The holes s in the doors are for leveling the coal when charged into the retorts. This elevation is at the end of a block of ovens and shows the brick end walls l, and the steel posts b support¬ ing the transverse steel stringers c, which, in turn, support the longitudinal steel floorbeams d. At one end of a block of ovens, there is a chamber con¬ taining the proper appliances for changing the flow of gas through the gas pipes /, Fig. 12 (a), {b), and (d) , from one end of the ovens to the other, and for reversing the air- current through the regenerators. There are two off¬ takes u, u' , Fig. 12 ( b) and (d) , to these retorts, which deliver the gas into the gas mains v, v' connected with each off-take. By this arrangement, the rich gas may be kept separate from the poorer gas. The gas coming off during the first period is treated for illuminating purposes and that coming off after this period is treated for fuel purposes. The flow of gas from the oven is regulated and directed to the proper gas main by a system of valves. There are six charging holes w in the top of these ovens, besides the two gas off-takes. This number of openings is made possible by the length of the oven, which is 43 feet. End-fired ovens could not be depended on for first-class coke if constructed of this length, although there would be economy in the additional length since fixed charges would be reduced by the increased output. 151 24 §71 BY-PRODUCT COKING 31 HORIZONTAE-FEUE BY-PRODUCT COKE OVENS SEMET-SOLVAY COKE OVENS 25. The general appearance of a Semet-Solvay by¬ product oven plant is shown in Figs. 13 and 14, which show the plant at Dunbar, Pennsylvania. Fig. 13 shows the wharf side and Fig. 14 the pusher side. The coal to be coked is stored in the oven bin a , Fig. 13, and is drawn off in larries when needed for oven charging. The arrangements that have previously been described for by-product oven charging may be applied to these ovens. The coke is pushed from the retort oven, by machine, on to the pan b, where it is quenched with water, as shown. The pan in this case is mounted on wheels and as the ovens are near the blast furnace where the coke is used, the pan is taken to the furnace-coke stock pile and there dumped, after which it is brought back to receive the coke from the next oven. There are two batteries c and d of twenty-five ovens each at this plant, separated by a space in which there are four tubular boilers e that utilize the heat from the waste gases before they pass into the stack /. The water needed for cooling the by-product apparatus^ and for watering the coke is impounded and pumped to the water tower from which it is drawn as needed. The front of the same oven plant is shown in Fig. 14. The coke pusher i is different, in detail, from those already described, but in a general way it consists of a long steel beam supplied with a rack with a ram j at one end. The rack is moved forwards by a pinion driven by a steam engine or an electric motor, and this movement pushes the coke from the oven. The sheet-iron oven doors k swing on hinges and are merely veils to prevent the radiation of heat from the oven door proper. The gas main l is connected with an off-take m at the top of each oven, and is also con¬ nected with a pipe n through which the gas passes to the by-product apparatus. 33 (c) Sect/on G-G 34 BY-PRODUCT COKING §71 26. Semet-Solvay Retort.—The retort chamber of the Semet-Solvay oven, Fig. 15 (a) and (b), is rectangular; although sometimes, in order to assist the coke pushing, the rear end is made about 1 inch wider than the front end. The dimensions of the retorts have been frequently varied so that the length ranges from 26 to 32 feet, the width from 16 to 20 inches, and the height from 5 feet 6 inches to 7 feet. The capacity of an oven having the smaller dimensions given will be 4 tons of coal; while the capacity of an oven constructed on the larger dimensions will be 6 tons of coal. There should be left a space of from 8 to 12 inches between the top of the coal and the retort arch in order that the gases may find egress through the off-take a, Fig. 15 (a), and to permit the swelling that occurs before the coal is coked. The sides of the coking chamber are constructed of rows of hollow fireclay tile b. These tile, called recuperator flue brick by some firebrick makers, are, as shown at Fig. 15 (d ), made in one piece with a bell end a and spigot end b, so as to fit into each other at the ends; they are grooved and tongued so that they will form gas-tight rabbeted joints with brick placed above and below. In order to fix the joints nicely, it may be necessary to smooth them by hand or by machine and use a thin fireclay mortar in addition. The firebrick arch c , Fig. 15 (a) and ( b ), above the retort rests on the flue bricks b, and it is about all the weight the latter have to sustain. In order to provide for the expansion and con¬ traction of the hollow tile b and the arch c, a space d above c is filled with sand. The next arch e above the sand is of fire¬ clay brick. Above the arch e> there is a red-brick arch /. The weight of the arch e and the load it carries come on the refrac¬ tory walls g, between two ovens and not on the tile b. In the top of the oven there are four openings, the off¬ take a at the front end, and three trunnel heads h. The coal is charged through the trunnel heads, for which reason they are fitted with iron covers and clamps i, Fig. 15 (b). After closing and clamping these covers, they are luted with clay to seal them air-tight. The oven floor j is made of fire¬ clay tile, and separates the retort from the hearth flue k, §71 BY-PRODUCT COKING 35 which extends the entire length of each oven. Below the hearth flue, there is an air flue / that extends the entire length of the battery of ovens. The oven foundation con¬ tains four masonry arches m and n that extend from one end of the battery to the other and which are utilized to pre¬ heat the air used for the combustion of the gases that heat the retorts. The outside air has access to the two inner arches n and must pass through them into the outer arches m before it can reach the air flue / and the combustion cham¬ bers. The air passages leading from the air flue to the com¬ bustion chambers are in the walls g between each two ovens, and reach the combustion chamber by offsets o , Fig. 15 (b ). 27. Oven Doors.—The ends of the retort have cast-iron door frames p that fit snugly to the ends of the flue bricks b. These frames are held in place by the buckstaves q and the expansion bolts and nuts r , which govern the longitudinal expansion of the masonry. The buckstaves are not screwed up tight to the walls until the oven masonry has become thoroughly dried out and heated. At the front and back ends of the retort are doors con¬ structed of firebrick and cast iron that are raised and lowered by jacks. In some cases they are raised by hydraulic arrangements situated between the two batteries and con¬ nected to the jacks that raise the doors. The front door of each oven has a sheet-iron screen that swings on hinges, making a sort of double door at this end. The doors are made air-tight by luting them with clay and wedging them against the retort-door frame. The hole s, Fig. 15 ( b ), shown in the door is for the purpose of leveling the charge; while through the hole /, the condition of the heat in the hearth flue k is examined. 28. Combustion Chambers.—The hollow tile b, Fig. 15 (d), forming the sides of the retort of a Semet- Solvay oven are arranged so as to form three flues u , u', u", as shown in Fig. 15 (c) . The gas is admitted to the top and middle flues by 2-inch gas pipes v, v' provided with suitable valves to regulate its flow. At the same ends of 36 BY-PRODUCT COKING 71 the flues, air is admitted for combustion, the air coming- from the air flue l through flues w shown by the dotted lines in Fig. 15 (c), to the points o shown in Fig. 15 {b) . The burning gases pass from the front to the rear of the top combustion chamber u, Fig. 15 (c), and thence into the flue u' through the opening x joining the two, as shown in the left-hand section DD of Fig. 15 (b) . The flame passes through this opening and with the additional flame produced by burning the gas entering at v', Fig. 15 (c), moves to the front of the middle combustion chamber u' and through openings x' in the tiles, as shown in section FF y Fig. 15 (b) , into the lower combustion chamber u ". From this point, the flame passes to the rear and down an open¬ ing x" connecting with the hearth flue k, thence to the stack flue y. The waste gas, after leaving the boilers, enters the stack with sufficient heat to cause a draft that will draw air into all the combustion flues of the ovens without the assist¬ ance of an exhaust fan. 29. Partition Walls. —Between the flues of two adja¬ cent ovens, solid 18-inch walls g y Fig. 15 (b) , of firebrick are constructed. The lining is thus practically independent of the walls separating the ovens. There being two sets of flue bricks and two sets of gas burners between each two retorts, it is evident that without thick walls separating the retorts there would be a loss of heat, particularly when there are no regenerators, as in this type of oven. In the Semet- Solvay ovens, the combustion of gases heats the sides and floor of the retort bright red and, by transmitting this heat, cokes the coal rapidly and completely in 24 hours. Owing to the thinness of the flue walls, the heat passes through them readily to the coal and to the walls between the ovens. Toward the end of the coking process, the coke becomes hotter than the gas and gives out heat that is absorbed by the division walls. After the ovens have been drawn and recharged, the division walls immediately deliver up a part of their heat, thus aiding the gas to supply quickly to the coal the heat required to start the operation of coking. §71 BY-PRODUCT COKING 37 30. Regulation of Combustion in tlie Retort Flues. The horizontal flues in the retort tiles have been termed combustion chambers because combustion of gas occurs in them. To regulate the flow of gas, the gas supply pipes v, v’ are provided with valves; and to regulate the flow of air for combustion, the air flues l are supplied with dampers at z , which are worked from outside the oven by an iron rod. When the oven gas and air are properly adjusted, flames should show in the combustion chambers but not in the hearth flue.' This condition can be ascertained by exam¬ ining the lower flue and the hearth flue through peep holes left in front and back walls for the purpose. The heat con¬ dition in the upper flues u cannot well be established, owing to their being filled with flames, unless the gas is shut off, and this course is recommended to be pursued twice in 24 hours. If carbon has been deposited on the walls, too much gas and not enough air for combustion has been admitted, and the supply of gas and air should then be properly regulated. This carbon must be burned off, as it prevents heat from radiating properly through the walls. The second flues u' should next be treated in a similar man¬ ner, and the air and gas regulated. The heat at the junction of the first and second flues should not be so great as to fuse the tile. As a rule, ovens having hot bottoms and somewhat cooler tops make good coke and furnish a better yield of by-products than ovens having cooler bottoms. It is stated that ovens with intensely hot tops tend to dissociate the elements form¬ ing the ammonia and to transform tar in the gas into soot, in which form it causes trouble by clogging the gas mains. COKE FROM RETORT OVENS 31. Owing to the fact that retorts are long and narrow and that the heat for the coking operation is supplied from the side walls, coking takes place from each side toward the center so that the coke has the appearance shown in Fig. 16. This figure is a vertical section through a retort showing the 38 BY-PRODUCT COKING §71 air chamber c , the passages o through which the preheated air enters the combustion chamber n, the vertical flues r, and the horizontal flues s, and trunnel-head section /. The coke has a very compact texture and is quite hard. It is used for blast-furnace or foundry smelting; and although it was thought by some to be too hard and dense to permit gases to permeate it or to permit combustion, actual tests do not indicate that it is inferior as a metallur¬ gical coke to beehive coke. It is stated that 85 per cent, of the coke made in beehive ovens will be compact and dense and 15 per cent, will be spongy; also that 81 per cent, of the coke from by¬ product ovens will be compact and dense and 19 per cent, will be spongy. By-prod¬ uct retort coke is in every way superior as a domestic fuel to gas-house coke, as the latter is spongy and is consumed quickly. Fig. 16 32. Preparing Coke for the Domestic Market.— In order to prepare coke for domestic use, it is crushed in toothed crushers and then sized in revolving screens that have different-sized openings in different sections of the screen. The sizes produced in screening are the following: Furnace . . . Over 2i-inch mesh Egg .... Over 2i-inch mesh, through 2a-inch mesh §71 BY-PRODUCT COKING 39 Stove .... Over 2-inch mesh, through 21-inch mesh Nut.Over i-inch mesh, through 2-inch mesh Breeze . . . Through i-inch mesh From the screens, the several sizes pass to loading bins; and in discharging from these bins, the coke passes over apron screens that remove any breeze or dirt that has accumulated after passing through the large screen. Cer¬ tain sizes, and particularly what is called nut , is packed in 20-pound bags for retail trade. There is a good demand for this size of coke in cities where anthracite is high priced. An extensive trade has also been built up in egg-size coke for heaters and furnaces, as this size is larger and will burn longer than nut. _ GAS FOR HEATING RETORTS 33. By-Product Gas. —The first gases that are distilled from the coal in the retorts are rich in illuminants, while those given off during the latter half of the coking operation are quite poor, in comparison; they are, however, suitable for heating coke ovens and for other fuel purposes. A coal having 28 per cent, of volatile matter should yield at least 10,000 cubic feet of gas per ton. During the first period of coking, lasting 9 hours, the marsh gas, which is the chief hydrocarbon in illuminating gas, diminishes, while the hydro¬ gen increases. The heating power of the gas also diminishes but not to such an extent as to cause the retorts to get cold. Prof. H. O. Hoffman, who made experiments with coke-oven gas, found that the calorific power of the gas per cubic foot dropped in 9 hours from 775 to 685 B. T. U.; the specific gravity from .55 to .49, and the candlepower from 18 to 13j. Further, he found that during the second period, from the ninth to the twenty-second hour, the amounts of gas given off during equal periods were almost constant and that during this period the calorific power, specific gravity, and candlepower were also almost constant. He found, also, that after the second period, the calorific value of the gas declined, as well as its specific gravity and candlepower; the quantity of gas also rapidly decreased. Experimenters differ 40 BY-PRODUCT COKING §71 in regard to the calorific value of retort-oven gas, which is no more than natural, owing to the different kinds of coal used in the experiments; but experimenters nearly all agree that it requires about 50 per cent, of the total gas evolved to coke the coal. Assuming, then, that the gas after the first period contains 450 htekf units and amounts to 5,000 cubic feet for every ton of coal coked, about 2,250,000 heat units are required to coke 1 ton of coal. 34. Producer Gas. —In some cases, the coke-oven gas is used entirely for illuminating purposes, and producer gas is substituted for it to heat the retorts. One ton of bituminous coal will furnish 130,000 cubic feei of producer gas, having a calorific power of 150 heat units per cubic foot. About 34.6 per cent, of producer gas is combustible while 65.4 per cent, is incombustible, which accounts for its low calorific power, and makes it necessary to have the oven flues and regenerators of larger size if this gas is to be used for heating the retorts. _ BY-PRODUCTS FROM RETORT OVENS 35. Principal Products. —The two principal products derived from coking coal in retort ovens are coke and gases. The former has been described. From the gases, other by-products, such as tar and ammonia, are obtained; and from the tar, still other products are obtained by the manu¬ facturing chemists. _ BY-PRODUCT OVEN GAS 36. The gas from retort ovens is practically the same as is obtained in a municipal gasworks using the same quality of coal. This gas is valued according to its illumi¬ nating power and heating capacity. 37. Candlepower of Gas.—The illuminating power of gas is reckoned in candlepower, a rather arbitrary standard based on the light that a spermaceti candle will emit when burning at the rate of 2 grains of sperm per minute, or 120 grains per hour. This standard is not entirely satisfactory, §71 BY-PRODUCT COKING 41 as it is claimed that one candle in 'burning - will emit more light than another. It is, however, the British Standard candlepower. In Germany, the Hefner amyl-acetate spirit lamp, is taken as a unit of light known as the Hefner unit , which is equivalent to .91 candlepower. A candle-foot is a measure of illumination and is the intensity of a standard candle at a dista7ice of 1 foot. In the manufacture of gas, the term candle-foot is, however, often used to express the number of cubic feet of gas of a known candlepower multiplied by that candlepower; for example, 5,000. cubic feet of gas having a candlepower of 18 is 5,000 X 18 = 90,000 candle feet. 38. Calorific Power of Gas. —The calorific value or heat units in a gas can be calculated from an analysis of the gas. Typical analyses of illuminating and fuel gases are given in Table II. TABLE II Kind of Gas Composition Calo¬ rific Value B.T.U. Unpu¬ rified Gas Can¬ C m H n C // 4 H, CO CO ; o 2 w 2 per cu. ft. dle power Illuminating 5-8 41.8 34-0 6.5 3.7 .3 7-9 736 18.4 Fuel .... 2.5 32-3 48.7 5-9 2.2 .4 8.0 583 10.3 The quantity of gas evolved depends on the percentage of volatile matter in the coal, and it may be assumed that a coal containing 28 per cent, volatile hydrocarbons will yield 10,000 cubic feet of gas per long ton of coal, and 35 to 40 per cent, of this will be surplus, or more than is needed for coking purposes. With coals of a low percentage of volatile matter, however, there is not sufficient surplus gas above oven requirements to be of importance. The cost of an 18-candlepower gas, unpurified, as delivered by the average coal gasworks varies between 15 and 40 cents per 1,000 cubic feet, according to the locality and size of plant. 42 BY-PRODUCT COKING §71 TAR 39. Tar is obtained from coke-oven gas during the proc¬ ess of condensation by cooling. The amount varies approx¬ imately from 2 to 5 per cent, of the weight of the coal carbonized. A very dry coal may fall short of, and a rich one exceed, these figures. Coke-oven tar usually contains 2 to 3 per cent, of ammoniacal liquor, which is with difficulty removed, particularly when the tar is repumped through the gas collecting mains to aid in keeping them clear of pitch. Coke-oven tar contains less free carbon than tar made from the same coal in gas-house retorts. This is possibly due to its coming less in contact with highly heated surfaces in the oven retort than in the gas retort. The separation of the ammoniacal liquor and the tar is usually effected by allowing the mixture to settle some time in a receiving tank, the higher specific gravity of the tar causing it to sink to the bottom, while the ammoniacal liquor gathers on top, and can be drawn off. Steam coils in the tank promote this action by keeping the tar fluid. In some works, a series of several smaller tanks is used through which the tar flows in turn, the bottom tar from the first tank passing to the top of the second and so on, the liquor being drawn off each one separately to a common receiver. The only really effective way is to heat the tar in a still until the water passes off and the first light oils appear, but this process is rather too expensive for general use. 40. Uses for Tar. —In the United States, tar is usually disposed of, as recovered, to the manufacturers of pitch and saturated felt, although a few of the by-product oven plants have installed their own tar-distilling or saturating plants. A certain amount of tar is used in its crude state in the manufacture of paints and varnishes, waterproofing, pipe dip, brick paving, tar concrete, and allied products. Some tar, as well as some of the oils distilled from tar, is burned in the manufacture of lampblack. But few of the tar works carry the distillation further than to separate the light and heavy §71 BY-PRODUCT COKING 43 oils from the soft pitch, which is used for roofing and paving. Hard pitch , as the term is understood abroad, is not usually made in the United -States and is in small demand here. The tar chemical industry, which is so highly developed in Germany, has made but little progress in the United States. Table III shows the various fractions obtained in coal tar distillation, and the temperatures at which they come off: TABLE III Fractions Commercial Product Up to 338 ° F. Ammoniacal liquor, solvent naphtha, burning naphtha From 338 ° to 446 ° F. Naphthalene, carbolic acid From 446 ° to 518 ° F. Creosote oil for impregnation, lubri¬ cating oil From 518 ° up . . . . Anthracene Residue . Pitch The market price of tar varies from 3 to 5 cents per United States gallon according to locality and conditions; at times it has fallen below 2 cents per gallon. In some districts, tar has been burned as fuel with excellent results. As fuel, 5 pounds of tar may be taken as equivalent to 7 pounds of coal, although the theoretical ratio is given as 10 to 11 , cal¬ culated on the chemical analysis. The first figure given is, however, correct in practice, because of the greater economy obtainable in using a liquid fuel, rather than a solid fuel. There is a further saving in labor in the use of tar as a fuel. The method of burning is usually to spray the tar in a finely divided condition into the furnace by means of a steam or air jet, specially constructed burners being used for this purpose. _ AMMONIA 41. Ammonia is recovered from the oven gas in the form of ammoniacal liquor during the processes of cooling and scrubbing. Some ammonia is also obtained from the 44 BY-PRODUCT COKING §71 distillation of tar. A part of the water forming the liquor is due to the moisture in the coal, the remainder is added in the scrubbing to aid in the final absorption of the ammonia. This liquor contains between 1 and 2 per cent, of ammonia, principally in the form of chloride, sulphate, sulphide, car¬ bonate, and hydrate. Of these, the carbonate, sulphide, and hydrate are regarded as free ammonia , or ammonia that may be driven off by heat alone. The chloride and sulphate are decomposed by heat only in the presence of an excess of an alkali, such as lime, sodium carbonate, or sodium hydrate, and are therefore classed as fixed salts. The proportion of these two forms of ammonia varies greatly in different liquors, being strongly influenced by the quality of both the coal coked and the water used for washing the gas. As the free ammonia is much more easily handled in distillation, it is desirable to obtain as much of it in this form as possible. The amount of ammonia, NH Z , recovered from ordinary coking coals may usually be reckoned as .25 per cent, of the weight of the coal, or roughly speaking, the equivalent of 1 per cent, of the weight of the coal reckoned as ammonium sulphate. Assuming the strength of the liquor to be 1 per cent. NH 3 , it is clear that the weight of liquor produced will be one-fourth of the weight of the coal carbonized; this figure is of use in approximately estimating the size necessary for liquor storage tanks and pumps. A stronger liquor than 1 per cent., say li or 2 per cent., is gener¬ ally more economical in concentration, as there is less water to heat. The concentration process consists in driving off the ammonia from the liquor by direct steam heating in a closed vertical tower of cast-iron sections, the escaping mix¬ ture of water and ammonia vapors being either condensed by cooling coils to form crude strong liquor of 15 to 20 per cent. A7/ 3 , or passed through lead boxes containing dilute sulphuric acid, if it is desired to make ammonium sulphate. The ammonium sulphate is dried and shipped in bulk or in bags to manufacturers of chemicals or fertilizers, while the ammonia water is shipped in drums or tank cars to similar industries. §71 BY-PRODUCT COKING 45 BY-PRODUCT COLLECTING APPARATUS 42. The nature of the apparatus used for collecting, cooling, and washing the gas has no connection with the type of oven in which the coal is treated. The general principles that govern the condensation of coal gas from gas-house retorts apply equally well in the case of coke-oven gas, except that the quantity of oven gas handled is usually larger. 43. Gas-Collecting Main.— The gas is drawn from each oven through an off-take, usually of cast iron, fitted over one of the openings in the oven roof and kept tightly sealed to the brickwork with clay. This off-take is provided with a valve that admits the gas to a single, large, gas-collecting main. This valve should be of simple and strong construction, so that it will stand the hard usage it receives. It should also be provided with means for freeing it of pitch, and for affording access to the off-take for the same purpose. The collecting main may be one of two types, wet or dry. 44. Wet Collecting Gas Main.— The wet type of col¬ lecting main is usually adopted on the Semet-Solvay ovens. It consists usually of a horizontal pipe a , Fig. 17, having a baffle plate b that divides it into two compartments c and d that are sealed from one another by water and tar. The gas enters one compartment, asr, and is drawn through the water and beneath the baffle plate into compartment d by the suction of a blower called an exhauster , and in this way a preliminary cooling and condensation of tar is effected. This keeps the gas in the ovens separate from that in the mains, a slight pressure being maintained on the oven side of the baffle, while the discharge side is under a slight suction. The level of tar and liquor is maintained in the main by an adjustable gate on a separate overflow passage connecting with the lowest part of the main, so that only the tar shall escape. The tar flows along the gas main to the condensers and then through drains to the tar well. The gas is taken by 151—25 Fig. 17 46 BY-PRODUCT COKING §71 an overhead connection from the upper part of the collect¬ ing main. 45. Dry Collecting Gas Main. —In the dry gas main system used in the Otto-Hoffman ovens, the main may be either horizontal or slightly inclined, and there is no baffle plate. The exhauster suction is maintained at such a gauge that all the ovens are under a slight pressure and the gas from them passes directly into the cooling system. In either the wet or the dry system, it is necessary to keep the mains clear of the pitch and tar that gathers in them as soon as the gas begins to cool a little, by pumping a constant stream of tar and liquor into one end and allowing it to escape at the other. In addition to this, openings are provided in the main through which it is possible to poke loose the accu¬ mulation of tar from the sides and top of the main, the stream of tar and liquor passing along the bottom serving to carry these to the seal pot provided for their removal. In a plant having but one battery of ovens, the seal pot should be at the nearest convenient point after the collecting main leaves the battery, or, as is the case in the wet main system there may be traps on the main through which hard pitch may be removed. If there are several batteries, it is usual to bring the mains together at a central point, toward which they all slope, and collect the hard tar there by means of the circulating method and by poking it loose in the mains. 46. Equalizing the Gas Pressure. —In order to make it possible to maintain a practically equal gas pressure on all the ovens, the collecting main must be of sufficient size to act as an equalizing reservoir between the ovens, at the same time delivering to the gas main. Where several bat¬ teries are connected to one system of gas mains, the pres¬ sure in the individual collecting mains on each battery is regulated by opening and closing the valves between them and the main gas system. With a single battery having but one main, the pressure may be regulated by regulating the exhauster. The pressure on the ovens is due to the fact that the gas is evolved more rapidly than it can escape §71 BY-PRODUCT COKING 47 through the openings. An exhauster relieves this pressure without going so far as to cause it to fall below the atmos¬ pheric pressure. For the best conditions, there should be a slight outward pressure of gas in the oven, as this avoids the entrance of air through cracks and the consequent dilu¬ tion of the oven gases and combustion of coke. Too great a pressure, however, causes the gas to force its way through the flue walls and burn there along with the heating gas, which not only results in a loss of the by-products, but also probably in the cooling off and choking of the flue with car¬ bon. Too much gas is as prejudicial to high heats as too little. For these reasons, it is desirable to carry as little suction on the heating flues or combustion chambers as pos¬ sible, so as not to facilitate the leakage of gas from the ovens. This is one argument in favor of the use of a pressure blower to supply the air for combustion, as otherwise the draft of the chimney stack must be depended on for this service. 47. Condensing House. —The gas mains lead to the condensing house, where the gas is usually first passed through air coolers, which condense a large portion of the tarry vapors, the remaining tarry vapors being removed in the tar scrubbers. These coolers consist of steel-plate or cast-iron vessels that expose a large cooling surface to the atmosphere, and thus allow the heat in the gas to be dif¬ fused. This cooling has already begun in the gas mains BY-PRODUCT COKING 48 §71 themselves, particularly when these mains are carried above ground. 48. Air Coolers. —There are a number of kinds of air coolers, the essential features of such a cooler being a large exposed surface in proportion to the volume of gas passing through the cooler and proper drainage of the con¬ densed tar liquor. One of the original forms known as a horizontal screw co7idenser , consisted of cast- iron pipes coupled end to end, as shown in Fig. 18, with return bends placed in a slightly inclined zigzag manner, so that gas passed in at a and out at b. Fig. 19 shows a vertical cooler , which consists of a tall steel cylinder contain¬ ing a number of vertical tubes placed as shown in the cross-section, so that cool air enters the tubes at the bottom and passes out at the top, the amount being regu¬ lated by the damper at the top. The gas passes into the condenser at the top or circulates around the air-cooled tubes and passes out at the bottom, as shown by the arrows. In the vertical pipe condenser , Fig. 20, the cooling pipes are arranged vertically, the lower ends of the pipes being fitted into partitioned boxes, or headers, of larger area than the pipes, through which water circulates. In the annular conde?iser , Fig. 21, the vertical tubes are of large size and additional cooling surfaces are supplied by §71 BY-PRODUCT COKING 49 enclosing an internal air pipe in the center, thus making the space through which the gas circulates annular in section. Annular condensers are sometimes made of steel plate and of large diameter. It is clear that atmospheric cooling is only practicable Fig. 20 while the gas is still considerably hotter than the air, so that the transmission of heat will be comparatively rapid; further¬ more, that this difference will vary from the same plant and apparatus, with the time of year. For this reason, the air coolers are sometimes provided with a water spray, to aid the cooling in warm weather, or they are placed in buildings having sides of movable slats, so that they may receive more or less wind as desired. When both these methods are employed, a consider¬ able cooling effect is obtained. Fig. 21 49. Tubular Water Coolers. —When wet gas mains are employed, air coolers other than the gas mains them¬ selves are usually omitted and recourse is had at once to the tubular water coolers. These vary in design, but are of 50 BY-PRODUCT COKING §71 the same general type, consisting of a vessel of steel plate through which water tubes are led, the gas being passed through the vessel around the tubes. A type of such a con¬ denser is shown in Fig. 22. The water spaces a and b are connected by a series of tubes c through which water circu¬ lates. The cool water enters at d and, passing up through the tubes that are in contact with the heated gases, absorbs heat and passes out at e. The upper part of this condenser is open to the atmosphere. The hot gas enters the shell at / and is forced by the baffle plate g and the tube sheets h to circulate to the top before it can find an entrance to the exit passage i. It is thus cooled by the water in pipes c, before it finally reaches the exit j. The condensed tar and ammo- niacal liquor trickle down the tubes and sides of the condenser, finding an out¬ let at k. The efficiency of a given amount of cooling surface is thus consider¬ ably increased because the gas just before exit comes in contact with the coolest surface, and the water when leaving comes in contact with the hottest surface. If the gas is to be divided into two parts for commercial use and oven-heating purposes, there should be two sets of mains and condensing apparatus, forming two distinct systems, which should be practically the same in construction. 50. Effect of Water in Gas.— Although the' gas is spoken of as being cooled, this is really a small matter 871 BY-PRODUCT COKING 51 compared with the cooling and condensation of the water vapor contained in it, as may be shown by the following exam¬ ple: Assume that in the carbonization of 2,000 pounds of coal, 10,000 cubic feet of gas is given off. This gas, if of a specific gravity of .5, will weigh .08073 X .5 = .040365 pound per cubic foot. The total weight will be 10,000 X .040365 = 403.65 pounds. If the coal, as charged into the oven, contained 2 per cent, of moisture, there being in addition 4 per cent, of chemically combined water, the weight of the water vapor in the resulting gas would be 6 per cent, of 2,000 pounds, or 120 pounds. Assume that the gas is to be cooled from 300° F. to 70° F.; the heat that must be absorbed in order to effect this cooling may be divided into three portions; namely, ( a ) that in the gas cooled through 230° F.; ( b) that in the water vapor cooled through the same range; and (c) the latent heat in the water vapor incident to its change from vapor to liquid water. Assuming .45 as the specific heat of the gas and .48 as that of the water vapor, (a) 403.65 pounds X .45 X 230° = 41,777.8 B. T. U. (b) 120 pounds X .48 X 230° = 13,248.0 B. T. U. In order to arrive at the value of (c), the amount of heat latent in the condensed vapor, first ascertain what portion of the vapor is actually condensed at 70° F. This may be found by determining the amount of water vapor that will saturate the given weight of gas at 70° F. From Table IV, it is found that at 70° F. 100 cubic feet of air saturated with vapor will contain 7.311 pounds of air and .114 pound of water; or as gas has but .5 the specific gravity of air, there will be 3.655 pounds of gas and .114 pound of water, or the water is 3.1 per cent, of the gas. Hence, in 403.65 pounds of gas, there will be 403.65 X .031 = 12.51 pounds of water, which subtracted from 120 pounds leaves 107.49 pounds of water actually condensed, and with the latent heat of vaporization at 965.8 B. T. U. the value of (c) is . 965.8 X 107.49 = 103,813.84 B. T. U. (a) + (b) + (c) = 158,839.64 B. T. U., of which the gas contained only about 26.3 per cent, and 52 BY-PRODUCT COKING 71 the water 73.7 per cent. This disparity is due to the latent heat given off in condensing the water vapor, as the pre¬ vious figures show. If instead of a coal having but 2 per cent, of sensible moisture, one having 5 to 8 per cent., as frequently met with, is used, it is clear that the work thrown on the cooling apparatus will be largely increased. 51. Table IV gives the weight of air and moisture at ordi¬ nary atmospheric pressure together with the weight of the mix¬ ture in 100 cubic feet of saturated air for various temperatures. TABLE IV Temperature of the Saturated Mixture Degrees Fahrenheit Weight of ioo Cubic Feet of Saturated Mixture; Also Weight of Water Vapor and Air in the Mixture Pounds 1 Temperature of the Saturated Mixture Degrees Fahrenheit Weight of 100 Cubic Feet of Saturated Mixture; Also Weight of Water Vapor and Air in the Mixture Pounds Vapor Air Saturated Mixture Vapor Air Saturated Mixture 32 .030 8.023 8-053 125 -554 5.9OO 6-454 35 •034 7-970 8.004 130 .630 5-717 6-347 40 .041 7.879 7.920 135 .714 5-524 6.238 45 .049 7-785 7.834 140 .806 5.325 6.131 50 •059 7-693 7-752 145 .909 5.106 6.015 55 .070 7-598 7.668 150 1.022 4.869 5.891 6o .082 7-507 7.589 155 I-I45 4.619 5.764 65 .097 7.410 7-507 160 1-333 4-346 5-679 70 .114 7-3 11 7-425 165 1.432 4-055 5.487 75 •134 7.208 7-342 170 1.602 3-739 5-341 8o .156 7- iq 6 7.262 175 1-774 3-402 5.176 to CO .182 6.996 7.178 180 1.970 3.036 5.006 90 .212 6.896 7.108 185 2.181 2.651 4-832 95 •245 6.764 7.OO9 190 2.411 2.231 4.642 IOO .283 6.641 6.924 195 2.662 1.781 4 443 105 .325 6.505 6.830 200 2-933 1.300 4-233 IIO •373 6.368 6.741 205 3-225 .785 4.010 ii 5 .426 6.224 6.650 210 3-543 .232 3-775 120 .488 6.063 6.551 212 3-683 .000 3-683 52. Cooling Surface Required. —The area of cooling surface required to sufficiently cool 1,000 cubic feet of gas per day under the ordinary conditions of manufacture in this §71 BY-PRODUCT COKING 53 country is assumed to be between 4 and 5 square feet; of this .5 to 1.5 square feet may be air cooled. Much depends on the difference in temperature between the gas and the cooling medium. If this difference is too great and too sudden cooling of the gas ensues, there will be a loss in its candlepower; hence, when the gas is used for illuminating purposes this point must be considered. If 5° F. is the maximum difference in temperature allowed between gas and the cooling water, 8 square feet of water-cooled surface will be necessary per 1,000 cubic feet of gas per day. If a maximum difference of 63° F. be allowed, as in the recently designed condensers for a London Gas Company, 1.71 square feet of water-cooled surface and 1.19 square feet of air¬ cooled surface may be considered sufficient, although for atmospheric condensers English practice prescribes 10 square feet per 1,000 cubic feet of gas. The first-mentioned figures are probably sufficient for all purposes. 53. Temperature Measurements. —The proper con¬ trol of the condensation process is entirely a matter of regulating the temperature of the condensers and mains. In order to control these temperatures, thermometers should be placed at the principal points where the gas enters and leaves the coolers, and where it leaves the condensing house. Ordinary thermometers may be used; these are generally inserted in mercury pockets at points where the temperatures are to be taken. They should be read hourly, and the read¬ ings noted on a printed form. A better method is to use recording thermometers. 54. Pressure Measurements. —The gas pressures are most easily observed by leading small pipes from different points in the system to a central gauge board, where all the needed gauges are arranged in the same order as the con¬ densing apparatus. Each gauge consists of a U-shaped glass tube filled with colored water, or contains water on which a glass float indicates the height of the water column. The point at which the pressure is measured should be indicated above each gauge, and the gauge board should be sufficiently 54 BY-PRODUCT COKING §71 lighted so that the gauges can be easily read day or night. Such a board greatly facilitates the control of the process and the prompt detection of stoppage in the apparatus. 55. Exhauster. —The exhauster, as has been stated, is used to move the gas through the mains to the condensing house by suction and to force it through the scrubbing and purifying apparatus to the gas holder. Some form of posi¬ tive rotary blower similar to that shown in Fig. 23, of which there are several on the market, is generally used. Blowers of the fan, or centrifugal, type, though frequently used for handling purified gas, are not in favor for use on foul gas, more especially as the pressures frequently used in scrubbing apparatus are higher than those easily attainable by this form of fan. In installing exhausters, the main point to be regarded is to get them of sufficiently large capacity to easily do the work, without requiring too high a speed. They are best driven by steam engines coupled directly to the shafts in preference to any other form of motor, as the speed can then be most easily regulated. If possible, two engines and two exhausters should be installed, one being kept for use when the other is being repaired. Cocks and pipe connec¬ tions should be provided for drawing off any accumulation of tar or liquor from either side of an exhauster. §71 BY-PRODUCT COKING 55 56 . TAR SCRUBBERS Pelouze & Audouin Scrubber. —The best known form of tar scrub¬ ber is that of Messrs. Pelouze & Audouin. The apparatus, Fig-. 24, consists of a vessel a in the middle of which is an annular tar cistern b. The lower and upper por- tions of a are gas chambers. In the upper portion of a is suspended the purify¬ ing apparatus, which consists of a bell c suspended by outside weights and ropes, as shown, having double cylindrical sides con¬ taining small perfora¬ tions. The holes in the outer wall are larger than those in the inner wall and are not opposite to them. The bell dips into a tar seal at the bottom. The gas enters the lower part of cham¬ ber a by the pipe d> passes up into the bell c , which by the pressure of the gas is lifted out of the tar sufficiently to allow some gas to escape and thus relieve 56 BY-PRODUCT COKING 71 the pressure. In this way, the pressure is kept constant and the flow of gas is automatically controlled. The gas now passes through the small perforations in the inner wall of the bell and strikes against the solid part of the outer wall, finally passing to the upper part of a through the larger perforations in the outer wall and out through the pipe e. The friction of the gas passing through the perforations and against the baffling walls causes the condensation of the tarry mist into large drops, which do not pass through the holes, but fall into the bottom of the vessel b } from which the tar is drawn off through suitable outlets. 57. Divesey Scrubber.—Another well-known form of tar scrubber is the Divesey, in which the gas is admitted to a closed vessel containing ammoniacal liquors, through which it bubbles to escape into funnel-shaped tubes, the larger ends of which dip into the liquor while the smaller ends connect with the main for the scrubbed gas. 58. Location of Scrubber.—The location of the scrub¬ ber in the condensing system varies in different plants. In some German works, it is placed immediately after the exhauster, where the temperature is nearly that of the dis¬ charged gas, or about 65° to 75° F. American and English practices agree in recommending that the heavy tar be removed from the gas before the temperature falls below 100° F., since below this temperature the tar absorbs illumi- nants at the expense of the gas. For this reason, a better location is immediately before the final cooler, preferably on the pressure side of the exhauster, as in this case the some¬ what higher specific gravity of the gas aids in the action. One advantage of running the Pelouze & Audouin scrubber at the higher temperature is the freedom from stoppage of the small holes by naphthalene. To facilitate clearing, the bells are frequently made polygonal in form instead of circular, and the impinging plates bolted to the frame so that they can readily be removed and clean ones substituted with but little delay. A partial cleaning may be effected by blowing in steam along with the gas, but this raises the gas §71 BY-PRODUCT COKING 57 temperature and is likely to interfere with the subsequent ammonia recovery. The presence of tar in the gas passing from the scrubber is detected by allowing a jet to blow on white paper. If tar is present, the paper will be blackened immediately; but if several minutes’ exposure produces no more than a brown stain, the gas is sufficiently clean. If a quantitative determi¬ nation of the tar present is desired, it can be made by pass¬ ing the gas through a weighed tube containing absorbent cotton, then through a meter, the increase in weight of the absorption tube being due to the tar removed from the gas. Before entering the absorption tube, the gas should be freed from water by being passed over caustic lime. AMMONIA SCRUBBERS 59. The removal of ammonia vapor from the gas depends on the great absorptive power of water for ammonia. The absorption of ammonia is accomplished in what are called scrubbers, or wasliers. There are two general classes of ammonia scrubbers. In one class, as the seal , or bell , scrubbers , the gas is forced by pressure through successive seals dipping into water or liquor; in the other class, represented by the tower and rotary scrubbers , the gas is passed through vessels containing a large amount of wetted surface, such as in a liquor spray or constantly moist¬ ened steel plates, wooden grids, gratings of parallel strips of wood, pieces of coke, or in revolving disks. The objection to seal, or bell, scrubbers is the amount of work they throw on the exhauster in forcing the gas through the seals; scrubbers of the tower class avoid that difficulty, but occupy considerable space. 60. Bell Washers. —The seal, or bell, washers con¬ sist, usually, of several cast-iron sections placed one above the other with the flanges bolted together. Each section contains a certain depth of liquor and has an opening for the passage of gas in its bottom, which opening is covered by a sealing hood, which may be quite simple or sometimes 58 BY-PRODUCT COKING §71 very complicated in form. The edges are usually saw-tooth shaped and dip below the liquor surface. The gas may pass either upwards or downwards, forcing its way through the seal and being divided into fine bubbles by the toothed edges. The water or liquor is fed into the top com¬ partment of the scrub¬ ber, through a seal of sufficient depth to with¬ stand the pressure due to the passage of the gas through the appara¬ tus. Two or more such scrubbers of several sec- tions each are usually placed in series, the compartment last trav¬ ersed by the gas being fed with fresh water, in order to complete the absorption of the ammo¬ nia. The weak liquor from the end compart¬ ments is used in those preceding them, and thus strengthened up to li to 2a per cent, of ammonia gas, NH 3 . The shape of the scrub¬ ber may be rectangular, circular, or octagonal, and the details of its construction differ with Fig. 25 every design. Wafer or Weak Liquor 61. Tower Scrubbers.—The tower scrubber usually consists of a metal cylinder, filled wholly or in part' with some loose material like coke or tile, or with wooden slats §71 BY-PRODUCT COKING 59 spaced regularly and closely; the surfaces of this filling material are wetted by a constant spray of liquor or water fed in at the top by some form of sprinkling device. In the scrubber shown in Fig. 25, the cylinder a contains perforated partitions on which coke or other loose material is placed. The water enters at the top as a spray through the pipe b. In descending, it encounters the ascending gas, which enters at the bottom through c and passes out at the top through d. The film of water on the surfaces exposed to the gas absorbs the ammonia from it, forming ammoniacal liquor, which passes out at e. The best results with such towers appear to be given by placing boards l inch wide 1 inch apart, this affording the greatest wetted surface with the least volume to obstruct the gas passages. Horizontal perforated plates placed at frequent intervals in the scrubber, with holes in the plates i inch in diameter, thus forming a series of plates, are used in some American plants with considerable success; this latter form of apparatus is called the sieve washer. If tower scrubbers are used, it is usually necessary to place two or more in series. 62 . Horizontal Rotary Scrubber. —The horizontal rotary scrubber, Fig. 26, or washer scrubber, as it is sometimes termed, consists of a cast-iron cylindrical case a placed horizontally. Through the axis runs a shaft b revolved by the belt pulley c and carrying a number of perforated steel plates, wooden grids, or brush wheels, according to the particular type of machine. The lower half of the cylinder is filled with weak ammonia water, which wets the surface of the plates or grids as these are slowly turned by the shaft. In the type of scrubber shown in Fig. 26, a number of brush wheels, each having its center filled with coke or other porous substance are mounted on the shaft b. The wheels are so arranged that the water is carried up on the circum¬ ference of the revolving wheel and filters through the per¬ forations shown in the wheel, keeping the coke thoroughly wet. This wetted surface is exposed to the action of the gas, which enters at d , passes through the apparatus from end to 60 BY-PRODUCT COKING §71 end above the water level, and out at the opposite end. By a special arrangement of the plates or grids, in some the gas is made to follow as tortuous a path as possible, in order to promote the absorption of ammonia. When metal plates are used, the inner surface of the cylinder and the edges of the plates are machined so that they come very close to each other without actually touching; this allows the liquor to form a film joint in this place and helps to stop the gas from pass¬ ing through by the shortest route. The main objection to the use of metal plates is the great weight of the moving parts and the size of shaft required to carry this weight without bending. The lower portion of the shell containing the liquor is usually divided into a number of compartments by partitions, as shown. These compartments are connected alternately top and bottom by openings in the partitions, so that the liquor must flow from one end to the other, and in this way become gradually stronger, the fresh water or weakest liquor entering at the end where the gas is discharged. At the bottom of each compartment are drain cocks for remov¬ ing any tar that may gather there. The entering water is fed in, usually, by a small jet discharging into a funnel, which extends sufficiently high above the liquor level inside to over¬ come the pressure of the gas and is provided with a seal of corresponding depth. The discharged liquor flows also through a sealed pipe to the liquor storage cistern. The §71 BY-PRODUCT COKING 61 motive power is usually furnished by a small upright steam engine or an electric motor geared down to give about five revolutions per minute to the main shaft. The whole appa¬ ratus is very compact and self-contained and requires little power to run it. It is efficient in its operation. The main objections to it are that it requires power for its operation and its initial cost is high. It adds but a few tenths of an inch to the pressure of the gas to be forced through it, which advan¬ tage, however, it shares with most of the scrubbers of the tower pattern. One pass through a rotary scrubber is usu¬ ally enough to absorb the ammonia in gas to within allowable limits, provided that the quantity of gas passing through the apparatus is not in excess of its rated capacity. 63. Ajiparatus for Concentrating tlie Ammonia. The usual form of concentration apparatus is shown in Fig. 27. It consists of the still, which includes two parts, one a for the ammonia gas, known as free ammonia , and one b for the ammonium compounds known as fixed ammonia . Each part is composed of cylindrical cast-iron sections bolted together by flanges, as shown, one above another, the sections being provided with internal heads and seals. The free-ammonia still a discharges into the fixed- ammonia still b , a lime chamber c being between the two. The weak liquor enters at the top of the free-ammonia still from the feed-tank d and passes down through the sections, encountering the steam, which enters at the bottom of the fixed-ammonia still at e and passes upwards. The free ammonia driven off by the steam in the upper section a and that set free by the action of the lime in c and steam in the fixed-ammonia section b pass out through a cooler /, which serves also as a preheater for the incoming weak liquor. If ammonium sulphate is to be made, the gases pass through pipes g to the lead-lined saturating boxes h , where the ammonia is absorbed by the dilute sulphuric acid placed in them. The ammonium sulphate is deposited in these boxes in the form of white crystals, accompanied by the evolution of considerable heat. When the acid is sufficiently neutralized, 151—26 §71 BY-PRODUCT COKING 63 the contents of the saturators h are discharged into the cooling tank i, where the liquid, which is called the mother liquor , is cooled and drawn off to the tank j. The sulphate is dried in the centrifugal drying machine k and afterwards taken by the conveyer belt / to the bagging room. If concentrated liquor is to be made, the gas passes through the pipes g to the second cooler m> termed an absorber , in which the ammonia and water vapors are con¬ densed to a strong liquor. In either case, there are certain non-condensible gases produced in the distillation, which are obnoxious in their nature and are led away by the pipe n to a smokestack, or are burned under the boilers. STORAGE OF TAR, LIQUOR, AND GAS 64 . Amount of Storage Room Required for Tar and Liquor. —It is essential in a by-product coke-oven plant to provide ample storage room for the tar and ammonia liquor. If the tar is to be shipped direct to the consumer, as is usually the case, it is imperative that it be given suffi¬ cient time to settle and allow the entrained ammoniacal liquor to separate from it. Otherwise, this liquor will not only be lost, but cause complaint by the purchasers. Steam heating coils on the bottom of the tar tank aid in the separa¬ tion of the liquor. Two weeks of quiet storage for settle¬ ment is by no means a too liberal allowance, though good results are obtained by allowing the tar to flow by gravity through three or more steam-heated vessels of moderate capacity so connected that the heaviest tar from the first will flow to the second, which discharges its heaviest tar into the third. In some plants, where commercial exigencies must also be considered, storage for 3 months’ output is not con¬ sidered excessive. In the case of ammoniacal liquor, so much capacity is not essential. In every complete by-product coke-oven plant, apparatus for the concentration of the weak liquor to strong crude liquor, or its conversion into ammonium sulphate is provided. The only need for storage, therefore, is that the 64 BY-PRODUCT COKING §71 liquor and lighter tars shall have opportunity to separate, and for this the storage of a week’s output suffices. This may be approximated, as already noted, by figuring it as one-quarter the weight of coal carbonized per day, for liquor having 1 per cent, of NH 3 , or 65 United States gallons per ton of coal coked. As this is a minimum strength for liquor, the resulting capacities should be ample. It must, however, be taken into account that there are usually liquors of various strengths made in the condensing and scrubbing processes, and that the weaker liquors must be passed through the apparatus again until they are of a proper strength for economical concentration. The weak liquors usually come from the first condensers, where the temperature is too high to permit of much absorption of ammonia in the water that is condensed from the gas, and from the last stage of the washing process, where fresh water is used for the final scrubbing. If a rotary scrubber is used, it delivers a strong, crude liquor, because of the successive compartments through which the liquor must pass, even though it be fed by fresh water. For this reason, it is feasible to collect the weak liquor from the condensers and feed it into the first few com¬ partments of the rotary scrubber, while fresh water is fed into the last compartments next the end where the gas is discharged. In this way, only two grades of liquor need be arranged for, the weak from the condensers and the strong from the scrubber, the latter liquor being pumped from the overflow receiver directly to the main storage tank. Where tower scrubbers or seal washers are used, it is necessary to handle three or even four strengths of liquor, the liquor from each tower or set of towers being kept separate and used for scrubbing in the apparatus next preceding. For the sake of convenience and reliability in operation, a certain amount of the intermediate liquors should be kept on hand, so that shut-downs on pumps, etc. will not interrupt the work. 65 . Storage Cisterns. —The necessary storage cisterns are usually sunk beneath the ground level and are built of concrete, or brick laid in cement, with arched or timber roofs. §71 BY-PRODUCT COKING 65 These are convenient, as the tar and liquor will then drain to them directly from the seal pots and apparatus, and they do not take up space above ground; but on the other hand they are difficult to construct so that they will not break, and the tar once in them is harder to raise by suction to the pumps than if the storage were above the ground level. The heavier tar sinks to the bottom of the cistern and after a year or two hardens to a rubbery substance that will not mix with the softer tar, and clogs the pumps. The cleaning out of such a cistern underground is a serious matter, whereas above ground it may be drained from time to time and kept free with little trouble. For these reasons, where the cost is not too great, a number of steel tanks set above ground seem to be preferable to a large underground cistern divided into sections by walls, for the different liquids. It is, however, impossible to do with¬ out some low-level cisterns of small capacity to receive the drips from the various seals and drains, but if these are of comparatively small size they can be kept free by pumps, and are not hard to clean. Steel storage tanks should be provided with bottom outlets and steam coils carried on sup¬ ports just above the tank bottom, so laid out as to drain any condensation to the outlet. A steam trap may then be placed at this point and the water thus removed without further attention. If this is not done, a jet of steam must be kept constantly blowing from the vent in order to be sure that water is not filling the pipe. An internal swinging suc¬ tion pipe that may be adjusted to draw either the upper liquor or the lower tar is frequently used in either steel or under¬ ground tanks, thus making only one pump connection neces¬ sary. Steel tanks are usually provided with self-supporting roofs of light plate with internal stays, though a better plan is to cover them with a tight wooden roof covered with tar and gravel, as the steel roof is ultimately attacked and spoiled by the ammonia fumes, which do not attack the wood. The gravel or tin covering practically obviates danger from fire, except from causes that would be as dangerous to a steel roof. The tighter it is made, the 66 BY-PRODUCT COKING §71 less loss will there be of ammonia in the form of vapor. There should be a manhole in the roof and one near the bottom of the shell, to allow access for cleaning and repairs. 66. Gas Holders.—In coke-oven plants, when the sur¬ plus gas is sold for outside purposes, a gas holder, Fig. 28, serves the same purposes as it does in the ordinary gas plant, that is, storage for times of maximum consumption or mini¬ mum production. The amount of this storage may, in gen¬ eral, be assumed to be 24-hours’ production, though with increased size of plant and consequent multiplication of units, the need for storage grows less. Local conditions also influence this question to a large extent. In works where the gas is divided into two portions, a storage holder of ample size is usually essential for the rich gas. A smaller holder, known as a relief holder , is also of great use on the poor-gas system, as it serves to regulate the pressure of the oven-heating gas and gives much better results in the oven heats. This holder need not be of great size, capacity for i or 1 hour’s output being sufficient for a plant not exceeding fifty ovens, and less in proportion for a larger plant. When but one grade of gas is made, a holder is essential for regu¬ lating purposes and should be installed at every plant, §71 BY-PRODUCT COKING 67 although it is true that a plant of moderate size can be run without a holder if the coal used is rich in gas. Such a plant, however, must either waste a great deal of its gas or dispose of it in some manner that is not seriously affected by varia¬ tions in supply, if such can be found. With a coal low in volatile matter, which soon yields its gas in the oven, a holder is necessary for the proper operation of the plant, as by its use alone can the gas supply be maintained. As the size, location, and special conditions under which each plant is built vary widely, it is not practicable to discuss the general arrangement more in detail. The most useful information in this line may be obtained by careful study of the arrangements adopted in the various important and modern works like that at Everett, Massachusetts, as shown in Fig. 1. ' •• BY-PRODUCT COKING EXAMINATION QUESTIONS (1) What is meant by by-product coking? (2) What are the advantages of by-product coking over coking in beehive ovens? (3) (a) How does the yield of coke from by-product ovens compare with that from beehive ovens? ( b) What is the cause of these differences? (4) What important factors must be taken into con¬ sideration in determining a suitable location for a by-product coking plant? (5) Explain briefly the general arrangement of the flues that distribute the burning gases about the retort in the Otto- Hoffman oven. (6) (a) What provision is made for preheating the air for burning the gas that heats the retorts? (b) How is the heat maintained in these regenerators? (7) What advantages are there in preheating the air for the combustion of the gas? (8) (a) By what indication can it be known that an oven is burning properly? ( b) What injury may result if the combustion in the oven flues is not complete? (9) Explain how the underfired retort ovens differ from the Otto-Hoffman ovens in principle. (10) What advantages do underfired retort ovens have over end-fired ovens? §71 151—41 2 BY-PRODUCT COKING §71 (11) What are the distinctive features of the Schniewind or United-Otto ovens? (12) How does the arrangement of the flues for heating the retorts in the Semet-Solvay oven differ from that in the Otto-Hoffman oven? (13) In what way is the absence of regeneration offset in the Semet-Solvay oven? (14) What are the principal by-products obtained from the gases from by-product ovens? (15) On what qualities does the value of by-product gas depend? (16) In what two ways are gas-collecting mains con¬ structed and in what respect do they differ from each other? (17) ( a ) What two kinds of coolers are used for con¬ densing the tar from the hot gases? (b) Explain the principle of each. (18) By what means are the last traces of tar removed from the gas? (19) On what principle does the removal of ammonia from the gas depend? (20) What are the advantages and disadvantages of having storage cisterns below the ground level? Mail your work on this lesson as soon as you have finished it and looked it over carefully. DO NOT HOLD IT until another lesson is ready. " ' SUPPLIES FOR STUDENTS In order to do good work, it is very necessary for our students to secure the best aterials, instruments, etc. used in their Courses. We have often found that inexperi- lced students have paid exorbitant prices for inferior supplies, and their progress has aen greatly retarded thereby. To insure our students against such error, arrangements ave been made with the Technical Supply Company, of Scranton, Pa., to furnish such as ssire them with all the supplies necessary in the different Courses. SEE PRICES ON SEPARATE LIST LIGHT-WEIGHT PRINTED. ANSWER PAPER With printed headings especially adapted for use of students of the I.C.S. Size '/ 2 " x 14". This paper is very tough, durable, and has a fine writing surface. It will last )r years, and the student is thus enabled to keep a permanent record of the work sent to le Schools. I.C.S. COLD-PRESSED DRAWING PAPER Size 15"x20". Buff color—easy on the eyes. It is unusually strong and tough; takes clean, clear line; is not brittle; is not easily soiled. Best for both ink and pencil. “TESCO” TRACING CLOTH Used extensively by draftsmen, architects, engineers, and contractors-—a high recom- Lendation of quality. It is transparent, strong, free from knots and other imperfections nd contains no air bubbles. I.C.S. instructors assure their students it is thoroughly ependable. Furnished in sheets 15"x20". PORTFOLIOS For keeping your Examination Papers and drawing plates neat and clean and in order. >on’t roll them up and then forget where they are, or leave them where they will become ailed or damaged. Some of these days an employer may ask to see them. “TESCO” LIQUID DRAWING INK “Tesco” Ink flows smoothly and evenly from the pen and leaves a clear, sharp line of niform intensity, free from cracks and bubbles. FOUNTAIN PENS As answers to Examination Questions must-be written in. ink, you can, with a fountain en, answer your papers any time—anywhere—whether it is in the office, shop, factory, r home. DICTIONARIES No matter which Course you are studying, no matter what kind of work you do, a ictionary is valuable. Keep it near you when you read and when you study. Don’t skip re words you don’t understand; look them up, for that is the best way to acquire a ocabulary. RUBBER HAND STAMPS Stamp your name, address, and class letters and number on every lesson and drawing ou send to the Schools. Useful for marking envelopes, books, papers, etc. DRAWING OUTFITS The I.C.S. Outfits are not simply “gotten up” to provide something for. the student to sev during his Course. These Outfits will last long after he has, gotten into actual work, 'hey are practical Outfits—made up from specifications furnished by I.C.S. Instructors. Naturally, then, such Outfits must be right. _ All instruments, must be of a high uality to give long and efficient service. All material must be honest, sincere, dependable, he busy man cannot be annoyed with poor, material, and the student must not be retarded y the use' of it. COMBINATION DRAWING AND STUDY TABLE The table is made of oak, and can be folded and placed out of the way; and, although : weighs but l9 l / 2 pounds, it will support a direct weight of 200 pounds. The braces are f nickeled rolled steel. 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