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T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 14, No. 9
By-product Coking By F. W. Sperr, Jr. CHIEFCHEMIST, THE KOPPERSCOMPANY LABORATORIES, MELLONINSTITUTE, PITTSBURGH, PA.
T
.HE BY-PRODUCT coke industry has found the past
1-The
alpha compounds are insoluble in pyridine,
2-The beta compounds are soluble in pyridine, but are left two years remarkably rich in technicalachievements as insoluble residue when the pyridine extract is treated with which promise a very prosperous development as busi- chloroform. ness recovers from its recent depression. It is gratifying 3-The gamma compounds comprise that part of the PYrito note that such achievements are more. and more the result of dine extract which is soluble in chloroform. planned scientific research in which chemisThe gamma compounds are considered try has a most important part. The field to correspond with the resinic substances. of research, comprising coal and its relation As to the nature of the alpha and beta to coke formation, the coking process, the compounds we may refer here to the hyproperties and utilization of coke, the repothesis of Fischer and Schradera that covery and utilization of the by-product,s, lignin degradation products, rather than and the materials of plant construction, is cellulosic substances, play an important so large, that a review of the subject conpart in coal constitution. densed to the limits of this article would The relation of these three groups of amount to a mere Sndex of the numerous substances to the coking property has been important papers that have appeared. It investigated by S. Roy Illingworth,4 who will, therefore, be more interesting and worked with the general idea of determinuseful to select for discussion a few subing the proportion of each group in the jects of investigation that may be considresidues obtained by heating typical coals ered typical of the general trend of research for different periods and at different temin this connection. peratures. He found the beta compounds PROPERTY AND PROCESS OF COKING to be less stable than the resinic compounds The various investigators who have and that in all probability the former are the first to decompose on heating. been working on the difficult and imporAssuming, as the majority of investigators tant problem of coal constitution have F. W. SPERR,JR. have done, that, the resinic compounds contributed much toward improving our conceptions of the coking property and the mechanism of constitute the “cementing” agency in the coking process, he coke formation. At the best, however, any such conccptions developed an interesting line of inquiry into the mechanism of must be regarded as working hypotheses which we must be coke formation on the basis of determining the minimum prepared to amend or to discard altogether in the light of amount of these compounds that could be present to produce additional information. Coal research is still in too early a a coherent coke, His results indicated a difference in the stage to formulate strict generalizations, and investigators cementing properties of the various resinic substances in the must not lose sight of the marked individuality possessed different coals-the higher volatile and more poorly coking coals having, as would be expected, resins with weaker cokeby each and every coa1.l The three general methods most used in recent investiga- producing quality than the better coking coals. Nevertheless, tions of coal constitution are exnmination with the micro- he took 5.5 per cent of resinic substances to be an average figure scope, solution in organic solvents, and low temperature dis- for the majority of coking coals representing the minimum tillation. It may be useful to attempt a brief correlation of amount of resinic substances capable of holding a residue together in the form of a coherent coke. He then constructed the work so far done. The study of coal wit,h the microscope has been of prime a picture of the coking process showing the formation of a importance with respect to the direct value of the results ob- plastic stage due to softening of the resinic substances, the tained. It has shown, what is now generalIy accepted, creation of a spongy state during the period when the mass that an important group of coal constituents are resinic com- contains more than the critical amount (e. Q., 5.5 per cent) pounds derived from plant resins that me resistant t o decay. of resins, and the stiffening and solidification of the mass These resinic compounds are believed to have a great influ- with the reduction of the resinic content below 5.5 per cent. ence on coke formation. Regarding the nature and influence Differences in the porosity of coke he considered to be due to of the other coal constituents our knowledge is most unsatis- differences in the stability of the beta substances. The factory. There WRS formally a disposition to classify these crucial characteristic of any coal as regards porosity of the as “cellulosic,’1 but it has been pointed out that cellulose resulting coke would be the amount of volatile matter evolved proper is unstable under the conditions of peat. formation, when the hot mass is in its most viscous state and about Taking advantage of the remarkable solvent action of pyridine to pass to a fixed structure by virtue of the destruction of on coal, and of the solubility of portions of the pyridine ex- the resins. He determined the rate of evolution of volatile tract in chloroform, it has been proposed2 to classify the coal matter during what might be considered its critical period, substances in the three groups-alpha, beta, and gamma and obtained “porosity factors” which came in the same compounds, without attempting to define the nature of each order as the actual porosity of the cokes from the coals group. This has constituted a useful working agreement, investigated. Some space has been given to this work of Illingworth bewhich it is well to get clearly in mind with the following definitions : a Brennsloff-Chem., 2 (1921), 37, 237. George Charpy and Gaston Decorps, Com9l. rend., 168 (1919), 1301. “Monograph on the Constitution of Coal,” by Stopes and Wheeler, London, 1918. 1
2
4 J . SOG. Chem. Ind., 89 (1920), 111T, 133T;Fuel, 1 (1922), 49. See also Bone, et 02.. Proc. Roy. SOC.,1OOA (1922), 682; reviewed and severely criticized by Wheeler in Fuel, 1 (1922), 49.
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T H E JOURNAL OF INDUXTRIAL AND ENGINEERING CHEMISTRY
cause it xs typical of that type of scientific investigation which is greatly needed in coke technology. Work of this sort should be continued to the point of enabling us to determine definitely by a laboratory examination of any given coal the quality of the coke that it will make in large-scale operation, and this should be accomplished without the necessity of largescale tests. The rnicroscopic examination of coal has developed certain nem terms with which coke technologists must become acquainted. Reference must first be made to the pioneer work of Dr. Reinhardt T h i e s ~ e n ,of~ the U. 8. Bureau of Mines, who has developed a technic of making thin sections of coal through which light can be transmitted to such a point that ordinary bituminous coal can be most thoroughly examined. The bright bands prominent in bituminous coal, he finds, represent parts of definite components of the woody parts of plants-that is, parts once pieces of logs or stems, branches, twigs, and rootq, but now much compressed. Such parts of the coal he calls unthruzylon, meaning coal wood, from unihraz, coal, and zylon, wood. Dr. Thiewsen is now making a study of the relation between the constitution of coal, as seen under the microscope, and it? coking quality, and has been making considerable progress in following this relation. For example, anthraxylous constituents of Illinois coal have been separated on the stage of the microscope and subsequently coked. The experiment showed that the mthraxylon swelled, fused, and acted a3 a coking constituent, whereas the attritus did not swell or fuse but merely sintered, retaining the original structure that it had in the coal. This line of investigation has been pursued in England by Marie C. Stopes,6 who distinguishes two constituents of the bright coal bands, viz., clurain and vitruin. Clarain has a bright, smooth structure but is so closely associated with fragments of the dull coal (durain) as to be difficult to separate. Vitrain occurs in brilliant, structureless, well-defined bands. It can readily be separated and is usually smaller in amount than the other constituents. The other two principal constituents she calls fusain and durain. Fusain is the familiar "mother-of-coal" or "mineral charcoal." Durain is the dull-appearing coal substance (Mattkohle) having a hard, close, firm texture and a lumpy, irregular surface of breakage across the bedding plane. Rudolph Lessing' has studied the behavior of these constituents on coking. Considerable fusion and merging of particles was shown by clarain which gave cokes with a peculiar brown sheen. Vitrain produces a characteristic silver-white coke, but the consolidation of particles did not go so far as with clarain. Durain was practically devoid of coking value, but the particles adhered to each other a little more than in the case of fussin which had absolutely no coking tendency. A study of the properties and process of by-product coking is not complete without consideration of the light shed by low-temperature distillation, in which field there has been considerable activity directed toward the development of commercial processes. So far, however, the by-product chemist is chiefly concerned with the theories of pyrogenesis and coal structure, such as are developed in the recent articles of J. J. Morgan and R. P. Soulea on tfhe composition of low-temperature tar, and their reference to earlier work of the same nature. The very important problem of the deterioration of coal in storage has been studied by William Seymour,g both in relafi
U.S. Bur. Mines, Bull. 117 (1920), and other publications.
fi
Proc. Roy. Soc., 90B (1919),470. J . Chem. SOG.,117 (1920), 247. Chem. Met. Ens., 26 (19221,923,977, 1025. Blast Furnace and Steel Plant, 1920, 435.
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tion to coke manufacture and to the utilization of the coke in the blast furnace. B brief research of an entirely new type into the carbonization of coal has been conducted by Eric Sinkinson,lo who has shown that the electrically nonconductor coal changes to a conductor (coke) n t a temperature in the region of 500" c. Reference should be made to theinvestigations of F. Kortenll into the expansion of certain types of coal during coking. Our own laboratories have done a large amount of work on this subject, and have developed a method which, on arelatively small sample, determines both the coking qualities and the contraction or expansion of a given coal. This work will be published in the near future.
BY-PRODUCT FORMATION
80 far, we have been considering that type of investigation which aims a t the elucidation of the coking property. Other investigations into the phenomena of carbonization have to do with the evolution of by-products and during the past two years attention has been paid principally to ammonia and sulfur. Extensive experiments in full-sized by-product ovens have been described by A. Thau.12 The characteristics of the coke, gas, light oil, etc., produced a t different temperatures were examined but the principal work was done on the conditions covering the yield of ammonia. The amount of free space above the coal in the oven did not appear to have so much influence in decreasing the yield of ammonia by secondary decomposition as has been generally believed. The hot surfaces of carbon appear to be more effective in general secondary decompositions than the hot oven walls. -4ir leaks were shown to diminish the yield of ammonia considerably. H. J. HodsmanI3refers to the work of Thau and others, and describes laboratory experiments made under his direction to examine further the decomposition of ammonia in the presence of oxygen. No destruction of ammonia was detected in coal-gas mixtures containing 1 per cent of oxygen at any temperature below 600" C. At 700" C. and higher, the loss of ammonia was very considerable. The results of these experiments agreed in general with Thau's observations. Another laboratory research into the formation of ammonia during carbonization was conducted by A. C. Monkhouse and J. W. Cobb.14 Cokes prepared at 500", 800", and 1100"C. were subjected to the action of hydrogen and nitrogen separately a t three different temperatures-600", 800°, and 1000" C . The hydrogen appeared to exerehe a specific action on the nitrogen in the 500" coke, with the formation of ammonia. Another series of experiments was made on the 500' coke treated successfully at 800" C. with nitrogen, hydrogen, and steam, the action of each gas being carried to completion before the next was allowed to act. Large quantities of ammonia were obtained by the use of hydrogen when heating with nitrogen had ceased to yield any ammonia, and further large quantities were obtained with steam when the hydrogen had become practically ineffective. Monkhouse and Cobb also obtained some data on the liberation of sulfur from the coke under the above conditione. The sulfur was evolved as hydrogen sulfide in a way similar to and parallel with that of ammonia. A much more extensive investigation of the behavior of sulfur during carbonization has been conducted by dlfred R. Powell, of the U. s. Bureau of Mines. U. 0. Hutton and C. C. Thomas,lS of J . Chem. Soc., 117 (l920),839. a. Eisen, 40 (1920), 1106. 12 Brennstof-Chem., 1 (1920),52. l a Gas World, 76 (19223,12 (Coking Section). 1 4 Gas J . , 166 (1921),234. 16 THISJOURNAL, 12 (1920), 1077;13 (1921),33;Gas A g e , 47 (1921),88.
10
11 StahE
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THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
Johns Hopkins University, have also carried on a line of research in cooperation. Powell's work has been OF great importance in showing the way in which different forms of sulfur decompose and the effect of hydrogen in removing sulfur from the coke, and has formed a basis for the study of methods for desulfurizing coke during the coking process which the Bureau of Mines is now conducting.
PROPERTIES AND UTILIZATION OF COKE I n the work of our own laboratories in the Mellon Institute, great emphasis is placed on the study of coke itself. This has a twofold relation-first, to the conditions of coking, and second, to the conditions under which coke is consumed, A thorough knowledge of the properties of coke is cssentinl. For qome time especial attcntion has been given to specific gravity, porosity, and cell structure. The correct determination of the true specific gravity of colrc is a problem, the difficulty of which is not generally recognized. The figures obtained vary with the method used, and since the porosity is calculated from thc specific gravity, the discrepancies may be equivalent to as much as 30 to 50 per cent of the total varktion in porosity found in different blast-furnace cokes. The subject has been fully discusaed by H. J. Roqe, of our laboratories, in a paper presented a t the last meeting of the ~ o C I E T Y . Methods of recording and AMERICAN CHEMICAL comparing the Gel1 structure of cokes have been developed, and much progress has been made toward a better understanding of this important characteristic. Studies have also been made of the volatile matter and occluded gases in coke, in which connection the large amount of research work recently done by different investigatorq on the properties of charcoal has been found especially helpful. A study of the combustibility of coke is also under way. The investigation of the effect of the conditions of by-product coke oven operation on coke quality has led conversely to the development of a, method that enables us to determine the maximum temperature to which a given piece of coke has been subjected. Since 90 per cent of all coke manufactured is consumed in the blast furnace, the study of the effect of coke quality on blast-furnace operation is of prime importance. The most outstanding contribution to our knowledge of this subject has been made by Heinrich Koppers.16 Extensive reference ismade by Koppers to the work of H. P. Howlandl' on American blast-furnace practice. Koppers agrees with the general opinion of experts in this country that the most important property 01 coke for blast-furnace purposes is combustibility. He then shows the remarkable fuel consumption figures obtained in charcoal furnace practice and the significance of such practice with relation to the optimum coke quality. The conibustibility of coke stands in close relation to the temperature of coking; the higher this temperature the less the combustibility. Good blast-furnace coke ought to be made of homogeneous coal coked a t moderate temperatures in such a way that the heating is uniform a t all points in the coking mass, and should be pushed out of the oven as soon R scolring is finished. Finally, it should be uniform in size. Koppers shows how the by-product coke oven structure may be modified to attain a greater uniformity of heat flow into the coking mass. Great progress has been made in this direction in recent American installations, and the Becker type ovens, which have recently been put into operation by The Koppers Company a t Chicago, may be cited as the newest development that has been made with remarkably successful results in the regulation of the quality of the coke produced. 16
17
Sfahl u. Ezsen., 1921, 1173. Trans. Am. Inst. M m Met. Eng , 66 (1917),339.
Vol. 14,No. 9
Koppers goes milch further than the regulation of coke oven conditions to produce the right sort of coke. He shows how the blast furnace itself may be iinproved by modifications, simple yet almost revolutionary in their conception, so as to obtain more uniform operation, increased capacity, and decreared coke consumption per ton of iron. The relation between the physical properties of coke and its utilization in the blast furnace is being made a wbject of study by the U. S. Bureau of Mines. The various physical tests, such as shatter, hardness, porosity, and combustibility, are being thoroughly invertigatcd a t both the Southern Experiment Station of the Bureau, located a t Tuscaloosa, Ala., and the Pittsburgh Experiment Station, as well as at the Experiment Station at Minneapolis, Minn. The rate of combustion of coke in various blast furnaces is being studied by taking samples of the hearth gases from a water-cooled sampling tube inserted in the tuyeres. By determining thc relative percentages of carbon monoxide, carbon dioxide, and oxygen a t various points in the hearth from the end of the tuyere to the center of the hearth, it is possible to note the variation in the rate of combustion in various blast furnaces using different kinds of coke. Laboratory experiments are also being made on the rate of combustion of coke of various physical properties. MATERIALSOF PLANT CONSTRUCTION The most importsnt materials in the construction of byproduct coke plants are the refractories. Testimony before the Federal Trade Commission18 shows that the byproduct coke oven industry in this country stands second only to the open hearth industry in the consumption of firebrick. Modern American coking practice uses silica, brick exclusively, which permits higher temperatures with consequent important decrease in coking time and increase in capacity. In this development, America is pioneer nnd the attention of the rest of the world is at present directed toward the adoption of this practice. Advances in the production and utilization of other materials of plant construction have occurred during the past few years, but such advances have been shared in common with a great many other industries which also use these materials, so a detailed description is not in place here. THERECOVERY O F BY-PRODUCTS -4KD OTHER DEVELOPMENTS The prepnration and utilization of the chief by-products, tar, ammonia, and benzol, each constitute an important, industry in itself and the developments cannot adequately be considered in detail. I n the tar industry, chief attention a t present i q given to the development of satisfactory processes for continuous distillr,tion. The major attention of the ammonia industries has been directed toward the improvement of the chief product, ammonium sulfate, to give a neutral friable salt. This development is going forward mainly in England. The enormous mar-time demands for benzol products have, of course, disappeared and research in this field has largely been confined to the development of a satisfactory motor fuel. Other recent developments which give important economic aid to the advance of the by-product coke oven industry are the utilization of by-product coke oven gas as a domestic fuel, the firing of by-product ovens by producer gas (with the consequent release of a large amount of high-grade gas), and the liquid purification of gas. 18
R.M. Howe, Trans A m Inst. M i n . Met. E n g , 62 (1819),14.
The Anaconda Copper Mining Company has purchased a $1,000,000 phosphate rock deposit, intending to use waste smelter gases for fertilizer making.
