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JOHN D.
PRICE and M. E. MADOR
The Colorado Fuel and Iron Corp., Pueblo, Colo.
Coal Carbonization Research A World-W i d e Problem Coke is currently a necessity in the smelting of iron ore. This article may assist the carbonization research engineer in developing an improved product from an inferior raw material D m m o THE EARLY DAYS of making metallurgical coke, large inroads were made into the reserves of the better grades of coking coals. This was true particularly in regard to coals of low ash and sulfur content and, as a result, the depletion of this high quality coal has increased the washing of coal before carbonization. The same condition has been true regarding the usage of the coals of better coke-producing properties. This has resulted in the present pmblem of producing satisfactory metallurgical cokes from coals which not many years ago would have been considered unsuitable for this purpose. This same condition also arose from building iron and steel plants in locations where only inferior grades of coal are available. These conditions are found not only in this counhy but also in many other wuntries throughout the world. Thus an increasing amount of research is being
conducted toward coke quality improvement. The threatened depletion of petroleum reserves and the increasing demand for chemicals of all kindspharmaceutical, agricultural, insecticidal, plastics, synthetic fibers, and others -have given a tremendous boost to coal chemical research (8, 70, 72, 27).
Cool Chemical Research
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Coal hydrogenation for the production of synthetic liquid fuels and low temperature carbonization for the production of tars of special properties as well as of boiler plant smokeless fuel are receiving much attention. Over 30 low-temperature carbonization units of some size and type now exist in the United States and Canada and several additional commercial plants are in the development stage. Production of improved grades of benzol products, by replacing acid washing of light oils with hydrogenation and the use of coke oven gas for the hydrogenation process, is fairly new as is also the application of the Udex process to toluol puriiication. Microsieve technique and azeotropic distillation for benzol refining is being investigated. Synthetic ammonia production utilizing the hydrogen
content of coke oven gas, is becoming prevalent. Several plants are replacing the customary production of ammonium sulfate by diammonium phosphate and are establishing control methods. Also, the pelletizing ofdiammonium phosphate is particularly intriguing because of the low t e m p e r a m e of decomposition of this material. Passing mention only can be made of the thousands of compounds made from the crude coal cbemicals and on which research is being continued.
Coking Coals I t is most difficult to give a definition for a “good coking coal.” Gradually the use of the word “good” is being replaced by “satisfactory.” And by satisfactory is-meant that a coal or blend of coals produces a coke which, in turn, permits a blast furnace practice rully competitive in quality, efIiciency, and cost. I t is only rarely that a single coal is available for making a satisfactory coke; blending of two or more coals of different properties is the rule at the great majority of coke plants. while a simple twosoal blend of high and low volatile coals is most common, there are cases in which the use of a third coal VOL. SO, NO. 1
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or other blending material is advantageous. As an example, the coking coals of Utah are of low fluidity and the use of medium-volatile high-fluidity coal has been found desirable as a third constituent. I n certain locations and with similar types of coals, coal tar pitch, petroleum coke breeze, asphaltite, and other bituminous materials have been tried and in some cases have been used commercially with success. Much material has been published on the blending of coal (7, 9, 77, 27, 23).
Availability of Satisfactory Coals In localities where satisfactory coals are not readily available, the greatest attention is given to ways and means of remedying the situation. Although this problem is encountered in many places throughout the world, five of them in particular are known to the author. They are 1. The Midlands District of England where a large supply of high volatile coal is available and where low volatile coal must be secured from South Wales; 2. The Lorraine District of France and the adjacent Saar, also having only high volatile coal deposits and where the nearest supply of low volatile coal is found in the Ruhr District of Germany; 3. Chile, where the coal is of low fluidity and where coal for blending is secured largely from the United States; 4. The far western section of the United States where the readily available coals are also of low fluidity and where the nearest source of low volatile coal is in Oklahoma; 5. Japan, where char was substituted for low volatile coal during and after World War 11, but where it is now thought to be more economical to import low volatile coal from the United States (76, 26). Each of these districts has its own particular problems and results secured in one do not necessarily apply in equal measure to the others. Regardless of the specific nature of the individual problems, in general it is the same, “What can be done to make a satisfactory coke from readily available coals?” This article describes some of the work being done throughout the world to find the ansbver to this question. Background I t must not be inferred that no successful results have been achieved in the past along this line of endeavor. The washing of coal, practiced for many years, definitely improves the chemical nature of the coke and generally improves its physical properties as well. Compacting the charge by stamping of the coal before charging into the ovens, in order to increase the bulk density of the charge, has been successful for many years,
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INDUSTRIAL AND ENGINEERING CHEMISTRY
particularly in Europe. The bulk density of the charge has also been increased, although not to the extent secured by stamping, either by adding oil or by controlling the moisture content of the coal. In this latter case, when working with a coal of the water content giving minimum bulk density, either increasing or decreasing the water content gives the same results-an increase in the gross and net bulk density of the coal. The proper degree of pulverization of the coal is important-the finer the pulverization, of course within reasonable limits, the better the coke. Proper charging of the ovens reduces variations in quality between coke produced in different sections of the ovens. All of these have been tried and their value has been determined; many of the practices so discovered are noJv used. I n many cases further work is necessary, and the rapid depletion of some grades of coal is an important factor in this opinion.
Research Organizations As expected, the type and amount of carbonization research now under way varies widely between the different countries. It should be pointed out that not all coal research organizations are devoting their full time to carbonization research. Many are ivorking on problems related to the use of coal as an industrial or domestic fuel and many are primarily interested in the application of coal as a raw material for the chemical industry. Various research organizations are listed, for want of a better method, under their sponsorship. First are those sponsored by the various governments; examples of which in this country are the United States Bureau of Mines and the Illinois State Geological Survey. Then there are the public organizations, usually endowed and where specific research work is performed under contract; prominent among such are Mellon and Battelle Institutes. This same group should probably include those sponsored by a number of colleges and universities, many of which are in a position to perform contract work. Pennsylvania State University, Colorado and Missouri Schools of Mines fall in this latter group. Industrial organizations may sponsor research work either through trade associations or individually. Bituminous Coal Research is an example of the first group although their work on carbonization problems is limited. While not actually operating as research laboratories, the American Iron and Steel Institute, the American Institute of Mining, Metallurgical Petroleum Engineers, the American Gas Association, the American Society of Testing Materials, the American Coke and Coal Chemicals Institute and others have carbonization committees, some of them dedi-
cated to and all of them interested in carbonization research. Outstanding among the laboratories operated by individual industries is U. S. Steel, Monroeville, Pa. Coke-oven contractors also are operating research laboratories, both Koppers and Willputte are active in this country. Private research laboratories are also operated, the Fuel Research Laboratory, Indianapolis, is an example. And a similar distribution of sponsorship and a long list of research laboratories are found throughout the European countries. Outstanding among these are-in England, the Fuel Research Station of the Department of Industrial and Scientific Research, the Stoke Orchard Laboratory of the National Coal Board, and the Pontppridd Laboratory of the British Coke Research Association. Outstanding among industrial laboratories is the United Coke and Chemicals Co., at Orgreave. In France, the Center for Study and Research on Carbonization, and in Germany, the Essen Laboratory of the German Coal Mining A4ssociation are outstanding examples on the Continent (3: 78, 79).
Basic Research The various items of basic research now in progress are studies on the petrographic constituents of coal and the conducting of spectrochemical analyses of coal and coal impurities. The nature of the bitumen content of coal and the effect of variations in this are also interesting subjects of basic research. Studies of plasticity and of the expansion characteristics of coal and the interrelationship of the tivo indicate that plasticity is by far the more important when considering coals for blending. Plasticity us. Volatile Evolution. A n interesting experiment conducted in both Germany and France consists of the determination of the temperature ranges of plasticity (as measured by the Gieseler or similar plastometer), and of volatile evolution. I n most cases the peak rate of each of these, for a given coal, was found to fall within the same range of temperature. Li’hen this condition is observed, the coals under consideration may be considered as compatible. But this condition does not always occur, and with certain coals the peak rate of volatile evolution may occur within a different temperature range from that of the maximum plasticity. In such cases, the quality of the coke produced from a blend of coals including a coal of this nature was found to be inferior to that produced when all coals are indicated to be compatible (28). Contraction. Another test of interest is the comparison of the temperature of solidification us. the degree of con-
COKING METHODS AND PRODUCTS traction of the solidified mass. T o determine these, a small sample of the coal is carbonized in a furnace so arranged that the heat travels in a horizontal direction from the walls toward the center of the charge. The coke blocks thus made from various coals and blends are compared by observing the nature of the coke formed and by counting the number of fissures appearing on the surface. Fissuring is taken to be an index of contraction, and as contraction is reduced by applying various blending techniques or by temperature control, so also does the number of fissures decrease (28). Solvent Extraction. Solvent extraction studies have been made on coking coals. Using pyridine as the solvent, these studies give information regarding the chemical constituents and structure of coals and may show the different behaviors of various coals during the coking process ( 3 ) . Use of Fine O r e Inert. Fine pyritic iron residues from sulfuric plants are used by mixing them with coking coal. Carbonization of coke so prepared, using mixtures of this very fine oxide up to a limit of 7%, improves the shatter index but generally impairs the resistance of the coke to abrasion (73). Coke Research. Fundamental research may also be applied to coke. Cgkes made from identical coals a t different coking plants do not always give the same results when used in a blast furnace. Therefore, the average analysis of coke may not always indicate the real differences which may exist between different portions or pieces, as these differences are concealed by averaging the samples or results. Accordingly, a system has been devised for sampling representative portions of coke produced at various but definite distances between the walls and center of the oven, These samples are taken by cutting the coke prisms on a plane parallel to the wall end of the piece by a brick saw or other suitable means. These small samples are then grouped into larger samples representing the coke produced a t definite distances from the oven wall and are tested individually. Tests to which they are subjected include the determination of the volatile content, the wetoxidation rate, and the microstrength. The data from these three tests are plotted on a single chart against the point of origin. By comparing the various charts, interesting and valuable conclusions can be reached regarding the efficiency of carbonization of the ovens in which the coke was produced ( 75)* Domestic Coke. Because of smoke conditions, the use of coal as a domestic fuel is discouraged in England and an effort is made to replace it with small
sizes of coke. The relatively low reactivity of coke, however, introduced problems both of ignition and of maintaining fires, particularly in open grates which are common in that country. The possibility of correcting this condition by blending with poorly coking coals was investigated (74). Practical Research. Research in coal carbonization practice is largely concerned with the methods of determination for satisfactorily reducing or eliminating the amount of low or medium volatile coal needed in the blends. Several methods of accomplishing this have been tried with varying degrees of success, all of which show sufficient promise. Use of Char. The fact that lowtemperature char can in many cases satisfactorily replace low volatile coal in blends for the preparation of metallurgical coke is not a new discovery and over 25 years ago was described by men from three different countries (30, 37, 33). I t still ranks high among the possibilities for solving the worldwide problem and is a common line of endeavor. The chief problem is not to determine if char will do the work but rather the best method to produce the char (22). One plant in the Northern Section of France has produced Carbolux for some 25 years for use as a domestic fuel. Carbolux is produced by first partially devolatilizing high volatile coking coal in oxidizing and carbonizing drums at low temperatures; one third of such char is then mixed with two thirds of the base coal and is coked in standard coke ovens. The result is a domestic fuel which has combustibility characteristics approaching charcoal. Char is now produced on an experimental basis at the Marienau Laboratory in Lorraine and a pilot plant test is under way in the Ruhr District of Germany. Several recent pilot plant installations have been made in the Midlands District of England and a commercial plant is reported to be ready for operation in Eastern France. Experimental work on char production and use has been conducted in the United States at a number of locations (20, 24, 25). Although coke made in blast furnaces from a mixture including char has not been used extensively other than for certain experience in Japan (76), two short runs, 6- and 30-day duration a t two locations, indicate that it is satisfactory. Precompression. As an alternative method to stamping for increasing the bulk density of the coal charge, a system of precompression has been tried for several years in Eastern France and a commercial installation has recently been installed. I t is known that when washed coal is crushed, its bulk density
is lowered because of the entrainment of air by the fine coal particles. This new system involves the passing of the fine washed coal between rolls at high pressure and its formation into a sheet or ribbon with a bulk density approaching 70 pounds per cubic foot. This compressed cake or ribbon is then broken, before charging, to whatever degree is necessary to give the desired bulk density in the oven. By this means, one case is recorded where the coal density was raised 20% (from 45 to 54 pounds) with the result that the amount of high volatile coal in the mixture increased from 30 to 60% without affecting the quality of the coke. Selective Crushing;. A selective crushing method was employed a t the Thionville plant in Lorraine. The washed coal, -10 mm. in size, is screened and separated at 2 and 4 mm. The fraction under 2 mm. contains mainly the concentrated vitrain and clairain. The 2- X 4-mm. fraction consists largely of durain. The fraction over 4 mm. consists of particles containing all three petrographic constituents. This fraction is subjected to mild crushing in order to separate these constituents and then is recirculated and is rescreened with the original coal. The two finer fractions are then treated separately. The purest coal is found in the -2-mm. fraction and this remains as is. The 2- X 4-mm. fraction is crushed to -1 mm. and is added to the -22-mm. fraction. Or, depending on the nature of the coal, this 2- X 4-mm. fraction may be partially devolatilized or further cleaned before being added to the cleaner coal fraction. In the first of these methods, finer pulverization of the durain, the Micum 40 index of the coke was increased from 60 to 76 and the 2-inch shatter index from 70 to 89 (6, 7). Ferro-Coke. Ferro-Coke is manufactured on a full commercial scale at one plant at Walsum in the Ruhr District (2). Fine magnetic iron ore is added to the high volatile coal in proportions of about 30% ore to 70% coal. The product is a very heavy and strong coke in which u p to 60% of the ore is reduced to metallic iron. Claims made for this process are improvement in strength of coke made from high volatile coal; disposal of fine ore or flue dust; reduction of the requirement of sintering plants for coke breeze; and reduction of fuel consumption in the blast furnace. Objections to the process are found: in the binding of a large portion of the original sulfur of coal in the coke in form of iron sulfide; limited uses to which the breeze can be put because of its iron content; and possible damage to silica oven walls. While it is claimed that no damage will VOL. 50, NO. 1
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occur to the silica brick walls if their temperatures are not allowed to exceed 2150’ or 2200°, this process is not favored in Britain because of this possibility. In the United States, an extensive test on the production and use of iron coke was made at a plant of one of the larger steel companies (29). D r y Quenching. The Ford Motor Co. at Dagenham, near London, is one of the few plants in the world using the Sulzer dry quenching process. The claim is made that the thermal shock caused by applying water to hot coke is avoided and that the resultant incipient fractures which tend to reduce its resistance to shatter loss are eliminated. As a result of rougher handling, the coke as produced is smaller in size but shows fewer indications of cross fracturing and has an improved shatter index than does wet-quenched coke made from the same coal mixture. Thus this process results in improved strength of coke, in an increased coke and decreased breeze yield a t the ovens, and in the generation of more steam in the dry quenching unit than is needed for the operation of the entire coke plant (77). Hot Water Quenching. The use of preheated water for quenching of coke has been advocated by a number of coke oven operators but considerable disagreement has been expressed regarding its benefits. Those in favor of its use report improved strength of coke with reduced residual moisture in the quenched coke as well as noticeable improvement in blast furnace practice (32). Briquetting. I n certain districts of Europe, including those now occupied by Russia, available coals are entirely lacking in coke producing qualities. At these locations, noncoking subbituminous coals and lignites are briquetted with a suitable binder, carbonized, and used as blast furnace fuel. Although the blast furnaces perform satisfactorily on this fuel, details are lacking (4). This same procedure has been carried out in Australia (5). International Cooperation. England, Germany, Holland, France, and possibly other countries in Europe have their own systems of classifying coals but none of these are the same as the system used currently in the United States. The rapid increase in international cooperarion which has occurred during the past few years and the increase in the number of international conferences make it highly desirable to eliminate the misunderstandings and confusion which arise from this condition. There are a number of organizations through which this cooperation is fostered-the Economic Commission for Europe, the Organization for European Economic Cooperation, the International Standards Organization, and the European
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Coal and Iron Community. One of the matters now under consideration is to establish an International Coal Classification System. The European countries also have their individual systems of coke classification and of coke testing. Physical strength may be determined by a number of different types of tromme1 or tumbler tests. The shatter test is also subject to a number of variations. The standardization of sampling procedures, the adoption of standard methods for testing chemical and physical properties, and the setting up of a uniform method of classifying coke, are all now under consideration. Hence, within a few years the International designation in these regards map be standardized.
Conclusion The use of low temperature char as a substitute for low volatile coal appears to be most widely favored in all of the countries investigating coke improvement methods. Although the use of rotary retorts of various types has by no means been ruled out, and several types of vertical retorts are in use, the fluidized bed process appears to be in highest favor. One reason for this is the potentially greater throughput capacity of a single retort of this type. The chief requirement for a low temperature process is that the char produced in it should make a satisfactory blast furnace coke. In spite of this apparent preference for char, there still are a large number who are not convinced that this is the only way. They still are hopeful to find another way, possibly more economical or more desirable for any of a dozen reasons. Finally, there are indications that the research engineer may come up with an entirely new process of smelting iron ore and that coke may be eliminated from the picture. If and when that day comes, the carbonization research engineer must turn his attention and energies toward other fields of research.
Literature Cited (1) Bardgett, H., J . Znst. Fuel (London) 27, 274 (June 1954). (2) Barking, H., Eymann, C., Gliickauf 39/40, 993 (Sept. 1953). 13) ~, Blavden, H. E., Yearbook of Coke Oven’ Managers’ Assoc. (British), Location 290, 1955. (4) Brit. Iron and Steel Fed., London, “Steel Developments in Eastern Germany,” October 1954. (5) Broadbent, R., Donnelly, R. P., Platell, N., J. Znst. Fuel (London) 28, 3, (January 1955). (6) Burstlein, E., Chaleur &3 ind., Paris, 36 (January 1955). (7) Coke and Gas (London), 18, 246, 288, “The petrographic preparation of coals for coking” (Editorial), (JulyAugust 1956). (8) Davidson, J. G., “Coal and the Chemical Industry,” National Coal Assoc., Washington,D. C., June 14: 1956.
INDUSTRIAL AND ENGINEERING CHEMISTRY
( 9 ) Dryden, I. G. C., Griffith, M., Kirby, R. .4., Coke and Gas (London) 17, 272, (July 1955). (10) Fleming, G. L., Bull. CEP-56, Operation Section, Am. Gas ASSOC., Philadelphia, Pa., May 1956. (11) Foxwell, G. E., J . Znst. Fuel (London) 22, 346 (October 1949). (12) Foy, F. C., “The potential use of coal fox. the production of chemicals,” Bituminous Coal Research, Pittsburgh, Pa., May 1956. (13) Fuel Research Station (Dept. of Industrial and Scientific Research, London), 1954 Rept., 11. , (14) Zbid., 1955, p. 3. (15) Hewett, F. J., Riley, H. L., Savage, P., Yearbook, Coke Oven Managers’ Assoc., (British), Benn Bras. Ltd., London, p. 185, 1953. (16) Hisada, K., Japan Scientific Rev., 2, No. 1 (1951). (17) Jackman, H. W.,Eissler, R. L., Reed, F. L., Illinois State Geol. Survey, Urbana, Ill., Circ. 219, 1956. (18) Loison, R., “Rapport sur l’activite de la station experimentale de Marienau en 1953,” Charbonnages de France, (Paris), May 1954. (19) McCabe, L. C., “Coal Research of the U. S. Bureau of Mines,” Bituminous Coal Research, Pittsburgh, Pa., April 1955. (20) Minet, R. G., “Continuous Fluidized Carbonization of Bituminous Coal,” Am. Coke and Coal Chem. Inst., Rye, h7.Y., May 1956. (21) Powell, A. R., United Nations Publication Sales No. 1954, 11. 6.3, vol. 11, p, 91, Economic Commission for Latin America, Bogota, Colombia, October 1952. (22) Price, J. D., Proceedings: Rocky Mountain Coal Minine Inst.. Glenwood Springs, Co10.y p. 30; June 1956. (23) Price. J. D., Trans. Am. Znst. Minin? Met. Engrs. 196, 726. (1953). (24) Price, J. D., Woody, G. V., Coal Division, Tech. Publ. 1745-F. 155, Am. Inst. Mining Met. E’ngrs.; h-ew York, February 1944. (25) Reed, F. H., Jackman, H. W., Henline, P. W., Illinois State Geol. Survey, Urbana, Ill., Rept. of Invest. 187, 1955. (26) Reid, W. T., U. S. Bur. Mines, (Supt. Documents, Washington 25, D. C.) Inf. Circ. 7430, 1948. (27) Rose, H. J., Glenn, R. A,, IND.ENG. CHEM.48, 350 (1955). (28) Riley, H. L., United Coke and Chemicals Co. (Sheffield), “Notes on the Carbonization Conference of the European Coal and Iron Community,” Paris, July 1953. (29) Russell, C. C., Whitstone, P., Liggett, R. P., Proceedings, Am. Inst. Mining Met. Engrs. 14, 93, (April 1955). (30) Shimomura, K., Chem. & Ind. (London) (June 8, 1921). “ A method for makin5 non-fingery coke from bituminous coal high in volatile matter.” (31) Thau, A . , “Die Schwelung von Braun und Steinkohle,” Wilhelm Knapp, Halle (Saale), 1927. (32) Thomas, J. Mi., Proceedings, Am. Inst. Mining Met. Engrs. 13, 96 (April 1954). (33) West, J. G., U. S. Patent 1,445,735 (1923).
RECEIVED for review April 10, 1957 ACCEPTED December 2, 1957 Division of Gas and Fuel Chemistry. 131st Meeting, ACS: Miami, Fla., April 1957.
