US3075889A - Two-stage coking psocess - Google Patents

Description

TWO-STAGE COKING PROCESS Filed Aug. 13, 1959 m 9* INVENTOR.

Ware

Filed Aug. 13, 1959, Ser. No. 833,504 7 Qlaims. ((Il. 202-22) The present invention relates generally to a process of producing metallurgical coke from carbonaceous material, and more particularly, to a two-stage process of producing metallurgical coke from a finely divided fusible coal wherein valuable by-products are recovered along with highquality metallurgical coke.

The production of a high-quality metallugical coke containing not substantially in excess of about 1% by weight volatile matter from coal, is conventionally achieved by heating the coal in a coking oven to relatively high temperature (1800 F), during which heating the particles of coal are agglomerated into a unitary solid structure and much of the organic volatile matter is thermally distilled as relatively low molecular weight hydrocarbon compounds and other compounds of varying economic value. The type of coal which has been considered usable for the production of metallurgical coal has heretofore been quite limited, and some coal, such as 100% lllinois coal, has never been considered useful for the production of high-grade metallurgical coke.

Where attempts are made to recover substantial amounts of the organic volatile matter contained in coal, the coal heretofore has been heated at relatively low temperatures (7001100 F). The residual char which remains, however, has a very frangible structure with a low compression strength index which is limited to use as a fuel in power plants or the like and cannot be used for the manufacture of metallurgical coke.

it is, therefore, a primary object of the present invention to provide a more economical process of producing high-grade metallurgical coke containing not substantially in excess of 1% in weight volatile matter.

it is another object of the present invention to provide an improved process for economically producing a highgrade metallur ical coke from coals which have heretofore been considered unsuitable for the production of highgrade metallurgical coke.

It is a still further object of the present invention to provide an improved process for making metallurgical coke from finely divided carbonaceous material while recovering substantial amounts of valuable volatile chemical by-products.

Other objects of the present invention will be apparent to those skilled in the art from the detailed description and claims to follow when taken with the accompanying drawing, wherein The FIGURE of the drawing shows a schematic view of suitable apparatus for carrying out the process of the invention.

The foregoing and other objects of the present invention are achieved by employing a two-stage coking operation wherein a quiescent mass of coal, or other fusible carbonaceous material in a finely divided form or a compressed form of finely divided carbonaceous matter, is first subjected to a relatively low temperature heating or first coking stage at a temperature between about 1200 and 1500 F., during which heating stage sufiicient internal agglomeration strength is imparted to the coal to enable the mass to withstand the stresses incidental to high temperature heating and to transfer to a high temperature heating or second coking stage without damaging the internal structure and without destroying significantly the valuable volatile organic products therein. Thereafter,

hired rates Patent ice the partially coked coal is subjected to a high temperature heating stage at a temperature of about 2000 F., and not substantially in excess of about 2400 F., during which treatment a high-grade metallurgical coke having not substantially in excess of 1% by weight volatile matter is formed.

An essential requirement of the instant two-stage coking process is that the freshly formed low-temperature coke produced in the first heating stage is not subjected to external stresses during the heating stage until the mass has been heated to a temperature of at least 1200 F, and preferably a temperature of 1400 F., in order to avoid interference with the agglomeration of the coke into a rigid mass. It is also essential in the practice of the instant invention, that one employ completely independent temperature segregated zones for the two stages of the coking operation, and that the heating be eifected by external means. When the coking process is performed in the above described two-stage manner, the average practical size of the resulting coke produced by the instant combined low-high temperature coking process is found to be approximately three times as large as the metallurgical coke produced by the conventional high-temperature coking process from the same coal. In addition, substantial amounts of valuable organic chemicals are obtained from the low-temperature tars and other volatile matter recovered during the coking operation. This is in marked contrast with the previous attempts to manufacture coke by distillation in two steps, since the quality of the coke obtained by the previous two-stage coking operations has not been essentialy different from the char obtained by the ordinary distillation procedure. Nor has full advantage heretofore been taken or" the chemicals produced during the production of metallurgical coke.

An important feature of the present invention which makes the process adaptable to commercial operation is the formation of coke of relatively high strength in the first or low temperature heating stage. The unusual strength imparted to the coke in the low-temperature stage is achieved by heating the pulverized coal or compressed pulverized coal to a temperature between about 1200 and 1500 F. and preferably to about 1400 F. before subjecting the coke to the high-temperature heating in the secondary heating zone. Unless the coke is thus heated in the first stage, there is insufficient binding or agglomeration of the coal particles to form a unitary structure and to permit transfer of the mass to the high temperature stage without destroying to a significant degree the agglomerated structure of the coke. The further heating of the coke in the second or high-temperature stage, up to a temperature of about 2000 F. but not substantially higher than about 24-00" F. fixes the desired structure and provides metallurgical coke of high strength, low volatile matter content, and unusually large particle size. It should, of course, be understod that the best operating temperatures for a particular coal will vary within the temperature ranges specified above depending upon the composition of the particular coal or blend of coal being coked.

The chemical composition of a typical low-temperature tar obtained in the instant two-stage distillation metallurgical coking operation is comprised generally on a weight basis of about 41.4% distillate oils, 51.8% pitch, with about 6.8% distillation loss. Most of the valuable chemicals are found in the distillate oils which are comprised of phenols, cresols, xylenols, resorcinols, oleiins, and other aromatics and parail'lns. In a typical operation in which the liquid and gaseous by-products of the separate high and low-temperature coking stages are combined prior to further processing, about 20 to 25 gallons of tar per ton of coal is recovered in the low-temperature coking stage, as compared with about 5.5 gallons of accuses 2% tar in a conventional high-coking temperature coking operation, and without any lowering of the quality or quantity of the metallurgical coke produced.

The data presented in Table I show a comprison between the coke and by-products produced by the herein disclosed process (Case A), a typical low-temperature cooking operation (Case B), and a typical high-temperature coking operation (Case C).

Table I Case A- Case B- Case Colre Composition, dry (100% Low-High Low High lllinois coal) Temp, Temp, Temp.,

percent by percent by percent by weight weight weight 1 10. 7 8. 52 10. 70 2 0.80 20. 00 0. 80 3. $7. 75 69. 80 87. 80 4. Sulfur 0.70 0.98 0.70 5. Yield (total, dry basis)... 62.00 81.00 65.0 6. Breeze 0.5 0.5 2.5 Size (average, inches) 3. 5 3.5 1.2 High Temperature Gompre Strength Index, p.s.1 3,740 1,000 3,900 Tumbler Stability.-- 57-59 20 42. 5 Tar Volume, gaL/ton 25. 5 22. O0 5. 5 Heating Value of Tar, 103 B.t.u.,'

gal 135 127 145 Gas Volume, ttfi/ton 7.. 0 6. 0 10. 5 Heating Value of Gas, Btu. 850 900 530 Benzol, Toluols, ete., gal/ton-.. 1.9 1.7 2.3

It is also possible in practicing the instant process, to divide the volatile distillation products into low-temperature and high-temperature components, so as to produce two distinct gaseous products. The low-temperature gas obtained would be comprised essentially of methane (65- 85% by volume) with small amounts of ethane, ethylene, and hydrogen. The high-temperature gas would be comprised of relatively large amounts of hydrogen with relatively low amounts of methane and other aliphatic hydrocarbons which would be of use as a fuel, or could be used for reduction purposes in metallurgical processes.

The process of the present invention which utilizes to the upmost limit the full agglomeration power of the coal can be carried out in a variety of equipment both conventional as well as equipment which is especially adapted for the process. One type of equipment which is capable of being used to carry out the instant process is shown in the accompanying schematic drawing wherein designates one of a plurality of low-temperature coking compartments generally rectangular in form and constructed of cast iron, silicon carbide, or refractory brick, or other relatively heat resistant material. Disposed above the compartments 10 are a plurality of coal charging hoppers 11 which feed pulverized coal into the compartments 1%. The pulverized coal 12 is supported in the compartment 19 by a stationary lower wall 13. The opposed lateral wall sections or doors 14, 15, respectively, are movable to permit a pusher and moving the coke in the lower portion laterally out of the said low-temperature coking compartment into the adjacent high-temperature heating compartment 17 which is in direct communication with the lower portion of the compartment it). When the coal in the low temperature zone 10 reaches its proper temperature (Le. 1400 F.) after about 7 hours heating, at which time it is in a solid agglomerate form, the pusher arm 16 engages one of the lateral faces of the mass of low-temperature coke or coal 12 and slides the mass laterally Without significantly disturbing the internal structure of the agglomerated coal particles into the high-temperature compartment 17 where it is heated to a temperature of about 2100 P. in a period of about 1.5 hours. The pusher arm 16 is so constructed that incompletely heated coal does not enter the lower section of the low temperature heating zone until the pusher arm 16 is retracted from the said zone 10. When the compartment 17 contains completely formed metallurgical coke, the coke is allowed to cool and the cooled metallurgical coke in compartment 17 is first arm 16 entering the compartment 10 removed by raising one of the discharge doors 18, to permit the coke to drop into a suitable skip car 19.

The volatile tars and gases from both the low-temperture compartments 10 and the high-temperature compart ment 17 are withdrawn through a. suitable common collection main 2d although separate collection mains can be used, if desired. Heating the coking compartments 1% and 17 should be by indirect means where the finely divided form of the coal is used in order to obtain a dense, high compression strength coke, and is preferably accomplished by providing a plurality of wall burners (not shown) in the high-temperature compartment 17 and conducting the combustion gases downwardly through wall ducts and thence into the lines of the low-temperature chamber which conduct the gases at a much lower temperature upwardly through wall ducts past the lowtemperature chamber 10 where additional wall burners are provided as required. Additional heating facilities may be provided for compartments 1% and 17 wherever required. It will be understood that the high-temperature compartment 17 is made of highly heat resistant refractory brick or similar heat resistant material. It has been found that in the low temperature zone the desired coking temperature of about 1400 F. proceeds inwardly from the walls at a total rate of /2 to 1 inch per hour. In the high-temperature zone the final coking temperature of about 2100 F. proceeds inwardly from the walls at a total rate of at least two inches per hour and often asmuch as six inches per hour. A rate of two inches per hour is not attainable in the present high temperature process where distillation must be effected before the high temperature of 18002000 F. is reached.

In one specific application, the apparatus illustrated herein is charged with a unit quantity of finely divided pulverized coal which is preferably crushed and screened and which has at least less than /s in diameter (6 mesh, U.S. St.), such as Illinois coal, with the walls of the low-temperature compartment it} being maintained at a temperature of about 1500 F. at the lower end and about 1200" F. at the upper end until the center of the charge of pulverized coal reaches a temperature of about 1400 F. in the low temperature zone, whereupon the pusher door 15 is opened and the low-- temperature charge is moved bodily into the high-temperature compartment 1'! by means of the pusher arm I6 moving inwardly. The walls of the high-temperature compartment 17 are maintained at a maximum temperature of about 2400 F. and the charge is retained thercirs until the center of the charge reaches a temperature of about 2000" R, whereupon the door 18 is moved inwardly to eject the completely coked charge into a car.

It should be understood that the herein disclosed lowhigh temperature process for producing high quality metallurgical coke is capable of being carried out in equipment other than that described herein. Thus, for example, both stages of heating could be carried out in a single retort having at spaced points therealong distinct temperature zones and the process carried out in a continuous or semi-continuous manner.

It will be apparent from the foregoing detailed description, that the present invention provides a process for making high-grade metallurgical coke from marginal coking coals which heretofore were considered unsuitable for use in making metallurgical coke. The present proc ess also makes it possible for the manufacturer to take full advantage of the valuable organic chemicals contained.

in the coal and which are normally destroyed to a large: high-- grade metallurgical coke. Also, applicants process pro-- vides a means for taking maximum advantage of the ag-- degree in the conventional process for producing glomeration powers of the coal by providing low-temperature coke with suificient internal strength so that the coke agglomerate or structure thereof is not destroyed or degraded when transferred to or heating in the hightemperature coking stage, thereby making it possible to use coals which heretofore could not be used to make high grade metallurgical coke. The improved structure of the metallurgical coke produced by the present process is fully evident from a comparison of the several types of coke as shown in Table 1 herein.

In the specification and claims, the term fusible carbonaceous material is intended to designate coals, mixtures of coals or lignite, or the like, which are capable of coking and which pass through a plastic state on heating and are therefore capable of forming an autogenous binding during carburization. In general, coals having at least about 12% volatile matter in the natural state (as mined) can be used in the present process to make high-grade metallurgical coke. Thus, while the present process is applicable to a wide variety of coals, it is particularly applicable to marginal coals which have heretofore not been used for making high grade metallurgical coke, such as 100% Illinois coal. If desired, the finely divided coal can be tamped in the low-temperature chamber before heating to increase the density or can be briquetted to any desired size.

I claim:

1. A process for producing metallurgical coke from Illinois-type coal which contains at least about 12% by weight volatile matter comprising; indirectly heating a quiescent mass of finely divided Illinois-type coal in a first stage heating zone at a temperature between 1200 F and about 1500 F. to provide a partially coked mass of carbonaceous material having internal agglomeration strength to withstand stresses incident to transfer to and treatment in a high temperature coking zone without damaging the internal structure thereof, and thereafter transferring the partially coked product of the first stage heating zone to a second stage heating zone and rapidly heating therein to a temperature of about 200 F. and not substantially above about 2400 F., and recovering a high grade metallurgical coke product containing not substantially in excess of about 1% volatile matter and volatile organic tars and gases.

2. A process for producing metallurgical coke from fusible carbonaceous material comprised essentially of Illinois No. 6 coal which has at least about 12% by weight volatile matter comprising; indirectly heating a quiescent mass of pulverized Illinois No. 6 type coal having at least 90% by Weight less than in diameter in a first stage heating zone to a temperature of between 1200 F. and 1500 F. to provide a partially coked mass having sufficient internal agglomeration strength to withstand transfer en masse to and heating in a second stage high temperature heating zone without damaging the internal structure thereof, transferring the partially coked coal from the first stage heating zone en masse to a completely independent temperature segregated second stage high temperature heating zone without disturbing the internal structure thereof, and rapidly heating the partially coked product in the said second stage heating zone at a temperature of about 2000 F. and not substantially above 2400 F. and recovering a high grade metallurgical coke containing not substantially in excess of about 1% volatile matter and volatile organic chemical products.

3. A process for producing metallurgical coke and volatile organic chemicals as in claim 2, wherein said Illinois coal is heated in the first stage heating zone to a temperature of about 1400 F. and the partially coked product is heated in the second stage heating zone to a temperature of about 2100 F.

4. A process for producing metallurgical coke and volatile organic chemicals as in claim 2 wherein the said volatile products from the said first heating zone are recovered separately from the volatile products from the said second stage heating zone.

5. A process for producing metallurgical coke and volatile organic chemicals as in claim 2 wherein the said volatile products from said first stage heating zone and said second stage heating zone are combined in a single recovery system.

6. A process for producing metallurgical coke as in claim 2 wherein said pulverized coal is heated in said firststage heating zone while in the form of a loose charge 'of finely divided coal.

7. A process for producing metallurgical coke as in claim 2 wherein said pulverized coal is heated in said first-stage heating zone while in a compressed form of finely divided coal.

References Cited in the file of this patent UNITED STATES PATENTS 1,496,053 Illingworth June 3, 1924 1,621,222 Robertson Mar. 15, 1927 2,066,083 Vanelesgrift et al Dec. 29, 1936 2,247,185 Caccioppoli June 24, 1941 2,922,752 Reintjes Jan. 26, 1960

Claims (1)

1. A PROCESS FOR PRODUCING METALLURGICAL COKE FROM ILLINOIS-TYPE COAL WHICH CONTAINS AT LEAST ABOUT 12% BY WEIGHT VOLATILE MATTER COMPRISING; INDIRECTLY HEATING A QUIESCENT MASS OF FINELY DIVIDED ILLINOIS-TYPE COAL IN A FIRST STAGE HEATING ZONE AT A TEMPERATURE BETWEEN 1200*F. AND ABOUT 1500*F. TO PRIVIDE A PARTIALLY COKED MASS OF CARBONACEOUS MATERIAL HAVING INTERNAL AGGLOMERATION STRENGTH TO WITHSTAND STRESS INCIDENT TO TRANSFER TO AND TREATMENT IN A HIGH TEMPERATURE COKING ZONE WITHOUT DAMAGING THE INTERNAL STRUCTURE THEREOF, AND THERAFTER TRANSFERRING THE PARTIALLY COKED PRODUCT OF THE FIRST STAGE HEATING ZONE TO A SECOND STAGE HEATING ZONE AND RAPIDLY HEATING THEREIN TO A TEMPERATURE OF ABOUT 200*F. AND NOT SUBSTANTIALLY ABOVE ABOUT 2400*F., AND RECOVERING A HIGH GRADE METALLURGICAL COKE PRODUCT CONTAINING NOT

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