US3073751A

US3073751A - Method of making formcoke

Info

Publication number: US3073751A
Application number: US46796A
Authority: US
Inventors: Gorin Everett; Robert J Friedrich
Original assignee: Consolidation Coal Co
Current assignee: Consolidation Coal Co
Priority date: 1960-08-01
Filing date: 1960-08-01
Publication date: 1963-01-15
Anticipated expiration: 1980-01-15

Description

Jan. 15, 1963 E. GORIN ETAL METHOD OF MAKING FORMCOKE Filed Aug. 1. 1960 NON-CONDENSABLE GAS S N M. OCONDENSABLE GAS N 8 E 0/ 7 w 8 CONDENSER m S S T M. EN.- 4 7 m s m m 7 H 0 2 m C 7 w m E O K N 8 O fi 5 CALC NER C 8 o m 4 5 V F CONDENSER O 7 6 z m 5 O CALC NER v 4 L M R 2 R 4 M 0 CONDENSER PM 4 F S w A w a 6 z w m G H 0M R N k E R E RM M L H L l 6 l B m D M R E CARBON ZER M E n H k L m INVENTORS EVERETT GORIN ROBERT J. FRIEDRICH BY Lpfl fiwgz PITCH ATTORNEY 3,073,751 METHGD 6F MAKING FORMCGKE Everett Gorin, Pittsburgh, and Robert J. Friedrich, Finleyville, Pa., assignors to Consolidation Coal Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. l, 1960, Ser. No. 46,7% 7 Claims. (Cl. 202-26) This invention relates to the production of formcoke from caking bituminous coals, and, more particularly, to the production of a formcoke which is suitable for use in conventional blast furnaces.

The supply of caking coals particularly suitable for making metallurgical coke in conventional coke ovens is limited. it would be highly desirable to develop a method of making coke that would be relatively independent of the restrictive specifications imposed upon the coals now employed in current coke plants. in particular, it would be desirable to make coke from any caking bituminous coal which would be equal to or superior to that coke which is now made from very special blends of coking coals. Such an accomplishment would extend the reserves of coal available for the metallurgical market.

This invention is primarily concerned with making coke from mixtures of a caking bituminous coal and the solid distillation residue of previously distilled coal, with or without the addition of pitch. Formulations of this general type have been used before in attempts to make coke. These formulations have been transformed by briquetting presses, by tumbling as in a rotary retort, or by other means into briquets or agglomerates of predetermined sizes. The term formcoke has been used to describe such products in a calcined state and is so used herein. In general, the formcokes so far produced have been inferior to conventional coke with respect to their porosity, density or strength. In particular, their strength has not been adequate to sustain the burden of a conventional blast furnace, albeit adequate in some instances for low shaft furnaces and the like. In the copending application of Friedrich et al., Serial No. 635,277, filed January 22, 1957, now abandoned, there is described a method of forming briquets from a narrowly defined formulation of the general type mentioned above, and thereafter subjecting the briquets to a critical heating schedule in the calcining step. While the resulting form'coke does have the requisite strength for blast furnace use, the rather precise heating schedule imposes economic deterrents upon its commercial use.

Accordingly, it is the primary object of this invention to provide a method of making agglomerates from a caking bituminous coal which, when calcined by conventional means, will yield formcoke suitable for blast furnace use.

Other objects of our invention will become apparent upon reference to the following description and to the accompanying drawing in which a preferred embodiment of our invention is shown schematically.

in accordance with our invention, crushed caking biturninous coal and finely divided char (is. the solid carbonaceous residue of coal which has been distilled between 800 and 1400 F.) are introduced into a substantially horizontal rotary retort to fill at least ten percent by volume of the retort, but preferably between thirty (30) and fifty (50) percent. If desired, pitch may be added at the same time to increase the degree of fluidity of the coal upon being heated and to supply some binder. The relative proportions of coal, char and pitch introduced into the retort are: to 60 parts by weight of coal, to 65 parts by weight of char, and 0 to 15 parts by weight of pitch. The temperature within the retort is maintained in the range of 750 to 825 F. The desired temperature of the mixture in the retort is maintained under essentially adiabatic conditions, that is by 3,Zi,75l Patented Jan. 15, 1933 ice preheating the raw materials before admittance to the retort to supply as sensible heat substantially all the heat required to achieve the desired temperature in the tumbling zone. The retort is rotated to effect tumbling and intimate mixing of the solids. As the mixture is tumbled in the retort, discrete agglomerates are formed while concurrently partial distillation of the coal occurs, thereby evoiving tar, the pitch portion of which when recycled serves as an additional binder for the agglomerates when pitch is included in the formulation. The residence time of the solids in the retort is generally between fifteen and thirty minutes. The hot agglomerates are recovered from the retort and thereafter calcined at an elevated temperature, e.g. between about 1500 and l800 F. During calcination no further agglomerate growth occurs. in fact, the agglomerates produce formcoke of somewhat smaller size due to shrinkage during the calcination. The product forrncoke has the density, strength and abrasion resistance of conventional blast furnace coke, and, in fact, the strength is generally superior to that of conventional coke if made under the conditions set forth hereinafter in the description of the preferred embodiment of our invention.

However, before describing the preferred embodiment of our invention, those features and conditions of our process which are essential to the production of a formcoke suitable for use in a blast furnace will be described. The success of our process is critically dependent upon the maintenance of narrowly defined conditions. Failure to observe the essential requirements set forth below results in no agglomerates at all, or in agglomerates too weak for blast furnace use, or in a single massive agglomerate.

The critical features of our process are as follows. The composition of the formulation must fall within the relative proportions of caking coal, char, and pitch set forth above. The coal must be a caking coal. However, it may be low volatile, medium volatile, or high volatile. Furthermore, the coal must not have been oxidized before use in our process, and must not be exposed to xygen during the process. If oxidized coal is used, weak, friable formcoke is produced. The amount of coal must not exceed that specified, for otherwise large and weak agglomerates, or even a single solidified mass will be obtained. The char employed in the process may be derived from eithercaking or non-caking coals including lignite and sub-bituminous coals by low temperature carbonization. Its cubic foot weight should be between 20 and 35 pounds if a porous formcoke is desired. In such a case, the char should be prepared from caking coal by a fluidized carbonization process, whereby a very porous char is produced. The amount of char must not exceed that specified since either no agglomerates will be formed, or small weak pellets will be obtained. The pitch may be any pitch which is free of constituents boiling below 400 C. and may be derived from high or low temperature carbonization of coal. Excessive amounts of pitch will have the same effect as too much caking coal.

The agglomerates must be formed in a tumbling zone, such as that provided by a rotary retort. To obtain the desired agglomerates, the mixture of coal and char must occupy at least l0 percent of the volume of the tumbling zone, and preferably between 35 and 50 percent. If the occupancy is less than 10 percent only a small yield of agglomerates under the conditions of our process is obtained. Furthermore, the major portion of the heat required, and preferably all, should be supplied adiabatically in the form of sensible preheat of the components of the formulation. That is, the equilibrium temperature of the components upon mixing should approach that desired in the tumbling zone, preferably not more than 25 F. below the desired zone temperature. If desired, some mixing may be effected before entry into the retort, but, if this is done, care should be exercised to avoid reaching a temperature at which agglomeration will prematurely occur; or if such temperature is reached, only a very short residence time should be allowed for the agglomerates in the tumbling zone.

It is essential for the formation of strong formcoke, in accordance with our invention, to maintain a temperature in the tumbling zone which is within the range 750 to 825 F. If the temperature is below 750 F, there is little or no a glomeration of the mixture. If the temperature is above 825 F., carbonization of the agglomerates is too rapid, with the result that the formcoke product is weak and friable. We have further found that it is particularly important that the temperature of the tumbling zone must not approach the temperature of maximum fluidity of the cakiitg coal used in the formulation, but must be below that point preferably at least 25 F. lower than the temperature of maximum fluidity. Otherwise, agglomerates are formed which are too weak and friable for blast furnace use. Still further we have found that the temperature of the walls of the retort which enclose the tumbling zone should not exceed 825 F. because of the resulting too high carbonization rate in the tumbling zone. Accordingly, only a very limited amount of heat may be supplied to the zone through the walls, thus the necessity for supplying the major portion of the heat adiabatically.

The resulting agglomerates, after being calcined, have properties quite similar to those of conventional blast furnace coke. Their stability factor (as determined by the ASTM Method No. 13294-50) is at least 50 and thus equal to that of the best blast furnace coke now in use.

Referring now to the drawing for a description of the preferred embodiment of our invention, finely divided caking bituminous coal having a size consist of, for example, 14 mesh x Tyler Standard screen is continuously fed through a conduit into a preheating zone 12 where the coal is heated by any conventional means to a temperature of about 400 to 500 F. The stream of preheated coal is conducted through a conduit 14 to a low temperature carbonization zone 16. In this zone the coal is heated to a temperature of about 900 to 1000 F., preferably in a dense phase fluidized bed. The operation of such a carbonization zone is now well known and does not form an essential part of this invention except to the extent that the char so produced in a fluidized bed has particularly desirable properties when a formcoke of low density is desired. Such char has a highly porous structure which is retained throughout the subsequent production of formcoke. The tar vapors evolved from the carbonization zone are conducted through a conduit 18 to a condenser 20. Non-condensable gases are recovered through a conduit 22 while tar condensate is recovered through a conduit 24. Hot char is transferred without intentional cooling through a conduit 26 to a rotary retort 28. If desired, the char may be initially distributed the length of the retort by suitable means such as an elongated screw.

Non-oxidized coal in the proper relative proportion to the char is supplied to the rotary retort 28 through a conduit 30 from a coal preheater 31. In contrast to the coal fed to the carbonizer 16, the coal in this case is preferred to be about A" x 0 size consist, that is, coarser than the coal fed to the carbonizer. It is preferably preheated to a temperature between 500 and 650 F. However, the raw coal feed for the entire integrated process may be screened into two fractions namely: 4 x 14 mesh and 14 mesh x 0 (Tyler Standard screen). The 14 mesh x 0 then becomes the feed to the carbonizer 16 while the coarser A x 14 mesh fraction is fed to the preheater 31 and thence to the retort. We have found that the formcoke of this invention is improved by the use of coal which is coarser than the char. Preferably the coal fed to the tumbling zone has a size consist between and 14 mesh Tyler Standard screen.

The tar from the aforementioned condenser 20 is fed through a continuation of conduit 24 to a heated fractionator 32. The latter serves to separate the tar into a pitch fraction and a fraction boiling below 400 C. which is recovered through a conduit 34. The pitch is withdrawn through a conduit 36. A portion of the withdrawn pitch is transferred through a conduit 38 to a preheater 43 and thence to the rotary retort 23 into which it is introduced through suitable spray nozzles 42 near the inlet end of the retort. The pitch is preferably heated to between 650 and 800 F. in the preheater 40.

The preferred proportions of char, coal and pitch fed to the rotating retort are as follows: 45 to parts by weight of char, 40 to 55 parts by weight of coal, and 0 to 15 parts by weight of pitch. The preheat temperatures of these three ingredients are preferably 900 to 1100 F. for the char, 400 to 650 F. for the coal, and 650 to 750 F. for the pitch. However, the preheat temperatures are suitably adjusted in accordance with the relative proportions of the three ingredients to yield an average temperature of the mixture of at least 725 F. but not higher than 825 F. Additional heat, if required, may be provided by external heating of the retort walls provided the temperature thereof is not allowed to exceed 825 F., or by internal heating as by a gas burner, to raise the temperature of the mixture in the retort to between 750 and 825 F. The atmosphere in the retort should be non-oxidizing; consequently any air employed in any burner should be completely consumed.

The total feed to the rotating retort 28 is regulated so as to fill at least 10 percent of the retort. However, sufficient free space must be afforded to permit intimate mixing of the ingredients upon rotation of the retort. A relatively deep bed of solids is thus maintained at all times in the retort. Such a deep bed is possible only because of the use of adiabatic heat in our process, since the use of externally supplied heat would require a shallow bed to permit adequate heat transfer. It is important that a deep bed he maintained, for otherwise uniformly sized coherent agglomerates are not obtained under the conditions of our process. The formation of the agglomerates is accompanied by distillation of tar from the caking coal. Some of this tar as produced serves as a binder in the formation of the agglomerates. Accordingly, the amount of pitch fed to the retort is regulated in accordance with the fluidity characteristics of the feed coal at the formation temperature; the greater the fluidity the less extraneous pitch is needed. The total feed to the rotating retort is also regulated to provide a residence time in the retort of about 15 to 30 minutes.

The tar vapors evolved in retort 28 are removed through a conduit 44 to a condenser 46. The non-condensable gases are recovered from the condenser 46 through a conduit 48. The tar condensate is withdrawn through a conduit 56 and transferred to the fractionator 32.

The hot raw agglomerates which, for the most part, range in size between /2 inch and 3 inches are removed from the retort 28 through a conduit 52. The stream of agglomerates is preferably separated by screening (not shown) into two streams which contain the /2" x 1 /2" agglomerates and the plus 1 /2 agglomerates, respectively. The purpose of this separation is to permit selection of optimum heating rates in the calciners. The smaller size agglomerates are carried through conduit 54 into the top of a calcincr 56 while the larger size agglomerates are carried through conduit 53 into the top of a calciner 64 Each of the calciners is adapted to operate under a pressure between 0 and pounds per square inch and at a temperature between about 1500 and 1800" F. A hot gas, preferably a reducing gas, is introduced into the bottoms of the calciners through conduits 62 and 64, respectively. The hot gaszpasses upwardly and in countercurrent heat exchange relationship to the downwardly moving stream of agglomerates. In calciner 56, the rate of heating is regulated so as to be substantially higher than that provided in calciner 60, for example 30 to 40 F. per minute in contrast to to 20 F. per minute in calciner 60. By such regulation the heating schedule best designed to produce strong formcoke is provided. However, the precise operation or the particular embodiment of such calciners is well known in the art and does not form an essential part of this invention. The purpose of the reducing gas is to lower the sulfur content of the product during the calcining step. The product forrncoke is withdrawn through conduits 65 and 68. Tar vapors and other gases are withdrawn from the top of the calciners through conduits 7t) and '72 into a conduit 74 which carries them to a condenser 76. The tar condensate is recovered through a conduit 78, while the non-condensables are recovered through conduit 80.

In the following Table l the pertinent data of a number of runs are tabulated which show the critical effect of temperature and composition of the feed formulation.

on a 3" screen; and 29.9 percent of the product after removal of the 31.2 percent was retained on a 2 screen, etc. The cumulative percentages amount to 98.9, leaving 1.1 percent of solids less than /2 in size.

In the last column of Table I is reported the tumbler index of the plus l-inch fraction of each of the respective product forrncokes where such index was obtainable. The forrncoke was produced by calcining the agglomerates from the tumbling zone at 1800 F. Except where otherwise indicated, this index was obtained as follows. One thousand grams of the coke were tumbled in an eight-inch diameter drum fitted with three 1 equally spaced lifting vanes which was rotated at 54 r.p.m. for 1080 revolutions. At the conclusion of the test the weight percent of forrncoke equal to or larger than /2 inch was determined. This figure is reported as sumbler index and is a measure of the strength of the formcoke. Comparison of this index with the Micum index showed that the two are substantially the same. On the other hand the ASTM tumbler index D294-29 is much lower since it is determined by a much more rigorous tumbling procedure.

T able I Formulation (weight percent) Temp. Product size (weight percent on) Run F. Tumbler index of No. tumbling +1 product Goal 1 Char Pitch zone 3" 2" 1 Oonven ionalkblast furnace 50 to 60 (ASTM) co e 1 3 50 I 50 0 800 1 7 32.6 42. 4 17.2 54 (ASTM) Conventionalkblast furnace 88 to 94.

co e 4.5 55 0 725 0 O 0 0 45 55 0 750 0 1. 5 4. 5 30 47. 5 47. 5 5 775 0 12. 5 67. 4 19. 3 95. 48. 0 42 10 775 34 20. 9 29. 9 13. 2 89. 60 0 800 0 0 .5 10 55 0 800 O 20 33 22 89. 50 0 800 1. 7 32. 6 42. 4 17.2 95. 5. 45 0 800 74. 7 17. 5 7. 7 95. 35 0 800 C'oked to solid mass e Maximum fiuidity60,000 DDPM at 830 1*. (determined by the Gieseler plast-ometer in accordanc with the published ASTM proposed procedure).

2 3 x 2 coke used for test. 3 Runs 1 and 8 are the same In these runs a caking bituminous coal from the Pittsburgh Seam was used. Its size consist was A x 0 Tyler Standard screen. The char was obtained by the distilla- They are included twice to facilitate comparison of ASTM tumbler index- In Table II, the pertinent data relative to the effect of percentage of retort volume occupied by solids are tabulated.

Table II Formulation (weight Solids 00- Product size (weight percent on) Tumbler index on product Run percent) Temp. cupancy sizes shown No. F. (percent of retort 01 Goal Char Pitch 3" 2 1" 3" 2 1" tion of a caking bituminous coal, likewise from the Pittsburgh Seam. its size consist was 8 x 0 mesh Tyler Standard screen. The pitch was a by-product oven pitch of 101 C. melting point obtained from the topping of high temperature tar. The resulting mixture occupied about 40 percent of the retort volume. The temperature of the final mixture in the rotating retort is given under the heading of Temp, F. The size distribution of the product from the rotating kiln is given under Product Size expressed as Wt. percent on the designated screen size. The percentages represent the percent of total yield of solid product. The diiference between the total of the percentages listed and 100 percent is the amount of solid product below /2 inch in size. For example, in

According to the provisions of the patent statutes, we have explained the principle, preferred construction, and mode of operation of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims, the in- ,vention may be practiced otherwise than as specifically illustrated and described.

We claim:

The method of making formcoke which comprises establishing and maintaining a tumbling zone in a retort, introducing finely divided caking bituminous coal and finely divided solid distillation residue of coal into said tumbling zone in the relative proportions of 35 to 60 by weight of said caking bituminous coal and 40 to 65 parts by weight of said distillation residue, maintaining at least ten percent of the volume of said retort filled with said coal and residue, maintaining the temperature of said tumblin" zone between 750 and 825 F., supplying substantially all the heat required to maintain. said temperature as sensible heat of the materials fed to the retort, tumbling said coal and residue in said tum bling zone under non-oxidative conditions until agglomerates are formed, and thereafter calcining said agglomeratesat an elevated temperature, whereby particulate formcoke of great strength is produced.

2. The method of making formcoke which comprises establishing and maintaining a tumbling zone in a retort, introducing finely divided caking bituminous coal, finely divided solid distillation residue of coal, and pitch into said tumbling zone in the relative proportions of 35 to 60 parts by weight of said caking bituminous coal, 40 to 65 parts by weight of said distillation residue, and up to parts by weight of said pitch, maintaining at least ten percent of the volume of said retort filled with said coal, residue and pitch, maintaining the temperature of said tumbling zone between 750 and 825 F., supplying substantially all the heat required to maintain said temperature as sensible heat of the materials fed to the retort, tumbling said coal, residue and pitch in said tumbling zone under non-oxidative conditions until agglomerates are formed, and thereafter calcining said agglomerates at an elevated temperature, whereby particulate formcoke of great strength is produced.

3. The method or" making formcoke which comprises establishing and maintaining a tumbling zone in a retort, introducing finely divided caking bituminous coal and finely divided solid distillation residue of coal into said tumbling zone in the relative roportions of to 60 parts by weight of said bituminous coal and to 65 parts by weight of said distillation residue, said residue having been heated prior to introduction into said tumbling zone to an elevated temperature such that upon admixture with said coal an average temperature of at least 725 F. and not more than 825 F. is achieved, maintaining at least ten percent of the volume of said retort filled with said coal and residue, maintaining the average temperature of the solids in the tumbling zone in the range of 750 to 825 F. and below the temperature of maximum fluidity of said coal, tumbling said coal and residue in said tumbling zone under non-Oxidative conditions until agglomerates are formed, withdrawing said agglomerates from said tumbling zone and thereafter calcining said agglomerates at an elevated temperature whereby particulate formcoke or" great strength is produced.

4. The method of making formcoke which comprises establishing and maintaining a tumbling zone in a retort, introducing finely divided caking bituminous coal, finely divided solid distillation residue of previously distilled coal, and pitch into said tumbling zone in the relative proportions of 35 to parts by weight of said bituminous coal, 40 to parts by weight of said distillation residue, and up to 15 parts by weight of said pitch, at least said residue having been heated prior to introduction into said tumbling zone to elevated temperatures such that upon admixture with said coal and pitch an average temperature of at least 725 F. and not more than 825 F. is achieved, maintaining at least ten percent of the volume of said retort filled with said three materials, maintaining the temperature of the materials in the tumbling zone in the range of 750 to 825 F. and below the temperature of maximum fluidity of said bituminous coal, tumbling said materials in said tumbling zone under non-oxidative conditions until agglomerates are formed, withdrawing said agglomerates from said tumbling zone, and thereafter calcining said agglomerates at an elevated temperature,

whereby particulate formcoke of great strength is produced.

5. The method of making formcoke which comprises establishing and maintaining an agglomeration zone under nonxidative conditions within a substantially horizontal rotary retort, introducing finely divided calzing bituminous coal and finely divided solid distillation residue of coal into said agglomeration zone in the relative proportions of 35 to 60 parts by weight of said coal and 40 to 65 parts by weight of said distillation residue, maintaining ten percent of the volume of said retort filled with solids, maintaining the temperature of the solids in said agglomeration zone between 750 and 825 F., supplying substantially all the heat required to maintain said temperature by the sensible heat of said solids, rotating the retort to efiect intimate mixing of coal and distillation residue by virtue of the rotary motion of the retort, recovering agglomerated solids from said agglomeration zone and thereafter calcining said agglomerated solids at an elevated temperature, whereby particulate formcoke of great strength is produced.

6. The method of making formcoke which comprises establishing and maintaining a tumbling zone in a retort, introducing into said tumbling zone the ingredients of a formulation consisting essentially of 40 to 55 parts by weight of a finely divided caking bituminous coal, 45 to 55 parts by weight of finely divided distillation residue of coal, and up to 15 parts by weight of pitch, maintaining between ten and fifty percent of the volume of said retort filled with said ingredients, maintaining the temperature of said tumbling zone between 750 and 825 F. and below the point of maximum fluidity of said bituminous coal, supplying substantially all the heat required to maintain said temperature by the sensible heat of said ingredients, maintaining the temperature of the walls of said retort below 825 F., tumbling said ingredients in said tumbling zone under non-oxidative conditions until agglomerates are formed, and thereafter calcining said agglomerates at an elevated temperature, whereby particulate formcoke of great strength is produced.

7. The method of making formcoke which comprises carbonizing finely divided coal in a dense fluidized bed at a temperature between 900 and 1000 F., separately recovering the products char and tar, fractionating the tar to recover a pitch fraction free of fractions boiling below 460 C. introducing said char and pitch along with a finely divided caking bituminous coal into a substantially horizontal rotary retort in the relative proportions of 40 to 55 parts by weight of coal, 45 to 55 parts by weight of char, and up to 15 parts by weight of pitch, said coal as fed being at a temperature between 400 and 650 F., said char between 900 and 1100 F., and said pitch between 650 and 756 F., maintaining between ten and fifty percent of the volume of said retort filled with said coal, chat and pitch, maintaining the temperature within said retort between 750 and 825 F. and below the point of maximum fluidity of said bituminous coal, supplying substantially all the heat required to maintain said temperature by the sensible heat of said coal, char and pitch, maintaining the temperature of the walls of said retort below 825 F., tumbling said coal, char and pitch under non-oxidative conditions in said rotary retort until agglomerates are formed, and thereafter calcining said agglomerates at a temperature between 1500 and 1800 F., and recovering particulate formcoke having a stability factor of at least 50 (ASTM No. D294-50).

Aspegrcn Apr. 9, 1957 MattoX et al. Feb. 28, 1956

Claims

1. THE METHOD OF MAKING FORMCOKE WHICH COMPRISES ESTABLISHING AND MAINTAINING A TUMBLING ZONE IN A RETORT, INTRODUCING FINELY DIVIDED CAKING BITUMINOUS COAL AND FINELY DIVIDED SOLID DISTILLATION RESIDUE OF COAL INTO SAID TUMBLING ZONE IN THE RELATIVE PROPORTIONS OF 35 TO 60 PARTS BY WEIGHT OF SAID CAKING BITUMINOUS COAL AND 40 TO 65 PARTS BY WEIGHT OF SAID DISTILLATION RESIDUE, MAINTAINING AT LEAST TEN PERCENT OF THE VOLUME OF SAID RETORT FILLED WITH SAID COAL AND RESIDUE, MAINTAINING THE TEMPERATURE OF SAID TUMBLING ZONE BETWEEN 750 AND 825* F., SUPPLYING SUBSTANTIALLY ALL THE HEAT REQUIRED TO MAINTAIN SAID TEMPERATURE AS SENSIBLE HEAT OF THE MATERIALS FED TO THE RETORT, TUMBLING SAID COAL AND RESIDUE IN SAID TUMBLING ZONE UNDER NON-OXIDATIVE CONDITIONS UNTIL AGGLOMERATES ARE FORMED, AND THEREAFTER CALCINING SAID AGGLOMERATES AT AN ELEVATED TEMPERATURE, WHEREBY PARTICULATE FORMCOKE OF GREAT STRENGTH IS PRODUCED.