US3018227A

US3018227A - Preparation of formcoke

Info

Publication number: US3018227A
Application number: US635421A
Authority: US
Inventors: Baum Kurt; Robert J Friedrich
Original assignee: Consolidation Coal Co
Current assignee: Consolidation Coal Co
Priority date: 1957-01-22
Filing date: 1957-01-22
Publication date: 1962-01-23
Anticipated expiration: 1979-01-23

Description

Jan. 23, 1962 K. BAUM ETAL PREPARATION OF FORMCOKE 4 Sheets-Sheet 1 Filed Jan. 22, 1957 ZOZ Jan. 23', 1962 K. BAUM lETAL PREPARATION OF FORMCOKE 4 Sheets-Sheet 2 Filed Jan. 22, 1957 N mDoE KURT BAUM ROBERT J. FRIEDRICH Jan. 23, y1962 K.BAUM ETAL PREPARATION OF' FORMCOKE 4 Sheets-Sheet 3 Filed Jan. 22, 1957 .m .mm-DDE mxOoEmOm KURT BAUM ROBERT J. FRIEDRICH 4 Sheets-Sheet 4 Filed Jan. 22, 1957 .v mnw KURT BAUM ROBERT J. FRIEDRICH 3,018,227 PREPARATION F FORMCOKE Kurt Baum, Essen, Germany, and Robert J. Friedrich,

Library, Pa., assignors to Consolidation Coal Company, a corporation of Pennsylsania Filed Jan. 22, 1957, Ser. No. 635,421 11 Claims. (Cl. 202-26) The present invention relates to formcoke and a method of preparing it. More particularly, the present invention is directed to a composition of matter useful as a metallurgical fuel and the method of preparing it.

At the present time virtually the exclusive metallurgical fuel is coke which has been prepared from caking coal in by-product coke ovens or beehive coke ovens.

By-product coke ovens require an initial high capital investment, result in high processing costs because of the inherent batch-Wise processing and impose rather severe limitations on the nature of the coal feed material. Beehive coke ovens similarly have high processing costs because of the batch-wise nature of the treatment and do not produce any valuable by-products.

Another disadvantage of current techniques for making coke is the rather substantial loss of useful solid coke product resulting from fragmentation which occurs when the coke product is discharged fro-m the oven whether of the beehive or by-product variety. For most metallurgical applications, only the large fragments of coke are marketable. It is possible, of course, to recycle into the coke oven a portion of the coke breeze resulting from fragmentation. A substantial portion of the product coke, however, is not saleable as a premium product because of the size requirements of the coke market.

According to the present invention, we have discovered a method for preparing a metallurgical fuel which has the desirable intrinsic properties of conventional coke with the following additional advantages: (l) the material is produced in a continuous or semi-continuous manner rather than in a batch process; (2) the product possesses substantially uniform size and configuration; (3) the overall yield of valuable liquid by-products is significantly greater than that obtained in conventional by-product coking; (4) the processing time required is significantly less than that required in conventional coke making processes; and (5) the process may be applied to any of the caking bituminous coals without regard to the swelling pressures which such coals would exhibit during conventional coking.

Essentially the formcoke of the present invention is prepared from a formulation comprising at least three ingredients which include (a) a caking bituminous coal; (b) a low temperature carbonization char which has been obtained by iluidized low temperature carbonization of a high volatile bituminous coal; and (c) a pitch binder obtained by pyrolytic treatment of carbonaceous solid fuels, at least a portion of which has a fixed carbon content exceeding 25 percent. The formulation has a volatile matter content greater than 22 percent. The mixture of starting materials is blended, kneaded, and briqueted under pressure into uniform shapes. The briquets possess a satisfactory raw strength which is necessary to permit their handling and movement into coking apparatus. The resulting briquets are shock heated to a temperature above the plastic range of the caking coal constituent to effect virtually instantaneous coking of the outer shell of the briquet, and are retained at a temperature of 900 to 1250 F. until the entire briquet mass has passed through the plastic temperature range of the caking coal and has achieved a temperature above 900 F. Thereafter the coked briquets are calcined by continued heating to a temperature suicient for reducing the volatile matter content to an acceptable value. The calcined briquets ted States Patent O ,Mice

thereupon are cooled to a temperature below their atmospheric kindling temperature and are recovered as a useful fuel for metallurgical purposes.

The formcoke produced by the present invention has dimensionally uniform structure, has a homogeneous cornposition, is highly porous, and has an apparent density equivalent to that of existing metallurgical coke. On microscopic inspection our new formcoke is virtually indistinguishable from existing strong metallurgical coke since the individual particles comprising the formulation completely lose their discrete identity during processing. The tumbler strength of our new formcoke is as high as that of existing strong metallurgical coke. Sulfur content and volatile matter content correspond to that of coke prepared from the same starting coal or coal blend.

We are aware that many prior investigators have proposed that coke-like materials be prepared in definite shapes by briqueting and subsequent coking and calcination. Such calcined briquets, however, have been of poor quality because of non-homogeneity, high density and low strength. The individual particles which were Vabout 20 to 25 pounds per cubic foot.

agglomerated .during prior art briquet preparation are only loosely bound in the calcined briquets. The discrete, loosely bound particles could be readily abraded from the calcined briquets. The weak bonding permitted l substantial shattering tooccur when the calcined briquets were subjected to mechanical stresses. Another defect of prior art calcined briquets, especially those produced from coal alone, was the distortion of shape and resultant cracks and fissures which occurred during the calcining and cooling stages. Prior art calcined briquets possess too high a density and too low a strength.

The formcoke of the present invention has substantially uniform undistorted shape; it is free from cracks and fissures; it appears to possess a homogeneous composition similar to that of premium metallurgical coke produced in coke ovens from good caking coals. The particulate starting materials are securely bound in and be` come part of a continuum of carbonaceous material whereby their initial character as discrete particulate ingredients is lost.

I. BRIQUET FEED FORMATION A. F liudized low temperature carbonization char.-One

of about 800 to about 0 F., volatile material is4 evolved in the form of gas and tar. The quantity of valuable liquid tar recoverable via low temperature carbonization is from about l5 to about 40 gallons per ton of coal in contrast to the yield of about Sto l0 gallons per ton of coal realized in by-product coke ovens. The solid residue remaining after evolution of volatile matter is Itermed chan The physical nature of the char is dependent upon the mechanical conditions of carbonization. Many low temperature carbonization processes known to the art will produce char having a bulk density of 30 pounds per cubic foot and higher. For our formcoke, the char must have a sponge-like porous composition and a density of less than 30 pounds per cubic foot.

To prepare our new formcoke, the char component must be produced by low temperature carbonization conducted under fluidized solids contacting conditions. When produced in fluidized low temperature carbonization processes, the char is swelled and expanded into uify, rounded solid particles. The sponge-like porous properties of the char particles result in a low bulk density of the material and a correspondingly low physical strength. The bulk density of the material is from The char resulting from fluidized low temperature carbonization,

moreover, is in discrete particulate form, -for example,

capable of passing through a 14 mesh Tyler standard screen. Y

It is possible to produce high density char from high volatile bituminous coal by fluidized low temperature carbonizaton process when the untreated coal is introduced directly into the iluidized carbonization stage and its operability (i.e., its ability to retain particulate configuration and avoid agglomeration) is forced by means of mechanical stirring devices. Such dense chars are not suited to the preparation of our formcoke. The uidized low temperature carbonization process required for the fiuidized low temperature carbonization char is one in which the coal achieves operability by virtue of preliminary treatments such as preoxidation, for example.

Throughout this specification, the abbreviation LTC refers to low temperature carbonization; the phrase fluidized LTC char refers to the solid particulate residue resulting from a low temperature carbonization ofV high volatile bituminous coal conducted under fluidized solids contacting techniques.

'I'he final carbonizing temperature determines to alarge extent the ultimate volatile material content of the char particles. For purposes of the present invention the carbonization temperature should not exceed 1350 F. 'If the char is to be thermally treated prior to briquet blending according to our invention, such thermal treatment should not be carried out at ternperatures above 1350 F. PreliminaryV treatment at excessive temperatures tends to graphitize the char, to destroy its porous character, increase its density and thereby to render it less desirable for formcoke preparation.

Low temperature carbonization char which has been prepared from processes which are not conducted under fluidized solids contacting conditions are unsuitable for preparing our new form'coke. These chars generally have a higher bulk density than fluidized LTC chars and do not possess the uffy, sponge-like composition we have found to be necessary.

The high volatile coal employed in preparing the fluidized LTC char need not be one normally considered as a caking coal. By that We mean that the char may be prepared from high volatile coal which would not exhibit satisfactory caking properties for metallurgical coke ovens. In many areas of the world such coal is readily available. Such coal, now has no utility in the preparation of metallurgical fuels, although it may be converted into a lluidized LTC char quite readily and be used in that form as a major constituent in the preparation of metallurgical fuels according to our present invention.

Fluidized LTC char comprises about 45 to 80 percent by weight of the briquet formulation.

`B. Cakng bituminous cal.-The caking bituminous coal employed in the briquet formulation has a volatile matter content exceeding about 30 percent by weight. Such coals are described as high volatile caking bituminous coals. Preferably, the caking bituminous coal is crushed to a size consist approximating that the fluidized LTC char. For example, high volatile caking bituminous coal ground to pass through a 28 mesh Tyler standard screen has been found quite satisfactory in preparing formcoke according to this invention. Where the coal is too finely ground, the resulting excess surface area introduces difficulties related to the pitch binder required for our new process. A small amount of residual moisture is not detrimental in the present process although excessive moisture is undesirable. Generally, coal which has been stored in open atmosphere acquires an equilibrium moisture content of about to 8 percent by weight which is satisfactory. If desired, the caking bituminous coal employed in the briquet formulation may be the same caking bituminous coal used as the feed material for the fluidized low temperature carbonization process which supplies the char for the briquet various coals provided the blend has sufficient caking properties and volatile matter content.

The briquet formulation from this invention comprises abolut 10 to 35 percent by weight of caking bituminous CO3 C. Pitch binden-*The briquet formulation according to this invention comprises about 6 to 20 weight percent of pitch obtained by pyrolysis of caking coals. The pitch should be free of materials boiling below about 350 C. and may additionally be `free of materials boiling below 400 C.V if desired. The melting point of the pitch should be below about C.V A ring and ball melting point of about 60 to 90 C. is satisfactory, (ASTM: E28-42T).

From about l to 12 weight percent of the briquet formulation should comprise a high carbon pitch having a fixed carbon content exceeding 25 percent. A pitch meeting these requirements can be obtained by thermal treatment of pitches at temperatures exceeding about 1500 F. An example of such a pitch would be the pitch obtained from high temperature carbonization of coal in a conventional coke oven or, more conveniently, it may be the pitch which is produced during the calcining of the briquets according to this invention.

Up to about 15 weight percent of the briquet formulation may comprise a low carbon pitch having a fixed carbon content of less than about 20 percent. Generally pitches which have not been exposed to thermal treatment at temperatures above 1400 F. are suitable. The pitch normally obtained from low temperature carbonization of caking bituminous coal meets these specifications. Fixed carbon content of pitches is determined by the technique employed in determining fixed carbon content of coals (ASTM: D27l-48, paragraph 16).

The pitch binder serves two functions in our invention. First, the pitch serves as an adhesive to bind the particles of caking coal and uidized LTC char Vinto shaped briquets. In this function the pitch must coat the surfaces of the particles in the raw briquet feed.

Second, the pitch serves as a flux in the thermal treating stage of the process to cause the components of the briquet to fuse together into a homogeneous mass. With proper fluxing action, the individual solid particulate constituents become securely bound in the product formcoke. The resulting formcoke product, like existing metallurgical coke of good quality, is relatively free of non-homogeneity.

The described high carbon pitch alone may serve both functions of the pitch binder. In fact, excellent formcoke may be prepared according to this invention from our briquet formulation wherein about 10 to l2 Weight percent of high carbon pitch is employed as the exclusive pitch binder. However, We prefer to provide an intetegrated self-sustaining formcoking process which employs the high carbon recycle pitch, autogenously obtained from the briquet coking and calcining stages, as' the high carbon pitch component of the briquet formulation. We have found that the quantity of high carbon pitch which may be recovered in this manner is sufficient to supply only up to about 6.5 percent by weight of fresh briquets under continuous processing conditions. This quantity of pitch is insufficient to serve the adhesive function of pitch binder, although it is adequate to serve the fluxing function. Additional high carbon pitch for the adhesive function may be obtained from extrinsic sources such as conventional coke oven processors or may be prepared by thermal treatments of low carbon pitch to supply the recycle deficiency inherent in continuous processing. Where additional high carbon pitch for the adhesive function may be obtained from extrinsic sources such as conventional coke oven processors or may be preing. Where additional high carbon pitch is obtained 5 extrinsically, the incremental quantity need be only l to 3 percent of the weight of the raw briquets.

As an alternative, however, a low carbon pitch may be employed to make up the intrinsic deficiency of recycle pitch. Low carbon pitch is readily available in the LTC tar which is obtained contemporaneously with the uidized LTC char. The presence of finely divided particles of coal and partially devolatilized coal in pitches obtained from uidized low temperature carbonization does not adversely affect their utility in the present invention. The low carbon pitch adequately serves the adhesive function of the pitch binder and does not interfere with the fluxing function provided by the high carbon pitch. Low carbon pitch alone is less effective for the fluxing function and also is of doubtful value alone for the adhesive function. Briquets formed from low carbon pitch alone tend to exhibit shape distortion and are readily deformable. Where low carbon pitch is employed as the incremental pitch, greater quantities are required than where high carbon pitch is selected as the incremental pitch. Up to about l5 percent by weight of LTC pitch may be employed in the briquets. In general, one incremental percent of high carbon pitch is about as effective in our invention as three incremental percent of low carbon pitch.

It is possible to convert low carbon pitches into high carbon pitches by selected thermal treatments. Such processes are beyond the scope of the present invention except for the following caveat. Simple thermal treatment of a low carbon pitch, while effective in increasing the fixed carbon content, also results in a significantly increased melting point of the treated pitch. The melting point of the entire pitch which is employed in our invention should be, as previously stated, from about 60 to 90 C. as measured by ring and ball determination.

D. Recycle coke.-Abrasion of the formcoke product obtained in the present process results in the production of only a small quantity of undersized coke particles. We have been able to recover all of the undersized coke particles for reblending with the briquet formulation. Generally the amount of recycle coke, which preferably is crushed to pass through a 28 mesh Tyler standard screen, will be about 5 percent of the briquet formulation. Unlike the other ingredients of our briquet formulation, these recycle coke particles retain their particulate identity in our process and are identifiable in the product formcolce. The recycle coke particles, however, are cornpletely surrounded with a continuum of homogeneous coke and do not adversely affect the formcoke properties. Up to about 8 percent by weight of crushed formcoke fragments may be added to the formulation without serious difficulty.

E. Preferred embodz'mentf-We have found that the following formulation Will produce satisfactory formcoke according to this invention.

Table I BRIQUET FORMULATION Constituent Weight Percent Fluidized low temperature carbonization cha 58. 5 High volatile caking bituminous coal... 25. 0 Low temperature carbonization pitch.. 5. 3 Pitch recovered from process 6.2 Recycle cnice 5.0

. 6 for example, to pass through a 200 mesh Tyler standard screen. The comminuted solid pitch is thereupon uniformly mixed with the iluidized LTC char and caking coal.

The blended formulation has a volatile matter content greater than 22 percent, preferably from about 24 to 30 percent by weight. (ASTM: D27148, paragraph 13a and 14a.)

G. Kneading.-Following the blending of ingredients, the formulation should be kneaded for a brief period in accordance with the well-known briqueting art. The kneading operation usually is carried out in a tank having agitation paddles rotatable in horizontal planes. Live steam is usually passed through the briquet formulation in the kneading apparatus. The function of the kneading operation is to cause emulsification of the pitch binder to assure that the binder becomes uniformly spread over the surfaces of the particles. Thus kneading is carried out at a temperature above the melting point of the pitch. We have found that from about 7 to 10 minutes residence time in a steam kneader is satisfactory for our present process.

The kneadedv raw briquet mixture preferably should be passed quickly from the kneading apparatus into briqueting apparatus.

mediately above the briqueting apparatus.

H. Briqueting.-The briqueting stage of the present` process preferably should be conducted at a temperature of about 25 to 40 F. above the melting point ofthe pitch employed in the briquet formulation. The application of live steam in the briqueting stage is a preferred method of supplying necessary heat. Thus the preferred briqueting temperature is about 200 F., a value readily attainable with inexpensive steam. Any well-known briqueting apparatus is suitable for the briqueting stage. We prefer to use roll presses.

We have found that the kneaded briquet formulation must be pressure-fed into such roll presses. Pressure feeding is required to assure that the pockets of the roll press be filled completely with briquet formulation. Cornpression pressure of 3000-5000 p.s.i.g. during actu-al briquet formulation has been found satisfactory.

Any desired geometric shape is satisfactory for the briquets. Ovoids, pillow blocks and cylinders have been found suitable. We have been successful in preparing formcoke from briquets having dimensions up to two inches and more. We prefer to employ briquet sizes such that each particle within the briquet is not more than about one inch from the nearest outer surface of the briquet.

The briquets leave the briqueting press at a temperature slightly above the melting point of the pitch. In this condiiton, they are somewhat pasty and Vare deformable. Severe mechanical shock will cause shape distortion of briquets in this condition. lf the briquets are allowed to cool to a temperature very slightly above the melting point of the pitch, a maximum mechanical shock resistance results. The briquet surface becomes hardened to resist deformation, yet the interior of the briquet remains resilient to resist fracture during handling. If the briquets are allowed to cool below the melting point of the pitch, they become brittle and susceptible to fracture. Accordingnly, we prefer to transport the briquets for further processing at a temperature of about 70 to 80 C. We have found that the briquets will possess a maximum raw strength during the period occurring from labout 2 to about l0 minutes following exposure to atmospheric temperature upon discharge from the briqueting apparatus. Accordingly, we prefer that the briquets be handled with gentleness to avoid deformation during the first two minutes or so after formation. Transportation and mechanical handling of the briquets should occur within the succeeding few minutes to avoid fractures and deformation.

In most briqueting plants, this is not a problem since the steam kneader usually is installed im-4 Any undersize fragments of briquets may be collected and returned to the blending stage for recombination in Y the raw briquet feed mixture.

I. Shock hearing-The briquets formed as described should be subjected to a shock heating treatment which virtually instantaneously raises their temperature above the plastic range of the caking coal. Preferably the briquets should be heated so that the outer surface of the briquet is virtually instantaneously elevated above the plastic temperature, i.e., to a temperature in the range of labout 900 to 1250 F. The inner portion of the briquet will attain the shock heating temperature somewhat more slowly.

The rapid heating of the outer shell of each briquet serves to form a crust of coke which is sufficiently strong to retain the form and shape of the briquet while the interior portions pass through the plastic range of temperature. When each briquet possesses a crust of coke, there is no tendency for individual briquets to fuse together since the coked surface is non-cohesive.

As the briquets pass through the coking stage, the thermal treatment causes evolution of volatile material from the briquet constituents in the form of gases and tars which can be recovered as valuable by-products. The evolved products escape from the briquets and yare carried away in a vapor phase for recovery. The high boiling volatile constituents can be recovered as the recycle pitch required in the briquet formulation. In a preferred formcoking process, these volatile materials are exposed to temperature in excess of about l550 F. prior to recovery to assure that the resultant pitch will be of the described high carbon type required in our briquet formulation.

Rapid heating through the plastic range is desirable from an economic standpoint since the briquets are thereby maintained under processing conditions for only a brief period of time in contrast to coke oven treatment, for example. However economic considerations are not the only criterion determining the shock heating rate. We have found that the plasticity of caking coals varies considerably according to the heating regime to which they are exposed. Where a caking coal is heated rapidly through its plastic range, its fluidity is greatly increased over that exhibited when heated slowly through its plastic range. This increased fluidity resulting from shock heating serves in our invention to produce a melted briquet mass in which the iluidized LTC char is engulfed by liquid coal. The succeeding coking of the coal forms a carbonaceous continuum in which the discrete particulate starting materials are securely bound as a homogeneous material.

The briquets should be retained under shock heating conditions at a temperature of about 900-1250 F. for sulicient time to permit the briquets to pass entirely through the plastic range and achieve a temperature above 900 F. throughout. Where small briquet shapes are employed, the retention time will not be great. When larger briquet shapes are desired, the retention time may be appreciable. A residence time of about 30 minutes at about 1100 F. has been found satisfactory in producing briquets of about 2-inch diameter. Attempts to subject the shock heated briquets to `a further heat treatment at higher temperatures before the entire mass has passed through the plastic temperature will cause severe fracturing of the briquets.

The shock heating may be effected in a variety of ways. One technique is to pass a hot inert gas at yabout 2200 F. through a downwardly moving bed of the briquets. Alternatively the briquets may be plunged into a lluidized bed of nely divided inert solid particles maintained at the desired shock heating temperature.

J. CaIcining.-When the briquets have been heated throughout to a temperature above 900 F., they can be further heated to a nal temperature above about 1550 F. Heating rates above about 50 F. per minute should be avoided. A heating rate of about 20 to 35 F. per minute is preferred. The nal temperature determines to a large extent the quantity of volatile matter remaining in the coke. The volatile material evolved from the coked briquets may be recovered in the vapor phase together with the volatile materials evolved from the shock heating stage.

K. Cooling-When the coked briquets have attained the desired calcining temperature, they should be gradually cooled to a temperature below the atmospheric kindling temperature of the formcoke. Cooling rates up to about 30 to 35 F. per minute have been found satisfactory. Excessive cooling rates, c g., 60 F. per minute, will introduce cracks and fissures in the product formcoke. We have found that the passage of relatively cool inert gases, e.g., flue gases at about 400 F., through a moving bed of formcoke will effect the desired cooling to a formcoke discharge temperature of Vabout 600 F.

L. Formcoke properties-The formcoke produced by our invention is virtually indistinguishable from metallurgical coke obtained from by-product coke ovens, except that our new formcoke has the definite advantage of uniform size and shape. Table II lists some of the properties of our new formcoke.

Table II PHYSICAL PROPERTIES OF FORMCOKE AND EXISTING METALLURGICAL COKES lRauge reported for 12 U.S. coke plants, Contribution To The Metallurgv cf Steel Number 43, Coke Evaluation Project, American Iron and Steel Institute, New York, 1953.

For a full understanding of the present invention, its object and advantages, reference should be had to the following description and accompanying drawing in which:

FIGURE l is a schematic ilow diagram illustrating apparatus adapted for use preparing formcoke according to this invention;

FIGURE 2 includes a photograph of coke oven coke as recovered from a by-product oven and four photomicrographs (15 power magnification) and three photomicrographs (3 power magnification) of thin sections of the coke;

FIGURE 3 includes a photograph of typical calcined formcoke prepared according to our invention together with a photograph of split formcoke, two photomicrographs (15 power magnication) and one photomicrograph (3 power magnification) of thin sections of the formcoke; and

FIGURE 4 includes three photomicrographs (3 power magnification) of low strength metallurgical coke, high strength metallurgical coke and typical formcoke prepared according to our invention together with two photomicrographs (l5 power magnification) of each of the identified materials.

Formcoke suitable for use as a metallurgical fuel may be prepared from caking bituminous coal in a continuous manner according to the ow diagram illustrated in FIG- URE 1.

The present process employs as starting material (a) a high volatile bituminous coal 10 which need not possess caking properties satisfactory for use as a metallurgical coke oven feed material and (b) a high volatile caking bituminous coal 11. Where high volatile caking coal is readily avaliable, it may be used exclusively.

High volatile bituminous coal is subjected to fluidized low temperature carbonization in a processing stage 12. The tar and gas products of low temperature carbonization are recovered through a conduit 14 for refining in a tar recovery stage 16. The product char from the fluidized low temperature carbonization stage 12 is introduced through a conduit 18 into a briquet blending stage 20. High volatile caking bituminous coal 11 is introduced directly without thermal treatment into the blending stage 20 through a conduit 22. The pitch obtained from low temperature carbonization may be withdrawn from the tar recovery stage 16 through a conduit 24 and employed as the low carbon pitch of the briquet formulation. High carbon pitch is introduced into the briquet blending stage 20 through a conduit 26.

The raw briquet mixture is homogeneously mixed in the blending stage 20 and transferred to a kneading stage 28. The kneaded, blended raw briquet mixture is transferred to a briqueting stage 30 which employs forced feeding apparatus (schematically indicated) 32 to assure that the briquet forming pockets are substantially filled with raw mixture.

VProduct briquets are recovered from the briqueting stage 30 and passed over a screen 34 through which briquet fragments may be recovered for recycle in the r'aw briquet blending stage 20 through a conduit 36. The integral briquets are transferred by conveying means 38, preferably during the period 2 to 10 minutes after leaving the briqueting press 30 to a thermal treatment vessel 40.

The thermal treatment vessel 40 comprises three separated zones including an upper shock heating zone 42, a center calcining zone 44, and a lower cooling zone 46. Hot inert gases are introduced into the shock heating zone 42 through a conduit 48 and into the calcining zone 44 through a conduit 50. The hot gases introduced through conduits 48 and 50 supply the heat required for the thermal processing. Relatively cool gases are recovered through a conduit 52 between the shock heating zone 42 and the calcining zone 44. Evolved gases and tars are carried with the spent heating gases to a condenser 54. Readily condensible tar is recovered from the bottom of the condenser 54 through a conduit S6 and flashed in a distillation zone 58. The high boiling portion of the recovered tars is recovered from the distillation zone 58 through a conduit 26 for use as the high carbon pitch in the briquet formulation. The lower boiling liquid tar constituents are recovered as distillates through a conduit 60 and may be combined with the LTC tar for recovery of valuable liquid products. Non-condensible gases exiting from the thermal treatment vessel 40 through the conduit 52 are eliminated from the condenser 54 through a conduit 62.

The briquets entering the shock heating zone 42 are rapidly heated on their surface through the plastic temperature 'of the caking coal which they contain. The briquets are retained in the shock heating zone 42 until the briquets attain throughout a temperature in excess of 900 F.

The briquets at a temperature of 900 to l250 F. pass downwardly as a moving bed from the shock heating zone 42 into the calcining zone 44 where they are gradually further heated to a calcining temperature above l550 F. The calcined briquets pass downwardly as a moving bed into the cooling zone 46 and are discharged from the bottom thereof at a temperature below the atmospheric kindling temperature of the briquet. Cool inert gases are introduced into the cooling zone 46 through a conduit 64. The heated gases are recovered from the cooling zone 46 through a conduit 66. The gases emanating through the conduit 66 may be employed in a heat exchange 68 for generating low pressure steam which might be used, for example, in the kneading stage 22'5.

A"Product formcoke is discharged from the cooling zone 10 46 onto a screen 70 through which formcoke fragments can pass for return through a conduit 72 to be recombined in the raw briquet blend. The intact product formcoke is recovered from the screen 70 for use as a metallurgical fuel.

The time required to prepare formcoke after the briquets have been formed is about two hours, including the shock heating, calcining and cooling stages. The product has properties comparable to metallurgical coke which requires about eighteen hours processing time in v typical by-product coke ovens.

The properties of the formcoke produced by our invention can be illustrated by the petrographic photomicrographs and photographs presented in FIGURES 2 through 4.

FIGURE 2(A) is a photograph of a complete fragment o-f coke obtained from a by-product coke oven. The complete fragment of coke in FIGURE 2(A) comprises the cauliflower end (a), the dense, good metallurgical coke (b), and the weak, friable envelope coke (c). FIGURE 2(B) is a photomicrograph taken at 3 power magnification of a thin section of envelope coke. FIGURE 2(G) is a photomicrograph taken at 3 power magnification of a thin section of the dense good coke. FIGURE 2(D) is a photomicrograph taken at 3 power magnification of a thin section of coke from the cauliflower end of the coke fragment. FIGURE 2(B) is a photomicrograph taken at 15 power magnification of a thin section of envelope coke. FIGURE 2(F) is a photomicrograph taken at 15 power magnification of a thin section of the dense good coke. FIGURES 2(G) and 2(H) are photomicrographs taken at 15 power magnification of two thin sections of the cauliflower end of the coke fragment.

FIGURE 2(A) is representative of the coke product resulting from the conventional by-product coke ovens. When this coke is transported and used in metallurgical operations, the principal shatter, breakage and loss of product results from the relatively weak coke which occurs at the cauliflower end and at the envelope end of each coke fragment. The good, strong coke which is produced between the cauliflower and the envelope is the desirable product which possesses a relatively hornogeneous texture and a relatively thick cell wall structure.

Throughout FIGURES 2(B) and 2(H), the black areas of the photomicrographs indicate coke material and the white or gray areas indicate void spaces or cells. The friability of envelope coke is apparent from viewing FIG- URE 2(B) which indicates the lack of homogeneity, the highly porous composition and the relatively thin cell wall structure of envelope coke. The thin wall structure and high porosity of envelope coke is more apparent from inspection of FIGURE 2(B) which was obtained at higher magnification.

Cauliflower coke, on the other hand, possesses a more homogeneous texture and a generally higher density as evidenced by the smaller cell structure and the relatively thick cell wall structure. The cauliflower end of the coke, however, is highly fissured and cracked from the severe thermal stresses introduced into this material during its formation. Gross cracks and fissures in the coke are evident from an inspection of the coke fragment in FIG- URE 2(A). Microscopic cracks are evident from an inspection of FIGURES 2(D) and 2(G). In addition, the weaknesses in cauliflower coke appear to align themselves as indicated in FIGURE 2(H) by the general lineation from the point m to the point n. Along this lineation, an area of extremely thin wall structure indicates potentially severe weaknesses and probable fracture of the material under mechanical shock.

The dense, good metallurgical coke which exists between the cauliflower end and the envelope end of coke oven product is illustrated in FIGURES 2(G) and 2(F) as having a relatively homogeneous texture, a high density as indicated by relatively small cells and appreciable strength as indicated by the relatively thick cell walls. This is the dense, good coke which forms the overwhelming bulk of the coke oven product available for use as a metallurgical fuel. Thus the principal losses which occur in potentially realizable metallurgical fuel from byproduct coke ovens result from abrasion and shattering of the highly porous, friable envelope coke and of theVV highly fissured cauliflower coke. The fine particles resulting from abrasion and shattering form the bulk of the socalled coke oven breeze which is not marketable as a premium metallurgical fuel.

FIGURE 3 presents photographs of a typical calcined formcoke produced in accordance with the present invention. FIGURE 3(A) is a photograph o-f a pillow block formcoke briquet. Figure 3(B) is a photograph of a pillow block formcoke briquet which has been split along a longitudinal plane. An inspection of the gross properties of the formcoke briquets and fragments illustrated in FIGURES 3(A) and 3(B) shows a striking similarity to the dense, good metallurgical coke which has been shown in FIGURE 2(A) at (b). The formcoke possesses the lustery appearance which is characteristic of the graphitization of good metallurgical coke. From a microscopic view Ythe'formcoke cell structure resembles that of dense, goed metallurgical coke rather than either envelope coke or cauliflower coke.

FIGURE 3(C) is a photomicrograph taken at 3 power magnification of an entire longitudinal plane of a thin section of a formcoke briquet prepared according to the present invention. FIGURES 3(D) and 3(E) are photomicrographs taken at power magnification of thin sections o-f our product formcoke taken along a longitudinal and a transverse plane of a formcoke briquet respectively. The relatively homogeneous character of our product formcoke is apparent from inspection of FIGURES 3 (C) 3(D) and 3(E). The desirable properties manifested in FIGURES 3(C), 3(D) and 3(E) include a homogeneous texture, a relatively thick cell wall structure and an absence of fissures or lineations of weak cell walls. In addition, the absence of identifiable particles of the starting materials should be noted. The individual discrete starting materials have merged into a continuum of carbonaceous material in which the starting particles of material have lost their discrete identity.

Comparison of FIGURE 3(C) with FIGURES 2(B), 2(C) and 2(D) (all taken at 3 power magnification) would indicate that the formcoke of FIGURE 3( C) possesses a generally different texture and structure than any portion of the metallurgical coke fragments. However, comparison of our formcoke in FIGURES 3 (D) and 3 (E) with metallurgical coke in FIGURES 2(E), 2(F), 2(G) and 2(H) (all taken at l5 power magnification) shows the similarity which exists between our formcoke and the dense, strong metallurgical coke FIGURE 2(F). While the individual cells of our formcoke appear to be generally smaller than the individual cells of the dense, strong coke, nevertheless, the formcoke cell Walls are equally thick and strong in appearance. Moreover, the fact that the bulk density of our formcoke compares with the bulk density of good, strong metallurgical coke indicates that the fractional void space of our formcoke is about the same as the fractional void space of good metallurgical coke.

FIGURE 4 presents a photomicrographic comparison of thin sections of low strength metallurgical coke, high strength metallurgical coke and formcoke prepared according to the present invention. A thin section of low strength metallurgical coke (prepared from poorly coking coal blends) is presented in FIGURE 4(A) at 3 power magnification and in FIGURES 4(B) and 4(C) at l5 power magnification. A high strength metallurgical coke is presented in FIGURE 4(D) at 3 power magnification and in FIGURES 4(B) and 4(F) at l5 power magnification. Formcoke according to the present invention is presented n FIGURE 4(G) at 3 power magnification and in FIGURES 4(H) and 4(1) at 15 power magnification.

Microscopic cracks of the low strength metallurgical coke are apparent in the photomicrograph in FIGURE 4(A).V The highly porous nature of the low strength metallurgical coke is apparent from inspection of FIG- URES 4(A), 4(B) and 4(C). A general lineation of large cells joined by thin cell walls can be detected in FIGURE 4(0) The high strength metallurgical coke illustrated in FIG- URES 4(B), 4(B) and 4(F)'has a more nearly homogeneous texture, has generally smaller cells with larger cell wall structure and a less porous composition.

The formcoke of our invention much moreV nearly resembles the high strength metallurgical coke than the low strength metallurgical coke. The l5 power photomicrographs of our formcoke in FIGURES 4(H) and 4(1) illustrates a porous composition, a homogeneous texture and a thick cell wall structure similar to that shown for the high strength metallurgical coke in FIGURES 4(E) and 4(F). While the individual cells of our formcoke appearY to be generally smaller than those found in the high strength metallurgical coke, nevertheless, the fractional void space in both materials is about the same as evidence by the nearly identical bulk densities of the two materials.

EXAMPLE I To illustrate the formcoke preparation of our invention, 331 lbs. of briquet formulation was prepared as follows:

20.5 lbs. (6.2 wt. percent) of high carbon pitch.

17.5 lbs. (5.3 wt. percent) of low carbon pitch obtained from tar produced by iiuidized low temperature carbonization of Montour coal, a typical high volatile caking coal from the Pittsburgh seam. The material was mixed as a crushed solid capable of passing through a 0.5 mm. screen.

16.5 lbs (5.'0 wt. percent) of recycle formcoke fragments crushed to pass through a 3.0 mm. screen.

82.5 lbs (24.9 wt. percent) of Montour coal, a typical high volatile caking coal from the Pittsburgh seam. The material was crushed to pass through a 0.5 mm.

Y screen.

193.8 lbs. (58.6 wt. percent) of uidized LTC char prepared from Montour coal at a carbonizing temperature of about 925 F.

The formulation was well mixed at 50-52 C., kneaded for about 8 minutes at 95 C. and briqueted in a roll press maintained at 92-96 C. The raw briquets had a measured average point crushing strength of 30 kilograms when the briquet rolls were forced-fed, but only 24 kilograms when the rolls were not forced-fed.

46.5 pounds of the raw briquets were selected by hand picking to insure that only whole briquets were Vfurther treated. The briquets were shock heated in a hot oven tofabout 500 C. in less than 30 minutes and thereafter heated to about 930 C. in an additional 270 minutes. The calcined briquets were cooled and recovered.

The product formcoke had a Micum abrasion index of l 95.9%. Micum abrasion indices above about 90% are considered to represent excellent metallurgical 5 coke. Values above Vabout are considered to represent acceptable metallurgical coke. The porosity was 50.34%. The true density was 1.80. The volatile matter content was 1.3%.

29.3 pounds of coke was produced from the 46.5 pounds of starting briquets. Only 1.9 pounds of the coked product was in the form of particles which would pass through a 10 mm. screen. 24.1 pounds of the coke appeared intact in the uniform shape of the original briquets. 3.3 pounds of the coke appeared as briquet fragments which were retained on a 10 mm. screen.

EXAMPLE II A briquet formulationwas prepared from low temperais" l ture carbonization char which was prepared in a rotating kiln (Disco process) instead of by a uidized process. The formulation was as follows:

5.3 weight percent of low carbon pitch obtained from tar produced by iiuidized low temperature carbonization of Montour coal, a typical high volatile caking coal from the Pittsburgh seam.

6.2 weight percent of high carbon pitch.

5.0 weight percent of recycle formcoke fragments crushed to pass through a 3.0 mm. screen.

25.0 weight percent of Montour coal, a typical high Volatile caking coal from the Pittsburgh seam, crushed to pass through a 0.5 mm. screen. L

58.5 weight percent of crushed LTC char prepared by the Disco process in a rotating kiln at S50-900 F. The crushed char passed through an 8 mesh Tyler standard screen; 5.7 percent was retained on a 14 mesh Tyler standard screen; 25.5 percent passed through a 325 mesh Tyler standard screen.

Ten briquets (one-inch pillow blocks) were prepared at 100 C. under 5000 p.s.i. pressure. The briquets were shock heated to 1l00 F. and thereafter calcined at 1800 F. for 30 minutes. The heating rate during calcining was 20 F. per minute. The resulting briquet product was severely cracked; not one briquet remained intact.

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 invention may be practiced otherwise than as specically illustrated and described.

We claim:

l. A porous formcoke of substantially uniform size and shape obtained by the coking of a composition having a volatile matter content in excess of 22 percent and containing to 35 percent by weight of a particulate bituminous caking coal, 80 to 45 percent by weight of a uidized low temperature carbonization char derived from bituminous coal, and 6 to 20 percent by weight of pitch derived by pyrolysis of bituminous coal, said formcoke having a substantially homogeneous carbonaceous continuum, a Micum abrasion index above 90 percent, an apparent density of 0.80 to 0.95, a volatile matter content less than 2 percent and being substantially free of discrete granular particles of the starting materials.

2. A composition for use as a raw material in the preparation of formcoke which comprises 10 to 35 percent by weight of a finely divided caking bituminous coal, 80 to 45 percent by weight of char having a bulk density less than 30 pounds per cubic foot and which has been produced by uidized low temperature carbonization of bituminous coal and 6 to 20 percent by weight of pitch obtained by pyrolysis of bituminous coals and having a melting point (ring and ball) of 60 to 90 C. including at least 1 to 12 percent by weight of a high carbon pitch which has a xed carbon content exceeding 25 percent and up to percent by weight of a low carbon pitch which has a fixed carbon content less than percent, said coal, char and pitch being substantially homogeneously intermixed and having a volatile matter content, when intermixed, in excess of 22 percent.

3. The composition of claim 2 in which the high carbon pitch is a product of coal pyrolysis and has been heated to a temperature above about 1500 F.

4. The composition of claim 2 in which the high carbon pitch is obtained from the evolved hydrocarbonaceous vapors resulting from coking of compositions as dened in claim 2.

5. The composition of claim 2 in which the low carbon pitch is obtained from the evolved hydrocarbonaceous vapors resulting from fluidized low temperature carbonization of high, volatile bituminous coal.

-6. *The* composition of claim 2 in whichV up to about 8` percent by weight of tinely divided fragments of calcined formcoke is homogeneously intermixed therewith.

7. A porous formcoke of substantially uniform size and shape obtained by shaping the composition of claim 2 and coking the shaped composition, said coking including the steps of shock heating the composition to a temperature above the plastic temperature of the coal, retaining the shaped composition at a temperature below about 1250 F. until the entire composition has attained a temperature above the plastic temperature of the coal and thereafter continuing to heat the resulting coked composition to a calcining temperature.

8. The composition of claim 2 in which the char has not been heated to a temperature above 1350 F. and has has been produced by the uidized low temperature carbonization of high volatile bituminous coal.

9. A method for preparing formcoke comprising substantially homogeneously intermixing 10 to 35 percent by weight of a finely divided caking bituminous coal, to 45 percent by weight of char having a bulk density less than 30 pounds per cubic foot which has not been exposed to a temperature above 1350 F. and which has been produced by fluidized low temperature carbonization of high volatile bituminous coal, 6 to 20 percent by weight of pitch obtained by pyrolysis of bituminous coal and having a melting point (ring and ball) of 60 to 90 C. including at least 1 to 12 parts by weight of a high carbon pitch obtained by pyrolysis of bituminous coal which has a ixe-d carbon content exceeding 25 percent and up to 15 percent by weight of a low carbon pitch obtained by pyrolysis of bituminous coal which has a fixed carbon content less than 20 percent, pressing a shaped briquet from the resulting mixture at a temperature slightly above the melting point of said pitches, coking the said shaped briquet by iirst shock heating to a temperature above the plastic temperature of the coal, retaining the briquet at a temperature below about 1250 F. until the entire briquet has attained a temperature above the plastic temperature of the coal, and thereafter continuing to heat the resulting coked briquet to a calcining temperature.

l0. A method for preparing formcoke comprising substantially homogeneously intermixing 10 to 35 percent by weight of a finely divided caking bituminous coal, 80 to 45 percent by weight of char, having a bulk density less than 30 pounds per cubic foot which has not been exposed to a temperature above 1350 F. and which has been produced by uidized low temperature carbonization of high volatile bituminous coal, 6 to 20 percent by weight of pitch obtained by pyrolysis of bituminous coal and having a melting point (ring and ball) of 60 to 90 C. including at least 1 to 12 percent by weight of a high carbon pitch obtained by pyrolysis of bituminous coal which has a fixed carbon content exceeding 25 percent and up to l5 percent by weight of a low carbon pitch obtained by pyrolysis of bituminous coal which has a fixed carbon content less than 20 percent, pressing a shaped briquet from the resulting mixture at a temperature slightly above the melting point of said pitches, coking the said shaped briquet by first shock heating to a temperature above the plastic temperature of the coal, retaining the briquet at a temperature below about 1250 F. until the entire briquet has attained a temperature above the plastic temperature of the coal, thereafter continuing to heat the resulting coked briquet to a calcining temperature above l550 F., recovering the resulting calcined briquet as product, recovering the evolved hydrocarbonaceous vapors resulting from the coking and calcining treatment, recovering from said evolved hydrocarbon vapors the high carbon pitch for use as the said high carbon pitch.

l1. A method for preparing formcoke from high volatile caking coal comprising subjecting a portion of high volatile caking coal to low temperature carbonization under fluidized conditions, recovering evolved hydrocarbonaceous LTC vapors and particulate uidized LTC char i5 having a bulk density less than 30 pounds per cubic foot, recovering low carbon pitch from said evolved hydrocarbonaceous LTC vapors, substantially homogeneously intermixing a briquet formulation comprising 10 to 35 percent by weight of nely divided high volatile caking coal, S0 to 45 percent by weight of said iluidized LTC char, 6 to 20 percent by weight of pitch including at least 1 to 12 percent by Weight of a high carbon pitch and up to 15 percent by weight of said low carbon pitch, pressing a shaped briquet from the resulting mixture at a temperature slightly above the melting point of said pitch, coking the said shaped briquet by first shock heating to a temperature above the plastic temperature of the coal, re taining the briquet at a temperature below about 1250 F. until the entire briquet has attained a temperature above the plastic temperature of the coal, thereafter continuing to heat the resulting coked briquet to a calcining temperature above 1550 F., recovering evolved hydro` carbonaceous vapors from the coking and calcining treat'- Y ments, recovering high carbon pitch from said last-mentioned hydrocarbonaceous vapors for use as the high carbon pitch component in said briquet formulation, and recovering a calcined coked briquet as product.

References Cited in the iile of this patent UNITED STATES PATENTS

Claims

11. A METHOD FOR PREPARING FORMCOKE FROM HIGH VOLATILE CAKING COAL COMPRISING SUBJECTING A PORTION OF HIGH VOLATILE CAKING COAL TO LOW TEMPERATURE CARBONIZATION UNDER FLUIDIZED CONDITIONS, RECOVERING EVOLVED HYDROCARBONACEOUS LTC VAPORS AND PARTICULATE FLUIDIZED LTC CHAR HAVING A BULK DENSITY LESS THAN 30 POUNDS PER CUBIC FOOT, RECOVERING LOW CARBON PITCH FROM SAID EVOLVED HYDROCARBONACEOUS LTC VAPORS, SUBSTANTIALLY HOMOGENEOUSLY INTERMIXING A BRIQUET FORMULATION COMPRISING 10 TO 35 PERCENT BY WEIGHT OF FINELY DIVIDED HIGH VOLATILE CAKING COAL, 80 TO 45 PERCENT BY WEIGHT OF SAID FLUIDIZED LTC CHAR, 6 TO 20 PERCENT BY WEIGHT OF PITCH INCLUDING AT LEAST 1 TO 12 PERCENT BY WEIGHT OF A HIGH CARBON PITCH AND UP TO 15 PERCENT BY WEIGHT OF SAID LOW CARBON PITCH, PRESSING A SHAPED BRIQUET FROM THE RESULTING MIXTURE AT A TEMPERATURE SLIGHTLY ABOVE THE MELTING POINT OF SAID PITCH, COKING THE SAID SHAPED BRIQUET BY FIRST SHOCK HEATING TO A TEMPERATURE ABOVE THE PLASTIC TEMPERATURE OF THE COAL, RETAINING THE BRIQUET AT A TEMPERATURE BELOW ABOUT 1250* F. UNTIL THE ENTIRE BRIQUET HAS ATTAINED A TEMPERATURE ABOVE THE PLASTIC TEMPERATURE OF THE COAL, THEREAFTER CONTINUING TO HEAT THE RESULTING COKED BRIQUET TO A CALCINING TEMPERATURE ABOVE 1550*F., RECOVERING EVOLVED HYDROCARBONACEOUS VAPORS FROM THE COKING AND CALCINING TREATMENTS, RECOVERING HIGH CARBON PITCH FROM SAID LAST-MENTIONED HYDROCARBONACEOUS VAPORS FOR USE AS THE HIGH CARBON PITCH COMPONENT IN SAID BRIQUET FORMULATION, AND RECOVERING A CALCINED COKED BRIQUET AS PRODUCT.