US3010882A - Process of extruding anthracite coal to form a metallurgical coke-like material - Google Patents

Description

Nov. 28, 1961 Filed July 14, 1952 A METALLURGICAL COKE-LIKE MATERIAL 2 Sheets-Sheet .2

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cAesomzms RETOQT a 4.:- J A f J P2 l INVENTOR KENNETH M. DAfiCl/l r 40m J/Voszcs ATTORNEY 3010 882 inmates or nxrnuhnsc A crrn COAL TO FORM A METALLURGICAL (IOKE-LIKE MATE Kenneth M. Barclay, Stockton, N.J., Elon John Nobles,

This invention relates to the production of solid fuels, more particularly to the production of metallurgical or foundry grade coke from anthracite coal.

As is known, the metallurgical coke which is used is largely produced in by-product coke ovens by high temperature distillation of blends of selected grades of bituminous coal. The physical structure of the by-product coke oven and the established specifications of metallurgical coke impose diificultly attainable criteria for the bituminous coals which are suitable for such coke production included among which are low sulfur content of the coal, suitable coking properties, low swelling characteristics and the like. These requirements seriously limit the potential supply of coal suitable for processing in byproduct ovens.

A long standing and still extant problem in the coal industry has been the economical or profitable disposition of anthracite fines formed during the course of mining and sizing the coal. An important tonnage of such fines are produced, for example, in the floatation process of treating coals.

A major objective of the present invention is to devise a method of converting anthracite coal into a metallurgical grade coke.

A further objective is to provide a method of treating culm or other finely particulated anthracite coal in an economical manner to produce therefrom an improved product of enhanced value in the industry.

An additional objective is to produce from anthracite coa-l a metallurgical grade coke of special physical structure and configuration whereby it is rendered particularly valuable in the metallurgical fields.

With these and other correlated objects in view, the concepts of the invention comprehend the treatment of anthracite coal in rather finely particulate form under special conditions to convert it into agglomerated units of defined configuration and adapted to function effectively as a metallurgical grade coke. The advantages accruing from this concept will be readily apparent and evaluated from a consideration of the operation as indicated in the accompanying drawings in which:

FIG. 1 is a simplified flow sheet of the process;

FIG. 2 is an enlarged cross-section of one type of briquette producible by the process;

FIG. 3 is an enlarged schematic detail of the extrusion die;

FIG. 4 is a schematic illustration of a modified form of apparatus which may be employed in carrying out the process;

FIG. 5 is a vertical cross section of the distillation and carbonizing retort.

Considered bn'efiy, the improved process of the invention involves the preforming of anthracite fines under conditions adjusted and controlled to produce a tough,

compact and rugged unit and the subsequent heat treatment of the preformed unit to produce a low volatile coke unit of predetermined configuration by reason of which it serves effectively as a solid fuel and is especially suitable for use, among other things, as foundry coke.

It is to be noted, initially, that the art is replete 'with proposed methods of briquetting carbonaceous materials I such "as Wood, peat, bituminous coal and mixtures of shortened depending 3,010,882 Patented Nov. 28, 1961 were concerned with the production of, a briquette which could be utilized as a household fuel. It is particularly to be observed that the present invention is concerned with the treatment of anthracite coal by a procedure and under conditions controlled to produce a product of such physical and chemical characteristics that it provides an excellent grade of metallurgical coke.

The starting material utilized in the process comprises anthracite coal. This may be derived from any source such as screenings, floatation concentrates and the like, and if not previously reduced to the desired fineness, are ground. Preferably the particle size of the anthracite fines should be such that 100% pass through a 20 mesh screen and 70 to are retained on a 200 mesh screen.

As shown in the drawings, the anthracite fines are passed from the hopper or other storage container 1 through the dryer 2 in which they are dried to the desired moisture content of between about 6 and 10 percent. Water vapors evolved during the drying pass off through flue 3 and the dried fines are discharged through a suitable conduit 4 to a mixing device 5 in which they are thoroughly mixed with a binder fed to the mixer from a binder supply tank 6.

It has been ascertained that in order to insure satisfactory subsequent extrusion of the coal-binder mix and the production of a formed unit of the desired physical characteristics, the step of incorporating the binderwith the coal fines should be carefully controlled. In a typical procedure of the order of about six to about fourteen parts of binder are mixed with about 94 to 86 parts by weight of coal. The binder preferably comprises hydrocarbon pitch although other binders may be utilized.

The mixing of the binder and coal fines is carried out under conditions which insure eflfective wetting of the coal particles by the binder and a homogeneous distribution of the binder through the mixture. For this purpose the binder should, preferably be in fluent condition.

As a result of extensive experimentation and tests, it has been ascertained that the most effective mixture from which to form improved compacted units is achieved when the mix contains between about 6% and 12% of water. The role or function. of water in the mix is not completely understood. It does appear that it insures better plasticity or lubricity of the coal particles, possibly because of some emulsification of the liquid binder phase. Whatever may be the mechanism of the action involved, it has been determined that the presence of a certain amount of water is an important factor, not only in respect to themixing operation, but also in subsequent extrusion. If the moisture content of the coal charged'to the mixer is below about 6%, water should be added to bring the moisture content to the above described range.

In the preferred method of operation, the preheated fluent binder, at a temperature of between about 300-350" F.,'is added to the coal through one or more; distributors 6' through which the binder may be forced or aspirated by steam. In the preferred operation the fluent binder is added in distributed or spray form continuously during the mixing operation.

wetting of the coal particles. It has been found that with a paddle mixer and utilizing the stated proportions of binder and coal, such uniform mixing is achieved in a period of about 15 minutes more or less. As will be appreciated, other types of mixing apparatus may be em ployed and the mixing period may be lengthened or on the efficiency of the particular machine.

to charge to the retort for final carbonization.

While the process will be described as a batch operation, it will be understood that by the proper design of the mixer insuring sufficient retention time therein, the mixing and extrusion operations may be carried out continuously. A a I I The coal-binder mix which is prepared in mixer Sis discharged through a conduit 7 to the extruder 8. While not shown, it will be understood that the conduit 7 is provided with any suitable type of measuring valve to control the input rate of the plastic mix to the extruder.

The extruder may be of any suitable standard type which is modified to produce the desired compactness and structure of the formed unit, i.e., one in which the mix is forced through a bore having a tapered or converging section associated with an axially positioned mandrel having a reversely tapered section opposite said converging section. Such a unit is more particularly disclosed in the copending application of Kenneth M. Barclay Serial No.

298,726, filed July 14, 1952. The simplified form shown With an extruder of this type Operating at low pressures,

i.e., below 500 psi. and preferably of the order of 100 p.s.i., dense tough and uniformly compacted cylinders are produced. It is to be observed that the uniform or even compaction of the unit is a factor of salient im-' .portance in the present invention because this uniformity is necessary if excessive cracking is to be avoided inthe subsequent carbonization of the unit. 7

While in the preferred mode of procedure, for reasons subsequently to appear, the unit is extruded in the form of a cylinder, it will be apparent that differently formed units may be produced such as polygonal shaped hollow units, solid cylinders and the like. ,7

The continuous compacted tube of bonded coal discharged'from the extruder is preferably cut into small,

readily handled units of the order of about three to five or more inches in length. This may be done by severing the discharged extruded tube at the nozzle and depositing the severed sections on a suitable continuous conveyor 15. As shown, a suitable automatic cutting mechanism illustrated by the knife 14 is positioned adjacent the end of the extrusion tube and isset or controlled to sever the tube into sections of the desired length. Whenever desired the tube may be out not only laterally but also longitudinally to produce one or more segments.

While for illustrative purposes'a longitudinal extruder has been shown and described, it will be understood that a vertical extruder may be employed; Similarly, if desired,

multiple head extrusion machines may-be used.

The raw units thus produced are subsequently carboriized to produce a dense, strong metallurgical coke-like product. There are a number of phy'sical characteristics which determine the-essential utility ofa fuel unit as a metallurgical coke, among which are,-the reaction rate or combustion behavior, volatile matter, bulk density, physical strength as indicated by'shatter strength, tumbler test and the like. It has been found that when raw head load strength during carbonization is limited, the initial stage of carbonization can best be done in a heating zone in which, by mechanical means, the head load is reduced to a point where undue deformation does'not take place.

In such first stage temperatures of the order of 370 C.

to 490 C. may be-utilized.1This treatment produces .firmly bonded strong units 'of sutlicient head load strength As shown on the drawings, the cut green units are preferably quickly transferred by any suitable conveyer-15 and are discharged through a chute 16 to a first stage carbonizer 17 of any suitable type in which the units are raised to the described temperature in a period of time sufiicient to develop strength and evolve gases at such a rate which is insuflicient to distort the units. The furnace may comprise, for example, one of the horizontal type provided with the continuous grate conveyer which transports the units through the furnace at a predetermined rate. The furnace may be heated in any desired manner as by gas entering through line 19 or from the retort 25. The furnace is provided with exhaust stack 20 in which suitable condensers (not shown) may be interposed to condense and recover volatile products evolved during the thermal treatment. A V

The preconditioned units are then charged through the passageway 21 to the carbonizing zone in which they are carbonized at a finishing temperature of from about 850 C. to 1000 C. or more to produce exceptionally tough,

' tubular or other shaped units of low volatile content, of

the order of from 1 to 2%. It will be understood that the finishing temperature is chosen in relation to the desired reactivity and volatile content of the coke.

The particular method of carbonizing the extruded units is specifically correlated with the character and configuration of such units. Such carbonization zone essentially comprises a retort in which theextruded units are progressively: heated up to the finishing temperature by direct contact with hot, non-reactive gas, that is a gas which has no material. action on the coke, which is comprised in part of gas evolved from the coal which is stripped of its volatile components and is then recycled.

As shown in FIG. 1, the units to be carbonized are fed through passageway 21 which may be provided with a suitable gas seal and are discharged into carbonizing retort 25. In the retort, in a manner to be more fully described, the hollow extruded units are directly contacted with an upwardly flowing stream of nonreactive gas made up, in effect, of two merged streams. One stream is fed through line 26 to a combustion chamber where it is suitably burned with added air or oxygen and then enters the tuyeres. This gas stream is preferably a stripped product gas, i.e., one derived from the distillation in the retortwhich has been stripped of condensable components. A stream of similarly derived gas is fed to the bottom of the retort through line 27. This enters at the bottom in controlled quantities serving first to quench the finished coke being thereby preheated and passing upwardly merges with the hot tuyere gas entering from the tuyere sections.

The gases and vapors distilled from the coal during the carbonizing pass overhead through a main 28 to a tar knockout or settling box 29. The gas from which a substantial amountv of tar and pitch has been separated in box 29, passes through line 30 and may be subjected to any conventional or suitable methods to'separate further quantities of tar and to separate condensable components such as light and heavy oils. The refined gas resulting from such partial or substantially complete purification serves as a recycle gas fed through lines 26 and 27.

The finished quenched coke units are discharged through a suitable gas seal 31 to a car loading conveyer quench gas in the described manner insures high thermal economies since the sensible heat abstracted from the finished coked extrusions is later transferred to the incoming charge of extruded units entering the upper section by the retort. The gas going through line 26 may, if desired, be indirectly heated.

As intimated previously, the correlation of the particular configuration of the extruded units and the carbonization of these by direct contact with hot gases produces notably improved results. In its passage through a bed of such tubular .bonded units, theggases contact a 'very susbtantial areaof, thejunits passing through the his to be noted that utilizing the product gas as a amuse centers as well as around the exteriors of such units. This insures rapid heat transfer from the gas to the solid units and insures a more uniform penetration of heat as compared to the ovoid shape of conventional briquettes. The shape of the extruded units imparts high permeability to the bed of units, not only in the carbonization zone but in later operations, as for example, when the coked product is employed as a fuel in a cupola. Similarly, the shape of the extruded units insuring a uniform dimension in cross-section assures a more even shrinkage during devolatization or distillation with a consequent reduction in cracking and an increase in toughness of the carbonized units, the enlarged exposed surface area of the tubular units also improves the effect of the hot gases in sweeping out the volatile material as it is evolved during passage of the tubular units through the carbonization zone.

While the bonded extruded units herein described may be carbonized in any type of retort in which they are brought into contact with hot gases, at sufliciently elevated temperature, it has been found that best results are secured by passing the units downwardly through a vertical retort in countercurrent contact with a stream of upwardly flowing gas having a low or negligible partial pressure of volatile evolvable from the coal. A particularly effective carbonizing retort for accomplishing this is illustrated more in detail in FIG. 5. The gas going through line 26 may, if desired, be indirectly heated.

As shown in FIG. 5, the extruded pieces after preconditioning in the first stage carbonization zone 18 are fed from the hopper 22 over screen 34 and through the rotary gas seal 23 to retort 25. As will be understood, the screen 34 separates out any fines that may have formed during previous handling of the extruded units.

The carbonizing retort may be of any suitable design and construction and of the desired capacity. Essentially such retort comprises a steel shell provided with a suitable refractory lining such as fire brick and, if desired, may be lagged on the exterior with insulating material. The contour and height of the various parts of the retort are determined by the rate of heating desired and the ultimate finishing temperature.

The extruded tubular units passing downwardly through the retort, as noted previously, are contacted with an upwardly flowing stream of hot, non-reactive gases, flowing into the retort through lines 26 and 27. The stream entering from line 26 is indirectly heated or heated by partial combustion in the combustion chamber 25' and fed through the tuyeres into the retort. Air for such partial combustion may be introduced under pressure through blower 35 and line 36.

In bringing the retort up to temperature preparatory to putting it on stream, the gas feed line 37 may be employed since for such preheating operation the volume and temperature of tuyere gas is not particularly important.

The stream of quench gas enters the lower quench section 38 of the retort in controlled quantities contacting and abstracting heat from the finished units being thereby preheated and then subsequently mixes with gas entering through the tuyeres.

In their passage down the retort the extruded units are subjected to an increasing temperature gradient during which passage condensable, volatile material and fixed gases are evolved. In operating the process, the quantities of gases fed through lines 26 and 27 and the temperature of the tuyere gas are so correlated and controlled that the volume of gas passing upwardly in the retort has a heat capacity which substantially balances that of the charge of briquettes being heated. In passage down the retort, the units are subjected to increasing temperatures and at such a rate as to avoid distortion and cracking of the extruded units. In the lower section of the retort the extruded units are subjected to the desired high finishing temperature of from 800 C. to 1000" C. and are thereafter quenched in the manner described.

6 The upwardly flowing gases sweep the evolved tars into the upper cooler section of the retort thereby minimizing cracking of these products.

If desired, an additional stream of product gas may be advantageously utilized in the carbonization. retort, if the first stage carbonizcr 17 is not used. This is fed into the upper section of the retort through line 50 after being preheated to a temperature of the order of 200 C. to 400 C. Because of its sensible heat, this gas serves to heat the incoming units and this minimizes or inhibits the condensation of tar from the tar-laden vapors which condensation would occur ifsuch vapors were contacted withcold briquettes. This entering stream of flush gas enters the retort in a direction countercurrent to the main stream of gas passing upwardly in the retort and thus checks the flow of the latter into the top cooler section of the retort where condensation of tar might otherwise occur.

The gases with their contained vapors and entrained material pass through a downcomer pipe 28 to the tar knock-out or settling box 29. As the gas stream enters the line 28, it is advantageously continuously sprayed with a coolant, such as water, entering through line 39. This coolant may be continuously recirculated by withdrawing it as a supernatantliquor from the knockout box 29 through line 40 and pump 41 and forced through line 39. Requisite make-up coolant may be admitted to the circuit through valve controlled line 40'.

The liquid tar which settles out in box 29 is withdrawn through line 42 and forced by pump 43, controlled by a variable speed controller 44, through the line 45 and after suitable fractionation a portion may be utilized for the binder requirements in the initial coal-binder mixing operations. Excess above such requirements may be directed through line 46 and processed in any desired manner. Additional fluent tar or pitch fractions may be added to the cycle through the binder make up tank 6.

The gas from which the tar has been scrubbed is passed overhead through line 30 and may be treated by conventional methodsto separate additional quantities of tar and to condense and fractionate the contained condensable components. The gas freed from such condensable component serves as a source of the recycle gas for the carbonizing retort and may, whenever required, be supplemented by gas introduced into the cycle from an extraneous source.

While previously described retort represents the presently preferred physical structure, it will be understood that other designs may be used and the invention is con sidered to comprehend any functional equivalent.

The process of the invention and the products produced are of marked technological significance and value. As noted previously, the potential supply of coking coals suitable for processing in a by-product coke oven are limited and are constantly diminishing. One of the factors that limits the choice of coal suitable for conversion to a metallurgical grade coke is the sulfur content of the coal. Although under the exigencies of high production demands during the last war the tolerable sulfur content of metallurgical coke was somewhat increased, it still remains a rather rigid specification which heretofore could be satisfied only by a careful choice of coking grades of low sulfur bituminous coal.

. There are certain substantial deposits of anthracite coal notably in the Pennsylvania anthracite region which arecharacterized by a low sulfur content of the order of 1% or less of sulfur. These coals may be processed and indeed are a preferred type of raw material for producing an excellent grade of metallurgical coke according to the described process. A specific objective and achievement of the invention is therefore the conversion of such low sulfur anthracite into more valuable products, namely,

' metallurgical coke. The economic significance of, ineffect, providing 'a new and relatively abundant raw ma- 7 terial for-the production of metallurgical coke will be luminously obvious to those skilled in the'art.

The product produced by the described method possesses many distinctive advantages. The carbonized extruded units are uniform in size and composition and this aids greatly in maintaining uniform operation during its use, as for example, in a cupola operation. Fuel size generally, as is known, is of importance because this is a factor of major importance in establishing the permeability of bed to the passage of gases. The new fuel of the invention,'because of its special configuration, i.e., with a central bore or hole, markedly increases the ease with which gases can pass through a bed of this fuel.

Another outstanding characteristic of this fuel is its controllable bulk density. Tests were conducted in which substantial samples of the order of 200 pounds and more were admitted to large cylindrical containers in such a manner as to produce random orientation. It was determined that the bulk density wasof the order of 33-34 pounds per cubic foot which compares most favorably with the 2830 pounds per cubic foot for typical foundry coke. This measurement of bulk density was confirmed by actual test in a cupola in which from the weight of fuel charged and the depth of bed the bulk density was estimated at 33 pounds per cubic foot. These tests were made on tubular extruded carbonized briquettes of 4 inch external diameter and a 1.5 inch bore and between 3' and 5 inches in length. As will be appreciated, the bulk density can be considerably varied 'by varying the sizeof the diameter of the bore. The central bore or hole increases the wall surface area per unit volume; this is, of course, of particular moment because such an increase in surface area speeds the rate of carbonization of the briquettes and also aids combustion of the coked briquettes when employed as a fuel.

.A series of operations carried out in standard cupolas following normal procedure but using the fuel of the invention in lieu of foundry coke definitely established the product as an effective fuel.

havior. The shape of the identifiable anthracite coke in the drop varied in size; but retained the exact shape of the original tubular units with substantially the same thickness of fuel burned off all faces,'i.e., the interior or bore, the exterior and ends. important property for it imparts an-increased permeability to the bed as the fuel is consumed. This result is produced because the volume of the center void in each cylinder increases at a rate greater than the decrease in overall volume of the cylinder. The remarkable mechanical strength ofthe carbonized product is demonstrated by the fact that units removed from the cupola 'in incandescent state with a full burden above still retain their shape and structure. I

It will be appreciated that wide permissive variations in procedure are inherent within the scopeof the invention. Thus if desired, in lieu of the separate stage heating disclosed in FIG. 1, the first stage carbonization may be directly associated with the final carbonization stage as shown,'for example, in FIG. 4. The first stage carbonization zone which may conveniently take the form of a horizontal furnace may comprise the continuous conveyor 18' which receives the green extrudedfunits from conveyor 15 and after heating to the desired temperature for the requisite period of time in furnace 17 may be heated by hot gases from retort 25' and preferably after such gases havebeen stripped of condensible material. r a

While a preferred mode of procedure has been described, it is to be understood that this may be modified within the scope of the invention .by utilizing functionally equivalent steps for the illustrative ones described. The

An interesting and impor-. tant characteristic of the new fuel is its combustion'be This is a particularly.

8 the results desired in a particular metallurgical operation. 7 We claim: a a '1. A process of producing metallurgical coke which comprises thoroughly admixing finely particulated anthracite coal with a fluent'carbonaceous binder preheated to a temperature of approximately 300 F. to 350 F. and in atomized form for a period of time sufiicient to effectively coat and the coal particles and produce a plastic mass of uniform consistency containing from about 6% to about 12% Water, said binder being gradually added during the mixing operation, extruding the plastic mass through a die orifice under a pressure of approximately 100 psi. to form a continuous tubular unit, cutting the unit into sections of selected length, carbonizing such units by passing them downwardly through a vertical carbonization zone in contact with a countercurrent stream of hot, non-reactive gas and withdrawing such units from the Zone after heating to a finishing temperature of between 850 C. and 1000 C.

2. A processof producing metallurgical coke which comprises admixing finely particulated anthracite coal with a heated fluent carbonaceous binder in atomized form for a period of time sufiicient to insure eifective coating of the coal particles by the binder and to produce a plastic mass of uniform consistency, said binder being gradually added during the mixing operation, extruding the plastic mass into a tubular unit of selected size and shape, severing the tubular unit into sections of predetermined length, and carbonizing the tubular sections by direct contact with a flowing stream of non-reactive gas and at a finishing tem-' perature of between about 850 C. and 1000 C.

3.- A process in accordance with claim 2 in which the binder is comprised of coal tar pitch preheated to a temperature above about 300 F.

4.'A process in accordance with claim 2 in which the binder is comprised of petroleum asphalt.

5. A process of producing metallurgical coke which comprises thoroughly admixing finely particulated anthracite coal with an atomized heated coal tar binder for a period of time sufiicient to efliectively coat the coal particles and produce a plastic mass of uniform consistency containing from about 6% to about 12% water, said binder being gradually added during the mixing operation, extruding the plastic mass through a die orifice under a pressure of approximately 100 psi. to form a continuous tubular unit, cutting the unit into sections of selected length, carbonizing such units by passing them downwardly through a vertical carbonization zone in contact with a countercurrent stream of hot, non-reactive gas and withdrawing such units from the zone after heating to a finishing temperature of between 850 C. and 1000 C.

6. A method of treating low sulfur anthracite coal to produce a metallurgical coke which comprises finely grindwith a flowing stream of hot non-reactive gas, continuing end product similarly is susceptible of wide permissive the heating to a finishing temperature of between about 850 C. and 1000 C. and removing the carbonized units from the carbonization zone.

References Cited in the file of this patent UNITED STATES PATENTS 42,163 Pierre Apr. 5, 1864 175,744 Penrose Apr. 4, 1876 846,958 Sheldon Mar. 12, 1907 1,618,248 Walton -c Feb. 22, 1927 (Other references on following page) UNITED STATES PATENTS Archbald Oct. 20, 1931 Trent Oct. 10, 1933 Archbald Oct. 10, 1933 Berry Sept. 27, 1938 Wulf Mar. 23, 1943 Storrs May 23, 1944 Otto July 18, 1944 10 Otto July 18, 1944 Otto Aug. 14, 1945 Van Ackeren June 6, 1950 Berl Apr. 1, 1952 OTHER REFERENCES US. Dept. of Interior Information Circular No. 7462, June 1948, pages 32 and 33.

Claims (1)

1. A PROCESS OF PRODUCING METALLURGICAL COKE WHICH COMPRISES THROUGHLY ADMIXING FINELY PARTICULATED ANTHRACITE COAL WITH A FLUENT CARBONACEOUS BINDER PREHEATED TO A TEMPERATURE OF APPROXIMATELY 300*F. TO 350*F. AND IN ATOMIZED FORM FOR A PERIOD OF TIME SUFFICIENT TO EFFECTIVELY COAT AND THE COAL PARTICLES AND PRODUCE A PLASTIC MASS OF UNIFORM CONSISTENCY CONTAINING FROM ABOUT 6% TO ABOUT 12% WATER, SAID BINDER BEING GRADUALLY ADDED DURING THE MIXING OPERATION, EXTRUDING THE PLASTIC MASS THROUGH A DIE ORIFICE UNDER A PRESSURE OF APPROXIMATELY 100 P.S.I. TO FORM A CONTINUOUS UNIT, CUTTING THE UNIT INTO SECTIONS OF SELECTED LENGTH, CARBONIZING SUCH UNITS BY PASSING THEM DOWNWARDLY THROUGH A VERTICAL CARBONIZATION ZONE IN

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