US2595234A - Process for the production of fuel gas from carbonaceous solid fuels - Google Patents

Description

Patented May 6, 1952 UNITED STATES PATENT OF F ICE Du Bois Eastman, Whittier, Calif., assignor to The. Texas Company, New York, N. Y., acon poration of Delaware Application June 15, 1949, sei-iai No. 99,182v

claims. (CI. 1s- 202) This invention relates to a process for the-production of fuel gas from a carbonaceous solid fuel. In one of its-more specific aspects this invention relates to an improvedl process for the distillation of coal and the simultaneousmethanizati'on of carbonY monoxide and hydrogen to produce a fuel gas of relatively high heating value. The process of this invention may beV applied to the gasification ofv coke, oil shale, and various grades off' coal including anthracite, lignite; and bituminousv coals.

Anobject of this invention is to provide an improved process for the `gasification of solid carbonaceousfuels.

Another object of this invention is to provide for the production offuelgas from` solid fuels.

Still another object of this invention is to provide for the distillation of volatilizable constituents from solid carbonaceous materials containing volatilizable constituents'.

Alfurther objectof` this invention is to provide for themethanization of carbon monoxide and hydrogento -produce a fuel gas of high heating value;

In aicopending application of du'Bois Eastman and Leon-V P. Gaucher, Serial No. 49,626, led September 16, 1948, (D#31,-208), a novel process for pulverizing carbonaceousv solidsis disclosed. Inaccordance Withthe-method disclosed in said application, particles of a solid -carbonaceous material, particularly coal, are admixed with a liquid to. form-a` suspension and the suspension `passed asa coniined stream through a-heating zone. The carbonaceo-us solid is heated in the heating zone to` an elevated temperature. Heatingoffparticles of..coal.under these conditions resultsA inrapid disintegrationof the particles to powder.

In accordance .with the presentinvention, this novel step" of heating .and pulverizing solid Acarbonaceous.. material is employed in connection withI gasification .of the `resulting powdered `fuel with QXygen and steam and conversion of the resulting, carbon monoxide and hydrogen to fuel gas.: The gasification with steam'and oxygen is carried out ina lliow type-gas .generatcr'at a temperature Within the-.rangeof vfrom about `2000 vto about 3000 F. Hotagasesfrom the gasication step are used tosupplyfheat for carbonization of the fuel in al fluidized bed in' a separate carbonizration and methanizationi zone.l The methanization zone is'operated' at Va temperature withinthe rangezof from about 900 to'about 1800 F; and preferably` within* the range'of yfrom about 1000 to about :1500F. Additional heat is liberated -by themethanization reaction, ige., the reactionof carbon monoxide-and hydrogen toproduce methane. that liberated from the fuel by distillation serve to enrich the product gases. Heat from thega'si'- cation is also used for heating the' slurry to vaporize thefliquid and-preheat andva'porizef the carbonaceo'us solid.

An important distinction'over processes" of the priorv art is the combination of anI unobstructed, now type generator'and a fluid bed carbonization zone. The results obtainedby this combination are quantitatively different from thosevobt'ained by fluid bed gasification processes and'thosefelnploying moving beds. In the iioW type' generator, thefquantity of solid luel supplied to the generatoi" is just suliicient' to react with the gases. Slag maybe Withdrawn fromthe generator asfaliquid or solid'ash maybe separated from' the product gases. Free heat transfer by'radiation is achieved so that the entire reaction zone operates at es'- sentially a single uniform temperature; For best results the internal surface area of the generator, as compared with the surface ofv av sphere of equal volume, is less than 1.5 times the surface area of the sphere. A

Methanization is most 'effectively carried out ata temperature considerably below the temperature eliective for' rapid and -eiiicient gasification. rlhe fluidized bed or solid fuel `andfresulting char provides an ideal reaction zone for the production of methane from carbon monoxide and vhydrogen, since the entire' reaction zone maybe maintained-at a uniform desired temperature.` As there is=no` appreciableconsumptionV of the Ac'oal particles in the vfiuidized fbed and no ash production, there kfisno problem of carbon loss aslthe conventional iiuid' bed gasifier.-v Heat transfer surfaceslmay. be provided in them'ethanization zone forl accurate control of the temperature therein. Heat from' -the'fmethahization zone may be used to vaporize the slurry: feed stream;A

Since the: bed of solid particles of carbonaceous material inthe methanization zoneismaintained in/ a`Y highly' turbulent condition. fresh coal is rapidly dispersed in a large volume-of carbonized coal or char. Under these conditions, araw caking, 'coal passes through the plastic vstage with a minimum of agglomeration.` Heat transfersurfacesa're kept Vclean 'by the abrasivel action "of the fiuidized particles.

The process of this invention' `produces a" fuel gas of Vequal or higher heating-valuethanfcomparable processes in which gasification Withsteam and oxygen is carried out in a dens'epliase, el g.; in a i-luidiized or moving bed,"with' an appreciable Methane produced by this reaction and saving in oxygen and steam. The permissible oXygen-to-steam ratio in the generator is considerably higher than for the conventional dense phase gasification reactors while, at the same time, the oxygen-to-fuel ratio is lower. Since oxygen and, to a lesser extent, steam requirements are significant factors in the cost of synthetic fuel production, the present process materially improves the economy of the production of fuel gas of high heating value.

The overall steam requirements for the process range from about 0.8 to about 2.0 pounds per pound of solid fresh fuel while the free oxygen requirements range from about 0.1 to about 0.8 pounds per pound of solid fresh fuel. Pressures may vary from about 150 to about 750 pounds per square inch gauge, or higher.

In a preferred embodiment of this invention, coal in particle form is mixed with suficient water to form a iiuid suspension or slurry. The slurry is passed through a tubular heating zone wherein it is heated to a temperature at least sufficient to vaporize the water. Combined water contained in the coal need not be completely removed in the heating step. The heating step produces a dispersion of powdered coal in steam and at the same time may distill some of the volatilizable constituents from the coal.

The quantity of liquid admixed with the coal to form the suspension may vary considerably depending upon process requirements and the feed material. A minimum of about percent water by Weight is required to form a fluid suspension of coal. The liquid content of the suspension may be controlled by first mixing the solid with a quantity of liquid in excess of the required quantity and adjusting the consistency to the desired value by removal of excess liquid in a conventional thickener. The suspension is readily pumped with suitable equipment, e. g., with a diaphragm type pump, of the type commonly used for handling similar suspensions of solids. The suspension may be made up at a point some distance away from the processing site and pumped to the site in a pipeline.

A catalyst for the methanization reaction, for example, iron oxide, may be added to the slurry. Also fluxing agents, e. g., lime, silica, alumina, etc., may be added to decrease the fusion temperature of the ash.

Some coals require substantial theoretical amounts of steam for the production of hydrogen and carbon monoxide by reaction with steam and oxygen at temperatures within commercially attainable limits 2000 F. to 3000 FJ. Others contain Water in suiiicient quantity or even in excess of the theoretical requirements. Anthracite is an example of the former, requiring a considerable quantity of steam, for example, 30 percent by Weight. Lignite is an example of the latter, often containing more than the theoretical requirement of water. Water in excess of the theoretical requirement is not detrimental to the gasification reaction. While anthracite, because of its relatively high steam requirement, is an excellent feed material for the process of this invention, lignite may also be used.

Anthracite silt may advantageously be used as a feed material for the present process. Anthracite silt is a term applied to the fine particles of coal and associated impurities, obtained as a by-product in the mining, handling, and sizing of anthracite coal. Anthracite silt may be used in the present process Without preliminary grinding.v It ranges in size from about 13e inch aver- 4 age diameter, to about 200 mesh, the bulk of the material falling Within the range of t inch to mesh.

The size of the coal particles fed to the heating step is not of especial importance to the successful operations of the invention. Particles of a size which may be passed through the heater tubes Without difculty may be used, i. e., particles having an effective diameter less than onethird the pipe diameter. Generally, it is preferable to use particles less than about one-quarter inch in average diameter. Since the heating of the dispersion under turbulent flow conditions results in disintegration of the coal, costly pulverization by mechanical means is eliminated. It is contemplated in most applications of this process that the coal will be reduced only to a particle size such that it may be readily handled as a suspension or slurry. The coal may be crushed mechanically to about one-fourth inch in average diameter with" a relatively small expenditure of power. Further mechanical reduction in size becomes progressively more expensive, pulverization requiring large expenditures of power. It is evident that this process possesses important advantages over conventional methods which involve separate pulverization and carbonization.

The linear' velocity of a liquid suspension at the inlet to the heating coil should be within the range of from about l/2 foot to about l0 feet per second, suitably about l to 2 feet per second. The velocity of gaseous dispersions as at the outlet of the coil depends upon the pressure and temperature of the dispersion.

The temperature at the outlet of the heating coil may range from about 250 to 1500 F. or higher. The temperature preferably is at least suflicient to insure vsubstantially complete vaporization of liquid present in the dispersion by the time it is discharged fromthe heating zone. Preferably a temperature within the range of 600 to 1400 F. is attained at the outlet of the coil. The higher temperatures, within practical limits, are usually advantageous. The extent of carbonization, i. e., distillation of volatilizable constituents from the coa-l, may be controlled by control of the temperature.

Pressure, in itself, is not critical in the heating step. The temperature and pressure relationships affecting vaporization are well known. 1t is desirable to operate the heating zone at a pressure somewhat higher than the operating pressure of the gasication zone. In the generation of fuel or synthesis gas, it is often desirable to operate the gasification step at an elevated pressure, for example, 300 to 600 pounds per square inch. The heating and pulverizing step may be operated at a corresponding pressure sufficient to insure flow through the heating coil and into the generator at the desired rate. A considerable pressure drop takes place in the heating zone due to resistance to flow. This drop may be on the order of, for example, 100 pounds per square inch. Often it is desirable to reduce the pressure suddenly in the heating zone or at its outlet to enhance the vaporization and disintegration actions of the heating step.

Part of the vapors may be separated from the powdered solid before it is fed into the generator or part of the solid may be separated from the gasiform dispersion. Separation of powdered solids from gases or vapors may be effected in a number of Ways. `A cyclone separator is generally effective for removal of solids from gases.

5 Very fine particles may be 'separated with a Cottrell precipitator. Less desirable are sepa.- rators of the filter or liquid contact type.

A number of advantages are obtained by this method of operation. Pulverization and preheating of the coal, and generationand preheating of the steam for the gasiiication reaction may be accomplished in a single heating step. Additionally, the coal may be subjected to distillation conditions. When dispersed in a liquid `to form a slurry, the carbonaceous solid maybe readily transported and subjected vto elevated pressure. Since the slurry mayv be handled as a liquid, troublesome lock hoppers and similar devices are eliminated and replaced simply by a slurry mixe-r and a pumpr Another advantage results from the fact that, in a dispersion, the quantity .of coal fed to the process may be accurately metered.

The. invention will .be more readily understood' from. the following detailed description and the. accompanying drawing. In Vthe detailed descrip` tion of illustrative operations involving the present invention, coal is taken as a preferred fuel and Water as a preferred liquid for forming the dispersion.

The ligure is a diagrammatic elevational view illustrating a preferred method of carrying out the process of the present invention.

With. reference to the gure, coal in particle form is introduced through line I into storage hopper 2 from which it may be passed through line 3 into mixer 4. Sufficient water to form a uid slurry of coal in water is admitted to the mixer through line E. The slurry is withdrawn from the mixer 4 .to a pump i and forced under pressure through a heating coil 8 wherein it is heated to a temperature at least suiiicient to vaporize the Water. The resulting dispersion of powdered coal in steam is introduced into conduit 9 and thence into vessel i Vessel I is a pressure vessel wherein hot gases comprising carbon oxides and hydrogen resulting from the gasification of solid fuels with oxygen and steam are contacted with fresh coal and its char in a dense phase fluidized bed. A cooling coil II is provided in vessel I0 to remove excess heat therefrom and to control the temperature at which the methanizationzone is operated. IIn the vessel I0, carbon monoxide and hydrogen interact in the presence of the solid fuel to produce methane. At the same time, volatilizable materials are distilled from the coal and admixed with the gases resulting from the gasification with steam and oxygen and the methanization reaction.

The resulting mixture of gases passes through line I2 to a cyclone separator I3. In the separator I3, solid particles of coal which may be carried over from the uidized bed in vessel I0 are separated from the gases. The fine particles so recovered are passed through line I4 to mixer 4 into admixture with particles of fresh coal from line 3. The gases from separator I3 pass through line I5 into heat exchange with the slurry in the heating coil 8 to provide at least a portion of the heat required for heating the slurry. The gases are then discharged from the system through line I6 as raw fuel which, after suitable purification steps for the removal of water, condensible oils and tars, is suitable for industrial and household heating.

Char from the vessel I0 is withdrawn through line I'I and introduced into the gasification zone I8 into admixture with oxygen and steam entering through line I9. The gasification zone is operated as a :lio-w generator with the reactants in dilute phase. The resulting gases from the gasification zone pass through line 9 into vessel Ill. Slag is discharged from the gasification zone I9 through line 2B.

Example Buckwheat coal having the following analysis is used in the process of this invention:

Percent Percent Percent Llggfe Dry and Proximate Analysis as Dried Y and As'h Mineral Received at .10590. Free Matter Free Moisture 3. 3' Volatile Matter.. 4. 7 4. 9 5. Fixed Carbon. 78.1 80. 7 94.

13. 9 14.4 Ultimate Analyst Ash 13.9 14.4 y Sulfur 0. 6 0.6 t). 7 Hydrogen 2. 5 2. 3 2. B Carbon--. 76. 7 79. 3 92. 7 Nitrogen.. 0. 8 .8 0. 9 Oxygen 5. 5 2. 6 3. 1 Calorie Value, B. t. u.

per lb l2, 730 l2, 730 14, 870 15,040

A slurry is made up using one pound of water per pound of coal. The slurry is charged through a heating coil wherein it is heated to about 1100 F. and charged into a iiuidized bed of char in a methanization zone maintained at about 1160 F. and 600 pounds per square inch gauge. The slurry is passed in indirect heat exchange with the iiuidized bed of char in the methanization zone.

The gasification zone is operated at about 2320 F. and 600 pounds per square inch gauge. Steam and oxygen are preheated to about 620 F. and admixed with char drawn directly from the methanization zone. The quantities of steam and oxygen fed to the gasier correspond to 0.773 pound steam and 0.760 pound of an oxygen concentrate containing 99.2 percent oxygen and 0.8 percent nitrogen, by volume, per pound of raw coal, as received, fed to the system. The slag is withdrawn from the gasier as a liquid in an amount corresponding to 0.150 pound per pound of feed.

The char from the methanization zone amounts to about 0.907 pound per pound of raw coal. About 0.021 pound of recovered fines is separated from the product gas and admixed with the fresh feed.

The gas from the gasication Zone at 2320 F. has the following approximate composition:

Volume percent lydrogen 26 Carbon monoxide 49 Water vapor 15 Carbon dioxide 10 All of this gas passes to the methanization zone. The total product gas from the methanization zone has the following approximate composition:

- Volume percent Hydrogen 1l Methane 12 Water vapor 44 Carbon monoxide 3 Carbon dioxide 30 equivalent to about 14.2 standard cubic feet per pound of raw coal of the following composition:

Volume percent Hydrogen 40 Methane 46 Carbon monoxide 12 Nitrogen 1 1 Water vapor and carbon dioxide 1 The fuel gas has a gross heating value of about 611 B. t. u. and a net heating value of 548 B. t. u. per standard cubic foot.

`Gloviously many modifications and variations of ;the invention as hereinabove setJ forth may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appendedclaims.

I claim:

1. In a process for the generation of fuel gas from a solid carbonaceous fuel containing volatilizable constituents, the improvement which comprises admixing said solid carbonaceous fuel in particle form with suiicient water to forma fiuid suspension, passing said suspension through a heating zone at an elevated temperature such that substantially all of the water is vaporized thereby -forrning a dispersion of coal in steam, passing the resulting dispersion into a fluidized bed of solid carbonaceous material in a methanization zone into contact with carbon monoxide and hydrogen at a temperature within the range of from about 900 1o about 1800" F. whereby carbon monoxide and hydrogen are converted to methane and Volatilable constituents of said solid carbonaceous material are distilled therefrom, withdrawing carbonaceous material from said methanization zone and passing it into contact with oxygen and steam in dilute phase in a gasification zone maintained at a temperature within the range of from about 2000 to about 3000 F., passing the resulting gases comprising carbon monoxide and hydrogen from the'gasiiication zone into the methanization zone as the source of carbon monoxide and hydrogen therefor, and discharging the gaseous products of the methanization zone as the raw product fuel gas.

2. A process as defined in claim 1 wherein at least a portion of the heat requirements of said heating zone is obtained from said methanization zone by indirect heat exchange.

3. A process as defined in claim 1 wherein said methanization zone is maintained at a temperature within the range of from about 1000 to about 1500 F.

4. A process as defined in claim 1 wherein the gasification zone and methanization zone are operated at a pressure within the range of from about to about 750 pounds per squareinch gauge.

5. In a process for the generation of fuel gas from a solid carbonaceous fuel containing volatilizable constituents, the improvement which comprises admixing said solid carbonaceous fuel in particle form with suicient Water to form a iiuid suspension, passing said suspens ion through a heating zone at an elevated temperature such that substantially all of the Water is vaporized thereby forming a dispersion of coal in steam, separating at least a portion of the steam from the solid carbonaceous particles, passing the solid carbonaceous Particles into a fluidized bed of solid carbonaceous material in a methanization zone into contact with carbon monoxide and hydrogen at a temperature within the range of from about 900 to about 1800 F. whereby carbon monoxide and hydrogen are converted to methane and volatilizable constituents of said solid carbonaceous material are distilled therefrom, withdrawing carbonaceous material -from said methanization zone and passing it into contact with oxygen and steam in dilute phase in a gasification zone maintained at a temperature within the range of from about 2000 to about 3000 F., passing the stream separated from the solid carbonaceous particles to the gasification zone to supply at least a portion of the steam thereto, passing the resulting gases comprising carbon monoxide and hydrogen from the gasification zone into the methanization zone as the source of carbon monoxide and hydrogen therefor, and discharging the gaseous products of the methanization zone as the raw product fuel gas.

DU BOIS EASTMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,414,586 Egloil Jan. 21, 1947 FOREIGN PATENTS Number Country Date 286,404 Great Britain Mar. 8, 1928 503,158 Great Britain Apr. 3, 1939 578,711 Great Britain vJuly 9, 1946

Claims (1)

1. IN A PROCESS FOR THE GENERAION OF FUEL GAS FROM A SOLID CARBONACEOUS FUEL CONTAINING VOLATILIZABLE CONSTITUENTS, THE IMPROVEMENT WHICH COMPRISES ADMIXING SAID SOLID CARBONACEOUS FUEL IN PARTICLE FORM WITH SUFFICIENT WATER TO FORM A FLUID SUSPENSION, PASSING SAID SUSPENSION THROUGH A HEATING ZONE AT AN ELEVATED TEMPERATURE SUCH THAT SUBSTANTIALLY ALL OF THE WATER IS VAPORIZED THEREBY FORMING A DISPERSION OF COAL IN STEAM, PASSING THE RESULTING DISPERSION INTO A FLUIDIZED BED OF SOLID CARBONACEOUS MATERIAL IN A METHANIZATION ZONE INTO CONTACT WITH CARBON MONOXIDE AND HYDROGEN AT A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 900 TO ABOUT 1800* F. WHEREBY CARBON MONOXIDE AND HYDROGEN ARE CONVERTED TO METHANE AND VOLATILABLE CONSTITUENTS OF SAID SOLID CARBONACEOUS MATERIAL ARE DISTILLED THERE-

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