US3715195A

US3715195A - Multihydrotorting of coal

Info

Publication number: US3715195A
Application number: US00158468A
Authority: US
Inventors: J Tassoney; W Schlinger
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1971-06-30
Filing date: 1971-06-30
Publication date: 1973-02-06
Anticipated expiration: 1990-02-06

Abstract

D R A W I N G
THIS IS A NONCATALYTIC MULTIHYDROTORTING PROCESS FOR MAXIMIZING THE CONVERSION OF COAL INTO NONPOLLUTING FUEL GAS. A PUMPABLE COAL-WATER SLURRY IN ADMIXTURE WITH A STREAM OF SYNTHESIS GAS IS PASSED THROUGH A TUBULAR RETORT WHERE IT IS HEATED TO A TEMPERATURE IN THE RANGE OF ABOUT 600 TO 1300*F. IN THE ABSENCE OF AIR. THE SOLID COAL PARTICLES ARE FRAGMENTIZED AND CARBONIZED IN THE TUBULAR RETORT. THE VOLATILE CONSTITUENTS IN SAID SLURRY ARE VOLATILIZED AND SIMULTANEOUSLY HYDROGENATION OF THE PROCESS STREAM TAKES PLACE. THE EFFLUENT FROM THE TUBULAR RETORT IS THEN INTRODUCED INTO A FLUIDIZED BED RETORT ALONG WITH A SECOND STREAM OF SYNTHESIS GAS. THERMAL DECOMPOSITION OF THE CARBONACEOUS MATERIALS TAKES PLACE IN THE ABSENCE OF AIR AND THE PROCESS STREAM IS HYDROGENATED FOR A SECOND TIME. OFF-GAS FROM THE FLUIDIZED BED IS THEN SCRUBBED AND PURIFIED TO PRODUCE NONPOLLUTING FUEL GAS HAVING A HIGH HEATING VALUE. SPENT CARBONACEOUS PARTICLES LEAVING THE FLUIDIZED BED RETORT ARE INTRODUCED INTO A FREE-FLOW NONCATALYTIC GAS GENERATOR FOR CONVERSION INTO PREFERABLY METHANE-RICH SYNTHESIS GAS BY PARTIAL OXIDATION FOR USE IN THE AFORESAID TWO HYDROTORTING STAGES.

Description

Feb. 6, 1973 J. P. TAssoNEY ET AL 3,715,195

MULTIHYDROTORTING 0F COAL Filed June 30. 1971 United States Patent Oce Patented Feb. 6, 1973 U.S. Cl. 48-197 R 12 Claims ABSTRACT OF THE DISCLOSURE This is a noncatalytic multihydrotorting process for maximizing the conversion of coal into nonpolluting fuel gas. A pumpable coal-water slurry in admixture with a stream of synthesis gas is passed through a tubular retort where it is heated to a temperature in the range of about 600 to 1300 F. in the absence of air. The solid coal particles are fragmentized and carbonized in the tubular retort, the volatile constituents in said slurry are volatilized and simultaneously hydrogenation of the process stream takes place. The eiuent from the tubular retort is then introduced into a uidized bed retort along with a second stream of synthesis gas. Thermal decomposition of the carbonaceous materials takes place in the absence of air and the process stream is hydrogenated for a second time. Off-gas from the uidized bed is then scrubbed and purified to produce nonpolluting fuel gas having a high heating value. Spent carbonaceous particles leaving the uidized bed retort are introduced into a free-tiow noncatalytic gas generator for conversion into preferably methane-rich synthesis gas by partial oxidation for use in the aforesaid two hydrotorting stages.

fuel gas from coal and other solid carbonaceous fuels.l

More specifically it relates to the hydroconversion of coal with synthesis gas in the absence of a catalyst to form a nonpolluting fuel gas.

'Description of the prior art The liquid phase catalytic hydrogenation of mixtures of ground coal, oil, and catalyst are known to the art. By this means heavy coal oil is produced which requires extensive processing to rid the oil of catalyst and to fractionate it into usuable liquid products. Off-gas from these processes contain substantial amounts f HZS and other acid gas constituents which pollute the environment. Further, such prior art processes are not too practical because of the deposition of asphalt and high polymers which foul and plug apparatus and rapidly deactivate the catalyst.

Batch hydrotorting of coal is uncconomical because of the slow heating time required to pass through the softening temperature point of the coal, the fusion of the coal to the retort wall, the poor rate of heat transfer into the lump coal, and the comparatively increased hydrogen consumption.

Other contemporary coal hydrogenation processes are unsatisfactory because of one or more of the following reasons: utilize extensive purification processes to make pure hydrogen for use in hydrogenation, require expensive rne grinding of the coal and pretreatment by oxidation to overcome agglomerating tendencies of raw coal, produce a great amount of oil in place of fuel gas, the product gas has a low gross heating value, and a large amount of heat from an external source must be supplied to the system.

The present invention overcomes the diiculties inherent in the above-described prior art processes. IFurther, there are achieved important economies in the production of a gas rich in hydrogen and methane for hydro- Y genating the coal.

SUMMARY This is a continuous process for the production of fuel-gas from coal. It is also applicable to other solid carbonaceous fuels such as oil shale, tar sands, and pctroleum coke. The process involves multihydrotorting of the carbonaceous fuel using synthesis gas produced subsequently in the process by partial oxidation of residue from the hydrotorting steps, producing a gaseous mixture substantially comprising hydrogen and carbon monoxide and preferably from about l0 to 30 mole percent methane.

In a preferred embodiment raw coal is ground to a size in the range of about 1/2 to 1A inch diameter and mixed with water to form a pumpable slurry having a solids content in the range of about 25-55 weight percent, and higher. The coal-water slurry is dispersed in a stream of synthesis gas and is then introduced into a tubular retort in the absence of air under conditions of turbulent flow and at a pressure in the range of 6 to 250 atmospheres and at a temperature in the range of about 600 to 1300" F. The solid coal particles are fragmented and carbonized in the tubular retort, the volatile constituents in the slurry are vaporized, and a dispersion of solid carbonaceous particles and 'volatilized coal products in a mixture of steam and synthesis gas is formed. Simultaneously hydrogenation of said dispersionis effected by the hydrogen in said synthesis gas.

The etliuent from the tubular retort is introduced into the top of a uidized-bed. Fluidizing is effected by a second stream of said synthesis gas entering at the bottom of said fluidized bed. By this means, intimate contacting and a second hydrogenation of the process stream is effected in the tiuidized bed in the absence of air at a temperature in the range of about 1200 to 2000 F. and a pressure in the range of about 6 to 250 atmospheres. Advantageously, at a temperature of 1300 F. and above, carbon and hydrogen react non-catalytically to increase the methane content in the process gas stream.

The process gas stream of raw fuel gas leaving from the top of the fluidized bed is cooled and scrubbed to remove a minor amount of any normally nonvolatile materials such as water, tar, oil, and particulate carbon in a separation zone. Then by conventional gas purification and drying, a product stream of nonpolluting fuel gas is produced. Solid carbonaceous matter from the bottom of the ltiuidized-bed hydrotort and the separation zone are reacted by partial oxidation with steam and oxygen in a free-how noncatalytie synthesis gas generator at a temperature in the range of 1200 to 2100 F. and a pressure in the range of about 1 to 250 atmospheres to produce the synthesis gas for use in the aforesaid two hydrotorting steps. Preferably, the synthesis gas is produced having a methane content in-the range of about 10 to 30 mole percent. This is done by operating the synthesis gas generator at a temperature in the range of about 1200 to 2000 F., a pressure in the range of about 15 to 250 atmospheres, and with a steam to fuel weight'1 ratio in the range of 3 to 5 parts of steam per part of fuel. Preferably, the multihydrotorting steps and the synthesis gas generator are operated at the same pressure. Further, the operating conditions of the process are such so as to produce a maximum quantity of nonpolluting fuel gas from coal. Since all of the carbon-containing by-products i.e. tar, coal oil, and particulate carbon are utilized in the production of synthesis gas, there is substantially no waste of the carbon values in the coal. i

It is therefore a principal object of the present inven- 3 tion to provide a continuous process for economically and efficiently producing nonpolluting fuel gas having a high gross heating value from a solid carbonaceous fuel. Another object of the invention is to produce a Stream synthesis gas having an improved heating value from coal and containing at least 10 mole percent of methane. A still further object is to produce a maximum amount of nonpolluting fuel gas from coal, utilizing substantially all of the carbon in the coal.

One further object of the invention is to manufacture from coal, fuel-gas having a sulfur concentration of less than 5 parts per million.

DESCRIPTION OF THE INVENTION The present invention involves a noncatalytic continuous process for making nonpolluting fuel-gas comprising essentially carbon monoxide, hydrogen and methane from a solid carbonaceous fuel.

The process of the present invention is especially useful for the gasification of coal and similar fuels containing volatilizable constituents. Various grades of coal may be treated including anthracite, bituminous coals and lignite. Waste coals, such as slack coal and the like, and cokes made from coal are suitable for use in the present process. The process is also applicable to the treatment of oil shale, tar sands, petroleum coke, asphalt, and pitch.

Sulfur levels in coal range from 0.2% or less to about 7 weight percent on a dry basis. In the manufacture of fuel gas from coal most of the sulfur is gasitied. Prevention of air pollution demands that the sulfur level in fuel gas be reduced to about 500 parts per million. This may be accomplished by the process of our invention.

The particle size of the raw coal, or other solid carbonaceous fuel fed to the subject process is not of particular importance. This is an important economic advantage; for, by our process it is not necessary to resort to costly -fine grinding or pulverization of the coal in the preparation of the feed. yIn comparison, conventional hydrogenation processes ordinarily require large expenditures of power to pulverize the coal to the size of powder.

In our process, coal may be crushed mechanically to a particle size of about 1/2 inch to A inch in average diameter or smaller with a relatively small expenditure of power and in conventional coarse grinding equipment. Further reduction in size of the coal particles and frag mentation occurs subsequently in the process, while simultaneously being hydrogenated in a tubular retort to be further described.

The coarse ground coal particles are mixed with a suitable carrier such as oil or water, and preferably water, to form a pumpable coal-water slurry containing about 25 to 55 weight percent of solids at ambient temperature. The coal-water slurry is pumped through the axial passage of an orifice-type mixer, e.g. venturi or nozzle mixer such as shown in the drawing or in Perrys Chemical Engineers Handbook, Fourth edition, McGraw-Hill 1963, pages 18-54 to 56.

Unshifted hot raw synthesis gas, a gaseous mixture substantially comprising H2 and CO preferably rich in methane, is produced subsequently in the process. The synthesis gas is injected into the coal-water slurry accelerating through the throat of the nozzle mixer to form a dispersion. The synthesis gas enters the mixer at a temperature in the range of about 1200-2100 F., a pressure in the range of about 1 to 250 atmospheres, and in an amount sufficient to provide about 1500 to 6500 standard cubic feet (s.c.f.) of hydrogen per ton of coal feed (dry basis).

The dispersion of coal, H2O, and synthesis gas at the inlet to the tubular retort is preferably at a velocity in the range of about 5 to 50 feet per second and suitably about feet per second. The velocity of the gaseous dispersion of particles of solid carbonaceous matter and vapor at the outlet of the coil is within the range of Y from about 25 to about 500 feet per second, and suitably about 60 feet per second. The tubular retort is an elongated tubular reactor of relatively great length in comparison with its cross-sectional area, eg, about 1 to 8 inches inside diameter and larger and about 500 to 4,000 feet long. It is more fully described in U.S. Pat. 2,989,461 issued to Du Bois Eastman and W. G. Schlinger. Advantageously by our process substantially all of the heat required for retorting may be supplied by the synthesis gas. However, if desired only a portion of the necessary heat may be provided by the sensible heat of the synthesis gas since the tubular retort may be externally heated if necessary. The temperature at the outlet of the tubular retort may range from about 600 to 1300 F., and preferably within the range of about 850 to 1100 F. The extent of pyrolysis and carbonization, i.e. thermal decomposition of the coal in the absence of air with distillation of volatilizable constituents in the coal may be controlled by control of the temperature. The distillation of volatilizable materials is also dependent to a limited extent on the amount of water in the coal-water slurry feed. Further, stream reacts with carbon and carbon monoxide to form hydrogen and carbon oxides. This later reaction reduces the amount of synthesis gas required at a great economic savings. Expansion of the water in the coal upon being converted into steam helps to rupture the coal particles. The particles of solid carbonaceous matter produced by devolatilization of the coal comprises principally carbon with a small amount of ash and relatively minor amounts 0f hydrogen, oxygen, nitrogen, and sulfur. Reaction between hydrogen and sulfur to produce hydrogen sulfide takes place.

The residence time in the tubular retort is long enough to permit the coal to fragmentize and carbonize, the volatile materials to volatilize, and for hydrogenation to commence. Thus, thc residence time is maintained in the range of about 1A minute to 5 minutes while at the previously mentioned conditions of temperature, pressure and feed composition.

The volume and velocity of the dispersion flowing within the tubular retort are such as to ensure highly turblent flow conditions, which combined with heat and pressure therein promotes the attrition and disintegration of the coal and the dispersal of tine carbonaceous solid particles in a uidized dispersion with steam and synthesis gas. The turbulence level, as defined by the ratio em/v, where em is t-he average apparent viscosity and v is the kinematic viscosity, is maintained in the range of about 25 to 100,000, and preferably at least 500. The pressure in the tubular retort is in the range of about to 3500 p.s.i.g. and preferably in the range of about 400 to 1600 p.s.i.g. Suitably, the pressure may be substantially that of the synthesis gas generator to be further described, less ordinary line drop.

The eiuent stream leaving the tubular retort is introduced into the upper end of a uidiZed-bed retort where second stage hydrotorting of the solid carbonaceous particles and the volatilized products in the efliuent -stream takes place in the absence of air. Suitably, the

uidized-bed retort comprises a vertical steel pressure vessel. A second portion of synthesis gas produced subsequently in the process is introduced at the bottom of the retort at a temperature in the range of about 1200 to 2000 F. and suitably in the range of about 1500 to 1800 F. Preferably, the uidizedbed retort is maintained at a temperature of at least 1300 F. so as toincrease the methane content in the process gas stream. The pressure in the uidized-bed retort is in the range of about 90 to 3500 p.s.i.g., and preferably in the range of about 400 to 1600 p.s.i.g. Suitably, the pressure may be substantially that of the synthesis gas generator, to be further described, less ordinary line drop. The synthesis gas is passed upwardly through the hydrogenation zone in contact with the fluidized-bed of solid carbonaceous particles.

The evolved vapor and the up-owing synthesis gas provide the uidizing medium for agitating the bed of fine carbonaceous particles. The synthesis gas entering at the bottom of the fluidized bed comprises from about 1500 to 6500 s.c.f. of hydrogen per ton of solid carbonaceous particles (dry basis). The velocity of the synthesis gas should be sufficient to uidize, that is to suspend but not to entrain, the mass of carbonaceous particles in the up-owing stream of gases.

Hydrogenation of the solid carbonaceous particles and the volatile products in the process gas stream takes place in the fluidized-bed retort along with som hydrocracking of hydrocarbons. Further, steam reacts with carbon and carbon monoxide to form hydrogen and carbon oxides. This later reaction reduces the amount of synthesis gas required at a great economic savings. Sul- -fur and nitrogen impurities react with hydrogen to produce hydrogen sulfide and ammonia. The particles of solid carbonaceous matter are reacted in the fluidizedbed until preferably about 40 to 9S weight percent of the carbon in the feed is gasified. Thus, the residence time in the uidized-bed retort may range from about to 55 minutes and preferably about 30 minutes.

The process gas stream leaving from the top of the tluidized-bed retort is cooled to a temperature below the dewpoint by indirect heat exchange with water. Steam for use in the process may be produced thereby. Water containing dissolved gaseous trace amounts such as NH3, H2S, COS and CO2 along with oil and tar are recovered and are recycled to the generator.

The process stream is then scrubbed by a standard gas scrubbing procedure preferably with water to knock out any entrained particulate carbon and other solid and liquid impurities. For example, the process stream is accelerated through the center passage of an orifice-type scrubber, such as a venturi, jet, or nozzle type scrubber and clear water is injected into the process stream at the throat of the nozzle scrubber. A mixture comprising the process gas stream and the scrubbing water is then passed into a separation zone where by conventional means, solids-free process gas is separated from the rest of the mixture. For example, the separation zone may include a gravity separator from which a solids-free process gas stream is drawn ofi` and separated from a mixture of water and a comparatively small amount of oil, tar, and particulate carbon. The later mixture is then introduced into a separation vessel from which clear water is drawn off and recycled to the nozzle scrubber for additional gas scrubbing. The residue consisting .of a concentrated carbonaceous slurry comprising about to 60 weight percent solids may be used in the production of the aforesaid synthesis gas to be described later.

The dry solids-free process gas stream from the separation zone having the analysis as shown in Table I is introduced into a gas purification unit where gaseous impurities such as H2S, COS, and CO2 are removed. The composition of the purified product fuel gas from the gas purification unit is shown in Table I. The nonpolluting product gas has a gross heating value in the range of about 500 to 600 b.t.u. per standard cubic foot.

For example, C02, H28, NH3 and COS may be removed from the process gas stream leaving the separation zone in an acid-gas separation zone by suitable conventional processes involving refrigeration and physical or chemical absorption with solvents, such as n-methylpyrrolidone, triethanolamine, propylene carbonate, or alternately with hot potassium carbonate. Methane should be substantially insoluble in the solvent selected. Most of the CO2 absorbed in the solvent can be released by simple flashing, the rest being removed by stripping. This may be done most economically with nitrogen that is available free of cost from the air-separation unit used to provide oxygen for the gasification step. The stream of CO2 has a purity of more than 98.5% and may therefore be used for organic synthesis. The regenerated solvent is then recycled to the absorption column for reuse. When necessary, nal cleanup may `be accomplished by passing the 6 process gas through iron oxide, zinc oxide, or activated carbon to remove residual traces of H28 or organic sulfide. Similarly H28 and COS are then converted into sulfur by a suitable process; for example, the Claus process for producing elemental sulfur from HZS as described in Kirk-Othmer Encyclopedia of Chemical Technology, Second edition volume 19, John Whiley, 1969, page 352. Ex- Cess SO2 may be removed and discarded in chemical combination with limestone, or by means of a suitable coml Ppm.

The concentrated carbonaceous slurry residue from the aforesaid separation zone is mixed with spent solid carbonaceous particles from the bottom of the uidizedbed retort and introduced into a conventional free-flow synthesis gas generator. The synthesis gas generator is a vertical, cylindrical shaped refractory lined steel pressure vessel that is free from packing, catalyst, or any other obstruction to flow of the gases therethrough. Preferably, the feed is introduced into the reaction zone by means of an axially aligned burner at one end of the gas generator and the hot raw synthesis gas is discharged from an axially aligned .exit port located at the other end of the gas generator.

Suitably, the aforesaid feed mixture is first dispersed in steam and then introduced into the reaction zone of the gas generator by way of either the annulus of an annulustype burner, or by way of the center passage in the burner. For example, a suitable burner is shown in coassigned U.S. Pat. No. 2,928,460 issued to Du Bois Eastman, Charles P. Marion, and William L. Slater. An oxygenrich gas, i.e. air, oxygen enriched air (22 mole percent O2 and higher), and preferably substantially pure oxygen mole percent O2 and more) in order to avoid subsequent removal of the impurities found in air is also passed into the refractory lined reaction zone by way of the other passage of the burner. The atomic ratio of free (uncombined) oxygen to carbon in the feed (O/C ratio) is maintained in the range of about 0.60 to 1.2, and preferably below 1.0.

The two streams leaving the burner impinge against each other in the reaction zone of the gas generator and are atomized. Partial oxidation of the carbonaceous fuel vthen takes place at an autogenous temperature in the range of about 1200 to 2100" F. and at a pressure in the range of about 1 to 250 atmospheres. Residence time in the gas generator is about 2 to 10 seconds. The weight ratio of H2O to carbonaceous fuel is in the range of about 0.5 to S, that is, 0.5 to 5 parts by weight of H2O for each part by weight of carbonaceous fuel. The H2O may be supplied to the generator in liquid or gaseous phase. It will react with the CO and carbonaceous fuel, and moderate the temperature in the reaction zone. The H2O may be introduced in admixture with the oxygen-rich gas or with the carbonaceous fuel.

In a preferred embodiment, the methane content in the raw synthesis gas is advantageously increased to a value in the range of about 10 to 30 mole percent by operating-` the synthesis gas generator at a temperature in the rangev of .about 1200 to 2000 F. and at a H2O to fuel weight ratio in the range of about 3 to 5. Further, the mole ratio of H2 to CO may be increased to 3 or higher when the steam to fuel weight ratio is increased to 4 or higher.

The hot raw synthesis gas discharged from the reaction zone of the synthesis gas generator has an analysis as shown in Table I. About 2 to l0 weight percent of particulate carbon (basis weight of carbon in the feed to the gas generator) are entrained in the stream of raw synthesis gas. The hot gas is passed through a refractory lined connector which joins the synthesis gas generator, and optionally is passed through a waste heat boiler. On the way to the waste heat boiler, solid ash is separated from the synthesis gas. The ash is collected, for example in a water-cooled ash chamber and periodically removed from the system. Ash is the residue resulting from the partial oxidation reaction. It consists principally of silica, alumina, ferric oxide, lime, unconverted particulate carbon, together with smaller amounts of maguesia, titanium oxide, alkali compounds and sulfur compounds. These compounds are derived largely from clay.

Whether or not the efliuent gas from the gas generator is cooled in a waste-heat boiler depends on material and heat balances. Such factors are considered as the desired operating temperature in each retort, the temperature of the effluent gas from the gas generator, the quantities and compositions of the various streams, and the desired methane content in the process gas streams.

If desired the methane content of the product fuel gas may be increased still further i.e. 4in the range of about 45 to 95 mole percent CH4, or higher. By this means the gross heating value of the fuel gas may be increased, or a stream of methane may be produced for organic synthesis.

This may be effected by the process of our invention further provided with the steps of producing the aforesaid dry process gas stream leaving the gas purification zone with a mole rat-io Hz/CO of about 2.5 to 5, and preferably about 3. The process gas stream is then introduced into a methanation catalytic reactor at a temperature n the range of about 390 to l000 F. For example, the preferable exit temperature for gases reacting over NiO-AlzOa methanation catalyst is about 662 F. Space velocities range from about 100 to 10,000 standard volumes of gas per volume of catalyst (hn-1) and pressures range from v1 to 250 atmospheres. 'H2 reacts with CO to produce CH4 and H2O. Water in the effluent gas leaving the methanator may be condensed out by cooling, leaving substantially pure methane (99 volume percent).

DESCRIPTION OF THE DRAWING AND EXAMPLE A more complete understand-ing of the invention may be had by reference to the accompanying schematic drawing which shows the previously described process in detail. Although the drawing illustrates a preferred embodiment of the process of this invention, it is not intended to limit the continuous process Iillustrated to the particular apparatus or materials described. Quantities have been assigned to the various streams so that the description may also serve as an example.

On an hourly basis, with reference to the drawing about 2000 pounds of raw bituminous lump coal in line 1 are introduced into grinder 2 having the following proximate analysis in weight percent, as received: moisture 4.8, volatile matter 42.8, fixed carbon 46.0 and ash 6.59. The coal has a heating value of 13,500 B.t.u. per pound and an ash softening temperature of 2,300 F.

Coal reduced in size from 6" lumps to a size range of about A to 1/2 inch average diameter by means of a conventional grinder 2, are passed through line 3 finto mixer 4. 2000 pounds of water from line 5 are added to the mixer and a coal-water slurry is produced. At ambient ternperature by means of pump 6, the slurry is pumped through lines 7 and 8, nozzle-mixer 9, and line 10 into tubular hydrotort 11 where fragmentizing and pyrolysis of the coal, volatilizing of the volatilizable materials in the slurry, and preliminary hydrogenation of the process stream is effected. 44,700 standard cubic feet per hour of methane-rich synthesis gas at a temperature of about 1700 F. and a pressure at about 1500 p.s.i.g. in line 13, as produced subsequently in the process, are passed through

lines

14 and 15 at the throat of nozzle mixer 9 and mixed with the coal-water slurry axially passing and accelerating through the throat of nozzle mixer 9.

Thus, about 4000 pounds per hour of coal-water slurry dispersed in synthesis gas iu line 10 at a temperature of about 500 F. are introduced at a velocity of about l0 ft./sec. into noncatalytic tubular retort l1 consisting of a 1 inch Schedule 80 pipe x 530 feet long. Conditions in tubular retort 11 include: pressure 1250 p.s..g., retorting period 50 seconds, turbulence level 810, exit temperature ll00 F., and hydrogen consumption 3300 s.c.f. per ton of raw coal feed in line 1.

The effluent process stream from the tubular retort is passed through line 16 into fluidized bed retort 17 where second-stage thermal decomposition and hydrotorting takes place in the absence of air. About 23,900 s.c.f. of methane-rich synthesis gas is introduced through line 18 at the bottom of uidized bed retort 17 to uidize but not to entrain the down moving solids. The synthesis gas is produced subsequently in the process and will be further described later.

The overhead effluent gas stream leaving uidized bed hydrotort 17 by way of line 19 is cooled below the dewpoint Iin heat exchanger 20 by indirect heat exchange with water entering by way of line 21 and leaving as steam by way of line 22. The process stream is passed through line 23 into the axial passage of nozzle scrubber 24. As the process gas stream is accelerated through the nozzle 27 it is scrubbed with about 720 lbs. per hour of make-up water which is introduced at the throat of the scrubber by way of lines 25-28. Thus the normally non-volatile matter including tar and particulate carbon are scrubbed from the process gas stream forming a carbonaceous slurry with water. The process stream is passed through line 29 into separation zone 30. 3893 lbs. per hour of clear Water are separated, and separate portions are recycled to nozzle scrubber 27 by way of lines 31 and 26-28, and to mixer 4 by way of lines S9 and 5. Further purified water may be supplied to cooler 20 by way of line 2.1 and to waste heat boiler 51 by way of line 52. 347 lbs. per hour of concentrated carbonaceous slurry is separated in separation zone 30 by gravity settling or filtration and passed through line 32 for subsequent use as a portion of the feed for the generation of synthesis gas, to be described later.

54,750 s.c.f.h. of process gas stream leaving separation zone 30 and having the analysis shown in Table II on a dry basis are then passed through line 33 into convention gas purification zone 34, as previously described. Gaseous impurities are removed from the process gas stream and leave by way of line 35. Non-polluting fuel gas having gross heating value of 585 B.t.u./s.c.f. and an analysis as shown in Table II are produced by the aforesaid process and leave by way of line 36.

TABLE II.-GAS ANALYSISQMOLE PERCENT [Dry basis] Off-gas Non-polluting from separafuel gas tion zone (line 33) Synthesis gas (line 12) oduct line 3G) ceous particles leaving liuidized bed retort 17 by way of line 38 at a temperature of about 1700u F. and about 347 pounds per hour of carbonaceous slurry at a temperature of about 100 F. leavin-g from separation zone 30 by way of line 32. The carbonaceous slurry is passed through line 32 and is mixed in line 39 with solid carbonaceous particles from line 38. The ultimate analysis of the fuel mixture in line 39 in wt. percent follows: C, 86.13; H, 7.84; O, 4.62; N, 0.97; S, 0.44; (Ash-Free Basis).

The fuel mixture in line 39 is passed through line 40 and into synthesis gas generator 37 by way of annulus 41 of an axially aligned annulus type burner 42 at a velocity of about 200 feet per second. 2613 pounds of steam from line 43 at a temperature of about 600 F. may be mixed in line 40 with the aforesaid fuel mixture from line 39 to provide a steam/fuel ratio of 5.0.

About 6285 s.c.f.h. of oxygen (99.5 mole percent O2) at a temperature of 130 F. from line 44 are passed through the center passage of burner 42 at a velocity of 600 feet per second providing an O/C mole ratio of about .928. The oxygen in line 44 is preferably made by passing air from line 45 into conventional air separation zone 46. Optionally, the fuel mixture may be passed through the center passage of burner 42 and the oxygen passed through annulus 4l.

Advantageously, by-product liquid nitrogen may be obtained from air separation zone 46 and by way of line 47v introduced into gas purification zone 34 as part of the gas purification process, as described previously. Optionally, the aforesaid steam may be mixed with the oxygen for introduction into the gas generator.

Upon impact within reaction zone 48 of gas generator 37, atomization of the feedstream takes place and by partial oxidation at an autogenous temperature of about 1730" F. and at a pressure of about 100 atmospheres, synthesis gas is produced having an unusually high methane content, .e. about mole percent. The hot effluent synthesis gas leaves gas generator 37 by way of axially aligned exit port 49 and passes through refractory lined connector 50 and waste-heat boiler 5l. The lcooled raw synthesis gas leaving the waste-heat boiler by way of line 12 has a gas analysis as shown in Table II. This gas also contains about 5.0 wt. percent (basis carbon in the feed) of unreacted particulate carbon. Cooling of the synthesis gas is effected by ind-irect heat exchange with water, entering waste-heat boiler f51 by way of line 52 and leaving as steam by way of line 53.

A portion of the steam is introduced into the synthesis gas generator by way of lines 43 and 40 as mentioned previously. Excess steam may be drawn off for use elsewhere in the system e.g. operation of grinder 2, or air separation unit 46 by way of lines 54-55 and valve 56. Periodically, ash is removed from the system by way of leg 57 of connector 50, and line 58 which lead to a watercooled ash chamber and lock-hopper unit not shown.

The compositions and process of the invention have been described generally and by example with reference to particular compositions for purposes of clarity and illustration only. It will be apparent to those skilled in the art from the foregoing that various modifications of the process and the compositions disclosed herein can be made without departure from the spirit of the invention.

We claim:

1. A process for producing nonpolluting fuel gas comprising hydrogen, carbon monoxide and methane from a solid carbonaceous fuel comprising (1) preparing a putnpable solid carbonaceous fuelwater slurry and introducing same in admixture with a rst stream of synthesis gas into a tubular retort where at a pressure in the range of about 90 to 3500 p.s.i.g. said mixture is heated to an exit temperature in the range of about 600 to l300 F. and hydrogenated with the hydrogen in said synthesis gas, producing a hydrogenated dispersion of solidy carbonaceous fuel particles and the volatilized products thereof in a mixture of steam and synthesis gas;

(2) introducing the dispersion from (l) into the top of a fluidizecl bed at a temperature in the range of about 600 to l300 F. and a pressure of about 90 to 3500 p.s.i.g, where it is intimately contacted and hydrogenated with a second stream of synthesis gas entering at the bottom of said fluidized bed, producing a process gas stream of raw gas which leaves from the top of said uidized bed and a separate stream of particles of solid carbonaceous fuel which leaves from the bottom of said uidized bed;

(3) separating entrained solids, water and substantially all of the normally nonvolatile matter from the process gas stream from (2);

(4) introducing at least a portion of the solid carbonaceous fuel particles from (2) and at least a portion of said solids and normally nonvolatile matter from (3) into the reaction zone of a free-flow noncatalytic synthesis gas generator where by the partital oxidation reaction with steam and an oxygen-rich gas selected from the group consisting of air, oxygen enriched air, and substantially pure oxygen at an autogenous temperature in the range of about 1200 to 2100* F. and a pressure in the range of about 1 to 250 atmospheres a stream of synthesis gas is produced for use 'in (l) and (2); and

(5) purifying the process gas stream from (3) to produce said product stream of nonpolluting fuel gas.

2. The process of claim 1 further provided with the steps of maintaining the reaction zone of the synthesis gas generator in step (4) at an autogenous temperature in the range of about 1200 to 2000 F., a steam to fuel weight ratio in the range of 3 to 5, providing said synthesis gas with a methane concentration in the range of about l0 to 30 mole percent.

3. The process of claim 1 further provided with the steps of preparing the pumpable solid carbonaceous fuelwater slurry in step (l) by grinding coal to a particle size of 1/2 to 1A: inch diameter and mixing same with water.

4. The process of claim l wherein said solid carbonaceous fuel is selected from the group consisting of bituninous coal, anthracite coal, cokes made from coal, oil shale, tar sands, petroleum coke, asphalt, pitch and lignite.

5. The process of claim 1 further provided with the step of passing the mixture of synthesis gas and solid carbonaceous fuel-water slurry through the tubular retort in step (1) at a turbulence level m/v in the range of 25 to 100,000 where em is the average apparent vis- Cosity and v is the kinematic viscosity.

6. The process of claim 1 further provided with the steps of introducing separate streams of synthesis gas into the tubular retort in step (l) and into the fludized bed in step (2), each stream of synthesis gas providing about 1500 to 6500 standard cubic feet of hydrogen per ton of solid carbonaceous fuel (dry basis).

7. In a process for producing fuel gas comprising hydrogen, carbon monoxide and methane by the hydrotorting of coal, the improvement comprising (1) grinding the coal to a l" diameter or smaller and mixing with water to produce a pumpable slurry containing about 25 to 55 weight percent solids;

(2) mixing the slurry of (l) with synthesis gas produced subsequently in the process at a temperature in the range of about 1200 to 2l00 F. and in an amount to provide about 1500 to 6500 standard cubic feet (s.c.f.) of hydrogen per tone of dry coal feed;

(3) passing the synthesis gas and-slurry mixture of (2) through a tubular retort under turbulent conditions to fragmentize and pyrolyze said coal particles, volatilize the volatile constituents in said slurry, and to simultaneously hydrogenate the process stream at a pressure in the range of about to 3500 p.s.i.g.;

(4) introducing the efliuent process stream from the tubular retort in (3) at a temperature in the range of about 600 to 1300" F. into a fluidized bed retort at a pressure in the range of about 90 to 3500 p.s.i,g. where thermal decomposition and hydrogenation take place with a separate stream of synthesis gas produced subsequently in the process and supplied at a temperature in the range of about 1200 to 2100 F. and in an amount to provide about 1500` to 6500 s.c.f. of hydrogen per ton of dry coal feed;

(5) withdrawing an overhead process stream from the uidized-bed retort of (4), cooling said process stream to below the dewpoint and separating Water, entrained solids as a carbonaceous slurry, and substantially all of the normally nonvolatile matter from the process gas stream;

(6) withdrawing spent particles of solid carbonaceous fuel from the fiuidized-bed retort of (4), mixing at least a portion of said spent carbonaceous particles with at least a portion of said rbonaceous slurry and nonvolatile matter from (5), introducing said mixture into the reaction zone of a free-flow, noneatalytic synthesis gas generator whereby the partial oxidationvreactiou with steam and substantially pure oxygen at an autogenous temperature in the range of about 1200 to 2100 F. and at a pressure in the range of about l to 250 atmospheres, a stream of synthesis gas is produced for use in (2) and (4); and

(7) purifying the process gas stream from =(5) to produce a product stream of nonpolluting fuel gas comprising hydrogen, carbon monoxide and methane.

8. The process of claim 7 further provided with the steps of preparing the pumpable solid carbonaceous fuelwater slurry in step (1) by grinding coal to a particle size of l/2 to 1A inch diameter and mixing same with water.

9. The process of claim 7 further provided with the step of maintaining the reaction temperature in the fluidized-bed retort in step (4) at a temperature of at least 1300" F. so as to increase the methane content in the process gas stream.

l0. The process of claim 7 further provided with the step of passing the synthesis gas produced in step (6) in indirect heat exchange with water thereby cooling said synthesis gas while simultaneously producing steam for use in step (6) in the generation of said synthesis gas.

11. The process of claim 7 further provided with the steps of increasing the methane content of the product gas stream from step (7) by introducing said product gas stream having a mole ratio Hz/CO in the range of 2.5 to 5 parts of H2 per part of CO into a methanation zone containing a suitable nickel oxide methanation catalyst, and at a temperature in the range of about 390 to 1000' F., reacting said CO and H2 to produce a product gas stream substantially comprising methane and H2O.

12. The process of claim l1 further provided with the steps of cooling said gas stream below the dewpoint, condensing out said water, and separating a stream of substantially pure methane.

References Cited UNITED STATES PATENTS JOSEPH SCOVRONEK, Primary Examiner U.S. Cl. X.R.