US3437561A - Agglomerating coal hydrocarbonization process - Google Patents

Description

April 8, 1969 A. M. SQUIRES 3,437,561

AGGLOMERATING COAL HYDROCARBONIZATION PROCESS Filed June 29, 1966 w FZUX C'UAL y Bm R 7 (FITTED FOR MIXING OF COAL AND FLUX) 17 HOPPER A661 OMFRAWA/G FL u/a/zzp i/M TEMPERATURE REGULATION PRESSURE REGULATION GAS/F/EP I NVENTOR. 4?;7/02 M Ska/R55 ATTORA/EV nited U.S. Cl. 201-8 8 Claims ABSTRACT OF THE DISCLOSURE There is provided an improved process for hydrocarbonizing coals, with production of methane and coke, in which advantage is taken of the agglomerating tendencies of most bituminous and subbituminous coals and lignites in hydrogen. Coal is finely ground and injected into a fluidized bed of coke pellets between about & and inch in size. The bed is fluidized with a gas containing hydrogen, preferably at high pres-sure. The temperature is controlled in a range such that the initial hydrocarbonization products, formed practically instantaneously, include methane and a sticky residue which adheres to the coke pellets and is itself converted to coke within a few seconds. The temperature control is effected by adjusting the rate of supply of the coal and the temperature and pressure of the hydrogen, and optionally by adding methane to the hydrogen to reduce the potential extent to which the hydrogen may react to form methane in accordance with the quasi-equilibrium which limits the reaction. Coke pellets are withdrawn to maintain a constant inventory in the bed. The coke may be gasified in a slagging gasifier with the advantage that ash constituents of the original coal are present in the coke in a finely divided form and can speedily react to form slag; the gasifier may advantageously be of the slagging-grate variety.

Background of the invention This application is a continuation-in-part of my application Ser. No. 337,900, filed Jan. 15, 1964, now US. Patent 3,276,203 (October 1966).

Summary of the invention This invention relates to the carbonization of coal in hydrogen.

An object of the invention is to provide an improved process for converting caking coals into a gaseous product and coke.

Another object of the invention is to provide a process for converting noncaking coals into methane-rich gas and coke pellets large enough to be used in a grate furnace.

Another object is to provide an improved economic process for the complete gasification of coals.

Another object is to provide a coal-carbonization process using apparatus of unusually great coal-processing capacity.

Another object is to provide an improved process for converting coal into synthetic pipeline gas.

Another object is to produce from coal a hydrogen rich fuel gas suitable for use in an advanced power cycle in which the temperature of steam is raised by direct addition of combustion products of the fuel gas with oxygen or air while also producing from the coal a hydrogen lean fuel gas for combustion with air to provide heat to raise steam.

The conventional method of carbonizing caking coals requires expensive apparatus for the indirect heating of coal across a heat-transfer surface, and the coal-processing capacity of the apparatus is small because of the slowtates Patent 3,437,561 Patented Apr. 8, 1969 ness of the heat transfer. It has long been recognized that the carbonization reactions are extremely rapid, and that apparatus of vastly improved capacity could be developed if means were available for the practically instantaneous heating of coal to carbonization temperatures. Early in the development of modern fluidized-bed techniques, it was recognized that the fluidized bed provides a means for the practically instantaneous heating of coal. Attempts to develop fluidized-bed coal-carbonization processes led to disappointment, however. Many American coals, particularly in the industrial East, are so strongly caking that it is diflicult in a simple one-step fluidized-bed carbonization process to avoid formation of massive agglomerates after a short period of operation. This difiiculty was got around by providing several fluidized carbonization stages at progressively higher temperatures, or by injecting raw coal at a relatively low rate into a rapidly moving stream of already-carbonized char conveyed at a relatively high rate by a gas. These expedients gave rise to added complications which greatly reduced the coal-treating capacity per unit volume of equipment, and fluidized-carbonization processes have not been widely adopted by industry.

Recently a great deal of attention has been given to the production of synthetic pipeline gas from coal in a multistep process in whch the first significant coal-treating step is the carbonization of coal in a hydrogen-rich gas at high pressure. (See, for example, US. Patent 3,194,644 (1965); also, a Report prepared by Institute of Gas Technology (IGT) for the Oflice of Coal Research (OCR): Process Design and Cost Estimate for Produc tion of 265 million sci/day of Pipeline Gas by the Hydrogasification of Bituminous Coal, OCR Contract 14 01-0001-381, covering July 1964 to October 1965, available from OCR and on deposit at many libraries.) The contacting of coal with the hydrogen-rich gas in this hydrocarbonization step is made difficult by the caking propensities of coal under the conditions of the step. Under operating conditions selected to obtain economically desirable results, many coals ordinarily considered to be noncakingi.e., noncaking under conventional carbonizing con ditions-are rendered s icky upon their initial exposure to the hydrogen. The opinion is generally held that many coals cannot practicably be subjected to the hydrocar bonization step in a fluidized bed unless the raw coal is first treated in a step at lower temperature which removes such a large portion of the volatile matter from the coal as to make the whole operation uneconomic.

The aforementioned IGT report outlined a state-of-theart plant-scale design in which the hydrocarbonization step would be conducted in a free-fall zone, i.c., coal would be fed to the top of the zone and allowed to fall freely downward in counter-current-flow relationship to an ascending stream of a hydrogen-rich gas. Even with this arrangement, the IGT report proposed that coal would first be subjected to a pretreatment step to overcome the coals agglomerating tendencies. In the pretreatment step the coal would be partially oxidized in a fluidized bed at substantially atmospheric pressure and 750 F. The coal-processing capacity of the proposed pretreatment bed would be only about 180 pounds of moisture-and-ash-free (M.A.F.) coal per hour per square foot of bed cross-section. The pretreatment step would serve no useful process functionother than drying the coal and rendering the hydrocarbonization step feasibleand indeed would hurt the overall economy of the pipeline-gas plant, since the pretreatment step would lower the volatile matter in the coal, the matter from which methane can be derived most cheaply.

I have found that pretreatment may be dispensed with and hydrocarbonization may be conducted in equipment of outstandingly small size by taking advantage of the agglornerating tendencies of a coal and by putting these tendencies to a constructive use. According to my invention there is provided a process for hydrocarbonizing a coal selected from the group consisting of bituminous and subbituminous coals and lignites, comprising: (a) grinding the coal to a fineness substantially smaller than 200 mesh; (b) injecting the ground coal into a fluidized bed operating at a temperature between about 1000 F. and 1700 F., the fluidized bed comprising coke pellets displaying a range of diameters, the substantially smallest pellet being larger than about & inch, the coal being heated practically instantaneously to substantially the temperature of the bed; (c) supplying to the fluidized bed a hot gas containing hydrogen; (d) adjusting the temperature of the bed within temperature limits such that the practically instantaneous heating of the coal in the aforementioned gas to a temperature within said limits causes the coal to decompose practically instantaneously into gaseous matter and a nongaseous semifluid residue displaying agglomerating tendencies, the adjusting being accomplished at least primarily by adjusting the temperature of the gas and/or by adjusting the rate of injection of the coal and/or by supplying a hot gas in step containing methane as well as hydrogen and by adjusting the hydrogen partial pressure and the methane partial pressure in the gas and thereby adjusting the extent to which the hydrogen can react in the bed to form methane in accordance with a chemical quasiequilibrium governing the reaction between hydrogen and the carbon of the coke pellets; (e) withdrawing gaseous product rich in methane from the fluidized bed; and (f) withdrawing coke pellets from the fluidized bed to maintain the inventory of coke pellets in the bed substantially constant.

Coal of a fineness smaller than about 200 mesh is heated practically instantaneously upon injection into the fluidized bed to the bed temperature. carbonization reactions occur practically instantaneously with the production of a gas and a sticky residue, which is almost immediately captured by coke pellets near the point of coal injection. Following capture by a coke pellet, the residue is converted within a matter of seconds to a dry coke, and the size of the coke pellet is increased by the addition of the newly formed coke.

Attention is directed to the fact that a solid of a fineness smaller than 200 mesh is not itself fluidized in the new process of this invention. No appreciable amount of coal as such is present in the bed at any given moment. This is important, for a coal can be treated in the new process which would become extremely sticky and would agglomerate badly if the coal were heated slowly through its plastic stage.

Although the process may be operated at atmospheric pressure if a strongly-caking coal is to be treated, in general operation at an elevated pressure is much more attractive. Coal-treating capacity is more or less proportional to the pressure, and the gaseous product is generally lighter in molecular weight at higher pressures and contains less troublesome tarry matter.

If a coal which is normally considered to be noncaking is to be treated, the process should be operated at a partial pressure of hydrogen appreciably higher than atmospheric. A wide range of coals, including subbituminous coals and some lignites, can be used. In general, a pressure higher than about 300 pounds per square inch absolute (p.s.i.a.) is preferable. If the process is used in conjunction with the production of synthetic pipeline gas, a pressure higher than about 1000 p.s.i.a. is advantageous.

No general rule can be given, valid for all coals, concerning the hydrogen partial pressure and the temperature limits within which the fluidized bed of the new process should operate. For a given coal, the operating temperature limits will depend upon the hydrogen partial pressure. For some coals, the operating temperature limits are wide. For other materials, such as for example some lignites, the limits are narrow. In general, the

preferred operating temperature will fall between about 1000 and 1700 F., and it will usually fall between about 1200 and 1500 F. At generally higher pressures and temperatures, a gaseous product can be produced which comprises substantially methane with little if any benzene or higher aromatics, for the carbonization is directed by the presence of hydrogen at high pressure into reaction paths which lead to methane, and coke as the primary carbonization products.

In planning operation for a given coal, one may conveniently resort to small-scale laboratory tests to determine the relationship between hydrogen pressure and the temperature limits dependent thereon within which the practically instantaneous heating of the coal causes it to carbonize with formation of a sticky residue. The operating temperature of the hydrocarbonization bed may most conveniently be controlled within the allowable limits by adjustment of one or more of four variables: (1) partial pressure of hydrogen in the fiuidizing gas; (2) partial pressure of methane in the gas; (3) rate of coal injection into the bed; and (4) temperature of the hydrogen-containing fluidizing gas. The operation of the hydrocarbon ization bed is thermoneutral, i.e., heat is supplied to the bed only in the hydrogen-containing gas and in the coaly solid, and heat is withdrawn from the bed substantially only in the gaseous and solid products. The hydrocarbonization reactions are exothermic, and in general the solid can most conveniently be supplied at atmospheric temperature, while proper temperature control of the bed can generally be achieved with use of a fluidizing-gas temperature which is appreciably below the operating temperature of the bed. The extent of the hydrocarbonization reactions is limited by an approach to a quasiequilibrium between hydrogen, methane, and carbon-stuff having the free energy of carbon in the coke pellets. (The quasiequilibrium is not a true thermodynamic equilibrium since the carbon in the pellets is not in an equilibrium state, the carbon having a free energy which is generally higher than the free energy of graphite by an amount which probably depends upon coke residence time in the bed as well as upon other factors. One need not know the free energy of the carbon in order to operate the new process successfully.) Accordingly, the extent of the hydrocarbonization reactions may be reduced by lowering hydrogen partial pressure or by raising methane partial pressure, either measure having a strong influence in the direction of lowering the operating temperature in the bed. The extent of the hydrocarbonization reactions can also be reduced by lowering the rate of injection of coal, thereby lowering operating temperature, and reducing the temperature of the hydrogen-containing fluidizing gas has the same effect.

The fluidized bed should contain a range of cokepellet sizes, and there should be a continuous gradation of sizes within this range. The range of coke-pellet sizes in the bed may be characterized in the following way: divide the coke into three size fractions, a fraction containing the smallest particles present and having a weight of one percent of the total coke; a fraction containing the largest particles present and also having a weight of one percent; and a middle fraction containing 98 percent of the total weight of the coke. The largest and smallest particle in the middle fraction characterize the range of coke-pellet sizes, and it is preferable that there be at least about a five-fold difference in diameter between the largest and smallest particle. The range of pellet sizes should be encompassed approximately within the limits and 4 inch. If particles are too small, catastrophic agglomeration of the bed is apt to occur. Unduly large pellets would require fluidizing velocities so high as to lead to mechanical difficulties. A preferred distribution of pellet sizes may be characterized thus: divide the bed .into two equal weight fractions, one of larger sizes and another of smaller sizes; the median diameter-Le, the smallest of the larger sizes and the largest of the smaller sizesis preferably between about /8 and inch.

The fluidizing velocity (based upon efiluent gases) is preferably below a velocity about 200% in excess of the minimum fluidizing velocity of the coke pellets. The bed is preferably housed in a frusto-conical chamber with a gradual taper and the smaller end at the bottom, so that the fluidizing velocity is less at the top of the bed than at the bottom. In a preferred design, the velocity is about 100% in excess of the minimum fiuidizing velocity at the bottom of the bed and about 20% in excess of the minimum fiuidizing velocity at the top.

From the foregoing discussion, it will be recognized that the fluidizing-gas velocity in the new process may range over fairly wide limits. In general, superficial velocities which meet the aforementioned conditions will be found to fall in the range between about 2 and 20 feet per second. Other factors being equal, it is advantageous to use a fluidizing-gas velocity between about 5 and ft./sec.

Gaseous product from the hydrocarbonization bed may be used as a fuel, or may be converted by known process steps to synthetic pipeline gas or to hydrogen or to synthesis gas for production of ammonia, methanol, or other synthetic products.

Coke pellets removed from the bed may be used in a variety of ways. They are an excellent fuel for combustion in a grate furnace. They are an excellent charge stock for a moving-bed hydrogasification process of the type described in the aforementioned IGT report, in which a portion of the carbon values in the coke are converted to methane, carbon monoxide, and hydrogen by the action of steam and hydrogen at high pressures under thermoneutral conditions. The coke pellets may be gasified in a fluidized bed supplied with steam and oxygen, or in a moving-bed steam-oxygen gasifier of the Lurgi type, discharging a dry ash. The pellets may be compacted into larger agglomerates and heated to a high temperature to drive off all residual volatile matter and to produce a coke suitable for metallurgical use.

A preferred use for the coke pelletsor for coke-containing residue from the aforementioned moving-bed hydrogasification processis as a charge stock to a moving-bed gasifier discharging ash in form of a molten slag. The term gasifier is here used to denote equipment suitable for conducting a gasification process, where, following C. G. von Fredersdorff and Martin A. Elliott (chapter 20, page 892, in Chemistry of Coal Utilization: Supplementary Volume, edited by H. H. Lowry, John Wiley & Sons, Inc., New York, 1963), the term gasification as used here signifies the reaction of solid fuels with air, oxygen, steam, carbon dioxide, or mixtures of these, to yield a gaseous product that is suitable for use either as a source of energy or as a raw material for the synthesis of chemicals, liquid fuels, or other gaseous fuels. These authorities (page 949) classify gasification processes in several ways, and one of the categories is a fixed bed process using fuel in form of lumps, with countercurrent movement of solid and gaseous reactants, and with discharge of noncombustible residue as slag in a slagging operation. These authorities (pages 949-950) use the term fixed bed to signify a fuel bed supported by a grate or by other means and maintained at a constant depth above the support. Thus, the upper and lower extremities of the bed are fixed in space, but within the bed fuel moves slowly from the top down through the gasification zone, and residue is discharged at the bottom. In the strictest sense, this is a moving bed with fixed extremities.

A preferred form of moving-bed gasifier discharging slag is the slagging-grate gasifier disclosed in U.S. Patent 3,253,906 (1966). See also Journal of the Institution of Gas Engineers, vol. 5 (1965), pages 444-469, for a description of this gasifier as well as descriptions of moving-bed slagging gasifiers of an earlier, better-known design, in which the gasification medium is introduced into the fuel bed in a concentrated stream at several points by means of tuyeres. In the slagging-grate gasifier of the aforementioned US. patent, the fuel bed rests upon a water-cooled grate through all of which the gasification medium is supplied, the rate of supply and the mediums composition being such that the temperature in the fuel 'bed directly above the grate is above the melting temperature of ash in the fuel. This gasifier has an unusually high capacity. In trials at atmospheric pressure, a gasification rate of 950 lbs./hr.-ft. of grate area was achieved, and a rate several times greater can be expected at a pressure higher than 300 p.s.i.a. The atmospheric-pressure trials disclosed a serious problem, however. The gasitication rate is so high and the residence time of the solid fuel in the high-temperature zone directly above the grate is so short that lumps of noncarbonaceous matter in the fuel are not properly slagged if this matter has a high fusion temperature. Attempts were made to overcome the problem by adding lumps of a fiuxing agent to the fuel, e.g., by adding blast-furnace slag to a fuel containing ashmatter high in silica, thereby lowering the ratio of silica to earthy constituents such as calcia and magnesia, and thereby lowering the viscosity of slag produced upon melting the ash. The attempts were not successful, and their failure was associated with the short time during which a lump of refractory dirt was present within the hightemperature zone, a time which was apparently too short for the slagging reactions to occur which would incorporate the lump into a molten slag. The lump apparently arrived at the grate in solid form, was cooled by the grate, and remained on the grate as a permanent obstruction to gas flow upward and slag flow downward across the grate. If many such lumps were present in the fuel, they accumulated on the grate and spoiled the operation of the slagging-grate gasifier.

My present invention provides a means of overcoming this difiiculty in the operation of the slagging-grate gasifier. By grinding all of the coal to a fineness smaller than 200 mesh, one avoids any possibility that lumps of refractory dirt will be present in the charge stock to the slagging-grate gasifier. The original ash-matter in the coal is distributed uniformly throughout all of the coke pellets produced in the hydrocarbonization bed, and the uniform melting of this matter at the lowest possible temperature is thereby promoted. If the fusion temperature of the ash-matter is still too high for efficient operation of the slagging-grate gasifier, a fiuxing agent can be blended into the coal and incorporated in the coke pellets. The fiuxing agent is preferably ground to a fineness such that it will substantially all pass through a 325- mesh screen, and is subsequently blended intimately with the coal lines to be charged to the hydrocarbonization bed. As coke pellets which contain the fiuxing agent move down through the high-temperature zone, fiuxing reactions are complete even in the short time available, because the fiuxing agent and the coal ash are present in an intimate intermingling of tiny particles.

The fiuxing of large amounts of refractory dirt is a problem even in a moving-bed slagging gasifier of the aforementioned earlier, better-known design; and so providing coke pellets in which ash-matter is finely divided, and which may contain a finely divided fiuxing agent as well, would improve the operation. The slagging-grate gasifier has several advantages, however, in addition to its capacity advantage. The slagging-grate gasifier is able to handle a fragile solid, which would quickly break apart into dust in the raceway in front of a tuyere, the dust being carried upward by gas and producing a blockage in the fuel bed above. The slagging-grate gasifier also has the advantage that the hottest zone, being closer to the .point at which slag leaves the fuel bed, can be at a lower temperature, thereby reducing the danger that silicon will volatilize as silicon monoxide, which forms a fume in the product gas rendering its cleaning difiicult.

The hydrogen-containing gas supplied to the hydrocarbonization bed may advantageously be derived from. H and CO produced by gasifying the coke pellets with steam and oxygen in a slagging-grate gasifier. Either this gas may be used directly without further treatment, or its hydrogen content may be increased by shifting CO with steam and removing C The gas may also be employed in a hydrogasification step interposed between the slagginggrate gasifier and the hydrocarbonization bed.

The hydrogen-containing gas may also be derived by reforming a part of the methane product with steam. If a strongly-caking coal is being treated, the hydrogen content of the gaseous product from the hydrocarbonization bed may be adequate, and this gas may be recycled to the bed.

Although the economic advantage usually lies in employing as-mined coal in my new process, untreated except possibly for cleaning to reduce the ash or drying to remove moisture, I do not wish my invention to be limited to the use of as-mined coal. A wide range of coaly matter wall serve, and a particular plant situation may make it advantageous to use a char from a. low-temperture carbonization process, for example, or a coal-like solid reconstituted from a low-ash liquid extract of coal, whose use would have the advantage of giving rise to a lowash coke.

Brief description of the drawing My invention including various novel features will be more fully understood by reference to the accompanying drawing, which diagrammatically illustrates apparatus suitable for carrying out the hydrocarbonization of coal and the gasification of coke product from the hydrocarbonization process.

Description of a preferred embodiment The following description of the drawing will provide an example of the operation of the process employing a bituminous coal which, for example, may contain the following ingredients, based on weight percent: moisture about ash about 9%, volatiles about 37.1%, and fixed carbon about 48.9%, having a higher heating value at 60 F. of about 12,550 British thermal units per pound, and containing about 3.2% sulfur. Coal of this kind is extensively used in this country for thermal power generation in large plants.

Coal is introduced via line 1 to grinding means 51, which grinds the coal to a fineness so that substantially all of the coal will pass through a ZOO-mesh screen. The coal is transferred from grinding means 51 to elevated bin 2, which is connected to a pair of lock hoppers 5 and 6 through valves 3 and 4- respectively. The lock hoppers are connected to discharge into drum 13 through valves 11 and 512 respectively. At any given time one of the lock hoppers 5 and 6 is at atmospheric pressure and is receiving coal from bin 2. At this time the other of the two lock hoppers is pressurized preferably by hydrogen supplied through line 7 or 8 through valves 9 or 10, and is discharging coal through valve 11 or 12 into drum 13. Drum 13 is also pressurized with hydrogen, from line 14, and the pressure in drum 13 is maintained at a sufficient increment above the pressure in vessel 17 to cause coal to be fed continuously from drum 13 through gentle curved lines 15 via nozzles 16 into fluidized bed 18 housed in vessel 17. Two lines 15 are shown in the drawing, but more lines may sometimes be advantageously used. To a degree, the rate of coal injection into the vessel '17 may be controlled by adjusting the pressure in drum 13, the adjustment being effected by pressure-regulating means 52. A more positive control of the rate of coal injection can be effected by using more or fewer of the lines 15. Each line 115 is provided with a shut-off plug-type valve 53, so that the flow of coal through a given line may be stopped by closing its respective valve 53. Accordingly, the rate of coal injection may be adjusted by opening or closing one or more of the valves 53. Pluidizing gas is supplied to vessel 17 through line 19, the temperature of the gas being adjusted by temperature-regulating-means 54. In the instant example of the operation of the process of the invention, the fiuidizing gas is substantially pure hydrogen, say. As previously explained, it may sometimes be advantageous to supply a gas in line 19 containing methane as well as hydrogen, the partial pressures of these gases being adjusted to regulate the extent to which hydrogen may react to form additional methane in bed 18. The adjustment of the partial pressures of methane and hydrogen in line 19 may be accomplished, for example, by supplying a gas rich in methane from line 55 and a gas rich in hydrogen from line 57, the flows in the two lines being governed by the settings of valves 56 and 58 respectively. Fluidized bed 18 comprises approximately spherical coke pellets in the size range from about to /2 inch, say. The bed is at 600 p.s.i.a. and 1400 F., say. As coal is injected into bed 18, it is hydrocarbonized practically instantaneously to form methane and coke as the primary carbonization products. The operation of bed 18 is thermoneutral, i.e., heat is added or withdrawn only via materials supplied to or taken from the bed. The coal is injected into the bed at substantially atmospheric temperature, say, and hydrogen is supplied at 960 F., say. Gas and coke products are withdrawn from the bed at substantially the bed temperature.

A rich fuel gas product leaves vessel 17 through line 20; this product is essentially free of heavy tar substances. The quantity of carbon present in the rich fuel gas corresponds substantially to the carbon present in volatiles in the coal, as determined by conventional assay.

Coke pellets are withdrawn by gravity flow downward through pipe 21, in order to maintain the inventory of coke in bed 18 substantially constant. The residence time of coke in bed '18 is so shortgenerally only a few minutes-that substantially no hydrogasification of fixed carbon in the coal takes place. The quantity of coke produced by the hydrocarbonization process corresponds substan tially to the amount of fixed carbon in the coal.

The hydrocarbonization reactions which convert volatile carbon substantially to methane are extremely rapid, and for all practical purposes these reactions are limited only by the systems ability to heat the feed coal particles to reaction temperature. Under the turbulent conditions which prevail near the bottom of fluidized bed where coal feed is introduced, the coal is heated to the bed temperature practically instantaneously. Substantially all of the coke produced is laid down as additional matter upon coke pellets near the point of coal entry into the bed.

The coal-processing capacity of vessel .17 is outstandingly high. At a fluidizing-gas superficial velocity of 5 ft./sec., the capacity is about 6 tons of M.A.F. coal per hour per square foot of reactor cross-section. The capacity of the free-fall hydrocarbonization zone in the aforementioned IGT design was only about one-fifth of this, although the operating pressure was considerably higher.

As the drawing indicates, vessel 17 preferably has the form of a frusto-conical chamber with a gradual taper and the smaller end at the bottom. The taper is preferably chosen so that the cross-sectional area at the top of bed 18 is about five-thirds greater than the area at the bottom of bed 18. The range of particle sizes in bed 18 is preferably controlled so that the fluidization velocity is about in excess of the minimum fiuidization velocity at the bottom of bed 18 and is about 20% in excess of this velocity at the top. If the particles display a tendency to grow too large, some finer particles may advantageously be introduced into the bed to act as seed for the growth of additional particles. A convenient method of introducing seed particles is to produce them by an attrition process taking place within bed 18 itself; for example, introducing a high-velocity gas stream into bed 18 from a nozzle (not shown in the drawing) will produce a raceway within which particle attrition will occur. As an alternative to introducing seed particles, one may prefer to selectively withdraw larger particles from the bed, the smaller and larger particles being separated by an elutriation technique in apparatus not shown in the drawing. In the unlikely event that particles tend to remain too small on the averagean indication of undue turbulence in the bed giving rise to too rapid production of seed particles by attrition-one may advantageously practice the selective withdrawal of smaller particles with the aid of an elutriation technique.

Coke pellets move downward through pipe 21 into vessel 22, a slagging-grate gasifier operated at a coke-consumption rate which is controlled to maintain the inventory of coke in bed 18 substantially constant. Pellets flow outward and downward from the lower end of pipe 21 to form moving-bed 23 of coke, which serves as a feeder of coke to downpipes 24. From downpipes 24, the coke moves into moving-bed 26, which preferably is only about 1 to 2 feet deep. Bed 26 is supported by slagging-grate 27, comprising closely-spaced parallel stainless-steel tubes, of A inch outside diameter, say, cooled by water flowing inside the tubes (the water being supplied to the tubes and withdrawn therefrom through pipes not shown in the drawing). A gasification medium, comprising primarily oxygen and steam, say, is caused to flow upward across the entire area of slagging-grate 27 and into bed 26 at a composition and rate such that a high-temperature reaction zone forms in bed 26 immediately above grate 27. The temperature of this zone should be such that ash in the coal is converted to a molten slag which flows downward through grate 27 and into space 28. Coke moving downward in bed 26 is gasified as it approaches the hightemperature zone. The gases flowing counter to the coke are cooled both by giving up heat to the endothermic gasification reactions and also by exchange of heat to the cooler coke. Gaseous product comprising primarily H and CO is withdrawn from the space formed around downpipes 24, leaving vessel 22 through line 25. Space 28 constitutes a forehearth serving primarily to supply heat to the underneath sides of grate-tubes 27, and also sometimes advantageously serving as a combustion or gasification Zone to consume fine sizes of coal. A gasification medium is supplied to forehearth 28 through pipes 29 from lines 30. A fuelwhich may be recycled product fuel gas from line 25, or pulverized coal, or other fuel as desiredis supplied to forehearth 28 through pipes 31 from lines 32. Two sets of pipes 29 and 31 are shown in the drawing, but more sets may sometimes be advantageously used. The rate of fuel supply to pipes 31 is adjusted to maintain a slagging temperature in forehearth 28, so that slag falling from slagging-grate 27 flows freely across the upper, sloping surface of partition 33 and downward through taphole 34 in the center of partition 33. Also, the gasification medium is heated in forehearth 28 so that the underneath sides of grate-tubes 27 are not cooled by the passage of this medium. Notice that most of the surface or gas space seen by grate-tubes 27 is maintained at a high temperature, so that little radiative cooling of these tubes can occur.

Slag falls from taphole 34 through space 35 into water pool 36. The sudden cooling of slag in pool 36 causes it to break apart into a frit. Water containing frit is withdrawn intermittently through valve 44 into chamber 45. With valve 44 closed, chamber 45 is depressured, and the slag frit and water are discharged through valve 46 for disposal. Water is supplied to pool 36 through line 37. In practice, there may be a tendency for slag beards to form, i.e., stalactites of solid slag hanging from the edge of taphole 34. Moveable arm 42 can advantageously be used to knock off such beards, when they are seen through sightglass 43. The tendency for beards to form can be reduced and the danger of the tapholes freezing over can be eliminated by playing a flame on the underside of taphole 34 from the combustion of air or oxygen supplied through pipe 38 from line 39 and a fuel supplied through pipe 40 from line 41.

If a coal is treated in bed 17 which contains ash-matter high in silica, a flux such as blast-furnace slag is advantageously added to bin 2, to be mixed therein with the coal. A flux may be supplied from line 59 to grinding means 60 and thence to bin 2, the flux being advantageously ground to a fineness of 325 mesh by means 60.

When operation of vessel 17 is initiated for the first time, a coke charge having a suitable range of particle size should be supplied from an outside source. The charge is heated to a temperature in the operating range by supplying a hot gas-first atmospheric flue gas, say, and finally high-pressure hydrogen-through line 19. With hydrogen flowing in line 19, coal is injected into the bed via one or more of the lines 15, first at a reduced rate, and finally at full rate, with appropriate adjustment of hydrogen pressure and temperature to keep the bed temperature within the proper limits. It is advantageous to provide an outlet from pipe 21 (not shown in the drawing) for temporary withdrawal of coke during start-up, so that the start-up of hydrocarbonizer 17 is not complicated by the simultaneous start-up of slagging-grate gasifier 22. If one desires to derive the hydrogen in line 19 from H and CO in line 25, the gasifier can advantageously be placed into service before the hydrocarbonizer with use of an external supply of coke introduced into vessel 22 by a connection not shown in the drawing.

In a power station incorporating an advanced power cycle in which the temperature of steam is raised by the direct addition of the products of combustion of a clean fuel gas with oxygen or air, the clean fuel gas may advantageously be derived from the product in line 20, the hydrogen in line 19 having been derived from H and CO in line 25. In this application of the present invention, it is advantageous to supply two slagging-grate gasifiers like 22, in one of which the gasification medium is oxygen and steam, to supply hydrogen for use in line 19, and in the other of which the gasification medium is air and carbon dioxide or flue gas, to supply a hydrogen-poor lean fuel gas for' combustion in a supercharged boiler to raise and superheat steam. In a power station incorporating a magnetohydrodynamic electricity-generating device, a superior fuel for use in the combustion supp-lying hot gas to this device can be produced from a gasifier like 22 in which the gasification medium is oxygen and carbon dioxide.

As mentioned previously, coke pellets may be withdrawn from pipe 21 for other uses, and a coke hydrogasification step may advantageously be interposed between vessel 17 and vessel 22 if ones purpose is to produce synthetic pipeline gas.

I now give an example of the process conducted in agglomerating fluidized hydrocarbonizer vessel 17:

EXAMPLE Bed 18 was operated at 600 p.s.i.a and 1400 F. The aforementioned bituminous coal was used in its natural condition, i.e., undriecl and at atmospheric temperature. Hydrogen was supplied at 960 F. and at a rate of 79.05 pound-moles of H per ton of M.A.F. coal. Product gases in line 20 contained 40.71 moles of CH 34.13 H 13.99 H 0, and 1.13 H 5 per ton of M.A.F. coal. Coke pellets in line 21 amounted to 0.597 ton of ash-free coke per ton of M.A.F. coal.

I do not wish my invention to be limited to the particular embodiment of the accompanying drawing and foregoing example. Those skilled in the art will recognize other arrangements and other modes of operation which differ from my example only in detail, not in spirit. Only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A process for hydrocarbonizing a coal selected from the group consisting of bituminous and subbituminous coals and lignites, comprising:

(a) grinding said coal to a fineness substantially smaller than 200 mesh;

(b) injecting said ground coal into a fluidized bed operating at a temperature between about 1000 F. and 1700 F., said fluidized bed comprising coke pellets displaying a range of diameters, the substantially smallest pellet being larger than about 6 inch, said coal being heated practically instantaneously in said bed to substantially said temperature;

(c) supplying to said fluidized bed a hot gas containing hydrogen;

(d) adjusting the temperature of said bed within temperature limits such that the practically instantaneous heating of said coal in said gas to a temperature within said limits causes the coal to decompose practically instantaneously into gaseous matter and a nongaseous semifluid residue displaying agglomerating tendencies, said adjusting being accomplished at least primarily by adjusting the temperature of said gas and/or by adjusting the rate of injection of said coal and/or by supplying a hot gas in step (c) containing methane as well as hydrogen and by adjusting the hydrogen partial pressure and the methane partial pressure in said gas and thereby adjusting the extent to which the hydrogen can react in said bed to form methane in accordance with a chemical quasiequilibrium governing the reaction between hydrogen and the carbon of said coke pellets;

(e) Withdrawing gaseous product rich in methane from said fluidized bed; and

(f) Withdrawing coke pellets from said fluidized bed to maintain the inventory of coke pellets in said bed substantially constant.

2. The process of claim 1 in which also said fluidized bed operates at a pressure not below about 300 p.s.i.a.

3. The process of claim 1 in which also said range of diameters is such that the largest of said coke pellets is not less than about 5 times larger in diameter than the smallest.

4. The process of claim 1 in which also the superficial velocity of fluidizing gas leaving the top of said fluidized bed is not greater than about 200 percent in excess of the minimum fluidizing velocity of said coke pellets in said gas.

5. The process of claim 1 in which also at least a portion of carbon contained in at least a portion of said coke pellets is gasified by a gasification medium selected from the group comprising oxygen, air, steam, carbon dioxide, and flue gas in a gasifier of the slagging, moving-bed type.

6. The process of claim 5 including the following additional steps: finely grinding a fiuxing agent such as blastfurnace slag, and mixing said ground fluxing agent with said ground coal from step (a) before injecting said coal into said fluidized bed in step (b).

7. The process of claim 5 in which also said gasifier is of the slagging-grate type.

8. The process of claim 5 in which also said gasification medium is primarily oxygen and steam, and including the step of deriving at least a portion of said hydrogen-containing gas in step (c) from gas produced in said gasifier.

References Cited UNITED STATES PATENTS 3,130,133 4/1964 Loevenstein 201-31 3,194,644 7/1965 Gorin et al 48-197 3,247,092 4/1966 Huntington t 208-10 3,253,906 5/ 1966 Secord 48-206 3,320,152 5/1967 Nathan et al. 201-31 NORMAN YUDKOFF, Primary Examiner.

DAVID EDWARDS, Assistant Examiner.

Us. or. x.R.

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