JPS623878B2 - - Google Patents

Description

[Detailed description of the invention]

The invention relates to the conversion of coal and similar carbonaceous solids in the presence of alkali metal-containing catalysts, in particular the recovery of alkali metal components from waste solids produced during the gasification of coal and similar operations, and the recovery of alkali metal components from waste solids produced during the gasification of coal and similar operations. Concerning their reuse as components of containing catalysts. Potassium carbonate, cerium carbonate and other alkali metal compounds have been recognized as useful catalysts for the gasification of coal and similar carbonaceous solids.
In addition, such compounds can be used for coal liquefaction, coal carbonization,
It has also been proposed for use in coal combustion and related methods. Bituminous coal, subbituminous coal, lignite, petroleum coke, oil shale, organic wastes and similar carbon materials are heated to elevated temperatures to ensure high reaction rates made possible by the presence of alkali metal compounds. Compounds of potassium, cerium, sodium or lithium, alone or with other metal components, are added to such materials before reacting with steam, hydrogen, oxygen or other agents to produce gaseous and/or liquid effluents. It has been proposed to mix or impregnate in combination with. Research has shown that a variety of different alkali metal compounds can be used for this purpose, including both organic and inorganic salts, oxides, hydroxides and the like. Generally, the above studies show that cerium compounds are the most effective gasification catalysts, followed by potassium,
Indicates the order of sodium and lithium compounds. Due to the relatively high cost of cerium compounds and the low effectiveness of lithium compounds, most of the experimental work in this field conducted in the past has been directed to the use of potassium and sodium compounds. This study showed that potassium compounds were substantially more effective than their sodium counterparts. Therefore, focus has been on the use of potassium carbonate. Coal gasification processes and similar operations carried out at high temperatures in the presence of alkali metal compounds generally result in the formation of char and alkali metal residues. Char typically includes unconverted carbonaceous components of coal or other feedstocks and various inorganic components commonly referred to as ash. It is generally desirable to withdraw a portion of the char from the reaction zone during gasification and similar operations to remove ash and prevent it from depositing in the reaction zone or other vessels of the system. Elutriation and other techniques are available to separate relatively high ash content particles and return relatively low ash content particles to the reaction zone to improve carbon utilization in such processes. It has been proposed. In the above gasification and other processes that utilize alkali metal-containing catalysts, the cost of the alkali metal component is an important factor in determining the overall cost of the process. In order to maintain catalyst costs at reasonable levels, it is essential to recover and reuse the alkali metal components. It has been proposed to recover the alkali metal components by leaching as they are withdrawn from the reaction zone along with the char during operations of the above type. Research indicates that these components generally exist in part as carbonates and other water-soluble compounds that can be recovered by washing with water. Experience has shown that only a portion of the potassium carbonate or other alkali metal component is usually recovered and that substantial amounts of make-up alkali metal compound are therefore required. This significantly increases the cost of such operations. The present invention provides an improved method for recovering alkali metal components from coal particles produced during coal gasification and other conversion processes conducted in the presence of alkali metal-containing catalysts. Thus, in accordance with the present invention, particles containing alkali metal residues produced during coal gasification and related high temperature conversion processes are treated with a calcium or magnesium containing compound in the presence of water so that the calcium or magnesium containing compound is alkali. from the particles by treatment under conditions such that water-insoluble compounds such as alkali metal aluminosilicates in the metal residue react to form a water-insoluble precipitate and an aqueous solution containing the water-soluble alkali metal components. It has been found that increased amounts of alkali metal compounds can be efficiently recovered. These alkali metal components are
It is then used in a conversion process as at least a portion of the alkali metal component that makes up the alkali metal-containing catalyst. Preferably, such use is accomplished by recycling the solution directly to the conversion process. However, if desired, the alkali metal component can be first recovered from the solution and then used in the conversion process. The aqueous solution produced in the processing step can contain significant amounts of water-soluble alkali metal aluminates. If this is the case,
of the solution before recycling it to the conversion process.
It is usually desirable to lower the pH and precipitate the aluminum in the form of aluminum hydroxide. The present invention is based in part on studies of the reactions that catalysts containing alkali metal components undergo during coal gasification and similar operations. Coal and other carbonaceous solids used in such operations typically contain mineral components that are converted to ash during the gasification process. Although the composition of the ash varies, the major components expressed as oxides are generally silica, alumina, and ferric oxide. Alumina is usually present in the ash in the form of aluminosilicates. Studies have shown that at least a portion of the alkali metal compounds used as gasification catalyst components, such as potassium carbonate, react with aluminosilicate and other ash components to form water-soluble alkali metal compounds such as carbonates, sulfates, etc. It has been found that alkali metal residues containing water-insoluble and catalytically inert materials such as metal aluminosilicates are produced. If the alkali metal components in this insoluble alkali metal residue cannot be recovered, they are lost from the process and must be replaced by make-up alkali metal compounds. The process of the present invention allows the recovery of these alkali metal components, thereby reducing the costs incurred by the use of large quantities of make-up alkali metal compounds. As a result, the present invention allows for considerable savings in gasification and other conversion operations carried out in the presence of alkali metal-containing catalysts, and at a significantly lower cost than would otherwise be the case. ) allows the production of liquid. The method illustrated in the accompanying drawings involves impregnating a feedstock solid with a solution of an alkali metal compound or a mixture of such compounds, after which the impregnated material is brought into interaction between the alkali metal and carbon present. Methane by steam gasification of bituminous coal, subbituminous coal, lignite or similar carbonaceous solids at elevated temperatures in the presence of an alkali metal catalyst prepared by heating to a temperature sufficient to This is the manufacturing method. It is noted that the disclosed alkali metal recovery system is not limited to this particular gasification process, and that it combines steam, hydrogen, oxygen or the like with a carbonaceous feedstock using an alkali metal compound or carbon-alkali metal catalyst. Various other conversion processes such as accelerating the reaction to produce a char, coke or similar solid product containing alkali metal residues and from which the alkali metal compound is recovered for reuse as a catalyst or a component thereof. It will be understood that it can be used in conjunction with any of the following. For example, this applies to coal, petroleum coke, which produces waste carbonaceous solids at temperatures below the ash melting point,
It can be used to recover alkali metal compounds from a variety of processes for the gasification of lignite, organic waste, and similar solid feed streams. Other conversion processes that can be used in conjunction include carbonization of coal and similar feedstock solids, liquefaction of coal and related carbonaceous feedstocks, carbonization (retorteng) of oil shale, partial combustion of carbonaceous feedstocks, etc. Examples include operations for Such methods are disclosed in the literature and will be apparent to those skilled in the art. In the method illustrated in the accompanying drawings, a solid carbonaceous feedstock, such as bituminous coal, subbituminous coal, lignite or the like, which has been pre-ground to a particle size of about 8 mesh or smaller on a U.S. sieve series basis, is It is sent to line 10 from a raw material preparation plant or storage facility (not shown). The solids introduced into line 10 are fed to a hopper or similar vessel 11 from where they are passed via line 12 to feed preparation zone 14. This zone consists of a screw conveyor or similar device 15 powered by a motor 16;
A series of spray nozzles or similar devices 17 for spraying the solids with an alkali metal-containing solution supplied via line 18 to the solids as they are moved through the preparation zone by the conveyor, and steam into the preparation zone. A similar set of nozzles or similar for introduction 1
Contains 9. The steam supplied via line 20 serves to heat the impregnated solids and drive out moisture. Steam flows from zone 14 to pipe 21
and sent to a condenser (not shown) from where it can be recovered for use as make-up water or the like. The majority of the alkali metal-containing solution is recycled via lines 13 and 76 from the alkali metal recovery section of the process, which is described in detail below. All required replenishment solutions can be introduced into line 13 via line 22. Sufficient alkali metal-containing solution is introduced into feed preparation zone 14 to provide from about 1 to about 50% by weight of the alkali metal compound or mixture of such compounds relative to the coal or other carbonaceous solids. is preferable. Generally, from about 1 to about 15% by weight is suitable. The dried impregnated solid particles prepared in zone 14 are drawn off via line 24 and sent to a closed hopper or similar container 25. As such, they contain sufficient water to enable their entrainment into the high pressure steam, recycle product stream, inert gas or other carrier gas stream introduced via line 28 into line 29. It is discharged at increased pressure via a star wheel feeder or equalizer 26 in line 27.
The carrier gas and entrained solids are conveyed via line 29 to manifold 30 and from the manifold to gasifier 32 via feed line 31 and nozzles (not shown). Instead of or in addition to the hopper 25 and starwheel feeder 26, the feed system may include:
Parallel lock hoppers, pressurized hoppers,
Continuously operated aerated standpipes or other equipment may be used. It is generally preferred that gasifier 32 operate at a pressure of about 500 to about 2000 psig. The carrier gas and entrained solids are typically introduced at a pressure somewhat in excess of the operating pressure of the gasifier. The carrier gas is approx.
It can be preheated to a temperature above 300°C but below the initial softening point of the coal or other feedstock used. The feedstock particles are 1 lb carrier gas
It can be suspended in the carrier gas at a concentration of about 0.2 to about 5.0 lb/solid feedstock. The optimum ratio for a particular system depends on the particle size and density of the feedstock,
It depends in part on the molecular weight of the gas used, the temperature of the solid feedstock and inlet gas stream, the amount of alkali metal compound used, and other factors. Generally, about 0.5 to about 4.0 lb of solid feedstock per lb of carrier gas
A ratio of . Gasifier 32 consists of a refractory lined vessel containing a fluidized bed of carbonaceous solids extending above an internal grate or similar distribution device (not shown). The bed is injected by steam introduced via line 33, manifold 34 and peripherally spaced injection pipes and nozzles 35, and by recycled hydrogen and carbon monoxide introduced via bottom inlet pipe 36. and maintained in a fluid state. The particular injection system shown is not critical; therefore, other methods for injecting steam and recycled hydrogen and carbon monoxide may also be used. In some cases, for example, it may be desirable to introduce both steam and recycle gas through multiple nozzles to obtain a more uniform distribution of the injected fluid and reduce the likelihood of channeling and related problems. The space velocity of the rising gas in the fluidized bed is typically about 300 to about 3000 volumes of steam and recycled hydrogen and carbon monoxide/
hr/fluid solids volume. The injected steam reacts with the feedstock carbon in the fluidized bed in gasifier 32 at a temperature in the range of about 800 to about 1600 psig and a pressure of about 300 to 2000 psig. Due to the recycled hydrogen and carbon monoxide injected near the lower end of the bed and the equilibrium conditions that exist in the bed as a result of the presence of the carbon-alkali metal catalyst, the reaction products are typically more essential than methane and carbon dioxide. Above. Competing reactions, reactions that would normally tend to produce additional hydrogen and carbon monoxide in the absence of catalyst and recycle gas, are suppressed. The ratio of methane to carbon dioxide in the crude product gas thus formed is preferably from about 1 to about 1.4 moles per mole depending on the amount of hydrogen and oxygen in the raw coal or other carbonaceous solids. is within the range of The coal used can be considered an oxygenated hydrocarbon for the purpose of describing the reaction. For example, coal from Wyodak can be considered to have the approximate formula CH ₀ . ₈₄ O ₀ . ₂₀ , based on the final analysis of the coal without moisture and ash and ignoring nitrogen and sulfur. The production of methane and carbon dioxide by the reaction between coal and steam is as follows. 1.24H ₂ O ₍ g ₎ + 1.8CH _{0 . 84} O ₀ . produces a high methane to carbon dioxide ratio. Gas leaving the fluidized bed of gasifier 32 passes through the upper part of the gasifier, which acts as a separation zone and
Particles that are too heavy to be entrained by the gas exiting the vessel are now returned to the bed. If desired, this separation zone can include one or more cyclone separators or the like to remove relatively large particles from the gas. The gas withdrawn from the upper part of the gasifier via line 37 typically contains recycle gas, unreacted steam, hydrogen sulfide, ammonia and other contaminants formed from sulfur and nitrogen contained in the feedstock. methane and carbon dioxide produced by the reaction of steam with carbon, hydrogen and carbon monoxide, which are introduced into the gasifier as gasifiers and entrained fines. This gas is introduced into a cyclone separator or similar device 38 for removal of larger fines.
The overhead gas then enters a second separator 41 via line 39 where smaller particles are removed. The gas from which the solids have been separated is taken out as overhead from the separator 41 via line 42, and the fine powder is discharged downward via depressures 40 and 43. These fines can be returned to the gasifier or sent to the alkali metal recovery zone of the process as described below. After separating the entrained solids from the crude product gas as described above, the gas stream can be passed through suitable heat exchange equipment for heat recovery and then treated for removal of acid gases. . Once this is achieved, the residual gas, consisting primarily of methane, hydrogen and carbon monoxide, is separated cryogenically from the product methane stream and the hydrogen and carbon monoxide recycle stream (which is (return to the gasifier via line 36). Conventional gas treatment equipment can be used. A detailed description of this downstream gas processing portion of the method is not necessary for understanding the invention and is therefore omitted. The fluidized bed of gasifier 32 consists of char particles that are formed when the solid carbonaceous feedstock undergoes gasification. The composition of the char particles depends on the amount of mineral matter present in the carbonaceous material fed to the gasifier, the amount of alkali metal compound or mixture of such compounds impregnated in the feedstock, and the amount of the char particles in the fluidized bed. It depends on the degree of gasification it undergoes while inside. Lighter char particles, which have a relatively high content of carbonaceous material, tend to remain in the upper part of the fluidized bed. Heavy char particles, which contain relatively small amounts of carbonaceous material and relatively large amounts of ash and alkali metal residues, are
It tends to migrate toward the bottom of the fluidized bed. A portion of the heavy char particles is usually withdrawn from the bottom of the fluidized bed to remove ash and thereby prevent it from accumulating in the gasifier and other vessels in the system. The method of the present invention is based in part on the fact that the alkali metal component of the gasification catalyst reacts with the mineral components of lime and other carbonaceous solids during the gasification process. Studies have shown that at least a portion of the alkali metal compounds used as gasification catalyst components, such as potassium carbonate, sodium carbonate, and the like, react with aluminosilicate and other ash components to form water-soluble compounds such as carbonates, sulfates, etc. It has been shown to produce alkali metal residues containing catalytically inert materials such as alkali metal compounds and catalytically inert materials such as alkali metal aluminosilicates and other water-insoluble compounds. From about 10 to about 50 weight percent of the potassium carbonate or other alkali metal compound used to impregnate coal or similar feedstock prior to gasification reacts with aluminosilicates and other ash components during gasification. It has been found that alkali metal aluminosilicates and other water-insoluble compounds are formed which cannot normally be recovered from the ash by washing with water. Preliminary studies indicate that when such potassium carbonate is used to impregnate coal, the majority of the water-insoluble portion of the alkali metal residue produced is a synthetic caryophyllite with the chemical formula _KAlSiO4 . Tend. In order to improve the economics of the catalytic gasification processes described above and other catalytic conversion processes where water-insoluble alkali metal residues are formed, it is necessary to recover as many alkali metal components as possible from the insoluble residue and to remove them. It would be desirable to reuse it as a catalyst component in the conversion process, thereby reducing the need for costly make-up alkali metal compounds. A substantial amount of the alkali metal component in the water-insoluble alkali metal residue withdrawn with the charcoal and ash from the reaction zone of the gasifier or other conversion process of the above process may cause the particles withdrawn from the reaction zone to It has been found that by treatment with a calcium- or magnesium-containing compound in the presence of the compound, it can be recovered for reuse in a conversion process. The treatment process is carried out under conditions such that the calcium- or magnesium-containing compound liberates the alkali metal components from the water-insoluble alkali metal residue to produce an aqueous solution containing these components. These water-soluble alkali metal components are then used in the conversion process as at least a portion of the alkali metal components that make up the alkali metal-containing catalyst. Preferably, such use is accomplished by recycling the solution directly to the conversion process. However, if desired, it is also possible to first recover the alkali metal component from the solution and then use it in the conversion process. The aqueous solution produced in the processing step can contain significant amounts of water-soluble alkali metal aluminates. In such cases, it is usually desirable to remove aluminum from the aqueous solution before recycling it to the conversion process. This is the solution
This can be achieved by lowering the PH sufficiently to cause precipitation of aluminum hydroxide. Referring again to the accompanying drawings, char particles containing carbonaceous material, ash and alkali metal residues are continuously withdrawn from the bottom of the fluidized bed of gasifier 32 via line 44. The particles flow downwardly through line 44 in countercurrent to the flow of steam or other separation gas introduced via line 45. Here,
A preliminary separation of the solids occurs based on size and density differences. Light particles with a relatively large amount of carbonaceous material tend to be returned to the gasifier, and heavy particles with a relatively high content of ash and alkali metal residues are sent via line 46 to a fluidized bed withdrawal zone 47.
flows downward. Steam or other fluidizing gas is introduced into the bottom of the withdrawal zone via line 48 to maintain the bed in a fluidized state. Conduit 4 is used to cool the particles and facilitate their further processing.
Water can be introduced via step 9. The rate of withdrawal is controlled by regulating the pressure in zone 47 by means of a throttle valve 50 in overhead line 51. Gas from line 51 can be returned to the gasifier via line 52 or exhausted via valve 53. From the container 47, the solid particles are transferred to the valve 55.
It is sent to a hopper 56 via a conduit 54 containing. The solid particles in hopper 56 are now ready for processing to recover the alkali metal components. Typically, the soluble alkali metal components are recovered by washing these particles with water. In addition to being used to recover alkali metal components from insoluble alkali metal residues formed during gasification or other conversion processes, the process of the present invention can also be used to recover water-soluble alkali metal residues present in these particles. It can also be used to recover soluble alkali metal components from materials. However, elimination of the water wash step may not be desirable. This is because the water-soluble alkali metal components that are normally removed in this step tend to be present and react with calcium- or magnesium-containing compounds when the particles are treated with the compounds, thereby reducing the The amount of calcium or magnesium compound required is substantially reduced compared to the amount that would be required if the alkali metal components were consumed solely by the reaction that solubilizes the alkali metal components from the insoluble alkali metal compounds present in the residue. Because it will be done. Thus, one of the factors in determining whether a water wash step should be eliminated is usually the cost of the increased requirement for calcium or magnesium containing compounds relative to the cost of the water wash step. The process shown in the accompanying figures uses a water washing step prior to processing the particles to recover alkali metal components or compounds from insoluble alkali metal residues. The solid particles in hopper 56 are combined with the char fines recovered from the crude product gas via depressures 40 and 43 and line 57;
It is then supplied to a washing zone 59 via a pipe 58. The water wash zone typically consists of a multi-stage countercurrent extraction system in which the particles are contacted countercurrently with water introduced via line 60. An aqueous solution of alkali metal compounds such as alkali metal carbonates, sulfates and the like is recovered from the apparatus and can be recycled to feed preparation zone 14 via lines 61, 13, 76 and 18. Here, coal or similar carbonaceous feedstock is impregnated with alkali metal compounds recovered from the soluble alkali metal residues of the water washing process and from the insoluble alkali metal residues as described below. The particles, from which substantially all of the soluble alkali metal components have been extracted, are withdrawn from the water washing zone via line 62 in the form of a slurry. Although the soluble alkali metal components have been removed from the particles, a significant amount of the alkali metal components are still present in the form of insoluble alkali metal residues. The slurry passes through the conduit 62,
Transferred to an autoclave or similar reaction vessel 63 equipped with a stirrer 66. Here, the alkali metal aluminosilicate and other insoluble alkali metal compounds in the alkali metal residue react in the presence of water with calcium- or magnesium-containing compounds introduced into the reactor via line 64 to become water-soluble. It produces alkali metal components and water-insoluble compounds such as calcium or magnesium silicates and the like. Apparently, the calcium or magnesium compound is at least partially dissolved in the slurry water, thus producing calcium or magnesium ions that displace or liberate the water-soluble alkali metal component from the insoluble alkali metal compound. The substituted alkali metal components are recovered in the steps described below and recycled to the gasification process where they serve as at least a portion of the alkali metal components that make up the alkali metal-containing catalyst. Agitator 66 is operated continuously during the reaction to at least partially prevent agglomeration of the reactants. An example of one hydrothermal (in the presence of hot water) reaction that would take place in autoclave 63 is described below. For the purpose of writing the reaction equation, it is assumed that the calcium-containing compound is present in the autoclave in the form of calcium hydroxide. The symbol "M" is used to represent an alkali metal cation. The actual alkali metal present will depend on the type of alkali metal compound used as a component of the alkali metal-containing gasification catalyst. As can be seen from the above formula (1), alkali metal aluminosilicate reacts with calcium hydroxide in the presence of hot water to produce water-soluble alkali metal aluminate and water-insoluble dicalcium silicate.
A portion of the alkali metal aluminate formed by reaction equation (1) reacts with water to form a water-insoluble precipitate of alkali metal hydroxide and aluminum hydroxide as shown in equation (2). . The amount of alkali metal aluminate actually found in solution depends in part on temperature, PH, and other reaction conditions of the autoclave. It will be appreciated that the above reaction equations represent only two reactions that may be performed in an autoclave. It is also possible that hydrothermal reactions involving more complex alkali metal aluminosilicates and other insoluble components in the alkali metal residue may occur to produce products other than those shown in the above formula. The actual role of water in the reaction of calcium- or magnesium-containing compounds with insoluble alkali metal residues is not clearly known. However, it is theorized that the primary role of water is to provide favorable reaction kinetics by acting as a medium through which calcium or magnesium ions are highly mobile. If the amount of water in the slurry drawn from wash zone 59 is insufficient to provide optimal kinetics, water can be added to the slurry in line 62 via line 65. Generally, the temperature of the autoclave 63 is approximately
It is maintained within the range of 250 to about 500〓. Since the water within the autoclave 63 must always be present in a liquid state to provide the medium for the hydrothermal reaction, the pressure within the autoclave is typically equal to or greater than the vapor pressure of water at the operating temperature. It should be high. The calcium or magnesium compound used as one of the reactants in the hydrothermal reaction carried out in an autoclave is any inorganic or organic calcium or magnesium containing compound that at least partially ionizes or dissociates in water to yield calcium or magnesium ions. It's good to be warm. Calcium-containing compounds may be, for example, calcium oxide, calcium hydroxide, calcium acetate, calcium oxalate, calcium formate, calcium carbonate, dolomite and the like. Similarly, the magnesium-containing compound may be magnesium oxide, magnesium hydroxide, magnesium acetate, magnesium oxalate, magnesium formate, magnesium carbonate, dolomite, and the like. The actual calcium- or magnesium-containing compound used will depend primarily on its availability, cost, and solubility in water. The amount of calcium- or magnesium-containing compound required depends in part on the amount of silicate and soluble alkali metal components in the granulate fed to autoclave 63. If desired, a mixture of two or more calcium- or magnesium-containing compounds can be used instead of a single compound. Slurry effluent from reactor 63 is routed to line 67
and sent to a rotator or other solid-liquid separator 68 where the water-soluble alkali metal components are extracted from the particulate matter and water-insoluble precipitate formed by the reaction carried out in the autoclave 63. An aqueous solution is separated. Solids are withdrawn from the filter via line 69 and contains small amounts of carbonaceous material ash, calcium silicate, and aluminum hydroxide, among other materials. These solids can be disposed of as landfill material or can be further processed to recover valuable components such as calcium silicate which can then be used in the manufacture of cement. The aqueous effluent from filter 68 contains alkali metal components in solution. As can be seen from formulas (1) and (2) above, these components usually consist of alkali metal hydroxides and alkali metal aluminates. If the effluent contains only small amounts of alkali metal aluminates, it can be recycled directly to feed preparation zone 14 where coal or similar carbonaceous feedstock is impregnated with the alkali metal component. Recirculation of the effluent may be accomplished by closing valve 83 and directing the effluent through line 70 to line 80, through valve 81 to line 84, and through lines 76 and 18. can. However, if the effluent from filter 68 contains significant amounts of alkali metal aluminate, it is usually desirable to remove the aluminum from the solution before recycling the aqueous effluent to the feed preparation zone. Removal of aluminum is desirable. This is because it can form additional alkali metal aluminosilicates in the gasifier by reacting with the silica in the feed and the alkali metal components in the catalyst. If aluminum removal is desired, valve 81 is closed and the aqueous effluent from filter 68 is sent from line 70 via line 82 to valve 83 to a contactor or similar vessel 71. In contactor 71, the PH of the effluent is reduced to about 10.0-10.0 by contacting it with a carbon dioxide-containing gas.
It is reduced to a value within the range of about 4.0, preferably about 9.0 to about 5.0. The aqueous solution contains carbon dioxide-containing gas in pipe 7.
2 into the bottom of the contactor and simultaneously passed down the contact zone of the contactor. As the carbon dioxide-containing gas rises through the downstream aqueous solution, the carbon dioxide in the gas reacts with the alkali metal aluminates to form alkali metal carbonates and water-insoluble aluminum hydroxide. Alkali metal bicarbonates may also be formed if the partial pressure of carbon dioxide is high enough and the contactor temperature is low. The gas depleted in carbon dioxide is drawn out as overhead from the contactor 71 via the line 73,
It is then emitted to the atmosphere, further processed for carbon dioxide capture and reuse, or otherwise disposed of. Any carbon dioxide-containing gas can be used, including pure carbon dioxide and air. However, it is preferred to use carbon dioxide removed from the crude product gas produced in gasifier 32. The contact vessel used is not necessarily of the type shown in the drawings, but may be of any type that allows reasonably good contact between the carbon dioxide-containing gas and the aqueous alkali metal aluminate solution. A simple tank bubbling carbon dioxide-containing gas into an aqueous solution will suffice for the purposes of this invention. The purpose of the above steps of the alkali metal recovery process is to lower the pH of the aqueous solution containing the alkali metal aluminate so that substantially all of the aluminum is removed from the solution in the form of a water-insoluble precipitate of aluminum hydroxide. The purpose is to leave in solution an alkali metal component that does not contain aluminum, which is then recovered and used as a component of the gasification catalyst. As previously described, removing aluminum from the alkali metal components prior to their use in the gasification catalyst allows the gasification to occur by reaction of the aluminum with the silica in the feedstock and the alkali metal component in the catalyst. This is desirable to help avoid the possibility of additional alkali metal aluminosilicate formation in the vessel. Any method of lowering the PH can be used for purposes of the present invention. For example, instead of contacting the effluent from filter 68 with a carbon dioxide-containing gas, the effluent may be
sulfuric acid in an amount sufficient to reduce the PH to the desired value,
It can also be mixed with formic acid, nitric acid or the like. Referring again to the drawings, the effluent from contactor 71, which contains alkali metal carbonate and aluminum hydroxide, is drawn from the bottom of the vessel via line 74 and sent to a rotator or similar fluid. It is sent to solid separator 75. Solid aluminum hydroxide is now removed from the aqueous solution containing the alkali metal carbonate, and the solution is passed through line 8.
6, 76 and 18 to feed preparation zone 14 where the gasification feed is impregnated with alkali metal carbonate. If the concentration of alkali metal carbonate in the recycled solution is undesirably low, the solution can be concentrated by removing excess water before returning it to the feed preparation zone. The exact alkali metal compounds present in the recycle solution are determined from the aqueous effluent from filter 68.
It will be appreciated that this depends on the substance used to lower the PH. For example, if nitric acid is used instead of carbon dioxide-containing gas, the recycled solution will contain alkali metal nitrates instead of carbonates. The aluminum hydroxide collected in filter 75 passes through line 77 to rotary kiln or similar equipment 78.
where it is calcined at high temperatures to produce alumina, which can be recovered via line 79 and sold as a by-product. Sale of this material can provide additional revenue from the process, thus lowering the overall cost of product gas. Embodiments of the present invention that include a PH adjustment step are those that allow alumina to be recovered as a by-product of an alkali metal recovery process. If recovery of alumina is not desired for any reason, this embodiment of the invention can be simplified by eliminating strainer 68 and rotary kiln 78. In such a case, the slurry from autoclave 63 is sent directly to vessel 71 without liquid-solid separation and contacted with carbon dioxide-containing gas. The effluent from the contactor undergoes liquid-solid separation in filter 75 and the resulting aqueous solution is recycled to the feed preparation zone. The solids, which contain carbonaceous material, ash, calcium silicate, and aluminum hydroxide, among other materials, can be used as landfill material or otherwise disposed of. The nature and objects of the present invention are further illustrated by the results of laboratory tests showing that soluble alkali metal compounds can be recovered from the insoluble components of the coal produced during catalytic gasification of coal. To test the effectiveness of the proposed alkali metal recovery method, a tubular bomb having an inner diameter of 1 inch was charged with approximately 5-15 grams of char ground to less than 100 mesh by US sieve series standards. The tube cylinder was rotated by a variable speed motor in a tube furnace equipped with a temperature controller and timer. Char is made of Illinois pre-impregnated with potassium carbonate.
Derived from fluidized bed catalytic gasification of No. 6 coal. Before the char was fed into the tubular bomb, it was analyzed for both water and acid soluble potassium. The amount of water-insoluble potassium present in the char was determined by subtracting these two values. In some of the experiments conducted, the feedstock cher was rinsed with water before charging it into the tubular bomb. Char contains calcium hydroxide and about 70 to about
A tubular bomb was fed in the form of a slurry containing 100 ml of distilled water. Sufficient calcium hydroxide was used so that the slurry contained a calcium to potassium molar ratio of about 2.0 to about 13.0. Approximately 201/4 inch carbon steel ball bearings were added to the tubular cylinder to ensure good agitation and prevent caking or agglomeration. Reaction temperatures of about 350 to about 500 °C and reaction times of 2 to 4 hours were studied. Solids and liquid were quantitatively recovered from the cylinder and separated by decantation. The solids from the bomb were washed with 150 ml of water and dried. Both the solid and the decant were analyzed for potassium content by X-ray fluorescence. The decant was then evaporated and the resulting residue was analyzed by X-ray diffraction to determine its composition. The results of these tests are shown in Table 1 below.

Table 1 shows that calcium hydroxide liberates a substantial amount of the water-insoluble potassium originally contained in the char. the percentage of insoluble potassium recovered is within the range of about 63 to about 95.2%;
And at temperatures higher than 420㎓, the lowest recovery percentage was 72.1. The relatively high difference in potassium residuals for runs 3-6 is due to possible leaks in the experimental setup. X-ray diffraction analysis of the residue produced from the evaporation of the decant liquid
It showed the presence of K ₂ CO ₃ , K ₂ CO ₃ , 11/2H ₂ O, K ₂ SO ₄ and possibly some unreacted Ca(OH) ₂ . The presence of potassium carbonate rather than potassium hydroxide is expected. This is because the former reacts with atmospheric carbon dioxide during evaporation of the decant to form carbonates. From the above, it can be seen that the process of the present invention provides improvements that allow for significantly increasing the amount of alkali metal components recovered from alkali metal residues produced during catalytic gasification and similar high temperature catalytic conversion processes. It will be obvious that the present invention provides a method for recovering alkali metals. As a result, the need for costly make-up alkali metal compounds is reduced, thereby lowering the overall cost of the conversion process.

[Brief explanation of the drawing]

The attached drawing is a schematic flow sheet of a catalytic coal gasification method for recovering and reusing the alkali metal components of the catalyst, and the reference numerals indicating the main parts are as follows. 14: Raw material preparation zone, 32: Gasifier, 59:
Water washing zone, 63: Reactor, 71: Contactor, 78:
Rotating kiln.

Claims (1)

[Claims] 1. During the conversion of a solid carbonaceous feedstock into a liquid and/or gas in the presence of an alkali metal-containing catalyst, char particles containing carbonaceous material, inorganic ash and alkali metal residues are formed. (a) treating the alkali metal residue-containing char particles with a calcium- or magnesium-containing compound in the presence of liquid water at a temperature of 250-500°C (121-260°C) to render them water-soluble; producing an aqueous solution containing an alkali metal component; and (b) using the alkali metal component from the aqueous solution as at least a portion of the alkali metal component constituting the alkali metal-containing catalyst in the conversion process. A method for converting solid carbonaceous feedstocks. 2. The method of claim 1 further characterized in that the conversion process comprises gasification. 3. The method of claim 1 or 2, further characterized in that the conversion process comprises liquefaction. 4. The method according to any one of claims 1 to 3, further characterized in that at least a portion of the alkali metal-containing catalyst consists of potassium carbonate. 5. A method according to any one of claims 1 to 4, further characterized in that the char particles containing alkali metal residues are treated with a calcium-containing compound. 6 Claim 5 further characterized in that the calcium-containing compound consists of calcium hydroxide.
The method described in section. 7. The method of claim 5, further characterized in that the calcium-containing compound comprises calcium oxide. 8. A method according to any one of claims 1 to 7, further characterized in that the carbonaceous feedstock consists of coal. 9. Lowering the pH of the water-soluble alkali metal component-containing aqueous solution in step (a) to a level sufficient to precipitate aluminum hydroxide, thereby forming a water-soluble alkali metal component-containing aqueous solution substantially free of aluminum. 9. A method according to any one of claims 1 to 8, further characterized by: 10 By bringing an aqueous solution containing a water-soluble alkali metal component into contact with a gas containing carbon dioxide, the pH of the aqueous solution can be adjusted.
, thereby forming a water-soluble aluminum hydroxide-containing precipitate and a water-soluble alkali metal carbonate-containing aqueous solution, and using said alkali metal carbonate as at least a portion of the alkali metal component constituting the alkali metal-containing catalyst. 10. The method of claim 9 further characterized by: 11. Claims 1 to 10 further comprising the additional step of washing the char particles containing alkali metal residues with water before treating the particles with a calcium- or magnesium-containing compound in the presence of liquid water. The method described in any of the paragraphs. 12. The method according to any one of claims 1 to 11, further characterized in that the alkali metal-containing catalyst comprises a carbon-alkali metal catalyst.