FR2478667A2 - Coal conversion using alkali metal catalyst - with catalyst recovery from ash - Google Patents

Abstract

Conversion of coal (or other solid carbonaceous material) to liq. and/or gaseous products is carried out in the presence of an alkali metal catalyst as described in the Parent Patent. The improvement comprises recovering catalyst values from the solid residue (ash) by (a) heating the ash particles with CaO or MgO (or a cpd. decomposable to CaO or MgO on heating in air) at a temp. sufficient to convert water-insoluble alkali metal cpds. to water-soluble cpds.; (b) leaching the water-soluble cpds. with water to obtain an aq. soln.; and (c) using the alkali metal cpds. derived from the aq. soln. as at least part of the catalyst in the conversion process. The process is esp. applicable to coal gasification catalysed by K2CO3, but can also be applied to liquefaction, carbonisation, combustion, etc. Catalyst recovery greatly improves the economy of the process.

Description

 The present invention relates to the conversion of hard coal and similar carbonaceous solids in the presence of catalysts containing an alkali metal2 and it relates more precisely to the recovery of the constituents of alkali metals from spent solids produced during the gasification of hard coal and other similar operations and their reuse as constituents of catalysts containing alkali metals.

 In the present text, "coal" is understood to mean both coal in the strict sense and other types of coal.

 Potassium carbonate, cesium carbonate and other alkali metal compounds have been recognized as useful catalysts for the gasification of coal and similar carbon solids. The use of these compounds has also been proposed in the liquefaction of hard coal, the carbonization of hard coal, the burning of hard coal and other similar processes. To guarantee the higher reaction rates made possible by the presence of compounds. of alkali metals, it has been suggested to mix or impregnate bituminous coal, sub-bituminous coal, lignite, petroleum coke, shale oil, organic residues and similar carbonaceous materials with potassium compounds , cesium, sodium or lithium, alone or in combination with other metallic constituents, before these materials react with vapor, hydrogen, oxygen or other agents, at elevated temperatures producing effluents gaseous and / or liquid. Studies have shown that a wide variety of different alkali metal compositions can be used for this purpose, including organic oxides, organic and inorganic hydroxides, and the like.

 In general, the studies discussed above indicate that cesium compounds are the most effective gasification catalysts and are followed, in order, by potassium, sodium and lithium compounds. Due to the relatively high cost of cesium compounds and the low efficiency of lithium compounds, most of the experimental work undertaken in the past in this field has concerned the use of potassium and sodium compounds. This work has shown that potassium compounds are much more effective than the corresponding sodium compounds. Attention therefore turned to the use of potassium carbonate.

 Coal gasification operations and similar operations carried out in the presence of alkali metal compounds at high temperature generally lead to the formation of carbonization products and alkali metal residues. Carbonization products normally include unconverted carbonaceous constituents of coal, or other treated material, and various inorganic constituents generally called as ash. It is generally desirable to extract some of the carbonization product from the reaction zone during gasification and the like to remove ash and prevent it from accumulating in the reaction zone or other tanks in the system. Eutriation and other techniques have been proposed for separating the particles of carbonization products with a relatively high ash content and returning the particles having a relatively low ash content to the reaction zone, in order to improve the use of carbon in these processes.

 In gasification and other processes mentioned above which use catalysts containing alkali metals, the cost of the alkali metal components is a significant factor in determining the overall cost of the process. In order to keep the cost of the catalyst at reasonable rates, it is essential to recover and reuse the constituents of alkali metals. To recover the alkali metals, leaching has been proposed when these metals are extracted from the reaction zone with the carbonization product during the operations indicated above. Studies indicate that these constituents are generally present partly in the form of carbonates and partly in the form of soluble compounds recoverable by water-based watering. In addition, experience has shown that only part of the potassium carbonate or other constituents of alkali metals is normally recovered and therefore high quantities of additional alkali metal compounds are required. The cost of these operations is considerably increased.

 There has already been described in patent application FR 78.01.725, to which reference should be made, an improved process for the recovery of the alkali metal constituents from the particles of carbonization products obtained during the gasification of the coal and of other conversion processes carried out in the presence of a catalyst containing an alkali metal. By this process, large amounts of alkali metal constituents can be recovered from particles containing residues of alkali metals produced during gasification coal and other relatively high temperature conversion processes, by mixing the particles with calcium oxide or a solid calcium-containing compound which decomposes on heating to form calcium oxide, and by heating the resulting mixture of solids to a temperature high enough for the calcium oxide to react with alkali metal aluminosilicates ins water-soluble, contained in alkali metal residues, to give reaction products containing water-insoluble calcium silicates and water-soluble alkali metal aluminates. contact with water ~ which leaches solids, alkali metal aluminates and other constituents of alkali metals soluble in water. The pH of the resulting aqueous solution containing the water-soluble alkali metal aluminates is lowered enough to cause precipitation of aluminum hydroxide, whereby a solution containing practically free alkali metal components is formed. aluminum.

These alkali metal constituents are then used as at least part of the alkali metal constituents which represent the catalyst containing an alkali metal.

Such use preferably presupposes recycling of the solution directly to the conversion process. If this proves useful, the constituents of alkali metals can however first be recovered from the solution and then used in the conversion process.

 There has now been unexpectedly found a further improved process for the recovery of alkali metal constituents from mixtures of carbonization products, ash and alkali metal residues obtained during the gasification of coal and other conversion processes carried out. in the presence of an alkali metal containing catalyst. In accordance with the present invention, it has now been found that increased amounts of alkali metal constituents can be efficiently recovered from particles containing alkali metal residues produced during gasification. carbon, and derivative conversion processes operating at high temperature, by bringing the particles into contact with a compound containing calcium or magnesium-at a sufficiently high temperature, in practice of the order of 8710C, to transform the constituents of alkali metals insoluble in water present in the residues of alkali metals in constituents of met to water-soluble alkalis. There is every reason to believe that the elevated temperature allows the calcium or magnesium containing compound to react with water-insoluble constituents, such as alkali metal aluminosilicates, in the residues of alkali metals and hence the obtaining reaction products containing compounds insoluble in batten, such as calcium silicates and constituents of alkali metals soluble in water. The reaction products are contacted with water which leaches the water-soluble alkali metal components from the solids and then forms an aqueous solution. The water-soluble alkali metal constituents present in this solution are then used to form at least a fraction of the alkali metal constituents of the catalyst containing alkali metals. This is done preferably by recycling the solution directly in the conversion process. If desired, however, the alkali metal constituents can be recovered from the solution first and then used in the conversion process.

The aqueous solution produced in the leaching step may contain a significant amount of water-soluble alkali metal aluminates. If this is the case, it is convenient in practice to lower the pH of the solution to precipitate the aluminum in the form of aluminum hydroxide before recycling the solution to the conversion process.

 The invention is based in part on studies of the reactions of catalysts containing alkali metal constituents during gasification of coal and other similar operations. Coal and other carbon solids used in these operations normally contain mineral constituents which are converted to ash during the gasification process. Although the composition of the ashes is variable, the main constituents, expressed as oxides, are generally silica, alumina and ferric oxide. Alumina is normally present in ash in the form of aluminosilicates. Studies have shown that at least some of the alkali metal compounds, such as potassium carbonate, which are used as constituents of the gasification catalyst, react with aluminosilicates and other ash constituents forming alkali metal residues containing water-soluble alkali metal compounds, such as carbonates, sulfates, sulfides and the like, and catalytically inactive materials, insoluble in water, such as alkali metal aluminosilicates. Unless the alkali metal constituents can be recovered from the insoluble alkali metal residues, these are lost to the process and must be replaced by complementary alkali metal compounds. The process according to the invention allows the recovery of these constituents of alkali metals and therefore reduces the costs inherent in the use of large amounts of complementary alkali metal compounds. The invention therefore makes it possible to achieve substantial savings during gasification and other conversion operations carried out in the presence of catalysts containing alkali metals, and makes it possible to produce gases and / or liquids at cost prices. much lower than what would otherwise have to be endured.

 The invention is illustrated in more detail with reference to the accompanying drawing board comprising a single figure representing a schematic diagram of a process for catalytic gasification of coal, in which the constituents of alkali metals of the carbon are recovered and reused. catalyst.

 The process illustrated in the appended drawing applies to the production of methane by gasification of quituminous coal, sub-bituminous coal, lignite or similar carbonaceous solids, by means of steam at high temperature in the presence of a catalyst with carbon and alkali metal base prepared by impregnating the solid charges with a solution of an alkali metal compound or a mixture of these compounds and subsequently heating the impregnated material to a temperature sufficient to produce an interaction between the metal alkaline and the carbon present. It is clear that the alkali metal recovery system described is not limited to this particular gasification process and that it can be used in conjunction with a variety of conversion processes in which compounds of alkali metals or carbon and alkali metal catalysts to initiate the reaction of steam, hydrogen, oxygen, or the like, with m carbonaceous feed materials in order to obtain a carbonization product, coke or a similar solid product containing alkali metal residues, from which the alkali metal compounds are recovered for re-use as catalyst or constituent of the catalyst. It can be used , for example, for the recovery of alkali metal compounds from various gasification processes of coal, petroleum coke, lignite, organic waste materials and charge streams of similar solids which produce carbonaceous solids exhausted at temperatures below the melting point of ash. As other conversion processes with which this recovery system can be used, there may be mentioned the operations of carbonization of hard coal and solids of similar charge, liquefaction of hard coal and similar carbonaceous charge materials, distillation of shale oil, partial combustion of carbonaceous feed materials, and the like. These processes have been described in the literature and are familiar to those skilled in the art.

 In the process illustrated by the appended figure, a carbonaceous filler material such as bituminous coal, sub-bituminous coal, lignite or the like, which has been ground to a particle size of about 2.38 mm or less, is introduced into the conduit 10 from a load preparation installation or from storage equipment, not shown in the drawing. The solids introduced into the conduit 10 are loaded into a hopper or similar tank 11 from which they are sent through the conduit 12 into the zone 14 for preparing the charge. This zone contains a conveyor screw 15 (or any similar device) not shown, controlled by a motor 16, a series of spray nozzles or similar device 17 for spraying a solution containing an alkali metal introduced by the pipe 18 onto the solids which pass through the preparation area on the conveyor screw, and a similar set of nozzles or the like 19 for introducing steam into the preparation area.

The steam, introduced through line 20, is used to heat the impregnated solids and to expel moisture. The vapor is ex treated from the zone 14 via the conduit 21 and is directed into a condenser (not shown) from where it can be recovered for use as complementary water or the like. Most of the alkali metal containing solution is recycled through line 79 from the alkali metal recovery section of the process, which is described in detail below. Any additional solution required can be introduced into line 79 through line 13.

It is preferred to introduce a sufficient solution containing the alkali metal into the preparation zone for the charge 14 in order to provide from 1 to 50% by weight of the alkali metal compound or of the mixture of such compounds on the coal or any other carbonaceous solid. A quantity of 1 to 15% - approximately by weight is generally adequate. The impregnated and dried solid particles, prepared in zone 14, are extracted through line 24 and sent to a closed hopper or similar tank near 25. From 1 to 1, they are discharged by a Maltese cross loader or an equivalent device 26 in stream 27, at a pressure high enough to allow them to be entrained in a stream of pressurized steam, recycling production gas, inert gas or any other carrier gas introduced into line 29 through line 28. vector and the entrained solids are sent to the collector 30 by the conduit 29, and, from the collector, to the gasifier 32 via the conduits 31 and nozzles, not shown in the accompanying drawing The hopper 25 and the cross loader of
Malté 26 can be supplemented or replaced in the supply system by hoppers mounted in parallel, hoppers under pressure, aerated supply columns operating in series, or any other device capable of carrying the stream of charge solids to the required pressure.

 It is generally preferred that the gasifier 32 operates at a gauge pressure of between 2.1 × 10 6 to 14 × 10 6 pascals. The carrier gas and entrained solids are normally - introduced at a pressure slightly higher than the operating pressure of the gasification device.

The carrier gas can be preheated to a temperature of about 1490C, but below the initial softening point of the coal or any other filler used. The filler particles can be suspended in the carrier gas at a concentration of between about 0.2 and 5.0 kg of solid filler material per kg of carrier gas. The optimal ratio for a particular system depends in part on the particle size of the filler and their density, the molecular weight of the gas used, the temperature of the solid filler material and the gas feed stream, the amount of alkali metal compound used and other factors. Generally, ratios of from about 0.5 to about 4.0 kg of solid filler per kg of carrier gas are preferred.

 The gasifier 32 comprises a tank lined with a refractory material, containing a fluidized bed of carbonaceous solids rising in the tank above an internal grid or a similar distribution device not shown in the accompanying drawing. The bed is maintained in the fluidized state by means of steam introduced through the pipe 33, the manifold 34 and the injection pipes, and nozzles 35 spaced apart from the periphery 1 and by means of recycled hydrogen and carbon monoxide introduced by the lower inlet duct 36. The particular injection system shown in the drawing is not critical and other methods of injecting recycled steam and hydrogen and carbon monoxide can also be used In some cases, for example, it may be preferable to introduce steam and recycling gases through multiple nozzles in order to obtain a more uniform distribution of the injected fluid and to reduce the possibility of creating preferential paths and other related problems. The space velocity of the ascending gases in the fluidized bed is normally between 300 and 3000 volumes of steam and hydrogen and carbon monoxide recycled per hour, per volume of fluidized solids.

0,8 C02 + CH4
Dans les mêmes conditions de gazéification, des houilles de teneur plus élevées en oxygène produisent normalement des rapports méthane/anhydride carbonique plus faibles et celles de teneur plus faible en oxygène donnent des rapports méthane/anhydride carbonique plus élevés.The injected vapor reacts with the carbon in the feedstock in the fluidized bed in the gasifier 32 at a temperature between about 426 and 8710C and at a gauge pressure between about 21 and 140 kg / cm2. Due to the equilibrium conditions prevailing in the bed, as a result of the presence of the carbon-alkali metal catalyst and of the recycled hydrogen and carbon monoxide injected near the lower end of the bed, the Reactions normally consist mainly of methane and carbon dioxide. Competitive reactions which, in the absence of the catalyst and recycled gases, generally tend to produce additional hydrogen and carbon monoxide, are suppressed. The ratio of methane to carbon dioxide in the raw production gas thus formed is preferably of the order of 1 to about 1.4 moles per mole, depending on the amount of hydrogen and o xylene in the coal or in the other carbon solids treated. The coal used can be considered as an oxygenated hydrocarbon, in the description of the reaction. Wyodak hard coal, for example, can be considered to have the approximate formula oe0.84O0.20 based on the final moisture and ashless coal analysis, neglecting nitrogen and sulfur. The reaction of this coal with steam to produce methane and carbon dioxide is as follows 1.24 H2O (g) + 1.8 CH0.84 0.20

0.8 C02 + CH4
Under the same gasification conditions, coal with a higher oxygen content normally produces lower methane / carbon dioxide ratios and those with a lower oxygen content give higher methane / carbon dioxide ratios.

 The gas leaving the fluidized bed in the gasifier 32 passes through the upper section of the gasifier which serves as a disengagement zone where the particles, too heavy to be entrained by the gas leaving the tank, return to the bed. If deemed useful, this disengagement zone may include one or more cyclone separators or the like to remove relatively large particles from the gas. The gas extracted from the top of the gasifier through line 37 normally contains -m6-thane and carbon dioxide produced by the reaction of steam with carbon, hydrogen and carbon monoxide introduced into the gasifier in the form of recycle gas, unreacted steam, sulfide d hydrogen, ammonia and other impurities formed from sulfur and nitrogen contained in the feedstock, and entrained fines. This gas is introduced into the cyclone separator or a similar device 38 to separate the larger fines. The top gas then passes through the conduit 39 into a second separator 41 where the smaller particles are separated. The gas which no longer contains solids exits at the top of the separator 41 via the conduit 42 and the fines are discharged from the bottom by descending conduits 40 and 43. These fines can be returned to the gasifier or to the recovery section alkali metals of the process, as discussed below.

 After separation of the entrained solids from the raw production gas as described above, the gas stream can pass through a heat exchanger suitable for heat recovery, and then be adequately treated for the separation of acid gases . Once these operations have been carried out, the remaining gas, mainly consisting of methane, hydrogen and carbon monoxide, can be separated by a cryogenic technique into a production methane stream and a hydrogen recycling stream and carbon monoxide which is returned to the gasifier through line 36. A conventional gas treatment equipment can be used for this purpose. This part of the downstream gas treatment will not be described here, since such a detailed description is not necessary for understanding the invention.

 The fluidized bed in the gasifier 32 consists of particles of carbonization product formed when the solid carbonaceous filler material is subjected to gasification. The composition of the carbonization product particles depends on the amount of mineral matter present in the carbonaceous matter charged in the gasifier, on the amount of the alkali metal compound, or on the mixture of these compounds, impregnated on the charge material, and on the degree gasification of the carbonization product particles in the fluidized bed. The lighter carbonaceous particles, which have a relatively high content of carbonaceous material, tend to remain in the upper part of the fluidized bed.The heavier carbonization particles, which contain a relatively small amount of material carbonaceous and a relatively large amount of ash and alkali metal residues, tend to migrate to the bottom of the fluidized bed. Some of the heavier carbonization particles are normally removed from the bottom of the fluidized bed to remove ash and prevent it from accumulating in the gasifier and other tanks in the system.

 The process according to the invention is based in part on the fact that the alkali metal constituents of the gasification catalyst react with the mineral constituents of coal or other carbonaceous solids during the gasification process. Studies have shown that at least a fraction of the alkali metal compounds such as potassium carbonate, sodium carbonate and the like, which are used as components of the gasification catalyst, react with the aluminosilicates and other constituents of the ash. to form alkali metal residues containing water-soluble alkali metal compounds such as carbonates, sulfates, sulfides and the like, and materials without catalytic activity such as alkali metal aluminosilicates and other insoluble compounds in water.

 It has been found that from about 10 to 50% by weight of the potassium carbonate or other alkali metal compound used to impregnate the coal or other similar filler before gasification reacts with the aluminosilicates and other constituents of the ash during gasification by forming alkali metal aluminosilicates and other water-insoluble compounds, which cannot normally be recovered by washing ash with water. Preliminary studies tend to indicate that when potassium carbonate is used to impregnate the coal, the major constituent of the water-insoluble fraction of the alkali metal residues produced is a synthetic kaliophilite having the chemical formula KAlSiO4 .

 In order to improve the economic characteristics of the gasification process described above and of other catalytic conversion processes in which water-insoluble alkali metal residues are formed, it is desirable to recover the highest proportion possible of the alkali metal constituents in the insoluble residues and to reuse them as constituents of the catalyst in the conversion process, whereby the amount of additional, expensive, expensive alkali metal compounds is reduced. It has been found that it is possible to recover a high amount of alkali metal constituents in the water-insoluble alkali metal residues, extracted with the residual carbon and the ash from the gasifier of the process described above or from the zone reaction methods of other conversion methods, and to reuse them in the conversion method by mixing the particles extracted from the reaction zone with a compound containing calcium or magnesium, and by heating the resulting mixture in the absence of liquid water, at a relatively high temperature.The heating process converts the water-insoluble alkali metal constituents in the alkali metal residues into water-soluble constituents and thus allows the formation of reaction products containing constituents water-soluble alkali metals that are free of water. The reaction products are brought into contact with water, which leaches the constituents of water-soluble metal or alkalines present in the solids and thus forms an aqueous solution. The water-soluble alkali metal constituents present in this solution in the conversion process are then used as at least a fraction of the alkali metal constituents which make up the catalyst containing alkali metals. preferably by recycling the aqueous solution directly into the conversion process. If desired, however, the alkali metal constituents can be recovered from the solution first and then used in the conversion process. The aqueous solution produced in the leaching step may contain a significant amount of water-soluble alkali metal aluminates. If this is the case, it is normally desired to remove the aluminum from the aqueous solution before recycling it in the conversion process. This can be done by lowering the pH of the solution enough to precipitate aluminum hydroxide.

 Referring again to the accompanying drawing, the particles of carbonization product containing a carbonaceous material, ashes and residues of alkali metals are continuously extracted by the conduit 44 from the bottom of the fluidized bed in the gasifier 32. The particles flow through line 44 against the flow of a vapor or other elutriation gas introduced through line 45. There then occurs a preliminary separation of the solids, based on the differences in dimensions and density. The lighter particles having a relatively large amount of carbonaceous material tend to be returned to the gasifier, and the heavier particles having a relatively high content of ash and alkali metal residues continue to flow through the conduit 46 containing a valve 55, in the hopper 56. The fines of carbonization product recovered from the raw production gas by the descending conduits 40 and 43 and the conduit 57 can also be returned to the hopper.

 The solid particles in the hopper 56, which contain residues of alkali metals which are soluble and insoluble in water, are entrained in the conduit 58 where they are mixed with a compound containing calcium or magnesium introduced into the conduit 58 from the hopper 59 via the conduit 66. The calcium-containing compound may be a calcium oxide calcium or any calcium compound which decomposes in air to form calcium oxide when subjected to relatively raised temperatures. The calcium-containing compound can be inorganic or organic and can, for example, be calcium hydroxide, calcium acetate, calcium oxalate, calcium formate, calcium carbonate, dolomite and the like. , the magnesium-containing compound may be magnesium oxide or any magnesium compound which decomposes in air to form magnesium oxide when subjected to relatively high temperatures. The magnesium-containing compound can be inorganic or organic and can, for example; be magnesium hydroxide, magnesium acetate, magnesium oxalate, magnesium formate, magnesium carbonate, dolomia and the like. In fact, the calcium or magnesium compound used is chosen first according to its availability and its price. The required amount of calcium-containing compound depends in part on the amount of silicates in the powdered material with which it is mixed. If this proves useful, a mixture of two or more calcium-containing compounds or magnesium instead of a single compound.

 The mixture of particles of carbonization product containing the residues of alkali metals and of the compound containing calcium or magnesium is sent via line 61 to the rotary furnace or a similar heater 62 oh it is subjected to sufficiently high temperatures. zero furnace alkali metal alminosilicates and other water-insoluble alkali metal compounds in / the residue may react with the calcium or magnesium of the calcium or magnesium containing compound. The reaction converts the water-insoluble alkali metal compounds into reaction products containing water-soluble alkali metal constituents and water-insoluble compounds. The reaction products are then treated as described below. , for the recovery of the water-soluble alkali metal constituents, which are recycled in the gasification process where they are used as at least part of the alkali metal constituents which make up the catalyst containing an alkali metal.

 The mixture of solids introduced into the rotary kiln is normally subjected to a temperature between about 871 and 14260C The mixture is preferably heated to the sintering temperature which causes the surface of the particles to soften, thereby increasing the tendency of particles to agglomerate or to stick together. Sintering gives mobility to the calcium or magnesium ions present and apparently allows them to easily saturate the atomic structure of alkali metal aluminosilicates and to displace the constituents of alkali metals. Sintering can effectively be carried out in a counter-current rotary kiln in which the fuel passes through the kiln in a direction opposite to that in which the mixture of solids circulates. The rotary kiln can be replaced by any heating appliance or similar, as long as they allow the required temperatures to be reached. If desired, the temperature in the heater can be raised above the sintering temperature to convert the mixture of solids to a liquid mass in which the desired reactions take place more quickly. However, this process may not be advantageous since the liquid, on cooling, forms a vitreous solid which makes it difficult to leach with water the constituents of soluble alkali metals.

 It has not been possible to fully elucidate the effective reactions which occur in the rotary kiln 62 to transform the water-insoluble compounds in the alkali metal residues into water-soluble alkali metal components. Apparently, the calcium or magnesium ions of the calcium or magnesium compound displace or release water-soluble alkali metal constituents from the water-insoluble compounds in the alkali metal residues. The liberation of these water soluble constituents is accompanied by the formation of solid constituents, insoluble in water, of calcium or magnesium, such as silicates, aluminates, aluminosilicates or other insoluble compounds of calcium or magnesium depending on the composition of the alkali metal residues.

 The sintered mixture of solids leaving the rotary kiln 62 is cooled and sent via the conduit 63 to a ball mill or any other similar grinding apparatus 64 where the solids are pulverized, crushed or otherwise crushed to a size suitable for water leaching.

 It is desirable to produce relatively small particles so as to provide a larger surface area for efficient water leaching. The actual size is determined in part by the balance between the cost of grinding and the efficiency of water leaching. The particles are preferably ground to a size of less than about 0.250 mm.

 The ground solids are extracted from the ball mill 64 and sent to the water washing zone 66, via the conduit 65, which zone normally includes a multi-stage counter-current extraction system in which the solids are brought into contact with water flowing against the current, introduced through line 67.

The water leached from the solids of the water-soluble alkali metal constituents, producing an aqueous solution of these constituents which is discharged from the water washing zone through line 68. The spent solids are discharged from the washing area with water via line 69 and contain, among other substances, ash and various types of calcium or magnesium silicates. These solids can be used as backfill or in construction, or used for other applications.

 The aqueous solution extracted from the water washing zone 66 by the conduit 68 contains constituents of alkali metals which are soluble in water. These constituents are normally composed of alkali metal hydroxides and alkali metal aluminates. If the solution contains only a small amount of alkali metal aluminates, it can be recycled to the charge preparation zone 14, where the coal or similar carbonaceous material is impregnated with the constituents of alkali metals. The solution can be recycled by closing the valve 70 and passing the solution through line 71, through valve 72, through line 73 and through lines 79 and 18, however, if the solution in line 68 contains a significant amount of alkali metal aluminates, it is normally desirable to remove the aluminum from the solution before recycling it to the charge preparation area. Removal of aluminum is desirable since it can form complementary alkali metal aluminosilicates in the gasification by reaction with the silica filler material and the alkali metal constituents of the catalyst. If the aluminum is to be eliminated, the valve 72 is closed and the solution of the conduit 68 is passed through the valve 70 and the conduit 74, into the contact tower 75 or a similar device.

 In the contact tower 75 the pH of the solution is then lowered to a value of between approximately 10.0 and 4.0, preferably between approximately 9.0 and 5.0, by contact with a gas containing anhydride carbonic. The aqueous solution crosses from top to bottom the contact zone in the contact tower 75 where it comes into contact with an ascending gas which contains carbon dioxide.

The gas containing carbon dioxide is injected into the bottom of the contact tower through line 76. When the gas containing carbon dioxide passes from bottom to top through the descending aqueous solution, the carbon dioxide contained in the gas reacts with the alkali metal aluminates in the solution to form alkali metal carbonates and water-insoluble aluminum hydroxide. If the partial pressure of carbon dioxide is high enough and the temperature in the contact tower low enough, bicarbonates of alkali metals can also form.

 A gas depleted in carbon dioxide is extracted at the top of the contact tower 75 through the conduit 77 and is either released into the atmosphere, or treated for recovery and reuse of carbon dioxide, or otherwise evacuated. Any gas containing carbon dioxide, including pure carbon dioxide and air, can between used. However, it is preferred to use the smoke gases from the combustion of the fuel in the rotary kiln 62. The contact container used may be of another type than that shown in the appended drawing, but may be of a type which allows fairly good contact between the gas containing carbon dioxide and the aqueous solution containing the alkali metal aluminates. A tank in which the gas containing carbon dioxide bubbles into the aqueous solution may be sufficient for the purposes of the invention.

 The purpose of the operation of the alkali metal recovery process, described above, is to lower the pH of the aqueous solution containing the alkali metal aluminates, so as to separate practically all of the aluminum from the solution. in the form of a precipitate of aluminum hydroxide insoluble in water, whereby the solution contains only constituents of alkali metals without aluminum, which are then recovered and used as constituents of the gasification catalyst. As noted above, it is desirable to separate the aluminum from the alkali metal constituents before use in the gasification catalyst to help avoid the possible formation of additional alkali metal aluminosilicates in the gasifier, by reaction of aluminum with silica in the filler and the alkali metal constituents of the catalyst. It is obvious that, to fulfill the object of the invention, any means can be used to lower the pH. For example, instead of contacting the aqueous solution of the water washing zone 66 with a gas containing carbon dioxide, the effluent can be mixed with sufficient quantities of sulfuric acid, of acid nitric, formic acid or the like to lower the pH to the desired value.

 Referring again to the accompanying drawing, the effluent leaving the contact tower 76 and which contains alkali metal carbonates and other constituents of water-soluble alkali metals, and aluminum hydroxide, is extracted from the tower through line 78 and passes through a rotary mill or other solid liquid separation device 80, where solid aluminum hydroxide is separated from the aqueous solution, and is then sent through line 81 into a rotary oven or similar heater 82 in which it is calcined at elevated temperatures to produce alumina which is recovered through line 83 and which can be sold as a by-product. The sale of this material can generate additional process income and reduce the overall cost of production gas accordingly.

 A substantially solids-free aqueous solution containing alkali metal carbonates and other water-soluble alkali metal compounds is removed from the filter 80 through line 84 and recycled through lines 79 and 18 to the preparation area for the charge 14, in which the coal or a similar carbonaceous charge material is impregnated with the alkali metal compounds contained in the solution. If the concentration of the alkali metal compounds in the recycled solution is too low, the solution can be concentrated in removing excess water before the solution is returned to the charge preparation area. It is obvious that the actual alkali metal compound or the alkali metal compounds present in the recycled solution depend on the substance used to lower the pH of the aqueous effluent from the water washing zone 66. For example, if the gas containing carbon dioxide is replaced by nitric acid, the recycled solution will contain alkali metal nitrates instead of carbonates.

 In the embodiments of the invention studied above and illustrated in the accompanying drawing, the calcium or magnesium compound is mixed with the particles containing residues of alkali metals after these have been extracted from the gasifier or from any similar conversion area. It should be noted that the method according to the invention is not limited to this mode of incorporating the compound containing calcium or magnesium, but also includes cases where the compost in question is added before or during the gasification. can be done by mixing the calcium or magnesium compound with the charge material consisting of hard coal or other carbonaceous materials, or by impregnating the hard coal with a solution of the compound.

 The mode of implementation of the invention which comprises the step of adjusting the pH constitutes a variant which allows - recovery of alumina recovery as subprocesses to the process, to alkali metals. not collect the alumina, for any reason, this variant of the invention can be simplified by eliminating the contact tower 75, the rotary filter 80 and the rotary oven 82, and by injecting the gas containing carbon dioxide, or any other acidifying agent, directly in the water washing zone 66 to lower the pH and thus precipitate aluminum hydroxide. The solid aluminum hydroxide is extracted from the water washing zone via line 69 together with other solids, and the aqueous solution containing the water-soluble alkali metal constituents, extracted from the water washing zone 66 through line 68 is sent to zone 14 of charge preparation.

 It is evident from the above that the process according to the invention provides an improved alkali metal recovery system, which makes possible a significant increase in the amount of alkali metal constituents recovered from the residues of alkali metals produced during catalytic gasification and similar methods of catalytic conversion at elevated temperatures. This results in a reduced consumption of additional, expensive alkali metal compounds, and therefore a reduction in the overall cost of the conversion process.

Claims (14)

 1. Process for the conversion of a solid filler material in the presence of an catalyst containing an alkali metal into liquids and / or gases, in which particles containing residues of alkali metals are produced, according to the claim 1 of the main patent, characterized in that it comprises: - -  a) bringing these particles containing alkali metal residues into contact with a compound containing calcium or magnesium chosen from calcium or magnesium oxide and a compound which decomposes by heating in air to give oxide calcium or magnesium;  b) heating these particles in contact with the calcium or magnesium-containing compound to a temperature high enough to convert the water-soluble alkali metal constituents in these alkali metal residues to the water-soluble alkali metal constituents water, thereby obtaining reaction products containing water soluble alkali metal constituents;  c) bringing these reaction products into contact with the batten, thus forming an aqueous solution containing the constituents of alkali metals soluble in water; and  d) the use of these alkali metal constituents from the aqueous solution in the conversion process as at least a fraction of the alkali metal constituents composing the catalyst containing alkali metals.  2. Method according to claim '13 characterized in that it implements a gasification.  3. Method according to claim 1, characterized in that it comprises a liquefaction.  4. Method according to claim 1, characterized in that at least a fraction of the catalyst containing alkali metals comprises potassium carbonate.  5. Method according to claim 1, characterized in that the particles containing dice residues of alkali metals are brought into contact with a compound containing calcium.  6. Method according to claim 5, characterized in that the calcium-containing compound comprises calcium carbonate, calcium hydroxide or calcium oxide.  7. Method according to claim 1, characterized in that it is heated to a temperature above about 871 OC particles in contact with the compound containing calcium or magnesium.  8. Method according to claim 1, characterized in that it further comprises a step of converting the reaction products into solid particles of a predetermined size before bringing the reaction products into contact with water.  9. Method according to claim 1, characterized in that the carbonaceous filler material comprises coal.  10. Method according to claim 1, characterized in that the aqueous solution is recycled in the conversion process where the constituents of alkali metals are used for at least a fraction of the constituents of alkali metals which comprises the catalyst containing alkali metals.  11. A process for the gasification of hard coal in the presence of a catalyst comprising carbon and alkali metals, in which particles containing residues of alkali metals are produced, characterized in that it comprises:  a) the mixture of these particles containing residues of alkali metals with a solid compound containing calcium to form a mixture of solids, this compound containing calcium being chosen from calcium oxide and a compound which decomposes by heating with l air to give calcium oxide: of said  b) heating / mixing solids to a temperature between about 8710C and about 14260C, with the formation of reaction products containing water-soluble alkali metal constituents;  c) bringing these solid reaction products into contact with water, thus forming an aqueous solution containing constituents of alkali metals soluble in liteau, in particular aluminates of alkali metals soluble in water;  d) lowering the pH of this aqueous solution sufficiently to cause precipitation of aluminum hydroxide, with the formation of an aqueous solution containing constituents of alkali metals soluble in water practically free of aluminum; and  e) the recycling of this aqueous solution formed in step d) in the conversion process in which the constituents of alkali metals practically free of aluminum are used to form at least a fraction of the constituents of alkali metals which the catalyst comprises carbon and alkali metals.  12. Method according to claim 11, characterized in that the calcium-containing compound comprises calcium deltoxide.  13. Method according to claim 11, characterized in that the solid reaction products are further ground before bringing them into contact with water.  14. Method according to claim 11, characterized in that the pH of the aqueous solution containing alkali metal aluminates soluble in water is lowered by bringing this solution into contact with a gas containing carbon dioxide, thus forming a water-insoluble precipitate containing aluminum hydroxide and an aqueous solution containing water-soluble alkali metal carbonates, and these alkali metal carbonates are used to form at least a fraction of the alkali metal constituents which includes the catalyst containing alkali metal.