Patent Application
20090165382
The present invention relates to a catalytic gasification process that involves the extraction and recovery of alkali metal from char that remains following catalytic gasification of a carbonaceous composition. Further, the invention relates to processes for extracting and recovering alkali metal from char by reacting a slurry of char particulate with carbon dioxide under suitable temperature and pressure so as to convert insoluble alkali metal compounds contained in the insoluble char particulate to soluble alkali metal compounds.
In view of numerous factors such as higher energy prices and environmental concerns, the production of value-added gaseous products from lower-fuel-value carbonaceous feedstocks, such as petroleum coke and coal, is receiving renewed attention. The catalytic gasification of such materials to produce methane and other value-added gases is disclosed, for example, in U.S. Pat. No. 3,828,474, U.S. Pat. No. 3,998,607, U.S. Pat. No. 4,057,512, U.S. Pat. No. 4,092,125, U.S. Pat. No. 4,094,650, U.S. Pat. No. 4,204,843, U.S. Pat. No. 4,468,231, U.S. Pat. No. 4,500,323, U.S. Pat. No. 4,541,841, U.S. Pat. No. 4,551,155, U.S. Pat. No. 4,558,027, U.S. Pat. No. 4,606,105, U.S. Pat. No. 4,617,027, U.S. Pat. No. 4,609,456, U.S. Pat. No. 5,017,282, U.S. Pat. No. 5,055,181, U.S. Pat. No. 6,187,465, U.S. Pat. No. 6,790,430, U.S. Pat. No. 6,894,183, U.S. Pat. No. 6,955,695, US2003/0167961A1, US2006/0265953A1, US2007/000177A1, US2007/083072A1, US2007/0277437A1 and GB 1599932.
Gasification of a carbonaceous material, such as coal or petroleum coke, can be catalyzed by loading the carbonaceous material with a catalyst comprising an alkali metal source. US2007/0000177A1 and US2007/0083072A1, both incorporated herein by reference, disclose the alkali-metal-catalyzed gasification of carbonaceous materials. Lower-fuel-value carbon sources, such as coal, typically contain quantities of inorganic matter, including compounds of silicon, aluminum, calcium, iron, vanadium, sulfur, and the like. This inorganic content is referred to as ash. Silica and alumina are especially common ash components. At temperatures above 500-600° C., alkali metal compounds can react with the alumina and silica to form alkali metal aluminosilicates. As an aluminosilicate, the alkali metal compound is substantially insoluble in water and has little effectiveness as a gasification catalyst.
At typical gasification temperatures, most components of ash are not gasified, and thus build up with other compounds in the gasification reactor as a solid residue referred to as char. For catalytic gasification, char generally includes ash, unconverted carbonaceous material, and alkali metal compounds (from the catalyst). The char must be periodically withdrawn from the reactor through a solid purge. The char may contain substantial quantities of alkali metal compounds. The alkali metal compounds may exist in the char as soluble species, such as potassium carbonate, but may also exist as insoluble species, such as potassium aluminosilicate (e.g., kaliophilite). It is desirable to recover the soluble and the insoluble alkali metal compounds from the solid purge for subsequent reuse as a gasification catalyst. A need remains for efficient processes for recovering soluble and insoluble alkali metal compounds from char. Such processes should effect substantial recovery of alkali metal compounds from the char, minimize the complexity of the processing steps, reduce the use of consumable raw materials, and generate few waste products that require disposal.
The present invention provides processes for converting a carbonaceous composition into a plurality of gaseous products with recovery of an alkali metal compounds that can be reused as a gasification catalyst. The invention further provides processes for extracting and recovering catalytically useful alkali metal compounds from soluble and insoluble alkali metal compounds contained in char, where the processes involve thermal quenching of the char in an aqueous medium followed by treatment of the char particulate with carbon dioxide gas under hydrothermal conditions.
In a first aspect, the invention provides a process for extracting and recovering alkali metal from a char, the char comprising (i) one or more soluble alkali metal compounds and (ii) insoluble matter comprising one or more insoluble alkali metal compounds, the process comprising the steps of: (a) providing the char at an elevated temperature ranging from 50° C. to about 600° C.; (b) quenching the char in an aqueous medium to fracture the char and form a quenched char slurry; (c) contacting the quenched char slurry with an alkali metal hydroxide under suitable pressure and temperature so as to convert at least a portion of the insoluble alkali metal compounds to one or more soluble alkali metal compounds, and produce a first leached slurry comprising the soluble alkali metal compounds and residual insoluble matter; (d) contacting the first leached slurry with carbon dioxide under suitable pressure and temperature so as to convert at least a portion of the insoluble alkali metal compounds to one or more soluble alkali metal compounds, and produce a second leached slurry comprising the soluble alkali metal compounds and residual insoluble matter; (e) degassing the second leached slurry under suitable pressure and temperature so as to remove a substantial portion of the excess carbon dioxide and hydrogen sulfide, if present, and produce a degassed second leached slurry; (f) separating the degassed second leached slurry into a first liquid stream and a residual insoluble matter stream, the first liquid stream comprising a predominant portion of the soluble alkali metal compounds from the degassed second leached slurry, and the residual insoluble matter stream comprising residual soluble alkali metal compounds and residual insoluble alkali metal compounds; (g) recovering the first liquid stream; and (h) washing the residual insoluble matter stream with an aqueous medium to produce a first wash stream comprising substantially all of the residual soluble alkali metal compounds from the residual insoluble matter stream, wherein the quenching and contacting is performed in the substantial absence of gaseous oxygen.
In a second aspect, the invention provides a process for catalytically converting a carbonaceous composition, in the presence of an alkali metal gasification catalyst, into a plurality of gaseous products, the process comprising the steps of: (a) supplying a carbonaceous composition to a gasification reactor, the carbonaceous composition comprising an ash; (b) reacting the carbonaceous composition in the gasification reactor in the presence of steam and an alkali metal gasification catalyst under suitable temperature and pressure to form (i) a char comprising alkali metal from the alkali metal gasification catalyst in the form of one or more soluble alkali metal compounds and one or more insoluble alkali metal compounds, and (ii) a plurality of gaseous products comprising methane and one or more of hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, ammonia, and other higher hydrocarbons; (c) removing a portion of the char from the gasification reactor; (d) extracting and recovering a substantial portion of the alkali metal from the char according to any process of the first aspect of the invention; and (e) at least partially separating the plurality of gaseous products to produce a stream comprising a predominant amount of one of the gaseous products.
The process can be run continuously, and the recovered alkali metal can be recycled back into the process to minimize the amount of makeup catalyst required.
The present invention relates to processes for the catalytic conversion of a carbonaceous composition into a plurality of gaseous products with substantial recovery of alkali metal used as the gasification catalyst. The alkali metal is recovered from char that develops as a result of the catalyzed gasification of a carbonaceous material in a gasification reactor. The alkali metal may exist in the char in either water-soluble or water-insoluble forms. The present invention provides efficient processes for extracting and recovering substantially all of the soluble and insoluble alkali metal from char. Among other steps, these processes include the quenching of the char in an aqueous solution to fracture the char, dissolving substantially all of the water-soluble alkali metal compounds, and forming a slurry of the quenched char, and the reacting of a char slurry with an alkali metal hydroxide followed by carbon dioxide at suitable pressures and temperatures to solubilize and extract insoluble alkali metal compounds. In this manner, soluble and insoluble alkali metal compounds are substantially removed from char using simplified processes that require few consumable raw materials.
The present invention can be practiced, for example, using any of the developments to catalytic gasification technology disclosed in commonly owned US2007/0000177A1, US2007/0083072A1 and US2007/0277437A1; and U.S. patent application Ser. No. 12/178,380 (filed 23 Jul. 2008), Ser. No. 12/234,012 (filed 19 Sep. 2008) and Ser. No. 12/234,018 (filed 19 Sep. 2008). Moreover, the present invention can be practiced using developments described in the following U.S. Patent Applications, each of which was filed on even date herewith and is hereby incorporated herein by reference: Ser. No. ______, entitled “PETROLEUM COKE COMPOSITIONS FOR CATALYTIC GASIFICATION” (attorney docket no. FN-0008 US NP1); Ser. No. ______, entitled “STEAM GENERATING SLURRY GASIFIER FOR THE CATALYTIC GASIFICATION OF A CARBONACEOUS FEEDSTOCK” (attorney docket no. FN-0017 US NP1); Ser. No. ______, entitled “PETROLEUM COKE COMPOSITIONS FOR CATALYTIC GASIFICATION” (attorney docket no. FN-0011 US NP 1); Ser. No. ______, entitled “COAL COMPOSITIONS FOR CATALYTIC GASIFICATION” (attorney docket no. FN-0009 US NP1); Ser. No. ______, entitled “PROCESSES FOR MAKING SYNTHESIS GAS AND SYNGAS-DERIVED PRODUCTS” (attorney docket no. FN-0010 US NP1); Ser. No. ______, entitled “CARBONACEOUS FUELS AND PROCESSES FOR MAKING AND USING THEM” (attorney docket no. FN-0013 US NP1); and Ser. No. ______, entitled “PROCESSES FOR MAKING SYNGAS-DERIVED PRODUCTS” (attorney docket no. FN-0012 US NP1).
All publications, patent applications, patents and other references mentioned herein, if not otherwise indicated, are explicitly incorporated by reference herein in their entirety for all purposes as if fully set forth.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. In case of conflict, the present specification, including definitions, will control.
Except where expressly noted, trademarks are shown in upper case.
Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described herein.
Unless stated otherwise, all percentages, parts, ratios, etc., are by weight.
When an amount, concentration, or other value or parameter is given as a range, or a list of upper and lower values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper and lower range limits, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the present disclosure be limited to the specific values recited when defining a range.
When the term “about” is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to.
As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).
The use of “a” or “an” to describe the various elements and components herein is merely for convenience and to give a general sense of the disclosure. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.
The materials, methods, and examples herein are illustrative only and, except as specifically stated, are not intended to be limiting.
The term “carbonaceous material” or “carbonaceous composition” as used herein includes a carbon source, typically coal, petroleum coke, asphaltene and/or liquid petroleum residue, but may broadly include any source of carbon suitable for gasification, including biomass. The carbonaceous composition will generally include at least some ash, typically at least about 3 wt % ash (based on the weight of the carbonaceous composition).
The term “petroleum coke” as used herein includes both (i) the solid thermal decomposition product of high-boiling hydrocarbon fractions obtained in petroleum processing (heavy residues—“resid petcoke”) and (ii) the solid thermal decomposition product of processing tar sands (bituminous sands or oil sands—“tar sands petcoke”). Such carbonization products include, for example, green, calcined, needle and fluidized bed petroleum coke.
Resid petcoke can be derived from a crude oil, for example, by coking processes used for upgrading heavy-gravity residual crude oil, which petroleum coke contains ash as a minor component, typically about 1.0 wt % or less, and more typically about 0.5 wt % of less, based on the weight of the coke. Typically, the ash in such lower-ash cokes predominantly comprises metals such as nickel and vanadium.
Tar sands petcoke can be derived from an oil sand, for example, by coking processes used for upgrading oil sand. Tar sands petcoke contains ash as a minor component, typically in the range of about 2 wt % to about 12 wt %, and more typically in the range of about 4 wt % to about 12 wt %, based on the overall weight of the tar sands petcoke. Typically, the ash in such higher-ash cokes predominantly comprises materials such as compounds of silicon and/or aluminum.
The petroleum coke can comprise at least about 70 wt % carbon, at least about 80 wt % carbon, or at least about 90 wt % carbon, based on the total weight of the petroleum coke. Typically, the petroleum coke comprises less than about 20 wt % percent inorganic compounds, based on the weight of the petroleum coke.
The term “asphaltene” as used herein is an aromatic carbonaceous solid at room temperature, and can be derived, from example, from the processing of crude oil and crude oil tar sands.
The term “liquid petroleum residue” as used herein includes both (i) the liquid thermal decomposition product of high-boiling hydrocarbon fractions obtained in petroleum processing (heavy residues—“resid liquid petroleum residue”) and (ii) the liquid thermal decomposition product of processing tar sands (bituminous sands or oil sands—“tar sands liquid petroleum residue”). The liquid petroleum residue is substantially non-solid; for example, it can take the form of a thick fluid or a sludge.
Resid liquid petroleum residue can be derived from a crude oil, for example, by processes used for upgrading heavy-gravity crude oil distillation residue. Such liquid petroleum residue contains ash as a minor component, typically about 1.0 wt % or less, and more typically about 0.5 wt % of less, based on the weight of the residue. Typically, the ash in such lower-ash residues predominantly comprises metals such as nickel and vanadium.
Tar sands liquid petroleum residue can be derived from an oil sand, for example, by processes used for upgrading oil sand. Tar sands liquid petroleum residue contains ash as a minor component, typically in the range of about 2 wt % to about 12 wt %, and more typically in the range of about 4 wt % to about 12 wt %, based on the overall weight of the residue. Typically, the ash in such higher-ash residues predominantly comprises materials such as compounds of silicon and/or aluminum.
The term “coal” as used herein means peat, lignite, sub-bituminous coal, bituminous coal, anthracite, or mixtures thereof. In certain embodiments, the coal has a carbon content of less than about 85%, or less than about 80%, or less than about 75%, or less than about 70%, or less than about 65%, or less than about 60%, or less than about 55%, or less than about 50% by weight, based on the total coal weight. In other embodiments, the coal has a carbon content ranging up to about 85%, or up to about 80%, or up to about 75% by weight, based on total coal weight. Examples of useful coals include, but are not limited to, Illinois #6, Pittsburgh #8, Beulah (N.D.), Utah Blind Canyon, and Powder River Basin (PRB) coals. Anthracite, bituminous coal, sub-bituminous coal, and lignite coal may contain about 10 wt %, from about 5 to about 7 wt %, from about 4 to about 8 wt %, and from about 9 to about 11 wt %, ash by total weight of the coal on a dry basis, respectively. However, the ash content of any particular coal source will depend on the rank and source of the coal, as is familiar to those skilled in the art. See, for example, “Coal Data: A Reference”, Energy Information Administration, Office of Coal, Nuclear, Electric and Alternate Fuels, U.S. Department of Energy, DOE/EIA-0064(93), February 1995.
The term “ash” as used herein includes inorganic compounds that occur within the carbon source. The ash typically includes compounds of silicon, aluminum, calcium, iron, vanadium, sulfur, and the like. Such compounds include inorganic oxides, such as silica, alumina, ferric oxide, etc., but may also include a variety of minerals containing one or more of silicon, aluminum, calcium, iron, and vanadium. The term “ash” may be used to refer to such compounds present in the carbon source prior to gasification, and may also be used to refer to such compounds present in the char after gasification.
As used herein, the terms “alkali metal compound” refers to a free alkali metal, as a neutral atom or ion, or to a molecular entity, such as a salt, that contains an alkali metal. Additionally, the term “alkali metal” may refer either to an individual alkali metal compound, as heretofore defined, or may also refer to a plurality of such alkali metal compounds. An alkali metal compound capable of being substantially solubilized by water is referred to as a “soluble alkali metal compound.” Examples of a soluble alkali metal compound include free alkali metal cations and water-soluble alkali metal salts, such as potassium carbonate, potassium hydroxide, and the like. An alkali metal compound incapable of being substantially solubilized by water is referred to as an “insoluble alkali metal compound.” Examples of an insoluble alkali metal compound include water-insoluble alkali metal salts and/or molecular entities, such as potassium aluminosilicate.
Alkali metal compounds suitable for use as a gasification catalyst include compounds selected from the group consisting of alkali metal carbonates, bicarbonates, formates, oxalates, amides, hydroxides, acetates, halides, nitrates, sulfides, and polysulfides. For example, the catalyst can comprise one or more of Na2CO3, K2CO3, Rb2CO3, Li2CO3, Cs2CO3, NaOh, KOH, RbOH, or CsOH, and particularly, potassium carbonate and/or potassium hydroxide.
The carbonaceous composition is generally loaded with an amount of an alkali metal. Typically, the quantity of the alkali metal in the composition is sufficient to provide a ratio of alkali metal atoms to carbon atoms ranging from about 0.01, or from about 0.02, or from about 0.03, or from about 0.04, to about 0.06, or to about 0.07, or to about 0.08. Further, the alkali metal is typically loaded onto a carbon source to achieve an alkali metal content of from about 3 to about 10 times more than the combined ash content of the carbonaceous material (e.g., coal and/or petroleum coke), on a mass basis.
Any methods known to those skilled in the art can be used to associate one or more gasification catalysts with the carbonaceous composition. Such methods include, but are not limited to, admixing with a solid catalyst source and impregnating the catalyst onto the carbonaceous solid. Several impregnation methods known to those skilled in the art can be employed to incorporate the gasification catalysts. These methods include, but are not limited to, incipient wetness impregnation, evaporative impregnation, vacuum impregnation, dip impregnation, and combinations of these methods. Gasification catalysts can be impregnated into the carbonaceous solids by slurrying with a solution (e.g., aqueous) of the catalyst.
That portion of the carbonaceous feedstock of a particle size suitable for use in the gasifying reactor can then be further processed, for example, to impregnate one or more catalysts and/or cocatalysts by methods known in the art, for example, as disclosed in U.S. Pat. No. 4,069,304 and U.S. Pat. No. 5,435,940; previously incorporated U.S. Pat. No. 4,092,125, U.S. Pat. No. 4,468,231 and U.S. Pat. No. 4,551,155; previously incorporated U.S. patent application Ser. Nos. 12/234,012 and 12/234,018; and previously incorporated U.S. patent applications Ser. No. ______, entitled “PETROLEUM COKE COMPOSITIONS FOR CATALYTIC GASIFICATION” (attorney docket no. FN-0008 US NP1), Ser. No. ______, entitled “PETROLEUM COKE COMPOSITIONS FOR CATALYTIC GASIFICATION” (attorney docket no. FN-0011 US NP1), Ser. No. ______, entitled “CONTINUOUS PROCESS FOR CONVERTING CARBONACEOUS FEEDSTOCK INTO GASEOUS PRODUCTS” (attorney docket no. FN-0018 US NP1), and Ser. No. ______, entitled “COAL COMPOSITIONS FOR CATALYTIC GASIFICATION” (attorney docket no. FN-0009 US NP1).
One particular method suitable for combining the coal particulate with a gasification catalyst to provide a catalyzed carbonaceous feedstock where the catalyst has been associated with the coal particulate via ion exchange is described in previously incorporated U.S. patent application Ser. No. 12/178,380 (filed 23 Jul. 2008). The catalyst loading by ion exchange mechanism is maximized (based on adsorption isotherms specifically developed for the coal), and the additional catalyst retained on the wet cake, including inside the pores, is controlled so that the total catalyst target value is obtained in a controlled manner. Such loading provides a catalyzed coal particulate as a wet cake. The catalyst loaded and dewatered wet coal cake typically contains, for example, about 50% moisture. The total amount of catalyst loaded is controlled by controlling the concentration of catalyst components in the solution, as well as the contact time, temperature and method, as can be readily determined by those of ordinary skill in the relevant art based on the characteristics of the starting coal.
The catalyzed feedstock can be stored for future use or transferred to a feed operation for introduction into the gasification reactor. The catalyzed feedstock can be conveyed to storage or feed operations according to any methods known to those skilled in the art, for example, a screw conveyer or pneumatic transport.
The extraction and recovery methods of the present invention are particularly useful in integrated gasification processes for converting carbonaceous feedstocks, such as petroleum coke, liquid petroleum residue and/or coal, to combustible gases, such as methane. The gasification reactors for such processes are typically operated at moderately high pressures and temperature, requiring introduction of a carbonaceous material (i.e. a feedstock) to the reaction zone of the gasification reactor while maintaining the required temperature, pressure, and flow rate of the feedstock. Those skilled in the art are familiar with feed systems for providing feedstocks to high pressure and/or temperature environments, including, star feeders, screw feeders, rotary pistons, and lock-hoppers. It should be understood that the feed system can include two or more pressure-balanced elements, such as lock hoppers, which would be used alternately.
Suitable gasification reactors include counter-current fixed bed, co-current fixed bed, fluidized bed, entrained flow, and moving bed reactors. The gasification reactor typically will be operated at moderate temperatures of at least about 450° C., or of at least about 600° C. or above, to about 900° C., or to about 750° C., or to about 700° C.; and at pressures of at least about 50 psig, or at least about 200 psig, or at least about 400 psig, to about 1000 psig, or to about 700 psig, or to about 600 psig.
The gas utilized in the gasification reactor for pressurization and reactions of the particulate composition typically comprises steam, and optionally, oxygen or air, and are supplied to the reactor according to methods known to those skilled in the art. For example, any of the steam boilers known to those skilled in the art can supply steam to the reactor. Such boilers can be powered, for example, through the use of any carbonaceous material such as powdered coal, biomass etc., and including but not limited to rejected carbonaceous materials from the particulate composition preparation operation (e.g., fines, supra). Steam can also be supplied from a second gasification reactor coupled to a combustion turbine where the exhaust from the reactor is thermally exchanged to a water source and produce steam.
Recycled steam from other process operations can also be used for supplying steam to the reactor. For example, when the slurried particulate composition is dried with a fluid bed slurry drier, as discussed previously, the steam generated through vaporization can be fed to the gasification reactor.
The small amount of required heat input for the catalytic coal gasification reaction can be provided by superheating a gas mixture of steam and recycle gas feeding the gasification reactor by any method known to one skilled in the art. In one method, compressed recycle gas of CO and H2 can be mixed with steam and the resulting steam/recycle gas mixture can be further superheated by heat exchange with the gasification reactor effluent followed by superheating in a recycle gas furnace.
A methane reformer can be included in the process to supplement the recycle CO and H2 fed to the reactor to ensure that the reaction is run under thermally neutral (adiabatic) conditions. In such instances, methane can be supplied for the reformer from the methane product, as described below.
Reaction of the particulate composition under the described conditions typically provides a crude product gas and a char. The char produced in the gasification reactor during the present processes typically is removed from the gasification reactor for sampling, purging, and/or catalyst recovery. Methods for removing char are well known to those skilled in the art. One such method taught by EP-A-0102828, for example, can be employed. The char can be periodically withdrawn from the gasification reactor through a lock hopper system, although other methods are known to those skilled in the art.
Crude product gas effluent leaving the gasification reactor can pass through a portion of the gasification reactor which serves as a disengagement zone where particles too heavy to be entrained by the gas leaving the gasification reactor (i.e., fines) are returned to the fluidized bed. The disengagement zone can include one or more internal cyclone separators or similar devices for removing fines and particulates from the gas. The gas effluent passing through the disengagement zone and leaving the gasification reactor generally contains CH4, CO2, H2 and CO, H2S, NH3, unreacted steam, entrained fines, and other contaminants such as COS.
The gas stream from which the fines have been removed can then be passed through a heat exchanger to cool the gas and the recovered heat can be used to preheat recycle gas and generate high pressure steam. Residual entrained fines can also be removed by any suitable means such as external cyclone separators followed by Venturi scrubbers. The recovered fines can be processed to recover alkali metal catalyst.
The gas stream exiting the Venturi scrubbers can be fed to COS hydrolysis reactors for COS removal (sour process) and further cooled in a heat exchanger to recover residual heat prior to entering water scrubbers for ammonia recovery, yielding a scrubbed gas comprising at least H2S, CO2, CO, H2 and CH4. Methods for COS hydrolysis are known to those skilled in the art, for example, see U.S. Pat. No. 4,100,256.
The residual heat from the scrubbed gas can be used to generate low pressure steam. Scrubber water and sour process condensate can be processed to strip and recover H2S, CO2 and NH3; such processes are well known to those skilled in the art. NH3 can typically be recovered as an aqueous solution (e.g., 20 wt %).
A subsequent acid gas removal process can be used to remove H2S and CO2 from the scrubbed gas stream by a physical absorption method involving solvent treatment of the gas to give a cleaned gas stream. Such processes involve contacting the scrubbed gas with a solvent such as monoethanolamine, diethanolamine, methyldiethanolamine, diisopropylamine, diglycolamine, a solution of sodium salts of amino acids, methanol, hot potassium carbonate or the like. One method can involve the use of Selexol® (UOP LLC, Des Plaines, Ill. USA) or Rectisol® (Lurgi AG, Frankfurt am Main, Germany) solvent having two trains; each train consisting of an H2S absorber and a CO2 absorber. The spent solvent containing H2S, CO2 and other contaminants can be regenerated by any method known to those skilled in the art, including contacting the spent solvent with steam or other stripping gas to remove the contaminants or by passing the spent solvent through stripper columns. Recovered acid gases can be sent for sulfur recovery processing. The resulting cleaned gas stream contains mostly CH4, H2 and CO and, typically, small amounts of CO2 and H2O. Any recovered H2S from the acid gas removal and sour water stripping can be converted to elemental sulfur by any method known to those skilled in the art, including the Claus process. Sulfur can be recovered as a molten liquid.
The cleaned gas stream can be further processed to separate and recover CH4 by any suitable gas separation method known to those skilled in the art including, but not limited to, cryogenic distillation and the use of molecular sieves or ceramic membranes. One method for recovering CH4 from the cleaned gas stream involves the combined use of molecular sieve absorbers to remove residual H2O and CO2 and cryogenic distillation to fractionate and recover CH4. Typically, two gas streams can be produced by the gas separation process, a methane product stream and a syngas stream (H2 and CO). The syngas stream can be compressed and recycled to the gasification reactor. If necessary, a portion of the methane product can be directed to a reformer, as discussed previously and/or a portion of the methane product can be used as plant fuel.
The term “char” as used herein includes mineral ash, unconverted carbonaceous material, and water-soluble alkali metal compounds and water-insoluble alkali metal compounds within the other solids. The char produced in the gasification reactor typically is removed from the gasification reactor for sampling, purging, and/or catalyst recovery. Methods for removing char are well known to those skilled in the art. One such method, described in previously incorporated EP-A-0102828, for example, can be employed. The char can be periodically withdrawn from the gasification reactor through a lock hopper system, although other methods are known to those skilled in the art.
Alkali metal salts, particularly sodium and potassium salts, are useful as catalysts in catalytic coal gasification reactions. Alkali metal catalyst-loaded carbonaceous mixtures are generally prepared and then introduced into a gasification reactor, or can be formed in situ by introducing alkali metal catalyst and carbonaceous particles separately into the reactor.
After gasification, the alkali metal may exist in the char as species that are either soluble or insoluble. In particular, alkali metal can react with mineral ash at temperatures above about 500-600° C. to form insoluble alkali metal aluminosilicates, such as kaliophilite. As an aluminosilicate, or other insoluble compounds, the alkali metal is ineffective as a catalyst.
As discussed, supra, char is periodically removed from the gasification reactor through a solid purge. Because the char has a substantial quantity of soluble and insoluble alkali metal, it is desirable to recover the alkali metal from the char for reuse as a gasification catalyst. Catalyst loss in the solid purge must generally be compensated for by a reintroduction of additional catalyst, i.e., a catalyst make-up stream. Processes have been developed to recover alkali metal from the solid purge in order to reduce raw material costs and to minimize environmental impact of a catalytic gasification process. For example, a recovery and recycling process is described in previously incorporated US2007/0277437A1.
The present invention provides a novel process for extracting and recovering soluble and insoluble alkali metal from char.
Referring to
The invention places no particular limits on the ratio of aqueous medium to char, or on the temperature of the aqueous medium. In some embodiments, however, the wt/wt ratio of water in the aqueous medium to the water-insoluble component of the char ranges from about 3:1, or from about 5:1, up to about 7:1, or up to about 15:1. Additionally, in some embodiments, the aqueous medium has a temperature that ranges from about 95° C. up to about 110° C., or up to about 140° C., or up to about 200° C., or up to about 300° C. The pressure need not be elevated above atmospheric pressure. In some embodiments, however, the quenching occurs at pressures higher than atmospheric pressure. For example, the quenching may occur at pressures up to about 25 psig, or up to about 40 psig, or up to about 60 psig, or up to about 80 psig, or up to about 400 psig (including the partial pressure of CO2). The quenching process preferably occurs under a stream of gas that is substantially free of oxygen or other oxidants and comprises carbon dioxide.
The quenching step fractures the heated char by dissolving the rather large amount of water soluble alkali metal compounds (e.g., carbonates) that holds it together such that a quenched char slurry results. The char leaves the gasification reactor at high temperature, and it is typically cooled down. For example, the temperature of the char may range from about 35° C., or from about 50° C., or from about 75° C., up to about 200° C., or up to about 300° C., or up to about 400° C. In some embodiments, the char has an elevated temperature ranging from about 50° C. to about 600° C. The quenched char slurry comprises both soluble alkali metal and insoluble alkali metal. As the char fractures, soluble alkali metal leaches into the aqueous solution.
The char quenching is preferably performed in the substantial absence of gaseous oxygen. For example, the leaching environment has less than about 1% gaseous oxygen, or less than about 0.5% gaseous oxygen, less than about 0.1% gaseous oxygen, less than about 0.01% gaseous oxygen, or less than about 0.005% gaseous oxygen, based on the total volume.
In some embodiments, the aqueous medium used in the quenching may comprise a wash stream that results from a washing step of the present invention, described, infra.
2. Contacting of Quenched Char Slurry with an Alkali Metal Hydroxide (200)
The quenched char slurry (20) can be contacted with an alkali metal hydroxide (25) under suitable pressure and temperature so as to convert at least a portion of the insoluble alkali metal compounds in the insoluble matter to one or more soluble alkali metal compounds and produce a first leached slurry (30) comprising soluble alkali metal compounds and a partially extracted insoluble matter comprising insoluble alkali metal compounds.
The contacting of the quenched char slurry (20) with the alkali metal hydroxide (25) typically involves contacting the slurry at an elevated temperature with an aqueous solution of the alkali metal hydroxide such that at least a portion of the alkali metal from the insoluble matter is extracted. Generally, the alkali metal hydroxide is provided to the quenched char slurry (20) as an aqueous solution having a concentration ranging form about 1 to about 10 M alkali metal hydroxide. The alkali metal hydroxide can comprise any of LiOH, NaOH, KOH, RbOH, and CsOH, as well as mixtures thereof, preferably, the alkali metal comprises NaOH or KOH. Most preferably the alkali metal hydroxide comprises KOH.
The quenched char slurry can be pressurized and heated by the introduction of heated and pressurized steam. For example, the temperature of the slurry can range from about 100° C., or from about 125° C., or from about 150° C., up to about 240° C., up to about 270° C., or up to about 300° C. In some embodiments, the slurry has an elevated temperature ranging from about 150° C. to about 240° C. In some embodiments, the slurry has an elevated temperature ranging from about 100° C. to about 150° C.
In any combination with the preceding temperature ranges, the slurry can be maintained at a pressure of from about 25 psig, or from about 35 psig, or from about 50 psig, up to about 250 psig, or up to 500 psig, or up to about 750 psig, or up to 1000 psig. In some embodiments, the slurry may be maintained at a pressure of from about 50 to 500 psig. In other embodiments, the slurry may be maintained at a pressure of from about 50 to 250 psig.
The slurry can be maintained at an appropriate temperature and pressure for a residence time ranging from about 1 minute, or about 5 minutes, or about 15 minutes, or about 30 minutes, up to about 60 minutes, or up to about 120 minutes, or up to about 150 minutes, or up to about 180 minutes. In some embodiments, the slurry may be maintained at an appropriate temperature and pressure for a residence time ranging from 30 minutes to 150 minutes.
In one embodiment, the contacting takes place in a pressurized leaching operation using at least 2, and preferably 3, continuous stirred-tank reactors (CSTRs), either in series (e.g., co-current), or a single horizontal pressure vessel with internal weirs and stirrers to provide 3-6 internal stages for the slurry (the gas phase may optionally be separated by stages).
3. Contacting of Quenched Char Slurry with Carbon Dioxide (300)
The contacting of the first leached slurry (30) with carbon dioxide (35) occurs under pressure and temperature suitable to convert at least a portion at least a portion, or even a predominant portion, of the insoluble alkali metal compounds to one or more soluble alkali metal compounds, and produce a second leached slurry comprising the soluble alkali metal compounds and a residual insoluble matter. In the alternative, this process step is referred to as a first leaching or a first hydrothermal leaching.
In some instances, as can be determined by one skilled in the art, prior to contacting the first leached slurry with carbon dioxide, the temperature and/or pressure of the first leached slurry (30) can be reduced according to those methods known to those skilled in the art. For example, the first leached slurry can be flashed into a flash drum. Water can also be evaporated from the first leached slurry (30) to increase the concentration of alkali metals in the slurry solution. In one embodiment, the first leached slurry may be cooled to a temperature ranging from about 120° C. to 145° C. and a pressure to 45 psig or less prior to contacting the first leached slurry with carbon dioxide.
The hydrothermal leaching process converts a portion of the insoluble alkali metal compounds in the partially extracted insoluble matter to one or more soluble alkali metal compounds, as well as neutralizes excess alkalinity, hydrolyzes carbonates, precipitates silica and/or alumina, and strips sulfidic sulfur as hydrogen sulfide to yield a second leached slurry (40) comprising soluble alkali metal compounds and a residual insoluble matter. The alkali metal in the second leached slurry (40) comprises at least potassium carbonate and the pH of the solution generally ranges from about 7, or about 8, or about 9, up to about 10, or up to about 11, or up to about 12.
The hydrothermal leaching may be performed by any suitable means known to those of skill in the art for performing hydrothermal leaching. For example, in some embodiments, the first hydrothermal leaching step is carried out in three pressurized continuous flow stirred tank reactors (CSTRs) in series (in three co-current stages). In other embodiments, for example, the first hydrothermal leaching step is carried out in a single horizontal pressure leaching vessel with internal weirs and stirrers to provide between 3-6 internal stages for the slurry.
The contacting of the carbon dioxide (35) with the first leached slurry (30) may occur by any means known to those of skill in the art suitable for introducing a gas into a slurry. Suitable methods include, but are not limited to, solubilizing the gas under pressure with gas-phase entrainment stirring or bubbling the gas through the slurry.
For the first hydrothermal leaching step, suitable temperatures and pressure (including partial pressures of various gases), and the duration of the leaching may be selected based on the knowledge of one skilled in the art. This choice may depend on, among other factors, the composition of the carbonaceous feedstock: Higher temperatures and/or pressures may be more suitable for carbonaceous feedstock having higher mineral ash content (e.g., Powder River Basin coal with 7-10% ash). Suitable temperatures may, for example, range from about 90° C., or from about 100° C., or from about 110° C., up to about 120° C., or up to about 130° C., or up to about 140° C., or up to about 160° C. The leaching is typically carried out in the presence of steam. Suitable partial pressures of steam, for example, range from about 3 psig, or from about 6 psig, up to about 14 psig, up to about 20 psig. Suitable total pressures, for example, range from about 30 psig, or from about 40 psig, or from about 50 psig, up to about 75 psig, or up to about 90 psig, or up to about 110 psig. Suitable partial pressures of carbon dioxide may, for example, range from about 25 psig, from about 40 psig, or from about 60 psig, to about 100 psig, to about 120 psig, to about 140 psig, or to about 170 psig. Suitable durations, for example, range from about 15 minutes, or from about 30 minutes, or from about 45 minutes, up to about 60 minutes, or up to about 90 minutes, or up to about 120 minutes.
The hydrothermal leaching is performed in the substantial absence of gaseous oxygen or other oxidants. For example, the leaching environment has less than about 1% gaseous oxygen, or less than about 0.5% gaseous oxygen, less than about 0.1% gaseous oxygen, less than about 0.01% gaseous oxygen, or less than about 0.005% gaseous oxygen, based on the total volume.
The first leaching process converts at least a portion, or even a predominant portion, of the insoluble alkali metal compounds to one or more soluble alkali metal compounds. As used in this first leaching process, the conversion of insoluble alkali metal compounds to soluble alkali metal compounds generally involves the chemical conversion of a water-insoluble alkali metal compound (such as potassium aluminosilicate) into a water-soluble alkali metal compound (such as potassium carbonate).
The amount of insoluble alkali metal compounds converted to soluble alkali metal compounds in this leaching step will depend on a variety of factors, including the composition of the char, the temperature, the pressure (including the partial pressures of steam and carbon dioxide), and the duration of the leaching operation. The amount of insoluble alkali metal compound converted will also depend on the composition of the insoluble alkali metal compounds present in the char. Some insoluble alkali metal compounds, such as kaliophilite, are more difficult to convert into soluble alkali metal compounds than others. For example, the first leaching step may convert at least about 5%, or at least about 10%, or at least about 20%, or at least about 40%, or at least about 50%, or at least about 60%, or at least about 70%, or at least about 80% of the insoluble alkali metal compounds from the insoluble matter, based on the total moles of insoluble alkali metal compounds in the quenched char.
In some embodiments of the invention, the alkali metal hydroxide contacting and/or the first hydrothermal leaching step is combined with the char quenching step into a single step. In these embodiments, the char quenching is performed at a pressure and temperature more typical for the first hydrothermal leaching step. Suitable temperatures may, for example, range from about 90° C., or from about 100° C., or from about 110° C., up to about 120° C., or up to about 130° C., or up to about 140° C., or up to about 160° C. Suitable total pressures, for example, range from about 30 psig, or from about 40 psig, or from about 50 psig, up to about 75 psig, or up to about 90 psig, or up to about 110 psig. At these elevated temperatures and pressures, the partial pressures of carbon dioxide and steam are similar to those for the first leaching step. By performing the char quenching under the temperature and pressure conditions typical of the first leaching step, the two steps are effectively combined. In these embodiments, the combined quenching/leaching step substantially leaches the water-soluble alkali metal compounds from the insoluble matter and converts at least a portion of the insoluble alkali metal compounds in the char to one or more soluble alkali metal compounds, and thereby produces a second leached slurry comprising soluble alkali metal compounds and residual insoluble matter.
By performing the alkali metal hydroxide hydrolysis and carbonation prior to before filtration of the slurry, the bulk of the slurry solids will act as a filtering aid for any fine (e.g., colloidal) silica and alumina precipitate.
The second leached slurry (40) is degassed under suitable pressures and temperatures so as to remove a substantial portion of the excess carbon dioxide and hydrogen sulfide, if present, and produce a degassed second leached slurry (50).
Any suitable degassing methods known to those of skill in the art may be used to perform the degassing step. The degassing may be performed by pumping and heating the leached slurry and flashing it into a flash drum. For these embodiments, a suitable temperature may be, for example, about 130° C. or higher, or about 140° C. or higher, or about 145° C. or higher, or about 150° C. or higher. For these embodiments, after flashing into the flash drum, the slurry temperature may drop to 120° C. or less, or 110° C. or less, or 100° C. or less, or 95° C. or less. For these embodiments, suitable pressures range from about 10 to about 20 psig, or at about atmospheric pressure.
As necessary, depending on the pressure and temperature at which any preceding steps are performed, the degassing may be performed by feeding a heated pressurized solution into a series of staged pressure let-down vessels equipped with stirring or other recirculation mechanisms. In some embodiments, the slurry may be cooled prior to being fed into a first pressure let-down vessel, for example to a suitable temperature of about 170° C. or below, or to about 150° C. or below, or to about 130° C. or below. Suitable pressures will depend on the pressure under which the first hydrothermal leaching was performed. Suitable pressures for degassing are, for example, about 300 psig or less, or about 100 psig or less, or about 50 psig or less, or about 25 psig or less.
The off-stream gas may be handled by any means known to those of skill in the art. For example, the off gases from a let-down vessel may be fed, as needed, through gas/water breakdown drums and the separated water recycled into the degassed slurry. In some embodiments, the degassing apparatus is equipped with safety features for handling hydrogen sulfide as an off gas.
The degassing step results in the substantial removal of excess carbon dioxide. For example, the partial pressure of carbon dioxide is reduced to less than about 10 psig, or less than about 5 psig, or less than about 2 psig. The degassing also results in the substantial removal of excess hydrogen sulfide, if present. For example, the partial pressure of hydrogen sulfide is reduced to less than about 1 psig, or less than about 0.1 psig, less than about 0.05 psig, or less than about 0.01 psig.
5. Separation and Recovery of Liquid from Partially Extracted Insoluble Matter (500)
The degassed second leached slurry (50) is separated into a first liquid stream (60) and a residual insoluble matter stream (65). The first liquid stream comprises recovered soluble alkali metal, including soluble alkali metal compounds that were converted from insoluble alkali metal compounds in the char.
The residual insoluble matter steam comprises at least a portion of the alkali metal contained in the insoluble matter of the char. For example, the residual insoluble matter steam comprises less than about 95 molar percent, or less than about 90 molar percent, or less than about 80 molar percent, or less than about 60 molar percent, or less than about 50 molar percent, or less than about 40 molar percent, or less than about 30 molar percent, of the alkali metal contained in the insoluble matter of the char. The residual insoluble matter stream may also comprise a residual amount of soluble alkali metal compounds in addition to residual insoluble alkali metal compounds.
The separation and recovery of the first liquid stream from the residual insoluble matter stream (65) may be carried out by typical methods of separating a liquid from a solid particulate. Illustrative methods include, but are not limited to, filtration (gravity or vacuum), centrifugation, use of a fluid press, decantation, and use of hydrocyclones.
Separation and recovery steps are generally performed following contacting of the insoluble matter with carbon dioxide and degassing to remove excess carbon dioxide and hydrogen sulfide.
The recovered first liquid stream will contain soluble alkali metal compounds that may be captured for reuse as a gasification catalyst. Methods for recovery of soluble alkali metal from an aqueous solvent for reuse as a gasification catalyst are known in the art. See, for example, previously incorporated US2007/0277437A1.
The recovered first liquid stream comprises a predominant portion of the soluble alkali metal compounds from the degassed second leached slurry. For example, the first liquid stream comprises at least about 50 molar percent, or at least about 55 molar percent, or at least about 60 molar percent, or at least about 65 molar percent, or at least about 70 molar percent, of the soluble alkali metal compounds from the degassed second leached slurry.
Following separation from the first liquid stream, the residual insoluble matter stream (65) is produced comprising a residual amount of soluble alkali metal compounds in addition to residual insoluble alkali metal compounds. The residual insoluble matter stream (65) can be washed with an aqueous medium (70) to substantially recover the residual soluble alkali metal compounds present in the residual insoluble matter as a first wash stream (75). The residual soluble alkali metal compounds consists of soluble alkali metal compounds that failed to separate into the first liquid stream during separation (e.g., entrained aqueous solution). The amount of entrained solution in the residual insoluble matter stream will depend on the particle size of the residual insoluble matter as well as the concentration of the soluble alkali metal compounds in the entrained solution, as are familiar to those skilled in the art.
In some embodiments of the invention, the residual insoluble matter stream is washed with an aqueous medium to produce a first wash stream comprising at least a portion, or even a predominant portion, or substantially all of the residual soluble alkali metal compounds in the residual insoluble matter stream. The first wash stream may, for example, comprise more than about 60%, or more than about 75%, or more than about 90%, or more than about 95%, of the residual alkali metal in the residual insoluble matter stream, based on the total weight of residual alkali metal.
As used herein, the term “washing” is not limited to a single flush of the insoluble matter with an aqueous medium, such as water. Rather, each washing step may include multiple staged counter-washings of the insoluble matter. In some embodiments of the invention, the washing of the residual insoluble matter stream comprises at least two staged counter-washings. In some embodiments, the washing of the residual insoluble matter stream comprises at least five staged counter-washings. The washing may be performed according to any suitable method known to those of skill in the art. For example, the washing step may be performed using a continuous multi-stage counter-current system whereby solids and liquids travel in opposite directions. As known to those of skill in the art, the multi-stage counter current wash system may include mixers/settlers (CCD or decantation), mixers/filters, mixers/hydrocyclones, mixers/centrifuges, belt filters, and the like.
The first wash stream (75) is recovered by typical means of separating a solid particulate from a liquid. Illustrative methods include, but are not limited to, filtration (gravity or vacuum), centrifugation, and use of a fluid press.
In some embodiments, the recovered first wash stream may be used as at least part of the aqueous medium used for quenching the char.
An agglomerate char material was provided having a composition especially concentrated in kaliophilite. By weight, the sample was approximately 90% ash (including soluble and insoluble potassium) and about 10% carbon. The material was ground to a particle size (Dp80) of 68.5 microns. The sample was subjected to water at 95° C. in a nitrogen atmosphere. The sample was filtered and dried. Analysis of the resulting sample indicated that the amount of water-soluble potassium removed from the sample amounted to 40.08 wt % (dry basis) of the original sample.
he post-treatment sample from Example 1 was used. The hot-water-washed sample consisted of 78.20 wt % of ash and 8.99 wt % fixed carbon. Analysis of the ash portion determined that the ash contained 36.42 wt % of silica, 15.72 wt % of alumina, 18.48 wt % of insoluble potassium oxide, 12.56 wt % of calcium oxide, 9.13 wt % of ferric oxide, and trace quantities of other inorganic oxides. SEM data confirmed that most of the insoluble potassium oxide in the ash is tied up in KAlSiO4, primarily as kaliophilite and kalsilite.
The post-treatment sample from Example 1 was provided to a 450 ml autoclave. KOH was added and supplemented with an amount of potassium carbonate to simulate a recycle stream from washing, the autoclave pressurized by the addition of CO2, and the system was heated to 200° C. for 3 hours. The leached slurries were filtered, the solids washed, and the solutions and solids analyzed to provide a material balance on potassium. The experimental conditions yielded an incremental extraction of the insoluble potassium species of 40%, based on the total weight of the starting char.
A char sample was provided from the gasification (87-89% carbon conversion) of Class B catalyzed Powder River Basin coal. The dry sample was determined to contain 34.4 wt % potassium. The char sample was crushed and added to water to form a slurry in a nitrogen atmosphere. The slurry sample was added to an autoclave with KOH and additional water. The system was pressurized with CO2 and heated for 90 minutes at 160° C. The autoclave was cooled to ambient temperature. The solid was filtered and washed three times with water. Thus, the soluble potassium was largely removed from the sample. The total potassium extraction was 92.0%.
This application claims priority under 35 U.S.C. §119 from U.S. Provisional Application Ser. No. 61/017,312 (filed Dec. 28, 2007), the disclosure of which is incorporated by reference herein for all purposes as if fully set forth. This application is related to commonly owned U.S. application Ser. No. 11/421,511, filed Jun. 1, 2006, entitled “CATALYTIC STEAM GASIFICATION PROCESS WITH RECOVERY AND RECYCLE OF ALKALI METAL COMPOUNDS”; U.S. application Ser. No. ______, (filed concurrently herewith), entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0007 US NP1); U.S. application Ser. No. ______, (filed concurrently herewith), entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0015 US NP1); and U.S. application Ser. No. ______, (filed concurrently herewith), entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0016 US NP1).
| Number | Date | Country | |
|---|---|---|---|
| 61017312 | Dec 2007 | US |
