Patent Application
20090165361
The present invention relates to carbonaceous fuels and processes for making them. Moreover, the invention also relates to processes using the carbonaceous fuels in the production of cement products.
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 GB1599932.
Catalytic gasification processes can result in relatively large quantities of waste materials. For example, formation of a particulate carbonaceous feedstock by grinding processes can result in quantities of small particulates (i.e., “fines”) that are too small in particle size to be effectively used in gasification processes. The amount of fines generated can be on the order of 15-40% of the input feedstock. Moreover, gasification of lower-fuel-value carbonaceous feedstocks will often result in large quantities of char residue in which unconverted carbonaceous material is intermixed with ash and catalyst. Both fines and char residue represent a loss of potentially useful carbon, and can present issues with respect to waste handling and disposal. Accordingly, processes are needed which can efficiently utilize fines and char residue.
In one aspect, the present invention provides a carbonaceous fuel comprising: (a) unconverted fines of a carbonaceous feedstock, the carbonaceous feedstock having an ash content of greater than 1 wt % (based on the weight of the carbonaceous feedstock), the fines having an average particle size less than about 45 μm; and (b) a char residue formed by catalytic gasification of the carbonaceous feedstock, the char residue having an ash content of greater than about 30 wt % (based on the weight of the char residue), wherein the ash includes at least one aluminum-containing compound or silicon-containing compound; and having a weight ratio of fines to char residue in the range of from about 4:1 to about 1:4, and a total dry basis wt % of carbon of least about 40 wt % (based on the weight of the carbonaceous fuel).
In a second aspect, the present invention provides a process for making one or more gaseous products and a carbonaceous fuel, the process comprising the steps of: (a) providing (1) unconverted fines of a carbonaceous feedstock, the carbonaceous feedstock having an ash content of greater than about 1 wt % (based on the weight of the carbonaceous feedstock), the fines having an average particle size less than about 45 μm, and (2) particulates of the carbonaceous feedstock suitable for gasification in a reactor; (b) reacting the particulates in the reactor in the presence of steam and a gasification catalyst under suitable temperature and pressure to form the one or more gaseous products and a char residue having an ash content greater than about 30 wt % (based on the weight of the char residue), wherein the ash includes at least one aluminum-containing compound or silicon-containing compound; and (c) combining the fines with the char residue in a weight ratio in the range of from about 4:1 to about 1:4 to form the carbonaceous fuel, wherein the carbonaceous fuel has a dry basis wt % carbon of at least about 40% (based on the weight of the carbonaceous fuel).
In a third aspect, the present invention provides a process of making a cement product comprising: (a) providing a carbonaceous fuel as described above, or a carbonaceous fuel made by the process as described above; (b) passing the carbonaceous fuel into a cement-making zone; and (c) at least partially combusting the carbonaceous fuel to provide heat for a cement producing reaction within the cement-making zone.
The present invention relates generally to carbonaceous fuels and to processes for making and using them. Generally, a carbonaceous fuel of the present invention includes unconverted fines of a carbonaceous feedstock and a char residue formed by catalytic gasification of the carbonaceous feedstock. This carbonaceous fuel can be used, for example, in a cement-making process. Such carbonaceous fuels and processes can provide for an economical and commercially practical process for catalytic gasification of carbonaceous feedstocks to yield methane and/or other value-added gases, as well as utilize the byproducts of gasification in an industrially-useful manner. The conversion of the fines and the char residue to a carbonaceous fuel can result in less overall waste and lower disposal costs. The carbonaceous fuel can be used, for example, to provide heat in a cement-making process, thereby yielding additional value-added products from the carbonaceous feedstock. Moreover, the carbonaceous fuels of the present invention can have a relatively high fuel value, and therefore can supply a significant portion, if not all, of the heat necessary for the cement-making process.
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 processes of the present invention can be practiced in conjunction with the subject matter of the following U.S. patent applications, each of which was filed on even date herewith: Ser. No. ______, entitled “CONTINUOUS PROCESSES FOR CONVERTING CARBONACEOUS FEEDSTOCK INTO GASEOUS PRODUCTS” (attorney docket no. FN-0018 US NP1); Ser. No. ______, entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0007 US NP1); Ser. No. ______, entitled “PETROLEUM COKE COMPOSITIONS FOR CATALYTIC GASIFICATION” (attorney docket no. FN-0011 US NP1); Ser. No. ______, entitled “PETROLEUM COKE COMPOSITIONS FOR CATALYTIC GASIFICATION” (attorney docket no. FN-0008 US NP1); Ser. No. ______, entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0014 US NP1); 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 “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0015 US NP1); Ser. No. ______, entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0016 US NP1); Ser. No. ______, entitled “STEAM GENERATING SLURRY GASIFIER FOR THE CATALYTIC GASIFICATION OF A CARBONACEOUS FEEDSTOCK” (attorney docket no. FN-0017 US NP1); and Ser. No. ______, entitled “PROCESSES FOR MAKING SYNGAS-DERIVED PRODUCTS” (attorney docket no. FN-0012 US NP1). All of the above are incorporated herein by reference for all purposes as if fully set forth.
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 invention 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 invention, 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 invention 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 invention 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 invention. 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 feedstock” as used herein refers to a carbonaceous material that is used as a feedstock in a catalytic gasification reaction. The carbonaceous feedstock can be formed, for example, from coal, petroleum coke, or a mixture of the two. The carbonaceous feedstock can come from a single source, or from two or more sources. For example, the carbonaceous feedstock can be formed from one or more tar sands petcoke materials, one or more coal materials, or a mixture of the two.
The term “petroleum coke” as used herein includes both (i) the carbonization product of high-boiling hydrocarbon fractions obtained in petroleum processing (heavy residues—“resid petcoke”) and (ii) the carbonization product of processing tar sands (bituminous sands or oil sands—“tar sands petcoke”). Such carbonization products include, for example, green, calcined, and needle 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 (either resid petcoke or tar sands petcoke) 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.
Petroleum coke in general has an inherently low moisture content typically in the range of from about 0.2 to about 2 wt %. (based on total petroleum coke weight); it also typically has a very low water soaking capacity to allow for conventional catalyst impregnation methods.
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 the total coal weight. Examples of useful coals include, but are not limited to, Illinois #6, Pittsburgh #8, Beulah (N. Dak.), Utah Blind Canyon, and Powder River Basin (PRB) coals. Anthracite, bituminous coal, sub-bituminous coal, and lignite coal may contain about 10 wt %, about 5 to about 7 wt %, about 4 to about 8 wt %, and 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 gasification processes referred to in the context of the present invention include reacting a particulate carbonaceous feedstock in a gasifying reactor in the presence of steam and a gasification catalyst under suitable temperature and pressure to form a plurality of gaseous products comprising methane and at least one or more of hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, ammonia and other higher hydrocarbons, and a solid char residue. Examples of such gasification processes are, disclosed, for example, in previously incorporated 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 GB1599932; commonly owned 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); as well as in previously incorporated U.S. patent applications Ser. No. ______, entitled “CONTINUOUS PROCESSES FOR CONVERTING CARBONACEOUS FEEDSTOCK INTO GASEOUS PRODUCTS” (attorney docket no. FN-0018 US NP1); Ser. No. ______, entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0014 US NP1); Ser. No. ______, entitled “PROCESSES FOR MAKING SYNTHESIS GAS AND SYNGAS-DERIVED PRODUCTS” (attorney docket no. FN-0010 US NP1); Ser. No. ______, entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0015 US NP1); Ser. No. ______, entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0016 US NP1); Ser. No. ______, entitled “STEAM GENERATING SLURRY GASIFIER FOR THE CATALYTIC GASIFICATION OF A CARBONACEOUS FEEDSTOCK” (attorney docket no. FN-0017 US NP1); and Ser. No. ______, entitled “PROCESSES FOR MAKING SYNGAS-DERIVED PRODUCTS” (attorney docket no. FN-0012 US NP1).
The gasification reactors for such processes are typically operated at moderately high pressures and temperatures, requiring introduction of the particulate carbonaceous feedstock to the reaction zone of the gasification reactor while maintaining the required temperature, pressure, and flow rate of the particulate carbonaceous 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.
In some instances, the particulate carbonaceous feedstock can be prepared at pressure conditions above the operating pressure of gasification reactor. Hence, the particulate carbonaceous feedstock can be directly passed into the gasification reactor without further pressurization.
Typically, the carbonaceous feedstock is supplied to the gasifying reactor as particulates having an average particle size of from about 250 microns, or from about 25 microns, up to about 500, or up to about 2500 microns. One skilled in the art can readily determine the appropriate particle size for the particulates. For example, when a fluid bed gasification reactor is used, the particulate carbonaceous feedstock can have an average particle size which enables incipient fluidization of the particulate petroleum coke feed material at the gas velocity used in the fluid bed gasification reactor. Processes for preparing particulates are described in more detail below.
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 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 carbonaceous feedstock typically comprises steam, and optionally oxygen, air, CO and/or H2, and is supplied to the reactor according to methods known to those skilled in the art. Typically, the carbon monoxide and hydrogen produced in the gasification is recovered and recycled. In some embodiments, however, the gasification environment remains substantially free of air, particularly oxygen. In one embodiment of the invention, the reaction of the carbonaceous feedstock is carried out in an atmosphere having less than 1% oxygen by volume.
Any of the steam boilers known to those skilled in the art can supply steam to the gasification reactor. Such boilers can be fuel, 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 carbonaceous feedstock 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 to produce steam. Steam may also be generated from heat recovered from the hot raw gasifier product gas.
Recycled steam from other process operations can also be used for supplying steam to the gasification reactor. For example, when the slurried particulate carbonaceous feedstock is dried with a fluid bed slurry drier (as discussed below), the steam generated through vaporization can be fed to the gasification reactor.
The small amount of required heat input for the catalytic 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 carbonaceous feedstock under the described conditions typically provides a crude product gas comprising a plurality of gaseous products comprising methane and at least one or more of hydrogen, carbon monoxide and other higher hydrocarbons, and a solid char residue. The char residue produced in the gasification reactor during the present processes is typically removed from the gasification reactor for sampling, purging, and/or catalyst recovery. In processes of the present invention, the char residue is combined with unconverted fines to form a carbonaceous fuel, as described in more detail below. Methods for removing char residue are well known to those skilled in the art. One such method taught by EP-A-0102828, for example, can be employed. The char residue 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 are returned to the fluidized bed. The disengagement zone can include one or more internal cyclone separators or similar devices for removing particulates from the gas. The gas effluent passing through the disengagement zone and leaving the gasification reactor generally contains CH4, CO2, H2, CO, H2S, NH3, unreacted steam, entrained particles, and other trace contaminants such as COS and HCN.
Residual entrained particles are typically removed by suitable means such as external cyclone separators followed by Venturi scrubbers. The recovered particles can be processed to recover alkali metal catalyst.
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. 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 or chemical 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.
In certain embodiments of the invention, the plurality of gaseous products are at least partially separated to form a gas stream comprising a predominant amount of one of the gaseous products. For example, 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.
Further process details can be had by reference to the previously incorporated publications and applications.
Gasification processes according to the present invention use a carbonaceous feed material (e.g., a coal and/or a petroleum coke) and further use an amount of a gasification catalyst, for example, an alkali metal component, as alkali metal and/or a compound containing alkali metal, as well as optional co-catalysts, as disclosed in the previous incorporated references. Typically, the quantity of the alkali metal component in the composition is sufficient to provide a ratio of alkali metal atoms to carbon atoms in the range of 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.
Suitable alkali metals are lithium, sodium, potassium, rubidium, cesium, and mixtures thereof. Particularly useful are potassium sources. Suitable alkali metal compounds include alkali metal carbonates, bicarbonates, formates, oxalates, amides, hydroxides, acetates, or similar compounds. 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.
Typically, carbonaceous feedstocks include a quantity of inorganic matter (e.g. including calcium, alumina and/or silica) which form inorganic oxides (“ash”) in the gasification reactor. At temperatures above about 500 to 600° C., potassium and other alkali metals can react with the alumina and silica in ash to form insoluble alkali aluminosilicates. In this form, the alkali metal is substantially water-insoluble and inactive as a catalyst. To prevent buildup of the residue in a coal gasification reactor, a solid purge of char residue, i.e., solids composed of ash, unreacted or partially-reacted carbonaceous feedstock, and various alkali metal compounds (both water soluble and water insoluble) are routinely withdrawn. Preferably, the alkali metal is recovered from the char residue for recycle; any unrecovered catalyst is generally compensated by a catalyst make-up stream. The more alumina and silica in the feedstock, the more costly it is to obtain a higher alkali metal recovery.
The ash content of the carbonaceous feedstock can be selected to be, for example, to be about 20 wt % or less, or about 15 wt % or less, or about 10 wt % or less.
In certain embodiments of the present invention, the gasification catalyst is substantially extracted (e.g., greater than 80%, greater than 90%, or even greater than 95% extraction) from the char residue. Processes have been developed to recover gasification catalysts (such as alkali metals) from the solid purge in order to reduce raw material costs and to minimize environmental impact of a catalytic gasification process. The char residue can be quenched with recycle gas and water and directed to a catalyst recycling operation for extraction and reuse of the alkali metal catalyst. Particularly useful recovery and recycling processes are described in U.S. Pat. No. 4,459,138, as well as previously incorporated U.S. Pat. No. 4,057,512, US2007/0277437A1, U.S. patent application Ser. No. ______, entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0007 US NP1), U.S. patent application Ser. No. ______, entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0014 US NP1), U.S. patent application Ser. No. ______, entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0015 US NP1), and U.S. patent application Ser. No. ______, entitled “CATALYTIC GASIFICATION PROCESS WITH RECOVERY OF ALKALI METAL FROM CHAR” (attorney docket no. FN-0016 US NP1). Reference can be had to those documents for further process details.
In certain embodiments of the invention, at least 70%, at least 80%, or even at least 90% of the water-soluble gasification catalyst is extracted from the char residue.
The carbonaceous feedstock for use in the gasification process can require initial processing.
The carbonaceous feedstock can be crushed and/or ground according to any methods known in the art, such as impact crushing and wet or dry grinding to yield particulates. Depending on the method utilized for crushing and/or grinding of the petroleum coke, the resulting particulates can need to be sized (e.g., separated according to size) to provide an appropriate particles of carbonaceous feedstock for the gasifying reactor. The sizing operation can be used to separate out the fines of the carbonaceous feedstock from the particles of carbonaceous feedstock suitable for use in the gasification process.
Any method known to those skilled in the art can be used to size the particulates. For example, sizing can be preformed by screening or passing the particulates through a screen or number of screens. Screening equipment can include grizzlies, bar screens, and wire mesh screens. Screens can be static or incorporate mechanisms to shake or vibrate the screen. Alternatively, classification can be used to separate the particulate carbonaceous feedstock. Classification equipment can include ore sorters, gas cyclones, hydrocyclones, rake classifiers, rotating trommels, or fluidized classifiers. The carbonaceous feedstock can be also sized or classified prior to grinding and/or crushing.
In one embodiment of the invention, the carbonaceous feedstock is crushed or ground, then sized to separate out fines of the carbonaceous feedstock having an average particle size less than about 45 microns from particles of carbonaceous feedstock suitable for use in the gasification process. As described in more detail below, the fines of the carbonaceous feedstock can remain unconverted (i.e., unreacted in a gasification or combustion process), then combined with char residue to provide a carbonaceous fuel of the present invention.
That portion of the carbonaceous feedstock suitable 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 previously incorporated U.S. Pat. No. 4,069,304; U.S. Pat. No. 4,092,125; U.S. Pat. No. 4,468,231; U.S. Pat. No. 4,551,155; U.S. Pat. No. 5,435,940; 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); and U.S. patent applications Ser. No. ______, entitled “CONTINUOUS PROCESSES FOR CONVERTING CARBONACEOUS FEEDSTOCK INTO GASEOUS PRODUCTS” (attorney docket no. FN-0018 US NP1), Ser. No. ______, entitled “PETROLEUM COKE COMPOSITIONS FOR CATALYTIC GASIFICATION” (attorney docket no. FN-0011 US NP1), Ser. No. ______, entitled “PETROLEUM COKE COMPOSITIONS FOR CATALYTIC GASIFICATION” (attorney docket no. FN-0008 US NP1), and Ser. No. ______, entitled “COAL COMPOSITIONS FOR CATALYTIC GASIFICATION” (attorney docket no. FN-0009 US NP1)
In one aspect of the present invention, a carbonaceous fuel comprises (a) unconverted fines of a carbonaceous feedstock, and (b) a char residue formed by catalytic gasification of the carbonaceous feedstock, in a weight ratio of fines to char residue in the range of from about 4:1 to about 1:4, for example, in the range of from about 2:1 to about 1:2. The carbonaceous fuel has a total dry basis wt % of carbon of at least about 40%, for example, at least about 55% (based on the weight of the carbonaceous fuel).
According to this aspect of the invention, the fines have an average particle size less than about 45 μm. For example, in one embodiment of the invention, the fines have an average particle size of less than about 25 μm. Moreover, according to this aspect of the invention, the char residue has an ash content greater than about 30 wt % (based on the weight of the char residue), and includes at least one aluminum-containing compound or silicon-containing compound. For example, the ash can contain one or more aluminum oxides, aluminates, silicon oxides and/or silicates. The carbonaceous feedstock according to this aspect of the invention has an ash content of greater than about 1 wt % (based on the weight of the carbonaceous feedstock). For example, the carbonaceous feedstock can be a tar sands petcoke material or a coal material, as described above.
The fines and the char residue can be formed, for example, as described above. The fines can also include the residual entrained particles removed from the gas effluent.
The fines and char residue can be combined in a weight ratio in the range of from about 4:1 to about 1:4 to form the carbonaceous fuel using any methods known to those skilled in the art including, but not limited to, kneading, and vertical or horizontal mixers, for example, single or twin screw, ribbon, or drum mixers.
The carbonaceous fuel of the present invention can take many forms. For example, in one embodiment of the invention, the carbonaceous fuel is a substantially dry particulate solid. In other embodiments of the invention, the carbonaceous fuel further comprises water in an amount sufficient to form a slurry. Water can be combined with the fines and the char residue (in any order) to make such a slurry. The slurry can have, for example, a ratio of fines and char residue to water, by weight, which ranges from about 5:95 to about 40:60; for example, the ratio can be in the range of from about 15:85 to about 35:65. In certain embodiments of the invention, the ratio of fines and char residue to water is about 15:85, about 20:80, about 25:75, about 30:70, about 35:65 or about 40:60. Any method known by the person of skill in the art can be used to form the slurry.
In certain embodiments, the carbonaceous fuel of the present invention can be used to make a cement product. The carbonaceous fuels of the present invention include at least one aluminum-containing compound or silicon-containing compound; when the carbonaceous fuel is at least partially combusted in a cement making zone, this aluminum-containing compound or silicon-containing compound can become part of the cement product. In certain embodiments of the invention, the carbonaceous fuel includes additional calcium-containing materials. For example, in processes that use calcium compounds as CO2 traps in the gasification process, for sulfur removal, or as reactants in an alkali removal step (e.g., using a lime digestion process), the char residue can contain a significant amount of calcium compounds such as calcium hydroxides, calcium carbonates, calcium silicates and calcium aluminosilicates. See, e.g., U.S. Pat. No. 4,260,421. Cement feedstocks such as calcium-containing materials, silicon-containing materials, or both can also be simply added to the fines and the char residue. For example, in certain embodiments of the invention, the carbonaceous fuel further comprises calcium carbonate, for example, in the form of limestone. An impure limestone that contains SiO2 can be used. In other embodiments of the invention, the carbonaceous fuel further comprises one or more cement feedstocks such as clay, shale, sand, gypsum, a silicate, a calcium silicate, an aluminate, an aluminosilicate, a calcium aluminosilicate, iron ore, bauxite, fly ash and slag.
One aspect of the invention provides a process of making a cement product. The process comprises providing a carbonaceous fuel as described above, or a carbonaceous fuel made according to a process as described above; passing the carbonaceous fuel into a cement-making zone, and at least partially combusting the carbonaceous fuel to provide heat for a cement producing reaction within the cement-making zone. The cement-making zone can include, for example, a cement kiln such as a rotary kiln. The cement producing reaction can, for example, incorporate the aluminum-containing compound or the silicon containing compound in the carbonaceous fuel into a cement product. The cement producing reaction can also incorporate a cement feedstock (either as part of the carbonaceous fuel, or passed separately into the cement-making zone) into a cement product. In certain embodiments of the invention, the cement-making zone further comprises a precalciner. In certain embodiments of the invention, additional fuel, such as, for example, coal, petcoke, or waste materials such as tires or garbage, can be passed into the cement-making zone to provide additional heat from combustion. Cement making processes are well known in the art, and can be modified according to the present invention in order to make a wide variety of cement products, such as Portland cement, pozzolan-lime cements, slag-lime cements, supersulfated cements, calcium aluminate cements, and calcium sulfoaluminate cements. Cement-making processes are described, for example, in U.S. Pat. No. 4,260,421.
In certain embodiments of the invention, the carbonaceous fuel includes sufficient cement precursor material to form a cement product without the addition of other cement feedstocks. For example, as described above the carbonaceous fuel itself can be formulated to include a calcium-containing material, a silicon-containing material, or both in addition to the fines and the char residue. In other embodiments of the invention, however, the process for making the cement product further comprises passing at least one cement feedstock (e.g., a calcium-containing material, a silicon-containing material) into the cement-making zone. The heat provided by the combustion of the carbonaceous fuel causes a cement producing reaction to incorporate the cement feedstock(s) into cement clinker. For example, in certain embodiments of the invention, the process further comprises passing into the cement-making zone calcium carbonate, for example, in the form of limestone. An impure limestone that contains SiO2 can be used. In other embodiments of the invention, the process further comprises passing into the cement-making zone one or more cement feedstocks such as clay, shale, sand, gypsum, a silicate, a calcium silicate, an aluminate, an aluminosilicate, a calcium aluminosilicate, iron ore, bauxite, fly ash and slag. As the person of skill in the art will appreciate, cement clinker can be ground and optionally admixed with other substances (e.g., gypsum) to provide the cement product.
In one example of a process for making a cement product, the carbonaceous fuel, and optionally one or more cement feedstocks, and optionally one or more additional fuels are passed into a precalciner, in which the carbonaceous fuel is at least partially combusted to provide the heat energy necessary to decarbonate any calcium carbonate present, and dry and heat the carbonaceous fuel and any optionally-added materials to a sufficiently high temperature to begin the chemical reactions that lead to the production of cement. In one embodiment of the invention, all of the combustible material in the carbonaceous fuel and optional additional fuel is combusted in the precalciner. The temperature in the precalciner is typically maintained in the range of about 130° F. to about 1800° F. If the carbonaceous fuel and any optional additional fuels are not sufficient to pass the hot exhaust gases from the cement kiln into the precalciner to provide the necessary makeup heat. The heated material from the precalciner is passed to a cement kiln (e.g., a rotary kiln). Here, the material is subjected to temperatures in the range of about 1700° F. to about 2700° F. in order to sinter the solids and convert them into cement clinker. The energy required in the cement kiln can be provide by, for example, by burning a supplementary fuel such as coal or gas that is introduced into the opposite end of the kiln. If, however, all of the combustible material in the carbonaceous fuel and optional additional fuel is not combusted in the precalciner, the remainder can be combusted in the kiln to reduce or even eliminate the need for supplementary fuel. Cement clinker is withdrawn from the kiln and further processed into a cement product.
In a first example, Powder River Basin coal can be ground, yielding 124.3 lb of unconverted coal fines having about 70 wt % carbon and about 6-7 wt % ash on a dry basis. The fines can be combined with 187.1 lb washed char residue, which has about 57 wt % carbon on a dry basis. This blend would have about 62 wt % carbon and about 28 wt % ash on a dry basis.
This blend can be combined with water (e.g., in a ratio of 30:60 blend:water by weight) to form a slurry, which can then be passed into a precalciner in a cement making process.
In a second example, Powder River Basin coal can be ground, yielding about 250.0 lb of unconverted coal fines having about 70 wt % carbon and about 6-7 wt % ash on a dry basis. The fines can be combined with 187.1 lb washed char residue, which has about 57 wt % carbon on a dry basis. This blend would have about 65 wt % carbon and about 22 wt % ash on a dry basis.
This blend can be combined with water (e.g., in a ratio of 30:60 blend:water by weight) to form a slurry, which can then be passed into a precalciner in a cement making process.
This application claims priority under 35 U.S.C. §119 from U.S. Provisional Application Ser. No. 61/017,311 (filed Dec. 28, 2007), the disclosure of which is incorporated by reference herein for all purposes as if fully set forth.
| Number | Date | Country | |
|---|---|---|---|
| 61017311 | Dec 2007 | US |
