A* + B → A*B	A* + C → A*C	A* + BC → A*BC
A + B* → AB*	AC + B* → (AC)B*
A + C* → AC*	AB + C* → (AB)C*
(AB)* + C → (AB)*C	(AC)* + B → (AC)*B	(BC)* + A → A(BC)*

(b) Two components treated with catalyst

A* + B* → AB	A* + C* → AC	A* + (BC)* → A(BC)
A* + B* + C → ABC	A* + B + C* → ABC
B* + (AC)* → B(AC)	C* + (AB)* → (AB)C

(c) Three components treated with catalyst

A* + B* + C* → A*B*C*

Any methods known to those skilled in the art can be used to associate one or more gasification catalysts with the biomass char, non-biomass, biomass particulates, and/or mixtures thereof to provide a catalyzed particulate thereof. Such methods include but are not limited to, ad-mixing with a solid catalyst source and impregnating the catalyst on to particulates. 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, ion exchanging, and combinations of these methods.

In one embodiment, an alkali metal gasification catalyst can be impregnated into one or more of the particulates by slurrying with a solution (e.g., aqueous) of the catalyst. When a particulate is slurried with a solution of the catalyst and/or co-catalyst, the resulting slurry can be dewatered to provide a catalyzed particulate, again typically, as a wet cake. The catalyst solution for slurrying the particulate can be prepared from any catalyst source in the present methods, including fresh or make-up catalyst and recycled catalyst or catalyst solution (infra). Methods for dewatering the slurry to provide a wet cake of the catalyzed particulate include filtration (gravity or vacuum), centrifugation, and a fluid press.

One particular method suitable for combining coal with a gasification catalyst to provide a catalyzed particulate is via ion exchange as described in in previously incorporated U.S. patent application Ser. No. 12/178,380 (filed 23 Jul. 2008). Catalyst loading by ion exchange mechanism may be maximized based on adsorption isotherms specifically developed for the coal, as discussed in the incorporated reference. Such loading provides a catalyzed particulate as a wet cake. Additional catalyst retained on the ion-exchanged particulate wet cake, including inside the pores, can be controlled so that the total catalyst target value can be obtained in a controlled manner. The catalyst loaded and dewatered wet cake may contain, for example, about 50 % moisture. The total amount of catalyst loaded can be 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.

Alternatively, the slurried particulates may be dried with a fluid bed slurry drier (i.e., treatment with superheated steam to vaporize the liquid), or the solution evaporated, to provide a dry catalyzed particulate.

The catalyzed particulates may comprise greater than about 10%, greater than about 20%, greater than about 30%, greater than about 40%, greater than about 50%, greater than about 70%, greater than about 85%, or greater than about 90% of the total amount of the gasification catalyst of the particulate composition. The percentage of total gasification catalyst that is associated with the particulates can be determined according to methods known to those skilled in the art.

Separate particulates, with or without catalyst, can be blended appropriately to control, for example, the total catalyst loading or other qualities of the particulate composition, as discussed previously. The appropriate ratios of the separate particulates will depend on the qualities of the feedstocks as well as the desired properties of the particulate composition. For example, a biomass char particulate and a catalyzed non-biomass particulate can be combined in such a ratio to yield a particulate composition having a predetermined ash content, as discussed previously.

Separate particulates, as one or more dry particulates and/or one or more wet cakes, can be combined by 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 resulting particulate composition can be stored for future use or transferred to a feed operation for introduction into a gasification reactor. The particulate composition 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.

Ultimately, the particulate composition may be dried, under a flow of an inert gas, with a fluid bed slurry drier (i.e., treatment with superheated steam to vaporize the liquid), or the solution evaporated, to provide a catalyzed particulate typically having a residual moisture content of, for example, less than about 8 wt %, or less than about 6 wt %, or less than about 4 wt %.

In an embodiment of the third aspect, the present invention provides a process for preparing a particulate composition according to the first aspect, the process comprising the steps of: (a) providing a first particulate carbonaceous feedstock that is a biomass char, a second particulate carbonaceous feedstock that is a biomass, non-biomass, or mixture thereof, and a gasification catalyst; (b) contacting the first carbonaceous feedstock and the second carbonaceous feedstock with an aqueous solution comprising at least a portion of the gasification catalyst to form a slurry; (c) dewatering the slurry to form a catalyst-loaded wet cake; and (d) thermally treating the wet coal cake under a flow of inert dry gas to form the particulate composition.

In another embodiment of the third aspect, the present invention provides a process for preparing a particulate composition according to the first aspect, the process comprising the steps of: (a) providing a first particulate carbonaceous feedstock that is a biomass char, a second particulate carbonaceous feedstock that is a biomass, non-biomass, or mixture thereof, and a gasification catalyst; (b) contacting the first carbonaceous feedstock with an aqueous solution comprising at least a portion of the gasification catalyst to form a slurry; (c) dewatering the slurry to form a catalyst-loaded wet cake; (d) mixing the catalyst-loaded wet cake with and the second carbonaceous feedstock to form a mixture; and (e) thermally treating the mixture under a flow of inert dry gas to form the particulate composition.

In another embodiment of the third aspect, the present invention provides a process for preparing a particulate composition according to the first aspect, the process comprising the steps of: (a) providing a first particulate carbonaceous feedstock that is a biomass char, a second particulate carbonaceous feedstock that is a biomass, non-biomass, or mixture thereof, and a gasification catalyst; (b) contacting the second carbonaceous feedstock with an aqueous solution comprising at least a portion of the gasification catalyst to form a slurry; (c) dewatering the slurry to form a catalyst-loaded wet cake; (d) mixing the catalyst-loaded wet cake with and the first carbonaceous feedstock to form a mixture; and (e) thermally treating the mixture under a flow of inert dry gas to form the particulate composition.

Catalytic Gasification Methods

The particulate compositions of the present disclosure are particularly useful in integrated gasification processes for converting biomass and non-biomass to combustible gases, such as methane. The gasification reactors for such processes are typically operated at moderately high pressures and temperature, requiring introduction of the particulate composition 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.

In some instances, the particulate composition can be prepared at pressures conditions above the operating pressure of gasification reactor. Hence, the particulate composition can be directly passed into the gasification reactor without further pressurization.

Any of several catalytic gasifiers can be utilized. Suitable gasification reactors include counter-current fixed bed, co-current fixed bed, fluidized bed, entrained flow, and moving bed reactors.

The particulate compositions are particularly useful for gasification 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. Alternatively, the steam may be provided to the gasification reactor as described previously incorporated U.S. patent applications Ser. No. ______, entitled “STEAM GENERATION PROCESSES UTILIZING BIOMASS FEEDSTOCKS” (attorney docket no. FN-0020 US NP1), and Ser. No. ______, entitled “REDUCED CARBON FOOTPRINT STEAM GENERATION PROCESSES” (attorney docket no. FN-0021 US NP1).

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 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 H₂can 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 carbon monoxide and hydrogen fed to the reactor to ensure that enough recycle gas is supplied to the reactor so that the net heat of reaction is as close to neutral as possible (only slightly exothermic or endothermic), in other words, that the reaction is run under thermally neutral 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. 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.

The char 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 and US2007/0277437A1, and previously incorporated U.S. patent application Ser. Nos. 12/342,554, 12/342,715, 12/342,736 and 12/343,143. Reference can be had to those documents for further process details.

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, H₂and 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, optionally followed by Venturi scrubbers. The recovered fines can be processed to recover alkali metal catalyst, or directly recycled back to feedstock preparation as described in previously incorporated U.S. patent application Ser. No. ______, entitled “CARBONACEOUS FINES RECYCLE” (attorney docket no. FN-0028 US NP1).

The gas stream from which the fines have been removed 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, CO₂and NH₃; such processes are well known to those skilled in the art. NH₃can typically be recovered as an aqueous solution (e.g., 20 wt %).

A subsequent acid gas removal process can be used to remove H₂S and CO₂from 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 A G, Frankfurt am Main, Germany) solvent having two trains; each train consisting of an H₂S absorber and a CO₂absorber. The spent solvent containing H₂S, CO₂and 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 CO₂and 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. One method for removing acid gases from the scrubbed gas stream is described in previously incorporated U.S. patent application Ser. No. ______, entitled “SELECTIVE REMOVAL AND RECOVERY OF ACID GASES FROM GASIFICATION PRODUCTS” (attorney docket no. FN-0023 US NP1).

The cleaned gas stream can be further processed to separate and recover CH₄by 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 separating and recovering methane from the cleaned gas stream is described in previously incorporated U.S. patent application Ser. No. ______, entitled “PROCESS AND APPARATUS FOR THE SEPARATION OF METHANE FROM A GAS STREAM” (attorney docket no. FN-0022 US NP1).

Typically, two gas streams can be produced by the gas separation process, a methane product stream and a syngas stream (H₂and 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.

EXAMPLESExample 1

Feedstock Preparation

Switchgrass can be dried and crushed to produce a particulate having an average size of about 250 microns. The biomass feedstock can be provided to a combustion reactor fed by an enriched oxygen source. The resulting exhaust gas from the combustion reactor would contain hot CO₂. The exhaust gas can be passed through a heat exchanger in contact with a water source to produce steam, a portion of which can be provided to a steam turbine to generate electricity. The biomass char produced from the biomass combustion reactor can be withdrawn and directed to a feedstock preparation operation where the biomass char can be crushed to a particle size ranging from about 0.85 to about 1.4 mm. Fines (<0.85 mm) can be separated from the crushed biomass char by vibratory screening.

Separately, as-received coal (Powder River Basin) can be stage-crushed to maximize the amount of material having particle sizes ranging from about 0.85 to about 1.4 mm. Fines (<0.85 mm) can be separated from the crushed materials by vibratory screening and the crushed coal can be slurried with an aqueous solution of potassium carbonate and dewatered to provided a wet cake of a catalyzed coal feedstock.

The wet cake of the catalyzed coal feedstock can be kneaded together, in a 9:1 w/w ratio on a dry basis, with the crushed biomass char to provide a blended feedstock which can be dried via a fluid bed slurry drier to a final state having about 5 wt % residual moisture.

Example 2

Catalytic Gasification

A portion of the generated steam from the heat exchanger of Example 1 can be superheated and then introduced to a fluidized bed gasification reactor (catalytic gasifier) supplied with the blended feedstock of Example 1. The blended feedstock can be introduced under a positive pressure of nitrogen. Typical conditions for the catalytic gasifier could be: total pressure, 500 psi and temperature, 1200° F. The effluent of the catalytic gasifier could contain methane, CO₂, H₂, CO, water, H₂S, ammonia, and nitrogen, which can be passed to a scrubber to remove ammonia and an acid gas removal unit to remove H₂S and CO₂. The CO₂can be recovered.

Claims

1. A particulate composition having a particle distribution size suitable for gasification in a fluidized bed zone, the particulate composition comprising an intimate mixture of:

(a) a first carbonaceous feedstock that is a biomass char;

(b) a second carbonaceous feedstock that is a biomass, non-biomass, or a mixture thereof, and

(c) a gasification catalyst which, in the presence of steam and under suitable temperature and pressure, exhibits gasification activity whereby a plurality of gases including methane and at least one or more of hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, ammonia and other higher hydrocarbons are formed,

wherein:

(i) the first carbonaceous feedstock and second carbonaceous feedstock are present in the particulate composition at a weight ratio of from about 5:95 to about 95:5; and

(ii) the gasification catalyst comprises a source of at least one alkali metal and is present in an amount sufficient to provide, in the particulate composition, a ratio of alkali metal atoms of the gasification catalyst to carbon atoms ranging from about 0.01 to about 0.10, wherein the biomass char comprises at least a portion of the source of at least one alkali metal.

2. The particulate composition according toclaim 1, wherein a portion of the gasification catalyst is loaded on at least one of the first carbonaceous feedstock and the second carbonaceous feedstock.

3. The particulate composition according toclaim 1, wherein the alkali metal comprises potassium, sodium or both.

4. The particulate composition according toclaim 1, wherein the alkali metal is potassium.

5. The particulate composition according toclaim 1, wherein the biomass char comprises all of the gasification catalyst.

6. The particulate composition according toclaim 5, wherein the alkali metal is potassium.

7. The particulate composition according toclaim 1, having a particle size ranging from about 25 microns to about 2500 microns.

8. The particulate composition according toclaim 1, having a residual moisture content of less than about 4 wt. %.

9. The particulate compositions according to theclaim 1, wherein the second carbonaceous feedstock is a non-biomass.

10. A process for converting a particulate composition into a plurality of gaseous products, the process comprising the steps of:

(a) supplying a particulate composition according toclaim 1 to a gasifying reactor;

(b) reacting the particulate composition in the gasifying reactor in the presence of steam and under suitable temperature and pressure to form a plurality of gaseous including methane and at least one or more of hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, ammonia and other higher hydrocarbons; and

(c) at least partially separating the plurality of gaseous products to produce a stream comprising a predominant amount of one of the gaseous products.

11. The process according toclaim 10, wherein the stream comprises a predominant amount of methane.

12. The process according toclaim 10, wherein a char is formed in step (b), and the char is removed from the gasifying reactor and sent to a catalyst recovery and recycle process.

13. The process according toclaim 12, wherein the gasification catalyst comprises gasification catalyst recycled from the catalyst recovery and recycle process.

14. A process for preparing a particulate composition, the process comprising the steps of:

(a) providing a first particulate carbonaceous feedstock that is a biomass char, a second particulate carbonaceous feedstock that is a biomass, non-biomass, or mixture thereof, and, optionally, an alkali metal gasification catalyst which, in the presence of steam and under suitable temperature and pressure, exhibits gasification activity whereby a plurality of gases including methane and at least one or more of hydrogen, carbon monoxide, carbon dioxide, hydrogen sulfide, ammonia and other higher hydrocarbons are formed from the particulate composition;

(b) mixing the first particulate carbonaceous feedstock, the second particulate carbonaceous feedstock and, optionally, the alkali metal gasification catalyst to form a mixture; and

(c) optionally thermally treating the mixture under a flow of inert dry gas to form the particulate composition, wherein

the gasification catalyst comprises a source of at least one alkali metal and is present in an amount sufficient to provide, in the particulate composition, a ratio of alkali metal atoms of the gasification catalyst to carbon atoms ranging from about 0.01 to about 0.10, wherein the biomass char comprises at least a portion of the source of at least one alkali metal.

15. The process according toclaim 14, wherein the first carbonaceous feedstock and second carbonaceous feedstock are contacted separately with an aqueous solution comprising at least a portion of the gasification catalyst to form first and second slurries; the first and second slurries are dewatered separately to form first and second catalyst-loaded wet cakes; and the first and second catalyst-loaded wet cakes are mixed to form the mixture.

16. The process according toclaim 14, wherein the first carbonaceous feedstock and second carbonaceous feedstock are contacted separately with an aqueous solution comprising at least a portion of the gasification catalyst to form first and second slurries; the first and second slurries are dewatered separately to form first and second catalyst-loaded wet cakes; the first and second catalyst-loaded wet cakes are separately thermally treated to form first and second dry particulates; and the first and second dry particulates are mixed to form the mixture.

17. The process according toclaim 14, wherein the first carbonaceous feedstock and second carbonaceous feedstock are mixed to form a blend; the blend is contacted with an aqueous solution comprising at least a portion of the gasification catalyst to form a slurry; and the slurry is dewatered to form a catalyst-loaded wet cake which is the mixture.

18. The process according toclaim 14, wherein the first carbonaceous feedstock is contacted with an aqueous solution comprising at least a portion of the gasification catalyst to form a slurry; the slurry is dewatered to form a catalyst-loaded wet cake; and the catalyst-loaded wet-cake is mixed with the second carbonaceous feedstock to form the mixture.

19. The process according toclaim 14, wherein the second carbonaceous feedstock is contacted with an aqueous solution comprising at least a portion of the gasification catalyst to form a slurry; the slurry is dewatered to form a catalyst-loaded wet cake; and the catalyst-loaded wet-cake is mixed with the first carbonaceous feedstock to form the mixture.

20. The process according toclaim 14, wherein the first carbonaceous feedstock and the second carbonaceous feedstocks are mixed to form the mixture.