US20130042824A1 - Hydromethanation of a carbonaceous feedstock - Google Patents

Abstract

The present invention relates to processes for hydromethanating a carbonaceous feedstock to a methane product stream and electrical power, in which heat energy from the hot methane-enriched synthesis gas is used to generate a dry saturated steam stream, the dry saturated steam stream is converted into a superheated steam stream via pressure drop for feeding into the hydromethanation reactor to satisfy the steam demand of the hydromethanation reaction, and heat generated from a downstream gas methanation processing is recovered to produce a superheated process steam stream which is used to generate the electric power.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This application claims priority under 35 U.S.C. §119 from U.S. Provisional Application Ser. No. 61/524,536 (filed 17 Aug. 2011), 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. patent application Ser. No. ______, (attorney docket no. FN-0070 US NP1, entitled HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK, concurrently filed herewith), the disclosure of which is incorporated by reference herein for all purposes as if fully set forth.
FIELD OF THE INVENTION
• The present invention relates to processes for hydromethanating a carbonaceous feedstock to a methane product stream and electrical power, in which heat energy from the hot methane-enriched synthesis gas is used to generate a dry saturated steam stream, and the dry saturated steam stream is converted into a superheated steam stream via pressure drop for feeding into the hydromethanation reactor to satisfy the steam demand of the hydromethanation reaction, and heat generated from a downstream gas methanation processing is recovered to produce a superheated process steam stream which is used to generate the electric power.
BACKGROUND OF THE INVENTION
• In view of numerous factors such as higher energy prices and environmental concerns, the production of value-added products (such as pipeline-quality substitute natural gas, hydrogen, methanol, higher hydrocarbons, ammonia and electrical power) from lower-fuel-value carbonaceous feedstocks (such as petroleum coke, resids, asphaltenes, coal and biomass) is receiving renewed attention.
• Such lower-fuel-value carbonaceous feedstocks can be gasified at elevated temperatures and pressures to produce a synthesis gas stream that can subsequently be converted to such value-added products.
• One advantageous gasification process is hydromethanation, in which the carbonaceous feedstock is converted in a fluidized-bed hydromethanation reactor in the presence of a catalyst source and steam at moderately-elevated temperatures and pressures to directly produce a methane-enriched synthesis gas stream (medium BTU synthesis gas stream) raw product. This is distinct from conventional gasification processes, such as those based on partial combustion/oxidation of a carbon source at highly-elevated temperatures and pressures (thermal gasification, typically non-catalytic), where a syngas (carbon monoxide +hydrogen) is the primary product (little or no methane is directly produced), which can then be further processed to produce methane (via catalytic methanation, see reaction (III) below) or any number of other higher hydrocarbon products.
• Hydromethanation processes and the conversion/utilization of the resulting methane-rich synthesis gas stream to produce value-added products are disclosed, for example, in U.S. Pat. No. 3828474, U.S. Pat. No. 3,958,957, 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. 4,243,639, 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. 4,604,105, 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, US2003/0167691A1, US2006/0265953A1, US2007/000177A1, US2007/083072A1, US2007/0277437A1, US2009/0048476A1, US2009/0090056A1, US2009/0090055A1, US2009/0165383A1, US2009/0166588A1, US2009/0165379A1, US2009/0170968A1, US2009/0165380A1, US2009/0165381A1, US2009/0165361A1, US2009/0165382A1, US2009/0169449A1, US2009/0169448A1, US2009/0165376A1, US2009/0165384A1, US2009/0217582A1, US2009/0220406A1, US2009/0217590A1, US2009/0217586A1, US2009/0217588A1, US2009/0218424A1, US2009/0217589A1, US2009/0217575A1, US2009/0229182A1, US2009/0217587A1, US2009/0246120A1, US2009/0259080A1, US2009/0260287A1, US2009/0324458A1, US2009/0324459A1, US2009/0324460A1, US2009/0324461A1, US2009/0324462A1, US2010/0071235A1, US2010/0071262A1, US2010/0120926A1, US2010/0121125A1, US2010/0168494A1, US2010/0168495A1, US2010/0179232A1, US2010/0287835A1, US2010/0287836A1, US2010/0292350A1, US2011/0031439A1, US2011/0062012A1, US2011/0062721A1, US2011/0062722A1, US2011/0064648A1, US2011/0088896A1, US2011/0088897A1, US20110146978A1, US20110146979A1, US2012/0046510A1, US2012/0060417A1, US2012/0102836A1, US2012/0102837A1, WO2011/029278A1, WO2011/029282A1, WO2011/029283A1, WO2011/029284A1, WO2011/029285A1, WO2011/063608A1 and GB1599932. See also Chiaramonte et al, “Upgrade Coke by Gasification”,Hydrocarbon Processing,September 1982, pp. 255-257; and Kalina et al, “Exxon Catalytic Coal Gasification Process Predevelopment Program, Final Report”, Exxon Research and Engineering Co., Baytown, Tex., FE236924, December 1978.
• The hydromethanation of a carbon source typically involves four theoretically separate reactions:
• 
  Steam carbon: C+HO→CO+H₂  (I)
• 
  Water-gas shift: CO+H₂O→H₂'CO₂  (II)
• 
  CO Methanation: CO+3H₂→CH₄+H₂O   (III)
• 
  Hydro-gasification: 2H₂+C→CH₄  (IV)
• In the hydromethanation reaction, the first three reactions (I-III) predominate to result in the following overall reaction:
• 
  2C+2H₂O→CH₄+CO₂  (V).
• The overall hydromethanation reaction is essentially thermally balanced; however, due to process heat losses and other energy requirements (such as required for evaporation of moisture entering the reactor with the feedstock), some heat must be added to maintain the thermal balance.
• The reactions are also essentially syngas (hydrogen and carbon monoxide) balanced (syngas is produced and consumed); therefore, as carbon monoxide and hydrogen are withdrawn with the product gases, carbon monoxide and hydrogen need to be added to the reaction as required to avoid a deficiency.
• In order to maintain the net heat of reaction as close to neutral as possible (only slightly exothermic or endothermic), and maintain the syngas balance, a superheated gas stream of steam, carbon monoxide and hydrogen is often fed to the hydromethanation reactor. Frequently, the carbon monoxide and hydrogen streams are recycle streams separated from the product gas, and/or are provided by reforming/partially oxidating a portion of the product methane. See, for example, previously incorporated U.S. Pat. No. 4,094,650, U.S. Pat. No. 6,955,595, US2007/083072A1, US2010/0120926A1, US2010/0287836A1, US2011/0031439A1, US2011/0062722A1 and US2011/0064648A1.
• In one variation of the hydromethanation process, required carbon monoxide, hydrogen and heat energy can also at least in part be generated in situ by feeding oxygen into the hydromethanation reactor. See, for example, previously incorporated US2010/0076235A1, US2010/0287835A1, US2011/0062721A1 US2012/0046510A1, US2012/0060417A1, US2012/0102836A1 and US2012/0102837A1.
• The result is a “direct” methane-enriched raw product gas stream also containing substantial amounts of hydrogen, carbon monoxide and carbon dioxide which can, for example, be directly utilized as a medium BTU energy source, or can be processed to result in a variety of higher-value product streams such as pipeline-quality substitute natural gas, high-purity hydrogen, methanol, ammonia, higher hydrocarbons, carbon dioxide (for enhanced oil recovery and industrial uses) and electrical energy.
• In addition to the heat and syngas demands of the hydromethanation reaction, steam is also a reactant in the process and the process thus also has a steam demand. A portion of the steam demand for the reaction can be satisfied by evaporation of moisture entering the reactor with the feedstock; however, the majority of the steam demand is satisfied by feeding superheated steam into the hydromethanation reactor. Desirably, the required superheated steam is generated substantially entirely from process heat recovery so that little or no imported steam is needed.
• Generating the required amount and type (temperature/pressure) of superheated steam solely from process heat recovery, however, is challenging, especially at or near the operating temperature of the hydromethanation reactor. While the superheated steam may in some cases desirably be fed at a temperature less than the operating temperature of the hydromethanation reactor (such as disclosed in previously incorporated US2012/0046510A1), more oxygen may be required for the hydromethanation reactor in order to maintain the heat balance, which could have an effect on the overall efficiency of the process.
• It would, therefore, be desirable to find a way to utilize lower temperature steam in order the satisfy the steam demand of the hydromethanation reaction without degrading the overall process efficiency in a material way.
SUMMARY OF THE INVENTION
• In one aspect, the invention provides a process for generating a cooled methane product stream and electrical power from a non-gaseous carbonaceous material, the process comprising the steps of:
• (a) preparing a carbonaceous feedstock from the non-gaseous carbonaceous material;
• (b) introducing the carbonaceous feedstock, a hydromethanation catalyst, a steam stream and an amount of oxygen into a hydromethanation reactor, wherein the hydromethanation reactor is operating at a first pressure condition;
• (c) reacting a portion of the carbonaceous feedstock in the hydromethanation reactor with oxygen to generate carbon monoxide, hydrogen and heat energy;
• (d) reacting a portion of the carbonaceous feedstock in the hydromethanation reactor in the presence of carbon monoxide, hydrogen, steam and hydromethanation catalyst to produce a methane-enriched raw product gas;
• (e) withdrawing a methane-enriched raw product gas stream of the methane-enriched raw product gas from the hydromethanation reactor, wherein the methane-enriched raw product gas stream comprises methane, carbon monoxide, hydrogen, carbon dioxide, hydrogen sulfide, steam and heat energy;
• (f) introducing the methane-enriched raw product stream into a first heat exchanger unit to recover heat energy and generate a cooled methane-enriched raw product stream and a dry saturated steam stream, wherein the dry saturated steam stream is at a second pressure condition that is higher than the first pressure condition;
• (g) providing at least a portion of the dry saturated steam stream to the hydromethanation reactor under a reduced pressure condition such that the portion of dry saturated steam stream provided to the hydromethanation reactor is converted to a first superheated steam stream at or prior to introduction into the hydromethanation reactor, wherein the reduced pressure condition is higher than the first pressure condition but lower than the second pressure condition;
• (h) steam shifting a portion of the carbon monoxide in the cooled methane-enriched raw product stream to generate a hydrogen-enriched raw product stream;
• (i) removing a substantial portion of the carbon dioxide and a substantial portion of the hydrogen sulfide from the hydrogen-enriched raw product stream to produce a sweetened gas stream, wherein the sweetened gas stream comprises a substantial portion of the hydrogen, carbon monoxide and methane from the hydrogen-enriched raw product stream;
• (j) methanating a substantial portion of the carbon monoxide in the sweetened gas stream with hydrogen in the sweetened gas stream to generate a methane-enriched treated product stream and heat energy;
• (k) recovering a portion of the heat energy from step (j) to generate the cooled methane product stream;
• (l) generating a second superheated steam stream from at least a portion of the heat energy recovered in step (k); and
• (m) generating electrical power from at least a portion of the second superheated steam stream generated in step (l),
• wherein
• (1) the reaction of step (d) has a steam demand and a heat demand,
• (2) the steam demand is substantially satisfied by the steam stream,
• (3) the steam stream substantially comprises steam from the dry saturated steam stream, and
• (4) the amount of oxygen introduced into the hydromethanation reactor is sufficient so that the heat demand of the reaction of step (d) is substantially satisfied by the reaction of step (c).
• The process in accordance with the present invention is useful, for example, for more efficiently producing higher-value products and by-products from various carbonaceous materials at a reduced capital and operating intensity.
• These and other embodiments, features and advantages of the present invention will be more readily understood by those of ordinary skill in the art from a reading of the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a diagram of an embodiment of the process for generating a cooled methane-enriched raw product gas stream and dry saturated steam stream in accordance with the present invention.
• FIG. 2 is a diagram of an embodiment for the further processing of the cooled methane-enriched raw product stream to generate the cooled methane product stream and electrical power in accordance with the present invention.
DETAILED DESCRIPTION
• The present invention relates to processes for converting a non-gaseous carbonaceous material ultimately into one or more value-added gaseous products. Further details are provided below.
• In the context of the present description, 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.
• Unless stated otherwise, all percentages, parts, ratios, etc., are by weight.
• Unless stated otherwise, pressures expressed in psi units are gauge, and pressures expressed in kPa units are absolute. Pressure differences, however, are expressed as absolute (for example,pressure 1 is 25 psi higher than pressure 2).
• 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” and “and/or” refers to an inclusive and not to an exclusive. For example, a condition A or B, or A and/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 term “substantial”, as used herein, unless otherwise defined herein, means that greater than about 90% of the referenced material, preferably greater than about 95% of the referenced material, and more preferably greater than about 97% of the referenced material. If not specified, the percent is on a molar basis when reference is made to a molecule (such as methane, carbon dioxide, carbon monoxide and hydrogen sulfide), and otherwise is on a weight basis (such as for entrained fines).
• The term “predominant portion”, as used herein, unless otherwise defined herein, means that greater than 50% of the referenced material. If not specified, the percent is on a molar basis when reference is made to a molecule (such as hydrogen, methane, carbon dioxide, carbon monoxide and hydrogen sulfide), and otherwise is on a weight basis (such as for entrained fines).
• The term “depleted” is synonymous with reduced from originally present. For example, removing a substantial portion of a material from a stream would produce a material-depleted stream that is substantially depleted of that material. Conversely, the term “enriched” is synonymous with greater than originally present.
• The term “carbonaceous” as used herein is synonymous with hydrocarbon.
• The term “carbonaceous material” as used herein is a material containing organic hydrocarbon content. Carbonaceous materials can be classified as biomass or non-biomass materials as defined herein.
• The term “biomass” as used herein refers to carbonaceous materials derived from recently (for example, within the past100 years) living organisms, including plant-based biomass and animal-based biomass. For clarification, biomass does not include fossil-based carbonaceous materials, such as coal. For example, see previously incorporated US2009/0217575A1, US2009/0229182A1 and US2009/0217587A1.
• The term “plant-based biomass” as used herein means materials derived from green plants, crops, algae, and trees, such as, but not limited to, sweet sorghum, bagasse, sugarcane, bamboo, hybrid poplar, hybrid willow, albizia trees, eucalyptus, alfalfa, clover, oil palm, switchgrass, sudangrass, millet, jatropha, and miscanthus (e.g.,Miscanthus×giganteus). Biomass further include wastes from agricultural cultivation, processing, and/or degradation such as corn cobs and husks, corn stover, straw, nut shells, vegetable oils, canola oil, rapeseed oil, biodiesels, tree bark, wood chips, sawdust, and yard wastes.
• The term “animal-based biomass” as used herein means wastes generated from animal cultivation and/or utilization. For example, biomass includes, but is not limited to, wastes from livestock cultivation and processing such as animal manure, guano, poultry litter, animal fats, and municipal solid wastes (e.g., sewage).
• The term “non-biomass”, as used herein, means those carbonaceous materials which are not encompassed by the term “biomass” as defined herein. For example, non-biomass include, but is not limited to, anthracite, bituminous coal, sub-bituminous coal, lignite, petroleum coke, asphaltenes, liquid petroleum residues or mixtures thereof. For example, see US2009/0166588A1, US2009/0165379A1, US2009/0165380A1, US2009/0165361A1, US2009/0217590A1 and US2009/0217586A1.
• “Liquid heavy hydrocarbon materials” are viscous liquid or semi-solid materials that are flowable at ambient conditions or can be made flowable at elevated temperature conditions. These materials are typically the residue from the processing of hydrocarbon materials such as crude oil. For example, the first step in the refining of crude oil is normally a distillation to separate the complex mixture of hydrocarbons into fractions of differing volatility. A typical first-step distillation requires heating at atmospheric pressure to vaporize as much of the hydrocarbon content as possible without exceeding an actual temperature of about 650° F., since higher temperatures may lead to thermal decomposition. The fraction which is not distilled at atmospheric pressure is commonly referred to as “atmospheric petroleum residue”. The fraction may be further distilled under vacuum, such that an actual temperature of up to about 650° F. can vaporize even more material. The remaining undistillable liquid is referred to as “vacuum petroleum residue”. Both atmospheric petroleum residue and vacuum petroleum residue are considered liquid heavy hydrocarbon materials for the purposes of the present invention.
• Non-limiting examples of liquid heavy hydrocarbon materials include vacuum resids; atmospheric resids; heavy and reduced petroleum crude oils; pitch, asphalt and bitumen (naturally occurring as well as resulting from petroleum refining processes); tar sand oil; shale oil; bottoms from catalytic cracking processes; coal liquefaction bottoms; and other hydrocarbon feedstreams containing significant amounts of heavy or viscous materials such as petroleum wax fractions.
• The term “asphaltene” as used herein is an aromatic carbonaceous solid at room temperature, and can be derived, for example, from the processing of crude oil and crude oil tar sands. Asphaltenes may also be considered liquid heavy hydrocarbon feedstocks.
• The liquid heavy hydrocarbon materials may inherently contain minor amounts of solid carbonaceous materials, such as petroleum coke and/or solid asphaltenes, that are generally dispersed within the liquid heavy hydrocarbon matrix, and that remain solid at the elevated temperature conditions utilized as the feed conditions for the present process.
• The terms “petroleum coke” and “petcoke” as used herein include 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 petcoke.
• Resid petcoke can also be derived from a crude oil, for example, by coking processes used for upgrading heavy-gravity residual crude oil (such as a liquid petroleum residue), which petcoke 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 silica and/or alumina.
• 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 % inorganic compounds, based on the weight of the petroleum coke.
• 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 coal include, but are not limited to, Illinois #6, Pittsburgh #8, Beulah (ND), 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 ash produced from combustion of a coal typically comprises both a fly ash and a bottom ash, as is familiar to those skilled in the art. The fly ash from a bituminous coal can comprise from about 20 to about 60 wt % silica and from about 5 to about 35 wt % alumina, based on the total weight of the fly ash. The fly ash from a sub-bituminous coal can comprise from about 40 to about 60 wt % silica and from about 20 to about 30 wt % alumina, based on the total weight of the fly ash. The fly ash from a lignite coal can comprise from about 15 to about 45 wt % silica and from about 20 to about 25 wt % alumina, based on the total weight of the fly ash. See, for example, Meyers, et al. “Fly Ash. A Highway Construction Material,” Federal Highway Administration, Report No. FHWA-IP-76-16, Washington, D.C., 1976.
• The bottom ash from a bituminous coal can comprise from about 40 to about 60 wt % silica and from about 20 to about 30 wt % alumina, based on the total weight of the bottom ash. The bottom ash from a sub-bituminous coal can comprise from about 40 to about 50 wt % silica and from about 15 to about 25 wt % alumina, based on the total weight of the bottom ash. The bottom ash from a lignite coal can comprise from about 30 to about 80 wt % silica and from about 10 to about 20 wt % alumina, based on the total weight of the bottom ash. See, for example, Moulton, Lyle K. “Bottom Ash and Boiler Slag,” Proceedings of the Third International Ash Utilization Symposium, U.S. Bureau of Mines, Information Circular No. 8640, Washington, D.C., 1973.
• A material such as methane can be biomass or non-biomass under the above definitions depending on its source of origin.
• A “non-gaseous” material is substantially a liquid, semi-solid, solid or mixture at ambient conditions. For example, coal, petcoke, asphaltene and liquid petroleum residue are non-gaseous materials, while methane and natural gas are gaseous materials.
• The term “unit” refers to a unit operation. When more than one “unit” is described as being present, those units are operated in a parallel fashion unless otherwise stated. A single “unit”, however, may comprise more than one of the units in series, or in parallel, depending on the context. For example, an acid gas removal unit may comprise a hydrogen sulfide removal unit followed in series by a carbon dioxide removal unit. As another example, a contaminant removal unit may comprise a first removal unit for a first contaminant followed in series by a second removal unit for a second contaminant. As yet another example, a compressor may comprise a first compressor to compress a stream to a first pressure, followed in series by a second compressor to further compress the stream to a second (higher) pressure.
• The term “a portion of the carbonaceous feedstock” refers to carbon content of unreacted feedstock as well as partially reacted feedstock, as well as other components that may be derived in whole or part from the carbonaceous feedstock (such as carbon monoxide, hydrogen and methane). For example, “a portion of the carbonaceous feedstock” includes carbon content that may be present in by-product char and recycled fines, which char is ultimately derived from the original carbonaceous feedstock.
• The term “superheated steam” in the context of the present invention refers to a steam stream that is non-condensing under the conditions utilized, as is commonly understood by persons of ordinary skill in the relevant art.
• The term “dry saturated steam” or “dry steam” in the context of the present invention refers to slightly superheated saturated steam that is non-condensing, as is commonly understood by persons of ordinary skill in the relevant art.
• The term “syngas demand” refers to the maintenance of syngas balance in the hydromethanation reactor for the hydromethanation reaction of step (d). As indicated above, in the overall desirable steady-state hydromethanation reaction (see equations (I), (II) and (III) above), hydrogen and carbon monoxide are generated and consumed in relative balance. Because both hydrogen and carbon monoxide are withdrawn as part of the gaseous products, hydrogen and carbon monoxide must be added to (via a superheated syngas feed stream as discussed below) and/or generated in situ in (via a combustion/oxidation reaction with supplied oxygen as discussed below) the hydromethanation reactor in an amount at least required to substantially maintain this reaction balance. For the purposes of the present invention, the amount of hydrogen and carbon monoxide that must be added to and/or generated in situ for the hydromethanation reaction (step (d)) is the “syngas demand”.
• The term “steam demand” refers to the amount of steam that must be added to the hydromethanation reactor via the steam stream (step (b), see also (12) inFIG. 1). Steam is consumed in the hydromethanation reaction and some steam must be added to the hydromethanation reactor. The theoretical consumption of steam is two moles for every two moles of carbon in the feed to produce one mole of methane and one mole of carbon dioxide (see equation (V)). In actual practice, the steam consumption is not perfectly efficient and steam is withdrawn with the product gases; therefore, a greater than theoretical amount of steam needs to be added to the hydromethanation reactor, which added amount is the “steam demand”. Steam can be added, for example, via the steam stream and the oxygen-rich gas stream (which are typically combined prior to introduction into the hydromethanation reactor as discussed below). The amount of steam to be added (and the source) is discussed in further detail below. Steam generated in situ from the carbonaceous feedstock (e.g., from vaporization of any moisture content of the carbonaceous feedstock, or from an oxidation reaction with hydrogen, methane and/or other hydrocarbons present in or generated from the carbonaceous feedstock) can assist in providing steam; however, it should be noted that any steam generated in situ or fed into the hydromethanation reactor at a temperature lower than the hydromethanation reaction temperature will have an impact on the “heat demand” for the hydromethanation reaction.
• The term “heat demand” refers to the amount of heat energy that must be added to the hydromethanation reactor and/or generated in situ (for example, via a combustion/oxidation reaction with supplied oxygen as discussed below) to keep the reaction of step (d) in substantial thermal balance, as discussed above and as further detailed below. In the context of the present invention, as discussed below, in steady-state operation of the process, all streams are typically fed into the hydromethanation reactor at a temperature below the operating temperature of the hydromethanation reaction (step (d)). In that case the “heat demand” will be satisfied by the in situ combustion/oxidation reaction (step (c)).
• 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. The materials, methods, and examples herein are thus illustrative only and, except as specifically stated, are not intended to be limiting.
General Process Information
• In one embodiment of the invention, a cooled methane product (99) and electrical power (92) are ultimately generated from a non-gaseous carbonaceous material (10) as illustrated inFIGS. 1 and 2.
• Referring toFIG. 1, in accordance with an embodiment of the invention, the non-gaseous carbonaceous material (10) is processed in a feedstock preparation unit (100) to generate a carbonaceous feedstock (32) which is fed to a catalyst application unit (350) where hydromethanation catalyst is applied to generate a catalyzed carbonaceous feedstock (31+32).
• In certain optional embodiments as discussed below, all or a portion of a recycle carbon-enriched and inorganic ash-depleted char stream (65) and/or all or a portion of a recovered fines stream (362) may be (i) fed to feedstock preparation unit (100) and co-processed with the non-gaseous carbonaceous material (10), (ii) combined with carbonaceous feedstock (32) for feeding to catalyst application unit (350), (iii) combined with catalyzed carbonaceous feedstock (31+32); or (iv) some combination of the above may be utilized.
• The hydromethanation catalyst will typically comprise a recycle catalyst from recycle catalyst stream (57) and a makeup catalyst from make-up catalyst stream (56). Further details are provided below.
• The catalyzed carbonaceous feedstock (31+32) is fed into a hydromethanation reactor (200) along with a steam stream (12) and an oxygen-rich gas stream (14), and optionally a superheated syngas feed stream (16).
• As discussed in further detail below, steam stream (12) is derived from a dry saturated steam stream (40) generated from process heat recovery (from heat energy recovery from the hot raw product gas), and is converted to superheated steam via pressure drop prior to or at introduction into hydromethanation reactor (200).
• The steam stream (12), oxygen-rich gas stream (14) and optional superheated syngas feed stream (16) may be a single feed stream which comprises, or multiple feed streams which comprise, in combination with the in situ generation of heat energy and syngas, steam and heat energy, and optionally hydrogen and carbon monoxide, as required to at least substantially satisfy, or at least satisfy, the syngas, steam and heat demands of the hydromethanation reaction that takes place in hydromethanation reactor (200).
• In the hydromethanation reactor (200), (i) a portion of the carbonaceous feedstock reacts with oxygen to generate heat energy and typically carbon monoxide, hydrogen and carbon dioxide (combustion/oxidation reaction), and (ii) a portion of the carbonaceous feedstock, steam, hydrogen and carbon monoxide react in the presence of the hydromethanation catalyst to generate a methane-enriched raw product gas (the hydromethanation reaction). The generated methane-enriched raw product gas is withdrawn as a methane-enriched raw product gas stream (50) from the hydromethanation reactor (200). The withdrawn methane-enriched raw product gas stream (50) typically comprises at least methane, carbon monoxide, carbon dioxide, hydrogen, hydrogen sulfide, steam, entrained solids fines and heat energy.
• The hydromethanation reactor (200) comprises a fluidized bed (202) with an upper portion (202b) and a lower portion (202a). Without being bound by any particular theory, the hydromethanation reaction predominates in upper portion (202b), and an oxidation reaction with the oxygen from oxygen-rich gas stream (14) predominates in lower portion (202a). It is believed that there is no specific defined boundary between the two portions, but rather there is a transition as oxygen is consumed (and heat energy and syngas are generated) in lower portion (202a). It is also believed that oxygen consumption is rapid under the conditions present in hydromethanation reactor (200); therefore, the predominant portion of fluidized bed (202) will be upper portion (202b).
• The steam stream (12) and oxygen-rich gas stream (14) may be fed separately into the hydromethanation reactor (200), but are typically combined prior to feeding into lower portion (202a) of fluidized bed (202). In one embodiment, as disclosed in previously incorporated US2012/0046510A1, optional superheated syngas feed stream (16) is not present, and the catalyzed carbonaceous feedstock (31+32), steam stream (12) and oxygen-rich gas stream (14) are all fed to hydromethanation reactor (200) at a temperature below the target operating temperature of the hydromethanation reaction.
• At least a portion of the carbonaceous feedstock in lower portion (202a) of fluidized bed (202) will react with oxygen from oxygen-rich gas stream (14) to generate heat energy, and also hydrogen and carbon monoxide (syngas). In one embodiment, this occurs in sufficient amounts to satisfy the heat and syngas demands of the hydromethanation reaction (no separate superheated syngas feed stream (16) is utilized in steady-state operation of the process). This includes the reaction of solid carbon from unreacted (fresh) feedstock, partially reacted feedstock (such as char and recycled fines), as well gases (carbon monoxide, hydrogen, methane and higher hydrocarbons) that may be generated from or carried with the feedstock and recycle fines in lower portion (202a). Generally some water (steam) may be produced, as well as other by-products such as carbon dioxide depending on the extent of combustion/oxidation.
• As indicated above, in hydromethanation reactor (200) (predominantly in upper portion (202b) of fluidized bed (202)) the carbonaceous feedstock, steam, hydrogen and carbon monoxide react in the presence of the hydromethanation catalyst to generate a methane-enriched raw product, which is ultimately withdrawn as a methane-enriched raw product stream (50) from the hydromethanation reactor (200).
• The reactions of the carbonaceous feedstock in fluidized bed (202) also result in a by-product char comprising unreacted carbon as well as non-carbon content from the carbonaceous feedstock (including entrained hydromethanation catalyst) as described in further detail below. To prevent buildup of the residue in the hydromethanation reactor (200), a solid purge of by-product char is routinely withdrawn (periodically or continuously) via char withdrawal line (58).
• The withdrawn by-product char can be processed in a catalyst recovery unit (300) to recover entrained catalyst, and optionally other value-added by-products such as vanadium and nickel (depending on the content of the non-gaseous carbonaceous material (10)), to generate a depleted char (59). Depleted char (59) may optionally processed in a carbon recovery unit (325) to generate the recycle carbon-enriched and inorganic ash-depleted char stream (65) and a carbon-depleted and inorganic ash-enriched stream (66), as disclosed in U.S. patent application Ser. No. 13/450,995 (incorporated below). In an alternative embodiment as discussed below, all or a portion of the recovered fines stream (362) may be co-processed with the withdrawn by-product char in catalyst recovery unit (300).
• In one embodiment of the present invention, as disclosed in previously incorporated US2012/0102836A1, carbonaceous feedstock (32) (or catalyzed carbonaceous feedstock (31+32)) is fed into lower portion (202a) of fluidized bed (202). Because catalyzed carbonaceous feedstock (31+32) is introduced into lower portion (202a) of fluidized bed (202), char withdrawal line (58) will be located at a point such that by-product char is withdrawn from fluidized bed (202) at one or more points above the feed location of catalyzed carbonaceous feedstock (31+32), typically from upper portion (202b) of fluidized bed (202).
• In this embodiment, due to the lower feed point of catalyzed carbonaceous feedstock (31+32) into hydromethanation reactor (200), and higher withdrawal point of by-product char from hydromethanation reactor (200), hydromethanation reactor (200) with be a flow-up configuration as discussed below.
• Hydromethanation reactor (200) also typically comprises a zone (206) below fluidized-bed (202), with the two sections typically being separated by a grid plate (208) or similar divider. Particles too large to be fluidized in fluidized-bed section (202), for example large-particle by-product char and non-fluidizable agglomerates, are generally collected in lower portion (202a) of fluidized bed (202), as well as zone (206). Such particles will typically comprise a carbon content (as well as an ash and catalyst content), and may be removed periodically from hydromethanation reactor (200) via char withdrawal lines (58) and (58a) for catalyst recovery and further processing as discussed below.
• Typically, the methane-enriched raw product passes through an initial disengagement zone (204) above the fluidized-bed section (202) prior to withdrawal from hydromethanation reactor (200). The disengagement zone (204) may optionally contain, for example, one or more internal cyclones and/or other entrained particle disengagement mechanisms. The “withdrawn” (see discussion below) methane-enriched raw product gas stream (50) typically comprises at least methane, carbon monoxide, carbon dioxide, hydrogen, hydrogen sulfide, steam, heat energy and entrained fines.
• The methane-enriched raw product gas stream (50) is initially treated to remove a substantial portion of the entrained fines, typically via a cyclone assembly (360) (for example, one or more internal and/or external cyclones), which may be followed if necessary by optional additional treatments such as Venturi scrubbers, as discussed in more detail below. The “withdrawn” methane-enriched raw product gas stream (50), therefore, is to be considered the raw product prior to fines separation, regardless of whether the fines separation takes place internal to and/or external of hydromethanation reactor (200).
• As specifically depicted inFIG. 1, the methane-enriched raw product stream (50) is passed from hydromethanation reactor (200) to a cyclone assembly (360) for entrained particle separation. While cyclone assembly (360) is shown inFIG. 1 as a single external cyclone for simplicity, as indicated above cyclone assembly (360) may be an internal and/or external cyclone, and may also be a series of multiple internal and/or external cyclones.
• The methane-enriched raw product gas stream (50) is treated in cyclone assembly (360) to generate the fines-depleted methane-enriched raw product gas stream (52) and a recovered fines stream (362).
• Recovered fines stream (362) may be fed back into hydromethanation reactor (202), for example, into upper portion (202b) of fluidized bed (202) via fines recycle line (364), and/or into lower portion (202a) of fluidized bed (202) via fines recycle line (366) (as disclosed in previously incorporated US2012/0060417A1). To the extent not fed back into fluidized bed (202), recovered fines stream (362) may, for example, be recycled back to feedstock preparation unit (100) and/or catalyst recovery unit (300), and/or combined with catalyzed carbonaceous feedstock (31+32).
• The fines-depleted methane-enriched raw product gas stream (52) typically comprises at least methane, carbon monoxide, carbon dioxide, hydrogen, hydrogen sulfide, steam, ammonia and heat energy, as well as small amounts of contaminants such as remaining residual entrained fines, and other volatilized and/or carried material (for example, mercury) that may be present in the carbonaceous feedstock. There are typically virtually no (total typically less than about 50 ppm) condensable (at ambient conditions) hydrocarbons present in fines-depleted methane-enriched raw product gas stream (52).
• The fines-depleted methane-enriched raw product gas stream (52) is then provided to a heat recovery unit, e.g., first heat exchanger unit (400), which removes at least a portion of the heat energy from the fines-depleted methane-enriched raw product stream (52) and reduces the temperature of the fines-depleted methane-enriched raw product stream (52) to generate a cooled methane-enriched raw product stream (70) having a temperature less than the fines-depleted methane-enriched raw product stream (52).
• The heat energy recovered by first heat exchanger unit (400) is used to generate a first process steam stream (40) from a boiler feed water stream (39a), with the resulting first process steam stream (40) being a dry saturated steam at a pressure (second pressure condition) higher than the operating pressure (first pressure condition) of hydromethanation reactor (200). At least a portion of the first process steam stream (40) is fed back to the hydromethanation reactor (200) as steam stream (12). Another portion of first process steam stream (40) (for example, that is excess to the steam demand of the hydromethanation reaction) can be withdrawn as steam stream (12a) and used, for example, in other process operations (such as catalyst application and recovery).
• As indicated above, steam stream (12) as fed into hydromethanation reactor (200) is superheated steam. As first process steam stream (40) is at a pressure higher than in the hydromethanation reactor (200), the conversion from dry saturated steam to superheated steam can occur due to the pressure drop across the feed point into hydromethanation reactor (200), or first process steam stream (40) can be passed through an expander or other similar pressure reduction device (405) to convert the dry saturated steam into superheated steam, as discussed in further detail below.
• The cooled fines-depleted methane-enriched raw product gas stream (70) is treated in one or more downstream processing steps to further recover heat energy, decontaminate and convert, to produce a cooled methane product stream, electrical power and, optionally, one or more value-added products such as, for example, substitute natural gas (pipeline quality), hydrogen, carbon monoxide, syngas, ammonia, methanol and other syngas-derived products, as disclosed in many of the documents referenced in the “Hydromethanation” section below and as further discussed below.
• Additional details and embodiments are provided below.
Hydromethanation
• Catalytic gasification/hydromethanation and/or raw product conversion processes and conditions are generally 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. 4,604,105, U.S. Pat. No. 4,617,027, U.S. Pat. No. 4609456, 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, US2003/0167691A1 and US2006/0265953A1, as well as in previously incorporated US2007/0000177A1, US2007/0083072A1, US2007/0277437A1, US2009/0048476A1, US2009/0090056A1, US2009/0090055A1, US2009/0165383A1, US2009/0166588A1, US2009/0165379A1, US2009/0170968A1, US2009/0165380A1, US2009/0165381A1, US2009/0165361A1, US2009/0165382A1, US2009/0169449A1, US2009/0169448A1, US2009/0165376A1, US2009/0165384A1, US2009/0217582A1, US2009/0220406A1, US2009/0217590A1, US2009/0217586A1, US2009/0217588A1, US2009/0218424A1, US2009/0217589A1, US2009/0217575A1, US2009/0229182A1, US2009/0217587A1, US2009/0246120A1, US2009/0259080A1, US2009/0260287A1, US2009/0324458A1, US2009/0324459A1, US2009/0324460A1, US2009/0324461A1, US2009/0324462A1, US2010/0076235A1, US2010/0071262A1, US2010/0121125A1, US2010/0120926A1, US2010/0179232A1, US2010/0168495A1, US2010/0168494A1, US2010/0292350A1, US2010/0287836A1, US2010/0287835A1, US2011/0031439A1, US2011/0062012A1, US2011/0062722A1, US2011/0062721A1, US2011/0064648A1, US2011/0088896A1, US2011/0088897A1, US20110146978A1, US20110146979A1, US2011/0207002A1, US2011/0217602A1, US2011/0262323A1, US2012/0046510A1, US2012/0060417A1, US2012/0102836A1 and US2012/0102837A1. See also commonly-owned U.S. patent applications Ser. No. 13/402,022 (attorney docket no. FN-0067 US NP1, entitled HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK WITH NICKEL RECOVERY, which was filed 22 Feb. 2012), Ser. No. 13/450,995 (attorney docket no. FN-0068 US NP1, entitled HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK, which was filed 19 Apr. 2012) and Ser. No. 13/484,918 (attorney docket no. FN-0069 US NP1, entitled HYDROMETHANATION OF A CARBONACEOUS FEEDSTOCK, which was filed 31 May 2012).
• In an embodiment in accordance with the present invention as illustrated inFIG. 1, catalyzed carbonaceous feedstock (31+32), steam stream (12) and, optionally, superheated syngas feed stream (16) are introduced into hydromethanation reactor (200). In addition, an amount of an oxygen-rich gas stream (14) is also introduced into hydromethanation reactor (200) for in situ generation of heat energy and syngas, as generally discussed above and disclosed in many of the previously incorporated references (see, for example, previously incorporated US2010/0076235A1, US2010/0287835A1, US2011/0062721A1, US2012/0046510A1, US2012/0060417A1, US2012/0102836A1 and US2012/0102837A1).
• Steam stream (12), oxygen-rich gas stream (14) and superheated syngas feed stream (16) (if present) are introduced into hydromethanation reactor at a temperature below the target operating temperature of the hydromethanation reaction, as disclosed in previously incorporated US2012/0046510A1. Although under those conditions this has a negative impact on the heat demand of the hydromethanation reaction, this advantageously allows full steam/heat integration of the hydromethanation portion of the process, without the use of fuel-fired superheaters (in steady-state operation of the process) that are typically fueled with a portion of the product from the process.
• Typically, superheated syngas feed stream (16) will not be present in steady-state operation of the process.
• Hydromethanation reactor (200) is a fluidized-bed reactor. Hydromethanation reactor (200) can, for example, be a “flow down” countercurrent configuration, where the catalyzed carbonaceous feedstock (31+32) is introduced at a higher point so that the particles flow down the fluidized bed (202) toward lower portion (202a) of fluidized bed (202), and the gases flow in an upward direction and are removed at a point above the fluidized bed (202).
• Alternatively, hydromethanation reactor (200) has a “flow up” co-current configuration, where the catalyzed carbonaceous feedstock (31+32) is fed at a lower point (bottom portion (202a) of fluidized bed (202)) so that the particles flow up the fluidized bed (202), along with the gases, to a char by-product removal zone, for example, near or at the top of upper portion (202b) of fluidized bed (202), to the top of fluidized bed (202). In one embodiment, the feed point of the carbonaceous feedstock (such as catalyzed carbonaceous feedstock (31+32)) should result in introduction into fluidized bed (200) as close to the point of introduction of oxygen (from oxygen-rich gas stream (14)) as reasonably possible. See, for example, previously incorporated US2012/0102836A1.
• Hydromethanation reactor (200) is typically operated at moderately high pressures and temperatures, requiring introduction of solid streams (e.g., catalyzed carbonaceous feedstock (31+32) and if present recycle fines) to the reaction chamber of the reactor while maintaining the required temperature, pressure and flow rate of the streams. Those skilled in the art are familiar with feed inlets to supply solids into the reaction chambers having high pressure and/or temperature environments, including star feeders, screw feeders, rotary pistons and lock-hoppers. It should be understood that the feed inlets can include two or more pressure-balanced elements, such as lock hoppers, which would be used alternately. In some instances, the carbonaceous feedstock can be prepared at pressure conditions above the operating pressure of the reactor and, hence, the particulate composition can be directly passed into the reactor without further pressurization. Gas for pressurization can be an inert gas such as nitrogen, or more typically a stream of carbon dioxide that can, for example be recycled from a carbon dioxide stream generated by an acid gas removal unit.
• Hydromethanation reactor (200) is desirably operated at a moderate temperature (as compared to “conventional” oxidation-based gasification processes), with a target operating temperature of at least about 1000° F. (about 538° C.), or at least about 1100° F. (about 593° C.), to about 1500° F. (about 816° C.), or to about 1400° F. (about 760° C.), or to about 1300° F. (704° C.); and a pressure (first operating pressure of step (c)) of about 250 psig (about 1825 kPa, absolute), or about 400 psig (about 2860 kPa), or about 450 psig (about 3204 kPa), to about 1000 psig (about 6996 kPa), or to about 800 psig (about 5617 kPa), or to about 700 psig (about 4928 kPa), or to about 600 psig (about 4238 kPa), or to about 500 psig (about 3549 kPa). In one embodiment, hydromethanation reactor (200) is operated at a pressure (first operating pressure) of up to about 600 psig (about 4238 kPa), or up to about 550 psig (about 3894 kPa).
• Typical gas flow velocities in hydromethanation reactor (200) are from about 0.5 ft/sec (about 0.15 m/sec), or from about 1 ft/sec (about 0.3 m/sec), to about 2.0 ft/sec (about 0.6 m/sec), or to about 1.5 ft/sec (about 0.45 m/sec).
• As oxygen-rich gas stream (14) is fed into hydromethanation reactor (200), a portion of the carbonaceous feedstock (desirably carbon from the partially reacted feedstock, by-product char and recycled fines) will be consumed in an oxidation/combustion reaction, generating heat energy as well as typically some amounts carbon monoxide and hydrogen (and typically other gases such as carbon dioxide and steam). The variation of the amount of oxygen supplied to hydromethanation reactor (200) provides an advantageous process control to ultimately maintain the syngas and heat balance. Increasing the amount of oxygen will increase the oxidation/combustion, and therefore increase in situ heat generation. Decreasing the amount of oxygen will conversely decrease the in situ heat generation. The amount of syngas generated will ultimately depend on the amount of oxygen utilized, and higher amounts of oxygen may result in a more complete combustion/oxidation to carbon dioxide and water, as opposed to a more partial combustion to carbon monoxide and hydrogen.
• The amount of oxygen supplied to hydromethanation reactor (200) must be sufficient to combust/oxidize enough of the carbonaceous feedstock to generate enough heat energy and syngas to meet the heat and syngas demands of the steady-state hydromethanation reaction.
• In one embodiment, the amount of molecular oxygen (as contained in the oxygen-rich gas stream (14)) that is provided to the hydromethanation reactor (200) can range from about 0.10, or from about 0.20, or from about 0.25, to about 0.6, or to about 0.5, or to about 0.4, or to about 0.35 pounds of O₂per pound of carbonaceous feedstock (32).
• The hydromethanation and oxidation/combustion reactions within hydromethanation reactor (200) will occur contemporaneously. Depending on the configuration of hydromethanation reactor (200), the two steps will typically predominate in separate zones—the hydromethanation in upper portion (202b) of fluidized bed (202), and the oxidation/combustion in lower portion (202a) of fluidized bed (202). The oxygen-rich gas stream (14) is typically mixed with steam stream (12) and the mixture introduced at or near the bottom of fluidized bed (202) in lower portion (202a) to avoid formation of hot spots in the reactor, and to avoid (minimize) combustion of the desired gaseous products. Feeding the catalyzed carbonaceous feedstock (31+32) with an elevated moisture content, and particularly into lower portion (202a) of fluidized bed (202), also assists in heat dissipation and the avoidance if formation of hot spots in reactor (200), as disclosed in previously incorporated US2012/0102837A1.
• If superheated syngas feed stream (16) is present, that stream will typically be introduced as a mixture with steam stream (12), with oxygen-rich gas stream (14) introduced separately into lower portion (202a) of fluidized bed (202) so as to not preferentially consume the syngas components.
• The oxygen-rich gas stream (14) can be fed into hydromethanation reactor (200) by any suitable means such as direct injection of purified oxygen, oxygen-air mixtures, oxygen-steam mixtures, or oxygen-inert gas mixtures into the reactor. See, for instance, U.S. Pat. No. 4,315,753 and Chiaramonte et al., Hydrocarbon Processing, September 1982, pp. 255-257.
• The oxygen-rich gas stream (14) is typically generated via standard air-separation technologies, and will be fed mixed with steam, and introduced at a temperature above about 250° F. (about 121° C.), to about 400° F. (about 204° C.), or to about 350° F. (about 177° C.), or to about 300° F. (about 149° C.), and at a pressure at least slightly higher than present in hydromethanation reactor (200). The steam in oxygen-rich gas stream (14) should be non-condensable during transport of oxygen-rich stream (14) to hydromethanation reactor (200), so oxygen-rich stream (14) may need to be transported at a lower pressure then pressurized (compressed) just prior to introduction into hydromethanation reactor (200).
• As indicated above, the hydromethanation reaction has a steam demand, a heat demand and a syngas demand. These conditions in combination are important factors in determining the operating conditions for the hydromethanation reaction as well as the remainder of the process.
• For example, the hydromethanation reaction requires a theoretical molar ratio of steam to carbon (in the feedstock) of at least about 1. Typically, however, the molar ratio is greater than about 1, or from about 1.5 (or greater), to about 6 (or less), or to about 5 (or less), or to about 4 (or less), or to about 3 (or less), or to about 2 (or less). The moisture content of the catalyzed carbonaceous feedstock (31+32), moisture generated from the carbonaceous feedstock in the hydromethanation reactor (200), and steam included in the steam stream (12), oxygen-rich gas stream (14) and recycle fines stream(s) (and optional superheated syngas feed stream (16)), all contribute steam for the hydromethanation reaction. The steam in steam stream (12) should be sufficient to at least substantially satisfy (or at least satisfy) the “steam demand” of the hydromethanation reaction.
• As also indicated above, the hydromethanation reaction (step (d)) is essentially thermally balanced but, due to process heat losses and other energy requirements (for example, vaporization of moisture on the feedstock), some heat must be generated in the hydromethanation reaction to maintain the thermal balance (the heat demand). The partial combustion/oxidation of carbon in the presence of the oxygen introduced into hydromethanation reactor (200) from oxygen-rich gas stream (14) should be sufficient to at least substantially satisfy (or at least satisfy) both the heat and syngas demand of the hydromethanation reaction.
• The gas utilized in hydromethanation reactor (200) for pressurization and reaction of the catalyzed carbonaceous feedstock (31+32) comprises the steam stream (12) and oxygen-rich gas stream (14) (and optional superheated syngas feed stream (16)) and, optionally, additional nitrogen, air, or inert gases such as argon, which can be supplied to hydromethanation reactor (200) according to methods known to those skilled in the art. As a consequence, steam stream (12) and oxygen-rich gas stream (14) must be provided at a higher pressure which allows them to enter hydromethanation reactor (200).
• All streams should be fed into hydromethanation reactor (200) at a temperature less than the target operating temperature of the hydromethanation reactor, such as disclosed in previously incorporated US2012/0046510A1.
• Steam stream (12) will be at a temperature above the saturation point at the feed pressure. When fed into hydromethanation reactor (200), steam stream (12) will be a superheated steam stream to avoid the possibility of any condensation occurring. Typical feed temperatures of steam stream (12) are from about 400° F. (about 204° C.), or from about 450° F. (about 232° C.), to about 650° F. (about 343° C.), or to about 600° F. (about 316° C.). Typical feed pressures of steam stream (12) are about 25 psi (about 172 kPa) or greater than the pressure within hydromethanation reactor (200).
• The actual temperature and pressure of steam stream (12) will ultimately depend on the level of heat recovery from the process and the operating pressure within hydromethanation reactor (200), as discussed below. In any event, desirably no fuel-fired superheater should be used in the superheating of steam stream (12) in steady-state operation of the process.
• When steam stream (12) and oxygen-rich stream (14) are combined for feeding into lower section (202a) of fluidized bed (202), the temperature of the combined stream will be controlled by the temperature of steam stream (12), and will typically range from about from about from about 400° F. (about 204° C.), or from about 450° F. (about 232° C.), to about 650° F. (about 343° C.), or to about 600° F. (about 316° C.).
• The temperature in hydromethanation reactor (200) can be controlled, for example, by controlling the amount and temperature of steam stream (12), as well as the amount of oxygen supplied to hydromethanation reactor (200).
• In steady-state operation, steam for the hydromethanation reaction is solely generated from other process operations through process heat capture (such as generated in a waste heat boiler, generally referred to as “process steam” or “process-generated steam”), specifically from the cooling of the raw product gas in heat first heat exchanger unit (400). Additional steam can be generated for other portions of the overall process, such as disclosed, for example, in previously incorporated US2010/0287835A1 and US2012/0046510A1.
• The overall process described herein is desirably steam positive, such that steam demand (pressure and amount) for the hydromethanation reaction can be satisfied via heat exchange in first heat exchange unit (400), with process heat recovery at the different stages allowing for production of excess steam that can be used for power generation and other purposes. Desirably, process-generated steam from first heat exchange unit (400) accounts for 100 wt % or greater of the steam demand of the hydromethanation reaction.
• The result of the hydromethanation reaction is a methane-enriched raw product, which is withdrawn from hydromethanation reactor (200) as methane-enriched raw product stream (50) typically comprising CH₄, CO₂, H₂, CO, H₂S, unreacted steam and, optionally, other contaminants such as entrained fines, NH₃, COS, HCN and/or elemental mercury vapor, depending on the nature of the carbonaceous material utilized for hydromethanation.
• If the hydromethanation reaction is run in syngas balance, the methane-enriched raw product stream (50), upon exiting the hydromethanation reactor (200), will typically comprise at least about 15 mol %, or at least about 18 mol %, or at least about 20 mol %, methane based on the moles of methane, carbon dioxide, carbon monoxide and hydrogen in the methane-enriched raw product stream (50). In addition, the methane-enriched raw product stream (50) will typically comprise at least about 50 mol % methane plus carbon dioxide, based on the moles of methane, carbon dioxide, carbon monoxide and hydrogen in the methane-enriched raw product stream (50).
• If the hydromethanation reaction is run in syngas excess, e.g., contains an excess of carbon monoxide and/or hydrogen above and beyond the syngas demand (for example, excess carbon monoxide and/or hydrogen are generated due to the amount of oxygen-rich gas stream (14) fed to hydromethanation reactor (200)), then there may be some dilution effect on the molar percent of methane and carbon dioxide in methane-enriched raw product stream (50).
• The non-gaseous carbonaceous materials (10) useful in these processes include, for example, a wide variety of biomass and non-biomass materials. The carbonaceous feedstock (32) is derived from one or more non-gaseous carbonaceous materials (10), which are processed in a feedstock preparation section (100) as discussed below.
• The hydromethanation catalyst (31) can comprise one or more catalyst species, as discussed below.
• The carbonaceous feedstock (32) and the hydromethanation catalyst (31) are typically intimately mixed (i.e., to provide a catalyzed carbonaceous feedstock (31+32)) before provision to the hydromethanation reactor (200), but they can be fed separately as well.
Gas ProcessingFines Removal
• The hot gas effluent leaving the reaction chamber of the hydromethanation reactor (200) can pass through a fines remover unit (such as cyclone assembly (360)), incorporated into and/or external of the hydromethanation reactor (200), which serves as a disengagement zone. Particles too heavy to be entrained by the gas leaving the hydromethanation reactor (200) (i.e., fines) are returned to the hydromethanation reactor (200), for example, to the reaction chamber (e.g., fluidized bed (202)).
• Residual entrained fines are substantially removed by any suitable device such as internal and/or external cyclone separators optionally followed by Venturi scrubbers. As discussed above, at least a portion of these fines can be returned to lower section (202a) of fluidized bed (202) via recycle line (366). A portion may also be returned to upper portion (202b) of fluidized bed (202) via recycle line (364). Any remaining recovered fines can be processed to recover alkali metal catalyst, and/or combined at some stage with carbonaceous feedstock (32), and/or directly recycled back to feedstock preparation as described in previously incorporated US2009/0217589A1.
• Removal of a “substantial portion” of fines means that an amount of fines is removed from the resulting gas stream such that downstream processing is not adversely affected; thus, at least a substantial portion of fines should be removed. Some minor level of ultrafine material may remain in the resulting gas stream to the extent that downstream processing is not significantly adversely affected. Typically, at least about 90 wt %, or at least about 95 wt %, or at least about 98 wt %, of the fines of a particle size greater than about 20 μm, or greater than about 10 μm, or greater than about 5 μm, are removed.
Heat Exchange and First Process Steam Stream
• Depending on the hydromethanation conditions, the fines-depleted methane-enriched raw product stream (52) can be generated having at a temperature ranging from about 1000° F. (about 538° C.) to about 1500° F. (about 816° C.), and more typically from about 1100° F. (about 593° C.) to about 1400° F. (about 760° C.); a pressure of from about 250 psig (about 1825 kPa) to about 1000 psig (about 6996 kPa), more typically from about 400 psig (about 2860 kPa), or from about 450 psig (about 3204 kPa), to about 800 psig (about 5617 kPa), or to about 600 psig (about 4238 kPa); and a velocity of from about 0.5 ft/sec (about 0.15 m/sec) to about 2.0 ft/sec (about 0.61 m/sec), more typically from about 1.0 ft/sec (0.30 m/sec) to about 1.5 ft/sec (about 0.46 m/sec).
• The fines-depleted methane-enriched raw product stream (52) is provided to a heat recovery unit, e.g., first heat exchanger unit (400) as shown inFIG. 1. First heat exchanger unit (400) removes a portion of the heat energy from the fines-depleted methane-enriched raw product stream (52) and reduces the temperature of the fines-depleted methane-enriched raw product stream (52) to generate a cooled methane-enriched raw product stream (70) having a temperature less than the fines-depleted methane-enriched raw product stream (52). The heat energy recovered by first heat exchanger unit (400) is used at least in part to generate a first process steam stream (40) which is a dry saturated steam stream. At least a portion of the first process steam stream (40) is fed back to the hydromethanation reactor (200) as steam stream (12).
• In one embodiment, first heat exchanger unit (400) is a steam boiler, for example, a shell and tube heat exchanger of a type well-known to those of ordinary skill in the relevant art. A stream of boiler feed water (39a) is passed through first heat exchanger unit (400) to generate first process steam stream (40), which is a dry saturated steam stream of a pressure higher than the pressure in hydromethanation reactor (200).
• The resulting cooled methane-enriched raw product stream (70) will typically exit first heat exchanger unit (400) at a temperature ranging from about 450° F. (about 232° C.) to about 1100° F. (about 593° C.), more typically from about 550° F. (about 288° C.) to about 950° F. (about 510° C.); a pressure of from about 250 psig (about 1825 kPa) to about 1000 psig (about 6996 kPa), more typically from about 400 psig (about 2860 kPa), or from about 450 psig (about 3204 kPa), to about 800 psig (about 5617 kPa), or to about 600 psig (about 4238 kPa); and a velocity of from about 0.5 ft/sec (about 0.15 m/sec) to about 2.0 ft/sec (about 0.61 m/sec), more typically from about 1.0 ft/sec (0.30 m/sec) to about 1.5 ft/sec (about 0.46 m/sec).
• The resulting first process steam stream (40) is a dry saturated steam stream that will exit first heat exchanger unit (400) at a pressure that is ultimately dependent on the operating pressure within hydromethanation reactor (200). The temperature of first process steam stream (40) will typically be slightly above the saturation temperature, for example, about 20% or less, or about 10% or less, or about 5% or less, above such saturation temperature.
• In one embodiment, the pressure of first process steam stream (40) at the exit of first heat exchanger unit (400) (second pressure condition) is at least about 25 psi (about 172 kPa), or at least about 50 psi (about 345 kPa), or at least about 100 psi (about 690 kPa), greater than the operating pressure of the hydromethanation reactor (200) (first pressure condition). In another embodiment, the pressure of first process steam stream (40) at the exit of first heat exchanger unit (400) (second pressure condition) is at least about 5%, or at least about 10%, greater than the operating pressure of the hydromethanation reactor (200) (first pressure condition).
• In another embodiment, the pressure of first process steam stream (40) at the exit of first heat exchanger unit (400) (second pressure condition) is about 200 psi (about 1379 kPa) or less greater than the operating pressure of the hydromethanation reactor (200) (first pressure condition). In another embodiment, the pressure of first process steam stream (40) at the exit of first heat exchanger unit (400) (second pressure condition) is at least about 20% or less greater than the operating pressure of the hydromethanation reactor (200) (first pressure condition).
• As indicated above, steam stream (12) substantially comprises, or fully comprises, steam from first process steam stream (40). To the extent not utilized as part of steam stream (12), an excess steam stream (12a) can be withdrawn for use elsewhere in the process.
• At or before feeding into hydromethanation reactor (200), steam stream is converted from a dry saturated steam stream to a superheated steam stream by pressure drop. For example, because steam stream (12) is at a pressure higher than the operating pressure of hydromethanation reactor (200), simply feeding steam stream (12) into hydromethanation reactor (200) will result in such conversion. To the extent necessary, steam stream (12) can also be processed through an expander or other pressure drop device (405) to reduce the pressure in steam stream (12) as appropriate for feeding into hydromethanation reactor (200).
Gas Purification/Conversion
• Referring toFIG. 2, raw product purification/conversion will typically comprise, for example, water-gas shift processes (700), dehydration (450), acid gas removal (800) and methanation (950), and other optional processes such as, for example, trace contaminant removal (500) and ammonia removal and recovery (600).
• Trace Contaminant Removal (500)
• As is familiar to those skilled in the art, the contamination levels of the gas stream, e.g., cooled methane-enriched raw product stream (70), will depend on the nature of the carbonaceous material used for preparing the carbonaceous feedstocks. For example, certain coals, such as Illinois #6, can have high sulfur contents, leading to higher COS contamination; and other coals, such as Powder River Basin coals, can contain significant levels of mercury which can be volatilized in hydromethanation reactor (200).
• COS can be removed from a gas stream, e.g. the cooled methane-enriched raw product stream (70), by COS hydrolysis (see, U.S. Pat. No. 3,966,875, U.S. Pat. No. 4,011,066, U.S. Pat. No. 4,100,256, U.S. Pat. No. 4,482,529 and U.S. Pat. No. 4,524,050), passing the gas stream through particulate limestone (see, U.S. Pat. No. 4,173,465), an acidic buffered CuSO₄solution (see, U.S. Pat. No. 4,298,584), an alkanolamine absorbent such as methyldiethanolamine, triethanolamine, dipropanolamine or diisopropanolamine, containing tetramethylene sulfone (sulfolane, see, U.S. Pat. No. 3,989,811); or counter-current washing of the cooled second gas stream with refrigerated liquid CO₂(see, U.S. Pat. No. 4,270,937 and U.S. Pat. No. 4,609,388).
• HCN can be removed from a gas stream, e.g., the cooled methane-enriched raw product stream (70), by reaction with ammonium sulfide or polysulfide to generate CO₂, H₂S and NH₃(see, U.S. Pat. No. 4,497,784, U.S. Pat. No. 4,505,881 and U.S. Pat. No. 4,508,693), or a two stage wash with formaldehyde followed by ammonium or sodium polysulfide (see, U.S. Pat. No. 4,572,826), absorbed by water (see, U.S. Pat. No. 4,189,307), and/or decomposed by passing through alumina supported hydrolysis catalysts such as MoO₃, TiO₂and/or ZrO₂(see, U.S. Pat. No. 4,810,475, U.S. Pat. No. 5,660,807 and U.S. Pat. No. 5,968,465).
• Elemental mercury can be removed from a gas stream, e.g., the cooled methane-enriched raw product stream (70), for example, by absorption by carbon activated with sulfuric acid (see, U.S. Pat. No. 3,876,393), absorption by carbon impregnated with sulfur (see, U.S. Pat. No. 4,491,609), absorption by a H₂S-containing amine solvent (see, U.S. Pat. No. 4,044,098), absorption by silver or gold impregnated zeolites (see, U.S. Pat. No. 4,892,567), oxidation to HgO with hydrogen peroxide and methanol (see, U.S. Pat. No. 5,670,122), oxidation with bromine or iodine containing compounds in the presence of SO₂(see, U.S. Pat. No. 6,878,358), oxidation with a H, Cl and O-containing plasma (see, U.S. Pat. No. 6,969,494), and/or oxidation by a chlorine-containing oxidizing gas (e.g., ClO, see, U.S. Pat. No. 7,118,720).
• When aqueous solutions are utilized for removal of any or all of COS, HCN and/or Hg, the waste water generated in the trace contaminants removal units can be directed to a waste water treatment unit (not depicted).
• When present, a trace contaminant removal of a particular trace contaminant should remove at least a substantial portion (or substantially all) of that trace contaminant from the so-treated gas stream (e.g., cooled methane-enriched raw product stream (70)), typically to levels at or lower than the specification limits of the desired product stream. Typically, a trace contaminant removal should remove at least 90%, or at least 95%, or at least 98%, of COS, HCN and/or mercury from a cooled first gas stream, based on the weight of the contaminant in the prior to treatment.
• Ammonia Removal and Recovery (600)
• As is familiar to those skilled in the art, gasification of biomass, certain coals, certain petroleum cokes and/or utilizing air as an oxygen source for hydromethanation reactor (200) can produce significant quantities of ammonia in the product stream. Optionally, a gas stream, e.g. the cooled methane-enriched raw product stream (70), can be scrubbed by water in one or more ammonia removal and recovery units (600) to remove and recover ammonia.
• The ammonia recovery treatment may be performed, for example, on the cooled methane-enriched raw product stream (70), directly from heat exchanger (400) or after treatment in one or both of (i) one or more of the trace contaminants removal units (500), and (ii) one or more sour shift units (700).
• After scrubbing, the gas stream, e.g., the cooled methane-enriched raw product stream (70), will typically comprise at least H₂S, CO₂, CO, H₂and CH₄. When the cooled methane-enriched raw product stream (70) has previously passed through a sour shift unit (700), then, after scrubbing, the gas stream will typically comprise at least H₂S, CO₂, H₂and CH₄.
• Ammonia can be recovered from the scrubber water according to methods known to those skilled in the art, can typically be recovered as an aqueous solution (61) (e.g., 20 wt %). The waste scrubber water can be forwarded to a waste water treatment unit (not depicted).
• When present, an ammonia removal process should remove at least a substantial portion (and substantially all) of the ammonia from the scrubbed stream, e.g., the cooled methane-enriched raw product stream (70). “Substantial” removal in the context of ammonia removal means removal of a high enough percentage of the component such that a desired end product can be generated. Typically, an ammonia removal process will remove at least about 95%, or at least about 97%, of the ammonia content of a scrubbed first gas stream, based on the weight of ammonia in the stream prior to treatment.
• Any recovered ammonia can be used as such or, for example, can be converted with other by-products from the process. For example, sulfur recovered from the acid gas removal unit can be used in conjunction with the ammonia to generate products such as ammonium sulfate.
• Water-Gas Shift (700)
• A portion or all of the methane-enriched raw product stream (e.g., cooled methane-enriched raw product stream (70)) is typically supplied to a water-gas shift reactor, such as sour shift reactor (700).
• In sour shift reactor (700), the gases undergo a sour shift reaction (also known as a water-gas shift reaction) in the presence of an aqueous medium (such as steam) to convert at least a predominant portion (or a substantial portion, or substantially all) of the CO to CO₂and to increase the fraction of H₂. The generation of increased hydrogen content is utilized, for example, to optimize hydrogen production, or to otherwise optimize H₂/CO ratios for downstream methanation.
• The water-gas shift treatment may be performed on the cooled methane-enriched raw product stream (70) passed directly from heat exchanger (400), or on the cooled methane-enriched raw product stream (70) that has passed through a trace contaminants removal unit (500) and/or an ammonia removal unit (600).
• A sour shift process is described in detail, for example, in U.S. Pat. No. 7,074,373. The process involves adding water, or using water contained in the gas, and reacting the resulting water-gas mixture adiabatically over a steam reforming catalyst. Typical steam reforming catalysts include one or more Group VIII metals on a heat-resistant support.
• Methods and reactors for performing the sour gas shift reaction on a CO-containing gas stream are well known to those of skill in the art. Suitable reaction conditions and suitable reactors can vary depending on the amount of CO that must be depleted from the gas stream. In some embodiments, the sour gas shift can be performed in a single stage within a temperature range from about 100° C., or from about 150° C., or from about 200° C., to about 250° C., or to about 300° C., or to about 350° C. In these embodiments, the shift reaction can be catalyzed by any suitable catalyst known to those of skill in the art. Such catalysts include, but are not limited to, Fe₂O₃-based catalysts, such as Fe₂O₃—Cr₂O₃catalysts, and other transition metal-based and transition metal oxide-based catalysts. In other embodiments, the sour gas shift can be performed in multiple stages. In one particular embodiment, the sour gas shift is performed in two stages. This two-stage process uses a high-temperature sequence followed by a low-temperature sequence. The gas temperature for the high-temperature shift reaction ranges from about 350° C. to about 1050° C. Typical high-temperature catalysts include, but are not limited to, iron oxide optionally combined with lesser amounts of chromium oxide. The gas temperature for the low-temperature shift ranges from about 150° C. to about 300° C., or from about 200° C. to about 250° C. Low-temperature shift catalysts include, but are not limited to, copper oxides that may be supported on zinc oxide or alumina. Suitable methods for the sour shift process are described in previously incorporated US2009/0246120A1.
• The sour shift reaction is exothermic so it is often carried out with a heat exchanger, such as second heat exchanger unit (401), to permit the efficient use of heat energy. Shift reactors employing these features are well known to those of skill in the art. An example of a suitable shift reactor is illustrated in previously incorporated U.S. Pat. No. 7,074,373, although other designs known to those of skill in the art are also effective.
• Following the sour gas shift procedure, the resulting hydrogen-enriched raw product stream (72) generally contains CH₄, CO₂, H₂, H₂S, steam, optionally CO and optionally minor amounts of other contaminants.
• As indicated above, the hydrogen-enriched raw product stream (72) can be provided to a heat recovery unit, e.g., second heat exchanger unit (401). While second heat exchanger unit (401) is depicted inFIG. 2 as a separate unit, it can exist as such and/or be integrated into the sour shift reactor (700), thus being capable of cooling the sour shift reactor (700) and removing at least a portion of the heat energy from the hydrogen-enriched raw product stream (72) to reduce the temperature and generate a cooled stream.
• At least a portion of the recovered heat energy can be used to generate a second process steam stream from a water/steam source.
• In a specific embodiment as depicted inFIG. 2, the hydrogen-enriched raw product stream (72), upon exiting sour shift reactor (700), is introduced into a superheater (401a) followed by a boiler feed water preheater (401b). Superheater (401a) can be used, for example, to superheat a stream (42a) which can be a portion of cooled methane-enriched raw product stream (70), to generate a superheated stream (42b) which is then recombined into cooled methane-enriched raw product stream (70). Alternatively, all of cooled methane-enriched product stream can be preheated in superheater (401a) and subsequently fed into sour shift reactor (700) as superheated stream (42b). Boiler feed water preheater (401b) can be used, for example, to preheat boiler feed water (46) to generate a preheated boiler water feed stream (39) for one or more of first heat exchanger unit (400) and third heat exchanger unit (403), as well as other steam generation operations.
• If it is desired to retain some of the carbon monoxide content of the methane-enriched raw product stream (50), a gas bypass loop (71) in communication with the first heat recovery unit (400) can be provided to allow some of the cooled methane-enriched raw product stream (70) exiting the first heat exchanger unit (400) to bypass the sour shift reactor (700) and second heat exchanger unit (401) altogether, and be combined with hydrogen-enriched raw product stream (72) at some point prior to dehydration unit (450) and/or acid gas removal unit (800). This is particularly useful when it is desired to recover a separate methane product, as the retained carbon monoxide can be subsequently methanated as discussed below.
• Dehydration (450)
• Subsequent to sour shift reactor (700) and second heat exchanger unit (401), and prior to acid gas removal unit (800), the hydrogen-enriched raw product stream (72) will typically be treated in a dehydration unit (450) to reduce water content. Dehydration unit (450) can, for example, be a knock-out drum or similar water separation device, and/or water absorption processes such as glycol treatment. Such dehydration units and processes are in a general sense well known to those of ordinary skill in the relevant art.
• A resulting waste water stream (47) (which will be a sour water stream) can be sent to a wastewater treatment unit (not depicted) for further processing. The resulting dehydrated hydrogen-enriched raw product stream (72a) is sent acid gas removal unit (800) as discussed below.
• Compressor Unit (452)
• The dehydrated raw sour gas stream, such as dehydrated hydrogen-enriched raw product stream (72a) may optionally be compressed prior to treatment in acid gas removal unit (800) to generate a compressed raw sour gas stream (72b), as disclosed in previously incorporated U.S. patent application Ser. No. 13/484,918. A compressor unit (452) compresses dehydrated raw sour gas stream (72a) to a third pressure condition which is higher than dehydrated raw sour gas stream (72a), and typically higher than the first pressure condition (the operating pressure of hydromethanation reactor (200)).
• Compressor unit (452) can be a single or series of gas compressors depending on the required extent of compression, as will be understood by a person of ordinary skill in the art. Suitable types of compressors are also generally well known to those of ordinary skill in the art, for example, compressors known suitable for use with syngas streams (carbon monoxide plus hydrogen) would also be suitable for use in connection with the present invention.
• As indicated above, compressed raw sour gas stream (72b) is at a pressure higher than dehydrated raw sour gas stream (72a). In one embodiment, the pressure of compressed raw sour gas stream (72b) (the third pressure condition) is about 20% higher or greater, or about 35% higher or greater, or about 50% higher or greater, to about 100% higher or less, than the pressure of dehydrated raw sour gas stream (72a).
• In another embodiment, the pressure of compressed raw sour gas stream (72b) (the third pressure condition) is about 720 psig (about 5066 kPa) or greater, or about 750 psig (about 5273 kPa) or greater, and about 1000 psig (about 6996 kPa) or less, or about 900 psig (about 6307 kPa) or less, or about 850 psig (about 5962 kPa) or less.
• In another embodiment, the pressure of dehydrated raw gas stream (72a) is about 600 psig (about 4238 kPa) or less, or about 550 psig (about 3894 kPa) or less, or about 500 psig (3549 kPa) or less, and about 400 psig (about 2860 kPa) or greater, or about 450 psig (about 3204 kPa) or greater.
• Acid Gas Removal (800)
• A subsequent acid gas removal unit (800) is used to remove a substantial portion of H₂S and a substantial portion of CO₂from the hydrogen-enriched raw product stream (72), or the dehydrated raw sour gas stream (72a) if present, or the compressed raw product stream (72b) if present, and generate a sweetened gas stream (80).
• Acid gas removal processes typically involve contacting a gas stream 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 to generate CO₂and/or H₂S laden absorbers. 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 containing an H₂S absorber and a CO₂absorber.
• One method for removing acid gases is described in previously incorporated US2009/0220406A1.
• At least a substantial portion (e.g., substantially all) of the CO₂and/or H₂S (and other remaining trace contaminants) should be removed via the acid gas removal processes. “Substantial” removal in the context of acid gas removal means removal of a high enough percentage of the component such that a desired end product can be generated. The actual amounts of removal may thus vary from component to component. For “pipeline-quality natural gas”, only trace amounts (at most) of H₂S can be present, although higher (but still small) amounts of CO₂may be tolerable.
• Typically, at least about 85%, or at least about 90%, or at least about 92%, of the CO₂should be removed from the stream fed into acid gas removal unit (800). Typically, at least about 95%, or at least about 98%, or at least about 99.5%, of such H₂S, should be removed.
• Losses of desired product (hydrogen and/or methane) in the acid gas removal step should be minimized such that the sweetened gas stream (80) comprises at least a substantial portion (and substantially all) of the methane and hydrogen from the stream fed into acid gas removal unit (800). Typically, such losses should be about 2 mol % or less, or about 1.5 mol % or less, or about 1 mol % of less, respectively, of the methane and hydrogen from the compressed raw product stream (72b).
• The resulting sweetened gas stream (80) will generally comprise CH₄, H₂and optionally CO (for the downstream methanation), and typically small amounts of CO₂and H₂O.
• Any recovered H₂S (78) from the acid gas removal (and other processes such as 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.
• Any recovered CO₂(79) from the acid gas removal can be compressed for transport in CO₂pipelines, industrial use, and/or sequestration for storage or other processes such as enhanced oil recovery, and can also be used for other process operations (such as in certain aspects catalyst recovery and feed preparation).
• The resulting sweetened gas stream (80) is further processed as described below.
• Hydrogen Separation Unit (850)
• Hydrogen may be separated from the sweetened gas stream (80) according to methods known to those skilled in the art, such as cryogenic distillation, the use of molecular sieves, gas separation (e.g., ceramic) membranes, and/or pressure swing adsorption (PSA) techniques. See, for example, previously incorporated US2009/0259080A1.
• In one embodiment, a PSA device is utilized for hydrogen separation. PSA technology for separation of hydrogen from gas mixtures containing methane (and optionally carbon monoxide) is in general well-known to those of ordinary skill in the relevant art as disclosed, for example, in U.S. Pat. No. 6,379,645 (and other citations referenced therein). PSA devices are generally commercially available, for example, based on technologies available from Air Products and Chemicals Inc. (Allentown, Pa.), UOP LLC (Des Plaines, Ill.) and others.
• In another embodiment, a hydrogen membrane separator can be used followed by a PSA device.
• Such separation provides a high-purity hydrogen product stream (85) and a hydrogen-depleted sweetened gas stream (82).
• The recovered hydrogen product stream (85) preferably has a purity of at least about 99 mole %, or at least 99.5 mole %, or at least about 99.9 mole %.
• The hydrogen product stream (85) can be used, for example, as an energy source and/or as a reactant. For example, the hydrogen can be used as an energy source for hydrogen-based fuel cells, for power and/or steam generation and/or for a subsequent hydromethanation process. The hydrogen can also be used as a reactant in various hydrogenation processes, such as found in the chemical and petroleum refining industries.
• The hydrogen-depleted sweetened gas stream (82) will comprise substantially methane, with optional minor amounts of carbon monoxide (depending primarily on the extent of the sour shift reaction and bypass), carbon dioxide (depending primarily on the effectiveness of the acid gas removal process) and hydrogen (depending primarily on the extent and effectiveness of the hydrogen separation technology). The hydrogen-depleted sweetened gas stream (82) can be utilized can be further processed/utilized as described below.
• Methanation (950)
• All or a portion of sweetened gas stream (80), or hydrogen-depleted sweetened gas stream (82) if present, is fed to a trim methanator (950) to generate additional methane from the carbon monoxide and hydrogen that may be present in those streams, resulting in a methane-enriched product stream (97).
• If a hydrogen separation unit (850) is present, a portion of sweetened gas stream (80) may bypass hydrogen separation unit (850) via bypass line (86) to adjust the hydrogen content of hydrogen-depleted sweetened gas stream (82) to optimize the H₂/CO ratio for methanation.
• The methanation reaction can be carried out in any suitable reactor, e.g., a single-stage methanation reactor, a series of single-stage methanation reactors or a multistage reactor. Methanation reactors include, without limitation, fixed bed, moving bed or fluidized bed reactors. See, for instance, U.S. Pat. No. 3,958,957, U.S. Pat. No. 4,252,771, U.S. Pat. No. 3,996,014 and U.S. Pat. No. 4,235,044. Methanation reactors and catalysts are generally commercially available. The catalyst used in the methanation, and methanation conditions, are generally known to those of ordinary skill in the relevant art, and will depend, for example, on the temperature, pressure, flow rate and composition of the incoming gas stream.
• As the methanation reaction is highly exothermic, the methane-enriched product gas stream (97) is provided to a heat recovery unit, e.g., third heat exchanger unit (403) to remove a portion of the heat energy and generate the cooled methane product stream (99). While third heat exchanger unit (403) is depicted as a separate unit, it can exist as such and/or be integrated into methanator (950), thus being capable of cooling the methanator unit and removing at least a portion of the heat energy from the methane-enriched gas stream to reduce the temperature of the methane-enriched gas stream. The recovered heat energy can be utilized to generate a third process steam stream (43) from a water and/or steam source (39b). Although not depicted as such inFIG. 2, third heat exchanger unit (403) may comprise a superheating section followed by a boiler section such as previously described for second heat exchanger unit (401). Because of the highly exothermic nature of the methanation reaction, second process stream (43) can be generated as a highly-superheated steam suitable, for example, for driving a steam turbine.
• Cooled methane product stream (99) can be utilized as the final methane product stream, or it can be further processed, when necessary, 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 gas separation (e.g., ceramic) membranes. Additional gas purification methods include, for example, the generation of methane hydrate as disclosed in previously incorporated US2009/0260287A1, US2009/0259080A1 and US2009/0246120A1.
• Pipeline-Quality Natural Gas
• The invention provides processes and systems that, in certain embodiments, are capable of generating “pipeline-quality natural gas” (or “pipeline-quality substitute natural gas”) from the hydromethanation of non-gaseous carbonaceous materials. A “pipeline-quality natural gas” typically refers to a methane-containing stream that is (1) within ±5% of the heating value of pure methane (whose heating value is 1010 btu/ft³under standard atmospheric conditions), (2) substantially free of water (typically a dew point of about −40° C. or less), and (3) substantially free of toxic or corrosive contaminants. In some embodiments of the invention, the cooled methane product stream (99) described in the above processes satisfies such requirements.
Waste Water Treatment
• Residual contaminants in waste water resulting from any one or more of the trace contaminant removal, sour shift, ammonia removal, acid gas removal and/or catalyst recovery processes can be removed in a waste water treatment unit to allow recycling of the recovered water within the plant and/or disposal of the water from the plant process according to any methods known to those skilled in the art. Depending on the feedstock and reaction conditions, such residual contaminants can comprise, for example, aromatics, CO, CO₂, H₂S, COS, HCN, ammonia, and mercury. For example, H₂S and HCN can be removed by acidification of the waste water to a pH of about 3, treating the acidic waste water with an inert gas in a stripping column, and increasing the pH to about 10 and treating the waste water a second time with an inert gas to remove ammonia (see U.S. Pat. No. 5,236,557). H₂S can be removed by treating the waste water with an oxidant in the presence of residual coke particles to convert the H₂S to insoluble sulfates which may be removed by flotation or filtration (see U.S. Pat. No. 4,478,425). Aromatics can be removed by contacting the waste water with a carbonaceous char optionally containing mono- and divalent basic inorganic compounds (e.g., the solid char product or the depleted char after catalyst recovery, supra) and adjusting the pH (see U.S. Pat. No. 4,113,615). Aromatics can also be removed by extraction with an organic solvent followed by treatment of the waste water in a stripping column (see U.S. Pat. No. 3,972,693, U.S. Pat. No. 4,025,423 and U.S. Pat. No. 4,162,902).
Process Steam
• The process steam streams (e.g.,40 and43) resulting from heat energy recovery can be generated by contacting a water/steam source (such as (39a) and (39b)) with the heat energy recovered from the various process operations using one or more heat recovery units, such as first and third heat exchanger units (400) and (403).
• Any suitable heat recovery unit known in the art may be used. For example, a steam boiler or any other suitable steam generator (such as a shell/tube heat exchanger) that can utilize the recovered heat energy to generate steam can be used. The heat exchangers may also function as superheaters for steam streams, such as (401a) inFIG. 2, so that heat recovery through one of more stages of the process can be used to superheat the steam to a desired temperature and pressure, thus eliminating the need for separate fuel fired superheaters.
• While any water source can be used to generate steam, the water commonly used in known boiler systems is purified and deionized (about 0.3-1.0 μS/cm) so that corrosive processes are slowed.
• If needed, a suitable steam boiler or steam generator can be used to provide any make-up steam stream. 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 feedstock preparation operations (e.g., fines, supra). In one embodiment, such an additional steam boiler/generator may be present, but is not used in steady state operation of the process.
• In one embodiment, the process steam streams supply at least all of the total steam demand for the entire process, in which during steady state operation there is substantially no make-up steam stream.
• In another embodiment, an excess of process steam is generated. The excess steam can be used, for example, for power generation via a steam turbine, for driving an air separation unit via a steam turbine, and/or drying the carbonaceous feedstock in a fluid bed drier to a desired moisture content (as discussed below).
• Power Generation
• In accordance with the present invention, at least a portion of third process steam stream (43) is provided to a steam turbine (986) to generate electrical power (92). The steam stream (43a) exiting steam turbine (986) may be utilized elsewhere in the process, for example, may be recycled to third heat exchanger unit (403) as part of an integrated combined cycle operation.
• In addition, a portion of the cooled methane product stream (99) can be utilized for combustion and steam generation, as can a portion of any recovered hydrogen (85). As indicated above, excess recycle steam may be provided to one or more power generators, such as a combustion or steam turbine.
• Any produced electrical power can, for example, be utilized within the plant or can be sold onto the power grid.
Preparation of Carbonaceous Feedstocks
• Carbonaceous Materials Processing (100)
• Particulate carbonaceous materials, such as biomass and non-biomass, can be prepared via crushing and/or grinding, either separately or together, according to any methods known in the art, such as impact crushing and wet or dry grinding to yield one or more carbonaceous particulates. Depending on the method utilized for crushing and/or grinding of the carbonaceous material sources, the resulting carbonaceous particulates may be sized (i.e., separated according to size) to provide the carbonaceous feedstock (32) for use in catalyst loading processes (350) to form a catalyzed carbonaceous feedstock (31+32) for the hydromethanation reactor (200).
• Any method known to those skilled in the art can be used to size the particulates. For example, sizing can be performed 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 carbonaceous particulates. Classification equipment can include ore sorters, gas cyclones, hydrocyclones, rake classifiers, rotating trommels or fluidized classifiers. The carbonaceous materials can be also sized or classified prior to grinding and/or crushing.
• The carbonaceous particulate can be supplied as a fine particulate having an average particle size of from about 25 microns, or from about 45 microns, up to about 2500 microns, or up to about 500 microns. One skilled in the art can readily determine the appropriate particle size for the carbonaceous particulates. For example, when a fluidized bed reactor is used, such carbonaceous particulates can have an average particle size which enables incipient fluidization of the carbonaceous materials at the gas velocity used in the fluidized bed reactor. Desirable particle size ranges for the hydromethanation reactor (200) are in the Geldart A and Geldart B ranges (including overlap between the two), depending on fluidization conditions, typically with limited amounts of fine (below about 25 microns) and coarse (greater than about 250 microns) material.
• Additionally, certain carbonaceous materials, for example, corn stover and switchgrass, and industrial wastes, such as saw dust, either may not be amenable to crushing or grinding operations, or may not be suitable for use as such, for example due to ultra fine particle sizes. Such materials may be formed into pellets or briquettes of a suitable size for crushing or for direct use in, for example, a fluidized bed reactor. Generally, pellets can be prepared by compaction of one or more carbonaceous material; see for example, previously incorporated US2009/0218424A1. In other examples, a biomass material and a coal can be formed into briquettes as described in U.S. Pat. No. 4,249,471, U.S. Pat. No. 4,152,119 and U.S. Pat. No. 4,225,457. Such pellets or briquettes can be used interchangeably with the preceding carbonaceous particulates in the following discussions.
• Additional feedstock processing steps may be necessary depending on the qualities of carbonaceous material sources. Biomass may contain high moisture contents, such as green plants and grasses, and may require drying prior to crushing. Municipal wastes and sewages also may contain high moisture contents which may be reduced, for example, by use of a press or roll mill (e.g., U.S. Pat. No. 4,436,028). Likewise, non-biomass, such as high-moisture coal, can require drying prior to crushing. Some caking coals can require partial oxidation to simplify operation. Non-biomass feedstocks deficient in ion-exchange sites, such as anthracites or petroleum cokes, can be pre-treated to create additional ion-exchange sites to facilitate catalyst loading and/or association. Such pre-treatments can be accomplished by any method known to the art that creates ion-exchange capable sites and/or enhances the porosity of the feedstock (see, for example, previously incorporated U.S. Pat. No. 4,468,231 and GB1599932). Oxidative pre-treatment can be accomplished using any oxidant known to the art.
• The ratio and types of the carbonaceous materials in the carbonaceous particulates can be selected based on technical considerations, processing economics, availability, and proximity of the non-biomass and biomass sources. The availability and proximity of the sources for the carbonaceous materials can affect the price of the feeds, and thus the overall production costs of the catalytic gasification process. For example, the biomass and the non-biomass materials can be blended in at about 5:95, about 10:90, about 15:85, about 20:80, about 25:75, about 30:70, about 35:65, about 40:60, about 45:55, about 50:50, about 55:45, about 60:40, about 65:35, about 70:20, about 75:25, about 80:20, about 85:15, about 90:10, or about 95:5 by weight on a wet or dry basis, depending on the processing conditions.
• Significantly, the carbonaceous material sources, as well as the ratio of the individual components of the carbonaceous particulates, for example, a biomass particulate and a non-biomass particulate, can be used to control other material characteristics of the carbonaceous particulates. Non-biomass materials, such as coals, and certain biomass materials, such as rice hulls, typically include significant quantities of inorganic matter including calcium, alumina and silica which form inorganic oxides (i.e., ash) in the catalytic gasifier. At temperatures above about 500° C. to about 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 the hydromethanation reactor (200), a solid purge of by-product char (58) (and (58a)) comprising ash, unreacted carbonaceous material, and various other compounds (such as alkali metal compounds, both water soluble and water insoluble) is withdrawn and processed as discussed below.
• In preparing the carbonaceous particulates, the ash content of the various carbonaceous materials can be selected to be, for example, about 20 wt % or less, or about 15 wt % or less, or about 10 wt % or less, or about 5 wt % or less, depending on, for example, the ratio of the various carbonaceous materials and/or the starting ash in the various carbonaceous materials. In other embodiments, the resulting the carbonaceous particulates can comprise an ash content ranging from about 5 wt %, or from about 10 wt %, to about 20 wt %, or to about 15 wt %, based on the weight of the carbonaceous particulate. In other embodiments, the ash content of the carbonaceous particulate can comprise less than about 20 wt %, or less than about 15 wt %, or less than about 10 wt %, or less than about 8 wt %, or less than about 6 wt % alumina, based on the weight of the ash. In certain embodiments, the carbonaceous particulates can comprise an ash content of less than about 20 wt %, based on the weight of processed feedstock where the ash content of the carbonaceous particulate comprises less than about 20 wt % alumina, or less than about 15 wt % alumina, based on the weight of the ash.
• Such lower alumina values in the carbonaceous particulates allow for, ultimately, decreased losses of catalysts, and particularly alkali metal catalysts, in the hydromethanation portion of the process. As indicated above, alumina can react with alkali source to yield an insoluble char comprising, for example, an alkali aluminate or aluminosilicate. Such insoluble char can lead to decreased catalyst recovery (i.e., increased catalyst loss), and thus, require additional costs of make-up catalyst in the overall process.
• Additionally, the resulting carbonaceous particulates can have a significantly higher % carbon, and thus btu/lb value and methane product per unit weight of the carbonaceous particulate. In certain embodiments, the resulting carbonaceous particulates can have a carbon content ranging from about 75 wt %, or from about 80 wt %, or from about 85 wt %, or from about 90 wt %, up to about 95 wt %, based on the combined weight of the non-biomass and biomass.
• In one example, a non-biomass and/or biomass is wet ground and sized (e.g., to a particle size distribution of from about 25 to about 2500 μm) and then drained of its free water (i.e., dewatered) to a wet cake consistency. Examples of suitable methods for the wet grinding, sizing, and dewatering are known to those skilled in the art; for example, see previously incorporated U.S. Pat. No. 2009/0048476A1. The filter cakes of the non-biomass and/or biomass particulates formed by the wet grinding in accordance with one embodiment of the present disclosure can have a moisture content ranging from about 40% to about 60%, or from about 40% to about 55%, or below 50%. It will be appreciated by one of ordinary skill in the art that the moisture content of dewatered wet ground carbonaceous materials depends on the particular type of carbonaceous materials, the particle size distribution, and the particular dewatering equipment used. Such filter cakes can be thermally treated, as described herein, to produce one or more reduced moisture carbonaceous particulates.
• Each of the one or more carbonaceous particulates can have a unique composition, as described above. For example, two carbonaceous particulates can be utilized, where a first carbonaceous particulate comprises one or more biomass materials and the second carbonaceous particulate comprises one or more non-biomass materials. Alternatively, a single carbonaceous particulate comprising one or more carbonaceous materials utilized.
• Catalyst Loading for Hydromethanation (350)
• The hydromethanation catalyst is potentially active for catalyzing at least reactions (I), (II) and (III) described above. Such catalysts are in a general sense well known to those of ordinary skill in the relevant art and may include, for example, alkali metals, alkaline earth metals and transition metals, and compounds and complexes thereof. Typically, the hydromethanation catalyst comprises at least an alkali metal, such as disclosed in many of the previously incorporated references.
• For the hydromethanation reaction, the one or more carbonaceous particulates are typically further processed to associate at least one hydromethanation catalyst, typically comprising a source of at least one alkali metal, to generate a catalyzed carbonaceous feedstock (31+32). If a liquid carbonaceous material is used, the hydromethanation catalyst may for example be intimately mixed into the liquid carbonaceous material.
• The carbonaceous particulate provided for catalyst loading can be either treated to form a catalyzed carbonaceous feedstock (31+32) which is passed to the hydromethanation reactor (200), or split into one or more processing streams, where at least one of the processing streams is associated with a hydromethanation catalyst to form at least one catalyst-treated feedstock stream. The remaining processing streams can be, for example, treated to associate a second component therewith. Additionally, the catalyst-treated feedstock stream can be treated a second time to associate a second component therewith. The second component can be, for example, a second hydromethanation catalyst, a co-catalyst, or other additive.
• In one example, the primary hydromethanation catalyst (alkali metal compound) can be provided to the single carbonaceous particulate (e.g., a potassium and/or sodium source), followed by a separate treatment to provide one or more co-catalysts and additives (e.g., a calcium source) to the same single carbonaceous particulate to yield the catalyzed carbonaceous feedstock (31+32). For example, see previously incorporated US2009/0217590A1 and US2009/0217586A1.
• The hydromethanation catalyst and second component can also be provided as a mixture in a single treatment to the single second carbonaceous particulate to yield the catalyzed carbonaceous feedstock (31+32).
• When one or more carbonaceous particulates are provided for catalyst loading, then at least one of the carbonaceous particulates is associated with a hydromethanation catalyst to form at least one catalyst-treated feedstock stream. Further, any of the carbonaceous particulates can be split into one or more processing streams as detailed above for association of a second or further component therewith. The resulting streams can be blended in any combination to provide the catalyzed carbonaceous feedstock (31+32), provided at least one catalyst-treated feedstock stream is utilized to form the catalyzed feedstock stream.
• In one embodiment, at least one carbonaceous particulate is associated with a hydromethanation catalyst and optionally, a second component. In another embodiment, each carbonaceous particulate is associated with a hydromethanation catalyst and optionally, a second component.
• Any methods known to those skilled in the art can be used to associate one or more hydromethanation catalysts with any of the carbonaceous particulates and/or processing streams. Such methods include but are not limited to, admixing with a solid catalyst source and impregnating the catalyst onto the processed carbonaceous material. Several impregnation methods known to those skilled in the art can be employed to incorporate the hydromethanation 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 hydromethanation catalyst can be impregnated into one or more of the carbonaceous particulates and/or processing streams by slurrying with a solution (e.g., aqueous) of the catalyst in a loading tank. When slurried with a solution of the catalyst and/or co-catalyst, the resulting slurry can be dewatered to provide a catalyst-treated feedstock stream, again typically, as a wet cake. The catalyst solution can be prepared from any catalyst source in the present processes, including fresh or make-up catalyst and recycled catalyst or catalyst solution. Methods for dewatering the slurry to provide a wet cake of the catalyst-treated feedstock stream include filtration (gravity or vacuum), centrifugation, and a fluid press.
• In another embodiment, as disclosed in previously incorporated US2010/0168495A1, the carbonaceous particulates are combined with an aqueous catalyst solution to generate a substantially non-draining wet cake, then mixed under elevated temperature conditions and finally dried to an appropriate moisture level.
• One particular method suitable for combining a coal particulate and/or a processing stream comprising coal with a hydromethanation catalyst to provide a catalyst-treated feedstock stream is via ion exchange as described in previously incorporated US2009/0048476A1 and US2010/0168494A1. Catalyst loading by ion exchange mechanism can be maximized based on adsorption isotherms specifically developed for the coal, as discussed in the incorporated reference. Such loading provides a catalyst-treated feedstock stream 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 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 disclosed in the aforementioned incorporated references, and as can otherwise be readily determined by those of ordinary skill in the relevant art based on the characteristics of the starting coal.
• In another example, one of the carbonaceous particulates and/or processing streams can be treated with the hydromethanation catalyst and a second processing stream can be treated with a second component (see previously incorporated US2007/0000177A1).
• The carbonaceous particulates, processing streams, and/or catalyst-treated feedstock streams resulting from the preceding can be blended in any combination to provide the catalyzed second carbonaceous feedstock, provided at least one catalyst-treated feedstock stream is utilized to form the catalyzed carbonaceous feedstock (31+32). Ultimately, the catalyzed carbonaceous feedstock (31+32) is passed onto the hydromethanation reactor(s) (200).
• Generally, each catalyst loading unit comprises at least one loading tank to contact one or more of the carbonaceous particulates and/or processing streams with a solution comprising at least one hydromethanation catalyst, to form one or more catalyst-treated feedstock streams. Alternatively, the catalytic component may be blended as a solid particulate into one or more carbonaceous particulates and/or processing streams to form one or more catalyst-treated feedstock streams.
• Typically, when the hydromethanation catalyst is solely or substantially an alkali metal, it is present in the catalyzed carbonaceous feedstock in an amount sufficient to provide a ratio of alkali metal atoms to carbon atoms in the catalyzed carbonaceous feedstock ranging from about 0.01, or from about 0.02, or from about 0.03, or from about 0.04, to about 0.10, or to about 0.08, or to about 0.07, or to about 0.06.
• With some feedstocks, the alkali metal component may also be provided within the catalyzed carbonaceous feedstock to achieve an alkali metal content of from about 3 to about 10 times more than the combined ash content of the carbonaceous material in the catalyzed carbonaceous feedstock, 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 sodium carbonate, potassium carbonate, rubidium carbonate, lithium carbonate, cesium carbonate, sodium hydroxide, potassium hydroxide, rubidium hydroxide or cesium hydroxide, and particularly, potassium carbonate and/or potassium hydroxide.
• Optional co-catalysts or other catalyst additives may be utilized, such as those disclosed in the previously incorporated references.
• The one or more catalyst-treated feedstock streams that are combined to form the catalyzed carbonaceous feedstock typically comprise greater than about 50%, greater than about 70%, or greater than about 85%, or greater than about 90% of the total amount of the loaded catalyst associated with the catalyzed carbonaceous feedstock (31+32). The percentage of total loaded catalyst that is associated with the various catalyst-treated feedstock streams can be determined according to methods known to those skilled in the art.
• Separate carbonaceous particulates, catalyst-treated feedstock streams, and processing streams can be blended appropriately to control, for example, the total catalyst loading or other qualities of the catalyzed carbonaceous feedstock (31+32), as discussed previously. The appropriate ratios of the various stream that are combined will depend on the qualities of the carbonaceous materials comprising each as well as the desired properties of the catalyzed carbonaceous feedstock (31+32). For example, a biomass particulate stream and a catalyzed non-biomass particulate stream can be combined in such a ratio to yield a catalyzed carbonaceous feedstock (31+32) having a predetermined ash content, as discussed previously.
• Any of the preceding catalyst-treated feedstock streams, processing streams, and processed feedstock streams, 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 catalyzed carbonaceous feedstock (31+32) can be stored for future use or transferred to one or more feed operations for introduction into the hydromethanation reactor(s). The catalyzed carbonaceous 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.
• In one embodiment, the carbonaceous feedstock as fed to the hydromethanation reactor contains an elevated moisture content of from greater than 10 wt %, or about 12 wt % or greater, or about 15 wt % or greater, to about 25 wt % or less, or to about 20 wt % or less (based on the total weight of the carbonaceous feedstock), to the extent that the carbonaceous feedstock is substantially free-flowing (see previously incorporated US2012/0102837A1).
• The term “substantially free-flowing” as used herein means the carbonaceous feedstock particulates do not agglomerate under feed conditions due to moisture content. Desirably, the moisture content of the carbonaceous feedstock particulates is substantially internally contained so that there is minimal (or no) surface moisture.
• A suitable substantially free-flowing catalyzed carbonaceous feedstock (31+32) can be produced in accordance with the disclosures of previously incorporated US2010/0168494A1 and US2010/0168495A1, where the thermal treatment step (after catalyst application) referred to in those disclosures can be minimized (or even potentially eliminated).
• To the extent necessary, excess moisture can be removed from the catalyzed carbonaceous feedstock (31+32). For example, the catalyzed carbonaceous feedstock (31+32) may be dried with a fluid bed slurry drier (i.e., treatment with superheated steam to vaporize the liquid), or the solution thermally evaporated or removed under a vacuum, or under a flow of an inert gas, to provide a catalyzed carbonaceous feedstock having a the required residual moisture content.
• Catalyst Recovery (300)
• Reaction of the catalyzed carbonaceous feedstock (31+32) under the described conditions generally provides the fines-depleted methane-enriched raw product stream (52) and a solid char by-product (58) (and (58a)) from the hydromethanation reactor (200). Unless otherwise indicated, reference to solid char by-product (58) also includes reference to solid char by-product (58a) as well.
• The solid char by-product (58) typically comprises quantities of unreacted carbon, inorganic ash and entrained catalyst. The solid char by-product (58) is removed from the hydromethanation reactor (200) for sampling, purging, and/or catalyst recovery via a char outlet.
• The term “entrained catalyst” as used herein means chemical compounds comprising the catalytically active portion of the hydromethanation catalyst, e.g., alkali metal compounds present in the char by-product. For example, “entrained catalyst” can include, but is not limited to, soluble alkali metal compounds (such as alkali metal carbonates, alkali metal hydroxides and alkali metal oxides) and/or insoluble alkali compounds (such as alkali metal aluminosilicates). The nature of catalyst components associated with the char extracted are discussed, for example, in previously incorporated US2007/0277437A1, US2009/0165383A1, US2009/0165382A1, US2009/0169449A1 and US2009/0169448A1.
• The solid char by-product is continuously or periodically withdrawn from the hydromethanation reactor (200) through a char outlet which can, for example, be a lock hopper system, although other methods are known to those skilled in the art. Methods for removing solid char product are well known to those skilled in the art. One such method taught by EP-A-0102828, for example, can be employed.
• The char by-product (58) from the hydromethanation reactor (200) may be passed to a catalytic recovery unit (300), as described below. Such char by-product (58) may also be split into multiple streams, one of which may be passed to a catalyst recovery unit (300), and another stream which may be used, for example, as a methanation catalyst (as described in previously incorporated US2010/0121125A1) and not treated for catalyst recovery.
• In certain embodiments, when the hydromethanation catalyst is an alkali metal, the alkali metal in the solid char by-product (58) can be recovered to produce a catalyst recycle stream (57), and any unrecovered catalyst can be compensated by a catalyst make-up stream (57) (see, for example, previously incorporated US2009/0165384A1). The more alumina plus silica that is in the feedstock, the more costly it is to obtain a higher alkali metal recovery.
• In one embodiment, the solid char by-product (58) from the hydromethanation reactor (200) can be quenched with a recycle gas and water to extract a portion of the entrained catalyst. The recovered catalyst (57) can be directed to the catalyst loading unit (350) for reuse of the alkali metal catalyst.
• Other particularly useful recovery and recycling processes are described in U.S. Pat. No. 4,459,138, as well as previously incorporated US2007/0277437A1 US2009/0165383A1, US2009/0165382A1, US2009/0169449A1 and US2009/0169448A1. Reference can be had to those documents for further process details.
• The recycle of catalyst can be to one or a combination of catalyst loading processes. For example, all of the recycled catalyst can be supplied to one catalyst loading process, while another process utilizes only makeup catalyst. The levels of recycled versus makeup catalyst can also be controlled on an individual basis among catalyst loading processes.
• The by-product char (58) can also be treated for recovery of other by-products, such as vanadium and/or nickel, in addition to catalyst recovery, as disclosed in previously incorporated US2011/0262323A1 and U.S. patent application Ser. No. 13/402,022.
• As indicated above, all or a portion of recovered fines stream (362) can be co-treated in catalyst recovery unit (300) along with by-product char (58).
• The result of treatment for catalyst and other by-product recovery is a “cleaned” depleted char (59), at least a portion of which can be provided to a carbon recovery unit (325) as discussed below.
• Carbon Recovery Unit (325)
• In one embodiment, at least a portion, or at least a predominant portion, or at least a substantial portion, or substantially all, of the depleted char (59) can be treated in a carbon recovery unit (325) to generate a carbon-enriched and inorganic ash-depleted stream (65) and a carbon-depleted and inorganic ash-enriched stream (66), as disclosed in previously incorporated U.S. patent application Ser. No. 13/450,995. At least a portion, or at least a predominant portion, or at least a substantial portion, or substantially all, of the carbon-enriched and inorganic ash-depleted stream (65) can be recycled back to feedstock preparation unit (100) for processing and ultimately feeding back to hydromethanation reactor (200) as part of carbonaceous feedstock (32).
• Because of the carbon content of depleted char (59), it can be treated by known coal beneficiation techniques to separate a higher carbon (lower ash) fraction from a lower carbon (higher ash) fraction. The particle size of the depleted char (59) will typically be similar to or smaller than the carbonaceous feedstock (32) as provided to hydromethanation reactor (200) (below 6 mm), and thus most suited for wet beneficiation and/or magnetic separation techniques. Such techniques and equipment suitable for use in connection therewith are generally known those of ordinary skill in the relevant art, and are readily available from many commercial sources. For example, techniques and equipment such as dense-medium cyclones, hydrocyclones, wet concentration tables, cone concentrators, spiral concentrators, centrifuges and froth flotation may be utilized.
• The resulting carbon-depleted and inorganic ash-enriched stream (66) will still retain some residual carbon content and can, for example, be combusted to power one or more steam generators (such as disclosed in previously incorporated US2009/0165376A1)), or used as such in a variety of applications, for example, as an absorbent (such as disclosed in previously incorporated US2009/0217582A1), or disposed of in an environmentally acceptable manner.
Multi-Train Processes
• In the processes of the invention, each process may be performed in one or more processing units. For example, one or more hydromethanation reactors may be supplied with the carbonaceous feedstock from one or more catalyst loading and/or feedstock preparation unit operations. Similarly, the methane-enriched raw product streams generated by one or more hydromethanation reactors may be processed or purified separately or via their combination at various downstream points depending on the particular system configuration, as discussed, for example, in previously incorporated US2009/0324458A1, US2009/0324459A1, US2009/0324460A1, US2009/0324461A1 and US2009/0324462A1.
• In certain embodiments, the processes utilize two or more hydromethanation reactors (e.g., 2-4 hydromethanation reactors). In such embodiments, the processes may contain divergent processing units (i.e., less than the total number of hydromethanation reactors) prior to the hydromethanation reactors for ultimately providing the catalyzed carbonaceous feedstock to the plurality of hydromethanation reactors, and/or convergent processing units (i.e., less than the total number of hydromethanation reactors) following the hydromethanation reactors for processing the plurality of methane-enriched raw product streams generated by the plurality of hydromethanation reactors.
• When the systems contain convergent processing units, each of the convergent processing units can be selected to have a capacity to accept greater than a 1/n portion of the total feed stream to the convergent processing units, where n is the number of convergent processing units. Similarly, when the systems contain divergent processing units, each of the divergent processing units can be selected to have a capacity to accept greater than a 1/m portion of the total feed stream supplying the convergent processing units, where m is the number of divergent processing units.
EXAMPLES OF SPECIFIC EMBODIMENTS
• A specific embodiment of the process is one in which the second pressure condition is at least about 25 psi (about 172 kPa), or at least 50 psi (about 345 kPa), or at least about 100 psi (about 690 kPa), and/or about 200 psi (about 1379 kPa) or less, greater than the first pressure condition.
• Another specific embodiment is one in which the pressure of first process steam stream (40) is at least about 5% or greater, or at least about 10% or greater, than the operating pressure of the hydromethanation reactor (200) (first pressure condition). In another specific embodiment, the pressure of first process steam stream (40) at the exit of first heat exchanger unit (400) (second pressure condition) is at least about 20% or less greater than the operating pressure of the hydromethanation reactor (200) (first pressure condition).
• Another specific embodiment is one in which the first pressure condition is about 400 psig (about 2860 kPa) or greater, or about 450 psig (about 3204 kPa) or greater; and/or about 1000 psig or less (about 6996 kPa), or about 900 psig (about 6307 kPa) or less, or about 600 psig (about 4238 kPa) or less.
• Another specific embodiment is one in which at least a portion of the superheated steam generated as a result of step (k) is, for example, used to drive an air separation unit (for example, for generating an oxygen-rich stream to be provided to the hydromethanation reactor). For example, the superheated steam can be supplied to a turbine (one or more) that mechanically drives a generator and an air separation unit.
• Another specific embodiment is on in which the steam demand of the hydromethanation reaction is at least satisfied by the steam stream.
• Another specific embodiment is one in which the steam stream comprises only steam from the dry saturated steam stream.

Claims (19)

1. A process for generating a cooled methane product stream and electrical power from a non-gaseous carbonaceous material, the process comprising the steps of:

(a) preparing a carbonaceous feedstock from the non-gaseous carbonaceous material;

(b) introducing the carbonaceous feedstock, a hydromethanation catalyst, a steam stream and an amount of oxygen into a hydromethanation reactor, wherein the hydromethanation reactor is operating at a first pressure condition;

(c) reacting a portion of the carbonaceous feedstock in the hydromethanation reactor with oxygen to generate carbon monoxide, hydrogen and heat energy;

(d) reacting a portion of the carbonaceous feedstock in the hydromethanation reactor in the presence of carbon monoxide, hydrogen, steam and hydromethanation catalyst to produce a methane-enriched raw product gas;

(e) withdrawing a methane-enriched raw product gas stream of the methane-enriched raw product gas from the hydromethanation reactor, wherein the methane-enriched raw product gas stream comprises methane, carbon monoxide, hydrogen, carbon dioxide, hydrogen sulfide, steam and heat energy;

(f) introducing the methane-enriched raw product stream into a first heat exchanger unit to recover heat energy and generate a cooled methane-enriched raw product stream and a dry saturated steam stream, wherein the dry saturated steam stream is at a second pressure condition that is higher than the first pressure condition;

(g) providing at least a portion of the dry saturated steam stream to the hydromethanation reactor under a reduced pressure condition such that the portion of dry saturated steam stream provided to the hydromethanation reactor is converted to a first superheated steam stream at or prior to introduction into the hydromethanation reactor, wherein the reduced pressure condition is higher than the first pressure condition but lower than the second pressure condition;

(h) steam shifting a portion of the carbon monoxide in the cooled methane-enriched raw product stream to generate a hydrogen-enriched raw product stream;

(i) removing a substantial portion of the carbon dioxide and a substantial portion of the hydrogen sulfide from the hydrogen-enriched raw product stream to produce a sweetened gas stream, wherein the sweetened gas stream comprises a substantial portion of the hydrogen, carbon monoxide and methane from the hydrogen-enriched raw product stream;

(j) methanating a substantial portion of the carbon monoxide in the sweetened gas stream with hydrogen in the sweetened gas stream to generate a methane-enriched treated product stream and heat energy;

(k) recovering a portion of the heat energy from step (j) to generate the cooled methane product stream;

(l) generating a second superheated steam stream from at least a portion of the heat energy recovered in step (k); and

(m) generating electrical power from at least a portion of the second superheated steam stream generated in step (l),

wherein

(1) the reaction of step (d) has a steam demand and a heat demand,

(2) the steam demand is substantially satisfied by the steam stream,

(3) the steam stream substantially comprises steam from the dry saturated steam stream, and

(4) the amount of oxygen introduced into the hydromethanation reactor is sufficient so that the heat demand of the reaction of step (d) is substantially satisfied by the reaction of step (c).

2. The process ofclaim 1, wherein the steam demand is at least satisfied by the steam stream.

3. The process ofclaim 1, wherein the steam stream comprises only steam from the dry saturated steam stream.

4. The process ofclaim 2, wherein the steam stream comprises only steam from the dry saturated steam stream.

5. The process ofclaim 1, wherein the second pressure condition is at least about 25 psi (about 172 kPa) greater than the first pressure condition.

6. The process ofclaim 5, wherein the second pressure condition is at least about 50 psi (about 345 kPa) greater than the first pressure condition.

7. The process ofclaim 6, wherein the second pressure condition is at least about 100 psi (about 690 kPa) greater than the first pressure condition.

8. The process ofclaim 7, wherein the second pressure condition is about 200 psi (about 1379 kPa) or less greater than the first pressure condition.

9. The process ofclaim 1, wherein the second pressure condition is at least about 5% greater than the first pressure condition.

10. The process ofclaim 9, wherein the second pressure condition is at least about 10% greater than the first pressure condition.

11. The process ofclaim 10, wherein the second pressure condition is about 20% or less greater than the first pressure condition.

12. The process ofclaim 1, wherein the first pressure condition is about 400 psig (about 2860 kPa) or greater.

13. The process ofclaim 12, wherein the first pressure condition is about 450 psig (about 3204 kPa) or greater.

14. The process ofclaim 1, wherein the first pressure condition is about 1000 psig or less (about 6996 kPa).

15. The process ofclaim 14, wherein the first pressure condition is about 900 psig (about 6307 kPa) or less.

16. The process ofclaim 15, wherein the first pressure condition is about 600 psig (about 4238 kPa) or less.

17. The process ofclaim 12, wherein the first pressure condition is about 1000 psig or less (about 6996 kPa).

18. The process ofclaim 17 wherein the second pressure condition is at least about 25 psi (about 172 kPa) greater than the first pressure condition.

19. The process ofclaim 17, wherein the second pressure condition is at least about 5% greater than the first pressure condition.

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