Method and system for oxygen transport membrane enhanced integrated gasifier combined cycle (IGCC)

Abstract

A system and method for oxygen transport membrane enhanced Integrated Gasifier Combined Cycle (IGCC) is provided. The oxygen transport membrane enhanced IGCC system is configured to generate electric power and optionally produce a fuel/liquid product from coal-derived synthesis gas or a mixture of coal-derived synthesis gas and natural gas derived synthesis gas.

Claims

1. An oxygen transport membrane based hydrogen-rich fuel gas production system comprising: a coal gasification subsystem configured to produce a coal-derived synthesis gas stream from a source of coal, steam and a first oxygen stream; an oxygen transport membrane based conversion subsystem configured to treat the coal-derived synthesis gas stream with at least a second oxygen stream to form a hydrogen-rich effluent stream, wherein said oxygen transport membrane-based conversion subsystem comprises an oxygen transport membrane reforming reactor comprising an oxygen transport membrane element having an oxidant side and a reactive side, the oxygen transport membrane element configured to transport oxygen ions at an elevated operational temperature where there is a difference in partial pressure of oxygen across the membrane element; a source of low pressure feed air in fluid communication with the oxidant side of the oxygen transport membrane element; a source of coal-derived synthesis gas in fluid communication with the reactive side of the oxygen transport membrane element; optionally a source of natural gas and steam in fluid communication with the reactive side of the oxygen transport membrane element; and a reforming catalyst disposed at or proximate to the reactive side of the oxygen transport membrane element; wherein oxygen from the feed air permeates through the oxygen transport membrane element and reacts with a portion of the coal-derived synthesis gas at the reactant side of the oxygen transport membrane element to produce reaction products and heat; wherein the oxygen transport membrane based reforming reactor assembly is further configured to reform unconverted hydrocarbons in the coal-derived synthesis gas and/or said optional natural gas in the presence of the steam, a portion of the heat and the catalyst to produce a hydrogen-rich effluent stream; a gas conditioning subsystem configured to treat the hydrogen-rich effluent stream to produce the hydrogen-rich fuel gas; wherein the first oxygen stream is provided by separation of oxygen from air at cryogenic temperatures and the second oxygen stream is provided by separation of oxygen from air at elevated temperatures within the oxygen transport membrane based conversion subsystem; and wherein the mass of the second oxygen stream divided by the total mass of the first and second oxygen streams is in the range of 0.1 to 0.7.

2. The system of claim 1 wherein the hydrogen-rich fuel gas is provided as a fuel to a gas turbine to generate electricity.

3. The system of claim 1 wherein the hydrogen-rich fuel gas is divided into at least a first portion and a second portion, the first portion provided to a gas turbine to generate electricity, and the second portion provided as a source of hydrogen in other industrial applications.

4. The system of claim 1 wherein the gas conditioning subsystem produces a carbon dioxide rich stream and the hydrogen-rich fuel gas.

5. The system of claim 2 wherein a nitrogen rich stream formed while separating oxygen from air at cryogenic temperature is provided to the gas turbine as a diluent.

6. The system of claim 5 wherein the coal-derived synthesis gas stream contains at least 5.0 volume % hydrocarbons and the hydrogen-rich synthesis gas stream contains less than about 2.0 volume % hydrocarbons.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other aspects, features, and advantages of the present invention will be more apparent from the following, more detailed description thereof, presented in conjunction with the following drawings, in which:

(2) FIG. 1 shows a schematic illustration of a prior art advanced power cycle with carbon capture for producing electric power from a coal-derived synthesis gas using an oxygen transport membrane based boiler;

(3) FIG. 2 shows a schematic illustration of a prior art advanced power cycle with carbon capture for producing electric power from a natural gas based oxygen transport membrane based reforming reactor and oxygen transport membrane based boiler;

(4) FIG. 3 shows a schematic illustration of a IGCC method and system with carbon capture for producing electric power from a coal-derived synthesis gas using an oxygen transport membrane based reforming reactor or converter in accordance with an embodiment of the invention;

(5) FIG. 4 shows an illustration of the oxygen transport membrane based reforming reactor or converter suitable for use with the embodiment of FIG. 3;

(6) FIG. 5 shows a schematic illustration of an oxygen transport membrane enhanced IGCC method and system with carbon capture for producing electric power from a mixture of a coal-derived synthesis gas and natural gas based synthesis gas produced from an oxygen transport membrane based reforming reactor or converter in accordance with another embodiment of the invention;

(7) FIG. 6 shows a schematic illustration of an oxygen transport membrane enhanced IGCC method and system with carbon capture for synthesizing a fuel/liquid product and producing electric power using a mixture of a coal-derived synthesis gas and natural gas based synthesis gas produced from an oxygen transport membrane based reforming reactor or converter in accordance with yet another embodiment of the invention;

(8) FIG. 7 shows an illustration of the oxygen transport membrane based reforming reactor or converter suitable for use with the embodiments of FIG. 5 and FIG. 6; and

(9) FIG. 8 shows an illustration of the oxygen transport membrane based reforming reactor or converter suitable for use with the embodiments of FIG. 5 and FIG. 6.

DETAILED DESCRIPTION

(10) Turning now to FIG. 3, there is shown a schematic illustration of one embodiment of the present oxygen transport membrane enhanced IGCC method and system that generates electric power from a coal-derived synthesis gas that is upgraded using an oxygen transport membrane based reforming reactor or converter. The oxygen transport membrane enhanced IGCC system comprises: (i) a coal gasification subsystem, preferably comprising an entrained flow coal gasifier, configured for generating a source of coal-derived synthesis gas; (ii) an oxygen transport membrane based subsystem containing an oxygen transport membrane based reforming reactor or converter configured for upgrading the quality of the coal-derived synthesis gas produced in the coal gasification subsystem; (iii) an air intake subsystem configured for supplying a heated air feed stream to the oxygen transport membrane based reforming reactor or converter; (iv) a synthesis gas conditioning subsystem that preferably includes a heat recovery train, a water-gas shift reactor, a synthesis gas separation and purification unit, and a carbon dioxide purification unit; and (v) a power generating subsystem.

(11) A key feature of the present system and method is the oxygen transport membrane based reforming reactor or converter. This converter is essentially an oxygen-blown secondary reformer, but it operates without a cryogenically produced oxygen supply. In this arrangement, the oxygen transport membrane based converter serves to further react the coal-derived synthesis gas at high temperatures effectively increasing the amount of carbon that is converted to carbon monoxide, and subsequently utilized to shift water vapor to hydrogen with resulting carbon dioxide available for capture. With this secondary conversion in the oxygen transport membrane enhanced IGCC system, the coal gasifier may be operated with reduced cryogenically produced oxygen input relative to the coal input.

(12) FIG. 4 depicts the preferred oxygen transport membrane based reforming reactor or converter configured to upgrade or convert the coal-derived synthesis gas produced in the coal gasification subsystem of FIG. 3. In this embodiment, the synthesis gas from the coal gasification subsystem is directed to the reactant side of the oxygen transport membrane reactor or converter after clean-up and desulfurization of the coal-derived synthesis gas. The oxygen transport membrane oxidizes a portion of the hydrogen and carbon monoxide with pure oxygen transported through the membrane to the reactant side releasing heat and producing some reaction products, namely H.sub.2O and carbon dioxide. In the presence of a suitable reforming catalyst and the heat generated by the oxidation process, residual methane present in the coal-derived synthesis gas converts to additional hydrogen and carbon monoxide while some H.sub.2O and carbon dioxide converts to hydrogen and carbon monoxide through steam-methane reforming, reverse water-gas shift, and dry-reforming reactions. Because of the high operating temperatures (e.g. 1000 C.) associated with the oxygen transport membrane the upgraded synthesis gas will equilibrate with a low methane slip (i.e. <1% by volume), and a higher content of carbon monoxide and hydrogen than the coal-derived synthesis gas fed to the oxygen transport membrane converter. As indicated above, oxygen transport membrane converter, integrated with a catalyst, operates much like an oxygen-blown secondary reformer; however, the source of oxygen is from a low-pressure air supply on the oxidant side of the membrane elements, and the heat for the reactions is provided by the oxidation of a portion of the hydrogen and carbon monoxide in the synthesis gas with pure oxygen transported through the membrane. In this mode, if there is an excess heat, it may be transferred via radiative heat transfer to a suitable load in the form of a process gas passing through adjacent heating tubes. The process gas can be a synthesis gas, steam, or any other suitable gas that requires preheating or reheating to a temperature in the 300 C. to 850 C. range.

(13) Turning now to FIG. 5, there is shown another embodiment of the present oxygen transport membrane enhanced IGCC method and system that generates electric power from a mixture of coal-derived synthesis gas and natural gas derived synthesis gas. The oxygen transport membrane enhanced IGCC system comprises: (i) a coal gasification subsystem, preferably comprising an entrained flow coal gasifier, configured for generating a source of coal-derived synthesis gas; (ii) a natural gas and steam combined feed subsystem adapted for providing a natural gas feed and steam feed to the oxygen transport membrane enhanced IGCC system; (iii) an oxygen transport membrane based subsystem configured for reforming the natural gas feed, mixing the natural gas derived synthesis gas with the coal-derived synthesis gas, and upgrading the mixed synthesis gas in an oxygen transport membrane based converter; (iv) an air intake subsystem configured for supplying a heated air feed stream to the oxygen transport membrane based reforming reactor or converter; (v) a synthesis gas conditioning subsystem that preferably includes a heat recovery train, a water-gas shift reactor, a synthesis gas separation and purification unit, and a carbon dioxide purification unit; and (vi) a power generating subsystem.

(14) FIG. 6 shows yet another embodiment of the present oxygen transport membrane enhanced IGCC method and system that is specifically configured or adapted to produce co-products including a fuel/liquid product, preferably in a Fischer-Tropsch synthesis process, and electric power from a mixture of coal-derived synthesis gas and natural gas derived synthesis gas. The oxygen transport membrane enhanced IGCC system shown in FIG. 6 comprises: (i) a coal gasification subsystem, preferably comprising an entrained flow coal gasifier, configured for generating a source of coal-derived synthesis gas; (ii) a natural gas and steam combined feed subsystem adapted for providing a natural gas feed and steam feed to the oxygen transport membrane enhanced IGCC system; (iii) an oxygen transport membrane based subsystem configured for reforming the natural gas feed, mixing the natural gas derived synthesis gas with the coal-derived synthesis gas, and upgrading the mixed synthesis gas in an oxygen transport membrane based converter; (iv) an air intake subsystem configured for supplying a heated air feed stream to the oxygen transport membrane based reforming reactor or converter; (v) a synthesis gas conditioning subsystem that preferably includes a heat recovery train, a water-gas shift reactor, a synthesis gas separation and purification unit, and a carbon dioxide purification unit; (vi) a power generating subsystem; and (vii) a liquid/fuel product synthesis subsystem.

(15) In the arrangements described with reference to FIG. 5 and FIG. 6, both coal and natural gas feedstocks may be used for increased efficiency and lower carbon dioxide emitting combined cycle plants within a framework of proven and available carbon dioxide capture technology. Additionally, for Fischer-Tropsch synthetic fuels or methanol synthesis, synthesis gas produced from coal is generally hydrogen deficient, and synthesis gas produced from natural gas is generally hydrogen rich. Blending the synthesis gas derived from both fuel sources allows for more flexibility and efficiency with respect to achieving the ideal synthesis gas characteristics to support downstream liquid product synthesis.

(16) FIG. 7 and FIG. 8 depict preferred arrangements or embodiments of the preferred oxygen transport membrane based reforming reactor or converter configured or adapted for use in the natural gas based oxygen transport membrane enhanced IGCC systems shown in FIG. 5 and FIG. 6. As with the earlier described embodiments, the coal-derived synthesis gas from the coal gasification subsystem is directed to the reactant side of the oxygen transport membrane based reforming reactor or converter after clean-up and desulfurization of the coal-derived synthesis gas. The combined feed stream comprising natural gas and steam, on the other hand, is directed to either a reforming tube (FIG. 7) or to the reactant side of the oxygen transport membrane based reforming reactor (FIG. 8) where it is mixed with the cleaned and desulfurized synthesis gas from the coal gasification subsystem.

(17) Within the oxygen transport membrane based reforming reactor or converter shown in FIG. 7, a portion of the hydrogen and carbon monoxide in the mixed synthesis gas is oxidized with pure oxygen transported through the membrane to the reactant side releasing heat and producing some reaction products, namely H.sub.2O and carbon dioxide. In the presence of a suitable reforming catalyst disposed within the oxygen transport membrane reforming tube and the heat generated by the oxidation reaction, the residual methane present in the mixed synthesis gas stream is converted to additional hydrogen and carbon monoxide while some H.sub.2O and carbon dioxide converts to hydrogen and carbon monoxide through steam-methane reforming, reverse water-gas shift, and dry-reforming reactions.

(18) In the embodiment of FIG. 7, process tubes are loaded with a reforming catalyst and are configured to convert or reform the natural gas with steam in the presence of radiant heat provided from the oxygen transport membrane elements or tubes. Since these reforming tubes operate at lower temperatures (i.e. 750 C. to 900 C.) than the oxygen transport membrane elements or tubes, the natural gas-derived synthesis gas produced in the reforming tubes will contain a significant amount of methane slip. This natural gas derived synthesis gas is combined with the coal-derived synthesis gas and this mixed synthesis gas stream is upgraded or converted using the oxygen transport membrane based reactor or converter, as generally described above with reference to FIG. 4. In this arrangement, the coal and cryogenically produced oxygen input to the cycle is further reduced compared to the coal-only embodiment of FIG. 3, while obtaining the same amount of hydrogen fuel to be supplied to the gas turbines, and with lower amounts of carbon dioxide produced for capture.

(19) In the embodiment of FIG. 8, a portion of the hydrogen and carbon monoxide in the coal-derived synthesis gas is oxidized with pure oxygen transported through the membrane to the reactant side also releasing heat and producing some reaction products. In the presence of a suitable reforming catalyst disposed within the oxygen transport membrane reforming tube and the heat generated by the oxidation reaction, the residual methane present in the coal-derived synthesis gas stream and the methane in the natural gas based combined feed stream are converted to hydrogen and carbon monoxide through various reactions including steam-methane reforming. The embodiment of FIG. 8 simulates a near autothermal reforming type operation and would require sufficient catalyst activity such that the coal-derived synthesis gas, together with the natural gas and steam feed may be converted within the oxygen transport membrane reforming tube in a once-through arrangement. In this arrangement, where Fischer-Tropsch synthesis is to be supported, the hydrogen post shift and acid gas removal or separation can be combined with the pre-shift synthesis gas to achieve the desired H.sub.2/CO ratio of about 2.0. As the natural gas input is increased, progressively less hydrogen is required to be separated and blended back to the synthesis gas to support Fischer-Tropsch liquids synthesis. This results in still more carbon and hydrogen from the feedstock available for conversion to liquid product, and less hydrogen liberated for power recovery, and less carbon dioxide produced for capture.

(20) The coal-derived synthesis gas when reacted in the oxygen transport membrane based converter or secondary reformer can be utilized in the same mode as traditional IGCC system configurations with or without carbon capture and sequestration (CCS). The further addition of a primary reformer using natural gas and steam upstream of the oxygen transport membrane based converter or secondary reformer, would enable the production of a mixed synthesis gas with higher H.sub.2/CO ratio that can be produced for: (i) use solely in the enhanced IGCC power generation process with or without CCS; (ii) use solely in a Fischer-Tropsch liquids synthesis process; or (iii) an IGCC power generation (with or without CCS) and with a Fischer-Tropsch liquids co-product; or (iv) an IGCC power generation (with or without CCS) and with a Fischer-Tropsch liquids off-peak product.

(21) Elements of each of the above-described subsystems shown in FIG. 3, FIG. 5 and FIG. 6 together with operational aspects of each subsystem are disclosed in detail below.

(22) Coal Gasifier Subsystem

(23) Various embodiments of the present inventions contemplate the use of a conventional coal gasification subsystem as generally shown in FIGS. 3, 5 and 6. In a typical coal gasification subsystem, a pulverized coal feedstock is fed to a gasification unit along with steam and oxygen supplied from a cryogenic air separation unit. In the disclosed embodiments, the cryogenic air separation unit is preferably a commercially available low purity, low to intermediate pressure air separation unit, known to those persons skilled in the art cryogenic air separation plants, although more complex air separation units can be employed to meet other industrial gas requirements of the plant or facility.

(24) In practice, the coal gasification unit may comprise a single coal gasification reactor or a plurality of reactors connected in a series of stages which collectively achieve the desired coal gasification, that is, the formation of a coal-derived synthesis gas stream. Preferably, the coal gasification unit is an entrained flow, fixed bed, or fluidized bed coal gasifier. In the coal gasification process, the steam and oxygen injected into the coal beds result in the partial oxidation of the coal at temperatures between about 750 C. and 1500 C. and pressures of between about 300 psia and 1000 psia. At these high temperatures and pressurized conditions, the molecular bonds of coal and steam are broken down, releasing a raw synthesis gas stream that contains at least hydrogen and carbon monoxide and which also typically contains other substances such as carbon dioxide, water vapor, hydrocarbons, volatilized tars, particulate matter, and sulfides. The portions of the coal feedstock which are not transformed into raw synthesis gas may become a slag material that resembles glass, sulfur byproducts or ammonia. There is also some ash generally formed in the coal gasifier which is removed later in the gasification process. The tars, oils, phenols, ammonia and water co-products are preferably condensed from the raw synthesis gas stream and purified, as appropriate. The synthesis gas is then directed to a filter or cleaning area where further impurities are removed. The resulting coal-derived synthesis gas is typically at a temperature of between about 500 C. and 1000 C. and at a pressure of between about 300 psia and 1000 psia.

(25) For some of the embodiments presented in this invention, the preferred coal gasifier type may be the entrained flow gasifier. Operating pressures for entrained flow coal gasifiers (e.g. those made by General Electric, Conoco Phillips, Shell, Siemens, etc.) typically range from 300 to 1500 psig and more typically from 500 to 1100 psig. In this case, coal may be fed in dry particulate form or may be mixed with water and fed as a slurry to the gasifier.

(26) The coal-derived synthesis gas may require a pretreatment subsystem for H.sub.2S and COS control that is disposed downstream of the coal gasifier and upstream of the oxygen transport membrane based reforming reactor or converter. The preferred coal-derived synthesis gas pretreatment process is solvent-based (MDEA) sulfur removal process, although a warm gas cleanup process using a solid regenerable sorbent may alternatively be used.

(27) Natural Gas and Steam Combined Feed Subsystem

(28) As shown in FIG. 5 and FIG. 6, the natural gas feed stream to be reformed within the oxygen transport membrane enhanced IGCC system is typically preheated in one or more heat exchangers that serve as a natural gas feed preheaters. Also, since the natural gas typically contains unacceptably high level of sulfur species, the natural gas feed stream undergoes a sulfur removal process such as hydro-desulfurization (HDS). HDS is a catalytic chemical process widely used to remove sulfur from the natural gas feedstock. To facilitate the desulfurization, a small amount of hydrogen or hydrogen-rich gas is added to natural gas feed upstream of the heat exchangers. Further, since the natural gas based mixed feed stream generally contains some higher hydrocarbons that will break down at high temperatures to form unwanted carbon deposits that adversely impact the reforming process, the natural gas based mixed feed stream may optionally be pre-reformed in an adiabatic pre-reformer (not shown), which converts higher hydrocarbons present in the mixed feed stream to methane, hydrogen, carbon monoxide, and carbon dioxide. An alternative pre-reformer suitable for use with the present embodiments would be a heated pre-reformer that is thermally coupled with the oxygen transport membrane based reforming subsystem.

(29) Steam is then added to the heated and desulfurized natural gas feed stream. The steam is preferably superheated steam at a pressure between about 15 bar to 80 bar and a temperature between about 300 C. and 600 C. and may be generated in a fired heater using a source of process steam or diverted from other portions of the system. The superheated steam is preferably added to the natural gas feed stream upstream of any pre-reformer to adjust the steam to carbon ratio and final temperature of the combined natural gas based feed stream. If required, the combined natural gas based feed stream may be further preheated to get the combined feed stream to the desired temperature. The temperature of the combined natural gas based feed stream directed to the oxygen transport membrane based reforming reactor or converter is preferably between about 300 C. and 750 C., and more preferably between about 450 C. and 600 C. The steam to carbon ratio of the combined natural gas based feed stream is preferably between about 1.0 and 2.5, and more preferably between about 1.2 and 2.2.

(30) Air Preheat Subsystem

(31) With reference again to FIGS. 3, 5 and 6, the air supply and preheating subsystem includes a source of feed air or other oxygen containing feed stream; an air preheater for example a continuously rotating regenerative air preheater configured to heat the source of feed air; and conduits for supplying the heated feed air stream from the regenerative air preheater to the oxygen transport membrane based reforming reactor. The air supply and preheat subsystem further includes a plurality of return conduits configured to return the heated, oxygen depleted air stream from the oxygen transport membrane based reforming reactor to the regenerative air preheater to heat the source of feed air or other oxygen containing feed stream and subsequently exhaust the cooled oxygen depleted stream.

(32) The heated and oxygen depleted stream can optionally be introduced into a duct burner region within the return conduits which include one or more duct burners used to support combustion of a supplemental fuel stream to produce supplemental heat introduced into the continuously rotating regenerative air preheater and preheat the feed air stream. Alternatively, the duct burner may also be disposed directly in the air intake duct downstream of the heat exchanger to pre-heat the incoming feed air stream. The supplemental fuel stream can be a source of natural gas or the tail gas routed from elsewhere in the plant or a combination thereof. As described in more detail below, the preferred tail gas is typically associated with the product synthesis subsystem or hydrogen production subsystem.

(33) The heated feed air stream is directed to the oxidant-side of the oxygen transport membrane reactor, and more particularly to the oxidant-side of the oxygen transport membrane elements or tubes within the oxygen transport membrane based reforming reactor. As the heated feed air stream flows across the oxidant-side surfaces of the oxygen transport membrane elements or tubes, oxygen ions from the heated feed air stream permeate through the oxygen transport membrane elements or tubes to the reactant side of the oxygen transport membrane elements or tubes. The oxygen ions recombine at the permeate side of the oxygen transport membrane elements or tubes and react with a hydrogen containing stream at the permeate side to create the heat and a difference in oxygen partial pressure across the oxygen transport membrane element which drives the oxygen transport.

(34) As a result of the reactively driven oxygen ion transport across the membranes, the feed air stream becomes generally depleted of oxygen and heated by the convective heat transfer between the oxygen transport membrane elements or tubes and the passing air stream. At the high temperatures within the oxygen transport membrane based reforming reactor, approximately 70% or more of the oxygen within the feed air stream is transported or permeated across the oxygen transport membrane elements or tubes. The residual stream is thus a heated, oxygen-depleted stream that exits the oxygen transport membrane based reforming reactor and is used to preheat the incoming feed air stream, via a ceramic regenerative air preheater. The air supply and preheat subsystem may also include a blower or fan required to convey an oxygen containing feed stream through the regenerative air preheater and the downstream oxygen transport membrane reforming reactors or converters.

(35) Oxygen Transport Membrane Based Reforming Reactor/Converter

(36) A schematic illustration of the concept behind the first embodiment of the oxygen transport membrane based reforming reactor or converter is shown in FIG. 4. As seen in FIG. 4, the oxygen transport membrane assembly comprises an oxygen transport membrane based reforming tube where secondary reforming of the coal-derived synthesis gas occurs.

(37) The oxygen transport membrane based reforming tube has an oxidant side and a reactive side and is capable of conducting oxygen ions at an elevated operational temperature where there is a difference in partial pressure of oxygen across the membrane. The oxidant side of the oxygen transport membrane reforming tubes is preferably the exterior surface of the ceramic tubes exposed to the heated oxygen containing stream and the reactant side or permeate side is preferably the interior surface of the ceramic tubes. Within the oxygen transport membrane reforming tube is catalysts that facilitate partial oxidation and further reforming of the coal-derived synthesis gas.

(38) The coal-derived synthesis gas stream produced by the coal gasification subsystem generally contains hydrogen, carbon monoxide, unconverted carbon species, steam, carbon dioxide and other constituents and is directed to the reactive side of the oxygen transport membrane based reforming tube. A portion of the hydrogen and carbon monoxide within the coal-derived synthesis gas reacts with the permeated oxygen on the reactive side of the oxygen transport membrane based reforming tubes to produce heat, a portion of which is used in-situ to facilitate the conversion or further reforming of the coal-derived synthesis gas within the oxygen transport membrane based reforming tubes. In addition, a portion of the heat produced through the reaction of hydrogen with the permeated oxygen is transferred as radiant heat to adjacent process gas heating tubes.

(39) Disposed in an adjacent or juxtaposed orientation relative to the oxygen transport membrane based reforming tube is the process gas heating tube (i.e. steam/fluid tubes). Although FIG. 4 shows a single oxygen transport membrane based reforming tube and a single process gas heating tube, there would be many of such oxygen transport membrane based reforming tubes and process gas heating tubes in each assembly or subsystem. An example of such multi-tube assembly is generally described with reference to FIG. 19 and associated detailed description in U.S. provisional patent application Ser. No. 61/932,974, the entire disclosure of which is incorporated by reference herein.

(40) The close packing arrangement of oxygen transport membrane based reforming tubes and process gas heating tubes provides for efficient heat transfer, primarily through radiation. Such arrangement is configured to prevent overheating of the system or otherwise to manage the thermal load of the oxygen transport membrane based reforming reactors or converter. This close packing arrangement also provides advantages with respect to packing density, modularization, low cost manufacturing, shop-fab modules, and scalability of oxygen transport membrane based systems described in U.S. provisional patent application Ser. No. 61/932,974.

(41) A schematic illustration of the concept behind a second embodiment of the oxygen transport membrane based reforming reactor or converter is shown in FIG. 7. In this embodiment, the heated feed stream comprising natural gas and steam first passes through primary reforming tubes, which contain conventional reforming catalysts configured to reform the natural gas based feed stream. The temperature of the reformed synthesis gas leaving the primary reforming tubes is designed to be between 650 C. and 850 C. This reformed synthesis gas is then fed along with the coal-derived synthesis gas to the oxygen transport membrane reforming tubes that are also filled with a reforming catalyst. Oxygen from the heated intake or feed air permeates through the oxygen transport membrane tubes and reacts with a portion of the mixed synthesis gas at the reactant side of the tubes. A portion of the energy or heat generated by this reaction is used for in-situ secondary reforming of the mixed synthesis gas. The rest of the energy or heat is transferred by radiation to the primary reforming tubes to drive the primary reforming reactions and by convection to the oxygen-depleted retentate stream. The upgraded synthesis gas leaving the oxygen transport membrane reforming tubes is preferably at a temperature between about 900 C. and about 1050 C. In other words, the endothermic heating requirements of the reforming process occurring in the primary reforming tubes is supplied through radiation of some of the heat from the oxidation reaction occurring in oxygen transport membrane reforming tubes together with the convective heat transfer provided by heated, oxygen depleted retentate stream.

(42) The upgraded synthesis gas stream produced by the oxygen transport membrane based reforming reactor assembly or subsystem of FIG. 7 generally contains hydrogen, carbon monoxide, unconverted methane, steam, carbon dioxide and other constituents. A significant portion of the sensible heat from the upgraded synthesis gas stream can be recovered using a heat exchange section or recovery train that is designed to cool the upgraded synthesis gas stream while preheating boiler feed water as well as generating process steam. Optionally, a portion of the sensible heat may also be used to preheat the natural gas based feed stream. The resulting cooled and upgraded synthesis gas generally has a module of between about 1.7 and 1.95 and a H.sub.2/CO ratio of between about 2.5 and 4.0. This cooled and upgraded synthesis gas is suitable for use as a feed stream to the power generation subsystem and/or the Fischer-Tropsch synthesis section, described in more detail below.

(43) Another alternate embodiment of the oxygen transport membrane based reforming reactor assembly or subsystem is shown in FIG. 8. The embodiment shown in FIG. 8 employs the same natural gas and steam conditioning process described above with reference to FIG. 7. However, in this embodiment, the natural gas based mixed feed stream containing natural gas and steam is mixed with the coal derived synthesis gas either upstream of the oxygen transport membrane reforming reactor assembly or subsystem or as the streams enter the oxygen transport membrane reforming reactor. The combined or mixed feed stream is fed to a reactant side of a reactively driven and catalyst containing oxygen transport membrane based reforming reactor assembly, generally represented as the illustrated oxygen transport membrane tube.

(44) As with the earlier described embodiments, the reactively driven, oxygen transport membrane based reforming reactor or assembly includes one or more oxygen transport membrane tubes each having an oxidant side and a reactant side. Each of the oxygen transport membrane tubes are configured to separate oxygen from the heated feed air stream contacting the oxidant side and transport the separated oxygen to the reactant side through oxygen ion transport. The oxygen ion transport occurs when the oxygen transport membrane tubes are subjected to elevated operational temperatures and there is a difference in oxygen partial pressure across the oxygen transport membrane elements or tubes.

(45) A portion of the hydrogen and carbon monoxide within the combined feed stream immediately reacts with the permeated oxygen at the reactant side of the tubes to produce the difference in oxygen partial pressure across the oxygen transport membrane elements which drives the oxygen ion transport and separation. This oxidation reaction also produces reaction products and heat that is used to facilitate the in-situ reforming of the combined feed stream in the presence of the reforming catalysts within the oxygen transport membrane reforming reactor or assembly. Specifically, the oxygen transport membrane based reforming reactor is configured to reform the natural gas as well as further reform any unconverted hydrocarbons from the coal-derived synthesis gas in the presence of the reaction products and heat to produce a synthesis gas product stream. The synthesis gas product stream leaving the oxygen transport membrane based reforming reactor is preferably at a temperature between about 900 C. and 1050 C.

(46) Again, a significant portion of the sensible heat from the produced synthesis gas stream can be recovered using a heat exchange section or recovery train that is designed to cool the produced synthesis gas stream while preheating boiler feed water as well as generating process steam. Optionally, the sensible heat can be used to preheat the natural gas based feed stream. The resulting cooled oxygen transport membrane derived synthesis gas generally has a module of between about 1.95 and 2.2 and a H.sub.2/CO ratio of between about 2.7 and 4.0. This cooled oxygen transport membrane derived synthesis gas is suitable for use as a feed stream to the oxygen transport membrane based power subsystem and/or the synthesis section, described in more detail below.

(47) As indicated above, one of the key advantages of the present systems and methods is the ability to modularize and/or scale the oxygen transport membrane based reforming reactors. In all three above-described embodiments, the oxygen transport membrane based reforming reactors are preferably arranged as sets of closely packed reforming tubes in close proximity to one another and in close proximity to the process gas heating tubes or primary reforming tubes, as the case may be. Such arrangement is generally shown and described in U.S. provisional patent application Ser. No. 61/887,751; 61/932,974 and 61/888,327 which are incorporated by reference herein.

(48) Synthesis Gas Conditioning Subsystem

(49) Like many IGCC systems, the present oxygen transport membrane enhanced IGCC system and process may include a water-gas shift reactor to generate additional hydrogen and carbon dioxide via the Water Gas Shift reaction: CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2

(50) Since the Water Gas Shift reaction is exothermic, the shifted synthesis gas leaves the shift reactor at a temperature greater than the directly cooled synthesis gas, and preferably at a temperature of around 435 C. A portion of the sensible energy in this shifted stream is preferably recovered by preheating or reheating boiler feed water or by preheating the natural gas and hydrogen feed stream. Although not shown, a portion of the shifted synthesis stream may be recycled back to the oxygen transport membrane feed streams to adjust the H.sub.2/CO of the synthesis gas feed. The shifted synthesis gas is then directed to the acid gas removal (AGR) process to strip carbon dioxide from the shifted synthesis gas.

(51) The illustrated AGR process is the Selexol process commercially offered by UOP, LLC, a solvent generally comprising a mixture of the dimethyl ethers of polyethylene glycol dissolves or absorbs the acid gases such as carbon dioxide from the conditioned synthetic gas at relatively high pressure, usually about 300 psia to 1000 psia. The rich solvent containing the carbon dioxide gas is then stripped to release and recover the carbon dioxide gas. The stripped carbon dioxide gas is directed to a carbon purification unit (CPU) while the remaining hydrogen-rich gas effluent is directed to the IGCC power generation subsystem. The preferred Selexol process is preferred for the present oxygen transport membrane enhanced IGCC process as it provides good selectivity for carbon dioxide over hydrogen contained within the synthesis gas and minimizes the need for hydrogen purification.

(52) The CPU subsystem is configured to purify the carbon dioxide containing effluent stream and produce a purified carbon dioxide-rich stream suitable for carbon dioxide capture and storage/sequestration (CCS) processing or direct use in processes such as enhanced oil recovery. In the illustrated embodiment, the CPU subsystem first compresses the carbon dioxide-rich effluent stream to roughly 375 psia in a multi-stage compression train. The compressed carbon-dioxide-rich stream is dried in a carbon dioxide dryer which is adapted to remove excess moisture and water through a temperature swing adsorption process thereby preventing or reducing corrosion of the gas handling components. The CPU subsystem also is configured to remove undesirable impurities such as mercury and selected acids from the carbon dioxide-rich stream and may also include an auto-refrigerative process for inert removal. A typical auto-refrigerative process purifies the carbon dioxide stream to about 95% or greater purity with 97% recovery of carbon dioxide. This cryogenic based process also produces a vent stream which is enriched in atmospheric gases (e.g., N.sub.2, O.sub.2, Ar). The purified carbon dioxide-rich effluent stream is then further compressed to about 2000 psia.

(53) Power Generation Subsystem

(54) The illustrated IGCC type power generation subsystems shown in FIGS. 3, 5 and 6 provide an arrangement that supply electric power from both a hydrogen fueled gas turbine or hydrogen-rich gas fueled turbine and from steam turbine generators, as is known by those skilled in the art. An additional source of electric power is also generated in the oxygen transport membrane enhanced IGCC system as a result of the expansion of the coal-derived synthesis gas to the low to moderate pressures required by the oxygen transport membrane based reforming reactor or converter.

(55) In the illustrated embodiments, the produced synthesis gas is cooled, cleaned and conditioned into a hydrogen-rich gaseous fuel that is directed to a suitable gas turbine. Gas turbines available from manufacturers like GE and Siemens typically need only minor modifications to use a hydrogen-rich synthesis gas as the fuel while further changes or modifications may be required to the gas turbine where hydrogen fuel is the preferred choice of fuel. Most of the sensible heat in the hot gas turbine exhaust gas is recovered in the heat recovery steam generator (HRSG) where it produces steam that drives a steam turbine in a manner or arrangement well known to those persons skilled in the art.

(56) While the performance and overall efficiency of the synthesis gas fueled or hydrogen fueled gas turbine may be lower than comparable natural gas fueled gas turbines due to the low heating values of synthesis gas based fuels and associated temperature limitations in the synthesis gas fueled gas turbines, the environmental advantages of the IGCC powerplant are notable. Such advantages of the IGCC system or powerplant include the ability to capture and sequester carbon dioxide (i.e. CCS enabled). In addition, like other IGCC powerplants, the oxygen transport membrane enhanced IGCC system or powerplant produces very low levels of NOx, SO.sub.2, particulates, and volatile mercury as the emission-forming constituents from the synthesis gas are removed prior to combustion in the IGCC power generation subsystem.

(57) Liquid/Fuel Product Synthesis Section

(58) Turning back to FIG. 6, the present oxygen transport membrane enhanced IGCC system and associated methods contemplate the production or synthesis of selected liquid/fuel co-products such as Fischer-Tropsch synthetic fuels or hydrogen.

(59) Where the liquid/fuel product synthesis is a Fischer-Tropsch gas to liquid (GTL) synthesis process, the combined synthesis gas stream is synthesized into selected liquid hydrocarbon products in a Fischer-Tropsch catalyst based reactor (e.g. fixed bed reactor, slurry phase reactor, or synthol reactor) and subsequently purified into a final liquid hydrocarbon product in a manner generally known to those skilled in the art. The liquid hydrocarbon product generally produced by the Fischer-Tropsch gas to liquid (GTL) synthesis process heavily depends on temperature, catalyst, pressure and, more importantly, the synthesis gas composition.

(60) For example, at high temperature Fischer-Tropsch reactions (i.e. 330 C.-350 C.) the liquid hydrocarbon product predominantly comprises gasoline and light olefins whereas at low temperature Fischer-Tropsch reactions (i.e. 220 C.-250 C.) the liquid hydrocarbon product predominantly comprises distillates and waxes, with some gasoline. Catalysts used in many Fischer-Tropsch gas to liquid (GTL) synthesis processes include cobalt-based catalysts or iron-based catalysts. The synthesis gas composition, and in particular, the ratio of hydrogen to carbon monoxide (H.sub.2/CO ratio) is an important variable that affects the Fischer-Tropsch gas to liquid (GTL) synthesis process one that can be controlled by aspects and features of the present invention. For FT reactors using iron-based catalyst, the target H2/CO ratio is around 1:1. For FT reactors using cobalt-based catalyst, the preferred embodiment for this invention, the target H2/CO ratio is around 2:1. The FT synthesis section also generates a tail gas comprising unconverted CO & H2, H2O as well as light hydrocarbons such as methane and/or C2-C5 hydrocarbons. All or a portion of the FT tail gas may be recycled back to the oxygen transport membrane based reforming subsystem or can be used as a supplemental fuel source for the duct burner in the air intake subsystem.

(61) Where the desired liquid/fuel product is hydrogen, the mixed stream of synthesis gas can be processed to produce a hydrogen gas product via a hydrogen product swing adsorption (PSA) process or via hydrogen membrane separation, as generally known to those skilled in the art. For example, in the hydrogen PSA based process, the mixed synthesis gas stream is first subjected to a water gas shift reaction, subsequently cooled and directed to a hydrogen pressure swing adsorption (PSA) unit which produces a higher purity hydrogen stream while the carbon oxides, methane and other impurities are rejected as a tail gas. When integrated with the embodiments of the present systems and methods, the hydrogen PSA tail gas may be recycled to use with the duct burners or other sections associated with the oxygen transport membrane based reforming subsystem while a portion of the hydrogen gas may be diverted and mixed with the natural gas feed prior to desulfurization to produce the natural gas based feed stream. Similarly, where hydrogen membrane separation process is used, a portion of the hydrogen can be used to condition the feed streams or used as a supplemental fuel source in the oxygen transport membrane based reforming subsystem.

Comparative Examples

(62) In Tables 1 and 2, a Base Case analysis is provided in the designated column. The base case is a coal-only case, with the coal-derived synthesis gas obtained from a system generally described in the U.S. Department of Energy's Cost and Performance Baseline for Fossil Energy Plants.

(63) Table 1 compares the Base Case against a coal-only case of the present IGCC system with the oxygen transport membrane based reforming reactor or converter as shown and described with reference to FIG. 3 and FIG. 4, referred to in Table 1 as Case 2. In Case 2, the specific oxygen is reduced to the gasifier and the coal split is adjusted between the two stages. Due to the reduced temperature of the second stage in the gasifier, the methane slip increases significantly in this case. Through the addition of the oxygen transport membrane based reforming reactor of converter to the cycle, additional non-cryogenically produced oxygen is provided to the coal-derived synthesis gas stream and a significant portion of the methane slip is reacted in the secondary reforming step to liberate carbon monoxide and hydrogen which is convertible to power with carbon dioxide capture.

(64) When comparing the Base Case with the Case 2, the present IGCC system with the oxygen transport membrane based reforming reactor or converter provides the following benefits and advantages:

(65) For the same overall specific oxygen, roughly 90% is cryogenically produced and 10% is provided by through the oxygen transport membrane elements. Relative to a unit of hydrogen available to the gas turbines, the cryogenically produced oxygen is reduced by about 30% versus the Base Case. This results in a large reduction in parasitic power to operate the air separation unit (ASU), and more power available as useful plant output.

(66) The corresponding carbon (in the coal) conversion to carbon monoxide increases from about 60% in the Base Case to about 75% in the oxygen transport membrane based reforming reactor or converter case. This increase in carbon monoxide represents more opportunity for hydrogen fuel to the gas turbines, and less carbon dioxide or unreacted methane passing through to capture. In fact, the methane slip is reduced by over 90% from the reduced-oxygen gasifier synthesis gas and about 85% from the Base Case synthesis gas. In addition, there is an increase in synthesis gas CO/CO.sub.2 ratio of about 70%. With the increase in carbon conversion to carbon monoxide and the resultant increase in hydrogen available to the gas turbines per unit of carbon input, there is an overall 20% reduction of carbon dioxide produced by the powerplant with an oxygen transport membrane based converter.

(67) TABLE-US-00001 TABLE 1 Base Case Case 2 IGCC IGCC w/OTM Converter Gasifier Out Gasifier Out OTM Out % Heating Value from NG 0.0% 0.0% scf NG/lb Dry Coal 0.0 0.0 Pressure (bar abs) 43 43 43 O.sub.2/C Ratio 0.46 0.41 0.46 H.sub.2O/C Ratio 0.68 0.68 0.68 CO/CO.sub.2 Ratio 1.90 1.60 3.20 H.sub.2/CO Ratio 0.91 0.88 0.92 C to CO Conversion 60% 52% 75% H.sub.2 Fuel/Unit Carbon In 1.13 0.98 1.44 C Converted/Unit Carbon In 80% 75% 87% Cryo O.sub.2/Total O.sub.2 100% 90% 10% CO.sub.2/Unit H.sub.2 Fuel 0.41 0.42 0.21 CO.sub.2 Produced CO.sub.2/CO.sub.2 .sub.base 100% 116% 79% Fischer-Tropsch Adjustment 0.64 0.63 0.64 N.sub.2 (Vol %) 3.4 3.7 3.2 O.sub.2 (Vol %) 0.0 0.0 0.0 H.sub.2 (Vol %) 27.1 24.6 32.3 H.sub.2O (Vol %) 19.1 18.0 17.8 CO (Vol %) 30.0 27.9 35.1 CO.sub.2 (Vol %) 15.8 17.5 11.0 CH.sub.4 (Vol %) 4.6 8.2 0.7

(68) Table 2 compares the Base Case against the embodiment of the present oxygen transport membrane enhanced IGCC system using coal and natural gas with the oxygen transport membrane based reforming reactor or converter as shown and described with reference to FIG. 5, referred to in Table 2 as Case 3. In Case 3, natural gas is supplied such that it comprises approximately 50% of the fuel heating value to the IGCC oxygen transport membrane enhanced plant. Table 2 also compares the Base Case to the oxygen transport membrane enhanced IGCC system configured to support co-product generation, and in particular Fischer-Tropsch synthesis, shown and described with reference to FIG. 6, and is referred to as Case 4.

(69) The oxygen transport membrane enhanced IGCC system with both coal and natural gas feeds and the oxygen transport membrane based reforming reactor provides significant advantages when compared to the Base Case. For example, the methane slip in both Case 3 and Case 4 is reduced by over 90% from the methane slip in the Case 2 synthesis gas, and about 85% from the methane slip in the Base Case synthesis gas. With respect to specific oxygen input for Case 3, about 50% of the oxygen is cryogenically-derived while about 50% is provided by through oxygen transport membranes. Relative to a unit of hydrogen available to the gas turbines, the cryogenically produced oxygen is reduced by 65% versus the base case. This results in a large reduction in parasitic power to operate the ASU, and more power available as useful plant output. In addition, the capacity of the ASU can be dramatically reduced which results in a capital cost savings compared to the Base Case.

(70) Also, the hydrogen available as a fuel to the gas turbine relative to a unit of carbon input increases from about 1.13 in the Base Case to about 1.86 in Case 3. This represents an increase of 43% over the Base Case and 30% increase over Case 2. This hydrogen fuel increase represents a progressively lower carbon input required for the same required power for the plant. Put another way, there is roughly a 40% reduction in carbon dioxide produced for Case 3 versus the Base Case.

(71) In Case 4, when the upgraded or combined synthesis gas is specifically adapted to achieve the desired characteristics to support Fischer-Tropsch synthesis, there is a slight loss of efficiency. In the Base Case, only 64% of the synthesis gas produced can be adjusted to achieve the desired ratio. The remaining 36% is preferably used to provide the hydrogen input for the ratio adjustment. For Case 2 (See Table 1) this efficiency does not improve because it is restricted to the inherent hydrogen-to-carbon ratio of the fuel and H.sub.2O/carbon ratio of the conversion.

(72) However, with the addition of natural gas (e.g. about 50% by heating value) as suggested in Case 3, the efficiency for downstream Fischer-Tropsch synthesis can be increased to about 87%. By further increasing the natural gas feed or input to approximately 70% by heating value as suggested by Case 4, no hydrogen adjustment is required, and 100% of the produced synthesis gas may be used for Fischer-Tropsch synthesis.

(73) TABLE-US-00002 TABLE 2 Base Case 3 Case 4 Case IGCC IGCC IGCC w/Natural Gas w/Natural Gas Gasifier Gasifier Gasifier Out Out OTM Out Out OTM Out % HeatingValue 0.0% 49.9% 70.6% from NG scf NG/lb Dry Coal 0.0 13.6 32.8 Pressure (bar abs) 43 43 30 43 30 O.sub.2/C Ratio 0.46 0.41 0.51 0.41 0.54 H.sub.2O/C Ratio 0.68 0.68 0.99 0.68 1.17 CO/CO.sub.2 Ratio 1.90 1.60 2.65 1.60 2.50 H.sub.2/CO Ratio 0.91 0.88 1.60 0.88 2.00 C to CO Conversion 60% 52% 71% 52% 70% H.sub.2 Fuel/Unit 1.13 0.98 1.86 0.98 2.10 Carbon In C Converted/Unit 80% 75% 87% 75% 87% Carbon In Cryo O.sub.2/Total O.sub.2 100% 50% 50% 31% 69% CO.sub.2/Unit H.sub.2 Fuel 0.41 0.42 0.14 0.42 0.08 CO.sub.2 Produced 100% 116% 61% 116% 54% (vs Base) FT Adjustment 0.64 0.63 0.87 0.63 1.00 N.sub.2 (Vol %) 3.4 3.7 1.6 3.7 1.1 O.sub.2 (Vol %) 0.0 0.0 0.0 0.0 0.0 H.sub.2 (Vol %) 27.1 24.6 38.8 24.6 40.9 H.sub.2O (Vol %) 19.1 18.0 25.7 18.0 28.8 CO (Vol %) 30.0 27.9 24.2 27.9 20.5 CO.sub.2 (Vol %) 15.8 17.5 9.1 17.5 8.2 CH.sub.4 (Vol %) 4.6 8.2 0.6 8.2 0.5

(74) While the inventions herein disclosed have been described by means of specific embodiments and processes associated therewith, numerous modifications and variations can be made thereto by those skilled in the art without departing from the scope of the invention as set forth in the appended claims or sacrificing all of its features and advantages.