WO2008123968A1 - Solid oxide fuel cell system with internal reformation - Google Patents

Solid oxide fuel cell system with internal reformation Download PDF

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Publication number
WO2008123968A1
WO2008123968A1 PCT/US2008/004216 US2008004216W WO2008123968A1 WO 2008123968 A1 WO2008123968 A1 WO 2008123968A1 US 2008004216 W US2008004216 W US 2008004216W WO 2008123968 A1 WO2008123968 A1 WO 2008123968A1
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WIPO (PCT)
Prior art keywords
fuel cell
insert
fuel
cell system
interconnect plate
Prior art date
Application number
PCT/US2008/004216
Other languages
French (fr)
Inventor
Deepak Bose
Emad El Batawi
Stephen Couse
Darren Hickey
James Mcelroy
Original Assignee
Bloom Energy Corporation
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Filing date
Publication date
Application filed by Bloom Energy Corporation filed Critical Bloom Energy Corporation
Publication of WO2008123968A1 publication Critical patent/WO2008123968A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
    • H01M8/0606—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants
    • H01M8/0612—Combination of fuel cells with means for production of reactants or for treatment of residues with means for production of gaseous reactants from carbon-containing material
    • H01M8/0637—Direct internal reforming at the anode of the fuel cell
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C01B3/38—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using catalysts
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04007—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
    • H01M8/04014—Heat exchange using gaseous fluids; Heat exchange by combustion of reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
    • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
    • H01M8/04097—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with recycling of the reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/06—Combination of fuel cells with means for production of reactants or for treatment of residues
    • H01M8/0662—Treatment of gaseous reactants or gaseous residues, e.g. cleaning
    • H01M8/0668—Removal of carbon monoxide or carbon dioxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0233—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a steam reforming step
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0415—Purification by absorption in liquids
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/042—Purification by adsorption on solids
    • C01B2203/043—Regenerative adsorption process in two or more beds, one for adsorption, the other for regeneration
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0435—Catalytic purification
    • C01B2203/0445—Selective methanation
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0465—Composition of the impurity
    • C01B2203/047—Composition of the impurity the impurity being carbon monoxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0465—Composition of the impurity
    • C01B2203/0475—Composition of the impurity the impurity being carbon dioxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0465—Composition of the impurity
    • C01B2203/0495—Composition of the impurity the impurity being water
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/06—Integration with other chemical processes
    • C01B2203/066—Integration with other chemical processes with fuel cells
    • C01B2203/067—Integration with other chemical processes with fuel cells the reforming process taking place in the fuel cell
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/10—Catalysts for performing the hydrogen forming reactions
    • C01B2203/1005—Arrangement or shape of catalyst
    • C01B2203/1029—Catalysts in the form of a foam
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/10—Catalysts for performing the hydrogen forming reactions
    • C01B2203/1041—Composition of the catalyst
    • C01B2203/1047—Group VIII metal catalysts
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/10—Catalysts for performing the hydrogen forming reactions
    • C01B2203/1041—Composition of the catalyst
    • C01B2203/1047—Group VIII metal catalysts
    • C01B2203/1052—Nickel or cobalt catalysts
    • C01B2203/1058—Nickel catalysts
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/14—Details of the flowsheet
    • C01B2203/148—Details of the flowsheet involving a recycle stream to the feed of the process for making hydrogen or synthesis gas
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/12—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte
    • H01M2008/1293—Fuel cells with solid oxide electrolytes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the present invention generally relates to a solid oxide fuel cell system that conducts internal reformation.
  • Internal reformation is advantageous in that it provides a reduced operation cost and a simplified design for a fuel cell system.
  • External reformers add cost and design complexity to fuel cell systems, such as solid oxide fuel cell systems. While solid oxide fuel cells are capable of internally reforming hydrocarbon fuels, complete internal reformation poses several challenges, such as thermal management and faster electrode degradation.
  • Internal reformation on the anode of a fuel cell itself is disadvantageous because there is essentially no control over the amount of reformation, which can create a problem for thermal management of the fuel cell system. Furthermore, internal reformation on the anode may reduce the life of the anode, such as through Ni dusting.
  • a fuel cell system comprises a fuel cell, an interconnect plate, and an insert, wherein the insert is disposed between the interconnect plate and the fuel cell, wherein the fuel cell system is configured to provide a serpentine fuel gas inlet flow stream that flows first between the insert and the interconnect plate and then flows between the insert and an anode of the fuel cell, wherein the fuel cell system is configured so that the fuel gas flowing between the insert and the interconnect plate contacts a reforming catalyst.
  • a method of internally reforming a fuel gas within a fuel cell system comprising the steps of providing a fuel cell system which comprises a fuel cell, an interconnect plate, and an insert, wherein the insert is disposed between the interconnect plate and the fuel cell, flowing a hydrocarbon fuel inlet stream between the insert and the interconnect plate, reforming the fuel inlet stream flowing between a first side of the insert and the interconnect plate, and flowing the reformed fuel stream between a second side of the insert and an anode of the fuel cell.
  • a method of operating a fuel cell system comprises the steps of providing a fuel cell system, which comprises a fuel cell, an interconnect plate, and a porous insert, wherein the insert contains a reforming catalyst and the insert is disposed between the interconnect plate and the fuel cell, and flowing a fuel inlet stream into the insert, wherein the insert creates a pressure difference for the fuel inlet stream between one side of the insert and another side of the insert.
  • a fuel cell system comprises a fuel cell, an interconnect plate comprising a fuel gas inlet in a fuel inlet plenum, and a barrier configured to direct a flow of fuel gas from the fuel gas inlet toward a periphery of the plenum, and a reformer catalyst located in the plenum.
  • a method of operating a fuel cell system comprises the steps of providing a fuel cell, providing an interconnect plate comprising a fuel gas inlet in a fuel inlet plenum and a barrier configured to direct a flow of fuel gas from the fuel gas inlet toward a periphery of the plenum, providing a reformer catalyst located in the plenum, and flowing fuel gas through the fuel gas inlet and around the barrier.
  • a fuel cell system comprises a fuel cell stack containing internal reformation catalyst regions, a Sabatier reactor configured to receive anode exhaust from the fuel cell stack and to produce methane, and a carbon dioxide scrubber configured to remove excess carbon monoxide from methanated anode exhaust produced by the reactor and to recycle the methane back to the fuel cell stack.
  • a method of recirculating anode exhaust gas comprises providing anode exhaust stream from a fuel cell stack, reacting the anode exhaust stream to provide a methanated anode exhaust stream, scrubbing the methanated anode exhaust stream to remove excess carbon dioxide, after removing the excess carbon dioxide, providing the methanated anode exhaust stream into a fuel inlet stream, and internally reforming the fuel inlet stream in the fuel cell stack.
  • Figure 1 is an exploded view of a stack of fuel cell plates as viewed from above, according to a first embodiment.
  • Figure 2 is an exploded view of the stack of fuel cell plates of Figure 1 as viewed from below, according to a first embodiment.
  • Figure 3 is an exploded side view of a fuel cell stack, according to a second embodiment.
  • Figure 4a shows an exploded side view of an insert, according to an embodiment.
  • Figure 4b shows an exploded side view of an insert, according to an embodiment.
  • Figure 4c shows an exploded side view of an insert, according to an embodiment.
  • Figure 4d shows an exploded side view of an insert, according to an embodiment.
  • Figure 4e shows an exploded side view of an insert, according to an embodiment.
  • Figure 5 is a plan view of an interconnect plate, according to a third embodiment.
  • Figure 6 is an enlarged view of a central region of the interconnect plate of Figure 5.
  • Figure 7a shows a top view of an interconnect plate according to the third embodiment.
  • Figure 7b shows a top schematic view of a fuel cell according to the third embodiment.
  • Figure 7c shows a plan view of an interconnect plate, according to the third embodiment.
  • Figure 8 shows a plan view of an interconnect plate, according to a further arrangement of the third embodiment.
  • Figure 9 shows an enlarged view of an inlet region of the interconnect plate of Figure 8.
  • Figure 10a shows a top view of an interconnect plate 200 according to a further arrangement of the third embodiment.
  • Figure 10b shows a top schematic view of a fuel cell according to a further arrangement of the third embodiment.
  • Figure 10c shows a plan view of an interconnect plate, according to a further arrangement of the third embodiment.
  • Figure 11 shows a schematic of a fuel cell system, according to a fourth embodiment.
  • Figure 12 shows a schematic of a fuel cell system, according to a further arrangement of the fourth embodiment.
  • One non- limiting object of the embodiments described herein is to provide a fuel cell system and method that provide internal reformation while overcoming the disadvantages discussed above. While a solid oxide fuel cell (SOFC) system is preferred, other fuel cell types may also be used.
  • SOFC solid oxide fuel cell
  • FIG. 1 is an exploded view of a repeating unit of a fuel cell stack 10 as viewed from above, according to a first embodiment.
  • the fuel cell stack 10 can include a solid oxide fuel cell 20 that includes an anode 26 (as shown in the example of Figure 1), a cathode 28 (as shown in the example of Figure 2), and an electrolyte 27 disposed between the anode 26 and the cathode 28.
  • the fuel cell 20 can include a fuel inlet 22 and a fuel outlet 24, such as in the arrangement of openings or holes shown in the examples of Figures 1 and 2.
  • a seal 23 can be arranged around fuel inlet 22 to prevent fuel gas from the fuel inlet 22 from flowing over an anode side of the fuel cell 20.
  • the fuel cell stack 10 can further include a insert 30 and interconnect plates 40, as shown in the examples of Figures 1 and 2.
  • a insert 30 can include a reforming side 38 where internal reformation of fuel gas flowing between the insert 30 and an interconnect plate 40 occurs.
  • the reforming side 38 faces away from anode 26 and faces toward interconnect plate 40.
  • a reformer catalyst can be disposed on the reforming side 38 of insert 30, between the insert 30 and the interconnect plate 40, or by other methods known in the art.
  • the insert 30 can be made of a high temperature conductive foam, ribs or corrugation, plate, a conductive ceramic plate or a metal plate, such as a Cr-Fe alloy plate. If desired, the insert 30 may contain ribs or corrugation to provide a degree of flexibility that mitigates the effect of a coefficient of thermal expansion mismatch between the insert 30 and other components of the fuel cell stack 10.
  • the insert 30 can include a fuel inlet 32, a fuel passage 34 to the anode 26, and a fuel outlet 36, such as in the arrangement shown in the examples of Figures 1 and 2.
  • the fuel inlet 32 and fuel outlet 36 of the insert 30 can be designed to engage with an adjacent component(s) of the fuel cell stack 10 in a sealing manner.
  • the fuel inlet 32 can form a protrusion on a bottom side (non-reforming side) of the insert 30 that engages with the fuel cell 20 in an sealing manner.
  • the fuel outlet 36 can be designed to be raised and protrude from the top side (reforming side) of the insert 30, as shown in the example of Figure 1, so that the fuel outlet 36 engages with an interconnect plate 40 in a sealing manner.
  • the protrusions around the openings form fuel inlet and outlet riser channels for an internally manifolded fuel stack configuration.
  • the fuel inlet 32 can be configured to permit fuel gas to exit the fuel inlet 32 and flow across the reformer side 38 of the insert 30 to permit internal reformation of the fuel gas on the reformer side 38 of the insert.
  • the reformed fuel gas can then flow through the insert 30 via the fuel passage 34 to the other, non-reforming side of the insert 30.
  • the non-reforming side of the insert 30 can be disposed facing the anode 26 of the fuel cell 20 to permit the reformed fuel gas to undergo an oxidation reaction as the fuel gas passes between the insert 30 and the anode 26 before exiting through the fuel outlet 36 of the insert 30.
  • An interconnect plate 40 can be arranged adjacent to the cathode 28 of a fuel cell 20 so that an air side 46 of interconnect plate 40 faces the cathode 28 and a stream of air can flow between the interconnect plate 40 and the cathode 28, as indicated by arrow A in the examples of Figures 1 and 2. Furthermore, the interconnect plate 40 can be arranged adjacent to the insert 30 so that a fuel reformer side 48 of the interconnect plate 40 faces the insert 30 and a stream of fuel can flow between the interconnect plate 40 and the insert, as indicated by arrow FS in the example of Figure 2. According to a further embodiment, the interconnect plate 40 can be made of a chromium-iron alloy, a conductive ceramic, or other materials known in the art.
  • current produced by the electrochemical reactions of the fuel cell stack can be conducted by the insert 30.
  • portions of the insert 30 can be welded to the interconnect plate 40 to reduce adverse effects upon current collection due to the presence of the insert 30 in a fuel cell stack.
  • a fuel gas inlet stream is introduced into a fuel cell stack 10 in the direction indicated by arrow FI in the examples of Figures 1 and 2.
  • the fuel gas flows through the inlet fuel riser channel made up of fuel inlets 42, 22, 32 of an interconnect plate 40, fuel cell 20, and insert 30, respectively, and is permitted to flow across the reformer side 38 of the insert 30, which faces an interconnect plate 40.
  • the fuel gas undergoes a reforming reaction as the fuel gas flows along the reformer side 38 of the insert 30, as indicated by arrows FS in the examples of Figures 1 and 2.
  • the reformed fuel gas then flows through the fuel passage 34 to the anode 26 of the fuel cell 20.
  • the reformed fuel gas undergoes an electrochemical oxidation reaction at the anode 26, flows to the outlet 24 of the fuel cell 20, and then flows out of the fuel cell stack 10 through the outlet fuel riser channel made up of outlets 24, 44, 36 in the direction indicated by arrow FO in the examples of Figures 1 and 2.
  • internal reformation can occur in a space formed between the insert 30 and the interconnect plate 40.
  • the fuel cell stack 10 can be configured to internally reform fuel gas within channels formed between a insert 30 and an interconnect plate 40 where the reformation catalyst is coated on the side 48 of interconnect plate 40 instead of, or in addition to, being coated on side 38 of insert 30.
  • a depth of the channels formed by the insert 30 and the interconnect plates 40 can be varied in order to control the reformation process.
  • the type of catalyst used in the channels and the placement of the catalyst in the channels can be varied to control the reformation process.
  • the reforming catalyst can be spread over an entire area encompassed by channels between an insert 30 and an interconnect plate 40 or the reforming catalyst may be preferentially placed in predetermined areas of the channels located between ribs on side 38 of insert 30 and/or side 48 of interconnect plate 40.
  • a reformer catalyst such as, for example, nickel and rhodium or other catalysts known in the art can be used within the channels formed by the insert 30 and the interconnect plates 40.
  • internal steam reformation of hydrocarbon fuels can be conducted over the entire cell area of an insert, especially if side 38 of insert 30 is flat.
  • a design made according to features of the first embodiment described above provides maximum thermal contact between an internal reforming region and an electrochemical oxidation region.
  • the addition of the insert 30 advantageously permits enhanced control over the reformation process.
  • the insert 30 can provide enhanced control over the reformation process in terms of residence time, catalyst choice, and/or thermal management.
  • the stack may be internally manifolded for air and/or externally manifolded for fuel.
  • the stack may also be semi-internally manifolded for fuel (i.e. contain an inlet fuel riser channel but vent the fuel exhaust stream outside the stack boundary without using an outlet fuel riser channel) and/or contain more than one inlet and/or outlet riser channel.
  • a fuel cell system can be arranged that includes one or more fuel cell stacks 10 according any of the embodiments described above.
  • FIG. 3 is an exploded side view of a repeating unit of a fuel cell stack 110, according to a second embodiment.
  • a fuel cell stack 110 can include a fuel cell 120, which includes a solid oxide fuel electrolyte 122, a cathode 124, and an anode 126.
  • the fuel cell stack 1 10 can further include a reformation insert 130 for an interconnect plate 140.
  • the insert 130 can be arranged to receive a flow of fuel gas inlet stream in an inlet direction, as indicated by the arrow IN of the example of Figure 3.
  • the reformed fuel stream is provided in an outlet direction, as indicated by the arrow EX of the example of Figure 3.
  • the insert 130 can be inserted into a fuel cavity in an interconnect plate 140, or the insert 130 can be located in a space between the anode 126 and the interconnect plate 150.
  • the insert 130 can include a first portion 132 and a second portion 134, as shown in the example of Figure 3.
  • the first portion 132 of the insert 130 can include a reforming catalyst and the second portion 134 of the insert 130 can be made of a metallic foam or other porous metallic material.
  • the first portion 132 can be made of a reforming catalyst foam or other porous material, such as, for example, a nickel foam or stainless steel foam coated with catalyst.
  • the second portion 134 can be made of a nickel foam or a stainless steel foam.
  • the first portion 132 and the second portion 134 are electrically connected.
  • the anode 126 may further be electrically connected to the second portion 134 for current collection during operation of a fuel cell stack 110.
  • the first portion 132 of an insert can create a lower pressure drop than the second portion 134 of the insert.
  • the first portion 132 and the second portion 134 are made of a foam or other porous material, the first portion 132 can have a greater porosity than the second portion 134 in order to produce a pressure difference between the first portion 132 and the second portion 134.
  • the arrangement can cause fuel gas to flow from the first portion 132 to the second portion 134 in a phased fashion.
  • fuel gas flow can be distributed between the first portion 132 and the second portion 134 as indicated by arrows CF in Figure 3.
  • Such an insert 130 can provide an enhanced fuel gas flow distribution across an anode 126 of a fuel cell 120 in comparison to an insert that simply flows fuel gas from one side of the insert to another. Furthermore, a phased flow produced by a pressure difference within an insert 130 can limit excessive current densities that lead to anode starvation, thus improving fuel cell performance and life, which in turn reduces the maintenance cost for a fuel cell system.
  • the first portion 132 and the second portion 134 can have a triangular or wedge-shaped cross section. The first portion 132 and the second portion 134 can be arranged to face one another so a wedge surface of the first portion 132 and the second portion 134 face one another.
  • the second portion 134 can be arranged with a cross section in the shape of an upside-down triangle that faces the first portion 132.
  • the first portion 132 and second portion 134 each have a cross-section in the shape of right triangle, as shown in the example of Figure 3, the first portion 132 and second portion 134 can be arranged so that the hypotenuse of each right triangle faces one another.
  • the first portion 132 and second portion 134 can be arranged to be in contact with one another to form an interface between the first portion 132 and the second portion 134.
  • a fuel gas can be introduced into the first portion 132 of an insert 130 as indicated by arrow IN of Figure 3.
  • a portion of the fuel gas flows through the first portion 132 along the direction indicated by the arrow IN.
  • the reformed fuel passes by the anode 126, exits the insert 130 along the direction indicated by arrow EX in Figure 3, and flows from the first portion 132 to the second portion 134 in the direction indicated by arrows CF in Figure 3.
  • Such a fuel gas flow in the CF direction may be made in a phased manner due to a pressure difference between the first portion 132 and the second portion 134.
  • the phased fuel gas flow made be arranged to provide an even flow distribution of fuel gas across an anode 126 of a fuel cell 120.
  • an interface between the first portion 132 and the second portion 134 of an insert 130 can have a different shape or geometry than that shown in Figure 3.
  • the interface can be nonlinear, curved, horizontal, or any other shape providing a sufficient pressure difference between the first portion 132 and the second portion 134.
  • Figure 4a shows an exploded side view of an insert 130 that includes a strip 138, according to a further embodiment.
  • a strip 138 can be inserted between the first portion 132 and the second portion 134 of an insert to control the flow distribution of fuel gas between the first portion 132 and the second portion 134.
  • a strip 138 is not necessary if a pressure drop difference between the first portion 132 and the second portion 134 is sufficient to produced a desired flow distribution.
  • a strip 138 can be made from a material, such as a high temperature adhesive, that aids in the joining of the first portion 132 and the second portion 134, such as when the first portion 132 and the second portion 134 are made of different materials.
  • Figure 4b shows an exploded side view of an insert 130 that includes a seal 136 impermeable to fuel gas, according to a further embodiment.
  • a seal 136 may be deposited on the second portion 134 of an insert 130, as shown in the example of Figure 4b (i.e. the seal 13b is positioned on the outlet side of insert, which is positioned perpendicular to the anode 126), to cause a fuel gas to flow into the first portion 132 of the insert 130 in the direction indicated by arrow IN, to flow from the first portion to the second portion 134, and out of the second portion 134, as indicated by arrow EX in the example of Figure 4b.
  • a seal 136 can be used to force an entirety of a fuel gas flow to exit through a top side of an insert 130 where an anode 126 of a fuel cell 120 is located. Such an arrangement advantageously provides more fuel for the anode by forcing fuel gas to exit the insert 130.
  • Figure 4c shows an exploded side view of an insert 130 that includes a seal 136A deposited on an output side of first portion 132 of an insert 130 and a seal 136B deposited on an input side of the second portion 134 of an insert 130, according to a further embodiment.
  • the first portion 132 is arranged so that the cross-section of the first portion 132 forms an upside-down triangle or wedge, as shown in the example of Figure 4c. Therefore, a fuel inlet for the insert 130 is positioned at a distance away from the anode 126 beneath seal 136B so that gas may flow into the first portion 132.
  • Such an arrangement may be provided to control a flow of fuel gas flowing into the second portion 134 by affixing a seal 136B at an input side of the second portion 134 and to control a flow of fuel gas flowing out of the first portion by affixing a seal 136A at an output side of first portion 132.
  • Figure 4d shows an exploded side view of an insert 130, according to a further embodiment, that is similar to the insert 130 of Figure 4c but includes first and second portions 132, 134 having a horizontal interface rather than a sloped interface.
  • the first portion 132 may be constructed of a material with a higher porosity than a material that the second portion 134 is constructed of.
  • a fuel gas can be introduced in a direction indicated by arrow IN of Figure 4d, flow from the first portion 132 to the second portion 134 of an insert 130, and flow out of the insert 130 in a direction indicated by arrow EX of Figure 4d while providing fuel gas to an anode 126 of a fuel cell 120.
  • Figure 4e shows an exploded side view of an insert 131 that is made of a single piece of material, according to a further embodiment.
  • An insert 131 can be constructed of a foam or other porous material to create a pressure drop within the insert 131.
  • an insert 131 may be constructed to have a graded porosity that decreases from the top of the insert 131 to the bottom of the insert 131 in order to provide a sufficient pressure difference as described in the embodiments above.
  • an insert 131 may have a lower porosity in a top portion of the insert 131 than in a bottom portion of the insert 131.
  • an insert 131 may have a graded porosity that decreases from one side of the insert 131 to another in a direction along a fuel gas flow into the insert 131 , as indicated by the arrows IN and EX of Figure 4e.
  • the insert 131 can include two portions, with a first portion of higher porosity arranged on an inlet side of the insert 131 and a second portion of lower porosity arranged on an outlet side of the insert 131.
  • a catalyst of the insert 130, 131 can be changed and selected to suit a specified fuel, according to a further embodiment.
  • Such an arrangement advantageously permits an expensive interconnect plate to be used for different fuel cell stacks that use different fuels.
  • an interconnect plate may be expensive because it is made of a pressed powder that is suitable for use in a fuel cell stack.
  • an interconnect plate is generally an expensive component of a fuel cell stack, it makes economic sense to increase the functionality of an interconnect plate because this may only increase the cost of the interconnect plate by a relatively small percent.
  • reformation of a fuel gas can be conducted internally, the cost of a fuel cell system is reduced because there is no need for an external reformer or anodes capable of reforming fuel gas.
  • a design made according to features of the second embodiment described above provides improved thermal control of a fuel cell system and permits a more uniform current density by incorporating a reforming function and a phased fuel inlet distribution to an anode of a fuel cell. Furthermore, such a design can improve fuel cell performance and improve fuel cell life by reducing areas of high fuel utilization.
  • FIG. 5 is a plan view of an interconnect plate 200, according to a third embodiment.
  • An interconnect plate 200 can include an inlet fuel distribution plenum 202, outlet fuel distribution plenum(s) 204, a flow field 210 containing flow channels separated by ribs, barriers 220, a fuel inlet 230, and fuel outlet(s) 240, as shown in the example of Figure 5.
  • Plenums 202, 204 may comprise recesses in the interconnect plate 200 and the flow fields 210 may contain ribs 211 that can be configured to form raised areas in relation to a bottom surface of an interconnect plate 200, thus forming channels 212 for fuel gas flow between the ribs 21 1.
  • barriers 220 may comprise fins which extend roughly perpendicular to the channels 21 1.
  • the barriers 220 can be arranged in plenum 202 around a fuel inlet 230 to direct a flow of fuel gas toward the periphery of plenum 202.
  • Figure 6 is an enlarged view of a central region of the interconnect plate of Figure 5.
  • barriers 220 can be arranged to direct a flow of fuel gas from a fuel inlet 230, along a central portion of an interconnect plate 200 between the barriers 220, and around the ends of barriers 220 to the channels 212 located between ribs 211, as indicated by arrows FFl in the example of Figure 6.
  • FIG. 7a shows a top view of an interconnect plate 200 according to the third embodiment.
  • Figure 7b shows a top schematic view of a fuel cell 300 according to the third embodiment.
  • a fuel cell 300 can include a central region 302 that includes a reformer catalyst formed on the electrolyte 301 of the cell. The catalyst is used for reforming fuel gas that is provided from inlet 230 gas over the central region 302 in the plenum 202 between the fuel cell 300 and an interconnect plate 200.
  • a fuel cell 300 also includes anode regions 304 outside of a central region 302 for oxidizing reformed fuel gas in an electrochemical reaction.
  • a fuel cell 300 can further include outlets 310 for exhaust from the anode regions 304.
  • the ribs 212 in flow fields 210 contact anode regions 304 while central region 302 is located opposite to plenum 202 in the interconnect plate 200.
  • anode regions 304 of a fuel cell 300 are in electrical contact with an interconnect plate 200.
  • Figure 7c shows a plan view of an in-use interconnect plate 200, according to the third embodiment.
  • an interconnect plate 200 can be arranged so that a region of internal reformation 206 is produced in plenum 202 when fuel gas flows through the interconnect plate 200.
  • regions of high current density 208 can be produced when reformate gas produced by the reforming reaction in the region of internal reformation 206 passes into channels 211 in flow fields lying between the interconnect plate 200 and a fuel cell.
  • reformer catalyst can be arranged in plenum 202 around a fuel inlet 230 and barriers 220 of an interconnect plate.
  • reformer catalyst can be coated in central region 302 in the fuel cell that faces an interconnect plate 200, in the plenum 202 in the interconnect plate 200, or in both the fuel cell and the interconnect plate 200.
  • Such a reformer catalyst can be arranged in plenum 202 within the area between barriers 220, or the reformer catalyst can also be arranged in plenum 202 outside of the barriers 220 in an area surrounding the barriers 220.
  • a fuel gas flowing from a fuel inlet 230 through a plenum 202 between barriers 220 can be subjected to a reforming reaction, due to the presence of a reformer catalyst in the central region, before the gas enters channels 212 located between ribs 211 in flow fields 210.
  • Plenum 202 of interconnect plate 200 that contains the reformer catalyst can be configured to not to be in electrical contact with a fuel cell, such as an anode of a fuel cell.
  • a reformer catalyst can be arranged in channels 211 between ribs 211.
  • reformer catalyst can be provided in the anode, in the flow fields 210 in the interconnect plate 200, or in both the fuel cell and the interconnect plate 200.
  • a reforming catalyst used in plenum 202 can be the same reforming catalyst used in between ribs 211 or it can be different. For example, it can be advantageous to provide a different reforming catalyst in order to provide process flexibility for an interconnect plate of a fuel cell system.
  • a fuel gas flow can be introduced through a center of a fuel cell, which is likely the hottest region of the fuel cell and the most difficult to withdraw heat from. Furthermore, by providing barriers that direct a flow of the fuel gas through a central plenum region around a fuel inlet that contains a reformer catalyst, a residence time of the fuel gas can be advantageously maximized to ensure full reformation of the fuel gas. Without the barriers, fuel gas could directly enter channels between ribs of an interconnect plate, thus causing the fuel gas to quickly exit areas containing reformer catalyst. Furthermore, when a fuel cell system has high current densities and thus large flow rates, there may not be sufficient residence time in the central region to fully reform fuel gas without the use of barriers arranged around a fuel inlet.
  • Figure 8 shows a plan view of an interconnect plate 200, according to a further arrangement of the third embodiment.
  • a fuel inlet 232 is arranged at one end of an interconnect plate 200 and a fuel outlet 240 is arranged at an opposite end of an interconnect plate 200.
  • a barrier 222 can be arranged around a fuel inlet 232 to direct a flow of fuel gas into the plenum 202 between an interconnect plate 200 and a fuel cell that faces the interconnect plate.
  • Figure 9 shows an enlarged view of an inlet region of the interconnect plate of Figure 8.
  • an interconnect plate 200 can be arranged so that fuel gas flows out of fuel inlet 232 into plenum 202 and is directed by a barrier 222 along the inlet plenum 202 in a direction indicated by arrows FF2, so that fuel gas flows around the end of the barriers 222 to channels 212 located between ribs 211 in flow fields 210.
  • Figure 10a shows a top view of an interconnect plate 200 according to the arrangement of Figure 8.
  • Figure 10b shows a top schematic view of a fuel cell 300 according to the third embodiment.
  • the fuel cell 300 can include an inlet region 302 that includes a reformer catalyst for reforming fuel gas that flows in the central region 302 between the fuel cell 300 and an interconnect plate 200.
  • the fuel cell 300 can include an anode region 304 located outside of an inlet region 302 for oxidizing reformed fuel gas in an electrochemical reaction.
  • the fuel cell 300 can further include outlet 320 for fuel exhaust from the anode regions 304.
  • an anode region 304 of a fuel cell 300 can be in electrical contact with an interconnect plate 200 because the fuel cell 300 is in contact with the interconnect plate 200 with a fuel cell stack.
  • Figure 10c shows a plan view of an in-use interconnect plate 200, according to the arrangement of Figure 8.
  • an interconnect plate 200 can be arranged so that a region of internal reformation 206 is produced in plenum 202 when fuel gas flows along the face of the interconnect plate 200.
  • a region of high current density 208 can be produced when reformate gas produced by the reforming reaction in the region of internal reformation 206 passes into channels 211 lying between the interconnect plate 200 and the anode 304 of the fuel cell.
  • the reformer catalyst can be provided in plenum 202, in region 302, in channels 211, and/or in anode 304.
  • a reforming catalyst used in the region around a fuel inlet 230 can be the same reforming catalyst used in between ribs 211 or can be different. For example, it can be advantageous to provide a different reforming catalyst in order to provide process flexibility for an interconnect plate of a fuel cell system.
  • a residence time of the fuel gas can be advantageously maximized to ensure full reformation of the fuel gas.
  • fuel gas could directly enter channels between ribs of an interconnect plate, thus causing the fuel gas to quickly exit areas containing reformer catalyst.
  • a barrier arranged around a fuel inlet.
  • thermal management of the center of the stack may be difficult.
  • interconnect plates that are made from high thermal conductivity materials, such as, for example, chromium based alloys and other high thermal conductivity materials known in the art.
  • Such interconnect plates may be further designed with a thin cross-section, such as a few millimeters, to enhance conduction of heat.
  • additional heat can be provided to the stack, such as by, for example, radiation heat sources, other stacks positioned close to one another in a hot box, or convectively flowing exhaust air around stack surfaces that correspond to an internal reformation region.
  • a design made according to features of the third embodiment described above allows spatial separation of internal reformation and electrochemical regions over the area of a fuel cell, thus potentially allowing the use of different catalysts for an anode and for internal reformation. Furthermore, such a design allows internal reformation to occur in the core of a stack where the temperature would be the highest and heat rejection would be difficult. Therefore, such a design can provide enhanced thermal management of a core of a fuel cell stack.
  • An object of the following embodiment is to reduce the cooling duty of an internal reforming operation by diluting an anode stream with anode recycled gas.
  • an anode recycle loop can be used to produce methane.
  • an anode stream containing gas species and heat can be processed to produce methane with the following reactions: CO + 3H 2 -» CH 4 + H 2 O (1)
  • the methane produced by the above reactions can then be used to cool a fuel cell stack due to an endothermic internal reformation reaction within the fuel cell stack.
  • a nickel-alumina catalyst could be used within the fuel cell stack as a reformer catalyst. Therefore, an additional cooling duty would be provided for the stack, providing a more efficient use of fuel and permitting the use of higher power densities.
  • increasing the rate of methane reformation, for additional cooling duty with a simple recirculation of an anode stream causes the use of additional natural gas and the deterioration of fuel cell efficiency.
  • anode exhaust can be methanated to provide additional methane for internal reforming.
  • carbon dioxide in the anode/methanated recycle stream tends to choke the fuel cell system because of its displacement of fuel from the input stream to the fuel cell, it can be advantageous to scrub the methanated recycle stream to remove excess carbon dioxide gas.
  • a fuel cell system can be operated with approximately 67% air utilization, which is only 1.5 times the stoichiometric level, and is more efficient than 25% air utilization. For example, such a higher air utilization rate reduces an air blower demand for cooling, which reduces the amount of parasitic electrical demand on the fuel cell system caused by the use of the air blower.
  • FIG 11 shows a schematic of a fuel cell system 400, according to a fourth embodiment.
  • a fuel cell system 400 can include a fuel cell stack 410 that is supplied with a source of methane, such as a natural gas tank or pipe as indicated by arrow Ml, and a source of water, as indicated by arrow Wl.
  • Anode exhaust is expelled from a fuel cell stack 410, as indicated by arrow E in the example of Figure 11.
  • Anode exhaust E can include carbon monoxide, carbon dioxide, and hydrogen gas in addition to unreformed methane.
  • Anode exhaust E can then be supplied to a reactor 420 that methanates the anode exhaust E, per reactions (1) and (2) discussed above.
  • reactor 420 can be a Sabatier reactor which contains a catalyst, such as, for example, a ruthenium catalyst.
  • the products produced by reactor 420 i.e. methanated anode exhaust, may then be supplied to a carbon dioxide scrubber 430, as indicated by arrow P in the example of Figure 11.
  • the products from a reactor 420 can include methane, carbon dioxide, and water.
  • Carbon dioxide scrubber 430 can be used to remove excess carbon dioxide, as indicated by arrow CO 2 in the example of Figure 11, from the methanated anode exhaust, which can then be combined with the input stream of methane, as indicated by arrow M2 in the example of Figure 11.
  • PPSA partial pressure swing adsoprtion
  • FIG. 12 shows a schematic of a fuel cell system 400, according to a further arrangement of the fourth embodiment.
  • a fuel cell system 400 can include a fuel cell stack 410 that is supplied with a source of methane, as indicated by arrow Ml.
  • Anode exhaust is expelled from a fuel cell stack 410, as indicated by arrow E in the example of Figure 12, and is methanated by a reactor 420 that methanates the anode exhaust E, per reactions (1) and (2) discussed above.
  • reactor 420 can be a Sabatier reactor which contains a catalyst, such as, for example, a ruthenium catalyst.
  • the products of reactor 420, i.e. methanated anode exhaust may then be supplied to a carbon dioxide scrubber 430, as indicated by arrow P in the example of Figure 12.
  • a water recycler 440 can be provided in the anode exhaust stream to remove water from the anode exhaust and recycle the water back into the input stream for the fuel cell stack 410, as indicated by arrow W2 in the example of Figure 12.
  • a water recycler 442 can be positioned in the methanated anode exhaust stream P to remove and recycle water.
  • an enthalpy wheel or absorbent beds can be provided as a water recycler.
  • a source of water can be provided, as indicated by arrow Wl in the example of Figure 12.
  • the embodiments of the fuel cell system 400 described above need not be reversible to produce hydrogen that can be stored for later use as fuel.
  • the fuel cell system 400 of the embodiments described above produces methane gas, not hydrogen gas, and therefore differs from reversible fuel cell systems known in the art.

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Abstract

A solid oxide fuel cell system conducts internal reformation. Internal reforming reactions can advantageously be used to affect cooling of a fuel cell stack and control the heat management of the fuel cell system. Internal reforming can be accomplished by providing a reforming catalyst within the fuel cell stack, such as between a fuel cell and an interconnect plate.

Description

SOLID OXIDE FUEL CELL SYSTEM WITH INTERNAL REFORMATION
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] The present application claims benefit of United States provisional application 60/907,524, filed April 5, 2007, which is incorporated herein by reference in its entirety.
[0002] The present invention generally relates to a solid oxide fuel cell system that conducts internal reformation.
BACKGROUND
[0003] Internal reformation is advantageous in that it provides a reduced operation cost and a simplified design for a fuel cell system. External reformers add cost and design complexity to fuel cell systems, such as solid oxide fuel cell systems. While solid oxide fuel cells are capable of internally reforming hydrocarbon fuels, complete internal reformation poses several challenges, such as thermal management and faster electrode degradation. Internal reformation on the anode of a fuel cell itself is disadvantageous because there is essentially no control over the amount of reformation, which can create a problem for thermal management of the fuel cell system. Furthermore, internal reformation on the anode may reduce the life of the anode, such as through Ni dusting.
SUMMARY
[0004] According to an embodiment, a fuel cell system comprises a fuel cell, an interconnect plate, and an insert, wherein the insert is disposed between the interconnect plate and the fuel cell, wherein the fuel cell system is configured to provide a serpentine fuel gas inlet flow stream that flows first between the insert and the interconnect plate and then flows between the insert and an anode of the fuel cell, wherein the fuel cell system is configured so that the fuel gas flowing between the insert and the interconnect plate contacts a reforming catalyst.
[0005] According to an embodiment, a method of internally reforming a fuel gas within a fuel cell system, comprising the steps of providing a fuel cell system which comprises a fuel cell, an interconnect plate, and an insert, wherein the insert is disposed between the interconnect plate and the fuel cell, flowing a hydrocarbon fuel inlet stream between the insert and the interconnect plate, reforming the fuel inlet stream flowing between a first side of the insert and the interconnect plate, and flowing the reformed fuel stream between a second side of the insert and an anode of the fuel cell.
[0006] According to an embodiment, a method of operating a fuel cell system comprises the steps of providing a fuel cell system, which comprises a fuel cell, an interconnect plate, and a porous insert, wherein the insert contains a reforming catalyst and the insert is disposed between the interconnect plate and the fuel cell, and flowing a fuel inlet stream into the insert, wherein the insert creates a pressure difference for the fuel inlet stream between one side of the insert and another side of the insert.
[0007] According to an embodiment, a fuel cell system comprises a fuel cell, an interconnect plate comprising a fuel gas inlet in a fuel inlet plenum, and a barrier configured to direct a flow of fuel gas from the fuel gas inlet toward a periphery of the plenum, and a reformer catalyst located in the plenum.
[0008] According to an embodiment, a method of operating a fuel cell system comprises the steps of providing a fuel cell, providing an interconnect plate comprising a fuel gas inlet in a fuel inlet plenum and a barrier configured to direct a flow of fuel gas from the fuel gas inlet toward a periphery of the plenum, providing a reformer catalyst located in the plenum, and flowing fuel gas through the fuel gas inlet and around the barrier.
[0009] According to an embodiment, a fuel cell system comprises a fuel cell stack containing internal reformation catalyst regions, a Sabatier reactor configured to receive anode exhaust from the fuel cell stack and to produce methane, and a carbon dioxide scrubber configured to remove excess carbon monoxide from methanated anode exhaust produced by the reactor and to recycle the methane back to the fuel cell stack.
[0010] According to an embodiment, a method of recirculating anode exhaust gas comprises providing anode exhaust stream from a fuel cell stack, reacting the anode exhaust stream to provide a methanated anode exhaust stream, scrubbing the methanated anode exhaust stream to remove excess carbon dioxide, after removing the excess carbon dioxide, providing the methanated anode exhaust stream into a fuel inlet stream, and internally reforming the fuel inlet stream in the fuel cell stack. BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Figure 1 is an exploded view of a stack of fuel cell plates as viewed from above, according to a first embodiment.
[0012] Figure 2 is an exploded view of the stack of fuel cell plates of Figure 1 as viewed from below, according to a first embodiment.
[0013] Figure 3 is an exploded side view of a fuel cell stack, according to a second embodiment.
[0014] Figure 4a shows an exploded side view of an insert, according to an embodiment.
[0015] Figure 4b shows an exploded side view of an insert, according to an embodiment.
[0016] Figure 4c shows an exploded side view of an insert, according to an embodiment.
[0017] Figure 4d shows an exploded side view of an insert, according to an embodiment.
[0018] Figure 4e shows an exploded side view of an insert, according to an embodiment.
[0019] Figure 5 is a plan view of an interconnect plate, according to a third embodiment.
[0020] Figure 6 is an enlarged view of a central region of the interconnect plate of Figure 5.
[0021] Figure 7a shows a top view of an interconnect plate according to the third embodiment.
[0022] Figure 7b shows a top schematic view of a fuel cell according to the third embodiment.
[0023] Figure 7c shows a plan view of an interconnect plate, according to the third embodiment.
[0024] Figure 8 shows a plan view of an interconnect plate, according to a further arrangement of the third embodiment.
[0025] Figure 9 shows an enlarged view of an inlet region of the interconnect plate of Figure 8. [0026] Figure 10a shows a top view of an interconnect plate 200 according to a further arrangement of the third embodiment.
[0027] Figure 10b shows a top schematic view of a fuel cell according to a further arrangement of the third embodiment.
[0028] Figure 10c shows a plan view of an interconnect plate, according to a further arrangement of the third embodiment.
[0029] Figure 11 shows a schematic of a fuel cell system, according to a fourth embodiment.
[0030] Figure 12 shows a schematic of a fuel cell system, according to a further arrangement of the fourth embodiment.
DETAILED DESCRIPTION
[0031] Embodiments will be described below with reference to the drawings. One non- limiting object of the embodiments described herein is to provide a fuel cell system and method that provide internal reformation while overcoming the disadvantages discussed above. While a solid oxide fuel cell (SOFC) system is preferred, other fuel cell types may also be used.
First Embodiment
[0032] Figure 1 is an exploded view of a repeating unit of a fuel cell stack 10 as viewed from above, according to a first embodiment. The fuel cell stack 10 can include a solid oxide fuel cell 20 that includes an anode 26 (as shown in the example of Figure 1), a cathode 28 (as shown in the example of Figure 2), and an electrolyte 27 disposed between the anode 26 and the cathode 28. The fuel cell 20 can include a fuel inlet 22 and a fuel outlet 24, such as in the arrangement of openings or holes shown in the examples of Figures 1 and 2. According to a further embodiment, a seal 23 can be arranged around fuel inlet 22 to prevent fuel gas from the fuel inlet 22 from flowing over an anode side of the fuel cell 20.
[0033] The fuel cell stack 10 can further include a insert 30 and interconnect plates 40, as shown in the examples of Figures 1 and 2. A insert 30 can include a reforming side 38 where internal reformation of fuel gas flowing between the insert 30 and an interconnect plate 40 occurs. Preferably, the reforming side 38 faces away from anode 26 and faces toward interconnect plate 40. For example, a reformer catalyst can be disposed on the reforming side 38 of insert 30, between the insert 30 and the interconnect plate 40, or by other methods known in the art. The insert 30 can be made of a high temperature conductive foam, ribs or corrugation, plate, a conductive ceramic plate or a metal plate, such as a Cr-Fe alloy plate. If desired, the insert 30 may contain ribs or corrugation to provide a degree of flexibility that mitigates the effect of a coefficient of thermal expansion mismatch between the insert 30 and other components of the fuel cell stack 10.
[0034] The insert 30 can include a fuel inlet 32, a fuel passage 34 to the anode 26, and a fuel outlet 36, such as in the arrangement shown in the examples of Figures 1 and 2. The fuel inlet 32 and fuel outlet 36 of the insert 30 can be designed to engage with an adjacent component(s) of the fuel cell stack 10 in a sealing manner. According to the example shown in Figures 1 and 2, the fuel inlet 32 can form a protrusion on a bottom side (non-reforming side) of the insert 30 that engages with the fuel cell 20 in an sealing manner. Furthermore, the fuel outlet 36 can be designed to be raised and protrude from the top side (reforming side) of the insert 30, as shown in the example of Figure 1, so that the fuel outlet 36 engages with an interconnect plate 40 in a sealing manner. The protrusions around the openings form fuel inlet and outlet riser channels for an internally manifolded fuel stack configuration.
[0035] The fuel inlet 32 can be configured to permit fuel gas to exit the fuel inlet 32 and flow across the reformer side 38 of the insert 30 to permit internal reformation of the fuel gas on the reformer side 38 of the insert. The reformed fuel gas can then flow through the insert 30 via the fuel passage 34 to the other, non-reforming side of the insert 30. The non-reforming side of the insert 30 can be disposed facing the anode 26 of the fuel cell 20 to permit the reformed fuel gas to undergo an oxidation reaction as the fuel gas passes between the insert 30 and the anode 26 before exiting through the fuel outlet 36 of the insert 30.
[0036] An interconnect plate 40 can be arranged adjacent to the cathode 28 of a fuel cell 20 so that an air side 46 of interconnect plate 40 faces the cathode 28 and a stream of air can flow between the interconnect plate 40 and the cathode 28, as indicated by arrow A in the examples of Figures 1 and 2. Furthermore, the interconnect plate 40 can be arranged adjacent to the insert 30 so that a fuel reformer side 48 of the interconnect plate 40 faces the insert 30 and a stream of fuel can flow between the interconnect plate 40 and the insert, as indicated by arrow FS in the example of Figure 2. According to a further embodiment, the interconnect plate 40 can be made of a chromium-iron alloy, a conductive ceramic, or other materials known in the art.
[0037] According to a further embodiment, current produced by the electrochemical reactions of the fuel cell stack can be conducted by the insert 30. According to a further embodiment, portions of the insert 30 can be welded to the interconnect plate 40 to reduce adverse effects upon current collection due to the presence of the insert 30 in a fuel cell stack.
[0038] According to a further embodiment, a fuel gas inlet stream is introduced into a fuel cell stack 10 in the direction indicated by arrow FI in the examples of Figures 1 and 2. The fuel gas flows through the inlet fuel riser channel made up of fuel inlets 42, 22, 32 of an interconnect plate 40, fuel cell 20, and insert 30, respectively, and is permitted to flow across the reformer side 38 of the insert 30, which faces an interconnect plate 40. The fuel gas undergoes a reforming reaction as the fuel gas flows along the reformer side 38 of the insert 30, as indicated by arrows FS in the examples of Figures 1 and 2. The reformed fuel gas then flows through the fuel passage 34 to the anode 26 of the fuel cell 20. The reformed fuel gas undergoes an electrochemical oxidation reaction at the anode 26, flows to the outlet 24 of the fuel cell 20, and then flows out of the fuel cell stack 10 through the outlet fuel riser channel made up of outlets 24, 44, 36 in the direction indicated by arrow FO in the examples of Figures 1 and 2.
[0039] According to a further embodiment, internal reformation can occur in a space formed between the insert 30 and the interconnect plate 40. For example, the fuel cell stack 10 can be configured to internally reform fuel gas within channels formed between a insert 30 and an interconnect plate 40 where the reformation catalyst is coated on the side 48 of interconnect plate 40 instead of, or in addition to, being coated on side 38 of insert 30.
[0040] According to a further embodiment, a depth of the channels formed by the insert 30 and the interconnect plates 40 can be varied in order to control the reformation process. Furthermore, the type of catalyst used in the channels and the placement of the catalyst in the channels can be varied to control the reformation process. For example, the reforming catalyst can be spread over an entire area encompassed by channels between an insert 30 and an interconnect plate 40 or the reforming catalyst may be preferentially placed in predetermined areas of the channels located between ribs on side 38 of insert 30 and/or side 48 of interconnect plate 40. A reformer catalyst, such as, for example, nickel and rhodium or other catalysts known in the art can be used within the channels formed by the insert 30 and the interconnect plates 40. According to a further embodiment, internal steam reformation of hydrocarbon fuels can be conducted over the entire cell area of an insert, especially if side 38 of insert 30 is flat.
[0041] A design made according to features of the first embodiment described above provides maximum thermal contact between an internal reforming region and an electrochemical oxidation region. The addition of the insert 30 advantageously permits enhanced control over the reformation process. For instance, the insert 30 can provide enhanced control over the reformation process in terms of residence time, catalyst choice, and/or thermal management.
[0042] While a fuel cell system that is internally manifolded for fuel and externally manifolded for air is described, other manifolding configurations may be used. For example, the stack may be internally manifolded for air and/or externally manifolded for fuel. The stack may also be semi-internally manifolded for fuel (i.e. contain an inlet fuel riser channel but vent the fuel exhaust stream outside the stack boundary without using an outlet fuel riser channel) and/or contain more than one inlet and/or outlet riser channel. According to a further embodiment, a fuel cell system can be arranged that includes one or more fuel cell stacks 10 according any of the embodiments described above.
Second Embodiment
[0043] Figure 3 is an exploded side view of a repeating unit of a fuel cell stack 110, according to a second embodiment. A fuel cell stack 110 can include a fuel cell 120, which includes a solid oxide fuel electrolyte 122, a cathode 124, and an anode 126. The fuel cell stack 1 10 can further include a reformation insert 130 for an interconnect plate 140. The insert 130 can be arranged to receive a flow of fuel gas inlet stream in an inlet direction, as indicated by the arrow IN of the example of Figure 3. The reformed fuel stream is provided in an outlet direction, as indicated by the arrow EX of the example of Figure 3. The insert 130 can be inserted into a fuel cavity in an interconnect plate 140, or the insert 130 can be located in a space between the anode 126 and the interconnect plate 150.
[0044] According to a further embodiment, the insert 130 can include a first portion 132 and a second portion 134, as shown in the example of Figure 3. According to a further embodiment, the first portion 132 of the insert 130 can include a reforming catalyst and the second portion 134 of the insert 130 can be made of a metallic foam or other porous metallic material. For example, the first portion 132 can be made of a reforming catalyst foam or other porous material, such as, for example, a nickel foam or stainless steel foam coated with catalyst. In another example, the second portion 134 can be made of a nickel foam or a stainless steel foam. According a further preferred embodiment, the first portion 132 and the second portion 134 are electrically connected. The anode 126 may further be electrically connected to the second portion 134 for current collection during operation of a fuel cell stack 110.
[0045] According to a further embodiment, the first portion 132 of an insert can create a lower pressure drop than the second portion 134 of the insert. For example, if the first portion 132 and the second portion 134 are made of a foam or other porous material, the first portion 132 can have a greater porosity than the second portion 134 in order to produce a pressure difference between the first portion 132 and the second portion 134. When such a first portion 132 and second portion 134 are joined together to form an insert 130, the arrangement can cause fuel gas to flow from the first portion 132 to the second portion 134 in a phased fashion. For example, fuel gas flow can be distributed between the first portion 132 and the second portion 134 as indicated by arrows CF in Figure 3. Such an insert 130 can provide an enhanced fuel gas flow distribution across an anode 126 of a fuel cell 120 in comparison to an insert that simply flows fuel gas from one side of the insert to another. Furthermore, a phased flow produced by a pressure difference within an insert 130 can limit excessive current densities that lead to anode starvation, thus improving fuel cell performance and life, which in turn reduces the maintenance cost for a fuel cell system. [0046] As shown in the example of Figure 3, the first portion 132 and the second portion 134 can have a triangular or wedge-shaped cross section. The first portion 132 and the second portion 134 can be arranged to face one another so a wedge surface of the first portion 132 and the second portion 134 face one another. As shown in the example of Figure 3, the second portion 134 can be arranged with a cross section in the shape of an upside-down triangle that faces the first portion 132. For example, if the first portion 132 and second portion 134 each have a cross-section in the shape of right triangle, as shown in the example of Figure 3, the first portion 132 and second portion 134 can be arranged so that the hypotenuse of each right triangle faces one another. Furthermore, the first portion 132 and second portion 134 can be arranged to be in contact with one another to form an interface between the first portion 132 and the second portion 134.
[0047] A fuel gas can be introduced into the first portion 132 of an insert 130 as indicated by arrow IN of Figure 3. A portion of the fuel gas flows through the first portion 132 along the direction indicated by the arrow IN. The reformed fuel passes by the anode 126, exits the insert 130 along the direction indicated by arrow EX in Figure 3, and flows from the first portion 132 to the second portion 134 in the direction indicated by arrows CF in Figure 3. Such a fuel gas flow in the CF direction may be made in a phased manner due to a pressure difference between the first portion 132 and the second portion 134. For example, the phased fuel gas flow made be arranged to provide an even flow distribution of fuel gas across an anode 126 of a fuel cell 120.
[0048] According to a further embodiment, an interface between the first portion 132 and the second portion 134 of an insert 130 can have a different shape or geometry than that shown in Figure 3. For example, the interface can be nonlinear, curved, horizontal, or any other shape providing a sufficient pressure difference between the first portion 132 and the second portion 134.
[0049] Figure 4a shows an exploded side view of an insert 130 that includes a strip 138, according to a further embodiment. A strip 138 can be inserted between the first portion 132 and the second portion 134 of an insert to control the flow distribution of fuel gas between the first portion 132 and the second portion 134. However, such a strip 138 is not necessary if a pressure drop difference between the first portion 132 and the second portion 134 is sufficient to produced a desired flow distribution. Furthermore, a strip 138 can be made from a material, such as a high temperature adhesive, that aids in the joining of the first portion 132 and the second portion 134, such as when the first portion 132 and the second portion 134 are made of different materials.
[0050] Figure 4b shows an exploded side view of an insert 130 that includes a seal 136 impermeable to fuel gas, according to a further embodiment. A seal 136 may be deposited on the second portion 134 of an insert 130, as shown in the example of Figure 4b (i.e. the seal 13b is positioned on the outlet side of insert, which is positioned perpendicular to the anode 126), to cause a fuel gas to flow into the first portion 132 of the insert 130 in the direction indicated by arrow IN, to flow from the first portion to the second portion 134, and out of the second portion 134, as indicated by arrow EX in the example of Figure 4b. Therefore, a seal 136 can be used to force an entirety of a fuel gas flow to exit through a top side of an insert 130 where an anode 126 of a fuel cell 120 is located. Such an arrangement advantageously provides more fuel for the anode by forcing fuel gas to exit the insert 130.
[0051] Figure 4c shows an exploded side view of an insert 130 that includes a seal 136A deposited on an output side of first portion 132 of an insert 130 and a seal 136B deposited on an input side of the second portion 134 of an insert 130, according to a further embodiment. In this embodiment, the first portion 132 is arranged so that the cross-section of the first portion 132 forms an upside-down triangle or wedge, as shown in the example of Figure 4c. Therefore, a fuel inlet for the insert 130 is positioned at a distance away from the anode 126 beneath seal 136B so that gas may flow into the first portion 132. Such an arrangement may be provided to control a flow of fuel gas flowing into the second portion 134 by affixing a seal 136B at an input side of the second portion 134 and to control a flow of fuel gas flowing out of the first portion by affixing a seal 136A at an output side of first portion 132.
[0052] Figure 4d shows an exploded side view of an insert 130, according to a further embodiment, that is similar to the insert 130 of Figure 4c but includes first and second portions 132, 134 having a horizontal interface rather than a sloped interface. For example, the first portion 132 may be constructed of a material with a higher porosity than a material that the second portion 134 is constructed of. A fuel gas can be introduced in a direction indicated by arrow IN of Figure 4d, flow from the first portion 132 to the second portion 134 of an insert 130, and flow out of the insert 130 in a direction indicated by arrow EX of Figure 4d while providing fuel gas to an anode 126 of a fuel cell 120.
[0053] Figure 4e shows an exploded side view of an insert 131 that is made of a single piece of material, according to a further embodiment. An insert 131 can be constructed of a foam or other porous material to create a pressure drop within the insert 131. For example, an insert 131 may be constructed to have a graded porosity that decreases from the top of the insert 131 to the bottom of the insert 131 in order to provide a sufficient pressure difference as described in the embodiments above. In a further example, an insert 131 may have a lower porosity in a top portion of the insert 131 than in a bottom portion of the insert 131. Furthermore, an insert 131 may have a graded porosity that decreases from one side of the insert 131 to another in a direction along a fuel gas flow into the insert 131 , as indicated by the arrows IN and EX of Figure 4e. In a further embodiment, the insert 131 can include two portions, with a first portion of higher porosity arranged on an inlet side of the insert 131 and a second portion of lower porosity arranged on an outlet side of the insert 131.
[0054] A catalyst of the insert 130, 131 can be changed and selected to suit a specified fuel, according to a further embodiment. Such an arrangement advantageously permits an expensive interconnect plate to be used for different fuel cell stacks that use different fuels. For example, an interconnect plate may be expensive because it is made of a pressed powder that is suitable for use in a fuel cell stack. Because an interconnect plate is generally an expensive component of a fuel cell stack, it makes economic sense to increase the functionality of an interconnect plate because this may only increase the cost of the interconnect plate by a relatively small percent. Furthermore, because reformation of a fuel gas can be conducted internally, the cost of a fuel cell system is reduced because there is no need for an external reformer or anodes capable of reforming fuel gas.
[0055] A design made according to features of the second embodiment described above provides improved thermal control of a fuel cell system and permits a more uniform current density by incorporating a reforming function and a phased fuel inlet distribution to an anode of a fuel cell. Furthermore, such a design can improve fuel cell performance and improve fuel cell life by reducing areas of high fuel utilization. Third Embodiment
[0056] Figure 5 is a plan view of an interconnect plate 200, according to a third embodiment. An interconnect plate 200 can include an inlet fuel distribution plenum 202, outlet fuel distribution plenum(s) 204, a flow field 210 containing flow channels separated by ribs, barriers 220, a fuel inlet 230, and fuel outlet(s) 240, as shown in the example of Figure 5. Plenums 202, 204 may comprise recesses in the interconnect plate 200 and the flow fields 210 may contain ribs 211 that can be configured to form raised areas in relation to a bottom surface of an interconnect plate 200, thus forming channels 212 for fuel gas flow between the ribs 21 1. As shown in the example of Figure 5, barriers 220 may comprise fins which extend roughly perpendicular to the channels 21 1. The barriers 220 can be arranged in plenum 202 around a fuel inlet 230 to direct a flow of fuel gas toward the periphery of plenum 202. Figure 6 is an enlarged view of a central region of the interconnect plate of Figure 5. As shown in the example of Figure 6, barriers 220 can be arranged to direct a flow of fuel gas from a fuel inlet 230, along a central portion of an interconnect plate 200 between the barriers 220, and around the ends of barriers 220 to the channels 212 located between ribs 211, as indicated by arrows FFl in the example of Figure 6.
[0057] Figure 7a shows a top view of an interconnect plate 200 according to the third embodiment. Figure 7b shows a top schematic view of a fuel cell 300 according to the third embodiment. A fuel cell 300 can include a central region 302 that includes a reformer catalyst formed on the electrolyte 301 of the cell. The catalyst is used for reforming fuel gas that is provided from inlet 230 gas over the central region 302 in the plenum 202 between the fuel cell 300 and an interconnect plate 200. A fuel cell 300 also includes anode regions 304 outside of a central region 302 for oxidizing reformed fuel gas in an electrochemical reaction. A fuel cell 300 can further include outlets 310 for exhaust from the anode regions 304. In the fuel cell stack, the ribs 212 in flow fields 210 contact anode regions 304 while central region 302 is located opposite to plenum 202 in the interconnect plate 200. Thus, anode regions 304 of a fuel cell 300 are in electrical contact with an interconnect plate 200.
[0058] Figure 7c shows a plan view of an in-use interconnect plate 200, according to the third embodiment. As shown in the example of Figure 7c, an interconnect plate 200 can be arranged so that a region of internal reformation 206 is produced in plenum 202 when fuel gas flows through the interconnect plate 200. Furthermore, regions of high current density 208 can be produced when reformate gas produced by the reforming reaction in the region of internal reformation 206 passes into channels 211 in flow fields lying between the interconnect plate 200 and a fuel cell.
[0059] According to a further embodiment, reformer catalyst can be arranged in plenum 202 around a fuel inlet 230 and barriers 220 of an interconnect plate. For example, reformer catalyst can be coated in central region 302 in the fuel cell that faces an interconnect plate 200, in the plenum 202 in the interconnect plate 200, or in both the fuel cell and the interconnect plate 200. Such a reformer catalyst can be arranged in plenum 202 within the area between barriers 220, or the reformer catalyst can also be arranged in plenum 202 outside of the barriers 220 in an area surrounding the barriers 220. Therefore, a fuel gas flowing from a fuel inlet 230 through a plenum 202 between barriers 220 can be subjected to a reforming reaction, due to the presence of a reformer catalyst in the central region, before the gas enters channels 212 located between ribs 211 in flow fields 210. Plenum 202 of interconnect plate 200 that contains the reformer catalyst can be configured to not to be in electrical contact with a fuel cell, such as an anode of a fuel cell.
[0060] According to a further embodiment, a reformer catalyst can be arranged in channels 211 between ribs 211. For example, reformer catalyst can be provided in the anode, in the flow fields 210 in the interconnect plate 200, or in both the fuel cell and the interconnect plate 200.
[0061] A reforming catalyst used in plenum 202 can be the same reforming catalyst used in between ribs 211 or it can be different. For example, it can be advantageous to provide a different reforming catalyst in order to provide process flexibility for an interconnect plate of a fuel cell system.
[0062] By providing a design according to the embodiments described above, a fuel gas flow can be introduced through a center of a fuel cell, which is likely the hottest region of the fuel cell and the most difficult to withdraw heat from. Furthermore, by providing barriers that direct a flow of the fuel gas through a central plenum region around a fuel inlet that contains a reformer catalyst, a residence time of the fuel gas can be advantageously maximized to ensure full reformation of the fuel gas. Without the barriers, fuel gas could directly enter channels between ribs of an interconnect plate, thus causing the fuel gas to quickly exit areas containing reformer catalyst. Furthermore, when a fuel cell system has high current densities and thus large flow rates, there may not be sufficient residence time in the central region to fully reform fuel gas without the use of barriers arranged around a fuel inlet.
[0063] When fuel gas is reformed in a central plenum 202 region around a fuel inlet 230, strong cooling of the core of a fuel cell stack can occur due to the internal reformation reaction and due to convective cooling caused by the fuel gas flow. Therefore, a design according to the embodiments described above can advantageously provide effective thermal management of a large-area interconnect plate and interconnect plates made of materials having a low thermal conductivity.
[0064] Figure 8 shows a plan view of an interconnect plate 200, according to a further arrangement of the third embodiment. In the example shown in Figure 8, a fuel inlet 232 is arranged at one end of an interconnect plate 200 and a fuel outlet 240 is arranged at an opposite end of an interconnect plate 200. A barrier 222 can be arranged around a fuel inlet 232 to direct a flow of fuel gas into the plenum 202 between an interconnect plate 200 and a fuel cell that faces the interconnect plate.
[0065] Figure 9 shows an enlarged view of an inlet region of the interconnect plate of Figure 8. As shown in the example of Figure 9, an interconnect plate 200 can be arranged so that fuel gas flows out of fuel inlet 232 into plenum 202 and is directed by a barrier 222 along the inlet plenum 202 in a direction indicated by arrows FF2, so that fuel gas flows around the end of the barriers 222 to channels 212 located between ribs 211 in flow fields 210.
[0066] Figure 10a shows a top view of an interconnect plate 200 according to the arrangement of Figure 8. Figure 10b shows a top schematic view of a fuel cell 300 according to the third embodiment. The fuel cell 300 can include an inlet region 302 that includes a reformer catalyst for reforming fuel gas that flows in the central region 302 between the fuel cell 300 and an interconnect plate 200. The fuel cell 300 can include an anode region 304 located outside of an inlet region 302 for oxidizing reformed fuel gas in an electrochemical reaction. The fuel cell 300 can further include outlet 320 for fuel exhaust from the anode regions 304. According to a further embodiment, an anode region 304 of a fuel cell 300 can be in electrical contact with an interconnect plate 200 because the fuel cell 300 is in contact with the interconnect plate 200 with a fuel cell stack.
[0067] Figure 10c shows a plan view of an in-use interconnect plate 200, according to the arrangement of Figure 8. As shown in the example of Figure 10c, an interconnect plate 200 can be arranged so that a region of internal reformation 206 is produced in plenum 202 when fuel gas flows along the face of the interconnect plate 200. Furthermore, a region of high current density 208 can be produced when reformate gas produced by the reforming reaction in the region of internal reformation 206 passes into channels 211 lying between the interconnect plate 200 and the anode 304 of the fuel cell.
[0068] As in the previous configuration, the reformer catalyst can be provided in plenum 202, in region 302, in channels 211, and/or in anode 304.
[0069] A reforming catalyst used in the region around a fuel inlet 230 can be the same reforming catalyst used in between ribs 211 or can be different. For example, it can be advantageous to provide a different reforming catalyst in order to provide process flexibility for an interconnect plate of a fuel cell system.
[0070] By providing a barrier to direct a flow of the fuel gas through an inlet plenum that contains a reformer catalyst, a residence time of the fuel gas can be advantageously maximized to ensure full reformation of the fuel gas. Without a barrier, fuel gas could directly enter channels between ribs of an interconnect plate, thus causing the fuel gas to quickly exit areas containing reformer catalyst. Furthermore, when a fuel cell system has high current densities and thus large flow rates, there may not be sufficient residence time in the inlet region to fully reform fuel gas without the use of a barrier arranged around a fuel inlet. However, because reformation of fuel gas occurs only to one side of a fuel cell stack, thermal management of the center of the stack may be difficult. Therefore, a design according to the above further arrangement is desirable for interconnect plates that are made from high thermal conductivity materials, such as, for example, chromium based alloys and other high thermal conductivity materials known in the art. Such interconnect plates may be further designed with a thin cross-section, such as a few millimeters, to enhance conduction of heat. Furthermore, additional heat can be provided to the stack, such as by, for example, radiation heat sources, other stacks positioned close to one another in a hot box, or convectively flowing exhaust air around stack surfaces that correspond to an internal reformation region.
[0071] A design made according to features of the third embodiment described above allows spatial separation of internal reformation and electrochemical regions over the area of a fuel cell, thus potentially allowing the use of different catalysts for an anode and for internal reformation. Furthermore, such a design allows internal reformation to occur in the core of a stack where the temperature would be the highest and heat rejection would be difficult. Therefore, such a design can provide enhanced thermal management of a core of a fuel cell stack.
Fourth Embodiment
[0072] As solid oxide fuel cell technology progresses, the demand for more efficient use of fuel increases. One way to increase fuel cell system efficiency is to recycle a portion of the anode exhaust stream back into the anode inlet stream at a defined recycling ratio. In addition to using anode gas recycling to boost system efficiency, the demand for higher power densities will inevitably lead to more cost-effective solid oxide fuel cell systems. A benefit for this higher fuel efficiency is lower CO and CO2 emissions. Such a demand for higher power densities will cause elevated temperatures in a fuel cell stack. If the heat caused by the elevated temperatures is not controlled, interconnect plates and other metallic components of the fuel cell could deform and even melt.
[0073] Internal reforming is an effective way of cooling a fuel cell reaction site. However, even if 100% direct internal reforming is achieved, the heat generated from the electrochemical reaction will still be too much at higher current densities.
[0074] An object of the following embodiment is to reduce the cooling duty of an internal reforming operation by diluting an anode stream with anode recycled gas.
[0075] According to the fourth embodiment, an anode recycle loop can be used to produce methane. For example, an anode stream containing gas species and heat can be processed to produce methane with the following reactions: CO + 3H2 -» CH4 + H2O (1)
CO2 + 4H2 -* CH4 + 2H2O (2)
[0076] The methane produced by the above reactions can then be used to cool a fuel cell stack due to an endothermic internal reformation reaction within the fuel cell stack. For example, a nickel-alumina catalyst could be used within the fuel cell stack as a reformer catalyst. Therefore, an additional cooling duty would be provided for the stack, providing a more efficient use of fuel and permitting the use of higher power densities. However, increasing the rate of methane reformation, for additional cooling duty, with a simple recirculation of an anode stream causes the use of additional natural gas and the deterioration of fuel cell efficiency. To maintain fuel cell efficiency and an increased amount of fuel cell cooling due to endothermic reforming, anode exhaust can be methanated to provide additional methane for internal reforming. Furthermore, because carbon dioxide in the anode/methanated recycle stream tends to choke the fuel cell system because of its displacement of fuel from the input stream to the fuel cell, it can be advantageous to scrub the methanated recycle stream to remove excess carbon dioxide gas.
[0077] By providing a fuel cell system according to the embodiments described herein, a fuel cell system can be operated with approximately 67% air utilization, which is only 1.5 times the stoichiometric level, and is more efficient than 25% air utilization. For example, such a higher air utilization rate reduces an air blower demand for cooling, which reduces the amount of parasitic electrical demand on the fuel cell system caused by the use of the air blower.
[0078] Figure 11 shows a schematic of a fuel cell system 400, according to a fourth embodiment. As shown in the example of Figure 11, a fuel cell system 400 can include a fuel cell stack 410 that is supplied with a source of methane, such as a natural gas tank or pipe as indicated by arrow Ml, and a source of water, as indicated by arrow Wl. Anode exhaust is expelled from a fuel cell stack 410, as indicated by arrow E in the example of Figure 11. Anode exhaust E can include carbon monoxide, carbon dioxide, and hydrogen gas in addition to unreformed methane. Anode exhaust E can then be supplied to a reactor 420 that methanates the anode exhaust E, per reactions (1) and (2) discussed above. For example, reactor 420 can be a Sabatier reactor which contains a catalyst, such as, for example, a ruthenium catalyst. The products produced by reactor 420, i.e. methanated anode exhaust, may then be supplied to a carbon dioxide scrubber 430, as indicated by arrow P in the example of Figure 11. The products from a reactor 420 can include methane, carbon dioxide, and water. Carbon dioxide scrubber 430 can be used to remove excess carbon dioxide, as indicated by arrow CO2 in the example of Figure 11, from the methanated anode exhaust, which can then be combined with the input stream of methane, as indicated by arrow M2 in the example of Figure 11. For example, a partial pressure swing adsoprtion (PPSA) system, such as that described in U.S. Patent Application No. 11/188,118 filed on July 25, 2005, which is incorporated herein by reference, can be used to scrub excess carbon dioxide from the methanated anode exhaust stream.
[0079] Figure 12 shows a schematic of a fuel cell system 400, according to a further arrangement of the fourth embodiment. A fuel cell system 400 can include a fuel cell stack 410 that is supplied with a source of methane, as indicated by arrow Ml. Anode exhaust is expelled from a fuel cell stack 410, as indicated by arrow E in the example of Figure 12, and is methanated by a reactor 420 that methanates the anode exhaust E, per reactions (1) and (2) discussed above. For example, reactor 420 can be a Sabatier reactor which contains a catalyst, such as, for example, a ruthenium catalyst. The products of reactor 420, i.e. methanated anode exhaust, may then be supplied to a carbon dioxide scrubber 430, as indicated by arrow P in the example of Figure 12.
[0080] Furthermore, a water recycler 440 can be provided in the anode exhaust stream to remove water from the anode exhaust and recycle the water back into the input stream for the fuel cell stack 410, as indicated by arrow W2 in the example of Figure 12. Alternatively, a water recycler 442 can be positioned in the methanated anode exhaust stream P to remove and recycle water. For example, an enthalpy wheel or absorbent beds can be provided as a water recycler. According to a further embodiment, a source of water can be provided, as indicated by arrow Wl in the example of Figure 12.
[0081] The embodiments of the fuel cell system 400 described above need not be reversible to produce hydrogen that can be stored for later use as fuel. In fact, it must be noted that the fuel cell system 400 of the embodiments described above produces methane gas, not hydrogen gas, and therefore differs from reversible fuel cell systems known in the art.
The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The description was chosen in order to explain the principles of the invention and its practical application. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.

Claims

What is claimed is:
1. A fuel cell system, comprising: a fuel cell, an interconnect plate, and an insert, wherein the insert is disposed between the interconnect plate and the fuel cell, wherein the fuel cell system is configured to provide a serpentine fuel gas inlet flow stream that flows first between the insert and the interconnect plate and then flows between the insert and an anode of the fuel cell, wherein the fuel cell system is configured so that the fuel gas flowing between the insert and the interconnect plate contacts a reforming catalyst.
2. The fuel cell system of claim 1, wherein the insert is welded to the interconnect plate.
3. The fuel cell system of claim 1, further comprising channels between the insert and the interconnect plate, wherein the channels contain the reforming catalyst.
4. The fuel cell system of claim 1, wherein the reforming catalyst is coated on a side of the insert facing the interconnect plate.
5. The fuel cell system of claim 1, wherein a the reforming catalyst is coated on a side of the interconnect plate facing the insert.
6. The fuel cell system of claim 1, wherein the reforming catalyst is coated on the insert and the interconnect plate.
7. A method of internally reforming a fuel gas within a fuel cell system, comprising: providing a fuel cell system which comprises a fuel cell, an interconnect plate, and an insert, wherein the insert is disposed between the interconnect plate and the fuel cell, flowing a hydrocarbon fuel inlet stream between the insert and the interconnect plate, reforming the fuel inlet stream flowing between a first side of the insert and the interconnect plate, and flowing the reformed fuel stream between a second side of the insert and an anode of the fuel cell.
8. A fuel cell system, comprising: a fuel cell, an interconnect plate, and a porous insert, wherein the insert contains a reforming catalyst, wherein the insert is disposed between the interconnect plate and the fuel cell, wherein the insert is configured to produce a pressure difference between one side of the insert and another side of the insert.
9. The fuel cell system of claim 8, wherein the insert comprises a first portion and a second portion, wherein the first portion is configured to receive a fuel gas flow, wherein the second portion is configured to receive the fuel gas flow from the first portion.
10. The fuel cell system of claim 9, wherein the first portion comprises the reforming catalyst.
11. The fuel cell system of claim 9, wherein the first portion comprises a higher amount of porosity than the second portion.
12. The fuel cell system of claim 9, further comprising a strip disposed between the first portion and the second portion.
13. The fuel cell system of claim 9, wherein the first portion and the second portion each have a cross section in the shape of a triangle.
14. The fuel cell system of claim 13, wherein one of the first portion and the second portion is arranged with a cross section in the shape of an upside-down triangle that faces the other of the first portion and the second portion.
15. The fuel cell system of claim 9, wherein at least one of the first portion and the second portion comprises a seal impermeable to the fuel gas flow.
16. A method of operating a fuel cell system, comprising: providing a fuel cell system, which comprises a fuel cell, an interconnect plate, and a porous insert, wherein the insert contains a reforming catalyst and the insert is disposed between the interconnect plate and the fuel cell, and flowing a fuel inlet stream into the insert, wherein the insert creates a pressure difference for the fuel inlet stream between one side of the insert and another side of the insert.
17. A fuel cell system, comprising: a fuel cell, an interconnect plate comprising a fuel gas inlet in a fuel inlet plenum, and a barrier configured to direct a flow of fuel gas from the fuel gas inlet toward a periphery of the plenum, and a reformer catalyst located in the plenum.
18. The fuel cell system of claim 17, wherein the fuel gas inlet is located in a central region of the interconnect plate.
19. The fuel cell system of claim 18, wherein the interconnect plate comprises a first barrier that is located on one side of the fuel gas inlet and a second barrier that is located on an opposite side of the fuel gas inlet.
20. The fuel cell system of claim 17, wherein the fuel gas inlet is located in a side region of the interconnect plate.
21. The fuel cell system of claim 17, wherein the interconnect plate comprises at least one flow field comprising ribs and channels extending along a first direction of the interconnect plate, wherein the barrier extends substantially perpendicular to the channels to direct fuel gas in a substantially perpendicular direction to the first direction of the interconnect plate.
22. A method of operating a fuel cell system, comprising: providing a fuel cell, providing an interconnect plate comprising a fuel gas inlet in a fuel inlet plenum and a barrier configured to direct a flow of fuel gas from the fuel gas inlet toward a periphery of the plenum, providing a reformer catalyst located in the plenum, and flowing fuel gas through the fuel gas inlet and around the barrier.
23. A fuel cell system, comprising: a fuel cell stack containing internal reformation catalyst regions, a Sabatier reactor configured to receive anode exhaust from the fuel cell stack and to produce methane, and a carbon dioxide scrubber configured to remove excess carbon dioxide from methanated anode exhaust produced by the reactor and to recycle the methane back to the fuel cell stack.
24. The fuel cell system of claim 23, further comprising a water recycler for removing water from the anode exhaust, wherein the water recycler is located upstream of the reactor or downstream of the reactor.
25. A method of recirculating anode exhaust gas, comprising: providing anode exhaust stream from a fuel cell stack, reacting the anode exhaust stream to provide a methanated anode exhaust stream, scrubbing the methanated anode exhaust stream to remove excess carbon dioxide, after removing the excess carbon dioxide, providing the methanated anode exhaust stream into a fuel inlet stream, and internally reforming the fuel inlet stream in the fuel cell stack.
26. The method of claim 25, further comprising the step of recycling water from the anode exhaust stream into the fuel inlet stream before the reacting step or after the reacting step.
27. The method of claim 25, wherein the methane provided from the fuel exhaust stream into the fuel inlet stream cools the stack during the step of internally reforming the fuel inlet stream.
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