WO2008137964A1

WO2008137964A1 - Solid oxide fuel processor

Info

Publication number: WO2008137964A1
Application number: PCT/US2008/062965
Authority: WO
Inventors: Glendon M. Benson
Original assignee: Benson Glendon M
Priority date: 2007-05-07
Filing date: 2008-05-07
Publication date: 2008-11-13

Abstract

A membrane reactor in which reactants are subjected to reverse flow and counterflows that permit reactants and products of one species, such as air and lean air, to be fed and discharged at one end of the reactor and another species, such as fuel and oxidized products, to be discharged at the opposite end of the reactor This arrangement permits the use of close-coupled, compact and integral counterflow heat exchangers and enables fuel recovery from exhaust Heat transport devices, such as heat pipes, are used to isothermalize the membrane reactor and to transfer heat, produced or required, to external heat transfer fluids Adaptations of this arrangement permit the integration of separate devices into compact units, such as the stacking of fuel-assisted electrolyzers and fuel cells for the simulation production of hydrogen and/or electric power that are modulated to meet load demands

Description

SOLID OXIDE FUEL PROCESSOR

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims the priority of U.S. provisional application No. 60/928,193 filed May 7, 2007, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] This invention relates generally to apparatus which convert carbonaceous fuels into two separate exhaust streams comprising hydrogen and carbon dioxide, and more particularly the invention relates to systems that provide this conversion in the most energy-efficient method within minimum cost, volume and weight constraints, with the option of producing electrical energy. Modifications of this system include solid oxide fuel cells, solid oxide electrolyzers, solid oxide fuel-assisted electrolyzers, solid oxide oxygen generators fed by air or carbon dioxide, solid oxide hydrogen pumps, solid oxide oxygen pumps and related or combined systems that all employ ion or mixed ion/electron conducting thin films. Of particular interest is that this invention converts carbonaceous fuels to exhaust streams of only hydrogen and carbon dioxide in which the hydrogen stream fuels either combustion engines or fuel cells with essentially zero exhaust emissions, while the carbon dioxide stream can be captured for use in making hydrocarbon fuels employing hydrogen produced by renewable energy for ultimate sequestration, thereby eliminating its effect on global warming.

BACKGROUND OF THE INVENTION

[0003] Emissions from hydrocarbon-fueled combustion engines produce smog and greenhouse gases. Exhaust after-treatment devices, such as catalytic mufflers and particulate filters, have been developed over the last several decades to reduce smog-producing emissions but fail to reduce greenhouse gas emissions. An innovation that eliminates these emissions is a solid-state electrochemical fuel processor that converts, without combustion, conventional hydrocarbon fuels to pure hydrogen and carbon dioxide which are then discharged in separate streams, with hydrogen fed to the engine (combustion engine or fuel cell) for emission-free operation and carbon dioxide fed to a liquefier and then to a storage tank. For vehicles, with on-board storage tanks, the liquefied carbon dioxide is off-loaded during refueling for subsequent transfer to either a sequestration site or to a renewable-energy (e.g. solar thermal) powered electrolyzer. This electrolyzer produces hydrogen from steam and carbon monoxide from the transferred carbon dioxide and then the carbon monoxide and hydrogen are reacted to form a hydrocarbon fuel (e.g. 3H₂ + CO CH₄ + H₂O) that again is fed to fuel processors for the hydrogen-fueling of engines - thereby fully recycling the carbon, using only solar as an energy source.

[0004] It is evident that this fuel processor also may be applied to stationary engines. However, emphasis is directed toward the transportation sector since it produces 35% of all greenhouse gas emissions and, being mobile, presents a more difficult challenge for carbon dioxide capture. The practicality of using this fuel processor in mobile applications is shown by the following example. An advanced hydrogen-fueled, lean-burn combustion engine or fuel cell would provide a 44 mile per gallon (iso-octane equivalent) fuel consumption for a standard passenger car which, for a 400-mile vehicle range, would produce 161 pounds of carbon dioxide (comparable to the battery weight in a Lexus hybrid) that is nearly invariant of the hydrocarbon fuel fed to the fuel processor. Decreasing fuel consumption or range would reduce the weight of carbon dioxide captured per refuel. Further, using solid oxide fuel cell technology, the fuel processor would produce hydrogen at a rate of 100 KW (lower heating value) per cubic foot of fuel processor volume. Since the fuel processor operates at nearly steady-state and feeds hydrogen to a pressurized tank (via a compressor) it is not subject to vehicle transient power demands and therefore needs to provide a much lower average rate of energy output than the peak output of the vehicle drive engine.

[0005] Solid oxide ion conducting films have been used for electrochemically oxidizing hydrocarbon fuels to produce electricity, reducing steam to produce hydrogen and oxygen, reducing carbon dioxide to produce oxygen and carbon monoxide while solid oxide mixed ion/electron conducting films have been used for non-gal vanically separating oxygen from air and hydrogen from hydrogen-containing streams. These films have been employed in either planar or tubular arrays in stand-alone reactors that are fed reactants in co-flow, counterflow or cross-flow arrangements using remote heat exchangers and fuel processors that lead to large and costly systems on a per-unit output basis. SUMMARY OF THE INVENTION

[0006] The present invention concerns a fuel processor that converts, without combustion, carbonaceous fuels to pure hydrogen and carbon dioxide which are discharged in separate streams. This fuel processor is based upon the use of a high-temperature electrochemical reactor which employs a solid state membrane electrolyte, where the electrolyte may be proton (hydrogen ion) conducting or mixed proton/electron conducting (both referred to as a protonic electrolyte) or oxygen ion conducting, or mixed oxygen ion/electron conducting (both referred to as an oxonic electrolyte) and where mixed ion/electron conducting electrolytes are referred to as MIEC electrolytes.

[0007] The present invention employs a membrane reactor in which reactants are subject to a reverse counterflow arrangement that permits reactants and products of one species, such as air and lean air, to be fed and discharged at one end of the reactor and another species, such as fuel and oxidized products, to be fed and discharged at the opposite end of the reactor. This arrangement permits the use of close-coupled, compact and integral counterflow heat exchangers and provides means for fuel recovery from exhaust. This arrangement also makes possible the use of heat transport devices, such as heat pipes, to isothermalize the membrane reactor and to transfer heat, produced or required, to external heat transfer fluids. Adaptations of this arrangement permit the integration of separate devices into compact units, such as the stacking of fuel-assisted electrolyzers and fuel cells for the simulation production of hydrogen and electric power that are modulated to meet load demands.

[0008] The fuel processor, in which single electrochemical cells have either protonic or oxonic electrolytes, is fed reformed gases (carbon dioxide and hydrogen ) produced in a reformer that is fueled (for illustration) by a simple hydrocarbon — methane (CH₄) mixture, along with steam (H₂O). In practice, the reformer is integral with the electrochemical reactor thereby providing in-situ reformation. Reformed gases are fed to a hydrogen producing cell (HC) where the hydrogen from the reformate is separated from carbon dioxide by being conducted (in ion form) through a solid-state protonic electrolyte and then recombined to hydrogen gas that is discharged. Reformed gases are fed to an electrolysis cell (EC) where the fed steam is dissociated into hydrogen and oxygen, and the oxygen is conducted (in ion form) through a solid-state oxonic electrolyte and then reacted with the hydrogen, supplied by the reformate, to form steam that is discharged along with carbon dioxide. Condensation of the steam separates the carbon dioxide and the condensed steam is reheated and refed to the cell. The chemical potential provided by the oxidation of hydrogen replaces the voltage potential commonly used in dissociation of water by conventional electrolysis. The heat (Q) required by the reformer and electrochemical cells is caused by the endothermic reactions produced therein and is provided by external heat sources, such as exhaust from combustion engines or heat rejection from high temperature fuel cells.

[0009] Reformed gases are fed to a protonic fuel cell (FC) where the hydrogen from the reformate is separated from carbon dioxide by being dissociated, conducted (in ion form) through a protonic electrolyte and then oxidized by the fed oxygen to form steam that is discharged. The electrochemical oxidation of hydrogen produces both heat and electrical energy. Reformed gases are fed to an oxonic fuel cell (FC) where the hydrogen from the reformate is oxidized by the fed oxygen that is first dissociated, then conducted (in ion form) through an oxonic electrolyte and then oxidized to form steam that is discharged along with carbon dioxide. Condensation of the steam separates the carbon dioxide, and the condensed steam is reheated and refed to the cell. The heat (Q) required by the reformers is caused by the endothermic reactions produced therein and is provided by the heat rejected from the respective fuel cells, yielding a net heat rejection that may be transported to the reformer and electrochemical cells.

[0010] One method of achieving this heat transport is to stack in electrical series the hydrogen producing cell and the fuel cell. This permits the use of a closely-coupled heat exchange means between cells, such as the use of static heat pipes or circulating fluids, including fuel cell exhaust gases. This stacking arrangement also produces an increase in voltage across the ion-conducting hydrogen producing cell, owing to the voltage output of the fuel cell, which increases the ion flux through the electrolytes of the hydrogen producing cell thereby reducing the cell volume required for a fixed hydrogen output flow rate. The process chemical reactions for this stacking arrangement along with the global reactions (based upon external inputs and outputs of the stack) show that the chemical reactions are identical for cells employing either protonic or oxonic electrolytes.

[0011] Replacing single cell stacks with stacks comprising n hydrogen producing cells for each fuel cell permits the stack to operate adiabatically, provided the value of n is correct. The global reactions for the hydrogen producing cells and the fuel cells are the same for the stack containing protonic electrolytes and the stack containing oxonic electrolytes. Thus, the enthalpy change ( H_Hc) for the n hydrogen producing cells and the enthalpy change ( H_Fc) for one fuel cell is the same for either stack and therefore may be uniquely calculated. Adding the values of H_Hc and H_Fc and equating this sum to zero (necessary for adiabatic operation), and then solving for n, yields the number of hydrogen producing cells per fuel cell that is required for adiabatic stack operation. This calculation is valid since the total energy (heat and electric) produced by the ion-conducting fuel cell is transferred to n ion-conducting hydrogen generating cells, with cell losses (e.g. polarization and ohmic) only reducing the hydrogen discharge rate from the hydrogen producing cells. These calculations yield n = 4.19235 for 1000 K and n = 4.12390 for 1200 K stack operating temperatures. Changes in reactant composition and the degree of reactant utilization in the stack changes the value of n obtained, with n = 4.00 being typical.

[0012] The enthalpy produced by the oxidation of the hydrogen produced by each of the stacks is based upon the reaction:

4nH₂ + 2nO₂ 4nH₂O and equals, at respective oxidation temperature of 1000 K and 1200 K:

H_H2)iooo = -4,156,413 J ; H_H2)i_2Oo = -4,107,355 J

[0013] The enthalpy produced by the oxidation of the methane fed to each of the stacks is based upon the reaction: (n + 1) CH₄ + 2 (n + 1) O₂ (n + 1) CO₂ +2 (n + 1) H₂O and equals, at respective oxidation temperatures of 1000 K and 1200 K: H_CH4)iooo = -4,156,413 J ; H_CH4)i₂oo = -4,107,355 J

[0014] Hence, the enthalpy produced by oxidizing the hydrogen produced by each of the stacks equals the enthalpy produced by oxidizing, at the same temperature, the methane fuel fed to each of the stacks. This result is independent of the type of fed fuel.

[0015] The terminal voltage produced by four (n = 4) serially connected ion-conducting hydrogen generating cells, using an open circuit voltage of .25 volts and an areal specific resistance (ASR) of .20 ohm cm² at a current density of j (amps/cm²), is:

V_HC = .25 - .20 j (volts) (1) whereas the terminal voltage produced by the ion-conducting fuel cell, using an open circuit voltage of 1.00 volts and the same ASR value, is:

V_FC = 1.00 - .2Oj (volts) (2) [0016] Equations 1 and 2 show that the combined voltages of the hydrogen generating cells and the fuel cell are zero at a current density of 2 Amps/cm² and represent a stack producing only hydrogen. In this mode, all of the heat and the electric energy produced by the fuel cell is consumed by the hydrogen generating cells resulting in an adiabatic stack. As the current density decreases, a positive voltage is thereby produced which, when connected to an electrical load, represents electric power, while hydrogen production has decreased. At zero current density, neither hydrogen nor electric power is produced and no fuel is consumed. As a result, this configuration is primarily a hydrogen producer with electric power a secondary product. Increasing the value of ASR, due to higher ohmic and polarization losses in both the hydrogen generating cells and fuel cell, decreases both the hydrogen production rate and the electric power produced.

[0017] In the stacks, the current through the ion-conducting fuel cell equals that in the ion- conducting hydrogen producing cells. The installation of a current shunt between the fuel cell and the hydrogen producing cells electrically disconnects the hydrogen producing cells from the fuel cell and connects the fuel cell to an electric load. For this operating mode, no hydrogen is generated in the ion-conducting hydrogen producing cells, unless they are electrically connected, and the fuel cell may be operated to match electrical load demand. Replacing the current shunt with a variable conductance switch provides modulation of the current to the hydrogen producing cells, independent of the current in the fuel cell. Such decoupling of the current in the fuel cell from the current in the hydrogen producing cells provides operating flexibility while still permitting the heat rejected from the fuel cell to flow to the hydrogen producing cells through use of side-mounted heat transfer conduits. As a result, the stack may continuously vary its output from all hydrogen production to all electric production. The disadvantage of this configuration is that the hydrogen producing cells are idled when only electric production is required.

[0018] For the stacks to produce both hydrogen and electricity without idling the hydrogen producing cells when only electricity is demanded requires that the cathodes of the ion- conducting hydrogen producing cells need to operate efficiently under both a reducing atmosphere (steam and hydrogen) for hydrogen production and an oxidizing atmosphere (oxygen) for electrical production, i.e. fuel cell operation. For producing only hydrogen, all the cathodes of the hydrogen producing cells are fed steam, or a steam-hydrogen mixture. Sequentially switching these cathodes from steam to oxygen (air) admission increases step- wise the electric power output and decreases hydrogen output. When all cathodes of the hydrogen generating cells are fed oxygen (air) then all of these cells produce electric power in combination with the electric power produced by the fuel cells. Therefore, with this design the stack output is incrementally varied from hydrogen only to electric power only, with the maximum hydrogen production occurring at zero electric power output and zero net heat output (i.e. adiabatic operation) and with the maximum electric power production occurring at zero hydrogen production and maximum heat rejection (since all cells are now operating as fuel cells).

[0019] For hydrogen only production, the stacks employ mixed ion/electron conducting

(MIEC) membrane electrolytes (protonic and oxonic). The output of the fuel cell - now just an electrochemical fuel oxidizer - is only heat, which is transferred to the hydrogen generating cells (for fuel reforming) by heat transport means, such as static heat pipes or circulating fluids, including fuel cell exhaust gases. The reactions are the same, as well as the number (n) of hydrogen generating cells to fuel cells required for adiabatic stack operation. The use of MIEC membrane electrolytes simplifies design by eliminating electrical connections between cells and provides an order of magnitude higher flux density than ion- conducting electrolytes, particularly for oxonic MIECs, viz. 5 x 10^"5 vs 5 x 10^"6 molo₂/sec cm² or 10 x 10^"5 vs 1 x 10^"5 molm/sec cm² equivalent. Further, in-situ steam reforming with excess steam provides a less reducing atmosphere than in syngas production and therefore aids in overcoming the inherent limited thermodynamic stability of highly conductive MIECs, particularly at the high temperatures required (typically 1520-1550⁰F for nickel- catalyzed steam reforming).

[0020] The hydrogen producing cells and fuel cells may also be combined axially, which is of advantage in using MIECs, as illustrated by the following. Admitting the combined feed stream, (n + 1) CH₄+ 2(n + I)H₂O, above an air-supplied oxonic MIEC membrane, transfers 2O₂ to the stream, which oxidizes a portion of the stream to CO₂ + 2H₂O, that in turn provides the energy required for reforming the stream, thereby producing a stream composed of (n + I)CO₂ + 4H₂O + 4nH₂. Admitting this stream above a protonic MIEC membrane transfers 4nH₂ from the stream to a hydrogen discharge channel below the membrane. The global reactions and the value of n are the same as those for an adiabatic stack.

[0021] For these high temperatures both protonic and oxonic membrane electrolytes (including MIECs) are solid oxides and therefore the hydrogen producing cells are termed Solid Oxide Electrolysis Cells (SOEC) or, when fuel-energized (as described and used herein), are termed Solid Oxide Fuel-energized Electrolysis Cells (SOFEC) and the fuel cells are termed Solid Oxide Fuel Cells (SOFC). This terminology will be used in the remainder of this application.

BRIEF DESCRIPTION OF THE DRAWINGS [0022] FIG. 1 is a diagrammatic illustration of a solid oxide fuel processor system.

[0023] FIG. 2 is a layout of the components of a solid oxide fuel processor.

[0024] FIG. 3 is a detailed illustration of a repeat unit of the solid oxide fuel cell in the fuel processor.

[0025] FIG. 4 is an illustration of one cell of the two-cell repeat unit.

[0026] FIG. 5 is a longitudinal cross-section of a side heat pipe for a solid oxide fuel processor.

[0027] FIG. 6 is an exploded assembly of a planar repeat unit.

[0028] FIG. 7 is a cross-section of an ion conducting membrane assembly.

[0029] FIG. 8 is a gas flow diagram for an ion conducting fuel processor.

[0030] FIG. 9 is an illustration of the operation of a cathode manifold purge valve.

[0031] FIG. 10 is a diagram of electrical switching means for a solid oxide fuel cell/solid oxide fuel-assisted fuel processor.

[0032] FIG. 11 is a diagram of the components of a mixed ion/electron conducting membrane reactor fuel processor.

[0033] FIG. 12 is a detailed illustration of the repeat unit in a mixed ion/electron conducting membrane reactor fuel processor.

[0034] FIG. 13 is a detailed illustration of the repeat unit in a mixed ion/electron conducting membrane reactor fuel processor with hydrogen separator. [0035] FIG. 14 is an illustration of the cross-section of the unit cell of the repeat unit in a mixed ion/electron conducting membrane reactor.

[0036] FIG. 15 is an illustration of three cross-sections of mixed ion/electron conducting membrane assemblies.

[0037] FIG. 16 is an illustration of the coupling between tubular membranes and tubular heat exchangers.

[0038] FIG. 17 is an illustration of the cross-sections of a finned hydrogen separator.

[0039] FIG. 18 is an illustration of an integrated fuel cell processor and fuel cell.

DESCRIPTION OF THE PREFERRED EMBODIMENTS [0040] FIG. 1 diagrammatically illustrates a system that incorporates the present invention (a solid oxide fuel processor) 1 which is fed heated water vapor (steam) 2, a heated carbonaceous fuel 3 and heated air 4 and exhausts hot lean air 5, pure hydrogen 6 and a composite gas (steam and carbon dioxide) 7, both at approximately the temperature in fuel processor 1. Details of fuel processor 1 are shown in FIGS. 2 and 3 and further discussed below.

[0041] The exhaust steam 6 is cooled in counterflow heat exchanger 8, and flows as cooled gas 9 to compressor 10 and then as a compressed gas 11 to storage tank 12. Tank 12 supplies pressurized hydrogen 13 to a combustion engine or fuel cell 14, and the engine exhausts a composite gas (steam and lean air) 17 after performing work output. Exhaust stream 17 is cooled in counterflow heat exchanger 18 and then is discharged to atmosphere as a cooled composite exhaust stream 19. A portion of gas stream 17 is condensed to liquid in 18 and then re-enters 18 as liquid stream 20 where it is vaporized and then discharged as steam 21 which is fed to heat exchanger 8 where it is heated and then is discharged as hot steam 22, partially supplying steam to 2. Intake air 23 is fed to counterflow heat exchanger 24 which provides hot air stream 4 to fuel processor 1, while hot lean air 5 is discharged from fuel processor 1, cooled by heat exchanger 24 and then discharged to atmosphere as exhaust stream 25. Composite gas stream 7 from fuel processor 1 is fed to heat exchanger 26 wherein the steam portion of gas stream 7 is condensed and then discharged as a liquid stream 27 that is then fed to counterflow heat exchanger 28 wherein it is vaporized and discharged as vapor stream 29. Stream 29 is fed to compressor 30 and then discharged as a compressed vapor 31. Vapor stream 31 is fed to superheater 32 wherein it is heated, by heat exchange with 26, and then discharged as a superheated stream 33. Stream 33 then combines with stream 22 to supply steam to 2. The portion of gas stream 7 not condensed in heat exchanger 26 is discharged as a carbon dioxide stream 34 and fed to carbon dioxide liquefier 35 where it is condensed and then discharged as liquid stream 36 to storage tank 37 for reuse or sequestration.

[0042] FIG. 2 diagrammatically depicts the construction of a solid oxide fuel processor 1 as shown in FIG. 1. It has a cathode manifold 50, a cathode gas counterflow heat exchanger 51, a solid oxide membrane reactor 52, a hydrogen separator 53, an anode gas counterflow heat exchanger 54, a steam heat exchanger 55 and an anode manifold 56. Ambient air 57 is fed to cathode manifold 50 which divides air stream 57 into multiple air streams 58 and then feeds airstreams 58 to plate heat exchangers within heat exchanger 51 wherein air streams 58 are heated and then discharged as hot air streams 59. Hot air streams 59 are fed to membrane reactor 52, which comprises a stack of at least one pair of solid oxide fuel cells (SOFC) 60, which remove oxygen from the air stream by oxygen-ion transport through an ion-transport membrane, and this air stream is discharged from SOFC 60 as a lean air stream 61 to heat exchanger 51 wherein lean air stream 61 is cooled to a cool lean air stream 62 which flows through cathode manifold 50 and then is discharged as exhaust air stream 63. Water vapor 64 is fed to cathode manifold 50 which divides vapor stream 64 into multiple vapor streams 65 and then feeds vapor streams 65 to plate heat exchangers within cathode heat exchanger 51 where vapor stream 65 is heated and then discharged as a hot steam stream 66. Hot steam stream 66 is fed to membrane reactor 52, which also comprises a stack of at least one pair of solid oxide fuel assisted electrolyzer cells (SOFEC) 67 wherein the steam stream 66 is reduced to hydrogen by electrochemical dissociation and transport of oxygen ion through an oxygen-ion transport membrane. The hydrogen so produced is discharged from SOFEC 67 as a hot hydrogen stream 68 to cathode heat exchanger 51 wherein hydrogen stream 68 is cooled to a cool water vapor stream 69 which flows through cathode manifold 50 and then is discharged as exhaust hydrogen stream 70. Fuel gas 71 is fed to anode manifold 56 which divides fuel gas stream 71 into multiple gas streams 72 and then feeds gas streams 72 to plate heat exchangers within 54 wherein gas streams 72 are heated and then discharged as hot gas streams 73. Hot gas stream 73 void of hydrogen is fed to hydrogen separator 53, which comprises a stack of at least one hydrogen separation cell 74 which infuses hydrogen into gas stream 73 thereby producing a hydrogen enriched gas stream 75. Water vapor 76 is fed to steam heat exchanger 55 which divides water vapor stream 76 into multiple water vapor streams 77 and then feeds those to plate heat exchangers within steam heat exchanger 55 wherein water vapor streams 77 are treated and then discharged as a hot steam stream 78. Hot steam stream 78 is mixed with hot fuel gas stream 75 to form, without reforming, a composite gas stream 79, comprising steam and fuel gas, at entrance to membrane reactor 52. Part of composite gas stream 79 is fed to SOFC 60 wherein it is in-situ reformed and then oxidized by reduction of air stream 59 to form a gas stream comprising steam 80, carbon dioxide 81 and residual hydrogen 82 (due to incomplete consumption of hydrogen), which is discharged from SOFC 60 and fed to hydrogen separator 53. The remainder of composite gas stream 79 is fed to SOFEC 67 wherein it is in-situ reformed and then oxidized by reduction of steam stream 66 to form a gas stream comprising steam 80, carbon dioxide 81 and residual hydrogen 82 (due to incomplete consumption of hydrogen), which is discharged from SOFEC 67 and fed to hydrogen separator 53. In hydrogen separator 53 gas streams of steam 80, carbon dioxide and residual hydrogen 82 flow through at least one hydrogen permeable membrane chamber 74 which separates the residual hydrogen 82 and transports it to the fuel gas stream 73 counterflowing (illustrated in FIG. 3) in the fuel gas inflow channel of chamber 74 which separates the residual hydrogen 82 and transports it to the fuel gas stream 73 counterflowing in the fuel gas inflow channel at chamber 74 in hydrogen separator 53. The hydrogen-free streams of steam 80 and carbon dioxide 81 are exhausted from hydrogen separator 53 and are fed to anode gas heat exchanger 54 where they are cooled by counterflow heat exchange with fuel gas stream 72 and water vapor stream 77, and then discharged as cool gas streams 83 and 84 to anode manifold 56 from which they are exhausted as a steam stream 85 and carbon dioxide stream 86. In the process of producing hydrogen, the SOFC/SOFEC membrane reactor 52 also produces a voltage.

[0043] FIG. 3 diagrammatically illustrates in detail one of the repeat units of the solid oxide fuel cell 60 of the assembly shown in FIG. 2. Ambient air 57 is fed to cathode manifold 50 and then is fed to cathode counterflow heat exchanger 51 as air stream 58 where heat Q is transferred to heat air stream 58 to the temperature of the solid oxide fuel cell reactor 52. The heated air stream 59 is discharged from cathode heat exchanger 51, conducted around fuel gas stream connecting channel 83 to form a reverse flow (as illustrated in FIG. 3) and is fed to the top cathode flow channel 84 where air is electrochemically reduced to oxygen ions, which in turn are transported through the top electrolyte membrane 85 to the top anode flow channel 86 where they oxidize a portion of the fuel contained therein. The air stream 59 is discharged from the top cathode flow channel 85 through air stream connecting channel 87 and into the bottom cathode flow channel 88 where air is electrochemically reduced to oxygen ions, which in turn are transported through the bottom electrolyte membrane 89 to the bottom anode flow channel 90 where they oxidize a major portion of the fuel contained therein. The air stream 61 is discharged from the bottom cathode flow channel 88, as oxygen-depleted (lean) air, into cathode heat exchange 51 where heat Q is transferred to air stream 58, thereby cooling hot lean air stream 61 to a near-ambient temperature lean air stream 62 which is exhausted through cathode manifold 50 as lean air exhaust stream 63. Fuel gas 71 is fed to anode manifold 56 and then is fed to anode counterflow heat exchanger 54 as gas stream 72 where heat Q is transferred to heat gas stream 72 to the temperature of the solid oxide fuel cell 52. The hydrogen-free heated gas stream 73 is discharged into the hydrogen separator's top flow channel 91 where hydrogen ions are transported through hydrogen permeable membrane 74 to gas stream 73, thereby producing a hydrogen-rich gas stream 75 that is discharged from 91. Water vapor 76 is fed into steam heat exchanger 55 and heated to produce a hot steam stream 78. At the entrance to the top anode flow channel 86 the hot gas stream 75 is mixed with the hot steam stream 78 and then combined into anode feed stream 79 without reforming. Oxygen ions transported through the top electrolyte 85 oxidize a portion of the fuel contained in top anode flow channel 86. The gas stream 79 is discharged from the top anode flow channel 86 through gas stream connecting channel 83 into the bottom electrolyte 89 to oxidize a major portion of the fuel contained therein, producing a composite exhaust gas containing steam stream 80, carbon dioxide stream 81 and a residual hydrogen stream 82. This composite gas stream is conducted around air stream connecting channel 87 and fed into the hydrogen separator bottom flow channel 92. The high partial pressure of hydrogen in the bottom flow channel 92 drives hydrogen ions through the hydrogen ion permeable membrane 74 into the initially hydrogen-free fed fuel gas stream in the top flow channel 91. The steam stream 80 and carbon dioxide stream 81, essentially hydrogen free, are discharged from the bottom flow channel 92 and fed as a composite gas to anode counterflow heat exchanger 54 where it is cooled by heat transport Q to the intake fuel gas stream 72 and steam stream 76. The near-ambient temperature composite gas stream comprising steam 82 and carbon dioxide 84 is discharged from anode heat exchanger 54, fed into anode manifold 56 and then discharged from manifold 56 as exhaust steam 85 and carbon dioxide 86. [0044] Exchanging the air feed in the repeat unit shown in FIG. 3 to steam feed changes the solid oxide fuel cell (SOFC) in FIG. 3 to a solid oxide fuel-assisted electrolyzer (SOFEC) in which the steam is reduced to hydrogen in the cathode and the co-produced oxygen is transported through oxygen ion conducting top electrolyte 85 and bottom electrolyte 89 and then oxidizes fuel gas in the top anode flow channel 86 and the bottom anode flow channel 90. The cathode manifold intakes air 57 and exhausts lean air 63 at its top, as shown in FIG. 2, and intakes steam 64 and exhausts hydrogen 70. The air stream feeds the anodes and the steam stream feeds the cathodes of the SOFEC. All other aspects of the SOFEC are identical to those of the SOFC shown in FIG. 2.

[0045] FIG. 4 illustrates cross-sections of one cell of the two-cell repeat unit for either the solid oxide fuel cell (SOFC) or the solid oxide fuel-assisted cell (SOFEC) shown in FIG. 3. FIG. 4A shows a lateral cross-section and FIG. 4B shows a longitudinal cross-section of one integral cell. The cathode current collector 100 is a perforated metal sheet with slots that are closely spaced in the longitudinal direction and match the width of the cathode flow channel 84 in the lateral direction. The cathode current collector is bonded to the flat top of the cathode interconnect 101. The flat bottom of 101 is brazed to the laterally grooved top face of the anode interconnect 102 to form a brazed interconnect assembly 112, and the flat bottom face is bonded to the anode current collector 103, which is identical to the cathode current collector 100. The anode interconnect 102 is longitudinally grooved to provide anode flow channels 86 in which the anode gas counterflows relative to the cathode gas. A glass- ceramic hermetic seal 104 provides a peripheral seal for the electrochemically active PEN 105 which comprises integral planar sheets of porous anode 106, solid ion conducting electrolyte 107 and porous cathode 108. The PEN's porous anode 106 is reactively brazed to the anode current collector 103. In vertically stacking these cells, the cell beneath that shown in FIG. 4 has its cathode current collector make contact with porous cathode 108 while the cell above that shown in FIG. 4 has its porous cathode make contact with cathode current collector 100 thereby providing a low electrical resistance between stacked cells. The lateral groves 109 in anode interconnect 102 form the heat pipe flow channels in which liquid metal, such as sodium, flows laterally from condensing chamber 110 by the capillary action produced by the porous coating 111 on lateral grooves 109. Heat produced within the cell vaporizes the liquid metal, which vapor then flows through grooves 109 to condensing chamber 110 in which the metal vapor condenses by heat exchange with a side-mounted heat exchanger, such as a heat pipe. The condensed metal is drawn back into the lateral grooves 109 by the capillary action produced by the porous coating 111 on the condensing chamber's walls. The heat pipe isothermalizes the cell by laterally transporting cell produced heat to condensing chamber 110 which longitudinally transports heat which, in turn, isothermalizes the chamber's external side wall. Hydrogen permeation through the metal interconnects 101 and 102 to the heat pipe channels 109 is impeded by precoating the channels and condensing chamber with a hydrogen impermeable barrier, such as a dense ceramic film. Residual hydrogen in the heat pipe is removed by hydrogen permeable membranes mounted on the ends of condensing chamber 110, which are coated with a catalyst to ensure rapid oxidation of hydrogen transported through the membranes. For long operating life all metal surfaces, except those interior to heat pipe, are coated with an electrically conductive oxidation-and- reduction-resistant oxide coating, such as a lanthanum-strontium-chromium-cobaltite film.

[0046] FIG. 5 illustrates a longitudinal cross-section through a vertical plane of a vertically short-sided heat pipe heat exchanger 120. Seven heat pipe chambers 121, formed in block 122 as longitudinal grooves and enclosed by sealing sheet 123, are filled with liquid metal through port 124 and sealed with a hydrogen permeable membrane inserted into both ends of 124 formed in ends of sealing sheet 123. Heat applied to the external flat face of sealing sheet 123 is transferred through sealing sheet 123 and vaporizes liquid metal entrained in porous coating 125. Metal vapor 126 so formed flows laterally to the longitudinal groove faces 127 in block 122 where it condenses. The heat of metal condensation heats block 122 to nearly the temperature of the stack side adjacent to the flat face of sealing sheet 123. Block 122 conducts heat laterally to fins 128 that are brazed to cover sheet 129 thereby forming longitudinal flow channels 130. A heat transfer fluid 131, preferably a gas or vaporizable liquid, flows into flow channels 130 at one end of heat exchanger 120, then longitudinally through channels 130, and exhausts from the opposite end of heat exchanger 120, thereby absorbing the heat generated in the stack. In addition to this heat transfer function of heat exchanger 120, the vertical slots 132 permit a vertical transport of liquid and vaporized metal contained in chambers 121, thereby isothermalizing the stack in the vertical direction. FIG. 6 illustrates an exploded assembly of a planar repeat unit (without a planar heat pipe) for either the solid oxide fuel cell (SOFC) or the solid oxide fuel-assisted electrolyzer cell (SOFEC). The assembly is stacked vertically and comprises, from bottom upward, anode current collector 103, brazed interconnect 112 containing anode interconnect 102 and cathode interconnect 101, cathode current collector 100, glass-ceramic hermetic seal 104 and PEN 105. PEN 105 is framed and sealed by glass-ceramic seal 104 which also provides a peripheral seal between cathode current collector 100 and anode current collector 103 of the next repeat unit. Cathode current collector 100 is brazed to interconnect 133 and interconnect 133 is brazed to anode current collector 103.

[0047] FIG. 7 schematically shows a through-plane cross-section of PEN 105 sandwiched between metal anode current collector 103 and metal cathode current collector 100 (both shown in phantom). PEN 105 comprises the following five bonded planar layers: a porous thick anode current collector 133 which typically acts as the support for the PEN and exhibits high open porosity and big electronic conductivity that provide an evenly distributed current to anode 106 from anode current collector 103; a porous functional anode 106 which exhibits high electrochemical activity, mixed ionic and electronic conductivities (MIEC) and comprises a dense open porous structure; an electrolyte 107 which exhibits high ion conductivity with minimum electronic conductivity and comprises a very thin solid structure; a porous functional cathode 108 which exhibits high electrochemical activity, mixed ionic and electronic conductivities (MIEC) and comprises a thin dense open porous structure; and a porous cathode current collector 134 which exhibits high open porosity and high electronic conductivity and evenly distributes current to cathode 108 from cathode current collector 100.

[0048] Excluded from the cross-section of PEN 105 are any functional or barrier layers between anode and electrolyte or between electrolyte and cathode.

[0049] FIG. 8 illustrates gas flows in an SOFC/SOFEC solid oxide fuel processor (without hydrogen separator) comprising SOFC cathode manifold 50', SOFC cathode counterflow heat exchanger 51', SOFC stack 60, SOFC anode counterflow heat exchanger 54', common anode manifold 56, SOFEC cathode manifold 50", SOFEC cathode counterflow heat exchanger 51", SOFEC stack 67 and SOFEC anode counterflow exchanger 54". Air is fed into SOFC cathode manifold 50' at air intake 57, is heated in SOFC cathode counterflow heat exchanger 51' to SOFC stack temperature and is then fed into SOFC 60. Lean air is discharged from SOFC 60, cooled in SOFC cathode heat exchanger 51', discharged into SOFC cathode manifold 50' and discharged to atmosphere at air exhaust 63. Vaporized water is fed into SOFEC cathode manifold 50" at steam intake 64, is heated in SOFEC cathode counterflow heat exchanger 51" to SOFEC stack temperature and is then fed into SOFEC 67. Hydrogen is discharged from SOFEC 67, cooled in SOFEC cathode heat exchanger 51", discharged into SOFEC cathode manifold 50" and discharged at hydrogen exhaust 70. Line 89 is an imaginary operating line that separates the stack into cells that operate as SOFCs and those that operate as SOFECs. Above line 89 the cathode manifold, cathode heat exchanger and SOFC cathodes have air flow, while below line 89 the cathode manifold, cathode heat exchanger and SOFEC cathode have a steam-hydrogen flow. The unique feature of this solid oxide fuel processor is that it produces both hydrogen and electric output. If all cathodes are fed air, line 89 moves to the bottom of the fuel processor and the SOFEC becomes an SOFC producing only electric output at the largest voltage potential (V_out - V_1n). If all cathodes are fed steam, line 89 moves to the top of the fuel processor and the SOFC becomes an SOFEC producing only hydrogen with zero voltage potential. Intermediate positions of line 89 indicate which portions of the complete stack operate as SOFCs and which portions operate as SOFECs, thereby regulating the electric and hydrogen output. Since both the SOFC and SOFEC anodes are fed a common fuel, movement of line 89 has no effect on anode operation. However, movement of line 89 upward by one cell height immediately drives hot steam into the hot air-filled cathode, while a downward movement of line 89 by one cell height immediately drives hot air into the hot hydrogen- filled cathode. To eliminate this dangerous condition the cathode that is being switched needs to be purged with stem and this purging must be available to each cell of the complete stack. An effective method of accomplishing this is to use one piston positioned in the intake bore of the cathode manifold and a second piston position in the discharge bore, with both piston strokes sufficient to traverse the entire stack height.

[0050] FIG. 9 illustrates the design and operation of the cathode manifold purge valve for use in an SOFC/SOFEC fuel processor. This valve, shown in FIG. 9A, comprises two pistons: intake piston 140 and exhaust piston 141, each coupled to a hollow tubular drive rod 142 and 143, respectively, with purge steam provided to rod 142 and leak steam provided to rod 143, with purge steam and leak steam provided by a common source, external the cathode manifold. Intake piston 140 and exhaust piston 141 are separately driven through respective drive rods 142 and 143, by linear stepper motors, external the cathode manifold. The cathode manifold contains an intake manifold sleeve 144 and an exhaust manifold sleeve 145 each with radial ports 146 and 147, respectively, axially that match the vertical spacings of the intake manifold ports 148 and the exhaust manifold ports 149. Each piston has a radial flow passage, 150 and 151, respectively, that flow communicates with its respective hollow drive rod, and also has two circumferential seals 152 and 153, respectively, that are axially equal- spaced from the centerline of the piston's radial flow passage. In FIG. 9A manifold sleeve ports 148, 149 and 149'are open and the two pistons are parked between adjacent ports. This condition represents steady state operation. In FIG. 9B the intake piston 140 downstrokes and aligns its radial flow passage 150 with the intake manifold port 148', formerly an air inlet port, which port is now steam purged by purge steam flowing through the intake piston's radial flow passage 150. This steam purge also purges all cathode flow channels connected to manifold intake port 148' and exhausts through manifold exhaust port 149' into the air side of the exhaust manifold sleeve 145. In FIG. 9C the exhaust piston 141 downstrokes and uncovers exhaust manifold port 149' thereby discharging purge steam to the hydrogen side of the exhaust manifold sleeve 145. In FIG. 9D the intake piston 140 downstrokes and uncovers intake manifold port 148', thereby feeding steam from the steam side of intake manifold sleeve 144 into all cathode flow channels connected to port 148'. Since exhaust manifold port 149' is open, hydrogen produced in the SOFEC flow channel now exhausts to the hydrogen side of the exhaust manifold sleeve 145. All ports are now open and the stack is operating in steady-state, but with one more SOFEC cells electrolyzing steam in hydrogen than shown in FIG. 9A. In FIG. 9E the intake piston 140 upstrokes from its position shown in FIG. 9A and aligns its radial flow passage 150 with the intake manifold port 148, formerly a steam inlet port, which port is now steam purged by purge steam flowing through the intake piston's radial flow passage 150. This steam purge also purges all cathode flow channels connected to manifold intake port 148 and exhausts through manifold exhaust port 149 into the hydrogen side of exhaust manifold sleeve 145. In FIG. 9F the exhaust piston 141 upstrokes and uncovers exhaust manifold port 149 thereby discharging purge steam from all cathode flow channels connected to intake manifold port 148 into the air side of the exhaust manifold sleeve 145. In FIG. 9G the exhaust piston 141 upstrokes and uncovers intake manifold port 148, thereby feeding air to all cathode flow channels connected to this port, and the exhaust air discharges to the air side of exhaust manifold sleeve 145. All ports are open and the stack is operating in steady state but with one more cell operating as a fuel cell than shown in FIG. 9A.

[0051] FIG. 10 illustrates an SOFC/SOFEC fuel processor comprising SOFC 60, SOFEC 67, conductive electrical buses 160 and 161, controller 162, electrical loads 163 and 164, and connecting electrical conductors 165, 166, 167 and 168. Both SOFC 60 and SOFEC 67 are commonly fueled and are thermally coupled. When bus 160 is electrically connected to bus 161, SOFC 60, SOFEC 67 and loads 163 and 164 are connected in series. For a stack comprising four SOFECs and one SOFC the terminal voltage output of the four SOFECs typically is: S_OFEC = .25 - .2Oj (volts), and that for the one SOFC typically is: V_SOFC = 1.00 - .2Oj (volts), where j is current density (amperes per square centimeter), noting that all current passes through all cells. The combined voltage output of all cells is zero at a current density of 2A/cm² and only hydrogen is produced. As current density decreases a positive voltage is produced while hydrogen production is reduced. At zero current density neither hydrogen nor electricity is produced and no fuel is consumed. Electrically decoupling SOFC 60 and SOFEC 67 through controller 162 permits SOFC 60 to drive load 164 independent of SOFEC 67 driving load 163. This decoupling provides operating flexibility relative to that provided without such decoupling.

[0052] FIG. 11 diagrammatically illustrates a solid oxide fuel processor comprising cathode manifold 50, cathode gas counterflow heat exchanger 51, solid oxide membrane reactor 52, anode gas counterflow heat exchanger 54, steam heat exchanger 55 and anode manifold 56. Ambient air 57 is fed to cathode manifold 50 which divides air stream 57 into multiple air streams 58 and then feeds air streams 58 to plate heat exchangers within heat exchanger 51 wherein air streams 51 are heated and then discharged as hot air streams 59. Hot air streams 59 are fed to membrane reactor 52, which comprises a stack of at least one pair of mixed ionic/electronic conducting (MIEC) membrane reactors 170 and then is discharged from membrane reactor 170 as a lean air stream 61 to heat exchanger 51 wherein air stream 61 is cooled to a cool lean air stream 62 which flows through cathode manifold 50 and then is discharged as exhaust air stream 63. Fuel gas 71 is fed to anode manifold 56 which divides fuel gas stream 71 into multiple gas streams 72 and then feeds gas streams 72 to plate heat exchangers within 54, wherein gas streams 72 are heated and then discharged as hot gas streams 73, and water vapor 76 is fed to steam heat exchanger 55 which divides water vapor stream 76 into multiple water vapor streams 77 and then feeds these to plate heat exchangers within steam heat exchanger 55, wherein water vapor streams 77 are heated and discharged as hot steam stream 78. Hot steam stream 78 is mixed with hot fuel gas stream 75, without reforming, into a composite steam-fuel gas stream 79 at entrance to membrane reactor 52 which comprises a stack of at least one pair of MIEC membrane reactors 170. Composite gas stream 79 is fed into the MIEC membrane reactor where it is adiabatically reformed to carbon dioxide and hydrogen, employing heat provided by oxidation of a portion of the fuel gas to carbon dioxide and steam using oxygen separated from the air stream by an oxygen ion conducting MIEC membrane. The carbon dioxide and hydrogen stream is separated into a hydrogen stream and a carbon dioxide stream using a proton conducting MIEC membrane. The resulting reaction products are discharged from the membrane reactor as steam stream 80, carbon dioxide stream 81 and hydrogen stream 82, which are fed to anode heat exchanger 54 where they are cooled, discharged through the anode manifold 56 and then exhausted as hydrogen stream 82 and a composite stream comprising a carbon dioxide stream 81 and water vapor stream 80. The only products produced are a pure hydrogen stream and a carbon dioxide stream, both at near-ambient temperature. No heat is produced since the reaction within the membrane reactor is adiabatic.

[0053] FIG. 12 diagrammatically illustrates in detail one of the repeat units contained in the assembly shown in FIG. 11. Ambient air 57 is fed to cathode manifold 50 and then is fed to cathode counterflow heat exchanger 51 as air stream 58 where heat Q is transferred to heat air stream 58 to the temperature of the membrane reactor 170. The heated air stream 59 is discharged from cathode heat exchanger 51, conducted first around hydrogen gas stream connecting channel 174, then around fuel gas stream connecting channel 83 and fed to the top cathode flow channel 84 where oxygen is separated from air by the oxygen ion conducting MIEC top membrane 171 and transported through membrane 171 to the top anode flow channel 86 where it oxidizes a portion of the fuel contained therein. The air stream 59 is discharged from the top cathode flow channel 84 through air stream connecting channel 87 and into bottom cathode flow channel 88 where oxygen is separated from air by the oxygen ion conducting MIEC bottom membrane 176 to the bottom anode flow channel 90 where it oxidizes the remaining portion of fuel contained therein. The air stream 61 is discharged from the bottom cathode flow channel 88 as oxygen-depleted (lean) air into cathode heat exchanger 51 where heat Q is transferred to air stream 58, thereby cooling hot lean air stream 61 to a near-ambient temperature lean air stream 62 which is exhausted through cathode manifold 50 as lean air exhaust stream 63. Fuel gas 71 is fed to anode manifold 56 and then is fed to anode counterflow heat exchanger 54 as gas stream 72 where heat Q is transferred to heat gas stream 72 to the temperature of the membrane reactor 170. Water vapor 76 is fed into steam heat exchanger 55 and heated to produce a hot steam stream 78. A portion of the hot steam stream 178 is fed into hydrogen flow channel 173 to serve as a sweep gas and the remainder of hot steam stream 78 is mixed with fuel gas stream 73 and then combined, without reforming, into anode feed stream 79. Oxygen ions transported through the top oxygen ion conducting MIEC 171 oxidize a portion of the fuel contained in the top anode flow channel 86. The gas stream 79 is discharged from the top anode flow channel 86 through gas stream connecting channel 83 into bottom anode flow channel 90 where oxygen ions transported through bottom oxygen ion conducting MIEC 176 oxidize the remaining portion of fuel contained therein, producing a composite exhaust gas containing steam stream 80 and carbon dioxide stream 81. This composite gas stream is conducted around air stream connecting channel 87 and fed into anode counterflow heat exchanger 54 where it is cooled by heat transport Q to the intake fuel gas stream 72. The near-ambient temperature composite gas stream (80 and 81) discharged from anode heat exchanger 54 is fed into anode manifold 56 and then discharged from manifold 56 in a separate stream as exhaust gases comprising steam 80 and carbon dioxide 81. The fuel gas 73 and steam 78, fed as a mixture 79 into the top anode channel 86, are thermally and catalytically reformed, producing carbon dioxide and hydrogen. The hydrogen, so produced, is transported through top proton conducting MIEC membrane 172 into hydrogen flow channel 173. The composite hydrogen and steam sweep gas 179 are discharged from channel 173 and are transported through connecting channel 174 to the bottom hydrogen flow channel 175. The hydrogen produced by reforming the remainder of fuel gas and steam in the bottom anode flow channel is transported through the bottom proton conducting MIEC membrane 177 into the bottom hydrogen flow channel 175. The composite gas (hydrogen 82 and steam 178) is discharged from bottom hydrogen flow channel 175, conducted around air stream connecting channel 87 and fed into anode heat exchanger 54 where it is cooled by heat transport to the intake fuel gas stream 72. The near-ambient temperature composite gas stream (comprising hydrogen 82 and steam 178) discharged from anode heat exchanger 54 is fed into anode manifold 56 and then discharged from manifold 56 in a composite stream of exhaust gases comprising hydrogen 82 and steam 178 - the sweep gas.

[0054] FIG. 13 diagrammatically illustrates in detail one of the repeat units contained in the assembly shown in FIG. 11 but includes a hydrogen separator which FIG. 12 excluded. The gas flows illustrated in FIG. 12 and FIG. 13 are identical except for that portion which involves the hydrogen separator, and therefore only this portion will be discussed. Composite gas 179, comprising hydrogen 82 and steam 178, is discharged from hydrogen flow channel 175, is conducted around air stream connecting channel 87, through bottom hydrogen stream connecting channel 180 and is discharged first into flow channel 183 and then into anode heat exchanger where composite gas 179 is cooled, fed to anode manifold and exhausted. Exhaust gas 181 is discharged from bottom anode flow channel, conducted first around air stream connecting channel 87 and then around bottom hydrogen stream connecting channel 180 and then discharged through flow channel 182 into hydrogen separator flow channel 184. The residual hydrogen in anode exhaust gas 181 is transported through proton conducting MIEC membrane 74 to the hot hydrogen-free fuel gas 73 fed into the hydrogen separator 53. The hydrogen-depleted anode exhaust gas 185 is discharged from the hydrogen separator flow channel 184 and fed into anode heat exchanger 54, where it is cooled by heat transport to the intake fuel gas stream 72. The near-ambient temperature composite gas stream (comprising steam 80 and carbon dioxide 81) is discharged from anode heat exchanger 54, fed into anode manifold 56 and then discharged from manifold 56 in a composite stream as exhaust gases comprising steam 80 and carbon dioxide 81.

[0055] FIG. 14 illustrates cross-sections of one cell of the two-cell repeat unit shown in FIG. 13. FIG. 14A shows a lateral cross-section and FIG. 14B shows a longitudinal cross-section of one integral cell. The membrane support 100 is a perforated metal sheet with slots that are closely-spaced in the longitudinal direction and match, in the lateral direction, the width of the air flow channel 84, fuel gas flow channel and hydrogen flow channel 173, all of equal width. Membrane support IOOA is bonded to hydrogen interconnect 191, membrane supports IOOB and IOOC are bonded to fuel interconnect 102, and membrane support IOOD is bonded to air interconnect 101. The air interconnect 101 is longitudinally grooved on one side to provide air flow channels 84 and on the opposite site to provide heat pipe channels 109 that have a porous coating 111. The hydrogen interconnect 191 is longitudinally grooved to provide hydrogen channels 173. The fuel interconnect 102 comprises longitudinal stripes that are bonded to membrane supports IOOB and IOOC to form an integral structure that forms longitudinal grooves to provide fuel flow channels. The membrane supports are joined to their respective mating MIEC membranes by reactive brazing, as is air interconnect 101 joined to heat pipe cover 192. In vertically stacking these cells, the cell beneath that shown in FIG. 14 has the flat face of hydrogen interconnect 191 contacting the flat face of heat pipe cover 192 which after stack assembly is brazed. Alternately, heat pipe cover 192 could be replaced with the hydrogen interconnect 191 and then air channel interconnect would be brazed to hydrogen interconnect 191. The longitudinal grooves 109 in air connect 109 form the heat pipe flow channels in which liquid metal, such as sodium, flows longitudinally by the capillary action produced by the porous coating 111 on longitudinal grooves 109. Heat produced within the hot section of the cell vaporizes the liquid metal, which vapor then flows through grooves 109 to condense in the cooler section of the cell thereby isothermalizing the cell, which operates adiabatically, thus eliminating the need for side-mounted heat pipes required for heat dissipation to a heat transfer fluid. Hydrogen permeation through the hydrogen interconnect 191 to the heat pipe channels 109 is impeded by precoating the channels with a hydrogen impermeable barrier, such as a dense ceramic film. Residual hydrogen in the heat pipe is removed by a hydrogen permeable membrane mounted in an end chamber of the heat pipe that commonly flow-connects all heat pipe grooves 109. The hydrogen permeable membrane is coated with a catalyst to ensure rapid oxidation of hydrogen transported through the membrane.

[0056] FIG. 15 illustrates lateral cross-sections of three MIEC membrane assemblies. FIG. 15A shows a planar assembly with MIEC membrane 200, either proton conducting or oxygen ion conducting, sandwiched between two porous supports 201 that are each faced with a perforated skin 202. The porous supports 201 and perforated skins 202 may be metal and brazed together with membrane 200, or the entire structure may be ceramic that is co-formed and co-fired. The porous supports provide uniform distribution of gases to the membrane faces and accommodate catalysts that enhance membrane surface reactions to increase ion flux through the membrane assembly. FIG. 15B shows a finned planar assembly with longitudinal finned structures extending through the full depth of the flow channels. Bottom finned structure 203 comprises a porous support 204 that is coated with a thin layer of oxygen ion conducting MIEC 205 that, together with planar solid wall 206, forms the air flow channel 207. Middle finned structure 208 comprises a porous support 209 that is coated with a thin layer of proton conducting MIEC 210 that, together with finned structure 203, forms the fuel flow channel 211. Top finned structure 212 comprises an integral solid fin 213 and solid planar wall 214 that, together with finned structure 208, forms the hydrogen flow channel 215. Air in channel 207 counterflows relative to fuel flow in channel 211 and hydrogen flow in channel 215. The porous support 204 may be reinforced with a solid vertical fin 216 and porous support 209 may be reinforced with a solid vertical fin 217. For rigidity, the tips of bottom finned structure 203 are bonded to the planar wall 206, the tips of middle finned structure 208 are bonded to the upper face of bottom finned structure 203, and the tips of top finned structure 212 are bonded to the upper face of middle finned structure

208. The entire structure shown in FIG. 15B may be formed of metal, except for coated films 205 and 210, or may be formed of ceramic, or may consist of discrete parts formed of metal or ceramic. Planar wall 206 may have fins extending from the surface opposite the air flow channel 207 to form a finned structure which when brazed to the non-finned surface of top finned structure 212 forms longitudinal sealed channels which, when filled with a vaporizable metal, create a planar heat pipe. FIG. 15C shows a finned tubular assembly with longitudinal finned structures extending through the full depth of the flow channels. The internally finned outer metal tube 218 when brazed to the inner metal tube 219 forms longitudinal sealed channels which, when filled with a vaporizable metal, create a tubular heat pipe that contains within it a membrane reactor composed of an outer tubular finned structure 220 and an inner tubular finned structure 221. The outer tubular finned structure 220 comprises a finned tubular porous support 222 that is coated with an oxygen ion conducting MIEC 223 which, together with inner metal tube 219, forms air flow channel 224. The inner tubular finned structure 221 comprises a finned tubular porous support 225 that is coated with a proton conducting MIEC 226 which, together with the internal diameter of outer finned tubular structure 220, forms fuel flow channel 227, while the internal diameter of inner tubular finned structure 221 forms the hydrogen flow channel 228. Air in channel 224 counterflows relative to fuel flow in channel 227 and hydrogen flow in channel 228. For rigidity, the tips of the outer finned tubular structure 220 are bonded to the inner surface of the inner metal tube 219 and the tips of the inner finned tubular structure 221 are bonded to the inner surface of the outer finned tubular structure 220. The entire structure, shown in FIG. 15C, may be formed of metal, except for coated films 223 and 226, or may be formed of ceramic, except for the internally finned outer metal tube 218 and inner metal tube 219.

[0057] FIG. 16 diagrammatically illustrates in planar cross-section the coupling of two finned tubular membrane reactors, shown in FIG. 15C with counterfiow heat exchangers mounted on opposite ends of the membrane reactors. The two reactors are coupled in series to provide a reverse flow of gases and each operates in counterflow of the reactive gases. The tubular counterflow heat exchanger for air flow is mounted on the left of the two membrane reactors, and the tubular counterflow heat exchanger for fed steam and fuel gas flows and discharged carbon dioxide, steam and hydrogen flows is mounted on the right of the two membrane reactors. For clarity, the finned structures of the tubular membrane reactors and the heat pipe that circumscribes each tubular membrane reactor are deleted and only the hot end of each heat exchanger with fins removed is shown. The air heat exchanger 230 comprises an outer annular channel 231 formed by outer tube 232 and middle tube 233 and an inner annular channel 234 formed by common middle tube 233 and inner tube 235. The outer channel 231 feeds air to the reactors and the inner channel 234 exhausts the lean air from the reactors. The air heat exchanger couples to the reactors through an air head that comprises three stacked rings. Ring one 236 comprises an axial extension of outer tube 232 and middle tube 233 that form annular chamber 237 bounded by first end plate 238 that joins to inner tube 235 and by second end plate 239 that has holes 240 and 241 that respectively conduct intake air and exhaust lean air. Ring two 242 comprises intake air cylindrical chamber 243 (bounded by second end plate 239, first reactor's outer tube 244 and front end plate 245) and the exhaust air cylindrical chamber 246 (bounded by second end plate 239, second reactor's outer tube 247 and front end plate 248). Ring three 249 comprises two concentric annular chambers 250 and 252 that circumscribe tubular chamber 254' for the second reactor. The first reactor's outer annular chamber 250 is bounded radially by the first reactor's outer tube 244 and inner cathode channel tube 251 and the inner annular chamber 252 is bounded radially by inner cathode channel tube 251 and inner anode channel tube 253. The second reactor's outer annular chamber 250' is bounded radially by second reactor's outer tube 247 and inner cathode channel tube 251' and the inner annular chamber 252' is bounded radially by inner cathode channel tube 251 ' and inner anode channel tube 253 '. The fuel head comprises four rings. Ring one 255 comprises the concentric annular chambers 256 and 257 that circumscribe tubular chamber 258 for first reactor and two concentric annular chambers 256' and 258' that circumscribe tubular chamber 258 for the second reactor. The first reactor's outer annular chamber 256 is bounded radially by first reactor's outer tube 244 and inner cathode channel tube 251 and the inner annular chamber 258 is bounded radially by inner cathode channel tube 251 and inner anode channel tube 253. The second reactor's outer annular chamber 256' is bounded radially by the second reactor's outer tube 247 and inner cathode channel tube 251' and the inner annular chamber 258' is bounded radially by inner cathode channel tube 251' and inner anode channel tube 253. Ring two 259 comprises inner annular chamber 260 and tubular chamber 261 for the first reactor and inner annular chamber 260' and tubular chamber 261 ' for the second reactor. These chambers are bounded identically as those in ring one. Ring three 262 comprises fuel intake chamber 263, steam intake chamber 264, carbon dioxide/steam exhaust chamber 265 and hydrogen exhaust chamber 266. Fuel intake chamber 263 is bounded by fuel heat exchanger outer wall 267 and inner wall 268. Steam intake chamber 264 is bounded by fuel heat exchanger inner wall 268 and steam inlet inner wall 269. Carbon dioxide/steam exhaust chamber 265 is bounded by steam intake outer wall 270 and an extension of second reactor's inner anode wall 253. Hydrogen exhaust chamber 266 is bounded by steam intake inner wall 269. Ring four 271 comprises three concentric annular chambers (fuel feed chamber 272, carbon dioxide/steam exhaust chamber 273 and steam intake chamber 274) that circumscribe the hydrogen exhaust chamber 275 and are radially bounded by respective tube walls 272, 268, 270 and 269. Ring four 271 mates with fuel counterflow heat exchanger 276 which comprises three concentric annular flow channels (fuel feed channel 272', carbon dioxide/steam exhaust channel 273' and steam intake channel 274') that circumscribe the hydrogen exhaust channel 275' and are radially bounded by respective tube walls 272, 268, 270 and 269. Gas composition and gas flow directions are shown in FIG. 16 using the following symbols for gases: A : air, CO₂ : carbon dioxide, F : fuel, H₂ : hydrogen, S : steam; and for perpendicular flow directions: + into paper and - out of paper.

[0058] FIG. 17 diagrammatically illustrates the hydrogen separator in lateral and longitudinal cross-sections. FIG. 17A shows the separator's anode exhaust assembly in lateral cross- section, FIG. 17B shows the separator's anode intake assembly in lateral cross-section, and FIG. 17C shows the separator's anode exhaust assembly in longitudinal cross-section. FIG. 17A illustrates the porous metal wedges 300 that are coated with a thin MIEC membrane 301 and brazed to mounting plate 302 having through slots 303 for hydrogen transport to lateral channels 305. Cover 306 is brazed to the mounting plate for sealing the longitudinal-flowing exhaust gases and to the wedge tips for providing rigidity. FIG. 17B shows the fins 307, which support cover 308, and base 309 having through holes for hydrogen transport from lateral channels 305 in anode exhaust assembly to intake gas flowing between fins 307. Base 309 is integral with fins 307 and both are brazed to cover 310 for sealing the longitudinal- flowing intake gases and for providing rigidity. FIG. 17C shows the longitudinally-separated porous wedges 300 and the laterally grooved mounting plate 302. The observed curve at the wedge base is caused by the radius at wedge ends.

[0059] FIG. 18 diagrammatically illustrates two versions of an ion transporting MIEC membrane reactor integrated with a solid oxide fuel cell (SOFC). In FIG. 18A the SOFC is based upon an oxygen-ion transporting (oxonic) membrane and in FIG. 18B the SOFC is based upon a proton transporting (protonic) membrane. FIG. 18A shows the oxonic- equipped 400 on the right with the heat pipe 401 beneath. Heat exhausted from SOFC 400 is transferred to heat pipe 401 by vaporizing liquid metal at the right side of heat pipe 401, transporting the metal vapor to the left side of heat pipe 401 and then condensing the metal vapor at the left side of heat pipe 401 which provides heat to the membrane reactor 402. This heat supplies the energy needed for reforming the fuel and steam in fuel flow channel 403 to carbon dioxide and hydrogen. The resulting hydrogen is transported through the proton conducting MIEC membrane 404 to the hydrogen flow channel 405, where the hydrogen flows laterally to the oxidation channel 406. Oxygen, contained in the air flowing in air flow channel 407, is transported as ions through ion conducting membrane 408 and then is discharged into oxidation channel 406 where it oxidizes the hydrogen discharged from hydrogen flow channel 405. Since the SOFC rejects more heat than that required for reforming the fuel to hydrogen for fueling the SOFC, the excess heat is rejected to a heat exchanger 409 mounted on the exposed side of the SOFC, where the side heat exchanger 409 is shown in phantom in FIG. 18 A. Alternately, a second SOFC with side heat exchanger could be mounted on the opposite side of the membrane reactor to provide a symmetric design and permit a greater heat exchanger surface area. FIG. 18B shows the protonic- equipped SOFC 410 with proton conducting membrane 411 located above the air flow channel 407. All components, except the ion conducting membranes, are identical to those shown in FIG. 18A and therefore are not repeatedly described. In function, the SOFC in FIG. 18A produces steam in oxidation chamber 406 which is exhausted by flowing longitudinally in this chamber, whereas the SOFC in FIG. 18B produces steam in air flow channel 407 which is exhausted by longitudinally co-flowing with air in air flow channel 407. In stacking the repeat units shown in FIG. 18 each repeat unit is electrically insulated since each unit produces a voltage potential.

Claims

WHAT IS CLAIMED IS:

L A membrane reactor comprising an ion permeable membrane, a first flow path directing ions from a reactant stream through the ion permeable membrane to form a product stream and a second flow path flowing the product stream as a counterflow relative to the reactant stream through the ion permeable membrane so that the streams reverse flow within the membrane reactor.

2. A membrane reactor according to claim 1 wherein the membrane comprises a galvanic ion conductor.

3. A membrane reactor according to claim 1 wherein the membrane comprises a non-galvanic mixed ion and electron conductor.

4. A membrane reactor according to claim 1 wherein the reactor is close- coupled to an adjacent counterflow heat exchanger for each reactant and product stream.

5. A membrane reactor according to claim 1 wherein the reactor is close- coupled to an adjacent membrane reactor that transports ions from the product stream to the reactant stream.

6. A membrane reactor according to claim 5 wherein the membrane comprises a galvanic ion conductor.

7. A membrane reactor according to claim 5 wherein the membrane comprises a non-galvanic mixed ion and electron conductor.

8. A membrane reactor according to claim 1 wherein the reactor includes a heat transport means within the reactor.

9. A membrane reactor according to claim 8 wherein the heat transport means comprises a heat pipe.

10. A membrane reactor according to claim 1 including a heat transport means adjoining the reactor.

I L A membrane reactor according to claim 10 wherein the heat transport means comprises a heat pipe.

12. A membrane reactor according to claim 1 including at least one pair of planar reactors that are stacked adjacently together.

13. A membrane reactor according to claim 1 including at least one pair of tubular reactors that are stacked adjacently together.

14. A membrane reactor comprising an ion permeable membrane, a first flow path from which ions of reactant stream migrate through the ion permeable membrane to react with a second stream, a second flow path flowing the second stream as a counterflow relative to the reactant stream past the ion permeable membrane, the first and second flow paths further reversing the flow of the streams within the membrane reactor, and a second permeable membrane through which ions of the reacted second stream migrate to form a product stream.

15. A membrane reactor according to claim 14 wherein the product stream also reverse flows within said membrane reactor.

16. A membrane reactor according to claim 14 wherein the membranes are galvanic ion conductors.

17. A membrane reactor according to claim 14 wherein the membranes comprise non-galvanic mixed ion and electron conductors.

18. A membrane reactor according to claim 1 comprising two reactant streams and two product streams in which a first reactant stream comprises air and a second reactant stream comprises a carbonaceous fuel, and in which the first product stream comprises lean air and the second product stream comprises an oxidized fuel, and wherein the first reactant stream counterflows relative to the first product stream, the second reactant stream counterflows relative to the second product stream, and the first reactant stream counterflows relative to the first product stream.

19. A membrane reactor according to claim 18 wherein a voltage potential is produced having a voltage output that is modulated relative to a product stream output.

20. A membrane reactor according to claim 18 in which the first reactant stream is steam and the first product stream is hydrogen.

21. A membrane reactor comprising an ion permeable membrane defining first and second flow paths on respective sides of the membrane, a cathode manifold directing a reactant stream including air into the first flow path, and an anode manifold directing an oxidizable gas including hydrocarbons and H₂O into the second flow path, the first and second flow paths being configured to flow the reactant stream and the gas in opposite directions past the membrane and to reverse the directions of the respective flows while ions from the reactant stream are transported through a second membrane to produce a stream including hydrogen.

22. A membrane reactor comprising an ion permeable membrane defining first and second flow paths on respective sides of the membrane, a cathode manifold directing a reactant stream including air into the first flow path, an anode manifold directing a second stream into the second flow path which counterflows relative to the reactant stream in the first flow path, the flow paths being arranged so that each stream also reverse flows along the permeable membrane, and a second ion permeable membrane arranged so that ions of the reacted second stream are transported through the second permeable membrane to form a product stream including hydrogen.