WO2014177336A1 - Solid oxide stack system with thermally matched stack integrated heat exchanger - Google Patents

Solid oxide stack system with thermally matched stack integrated heat exchanger Download PDF

Info

Publication number
WO2014177336A1
WO2014177336A1 PCT/EP2014/056520 EP2014056520W WO2014177336A1 WO 2014177336 A1 WO2014177336 A1 WO 2014177336A1 EP 2014056520 W EP2014056520 W EP 2014056520W WO 2014177336 A1 WO2014177336 A1 WO 2014177336A1
Authority
WO
WIPO (PCT)
Prior art keywords
stack
heat exchanger
solid oxide
heat
hsa
Prior art date
Application number
PCT/EP2014/056520
Other languages
French (fr)
Inventor
Claus FRIIS PEDERSEN
Original Assignee
Haldor Topsøe A/S
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Haldor Topsøe A/S filed Critical Haldor Topsøe A/S
Publication of WO2014177336A1 publication Critical patent/WO2014177336A1/en

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/02—Process control or regulation
    • 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
    • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
    • H01M8/241—Grouping of fuel cells, e.g. stacking of fuel cells with solid or matrix-supported electrolytes
    • H01M8/2425—High-temperature cells with solid electrolytes
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/70—Assemblies comprising two or more cells
    • C25B9/73—Assemblies comprising two or more cells of the filter-press type
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D9/00—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
    • F28D9/0093—Multi-circuit heat-exchangers, e.g. integrating different heat exchange sections in the same unit or heat-exchangers for more than two fluids
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F3/00—Plate-like or laminated elements; Assemblies of plate-like or laminated elements
    • F28F3/08—Elements constructed for building-up into stacks, e.g. capable of being taken apart for cleaning
    • F28F3/083—Elements constructed for building-up into stacks, e.g. capable of being taken apart for cleaning capable of being taken apart
    • 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
    • H01M8/04037—Electrical heating
    • 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
    • H01M8/04067—Heat exchange or temperature measuring elements, thermal insulation, e.g. heat pipes, heat pumps, fins
    • H01M8/04074—Heat exchange unit structures specially adapted for fuel cell
    • 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
    • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
    • H01M8/241—Grouping of fuel cells, e.g. stacking of fuel cells with solid or matrix-supported electrolytes
    • H01M8/2425—High-temperature cells with solid electrolytes
    • H01M8/2428—Grouping by arranging unit cells on a surface of any form, e.g. planar or tubular
    • 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
    • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
    • H01M8/241—Grouping of fuel cells, e.g. stacking of fuel cells with solid or matrix-supported electrolytes
    • H01M8/2425—High-temperature cells with solid electrolytes
    • H01M8/2432—Grouping of unit cells of planar configuration
    • 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
    • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
    • H01M8/2465—Details of groupings of fuel cells
    • H01M8/247—Arrangements for tightening a stack, for accommodation of a stack in a tank or for assembling different tanks
    • H01M8/248—Means for compression of the fuel cell stacks
    • 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
    • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
    • H01M8/2465—Details of groupings of fuel cells
    • H01M8/2484—Details of groupings of fuel cells characterised by external manifolds
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D21/00—Heat-exchange apparatus not covered by any of the groups F28D1/00 - F28D20/00
    • F28D2021/0019—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for
    • F28D2021/0043—Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for for fuel cells
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F2265/00—Safety or protection arrangements; Arrangements for preventing malfunction
    • F28F2265/24—Safety or protection arrangements; Arrangements for preventing malfunction for electrical insulation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F2265/00—Safety or protection arrangements; Arrangements for preventing malfunction
    • F28F2265/26—Safety or protection arrangements; Arrangements for preventing malfunction for allowing differential expansion between elements
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines

Definitions

  • Solid Oxide Cells are used for a wide range of purposes in- eluding the generation of electricity from different fuels (fuel cell mode) and the generation of synthesis gas (CO + H2) from water and carbon dioxide (electrolysis mode) .
  • fuel cell mode fuel cell mode
  • CO + H2 synthesis gas
  • water and carbon dioxide electrolysis mode
  • the solid oxide stacks typically operate at temperatures in the range from 600 to 1000 °C . At these temperatures reduction of heat loss is essential to ob ⁇ tain a good efficiency.
  • Thermal insulation is used to reduce heat loss to the environment and heat ex ⁇ changers are used to transfer heat from the outlet gas flows to the inlet gas flows.
  • Heat exchangers are therefore criti ⁇ cal components in almost any solid oxide stack system (SOSS) and it is essential to optimise these to enhance heat trans- fer and reduce heat loss.
  • SOSS solid oxide stack system
  • This invention relates to the design and integration of thermally matched heat exchangers and their integration with sol ⁇ id oxide stacks and systems to enhance the overall efficacy of these systems.
  • FIG. 1 An example of a non-integrated system is shown in figure 1.
  • a solid oxide stack in electrolysis mode is fed via an input/output heat exchanger in series with an electrical heater.
  • HSA hot surface area
  • T (A) is the temperature for a given area
  • T Ma x is the maximum temperature across the entire area
  • T ext (A) is the temperature of the adjacent components and surroundings ex ⁇ ternal environment
  • ⁇ ⁇ ⁇ ⁇ is the minimum external tempera ⁇ ture (typically room temperature) .
  • the x hot surface area' can be interpreted as the actual surface temperature difference integrated for the entire device area and normalised with the maximum temperature difference.
  • the active area measures 8 cm x 8 cm x 12 cm giving it a surface area of 500 cm 2 .
  • the temperature of the heat exchanger howev ⁇ er varies (linearly) from the maximum temperature to the cold input temperature. If the cold input temperature is similar to the external temperature, then the hot surface area of the heat exchanger is 250 cm 2 . This number does not include the manifolding and the piping which adds additional 250 cm 2 of hot surface area.
  • the stack (without enclosure and compression system) measures 12 cm x 12 cm x 10 cm and has a (hot) surface area of 750 cm 2 .
  • To reduce the heat loss of solid oxide stack systems it has been proposed to integrate the heat exchangers with the stacks and thereby to reduce the heat losses from hot mani ⁇ folding and hot piping.
  • US20100200422 Discloses an electrolyser including a stack of a plurality of elementary electrolysis cells, each cell in ⁇ cluding a cathode, an anode, and an electrolyte provided be ⁇ tween the cathode and the anode.
  • An interconnection plate is interposed between each anode of an elementary cell and a cathode of a following elementary cell, the interconnection plate being in electric contact with the anode and the cath ⁇ ode.
  • a pneumatic fluid is to be brought into contact with the cathodes, and the electrolyser further includes a mechanism ensuring circulation of the pneumatic fluid in the electro ⁇ lyser for heating it up before contacting the same with the cathodes .
  • EP1602141 is an example of such a proposed invention and re- veals a Solid Oxide Stack System that is modularly built, wherein the additional components such as the heat exchangers are directly arranged in the high-temperature fuel cell stack to avoid piping.
  • FIG 2 (figure 4 from
  • FIG. 2 shows that the heat exchanger (luftvor- warmer) in EP1602141 is based on a traditional cross flow heat exchanger. In this case the heat exchanger will have a hot x left' side and a cold x right' side as indicated in ital ⁇ ics on figure 2. The heat exchanger is facing a hot component (nachverbrenner) on top and a cold component (Vorreformer) at the bottom. This distribution of hot and cold surfaces leads to two issues.
  • the heat exchanger will on the left side have hot surfaces (A) facing the relatively cold prereformer ("vorreformer”) and have cold surfaces (B) facing the hot post combustor ("nachverbrenner”) .
  • Thermal insulation materials are therefore necessary between the different elements to avoid high heat loss at the hot/cold interfaces A) and B) .
  • typically at least 0.1 mm/K of insulation materials will have to be used 1 .
  • ⁇ is the temperature difference across the heat exchanger (hot inlet tempera- ture - cold inlet temperature)
  • thermally matched is here understood that the thermal gradients of the heat exchanger are oriented in the same direction as those of the adjacent stack components. This can also be expressed as a criterion that the maximum temperature difference ⁇ between two adj acent /touching points of the heat exchanger and the adjacent components is substantially smaller than the maximum temperature difference ⁇ across the heat exchangers, please refer to figure 4.
  • Such heat exchangers have the advantages of being able to practically eliminate the heat loss from manifolding and pip ⁇ ing. Furthermore, they can also be used to:
  • Hex A thermally matched heat exchanger
  • the heat exchanger is in principle a x bended' counter flow plate heat exchanger. The flow propagates from one side ( x left' or x right' ) to the oth- er side ( x right' or x left' ) and at the left and right edges, the flow is directed to another layer in the heat exchanger and the flow direction is reversed.
  • thermally insulation layer is inserted between each x layer' of the heat exchanger.
  • This layer could for example be just a hollow section using still air as insulation material.
  • N The number of layers ⁇ ⁇ ' used in such a heat exchanger is de ⁇ termined by the maximum acceptable temperature difference ⁇ .
  • N can be expressed as N > ⁇ / ⁇ .
  • the heat exchanger proposed here is not only characterised by eliminating the heat loss from manifolding and piping, but it also have a very low effective surface area when integrated into solid oxide stack systems.
  • this equation 1 shows that if T (A) - T ext (A) is low for a given surface, then the effective hot surface area from this surface is also low. This basically indicates that if two hot surfaces are placed face to face, then the heat loss of both can be eliminated.
  • a 'Hex A' type heat exchanger with a height of 3 cm is connect- ed to a 12 x 12 cm stack operating at 775°C.
  • the heat exchanger is assumed to have a 25°C inlet from an adjacent man ⁇ ifold ⁇ is assumed to be 75°C towards both the manifold and the stack facets.
  • this heat exchanger can become an integrated part of the stack compression system and help to reduce the heat loss from the compression system, which in most solid oxide stack systems are substantial. Due to differences in thermal expansion coefficients between dif- ferent stack components (e.g. cells and interconnects), ex ⁇ ternal compression systems are typically applied to the two endplates of the stack.
  • a steel shield is used to provide the stack compression. The steel shield is bolted to a bottom plate and provides the compression pressure through the stack through a compression mat. As this compression mat has a relatively high thermal conductivity, the steel shield has the same tem ⁇ perature as the stack inside. The surface area of the steel shield is 2000 cm2 or almost 3 times higher than the surface area of the stack. This implies that the hot compression sys- tern will add significantly to the heat loss of the solid ox ⁇ ide stack system.
  • Solid Oxide Stack System configuration which is very popular when several stacks are need is the so-called 'boxer' config ⁇ uration.
  • two stacks are placed on top of each other with a centre manifold and compression provided from the two ends as shown in figure 8a and 8b.
  • One advantages of the 'boxer' configuration is that two hot stack surfaces are facing each other, thereby reducing the system heat loss compared to a configuration with two individual stacks.
  • a sim ⁇ ple compression system providing compression from the two ends can be used to compress the two stacks simultaneously.
  • the electrical wiring is connected to the hot bottom and top-plates of the stacks as indicated on figure 9A. To reduce the ohmic losses of these wires they typically have a relatively broad cross section and hence a considerable thermal conductivity.
  • Hex A heat exchanger can be assembled in the same assembly processes used for assembling the stacks.
  • Hex A can be manufac- tured by stacking of metal plates and spacers with the same foot print and from the same materials as those used for in ⁇ terconnects and spacers in the stack.
  • the heat exchanger can be assembled by the same process (e.g. robot controlled stacking) as the fuel cell stack and the heat exchanger ele ⁇ ments can be joined by the same methods used for the stack, e.g. glass soldering, Ni-brazing or diffusion bonding.
  • thermally matched, stack in ⁇ tegrated heat exchangers is shown in Figure 10.
  • This thermal ⁇ ly matched stack integrated heat exchanger is placed at one of the sides of the stack and uses a counter flow plate heat exchanger configuration.
  • the cold inlet is connected to the top of the heat exchanger at the x cold' right side and the hot x left' side of the heat exchanger faces the stack.
  • the hot flow be- tween the stack and the heat exchanger goes through a manifolding plate at the bottom of the stack.
  • Hex B can be sepa ⁇ rate from the stack and for example an external heater can be inserted between Hex B and the stack.
  • Hex B can also be an integrated part of the stack and for example share components such as spacers and interconnects. This will require electri ⁇ cally insulating parts to be included in the heat exchanger design as described in the following.
  • FIG 11 shows an embodiment of this invention, where the heat exchanger is realised from stack components by extending the length of interconnects and spacers.
  • One set of heat ex- changer plates can then be based on extensions of the inter ⁇ connects.
  • every other set of heat exchanger plates (corresponding to the extensions of the cells) have to be based on a material which is electrically nonconductive in the vertical direction. This could for example be a ceramic plate or a ceramically coated metal sheet.
  • the two sets of heat exchanger plates can be separated by extended spacers, which are also used to lead the desired flows across the dif- ferent heat exchangers plates.
  • the heat exchanger plates of Hex B can be as ⁇ Sild in exactly the same process as the stack and similar methods can be used for joining the heat exchanger and stack components. Such joining methods could for example be glass sealing/soldering, brazing or diffusion bonding.
  • Hex B also can also have a low hot surface ar ⁇ ea .
  • a 'Hex B' type heat exchanger with a length of 6 cm is connect ⁇ ed to a 12 x 12 cm stack with a height of 10 cm operating at 775°C.
  • the heat exchanger is assumed to have inlet and outlet flow temperatures of 25 and 50°C, respectively.
  • the Hex B heat exchanger can also be realised with low elec- trical resistance. Every other heat exchanger plate can be realised as a metal plate and thereby be electrically conduc ⁇ tive. This makes it possible for example to have cold elec ⁇ trical connections to the top or bottom plates of the stack from the top or bottom plate on the heat exchanger.
  • a very interesting feature of this heat exchanger embodiment is that it is possible to have cold electrical connections to each interconnect in the stack. This can be used to provide a cold environment for electrical components used to control the current through individual cell or groups of cells. Such current control can for example be used to adjust the current over individual cells or cell groups in order to obtain very high fuel utilisations for all cells or cell groups in a stack. Another application could be to switch off the current in SOEC mode for cell or cell groups with defect (leaking) cells. This would avoid the excessive heating of defect cells to destroy adjacent cells.
  • the proposed heat exchanger embodiments can be used in many configurations to realise different SOFC, SOEC and even com ⁇ bined SOFC/SOEC configurations.
  • One example is shown in fig ⁇ ure 12.
  • four stacks are placed close to each other each sharing two hot sides with neighbouring stacks.
  • Each stack is also connected to one Hex A and one Hex B, providing cold external interfaces for all in-plane sides of this configuration.
  • stack integrated heaters between the stacks these are also indi ⁇ cated on figure 12.
  • Solid oxide stack configurations with two heat exchangers are relevant for both SOEC and SOFC systems. This is exemplified on figure 13 and 14.
  • Figure 13 shows a simple SOEC configuration which can be re ⁇ alised with two (integrated) heat exchangers and a heater.
  • Fuel e.g. H20
  • the cold flow e.g.
  • 101°C steam) from fuel inlet 1 is heated in Hexla by the hot fuel outlet flow coming from the stack.
  • the cold flow from fuel inlet 2 is heated in Hex2 by the hot oxygen outlet flow from the stack.
  • No inlet flushing of the oxygen side is used and the output from the oxygen side is therefore 100% 02.
  • the two fuel inlets are combined and the temperature of the combined flow is increased in a heater before the fuel fed to the stack.
  • the stack is assumed to operate close to the ther- mo-neutral point and the temperatures of the output flows will therefore be close to the stack operating temperature.
  • the heat exchangers are not ideal and some heat will be lost to the environment, and these heat losses are compensated by the heater.
  • the stack can operate at currents up to 70A with a fuel utilisation up to 70%.
  • the fuel in ⁇ put flow to the stack should be 3.4 Nm3/h (steam) .
  • Figure 14 shows a simple SOFC configuration which can be re ⁇ alised with two (integrated) heat exchangers.
  • Fuel e.g. H2
  • Fuel inlet 1 is fed to the stack through fuel inlet 1 and the cold inlet flow is heated in Hexl by the hot fuel outlet from the stack.
  • the cold air inlet flow is heated in Hex2 by the hot air outlet flow from the stack.
  • This configuration is the common denominator of the SOEC and SOFC configurations shown in figure 13 and 14.
  • SOEC mode the air inlet and outlets are shut off (on the cold side of Hex3) and the system is operating exactly as the SOEC system in figure 13.
  • Hex B type heat exchangers for the air flow (Hex 3) as Hex B type heat exchangers can easily be designed for low pressure drop, which is less simple with the Hex A type de ⁇ sign .
  • Hex A type heat exchangers for the main fuel heat exchangers are used in both SOEC and SOFC mode and therefore can provide cold interfaces for the compression system for both operating modes.
  • a solid oxide electrolysis cell (SOEC) system comprising one or more SOEC stack (s) and one or more stack- integrated, temperature-matched heat exchanger (s) in di- rect physical contact on at least 1/12, preferably at least 1/6, preferably at least 1/3 of the heat exchanger surface area with the SOEC stack (s), wherein the maximum temperature difference ⁇ between two adjacent and con ⁇ tacting points of the heat exchanger and the adjacent SOEC stack (s) is smaller than the maximum temperature difference ⁇ across the heat exchanger ( s ) , wherein ⁇ / ⁇ ⁇ 50%, preferably ⁇ / ⁇ ⁇ 20% preferably ⁇ / ⁇ ⁇ > o ⁇
  • SOEC solid oxide electrolysis cell
  • HSAgy ste m relative to the hot surface area of the heat exchanger (s) in a not integrated, stand-alone (HSA sa ) situation
  • HSA system /HSA sa ⁇ 1 preferably HSA System /HSA sa *C 0.3, preferably HSA system /HSA sa ⁇ 0.1.
  • a solid oxide electrolysis cell system according to fea ⁇ ture 1, wherein the heat exchanger (s) have a temperature difference, ⁇ , between the maximum and minimum inlet temperatures of ⁇ > 300°C, preferably ⁇ > 450°C, preferably ⁇ > 600°C.
  • a solid oxide electrolysis cell system according to fea ⁇ ture 1, wherein at least one of the heat exchangers is used for feeding current to the stack (s) or to and from the stack (s) and the at least one of the heat exchangers has an electrical resistance R He x between an cold surface and a stack element of R He x ⁇ 1 mOhm, preferably R He x ⁇ 0.1 mOhm, preferably R He x ⁇ 0.01 mOhm.
  • a solid oxide electrolysis cell system according to fea- ture 4 wherein the stack element is the top or the bot- torn plates of the stack.
  • a solid oxide electrolysis cell system according to fea ⁇ ture 4, wherein the stack element is cells or cell groups and current control of these is performed at cold interfaces of the at least one heat exchanger.
  • a solid oxide electrolysis cell system according to fea ⁇ ture 8 wherein the stack compression is at least 200 mBar .
  • a solid oxide electrolysis system according to fea ⁇ ture 1, wherein the hot surfaces of the heat exchang- er(s) are at the stack operating temperature or at maxi ⁇ mum 50°C colder.
  • a solid oxide stack system applying at least on heat exchanger according to feature 1, where the thermal management system is designed in a way where the system can operate with high efficiency in both SOEC and SOFC mode .
  • a solid oxide stack system according to feature 12 wherein the thermal management system can operate with as few as three heat exchangers .

Abstract

Abstract. A Solid oxide electrolysis cell (SOEC) system has at least one integrated heat exchanger which minimizes the hot surface area of the heat exchanger and the system.

Description

Title: Solid Oxide stack system with thermally matched stack integrated Heat Exchanger.
Solid Oxide Cells are used for a wide range of purposes in- eluding the generation of electricity from different fuels (fuel cell mode) and the generation of synthesis gas (CO + H2) from water and carbon dioxide (electrolysis mode) . Re¬ gardless of the application, the solid oxide stacks typically operate at temperatures in the range from 600 to 1000 °C . At these temperatures reduction of heat loss is essential to ob¬ tain a good efficiency.
The two essential components to reduce heat loss are thermal insulation materials and heat exchangers. Thermal insulation is used to reduce heat loss to the environment and heat ex¬ changers are used to transfer heat from the outlet gas flows to the inlet gas flows. Heat exchangers are therefore criti¬ cal components in almost any solid oxide stack system (SOSS) and it is essential to optimise these to enhance heat trans- fer and reduce heat loss.
This invention relates to the design and integration of thermally matched heat exchangers and their integration with sol¬ id oxide stacks and systems to enhance the overall efficacy of these systems.
In traditional non-integrated solid oxide stack system con¬ figurations a significant amount of heat is lost through hot surfaces and piping between components.
An example of a non-integrated system is shown in figure 1. On both the fuel and the oxygen side a solid oxide stack in electrolysis mode is fed via an input/output heat exchanger in series with an electrical heater.
To be able to compare heat losses of different set-up a pa¬ rameter called the xhot surface area' (HSA) can be defined as :
Figure imgf000003_0001
Where T (A) is the temperature for a given area, TMax is the maximum temperature across the entire area and Text (A) is the temperature of the adjacent components and surroundings ex¬ ternal environment and ΤΜ±η is the minimum external tempera¬ ture (typically room temperature) . The xhot surface area' can be interpreted as the actual surface temperature difference integrated for the entire device area and normalised with the maximum temperature difference.
Considering, the large left heat exchangers on figure 1, the active area measures 8 cm x 8 cm x 12 cm giving it a surface area of 500 cm2. The temperature of the heat exchanger howev¬ er varies (linearly) from the maximum temperature to the cold input temperature. If the cold input temperature is similar to the external temperature, then the hot surface area of the heat exchanger is 250 cm2. This number does not include the manifolding and the piping which adds additional 250 cm2 of hot surface area. For reference the stack (without enclosure and compression system) measures 12 cm x 12 cm x 10 cm and has a (hot) surface area of 750 cm2. To reduce the heat loss of solid oxide stack systems it has been proposed to integrate the heat exchangers with the stacks and thereby to reduce the heat losses from hot mani¬ folding and hot piping.
US20100200422 Discloses an electrolyser including a stack of a plurality of elementary electrolysis cells, each cell in¬ cluding a cathode, an anode, and an electrolyte provided be¬ tween the cathode and the anode. An interconnection plate is interposed between each anode of an elementary cell and a cathode of a following elementary cell, the interconnection plate being in electric contact with the anode and the cath¬ ode. A pneumatic fluid is to be brought into contact with the cathodes, and the electrolyser further includes a mechanism ensuring circulation of the pneumatic fluid in the electro¬ lyser for heating it up before contacting the same with the cathodes .
EP1602141 is an example of such a proposed invention and re- veals a Solid Oxide Stack System that is modularly built, wherein the additional components such as the heat exchangers are directly arranged in the high-temperature fuel cell stack to avoid piping. Referring to figure 2 (figure 4 from
EP1602141) cold air (luft) is being preheated by exchanging heat with warm off gas (abgas) coming from a post-combustion (nachverbrenner) unit.
There are however fundamental limitation to the heat loss im¬ provements which can be obtained with the invention in
EP1602141. Figure 2 shows that the heat exchanger (luftvor- warmer) in EP1602141 is based on a traditional cross flow heat exchanger. In this case the heat exchanger will have a hot xleft' side and a cold xright' side as indicated in ital¬ ics on figure 2. The heat exchanger is facing a hot component (nachverbrenner) on top and a cold component (Vorreformer) at the bottom. This distribution of hot and cold surfaces leads to two issues.
1) In the configuration shown in EP1602141, the heat exchanger will on the left side have hot surfaces (A) facing the relatively cold prereformer ("vorreformer") and have cold surfaces (B) facing the hot post combustor ("nachverbrenner") . Thermal insulation materials are therefore necessary between the different elements to avoid high heat loss at the hot/cold interfaces A) and B) . To obtain a good thermal insu¬ lation between adjacent hot and cold surfaces, typically at least 0.1 mm/K of insulation materials will have to be used1.
2) Due to thermal expansion and the different temperatures across the heat exchanger in the contact plane, the heat ex¬ changer will move relative to the adjacent components during start up and cool-down of the system. With a 12 x 12 cm stack and a (steel) thermal expansion coefficient of 15 E-6 (K-1) , this relatively movement will be of the order of 1.5 mm if the post combustor reaches the stack operating temperature of 750°C.
If the prereformer, heat exchanger and post combustor are free to move relative to each other this is not necessarily an issue. However gas needs to flow between the adjacent com¬ ponents and the three elements therefore have to be fixed to each other as indicated on figure 3, where the prereformer, heat exchanger and post combustor are shown together with the necessary connections between these. Figure 3 also indicate hot areas with xblack' colour and cold areas with xwhite' colour . To summarise, the heat exchanger of invention in EP1602141 is therefore characterised by:
■ At points A and B at least 0.1 mm x ΔΤ of insulation ma¬ terials have to be inserted. Here ΔΤ is the temperature difference across the heat exchanger (hot inlet tempera- ture - cold inlet temperature)
■ At points C and D the heat exchangers have to be fixed to the adjacent components. Since the heat exchanger moves relative to the adjacent components during start¬ up and cool down cycles, this fixation have to be of a solid nature e.g. with steel connections brazed to the heat exchanger and to the adjacent component.
Assuming a ΔΤ of 750°C and a simple realisation of the steel connection along the side of the stack measuring 12 cm (stack length) x 1.5 cm (for air holes and brazing zones) x 7.5 cm (insulation height) then the hot surface area of these steel connections become 135 cm. This is comparable to the surface area of the piping and manifolding of the traditional bulk heat exchanger design of figure 1.
Another challenge of the invention of EP1602141 is that figure 2 indicates flow transfer also at the hot/cold interfaces A and B, which are therefore not free to move. Consequently, the invention of EP1602141 is only suited to deliver the desired flows and provide the desired reduction in piping and
1 Using for example high insulation materials from microthermgroup.com manifolding surface areas for relatively low values of in¬ let/outlet temperature differences (ΔΤ) .
The maximum operating temperature and efficiencies of the heat exchanger of invention EP1602141 and similar designs are limited by the fact that the heat exchanger thermal gradient (left to right) is perpendicular to the thermal gradient (top to bottom) of the adjacent components in the stack assembly. Alternative system and heat exchanger designs are proposed in this invention which has thermal gradients oriented in the same direction (thermally matched) as those of the adjacent stack components. This allows the heat exchangers to operate efficiently also in systems with relatively high values of inlet/outlet temperature differences (ΔΤ) .
Here we propose to use thermally matched heat exchangers closely integrated with the other components of solid oxide stack systems. By thermally matched is here understood that the thermal gradients of the heat exchanger are oriented in the same direction as those of the adjacent stack components. This can also be expressed as a criterion that the maximum temperature difference δΤ between two adj acent /touching points of the heat exchanger and the adjacent components is substantially smaller than the maximum temperature difference ΔΤ across the heat exchangers, please refer to figure 4.
Such heat exchangers have the advantages of being able to practically eliminate the heat loss from manifolding and pip¬ ing. Furthermore, they can also be used to:
1. Reduce heat loss from the compression system
2. Reduce the overall heat loss of the system as they can reduce the hot surface area of the system 3. Improve the efficiency of the electrical system
4. Reduce the heat exchanger cost as the assembly of these can be integrated with the stack assembly.
One example of an embodiment (Hex A) of thermally matched heat exchanger is shown in figure 5. The heat exchanger is in principle a xbended' counter flow plate heat exchanger. The flow propagates from one side ( xleft' or xright' ) to the oth- er side ( xright' or xleft' ) and at the left and right edges, the flow is directed to another layer in the heat exchanger and the flow direction is reversed.
Between each xlayer' of the heat exchanger, a thermally insulation layer is inserted. This layer could for example be just a hollow section using still air as insulation material.
The number of layers λΝ' used in such a heat exchanger is de¬ termined by the maximum acceptable temperature difference δΤ . As each layer handles 1/Nth of the overall temperature dif¬ ference ΔΤ, N can be expressed as N > ΔΤ/δΤ.
The heat exchanger proposed here is not only characterised by eliminating the heat loss from manifolding and piping, but it also have a very low effective surface area when integrated into solid oxide stack systems. To understand this equation 1 shows that if T (A) - Text (A) is low for a given surface, then the effective hot surface area from this surface is also low. This basically indicates that if two hot surfaces are placed face to face, then the heat loss of both can be eliminated.
To exemplify this, please consider the system on figure 6. A 'Hex A' type heat exchanger with a height of 3 cm is connect- ed to a 12 x 12 cm stack operating at 775°C. The heat exchanger is assumed to have a 25°C inlet from an adjacent man¬ ifold δΤ is assumed to be 75°C towards both the manifold and the stack facets.
For the stand alone heat exchanger integration according to equation (1) of the 6 sides' yields:
12 cm x 12 cm x (775 -75/2 - 25) °C = 10.3 m2 K (TOP) 12 cm x 12 cm x (75/2) °C = 0.5 m2 K (bottom)
4 x 12 cm x 3 cm x (775 - 25) /2 °C = 5.4 m2 K (sides)
Leading to a hot surface area of (10.3 + 0.5 + 5.4) m2 K / (775 - 25) K = 216 cm2 In the stack integrated configuration, the heat loss from the hot side is reduced to 0.5 m2 K and the system hot surface are is found as (0.5 + 0.5 + 5.4) m2 K / (775 - 25) K = 85 cm2
An interesting aspect of this heat exchanger is that it can become an integrated part of the stack compression system and help to reduce the heat loss from the compression system, which in most solid oxide stack systems are substantial. Due to differences in thermal expansion coefficients between dif- ferent stack components (e.g. cells and interconnects), ex¬ ternal compression systems are typically applied to the two endplates of the stack. One example of heat loss from a com¬ pression system is shown in figure 7 and used for the system on figure 1. Here a steel shield is used to provide the stack compression. The steel shield is bolted to a bottom plate and provides the compression pressure through the stack through a compression mat. As this compression mat has a relatively high thermal conductivity, the steel shield has the same tem¬ perature as the stack inside. The surface area of the steel shield is 2000 cm2 or almost 3 times higher than the surface area of the stack. This implies that the hot compression sys- tern will add significantly to the heat loss of the solid ox¬ ide stack system.
A very attractive alternative would be to use the proposed embodiment of a stack integrated thermally matched heat ex- changer as an integrated part of the compression system. A
Solid Oxide Stack System configuration which is very popular when several stacks are need is the so-called 'boxer' config¬ uration. Here two stacks are placed on top of each other with a centre manifold and compression provided from the two ends as shown in figure 8a and 8b. One advantages of the 'boxer' configuration is that two hot stack surfaces are facing each other, thereby reducing the system heat loss compared to a configuration with two individual stacks. Furthermore, a sim¬ ple compression system providing compression from the two ends can be used to compress the two stacks simultaneously.
This is shown for a standard configuration on figure 8a, indicating that in this case a xhot' compression system is needed as the compression will be applied directly at the two hot stack top/bottoms.
An alternative and attractive configuration is shown on fig¬ ure 8b. Here, the proposed heat exchanger (Hex a) is inserted between the stacks and the compression system. The heat ex¬ changers have hot end surfaces towards the stacks and cold end surfaces opposite the stacks towards the compression sys¬ tems. Such heat exchangers could provide cold interfaces for the compression system and thereby in practise eliminate the heat loss from the compression system.
Another source of heat loss in Solid Oxide Stack Systems is the electrical wiring. Typically, the electrical wiring is connected to the hot bottom and top-plates of the stacks as indicated on figure 9A. To reduce the ohmic losses of these wires they typically have a relatively broad cross section and hence a considerable thermal conductivity.
By using electrically conductive stack integrated heat ex¬ changers like Hex A and connecting the electrical wires to the cold surfaces, this heat loss would be eliminated as in¬ dicated on figure 9B .
To give an example of the typical ohmic loss of a heat ex¬ changer, consider again a heat exchanger measuring 12 x 12 x 3 cm. As the thermally matched heat exchangers can be con¬ nected directly to the stacks without the use of gaskets, the electrical resistance to the stack is identical to the elec- trical resistance of the heat exchanger. The heat exchanger plates will be electrically connected in the joining areas which can be assumed to be 12 cm long and a 1 cm width. Using a resistivity of steel of 12E-6 Ohm cm, the Hex A resistance RHex to the stack from the cold heat exchanger surface is found to be:
RHex = 12E-6 Ohm cm x 3 cm / (12 cm x 1 cm) = 3 E-6 Ohm
Transmission of even a relative large SOEC current of 100A across the heat exchanger will hence only cause a negligible additional voltage drop. A further and quite significant loss mechanism of Solid Oxide Stack Systems is the DC/AC conversion part of the system, where the power loss can easily be of the order of 5%. Here it is well-known that for both DC/AC and AC/DC conversion, the highest conversion efficiencies for a given electrical power is obtained for the highest possible (switching) volt¬ ages. This is similar to the well-known phenomena that the lowest transmission loss of electrical power is achieved for high voltage transmission lines.
To reduce switching loss it is therefore advantageous to con¬ nect several stacks in series electrically to obtain a high voltage for the DC/AC converter, as indicated for an extended boxer configuration in figure 9b. Typically, the compression system has to be electrically grounded, which leads to rela- tively high voltages between the end stack facets and the compression system, point I) and II) on figure 9b. This set limits to the maximum voltage in traditional configurations as there are practical limitations to finding electrical in¬ sulation materials which can operate simultaneously at high voltages, high temperatures and at high pressure during tem¬ perature cycles.
By applying an electrically conductive stack integrated heat exchanger with a hot side against the stack and a cold sur¬ face towards the compression system, it is however possible to have the electrical interfaces of the stack at a cold sur¬ face and hence to provide the insulation between the stacks and the compression system at much colder temperatures.
A significant advantage of the Hex A heat exchanger is that it can be assembled in the same assembly processes used for assembling the stacks. As an example Hex A can be manufac- tured by stacking of metal plates and spacers with the same foot print and from the same materials as those used for in¬ terconnects and spacers in the stack. The heat exchanger can be assembled by the same process (e.g. robot controlled stacking) as the fuel cell stack and the heat exchanger ele¬ ments can be joined by the same methods used for the stack, e.g. glass soldering, Ni-brazing or diffusion bonding. By using metal components for the heat exchangers it is assured that they as generally desired are electrically conductive.
Another preferred embodiment of thermally matched, stack in¬ tegrated heat exchangers is shown in Figure 10. This thermal¬ ly matched stack integrated heat exchanger is placed at one of the sides of the stack and uses a counter flow plate heat exchanger configuration.
On figure 10, the cold inlet is connected to the top of the heat exchanger at the xcold' right side and the hot xleft' side of the heat exchanger faces the stack. The hot flow be- tween the stack and the heat exchanger goes through a manifolding plate at the bottom of the stack. Hex B can be sepa¬ rate from the stack and for example an external heater can be inserted between Hex B and the stack. Hex B can also be an integrated part of the stack and for example share components such as spacers and interconnects. This will require electri¬ cally insulating parts to be included in the heat exchanger design as described in the following.
Figure 11 shows an embodiment of this invention, where the heat exchanger is realised from stack components by extending the length of interconnects and spacers. One set of heat ex- changer plates can then be based on extensions of the inter¬ connects. To avoid electrical short circuiting between the cells in the stack, every other set of heat exchanger plates (corresponding to the extensions of the cells) have to be based on a material which is electrically nonconductive in the vertical direction. This could for example be a ceramic plate or a ceramically coated metal sheet. The two sets of heat exchanger plates can be separated by extended spacers, which are also used to lead the desired flows across the dif- ferent heat exchangers plates.
As for Hex A, the heat exchanger plates of Hex B can be as¬ sembled in exactly the same process as the stack and similar methods can be used for joining the heat exchanger and stack components. Such joining methods could for example be glass sealing/soldering, brazing or diffusion bonding.
As for Hex A, Hex B also can also have a low hot surface ar¬ ea .
To exemplify this, please consider the system on figure 10. A 'Hex B' type heat exchanger with a length of 6 cm is connect¬ ed to a 12 x 12 cm stack with a height of 10 cm operating at 775°C. The heat exchanger is assumed to have inlet and outlet flow temperatures of 25 and 50°C, respectively.
For the stand alone heat exchanger, integral of the hot sur¬ face area according to equation (1) can be found as:
12 cm x 10 cm x (775 - 25) °C = 9 m2 K (hot surface) 12 cm x 10 cm x (50 - 25) °C = 0.3 m2 K (cold surface)
4 x 10 cm x 5 cm x (775 - 25) /2 °C = 7.5 m2 K (sides) This gives a hot surface area of:
(9 + 0.3 + 7.5) m2 K/ (775 - 25) = 225 cm2
In the stack integrated configuration, the heat loss from the hot surface is eliminated and the system hot surface are is found as 105 cm2
The Hex B heat exchanger can also be realised with low elec- trical resistance. Every other heat exchanger plate can be realised as a metal plate and thereby be electrically conduc¬ tive. This makes it possible for example to have cold elec¬ trical connections to the top or bottom plates of the stack from the top or bottom plate on the heat exchanger.
To give an example of the typical ohmic loss, consider again a heat exchanger measuring 12 x 10 x 5 cm. The heat exchanger plates are assumed to be 0.3 mm thick. In this case the Hex B resistance RHex to the stack from the cold heat exchanger sur¬ face is found to be:
RHex = 12E-6 Ω cm x 5 cm / (12 cm x 0.03 cm) = 1.7 E-4 Ω
A very interesting feature of this heat exchanger embodiment is that it is possible to have cold electrical connections to each interconnect in the stack. This can be used to provide a cold environment for electrical components used to control the current through individual cell or groups of cells. Such current control can for example be used to adjust the current over individual cells or cell groups in order to obtain very high fuel utilisations for all cells or cell groups in a stack. Another application could be to switch off the current in SOEC mode for cell or cell groups with defect (leaking) cells. This would avoid the excessive heating of defect cells to destroy adjacent cells.
The proposed heat exchanger embodiments can be used in many configurations to realise different SOFC, SOEC and even com¬ bined SOFC/SOEC configurations. One example is shown in fig¬ ure 12. In figure 12a four stacks are placed close to each other each sharing two hot sides with neighbouring stacks. Each stack is also connected to one Hex A and one Hex B, providing cold external interfaces for all in-plane sides of this configuration. It is furthermore possible to cascade several similar configurations in the out-off-plane direction thereby realising a system with very few hot external surfac¬ es. For SOEC purposes it can be advantageous to include stack integrated heaters between the stacks, these are also indi¬ cated on figure 12.
Solid oxide stack configurations with two heat exchangers are relevant for both SOEC and SOFC systems. This is exemplified on figure 13 and 14.
Figure 13 shows a simple SOEC configuration which can be re¬ alised with two (integrated) heat exchangers and a heater. Fuel (e.g. H20) is fed to the stack through two inlets, where the flows can be adjusted independently. The cold flow (e.g.
101°C steam) from fuel inlet 1 is heated in Hexla by the hot fuel outlet flow coming from the stack. In the same manner the cold flow from fuel inlet 2 is heated in Hex2 by the hot oxygen outlet flow from the stack. No inlet flushing of the oxygen side is used and the output from the oxygen side is therefore 100% 02. The two fuel inlets are combined and the temperature of the combined flow is increased in a heater before the fuel fed to the stack. The stack is assumed to operate close to the ther- mo-neutral point and the temperatures of the output flows will therefore be close to the stack operating temperature. The heat exchangers are not ideal and some heat will be lost to the environment, and these heat losses are compensated by the heater.
The main motivation for this configuration is that it makes it possible to balance the inlet thermal mass to the outlet thermal mass for all current levels. This is probably best demonstrated by two examples.
Assuming that a 75 cell stack, with a 100 cm2 active area per cell is used. The stack can operate at currents up to 70A with a fuel utilisation up to 70%. In this case the fuel in¬ put flow to the stack should be 3.4 Nm3/h (steam) .
When the system is operating at maximum load, then 2.4 Nm3/h H20 is converted to H2 and at the same time 1.2 Nm3/h 02 is produced. To achieve the most efficient heat recovery in the two heat exchangers, the thermal mass of the inlet flows should be adjusted to match the thermal mass of the outlet flows. With the specific heat of steam being 37.5 J/ (mol K) and the specific heat of oxygen being 29.4 J/ (mol K) , then the thermal mass balancing flow of inlet 2 should be 1.2 Nm3/h x 29.4/37.5 = 0.94 Nm3/h. The balanced flow of inlet 1 then becomes 3.4 Nm3/h - 0.94 Nm3/h = 2.46 Nm3/h If no electrolysis is applied (the system is idle) then the most efficient heat recovery is obtained if all the fuel is fed through fuel inlet 1, where it in Hexl can interact with a similar hot outlet flow.
Figure 14 shows a simple SOFC configuration which can be re¬ alised with two (integrated) heat exchangers. Fuel (e.g. H2) is fed to the stack through fuel inlet 1 and the cold inlet flow is heated in Hexl by the hot fuel outlet from the stack. In the same manner the cold air inlet flow is heated in Hex2 by the hot air outlet flow from the stack.
In contrast to the situation in SOEC mode, then it is desira¬ ble that the two inlet flows are colder than the stack oper¬ ating temperature as the colder inlet flows provide the nec- essary cooling of the stack. To give an example of typical operating parameters then a 75 cell stack, with an electrical output of 1.5 kW, an electrical efficiency of 50% and a fuel utilisation of 70% can be considered. With a lower heating value of hydrogen of 3.5 kWh/Nm3, then the SOFC needs a hy- drogen input of
1.5 kW / 3.5 kWh/Nm3 / 50%/ 70% = 1.8 Nm3/h H2
Assuming a stack inlet temperature of 650°C, a outlet temper¬ ature of 850°C, and a specific heat of air of 29 J(mol K) then it is found that roughly 21 Nm3/h of air is needed to provide cooling for the 1.5 kW of heat produced by the stack.
In practise this will be somewhat lower as some cooling typi¬ cally also will be provided by the fuel inlet and there will be some heat lost to the environment. It is also possible to realise solid oxide stack system with more than two heat exchangers per stack using these integrat¬ ed heat exchangers. One possible embodiment is shown in fig- ure 12b. Here there are 12 stacks and 14 heat exchangers ar¬ ranged in a very compact configuration. Using manifolding plates for fuel, air and oxygen distribution, it is possible for several stacks to share one heat exchanger and thereby realise for example the combined SOEC and SOFC system shown on figure 15.
This configuration is the common denominator of the SOEC and SOFC configurations shown in figure 13 and 14. When operating in SOEC mode the air inlet and outlets are shut off (on the cold side of Hex3) and the system is operating exactly as the SOEC system in figure 13.
When operating in SOFC mode the Oxy outlet and the fuel inlet 2 are shut off (on the cold side of Hex 2), the heater is shut off and the system is operating in a way very similar to the configuration of figure 14. The only difference is that in most cases Hexla is larger than Hexlb, implying that the temperature of the fuel fed to the stack is higher in figure 15 than in the typical SOFC configuration. This means that a marginally higher air flow is needed to cool the stack. How¬ ever, as the fuel flow is much smaller (more than one order of magnitude) than the airflow this increased airflow will only have a negligible influence on the SOFC system efficien¬ cy . To implement the system configuration of figure 15 with the integrated stacks shown in figure 12b, then it is possible to use hex B type heat exchangers for the air flow (Hex 3) as Hex B type heat exchangers can easily be designed for low pressure drop, which is less simple with the Hex A type de¬ sign .
On the other hand in might be advisable to use Hex A type heat exchangers for the main fuel heat exchangers (hex lb) as these are used in both SOEC and SOFC mode and therefore can provide cold interfaces for the compression system for both operating modes.
Features of the invention
1. A solid oxide electrolysis cell (SOEC) system comprising one or more SOEC stack (s) and one or more stack- integrated, temperature-matched heat exchanger (s) in di- rect physical contact on at least 1/12, preferably at least 1/6, preferably at least 1/3 of the heat exchanger surface area with the SOEC stack (s), wherein the maximum temperature difference δΤ between two adjacent and con¬ tacting points of the heat exchanger and the adjacent SOEC stack (s) is smaller than the maximum temperature difference ΔΤ across the heat exchanger ( s ) , wherein δΤ/ΔΤ < 50%, preferably δΤ/ΔΤ < 20% preferably δΤ/ΔΤ < > o ·
A solid oxide electrolysis cell system according to fea¬ ture 1, wherein the hot surface area of the system
(HSAgystem) relative to the hot surface area of the heat exchanger (s) in a not integrated, stand-alone (HSAsa) situation is HSAsystem/HSAsa< 1, preferably HSASystem/HSAsa *C 0.3, preferably HSAsystem/HSAsa < 0.1.
A solid oxide electrolysis cell system according to fea¬ ture 1, wherein the heat exchanger (s) have a temperature difference, ΔΤ, between the maximum and minimum inlet temperatures of ΔΤ > 300°C, preferably ΔΤ > 450°C, preferably ΔΤ > 600°C.
. A solid oxide electrolysis cell system according to fea¬ ture 1, wherein at least one of the heat exchangers is used for feeding current to the stack (s) or to and from the stack (s) and the at least one of the heat exchangers has an electrical resistance RHex between an cold surface and a stack element of RHex < 1 mOhm, preferably RHex < 0.1 mOhm, preferably RHex < 0.01 mOhm.
5. A solid oxide electrolysis cell system according to fea- ture 4, wherein the stack element is the top or the bot- torn plates of the stack.
6. A solid oxide electrolysis cell system according to fea- ture 4, wherein the stack element is a heater.
7. A solid oxide electrolysis cell system according to fea¬ ture 4, wherein the stack element is cells or cell groups and current control of these is performed at cold interfaces of the at least one heat exchanger.
8. A solid oxide electrolysis cell system according to fea¬ ture 1, wherein stack compression is applied to the cold surface of at least one of the heat exchangers.
9. A solid oxide electrolysis cell system according to fea¬ ture 8, wherein the stack compression is at least 200 mBar . 10. A solid oxide electrolysis system according to fea¬ ture 1, wherein the assembly of the integrated heat ex¬ changers is integrated with the stack assembly, at least one of the heat exchangers share at least an intercon¬ nect or a spacer.
11. A solid oxide electrolysis system according to fea¬ ture 1, wherein the hot surfaces of the heat exchang- er(s) are at the stack operating temperature or at maxi¬ mum 50°C colder.
12. A solid oxide stack system, applying at least on heat exchanger according to feature 1, where the thermal management system is designed in a way where the system can operate with high efficiency in both SOEC and SOFC mode . 13. A solid oxide stack system according to feature 12, wherein the thermal management system can operate with as few as three heat exchangers .
14. A solid oxide stack system according to feature 12, where the thermal management system can operate without any hot valves.

Claims

Claims
A solid oxide electrolysis cell (SOEC) system com¬ prising one or more SOEC stack (s) and one or more stack-integrated, temperature-matched heat exchang¬ er (s) in direct physical contact on at least 1/12, preferably at least 1/6, preferably at least 1/3 of the heat exchanger surface area with the SOEC stack (s), wherein the maximum temperature difference δ between two adjacent and contacting points of the heat exchanger and the adjacent SOEC stack (s) is smaller than the maximum temperature difference ΔΤ across the heat exchanger ( s ) , wherein δΤ/ΔΤ < 50%, preferably δΤ/ΔΤ < 20% preferably δΤ/ΔΤ < 5% and the hot surface area of the system (HSAsystem) relative to the hot surface area of the heat exchanger (s) in a not integrated, stand-alone (HSAsa) situation is HSAsystem/HSAsa< 1, preferably HSASystem/HSAsa < 0.3, preferably HSAsystem/HSAsa < 0.1.
A solid oxide electrolysis cell system according to claim 1, wherein the heat exchanger (s) have a temper¬ ature difference, ΔΤ, between the maximum and minimum inlet temperatures of ΔΤ > 300°C, preferably ΔΤ > 450°C, preferably ΔΤ > 600°C.
3. A solid oxide electrolysis cell system according to claim 1, wherein at least one of the heat exchangers is used for feeding current to the stack (s) or to and from the stack (s) and the at least one of the heat exchangers has an electrical resistance RHex between an cold surface and a stack element of RHex < 1 mOhm, preferably RHex < 0.1 mOhm, preferably RHex < 0.01 mOhm.
A solid oxide electrolysis cell system according to claim 3, wherein the stack element is the top or the bottom plates of the stack.
A solid oxide electrolysis cell system according to claim 3, wherein the stack element is a heater.
A solid oxide electrolysis cell system according to claim 3, wherein the stack element is cells or cell groups and current control of these is performed at cold interfaces of the at least one heat exchanger.
A solid oxide electrolysis cell system according to claim 1, wherein stack compression is applied to the cold surface of at least one of the heat exchangers.
A solid oxide electrolysis cell system according to claim 7, wherein the stack compression is at least 200 mBar.
A solid oxide electrolysis system according to claim 1, wherein the assembly of the integrated heat ex¬ changers is integrated with the stack assembly, at least one of the heat exchangers share at least an interconnect or a spacer.
10. A solid oxide electrolysis system according to claim 1, wherein the hot surfaces of the heat ex¬ changer (s) are at the stack operating temperature or at maximum 50 °C colder.
PCT/EP2014/056520 2013-05-01 2014-04-01 Solid oxide stack system with thermally matched stack integrated heat exchanger WO2014177336A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EPPCT/EP2013/059066 2013-05-01
EP2013059066 2013-05-01

Publications (1)

Publication Number Publication Date
WO2014177336A1 true WO2014177336A1 (en) 2014-11-06

Family

ID=48236951

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2014/056520 WO2014177336A1 (en) 2013-05-01 2014-04-01 Solid oxide stack system with thermally matched stack integrated heat exchanger

Country Status (3)

Country Link
AR (1) AR096120A1 (en)
TW (1) TW201505248A (en)
WO (1) WO2014177336A1 (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2019158307A1 (en) * 2018-02-15 2019-08-22 Siemens Aktiengesellschaft Electrochemical production of a gas comprising co with intermediate cooling of the electrolyte flow
US11145880B2 (en) * 2017-12-22 2021-10-12 Colorado School Of Mines High efficiency solid oxide fuel cell—internal combustion engine hybrid power system
DE102021203513A1 (en) 2021-04-09 2022-10-13 Robert Bosch Gesellschaft mit beschränkter Haftung Solid oxide electrolytic cell device and method of operating the solid oxide electrolytic cell device
WO2023222504A1 (en) * 2022-05-18 2023-11-23 Topsoe A/S Solid oxide electrolysis unit

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI755647B (en) * 2019-11-04 2022-02-21 財團法人工業技術研究院 Fuel cell system and control method thereof

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20010049041A1 (en) * 1998-08-10 2001-12-06 Peter Buchner Apparatus and method for utilizing the waste heat of an air-cooled fuel cell battery
US20050014046A1 (en) * 2001-03-17 2005-01-20 Bayerische Motoren Werke Aktiengesellschaft Fuel cell with integrated heat exchanger
US20070287045A1 (en) * 2006-06-09 2007-12-13 Samsung Sdi Co., Ltd. Fuel cell having heat exchanger built in stack
DE102006049252A1 (en) * 2006-10-19 2008-04-30 Robert Bosch Gmbh Fuel cell for motor vehicle, has multiple single cell units, which are supplied by gas flow comprising hydrogen and gas flow comprising oxygen, and heat exchanger integrated in one of single cell units
US20100200422A1 (en) * 2007-09-25 2010-08-12 Commissariat A L' Energie Atomique High temperature electrolyser with temperature homogenisation device

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20010049041A1 (en) * 1998-08-10 2001-12-06 Peter Buchner Apparatus and method for utilizing the waste heat of an air-cooled fuel cell battery
US20050014046A1 (en) * 2001-03-17 2005-01-20 Bayerische Motoren Werke Aktiengesellschaft Fuel cell with integrated heat exchanger
US20070287045A1 (en) * 2006-06-09 2007-12-13 Samsung Sdi Co., Ltd. Fuel cell having heat exchanger built in stack
DE102006049252A1 (en) * 2006-10-19 2008-04-30 Robert Bosch Gmbh Fuel cell for motor vehicle, has multiple single cell units, which are supplied by gas flow comprising hydrogen and gas flow comprising oxygen, and heat exchanger integrated in one of single cell units
US20100200422A1 (en) * 2007-09-25 2010-08-12 Commissariat A L' Energie Atomique High temperature electrolyser with temperature homogenisation device

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11145880B2 (en) * 2017-12-22 2021-10-12 Colorado School Of Mines High efficiency solid oxide fuel cell—internal combustion engine hybrid power system
WO2019158307A1 (en) * 2018-02-15 2019-08-22 Siemens Aktiengesellschaft Electrochemical production of a gas comprising co with intermediate cooling of the electrolyte flow
CN111727275A (en) * 2018-02-15 2020-09-29 西门子股份公司 Electrochemical production of gases containing CO using intercooling of the electrolyte stream
DE102021203513A1 (en) 2021-04-09 2022-10-13 Robert Bosch Gesellschaft mit beschränkter Haftung Solid oxide electrolytic cell device and method of operating the solid oxide electrolytic cell device
WO2023222504A1 (en) * 2022-05-18 2023-11-23 Topsoe A/S Solid oxide electrolysis unit

Also Published As

Publication number Publication date
AR096120A1 (en) 2015-12-09
TW201505248A (en) 2015-02-01

Similar Documents

Publication Publication Date Title
JP6517835B2 (en) Fuel cell stack configuration
US20160006047A1 (en) Sofc stack with integrated heater
WO2014177336A1 (en) Solid oxide stack system with thermally matched stack integrated heat exchanger
US10218011B2 (en) High-temperature or fuel-cell electrochemical system having improved thermal management
US20050106446A1 (en) Fuel cell system
JP5318506B2 (en) Fuel cell system
JP5981379B2 (en) Fuel cell
EP2254182B1 (en) Process of running a serial connected fuel cell stack module assembly
EP2845254A1 (en) A current collector component for a fuel cell
JP6776201B2 (en) Multi-stack fuel cell system and heat exchanger assembly
JP4494409B2 (en) Multi-cell fuel cell layer and system
US20210391585A1 (en) Solid oxide electrochemical system having integrated heating means
US20090169969A1 (en) Bipolar plate of solid oxide fuel cell
US8778550B2 (en) Battery of fuel cells
WO2014177207A1 (en) Heat exchanger in sofc stack
JP6277113B2 (en) Fuel cell module
US20230335762A1 (en) Fuel cell, a full cell vehicle including the same, and a method of controlling a temperature of a vehicle
JP2015032489A (en) Solid oxide fuel cell stack
JP2004165030A (en) Fuel cell
KR20220091940A (en) Structure of thermoelectric module for thermoelectric generator using wasted heat of fuel cell
JPH03263881A (en) Thermoelectric generation method and device
KR20220091938A (en) Thermoelectric generator using wasted heat of fuel cell
JP2011204602A (en) Flat plate lamination type fuel cell

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 14715261

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 14715261

Country of ref document: EP

Kind code of ref document: A1