JP5315400B2 - Solid oxide fuel cell stack - Google Patents

Description

  The present invention relates to a solid oxide fuel cell stack in which a plurality of cells of a solid oxide fuel cell are arranged.

  In recent years, fuel cells have been actively developed for reasons such as clean exhaust gas and relatively high power generation efficiency. There are several types of fuel cells. In any type, it is required to further improve the energy conversion efficiency or the power generation efficiency.

  A solid oxide fuel cell (Solid Oxide Fuel Cell, hereinafter referred to as SOFC in some cases) has a high operating temperature of about 500 to 1000 ° C. Patent Document 1 discloses that a thermoelectric conversion element is disposed around the SOFC stack in order to effectively use this heat to improve energy conversion efficiency.

  In Patent Document 2, in a polymer electrolyte fuel cell operating at a low temperature, an oxygen electrode-side field plate is provided in order to provide a fuel cell with high energy utilization efficiency using thermal energy generated by an electrochemical reaction. It is disclosed that a thermoelectric conversion element is disposed in contact therewith.

JP 2002-358997 A JP 2002-141077 A

  However, in the technique described in Patent Document 1, since a thermoelectric conversion element is arranged around the SOFC stack, there is room for further improvement in terms of effective use of heat.

  Further, the technique described in Patent Document 2 cannot be said to be excellent in terms of the amount of power generated by the thermoelectric conversion element because the operating temperature is low.

  An object of the present invention is to provide an SOFC stack that can more effectively utilize the heat generated by the SOFC and obtain higher power generation efficiency.

According to the present invention, it has a plurality of cells of a solid oxide fuel cell,
A solid oxide fuel cell stack having a thermoelectric conversion element between the cells ,
The cell has a cylindrical shape, and the thermoelectric conversion element has a hollow cylindrical shape.
A solid oxide fuel cell stack is provided.

The solid oxide fuel cell stack is
Furthermore, it can have a flow path for flowing a cooling medium for cooling one side of the thermoelectric conversion element.

  The present invention provides an SOFC stack that can more effectively utilize the heat generated by the SOFC and obtain higher power generation efficiency.

It is a partial schematic diagram which shows an example of the SOFC stack for reference . It is a partial schematic diagram which shows another example of the SOFC stack for reference . It is a partial schematic diagram which shows another example of the SOFC stack for reference . It is a partial schematic diagram which shows another example of the SOFC stack for reference . It is a partial schematic diagram which shows another example of the SOFC stack for reference . It is a partial schematic diagram which shows an example of the SOFC stack of this invention, (a) is a cross-sectional view, (b) is an AA longitudinal cross-sectional view. It is a partial schematic diagram which shows another example of the SOFC stack of this invention. It is a schematic diagram which shows the example of the thermoelectric conversion element modularized. It is a schematic diagram which shows another example of the thermoelectric conversion element modularized. It is a schematic diagram which shows another example of the thermoelectric conversion element modularized, (a) is a cross-sectional view, (b) is a longitudinal cross-sectional view.

The SOFC stack is electrically connected by a plurality of cells (single cells) sandwiching an electrolyte between an anode electrode and a cathode electrode, an electronic conductive member called a separator or an interconnector, an electronic conductive member called a current collector, and the like. It has the structure connected to.
In the present invention, the cell has a cylindrical shape, and the thermoelectric conversion element has a hollow cylindrical shape. Other cases may be mentioned below, but this is for reference only.

In SOFC, oxygen ion conductive ceramics or proton ion conductive ceramics are used as an electrolyte, and hydrogen and oxygen are electrochemically reacted. At this time, H ₂ O is generated at the anode or the cathode and generates heat.

  In the SOFC stack, there is a temperature difference between the portion where the heat generation occurs and the other portions.

  In the present invention, the thermoelectric conversion element is arranged between the cells, so that the temperature difference is effectively used, and in addition to the power generation by the electrochemical reaction, the thermoelectric conversion element generates power. This can improve power generation efficiency.

  Moreover, since the thermoelectric conversion element converts heat energy into electric energy, it has a cooling effect. By disposing the thermoelectric change element between the cells, it is possible to cool the inside of the SOFC stack. Conventionally, the stack is cooled by supplying a large amount of gas (usually cathode gas). However, since a large amount of gas is supplied, the required power (power consumption of a blower or the like) increases, and the efficiency of the SOFC system decreases. In the present invention, the electric energy can be taken out simultaneously with the thermoelectric conversion element, and at the same time, the cell can be cooled. Therefore, the power required for cooling can be reduced, and the blower, piping, and the like can be downsized. As a result, the SOFC system can be highly efficient and downsized.

  Furthermore, since the operating temperature of SOFC is higher than that of polymer electrolyte fuel cells that operate at a low temperature of about 80 ° C., it is possible to obtain a large temperature difference, and higher efficiency can be achieved by power generation using thermoelectric conversion elements. Can be planned.

The material of the thermoelectric conversion element can be appropriately selected from known thermoelectric conversion element materials that can be used at the operating temperature of the SOFC. For example, as a p-type thermoelectric conversion element, SiGe, Si _0.8 Ge _0.2 , β-FeSi ₂ , PbTe, GeTe, GeTe-AgSbTe ₂ , β-Zn ₄ Sb ₃ , Ce (Fe _3.5 Co _0.5 ) Sb ₁₂ , n-type thermoelectric. As the conversion element, SiGe, β-FeSi ₂ , PbTe, Ba _0.3 Co _3.7 Sb ₁₂ , Zn _0.98 Al _0.02 O can be used.

  The shape of the thermoelectric conversion element can be appropriately selected from known thermoelectric conversion element shapes such as a bulk, a thin film, a thick film, a cylinder, and a flat plate in accordance with the shape of the SOFC stack. As for the thermoelectric conversion element, a plurality of thermoelectric conversion elements may be modularized.

  FIG. 8 shows an example of a flat plate type thermoelectric conversion element module in which a plurality of p-type or n-type thermoelectric conversion elements are arranged. A plurality of p-type or n-type thermoelectric conversion elements 1001 are connected in parallel between the conductor plates 1002.

  FIG. 9 shows an example of a flat plate type thermoelectric conversion element module in which p-type and n-type thermoelectric conversion elements are alternately arranged. A plurality of thermoelectric conversion elements 1001 are connected in series by a conductor 1003. At this time, p-type and n-type thermoelectric conversion elements are alternately connected. In addition, an insulator 1004 is provided, and one electrical path is formed between the two conductor plates 1002.

  FIG. 10 shows an example of a cylindrical thermoelectric conversion element module in which a plurality of p-type or n-type thermoelectric conversion elements are arranged. A hollow cylindrical p-type or n-type thermoelectric conversion element 2001 is connected in series by a conductive member 2002 and a conductive member 2003. The conductive member 2002 is electrically connected to the outside of the cylindrical thermoelectric conversion element, and the conductive member 2003 is electrically connected to the inside of the cylindrical thermoelectric conversion element.

  About the member and structure of SOFC stacks other than a thermoelectric conversion element, it can select suitably from the member and structure of a well-known SOFC stack, and can employ | adopt. For example, as the SOFC stack, various shapes such as a flat plate shape and a cylindrical shape can be appropriately selected and employed.

  In an SOFC stack, practically, many cells are often stacked or aligned. In this case, the thermoelectric conversion elements may be arranged in all between the cells, or the thermoelectric conversion elements may be arranged only in a part. For example, in the case of a flat plate type SOFC, a thermoelectric conversion element can be arranged for each cell, or a plurality of cells may be arranged as a block, and a thermoelectric conversion element may be arranged for each block. .

  In order to suppress the thermal stress applied to the SOFC stack due to the temperature difference, it is effective to make the cell cylindrical. In the case of a flat type stack, for example, stacked cells and separators are sandwiched between two metal (electrically conductive) plates called end plates and bolted. The cylindrical stack has a structure in which, for example, a part of the electrode surface is electrically connected by an interconnector. For this reason, the cylindrical stack has a smaller restraint area than the flat plate stack, and it is relatively easy to relieve thermal stress. It is also effective to use a material having a cushioning effect for the current collector for electrically connecting the cylindrical cells. For example, a metal porous body (Metal-foam, foam metal) is easily deformed by an external force and has a small contact area. For this reason, since the thermal expansion of a cell, a separator, and an interconnector can be absorbed and thermal stress can be relieved, a metal porous body is suitable as a current collector.

  Next to the thermoelectric conversion element, a cooling medium flow path that is a flow path for flowing the cooling medium can be provided. In particular, the amount of power generation in the thermoelectric conversion element can be increased by providing a cooling medium flow path on one side of the thermoelectric conversion element (the side where the temperature is desired to be lowered) and cooling one side of the thermoelectric conversion element. At this time, it is preferable to provide a cooling medium flow path adjacent to the side where the water generation reaction does not occur, of the anode side and the cathode side.

  As the cooling medium, a gas having a temperature and a flow rate capable of cooling the side of the thermoelectric conversion element that is desired to have a lower temperature during power generation can be appropriately used. As the cooling medium, anode gas or cathode gas supplied to the stack can be used, or other gas can be used separately from these gases. For example, air can be used as the other gas. Alternatively, when there is a gas to be preheated in the SOFC system, the gas can be used as a cooling medium, and the gas can be preheated simultaneously with the cooling of the thermoelectric conversion element.

  Note that gas can be supplied to or discharged from the cell or the like by appropriately using a header or a manifold structure.

  In the case of a cylindrical SOFC, in order to electrically connect thermoelectric conversion elements and cells, or to form a module by electrically connecting cylindrical thermoelectric conversion elements as shown in FIG. Known interconnectors and current collectors used for SOFC, and known conductive members can be used as appropriate.

EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited by this. Examples 1 to 5 are for reference.

[Example 1]
In this embodiment, a flat SOFC is employed, and cells and thermoelectric conversion elements are alternately arranged one by one. FIG. 1 is a partial schematic diagram for explaining the flat plate type SOFC stack of this example. The electrolyte plate 1 is an oxygen ion conductive ceramic. An anode electrode 2a and a cathode electrode 2c are disposed at positions sandwiching the electrolyte plate 1. An anode side separator 3a is disposed on the opposite side of the anode electrode 2a from the electrolyte plate, and a cathode side separator 3c is disposed on the opposite side of the cathode electrode 2c from the electrolyte plate. That is, the separators 3a and 3c are arranged at a position sandwiching a cell (single cell) 4 composed of the electrolyte plate 1 and the electrodes 2a and 2c.

  A thermoelectric conversion element 5 (here, an n-type thermoelectric conversion element is used) is arranged on the opposite side of the separator 3c from the cell, and an adjacent cell (not shown) is sandwiched on the opposite side of the thermoelectric conversion element to the separator 3c. An anode side separator 3a-1 is disposed. The outer shape of the thermoelectric conversion element is a flat plate. In this way, the cells sandwiched between the anode side separator and the cathode side separator and the thermoelectric conversion elements are alternately stacked.

An anode gas containing hydrogen is supplied to the anode electrode, and a cathode gas containing oxygen is supplied to the cathode electrode. Since the reaction for generating H ₂ O on the anode side progresses during power generation by SOFC and a large amount of heat is generated, the anode side separator 3a-1 becomes hotter than the cathode side separator 3c, and a temperature difference ΔT is created in the thermoelectric conversion element. . In FIG. 1, the broken line schematically shows a temperature gradient in the thermoelectric conversion element. This ΔT enables the thermoelectric conversion element to generate power.

[Example 2]
In this embodiment, a cooling medium flow path 6 which is a flow path for flowing a cooling medium is added to the flat plate type SOFC stack of the first embodiment. By cooling the thermoelectric conversion element on the anode side (right side in FIG. 2) or the cathode side (left side in FIG. 2) where water generation reaction does not occur (here, the cathode side) with a cooling medium, The temperature difference in the conversion element can be made larger. For this reason, in this embodiment, the cooling medium flow path 6 is provided between the thermoelectric conversion element 5 and the cathode side separator 3c.

  In order to provide the cooling medium flow path, a member (cooling medium flow path forming member) 7 that has electronic conductivity, has a flat outer shape, and has a groove that becomes a cooling medium flow path can be used. You may integrate this member with a separator or a thermoelectric conversion element.

  As the cooling medium, the anode inlet gas or the cathode inlet gas supplied to the stack can be branched as required, or another gas (for example, air) can be used separately.

Example 3
As shown in FIG. 3, the present embodiment is an example in which a heat insulating material 8 is added between the cathode side separator 3c of the flat plate type SOFC stack of the second embodiment and the cooling medium flow path forming member 7. With the heat insulating material, heat transfer from the cell (cathode side) to the cooling medium, and hence to the low temperature side of the thermoelectric conversion element, can be suppressed, the low temperature side of the thermoelectric conversion element can be made lower, and ΔT can be increased. .

Example 4
As shown in FIG. 4, in this embodiment, the anode side (right side in the figure) of the thermoelectric conversion element is cooled to a low temperature by the cooling medium, and the cathode side (left side in the figure) is raised to a high temperature. In this case, it is preferable to dispose the heat insulating material 8 between the anode and the cooling medium in order to prevent heat generated in the anode from being transferred from the anode side separator 3a-1 to the cooling medium and reducing ΔT. In this example, a p-type thermoelectric conversion element is used.

Example 5
In the flat plate type SOFC, at least one of the anode side separator and the cathode side separator can include a thermoelectric conversion element. Either the anode-side separator or the cathode-side separator may be composed of a thermoelectric conversion element, or both separators may be integrated into a single thermoelectric conversion element. Alternatively, a part of either or both separators may be formed of a thermoelectric conversion element.

  As shown in FIG. 5, in this example, the cathode-side separator 3c is made of a thermoelectric conversion element, and the cathode-side separator also serves as the thermoelectric conversion element.

Example 6
In this embodiment, a cylindrical SOFC is employed, and the thermoelectric conversion element has a hollow cylindrical shape (pipe shape) having openings at both ends. As shown in FIG. 6, the thermoelectric conversion element 25-1 is arranged between the cell 21-1 and the adjacent cell 21-2. The thermoelectric conversion element 25-2 is also arranged on the opposite side of the cell 21-2 from the thermoelectric conversion element 25-1. Here, an n-type thermoelectric conversion element is used.

  The cell has an inner pipe 22, and an anode gas containing hydrogen is supplied from the inner pipe. A cathode gas containing oxygen is supplied to the outside of the cell. The cell has a structure in which an anode electrode is provided on the inner side and a cathode electrode is provided on the outer side with a cylindrical electrolyte closed at one end. Both the cell and thermoelectric conversion element have a positive pole on the outside and a negative pole on the inside. A current collector 23 is in contact with the outside of the cell and the thermoelectric conversion element, an interconnector 24 is electrically connected to the inside, and the current collector and the interconnector are in contact with each other to form an electrical path.

  Cathode gas flows both inside and outside the thermoelectric conversion element. Each cell generates heat during power generation, whereby the thermoelectric conversion element is heated from the outside. On the other hand, the inside of the hollow cylindrical thermoelectric conversion element is a cooling medium flow path. A part of the cathode gas is used as a cooling medium, and the cooling medium flows inside, whereby the thermoelectric conversion element is cooled from the inside. Therefore, the thermoelectric conversion element has a high temperature on the outside and a low temperature on the inside, causing a temperature difference. This temperature difference enables power generation by the thermoelectric conversion element.

Example 7
In Example 6, a hollow cylindrical thermoelectric conversion element having both ends opened was used, but this is not restrictive. In this example, a hollow cylindrical thermoelectric conversion element in which one end of the thermoelectric conversion element is closed and the other end is opened is used. FIG. 7 shows one cell 21 and one thermoelectric conversion element 25. One end of the thermoelectric conversion element (the upper end in the drawing in the drawing) is closed, and the inner tube 26 is disposed in the thermoelectric conversion element. Cathode gas is supplied from the inner pipe 26 as a cooling medium, and the inside of the thermoelectric conversion element is cooled. A cooling medium (cathode gas) discharged from the thermoelectric conversion element can be supplied to the outside of the cell and used as a cathode gas for a battery reaction.

  Although several examples have been described above, in the present invention, the fuel cell stack is flat or cylindrical, the thermoelectric conversion element (which may be modularized) is flat or cylindrical Various choices are possible, such as using p-type or n-type as the thermoelectric conversion element, using anode gas or cathode gas as the cooling medium, or using other gas, There can be various forms depending on the selection.

  The SOFC system of the present invention can be used for, for example, a stationary or mobile power generation system and a cogeneration system.

DESCRIPTION OF SYMBOLS 1 Electrolyte plate 2a Anode electrode 2c Cathode electrode 3a Anode side separator 3c Cathode side separator 4 Cell (single cell)
5 Thermoelectric Conversion Element 6 Cooling Medium Channel 7 Cooling Medium Channel Forming Member 8 Heat Insulating Material 21 Cell (Single Cell)
22 Anode gas supply inner pipe 23 Current collector 24 Interconnector 25 Thermoelectric conversion element 26 Cooling medium supply inner pipe 1001 Thermoelectric conversion element 1002 Conductor plate 1003 Conductor 1004 Insulator 2001 Thermoelectric conversion element 2002 Conductive member 2003 Conductive member

Claims (2)

Having a plurality of cells of a solid oxide fuel cell,
A solid oxide fuel cell stack having a thermoelectric conversion element between the cells,
The cell has a cylindrical shape, and the thermoelectric conversion element has a hollow cylindrical shape.
Solid body oxide fuel cell stack. Further, the solid oxide fuel cell stack according to claim 1, further comprising a flow path for flowing a cooling medium for cooling the one side of the thermoelectric conversion element.

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