JP2008218279A - Solid oxide fuel cell, and supplying method of fuel gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize improvement in power generation efficiency and durability by uniformalizing cell voltage of respective power generating cells in a fuel cell stack. <P>SOLUTION: In a supplying method of a fuel gas of a solid oxide fuel cell in which the fuel cell stack 1 is constituted by collecting a plurality of the power generating cells 5 wherein a fuel electrode layer and an air electrode layer are arranged at both faces of a solid electrolyte layer and in which power generating reaction is made to be formed by supplying the fuel gas and an oxidizer gas to the respective power generating cells 5, the fuel gas supply amount to the power generating cells 5 positioned at the end part of the fuel cell stack 1 is increased compared with other power generating cells 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid oxide fuel cell in which a plurality of power generation cells each having a fuel electrode layer and an air electrode layer disposed on both sides of a solid electrolyte layer are stacked, and in particular, to uniformize the voltage of each power generation cell. Thus, the present invention relates to a solid oxide fuel cell that improves power generation efficiency and durability.

  In recent years, solid oxide fuel cells that directly convert chemical energy of fuel into electrical energy have attracted attention as high-efficiency and clean power generators. This solid oxide fuel cell has been proposed as a cylindrical type, a monolith type, and a flat plate type, and each has a solid electrolyte layer made of an oxide ion conductor sandwiched between the air electrode layer and the fuel electrode layer from both sides. It has a laminated structure.

During power generation, an oxidant gas (oxygen) is supplied to the air electrode layer side and a fuel gas (H ₂ , CO, CH _4, etc.) is supplied to the fuel electrode layer side as a reaction gas. The air electrode layer and the fuel electrode layer are both porous layers so that the reaction gas can reach the interface with the solid electrolyte layer.

Oxygen supplied to the air electrode layer passes through the pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte layer, and receives electrons from the air electrode layer at this portion to receive oxide ions (O ²⁻ ). Is ionized. The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode layer, and the oxide ions that reach the vicinity of the interface with the fuel electrode layer react with the fuel gas at this portion to react with the reaction product (H ₂ O, CO _2, etc.) and electrons are emitted to the fuel electrode layer. Electrons generated in the electrode reaction (power generation reaction) can be taken out as an electromotive force at an external load on another route.

  By the way, a flat plate type fuel cell stack is configured by stacking a large number of power generation cells and separators alternately. The temperature distribution in the stacking direction is shown by a solid line (A) in FIG. Thus, there is a tendency that the temperature in the vicinity of both ends of the fuel cell stack is extremely lowered as compared with the temperature in the middle portion.

This is because the fuel cell stack has a structure in which each power generation cell is sandwiched between upper and lower power generation cells, so that the Joule heat of the power generation cell is difficult to dissipate outside. This is because the power generation cell is in direct contact with the atmosphere in the module, and thus Joule heat is easily dissipated.
In the case of a solid oxide fuel cell, when the temperature of the power generation cell decreases, the electrical resistance of the solid electrolyte layer mainly increases and the heat loss increases, so that the broken line (b) in FIG. Thus, the cell voltage is lower than that of the power generation cell in the high temperature portion.

As described above, when the cell voltages are non-uniform in a plurality of power generation cells, the total power generation performance of the fuel cell is limited by the power generation performance (cell voltage) of the power generation cell in the low temperature part, which is efficient. There was a problem that it was impossible to generate electricity. In addition, when the cell voltage drops below a predetermined value, the internal resistance increases, so that the amount of heat generated by the power generation cell increases, causing a temperature difference in the cell plane and causing the problem of damage to the power generation cell.
Such a problem can also occur in a fuel cell stack having a bundle structure in which a large number of cylindrical power generation cells are collected.

Note that Patent Document 1 is disclosed as a technique for uniformizing the temperature distribution in the stacking direction of the fuel cell stack. In Patent Document 1, a heat radiating portion is provided in each separator in the stacking direction, and the stack temperature is controlled by the heat radiating action, and the cross-sectional area of the heat radiating portion is changed according to the position where the separator is arranged. The structure of the heat dissipating part is extremely complicated.
As another method, it is conceivable to install a heat insulating material in a portion where the stack temperature is lowered, but it is difficult to completely suppress the heat radiation of the power generation cell by the heat insulating material.
JP 2004-273140 A

  The present invention has been made in view of the above-described problems, and prevents a decrease in cell voltage due to a decrease in the temperature of the fuel cell stack and makes each cell voltage uniform to improve power generation efficiency and durability. It is an object of the present invention to provide a solid oxide fuel cell and a preferable fuel gas supply method therefor.

  That is, the fuel gas supply method according to claim 1 comprises a plurality of power generation cells each having a fuel electrode layer and an air electrode layer arranged on both sides of a solid electrolyte layer to constitute a fuel cell stack, and A fuel gas supply method for a solid oxide fuel cell that generates a power generation reaction by supplying a fuel gas and an oxidant gas, the fuel gas supply amount to the power generation cell located at an end of the fuel cell stack It is characterized in that it is increased compared to other power generation cells.

  According to a second aspect of the present invention, there is provided a solid oxide fuel cell comprising a plurality of power generation cells each having a fuel electrode layer and an air electrode layer disposed on both sides of a solid electrolyte layer to constitute a fuel cell stack, A solid oxide fuel that generates a power generation reaction by supplying a fuel gas and an oxidant gas to each power generation cell via a fuel gas flow path that communicates with the oxidant gas manifold and an oxidant gas flow path that communicates with the oxidant gas manifold In the battery, a flow resistance reduction means for reducing a flow resistance of the fuel gas flow path is provided in the fuel gas flow path of the power generation cell located at the end of the fuel cell stack, and the flow resistance resistance means Thus, the amount of fuel gas supplied to the power generation cell is increased compared to other power generation cells.

  According to a third aspect of the present invention, in the solid oxide fuel cell according to the second aspect of the present invention, each power generation unit is provided with a heat dissipating means inside the fuel cell stack and is located in the vicinity of the heat dissipating means. The flow resistance reduction means is provided in the fuel gas flow path of the cell.

  According to a fourth aspect of the present invention, there is provided the solid oxide fuel cell according to the second or third aspect, wherein the flow resistance is reduced by a throttle mechanism of a fuel supply port of the fuel gas flow path. It is characterized by having a channel resistance relaxation means that decreases.

  Further, the invention according to claim 5 is the solid oxide fuel cell according to claim 2 or 3, wherein the flow path resistance is reduced by the cross-sectional area of the fuel gas flow path. It has a resistance relaxation means.

  In the solid oxide fuel cell according to any one of claims 2 and 3, the flow resistance of the fuel gas flow path is reduced by the length of the fuel gas flow path. It has a flow path resistance relaxation means.

  The invention according to claim 7 is the solid oxide fuel cell according to any one of claims 2 to 6, wherein the sealless structure for discharging unused fuel gas from the outer periphery of the power generation cell is provided. It is characterized by having.

According to the first to seventh aspects of the present invention, the amount of fuel gas supplied to the power generation cell located at a portion where the stack temperature is relatively lowered, such as the end of the fuel cell stack or the vicinity of the heat dissipation means, is supplied to another power generation. Since the number of cells is higher than that of cells, in the power generation cells with low temperature, the overvoltage of the fuel electrode layer decreases and the cell voltage increases, so the voltage of each power generation cell can be made uniform and efficient. Power generation is possible.
In addition, since the internal resistance of the power generation cell decreases and the Joule heat generation decreases due to an increase in the cell voltage, the temperature difference within the same cell surface decreases, preventing damage to the power generation cell and improving the durability of the fuel cell. improves.

  In particular, as in the invention according to claim 7, in the case of a fuel cell having a sealless structure, unused fuel gas is present in the outer peripheral portion of the power generation cell located at the end of the stack as compared with other power generation cells. Since a large amount is released and burned in the vicinity of the cell, the temperature of the power generation cell at the stack end can be raised by this combustion heat. As a result, the internal resistance of the heated power generation cell decreases and the cell voltage increases, so that more efficient power generation can be performed.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 shows a flat plate type solid oxide fuel cell to which the present invention is applied, FIG. 2 shows the structure of a single cell according to the present invention, FIG. 3 shows an example of a separator, and FIG. FIG. 5 and FIG. 6 show a method of supplying fuel gas to each power generation cell in the fuel cell stack.

  As shown in FIG. 2, the unit cell 10 includes a power generation cell 5 in which a fuel electrode layer 3 and an air electrode layer 4 are disposed on both surfaces of a solid electrolyte layer 2, and a fuel electrode current collector disposed outside the fuel electrode layer 3. 6, an air electrode current collector 7 disposed outside the air electrode layer 4, and a separator 8 disposed outside each current collector 6, 7.

Among these components, the solid electrolyte layer 2 is composed of stabilized zirconia (YSZ) or the like to which yttria is added, and the fuel electrode layer 3 is composed of a metal such as Ni or a cermet such as Ni—YSZ, and the air electrode. The layer 4 is made of LaMnO ₃ , LaCoO ₃ or the like, the fuel electrode current collector 6 is made of a sponge-like porous sintered metal plate such as Ni, and the air electrode current collector 7 is made of a sponge-like porous material such as Ag. It consists of a sintered metal plate.

  The separator 8 is formed of a square stainless steel plate having a thickness of several millimeters and has a function of electrically connecting the power generation cells 5 and supplying a reaction gas to the power generation cells 5 as shown in FIG. As described above, the fuel gas flow path 11 for introducing the fuel gas into the inside from the edge of the separator 8 and discharging it from the gas discharge hole 11a at the substantially center of the surface facing the fuel electrode current collector 6 of the separator 8, and the oxidant And an oxidant gas passage 12 that introduces gas from the edge of the separator 8 and discharges it from the gas discharge hole 12a at the substantially center of the surface of the separator 8 that faces the air electrode current collector 7. The path is formed in a spiral shape.

  As shown in FIGS. 2 and 3, a pair of gas holes 13, 14 penetrating in the plate thickness direction are provided in the left and right edges of the separator 8, and one gas hole 13 is formed in the fuel gas channel 11. The other gas hole 14 communicates with the oxidant gas flow path 12, and fuel gas and oxidant gas are passed from the gas holes 13, 14 to the electrode surfaces of the power generation cells 5 through the gas flow paths 11, 12. To be supplied.

  As shown in FIG. 1, the solid oxide fuel cell (fuel cell stack 1) according to the present embodiment is formed by laminating a large number of unit cells 10 having the above-described configuration with ring-shaped insulating gaskets 15 and 16 interposed therebetween. In addition, end plates 20 and 20 are arranged at both upper and lower ends, and a peripheral portion is fastened with a bolt 21 so that the respective components are brought into close contact with each other. Reference numeral 16 denotes a fuel gas manifold 17 for introducing a fuel gas and an oxidant which are connected in the stacking direction in a state in which the gas holes 13 and 14 of the separator 8 are mechanically closely contacted and fixed in the stacking direction. An oxidant gas manifold 18 for introducing gas is formed.

In the above configuration, during operation, the fuel gas is introduced into the fuel gas manifold 17 from the outside, and this fuel gas passes from the gas holes 13 of the separators 8 to the fuel electrode current collector 6 side through the fuel gas passages 11. The ejected gas and the ejected gas permeate and diffuse inside the fuel electrode current collector 6 and are guided to the fuel electrode layer 3 of each power generation cell 5. The air is introduced from the gas holes 14 of the separators 8 through the oxidant gas passages 12 to the side of the air electrode current collector 7, and the ejected gas permeates and diffuses inside the air electrode current collector 7. It is induced by the air electrode layer 4 of each power generation cell 5 to cause an electrode reaction (power generation reaction).
During this power generation reaction, Joule heat is generated by the internal resistance of the power generation cell 5 and the thermal energy is released to the outside mainly from the side surface of the separator.

  The fuel cell stack 1 has a sealless structure in which a gas leakage prevention seal is not provided on the outer periphery of the power generation cell 5, and the remaining fuel gas that has not been used in the power generation reaction flows from the periphery of the power generation cell 5. It is designed to be released freely outside.

  By the way, in the flat stack type fuel cell stack 1, a temperature difference is generated in the stack stacking direction due to the unbalance of the heat radiation amount in the stacking direction, and the cell voltage in the low temperature portion is extremely lowered, so that efficient power generation is not performed. As described above, there is a problem.

  Therefore, conventionally, the amount of fuel gas supplied to each power generation cell has been made uniform. However, in the present invention, the single cell 10 (that is, the power generation cell 5) located at both ends of the stack where the temperature is significantly reduced is the separator 8. As shown by the broken line in FIG. 5B, the amount of fuel gas supplied to the power generation cell 5 can be changed by providing a flow resistance reducing means for reducing the flow resistance in the fuel gas flow path 11. It was made to increase compared with the power generation cell 5 of.

In the present embodiment, the amount of fuel gas supplied to the power generation cell 5 in the low temperature portion of the stack is about 1.1 to 2 times that of the power generation cell 5 in the other high temperature portion, but the increase in fuel gas is 5 Set according to the temperature drop. In addition, since a large amount of fuel gas is supplied to the power generation cell 5 in this portion, there is a risk of a shortage of oxidant gas. There is no danger of explosion. On the other hand, in the case of the seal structure, since the fuel gas is circulated, no problem occurs.
In this embodiment, the power generation cells 5 that increase the fuel gas are two to three stages from both ends of the fuel cell stack. However, it is not necessary to increase the amount of fuel gas in the power generation cells 5 at both ends of the stack. However, depending on the lowering state of the stack temperature (cell voltage state), only the power generation cell 5 at one end may be used.
In the stacked fuel cell stack 1, since the temperature drop at the lower end of the stack is significant compared to the upper end of the stack, it is preferable to increase the fuel gas at least for the power generation cell 5 at the lower end of the stack.

  Here, in the present embodiment, as shown in FIG. 4, (1) the communication portion (fuel supply port 19) between the fuel gas manifold 17 and the fuel gas flow channel 11 of the separator 8 is used as the flow resistance reducing means. A flow path structure in which the orifice diameter d is increased to increase the amount of fuel gas flowing through the fuel gas flow path 11, and (2) the flow path length L of the fuel gas flow path 11 (from the fuel supply port 19 to the gas) The length of the discharge hole 11a) is constant, and the flow path cross-sectional area (that is, the flow path diameter D) is increased to increase the supply amount of fuel gas. (3) The flow path cross-sectional area is constant. Further, it is possible to adopt a flow path structure in which the flow length L of the fuel gas flow path 11 is increased to increase the fuel supply amount.

  As described above, when the amount of the fuel gas to the power generation cell 5 is increased by the flow path resistance relaxation means, the chemical reaction in the fuel electrode layer 3 becomes active, the overvoltage of the fuel electrode layer 3 is reduced, and the cell voltage is reduced. As shown in the broken line (c) in FIG. 5 (a), the cell voltage at both ends of the stack rises compared to the broken line (b), and the cell voltage of each power generation cell 5 in the stacking direction becomes uniform. Is done. As a result, efficient power generation becomes possible, and the internal resistance of the power generation cell 5 decreases due to the increase in cell voltage, and Joule heat generation decreases. Therefore, the temperature difference in the same cell plane decreases, and the power generation cell 5 Is prevented and durability is improved.

  Further, as described above, the fuel cell stack 1 of the present embodiment employs a sealless structure, and therefore, the outer peripheral portion of the power generation cell 5 located in the vicinity of the stack end is larger than the other power generation cells 5. Since the used fuel gas is released and the released gas is burned in the vicinity of the cell, the power generation cell 5 in the vicinity of the stack end can be heated by the combustion heat. As a result, the internal resistance of the heated power generation cell 5 decreases and the cell voltage increases, so that more efficient power generation can be performed.

  In the above embodiment, the fuel gas supply amount of the power generation cells 5 located in the vicinity of the end portion of the fuel cell stack 1 is increased. For example, as shown in FIG. For the purpose of equalizing the stack temperature, when the heat sink 30 is disposed in the middle part of the fuel cell stack 1, as shown by the solid line in FIG. The temperature may decrease too much, which leads to a decrease in cell voltage as shown by the broken line (b) in FIG. 6A. In order to suppress this, as shown by the broken line in FIG. 6 (b), it is of course possible to apply the present invention to this temperature drop portion and increase the amount of fuel gas supplied to the power generation cell 5, thereby As shown by the broken line (c) in FIG. It can be made uniform in the cell voltage by eliminating the influence of the plate 30.

  As described above, in the present embodiment, the flat plate type fuel cell has been described. However, it is needless to say that the present invention can be applied to a fuel cell stack having a bundle structure in which a large number of cylindrical power generation cells are assembled.

  7 shows a fuel cell stack 50 having a bundle structure. In FIG. 7, reference numeral 41 denotes a fuel manifold, reference numeral 42 denotes a fuel gas flow path, reference numeral 40 denotes a power generation cell, reference numeral 43 denotes a fuel electrode layer, and reference numeral 44 denotes a solid electrolyte. Reference numeral 45 denotes an air electrode layer, and reference numeral 46 denotes an oxidant gas flow path.

In the fuel cell stack 50 having the above-described configuration, the power generation cells 40 at the outer periphery of the bundle easily radiate Joule heat as compared with the power generation cells 40 at the center, so that the cell temperature at the outer periphery of the bundle is lower than that at the center. Therefore, for the power generation cells 40 arranged on the outer periphery of the bundle, the present invention is applied to supply more fuel gas than the power generation cells 40 in other portions, thereby reducing the cell voltage in this portion. It is possible to suppress the cell voltage and make the cell voltage uniform.
In addition, the power generation cells 40 located at the corners of the outer periphery of the bundle have a particularly large amount of heat radiation and a large decrease in cell voltage. Therefore, by supplying more fuel gas to the power generation cells 40 in this portion, It is possible to suppress an extreme voltage drop and further uniform the cell voltage.

The figure which shows the external appearance of the flat plate type solid oxide fuel cell to which this invention is applied. The figure which shows the structure of the single cell which concerns on this invention. The top view which shows an example of a separator. The figure which shows the gas introduction part of a separator. Explanatory drawing which shows the supply method of the fuel gas to each cell in a fuel cell stack. Explanatory drawing which shows the supply method different from FIG. 5 of the fuel gas to each cell in a fuel cell stack. 1 shows a cylindrical solid oxide fuel cell to which the present invention is applied, in which (a) is a side sectional view and (b) is a plan view.

Explanation of symbols

1 Solid oxide fuel cell (fuel cell stack)
2 solid electrolyte layer 3 fuel electrode layer 4 air electrode layer 5 power generation cell 11 fuel gas channel 12 oxidant gas channel 13 fuel gas manifold 14 oxidant gas manifold

Claims (7)

A plurality of power generation cells each having a fuel electrode layer and an air electrode layer disposed on both sides of the solid electrolyte layer constitute a fuel cell stack, and a fuel gas and an oxidant gas are supplied to each power generation cell to generate a power generation reaction. A method of supplying fuel gas for a solid oxide fuel cell, comprising:
A fuel gas supply method, wherein a fuel gas supply amount to the power generation cells located at an end of the fuel cell stack is increased as compared with other power generation cells. A plurality of power generation cells each having a fuel electrode layer and an air electrode layer arranged on both sides of the solid electrolyte layer constitute a fuel cell stack, and each communicates with a fuel gas flow path that communicates with the fuel manifold and an oxidant gas manifold. In a solid oxide fuel cell that generates a power generation reaction by supplying a fuel gas and an oxidant gas to each power generation cell through an oxidant gas flow path,
A flow resistance reducing means for reducing the flow resistance of the fuel gas flow path is provided in the fuel gas flow path of the power generation cell located at the end of the fuel cell stack, and the power generation by the flow resistance resistance means A solid oxide fuel cell characterized in that the amount of fuel gas supplied to the cell is larger than that of other power generation cells. The heat dissipation means is provided inside the fuel cell stack, and the flow path resistance relaxation means is provided in a fuel gas flow path of each power generation cell located in the vicinity of the heat dissipation means. 3. The solid oxide fuel cell according to 2. 4. The solid oxide fuel according to claim 2, further comprising flow path resistance relaxation means for reducing flow path resistance by a throttle mechanism of a fuel supply port of the fuel gas flow path. battery. 4. The solid oxide fuel cell according to claim 2, further comprising flow path resistance relaxation means for reducing flow path resistance by a cross-sectional area of the fuel gas flow path. 4. The solid oxide fuel cell according to claim 2, further comprising flow path resistance relaxation means for decreasing a flow path resistance by a flow path length of the fuel gas flow path. The solid oxide fuel cell according to any one of claims 2 to 6, further comprising a sealless structure that discharges unused fuel gas from the outer periphery of the power generation cell.

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