JP2008226704A - Solid oxide fuel cell, and supplying method of oxidizing gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize improvement in power generation efficiency and improvement in durability by uniformizing the temperature in lamination direction of a fuel cell stack. <P>SOLUTION: This is a supply method of an oxidizer gas of a solid oxide fuel cell, in which a fuel cell stack 1 is constructed, by laminating a plurality of power generation cells 5 where a fuel electrode layer and an air electrode layer are arranged on both sides of a solid electrolyte layer and power generation reaction is caused, by supplying a fuel gas and an oxidizer gas to each power generation cell 5. The amount of oxidizer gas supplied to the power generation cells 5, located at an intermediate stage of the fuel cell stack 1, is made larger than the standard amount, and the amount of the oxidizer gas supplied to the power generation cells 5, located at the end parts of the fuel cell stack 1, is made smaller than the standard amount. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell having a structure in which power generation cells and separators are alternately stacked, and in particular, solid oxide that improves power generation efficiency and durability by uniformizing the temperature in the stacking direction of the fuel cell stack. The present invention relates to a physical fuel cell.

  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 fuel cell stack is high in the middle portion and low in both end portions.

  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. Because the power generation cell is in direct contact with the atmosphere inside the module, Joule heat is likely to dissipate. The power generation cell in the low temperature part has a high internal resistance and a low cell voltage. The electrode reaction is inactive compared with the partial power generation cells, and the power generation performance is reduced.

  As described above, when temperature non-uniformity occurs in the stacking direction of the fuel cell stack, the overall power generation performance of the fuel cell is limited by the power generation performance of the power generation cells in the low temperature part, and efficient power generation is achieved. There was a problem that could not be done. Moreover, although the power generation cell in the high temperature portion has good power generation performance, there is a problem that the stack components such as the power generation cell and the metal separator are easily deteriorated by being exposed to a high temperature atmosphere.

For example, Patent Literature 1 and Patent Literature 2 are disclosed as techniques for equalizing the temperature 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 dissipation part is complicated.
Patent Document 2 diverts a part of the cooling water supplied to the fuel cell main body and suppresses the temperature drop of the unit battery cells located at both ends of the fuel cell main body using the diverted cooling water. The cooling water piping structure is complicated.
JP 2004-273140 A JP 2005-203189 A

  The present invention has been made in view of the above problems, and a solid oxide fuel cell that improves power generation efficiency and durability by uniformizing the temperature in the stacking direction of the fuel cell stack, and therefore It is an object of the present invention to provide a preferable method for supplying an oxidant gas.

  That is, the supply method of the oxidant gas according to claim 1 is configured such that a plurality of power generation cells in which a fuel electrode layer and an air electrode layer are arranged on both sides of a solid electrolyte layer are stacked to constitute a fuel cell stack, and each power generation cell A method for supplying an oxidant gas of a solid oxide fuel cell in which a fuel gas and an oxidant gas are supplied to cause a power generation reaction, the oxidant being supplied to a power generation cell located in a middle stage of the fuel cell stack It is characterized by making the amount of gas larger than the standard amount.

  According to a second aspect of the present invention, there is provided an oxidizing gas supply method comprising a fuel cell stack in which a plurality of power generation cells having a fuel electrode layer and an air electrode layer disposed on both sides of a solid electrolyte layer, and each power generation cell. A method for supplying an oxidant gas of a solid oxide fuel cell in which a fuel gas and an oxidant gas are supplied to cause a power generation reaction, the oxidant being supplied to a power generation cell located in a middle stage of the fuel cell stack It is characterized in that the amount of gas is made larger than the standard amount and the amount of oxidant gas supplied to the power generation cells located at the end of the fuel cell stack is made smaller than the standard amount.

  The solid oxide fuel cell according to claim 3 includes a power generation cell configured by disposing a fuel electrode layer and an air electrode layer on both surfaces of the body electrolyte layer, and a fuel gas flow path and an oxidant gas flow therein. A fuel cell stack is configured by alternately laminating separators having paths, and a power generation reaction is generated by supplying fuel gas and oxidant gas to each power generation cell via the fuel gas flow path and oxidant gas flow path. In the solid oxide fuel cell to be operated, a gas flow rate adjusting means for adjusting a gas flow rate of the oxidant gas flow path is provided in the oxidant gas flow path, and the middle stage of the fuel cell stack is provided by the gas flow rate adjusting means. The amount of the oxidant gas supplied to the power generation cell located in the section is increased from the standard amount.

  The solid oxide fuel cell according to claim 4 is a power generation cell configured by arranging a fuel electrode layer and an air electrode layer on both surfaces of a solid electrolyte layer, and a fuel gas flow path and an oxidant gas flow inside. A fuel cell stack is configured by alternately laminating separators having paths, and a power generation reaction is generated by supplying fuel gas and oxidant gas to each power generation cell via the fuel gas flow path and oxidant gas flow path. In the solid oxide fuel cell to be operated, a gas flow rate adjusting means for adjusting a gas flow rate of the oxidant gas flow path is provided in the oxidant gas flow path, and the middle stage of the fuel cell stack is provided by the gas flow rate adjusting means. The amount of oxidant gas supplied to the power generation cell located in the section is made larger than the standard amount, and the amount of oxidant gas supplied to the power generation cell located at the end of the fuel cell stack is made smaller than the standard amount. Features

  The invention according to claim 5 is the solid oxide fuel cell according to any one of claim 3 or claim 4, wherein the flow path is provided by a throttle mechanism of a gas supply port of the oxidant gas flow path. It has a gas flow rate adjusting means for controlling resistance.

  The invention according to claim 6 is a gas which controls flow path resistance by a cross-sectional area of the oxidant gas flow path in the solid oxide fuel cell according to claim 3 or 4. It has a flow rate adjusting means.

  The invention according to claim 7 is the solid oxide fuel cell according to any of claim 3 or claim 4, wherein the flow path resistance is controlled by the flow path length of the oxidant gas flow path. And a gas flow rate adjusting means.

Here, in a solid oxide fuel cell, for example, when hydrogen is used as the fuel gas, the amount of oxidant gas (air) supplied to the power generation cell is 2.5 times the amount of fuel gas supplied stoichiometrically. This amount is the minimum flow rate (theoretical value) required for the electrochemical reaction, but the amount of air (standard amount) that is the oxidant gas that is actually supplied to the power generation cell is usually fuel gas. The supply amount of H ₂ (hydrogen) is 4 to 5 times, but it is 7 to 8 times under the condition of a high power density of 0.5 W / cm ² or more. The maximum temperature is controlled within a certain temperature.
The standard amount of air, which is an oxidant gas when the fuel gas is hydrocarbon methane, is 16 to 20 times.

According to the first and third aspects of the invention, the amount of the oxidant gas supplied to the power generation cell in the portion where the stack temperature is higher than the others, such as the middle stage portion of the fuel cell stack, is larger than the standard amount. The cooling effect of the middle part of the fuel cell stack due to the oxidant gas becomes significant. As a result, the temperature of the middle part of the stack decreases, and the temperature distribution in the stacking direction of the fuel cell stack is relaxed, enabling efficient power generation. It becomes.
Moreover, since the thermal stress with respect to stack component parts, such as a power generation cell and a separator, is eased because the temperature of a stack | stuck middle stage part falls, deterioration of these parts is prevented and durability improves.

Further, according to the inventions of claims 2 and 4, the amount of the oxidant gas supplied to the power generation cell in the portion where the stack temperature becomes high, such as the middle portion of the fuel cell stack, is made larger than the standard amount, and Since the amount of oxidant gas supplied to the power generation cells in the part where the stack temperature decreases, such as the end of the fuel cell stack, is smaller than the standard amount, the cooling effect by air becomes significant in the middle stage of the fuel cell stack. As the temperature of the middle stage of the stack decreases and the cooling power by air decreases at the end of the fuel cell stack, and the temperature of the stack end increases accordingly, the temperature in the stacking direction of the fuel cell stack increases. It becomes uniform and enables more efficient power generation.
Moreover, since the thermal stress with respect to stack components, such as a power generation cell and a separator, will be relieved if the temperature of a stack | stuck middle stage part falls, deterioration of these components will be prevented and durability will improve.

  In addition, according to the inventions described in claims 5 to 7, the stack temperature can be made uniform without using a complicated heat dissipation mechanism or piping structure as in the prior art, which can contribute to downsizing and cost reduction of the apparatus.

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

  FIG. 1 shows a flat-stacked solid oxide fuel cell to which the present invention is applied, FIG. 2 shows the configuration of a single cell according to the present invention, FIG. 3 shows an example of a separator, and FIG. FIG. 5 shows a method of supplying an oxidant 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. 3, a fuel gas flow path 11 that introduces fuel gas into the inside from the edge of the separator 8 and discharges it from the gas discharge hole 11 a at the substantially center of the surface of the separator 8 facing the anode current collector 6; And an oxidant gas flow path 12 that introduces oxidant 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 gas flow 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 the fuel gas and the oxidant gas pass from the gas holes 13 and 14 to the electrode surfaces of the power generation cells 5 through the gas flow paths 11 and 12. Is 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, fuel gas (hydrogen) is introduced from the outside into the fuel gas manifold 17, and this fuel gas passes through the fuel gas passages 11 from the gas holes 13 of the separators 8. 6, and the jet gas permeates and diffuses inside the fuel electrode current collector 6 and is guided to the fuel electrode layer 3 of each power generation cell 5, and the oxidant gas ( Air) is introduced from the gas holes 14 of the separators 8 through the oxidant gas flow passages 12 to the air electrode current collector 7, and the discharged gas permeates through the air electrode current collector 7. It diffuses and is induced to the air electrode layer 4 of each power generation cell 5, and an electrode reaction (power generation reaction) occurs at each electrode.
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 8.

  By the way, in the flat plate type fuel cell stack 1, a temperature distribution is generated in the stack stacking direction due to the unbalance of the heat radiation amount in the stacking direction. As described above, there is a problem that the power generation is not performed and the stack components are likely to be deteriorated due to thermal stress in the high temperature portion of the middle stage of the stack.

  Therefore, conventionally, as shown by the broken line (A) in FIG. 5B, the amount of the oxidant gas supplied to each power generation cell 5 is all uniform (standard amount). However, in the present invention, the oxidation of the separator 8 is performed. A gas flow rate adjusting means for adjusting the gas flow rate by changing the flow channel resistance is provided in the oxidant gas flow channel 12. As shown by the solid line (b) in FIG. 5B, the amount of the oxidant gas supplied to the power generation cell 5 through the oxidant gas flow path 12 is reduced by the broken line (FIG. For the power generation cells 5 at both ends of the stack having a low temperature, the flow resistance of the oxidant gas flow channel 12 is increased and the oxidant gas supplied to the power generation cell 5 is increased. The amount was made smaller than the standard amount.

  In the present embodiment, the amount of oxidant gas supplied to the power generation cell 5 in the high temperature portion of the stack is 1.1 to 3 times the standard amount. Further, the amount of the oxidant gas supplied to the power generation cell 5 in the stack low temperature portion is set to the above standard amount of 0.6 to 0.9, and at least a flow rate at which normal power generation can be performed (that is, in the case of air, the flow rate of hydrogen (2.5 times or more, preferably 3.5 times or more) must be secured. In any case, the supply amount (increase and decrease) of the oxidant gas is set according to the stack temperature.

Further, in the present embodiment, the power generation cell 5 in which the supply amount of the oxidant gas is reduced is set to two to three cells from both ends of the fuel cell stack 1, but the power generation cells 5 at both ends of the stack are not necessarily limited. There is no need to reduce the amount of the oxidant gas, and depending on the state of the decrease in the stack temperature, the amount of the power generation cell 5 at either end may be reduced.
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 reduce the oxidant gas at least for the power generation cell 5 at the lower end of the stack.

  Here, in this embodiment, as the gas flow rate adjusting means, as shown in FIG. 4, (1) a communicating portion (oxidant gas supply port 19) of the oxidant gas manifold 14 and the oxidant gas flow path 12 of the separator 8. ) Is an orifice restrictor, and the orifice diameter d is changed to adjust the amount of the oxidant gas flowing through the oxidant gas flow path 12; (2) the flow path length L ( (A length from the oxidant gas supply port 19 to the gas discharge hole 12a), and a flow path structure for adjusting the supply amount of the oxidant gas by increasing the flow path cross-sectional area (that is, the flow path diameter D); 3) Any one of the flow channel structures that adjust the supply amount of the oxidant gas by increasing the flow channel length L of the oxidant gas flow channel 12 while keeping the flow channel cross-sectional area constant can be adopted.

As described above, in the present embodiment, the gas flow rate adjusting means increases the amount of oxidant gas supplied to the power generation cells in the middle stage of the high temperature fuel cell stack, and the end of the low temperature fuel cell stack. By reducing the amount of oxidant gas supplied to the power generation cell of the part, as shown by the broken line (b) in FIG. 5 (a), power generation due to the circulation of oxidant gas in the middle part of the fuel cell stack The cooling effect of the cells 5 and separators 8 becomes remarkable, and the temperature of the middle stage of the stack can be lowered. At the end of the fuel cell stack, the cooling power by the oxidant gas is lowered and the temperature of the stack end is raised. Therefore, the temperature in the stacking direction in the fuel cell stack 1 is made uniform, and more efficient power generation is possible.
In addition, since the temperature of the middle stage of the stack is lowered, the thermal stress on the stack components such as the power generation cell 5 and the separator 8 is alleviated. Will improve.

  In addition, by using the gas flow rate adjusting means, the stack temperature can be made uniform without using a complicated heat dissipation mechanism and piping structure as shown in Patent Document 1 and Patent Document 2, so that the apparatus can be made smaller and less expensive. Can contribute to

  In addition, although not shown in the drawings, the present invention is also provided in which a heat sink is provided in the middle part of the fuel cell stack 1 every several stages or every several tens of stages, and the temperature of the part is lowered to make the stack temperature uniform. Of course, the present invention can be applied. In this case, the gas flow path adjusting means is provided in an intermediate portion between the heat radiating plate and the amount of the oxidant gas supplied to the power generation cell 5 in that portion is increased. Due to the cooling effect of both the plate and the oxidant gas, the temperature non-uniformity in the middle stage of the stack can be more reliably eliminated.

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 oxidant gas to each cell in a fuel cell stack.

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 flow path 12 Oxidant gas flow path

Claims (7)

A fuel cell stack is configured by laminating a plurality of power generation cells having a fuel electrode layer and an air electrode layer on both sides of a solid electrolyte layer, and a fuel gas and an oxidant gas are supplied to each power generation cell to generate a power generation reaction. A method for supplying an oxidant gas of a solid oxide fuel cell, comprising:
A method for supplying an oxidant gas, characterized in that the amount of oxidant gas supplied to a power generation cell located in the middle stage of the fuel cell stack is made larger than a standard amount. A fuel cell stack is configured by laminating a plurality of power generation cells having a fuel electrode layer and an air electrode layer on both sides of a solid electrolyte layer, and a fuel gas and an oxidant gas are supplied to each power generation cell to generate a power generation reaction. A method for supplying an oxidant gas of a solid oxide fuel cell, comprising:
The amount of oxidant gas supplied to the power generation cells located in the middle stage of the fuel cell stack is made larger than the standard amount, and the amount of oxidant gas supplied to the power generation cells located at the end of the fuel cell stack is standardized. A method for supplying an oxidant gas, wherein the amount is less than the amount. A fuel cell stack is constructed by alternately laminating a power generation cell configured with a fuel electrode layer and an air electrode layer on both sides of a solid electrolyte layer, and a separator having a fuel gas channel and an oxidant gas channel inside. In the solid oxide fuel cell in which fuel gas and oxidant gas are supplied to each power generation cell through the fuel gas channel and oxidant gas channel to generate a power generation reaction,
The oxidant gas flow path is provided with gas flow rate adjusting means for adjusting the gas flow rate of the oxidant gas flow path,
A solid oxide fuel cell characterized in that the amount of oxidant gas supplied to a power generation cell located in the middle part of the fuel cell stack is made larger than the standard amount by the gas flow rate adjusting means. A fuel cell stack is constructed by alternately laminating a power generation cell comprising a fuel electrode layer and an air electrode layer on both sides of a solid electrolyte layer and a separator having a fuel gas channel and an oxidant gas channel inside. In the solid oxide fuel cell in which fuel gas and oxidant gas are supplied to each power generation cell via the fuel gas channel and oxidant gas channel to generate a power generation reaction,
The oxidant gas flow path is provided with gas flow rate adjusting means for adjusting the gas flow rate of the oxidant gas flow path,
By the gas flow rate adjusting means, the amount of oxidant gas supplied to the power generation cell located in the middle stage of the fuel cell stack is made larger than the standard amount and supplied to the power generation cell located at the end of the fuel cell stack. A solid oxide fuel cell characterized in that the amount of oxidant gas is less than the standard amount. 5. The solid oxide fuel according to claim 3, further comprising gas flow rate adjusting means for controlling flow path resistance by a throttle mechanism of a gas supply port of the oxidant gas flow path. battery. 5. The solid oxide fuel cell according to claim 3, further comprising gas flow rate adjusting means for controlling flow path resistance by a cross-sectional area of the oxidant gas flow path. 5. The solid oxide fuel cell according to claim 3, further comprising gas flow rate adjusting means for controlling flow path resistance by a flow path length of the oxidant gas flow path.

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