fuel cell device

Abstract

To provide a fuel cell device that can effectively reduce the maximum temperature of the fuel cell. [Solution] In a fuel cell device, fuel gas is supplied to the fuel electrode 7 of a fuel cell cell C sandwiched between two interconnectors 15 through a fuel electrode side passage 17 formed between one interconnector 15 and the fuel electrode 7, and air is supplied to the air electrode 8 of the fuel cell cell C through an air electrode side passage 18 formed between the other interconnector 15 and the air electrode 8. Between the two interconnectors 15 that do not have a fuel cell C in between, a porous layer 16 is provided, which has a porous body 19 that is in contact with both of the two interconnectors 15, and fuel gas before it is supplied to the fuel electrode side passage 17, or air before it is supplied to the air electrode side passage 18, flows through the porous layer 16 between the inlet 16a and the outlet 16b.

Description

Technical Field

[0001] The present invention relates to a fuel cell device.

Background Art

[0002] Patent Document 1 (International Publication No. 2013 / 065757) describes a fuel cell stack in which a flat power generation cell having an electrolyte layer, an air electrode, and a fuel electrode arranged with the electrolyte layer therebetween and generating power using an oxidant gas and a fuel gas is stacked in a plurality along the thickness direction of the power generation cell. Further, this fuel cell stack includes a heat exchanger provided in contact with the power generation cell between two adjacent power generation cells in the stacking direction, and a first flow path through which an oxidant gas or a fuel gas supplied from the outside passes is provided inside the heat exchanger. In Patent Document 1, by providing a heat exchanger as described above in the fuel cell stack, an attempt is made to lower the temperature of the power generation cell adjacent to the heat exchanger.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The heat exchanger provided in the fuel cell stack described in Patent Document 1 simply has a first flow path through which an oxidant gas or a fuel gas supplied from the outside passes. Therefore, there is a limit to lowering the temperature of the power generation cell.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a fuel cell device capable of effectively achieving reduction of the maximum temperature of a fuel cell.

Means for Solving the Problems

[0006] A characteristic configuration of the fuel cell device according to the present invention for achieving the above objective is a fuel cell device comprising a cell stack formed by stacking a plurality of flat-plate type solid oxide fuel cell cells, each of which is configured by providing a fuel electrode on one plane of a flat solid electrolyte membrane and an air electrode on the other plane, with interconnectors sandwiched between the fuel cell cells. Fuel gas is supplied to the fuel electrode of the fuel cell, which is sandwiched between two interconnectors, through a fuel electrode side passage formed between one interconnector and the fuel electrode, and air is supplied to the air electrode of the fuel cell, through an air electrode side passage formed between the other interconnector and the air electrode. Between the two interconnectors that do not have a fuel cell in between, there is a porous layer provided in which a thermally conductive porous material is provided that is in contact with both of the two interconnectors. The porous layer is located at a point between the inlet and outlet through which the fuel gas, before being supplied to the fuel electrode side flow path, or the air, before being supplied to the air electrode side flow path, flows. Here, the porous body may be composed of foamed metal. Furthermore, the foamed metal material may also include stainless steel. Furthermore, the porous body may be provided such that the porosity in each part of the porous layer differs between the inlet and outlet of the porous layer. Here, the porosity is the proportion of space (empty space) that occupies in the porous layer.

[0007] According to the above characteristic configuration, heat exchange occurs in the porous layer between the fuel gas or air and the thermally conductive porous material that is in contact with both interconnectors sandwiching the porous layer. In other words, the fuel gas or air flowing through any part of the porous layer can come into contact with the porous material and undergo heat exchange. Furthermore, since the thermally conductive porous material is in contact with both interconnectors sandwiching the porous layer, good heat exchange occurs between the porous material and the two interconnectors. As a result, good heat exchange occurs between the fuel gas or air flowing through the porous layer and both interconnectors sandwiching the porous layer. Therefore, the two interconnectors sandwiching the porous layer, which are relatively hotter, are effectively cooled by the relatively cooler fuel gas flowing through the porous layer before being supplied to the fuel electrode side flow path, or the relatively cooler air before being supplied to the air electrode side flow path. Therefore, it is possible to provide a fuel cell device that can effectively reduce the maximum temperature of the fuel cell.

[0008] Another characteristic configuration of the fuel cell device according to the present invention is that the porous body is provided such that the average void ratio between the inlet and outlet of the porous layer is 50% or more and 99% or less.

[0009] According to the above-described configuration, since the porosity of the porous layer is sufficiently ensured, a sufficient amount of fuel gas or air can be flowed through the porous layer, while the two interconnectors, which are relatively hotter and sandwich the porous layer, can be effectively cooled by that fuel gas or air. [Brief explanation of the drawing]

[0010] [Figure 1] This is a diagram showing the configuration of a fuel cell system. [Figure 2] This diagram shows a part of the configuration of the cell stack in a fuel cell device. [Figure 3] This figure shows an example of the cell stack structure used in the simulation. [Figure 4] This figure shows an example of the cell stack structure used in the simulation. [Figure 5]This figure shows an example of the cell stack structure used in the simulation. [Figure 6] This figure shows an example of the cell stack structure used in the simulation. [Figure 7] This figure shows the simulation results. [Modes for carrying out the invention]

[0011] An embodiment of the fuel cell device of the present invention will be described below with reference to the drawings. Figure 1 is a diagram showing the configuration of a fuel cell device. Figure 2 is a diagram showing a part of the configuration of the cell stack 6 provided in the fuel cell device. As shown in the figures, the fuel cell device includes a cell stack 6 formed by stacking multiple flat-plate type solid oxide fuel cell cells C, each consisting of a flat solid electrolyte membrane 9 with a fuel electrode 7 facing one plane and an air electrode 8 facing the other plane, with interconnectors 15 sandwiched between the fuel cell cells C.

[0012] Furthermore, as will be described in detail later, the fuel cell device includes a porous layer 16 between two interconnectors 15 that do not have a fuel cell cell C in between, with a porous body 19 in contact with both of the two interconnectors 15. The interconnectors 15 and the porous body 19 can be joined using a bonding material. For example, spinel-based (AB2O4) oxides containing Co and Mn, or LSCF, which is also used as a material for the air electrode 8, can be used as bonding materials.

[0013] The fuel cell device of this embodiment includes a raw fuel supply unit 1 such as a pump, a desulfurization unit 2, a vaporization unit 3, a reforming unit 4, a combustion unit 5, a reforming water supply unit 12 such as a pump, and an air supply unit 13 such as a pump. Of these, the vaporization unit 3, the reforming unit 4, the combustion unit 5, and the cell stack 6 are housed inside the container 10, and the inside of the container 10 is kept at a high temperature.

[0014] In the desulfurization section 2, sulfur compounds contained in the raw fuel gas (e.g., city gas, etc.) containing hydrocarbon gas supplied through the raw fuel gas flow path L1 by the raw fuel supply section 1 are removed. In the vaporization section 3, reforming water supplied through the reforming water flow path L4 by the reforming water supply section 12 and the raw fuel gas after passing through the desulfurization section 2 are supplied. The vaporization section 3 heats and evaporates the supplied reforming water using the combustion heat transferred from the combustion section 5. The mixed gas of the raw fuel gas and steam generated in the vaporization section 3 is supplied to the reforming section 4. Combustion heat generated in the combustion section 5 is also transferred to the reforming section 4. Then, the reforming section 4 performs steam reforming treatment of the raw fuel gas contained in the mixed gas supplied from the vaporization section 3 to generate a fuel gas mainly composed of hydrogen. The generated fuel gas is supplied to the fuel cell stack C through the fuel gas flow path L2.

[0015] To the fuel electrode 7 of each fuel cell stack C, a fuel gas mainly composed of hydrogen generated in the reforming section 4 is supplied through the fuel gas flow path L2, and to the air electrode 8, air (oxygen) is supplied through the air flow path L3 by the air supply section 13. Then, in each fuel cell stack C, a power generation reaction is performed by the fuel gas supplied to the fuel electrode 7 and the air (oxygen) supplied to the air electrode 8.

[0016] From the fuel cell stack C, a gas containing hydrogen not used in the power generation reaction (fuel electrode exhaust gas) is discharged to the fuel electrode exhaust gas path L5, and air not used in the power generation reaction (air electrode exhaust gas) is discharged to the air electrode exhaust gas path L6.

[0017] The fuel electrode exhaust gas flowing through the fuel electrode exhaust gas path L5 and the air electrode exhaust gas flowing through the air electrode exhaust gas path L6 are supplied to the combustion section 5 and burned. Then, the combustion exhaust gas discharged from the combustion section 5 is exhausted to the outside of the container 10 through the combustion exhaust gas path L7.

[0018] The control unit 11 controls the operation of the fuel cell device. For example, the control unit 11 adjusts the amount of raw fuel gas per unit time supplied to the desulfurization unit 2, the amount of reforming water per unit time supplied to the vaporization unit 3, the current output from the cell stack 6, etc., to control the temperature of the reforming unit 4, the power generation reaction in the cell stack 6, the temperature of the combustion unit 5, etc. Although not shown in the figure, information such as the temperature of the vaporization unit 3, the temperature of the reforming unit 4, and the temperature of the combustion unit 5 can also be transmitted to the control unit 11 and used for the operation control of the fuel cell device.

[0019] In the fuel cell device of this embodiment, fuel gas is supplied to the fuel electrode 7 of the fuel cell C sandwiched between the two interconnectors 15 through the fuel electrode side flow path 17 formed between one interconnector 15 and the fuel electrode 7, and air is supplied to the air electrode 8 of the fuel cell C through the air electrode side flow path 18 formed between the other interconnector 15 and the air electrode 8.

[0020] Specifically, the fuel gas supplied to the cell stack 6 flows into the fuel electrode side flow path 17 formed between the surface of the fuel electrode 7 and the surface of the fuel electrode 7 side of the interconnector 15. The fuel gas is supplied to the fuel electrode 7 while flowing through the fuel electrode side flow path 17, and the remaining fuel gas and the fuel electrode exhaust gas containing the reaction product gas (water vapor, carbon dioxide gas) that has flowed through the fuel electrode side flow path 17 are configured to flow out of the outside of the fuel electrode side flow path 17.

[0021] The air supplied to the cell stack 6 flows into the air electrode side flow path 18 formed between the surface of the air electrode 8 and the surface of the air electrode 8 side of the interconnector 15. The air is supplied to the air electrode 8 while flowing through the air electrode side flow path 18, and the remaining air that has flowed through the air electrode side flow path 18 is configured to flow out of the outside of the air electrode side flow path 18.

[0022] The fuel cell device of this embodiment includes a porous layer 16 provided between two interconnectors 15 that do not have a fuel cell C in between, with a porous body 19 in contact with both of the two interconnectors 15. Air flows through the porous layer 16 between the inlet 16a and the outlet 16b before being supplied to the air electrode side flow path 18. The air that has flowed through the porous layer 16 is then distributed to the air electrode side flow paths 18 of the multiple fuel cell cells C. Alternatively, fuel gas before being supplied to the fuel electrode side flow path 17 may flow through the porous layer 16 between the inlet 16a and the outlet 16b instead of the air described above.

[0023] The porous body 19 is made of foamed metal. Because the foamed metal has a three-dimensional network structure, it has a large surface area. For example, the material of the foamed metal includes stainless steel. The porous body 19 is provided such that the average porosity between the inlet 16a and outlet 16b of the porous layer 16 is 50% or more and 99% or less. Here, the porosity is the proportion of gaps (spaces) that occupy the porous layer 16. In other words, the porous body 19 is provided such that the proportion of gaps in the total volume of the porous layer 16 is 50% or more and 99% or less. In this way, because the porosity of the porous layer 16 is sufficiently ensured, a sufficient amount of air can be flowed into the porous layer 16, and the two interconnectors 15, which are relatively high in temperature and sandwich the porous layer 16 between them, can be cooled well by that air. Alternatively, the porous body 19 may be provided such that the average porosity between the inlet 16a and outlet 16b of the porous layer 16 is 80% or more. Alternatively, the porous body 19 may be provided such that the average void ratio between the inlet 16a and outlet 16b of the porous layer 16 is 95% or less.

[0024] As shown in Figure 2, the air supplied through the air channel L3 first flows into the inlet 16a of the porous layer 16, flows through the porous layer 16 while in contact with the porous body 19, and then flows out from the outlet 16b. The air that flows out from the outlet 16b of the porous layer 16 is then distributed to the multiple fuel cell cells C and flows into each air electrode side channel 18.

[0025] By adopting this configuration, preheating of the air before it flows into the air electrode side channel 18 is performed in the porous layer 16. In other words, there is the advantage that the cell stack 6 is cooled via the interconnector 15 that is in contact with the porous layer 16.

[0026] Next, we will describe experimental examples (computer simulations) conducted to confirm the effects of providing the porous layer 16 in the fuel cell device of this embodiment. Figure 3 shows the structure of the cell stack 6 of Example 1, which includes a porous layer 16 containing a porous body 19 having a uniform porosity. Figure 4 shows the structure of the cell stack 6 of Example 2, which includes a porous layer 16 containing porous bodies 19 having different porosities. Figure 5 shows the structure of the cell stack 6 of Comparative Example 1, which includes an empty layer 20 that does not contain a porous body 19. Figure 6 shows the structure of the cell stack 6 of Comparative Example 2, which does not include the porous layer 16 or the empty layer 20.

[0027] In all of the cell stacks 6 of Examples 1 and 2 and Comparative Examples 1 and 2, the number of stacked fuel cell cells C is 20. In Examples 1 and 2, a porous layer 16 is provided between 10 layers of fuel cell C and another 10 layers of fuel cell C, and in Comparative Example 1, a space layer 20 is provided between 10 layers of fuel cell C and another 10 layers of fuel cell C. In all cases, in the fuel cell C, the direction of fuel gas flow in the fuel electrode side flow path 17 and the direction of air flow in the air electrode side flow path 18 are in a counterflow configuration, facing each other.

[0028] The size of fuel cell cell C in a plane perpendicular to the stacking direction is a rectangle measuring 10 cm x 15 cm. Furthermore, the manifold supplying fuel gas and air to multiple fuel cell cells C, and the manifold from which fuel electrode exhaust gas and air electrode exhaust gas are discharged from multiple fuel cell cells C, were excluded from the analysis.

[0029] In Example 1, a porous body 19, which is a foamed metal with a uniform porosity (95%) formed from stainless steel equivalent to SUS430, is provided in the porous layer 16. In Example 2, the porous body 19 is provided such that the porosity differs in each part of the porous layer 16 between the inlet 16a and the outlet 16b of the porous layer 16. Specifically, in Example 2, a first porous body 19a, which is a foamed metal with a relatively high porosity (porosity = 99%) formed from stainless steel equivalent to SUS430, is provided on the upstream side, and a second porous body 19b, which is a foamed metal with a relatively low porosity (porosity = 91%) formed from stainless steel equivalent to SUS430, is provided on the downstream side. In other words, in Example 2, the average porosity in the porous layer 16 is 95%.

[0030] Table 1 and Figure 7 below show other conditions and results of the computer simulation. Figure 7 shows the temperature distribution and current density distribution of each cell stack 6 in Examples 1 and 2 and Comparative Examples 1 and 2.

[0031] In Examples 1 and 2 and Comparative Examples 1 and 2, the fuel gas was a reformed gas obtained by steam reforming city gas 13A at 600°C with an S / C ratio of 2.5, the air was a gas containing 21% oxygen and 79% nitrogen, the fuel utilization rate was 80%, the air utilization rate was 40%, and the current density of the cell stack 6 was 0.350 A / cm². 2 The heat dissipation conditions are an emissivity of 0.5 and a virtual surface temperature outside the cell stack 6 of 600°C. The thickness of the porous layer 16 and the space layer 20 in the stacking direction of the fuel cell cell C is 2 mm.

[0032] [Table 1]

[0033] As shown in Table 1 and Figure 7, in Examples 1 and 2, the maximum temperature of the cell stack 6 is lower and the average temperature of the cell stack 6 is higher than in Comparative Examples 1 and 2. This is thought to be an effect obtained by providing the porous layer 16. Looking at the maximum temperature of the cell stack 6, Comparative Example 2 is 784°C, while Comparative Example 1, which has a space layer 20, is reduced to 728°C, indicating that providing the space layer 20 lowers the maximum temperature of the cell stack 6. Furthermore, on the outlet side of the fuel electrode side flow path 17, where the temperature is relatively lower, the temperature rises due to the transfer of heat from the preheated air in the space layer 20, and as a result, the temperature distribution in the plane perpendicular to the stacking direction of the fuel cell cells C is made uniform.

[0034] Furthermore, in Examples 1 and 2, compared to Comparative Example 1, the maximum temperature of the cell stack 6 was reduced by more than 18°C ​​while maintaining the average voltage (i.e., power generation performance) of the fuel cell C. This is thought to be because the porous body 19 in the porous layer 16 promotes heat conduction in the plane perpendicular to the stacking direction of the fuel cell C, resulting in a more uniform temperature and current distribution. In Comparative Example 1, the power generation reaction occurred unevenly on the fuel gas inlet side of the fuel electrode side flow path 17, resulting in a high current density and high temperature in that area. However, in Examples 1 and 2, the reaction occurred throughout the entire plane perpendicular to the stacking direction of the fuel cell C (i.e., there was no extreme bias in the current density within the plane), and the effective reaction region was expanded. This is thought to be because, in Examples 1 and 2, the air preheating is performed more effectively in the porous layer 16, and high-temperature air is supplied to the air electrode side flow path 18 of each fuel cell C. Furthermore, by lowering the maximum temperature of the cell stack 6, it is possible to further increase the current density, and by strengthening the insulation around the cell stack 6, the average temperature of the cell stack 6 can be increased, thereby allowing the cell stack 6 to perform even better.

[0035] As described above, heat exchange occurs in the porous layer 16 between the air and the thermally conductive porous material 19 that is in contact with both of the two interconnectors 15 sandwiching the porous layer 16. In other words, air flowing through any part of the porous layer 16 can come into contact with the porous material 19 and perform heat exchange. Furthermore, since the thermally conductive porous material 19 is in contact with both of the two interconnectors 15 sandwiching the porous layer 16, good heat exchange occurs between the porous material 19 and the two interconnectors 15. As a result, good heat exchange occurs between the air flowing through the porous layer 16 and both of the two interconnectors 15 sandwiching the porous layer 16. Therefore, the two interconnectors 15, which are relatively hotter and sandwich the porous layer 16, are effectively cooled by the relatively cooler air flowing through the porous layer 16 before it is supplied to the air electrode side flow path 18. Thus, a fuel cell device can be provided that can effectively reduce the maximum temperature of the fuel cell cell C.

[0036] <Another Embodiment> In the above embodiments, the configuration of the fuel cell device of the present invention has been described with specific examples, but the configuration can be modified as appropriate.

[0037] In the above embodiment, the fuel cell C may have a metal-supported structure supported by a metal plate such as stainless steel. When such a metal-supported structure is adopted, strength can be ensured by the metal plate, so the total thickness of the cell stack 6 can be reduced compared to, for example, when a fuel electrode-supported structure is adopted in which the ceramic constituting the fuel electrode 7 is used as a support. In addition, the fuel cell C may have a fuel electrode-supported structure in which the fuel electrode 7 is given structural strength.

[0038] In the above embodiment, a configuration was described in which air is flowed through the porous layer 16 and the air discharged from the porous layer 16 is supplied to the air electrode side flow path 18 formed between the interconnector 15 and the air electrode 8 (i.e., supplied to the fuel cell cell C). However, fuel gas may also be flowed through the porous layer 16. That is, a configuration may be described in which fuel gas is flowed through the porous layer 16 and the fuel gas discharged from the porous layer 16 is supplied to the fuel electrode side flow path 17 formed between the interconnector 15 and the fuel electrode 7 (i.e., supplied to the fuel cell cell C). In that case, as the porous body 19 provided in the porous layer 16, for example, a Ni mesh, Ni-Co plating, or foamed metal of ferritic stainless steel with Co plating can be used. Alternatively, the cell stack 6 may be provided with both a porous layer 16 through which fuel gas flows and a porous layer 16 through which air flows.

[0039] In the above embodiment, the case in which the fuel cell cell C is rectangular in a plane perpendicular to the stacking direction of the fuel cell cell C was described, but its shape may also be square and can be changed as appropriate.

[0040] In the above embodiment, an example was described in which one porous layer 16 is provided in the cell stack 6, but the number of porous layers 16 provided can be one or more, and the number can be changed as appropriate.

[0041] In the above embodiment, an example was described in which, in a single fuel cell cell C, the direction of fuel gas flow in the fuel electrode side passage 17 and the direction of air flow in the air electrode side passage 18 are opposite each other, forming a counterflow. However, the directions of fuel gas and air flow can be changed as appropriate. For example, in a single fuel cell cell C, the direction of fuel gas flow in the fuel electrode side passage 17 and the direction of air flow in the air electrode side passage 18 may be parallel (i.e., coflow), or they may be orthogonal (i.e., crossflow).

[0042] In the above embodiment, an example was described in which two types of porous materials 19 with different porosities are provided in the porous layer 16, as in Example 2. However, three or more types of porous materials 19 with different porosities may also be provided in the porous layer 16.

[0043] The configurations disclosed in the above embodiments (including other embodiments) can be applied in combination with configurations disclosed in other embodiments, provided that no inconsistencies arise. Furthermore, the embodiments disclosed herein are illustrative, and the embodiments of the present invention are not limited thereto and can be modified as appropriate without departing from the object of the present invention. [Industrial applicability]

[0044] This invention can be used in fuel cell devices that can effectively reduce the maximum temperature of the fuel cell. [Explanation of Symbols]

[0045] 6: Cell stack 7:Fuel electrode 8: Air pole 9: Solid electrolyte membrane 15: Interconnector 16: Porous layer 16a:Inlet 16b: Outlet 17:Fuel electrode side flow path 18: Air electrode side channel 19: Porous material C: Fuel cell

Claims

1. A fuel cell device comprising a cell stack formed by stacking multiple flat-plate type solid oxide fuel cell cells, each of which is configured with a fuel electrode on one plane of a flat solid electrolyte membrane and an air electrode on the other plane, with interconnectors in between the fuel cell cells, Fuel gas is supplied to the fuel electrode of the fuel cell, which is sandwiched between two interconnectors, through a fuel electrode side passage formed between one interconnector and the fuel electrode, and air is supplied to the air electrode of the fuel cell, through an air electrode side passage formed between the other interconnector and the air electrode. Between the two interconnectors that do not have a fuel cell in between, there is a porous layer provided in which a thermally conductive porous material is provided that is in contact with both of the two interconnectors. A fuel cell device in which the fuel gas before being supplied to the fuel electrode side flow path, or the air before being supplied to the air electrode side flow path, flows through the porous layer between the inlet and outlet.

2. The fuel cell apparatus according to claim 1, wherein the porous body is made of foamed metal.

3. The fuel cell device according to claim 2, wherein the foamed metal material includes stainless steel.

4. The fuel cell device according to any one of claims 1 to 3, wherein the porous body is provided such that the average void ratio between the inlet and outlet of the porous layer is 50% or more and 99% or less.

5. The fuel cell device according to any one of claims 1 to 3, wherein the porous body is provided such that the porosity in each part of the porous layer differs between the inlet and outlet of the porous layer.

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