fuel cell system

Abstract

To provide a solid oxide fuel cell system preventing an excessive temperature rise in a cell stack, thereby achieving a stable activated operation for a long period of time.SOLUTION: Provided is a solid oxide fuel cell system including: a cell stack 2; an anode gas supply passage 4 and an anode gas exhaust passage 6 connected respectively to an anode inflow side and an anode outflow side of the cell stack 2; a cathode gas supply passage 8 and a cathode gas exhaust passage 10 connected respectively to a cathode inflow side and a cathode outflow side of the cell stack 2; and passage switching means 12 (14) provided in the anode gas supply passage 4 and the anode gas exhaust passage 6 (the cathode gas supply passage 8 and the cathode gas exhaust passage 10). Deterioration determination means of a controller 46 performs a local deterioration determination based on temperatures related to the cell stack 2, and the controller 46 switches, based on the local deterioration determination, the passage switching means 12, 14 to change the flow direction of anode gas (cathode gas).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system including a cell stack in which a plurality of fuel cells are stacked. [Background technology]

[0002] A solid oxide fuel cell system equipped with a solid oxide cell stack using a solid electrolyte as a membrane that conducts oxide ions is known (see, for example, Patent Document 1). In this solid oxide fuel cell system, the cell stack is constructed by stacking a plurality of fuel cells, and each fuel cell has an anode (fuel electrode) on one side of the solid electrolyte and a cathode (oxygen electrode) on the other side. The operating temperature of the cell stack in this solid oxide fuel cell system is high, approximately 500 to 900°C, and at such high temperatures, hydrogen, carbon monoxide, and hydrocarbons in the anode gas (e.g., steam-reformed gas) undergo an electrochemical reaction with the cathode gas (e.g., oxygen in the air), thereby generating electricity.

[0003] In such a solid oxide fuel cell system, a heat conductive part formed from a material with higher thermal conductivity than the connecting parts has been proposed within the gaps between the connecting parts of stacked fuel cell cells (see, for example, Patent Document 2). In this solid oxide fuel cell system, the heat generated by power generation in the cell stack is conducted by the heat conductive part, thereby making it possible to uniform the temperature distribution within the fuel cell cells.

[0004] Meanwhile, a known fuel cell system is provided with an anode gas flow path switching means in an anode gas supply flow path that supplies anode gas and an anode gas discharge flow path that discharges anode gas (reactive anode gas), and with a cathode gas flow path switching means in a cathode gas supply flow path that supplies cathode gas and a cathode gas discharge flow path that discharges cathode gas (reactive cathode gas) (see, for example, Patent Document 3). In this fuel cell system, by switching the anode gas flow path switching means, the anode gas supply flow path is switched to the anode outflow side and the anode gas discharge flow path is switched to the anode inflow side, and by switching the cathode gas flow path switching means, the cathode gas supply flow path is switched to the cathode outflow side and the cathode gas discharge flow path is switched to the cathode inflow side. By switching the connections in this manner, water retention in the electrodes of the cell stack is prevented, and temporary degradation of the cell stack performance is suppressed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-285340 [Patent Document 2] Japanese Patent Application Publication No. 2017-552322 [Patent Document 3] Patent No. 5009168 Summary of the Invention [Problem to be solved by the invention]

[0006] In such fuel cell systems, cell stack degradation occurs when power generation continues. Here, degradation refers to an increase in the internal resistance of the cell stack. As this internal resistance increases, the heat generated during power generation increases, causing the temperature of the cell stack to rise. In particular, solid oxide cell stacks have high operating temperatures (power generation temperatures) of approximately 500 to 900°C. Therefore, the temperature of the cell stack may become excessively high as the amount of heat generated during power generation increases. When the temperature of the cell stack becomes excessive, it reaches a temperature range where the metal components inside the cell stack rapidly oxidize, leading to damage to the cell stack.

[0007] In this cell stack, temperatures tend to be particularly high near the anode and cathode outlets, i.e., near the anode gas outlet and cathode gas outlet of the cell stack. This is because the fuel cell absorbs heat generated during power generation as gas (anode gas and cathode gas are sometimes referred to as "gas") flows through the cell stack, and from the early stage of power generation, a temperature distribution occurs within the stack in which the temperature gradually increases from the gas inlets (anode gas inlet, cathode gas inlet) to the gas outlets (anode gas outlet, cathode gas outlet).

[0008] It is known that the higher the temperature of the fuel cells that make up a cell stack, the faster the deterioration progresses. Therefore, fuel cell deterioration tends to progress faster near the gas outlet of the cell stack than in other areas. After a certain period of operation and power generation (in other words, after a certain degree of deterioration has progressed), the deterioration near the gas outlet of the cell stack progresses locally, the heat generation amount increases, and the temperature near the gas outlet of the cell stack tends to become particularly high. Therefore, once the deterioration of the cell stack has progressed to a certain extent, the temperature near the gas outlet tends to become even higher due to heat transport from the upstream side of the cell stack and the increase in the heat generation amount near the gas outlet.

[0009] Cell stacks deteriorate over time as they are operated, but even within a single fuel cell, the upstream and downstream portions of the anode's internal flow path (and cathode's internal flow path) within the cell are more susceptible to deterioration than the downstream portion, and the portion with the fastest rate of deterioration becomes the rate-limiting factor, shortening the lifespan of the cell stack. As this deterioration progresses, localized temperature increases near the gas outlets (anode gas outlet, cathode gas outlet) of the cell stack can pose a major problem, leading to oxidation of metal components and cell cracking.

[0010] An object of the present invention is to provide a fuel cell system that can operate stably for a long period of time by suppressing excessive temperature rise in the cell stack. [Means for solving the problem]

[0011] A fuel cell system according to a first aspect of the present invention comprises: a cell stack having fuel cells each having an anode, a cathode, and an electrolyte layer interposed therebetween; an anode gas supply flow path connected to the anode inlet side of the cell stack; an anode gas discharge flow path connected to the anode outlet side; a cathode gas supply flow path connected to the cathode inlet side of the cell stack; a cathode gas discharge flow path connected to the cathode outlet side; flow path switching means provided in at least one of the anode gas supply flow path and the anode gas discharge flow path and the cathode gas supply flow path and the cathode gas discharge flow path; and a controller for controlling the switching of the flow path switching means; a gas temperature measuring means for measuring a gas temperature is provided on both the anode inlet side and outlet side of the cell stack and / or on both the cathode inlet side and outlet side of the cell stack; The controller includes a deterioration determination means for determining local deterioration of the cell stack, the deterioration determination means comprising: Based on the temperature measured by the gas temperature measuring means The cell stack is characterized in that a local deterioration determination is performed, and the controller switches the flow path switching means based on the local deterioration determination by the deterioration determination means.

[0015] Furthermore, the claims of the present invention 2In the fuel cell system described in the above, the deterioration determination means determines local deterioration of the cell stack based on the temperature difference between the temperature of the reactive anode gas on the anode outlet side and the temperature of the anode gas on the anode inlet side and / or the temperature difference between the temperature of the reactive cathode gas on the cathode outlet side and the temperature of the cathode gas on the cathode inlet side.

[0016] Furthermore, the claims of the present invention 3 In the fuel cell system described above, the controller includes a criterion change means for changing a deterioration criterion that serves as a criterion for determining local deterioration of the cell stack, and the criterion change means changes the deterioration criterion each time the flow path switching means is switched by the controller. [Effects of the Invention]

[0017] According to the fuel cell system of claim 1 of the present invention, a flow path switching means is provided in at least one of the anode gas supply flow path and the anode gas discharge flow path and the cathode gas supply flow path and the cathode gas discharge flow path, and the controller includes a deterioration determination means for determining local deterioration of the cell stack, and this deterioration determination means determines local deterioration based on a temperature related to the cell stack, and the flow path switching means is switched based on this local deterioration determination by the deterioration determination means, so that the flow of at least one of the anode gas and the cathode gas can be switched.

[0018] For example, when a flow path switching means (anode gas flow path switching means) is provided in the anode gas supply flow path and the anode gas discharge flow path, before switching, the anode gas flowing through the anode gas supply flow path flows in from the anode inlet side of the cell stack, and the reacted anode gas that has flowed through the cell stack is discharged from this anode outlet side through the anode gas discharge flow path, but after switching, the anode gas flowing through the anode gas supply flow path flows in from the anode outlet side of the cell stack, and the reacted anode gas that has flowed through the cell stack is discharged from this anode inlet side through the anode gas discharge flow path.

[0019] Furthermore, for example, when a flow path switching means (cathode gas flow path switching means) is provided in the cathode gas supply flow path and the cathode gas discharge flow path, before switching, the cathode gas flowing through the cathode gas supply flow path flows in from the cathode inlet side of the cell stack, and the reacted cathode gas that has flowed through this cell stack is discharged from the cathode outlet side through the cathode gas discharge flow path, but after switching, the cathode gas flowing through the cathode gas supply flow path flows in from the cathode outlet side of the cell stack, and the reacted anode gas that has flowed through this cell stack is discharged from the cathode inlet side through the cathode gas discharge flow path.

[0020] By switching the gas flow in this way and positioning the locally deteriorated portion of the cell stack upstream in the gas flow direction, it is possible to supply a relatively low-temperature gas to this deteriorated portion, which reduces the temperature of the locally deteriorated portion, which is prone to become high temperature, thereby suppressing the maximum temperature inside the cell stack and preventing rapid oxidation of the metal components used in the cell stack, as well as the resulting temperature differences and thermal stress inside the cell stack.

[0023] Furthermore, the cell stack Gas temperature measuring means are provided on the anode inlet and outlet sides (and / or cathode inlet and outlet sides of the cell stack), and localized deterioration of the cell stack can be determined based on the temperatures measured by this gas temperature measuring means.

[0024] As localized deterioration progresses near the anode outlet side (cathode outlet side) of the cell stack, the temperature near the anode outlet side (cathode outlet side) rises, and as a result, the temperature of the reacted anode gas (reacted cathode gas) discharged from the anode outlet side (cathode outlet side) of the cell stack also rises. On the other hand, the temperature of the anode gas (cathode gas) supplied to the anode inlet side (cathode inlet side) of the cell stack is measured before it comes into contact with the cell stack, and is therefore less affected by the temperature of the cell stack. Therefore, as deterioration of the cell stack progresses, the temperature rise of the reacted anode gas (reacted cathode gas) from the outlet side becomes greater than that of the anode gas (cathode gas) on the inlet side. Therefore, by measuring the temperatures of the anode gas (cathode gas) on the inlet side of the stack and the reacted anode gas (reacted cathode gas) on the outlet side, the state of localized deterioration of the cell stack can be monitored.

[0025] In this case, it is sufficient to provide a gas temperature measurement means on the anode inlet and outlet sides of the cell stack (and / or the cathode inlet and outlet sides of the cell stack), which requires fewer measurement points than measuring the temperature distribution of the cell stack.In addition, the configuration required for temperature measurement and local deterioration determination is simplified, which makes it possible to reduce costs such as manufacturing costs and maintenance costs.

[0026] Furthermore, the claims of the present invention 2 In the fuel cell system described in the above, the degradation determination means uses the temperature difference between the temperature of the reacted anode gas on the anode outlet side and the temperature of the anode gas on the anode inlet side (and / or the temperature difference between the temperature of the reacted cathode gas on the cathode outlet side and the temperature of the cathode gas on the cathode inlet side), and can determine local degradation of the cell stack based on this temperature difference. As local degradation of the cell stack progresses, the temperature of the reacted anode gas (reacted cathode gas) rises compared to the anode gas (cathode gas), and this temperature difference becomes larger, and therefore it is possible to determine local degradation of the cell stack using this temperature difference.

[0027] Furthermore, the claims of the present invention3 According to the fuel cell system described above, the controller includes a judgment criterion changing means which changes the deterioration judgment criterion each time the flow path switching means is switched, so that the flow path switching means can change the flow path multiple times depending on the progress of local deterioration of the cell stack. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a simplified diagram showing a first embodiment of a fuel cell system according to the present invention; [Figure 2] 2 is a cross-sectional view showing a simplified view of the cell stack and the related configuration of the fuel cell system of FIG. 1. FIG. [Figure 3] FIG. 3(a) is a diagram showing the gas flow direction in the cell stack of FIG. 2, and FIG. 3(b) is a diagram showing the temperature distribution in the cell stack at that time. [Figure 4] 4(a) is a diagram showing the flow direction when the gas flow direction is switched in the cell stack of FIG. 2, and FIG. 4(b) is a diagram showing the temperature distribution in the cell stack at that time. [Figure 5] FIG. 3 is a diagram showing a state when the flow direction of the cathode gas is switched in the cell stack of FIG. 2. [Figure 6] FIG. 3 is a diagram showing a state when the flow direction of the anode gas in the cell stack of FIG. 2 is switched. [Figure 7] 2 is a simplified cross-sectional view showing a temperature distribution measuring means provided in the cell stack of the fuel cell system of FIG. 1. FIG. [Figure 8] FIG. 2 is a block diagram showing a simplified control system of the fuel cell system according to the first embodiment. [Figure 9] 9 is a flowchart showing the flow of control by the control system of FIG. 8; [Figure 10] FIG. 10(a) is a simplified diagram showing a first switching state of the flow path switching means applied to the fuel cell system of the first embodiment, and FIG. 10(b) is a simplified diagram showing a second switching state of this flow path switching means. [Figure 11] FIG. 6 is a block diagram showing a simplified control system of a fuel cell system according to a second embodiment. [Figure 12] FIG. 11(b) is a simplified diagram showing a first switching state of the flow path switching means applied to the fuel cell system of the second embodiment, and FIG. 11(b) is a simplified diagram showing a second switching state of this flow path switching means. [Figure 13] 12 is a flowchart showing the flow of control by the control system of FIG. 11; [Figure 14] FIG. 10 is a simulation diagram showing the relationship between the power generation time of the cell stack and the temperature difference within the cell stack when the flows of the anode gas and cathode gas are switched and when the flows of the anode gas and cathode gas are not switched. DETAILED DESCRIPTION OF THE INVENTION

[0029] Next, various embodiments of a fuel cell system according to the present invention will be described with reference to the accompanying drawings. Note that in the following embodiments, the present invention will be described as being applied to a solid oxide fuel cell system as an example of a fuel cell system, but is not limited to this solid oxide fuel cell system and can be similarly applied to other types of fuel cell systems such as a polymer electrolyte fuel cell system and a phosphoric acid fuel cell system.

[0030] First, a fuel cell system of a first embodiment will be described with reference to Figures 1 to 11. In Figures 1 and 2, the solid oxide fuel cell system shown as an example of a fuel cell system includes a cell stack 2 that generates electricity through an electrochemical reaction between an anode gas (fuel gas, reformed gas, etc.) and a cathode gas (oxygen in the air, etc.), and an anode gas supply flow path 4 is connected to the anode inlet side of the cell stack 2, and an anode gas discharge flow path 6 is connected to the anode outlet side thereof. Furthermore, a cathode gas supply flow path 8 is connected to the cathode inlet side of the cell stack 2, and a cathode gas discharge flow path 10 is connected to the cathode outlet side thereof.

[0031] In this embodiment, anode gas flow path switching means 12 (anode gas flow path switching means) are provided in the anode gas supply flow path 4 and the anode gas discharge flow path 6, and cathode gas flow path switching means 14 (cathode gas flow path switching means) are provided in the cathode gas supply flow path 8 and the cathode gas discharge flow path 10. These flow path switching means 12, 14 have a configuration such as that shown in Fig. 10, and will be described in detail later.

[0032] To explain the cell stack 2, the cell stack 2 is configured by stacking a plurality of fuel cells 16, with flow path walls 18 provided between each of the fuel cells 16. Each fuel cell 16 has a solid electrolyte layer 20 as an electrolyte layer that conducts oxide ions, with an anode 22 (fuel electrode) provided on one side (the lower side in FIGS. 2 to 6) of the solid electrolyte 20 and a cathode 24 (oxygen electrode) provided on the other side (the upper side in FIGS. 2 to 6).

[0033] Anode inlets 26 are provided on the anode inflow side of the cell stack 2, and these anode inlets 26 are connected to the anode gas supply flow path 4. Furthermore, anode outlets 28 are provided on the anode outflow side of the cell stack 2, and these anode outlets 28 are connected to the anode discharge flow path 6. With this configuration, as shown by the two-dot chain line in Figure 2, the anode gas supplied through the anode gas supply flow path 4 flows through the anode inlet 26 into the anode internal flow path 30, and the reacted anode gas that has flowed through this anode internal flow path 30 is discharged from the anode outlet 28 to the anode gas discharge flow path 6.

[0034] A cathode inflow port 32 is provided on the cathode inflow side of the cell stack 2, and a cathode gas supply flow path 8 is connected to the cathode inflow port 32. A cathode outflow port 34 is provided on the cathode outflow side of the cell stack 2, and a cathode exhaust flow path 10 is connected to the cathode outflow port 34. With this configuration, as shown by the dashed dotted line in Figure 2, the cathode gas supplied through the cathode gas supply flow path 8 flows through the cathode inflow port 32 into the cathode internal flow path 36, and the reacted cathode gas that has flowed through the cathode internal flow path 36 is discharged from the cathode outflow port 34 to the cathode gas exhaust flow path 10.

[0035] In this embodiment, as will be described later, the flow path switching means 12, 14 are switched between a first switching state (for example, the state shown in FIG. 10(a)) and a second switching state (for example, the state shown in FIG. 10(b)). When both of the flow path switching means 12, 14 are in the first switching state, the anode gas and the cathode gas flow into the cell stack 2 from the anode inlet 26 and the cathode inlet 32, as shown in FIGS. 2 and 3(a), and are discharged from the anode outlet 28 and the cathode outlet 34. At this time, the temperature distribution in the cell stack 2 in the flow direction of the gases (anode gas, cathode gas) is as shown in FIG. 3(b), and the temperature tends to be higher toward the discharge side of the anode gas and the cathode gas, i.e., near the anode outlet 28 and the cathode outlet 34, in other words, toward the right end in FIG. 3.

[0036] Furthermore, when both flow path switching means 12, 14 are in the second switching state, the flow directions of the anode gas and cathode gas are reversed, and the anode gas and cathode gas flow into the cell stack 2 from the anode outlet 28 and the cathode outlet 34, as shown in Figure 4(a), and are discharged from the anode inlet 26 and the cathode inlet 32. At this time, the temperature distribution in the cell stack 2 in the flow direction of the gases (anode gas, cathode gas) is as shown in Figure 4(b), and the temperature tends to be higher towards the discharge side of the anode gas and cathode gas, i.e., near the anode inlet 26 and the cathode inlet 32, in other words, towards the left end in Figure 4.

[0037] In the above explanation, both flow path switching means 12, 14 (flow path switching means for anode gas and cathode gas) are switched, but for example, when the anode gas flow path switching means 12 is switched, as shown in Fig. 5, the cathode gas flows from the cathode inlet 32 ​​into the cell stack 2 and is discharged from the cathode outlet 34, but the flow direction of the anode gas is switched and it flows from the anode outlet 28 into the cell stack 2 and is discharged from the anode inlet 26. When the flow of the anode gas is switched in this way, for example, the cathode gas flow path switching means 14 provided in the cathode gas supply flow path 8 and the cathode gas discharge flow path 10 can be omitted.

[0038] For example, when the cathode gas flow path switching means 14 is switched, as shown in Fig. 6, the anode gas flows from the anode inlet 26 into the cell stack 2 and is discharged from the anode outlet 28, but the flow direction of the cathode gas is switched, and the cathode gas flows from the cathode outlet 28 into the cell stack 2 and is discharged from the cathode inlet 26. When the flow of the cathode gas is switched in this way, for example, the anode gas flow path switching means 12 provided in the anode gas supply flow path 4 and the anode gas discharge flow path 6 can be omitted.

[0039] In this solid oxide fuel cell system, the occurrence of localized deterioration in the cell stack 2 is determined by utilizing the temperature distribution inside the cell stack to monitor the progress of localized deterioration in the cell stack 2. Referring to Figs. 7 and 8 as well as Fig. 1, a temperature distribution measuring means 42 for measuring the temperature distribution is provided in the cell stack 2, and this temperature distribution measuring means 42 measures the temperature distribution as a function of distance in the flow direction of the gases (anode gas, cathode gas). Such temperature distribution measuring means 42 is composed of, for example, a thermocouple 44, and measures the temperature at, for example, eight locations (measurement points P1 to P8) in the cell stack 2. Note that this temperature distribution measurement may be performed by measuring the temperature at any number of measurement locations other than eight (for example, four to six locations).

[0040] The measured temperatures (measured temperatures at measurement points P1 to P8) from this temperature distribution measuring means 42 (thermocouple 44) are sent to a controller 46 that controls the system, and the controller 46 determines the occurrence of localized deterioration in the cell stack 2 based on the measured temperature distribution of this temperature distribution measuring means 42.

[0041] 8, the illustrated controller 46 is composed of, for example, a microprocessor, and in this embodiment includes a temperature gradient calculation means 48, a deterioration determination means 50, a valve switching signal generation means 52, a valve control means 54, and a memory means 56. The temperature gradient calculation means 48 uses the temperature distribution measured by the temperature distribution measurement means 42 (i.e., the temperatures measured at measurement points P1 to P8) to calculate the slope of an approximate line between the distance in the gas flow direction and the measured temperature distribution. This slope can be calculated using, for example, the least squares method. If the temperature near the outlet side of the cell stack 2 (the temperature measured at measurement point P8) rises and localized deterioration occurs, the slope of this approximate line increases. Therefore, the occurrence of localized deterioration in the cell stack 2 can be detected based on the magnitude of the slope of the approximate line based on this measured temperature distribution.

[0042] The memory means 56 stores a reference gradient value that serves as the basis for the gradient of this approximate straight line, and when the magnitude of the gradient of the approximate straight line based on this measured temperature distribution exceeds this reference gradient value, the deterioration determination means 50 determines that local deterioration has occurred in the cell stack 2 and performs a local deterioration determination.

[0043] Valve switching signal generating means 52 generates a valve switching signal based on the local deterioration determination by deterioration determining means 50, and valve control means 54 controls the switching of flow path switching means 12, 14 (flow path switching means for anode gas and cathode gas) based on this valve switching signal. For example, when flow path switching means 12, 14 are in the first switching state (switching state shown in FIG. 3), they are switched to the second switching state (switching state shown in FIG. 4), and when in the second switching state, they are switched to the first switching state.

[0044] In this embodiment, the flow path switching means 12, 14 have substantially the same configuration, and are configured, for example, as shown in Figure 10. Regarding the anode gas flow path switching means 12 (cathode gas flow path switching means 14), the anode gas supply flow path 4 (cathode gas supply flow path 8) and anode gas discharge flow path 6 (cathode gas discharge flow path 10) of the cell stack 2 are connected by a first connection flow path 62 and a second connection flow path 64. A first anode gas three-way valve 68 (first cathode gas three-way valve 70) is disposed at the connection between the first connection flow path 62 and the anode gas supply flow path 4 (cathode gas supply flow path 8), and a second anode gas three-way valve 72 (second cathode gas three-way valve 74) is disposed at the connection between the second connection flow path 64 and the anode gas discharge flow path 6 (cathode gas discharge flow path 10).

[0045] When the anode gas flow path switching means 12 (cathode gas flow path switching means 14) is in the first switching state, the first anode gas three-way valve 68 (first cathode gas three-way valve 70) and the second anode gas three-way valve 72 (second cathode gas three-way valve 74) are in the first switching state shown in Figure 10(a). That is, the first anode gas three-way valve 68 (first cathode gas three-way valve 70) connects the anode gas supply flow path 4 (cathode gas supply flow path 8) to the anode inlet 26 (cathode inlet 32) of the cell stack 2, and the second anode gas three-way valve 72 (second cathode gas three-way valve 74) connects the anode exhaust port 28 (cathode exhaust port 34) of the cell stack 2 to the anode gas exhaust flow path 6 (cathode gas exhaust flow path 10).

[0046] Because of this communication, as shown by the arrows in Figure 10(a), the anode gas (cathode gas) from the anode gas supply flow path 4 (cathode gas supply flow path 8) flows into the anode inlet side (cathode inlet side) of the cell stack 2, flows through the internal flow path 30 (34) of the anode 22 (cathode 24) of this cell stack 2, and then is discharged from the anode outlet side (cathode outlet side) of the cell stack 2 through the anode gas discharge flow path 6 (cathode gas discharge flow path 10).

[0047] Furthermore, when the flow path switching means 12 for anode gas (flow path switching means 14 for cathode gas) is in the second switching state, the first anode gas three-way valve 68 (first cathode gas three-way valve 70) and the second anode gas three-way valve 72 (second cathode gas three-way valve 74) are in the second switching state shown in Figure 10(b). That is, the first anode gas three-way valve 68 (first cathode gas three-way valve 70) connects the anode gas supply flow path 4 (cathode gas supply flow path 8) to the anode outlet 28 (cathode gas outlet 34) of the cell stack 2 via the first connection flow path 62, and the second anode gas three-way valve 72 (second cathode gas three-way valve 74) connects the anode inlet 26 (cathode inlet 32) of the cell stack 2 to the anode gas discharge flow path 6 (cathode gas discharge flow path 10) via the second connection flow path 64.

[0048] Because they are connected in this manner, as shown by the arrows in Figure 10(b), the anode gas (cathode gas) from the anode gas supply flow path 4 (cathode gas supply flow path 8) flows into the anode outlet side (cathode outlet side) of the cell stack 2 through the first connection flow path 62, flows through the internal flow path 30 (34) of the anode 22 (cathode 24) of this cell stack 2, and then is discharged from the anode inlet side (cathode inlet side) of the cell stack 2 through the second connection flow path 64 and the anode gas discharge flow path 6 (cathode gas discharge flow path 10).

[0049] By configuring the flow path switching means 12 for anode gas (flow path switching means 14 for cathode gas) in this manner, the flow direction of the anode gas (cathode gas) in the first switching state can be switched to the opposite direction from the flow direction of the anode gas (cathode gas) in the second switching state.

[0050] Next, flow path switching control in the above-mentioned solid oxide fuel cell system will be described mainly with reference to Figures 1 and 8 to 9. When operation of the solid oxide fuel cell system is started, the process proceeds from step S1 to step S2, and an approximate linear gradient, i.e., a temperature gradient, is calculated based on the measured temperature distribution of the cell stack 2. Temperature distribution measurement means 42 measures the internal temperature at predetermined locations (predetermined measurement locations P1 to P8 in this embodiment) of the cell stack 2, and temperature gradient calculation means 48 of the controller 46 calculates a temperature gradient value of the internal temperature of the cell stack 2 based on the measured temperature distribution measured by the temperature distribution measurement means 42.

[0051] If the temperature gradient value calculated by the temperature gradient calculation means 48 exceeds the reference gradient value registered in the memory means 56, the process proceeds from step S3 to step S4. If this calculated temperature gradient value exceeds the reference gradient value, it means that the internal resistance of the anode outflow side and / or cathode outflow side of the cell stack 2 is increasing, causing a rise in temperature. This indicates that localized deterioration has occurred on the anode outflow side and / or cathode outflow side of the cell stack 2. In such a case, the deterioration determination means 50 determines that localized deterioration has occurred in the cell stack 2 and determines that localized deterioration has occurred. If this calculated temperature gradient value is equal to or less than the reference gradient value, the process proceeds from step S3 to step S7.

[0052] When localized deterioration is determined in this manner, the valve switching signal generating means 52 generates a valve switching signal (step S5), and the valve control means 54 switches the flow path switching means 12, 14 from the first switching state to the second switching state based on this valve switching signal (step S6). That is, based on this valve switching signal, the valve control means 54 switches the first anode gas three-way valve 68 from the first switching state to the second switching state, and switches the second anode gas three-way valve 72 from the first switching state to the second switching state, and by switching in this way, the flow direction of the anode gas is switched to the opposite direction. Furthermore, based on this valve switching signal, the valve control means 54 switches the first cathode gas three-way valve 70 from the first switching state to the second switching state, and switches the second cathode gas three-way valve 74 from the first switching state to the second switching state, and by switching in this manner, the flow direction of the cathode gas is also switched to the opposite direction.

[0053] When the flow directions of the anode gas and cathode gas are switched in this way, the anode gas from the anode gas supply flow path 4 flows into the cell stack 2 from the anode outlet side, and the cathode gas from the cathode gas supply flow path 8 flows into the cell stack 2 from the cathode outlet side. The anode gas from the anode gas supply flow path 4 has a lower temperature than the reacted anode gas that was discharged from the anode outlet side of the cell stack 2, and by switching the flow of the anode gas in the opposite direction, this lower-temperature anode gas is supplied from the anode outlet side of the cell stack 2. The cathode gas from the cathode gas supply flow path 8 has a lower temperature than the reacted cathode gas that was discharged from the cathode outlet side of the cell stack 2, and by switching the flow of the cathode gas in the opposite direction, this lower-temperature cathode gas is supplied from the cathode outlet side of the cell stack 2.

[0054] Therefore, since low-temperature anode gas and low-temperature cathode gas flow into the cell stack 2 from the side where localized deterioration is occurring, the temperature rise in the part of the cell stack 2 where localized deterioration is occurring is suppressed, thereby suppressing the progression of localized deterioration.

[0055] This determination of localized deterioration of the cell stack 2 continues until operation of the solid oxide fuel cell system is terminated, and steps S2 to S7 are repeatedly performed. When operation of the system is terminated, the process moves from step S7 to step S8, and operation of the fuel cell system is terminated.

[0056] In this embodiment, local deterioration of the cell stack 2 is determined by calculating the approximate linear slope (i.e., the temperature gradient that linearly shows the relationship between the distance in the gas flow direction and the measured temperature distribution) based on the measured temperature distribution of the cell stack 2 measured by the temperature distribution measuring means 44. However, instead of this configuration, the measured temperature distribution of the cell stack 2 measured by the temperature distribution measuring means 44, i.e., the measured temperatures at specified measurement points (P1 to P8) of the cell stack 2, may be used to determine local deterioration of the cell stack 2 based on the temperature difference between the highest and lowest temperatures of these measured temperatures.

[0057] When localized deterioration occurs in the cell stack 2, the internal resistance of that area increases, causing the temperature of that area to rise and become higher than that of other areas, and therefore the temperature difference between the highest and lowest temperatures in the measured temperature distribution of the cell stack 2 also increases.Therefore, the occurrence of localized deterioration in the cell stack 2 can be determined based on this temperature difference.

[0058] Next, a second embodiment of a solid oxide fuel cell system according to the present invention will be described with reference to Figures 11 to 13. In this second embodiment, instead of measuring the internal temperature of the cell stack, the temperatures of the anode gas flowing through the anode inlet side and anode outlet side of the cell stack are measured, and the temperatures of the cathode gas flowing through the cathode inlet side and cathode outlet side of the cell stack are measured. Also, instead of using two three-way valves as flow path switching means for the anode gas and cathode gas, four on-off valves are used to switch the gas flow paths. In this second embodiment, components that are substantially the same as those in the first embodiment described above are given the same reference numerals, and their description will be omitted.

[0059] 11 and 12, in the second embodiment, an anode gas temperature measuring means 82 for measuring the temperature of the anode gas is provided, and this anode gas temperature measuring means 82 is composed of a first anode gas temperature sensor 84 that measures the temperature of the anode gas flowing on the anode inlet side of the cell stack 2 and a second anode gas temperature sensor 86 that measures the temperature of the reacted anode gas flowing on the anode outlet side. Also, a cathode gas temperature measuring means 88 for measuring the temperature of the cathode gas is provided, and this cathode gas measuring and detecting means 88 is composed of a first cathode gas temperature sensor 90 that measures the temperature of the cathode gas flowing on the cathode inlet side of the cell stack 2 and a second cathode gas temperature sensor 92 that measures the temperature of the reacted cathode gas flowing on the cathode outlet side.

[0060] In this second embodiment, local deterioration of the cell stack 2 is determined based on the temperature difference between the anode gas temperature on the anode outlet side of the cell stack 2 (temperature measured by the second anode gas temperature sensor 86) and the anode gas temperature on the anode inlet side (temperature measured by the first anode gas temperature sensor 84), and also based on the temperature difference between the cathode gas temperature on the cathode outlet side of the cell stack 2 (temperature measured by the second cathode gas temperature sensor 92) and the cathode gas temperature on the cathode inlet side of the cell stack 2 (temperature measured by the first cathode gas temperature sensor 90).

[0061] If localized deterioration occurs near the anode outflow side (near the cathode outflow side) of the cell stack 2 and the internal resistance increases, the temperature near this anode outflow side (near the cathode outflow side) will rise, and the temperature of the reacted anode gas (reacted cathode gas) discharged from the anode outflow side (cathode outflow side) will rise. As a result, the temperature difference between the temperature measured by the second anode gas temperature sensor 86 (second cathode gas temperature sensor 92) and the temperature measured by the first anode gas temperature sensor 84 (first cathode gas temperature sensor 90) will increase, and localized deterioration of the cell stack 2 can be determined based on this temperature difference.

[0062] In this second embodiment, in order to determine the progress of localized deterioration of the cell stack 2 using the temperatures measured by the anode gas temperature measuring means 82 and the cathode gas temperature measuring means 88, the controller 46A is equipped with an anode gas temperature difference calculating means 94 and a cathode gas temperature difference calculating means 96 instead of the temperature gradient calculating means. The anode gas temperature difference calculating means 94 calculates the temperature difference between the temperature measured by the second anode gas temperature sensor 86 and the temperature measured by the first anode gas temperature sensor 84, and the cathode gas temperature difference calculating means 96 calculates the temperature difference between the temperature measured by the second cathode gas temperature sensor 92 and the temperature measured by the first cathode gas temperature sensor 90.

[0063] In this embodiment, the memory means 56A stores an anode gas temperature difference reference value, which serves as a reference value when determining whether localized deterioration has occurred based on the anode gas temperature difference, and a cathode gas temperature difference reference value, which serves as a reference value when determining whether localized deterioration has occurred based on the cathode gas temperature difference.

[0064] The deterioration determination means 50 determines that local deterioration has occurred in the cell stack 2 when the anode gas temperature difference calculated by the anode gas temperature difference calculation means 94 exceeds the anode gas temperature difference reference value, and also determines that local deterioration has occurred in the cell stack 2 when the cathode gas temperature difference calculated by the cathode gas temperature difference calculation means 96 exceeds the cathode gas temperature difference reference value.

[0065] The anode gas and cathode gas flow path switching means 12A, 14A are configured, for example, as shown in Figure 12. Referring to Figure 12, the anode gas flow path switching means 12A (cathode gas flow path switching means 14A) will be described. The anode gas supply flow path 4 (cathode gas supply flow path 8) and anode gas discharge flow path 6 (cathode gas discharge flow path 10) of the cell stack 2 are connected by a first connection flow path 62 and a second connection flow path 64. A first anode gas on / off valve 102 (first cathode gas on / off valve 110) is provided in the anode gas supply flow path 4 (cathode gas supply flow path 8) downstream of a connection between the first connection flow path 62 and the anode gas supply flow path 4 (cathode gas supply flow path 8), and a second anode gas on / off valve 104 (second cathode gas on / off valve 112) is provided in the first connection flow path 62 downstream of this connection. In addition, a third anode gas on-off valve 106 (third cathode gas on-off valve 114) is arranged in the anode gas discharge flow path 6 (cathode gas discharge flow path 10) upstream of the connection between the second connection flow path 64 and the anode gas discharge flow path 6 (cathode gas discharge flow path 10), and a fourth cathode gas on-off valve 108 (fourth cathode gas on-off valve 116) is arranged in the second connection flow path 64 upstream of this connection.

[0066] When the anode gas flow path switching means 12A (cathode gas flow path switching means 14A) is in the first switching state, as shown in Figure 12(a), the first anode gas on / off valve 102 (first cathode gas on / off valve 110) is held in an open state, the second anode gas on / off valve 104 (second cathode gas on / off valve 112) is held in a closed state, the third anode gas on / off valve 106 (third cathode gas on / off valve 114) is held in an open state, and the fourth anode gas on / off valve 108 (fourth cathode gas on / off valve 116) is held in a closed state, thereby connecting the anode gas supply flow path 4 (cathode gas supply flow path 8) to the anode inlet (cathode inlet) of the cell stack 2, and connecting the anode outlet (cathode outlet) of the cell stack 2 to the anode gas discharge flow path 6 (cathode gas discharge flow path 10).

[0067] Furthermore, when the anode gas flow path switching means 12A (cathode gas flow path switching means 14A) is in the second switching state, as shown in FIG. 12(b), the first anode gas on-off valve 102 (first cathode gas on-off valve 110) is held in a closed state, the second anode gas on-off valve 104 (second cathode gas on-off valve 112) is held in an open state, the third anode gas on-off valve 106 (third cathode gas on-off valve 114) is held in a closed state, and the fourth anode gas on-off valve 108 (fourth cathode gas on-off valve 116) is held in an open state, so that the anode gas supply flow path 4 (cathode gas supply flow path 8) and the anode outlet (cathode outlet) of the cell stack 2 are connected via the first connecting flow path 62, and the anode inlet (cathode inlet) of the cell stack 2 and the anode gas discharge flow path 6 (cathode gas discharge flow path 10) are connected via the second connecting flow path 64. Even if the flow path switching means 12A for anode gas and 14A for cathode gas are configured in this way, the same effects as those described above can be achieved.

[0068] Flow path switching control in the solid oxide fuel cell system of this second embodiment will now be described. When operation of the solid oxide fuel cell system is started, the process proceeds from step S11 to step S12, where the anode gas temperature difference is calculated. A first anode gas temperature sensor 84 measures the anode gas temperature on the anode inflow side of the cell stack 2, and a second anode gas temperature sensor 86 measures the anode gas temperature on the anode outflow side of the cell stack 2 (i.e., the reaction anode gas temperature). An anode gas temperature difference calculation means 94 calculates the anode gas temperature difference based on the temperatures measured by these temperature sensors 84, 86.

[0069] Then, when the anode gas temperature difference calculated by the anode gas temperature difference calculation means 94 exceeds the anode gas temperature difference reference value registered in the memory means 56A, the process proceeds from step S13 to step S14, and the deterioration determination means 50 determines that localized deterioration has occurred in the cell stack 2 and that partial deterioration has occurred.

[0070] In step S13, if the anode gas temperature difference calculated by the anode gas temperature difference calculation means 94 is equal to or less than this anode gas temperature difference reference value, the process proceeds to step S15, where the cathode gas temperature difference is calculated. The first cathode gas temperature sensor 90 measures the cathode gas temperature on the cathode inlet side of the cell stack 2, and the second cathode gas temperature sensor 92 measures the cathode gas temperature on the cathode outlet side of the cell stack 2 (i.e., the reaction cathode gas temperature). The cathode gas temperature difference calculation means 96 calculates the cathode gas temperature difference based on the temperatures measured by these temperature sensors 90, 92.

[0071] Then, when the cathode gas temperature difference calculated by the cathode gas temperature difference calculation means 96 exceeds the cathode gas temperature difference reference value registered in the memory means 56A, the process proceeds from step S16 to step S14, and in this case too, the deterioration determination means 50 determines that local deterioration has occurred in the cell stack 2 and that partial deterioration has occurred.

[0072] When the anode gas temperature difference (cathode gas temperature difference) exceeds the anode gas temperature difference reference value (cathode gas temperature difference reference value), it means that the internal resistance of the anode outflow side (cathode outflow side) of the cell stack 2 is increasing and its temperature is rising, which indicates that localized deterioration has occurred around the anode outflow side (cathode outflow side) of the cell stack 2. In such a case, the deterioration determination means 50 determines that localized deterioration has occurred in the cell stack 2. In this embodiment, the anode gas temperature difference reference value and the cathode gas temperature difference reference value are set separately, but these two reference values ​​may also be set as a common gas temperature difference reference value.

[0073] When localized deterioration is determined in this manner, similarly to the first embodiment described above, the valve switching signal generating means 52 generates a valve switching signal (step S17), and the valve control means 54 switches the flow path switching means 12A, 14A from the first switching state to the second switching state based on this valve switching signal (step S18). That is, based on this valve switching signal, the valve control means 54 switches the first anode gas on-off valve 102 from an open state to a closed state, the second anode gas on-off valve 104 from a closed state to an open state, the third anode gas on-off valve 106 from an open state to a closed state, and the fourth anode gas on-off valve 108 from a closed state to an open state, and by switching in this manner, the flow direction of the anode gas is switched to the opposite direction.

[0074] Furthermore, based on this valve switching signal, the valve control means 54 switches the first cathode gas on-off valve 110 from an open state to a closed state, the second cathode gas on-off valve 112 from a closed state to an open state, the third cathode gas on-off valve 114 from an open state to a closed state, and the fourth cathode gas on-off valve 116 from a closed state to an open state, and by switching in this manner, the flow direction of the cathode gas is switched in the opposite direction.

[0075] When the flow directions of the anode gas and cathode gas are switched in this way, as described above, the anode gas from the anode gas supply flow path 4 flows into the cell stack 2 from the anode outflow side, and the cathode gas from the cathode gas supply flow path 8 flows into the cell stack 2 from the cathode outflow side, so that low-temperature anode gas is supplied from the anode outflow side of the cell stack 2, and low-temperature cathode gas is supplied from the cathode outflow side of the cell stack 2. This prevents temperature increases in areas of the cell stack 2 where localized deterioration is occurring, and as a result, the progression of localized deterioration can be suppressed.

[0076] This determination of localized deterioration of the cell stack 2 continues until operation of the solid oxide fuel cell system is terminated, and steps S12 to S19 are repeatedly performed. When operation of the system is terminated, the process moves from step S19 to step S20, and operation of the fuel cell system is terminated.

[0077] In the second embodiment, localized deterioration of the cell stack 2 is determined using both the anode gas temperature difference calculated by the anode gas temperature difference calculation means 94 and the cathode gas temperature difference calculated by the cathode gas temperature difference calculation means 96, but it is not necessary to use these two temperature differences, and localized deterioration of the cell stack 2 may be determined using either the anode gas temperature difference calculated by the anode gas temperature difference calculation means 94 or the cathode gas temperature difference calculated by the cathode gas temperature difference calculation means 96. When localized deterioration is determined using the anode gas temperature difference, the cathode gas temperature measurement means 88 (first and second cathode gas temperature sensors 90, 92) can be omitted, and when localized deterioration is determined using the cathode gas temperature difference, the anode gas temperature measurement means 82 (first and second anode gas temperature sensors 84, 86) can be omitted.

[0078] In the first embodiment, a reference gradient value is used as a deterioration determination reference value that serves as a criterion for determining local deterioration of the cell stack 2, but multiple reference gradient values ​​may be set as this deterioration determination reference value, and the deterioration determination criterion may be changed by changing the reference gradient value each time the flow path is switched by the flow path switching means 12, 14.

[0079] In addition, in the second embodiment, the anode gas temperature difference reference value and the cathode gas temperature difference reference value are used as the deterioration determination reference values ​​that serve as the criteria for determining local deterioration of the cell stack 2, but it is also possible to set multiple anode gas temperature difference reference values ​​and cathode gas temperature difference reference values ​​as these anode gas temperature difference reference values ​​and cathode gas temperature difference reference values, and change the anode gas temperature difference reference value and the cathode gas temperature difference reference value each time the flow path switching means 12A, 14A switches the flow path, thereby changing the deterioration determination criteria.

[0080] In these cases, the controller 46 (46A) may include a judgment criterion changing means (not shown), and this judgment criterion changing means may be configured to change the reference gradient values ​​(anode gas temperature difference reference value and cathode gas temperature difference reference value) as deterioration judgment criteria each time the flow path switching means 12, 14 (12A, 14A) is switched by the controller.

[0081] To confirm the effects of the present invention, the following simulation was performed. As an example, the temperature difference between the maximum and minimum temperatures in the temperature distribution inside the cell stack was calculated, and a numerical simulation was performed on the transition of the temperature difference between the maximum and minimum temperatures inside the cell stack under the condition that when this temperature difference reached 120°C, the flow path switching means was switched only once to reverse the flow directions of the anode gas and cathode gas. The results of this simulation were as shown as an example in Figure 14 (in the graph of Figure 14, the gas flow path was switched by the flow path switching means at the third point from the left (marked with a black circle)).

[0082] As a comparative example, a numerical simulation was performed on the transition of the temperature difference between the maximum and minimum temperatures in the cell stack when the flow path switching means was not performed even once (i.e., the flow directions of the anode gas and cathode gas were not switched). The results of this simulation are shown in Figure 14 as a comparative example.

[0083] As is clear from these simulation results, in the example, at the time when the gas flow path was switched by the flow path switching means, there was almost no change in the temperature difference between the maximum and minimum temperatures within the cell stack, and even after 50,000 hours of power generation operation, this temperature difference within the cell stack was lower than in the comparative example, confirming that the progression of localized deterioration of the cell stack was suppressed. [Explanation of symbols]

[0084] 2 Cell stack 4 Anode gas supply channel 6 Anode gas discharge passage 8 Cathode gas supply channel 10 Cathode gas exhaust flow path 12, 12A, 14, 14A Flow path switching means 16 fuel cell 20 Solid electrolyte 22 Anode 24 cathode 42 Temperature distribution measurement means 46,46A Controller 48 Temperature gradient calculation means 50 Deterioration judgment means 52 Valve switching signal generating means 54 Valve control means 82 Anode gas temperature measuring means 88 Cathode gas temperature measuring means 94 Anode gas temperature difference calculation means 96 Cathode gas temperature difference calculation means

Claims

1. the fuel cell includes a cell stack having fuel cells each having an anode, a cathode, and an electrolyte layer interposed therebetween; an anode gas supply flow path connected to the anode inlet side of the cell stack; an anode gas discharge flow path connected to the anode outlet side; a cathode gas supply flow path connected to the cathode inlet side of the cell stack; a cathode gas discharge flow path connected to the cathode outlet side; flow path switching means provided in at least one of the anode gas supply flow path and the anode gas discharge flow path and the cathode gas supply flow path and the cathode gas discharge flow path; and a controller for controlling the switching of the flow path switching means, A fuel cell system characterized in that a gas temperature measuring means for measuring gas temperature is provided on both the anode inlet and outlet sides of the cell stack and / or both the cathode inlet and outlet sides of the cell stack, the controller includes a deterioration determination means for determining local deterioration of the cell stack, the deterioration determination means determines local deterioration of the cell stack based on the temperature measured by the gas temperature measuring means, and the controller switches the flow path switching means based on the local deterioration determination of the deterioration determination means.

2. 2. The fuel cell system according to claim 1, wherein the deterioration determination means determines local deterioration of the cell stack based on the temperature difference between the temperature of the reacted anode gas on the anode outlet side and the temperature of the anode gas on the anode inlet side and / or the temperature difference between the temperature of the reacted cathode gas on the cathode outlet side and the temperature of the cathode gas on the cathode inlet side.

3. 3. The fuel cell system according to claim 1, wherein the controller includes a criterion change means for changing a deterioration criterion that serves as a criterion for determining local deterioration of the cell stack, and the criterion change means changes the deterioration criterion each time the flow path switching means is switched by the controller.

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