Fuel cell system and control method thereof

Abstract

A fuel cell system includes a fuel cell having: a single cell stack having an internal reforming catalyst for generating hydrogen from a hydrocarbon; a first flow path for supplying a hydrocarbon-containing fuel to the single cell stack; and a second flow path for supplying an oxidant gas to the single cell stack in such a manner that the oxidant gas flows in a direction opposite to or orthogonal to the fuel. Further, the temperature of the oxidant gas discharged from the fuel cell, i.e., the discharged oxidant gas, is detected, and the temperature control of the fuel cell is performed based on the temperature of the discharged oxidant gas.

Description

Technical Field

[0001] The present invention relates to a fuel cell system having a fuel cell and a control method for the fuel cell system. Background Art

[0002] JP2017-117550A discloses the following method: detecting the temperature of the central portion of the single cell stack that becomes the highest temperature, and performing control to make the temperature distribution of the entire fuel cell uniform. This fuel cell system supplies an inert gas to the central portion of the single cell stack that becomes the highest temperature to lower the temperature of the central portion of the single cell stack, thereby achieving uniformization of the temperature distribution of the entire fuel cell. Summary of the Invention

[0003] As described above, JP2017-117550A is premised on the central portion of the single cell stack being the highest temperature, but depending on the structure and / or operating scenario of the fuel cell, the central portion of the single cell stack is not necessarily always the highest temperature compared to other portions of the single cell stack. For example, in a fuel cell having a catalyst (hereinafter referred to as a reforming catalyst) configured to reform fuel inside the single cell stack, in the case of partial oxidation reforming, the end portion on the inlet side of the anode becomes relatively the highest temperature compared to the central portion of the single cell stack. Thus, in this internally reforming type fuel cell, if temperature control is performed based on the temperature of the central portion of the single cell stack, it is possible for a part of the single cell stack to exceed the heat resistance upper limit temperature.

[0004] An object of the present invention is to provide a fuel cell system and a control method thereof that can perform temperature control within a range not exceeding the heat resistance upper limit temperature of the fuel cell when a single cell stack having a reforming catalyst is provided.

[0005] A control method for a fuel cell system according to one aspect of the present invention is a control method for a fuel cell system having a fuel cell, the fuel cell including: a single cell stack having a reforming catalyst for generating hydrogen from a hydrocarbon; a first flow path for supplying a hydrocarbon-containing fuel to the single cell stack; and a second flow path for supplying the oxidant gas to the single cell stack in such a manner that the oxidant gas flows toward or orthogonally to the fuel. In the control method for the fuel cell system, the temperature of the oxidant gas discharged from the second flow path, that is, the temperature of the discharged oxidant gas, is detected, and the temperature control of the fuel cell is performed based on the temperature of the discharged oxidant gas. Brief Description of the Drawings

[0006] Figure 1 is a block diagram showing the structure of the fuel cell system according to the first embodiment.

[0007] Figure 2 is an explanatory diagram showing the flow path of the fuel and the flow path of the oxidant gas in the single cell stack.

[0008] Figure 3 It is a graph showing the temperature distribution inside a fuel cell in the case of performing partial oxidation reforming.

[0009] Figure 4 It is a flowchart related to the temperature control of the fuel cell.

[0010] Figure 5 It is a graph schematically showing the temperature control during warm-up operation.

[0011] Figure 6 It is a graph schematically showing the temperature control during steady operation.

[0012] Figure 7 It is a block diagram showing the structure of the fuel cell system according to the second embodiment.

[0013] Figure 8 It is an explanatory diagram of a modified example in which the installation position of the temperature sensor is changed.

[0014] Figure 9 It is an explanatory diagram of a modified example in which the structure of the flow paths of the fuel and the oxidant gas is changed.

[0015] Figure 10 It is an explanatory diagram of a modified example in which the structure of the flow paths of the fuel and the oxidant gas and the installation position of the temperature sensor are changed. Detailed Description of the Invention

[0016] (First Embodiment)

[0017] Figure 1 It is a block diagram showing the structure of the fuel cell system 10 according to the first embodiment. As Figure 1 shown, the fuel cell system 10 includes a power generation device 11 and a controller 12. The power generation device 11 is a device that generates power using the fuel cell 20, and in addition to the fuel cell 20, it also includes a fuel flow rate adjustment device 31, an air flow rate adjustment device 33, an oxidant gas supply device 41, a heat exchanger 43, a burner 51, a temperature sensor 60, and the like. The controller 12 is a control device that uniformly controls the power generation device 11 and each part constituting the power generation device 11.

[0018] The fuel cell 20 includes a fuel cell single cell (hereinafter, simply referred to as a single cell) configured to generate power through an electrochemical reaction using a fuel and an oxidant gas. In the present embodiment, the fuel cell 20 includes a single cell stack 21, which is composed of a single single cell or a plurality of single cells stacked, and is configured to generate the required power as a whole.

[0019] The single cell stack 21 has a reforming catalyst (hereinafter referred to as the internal reforming catalyst) inside it. The internal reforming catalyst 22 reforms the fuel (hereinafter referred to as the raw fuel) supplied to the fuel cell 20 by causing or promoting a specific chemical reaction, and generates a fuel (hereinafter referred to as the reformed fuel (anode gas)) that can be directly used for power generation from the raw fuel. The raw fuel is, for example, a fuel containing a raw material containing a hydrocarbon group such as an alkyl group as a main component, and specifically, is a hydrocarbon such as methane or an alcohol such as methanol. The internal reforming catalyst 22 causes a hydrogen-containing reformed fuel for power generation to be generated from the hydrocarbon-containing raw fuel. Thus, the fuel cell 20 is a so-called direct internal reforming type, and in principle, no additional reformer is required, and the fuel cell 20 itself can accept the supply of un-reformed raw fuel or incompletely reformed raw fuel to generate power.

[0020] For the fuel reforming that the single cell stack 21 can perform, there are, for example, partial oxidation reforming (POX), steam reforming (SR), and carbon dioxide reforming. The internal reforming catalyst 22 contributes to some or all of these reforming reactions.

[0021] Partial oxidation reforming is a reforming reaction in which the raw fuel is partially oxidized by mixing oxygen (O2) in the raw fuel to obtain a reformed fuel. For example, when the raw fuel is methane (CH4), the partial oxidation reforming is mainly carried out by the partial oxidation reaction shown in the following (1). In addition, excluding the case that occurs on a catalyst that is extremely exceptional in part, in the partial oxidation reforming, for example, complete combustion (complete oxidation) shown in the following (2) occurs and proceeds in the initial stage. Therefore, in the partial oxidation reforming, in addition to hydrogen (H2), water (H2O) is also generated. Both the partial oxidation reaction of (1) and the complete combustion of (2) are exothermic reactions. Therefore, the partial oxidation reforming is an exothermic reaction. In addition, as can be seen from (1) and (2), the partial oxidation reforming is a reaction that consumes oxygen. Therefore, the partial oxidation reforming does not occur uniformly throughout the single cell stack 21, but relatively more occurs in the upstream part of the fuel flow path (the first flow path 23 described later), and relatively less occurs in the downstream part of the fuel flow path where oxygen is consumed. This is because oxygen is abundant in the upstream part, but in the downstream part, oxygen is consumed successively due to the partial oxidation reforming, and the amount of oxygen contained becomes relatively less. In this way, in the single cell stack 21, along the fuel flow path, the amount of the partial oxidation reforming occurring changes obliquely, and thus a large temperature gradient may be generated in the single cell stack 21.

[0022] CH4 + 1 / 2O2 → CO + 2H2…(1)

[0023] CH4 + 2O2 → CO2 + 2H2O…(2)

[0024] Steam reforming is a reforming reaction in which the original fuel or the reformed fuel is partially oxidized by reacting the original fuel with water (steam) to obtain the reformed fuel. For example, when the original fuel is methane, steam reforming mainly proceeds through the oxidation reaction shown in the following (3) or (4). Steam reforming can be carried out using newly supplied water or water generated by partial oxidation reforming (especially complete combustion). In the present embodiment, the single cell stack 21 performs steam reforming using the water generated by partial oxidation reforming. Steam reforming is an endothermic reaction.

[0025] CH4+H2O→CO+3H2…(3)

[0026] CH4+2H2O→CO2+4H2…(4)

[0027] Carbon dioxide reforming is a reforming reaction in which the original fuel or the reformed fuel is partially oxidized by reacting the original fuel or the reformed fuel with carbon dioxide (CO2) to obtain the reformed fuel, and the reformed fuel is obtained by reforming through partial oxidation reforming or steam reforming. For example, when the original fuel is methane, carbon dioxide reforming mainly proceeds through the partial oxidation reaction shown in the following (5). Carbon dioxide reforming can be carried out using newly supplied carbon dioxide or carbon dioxide generated by partial oxidation reforming (especially complete combustion) or steam reforming. In the present embodiment, the single cell stack 21 performs carbon dioxide reforming using the carbon dioxide generated by partial oxidation reforming and / or steam reforming. Carbon dioxide reforming is an endothermic reaction.

[0028] CH4+CO2→2CO+2H2…(5)

[0029] In addition, the fuel cell 20 is, for example, a solid oxide fuel cell (SOFC). When the fuel cell 20 is an SOFC, the single cell stack 21 has a first flow path 23, a second flow path 24, and an electrolyte (not shown) made of solid oxide. The first flow path 23 is a flow path for raw fuel and / or reformed fuel (hereinafter, simply referred to as fuel unless distinction is required), and the second flow path 24 is a flow path for oxidant gas. Moreover, the single cell stack 21 has a structure in which the first flow path 23 and the second flow path 24 are adjacent to each other with the electrolyte therebetween. Thus, the internal reforming catalyst 22 is provided in the first flow path 23 which is a flow path for fuel. In addition, an electrode configured to function as a negative electrode (hereinafter, referred to as an anode) is provided on the surface of the electrolyte in the first flow path 23, and an electrode configured to function as a positive electrode (hereinafter, referred to as a cathode) is provided on the surface of the electrolyte in the second flow path 24. Further, in the present embodiment, the internal reforming catalyst 22 is separate from the anode, but sometimes a part or all of the anode functions as the internal reforming catalyst 22. In addition, the internal reforming catalyst 22 is substantially provided in the same manner throughout the single cell stack 21. That is, the internal reforming catalyst 22 is not provided only in a specific portion of the first flow path 23 or the like, and the raw fuel can be reformed substantially at any portion of the first flow path 23 within the single cell stack 21.

[0030] The fuel cell 20 has an anode inlet A1, an anode outlet A2, a cathode inlet C3, and a cathode outlet C4.

[0031] The anode inlet A1 is the upstream end of the first flow path 23 and is an inlet for supplying raw fuel to the fuel cell 20. Thus, the anode inlet A1 is connected to the fuel flow rate adjusting device 31 via the fuel supply path 32. On the other hand, the anode outlet A2 is the downstream end of the first flow path 23 and is used to discharge the used fuel and the gas generated by power generation (hereinafter, referred to as discharged fuel (anode exhaust gas)) to the outside of the fuel cell 20. In the present embodiment, the anode outlet A2 is connected to the burner 51 via the fuel discharge path 34.

[0032] The cathode inlet C3 is the upstream end of the second flow path 24 and is an inlet for supplying oxidant gas to the fuel cell 20. In the present embodiment, the cathode inlet C3 is connected to the oxidant gas supply device 41 via the oxidant gas supply path 42. On the other hand, the cathode outlet C4 is the downstream end of the second flow path 24 and is used to discharge the oxidant gas used in power generation and the gas generated by power generation (hereinafter, referred to as discharged oxidant gas (cathode exhaust gas)) to the outside of the fuel cell 20. In the present embodiment, the cathode outlet C4 is connected to the burner 51 via the oxidant gas discharge path 44.

[0033] In addition, the fuel cell 20 supplies power to devices or apparatuses connected to the fuel cell 20. Devices or apparatuses connected to the fuel cell 20 are, for example, a storage battery or a motor that serves as a drive source for an electric vehicle. In the present embodiment, although not shown in the drawings, the fuel cell 20 is connected to a storage battery, and the storage battery is connected to a motor for driving an electric vehicle. Therefore, the fuel cell 20 functions as an energy source for indirectly driving an electric vehicle.

[0034] The fuel flow rate regulating device 31 is a device (fuel supply device) that supplies a raw fuel to the fuel cell 20 and is a device that regulates the flow rate of the raw fuel supplied to the fuel cell 20. The fuel flow rate regulating device 31 is connected to the anode inlet A1 via a fuel supply path 32. The fuel flow rate regulating device 31 includes a fuel tank and an injector. The fuel tank stores the raw fuel in a liquid state, for example. The injector ejects the raw fuel from the fuel tank into the fuel supply path 32. Thus, the fuel flow rate regulating device 31 supplies the raw fuel to the fuel cell 20. The timing of supplying the raw fuel to the fuel cell 20 and the supply amount of the raw fuel, etc. are controlled by the controller 12. In addition, the fuel flow rate regulating device 31 may sometimes include a heat exchanger or the like. In this case, the fuel flow rate regulating device 31 can adjust the temperature, phase, pressure, etc. of the raw fuel by heating or heat exchange, etc. In the present embodiment, the fuel flow rate regulating device 31 vaporizes the raw fuel and supplies it to the fuel cell 20.

[0035] The air flow rate regulating device 33 is connected to the fuel supply path 32 and is a device (air supply device) that mixes air with the raw fuel supplied to the fuel cell 20 by the fuel flow rate regulating device 31 as needed and is a device that regulates the flow rate of the air mixed with the raw fuel. The air flow rate regulating device 33 is, for example, a blower. The purpose of mixing air with the raw fuel by the air flow rate regulating device 33 is to cause partial oxidation reforming to occur in the single cell stack 21 or to promote the partial oxidation reforming that occurs in the single cell stack 21 by making the raw fuel contain oxygen. Thus, the air flow rate regulating device 33 only needs to be able to mix oxygen with the raw fuel as needed. Therefore, the air flow rate regulating device 33 may also be configured to mix only oxygen, a gas other than oxygen-containing air, air whose composition, temperature, etc. have been adjusted, etc. with the raw fuel instead of natural air. The timing of mixing air with the raw fuel and the amount of air mixed with the raw fuel, etc. are controlled by the controller 12.

[0036] The oxidant gas supply device 41 is a device that supplies an oxidant gas to the fuel cell 20 and is connected to the cathode inlet C3 via an oxidant gas supply path 42. In the present embodiment, the oxidant gas is oxygen-containing air used for power generation of the fuel cell 20. That is, in the present embodiment, the oxidant gas supply device 41 is a blower.

[0037] The heat exchanger 43 is disposed in the oxidant gas supply path 42 and heats the oxidant gas through heat exchange. Thus, the heat exchanger 43 supplies the heated oxidant gas to the fuel cell 20. Heat exchange for heating the oxidant gas is performed with the gas discharged from the burner 51 (hereinafter referred to as exhaust gas).

[0038] The discharged fuel is supplied from the fuel cell 20 to the burner 51 via the fuel discharge path 34. In addition, the discharged oxidant gas is supplied from the fuel cell 20 to the burner 51 via the oxidant gas discharge path 44. Then, the burner 51 burns the discharged fuel and the discharged oxidant gas by catalytic combustion, for example. The exhaust gas generated as a result of this combustion is discharged to the outside of the fuel cell system 10 via the heat exchanger 43 from the exhaust path 52. Therefore, the heat generated due to the electrochemical reaction, the generation of exhaust gas, etc. in the fuel cell 20 is used to heat the oxidant gas in the oxidant gas supply path 42 through heat exchange in the heat exchanger 43.

[0039] The temperature sensor 60 is disposed in the oxidant gas discharge path 44. The temperature sensor 60 detects the temperature of the oxidant gas discharged from the fuel cell 20, more specifically, the discharged oxidant gas that is discharged from the second flow path 24. The temperature sensor 60 inputs the detected temperature of the discharged oxidant gas to the controller 12.

[0040] The controller 12 performs temperature control of the fuel cell 20 based on the temperature of the discharged oxidant gas detected by the temperature sensor 60. In particular, in the present embodiment, the controller 12 performs temperature control of the fuel cell 20 by the heat release of partial oxidation reforming in the cell stack 21. Details of the specific method by which the controller 12 performs temperature control of the fuel cell 20 will be described later. In addition, the controller 12 is a computer or a microcomputer constituted by a processor such as a CPU or a GPU, a memory, etc. The controller 12 can be configured not only as a dedicated computer for controlling the fuel cell system 10, but also as a part of a computer that controls other devices or systems, etc. For example, when the fuel cell system 10 is mounted on an electric vehicle, the vehicle controller that controls the driving, etc. of the electric vehicle can function as the controller 12 of the fuel cell system 10. In addition, the controller 12 can be configured as a server-type computer that controls the power generation device 11 by communicating with the power generation device 11.

[0041] Figure 2 It is an explanatory diagram showing the flow path of fuel and the flow path of oxidant gas in the cell stack 21 of the present embodiment. As Figure 2As shown, the first flow path 23 is a flow path for supplying fuel to the single cell stack 21. In addition, the second flow path 24 is a flow path for supplying an oxidant gas to the single cell stack 21 in such a manner that the oxidant gas flows facing the fuel. The shapes of the first flow path 23 and the second flow path 24 as flow paths are parallel, but the direction in which the fuel flows in the first flow path 23 is opposite to the direction in which the oxidant gas flows in the second flow path 24. Therefore, considering the flow directions of the fuel and the oxidant gas, the first flow path 23 and the second flow path 24 are anti-parallel or counter-parallel, and the fuel and the oxidant gas become so-called counterflow. In addition, as will be described later, the second flow path 24 can be a flow path for supplying an oxidant gas to the single cell stack 21 in such a manner that the oxidant gas flows orthogonally to the fuel.

[0042] Figure 3 is a schematic graph showing the temperature distribution in the fuel cell 20 in the case of performing partial oxidation reforming. In Figure 3 it shows the temperature distribution of the fuel cell 20 formed when the entire single cell stack 21 reaches a temperature above the level at which partial oxidation reforming can occur and partial oxidation reforming is performed in the single cell stack 21 on top of that. The temperature at which partial oxidation reforming can occur is, for example, about 300 degrees or higher. In addition, the horizontal axis represents the positions along the first flow path 23 and the second flow path 24. Each single cell constituting the single cell stack 21 is stacked in the direction of this vertical axis. In addition, the curve 101 shown by the solid line represents the temperature of the fuel in the fuel cell 20, and the curve 102 shown by the dashed line represents the temperature of the oxidant gas. The temperatures of the fuel and the oxidant gas in the single cell stack 21 can be regarded as substantially the same as the temperature of the fuel cell 20.

[0043] Raw fuel is supplied, for example, at room temperature from the anode inlet A1. When the raw fuel reaches the single cell stack 21, partial oxidation reforming, which is an exothermic reaction, occurs. As a result, as shown by the curve 101, the temperature of the fuel and the fuel cell 20 rises corresponding to the amount of partial oxidation reforming that occurs. As described above, partial oxidation reforming occurs relatively more on the anode inlet A1 side where oxygen is abundant, and the amount of occurrence becomes relatively less on the anode outlet A2 side where oxygen is consumed. Therefore, as shown by the curve 101, partial oxidation reforming forms a temperature distribution in the fuel cell 20 that generally decreases from the anode inlet A1 to the anode outlet A2. Due to this temperature distribution, the fuel cell 20 does not reach the highest temperature Tp at the position in the central part of the fuel cell 20, but reaches the highest temperature Tp at a specified position (the anode inlet A1 or a position near the anode inlet A1) biased towards the anode inlet A1 side.

[0044] As shown by curve 102, the temperature distribution of the oxidant gas follows the temperature distribution formed by partial oxidation reforming as described above and becomes substantially the same temperature distribution at least within the single cell stack 21. This is because the fuel and the oxidant gas flow integrally within the single cell stack 21 via the electrolyte which is a thin film, and thus become substantially the same temperature through mutual heat exchange. Therefore, the discharged oxidant gas discharged from the cathode outlet C4 is discharged after becoming a temperature substantially equal to the highest temperature of the temperature distribution formed by partial oxidation reforming or a temperature correlated with the highest temperature in the temperature distribution formed by partial oxidation reforming. The temperature correlated with the highest temperature means a temperature that can calculate or estimate the highest temperature within the fuel cell 20 based on this temperature due to having a certain relationship with the highest temperature within the fuel cell 20.

[0045] The temperature sensor 60 detects the temperature of the discharged oxidant gas. As a result, the temperature sensor 60 detects the highest temperature within the fuel cell 20 or a temperature correlated with the highest temperature within the fuel cell 20. The controller 12 performs temperature control of the fuel cell 20 based on the temperature of the discharged oxidant gas detected by the temperature sensor 60, and thereby performs temperature control of the fuel cell 20 based on the highest temperature within the fuel cell 20.

[0046] In the present embodiment, since the fuel and the oxidant gas are in a countercurrent flow, the temperature of the discharged oxidant gas is a temperature substantially equal to the highest temperature of the temperature distribution formed by partial oxidation reforming. Therefore, the temperature sensor 60 substantially detects the highest temperature within the fuel cell 20 by detecting the temperature of the discharged oxidant gas. Then, the controller 12 directly performs temperature control of the fuel cell 20 based on the highest temperature within the fuel cell 20 by using the temperature of the discharged oxidant gas detected by the temperature sensor 60.

[0047] In addition, the temperature of the fuel cell 20 decreases in the central portion of the single cell stack 21 due to the progress of steam reforming and / or carbon dioxide reforming which are endothermic reactions. Further, the temperature of the fuel cell 20 increases from the central portion of the single cell stack 21 to the anode outlet A2 and the cathode inlet C3 because the heated oxidant gas is supplied from the cathode inlet C3.

[0048] Next, a method for the controller 12 to control the temperature of the fuel cell 20 by the heat release of partial oxidation reforming in the single cell stack 21 will be described. Figure 4It is a flowchart related to the temperature control of the fuel cell 20. That is, in the case of controlling the temperature of the fuel cell 20 by the heat release of partial oxidation reforming in the single cell stack 21, the controller 12 sequentially repeats the execution of the oxidant gas discharge temperature acquisition step S101, the determination step S102, the temperature rise limit calculation step S103, the target heat release amount calculation step S104, the fuel flow rate calculation step S105, the mixed air flow rate calculation step S106, and the control execution step S107 at a prescribed time interval, thereby controlling the temperature of the fuel cell 20. In addition, the "temperature control of the fuel cell 20" particularly refers to the control performed in the temperature rise limit calculation step S103, the target heat release amount calculation step S104, the fuel flow rate calculation step S105, the mixed air flow rate calculation step S106, and the control execution step S107.

[0049] In the oxidant gas discharge temperature acquisition step S101, the controller 12 acquires the temperature of the discharged oxidant gas detected by the temperature sensor 60. That is, the controller 12 is configured to function as an oxidant gas discharge temperature acquisition unit. During the warm-up operation of the fuel cell system 10 (before the start of partial oxidation reforming), the temperature on the cathode outlet C4 side (anode inlet A1 side) becomes low. Therefore, in the case of warm-up operation, the controller 12 can determine whether the temperature inside the fuel cell 20 has reached the temperature at which partial oxidation reforming can be performed based on the temperature of the discharged oxidant gas detected by the temperature sensor 60 that reflects this temperature. On the other hand, when partial oxidation reforming starts, the temperature of the discharged oxidant gas detected by the temperature sensor 60 reflects the heat release caused by partial oxidation reforming and thus becomes a temperature approximately equal to the highest temperature inside the fuel cell 20. Therefore, after the start of partial oxidation reforming, the controller 12 regards the temperature of the discharged oxidant gas obtained from the temperature sensor 60 as the highest temperature inside the fuel cell 20 and executes the subsequent steps for controlling the temperature of the fuel cell 20. In addition, in the case where the temperature of the discharged oxidant gas may deviate from the highest temperature inside the fuel cell 20 due to the operating state of the fuel cell 20 or the like to an extent that causes a control error, the detected temperature of the discharged oxidant gas can be corrected as needed. In this case, the controller 12 performs the following steps considering the correlation between the temperature of the discharged oxidant gas and the highest temperature inside the fuel cell 20. Additionally, in the case of using the temperature of the discharged oxidant gas to estimate the highest temperature inside the fuel cell 20, for example, a graph obtained by correlating the temperature of the discharged oxidant gas with the highest temperature inside the fuel cell 20 can be used.

[0050] In determination step S102, the controller 12 determines whether the temperature of the discharged oxidant gas is equal to or higher than the temperature at which partial oxidation reforming can be performed. That is, the controller 12 is configured to function as a determination unit. When the temperature of the discharged oxidant gas is lower than the temperature at which partial oxidation reforming can be performed, the controller 12 does not execute the steps following determination step S102, but continues to acquire the temperature of the discharged oxidant gas at a prescribed period. This is because when the temperature of the discharged oxidant gas, i.e., the maximum temperature of the fuel cell 20, does not reach the temperature at which partial oxidation reforming can be performed, partial oxidation reforming does not occur, and thus the heat cannot be used for the temperature control of the fuel cell 20. When the temperature of the discharged oxidant gas is equal to or higher than the temperature at which partial oxidation reforming can be performed, the controller 12 executes the temperature rise limit calculation step S103.

[0051] In the temperature rise limit calculation step S103, the controller 12 calculates the temperature rise limit ΔTm using the detected temperature Tq of the discharged oxidant gas. That is, the controller 12 is configured to function as a temperature rise limit calculation unit. The temperature rise limit ΔTm is the temperature obtained by subtracting the detected temperature Tq of the discharged oxidant gas from the heat-resistant upper limit temperature (hereinafter, simply referred to as the heat-resistant upper limit temperature) of the component with the lowest heat resistance among the single cell stack 21 and the other components constituting the fuel cell 20. In the present embodiment, the heat-resistant upper limit temperature Tk of the internal reforming catalyst 22 is the lowest among the heat-resistant upper limit temperatures of the single cell stack 21 and the other components of the fuel cell 20. Therefore, the controller 12 calculates the temperature rise limit ΔTm by ΔTm = Tk - Tq.

[0052] In the target heat release amount calculation step S104, the controller 12 calculates a prescribed target heat release amount Qt based on the temperature Tq of the discharged oxidant gas. Thereby, in the temperature control of the fuel cell 20, the controller 12 sets the target heat release amount Qt such that the temperature Tq of the discharged oxidant gas does not exceed the heat-resistant upper limit temperature Tk of the internal reforming catalyst 22. That is, the controller 12 is configured to function as a target heat release amount calculation unit and / or a target heat release amount setting unit. The target heat release amount Qt is the target value of the heat release amount caused by partial oxidation reforming. In addition, the target heat release amount Qt is the target value of the heat release amount per prescribed time (for example, the detection period of the temperature Tq of the discharged oxidant gas). Regarding the target heat release amount Qt, for example, the target heat release amount Qt can be obtained by Qt = ΔTm × Sh × Mc, where Sh is the specific heat of the single cell stack 21 or each single cell and Mc is the mass of the single cell in which partial oxidation reforming occurs. The controller 12 calculates the flow rate of the fuel (oxygen) for achieving the target heat release amount Qt based on the heat release amount obtained from the reaction formula of partial oxidation reforming.

[0053] In the fuel flow rate calculation step S105, the controller 12 calculates the flow rate of the raw fuel, i.e., the fuel flow rate Ff, based on the target heat release amount Qt. That is, the controller 12 is configured to function as a fuel flow rate calculation unit. The fuel flow rate Ff is the flow rate of the raw fuel required to achieve the target heat release amount Qt through partial oxidation reforming. When power generation starts in the single cell stack 21, the fuel flow rate Ff calculated in the fuel flow rate calculation step S105 is the flow rate of the raw fuel for maintaining power generation while achieving the target heat release amount Qt.

[0054] In the mixed air flow rate calculation step S106, the controller 12 calculates the amount of air mixed with the raw fuel, i.e., the mixed air flow rate Fa, based on the target heat release amount Qt. That is, the controller 12 is configured to function as a mixed air flow rate calculation unit. The mixed air flow rate Fa is the flow rate of air required to be mixed with the raw fuel to achieve the target heat release amount Qt through partial oxidation reforming. When power generation starts in the single cell stack 21, the mixed air flow rate Fa is the flow rate of oxygen-containing air corresponding to the amount of partial oxidation reforming that occurs.

[0055] In the control execution step S107, the controller 12 controls the fuel flow rate adjustment device 31 and the air flow rate adjustment device 33 respectively so as to achieve the calculated fuel flow rate Ff and mixed air flow rate Fa. That is, the controller 12 operates the fuel flow rate Ff and the mixed air flow rate Fa so that the heat release amount of partial oxidation reforming in the single cell stack 21 becomes the target heat release amount Qt. Therefore, the controller 12 is configured to function as a fuel flow rate control unit that controls the flow rate of the raw fuel supplied to the fuel cell 20 by the fuel flow rate adjustment device 31. In addition, the controller 12 is configured to function as a mixed air flow rate control unit that controls the flow rate of the air mixed into the raw fuel by the air flow rate adjustment device 33. In this way, by controlling the fuel flow rate Ff and the mixed air flow rate Fa, even when a temperature distribution that decreases from the anode inlet A1 to the anode outlet A2 is generated inside the fuel cell 20 due to partial oxidation reforming, the temperature of the fuel cell 20 is controlled within a range not exceeding the heat resistance upper limit temperature Tk of the internal reforming catalyst 22. Therefore, the fuel cell system 10 can continuously and efficiently operate without damaging the internal reforming catalyst 22 even when fuel reforming is performed by partial oxidation reforming inside the single cell stack 21.

[0056] As described above, in the operation scenario of performing warm-up operation at the start of the fuel cell system 10 and the operation scenario of restoring the temperature of the single cell stack 21 when the temperature of the single cell stack 21 decreases due to steam reforming or the like, the temperature control of the fuel cell 20 by the heat release of partial oxidation reforming in the single cell stack 21 is particularly useful. Hereinafter, these operation scenarios will be described in detail.

[0057] Figure 5is a graph schematically showing temperature control during warm-up operation. Temperature Ta is the temperature at which partial oxidation reforming can be performed, for example, about 300 degrees. Temperature Tb is the temperature at which power generation can be performed when the fuel cell 20 is a solid oxide fuel cell, for example, about 500 degrees. Temperature Tc is the temperature maintained during stable operation considering power generation efficiency when the fuel cell 20 is a solid oxide fuel cell, for example, about 800 degrees to 1000 degrees. Additionally, Figure 5 Each of the curves G1 to G6 represents the temperature of the oxidant gas when measured at a prescribed time interval or the like.

[0058] When starting the fuel cell system 10 and performing warm-up operation until the temperature region where the fuel cell 20 can generate power is reached, the temperature of the fuel cell 20 is low compared to the temperature at which power generation is possible. Therefore, the controller 12 supplies the oxidant gas and the raw fuel to the burner 51 and at the same time causes the heated oxidant gas to flow to the fuel cell 20, thereby warming up the fuel cell 20. As a result, as shown by the curves G1 and G2, the temperature of the fuel cell 20 gradually rises and approaches the temperature at which power generation is possible. Temperature Td1 is the temperature Tq of the discharged oxidant gas at the time point of curve G1. Temperature Td2 is the temperature Tq of the discharged oxidant gas at the time point of curve G2.

[0059] Here, when continuing the above-described warm-up operation using the overheated oxidant gas, as shown by the intervals between the curves G1 to G3, the rate of temperature rise of the fuel cell 20 is slow, and it takes a long time until the fuel cell 20 reaches the temperature at which power generation is possible. Therefore, as shown by curve G3, when the temperature Tq of the discharged oxidant gas reaches temperature Td3 and becomes a temperature above the temperature Ta at which partial oxidation reforming can be performed, the controller 12 calculates the temperature rise limit ΔTm, that is, the temperature rise limit δ3, at the time point of curve G3 by subtracting the detected temperature Td3 of the discharged oxidant from the heat-resistant upper limit temperature Tk. The controller 12 calculates the target heat release amount Qt based on the temperature rise limit δ3, and calculates the fuel flow rate Ff and the mixed air flow rate Fa based on the calculated target heat release amount Qt. After that, if the controller 12 controls the fuel flow rate adjusting device 31 and the air flow rate adjusting device 33 according to the calculated fuel flow rate Ff and the mixed air flow rate Fa respectively, then as shown by curve G3*, partial oxidation reforming is performed within the prescribed range Rpox of the single cell stack 21. As a result, the temperature of the prescribed range Rpox rises due to the heat release of partial oxidation reforming. However, within the prescribed range Rpox, the maximum temperature of the fuel cell 20 is also below the heat-resistant upper limit temperature Tk.

[0060] The heat generated by the partial oxidation reforming of the curve G3* propagates in the single cell stack 21. Therefore, as shown by the curve G4, at the timing when the temperature Tq of the discharged oxidant gas is to be detected next, the interval from the curve G3 to the curve G4 becomes larger compared to the intervals of the respective curves from the curve G1 to the curve G3. That is, in the operation scenario of warm-up operation, the warm-up of the fuel cell 20 is promoted by the occurrence of partial oxidation reforming.

[0061] At the time point of the curve G4, the temperature Tq of the discharged oxidant gas is the temperature Td4, which is lower than the power generation temperature Tb but higher than the temperature Ta at which partial oxidation reforming can occur. Therefore, the controller 12 performs partial oxidation reforming again in the single cell stack 21 in the same manner as described above, and promotes the warm-up of the fuel cell 20 by the heat of this partial oxidation reforming. That is, the controller 12 calculates the temperature rise limit δ4 at the time point of the curve G4. Then, the controller 12 calculates the target heat release amount Qt based on the temperature rise limit δ4, and calculates and controls the fuel flow rate Ff and the mixed air flow rate Fa based on the calculated target heat release amount Qt. As a result, as shown by the curve G4*, partial oxidation reforming occurs within the specified range Rpox of the single cell stack 21, and the warm-up of the fuel cell 20 is promoted again by the propagation of the heat of this partial oxidation reforming.

[0062] The temperature rise limit δ4 at the time point of the curve G4 is smaller than the temperature rise limit δ3 at the time point of the curve G3. Therefore, the target heat release amount Qt at the time point of the curve G4 is naturally smaller than the target heat release amount Qt at the time point of the curve G3. In addition, the fuel flow rate Ff and the mixed air flow rate Fa at the time point of the curve G4 are also smaller than the fuel flow rate Ff and the mixed air flow rate Fa at the time point of the curve G3. As a result, regarding the heat release amount of the partial oxidation reforming occurring within the specified range Rpox of the single cell stack 21, the heat release amount at the time point of the curve G4 is suppressed compared to the heat release amount at the time point of the curve G3. As a result, even if partial oxidation reforming is additionally performed at the time point of the curve G4, the maximum temperature of the fuel cell 20 is maintained below the heat resistance upper limit temperature Tk.

[0063] Thereafter, as shown by curve G5, when the temperature Tq of the discharged oxidant gas becomes temperature Td5 and exceeds the temperature Tb at which power generation is possible, power generation is started in the single cell stack 21 by supplying fuel and the oxidant gas. Generally, the higher the temperature of the fuel cell 20, the higher the power generation efficiency of the fuel cell 20. Therefore, the fuel cell 20 operates while maintaining as high a temperature as possible within the range below the heat resistance upper limit temperature Tk. Thus, even when the temperature Tc, which is the target for stable operation, is not reached as shown by curve G5 even after the start of power generation, the controller 12 continues the warm-up of the fuel cell 20 in the same manner as described above. That is, the controller 12 calculates the temperature rise limit δ5 at the time point of curve G5. Then, the controller 12 calculates the target heat release amount Qt based on the temperature rise limit δ5, and calculates and controls the fuel flow rate Ff and the mixed air flow rate Fa based on the calculated target heat release amount Qt. As a result, as shown by curve G4*, partial oxidation reforming occurs within the specified range Rpox of the single cell stack 21, and the warm-up of the fuel cell 20 is promoted by propagating the heat of the partial oxidation reforming. As a result, at the time point of curve G6, the temperature Tq of the discharged oxidant gas becomes temperature Td6, and the overall temperature of the fuel cell 20 also exceeds the temperature Tc maintained during stable operation. Thus, compared with the case where warm-up operation is performed by flowing only the oxidant gas heated by the heater or the burner 51 as in the past, the warm-up operation can be completed in a short time, and the fuel cell system 10 can shift to stable operation in which power generation is performed in the single cell stack 21.

[0064] Figure 6It is a graph schematically showing temperature control during stable operation. Even when the temperature of the fuel cell 20 substantially exceeds the temperature Tc maintained during stable operation and stable operation continues, the temperature of the fuel cell 20 sometimes decreases depending on the heat absorption amount generated by steam reforming or the like, the load applied to the fuel cell 20, and the like. For example, when the output power required for the fuel cell 20 is medium or low and the load applied to the fuel cell 20 is a low load or a medium load and stable operation is performed, the temperature distribution inside the fuel cell 20 becomes a temperature distribution in which the temperature substantially rises from the cathode inlet C3 to the cathode outlet C4. This is because, in the fuel cell 20 of the present embodiment, in the case of a low load or a medium load, the heat generated by power generation is small, but the heat absorption amount generated by steam reforming or the like is even smaller, so the heat release amount generated by power generation exceeds the heat absorption amount generated by steam reforming or the like. On the other hand, when the output power required for the fuel cell 20 is large and the load applied to the fuel cell 20 is high, the temperature distribution inside the fuel cell 20 sometimes becomes a temperature distribution in which the temperature decreases from the cathode inlet C3 to the cathode outlet C4. This is because, in the fuel cell 20 of the present embodiment, in the case of a high load, the heat generated by power generation is large, but the heat absorption amount generated by steam reforming or the like is even larger, so the heat release amount generated by power generation is lower than the heat absorption amount generated by steam reforming or the like. Thus, if the fuel cell 20 continues stable operation in a high-load state, for example, as shown by the curve G7, although after the start of stable operation, the temperature of the fuel cell 20 sometimes becomes lower than the temperature Tc that should be maintained during stable operation. In such a state, if stable operation is simply continued, the temperature of the fuel cell 20 will also be lower than the temperature Tb at which power generation can be performed, and it may be impossible to continue power generation.

[0065] Therefore, even after the controller 12 transitions to stable operation, it continues to detect the temperature Tq of the exhausted oxidant gas. Moreover, when the temperature Tq of the exhausted oxidant gas is below the temperature Tc that should be maintained during stable operation, the controller 12 heats the fuel cell 20 by the exotherm of partial oxidation reforming. For example, when the temperature Tq of the exhausted oxidant gas is the temperature Td7 as shown by the curve G7 and is lower than the temperature Tc that should be maintained during stable operation, the controller 12 calculates the temperature increase limit δ7. Then, the controller 12 calculates the target heat release amount Qt based on the temperature increase limit δ7, and calculates and controls the fuel flow rate Ff and the mixed air flow rate Fa based on the calculated target heat release amount Qt. As a result, as shown by the curve G7*, partial oxidation reforming occurs within the specified range Rpox of the single cell stack 21. Then, by propagating the heat of the partial oxidation reforming that has occurred, as shown by the curve G8, the temperature of the fuel cell 20 becomes a temperature above the temperature Tc that should be maintained during stable operation. As a result of this temperature control, even when the fuel cell 20 continues to be in a high-load state, it is possible to continue power generation while satisfying the required output power. In addition, in the case of performing temperature control to maintain the temperature of the fuel cell 20 at a temperature above the temperature Tc that should be maintained during stable operation in this way, the controller 12 also performs temperature control based on the temperature Tq of the exhausted oxidant gas. Therefore, even when observed locally, the temperature of the fuel cell 20 does not exceed the heat-resistant upper limit temperature Tk. Thus, the fuel cell system 10 can stably continue stable operation without damaging the fuel cell 20 or the like.

[0066] As described above, the control method of the fuel cell system 10 according to one embodiment is a control method of the fuel cell system 10 including the fuel cell 20. The fuel cell 20 includes: a single cell stack 21 having an internal reforming catalyst 22, which is a reforming catalyst for generating hydrogen from a hydrocarbon; a first flow path 23 for supplying a hydrocarbon-containing fuel to the single cell stack 21; and a second flow path 24 for supplying the oxidant gas to the single cell stack 21 in such a manner that the oxidant gas and the fuel flow either in opposite directions or orthogonally. In the control method of the fuel cell system 10, the temperature Tq of the oxidant gas exhausted from the second flow path 24, that is, the exhausted oxidant gas, is detected, and the temperature of the fuel cell 20 is controlled based on the temperature Tq of the exhausted oxidant gas.

[0067] In the control method of the fuel cell system 10, as described above, since the fuel cell 20 is of the internally reforming type, the vicinity of the anode inlet A1 sometimes becomes relatively hotter compared to the central portion of the single cell stack 21. In addition, the fuel cell 20 is a so-called counterflow or crossflow type, and the temperature of the cathode outlet C4 can be regarded as the temperature of the anode inlet A1, which is a relatively hot portion. Moreover, the controller 12 of the fuel cell system 10 performs temperature control of the fuel cell 20 based on the temperature Tq of the discharged oxidant gas detected at the cathode outlet C4 near the anode inlet A1. That is, in the control method of the fuel cell system 10 according to the above-described embodiment, temperature control is performed based on the temperature of the relatively hot portion within the fuel cell 20, so that stable control that complies with the heat-resistant upper limit temperature Tk as the heat-resistant reference can be more reliably achieved.

[0068] On the other hand, in the case of performing temperature control of the fuel cell 20 based on the temperature of the central portion of the fuel cell 20 as in the past, in an operating scenario where the fuel cell 20 is of the internally reforming type and the vicinity of the anode inlet A1 becomes relatively hotter compared to the central portion of the single cell stack 21, the relatively hot portion near the anode inlet A1 exceeds the heat-resistant upper limit temperature Tk as the heat-resistant reference, and there is a possibility that the fuel cell 20 may be damaged or the like. Therefore, compared with the control method of the conventional fuel cell system, the control method of the fuel cell system 10 according to the above-described embodiment does not cause damage to the fuel cell 20 or the like and can operate more reliably and stably.

[0069] As an example of a scenario where the vicinity of the anode inlet A1 is more likely to become a relatively hot portion compared to the central portion of the single cell stack 21, there is an operating scenario in which partial oxidation reforming occurs. Therefore, the above-described control method of the fuel cell system 10 is particularly suitable for the case where partial oxidation reforming occurs in the single cell stack 21.

[0070] For example, when partial oxidation reforming is actively carried out starting from a low temperature region of about 300 degrees Celsius to promote the warm-up (temperature rise) of the fuel cell 20, due to the heat release of partial oxidation reforming, the anode inlet A1 side becomes the highest temperature in the temperature distribution within the fuel cell 20. Therefore, when partial oxidation reforming is carried out for the warm-up of the fuel cell 20, the temperature Tq of the discharged oxidant gas is also detected by the temperature sensor 60 provided at the cathode outlet C4 as described above, and the temperature control of the fuel cell 20 is performed based on the detected temperature Tq of the discharged oxidant gas. Thus, the warm-up of the fuel cell 20 can be promoted within a range where the heat-resistant upper limit temperature Tk is not exceeded even when observed locally. In addition, as in the above-described embodiment, when the fuel and the oxidant gas are in a countercurrent flow, the temperature Tq of the discharged oxidant gas detected by the temperature sensor 60 is substantially equal to the highest temperature of the fuel cell 20. Therefore, the above-described temperature control can be performed particularly accurately.

[0071] In addition, in the control method of the fuel cell system 10 according to the above-described embodiment, the temperature control of the fuel cell 20 is particularly performed so that the temperature of the fuel cell 20 becomes equal to or lower than the heat-resistant upper limit temperature Tk which is a specified temperature. Moreover, the heat-resistant upper limit temperature Tk is arbitrary. Therefore, the control method of the fuel cell system 10 according to the above-described embodiment is particularly suitable for the case where the temperature of the fuel cell 20 is controlled to be equal to or lower than a specified temperature, and stable control with reduced risks such as damage to the fuel cell 20 and the fuel cell system 10 can be achieved.

[0072] In addition to the above-described basic structure, the fuel cell system 10 of the above-described embodiment further includes: a fuel flow rate adjusting device 31 that adjusts the flow rate of the fuel supplied to the fuel cell 20; and an air flow rate adjusting device 33 that adjusts the flow rate of the air mixed with the fuel. Moreover, in the control method of the fuel cell system 10 of the above-described embodiment, in the temperature control of the fuel cell 20, specifically, the flow rate of the fuel, i.e., the fuel flow rate Ff, and the flow rate of the air mixed with the fuel, i.e., the mixed air flow rate Fa, are operated so that the heat release amount of partial oxidation reforming in the cell stack 21 becomes a specified target heat release amount Qt based on the temperature Tq of the discharged oxidant gas. Therefore, the control method of the fuel cell system 10 of the above-described embodiment realizes the temperature control of the fuel cell 20 by using the method of partial oxidation reforming that inevitably occurs due to the properties of the internal reforming catalyst 22. That is, in the control method of the fuel cell system 10 of the above-described embodiment, the temperature control of the fuel cell 20 is realized without the need to prepare a special heat source or cold heat source.

[0073] Further, in the fuel cell system 10, partial oxidation reforming is actively carried out by mixing air with fuel using the air flow regulating device 33. Moreover, in the fuel cell system 10, the target heat release amount Qt is determined based on the temperature Tq of the exhausted oxidant gas, and the fuel flow rate Ff and the mixed air flow rate Fa are controlled. As a result, in the fuel cell system 10, the temperature of the fuel cell 20 is controlled by controlling the heat release amount of the partial oxidation reforming that occurs. In this way, when controlling the heat release of the partial oxidation reforming based on the temperature Tq of the exhausted oxidant gas, the temperature control of the fuel cell 20 can be appropriately performed. In particular, in the case of warming up the fuel cell 20 and in the case of wanting to maintain the temperature of the fuel cell 20 for continuous use at a high load, the fuel cell system 10 can particularly appropriately control the temperature of the fuel cell 20 within a range not exceeding the heat resistance upper limit temperature Tk even when observed locally. Regarding the warming up of the fuel cell 20, the above temperature control using the heat release of the partial oxidation reforming can promote the warming up. In addition, in the case of using the fuel cell 20 at a high load, the temperature Tc that should be maintained for stable operation can be maintained.

[0074] In the control method of the fuel cell system 10 of the above embodiment, specifically, the target heat release amount Qt is set such that the temperature Tq of the exhausted oxidant gas does not exceed the heat resistance upper limit temperature Tk of the internal reforming catalyst 22 that is the reforming catalyst. Thereby, the temperature of the fuel cell 20 can be particularly appropriately controlled within a range not exceeding the heat resistance upper limit temperature Tk even when observed locally.

[0075] In the control method of the fuel cell system 10 of the above embodiment, specifically, when the temperature Tq of the exhausted oxidant gas is equal to or higher than the temperature at which partial oxidation reforming can be carried out in the single cell stack 21, the temperature control of the fuel cell 20 for supplying fuel and air mixed with the fuel is performed. Thereby, only when reaching the temperature region where partial oxidation reforming can be carried out, the mixed gas of fuel and air is appropriately supplied, so that the temperature control of the fuel cell 20 using the heat release of the partial oxidation reforming can be implemented. As a result, waste of fuel can be avoided, and adverse conditions such as carbon precipitation can also be prevented.

[0076] In addition, the fuel cell system 10 of the above-described embodiment includes a fuel cell 20, a temperature sensor 60, and a controller 12. The fuel cell 20 includes: a single cell stack 21 having an internal reforming catalyst 22 that generates hydrogen from a hydrocarbon; a first flow path 23 for supplying a hydrocarbon-containing fuel to the single cell stack 21; and a second flow path 24 for supplying an oxidant gas to the single cell stack 21 such that the oxidant gas flows in a direction facing or orthogonal to the fuel. The temperature sensor 60 detects the temperature Tq of the oxidant gas discharged from the second flow path 24, i.e., the discharged oxidant gas. The controller 12 controls the temperature of the fuel cell 20 based on the temperature Tq of the discharged oxidant gas.

[0077] The fuel cell system 10 can change its structure within the scope not departing from the gist of the temperature control of the fuel cell 20 according to the above-described embodiment. For example, in the above-described embodiment, an example of controlling the temperature of the fuel cell 20 by using the heat released by partial oxidation reforming is described. However, as long as the temperature of the fuel cell 20 can be controlled based on the temperature Tq of the discharged oxidant gas, the temperature of the fuel cell 20 can be controlled by a method other than using the heat released by partial oxidation reforming, such as heating with a heater. For example, instead of using the heat released by partial oxidation reforming, the controller 12 can also control the supply amount of air supplied by the oxidant gas supply device 41 or the supply amounts of fuel, exhaust gas, and / or fresh air supplied to the burner 51 so that the temperature Tq of the discharged oxidant gas becomes a desired temperature (e.g., comply with a specified upper limit temperature). However, the temperature control of the fuel cell 20 using partial oxidation reforming as in the above-described embodiment does not require a special structure for controlling the temperature of the fuel cell 20, and thus is particularly preferred.

[0078] (Second Embodiment)

[0079] The fuel cell system 10 of the above-described first embodiment includes an internally reforming type fuel cell 20 having a single cell stack 21 with an internal reforming catalyst 22. Such an internally reforming type fuel cell 20 is used by supplying a slightly excessive amount of raw fuel to prevent carbon precipitation and the like. Therefore, the fuel utilization rate is low. Therefore, the fuel cell system 10 of the above-described first embodiment can improve the fuel utilization rate by also using other fuel cells as follows.

[0080] Figure 7 It is a block diagram showing the structure of the fuel cell system 210 of the second embodiment. The fuel cell system 210 of the second embodiment uses the fuel cell 20 of the fuel cell system 10 of the first embodiment as the first fuel cell and adds a second fuel cell 220. Therefore, the same structures as those of the fuel cell system 10 of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and the description thereof is omitted.

[0081] The second fuel cell 220 is a fuel cell having fewer single cell stacks 221 than the fuel cell 20 which is the first fuel cell. In the present embodiment, the single cell stack 221 of the second fuel cell 220 is a solid oxide type fuel cell not having the internal reforming catalyst 22. That is, the second fuel cell 220 generates electricity by being supplied with reformed fuel.

[0082] The anode inlet A3 of the second fuel cell 220 is connected to the anode outlet A2 of the fuel cell 20. In addition, the anode outlet A4 of the second fuel cell 220 is connected to the burner 51 via the fuel discharge path 34. That is, the fuel discharged from the fuel cell 20 is supplied to the second fuel cell 220 as fuel. Since the raw fuel is supplied slightly in excess, the discharged fuel of the fuel cell 20 is not completely used as fuel, but hydrogen remains and it can still be used as fuel. On the other hand, the discharged fuel of the fuel cell 20 reforms almost all of the raw fuel into hydrogen through internal reforming in the fuel cell 20. Thus, the discharged fuel of the fuel cell 20 is used as reformed fuel in the second fuel cell 220.

[0083] The cathode inlet C1 of the second fuel cell 220 is connected to the oxidant gas supply device 41 via the oxidant gas supply path 42. In addition, the cathode outlet C2 of the second fuel cell 220 is connected to the cathode inlet C3 of the fuel cell 20. That is, the second fuel cell 220 uses the oxidant gas supplied from the oxidant gas supply device 41 for power generation. After that, the second fuel cell 220 supplies the oxidant gas (discharged oxidant gas) discharged from the second fuel cell 220 to the fuel cell 20 as oxidant gas. The discharged oxidant gas of the second fuel cell 220 contains oxygen and can sufficiently function as oxidant gas also in the fuel cell 20.

[0084] As described above, the fuel cell system 210 of the second embodiment includes, in addition to the fuel cell 20 which is the first fuel cell, a second fuel cell 220. Moreover, the fuel discharged from the fuel cell 20 is supplied to the second fuel cell 220. As a result, in the internally reforming type fuel cell 20, the raw fuel is supplied slightly in excess for use, so the fuel utilization rate is low, but the discharged fuel of the fuel cell 20 is reused in the second fuel cell 220 for power generation. Thus, the fuel cell system 210 can use the raw fuel with almost no remainder for power generation and can improve the fuel utilization rate compared with the fuel cell system 10 of the first embodiment.

[0085] In addition, the fuel cell system 210 of the second embodiment supplies, as the oxidant gas, the exhaust oxidant gas, which is the oxidant gas discharged from the second fuel cell 220, to the fuel cell 20. When an endothermic reaction such as steam reforming occurs inside the fuel cell 20, the temperature of the fuel cell 20 decreases. However, as described above, the exhaust oxidant gas heated by power generation in the second fuel cell 220 is supplied to the fuel cell 20 as the oxidant gas, making it easy to maintain the heat balance between the heat release caused by power generation in the fuel cell 20 and the endotherm caused by fuel reforming. In addition, it is easy to maintain the heat balance even when looking at the fuel cell system 210 as a whole. Therefore, the controller 12 can more stably and efficiently maintain the stable operation of the internally reforming type fuel cell 20.

[0086] In addition, the second fuel cell 220 added to the fuel cell system 210 of the second embodiment uses a fuel cell with fewer internal reforming catalysts 22 than the fuel cell 20. Therefore, in the second fuel cell 220, endothermic reactions such as steam reforming rarely occur. Thus, by supplying the exhaust oxidant gas of the second fuel cell 220 to the fuel cell 20, the controller 12 can particularly easily maintain the heat balance between the heat release caused by power generation in the fuel cell 20 and the endotherm caused by fuel reforming. In addition, it is easy to maintain the heat balance even when looking at the fuel cell system 210 as a whole. Moreover, when the second fuel cell 220 does not have the internal reforming catalyst 22 as in the second embodiment described above, it is easiest to maintain their heat balance.

[0087] (Modified Example)

[0088] In the above-described first and second embodiments, the temperature sensor 60 is provided at the cathode outlet C4 where the second flow paths 24 branched into a plurality of paths inside the cell stack 21 are merged into one flow path again. However, the arrangement of the temperature sensor 60 can be arbitrarily changed within the range where the maximum temperature in the temperature distribution inside the fuel cell 20 can be detected or estimated. For example, Figure 8 FIG. is an explanatory diagram of a modified example in which the installation position of the temperature sensor 60 is changed. As Figure 8 shown, a flow path 301 can be provided and the temperature sensor 60 can be provided in the flow path 301. The flow path 301 leads out a part of the second flow path 24 branched inside the cell stack 21 and merges it into the cathode outlet C4. In this way, if the temperature sensor 60 is provided in the flow path 301 that leads out a part of the second flow path 24, even when a temperature distribution is formed in the fuel cell 20 in the Y direction perpendicular to the first flow path 23 and the second flow path 24 due to the overall structure of the fuel cell 20, the controller 12 can easily and accurately detect or estimate the maximum temperature of the fuel cell 20 regardless of the temperature distribution in the Y direction.

[0089] In the above-described first and second embodiments, the fuel and the oxidant gas of the fuel cell 20 are in a counter flow, but the fuel and the oxidant gas of the fuel cell 20 can be changed to a so-called cross flow. For example, Figure 9 FIG. is an explanatory diagram of a modified example in which the structure of the flow paths of the fuel and the oxidant gas is changed. That is, the fuel cell 20 can employ a single cell stack 302 instead of the counter-flow single cell stack 21. The single cell stack 302 changes the second flow path 24 into a flow path that supplies the oxidant gas to the single cell stack 21 in such a manner that the oxidant gas flows orthogonally to the fuel. Thus, even when the single cell stack 302 in which the fuel and the oxidant gas are in a so-called cross flow is employed, the control methods of the above-described first and second embodiments can be executed and the effects thereof can be obtained. This is because, in the cross-flow single cell stack 302, the temperature of the discharged oxidant gas also has a certain correlation with the highest temperature in the temperature distribution within the fuel cell 20. Therefore, the controller 12 can estimate the highest temperature within the fuel cell 20 based on the temperature of the discharged oxidant gas.

[0090] In addition, a single cell stack with a parallel flow in which the first flow path 23 and the second flow path 24 are parallel and the fuel and the oxidant gas flow in parallel in these flow paths can also be employed. In this case, the control methods of the above-described first and second embodiments can be executed and the effects thereof can be obtained. However, in order to make the temperature distribution within the fuel cell 20 closer to uniform to improve the power generation efficiency, whether or not partial oxidation reforming is performed, it is preferable to employ the counter-flow single cell stack 21 or the cross-flow single cell stack 302, and it is particularly preferable to employ the counter-flow single cell stack 21.

[0091] Figure 10 FIG. is an explanatory diagram of a modified example in which the structure of the flow paths of the fuel and the oxidant gas and the installation position of the temperature sensor 60 are changed with respect to the above-described first and second embodiments. Figure 10 In a modified example of the fuel cell 20, on the basis of employing the cross-flow single cell stack 302, a flow path 303 that leads out a part of the second flow path 24 and joins the cathode outlet C4 is provided. Moreover, the temperature sensor 60 is provided in this flow path 303. Thus, in the case of employing the cross-flow single cell stack 302, if the flow path 303 that leads out a part of the second flow path 24 is provided and the temperature sensor 60 is provided in this flow path, the correlation between the highest temperature in the temperature distribution within the fuel cell 20 and the temperature Tq of the discharged oxidant gas to be detected becomes higher. Therefore, the accuracy is improved when the controller 12 estimates the highest temperature within the fuel cell 20. As a result, the accuracy of the temperature control of the fuel cell 20 is improved. In particular, if Figure 10If the flow path 303 is provided on the anode inlet A1 side where partial oxidation reforming occurs relatively frequently as shown, in the case where the highest temperature part is generated on the anode inlet A1 side in the fuel cell 20 due to the heat release of partial oxidation reforming, the temperature can be directly and accurately detected. Therefore, the temperature control of the fuel cell 20 by the controller 12 can be particularly accurately implemented.

[0092] The embodiments of the present invention have been described above. The above embodiments only show a part of the application examples of the present invention. It is not intended to limit the technical scope of the present invention to the specific structures of the above embodiments. Various changes and modifications can be made to the above embodiments within the scope of the matters described in the claims. In addition, the technical ideas described in the above embodiments and modification examples can be appropriately combined.

Claims

1. A control method for a fuel cell system, the fuel cell system comprising a fuel cell having: a single cell stack having a reforming catalyst for generating hydrogen from a hydrocarbon; a first flow path for supplying a hydrocarbon-containing fuel to the single cell stack; and a second flow path for supplying an oxidant gas to the single cell stack in such a manner that the oxidant gas flows toward or orthogonally to the fuel, in the control method of the fuel cell system, detect the temperature of the oxidant gas discharged from the second flow path, i.e., the temperature of the discharged oxidant gas; when supplying air to the first flow path to perform partial oxidation reforming in the single cell stack, perform temperature control of the fuel cell based on the temperature of the discharged oxidant gas; the fuel cell system further comprises: a fuel flow rate adjusting device for adjusting the flow rate of the fuel supplied to the fuel cell; and an air flow rate adjusting device for adjusting the flow rate of the air mixed with the fuel; in the temperature control of the fuel cell, operate the flow rate of the fuel and the flow rate of the air such that the heat release amount of the partial oxidation reforming in the single cell stack becomes a prescribed target heat release amount based on the temperature of the discharged oxidant gas.

2. The control method for a fuel cell system according to claim 1, wherein, in the temperature control of the fuel cell, set the target heat release amount such that the temperature of the discharged oxidant gas does not exceed the heat-resistant upper limit temperature of the reforming catalyst.

3. The control method for a fuel cell system according to claim 1 or 2, wherein, when the temperature of the discharged oxidant gas is equal to or higher than the temperature at which partial oxidation reforming can be performed in the single cell stack, perform the temperature control of the fuel cell.

4. A fuel cell system, comprising: The first fuel cell includes a single cell stack, a first flow path, and a second flow path, where the single cell stack has a reforming catalyst for generating hydrogen from a hydrocarbon, the first flow path is for supplying a hydrocarbon-containing fuel to the single cell stack, and the second flow path is for supplying the oxidant gas to the single cell stack in such a manner that the oxidant gas flows toward or orthogonally to the fuel; a temperature sensor for detecting the temperature of the oxidant gas discharged from the second flow path, i.e., the temperature of the discharged oxidant gas; and a controller that, when supplying air to the first flow path to perform partial oxidation reforming in the single cell stack, performs temperature control of the first fuel cell based on the temperature of the discharged oxidant gas, the fuel cell system further comprises: a fuel flow rate adjusting device for adjusting the flow rate of the fuel supplied to the first fuel cell; and an air flow rate adjusting device for adjusting the flow rate of the air mixed with the fuel; in the temperature control of the first fuel cell, operate the flow rate of the fuel and the flow rate of the air such that the heat release amount of the partial oxidation reforming in the single cell stack becomes a prescribed target heat release amount based on the temperature of the discharged oxidant gas.

5. The fuel cell system according to claim 4, wherein, it further comprises a second fuel cell, and the second fuel cell is supplied with the fuel discharged from the first fuel cell.

6. The fuel cell system according to claim 5, wherein, The oxidant gas discharged from the second fuel cell is supplied to the first fuel cell.

7. The fuel cell system according to claim 5 or 6, wherein, The second fuel cell has less reforming catalyst than the first fuel cell.

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