Fuel cell system

Abstract

A fuel cell system (1) comprises a first sub-fuel cell system (100) and a second sub-fuel cell system (200). The first sub-fuel cell system (100) comprises a first fuel cell stack (110) and a first cooling path (150). The second sub-fuel cell system (200) comprises a second fuel cell stack (210) and a second cooling path (250). A first cooling medium (15) for cooling the first fuel cell stack (110) flows through the first cooling path (150). A second cooling medium (25) for cooling the second fuel cell stack (210) flows through the second cooling path (250). The first cooling path (150) and the second cooling path (250) are independent of each other. The temperature of the second fuel cell stack (210) during power generation is higher than the temperature of the first fuel cell stack (110) during power generation.

Description

Fuel cell system

[0001] The present disclosure relates to a fuel cell system.

[0002] As a power generation device, a fuel cell is known. A fuel cell generates heat during power generation. Patent Documents 1 and 2 describe a fuel cell system in which heat is extracted together with the power generated by a plurality of fuel cells.

[0003] Japanese Patent Application Laid-Open No. 2008-277017 Japanese Patent Application Laid-Open No. 2020-136041

[0004] The present disclosure provides a fuel cell system suitable for achieving both stable extraction of power and supply of high-temperature heat.

[0005] The fuel cell system according to the present disclosure includes a first sub-fuel cell system including a first fuel cell stack and a first cooling path through which a first cooling medium for cooling the first fuel cell stack flows, and a second sub-fuel cell system including a second fuel cell stack and a second cooling path through which a second cooling medium for cooling the second fuel cell stack flows. The first cooling path and the second cooling path are independent of each other, and the temperature of the second fuel cell stack during power generation is higher than the temperature of the first fuel cell stack during power generation. A fuel cell system is provided.

[0006] The fuel cell system according to the present disclosure is suitable for achieving both stable extraction of power and supply of high-temperature heat.

[0007] Configuration diagram of the fuel cell system according to Embodiment 1, Explanation diagram of the humidifier and the gas-liquid separator according to Embodiment 1, Configuration diagram of the fuel cell system according to Embodiment 2, Explanation diagram of the humidifier and the gas-liquid separator according to Embodiment 2, Configuration diagram of the fuel cell system according to Embodiment 3, Configuration diagram of the fuel cell system according to Embodiment 4, Configuration diagram of the fuel cell system according to Embodiment 5, Configuration diagram of the fuel cell system according to Embodiment 6

[0008] (Knowledge and other information forming the basis of this disclosure) A low temperature of the fuel cell stack is advantageous from the viewpoint of suppressing the deterioration of the power generation performance of the fuel cell stack. A high temperature of the fuel cell stack is advantageous from the viewpoint of utilizing the heat generated by the fuel cell stack. Furthermore, separating the path through which the medium that exchanges heat with the relatively low temperature fuel cell stack flows from the path through which the medium that exchanges heat with the relatively high temperature fuel cell stack flows is advantageous from the viewpoint of supplying high-temperature heat originating from the high-temperature fuel cell stack. Taking these factors into consideration, the inventors have investigated a technology suitable for achieving both stable power extraction and high-temperature heat supply. This disclosure is based on such investigations.

[0009] Embodiments will be described in detail below with reference to the drawings. However, descriptions that are unnecessarily detailed may be omitted. For example, detailed descriptions of already well-known matters or redundant descriptions of substantially identical configurations may be omitted. The accompanying drawings and the following description are provided for the full understanding of the disclosure by those skilled in the art and are not intended to limit the subject matter described in the claims.

[0010] (Embodiment 1) Figure 1A is a diagram showing the configuration of a fuel cell system 1 according to Embodiment 1. The fuel cell system 1 includes a first sub-fuel cell system 100, a second sub-fuel cell system 200, a fuel path 300, an oxidizer path 400, and a control device 10.

[0011] For example, the first sub-fuel cell system 100 and the second sub-fuel cell system 200 are stationary subsystems. For example, the first sub-fuel cell system 100 and the second sub-fuel cell system 200 are separated from each other by different enclosures.

[0012] The fuel path 300 is shared by the first sub-fuel cell system 100 and the second sub-fuel cell system 200. The fuel path 300 supplies fuel gas 13 to the first sub-fuel cell system 100 and the second sub-fuel cell system 200. In Embodiment 1, the fuel path 300 is constructed using piping.

[0013] The oxidizer path 400 is shared by the first sub-fuel cell system 100 and the second sub-fuel cell system 200. The oxidizer path 400 supplies oxidizer gas 14 to the first sub-fuel cell system 100 and the second sub-fuel cell system 200. In Embodiment 1, the oxidizer path 400 is configured using piping.

[0014] The first sub-fuel cell system 100 includes a first fuel cell stack 110, a first cooling path 150, and a first heat exhaust path 160. The first sub-fuel cell system 100 also includes a pump 120, a first tank 151, a first pump 152, and a first heat exchanger 161. Furthermore, the first sub-fuel cell system 100 includes a first blower 130.

[0015] The first fuel cell stack 110 includes a pair of first current collector plates and a plurality of first fuel cell cells. The plurality of first fuel cell cells are stacked between the pair of first current collector plates. Each first fuel cell includes a first membrane electrode assembly (MEA). The first membrane electrode assembly includes a first anode, a first cathode, and a first electrolyte membrane. The first electrolyte membrane is sandwiched between the first anode and the first cathode. Each of the first anode and the first cathode contains a catalyst.

[0016] In Embodiment 1, the first fuel cell stack 110 is a polymer electrolyte fuel cell. The first cooling path 150 is configured using piping. The first heat exhaust path 160 is configured using piping. The pump 120 is a booster pump.

[0017] The second sub-fuel cell system 200 includes a second fuel cell stack 210, a second cooling path 250, and a second heat exhaust path 260. The second sub-fuel cell system 200 also includes a pump 220, a second tank 251, a second pump 252, and a second heat exchanger 261.

[0018] The second fuel cell stack 210 includes a pair of second current collector plates and a plurality of second fuel cell cells. The plurality of second fuel cell cells are stacked between the pair of second current collector plates. The second fuel cell cell includes a second membrane electrode assembly (MEA). The second membrane electrode assembly includes a second anode, a second cathode, and a second electrolyte membrane. The second electrolyte membrane is sandwiched between the second anode and the second cathode. Each of the second anode and the second cathode contains a catalyst.

[0019] In Embodiment 1, the second fuel cell stack 210 is a polymer electrolyte fuel cell. The second cooling path 250 is configured using piping. The second heat exhaust path 260 is configured using piping. The pump 220 is a booster pump.

[0020] In Embodiment 1, the catalyst contained in the first anode and the catalyst contained in the second anode have different compositions. However, the catalyst contained in the first anode and the catalyst contained in the second anode may have the same composition.

[0021] In Embodiment 1, the catalyst contained in the first cathode and the catalyst contained in the second cathode have different compositions. However, the catalyst contained in the first cathode and the catalyst contained in the second cathode may have the same composition.

[0022] The first fuel cell stack 110 includes a first fuel supply unit 111, a first fuel discharge unit 112, a first oxidizer supply unit 113, a first oxidizer discharge unit 114, a first cooling medium supply unit 115, and a first cooling medium discharge unit 116.

[0023] The second fuel cell stack 210 includes a second fuel supply unit 211, a second fuel discharge unit 212, a second oxidizer supply unit 213, a second oxidizer discharge unit 214, a second cooling medium supply unit 215, and a second cooling medium discharge unit 216.

[0024] Fuel gas 13 flows through the fuel path 300. In Embodiment 1, the fuel gas 13 is a hydrogen-containing gas. Specifically, the fuel gas 13 is pure hydrogen gas. Here, pure hydrogen gas is a gas in which the hydrogen concentration is 90% by volume or more and 100% by volume or less.

[0025] Fuel gas 13 is supplied to the fuel path 300 from a fuel gas source (not shown). In Embodiment 1, the fuel gas source is a hydrogen tank. The fuel gas source may also be infrastructure.

[0026] The fuel path 300 includes a supply path 316, a supply path 326, a circulation path 317, and a circulation path 327.

[0027] In the supply path 316, positions 301, 302, and the first fuel supply unit 111 appear in this order. In the supply path 316, the fuel gas 13 flows through positions 301, 302, and the first fuel supply unit 111 in this order. As a result, the fuel gas 13 is supplied to the first fuel cell stack 110.

[0028] The supply path 326 is connected to the supply path 316 at position 301. In the supply path 326, position 301, position 303, and the second fuel supply unit 211 appear in this order. In the supply path 326, the fuel gas 13 that branches off from the supply path 316 at position 301 flows through position 303 and the second fuel supply unit 211 in this order. As a result, the fuel gas 13 is supplied to the second fuel cell stack 210.

[0029] The circulation path 317 is connected to the supply path 316 at position 302. In the circulation path 317, the first fuel discharge section 112, the pump 120, and position 302 appear in this order. In the circulation path 317, the fuel gas 13 is pressurized by the pump 120, causing the fuel gas 13 to flow through the first fuel discharge section 112, the pump 120, and position 302 in this order. As a result, the anode off gas from the first fuel cell stack 110 discharged from the first fuel discharge section 112 is returned to the supply path 316 as fuel gas 13.

[0030] The anode off-gas of a fuel cell stack is the fuel gas containing unreacted fuel gas components in that fuel cell stack. In Embodiment 1, the unreacted fuel gas component is unreacted hydrogen.

[0031] The circulation path 327 is connected to the supply path 326 at position 303. In the circulation path 327, the second fuel discharge section 212, the pump 220, and position 303 appear in this order. In the circulation path 327, the fuel gas 13 is pressurized by the pump 220, causing the fuel gas 13 to flow through the second fuel discharge section 212, the pump 220, and position 303 in this order. As a result, the anode off gas from the second fuel cell stack 210 discharged from the second fuel discharge section 212 is returned to the supply path 326 as fuel gas 13.

[0032] In the oxidizing agent path 400, the oxidizing agent gas 14 flows. In Embodiment 1, the oxidizing agent gas 14 is air.

[0033] Oxidizing gas 14 is supplied to the oxidizing pathway 400 from an oxidizing gas source (not shown). In Embodiment 1, the oxidizing gas source is the atmosphere.

[0034] The oxidizing agent pathway 400 includes a supply pathway 416, a connection pathway 450, and a discharge pathway 428.

[0035] In the supply path 416, the first blower 130 and the first oxidant supply unit 113 appear in that order. In the supply path 416, the oxidant gas 14 is pressurized by the first blower 130, causing the oxidant gas 14 to flow through the first blower 130 and the first oxidant supply unit 113 in that order. As a result, the oxidant gas 14 is supplied to the first fuel cell stack 110.

[0036] The connection path 450 connects the first oxidant discharge unit 114 and the second oxidant supply unit 213. In the connection path 450, the cathode-off gas from the first fuel cell stack 110 discharged from the first oxidant discharge unit 114 flows from the first oxidant discharge unit 114 to the second oxidant supply unit 213 as oxidant gas 14. As a result, oxidant gas 14 is supplied to the second fuel cell stack 210.

[0037] The cathode-off gas of a fuel cell stack is an oxidizing gas containing unreacted oxidizing gas components in the fuel cell stack. In Embodiment 1, the unreacted oxidizing gas component is unreacted air.

[0038] In the exhaust path 428, the cathode off-gas of the second fuel cell stack 210 discharged from the second oxidant discharge portion 214 flows as the oxidant gas 14.

[0039] In the first cooling path 150, the first cooling medium 15 flows. In Embodiment 1, the first cooling medium 15 is water.

[0040] In the first cooling path 150, the first tank 151, the first pump 152, the first cooling medium supply portion 115, the first cooling medium discharge portion 116, the first heat exchanger 161, and the first tank 151 appear in this order. When the first cooling medium 15 is pressurized by the first pump 152, the first cooling medium 15 flows through the first tank 151, the first pump 152, the first cooling medium supply portion 115, the first cooling medium discharge portion 116, the first heat exchanger 161, and the first tank 151 in this order.

[0041] In the first exhaust heat path 160, the first heat medium 16 flows. In Embodiment 1, the first heat medium 16 is water. Tanks and pumps (not shown) are provided in the first exhaust heat path 160.

[0042] In the first exhaust heat path 160, the first heat exchanger 161 appears. In the first heat exchanger 161, the first cooling medium 15 in the first cooling path 150 and the first heat medium 16 in the first exhaust heat path 160 exchange heat. The first heat medium 16 carries heat to the first heat load.

[0043] Hereinafter, the terms first discharge temperature To1, first supply temperature Ti1, and first temperature difference ΔT1 are used. These terms are explained as follows.

[0044] In the first cooling path 150, the first cooling medium 15 is discharged from the first fuel cell stack 110 through the first cooling medium discharge portion 116. The first discharge temperature To1 is the temperature of the first cooling medium 15 at the first cooling medium discharge portion 116 in this discharge.

[0045] In the first cooling path 150, the first cooling medium 15 is supplied to the first fuel cell stack 110 through the first cooling medium supply portion 115. The first supply temperature Ti1 is the temperature of the first cooling medium 15 at the first cooling medium supply portion 115 in this supply.

[0046] The first temperature difference ΔT1 is the difference obtained by subtracting the first supply temperature Ti1 from the first discharge temperature To1, as shown in the following Equation 1. Equation 1: ΔT1 = To1 - Ti1

[0047] The first cooling medium 15 cools the first fuel cell stack 110. During this cooling, the first cooling medium 15 is heated. The first discharge temperature To1 becomes higher than the first supply temperature Ti1. That is, the first temperature difference ΔT1 becomes greater than zero. The heated first cooling medium 15 heats the first heat medium 16 by heat exchange in the first heat exchanger 161.

[0048] In the second cooling path 250, the second cooling medium 25 flows. In Embodiment 1, the second cooling medium 25 is water.

[0049] In the second cooling path 250, the second tank 251, the second pump 252, the second cooling medium supply section 215, the second cooling medium discharge section 216, the second heat exchanger 261, and the second tank 251 appear in this order. When the second cooling medium 2 is pressurized by the second pump 252, the second cooling medium 25 flows through the second tank 251, the second pump 252, the second cooling medium supply section 215, the second cooling medium discharge section 216, the second heat exchanger 261, and the second tank 251 in this order.

[0050] In the second exhaust heat path 260, the second heat medium 26 flows. In Embodiment 1, the second heat medium 26 is water. Tanks and pumps (not shown in the figure) are provided in the second exhaust heat path 260.

[0051] In the second exhaust heat path 260, the second heat exchanger 261 appears. In the second heat exchanger 261, the second cooling medium 25 in the second cooling path 250 and the second heat medium 26 in the second exhaust heat path 260 exchange heat. The second heat medium 26 carries heat to the second heat load.

[0052] Hereinafter, the terms the second discharge temperature To2, the second supply temperature Ti2, and the second temperature difference ΔT2 are used. These terms are explained as follows.

[0053] In the second cooling path 250, the second cooling medium 25 is discharged from the second fuel cell stack 210 via the second cooling medium discharge section 216. The second discharge temperature To2 is the temperature of the second cooling medium 25 at the second cooling medium discharge section 216 during this discharge.

[0054] In the second cooling path 250, the second cooling medium 25 is supplied to the second fuel cell stack 210 via the second cooling medium supply unit 215. The second supply temperature Ti2 is the temperature of the second cooling medium 25 in the second cooling medium supply unit 215 during this supply.

[0055] The second temperature difference ΔT2 is the difference obtained by subtracting the second supply temperature Ti2 from the second discharge temperature To2, as shown in Equation 2 below. Equation 2: ΔT2 = To2 - Ti2

[0056] The second cooling medium 25 cools the second fuel cell stack 210. During this cooling, the second cooling medium 25 is heated. The second discharge temperature To2 becomes higher than the second supply temperature Ti2. That is, the second temperature difference ΔT2 becomes greater than zero. The heated second cooling medium 25 heats the second heat medium 26 in the second heat exchanger 261 through heat exchange.

[0057] Hereafter, the temperature of the first fuel cell stack 110 will be denoted as Ts1. The temperature of the second fuel cell stack 210 will be denoted as Ts2. As shown in Equation 3 below, the difference (temperature difference) obtained by subtracting temperature Ts1 from temperature Ts2 will be denoted as ΔTs. Equation 3: ΔTs = Ts2 - Ts1

[0058] In Embodiment 1, the temperature Ts2 of the second fuel cell stack 210 during power generation is higher than the temperature Ts1 of the first fuel cell stack 110 during power generation. In this case, degradation of the power generation performance of the relatively lower temperature first fuel cell stack 110 is less likely to occur. On the other hand, because the second fuel cell stack 210 is relatively hot, it is easier to heat the second cooling medium 25 to a high temperature. Furthermore, in Embodiment 1, as shown in Figure 1A, the first cooling path 150 and the second cooling path 250 are independent of each other. Therefore, it is possible to prevent a temperature drop caused by the second cooling medium 25, which has been heated to a high temperature, mixing with the first cooling medium 15. For these reasons, according to Embodiment 1, power can be stably extracted by the first fuel cell stack 110. Moreover, due to the independence of the second fuel cell stack 210 and the cooling paths 150 and 250, a high temperature second cooling medium 25 can be obtained, and this high temperature second cooling medium 25 can be used for high-temperature heat supply.

[0059] The low temperature of the first fuel cell stack 110 also has the advantage of making it easier to increase the power generated by the first fuel cell stack 110, depending on its specifications. Specifically, the low temperature of the first fuel cell stack 110 can increase the partial pressure of the reaction gas, which can increase the power generated.

[0060] The above-mentioned "temperature Ts1" and "temperature Ts2" will be explained below.

[0061] In the first example, the temperature Ts1 is the temperature value detected by a temperature sensor located near the first fuel cell stack 110. The temperature Ts2 is the temperature value detected by a temperature sensor located near the second fuel cell stack 210.

[0062] In the second example, the temperature Ts1 is the temperature detected by a temperature sensor installed in the first cooling path 150, which is the temperature of the first cooling medium 15. Specifically, this temperature sensor is installed in the first cooling path 150 downstream of the first cooling medium discharge section 116 and upstream of the first heat exchanger 161. The temperature Ts2 is the temperature detected by a temperature sensor installed in the second cooling path 250, which is the temperature of the second cooling medium 25. Specifically, this temperature sensor is installed in the second cooling path 250 downstream of the second cooling medium discharge section 216 and upstream of the second heat exchanger 261.

[0063] In Embodiment 1, the deterioration of the power generation performance of the first fuel cell stack 110 includes a decrease in the power generation voltage of the first fuel cell stack 110. The deterioration of the power generation performance of the first fuel cell stack 110 is mainly caused by the deterioration of the catalyst of the first fuel cell stack 110.

[0064] In Embodiment 1, the deterioration of the power generation performance of the second fuel cell stack 210 includes a decrease in the power generation voltage of the second fuel cell stack 210. The deterioration of the power generation performance of the second fuel cell stack 210 is mainly caused by the deterioration of the catalyst of the second fuel cell stack 210.

[0065] In Embodiment 1, the degradation of the power generation performance of the first fuel cell stack 110 is easier to suppress than the degradation of the power generation performance of the second fuel cell stack 210. The decrease in the power generation voltage of the first fuel cell stack 110 is easier to suppress than the decrease in the power generation voltage of the second fuel cell stack 210. The degradation of the catalyst in the first fuel cell stack is easier to suppress than the degradation of the catalyst in the second fuel cell stack.

[0066] As described above, suppressing the degradation of the power generation performance of the first fuel cell stack 110 is advantageous from the standpoint of stably extracting power from the first fuel cell stack 110. On the other hand, the degradation of the power generation performance of the second fuel cell stack 210 is unlikely to be a problem when supplying high-temperature heat using the second fuel cell stack 210.

[0067] The thickness of the second electrolyte membrane in the second fuel cell stack 210 may be greater than the thickness of the first electrolyte membrane in the first fuel cell stack 110. In the first fuel cell stack 110, a smaller thickness of the first electrolyte membrane may be advantageous from the viewpoint of improving power generation efficiency. In contrast, in the second fuel cell stack 210, high-temperature extraction is prioritized over power generation efficiency. In the second fuel cell stack 210, increasing the thickness of the second electrolyte membrane may be advantageous in making the second electrolyte membrane less prone to rupture.

[0068] Let me explain the above statement that "the first cooling path 150 and the second cooling path 250 are independent of each other." Specifically, this statement means that in the fuel cell system 1, the first cooling path 150 and the second cooling path 250 are distinguished so that the first cooling medium 15 and the second cooling medium 25 do not mix.

[0069] In Embodiment 1, the control device 10 controls the first pump 152 and the second pump 252 such that the temperature Ts2 of the second fuel cell stack 210, which is generating power, becomes higher than the temperature Ts1 of the first fuel cell stack 110, which is also generating power.

[0070] Specifically, the control device 10 can: - Reduce the first temperature difference ΔT1 and lower the temperature Ts1 by controlling the first pump 152 to increase the flow rate of the first cooling medium 15 in the first cooling path 150; - Increase the first temperature difference ΔT1 and raise the temperature Ts1 by controlling the first pump 152 to decrease the flow rate of the first cooling medium 15 in the first cooling path 150; - Reduce the second temperature difference ΔT2 and lower the temperature Ts2 by controlling the second pump 252 to increase the flow rate of the second cooling medium 25 in the second cooling path 250; - Increase the second temperature difference ΔT2 and raise the temperature Ts2 by controlling the second pump 252 to decrease the flow rate of the second cooling medium 25 in the second cooling path 250.

[0071] In a specific control example, when the temperature difference ΔTs is smaller than the target value, the control device 10 controls the first pump 152 to increase the flow rate of the first cooling medium 15 in the first cooling path 150, and / or controls the second pump 252 to decrease the flow rate of the second cooling medium 25 in the second cooling path 250.

[0072] In a specific control example, when the temperature difference ΔTs is greater than the target value, the control device 10 controls the first pump 152 to decrease the flow rate of the first cooling medium 15 in the first cooling path 150, and / or controls the second pump 252 to increase the flow rate of the second cooling medium 25 in the second cooling path 250.

[0073] The target value is greater than zero. According to a specific control example, the temperature Ts2 of the second fuel cell stack 210 during power generation can be maintained at a higher temperature Ts1 of the first fuel cell stack 110 during power generation.

[0074] For example, the target temperature is 5°C or higher. More specifically, the target temperature could be between 5°C and 40°C. More specifically, the target temperature could be between 10°C and 35°C.

[0075] As described above, in the oxidizer path 400 of Embodiment 1, the cathode-off gas of the first fuel cell stack 110 is supplied to the second fuel cell stack 210 as oxidizer gas 14. With this configuration, the oxygen concentration of the oxidizer gas 14 supplied to the second fuel cell stack 210 can be lowered compared to the oxygen concentration of the oxidizer gas 14 supplied to the first fuel cell stack 110. A lower oxygen concentration of the oxidizer gas 14 supplied to the second fuel cell stack 210 is advantageous from the viewpoint of lowering the power generation efficiency of the second fuel cell stack 210 and increasing the heat generation efficiency of the second fuel cell stack 210. Furthermore, this is advantageous from the viewpoint of raising the temperature Ts2 of the second fuel cell stack 210 during power generation.

[0076] Although not shown in Figure 1A, the fuel cell system 1 in Embodiment 1 includes a humidifier and a gas-liquid separator. Figure 1B is an explanatory diagram of the humidifier and gas-liquid separator according to Embodiment 1. As shown in Figure 1B, the fuel cell system 1 includes a fuel humidifier 360, an oxidizer humidifier 460, and an oxidizer gas-liquid separator 470.

[0077] The fuel humidifier 360 humidifies the fuel gas 13 supplied to the first fuel cell stack 110. The oxidizer humidifier 460 humidifies the oxidizer gas 14 supplied to the first fuel cell stack 110. By humidifying the fuel gas 13 and oxidizer gas 14 supplied to the first fuel cell stack 110, the power generation efficiency of the first fuel cell stack 110 can be increased and the deterioration of the power generation performance of the first fuel cell stack 110 can be suppressed.

[0078] In the example shown in Figure 1B, the fuel humidifier 360 is located in the supply path 316. The oxidizer humidifier 460 is located in the supply path 416. Specifically, the oxidizer humidifier 460 is located in the supply path 416 between the first blower 130 and the first oxidizer supply unit 113.

[0079] In the example shown in Figure 1B, the oxidizer gas-liquid separator 470 is installed in the connection path 450. The oxidizer gas-liquid separator 470 separates the oxidizer gas 14 in the connection path 450 into gas and liquid phases. By separating the oxidizer gas 14 in the connection path 450 into gas and liquid phases, it is possible to suppress the phenomenon of condensation occurring in the piping constituting the connection path 450 due to the cathode off containing a large amount of water vapor in the first fuel cell stack 110, thereby blocking the piping.

[0080] In the example in Figure 1B, there are no humidifiers located in the supply path 326. There are no humidifiers located in the connection path 450.

[0081] In Embodiment 1, the current density of the second fuel cell stack 210 during power generation is higher than the current density of the first fuel cell stack 110 during power generation. The higher current density of the second fuel cell stack 210 can increase the heat generation efficiency of the second fuel cell stack 210.

[0082] By increasing the current density of the second fuel cell stack 210, it is possible to lower the power generation voltage of the second fuel cell stack 210 and increase the heat output of the second fuel cell stack 210. Specifically, the theoretical voltage of the fuel cell stack is fixed. When the actual power generation voltage decreases, the loss from the theoretical voltage is converted into heat output. Also, when the current density increases, the power generation output increases. Therefore, by increasing the current density of the second fuel cell stack 210, it is possible to reduce the size of the second fuel cell stack 210, thereby simultaneously achieving cost reduction and compactness.

[0083] The "current density of the first fuel cell stack 110" will now be explained. As described above, the first fuel cell stack 110 consists of multiple first fuel cell cells stacked on top of each other. The current density of the first fuel cell stack 110 is the current density per unit area of ​​the catalyst layer region of the first membrane electrode assembly of each first fuel cell in the first fuel cell stack 110, when the first fuel cell is viewed in plan.

[0084] The "current density of the second fuel cell stack 210" will now be explained. As mentioned above, the second fuel cell stack 210 consists of multiple second fuel cell cells stacked on top of each other. The current density of the second fuel cell stack 210 is the current density per unit area of ​​the catalyst layer region of the second membrane electrode assembly of each second fuel cell in the second fuel cell stack 210, when the second fuel cell is viewed in plan.

[0085] For example, catalysts for the first fuel cell stack and the second fuel cell stack are selected. This makes it possible to achieve a state in which the current density of the second fuel cell stack 210 during power generation is higher than the current density of the first fuel cell stack 110 during power generation.

[0086] Furthermore, for example, the electrode area of ​​the membrane electrode junctions of the first fuel cell stack 110 and the second fuel cell stack 210 can be adjusted. Since the specifications of the power cables and other components used can be standardized, the current value for each subsystem can be set to a constant value. Therefore, by making the electrode area of ​​the second fuel cell stack 210 smaller than that of the first fuel cell stack 110, a high current density state can be achieved in the second fuel cell stack 210. Since the second fuel cell stack 210 has a smaller electrode area, the separators and fastening members that make up the stack can also be made smaller, thus achieving both cost reduction and compactness at the same time.

[0087] In one configuration example, the second sub-fuel cell system 200 includes a converter that converts the power generated by the second fuel cell stack 210 into heat. The heat generated by the converter is supplied to the second heat medium 26. According to this configuration example, the heat supplied from the second fuel cell stack 210 to the second heat load can be extracted not only via the second cooling medium 25 but also via the converter. This can contribute to the supply of high-temperature heat based on the second fuel cell stack 210. Note that the phrase "the heat generated by the converter is supplied to the second heat medium 26" is intended to encompass both a form in which heat is directly supplied from the converter to the second heat medium 26 and a form in which heat is indirectly supplied from the converter to the second heat medium 26 via an intervening material.

[0088] Specifically, the first fuel cell stack 110 is more likely to generate stable power because the degradation of its power generation performance is suppressed. On the other hand, compared to the first fuel cell stack 110, the second fuel cell stack 210 has a higher temperature during operation, which degrades its power generation performance and makes it more likely to generate unstable power. Therefore, it is rational to convert the power generated by the second fuel cell stack 210 into heat using a converter and to use the second fuel cell stack 210 more intensively for heat extraction.

[0089] In the above example configuration using a converter, it is possible to apply a configuration in which the thickness of the second electrolyte membrane of the second fuel cell stack 210 is greater than the thickness of the first electrolyte membrane of the first fuel cell stack 110. In the above example configuration, the second fuel cell stack 210 may be intended for high-temperature heat supply. In that case, as described above, even if the power generation performance of the second fuel cell stack 210 deteriorates and unstable power is generated, that power is converted into thermal energy, so the instability of the generated power is unlikely to be a problem. However, if the second fuel cell stack 210 is operated at a higher temperature than the first fuel cell stack 110, the deterioration rate of the second electrolyte membrane of the second fuel cell stack 210 may be faster. In this respect, increasing the thickness of the second electrolyte membrane makes it easier to ensure the required lifespan of the second fuel cell stack 210. In the first fuel cell stack 110, increasing the thickness of the first electrolyte membrane raises concerns that resistance will increase and power generation performance will decrease. However, if the purpose of the second fuel cell stack 210 is high-temperature heat supply, the above concerns are limited.

[0090] Furthermore, considering that additional heat is extracted via the converter, it is possible to set the temperature Ts2 of the second fuel cell stack 210 during power generation to a lower temperature to suppress the deterioration of the power generation performance of the second fuel cell stack 210.

[0091] For example, the converter is an electric heater. For example, the converter is attached to the second heat exchanger 261. Also, for example, the converter is attached to the piping that constitutes the second heat exhaust path 260.

[0092] Let's assume that both electricity and heat are extracted from a single fuel cell stack. As can be understood from the above explanation, in this case, if priority is given to suppressing the degradation of the power generation performance of the fuel cell stack, it becomes difficult to supply high-temperature heat based on the fuel cell stack. This means that the applications for heat supply based on the fuel cell stack are limited. In this regard, according to Embodiment 1, one of the two fuel cell stacks 110 and 210 is responsible for stable electricity extraction, and the other is responsible for high-temperature heat supply. Through this division of roles, it is possible to ensure a period during which stable electricity extraction is possible while mitigating the above limitations and increasing the applications for heat supply. This can contribute to improving the marketability of the fuel cell system 1.

[0093] For example, according to Embodiment 1, the second heat transfer medium 26 can be heated to 80°C or higher through heating including heat exchange by the second heat exchanger 261. Having the second heat transfer medium 26 at such a high temperature is advantageous from the viewpoint of increasing the range of applications for heat supply. Specifically, the second heat transfer medium 26 can be heated to 80°C or higher and 100°C or lower through heating including heat exchange by the second heat exchanger 261. More specifically, the second heat transfer medium 26 can be heated to 90°C or higher and 100°C or lower through heating including heat exchange by the second heat exchanger 261.

[0094] The "heating including heat exchange by the second heat exchanger 261" described above may be heating by heat exchange by the second heat exchanger 261 alone, or it may include heat exchange by the second heat exchanger 261 and heating by the converter described above.

[0095] In Embodiment 1, the applications of the heat supply based on the second fuel cell stack 210 include, for example, at least one selected from the group consisting of hot water supply, heating, sterilization, drying, cleaning, and chemical processes. Specifically, in chemical processes, high-temperature heat supply can be applied to melting, high-temperature maintenance, etc. For example, heat can be supplied to the heat load at these applications via the second heat transfer medium 26.

[0096] Other embodiments will be described below. In the following, elements common to embodiments already described and those described later will be given the same reference numerals, and their descriptions may be omitted. The descriptions of each embodiment may be mutually applicable, as long as they do not technically contradict each other. As long as they do not technically contradict each other, each embodiment may be combined with each other.

[0097] (Embodiment 2) Figure 2A is a diagram showing the configuration of a fuel cell system 2 according to Embodiment 2. In the fuel cell system 2, the fuel path 300 includes a supply path 316, a connection path 350, and a circulation path 329.

[0098] In the supply path 316, position 304 and the first fuel supply unit 111 appear in this order. In the supply path 316, the fuel gas 13 flows through position 304 and the first fuel supply unit 111 in this order. As a result, the fuel gas 13 is supplied to the first fuel cell stack 110.

[0099] The connection path 350 connects the first fuel discharge section 112 and the second fuel supply section 211. In the connection path 350, the anode off gas from the first fuel cell stack 110 discharged from the first fuel discharge section 112 flows as fuel gas 13 from the first fuel discharge section 112 to the second fuel supply section 211. As a result, fuel gas 13 is supplied to the second fuel cell stack 210.

[0100] The circulation path 329 is connected to the supply path 316 at position 304. In the circulation path 329, the second fuel discharge section 212, the pump 220, and position 304 appear in this order. In the circulation path 329, the fuel gas 13 is pressurized by the pump 220, causing the fuel gas 13 to flow through the second fuel discharge section 212, the pump 220, and position 304 in this order. As a result, the anode off gas from the second fuel cell stack 210 discharged from the second fuel discharge section 212 is returned to the supply path 316 as fuel gas 13.

[0101] Although not shown in Figure 2A, the fuel cell system 2 in Embodiment 2 includes a humidifier and a gas-liquid separator. Figure 2B is an explanatory diagram of the humidifier and gas-liquid separator according to Embodiment 2. As shown in Figure 2B, the fuel cell system 2 includes a fuel humidifier 360, an oxidizer humidifier 460, a fuel gas-liquid separator 370, and an oxidizer gas-liquid separator 470.

[0102] In fuel cell system 2, the fuel humidifier 360 is located in the supply path 316. The oxidizer humidifier 460 is located in the supply path 416 between the first blower 130 and the first oxidizer supply unit 113. The fuel gas-liquid separator 370 is located in the connection path 350. The oxidizer gas-liquid separator 470 is located in the connection path 450. In a typical example, there are no humidifiers located in the connection path 350 and the connection path 450.

[0103] The fuel gas-liquid separator 370 separates the fuel gas 13 in the connection path 350 into gas and liquid phases. By separating the fuel gas 13 in the connection path 350 into gas and liquid phases, it is possible to suppress the phenomenon in which anode off-off containing a large amount of water vapor in the first fuel cell stack 110 condenses in the piping constituting the connection path 350 and blocks the piping.

[0104] (Embodiment 3) Figure 3 is a diagram showing the configuration of a fuel cell system 3 according to Embodiment 3. In the fuel cell system 3, the second sub-fuel cell system 200 includes a second blower 230. The oxidizer path 400 includes a supply path 416, a discharge path 418, a supply path 426, and a discharge path 428.

[0105] In the supply path 416, position 401, the first blower 130, and the first oxidizer supply unit 113 appear in this order.

[0106] In the discharge path 418, the cathode-off gas from the first fuel cell stack 110 discharged from the first oxidant discharge section 114 flows as the oxidant gas 14.

[0107] The supply path 426 is connected to the supply path 416 at position 401. In the supply path 426, position 401, the second blower 230, and the second oxidant supply unit 213 appear in this order. In the supply path 426, the oxidant gas 14 is pressurized by the second blower 230, causing the oxidant gas 14 that branched off from the supply path 416 at position 401 to flow through the second blower 230 and the second oxidant supply unit 213 in this order. As a result, the oxidant gas 14 is supplied to the second fuel cell stack 210.

[0108] In the fuel cell system 3, the fuel humidifier 360 is located in the supply path 316. The oxidizer humidifier 460 is located in the supply path 416 between the first blower 130 and the first oxidizer supply unit 113.

[0109] (Embodiment 4) Figure 4 is a diagram showing the configuration of a fuel cell system 4 according to Embodiment 4. In Embodiment 4, a fuel path 300 is configured in the same way as in Embodiment 2. In Embodiment 4, an oxidizer path 400 is configured in the same way as in Embodiment 3.

[0110] In the fuel cell system 4, the fuel humidifier 360 is located in the supply path 316. The fuel gas-liquid separator 370 is located in the connection path 350. The oxidizer humidifier 460 is located in the supply path 416 between the first blower 130 and the first oxidizer supply unit 113. In a typical example, there is no humidifier located in the connection path 350.

[0111] (Embodiment 5) Figure 5 is a diagram showing the configuration of the fuel cell system 5 according to Embodiment 5. In Embodiments 1 to 4 described above, a first heat exchanger 161 is used. In contrast, in Embodiment 5, a first heat exchanger 165 is used instead of the first heat exchanger 161.

[0112] The first heat exchanger 165 is an air-cooled heat exchanger. The first heat exchanger 165 cools the first cooling medium 15 by air cooling. With this configuration, the tank and pump in the first heat exhaust path 160 can be omitted. This is advantageous from the viewpoint of constructing the fuel cell system 5 at low cost. In the example in Figure 5, the first heat exchanger 165 includes a fan.

[0113] (Embodiment 6) Figure 6 is a diagram showing the configuration of a fuel cell system 6 according to Embodiment 6.

[0114] The fuel cell system 6 includes a first subsystem group 500 and a second subsystem group 600. Each subsystem in the first subsystem group 500 is composed of a first sub-fuel cell system 100. Each subsystem in the second subsystem group 600 is composed of a second sub-fuel cell system 200.

[0115] Hereinafter, the number of first sub-fuel cell systems 100 in the first subsystem group 500 will be denoted as M1. M1 is a natural number greater than or equal to 2, for example, between 2 and 100.

[0116] Hereinafter, the number of second sub-fuel cell systems 200 in the second subsystem group 600 will be denoted as M2. M2 is a natural number greater than or equal to 2, for example, between 2 and 100.

[0117] M1 and M2 may be the same or they may be different.

[0118] In Embodiment 6, any of the first sub-fuel cell systems 100 from Embodiments 1 to 5 may be used as the first sub-fuel cell system 100 of M1. In Embodiment 6, any of the second sub-fuel cell systems 200 from Embodiments 1 to 5 may be used as the second sub-fuel cell system 200 of M2.

[0119] The M1 first sub-fuel cell system 100 may include two or more different first sub-fuel cell systems 100 from any embodiment among embodiments 1 to 5. The M2 second sub-fuel cell system 200 may include two or more different second sub-fuel cell systems 200 from any embodiment among embodiments 1 to 5.

[0120] The first sub-fuel cell system 100 (M1 unit) and the second sub-fuel cell system 200 (M2 unit) may be associated in a one-to-one correspondence. The corresponding first sub-fuel cell system 100 and second sub-fuel cell system 200 may constitute any of the fuel cell systems of embodiments 1 to 5 described with reference to Figures 1 to 5.

[0121] In the fuel cell system 6, fuel gas 13 is supplied to each first sub-fuel cell system 100 in the first subsystem group 500 and each second sub-fuel cell system 200 in the second subsystem group 600 via the fuel path 300. Oxidizer gas 14 is supplied to each first sub-fuel cell system 100 in the first subsystem group 500 and each second sub-fuel cell system 200 in the second subsystem group 600 via the oxidizer path 400.

[0122] In Embodiment 6, following Embodiments 2 and 4, the anode-off gas of the M1 first fuel cell stack 110 may be supplied to the M2 second fuel cell stack 210 as fuel gas 13. Following Embodiments 1, 3 and 5, fuel gas 13 that has not passed through the M1 first fuel cell stack 110 may be supplied to the M2 second fuel cell stack 210. Fuel gas 13 that is part or all of the anode-off gas of the M1 first fuel cell stack 110 and fuel gas 13 that has not passed through the M1 first fuel cell stack 110 may be supplied to the M2 second fuel cell stack 210.

[0123] In Embodiment 6, following Embodiments 1, 2, and 5, the cathode-off gas of the M1 first fuel cell stack 110 may be supplied to the M2 second fuel cell stack 210 as the oxidizer gas 14. Following Embodiments 3 and 4, the oxidizer gas 14 that has not passed through the M1 first fuel cell stack 110 may be supplied to the M2 second fuel cell stack 210. The oxidizer gas 14 that is part or all of the cathode-off gas of the M1 first fuel cell stack 110 and the oxidizer gas 14 that has not passed through the M1 first fuel cell stack 110 may be supplied to the M2 second fuel cell stack 210.

[0124] According to Embodiment 6, the necessary power and heat can be extracted by appropriately setting M1 and M2.

[0125] (Technologies applicable to Embodiments 1 to 6) In Embodiments 1 to 6, the fuel humidifier 360 may be omitted. The oxidizer humidifier 460 may be omitted. The fuel gas-liquid separator 370 may be omitted. The oxidizer gas-liquid separator 470 may be omitted.

[0126] In embodiments 1 to 4 and 6, the first heat exchanger 165 of embodiment 5 may be used.

[0127] In embodiments 1 to 6, the first fuel cell stack 110 and the second fuel cell stack 210 may be of solid oxide type.

[0128] In embodiments 1 to 6, the type of the first fuel cell stack 110 and the type of the second fuel cell stack 210 are the same. Specifically, the first fuel cell stack 110 and the second fuel cell stack 210 are of the polymer electrolyte type.

[0129] The types of the first fuel cell stack 110 and the second fuel cell stack 210 may be different. For example, one of the first fuel cell stack 110 and the second fuel cell stack 210 may be a polymer electrolyte type, and the other may be a solid oxide type.

[0130] In embodiments 1 to 6, the fuel gas 13 may be a hydrogen-containing gas obtained by steam reforming.

[0131] In embodiments 1 to 6, the control device 10 may perform partial load operation of the first fuel cell stack 110 and the second fuel cell stack 210. Partial load operation is operation in which power is output that is greater than zero but less than the rated power.

[0132] In Embodiment 6, the fuel cell system 6 includes both the first subsystem group 500 and the second subsystem group 600. However, the fuel cell system may include only one of the first subsystem group 500 and the second subsystem group 600. In one example, the number of first sub-fuel cell systems 100 in the fuel cell system is one, and the fuel cell system includes the second subsystem group 600. In another example, the number of second fuel cell stacks 210 in the fuel cell system is one, and the fuel cell system includes the first subsystem group 500.

[0133] (Note) This disclosure discloses the following technologies.

[0134] (Technology 1) A fuel cell system comprising: a first sub-fuel cell system including a first fuel cell stack and a first cooling path through which a first cooling medium for cooling the first fuel cell stack flows; and a second sub-fuel cell system including a second fuel cell stack and a second cooling path through which a second cooling medium for cooling the second fuel cell stack flows, wherein the first cooling path and the second cooling path are independent of each other, and the temperature of the second fuel cell stack during power generation is higher than the temperature of the first fuel cell stack during power generation.

[0135] (Technology 2) The fuel cell system according to Technology 1, comprising an oxidizer path for flowing an oxidizer gas through the first fuel cell stack and the second fuel cell stack, wherein the cathode-off gas of the first fuel cell stack is supplied to the second fuel cell stack as the oxidizer gas through the oxidizer path.

[0136] (Technology 3) The fuel cell system according to Technology 1 or 2, wherein the second sub-fuel cell system includes a heat exchanger provided in the second cooling path and a converter that converts the power generated by the second fuel cell stack into heat, the heat exchanger exchanges heat between the second cooling medium and a heat medium, and the heat generated by the conversion in the converter is supplied to the heat medium.

[0137] (Technical 4) A fuel cell system according to any one of Technical 1 to 3, comprising at least one of a fuel humidifier for humidifying the fuel gas supplied to the first fuel cell stack and an oxidizer humidifier for humidifying the oxidizer gas supplied to the first fuel cell stack.

[0138] (Technical 5) The fuel cell system according to any one of Technical 1 to 4, wherein the first sub-fuel cell system includes a heat exchanger provided in the first cooling path, and the heat exchanger cools the first cooling medium by air cooling.

[0139] (Technology 6) The fuel cell system according to any one of Technology 1 to 5, wherein the current density of the second fuel cell stack during power generation is higher than the current density of the first fuel cell stack during power generation.

[0140] (Technical 7) A fuel cell system according to any one of Technical 1 to 6, comprising at least one of a first subsystem group and a second subsystem group, wherein each subsystem in the first subsystem group is composed of the first sub-fuel cell system, and each subsystem in the second subsystem group is composed of the second sub-fuel cell system.

[0141] According to the technology disclosed herein, one of two fuel cell stacks can be responsible for stable power extraction, while the other is responsible for high-temperature heat supply. Through this division of roles, a fuel cell system that can achieve both stable power extraction and high-temperature heat supply can be realized.

Claims

1. A fuel cell system comprising: a first sub-fuel cell system including a first fuel cell stack and a first cooling path through which a first cooling medium for cooling the first fuel cell stack flows; and a second sub-fuel cell system including a second fuel cell stack and a second cooling path through which a second cooling medium for cooling the second fuel cell stack flows, wherein the first cooling path and the second cooling path are independent of each other, and the temperature of the second fuel cell stack during power generation is higher than the temperature of the first fuel cell stack during power generation.

2. The fuel cell system according to claim 1, comprising an oxidizer path for flowing an oxidizer gas through the first fuel cell stack and the second fuel cell stack, wherein the cathode-off gas of the first fuel cell stack is supplied to the second fuel cell stack as the oxidizer gas through the oxidizer path.

3. The fuel cell system according to claim 1, wherein the second sub-fuel cell system includes a heat exchanger provided in the second cooling path and a converter that converts the power generated by the second fuel cell stack into heat, the heat exchanger exchanges heat between the second cooling medium and a heat medium, and the heat generated by the conversion in the converter is supplied to the heat medium.

4. The fuel cell system according to claim 1, comprising at least one of a fuel humidifier for humidifying the fuel gas supplied to the first fuel cell stack and an oxidizer humidifier for humidifying the oxidizer gas supplied to the first fuel cell stack.

5. The fuel cell system according to claim 1, wherein the first sub-fuel cell system includes a heat exchanger provided in the first cooling path, and the heat exchanger cools the first cooling medium by air cooling.

6. The fuel cell system according to claim 1, wherein the current density of the second fuel cell stack during power generation is higher than the current density of the first fuel cell stack during power generation.

7. The fuel cell system according to claim 1, comprising at least one of a first subsystem group and a second subsystem group, wherein each subsystem in the first subsystem group is composed of the first sub-fuel cell system, and each subsystem in the second subsystem group is composed of the second sub-fuel cell system.

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