Fuel cell system and method of operating the same

Abstract

A fuel cell system (100) comprises a fuel cell stack (4), a cooling water path (40), a cooling water tank (30), a cooling water pump (10), an oxidant gas supply unit (15), an oxidant gas supply path (11), an oxidant gas humidification path (12), an oxidant gas discharge path (13) and an exhaust gas path (14). The fuel cell system (100) is configured such that when the fuel cell stack (4) stops generating electricity, the inlet of the oxidant gas humidification path (12) is completely immersed in water, but the temperature of the remaining oxidant gas is controlled, and the cathode (4b) is not filled with cooling water (30r).

Description

Technical Field

[0001] The present disclosure relates to a fuel cell system including a cooling water tank for recovering water generated in a fuel cell stack and an operating method thereof. Background Art

[0002] Patent Document 1 discloses a fuel cell system in which, when power generation is stopped, an on-off valve is switched to supply part of cooling water to the cathode so that the cathode is filled with cooling water, thereby suppressing the inflow of air into the cathode.

[0003] The fuel cell system comprises: a fuel gas supply path, a fuel cell stack, an unreacted fuel gas exhaust path, an oxidant gas supply path, an oxidant gas exhaust path, a cooling water path, a cooling water pump, a cooling water tank, a cooling water supply pipeline, a first water valve, a cooling water exhaust pipeline and a second water valve.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2013-26182 Summary of the invention

[0007] The present disclosure provides a fuel cell system and an operating method thereof that can suppress the inflow of air into the cathode when power generation stops without filling the cathode with cooling water when the fuel cell system stops power generation.

[0008] The fuel cell system disclosed in the present invention includes a fuel cell stack, a cooling water path, a cooling water tank, a cooling water pump, an oxidant gas supply unit, an oxidant gas supply path, an oxidant gas humidification path, an oxidant gas exhaust path, and an exhaust gas path.

[0009] The fuel cell stack is a solid polymer type, and is configured to generate electricity by reacting a fuel gas supplied to an anode and an oxidant gas supplied to a cathode.

[0010] The cooling water path is configured to circulate cooling water that exchanges heat with the fuel cell stack.

[0011] The cooling water tank is a generally closed tank provided in a portion of the cooling water path that is lower than the fuel cell stack in the vertical direction. The cooling water tank has a gas storage portion above a cooling water storage portion that stores cooling water when in the installed state, and the gas storage portion is divided into a first space and a second space in a manner that is not connected to each other regardless of the operating state of the fuel cell stack.

[0012] The cooling water pump is provided in the cooling water path to draw cooling water from the cooling water tank and supply the cooling water to the fuel cell stack.

[0013] The oxidant gas supply unit is configured to supply oxidant gas. The oxidant gas supply path is a path configured to supply oxidant gas to the cooling water in the cooling water storage unit below the first space, and is a path connecting the oxidant gas supply unit and the cooling water tank.

[0014] The oxidant gas humidifying path is a path configured to supply the oxidant gas discharged from the oxidant gas supply path and humidified and accumulated in the first space to the cathode, and is a path having an inlet opening to the first space and an outlet connected to the inlet of the cathode.

[0015] The oxidant gas discharge path is a path configured to supply the oxidant gas discharged from the cathode outlet without being used for the reaction of the fuel cell stack to the cooling water in the cooling water storage part below the second space. The oxidant gas discharge path is a path having an inlet connected to the cathode outlet and an outlet opening in the cooling water in the cooling water storage part below the second space.

[0016] The exhaust gas passage is a passage configured to discharge the oxidizing gas discharged from the oxidizing gas discharge passage, separated into gas and liquid and stored in the second space to the outside, and has an inlet opening to the second space and an outlet opening to the outside.

[0017] Furthermore, the fuel cell system of the present disclosure is configured such that when the fuel cell stack stops generating power, the inlet of the oxidant gas humidification path is completely submerged in water, but the temperature of the remaining oxidant gas is controlled without filling the cathode with cooling water.

[0018] In addition, the operating method of the fuel cell system disclosed in the present invention is an operating method of a fuel cell system having a fuel cell stack, a cooling water path, a cooling water tank, a cooling water pump, an oxidant gas supply unit, an oxidant gas supply path, an oxidant gas humidification path, an oxidant gas exhaust path, an exhaust gas path and a heater. The fuel cell stack is a solid polymer type, which generates electricity by reacting the fuel gas supplied to the anode and the oxidant gas supplied to the cathode. The cooling water path is a cooling water circulation for heat exchange with the fuel cell stack. The cooling water tank is a roughly closed box arranged in a portion of the cooling water path that is lower than the fuel cell stack in the vertical direction. The cooling water tank has a gas storage unit above the cooling water storage unit for storing cooling water in the setting state, and the gas storage unit is divided into a first space and a second space in a manner that is not connected to each other regardless of the operating state of the fuel cell stack. The cooling water pump is arranged in the cooling water path to draw cooling water in the cooling water tank and supply it to the fuel cell stack. The oxidant gas supply unit supplies oxidant gas. The oxidant gas supply path connects the oxidant gas supply unit and the cooling water tank in a manner that the oxidant gas is supplied to the cooling water of the cooling water storage unit below the first space. The oxidant gas humidification path has an inlet opening to the first space and an outlet connected to the inlet of the cathode, so as to supply the oxidant gas discharged from the oxidant gas supply path and humidified and accumulated in the first space to the cathode. The oxidant gas discharge path is a path configured to supply the oxidant gas discharged from the outlet of the cathode not used for the reaction of the fuel cell stack to the cooling water of the cooling water storage unit below the second space. The oxidant gas discharge path has an inlet connected to the outlet of the cathode and an outlet opening to the cooling water of the cooling water storage unit below the second space. The exhaust gas path has an inlet opening to the second space and an outlet opening to the outside, so that the oxidant gas discharged from the oxidant gas discharge path and accumulated in the second space by gas-liquid separation can be discharged to the outside. The heater is arranged in the cooling water tank to adjust the temperature of the cooling water. In addition, in the operation method of the fuel cell system disclosed in the present invention, the fuel cell system also operates the cooling water pump after the fuel cell stack stops generating electricity. In addition, in the operating method of the fuel cell system disclosed in the present invention, when the fuel cell stack stops generating electricity, the fuel cell system uses a heater to adjust the temperature of the cooling water so that although the inlet of the oxidant gas humidification path is completely immersed in water, the cathode is not filled with cooling water.

[0019] In the fuel cell system and the operating method of the fuel cell system of the present disclosure, when the fuel cell stack stops generating power, it is possible to suppress the inflow of air into the cathode when power generation stops without filling the cathode with cooling water. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a block diagram showing the configuration of the fuel cell system in Embodiment 1 of the present disclosure.

[0021] Figure 2 This is a diagram showing the relationship between the pressure of the residual oxidant gas and the volume of the residual oxidant gas with respect to the temperature of the residual oxidant gas in Embodiment 1 of the present disclosure.

[0022] Figure 3 This is a block diagram showing the configuration of a fuel cell system in Embodiment 2 of the present disclosure. DETAILED DESCRIPTION

[0023] The fuel cell system disclosed in the present invention comprises a fuel cell stack, a cooling water path, a cooling water tank, a cooling water pump, an oxidant gas supply unit, an oxidant gas supply path, an oxidant gas humidification path, an oxidant gas discharge path and an exhaust gas path. The fuel cell stack is a solid polymer type, which generates electricity by reacting the fuel gas supplied to the anode and the oxidant gas supplied to the cathode. The cooling water path is a cooling water circulation for heat exchange with the fuel cell stack. The cooling water tank is a generally closed box arranged in a portion of the cooling water path that is lower than the fuel cell stack in the vertical direction. In the cooling water tank, a gas storage unit is provided above a cooling water storage unit for storing cooling water in a setting state, and the gas storage unit is divided into a first space and a second space in a manner that is not connected to each other regardless of the operating state of the fuel cell stack. The cooling water pump is arranged in the cooling water path to draw cooling water in the cooling water tank and supply it to the fuel cell stack. The oxidant gas supply unit supplies oxidant gas. The oxidant gas supply path connects the oxidant gas supply unit and the cooling water tank in a manner that supplies oxidant gas to the cooling water in the cooling water storage unit below the first space. The oxidant gas humidification path has an inlet opening to the first space and an outlet connected to the inlet of the cathode, so that the oxidant gas discharged from the oxidant gas supply path and humidified and accumulated in the first space is supplied to the cathode. The oxidant gas discharge path is a path configured to supply the oxidant gas discharged from the outlet of the cathode without being used for the reaction of the fuel cell stack to the cooling water of the cooling water storage part below the second space. The oxidant gas discharge path has an inlet connected to the outlet of the cathode and an outlet opening to the cooling water of the cooling water storage part below the second space. The exhaust gas path has an inlet opening to the second space and an outlet opening to the outside, so that the oxidant gas discharged from the oxidant gas discharge path and accumulated in the second space by gas-liquid separation can be discharged to the outside. The fuel cell system disclosed in the present invention is configured so that when the fuel cell stack stops generating electricity, the inlet of the oxidant gas humidification path is completely submerged in water, but the temperature of the remaining oxidant gas is controlled without filling the cathode with cooling water.

[0024] In the fuel cell system of the present disclosure, the cathode path can be sealed without filling the cathode with cooling water when the fuel cell stack stops generating power.

[0025] Therefore, since the inflow of air is suppressed without causing cooling water to stagnate inside the cathode during shutdown, water clogging during startup (when power generation starts) can be suppressed, and stable power generation can be performed.

[0026] In addition, the fuel cell system of the present disclosure may also include a heater and a control unit. The heater may be provided in the cooling water tank to adjust the temperature of the cooling water. The control unit may also operate the cooling water pump after the fuel cell stack stops generating electricity. In addition, the control unit may also use the heater to adjust the temperature of the cooling water when the fuel cell stack stops generating electricity, thereby controlling the temperature of the residual oxidant gas, so that although the inlet of the oxidant gas humidification path is completely submerged in water, the cathode is not filled with cooling water.

[0027] In addition, the fuel cell system of the present disclosure may also include a temperature measuring device. The temperature measuring device may measure the temperature of cooling water discharged from the fuel cell stack or the temperature of oxidant gas discharged from the fuel cell stack. The control unit may also estimate the temperature of the oxidant gas in the cathode based on the value of the temperature measuring device.

[0028] In addition, the fuel cell system of the present disclosure may also be provided with a water level gauge. The water level gauge may be provided in the oxidant gas discharge path to detect the water level of the cooling water in the oxidant gas discharge path. The control unit may also adjust the heating amount of the heater when the fuel cell stack stops generating electricity so that the water level gauge detects a predetermined water level.

[0029] In addition, the operating method of the fuel cell system disclosed in the present invention is an operating method of a fuel cell system having a fuel cell stack, a cooling water path, a cooling water tank, a cooling water pump, an oxidant gas supply unit, an oxidant gas supply path, an oxidant gas humidification path, an oxidant gas exhaust path, an exhaust gas path and a heater. The fuel cell stack is a solid polymer type, which generates electricity by reacting the fuel gas supplied to the anode and the oxidant gas supplied to the cathode. The cooling water path is a cooling water circulation for heat exchange with the fuel cell stack. The cooling water tank is a roughly closed box arranged in a portion of the cooling water path that is lower than the fuel cell stack in the vertical direction. The cooling water tank has a gas storage unit above the cooling water storage unit for storing cooling water in the setting state, and the gas storage unit is divided into a first space and a second space in a manner that is not connected to each other regardless of the operating state of the fuel cell stack. The cooling water pump is arranged in the cooling water path to draw cooling water in the cooling water tank and supply it to the fuel cell stack. The oxidant gas supply unit supplies oxidant gas. The oxidant gas supply path connects the oxidant gas supply unit and the cooling water tank in a manner that the oxidant gas is supplied to the cooling water of the cooling water storage unit below the first space. The oxidant gas humidification path has an inlet opening to the first space and an outlet connected to the inlet of the cathode, so as to supply the oxidant gas discharged from the oxidant gas supply path and humidified and accumulated in the first space to the cathode. The oxidant gas discharge path is a path configured to supply the oxidant gas discharged from the outlet of the cathode not used for the reaction of the fuel cell stack to the cooling water of the cooling water storage unit below the second space. The oxidant gas discharge path has an inlet connected to the outlet of the cathode and an outlet opening to the cooling water of the cooling water storage unit below the second space. The exhaust gas path has an inlet opening to the second space and an outlet opening to the outside, so that the oxidant gas discharged from the oxidant gas discharge path and accumulated in the second space by gas-liquid separation can be discharged to the outside. The heater is arranged in the cooling water tank to adjust the temperature of the cooling water. In addition, in the operation method of the fuel cell system disclosed in the present invention, the fuel cell system also operates the cooling water pump after the fuel cell stack stops generating electricity. In addition, in the operating method of the fuel cell system disclosed in the present invention, when the fuel cell stack stops generating electricity, the fuel cell system uses a heater to adjust the temperature of the cooling water so that although the inlet of the oxidant gas humidification path is completely immersed in water, the cathode is not filled with cooling water.

[0030] (Insights, etc., which are the basis of this disclosure)

[0031] Since the inventors conceived of the present disclosure, in a fuel cell system, by blocking the flow of air into the cathode of the fuel cell stack when power generation is stopped, degradation of the catalyst of the fuel cell stack is suppressed.

[0032] Therefore, in this industry, in order to suppress the decrease in power generation efficiency and the increase in cost and to suppress the inflow of air into the cathode when power generation is stopped, a product design is usually performed in which a part of the cooling water is supplied to the cathode to fill the cathode with cooling water.

[0033] However, it was discovered that there is a new problem that when the cathode is filled with cooling water, the cooling water that fills the cathode must be fully drained before restarting power generation. In order to solve this problem, the subject matter of the present disclosure is formed.

[0034] Therefore, the present disclosure provides a fuel cell system and an operating method thereof that can suppress the inflow of air into the cathode when power generation stops without filling the cathode with cooling water when the fuel cell system stops power generation.

[0035] The following describes the embodiments in detail with reference to the accompanying drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of already known matters are omitted, or where repeated descriptions of substantially the same structures are omitted.

[0036] In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims through the drawings and the following description.

[0037] (Implementation Method 1)

[0038] Below, use Figure 1-2 A fuel cell system 100 in Embodiment 1 as an example of the fuel cell system of the present disclosure will be described.

[0039] [1-1. Structure]

[0040] Figure 1 is a block diagram showing the structure of the fuel cell system 100 in Embodiment 1. Figure 1 As shown, the fuel cell system 100 includes: a fuel gas supply path 1a, a fuel cell stack 4, an unreacted fuel gas exhaust path 5, a control unit 8, a cooling water pump 10, an oxidant gas supply path 11, an oxidant gas humidification path 12, an oxidant gas exhaust path 13, an exhaust gas path 14, an oxidant gas supply unit 15, an atmospheric pressure gauge 20, a cooling water tank 30, a cooling water path 40, a heater 60 and a first temperature measuring device 61.

[0041] G in the figure indicates the direction of gravity. That is, the elements recorded on the upper side of the figure indicate that they are located at a relatively high position in the vertical direction, and the elements recorded on the lower side of the figure indicate that they are located at a relatively low position in the vertical direction. Figure 1As shown, in some cases, the vertical direction in a state where the fuel cell system 100 is installed with the cooling water tank 30 located below (corresponding to the installation state of the present disclosure) is described as the up-down direction. This is also the case in the fuel cell system 200 in Embodiment 2 described later.

[0042] The fuel cell stack 4 is, for example, a solid polymer type, and is configured to generate electricity by reacting a fuel gas supplied from a fuel gas supplier 1 to an anode 4 a and an oxidant gas supplied to a cathode 4 b .

[0043] The fuel cell stack 4 is a solid polymer fuel cell stack as described above, and has the following structure: Figure 1 A plurality of single cells are stacked on the anode 4a (in the horizontal direction) and the single cells are electrically connected in series. The fuel cell stack 4 is configured to generate electricity by reacting a fuel gas supplied to the anode 4a and an oxidant gas (air) supplied to the cathode 4b.

[0044] The single cell has an electrolyte membrane-electrode assembly in which an electrolyte membrane 4c composed of a hydrogen ion conductive polymer is sandwiched between an anode electrode and a cathode electrode. In addition, the single cell has a structure in which the electrolyte membrane-electrode assembly is sandwiched between an anode separator and a cathode separator, wherein the anode separator has a groove-shaped anode flow path formed on the surface in contact with the anode electrode, and the cathode separator has a groove-shaped cathode flow path formed on the surface in contact with the cathode electrode.

[0045] Figure 1 The anode 4 a of the fuel cell stack 4 shown is an anode obtained by combining an anode electrode and an anode separator, and the cathode 4 b of the fuel cell stack 4 is a cathode obtained by combining a cathode electrode and a cathode separator.

[0046] The fuel cell stack 4 is used in an orientation in which both main surfaces of the electrolyte membrane 4 c are substantially parallel to the vertical direction.

[0047] The anode 4a is provided with an inlet and an outlet. The inlet of the anode 4a is a hole for supplying hydrogen-containing gas to the anode 4a. The outlet of the anode 4a is a hole for discharging hydrogen-containing gas not used for power generation (unreacted) from the anode 4a among the hydrogen-containing gas supplied to the anode 4a.

[0048] Furthermore, the anode flow path is formed so that the hydrogen-containing gas flowing into the anode flow path from the inlet flows toward the outlet without resisting gravity while meandering.

[0049] The cathode 4b is provided with an inlet and an outlet. The inlet of the cathode 4b is a hole for supplying the oxidant gas to the cathode 4b. The outlet of the cathode 4b is a hole for discharging the oxidant gas (unreacted) not used for power generation and the water (water vapor) generated by the electrochemical reaction of the fuel cell stack 4 from the cathode 4b.

[0050] The cathode flow path is formed so that the oxidant gas flowing into the cathode flow path from the inlet and the water (steam) generated in the cathode 4 b by the electrochemical reaction of the fuel cell stack 4 flow toward the outlet without resisting gravity while serpentine motion.

[0051] The cooling water passage 40 is configured in a ring shape so as to circulate the cooling water 30 r that performs heat exchange with the fuel cell stack 4 (for adjusting the operating temperature of the fuel cell stack 4 ).

[0052] The cooling water tank 30 is a generally closed tank provided in a portion of the cooling water path 40 that is lower than the fuel cell stack 4 in the vertical direction (gravity direction). The cooling water tank 30 has a gas storage portion 30e above a cooling water storage portion 30d storing cooling water 30r, and the gas storage portion 30e is divided into a first space 30f and a second space 30g by a shielding plate 30s. The shielding plate 30s divides the first space 30f and the second space 30g in a manner that they are not connected to each other.

[0053] When the fuel cell stack 4 stops generating electricity (when fuel gas and oxidant gas are not supplied to the fuel cell stack 4), the height of the liquid level at the lower surface of the first space 30f and the height of the liquid level at the lower surface of the second space 30g are both the same height of the liquid level 30a when stopping.

[0054] When the fuel cell stack 4 generates electricity (when the fuel gas and the oxidant gas are supplied to the fuel cell stack 4), the height of the first operation liquid level 30b, which is the lower surface of the first space 30f, is lower than the second operation liquid level 30c, which is the lower surface of the second space 30g. However, the shielding plate 30s extends downward from the upper part of the gas storage part 30e (the top surface in the cooling water tank 30) and extends to a position lower than the first operation liquid level 30b, so the first space 30f and the second space 30g are not connected to each other.

[0055] In the cooling water tank 30, the inlet of the cooling water 30r based on the cooling water path 40 is provided at a portion of the side wall on the first space 30f side that is lower than the first operation liquid level 30b. In addition, in the cooling water tank 30, the outlet of the cooling water 30r based on the cooling water path 40 is provided at a portion of the side wall on the second space 30g side that is lower than the stop liquid level 30a. In addition, the cooling water tank 30 is configured so that the inlet of the cooling water 30r based on the cooling water path 40 and the outlet of the cooling water 30r based on the cooling water path 40 are opposite to each other.

[0056] The cooling water pump 10 is provided in the cooling water path 40 at a position higher than the fuel cell stack 4 in the vertical direction, and is configured to draw cooling water 30 r in the cooling water tank 30 and supply the cooling water to the fuel cell stack 4 .

[0057] The fuel gas supplier 1 is a fuel gas infrastructure having a predetermined supply pressure. In the present embodiment, a hydrogen-containing gas having hydrogen as a main component is used as an example of the fuel gas of the present disclosure.

[0058] The fuel gas supply path 1 a is a path configured to supply the fuel gas from the fuel gas supplier 1 to the anode 4 a of the fuel cell stack 4 , and is a path connecting the fuel gas outlet in the fuel gas supplier 1 and the inlet of the anode 4 a of the fuel cell stack 4 .

[0059] The unreacted fuel gas exhaust path 5 is a path for exhausting unused fuel gas that is not used for power generation (electrochemical reaction) in the fuel gas supplied to the fuel cell stack 4 and is discharged from the outlet of the anode 4a to the outside of the fuel cell system 100. The inlet of the unreacted fuel gas exhaust path 5 is connected to the outlet of the anode 4a.

[0060] The oxidizing gas supply unit 15 is provided at the inlet of the oxidizing gas supply path 11 and is constituted by a pump. The oxidizing gas supply unit 15 increases the pressure of the outside air and supplies the air for power generation to the cathode 4b.

[0061] In addition, the oxidant gas supply unit 15 does not have a function of blocking the oxidant gas, and when the oxidant gas supply unit 15 is stopped, the oxidant gas can pass through the oxidant gas supply unit 15 by utilizing convection and pressure difference.

[0062] The oxidant gas supply path 11 is a path configured to supply the oxidant gas from the oxidant gas supply unit 15 to the cooling water 30r of the cooling water storage unit 30d below the first space 30f of the cooling water tank 30. The oxidant gas supply path 11 is a path connecting the oxidant gas supply unit 15 and the cooling water tank 30. The oxidant gas supply path 11 extends downward through the top surface of the cooling water tank 30 on the first space 30f side, and has an outlet at a position lower than the liquid level 30b during the first operation and away from the shielding plate 30s.

[0063] The oxidizing gas supplied to the cooling water 30r of the cooling water tank 30 through the oxidizing gas supply path 11 is bubbled and supplied to the first space 30f. Therefore, when the oxidizing gas supply unit 15 is operated, the humidity of the first space 30f is higher than that of the outside air.

[0064] Furthermore, since the oxidizing gas supply passage 11 has an outlet at a position away from the shielding plate 30s, it is possible to suppress the oxidizing gas supplied from the oxidizing gas supply passage 11 from passing over the shielding plate 30s and being supplied to the second space 30g.

[0065] The oxidizing gas humidifying passage 12 is a passage configured to supply the oxidizing gas discharged from the oxidizing gas supply passage 11 into the cooling water 30r and humidified and accumulated in the first space 30f to the cathode 4b. The oxidizing gas humidifying passage 12 is a passage having an inlet opening into the first space 30f and an outlet connected to the inlet of the cathode 4b.

[0066] The oxidizing gas humidifying passage 12 extends downward through the ceiling surface of the cooling water tank 30 on the first space 30f side, and has an inlet below the stop liquid level 30a and above the first operation liquid level 30b.

[0067] The oxidant gas discharge path 13 is a path for supplying the unused oxidant gas discharged from the outlet of the cathode 4b and the water (water vapor) generated in the cathode 4b by the electrochemical reaction of the fuel cell stack 4 to the cooling water tank 30. The unused oxidant gas discharged from the outlet of the cathode 4b is the oxidant gas that is not used for power generation (electrochemical reaction) among the oxidant gas supplied to the fuel cell stack 4. The oxidant gas discharge path 13 is a path configured to supply the unused oxidant gas from the outlet of the cathode 4b and the water (water vapor) generated in the cathode 4b to the cooling water 30r of the cooling water storage portion 30d below the second space 30g.

[0068] The oxidizing gas discharge path 13 has an inlet connected to the outlet of the cathode 4b and an outlet opening into the cooling water 30r in the cooling water reservoir 30d below the second space 30g. The oxidizing gas discharge path 13 is configured to slope downward from the inlet toward the outlet.

[0069] The oxidizing gas discharge path 13 extends downward through the ceiling surface of the cooling water tank 30 on the second space 30g side, and has an outlet below the stop liquid level 30a and the second operation liquid level 30c.

[0070] The exhaust gas path 14 is a path configured to discharge the oxidant gas discharged from the oxidant gas discharge path 13 into the cooling water 30r and accumulated in the second space 30g after gas-liquid separation to the outside of the fuel cell system 100. The exhaust gas path 14 is a path having an inlet opening at the top surface of the cooling water tank 30 on the second space 30g side and an outlet opening to the outside.

[0071] The control unit 8 only needs to be a control unit with a control function, and it has a computer system (not shown), and the computer system has a processing unit (not shown) and a storage unit (not shown) for storing a control program. As the processing unit, a CPU (Central Processing Unit) can be exemplified. As the storage unit, a memory can be exemplified. The CPU executes the control program stored in the memory, whereby the computer system functions as the control unit 8. It is assumed here that the control program executed by the CPU is pre-recorded in the memory of the computer system, but it can also be recorded in a non-temporary recording medium such as a memory card and provided, or it can be provided through an electrical communication line such as the Internet.

[0072] The atmospheric pressure gauge 20 is a pressure measuring device for measuring the atmospheric pressure.

[0073] The cooling water tank 30 is a water tank that stores the generated water generated by the operation of the fuel cell stack 4 as cooling water 30r. The cooling water tank 30 is arranged at a position lower than the fuel cell stack 4, and can make the generated water discharged through the oxidant gas discharge path 13 fall under the action of gravity, and the fallen generated water is recovered as cooling water 30r.

[0074] The cooling water tank 30 has a substantially sealed structure except for the connection portions with the oxidant gas supply path 11 , the oxidant gas humidification path 12 , the oxidant gas discharge path 13 , the exhaust gas path 14 , and the cooling water path 40 .

[0075] The oxidant gas flow space inside the cooling water tank 30 is divided by the shielding plate 30s into a first space 30f through which the humidified oxidant gas flows, and a second space 30g which is open to the atmosphere and through which unused oxidant gas flows.

[0076] The first space 30f is connected to an oxidant gas supply path 11 and an oxidant gas humidification path 12 for supplying oxidant gas to the fuel cell stack 4. The second space 30g is connected to an oxidant gas discharge path 13 and an exhaust gas path 14.

[0077] The cooling water path 40 connects the cooling water tank 30, the fuel cell stack 4 and the cooling water pump 10 in a ring shape. In addition, the cooling water path 40 is a path configured such that the cooling water 30r in the cooling water tank 30 is supplied to the fuel cell stack 4 by the cooling water pump 10 (through the cooling water pump 10), and the cooling water 30r after heat exchange with the fuel cell stack 4 returns to the cooling water tank 30.

[0078] The heater 60 is located in the cooling water storage portion 30 d (a portion immersed in the cooling water 30 r ) in the cooling water tank 30 , and is a heater for heating the cooling water 30 r (adjusting the temperature of the cooling water 30 r ).

[0079] The first temperature measuring device 61 is a temperature measuring device provided in a path in the cooling water path 40 where the cooling water 30 r flows after completing heat exchange with the fuel cell stack 4 and returns to the cooling water tank 30 , and measures the temperature of the cooling water 30 r passing through the cooling water path 40 .

[0080] The fuel cell system 100 is configured such that, when the fuel cell stack 4 stops power generation, the inlet of the oxidant gas humidification path 12 is completely submerged in water, but the cathode 4b is not filled with the cooling water 30r.

[0081] [1-2. Action]

[0082] The operation and effects of the fuel cell system 100 configured as described above will be described below.

[0083] First, based on Figure 1 The operation of the fuel cell system 100 when power generation is stopped will be described.

[0084] In the first embodiment, the fuel gas supplied from the fuel gas supplier 1 is a gas mainly containing hydrogen. In the case where the fuel gas is generated by reforming a hydrocarbon raw gas, the fuel gas supplied from the fuel gas supplier 1 may contain carbon dioxide, carbon monoxide, methane, nitrogen, argon, water vapor, and other gases as impurities. In addition, the oxidant gas supplied from the oxidant gas supplier 15 is air, which is mainly composed of nitrogen, oxygen, argon, and carbon dioxide.

[0085] When the fuel cell stack 4 stops generating electricity, the fuel gas for generating electricity from the fuel gas supplier 1 to the anode 4a is stopped, and the unreacted fuel gas exhaust path 5 is also closed. However, in order to keep the anode 4a at a positive pressure, the fuel gas is regularly supplied to the anode 4a from the fuel gas supplier 1 even after the fuel cell stack 4 stops generating electricity, to prevent the oxidant gas from invading the anode 4a from the outside of the fuel cell system 100.

[0086] In addition, when the fuel cell stack 4 stops generating electricity, the fuel cell system 100 stops the oxidant gas supply unit 15. When the fuel cell system 100 stops the oxidant gas supply unit 15, the pressures of the first space 30f and the second space 30g of the cooling water tank 30 both become atmospheric pressure. This is because the oxidant gas supply unit 15 does not have a function of blocking the oxidant gas, and because the exhaust gas path 14 connects the second space 30g of the cooling water tank 30 to the outside air (atmosphere).

[0087] Therefore, the liquid level of the cooling water tank 30 when the fuel cell stack 4 stops generating electricity is consistent with the liquid level 30a when the fuel cell stack 4 stops generating electricity in both the first space 30f and the second space 30g. When the fuel cell stack 4 stops generating electricity, the outlet (downstream end) of the oxidant gas supply path 11, the inlet (upstream end) of the oxidant gas humidification path 12, and the outlet (downstream end) of the oxidant gas discharge path 13 are respectively located below the liquid level 30a when the fuel cell stack 4 stops generating electricity, and are immersed in the cooling water 30r.

[0088] By adopting such a state, the oxidant gas remaining in the cathode 4 b , the oxidant gas humidification passage 12 , and the oxidant gas discharge passage 13 can be sealed.

[0089] Next, the oxidant gas remaining in the cathode 4b, the oxidant gas humidification path 12, and the oxidant gas exhaust path 13 after the fuel cell stack 4 stops generating electricity is defined as residual oxidant gas, and a method of controlling the pressure of the residual oxidant gas is described.

[0090] As the first condition, the pressure of the residual oxidant gas at a high temperature T0 (K) after the fuel cell stack 4 is stopped is set to P0 (Pa), and the volume is set to V0 (m 3 ). Immediately after the fuel cell stack 4 stops generating electricity, the pressure P0 (kPa) of the residual oxidant gas can be approximately the same as the atmospheric pressure. That is, the pressure P0 (Pa) can be translated as the atmospheric pressure P0 (Pa). The temperature T0 (K) is approximately the same as the temperature when the fuel cell stack 4 is operating.

[0091] As the second condition, the pressure of the residual oxidant gas when the oxygen in the residual oxidant gas is completely consumed by the fuel gas of the anode 4a is denoted as P1 (Pa), and the volume is denoted as V1 (m 3 ). When the oxidant gas is air, the nitrogen concentration in the air is 79(%) and the oxygen concentration is 21(%), so the pressure P1 (Pa) is expressed by the following (Formula 1).

[0092] [Formula 1]

[0093] P1=0.79×P0

[0094] Since only oxygen consumption is considered, the volume V1 (m 3 ) and volume V0(m 3 )equal.

[0095] As a third condition, in addition to studying the consumption of oxygen in the residual oxidant gas, the temperature reduction of the fuel cell stack 4 was also studied. The pressure of the residual oxidant gas at this time was set to P2 (Pa) and the temperature was set to T2 (K). In order to find the degree of reduction in the pressure P2 (Pa), the volume V2 (m 3 ) and V0(m 3 ) are equal. The pressure P2 (Pa) of the residual oxidant gas at this time is expressed by the following (Formula 2).

[0096] [Formula 2]

[0097]

[0098] Since T2(K)<T0(K), the pressure P2(Pa) is smaller than P0(Pa), and a negative pressure is generated. The generated negative pressure sucks the cooling water 30r in the cooling water tank 30 through the oxidant gas humidification path 12 and the oxidant gas discharge path 13 until it reaches equilibrium with the atmospheric pressure P0(Pa). The height of the sucked cooling water 30r at this time, i.e., the water head difference, is set to h(m).

[0099] As the fourth condition, the balance between the pressure P2 (Pa) of the residual oxidant gas calculated under the third condition and the atmospheric pressure P0 (Pa) was investigated. The density of the cooling water 30r in the cooling water tank 30 was set to ρ (kg / m 3 ), set the acceleration due to gravity to g(m / s 2 ), the head difference from the liquid surface 30a when stopped due to negative pressure is set to h (m), and the pressure of the residual oxidant gas when balanced with the atmospheric pressure is set to P3 (Pa). The pressure P3 (Pa) of the residual oxidant gas at this time is expressed by the following (Formula 3).

[0100] [Formula 3]

[0101] P3=P0-ρgh

[0102] The cross-sectional area of ​​the pipes of the oxidizing gas humidifying passage 12 and the oxidizing gas exhaust passage 13 is S (m 2 ). When the volume of the residual oxidant gas when the water head difference h (m) is balanced with the atmospheric pressure at a pressure of P3 (Pa) is set to V3 (m 3 ), volume V3(m 3 ) is expressed by the following (Formula 4).

[0103] [Formula 4]

[0104] V3=V0-Sh

[0105] Based on the above, using the Boyle-Charles equation and (Formula 4), the pressure P3 (Pa) of the residual oxidant gas in equilibrium with the atmospheric pressure is expressed by the following (Formula 5).

[0106] [Formula 5]

[0107]

[0108] According to (Formula 5), ​​if the temperature T2 (K) of the residual oxidant gas is set high, the pressure P3 (Pa) increases, and if the temperature T2 (K) decreases, the pressure P3 (Pa) decreases.

[0109] Since (Formula 3) and (Formula 5) are equal, if the water head difference h(m) is solved as a quadratic equation, the water head difference h(m) can be obtained by adjusting the temperature T2(K) of the residual oxidant gas. Therefore, the pressure P3(Pa) can be controlled according to (Formula 3), and the volume V3(m 3 ).

[0110] When the temperature measured by the first temperature measuring device 61 is set to TK (K), the temperature TK (K) of the cooling water 30r passing through the cooling water path 40 in the fuel cell stack 4 and the temperature T2 (K) of the residual oxidant gas can be considered to be substantially the same. Therefore, by adjusting the temperature of the cooling water 30r in the cooling water tank 30, the temperature T2 (K) of the residual oxidant gas can be made variable, and the pressure P3 (Pa) of the residual oxidant gas and the volume V3 (m 3 ) for control.

[0111] Next, a method for controlling the temperature of the cooling water 30r in the cooling water tank 30 to a predetermined temperature TS (K) is described. The rated calorific value of the heater 60 is Q (W), the operation amount of the heater 60 is H (%), and the heat transfer efficiency from the heater 60 to the cooling water 30r is γ (-). In addition, the specific heat of the cooling water 30r is Cp (J / kg·K), and the mass is W (kg). At this time, the heating amount Q1 (W) that can be heated from the heater 60 to the cooling water 30r is expressed by the following (Formula 6).

[0112] [Formula 6]

[0113] Q1=γ×H×Q

[0114] Furthermore, when the cooling water 30r is heated by the heating amount Q1 (W) for a period of time t (s), the following relationship (Formula 7) is approximately obtained.

[0115] [Formula 7]

[0116] Q1×t=Cp×W×(TS-T2)

[0117] Regarding (Formula 6) and (Formula 7), since the amount of heating Q1 (W) is equal, the following (Formula 8) can be derived.

[0118] [Formula 8]

[0119]

[0120] Therefore, the operation amount H(%) of the heater 60 can be operated to adjust the heating amount Q1(W) of the heater 60. Thus, the temperature difference TS-T2(K) until the temperature of the cooling water 30r in the cooling water tank 30 reaches the predetermined temperature TS(K) can be changed, and the temperature T2(K) of the residual oxidant gas can be controlled to the predetermined temperature TS(K).

[0121] When the volume of cathode 4b is set to VC (m 3 ) is to prevent the cooling water 30r drawn through the oxidant gas humidification path 12 and the oxidant gas discharge path 13 from intruding into the cathode 4b, and to form VC (m 3 )=V3(m 3 Therefore, the temperature of the cooling water 30r is controlled to a predetermined temperature TS (K) so that the volume of the residual oxidant gas becomes VC (m 3 ).

[0122] Figure 2 The pressure P3 (Pa) and volume V3 (m 3 ) relative to the temperature T2 (K) of the residual oxidant gas. Figure 2 , the pressure P3 (Pa) of the residual oxidant gas and the volume V3 (m 3 ) for explanation.

[0123] When the temperature T2 (K) of the residual oxidant gas decreases, according to (Formula 4) and (Formula 5), ​​the pressure P3 (Pa) and volume V3 (m 3 )reduce.

[0124] If the volume of the residual oxidant gas V3 (m 3 ) is smaller than the volume VC (m 3 ) is small, the attracted cooling water 30r penetrates into the cathode 4b. Therefore, the volume V3 (m 3) and the volume VC (m 3 ) is equal to the target predetermined temperature TS (K) of the cooling water 30r.

[0125] That is, by operating the operation amount H(%) of the heater 60 in accordance with (Formula 8) so as to reach a predetermined temperature TS(K) or higher, the cooling water 30r having a predetermined temperature TS(K) or higher is supplied to the fuel cell stack 4 by the cooling water pump 10 .

[0126] Thus, the temperature T2 (K) of the residual oxidant gas can be made higher than the predetermined temperature TS (K), and the volume V3 (m 3 ) is the volume VC (m 3 ) or more, so that the cathode 4b can be sealed without filling it with cooling water 30r.

[0127] The above describes the behavior of the fuel cell stack 4 after stopping power generation. If the power generation of the fuel cell stack 4 is stopped for a long time, the fuel gas is supplied to keep the anode 4a at a positive pressure, but a part of the fuel gas supplied to the anode 4a passes through the electrolyte membrane 4c and mixes with the residual oxidant gas of the cathode 4b. The pressure P3 (Pa) of the residual oxidant gas after mixing is equal to the atmospheric pressure due to the fuel gas passing through the electrolyte membrane 4c from the anode 4a to the cathode 4b.

[0128] As a result, the head difference h (m) from the liquid surface 30 a when stopped due to the generation of negative pressure becomes substantially 0, and the cooling water 30 r sucked through the oxidant gas humidification path 12 and the oxidant gas discharge path 13 is recovered again in the cooling water tank 30 .

[0129] Next, based on Figure 1 , the operation of the fuel cell system 100 during operation will be described.

[0130] As described above, in Embodiment 1, the fuel gas supplied from the fuel gas supplier 1 is a gas mainly containing hydrogen. In the case where the fuel gas is generated by reforming a hydrocarbon raw gas, the fuel gas supplied from the fuel gas supplier 1 may contain carbon dioxide, carbon monoxide, methane, nitrogen, argon, water vapor, and other gases as impurities. In addition, the oxidant gas supplied from the oxidant gas supplier 15 is air, which is mainly composed of nitrogen, oxygen, argon, and carbon dioxide.

[0131] When the fuel cell stack 4 is in operation, the fuel gas is supplied from the fuel gas supplier 1 to the anode 4 a of the fuel cell stack 4 , and the oxidant gas is supplied from the oxidant gas supplier 15 to the cathode 4 b of the fuel cell stack 4 .

[0132] When the fuel cell stack 4 is in operation, the oxidant gas is humidified by the cooling water 30 r in the cooling water tank 30 via the oxidant gas supply path 11 , and is supplied to the cathode 4 b via the first space 30 f and the oxidant gas humidification path 12 .

[0133] The unreacted oxidant gas and produced water not used in the cathode 4b are supplied to the cooling water tank 30 via the oxidant gas discharge path 13. The unreacted oxidant gas and produced water supplied to the cooling water tank 30 are recovered as cooling water 30r in the cooling water tank 30. The remaining unreacted oxidant gas is discharged to the outside of the fuel cell system 100 via the second space 30g and the exhaust gas path 14.

[0134] The cooling water tank 30 is partitioned in the middle by the shielding plate 30s, but the cooling water 30r in the cooling water tank 30 can flow between the first space 30f and the second space 30g through the gap between the bottom surface of the cooling water tank 30 and the lower end of the shielding plate 30s.

[0135] The liquid level of the cooling water 30r existing in the first space 30f side when the fuel cell stack 4 is operating is referred to as a first operating liquid level 30b, and the liquid level of the cooling water 30r existing in the second space 30g side when the fuel cell stack 4 is operating is referred to as a second operating liquid level 30c.

[0136] When the fuel cell stack 4 is in operation, the first space 30f is supplied with the oxidant gas whose pressure is increased by the oxidant gas supply unit 15. On the other hand, the oxidant gas is similarly supplied from the oxidant gas supply unit 15 to the second space 30g, and thus the pressure is increased. However, since the second space 30g is located downstream of the first space 30f in the flow direction of the oxidant gas, the pressure mainly decreases according to the pressure loss of the cathode 4b.

[0137] Therefore, when the fuel cell stack 4 is operating, the second operating liquid level 30c is higher than the first operating liquid level 30b which is the liquid level when the fuel cell stack 4 is operating. When the fuel cell stack 4 is operating, the outlet (downstream end) of the oxidant gas supply path 11 is located below the first operating liquid level 30b and is immersed in the cooling water 30r.

[0138] When the fuel cell stack 4 is in operation, the inlet (upstream end) of the oxidant gas humidification path 12 is located at a position higher than the first operation liquid level 30b, and is not immersed in the cooling water 30r but exists in the first space 30f. When the fuel cell stack 4 is in operation, the outlet (downstream end) of the oxidant gas discharge path 13 is located at a position lower than the second operation liquid level 30c, and is immersed in the cooling water 30r.

[0139] [1-3. Effects, etc.]

[0140] As described above, in this embodiment, the fuel cell system 100 includes: a fuel cell stack 4, a cooling water path 40, a cooling water tank 30, a cooling water pump 10, an oxidant gas supply unit 15, an oxidant gas supply path 11, an oxidant gas humidification path 12, an oxidant gas exhaust path 13 and an exhaust gas path 14.

[0141] The fuel cell stack 4 is a solid polymer type, and is configured to generate electricity by reacting a fuel gas supplied to an anode 4 a and an oxidant gas supplied to a cathode 4 b .

[0142] The cooling water passage 40 is configured to circulate the cooling water 30 r that exchanges heat with the fuel cell stack 4 .

[0143] The cooling water tank 30 is a substantially sealed tank provided in a portion of the cooling water path 40 that is lower than the fuel cell stack 4 in the vertical direction. The cooling water tank 30 has a gas storage portion 30e above a cooling water storage portion 30d that stores cooling water 30r when installed. The gas storage portion 30e is divided into a first space 30f and a second space 30g so as not to communicate with each other regardless of the operating state of the fuel cell stack 4.

[0144] The cooling water pump 10 is provided in the cooling water path 40 to pump the cooling water 30 r in the cooling water tank 30 and supply the cooling water to the fuel cell stack 4 .

[0145] The oxidizing gas supply unit 15 is configured to supply oxidizing gas. The oxidizing gas supply path 11 is a path that connects the oxidizing gas supply unit 15 and the cooling water tank 30 so as to supply oxidizing gas to the cooling water 30r in the cooling water storage unit 30d below the first space 30f.

[0146] The oxidant gas humidifying passage 12 is a passage whose inlet opens to the first space 30f and whose outlet is connected to the inlet of the cathode 4b, so as to supply the oxidant gas discharged from the oxidant gas supply passage 11 and humidified and accumulated in the first space 30f to the cathode 4b.

[0147] The oxidant gas discharge path 13 is a path configured to supply the oxidant gas discharged from the outlet of the cathode 4b without being used for the reaction of the fuel cell stack 4 to the cooling water 30r in the cooling water storage part 30d below the second space 30g. The oxidant gas discharge path 13 is a path whose inlet is connected to the outlet of the cathode 4b and whose outlet is open to the cooling water 30r in the cooling water storage part 30d below the second space 30g.

[0148] The exhaust gas passage 14 is a passage configured to discharge the oxidizing gas discharged from the oxidizing gas discharge passage 13 and accumulated in the second space 30g after gas-liquid separation to the outside, and has an inlet opening to the second space 30g and an outlet opening to the outside.

[0149] Furthermore, the fuel cell system 100 of this embodiment is configured such that when the fuel cell stack 4 stops generating power, the inlet of the oxidant gas humidification path 12 is completely submerged in water, but the temperature of the remaining oxidant gas is controlled so that the cathode 4b is not filled with the cooling water 30r.

[0150] When the fuel cell stack 4 stops generating electricity, the cathode 4b, the oxidant gas humidification path 12, and the oxidant gas exhaust path 13 become negative pressure, and thus the cooling water 30r in the cooling water tank 30 is sucked up from the oxidant gas humidification path 12 and the oxidant gas exhaust path 13. In contrast, those skilled in the art can also appropriately design the dimensions of each structure in the fuel cell system 100 without filling the cathode 4b with the cooling water 30r. The dimensions of each structure in the fuel cell system 100 refer to, for example, the dimensions of the interior (including the path) of the cooling water tank 30, the amount of cooling water 30r in the cooling water tank 30, the inner diameter and length of the oxidant gas humidification path 12 and the oxidant gas exhaust path 13, the volume (capacity) of the cathode 4b, and the distance in the height direction between the fuel cell stack 4 and the cooling water tank 30. In the fuel cell system designed in this way, when the fuel cell stack 4 stops generating electricity, even if the cooling water 30r is not circulated by the cooling water pump 10 or heated by the heater 60, the cathode 4b can be prevented from being filled with the cooling water 30r.

[0151] In contrast, the fuel cell system 100 of the present embodiment is configured such that when the fuel cell stack 4 stops generating power, the inlet of the oxidant gas humidification path 12 is completely submerged in water, but the temperature of the remaining oxidant gas is controlled without filling the cathode 4b with the cooling water 30r. Therefore, in the fuel cell system 100 of the present embodiment, when the fuel cell stack 4 stops generating power, the cathode path can be sealed without filling the cathode 4b with the cooling water 30r.

[0152] Therefore, in the fuel cell system 100, when power generation is stopped, the inflow of air is suppressed without causing the cooling water 30r to stagnate inside the cathode 4b, so that water clogging at startup (at the start of power generation) can be suppressed and stable power generation can be performed.

[0153] In addition, in the fuel cell system 100, there is no restriction on the size of each structure for making the cathode 4b not be filled with cooling water 30r even though the inlet of the oxidant gas humidification path 12 is completely submerged in water when the fuel cell stack 4 stops generating electricity. Therefore, in the fuel cell system 100, the degree of freedom in designing each structure in the fuel cell system 100 can be increased.

[0154] In addition, as in the present embodiment, the fuel cell system 100 includes a heater 60 and a control unit 8. The heater 60 is disposed in the cooling water tank 30 to adjust the temperature of the cooling water 30r. The control unit 8 operates the cooling water pump 10 even after the fuel cell stack 4 stops generating electricity, and uses the heater 60 to adjust the temperature of the cooling water 30r when the fuel cell stack 4 stops generating electricity, so that although the inlet of the oxidant gas humidification path 12 is completely submerged in water, the cathode 4b is not filled with the cooling water 30r.

[0155] If, when the fuel cell stack 4 stops generating electricity, the cooling water 30r heated to a predetermined temperature by the heater 60 is not circulated by the cooling water pump 10, the cathode 4b may be filled with the cooling water 30r. In contrast, in the fuel cell system 100, when the fuel cell stack 4 stops generating electricity, the cooling water 30r heated to a predetermined temperature by the heater 60 is circulated by the cooling water pump 10. Thus, in the fuel cell system 100, when generating electricity is stopped, the cooling water 30r can be sucked and introduced from the cooling water tank 30 to the oxidant gas humidification path 12 and the oxidant gas exhaust path 13 while adjusting the temperature of the residual oxidant gas of the cathode 4b. As a result, in the fuel cell system 100, the cathode 4b can be sealed without being filled with the cooling water 30r. Therefore, in the fuel cell system 100, since the inflow of air is suppressed without causing the cooling water 30r to remain inside the cathode 4b when generating electricity is stopped, the water clogging of the cathode 4b at the start (at the start of generating electricity) can be suppressed, and stable generating electricity can be implemented.

[0156] Furthermore, as in the present embodiment, the fuel cell system 100 includes the first temperature measuring device 61 , which is an example of a temperature measuring device of the present disclosure and measures the temperature of the cooling water 30 r discharged from the fuel cell stack 4 .

[0157] More specifically, the first temperature measuring device 61 measures the temperature of the cooling water 30r in the cooling water path 40 returning from the fuel cell stack 4 to the cooling water tank 30. The control unit 8 estimates the temperature of the cathode 4b (sealed residual oxidant gas) based on the value of the first temperature measuring device 61.

[0158] Thus, in the fuel cell system 100, it is possible to measure the temperature inside the fuel cell stack 4 at a position upstream of the first temperature measuring device 61. Therefore, in the fuel cell system 100, it is possible to estimate the temperature of the cathode 4b (sealed residual oxidant gas) based on the value of the first temperature measuring device 61, and to adjust the temperature of the cooling water 30r using the heater 60 based on the estimated value, thereby controlling the pressure of the residual oxidant gas.

[0159] In the present embodiment, the fuel cell system 100 may be modified such that the first temperature measuring device 61 measures the temperature of the oxidizing gas in the oxidizing gas exhaust path 13 instead of measuring the temperature of the cooling water 30 r in the cooling water path 40 .

[0160] Therefore, in this deformed fuel cell system, the temperature of the cathode 4b (sealed residual oxidant gas) can be estimated based on the measurement value of the first temperature measuring device 61, and the temperature of the cooling water 30r can be adjusted using the heater 60 based on the estimated value, thereby controlling the pressure of the residual oxidant gas.

[0161] (Implementation Method 2)

[0162] Below, use Figure 2-3 A fuel cell system 200 according to Embodiment 2 as an example of the fuel cell system of the present disclosure will be described.

[0163] [2-1. Structure]

[0164] Figure 3 2 is a block diagram showing the structure of the fuel cell system 200 in Embodiment 2. Figure 3 As shown, the fuel cell system 200 includes: a fuel gas supply path 1a, a fuel cell stack 4, an unreacted fuel gas exhaust path 5, a control unit 8, a cooling water pump 10, an oxidant gas supply path 11, an oxidant gas humidification path 12, an oxidant gas exhaust path 13, an exhaust gas path 14, an oxidant gas supply unit 15, an atmospheric pressure gauge 20, a cooling water tank 30, a cooling water path 40, a heater 60, a first temperature measuring device 61, a second temperature measuring device 62 and a water level meter 70.

[0165] G in the figure indicates the direction of gravity. That is, the elements written on the upper side of the figure indicate that they are located at a relatively high position in the vertical direction, and the elements written on the lower side of the figure indicate that they are located at a relatively low position in the vertical direction.

[0166] The fuel cell system 200 in the second embodiment is different from the fuel cell system 100 in the first embodiment in that, in addition to the structure of the fuel cell system 100, it also includes a second temperature measuring device 62 and a water level gauge 70. The same reference numerals are given to the same structures as those of the fuel cell system 100 in the first embodiment, and the description thereof is omitted.

[0167] The second temperature measuring device 62 is a temperature measuring device that measures the temperature of the cooling water 30r flowing into the fuel cell stack 4 (at a position upstream of the fuel cell stack 4). The second temperature measuring device 62 is provided in a path upstream of the fuel cell stack 4 in the cooling water path 40 (a path between the fuel cell stack 4 and the cooling water pump 10).

[0168] The water level meter 70 is provided on the path of the oxidant gas exhaust path 13, measures the water level of the cooling water 30r sucked from the cooling water tank 30, and detects that the cooling water 30r is sucked to a certain water level.

[0169] [2-2. Action]

[0170] The operation and effects of the fuel cell system 200 configured as described above will be described below.

[0171] First, based on Figure 3 The operation when power generation is stopped in the fuel cell system 200 will be described.

[0172] In the second embodiment, the fuel gas supplied from the fuel gas supplier 1 is also a gas mainly containing hydrogen. In the case where the fuel gas is generated by reforming a hydrocarbon raw gas, the fuel gas supplied from the fuel gas supplier 1 may contain carbon dioxide, carbon monoxide, methane, nitrogen, argon, water vapor and other gases as impurities. In addition, the oxidant gas supplied from the oxidant gas supplier 15 is air, which is mainly composed of nitrogen, oxygen, argon and carbon dioxide.

[0173] When the fuel cell stack 4 stops generating electricity, the fuel gas for generating electricity from the fuel gas supplier 1 to the anode 4a is stopped, and the unreacted fuel gas exhaust path 5 is also closed. However, in order to keep the anode 4a at a positive pressure, the fuel gas is regularly supplied to the anode 4a from the fuel gas supplier 1 even after the fuel cell stack 4 stops generating electricity, to prevent the oxidant gas from invading the anode 4a from the outside of the fuel cell system 100.

[0174] In addition, when the fuel cell stack 4 stops generating electricity, the fuel cell system 200 stops the oxidant gas supply unit 15. When the fuel cell system 200 stops the oxidant gas supply unit 15, the pressures of the first space 30f and the second space 30g of the cooling water tank 30 both become atmospheric pressure. This is because the oxidant gas supply unit 15 does not have a function of blocking the oxidant gas, and because the exhaust gas path 14 connects the second space 30g of the cooling water tank 30 to the outside air (atmosphere).

[0175] Therefore, the liquid level of the cooling water tank 30 when the fuel cell stack 4 stops generating electricity is consistent with the liquid level 30a when the fuel cell stack 4 stops generating electricity in both the first space 30f and the second space 30g. When the fuel cell stack 4 stops generating electricity, the outlet (downstream end) of the oxidant gas supply path 11, the inlet (upstream end) of the oxidant gas humidification path 12, and the outlet (downstream end) of the oxidant gas discharge path 13 are respectively located below the liquid level 30a when the fuel cell stack 4 stops generating electricity, and are immersed in the cooling water 30r.

[0176] By adopting such a state, the oxidant gas remaining in the cathode 4 b , the oxidant gas humidification passage 12 , and the oxidant gas discharge passage 13 can be sealed.

[0177] Next, the oxidant gas remaining in the cathode 4b, the oxidant gas humidification path 12, and the oxidant gas exhaust path 13 after the fuel cell stack 4 stops generating electricity is defined as residual oxidant gas, and a method of controlling the pressure of the residual oxidant gas is described.

[0178] As the first condition, the pressure of the residual oxidant gas at a high temperature T0 (K) after the fuel cell stack 4 is stopped is set to P0 (Pa), and the volume is set to V0 (m 3 ). Immediately after the fuel cell stack 4 stops generating electricity, the pressure P0 (kPa) of the residual oxidant gas can be approximately the same as the atmospheric pressure. That is, the pressure P0 (Pa) can be translated as the atmospheric pressure P0 (Pa). The temperature T0 (K) is approximately the same as the temperature when the fuel cell stack 4 is operating.

[0179] As the second condition, the pressure of the residual oxidant gas when the oxygen in the residual oxidant gas is completely consumed by the fuel gas of the anode 4a is denoted as P1 (Pa), and the volume is denoted as V1 (m 3 ). When the oxidant gas is air, the nitrogen concentration in the air is 79(%) and the oxygen concentration is 21(%), so the pressure P1 (Pa) is expressed by (Formula 1).

[0180] Since only oxygen consumption is considered, the volume V1 (m 3 ) and volume V0(m 3 )equal.

[0181] As a third condition, in addition to studying the consumption of oxygen in the residual oxidant gas, the temperature reduction of the fuel cell stack 4 was also studied. The pressure of the residual oxidant gas at this time was set to P2 (Pa) and the temperature was set to T2 (K). In order to find the degree of reduction in the pressure P2 (Pa), the volume V2 (m 3 ) and V0(m 3 ) are equal. The pressure P2 (Pa) of the residual oxidant gas at this time is expressed by (Formula 2).

[0182] Since T2(K)<T0(K), the pressure P2(Pa) is smaller than P0(Pa), and a negative pressure is generated. The generated negative pressure sucks the cooling water 30r in the cooling water tank 30 through the oxidant gas humidification path 12 and the oxidant gas discharge path 13 until it reaches equilibrium with the atmospheric pressure P0(Pa). The height of the sucked cooling water 30r at this time, i.e., the water head difference, is set to h(m).

[0183] As the fourth condition, the balance between the pressure P2 (Pa) of the residual oxidant gas calculated under the third condition and the atmospheric pressure P0 (Pa) was investigated. The density of the cooling water 30r in the cooling water tank 30 was set to ρ (kg / m 3 ), set the acceleration due to gravity to g(m / s 2 ), the head difference from the liquid surface 30a when stopped due to negative pressure is set to h (m), and the pressure of the residual oxidant gas when balanced with the atmospheric pressure is set to P3 (Pa). The pressure P3 (Pa) of the residual oxidant gas at this time is expressed by (Formula 3).

[0184] The cross-sectional area of ​​the pipes of the oxidizing gas humidifying passage 12 and the oxidizing gas exhaust passage 13 is S (m 2 ). When the volume of the residual oxidant gas when the water head difference h (m) is balanced with the atmospheric pressure at a pressure of P3 (Pa) is set to V3 (m 3 ), volume V3(m 3 ) is expressed by (Formula 4).

[0185] Based on the above, using the Boyle-Charles equation and (Formula 4), the pressure P3 (Pa) of the residual oxidant gas in equilibrium with the atmospheric pressure is expressed by (Formula 5).

[0186] According to (Formula 5), ​​if the temperature T2 (K) of the residual oxidant gas is set high, the pressure P3 (Pa) increases, and if the temperature T2 (K) decreases, the pressure P3 (Pa) decreases.

[0187] Since (Formula 3) and (Formula 5) are equal, if the water head difference h(m) is solved as a quadratic equation, the water head difference h(m) can be obtained by adjusting the temperature T2(K) of the residual oxidant gas. Therefore, the pressure P3(Pa) can be controlled according to (Formula 3), and the volume V3(m 3 ).

[0188] When the temperature measured by the first temperature measuring device 61 is set to TK (K), the temperature TK (K) of the cooling water 30r passing through the cooling water path 40 in the fuel cell stack 4 and the temperature T2 (K) of the residual oxidant gas can be considered to be substantially the same. Therefore, by adjusting the temperature of the cooling water 30r in the cooling water tank 30, the temperature T2 (K) of the residual oxidant gas can be made variable, and the pressure P3 (Pa) of the residual oxidant gas and the volume V3 (m 3 ) for control.

[0189] Next, a method for controlling the temperature of the cooling water 30r in the cooling water tank 30 to a predetermined temperature TS (K) is described. The rated calorific value of the heater 60 is Q (W), the operation amount of the heater 60 is H (%), and the heat transfer efficiency from the heater 60 to the cooling water 30r is γ (-). In addition, the specific heat of the cooling water 30r is Cp (J / kg·K), and the mass is W (kg). At this time, the amount of heat Q1 (W) that can be heated from the heater 60 to the cooling water 30r is expressed by (Formula 6).

[0190] Furthermore, when the cooling water 30r is heated by the heating amount Q1 (W) for a period of time t (s), the relationship represented by (Formula 7) is approximately achieved.

[0191] Since the heating amount Q1 (W) is equal to that of (Formula 6) and (Formula 7), (Formula 8) can be derived.

[0192] Therefore, the operation amount H(%) of the heater 60 can be operated to adjust the heating amount Q1(W) of the heater 60. Thus, the temperature difference TS-T2(K) until the temperature of the cooling water 30r in the cooling water tank 30 reaches the predetermined temperature TS(K) can be changed, and the temperature T2(K) of the residual oxidant gas can be controlled to the predetermined temperature TS(K).

[0193] When the volume of cathode 4b is set to VC (m 3 ) is to prevent the cooling water 30r drawn through the oxidant gas humidification path 12 and the oxidant gas discharge path 13 from intruding into the cathode 4b, and to form VC (m 3 )=V3(m 3Therefore, the temperature of the cooling water 30r is controlled to a predetermined temperature TS (K) so that the volume of the residual oxidant gas becomes VC (m 3 ).

[0194] A water level gauge 70 is provided on the oxidant gas discharge path 13. Here, the distance from the liquid level 30a at the time of stop to the water level gauge 70 is set to J(m). The temperature T2(K) of the residual oxidant gas is adjusted so that the water head difference h(m) is consistent with J(m), thereby preventing the cooling water 30r sucked from the cooling water tank 30 from intruding into the cathode 4b in the fuel cell system 200.

[0195] based on Figure 2 , the pressure P3 (Pa) of the residual oxidant gas and the volume V3 (m 3 ) for explanation.

[0196] When the temperature T2 (K) of the residual oxidant gas decreases, according to (Formula 4) and (Formula 5), ​​the pressure P3 (Pa) and volume V3 (m 3 )reduce.

[0197] If the volume of the residual oxidant gas V3 (m 3 ) is smaller than the volume VC (m 3 ) is small, the attracted cooling water 30r penetrates into the cathode 4b. Therefore, the volume V3 (m 3 ) and the volume VC (m 3 ) is equal to the target predetermined temperature TS (K) of the cooling water 30r.

[0198] That is, by operating the heater 60 at an operating amount H (%) in accordance with (Formula 8) so as to reach a predetermined temperature T2 (K) or higher, the cooling water 30r having a predetermined temperature TS (K) or higher is supplied to the fuel cell stack 4 by the cooling water pump 10. As a result, the temperature T2 (K) of the residual oxidant gas can be made higher than the predetermined temperature TS (K), and the volume V3 (m 3 ) is the volume VC (m 3 ) or more, so that the cathode 4b can be sealed without filling it with cooling water 30r.

[0199] The above describes the behavior of the fuel cell stack 4 after stopping power generation. If the power generation of the fuel cell stack 4 is stopped for a long time, the fuel gas is supplied to keep the anode 4a at a positive pressure, but a part of the fuel gas supplied to the anode 4a passes through the electrolyte membrane 4c and mixes with the residual oxidant gas of the cathode 4b. The pressure P3 (Pa) of the residual oxidant gas after mixing is equal to the atmospheric pressure due to the fuel gas passing through the electrolyte membrane 4c from the anode 4a to the cathode 4b.

[0200] As a result, the head difference h (m) from the liquid surface 30 a when stopped due to the generation of negative pressure becomes substantially 0, and the cooling water 30 r sucked through the oxidant gas humidification path 12 and the oxidant gas discharge path 13 is recovered again in the cooling water tank 30 .

[0201] Next, based on Figure 3 , the operation of the fuel cell system 200 during operation will be described.

[0202] As described above, in Embodiment 2, the fuel gas supplied from the fuel gas supplier 1 is a gas mainly containing hydrogen. In the case where the fuel gas is generated by reforming a hydrocarbon raw gas, the fuel gas supplied from the fuel gas supplier 1 may contain carbon dioxide, carbon monoxide, methane, nitrogen, argon, water vapor, and other gases as impurities. In addition, the oxidant gas supplied from the oxidant gas supplier 15 is air, which is mainly composed of nitrogen, oxygen, argon, and carbon dioxide.

[0203] When the fuel cell stack 4 is in operation, the fuel gas is supplied from the fuel gas supplier 1 to the anode 4 a of the fuel cell stack 4 , and the oxidant gas is supplied from the oxidant gas supplier 15 to the cathode 4 b of the fuel cell stack 4 .

[0204] When the fuel cell stack 4 is in operation, the oxidant gas is humidified by the cooling water 30 r in the cooling water tank 30 via the oxidant gas supply path 11 , and is supplied to the cathode 4 b via the first space 30 f and the oxidant gas humidification path 12 .

[0205] The unreacted oxidant gas and produced water not used in the cathode 4b are supplied to the cooling water tank 30 via the oxidant gas discharge path 13. The produced water of the unreacted oxidant gas and produced water supplied to the cooling water tank 30 is recovered as cooling water 30r in the cooling water tank 30. The remaining unreacted oxidant gas is discharged to the outside of the fuel cell system 200 via the second space 30g and the exhaust gas path 14.

[0206] The cooling water tank 30 is partitioned in the middle by the shielding plate 30s, but the cooling water 30r in the cooling water tank 30 can flow between the first space 30f and the second space 30g through the gap between the bottom surface of the cooling water tank 30 and the lower end of the shielding plate 30s.

[0207] The liquid level of the cooling water 30r existing in the first space 30f side when the fuel cell stack 4 is operating is referred to as a first operating liquid level 30b, and the liquid level of the cooling water 30r existing in the second space 30g side when the fuel cell stack 4 is operating is referred to as a second operating liquid level 30c.

[0208] When the fuel cell stack 4 is in operation, the first space 30f is supplied with the oxidant gas whose pressure is increased by the oxidant gas supply unit 15. On the other hand, the oxidant gas is similarly supplied from the oxidant gas supply unit 15 to the second space 30g, and thus the pressure is increased. However, since the second space 30g is located downstream of the first space 30f in the flow direction of the oxidant gas, the pressure mainly decreases according to the pressure loss of the cathode 4b.

[0209] Therefore, when the fuel cell stack 4 is operating, the second operating liquid level 30c is higher than the first operating liquid level 30b which is the liquid level when the fuel cell stack 4 is operating. When the fuel cell stack 4 is operating, the outlet (downstream end) of the oxidant gas supply path 11 is located below the first operating liquid level 30b and is immersed in the cooling water 30r.

[0210] When the fuel cell stack 4 is in operation, the inlet (upstream end) of the oxidant gas humidification path 12 is located at a position higher than the first operation liquid level 30b, and is not immersed in the cooling water 30r but exists in the first space 30f. When the fuel cell stack 4 is in operation, the outlet (downstream end) of the oxidant gas discharge path 13 is located at a position lower than the second operation liquid level 30c, and is immersed in the cooling water 30r.

[0211] [2-3. Effects, etc.]

[0212] As described above, in this embodiment, the fuel cell system 200 includes: a fuel cell stack 4, a cooling water path 40, a cooling water tank 30, a cooling water pump 10, an oxidant gas supply unit 15, an oxidant gas supply path 11, an oxidant gas humidification path 12, an oxidant gas exhaust path 13, an exhaust gas path 14, a heater 60, a water level gauge 70 and a control unit 8.

[0213] The fuel cell stack 4 is a solid polymer type, and is configured to generate electricity by reacting a fuel gas supplied to an anode 4 a and an oxidant gas supplied to a cathode 4 b .

[0214] The cooling water passage 40 is configured to circulate the cooling water 30 r that exchanges heat with the fuel cell stack 4 .

[0215] The cooling water tank 30 is a substantially sealed tank provided in a portion of the cooling water path 40 that is lower than the fuel cell stack 4 in the vertical direction. The cooling water tank 30 has a gas storage portion 30e above a cooling water storage portion 30d that stores cooling water 30r when installed. The gas storage portion 30e is divided into a first space 30f and a second space 30g so as not to communicate with each other regardless of the operating state of the fuel cell stack 4.

[0216] The cooling water pump 10 is provided in the cooling water path 40 to pump the cooling water 30 r in the cooling water tank 30 and supply the cooling water to the fuel cell stack 4 .

[0217] The oxidizing gas supply unit 15 is configured to supply oxidizing gas. The oxidizing gas supply path 11 is configured to supply oxidizing gas to the cooling water 30r in the cooling water storage unit 30d below the first space 30f, and is a path connecting the oxidizing gas supply unit 15 and the cooling water tank 30.

[0218] The oxidant gas humidifying passage 12 is a passage configured to supply the oxidant gas discharged from the oxidant gas supply passage 11 and accumulated in the first space 30f after being humidified to the cathode 4b. The inlet of the oxidant gas humidifying passage 12 opens to the first space 30f and the outlet is connected to the inlet of the cathode 4b.

[0219] The oxidant gas discharge path 13 is a path configured to supply the oxidant gas discharged from the outlet of the cathode 4b without being used for the reaction of the fuel cell stack 4 to the cooling water 30r in the cooling water storage part 30d below the second space 30g. The oxidant gas discharge path 13 is a path whose inlet is connected to the outlet of the cathode 4b and whose outlet is open to the cooling water 30r in the cooling water storage part 30d below the second space 30g.

[0220] The exhaust gas passage 14 is a passage configured to discharge the oxidizing gas discharged from the oxidizing gas discharge passage 13 and accumulated in the second space 30g after gas-liquid separation to the outside, and has an inlet opening to the second space 30g and an outlet opening to the outside.

[0221] The heater 60 is disposed in the cooling water tank 30 and is configured to adjust the temperature of the cooling water 30 r.

[0222] The water level gauge 70 is provided in the path of the oxidant gas discharge path 13 to detect the water level of the cooling water 30r in the oxidant gas discharge path 13. More specifically, the water level gauge 70 is configured to measure the water level of the cooling water 30r sucked from the cooling water tank 30 and detect that the cooling water 30r is sucked to a certain water level.

[0223] The control unit 8 also operates the cooling water pump 10 after the fuel cell stack 4 stops generating electricity. When the fuel cell stack 4 stops generating electricity, the control unit 8 adjusts the temperature of the cooling water 30r using the heater 60 so that the water level gauge 70 detects a predetermined water level at which the cathode 4b is not filled with the cooling water 30r even though the inlet of the oxidant gas humidification path 12 is completely submerged in water. By adjusting the temperature of the cooling water 30r using the heater 60, the control unit 8 controls the temperature of the remaining oxidant gas.

[0224] Thus, in the fuel cell system 200, when power generation is stopped, the cooling water 30r introduced into the cooling water tank 30 is sucked into the oxidant gas humidification path 12 and the oxidant gas exhaust path 13, but the sucked cooling water 30r can be reliably stopped at a predetermined height. Therefore, in the fuel cell system 200, the cathode 4b can be sealed without being filled with the cooling water 30r.

[0225] Therefore, in the fuel cell system 200, the pressure of the residual oxidant gas in the cathode 4b can be controlled with high accuracy, and the intrusion of the cooling water 30r into the cathode 4b can be reliably suppressed when power generation is stopped. Therefore, in the fuel cell system 200, water clogging of the cathode 4b at startup (when power generation starts) can be suppressed, and stable power generation can be implemented.

[0226] As in the present embodiment, the fuel cell system 200 includes: a first temperature measuring device 61 as an example of a temperature measuring device disclosed in the present invention, and a second temperature measuring device 62 as an example of a temperature measuring device disclosed in the present invention. The first temperature measuring device 61 measures the temperature of the cooling water 30r (after heat exchange with the fuel cell stack 4) in the path from the fuel cell stack 4 to the cooling water tank 30 in the cooling water path 40. The second temperature measuring device 62 measures the temperature of the cooling water 30r (before heat exchange with the fuel cell stack 4) in the path between the cooling water pump 10 and the fuel cell stack 4 in the cooling water path 40. Then, the control unit 8 estimates the temperature of the cathode 4b (sealed residual oxidant gas) based on the values ​​of the first temperature measuring device 61 and the second temperature measuring device 62.

[0227] Thus, in the fuel cell system 200, the temperature inside the fuel cell stack 4 can be measured. Therefore, in the fuel cell system 200, the temperature of the cathode 4b (sealed residual oxidant gas) can be estimated with high accuracy based on the values ​​of the first temperature measuring device 61 and the second temperature measuring device 62, and the temperature of the cooling water 30r can be adjusted based on the estimated value using the heater 60. Therefore, in the fuel cell system 200, the pressure of the residual oxidant gas can be controlled, and the cooling water 30r can be reliably prevented from intruding into the cathode 4b.

[0228] (Other embodiments)

[0229] As described above, as an illustration of the technology disclosed in the present invention, Embodiment 1 and Embodiment 2 are described. However, the technology disclosed in the present invention is not limited thereto, and can also be applied to embodiments that have been changed, replaced, added, omitted, etc. In addition, it is also possible to combine the various components described in Embodiment 1 and Embodiment 2 as a new embodiment.

[0230] Therefore, other embodiments are exemplified below.

[0231] In Embodiment 1 and Embodiment 2, the fuel cell systems 100 and 200 using the first temperature measuring device 61 are described.

[0232] The temperature of the cooling water 30r can be estimated based on the amount of heat generated when the operating amount is applied to the heater 60. Therefore, the method of measuring the temperature of the cooling water 30r is not limited to the first temperature measuring device 61. However, if a sheathed thermocouple is used as the first temperature measuring device 61, the temperature of the cooling water 30r can be measured in real time and simply. Therefore, in a fuel cell system of another embodiment using a sheathed thermocouple as the first temperature measuring device 61, the responsiveness of the temperature control corresponding to the temperature change after stopping power generation can be accelerated.

[0233] Industrial Applicability

[0234] The present disclosure can be applied to a fuel cell system that recovers water generated in a fuel cell stack. Specifically, for example, the present disclosure can be applied to a pure hydrogen fuel cell system that generates electricity using hydrogen as fuel gas.

[0235] Description of Reference Numerals

[0236] 1. Fuel gas supplier; 1a. Fuel gas supply path; 4. Fuel cell stack; 4a. Anode; 4b. Cathode; 4c. Electrolyte membrane; 5. Unreacted fuel gas exhaust path; 8. Control unit; 10. Cooling water pump; 11. Oxidant gas supply path; 12. Oxidant gas humidification path; 13. Oxidant gas exhaust path; 14. Exhaust gas path; 15. Oxidant gas supply unit; 20. Barometer; 30. Cooling water tank; 30a. Liquid level when stopped; 30b. Liquid level during the first operation; 30c. Liquid level during the second operation; 30d. Cooling water storage unit; 30e. Gas storage unit; 30f. First space; 30g. Second space; 30r. Cooling water; 30s. Shielding plate; 40. Cooling water path; 60. Heater; 61. First temperature measuring device; 62. Second temperature measuring device; 70. Water level gauge; 100. Fuel cell system; 200. Fuel cell system

Claims

1. A fuel cell system, characterized in that: The fuel cell system has: A solid polymer fuel cell stack that generates electricity by reacting a fuel gas supplied to an anode and an oxidant gas supplied to a cathode; a cooling water path for circulating cooling water for heat exchange with the fuel cell stack; A substantially sealed cooling water tank, wherein in a set state, a gas storage portion is provided above a cooling water storage portion storing the cooling water, the gas storage portion being divided into a first space and a second space in a manner that the two spaces are not connected to each other regardless of the operating state of the fuel cell stack, and the cooling water tank is provided at a position in the cooling water path that is lower than the fuel cell stack in a vertical direction; a cooling water pump, which is arranged in the cooling water path to draw the cooling water in the cooling water tank and supply it to the fuel cell stack; an oxidant gas supply unit that supplies the oxidant gas; an oxidant gas supply path connecting the oxidant gas supply unit and the cooling water tank in such a manner that the oxidant gas is supplied to the cooling water in the cooling water storage unit below the first space; an oxidant gas humidification path, the inlet of which is open to the first space and the outlet of which is connected to the inlet of the cathode, so as to supply the oxidant gas discharged from the oxidant gas supply path and humidified and accumulated in the first space to the cathode; an oxidant gas discharge path, the inlet of which is connected to the outlet of the cathode and the outlet of which opens into the cooling water in the cooling water reservoir below the second space, so as to supply the oxidant gas discharged from the outlet of the cathode without being used for the reaction of the fuel cell stack to the cooling water in the cooling water reservoir below the second space; and an exhaust gas path, the inlet of which is open to the second space and the outlet of which is open to the outside, so that the oxidant gas discharged from the oxidant gas discharge path and accumulated in the second space after gas-liquid separation can be discharged to the outside, The fuel cell system is configured such that when the fuel cell stack stops generating power, the inlet of the oxidant gas humidification path is completely submerged in water, but the temperature of the remaining oxidant gas is controlled so that the cathode is not filled with the cooling water.

2. The fuel cell system according to claim 1, characterized in that: The fuel cell system further comprises: a heater, disposed in the cooling water tank, for adjusting the temperature of the cooling water; and a control unit that operates the cooling water pump even after the fuel cell stack stops generating power, The control unit uses the heater to adjust the temperature of the cooling water when the fuel cell stack stops generating electricity, thereby controlling the temperature of the remaining oxidant gas, so that although the inlet of the oxidant gas humidification path is completely submerged in water, the cathode is not filled with the cooling water.

3. The fuel cell system according to claim 2, characterized in that: The fuel cell system further includes a temperature measuring device that measures the temperature of the cooling water discharged from the fuel cell stack or the temperature of the oxidant gas discharged from the fuel cell stack. The control unit estimates the temperature of the oxidant gas in the cathode based on the value of the temperature measuring device.

4. The fuel cell system according to claim 2 or claim 3, characterized in that: The fuel cell system further includes a water level meter provided in the oxidant gas discharge path for detecting a water level of the cooling water in the oxidant gas discharge path. The control unit adjusts the heating amount of the heater so that the water level gauge detects a predetermined water level when the fuel cell stack stops generating power.

5. A method for operating a fuel cell system, The fuel cell system has: A solid polymer fuel cell stack that generates electricity by reacting a fuel gas supplied to an anode and an oxidant gas supplied to a cathode; a cooling water path for circulating cooling water for heat exchange with the fuel cell stack; A substantially sealed cooling water tank, wherein in a set state, a gas storage portion is provided above a cooling water storage portion storing the cooling water, the gas storage portion being divided into a first space and a second space in a manner that the two spaces are not connected to each other regardless of the operating state of the fuel cell stack, and the cooling water tank is provided at a position in the cooling water path that is lower than the fuel cell stack in a vertical direction; a cooling water pump, which is arranged in the cooling water path to draw the cooling water in the cooling water tank and supply it to the fuel cell stack; an oxidant gas supply unit that supplies the oxidant gas; an oxidant gas supply path connecting the oxidant gas supply unit and the cooling water tank in such a manner that the oxidant gas is supplied to the cooling water in the cooling water storage unit below the first space; an oxidant gas humidification path, the inlet of which is open to the first space and the outlet of which is connected to the inlet of the cathode, so as to supply the oxidant gas discharged from the oxidant gas supply path and humidified and accumulated in the first space to the cathode; an oxidant gas discharge path, the inlet of which is connected to the outlet of the cathode and the outlet of which opens into the cooling water in the cooling water reservoir below the second space, so as to supply the oxidant gas discharged from the outlet of the cathode without being used for the reaction of the fuel cell stack to the cooling water in the cooling water reservoir below the second space; an exhaust gas passage having an inlet opening to the second space and an outlet opening to the outside so as to be able to discharge the oxidizing gas discharged from the oxidizing gas discharge passage and accumulated in the second space after being separated into gas and liquid to the outside; and A heater is arranged in the cooling water tank to adjust the temperature of the cooling water. The operating method of the fuel cell system is characterized by: The cooling water pump is also operated after the fuel cell stack stops generating electricity. When the fuel cell stack stops generating power, the temperature of the cooling water is adjusted by the heater so that the cathode is not filled with the cooling water although the inlet of the oxidant gas humidification path is completely immersed in water.

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