Fuel cell system and operation method thereof

Abstract

To provide a fuel cell system that can simply and efficiently suppress the effect of high-pressure oxygen-containing gas supplied into a fuel cell on other fluids, and can simply and efficiently operate at an appropriate high power output.SOLUTION: A fuel cell system S1 supplies high-pressure oxygen to a fuel cell 10 by a compressor unit 60 in which a compressor 61 and a turbine 62 work in conjunction with each other. The oxygen-containing gas flowing out from an oxygen-containing gas flow path 18 in the fuel cell 10 flows into a cooling water tank 50 and is then discharged. Cooling water is supplied from the cooling water tank 50 to a cooling water flow path 19 in the fuel cell 10.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] 1. Field of the Invention The present invention relates to a fuel cell system and an operating method thereof. [Background technology]

[0002] A polymer electrolyte fuel cell, as an example of a fuel cell, generally includes a plurality of unit cells each having a membrane electrode assembly including an electrolyte membrane and two electrodes sandwiching the electrolyte membrane, and two separators sandwiching the membrane electrode assembly. A stack of a plurality of unit cells is generally called a cell stack.

[0003] One of the two electrodes is sometimes called the anode, and the other is sometimes called the cathode. The anode is supplied with a fuel gas containing hydrogen, which causes an electrochemical reaction. The cathode is supplied with an oxygen-containing gas, which causes an electrochemical reaction.

[0004] In a polymer electrolyte fuel cell, one of the two separators may be provided with a flow path for passing a fuel gas, and the other may be provided with a flow path for passing an oxygen-containing gas. The separator having the flow path for the fuel gas is sometimes called an anode separator, and the separator having the flow path for the oxygen-containing gas is sometimes called a cathode separator. Such a separator may be made of a porous material.

[0005] In addition, either the anode separator or the cathode separator may be provided with a cooling water flow path for removing reaction heat generated by the electrochemical reaction. In this case, a flow path for a reaction gas (hydrogen gas or oxygen-containing gas) is generally provided on one side of the separator, and a cooling water flow path is provided on the other side.

[0006] When a fuel cell system with a power output of, for example, 100 kW or more is constructed using the above-mentioned polymer electrolyte fuel cells, it is required to supply a large amount of oxygen to the cathode. In this case, compressed oxygen-containing gas may be supplied to the cathode of each unit cell of the cell stack from a turbine-equipped compressor that can be driven at high power.

[0007] However, when a large amount of oxygen-containing gas is supplied from the turbine compressor as described above, the pressure of the oxygen-containing gas flowing through the flow path of the single cell increases. When the separator is made of a porous material as described above, such an increase in pressure of the oxygen-containing gas may affect the state of the cooling water flowing through the separator. For example, there is a risk that the water level of the cooling water in the tank that stores the cooling water may undesirably rise. In addition, there is a risk that the cooling water may flow into the fuel gas flow path due to the oxygen-containing gas, preventing the fuel gas from flowing properly and affecting power generation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 6881240 Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the problem that the present invention aims to solve is to provide a fuel cell system and an operating method thereof that can easily and efficiently suppress the effect of high-pressure oxygen-containing gas supplied into the fuel cell on other fluids, and can easily and efficiently perform operation with appropriate high power generation output. [Means for solving the problem]

[0010] A fuel cell system according to one embodiment includes a fuel cell provided with a fuel gas flow path for flowing a fuel gas to be supplied to an anode electrode, an oxygen-containing gas flow path for flowing an oxygen-containing gas containing oxygen to be supplied to a cathode electrode, and a cooling water flow path for flowing cooling water, in which at least the oxygen-containing gas flow path and the cooling water flow path are isolated by a conductive porous body; a cooling water tank for storing the cooling water; an upstream cooling water flow path connecting an upstream end of the cooling water flow path to the cooling water tank and allowing the cooling water to flow from the cooling water tank to the cooling water flow path; a downstream cooling water flow path connecting the downstream end of the cooling water flow path to the cooling water tank and returning the cooling water that has flowed out of the cooling water flow path to the cooling water tank; the cooling water tank; a second downstream oxygen flow pipe connected to the cooling water tank and discharging, from the cooling water tank, the oxygen-containing gas that has flowed into the cooling water tank from the first downstream oxygen flow pipe; a compressor disposed inside the upstream oxygen flow pipe and compressing the oxygen-containing gas and sending it downstream; a turbine disposed inside the second downstream oxygen flow pipe and rotated by the oxygen-containing gas discharged from the cooling water tank; and a compressor unit having a drive shaft connecting the compressor and the turbine, the drive shaft being driven by a motor.

[0011] A method for operating a fuel cell system according to one embodiment includes providing a fuel cell having a fuel gas flow path for flowing a fuel gas to be supplied to an anode electrode, an oxygen-containing gas flow path for flowing an oxygen-containing gas containing oxygen to be supplied to a cathode electrode, and a cooling water flow path for flowing cooling water, wherein at least the oxygen-containing gas flow path and the cooling water flow path are isolated by a conductive porous body, a cooling water tank for storing the cooling water, an upstream cooling water flow path connecting an upstream end of the cooling water flow path to the cooling water tank and allowing the cooling water to flow from the cooling water tank to the cooling water flow path, a downstream cooling water flow path connecting the downstream end of the cooling water flow path to the cooling water tank and returning the cooling water that has flowed out of the cooling water flow path to the cooling water tank, and a compressor unit that is disposed inside the upstream oxygen flow pipe and that has a turbine that is rotated by the oxygen-containing gas discharged from the cooling water tank, and a drive shaft that connects the compressor and the turbine, and that drives the drive shaft by a motor, and the fuel cell system is operated such that a pressure difference between an internal pressure of the fuel gas flow passage and an internal pressure of the oxygen-containing gas flow passage is equal to or less than a predetermined pressure value. Effect of the Invention

[0012] According to the present invention, the influence of the high-pressure oxygen-containing gas supplied into the fuel cell on other fluids can be easily and efficiently suppressed, and appropriate high power output operation can be easily and efficiently performed. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating a fuel cell system according to a first embodiment. [Diagram 2] 2 is a schematic cross-sectional view of a fuel cell in the fuel cell system shown in FIG. [Diagram 3] 2 is a flowchart illustrating an example of the operation of the fuel cell system shown in FIG. [Figure 4] FIG. 13 is a diagram illustrating a fuel cell system according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, each embodiment will be described with reference to the accompanying drawings.

[0015] <First embodiment> Fig. 1 shows a schematic diagram of a fuel cell system S1 according to a first embodiment. As shown in Fig. 1, the fuel cell system S1 includes a fuel cell 10. The fuel cell 10 takes in a fuel gas containing hydrogen from a hydrogen supply source 20, and takes in an oxygen-containing gas containing oxygen from an oxygen supply source 30. The fuel cell 10 is also supplied with cooling water from a cooling water tank 50. A plurality of piping members (21, 22, 31-33, 51, 52) for circulating a fluid (fuel gas, oxygen-containing gas, or cooling water) are connected to the fuel cell 10, the hydrogen supply source 20, the oxygen supply source 30, and the cooling water tank 50.

[0016] The compressor unit 60 compresses the oxygen-containing gas from the oxygen supply source 30 and supplies it to the fuel cell 10. This increases the amount of oxygen supplied to the fuel cell 10 per unit time compared to when the oxygen-containing gas is not compressed, thereby increasing the power generation output. The radiator 70 is provided to cool the oxygen-containing gas and cooling water. The control device 80 controls the pressure, flow rate, etc. of the fluids (fuel gas, oxygen-containing gas, cooling water) flowing within the fuel cell system S1.

[0017] Fig. 2 is a schematic cross-sectional view of a fuel cell 10. As shown in Fig. 2, the fuel cell 10 has a cell stack in which a plurality of unit cells SC are stacked. Each unit cell SC includes a membrane 11, an anode electrode 12, a cathode electrode 13, an anode electrode separator 14, and a cathode electrode separator 15.

[0018] In this embodiment, the fuel cell 10 is a solid polymer fuel cell. Therefore, the diaphragm 11 is a solid polymer membrane (ion exchange membrane) having ion conductivity. The anode 12 is disposed so as to be in contact with one surface of the diaphragm 11, and the cathode 13 is disposed so as to be in contact with the other surface of the diaphragm 11. Hereinafter, a laminate of the diaphragm 11, the anode 12, and the cathode 13 may be referred to as a membrane electrode assembly.

[0019] The anode 12 is supplied with a fuel gas containing hydrogen from a hydrogen supply source 20. The cathode 13 is supplied with an oxygen-containing gas containing oxygen from an oxygen supply source 30. The anode 12 reacts with hydrogen and the cathode 13 reacts with oxygen, causing the fuel cell 10 to generate electricity.

[0020] The anode separator 14 and the cathode separator 15 are disposed so as to sandwich the membrane electrode assembly (11, 12, 13). The anode separator 14 is disposed so as to be in contact with the anode 12, and the cathode separator 15 is disposed so as to be in contact with the cathode 13. In this embodiment, the anode separator 14 and the cathode separator 15 are formed from a porous material such as a conductive metal, carbon, or ceramic. The anode separator 14 and the cathode separator 15 are plate-shaped.

[0021] When the unit cells SC described above are stacked, the unit cells SC are stacked such that the anode electrode separator 14 of one of two adjacent unit cells SC is in contact with the cathode electrode separator 15 of the other unit cell SC.

[0022] The fuel cell 10 is provided with a fuel gas flow path 17 that at least partially faces the anode electrode 12, through which the above-mentioned fuel gas flows and supplies it to the anode electrode 12, an oxygen-containing gas flow path 18 that at least partially faces the cathode electrode 13, through which the above-mentioned oxygen-containing gas flows and supplies it to the cathode electrode 13, and a cooling water flow path 19 that flows cooling water.

[0023] More specifically, a plurality of fuel gas flow channels 17 are formed in the anode separator 14. The fuel gas flow channels 17 are, for example, groove-shaped, and are formed on the surface of the anode separator 14 that faces the anode 12. In addition, a plurality of oxygen-containing gas flow channels 18 and a plurality of cooling water flow channels 19 are formed in the cathode separator 15.

[0024] The oxygen-containing gas flow passage 18 is, for example, groove-shaped and formed on the surface of the cathode separator 15 facing the cathode 13. The cooling water flow passage 19 is, for example, groove-shaped and formed on the surface of the cathode separator 15 opposite to the surface on which the oxygen-containing gas flow passage 18 is formed. The oxygen-containing gas flow passage 18 and the cooling water flow passage 19 are separated from each other in the thickness direction of the cathode separator 15.

[0025] As described above, in the fuel cell 10, the unit cells SC are stacked such that the anode separator 14 of one of the two adjacent unit cells SC is in contact with the cathode separator 15 of the other. The anode separator 14 and the cathode separator 15 are conductive porous bodies. Therefore, in the fuel cell 10, the fuel gas flow path 17 and the coolant flow path 19 are separated by the porous body, and the oxygen-containing gas flow path 18 and the coolant flow path 19 are separated by the porous body.

[0026] The cooling water flow path 19 may be formed in the anode separator 14 instead of the cathode separator 15. Furthermore, a separator having the cooling water flow path 19 formed therein may be provided in addition to the anode separator 14 and the cathode separator 15, and the separator may be provided, for example, between the anode separator 14 and the cathode separator 15.

[0027] For ease of explanation, FIG. 1 partially shows an anode 12 of one of adjacent single cells SC in a fuel cell 10, a cathode 13 of the other single cell, and a separator portion 16 between them, consisting of an anode separator 14 and a cathode separator 15.

[0028] The hydrogen supply source 20 is a portion for storing fuel gas containing hydrogen. The hydrogen supply source 20 is connected to the upstream end of the fuel gas flow passage 17 by an upstream hydrogen flow pipe 21. A downstream hydrogen flow pipe 22 is connected to the downstream end of the fuel gas flow passage 17. The fuel gas from the hydrogen supply source 20 passes through the upstream hydrogen flow pipe 21 and flows into the fuel gas flow passage 17 from the upstream end of the fuel gas flow passage 17, and is supplied from the fuel gas flow passage 17 to the anode electrode 12. Unreacted fuel gas out of the fuel gas that flows into the fuel gas flow passage 17 flows into the downstream hydrogen flow pipe 22 from the downstream end of the fuel gas flow passage 17. In FIG. 1, the upstream hydrogen flow pipe 21 and the downstream hydrogen flow pipe 22 are illustrated as being connected to the anode electrode 12, but in reality, they are connected to the fuel gas flow passage 17 as described above.

[0029] A hydrogen supply cutoff valve 23 and an anode inlet adjustment valve 24 are provided in the upstream hydrogen flow pipe 21 in this order from the upstream side to the downstream side. The hydrogen supply cutoff valve 23 switches between opening and closing to switch between supplying and stopping the supply of fuel gas to the fuel cell 10. The anode inlet adjustment valve 24 adjusts the flow rate of the fuel gas flowing through the upstream flow pipe 21, thereby adjusting the flow rate and pressure of the fuel gas (hydrogen) supplied to the fuel cell 10. The hydrogen supply cutoff valve 23 and the anode inlet adjustment valve 24 are electrically connected to a control device 80, and their opening and closing or opening degree are controlled by the control device 80.

[0030] A hydrogen circulation pump 25 and a discharge cutoff valve 26 are provided in this order in the downstream hydrogen flow pipe 22 from the upstream side to the downstream side. The hydrogen circulation pump 25 generates a force for circulating the fuel gas. The discharge cutoff valve 26 switches between discharging and not discharging the fuel gas flowing out from the fuel cell 10 by switching between opening and closing. When the discharge cutoff valve 26 is closed and the fuel cell 10 is in a state where the fuel gas is not discharged, the fuel gas flowing out from the fuel cell 10 is returned to the upstream hydrogen flow passage 21 via a recycle flow passage 29. The recycle flow passage 29 is connected to a portion of the downstream hydrogen flow pipe 22 between the hydrogen circulation pump 25 and the discharge cutoff valve 26 and to a portion of the upstream hydrogen flow pipe 21 downstream of the anode inlet adjustment valve 24.

[0031] In this embodiment, the fuel gas flowing out from the downstream end of the downstream hydrogen flow pipe 22 is discharged to the atmosphere. More specifically, the downstream end of the downstream hydrogen flow pipe 22 is connected to a second downstream oxygen flow pipe 33, which will be described later, as indicated by "*A" in Fig. 1. When the exhaust cutoff valve 26 opens and the fuel cell 10 enters a state in which it discharges fuel gas, the fuel gas flowing out from the downstream end of the downstream hydrogen flow pipe 22 merges with the oxygen-containing gas that has flowed out of the fuel cell 10 and is flowing through the second downstream oxygen flow pipe 33, and is then discharged.

[0032] The hydrogen circulation pump 25 and the discharge cutoff valve 26 are electrically connected to a control device 80. The rotation speed of the hydrogen circulation pump 25 is controlled by the control device 80, and the opening and closing of the discharge cutoff valve 26 is controlled by the control device 80.

[0033] Furthermore, an anode inlet pressure sensor 27 is provided in the upstream hydrogen flow pipe 21, and an anode outlet pressure sensor 28 is provided in the downstream hydrogen flow pipe 22. The anode inlet pressure sensor 27 detects the pressure of the fuel gas flowing in the portion of the upstream hydrogen flow pipe 21 downstream of the connection position of the recycle flow path 29. The anode outlet pressure sensor 28 detects the pressure of the fuel gas flowing in the portion of the downstream hydrogen flow pipe 22 upstream of the hydrogen circulation pump 25. The anode inlet pressure sensor 27 and the anode outlet pressure sensor 28 are electrically connected to the control device 80, and provide the detection results to the control device 80.

[0034] The oxygen supply source 30 is a location where an oxygen-containing gas containing oxygen exists, for example, the atmosphere. An upstream oxygen flow pipe 31 is connected to the upstream end of the oxygen-containing gas flow passage 18, and the upstream oxygen flow pipe 31 allows the oxygen-containing gas from the oxygen supply source 30 to flow into the oxygen-containing gas flow passage 18. The downstream end of the oxygen-containing gas flow passage 18 is connected to a cooling water tank 50 by a downstream first oxygen flow pipe 32. The oxygen-containing gas from the oxygen supply source 30 flows into the oxygen-containing gas flow passage 18 from the upstream end of the oxygen-containing gas flow passage 18 through the upstream oxygen flow pipe 31, and is supplied from the oxygen-containing gas flow passage 18 to the cathode 13. Unreacted oxygen-containing gas out of the oxygen-containing gas that has flowed into the oxygen-containing gas flow passage 18 flows into the downstream first oxygen flow pipe 32 from the downstream end of the oxygen-containing gas flow passage 18. In FIG. 1, the upstream oxygen flow pipe 31 and the first downstream oxygen flow pipe 32 are illustrated as being connected to the cathode electrode 13, but in reality, they are connected to the oxygen-containing gas flow passage 18 as described above.

[0035] Further, the cooling water tank 50 is connected to the downstream second oxygen flow pipe 33, and the downstream second oxygen flow pipe 33 discharges the oxygen-containing gas that has flowed into the cooling water tank 50 from the downstream first oxygen flow pipe 32 from the cooling water tank 50. In this embodiment, the lower end of the downstream second oxygen flow pipe 33 is open to the atmosphere. Therefore, the oxygen-containing gas that flows from the cooling water tank 50 into the downstream second oxygen flow pipe 33 is discharged to the atmosphere.

[0036] A supply cutoff valve 34, a filter 35, and an intercooler 36 are provided in this order from upstream to downstream in the upstream oxygen flow pipe 31. The supply cutoff valve 34 switches between supplying and stopping the supply of oxygen-containing gas to the fuel cell 10 by switching between opening and closing. The supply cutoff valve 34 is electrically connected to a control device 80, and its opening and closing is controlled by the control device 80.

[0037] The filter 35 removes foreign matter from the oxygen-containing gas taken in from the oxygen supply source 30. The intercooler 36 cools the oxygen-containing gas. Although details will be described later, in this embodiment, a compressor 61 in a compressor unit 60 is disposed between the filter 35 and the intercooler 36 in the upstream oxygen flow pipe 31. The compressor 61 compresses the oxygen-containing gas, and therefore can increase the temperature of the oxygen-containing gas. At this time, the intercooler 36 cools the oxygen-containing gas, thereby making it possible to further increase the density of the air in the oxygen-containing gas.

[0038] The downstream end of the first downstream oxygen flow pipe 32 is connected to the upper surface of the cooling water tank 50. The position where the first downstream oxygen flow pipe 32 is connected to the cooling water tank 50 is not particularly limited, but it is preferable that the connection position is on the upper side of the cooling water tank 50 and that the first downstream oxygen flow pipe 32 opens into the gas phase portion in the cooling water tank 50.

[0039] The upstream end of the downstream second oxygen flow pipe 33 is connected to the upper surface of the cooling water tank 50. The position where the downstream second oxygen flow pipe 33 is connected to the cooling water tank 50 is not particularly limited, but it is preferable that the downstream second oxygen flow pipe 33 is connected to the upper side of the cooling water tank 50 at a position where it is open to the gas phase portion in the cooling water tank 50.

[0040] A gas-liquid separator 40 and a discharge shutoff valve 45 are provided in this order in the downstream second oxygen flow pipe 33 in the direction from the upstream side to the downstream side. The gas-liquid separator 40 separates moisture contained in the oxygen-containing gas discharged from the cooling water tank 50 from the gas components of the oxygen-containing gas. As will be described in detail later, the turbine 62 in the compressor unit 60 is disposed in the downstream second oxygen flow pipe 33, and the gas-liquid separator 40 is provided in a portion upstream of the position of the turbine 62 in the downstream second oxygen flow pipe 33. This can prevent moisture from flowing into the turbine 62 and affecting the rotation of the turbine 62.

[0041] The gas-liquid separator 40, for example, has a cooling water reservoir 41 and a cooling medium pipe 42 disposed in the cooling water reservoir 41. The cooling water reservoir 41 constitutes a part of the flow path of the downstream second oxygen flow pipe 33. The cooling medium pipe 42 circulates a cooling medium and cools the oxygen-containing gas that has flowed into the cooling reservoir 41, thereby condensing moisture contained in the oxygen-containing gas.

[0042] The moisture separated by the gas-liquid separator 40 mainly contains cooling water to be supplied to the fuel cell 10. The moisture separated by the gas-liquid separator 40 is returned to the cooling water tank 50. This makes it possible to suppress the discharge of cooling water and to effectively utilize the cooling water. The gas-liquid separator 40 and the cooling water tank 50 are connected by a return pipe 43. A drain trap 44 is provided in the return pipe 43. The drain trap 44 allows the flow of moisture from the gas-liquid separator 40 to the cooling water tank 50 and blocks the flow of gas and liquid in the opposite direction.

[0043] The discharge cutoff valve 45 switches between discharging and not discharging the oxygen-containing gas flowing out from the fuel cell 10 by switching between opening and closing. The discharge cutoff valve 45 is electrically connected to the control device 80, and the opening and closing are controlled by the control device 80. When the discharge cutoff valve 45 is opened to discharge the oxygen-containing gas flowing out from the fuel cell 10, the oxygen-containing gas is discharged from the downstream end of the downstream second oxygen flow pipe 33 through the turbine 62 from the discharge cutoff valve 45. Here, in this embodiment, as shown by "*A" in FIG. 1, the downstream end of the downstream hydrogen flow pipe 22 is connected to a portion of the downstream second oxygen flow pipe 33 downstream of the arrangement position of the turbine 62. Therefore, the oxygen-containing gas flowing from the discharge cutoff valve 45 through the turbine 62 is merged with the fuel gas flowing out from the downstream end of the downstream hydrogen flow pipe 22 downstream of the turbine 62 and discharged.

[0044] In this embodiment, the upstream oxygen flow pipe 31 and the downstream second oxygen flow pipe 33 are connected by an oxygen-containing gas bypass pipe 47. The oxygen-containing gas bypass pipe 47 allows the oxygen-containing gas to flow from the upstream oxygen flow pipe 31 to the downstream second oxygen flow pipe 33. The oxygen-containing bypass pipe 47 is provided with a bypass adjustment valve 48 that adjusts the flow rate of the oxygen-containing gas flowing through the oxygen-containing gas bypass pipe 47 toward the downstream second oxygen flow pipe 33.

[0045] In this embodiment, the oxygen-containing bypass pipe 47 connects a portion of the upstream oxygen flow pipe 31 downstream of the compressor 61 to a portion of the downstream second oxygen flow pipe 33 upstream of the turbine 62. In detail, the oxygen-containing bypass pipe 47 connects a portion of the upstream oxygen flow pipe 31 downstream of the intercooler 36 to a portion of the downstream second oxygen flow pipe 33 between the gas-liquid separator 40 and the turbine 62. However, the connection position of the oxygen-containing bypass pipe 47 may be different from that shown in FIG. 1.

[0046] The bypass adjustment valve 48 is electrically connected to the control device 80, and its opening degree is controlled by the control device 80. The bypass adjustment valve 48 is controlled to an open state when it is desired to reduce the amount of oxygen-containing gas supplied to the main fuel cell 10.

[0047] Further, the upstream oxygen flow pipe 31 is provided with an oxygen inlet pressure sensor 37, and the downstream second oxygen flow pipe 33 is provided with an oxygen outlet pressure sensor 46. The oxygen inlet pressure sensor 37 detects the pressure of the oxygen-containing gas flowing through a portion of the upstream oxygen flow pipe 31 downstream of the compressor 61, more specifically, a portion downstream of the intercooler 36, and downstream of the connection position of the oxygen-containing gas bypass pipe 47. The oxygen outlet pressure sensor 46 detects the pressure of the oxygen-containing gas flowing through a portion of the downstream second oxygen flow pipe 33 upstream of the turbine 62, more specifically, a portion of the downstream second oxygen flow pipe 33 between the gas-liquid separator 40 and the turbine 62, and downstream of the connection position of the oxygen-containing gas bypass pipe 47. The oxygen inlet pressure sensor 37 and the oxygen outlet pressure sensor 46 are electrically connected to the control device 80, and provide the detection results to the control device 80.

[0048] The cooling water tank 50 is a container for storing cooling water, and an upstream cooling water circulation pipe 51 and a downstream cooling water circulation pipe 52 are connected to the cooling water tank 50. The upstream cooling water circulation pipe 51 connects the upstream end of the cooling water flow path 19 to the cooling water tank 50, and allows cooling water to flow from the cooling water tank 50 to the cooling water flow path 19. The downstream cooling water circulation pipe 52 connects the downstream end of the cooling water flow path 19 to the cooling water tank 50, and returns the cooling water that has flowed out of the cooling water flow path 19 to the cooling water tank 50. The cooling water may be water.

[0049] The upstream cooling water circulation pipe 51 is connected to the bottom surface of the cooling water tank 50. The position where the upstream cooling water circulation pipe 51 is connected to the cooling water tank 50 is not particularly limited, but it is preferable that the upstream cooling water circulation pipe 51 is connected to the bottom side at a position where the upstream cooling water circulation pipe 51 opens into the liquid phase portion (inside the cooling water) in the cooling water tank 50.

[0050] A cooling water pump 53, a cooling water cooling heat exchanger 54, and a water treatment device 55 are provided in this order from the upstream side to the downstream side in the downstream cooling water circulation pipe 52. The cooling water pump 53 generates a force for circulating the cooling water. The cooling water pump 53 is electrically connected to a control device 80, and the rotation speed of the cooling water pump 53 is controlled by the control device 80.

[0051] Also, the cooling water pump 53 may be provided in the upstream cooling water flow pipe 51. However, in this embodiment, it is assumed that a state is created in which the pressure of the cooling water in the fuel cell 10 is lower than the fuel gas and the oxygen-containing gas, and this state is difficult to create when the cooling water pump 53 is provided in the upstream cooling water flow pipe 51. Therefore, it is desirable to provide the cooling water pump 53 in the downstream cooling water flow pipe 52.

[0052] The cooling water discharged from the fuel cell 10 absorbs heat from the fuel cell 10, so the cooling water cooling heat exchanger 54 cools the cooling water with a cooling medium. The water treatment device 55 also removes impurities from the cooling water. By the water treatment device 55 removing impurities from the cooling water, deterioration of the fuel cell 10 is suppressed.

[0053] The cooling water tank 50 is also provided with a cooling water tank pressure sensor 56A, a water level sensor 56B, a drain pipe 57, and a drain opening / closing valve 58. The cooling water tank pressure sensor 56A detects the pressure of the gas phase portion in the cooling water tank 50. The cooling water tank pressure sensor 56A is electrically connected to the control device 80, and provides the control device 80 with the detection result.

[0054] The water level sensor 56B detects the water level of the cooling water in the cooling water tank 50. The drain pipe 57 is connected to the bottom of the cooling water tank 50, and is provided to drain the cooling water in the cooling water tank 50. The drain opening / closing valve 58 is provided in the drain pipe 57, and switches between discharging and not discharging the cooling water in the drain pipe 57.

[0055] In this embodiment, the water level sensor 56B, the drain pipe 57, and the drain opening / closing valve 58 constitute a water level maintaining mechanism 59. The water level maintaining mechanism 59 controls the opening and closing of the drain opening / closing valve 58 so that the water level of the cooling water stored in the cooling water tank 50 is maintained at a predetermined height based on the detection result of the water level sensor 56B. In detail, the water level sensor 56B is electrically connected to the control device 80, and provides the detection result to the control device 80. The drain opening / closing valve 58 is electrically connected to the control device 80, and controls the drain opening / closing valve 58 based on the detection result of the water level sensor 56B. The water level maintaining mechanism 59 may include a cooling water filling section, and may fill the cooling water based on the detection result of the water level sensor 56B.

[0056] In this embodiment, as described above, the oxygen-containing gas from the oxygen supply source 30 is compressed and supplied to the fuel cell 10, and after flowing out from the fuel cell 10, is discharged via the cooling water tank 50. The compressor unit 60 has a compressor 61, a turbine 62, a drive shaft 63 connecting the compressor 61 and the turbine 62, and a motor 64 driving the drive shaft 63. The compressor 61 is disposed inside the upstream oxygen flow pipe 31, and compresses the oxygen-containing gas and sends it downstream. The turbine 62 is disposed inside the downstream second oxygen flow pipe 33, and rotates by the oxygen-containing gas (its pressure) discharged from the cooling water tank 50.

[0057] Specifically, the compressor 61 is disposed between the filter 35 and the intercooler 36 in the upstream oxygen flow pipe 31 as described above. The turbine 62 is provided in a portion of the downstream second oxygen flow pipe 33 upstream of the gas-liquid separator 40. More specifically, the turbine 62 is provided in a portion of the downstream second oxygen flow pipe 33 downstream of the connection position of the oxygen-containing gas bypass pipe 47.

[0058] The motor 64 is electrically connected to the control device 80, and its rotation speed is controlled by the control device 80. The flow rate of the oxygen-containing gas supplied to the downstream side from the compressor 61 increases or decreases according to an increase or decrease in the rotation speed of the motor 64. The turbine 62 rotates by the exhaust pressure of the oxygen-containing gas discharged from the fuel cell 10, and assists the power of the motor 64. This allows the compressor unit 60 to rotate the compressor 61 efficiently.

[0059] 1, the radiator 70 is connected to the intercooler 36, the gas-liquid separator 40, and the coolant cooling heat exchanger 54. The radiator 70 cools the cooling medium, and the cooled cooling medium is branched into three flow paths by the drive of a cooling medium pump 71 and passes through the intercooler 36, the gas-liquid separator 40, and the coolant cooling heat exchanger 54. Note that three radiators 70 may be provided, and each may be connected separately to the intercooler 36, the gas-liquid separator 40, and the coolant cooling heat exchanger 54.

[0060] As described above, the control device 80 controls the pressure, flow rate, etc. of the fluids (fuel gas, oxygen-containing gas, coolant) flowing through the fuel cell system S1. The control device 80 can adjust the flow rate and / or pressure of the oxygen-containing gas flowing through the fuel gas flow passage 17 by controlling the rotation speed of the compressor 61 and / or the opening degree of the bypass control valve 48 based on at least one of the detection results of the oxygen inlet pressure sensor 37, the oxygen outlet pressure sensor 46, and the coolant tank pressure sensor 56A, for example.

[0061] The control device 80 can adjust the flow rate and / or pressure of the fuel gas flowing through the oxygen-containing gas flow path 18 by controlling the opening degree of the hydrogen circulation pump 25 and / or the anode inlet control valve 24, for example, based on the detection results of the anode inlet pressure sensor 27 and / or the anode outlet sensor 28.

[0062] More specifically, the control device 80 in this embodiment controls at least one of the flow rate of the fuel gas flowing through the fuel gas flow passage 17, the rotation speed of the compressor 61, and the opening degree of the bypass control valve 48 so that the pressure difference between the internal pressure of the fuel gas flow passage 17 and the internal pressure of the oxygen-containing gas flow passage 18 is equal to or less than a predetermined pressure value. When performing this control, in this embodiment, the pressure detected by the anode outlet pressure sensor 28 is treated as the internal pressure of the fuel gas flow passage 17, and the pressure detected by the cooling water tank pressure sensor 56A is treated as the internal pressure of the oxygen-containing gas flow passage 18. However, the internal pressure of the fuel gas flow passage 17 and the internal pressure of the oxygen-containing gas flow passage 18 may be determined by the detection results of other sensors.

[0063] In addition, in this embodiment, the control device 80 opens the bypass control valve 48 when the flow rate of the fuel gas supplied to the fuel gas flow path 17 is changed to a value greater than or equal to a predetermined value in the direction of decreasing the flow rate. The state in which the flow rate of the fuel gas is changed to a value greater than or equal to a predetermined value in the direction of decreasing the flow rate is, for example, a state in which the supply of the fuel gas is stopped or significantly decreased in the event of an abnormality. In this case, if the supply amount of oxygen to the fuel cell 10 is not significantly decreased, the deterioration of the fuel cell 10 may progress. However, even if the rotation speed of the motor 64 is decreased, the rotation speed of the motor 64 may not decrease rapidly due to inertia. Therefore, in this embodiment, when the flow rate of the fuel gas is changed to a value greater than or equal to a predetermined value in the direction of decreasing the flow rate, the bypass control valve 48 is opened widely to a value greater than or equal to a predetermined opening. In this control, pressure fluctuations in the oxygen flow path (31-33) accompanying changes in the flow rate of the oxygen-containing gas supplied to the fuel cell 10 can be suppressed, and the burden on the compressor unit 60 can also be reduced.

[0064] The control device 80 also controls the drain opening / closing valve 58, the supply cutoff valves 23 and 34, the discharge cutoff valve 45, etc. The control device 80 may be configured as a computer including a CPU, a ROM, etc. The control device 80 may also be configured as another processor, an electric circuit, etc.

[0065] In the fuel cell system S1 according to this embodiment, as described above, the compressor unit 60 in which the compressor 61 and the turbine 62 work together can supply high-pressure oxygen to the fuel cell 10. Here, in the fuel cell 10, the pressure of the oxygen-containing gas flowing through the oxygen-containing gas flow passage 18 becomes higher than the pressure of the cooling water flowing through the cooling water flow passage 19, and the pressure difference between the pressure of the oxygen-containing gas and the pressure of the cooling water in the fuel cell 10 becomes lower than the capillary force of the cooling water that has permeated the cathode separator 15, which is a porous body, to form a sealed state. This sealed state means a state in which the cooling water is prevented from flowing into the oxygen-containing gas flow passage 18 and the oxygen-containing gas is prevented from flowing into the cooling water flow passage 19.

[0066] In this embodiment, the compressor 61 and the turbine 62 work in conjunction with each other to efficiently compress the oxygen-containing gas by the compressor 61. Therefore, when forming the above-mentioned sealed state, a state in which the pressure of the oxygen-containing gas flowing through the oxygen-containing gas flow passage 18 is greater than the pressure of the cooling water flowing through the cooling water flow passage 19 can be easily formed.

[0067] In addition, the pressure of the oxygen-containing gas flowing through the oxygen-containing gas flow passage 18 may become large, but in this embodiment, the oxygen-containing gas flowing out from the oxygen-containing gas flow passage 18 flows into the cooling water tank 50 and is then discharged. In this case, when the cooling water pump 53 is driven, the pressure in the cooling water tank 50 does not drop significantly below the pressure of the oxygen-containing gas at the downstream end of the oxygen-containing gas flow passage 18, and the pressure of the cooling water at the upstream end of the cooling water flow passage 19 does not drop significantly below the pressure in the cooling water tank 50. Therefore, the pressure of the cooling water flowing through the cooling water flow passage 19 does not become significantly smaller than the pressure of the oxygen-containing gas flowing through the oxygen-containing gas flow passage 18. Therefore, the pressure difference between the pressure of the oxygen-containing gas and the pressure of the cooling water in the fuel cell 10 can also be easily and efficiently controlled within a desired range. That is, with a simple mechanical configuration in which the oxygen-containing gas discharged from the fuel cell 10 is discharged via the cooling water tank 50, a desired pressure difference between the oxygen-containing gas and the cooling water can be obtained, for example, without increasing the output of the cooling water pump 53 or by suppressing the increase in the output of the cooling water pump 53, so that a sealed state can be easily and efficiently formed. This makes it possible to easily and efficiently suppress the effect of the oxygen-containing gas on other fluids (cooling water) flowing through the fuel cell 10, and to easily and efficiently perform an appropriate high power output operation.

[0068] On the other hand, in order to form a sealed state between the fuel gas and the cooling water, in the fuel cell 10 of this embodiment, a state is formed in which the pressure of the fuel gas flowing through the fuel gas flow passage 17 is greater than the pressure of the cooling water flowing through the cooling water flow passage 19, and the pressure difference between the fuel gas pressure and the cooling water pressure in the fuel cell 10 is smaller than the capillary force of the cooling water that has permeated the porous cathode electrode separator 15. In contrast, in this embodiment, at least one of the flow rate of the fuel gas flowing through the fuel gas flow passage 17, the rotation speed of the compressor 61, and the aperture of the bypass control valve 48 is controlled so that the pressure difference between the internal pressure of the fuel gas flow passage 17 and the internal pressure of the oxygen-containing gas flow passage 18 becomes equal to or less than a predetermined pressure value.

[0069] Fig. 3 is a flow chart for explaining an example of the operation of the fuel cell system S1 according to this embodiment, specifically showing the operation of controlling the pressure difference between the internal pressure of the fuel gas flow channel 17 and the internal pressure of the oxygen-containing gas flow channel 18 to be equal to or less than a predetermined pressure value. The operation shown in Fig. 3 is performed when operation at a predetermined power generation output is started, or when, for example, the power generation output setting is changed during normal operation (power generation).

[0070] 3, first, step S31 shows a process of controlling at least one of the flow rate of the fuel gas by adjusting the aperture of the anode inlet adjustment valve 24 on the upstream hydrogen flow pipe 21, the output (rotation speed) of the compressor 61, and the flow rate or pressure of the oxygen-containing gas supplied to the fuel cell 10 by adjusting the aperture of the bypass adjustment valve 48 on the oxygen-containing gas bypass pipe 47, so as to make the pressure difference between the internal pressure of the fuel gas flow passage 17 and the internal pressure of the oxygen-containing gas flow passage 18 equal to or less than a predetermined pressure value. Immediately after the start of the operation shown in FIG. 3, the aperture of the anode inlet adjustment valve 24, the output of the compressor 61, etc. are controlled so that the fuel gas and oxygen-containing gas corresponding to the set power generation output are supplied to the fuel cell 10, and thereafter, feedback control is performed via the subsequent steps S31 and S32.

[0071] In step S32 after the process in step S31, the pressure detected by the cooling water tank pressure sensor 56A and the anode outlet pressure sensor 28 are detected. In this embodiment, the pressure detected by the anode outlet pressure sensor 28 is treated as the internal pressure of the fuel gas flow path 17, and the pressure detected by the cooling water tank pressure sensor 56A is treated as the internal pressure of the oxygen-containing gas flow path 18.

[0072] Next, in step S33, the difference between the pressure detected by the cooling water tank pressure sensor 56A and the pressure detected by the anode outlet pressure sensor 28 is calculated as the pressure difference between the internal pressure of the fuel gas flow path 17 and the internal pressure of the oxygen-containing gas flow path 18. If the calculated pressure difference is within the threshold, the process ends (END). On the other hand, if the calculated pressure difference is not within the threshold, the process of step S31 is performed.

[0073] In the fuel cell system S1 according to the present embodiment described above, the compressor unit 60 in which the compressor 61 and the turbine 62 work in conjunction with each other makes it possible to supply high-pressure oxygen to the fuel cell 10. Meanwhile, the oxygen-containing gas flowing out from the oxygen-containing gas flow passage 18 flows into the cooling water tank 50 and is then discharged. In this case, when the cooling water pump 53 is driven, the pressure of the cooling water flowing through the cooling water flow passage 19 is not significantly smaller than the pressure of the oxygen-containing gas flowing through the oxygen-containing gas flow passage 18. Therefore, the pressure difference between the pressure of the oxygen-containing gas and the pressure of the cooling water in the fuel cell 10 can be easily and efficiently controlled to within a desired range.

[0074] That is, with a simple mechanical configuration in which the oxygen-containing gas discharged from the fuel cell 10 is discharged via the cooling water tank 50, a desired pressure difference between the oxygen-containing gas and the cooling water can be obtained, for example, without increasing the output of the cooling water pump 53 or by suppressing the increase in the output of the cooling water pump 53, so that a sealed state can be easily and efficiently formed. This makes it possible to easily and efficiently suppress the effect of the oxygen-containing gas on other fluids (cooling water) flowing through the fuel cell 10.

[0075] Therefore, according to this embodiment, the effect of the high-pressure oxygen-containing gas supplied into the fuel cell 10 on other fluids (cooling water in this embodiment) can be easily and efficiently suppressed, and appropriate high power output operation can be easily and efficiently performed.

[0076] The fuel cell system S1 further includes a water level maintaining mechanism 59 that maintains the water level of the cooling water stored in the cooling water tank 50 at a predetermined height. This makes it possible to suppress the discharge of an undesirably large amount of cooling water accompanying the discharge of the oxygen-containing gas, and to avoid a situation in which the pressure of the cooling water becomes excessively low relative to the oxygen-containing gas as a result of a decrease in the supply amount of cooling water, thereby making it possible to maintain proper operating and cooling states.

[0077] The fuel cell system S1 further includes an oxygen-containing gas bypass pipe 47 that connects the upstream oxygen flow pipe 31 and the downstream second oxygen flow pipe 33, and a bypass adjustment valve 48 that adjusts the flow rate of the oxygen-containing gas flowing through the oxygen-containing gas bypass pipe 47. This makes it possible to flexibly adjust the flow rate or pressure of the oxygen-containing gas supplied to the fuel cell 10.

[0078] Furthermore, the fuel cell system S1 controls at least one of the flow rate of the fuel gas flowing through the fuel gas flow passage 17, the rotation speed of the compressor 61, and the opening degree of the bypass control valve 48 so that the pressure difference between the internal pressure of the fuel gas flow passage 17 and the internal pressure of the oxygen-containing gas flow passage 18 is equal to or less than a predetermined pressure value, thereby maintaining an appropriate operating state.

[0079] Furthermore, the fuel cell system S1 opens the bypass adjustment valve 48 when the flow rate of the fuel gas supplied to the fuel gas flow path 17 is decreased by a predetermined value or more. This makes it possible to quickly avoid a situation in which deterioration of the fuel cell 10 progresses due to the oxygen flow rate being greater than the fuel gas flow rate.

[0080] <Second embodiment> Next, a fuel cell system S2 according to a second embodiment will be described with reference to Fig. 4. The same components in this embodiment as those in the first embodiment are designated by the same reference numerals, and duplicated descriptions will be omitted.

[0081] 4, the fuel cell system S2 according to this embodiment further includes an exhaust control valve 49, which is located downstream of the turbine 62 in the second downstream oxygen flow pipe 33, for controlling the flow rate of the oxygen-containing gas flowing out from the turbine 62. The exhaust control valve 49 is electrically connected to a control device 80, and its opening degree is controlled by the control device 80.

[0082] When the bypass control valve 48 opens, the exhaust control valve 49 increases its opening degree. This allows the oxygen-containing gas that has flowed into the downstream second oxygen flow pipe 33 through the bypass control valve 48 to flow smoothly. As described in the first embodiment, the bypass control valve 48 is opened, for example, when the flow rate of the fuel gas supplied to the fuel gas flow passage 17 is changed in the decreasing direction by a predetermined value or more.

[0083] Furthermore, the exhaust control valve 49 may change the opening degree thereof in response to a change in the flow rate of the fuel gas supplied to the fuel gas flow path 17 with the bypass control valve 48 closed. In detail, the exhaust control valve 49 may increase the opening degree when the flow rate of the fuel gas supplied to the fuel gas flow path 17 is increased, and may decrease the opening degree when the flow rate of the fuel gas supplied to the fuel gas flow path 17 is decreased.

[0084] According to the second embodiment, the same effects as those of the first embodiment can be obtained. Also, the exhaust adjustment valve 49 can increase the variation of the control of the fluid.

[0085] Although each embodiment has been described above, the above-mentioned embodiments are presented as examples and are not intended to limit the scope of the invention. Such novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. Other modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0086] S1, S2... fuel cell system, 10... fuel cell, 11... diaphragm, 12... anode electrode, 13... cathode electrode, 14... anode electrode separator, 15... cathode electrode separator, 16... separator portion, 17... fuel gas flow path, 18... oxygen-containing gas flow path, 19... cooling water flow path, SC... single cell, 20... hydrogen supply source, 21... upstream hydrogen flow pipe, 22... downstream hydrogen flow pipe, 23... hydrogen supply cutoff valve, 24... anode inlet control valve, 25... hydrogen circulation pump, 26... discharge cutoff valve, 27... anode inlet pressure sensor, 28... anode outlet pressure sensor, 29... recycle flow path, 30... oxygen supply source, 31... upstream oxygen flow pipe, 32... downstream first oxygen flow pipe, 33... downstream second oxygen flow pipe, 34... supply cutoff valve, 35... filter, 36... intercooler , 37...oxygen inlet pressure sensor, 40...gas-liquid separator, 41...cooling water reservoir, 42...cooling medium pipe, 43...return pipe, 44...drain trap, 45...discharge shutoff valve, 46...oxygen outlet pressure sensor, 47...oxygen-containing gas bypass pipe, 48...bypass control valve, 49...exhaust control valve, 50...cooling water tank, 51...upstream cooling water distribution pipe, 52...downstream cooling water distribution pipe, 53...cooling water pump, 54...cooling water cooling heat exchanger, 55...water treatment device, 56A...cooling water tank pressure sensor, 56B...water level sensor, 57...drain pipe, 58...drain opening / closing valve, 59...water level maintaining mechanism, 60...compressor unit, 61...compressor, 62...turbine, 63...drive shaft, 64...motor, 70...radiator, 71...cooling medium pump, 80...control device

Claims

1. a fuel cell including a fuel gas flow path through which a fuel gas to be supplied to an anode electrode flows, an oxygen-containing gas flow path through which an oxygen-containing gas containing oxygen to be supplied to a cathode electrode flows, and a cooling water flow path through which cooling water flows, wherein at least the oxygen-containing gas flow path and the cooling water flow path are separated by a conductive porous body; A cooling water tank that stores the cooling water; an upstream cooling water flow pipe that connects an upstream end of the cooling water flow passage and the cooling water tank and allows the cooling water to flow from the cooling water tank into the cooling water flow passage; a downstream cooling water flow pipe that connects a downstream end of the cooling water flow passage and the cooling water tank, and returns the cooling water that has flowed out of the cooling water flow passage to the cooling water tank; an upstream oxygen flow pipe connected to an upstream end of the oxygen-containing gas flow passage and allowing an oxygen-containing gas to flow into the oxygen-containing gas flow passage; a downstream first oxygen flow pipe connecting a downstream end of the oxygen-containing gas flow passage and the cooling water tank; a downstream second oxygen flow pipe connected to the cooling water tank and discharging the oxygen-containing gas that has flowed into the cooling water tank from the downstream first oxygen flow pipe from the cooling water tank; a compressor unit that is disposed inside the upstream oxygen flow pipe and that compresses the oxygen-containing gas and sends it downstream, a turbine that is disposed inside the downstream second oxygen flow pipe and that is rotated by the oxygen-containing gas discharged from the cooling water tank, and a drive shaft that connects the compressor and the turbine, the drive shaft being driven by a motor.

2. 2. The fuel cell system according to claim 1, further comprising a water level maintaining mechanism that maintains a water level of the cooling water stored in the cooling water tank at a predetermined height.

3. an oxygen-containing gas bypass pipe connecting the upstream oxygen flow pipe and the downstream second oxygen flow pipe; 2. The fuel cell system according to claim 1, further comprising a bypass regulating valve that regulates a flow rate of the oxygen-containing gas flowing through the oxygen-containing gas bypass pipe toward the downstream second oxygen flow pipe.

4. 4. The fuel cell system according to claim 3, wherein at least one of a flow rate of the fuel gas flowing through the fuel gas flow passage, a rotation speed of the compressor, and an opening degree of the bypass control valve is controlled so that a pressure difference between an internal pressure of the fuel gas flow passage and an internal pressure of the oxygen-containing gas flow passage is equal to or less than a predetermined pressure value.

5. 4. The fuel cell system according to claim 3, wherein the bypass control valve is opened when the flow rate of the fuel gas supplied to the fuel gas flow channel is changed in a decreasing direction by a predetermined value or more.

6. an exhaust control valve configured to control a flow rate of the oxygen-containing gas flowing out from the turbine, the exhaust control valve being disposed in a portion of the downstream second oxygen flow pipe downstream of the turbine; 6. The fuel cell system according to claim 5, wherein the exhaust control valve increases its opening degree when the bypass control valve is opened.

7. an exhaust control valve configured to control a flow rate of the oxygen-containing gas flowing out from the turbine, the exhaust control valve being disposed in a portion of the downstream second oxygen flow pipe downstream of the turbine; 2. The fuel cell system according to claim 1, wherein the opening degree of the exhaust control valve is changed in response to a change in the flow rate of the fuel gas supplied to the fuel gas flow channel.

8. 8. The fuel cell system according to claim 7, wherein the exhaust control valve increases its opening degree when the flow rate of the fuel gas is increased, and decreases its opening degree when the flow rate of the fuel gas is decreased.

9. 2. The fuel cell system according to claim 1, further comprising a gas-liquid separator, disposed in a portion of the downstream second oxygen flow pipe upstream of the turbine, for separating moisture contained in the oxygen-containing gas discharged from the cooling water tank.

10. a fuel cell including a fuel gas flow path through which a fuel gas to be supplied to an anode electrode flows, an oxygen-containing gas flow path through which an oxygen-containing gas containing oxygen to be supplied to a cathode electrode flows, and a cooling water flow path through which cooling water flows, wherein at least the oxygen-containing gas flow path and the cooling water flow path are separated by a conductive porous body; A cooling water tank that stores the cooling water; an upstream cooling water flow pipe that connects an upstream end of the cooling water flow passage and the cooling water tank and allows the cooling water to flow from the cooling water tank into the cooling water flow passage; a downstream cooling water flow pipe that connects a downstream end of the cooling water flow passage and the cooling water tank, and returns the cooling water that has flowed out of the cooling water flow passage to the cooling water tank; an upstream oxygen flow pipe connected to an upstream end of the oxygen-containing gas flow passage and allowing an oxygen-containing gas to flow into the oxygen-containing gas flow passage; a downstream first oxygen flow pipe connecting a downstream end of the oxygen-containing gas flow passage and the cooling water tank; a downstream second oxygen flow pipe connected to the cooling water tank and discharging the oxygen-containing gas that has flowed into the cooling water tank from the downstream first oxygen flow pipe from the cooling water tank; a compressor unit that is disposed inside the upstream oxygen flow pipe, the compressor unit compressing the oxygen-containing gas and sending the oxygen-containing gas downstream; a turbine that is disposed inside the downstream second oxygen flow pipe, the turbine being rotated by the oxygen-containing gas discharged from the cooling water tank; and a drive shaft that connects the compressor and the turbine, the drive shaft being driven by a motor, the method comprising: A method for operating a fuel cell system, the method comprising the steps of: operating the fuel cell system so that a pressure difference between an internal pressure of the fuel gas flow channel and an internal pressure of the oxygen-containing gas flow channel is equal to or less than a predetermined pressure value.

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