Fuel Cell Systems

Abstract

To provide a fuel cell system which is capable of venting air from cooling water even when pressure in a passage of the cooling water is lower than the ambient pressure.SOLUTION: A fuel cell system 1 comprises: a fuel cell stack 10 which generates electricity with hydrogen and oxygen; a cooling water discharge pipe 56 connected to the fuel cell stack 10; and a cooling water pump 57 which discharges cooling water from the fuel cell stack 10 via the cooling water discharge pipe 56. When the cooling water pump 57 is in operation, pressure inside the cooling water discharge pipe 56 is lower than the ambient pressure at least between the fuel cell stack and the cooling water pump 57. To the cooling water discharge pipe 56, there is connected an air vent pipe 60 which extends substantially in the vertical direction between the fuel cell stack 10 and the cooling water pump 57.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to a fuel cell system. [Background technology]

[0002] The fuel cell stack includes a stack of multiple single-cell batteries. The stack has flow paths for fuel gas, oxidant gas, and coolant. The fuel cell stack generates electricity through an electrochemical reaction between the fuel gas and oxidant gas introduced into the stack. Coolant for cooling the heated stack is also introduced into the stack. As disclosed in JP 2014-049267 A, the coolant that has cooled the stack is discharged from the fuel cell stack using a coolant pump. The coolant pump is located downstream of the fuel cell stack in the direction of the coolant flow.

[0003] Here, the cooling water discharged from the fuel cell stack may contain air bubbles. If cooling water containing air bubbles is introduced into the cooling water pump, the operating efficiency of the cooling water pump may decrease. As a result, the cooling water may not be supplied sufficiently to the fuel cell stack, and the fuel cell stack may not be sufficiently cooled. If the fuel cell stack cannot be sufficiently cooled, the performance of the fuel cell stack may be impaired. To solve this problem, an air vent valve is installed at the cooling water inlet of the cooling water pump to release air bubbles in the cooling water into the atmosphere and prevent air bubbles from being introduced into the cooling water pump. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-049267 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the pressure in the cooling water flow path is lower than atmospheric pressure, it is difficult to release the air bubbles in the cooling water into the atmosphere using the air vent valve. This requires the use of a special pump as the cooling water pump. Such pumps are expensive, which increases the installation cost of the fuel cell system.

[0006] The present invention has been made in consideration of these points, and aims to provide a fuel cell system that is capable of bleeding the cooling water even when the pressure in the cooling water flow path is lower than atmospheric pressure. [Means for solving the problem]

[0007] The fuel cell system according to the embodiment includes: a fuel cell stack that generates electricity using hydrogen and oxygen; a cooling water discharge pipe connected to the fuel cell stack; a cooling water pump that discharges cooling water from the fuel cell stack through the cooling water discharge pipe; Equipped with During operation of the cooling water pump, the pressure in the cooling water discharge pipe is lower than atmospheric pressure at least between the fuel cell stack and the cooling water pump; An air vent pipe extending generally in the vertical direction is connected to the cooling water discharge pipe between the fuel cell stack and the cooling water pump. [Effects of the Invention]

[0008] According to the fuel cell system of the embodiment, it is possible to bleed air from the cooling water even when the pressure in the cooling water flow path is lower than atmospheric pressure. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing the configuration of a fuel cell system according to an embodiment. [Figure 2] FIG. 2 is a diagram for explaining the flow of fluid inside the fuel cell stack shown in FIG. [Figure 3]FIG. 3 is a cross-sectional view taken along line III-III of the laminate of the fuel cell stack shown in FIG. [Figure 4] FIG. 4 is a flowchart illustrating a control method for the fuel cell system shown in FIG. [Figure 5] FIG. 5 is a diagram for explaining the operation of the valve provided in the vent pipe. [Figure 6] FIG. 6 is a diagram for explaining the operation of the valve provided in the vent pipe. [Figure 7] FIG. 7 is a diagram for explaining the operation of the valve provided in the vent pipe. [Figure 8] FIG. 8 is a diagram for explaining the operation of the valve provided in the vent pipe. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will be described below with reference to the accompanying drawings. First, the overall configuration of a fuel cell system will be described with reference to FIG.

[0011] 1, the fuel cell system 1 includes a fuel cell stack 10, a fuel gas supply system 30, a fuel gas discharge system 35, an oxidant gas supply system 40, an oxidant gas discharge system 45, a cooling water supply system 50, and a cooling water discharge system 55. The fuel cell stack 10 generates electricity using hydrogen and oxygen. The fuel gas is hydrogen, and the oxidant gas is air.

[0012] The fuel gas supply system 30 includes a fuel gas supply source (not shown), such as a fuel gas tank, and a fuel gas supply pipe 31. The fuel gas supply pipe 31 connects the fuel gas supply source to the fuel cell stack 10. The fuel gas discharge system 35 includes a fuel gas discharge pipe 36. One end of the fuel gas discharge pipe 36 is connected to the fuel cell stack 10.

[0013] The oxidizing gas supply system 40 includes an oxidizing gas supply source (not shown), such as a blower, and an oxidizing gas supply pipe 41. The oxidizing gas supply pipe 41 connects the oxidizing gas supply source to the fuel cell stack 10. The oxidizing gas discharge system 45 includes an oxidizing gas discharge pipe 46. One end of the oxidizing gas discharge pipe 46 is connected to the fuel cell stack 10.

[0014] The cooling water supply system 50 includes a cooling water supply source 51 and a cooling water supply pipe 52. The cooling water supply pipe 52 connects the cooling water supply source 51 to the fuel cell stack 10. In the illustrated example, the cooling water supply source 51 is a cooling water tank. The top of the cooling water tank 51 is open to atmospheric pressure. The cooling water supply pipe 52 is connected to the bottom of the cooling water tank 51.

[0015] The cooling water discharge system 55 includes a cooling water discharge pipe 56 and a cooling water pump 57. One end of the cooling water discharge pipe 56 is connected to the fuel cell stack 10. In the example shown, the other end of the cooling water discharge pipe 56 is connected to the top of the cooling water tank 51. When the cooling water pump 57 is operated, the pressure in the cooling water discharge pipe 56 decreases, and the cooling water in the fuel cell stack 10 is discharged into the cooling water discharge pipe 56 and then into the cooling water tank 51.

[0016] 1 to 3, the fuel cell stack 10 is a polymer electrolyte fuel cell stack. The fuel cell stack 10 includes a plurality of unit cells 11 and manifolds 21, 22, 23, 24, 25, and .

[0017] A plurality of single-cell batteries 11 are stacked in a direction perpendicular to the plane of the paper in FIGS. 1 and 2 to form a stack 12. The stack 12 has an overall rectangular parallelepiped shape. The stack 12 has a first side surface 12a, a second side surface 12b, a third side surface 12c, and a fourth side surface 12d that extend along the stacking direction of the single-cell batteries 11. The first side surface 12a and the second side surface 12b face each other. The third side surface 12c and the fourth side surface 12d face each other. Manifolds 21, 22, 23, 24, 25, and 26 are attached to the sides 12a, 12b, 12c, and 12d of the stack 12.

[0018] As shown in FIG. 3, each single-cell battery 11 includes a membrane electrode assembly (MEA) 13, a fuel separator 14, and an oxidant separator 15 disposed on either side of the membrane electrode assembly 13. The membrane electrode assembly 13 includes a polymer electrolyte membrane 13a and a pair of electrodes (a fuel electrode 13b and an oxidant electrode 13c) disposed on either side of the polymer electrolyte membrane 13a. The fuel separator 14 and the oxidant separator 15 are made of a conductive porous material. The fuel separator 14 and the oxidant separator 15 may be, for example, a conductive porous carbon plate.

[0019] A fuel gas flow channel 16 is provided on the surface of the fuel separator 14 that contacts the membrane electrode assembly 13. One end of the fuel gas flow channel 16 opens to the first side surface 12a of the stack 12. The other end of the fuel gas flow channel 16 opens to the second side surface 12b of the stack 12.

[0020] An oxidant gas channel 17 is provided on the surface of the oxidant separator 15 that contacts the membrane electrode assembly 13. One end of the oxidant gas channel 17 opens to the third side surface 12c of the stack 12. The other end of the oxidant gas channel 17 opens to the fourth side surface 12d of the stack 12.

[0021] A cooling water flow path 18 is provided on the other surface of the fuel separator 14 or the other surface of the oxidant separator 15. In the illustrated example, the cooling water flow path 18 is provided on the surface of the oxidant separator 15. One end of the cooling water flow path 18 opens to the fourth side surface 12d of the stack 12. The other end of the cooling water flow path 18 opens to the third side surface 12c of the stack 12.

[0022] The fuel gas supply manifold 21 is provided facing the first side surface 12a of the stack 12. The internal space 21a of the fuel gas supply manifold 21 is connected to one end of the fuel gas flow path 16. A fuel gas supply pipe 31 is connected to the fuel gas supply manifold 21, and the fuel gas is introduced into the internal space 21a through the fuel gas supply pipe 31.

[0023] The fuel gas discharge manifold 22 is provided facing the second side surface 12b of the stack 12. The internal space 22a of the fuel gas discharge manifold 22 is connected to the other end of the fuel gas flow path 16. A fuel gas discharge pipe 36 is connected to the fuel gas discharge manifold 22, and the fuel gas is discharged from the internal space 22a through the fuel gas discharge pipe 36.

[0024] The oxidizing gas supply manifold 23 is provided facing the third side surface 12c of the stack 12. An internal space 23a of the oxidizing gas supply manifold 23 communicates with one end of the oxidizing gas flow path 17. An oxidizing gas supply pipe 41 is connected to the oxidizing gas supply manifold 23, and the oxidizing gas is introduced into the internal space 23a through the oxidizing gas supply pipe 41.

[0025] The oxidant gas discharge manifold 24 is provided facing the fourth side surface 12d of the stack 12. An internal space 24a of the oxidant gas discharge manifold 24 communicates with the other end of the oxidant gas flow path 17. An oxidant gas discharge pipe 46 is connected to the oxidant gas discharge manifold 24, and the oxidant gas is discharged from the internal space 24a through the oxidant gas discharge pipe 46.

[0026] The cooling water supply manifold 25 is provided facing the fourth side surface 12d of the laminate 12. An internal space 25a of the cooling water supply manifold 25 communicates with one end of the cooling water flow path 18. A cooling water supply pipe 52 is connected to the cooling water supply manifold 25, and cooling water is introduced into the internal space 25a through the cooling water supply pipe 52.

[0027] The cooling water discharge manifold 26 is provided facing the third side surface 12c of the laminate 12. An internal space 26a of the cooling water discharge manifold 26 communicates with the other end of the cooling water flow path 18. A cooling water discharge pipe 56 is also connected to the cooling water discharge manifold 26, and the cooling water is discharged from the internal space 26a through the cooling water discharge pipe 56.

[0028] In FIG. 2, the flows of fuel gas, oxidant gas, and coolant in the fuel cell stack 10 are indicated by dashed arrows, dashed-dotted arrows, and solid arrows, respectively. As shown in FIG. 2, fuel gas is supplied from a fuel gas supply pipe 31 to the stack 12 through the internal space 21a of the fuel gas supply manifold 21. The fuel gas supplied to the stack 12 is introduced into the fuel gas flow path 16 of each single-cell battery 11. The oxidant gas is supplied from an oxidant gas supply pipe 41 to the stack 12 through the internal space 23a of the oxidant gas supply manifold 23. The oxidant gas supplied to the stack 12 is introduced into the oxidant gas flow path 17 of each single-cell battery 11. The hydrogen in the fuel gas and the oxygen in the oxidant gas then react in the single-cell battery 11 to generate electricity and water. The fuel gas discharged from the fuel gas flow path 16 flows into the fuel gas discharge pipe 36 through the fuel gas discharge manifold 22. The oxidizing gas discharged from the oxidizing gas flow channel 17 flows into the oxidizing gas discharge pipe 46 through the oxidizing gas discharge manifold 24 .

[0029] Cooling water is supplied to the stack 12 from the cooling water supply pipe 52 through the cooling water supply manifold 25. The cooling water supplied to the stack 12 is introduced into the cooling water flow path 18 of each single-cell battery 11 and is used to cool the single-cell battery 11. The cooling water discharged from the cooling water flow path 18 flows into the cooling water discharge pipe 56 through the cooling water discharge manifold 26.

[0030] The illustrated fuel cell system 1 is configured so that, when the cooling water pump 57 is operating, the pressure in the cooling water discharge pipe 56 becomes lower than the atmospheric pressure at least between the fuel cell stack 10 and the cooling water pump 57. As a result, in the fuel cell stack 10, the pressure in the cooling water flow path 18 becomes sufficiently lower than the pressure in the fuel gas flow path 16 and the oxidant gas flow path 17. As a result, the risk of the cooling water in the cooling water flow path 18 leaking into the fuel gas flow path 16 or the oxidant gas flow path 17 is effectively suppressed. In addition, the above-mentioned pressure difference causes the water generated at the oxidizer electrode 13c to move from the oxidizer electrode 13c through the porous gas diffusion layer and separator into the cooling water flow path 18 and then be removed from the fuel cell stack 10.

[0031] However, the cooling water discharged from the fuel cell stack may contain air bubbles. If cooling water containing air bubbles is introduced into the cooling water pump, the pump's operating efficiency may decrease. As a result, the cooling water may not be supplied sufficiently to the fuel cell stack, and the fuel cell stack may not be sufficiently cooled. If the fuel cell stack cannot be sufficiently cooled, the performance of the fuel cell may be impaired. To solve this problem, an air vent valve is installed at the cooling water inlet of the cooling water pump to release air bubbles in the cooling water into the atmosphere and prevent air bubbles from being introduced into the cooling water pump.

[0032] However, when the pressure in the cooling water discharge pipe is lower than atmospheric pressure, it is difficult to release the air bubbles in the cooling water into the atmosphere using the air vent valve. This requires the use of a special pump as the cooling water pump. Such pumps are expensive, which increases the installation cost of the fuel cell system.

[0033] Taking these circumstances into consideration, the fuel cell system 1 of this embodiment is designed to enable deaeration of the cooling water even when the pressure in the cooling water discharge pipe 56 is lower than atmospheric pressure.

[0034] Specifically, a vent pipe 60 is connected to the cooling water discharge pipe 56. The vent pipe 60 is connected to the cooling water discharge pipe 56 between the fuel cell stack 10 and the cooling water pump 57. The vent pipe 60 extends generally in the vertical direction. The lower end of the vent pipe 60 is connected to the cooling water discharge pipe 56. Air bubbles in the cooling water flowing through the cooling water discharge pipe 56 can be released to the outside of the cooling water discharge system 55 through the vent pipe 60.

[0035] In the illustrated example, the cooling water discharge pipe 56 extends generally horizontally at the connection portion with the vent pipe 60. In other words, the cooling water discharge pipe 56 has a horizontal portion 56a that extends generally horizontally between the fuel cell stack 10 and the cooling water pump 57, and the vent pipe 60 is connected to the horizontal portion 56a. Air bubbles in the cooling water flowing through the cooling water discharge pipe 56 tend to move toward the upper half of the cooling water discharge pipe 56 in the horizontal portion 56a. The vent pipe 60 is connected to the upper half of the horizontal portion 56a. This allows air bubbles in the cooling water flowing through the horizontal portion 56a to be efficiently captured within the vent pipe 60.

[0036] The cross-sectional area of ​​the cooling water discharge pipe 56 is determined as follows: the cross-sectional area of ​​the cooling water discharge pipe 56 at the connection with the vent pipe 60 is larger than the cross-sectional area of ​​the cooling water discharge pipe 56 at the connection with the fuel cell stack 10. This causes the flow rate of the cooling water that flows from the fuel cell stack 10 into the cooling water discharge pipe 56 to decrease at the connection between the cooling water discharge pipe 56 and the vent pipe 60. As a result, more air bubbles in the cooling water move upward at this connection. Therefore, more air bubbles in the cooling water can be captured in the vent pipe 60.

[0037] In the illustrated example, the horizontal portion 56a has a swollen portion 56b (see FIGS. 5 to 8). The cross-sectional area of ​​the swollen portion 56b is larger than the cross-sectional area of ​​the cooling water discharge pipe 56 other than the swollen portion 56b. The vent pipe 60 is connected to the upper half of the swollen portion 56b.

[0038] The cooling water tank 51 is located above the vent pipe 60. The upper end of the vent pipe 60 is connected to the bottom of the cooling water tank 51. A first on-off valve 61 is provided between the lower and upper ends of the vent pipe 60. A second on-off valve 62 is provided between the lower end of the vent pipe 60 and the first on-off valve 61. The first on-off valve 61 is located above the second on-off valve 62. By providing the vent pipe 60 and the on-off valves 61 and 62, the fuel cell system 1 can efficiently discharge air bubbles in the cooling water flowing through the cooling water discharge pipe 56 through the vent pipe 60. Specifically, by controlling the first on-off valve 61 and the second on-off valve 62 using a control method described with reference to FIGS. 4 to 8, air bubbles in the cooling water flowing through the cooling water discharge pipe 56 can be discharged through the vent pipe 60. In the illustrated example, the fuel cell system 1 has a control device 65 that controls the first on-off valve 61 and the second on-off valve 62.

[0039] The first on-off valve 61 and the second on-off valve 62 are not particularly limited as long as they are valves that can close / open the vent pipe 60 as needed. The first on-off valve 61 and the second on-off valve 62 may be, for example, electromagnetic valves.

[0040] A control method for the fuel cell system 1 will be described with reference to Figures 4 to 8. The following description will focus on a control method for the first on-off valve 61 and the second on-off valve 62. For simplicity of illustration, the cooling water supply pipe 52 is omitted from Figures 5 to 8.

[0041] When starting power generation by the fuel cell system 1, first, the first on-off valve 61 and the second on-off valve 62 are opened in response to a control signal from the control device 65. This causes the cooling water in the cooling water tank 51 to flow into the vent pipe 60, filling the vent pipe 60 with cooling water (step S1 in FIG. 4).

[0042] Next, as shown in Fig. 5, in response to a control signal from the control device 65, the first on-off valve 61 is closed while the second on-off valve 62 remains open (step S2 in Fig. 4). This prevents the area of ​​the vent pipe 60 below the first on-off valve 61 from being affected by atmospheric pressure through the cooling water tank 51. Hereinafter, the state in which the first on-off valve 61 is closed and the second on-off valve 62 is open will also be referred to as the "first state."

[0043] Next, the supply of fuel gas, oxidant gas, and coolant to the fuel cell stack 10 is started. The supply of coolant to the fuel cell stack 10 is performed by operating the coolant pump 57 to reduce the pressure in the coolant discharge pipe 56. In the illustrated example, the pressure in the coolant discharge pipe 56 is made lower than atmospheric pressure at least between the fuel cell stack 10 and the coolant pump 57. This sufficiently reduces the pressure in the coolant flow path 18 of the fuel cell stack 10, allowing coolant to be supplied from the coolant tank 51 to the coolant flow path 18. The coolant in the fuel cell stack 10 is also discharged to the coolant discharge pipe 56. The coolant flowing through the coolant discharge pipe 56 is then discharged to the coolant tank 51 via the coolant pump 57. In this manner, the coolant circulates through the coolant supply system 50, the fuel cell stack 10, and the coolant discharge system 55.

[0044] Air bubbles in the cooling water flowing through the cooling water discharge pipe 56 rise within the cooling water discharge pipe 56 and are trapped in the air vent pipe 60 that opens into the cooling water discharge pipe 56. The air bubbles trapped in the air vent pipe 60 accumulate in the region of the air vent pipe 60 between the first on-off valve 61 and the second on-off valve 62.

[0045] Next, when a predetermined time has elapsed since the first on-off valve 61 and the second on-off valve 62 were set to the first state and a certain amount of gas has accumulated in the vent pipe 60 (YES in step S4 in FIG. 4), as shown in FIG. 6, a control signal is received from the control device 65, and the second on-off valve 62 is closed while the first on-off valve 61 remains closed (step S5). Herein, the predetermined time may be a time length that does not allow too much gas to accumulate in the vent pipe 60. For example, it may be a time length that allows the amount of gas trapped in the vent pipe 60 to be contained in the region of the vent pipe 60 between the first on-off valve 61 and the second on-off valve 62. Hereinafter, the state in which both the first on-off valve 61 and the second on-off valve 62 are closed will also be referred to as an "intermediate state."

[0046] Next, as shown in FIG. 7 , in response to a control signal from the control device 65, the first on-off valve 61 is opened while the second on-off valve 62 remains closed (step S6). As a result, air bubbles trapped in the region between the first on-off valve 61 and the second on-off valve 62 rise and are released into the cooling water tank 51, and at the same time, cooling water from the cooling water tank 51 is introduced into the region of the ventilation pipe 60 above the second on-off valve 62. Note that, by keeping the second on-off valve 62 closed while the first on-off valve 61 is open, the region of the ventilation pipe 60 below the second on-off valve 62 is prevented from being affected by atmospheric pressure through the cooling water tank 51. Therefore, air bubbles in the cooling water flowing through the cooling water discharge pipe 56 continue to be trapped in the ventilation pipe 60. Hereinafter, the state in which the first on-off valve 61 is open and the second on-off valve 62 is closed will also be referred to as the “second state.”

[0047] 8, upon receiving a control signal from the control device 65, the first on-off valve 61 is closed while the second on-off valve 62 remains closed (step S7). That is, the first on-off valve 61 and the second on-off valve 62 are set to an intermediate state.

[0048] 5, in response to a control signal from the control device 65, the second on-off valve 62 is opened while the first on-off valve 61 remains closed (step S8). That is, the first on-off valve 61 and the second on-off valve 62 are set to the first state. Since the first on-off valve 61 remains closed while the second on-off valve 62 is open, the region of the vent pipe 60 below the first on-off valve 61 is prevented from being affected by atmospheric pressure through the cooling water tank 51. Therefore, air bubbles in the cooling water flowing through the cooling water discharge pipe 56 continue to be trapped in the vent pipe 60. The bubbles (gas) trapped in the vent pipe 60 accumulate in the region of the vent pipe 60 between the first on-off valve 61 and the second on-off valve 62.

[0049] Here, if power generation by the fuel cell system 1 continues, the supply of fuel gas, oxidant gas, and coolant to the fuel cell stack 10 continues. Therefore, the operation of the coolant pump 57 also continues. If the operation of the coolant pump 57 continues in step S9 (YES in step S9), the process returns to step S4, and the control of the first on-off valve 61 and the second on-off valve 62 continues.

[0050] On the other hand, when power generation by the fuel cell system 1 is terminated, the supply of fuel gas, oxidant gas, and coolant to the fuel cell stack 10 is stopped. Therefore, the operation of the cooling water pump 57 is also stopped. When the operation of the cooling water pump 57 is stopped, no more cooling water is introduced into the cooling water pump 57. Therefore, if the operation of the cooling water pump 57 is not continuing in step S9 (NO in step S9), the control of the first on-off valve 61 and the second on-off valve 62 is terminated.

[0051] Also, in step S4, if the certain time has not elapsed (NO in step S4), the process returns to step S4.

[0052] In the above-described embodiment, the separator 15 provided with the cooling water flow path 18 is made of a porous material, but this is not limiting. The separator 15 provided with the cooling water flow path 18 may be made of a material that does not allow water to pass through, such as a metal plate. In this case, too, the pressure in the cooling water discharge pipe 56 may be made lower than atmospheric pressure in order to prevent the cooling water from leaking from the cooling water supply system 50 or the cooling water discharge system 55, which may cause problems similar to those described above.

[0053] In the above-described embodiment, the first on-off valve 61 and the second on-off valve 62 are switched to the intermediate state after a predetermined time has elapsed since they were switched to the first state, but this is not limited to this. The first on-off valve 61 and the second on-off valve 62 may be switched to the intermediate state after a predetermined amount of gas has accumulated in the vent pipe 60 after being switched to the first state. In this case, a liquid level gauge or level sensor (a level switch or a level gauge) that measures the water level of the cooling water in the vent pipe 60 may be provided in the vent pipe 60, and the first state may be switched to the intermediate state based on the measurement result from the liquid level gauge or level sensor.

[0054] In the above-described embodiment, the first on-off valve 61 and the second on-off valve 62 are controlled using the control device 65, but this is not limiting. The first on-off valve 61 and the second on-off valve 62 may also be controlled manually.

[0055] Furthermore, in the above-described embodiment, the upper end of the vent pipe 60 is connected to the cooling water tank 51 included in the cooling water supply system 50, but this is not limited to this. The upper end of the vent pipe 60 may be connected to a cooling water tank separate from the cooling water tank 51 of the cooling water supply system 50. When the vent pipe 60 is connected to the cooling water tank 51 of the cooling water supply system 50, the fuel cell system 1 can be made more compact than when the vent pipe 60 is connected to a cooling water tank separate from the cooling water tank 51.

[0056] As described above, the fuel cell system 1 according to this embodiment includes the fuel cell stack 10, which generates electricity using hydrogen and oxygen, the cooling water discharge pipe 56 connected to the fuel cell stack 10, and the cooling water pump 57, which discharges cooling water from the fuel cell stack 10 through the cooling water discharge pipe 56. While the cooling water pump 57 is operating, the pressure in the cooling water discharge pipe 56 is lower than atmospheric pressure at least between the fuel cell stack and the cooling water pump 57. In addition, the cooling water discharge pipe 56 is connected to a vent pipe 60, which extends generally vertically, between the fuel cell stack 10 and the cooling water pump 57. With this fuel cell system 1, air bubbles in the cooling water flowing through the cooling water discharge pipe 56 can be discharged through the vent pipe 60 before the cooling water is introduced into the cooling water pump 57.

[0057] Furthermore, in the fuel cell system 1 according to this embodiment, the cooling water discharge pipe 56 extends substantially horizontally at the connection portion with the vent pipe 60. Furthermore, the vent pipe 60 is connected to the upper half of the cooling water discharge pipe 56. This allows air bubbles in the cooling water flowing through the cooling water discharge pipe 56 to be efficiently discharged through the vent pipe 60.

[0058] Furthermore, in the fuel cell system 1 according to this embodiment, the cross-sectional area of ​​the cooling water discharge pipe 56 at the connection with the vent pipe 60 is larger than the cross-sectional area of ​​the cooling water discharge pipe 56 at the connection with the fuel cell stack 10. This allows more air bubbles in the cooling water flowing through the cooling water discharge pipe 56 to be discharged through the vent pipe 60.

[0059] In the fuel cell system 1 according to this embodiment, the lower end of the vent pipe 60 is connected to the cooling water discharge pipe 56. The upper end of the vent pipe 60 is connected to the cooling water tank 51. A first on-off valve 61 is provided between the lower and upper ends of the vent pipe 60. A second on-off valve 62 is provided between the lower end of the vent pipe 60 and the first on-off valve 61. Since the fuel cell system 1 has such vent pipe 60 and on-off valves 61, 62, air bubbles in the cooling water flowing through the cooling water discharge pipe 56 can be efficiently discharged through the vent pipe 60.

[0060] Specifically, the first on-off valve 61 and the second on-off valve 62 transition from a first state in which the first on-off valve 61 is closed and the second on-off valve 62 is open, to an intermediate state in which the first on-off valve 61 and the second on-off valve 62 are both closed, and then to a second state in which the first on-off valve 61 is open and the second on-off valve 62 is closed, thereby removing air bubbles from the cooling water flowing through the cooling water discharge pipe 56.

[0061] The fuel cell system 1 according to this embodiment further includes a cooling water supply pipe 52 having one end connected to the fuel cell stack 10 and the other end connected to the cooling water tank 51. In other words, the vent pipe 60 is connected to the cooling water tank 51 of the cooling water supply system 50. In this case, the fuel cell system 1 can be made smaller than when the vent pipe 60 is connected to a cooling water tank separate from the cooling water tank 51.

[0062] In the fuel cell system 1 according to this embodiment, the first on-off valve 61 and the second on-off valve 62 are switched to the intermediate state after the first state is maintained for a predetermined time, thereby preventing excessive gas from accumulating in the gas vent pipe 60.

[0063] Alternatively, in the fuel cell system 1 according to this embodiment, the first on-off valve 61 and the second on-off valve 62 are switched to the intermediate state after the first state is maintained until a predetermined amount of gas accumulates between the lower end of the vent pipe 60 and the first on-off valve 61. This also prevents excessive gas from accumulating in the vent pipe 60.

[0064] Furthermore, in the fuel cell system 1 according to this embodiment, the fuel cell stack 10 includes a membrane electrode assembly 13 including a polymer electrolyte membrane 13a, a fuel electrode 13b, and an oxidizer electrode 13c disposed on either side of the polymer electrolyte membrane 13a, and a fuel separator 14 and an oxidizer separator 15 disposed on either side of the membrane electrode assembly 13. A fuel gas flow path 16 is provided on one side of the fuel separator 14. An oxidizer gas flow path 17 is provided on one side of the oxidizer separator 15. A cooling water flow path 18 is provided on the other side of the fuel separator 14 or the oxidizer separator 15. The separator provided with the cooling water flow path 18 is made of a porous material. In this fuel cell system 1, when the pressure in the cooling water discharge pipe 56 is made lower than the atmospheric pressure, the pressure in the cooling water flow path 18 in the fuel cell stack 10 becomes sufficiently lower than the pressure in the fuel gas flow path 16 or the oxidizer gas flow path 17. As a result, it is possible to effectively prevent the cooling water in the cooling water flow path 18 from leaking into the fuel gas flow path 16 or the oxidant gas flow path 17. Furthermore, the water generated at the oxidant electrode 13c moves from the oxidant electrode 13c through the porous gas diffusion layer and separator due to the pressure difference, to the cooling water flow path 18, and is then removed to the outside of the fuel cell stack 10.

[0065] Although the present invention has been described with reference to an embodiment and several modifications thereof, these embodiments and modifications are presented as examples and are not intended to limit the scope of the invention. These novel embodiments and modifications may be embodied in various other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, it is of course possible to combine these embodiments and modifications in part as appropriate within the spirit of the invention. [Explanation of symbols]

[0066] 1: fuel cell system, 10: fuel cell stack, 12: stack, 30: fuel gas supply system, 31: fuel gas supply piping, 35: fuel gas exhaust system, 36: fuel gas exhaust piping, 40: oxidizer gas supply system, 41: oxidizer gas supply piping, 45: oxidizer gas exhaust system, 46: oxidizer gas exhaust piping, 50: cooling water supply system, 51: cooling water tank, 52: cooling water supply piping, 55: cooling water exhaust system, 56: cooling water exhaust piping, 57: cooling water pump, 60: vent piping, 61: first on-off valve, 62: second on-off valve, 65: control device

Claims

1. a fuel cell stack that generates electricity using hydrogen and oxygen; a cooling water discharge pipe connected to the fuel cell stack; a cooling water pump that discharges cooling water from the fuel cell stack through the cooling water discharge pipe; Equipped with During operation of the cooling water pump, the pressure in the cooling water discharge pipe is lower than atmospheric pressure at least between the fuel cell stack and the cooling water pump; a vent pipe extending generally in a vertical direction between the fuel cell stack and the cooling water pump is connected to the cooling water discharge pipe, The lower end of the vent pipe is connected to the cooling water discharge pipe, The upper end of the vent pipe is connected to a cooling water tank, A first on-off valve is provided between the lower end and the upper end of the vent pipe, a second on-off valve is provided between a lower end of the vent pipe and the first on-off valve,

2. The cooling water discharge pipe extends substantially horizontally at a connection portion with the air vent pipe, 2. The fuel cell system according to claim 1, wherein the ventilation pipe is connected to an upper half of the cooling water discharge pipe.

3. 3. The fuel cell system according to claim 1, further comprising a cooling water supply pipe having one end connected to said fuel cell stack and the other end connected to said cooling water tank.

4. 4. The fuel cell system according to claim 1, wherein the first and second on-off valves transition from a first state in which the first on-off valve is closed and the second on-off valve is open, through an intermediate state in which the first and second on-off valves are both closed, to a second state in which the first on-off valve is open and the second on-off valve is closed, thereby removing air bubbles in the cooling water flowing through the cooling water discharge piping.

5. 5. The fuel cell system according to claim 4, wherein the first and second on-off valves are switched to the intermediate state after the first state is maintained for a predetermined time.

6. 5. The fuel cell system of claim 4, wherein the first and second opening / closing valves are switched to the intermediate state after the first state is maintained until a predetermined amount of gas accumulates between the lower end of the vent pipe and the first opening / closing valve.

7. 7. The fuel cell system according to claim 1, further comprising a control unit that controls opening and closing of the first on-off valve and the second on-off valve.

8. The fuel cell stack comprises: A membrane electrode assembly including a polymer electrolyte membrane and a fuel electrode and an oxidizer electrode disposed on either side of the polymer electrolyte membrane; a fuel separator and an oxidant separator disposed on either side of the membrane electrode assembly; Including, A fuel gas flow path is provided on one surface of the fuel separator, an oxidant gas flow channel is provided on one surface of the oxidant separator; a cooling water flow path is provided on the other surface of the fuel separator or the oxidizer separator; 8. The fuel cell system according to claim 1, wherein the separator provided with the cooling water flow passage is made of a porous material.

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