JP6135590B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  A fuel cell stack for generating electricity by reaction of hydrogen gas and air, a fuel supply system for supplying hydrogen gas to the fuel cell stack, a fuel circulation system for returning anode off-gas discharged from the fuel cell stack to the fuel cell stack, and fuel A fuel discharge system for discharging a part of the anode off-gas from the circulation system, an oxidant discharge system for discharging the cathode off-gas discharged from the fuel cell stack, a diluter connected to the fuel discharge system and the oxidant discharge system, Is known (see Patent Document 1).

  In the polymer electrolyte fuel cell, moisture, nitrogen gas or the like permeates from the cathode electrode to the anode electrode. These moisture, nitrogen gas and the like are returned to the fuel cell stack by the fuel circulation system together with the anode off gas. However, these moisture and nitrogen gas reduce the power generation efficiency of the fuel cell stack. Therefore, when a substance that reduces the power generation efficiency of the fuel cell stack is referred to as a power generation inhibitor, it is necessary to remove the power generation inhibitor from the hydrogen gas flow path. Therefore, in the fuel cell system of Patent Document 1, a part of the anode off gas containing the power generation inhibiting substance is discharged as a purge gas by a fuel discharge system.

  However, in order to release the purge gas to the atmosphere, it is necessary to make the hydrogen concentration in the purge gas lower than the explosion limit concentration for safety. Therefore, it is necessary to dilute the purge gas before releasing the purge gas into the atmosphere. Therefore, in the fuel cell system of Patent Document 1, the anode offgas discharged by the fuel discharge system is temporarily stored in a buffer tank, and the stored anode offgas is diluted using at least one of an injector and a pump. Is supplied to the vessel and diluted with cathode off-gas (including air).

JP 2012-252796 A

  However, in the fuel cell system described in Patent Document 1, an injector and a pump are required to supply the anode off gas stored in the buffer tank to the diluter, so that the system becomes complicated and the injector and the pump are driven. Electric energy is necessary to do this.

  According to the present invention, a fuel cell stack that generates electric power by an electrochemical reaction between a fuel gas and an oxidant gas, an anode offgas pipe connected to an outlet of a fuel gas passage formed in the fuel cell stack, A cathode offgas pipe connected to an outlet of an oxidant gas passage formed in the fuel cell stack, a buffer tank for temporarily storing purge gas from the anode offgas pipe, and an outlet or a halfway of the anode offgas pipe A purge gas introduction pipe connected to the inlet of the buffer tank, a purge gas introduction valve arranged in the purge gas introduction pipe, and a fuel gas in the exhaust gas arranged in the cathode off gas pipe by mixing the cathode off gas and the purge gas with each other A diluter for reducing the concentration, the outlet of the buffer tank and the inlet or the diluter. A purge gas discharge pipe connected to the cathode offgas pipe upstream of the diluter, and a purge gas discharge valve disposed in the purge gas discharge pipe, wherein the buffer tank is elastically expandable and contractible, and the purge gas discharge valve When the purge gas introduction valve is opened while being closed, purge gas flows into the buffer tank from the anode off-gas pipe through the purge gas introduction pipe, and at this time, the buffer tank elastically expands, When the purge gas introduction valve is closed and the purge gas discharge valve is opened, the buffer tank is elastically contracted so that the purge gas in the buffer tank passes through the purge gas discharge pipe into the diluter or the A fuel cell system is provided that is discharged into the cathode offgas pipe upstream of the diluter. .

  A power generation inhibiting substance can be removed from the fuel cell stack and the anode offgas pipe using a simpler configuration.

1 is an overall view of a fuel cell system. It is a fragmentary sectional view of a buffer tank. It is a fragmentary sectional view showing operation of a buffer tank. It is a fragmentary sectional view showing operation of a buffer tank. It is a fragmentary sectional view showing operation of a buffer tank. It is a time chart explaining a purge action. It is a figure which shows the map of the interval T. It is a flowchart which shows the routine which performs purge control. It is a fragmentary sectional view of another Example of a buffer tank. It is a fragmentary sectional view of another Example of a buffer tank. FIG. 3 is a schematic diagram showing another embodiment according to the present invention.

  Referring to FIG. 1, the fuel cell system 1 includes a fuel cell stack 10. The fuel cell stack 10 includes a plurality of fuel cell single cells (not shown) stacked in the stacking direction. Each single fuel cell includes a membrane electrode assembly 20. The membrane electrode assembly 20 includes a membrane electrolyte, an anode electrode formed on one side of the electrolyte, and a cathode electrode formed on the other side of the electrolyte.

  The anode electrode and the cathode electrode of the single fuel cell are electrically connected in series, and constitute an electrode of the fuel cell stack 10. The electrode of the fuel cell stack 10 is electrically connected to an inverter via a DC / DC converter, for example, and the inverter is electrically connected to a motor generator. Moreover, in another Example, the fuel cell system 1 is provided with an electrical storage device like a battery. Illustration of these electrical configurations is omitted.

  Further, in the single fuel cell, a hydrogen gas flow passage for supplying hydrogen gas as fuel gas to the anode electrode, an air flow passage for supplying air as oxidant gas to the cathode electrode, and a single fuel cell. A cooling water flow passage for supplying cooling water to the cell is formed. By connecting the hydrogen gas flow passage, the air flow passage, and the cooling water flow passage of the plurality of fuel cell single cells in series, the fuel cell stack 10 includes the hydrogen gas passage 30, the air passage 40, and the cooling water passage 50. Each is formed.

  A hydrogen gas supply pipe 31 is connected to the inlet of the hydrogen gas passage 30, and the hydrogen gas supply pipe 31 is connected to a hydrogen tank 32 that is a fuel gas source. In the hydrogen gas supply pipe 31, in order from the upstream side, a shutoff valve 33, a regulator 34 for adjusting the pressure of the hydrogen gas in the hydrogen gas supply pipe 31, and a pressure sensor PA for measuring the pressure in the hydrogen gas supply pipe 31. And are arranged. On the other hand, one end of an anode off gas pipe 36 is connected to the outlet of the hydrogen gas passage 30. One end of a purge gas introduction pipe 64 is connected to the other end of the anode off gas pipe 36, and an elastically expandable / contractible buffer tank 60 is connected to the other end of the purge gas introduction pipe 64. For example, an electromagnetic purge gas introduction valve 61 is disposed in the purge gas introduction pipe 64. When the shut-off valve 33 is opened, the hydrogen gas in the hydrogen tank 32 is regulated by the regulator 34 and supplied into the hydrogen gas passage 30 in the fuel cell stack 10 via the hydrogen gas supply pipe 31. In the embodiment shown in FIG. 1, hydrogen gas is supplied to the hydrogen gas supply pipe 31 so that the pressure of the hydrogen gas supply pipe 31 is maintained at a target pressure determined according to, for example, the load of the fuel cell system 1. In other words, when the purge gas introduction valve 61 is closed, the hydrogen gas is supplied to the hydrogen gas supply pipe 31 so that the hydrogen gas consumed by the fuel cell stack 10 is replenished. In this case, there is no anode off-gas flow in the anode off-gas pipe 36. On the other hand, when the purge gas introduction valve 61 is opened while the purge gas discharge valve 62 (described later) is closed, the hydrogen gas flow path composed of the hydrogen gas passage 30 and the anode off-gas pipe 36 of the fuel cell stack 10 becomes hydrogen gas. Scavenged by. At this time, the anode off gas flowing out from the anode off gas pipe 36, that is, the purge gas is supplied to the buffer tank 60 through the purge gas introduction pipe 64.

  An outlet of the purge gas discharge pipe 65 is connected to the outlet of the buffer tank 60, and an outlet of the purge gas discharge pipe 65 is connected to an inlet of a diluter 49 described later. For example, an electromagnetic purge gas discharge valve 62 is disposed in the purge gas discharge pipe 65. When the purge gas discharge pipe 65 is opened, the purge gas in the buffer tank 60 is supplied to the diluter 49.

  FIG. 2 is a cross-sectional view of an example of the buffer tank 60. In the example shown in FIG. 2, the buffer tank 60 includes a cylindrical member 71 that can elastically expand and contract and a plate member 72 having rigidity. The cylindrical member 71 and the plate-like member 72 are made of, for example, resin or metal. Further, the buffer tank 60 is accommodated in the hermetically sealed container 70, and thus is tightly surrounded by the container 70. The opening of the buffer tank 60 is hermetically fixed to the inner surface of the storage container 70. The purge gas introduction pipe 64 and the purge gas discharge pipe 65 described above pass through the storage container 70 and communicate with the buffer tank 60. In this case, when the cylindrical member 71 expands and contracts in the longitudinal direction of the buffer tank 60, the capacity of the buffer tank 60 is changed. A capacity sensor 74 that detects the capacity of the buffer tank 60 is also provided. The amount of gas stored in the buffer tank 60, that is, the capacity of the buffer tank 60 is represented by the position of the plate-like member 72. Therefore, in the embodiment shown in FIG. 2, the capacitance sensor 74 is composed of a position sensor that detects the position of the plate-like member 72. Specifically, the capacitance sensor 74 is configured by a contact type position sensor having a sensor head 74a. In another embodiment, the capacitive sensor 74 comprises an optical position sensor or an eddy current position sensor.

  Referring to FIGS. 1 and 2, the storage container 70 is provided with a breathing hole 73 communicating with the enclosed space A formed between the buffer tank 60 and the storage container 70. The breathing hole 73 is connected to the diluter 49 through a pipe 66. When the capacity of the buffer tank 60 increases, gas flows out from the surrounding space A through the breathing hole 73, and when the capacity of the buffer tank 60 decreases, gas flows into the surrounding space A through the breathing hole 73. In another embodiment, the breathing hole 73 is connected to the atmosphere.

  An air supply pipe 41 is connected to the inlet of the air passage 40, and the air supply pipe 41 is connected to the atmosphere 42 as an air source. In the air supply pipe 41, an air cleaner 43, an air supply unit or compressor 44 that pumps air, and an intercooler 45 that cools the air sent from the compressor 44 to the fuel cell stack 10 are sequentially provided from the upstream side. Be placed. On the other hand, a cathode offgas pipe 46 is connected to the outlet of the air passage 40. A cathode offgas control valve 47 is disposed in the cathode offgas pipe 46. The outlet of the cathode off-gas pipe 46 is connected to the inlet of the diluter 49, and the exhaust gas pipe 46 a is connected to the outlet of the diluter 49. Further, the inlet of the air bypass pipe 41 a is connected to the air supply pipe 41 downstream of the intercooler 45, and the outlet of the air bypass pipe 41 a is connected to the inlet of the diluter 49. An air bypass control valve 48 is disposed in the air bypass pipe 41a. When the compressor 44 is driven, air is supplied into the air passage 40 in the fuel cell stack 10 through the air supply pipe 41. At this time, the gas flowing out from the air passage 40, that is, the cathode off gas, flows into the cathode off gas pipe 46. The cathode offgas in the cathode offgas pipe 46 is then supplied to the diluter 49. When the air bypass control valve 48 is opened, part or all of the air discharged from the compressor 44 is supplied to the diluter 49 via the air bypass pipe 41a. In another embodiment, the outlet of the air bypass pipe 41 is connected to the cathode offgas pipe 46 upstream of the diluter 49 instead of the diluter 49.

  In the diluter 49, the hydrogen gas contained in the purge gas is diluted using the cathode offgas from the cathode offgas pipe 46 and the air from the air bypass pipe 41a as dilution gases. In another embodiment, the outlet of the purge gas discharge pipe 65 is connected to the cathode offgas pipe 46 or the air bypass pipe 41a.

  Further, referring to FIG. 1, one end of the cooling water supply pipe 51 is connected to the inlet of the cooling water passage 50, and the other end of the cooling water supply pipe 51 is connected to the outlet of the cooling water passage 50. A cooling water pump 52 that pumps the cooling water and a radiator 53 that cools the cooling water are disposed in the cooling water supply pipe 51. The cooling water supply pipe 51 between the radiator 53 and the cooling water pump 52 and the cooling water supply pipe 51 upstream of the radiator 53 are connected to each other by a radiator bypass passage 54. Further, a radiator bypass control valve 55 that controls the amount of cooling water flowing in the radiator bypass passage 54 is provided. In the fuel cell system 1 shown in FIG. 1, the radiator bypass control valve 55 is formed of a three-way valve and is disposed at the outlet of the radiator bypass passage 54. When the cooling water pump 52 is driven, the cooling water discharged from the cooling water pump 52 flows into the cooling water passage 50 in the fuel cell stack 10 through the cooling water supply pipe 51, and then passes through the cooling water passage 50. Then, it flows into the cooling water supply pipe 51 and returns to the cooling water pump 52 via the radiator 53 or the radiator bypass passage 54.

  The electronic control unit 90 is composed of a digital computer and includes a ROM (read only memory) 92, a RAM (random access memory) 93, a CPU (microprocessor) 94, an input port 95 and an output port 96 which are connected to each other by a bidirectional bus 91. It comprises. The fuel cell stack 10 is provided with an output sensor 99 that measures the output voltage or output current of the fuel cell stack 10. The output signal of the output sensor 99, the output signal of the pressure sensor PA, and the output signal of the capacitance sensor 74 are input to the input port 95 via the corresponding AD converter 97. On the other hand, the output port 96 is connected to the shut-off valve 33, the regulator 34, the purge gas introduction valve 61, the purge gas discharge valve 62, the compressor 44, the cathode offgas control valve 47, the air bypass control valve 48, and the cooling water pump 52 via the corresponding drive circuit 98. , And the radiator bypass control valve 55 are electrically connected.

  When hydrogen gas and air are supplied to the fuel cell stack 10, electric energy is generated in the fuel cell stack 10 by an electrochemical reaction of hydrogen and oxygen. This electric energy is supplied to, for example, an electric motor for driving the vehicle.

  As described at the beginning, the power generation inhibitor reaches the anode electrode of the fuel cell stack 10 from the cathode electrode. The amount of the power generation inhibiting substance in the hydrogen gas passage 30 and the cathode offgas pipe 36 of the fuel cell stack 10 increases as the operation time of the fuel cell system 1 becomes longer. Therefore, in the fuel cell system 1 shown in FIG. 1, the purge action for removing the power generation inhibiting substance from the hydrogen gas passage 30 and the cathode offgas pipe 36 of the fuel cell stack 10 is repeatedly performed. This will be described with reference to FIGS.

  FIG. 3 shows a state before the purge action is performed. In this case, the buffer tank 60 is in a contracted state, and almost no gas is stored in the buffer tank 60.

  When the purge action is to be performed, the purge gas introduction valve 61 is opened while the purge gas discharge valve 62 is closed. As a result, due to the difference between the pressure of the purge gas and the pressure inside the buffer tank 60, the purge gas, that is, the anode off gas containing a power generation inhibiting substance flows from the anode off gas pipe 36 to the buffer tank 60 through the purge gas introduction pipe 64. As a result, as shown in FIG. 4, the cylindrical member 71 elastically expands, and the purge gas is stored in the buffer tank 60. At this time, the cylindrical member 71 accumulates a restoring force for returning to the contracted state.

  Thereafter, the purge gas introduction valve 61 is closed and the purge gas discharge valve 62 is opened. As a result, as shown in FIG. 5, the tubular member 71 contracts due to the restoring force of the tubular member 71. Accordingly, the purge gas is discharged from the buffer tank 60 through the purge gas discharge pipe 65.

  Thereafter, the buffer tank 60 contracts to the state shown in FIG. At this time, the buffer tank 60 hardly stores the purge gas.

  Thereafter, the purge gas introduction valve 61 is opened while the purge gas discharge valve 62 is closed, so that the purge gas is reintroduced into the buffer tank 60. Thereafter, the purge gas introduction valve 61 is closed and the purge gas discharge valve 62 is opened, so that the purge gas buffer tank 60 is discharged. As described above, in the purge operation of the fuel cell system 1 shown in FIG. 1, the introduction of the purge gas into the buffer tank 60 and the discharge of the purge gas from the buffer tank 60 are alternately repeated.

  Thus, the purge gas is temporarily stored in the buffer tank 60, and the stored purge gas is discharged from the buffer tank 60 due to the elasticity of the buffer tank 60. That is, the purge action can be performed with a simple configuration. In addition, the amount of electric power required for the purge action can be reduced.

  The maximum possible capacity of the buffer tank 60 is preferably substantially the same as the amount of purge gas introduced by one purge gas introduction operation. If it does in this way, the size of buffer tank 60 can be made small and the space required for installing buffer tank 60 can be made small.

  In the fuel cell system 1 shown in FIG. 1, a purge action is performed when the fuel cell stack 1 is operated. In another embodiment, for example, when the output voltage or output current of the fuel cell stack 10 detected by the output sensor 99 is larger than the allowable lower limit, the purge action is not performed, and the output voltage or output current of the fuel cell stack 10 is not higher than the allowable lower limit. The purge action is performed when the value falls below.

  The purge action of the fuel cell system 1 shown in FIG. 1 will be further described with reference to FIG. Referring to FIG. 6, time t11 indicates when the purge action should be started. At this time, the buffer tank 60 is in a contracted state as shown in FIG. In this contracted state, the purge gas amount stored in the buffer tank 60 is almost zero.

  At time t11, the purge gas introduction valve 61 is opened while the purge gas discharge valve 62 is closed. As a result, the purge gas storage amount increases from almost zero.

  Next, when the introduction time Δt1 elapses and time t12 is reached, the purge gas introduction valve 61 is closed and the purge gas discharge valve 62 is opened. As a result, the purge gas is discharged from the buffer tank 60, and the purge gas storage amount gradually decreases from QP.

  Next, when the discharge time Δt2 elapses and time t21 is reached, the purge gas storage amount returns to almost zero. At this time, the purge gas introduction valve 61 is opened and the purge gas discharge valve 62 is closed. As a result, the purge gas is again introduced into the buffer tank 60. Next, at time t22, the purge gas introduction operation is ended and the purge gas discharge operation is started. At time t31, the purge gas discharge operation is ended and the purge gas introduction operation is started.

  Therefore, if the sum of the introduction time Δt1 and the discharge time Δt2 is referred to as an interval T, the purge action is repeated at the interval T. Alternatively, it can be considered that the operation of introducing the purge gas into the buffer tank 60 is repeated at an interval T, and the purge gas is discharged during a period when the introduction operation is not performed.

  The interval T is set as follows, for example. That is, the amount of power generation inhibiting substances in the hydrogen gas passage 30 and the anode off gas pipe 36 of the fuel cell stack 10 increases as the load or required power generation amount of the fuel cell system 1 increases, for example. Therefore, in the fuel cell system 1 shown in FIG. 1, the interval T is shortened as the load increases, as shown in FIG. The interval T is stored in advance in the ROM 92 in the form of a map shown in FIG. Note that the load of the fuel cell system 1 is represented by, for example, the amount of depression of the accelerator pedal.

  On the other hand, the introduction time Δt1 is set to a relatively short fixed time, for example. This is to reduce the amount of unused hydrogen gas discharged from the fuel cell system 10 in the form of purge gas as much as possible. On the other hand, the discharge time Δt2 is calculated by subtracting the introduction time Δt1 from the interval T (Δt2 = T−Δt1).

  In another embodiment, the interval T is set to a constant value. In yet another embodiment, the introduction time Δt1 is changed according to the load of the fuel cell system 1, for example.

  In the embodiment shown in FIG. 6, the purge gas discharge speed during the purge gas discharge operation, that is, the purge gas, so that the purge gas storage amount returns to almost zero when the discharge time Δt2 has elapsed since the purge gas discharge valve 62 was opened. The opening degree of the discharge valve 62 is set. That is, when the purge gas storage amount when the purge gas discharge valve 62 should be opened is QP, the purge gas discharge speed vp is expressed by (QP / Δt2). In this way, the hydrogen gas concentration discharged from the buffer tank 60 can be kept low.

  The purge gas discharged from the buffer tank 60 then flows into the diluter 49. As a result, the hydrogen gas contained in the purge gas is diluted by the cathode offgas from the cathode offgas pipe 46 and the air from the air bypass pipe 41a, that is, the dilution gas. In this case, in the fuel cell system 1 shown in FIG. 1, the required dilution gas amount is required to maintain the hydrogen gas concentration in the exhaust gas discharged from the exhaust gas pipe 46a, for example, lower than the explosion limit concentration. The amount of air from the compressor 44 and the air bypass control valve 48 are controlled so that the actual amount of dilution gas becomes the required amount of dilution gas. That is, when the cathode off gas amount from the cathode off gas pipe 46 is smaller than the required dilution gas amount, the air supply amount from the compressor 44 is increased and the air bypass control valve 48 is opened. On the other hand, when the amount of cathode offgas from the cathode offgas pipe 46 is larger than the required dilution gas amount, the air bypass control valve 48 is closed and the air increasing action of the compressor 44 is not performed. That is, the air supply amount from the compressor 44 is set to an air amount determined according to the required power generation amount of the fuel cell stack 10. As a result, the purge gas is safely released into the atmosphere.

  As described above, in the embodiment shown in FIGS. 1 and 2, the buffer tank 60 is accommodated in the accommodating container 70, and the breathing hole 73 is connected to the diluter 49. Therefore, even if purge gas containing hydrogen gas leaks from the buffer tank 60 for some reason, this purge gas first stays in the enclosed space A, and then is supplied to the diluter 49 and diluted. Therefore, the purge gas leaking from the buffer tank 60 is safely released into the atmosphere.

FIG. 8 shows a routine for executing the purge action described above. This routine is executed by interruption every predetermined time.
Referring to FIG. 8, in step 100, the load of the fuel cell system 1 is read. In the subsequent step 101, the interval T and the discharge time Δt2 are calculated. In the subsequent step 102, the purge gas introduction valve 61 is opened and the purge gas discharge valve 62 is closed over the introduction time Δt1. In the subsequent step 103, the purge gas storage amount is calculated by the capacity sensor 74, the opening degree of the purge gas discharge valve 62 is calculated, and the required dilution gas amount is calculated. In the subsequent step 105, the purge gas introduction valve 61 is closed and the purge gas discharge valve 62 is opened over the discharge time Δt2. Further, the compressor 44 and the air bypass control valve 48 are controlled so that the amount of dilution gas becomes the required amount of dilution gas.

  FIG. 9 shows another embodiment of the buffer tank 60. In this embodiment, an elastic body 75 such as a spring is inserted between the buffer tank 60 and the container 70 so that the buffer tank 60 can be elastically expanded and contracted. In this case, the cylindrical member 71 itself may not have elasticity.

  FIG. 10 shows still another embodiment of the buffer tank 60. In this embodiment, the buffer tank 60 is formed from an expandable / contractible bag 71a. In this embodiment, the position sensor 74 is composed of an optical position sensor, emits laser light with the sensor head 74b, and receives reflected light from the bag 71b.

  FIG. 11 shows another embodiment according to the present invention. Referring to FIG. 11, the storage container 70 and the diluter 49 are integrally formed. Alternatively, the container 70 and the diluter 49 are arranged so as to contact each other. Since the temperature of the cathode off gas is considerably high, the buffer tank 60 is easily heated by the cathode off gas.

  In the embodiment shown in FIG. 11, the cathode offgas inflow hole h <b> 1 is formed on one side of the storage container 70, and the cathode offgas outflow hole h <b> 2 is provided on the other side of the storage container 70. The cathode offgas inflow hole h1 and the cathode offgas outflow hole h2 communicate with the enclosed space A. The cathode off gas inflow hole h 1 is connected to the cathode off gas pipe 46 through the supply pipe 81. The cathode off-gas outflow hole h <b> 2 communicates with the interior space of the diluter 49. As a result, the cathode offgas in the cathode offgas pipe 46 flows into the enclosed space A through the supply pipe 81 and the cathode offgas inflow hole h1. This cathode off gas flows in the enclosed space A around the buffer tank 60 and then flows out into the diluter 49 through the cathode off gas outflow hole h2. As a result, the buffer tank 60 is easily heated by the cathode off gas.

  When cold, the water remaining in the buffer tank 60 may freeze. If the remaining water freezes, the buffer tank 60 may not be able to expand and contract well. Therefore, in the embodiment shown in FIG. 11, the buffer tank 60 is quickly heated by the cathode off gas, and the frozen water is quickly thawed. As a result, good expansion and contraction of the buffer tank 60 is ensured. In addition, vaporization of the residual moisture in the buffer tank 60 is promoted, and thus the residual moisture content in the buffer tank 60 is reduced.

  In another embodiment, the container 70 is formed integrally with the cathode offgas pipe 46 or the exhaust gas pipe 46a. In yet another embodiment, the cathode offgas outflow hole h2 is connected to the exhaust gas pipe 46a.

  In the embodiment described so far, the purge gas introduction pipe 64 is connected to the outlet of the cathode off gas pipe 36. In another embodiment, the outlet of the cathode offgas pipe 36 is connected to the hydrogen gas supply pipe 31 so that the cathode offgas is returned to the hydrogen gas supply pipe 31. In addition, a purge gas introduction pipe 64 is connected to the middle of the cathode off gas pipe 36.

DESCRIPTION OF SYMBOLS 1 Fuel cell system 10 Fuel cell stack 36 Anode offgas pipe 46 Cathode offgas pipe 49 Diluter 60 Buffer tank 61 Purge gas introduction valve 62 Purge gas discharge valve 64 Purge gas introduction pipe 65 Purge gas discharge pipe

Claims (4)

A fuel cell stack that generates electric power by an electrochemical reaction between a fuel gas and an oxidant gas;
An anode off-gas pipe connected to an outlet of a fuel gas passage formed in the fuel cell stack;
A cathode off-gas pipe connected to an outlet of an oxidant gas passage formed in the fuel cell stack;
A buffer tank for temporarily storing purge gas from the anode off-gas pipe;
A purge gas introduction pipe connecting the outlet or the middle of the anode off gas pipe to the inlet of the buffer tank;
A purge gas introduction valve disposed in the purge gas introduction pipe;
A diluter disposed in the cathode offgas pipe and reducing the fuel gas concentration in the exhaust gas by mixing the cathode offgas and the purge gas with each other;
A purge gas exhaust pipe connected to an outlet of the buffer tank and an inlet of the diluter or the cathode offgas pipe upstream of the diluter;
A purge gas discharge valve disposed in the purge gas discharge pipe;
With
The buffer tank is elastically extendable and contractible,
When the purge gas introduction valve is opened while the purge gas discharge valve is closed, purge gas flows into the buffer tank from the anode off-gas pipe through the purge gas introduction pipe. At this time, the buffer tank is elastically moved. When the purge gas introduction valve is closed and the purge gas discharge valve is opened, the buffer tank is elastically contracted to cause the purge gas in the buffer tank to pass through the purge gas discharge pipe. Discharged into the cathode offgas pipe in the diluter or upstream of the diluter,
Fuel cell system.   And a cathode offgas inflow hole and a cathode offgas outflow hole communicating with an enclosed space formed between the buffer tank and the container, the cathode offgas inflow being further provided. A hole is connected to the cathode offgas pipe so that the cathode offgas flows into the enclosed space through the cathode offgas inflow hole and then flows through the enclosed space and then through the cathode offgas outflow hole. The fuel cell system according to claim 1, wherein the fuel cell system flows out of the space.   The fuel cell system according to claim 2, wherein the cathode offgas inflow hole is connected to the cathode offgas pipe upstream of the diluter, and the cathode offgas outflow hole is connected to the diluter. The fuel cell system according to claim 2 , wherein the container and the diluter are integrally formed.

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