JP5417812B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system for generating power from a fuel cell.

2. Description of the Related Art Conventionally, a fuel cell system including a fuel cell that generates power by electrochemically reacting a reaction gas supplied to a reaction electrode is known in Patent Document 1 below. In such a fuel cell system, when the fuel cell is started below zero, the fuel cell and the circulating water in the gas circulation channel may not start due to freezing. It is necessary to discharge residual water in the road. Therefore, the fuel cell system described in Patent Document 1 is configured to introduce air into the anode electrode and discharge moisture remaining in the anode electrode.
JP 2005-116269 A

  However, even in the fuel cell system described in Patent Document 1 described above, the diameter of the discharge valve (purge valve) for discharging the reaction gas (hydrogen gas) is increased because the reaction gas needs to be limited. There is a problem that condensed water accumulates in the discharge valve.

  Therefore, the present invention has been proposed in view of the above-described situation, and an object thereof is to improve the amount of condensed water removed from the discharge valve when the fuel cell system is stopped.

  In the present invention, a fuel cell that is supplied with a reaction gas to generate power, a first circulation passage that returns the reaction gas discharged from the fuel cell to the fuel cell again, and the reaction gas in the first circulation passage is circulated. A circulation pump, a dewatering means connected to the first circulation flow path for discharging water contained in the reaction gas flowing through the first circulation flow path, and a discharge valve for discharging the reaction gas in the first circulation flow path In order to solve the above-mentioned problem, the discharge valve is connected to the upstream portion of the circulation pump in the first circulation channel. Two circulation channels are provided. In such a fuel cell system, the reaction gas is circulated through the first circulation channel and the second circulation channel.

  According to the fuel cell system of the present invention, since the reaction gas is circulated through the first circulation channel and the second circulation channel by driving the circulation pump, the generated water of the fuel cell is removed by the water removal means, At the same time, the reaction gas can be circulated through the second circulation channel to remove the condensed water of the discharge valve. Therefore, according to this fuel cell system, the amount of condensed water removed from the discharge valve can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
The fuel cell system shown as the first embodiment of the present invention is configured, for example, as shown in FIG. The fuel cell system includes a hydrogen system for supplying hydrogen to the fuel cell stack 1 and an air system for supplying air to the fuel cell stack 1. The operation of the hydrogen system and the air system is controlled by the control unit 2.

A fuel cell system is a fuel cell configured by stacking a plurality of fuel cell structures each having a pair of reaction electrodes (a fuel electrode and an oxidant electrode) through a solid polymer electrolyte membrane through a separator. A stack (fuel cell) 1 is provided. In the fuel cell stack 1, fuel gas (reactive gas) is supplied to the anode (fuel electrode) and oxidant gas (reactive gas) is supplied to the cathode (oxidant electrode), so that the fuel gas and the oxidizing gas are supplied. Electric power is generated by electrochemical reaction of the agent gas. In this embodiment, a case where hydrogen is used as the fuel gas and air is used as the oxidant gas will be described. In the fuel cell stack 1, hydrogen gas is supplied to the anode and air is supplied to the cathode, respectively, and power is generated by the electrochemical reaction of the electrodes shown in the following (1) and (2).
Anode (hydrogen electrode): H ₂ → 2H ⁺ + 2e ⁻ (1)
Cathode (oxygen electrode): 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O (2)

  The hydrogen system includes a hydrogen tank 3 that stores hydrogen gas, a hydrogen pressure regulating valve 4 that controls the supply of hydrogen gas to the fuel cell stack 1, and a fuel cell in a hydrogen supply channel L1 that supplies hydrogen gas to the fuel cell stack 1. A hydrogen gas pressure sensor 5 that detects the pressure of the hydrogen gas supplied to the stack 1 is provided.

  The hydrogen system includes a first hydrogen circulation passage L2 that recirculates hydrogen gas that has not been consumed in the fuel cell stack 1. The first hydrogen circulation passage L2 includes a gas-liquid separator 6 and a water discharge valve 7 (water removal means) for removing moisture contained in the hydrogen gas in the first hydrogen circulation passage L2, a first hydrogen circulation passage. A circulation pump 8 for circulating the hydrogen gas in L2 is provided.

  In the hydrogen system, an introduction flow path L4 and a second hydrogen circulation flow path L3 are provided branched from the first hydrogen circulation flow path L2, and an orifice 10 is provided in the second hydrogen circulation flow path L3. A hydrogen discharge flow path L5 is provided that branches from the second hydrogen circulation flow path L3 and the introduction flow path L4 and discharges the hydrogen gas discharged from the anode of the fuel cell stack 1 to the outside. A hydrogen discharge valve 9 that controls the discharge of hydrogen gas is provided in the hydrogen discharge flow path L5.

  The hydrogen tank 3 stores high-pressure hydrogen gas as fuel gas.

  The opening of the hydrogen pressure regulating valve 4 is controlled by a control signal from the control unit 2 to control the flow rate of the hydrogen gas supplied to the fuel cell stack 1, whereby the hydrogen gas at the inlet of the fuel cell stack 1 is controlled. The pressure is controlled.

  The hydrogen gas pressure sensor 5 detects the pressure of hydrogen gas at the anode inlet of the fuel cell stack 1 and outputs a detected value to the control unit 2.

  The circulation pump 8 has its rotation speed controlled by a control signal from the control unit 2, sucks the hydrogen gas discharged from the fuel cell stack 1 into the first hydrogen circulation passage L 2, and supplies it again to the fuel cell stack 1. ing. The circulating pump 8 may be an electric type described in the present embodiment or a known mechanical type described later.

  The gas-liquid separator 6 separates gaseous water contained in the hydrogen gas discharged from the fuel cell stack 1 into a liquid state. The moisture discharge valve 7 opens and closes in response to a control signal from the control unit 2 and discharges the liquid moisture separated by the gas-liquid separator 6 to the outside.

  The orifice 10 adjusts the flow rate in the second hydrogen circulation passage L3. Accordingly, the flow rate of hydrogen gas flowing from the first hydrogen circulation passage L2 into the introduction passage L4 and the second hydrogen circulation passage L3 is determined by the diameter of the orifice 10. Note that the ratio of the flow rates of the first hydrogen circulation passage L2 and the second hydrogen circulation passage L3 is approximately 50: 1, although it varies depending on the operating conditions.

  The hydrogen discharge flow path L5 discharges hydrogen gas to the outside through the hydrogen discharge valve 9. The opening and closing operation of the hydrogen discharge valve 9 is controlled in accordance with a control signal from the control unit 2 to purge hydrogen gas.

  The air system includes a compressor 11 that pressurizes air, which is an oxidant gas, on the air supply flow path L6 and supplies the air to the cathode of the fuel cell stack 1, and air that detects the pressure of the air supplied to the fuel cell stack 1. A pressure sensor 12 and an air pressure regulating valve 13 for adjusting the pressure of air in the fuel cell stack 1 are provided.

  The rotation speed of the compressor 11 is controlled by a control signal from the control unit 2, and air, which is an oxidant gas, is sucked from the outside, compressed, and supplied to the fuel cell stack 1. At this time, the flow rate of the supplied air is controlled, thereby controlling the pressure of the air at the inlet of the fuel cell stack 1.

  The air pressure sensor 12 detects the pressure of air at the cathode inlet of the fuel cell stack 1 and outputs a detection value to the control unit 2.

  The air pressure regulating valve 13 has its opening degree controlled by a control signal from the control unit 2 and controls the flow rate of air supplied to the fuel cell stack 1, thereby controlling the air pressure in the fuel cell stack 1. ing.

  The control unit 2 reads the signal from each sensor in the fuel cell system and sends a control signal to each component in accordance with the control logic stored in advance to control this system. In particular, based on the detection values of the hydrogen gas pressure sensor 5 and the air pressure sensor 12, the opening degree of the hydrogen pressure regulating valve 4, the hydrogen discharge valve 9, and the air pressure regulating valve 13 is controlled, and the rotation speed of the circulation pump 8 and the compressor 11 is controlled. It controls the power generation by the fuel cell system and the operation of removing moisture described later.

  In the fuel cell system configured as described above, an operation command such as a power generation start command, a power generation end command, and a target power generation amount supplied to the control unit 2 from the fuel cell stack 1 is supplied from the outside. During normal operation, the control unit 2 refers to the hydrogen gas pressure detected by the hydrogen gas pressure sensor 5 and the air pressure detected by the air pressure sensor 12 in accordance with the target power generation amount included in this operation command. A control signal is output to each part of the fuel cell system.

  Hydrogen gas is supplied to the fuel cell stack 1 from the hydrogen tank 3 through the hydrogen pressure regulating valve 4 during normal operation. The hydrogen gas discharged from the fuel cell stack 1 is supplied to the circulation pump 8, mixed with the hydrogen gas supplied to the fuel cell stack 1 from the hydrogen supply flow path L 1, and circulated to the anode of the fuel cell stack 1. During this normal operation, the circulation pump 8 is driven to circulate hydrogen gas through the first hydrogen circulation passage L2 and also through the introduction passage L4 and the second hydrogen circulation passage L3. Here, the hydrogen circulation amount of the introduction flow path L4 and the second hydrogen circulation flow path L3 is significantly smaller than that of the first hydrogen circulation flow path L2 due to the pressure loss due to the small diameter of the orifice 10. Further, hydrogen gas does not flow to the hydrogen discharge valve 9 of the hydrogen discharge flow path L5 branched from the introduction flow path L4 and the second hydrogen circulation flow path L3.

  On the other hand, air is taken in from the outside by the compressor 11 during normal operation, pressurized, and supplied to the cathode of the fuel cell stack 1. In the fuel cell stack 1, the supplied hydrogen gas and air are reacted to generate power.

  During this normal operation, the condensed water generated by the power generation reaction at the anode of the fuel cell stack 1 is discharged while being contained in hydrogen gas. The moisture is made liquid by the gas-liquid separator 6 and is discharged to the outside by opening the moisture discharge valve 7 by the control unit 2.

  When impurities such as nitrogen accumulate in the anode of the fuel cell stack 1 during normal operation, the hydrogen discharge valve 9 is opened to discharge nitrogen as an impurity from the hydrogen discharge flow path L5. Further, the hydrogen discharge valve 9 is opened in order to blow off the clogged water even when the cell voltage is lowered due to the clogging of the fuel cell stack 1. Further, when the fuel cell stack 1 is started, the hydrogen discharge valve 9 is opened to discharge the gas in the hydrogen supply system in order to replace the hydrogen supply system with hydrogen gas.

  Further, when the fuel cell system is stopped, the following processing is performed.

  The operation at the time of stopping will be described based on the flowchart of FIG. As shown in FIG. 3, first, when a signal for stopping the operation of the fuel cell stack 1 is input to the control unit 2 (S1), the control unit 2 closes the hydrogen pressure regulating valve 4 and supplies the fuel cell stack 1 to the fuel cell stack 1. The supply of hydrogen gas is stopped (S2). On the other hand, the circulation pump 8 is driven so that power generation in the fuel cell stack 1 is continuously performed for a predetermined time, and the hydrogen gas remaining in the fuel cell stack 1 and the first hydrogen circulation passage L2 is consumed (S3). ), The first hydrogen circulation passage L2 is set to a negative pressure.

  Thereafter, the control unit 2 monitors whether or not a predetermined time has elapsed (S4). When the predetermined time has elapsed, the hydrogen discharge valve 9 is opened (S5), and then the hydrogen discharge valve 9 is closed (S6). The stop process by the fuel cell system is terminated.

  Here, when the flow rate (orifice diameter) of the hydrogen discharge valve 9 is small and there is almost no flow velocity, the water vapor contained in the hydrogen gas is condensed in the introduction flow path L4 due to the temperature drop during operation of the fuel cell stack 1. It becomes water and accumulates. When the amount of the condensed water increases, the introduction flow path L4 is closed, and the fuel cell stack 1 cannot be operated when the temperature at the next startup of the fuel cell system is below zero.

  On the other hand, in the fuel cell system, when the second hydrogen circulation passage L3 is added and the circulation pump 8 is operated, hydrogen gas passes from the introduction passage L4 through the second hydrogen circulation passage L3 to the upstream of the circulation pump 8. To discharge. For this reason, even when the flow rate (orifice diameter) of the hydrogen discharge valve 9 is small and there is almost no flow velocity, the condensed water is blown off and the condensed water does not accumulate in the introduction flow path L4. Accordingly, the introduction flow path L4 and the hydrogen discharge valve 9 do not freeze even when starting below zero. Note that the ratio of the flow rates of the first hydrogen circulation passage L2 and the second hydrogen circulation passage L3 is approximately 50: 1, although it varies depending on the operating conditions.

  Further, the fuel cell system opens the hydrogen discharge valve 9 in step S5 when the fuel cell system is stopped, and operates the circulation pump 8 for a predetermined time or longer to remove moisture in the introduction flow path L4. When the circulation pump 8 is operated when the fuel cell system is stopped, the condensed water accumulated in the circulation pump 8, the fuel cell stack 1, and the first hydrogen circulation flow path L <b> 2 during a certain time during which the circulation pump 8 is operated. The gas is gradually discharged from the hydrogen discharge passage L5 through the hydrogen discharge valve 9. For example, as shown in FIG. 3, in the fuel cell system, the longer the opening time (stop purge time) of the hydrogen discharge valve 9 at the time of stop, the less the degree of water clogging in the introduction flow path L4 and the like, and the approximate time T1 is reached. It becomes a constant value. Therefore, the fuel cell system gas-liquid-separates the generated water of the fuel cell stack 1 by driving the circulation pump 8 with the hydrogen discharge valve 9 opened and circulating the hydrogen gas in the first hydrogen circulation passage L2. Remove with vessel 6. At the same time, the condensed water adhering to the introduction flow path L4 and the hydrogen discharge valve 9 can be removed by circulating the hydrogen gas through the second hydrogen circulation flow path L3.

  Further, the fuel cell system drives the circulation pump 8 and opens the hydrogen discharge valve 9 when the fuel cell system is stopped. When the hydrogen discharge valve 9 is opened when the fuel cell stack 1 is stopped, the amount of hydrogen gas flowing through the introduction flow path L4 increases, so that the condensed water adhering to the introduction flow path L4 is further blown away. Thereby, the state where condensed water accumulates in the introduction flow path L4 and the hydrogen discharge valve 9 is eliminated. For example, as shown in FIG. 4, the larger the diameter of the orifice 10 in the second hydrogen circulation passage L3, the larger the flow rate flowing through the second hydrogen circulation passage L3, but when the hydrogen discharge valve 9 is closed. Compared with the flow rate, the flow rate becomes higher when the hydrogen discharge valve 9 is opened. Here, assuming that the flow rate at which the condensed water in the introduction flow path L4 and the hydrogen discharge valve 9 can be removed is TH, the flow rate can be increased to TH or more by opening the hydrogen discharge valve 9.

  Furthermore, the fuel cell system repeatedly operates the hydrogen discharge valve 9 between the open state and the closed state in step S5 when the fuel cell system is stopped. When the opening and closing operation is repeated, pulsation occurs in the hydrogen gas flowing through the introduction flow path L4, and the condensed water adhering to the introduction flow path L4 and the hydrogen discharge valve 9 is blown off more effectively.

  As described above, according to the fuel cell system shown as the first embodiment, the second hydrogen circulation flow connected to the hydrogen discharge channel L5 and the upstream portion of the circulation pump 8 in the first hydrogen circulation channel L2. By providing the path L3 and driving the circulation pump 8, the hydrogen gas is circulated in the first hydrogen circulation flow path L2. Thereby, the water generated in the fuel cell stack 1 is removed by the gas-liquid separator 6. At the same time, the condensed water adhering to the introduction flow path L4 and the hydrogen discharge valve 9 can be removed by circulating the hydrogen gas through the second hydrogen circulation flow path L3. Therefore, according to this fuel cell system, the condensed water in the hydrogen discharge valve 9 can be surely removed when the fuel cell system is stopped, and the introduction flow path L4 and the hydrogen discharge valve 9 are closed even when starting below zero. The fuel cell system can be started without any problems.

  In addition, according to this fuel cell system, since the orifice 10 for adjusting the flow rate of the hydrogen gas in the second hydrogen circulation passage L3 is provided, most of the hydrogen gas is passed through the first hydrogen circulation passage L2 during normal operation. The condensed water in the introduction flow path L4 and the hydrogen discharge valve 9 can be removed when stopped.

  Furthermore, according to this fuel cell system, when the fuel cell system is stopped, the circulation pump 8 is operated for at least a predetermined time, so that the generated water is removed from the first hydrogen circulation passage L2 and the second hydrogen circulation passage. The condensed water in L3 can be removed over a certain period of time, and the condensed water in the introduction flow path L4 and the hydrogen discharge valve 9 can be reliably removed.

  Furthermore, according to this fuel cell system, since the hydrogen discharge valve 9 is opened during the purge operation when the fuel cell system is stopped, the condensate of the introduction flow path L4 and the fuel cell system is discharged to the outside. The condensed water of the introduction flow path L4 and the hydrogen discharge valve 9 can be removed.

  Furthermore, according to this fuel cell system, since the hydrogen discharge valve 9 is operated repeatedly between the open state and the closed state during the purge operation when the fuel cell system is stopped, the first hydrogen circulation passage L2, the introduction flow The pulsation is given to the hydrogen gas flowing through the passage L4 and the second hydrogen circulation passage L3, so that the condensed water can be removed more efficiently.

[Second Embodiment]
Next, a fuel cell system shown as a second embodiment of the present invention will be described. Note that the same portions as those in the above-described embodiment are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 5, the fuel cell system shown as the second embodiment includes a mechanical circulation pump 21 instead of the circulation pump 8 in the first embodiment. Further, in the fuel cell system shown as the second embodiment, the introduction flow path L4 branches from the gas discharge side of the mechanical circulation pump 21, and the second hydrogen circulation flow path L3 branches from the introduction flow path L4. The second hydrogen circulation passage L3 is connected to the gas inflow side of the mechanical circulation pump 21. The hydrogen discharge channel L5 is connected to a branch between the second hydrogen circulation channel L3 and the introduction channel L4.

  Even in such a fuel cell system, the hydrogen gas is circulated in the first hydrogen circulation passage L2 and the second hydrogen circulation passage L3 to remove the condensed water in the introduction passage L4 and the hydrogen discharge valve 9. The same operation and effect as the fuel cell system shown as a 1st embodiment mentioned above can be exhibited.

[Third Embodiment]
Next, a fuel cell system shown as a third embodiment of the present invention will be described. Note that the same portions as those in the above-described embodiment are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 6, the fuel cell system shown as the third embodiment is different from the fuel cell system shown as the first embodiment in that a filter 31 is added to the introduction flow path L4. This filter 31 is provided upstream of the orifice 10 in the second hydrogen circulation flow path L3 by being provided in the introduction flow path L4. Moreover, as shown in FIG. 7, the filter 31 may be provided in the introduction flow path L4 in the fuel cell system including the mechanical circulation pump 21 as in the second embodiment.

  The filter 31 gives pressure loss to the hydrogen gas flowing through the introduction flow path L4. The diameter of the filter 31 is smaller than the diameter of the hydrogen discharge valve 9.

  In such a fuel cell system, even if the flow rate flowing through the hydrogen discharge valve 9 is lowered by the filter 31, the circulation pump 8 is operated and the hydrogen gas reacted in the fuel cell stack 1 is made to react with the second hydrogen circulation passage L3. Shed. Thereby, the fuel cell system can blow off the condensed water in the 2nd hydrogen circulation flow path L3, and can remove the condensed water in the filter 31 which exists in the introduction flow path L4. Therefore, according to this fuel cell system, the condensed water in the introduction flow path L4 and the hydrogen discharge valve 9 can be removed.

  Further, by making the diameter of the filter 31 smaller than the diameter of the hydrogen discharge valve 9, the flow rate of the hydrogen gas flowing through the filter 31 and the introduction flow path L4 when the hydrogen discharge valve 9 is opened when the fuel cell system is stopped. And the condensed water in the introduction flow path L4 and the hydrogen discharge valve 9 can be efficiently removed.

[Fourth Embodiment]
Next, a fuel cell system shown as a fourth embodiment of the present invention will be described. Note that the same portions as those in the above-described embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the fuel cell system shown as the fourth embodiment, as shown in FIG. 8, a circulation cutoff valve 41 is provided downstream of the orifice 10 in the second hydrogen circulation passage L3. In this fuel cell system, under the control of the control unit 2, the circulation cutoff valve 41 is opened or closed when the fuel cell system is in operation, and the circulation cutoff valve 41 is opened when the fuel cell system is stopped.

  Such a fuel cell system closes the circulation shut-off valve 41 when it is not necessary to remove the condensed water in the introduction flow path L4 during normal operation of the fuel cell system. As a result, during normal operation, the hydrogen gas flowing through the second hydrogen circulation passage L3 can be eliminated, and the drive amount of the circulation pump 8 corresponding to the flow rate flowing through the second hydrogen circulation passage L3 can be reduced. it can.

  On the other hand, when removing the condensed water in the introduction flow path L4, the fuel cell system opens the circulation cutoff valve 41 in accordance with the control of the control unit 2. Then, the hydrogen gas circulated through the first hydrogen circulation passage L2 flows into the second hydrogen circulation passage L3, and the condensed water in the introduction passage L4 can be blown off. In addition, when the fuel cell system is stopped, by opening the circulation cutoff valve 41, the condensed water in the introduction flow path L4 and the hydrogen discharge valve 9 can be removed when the fuel cell system is stopped.

  According to such a fuel cell system, when it is desired to discharge residual water during operation of the fuel cell stack 1, the same effect as that of the first to third embodiments described above can be obtained with the circulation cutoff valve 41 opened. be able to. That is, by circulating the hydrogen gas through the second hydrogen circulation passage L3, the condensed water in the introduction passage L4 and the hydrogen discharge valve 9 can be removed, and freezing at the time of starting below zero can be avoided.

  The above-described embodiment is an example of the present invention. For this reason, the present invention is not limited to the above-described embodiment, and various modifications can be made depending on the design and the like as long as the technical idea according to the present invention is not deviated from this embodiment. Of course, it is possible to change.

1 is a block diagram showing a configuration of a fuel cell system shown as a first embodiment of the present invention. It is a flowchart which shows the operation | movement procedure at the time of the stop of the fuel cell system shown as 1st Embodiment of this invention. It is a figure which shows the degree of water clogging with respect to the stop purge time in the fuel cell system shown as 1st Embodiment of this invention. It is a figure which shows the relationship between the orifice diameter and flow volume in the 2nd hydrogen circulation flow path in the fuel cell system shown as 1st Embodiment of this invention. It is a block diagram which shows the structure of the fuel cell system shown as 2nd Embodiment of this invention. It is a block diagram which shows the structure of the fuel cell system shown as 3rd Embodiment of this invention. It is a block diagram which shows the other structure of the fuel cell system shown as 3rd Embodiment of this invention. It is a block diagram which shows the structure of the fuel cell system shown as 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Control unit 3 Hydrogen tank 4 Hydrogen pressure control valve 5 Hydrogen gas pressure sensor 6 Gas-liquid separator 7 Water discharge valve 8 Circulation pump 9 Hydrogen discharge valve 10 Orifice 11 Compressor 12 Air pressure sensor 13 Air pressure control valve 21 Mechanical type Circulation pump 31 Filter 41 Circulation shutoff valve L1 Hydrogen supply flow path L2 First hydrogen circulation flow path L3 Second hydrogen circulation flow path L4 Introduction flow path L5 Hydrogen discharge flow path L6 Air supply flow path

Claims (8)

A fuel cell that is supplied with a reaction gas to generate electricity;
A first circulation passage for returning the reaction gas discharged from the fuel cell to the fuel cell again;
A circulation pump for circulating the reaction gas in the first circulation channel;
A dewatering means connected to the first circulation channel and for discharging moisture contained in the reaction gas flowing through the first circulation channel;
A discharge valve for discharging the reaction gas in the first circulation channel;
An introduction flow path connected to a downstream portion of the circulation pump in the first circulation flow path;
A discharge flow path connecting the discharge valve and the introduction flow path ;
A second circulation passage connected to the discharge passage and an upstream portion of the circulation pump in the first circulation passage;
A fuel cell system comprising:
  2. The fuel cell system according to claim 1, wherein the second circulation channel is provided with an orifice for adjusting a flow rate of the reaction gas in the second circulation channel.   The fuel cell system according to claim 2, wherein a filter is provided upstream of the orifice.   The fuel cell system according to claim 3, wherein a diameter of the filter is smaller than a diameter of the discharge valve. A circulation cutoff valve provided in the second circulation channel;
During operation of the fuel cell system, the circulation shut-off valve is opened or closed,
The fuel cell system according to any one of claims 1 to 4, wherein when the fuel cell system is stopped, the circulation cutoff valve is opened.   5. The fuel cell system according to claim 1, wherein when the fuel cell system is stopped, the circulation pump is operated for at least a predetermined time.   The fuel cell system according to any one of claims 1 to 6, wherein the discharge valve is opened during a purge operation when the fuel cell system is stopped.   The fuel cell system according to any one of claims 1 to 6, wherein the discharge valve is repeatedly opened and closed during a purge operation when the fuel cell system is stopped.

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