WO2012091127A1

WO2012091127A1 - Fuel cell system

Info

Publication number: WO2012091127A1
Application number: PCT/JP2011/080484
Authority: WO
Inventors: 洋平水野; 修平咲間
Original assignee: Ｊｘ日鉱日石エネルギー株式会社
Priority date: 2010-12-28
Filing date: 2011-12-28
Publication date: 2012-07-05
Also published as: JP5728497B2; JPWO2012091127A1

Abstract

The purpose is to prevent the backward flow of exhaust gas with a cathode air power increase process, in the case that a current direction detection unit (23) detects that exhaust gas flowing toward an exhaust opening (26) is flowing backward in an exhaust system for discharging combustion gas of off gas emitted from a power generation unit (21) in this fuel cell system (1). Hence, with this fuel cell system (1) it is possible to prevent life-shortening, caused by the backward flow of exhaust gas to the power generation unit (21) side, for a fuel cell stack (5), various catalysts, absorbing agents, ion-exchange resins, various auxiliaries, or the like.

Description

Fuel cell system

The present invention relates to a fuel cell system.

As a technology in this type of field, for example, there is a fuel cell system described in Patent Document 1. This conventional fuel cell system includes an exhaust port for exhausting the exhaust gas after heat exchange with the heat exchanger to the outside of the case. A separate member for collecting impurities is provided in front of the exhaust port to prevent impurities from entering the heat exchanger side from the exhaust port.

JP 2009-181701 A

As an example of the installation mode of the fuel cell system, there is a case where the fuel cell system is installed indoors and the exhaust port is connected to the chimney. When the chimney is shared with other devices, the external exhaust gas that fills the chimney may contain components that are undesirable for the fuel cell system and dust in the chimney stack. At this time, if exhaust pressure rises from other devices or the chimney itself becomes blocked, the external exhaust gas in the chimney may flow into the fuel cell system.

In the conventional fuel cell system as described above, a single exhaust port is provided for the heat exchanger. However, it is difficult to sufficiently suppress exhaust gas (external exhaust gas) from other devices from flowing into the fuel cell system. When a component undesirable for the fuel cell system or external exhaust gas containing dust flows into the fuel cell system, the cell stack, various catalysts or adsorbents, ion exchange resins, various supplements, which are components of the fuel cell system. There is a risk that the machinery and the like will have a short life. Therefore, a technique for suppressing the inflow of external exhaust gas to the fuel cell system side is required.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a fuel cell system capable of suppressing the inflow of external exhaust gas to the fuel cell system side.

In order to solve the above problems, a fuel cell system according to one aspect of the present invention includes a power generation unit including a cell stack that generates power using a hydrogen-containing gas, a cathode blower that supplies cathode air to the cathode of the cell stack, A flow direction that is disposed in an exhaust port that discharges at least exhaust gas discharged from the power generation unit to the outside of the system, and an exhaust path between the power generation unit and the exhaust port, and detects the flow direction of the circulating gas in the exhaust path A detection unit, and a control unit that executes a first output increase process for increasing the supply output of the cathode air by the cathode blower compared to that during normal operation when the backflow of the flowing gas is detected by the flow direction detection unit. Prepare.

In this fuel cell system, in the exhaust path for exhausting the exhaust gas discharged from the power generation unit, when the backflow of the flowing gas flowing in the exhaust path is detected by the flow direction detection unit, external exhaust gas flows in, or Therefore, it is determined that there is a risk of inflow, and suppression of inflow of external exhaust gas is executed by the first output increase process of the cathode air. Therefore, in this fuel cell system, it is possible to suppress the shortening of the service life of the cell stack, various catalysts or adsorbents, various auxiliary machines and the like due to the flow of external exhaust gas to the fuel cell system side.

This fuel cell system can suppress the flow of external exhaust gas to the fuel cell system side.

1 is a diagram showing an embodiment of a fuel cell system according to the present invention. It is a figure which shows an example of the exhaust route of the fuel cell system shown in FIG. It is a figure which shows the other example of the exhaust route of the fuel cell system shown in FIG. It is a figure which shows an example of a flow direction detection part. It is a figure which shows the other example of a flow direction detection part. It is a flowchart which shows the operation | movement which concerns on the 1st form of a control part. It is a flowchart which shows the operation | movement which concerns on the 2nd form of a control part. It is a flowchart which shows the operation | movement which concerns on the 3rd form of a control part.

Hereinafter, preferred embodiments of a fuel cell system according to the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same or an equivalent part, and the overlapping description is abbreviate | omitted.

As shown in FIG. 1, the fuel cell system 1 includes a desulfurization unit 2, a water vaporization unit 3, a hydrogen generation unit 4, a cell stack 5, an off-gas combustion unit 6, a hydrogen-containing fuel supply unit 7, The water supply part 8, the oxidizing agent supply part 9, the power conditioner 10, the control part 11, and the heat exchange part 15 are provided. The fuel cell system 1 generates power in the cell stack 5 using a hydrogen-containing fuel and an oxidant. The type of the cell stack 5 in the fuel cell system 1 is not particularly limited, and examples thereof include a polymer electrolyte fuel cell (PEFC), a solid oxide fuel cell (SOFC), and phosphoric acid. A fuel cell (PAFC: Phosphoric Acid Fuel Cell), a molten carbonate fuel cell (MCFC: Molten Carbonate Fuel Cell), and other types can be employed. 1 may be appropriately omitted depending on the type of cell stack 5, the type of hydrogen-containing fuel, the reforming method, and the like.

As the hydrogen-containing fuel, for example, a hydrocarbon fuel is used. As the hydrocarbon fuel, a compound containing carbon and hydrogen in the molecule (may contain other elements such as oxygen) or a mixture thereof is used. Examples of hydrocarbon fuels include hydrocarbons, alcohols, ethers, and biofuels. These hydrocarbon fuels are derived from conventional fossil fuels such as petroleum and coal, and synthetic systems such as synthesis gas. Those derived from fuel and those derived from biomass can be used as appropriate. Specific examples of hydrocarbons include methane, ethane, propane, butane, natural gas, LPG (liquefied petroleum gas), city gas, town gas, gasoline, naphtha, kerosene, and light oil. Examples of alcohols include methanol and ethanol. Examples of ethers include dimethyl ether. Examples of biofuels include biogas, bioethanol, biodiesel, and biojet.

As the oxidizing agent, for example, air, pure oxygen gas (which may contain impurities that are difficult to remove by a normal removal method), or oxygen-enriched air is used.

The desulfurization unit 2 desulfurizes the hydrogen-containing fuel supplied to the hydrogen generation unit 4. The desulfurization part 2 has a desulfurization catalyst for removing sulfur compounds contained in the hydrogen-containing fuel. As the desulfurization method of the desulfurization unit 2, for example, an adsorptive desulfurization method that adsorbs and removes sulfur compounds and a hydrodesulfurization method that removes sulfur compounds by reacting with hydrogen are employed. The desulfurization unit 2 supplies the desulfurized hydrogen-containing fuel to the hydrogen generation unit 4.

The water vaporization unit 3 generates water vapor supplied to the hydrogen generation unit 4 by heating and vaporizing water. For the heating of the water in the water vaporization unit 3, for example, heat generated in the fuel cell system 1 such as recovering the heat of the hydrogen generation unit 4, the heat of the off-gas combustion unit 6, or the heat of the exhaust gas may be used. Moreover, you may heat water using other heat sources, such as a heater and a burner separately. In FIG. 1, only heat supplied from the off-gas combustion unit 6 to the hydrogen generation unit 4 is described as an example, but the present invention is not limited to this. The water vaporization unit 3 supplies the generated water vapor to the hydrogen generation unit 4.

The hydrogen generation unit 4 generates a hydrogen rich gas using the hydrogen-containing fuel from the desulfurization unit 2. The hydrogen generator 4 has a reformer that reforms the hydrogen-containing fuel with a reforming catalyst. The reforming method in the hydrogen generating unit 4 is not particularly limited, and for example, steam reforming, partial oxidation reforming, autothermal reforming, and other reforming methods can be employed. The hydrogen generator 4 may have a configuration for adjusting the properties in addition to the reformer reformed by the reforming catalyst depending on the properties of the hydrogen rich gas required for the cell stack 5. For example, when the type of the cell stack 5 is a polymer electrolyte fuel cell (PEFC) or a phosphoric acid fuel cell (PAFC), the hydrogen generation unit 4 is configured to remove carbon monoxide in the hydrogen-rich gas. (For example, a shift reaction part and a selective oxidation reaction part). The hydrogen generation unit 4 supplies a hydrogen rich gas to the anode 12 of the cell stack 5.

The cell stack 5 generates power using the hydrogen rich gas from the hydrogen generation unit 4 and the oxidant from the oxidant supply unit 9. The cell stack 5 includes an anode 12 to which a hydrogen-rich gas is supplied, a cathode 13 to which an oxidant is supplied, and an electrolyte 14 disposed between the anode 12 and the cathode 13. The cell stack 5 supplies power to the outside via the power conditioner 10. The cell stack 5 supplies the hydrogen rich gas and the oxidant, which have not been used for power generation, to the off gas combustion unit 6 as off gas. Note that a combustion section (for example, a combustor that heats the reformer) provided in the hydrogen generation section 4 may be shared with the off-gas combustion section 6.

The off gas combustion unit 6 burns off gas supplied from the cell stack 5. The heat generated by the off-gas combustion unit 6 is supplied to the hydrogen generation unit 4 and used for generation of a hydrogen rich gas in the hydrogen generation unit 4.

The hydrogen-containing fuel supply unit 7 supplies hydrogen-containing fuel to the desulfurization unit 2. The water supply unit 8 supplies water to the water vaporization unit 3. The oxidant supply unit 9 supplies an oxidant to the cathode 13 of the cell stack 5. The hydrogen-containing fuel supply unit 7, the water supply unit 8, and the oxidant supply unit 9 are configured by a pump, for example, and are driven based on a control signal from the control unit 11.

For example, when using a hydrogen-containing fuel that does not require a reforming process, such as pure hydrogen gas or hydrogen-enriched gas, one of the desulfurizer 2, the water supply unit 8, the water vaporization unit 3, and the hydrogen generation unit 4. One or more can be omitted.

The power conditioner 10 adjusts the power from the cell stack 5 according to the external power usage state. For example, the power conditioner 10 performs a process of converting a voltage and a process of converting DC power into AC power.

The control unit 11 performs control processing for the entire fuel cell system 1. The control unit 11 is configured by a device including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an input / output interface, for example. The control unit 11 is electrically connected to a hydrogen-containing fuel supply unit 7, a water supply unit 8, an oxidant supply unit 9, a power conditioner 10, and other sensors and auxiliary equipment not shown. The control unit 11 acquires various signals generated in the fuel cell system 1 and outputs a control signal to each device in the fuel cell system 1.

The heat exchange unit 15 moves the heat from the combustion gas to the water by circulating the off-gas combustion gas discharged from the cell stack 5 (that is, the exhaust gas from the off-gas combustion unit 6) and water (heat medium). Heat the water. This water is stored, for example, in a hot water storage tank for supplying hot water to a facility where the fuel cell system 1 is installed, and is circulated and supplied from the hot water storage tank to the heat exchanging unit 15.

Subsequently, the exhaust path of the fuel cell system 1 will be described. FIG. 2 is a diagram illustrating an example of an exhaust path of the fuel cell system 1.

As shown in FIG. 2, the exhaust path of the fuel cell system 1 includes a power generation unit 21, the heat exchange unit 15 described above, a damper 22, a flow direction detection unit 23, and a control unit 24. Housed in the housing 25. The casing 25 is provided with a circulation gas passage 27 and an exhaust port 26 through which exhaust gas (FC exhaust gas) discharged from at least the power generation unit 21 side flows. Although not shown in detail, the exhaust path is airtight with respect to outside air. Here, the airtightness means airtightness with respect to outside air other than the gas scheduled to be discharged from the housing 25. Specifically, it means a structure in which gas is discharged from the housing 25 only from a dedicated gas discharge path.

As the heat recovery water system, for example, a water flow path through which water circulated and supplied from the hot water storage tank flows into the heat exchange section 15 and a water flow path through which the water flows out from the heat exchange section 15 are respectively connected to the heat exchange section 15 as pumps. Connected through. From the heat exchange unit 15, the exhaust gas after heat exchange is discharged toward the exhaust port 26 of the housing 25.

The flow direction detection unit 23 is a part that detects the flow direction of the flow gas flowing in the flow gas channel 27. For example, as shown in FIG. 4, the flow direction detection unit 23 is configured by a fan 28 provided in a circulation gas flow path 27 toward the exhaust port 26. Since the rotation direction of the fan 28 changes depending on the flow direction of the flow gas flowing in the flow gas flow path 27, the flow direction of the flow gas can be determined from the rotation direction of the fan 28. Then, the fan 28 outputs a signal indicating the rotation direction to the control unit 24.

Note that the flow direction detection unit 23 may be a flap 29 provided in a circulation gas flow path 27 toward the exhaust port 26, for example, as shown in FIG. The flap 29 is inclined toward the exhaust port 26 when the circulating gas is flowing toward the exhaust port 26, and is inclined toward the opposite side of the exhaust port 26 when the circulating gas is flowing backward. The inclination of the flap 29 may be determined by, for example, ON / OFF of a switch provided at the base of the flap 29, or laser detection or the like may be used. Alternatively, image detection by a camera or the like may be performed, and detection by a strain gauge may be performed in a state where the base of the flap 29 is fixed.

The control unit 24 is a part that performs diagnosis processing of the flow direction of the circulating gas in the discharge path. In FIG. 2, the control unit 24 is disposed in the housing 25, but may be configured such that the function of the control unit 24 is added to the control unit 11 of the fuel cell system 1. The diagnosis process by the control unit 24 is repeatedly performed at predetermined intervals, for example, during operation of the fuel cell system 1.

FIG. 6 is a flowchart showing a first mode of operation of the control unit 24. In the example of the figure, when the diagnostic process is started, a signal indicating the flow direction of the flowing gas is output from the flow direction detection unit 23 to the control unit 24. The control unit 24 that has received the signal determines whether or not a backflow of the flowing gas has been detected (step S101), and if the backflow of the flowing gas is not detected, step S101 is repeatedly executed. On the other hand, if a backflow of the flowing gas is detected in step S101, a first output increase process is executed (step S102). In the first output increase process, the cathode air supply output by the cathode blower 20 is increased from that during normal operation within a range in which power generation of the system can be continued.

After the first output increase process, it is determined again whether or not a backflow of the flowing gas is detected (step S103). In step S103, when the backflow of the flowing gas is not detected, an output reduction process is executed (step S104). In the output reduction process, the cathode air supply output by the cathode blower 20 is reduced from the output during the first output increase process to the output during normal operation. Thereafter, the process returns to step S101 again, and the determination of the backflow detection of the circulating gas is repeatedly executed.

In step S103, if the backflow of the circulating gas is still detected, it is determined that the external exhaust gas is inflow or inflow. Then, the power generation by the fuel cell system 1 is stopped (step S105), and the fuel cell system 1 is stopped after a predetermined first stop step (step S106). Note that the first stop step here includes at least a second output increase process for increasing the supply output of the cathode air by the cathode blower 20 to the extent that the system can continue power generation. In addition, for example, the fuel cell system 1 is stopped through a predetermined procedure such as supply stop of the hydrogen-containing fuel, purge processing of the gas filling the power generation unit, cooling process of the cell stack 5 and the like.

In this embodiment, in the exhaust path for exhausting the FC exhaust gas, when the backflow of the circulating gas is detected by the flow direction detection unit 23, the backflow is performed by executing the first output increase processing of the cathode air. The circulating gas is pushed back, and the inflow of external exhaust gas is suppressed. In addition, after the execution of the output increase process by the control unit 24, when the backflow of the flow gas is still detected by the flow direction detection unit 23, the system is stopped through a predetermined first stop step. . Therefore, in this fuel cell system 1, various catalysts or adsorbents mounted on the cell stack 5 and the fuel cell system 1 due to the backflow of external exhaust gas to the fuel cell system 1 side, ion exchange resins, and various auxiliary machines Etc. can be shortened.

FIG. 3 is a view showing another example of the exhaust path of the fuel cell system 1. As shown in FIG. 3, this exhaust path is mainly different from the above example in that a damper 22 is provided. The damper 22 is for controlling the flow of circulation gas (FC exhaust gas, external exhaust gas, or mixed gas thereof) in the exhaust path. For example, an impeller in which blades are attached around a rotating shaft, or a guillotine damper in which a valve body crosses at right angles to a flow path. The damper 22 is provided at a position in front of the exhaust port 26 on the downstream side of the heat exchanging unit 15 and the flow direction detecting unit 23 described later in the circulation gas flow path 27, and switches between opening and closing of the exhaust port 26. A valve can be used instead of the damper.

FIG. 7 is a flowchart showing a second mode of operation of the control unit 24. In the example of the figure, when the diagnostic process is started, a signal indicating the flow direction of the flowing gas is output from the flow direction detection unit 23 to the control unit 24. The control unit 24 that has received the signal determines whether or not the backflow of the flowing gas has been detected (step S201), and if the backflow of the flowing gas is not detected, step S201 is repeatedly executed. On the other hand, if a backflow of the flowing gas is detected in step S201, a first output increase process is executed (step S202). In the first output increase process, the cathode air supply output by the cathode blower 20 is increased from that during normal operation within a range in which power generation of the system can be continued.

After the first output increase process, it is determined again whether or not the backflow of the flowing gas is detected (step S203). In step S203, when the backflow of the flowing gas is not detected, output reduction processing is executed (step S204). In the output reduction process, the cathode air supply output by the cathode blower 20 is reduced from the output during the first output increase process to the output during normal operation. Thereafter, the process returns to step S201 again, and the determination of the backflow detection of the circulating gas is repeatedly performed.

In step S203, if the backflow of the circulating gas is still detected, it is determined that the external exhaust gas is inflow or inflow. Then, the damper 22 is closed and the fuel cell system 1 is urgently stopped (step S205). Here, the emergency stop means that the fuel cell system 1 is stopped by omitting at least a part of the predetermined first stop step.

Also in this embodiment, in the exhaust path for exhausting the FC exhaust gas, when the backflow of the circulating gas is detected by the flow direction detection unit 23, the backflow is performed by executing the first output increase processing of the cathode air. The flowing gas is pushed back, and the inflow of external exhaust gas is suppressed. Accordingly, it is possible to suppress the shortening of the service life of various catalysts or adsorbents, ion exchange resins, various auxiliary machines and the like mounted on the cell stack 5 and the fuel cell system 1 due to the backflow of the flowing gas to the fuel cell system 1 side. it can. Moreover, in this embodiment, when the backflow of the flow gas is still detected by the flow direction detection unit 23 after the output increase process by the control unit 24, the damper 22 is closed and the system is urgently stopped. It has become.

FIG. 8 is a flowchart showing a third form of operation of the control unit 24. In the example of the figure, when the diagnostic process is started, a signal indicating the flow direction of the flowing gas is output from the flow direction detection unit 23 to the control unit 24. The control unit 24 that has received the signal determines whether or not a backflow of the flowing gas has been detected (step S301), and if the backflow of the flowing gas is not detected, step S301 is repeatedly executed. On the other hand, if a backflow of the circulating gas is detected in step S301, a first output increase process is executed (step S302). In the first output increase process, the cathode air supply output by the cathode blower 20 is increased from that during normal operation within a range in which power generation of the system can be continued.

After the first output increase process, it is determined again whether the backflow of the flowing gas is detected (step S303). In step S303, when the backflow of the flowing gas is not detected, output reduction processing is executed (step S304). In the output reduction process, the cathode air supply output by the cathode blower 20 is returned from the output during the first output increase process to the output during normal operation. Thereafter, the process returns to step S301 again, and the determination of the backflow detection of the circulating gas is repeatedly performed.

In step S303, if the backflow of the circulating gas is still detected, it is determined that the external exhaust gas is inflow or inflow. Then, the power generation by the fuel cell system 1 is stopped (step S305), and the first stop process of the system including the second output increase process is executed while the damper 22 is kept open (step S306). In the second output increase processing, the supply output of the cathode air by the cathode blower 20 is increased from the normal operation to the extent that the system can continue the power generation.

Further, along with the execution of the first stop process of the system, it is further determined whether or not the backflow of the circulating gas is detected (step S307). In step S307, when the backflow of the flowing gas is not detected, the first stop process of the fuel cell system 1 is completed as it is. On the other hand, in step S307, when the backflow of the circulating gas is detected, the first stop process is interrupted, the damper 22 is closed, and the fuel cell system 1 is urgently stopped (step S308).

Also in this embodiment, in the exhaust path for exhausting the FC exhaust gas, when the backflow of the circulating gas is detected by the flow direction detection unit 23, the backflow is performed by executing the first output increase processing of the cathode air. The flowing gas is pushed back, and the inflow of external exhaust gas is suppressed. Accordingly, it is possible to suppress the shortening of the service life of various catalysts or adsorbents, ion exchange resins, various auxiliary machines and the like mounted on the cell stack 5 and the fuel cell system 1 due to the backflow of the flowing gas to the fuel cell system 1 side. it can.

Further, in this embodiment, when the backflow of the circulating gas is not eliminated even by the first output increase process that is executed while the power generation of the fuel cell system 1 is continued, the power generation of the fuel cell system 1 is stopped, and the first stop step At the same time, the second output increase processing is performed. Although there is a limit to the amount of cathode air that can be increased while stably maintaining the power generation of the fuel cell system 1, the power generation can be stabilized by stopping the power generation of the fuel cell system 1 when the second output increase process is executed. Therefore, the supply amount of cathode air can be further increased. Thereby, the circulating gas flowing backward can be pushed back more strongly. Moreover, since the 1st stop process including a 2nd output increase process is tried before performing an emergency stop process, the emergency stop frequency of the fuel cell system 1 can be reduced. This contributes to extending the life of the fuel cell system 1.

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system, 5 ... Cell stack, 15 ... Heat exchange part, 20 ... Cathode blower, 21 ... Power generation part, 22 ... Damper, 23 ... Flow direction detection part, 24 ... Control part, 26 ... Exhaust port, 28 ... Fan, 29 ... flap.

Claims

A power generation unit including a cell stack that generates power using a hydrogen-containing gas;
A cathode blower for supplying cathode air to the cathode of the cell stack;
An exhaust port for discharging exhaust gas discharged from at least the power generation unit to the outside of the system;
A flow direction detection unit that is disposed in an exhaust path between the power generation unit and the exhaust port and detects a flow direction of the flow gas in the exhaust path;
A control unit that executes a first output increase process for increasing the supply output of the cathode air by the cathode blower compared to during normal operation when the flow direction detection unit detects a backflow of the flow gas. A fuel cell system provided.
2. The fuel cell system according to claim 1, wherein the control unit executes the first output increase processing with the supply output of the cathode air in a range in which the power generation of the system can be continued while continuing the power generation of the system.
The control unit sets the cathode air supply output to an output during normal operation when the flow direction detection unit no longer detects the backflow of the flow gas after the first output increase process. The fuel cell system according to claim 2.
The control unit stops the power generation of the system when the backflow of the circulation gas is still detected after the first output increasing process, and the cathode air exceeds a range in which the power generation of the system can be continued. The fuel cell system according to claim 2 or 3, wherein a first stop step including a second output increase process for supplying the fuel is executed.
A damper for switching opening and closing of the exhaust port in the exhaust path;
The control unit closes the damper and urgently stops the system when the backflow of the flow gas is still detected by the flow direction detection unit after the execution of the first output increase process. 3. The fuel cell system according to 3.
A damper for switching opening and closing of the exhaust port in the exhaust path;
The control unit executes the first stop process after stopping the power generation of the system when the backflow of the circulating gas is still detected by the flow direction detection unit after the execution of the first output increase process. 5. The fuel according to claim 4, wherein when the backflow of the flow gas is still detected by the flow direction detection unit while the first stop process is being performed, the damper is closed and the system is urgently stopped. Battery system.
The exhaust port further comprises a heat exchanging unit that circulates an off-gas combustion gas discharged from the cell stack and a liquid heat medium, transfers heat from the combustion gas to the heat medium, and heats the heat medium. The exhaust gas discharged to the outside of the fuel cell system is the combustion gas exhausted from a heat exchange unit, and the gas detected by the flow direction detection unit is the combustion gas flowing toward the exhaust port. Item 4. The fuel cell system according to Item 1.
A damper that switches between opening and closing of the exhaust port, and the controller closes the damper when the backflow of the combustion gas is still detected by the flow direction detection unit after the output increase process is performed. The fuel cell system according to claim 7, wherein the fuel cell system is stopped through a second stop step in which at least a part of the predetermined first stop step is omitted.
The control unit, after the execution of the output increase process, when the backflow of the combustion gas is no longer detected by the flow direction detection unit, the cathode blower supply output to the output during normal operation The output increasing process is performed again when the output decreasing process to be decreased is executed, and the backflow of the combustion gas is detected again by the flow direction detection unit after the output decreasing process is executed. The fuel cell system described.