JP7775112B2 - Fuel cell system and fuel cell system operating method - Google Patents

Description

The present invention relates to a fuel cell system and a method for operating such a fuel cell system.

Fuel cell systems are sometimes installed in environments where the air contains a large amount of impurities. If air containing impurities is continuously supplied to the cathode of the fuel cell stack for power generation, deterioration such as catalyst poisoning and corrosion of component parts in the fuel cell stack will accelerate, potentially leading to system failure or a shortened lifespan.

In order to remove impurities, Patent Document 1 provides a filter upstream of the blower that sends air to the fuel cell. However, even with a filter, if the impurity concentration temporarily increases, the amount of impurities that cannot be removed by the filter increases and ends up flowing into the fuel cell.

JP 2018-10763 A

The present invention was made in consideration of the above, and aims to reduce impurities in the air supplied to the air electrode of a fuel cell.

The fuel cell system according to claim 1 comprises a fuel cell that generates electricity using fuel gas supplied to an anode and air supplied to an cathode, a combustor that burns combustible gas, a combustion air inlet passage provided with a filter for removing foreign matter and that introduces external air that has passed through the filter into the combustor, a circulation flow passage that sends combustion exhaust gas from the combustor to the cathode, and a circulation flow rate adjustment unit that controls the circulation flow rate of the combustion exhaust gas sent to the circulation flow passage to increase in accordance with the voltage when the voltage of the fuel cell during power generation falls below a voltage at which it can be determined that the fuel cell is being affected by foreign matter mixed in with the external air.

In the fuel cell system of claim 1, the combustion exhaust gas obtained after combustible gas combustion is returned to the air electrode through the circulation flow path, and the oxygen in the combustion exhaust gas is used in the power generation reaction. Because the combustion exhaust gas is obtained after external air, from which foreign matter has been removed by a filter, is used for combustion, the amount of foreign matter mixed in is reduced. By controlling the circulation flow rate of the combustion exhaust gas using a circulation flow rate adjustment unit based on the voltage of the fuel cell during power generation, the amount of new external air used at the air electrode can be reduced, and the amount of impurities flowing into the air electrode can be reduced.

In the fuel cell system according to claim 2, the circulation flow rate adjustment unit controls the circulation flow rate so that the combustion exhaust gas is sent to the circulation flow path when the voltage is equal to or lower than a predetermined low voltage.

According to the fuel cell system of claim 2, when the voltage of the fuel cell during power generation is below a predetermined low voltage, it is determined that the fuel cell is being affected by external air containing impurities, and combustion exhaust gas is sent to the circulation flow path, thereby reducing the amount of external air taken in.

In the fuel cell system according to claim 3, the circulation flow rate adjustment unit adjusts the circulation flow rate in accordance with the voltage.

The fuel cell system according to claim 3 can determine the degree of influence of external air containing impurities based on the voltage of the fuel cell during power generation and adjust the circulation flow rate.

The fuel cell system according to claim 4 includes a water removal unit provided in the circulation flow path that removes water from the combustion exhaust gas.

The fuel cell system according to claim 4 removes water from the combustion exhaust gas, thereby preventing excess water from flowing into the air electrode.

The fuel cell system according to claim 5 includes an air electrode off-gas circulation flow path that sends off-gas discharged from the air electrode to the air electrode.

According to the fuel cell system of claim 5, off-gas from the air electrode can be returned to the air electrode via the air electrode off-gas circulation flow path.

The fuel cell system operating method according to claim 6 is a method for operating a fuel cell system equipped with a fuel cell that generates electricity using fuel gas supplied to the fuel electrode and air supplied to the air electrode, in which the flow rate of combustion exhaust gas from a combustor that introduces filtered combustion air to combustible gas is adjusted based on the voltage of the fuel cell during power generation, and the combustion exhaust gas is supplied to the air electrode.

In the fuel cell system operating method according to claim 6, the combustion exhaust gas obtained after combustible gas combustion is returned to the air electrode, and the oxygen in the combustion exhaust gas is used in the power generation reaction. Because the combustion exhaust gas is obtained after external air, from which foreign matter has been removed by a filter, is used for combustion, the amount of foreign matter mixed in is reduced. By controlling the circulating flow rate of the combustion exhaust gas based on the voltage of the fuel cell during power generation, the amount of new external air used at the air electrode can be reduced, and the amount of impurities flowing into the air electrode can be reduced.

The fuel cell system operating method according to claim 7 supplies the combustion exhaust gas to the air electrode when the voltage is equal to or lower than a predetermined low voltage.

According to the fuel cell system operating method of claim 7, when the voltage of the fuel cell during power generation is below a predetermined low voltage, it is determined that the fuel cell is being affected by external air containing impurities, and the combustion exhaust gas is returned to the air electrode, thereby reducing the amount of external air taken in.

The fuel cell system operating method according to claim 8 adjusts the flow rate of the combustion exhaust gas supplied to the air electrode in accordance with the voltage.

According to the fuel cell system operating method of claim 8, the degree of influence of external air containing impurities can be determined based on the voltage of the fuel cell during power generation, and the flow rate supplied to the air electrode can be adjusted.

The fuel cell system operating method according to claim 9 removes water from the combustion exhaust gas before sending it to the air electrode.

According to the fuel cell system operating method of claim 9, water is removed from the combustion exhaust gas, thereby preventing excess water from flowing into the air electrode.

The fuel cell system operating method according to claim 10 sends off-gas discharged from the air electrode to the air electrode.

According to the fuel cell system operating method of claim 10, off-gas from the air electrode can be returned to the air electrode.

The fuel cell system and fuel cell system operating method of the present invention can use combustion exhaust gas to reduce impurities in the air supplied to the fuel cell's air electrode.

1 is a configuration diagram of a fuel cell system according to a first embodiment. FIG. 2 is a block diagram of a control unit and related components of the fuel cell system according to the first embodiment. 10 is an example of a circulation flow rate adjustment table that defines the relationship between voltage and circulation flow rate. 10 is a flowchart of a circulation adjustment process. FIG. 10 is a configuration diagram of a fuel cell system according to a second embodiment. 10 is a flowchart of a circulation control process. FIG. 10 is a configuration diagram of a fuel cell system according to a third embodiment. FIG. 10 is a configuration diagram of a fuel cell system according to a fourth embodiment.

First Embodiment
A first embodiment of the present invention will be described with reference to the drawings.

The fuel cell system 10A is a power generation system installed in a user's home, apartment building, factory, etc.

Figure 1 shows an outline of the main components of a fuel cell system 10A according to an embodiment of the present invention. The main components of the fuel cell system 10A according to an embodiment of the present invention include a fuel cell stack 12, a reformer 14, a combustor 16, a condenser 18, a reforming water tank 20, an ion exchange resin 22, an air electrode filter 24, a combustor filter 26, and a control unit 30.

A raw material gas supply pipe P1 is connected to the reformer 14, and raw material gas is supplied from the raw material gas supply pipe P1 to the reformer 14 by a raw material gas supply blower B1. The raw material gas is not particularly limited as long as it can be reformed, and hydrocarbon fuels can be used. Examples of hydrocarbon fuels include methane, city gas, natural gas, LP gas (liquefied petroleum gas), coal-reformed gas, and lower hydrocarbon gases. Biogas may also be used.

The reformer 14 reforms the raw material gas to produce fuel gas containing hydrogen. The reformer 14 is connected to the fuel electrode 12A of the fuel cell stack 12. The fuel gas produced in the reformer 14 is supplied to the fuel electrode 12A of the fuel cell stack 12 via the fuel gas pipe P2.

The fuel cell stack 12 is a cell stack having multiple stacked fuel cells. The fuel cell stack 12 is an example of a fuel cell in the present invention, and each fuel cell has an electrolyte layer (not shown) and a fuel electrode 12A and an air electrode 12B stacked on the front and back surfaces of the electrolyte layer, respectively. Various fuel cells can be used as the fuel cell stack 12, including solid oxide fuel cells (SOFCs), molten carbonate fuel cells (MCFCs), and polymer electrolyte fuel cells (PEFCs). In this embodiment, a PEFC will be used as an example.

One end of an air supply pipe P3 is connected to the air electrode 12B of the fuel cell stack 12, and an air supply blower B2 is connected to the air supply pipe P3. An air electrode filter 24 is provided on the air supply pipe P3 upstream of the air supply blower B2. External air that has passed through the air electrode filter 24 is supplied to the air electrode 12B by the air supply blower B2. The air electrode filter 24 removes foreign matter from the external air. In the fuel cell stack 12, power is generated through a power generation reaction at the fuel electrode 12A and the air electrode 12B. The power is output to a circuit (not shown), and the voltage of the power output to the circuit is detected by a voltage detection unit 13. The voltage detection unit 13 is connected to a control unit 30 (described below) and outputs the detected voltage to the control unit 30.

Anode offgas is discharged from the anode 12A to anode offgas channel P5, and cathode offgas is discharged from the cathode 12B to cathode offgas channel P4. The anode offgas contains fuel gas that has not reacted in the power generation reaction, and is supplied from the anode offgas channel P5 to the combustor 16 for combustion. The cathode offgas contains oxygen that has not reacted in the power generation reaction and water produced in the power generation reaction. The cathode offgas is combined with the combustion exhaust gas, described below, in the cathode offgas channel P4 and sent to the condenser 18.

The combustor 16 is located adjacent to the reformer 14 and heats the reformer 14 with combustion heat. One end of a combustion air supply pipe P6 is connected to the combustor 16, and a combustion air supply blower B3 is connected to the combustion air supply pipe P6. A combustor filter 26 is located on the combustion air supply pipe P6 upstream of the combustion air supply blower B3. External air that has passed through the combustor filter 26 is supplied to the combustor 16 by the combustion air supply blower B3. The combustor filter 26 removes foreign matter from the external air. Anode off-gas is supplied to the combustor 16 from the anode off-gas passage P5, and combustible components in the anode off-gas are combusted by reaction with the oxygen contained in the air from the combustion air supply pipe P6.

One end of the combustion exhaust gas passage P7 is connected to the combustor 16, and the other end of the combustion exhaust gas passage P7 merges with the air electrode off-gas passage P4. The combustion exhaust gas discharged from the combustor 16 merges with the air electrode off-gas (hereinafter, the combined gas is referred to as "mixed gas") and is sent to the condenser 18.

The other end of the cathode off-gas passage P4 is connected to the condenser 18, where the gas-phase water in the mixed gas is condensed and separated into gas and liquid. The liquid water is sent to the reforming water tank 20 via flow passage P11. A check valve 11 is provided in flow passage P11.

The mixed gas from which the water has been removed is sent to the mixing channel P8. A flow rate adjustment three-way valve 19 is provided in the mixing channel P8, which branches into a circulation channel P9 and a discharge channel P10. The downstream end of the circulation channel P9 is connected to the air supply pipe P3 downstream of the cathode filter 24 and upstream of the air supply blower B2. The discharge channel P10 discharges the mixed gas from which the water has been removed to the outside. The flow rate adjustment three-way valve 19 is connected to the control unit 30, which will be described later, and adjusts the amount of mixed gas sent to the circulation channel P9 based on a signal from the control unit 30.

A specified amount of water (liquid phase) is sent to the reforming water tank 20, where it is stored, and any amount exceeding the specified amount is discharged to the outside through the discharge pipe P13. Driven by the pump 21, the water stored in the reforming water tank 20 is supplied as reforming water from the reforming water supply passage P12 through the ion exchange resin 22 to the reformer 14. The ion exchange resin 22 removes impurities from the passing water through ion exchange.

As shown in FIG. 2, the control unit 30 includes, as hardware, a processor 32 and memory 34. The processor 32 includes a CPU (Central Processing Unit) and the like. The memory 34 includes a ROM (Read Only Memory), RAM (Random Access Memory), storage, and the like.

The ROM stores various programs and data. The RAM serves as a working area and temporarily stores programs or data. The storage is composed of a hard disk drive (HDD) or solid state drive (SSD), and stores various programs and data, including the operating system. The ROM or storage stores a program for controlling the fuel cell system 10A. The processor 32 reads the program 35 and executes the program 35 using the RAM as a working area.

The storage area 36 of the memory 34 stores the circulation flow rate adjustment table T1 (described below), voltage data D output from the voltage detection unit 13, operating data of the fuel cell system 10, etc.

The circulation flow rate adjustment table T1 is used to adjust the amount of mixed gas (hereinafter referred to as "circulation flow rate C") sent to the circulation flow path P9 in accordance with the voltage data D output from the voltage detection unit 13. As an example, as shown in FIG. 3, the "circulation flow rate C" can be adjusted by starting at a circulation flow rate C1 when the voltage is V2, increasing the circulation flow rate C in proportion to the voltage drop, and adjusting to a circulation flow rate C2 when the voltage is V1. Voltage V2 is set taking into account the voltage drop that occurs when foreign matter is mixed in the outside air. In other words, when the voltage V of the voltage data D falls below voltage V2, it is determined that the device is being affected by foreign matter mixed in the outside air. Voltage V2 is set to a value greater than voltage V1. Voltage V1 can be set to an abnormally low voltage that exceeds the voltage drop caused by foreign matter mixed in the outside air.

An end-of-adjustment voltage V3 is also set, and if the voltage V exceeds V3 during the circulation adjustment process described below, this is used as an indicator to stop the supply of mixed gas to the air electrode 12B. Voltage V3 is set to a value greater than voltage V2, at which it can be determined that the supply is not affected by foreign matter mixed in the external air.

The processor 32 has a circulation flow rate adjustment unit 38 as a functional component. The functional components of the circulation flow rate adjustment unit 38 are realized by the processor 32 executing the program 35.

The operation panel 40 has displays, lamps, switches, etc. The operation panel 40 has switches that can change the operation and settings of the fuel cell system 10A. The communicator 42 is, for example, a modem. The communicator 42 has the function of connecting the fuel cell system 10A to other devices so that they can communicate with each other via the network N.

Next, the operation of the fuel cell system 10A of this embodiment will be described.

In the fuel cell system 10A, the raw material gas supply blower B1 sends raw material gas to the reformer 14. In the reformer 14, a reforming reaction occurs to generate fuel gas containing hydrogen from the raw material gas. The fuel gas is supplied to the fuel electrode 12A of the fuel cell stack 12 via the fuel gas pipe P2. External air, from which foreign matter has been removed through the air electrode filter 24, is supplied to the air electrode 12B of the fuel cell stack 12 by the air supply blower B2. In the fuel cell stack 12, the voltage of the power output by the power generation reaction at the fuel electrode 12A and the air electrode 12B is detected by the voltage detection unit 13, and the detected voltage is output to the control unit 30. The control unit 30 stores the received voltage data D in the memory area 36.

During operation of the fuel cell system 10A, the control unit 30 reads the circulation adjustment processing program shown in Figure 4 and executes it via the processor 32.

First, in step S10, the latest voltage data D is read from memory area 36, and in step S11, it is determined whether the voltage is V3 or higher. If the voltage is V3 or lower, in step S12, it is determined whether the voltage is V2 or higher. If the voltage is V2 or lower, in step S14, it is determined whether the voltage is V1 or higher. If the voltage is determined to be lower than V1, it is determined to be an abnormally low voltage, and an abnormality warning is issued in step S20, and processing ends. The abnormality warning can be issued by displaying a warning on the operation panel 40, emitting a warning sound, or the like.

If step S14 determines that the voltage is V1 or higher, it can be determined that the voltage V is being affected by foreign matter mixed in the external air, and the process proceeds to step S16 to reduce the amount of external air being taken in. In step S16, the circulation flow rate adjustment table T1 is referenced to determine the circulation flow rate C corresponding to the read voltage. Then, in step S18, a signal is output to the flow rate adjustment three-way valve 19 to adjust the circulation flow rate C. This allows the mixed gas to be supplied to the air electrode 12B at an appropriate flow rate, and the amount of external air being taken in can be reduced according to this supply rate.

In step S19, it is determined whether an instruction to end operation has been received, and if an instruction to end operation has been received, this process ends. If operation continues, the process returns to step S10 and repeats the process.

After the determination in step S19 is negative, the process returns to step S10. If the determination in step S11 is that the voltage is greater than V3, the voltage V exceeds the indicator for stopping the supply of mixed gas to the air electrode 12B. Therefore, in step S13, a signal is output to the flow rate adjustment three-way valve 19 to set the circulation flow rate C to zero. The process then returns to step S10.

If the determination in step S19 is negative, the process returns to step S10. If the determination in step S11 is positive and the voltage is determined to be greater than V2 in step S12, the process returns to step S10 without going through step S13 to continue supplying the mixed gas to the air electrode 12B.

In this way, the circulation adjustment process adjusts the flow rate of the mixed gas sent to the circulation flow path P9 in accordance with the voltage V, allowing the appropriate flow rate of the mixed gas to be supplied to the air electrode 12B and the oxygen in the mixed gas to be utilized at the air electrode 12B. This reduces the amount of external air taken in that corresponds to the amount of mixed gas supplied.

In addition, in this embodiment, water contained in the mixed gas is removed by the condenser 18 and supplied to the air electrode 12B, thereby preventing excess water from flowing into the air electrode 12B.

Second Embodiment
Next, a second embodiment of the present invention will be described. In this embodiment, the same parts as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

In place of the three-way flow rate regulating valve 19 of the fuel cell system 10A of the first embodiment, the fuel cell system 10B of this embodiment is equipped with a solenoid valve 44A and an orifice 44B in the circulation flow path P9. Other than the solenoid valve 44A and orifice 44B, the configuration is the same as that of the fuel cell system 10A of the first embodiment shown in FIG. 1.

As shown in FIG. 5, the fuel cell system 10B is equipped with a solenoid valve 44A and an orifice 44B in the circulation flow path P9. The solenoid valve 44A is located upstream of the orifice 44B, and when the solenoid valve 44A is open, the orifice 44B throttles the flow rate of the mixed gas flowing into the circulation flow path P9 to a constant amount. The flow rate of the mixed gas flowing into the circulation flow path P9 is set to the circulation flow rate required by a drop in voltage V. The solenoid valve 44A is connected to the control unit 30, and its opening and closing is controlled by the control unit 30.

Next, the operation of the fuel cell system 10B of this embodiment will be described.

During operation of the fuel cell system 10B, the control unit 30 reads the circulation control processing program shown in Figure 6 and executes it via the processor 32.

First, steps S10 to S14 are performed in the same manner as in the first embodiment. If step S14 determines that the voltage is equal to or greater than V1, it can be determined that the voltage V is being affected by foreign matter mixed in with the outside air. Therefore, in order to reduce the amount of outside air taken in, solenoid valve 44A is opened in step S15. This allows a predetermined circulation flow rate of mixed gas to be supplied to the air electrode 12B, reducing the amount of outside air taken in corresponding to this supply amount.

In step S18, it is determined whether an instruction to end operation has been received. If an instruction to end operation has been received, solenoid valve 44A is closed in step S19, and this process ends. If operation is to continue, the process returns to step S10 and repeats the process.

After the determination in step S18 is negative, the process returns to step S10. If the determination in step S11 is that the voltage is greater than V3, the voltage V exceeds the indicator for stopping the supply of mixed gas to the air electrode 12B. Therefore, in step S17, a signal is output to the solenoid valve 44A to close the solenoid valve 44A. The process then returns to step S10.

If the determination in step S18 is negative, the process returns to step S10. If the determination in step S11 is positive and the voltage is determined to be greater than V2 in step S12, the process returns to step S10 without going through step S17 to continue supplying the mixed gas to the air electrode 12B.

In this way, by controlling whether or not mixed gas is supplied to the circulation flow path P9 using the circulation control process, the mixed gas can be supplied to the air electrode 12B, and the intake of external air can be reduced by an amount corresponding to the amount supplied.

Third Embodiment
Next, a third embodiment of the present invention will be described. In this embodiment, the same parts as those in the first and second embodiments are designated by the same reference numerals, and detailed description thereof will be omitted.

The fuel cell system 10C of this embodiment has a combustion exhaust gas circulation flow path P14 instead of the circulation flow path P9 of the fuel cell system 10A of the first embodiment. It also has a flow rate adjustment three-way valve 46 instead of the flow rate adjustment three-way valve 19. Other than these, the configuration is the same as that of the fuel cell system 10A of the first embodiment shown in FIG. 1.

As shown in Figure 7, the combustion exhaust gas circulation flow path P14 is connected to a branch in the middle of the combustion exhaust gas path P7. The downstream end of the combustion exhaust gas circulation flow path P14 is connected to the air supply pipe P3 downstream of the air electrode filter 24 and upstream of the air supply blower B2.

A three-way flow rate control valve 46 is provided at the connection point between the combustion exhaust gas passage P7 and the combustion exhaust gas circulation passage P14. The three-way flow rate control valve 46 is connected to the control unit 30 and adjusts the amount of combustion exhaust gas sent to the combustion exhaust gas circulation passage P14 based on a signal from the control unit 30.

In the fuel cell system 10C of this embodiment, the circulation adjustment process (see Figure 4) is performed during operation, as in the first embodiment. In this way, the circulation adjustment process adjusts the flow rate of the combustion exhaust gas sent to the combustion exhaust gas circulation flow path P14 in accordance with the voltage V, allowing the oxygen in the combustion exhaust gas to be used at the air electrode 12B. This makes it possible to reduce the amount of external air taken in that corresponds to the amount of combustion exhaust gas supplied.

Fourth Embodiment
Next, a fourth embodiment of the present invention will be described. In this embodiment, the same parts as those in the first to third embodiments are designated by the same reference numerals, and detailed description thereof will be omitted.

In place of the three-way flow rate regulating valve 46 of the fuel cell system 10C of the third embodiment, the fuel cell system 10D of this embodiment is equipped with a solenoid valve 48A and an orifice 48B in the combustion exhaust gas circulation flow path P14. Other than the solenoid valve 48A and orifice 48B, the configuration is the same as that of the fuel cell system 10C of the third embodiment shown in FIG. 7.

As shown in FIG. 8, the fuel cell system 10D is equipped with a solenoid valve 48A and an orifice 48B in the combustion exhaust gas circulation flow path P14. The solenoid valve 48A is located upstream of the orifice 48B, and when the solenoid valve 48A is open, the orifice 48B throttles the flow rate of the combustion exhaust gas flowing into the combustion exhaust gas circulation flow path P14 to a constant amount. The flow rate of the combustion exhaust gas flowing into the combustion exhaust gas circulation flow path P14 is set to the circulation flow rate required by a drop in voltage V. The solenoid valve 48A is connected to the control unit 30, and its opening and closing is controlled by the control unit 30.

In the fuel cell system 10D of this embodiment, the circulation control process (see FIG. 6) is executed during operation, as in the second embodiment. In this way, the circulation control process controls whether or not combustion exhaust gas is supplied to the combustion exhaust gas circulation flow path P14, thereby supplying combustion exhaust gas to the air electrode 12B and reducing the intake of external air by an amount corresponding to the amount of supply.

The above describes an embodiment of the present invention, but the present invention is not limited to the above, and it goes without saying that various modifications and variations are possible within the scope of the present invention.

10A, 10B, 10C, 10D Fuel cell system 12 Fuel cell stack (fuel cell)
12A fuel electrode 12B air electrode 16 combustor 18 condenser (water removal section)
19, 46 Flow rate adjusting three-way valve (circulation flow rate adjusting section)
26 Combustor filter 30 Control unit (circulation flow rate adjustment unit)
38 Circulation flow rate adjusting unit 44A, 48A Solenoid valve (circulation flow rate adjusting unit)
44B, 48B Orifice (circulation flow rate adjustment part)
C Circulation flow rate D Voltage data P4 Air electrode off-gas path (air electrode off-gas circulation path)
P6 Combustion air supply pipe (combustion air introduction passage)
P9 Circulation flow path P14 Combustion exhaust gas circulation flow path (circulation flow path)

Claims (10)

a fuel cell that generates electricity using a fuel gas supplied to the fuel electrode and air supplied to the air electrode;
a combustor that burns combustible gas;
a combustion air introduction passage provided with a filter for removing foreign matter, and introducing external air that has passed through the filter into the combustor;
a circulation flow path for sending the combustion exhaust gas from the combustor to the air electrode;
a circulation flow rate adjusting unit that, when the voltage of the fuel cell during power generation falls below a voltage at which it can be determined that the fuel cell is being affected by foreign matter mixed in the external air, controls the fuel cell to increase the circulation flow rate at which the combustion exhaust gas is sent to the circulation flow path in accordance with the voltage; and
A fuel cell system comprising: the circulation flow rate adjusting unit controls the circulation flow rate so that the combustion exhaust gas is sent to the circulation flow path when the voltage is equal to or lower than a predetermined low voltage.
The fuel cell system according to claim 1 . The circulation flow rate adjusting unit adjusts the circulation flow rate in accordance with the voltage.
3. The fuel cell system according to claim 1 or 2. A water removal unit is provided in the circulation flow path and removes water from the combustion exhaust gas.
The fuel cell system according to any one of claims 1 to 3. an air electrode off-gas circulation flow path that sends the off-gas discharged from the air electrode to the air electrode,
The fuel cell system according to any one of claims 1 to 4. A method for operating a fuel cell system including a fuel cell that generates electricity using a fuel gas supplied to an anode and air supplied to an cathode, comprising:
When the voltage of the fuel cell during power generation falls below a voltage at which it can be determined that the voltage is being affected by foreign matter mixed in the external air, the flow rate of the combustion exhaust gas from the combustor, which introduces combustion air that has passed through a filter and burns the combustible gas, is adjusted so as to increase in accordance with the voltage and supplied to the air electrode.
A method for operating a fuel cell system. supplying the combustion exhaust gas to the air electrode when the voltage is equal to or lower than a predetermined low voltage;
The method for operating a fuel cell system according to claim 6. adjusting the flow rate of the combustion exhaust gas supplied to the air electrode in accordance with the voltage;
8. The method for operating a fuel cell system according to claim 6 or 7. removing water from the flue gas before delivering it to the cathode;
The method for operating a fuel cell system according to any one of claims 6 to 8. sending off-gas discharged from the air electrode to the air electrode;
The method for operating a fuel cell system according to any one of claims 6 to 9.