Fuel cell system and fuel cell system operating method

Abstract

To reduce impurities of the air supplied to the cathode of a fuel cell stack, using a combustion exhaust gas.SOLUTION: A fuel battery system 10A comprises: a fuel battery cell stack 12 that generates electricity by the fuel gas supplied to a fuel electrode 12A and the air supplied to an air electrode 12B; a combustor 16 that burns a combustible gas; a combustion air introduction path P6 that guides the external air having passed through a combustor filter 26 for removing foreign matter to the combustor 16; a circulation flow path P9 that sends out a combustion exhaust gas from the combustor 16 to the air electrode 12B, adding an external air thereto; and a circulation flow rate adjustment unit 38 that controls a circulation flow rate at which the combustion exhaust gas is sent out to the circulation flow path P9, on the basis of the voltage of the fuel battery cell stack 12 during electricity generation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system and a method for operating the fuel cell system. [Background technology]

[0002] Fuel cell systems are often 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.

[0003] Therefore, in Patent Document 1, a filter is provided upstream of the blower that sends air to the fuel cell to remove impurities. 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-10763 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in consideration of the above circumstances, and has as its object to reduce impurities in the air supplied to the air electrode of a fuel cell. [Means for solving the problem]

[0006] 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 introduction passage that is provided with a filter for removing foreign matter and introduces external air that has passed through the filter into the combustor, a circulation passage that sends combustion exhaust gas from the combustor to the cathode, and a voltage of the fuel cell during power generation. When the voltage drops below a level at which it can be determined that the device is being affected by foreign matter mixed in the external air, The circulation flow rate of the combustion exhaust gas sent to the circulation flow path is To increase and a circulation flow rate adjusting unit that controls the circulation flow rate.

[0007] In the fuel cell system according to claim 1, the combustion exhaust gas obtained after combustible gas combustion is returned to the air electrode through a circulation flow path, and the oxygen in the combustion exhaust gas is utilized in the power generation reaction. The combustion exhaust gas is obtained by subjecting external air, from which foreign matter has been removed by a filter, to combustion, and therefore 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.

[0008] In the fuel cell system according to claim 2, 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.

[0009] 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.

[0010] In the fuel cell system according to claim 3, the circulation flow rate adjusting unit adjusts the circulation flow rate in accordance with the voltage.

[0011] According to the fuel cell system of claim 3, the degree of influence of external air containing impurities can be determined in accordance with the voltage of the fuel cell during power generation, and the circulation flow rate can be adjusted.

[0012] The fuel cell system according to claim 4 includes a water removal section that is provided in the circulation flow path and removes water from the combustion exhaust gas.

[0013] According to the fuel cell system of claim 4, water is removed from the combustion exhaust gas, so that the inflow of excess water into the air electrode can be suppressed.

[0014] The fuel cell system according to claim 5 includes an air electrode off-gas circulation flow path that sends the off-gas discharged from the air electrode to the air electrode.

[0015] According to the fuel cell system of claim 5, the off-gas from the air electrode can be returned to the air electrode via the air electrode off-gas circulation channel.

[0016] The method of operating a fuel cell system according to claim 6 is a method of operating a fuel cell system equipped with a fuel cell that generates electricity using fuel gas supplied to an anode and air supplied to an cathode, in which the flow rate of combustion exhaust gas from a combustor that introduces filtered combustion air to burn combustible gas is adjusted based on the voltage of the fuel cell during power generation, and the combustion exhaust gas is supplied to the cathode.

[0017] In the fuel cell system operating method according to claim 6, the combustion exhaust gas after combusting combustible gas is returned to the air electrode, and the oxygen in the combustion exhaust gas is used in the power generation reaction. The combustion exhaust gas is a gas obtained after combustion of external air from which foreign matter has been removed by a filter, so the amount of foreign matter mixed in is reduced. By controlling the circulation 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.

[0018] A method for operating a fuel cell system according to a seventh aspect of the present invention supplies the combustion exhaust gas to the air electrode when the voltage is equal to or lower than a predetermined low voltage.

[0019] 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.

[0020] 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.

[0021] According to the fuel cell system operating method of claim 8, the degree of influence of external air containing impurities can be determined according to the voltage of the fuel cell during power generation, and the flow rate supplied to the air electrode can be adjusted.

[0022] In the fuel cell system operating method according to claim 9, water is removed from the combustion exhaust gas before it is sent to the air electrode.

[0023] According to the fuel cell system operating method of claim 9, water is removed from the combustion exhaust gas, so that the inflow of excess water into the air electrode can be suppressed.

[0024] In the fuel cell system operating method according to claim 10, the off-gas discharged from the air electrode is sent to the air electrode.

[0025] According to the fuel cell system operating method of claim 10, the off-gas from the air electrode can be returned to the air electrode. [Effects of the Invention]

[0026] According to the fuel cell system and the method for operating the fuel cell system of the present invention, it is possible to reduce impurities in the air supplied to the air electrode of the fuel cell by using the combustion exhaust gas. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a configuration diagram of a fuel cell system according to a first embodiment. [Figure 2]FIG. 2 is a configuration diagram of a control unit and related components of the fuel cell system according to the first embodiment. [Figure 3] 10 is an example of a circulation flow rate adjustment table that defines the relationship between voltage and circulation flow rate. [Figure 4] 10 is a flowchart of a circulation adjustment process. [Figure 5] FIG. 10 is a configuration diagram of a fuel cell system according to a second embodiment. [Figure 6] 10 is a flowchart of a circulation control process. [Figure 7] FIG. 10 is a configuration diagram of a fuel cell system according to a third embodiment. [Figure 8] FIG. 10 is a configuration diagram of a fuel cell system according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0028] First Embodiment A first embodiment of the present invention will be described with reference to the drawings.

[0029] The fuel cell system 10A is a power generation system installed in a user's home, an apartment building, a factory, or the like.

[0030] 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.

[0031] 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.

[0032] The reformer 14 reforms the raw material gas to generate a fuel gas containing hydrogen. The reformer 14 is connected to the fuel electrode 12A of the fuel cell stack 12. The fuel gas generated in the reformer 14 is supplied to the fuel electrode 12A of the fuel cell stack 12 via a fuel gas pipe P2.

[0033] The fuel cell stack 12 is a cell stack having a plurality of 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. Note that various fuel cells can be used as the fuel cell stack 12, such as a solid oxide fuel cell (SOFC), a molten carbonate fuel cell (MCFC), and a polymer electrolyte fuel cell (PEFC). In this embodiment, a PEFC will be described as an example.

[0034] 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 by a power generation reaction at the fuel electrode 12A and the air electrode 12B, and the power is output to a circuit (not shown). 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 later) and outputs the detected voltage to the control unit 30.

[0035] Anode offgas is discharged from the anode 12A to anode offgas channel P5, and cathode offgas is discharged from the cathode 12B to anode offgas channel P4. The anode offgas contains fuel gas that has not reacted in the power generation reaction, and this anode offgas is supplied from anode offgas channel P5 to 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 combustion exhaust gas, which will be described later, at cathode offgas channel P4 and sent to condenser 18.

[0036] The combustor 16 is provided adjacent to the reformer 14 and heats the reformer 14 with the heat of combustion. 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 provided 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 an anode off-gas passage P5, and combustible components in the anode off-gas are combusted by reaction with oxygen contained in the air from the combustion air supply pipe P6.

[0037] One end of a 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 merged gas is referred to as "mixed gas") and is sent to the condenser 18.

[0038] The other end of the cathode off-gas passage P4 is connected to the condenser 18, where gas-phase water in the mixed gas is condensed and separated into gas and liquid. The liquid-phase water is sent to the reforming water tank 20 via a passage P11. A check valve 11 is provided in the passage P11.

[0039] The mixed gas from which water has been removed is sent to a mixing channel P8. A flow rate regulating three-way valve 19 is provided in the mixing channel P8, and the mixing channel P8 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 air electrode filter 24 and upstream of the air supply blower B2. The discharge channel P10 discharges the mixed gas from which water has been removed to the outside. The flow rate regulating three-way valve 19 is connected to a 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.

[0040] A specified amount of water (liquid phase) is sent to the reforming water tank 20 and stored there, and any amount exceeding the specified amount is discharged to the outside through a discharge pipe P13. The water stored in the reforming water tank 20 is supplied as reforming water to the reformer 14 through the reforming water supply passage P12 and the ion exchange resin 22 by driving the pump 21. The ion exchange resin 22 removes impurities from the passing water by ion exchange.

[0041] 2, the control unit 30 includes, as hardware, a processor 32 and a memory 34. The processor 32 includes a CPU (Central Processing Unit), etc. The memory 34 includes a ROM (Read Only Memory), a RAM (Random Access Memory), and storage, etc.

[0042] The ROM stores various programs and various data. The RAM temporarily stores programs or data as a working area. The storage is composed of an HDD (Hard Disk Drive) or SSD (Solid State Drive), etc., and stores various programs including the operating system and various data. The ROM or storage stores a program for controlling the fuel cell system 10A. The processor 32 reads out the program 35 and executes the program 35 using the RAM as a working area.

[0043] A storage area 36 of the memory 34 stores a circulation flow rate adjustment table T1 (to be described later), voltage data D output from the voltage detection unit 13, operating data of the fuel cell system 10, and the like.

[0044] 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 with 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. The voltage V2 is set taking into consideration 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 becomes equal to or lower than V2, it is determined that the device is being affected by foreign matter mixed in the outside air. The voltage V2 is set to a value greater than the voltage V1. Note that the voltage V1 can be set to an abnormally low voltage that exceeds the voltage drop caused by foreign matter mixed in the outside air.

[0045] In addition, an adjustment end voltage V3 is set, and when the voltage V exceeds V3 in the circulation adjustment process described below, this voltage V3 is used as an indicator to stop the supply of the mixed gas to the air electrode 12B. The voltage V3 is set to a value greater than the voltage V2 at which it can be determined that there is no influence from foreign matter mixed in the external air.

[0046] The processor 32 includes, as a functional component, a circulation flow rate adjustment unit 38. The functional components of the circulation flow rate adjustment unit 38 are realized by the processor 32 executing the program 35.

[0047] The operation panel 40 has a display, lamps, switches, etc. The operation panel 40 has switches that can change the operation and settings of the fuel cell system 10A. The communication device 42 is, for example, a modem. The communication device 42 has a function of connecting the fuel cell system 10A to other devices so that they can communicate with each other via the network N.

[0048] Next, the operation of the fuel cell system 10A of this embodiment will be described.

[0049] In the fuel cell system 10A, a raw material gas supply blower B1 sends raw material gas to the reformer 14. In the reformer 14, a fuel gas containing hydrogen is produced from the raw material gas by a reforming reaction. The fuel gas is supplied to the fuel electrode 12A of the fuel cell stack 12 via a fuel gas pipe P2. External air, from which foreign matter has been removed through a cathode filter 24, is supplied to the cathode 12B of the fuel cell stack 12 by an 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 cathode 12B is detected by a voltage detection unit 13, and the detected voltage is output to a control unit 30. The control unit 30 stores the received voltage data D in a memory area 36.

[0050] In the control unit 30, the circulation adjustment processing program shown in FIG.

[0051] 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 it is determined that the voltage is lower than V1, it is determined that the voltage is abnormally low, and an abnormality warning is issued in step S20, and the process ends. The abnormality warning can be issued by displaying a warning on operation panel 40, emitting a warning sound, or the like.

[0052] If it is determined in step S14 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 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 at an appropriate flow rate to the air electrode 12B, and the amount of external air being taken in can be reduced according to the supply rate.

[0053] In step S19, it is determined whether an instruction to end operation has been given, and if an instruction to end operation has been given, the process ends. If operation is to continue, the process returns to step S10 and repeats the process.

[0054] After the determination in step S19 is negative, the process returns to step S10. If it is determined in step S11 that the voltage is greater than V3, the voltage V exceeds the index for stopping the supply of the mixed gas to the air electrode 12B, so in step S13, a signal is output to the flow rate regulating three-way valve 19 to set the circulation flow rate C to zero. Then, the process returns to step S10.

[0055] 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 in order to continue supplying the mixed gas to the air electrode 12B.

[0056] In this way, by adjusting the flow rate of the mixed gas sent to the circulation flow path P9 according to the voltage V through the circulation adjustment process, an appropriate flow rate of the mixed gas can be supplied to the air electrode 12B, and the oxygen in the mixed gas can be utilized at the air electrode 12B. This reduces the intake of external air by an amount corresponding to the amount of mixed gas supplied.

[0057] Furthermore, in this embodiment, water contained in the mixed gas is removed by the condenser 18 before being supplied to the air electrode 12B, so that excess water can be prevented from flowing into the air electrode 12B.

[0058] Second Embodiment Next, a second embodiment of the present invention will be described. In this embodiment, the same parts as in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

[0059] The fuel cell system 10B of this embodiment is provided with a solenoid valve 44A and an orifice 44B in the circulation flow path P9 instead of the three-way flow rate regulating valve 19 of the fuel cell system 10A of the first embodiment. The configuration other than the solenoid valve 44A and the orifice 44B is the same as that of the fuel cell system 10A of the first embodiment shown in FIG.

[0060] 5, the fuel cell system 10B is provided with a solenoid valve 44A and an orifice 44B in the circulation flow path P9. The solenoid valve 44A is provided 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 a 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.

[0061] Next, the operation of the fuel cell system 10B of this embodiment will be described.

[0062] In the control unit 30, a circulation control processing program shown in FIG.

[0063] First, steps S10 to S14 are performed in the same manner as in the first embodiment. If it is determined in step S14 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 the external air, and so in order to reduce the amount of external air taken in, the solenoid valve 44A is opened in step S15. This allows the mixed gas to be supplied to the air electrode 12B at a predetermined circulation flow rate, and the amount of external air taken in corresponding to this supply amount can be reduced.

[0064] In step S18, it is determined whether an instruction to end operation has been given, and if an instruction to end operation has been given, the 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.

[0065] After the determination in step S18 is negative, the process returns to step S10. If it is determined in step S11 that the voltage is greater than V3, the voltage V exceeds the indicator for stopping the supply of the mixed gas to the air electrode 12B, so in step S17, a signal is output to the solenoid valve 44A to close the solenoid valve 44A. Then, the process returns to step S10.

[0066] 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 in order to continue supplying the mixed gas to the air electrode 12B.

[0067] In this way, by controlling whether or not the mixed gas is supplied to the circulation flow path P9 through 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 of supply.

[0068] <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 denoted by the same reference numerals, and detailed description thereof will be omitted.

[0069] The fuel cell system 10C of this embodiment includes 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. Also, a flow rate adjustment three-way valve 46 instead of the flow rate adjustment three-way valve 19. Other configurations are the same as those of the fuel cell system 10A of the first embodiment shown in FIG.

[0070] 7, a combustion exhaust gas circulation flow path P14 is connected to a branch in the middle of the combustion exhaust gas flow 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.

[0071] A three-way flow rate regulating valve 46 is provided at the connection point of the combustion exhaust gas passage P7 with the combustion exhaust gas circulation passage P14. The three-way flow rate regulating 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.

[0072] Similarly to the first embodiment, the fuel cell system 10C of this embodiment also performs a circulation adjustment process (see FIG. 4) during operation. 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, thereby allowing the oxygen in the combustion exhaust gas to be used at the air electrode 12B. This makes it possible to reduce the intake of external air in an amount corresponding to the supply amount of combustion exhaust gas.

[0073] <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 given the same reference numerals, and detailed descriptions thereof will be omitted.

[0074] The fuel cell system 10D of this embodiment is provided with a solenoid valve 48A and an orifice 48B in the combustion exhaust gas circulation passage P14 instead of the three-way flow rate regulating valve 46 of the fuel cell system 10C of the third embodiment. The configuration other than the solenoid valve 48A and the orifice 48B is the same as that of the fuel cell system 10C of the third embodiment shown in FIG.

[0075] 8, the fuel cell system 10D is provided with a solenoid valve 48A and an orifice 48B in the combustion exhaust gas circulation flow path P14. The solenoid valve 48A is provided 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 a 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.

[0076] In the fuel cell system 10D of this embodiment, the circulation control process (see FIG. 6) is also executed during operation, as in the second embodiment. In this way, the circulation control process controls whether or not the combustion exhaust gas is supplied to the combustion exhaust gas circulation flow path P14, thereby supplying the combustion exhaust gas to the air electrode 12B and reducing the intake of external air by an amount corresponding to the supply amount.

[0077] 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 the present invention can be implemented in various modified forms within the scope of the gist of the present invention. [Explanation of symbols]

[0078] 10A, 10B, 10C, 10D Fuel Cell Systems 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 part) 26 Combustor filter 30 Control unit (circulation flow rate adjustment unit) 38 Circulation flow rate adjustment section 44A, 48A solenoid valve (circulation flow rate adjustment part) 44B, 48B Orifice (circulation flow rate adjustment part) C circulation flow rate D Voltage Data P4 Air electrode off-gas passage (air electrode off-gas circulation passage) P6 Combustion air supply pipe (combustion air introduction passage) P9 Circulation flow path P14 Combustion exhaust gas circulation flow path (circulation flow path)

Claims

1. 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:

2. 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 .

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

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