Fuel cell system

Abstract

To provide a fuel cell system which comprises a fuel cell part and materializes shortening of the stop time of the system while preventing deterioration of the fuel cell part due to rapid temperature drop.SOLUTION: A fuel cell system includes: a hot module including a fuel cell part having an anode and a cathode; and a combustion part that combusts anode off-gas discharged from the anode and cathode off-gas discharged from the cathode; and an operation control part that stops an operation by lowering a temperature of the fuel cell part to a target temperature. The hot module further includes: a first anode off-gas flow passage for guiding the anode off-gas to the combustion part, and a first flow volume adjustment part capable of adjusting a flow volume of the anode off-gas flowing through the first anode off-gas flow passage. The operation control part adjusts the flow volume of the anode off-gas flowing from the fuel cell part to the combustion part by controlling the operation of the first flow volume adjustment part so that an actual temperature decrease rate, which is a rate at which the temperature of the fuel cell part decreases, becomes a target temperature decrease rate in the operation stop process.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system. [Background technology]

[0002] Patent Document 1 discloses a fuel cell power generation system that reduces the duration of shutdown while suppressing the progression of fatigue and deterioration of the cell stack due to a sudden drop in temperature during shutdown. The fuel cell power generation system disclosed in Patent Document 1 has a cell stack made up of multiple stacked solid oxide fuel cells that generate electricity through an electrochemical reaction between reformed fuel gas obtained by reforming fuel gas and an oxidant gas containing air, and is equipped with a fuel cell unit that outputs the electromotive force of the cell stack as generated power, an operation control unit that executes a shutdown process to stop operation by lowering the temperature of the fuel cell unit to a target temperature, and a temperature drop rate adjustment means that can freely adjust the temperature drop rate of the fuel cell unit. The temperature drop rate adjustment means can freely adjust the temperature drop rate of the fuel cell unit by adjusting the flow rate of air supplied to the fuel cell unit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-141569 Summary of the Invention [Problem to be solved by the invention]

[0004] As disclosed in Patent Document 1, increasing the flow rate of air supplied to the fuel cell unit may cause a sudden drop in the temperature of the fuel cell unit, which may lead to deterioration. Furthermore, in a fuel cell system equipped with solid oxide fuel cells as disclosed in Patent Document 1, in order to prevent oxidation of the anodes that constitute the fuel cell cells, a small amount of fuel gas (less than during power generation operation) continues to be supplied to the anodes even during shutdown processing until operation completely stops. Therefore, if the time until operation completely stops is long, fuel gas not used for power generation will be wasted, which is undesirable from an economic standpoint.

[0005] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a fuel cell system that prevents deterioration of the fuel cell section due to a sudden drop in temperature while shortening the downtime. [Means for solving the problem]

[0006] The fuel cell system according to the present invention, which achieves the above object, has the following characteristic configuration: a hot module including: a fuel cell section configured by stacking a plurality of fuel cell units each having an anode and a cathode; a reforming section that generates fuel gas by steam reforming a raw fuel supplied from a raw fuel supply section; a fuel gas flow passage that guides the fuel gas generated by the reforming section to the anode; an oxidant gas flow passage that guides oxidant gas supplied from an oxidant gas supply section to the cathode; a combustion section that combusts anode off-gas discharged from the anode and cathode off-gas discharged from the cathode; and a cathode off-gas flow passage that guides the cathode off-gas discharged from the cathode to the combustion section; an operation control unit capable of executing an operation stop process to stop operation by lowering the temperature of the fuel cell unit to a target temperature; A fuel cell system comprising: The hot module comprises: a first anode off-gas flow passage that guides the anode off-gas to the combustion section; a first flow rate adjusting unit capable of adjusting the flow rate of the anode off-gas flowing through the first anode off-gas flow passage; a second anode off-gas flow passage that branches off from the first anode off-gas flow passage and guides the anode off-gas to the raw fuel supply section; a second flow rate adjusting unit capable of adjusting the flow rate of the anode off-gas flowing through the second anode off-gas flow passage; and The operation control unit adjusts the flow rate of the anode off-gas flowing from the fuel cell unit to the combustion unit by controlling the operation of the first flow rate adjustment unit and the second flow rate adjustment unit so that the actual temperature drop rate, which is the rate at which the temperature of the fuel cell unit drops, becomes the target temperature drop rate during the operation shutdown process.

[0007] According to the above characteristic configuration, during the operation shutdown process, the flow rate of anode offgas flowing from the fuel cell unit to the raw fuel supply unit via the second anode offgas flow passage is adjusted by controlling the operation of the second flow rate adjuster so that the actual temperature drop rate, which is the rate at which the temperature of the fuel cell unit drops, matches the target temperature drop rate. The flow rate of anode offgas flowing from the fuel cell unit to the combustion unit via the first anode offgas flow passage is also adjusted by controlling the operation of the first flow rate adjuster, thereby controlling combustion in the combustion unit. As a result, the accuracy of adjusting the actual temperature drop rate of the fuel cell unit can be improved. Therefore, a sudden drop in temperature of the fuel cell unit can be prevented, and a slowdown in the actual temperature drop rate (a decrease in the actual temperature drop rate) can be suppressed. In other words, deterioration of the fuel cell unit due to a sudden drop in temperature can be prevented, and the shutdown time can be shortened.

[0008] Another characteristic configuration of the fuel cell system according to the present invention is: When the actual temperature decreasing rate is slower than the target temperature decreasing rate, the operation control unit controls the operation of the first flow rate adjustment unit and the second flow rate adjustment unit to reduce the flow rate of the anode off-gas flowing from the anode to the combustion unit via the first anode off-gas flow passage, while increasing the flow rate of the anode off-gas flowing from the anode to the raw fuel supply unit via the second anode off-gas flow passage.

[0009] According to the above characteristic configuration, the flow rate of fuel gas supplied to the combustion section can be reduced from the current rate (for example, when comparing the target temperature drop rate with the actual temperature drop rate), thereby suppressing combustion by the combustion section and increasing (speeding up) the actual temperature drop rate. In other words, the downtime can be shortened. Furthermore, the flow rate of anode offgas supplied from the fuel cell section to the raw fuel supply section via the second anode offgas flow passage can be increased from the current rate, which contributes to saving fuel (raw fuel) used for power generation.

[0010] Another characteristic configuration of the fuel cell system according to the present invention is: the oxidant gas supply unit has an oxidant gas supply amount adjustment unit that can adjust the amount of the oxidant gas supplied to the cathode, When the actual temperature drop rate is slower than the target temperature drop rate, the operation control unit controls the operation of the oxidant gas supply amount adjustment unit to increase the flow rate of the cathode offgas flowing from the cathode to the combustion unit via the cathode offgas flow passage.

[0011] According to the above characteristic configuration, the flow rate of oxidant gas supplied to the fuel cell section can be increased from the current level, and the cooling effect of the oxidant gas can increase the actual temperature drop rate, thereby shortening the shutdown time from the start of the shutdown process to the end of the shutdown process (completion of shutdown).

[0012] Another characteristic configuration of the fuel cell system according to the present invention is: When the actual temperature decreasing rate is faster than the target temperature decreasing rate, the operation control unit controls the operation of the first flow rate adjustment unit and the second flow rate adjustment unit to increase the flow rate of the anode off-gas flowing from the anode to the combustion unit via the first anode off-gas flow passage, while decreasing the flow rate of the anode off-gas flowing from the anode to the raw fuel supply unit via the second anode off-gas flow passage.

[0013] According to the above characteristic configuration, by controlling the operation of the second flow rate adjuster, the flow rate of the anode off-gas flowing from the fuel cell unit to the raw fuel supply unit via the second anode off-gas flow passage can be reduced from the current level, and by controlling the operation of the first flow rate adjuster, the flow rate of the anode off-gas flowing from the fuel cell unit to the combustion unit via the first anode off-gas flow passage can be increased from the current level, thereby promoting combustion in the combustion unit and reducing (slowing down) the actual temperature drop rate from the current level, thereby suppressing deterioration of the fuel cell unit due to a sudden drop in temperature.

[0014] Another characteristic configuration of the fuel cell system according to the present invention is: the oxidant gas supply unit has an oxidant gas supply amount adjustment unit that can adjust the amount of the oxidant gas supplied to the cathode, When the actual temperature drop rate is faster than the target temperature drop rate, the operation control unit controls the operation of the oxidant gas supply amount adjustment unit to reduce the flow rate of the cathode off-gas flowing from the cathode to the combustion unit via the cathode off-gas flow passage.

[0015] According to the above-described characteristic configuration, the supply of oxidant gas to the fuel cell unit is suppressed, thereby suppressing the cooling effect of the oxidant gas, thereby making it possible to reduce the actual temperature drop rate compared to the current rate, thereby suppressing deterioration of the fuel cell unit due to a sudden drop in temperature.

[0016] Another characteristic configuration of the fuel cell system according to the present invention is: the hot module further includes a container that houses the reforming unit, the fuel cell unit, the combustion unit, the fuel gas flow channel, the oxidant gas flow channel, and the cathode off-gas flow channel; The first flow rate adjusting unit and the second flow rate adjusting unit are disposed outside the container.

[0017] According to the above characteristic configuration, there is no need to use a first flow rate adjusting unit and a second flow rate adjusting unit that can withstand the temperature (high temperature) inside the hot module, and the degree of freedom in designing the fuel cell system is improved.

[0018] Another characteristic configuration of the fuel cell system according to the present invention is: When the operation control unit determines that the combustion unit has misfired, it controls the operation of the first flow rate adjustment unit and the second flow rate adjustment unit so that the combustion unit can ignite, thereby increasing the flow rate of the anode off-gas flowing from the anode to the combustion unit via the first anode off-gas flow passage and decreasing the flow rate of the anode off-gas flowing from the anode to the raw fuel supply unit via the second anode off-gas flow passage.

[0019] However, with the above-described characteristic configuration, it is determined whether or not a misfire has occurred, and if so, the first flow rate regulator and the second flow rate regulator are controlled so that the combustion unit can ignite, thereby improving the accuracy of adjusting the actual temperature drop rate of the fuel cell unit. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic configuration diagram showing a fuel cell system according to an embodiment; [Figure 2] 10 is a flowchart illustrating an operation stop process according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] A fuel cell system 1 according to an embodiment of the present invention will be described below with reference to the drawings. FIG.

[0022] [Fuel cell system] As shown in FIG. 1, the fuel cell system 1 includes a reforming water supply unit 2, a raw fuel supply unit 3, an oxidizing gas supply unit 4, a hot module 5, and a control unit 10 (an example of an operation control unit).

[0023] [Reformed Water Supply Department] The reforming water supply unit 2 supplies reforming water to the hot module 5. The reforming water is, for example, tap water from which impurities have been removed. The reforming water supply unit 2 includes a reforming water supply path L2 through which the reforming water can flow, a pump 21 that can pump the reforming water, a water tank (not shown) that can store the reforming water, and the like.

[0024] [Raw and fuel supply department] The raw fuel supply unit 3 supplies raw fuel (raw fuel gas) to the hot module 5. The raw fuel contains hydrocarbons, such as city gas or LP gas. The raw fuel supply unit 3 includes a raw fuel supply path L3 through which the raw fuel can flow, a raw fuel blower 31 capable of supplying the raw fuel to the hot module 5, a desulfurization unit 32 that removes sulfur contained in the raw fuel, a raw fuel check valve 33 that prevents backflow of the raw fuel, and a raw fuel pressure gauge 34 that measures the pressure of the raw fuel flowing through the raw fuel supply path L3. The raw fuel pressure gauge 34 is a pressure sensor that transmits information indicating the measured pressure to the control unit 10.

[0025] [Oxidant gas supply unit] The oxidant gas supply unit 4 supplies an oxidant gas (oxidant) to the hot module 5 (cell stack 54). The oxidant gas contains oxygen, and is, for example, air. The oxidant gas supply unit 4 includes an oxidant gas supply channel L4 through which the oxidant gas can flow, an oxidant gas blower 41 (an example of an oxidant gas flow rate adjuster) that can supply the oxidant gas to the hot module 5, and an oxidant gas pressure gauge 42 that measures the pressure of the oxidant gas flowing through the oxidant gas supply channel L4. The oxidant gas pressure gauge 42 is a pressure sensor that transmits information indicating the measured pressure to the control unit 10.

[0026] [Hot Module] The hot module 5 is a fuel cell module that generates electricity by reacting hydrogen and oxygen. The hot module 5 has an inner container 51 (an example of a container), a vaporization section 52, a reforming section 53, a cell stack 54 (an example of a fuel cell section), a combustion section 55, a thermometer T, a fuel gas flow channel L51, an oxidant gas flow channel L52, a cathode offgas flow channel L53, a first anode offgas flow channel L54, a second anode offgas flow channel L55, a first adjustment valve V1 (an example of a first flow rate adjustment section), a second adjustment valve V2 (an example of a second flow rate adjustment section), a check valve V3, a first condenser section C1, a second condenser section C2, and an offgas blower B1.

[0027] A reforming water supply unit 2 (reforming water supply channel L2), a raw fuel supply unit 3 (raw fuel supply channel L3), and an oxidant gas supply unit 4 (oxidant gas supply channel L4) are connected to the hot module 5, and reforming water, raw fuel, and oxidant gas are supplied to the hot module 5. In this embodiment, the raw fuel is supplied to the vaporization unit 52, and the oxidant gas is supplied to the cell stack 54.

[0028] [Inner container] The internal vessel 51 has thermal insulation properties and accommodates the vaporization section 52, the reforming section 53, the cell stack 54, the combustion section 55, the thermometer T, the fuel gas flow passage L51, the oxidant gas flow passage L52, the cathode offgas flow passage L53, and part of the first anode offgas flow passage L54. In other words, the remainder of the first anode offgas flow passage L54, the second anode offgas flow passage L55, the first adjustment valve V1, the second adjustment valve V2, the check valve V3, the first condenser C1, the second condenser C2, and the offgas blower B1 are disposed outside the internal vessel 51.

[0029] [Vaporization section] In addition to the raw fuel and reforming water, combustion heat generated in the combustion unit 55 (described later) is supplied to the vaporization unit 52. The vaporization unit 52 vaporizes the reforming water by utilizing the combustion heat to generate steam. The vaporization unit 52 supplies a mixed gas obtained by mixing the generated steam and raw fuel to the reforming unit 53.

[0030] [Modification section] The reforming unit 53 generates fuel gas by steam reforming the mixed gas (raw fuel). The reforming unit 53 generates fuel gas by steam reforming the mixed gas by utilizing the combustion heat generated in the combustion unit 55. The fuel gas generated in the reforming unit 53 is supplied to the cell stack 54 via the fuel gas flow path L51.

[0031] [Cell stack] The cell stack 54 generates electricity based on the fuel gas and the oxidant gas. The cell stack 54 is composed of a plurality of stacked cells. Each cell generates electricity by chemically reacting hydrogen contained in the fuel gas with oxygen contained in the oxidant gas. In this embodiment, the cell is a solid oxide fuel cell and includes an anode 541 (combustion electrode), a cathode 542 (air electrode), and an electrolyte 543. For this reason, the fuel cell system 1 in this embodiment is also referred to as a solid oxide fuel cell system. The thermometer T is a temperature sensor and is disposed in a position where it can measure the temperature of the cell stack 54. The thermometer T measures the temperature of the cell stack 54 and transmits information indicating the measured temperature to the control unit 10. The temperature of the cell stack 54 during power generation operation is, for example, not lower than 600°C and lower than 800°C. When operation is completely stopped, the temperature of the cell stack 54 drops to approximately room temperature.

[0032] Fuel gas is supplied to the anode 541 via a fuel gas flow passage L51. The anode 541 is also connected to the combustion unit 55 via a first anode offgas flow passage L54, through which anode offgas can flow. Fuel gas (anode offgas) not used for power generation at the anode 541 is supplied to the combustion unit 55 via the first anode offgas flow passage L54. In the first anode offgas flow passage L54, a check valve V3, a first adjustment valve V1, and a first condenser C1 (steam condenser) are arranged in this order from upstream to downstream in the flow direction of the anode offgas. The fuel gas (anode offgas) not used for power generation at the anode 541 can also be supplied to the raw fuel supply unit 3 via a second anode offgas flow passage L55. The second anode offgas flow passage L55 branches off from the first anode offgas flow passage L54 between the check valve V3 and the first adjustment valve V1. In the second anode off-gas flow passage L55, a second adjustment valve V2, an off-gas blower B1, and a second condenser C2 (steam condenser) are arranged in this order from upstream in the flow direction of the anode off-gas. The off-gas blower B1 sends the anode off-gas to the raw fuel supply unit 3. The anode off-gas sent to the raw fuel supply unit 3 is supplied to the vaporization unit 52. The first condenser C1 and the second condenser C2 condense the moisture contained in the anode off-gas and separate it into a gas phase (anode off-gas) and a liquid phase (water).

[0033] The cathode 542 is supplied with an oxidant gas through an oxidant gas flow passage L52. The cathode 542 is also connected to the combustion unit 55 through a cathode offgas flow passage L53 through which cathode offgas can flow. The oxidant gas (cathode offgas) not used for power generation at the cathode 542 is supplied to the combustion unit 55 through the cathode offgas flow passage L53.

[0034] [Combustion section] The combustion section 55 generates combustion heat by combusting the anode off-gas and the cathode off-gas (the combustible components contained in the anode off-gas and the oxygen contained in the cathode off-gas).

[0035] The combustion section 55 has an ignition section 551 that can be ignited, and the combustion section 55 is ignited by the ignition section 551 and starts combustion. When the combustion section 55 starts combustion, it generates combustion heat to raise the temperature of the internal space (vaporization section 52 and reforming section 53) of the hot module 5 and generate combustion exhaust gas. The combustion exhaust gas is led to the outside of the hot module 5 via a combustion exhaust gas flow passage (not shown) and a combustion catalyst section (not shown).

[0036] The combustion unit 55 further includes an unburned gas detection unit 552 that detects unburned gas in the combustion unit 55. The unburned gas detection unit 552 measures the concentration of unburned gas, for example, and transmits information indicating the concentration of unburned gas to the control unit 10.

[0037] [Control Unit] The control unit 10 is composed of a microcontroller including a processor, a semiconductor memory, etc. The control unit 10 controls the operation of each of the reforming water supply unit 2, the raw fuel supply unit 3, the oxidant gas supply unit 4, and the hot module 5. During power generation operation, the control unit 10 controls the generated power from the cell stack 54 to be the rated output (e.g., 700 W).

[0038] In this embodiment, at a predetermined timing during power generation operation, the control unit 10 executes a shutdown process to completely stop operation by lowering the temperature of the cell stack 54 to a target temperature. The predetermined timing is, for example, a timing scheduled in advance for shutdown, a timing when a user or maintenance worker issues an instruction to shut down operation, etc.

[0039] The control unit 10 also has a storage unit 101 configured with a semiconductor memory or the like, and various data, program data, etc. are stored in the storage unit 101. By executing the programs stored in the storage unit 101, the control unit 10 functions as a target temperature drop rate setting unit 102, a temperature drop rate calculation unit 103, a temperature drop rate comparison unit 104, a misfire determination unit 105, and an end determination unit 106.

[0040] The target temperature decreasing rate setting unit 102 sets a target temperature decreasing rate T1 that is a target for the temperature decreasing rate of the cell stack 54. The target temperature decreasing rate setting unit 102 sets the target temperature decreasing rate T1 based on information such as the flow rate of the fuel gas (raw fuel), the flow rate of the oxidant gas, the actual operating time of the hot module 5, the outside air temperature, the temperature of the cell stack 54 (current temperature), and the time elapsed since the operation shutdown process. Information indicating the target temperature decreasing rate T1 is stored in the memory unit 101.

[0041] The temperature drop rate calculation unit 103 calculates the rate at which the temperature of the cell stack 54 is actually dropping (hereinafter referred to as the actual temperature drop rate T2) based on information indicating the temperature of the cell stack 54 transmitted from the thermometer T. More specifically, the temperature drop rate calculation unit 103 calculates the actual temperature drop rate T2 based on changes in the temperature of the cell stack 54 over a preset measurement interval. Specifically, the temperature drop rate calculation unit 103 calculates the actual temperature drop rate T2 by dividing the difference between information (value) indicating the temperature of the cell stack 54 at a certain timing and information (value) indicating the temperature of the cell stack 54 after the measurement interval (e.g., 5 seconds, 10 seconds) has elapsed by the value of the measurement interval (e.g., 5, 10).

[0042] The temperature drop rate comparison unit 104 compares information indicating the target temperature drop rate T1 stored in the memory unit 101 with the actual temperature drop rate T2 calculated by the temperature drop rate calculation unit 103, and transmits information indicating the comparison result to the control unit 10.

[0043] The misfire determination unit 105 determines whether or not the combustion unit 55 has misfired based on the information transmitted from the unburned gas detection unit 552 .

[0044] The termination determination unit 106 determines whether the temperature of the cell stack 54 has dropped to the target temperature. If the termination determination unit 106 determines that the temperature of the cell stack 54 has dropped to the target temperature, it terminates the operation shutdown process. Note that information indicating the target temperature is set in advance by the designer of the fuel cell system 1 and is stored in the storage unit 101.

[0045] Next, the operation stop process will be described with reference to Figures 1 and 2. Figure 2 is a flowchart showing the operation stop process.

[0046] 1 and 2, when the operation shutdown process is started, the control unit 10 fully opens the first adjustment valve V1 and fully closes the second adjustment valve V2 (step S101), and stops power generation by the cell stack 54 (step S103). The raw fuel blower 31 and the oxidant gas blower 41 are operated in a preset operating state during the operation shutdown process. Specifically, the raw fuel blower 31 is controlled so that the flow rate of the raw fuel is smaller than during normal operation (power generation operation), and the oxidant gas blower 41 is controlled so that the flow rate of the oxidant gas is smaller than during normal operation (power generation operation). The pump 21 is stopped.

[0047] Next, the control unit 10 (target temperature decreasing rate setting unit 102) sets the target temperature decreasing rate T1 (step S105). Information indicating the set target temperature decreasing rate T1 is stored in the storage unit 101.

[0048] Next, the control unit 10 (temperature decreasing rate calculation unit 103) calculates the actual temperature decreasing rate T2 (step S107). As described above, the control unit 10 calculates the actual temperature decreasing rate T2 by acquiring the temperature of the cell stack 54 at measurement intervals.

[0049] Next, the control unit 10 (temperature decreasing rate comparison unit 104) compares the target temperature decreasing rate T1 with the actual temperature decreasing rate T2 calculated in step S107 (step S109). Specifically, the control unit 10 determines whether the target temperature decreasing rate T1 is equal to or greater than the actual temperature decreasing rate T2. Hereinafter, the time when step S109 is performed will be referred to as the time of comparison and determination.

[0050] When the control unit 10 determines that the target temperature decreasing rate T1 is equal to or greater than the actual temperature decreasing rate T2, that is, that the actual temperature decreasing rate T2 is slower than the target temperature decreasing rate T1 (step S109; Yes), it reduces the flow rate of the anode offgas flowing from the anode 541 to the combustion unit 55 via the first anode offgas flow passage L54 from the current value (for example, at the time of the comparison or execution of the step) (in this embodiment, it increases the flow rate of the anode offgas flowing from the anode 541 to the raw fuel supply unit 3 via the second anode offgas flow passage L55 from the current value), and further increases the flow rate of the cathode offgas supplied from the cathode 542 of the cell stack 54 to the combustion unit 55 from the current value. Specifically, it throttles the first adjustment valve V1 to reduce its opening from the current value, while loosening the second adjustment valve V2 to increase its opening from the current value, thereby increasing the output of the oxidant gas blower 41 of the oxidant gas supply unit 4 (step S111). The first adjusting valve V1 may be in a closed state, and the second adjusting valve V2 may be in a fully open state.

[0051] On the other hand, when the control unit 10 (temperature decreasing rate comparison unit 104) determines that the target temperature decreasing rate T1 is not equal to or greater than the actual temperature decreasing rate T2 (step S109; No), it determines whether the target temperature decreasing rate T1 is less than the actual temperature decreasing rate T2 (step S113).

[0052] When the control unit 10 determines that the target temperature drop rate T1 is less than the actual temperature drop rate T2, that is, that the actual temperature drop rate T2 is faster than the target temperature drop rate T1 (step S113; Yes), it controls the operation of the oxidant gas blower 41 of the oxidant gas supply unit 4 to reduce the flow rate of the oxidant gas flowing from the cathode 542 to the combustion unit 55 from the current level (step S115).

[0053] Next, if the flow rate of the anode off gas flowing from the anode 541 to the combustion section 55 can be increased, the control section 10 increases the flow rate of the anode off gas flowing from the anode 541 to the combustion section 55 from the current rate. Also, if the flow rate of the anode off gas flowing from the anode 541 to the raw fuel supply section 3 can be decreased, the control section 10 decreases the flow rate of the anode off gas flowing from the anode 541 to the raw fuel supply section 3 from the current rate. Specifically, if the first regulating valve V1 can be loosened, the first regulating valve V1 is loosened to increase the opening degree from the current rate, and if the second regulating valve V2 can be throttled, the second regulating valve V2 is throttled to a smaller opening degree from the current rate (step S117).

[0054] Next, the control unit 10 (misfire determination unit 105) determines whether the combustion unit 55 has misfired (step S119). When the control unit 10 determines that the combustion unit 55 has misfired (step S119; Yes), the process returns to step S117. Specifically, the control unit 10 controls the operation of the first adjustment valve V1 to increase the flow rate of anode offgas flowing from the anode 541 to the combustion unit 55 via the first anode offgas flow passage L54 from the current level so that the combustion unit 55 can ignite. Note that in this embodiment, the control unit 10 also controls the operation of the second adjustment valve V2 to decrease the flow rate of anode offgas flowing from the anode 541 to the raw fuel supply unit 3 via the second anode offgas flow passage L55 from the current level.

[0055] If it is determined that the combustion unit 55 has not misfired (step S119; No), if it is determined that the target temperature drop rate T1 is not less than the actual temperature drop rate T2 (step S113; No), or after processing step S111, the control unit 10 (termination determination unit 106) determines whether the temperature of the cell stack 54 has dropped to the target temperature (step S121).

[0056] If the control unit 10 determines that the temperature of the cell stack 54 has not dropped to the target temperature (step S121; No), the control unit 10 returns to step S105 and repeats the processing from step S105 onwards. On the other hand, if the control unit 10 determines that the temperature of the cell stack 54 has dropped to the target temperature (step S121; Yes), the control unit 10 ends the operation shutdown processing.

[0057] As described above, the temperature of the cell stack 54 during power generation operation is, for example, between 600°C and 800°C. By the time the fuel cell system 1 is completely shut down, the temperature of the cell stack 54 has dropped to room temperature (for example, between 10°C and 40°C). Therefore, if the temperature of the cell stack 54 is lowered from the operating temperature to approximately room temperature in a short period of time during the operation shutdown process, thermal stress may be generated in the cell stack 54, which may cause deterioration of the cell stack 54 and lead to breakage. Therefore, it is necessary to gradually (over time) lower the temperature of the cell stack 54. However, during the operation shutdown process, a small amount of fuel gas (less than during power generation operation) is continuously supplied to prevent oxidation of the anode 541 (combustion electrode). In other words, if it takes a long time for the operation to be completely shut down, fuel gas not used for power generation will continue to be supplied, which is undesirable from an economical standpoint. However, according to the present embodiment, the flow rate of anode offgas flowing from the cell stack 54 to the raw fuel supply unit 3 via the second anode offgas flow passage L55 is adjusted by controlling the operation of the second adjustment valve V2, and the flow rate of anode offgas flowing from the cell stack 54 to the combustion unit 55 is adjusted by controlling the operation of the first adjustment valve V1, thereby controlling combustion (generation of combustion heat) in the combustion unit 55. This also reduces heat transfer (heat input) from the combustion unit 55 to the cell stack 54. As a result, the accuracy of adjusting the actual temperature decrease rate T2 of the cell stack 54 can be improved. In other words, a sudden temperature drop in the cell stack 54 can be prevented, and there is no need to unnecessarily reduce the actual temperature decrease rate T2. In other words, deterioration of the cell stack 54 due to a sudden temperature drop can be prevented, and downtime can be shortened.

[0058] <Another embodiment> The configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradictions arise. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention.

[0059] (1) The configuration of the hot module 5 in the above embodiment is an example, and the configuration within the hot module 5 can be changed as appropriate. For example, the raw fuel may be directly supplied to the reforming unit 53 from the raw fuel supply unit 3 without passing through the vaporization unit 52.

[0060] (2) In the above embodiment, the control unit 10 adjusted (decreased or increased) the flow rate of the anode off-gas flowing from the anode 541 of the cell stack 54 to the combustion unit 55 by controlling the operation of the first adjustment valve V1 and the second adjustment valve V2, but the control unit 10 may also adjust (decreased or increased) the flow rate of the anode off-gas flowing from the anode 541 of the cell stack 54 to the combustion unit 55 by controlling the operation of only the first adjustment valve V1.

[0061] (3) In step S111 of the operation shutdown process in the above embodiment, the flow rate of the anode offgas flowing from the anode 541 of the cell stack 54 to the combustion section 55 is decreased while the flow rate of the cathode offgas flowing from the cathode 542 of the cell stack 54 to the combustion section 55 is increased. However, after the flow rate of the anode offgas is decreased, the target temperature decrease rate T1 may be compared with the actual temperature decrease rate T2 calculated in step S107 (step S109), and the flow rate of the cathode offgas flowing from the cathode 542 of the cell stack 54 to the combustion section 55 may be increased. Specifically, the actual temperature decrease rate T2 may be calculated again, and the target temperature decrease rate T1 may be compared with the actual temperature decrease rate T2 again, and the flow rate of the cathode offgas flowing from the cathode 542 of the cell stack 54 to the combustion section 55 may be increased depending on the result of the calculation. Furthermore, in step S115 of the operation shutdown process, the flow rate of the cathode offgas flowing from the cathode 542 of the cell stack 54 to the combustion section 55 may be reduced, and the flow rate of the anode offgas flowing from the anode 541 of the cell stack 54 to the combustion section 55 may be increased. In other words, step S115 and step S117 may be executed simultaneously. [Industrial Applicability]

[0062] The present invention can be used in a fuel cell system. [Explanation of symbols]

[0063] 1: Fuel cell system 3: Raw fuel supply section 4: Oxidant gas supply section 5: Hot Module 10: Control unit (operation control unit) 41: Oxidant gas blower (oxidant gas flow rate adjusting unit) 51: Inner container (container) 53: Modification section 54: Cell stack (fuel cell section) 55: Combustion section 541: Anode 542: Cathode L51: Fuel gas flow passage L52: Oxidant gas flow passage L53: Cathode off-gas flow passage L54: First anode off-gas passage L55: Second anode off-gas passage T1:Target cooling rate T2:Actual cooling rate V1: First adjusting valve (first flow rate adjusting part) V2: Second adjustment valve (second flow rate adjustment part)

Claims

1. a hot module including: a fuel cell section configured by stacking a plurality of fuel cell units each having an anode and a cathode; a reforming section that generates fuel gas by steam reforming a raw fuel supplied from a raw fuel supply section; a fuel gas flow passage that guides the fuel gas generated by the reforming section to the anode; an oxidant gas flow passage that guides oxidant gas supplied from an oxidant gas supply section to the cathode; a combustion section that combusts anode off-gas discharged from the anode and cathode off-gas discharged from the cathode; and a cathode off-gas flow passage that guides the cathode off-gas discharged from the cathode to the combustion section; an operation control unit capable of executing an operation stop process to stop operation by lowering the temperature of the fuel cell unit to a target temperature; A fuel cell system comprising: The hot module comprises: a first anode off-gas flow passage that guides the anode off-gas to the combustion section; a first flow rate adjusting unit capable of adjusting the flow rate of the anode off-gas flowing through the first anode off-gas flow passage; a second anode off-gas flow passage branching from the first anode off-gas flow passage and guiding the anode off-gas to the raw fuel supply section; a second flow rate adjusting unit capable of adjusting the flow rate of the anode off-gas flowing through the second anode off-gas flow passage; and In the fuel cell system, the operation control unit adjusts the flow rate of the anode off-gas flowing from the fuel cell unit to the combustion unit by controlling the operation of the first flow rate adjustment unit and the second flow rate adjustment unit so that an actual temperature drop rate, which is the rate at which the temperature of the fuel cell unit drops, becomes a target temperature drop rate during the operation shutdown process.

2. 2. The fuel cell system according to claim 1, wherein, when the actual temperature decreasing rate is slower than the target temperature decreasing rate, the operation control unit controls the operation of the first flow rate adjustment unit and the second flow rate adjustment unit to decrease the flow rate of the anode off gas flowing from the anode to the combustion unit via the first anode off gas flow passage, while increasing the flow rate of the anode off gas flowing from the anode to the raw fuel supply unit via the second anode off gas flow passage.

3. the oxidant gas supply unit has an oxidant gas supply amount adjustment unit that can adjust the amount of the oxidant gas supplied to the cathode, 3. The fuel cell system according to claim 2, wherein, when the actual temperature decreasing rate is slower than the target temperature decreasing rate, the operation control unit controls the operation of the oxidant gas supply amount adjustment unit to increase the flow rate of the cathode offgas flowing from the cathode to the combustion unit via the cathode offgas flow passage.

4. 2. The fuel cell system according to claim 1, wherein, when the actual temperature decreasing rate is faster than the target temperature decreasing rate, the operation control unit controls the operation of the first flow rate adjustment unit and the second flow rate adjustment unit to increase the flow rate of the anode off gas flowing from the anode to the combustion unit via the first anode off gas flow passage, while decreasing the flow rate of the anode off gas flowing from the anode to the raw fuel supply unit via the second anode off gas flow passage.

5. the oxidant gas supply unit has an oxidant gas supply amount adjustment unit that can adjust the amount of the oxidant gas supplied to the cathode, 5. The fuel cell system according to claim 4, wherein, when the actual temperature decreasing rate is faster than the target temperature decreasing rate, the operation control unit controls the operation of the oxidant gas supply amount adjustment unit to reduce the flow rate of the cathode offgas flowing from the cathode to the combustion unit via the cathode offgas flow passage.

6. the hot module further includes a container that houses the reforming unit, the fuel cell unit, the combustion unit, the fuel gas flow channel, the oxidant gas flow channel, and the cathode off-gas flow channel; The fuel cell system according to claim 1 , wherein the first flow rate adjusting unit and the second flow rate adjusting unit are disposed outside the container.

7. 7. The fuel cell system according to claim 1, wherein, when the operation control unit determines that the combustion unit has misfired, the operation control unit controls the operation of the first flow rate adjustment unit and the second flow rate adjustment unit so that the combustion unit can ignite, thereby increasing the flow rate of the anode offgas flowing from the anode to the combustion unit via the first anode offgas flow passage and decreasing the flow rate of the anode offgas flowing from the anode to the raw fuel supply unit via the second anode offgas flow passage.

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