Fuel battery system

Abstract

To provide a fuel battery system capable of performing a temperature raising process under a preferred condition.SOLUTION: An operation control part 21 of a fuel battery system performs a reference flow rate determination process of determining, as a reference raw fuel flow rate and a reference air flow rate, the raw fuel flow rate and the air flow rate, respectively, in a first temperature raising process in which a required time until a temperature of a predetermined portion reaches a predetermined target temperature is short while the first temperature raising process is performed after the first temperature raising process is started among a plurality of first temperature raising processes in which at least one of the raw fuel flow rate and the air flow rate performed in the past is different from each other. In a start-up step after the reference flow rate determination process is performed, a second temperature raising process is performed in which an off-gas discharged from a cell stack is combusted in a combustion part 9 in a state where the flow rate per unit time of the raw fuel supplied to a reforming part 8 is constant at the reference raw fuel flow rate and the flow rate per unit time of the air supplied to the cell stack is constant at the reference air flow rate, thereby raising the temperature inside a hot module 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 (JP 2019-121466 A) describes a fuel cell system having a combustion section (4) that combusts offgas discharged from a cell stack (fuel cell G) and a combustion exhaust gas path (combustion gas path 27) that guides the combustion exhaust gas generated in the combustion section. Then, in a startup process that transitions the cell stack to a state where it can generate electricity, a temperature rise process is performed to raise the temperature in the hot module to a predetermined temperature. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-121466 Summary of the Invention [Problem to be solved by the invention]

[0004] In a fuel cell system, a heating process is required to raise the temperature in the hot module to a predetermined temperature during the startup process, for example, for several hours. In other words, the heating process takes up most of the time required from the start of the startup process to the start of power generation. Therefore, it is preferable to shorten the time required for the heating process.

[0005] Furthermore, when a raw fuel containing hydrocarbons, such as city gas, used in a fuel cell system is supplied via a microcomputer meter with a gas leak detection function, the supply of the raw fuel to the fuel cell system must be stopped periodically, such as approximately once a month, to avoid erroneous determination that the raw fuel has leaked. Therefore, if the time required for the temperature rise process can be shortened, this is advantageous because it will extend the period of time during which the fuel cell system can generate electricity per month.

[0006] The temperature rise process is performed by combustion in the combustion section inside the hot module, but the combustibility of the combustion section is significantly affected by variations in mass production, so there is a problem that the desirable flow rates per unit time of the combustible components and the air (oxygen) supplied to the combustion section to efficiently raise the temperature inside the hot module vary from one fuel cell system to another.

[0007] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a fuel cell system that can perform a temperature increase process under favorable conditions. [Means for solving the problem]

[0008] The fuel cell system according to the present invention for achieving the above object comprises a hot module having a cell stack with a container in which a plurality of fuel cell units, each having an anode and a cathode, are provided inside the container, a reforming unit that generates fuel gas by steam reforming a raw fuel, a fuel gas supply path that supplies the fuel gas from the reforming unit to the anode, and a combustion unit that combusts off-gas discharged from the cell stack; a raw fuel supply unit that supplies the raw fuel from outside the container to the reforming unit; an air supply unit that supplies air from the outside of the container to the cell stack; a reforming water supply unit that supplies reforming water from the outside of the container to the reforming unit; an operation control unit; A fuel cell system configured so that heat generated in the combustion section is transferred to the reforming section, a temperature measuring device for determination that measures the temperature of a predetermined portion inside the hot module; The operation control unit In the start-up process of the cell stack, a raw fuel flow rate, which is the flow rate per unit time of the raw fuel supplied to the reforming section, is kept constant, and an air flow rate, which is the flow rate per unit time of the air supplied to the cell stack, is kept constant, and a first temperature-raising process is performed to raise the temperature inside the hot module by combusting the off-gas discharged from the cell stack in the combustion section, performing a reference flow rate determination process to determine, as a reference raw fuel flow rate and a reference air flow rate, respectively, the raw fuel flow rate and the air flow rate in the first temperature-raising process in which, after the start of the first temperature-raising process, a required time for the temperature of the predetermined portion to reach a predetermined target temperature during the first temperature-raising process was short among a plurality of first temperature-raising processes that have been performed in the past in which at least one of the raw fuel flow rate and the air flow rate differ from one another; In the startup process after the reference flow rate determination process, the flow rate per unit time of the raw fuel supplied to the reforming section is kept constant at the reference raw fuel flow rate, and the flow rate per unit time of the air supplied to the cell stack is kept constant at the reference air flow rate, and a second heating process is performed to increase the temperature inside the hot module by burning the off-gas discharged from the cell stack in the combustion section.

[0009] According to the above-described characteristic configuration, the reference flow rate determination process determines the reference raw fuel flow rate and the reference air flow rate, respectively, of the first heating process performed multiple times during the cell stack startup process, in which the off-gas discharged from the cell stack is combusted in the combustion unit to raise the temperature inside the hot module. The first heating process, which took the shortest time for the temperature of a predetermined location inside the hot module to reach the predetermined target temperature after the first heating process was started, i.e., the first heating process that efficiently raised the temperature inside the hot module. The second heating process uses the reference raw fuel flow rate and the reference air flow rate determined in the reference flow rate determination process to combust the off-gas discharged from the cell stack in the combustion unit to raise the temperature inside the hot module. In other words, the heating process is performed with a raw fuel flow rate and an air flow rate appropriate for each individual fuel cell system. Therefore, it is possible to provide a fuel cell system that can perform the temperature increase process under favorable conditions.

[0010] Another characteristic configuration of the fuel cell system of the present invention is that when the reference raw fuel flow rate and the reference air flow rate are determined by the reference flow rate determination process, the operation control unit performs the second temperature rise process using the reference raw fuel flow rate and the reference air flow rate in the startup process that is performed during a predetermined period thereafter.

[0011] According to the above-described characteristic configuration, the reference raw fuel flow rate and the reference air flow rate determined by the reference flow rate determination process are used in the start-up process that is performed during a predetermined period thereafter, so that the temperature inside the hot module can be increased efficiently and with a certain degree of certainty during that predetermined period.

[0012] Another characteristic configuration of the fuel cell system of the present invention is that the operation control unit performs the first temperature rise process in which at least one of the raw fuel flow rate and the air flow rate is different from each other during the multiple startup processes that are performed after the predetermined period has elapsed.

[0013] According to the above characteristic configuration, a reference flow rate determination process can be performed based on the results of multiple startup processes newly performed after a predetermined period of time has elapsed.The reference raw fuel flow rate and reference air flow rate determined in the reference flow rate determination process are then used to perform the second temperature rise process for the subsequent predetermined period of time.In other words, by periodically updating the reference raw fuel flow rate and reference air flow rate, even if the fuel cell system has deteriorated over time, for example, the temperature rise process can be performed with a raw fuel flow rate and air flow rate appropriate for that deterioration state.

[0014] Another characteristic configuration of the fuel cell system of the present invention is that, in the reference flow rate determination process, the operation control unit determines the reference raw fuel flow rate and the reference air flow rate to be the raw fuel flow rate and the air flow rate, respectively, in the first heating process that took the shortest time among multiple first heating processes performed in the startup process after the cell stack's power generation stop period was longer than a set period.

[0015] The temperature inside the hot module at the start of the cell stack startup process varies depending on the length of the previous cell stack power generation suspension period. Therefore, if the cell stack power generation suspension period is short, i.e., if the temperature inside the hot module is high at the start of the cell stack startup process, the time required for the first heating process to raise the temperature of a specific location inside the hot module to the target temperature is likely to be short. On the other hand, if the cell stack power generation suspension period is long, i.e., if the temperature inside the hot module is low at the start of the cell stack startup process, the time required for the first heating process to raise the temperature of a specific location inside the hot module to the target temperature is likely to be long. Therefore, if the above-mentioned required time (i.e., the time it takes for the temperature of a specific location during the first heating process to reach the target temperature after the start of the first heating process) is measured during a first heating process performed during a startup process following significantly different cell stack power generation suspension periods, the reliability of the reference raw fuel flow rate and the reference air flow rate determined in the reference flow rate determination process will be low. Therefore, in this characteristic configuration, in the reference flow rate determination process, the operation control unit determines the reference raw fuel flow rate and the reference air flow rate, respectively, from the first heating process that took the shortest time among multiple first heating processes performed in the startup process after the cell stack power generation stop period was equal to or longer than the set period, i.e., after the temperature inside the hot module had dropped to a certain low level at the time the cell stack startup process was started.As a result, the second heating process can be performed using a reference raw fuel flow rate and a reference air flow rate that are somewhat reliable.

[0016] Another characteristic configuration of the fuel cell system of the present invention is that, in the reference flow rate determination process, the operation control unit determines the reference raw fuel flow rate and the reference air flow rate for each temperature range of the specified portion when the first heating process is started, and performs the second heating process using the reference raw fuel flow rate and the reference air flow rate corresponding to the temperature range of the specified portion when the second heating process is started.

[0017] If the internal temperature of the hot module is high when the cell stack startup process is initiated, the time required for the temperature of a predetermined location inside the hot module to reach the target temperature through the first heating process is likely to be shorter. Conversely, if the internal temperature of the hot module is low when the cell stack startup process is initiated, the time required for the temperature of a predetermined location inside the hot module to reach the target temperature through the first heating process is likely to be longer. Therefore, if the above-mentioned required time (i.e., the time it takes for the temperature of a predetermined location during the first heating process after the start of the first heating process to reach the target temperature) is measured during a first heating process when the internal temperature of the hot module at the start of the cell stack startup process varies greatly, the reliability of the reference raw fuel flow rate and reference air flow rate determined in the reference flow rate determination process will be low. Therefore, in this characteristic configuration, the operation control unit determines a reference raw fuel flow rate and a reference air flow rate for each temperature range of the predetermined portion when the first heating process is started in the reference flow rate determination process, and performs the second heating process using the reference raw fuel flow rate and the reference air flow rate corresponding to the temperature range of the predetermined portion when the second heating process is started. As a result, the second heating process can be performed using a reference raw fuel flow rate and a reference air flow rate with a certain degree of reliability. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram illustrating the configuration of a fuel cell system. [Figure 2] 4 is a flowchart illustrating the operation of a startup process of the fuel cell system. DETAILED DESCRIPTION OF THE INVENTION

[0019] BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram illustrating the configuration of a fuel cell system according to an embodiment of the present invention.

[0020] The fuel cell system has a container 1, and inside the container 1 is a cell stack 7 having a plurality of fuel cell cells 3 each having an anode 4 and a cathode 6, a reforming section 8 that generates fuel gas by steam reforming a raw fuel containing hydrocarbons such as city gas, a fuel gas supply path 15 that supplies fuel gas from the reforming section 8 to the anode 4, and a hot module 2 that has a combustion section 9 that combusts off-gas discharged from the cell stack 7.

[0021] The fuel cell system also includes a raw fuel supply unit 10 that supplies raw fuel to the reforming unit 8 from outside the container 1, an air supply unit 11 that supplies air to the cell stack 7 from outside the container 1, a reforming water supply unit 12 that supplies reforming water to the reforming unit 8 from outside the container 1, and an operation control unit 21.

[0022] Reforming water is supplied to the reforming section 8 via a reforming water supply channel 14. The reforming water supply channel 14 is provided with a reforming water supply unit 12, which is realized using a pump, a flow meter, etc. and supplies reforming water. The reforming water supply unit 12 can adjust the flow rate of reforming water per unit time supplied to the reforming section 8. In the reforming section 8, combustion heat generated in a combustion section 9, which will be described later, is transferred to vaporize the reforming water supplied from the reforming water supply unit 12. Note that a vaporizer that vaporizes the reforming water supplied by the reforming water supply unit 12 may be provided separately from the reforming section 8. In this case, the water vapor vaporized by the vaporizer is supplied to the reforming section 8. The operation of the reforming water supply unit 12 is controlled by an operation control unit 21 .

[0023] Furthermore, a raw fuel containing hydrocarbons is supplied to the reforming unit 8 via a raw fuel supply path 13. A raw fuel supply path 13 is provided with a raw fuel supply unit 10 that supplies the raw fuel and is realized using a blower, a flow meter, or the like. The raw fuel supply unit 10 can adjust the flow rate of the raw fuel per unit time that is supplied to the reforming unit 8. When a vaporization unit as described above is provided, the raw fuel may be supplied to the vaporization unit, and the steam generated in the vaporization unit and the supplied raw fuel may be mixed in the vaporization unit. The operation of the raw fuel supply unit 10 is controlled by an operation control unit 21 .

[0024] The reforming section 8 is supplied with combustion heat generated in the combustion section 9, which will be described later. The reforming section 8 then steam reforms the raw fuel supplied from the raw fuel supply section 10 to generate fuel gas containing hydrogen. The fuel gas generated in the reforming section 8 flows toward the cell stack 7 via a fuel gas supply path 15. When fuel gas is not being generated in the reforming section 8, the raw fuel flows through the fuel gas supply path 15.

[0025] The cell stack 7 includes a plurality of fuel cells 3 each having an anode 4, a cathode 6, and an electrolyte 5. For example, the fuel cells 3 are solid oxide fuel cells 3 that use a solid electrolyte.

[0026] Each fuel cell 3 generates power using the fuel gas produced in the reforming unit 8 and air (oxygen) supplied from the air supply unit 11. Specifically, fuel gas is supplied to the anode 4 via a fuel gas supply path 15, and air (oxygen) is supplied to the cathode 6 via an air supply path 19. The air supply path 19 is provided with an air supply unit 11 that supplies air and is realized using a pump, a flow meter, etc. The air supply unit 11 can adjust the flow rate of air per unit time that is supplied to the cell stack 7. The operation of the air supply unit 11 is controlled by an operation control unit 21 .

[0027] Note that not all of the hydrogen and other components contained in the fuel gas supplied to the anode 4 are used for power generation; the anode off-gas discharged from the anode 4 also contains hydrogen. When fuel gas is not being generated in the reforming unit 8, the raw fuel flows through the fuel gas supply path 15. In this case, the anode off-gas discharged from the anode 4 contains the raw fuel. The cathode off-gas discharged from the cathode 6 also contains oxygen. The anode off-gas is supplied from the cell stack 7 to the combustion unit 9 via the anode off-gas path 16, and the cathode off-gas is supplied from the cell stack 7 via the cathode off-gas path 17. In the combustion unit 9, the off-gas (anode off-gas) discharged from the cell stack 7 is ignited by the igniter 20 and combusted. The combustion heat generated in the combustion unit 9 increases the temperature of the internal space of the container 1 and is transferred to the reforming unit 8. The combustion exhaust gas discharged from the combustion unit 9 is discharged to the outside of the container 1 via the combustion exhaust gas path 18. The operation of the igniter 20 is controlled by an operation control unit 21 .

[0028] In addition, the fuel cell system includes a reformer temperature measuring device 22 that measures the temperature of the reformer 8. The fuel cell system also includes a combustion section temperature measuring device 23 that measures the temperature inside the combustion section 9. The fuel cell system also includes a stack temperature measuring device 24 that measures the temperature of the cell stack 7. The measurement results of the reformer temperature measuring device 22, the combustion section temperature measuring device 23, and the stack temperature measuring device 24 are transmitted to the operation control unit 21. As will be described later, in this embodiment, the stack temperature measuring device 24 is used as a determination temperature measuring device T that measures the temperature of a predetermined location inside the hot module 2. Note that another temperature measuring device may be used as the determination temperature measuring device T. For example, the reformer temperature measuring device 22 may be used as the determination temperature measuring device T. In other words, the above-mentioned "predetermined location" may be, for example, the cell stack 7, the reformer section 8, etc., or it may be a different location.

[0029] Next, the operation of the start-up process of the fuel cell system will be described. During the startup process for starting the operation of the cell stack 7, the operation control unit 21 supplies raw fuel and reforming water to the reforming unit 8 and supplies air to the cell stack 7. Then, during startup of the cell stack 7, the operation control unit 21 performs an ignition process by activating the igniter 20 while supplying raw fuel to the reforming unit 8 and air to the cathode 6 of the cell stack 7, and combusts the off-gas discharged from the cell stack 7 in the combustion unit 9. As the off-gas is combusted in the combustion unit 9, combustion heat is transferred to the inside of the hot module 2, causing the temperature inside the hot module 2 to rise. Then, when the temperature of a predetermined portion inside the hot module 2 (e.g., the temperature of the reforming unit 8, the temperature of the cell stack 7, etc.) rises, the operation control unit 21 can determine that the startup process of the fuel cell system has ended. The operation control unit 21 also measures the time required after performing the ignition process.

[0030] After performing the ignition process, if the temperature inside the combustion section 9 measured by the combustion section temperature measuring device 23 shows a predetermined temperature change trend, the operation control device 21 determines that normal ignition has occurred in the combustion section 9, and if the temperature inside the combustion section 9 measured by the combustion section temperature measuring device 23 does not show the above-mentioned temperature change trend, the operation control device 21 determines that normal ignition has not occurred in the combustion section 9 and repeats the ignition process to activate the igniter 20. For example, if normal ignition has occurred in the combustion section 9, the temperature inside the combustion section 9 measured by the combustion section temperature measuring device 23 will increase monotonically and then reach a predetermined temperature.

[0031] In such a fuel cell system, the startup process requires a temperature-raising process, for example, several hours, to raise the temperature inside the hot module 2 to a predetermined temperature. In other words, the temperature-raising process takes up most of the time required from the start of the startup process to the start of power generation. Therefore, it would be preferable to shorten the time required for the temperature-raising process. Furthermore, when the raw fuel containing hydrocarbons, such as city gas, used in the fuel cell system is supplied via a microcomputer meter with a gas leak detection function, the supply of raw fuel to the fuel cell system must be stopped periodically, such as approximately once a month, to avoid erroneous determination that the raw fuel has leaked. Therefore, shortening the time required for the temperature-raising process is preferable, as it would extend the period of time during which the fuel cell system can generate power per month.

[0032] The temperature increase process is performed by combustion in the combustion section 9 inside the hot module 2, but the combustibility of the combustion section 9 is affected by variations due to mass production. Therefore, there is a problem that the preferable values ​​of the flow rate per unit time of the combustible components (e.g., raw fuel, fuel gas, etc.) and the flow rate per unit time of air (oxygen) supplied to the combustion section 9 for efficiently increasing the temperature inside the hot module 2 vary from one fuel cell system to another. The flow rate per unit time of the combustible components supplied to the combustion section 9 can be adjusted by the flow rate per unit time of the raw fuel supplied to the reformer 8.

[0033] Therefore, the fuel cell system of this embodiment is configured to perform a process (multiple first heating processes and a reference flow rate determination process, which will be described later) to find a desirable value for the flow rate per unit time of the combustible components to be supplied to the combustion section 9 in order to efficiently raise the temperature inside the hot module 2, and then to perform a second heating process to supply the combustible components to the combustion section 9 at the flow rate determined by that process.

[0034] Specifically, in the startup process of the cell stack 7, the operation control unit 21 performs a first temperature-raising process in which the raw fuel flow rate, which is the flow rate per unit time of the raw fuel supplied to the reforming unit 8, is kept constant, and the air flow rate, which is the flow rate per unit time of the air supplied to the cell stack 7, is kept constant, by burning the off-gas discharged from the cell stack 7 in the combustion unit 9, thereby raising the temperature inside the hot module 2. Of the multiple first temperature-raising processes that have been performed in the past in which at least one of the raw fuel flow rate and the air flow rate is different from each other, after starting the first temperature-raising process (i.e., after performing the above-mentioned ignition process (however, if the ignition process has been performed multiple times, after performing the final ignition process)), the operation control unit 21 During the heating process, a reference flow rate determination process is performed in which the raw fuel flow rate and air flow rate in the first heating process, in which the time required for the temperature of a predetermined part inside the hot module 2 (for example, the temperature of the cell stack 7) to reach a predetermined target temperature was short, are determined to be a reference raw fuel flow rate and a reference air flow rate, respectively.In the startup process after the reference flow rate determination process, a second heating process is performed in which the flow rate per unit time of the raw fuel supplied to the reforming section 8 is kept constant at the reference raw fuel flow rate, and the flow rate per unit time of the air supplied to the cell stack 7 is kept constant at the reference air flow rate, and the off-gas discharged from the cell stack 7 is combusted in the combustion section 9 to raise the temperature inside the hot module 2.

[0035] 2 is a flowchart illustrating the operation of the startup process of the fuel cell system. The operation control unit 21 starts this flowchart when it is time to start the startup process of the fuel cell system.

[0036] In step #10, the operation control unit 21 determines whether there are valid reference raw fuel flow rates and reference air flow rates. For example, when the reference raw fuel flow rate and reference air flow rate are determined in the reference flow rate determination process described below, a validity period is set for the reference raw fuel flow rate and reference air flow rate. In other words, when the reference raw fuel flow rate and reference air flow rate are determined in the reference flow rate determination process, the second temperature rise process is performed using the reference raw fuel flow rate and reference air flow rate in the startup process that is performed during a predetermined period thereafter. Therefore, when the operation control unit 21 determines that there are valid reference raw fuel flow rates and reference air flow rates in step #10, it proceeds to step #14 and performs the startup process in which the second temperature rise process is performed.

[0037] On the other hand, if the operation control unit 21 determines in step #10 that there are no valid reference raw fuel flow rates and reference air flow rates, it proceeds to step #11 and determines whether the startup process in which the first temperature increase process is performed has been performed a set number of times. If the startup process in which the first temperature increase process is performed has not been performed a set number of times, the operation control unit 21 proceeds to step #12 and performs the startup process in which the first temperature increase process is performed. In this way, the operation control unit 21 performs the first temperature increase process in which at least one of the raw fuel flow rate and the air flow rate is different from each other in multiple startup processes that are performed after a predetermined period of time has passed or when the reference flow rate determination process has not yet been performed. Note that the raw fuel flow rate and the air flow rate used in the first temperature increase process can be freely selected as long as they are within the respective predetermined flow rate ranges. A plurality of candidate values ​​for the raw fuel flow rate within the predetermined flow rate range and a plurality of candidate values ​​for the air flow rate within the predetermined flow rate range may be stored in a memory unit (not shown) in advance, and the operation control unit 21 may select the raw fuel flow rate and the air flow rate to be used in the first temperature increase process from among them.

[0038] Furthermore, if the operation control unit 21 determines in step #11 that the startup step of performing the first temperature increase process has been performed a set number of times, it proceeds to step #13 and performs a reference flow rate determination process. As a result, a preferred value for the flow rate per unit time of the raw fuel to be supplied to the reforming unit 8 (i.e., supplied to the combustion unit 9) and a preferred value for the flow rate per unit time of the air to be supplied to the cell stack 7 are determined.

[0039] Then, in the next step #14, in the startup step after performing the reference flow rate determination process, the operation control unit 21 performs a second heating process in which the flow rate per unit time of the raw fuel supplied to the reforming unit 8 is kept constant at the reference raw fuel flow rate, and the flow rate per unit time of the air supplied to the cell stack 7 is kept constant at the reference air flow rate, and the off-gas discharged from the cell stack 7 is combusted in the combustion unit 9 to raise the temperature inside the hot module 2.

[0040] As described above, in the reference flow rate determination process, of the multiple first temperature-raising processes that increase the temperature inside the hot module 2 by combusting the off-gas discharged from the cell stack 7 in the combustion unit 9 during the startup process of the cell stack 7, the first temperature-raising process that took the shortest time for the temperature of a predetermined location inside the hot module 2 to reach the predetermined target temperature after the start of the first temperature-raising process is performed, i.e., the first temperature-raising process that efficiently increased the temperature inside the hot module 2, is determined as the reference raw fuel flow rate and the reference air flow rate, respectively. Then, in the second temperature-raising process, the reference raw fuel flow rate and the reference air flow rate determined in the reference flow rate determination process are used to combust the off-gas discharged from the cell stack 7 in the combustion unit 9, thereby increasing the temperature inside the hot module 2. In other words, the temperature-raising process is performed at a raw fuel flow rate and air flow rate appropriate for each individual fuel cell system.

[0041] Furthermore, the reference raw fuel flow rate and the reference air flow rate determined by the reference flow rate determination process are used in the startup process that is performed during a subsequent predetermined period, so that the temperature inside the hot module 2 can be raised efficiently and with a certain degree of certainty during that predetermined period. Furthermore, a valid period (i.e., the above-mentioned predetermined period) is set for the reference raw fuel flow rate and the reference air flow rate, and a new reference flow rate determination process is performed based on the results of multiple new startup processes that are performed after that valid period has elapsed. Then, the reference raw fuel flow rate and the reference air flow rate determined by the reference flow rate determination process are used to perform a second heating process for a subsequent predetermined period. In other words, by periodically updating the reference raw fuel flow rate and the reference air flow rate, even if the fuel cell system has deteriorated over time, for example, the heating process can be performed using a raw fuel flow rate and an air flow rate that are appropriate for that deterioration state.

[0042] <Another embodiment> In the above embodiment, a specific example of the configuration of the fuel cell system of the present invention has been described, but the configuration can be modified as appropriate.

[0043] In the above embodiment, the content of the reference flow rate determination process can be changed as appropriate. For example, in the reference flow rate determination process, the operation control unit 21 may determine the raw fuel flow rate and the air flow rate, respectively, in the first temperature rise process that took the shortest time among multiple first temperature rise processes performed in the startup process after the cell stack 7 had been power generation stopped for a set period or longer as the reference raw fuel flow rate and the reference air flow rate.

[0044] Specifically, in a fuel cell system, the temperature inside the hot module 2 at the time the start-up process of the cell stack 7 is initiated varies depending on the length of the previous period during which power generation by the cell stack 7 was stopped. Therefore, if the period during which power generation by the cell stack 7 was stopped is short, i.e., if the temperature inside the hot module 2 is high at the time the start-up process of the cell stack 7 is initiated, the time required for the temperature of a predetermined location inside the hot module 2 to reach the target temperature by the first heating process is likely to be short. On the other hand, if the period during which power generation by the cell stack 7 was stopped is long, i.e., if the temperature inside the hot module 2 is low at the time the start-up process of the cell stack 7 is initiated, the time required for the temperature of a predetermined location inside the hot module 2 to reach the target temperature by the first heating process is likely to be long. Therefore, if the above-mentioned required time (i.e., the time it takes for the temperature of a predetermined location during the first heating process after the start of the first heating process to reach the predetermined target temperature) is measured using a first heating process that is inconsistent with the length of the period during which power generation by the cell stack 7 was stopped, the reliability of the reference raw fuel flow rate and the reference air flow rate determined in the reference flow rate determination process will be low. However, as described above, when the operation control unit 21 determines the reference raw fuel flow rate and the reference air flow rate in the reference flow rate determination process to be the raw fuel flow rate and the air flow rate in the first heating process that took the shortest time out of multiple first heating processes performed in the startup process after the cell stack 7 had been power generation stopped for a period longer than the set period, the second heating process can be performed using the reference raw fuel flow rate and the reference air flow rate that have a certain degree of reliability.

[0045] Alternatively, in the reference flow rate determination process, operation control unit 21 may determine the reference raw fuel flow rate and the reference air flow rate for each temperature range of the predetermined portion when the first temperature increase process is started. Then, operation control unit 21 may perform the second temperature increase process using the reference raw fuel flow rate and the reference air flow rate corresponding to the temperature range of the predetermined portion when the second temperature increase process is started.

[0046] Specifically, if the internal temperature of the hot module 2 is high at the start of the startup process of the cell stack 7, the time required for the temperature of a predetermined location inside the hot module 2 to reach the target temperature through the first heating process is likely to be shorter. Conversely, if the internal temperature of the hot module 2 is low at the start of the startup process of the cell stack 7, the time required for the temperature of a predetermined location inside the hot module 2 to reach the target temperature through the first heating process is likely to be longer. Therefore, if the above-mentioned required time (i.e., the time required for the temperature of a predetermined location during the first heating process after the start of the first heating process to reach the predetermined target temperature) is measured using a first heating process that is inconsistent with the internal temperature of the hot module 2 at the start of the startup process of the cell stack 7, the reliability of the reference raw fuel flow rate and the reference air flow rate determined in the reference flow rate determination process will be low. However, as described above, in the reference flow rate determination process, the operation control unit 21 determines the reference raw fuel flow rate and the reference air flow rate for each temperature range of a specified location when the first heating process is started, and performs the second heating process using the reference raw fuel flow rate and the reference air flow rate corresponding to the temperature range of the specified location when the second heating process is started, thereby making it possible to perform the second heating process using a reference raw fuel flow rate and a reference air flow rate that have a certain degree of reliability.

[0047] The following Table 1 shows examples of reference raw fuel flow rates Q1a to Q1i and reference air flow rates Q2a to Q2i corresponding to each temperature range. The second temperature increase process can be performed using such reference raw fuel flow rates and reference air flow rates that are reliable to a certain extent.

[0048] [Table 1]

[0049] In the above embodiment, the timing of the ignition process is set as the start timing of the first temperature rise process, and the time required from that timing until the temperature of a predetermined part reaches a predetermined target temperature is measured. However, other timing may be set as the start timing of the first temperature rise process. For example, the timing when it is determined that normal ignition has occurred in the combustion unit 9 may be set as the start timing of the first temperature rise process, and the time required from that point may be measured.

[0050] 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. [Industrial Applicability]

[0051] The present invention can be used in a fuel cell system that can perform a temperature increase process under favorable conditions. [Explanation of symbols]

[0052] 1: Container 2: Hot module 3: Fuel cell 4: Anode 6: Cathode 7: Cell stack 8: Modification section 9: Combustion section 10: Raw fuel supply department 11: Air supply section 12: Reformed water supply section 15: Fuel gas supply line 21: Operation control section 22: Reforming section temperature measuring device (judgment temperature measuring device T) 23: Combustion section temperature measuring instrument 24: Stack temperature measuring device (judgment temperature measuring device T)

Claims

1. a hot module having a container, a cell stack in which a plurality of fuel cells each having an anode and a cathode are provided inside the container, a reforming unit that generates fuel gas by steam reforming a raw fuel, a fuel gas supply path that supplies the fuel gas from the reforming unit to the anode, and a combustion unit that combusts off-gas discharged from the cell stack; a raw fuel supply unit that supplies the raw fuel from outside the container to the reforming unit; an air supply unit that supplies air from the outside of the container to the cell stack; a reforming water supply unit that supplies reforming water from the outside of the container to the reforming unit; an operation control unit; A fuel cell system configured so that heat generated in the combustion section is transferred to the reforming section, a temperature measuring device for determination that measures the temperature of a predetermined portion inside the hot module; The operation control unit In the start-up process of the cell stack, a raw fuel flow rate, which is the flow rate per unit time of the raw fuel supplied to the reforming section, is kept constant, and an air flow rate, which is the flow rate per unit time of the air supplied to the cell stack, is kept constant. In this state, the off-gas discharged from the cell stack is combusted in the combustion section, thereby performing a first temperature increase process to increase the temperature inside the hot module; performing a reference flow rate determination process for determining, as a reference raw fuel flow rate and a reference air flow rate, the raw fuel flow rate and the air flow rate in the first temperature-raising process in which, after the start of the first temperature-raising process, a time required for the temperature of the predetermined portion to reach a predetermined target temperature was shortest during the first temperature-raising process among a plurality of first temperature-raising processes that have been performed in the past in which at least one of the raw fuel flow rate and the air flow rate differ from one another; In the startup process after the reference flow rate determination process, the flow rate per unit time of the raw fuel supplied to the reforming section is kept constant at the reference raw fuel flow rate, and the flow rate per unit time of the air supplied to the cell stack is kept constant at the reference air flow rate. In this state, the fuel cell system performs a second heating process to raise the temperature inside the hot module by combusting the off-gas discharged from the cell stack in the combustion section.

2. 2. The fuel cell system according to claim 1, wherein, when the reference raw fuel flow rate and the reference air flow rate are determined by the reference flow rate determination process, the operation control unit performs the second temperature rise process using the reference raw fuel flow rate and the reference air flow rate during the startup process, which is performed during a subsequent predetermined period.

3. 3. The fuel cell system according to claim 2, wherein the operation control unit performs the first temperature increase process in which at least one of the raw fuel flow rate and the air flow rate is different from one another during the multiple startup processes that are performed after the predetermined period has elapsed.

4. 4. The fuel cell system according to claim 1, wherein the operation control unit, in the reference flow rate determination process, determines the reference raw fuel flow rate and the reference air flow rate to be the raw fuel flow rate and the air flow rate, respectively, in the first heating process that took the shortest time among multiple first heating processes performed in the startup process after the cell stack's power generation stop period was longer than a set period.

5. 4. The fuel cell system according to claim 1, wherein the operation control unit, in the reference flow rate determination process, determines the reference raw fuel flow rate and the reference air flow rate for each temperature range of the specified portion when the first heating process is started, and performs the second heating process using the reference raw fuel flow rate and the reference air flow rate corresponding to the temperature range of the specified portion when the second heating process is started.

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