Fuel cell system

Abstract

To provide a fuel cell system capable of suppressing explosive ignition in a combustion part as much as possible.SOLUTION: The fuel cell system includes: a specific ignition detection unit 25 configured to detect at least one of occurrence of ignition of a high-concentration combustible component in a combustion part 9 and a state in which a possibility of ignition of a high-concentration combustible component in the combustion part 9 becomes high. An operation control unit 21 performs first gas stop processing of stopping supply of a first gas to an anode 4, in a case where, after executing an ignition process of causing an igniter 20 to perform ignition operation while supplying a first gas to the anode 4 and supplying a second gas to a cathode 6 at startup of a cell stack 7, at least one of the occurrence of ignition of the high-concentration combustible component in the combustion part 9 and the state in which the possibility of ignition of the high-concentration combustible component in the combustion part 9 becomes high is detected by the specific ignition detection unit 25.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 (JP 2008-135268 A) describes a fuel cell system including a cell stack (4) having a plurality of fuel cell units (4a) each having an anode and a cathode, a first gas supply unit (gas pump 2) that supplies a first gas containing hydrocarbon or hydrogen to the anode, a second gas supply unit (air blower 5) that supplies air to the cathode, a combustion unit (combustion region F) that receives off-gas discharged from the anode and cathode and combusts combustible components contained in the off-gas, and an igniter (ignition heater 7) that ignites the combustible components inside the combustion unit. In this fuel cell system, after an ignition operation is performed by the igniter, if it is not determined that ignition has occurred within a predetermined ignition determination time, it is determined that ignition has not occurred, and the igniter performs the ignition operation again. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-135268 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional fuel cell systems such as those described in Patent Document 1, if ignition of combustible components in the combustion section cannot be confirmed, the ignition operation using an igniter is repeatedly performed. Furthermore, if the period during which ignition of combustible components in the combustion section cannot be performed becomes long, the concentration of combustible components remaining in the combustion section increases. If an ignition operation using an igniter is performed in this state, there is a possibility that explosive combustion of the high concentration of combustible components remaining in the combustion section will occur.

[0005] When such explosive combustion occurs in the combustion section, it causes sudden pressure fluctuations and vibrations in the combustion section and the gas path leading to the combustion section, which may damage the combustion section, the gas path leading to the combustion section, or the cell stack connected to the combustion section.

[0006] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a fuel cell system that can minimize the occurrence of explosive ignition in the combustion section. [Means for solving the problem]

[0007] A characteristic configuration of a fuel cell system according to the present invention for achieving the above object is a fuel cell system comprising: a cell stack having a plurality of fuel cell units each having an anode and a cathode; a first gas supply unit that supplies a first gas containing hydrocarbon or hydrogen to the anode; a second gas supply unit that supplies a second gas containing oxygen to the cathode; a combustion unit that receives off-gas discharged from the anode and the cathode and combusts combustible components contained in the off-gas; an igniter that ignites the combustible components inside the combustion unit; and an operation control unit, a specific ignition detection unit that detects at least one of the occurrence of ignition of the high concentration of combustible components in the combustion unit and a state in which the possibility of ignition of the high concentration of combustible components in the combustion unit is increasing, The operation control unit is configured to perform an ignition process in which the igniter is activated to ignite while the first gas is supplied to the anode and the second gas is supplied to the cathode when the cell stack is started, and then, if the specific ignition detection unit detects at least one of the occurrence of ignition of a high concentration of the flammable component in the combustion unit and a state in which the possibility of ignition of a high concentration of the flammable component in the combustion unit is increasing, perform a first gas stop process in which the supply of the first gas to the anode is stopped.

[0008] According to the above-described characteristic configuration, the off-gas contains hydrocarbons or hydrogen discharged from the anode, and the hydrocarbons or hydrogen are combusted in the combustion section as combustible components. After performing the ignition process, the operation control unit performs a first gas stop process to stop the supply of the first gas (i.e., hydrocarbons or hydrogen) to the anode if the specific ignition detection unit detects at least one of the following: that a high concentration of combustible components has ignited in the combustion section; and that a high concentration of combustible components is likely to ignite in the combustion section. In other words, after performing the first gas stop process, the oxygen-containing off-gas discharged from the cathode can gradually reduce the concentration of combustible components in the combustion section downstream of the anode. As a result, even if the ignition process is subsequently performed, the occurrence of explosive ignition in the combustion section can be suppressed. Therefore, it is possible to provide a fuel cell system that can minimize the occurrence of explosive ignition in the combustion section.

[0009] Another characteristic configuration of the fuel cell system according to the present invention is to include a combustion section temperature measuring device that measures the temperature inside the combustion section, If, after performing the ignition process, the temperature inside the combustion section measured by the combustion section temperature measuring device does not show a predetermined temperature change trend, the operation control unit performs the ignition process again, activating the igniter to ignite while supplying the first gas to the anode and the second gas to the cathode.

[0010] When the ignition process is performed and the combustion of the combustible components starts normally, the temperature inside the combustion section will show a temperature change tendency, such as rising at a predetermined rate. However, if such a temperature change tendency is not shown, there is a high possibility that the combustion of the combustible components has not started normally, such as a misfire occurring in the combustion section. Therefore, in this characteristic configuration, if the temperature inside the combustion unit does not show a predetermined temperature change trend after the ignition process, the operation control unit performs the ignition process again to activate the igniter while supplying the first gas to the anode and the second gas to the cathode, thereby starting combustion of the combustible components in the combustion unit.

[0011] Another characteristic configuration of the fuel cell system according to the present invention is that the specific ignition detection unit has a concentration measuring device that measures the concentration of the combustible component present inside the combustion unit, When the concentration of the combustible component measured by the concentration measuring device is equal to or greater than a predetermined first threshold, it is determined that there is an increased possibility of ignition of the combustible component at a high concentration in the combustion section.

[0012] According to the above characteristic configuration, by using a concentration measuring device that measures the concentration of combustible components present inside the combustion section as a specific ignition detection section, if the concentration of the combustible components measured by the concentration measuring device is equal to or greater than a predetermined first threshold, it can be determined that there is a high possibility of ignition of high concentrations of combustible components in the combustion section.

[0013] Another characteristic configuration of the fuel cell system of the present invention is that, after performing the first gas stop processing, if the concentration of the combustible component measured by the concentration measuring device becomes less than the first threshold value while continuing to supply the second gas to the cathode, the operation control unit performs the ignition processing to activate the igniter to ignite while supplying the first gas to the anode and the second gas to the cathode.

[0014] According to the above characteristic configuration, after performing the first gas stop process, the operation control unit can ignite flammable components that are not at high concentrations by activating the igniter to ignite after the concentration of the flammable components measured by the concentration measuring device has fallen below the first threshold value and while supplying the first gas to the anode and the second gas to the cathode.

[0015] Another characteristic configuration of the fuel cell system according to the present invention is that the specific ignition detection unit has a pressure measuring device that measures a pressure inside the combustion unit, When abnormal pressure conditions are satisfied, including at least one of the pressure inside the combustion section measured by the pressure measuring instrument being equal to or greater than a predetermined second threshold and the change in pressure inside the combustion section within a predetermined period being equal to or greater than a third threshold, it is determined that ignition of a high concentration of the combustible component has occurred in the combustion section.

[0016] According to the above characteristic configuration, by using a pressure measuring device that measures the pressure inside the combustion section as the specific ignition detection section, if abnormal pressure conditions are satisfied, including at least one of the following: the pressure inside the combustion section measured by the pressure measuring device is equal to or greater than a predetermined second threshold value; and the range of change in the pressure inside the combustion section within a predetermined period of time is equal to or greater than a third threshold value, it can be determined that ignition of a high concentration of flammable components has occurred in the combustion section.

[0017] Another characteristic configuration of the fuel cell system of the present invention is that, after performing the first gas stop processing, if the abnormal pressure condition is no longer satisfied while the second gas is continuing to be supplied to the cathode, the operation control unit performs the ignition processing to activate the igniter to ignite while the first gas is being supplied to the anode and the second gas is being supplied to the cathode.

[0018] According to the above characteristic configuration, after the first gas stop processing is performed, the operation control unit supplies the first gas to the anode and the second gas to the cathode after the abnormal pressure condition is no longer satisfied, and thereby activates the igniter to ignite flammable components that are not highly concentrated.

[0019] Another characteristic configuration of the fuel cell system according to the present invention is to include a combustion section temperature measuring device that measures the temperature inside the combustion section, The operation control unit, after performing the ignition process, if the temperature inside the combustion unit measured by the combustion unit temperature measuring device shows a predetermined temperature change tendency, The feature is that a flow rate increasing process is performed to increase the flow rate per unit time of the first gas supplied to the anode and the flow rate per unit time of the second gas supplied to the cathode.

[0020] According to the above-described characteristic configuration, if the temperature inside the combustion unit measured by the combustion unit temperature measuring device shows a predetermined temperature change trend after the ignition process, it can be considered that the combustion unit has been ignited normally. In this state, the operation control unit performs a flow rate increase process, which increases the combustion heat generated in the combustion unit and quickly raises the temperature inside the hot module that houses the combustion unit.

[0021] Another characteristic configuration of the fuel cell system according to the present invention is that, in the flow rate increasing process, the operation control unit increases the flow rate of the first gas supplied to the anode and the flow rate of the second gas supplied to the cathode while maintaining the ratio of the flow rate per unit time of the first gas supplied to the anode and the flow rate per unit time of the second gas supplied to the cathode at a predetermined value.

[0022] According to the above characteristic configuration, the ratio of the flow rate of the first gas supplied to the anode and the flow rate of the second gas supplied to the cathode is maintained at a predetermined value during the flow rate increase process, so that the temperature inside the hot module can be quickly increased while combustion in the combustion section remains stable. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram illustrating the configuration of a fuel cell system according to a first embodiment. [Figure 2] 4 is a flowchart illustrating a start-up process of the fuel cell system according to the first embodiment. [Figure 3] FIG. 4 is a diagram illustrating the configuration of a fuel cell system according to a second embodiment. [Figure 4] 10 is a flowchart illustrating a start-up process of a fuel cell system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] First Embodiment A fuel cell system according to a first embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a diagram illustrating the configuration of the fuel cell system according to the first embodiment.

[0025] The fuel cell system has a container 1, inside which are arranged 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 produces 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, a combustion section 9 that combusts off-gas discharged from the cell stack 7, and a combustion exhaust gas path 18 that leads combustion exhaust gas generated in the combustion section 9 to the outside of the container 1.

[0026] 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.

[0027] 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 .

[0028] 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 .

[0029] Combustion heat generated in the combustion unit 9, which will be described later, is transferred to the reforming unit 8. The reforming unit 8 then steam reforms the raw fuel supplied from the raw fuel supply unit 10 to generate fuel gas containing hydrogen. The fuel gas generated in the reforming unit 8 flows toward the cell stack 7 via a fuel gas supply path 15. Note that if the reforming process of the raw fuel is not performed sufficiently in the reforming unit 8, such as during startup, the raw fuel is also supplied from the reforming unit 8 to the cell stack 7 via the fuel gas supply path 15.

[0030] 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 that use a solid electrolyte.

[0031] The fuel cell system includes a fuel gas supply path 15 through which fuel gas generated in the reforming section 8 flows toward the anode 4 of the cell stack 7, and an air supply path 19 through which air flows to be supplied to the cell stack 7. When fuel gas is not being generated in the reforming section 8, raw fuel flows through the fuel gas supply path 15, and as a result, raw fuel is supplied to the anode 4.

[0032] Each fuel cell 3 generates power using the fuel gas generated 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 channel 15, and air (oxygen) is supplied to the cathode 6 via an air supply channel 19. Note that if the reforming process of the raw fuel is not performed sufficiently in the reforming unit 8, such as during startup, the raw fuel is also supplied from the reforming unit 8 to the anode 4. In this way, the raw fuel supply unit 10 that supplies the raw fuel to the reforming unit 8 functions as a first gas supply unit that supplies a first gas containing hydrocarbon or hydrogen to the anode 4. The air supply channel 19 is provided with an air supply unit 11 that supplies air and is realized using a pump, a flow meter, or the like. The air supply unit 11 can adjust the flow rate of air per unit time supplied to the cell stack 7. In other words, the air supply unit 11 functions as a second gas supply unit that supplies a second gas containing oxygen to the cathode 6. The operation of the air supply unit 11 is controlled by an operation control unit 21 .

[0033] 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 flammable components such as hydrogen. When fuel gas is not 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, flammable components (e.g., hydrocarbons, hydrogen, etc.) in the off-gas (anode off-gas) discharged from the cell stack 7 are ignited and burned by the igniter 20. The combustion heat generated in the combustion unit 9 increases the temperature of the internal space of the container 1 and is transferred, in particular, to the reforming unit 8. The combustion exhaust gas discharged from the combustion section 9 is discharged to the outside of the vessel 1 via a combustion exhaust gas passage 18 . The operation of the igniter 20 is controlled by an operation control unit 21 .

[0034] Additionally, the fuel cell system includes a combustion section temperature measuring device 22 that measures the temperature inside the combustion section 9. The fuel cell system also includes a concentration measuring device 23 that measures the concentration of combustible components present inside the combustion section 9. The measurement results of the combustion section temperature measuring device 22 and the concentration measuring device 23 are transmitted to the operation control unit 21.

[0035] Next, a method for starting up the fuel cell system will be described. 2 is a flowchart illustrating the start-up process of the fuel cell system of the first embodiment. As will be described later, this embodiment is characterized in that, at the start-up of the cell stack 7, the operation control unit 21 performs an ignition process in which the igniter 20 is activated to ignite while a first gas containing hydrocarbon or hydrogen is supplied to the anode 4 and air is supplied to the cathode 6, and then, if the possibility of ignition of a high concentration of flammable components (e.g., hydrocarbons, hydrogen, etc.) in the combustion unit 9 becomes high, the operation control unit 21 performs a first gas stop process in which the supply of the first gas to the anode 4 is stopped.

[0036] The fuel cell system is provided with a specific ignition detection unit 25 that detects at least one of the occurrence of ignition of a high concentration of combustible components in the combustion unit 9 and a state in which the possibility of ignition of a high concentration of combustible components in the combustion unit 9 is increasing.

[0037] In this embodiment, the specific ignition detection unit 25 has a concentration measuring device 23 that measures the concentration of combustible components present inside the combustion unit 9, and if the concentration of the combustible components measured by the concentration measuring device 23 is equal to or greater than a predetermined first threshold, it is determined that there is an increased possibility of ignition of high concentrations of combustible components in the combustion unit 9.

[0038] As described above, the fuel cell system includes a cell stack 7 having a plurality of fuel cell cells 3 each having an anode 4 and a cathode 6, a raw fuel supply unit 10 serving as a first gas supply unit that supplies a first gas containing hydrocarbon or hydrogen to the anode 4, an air supply unit 11 serving as a second gas supply unit that supplies air to the cathode 6, a combustion unit 9 that receives the off-gas discharged from the anode 4 and the cathode 6 and combusts the combustible components contained in the off-gas, an igniter 20 that ignites the combustible components inside the combustion unit 9, and an operation control unit 21.

[0039] Then, in step #10, when the cell stack 7 is started up, the operation control unit 21 controls the operation of the raw fuel supply unit 10 and the air supply unit 11 to supply a raw fuel containing hydrocarbon to the anode 4 and supply air to the cathode 6. In this case, the operation control unit 21 controls the operation of the raw fuel supply unit 10 and the air supply unit 11 so that the flow rate of the raw fuel per unit time and the flow rate of the air per unit time are a predetermined ratio. The operation control unit 21 also controls the operation of the raw fuel supply unit 10 and the air supply unit 11 so that the flow rate of the raw fuel per unit time and the flow rate of the air per unit time are maintained at constant values.

[0040] Thereafter, in step #11, the operation control unit 21 performs the ignition process of activating the igniter 20 to ignite while supplying raw fuel to the anode 4 and air to the cathode 6 as described above.

[0041] In step #12, the operation control unit 21 determines whether normal ignition of the combustible components has occurred in the combustion unit 9. Specifically, after performing the ignition process, if the temperature inside the combustion unit 9 measured by the combustion unit temperature measuring device 22 shows a predetermined temperature change trend, the operation control unit 21 determines that normal ignition of the combustible components has occurred in the combustion unit 9 and proceeds to step #13, but if the temperature inside the combustion unit 9 measured by the combustion unit temperature measuring device 22 does not show the above-mentioned temperature change trend, the operation control unit 21 determines that normal ignition of the combustible components has not occurred in the combustion unit 9 and proceeds to step #14.

[0042] For example, the predetermined temperature change tendency is that the rate of temperature increase after the ignition process is equal to or greater than a set value, or that the range of temperature increase after the ignition process is equal to or greater than a set value, etc. Therefore, when the temperature of the combustion section 9 shows such a temperature change tendency, it can be assumed that the combustible components are being ignited normally in the combustion section 9, that is, that the combustible components are being continuously burned in the combustion section 9.

[0043] In step #13, if the temperature inside combustion section 9 measured by combustion section temperature measuring device 22 after the ignition process shows a predetermined temperature change trend, i.e., if combustible components are being ignited normally in combustion section 9, operation control section 21 controls the operation of raw fuel supply section 10 as the first gas supply section and air supply section 11 as the second gas supply section to perform a flow rate increase process to increase the flow rate per unit time of the first gas containing hydrocarbon or hydrogen that is supplied to anode 4 and the flow rate per unit time of air that is supplied to cathode 6. The flow rate per unit time of the first gas containing hydrocarbon or hydrogen that is supplied to anode 4 can be adjusted by the flow rate per unit time of the raw fuel that is supplied to reformer 8.

[0044] In this flow rate increasing process, the operation control unit 21 may increase the flow rate of the first gas supplied to the anode 4 and the flow rate of the air supplied to the cathode 6 while maintaining the ratio of the flow rate per unit time of the first gas (i.e., the raw fuel supplied to the reforming unit 8) supplied to the anode 4 and the flow rate per unit time of the air supplied to the cathode 6 at a predetermined value. By performing this flow rate increasing process, the combustion heat generated in the combustion unit 9 increases, and the rate at which the temperature inside the hot module 2 rises can be increased.

[0045] In step #14, the operation control unit 21 determines whether the concentration of combustible components present inside the combustion unit 9 measured by the concentration measuring device 23 is equal to or greater than a predetermined first threshold. If the concentration of the combustible components is less than the first threshold, the operation control unit 21 proceeds to step #10 and performs the ignition process (step #11) again, in which the igniter 20 is activated to ignite while the first gas is supplied to the anode 4 (i.e., raw fuel is supplied to the reforming unit 8) and air is supplied to the cathode 6. In this way, if the temperature inside the combustion unit 9 measured by the combustion unit temperature measuring device 22 after performing the ignition process does not show a predetermined temperature change trend, the operation control unit 21 performs the ignition process again, in which the igniter 20 is activated to ignite while the first gas is supplied to the anode 4 (i.e., raw fuel is supplied to the reforming unit 8) and air is supplied to the cathode 6.

[0046] However, if the above ignition process is performed when the concentration of combustible components present inside the combustion unit 9 measured by the concentration measuring device 23 is equal to or higher than a predetermined first threshold, that is, when there is a high possibility of ignition of high-concentration combustible components in the combustion unit 9, there is a possibility that explosive combustion of the high-concentration combustible components will occur. If such explosive combustion occurs in the combustion unit 9, sudden pressure fluctuations and vibrations will be caused in the combustion unit 9 and in the gas path connected to the combustion unit 9. This may result in damage to the combustion unit 9, the gas path connected to the combustion unit 9, the cell stack 7 connected to the combustion unit 9, and the like.

[0047] Therefore, in this embodiment, if the operation control unit 21 determines in step #14 that the concentration of combustible components present inside the combustion unit 9 measured by the concentration measuring device 23 is equal to or higher than a predetermined first threshold, the operation control unit 21 proceeds to step #15 and performs a first gas stop process to stop the supply of the first gas to the anode 4 (i.e., the supply of raw fuel to the reforming unit 8). That is, the operation control unit 21 is configured to perform an ignition process to operate the igniter 20 for ignition while supplying the first gas to the anode 4 (i.e., supplying raw fuel to the reforming unit 8) and supplying air to the cathode 6 at the start-up of the cell stack 7, and then, if the possibility of ignition of a high concentration of combustible components in the combustion unit 9 becomes high, perform the first gas stop process (i.e., a process to continue only the supply of air to the cathode 6).

[0048] By performing this first gas supply stop process, i.e., by continuing only the supply of air to the cathode 6, it is expected that the concentration of combustible components in the combustion section 9 downstream of the cathode 6 will gradually decrease. Then, the operation control section 21 continues only the supply of air to the cathode 6 in step #15 while the concentration of combustible components present inside the combustion section 9 measured by the concentration measuring device 23 is equal to or greater than a predetermined first threshold. On the other hand, after performing this first gas supply stop process, if the concentration of combustible components measured by the concentration measuring device 23 becomes less than the first threshold while continuing to supply air to the cathode 6, the operation control section 21 proceeds to step #10 and again performs the ignition process (step #11) of supplying the first gas to the anode 4 (i.e., supplying raw fuel to the reforming section 8) and activating the igniter 20 to ignite while supplying air to the cathode 6.

[0049] As described above, after performing the ignition process, if the concentration measuring device 23 serving as the specific ignition detection unit 25 detects a state in which there is an increased possibility of ignition of a high concentration of combustible components in the combustion unit 9, the operation control unit 21 performs a first gas stop process that stops the supply of the first gas (i.e., hydrocarbon or hydrogen) to the anode 4. In other words, after performing the first gas stop process, the oxygen-containing off-gas discharged from the cathode 6 can gradually lower the concentration of combustible components in the combustion unit 9 downstream of the anode 4. As a result, even if the ignition process is performed thereafter, the occurrence of explosive ignition in the combustion unit 9 can be suppressed.

[0050] Second Embodiment The fuel cell system of the second embodiment differs from the above-described embodiments in that, instead of performing the first gas stop process when there is an increased possibility of ignition of a high concentration of combustible components in the combustion section 9 as in the above-described embodiments, the fuel cell system of the second embodiment performs the first gas stop process when ignition of a high concentration of combustible components occurs in the combustion section 9. The fuel cell system of the second embodiment will be described below, but a description of the same configuration as in the above-described embodiments will be omitted.

[0051] FIG. 3 is a diagram illustrating the configuration of a fuel cell system according to the second embodiment. As shown in the figure, the fuel cell system of this embodiment includes a pressure measuring device 24 that measures the pressure inside the combustion section 9.

[0052] In the fuel cell system of this embodiment, the specific ignition detection unit 25 has a pressure measuring instrument 24 that measures the pressure inside the combustion unit 9, and when abnormal pressure conditions are satisfied, including at least one of the following: the pressure inside the combustion unit 9 measured by the pressure measuring instrument 24 becomes equal to or greater than a predetermined second threshold value; and the change in the pressure inside the combustion unit 9 within a predetermined period of time becomes equal to or greater than a third threshold value, it is determined that ignition of a high concentration of combustible components has occurred in the combustion unit 9.

[0053] The operation control unit 21 is configured to perform an ignition process in which the first gas is supplied to the anode 4 (i.e., raw fuel is supplied to the reforming unit 8) and the igniter 20 is activated while air is being supplied to the cathode 6 at the start of the cell stack 7, and then, if ignition of a high concentration of combustible components occurs in the combustion unit 9, to perform a first gas stop process in which the supply of the first gas to the anode 4 (i.e., supply of raw fuel to the reforming unit 8) is stopped. Specifically, the operation control unit 21 determines that ignition of a high concentration of combustible components has occurred in the combustion unit 9 when abnormal pressure conditions are satisfied, including at least one of the pressure inside the combustion unit 9 measured by the pressure measuring device 24 becoming equal to or higher than a predetermined second threshold and the change in the pressure inside the combustion unit 9 within a predetermined period becoming equal to or higher than a third threshold.

[0054] 3 is a flowchart illustrating the startup process of the fuel cell system of the first embodiment. In step #20, the operation control unit 21 controls the operation of the raw fuel supply unit 10 and the air supply unit 11 during startup of the cell stack 7 to supply a hydrocarbon-containing raw fuel to the anode 4 and air to the cathode 6. In this case, the operation control unit 21 controls the operation of the raw fuel supply unit 10 and the air supply unit 11 so that the flow rate of the raw fuel per unit time and the flow rate of the air per unit time are a predetermined ratio. The operation control unit 21 also controls the operation of the raw fuel supply unit 10 and the air supply unit 11 so that the flow rate of the raw fuel per unit time and the flow rate of the air per unit time are maintained at constant values.

[0055] Thereafter, in step #21, the operation control unit 21 performs an ignition process in which the igniter 20 is activated to ignite while the raw fuel is being supplied to the anode 4 and air is being supplied to the cathode 6 as described above.

[0056] In step #22, the operation control unit 21 determines whether normal ignition of the combustible components has occurred in the combustion unit 9. Specifically, after performing the ignition process, if the temperature inside the combustion unit 9 measured by the combustion unit temperature measuring device 22 shows a predetermined temperature change trend, the operation control unit 21 determines that normal ignition of the combustible components has occurred in the combustion unit 9 and proceeds to step #23, but if the temperature inside the combustion unit 9 measured by the combustion unit temperature measuring device 22 does not show the above-mentioned temperature change trend, the operation control unit 21 determines that normal ignition of the combustible components has not occurred in the combustion unit 9 and proceeds to step #24.

[0057] For example, the predetermined temperature change tendency is that the rate of temperature increase after the ignition process is equal to or greater than a set value, or that the range of temperature increase after the ignition process is equal to or greater than a set value, etc. Therefore, when the temperature of the combustion section 9 shows such a temperature change tendency, it can be assumed that the combustible components are being ignited normally in the combustion section 9, that is, that the combustible components are being continuously burned in the combustion section 9.

[0058] In step #23, if the temperature inside the combustion section 9 measured by the combustion section temperature measuring device 22 after the ignition process shows a predetermined temperature change trend, i.e., if the combustible components are being ignited normally in the combustion section 9, the operation control section 21 controls the operation of the raw fuel supply section 10 as the first gas supply section and the air supply section 11 as the second gas supply section to perform a flow rate increase process to increase the flow rate per unit time of the first gas (i.e., the raw fuel supplied to the reforming section 8) supplied to the anode 4 and the flow rate per unit time of the air supplied to the cathode 6. In this flow rate increase process, the operation control section 21 may increase the flow rate of the first gas (i.e., the raw fuel supplied to the reforming section 8) supplied to the anode 4 and the flow rate of the air supplied to the cathode 6 while maintaining the ratio per unit time of the first gas (i.e., the raw fuel supplied to the reforming section 8) supplied to the anode 4 and the flow rate per unit time of the air supplied to the cathode 6 at a predetermined value. By performing this flow rate increase process, the combustion heat generated in the combustion section 9 increases, and the rate at which the temperature inside the hot module 2 rises can be increased.

[0059] In steps #24 and #25, the operation control unit 21 determines whether or not an abnormal pressure condition is satisfied (i.e., whether or not ignition of a high concentration of combustible components has occurred in the combustion unit 9), which includes at least one of the following: the pressure inside the combustion unit 9 measured by the pressure measuring device 24 is equal to or greater than a predetermined second threshold (step #24); and the change in the pressure inside the combustion unit 9 within a predetermined period is equal to or greater than a third threshold (step #25). If the abnormal pressure condition is not satisfied, the operation control unit 21 proceeds to step #20, and again performs the ignition process (step #21) of activating the igniter 20 to ignite while supplying the first gas to the anode 4 (i.e., supplying raw fuel to the reformer 8) and supplying air to the cathode 6. In this way, if the temperature inside the combustion section 9 measured by the combustion section temperature measuring device 22 does not show a predetermined temperature change trend after performing the ignition process, the operation control section 21 performs the ignition process again, supplying the first gas to the anode 4 (i.e., supplying raw fuel to the reforming section 8) and activating the igniter 20 to ignite while supplying air to the cathode 6.

[0060] However, if the above ignition process is performed when the abnormal pressure condition is satisfied, i.e., when ignition of a high concentration of combustible components has occurred in the combustion section 9, there is a possibility that explosive combustion of the high concentration of combustible components will occur again.

[0061] Therefore, in this embodiment, if the operation control unit 21 determines in steps #24 and #25 that the abnormal pressure condition is satisfied (i.e., if it determines that ignition of a high concentration of combustible components has occurred in the combustion unit 9), the operation control unit 21 proceeds to step #26 and performs a first gas stop process to stop the supply of the first gas to the anode 4 (i.e., the supply of raw fuel to the reforming unit 8). In other words, the operation control unit 21 is configured to perform an ignition process to operate the igniter 20 for ignition while supplying the first gas to the anode 4 (i.e., supplying raw fuel to the reforming unit 8) and supplying air to the cathode 6 at the start-up of the cell stack 7, and then, if there is a possibility of ignition of a high concentration of combustible components in the combustion unit 9, to perform the first gas stop process (i.e., a process to continue only the supply of air to the cathode 6).

[0062] By performing this first gas supply stop process, i.e., by continuing only the supply of air to the cathode 6, it is expected that the concentration of combustible components in the combustion section 9 downstream of the cathode 6 will gradually decrease. Then, the operation control section 21 continues only the supply of air to the cathode 6 in step #26 while the abnormal pressure condition is satisfied. On the other hand, if the abnormal pressure condition is no longer satisfied after performing this first gas supply stop process, the operation control section 21 proceeds to step #20 and again performs the ignition process (step #21) of activating the igniter 20 to ignite while supplying the first gas to the anode 4 (i.e., supplying raw fuel to the reforming section 8) and supplying air to the cathode 6.

[0063] As described above, after performing the ignition process, if the pressure measuring device 24 serving as the specific ignition detection unit 25 detects that a high concentration of flammable components has ignited in the combustion unit 9, the operation control unit 21 performs a first gas stop process that stops the supply of the first gas (i.e., hydrocarbon or hydrogen) to the anode 4. In other words, after performing the first gas stop process, the concentration of flammable components in the combustion unit 9 downstream of the anode 4 can be gradually reduced. As a result, even if the ignition process is performed thereafter, the occurrence of explosive ignition in the combustion unit 9 can be suppressed.

[0064] <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.

[0065] In the above embodiment, an example was described in which the fuel cell system is equipped with either a concentration measuring device 23 or a pressure measuring device 24 as the specific ignition detection unit 25, but the fuel cell system may also be equipped with both a concentration measuring device 23 and a pressure measuring device 24 as the specific ignition detection unit 25.

[0066] In the above embodiment, an example has been described in which the fuel cell system includes a reforming unit that reforms a raw fuel containing hydrocarbons, but the fuel cell system may be configured without a reforming unit. For example, the fuel cell system may be configured such that the first gas supply unit directly supplies hydrogen to the anode 4.

[0067] In the above embodiment, an example was described in which the fuel cell system was equipped with a combustion section temperature measuring device 22 as a means for determining whether normal ignition has occurred in the combustion section 9 and whether continuous combustion is occurring, but the configuration may also be such that the ignition state of the combustion section 9 is determined based on the detection results of the flame state inside the combustion section 9 using a flame rod or the like.

[0068] 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]

[0069] The present invention can be used in a fuel cell system that can minimize the occurrence of explosive ignition in the combustion section. [Explanation of symbols]

[0070] 3: Fuel cell 4: Anode 6: Cathode 7: Cell stack 9: Combustion section 20: Fire igniter 21: Operation control section 22: Combustion section temperature measuring instrument 23: Concentration measuring device 24: Pressure measuring instrument 25: Specific ignition detection unit

Claims

1. A fuel cell system comprising: a cell stack having a plurality of fuel cell units each having an anode and a cathode; a first gas supply unit that supplies a first gas containing hydrocarbon or hydrogen to the anode; a second gas supply unit that supplies a second gas containing oxygen to the cathode; a combustion unit that receives off-gas discharged from the anode and the cathode and combusts combustible components contained in the off-gas; an igniter that ignites the combustible components inside the combustion unit; and an operation control unit, a specific ignition detection unit that detects at least one of the occurrence of ignition of the high concentration of combustible components in the combustion unit and a state in which the possibility of ignition of the high concentration of combustible components in the combustion unit is increasing, The operation control unit performs an ignition process to activate the igniter while supplying the first gas to the anode and the second gas to the cathode when the cell stack is started, and then, if the specific ignition detection unit detects at least one of the occurrence of ignition of a high concentration of the flammable component in the combustion unit and a state in which the possibility of ignition of a high concentration of the flammable component in the combustion unit is increasing, performs a first gas stop process to stop the supply of the first gas to the anode.

2. a combustion section temperature measuring device for measuring the temperature inside the combustion section; 2. The fuel cell system of claim 1, wherein, after performing the ignition process, if the temperature inside the combustion section measured by the combustion section temperature measuring device does not show a predetermined temperature change trend, the operation control unit performs the ignition process again, activating the igniter to ignite while supplying the first gas to the anode and the second gas to the cathode.

3. the specific ignition detection unit has a concentration measuring device that measures the concentration of the combustible component present inside the combustion unit, 3. A fuel cell system as described in claim 1 or 2, wherein when the concentration of the combustible components measured by the concentration measuring device is equal to or greater than a predetermined first threshold, it is determined that there is an increased possibility of ignition of the high concentration of the combustible components in the combustion section.

4. 4. The fuel cell system according to claim 3, wherein, after performing the first gas stop process, if the concentration of the combustible component measured by the concentration measuring device becomes less than the first threshold value while the second gas is continuing to be supplied to the cathode, the operation control unit performs the ignition process of activating the igniter to ignite while the first gas is being supplied to the anode and the second gas is being supplied to the cathode.

5. the specific ignition detection unit has a pressure measuring device that measures the pressure inside the combustion unit, 3. The fuel cell system according to claim 1, wherein when an abnormal pressure condition is satisfied, the abnormal pressure condition includes at least one of the pressure inside the combustion unit measured by the pressure measuring device being equal to or greater than a predetermined second threshold value and the pressure inside the combustion unit changing by a range equal to or greater than a third threshold value within a predetermined period of time.

6. 6. The fuel cell system according to claim 5, wherein, after performing the first gas stop process, if the abnormal pressure condition is no longer satisfied while the second gas is being continuously supplied to the cathode, the operation control unit performs the ignition process of activating the igniter to ignite while the first gas is being supplied to the anode and the second gas is being supplied to the cathode.

7. a combustion section temperature measuring device for measuring the temperature inside the combustion section; The operation control unit, after performing the ignition process, if the temperature inside the combustion unit measured by the combustion unit temperature measuring device shows a predetermined temperature change tendency, 3. The fuel cell system according to claim 1, wherein a flow rate increasing process is performed to increase the flow rate per unit time of the first gas supplied to the anode and the flow rate per unit time of the second gas supplied to the cathode.

8. 8. The fuel cell system according to claim 7, wherein, in the flow rate increasing process, the operation control unit increases the flow rate of the first gas supplied to the anode and the flow rate of the second gas supplied to the cathode while maintaining a ratio of the flow rate per unit time of the first gas supplied to the anode and the flow rate per unit time of the second gas supplied to the cathode at a predetermined value.

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