Fuel cell system

Abstract

This invention provides a fuel cell system with a simple structure that prevents excessive temperature rise in the vaporization section and maintains an optimal temperature. [Solution] The fuel cell system includes a second water supply unit 26 that can supply water to the combustion exhaust gas space of the heat exchange unit 11, a vaporization unit 8 which includes a vaporization space into which water supplied from the first water supply unit 25 flows, and is configured such that the water supplied to the vaporization space comes into contact with a lower surface member 8b which constitutes the lower surface of the vaporization space, the heat exchange unit 11 which includes a combustion exhaust gas space through which combustion exhaust gas flows, and is configured such that heat exchange occurs between the combustion exhaust gas space and the vaporization space via the lower surface member 8b, and is configured so that water can be supplied to the combustion exhaust gas space from the second water supply unit 26.

Description

Technical Field

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[0003]

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

Background Art

[0002] In a fuel cell system, a raw fuel gas containing hydrocarbons is steam reformed, and a fuel gas containing hydrogen generated by the steam reforming is supplied to the anode. For example, in the case of steam reforming of methane, a steam reforming reaction for converting methane into hydrogen and carbon monoxide is performed as follows.

[0003] CH4+H2O→CO+3H2

[0004] Therefore, in a fuel cell system, it is necessary to stably supply steam. However, one of the major problems in a fuel cell system is the risk of carbon deposition. For example, when methane is heated without steam at a high temperature of about 650°C or higher, the following reaction (Boudouard reaction) proceeds and carbon is deposited.

[0005] CH4→C+2H2

[0006] When carbon deposition progresses on the anode of the fuel cell, it leads to a decrease in power generation performance. When carbon deposition progresses in the reforming section, it causes clogging of the gas flow path and fouling of the reforming catalyst, leading to a failure of the fuel cell.

[0007] The amount of water for generating the steam used in the reforming reaction is very small. On the other hand, since the inside of the vaporizer is in a high-temperature state of several hundred °C, there is a possibility that a flashing phenomenon occurs in which water droplets vaporize instantly when they come into contact with the evaporation surface. When water flashing occurs, the pressure inside the vaporization section rises rapidly, the raw fuel gas is not supplied to the inside of the vaporization section, and it develops into a phenomenon of fuel starvation in which fuel gas (hydrogen) is not supplied to the anode of the fuel cell, leading to a failure of the fuel cell.

[0008] Patent Document 1 (Japanese Patent Publication No. 2020-92096) describes a fuel cell system comprising a combustion section (combustion chamber 18) to which anode exhaust gas discharged from the anode and cathode exhaust gas discharged from the cathode are supplied to burn flammable components contained in the anode exhaust gas, a vaporization section (first container 143) to which water is supplied, and a heat exchange section (second container 144) to which combustion exhaust gas discharged from the combustion section is supplied, wherein heat from the heat exchange section (second container 144) is supplied to the vaporization section (first container 143) to vaporize the water. In this fuel cell system, the direction of gas flow in the vaporization section (first container 143) and the direction of gas flow in the heat exchange section (second container 144) are opposite, so that the downstream side of the vaporization section becomes hot, but the upstream side of the vaporization section is prevented from becoming excessively hot. As a result, the water in the vaporization section can be gradually heated and stably evaporated.

[0009] Patent Document 2 (Japanese Patent Publication No. 2024-20904) describes a fuel cell system comprising a combustion section (43) to which anode exhaust gas discharged from the anode and cathode exhaust gas discharged from the cathode are supplied to burn combustible components contained in the anode exhaust gas, a vaporization section (evaporation section 30) to which water is supplied, and a heat exchange section (exhaust gas flow section 35) to which combustion exhaust gas discharged from the combustion section is supplied, wherein heat from the heat exchange section (exhaust gas flow section 35) located below is supplied to the vaporization section (evaporation section 30) located above to vaporize the water. In addition, the internal space of the vaporization section (evaporation section 30) is filled with multiple metal heat storage members (32), and water supplied from above reaches the heat storage members (32) through perforated metal (33a). In other words, the water supplied from above first comes into contact with the relatively low-temperature heat storage member (32), which is located away from the heat exchange section (exhaust gas flow section 35) below, so it is expected that the boiling of the water will be suppressed. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2020-92096 [Patent Document 2] Japanese Patent Publication No. 2024-20904 [Overview of the project] [Problems that the invention aims to solve]

[0011] Conventional fuel cell systems employ a vaporization section that suffers from a complex structure.

[0012] This invention has been made in view of the above-mentioned problems, and its purpose is to provide a fuel cell system that can prevent excessive temperature rise in the vaporization section with a simple structure and maintain an optimal temperature. [Means for solving the problem]

[0013] A characteristic configuration of the fuel cell system according to the present invention for achieving the above objective is a raw fuel gas supply unit that supplies raw fuel gas containing hydrocarbons, A reforming unit that steam reforms the aforementioned raw fuel gas to produce a fuel gas containing hydrogen, A first water supply unit that supplies water used in the steam reforming process, A vaporization unit that vaporizes the water supplied from the first water supply unit and supplies water vapor to the reforming unit, A fuel cell unit comprising a fuel cell cell having an anode to which the fuel gas generated in the reforming unit is supplied, a cathode to which an oxidizing gas is supplied, and an electrolyte provided between the anode and the cathode, An oxidizing gas supply unit that supplies the oxidizing gas to the cathode, A combustion section is supplied with anode exhaust gas discharged from the anode and cathode exhaust gas discharged from the cathode, which can burn the combustible components contained in the anode exhaust gas. A fuel cell system comprising a heat exchange unit to which combustion exhaust gas discharged from the combustion unit is supplied, The heat exchange section includes a combustion exhaust gas space through which the combustion exhaust gas flows. The vaporization unit includes a vaporization space into which the water supplied from the first water supply unit flows, The water supplied to the vaporization space comes into contact with the lower surface member that constitutes the lower surface of the vaporization space. The combustion exhaust gas space and the vaporization space exchange heat through the lower surface member. The system includes a second water supply unit capable of supplying water to the combustion exhaust gas space, The combustion exhaust gas space is configured to be supplied with water from the second water supply unit.

[0014] According to the above characteristic configuration, the heat exchange unit is equipped with a combustion exhaust gas space through which combustion exhaust gas flows, and the combustion exhaust gas space and the vaporization space are configured to exchange heat via a lower surface member of the vaporization space that comes into contact with the supplied water. In other words, the heat transferred from the combustion exhaust gas to the lower surface member can be used to effectively vaporize the water that comes into contact with the lower surface member. In addition, since the system is configured to allow water to be supplied to the combustion exhaust gas space from a second water supply unit, supplying water to the combustion exhaust gas space prevents the temperature of the combustion exhaust gas space from becoming too high. Furthermore, since it is only necessary to supply water to the combustion exhaust gas space, the configuration of the fuel cell system does not become complicated. Therefore, a fuel cell system can be provided that prevents excessive temperature rise in the vaporization section with a simple structure and maintains an optimal temperature.

[0015] Another characteristic configuration of the fuel cell system according to the present invention is a bottom surface temperature sensor that measures the temperature of the bottom surface member of the vaporization space, It includes an operation control unit, The operation control unit controls the operation of the second water supply unit by referring to the temperature of the lower surface member measured by the lower surface temperature sensor, thereby adjusting the amount of water supplied per unit time to the combustion exhaust gas space.

[0016] According to the above-described configuration, the operation control unit can maintain the optimal temperature of the lower member of the vaporization section by adjusting the amount of water supplied per unit time to the combustion exhaust gas space by referring to the temperature of the lower member.

[0017] Another characteristic configuration of the fuel cell system according to the present invention is that the combustion exhaust gas space includes a first space facing the lower surface member and a second space not facing the lower surface member but facing the first space. It includes a combustion exhaust gas amount adjustment unit that adjusts the amount of the combustion exhaust gas supplied to the first space per unit time and the amount of the combustion exhaust gas supplied to the second space per unit time. The second water supply unit can supply water to the first space.

[0018] According to the above characteristic configuration, the combustion exhaust gas space is composed of a first space facing the lower surface member of the vaporization space where the supplied water contacts and a second space not facing the lower surface member. And the combustion exhaust gas amount adjustment unit can adjust the amount of the combustion exhaust gas supplied to the first space per unit time and the amount of the combustion exhaust gas supplied to the second space per unit time, and the second water supply unit can supply water to the first space. As a result, by the combustion exhaust gas amount adjustment unit adjusting the amount of the combustion exhaust gas supplied to the first space per unit time and the amount of the combustion exhaust gas supplied to the second space per unit time, the temperature of the lower surface member can be adjusted. Also, by the second water supply unit supplying water to the first space, the temperature of the lower surface member can be adjusted.

[0019] Another characteristic configuration of the fuel cell system according to the present invention is a lower surface temperature sensor that measures the temperature of the lower surface member of the vaporization space, and an operation control unit. The operation control unit, when the temperature of the lower surface member measured by the lower surface temperature sensor is lower than the target temperature, controls the operation of the combustion exhaust gas amount adjustment unit to increase the amount of the combustion exhaust gas supplied to the first space per unit time, when the temperature of the lower surface member measured by the lower surface temperature sensor is above the target temperature, controls the operation of the combustion exhaust gas amount adjustment unit to decrease the amount of the combustion exhaust gas supplied to the first space per unit time.

[0020] According to the above characteristic configuration, the operation control unit can control the operation of the combustion exhaust gas amount adjustment unit to bring the temperature of the lower surface member closer to the target temperature.

[0021] Another characteristic configuration of the fuel cell system according to the present invention is that the operation control unit controls the operation of the second water supply unit to supply water to the combustion exhaust gas space when the temperature of the lower surface member measured by the lower surface temperature sensor is above a predetermined threshold temperature that is higher than the target temperature.

[0022] According to the above-described configuration, the operation control unit controls the operation of the second water supply unit to supply water to the combustion exhaust gas space, thereby lowering the temperature of the lower member and bringing it closer to the target temperature.

[0023] Another characteristic configuration of the fuel cell system according to the present invention is that the operation control unit controls the operation of the second water supply unit to supply water to the combustion exhaust gas space when the rate of temperature rise of the lower surface member measured by the lower surface temperature sensor is equal to or greater than a predetermined threshold rate.

[0024] According to the above-described configuration, the operation control unit controls the operation of the second water supply unit to supply water to the combustion exhaust gas space, thereby reducing the rate at which the temperature of the lower surface member rises. [Brief explanation of the drawing]

[0025] [Figure 1] This is a diagram showing the configuration of a fuel cell system. [Figure 2] This is a diagram showing the configuration of the heat exchange section. [Figure 3] This is a flowchart illustrating the heat exchange process of the first embodiment. [Figure 4] This is a flowchart illustrating the heat exchange process of the second embodiment. [Figure 5] This is a flowchart illustrating the heat exchange process of the third embodiment. [Figure 6] This is a flowchart illustrating the heat exchange process of the fourth embodiment. [Modes for carrying out the invention]

[0026] <First Embodiment> A fuel cell system according to the first embodiment of the present invention will be described below with reference to the drawings. Figure 1 is a diagram illustrating the configuration of the fuel cell system.

[0027] The fuel cell system has a container 1, and inside the container 1 is a fuel cell section 7 in which multiple fuel cell cells 3 having anodes 4 and cathodes 6 are provided; a vaporization section 8 that generates water vapor; a reforming section 9 that steam reforms raw fuel gas containing hydrocarbons such as city gas to produce fuel gas containing hydrogen; a fuel gas supply passage 16 that supplies fuel gas from the reforming section 9 to the anodes 4; a combustion section 10 that burns the exhaust gas discharged from the fuel cell section 7; and a combustion exhaust gas passage 22 that guides the combustion exhaust gas generated in the combustion section 10 to the outside of the container 1. The container 1 and the equipment housed in the container 1 together are sometimes called a hot module 2.

[0028] A heat exchange section 11 is provided in the middle of the combustion exhaust gas passage 22, to which the combustion exhaust gas discharged from the combustion section 10 is supplied. In the heat exchange section 11, the heat from the combustion exhaust gas is transferred to the vaporization section 8 and the reforming section 9.

[0029] The fuel cell system also includes a raw fuel gas supply unit 23 that supplies raw fuel gas containing hydrocarbons to the reforming unit 9 from outside the container 1, an oxidant gas supply unit 24 that supplies air as an oxidant gas to the fuel cell unit 7 from outside the container 1, a first water supply unit 25 that supplies water used for steam reforming (hereinafter sometimes referred to as reforming water) from outside the container 1, and an operation control unit 13. The fuel cell system also includes a storage unit 14 for storing information. For example, the first water supply unit 25 supplies water from a water tank that stores water purified using an ion exchange resin or the like.

[0030] Water for reforming is supplied to the reforming section 9 via the first water supply channel 20. In this embodiment, a configuration is adopted in which the vaporization section 8 is located upstream of the reforming section 9, so the water for reforming is first supplied to the vaporization section 8. The vaporization section 8 vaporizes the supplied water for reforming and supplies steam to the reforming section 9. The first water supply channel 20 is provided with a first water supply section 25, which supplies water for reforming used in steam reforming, and is realized using a pump, flow meter, etc. The first water supply section 25 can adjust the flow rate of water for reforming per unit time supplied to the vaporization section 8 and the reforming section 9. In the vaporization section 8, the heat of combustion generated in the combustion section 10, which will be described later, is transferred to vaporize the water for reforming supplied from the first water supply section 25. The operation of the first water supply unit 25 is controlled by the operation control unit 13.

[0031] Furthermore, the vaporization section 8 is supplied with raw fuel gas containing hydrocarbons via the raw fuel gas supply passage 15. In other words, the reforming section 9, located downstream of the vaporization section 8, is supplied with raw fuel gas containing hydrocarbons via the raw fuel gas supply passage 15. The raw fuel gas supply passage 15 is provided with a raw fuel gas supply section 23, which supplies the raw fuel gas using a blower, flow meter, etc. The raw fuel gas supply section 23 can adjust the flow rate of raw fuel gas per unit time supplied to the reforming section 9. In this embodiment, since the vaporization section 8 is located upstream of the reforming section 9, the water vapor generated in the vaporization section 8 and the supplied raw fuel gas are mixed in the vaporization section 8. The operation of the raw fuel gas supply unit 23 is controlled by the operation control unit 13.

[0032] In the reforming unit 9, heat from the combustion exhaust gas is transferred by the heat exchange unit 11. Then, in the reforming unit 9, the raw fuel gas supplied from the raw fuel gas supply unit 23 is steam reformed to produce a fuel gas containing hydrogen. The fuel gas produced in the reforming unit 9 flows to the fuel cell unit 7 via the fuel gas supply passage 16. In addition, if the reforming process of the raw fuel gas is not sufficiently performed in the reforming unit 9, such as during startup, the raw fuel gas is also supplied from the reforming unit 9 to the fuel cell unit 7 via the fuel gas supply passage 16.

[0033] The fuel cell unit 7 comprises a fuel cell cell 3 having an anode 4 to which the fuel gas produced in the reforming unit 9 is supplied, a cathode 6 to which an oxidizing gas is supplied, and an electrolyte 5 provided between the anode 4 and the cathode 6. For example, the fuel cell cell 3 is a solid oxide type fuel cell cell using a solid electrolyte.

[0034] The fuel cell system includes a fuel gas supply passage 16 through which the fuel gas generated in the reforming unit 9 flows toward the anode 4 of the fuel cell unit 7, and an oxidizer gas supply passage 17 through which air supplied to the fuel cell unit 7 flows. If fuel gas is not generated in the reforming unit 9, raw fuel gas flows through the fuel gas supply passage 16, and as a result, raw fuel gas is supplied to the anode 4.

[0035] Each fuel cell cell 3 generates electricity using the fuel gas produced in the reforming unit 9 and air (oxygen) supplied as an oxidizer gas from the oxidizer gas supply unit 24. Specifically, the anode 4 is supplied with fuel gas via the fuel gas supply passage 16, and the cathode 6 is supplied with air (oxygen) via the oxidizer gas supply passage 17. In addition, if the raw fuel gas is not sufficiently reformed in the reforming unit 9, such as during startup, the raw fuel gas is also supplied from the reforming unit 9 to the anode 4. The oxidizer gas supply passage 17 is equipped with an oxidizer gas supply unit 24, which supplies air as an oxidizer gas, and is implemented using a pump, flow meter, etc. The oxidizer gas supply unit 24 can adjust the flow rate of air per unit time supplied to the fuel cell unit 7. The operation of the oxidizer gas supply unit 24 is controlled by the operation control unit 13.

[0036] Furthermore, not all of the fuel gas supplied to the anode 4, such as hydrogen, is used for power generation; the anode exhaust gas discharged from the anode 4 also contains flammable components such as hydrogen. If fuel gas is not generated in the reforming unit 9, the raw fuel gas flows through the fuel gas supply passage 16, in which case the anode exhaust gas discharged from the anode 4 contains the raw fuel gas. Oxygen is also contained in the cathode exhaust gas discharged from the cathode 6. The combustion unit 10 receives the anode exhaust gas from the fuel cell unit 7 via the anode exhaust gas passage 18, and the cathode exhaust gas from the fuel cell unit 7 via the cathode exhaust gas passage 19. In the combustion unit 10, the anode exhaust gas discharged from the anode 4 and the cathode exhaust gas discharged from the cathode 6 are supplied to burn the flammable components contained in the anode exhaust gas. Ignition of the flammable components is performed by the igniter 12. The heat of combustion generated in the combustion unit 10 raises the temperature of the internal space of the container 1. In addition, the combustion exhaust gas is supplied to the heat exchange section 11, where heat is transferred to the vaporization section 8 and the reforming section 9. The combustion exhaust gas discharged from the heat exchange section 11 is discharged to the outside of the container 1 via a combustion catalyst section 37 located in the combustion exhaust gas passage 22 downstream of the heat exchange section 11. In the combustion catalyst section 37, hydrogen, hydrocarbons, carbon monoxide, etc., contained in the gas flowing through the combustion exhaust gas passage 22 are catalytically combusted using oxygen. The operation of the igniter 12 is controlled by the operation control unit 13.

[0037] In the fuel cell system of this embodiment, the heat exchange unit 11 includes a combustion exhaust gas space 36 through which combustion exhaust gas flows. The vaporization unit 8 includes a vaporization space 8a into which water supplied from the first water supply unit 25 flows, and the water supplied to the vaporization space 8a comes into contact with a lower surface member 8b that constitutes the lower surface of the vaporization space 8a, causing heat exchange between the combustion exhaust gas space 36 and the vaporization space 8a via the lower surface member 8b, and includes a second water supply unit 26 that can supply water to the combustion exhaust gas space 36, and is configured so that water can be supplied to the combustion exhaust gas space 36 from the second water supply unit 26. The second water supply unit 26 may supply, for example, tap water to the combustion exhaust gas space 36.

[0038] In addition, the fuel cell system is equipped with a bottom temperature sensor 35 that measures the temperature of the bottom member 8b of the vaporization space 8a, and the operation control unit 13 controls the operation of the second water supply unit 26 by referring to the temperature of the bottom member 8b measured by the bottom temperature sensor 35 to adjust the amount of water supplied per unit time to the combustion exhaust gas space 36.

[0039] Figure 2 shows the configuration of the heat exchange section 11. As shown in the figure, the heat exchange section 11 of this embodiment comprises a first heat exchange section 11a and a second heat exchange section 11b. The combustion exhaust gas space 36 of the heat exchange section 11 comprises a first space 36a facing the lower surface member 8b and a second space 36b that does not face the lower surface member 8b but faces the first space 36a. In other words, the first heat exchange section 11a has the first space 36a, and the second heat exchange section 11b has the second space 36b. Furthermore, a combustion exhaust gas amount adjustment unit 34 is provided to adjust the amount of combustion exhaust gas supplied per unit time to the first space 36a and the amount of combustion exhaust gas supplied per unit time to the second space 36b.

[0040] The combustion exhaust gas passage 22 branches into a first combustion exhaust gas passage 22a and a second combustion exhaust gas passage 22b. The combustion exhaust gas volume adjustment unit 34 includes a first combustion exhaust gas volume adjustment unit 34a located in the middle of the first combustion exhaust gas passage 22a, and a second combustion exhaust gas volume adjustment unit 34b located in the middle of the second combustion exhaust gas passage 22b. For example, the first combustion exhaust gas volume adjustment unit 34a and the second combustion exhaust gas volume adjustment unit 34b are valves whose opening degree can be adjusted. The operation control unit 13 can adjust the amount of combustion exhaust gas per unit time supplied to the first space 36a and the amount of combustion exhaust gas per unit time supplied to the second space 36b by adjusting the opening degrees of the first combustion exhaust gas volume adjustment unit 34a and the second combustion exhaust gas volume adjustment unit 34b. Furthermore, since the second water supply passage 21 is connected to the first combustion exhaust gas passage 22a, the second water supply unit 26 can supply water to the first space 36a.

[0041] Figure 3 is a flowchart illustrating the heat exchange process performed by the operation control unit 13. The operation control unit 13 repeatedly performs the heat exchange process shown in this flowchart while the raw fuel gas is undergoing steam reforming in the reforming unit 9.

[0042] As shown in the figure, in step #10, the operation control unit 13 determines whether the temperature of the lower member 8b is lower than the target temperature (for example, 200°C). If the temperature of the lower member 8b is lower than the target temperature (if the answer in step #10 is "Yes"), the operation control unit 13 proceeds to step #11; if the temperature of the lower member 8b is equal to or higher than the target temperature (if the answer in step #10 is "No"), the operation control unit 13 proceeds to step #12.

[0043] In step #11, if the temperature of the lower member 8b measured by the lower temperature sensor 35 is lower than the target temperature, the operation control unit 13 controls the operation of the combustion exhaust gas amount adjustment unit 34 to increase the amount of combustion exhaust gas supplied per unit time to the first space 36a. As a result, the temperature of the lower member 8b rises.

[0044] In contrast, in step #12, if the temperature of the lower member 8b measured by the lower temperature sensor 35 is above the target temperature, the operation control unit 13 controls the operation of the combustion exhaust gas amount adjustment unit 34 to reduce the amount of combustion exhaust gas supplied to the first space 36a per unit time. As a result, the temperature of the lower member 8b decreases.

[0045] Subsequently, in step #13, the operation control unit 13 determines whether the temperature of the lower member 8b measured by the lower temperature sensor 35 is above a predetermined threshold temperature, which is higher than the target temperature. In other words, the operation control unit 13 determines whether the temperature of the lower member 8b is excessively high. If the temperature of the lower member 8b measured by the lower temperature sensor 35 is above the threshold temperature, the operation control unit 13 proceeds to step #14 and controls the operation of the second water supply unit 26 to supply water to the combustion exhaust gas space 36 (first space 36a). By supplying water to the combustion exhaust gas space 36 (first space 36a), the temperature of the combustion exhaust gas space 36 (first space 36a) is rapidly reduced, and as a result, the temperature of the lower member 8b is rapidly reduced.

[0046] In response, the operation control unit 13 terminates the heat exchange process if the temperature of the lower surface member 8b, as measured by the lower surface temperature sensor 35, is lower than the threshold temperature.

[0047] As described above, the heat exchange unit 11 is equipped with a combustion exhaust gas space 36 through which combustion exhaust gas flows, and the combustion exhaust gas space 36 and the vaporization space 8a of the vaporization unit 8 are configured to exchange heat via the lower surface member 8b of the vaporization space 8a, which is in contact with the supplied water. In other words, the heat transferred from the combustion exhaust gas to the lower surface member 8b can be used to effectively vaporize the water in contact with the lower surface member 8b. In addition, since the combustion exhaust gas space 36 is configured to be supplied with water from the second water supply unit 26, supplying water to the combustion exhaust gas space 36 prevents the temperature of the combustion exhaust gas space 36 from becoming too high. Furthermore, since it is only necessary to supply water to the combustion exhaust gas space 36, the configuration of the fuel cell system does not become complicated.Therefore, a fuel cell system can be provided that prevents excessive temperature rise in the vaporization unit 8 with a simple structure and maintains an optimal temperature.

[0048] <Second Embodiment> The fuel cell system of the second embodiment differs from the embodiment described above in its heat exchange process. The fuel cell system of the second embodiment will be described below, but the same configuration as in the embodiment described above will be omitted.

[0049] Figure 4 is a flowchart illustrating the heat exchange process of the second embodiment. Steps #20, #21, and #22 shown in Figure 4 are the same as steps #10, #11, and #12 shown in Figure 3, so their explanation is omitted.

[0050] In step #23, the operation control unit 13 determines whether the rate of temperature rise of the lower member 8b, as measured by the lower temperature sensor 35, is equal to or greater than a predetermined threshold rate. If the rate of temperature rise of the lower member 8b, as measured by the lower temperature sensor 35, is equal to or greater than the threshold rate, the operation control unit 13 proceeds to step #24 and controls the operation of the second water supply unit 26 to supply water to the combustion exhaust gas space 36 (first space 36a). In other words, if a rapid temperature rise occurs in the lower member 8b of the vaporization unit 8, supplying water to the combustion exhaust gas space 36 (first space 36a) reduces the rate of temperature rise of the lower member 8b, that is, it suppresses a rapid temperature rise in the lower member 8b.

[0051] In response, the operation control unit 13 terminates the heat exchange process if the rate of temperature rise of the lower surface member 8b, as measured by the lower surface temperature sensor 35, is lower than a threshold rate.

[0052] <Third Embodiment> In the first and second embodiments, an example was described in which the combustion exhaust gas space 36 of the heat exchange unit 11 comprises a first space 36a and a second space 36b facing the lower surface member 8b, but the combustion exhaust gas space 36 may be composed of a single space. In other words, in this embodiment, the amount of combustion exhaust gas supplied to the combustion exhaust gas space 36 per unit time cannot be adjusted. The fuel cell system of the third embodiment will be described below, but the same configuration as in the above embodiments will not be described.

[0053] Figure 5 is a flowchart illustrating the heat exchange process of the third embodiment. In step #30, the operation control unit 13 determines whether the temperature of the lower member 8b measured by the lower temperature sensor 35 is above a predetermined threshold temperature, which is higher than the target temperature. If the temperature of the lower member 8b measured by the lower temperature sensor 35 is above the threshold temperature, the operation control unit 13 proceeds to step #31 and controls the operation of the second water supply unit 26 to supply water to the combustion exhaust gas space 36. By supplying water to the combustion exhaust gas space 36, the temperature of the combustion exhaust gas space 36 is rapidly reduced, and as a result, the temperature of the lower member 8b is rapidly reduced.

[0054] In response, the operation control unit 13 terminates the heat exchange process if the temperature of the lower surface member 8b, as measured by the lower surface temperature sensor 35, is lower than the threshold temperature.

[0055] <Fourth Embodiment> The fuel cell system of the fourth embodiment differs from that of the third embodiment in the heat exchange process. The fuel cell system of the fourth embodiment will be described below, but the same configuration as in the above embodiments will not be described.

[0056] Figure 6 is a flowchart illustrating the heat exchange process of the fourth embodiment. In step #40, the operation control unit 13 determines whether the rate of temperature rise of the lower member 8b, as measured by the lower temperature sensor 35, is equal to or greater than a predetermined threshold rate. If the rate of temperature rise of the lower member 8b, as measured by the lower temperature sensor 35, is equal to or greater than the threshold rate, the operation control unit 13 proceeds to step #41 and controls the operation of the second water supply unit 26 to supply water to the combustion exhaust gas space 36. In other words, if a rapid temperature rise occurs in the lower member 8b of the vaporization unit 8, supplying water to the combustion exhaust gas space 36 can reduce the rate of temperature rise of the lower member 8b, that is, it can suppress a rapid temperature rise in the lower member 8b.

[0057] In response, the operation control unit 13 terminates the heat exchange process if the rate of temperature rise of the lower surface member 8b, as measured by the lower surface temperature sensor 35, is lower than a threshold rate.

[0058] <Another Embodiment> In the above embodiment, specific examples of the fuel cell system configuration have been given, but the configuration can be modified as appropriate. For example, in the above embodiment, a configuration was described in which the second water supply unit 26 supplies tap water or the like to the combustion exhaust gas space 36. However, the second water supply unit 26 may also supply purified water to the combustion exhaust gas space 36, similar to the first water supply unit 25. Furthermore, in the above embodiment, an example was described in which the combustion exhaust gas volume adjustment unit 34 is realized using two valves, a first combustion exhaust gas volume adjustment unit 34a and a second combustion exhaust gas volume adjustment unit 34b, but other configurations are also possible. For example, the combustion exhaust gas volume adjustment unit 34 may be realized by a single valve provided at the branching point between the first combustion exhaust gas passage 22a and the second combustion exhaust gas passage 22b, which can adjust the amount of combustion exhaust gas supplied to the first combustion exhaust gas passage 22a and the amount of combustion exhaust gas supplied to the second combustion exhaust gas passage 22b.

[0059] In the above embodiment, the target temperature may be set as a numerical value with a range (i.e., a target temperature range).

[0060] The configurations disclosed in the above embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, as long as no inconsistencies arise. Furthermore, the embodiments disclosed herein are illustrative, and the embodiments of the present invention are not limited thereto and can be modified as appropriate without departing from the purpose of the present invention. [Industrial applicability]

[0061] This invention can be used in fuel cell systems that have a simple structure to prevent excessive temperature rise in the vaporization section and maintain an optimal temperature. [Explanation of symbols]

[0062] 3: Fuel cell 4: Anode 5: Electrolyte 6: Cathode 7:Fuel cell section 8: Vaporization section 8a: Vaporization space 8b:Bottom member 9: Modification section 10: Combustion section 11:Heat exchange part 13: Operation Control Unit 23: Raw Material and Fuel Gas Supply Department 24: Oxidizer gas supply unit 25: 1st water supply section 26:Second water supply section 26: Combustion exhaust gas space 34: Combustion exhaust gas volume adjustment unit 34a: First combustion exhaust gas volume adjustment unit 34b: Second combustion exhaust gas volume adjustment unit 35: Bottom temperature sensor 36: Combustion exhaust gas space 36a: 1st space 36b: 2nd space

Claims

1. A raw fuel gas supply unit that supplies raw fuel gases containing hydrocarbons, A reforming unit that steam reforms the aforementioned raw fuel gas to produce a fuel gas containing hydrogen, A first water supply unit that supplies water used in the steam reforming process, A vaporization unit that vaporizes the water supplied from the first water supply unit and supplies water vapor to the reforming unit, A fuel cell unit comprising a fuel cell cell having an anode to which the fuel gas generated in the reforming unit is supplied, a cathode to which an oxidizing gas is supplied, and an electrolyte provided between the anode and the cathode, An oxidizing gas supply unit that supplies the oxidizing gas to the cathode, A combustion section is supplied with anode exhaust gas discharged from the anode and cathode exhaust gas discharged from the cathode, which can burn the combustible components contained in the anode exhaust gas. A fuel cell system comprising a heat exchange unit to which combustion exhaust gas discharged from the combustion unit is supplied, The heat exchange section includes a combustion exhaust gas space through which the combustion exhaust gas flows. The vaporization unit includes a vaporization space into which the water supplied from the first water supply unit flows, The water supplied to the vaporization space comes into contact with the lower surface member that constitutes the lower surface of the vaporization space. The combustion exhaust gas space and the vaporization space exchange heat through the lower surface member. The system includes a second water supply unit capable of supplying water to the combustion exhaust gas space, A fuel cell system configured to supply water to the combustion exhaust gas space from the second water supply unit.

2. A bottom surface temperature sensor for measuring the temperature of the bottom surface member in the vaporization space, It includes an operation control unit, The fuel cell system according to claim 1, wherein the operation control unit controls the operation of the second water supply unit by referring to the temperature of the lower member measured by the lower surface temperature sensor to adjust the amount of water supplied per unit time to the combustion exhaust gas space.

3. The combustion exhaust gas space comprises a first space facing the lower surface member and a second space that does not face the lower surface member but faces the first space. The system includes a combustion exhaust gas quantity adjustment unit that adjusts the amount of combustion exhaust gas supplied per unit time to the first space and the amount of combustion exhaust gas supplied per unit time to the second space. The fuel cell system according to claim 1, wherein the second water supply unit can supply water to the first space.

4. A bottom surface temperature sensor for measuring the temperature of the bottom surface member in the vaporization space, It includes an operation control unit, The aforementioned operation control unit, If the temperature of the lower surface member measured by the lower surface temperature sensor is lower than the target temperature, the operation of the combustion exhaust gas volume adjustment unit is controlled to increase the amount of combustion exhaust gas supplied to the first space per unit time. The fuel cell system according to claim 3, wherein if the temperature of the lower surface member measured by the lower surface temperature sensor is equal to or greater than the target temperature, the operation of the combustion exhaust gas volume adjustment unit is controlled to reduce the amount of combustion exhaust gas supplied to the first space per unit time.

5. The fuel cell system according to claim 2 or 4, wherein the operation control unit controls the operation of the second water supply unit to supply water to the combustion exhaust gas space when the temperature of the lower member measured by the lower surface temperature sensor is above a predetermined threshold temperature that is higher than the target temperature.

6. The fuel cell system according to claim 2 or 4, wherein the operation control unit controls the operation of the second water supply unit to supply water to the combustion exhaust gas space when the rate of temperature rise of the lower surface member measured by the lower surface temperature sensor is equal to or greater than a predetermined threshold rate.

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