Solid oxide-type fuel battery system

Abstract

To provide a solid oxide-type fuel battery system capable of sufficiently securing water used for steam reforming and outputting large power during a time zone in which a power demand increases.SOLUTION: A solid oxide-type fuel battery system S includes: a combustion unit 11 that combusts off-gas discharged from a plurality of fuel battery cells 8; a heat recovery device H that recovers heat from combustion exhaust gas discharged from the combustion unit 11; and a water tank 19 that stores recovered water recovered from the combustion exhaust gas by the heat recovery device H. The water stored in the water tank 19 is used for steam reforming of raw fuel in a reforming unit 6. An operation control unit 26 operates a cell stack 9 in a water amount-increase mode during a predetermined advance time zone before a high-demand time zone when at least a high-demand condition is satisfied in the high-demand condition in which it is predicted that a power demand in a power system increases and a high-temperature condition in which it is predicted that a temperature rises during the high-demand time zone in which a power demand in the power system increases.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Patent Document 1 (Japanese Patent No. 5438420) describes a solid oxide fuel cell system including a reforming section that generates fuel gas by steam reforming a supplied raw fuel, and a cell stack in which multiple solid oxide fuel cells that generate power using the fuel gas generated in the reforming section are stacked. In this solid oxide fuel cell system, off-gas discharged from the cell stack is combusted, and the resulting combustion exhaust gas is cooled to condense water, and the condensed water is collected in a tank. The water collected in the tank is then used to steam reform the raw fuel.

[0003] Therefore, in the solid oxide fuel cell system described in Patent Document 1, when the water level sensor detects that the water level in the tank is lower than the high water level, the output of the cell stack is limited to a low value regardless of the magnitude of the power load. When the output of the cell stack decreases, for example, the amount of reforming water required per unit time for steam reforming decreases, and it is expected that the water level in the tank will return to above the high water level. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5438420 Summary of the Invention [Problem to be solved by the invention]

[0005] In a solid oxide fuel cell system, the higher the outside temperature, the lower the ability to cool the combustion exhaust gas, so the tank water level is more likely to drop during times when the outside temperature is high. Therefore, in the solid oxide fuel cell system described in Patent Document 1, the tank water level is more likely to drop during daytime hours in summer, for example, and the output of the fuel cell is more likely to be suppressed or stopped.

[0006] In addition, since the electricity usage rate is high during the daytime in summer, the electricity value can be said to be high during those times. Therefore, the solid oxide fuel cell system described in Patent Document 1 is likely to have its output suppressed or stopped during times when the electricity value is high, and therefore, there is a high possibility that the economic benefits of installing the solid oxide fuel cell system cannot be fully enjoyed.

[0007] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a solid oxide fuel cell system that can output large amounts of power during periods of high power demand while ensuring sufficient water for steam reforming. [Means for solving the problem]

[0008] A characteristic configuration of a solid oxide fuel cell system according to the present invention for achieving the above object is a solid oxide fuel cell comprising: a reforming section which generates fuel gas by steam reforming a raw fuel; a cell stack in which a plurality of solid oxide fuel cells which generate power using the fuel gas generated in the reforming section are stacked; a combustion section which combusts off-gas discharged from the plurality of fuel cells; a heat recovery device which recovers heat from the combustion exhaust gas discharged from the combustion section; a water tank which stores water recovered from the combustion exhaust gas by cooling the combustion exhaust gas with the heat recovery device; and an operation control section which controls operation, wherein the water stored in the water tank is used for steam reforming of the raw fuel in the reforming section, and the operation control section is configured to stop the power generation operation of the cell stack or suppress the power generation output when the amount of water stored in the water tank falls below a predetermined lower limit water amount, The operation control unit operates the cell stack in a water volume increase mode to increase the amount of water in the water tank for a predetermined advance time period prior to the high demand time period when at least one of a high demand condition in which an increase in power demand in the power system is predicted and a high temperature condition in which an increase in temperature in the area in which the cell stack is installed is predicted during a high demand time period when power demand in the power system increases is satisfied.

[0009] According to the above characteristic configuration, when at least the high demand condition is satisfied, the operation control unit operates the cell stack in a water volume increase mode for increasing the amount of water in the water tank during a predetermined advance time period before the high demand time period. In other words, the amount of water in the water tank is increased before the high demand time period when the power demand in the power system increases. As a result, it is possible to prevent the amount of water stored in the water tank from falling below a predetermined lower limit during the high demand time period, and it is expected that the power generation operation of the cell stack will continue during the high demand time period. Therefore, it is possible to provide a solid oxide fuel cell system that can output a large amount of electric power during periods of high demand for electric power while ensuring a sufficient amount of water for steam reforming.

[0010] Another characteristic feature of the solid oxide fuel cell system according to the present invention is that, in the water amount increase mode, the operation control unit controls the output power of the cell stack to a predetermined power that is less than a rated power. Here, the predetermined power may be the minimum output power that the cell stack can output.

[0011] According to the above characteristic configuration, by setting the output power of the cell stack to a predetermined power less than the rated power, the amount of reforming water required per unit time for steam reforming is reduced compared to when the output power of the cell stack is set to the rated power. As a result, it is expected that the amount of recovered water recovered from the combustion exhaust gas per unit time will be greater than the amount of reforming water used per unit time in steam reforming, and the amount of water stored in the water tank is expected to increase.

[0012] Another characteristic configuration of the solid oxide fuel cell system of the present invention is that the operation control unit is configured to operate the cell stack in the water increase mode during the advance time period when the high demand condition and the high temperature condition are satisfied, and determines that the high temperature condition is satisfied when the predicted maximum temperature during the high demand time period is equal to or higher than a predetermined temperature.

[0013] In a solid oxide fuel cell system, the higher the temperature, the lower the system's ability to cool the combustion exhaust gas, so there is a high possibility that the water level in the water tank will drop during hot periods. Therefore, in this characteristic configuration, the operation control unit determines that the high temperature condition is met when the predicted maximum temperature during the high demand time period is equal to or higher than a predetermined temperature, and operates the cell stack in the increased water volume mode before the high demand time period when power demand in the power system increases. As a result, it is expected that the amount of water stored in the water tank during the high demand time period will not fall below a predetermined lower limit, and the power generation operation of the cell stack will continue during the high demand time period.

[0014] Another characteristic configuration of the solid oxide fuel cell system of the present invention is that the operation control unit is configured to operate the cell stack in the water increase mode during the advance time period when the high demand condition and the high temperature condition are satisfied, and to determine that the high temperature condition is satisfied when a day including the high demand time period falls on a day that is predetermined to have high air temperatures.

[0015] For example, in summer, the temperature is likely to be higher than in winter, spring, autumn, etc., and therefore the solid oxide fuel cell system is likely to have a reduced ability to cool the combustion exhaust gas. In other words, summer can be predetermined as days when the temperature is high, and these days can be predetermined as days when the water level in the water tank is likely to drop. Therefore, in this characteristic configuration, the operation control unit determines that the high temperature condition is met if a day including a high demand time period falls on a day that is predetermined to be associated with high temperatures, and operates the cell stack in increased water volume mode prior to the high demand time period when power demand in the power grid increases. As a result, it is expected that the amount of water stored in the water tank during the high demand time period will not fall below a predetermined lower limit, and that the cell stack will continue to operate as a generator during the high demand time period.

[0016] Another characteristic configuration of the solid oxide fuel cell system according to the present invention is that the heat recovery device has a heat exchange section to which the combustion exhaust gas discharged from the combustion section is supplied, and a hot water storage tank for storing hot water, and is configured to circulate hot water by supplying hot water taken out from a lower part of the hot water storage tank to the heat exchange section and returning the hot water that has flowed through the heat exchange section to an upper part of the hot water storage tank, thereby storing the heat of the combustion exhaust gas recovered by the heat exchange section in the hot water storage tank, A hot water outlet passage is connected to the top of the hot water storage tank for discharging the hot water stored in the hot water storage tank to the outside, and a water supply passage is connected to the bottom of the hot water storage tank for supplying water to the hot water storage tank.A predetermined water supply pressure is applied to the hot water inside the hot water storage tank by the water supply passage, so that water is supplied from the water supply passage into the hot water storage tank in response to the hot water being discharged from the hot water storage tank into the hot water outlet passage.

[0017] According to the above characteristic configuration, the heat recovered by the heat recovery device can be stored in the hot water storage tank, and the heat can be supplied from the hot water outlet passage.

[0018] Another characteristic feature of the solid oxide fuel cell system according to the present invention is a heat dissipation unit that can perform a heat dissipation operation to dissipate heat from hot water taken out from a lower part of the hot water storage tank and supplied to the heat exchange unit, The operation control unit causes the heat radiating unit to perform the heat radiating operation in the water amount increase mode.

[0019] According to the above-mentioned characteristic configuration, by operating the heat dissipation section in the heat dissipation mode, it is possible to promote heat dissipation from the combustion exhaust gas in the heat exchange section, thereby promoting cooling of the combustion exhaust gas in the heat exchange section and promoting condensation of water from the combustion exhaust gas.

[0020] Another characteristic feature of the solid oxide fuel cell system according to the present invention is that, in the water volume increase mode, the operation control unit causes hot water or water in an amount greater than a set amount to be discharged from the hot water storage tank through the hot water outlet path.

[0021] According to the above characteristic configuration, by discharging hot water at a set amount or more from the hot water storage tank through the hot water outlet passage, water is supplied from the water supply passage to the lower part of the hot water storage tank, and the water is supplied to the heat exchanger. In other words, the relatively high temperature hot water originally stored in the hot water storage tank is not supplied to the heat exchanger, but the relatively low temperature water supplied from the water supply passage is supplied to the heat exchanger and used to cool the combustion exhaust gas. As a result, the cooling of the combustion exhaust gas is promoted in the heat exchanger, and the condensation of water from the combustion exhaust gas is promoted. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing a configuration of a system including a facility in which a solid oxide fuel cell system is installed. [Diagram 2] FIG. 1 is a diagram showing a configuration of a solid oxide fuel cell system. [Diagram 3] 4 is a flowchart illustrating an operation mode determination process for a solid oxide fuel cell system. [Figure 4] FIG. 2 is a diagram illustrating a schematic diagram of a high-demand time period and an advance time period. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] A solid oxide fuel cell system S according to an embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a diagram showing the configuration of a system including a facility F in which the solid oxide fuel cell system S is installed. Fig. 2 is a diagram showing the configuration of the solid oxide fuel cell system S.

[0024] As shown in FIG. 1, a solid oxide fuel cell system S is provided in a facility F such as a residence or a business office. A power line 32 connected to a power grid is provided in the facility F. A power consumption device L and a solid oxide fuel cell system S are connected to the power line 32. The power consumption device L and the solid oxide fuel cell system S are connected to the power line 32 linked to the power grid and can receive power from the power grid. In addition, the power generated by the solid oxide fuel cell system S can be supplied to the power grid via the power line 32. A gas containing a hydrocarbon, such as city gas, is supplied from a gas pipe 33 to the solid oxide fuel cell system S and a gas consumption device G provided in the facility F. The gas, such as city gas, supplied from the gas pipe 33 corresponds to the "raw fuel" of the present invention and may be referred to as the raw fuel in the following description.

[0025] The communication unit 28 of the solid oxide fuel cell system S is connected to an information and communication network N, and can communicate information with devices outside the facility F. The solid oxide fuel cell system S can communicate information with an information providing server P that provides, for example, information on the weather and information on the power supply and demand situation in the power grid.

[0026] As shown in FIG. 2, the solid oxide fuel cell system S includes various components in an outer container 1. A hot module 31 is provided in the outer container 1. The hot module 31 includes an inner container 2 that houses devices such as a cell stack 9 that operate in a high-temperature environment. Specifically, an evaporation section 5, a reforming section 6, a manifold 7, a cell stack 9, and the like are provided in the inner container 2. The evaporation section 5 generates steam by evaporating reforming water supplied from a water tank 19 through a reforming water supply passage L6, and supplies the steam to the reforming section 6. The reforming section 6 generates fuel gas by steam reforming a raw fuel (such as city gas) containing hydrocarbons supplied through a raw fuel supply passage L1 using the steam generated in the evaporation section 5. That is, the water stored in the water tank 19 is used for steam reforming of the raw fuel in the reforming section 6.

[0027] The cell stack 9 is configured by stacking multiple solid oxide fuel cells 8 that generate electricity using the fuel gas produced in the reforming unit 6. For example, the fuel gas produced in the reforming unit 6 passes through a fuel gas supply path L3 to reach a manifold 7, where the fuel gas is distributed to each of the fuel cells 8. The cell stack 9 is connected to a power line 32 via a power conversion unit 18.

[0028] The space above the cell stack 9 serves as a combustion section 11 that combusts off-gas discharged from the multiple fuel cell units 8. The heat of this combustion is transferred to the vaporization section 5 and reforming section 6 above it. The ignition section 10 ignites the off-gas.

[0029] An air supply passage L2 is connected to the air inlet 12 of the inner container 2, and air (oxygen) is supplied to the inside of the inner container 2. Gas present inside the inner container 2 is exhausted to the outside of the inner container 2 from the exhaust port 13 of the inner container 2. The exhaust gas exhausted from the inside of the inner container 2 contains the combustion exhaust gas exhausted from the combustion section 11. The exhaust port 13 is provided with a combustion catalyst section 14 that catalytically combusts hydrogen, carbon monoxide, etc. contained in the exhaust gas using oxygen.

[0030] The solid oxide fuel cell system S includes a heat recovery device H that recovers heat from the combustion exhaust gas discharged from the combustion section 11. Specifically, the heat recovery device H includes a heat exchange section 16 to which exhaust gas discharged from the inner vessel 2, including the combustion exhaust gas discharged from the combustion section 11, a hot water storage tank 23 that stores hot water, and a hot water circulation path L9 that circulates hot water between the heat exchange section 16 and the hot water storage tank 23, and is configured to supply hot water taken out from the lower part of the hot water storage tank 23 to the heat exchange section 16 and return the hot water that has flowed through the heat exchange section 16 to the upper part of the hot water storage tank 23, thereby circulating the hot water, thereby storing the heat of the combustion exhaust gas recovered by the heat exchange section 16 in the hot water storage tank 23.

[0031] The exhaust gas that has passed through the combustion catalyst section 14 is discharged to the outside of the inner vessel 2, flows through the exhaust gas flow path L4, and is supplied to the heat exchange section 16. In the heat exchange section 16, heat is exchanged between the exhaust gas and hot water flowing through the hot water circulation path L9 as a heat medium for exhaust heat recovery, i.e., the exhaust gas is cooled, and the moisture contained in the exhaust gas is condensed.

[0032] A branching section 17 is provided in the exhaust gas flow path L4 downstream of the heat exchange section 16, and a water recovery path L5 branches off from the exhaust gas flow path L4. Then, the gas phase components in the exhaust gas are discharged to the outside of the outer container 1 through the exhaust gas flow path L4, and the liquid phase components (condensed water) in the exhaust gas reach the water tank 19 through the water recovery path L5 and are stored in the water tank 19. In other words, the water tank 19 stores the recovered water recovered from the combustion exhaust gas by cooling the combustion exhaust gas in the heat recovery device H.

[0033] The raw fuel is supplied to the vaporization unit 5 through the raw fuel supply line L1. In the example shown in FIG. 2, the raw fuel supply unit 3 and the desulfurization unit 4 are provided in the raw fuel supply line L1. The raw fuel supply unit 3 flows a predetermined target amount of raw fuel into the raw fuel supply line L1. For example, the raw fuel supply unit 3 includes a raw fuel flow meter 3a that measures the flow rate per unit time of the raw fuel flowing through the raw fuel supply line L1, and a raw fuel pump 3b that flows the raw fuel into the raw fuel supply line L1 so that the flow rate per unit time of the raw fuel measured by the raw fuel flow meter 3a becomes the target raw fuel amount. The operation control unit 26 that controls the operation of the solid oxide fuel cell system S operates the raw fuel pump 3b so that the flow rate per unit time of the raw fuel measured by the raw fuel flow meter 3a becomes the target raw fuel amount. The desulfurization unit 4 removes sulfur compounds and the like contained in the raw fuel.

[0034] Air is supplied to the inside of the inner container 2 via an air supply path L2. An air pump 22 serving as an air supplier is provided in the air supply path L2. For example, the operation control unit 26 operates the air pump 22 so that the flow rate of air per unit time becomes a target flow rate.

[0035] The condensed water recovered using the water recovery passage L5 is supplied to the water tank 19. The water tank 19 is provided with a water amount measuring unit 20 that measures the amount of water stored in the water tank 19. The stored water stored in the water tank 19 is supplied to the vaporization unit 5 via the reforming water supply passage L6. A reforming water pump 21 as a reforming water supply unit and a water detection sensor 15 are provided in the reforming water supply passage L6. The operation control unit 26 operates the reforming water pump 21 so that the amount of water per unit time supplied to the vaporization unit 5 becomes a target flow rate. For example, the reforming water pump 21 operates at a target output determined according to the target water amount, and flows a predetermined target amount of reforming water into the reforming water supply passage L6.

[0036] The water detection sensor 15 is provided in the reforming water supply passage L6 between the reforming water pump 21 and the vaporization section 5, and measures the presence or absence of reforming water supplied to the vaporization section 5.

[0037] As described above, in the heat exchanger 16, heat exchange is performed between the exhaust gas and hot water as a heat medium for exhaust heat recovery flowing through the hot water circulation path L9. The hot water is stored in the hot water tank 23 and circulates between the hot water tank 23 and the heat exchanger 16 through the hot water circulation path L9. A hot water pump 24, a heat radiator 25, and a temperature sensor T2 are provided in the hot water circulation path L9 from the hot water tank 23 to the heat exchanger 16. The heat radiator 25 can perform a heat radiating operation to radiate heat from the hot water taken out from the lower part of the hot water tank 23 and supplied to the heat exchanger 16. For example, the heat radiator 25 can be realized by using a fan or the like. A temperature sensor T1 is provided in the hot water circulation path L9 from the heat exchanger 16 to the hot water tank 23.

[0038] For example, the operation control unit 26 controls the operation of the heat dissipation unit 25 so that the temperature of hot and cold water measured by the temperature sensor T2 becomes less than a predetermined upper limit hot and cold water temperature. The operation control unit 26 also controls the operation of the hot and cold water pump 24 so that the temperature of hot and cold water measured by the temperature sensor T1 becomes the target hot water storage temperature.

[0039] With this configuration, hot water supplied from the lower part of the hot water storage tank 23 to the heat exchange section 16 via the hot water circulation path L9 is heated in the heat exchange section 16, and the heated hot water is supplied via the hot water circulation path L9 to the upper part of the hot water storage tank 23. In this way, hot water is stored in the hot water storage tank 23 in a state that forms temperature stratification, i.e., heat is stored, such that relatively high temperature hot water exists in the upper part of the hot water storage tank 23 and relatively low temperature hot water exists in the lower part of the hot water storage tank 23.

[0040] A water supply line L7 for supplying water (clean water) to the hot water storage tank 23 is connected to the bottom of the hot water storage tank 23, and a hot water outlet line L8 for discharging the hot water stored in the hot water storage tank 23 to the outside is connected to the top of the hot water storage tank 23. A predetermined water supply pressure is also applied to the hot water inside the hot water storage tank 23 by the water supply line L7 to which supply pressure is applied. With this configuration, in the hot water storage tank 23, for example, when a water faucet (not shown) connected to the hot water outlet line L8 is opened, hot water is discharged from the hot water storage tank 23 to the hot water outlet line L8, and water is supplied from the water supply line L7 into the hot water storage tank 23.

[0041] In addition, the solid oxide fuel cell system S includes an operation control unit 26, a memory unit 27 that stores information handled by the solid oxide fuel cell system S, and a communication unit 28. The operation control unit 26 controls the operation of various devices such as the ignition unit 10, the raw fuel pump 3b, the reforming water pump 21, the air pump 22, the hot and cold water pump 24, the heat dissipation unit 25, and the communication unit 28.

[0042] Next, a water volume increase mode for increasing the amount of water in the water tank 19 will be described.

[0043] In the solid oxide fuel cell system S, when the amount of water stored in the water tank 19 falls below a predetermined lower limit water amount, the operation control unit 26 stops the power generation operation of the cell stack 9 or limits the power generation output to a predetermined output (such as the minimum output power that the cell stack 9 can output). For this reason, it is preferable that the solid oxide fuel cell system S is operated so that the amount of water stored in the water tank 19 is maintained at or above the lower limit water amount. In particular, it is preferable to be able to output large amounts of power during times when power demand is high in the power grid while securing a sufficient amount of water to be used for steam reforming.

[0044] Therefore, in the solid oxide fuel cell system S of this embodiment, when at least one of the high demand condition, that is, a high demand condition that an increase in the demand for electricity in the power system is predicted, and a high temperature condition that an increase in the temperature of the area in which the cell stack 9 is installed is predicted during a high demand time period when the demand for electricity in the power system is high, is satisfied, the operation control unit 26 operates the cell stack 9 in a water amount increase mode for increasing the amount of water in the water tank 19 during a predetermined advance time period before the high demand time period. In other words, the amount of water in the water tank 19 is increased before the high demand time period when the demand for electricity in the power system is high. As a result, it is possible to prevent the amount of water stored in the water tank 19 from falling below a predetermined lower limit amount during the high demand time period, and it is expected that the power generating operation of the cell stack 9 will continue during the high demand time period.

[0045] Fig. 3 is a flowchart explaining the operation mode determination process of the solid oxide fuel cell system S. The operation control unit 26 executes this operation mode determination process at set timings (e.g., every hour, etc.). Note that, although the flowchart shown in Fig. 3 explains an example in which the cell stack 9 is operated in the water amount increase mode when both the high demand condition and the high temperature condition are satisfied, the cell stack 9 may also be operated in the water amount increase mode when only the high demand condition is satisfied.

[0046] In this embodiment, the information providing server P stores information about power demand, such as a predicted future power usage rate (= predicted demand power / predicted supplyable power), and transmits information about the power demand to the solid oxide fuel cell system S at a set timing or in response to an information transmission request from the solid oxide fuel cell system S. The operation control unit 26 then determines that the high demand condition is met when the predicted power usage rate is equal to or greater than a set value (e.g., 85%), and determines the time period during which the predicted power usage rate is equal to or greater than the set value as a high demand time period.

[0047] The information providing server P also stores information about future predicted temperatures, and transmits the information about the predicted temperatures to the solid oxide fuel cell system S at a set timing or in response to an information transmission request from the solid oxide fuel cell system S. The operation control unit 26 then determines that the high temperature condition is satisfied when the predicted maximum temperature during the high demand time period is equal to or higher than a predetermined temperature.

[0048] Here, in the solid oxide fuel cell system S, the higher the temperature, the lower the ability to cool the combustion exhaust gas, so there is a high possibility that the water level in the water tank 19 will drop during high temperature time periods. However, in this embodiment, the operation control unit 26 determines that the high temperature condition is met when the predicted maximum temperature during the high demand time period is equal to or higher than a predetermined temperature, and attempts to operate the cell stack 9 in the water amount increase mode before the high demand time period when the power demand in the power system increases. As a result, it is expected that the power generation operation of the cell stack 9 will continue during the high demand time period, preventing the amount of water stored in the water tank 19 from falling below a predetermined lower limit water amount during the high demand time period.

[0049] In step #10, the operation control unit 26 determines whether or not the high demand condition will be met within a predetermined time period in the future (e.g., within five hours in the future). When the solid oxide fuel cell system S is operated in the water amount increase mode, it takes a certain amount of time for the amount of water in the water tank 19 to increase to a certain level, so it is preferable to operate the solid oxide fuel cell system S in the water amount increase mode a predetermined period before the high demand time period. Therefore, in step #10, it is determined whether or not the high demand condition will be met within a predetermined time period in the future (e.g., within five hours in the future).

[0050] Then, if the operation control unit 26 determines that the high demand condition will be satisfied within a predetermined future period (i.e., if the answer is "Yes" in step #10), the operation control unit 26 proceeds to step #11. On the other hand, if the operation control unit 26 determines that the high demand condition will not be satisfied within a predetermined future period (i.e., if the answer is "No" in step #10), the operation control unit 26 proceeds to step #13 and operates the solid oxide fuel cell system S in the normal mode. For example, the normal mode is an operation mode in which power generation is performed at rated output, or a load following mode in which the power generation output follows the power consumption of the power consuming device L, and the content of the normal mode can be set as appropriate.

[0051] In step #11, the operation control unit 26 determines whether or not the high temperature condition is satisfied during the high demand time period. If the operation control unit 26 determines that the high temperature condition is satisfied during the high demand time period, the operation control unit 26 proceeds to step #12, and if the operation control unit 26 determines that the high temperature condition is not satisfied during the high demand time period, the operation control unit 26 proceeds to step #13.

[0052] In step #12, the operation control unit 26 operates the cell stack 9 in a water volume increase mode for increasing the amount of water in the water tank 19 during a predetermined advance time period before the high demand time period. Fig. 4 is a diagram that illustrates a high demand time period and an advance time period. In this case, the operation control unit 26 determines, at the current stage (time 7:00), that the high demand condition will be satisfied between 12:00 and 16:00, which is included in a future five-hour period (an example of a predetermined period), and operates the cell stack 9 in the water volume increase mode during a advance time period (time 8:00 to 12:00), for example, four hours before the high demand time period (time 12:00 to 16:00).

[0053] Specifically, in the water amount increase mode, the operation control unit 26 sets the output power of the cell stack 9 to a predetermined power that is less than the rated power. For example, the predetermined power is the minimum output power that the cell stack 9 can output. By setting the output power of the cell stack 9 to a predetermined power that is less than the rated power in this way, the amount of reforming water required per unit time for steam reforming is reduced compared to when the output power of the cell stack 9 is set to the rated power. As a result, it is expected that the amount of recovered water recovered from the combustion exhaust gas per unit time will be greater than the amount of reforming water used per unit time in steam reforming, and the amount of water stored in the water tank 19 is expected to increase.

[0054] <Another embodiment> In the above embodiment, a specific example of the configuration of the solid oxide fuel cell system S has been given and explained, but the configuration can be modified as appropriate.

[0055] In the above embodiment, the operation control unit 26 may determine that the high temperature condition is satisfied when the day including the high demand time period corresponds to a day that is predetermined to have a high temperature. To be more specific, in summer, etc., the temperature is naturally more likely to be high compared to winter, spring, and autumn, etc., and therefore the solid oxide fuel cell system S is more likely to have a low ability to cool the combustion exhaust gas. That is, the summer, etc. can be predetermined as a day on which the temperature is high, and the day can be predetermined as a day on which the water level of the water tank 19 is more likely to drop. For example, the memory unit 27 of the solid oxide fuel cell system S stores July, August, and September as days that are predetermined to have a high temperature. The operation control unit 26 can determine that the high temperature condition is satisfied when the day including the high demand time period corresponds to any of July, August, and September.

[0056] In the above embodiment, the operation control unit 26 may operate the heat radiating unit 25 in the water amount increase mode. That is, by operating the heat radiating unit 25 in the heat radiating mode, it is possible to promote heat radiation from the combustion exhaust gas in the heat exchange unit 16. As a result, it is possible to promote cooling of the combustion exhaust gas in the heat exchange unit 16 and promote condensation of water from the combustion exhaust gas.

[0057] In the above embodiment, the operation control unit 26 may discharge a set amount or more of hot water from the hot water storage tank 23 through the hot water outlet passage L8 in the water amount increase mode. By discharging a set amount or more of hot water from the hot water storage tank 23 through the hot water outlet passage L8, water is supplied from the water supply passage L7 to the lower part of the hot water storage tank 23, and the water is supplied to the heat exchanger 16. In other words, the relatively high temperature hot water originally stored in the hot water storage tank 23 is not supplied to the heat exchanger 16, but the relatively low temperature water supplied from the water supply passage L7 is supplied to the heat exchanger 16 and used for cooling the combustion exhaust gas. As a result, the cooling of the combustion exhaust gas is promoted in the heat exchanger 16, and the condensation of water from the combustion exhaust gas can be promoted.

[0058] In the above embodiment, the solid oxide fuel cell system S of the present invention has been described using specific numerical examples, but these numerical values ​​are given for illustrative purposes only and can be changed as appropriate.

[0059] 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, provided that no contradiction arises. Furthermore, the embodiments disclosed in this specification are illustrative, and the embodiments of the present invention are not limited thereto, and can be appropriately modified within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0060] INDUSTRIAL APPLICABILITY The present invention can be used in a solid oxide fuel cell system that can output large amounts of electric power during periods of high demand for electric power while ensuring a sufficient amount of water for steam reforming. [Explanation of symbols]

[0061] 6: Modification section 8: Fuel cell 9: Cell stack 11: Combustion section 16:Heat exchange section 19: Water tank 23: Hot water tank 25: Heat dissipation part 26: Operation control unit H: Heat recovery device L7: Water supply channel L8: Outlet S: Solid oxide fuel cell system

Claims

1. a cell stack including a plurality of stacked solid oxide fuel cell cells that generate power using the fuel gas produced in the reforming section; a combustion section that combusts off-gas discharged from the plurality of fuel cell cells; a heat recovery device that recovers heat from the combustion exhaust gas discharged from the combustion section; a water tank that stores water recovered from the combustion exhaust gas by cooling the combustion exhaust gas with the heat recovery device; and an operation control section that controls operation, wherein the water stored in the water tank is used for steam reforming of the raw fuel in the reforming section, and the operation control section is configured to stop the power generation operation of the cell stack or suppress the power generation output when the amount of water stored in the water tank falls below a predetermined lower limit water amount, The operation control unit of the solid oxide fuel cell system operates the cell stack in a water increase mode to increase the amount of water in the water tank during a predetermined advance time period prior to the high demand time period when at least one of a high demand condition in which an increase in demand for electricity in the power system is predicted and a high temperature condition in which an increase in temperature in the area in which the cell stack is installed is predicted during a high demand time period when demand for electricity in the power system increases is satisfied.

2. The solid oxide fuel cell system according to claim 1 , wherein the operation control unit, in the water amount increase mode, controls the output power of the cell stack to a predetermined power that is less than a rated power.

3. 3. The solid oxide fuel cell system according to claim 2, wherein the predetermined power is a minimum output power that the cell stack can output.

4. The operation control unit is if the high demand condition and the high temperature condition are met, operating the cell stack in the increased water flow mode during the advance time period; 4. The solid oxide fuel cell system according to claim 1, wherein the high temperature condition is determined to be satisfied when a predicted maximum temperature during the high demand time period is equal to or higher than a predetermined temperature.

5. The operation control unit is if the high demand condition and the high temperature condition are met, operating the cell stack in the increased water flow mode during the advance time period; The solid oxide fuel cell system according to any one of claims 1 to 3, wherein the high temperature condition is determined to be satisfied when a day including the high demand time period corresponds to a day that is predetermined to have a high temperature.

6. The heat recovery device has a heat exchange section to which the combustion exhaust gas discharged from the combustion section is supplied, and a hot water storage tank for storing hot water, and is configured to store the heat of the combustion exhaust gas recovered by the heat exchange section in the hot water storage tank by circulating hot water by supplying hot water taken out from a lower part of the hot water storage tank to the heat exchange section and returning the hot water that has flowed through the heat exchange section to an upper part of the hot water storage tank, A solid oxide fuel cell system as described in any one of claims 1 to 3, wherein a hot water outlet passage is connected to the upper part of the hot water storage tank for discharging hot water stored in the hot water storage tank to the outside, and a water supply passage is connected to the lower part of the hot water storage tank for supplying water to the hot water storage tank, and a predetermined water supply pressure is applied to the hot water inside the hot water storage tank by the water supply passage, so that water is supplied from the water supply passage into the hot water storage tank in response to the hot water being discharged from the hot water storage tank into the hot water outlet passage.

7. A heat dissipation unit is provided that can perform a heat dissipation operation to release heat from hot water taken out from a lower portion of the hot water storage tank and supplied to the heat exchange unit, The solid oxide fuel cell system according to claim 6 , wherein the operation control unit causes the heat dissipation unit to perform the heat dissipation operation in the water amount increase mode.

8. The solid oxide fuel cell system according to claim 6 , wherein the operation control unit, in the water amount increase mode, causes the hot water to be discharged from the hot water storage tank through the hot water outlet path in an amount equal to or greater than a set amount.

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