Solid oxide type fuel battery system

Abstract

To provide a solid oxide type fuel battery system capable of determining whether or not a modification of an original fuel in a modification part is appropriately performed.SOLUTION: A solid oxide fuel battery system comprises: a vaporization part 5 that generates a moisture vapor by vaporizing a modified water; a modification part 6 that generates a fuel gas by modifying an original fuel in a moisture vapor modification by using the moisture vapor generated in the vaporization part 5; and a cell stack 9 in which a plurality of fuel battery cells 8 with a solid oxide type that generates a power by using the fuel gas generated in the modification part 6 is laminated, and comprises a voltage measurement part 29 that measures a power generation voltage of the cell stack 9. An operation control part 26 determines that at least one of a water shortage state that a modified water supplied to the vaporization part 5 is less than a target water amount and an original fuel shortage state that the original fuel supplied to the modification part 6 is less than a target original fuel amount in the case a power generation voltage measured under a predetermined reference measurement condition by the voltage measurement part 29 is a reference power generation voltage or larger.SELECTED DRAWING: Figure 1

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 raw fuel containing a hydrocarbon that is supplied to the reforming section, and a cell stack in which multiple solid oxide fuel cells that generate power using the fuel gas produced in the reforming section are stacked. In this solid oxide fuel cell system, the supply amounts of raw fuel and steam are adjusted so that the amounts of raw fuel and steam supplied to the reforming section reach target amounts. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5438420 Summary of the Invention [Problem to be solved by the invention]

[0004] In a solid oxide fuel cell system, if the amount of steam supplied to the reforming section is insufficient relative to the target amount, or if the amount of raw fuel supplied to the reforming section is insufficient relative to the target amount, the raw fuel will be supplied to the anode of the fuel cell in an insufficiently reformed state. If the system operates in an insufficiently reformed state, the hydrocarbons contained in the raw fuel will decompose, causing carbon to precipitate on the anode and possibly causing the cell stack to fail.

[0005] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a solid oxide fuel cell system that can determine whether or not reforming of raw fuel is being performed appropriately in the reforming section. [Means for solving the problem]

[0006] 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 system comprising: a vaporization unit that vaporizes reforming water supplied from a water tank through a reforming water supply channel to generate steam; a reforming water supply unit that flows a predetermined target amount of the reforming water through the reforming water supply channel; a reforming unit that steam reforms a raw fuel supplied through a raw fuel supply channel using the steam generated in the vaporization unit to generate fuel gas; a raw fuel supply unit that flows a predetermined target amount of the raw fuel through the raw fuel supply channel; a cell stack in which a plurality of solid oxide fuel cell cells that generate electricity using the fuel gas generated in the reforming unit are stacked; and an operation control unit that controls operation, a voltage measuring unit for measuring a power generation voltage of the cell stack, The operation control unit determines that at least one of a water shortage state in which the reforming water supplied to the vaporization unit is less than the target water amount, and a raw fuel shortage state in which the raw fuel supplied to the reforming unit is less than the target raw fuel amount, has occurred when the generated power voltage measured by the voltage measuring unit under specified standard measurement conditions is equal to or higher than the standard generated power voltage.

[0007] According to the above characteristic configuration, when the power generation voltage measured by the voltage measuring unit is equal to or higher than the reference power generation voltage, the operation control unit can determine that at least one of a water shortage state in which the amount of reforming water supplied to the vaporization unit is less than the target water amount, and a raw fuel shortage state in which the amount of raw fuel supplied to the reforming unit is less than the target raw fuel amount has occurred. Therefore, it is possible to provide a solid oxide fuel cell system that is capable of determining whether or not the reforming of the raw fuel is being performed appropriately in the reforming section.

[0008] Another characteristic configuration of the solid oxide fuel cell system according to the present invention is that the reforming water supply unit includes a reforming water pump that operates at a target output determined according to the target water amount to flow the reforming water into the reforming water supply path, the raw fuel supply unit includes a raw fuel flow meter that measures a flow rate per unit time of the raw fuel flowing through the raw fuel supply path, and a raw fuel pump that causes the raw fuel to flow through the raw fuel supply path so that the flow rate per unit time of the raw fuel measured by the raw fuel flow meter becomes the target raw fuel amount, The operation control unit determines that the water shortage state has occurred when the power generation voltage measured by the voltage measuring unit under the standard measurement conditions is equal to or higher than the standard power generation voltage and the flow rate of the raw fuel measured by the raw fuel flow meter is within a predetermined range of the target raw fuel amount.

[0009] According to the above-described characteristic configuration, when the flow rate of the raw fuel measured by the raw fuel flow meter is within a predetermined range from the target raw fuel amount, i.e., when a raw fuel shortage state has not occurred, it can be determined that a water shortage state has occurred and the generated power generation voltage measured by the voltage measuring unit is equal to or higher than the reference generated power generation voltage.

[0010] Another characteristic configuration of the solid oxide fuel cell system of the present invention is that the operation control unit determines that the water shortage condition has occurred and, when it is assumed that the reforming water pump is operating at the target output, determines that the water shortage condition has occurred due to leakage of the reforming water in the reforming water supply path between the reforming water pump and the evaporation unit.

[0011] According to the above characteristic configuration, when it is assumed that the reforming water pump is operating at the target output, i.e., when an appropriate amount of reforming water is being supplied from the reforming water pump, it can be determined that a water shortage condition is occurring due to a leakage of reforming water in the reforming water supply path between the reforming water pump and the evaporation section.

[0012] Another characteristic configuration of the solid oxide fuel cell system according to the present invention is a water detection sensor that is provided in the reforming water supply passage between the reforming water pump and the vaporization section and that detects the presence or absence of the reforming water supplied to the vaporization section, The operation control unit determines that the water shortage condition has occurred, and if it is assumed that the reforming water pump is operating at the target output and the water detection sensor determines that the reforming water is present, it determines that the water shortage condition has occurred due to leakage of the reforming water in the reforming water supply path between the water detection sensor and the evaporation unit.

[0013] According to the above characteristic configuration, when it is assumed that the reforming water pump is operating at the target output and the water detection sensor determines that there is reforming water, i.e., when an appropriate amount of reforming water is being supplied from the reforming water pump and reforming water is being supplied to the location where the water detection sensor is installed, it can be determined that a water shortage condition is occurring due to a leakage of reforming water in the reforming water supply path between the water detection sensor and the evaporation section.

[0014] Another characteristic feature of the solid oxide fuel cell system according to the present invention is that the operation control unit stops the power generation operation of the cell stack when it determines that the water shortage state is occurring due to leakage of the reforming water.

[0015] According to the above-described characteristic configuration, it is possible to prevent the cell stack from continuing to operate for power generation in a state where there is a possibility of a water shortage condition occurring due to leakage of reforming water, i.e., a state in which the cell stack cannot operate for power generation normally.

[0016] Another characteristic feature of the solid oxide fuel cell system according to the present invention is that the reference measurement condition is that the target water amount and the target raw fuel amount are constant for a predetermined period of time.

[0017] According to the above-described characteristic configuration, when the target water amount and the target raw fuel amount are constant for a predetermined period of time, the voltage measured by the voltage measuring unit should also be stable during that period, and the generated voltage in such a stable state can be compared with the reference generated voltage.

[0018] Another characteristic feature of the solid oxide fuel cell system according to the present invention is that the reference generated voltage is set to a value that decreases over time.

[0019] According to the above characteristic configuration, the reference generated voltage can be set to an appropriate value in consideration of the decrease in generated voltage that occurs with the progression of aging degradation. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram showing a configuration of a solid oxide fuel cell system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] A solid oxide fuel cell system 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 solid oxide fuel cell system. The solid oxide fuel cell system includes various components inside an outer container 1.

[0022] A hot module 31 is provided inside the outer vessel 1. The hot module 31 is provided with an inner vessel 2 that houses devices such as a cell stack 9 that operate in a high-temperature environment. Specifically, a vaporizer 5, a reformer 6, a manifold 7, a cell stack 9, and the like are provided inside the inner vessel 2. The vaporizer 5 vaporizes reforming water supplied from a water tank 19 through a reforming water supply passage L6 to generate steam, and supplies the steam to the reformer 6. The reformer 6 steam-reforms a raw fuel (such as city gas) containing hydrocarbons supplied through a raw fuel supply passage L1 using the steam generated by the vaporizer 5 to generate fuel gas. That is, the water stored in the water tank 19 is used for steam reforming of the raw fuel in the reformer 6.

[0023] 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 section 6. For example, the fuel gas produced in the reforming section 6 passes through a fuel gas supply passage L3 to reach a manifold 7, where the fuel gas is distributed to each of the fuel cells 8.

[0024] 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.

[0025] 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.

[0026] The solid oxide fuel cell system 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 a 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 an 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.

[0027] 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.

[0028] 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.

[0029] The raw fuel is supplied to the vaporization unit 5 through a raw fuel supply line L1. In the example shown in FIG. 1, a raw fuel supply unit 3 and a 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 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] In addition, the solid oxide fuel cell system includes an operation control unit 26, a memory unit 27 that stores information handled in the solid oxide fuel cell system, and a voltage measurement unit 29 that measures the power generation voltage of the cell stack 9. The operation control unit 26 controls the operations 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, and the heat dissipation unit 25 described above.

[0038] In a solid oxide fuel cell system configured as described above, if the amount of steam supplied to the reforming unit 6 is insufficient relative to a target amount, or if the amount of raw fuel supplied to the reforming unit 6 is insufficient relative to a target amount, the raw fuel will be supplied to the anode of the fuel cell 8 in an insufficiently reformed state. If the system operates in an insufficiently reformed state, decomposition of the hydrocarbons contained in the raw fuel will occur, causing carbon to precipitate at the anode, which may cause a breakdown of the cell stack 9. For this reason, it is necessary to determine whether the raw fuel is being properly reformed in the reforming unit 6.

[0039] Next, a process for determining whether the reforming of the raw fuel is being performed appropriately in the reforming unit 6, that is, whether at least one of a water shortage state in which the amount of reforming water supplied to the vaporization unit 5 is less than a target water amount and a raw fuel shortage state in which the amount of raw fuel supplied to the reforming unit 6 is less than a target raw fuel amount, is occurring will be described. The operation control unit 26 may perform such a determination process at a predetermined timing. For example, the operation control unit 26 may perform such a determination process at regular intervals, or may perform it every time the solid oxide fuel cell system is started up.

[0040] When the power generation voltage measured by the voltage measuring unit 29 under predetermined reference measurement conditions is equal to or higher than the reference power generation voltage, the operation control unit 26 determines that at least one of the following has occurred: a water shortage state in which the amount of reforming water supplied to the vaporizing unit 5 is less than a target water amount, and a raw fuel shortage state in which the amount of raw fuel supplied to the reforming unit 6 is less than a target raw fuel amount. Therefore, it can be determined whether the raw fuel is being reformed appropriately in the reforming unit 6.

[0041] In a solid oxide fuel cell system, the target amount of reforming water supplied to the vaporization unit 5 and the target amount of raw fuel supplied to the reforming unit 6 are changed according to the power generation state (load fluctuation), and the power generation voltage of the cell stack 9 also changes accordingly. Therefore, the reference measurement condition is that the target amount of water and the target amount of raw fuel are constant for a predetermined period, such as 30 minutes. In other words, when the target amount of water and the target amount of raw fuel are constant for a predetermined period, the voltage measured by the voltage measurement unit 29 during that period should also be stable, and the power generation voltage in such a stable state can be compared with the reference power generation voltage.

[0042] The operation control unit 26 determines that a raw fuel shortage state does not occur when the flow rate of the raw fuel measured by the raw fuel flow meter 3a is within a predetermined range from the target raw fuel amount. On the other hand, the operation control unit 26 determines that a raw fuel shortage state occurs when the flow rate of the raw fuel measured by the raw fuel flow meter 3a is smaller than the target raw fuel amount and is not within a predetermined range from the target raw fuel amount.

[0043] In addition, the operation control unit 26 determines that a water shortage condition is occurring when the power generation voltage of the cell stack 9 measured by the voltage measurement unit 29 under standard measurement conditions is equal to or higher than the standard power generation voltage and the flow rate of the raw fuel measured by the raw fuel flow meter 3a is within a predetermined range from the target raw fuel amount, i.e., when the raw fuel is being normally supplied to the reforming unit 6.

[0044] In addition, when the operation control unit 26 determines that a water shortage state has occurred and it is assumed that the reforming water pump 21 is operating at the target output, i.e., when an appropriate amount of reforming water is being supplied from the reforming water pump 21, it determines that a water shortage state has occurred due to leakage of reforming water in the reforming water supply passage L6 between the reforming water pump 21 and the vaporization unit 5. For example, when a command value given to the reforming water pump 21 is the target output and when the actual output of the reforming water pump 21 is the target output, the operation control unit 26 can determine that the reforming water pump 21 is operating at the target output.

[0045] Furthermore, when the operation control unit 26 determines that a water shortage state has occurred, and it is assumed that the reforming water pump 21 is operating at the target output, and the water detection sensor 15 determines that there is reforming water, it determines that a water shortage state has occurred due to a leakage of reforming water in the reforming water supply path L6 between the water detection sensor 15 and the evaporation unit 5.

[0046] Then, when the operation control unit 26 determines that a water shortage state has occurred due to the leakage of reforming water, it stops the power generation operation of the cell stack 9. In other words, it is possible to prevent the power generation operation of the cell stack 9 from being continued in a state where a water shortage state may have occurred due to the leakage of reforming water, that is, in a state where the cell stack 9 cannot normally perform power generation operation.

[0047] As a specific example, the target water amount and the target raw fuel amount are the same in the following operation example 1 (normal) and operation example 2 (when the reforming water is leaking). However, in the operation example 2, the reforming water actually supplied to the vaporization unit 5 is intentionally made less than the target water amount. Therefore, the amount of steam supplied to the reforming unit 6 in the operation example 2 is less than the amount of steam supplied to the reforming unit 6 in the operation example 1. The power generation voltage (here, the open circuit voltage (OCV)) measured by the voltage measurement unit 29 is higher in the operation example 2 than in the operation example 1. In this way, when the power generation voltage measured by the voltage measurement unit 29 is equal to or higher than the reference power generation voltage (e.g., 51 V, etc.), the operation control unit 26 can determine that at least one of a water shortage state in which the reforming water supplied to the vaporization unit 5 is less than the target water amount and a raw fuel shortage state in which the raw fuel supplied to the reforming unit 6 is less than the target raw fuel amount has occurred.

[0048] Operation example 1 (normal) The target raw fuel amount is 2.0 L / min, the target water amount is 4 mL / min, and the generated voltage is 50 V. Example 2 (when reforming water leaks) The target raw fuel amount is 2.0 L / min, the target water amount is 4 mL / min, and the generated voltage is 52 V.

[0049] <Another embodiment> In the above embodiment, a specific example of the configuration of the solid oxide fuel cell system has been described, but the configuration can be modified as appropriate.

[0050] In the above embodiment, the case where the voltage measurement unit 29 measures the open circuit voltage of the cell stack 9 has been exemplified, but the generated voltage measured by the voltage measurement unit 29 does not have to be the open circuit voltage. For example, the voltage measurement unit 29 may measure the generated voltage when generating electricity of, for example, 500 W.

[0051] In the above embodiment, the value of the reference generated voltage can be set appropriately. For example, the reference generated voltage may be a constant value, or may be set to a value that decreases over time. In other words, the reference generated voltage can be set to an appropriate value, taking into consideration that the generated voltage decreases with the progress of aging deterioration. As one example, the reference generated voltage may be set to a value of V=V0×(1−0.01X), where V0 is the initial reference generated voltage and X is the year. In other words, the reference generated voltage in this case is set to a value that decreases by 1% every year.

[0052] In the above embodiment, the solid oxide fuel cell system 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.

[0053] 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]

[0054] INDUSTRIAL APPLICABILITY The present invention can be used in a solid oxide fuel cell system capable of determining whether or not reforming of raw fuel is being performed appropriately in a reforming section. [Explanation of symbols]

[0055] 3a: Raw fuel flow meter (raw fuel supply section 3) 3b: Raw fuel pump (raw fuel supply section 3) 3b: Raw fuel pump 5: Vaporizing section 6: Modification section 8: Fuel cell 9: Cell stack 15: Water detection sensor 19: Water tank 21: Reformed water pump (reformed water supply section) 26: Operation control unit 29: Voltage measurement section L1: Raw fuel supply path L6: Reforming water supply path

Claims

1. a reforming water supply unit that supplies a predetermined target amount of the reforming water to the reforming water supply line; a reforming unit that steam-reforms a raw fuel supplied through a raw fuel supply line using the steam generated in the vaporization unit to generate a fuel gas; a raw fuel supply unit that supplies a predetermined target amount of the raw fuel to the raw fuel supply line; a cell stack in which a plurality of solid oxide fuel cell units are stacked to generate electricity using the fuel gas generated in the reforming unit; and an operation control unit that controls operation, a voltage measuring unit for measuring a power generation voltage of the cell stack, The operation control unit determines that at least one of a water shortage state in which the reforming water supplied to the vaporization unit is less than the target water amount, and a raw fuel shortage state in which the raw fuel supplied to the reforming unit is less than the target raw fuel amount, has occurred when the generated power voltage measured by the voltage measuring unit under specified standard measurement conditions is equal to or greater than the standard generated power voltage.

2. the reforming water supply unit includes a reforming water pump that operates at a target output determined according to the target water volume to cause the reforming water to flow through the reforming water supply path, the raw fuel supply unit includes a raw fuel flow meter that measures a flow rate per unit time of the raw fuel flowing through the raw fuel supply path, and a raw fuel pump that causes the raw fuel to flow through the raw fuel supply path so that the flow rate per unit time of the raw fuel measured by the raw fuel flow meter becomes the target raw fuel amount, 2. The solid oxide fuel cell system of claim 1, wherein the operation control unit determines that the water shortage state is occurring when the power generation voltage measured by the voltage measurement unit under the standard measurement conditions is equal to or higher than the standard power generation voltage and the flow rate of the raw fuel measured by the raw fuel flow meter is within a predetermined range from the target raw fuel amount.

3. The solid oxide fuel cell system of claim 2, wherein the operation control unit determines that the water shortage state has occurred and, when it is assumed that the reforming water pump is operating at the target output, determines that the water shortage state has occurred due to leakage of the reforming water in the reforming water supply path between the reforming water pump and the evaporation unit.

4. a water detection sensor for detecting the presence or absence of the reforming water supplied to the vaporization unit, the water detection sensor being provided in the reforming water supply passage between the reforming water pump and the vaporization unit; The solid oxide fuel cell system of claim 3, wherein the operation control unit determines that the water shortage state has occurred, and when it is assumed that the reforming water pump is operating at the target output and the water detection sensor determines that the reforming water is present, the operation control unit determines that the water shortage state has occurred due to leakage of the reforming water in the reforming water supply path between the water detection sensor and the evaporation unit.

5. 5. The solid oxide fuel cell system according to claim 3, wherein the operation control unit stops the power generation operation of the cell stack when it determines that the water shortage state is occurring due to leakage of the reforming water.

6. 5. The solid oxide fuel cell system according to claim 1, wherein the reference measurement condition is that the target water amount and the target raw fuel amount are constant for a predetermined period of time.

7. 5. The solid oxide fuel cell system according to claim 1, wherein the reference generated voltage is set to a value that decreases over time.

Images