Fuel cell system

Abstract

To provide a fuel cell system that can maintain high power generation efficiency in the fuel cell section while securing sufficient water storage. [Solution] The operation control unit 26 of the fuel cell system determines a target power generation pattern for the fuel cell unit 9 over a predetermined period, based on a first correlation between the amount of power generated by the fuel cell unit 9 and the power generation efficiency, a second correlation between the amount of power generated by the fuel cell unit 9 and the increase or decrease in stored water, and the current amount of stored water measured by the water amount measuring unit 20, such that the amount of stored water after the predetermined period becomes the target amount and the average power generation efficiency of the fuel cell unit 9 over the predetermined period is high.

Description

[Technical Field]

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

[0002] Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2011-34701) describes a fuel cell system that controls the power generation output of a fuel cell without limiting the maximum power generation output when the water level in a tank is equal to or higher than a predetermined high water level, and limits the maximum power generation output of the fuel cell to less than the rated power regardless of the magnitude of the power load when the water level in the tank is lower than the high water level. That is, in the fuel cell system described in Patent Document 1, an attempt is made to adjust the water level in the tank by changing the output of the fuel cell. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2011-34701 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] In the fuel cell system described in Patent Document 1, output is suppressed when the water balance indicating the amount of increase or decrease in stored water during operation deteriorates, but power generation efficiency may decrease depending on the amount of output suppression. FIG. 2 is a diagram showing an example of a first correlation between the power generation amount of a fuel cell unit and power generation efficiency, and FIG. 3 is a diagram showing an example of a second correlation between the power generation amount of the fuel cell unit and the amount of increase or decrease in stored water. As shown in FIGS. 2 and 3, in a fuel cell system, the smaller the power generation amount is, the lower the power generation efficiency becomes, and the amount of increase or decrease in stored water also varies depending on the power generation amount.

[0005] Therefore, even if the increase or decrease in stored water over a certain period of time is the same, the average power generation efficiency over that period will vary depending on the power generation pattern within that period. For example, based on the graphs in Figures 2 and 3, the increase or decrease in stored water when operating at 700W for 3 hours and 200W for 15 hours is almost the same as the increase or decrease in stored water when operating at 400W for 18 hours, both being around ±0. However, in the former case, the average power generation efficiency over 18 hours is 30%, while in the latter case it is 44%. In other words, the latter allows the fuel cell system to be operated more efficiently.

[0006] This invention has been made in view of the above-mentioned problems, and its purpose is to provide a fuel cell system that can secure sufficient stored water while maintaining a high power generation efficiency in the fuel cell section. [Means for solving the problem]

[0007] A characteristic configuration of the fuel cell system according to the present invention for achieving the above objective is a reforming unit that generates fuel gas by steam reforming raw fuel, A fuel cell unit that generates electricity by reacting the aforementioned fuel gas and oxygen gas, A combustion unit that burns the combustible gas present in the gas discharged from the fuel cell unit after it has been used in the power generation reaction to produce exhaust gas, A heat exchange unit that recovers the heat of the exhaust gas discharged from the combustion unit using a heat transfer medium, A water tank for recovering and storing condensed water generated from the exhaust gas by heat recovery in the heat exchange section, A water supply unit capable of supplying the stored water in the water tank to the reforming unit, A water volume measuring unit for measuring the amount of water stored in the water tank, It includes an operation control unit, The operation control unit determines a target power generation pattern for the fuel cell unit during a predetermined period, based on a first correlation between the power generation amount and power generation efficiency of the fuel cell unit, a second correlation between the power generation amount of the fuel cell unit and the increase or decrease in the amount of stored water, and the current amount of stored water measured by the water volume measuring unit, such that the amount of stored water after the predetermined period becomes the target amount and the average power generation efficiency of the fuel cell unit during the predetermined period is high.

[0008] According to the above characteristic configuration, the operation control unit can determine a target power generation pattern for the fuel cell unit over a predetermined period such that the amount of stored water after the predetermined period approaches the target amount, and the average power generation efficiency of the fuel cell unit over the predetermined period is high. Therefore, it is possible to provide a fuel cell system that can secure sufficient water storage while maintaining high power generation efficiency in the fuel cell section.

[0009] Another characteristic configuration of the fuel cell system according to the present invention is that the operation control unit acquires fuel consumption information, which includes information on the amount of power generated by the fuel cell unit and information on the amount of fuel consumed by the fuel cell unit to obtain the amount of power generated, during the operation of the fuel cell unit, and determines the first correlation relationship based on the fuel consumption information.

[0010] According to the above characteristic configuration, the operation control unit determines a first correlation based on the fuel consumption information, which includes information on the amount of power generated by the fuel cell unit and information on the amount of raw fuel consumed by the fuel cell unit to obtain the said amount of power generated, acquired during the operation of the fuel cell unit. In other words, the operation control unit can determine a first correlation suitable for that fuel cell unit.

[0011] Another characteristic configuration of the fuel cell system according to the present invention is that the operation control unit acquires information on the amount of power generated by the fuel cell unit and information on the increase or decrease in the amount of stored water when the amount of power generated by the fuel cell unit is generated, during the operation of the fuel cell unit, and determines the second correlation relationship based on the increase or decrease in the amount of power generated.

[0012] According to the above characteristic configuration, the operation control unit can determine a second correlation based on information acquired during the operation of the fuel cell unit, including information on the amount of power generated by the fuel cell unit and information on the increase or decrease in the amount of stored water when the power is generated by the fuel cell unit. In other words, the operation control unit can determine a second correlation suitable for that fuel cell unit.

[0013] Another characteristic configuration of the fuel cell system according to the present invention is that the second correlation is provided in multiple types depending on the ambient temperature or the temperature of the exhaust gas. Equipped with a temperature sensor that measures the ambient temperature or the temperature of the exhaust gas, The operation control unit determines the target power generation pattern based on the second correlation relationship corresponding to the current temperature measured by the temperature sensor.

[0014] According to the above characteristic configuration, the operation control unit can determine the target power generation pattern based on the second correlation corresponding to the current temperature, from among several types of second correlations provided depending on the ambient temperature or exhaust gas temperature.

[0015] Another characteristic configuration of the fuel cell system according to the present invention is that the operation control unit acquires increase / decrease information, which includes temperature information measured by the temperature sensor, power generation information from the fuel cell unit, and information on the increase / decrease in the amount of stored water when the power generation is generated in the fuel cell unit, during the operation of the fuel cell unit, and determines a plurality of types of second correlation relationships according to the ambient temperature or the temperature of the exhaust gas based on the increase / decrease information.

[0016] According to the above characteristic configuration, the operation control unit can determine multiple types of second correlations corresponding to the ambient temperature or exhaust gas temperature based on the temperature information measured by the temperature sensor, the amount of power generated by the fuel cell unit, and the increase / decrease information, which includes information on the increase / decrease in the amount of stored water when the amount of power generated by the fuel cell unit is generated. [Brief explanation of the drawing]

[0017] [Figure 1] This is a diagram showing the configuration of a fuel cell system. [Figure 2] It is a diagram showing a first correlation between the power generation amount of the fuel cell unit and power generation efficiency. [Figure 3] It is a diagram showing a second correlation between the power generation amount of the fuel cell unit and the increase / decrease amount of stored water. [Figure 4] It is a diagram showing a second correlation between the power generation amount of the fuel cell unit and the increase / decrease amount of stored water. MODE FOR CARRYING OUT THE INVENTION

[0018] Hereinafter, a fuel cell system according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the configuration of the fuel cell system. The fuel cell system includes various components inside an outer container 1.

[0019] A hot module 31 is provided inside the outer container 1. The hot module 31 is provided with an inner container 2 that accommodates equipment such as a cell stack 9 that operates in a high-temperature environment. Specifically, inside the inner container 2, there are provided a vaporization unit 5, a reforming unit 6, a manifold 7, a cell stack (an example of the fuel cell unit of the present invention) 9, and the like. The vaporization unit 5 vaporizes reforming water and supplies the vaporized water to the reforming unit 6. The reforming unit 6 performs steam reforming on raw fuel to generate fuel gas.

[0020] A temperature sensor T4 that measures the temperature of the space inside the outer container 1 is provided inside the outer container 1. Since the air inside the outer container 1 is ventilated by air outside the outer container 1 (that is, outside air), the temperature of the air measured by the temperature sensor T4 can be regarded as the temperature of the air outside the outer container 1 (outside air temperature).

[0021] The cell stack 9 has a plurality of fuel cells 8 that generate electricity by reacting the fuel gas generated in the reforming unit 6 and oxygen gas, which are supplied via a fuel gas supply passage L3. For example, the fuel gas generated in the reforming unit 6 reaches the manifold 7 through the fuel gas supply passage L3, and is distributed to each of the fuel cells 8 by the manifold 7.

[0022] The space above the cell stack 9 becomes a combustion section 11 where the off-gas (gas containing combustible gases such as residual fuel gas) discharged from the cell stack 9 is burned. This heat of combustion is transferred to the vaporization section 5 and the reforming section 6 above it. The ignition section 10 ignites the off-gas. In other words, the combustion section 11 burns the combustible gas present in the gas discharged from the cell stack 9 after it has been used in the power generation reaction, thereby producing exhaust gas.

[0023] An air supply passage L2 is connected to the air inlet 12 of the inner container 2, and air (oxygen gas) is supplied to the inside of the inner container 2. The gas present inside the inner container 2 is discharged to the outside of the inner container 2 from the exhaust port 13 of the inner container 2. The exhaust port 13 is equipped with a combustion catalyst section 14 that uses oxygen to catalytically combust hydrogen, carbon monoxide, etc. contained in the discharged gas.

[0024] The exhaust gas that has passed through the combustion catalyst section 14 is discharged to the outside of the inner container 2, flows through the exhaust gas flow path L4, and is supplied to the heat exchange section 16. The heat exchange section 16 recovers the heat from the exhaust gas discharged from the combustion section 11 using a heat transfer medium. The temperature of the exhaust gas supplied to the heat exchange section 16 is measured by a temperature sensor T3 installed in the middle of the exhaust gas flow path L4. In other words, in the heat exchange section 16, heat exchange takes place between the exhaust gas and the hot water flowing through the hot water circulation path L9 as a heat transfer medium, that is, the exhaust gas is cooled, and the water contained in the exhaust gas condenses.

[0025] In this embodiment, the temperature of the hot water flowing into the heat exchange unit 16 is measured by a temperature sensor T2 located in the middle of the hot water circulation path L9. For example, if a correspondence table is stored in the storage unit 27 that determines the amount of condensation per unit time from the temperature of the exhaust gas flowing into the heat exchange unit 16 and the temperature of the hot water flowing into the heat exchange unit 16, the operation control unit 26 can derive the amount of water condensation per unit time from the temperature of the hot water measured by the temperature sensor T2 and the temperature of the exhaust gas measured by the temperature sensor T3.

[0026] 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. The gaseous components of the exhaust gas are discharged to the outside of the outer container 1 through the exhaust gas flow path L4, and the liquid components (condensed water) of the exhaust gas are discharged to the water tank 19 through the water recovery path L5 and stored in the water tank 19. In other words, the water tank 19 recovers and stores the condensed water generated from the exhaust gas by heat recovery in the heat exchange section 16.

[0027] The raw fuel is supplied to the vaporization unit 5 via the raw fuel supply line L1. In the example shown in Figure 1, a raw fuel supply unit 3 and a desulfurization unit 4 are provided along the raw fuel supply line L1. For example, the operation control unit 26 operates the raw fuel supply unit 3 so that the flow rate of the raw fuel per unit time becomes the target flow rate. The desulfurization unit 4 removes sulfur compounds and other substances contained in the raw fuel.

[0028] Air is supplied to the inside of the inner container 2 via the air supply passage L2. An air supply unit 22 is provided along the air supply passage L2. For example, the operation control unit 26 operates the air supply unit 22 so that the air flow rate per unit time reaches the target flow rate.

[0029] The water tank 19 is equipped with a water volume measuring unit 20 for measuring the amount of water stored in the water tank 19. The stored water in the water tank 19 is supplied to the vaporization unit 5 via a water supply passage L6. A water supply unit 21 is provided along the water supply passage L6, which can supply the stored water from the water tank 19 to the reforming unit 6. For example, the operation control unit 26 operates the water supply unit 21 so that the amount of water supplied to the vaporization unit 5 per unit time becomes the target flow rate.

[0030] In the heat exchange section 16, heat exchange takes place between the exhaust gas and the hot water flowing through the hot water circulation path L9, which acts as a heat transfer medium. The hot water is stored in the hot water storage tank 23 and circulates between the hot water storage tank 23 and the heat exchange section 16 via the hot water circulation path L9. A temperature sensor T1 is installed along the hot water circulation path L9 between the heat exchange section 16 and the hot water storage tank 23.

[0031] The temperature sensor T1 measures the temperature of the hot water flowing into the hot water storage tank 23. For example, the operation control unit 26 controls the operation of the hot water circulation unit 24 so that the temperature of the hot water measured by the temperature sensor T1 reaches the target hot water storage temperature.

[0032] With this configuration, the hot water supplied from the bottom of the hot water storage tank 23 to the heat exchange unit 16 via the hot water circulation path L9 is heated in the heat exchange unit 16, and the heated hot water is supplied to the top of the hot water storage tank 23 via the hot water circulation path L9. In this way, the hot water is stored, or rather, heat is accumulated, in a state that forms a temperature stratification in the hot water storage tank 23, with relatively high-temperature hot water at the top of the tank and relatively low-temperature hot water at the bottom of the tank.

[0033] A water supply channel L7 for supplying tap water to the hot water storage tank 23 is connected to the lower part of the hot water storage tank 23, and a hot water outlet channel L8 for discharging the hot water stored in the hot water storage tank 23 is connected to the upper part of the hot water storage tank 23. The hot water stored in the hot water storage tank 23 is subjected to the water supply pressure applied inside the water supply channel L7. With this configuration, in the hot water storage tank 23, for example, when a faucet (not shown) connected to the hot water outlet channel L8 is opened, hot water is discharged from the hot water storage tank 23 to the hot water outlet channel L8, and tap water is supplied to the hot water storage tank 23 from the water supply channel L7.

[0034] The fuel cell system comprises an operation control unit 26 and a storage unit 27 that stores information handled by the fuel cell system. The operation control unit 26 controls the operation of various devices such as the ignition unit 10, raw fuel supply unit 3, water supply unit 21, air supply unit 22, and hot water circulation unit 24.

[0035] Changing the power output of the cell stack 9 may reduce the power generation efficiency. Therefore, in this embodiment, the operation control unit 26 determines a target power output pattern for the cell stack 9 over a predetermined period, based on a first correlation between the power output of the cell stack 9 and the power generation efficiency, a second correlation between the power output of the cell stack 9 and the increase or decrease in stored water, and the current amount of stored water measured by the water volume measuring unit 20, such that the amount of stored water after the predetermined period reaches the target amount and the average power generation efficiency of the cell stack 9 over the predetermined period is high. This target power output pattern includes one or more combinations of a target power output and the operating period at that target power output.

[0036] Figure 2 shows the first correlation between the power generation amount and power generation efficiency of the cell stack 9, and Figure 3 shows the second correlation between the power generation amount and the increase / decrease in stored water. For example, the first and second correlations are stored in the memory unit 27. As shown in Figures 2 and 3, in a fuel cell system, the power generation efficiency decreases as the power generation amount decreases, and the increase / decrease in stored water also fluctuates with the power generation amount.

[0037] Therefore, even if the increase or decrease in stored water over a certain period of time is the same, the average power generation efficiency over that period will vary depending on the power generation pattern within that period. For example, based on the graphs in Figures 2 and 3, the increase or decrease in stored water when operating at 700W for 3 hours and 200W for 15 hours is almost the same as the increase or decrease in stored water when operating at 400W for 18 hours, both being around ±0. However, in the former case, the average power generation efficiency over 18 hours is 30%, while in the latter case it is 44%. In other words, the latter allows the fuel cell system to be operated more efficiently. Therefore, the operation control unit 26 adopts an operation of 400W (target power generation) for 18 hours (operating period) as the target power generation pattern for the cell stack 9 over a predetermined period of 18 hours.

[0038] The first correlation shown in Figure 2 may be updated as needed, taking into account the deterioration of the fuel cell system over time. For example, the operation control unit 26 can acquire fuel consumption information, which includes information on the amount of power generated by the cell stack 9 and information on the amount of raw materials consumed by the cell stack 9 to obtain that amount of power (i.e., information on the amount of raw materials supplied by the raw material supply unit 3), while the cell stack 9 is in operation, and can determine the first correlation based on the fuel consumption information. To give a specific example, for instance, the control unit can operate the cell stack 9 by changing the amount of power generated from 100Wh to 700Wh in 100Wh increments at a predetermined frequency, such as once a year, and determine the first correlation by referring to the power generation efficiency derived based on the amount of raw materials consumed by the cell stack 9 to obtain each amount of power generated.

[0039] Furthermore, the second correlation shown in Figure 3 may be updated as needed, taking into account the deterioration of the fuel cell system over time. For example, the operation control unit 26 may acquire information on the amount of power generated by the cell stack 9 and information on the increase or decrease in the amount of stored water when the amount of power generated by the cell stack 9 is generated (i.e., information on the increase or decrease in the amount of stored water measured by the water volume measuring unit 20) while the cell stack 9 is in operation, and determine the second correlation based on the increase or decrease information.

[0040] Furthermore, multiple types of second correlations may be prepared and stored in the memory unit 27 depending on the ambient temperature or exhaust gas temperature. As described above, the fuel cell system of this embodiment is equipped with a temperature sensor T4 for measuring ambient temperature and a temperature sensor T3 for measuring exhaust gas temperature. Therefore, the operation control unit 26 can determine the target power generation pattern based on the second correlation corresponding to the current temperature measured by the temperature sensor T3 or temperature sensor T4.

[0041] Figure 4 shows examples of the second correlation relationships, of which several types are available depending on the ambient temperature. As shown in the figure, several types of second correlation relationships are available such that the water balance (increase or decrease in stored water) shifts to the positive side as the ambient temperature decreases. The operation control unit 26 then simply selects the second correlation relationship that is closest to the current temperature (ambient temperature) measured by the temperature sensor T4. Although Figure 4 shows examples of second correlation relationships for ambient temperatures of 30°C, 35°C, and 40°C, the number and types of second correlation relationships corresponding to each temperature can be set as appropriate.

[0042] Furthermore, the operation control unit 26 can acquire increase / decrease information during the operation of the cell stack 9, which includes temperature information measured by temperature sensor T3 or temperature sensor T4, information on the amount of power generated by the cell stack 9, and information on the increase / decrease in the amount of stored water when the amount of power generated by the cell stack 9. Based on the increase / decrease information, it can also determine multiple types of second correlations corresponding to the ambient temperature measured by temperature sensor T4 or the exhaust gas temperature measured by temperature sensor T3.

[0043] <Another Embodiment> In the above embodiment, the configuration of the fuel cell system was described with specific examples, but the configuration can be changed as appropriate.

[0044] In the above embodiments, the fuel cell system of the present invention was described with specific numerical examples, but these numerical values ​​are provided for illustrative purposes only and can be changed as appropriate.

[0045] 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]

[0046] This invention can be used in fuel cell systems that can secure sufficient stored water while maintaining high power generation efficiency in the fuel cell section. [Explanation of symbols]

[0047] 6: Modified section 9: Cell stack (fuel cell section) 11: Combustion section 16:Heat exchange section 19: Water tank 20: Water measurement part 21:Water supply section 26: Operation Control Unit T1: Temperature sensor T2: Temperature sensor T3: Temperature sensor T4: Temperature sensor

Claims

1. A reforming unit that generates fuel gas by steam reforming raw fuel, A fuel cell unit that generates electricity by reacting the aforementioned fuel gas and oxygen gas, A combustion unit that burns the combustible gas present in the gas discharged from the fuel cell unit after it has been used in the power generation reaction to produce exhaust gas, A heat exchange unit that recovers the heat of the exhaust gas discharged from the combustion unit using a heat transfer medium, A water tank for recovering and storing condensed water generated from the exhaust gas by heat recovery in the heat exchange section, A water supply unit capable of supplying the stored water in the water tank to the reforming unit, A water volume measuring unit for measuring the amount of water stored in the water tank, It includes an operation control unit, A fuel cell system in which the operation control unit determines a target power generation pattern for the fuel cell unit during a predetermined period, based on a first correlation between the amount of power generated by the fuel cell unit and the power generation efficiency, a second correlation between the amount of power generated by the fuel cell unit and the increase or decrease in the amount of stored water, and the current amount of stored water measured by the water amount measuring unit, such that the amount of stored water after the predetermined period becomes a target amount and the average power generation efficiency of the fuel cell unit during the predetermined period is high.

2. The fuel cell system according to claim 1, wherein the operation control unit acquires information on the amount of power generated by the fuel cell unit and information on the amount of raw materials consumed by the fuel cell unit to obtain the amount of power generated, and determines the first correlation based on the raw materials consumed information.

3. The fuel cell system according to claim 1, wherein the operation control unit acquires information on the amount of power generated by the fuel cell unit and information on the increase or decrease in the amount of stored water when the amount of power generated is generated by the fuel cell unit, and determines the second correlation based on the increase or decrease in the amount of power generated.

4. Multiple types of the second correlation are available depending on the ambient temperature or the temperature of the exhaust gas. Equipped with a temperature sensor that measures the ambient temperature or the temperature of the exhaust gas, The fuel cell system according to claim 1, wherein the operation control unit determines the target power generation pattern based on the second correlation corresponding to the current temperature measured by the temperature sensor.

5. The fuel cell system according to claim 4, wherein the operation control unit acquires, during the operation of the fuel cell unit, information on the temperature measured by the temperature sensor, information on the amount of power generated by the fuel cell unit, and information on the increase or decrease in the amount of stored water when the amount of power generated is generated by the fuel cell unit, and determines a plurality of types of second correlations according to the ambient temperature or the temperature of the exhaust gas based on the increase or decrease in the amount of power generated.

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