fuel cell system

Abstract

To provide a fuel cell system capable of preventing freezing of a circulation flow path for circulating hot water between a hot water storage tank and a heat exchanger even in the absence of an electric heater.SOLUTION: In a fuel cell system including a fuel cell 1, an operation control device C, a leak detection device Y, a hot water storage tank 2, and a circulation flow path 6, the operation control device C includes a storage unit 31 that stores a scheduled stop period during which the operation of the fuel cell 1 is stopped for a predetermined period in order to reset a cumulative time, and a determination unit 32 that determines the risk of freezing of the circulation flow path 6 during the scheduled stop period, and when the timing at which it is determined that there is a risk of freezing during the scheduled stop period is a timing that goes back a determination period that is larger than the predetermined period from the start of the scheduled stop period, and the freezing risk during the scheduled stop period exceeds a threshold value, the scheduled stop period stored in the storage unit 31 is brought forward.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system including a fuel cell, a hot water storage tank, and a heat exchanger that exchanges heat between the exhaust heat of the fuel cell and the hot water in the hot water storage tank. [Background technology]

[0002] Conventionally, fuel cell systems with high power generation efficiency that use solid oxide fuel cells (SOFCs) as fuel cells have been known. In these fuel cell systems, a reformer generates electricity by reacting hydrogen produced by reforming raw fuel with oxygen-containing air. The electricity is supplied to a power load, and the heat generated by the reaction is supplied to a heat load for hot water supply or space heating via a heat exchanger. Gas appliances such as reformers for solid oxide fuel cells are supplied with commercial gas (e.g., city gas 13A). This commercial gas is generally supplied via a gas leak detection device equipped with a protective function that detects gas leaks and issues an alarm or shuts off the gas. Conventionally, a gas meter with a microcomputer function (hereinafter referred to as a "microcomputer meter") installed in a gas supply pipe has been used as the gas leak detection device (see, for example, Patent Documents 1 and 2).

[0003] Microcomputer meters are equipped with various safety functions, one of which is the "function to sound an alarm or cut off the gas supply if gas continues to flow for a specified period of time." This function is intended to detect gas leaks, for example, if a rubber tube or gas pipe is damaged and a small amount of gas continues to leak, and it detects a small amount of gas leaking continuously for more than a certain period of time (for example, 30 days), and sounds an alarm or cuts off the gas supply.

[0004] When this alarm is issued or the gas supply is cut off, an inspection by the gas supplier is often required to clear the alarm, which also requires a certain period of time without gas flow. This process of clearing the alarm not only places a burden on the user, but also requires the fuel cell, which continuously uses gas, to be temporarily shut down. Once a fuel cell stops operating, it takes time to return to normal operation. In particular, in the case of solid oxide fuel cells, the shutdown process can take approximately 10 to 20 hours, and the restart process can take approximately 2 to 4 hours, causing unintended inconvenience to the user. Therefore, the fuel cell systems described in Patent Documents 1 and 2 provide planned shutdown periods during which the fuel cell is shut down in order to avoid alarms from gas leak detection devices.

[0005] The fuel cell system described in Patent Document 1 includes a shutdown schedule changing unit that changes the scheduled shutdown period of the fuel cell so that the fuel cell can operate independently at least during the predicted power outage period.

[0006] The fuel cell system described in Patent Document 2 comprises a heat exchanger that exchanges heat between the exhaust heat of the fuel cell and hot water in a hot water storage tank, and a circulation flow path that circulates the hot water between the hot water storage tank and the heat exchanger. An electric heater is provided in the water pipe that supplies tap water to the hot water storage tank to prevent the water pipe and peripheral equipment from freezing while the fuel cell is stopped. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-42411 [Patent Document 2] Japanese Patent Application Publication No. 2020-46090 Summary of the Invention [Problem to be solved by the invention]

[0008] The circulation path that circulates hot water between the hot water storage tank and the heat exchanger is sometimes equipped with a radiator that radiates heat that cannot be stored in the hot water storage tank by exchanging it with the outside air. In particular, the area around this radiator is at risk of failure due to freezing of the circulation path, which hinders efficient independent operation of the fuel cell system.

[0009] On the other hand, the fuel cell system described in Patent Document 1 controls the predicted power outage period so that the fuel cell shutdown period does not overlap, but it does not use technology to prevent the circulation flow path from freezing. Also, the fuel cell system described in Patent Document 2 requires the installation of a separate electric heater to prevent the water pipes from freezing, which incurs a certain amount of cost.

[0010] Therefore, there is a demand for a fuel cell system that can prevent freezing of the circulation flow path that circulates hot water between the hot water storage tank and the heat exchanger even when an electric heater is not provided. [Means for solving the problem]

[0011] A characteristic configuration of a fuel cell system according to the present invention is a fuel cell system including a fuel cell capable of supplying electric power generated by operation to a power load section, an operation control device for controlling the operation of the fuel cell, a leak detection device for detecting a leak in a fuel supply line that supplies fuel to the fuel cell, a hot water storage tank for storing hot water that can be supplied to a heat load section, a heat exchanger for exchanging heat between exhaust heat of the fuel cell and the hot water in the hot water storage tank, and a circulation flow path for circulating the hot water between the hot water storage tank and the heat exchanger, wherein the leak detection device detects a cumulative time during which the flow rate of fuel in the fuel supply line is equal to or less than a predetermined flow rate during a predetermined leak determination period. The operation control device is configured to determine that a leak has occurred when the cumulative time is less than a predetermined time, and the operation control device has a memory unit that stores a planned shutdown period during which operation of the fuel cell is stopped for a predetermined period to reset the accumulated time, and a judgment unit that judges the risk of freezing of the circulation flow path during the planned shutdown period, and when the timing at which it is judged that there is a risk of freezing during the planned shutdown period is a timing that goes back a judgment period that is greater than the predetermined period from the start of the planned shutdown period, and when the risk of freezing during the planned shutdown period exceeds a threshold, the planned shutdown period stored in the memory unit is brought forward.

[0012] In this configuration, the operation control device has a determination unit that determines whether there is a risk of freezing of the circulation flow path during the scheduled shutdown period of the fuel cell, and when this determination unit determines that there is a risk of freezing during the scheduled shutdown period and the risk of freezing exceeds a threshold, the scheduled shutdown period stored in the memory unit is brought forward.As a result, even if the fuel cell is shut down as planned (shut down during the brought-forward scheduled shutdown period), the risk of freezing of the circulation flow path that circulates hot water between the hot water storage tank and the heat exchanger can be reduced.

[0013] In addition, with this configuration, if the timing at which it is determined that there is a risk of freezing during the planned shutdown period is a determination period that is longer than the predetermined period from the start of the planned shutdown period, the planned shutdown period is advanced, allowing the fuel cell to restart before the predetermined period during which there is a risk of freezing (the planned shutdown period before the advancement). Furthermore, as with this configuration, by not advancing the planned shutdown period when the risk of freezing of the circulation flow path is low (the risk of freezing does not exceed the threshold), and by advancing the planned shutdown period only when the risk of freezing of the circulation flow path is high (the risk of freezing exceeds the threshold), freezing of the circulation flow path can be more efficiently prevented. Therefore, even without an electric heater, freezing of the circulation flow path that circulates hot water between the hot water storage tank and the heat exchanger can be prevented.

[0014] Another characteristic feature is that the determination unit determines the risk of freezing based on the outside air temperature included in the weather data.

[0015] As in this configuration, by utilizing weather data to determine the risk of freezing based on the outside temperature, it is possible to plan ahead and bring forward the planned shutdown period. Moreover, since weather data can be obtained anywhere, it is highly versatile.

[0016] Another characteristic feature is that when the total time during the planned shutdown period during which the outside air temperature is below a predetermined temperature is equal to or greater than a set value, the operation control device determines that the risk of freezing has exceeded a threshold value and advances the planned shutdown period stored in the memory unit.

[0017] As in this configuration, if the total time during a specified period during which the outside air temperature is below a specified temperature is greater than or equal to a set value, it is determined that there is a high risk of freezing of the circulation flow path (the risk of freezing exceeds a threshold value) and the scheduled shutdown period is brought forward, thereby reducing the computational load.

[0018] Another characteristic feature is that the memory unit stores a plurality of target temperatures including a first temperature and a second temperature higher than the first temperature, and the operation control device is configured to be capable of executing a heat storage mode in which the hot water stored in the hot water storage tank is raised to one selected target temperature.

[0019] In this configuration, a heat storage mode can be implemented in which the hot water stored in the hot water storage tank is heated to a target temperature using exhaust heat from the fuel cell, so that freezing can be prevented by simply circulating the hot water in the hot water storage tank through the circulation flow path during the planned shutdown period of the fuel cell, providing the heat stored in the heat storage mode to the circulation flow path.In this case, if the memory unit stores multiple target temperatures, including a first temperature and a second temperature higher than the first temperature, the optimal target temperature can be selected depending on the degree of risk of freezing.

[0020] Another characteristic configuration is that when it is determined that there is a risk of freezing and the total time during which the outside air temperature is below the predetermined temperature during the planned shutdown period is less than the set value, the operation control device selects the first temperature as the target temperature and executes the heat storage mode without advancing the planned shutdown period stored in the memory unit.

[0021] In this configuration, when it is determined that there is a risk of freezing and the total time during the planned shutdown period during which the outside air temperature is at or below a predetermined temperature is less than a set value, a relatively low first temperature is selected as the target temperature in the heat storage mode (for example, the normal target temperature during rated output operation of the fuel cell), so that heat can be stored in the hot water storage tank without special control.The heat stored in the hot water storage tank in this heat storage mode can then be provided to the circulation flow path during the planned shutdown period that was not brought forward, thereby preventing freezing.

[0022] Another characteristic configuration is that when the timing at which it is determined that there is a risk of freezing during the planned shutdown period is a timing that goes back a period equal to or shorter than the specified period from the start of the planned shutdown period, the operation control device selects the second temperature as the target temperature and executes the heat storage mode without advancing the planned shutdown period stored in the memory unit.

[0023] In this configuration, if the determined timing is a timing that is less than a predetermined period before the start of the planned shutdown period, advancing the planned shutdown period would prevent the fuel cell from restarting by the predetermined period during which there is a risk of freezing (the planned shutdown period before it was advanced), and there is a risk of the circulation flow path freezing. Therefore, the planned shutdown period stored in the memory unit is not advanced. On the other hand, because the relatively high second temperature is selected as the target temperature in the heat storage mode, heat can be stored in the hot water storage tank relatively early. Then, the heat stored in the hot water storage tank in this heat storage mode can be provided to the circulation flow path during the planned shutdown period that was not advanced, preventing freezing. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is an overall configuration diagram of a fuel cell system. [Figure 2] This is an example of determining the risk of freezing. [Figure 3] FIG. 2 is a control flow diagram of the operation control device. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of a fuel cell system according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0026] As shown in Fig. 1, a facility such as an ordinary home is provided with a fuel cell system X and a power load unit 3. The fuel cell system X and the power load unit 3 are connected to a power line PL that is linked to a power grid 15. A power meter (not shown) is installed on the power line PL to measure the power received by the facility.

[0027] Information about the power receiving point power measured by the power meter is transmitted to a management device (not shown). For example, the information about the power receiving point power is transmitted to the management device at a predetermined timing, such as every 10 seconds. The management device is a main server that can centrally manage each of the fuel cell systems X installed in multiple facilities.

[0028] The power load unit 3 is various devices such as lighting equipment and air conditioning equipment, and can receive power supply from at least one of the fuel cell system X and the power grid 15 installed in the facility.

[0029] The fuel cell system X includes a solid oxide fuel cell 1 (an example of a fuel cell) connected to an electric power grid 15. The power generated by the solid oxide fuel cell 1 is converted into a predetermined voltage, frequency, and phase by a power conversion unit 12 and supplied to a power line PL. The operations of the fuel cell system X and the power conversion unit 12 are controlled by an operation control device C.

[0030] The operation control device C can adjust the output power from the fuel cell system X to the power line PL between a predetermined upper limit output power and a predetermined lower limit output power. For example, the operation control device C can maintain the output power of the fuel cell system X at the upper limit output power to perform continuous operation (rated output operation). The operation control device C can also perform an operation (load following operation) in which the output power of the fuel cell system X follows the load power of the power load unit 3. For example, the operation control device C can perform an operation in which the output power of the fuel cell system X follows the load power of the power load unit 3 by adjusting the output power of the fuel cell system X so that the power supplied from the power grid 15 becomes zero or close to zero.

[0031] The operation control device C has information about the output power supplied from the power conversion unit 12 to the power line PL and information about the power measured by the power meter, and is therefore able to derive the load power of the power load unit 3. When the sign of the power measured by the power meter is positive (forward flow), this means that the load power is greater than the output power of the fuel cell system X, and when the sign of the power measured by the power meter is negative (reverse flow), this means that the output power of the fuel cell system X is greater than the load power.

[0032] 1 is a diagram showing the configuration of a fuel cell system X. The fuel cell system X includes a fuel meter Y (an example of a leakage detection device), an operation control device C that controls the operation of the fuel cell system X including a solid oxide fuel cell 1, a hot water storage tank 2, and a heat exchanger E.

[0033] The fuel cell system X includes a solid oxide fuel cell 1 that supplies power generated during operation to a power load unit 3 and supplies heat generated during operation to a heat load unit 4. The power load unit 3 is capable of consuming power supplied from a power grid 15 in addition to power supplied from the solid oxide fuel cell 1. In other words, the solid oxide fuel cell 1 is connected to the power grid 15 in a state in which it can supply power generated during operation to the power load unit 3, and in a state in which it can supply power from the power grid 15 to the power load unit 3 and in which it can supply power generated during operation to the power grid 15.

[0034] In addition to the heat generated from the solid oxide fuel cell 1, the heat load section 4 can also consume heat supplied from an auxiliary heat source device 11 that generates heat by burning raw fuel.

[0035] The solid oxide fuel cell 1 includes, inside the container 1A, a vaporizer 1b that evaporates the supplied reforming water, a reformer 1a that generates fuel gas (gas containing hydrogen) by steam reforming a raw fuel (gas containing hydrocarbons, for example, city gas 13A), a cell stack having multiple fuel cell units S that generate electricity using the fuel gas generated by the reformer 1a, and a combustion unit 1c that combusts off-gas from the cell stack. The cell stack is electrically connected to a power conversion unit 12.

[0036] The cell stack comprises a plurality of fuel cell units S electrically connected in series, each unit comprising an anode 50 having a fuel flow section (not shown) through which the fuel gas generated in the reformer 1a flows, and a cathode 60 having an air flow section (not shown) through which oxygen (air) flows. Although not shown, the fuel cell units S are configured as a solid oxide type having a solid electrolyte layer between the anode 50 and the cathode 60. Fuel gas is supplied to the anode 50, and oxygen is supplied to the cathode 60.

[0037] A gas manifold 1e is provided at the bottom of the cell stack to receive fuel gas supplied from the reformer 1a through a fuel gas flow path L4. The fuel gas supplied to this gas manifold 1e flows from the lower ends of the plurality of fuel cell cells S to the upper side and is used for the power generation reaction. After being used for the power generation reaction, the discharged fuel gas is discharged from a fuel gas outlet 50a at the upper end.

[0038] The solid oxide fuel cell 1 is provided with an air inlet 70 connected to an air supply passage L5, and an air filter 21, an air blower 22, and an air flow meter 23 are provided along the air supply passage L5. By operating the air blower 22, air is supplied into the container 1A through the air supply passage L5. The air filter 21 captures foreign matter such as dust in the air sucked into the air supply passage L5 by the air blower 22. The air flow meter 23 measures the flow rate per unit time of the air supplied into the container 1A. Air from within the container 1A flows from the lower side to the upper side in each of the multiple fuel cell units S and is used for the power generation reaction. After being used for the power generation reaction, the exhaust air is discharged from the air outlet 60a at the upper end.

[0039] A combustion space is formed above the cell stack to combust the exhaust fuel gas, which contains hydrogen not used in the power generation reaction and is discharged from the fuel gas outlet 50a, and the exhaust air, which is discharged from the air outlet 60a. This exhaust fuel gas and exhaust air become off-gas from the cell stack. An igniter 1d is also provided in this combustion space. In other words, the combustion space above the cell stack provides a combustion unit 1c that combusts the off-gas from the cell stack. Additionally, an integrated vaporizer 1b and reformer 1a are provided adjacent to the combustion space above the cell stack, which functions as the combustion unit 1c.

[0040] An exhaust section 80 is formed in the bottom of the container 1A for discharging the combustion exhaust gas generated in the combustion section 1c to the outside via a heat exchanger E. A combustion catalyst section 90 (e.g., a platinum-based catalyst) is provided in the container 1A for removing carbon monoxide gas and the like from the combustion exhaust gas discharged to the outside from the exhaust section 80.

[0041] The vaporizer 1b heats and evaporates the supplied reforming water using combustion heat transferred from the combustion section 1c. The reforming water stored in the reforming water tank 24 is supplied to the vaporizer 1b via a reforming water flow path L2 connected to the reforming water tank 24. Specifically, when the reforming water pump P operates, the reforming water stored in the reforming water tank 24 flows through the reforming water flow path L2 and into the vaporizer 1b.

[0042] Raw fuel is also supplied to the vaporizer 1b via a raw fuel flow path L1. A mass flow meter Fa and a raw fuel blower B are provided along the raw fuel flow path L1. The mass flow meter Fa is, for example, a thermal mass flow meter that performs measurements by utilizing the thermal diffusion effect of the raw fuel. Furthermore, a desulfurizer 20 is provided downstream of the raw fuel blower B in the raw fuel flow path L1 to remove sulfur compounds contained in the raw fuel (e.g., city gas). When the raw fuel blower B operates, the raw fuel flows through the raw fuel flow path L1, is desulfurized by the desulfurizer 20, and then flows into the vaporizer 1b. The operation control device C controls the operation of the raw fuel blower B and the on-off valve V1 so that the flow rate of the raw fuel measured using the mass flow meter Fa becomes a target flow rate. In this way, the vaporizer 1b generates a mixed gas containing raw fuel and steam, the supply amount of which per unit time is controlled by the operation control device C, and the mixed gas is supplied to the reformer 1a via the mixed gas flow path L3.

[0043] The reformer 1a performs steam reforming of the raw fuel contained in the mixed gas supplied from the vaporizer 1b. Although not shown, the reformer 1a is filled with a reforming catalyst, and the raw fuel is reformed by the catalytic action of this reforming catalyst.

[0044] The power generated by the solid oxide fuel cell 1 is supplied to a power conversion unit 12. The power conversion unit 12 converts the power generated by the solid oxide fuel cell 1 to the same voltage and frequency as the received power received from a power grid 15. The operation of the power conversion unit 12 is controlled by an operation control device C. The power conversion unit 12 is electrically connected to a received power supply line 14 via a generated power supply line 13. The generated power from the solid oxide fuel cell 1 is supplied to the power load unit 3 via the power conversion unit 12, the generated power supply line 13, and a received power supply line 14 (corresponding to the above-mentioned power line PL). This received power supply line 14 is connected to the power grid 15. In other words, the solid oxide fuel cell 1 is interconnected with the power grid 15 in a state in which it is able to supply the power generated by its operation to the power grid 15.

[0045] The receiving power supply line 14 is provided with a power load measuring unit 16 that measures the power load of the power load unit 3, and the measurement result is transmitted to the operation control device C. The operation control device C then adjusts the output power of the fuel cell system X so that the power supplied from the power grid 15 becomes zero or close to zero, thereby performing an operation (load following operation) in which the power follows the load power of the power load unit 3. This load following operation may control the power generated by the solid oxide fuel cell 1 based on the measurement value of the power at the receiving point near the above-mentioned power meter, or may control the power load detected by the power load measuring unit 16 to be equal to the power generated by the solid oxide fuel cell 1 and supplied to the receiving power supply line 14. The operation control device C can also operate the solid oxide fuel cell 1 at its rated output. However, during load following operation, if the power load measured by the power load measuring unit 16 is smaller than the minimum power generated by the solid oxide fuel cell 1 (the minimum power generated and supplied to the receiving power supply line 14 by the power conversion unit 12), surplus power is generated. In addition, surplus power is also generated when the solid oxide fuel cell 1 is operated at the rated output and the output power from the power conversion unit 12 is greater than the power load during rated output operation. If reverse power flow of power to the power grid 15 is possible, the surplus power may be supplied to the power grid 15.

[0046] The power load unit 3 is various devices such as lighting equipment and air conditioning equipment, and can receive power supply from at least one of the fuel cell system X and the power grid 15 installed in the facility. The types of devices to be included in the power load unit 3 can be set as appropriate. For example, it is possible to set the power load unit 3 to exclude auxiliary equipment used to operate the solid oxide fuel cell 1. Furthermore, the standby power of the power load unit 3 may be subtracted from the power load measured by the power load measurement unit 16.

[0047] The hot water storage tank 2 stores the heat generated by the solid oxide fuel cell 1 in the form of hot water. In other words, the hot water storage tank 2 stores hot water that has been heated using the heat generated by the operation of the solid oxide fuel cell 1. Clean water is supplied to the bottom of the hot water storage tank 2 via a water supply line 17. The inside of the hot water storage tank 2 is configured so that relatively low temperature hot water is stored in the bottom, and relatively high temperature hot water is stored in the top.

[0048] By operating the exhaust heat recovery pump 7, the hot water stored in the hot water storage tank 2 is circulated through a circulation flow path 6 between the hot water storage tank 2 and a heat exchanger E, through which the combustion exhaust gas from the solid oxide fuel cell 1 flows. A radiator 8 is installed along the circulation flow path 6 to radiate heat from the hot water flowing from the hot water storage tank 2 to the heat exchanger E through the circulation flow path 6. The relatively high-temperature hot water stored in the upper part of the hot water storage tank 2 is supplied to the heat load section 4 via a hot water supply path 5 and an auxiliary heat source device 11, which are connected to the upper part of the hot water storage tank 2. In addition, a first connection path 18 and a second connection path 19 are provided to connect the water supply path 17 and the hot water supply path 5. A three-way valve V2 is arranged at the connection between the first connection path 18 and the hot water supply path 5, and a shut-off valve V3 is arranged in the second connection path 19. The three-way valve V2 can be switched between a shutoff position that shuts off high-temperature hot water, a temperature control position that mixes water from the water supply line 17 with high-temperature hot water, and a high-temperature position that allows only high-temperature hot water to flow through the hot water supply line 5. The shutoff valve V3 is an on-off valve that can switch between communication and non-communication between the second connection line 19 and the hot water supply line 5.

[0049] The heat exchanger E is a known heat exchanger that exchanges heat between the exhaust heat of the solid oxide fuel cell 1 and the hot water in the hot water storage tank 2. In this embodiment, the heat exchanger E is provided in the circulation flow path 6, downstream of the radiator 8. The hot water stored in the lower part of the hot water storage tank 2 is heated through the heat exchanger E by circulating through the circulation flow path 6, and returned to the upper part of the hot water storage tank 2. A known temperature sensor T is provided in the circulation flow path 6, downstream of the heat exchanger E, and this temperature sensor T measures the temperature of the hot water heated by the heat exchanger E and outputs the temperature of the heated hot water to the operation control device C.

[0050] The thermal load section 4 is used for hot water supply, heating, etc. When the thermal load section 4 is used for hot water supply, the hot water does not return to the hot water storage tank 2. When the thermal load section 4 is used for heating, only the heat contained in the hot water is consumed, and the hot water may return to the hot water storage tank 2.

[0051] The fuel meter Y includes a volumetric flow meter Fb that measures the total volume of raw fuel (fuel) supplied to the solid oxide fuel cell 1 via a raw fuel flow path L1 (an example of a fuel supply path) and raw fuel (fuel) supplied to other fuel consumption appliances K, such as the auxiliary heat source device 11 and a gas stove, via a raw fuel flow path L6 (an example of a fuel supply path). The fuel meter Y detects leakage in the raw fuel flow paths L1 and L6 that supply raw fuel to the solid oxide fuel cell 1. This volumetric flow meter Fb is configured as a membrane-type gas meter that measures the amount of raw fuel used (total volume) from the number of operations of a movable membrane that separates two measuring chambers, or an ultrasonic gas meter that measures the amount of raw fuel used (total volume) by measuring the gas flow rate with an ultrasonic sensor.

[0052] The volumetric flow meter Fb is configured with a microcomputer meter having safety functions, including at least the function of issuing an alarm or cutting off the gas supply when gas continues to flow for a predetermined time. One of these safety functions is to determine that a leak has occurred and issue an alarm or cut off the gas supply if the cumulative time during which the flow rate (total volume) is below a very small amount (predetermined flow rate) does not reach a predetermined time (e.g., 1 hour) during a predetermined leak determination period (e.g., 30 days), and to reset the cumulative time (to zero) if the predetermined time has been reached. In this embodiment, to reset the cumulative time, a scheduled shutdown period is set at predetermined intervals (e.g., every 27 days) during which the operation of the solid oxide fuel cell 1 is stopped for a predetermined period (12 to 24 hours, including shutdown and startup, depending on the model).

[0053] Next, the operation control device C of the fuel cell system X will be described in detail with reference to FIGS.

[0054] As shown in Fig. 1, the operation control device C controls the operation of at least the solid oxide fuel cell 1. This operation control device C has a memory unit 31 that stores the planned shutdown period of the solid oxide fuel cell 1, a determination unit 32 that determines the risk of freezing during the planned shutdown period, and a control unit 33 that executes shutdown control of at least the solid oxide fuel cell 1. The operation control device C is composed of hardware and software having information processing functions, information storage functions, information communication functions, etc., and is provided in the facility, but may be provided in part or in whole in the management device. The memory unit 31 is composed of a storage medium that stores programs, etc. that operate the operation control device C, and is provided in each facility, but may be provided in part or in whole in the management device.

[0055] The memory unit 31 stores a scheduled shutdown period during which the operation of the solid oxide fuel cell 1 is stopped for a predetermined period (e.g., 24 hours) at predetermined intervals (e.g., every 27 days) to reset the cumulative time counted by the volumetric flow meter Fb. The memory unit 31 also stores multiple target temperatures (e.g., 60°C as a first temperature and 80°C as a second temperature) to execute a heat storage mode (described later). Because the solid oxide fuel cell 1 requires a long time (e.g., 24 hours) from shutdown to startup, the operation control device C in this embodiment can change (advance) the scheduled shutdown period stored in the memory unit 31 when the timing at which it is determined that there is a risk of freezing during the scheduled shutdown period (e.g., 24 hours) is a determination period (e.g., two days or more) earlier than the start of the scheduled shutdown period. The changed scheduled shutdown period can be set to a period earlier than the start of the previous scheduled shutdown period by a determination period (e.g., two days or more).

[0056] The determination unit 32 determines the risk of freezing during the planned shutdown period based on the outside air temperature (forecasted outside air temperature) included in the weather data. The weather data is forecast data for each measurement point (forecast area) published by the Japan Meteorological Agency, and includes outside air temperature, precipitation, wind speed, etc. The outside air temperature included in the weather data may be received by the operation control device C via a management device, or may be received directly by the operation control device C. The determination unit 32 determines the risk of freezing during the planned shutdown period based on the forecast data for the outside air temperature at the forecast point closest to the point where the fuel cell system X is located.

[0057] FIG. 2 shows an example in which the determination unit 32 determines the risk of freezing. In September 2021, the predicted minimum temperature for all days exceeds a first predetermined temperature (e.g., 3°C), so the determination unit 32 determines that there is "no risk of freezing." In this case, for example, the planned shutdown period included in September 2021 is determined to have "no risk of freezing." On the other hand, in January 2022, the predicted minimum temperature for most days is equal to or lower than the first predetermined temperature, so the determination unit 32 determines that there is "risk of freezing." In this case, for example, the planned shutdown period included in January 2022 is determined to have "risk of freezing." In addition, the risk of freezing may be determined to be "risk of freezing" if there are a specified number of days (e.g., 20 days) or more in a month when the minimum temperature is below the first specified temperature, or if the minimum temperature on the day including the planned shutdown period and a specified number of days before that (e.g., about three days before) is below the first specified temperature.

[0058] When the determination unit 32 determines that there is a risk of freezing, it further determines whether the risk of freezing during the planned shutdown period exceeds a threshold. As an example of a criterion for determining whether the risk of freezing exceeds a threshold, it uses whether the total time during which the outside air temperature is equal to or lower than a second predetermined temperature (e.g., 3°C, corresponding to the predetermined temperature) is equal to or greater than a set value (e.g., 8 hours) during a predetermined period (e.g., 24 hours) during which operation of the solid oxide fuel cell 1 is stopped within the planned shutdown period previously stored in the storage unit 31. The determination unit 32 determines January 10, 2022, on which the total time during which the outside air temperature is equal to or lower than the second predetermined temperature is less than the set value, as a "low risk of freezing," and determines January 21, 2022, on which the total time during which the outside air temperature is equal to or lower than the second predetermined temperature is equal to or greater than the set value, as a "high risk of freezing."

[0059] When the determination unit 32 determines that there is a "risk of freezing" and the total time during which the outside air temperature is at or below a second predetermined temperature (e.g., 3°C) within a predetermined period is equal to or greater than a set value (e.g., 8 hours), the operation control device C determines that there is a "high risk of freezing." If the timing at which the determinations of "risk of freezing" and "high risk of freezing" were made is a determination period (e.g., two days or more) longer than the predetermined period, going back from the start of the planned shutdown period (e.g., at least two days before the shutdown start date), the operation control device C advances the planned shutdown period stored in the memory unit 31. To advance the planned shutdown period, the operation control device C deletes or overwrites the planned shutdown period before correction, and stores it in the memory unit 31 as a corrected planned shutdown period. The next planned shutdown period is updated from this corrected planned shutdown period at predetermined intervals (e.g., every 27 days). This corrected planned stop period is selected as the period immediately preceding the original planned stop period, during which the total time during which the outside air temperature is below a second predetermined temperature (e.g., 3°C) is less than a set value (e.g., 8 hours).

[0060] When the start of the scheduled shutdown period or the corrected scheduled shutdown period of the solid oxide fuel cell 1 stored in the memory unit 31 arrives, the control unit 33 stops the operation of the solid oxide fuel cell 1 for a predetermined period (12 to 24 hours, including shutdown and startup, depending on the model). The control unit 33 is also configured to be able to execute a heat storage mode in which the hot water stored in the hot water storage tank 2 is raised to one target temperature selected from multiple target temperatures (e.g., 60°C as a first temperature and 80°C as a second temperature) stored in the memory unit 31. In this heat storage mode, the control unit 33 controls the exhaust heat recovery pump 7 to adjust the flow rate of the hot water flowing through the circulation flow path 6 so that the temperature (measured value of the temperature sensor T) of the hot water flowing through the heat exchanger E becomes the target temperature. For example, when the target temperature is higher than the measured value of the temperature sensor T, the control unit 33 reduces the flow rate of the hot water flowing through the circulation flow path 6. On the other hand, when the target temperature is lower than the measurement value of the temperature sensor T, the control unit 33 increases the flow rate of the hot water circulating through the circulation flow path 6, or controls the radiator 8 to remove heat from the hot water circulating through the circulation flow path 6. Here, the "heat storage mode" is a mode in which the unit is operated for a predetermined time (e.g., 8 hours) so that the measurement value of the temperature sensor T reaches the target temperature, and the hot water stored in the hot water storage tank 2 is controlled to a full storage state where almost all of the hot water has reached the target temperature by the start of the scheduled shutdown period. Note that the heat storage mode may be executed until a predetermined amount of heat is stored, even if almost all of the hot water stored in the hot water storage tank 2 has not reached the target temperature by the start of the scheduled shutdown period.

[0061] When the judgment unit 32 judges that there is a "risk of freezing" and the total time during a specified period during which the outside air temperature is below a second specified temperature (e.g., 3°C) is less than a set value (e.g., 8 hours), the operation control device C judges that there is a "low risk of freezing," selects a relatively low first temperature as the target temperature (e.g., 60°C, which is the normal target temperature for rated output operation of a fuel cell), and the control unit 33 controls the exhaust heat recovery pump 7 or the radiator 8 to execute the heat storage mode (low heat storage mode). On the other hand, when the judgment unit 32 judges that there is a "risk of freezing" and this judgment timing is a timing that goes back a period shorter than the judgment period (for example, two days) from the start of the planned shutdown period, particularly a timing that goes back a period shorter than a predetermined period from the start of the planned shutdown period (for example, a period within 24 hours before the start of the planned shutdown period), the operation control device C selects a relatively high second temperature as the target temperature (for example, 80°C), and the control unit 33 controls the exhaust heat recovery pump 7 or the radiator 8 to execute the heat storage mode (high heat storage mode).

[0062] When the operation control device C executes the heat storage mode, the control unit 33 stops the operation of the solid oxide fuel cell 1 during the scheduled shutdown period of the solid oxide fuel cell 1 stored in the memory unit 31 (i.e., during the original scheduled shutdown period without bringing forward the scheduled shutdown period), and operates the exhaust heat recovery pump 7 during the scheduled shutdown period to circulate the hot water stored in the hot water storage tank 2 through the circulation flow path 6. As a result, when the determination unit 32 determines that there is a "risk of freezing," the heat stored in the hot water storage tank 2 in the heat storage mode is given to the circulation flow path 6, thereby preventing the circulation flow path 6 from freezing.

[0063] Next, the control mode of the operation control device C will be described with reference to Fig. 3. First, the operation control device C operates the solid oxide fuel cell 1 (#31).

[0064] Next, the determination unit 32 of the operation control device C determines whether there is a risk of freezing of the circulation flow path 6 during the planned shutdown period (#32). If the minimum outside temperature during the planned shutdown period is equal to or lower than a first predetermined temperature (e.g., 3°C), the determination unit 32 determines that there is a "risk of freezing" (#32 Yes). If the minimum outside temperature is higher than the first predetermined temperature, the determination unit 32 determines that there is no "risk of freezing" (#32 No). Next, if the determination unit 32 determines that there is a "risk of freezing" (#32 Yes), and if the timing of the determination that there is a "risk of freezing" is a determination period (e.g., two days or more) longer than a predetermined period (e.g., 24 hours) going back from the start of the planned shutdown period (e.g., N days or more before the power generation shutdown date), the determination unit 32 determines the magnitude of the risk of freezing (#33 No, #34). For example, if the total time during the predetermined period during which the outside temperature is equal to or lower than a second predetermined temperature (e.g., 3°C) is equal to or higher than a set value (e.g., 8 hours), the determination unit 32 determines that there is a "high risk of freezing" (#34 Yes). If it is determined that there is a "high risk of freezing" (#34 Yes), the planned shutdown period stored in the memory unit 31 is brought forward and changed to a corrected planned shutdown period (#35). Then, when the start date of the corrected planned shutdown period of the solid oxide fuel cell 1 arrives, the control unit 33 suspends operation of the solid oxide fuel cell 1 for a predetermined period (#36).

[0065] In this way, by utilizing weather data information to determine the risk of freezing based on the outside air temperature, it is possible to systematically advance the planned shutdown period. Moreover, weather data is available anywhere, making it highly versatile. The operation control device C in this embodiment has a determination unit 32 that determines whether there is a risk of freezing in the circulation flow path 6 during the planned shutdown period of the solid oxide fuel cell 1. When this determination unit 32 determines that there is a risk of freezing during the planned shutdown period and the risk of freezing exceeds a threshold, the planned shutdown period stored in the memory unit 31 is advanced. As a result, even if the solid oxide fuel cell 1 is shut down systematically (shut down during the advanced planned shutdown period), the risk of freezing in the circulation flow path 6, which circulates hot water between the hot water storage tank 2 and the heat exchanger E, can be reduced.

[0066] Furthermore, in this embodiment, when the timing at which it is determined that there is a risk of freezing during the planned shutdown period is a timing that predates the start of the planned shutdown period by a determination period that is greater than the predetermined period, the planned shutdown period is advanced, so that the solid oxide fuel cell 1 can be restarted by the predetermined period during which there is a risk of freezing (the planned shutdown period before being advanced). Furthermore, by not advancing the planned shutdown period when the risk of freezing of the circulation flow path 6 is low (the risk of freezing does not exceed a threshold), and by advancing the planned shutdown period only when the risk of freezing of the circulation flow path 6 is high (the risk of freezing exceeds a threshold), freezing of the circulation flow path 6 can be more efficiently prevented. Furthermore, by determining that there is a high risk of freezing of the circulation flow path 6 when the total time of the risk of freezing within the predetermined period is equal to or greater than a set value, as in this embodiment, and advancing the planned shutdown period, the calculation load on the operation control device C is reduced.

[0067] Returning to FIG. 3 , if the determination unit 32 determines in step #34 that there is a “low risk of freezing” (No in step #34), it selects a relatively low first temperature in the heat storage mode as the target temperature (for example, 60°C, which is the normal target temperature for rated output operation of the fuel cell), and the control unit 33 controls the exhaust heat recovery pump 7 or the radiator 8 (low heat storage mode in step #37). Next, when the planned shutdown period of the solid oxide fuel cell 1 stored in the memory unit 31 arrives, the control unit 33 stops the operation of the solid oxide fuel cell 1 and activates the exhaust heat recovery pump 7 to circulate the hot water stored in the hot water storage tank 2 in the low heat storage mode through the circulation flow path 6 (#39). This allows heat to be stored in the hot water storage tank 2 without any special control. The heat stored in the hot water storage tank 2 in this low heat storage mode can then be provided to the circulation flow path 6 during the planned shutdown period that was not brought forward, thereby preventing freezing.

[0068] If the determination result in #33 indicates that the timing at which the determination unit 32 determined there was a "risk of freezing" is a longer determination period (e.g., two days or more) than the timing prior to the start of the planned shutdown period (e.g., within N days of the power generation shutdown date) (#33 Yes), the control unit 33 selects a relatively high second temperature in the heat storage mode as the target temperature (e.g., 80°C), and controls the exhaust heat recovery pump 7 or the radiator 8 (#38 high heat storage mode). Next, when the planned shutdown period of the solid oxide fuel cell 1 stored in the memory unit 31 arrives, the control unit 33 stops operation of the solid oxide fuel cell 1 and activates the exhaust heat recovery pump 7 to circulate the hot water stored in the hot water storage tank 2 through the circulation flow path 6 in the high heat storage mode (#39). In other words, when the determined timing is a timing that precedes the start of the planned shutdown period by a period shorter than the determined period, particularly if the timing is a period that precedes the start of the planned shutdown period by a period equal to or shorter than a predetermined period, if the planned shutdown period is advanced, the solid oxide fuel cell 1 will not be able to restart by the predetermined period when there is a risk of freezing (the planned shutdown period before being advanced), and there is a risk of freezing. Therefore, the planned shutdown period stored in the memory unit 31 is not advanced. On the other hand, since the relatively high second temperature is selected as the target temperature in the heat storage mode, heat can be stored in the hot water storage tank 2 relatively early. Then, the heat stored in the hot water storage tank 2 in this high heat storage mode can be provided to the circulation flow path 6 during the planned shutdown period that was not advanced, thereby preventing freezing.

[0069] [Other embodiments] <1> In the above-described embodiment, the fuel cell system X includes a solid oxide fuel cell 1, but the fuel cell system X may also include a polymer electrolyte fuel cell (PEFC), a phosphoric acid fuel cell (PAFC), or a molten carbonate fuel cell (MCFC).

[0070] <2> When storing the exhaust heat of the solid oxide fuel cell 1 in the hot water storage tank 2 in the heat storage mode described above, it is preferable to set the three-way valve V2 to the shutoff position and open the shutoff valve V3 to restrict the use of the heat in the hot water storage tank 2 for other purposes. Furthermore, when preventing freezing of the circulation flow path 6 by stopping the operation of the solid oxide fuel cell 1 and circulating the hot water in the hot water storage tank 2 through the circulation flow path 6 during a scheduled shutdown period after the heat storage mode has been executed, the hot water may be circulated intermittently or continuously.

[0071] <3> In the above-described embodiment, the determination unit 32 determines the risk of freezing during the planned shutdown period based on the outside air temperature (forecasted outside air temperature) included in the weather data. Alternatively, the determination unit 32 may determine the risk of freezing based on the temperature of tap water, which is the water temperature of the water supply passage 17, and is not particularly limited thereto.

[0072] <4> In the above-described embodiment, the planned shutdown period of the fuel cell system X is changed to avoid a leak determination by the fuel gauge Y, but the reason for changing the planned shutdown period of the fuel cell system X is not particularly limited. For example, if there has been no actual usage of gas or electricity for a long period of time, the planned shutdown period of the fuel cell system X may be scheduled taking into consideration the benefit of utility costs. In other words, the planned shutdown period may be in any form as long as it is planned to stop the operation of the fuel cell system X for a predetermined period of time.

[0073] <5> In the above embodiment, specific numerical values ​​are used to explain examples of control performed by the fuel cell system X, but these numerical values ​​are given for illustrative purposes and can be changed as appropriate. For example, the predetermined period and planned period for stopping the fuel cell system X may be 12 hours.

[0074] The configurations disclosed in the above-described embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, unless a contradiction arises. Furthermore, the embodiments disclosed in this specification are merely examples, and the present invention is not limited to these, and can be modified as appropriate within the scope of the purpose of the present invention. [Industrial Applicability]

[0075] The present invention can be used in a fuel cell system that includes a heat exchanger that exchanges heat between the exhaust heat of a fuel cell and hot water in a hot water storage tank, and a circulation flow path that circulates the hot water between the hot water storage tank and the heat exchanger. [Explanation of symbols]

[0076] 1: Solid oxide fuel cell (fuel cell) 2: Hot water tank 3: Power load section 4:Heat load section 6: Circulation channel 31: Storage section 32: Judgment section C: Operation control device E: Heat exchanger L1: Raw fuel flow path (fuel supply path) L6: Raw fuel flow path (fuel supply path) X: Fuel cell system Y: Fuel gauge (leak detection device)

Claims

1. A fuel cell system comprising: a fuel cell capable of supplying electric power generated by operation to a power load; an operation control device for controlling the operation of the fuel cell; a leak detection device for detecting leaks in a fuel supply line that supplies fuel to the fuel cell; a hot water storage tank for storing hot water that can be supplied to a heat load; a heat exchanger for exchanging heat between exhaust heat from the fuel cell and the hot water in the hot water storage tank; and a circulation flow path for circulating the hot water between the hot water storage tank and the heat exchanger, the leakage detection device is configured to determine that a leakage has occurred when a cumulative time during which the flow rate of fuel in the fuel supply path is equal to or less than a predetermined flow rate is less than a predetermined time during a predetermined leakage determination period, The operation control device has a memory unit that stores a planned shutdown period during which operation of the fuel cell is stopped for a predetermined period to reset the accumulated time, and a judgment unit that judges the risk of freezing of the circulation flow path during the planned shutdown period, and when the timing at which it is judged that there is a risk of freezing during the planned shutdown period is a timing that goes back a judgment period that is greater than the predetermined period from the start of the planned shutdown period, and when the risk of freezing during the planned shutdown period exceeds a threshold, the planned shutdown period stored in the memory unit is brought forward.

2. The fuel cell system according to claim 1 , wherein the determining unit determines the risk of freezing based on an outside air temperature included in meteorological data.

3. 3. The fuel cell system of claim 2, wherein when the total time during the planned shutdown period during which the outside air temperature is below a predetermined temperature is equal to or greater than a set value, the operation control device determines that the risk of freezing exceeds a threshold and brings forward the planned shutdown period stored in the memory unit.

4. the storage unit stores a plurality of target temperatures including a first temperature and a second temperature higher than the first temperature; 4. The fuel cell system according to claim 3, wherein the operation control device is configured to be capable of executing a heat storage mode in which the hot water stored in the hot water storage tank is raised to one selected target temperature.

5. 5. The fuel cell system according to claim 4, wherein when it is determined that there is a risk of freezing and the total time during which the outside air temperature is at or below the predetermined temperature during the planned shutdown period is less than the set value, the operation control device selects the first temperature as the target temperature and executes the heat storage mode without bringing forward the planned shutdown period stored in the memory unit.

6. 5. The fuel cell system according to claim 4, wherein when the timing at which it is determined that there is a risk of freezing during the planned shutdown period is a timing that goes back a period equal to or shorter than the predetermined period from the start of the planned shutdown period, the operation control device selects the second temperature as the target temperature and executes the heat storage mode without bringing forward the planned shutdown period stored in the memory unit.

Images