Fuel cell system

Abstract

This invention provides a fuel cell system that prevents the activation of alarms by microcomputer meters and does not generate a history of temperature rises and falls. [Solution] The fuel cell system S comprises a hot module 1 having a reforming unit 13 that reforms raw fuel to generate reformed gas, an electrochemical reaction unit 14 capable of performing a power generation reaction by reacting the reformed gas with an oxidizing gas and an electrolytic reaction of water vapor using external power, and a combustion unit 15 that burns the exhaust gas discharged from the electrochemical reaction unit 14; a raw fuel supply unit 2 that supplies raw fuel to the reforming unit 13 via a microcomputer meter; an oxidizing gas supply unit 3 that supplies oxidizing gas to the electrochemical reaction unit 14; a water supply unit 4 that supplies water to the reforming unit 13; and a control unit 5 that switches between a first state in which the electrochemical reaction unit 14 performs a power generation reaction and a second state in which the electrochemical reaction unit 14 performs an electrolytic reaction. The control unit 5 switches from the first state to the second state after a predetermined period has elapsed during the leak detection period.

Description

[Technical Field]

[0001] This invention relates to a fuel cell system. [Background technology]

[0002] Conventionally, fuel cell systems equipped with an electrochemical reaction section consisting of a solid oxide fuel cell (SOFC) are known. In such fuel cell systems, an oxidizing gas is supplied to the cathode of the electrochemical reaction section, and a reformed gas obtained by reforming the raw fuel is supplied to the anode, causing a chemical reaction between the cathode and anode to generate electricity.

[0003] The raw fuel (e.g., city gas 13A) is supplied via a microcomputer meter. The microcomputer meter detects a leak and issues an alarm or shuts off the supply of raw fuel if the raw fuel continues to flow beyond a leak detection period (e.g., 30 days). When a leak is detected, an inspection by the gas supplier is often required to clear the alarm, and clearing the alarm requires that the flow rate of raw fuel be suspended for a predetermined period of time. This clearing process is burdensome for the user and also requires measures to temporarily stop the power generation reaction, which uses gas continuously. Therefore, fuel cell systems that stop the power generation reaction at predetermined intervals have been disclosed to avoid alarm activation and raw fuel supply shutoff by the microcomputer meter (see, for example, Patent Documents 1-2).

[0004] Patent Document 1 discloses a fuel cell system equipped with a control device that avoids the microcomputer meter's leak detection by stopping the power generation reaction in the electrochemical reaction section for a second predetermined time while a first predetermined time has elapsed before the microcomputer meter makes a leak detection.

[0005] Patent Document 2 discloses a fuel cell system that stops the power generation reaction in the electrochemical reaction section at a time that is three predetermined times prior to the start of a second predetermined time set during the non-use period, which is the time required before the supply of raw materials to the fuel cell is stopped.

[0006] On the other hand, since the electrochemical reaction unit generates electricity at a high temperature of 600-800°C, when the electricity generation reaction stops and restarts, the temperature of the electrochemical reaction unit fluctuates between room temperature and 600-800°C due to rising and falling temperatures. When a rapid temperature change occurs in the electrochemical reaction unit at this time, thermal stress may be generated, potentially causing mechanical damage such as cracking and fatigue. Therefore, various measures are being taken to avoid such mechanical damage (see, for example, Patent Documents 3-4).

[0007] Patent Document 3 discloses a fuel cell system that, when the power generation reaction is stopped, supplies water vapor to the anode and an oxidizing gas (air in Patent Document 3) to the cathode, and controls the amount of water vapor and air supplied so that the temperature difference between the anode and the cathode remains within a certain range.

[0008] Patent Document 4 discloses a fuel cell system that monitors the rate of temperature decrease in the electrochemical reaction section when the power generation reaction is stopped, and controls a temperature decrease rate adjustment means so that the rate reaches a predetermined set rate of decrease. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2005-353292 [Patent Document 2] Japanese Patent Publication No. 2011-175816 [Patent Document 3] Japanese Patent Publication No. 2011-076846 [Patent Document 4] Japanese Patent Publication No. 2023-141569 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] From a safety standpoint, it is difficult to disable the alarm function of the microcomputer meter. Therefore, in order to avoid alarm activation, it is necessary to temporarily stop the power generation reaction of the fuel cell system at each leakage detection period. In this case, even if the heating and cooling rate of the electrochemical reaction section is controlled when the power generation reaction is stopped and restarted, as in the fuel cell systems described in Patent Documents 3 and 4, to suppress mechanical damage to the electrochemical reaction section, it was not possible to avoid the occurrence of heating and cooling history itself. Therefore, there was a risk of cumulative damage to the electrochemical reaction section due to repeated heating and cooling. In addition, the time required for heating and cooling prevented the power generation reaction from taking place, making it impossible to operate the fuel cell system efficiently.

[0011] This invention has been made in view of the above-mentioned problems, and its purpose is to provide a fuel cell system that does not generate a temperature rise / fall history while preventing alarms from being triggered by a microcomputer meter. [Means for solving the problem]

[0012] The characteristic configuration of the fuel cell system according to the present invention is a hot module having a reforming unit that reforms raw fuel to produce reformed gas, an electrochemical reaction unit capable of performing a power generation reaction by reacting the reformed gas with an oxidizing gas and an electrolytic reaction of water vapor using external power, and a combustion unit that burns the exhaust gas discharged from the electrochemical reaction unit. A raw fuel supply unit that supplies the raw fuel via a microcomputer meter to the reforming unit, An oxidizing gas supply unit that supplies the oxidizing gas to the electrochemical reaction unit, A water supply unit that supplies water to the modification unit, The system includes a control unit that switches between a first state in which the electrochemical reaction unit performs the power generation reaction and a second state in which the electrochemical reaction unit performs the electrolytic reaction, The microcomputer meter is configured to issue an alarm or shut off the supply of the raw materials if the flow rate of the raw materials is below the first set determination amount for a set determination period or longer, or if the state satisfying the non-leakage condition, which is that the cumulative flow rate of the raw materials during the set determination period is below the second set determination amount, does not occur a set number of times during the leakage determination period. The control unit switches from the first state to the second state after a predetermined period has elapsed during the leakage determination period.

[0013] According to this configuration, the control unit switches from a first state in which the electrochemical reaction unit performs a power generation reaction to a second state in which the electrochemical reaction unit performs an electrolytic reaction after a predetermined period has elapsed during the leak detection period, and stops the supply of raw fuel to the hot module. This avoids the activation of alarms by the microcomputer meter and the interruption of the raw fuel supply. Furthermore, by burning the exhaust gas generated by the electrolytic reaction in the combustion unit, the temperature of the electrochemical reaction unit can be maintained even when the supply of raw fuel to the hot module is stopped. This suppresses the occurrence of temperature rise and fall history in the electrochemical reaction unit caused by the cessation of the power generation reaction, thereby reducing mechanical damage to the electrochemical reaction unit associated with temperature rise and fall. In addition, compared to the case where the power generation reaction is stopped and temperature rise and fall occurs each time the supply of raw fuel is stopped, the time that was previously required for temperature rise and fall can be used for the power generation reaction, improving the power generation efficiency of the fuel cell system.

[0014] Another characteristic feature is that the control unit switches from the second state to the first state when the setting determination period has elapsed in the second state.

[0015] According to this configuration, when the setting determination period elapses, the control unit switches the fuel cell system from the second state to the first state, and thus the supply of the original fuel to the hot module is resumed. Thereby, it is possible to avoid the issuance of an alarm by the microcomputer meter and the interruption of the supply of the original fuel, and since the temperature of the electrochemical reaction unit is maintained, the power generation reaction of the electrochemical reaction unit can be started immediately after the setting determination period elapses. Therefore, compared with the case where the power generation reaction is stopped for each leakage determination period to raise and lower the temperature, it becomes possible to allocate the time required for raising and lowering the temperature to the power generation reaction, and the power generation efficiency of the fuel cell system can be improved.

[0016] As another characteristic configuration, in the first state, the exhaust gas is the off-gas discharged from the electrochemical reaction unit, In the second state, the exhaust gas includes the hydrogen-rich gas discharged from the electrochemical reaction unit.

[0017] According to this configuration, the combustion unit burns the off-gas discharged from the electrochemical reaction unit in the first state and burns the exhaust gas including the hydrogen-rich gas discharged from the electrochemical reaction unit in the second state. Therefore, the combustion heat by the combustion unit can be utilized in any state, and it becomes possible to maintain the temperature of the electrochemical reaction unit even in a state where the supply of the original fuel is stopped. Further, even in a state where the power generation reaction is stopped, the combustion heat by the combustion unit can be utilized, so that the fuel cell system can be used efficiently.

[0018] As another characteristic configuration, the water supplied by the water supply unit to the reforming unit is reforming water.

[0019] According to this configuration, since the water supply unit supplies reforming water to the reforming unit, reformed gas can be generated in the first state, and the electrolysis reaction of water vapor can be performed in the second state.

Brief Description of the Drawings

[0020] [Figure 1]This is a schematic diagram showing a fuel cell system in the first state. [Figure 2] This is a flowchart illustrating the transition between the first and second states. [Figure 3] This is a schematic diagram showing a fuel cell system in the second state. [Figure 4] This figure shows an example of the internal temperature of a hot module when a fuel cell system is shut down. [Figure 5] This figure shows an example of the internal temperature of a hot module during the switching between the first and second states. [Modes for carrying out the invention]

[0021] Embodiments of the fuel cell system according to the present invention will be described below with reference to the drawings. However, the invention is not limited to the embodiments described below, and various modifications are possible without departing from the spirit of the invention.

[0022] Figure 1 is a schematic diagram showing a fuel cell system S. The fuel cell system S comprises a hot module 1, a raw fuel supply unit 2, an oxidizer gas supply unit 3, a reforming water supply unit 4 (an example of a water supply unit), a control unit 5, and a hot water supply unit 6.

[0023] The raw fuel supply unit 2 supplies raw fuel, including hydrocarbons, to the hot module 1. The raw fuel is, for example, city gas or LP gas, and is supplied to the hot module 1 via the microcomputer meter 20. The raw fuel supply unit 2 also supplies raw fuel to gas appliances 71, such as gas stoves and gas-burning fan heaters, and to heat source devices 72, via the microcomputer meter 20.

[0024] The microcomputer meter 20 will issue an alarm and shut off the supply of raw materials if the flow rate of raw materials is below the first set judgment amount for a set time (an example of a setting judgment period, e.g., 2 hours) or longer, or if the cumulative flow rate of raw materials during the set time is below the second set judgment amount, and this condition does not occur a set number of times during the leak detection period (e.g., 30 days), for example, if the raw materials continue to flow above the first set judgment amount during the leak detection period. In other words, when the non-leak condition is met, no alarm will be issued and the supply of raw materials will not be shut off. Also, when the non-leak condition is met, the microcomputer meter 20 will reset the count for the leak detection period at that time and start counting for a new leak detection period from the beginning.

[0025] The raw fuel supply unit 2 includes a raw fuel supply channel L2, a solenoid valve 21, a fuel flow meter 22, a gas blower 23, and a desulfurizer 24. The raw fuel supply channel L2 branches into raw fuel supply channels L2a, L2b, and L2c downstream of the microcomputer meter 20 in the direction of raw fuel flow (hereinafter, the upstream and downstream sides in the direction of raw fuel flow will be simply referred to as the upstream side and the downstream side). Raw fuel supply channel L2a supplies raw fuel to the gas appliance 71. Raw fuel supply channel L2c supplies raw fuel to the heat source device 72.

[0026] The raw fuel supply channel L2b supplies raw fuel to the hot module 1. The raw fuel supply channel L2b is equipped with a solenoid valve 21, a fuel flow meter 22, a gas blower 23, and a desulfurizer 24 in that order from upstream to downstream. The solenoid valve 21 can adjust the flow rate of raw fuel through the raw fuel supply channel L2b. The fuel flow meter 22 measures the flow rate of raw fuel through the raw fuel supply channel L2. The gas blower 23 supplies raw fuel to the hot module 1 via the raw fuel supply channel L2 and the desulfurizer 24. In other words, the amount of raw fuel supplied to the hot module 1 per unit time can be adjusted by controlling the operation of the solenoid valve 21 and the gas blower 23. The desulfurizer 24 is located upstream of the hot module 1 in the raw fuel flow direction and removes sulfur from the raw fuel. As a result, sulfur-free raw fuel is supplied to the hot module 1. Furthermore, the raw fuel supply unit 2 may also function as a desulfurizer 24, or, in addition to the desulfurizer 24, may have an adsorption unit capable of adsorbing and desorbing raw fuel according to temperature.

[0027] The oxidant gas supply unit 3 supplies an oxidant gas containing oxygen to the hot module 1. The oxidant gas is, for example, air. The oxidant gas supply unit 3 includes an oxidant gas supply passage L3, an oxidant gas blower 31, and an oxidant gas flow meter 32. The oxidant gas blower 31 supplies the oxidant gas to the hot module 1 via the oxidant gas supply passage L3. The oxidant gas flow meter 32 measures the flow rate of the oxidant gas flowing through the oxidant gas supply passage L3. The amount of oxidant gas supplied to the hot module 1 per unit time is adjusted by controlling the operation of the oxidant gas blower 31.

[0028] The water reforming supply unit 4 supplies water reforming to the hot module 1. The water reforming is, for example, tap water from which impurities have been removed. The water reforming supply unit 4 includes a water reforming supply channel L4, a water tank 41, and a pump 42. In this embodiment, the water reforming supply channel L4 connects the water tank 41 to the raw fuel supply channel L2b, but it may also connect the water tank 41 to the vaporization unit 12. The water tank 41 stores the water reforming. The pump 42 pumps the water reforming stored in the water tank 41. As a result, the water reforming is supplied to the hot module 1 via the water reforming supply channel L4. The amount of water reforming per unit time supplied to the hot module 1 is adjusted by controlling the operation of the pump 42.

[0029] Next, we will describe the hot module 1. The hot module 1 is a fuel cell module that performs a power generation reaction by reacting a reformed gas with an oxidizing gas, and is also an electrolytic module that performs an electrolytic reaction by electrolyzing water vapor, carbon dioxide, etc. The hot module 1 has a container 11, a vaporization section 12, a reforming section 13, an electrochemical reaction section 14, a combustion section 15, a reformed gas flow path L11, an off-gas flow path L12, and a combustion exhaust gas flow path L13.

[0030] The container 11 has thermal insulation properties and houses the vaporization section 12, the reforming section 13, the electrochemical reaction section 14, the combustion section 15, the reformed gas flow path L11, the off-gas flow path L12, and the combustion exhaust gas passage L13.

[0031] The hot module 1 is connected to a raw fuel supply line L2b and an oxidizer gas supply line L3, through which raw fuel, reforming water, and oxidizer gas are supplied. In this embodiment, the raw fuel and reforming water are supplied to the vaporization section 12, and the oxidizer gas is supplied to the electrochemical reaction section 14.

[0032] The vaporization unit 12 is supplied with reforming water and raw fuel, as well as the heat of combustion generated in the combustion unit 15. The vaporization unit 12 vaporizes the reforming water by utilizing the heat of combustion to generate steam. In this embodiment, the vaporization unit 12 supplies a mixed gas, which is a mixture of the steam obtained by vaporizing the reforming water and the raw fuel, to the reforming unit 13. If raw fuel is not supplied to the vaporization unit 12, the vaporization unit 12 supplies only steam to the reforming unit 13.

[0033] The reforming unit 13 is supplied with a mixed gas from the vaporization unit 12. In addition to the mixed gas, the reforming unit 13 is also supplied with the heat of combustion generated in the combustion unit 15. The reforming unit 13 uses the heat of combustion to produce reformed gas by steam reforming the mixed gas (raw fuel). The reformed gas produced in the reforming unit 13 is supplied to the electrochemical reaction unit 14 via the reformed gas flow path L11. If the reforming unit 13 does not produce reformed gas, the raw fuel flows through the reformed gas flow path L11. Also, if no raw fuel is supplied to the vaporization unit 12, water vapor flows through the reformed gas flow path L11.

[0034] The electrochemical reaction unit 14 is composed of multiple electrochemical cells stacked on top of each other. Each electrochemical cell has an anode to which the reformed gas produced in the reforming unit 13 is supplied, a cathode to which the oxidizing gas is supplied, and an electrolyte layer provided between them. The electrolyte layer is, for example, a solid oxide, in which case the electrochemical reaction unit 14 has a solid oxide type electrochemical cell.

[0035] The electrochemical cell relating to the electrochemical reaction unit 14 can function as an electrochemical power generation cell that converts chemical energy into electrical energy, and can also function as an electrolytic cell that converts electrical energy into chemical energy. When the electrochemical cell relating to the electrochemical reaction unit 14 is operated as an electrochemical power generation cell, oxygen molecules O2 contained in the oxidizing gas in the cathode are converted into electrons e - It reacts with oxygen ions O 2- This is generated, and the generated oxygen ions O 2- The hydrogen molecules H2 contained in the reformed gas move through the electrolyte layer to the anode. At the anode, the hydrogen molecules H2 in the reformed gas are replaced by oxygen ions O 2-react with it to produce water H2O and electrons e - are generated. As a result, an electromotive force is generated between the anode and the cathode, and power generation is performed. The power generated by the electrochemical reaction unit 14 is taken out by the power converter 81. The reformed gas (anode off-gas) and the oxidant gas (cathode off-gas) that have not been used for power generation are supplied to the combustion unit 15 as off-gas (an example of exhaust gas) through the off-gas flow path L12.

[0036] When the electrochemical cell related to the electrochemical reaction unit 14 is made to act as an electrolytic cell, the supply of the raw fuel from the raw fuel supply unit 2 is not performed, a gas containing water vapor is circulated to the cathode, and a voltage is applied from the power converter 81 between the anode and the cathode (see FIG. 3). Then, at the cathode, electrons e - react with water molecules H2O to produce hydrogen molecules H2 and oxygen ions O 2- are generated. The generated oxygen ions O 2- move through the electrolyte layer to the anode, and the oxygen ions O 2- release electrons to become oxygen molecules O2. By the above reactions, water molecules H2O are electrolyzed into hydrogen H2 and oxygen O2 by external power. The hydrogen H2 and oxygen O2 generated by electrolysis are supplied to the combustion unit 15 through the off-gas flow path L12. Therefore, the exhaust gas discharged from the electrochemical reaction unit 14 contains a hydrogen-rich gas. Note that a gas containing carbon dioxide may be circulated to the cathode, and the fuel cell system S may have a fuel converter that synthesizes various compounds such as hydrocarbons from hydrogen H2 and carbon monoxide CO generated by electrolysis of carbon dioxide.

[0037] The combustion section 15 is positioned between the vaporization section 12 and the reforming section 13 and the electrochemical reaction section 14, and is connected to an off-gas flow path L12. The combustion section 15 generates combustion heat by burning off-gas or hydrogen-rich gas. The combustion heat generated in the combustion section 15 raises the temperature of the internal space of the container 11. The combustion section 15 also discharges combustion exhaust gas as the off-gas burns. The combustion exhaust gas flows through the combustion exhaust gas passage L13 and then through the combustion exhaust gas passage L5, which is connected to the combustion exhaust gas passage L13 outside the container 11. A heat exchanger 60, which will be described later, is provided in the middle of the combustion exhaust gas passage L5. After heat is removed from the combustion exhaust gas in the heat exchanger 60, it is discharged as exhaust gas.

[0038] Next, the hot and cold water supply unit 6 will be described. The hot and cold water supply unit 6 includes a hot water storage tank 61 for storing hot and cold water, a hot and cold water circulation path L61 for circulating the hot and cold water, a water supply path L62 for supplying tap water to the hot water storage tank 61, and a hot water outlet path L63 for discharging the hot and cold water stored in the hot water storage tank 61.

[0039] The hot water storage tank 61 stores hot water in a state that forms a temperature stratification, with relatively low-temperature hot water stored at the bottom and relatively high-temperature hot water stored at the top. The hot water circulation path L61 has a forward path L61a connecting the lower part of the hot water storage tank 61 to the heat exchanger 60, and a return path L61b connecting the heat exchanger 60 to the upper part of the hot water storage tank 61. The heat exchanger 60 performs heat exchange between the combustion exhaust gas discharged from the combustion section 15 and the hot water.

[0040] A circulation pump 62 is provided along the outbound path L61a to circulate hot water in the hot water circulation path L61. This circulates hot water between the hot water storage tank 61 and the heat exchanger 60. Additionally, a temperature measuring unit 63 is provided along the return path L61b to measure the temperature of the hot water.

[0041] Hot water flowing from the bottom of the hot water storage tank 61 through the forward path L61a of the hot water circulation path L61 into the heat exchanger 60 is heated in the heat exchanger 60 by absorbing heat from the combustion exhaust gas. Then, the hot water flowing out of the heat exchanger 60 flows through the return path L61b of the hot water circulation path L61 into the top of the hot water storage tank 61. The temperature of the hot water flowing into the hot water storage tank 61 (the temperature of the hot water measured by the temperature measuring unit 63) is controlled by controlling the operation of the circulation pump 62 so that it reaches a predetermined target hot water storage temperature (for example, 65°C). In this way, hot water is stored, i.e., heat is accumulated, in a state where a temperature stratification is formed in the hot water storage tank 61.

[0042] The water supply channel L62 is connected to the lower part of the hot water storage tank 61 and supplies tap water to the hot water storage tank 61. The hot water outlet channel L63 is connected to the upper part of the hot water storage tank 61 and discharges the hot water stored in the hot water storage tank 61. A temperature measuring unit 64 for measuring the temperature of the hot water is provided in the middle of the hot water outlet channel L63. The water supply channel L64 branches off from the water supply channel L62 and connects to the hot water outlet channel L63 upstream of the temperature measuring unit 64 in the hot water outlet channel L63. Therefore, tap water can be mixed with the hot water discharged from the hot water storage tank 61 by the water supply channel L64. In addition, a control valve 65 is provided in the middle of the water supply channel L64 that can adjust the amount of tap water mixed with the hot water flowing through the hot water outlet channel L63. The temperature of the mixed hot water, measured by the temperature measuring unit 64, is adjusted to a predetermined temperature (for example, 30°C) by controlling the operation of the control valve 65.

[0043] In this embodiment, a heat source device 72 for heating the hot water is provided downstream of the temperature measuring unit 64 in the hot water outlet L63. The heat source device 72 burns raw fuel supplied via the microcomputer meter 20 and heats the hot water with the heat of combustion. The heat source device 72 heats the hot water to the temperature required by the user and supplies it to the user.

[0044] The combustion exhaust gas used to heat the hot water in the heat exchanger 60 also contains water vapor. Therefore, when the combustion exhaust gas is cooled in the heat exchanger 60, the contained water vapor condenses. To recover this condensed water, the fuel cell system S is equipped with a water recovery channel L91 and a water purifier 90. The condensed water flows into the water recovery channel L91, passes through the water purifier 90, and is supplied to the water tank 41. The water purifier 90 is a device for removing impurities contained in the recovered condensed water. For example, the water purifier 90 is filled with ion exchange resin, and removes electrolyte ions (for example, ionized and dissolved salts and ammonia, etc.) contained in the recovered condensed water using, for example, H + , OH - By replacing it with this, it performs the function of relatively lowering the concentration of electrolytes contained in the recovered condensed water (i.e., lowering the electrical conductivity).

[0045] Next, the control unit 5 will be described. The control unit 5 is composed of a microcontroller including a processor and semiconductor memory. The control unit 5 controls the operation of the hot module 1, the raw fuel supply unit 2, the oxidizer gas supply unit 3, the reforming water supply unit 4, and the hot water supply unit 6. Specifically, the control unit 5 controls the operation of the solenoid valve 21, gas blower 23, oxidizer gas blower 31, pump 42, circulation pump 62, control valve 65, etc., to adjust the flow rate of raw fuel and reforming water supplied to the hot module 1.

[0046] Furthermore, the control unit 5 is configured to switch the operating state of the fuel cell system S. In this embodiment, the control unit 5 switches between a first state in which the electrochemical reaction unit 14 performs a power generation reaction and a second state in which the electrochemical reaction unit 14 performs an electrolytic reaction. Specifically, the control unit 5 switches between the first state and the second state according to the flow shown in Figure 2. The switching between the first state and the second state will be described in detail.

[0047] First, the first state of the fuel cell system S will be explained using Figure 1. In the first state, the electrochemical reaction unit 14 acts as a fuel cell that performs a power generation reaction, converting chemical energy such as fuel into electrical energy. In the first state, the solenoid valve 21 is open, and the raw fuel supplied from the raw fuel supply unit 2 is reformed in the vaporization unit 12 and the reforming unit 13, becoming a reformed gas containing hydrogen, which is supplied to the anode of the electrochemical reaction unit 14. In addition, the oxidizer gas supplied from the oxidizer gas supply unit 3 is supplied to the cathode of the electrochemical reaction unit 14. At this time, the hot module 1 is maintained at an operating temperature of, for example, 600°C to 800°C. An electromotive force is generated by the reaction between the reformed gas and the oxidizer gas, and the electricity generated by the electrochemical reaction unit 14 is extracted by the power converter 81. In addition, the heat of the combustion exhaust gas discharged from the combustion unit 15 is recovered by hot water in the heat exchanger 60.

[0048] Next, the second state of the fuel cell system S will be explained using Figure 3. In the second state, the electrochemical reaction unit 14 acts as an electrolytic cell that performs an electrolytic reaction, converting electrical energy into chemical energy. In the second state, the solenoid valve 21 is closed, and no raw fuel is supplied to the vaporization unit 12. On the other hand, reforming water is supplied to the vaporization unit 12 from the reforming water supply unit 4, and the reforming water is vaporized in the vaporization unit 12 to become a gas containing water vapor. The water vapor flows through the reforming gas flow path L11 and is supplied to the cathode of the raw fuel, and a voltage is applied between the anode and the cathode from the power converter 81. As a result, an electrolytic reaction of water molecules occurs and external power is consumed. At this time, the exhaust gas containing hydrogen and oxygen produced by the electrolytic reaction is burned in the combustion unit 15, so that the hot module 1 is maintained at an operating temperature of, for example, 600°C to 800°C, similar to the first state. Furthermore, the heat from the combustion exhaust gas discharged from the combustion section 15 is recovered by hot water in the heat exchanger 60.

[0049] Next, we will explain the switching between the first and second states. As shown in Figure 2, the fuel cell system S in this embodiment enters the first state after startup (#1 in Figure 2).

[0050] The first state is when raw fuel is supplied to the hot module 1 and the electrochemical reaction unit 14 performs a power generation reaction, that is, when raw fuel is constantly supplied via the microcomputer meter 20. Therefore, if the flow rate of raw fuel continues to exceed the first set judgment amount during the leak detection period, or if the cumulative flow rate of raw fuel exceeds the second set judgment amount, the microcomputer meter 20 will determine that the non-leak condition is not met and will make a leak detection, triggering an alarm and shutting off the supply of raw fuel, temporarily stopping the power generation reaction of the electrochemical reaction unit 14. When the power generation reaction of the electrochemical reaction unit 14 stops, the internal temperature of the hot module 1, which operates at 600°C to 800°C, drops to room temperature. At this time, if a temperature difference occurs inside and outside the hot module 1 due to the rapid drop in temperature, there is a risk of mechanical damage to the electrochemical reaction unit 14 due to thermal stress. For this reason, in conventional fuel cell systems, control was implemented to ensure that the rate of heating and cooling during the stopping and restarting of the power generation reaction was at a predetermined value. Specifically, in order to ensure that the non-leakage condition is met during the leakage detection period of the microcomputer meter 20 (e.g., 30 days), as shown in Figure 4, power generation by the electrochemical reaction unit 14 was stopped at predetermined intervals (e.g., 27 days) that were shorter than the leakage detection period, and a waiting period (e.g., 4 hours) was set to allow the hot module 1 to cool to room temperature at a predetermined rate. After the waiting period had elapsed, the solenoid valve 21 was closed so that the flow rate of the raw fuel was below the first set determination amount for a set time (e.g., 2 hours), or so that the cumulative flow rate of the raw fuel was below the second set determination amount at the set time, thereby avoiding leakage detection. After the set time had elapsed, another waiting period (e.g., 4 hours) was set to raise the temperature of the hot module 1 to the operating temperature (approximately 700°C in Figure 4) at a predetermined heating rate, and the power generation reaction of the electrochemical reaction unit 14 was restarted. Furthermore, the microcomputer meter 20 resets the leak detection period count after the set time has elapsed, and restarts the leak detection period count from the beginning. Also, during the standby time, a small amount of raw fuel is supplied to the hot module 1 to prevent oxidation of the anode and to control the cooling rate.

[0051] Thus, in conventional fuel cell systems, in addition to the set time required to maintain the flow rate of raw fuel below the first set judgment amount, or to maintain the cumulative flow rate of raw fuel below the second set judgment amount, a waiting time is required to set the heating and cooling rate to a predetermined value, which reduces the power generation time of the electrochemical reaction unit 14. Furthermore, because the electrochemical reaction unit 14 needs to be stopped once within the leak detection period, a heating and cooling history is created in the electrochemical reaction unit 14, which may cause cumulative damage to the electrochemical reaction unit 14. Therefore, in this embodiment, even if the supply of raw fuel is stopped once within the leak detection period of the microcomputer meter 20, control is performed to prevent a heating and cooling history from being created in the electrochemical reaction unit 14. Specifically, as shown in Figure 2, in a fuel cell system S in the first state, if no leak detection is performed during the leak detection period (e.g., 30 days) (Figure 2, #2 No), and a predetermined period shorter than the leak detection period (e.g., 27 days) has elapsed (Figure 2, #3 Yes), the control unit 5 closes the solenoid valve 21 and applies voltage to the electrochemical reaction unit 14 to control the fuel cell system S to the second state (Figure 2, #4). If the predetermined period has not elapsed (Figure 2, #3 No), the control unit 5 maintains the first state (Figure 2, #1). Also, if a leak is detected in the first state (Figure 2, #2 Yes), the fuel cell system S is shut down immediately. A case in which a leak is detected in the first state is, for example, when, in the second state, raw fuel is not supplied to the hot module 1, but raw fuel is continuously supplied to other gas-consuming devices such as the gas appliance 71 and the heat source device 72 for a set time. The predetermined period may be stored in the memory unit of the fuel cell system S, and the control unit 5 may perform control based on the information stored in the memory unit. Furthermore, the predetermined period may differ for each leak detection period, as long as it is within the leak detection period, and may be changed according to the usage status of the fuel cell system S or the usage status of other gas-consuming devices. That is, if the predetermined period in one leak detection period is 27 days, the predetermined period in the next leak detection period may be set to 20 days.

[0052] In the second state, the electrochemical reaction unit 14 performs an electrolytic reaction, and the exhaust gas generated by the electrolytic reaction is burned in the combustion unit 15, so that the internal temperature of the hot module 1 is maintained at approximately 700°C, the same as in the first state. Therefore, even if the supply of raw fuel is cut off and the power generation reaction of the electrochemical reaction unit 14 is stopped in order to avoid leakage detection by the microcomputer meter 20, the internal temperature of the hot module 1 can be maintained for the set time, as shown in Figure 5, so that the electrochemical reaction unit 14 does not experience a history of temperature rise and fall. This prevents cumulative damage to the electrochemical reaction unit 14. In addition, since there is no waiting time required to raise or cool the electrochemical reaction unit 14 at a constant temperature rise or fall rate, the power generation reaction of the electrochemical reaction unit 14 can be started by opening the solenoid valve 21 almost simultaneously with the elapsed time of the set time, thereby increasing the power generation time of the electrochemical reaction unit 14. After the elapsed time of the set time, the microcomputer meter 20 resets the count for the leakage detection period and starts the count for the leakage detection period from the beginning. As a result, the start dates for the period used for leak detection and the predetermined period will be the same.

[0053] When the set time has elapsed in the second state, the fuel cell system S switches to the first state, and the electrochemical reaction unit 14 performs the power generation reaction (Figure 2, #1). In this way, by switching the fuel cell system S in this embodiment to the second state at predetermined intervals, leakage detection by the microcomputer meter 20 can be avoided, the occurrence of temperature rise and fall history can be suppressed, and the power generation time can be increased. [Other Embodiments]

[0054] In the above embodiment, the control unit 5 switches between the first and second states to avoid leak detection by the microcomputer meter 20. However, it may also switch from the first state to the second state when the supply of raw materials is stopped due to piping work for raw materials, etc. Furthermore, the switching between the first and second states may be performed in conjunction with the opening and closing of the solenoid valve 21. [Industrial applicability]

[0055] This invention is applicable to fuel cell systems that include a hot module having an electrochemical reaction section capable of performing power generation and electrolytic reactions. [Explanation of Symbols]

[0056] 1: Hot Module 2: Raw fuel supply section 3: Oxidizer gas supply unit 4: Water supply unit for water treatment (water supply unit) 5: Control Unit 13: Modification section 14: Electrochemical reaction section 15: Combustion section 20: Microcomputer meter S: Fuel cell system

Claims

1. A hot module comprising: a reforming unit that reforms raw fuel to produce reformed gas; an electrochemical reaction unit capable of generating electricity by reacting the reformed gas with an oxidizing gas, and performing an electrolytic reaction of water vapor using external power; and a combustion unit that burns the exhaust gas discharged from the electrochemical reaction unit, A raw fuel supply unit that supplies the raw fuel via a microcomputer meter to the reforming unit, An oxidizing gas supply unit that supplies the oxidizing gas to the electrochemical reaction unit, A water supply unit that supplies water to the modification unit, The system includes a control unit that switches between a first state in which the electrochemical reaction unit performs the power generation reaction and a second state in which the electrochemical reaction unit performs the electrolytic reaction, The microcomputer meter is configured to issue an alarm or shut off the supply of the raw materials if the flow rate of the raw materials is below the first set determination amount for a set determination period or longer, or if the state satisfying the non-leakage condition, which is that the cumulative flow rate of the raw materials during the set determination period is below the second set determination amount, does not occur a set number of times during the leakage determination period. The control unit switches from the first state to the second state after a predetermined period has elapsed during the leakage detection period.

2. The fuel cell system according to claim 1, wherein the control unit switches from the second state to the first state when the setting determination period has elapsed in the second state.

3. In the first state, the exhaust gas is an off-gas discharged from the electrochemical reaction unit. The fuel cell system according to claim 1, wherein in the second state, the exhaust gas includes hydrogen-rich gas discharged from the electrochemical reaction unit.

4. The fuel cell system according to any one of claims 1 to 3, wherein the water supplied by the water supply unit to the reforming unit is reforming water.

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