JP2006024430A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system which can utilize effectively exhaust gas from a solid electrolyte fuel cell. <P>SOLUTION: The fuel cell system comprises: the solid electrolyte fuel cell 1 ; a heat exchanger 5 which carries out heat exchange between the exhaust gas from the solid electrolyte fuel cell 1 and water ; a hot water storing tank 6 which stores the water ; a circulation piping 7 which connects a bottom of the hot water storing tank 6 with the heat exchanger 5, and an upper portion of the hot water storing tank 6 with the heat exchanger 5, respectively, and circulates the water between the hot water storing tank 6 and the heat exchanger 5 ; a circulation pump 8 which is disposed in the circulation piping 7 and circulates the water compulsorily ; temperature detectors 11 and 12 which detect temperatures of the water at an inlet and outlet of the heat exchanger 5 respectively, and a control unit 13 which controls output of the circulation pump 8 in order that the temperature of the water at the outlet of the heat exchanger 5 becomes higher than the temperature of the water at the inlet of the heat exchanger 5 by a predetermined temperature or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid oxide fuel cell, a heat exchanger that exchanges heat between exhaust gas from the solid oxide fuel cell and water, a hot water storage tank that stores water, and a hot water storage tank and a heat exchanger. The present invention relates to a fuel cell system including a circulation pipe for circulating water and a circulation pump provided in the circulation pipe.

  A conventional polymer electrolyte fuel cell system will be described with reference to FIG. In this fuel cell system, a battery temperature detector 33 such as a thermistor for detecting the temperature of cooling water for recovering heat generated from the fuel cell 31 is installed on the outlet side of the cooling pipe 35 from the fuel cell 31. Reference numeral 36 indicates that when the temperature of the cooling water detected by the battery temperature detector 33 is less than the upper limit value of the operating temperature, the flow rate of water in the exhaust heat recovery pipe 37 is set to a predetermined flow rate according to the power generation amount of the fuel cell 31. The output of the circulation pump 39 is controlled so that the output of the circulation pump 39 is forcibly controlled regardless of the amount of power generated by the fuel cell 31 when the temperature exceeds the upper limit value of the operating temperature. This is a control device that controls to a value that does not reach a temperature at which deterioration of members such as the pump 41 and the battery temperature detector 33 arranged in the pipe 35 becomes severe.

  During the operation of such a fuel cell system, the fuel processing device 43 steam-reforms a raw material such as natural gas, generates a gas containing hydrogen as a main component, and supplies the gas to the fuel cell 31. Further, the oxidant gas is humidified by the oxidation side humidifier 47 by the air supply device 45 and supplied to the fuel cell 31. On the other hand, the heat generated by the power generation of the fuel cell 31 is recovered by the cooling water flowing in the cooling pipe 35. The cooling water is circulated by the pump 41, and the heat recovered in the cooling water moves to the water circulating in the exhaust heat recovery pipe 37 via the heat exchanger 49.

  When the temperature of the cooling water detected by the battery temperature detector 33 is less than the upper limit value of the operating temperature, the control device 36 sets the flow rate of water in the heat recovery pipe 37 according to the power generation amount of the fuel cell 31 to a predetermined flow rate. The output of the circulation pump 39 is controlled so that In addition, when the temperature of the cooling water becomes equal to or higher than the upper limit value of the operating temperature, the control device 36 forcibly outputs the output of the circulation pump 39 and detects the temperature of the pump 41 and the battery that are arranged in the fuel cell 31 or the cooling pipe 35. The value is controlled so as not to reach a temperature at which the deterioration of the member such as the vessel 33 becomes severe. For example, if the polymer electrolyte fuel cell is normally operated at 70 to 85 ° C., the output of the circulation pump 39 is forced when the operating temperature reaches 90 ° C., which is the upper limit value. Increase the cooling water temperature to a value that does not reach around 100 ° C. where the deterioration of the components such as the pump 41 and the battery temperature detector 33 arranged in the fuel cell 31 or the cooling pipe 35 becomes severe, and quickly normal operation Return to temperature.

  With such a configuration, it is possible to prevent an increase in pressure loss due to generation of bubbles in the exhaust heat recovery pipe 37, clogging of dust, and the like, and it is possible to prevent an increase in the temperature of the fuel cell 31 associated therewith. Further, since it is not necessary to perform an operation stop operation such as an emergency stop due to the temperature rise of the fuel cell 31, stable power generation can be maintained for a long time (see Patent Document 1).

Conventionally, in a polymer electrolyte fuel cell system, a gear pump that can reliably circulate a small amount of water at a high pressure is generally used as a circulation pump for circulating water in an exhaust heat recovery pipe.
JP 2003-282108 A

  However, although exhaust heat recovery systems have been developed for polymer electrolyte fuel cell systems, no solid heat recovery systems have been proposed for solid electrolyte fuel cell systems, and the electrolyte is a solid electrolyte type. Therefore, the exhaust heat recovery system of the polymer electrolyte fuel cell system cannot be directly applied to the solid electrolyte fuel cell system.

  That is, in the polymer electrolyte fuel cell system, since the polymer electrolyte is used, it is necessary to cool the fuel cell. For this reason, cooling water is used. If cooling with this cooling water is not performed, the fuel cell itself Since it breaks, it is necessary to control the temperature of the cooling water.

  On the other hand, in a solid oxide fuel cell system, fuel gas and oxygen-containing gas are used to generate power with a solid electrolyte. Excess fuel gas or oxygen-containing gas is burned to discharge combustion gas. It is intended to make effective use of energy.

  Therefore, in the polymer electrolyte fuel cell system, it is necessary to control the exhaust heat recovery system based on the temperature of the cooling water that cools the fuel cell, but in the solid oxide fuel cell system, it is necessary to cool the fuel cell. The control method is also different.

  In general, in a polymer electrolyte fuel cell system, a gear pump capable of reliably circulating a small amount of water at a high pressure is used, but this gear pump has a problem that it is expensive.

  It is an object of the present invention to provide a fuel cell system that can effectively use exhaust gas from a solid oxide fuel cell.

  In the fuel cell system of the present invention, a solid oxide fuel cell, a heat exchanger for exchanging heat between the exhaust gas from the solid electrolyte fuel cell and water, a hot water storage tank for storing water, a bottom portion of the hot water storage tank, A circulation pipe that connects between the heat exchanger and between the upper part of the hot water storage tank and the heat exchanger, and circulates water between the hot water storage tank and the heat exchanger; and A circulation pump that forcibly circulates the water, a temperature detector that detects the inlet water temperature and the outlet water temperature of the heat exchanger, and the outlet water temperature of the heat exchanger is equal to or higher than the inlet water temperature. And a control device for controlling the output of the circulation pump.

  In such a fuel cell system, by controlling the output of the circulation pump so that the outlet water temperature of the heat exchanger is equal to or higher than the inlet water temperature, heat exchange between water and exhaust gas can be performed effectively, High temperature hot water can be supplied stably. For example, when there is little power generated by a solid oxide fuel cell, the amount of exhaust gas also decreases, but in this case, the circulation pump is rotated slowly to reduce the amount of circulation per fixed time and heat exchange in the heat exchanger is sufficient. By carrying out to, the temperature of the water supplied in a hot water storage tank can be made high.

  The fuel cell system of the present invention includes a solid oxide fuel cell, a heat exchanger for exchanging heat between the exhaust gas from the solid electrolyte fuel cell and water, a hot water storage tank for storing water, and a bottom portion of the hot water storage tank. A circulation pipe for connecting water between the hot water storage tank and the heat exchanger, and for circulating water between the hot water storage tank and the heat exchanger, and the circulation A circulation pump that is provided in the piping and forcibly circulates water, a rotation speed detector that detects the rotation speed of the circulation pump, a temperature detector that detects the outlet water temperature of the heat exchanger, and the rotation speed detection The circulation flow rate of water in the circulation pipe is calculated from the rotation speed of the circulation pump of the condenser, and the outlet water temperature of the heat exchanger is calculated from the circulation flow rate and the heat amount of the exhaust gas of the solid oxide fuel cell, and is actually detected. The heat exchanger outlet temperature is calculated. Characterized by comprising a heat exchanger and a controller for controlling the output of the circulation pump so that the outlet temperature.

  In such a fuel cell system, the circulation flow rate of the water in the circulation pipe is obtained from the rotation speed of the circulation pump, and the theoretical outlet water temperature of the heat exchanger obtained from this circulation flow rate and the calorific value of the exhaust gas of the solid oxide fuel cell is calculated. Compare the actual detected outlet temperature of the heat exchanger and control the rotation speed of the circulation pump so that the actual outlet temperature becomes the theoretical outlet temperature. It is possible to stably supply hot hot water.

  That is, the rotation speed of the circulation pump and the circulation flow rate are in a proportional relationship, and in normal operation, they are determined by the pressure loss of the circulation pipe corresponding to the installation situation. Since the pressure loss of the circulation pipe according to the installation situation is determined by the pipe diameter and the pipe length, if the range of the pipe diameter and the pipe length is determined in advance, the circulation flow rate with respect to the rotation speed of the circulation pump is calculated. The Therefore, the temperature rise in the heat exchanger is calculated from the circulation flow rate calculated from the rotation speed of the circulation pump and the amount of exhaust heat calculated from the output of the fuel cell. Compare the temperature rise detected by the temperature detector that detects the water temperature at the inlet and outlet of the heat exchanger with the temperature rise calculated from the amount of heat, and when the difference of more than a predetermined value continues for a predetermined time, the circulation pump is forced to be above a certain level It has the control device which controls operation with the output of.

  Therefore, if the actual flow rate is less than the circulation flow rate calculated from the rotation speed of the circulation pump, the outlet temperature of the heat exchanger becomes high, and the temperature rise detected by the temperature detector is larger than the temperature rise obtained from the calculation. . In this way, when a difference of a predetermined value or more continues for a predetermined time, it is determined that the circulation is hindered for some reason, and the circulation pump can be prevented from being stopped in advance by operating the circulation pump at an output higher than a certain time. it can.

  In the fuel cell system of the present invention, the control device stops supplying the exhaust gas to the heat exchanger when the water in the hot water storage tank becomes equal to or higher than a predetermined temperature (a temperature close to the boiling temperature). And When the supply of the exhaust gas to the heat exchanger is stopped, the supply of high-temperature water to the hot water storage tank is stopped. In addition, unlike the polymer type, the solid oxide fuel cell does not need to be cooled internally, so that the solid oxide fuel cell itself is not affected even if the circulation pump is stopped.

  The control device desirably stops the circulation pump when the water in the hot water storage tank becomes equal to or higher than a predetermined temperature (a temperature close to the boiling temperature). By stopping the circulation pump, the water in the hot water storage tank can be prevented from approaching the boiling temperature.

  Furthermore, the fuel cell system of the present invention is characterized in that the control device is forcibly operated for a predetermined time with an output of a certain level or more at the start of re-operation after the circulation pump is stopped.

  As described above, in order to prevent boiling of the water in the hot water storage tank, the supply of exhaust gas to the heat exchanger is stopped and the circulation pump is stopped, which lowers the temperature of the heat exchanger. Therefore, even if high-temperature water from the hot water tank flows back to the heat exchanger, and from this heat exchanger to the hot water tank through the circulation pump, the circulation pump cannot be rotated even if the circulation pump is started again. It was difficult to return the water in the circulation pipe to a normal flow. In the present invention, when the recirculation operation is started after the circulation pump is stopped, the flow of water in the circulation pipe can be returned to a normal state by forcibly operating the circulation pump for a predetermined time with an output of a certain level or more.

  That is, when the water in the hot water storage tank exceeds a temperature close to the boiling temperature (for example, 90 ° C.), the circulation pump is stopped and the exhaust gas is discharged to another place without passing through the heat exchanger in order to prevent boiling. As a result of this operation, the temperature of the heat exchanger gradually decreases and the water temperature in the circulation pipe connected to the hot water storage tank also gradually decreases. Natural convection occurs in the opposite direction. Similarly, when the circulation pump is stopped at the time of boiling prevention, natural convection in the opposite direction is generated as the temperature of the heat exchanger decreases.

  When hot water in the hot water storage tank is used for hot water supply and cold tap water enters the bottom of the hot water storage tank, it returns to normal exhaust heat recovery operation. Since the outlet temperature of the heat exchanger is low, the control device attempts to increase the outlet temperature of the heat exchanger by controlling the flow rate of the circulation to sufficiently perform heat exchange in the heat exchanger. That is, the circulation pump is operated so that water flows through the circulation pipe at a minimum flow rate.

  Therefore, in the control as in normal operation, the pushing force of the circulation pump cannot overcome the natural convection (reverse flow) of water, the water flow in the circulation pipe cannot be made normal, and the heat It becomes a boiling state inside the exchanger and bubbles are rapidly generated. After such a state is reached, it is difficult to recover the circulation even if the outlet water temperature is detected to be above a predetermined level and the circulation pump is controlled. This tendency is particularly strong when a spiral pump is used as the circulation pump.

  In the present invention, when the circulation pump is temporarily stopped to prevent boiling and the operation is started again, even if the spiral pump is used as the circulation pump by strongly rotating the circulation pump for a certain period of time, By overcoming the above-mentioned natural convection in the reverse direction, normal flow can be restored, and then, by shifting to the output control of the circulation pump based on the heat exchanger outlet temperature, it is possible to prevent poor circulation after water boiling prevention control. It is possible to supply hot hot water with stability.

  In the fuel cell system of the present invention, a bypass pipe connected to the middle layer of the hot water storage tank is provided in a circulation pipe provided between the outlet side of the heat exchanger and the hot water storage tank, and the bypass pipe is switched to the bypass pipe. The control device is provided with a valve, and after the circulation pump is stopped, at the start of re-operation, the control device is forcibly operated for a predetermined time with an output of a certain level or more, and is switched to the bypass pipe, and the circulating water is placed in the middle layer of the hot water storage tank. It is characterized by returning.

  In such a fuel cell system, as described above, when the circulation pump is operated for a predetermined time with a predetermined output or more at the start of operation, the natural convection in the reverse direction is overcome and the circulation starts. Since the water in the hot water storage tank is supplied to the hot water storage tank as it is, a low temperature water layer is formed on the high temperature water layer, which disturbs the temperature stratification in the hot water storage tank. In the present invention, at the start of re-operation of the circulation pump, the operation is forcibly operated for a predetermined time with an output of a certain level or more, and the bypass water is switched to return the circulating water to the middle layer of the hot water tank. Without disturbing the stratification, it is possible to effectively use the hot water accumulated in the upper part of the hot water storage tank.

  In the fuel cell system of the present invention, the circulation pump is a spiral pump. Such a fuel cell system can be inexpensive.

  Furthermore, in the fuel cell system of the present invention, it is desirable that the fuel cell is a solid oxide fuel cell used for home use. Since such a fuel cell is required to be downsized, the fuel cell system of the present invention can be used effectively.

  In the fuel cell system of the present invention, exhaust heat from the solid oxide fuel cell can be used effectively. In addition, when the circulation pump is stopped and restarted, the circulation pump is forcibly operated for a predetermined time with a certain level of output, so that water in the circulation pipe can be used even when a spiral pump is used as the circulation pump. The flow can be returned to a normal state.

  The fuel cell system of the present invention will be described in detail with reference to FIG. As shown in FIG. 1, a solid oxide fuel cell system according to the present invention includes a solid oxide fuel cell 1, a fuel supply device 2 for supplying city gas, natural gas, and the like to the fuel cell 1, and oxidant air. An air supply device 3 for supplying the fuel cell 1 with fuel, and a fuel humidifier 4 for humidifying the fuel gas supplied to the fuel cell 1.

  The fuel cell 1 is connected to a heat exchanger 5 that recovers exhaust heat generated by power generation. The heat exchanger 5 is further connected to a circulation pipe 7 for circulating water in the hot water storage tank 6. 7 is provided with a circulation pump 8 for supplying water in the circulation pipe 7 to the heat exchanger 5. That is, the circulation pipe 7 includes a circulation pipe 7 a that connects between the heat exchanger 5 and the upper part of the hot water storage tank 6, and a circulation pipe 7 b that connects between the heat exchanger 5 and the bottom of the hot water storage tank 6. The water at the bottom of the hot water storage tank is returned to the upper part of the hot water storage tank 6 through the heat exchanger 5 by a circulation pump 8 comprising a spiral pump provided in the circulation pipe 7b.

  A switching damper 10 is provided in the pipe 9 for supplying the exhaust gas from the fuel cell 1 to the heat exchanger 5, and the damper 10 is configured so that the exhaust gas can be supplied to the heat exchanger 5 or other places.

  In the fuel cell system of the present invention, the circulation pipe 7b is provided with an inlet temperature detector 11 that detects the inlet water temperature of the heat exchanger 5, and the circulation pipe 7a has an outlet that detects the outlet water temperature of the heat exchanger 5. A temperature detector 12 is provided, and a control device 13 is provided for controlling the output of the circulation pump 8 based on information on the temperature detectors 11 and 12. Reference numeral 14 denotes a tank temperature detector that detects the water temperature of the hot water storage tank 6.

  In the operation of the fuel cell system as described above, the fuel supply device 2 supplies city gas, natural gas, or the like as fuel to the fuel cell 1. Further, an oxidant gas is supplied to the fuel cell 1 by the air supply device 3. First, fuel gas is combusted inside the fuel cell 1, and the fuel cell 1 itself is heated to a temperature at which power can be generated by the combustion heat. When the temperature reaches a predetermined temperature, power generation starts, and the temperature of the fuel cell 1 is maintained by heat generated by the power generation. Furthermore, the heat generated by the power generation is excessive and is released to the outside as exhaust heat. This exhaust heat is guided to the heat exchanger 5, and the heat is transferred to the water circulating in the circulation pipe 7 through the heat exchanger 5. When the tank water temperature detected by the tank temperature detector 14 is lower than the upper limit value of the hot water storage operation temperature, the control device 13 determines the flow rate of water in the circulation pipe per predetermined time according to the power generation amount of the fuel cell 1. The output of the circulation pump 8 is controlled so as to obtain a predetermined flow rate.

  However, when the hot water supply load is small and the amount of exhaust heat recovery is large, the hot water storage tank 6 is in a state of exceeding 90 ° C. If the operation is continued in such a state, the circulating water tends to boil in the heat exchanger 5, so the exhaust gas is discharged to another place by the switching damper 10 and the circulation pump 8 is stopped to prevent boiling.

  Thereafter, hot water in the hot water storage tank 6 is used for hot water supply or the like, the tank water temperature becomes lower than the upper limit of the hot water storage operation possible temperature, and the operation of the circulation pump 8 is started. However, while the exhaust heat of the fuel cell 1 is released elsewhere to prevent boiling and the circulation pump 8 is stopped, the temperature of the heat exchanger 5 decreases and becomes lower than the water temperature in the hot water storage tank 6, causing a temperature difference. Has occurred.

  In such a state, a natural convection force is generated in the direction opposite to the circulation direction during normal hot water storage operation. Even if the operation command for the circulation pump 8 is entered there and the switching damper 10 switches the exhaust gas to the heat exchanger 5, the outlet temperature of the heat exchanger 5 is low so that the circulation pump 8 is controlled in a direction in which the flow rate decreases. Will be. Since the head of the circulation pump 8 at this time is as small as about 1/10 of the rated operation, it is impossible to secure normal circulation under the force of natural convection.

  If the state in which normal circulation cannot be performed in this way continues, the circulating water boils inside the heat exchanger 5. Therefore, when the operation command for the circulation pump 8 is issued, the circulation is maintained normally by forcibly operating for a predetermined time with an output higher than a certain value, and then the inlet temperature detector 11 and the outlet temperature detector 12 of the heat exchanger 5. Thus, it is possible to shift to a predetermined temperature control, to prevent an abnormally high temperature and abnormal pressure increase of the heat exchanger due to poor circulation, and to continue stable operation.

  In FIG. 1, when the tank water temperature detected by the tank temperature detector 11 is less than the upper limit value of the hot water storage operation temperature, the output of the circulation pump 8 is controlled so that the temperature of the outlet temperature detector 12 becomes a predetermined temperature. To do. Assuming that the outlet water temperature to be controlled by the heat exchanger 5 is Wout, the inlet water temperature is Win, and the value of Wout−Win is ΔT, the lower the inlet water temperature Win is, the larger ΔT becomes, so the circulating flow rate becomes smaller.

  On the other hand, the circulating water circulating inside the heat exchanger 5 is heated by the exhaust gas, and as the temperature rises, the air dissolved in the water is generated as bubbles. These generated bubbles cannot be pushed out unless a predetermined flow rate is maintained, and stay in the heat exchanger 5.

  If such a state continues for a long time, eventually the pipe line of the heat exchanger 5 is blocked and the circulation stops. When the circulation stops, the circulating water boils inside the heat exchanger 5 and is in a dangerous state. Therefore, the control unit 13 controls the ΔT to be equal to or less than a predetermined value so as not to fall below a flow rate that does not cause poor circulation that has been empirically derived. With such a configuration, the circulation can be maintained normally, the abnormally high temperature and abnormal pressure increase of the heat exchanger due to poor circulation can be prevented, and stable operation can be continued.

  FIG. 2 is a configuration diagram of another fuel cell system of the present invention. In this fuel cell system, a bypass pipe 16 is branched from a circulation pipe 7 a that connects the heat exchanger 5 and the upper part of the hot water storage tank 6, and is connected to the middle layer of the hot water storage tank 6. A switching valve 15 is provided at a branch portion of the bypass pipe 16 from the circulation pipe 7a.

  When the tank water temperature detected by the tank temperature detector 14 is less than the upper limit value of the hot water storage operation temperature, the control device 13 determines that the difference between the temperature of the outlet temperature detector 12 and the temperature of the inlet temperature detector 11 is a predetermined value. The output of the circulation pump 8 is controlled so as to reach a temperature. However, when the tank hot water temperature is high and restarting after stopping the hot water storage operation to prevent danger, the circulation cannot be normally started as described above. For this reason, the circulation pump 8 is forcibly operated for a predetermined time with an output of a certain level or more, and at the same time, the switching valve 15 is switched to the bypass pipe 16 to return the circulating water to the middle layer of the hot water storage tank 6. By adopting such a configuration, it is possible to prevent low temperature water from returning to the upper part of the hot water storage tank 6, and to effectively use the hot water accumulated in the upper part of the hot water storage tank 6 without disturbing the temperature stratification in the hot water storage tank 6. It can be used for hot water supply and stable operation can be continued.

It is a block diagram which shows the fuel cell system of this invention. It is a block diagram which shows the other fuel cell system of this invention. It is a block diagram which shows the conventional fuel cell system.

Explanation of symbols

1: Fuel cell 5: Heat exchanger 6: Hot water storage tank 7: Circulation pipe 8: Circulation pump 10: Switching damper 11: Inlet temperature detector 12: Outlet temperature detector 13: Controller 14: Tank temperature detector 15: Switching Valve 16: Bypass piping

Claims (7)

A solid oxide fuel cell; a heat exchanger that exchanges heat between the exhaust gas from the solid oxide fuel cell and water; a hot water storage tank that stores water; a bottom of the hot water storage tank; and the heat exchanger; and An upper part of the hot water storage tank and the heat exchanger are connected to each other, a circulation pipe for circulating water between the hot water storage tank and the heat exchanger, and a circulation pipe provided in the circulation pipe for forcing water. Circulating a circulation pump, a temperature detector for detecting the inlet water temperature and the outlet water temperature of the heat exchanger, and controlling the output of the circulation pump so that the outlet water temperature of the heat exchanger is equal to or higher than the inlet water temperature. A fuel cell system. A solid oxide fuel cell; a heat exchanger that exchanges heat between the exhaust gas from the solid oxide fuel cell and water; a hot water storage tank that stores water; a bottom of the hot water storage tank; and the heat exchanger; and An upper part of the hot water storage tank and the heat exchanger are connected to each other, a circulation pipe for circulating water between the hot water storage tank and the heat exchanger, and a circulation pipe provided in the circulation pipe for forcing water. A circulation pump for circulation; a rotation speed detector for detecting the rotation speed of the circulation pump; a temperature detector for detecting the outlet water temperature of the heat exchanger; and the circulation pipe from the circulation pump rotation speed of the rotation speed detector Calculate the circulating flow rate of the water inside, calculate the outlet water temperature of the heat exchanger from the circulating flow rate and the amount of heat of the exhaust gas of the solid oxide fuel cell, and calculate the outlet temperature of the heat exchanger that is actually detected So that the outlet temperature of the heat exchanger Fuel cell system characterized by comprising a controller for controlling the output of the serial circulation pump. 3. The fuel according to claim 1, wherein the control device stops supplying the exhaust gas to the heat exchanger when the water in the hot water storage tank becomes equal to or higher than a predetermined temperature (a temperature close to the boiling temperature). Battery system. 4. The fuel cell according to claim 1, wherein the control device stops the circulation pump when the water in the hot water storage tank becomes equal to or higher than a predetermined temperature (a temperature close to a boiling temperature). system. The fuel cell system according to any one of claims 1 to 4, wherein the control device is forcibly operated at a predetermined output or more for a predetermined time at the start of re-operation after the circulation pump is stopped. A circulation pipe provided between the outlet side of the heat exchanger and the hot water storage tank is provided with a bypass pipe connected to the middle layer of the hot water storage tank, and a switching valve is provided in the bypass pipe. 2. After the circulation pump is stopped, at the start of re-operation, the operation is forcibly performed for a predetermined time with an output of a certain level or more, and is switched to the bypass pipe to return the circulating water to the middle layer of the hot water storage tank. The fuel cell system according to any one of 1 to 5. 7. The fuel cell system according to claim 1, wherein the circulation pump is a spiral pump.

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