JP2006024431A - 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 ; a circulation pump 8 disposed in the circulation piping 7 ; a rotational frequency detector which detects rotational frequency of the circulation pump 8 ; a circulating water flow quantity detector 9 disposed in the circulation piping 7, and a control unit 10 which compares theoretical quantity of the water flow corresponding the rotational frequency detected with the rotational frequency detector with real quantity of the water flow detected with the circulating water flow quantity detector 9, and when the real quantity of the water flow becomes less than the theoretical quantity of the water flow by a predetermined value, controls output of the circulation pump 8 compulsorily in order that the output of the pump 8 becomes a predetermined value or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid oxide fuel cell, a heat exchanger for exchanging heat between the exhaust gas from the solid oxide fuel cell and water, a hot water storage tank for storing water, and a connection between the heat exchanger and the hot water storage tank. The present invention relates to a fuel cell system including a circulation pipe that performs circulation 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 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 the polymer electrolyte fuel cell system, the temperature in the fuel cell is 70 to 85 ° C. and the temperature of the cooling water introduced into the heat exchanger is low, but in the solid oxide fuel cell system, the power generation temperature is Is at least 600 ° C. or higher, the exhaust gas introduced into the heat exchanger is at a higher temperature than the polymer type, and water is rapidly heated in the heat exchanger. For this reason, in the solid electrolyte form, for example, many bubbles present in water tend to be generated.

  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 electrolyte 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 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 circulating pump that forcibly circulates the water, a rotational speed detector that detects the rotational speed of the circulating pump, a circulating flow rate detector that is provided in the circulating pipe, and the rotational speed detector. The theoretical flow rate corresponding to the number of revolutions is compared with the actual flow rate detected by the circulation flow detector, and if the actual flow rate falls below the theoretical flow rate by a predetermined amount, the output of the circulation pump is forcibly increased to a predetermined value or more. A control device for controlling The features.

  In a solid oxide fuel cell, an oxygen-containing gas and a fuel gas are supplied, and the surplus oxygen-containing gas and surplus fuel gas that have not been used for the reaction are burned and discharged to the outside as exhaust gas. While being supplied to the heat exchanger, water is supplied to the heat exchanger, the exhaust gas and water are heat-exchanged, and the heat-exchanged water is sent to the upper part of the hot water storage tank via the circulation pipe. Further, water is supplied from the bottom of the hot water storage tank to the heat exchanger via a circulation pipe. In the heat exchanger, the heat energy of the exhaust gas discharged from the fuel cell can be used for heating water by the heat exchanger, and the heated water is supplied to the hot water storage tank.

  In the fuel cell system of the present invention, the theoretical flow rate corresponding to the rotation speed of the circulation pump detected by the rotation speed detector is compared with the actual flow rate flowing through the circulation pipe detected by the circulation flow detector. If the flow rate is lower than the theoretical flow rate by a predetermined amount, it is determined that bubbles or the like are present in the heat exchanger or the circulation pipe, impeding the flow of water, and the output of the circulation pump is forcibly exceeded the predetermined value. By controlling, bubbles or the like in the circulation pipe can be strongly pushed out by the circulation pump.

  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 for the rotation speed of the circulation pump is calculated . Therefore, the theoretical flow rate calculated from the rotation speed of the circulation pump is compared with the actual detected actual flow rate. If the actual flow rate is lower than the theoretical flow rate by a predetermined amount, for example, the air flow suddenly stops the circulation flow. Even in such a case, by immediately controlling the output of the circulation pump to the maximum, bubbles can be pushed out and the circulation can be maintained normally.

  The fuel cell 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 heat exchanger and between the upper part of the hot water storage tank and the heat exchanger, and circulating water between the hot water storage tank and the heat exchanger; A circulation pump for forcibly circulating water, a rotation speed detector for detecting the rotation speed of the circulation pump, a circulation flow rate detector provided in the circulation pipe, and the rotation speed detector The output of the circulation pump is forcibly controlled to a predetermined value or more when a change in the flow rate detected by the circulation flow rate detector is equal to or greater than a predetermined value for a predetermined time with respect to the change in rotation speed per time. And a control device To.

  In such a fuel cell system, when the state in which the flow rate change detected by the circulating flow rate detector is greater than or equal to a predetermined value continues for a predetermined time with respect to the change in rotational frequency detected by the rotational rate detector, Since the output of the pump is forcibly controlled to a predetermined value or more, bubbles can be pushed out, and hot water can be stably stored in the hot water storage tank at a constant temperature. That is, if the flow rate change detected by the flow rate detector exceeds a predetermined value rather than the change in the number of revolutions of the circulation pump per certain time, the pipe line resistance of the circulation pipe is increased. By largely controlling the output of the pump, the circulation stop can be prevented beforehand.

  Further, 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. Heat exchanger outlet temperature is calculated And a control device that controls the output of the circulation pump so that the outlet temperature of the heat exchanger is adjusted, and the control device is configured so that the detected outlet temperature of the heat exchanger is the calculated heat. When the state more than the predetermined temperature than the outlet temperature of the exchanger continues for a predetermined time, the circulation pump is forcibly controlled for a predetermined time with an output higher than the predetermined time.

  Even in such a fuel cell system, since the output of the circulation pump is forcibly controlled to a predetermined value or more, the hot water can be stored in the hot water storage tank stably at a constant temperature. In other words, if the detected outlet temperature of the heat exchanger is higher than the calculated outlet temperature of the heat exchanger for a predetermined time, bubbles are stagnated in the circulation pipe and the pipe resistance increases. Since the circulation flow rate is reduced, for example, by controlling the output of the circulation pump to the maximum, bubbles in the circulation pipe can be pushed out and the circulation stop can be prevented beforehand.

  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, 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 provided in the pipe for forcibly circulating water; a rotation speed detector for detecting the rotation speed of the circulation pump; a circulation flow rate detector provided in the circulation pipe; and an outlet of the heat exchanger A temperature detector for detecting the water temperature, a circulation pipe provided between the outlet side of the heat exchanger and the hot water storage tank, a bypass pipe connected to the middle layer of the hot water storage tank is provided, and the bypass pipe Provided in the switching valve, the rotation The theoretical flow rate corresponding to the rotational speed detected by the detector is compared with the actual flow rate detected by the flow rate detector, and if the actual flow rate falls below the theoretical flow rate by a predetermined amount, the output of the circulation pump is forcibly While controlling to more than a predetermined value, it switches to the said bypass piping, and circulating water is returned to the middle layer part of the said hot water storage tank, It is characterized by the above-mentioned.

  In such a fuel cell system, when bubbles are stagnated in the circulation pipe, the pipe resistance is increased, and the circulation flow rate is reduced, the output of the circulation pump is controlled to the maximum, for example, to reduce the bubbles in the circulation pipe. Pushing and stopping circulation can be prevented, and low temperature water can be returned to the upper part of the hot water tank by operating the switching valve provided in the bypass pipe and returning the circulating water to the middle part of the hot water tank. The hot water accumulated in the upper part of the hot water storage tank can be used effectively without disturbing the temperature stratification in 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.

  According to the fuel cell system of the present invention, it is possible to prevent poor circulation caused by fluctuations in pressure loss between the heat exchanger that collects exhaust gas generated by driving the solid oxide fuel cell and the circulation pipe, and high temperature. Water can be supplied stably.

  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 fuel cell 1, a fuel supply device 2 that supplies city gas, natural gas, and the like to the fuel cell 1, and oxidant air as the fuel cell. An air supply device 3 for supplying to the fuel cell 1 and a fuel humidifier 4 for humidifying the fuel gas to be supplied to the fuel cell 1 are provided.

  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.

  In the fuel cell system of the present invention, the circulation pipe 7b is provided with a flow rate detector 9 for detecting the amount of water flowing in the circulation pipe 7b. The flow rate detector 9 is circulated in the circulation pipe 7b. It is provided in the vicinity of the circulation pump 8 having the lowest water temperature. Further, a control device 10 for controlling the output of the circulation pump 8 is provided, and the pump output necessary for recovering the exhaust heat generated according to the power generation amount of the fuel cell 1 is controlled. Reference numeral 11 denotes a tank temperature detector that detects the water temperature in 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 11 is lower than the upper limit value of the hot water storage operation temperature, the control device 10 sets the flow rate of water in the circulation pipe to a predetermined flow rate according to the power generation amount of the fuel cell 1. The output of the circulation pump 8 is controlled. For example, if the upper limit value of the hot water storage operation temperature is 90 ° C. and the tank water temperature is 70 ° C., the output of the circulation pump 8 is set so that the flow rate of water in the circulation pipe is 0.3 liter / min. Be controlled.

  Further, the control device 10 compares the theoretical flow rate calculated from the rotational speed of the circulation pump 8 with the actual flow rate detected by the flow rate detector 9. When the actual flow rate detected by the flow rate detector 9 is smaller than the theoretical flow rate by a predetermined value or more (for example, 50%), or when the circulating flow rate suddenly stops due to an air lock or the like (the actual flow rate becomes 0 or close to 0) In this case, air or water vapor dissolved in the water circulating in the circulation pipe 7 is generated as bubbles, and the bubbles gradually increase and stagnate in the circulation pipe 7 so that water passes through the circulation pipe. 7 is a case where the flow path 7 becomes narrow and the pressure loss of the circulation pipe 7 increases.

  In this case, the control device 10 immediately controls the output of the circulation pump 8 to be larger than normal or maximized. As a result, the water pressure in the circulation pipe 7 is increased, and the bubbles are pushed out by the water pressure of the circulation pump 8 and pushed into the hot water storage tank. When the bubbles in the circulation pipe 7 are pushed out, the theoretical flow rate calculated from the number of revolutions of the circulation pump 8 and the actual flow rate detected by the flow rate detector 9 become substantially the same amount. Thus, the rotational speed of the circulation pump 8 is controlled.

  Therefore, in the fuel cell system of the present invention, even when a large amount of bubbles stagnates in the circulation pipe 7, the rotation speed of the circulation pump 8 is increased by the control device 10 and the water pressure in the circulation pipe 7 is increased. Therefore, even if a spiral pump is used, bubbles can be pushed out, circulation can be maintained normally, abnormal heat temperature and abnormal pressure rise of the heat exchanger due to poor circulation can be prevented, and stable operation can be achieved. Can continue.

  In addition, an inexpensive spiral pump that increases the water pressure by rotating at a high speed without using an expensive gear pump can be used as the circulation pump, and an inexpensive fuel cell system can be provided.

  FIG. 2 shows another fuel cell system of the present invention. In this fuel cell system, an outlet water temperature of the heat exchanger 5 is detected in a circulation pipe 7a connecting the heat exchanger 5 and the upper part of the hot water storage tank 6. A recovery temperature detector 12 is provided.

  In this fuel cell system, 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 control device 10 sets the temperature of the recovery temperature detector 12 to a predetermined temperature, for example, 60 to The output of the circulation pump 8 is controlled so as to be 90 ° C.

  In this fuel cell system, as in FIG. 1, when the actual flow rate detected by the flow rate detector 9 is smaller than the theoretical flow rate calculated from the rotational speed of the circulation pump 8, a sudden air lock occurs. When the circulation flow rate stops, the control device 10 immediately controls the output of the circulation pump 8 to be larger than usual or maximizes the pressure, thereby increasing the water pressure in the circulation pipe 7 and causing bubbles. Is pushed out by the water pressure of the circulation pump 8, pushed into the hot water storage tank, and can be quickly returned to the normal flow rate.

  In the fuel cell system of this embodiment, 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 temperature of the recovery temperature detector 12 is a predetermined temperature. Since the output of the circulation pump 8 is controlled so as to become, stacking and boiling can be achieved without disturbing the temperature stratification of the hot water storage tank 6 as compared with the system of FIG.

  FIG. 3 shows another fuel cell system of the present invention. In this fuel cell system, the control device 10 has the following functions. That is, the change per unit time of the rotation speed of the circulation pump 8 is ΔN, and the change per unit time of the actual flow rate detected by the flow rate detector 9 is ΔL. The ratio ΔN / ΔL between ΔN and ΔL is within a certain range during normal operation of the fuel cell 1. However, if bubbles or the like are generated in the circulation pipe 7 and the residual amount of bubbles increases, the resistance of the pipe 7 increases, and if the circulation flow rate decreases, the ΔN / ΔL value becomes equal to or greater than the limit value during normal operation. When this state continues for a predetermined time, the output (control voltage) of the circulation pump 8 is forcibly controlled to a predetermined value or more. Thereby, the water pressure in the circulation piping 7 can be made high, and a bubble can be extruded.

  Further, even when the flow rate detector 9 detects a decrease in the circulation flow rate and increases the number of revolutions of the pump so as to achieve a predetermined circulation flow rate, the ΔN / ΔL value exceeds the limit value for normal operation. When the state continues for a predetermined time, the output of the circulation pump 8 is forcibly controlled to a predetermined value or more.

  By adopting such a configuration, even when bubbles are stagnated in the circulation pipe 7, the circulation can be maintained normally, and the abnormally high temperature and abnormal pressure rise of the heat exchanger due to the poor circulation can be prevented. And stable operation can be continued.

  Moreover, the case where the function of the control apparatus 10 has the following functions may be sufficient. That is, the heat quantity of the exhaust gas of the fuel cell 1 is Q, the tank water temperature detected by the tank temperature detector 11 is W1, the heat exchanger inlet water temperature is Win, and the heat exchanger outlet water temperature detected by the outlet temperature detector 12 is Wout. The circulation flow rate P can be expressed by P = τN, where N is the number of rotations detected by the number detector and τ is a flow factor such as pressure loss of the circulation pipe 7.

  If the heat exchange factor of the heat exchanger 5 is α, the theoretical temperature rise ΔT ′ of the heat exchanger 5 can be expressed by ΔT ′ = αQ / P. On the other hand, the actual ΔT of the heat exchanger 5 can be expressed as ΔT = Wout−Win, and ΔT′≈ΔT during a steady operation, which falls within a certain range. However, if bubbles or the like are generated in the circulation pipe 7 and the residual amount of bubbles increases, the resistance of the pipe increases, and if the circulation flow rate decreases, ΔT ′ <ΔT, which exceeds the limit value during normal operation.

  When this state continues for a predetermined time, the circulation pump 8 is forcibly controlled at a rated output for a predetermined time. 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. 3 shows another fuel cell system of the present invention. In this fuel cell system, a bypass pipe 14 is branched from a circulation pipe 7a connecting the heat exchanger 5 and the upper part of the hot water storage tank 6. The bypass pipe 14 is connected to the middle layer of the hot water storage tank 6. Reference numeral 13 denotes a switching valve provided in the bypass pipe 14.

  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 control device 10 controls the output of the circulation pump 8 so that the temperature of the recovery temperature detector 12 becomes a predetermined temperature. To do. Further, the control device 10 compares the theoretical flow rate calculated from the rotational speed of the circulation pump 8 with the actual flow rate detected by the flow rate detector 9, and the actual flow rate detected by the flow rate detector 9 is equal to or greater than a predetermined value from the theoretical flow rate. When the circulation flow is suddenly stopped due to an air lock or the like, the output of the circulation pump 8 is immediately controlled to be maximized. At the same time, the switching valve 13 is switched to the bypass pipe 14 to circulate in the middle layer of the hot water storage tank 6. Return the water.

  When the actual flow rate is smaller than the theoretical flow rate by a predetermined value or when the circulation flow stops, heat is radiated in the circulation pipe 7a, the water in the circulation pipe 7a is cooled, and the cooled water is stored in the hot water storage tank 11. When the water flows into the upper part of the hot water tank, low temperature water is supplied onto the hot water layer of the hot water storage tank 6 and the temperature stratification in the hot water storage tank 6 is disturbed. In the present invention, the actual flow rate is the theoretical flow rate. If the circulating flow stops when the flow is smaller than a predetermined value, the switching valve 13 causes water to flow into the middle layer of the hot water storage tank 6 via the bypass pipe 14, and temperature stratification in the hot water storage tank 6 is performed. The hot water accumulated in the upper part of the hot water storage tank 6 can be effectively used for hot water supply without disturbing the water.

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 further another 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 tanks 7, 7a, 7b: Circulation piping 8: Circulation pump 9: Circulation flow rate detector 10: Controller 11: Tank temperature detector 12: Recovery temperature detector 13: Switching Valve 14: Bypass piping

Claims (5)

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 circulating pump to be circulated, a rotational speed detector for detecting the rotational speed of the circulating pump, a circulating flow rate detector provided in the circulating pipe, and a theoretical flow rate corresponding to the rotational speed detected by the rotational speed detector; And a control device for forcibly controlling the output of the circulation pump to a predetermined value or more when the actual flow rate falls below a predetermined amount below the theoretical flow rate. 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 circulating pump to be circulated, a rotational speed detector for detecting the rotational speed of the circulating pump, a circulating flow rate detector provided in the circulating pipe, and a change in rotational speed detected by the rotational speed detector per time. On the other hand, it comprises a control device for forcibly controlling the output of the circulation pump to a predetermined value or more when a state in which the flow rate change detected by the circulation flow detector is a predetermined value or more continues for a predetermined time. 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 A control device for controlling the output of the circulation pump, and the control device has a state where the actually detected outlet temperature of the heat exchanger is not lower than the calculated outlet temperature of the heat exchanger. When the fuel cell system continues for a predetermined time, the circulation pump is forcibly controlled for a predetermined time with a predetermined output or more. 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 to circulate, a rotation speed detector for detecting the rotation speed of the circulation pump, a circulation flow rate detector provided in the circulation pipe, a temperature detector for detecting an outlet water temperature of the heat exchanger, The 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 portion of the hot water storage tank, the bypass pipe is provided with a switching valve, and the rotation speed detector Corresponding to the number of revolutions detected in The theoretical flow rate is compared with the actual flow rate detected by the flow rate detector, and when the actual flow rate falls below the theoretical flow rate by a predetermined amount, the output of the circulation pump is forcibly controlled to a predetermined value or more, and the bypass pipe And circulating water is returned to the middle layer of the hot water storage tank. The fuel cell system according to any one of claims 1 to 4, wherein the circulation pump is a spiral pump.

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