JP5212895B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system that uses heat generated in a fuel cell module including a solid oxide fuel cell (SOFC).

  Conventionally, as a fuel cell system using exhaust gas from a fuel cell, for example, a fuel cell system as described in Patent Document 1 has been proposed. The fuel cell system described in Patent Document 1 below uses a solid electrolyte type fuel cell, and is for effectively using exhaust gas in the fuel cell module. Specifically, a solid oxide fuel cell module, a heat exchanger that exchanges heat between exhaust gas and water from the solid oxide fuel cell module, a hot water storage tank that stores water, and a heat exchange with the bottom of the hot water storage tank And a circulation pipe that circulates water between the hot water tank and the heat exchanger, and a circulation pipe that circulates water between the hot water tank and the heat exchanger. The circulation pump to be circulated, a temperature detector for detecting the inlet water temperature and the outlet water temperature of the heat exchanger, and the output of the circulation pump to control the outlet water temperature of the heat exchanger to be equal to or higher than the inlet water temperature. And a control device.

  In the fuel cell system described in Patent Document 1 described below, the output of the circulation pump can be controlled so that the outlet water temperature of the heat exchanger is equal to or higher than the inlet water temperature. As a result, heat exchange between water and exhaust gas can be effectively performed to stably supply hot hot water. More specifically, when the amount of power generated by the solid oxide fuel cell is small, the amount of exhaust gas also decreases. In this case, the circulation pump is slowly rotated to reduce the circulation amount per fixed time, and the heat exchanger By sufficiently performing heat exchange, the temperature of the water supplied into the hot water storage tank can be increased.

  Furthermore, a combine system of a fuel cell and a hot water supply device as described in Patent Document 2 below has also been proposed. The system described in Patent Document 2 below performs heat exchange between the exhaust gas from the fuel cell and the water in the hot water storage tank using a heat exchanger, and collects the condensed water that accompanies the cooling of the exhaust gas in the condensed water tank. Hot water is stored in a hot water tank. Water (hot water) in the hot water storage tank is circulated through the circulation channel so that the circulating flow rate becomes larger as the water level of the condensed water tank is lower, the hot water temperature of the hot water storage tank is lower, and the hot water supply amount is larger. And when the heat exchange with a heat exchanger cannot fully be performed, the radiator is taken in into the circulation flow path and the water in the hot water storage tank is cooled and used. As a result, the fuel cell and the hot water supply apparatus can be operated more appropriately, and the thermal efficiency and resource utilization efficiency can be increased.

Further, as a fuel cell system that uses exhaust gas from a fuel cell, a fuel cell system described in Patent Document 3 below has been proposed.
JP 2006-24430 A JP 2001-325882 A JP 2002-81743 A

  By the way, in the fuel cell system described in Patent Document 1 described above, the water in the hot water storage tank is heated by circulating between it and the heat exchanger. However, since the solid electrolyte fuel cell has high power generation efficiency and low fuel consumption, the exhaust gas temperature is high but the exhaust amount is small, and the exhaust gas contains a small amount of heat. Therefore, in a fuel cell system having a circulation path as described in Patent Document 1 described above, it is necessary to circulate water many times or to circulate water at a considerably low speed with respect to the heat exchanger. In order to prevent the hot water from being circulated many times, it is necessary to reduce the flow rate when boiling the hot water. However, as described in Patent Document 2, it is necessary to circulate water or hot water in order to dissipate the exhaust gas in the heat exchanger even after boiling the hot water. In this case, it is necessary to increase the flow rate in order to increase the cooling efficiency. In this way, in the fuel cell system that boils hot water using the exhaust gas of the fuel cell, it is necessary to increase or decrease the flow velocity of the pipe line, but in particular in the case of a solid oxide fuel cell Since the amount of heat generated is small, the lower limit of the flow rate of the pipe line becomes extremely low, and the control of the flow rate becomes extremely difficult.

  Therefore, in the present invention, there is provided a fuel cell system capable of appropriately controlling the flow velocity of a pipe line in both cases of boiling water and mainly radiating exhaust gas in a heat exchanger. The purpose is to provide.

  In order to solve the above-described problems, a fuel cell system according to the present invention includes a fuel cell module including a plurality of solid oxide fuel cells operated by a fuel gas and an oxidant gas, and the solid oxide fuel cell. Heat exchanger that performs heat exchange using exhaust gas containing gas generated by combustion of residual fuel gas and residual oxidant gas that did not contribute to power generation reaction in the process, and heats the water into hot water A tank for storing water and hot water for heating the water, a first pipe configured to re-feed the water fed to the heat exchanger to the heat exchanger, and a tank fed from the tank. A second pipe configured to feed the hot water to the heat exchanger and return the hot water heat-exchanged in the heat exchanger to the tank; and the first pipe and the second pipe Pump that generates water flow , Wherein the first pipeline and the second pipeline have a shared pipeline portion that shares a part of each, and the second pipeline is the shared pipeline portion And a supply line part for supplying water fed from the tank to the shared line part, and a reflux line part for refluxing hot water from the shared line part to the tank, The first pipe connects, together with the shared pipe section, a junction where the supply pipe section is connected to the shared pipe section and a branch point where the reflux pipe section branches from the shared pipe section. And a switching section for switching the pipeline between the reflux pipeline section and the circulation pipeline section is provided at the branch point, and the supply pipeline section and the reflux pipeline are provided. At least one of the pipe parts is provided with a pressure loss part so that the pressure loss of the pipe line is higher than that of the first pipe line. The switching unit is switched to the circulation pipeline unit side, the switching unit is switched to the reflux pipeline unit side rather than the flow rate flowing through the first pipeline by the water flow generated by the pump, and the pump is generated. It is configured such that the flow rate flowing through the second pipeline is reduced by the water flow to be performed.

  According to the present invention, a fuel cell system capable of appropriately controlling the flow rate of a pipe line in both cases of boiling water and mainly radiating exhaust gas in a heat exchanger. Can be provided.

  Prior to describing the best mode for carrying out the present invention, the function and effect of the present invention will be described.

  A fuel cell system according to the present invention does not contribute to a power generation reaction in a fuel cell module including a plurality of solid oxide fuel cells operated by a fuel gas and an oxidant gas, and the solid oxide fuel cells. Heat exchange using exhaust gas containing gas generated by combustion of the remaining fuel gas and the remaining oxidant gas, heat the water into hot water, water and the water A tank for storing heated hot water, a first conduit configured to allow water sent to the heat exchanger to reach the heat exchanger again, and water sent from the tank to the heat exchanger A second pipe configured to recirculate hot water exchanged in the heat exchanger to the tank, and a pump for generating a water flow in the first pipe and the second pipe, Fuel cell system with The first pipeline and the second pipeline have a shared pipeline portion that shares a part of each of the first pipeline and the second pipeline, together with the shared pipeline portion, from the tank. A supply line part that supplies the fed water to the shared line part, and a reflux line part that recirculates hot water from the shared line part to the tank, wherein the first line is And a circulation pipe section that connects, together with the common pipe section, a junction where the supply pipe section is connected to the common pipe section and a branch point where the reflux pipe section branches from the common pipe section. The branching point is provided with a switching unit for switching the pipeline between the reflux pipeline and the circulation pipeline, and at least of the supply pipeline and the reflux pipeline On one side, a pressure loss part is provided so that the pressure loss of the pipe line is higher than that of the first pipe line, and the switching part is connected to the circulation pipe. The switching portion is switched to the return conduit portion side rather than the flow rate flowing through the first conduit by the water flow generated by the pump, and the second conduit is generated by the water flow generated by the pump. It is comprised so that the flow volume which flows through may become small.

  According to the fuel cell system of the present invention, the first pipe is configured such that the water sent to the heat exchanger reaches the heat exchanger again, and the second pipe is sent from the tank. The heated water is sent to the heat exchanger, and the hot water heat-exchanged in the heat exchanger is returned to the tank. In addition, the first pipeline and the second pipeline share a part of each pipeline, and the water sent out from the tank is supplied from the supply pipeline of the second pipeline, the first pipeline and the second pipeline. It reaches the heat exchanger via the shared pipe section of two pipes. After the heat is exchanged in the heat exchanger to become hot water, the hot water reaches the branch point via the shared pipeline portion of the first pipeline and the second pipeline. A switching part is arranged at the branch point, and the switching part returns to the tank via the reflux pipe part of the second pipe or the junction point via the circulation pipe part of the first pipe. Thus, it is controlled whether to return to the shared pipeline section of the first pipeline and the second pipeline again. In such a pipeline configuration, in the present invention, a pressure loss portion is provided in at least one of the supply pipeline portion and the reflux pipeline portion, and the pressure loss of the pipeline stands in the portion where the pressure loss portion is provided. It is configured. In other words, the pressure loss portion is formed in a portion of the second pipeline that is formed independently of the first pipeline. Therefore, when the pump is driven in a state where the switching portion is switched to the circulation pipeline portion side of the first pipeline, the pressure loss does not increase more than necessary, and a water flow corresponding to the pump driving speed is generated, and the fuel cell The heat of exhaust gas from the module can be taken away appropriately. On the other hand, when the pump is driven in a state in which the switching unit is switched to the reflux pipeline side of the second pipeline, the pressure loss of the second pipeline is higher than the first pipeline by the pressure loss unit. The flow velocity of the water flow is lower than when no is provided. Therefore, the heat of the exhaust gas can be effectively received in the heat exchanger to boil the hot water.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same constituent elements in the drawings will be denoted by the same reference numerals as much as possible, and redundant description will be omitted.

  The fuel cell system FCS according to this embodiment will be described with reference to FIG. FIG. 1 is a block diagram schematically showing the configuration of the fuel cell system FCS. As shown in FIG. 1, the fuel cell system FCS includes a fuel cell unit FCU and a hot water storage unit WPU.

  Next, the fuel cell unit FCU will be described. The fuel cell unit FCU includes a fuel cell module FCM, an air supply unit AP, a fuel supply unit FP, a water supply unit WP, a power extraction unit EP, and a fuel cell unit control unit FS.

  The fuel cell module FCM includes a fuel cell stack 10, a preheater / evaporator 11, a reformer 12, and an air heat exchanger 13. The fuel cell module FCM oxidizes a fuel gas such as a reformed gas obtained by reforming hydrogen or a hydrocarbon fuel into a plurality of electrically connected fuel cells (not shown) constituting the fuel cell stack 10. Electric power is generated by supplying the agent gas to generate electricity. Each component of the fuel cell module FCM will be further described.

  The air supply unit AP includes elements such as a filter, a flow sensor, a buffer tank, and an air blower. The air as the oxidant gas supplied from the air supply unit AP is introduced into the air heat exchanger 13 through the preheater / evaporator 11. The air heat exchanger 13 includes an exhaust gas including a residual fuel gas that has not contributed to the power generation reaction in the fuel cell stack 10 and a gas obtained by burning the air, and air introduced through the preheater / evaporator 11. It is comprised so that heat may be exchanged between. The air preheated in the air heat exchanger 13 is supplied to the fuel cell stack 10. Further, a thermistor 14 for measuring the temperature of the exhaust gas that has passed through the air heat exchanger 13 is between the air heat exchanger 13 and the outlet of the discharge path, and in the vicinity of the air heat exchanger 13. Is arranged.

  The fuel supply unit FP includes a path through which city gas as hydrocarbon fuel flows and a path through which air flows. The city gas inflow path is composed of elements such as a solenoid valve, governor, fuel pump, buffer tank, flow sensor, desulfurizer, and check valve. A path through which the air flows is configured by elements such as a filter, an air blower, a buffer tank, a flow rate sensor, a check valve, and a solenoid valve. The city gas flowing in from these two paths and the atmosphere are mixed and introduced into the preheater / evaporator 11. The air-fuel mixture introduced into the preheater / evaporator 11 is introduced into the reformer 12, and the hydrocarbon gas is steam-reformed in the reformer 12 to become a hydrogen-rich fuel gas. The reformed fuel gas is supplied to the fuel cell stack 10.

  The water supply unit WP is a part that supplies water to be steam used when steam reforming city gas, and is configured by elements such as a purifier, a water pump, a check valve, a flow sensor, and an electromagnetic valve. Yes. The water supplied by the water supply unit WP is introduced into the preheater / evaporator 11 to form steam, and then introduced into the reformer 12.

  The fuel gas and air supplied to the fuel cell stack 10 cause a power generation reaction in each fuel cell constituting the fuel cell stack 10 and can generate power. Although the form of the fuel cell is not particularly limited, for example, a cylindrical fuel cell is preferably used. A cylindrical fuel cell includes an electrolyte layer, and an inner electrode layer and an outer electrode layer that sandwich the electrolyte layer. The inner electrode layer is, for example, a mixture of Ni and zirconia doped with at least one selected from rare earth elements such as Ca, Y, and Sc, and Ni and ceria doped with at least one selected from rare earth elements. It is formed from at least one of a mixture, a mixture of Ni, and a lanthanum gallate doped with at least one selected from Sr, Mg, Co, Fe, and Cu. The electrolyte layer includes, for example, zirconia doped with at least one selected from rare earth elements such as Y and Sc, ceria doped with at least one selected from rare earth elements, and lanthanum gallate doped with at least one selected from Sr and Mg. It is formed from at least one kind. The outer electrode layer is, for example, selected from lanthanum manganite doped with at least one selected from Sr and Ca, lanthanum ferrite doped with at least one selected from Sr, Co, Ni and Cu, Sr, Fe, Ni and Cu And at least one kind of samarium cobalt doped with at least one kind, silver, and the like.

  The electricity generated in the fuel cell stack 10 is taken out from the power take-out part EP. The power extraction unit EP includes a power conversion device such as an inverter, and outputs the electricity generated in the fuel cell stack 10 to the outside as an AC output.

  Here, the relationship among the fuel cell unit control unit FS, the fuel cell module FCM, the air supply unit AP, the fuel supply unit FP, the water supply unit WP, and the power extraction unit EP will be described with reference to FIG. FIG. 2 is a block configuration diagram for explaining the relationship among the fuel cell unit control unit FS, the fuel cell module FCM, the air supply unit AP, the fuel supply unit FP, the water supply unit WP, and the power extraction unit EP. .

  As shown in FIG. 2, the fuel supply unit FP, the air supply unit AP, the water supply unit WP, and the power extraction unit EP constitute an auxiliary device AD of the fuel cell unit FCU. The fuel cell unit control unit FS is a part for controlling each of the fuel supply unit FP, the air supply unit AP, the auxiliary device AD, and the power extraction unit EP, and includes a CPU and a ROM. The operation of the fuel cell module FCM is executed based on an instruction signal from the fuel cell unit controller FS.

  Returning to FIG. 1, of the fuel gas and air supplied to the fuel cell stack 10, the remaining fuel gas and the remaining air that did not contribute to the power generation reaction are burned, and exhaust gas is generated. Heat is given to the reformer 12 and the air heat exchanger 13 by the combustion and exhaust gas. The exhaust gas is heated to the reformer 12 and the air heat exchanger 13, and is then discharged to the outside after the temperature is lowered to a sufficiently safe temperature through the exhaust gas heat recovery heat exchanger 72. The The exhaust gas heat recovery heat exchanger 72 is a heat exchanger for boiling hot water stored in the hot water storage unit WPU. Therefore, the exhaust gas heat recovery heat exchanger 72 corresponds to the heat exchanger of the present invention.

  Next, the hot water storage unit WPU will be described. The hot water storage unit WPU includes a hot water storage tank WT, a hot water heater HU as an auxiliary heat source, and a hot water storage unit control unit WS. The hot water storage unit WPU boils water stored in the hot water storage tank WT to store hot water, and supplies the stored hot water to the hot water tap CL and the bathtub BT through the water heater HU. More specifically, when hot water is sufficiently stored in the hot water storage tank WT, it is not heated by the hot water heater HU but is passed through the hot water heater HU as it is and supplied to the hot water tap CL or the bathtub BT. . When hot water is not sufficiently stored in the hot water storage tank WT, it is heated by the hot water heater HU and supplied to the hot water tap CL and the bathtub BT.

  Next, the piping configuration of the hot water storage unit WPU will be described. A pipe 61, a pipe 51, a pipe 52, a pipe 56, and a pipe 57 are connected to the hot water storage tank WT. With respect to the hot water storage tank WT, the pipeline 61, the pipeline 51, and the pipeline 52 are connected to the lower side, and the pipeline 56 and the pipeline 57 are connected to the upper side, respectively.

  The pipe 61 is a pipe for supplying water from the outside to the hot water storage tank WT. A check valve 80, a pressure reducing valve 81, a check valve 82, a vacuum breaker 83, and a stop cock 84 are provided on the upstream side of the conduit 61 when viewed from the hot water storage tank WT. With such a configuration, when hot water in the hot water storage tank WT is used, water is supplied from the lower side of the hot water storage tank WT.

  The pipe 51 is a pipe for sending the water in the hot water storage tank WT to the exhaust gas heat recovery heat exchanger 72. The pipe line 52 is a pipe line for draining water in the hot water storage tank WT. A drain valve 70 is provided in the pipe line 52. The pipeline 51 joins a pipeline 55 to be described later and is connected to the pipeline 53. The pipe line 53 includes a pipe line 53a in the hot water storage unit WPU and a pipe line 53b in the fuel cell unit FCU. The pipe 53a is provided with a pump 71 that feeds the water in the hot water storage tank WT to the exhaust gas heat recovery heat exchanger 72. The pipe line 53b is connected to a heat exchanger 72 for exhaust gas heat recovery.

  From the exhaust gas heat recovery heat exchanger 72, a conduit 54b is connected as a conduit on the outlet side. The pipe 54b is a pipe in the fuel cell unit FCU, and a pipe 54a in the hot water storage unit WPU is connected to the pipe 54b. The pipeline 54a and the pipeline 54b constitute a pipeline 54. The pipe line 54 (pipe line 54 a) is connected to the three-way valve 73.

  In addition to the pipe line 54 (pipe line 54a), a pipe line 55 and a pipe line 56 are connected to the three-way valve 73. The pipe 55 joins the pipe 51 and is connected to the pipe 53 as described above. Therefore, the conduit 53, the conduit 54, and the conduit 55 form a circulation conduit that passes through the heat exchanger 72 for exhaust gas heat recovery. The pipe 55 is provided with a radiator 74 so that the hot water passing through the pipe 55 can be dissipated.

  The pipe 56 is a pipe for supplying hot water to the hot water storage tank WT, and is connected above the hot water storage tank WT. The pipe 56 is provided with a pressure loss portion 56a. The pressure loss part 56 a is a part configured such that the pressure loss of the pipe line in the part where the pressure loss part 56 a is provided is higher than the pipe line 53, the pipe line 54, and the pipe line 55. The pressure loss portion 56a may be a throttle-like one whose pipe is narrowed, or may be provided with a valve body such as a check valve or a flow rate adjustment valve. Further, in the present embodiment, the pressure loss portion 56 a is provided in the pipeline 56, but it is also preferable to provide the pressure loss portion 56 a in the pipeline 51. It is also preferable to provide one for each of the pipeline 56 and the pipeline 51. The pipe 57 is a pipe for supplying hot water from the hot water storage tank WT, and is connected above the hot water storage tank WT. The pipe 57 is connected to a mixing valve 76, and is provided with a check valve 79 and a hot water storage amount sensor 75. A pipe 59 branched from the pipe 61 is connected to the mixing valve 76. The mixing valve 76 mixes the hot water supplied from the pipe 57 and the water supplied from the pipe 59 and sends them to the pipe 58. The pipe line 58 is connected to the water heater HU. A water supply amount sensor 77 is provided in the pipeline 59.

  Next, the arrangement of the thermistor as a temperature measuring unit provided in each pipe line and hot water storage tank WT will be described. The hot water storage tank WT is provided with a thermistor 31, a thermistor 32, and a thermistor 33 in order from above. The thermistor 40 is provided in the pipe line 57. These thermistors 31, 32, 33, and 40 are thermistors for measuring the amount of hot water stored in the hot water storage tank WT. In the case of the present embodiment, the hot water storage tank WT has a configuration in which hot water is accumulated upward and water is accumulated downward. Therefore, the hot water storage amount can be grasped by the temperature of the thermistor.

  A thermistor 36 is provided in the pipe line 53 a of the pipe line 53. With this thermistor 36, it can be determined whether the hot water that is sufficiently heated or the water that has flowed out of the hot water storage tank WT is flowing through the pipe line 53, and a heat exchanger for exhaust gas heat recovery. The temperature of the water sent to 72 can also be measured. The thermistor 37 is provided in the pipeline 54b of the pipeline 54 in the fuel cell unit FCU, and the thermistor 34 and the thermistor 38 are provided in the pipeline 54a. That is, the thermistor 37 is provided on the side of the heat exchanger 72 for exhaust gas heat recovery of the pipe line 54, and the thermistor 34 and the thermistor 38 are provided on the three-way valve 73 side of the pipe line 54. The thermistor 37 can measure the temperature of hot water immediately after being heated by the exhaust gas heat recovery heat exchanger 72, and the thermistor 34 and the thermistor 38 can measure the temperature of hot water immediately before entering the three-way valve 73.

  A thermistor 39 is provided in the pipeline 56. The thermistor 39 is provided in the vicinity of the portion connected to the hot water storage tank WT, and can measure the temperature of the hot water introduced into the hot water storage tank WT.

  Next, the hot water storage unit control unit WS will be described with reference to FIG. FIG. 3 is a block configuration diagram for explaining functions of the hot water storage unit control unit WS. As shown in FIG. 3, the hot water storage unit control unit WS receives a signal indicating the temperature measurement value output from the thermistors 31, 32, 33, 34, 36, 37, 38, 39, 40, and stores the hot water storage amount sensor. 75 and the feed water amount sensor 77 receive signals indicating the amount of water that has passed through the respective portions. The hot water storage unit control unit WS outputs a control signal for driving the pump 71, the three-way valve 73, and the mixing valve 76 based on information processing based on those input signals or information processing based on a predetermined routine. To do. As described above, the hot water storage unit control unit WS is a part for controlling each of the pump 71, the three-way valve 73, and the mixing valve 76, and includes a CPU and a ROM. The operation of the hot water storage unit WPU is executed based on an instruction signal from the hot water storage unit control unit WS.

  This fuel cell system FCS includes, as constituent elements, a fuel cell module FCM including a plurality of solid oxide fuel cells that are operated by fuel gas and oxidant gas, and a fuel gas and oxidant gas that are burned by burning the fuel gas and oxidant gas. Heat exchange is performed using the exhaust gas discharged from the battery module FCM, and the heat exchanger 72 for exhaust gas heat recovery, which is a heat exchanger that heats water to make hot water, water and hot water that heats the water A hot water storage tank WT which is a tank to be stored.

  Further, this fuel cell system FCS includes the following pipe lines as pipes through which water and hot water pass. First, the pipe 53 (the pipes 53a and 53a) is a first pipe configured such that the water sent to the exhaust gas heat recovery heat exchanger 72 reaches the exhaust gas heat recovery heat exchanger 72 again. A pipe line 53b), a pipe line 54 (the pipe line 54a and the pipe line 54b), and a pipe line 55. Further, the water sent from the hot water storage tank WT is sent to the exhaust gas heat recovery heat exchanger 72, and the hot water exchanged in the exhaust gas heat recovery heat exchanger 72 is returned to the hot water storage tank WT. The pipe 51, the pipe 53 (the pipe 53a and the pipe 53b), the pipe 54 (the pipe 54a and the pipe 54b), and the pipe 56 are provided as the second pipe.

  Accordingly, the pipeline 53 (the pipeline 53a and the pipeline 53b) and the pipeline 54 (the pipeline 54a and the pipeline 54b) are configured as a shared pipeline section of the first pipeline and the second pipeline. Further, the pipeline 51 is configured as a supply pipeline section, and the pipeline 56 is configured as a reflux pipeline section. Further, the pipe line 55 is configured as a circulation pipe part.

  Further, the fuel cell system FCS includes a three-way valve 73 as a switching unit that switches a pipeline between a pipeline 55 that is a circulation pipeline and a pipeline 56 that is a reflux pipeline. The fuel cell system FCS further includes a pump 71 disposed in the pipe line 53 so as to generate the water flow of the first pipe line and the second pipe line described above. The fuel cell system FCS further includes a three-way valve 73 as a switching unit and a hot water storage unit control unit WS as a control unit that controls the pump 71.

  With such a configuration, when the operation of the fuel cell unit FCU is started, the water sent to the exhaust gas heat recovery heat exchanger 72 reaches the exhaust gas heat recovery heat exchanger 72 again. In the first pipeline, the pipeline 53 (the pipeline 53a and the pipeline 53b), the pipeline 54 (the pipeline 54a and the pipeline 54b), the pipeline 55, and the first pipeline A certain pipe line 53 (pipe line 53a and pipe line 53b), a pipe line 54 (pipe line 54a and pipe line 54b), and a pipe line which is a reflux pipe line part for refluxing hot water flowing through the pipe line 55 to the hot water storage tank WT. 56, it can comprise so that the 2nd pipe line which consists of the pipe line 51 which is a supply pipe line part may be provided. Therefore, heat exchange for exhaust gas heat recovery is performed by circulating the pipes 53 (the pipes 53a and 53b), the pipes 54 (the pipes 54a and 54b), and the pipes 55, which are the first pipes. A sufficient amount of heat can be obtained from the vessel 72, and the water can be heated to a desired temperature.

  In particular, when a solid oxide fuel cell is used as in the present embodiment, such a configuration is more effective. A solid oxide fuel cell has good power generation efficiency, and therefore consumes less fuel and has a high exhaust gas temperature of 200 to 400 ° C. However, since the amount of exhaust gas is small, the amount of heat of the exhaust gas itself is small. Therefore, a large amount of hot water cannot be immediately boiled and stored by heat exchange with exhaust gas, and it is necessary to store a small amount of hot water little by little. Therefore, as in the present embodiment, while boiling water at the start of operation of the fuel cell unit FCU, the pipes 53 (the pipes 53a and 53b) and the pipes 54 (the pipes 54a and 54a) are the first pipes. When the pipe 54b) and the pipe 55 are flown, and the water is springed up, the pipe is switched to the pipe 56 which is a reflux pipe section, and hot water can be fed into the hot water storage tank WT.

  Moreover, since the pressure loss part 56a is provided in the pipe line 56, there is no part which produces pressure loss in the part which comprises a 1st pipe line, and pressure loss is only given to the part which comprises a 2nd pipe line. It is comprised so that the part to produce may exist. Therefore, if the pump is driven in a state where the three-way valve 73 serving as the switching unit is switched to the pipeline 55 serving as the circulation pipeline of the first pipeline, the pressure loss does not increase more than necessary, and the pump 71 is driven. A water flow corresponding to the speed is generated, and the heat of the exhaust gas from the fuel cell module FCM can be appropriately taken. On the other hand, when the pump 71 is driven in a state where the three-way valve 73 serving as the switching unit is switched to the pipeline 56 serving as the reflux pipeline of the second pipeline, the pressure loss due to the pressure loss 56a is greater than that of the first pipeline. Since it is raised, the flow velocity of the water flow is lower than when the pressure loss portion 56a is not provided. Therefore, the exhaust gas heat recovery heat exchanger 72 can effectively receive the heat of the exhaust gas to boil the hot water.

  According to the fuel cell system FCS as described above, the following suitable operation control can be performed. FIG. 4 shows a flowchart for explaining this control routine. In the example shown in FIG. 4, the water temperature is input from the thermistor 36 to the hot water storage unit controller WS (step S01).

  Subsequently, the hot water storage unit control unit WS determines whether or not the water temperature input from the thermistor 36 is high (step S02). If the temperature of the water input from the thermistor 36 is high, the hot water storage tank WT is filled with boiled hot water, and if it is not high, water enters at least below the hot water storage tank WT. It is judged that Therefore, if the water temperature input from the thermistor 36 is not high, the hot water storage unit control unit WS returns to the process of step S01. On the other hand, if the water temperature input from the thermistor 36 is high, the process proceeds to step S03.

  If the water temperature input from the thermistor 36 is high, the hot water storage unit control unit WS is the first pipeline from the side of the pipeline 56 that is the second pipeline to the three-way valve 73 that is the switching unit. An instruction signal is output so that the pipeline is switched to the pipeline 55 side (step S03). In this case, the hot water storage unit control unit WS also preferably increases the drive speed of the pump 71.

  If such control is performed, the water is circulated to form the pipe 53 (the pipe 53a and the pipe 53b), the pipe 54 (the pipe 54a and the pipe 54b), and the pipe 55 which are in the first pipe. Can be appropriately switched between circulating the water and switching to the pipeline 56, which is the reflux pipeline section, to reflux the hot water storage tank WT. Since this switching is made based on the water temperature measured by the thermistor 36 which is a temperature measuring unit, if the hot water boiled up in the hot water storage tank WT is not filled, it is switched to the pipeline 56 side. A water flow is generated according to the rotation of the pump 71, and hot water is sent to the hot water storage tank WT. Since the pressure loss portion 56a is provided in the pipe 56, the flow velocity is lower than that when the pipe 56 is switched to the pipe 55, and the heat exchange in the exhaust gas heat recovery heat exchanger 72 is sufficiently performed. Yes, hot water is heated efficiently. On the other hand, if the hot water boiled in the hot water storage tank WT is filled, the hot water is switched to the pipe 55 side, and the hot water is discharged via the radiator 74 as the temperature of the pump 71 is reduced. It is sent to the heat exchanger 72 for gas heat recovery. Since the flow velocity increases compared with the case where the pipe 56 is switched, the radiator 74 effectively dissipates heat, and as a result, the exhaust gas heat recovery heat exchanger 72 effectively reduces the heat of the exhaust gas. Can be taken away.

  As in this embodiment, the first pipe and the second pipe are configured such that the flow velocity differs depending on the difference in the pipe configuration (the presence or absence of a pressure loss part), so that only one pump 71 is provided. Even if it exists, the flow rate variable range can be changed for each pipe line, which is also effective in pump selection.

It is a figure which shows the fuel cell system which concerns on this embodiment. It is a block block diagram which shows the control structure of the fuel cell unit shown in FIG. It is a block block diagram which shows the control structure of the hot water storage unit shown in FIG. It is a flowchart which shows an example of the control routine of the fuel cell system which concerns on this embodiment.

Explanation of symbols

10: Fuel cell stack 11: Preheating / evaporator 12: Reformer 13: Air heat exchangers 14, 31, 32, 33, 34, 36, 37, 38, 39, 40: Thermistors 51, 52, 53 53a, 53b, 54, 54a, 54b, 55, 56, 57, 58, 59, 61: Pipe 70: Drain valve 71: Pump 72: Heat exchanger 73 for exhaust gas heat recovery 73: Three-way valve 74: Radiator 75 : Hot water storage amount sensor 76: Mixing valve 77: Water supply amount sensor 79: Check valve 80: Check valve 81: Pressure reducing valve 82: Check valve 83: Vacuum breaker 84: Stopcock AD: Auxiliary device AP: Air supply section BT: Bathtub CL: Hot water tap EP: Electric power take-out unit FCM: Fuel cell module FCS: Fuel cell system FCU: Fuel cell unit FP: Fuel supply unit FS: Fuel cell unit control unit HU: Water heater P: Water supply unit WPU: hot-water storage unit WS: hot water storage unit controller WT: hot water tank

Claims (1)

A fuel cell module including a plurality of solid oxide fuel cells operated by a fuel gas and an oxidant gas;
In the solid oxide fuel cell, heat is exchanged using the exhaust gas including the gas generated by the combustion of the remaining fuel gas that did not contribute to the power generation reaction and the remaining oxidant gas, and heats the water Heat exchanger to make hot water,
A tank for storing water and hot water for heating the water;
A first conduit configured such that water sent to the heat exchanger reaches the heat exchanger again;
A second pipe configured to send water sent from the tank to the heat exchanger, and to return the hot water heat-exchanged in the heat exchanger to the tank;
A fuel cell system comprising: a pump for generating a water flow in the first pipeline and the second pipeline,
The first pipeline and the second pipeline have a shared pipeline section that shares a part of each,
The second pipe, together with the shared pipe section, supplies a water pipe fed from the tank to the shared pipe section, and returns hot water from the shared pipe section to the tank. A reflux conduit section to be
The first pipe line includes, together with the shared pipe line part, a merging point where the supply pipe line part is connected to the shared pipe line part and a branch point where the reflux pipe line part branches from the shared pipe line part. It has a circulation line part that connects,
The branching point is provided with a switching unit for switching the pipeline between the reflux pipeline and the circulation pipeline,
At least one of the supply line part and the reflux line part is provided with a pressure loss part so that the pressure loss of the line is higher than that of the first line,
The switching unit is switched to the circulation pipeline unit side, and the flow rate flowing through the first pipeline by the water flow generated by the pump is more than
The fuel cell system is characterized in that the switching unit is switched to the reflux pipeline unit side, and the flow rate flowing through the second pipeline is reduced by the water flow generated by the pump.

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