JP5025929B2 - Fuel cell power generation system - Google Patents

Description

  The present invention relates to a fuel cell power generation system, and more particularly to a fuel cell power generation system in which a reduction in exhaust heat recovery efficiency is suppressed.

  With the recent increase in awareness of global environmental conservation, fuel cell systems that generate electricity with fuel cells that contribute to the prevention of global warming are attracting attention. A fuel cell is a device that generates electricity by an electrochemical reaction between hydrogen and oxygen. Since this electrochemical reaction is an exothermic reaction, a fuel cell system is generally equipped with a hot water storage tank to effectively use this heat. In many cases, the system is configured. Heat generated from the fuel cell is lost to the stack cooling water, and the temperature of the stack cooling water whose temperature has risen is lowered by heat exchange with the exhaust heat recovery hot water and the heat exchanger, and is used again for cooling the fuel cell. On the other hand, the exhaust heat recovery hot water that has exchanged heat with the stack cooling water is guided to the hot water storage tank to be stored, and used according to the heat demand.

  The exhaust heat recovery warm water is heated by the stack cooling water that has taken heat from the fuel cell. During this heating, the air dissolved in the exhaust heat recovery warm water is released, and air pools are likely to occur in the pipe. For this reason, by supplying exhaust heat recovery hot water to the heat exchanger so that it flows upward from below, it is common to remove the air pocket generated in the pipe together with the flow of exhaust heat recovery hot water and lead it to the hot water storage tank. is there. On the other hand, the heat exchanger used for heat exchange between the stack cooling water and the exhaust heat recovery hot water is configured such that the stack cooling water and the exhaust heat recovery hot water flow in a counterflow to improve heat exchange efficiency. Preferably it is. When the exhaust heat recovery hot water flows from the lower side to the upper side and the stack cooling water flows in the opposite flow, the stack cooling water flows from the upper side to the lower side of the heat exchanger.

  However, the stack cooling water is often in a state in which nitrogen, oxygen, or carbon dioxide is dissolved, and gas may be generated from the stack cooling water. As described above, if the stack cooling water is passed through the heat exchanger from the upper side to the lower side, a gas pool is generated in the upper part of the heat exchanger. When a gas pool is generated in the heat exchanger, the portion in contact with the gas does not contribute to the heat exchange. As a result, the heat transfer area is reduced, and the temperature balance in the system is lost. In addition, it is difficult to directly recognize that a gas pool is generated in the heat exchanger, and excessive incidental facilities are required to recognize it.

  In view of the above-described problems, an object of the present invention is to provide a fuel cell power generation system that suppresses reduction in exhaust heat recovery efficiency without requiring an excessive incidental facility.

In order to achieve the above object, a fuel cell power generation system according to the invention described in claim 1 includes a reformed gas g containing hydrogen and an oxidant gas t containing oxygen as shown in FIG. A fuel cell 10 that generates electricity and generates heat; a cooling water c that takes away heat generated in the fuel cell 10 and a heat recovery water h that takes heat away from the cooling water c; and the cooling water c and the heat recovery water h The heat exchanger 36 for deriving the cooling water c and the heat recovery water h after heat exchange by flowing in a counter flow; and the temperature of the cooling water c introduced into the heat exchanger 36 and the heat exchanger 36 Temperature difference detection means 63 for detecting the temperature difference between the temperature of the heat recovery water h or the temperature difference between the temperature of the heat recovery water h introduced into the heat exchanger 36 and the temperature of the cooling water c derived from the heat exchanger 36. 65, 64, 66; the temperature detected by the temperature difference detection means 63, 65, 64, 66 Difference and a control unit 60 for controlling so when a predetermined condition is satisfied, the flow rate of the cooling water c flowing through the heat exchanger 36 is increased. The heat exchanger 36 introduces the cooling water c from the upper part, flows from the upper part to the lower part and is derived from the lower part, introduces the heat recovery water h from the lower part, flows from the lower part to the upper part, and derives from the upper part. The predetermined condition is that when the detected temperature difference is equal to or greater than the predetermined temperature difference, the first predetermined time is added to the accumulated time, the detected temperature difference is less than the predetermined temperature difference, the accumulated time is 0 and negative. When the first predetermined time is not subtracted from the accumulated time, the accumulated time reaches the second predetermined time. The cooling water c flowing through the heat exchanger 36 flows according to gravity. “According to gravity” refers to the relationship between the height of the inlet / outlet of the fluid flowing through the heat exchanger, which means that the position of the inlet is above the position of the outlet. It does not mean that the external force is not received.

  If comprised in this way, when the temperature difference detected with the temperature difference detection means satisfy | fills predetermined conditions, the flow volume of the direction which flows according to gravity among the cooling water which flows through a heat exchanger, or heat recovery water will increase. Therefore, when the predetermined condition of the temperature difference is due to a decrease in the amount of heat transfer associated with the occurrence of gas accumulation in the heat exchanger, the flow volume flowing according to gravity can be increased to remove the gas accumulation. it can.

As described above, the fuel cell power generation system according to the first aspect of the present invention, for example, as shown in FIG. 1, the heat exchanger 36 has a cooling water c is configured to flow by gravity.

  If constituted in this way, it will flow against the gravity heat recovery water which is easy to generate gas contrary to flowing cooling water according to gravity, and the quantity of the gas which stays in a heat exchanger decreases. A decrease in heat transfer area can be suppressed, and a decrease in exhaust heat recovery efficiency can be suppressed. Here, “against gravity” refers to the relationship between the height of the inlet and outlet of the fluid flowing through the heat exchanger, and means that the outlet position is above the inlet position. It does not mean that it does not receive external force such as mechanical force.

In addition, the fuel cell power generation system according to the invention described in claim 3 is the fuel cell power generation system 1 according to claim 1 or 2, as shown in FIG. 1, for example. A cooling water flow path 83 that introduces and leads out and introduces and discharges the cooling water c to and from the heat exchanger 36; a cooling water flow path 83 upstream of the fuel cell 10 and downstream of the heat exchanger 36; a cooling water pump 43 that circulates c; and gas venting means 58, 88, 59, 89 disposed in at least one cooling water flow path 83 upstream of the cooling water pump 43 and downstream of the cooling water pump 43. Prepare.

  If comprised in this way, the gas removed from the heat exchanger by the increase in the flow rate can be removed from the inside of the cooling water flow path, and the reduction of exhaust heat recovery efficiency can be suppressed and the cavitation of the cooling water pump can be prevented. can do.

As described above, the fuel cell power generation system according to the first aspect of the present invention, for example, as shown in FIGS. 1 and 2, the control device 60, the first temperature difference detecting means 63 every predetermined time, The temperature difference is detected by 65 (S1), and when the detected temperature difference is equal to or greater than the predetermined temperature difference , the first predetermined time is added to the accumulated time (S4), and the detected temperature difference is the predetermined temperature. The first predetermined time is subtracted from the integration time when the integration time is less than 0 and the negative value is not a negative value (S5, S6), and when the integration time reaches the second predetermined time, the cooling water c The flow rate is increased (S8).

  If comprised in this way, the presence of the gas which generate | occur | produces and retains in a heat exchanger without requiring an excessive incidental installation can be recognized, and the gas in a heat exchanger can be removed at an appropriate timing.

  According to the fuel cell power generation system of the present invention, the cooling water flowing through the heat exchanger or the heat recovery water flowing according to gravity when the temperature difference detected by the temperature difference detecting means satisfies a predetermined condition. Therefore, if the predetermined condition of the temperature difference is due to a decrease in the amount of heat transfer caused by the accumulation of gas in the heat exchanger, the flow rate of the gas flowing in accordance with gravity is increased. The pool can be removed.

Embodiments of the present invention will be described below with reference to the drawings. In each drawing, the same or corresponding members are denoted by the same or similar reference numerals, and redundant description is omitted. In FIG. 1, a broken line represents a control signal.
FIG. 1 is a system diagram illustrating a fuel cell power generation system 1 according to an embodiment of the present invention. The fuel cell power generation system 1 includes a “cooling water” in order to facilitate the distinction between the fuel cell 10, the reformer 20, the three-fluid heat exchanger 31, and the heat exchanger 36 (the three-fluid heat exchanger 31. A heat exchanger 36 ”, a hot water storage tank 41, a cooling water pump 43, a heat recovery water pump 44, and a control device 60.

  The fuel cell 10 introduces the reformed gas g and the oxidant gas t, and generates water and heat by generating electricity through an electrochemical reaction between hydrogen in the reformed gas g and oxygen in the oxidant gas t. Device. The fuel cell 10 is typically a polymer electrolyte fuel cell. The fuel cell 10 includes an anode part 11 for introducing a reformed gas g, a cathode part 12 for introducing an oxidant gas t, and a cooling part 13 for removing heat generated by an electrochemical reaction. . Although the fuel cell 10 is illustrated in a simplified manner in FIG. 1, typically, a single layer is formed by sandwiching a solid polymer film between an anode portion 11 and a cathode portion 12, and this is formed by stacking multiple layers. ing. An anode exhaust gas p containing hydrogen that was not used for the electrochemical reaction in the fuel cell 10 is discharged from the anode portion 11, and a cathode exhaust gas containing oxygen that was not used for the electrochemical reaction in the fuel cell 10 from the cathode portion 12. q is configured to be discharged.

  The reformer 20 introduces raw material fuel r and process water s such as city gas, LPG, digestion gas, methanol, GTL (Gas to Liquid) and kerosene, and reforms the raw material fuel r to improve the hydrogen. It is an apparatus for producing a quality gas g. The reformed gas g rich in hydrogen is a gas supplied to the fuel cell 10 containing hydrogen in an amount of 40% by volume or more, typically about 70 to 80% by volume. The hydrogen concentration in the reformed gas g may be 80% by volume or more, that is, any concentration that allows power generation by an electrochemical reaction with oxygen in the oxidant gas t when supplied to the fuel cell 10. The reformer 20 has a reforming catalyst packed bed and is configured to promote the reforming reaction. Since the steam reforming reaction for reforming the raw material fuel r is an endothermic reaction, the reformer 20 has a reforming heat generator 21 for obtaining reforming heat necessary for reforming. The reforming heat generator 21 typically has a burner, and is configured to be able to obtain reforming heat by burning fuel. As the fuel burned by the reforming heat generator 21, the raw material fuel r and the anode exhaust gas p are used. The reforming heat generator 21 is connected to a combustion exhaust gas line 21e that exhausts exhaust gas after burning the fuel.

  The three-fluid heat exchanger 31 exchanges heat between the stack cooling water c and the oxidant gas t, and further exchanges heat between the stack cooling water c and the reformed gas g derived from the reformer 20. A heat exchanger and a multi-tubular heat exchanger is preferably used. More preferably, a multi-tube heat exchanger having a pipe provided with fins is used for the flow path between the oxidizing gas t and the reformed gas g. Alternatively, a triple tube heat exchanger is also preferably used.

  The cooling water heat exchanger 36 is a device that exchanges heat between the stack cooling water c that has deprived of the heat generated in the fuel cell 10 and the heat recovery water h at a lower temperature in the hot water storage tank 41. A plate heat exchanger is preferably used. The cooling water heat exchanger 36 is formed by laminating a plurality of plates having heat transfer surfaces formed in a wave shape, and is configured to alternately flow the stack cooling water c and the heat recovery water h for each layer. . In FIG. 1, for convenience, the stack cooling water c and the heat recovery water h are shown to pass between the upper surface and the bottom surface of the cooling water heat exchanger 36, but actually, the cooling water heat exchanger 36 is The stack cooling water c flows from the upper side surface, flows through the cooling water forward passage hole formed in the upper part of the inside, and is distributed to every other plate communicating with the cooling water forward passage hole, and flows through each plate downward from the upper side. Then, after gathering in the cooling water return passage hole formed in the lower part of the interior, it flows out from the lower side surface. Further, the cooling water heat exchanger 36 is provided with every other plate in which the heat recovery water h flows from the lower side surface and flows through the heat recovery water forward hole formed in the lower part of the interior and communicates with the heat recovery water forward hole. It is configured to flow out from the upper side surface after flowing through the plates from below to gather in the heat recovery water return passage holes formed in the upper part of the interior. That is, the cooling water heat exchanger 36 is configured to flow the stack cooling water c and the heat recovery water h in a counter flow, and typically heat that is likely to generate dissolved air by heating. The recovered water h is flowed from below to above, and the stack cooling water c is flowed from above to below. The cooling water heat exchanger 36 cools the stack cooling water c and heats the heat recovery water h.

  The hot water storage tank 41 is a tank for storing the heat recovery water h recovered from the heat by the cooling water heat exchanger 36. The heat recovery water h stored in the hot water storage tank 41 has a higher temperature in the upper part than in the lower part. The hot water storage tank 41 derives the heat recovery water h stored in the lower part toward the cooling water heat exchanger 36 and recovers the heat generated in the fuel cell 10 by the cooling water heat exchanger 36 to increase the temperature. The heat recovery water h is introduced into the upper part so that the heat can be recovered and stored. The hot water storage tank 41 is connected to a hot water outlet pipe 87 for deriving the hot water w toward the heat demand (heat load) such as hot water supply and heating at the upper part, and the hot water w returned from the heat demand is introduced to the lower part. A hot water return pipe 86 is connected.

  A reformed gas line 81 for introducing the reformed gas g generated by the reformer 20 and an anode exhaust gas line 91 for discharging the anode exhaust gas p are connected to the anode portion 11 of the fuel cell 10. The quality gas line 81 is connected to the reformer 20 via the three-fluid heat exchanger 31, and the anode exhaust gas line 91 is connected to the reforming heat generator 21 of the reformer 20. A reformed gas three-way valve 51 serving as a branch point is disposed in the reformed gas line 81 on the downstream side of the three-fluid heat exchanger 31. The branch port of the reformed gas three-way valve 51 and the anode exhaust gas line 91 are connected by a reformed gas bypass line 81B. The reformed gas three-way valve 51 receives a signal from the control device 60 and continues to pass the reformed gas g flowing from the three-fluid heat exchanger 31 through the reformed gas line 81 or the reformed gas bypass line. It is comprised so that it can switch whether 81B is flowed. An anode shut-off valve 52 is disposed in the anode exhaust gas line 91 upstream from the junction with the reformed gas bypass line 81B. The anode cutoff valve 52 is configured to receive a signal from the control device 60 and to open and close.

  An air line 82 for introducing the stack air t as an oxidant gas and a cathode exhaust gas line 92 for discharging the cathode exhaust gas q are connected to the cathode portion 12. The air line 82 connects the three-fluid heat exchanger 31. The cathode exhaust gas line 92 is open to the outside of the system. In the air line 82 on the downstream side of the three-fluid heat exchanger 31, an oxidant gas three-way valve 53 serving as a branch point is disposed. The branch port of the oxidant gas three-way valve 53 and the cathode exhaust gas line 92 are connected by an air bypass line 82B. The oxidant gas three-way valve 53 receives the signal from the control device 60 and determines whether the stack air t flowing from the three-fluid heat exchanger 31 continues to flow through the air line 82 or the air bypass line 82B. It is configured so that it can be switched. A cathode shut-off valve 54 is disposed in the cathode exhaust gas line 92 upstream from the junction with the air bypass line 82B. The cathode cutoff valve 54 is configured to receive a signal from the control device 60 and to open and close.

  The cooling unit 13 is connected to a cooling water line 83 through which the stack cooling water c that takes heat generated in the fuel cell 10 is flowed. The cooling water line 83 supplies the stack cooling water c to the cooling unit 13, a cooling water heat exchanger. 36, a circulation flow path is formed which flows through the three-fluid heat exchanger 31 in this order and returns to the cooling unit 13 again. That is, the cooling water heat exchanger 36 and the three-fluid heat exchanger 31 are disposed in the cooling water line 83 that exits from the cooling unit 13 and returns to the cooling unit 13. A cooling water line 43 between the cooling water heat exchanger 36 and the three-fluid heat exchanger 31 is provided with a cooling water pump 43 that circulates the stack cooling water c. The cooling water pump 43 is configured to receive a signal from the control device 60 and adjust the flow rate of the circulating stack cooling water c by changing the rotation speed. A suction deaeration pipe 88 is branched from the cooling water line 83 between the cooling water pump 43 and the cooling water heat exchanger 36, and air existing in the cooling water line 83 is discharged to the tip of the suction deaeration pipe 88. An air vent valve 58 is provided. The suction deaeration pipe 88 and the air vent valve 58 constitute gas venting means. The air vent valve 58 has a floating ball inserted in a casing in which a vent is formed in the upper part. When the casing is full of water, the floating ball rises by buoyancy and closes the vent to prevent water leakage. When the gas flows into the gas, the floating ball descends so that the gas is discharged from the vent hole. Further, instead of the air vent valve 58 or together with the air vent valve 58, the delivery deaeration pipe 89 is branched from the cooling water line 83 between the cooling water pump 43 and the three-fluid heat exchanger 31, and the delivery deaeration pipe 89 The air vent valve 59 may be provided first. The delivery deaeration pipe 89 and the air vent valve 59 are also gas venting means. The air vent valve 59 is configured in the same manner as the air vent valve 58.

  A makeup water line 93 is connected to the cooling water line 83 between the cooling water heat exchanger 36 and the suction deaeration pipe 88. A makeup water cutoff valve 55 is disposed in the makeup water line 93. The makeup water cutoff valve 55 is configured to receive a signal from the control device 60 and to open and close. A pressure detector 61 that detects the pressure in the cooling water line 83 is installed in the cooling water line 83 between the cooling unit 13 and the cooling water heat exchanger 36. The pressure detected by the pressure detector 61 is transmitted as a signal to the control device 60, and is configured to be a basis for determining the opening / closing operation of the makeup water cutoff valve 55. In addition, a temperature detector 62 that detects the temperature of the stack cooling water c is disposed in the cooling water line 83 near the inlet of the cooling unit 13. As the temperature detector 62, a thermistor, a thermocouple, a resistance temperature sensor, or the like is used. The temperature detector 62 may be disposed in the cooling unit 13. In this case, the temperature of the stack cooling water c introduced into the cooling unit 13 can be detected. The temperature detector 62 may be disposed in the cooling water line 83 between the cooling water pump 43 and the three-fluid heat exchanger 31. The temperature detected by the temperature detector 62 is transmitted as a signal to the control device 60, and is configured to serve as a basis for determining the rotation speed of the heat recovery water pump 44.

  A heat recovery line 84 for flowing the heat recovery water h is connected to the hot water storage tank 41. The heat recovery line 84 forms a circulation channel that exits from the lower part of the hot water tank 41 and returns to the upper part of the hot water tank 41 via the cooling water heat exchanger 36. That is, the cooling water heat exchanger 36 is disposed in the heat recovery line 84. A heat recovery water pump 44 is disposed in the heat recovery line 84 from the hot water storage tank 41 to the cooling water heat exchanger 36. The heat recovery water pump 44 is configured to receive a signal from the control device 60 and adjust the flow rate of the heat recovery water h that circulates by changing the rotation speed.

  A temperature detector 63 that detects the temperature of the stack cooling water c is disposed in the cooling water line 83 on the inlet side of the stack cooling water c of the cooling water heat exchanger 36. Further, a temperature detector 65 that detects the temperature of the heat recovery water h is disposed in the heat recovery line 84 on the heat recovery water h outlet side of the cooling water heat exchanger 36. For the temperature detectors 63 and 65, a thermistor, a thermocouple, a resistance temperature sensor, or the like is used. The temperature detector 63 may be disposed in the cooling water heat exchanger 36 on the stack cooling water c inlet side, and the temperature detector 65 may be disposed in the cooling water heat exchanger 36 on the heat recovery water h outlet side. That is, it is only necessary to detect the temperature of the stack cooling water c entering the cooling water heat exchanger 36 and the temperature of the heat recovery water h exiting from the cooling water heat exchanger 36. The temperature detected by the temperature detectors 63 and 65 is transmitted to the control device 60 as a signal. Based on the temperature detected by the temperature detectors 63, 65, the temperature of the stack cooling water c entering the cooling water heat exchanger 36 and the temperature of the heat recovery water h exiting from the cooling water heat exchanger 36 are controlled by the control device 60. The temperature difference is calculated, and the temperature detectors 63 and 65 and the control device 60 constitute a temperature difference detection means. Further, the temperature signal detected by the temperature detector 63 is configured to be a basis for determining the rotation speed of the cooling water pump 43.

  The control device 60 receives the pressure signal and the temperature signal from the pressure detector 61 and the temperature detectors 62, 63, 65, and adjusts the rotation speed of the cooling water pump 43 and the heat recovery water pump 44 based on the received signals. Alternatively, the switching operation of the reformed gas three-way valve 51 and the oxidant gas three-way valve 53 and the opening / closing operation of the anode cutoff valve 52, the cathode cutoff valve 54, and the makeup water cutoff valve 55 can be performed. The control device 60 adjusts the amount of the reformed gas g generated in the reformer 20 and the flow rate of the reformed gas g introduced into the fuel cell 10, the stack air t, and the cooling water c, etc. The operation of the fuel cell power generation system 1 can be controlled by adjusting the electric power and the amount of heat stored in the hot water storage tank 41. Moreover, the control apparatus 60 is provided with the timer which can measure time. Further, the control device 60 is configured to perform various calculations based on the received pressure signal and temperature signal.

With continued reference to FIG. 1, the operation of the fuel cell power generation system 1 will be described.
When the operation of the fuel cell power generation system 1 is started, a part of the raw material fuel r is introduced into the reforming heat generator 21 and burned to generate reforming heat, and the raw material fuel r and the process are supplied to the reformer 20. Water s is introduced, the raw material fuel r is reformed in the reformer 20, and a reformed gas g is generated. The generated reformed gas g flows through the reformed gas line 81 toward the anode unit 11. Here, since the reforming reaction of the raw material fuel r in the reformer 20 is unstable when the fuel cell system 1 is started up, the reformed gas three-way valve 51 is set until the reformed gas g has a desired composition. Switching to the reformed gas bypass line 81B side, the reformed gas g is guided to the anode exhaust gas line 91 by bypassing the anode portion 11, and at the same time, the anode cutoff valve 52 is closed. The reformed gas g introduced to the anode exhaust gas line 91 is introduced into the reformed heat generator 21 and used as a combustion fuel. When the carbon monoxide concentration in the reformed gas g decreases to an extent that the fuel cell 10 can accept, the reformed gas three-way valve 51 is switched to guide the reformed gas g to the anode portion 11. Whether or not the composition of the reformed gas g has become a desired one may be detected by a concentration detector (not shown), or by measuring in advance the time during which the reformed gas g has the desired composition. Alternatively, the reformed gas three-way valve 51 may be switched after a predetermined time has elapsed since the start of the operation.

  On the other hand, the stack air t is sent into the air line 82 by a blower (not shown). During operation of the fuel cell system 1, the oxidant gas three-way valve 53 blocks communication with the air bypass line 82B, and the stack air t flowing through the air line 82 is humidified by a humidifier (not shown). Then, it is guided to the cathode portion 12. Further, the cooling water pump 43 is activated and the stack cooling water c passes through the inside of the cooling water line 83. The reformed gas g, the stack air t, and the stack cooling water c are made to have the same outlet temperature by flowing through the three-fluid heat exchanger 31 before being introduced into the fuel cell 10.

  In the fuel cell 10, electricity is generated by an electrochemical reaction between hydrogen in the reformed gas g introduced into the anode portion 11 and oxygen in the stack air t introduced into the cathode portion 12 to generate heat and water. To do. Hydrogen in the reformed gas g is consumed at the anode portion 11 as the fuel cell 10 generates power, but is operated at a constant utilization rate to prevent fuel shortage at the anode portion 11, and some hydrogen is discharged from the anode exhaust gas p. And discharged from the anode portion 11. On the other hand, oxygen in the stack air t is consumed as the fuel cell 10 generates power, and the stack air t after consumption of oxygen is discharged from the cathode portion 12 as cathode exhaust gas q. During the operation of the fuel cell system 1, the anode cutoff valve 52 and the cathode cutoff valve 54 are open. The anode exhaust gas p discharged from the anode section 11 is removed from excess moisture by a condenser (not shown), and then led to the reforming heat generator 21 to be used as fuel for combustion. The cathode exhaust gas q discharged from the cathode portion 12 is discharged to the atmosphere after excess moisture is removed by a condenser (not shown). The power generated by the fuel cell 10 is DC power, and this power is supplied to the power demand after being converted to AC power or as DC power.

  Further, the heat generated by the power generation is taken away from the fuel cell 10 by the stack cooling water c introduced into the cooling unit 13. The control device 60 changes the rotation speed of the cooling water pump 43 so that the temperature detected by the temperature detector 63 becomes a constant temperature. When the temperature detected by the temperature detector 63 is higher than a certain temperature, the rotation speed of the cooling water pump 43 is increased. Conversely, when the temperature is lower than the certain temperature, the rotation speed is decreased. Thus, the temperature of the fuel cell 10 is maintained at 70 to 100 ° C. by changing the flow rate of the stack cooling water c introduced into the cooling unit 13. In addition, the control device 60 detects the pressure in the cooling water line 83 with the pressure detector 61. When the pressure in the cooling water line 83 falls below a predetermined pressure, the replenishing water shut-off valve 55 is opened to open the cooling water. The makeup water is pumped to the line 83 by a makeup water pump (not shown), and when the predetermined pressure is recovered, the makeup water shutoff valve 55 is closed.

  The stack cooling water c whose temperature has been increased due to the removal of heat from the fuel cell 10 is cooled by heat exchange with the heat recovery water h in the cooling water heat exchanger 36. The heat recovery water h is sampled from the lower part of the hot water storage tank 41 when the heat recovery water pump 44 is activated, flows through the heat recovery line 84 and is introduced into the cooling water heat exchanger 36. The control device 60 changes the rotational speed of the heat recovery water pump 44 based on the temperature detected by the temperature detector 62. When the temperature detected by the temperature detector 62 is higher than the predetermined temperature, the rotational speed of the heat recovery water pump 44 is increased. Conversely, when the temperature is lower than the predetermined temperature, the rotational speed is decreased. In the cooling water heat exchanger 36, the stack cooling water c is introduced from above and led out from below, and the heat recovery water h is introduced from below and led out from above, and between the stack cooling water c and the heat recovery water h. In the counter flow, heat is exchanged efficiently. Further, since the heat recovery water h heated by the cooling water heat exchanger 36 is introduced into the cooling water heat exchanger 36 from below and led out from above, heat recovery water in which a gas such as dissolved oxygen is likely to be generated by heating. h flows against gravity, and even if a gas (generally having a lower density than water) is generated, it is discharged from the cooling water heat exchanger 36 along with the flow of the heat recovery water h.

  The heat recovery water h whose temperature has increased by exchanging heat with the stack cooling water c flows through the heat recovery line 84 and is returned to the upper part of the hot water storage tank 41. The heat recovery water h whose temperature has risen is returned to the hot water storage tank 41, so that the heat taken from the fuel cell 10 is stored in the hot water storage tank 41 as hot water. The hot water in the hot water storage tank 41 has a high temperature at the top and a low temperature at the bottom. The heat stored in the hot water storage tank 41 is consumed as hot water w by heat demand (not shown) such as hot water supply or heating. The hot water w sent to the heat demand is collected from the upper part of the heat storage tank 41 in which hot water having a high temperature is stored. On the other hand, when hot water is returned from the heat demand or when hot water is consumed due to the heat demand, the consumed water is introduced into the lower part of the hot water tank 41.

  By the way, during operation of the fuel cell power generation system 1, gas may be generated from the stack cooling water c. As the stack cooling water c, so-called ion-exchanged water in which impurities are removed to reduce electrical conductivity in order to suppress the discharge phenomenon in the cooling unit 13 is used. The cooling water line 83 is initially filled with pure water as the stack cooling water c, but when it is replenished after the operation of the fuel cell power generation system 1 is started, the water generated by the power generation of the fuel cell 10 is condensed. The material collected in (not shown) is reused, or tap water that has passed through an ion exchange resin layer is used. Tap water contains dissolved oxygen. The condenser (not shown) also includes condensed and recovered water that recovers the moisture contained in the anode exhaust gas p and the cathode exhaust gas q. The condensed and recovered water is nitrogen or oxygen that is a component of the stack air t, or reforming. Carbon dioxide contained in the gas g is dissolved. Therefore, various gases are dissolved in the stack cooling water c, and gas may be generated in the cooling water line 83.

  As described above, the stack cooling water c is introduced into the cooling water heat exchanger 36 from above and led out from below. When gas is generated in the cooling water line 83, the generated gas may appear as a gas pool above the cooling water heat exchanger 36. When a gas pool is generated above the cooling water heat exchanger 36, the portion in contact with the gas in the cooling water heat exchanger 36 does not contribute to heat exchange, and the heat transfer area in the cooling water heat exchanger 36 is reduced. Will be. The reduction of the heat transfer area in the cooling water heat exchanger 36 brings about a problem that the temperature balance of the fuel cell power generation system 1 is lost. On the other hand, it is difficult to recognize that a gas pool has occurred in the cooling water heat exchanger 36.

  As a result of intensive studies, the present inventors have found that the temperature difference between the stack cooling water c and the heat recovery water h, in which the generation of a gas pool in the cooling water heat exchanger 36 enters and exits the cooling water heat exchanger 36, The present inventors have found that there is a correlation and have completed the present invention. Therefore, hereinafter, the control for stably operating the fuel cell power generation system 1 by removing the gas accumulated in the cooling water heat exchanger 36 will be described with reference to FIG. 2 in addition to FIG.

  FIG. 2 is a flowchart for explaining the operation for correcting the collapse of the temperature balance of the fuel cell power generation system 1. The control device 60 detects the temperature of the stack cooling water c on the inlet side and the temperature of the heat recovery water h on the outlet side of the cooling water heat exchanger 36 at predetermined time intervals using the temperature detectors 63 and 65 (S1). The interval at which this temperature is detected is the first predetermined time. When the temperature detectors 63 and 65 detect each temperature, the control device 60 calculates a difference between the two temperatures (temperature difference) (S2). That is, the control device 60 calculates the temperature difference every first predetermined time. When the temperature difference is calculated, it is determined whether the temperature difference is equal to or greater than a predetermined temperature difference (S3). In addition, since the temperature difference is large compared with the time of steady operation for a while after starting of the fuel cell power generation system 1, it often becomes equal to or more than a predetermined temperature difference. Therefore, the step (S3) for determining whether or not the temperature difference is equal to or greater than the predetermined temperature difference is executed after a certain period of time (this is referred to as a third predetermined time), or once the temperature difference is equal to the predetermined temperature. It is better to execute after the difference becomes smaller.

  A step of determining whether or not the temperature difference is equal to or greater than a predetermined temperature difference (S3) is executed. If the temperature difference is equal to or greater than the predetermined temperature difference, the temperature detection interval (first predetermined time) is added to the integrated value (S4). ). The integrated value is 0 when the fuel cell power generation system 1 is started. On the other hand, if it is less than the predetermined temperature difference, it is determined whether or not the integrated value is 0 (S5). Here, the minimum value of the integrated value is set to 0 so that the integrated value does not become a negative value. In the step of determining whether or not the integrated value is 0 (S5), if the integrated value is 0, the process returns to the step of detecting the temperature with the temperature detectors 63 and 65 (S1). If the integrated value is not 0, the temperature detection interval (first predetermined time) is subtracted from the integrated value (S6). When the first predetermined time is subtracted from the integrated value, the process returns to the step (S1) in which the temperature detectors 63 and 65 detect the temperature again.

  When the step (S3) of determining whether or not the temperature difference is equal to or greater than the predetermined temperature difference is executed and the first predetermined time is added assuming that the temperature difference is equal to or greater than the predetermined temperature difference (S4), the integrated value is equal to the predetermined value. It is determined whether or not this is the case (S7). The predetermined time of the integrated value is the second predetermined time. If the integrated value is smaller than the predetermined value, the process returns to the step (S1) where the temperature detectors 63 and 65 detect the temperature again. On the other hand, if the integrated value is equal to or greater than the predetermined value, the control device 60 estimates that the gas transfer has occurred in the cooling water heat exchanger 36 on the cooling water line 83 side and the heat transfer area has decreased, and the cooling water The rotational speed of the pump 43 is increased, and the flow rate of the stack cooling water c flowing through the cooling water line 83 is increased (S8). The amount by which the stack cooling water c is increased varies depending on the equipment used, but may be any flow rate that can discharge the gas pool in the cooling water heat exchanger 36 on the cooling water line 83 side. Further, it is preferable to check how long the time is increased by performing a test operation in advance.

  When the flow rate of the stack cooling water c is increased, the gas pool generated in the cooling water heat exchanger 36 is pushed out to the stack cooling water c and flows through the cooling water line 83. When the gas pool reaches the branch of the suction deaeration pipe 88, a gas having a density lower than that of water passes through the suction deaeration pipe 88 branched from the upper part of the cooling water line 83 and reaches the air vent valve 58. Is discharged from the system. Note that the cooling water line 83 is a closed circuit and is pressurized with makeup water supplied from the makeup water line 93, and the suction side of the cooling water pump 43 is also at a positive pressure. Air does not enter the cooling water line 83 through the suction deaeration pipe 88. Thus, since gas is discharged | emitted by the suction side of the cooling water pump 43, the cavitation of the cooling water pump 43 can be prevented. The gas remaining without being removed by the air vent valve 58 is discharged from the delivery deaeration pipe 89 and the air vent valve 59 on the discharge side of the cooling water pump 43.

  The stack cooling water c flowing through the cooling water line 83 is increased to the extent that it is estimated that the gas pool has been discharged, and when completed, the flow rate of the stack cooling water c is returned to the flow rate during steady operation (S9). When the flow rate of the stack cooling water c is returned to the flow rate during steady operation, the flow returns to the step of detecting the temperature with the temperature detectors 63 and 65 (S1), and the same flow is repeated thereafter. The integrated value is reset when the fuel cell power generation system 1 is stopped.

  Although the fuel cell 10 has been described as a solid polymer fuel cell in the above description, it may be a fuel cell other than a solid polymer fuel cell such as a phosphoric acid fuel cell.

  In the above description, the discharge flow rate of the cooling water pump is controlled based on the temperature difference between the inlet temperature of the stack cooling water c to the cooling water heat exchanger 36 and the outlet temperature of the heat recovery water h. A temperature detector 64 for detecting the temperature of the stack cooling water c on the outlet side of the cooling water heat exchanger 36 is provided in place of the condenser 63, and the heat on the inlet side of the cooling water heat exchanger 36 is provided in place of the temperature detector 65. A temperature detector 66 for detecting the temperature of the recovered water h is provided, and the temperature detector 64 and the temperature detector 66 constitute a temperature difference detection means, and the outlet temperature and heat of the stack cooling water c with respect to the cooling water heat exchanger 36. The discharge flow rate of the cooling water pump may be controlled based on the temperature difference from the inlet temperature of the recovered water h.

  In the above description, the stack cooling water c is introduced into the cooling water heat exchanger 36 from above and led out from below, and the heat recovery water h is introduced from below and led out from above. , The stack cooling water c is introduced from below and led out from above, and the heat recovery water h is introduced from above and led out from below. Also good. In this case, it is preferable to increase the flow rate of the heat recovery water h when it is recognized from the temperature difference described above that a gas pool has occurred in the cooling water heat exchanger 36.

  FIG. 3 is a graph showing the temperature difference between the cooling water and the heat recovery water and the fluctuation of the flow rate of the cooling water pump in the example of the present invention. In FIG. 3, T63 represents the transition of the temperature of the stack cooling water c at the inlet of the cooling water heat exchanger 36 (typically the temperature detected by the temperature detector 63), and T65 represents the heat recovery at the outlet of the cooling water heat exchanger 36. The transition of the temperature of the water h (typically the temperature detected by the temperature detector 65) is shown. Qc indicates the transition of the flow rate of the stack cooling water c. FIG. 3 shows the transition Pc of the output of the cooling water pump 43 and the transition T62 of the temperature of the stack cooling water c at the inlet of the cooling unit 13 (typically the temperature detected by the temperature detector 62). In the example shown in the graph of FIG. 3, the first predetermined time is 1 second, the predetermined temperature difference ΔT (T63−T65) is 2 ° C., and the predetermined integrated value is 7200 seconds. That is, the temperature difference ΔT is calculated every second, and if the temperature difference ΔT is 2 ° C. or more, 1 second is added to the integrated value, and if it is less than 2 ° C., 1 second is subtracted unless the integrated value is 0, and the integrated value This was repeated until 7200 seconds were reached, and when 7200 seconds were reached, the flow rate of the stack cooling water c was increased by 2.5 to 3.3 times.

  According to FIG. 3, since the temperature difference ΔT exceeded 2 ° C. at 21:45, 1 second was added to the integrated value. The temperature difference ΔT was calculated and added / subtracted every second, and since the integrated value reached 7200 seconds after 23:35, the flow rate of the stack cooling water c was increased about three times. It took about 3-5 minutes for the flow rate to increase about 3 times. The gas reservoir was removed by increasing the flow rate of the stack cooling water c. In FIG. 3, the rapid decrease after the flow rate of the stack cooling water c once increases reflects that the gas is discharged. In addition, it can be seen from FIG. 3 that the heat transfer area in the cooling water heat exchanger 36 is restored by removing the gas reservoir, and the detected and calculated temperature difference ΔT is extremely small. That is, it is clear from FIG. 3 that by executing a series of controls, the output of the cooling water pump 43 is stabilized and the operation state of the fuel cell system 1 is recovered smoothly by eliminating the gas accumulation. It is.

1 is a system diagram illustrating a fuel cell power generation system according to an embodiment of the present invention. It is a flowchart explaining the driving | operation which corrects collapse of the temperature balance of the fuel cell power generation system which concerns on embodiment of this invention. It is a graph which shows the temperature difference of the cooling water and heat recovery water in the Example of this invention, and the fluctuation | variation of the flow volume of a cooling water pump.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell power generation system 10 Fuel cell 36 Heat exchanger 43 Cooling water pump 58, 59 Gas vent valve 60 Control apparatus 63, 64, 65, 66 Temperature detector 83 Cooling water flow path c Cooling water g Reformed gas h Heat recovery water t Oxidizing gas

Claims (3)

A fuel cell for generating heat by introducing a reformed gas containing hydrogen and an oxidant gas containing oxygen;
The cooling water that takes away the heat generated in the fuel cell is introduced from the upper part, the heat recovery water that takes heat from the cooling water is introduced from the lower part , the introduced cooling water flows from the upper part to the lower part, and the introduced heat the collected water to flow upward from below, after the said heat recovery water and the cooling water was heat exchange by flowing in countercurrent, the cooling water from the bottom, the heat recovery water from the top, derived respectively A heat exchanger;
The temperature difference between the temperature of the cooling water introduced into the heat exchanger and the temperature of the heat recovery water derived from the heat exchanger, or the temperature of the heat recovery water introduced into the heat exchanger and the heat exchanger A temperature difference detecting means for detecting a temperature difference from the temperature of the cooling water;
The temperature difference is detected by the temperature difference detection means every first predetermined time, and when the detected temperature difference is greater than or equal to a predetermined temperature difference, the first predetermined time is added to the accumulated time, When the detected temperature difference is less than a predetermined temperature difference and the integration time is not 0 or a negative value, the first predetermined time is subtracted from the integration time, and the integration time is a second predetermined time. wherein and a Ru controller increases the flow rate of the cooling water when it is;
Fuel cell power generation system. Before SL temperature difference detecting means, it is configured to detect the temperature difference between the temperature temperature of the cooling water and the heat recovery water derived from the heat exchanger to be introduced to the heat exchanger;
The fuel cell power generation system according to claim 1. A cooling water flow path for introducing and deriving the cooling water to the fuel cell, and introducing and deriving the cooling water to the heat exchanger;
A cooling water pump disposed in the cooling water flow path upstream of the fuel cell and downstream of the heat exchanger, and circulating the cooling water;
Degassing means disposed in at least one of the cooling water flow paths upstream of the cooling water pump and downstream of the cooling water pump;
The fuel cell power generation system according to claim 1 or 2.

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