JP2006032153A - Fuel cell cogeneration system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell cogeneration system having water independence, high exhaust heat recovery efficiency and a high system utilization rate. <P>SOLUTION: This fuel cell cogeneration system is provided with a hot-water storage tank 120 used for storing exhaust heat hot water 43a for executing heat exchange with cooling water 24a having cooled a fuel cell 30 and having a temperature sensor 124; an exhaust gas cooling heat exchanger 100 for executing heat exchange between an off-gas 63a discharged from the fuel cell 30 and the exhaust heat hot water 43a; and a water storage tank 70 used for recovering useful water 42a for humidifying an oxidizer gas 61a introduced into the fuel cell 30 from the off-gas 63a to store it and having a level sensor 132 for sensing the level of the useful water 42a. The fuel cell cogeneration system is so structured that the heat exchange between the off-gas 63a discharged from the fuel cell 30 and the exhaust heat hot water 43a is avoided when the temperature of the exhaust heat hot water 43a is above a predetermined temperature and the level of the water storage tank 70 is above a predetermined level. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell cogeneration system, and more particularly to a fuel cell cogeneration system having water independence, high exhaust heat recovery efficiency, and high system operation rate.

  The fuel cell cogeneration system introduces a fuel gas rich in hydrogen and an oxidant gas containing oxygen to generate electricity and generate heat and water through an electrochemical reaction between hydrogen in the fuel gas and oxygen in the oxidant gas. The system includes a fuel cell to be generated and a hot water storage tank that collects and stores heat generated during the electrochemical reaction of the fuel cell using hot water as a medium, and can simultaneously obtain electric power and heat. The heat generated in the fuel cell is cooled by the cooling water and stored in the hot water storage tank through hot water that exchanges heat with the cooling water. The exhaust heat from the fuel cell stored in the hot water storage tank is used for heat demand such as hot water supply and heating. Also, not all of the fuel gas and oxidant gas introduced into the fuel cell are used for the electrochemical reaction, and the fuel gas and oxidant gas that were not used for the reaction are mixed later and mixed as exhaust gas. Is discharged. The mixed exhaust gas discharged out of the system contains moisture generated in the fuel cell, and also includes a part of the heat generated in the fuel cell.

On the other hand, when the fuel cell is a polymer electrolyte fuel cell, it is necessary to humidify the oxidant gas to a humidity corresponding to a predetermined dew point in order to maintain high conductivity of the proton exchange membrane. The humidification of the oxidant gas is performed with water obtained by condensing and recovering moisture contained in the mixed exhaust gas. Further, the heat released from the mixed exhaust gas to condense moisture is used for heating moisture that humidifies the oxidant gas. In this way, the exhaust heat recovered from the fuel cell is supplied to heat demand such as hot water supply and heating, and the recovered water is used for humidifying the oxidant gas, thereby increasing the overall energy efficiency of the fuel cell cogeneration system. (For example, refer to Patent Document 1).
JP 2003-338304 A (FIG. 3 etc.)

  When the moisture recovered from the mixed exhaust gas is insufficient as the moisture used for humidifying the oxidant gas described above, water must be supplied from outside the system. When impurities are contained, the treatment load of the impurities increases, and the life of the water treatment apparatus for treating the impurities is shortened.

  On the other hand, there is room to recover the heat contained in the mixed exhaust gas even after raising the temperature of the recovered water that humidifies the oxidant gas. By recovering as much heat as possible from the mixed exhaust gas, the heat recovery efficiency can be improved. It can be increased and more water can be recovered.

  However, even if the exhaust heat recovery efficiency is increased, the fuel cell cannot be cooled to a predetermined operating temperature when the tank for storing the exhaust heat reaches a so-called full storage state. In such a case, a separate radiator or the like is installed. The fuel cell must be cooled to a predetermined operating temperature or the system must be stopped, and the improvement of the overall energy efficiency of the fuel cell cogeneration system will reach its peak.

  Accordingly, the present invention provides a fuel cell cogeneration system having water independence, high exhaust heat recovery efficiency, and high system operation rate in consideration of the balance among water independence, exhaust heat recovery rate, and system operation rate. The purpose is to do.

  In order to achieve the above object, the fuel cell cogeneration system according to the first aspect of the present invention includes, as shown in FIG. 1, for example, exhaust heat hot water 43 a that exchanges heat with cooling water 24 a that has cooled the fuel cell 30. A hot water storage tank 120 having a temperature detector 124 for detecting the temperature of the exhaust heat hot water 43 a stored in the hot water storage tank 120 or derived from the hot water storage tank 120; An exhaust gas cooling heat exchanger 100 for exchanging heat between the off gas 63a and the exhaust hot water 43a; and a water storage tank 70 for recovering and storing useful water 42a for humidifying the oxidant gas 61a introduced into the fuel cell 30 from the off gas 63a. A water storage tank 70 having a water level detector 132 for detecting the water level of the stored useful water 42a; When the temperature of the known exhaust heat hot water 43a is equal to or higher than a predetermined temperature and the water level detected by the water level detector 132 is equal to or higher than the predetermined water level, the heat of the off gas 63a discharged from the fuel cell 30 and the exhaust heat hot water 43a. Configured to avoid replacement.

  With this configuration, when the temperature of the exhaust heat hot water detected by the temperature detector is equal to or higher than the predetermined temperature and the water level detected by the water level detector is equal to or higher than the predetermined water level, the off-gas and exhaust discharged from the fuel cell are discharged. Since it is configured so as to avoid heat exchange with hot water, fuel is saved by preventing exhaust heat recovery when the hot water storage tank is becoming fully charged and there is a predetermined amount of water in the water storage tank. It is possible to recover as much exhaust heat as possible while increasing the operating rate of the battery cogeneration system and making the water independent. Here, the “predetermined temperature” is typically a temperature that takes into consideration the efficiency of heat exchange between the cooling water and the exhaust hot water at a temperature at which the cooling water can cool the fuel cell. “Full storage” refers to a state in which the temperature of the exhaust heat water in the hot water storage tank increases so that the cooling water cannot be cooled to a temperature necessary for cooling the fuel cell to a predetermined temperature.

  Moreover, the fuel cell cogeneration system according to the invention described in claim 2 is, for example, as shown in FIG. 1, in the fuel cell cogeneration system 1 described in claim 1, the exhaust hot water that circulates the exhaust hot water 43 a. A circulation channel 128; a bypass channel 129 that is disposed in the exhaust heat hot water circulation channel 128 and has a switching means 131 that avoids the flow of the exhaust heat hot water 43a to the exhaust gas cooling heat exchanger 100; and a temperature detector 124. When the temperature of the exhaust heat hot water 43a detected in step S is equal to or higher than a predetermined temperature and the water level detected by the water level detector 132 is equal to or higher than the predetermined water level, the flow of the exhaust heat hot water 43a to the exhaust gas cooling heat exchanger 100 is avoided. And a control device 130 for controlling the switching means 131.

  With this configuration, when the temperature of the exhaust heat hot water detected by the temperature detector is equal to or higher than the predetermined temperature and the water level detected by the water level detector is equal to or higher than the predetermined water level, the exhaust heat to the exhaust gas cooling heat exchanger is Since the switching means is controlled so as to avoid the flow of hot water, the fuel cell is controlled so that exhaust heat recovery is not performed when the hot water storage tank is becoming fully charged and the water storage tank has a predetermined amount of water. It is possible to recover as much exhaust heat as possible while increasing the operation rate of the cogeneration system and making the water independent.

  Further, the fuel cell cogeneration system according to the invention described in claim 3 introduces cooling water 24a in the fuel cell cogeneration system 1 described in claim 1 or 2, as shown in FIG. A fuel cell 30 that transfers the generated heat to the cooling water 24a; and a reformer 7 that introduces the raw material fuel 2a and the useful water 65a to generate the fuel gas 3a to be supplied to the fuel cell 30.

  If comprised in this way, since the fuel cell and the reformer which produces | generates fuel gas are provided, it will become a fuel cell cogeneration system which can generate electric power with a fuel cell based on raw material fuels, such as city gas and kerosene.

  Further, the fuel cell cogeneration system according to the invention described in claim 4 is the temperature of the fuel cell cogeneration system 1 described in any one of claims 1 to 3, as shown in FIG. The detector 124 is configured to detect the temperature of the exhaust heat hot water 43a stored below the middle in the vertical direction of the water level when the exhaust heat hot water 43a stored in the hot water storage tank 120 is full.

  With this configuration, the temperature detector is configured to detect the temperature of the exhaust heat hot water stored below the middle in the vertical direction of the water level when the exhaust heat hot water stored in the hot water storage tank is full. , The temperature detected is almost equal to the temperature of the exhaust heat hot water derived from the hot water tank and exchanged with off-gas, and the fuel cell avoids the hot water storage tank becoming full while collecting as much exhaust heat as possible The operation rate of the cogeneration system can be increased.

  A fuel cell cogeneration system according to the invention described in claim 5 is the fuel cell cogeneration system 1 according to any one of claims 1 to 4, for example, as shown in FIG. The water level is a water level corresponding to the amount of water consumed in the fuel cell cogeneration system 1 during a predetermined time.

  If comprised in this way, even if a water | moisture content cannot be collect | recovered during predetermined time, a fuel cell cogeneration system can be operated, without receiving supply of water from the outside. The “predetermined time” is typically 0.5 to 4 hours, and the lower limit is preferably about 1 hour from the viewpoint of operating time of the fuel cell cogeneration system. From the viewpoint of making the water tank as small as possible. The upper limit is preferably about 2 hours.

  According to the present invention, when the temperature of the exhaust heat hot water detected by the temperature detector is equal to or higher than the predetermined temperature and the water level detected by the water level detector is equal to or higher than the predetermined water level, the off gas and exhaust gas discharged from the fuel cell are discharged. Since it is configured to avoid heat exchange with hot water, it is possible to recover as much exhaust heat as possible while increasing the operation rate of the fuel cell cogeneration system and making the water independent.

  Embodiments of the present invention will be described below with reference to the drawings. In each figure, the same or equivalent devices are denoted by the same reference numerals, and redundant description is omitted. In FIGS. 1 and 3, a broken line represents a control signal.

  First, the configuration of the fuel cell cogeneration system 1 according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating a fuel cell cogeneration system 1 according to a first embodiment of the present invention. The fuel cell cogeneration system 1 includes a reformer 7, a water storage tank 70, a blower 84, a three-fluid heat exchanger 114, gas-liquid separators 45 and 55, a fuel cell 30, and a cooling water heat exchanger. 110, pump 108, mixed exhaust gas heat exchanger 83, exhaust gas cooling heat exchanger 100, gas-liquid separator 89, pumps 82 and 85, pure water device 86, water treatment device 93, and hot water storage tank. 120, a pump 125, and a control device 130.

  The reformer 7 has a combustion unit 107 for obtaining reforming heat necessary for reforming. The reformer 7 is generated by a reforming reaction with a nozzle that introduces a raw material fuel 2a such as natural gas, naphtha, methanol, and kerosene, a nozzle that introduces reforming water 65a sent from a pure water device 86, and the like. And a nozzle for deriving the fuel gas 3a. Furthermore, a nozzle for introducing the anode off-gas 21a discharged from the fuel cell 30 into the combustion unit 107, a nozzle for introducing combustion air 4a that is an oxygen-containing gas as a combustion support gas, and a nozzle for discharging the combustion exhaust gas 6a Furthermore, the reformer 7 has a nozzle for introducing the combustion fuel 5a supplied for combustion as an auxiliary fuel at the time of start-up or when the reforming heat necessary for the reforming reaction is insufficient. The nozzle for deriving the fuel gas 3 a generated by the reformer 7 is connected to the fuel electrode 32 of the fuel cell 30 through the three-fluid heat exchanger 114 and the gas-liquid separator 45. Note that the phrase “connected to two devices” includes a case where they are connected via a flow path.

  The water storage tank 70 also serves as a humidifier for humidifying the oxidant gas 61 a introduced into the fuel cell 30, and below the recovered water 42 </ b> A sent from the gas-liquid separator 45 and the gas-liquid separator 55. The recovered water 42B sent out, the recovered water inlet 73 into which the recovered water 42C sent out from the gas-liquid separator 89 enters, and the liquid storage unit 71 for storing the introduced recovered water 42A, 42B, 42C as useful water 42a. Have. The liquid storage part 71 is provided with a water level detector 132 that detects the water level of the useful water 42 a stored in the liquid storage part 71. A signal cable is laid between the water level detector 132 and the control device 130, and the water level detector 132 is configured to transmit the water level of the liquid storage unit 71 to the control device 130 as a signal i2.

  Further, since the liquid storage part 71 in the water storage tank 70 is in an atmospheric pressure state by maintaining the open state to the atmosphere through the oxidant gas inlet 72, the liquid storage part 71 has a gas difference due to the level difference from the gas-liquid separators 45, 55, and 89. The recovered water 42A, 42B, 42C can be introduced from the liquid separators 45, 55, 89 into the liquid storage unit 71. Therefore, a liquid feed pump for feeding the recovered water 42A, 42B, and 42C can be made unnecessary. The surplus useful water 42a can be discharged out of the system from a branch (not shown) provided on the discharge side of the pump 82.

  The lower part of the water storage tank 70 further has a useful water outlet 74 through which useful water 42a is led out, and an oxidant gas inlet 72 through which the oxidant gas 61a is introduced. Note that the oxidant gas inlet 72 exemplified in this embodiment is open to the atmosphere, and air in the atmosphere is used as the oxidant gas 61a. In the upper part of the water storage tank 70, an oxidant gas outlet 77 from which the oxidant gas 61a flows toward the air electrode 33 of the fuel cell 30 and useful water 42a returned from the mixed exhaust gas heat exchanger 83 are injected as humidification water. A useful water inlet 78 and a water disperser 79 for spraying the useful water 42a injected into the useful water inlet 78 as fine water droplets into the water storage tank 70 are provided. Between the upper and lower parts of the water storage tank 70, a filling part 80 filled with a filling for promoting gas-liquid contact between the injected useful water 42a and the oxidant gas 61a, and the filling part 80 are supported. And a filling support plate 81 is provided.

  The tip of the useful water outlet 74 is connected to a water disperser 79 above the water storage tank 70 via a pump 82, a water treatment device 93 and a mixed exhaust gas heat exchanger 83. As described above, the liquid storage unit 71 passes through the useful water outlet 74, the pump 82, the water treatment device 93, the mixed exhaust gas heat exchanger 83, the useful water inlet 78, the water disperser 79, and the filling unit 80. A circulation channel for circulating the useful water 42a is configured.

  A blower 84 that pressure-feeds the oxidant gas 61 a to the fuel cell 30 is connected to the oxidant gas outlet 77 of the water storage tank 70. The oxidant gas 61 a in the water storage tank 70 is sucked by the blower 84. The oxidant gas 61 a sucked from the oxidant gas inlet 72 and the useful water 42 a injected from the useful water inlet 78 are configured to make countercurrent contact at the filling portion 80.

  The outlet of the blower 84 is connected to the air electrode 33 of the fuel cell 30 via the three-fluid heat exchanger 114 and the gas-liquid separator 55. The oxidant gas 61 a pressurized by the blower 84 is configured to be introduced into the air electrode 33 of the fuel cell 30.

  The three-fluid heat exchanger 114 exchanges heat between the cooling water 24a and the oxidant gas 61a delivered from the water storage tank 70, and further heats the cooling water 24a and the fuel gas 3a delivered from the reformer 7. A three-fluid heat exchanger to be exchanged is preferably used. The three-fluid heat exchanger 114 is configured such that the fuel gas 3a, the oxidant gas 61a, and the cooling water 24a are heat-exchanged in parallel flow so that these three fluids have substantially the same temperature at the outlet of the three-fluid heat exchanger 114. Has been.

  The outlet nozzle of the fuel gas 3 a of the three-fluid heat exchanger 114 is connected to the fuel electrode 32 of the fuel cell 30 via the gas-liquid separator 45. The outlet nozzle of the oxidant gas 61 a of the three-fluid heat exchanger 114 is connected to the air electrode 33 of the fuel cell 30 via the gas-liquid separator 55. The outlet nozzle of the cooling water 24 a of the three-fluid heat exchanger 114 is connected to the cooling water passage 31 of the fuel cell 30.

  The gas-liquid separator 45 is a device that separates the condensed water in the fuel gas 3a. The gas-liquid separator 45 is connected to a flow path 145 for introducing the separated recovered water 42 </ b> A into the water storage tank 70. The gas-liquid separator 55 is a device that separates the condensed water in the oxidant gas 61a. The gas-liquid separator 55 is connected to a flow path 155 for introducing the separated recovered water 42 </ b> B into the water storage tank 70.

  The fuel cell 30 is a polymer electrolyte fuel cell, and includes a cooling water channel 31, a fuel electrode 32, and an air electrode 33. In the cooling water channel 31, a nozzle for introducing the cooling water 24a pumped by the pump 108 and a nozzle for deriving the cooling water 24a are arranged. The fuel electrode 32 includes a nozzle for introducing the fuel gas 3a generated and supplied by the reformer 7, and a nozzle for discharging the anode offgas 21a that is an offgas that has not been used for the electrochemical reaction in the fuel gas 3a. Has been placed. The air electrode 33 is provided with a nozzle for introducing the oxidant gas 61a delivered from the water storage tank 70 and a nozzle for discharging the cathode offgas 22a, which is an offgas not used in the electrochemical reaction, of the oxidant gas 61a. Has been. In the present specification, the anode off-gas 21a and the cathode off-gas 22a are collectively referred to as off-gas. In addition, the combustion exhaust gas 6 a discharged after burning the anode off gas 21 a introduced into the combustion unit 107 of the reformer 7 is also a kind of off gas discharged from the fuel cell 30.

  The fuel cell 30 outputs electric power by the electrochemical reaction between the fuel gas 3a and the oxidant gas 61a to generate water. This electrochemical reaction is an exothermic reaction, and the cooling water 24a is introduced into the cooling water channel 31 to cool the fuel cell 30, and the cooling water 24a flows into the cooling water channel 31 to cool the fuel cell 30. The heat generated by the electrochemical reaction is absorbed. The heat generated by the electrochemical reaction is carried out of the fuel cell 30 by the cooling water 24a or exhausted exhaust gas (the anode offgas 21a and the cathode offgas 22a). Further, in the polymer electrolyte fuel cell, it is necessary to humidify the oxidant gas 61a supplied to the air electrode in order to maintain high electrical conductivity of the proton exchange membrane (not shown). The required dew point of the oxidant gas 61a varies depending on the operating conditions such as the operating temperature of the fuel cell to be used, but is generally in the range of 50 to 80 ° C.

  An air electrode offgas flow path 141 that carries the cathode offgas 22a discharged from the air electrode 33 of the fuel cell 30 and a flow path 142 that carries the combustion exhaust gas 6a discharged from the combustion unit 107 of the reformer 7 are branched pipes. And a flow path 143 for conveying the mixed exhaust gas 63a as a gas having exhaust heat and moisture. Here, the mixed exhaust gas 63a in which the cathode off gas 22a, which is an off gas, and the combustion exhaust gas 6a merge is also an off gas discharged from the fuel cell 30. The flow path 143 passes through the mixed exhaust gas heat exchanger 83, the exhaust gas cooling heat exchanger 100, and the gas-liquid separator 89, and reaches an exhaust port (not shown) outside the system 102.

  The cooling water heat exchanger 110, the pump 108, and the three-fluid heat exchanger 114 are arranged in the flow path through which the cooling water 24a discharged from the cooling water flow path 31 of the fuel cell 30 flows, and the flow path of the cooling water 24a is The cooling fluid channel is a circulation channel that returns to the cooling water channel 31 via these devices. The pump 108 pumps and circulates the cooling water 24a, and is disposed on the flow path of the circulating cooling water 24a, not between the cooling water heat exchanger 110 and the three-fluid heat exchanger 114. Just do it.

  The cooling water heat exchanger 110 is a heat exchanger for exchanging heat between the exhaust heat hot water 43a stored in the hot water storage tank 120 and the cooling water 24a, and a plate heat exchanger is preferably used. In the cooling water heat exchanger 110, the exhaust heat hot water 43a is heated, and the cooling water 24a is cooled. That is, the exhaust heat of the fuel cell 30 transferred into the cooling water 24a by the exhaust heat hot water 43a is recovered. The outlet nozzle of the exhaust heat hot water 43 a of the cooling water heat exchanger 110 is connected to the upper part of the hot water storage tank 120.

  The mixed exhaust gas heat exchanger 83 is a heat exchanger that exchanges heat between the mixed exhaust gas 63a and the useful water 42a, and has a relatively small temperature difference between the gas that is the mixed exhaust gas 63a and the liquid that is the useful water 42a. Therefore, a plate heat exchanger is preferably used. In the mixed exhaust gas heat exchanger 83, the useful water 42a is heated, and the mixed exhaust gas 63a is cooled. As the useful water 42a is heated, the temperature of the sprayed water sprayed from the water disperser 79 of the water storage tank 70 is increased. As a result, the dew point of the oxidant gas 61a can be raised, and the mixed exhaust gas 63a is cooled. Thus, a part of the water in the mixed exhaust gas 63a is condensed.

  The exhaust gas cooling heat exchanger 100 is a heat exchanger for exchanging heat between the exhaust heat hot water 43a stored in the hot water storage tank 120 and the mixed exhaust gas 63a, and a plate heat exchanger is preferably used. In the exhaust gas cooling heat exchanger 100, the exhaust hot water 43a is heated, and the mixed exhaust gas 63a is cooled. That is, the exhaust heat of the fuel cell 30 transferred into the mixed exhaust gas 63a by the exhaust heat hot water 43a is recovered. Moreover, a part of the water | moisture content in the mixed exhaust gas 63a condenses by cooling the mixed exhaust gas 63a.

  A gas-liquid separator 89 is installed on the downstream side of the exhaust gas cooling heat exchanger 100 as viewed from the flow direction of the mixed exhaust gas 63a. The gas-liquid separator 89 separates the condensed water 42C from the mixed exhaust gas 63a cooled by the mixed exhaust gas heat exchanger 83 and the exhaust gas cooling heat exchanger 100. The gas-liquid separator 89 is connected to a flow path 189 for introducing the separated recovered water 42C into the water storage tank 70, and is introduced into the water storage tank 70 from the recovered water inlet 73 together with the recovered water 42A and 42B. The gas-liquid separator 89 is connected to a flow path 104 that discharges the exhaust gas 64a, which is a mixed exhaust gas after the condensed water is recovered, to the atmosphere (outside the system) 102.

  The pure water device 86 is disposed on the downstream side of the pump 85 in the flow path leading the useful water 42a as the reforming water 65a to the reforming device 7, and includes an ion exchange resin-filled column 87. The pure water device 86 purifies the useful water 42a used as the reforming water 65a into pure water. The outlet nozzle of the pure water device 86 is connected to the reforming device 7, and the reforming water 65 a purified to pure water is sent to the reforming device 7. Further, in order to prevent the ion exchange resin from being mixed into the reforming water 65a, a filter 88 may be installed on the downstream side of the ion exchange resin packed column 87.

The water treatment device 93 is disposed on the downstream side of the pump 82 in the circulation channel of the useful water 42 a connected to the useful water outlet 74 of the water storage tank 70, and has an ion exchange resin-filled column 94. As the ion exchange resin used for the ion exchange resin packed column 94 of the water treatment device 93, an anion exchange resin is desirable. Further, by installing a filter 95 on the downstream side of the ion exchange resin packed column 94, the ion exchange resin is prevented from being mixed into the useful water 42a. In the present embodiment, by providing a water treatment device 93 using an anion exchange resin in the circulation channel through which the useful water 42a circulates, the useful water 42a in gas-liquid contact with the oxidant gas 61a is stored in the water storage tank 70. The hydroxide ion OH ⁻ is always supplied. Thereby, the circulating useful water 42a is always kept alkaline, and pollutants such as NOx and SOx contained in the oxidant gas 61a are effectively removed.

  The hot water storage tank 120 is a tank for storing the exhaust heat hot water 43a. The exhaust hot water 43a stored in the hot water storage tank 120 forms a so-called temperature stratification in which the upper part has a relatively high temperature and the lower part has a relatively low temperature. The hot water storage tank 120 is connected to a device (not shown) for supplying heat to an external heat demand by supplying or circulating the exhaust heat hot water 43a. For example, the exhaust hot water 43a stored in the hot water storage tank 120 circulates between the external devices, and the exhaust hot water 43a derived from the hot water storage tank 120 supplies heat to the external devices, and then the hot water hot water 43a is supplied to the hot water storage tank 120. Returned. That is, the exhaust heat of the fuel cell 30 stored in the hot water storage tank 120 via the exhaust heat hot water 43a is effectively used for the heat demand.

  In addition to the circulation path (not shown) for supplying heat to the external device described above, the hot water storage tank 120 circulates the exhaust heat hot water 43a for recovering exhaust heat in the fuel cell cogeneration system 1. An exhaust heat hot water circulation channel 128 which is a channel is connected. A pump 125, a three-way valve 131 as switching means, an exhaust gas cooling heat exchanger 100, and a cooling water heat exchanger 110 are arranged in this order in the exhaust heat hot water circulation channel 128 in the direction in which the exhaust heat hot water 43a flows. Yes. The waste heat hot water 43a stored in the hot water storage tank 120 flows through the waste heat hot water circulation flow path 128, exchanges heat with the mixed exhaust gas 63a in the exhaust gas cooling heat exchanger 100, and moves to the mixed exhaust gas 63a. The combustion heat in the combustion unit 107 is recovered, the heat exchange with the cooling water 24a is performed in the cooling water heat exchanger 110, and the exhaust heat of the fuel cell 30 that has moved to the cooling water 24a is recovered and returned to the hot water storage tank 120. The recovered exhaust heat can be stored in the hot water storage tank 120. Further, the exhaust heat hot water circulation channel 128 is provided with a bypass channel 129 for switching the three-way valve 131 to prevent the exhaust heat hot water 43a from passing through the exhaust gas cooling heat exchanger 100, When the exhaust heat hot water 43a passes through the bypass channel 129, the exhaust gas cooling heat exchanger 100 is configured not to perform exhaust heat recovery. A signal cable is laid between the three-way valve 131 and the control device 130. The three-way valve 131 receives the signal i3 from the control device 130 and determines whether the exhaust hot water 43a passes through the bypass flow path 129. It is configured to be able to perform a switching operation.

    A temperature detector 124 is installed below the hot water storage tank 120. The temperature detector 124 is installed in the lower part of the hot water storage tank 120 in order to measure the temperature of the exhaust heat hot water 43a circulating through the cooling water heat exchanger 110. Or you may arrange | position so that the temperature of the waste heat hot water 43a derived | led-out from the hot water storage tank 120 may be measured. A signal cable is laid between the temperature detector 124 and the control device 130, and the temperature detected by the temperature detector 124 can be transmitted to the control device 130 as a signal i1.

  The control device 130 receives the temperature detected by the temperature detector 124 as a signal i1, and receives the water level detected by the water level detector 132 as a signal i2, and the received temperature is equal to or higher than a predetermined temperature. Further, when the received water level is equal to or higher than the predetermined water level, a signal i3 is transmitted to the three-way valve 131 so as to avoid the exhaust hot water 43a flowing through the exhaust heat hot water circulation passage 128 from flowing through the exhaust gas cooling heat exchanger 100. In other words, the flow of the three-way valve 131 can be switched.

Next, the operation of the fuel cell cogeneration system 1 according to the first embodiment of the present invention will be described.
In the reformer 7, the fuel gas 3a mainly composed of hydrogen is formed by a reforming reaction between the reforming water 65a purified from the useful water 42a and the raw material fuel 2a supplied from outside the fuel cell cogeneration system 1. Is generated. Usually, the reforming water 65a is supplied in excess of the necessary amount, so that the fuel gas 3a contains a large amount of moisture. The reformer 7 further introduces the air 4a as a combustion support agent from the outside of the system and the anode offgas 21a discharged from the fuel electrode 32 into the combustion section 107 and burns it, for the reforming reaction of the raw fuel 2a. The reforming heat is generated and the combustion exhaust gas 6a is discharged. Combustion fuel 5a is supplied to the combustion unit 107 from outside the system for assisting when the anode off gas 21a is insufficient. The fuel gas 3a generated by the reformer 7 is sent to the three-fluid heat exchanger 114 and cooled by the cooling water 24a, and the temperature and absolute humidity are adjusted as appropriate. The temperature of the fuel gas 3a before entering the three-fluid heat exchanger 114 is 65 to 100 ° C., and the temperature of the fuel gas 3a leaving the three-fluid heat exchanger 114 is 50 to 70 ° C. The cooled fuel gas 3 a condenses water, and the condensed water is separated as recovered water 42 A in the gas-liquid separator 45 and introduced into the water storage tank 70 from the recovered water inlet 73. The fuel gas 3 a from which excess water has been separated as the recovered water 42 </ b> A by the gas-liquid separator 45 is supplied to the fuel electrode 32 of the fuel cell 30.

  On the other hand, the oxidant gas 61a introduced into the water storage tank 70 is guided to the filling unit 80 and comes into gas-liquid contact with the useful water 42a sprayed from the water disperser 79 while passing through the filling unit 80. While being cleaned, it is heated and humidified. The oxidant gas 61 a that has been cleaned, heated, and humidified flows out of the water storage tank 70. The temperature of the oxidant gas 61a entering the water storage tank 70 is 5 to 40 ° C., and the temperature of the oxidant gas 61a flowing out of the water storage tank 70 is 50 to 65 ° C.

  The oxidant gas 61 a flowing out of the water storage tank 70 is pressurized by the blower 84. As a result of the pressure increase by the blower 84, the dew point of the oxidant gas 61a increases. For example, when the pressure increase of the oxidant gas 61a by the blower 84 is 12 kPa and the dew point of the oxidant gas 61a at the oxidant gas outlet 77 is 50 ° C., the dew point of the oxidant gas 61a is increased by about 2 ° C. and about 52 ° C. become. Therefore, when the dew point to be achieved by the oxidant gas 61a is constant, the humidifier load of the water storage tank 70 can be reduced and the water storage tank 70 can be made compact by disposing the blower 84 on the downstream side of the water storage tank 70. it can. Unlike the case where the blower 84 is disposed on the oxidant gas inlet 72 side, the inside of the water storage tank 70 is not pressurized by the blower 84.

  The oxidant gas 61a pressurized by the blower 84 is pumped to the three-fluid heat exchanger 114, and is cooled by heat exchange with the cooling water 24a in the three-fluid heat exchanger 114. The oxidant gas 61a cooled by the three-fluid heat exchanger 114 condenses excess water, and the condensed water is separated as recovered water 42B in the gas-liquid separator 55 and introduced into the water storage tank 70 from the recovered water inlet 73. Is done. The oxidant gas 61 a from which excess water is separated by the gas-liquid separator 55 is supplied to the air electrode 33 of the fuel cell 30. The temperature of the oxidant gas 61a before entering the three-fluid heat exchanger 114 is 55 to 85 ° C., and the temperature of the oxidant gas 61a exiting the three-fluid heat exchanger 114 is 50 to 70 ° C. Moreover, the temperature of the cooling water 24a before entering the three-fluid heat exchanger 114 is 50 to 70 ° C., and the temperature of the cooling water 24a exiting the three-fluid heat exchanger 114 is 50 to 70 ° C. Here, in the three-fluid heat exchanger 114, the specific heats of the cooling water 24a, the oxidant gas 61a, and the fuel gas 3a are greatly different. Therefore, even if the oxidant gas 61a and the fuel gas 3a are cooled, the cooling water 24a The temperature is almost unchanged. The cooling water 24 a, the oxidant gas 61 a, and the fuel gas 3 a are sent in parallel to each other in the three-fluid heat exchanger 114 so that the outlet temperatures thereof are the same.

  The cooling water 24a undergoes heat exchange with the exhaust heat hot water 43a in the cooling water heat exchanger 110, is led to the pump 108, is pressurized, and is sent to the three-fluid heat exchanger 114. In the cooling water heat exchanger 110, the cooling water 24a heats the exhaust hot water 43a, and the exhaust hot water 43a cools the cooling water 24a. Here, the temperature of the cooling water 24a before entering the cooling water heat exchanger 110 is 60 to 80 ° C., and the temperature of the cooling water 24a exiting the cooling water heat exchanger 110 is 50 to 70 ° C. Moreover, the temperature of the waste heat hot water 43a before entering the cooling water heat exchanger 110 is 10 to 45 ° C, and the temperature of the waste heat hot water exiting the cooling water heat exchanger 110 is 59 to 79 ° C. As described above, the cooling water 24a introduced into the three-fluid heat exchanger 114 is sent to the fuel cell 30 after adjusting the temperature and humidity of the fuel gas 3a and the oxidant gas 61a.

  In the fuel cell 30, electric power is output by an electrochemical reaction between hydrogen in the fuel gas 3a supplied to the fuel electrode 32 and oxygen in the oxidant gas 61a supplied to the air electrode 33 to generate heat and water. . The heat generated by the electrochemical reaction is absorbed by the cooling water 24a and the fuel cell 30 is cooled. Further, in the fuel cell 30, the anode off-gas 21a, which is the off-gas of the fuel gas 3a that has not been used for the electrochemical reaction from the fuel electrode 32, is generated from the oxidant gas 61a that has not been used for the electrochemical reaction from the air electrode 33. Cathode off-gas 22a which is off-gas is discharged | emitted, respectively. In addition, the water | moisture content produced | generated by the electrochemical reaction is contained in the cathode offgas 22a discharged | emitted. Therefore, the mixed exhaust gas 63a as the off gas also contains moisture.

  The mixed exhaust gas 63a is first guided to the mixed exhaust gas heat exchanger 83. In the mixed exhaust gas heat exchanger 83, heat is exchanged between the mixed exhaust gas 63a and the useful water 42a, and the useful water 42a is heated by the mixed exhaust gas 63a, so that the exhaust heat in the mixed exhaust gas 63a becomes the useful water 42a. To be recovered. The temperature of the mixed exhaust gas 63a before entering the mixed exhaust gas heat exchanger 83 is 60 to 80 ° C., and the temperature of the mixed exhaust gas 63a exiting the mixed exhaust gas heat exchanger 83 is 35 to 55 ° C. Moreover, the temperature of the useful water 42a before entering the mixed exhaust gas heat exchanger 83 in this case is 30 to 50 ° C., and the temperature of the useful water 42a exiting the mixed exhaust gas heat exchanger 83 is 55 to 70 ° C. . Since the temperature of the mixed exhaust gas 63a whose heat has been recovered by the useful water 42a is lowered, the moisture in the mixed exhaust gas 63a is condensed.

  The mixed exhaust gas 63a emitted from the mixed exhaust gas heat exchanger 83 is guided to the exhaust gas cooling heat exchanger 100, and the mixed exhaust gas 63a and the exhaust heat hot water 43a exchange heat, whereby the mixed exhaust gas 63a has the fuel cell 30. Waste heat is further recovered. The temperature of the mixed exhaust gas 63a before entering the exhaust gas cooling heat exchanger 100 is 35 to 55 ° C, and the temperature of the mixed exhaust gas 63a exiting the exhaust gas cooling heat exchanger 100 is 10 to 45 ° C. In this case, the temperature of the exhaust heat hot water 43a before entering the exhaust gas cooling heat exchanger 100 is 5 to 40 ° C., and the temperature of the exhaust heat hot water 43a exiting the exhaust gas cooling heat exchanger 100 is 10 to 45 ° C. It is. Since the temperature of the mixed exhaust gas 63a from which heat has been recovered by the exhaust hot water 43a is lowered, the moisture in the mixed exhaust gas 63a is further condensed.

  The mixed exhaust gas 63a cooled in the mixed exhaust gas heat exchanger 83 and the exhaust gas cooling heat exchanger 100 and condensed with water is led to the gas-liquid separator 89 to separate the condensed water. The separated condensed water is introduced into the water storage tank 70 from the recovered water inlet 73 as recovered water 42C. Further, the exhaust gas 64a from which the condensed water has been separated passes through the flow path 104 as exhaust gas and is discharged to the outside of the system 102 that is the atmosphere.

  The recovered water 42A, 42B, 42C introduced from the recovered water inlet 73 of the water storage tank 70 is stored in the liquid storage unit 71 as useful water 42a, and then sucked in by the pump 82 from the useful water outlet 74, and is then used in the water treatment device. It is pumped to 93. The useful water 42a pumped to the water treatment device 93 is freed of acid gas contaminants contained by the ion exchange resin-filled column 94 of the water treatment device 93. The useful water 42a exiting the water treatment device 93 is heated by the mixed exhaust gas 63a in the mixed exhaust gas heat exchanger 83, and the exhaust heat in the mixed exhaust gas 63a is recovered. The useful water 42a from which the exhaust heat has been recovered is injected into the water storage tank 70 through the useful water injection port 78, dispersed in the filling portion 80 by the water disperser 79, where it is brought into gas-liquid contact with the oxidant gas 61a and oxidized. The agent gas 61a is humidified, heated and washed. On the other hand, the useful water 42a is decarboxylated by the oxidant gas 61a and cooled. The useful water 42a decarboxylated and cooled is returned to the liquid storage unit 71 and stored. Therefore, the useful water 42a stored in the liquid storage part 71 is decarboxylated. Although a small amount of carbon dioxide gas is mixed in the oxidant gas 61a by the decarbonation process of the useful water 42a, the carbon dioxide gas has almost no catalyst poisoning action on the air electrode catalyst (not shown) in the fuel cell 30. Does not affect the deterioration and life of the fuel cell 30

  A part of the useful water 42a is used as the reforming water 65a. The useful water 42 a used as the reforming water 65 a is sucked by the pump 85 from the useful water outlet 74 and is pumped to the pure water device 86. The reforming water 65a purified to pure water in the pure water device 86 is supplied to the reforming device 7 and used for the reforming reaction. The reforming water 65a used for the reforming reaction is required to be pure water. Here, when the useful water 42a is decarboxylated in advance, that is, when the reforming water 65a is decarboxylated, the life of the ion exchange resin 87 can be extended, and the maintenance period of the pure water device 86 can be extended. . In addition, since the fuel cell cogeneration system 1 is water-independent, the water treatment load is small and the maintenance period of the pure water device 86 is further extended while no external water supply is received.

  Now, the waste heat hot water 43a which collect | recovered waste heat from the cooling water 24a with the cooling water heat exchanger 110 is stored by the hot water storage tank 120. FIG. As described above, the waste heat hot water 43a stored in the hot water storage tank 120 forms a temperature stratification, and the high temperature waste heat hot water 43a is used for heat demand outside the system, and the low temperature of the lower layer is low. Exhaust hot water 43a is used to cool the cooling water 24a. The exhausted hot water 43 a led out from the lower part of the hot water storage tank 120 is pumped through the exhausted hot water circulating flow path 128 by the pump 125 and reaches the three-way valve 131. In principle, the three-way valve 131 does not allow the exhaust hot water 43a to flow into the bypass flow path 129, so the exhaust hot water 43a flows through the exhaust hot water circulation path 128 and is introduced into the exhaust gas cooling heat exchanger 100. Is done.

  The exhaust heat hot water 43a introduced into the exhaust gas cooling heat exchanger 100 performs heat exchange with the mixed exhaust gas 63a, and recovers the exhaust heat of the fuel cell 30. The exhaust heat hot water 43a that has been recovered from the exhaust heat and exited from the exhaust gas cooling heat exchanger 100 is introduced into the cooling water heat exchanger 110, exchanges heat with the cooling water 24a, and is absorbed into the cooling water 24a. The exhaust heat of the battery 30 is recovered. The exhaust heat hot water 43 a obtained by recovering the exhaust heat of the fuel cell 30 by the exhaust gas cooling heat exchanger 100 and the coolant heat exchanger 110 is returned to the upper part of the hot water storage tank 120. In this way, most of the exhaust heat of the fuel cell 30 is collected and stored in the hot water storage tank 120, and the stored heat is supplied to the heat demand outside the system as needed and used effectively.

  It is preferable from the viewpoint of improving the total energy efficiency of the fuel cell cogeneration system 1 to recover as much waste heat as possible of the fuel cell 30 that should be discharged outside the system. However, since the exhaust hot water 43a stored in the hot water storage tank 120 is used to cool the cooling water 24a that cools the fuel cell 30, the cooling water 24a cannot be cooled, that is, the fuel cell 30 is cooled. Therefore, it is necessary to avoid the temperature of the exhaust heat hot water 43a in the hot water storage tank 120 from rising so much that the heat cannot be generated. That is, in order to increase the operating rate of the fuel cell cogeneration system 1, it is necessary to avoid the hot water storage tank 120 being fully stored.

  Since the fuel cell 30 cannot be cooled when it is fully charged, in such a case, a separate radiator or the like must be installed to cool the fuel cell 30 to a predetermined operating temperature or to stop the fuel cell cogeneration system 1. If a separate radiator or the like is provided, the initial cost increases and installation space is required. Moreover, the energy which operates this is needed and the total energy efficiency of a system will fall. On the other hand, when the system is shut down, the operating rate decreases, and when power demand is generated during that time, the hot water storage tank 120 is fully stored and the fuel cell 30 is shut down while the fuel cell 30 is stopped. ) Need to be supplied with power. On the other hand, if the exhaust heat recovery is not performed, the recovered water obtained is reduced, and water outside the system containing impurities such as silica must be introduced into the system. Therefore, the flow of the exhaust heat hot water 43a is controlled according to the flow shown below in consideration of the balance among water self-supporting, exhaust heat recovery rate, and system operation rate.

  FIG. 2 is a flowchart for explaining the switching operation of the three-way valve 131 as switching means for switching the flow of the waste heat hot water 43a in the waste heat hot water circulation passage 128. For convenience of the following description, a state in which the three-way valve 131 is open in the direction in which the exhaust heat hot water 43 a flows toward the exhaust gas cooling heat exchanger 100 is referred to as “normal”, and the exhaust heat warm water toward the bypass channel 129. The state in which the three-way valve 131 is open in the direction in which 43a flows is referred to as “bypass”.

  The control device 130 receives the temperature signal i1 from the temperature detector 124 as needed, and receives the water level signal i2 from the water level detector 132 as needed. When the three-way valve 131 does not receive the signal i3 from the control device 130, the three-way valve 131 is normal (S201). When the three-way valve 131 is normal, the exhaust heat hot water 43a passes through the exhaust heat hot water circulation passage 128 to recover the exhaust heat of the fuel cell 30 in the exhaust gas cooling heat exchanger 100 and the cooling water heat exchanger 110, thereby storing the hot water storage tank 120. Return to.

  The control device 130 determines whether or not the temperature of the exhaust heat water 43a detected by the temperature detector 124 is equal to or higher than a predetermined temperature based on the temperature signal i1 received as needed (S202). If the temperature is not higher than the predetermined temperature, the three-way valve 131 is maintained in a normal state (S201). The predetermined temperature is a temperature that takes into consideration the efficiency of heat exchange between the cooling water and the exhaust hot water with the temperature at which the cooling water can cool the fuel cell, and is 40 ° C. in the present embodiment. When this temperature is set to a predetermined temperature, the cooling water 24a can be cooled by the cooling water heat exchanger 110, and the operable time of the fuel cell 30 can be extended.

  When the temperature of the exhaust heat hot water 43a detected by the temperature detector 124 is equal to or higher than a predetermined temperature, it is stored in the liquid storage unit 71 detected by the water level detector 132 based on the water level signal i2 received as needed. It is determined whether or not the water level of the irrigation water 42a is equal to or higher than a predetermined water level (S203). If it is not higher than the predetermined water level, the three-way valve 131 is maintained in the normal state (S201), and if it is higher than the predetermined water level, the process proceeds to the next step. The predetermined water level is typically when the reforming water 65a as useful water used in the reformer 7 is stored between the time when the fuel cell cogeneration system 1 is activated and the time when power generation is started. Is the water level. In the present embodiment, the reforming water 65a used in the reformer 7 has an average of 6 mL per minute, and the time from the start of the fuel cell cogeneration system 1 to the start of power generation is 50 minutes. Accordingly, when a margin of 10 minutes is seen, the predetermined water level is the water level when the water storage tank 70 stores 6 mL / min × (50 + 10) min = 360 mL of water.

  When the temperature of the exhaust heat hot water 43a detected by the temperature detector 124 is equal to or higher than a predetermined temperature and the water level of the useful water 42a detected by the water level detector 132 is equal to or higher than the predetermined water level, the control device 130 controls the three-way valve 131. The signal i3 is transmitted to the three-way valve 131 to the bypass side (S204). When the three-way valve 131 is bypassed, the exhaust heat hot water 43a is not directly introduced into the exhaust gas cooling heat exchanger 100, but is directly introduced into the cooling water heat exchanger 110 through the bypass passage 129. Thereby, since the exhaust heat warm water 43a introduced into the cooling water heat exchanger 110 is not recovered in the exhaust gas cooling heat exchanger 100, the heat storage speed in the hot water storage tank 120 is suppressed. Therefore, it is possible to extend the time until the operation of the fuel cell 30 cannot be continued due to the hot water storage tank 120 becoming full. If the heat demand outside the system is generated while the operation time of the fuel cell 30 is extended and the heat stored in the hot water storage tank 120 is consumed, the operation of the fuel cell 30 can be continued without stopping. Become.

  However, if the exhaust heat hot water 43a bypasses the exhaust gas cooling heat exchanger 100, exhaust heat recovery cannot be performed by the exhaust gas cooling heat exchanger 100, and the recovered water separated by the gas-liquid separator 89 is also reduced. Therefore, when the temperature of the exhaust hot water 43a detected by the temperature detector 124 reaches a temperature at which the temperature of the exhaust hot water 43a is returned to a normal state lower than a predetermined temperature (hereinafter referred to as “recovery temperature”) (that is, in the hot water storage tank 120). When the amount of stored heat decreases and there is room in the remaining heat storage capacity), the bypass of the exhaust heat hot water 43a is released and the exhaust heat hot water 43a is introduced into the exhaust gas cooling heat exchanger 100 to recover the exhaust heat and moisture. It is preferable to do. Therefore, after switching the three-way valve 131 to the bypass side (S204), the process proceeds to a step (S205) for determining whether or not the temperature of the exhaust hot water 43a detected by the temperature detector 124 is equal to or lower than the return temperature. The reason why the return temperature is set lower than the predetermined temperature is to allow a sufficient amount of heat storage in the hot water storage tank 120.

  The control device 130 determines whether or not the temperature of the exhaust heat water 43a detected by the temperature detector 124 is equal to or lower than the return temperature based on the temperature signal i1 received as needed (S205). If the temperature has decreased to the return temperature, the process returns to the step of setting the three-way valve 131 to the normal state (S201). If the temperature does not fall to the return temperature, it is determined whether or not the water level of the useful water 42a stored in the liquid storage unit 71 detected by the water level detector 132 is equal to or higher than a predetermined water level, based on the water level signal i2 received as needed. The process returns to step (S203). In the step of determining whether or not the level of useful water 42a stored in the liquid storage unit 71 is equal to or higher than a predetermined level (S203), if the level is equal to or higher than the predetermined level, the three-way valve 131 is maintained in a bypass state (S204). If the water level is not higher than the predetermined level, the process returns to the step of setting the three-way valve 131 to the normal state (S201).

  When the three-way valve 131 returns to the normal state, the exhaust heat hot water 43a is again introduced into the exhaust gas cooling heat exchanger 100, so that more exhaust heat is recovered and moisture is also recovered. In this way, while increasing the operating rate of the fuel cell cogeneration system 1, as much exhaust heat as possible is recovered to improve the overall energy efficiency of the system and to satisfy the water self-supporting in the system as much as possible. In the present invention, even if the temperature of the exhaust heat hot water 43a detected by the temperature detector 124 is equal to or higher than a predetermined temperature, the water level of the useful water 42a detected by the water level detector 132 is lower than the predetermined water level. When the exhaust heat hot water 43a does not bypass the exhaust gas cooling heat exchanger 100, in this case, the fuel cell cogeneration system 1 is stopped after the exhaust heat is recovered to the maximum and the hot water storage tank 120 is fully stored. Will be. When the temperature detector 124 detects a predetermined temperature, the hot water storage tank 120 is not yet fully charged, but when the water level of the useful water 42a in the water storage tank 70 is less than the predetermined water level, In order to continue the operation of the generation system 1, water must be replenished from outside the system. However, in order to use water introduced from outside the system, impurities such as silica must be removed. The fuel cell cogeneration system after the hot water storage tank 120 is fully stored by recovering the exhaust heat to the maximum without bypassing the three-way valve 131 when the water level of the useful water 42a in the water storage tank 70 is less than a predetermined water level. If 1 is stopped, the life of the water treatment device 93 can be extended.

  Subsequently, a fuel cell cogeneration system 2 according to a second embodiment of the present invention will be described with reference to FIG. In the fuel cell cogeneration system 2 according to the second embodiment shown in FIG. 3, the fuel cell cogeneration system 1 according to the first embodiment includes a bypass flow path 129 and switching means in the exhaust heat hot water circulation flow path 128. The mixed exhaust gas flow path 143 is provided with a bypass flow path 144 and a three-way valve 136 serving as switching means. A signal cable is laid between the three-way valve 136 and the control device 130. The three-way valve 136 receives the signal i4 from the control device 130 and switches whether the mixed exhaust gas 63a passes through the bypass flow path 144 or not. It is configured to be able to operate.

  In the fuel cell cogeneration system 2, the exhaust heat hot water 43a always passes through the exhaust gas cooling heat exchanger 100 and the cooling water heat exchanger 110. However, when the temperature of the exhaust heat hot water 43a detected by the temperature detector 124 is equal to or higher than the predetermined temperature and the water level of the useful water 42a detected by the water level detector 132 is equal to or higher than the predetermined water level, the control device 130 is The signal i4 is transmitted to the valve 136, and the three-way valve 136 is switched to the bypass side. When the three-way valve 136 is switched to the bypass side, the mixed exhaust gas 63a does not pass through the exhaust gas cooling heat exchanger 100. Therefore, heat exchange is not performed between the exhaust hot water 43a and the mixed exhaust gas 63a. Therefore, the exhaust heat of the fuel cell 30 is not recovered in the exhaust heat hot water 43a. The control of the three-way valve 136 is the same as the flow when the three-way valve 131 is replaced with the three-way valve 136 in FIG.

  In the above description, the reforming method has been described as the steam reforming method, but it may be a partial oxidation reforming method or an autothermal reforming method. When the partial oxidation reforming method or the autothermal reforming method is adopted, the combustion unit 107 is not necessary, and the reforming device 7 can be made compact.

  In the above description, the fuel cell 30 has been described as a polymer electrolyte fuel cell, but it may be a fuel cell other than a polymer electrolyte fuel cell such as a phosphoric acid fuel cell.

  In the above description, the switching unit 131 (136) is described as a three-way valve, but the exhaust heat / hot water circulation channel 128 (mixed exhaust gas channel 143) on the downstream side of the branching portion with the bypass channel 129 (144). ) And bypass flow path 129 (144) may be provided with a two-way valve. Further, a two-way valve may be provided only in the bypass channel 129 depending on pressure loss in the exhaust heat hot water circulation channel 128 and the exhaust gas cooling heat exchanger 100.

1 is a block diagram illustrating a fuel cell cogeneration system according to a first embodiment of the present invention. It is a flowchart explaining the switching operation | movement of a switching means. It is a block diagram explaining the fuel cell cogeneration system which is the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell cogeneration system 2a Raw material fuel 3a Fuel gas 7 Reformer 24a Cooling water 30 Fuel cell 42a Useful water 43a Waste hot water 61a Oxidant gas 63a Off gas (mixed exhaust gas)
70 Water storage tank 100 Exhaust gas cooling heat exchanger 120 Hot water storage tank 124 Temperature detector 128 Waste heat hot water circulation flow path 129 Bypass flow path 130 Control device 131 Switching means 132 Water level detector

Claims (5)

A hot water storage tank for storing hot exhaust hot water that exchanges heat with cooling water that has cooled the fuel cell, and a temperature detector that detects the temperature of the exhaust hot water stored in or derived from the hot water storage tank. Having a hot water storage tank;
An exhaust gas cooling heat exchanger for exchanging heat between the off-gas discharged from the fuel cell and the exhaust hot water;
A water storage tank for recovering and storing useful water for humidifying the oxidant gas introduced into the fuel cell from the off gas, the water storage tank having a water level detector for detecting the water level of the stored useful water;
The off-gas discharged from the fuel cell and the exhaust heat hot water when the temperature of the exhaust heat hot water detected by the temperature detector is equal to or higher than a predetermined temperature and the water level detected by the water level detector is equal to or higher than a predetermined water level. Configured to avoid heat exchange with
Fuel cell cogeneration system. A waste heat and hot water circulation passage for circulating the waste heat and hot water;
A bypass flow path having switching means arranged in the exhaust heat hot water circulation flow path and avoiding the flow of the exhaust heat hot water to the exhaust gas cooling heat exchanger;
When the temperature of the exhaust heat hot water detected by the temperature detector is equal to or higher than a predetermined temperature and the water level detected by the water level detector is equal to or higher than a predetermined water level, the exhaust heat hot water to the exhaust gas cooling heat exchanger is A control device for controlling the switching means so as to avoid flow;
The fuel cell cogeneration system according to claim 1. A fuel cell that introduces the cooling water and transfers the generated heat to the cooling water;
A reformer that introduces raw fuel and the useful water and generates fuel gas to be supplied to the fuel cell;
The fuel cell cogeneration system according to claim 1 or 2. The temperature detector is configured to detect the temperature of the exhaust heat hot water stored below the middle in the vertical direction of the water level when the exhaust heat warm water stored in the hot water storage tank is full;
The fuel cell cogeneration system according to any one of claims 1 to 3. The predetermined water level is a water level corresponding to an amount of water consumed during a predetermined time in the fuel cell cogeneration system;
The fuel cell cogeneration system according to any one of claims 1 to 4.

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