JP2008277017A - Heat exchange system and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently carry out heat and electricity supply in a heat exchange system equipped with a fuel cell and a heater unit. <P>SOLUTION: In the heat exchange system 100, cooling water is circulated among a low temperature type fuel cell stack 20 operated in a low temperature region and having high power generation efficiency, a high temperature type fuel cell stack 30 operated in a high temperature region and having high heat recovery efficiency, and the heater unit 90 for heating equipped with a heat pump 94 as a heat source assist mechanism. In an operation control unit 60 of the heat exchange system 100, by controlling the low temperature type fuel cell stack 20 according to the power output demand of the heater unit 90, the inlet temperature of the cooling water in the heater unit 90 is controlled so as to become hot simultaneously with elevating the temperature of the cooling water supplied from the low temperature type fuel cell stack 20 to the high temperature type fuel cell stack 30. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heat exchange system including a heat source and a heater unit that exchanges heat from the heat source.

  In a fuel cell, waste heat can be used as energy in addition to electrical energy generated by an electrochemical reaction. As described above, various techniques using electric energy and thermal energy have been developed. For example, Patent Document 1 below discloses a combined heat and power supply system that supplements a shortage of heat with electric energy while utilizing exhaust heat of a fuel cell.

JP-A-7-65849

  As a specific example of the above-described combined heat and power system, for example, there is a heater unit including a heater core and a heat pump for heating a passenger compartment of a vehicle. In such a heater unit, the fuel cell cooling water and the blown air are heat-exchanged in the heater core to generate warm air for heating, but if the heater core alone cannot provide the required heating capacity, electric energy is supplied. By using the heat pump, the heating capacity is improved.

  Here, when the fuel cell is a polymer electrolyte fuel cell, the operating temperature range in which a high output can be obtained is generally around 80 ° C., so that the fuel cell cooling used for heat exchange in the heater unit is performed. Water becomes, for example, about 75 ° C. In this case, in the example of the heater unit described above, heat exchange is performed with the fuel cell coolant at about 75 ° C. in the heat core. On the other hand, when a similar heater unit is mounted on an engine vehicle, the heat core exchanges heat with engine coolant at about 120 ° C. Therefore, it can be said that the fuel cell vehicle equipped with the solid polymer fuel cell has lower heat exchange efficiency in the heater core than the engine vehicle.

  Thus, in a heater unit using a polymer electrolyte fuel cell, when the exhaust heat temperature of the fuel cell is low, the auxiliary burden of the heat pump increases, and a heat engine such as an engine is used as the heat source. As a result, there is a problem that the fuel efficiency is lowered. This problem is particularly noticeable when a considerable amount of heat is required in the heater unit, for example, when rapid heating is performed at the start of vehicle operation or the like.

  Such a problem is not limited to the heater unit for heating a fuel cell vehicle equipped with the above-described polymer electrolyte fuel cell. This is a problem common to a heat exchange system including a fuel cell that operates in a low-temperature region and a heater unit that generates hot air or hot water using exhaust heat of the fuel cell or electric power energy generated by power generation.

  In view of the above problems, the problem to be solved by the present invention is to increase the efficiency of a heat exchange system including a fuel cell and a heater unit.

The heat exchange system of the present invention that solves the above problems is as follows.
A heat exchange system having a heat source and a heater unit for exchanging heat from the heat source,
The heat source includes a first fuel cell that generates power in a predetermined temperature region, and a second fuel cell in a temperature region in which an operating temperature during power generation is higher than that of the first fuel cell.
A cooling medium supply mechanism that supplies a cooling medium to the first and second fuel cells and the heater unit, and supplies heat generated in the first and second fuel cells to the heat exchange in the heater unit;
The present invention is characterized in that it comprises at least an operation control unit that controls the first fuel cell or the second fuel cell based on the temperature of the cooling medium flowing through the heater unit.

  In the heat exchange system having such a configuration, the operation control unit controls at least the first fuel cell or the second fuel cell based on the temperature of the cooling medium flowing through the heater unit. Therefore, if the first fuel cell is a type that operates in a predetermined temperature range and has a high power generation efficiency, and the second fuel cell is a type that operates in a high temperature range and has a high exhaust heat temperature, the situation of the heater unit can be obtained. Accordingly, efficient thermoelectric supply can be performed.

  In the heat exchange system configured as described above, the cooling medium supply mechanism supplies the cooling medium flowing through the cooling path of the second fuel cell to the heater unit after flowing through the cooling path for cooling the first fuel cell. Then, after being subjected to heat exchange, the first fuel cell may be circulated. With such a configuration, the second fuel that operates at a higher temperature than the first fuel cell after the cooling medium that has become a low temperature due to heat exchange in the heater unit is warmed by the first fuel cell. Since it is supplied to the battery, the second fuel cell is not excessively cooled by the cooling medium. Therefore, the second fuel cell having high heat recovery efficiency can be stably operated on the high temperature side. In addition, the cooling medium supply mechanism supplies the heater unit with a high-temperature cooling medium from which heat has been recovered in two stages of the first fuel cell and the second fuel cell, so that the heat energy that can be efficiently used can be supplied. .

  In the heat exchange system configured as described above, the temperature difference between the outlet and the inlet of the cooling medium in the second fuel cell may be larger than the temperature difference between the outlet and the inlet of the cooling medium in the first fuel cell. Good. With such a configuration, the first fuel cell operates in a narrow temperature range, so that stable and efficient power generation can be performed. Further, since the second fuel cell operates in a wide temperature range, the heat recovery amount can be increased. Therefore, efficient thermoelectric supply utilizing each other's features becomes possible.

  In the heat exchanging system having such a configuration, the heater unit may include an assist mechanism that assists the insufficient amount of heat when the amount of heat recovered by heat exchange is insufficient with respect to the necessary amount of heat. With such a configuration, the second fuel cell that has risen efficiently due to the combination with the first fuel cell supplies heat energy that can be efficiently used to the heater unit. Can be reduced or stopped. Therefore, the fuel efficiency of the heat exchange system can be improved.

  Further, in the heat exchange system having such a configuration, the assist mechanism is a mechanism that assists the insufficient amount of heat using at least the electric power generated in the first fuel cell, and the operation control unit is configured to request the power output of the assist mechanism. The output of the first fuel cell may be changed to cope with the fluctuation. With such a configuration, since the first fuel cell capable of efficient power generation responds to fluctuations in the power output request of the assist mechanism, efficient thermoelectric supply can be performed. If the power output requirement of the assist mechanism is large when the heat exchange system is started up and then decreases, the transition of the power output requirement controls the temperature of the cooling medium supplied to the heater unit. This is compatible with the transition of operation required for the first fuel cell. Therefore, efficient thermoelectric supply can be performed.

  In the heat exchange system having such a configuration, the first fuel cell and the second fuel cell may be solid polymer fuel cells. With such a configuration, even in a polymer electrolyte fuel cell that operates in a relatively low temperature region, it is possible to supply high-temperature exhaust heat and perform efficient thermoelectric supply.

  Further, the heat exchange system having such a configuration may include an oxidizing gas flow path for supplying the oxidizing gas exhaust gas supplied to the first fuel cell to the second fuel cell for the oxidation reaction. With such a configuration, the oxidizing gas humidified by the water generated by the fuel cell reaction in the first fuel cell operates at a high temperature and is supplied to the second fuel cell that is easy to dry. It is possible to suppress the dry-up of the fuel cell and to operate stably.

  Further, in the heat exchange system configured as described above, the operation control unit is configured such that when the first fuel cell is stopped and the second fuel cell is in operation, the amount of heat required for the heater unit becomes a predetermined value or less. At this time, the temperature difference between the outlet and the inlet of the cooling medium in the second fuel cell may be controlled to be a predetermined value or less. With such a configuration, when the first fuel cell is stopped and the amount of heat necessary for the heater unit becomes a predetermined value or less, the temperature difference between the outlet and the inlet of the cooling medium in the second fuel cell becomes small. Thus, the operation temperature range of the second fuel cell is narrowed, so that the operation is stabilized and efficient thermoelectric supply can be performed.

The fuel cell used in the heat exchange system of the present invention is
The flow path of the cooling medium flowing inside the second fuel cell is formed in a predetermined one direction, and is a member of the second fuel cell that is generated by the temperature distribution formed along the predetermined one direction. The gist is that the change in thickness is fastened using a structure that can absorb the laminated surface of the laminated body constituting the second fuel cell.

  Alternatively, the flow path of the cooling medium flowing inside the second fuel cell is formed in a predetermined direction, and constitutes the second fuel cell generated by the temperature distribution formed along the predetermined direction. The gist is that a means for changing the fastening load of the second fuel cell so as to increase on the low temperature side of the temperature distribution according to the change in the thickness of the member is provided.

  The fuel cell having such a configuration has high heat recovery efficiency, that is, even when the temperature difference between the inlet and outlet of the cooling medium is large, the thickness of the members constituting the fuel cell generated by the temperature distribution formed in a predetermined direction. Can absorb changes. Or according to the change of the thickness of a member, the fastening load of a fuel cell is changed so that it may become large in the low temperature side of the said temperature distribution. Therefore, it is possible to alleviate the uneven surface pressure of each laminate constituting the fuel cell and suppress the leakage of fuel gas and the like.

An embodiment of the present invention will be described in the following procedure.
A. Heat exchange system configuration:
B. Operation of the heat exchange system:
C. Configuration of high-temperature fuel cell stack:

A. Heat exchange system configuration:
FIG. 1 is an explanatory diagram showing a schematic configuration of a heat exchange system 100 as an embodiment of the present invention. The heat exchange system 100 of the present embodiment is a system for supplying exhaust heat and electric energy of a fuel cell reaction to a heater unit mounted on a fuel cell vehicle, and is installed separately from a drive system fuel cell system. The fuel cell is used as a heat source.

  The heat exchange system 100 includes a fuel cell system 10 and a heater unit 90. The heater unit 90 is a vehicle interior heating system mounted on a fuel cell vehicle, and includes a heater core 92 and a heat pump 94. The heater core 92 is a heat exchanger for generating hot air by exchanging heat between the air blown for heating and the cooling water that has recovered the exhaust heat of the fuel cell system 10. The heat pump 94 is a heat pump system that supplementarily supplies heat using the electric energy generated by the fuel cell system 10 when the above-described heater core 92 alone does not provide sufficient hot air necessary for heating. Equipped with an evaporator, a condenser, a compressor, etc. (not shown). In the present embodiment, the heat pump 94 is used as the heat source assist mechanism of the heater core 92, but is not limited thereto. Various heat source devices such as an electric heater can be used.

  The fuel cell system 10 includes two types of fuel cell stacks, that is, a low temperature fuel cell stack 20 and a high temperature fuel cell stack 30. The fuel cell system 10 includes a low-temperature hydrogen supply mechanism 22, a low-temperature hydrogen discharge mechanism 24, a high-temperature hydrogen supply mechanism 32, a high-temperature hydrogen discharge mechanism 34, a cooling water circulation mechanism 40, an air supply mechanism 52, An air discharge mechanism 54 and an operation control unit 60 are provided.

  Among the elements constituting the fuel cell system 10, first, the low temperature fuel cell stack 20 and the high temperature fuel cell stack 30 will be described. Each of these is a polymer electrolyte fuel cell stack, and a plurality of laminated assemblies are sandwiched from both ends by terminals, insulators, and end plates. The laminate assembly described above functions as an electrode having a catalyst layer and a water repellent layer, an electrolyte membrane of a solid polymer member, a gas diffusion layer serving as a flow path for fuel gas and oxidizing gas, and a partition wall, and a cooling medium therein It is comprised from the separator provided with this flow path. As described above, these fuel cell stacks are installed separately from the drive fuel cell system for heating, and the output thereof is, for example, about 3 kW for both stacks. Therefore, it can be said that it is a small stack of about 1/30 to 1/40, for example, as compared with the fuel cell stack of the drive system.

  In the present application, the “low temperature type” and the “high temperature type” in the fuel cell stack described above refer to the operating temperature level at which the output of each fuel cell is maximized, and the level is a plurality of levels constituting the fuel cell system 10. Relative in fuel cells.

  FIG. 2 shows an example of temperature-output characteristics representing the relationship between operating temperature and voltage (output) for the low temperature fuel cell stack 20 and the high temperature fuel cell stack 30 in the present embodiment. In this example, the low-temperature fuel cell stack 20 can exhibit the maximum output V1 at the operating temperature of 80 ° C., but has a feature that the output is remarkably lowered as the operating temperature moves away from 80 ° C. On the other hand, the high temperature fuel cell stack 30 can exhibit the maximum output V2 at an operating temperature of 120 ° C. Although this output is smaller than the maximum output V1 of the low-temperature fuel cell stack 20, even when the operating temperature fluctuates from 120 ° C., the output gradually decreases.

  Such a difference in temperature-output characteristics can be realized by selecting fuel cell members or operating conditions. For example, if the thickness of the diffusion layer is increased, the water-repellent layer formed on the electrode is made dense, or the fuel gas or oxidizing gas is pressurized (for example, 100 kPa gauge), the maximum output point is obtained. Move to high temperature side.

  FIG. 3 shows the relationship between the chemical energy of hydrogen that can be extracted by the fuel cell reaction, and the electrical energy and thermal energy obtained. The so-called fuel cell reaction is a reaction that converts chemical energy of hydrogen into electric energy and thermal energy. Further, the chemical energy of hydrogen that can be extracted by the fuel cell reaction is constant. On the other hand, in the fuel cell reaction, as shown, the voltage drop increases and the voltage decreases as the current density increases. Therefore, as the current density increases, the rate of conversion to electrical energy in the chemical energy of hydrogen decreases, and the rate of conversion to thermal energy increases.

  Therefore, based on the temperature-output characteristics of the fuel cell stack shown in FIG. 2 and the energy relationship shown in FIG. 3, the low-temperature fuel cell stack 20 has a higher hydrogen content than the high-temperature fuel cell stack 30. It can be said that this is a fuel cell stack that can efficiently convert the chemical energy it has into electrical energy (high power generation efficiency), but produces less heat energy (not high heat recovery efficiency). On the other hand, the high-temperature fuel cell stack 30 is not so high in power generation efficiency as the low-temperature fuel cell stack 20, but has a high heat recovery efficiency and is easy to use because the exhaust heat is high temperature. It can be said that it is a battery stack.

  Next, other elements constituting the fuel cell system 10 will be described. The low temperature type hydrogen supply mechanism 22 is a mechanism for supplying hydrogen as a fuel gas to the low temperature type fuel cell stack 20, and includes a hydrogen tank, a shut valve, a regulator, a circulation pump, piping, and the like (not shown). The low-temperature hydrogen discharge mechanism 24 is a mechanism that discharges exhaust gas (anode off gas) from the low-temperature fuel cell stack 20 to the outside of the system, and includes a pipe or the like. Similarly, the high-temperature hydrogen supply mechanism 32 and the high-temperature hydrogen discharge mechanism 34 are also mechanisms for supplying or discharging hydrogen to the high-temperature fuel cell stack 30.

  The cooling water circulation mechanism 40 circulates a cooling medium (cooling water here) for cooling the low temperature type fuel cell stack 20 and the high temperature type fuel cell stack 30, and the low temperature type fuel cell stack 20 and the high temperature type fuel cell stack 30. This is a mechanism for adjusting the operating temperature, and includes a cooling water circulation pump 42, a cooling water circulation pipe 44, a radiator 46, and valves 47 and 48.

  The cooling water flow path connects the low temperature fuel cell stack 20 and the high temperature fuel cell stack 30 in series so that the high temperature fuel cell stack 30 is on the downstream side, and further on the downstream side, The heater unit 90 is connected. The cooling water is circulated between the low temperature fuel cell stack 20, the high temperature fuel cell stack 30 and the heater unit 90 by the cooling water circulation pump 42, and fuel in the low temperature fuel cell stack 20 and the high temperature fuel cell stack 30. Heat generated by the battery reaction is recovered and radiated by the heater core 92 of the heater unit 90. Further, the cooling water circulation pipe 44 is provided with a bypass line to the radiator 46, and the temperature of the cooling water can be adjusted according to the situation by opening and closing the valves 47 and 48.

  The air supply mechanism 52 is a mechanism for supplying air as an oxidizing gas to the low-temperature fuel cell stack 20 and the high-temperature fuel cell stack 30, and includes an air cleaner, an air compressor, piping, and the like (not shown). The air discharge mechanism 54 is a mechanism that discharges exhaust gas (cathode off-gas) from the low-temperature fuel cell stack 20 and the high-temperature fuel cell stack 30 to the outside of the system, and includes a diluter, a pipe, and the like (not shown). The air supply mechanism 52 and the air discharge mechanism 54 are mechanisms commonly used for the low temperature type fuel cell stack 20 and the high temperature type fuel cell stack 30, and the air flow paths are the low temperature type fuel cell stack 20 and the high temperature type fuel cell stack 30. The fuel cell stack 30 is connected in series so that the high-temperature fuel cell stack 30 is on the downstream side.

  The operation control unit 60 is a microcomputer that receives an output request from the heater unit 90 and input signals from various sensors, sends instruction signals to various loads, and controls the overall functions of the heat exchange system 100.

B. Operation of the heat exchange system:
Next, an operation example of the heat exchange system 100 will be described with reference to FIG. In this system, when the operation control unit 60 receives an output request from the heater unit 90, the fuel cell system 10 starts operating. That is, hydrogen and air are supplied to the low temperature fuel cell stack 20 and the high temperature fuel cell stack 30, and power generation is started. When power generation is started and the fuel cell reaction proceeds, the low temperature fuel cell stack 20 and the high temperature fuel cell stack 30 are gradually warmed up.

  FIG. 4A shows an example of the relationship between the position and temperature of the cooling water circulating through the low temperature fuel cell stack 20, the high temperature fuel cell stack 30, and the heater unit 90 at this time. As indicated by the solid line in the figure, the cooling water at temperature T01 is supplied to the low temperature fuel cell stack 20, recovers heat, is warmed to temperature T02, and is further supplied to the high temperature fuel cell stack 30. After recovering the heat and warming up to the temperature T03, the heat is supplied to the heater unit 90 to exchange heat with the heater core 92, cooled to the temperature T01, and supplied again to the low temperature fuel cell stack 20. Then, when the passenger compartment is gradually warmed and the required amount of heat in the heater unit 90 decreases, the temperature of the circulating cooling water rises as a whole as shown by the one-dot chain line in the figure. The temperature of the cooling water at this time is, for example, 65 ° C. at the inlet temperature T11 of the low temperature fuel cell stack 20, 75 ° C. at the inlet temperature T12 of the high temperature fuel cell stack 30, and 105 ° C. at the inlet temperature T13 of the heater unit 90. Become.

  Here, the temperature difference between the inlet and outlet of the cooling water in the low temperature fuel cell stack 20 and the high temperature fuel cell stack 30 is higher than that in the low temperature fuel cell stack 20 as shown in FIG. I am driving so that 30 becomes large. In order to operate in this way, for example, the number of stacks in the stack assembly may be increased in the high temperature fuel cell stack 30 than in the low temperature fuel cell stack 20. The cooling water carry-out heat quantity Q is expressed by the following equation (1) using the temperature difference ΔT at the inlet / outlet of the cooling water, the number n of the laminated assemblies, the flow rate L of the cooling water per laminated assembly, and the specific heat capacity C of the water. Therefore, the temperature difference ΔT at the inlet / outlet of the cooling water can be increased by reducing the cooling water flow rate L per laminate assembly.

  Q = ΔT × n × L × C (1)

  Thus, by reducing the temperature difference between the inlet and outlet of the cooling water in the low-temperature fuel cell stack 20, stable and efficient power generation is performed around the output peak of the temperature-output characteristics shown in FIG. be able to. Further, since the high temperature fuel cell stack 30 operates in a wide temperature range, the power generation cannot be performed as stably and efficiently as the low temperature fuel cell stack 20, but the temperature difference between the inlet and outlet of the cooling water is greatly increased. Therefore, the amount of heat recovery can be increased. Therefore, it is possible to efficiently supply thermoelectric power by utilizing the mutual characteristics of the low temperature fuel cell stack 20 having excellent power generation efficiency and the high temperature fuel cell stack 30 having excellent heat recovery efficiency.

  However, for the high-temperature fuel cell stack 30, it is desirable to adopt a type with a small output temperature dependency in order to perform the stable operation by making the electrolyte membrane wet as uniform as possible. The temperature dependence can be reduced, for example, by increasing the thickness of the diffusion layer constituting the high-temperature fuel cell stack 30 or by densifying the water-repellent layer formed on the electrode.

  FIG. 4B shows an example of the relationship between the change in temperature at the inlet of the cooling water heater unit 90 and the change in the outputs of the low temperature fuel cell stack 20 and the high temperature fuel cell stack 30. At the beginning of operation, the interior of the vehicle is not warmed, and it is necessary to heat it quickly, the temperature of the cooling water is low, the necessity of assisting the heat pump 94 is large, and for efficient thermoelectric supply. Therefore, the operation control unit 60 outputs the low temperature fuel cell stack 20 with high power generation efficiency (low temperature output in the figure), heat Control is performed so that the output (high-temperature output in the figure) of the high-temperature fuel cell stack 30 with high recovery efficiency becomes the maximum value. At this time, the output obtained from the low temperature fuel cell stack 20 and the high temperature fuel cell stack 30 is used for a heat pump 94 as a heat source assist mechanism, and the heat energy recovered through the cooling water is heat exchanged by the heater core 92. To be served.

  When the heater unit inlet temperature rises as the operation time elapses, the passenger compartment gradually warms and the necessary heat amount of the heater unit 90 decreases, the temperature of the cooling water rises, and efficiently Since it becomes possible to recover heat and the necessary assist heat source is reduced accordingly, the operation control unit 60 gradually decreases the output of the low-temperature fuel cell stack 20. When the passenger compartment is sufficiently warmed and the inlet temperature of the cooling water in the heater unit 90 reaches a predetermined temperature, the operation control unit 60 uses only the heat energy and power energy generated in the high-temperature fuel cell stack 30 to generate the heater. The unit 90 is controlled.

  Then, when the low temperature fuel cell stack 20 is stopped and the amount of heat required by the heater unit 90 becomes a predetermined value or less, the operation control unit 60 increases the flow rate of the cooling water flowing through the high temperature fuel cell stack 30. The reason why the flow rate of the cooling water is increased in this way is that the heater unit 90 can be controlled only by supplying the exhaust heat of the high-temperature fuel cell stack 30, and it is no longer necessary to increase the temperature of the cooling water. By reducing the temperature difference between the inlet and outlet of the cooling water in the high-temperature fuel cell stack 30 and narrowing the operating temperature range of the high-temperature fuel cell stack 30, power generation can be stabilized and efficient power recovery can be performed. It is.

  In the heat exchange system 100 having such a configuration, at least the low temperature fuel cell stack 20 or the high temperature fuel cell stack 30 is controlled based on the inlet temperature of the cooling water to the heater unit 90. The low temperature type fuel cell stack 20 is a type with high power generation efficiency, and the high temperature type fuel cell stack 30 is a type that operates in a high temperature range (high exhaust heat temperature). Depending on the energy, efficient thermoelectric supply can be performed.

  In the heat exchange system 100 having such a configuration, the cooling water circulation mechanism 40 circulates the cooling water in the order of the low temperature fuel cell stack 20, the high temperature fuel cell stack 30, and the heater unit 90. Therefore, in addition to the function that the low-temperature fuel cell stack 20 generates electrical energy that serves as an assist heat source for the heat pump 94, the cooling water that has become a low temperature due to heat exchange in the heater unit 90 is warmed, and the high-temperature fuel cell stack Also fulfills the function of supplying to 30. As a result, the high temperature fuel cell stack 30 can be stably operated on the high temperature side. In addition, since heat is recovered in two stages of the low-temperature fuel cell stack 20 and the high-temperature fuel cell stack 30, higher-temperature cooling water is supplied to the heater unit 90. Can be supplied to the unit.

  Further, in the heat exchange system 100 configured as described above, since the output of the low-temperature fuel cell stack 20 that excels in power generation efficiency is responded to fluctuations in the power output requirement of the heat pump 94, efficient thermoelectric supply can be performed. . In addition, the power output request of the heat pump 94 as an assist heat source requires rapid heating, and since there is a great need to assist the amount of heat that can be recovered from cooling water having a low temperature, the heat exchange system 100 is started up. Although sometimes large and then decreasing, the transition of the power output requirement is compatible with the transition of operation required for the low-temperature fuel cell stack 20 that functions to warm the cooling water supplied to the high-temperature fuel cell stack 30. Therefore, efficient heat supply can be performed.

  Further, in the heat exchange system 100 having such a configuration, air as an oxidizing gas is supplied to the low temperature fuel cell stack 20 by the air supply mechanism 52. The humidified air containing water generated by the fuel cell reaction in the low temperature fuel cell stack 20 is supplied to the high temperature fuel cell stack 30. Therefore, since humidified air can be supplied to the high-temperature fuel cell stack 30 that operates in a high temperature region and the electrolyte membrane is easy to dry, it is possible to suppress dry-up of the electrolyte membrane and perform stable operation. it can.

  In the heat exchange system 100 of the present embodiment, as described above, the small-scale low-temperature fuel cell stack 20 and the high-temperature fuel cell stack installed separately from the drive-system fuel cell stack as the heat source of the heater unit 90. 30 is used. Therefore, compared with the case where a drive system fuel cell stack is used as a heat source, the heat capacity of the fuel cell stack is very small, so that warming can be performed quickly and the heater unit 90 can be quickly started up, and heat exchange can be performed. The system 100 can be operated efficiently.

C. Configuration of high-temperature fuel cell stack:
C-1. High temperature fuel cell stack features:
As a premise of the configuration of the high temperature fuel cell stack 30, temperature distribution and thermal expansion in the high temperature fuel cell stack 30 will be described with reference to FIGS. FIG. 6A is an explanatory view showing a cooling water flow path 37 provided in the separator 38 used in the multilayer assembly 35 constituting the high temperature fuel cell stack 30 of the present embodiment. As illustrated, each of the plurality of cooling water flow paths 37 has a structure that linearly flows in the long side direction (ab direction) of the separator. The cooling water flowing through the cooling water flow path 37 is supplied to the separator from the cooling water inlet side (ad side), absorbs heat generated by the fuel cell reaction, and gradually increases the temperature while the cooling water outlet side (b -C side).

  The temperature difference at the inlet / outlet of the cooling water here is 30 ° C. (inlet: 75 ° C., outlet: 105 ° C.) in the above-described operation example. This temperature difference is generally about 10 to 15 ° C. for obtaining a stable output in the polymer electrolyte fuel cell (in the above operation example, the temperature difference between the inlet and outlet of the cooling water in the low temperature type fuel cell stack 20). The temperature difference is very large compared to 10 ° C.). As described above, the high-temperature fuel cell stack 30 efficiently recovers heat and supplies the heater unit 90 with heat energy that can be efficiently used at high temperatures. This is because a large temperature difference is secured.

  In this way, the cooling water flows in one direction, and by taking a large temperature difference between the inlet and outlet of the cooling water, in the high-temperature fuel cell stack 30, as shown in FIG. A large temperature distribution is formed in the flow direction of the cooling water passage 37 (the direction from a to b in the figure) so that the outlet side (bc side) of the cooling water becomes high temperature. As a result, the thermal expansion of the members constituting the laminate assembly 35 due to the heat generated with the power generation in the high-temperature fuel cell stack 30 is small on the cooling water inlet side (ad side), and the cooling water outlet side (b -C side). Since this phenomenon occurs in all the stacked bodies 36 in which a large number of the stacked body assemblies 35 are stacked, when viewed as a whole, a large deviation is generated in the amount of thermal expansion.

  As described above, the phenomenon of thermal expansion unevenness at the inlet side and the outlet side of the cooling water is not limited to the linear cooling water flow path shown in FIG. For example, it may be a serpentine type channel shown in FIG. In FIG. 6B, although there are a part where the cooling water flows in the ab direction and a part where the cooling water flows in the ad direction, it can be said that the cooling water generally flows in the ab direction. As described above, if the flow is generally directed in a predetermined direction, the same uneven phenomenon can occur.

C-2. Example:
Based on the characteristics of the high-temperature fuel cell stack 30 described above, the configuration of the high-temperature fuel cell stack 30 as an embodiment will be described with reference to FIG. As shown in the drawing, the high temperature fuel cell stack 30 is configured by sandwiching both ends of a laminate 36 in which a large number of laminate assemblies 35 are laminated with terminals 73a and 73b, insulators 72a and 72b, and end plates 71a and 71b. Yes.

  Fastening portions 74a and 74b are provided on upper portions of the end plates 71a and 71b constituting both ends of the high-temperature fuel cell stack 30, and these are connected to the connecting rod 77a. Fastening portions 74c and 74d (not shown) and a connecting rod 77b (not shown) having the same structure as the upper part are also provided at the lower portions of the end plates 71a and 71b. By adjusting the lengths of the connecting rods 77a and 77b, the end plates 71a and 71b pressurize the terminals 73a and 73b, the insulators 72a and 72b, and the stacked body 36 from both ends, and the high-temperature fuel cell stack 30 is pressed. The whole is fixed.

  The fastening portions 74a and 74b and the connecting rod 77a provided on the upper portions of the end plates 71a and 71b will be described in more detail with reference to FIG. FIG. 8 is an explanatory view showing a top view of the high-temperature fuel cell stack 30 shown in FIG. As shown in the drawing, the fastening portion 74b has a hole through which the tip of the connecting rod 77a passes. The fastening portion 74b and the connecting rod 77a are fixedly connected by fastening the nut 76b to the tip of the connecting rod 77a penetrating this hole. On the other hand, the fastening portion 74a has a spherical recess. A ball joint 75a that can be fitted and rotated in the recess is attached to the tip of the connecting rod 77a, and the fastening portion 74a and the connecting rod 77a can be rotated in the left-right direction via the ball joint 75a. It is connected to. The fastening portions 74c and 74d (not shown) and the connecting rod 77b (not shown) provided below the end plates 71a and 71b have the same structure as the fastening portions 74a and 74b and the connecting rod 77a. .

  As described above, the end plate 71b, the connecting rod 77a and the connecting rod 77b (not shown) are fixedly connected, and the end plate 71a, the connecting rod 77a and the connecting rod 77b (not shown) are rotatable. By connecting, the end plate 71a can be rotated and moved by a predetermined angle in the lateral direction. Accordingly, when the amount of thermal expansion of the member on the high temperature side (cooling water outlet side) of the high temperature fuel cell stack 30 is larger than that on the low temperature side (cooling water inlet side), the end plate 71a has a high temperature as shown in the figure. On the side, the end plate 71a and the end plate 71b rotate and move in a direction in which the distance becomes longer.

  In the high-temperature fuel cell stack 30 having such a configuration, even if the thermal expansion amount of the member is uneven due to ensuring a large temperature difference between the inlet and outlet of the cooling water, the end plate 71a follows the uneven expansion amount. Rotate and move. Therefore, the surface pressure inside the laminate assembly 35 can be made uniform, and leakage of hydrogen and the like can be prevented.

C-3. Variation:
A detailed configuration of the high-temperature fuel cell stack 30 as a modification will be described with reference to FIG. As shown in the drawing, in the high temperature fuel cell stack 30, as in the embodiment, both ends of a laminate 36 in which a large number of laminate assemblies 35 are laminated are terminals 73a and 73b, insulators 72a and 72b, and end plates 71a and 71b. It is configured to be sandwiched. The difference from the embodiment is that the structures of the fastening portions 84a and 84c provided at the upper and lower portions of the end plate 71a are the same as the fastening portions 74b and 74d, and the end plate 71a is fixed to the connecting rods 77a and 77b. And springs 88a to 88e are provided between the end plate 71b and the insulator 72b.

  In this example, the temperature distribution of the stacked body 36 becomes higher from the bottom to the top, so that the thermal expansion amount of the stacked body assembly 35 also increases from the bottom to the top. Correspondingly, the springs 88a to 88e are displaced largely in the order of 88a, 88b, 88c, 88d, and 88e, and absorb the change in the thickness in the stacking direction due to the thermal expansion of the stacked body 36.

  In the present embodiment, five springs are used as a structure that can absorb a change in thickness in the stacking direction due to thermal expansion, but the number of springs is not limited to five. Of course, it is not limited to a spring, and a shape memory alloy, a resin elastic body, or the like may be used to absorb a change in thickness due to thermal expansion.

  In the high-temperature fuel cell stack 30 having such a configuration, the springs 88 a to 88 e absorb changes in the thickness of the stacked body assembly 35 caused by thermal expansion along the stacked surface of the stacked body 36. Therefore, the difference in the surface pressure inside the laminate assembly 35 can be alleviated and leakage of hydrogen or the like can be prevented.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an example, and it is needless to say that the present invention can be implemented in various modes without departing from the gist of the present invention. For example, in the present embodiment, the heater unit 90 is provided with the heater core 92 as the assist mechanism, but may not include the assist mechanism. Naturally, the heat exchange system is not limited to the heat exchange system used for heating the fuel cell vehicle, and can be configured as various heat exchange systems such as a heating using a fuel cell cogeneration system at home and a heat exchange system for hot water supply. The cooling medium is not limited to a configuration that circulates between the fuel cell and the heater unit, but may be a configuration that only supplies the cooling medium.

It is explanatory drawing which shows schematic structure of the heat exchange system 100 as an Example of this invention. It is explanatory drawing which shows the relationship between the operating temperature of a fuel cell stack, and a voltage. It is explanatory drawing which shows the relationship between the chemical energy which the hydrogen which can be taken out by fuel cell reaction has, and the electrical energy and heat energy which are obtained. 3 is an explanatory diagram illustrating an operation example of the heat exchange system 100. FIG. It is explanatory drawing which shows the relationship between the temperature distribution in a fuel cell stack, and expansion of a member. It is explanatory drawing regarding the flow path direction of a cooling medium. It is a perspective view which shows the structure of the high temperature type fuel cell stack 30 as an Example. It is a top view which shows the structure of the high temperature type fuel cell stack 30 as an Example. It is explanatory drawing which shows the structure of the high temperature type fuel cell stack 30 as a modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 20 ... Low temperature type fuel cell stack 22 ... Low temperature type hydrogen supply mechanism 24 ... Low temperature type hydrogen discharge mechanism 30 ... High temperature type fuel cell stack 32 ... High temperature type hydrogen supply mechanism 34 ... High temperature type hydrogen discharge Mechanism 35 ... Laminated body assembly 36 ... Laminated body 37 ... Cooling water flow path 38 ... Separator 40 ... Cooling water circulation mechanism 42 ... Cooling water circulation pump 44 ... Cooling water circulation piping 46 ... Radiator 47, 48 ... Valve 52 ... Air supply mechanism 54 ... Air discharge Mechanism 60 ... Operation control unit 71a, 71b ... End plate 72a, 72b ... Insulator 73a, 73b ... Terminal 74a-74d ... Fastening part 75a ... Ball joint 76b ... Nut 77a, 77b ... Connecting rod 84a, 84c ... Fastening part 88a-88e ... Spring 90 ... Heater unit 92 ... H Stator core 94 ... heat pump 100 ... heat exchange system

Claims (10)

A heat exchange system having a heat source and a heater unit for exchanging heat from the heat source,
The heat source includes a first fuel cell that generates power in a predetermined temperature region, and a second fuel cell in a temperature region in which an operating temperature during power generation is higher than that of the first fuel cell.
A cooling medium supply mechanism that supplies a cooling medium to the first and second fuel cells and the heater unit, and supplies heat generated in the first and second fuel cells to the heat exchange in the heater unit;
A heat exchange system comprising: an operation control unit that controls at least the first fuel cell or the second fuel cell based on the temperature of the cooling medium flowing through the heater unit. The heat exchange system according to claim 1,
The cooling medium supply mechanism supplies the cooling medium flowing through the cooling path of the second fuel cell to the heater unit after flowing through the cooling path for cooling the first fuel cell for the heat exchange. A heat exchange system that is circulated to the first fuel cell after being provided. The heat exchange system according to claim 2,
The heat exchange system in which a temperature difference between an outlet and an inlet of the cooling medium in the second fuel cell is larger than a temperature difference between an outlet and an inlet of the cooling medium in the first fuel cell. The heat exchange system according to any one of claims 1 to 3,
The said heater unit is a heat exchange system provided with the assist mechanism which assists the insufficient heat quantity, when the heat recovery amount by the said heat exchange is insufficient with respect to the required heat quantity. The heat exchange system according to claim 4,
The assist mechanism is a mechanism that assists the insufficient amount of heat using at least the electric power generated in the first fuel cell.
The operation control unit is a heat exchange system that responds by changing the output of the first fuel cell in response to fluctuations in the power output request of the assist mechanism. A heat exchange system according to any one of claims 1 to 5,
The heat exchange system, wherein the first fuel cell and the second fuel cell are solid polymer fuel cells. The heat exchange system according to claim 6,
A heat exchange system comprising an oxidizing gas flow path for supplying an oxidizing gas exhaust gas supplied to the first fuel cell to the second fuel cell for an oxidation reaction. A heat exchange system according to any one of claims 1 to 7,
The operation control unit is configured such that when the first fuel cell is stopped and the second fuel cell is in operation, when the amount of heat necessary for the heater unit becomes a predetermined value or less, A heat exchange system that controls a temperature difference between an outlet and an inlet of the cooling medium in a fuel cell to be small. A second fuel cell used in the heat exchange system according to claim 1,
The flow path of the cooling medium flowing inside the second fuel cell is formed in a predetermined direction,
A change in the thickness of the member constituting the second fuel cell caused by the temperature distribution formed along the predetermined direction can be absorbed along the laminate surface of the laminate constituting the second fuel cell. A fuel cell that is fastened using a simple structure. A second fuel cell used in the heat exchange system according to claim 1,
The flow path of the cooling medium flowing inside the second fuel cell is formed in a predetermined direction,
The fastening load of the second fuel cell is changed to the low temperature side of the temperature distribution according to the change in the thickness of the member constituting the second fuel cell caused by the temperature distribution formed along the predetermined direction. A fuel cell equipped with means to change the size of the fuel cell.

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