JP2009238628A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To warm up a fuel-cell stack by effectively use heat generated in a system. <P>SOLUTION: A heat exchanger 40 is attached to a fuel-cell stack 2, air compressed by an air compressor 10 and raised in temperature is supplied to the heat exchanger 40. The air used for heat exchange in the heat exchanger 40 is supplied to the fuel-cell stack 2 as an oxidizer gas for power generation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell system having a fuel cell stack, and more particularly to a fuel cell system capable of preventing a temperature drop of the fuel cell stack due to heat dissipation.

  A fuel cell is used as a fuel cell stack in which a membrane electrode assembly formed by sandwiching an electrolyte membrane between catalyst electrodes is a minimum unit (hereinafter referred to as a cell), and several tens to several hundreds of cells are stacked. . Each cell is supplied with an oxidant gas and a fuel gas, and the reaction gas reacts with the membrane electrode assembly interposed therebetween to generate a cell voltage. The sum of the cell voltages becomes the output voltage of the fuel cell stack.

  There is an appropriate temperature range for the power generation reaction that causes voltage to occur in the cell in order for it to occur efficiently. Although this appropriate temperature range is higher than normal temperature, since the power generation reaction is an exothermic reaction, the temperature of the membrane electrode assembly rises due to self-heating. For this reason, during power generation, cooling with cooling water is performed so that the temperature of the membrane electrode assembly does not exceed the appropriate temperature range. However, in a situation where the outside air temperature is low as in winter, the amount of heat released to the outside may exceed the amount of heat generated inside, and the appropriate temperature range may not be maintained. In particular, the cells near both ends of the fuel cell stack are deprived of large amounts of heat by current collector plates with large heat capacity and thermal conductivity. The temperature of the electrode assembly is likely to decrease. In addition, a special operation method is adopted to quickly increase the temperature of the membrane electrode assembly at the time of cold start of the fuel cell stack, but also in this case, the temperature increase of the outer cell is slower than that of the inner cell. Therefore, it takes time until the fuel cell stack as a whole has sufficient power generation performance.

  For this reason, conventionally, in a fuel cell system considering use in a low temperature environment or starting from a low temperature state, a means for preventing a temperature drop of the fuel cell stack due to heat radiation by external heat supply has been adopted. The most common example is an electric heater. The fuel cell stack is warmed up by attaching an electric heater to the fuel cell stack and causing the electric heater to generate heat.

  However, electric power is required to generate heat from the electric heater, and the electric power is supplied directly from the battery when the system is started and directly from the fuel cell stack when generating power. That is, a part of the electric power generated by the fuel cell stack must be consumed. For this reason, in the system which warms up with an electric heater, there existed a problem that a fuel consumption will deteriorate by the part for the electric power consumption by an electric heater.

On the other hand, the patent documents listed below disclose technologies that utilize heat generated by power generation of the fuel cell stack. In particular, Patent Document 2 discloses a technique for warming air as an oxidant gas using heat of a fuel cell stack. However, since these technologies are based on the premise that there is extra heat in the fuel cell stack, the fuel cell stack needs heat like use in a low temperature environment or starting from a low temperature state. Useless in the situation.
Japanese translation of PCT publication No. 2002-522891 JP 2005-005074 A JP 2006-252982 A

  As described above, when an electric heater is used as a heat source for warming up the fuel cell stack, the problem of deterioration in fuel consumption is inevitable. However, the fuel cell stack itself cannot be used as a heat source for warming up. In order to warm up the fuel cell stack without deteriorating the fuel consumption, it is necessary to supply heat to the fuel cell stack from a heat source other than the fuel cell stack existing in the system.

  The present invention has been made to solve the above-described problems, and provides a fuel cell system that can warm up a fuel cell stack by effectively using heat generated in the system. Objective.

In order to achieve the above object, a fuel cell system according to a first invention comprises:
A fuel cell stack that generates power by receiving supply of oxidant gas and fuel gas; and
An air compressor for supplying air as an oxidant gas to the fuel cell stack;
A heat exchanger attached to the fuel cell stack, through which air heated by compression by the air compressor is passed;
It is characterized by having.

According to a second invention, in the first invention,
The air that has passed through the heat exchanger is supplied to the fuel cell stack as an oxidant gas.

According to a third invention, in the second invention,
An air supply passage from the air compressor to the fuel cell stack includes a main passage that directly connects the air compressor and the fuel cell, a branch from the main passage, the heat exchanger, and the main passage again. It is characterized by comprising a branch passage that joins the passage.

According to a fourth invention, in the third invention,
The main passage is provided with a cooler that cools the air that has been compressed by the air compressor and heated, and the sub-passage is branched from the main passage upstream of the cooler and again upstream of the cooler. It is characterized by merging with the main passage.

A fifth invention is the fourth invention,
A flow rate adjusting means is provided for adjusting the flow rate of the air supplied from the air compressor to the fuel cell stack through the sub-passage in the air supplied to the fuel cell stack.

According to a sixth invention, in the fifth invention,
The flow rate adjusting means adjusts the flow rate of air passed through the heat exchanger based on the temperature of air at the inlet and outlet of the heat exchanger.

A seventh invention is the invention according to any one of the first to sixth inventions,
The heat exchanger is arranged in the fuel cell stack side by side with a plurality of cells constituting the fuel cell stack.

In an eighth aspect based on the seventh aspect,
The heat exchanger is arranged inside the end plate at the end of the fuel cell stack.

In a ninth aspect based on the eighth aspect,
The heat exchanger is integrated with a current collector plate provided at an end of the fuel cell stack.

  According to the first aspect of the invention, the fuel cell stack can be warmed up using the air compressed by the air compressor and heated.

  According to the second aspect of the invention, since the air used for warming up is supplied to the fuel cell stack as an oxidant gas for power generation, work performed by the air compressor is not wasted.

  According to the third aspect of the invention, since the air that is turned to the heat exchanger is part of the air that is supplied from the air compressor to the fuel cell stack, the pressure loss of the air due to the heat exchanger can be suppressed.

  According to the fourth aspect of the invention, the high-temperature air before cooling can be passed through the heat exchanger to effectively warm up the fuel cell stack. Can send.

  According to the fifth aspect, the amount of heat supplied to the fuel cell stack can be controlled by adjusting the flow rate of air passing through the heat exchanger.

  According to the sixth aspect of the invention, the temperature state of the fuel cell stack can be accurately grasped by looking at the air temperature at the inlet and the air temperature at the outlet of the heat exchanger. And based on the exact grasp, the flow volume of the air supplied to a heat exchanger can be adjusted appropriately.

  According to the seventh aspect, since the heat exchanger is arranged alongside the cells in the fuel cell stack, heat can be supplied to the adjacent cells from the inside of the fuel cell stack.

  According to the eighth aspect of the invention, it is possible to prevent a temperature drop of the cell at the end which is particularly easy to cool.

  According to the ninth aspect, the heat exchange efficiency with respect to the cell at the end can be increased by integrating the current collector plate and the heat exchanger.

  FIG. 1 is a diagram showing a configuration of a fuel cell system as an embodiment of the present invention. This fuel cell system includes a fuel cell stack 2 configured by stacking a large number of cells 4. Although not shown, each cell 4 is configured by sandwiching both sides of a membrane electrode assembly with a separator. A current collector plate and an insulator (not shown) are sequentially arranged on both outer sides of the stacked cell group. In the fuel cell system of the present embodiment, a heat exchanger 40 to be described later is arranged on the outer side, and the end plate 6 is arranged on the outer side. The laminated bodies including the cells 4 are positioned and fixed by fastening the end plates 6 on both sides with fastening members (not shown).

An air supply passage 12 and an air discharge passage 14 are connected to the fuel cell stack 2. The air supply passage 12 is a passage for supplying air as an oxidant gas necessary for power generation reaction to the fuel cell stack 2, and is connected to the air compressor 10. The air compressor 10 compresses the sucked air and sends it to the air supply passage 12. Air compressor 10
There is no particular limitation on the format. Roots type, screw type, or other types may be used. An intercooler 16 for cooling the air that has been compressed by the air compressor 10 and has reached a high temperature is disposed in the air supply passage 12. The air supplied from the air supply passage 12 to the fuel cell stack 2 is distributed to the cathode-side gas flow path provided in each of the stacked cells 4. The air distributed in this way flows along the cathode side surface of each membrane electrode assembly and is then discharged to the air discharge passage 14.

  The fuel cell stack 2 generates water on the cathode side of each cell 4 when generating power by reacting oxygen and hydrogen. For this reason, the gas discharged from the air discharge passage 14 contains moisture. A humidifier 18 is disposed downstream of the intercooler 16 in the air supply passage 12. The humidifier 18 has a function of humidifying the air on the air supply passage 12 side using moisture contained in the air discharge passage 14. Further, a pressure regulating valve 20 is disposed upstream of the humidifier 18 in the air discharge passage 14.

  A hydrogen supply passage 26 and a hydrogen discharge passage 28 are connected to the fuel cell stack 2. The hydrogen supply passage 28 is a passage for supplying hydrogen as a fuel gas necessary for power generation reaction to the fuel cell stack 2, and is connected to the hydrogen tank 30. Hydrogen supplied from the hydrogen supply passage 26 to the fuel cell stack 2 is distributed to the anode-side gas flow path provided in each of the stacked cells 4. The hydrogen supplied to the anode side flows through the surface of each membrane electrode assembly and then is discharged to the hydrogen discharge passage 28.

  The hydrogen discharge passage 28 is connected to the hydrogen supply passage 26 via a hydrogen circulation pump 32 with a reversely supported valve. Thus, by rotating the hydrogen circulation pump 32, the hydrogen discharged from the fuel cell stack 2 is sent to the hydrogen supply passage 26 and supplied again to the fuel cell stack 2. A gas-liquid separator 36 is disposed upstream of the hydrogen circulation pump 32 in the hydrogen discharge passage 28. An exhaust valve 38 is connected to the gas-liquid separator 36. The exhaust valve 38 is controlled to open only when a predetermined purge condition is satisfied with the closed state as its basic state.

  One feature of the system configuration shown in FIG. 1 is that a heat exchanger 40 is arranged in the fuel cell stack 2 along with the cells 4. The heat exchanger 40 has substantially the same size (height and width) as the cell 4 and the current collector plate, and is externally integrated with the cell 4 and the current collector plate. When a high-temperature gas is introduced into the heat exchanger 40, the heat exchanger 40 takes heat of the gas and dissipates heat from the inner side surface of the heat exchanger 40, that is, the side surface on which the cell 4 is disposed. It has a structure.

  A heat exchanger air introduction passage 42 branched from the air supply passage 12 is connected to the inlet side of the heat exchanger 40. In the heat exchanger 40, high-temperature air taken out from the air supply passage 12 by the introduction passage 42 is used for heat exchange. The introduction passage 42 is branched from the air supply passage 12 upstream of the intercooler 16. On the other hand, a return passage 44 for returning air used for heat exchange to the air supply passage 12 is connected to the outlet side of the heat exchanger 40. The connection point of the return passage 44 to the air supply passage 12 is upstream of the intercooler 16 and downstream of the branch point of the introduction passage 42. The air supply passage 12 corresponds to a “main passage” according to the present invention, and the heat exchanger air introduction passage 42 and the return passage 44 correspond to a “sub-passage”.

  A flow rate adjusting valve 50 for adjusting the flow rate of air flowing therethrough is arranged in the heat exchanger air introduction passage 42. Further, a temperature sensor 46 for measuring the temperature of the air entering the heat exchanger 40 is disposed in the introduction passage 42 near the inlet of the heat exchanger 40. In the return passage 44, a temperature sensor 48 for measuring the temperature of the air exiting from the heat exchanger 40 is disposed near the outlet of the heat exchanger 40. The opening degree of the flow rate adjusting valve 50 is controlled by the control device 52 of the fuel cell system. The control device 52 estimates the internal temperature of the fuel cell stack 2 from the inlet air temperature measured by the temperature sensor 46 and the outlet air temperature measured by the temperature sensor 48, and the flow rate adjusting valve 50 according to the estimated internal temperature. The degree of opening is controlled. The flow rate adjusting valve 50, the temperature sensors 46 and 48, and the control device 52 constitute the “flow rate adjusting means” according to the present invention.

  The above is the description of the configuration of the fuel cell system according to the present embodiment. According to such a configuration, the fuel cell stack 2 can be warmed up using the air compressed by the air compressor 10 and heated to a high temperature. Further, since the heat exchanger 40 is arranged in the fuel cell stack 2 along with the cells 4, heat can be supplied to the cells 4 from the inside of the fuel cell stack 2. Further, it is possible to prevent a temperature drop of the cell 4 at the end portion that easily dissipates heat among the cells 4, and to make the temperature distribution between the cells 4 in the stacking direction uniform.

  Furthermore, according to the configuration of the fuel cell system of the present embodiment, the air used for heat exchange in the heat exchanger 40 is returned again to the air supply passage 12 and supplied to the fuel cell stack 2. Therefore, the compression work performed by the air compressor 10 is not wasted. Further, since the air compressed by the air compressor 10 is too hot to be supplied to the fuel cell stack 2 as it is, it is cooled by the intercooler 16. At this time, a part of the heat energy of the air is discarded. However, according to the configuration of the fuel cell system of the present embodiment, a part of the air compressed by the air compressor 10 is passed through the heat exchanger 40 before being cooled by the intercooler 16, so that waste of heat energy is eliminated. Can be suppressed. That is, the fuel cell system of the present embodiment can not only prevent a temperature drop of the cell 4 due to heat dissipation but also has a great advantage from the viewpoint of fuel consumption.

  Furthermore, according to the fuel cell system of the present embodiment, the size of the intercooler 16 can be reduced. This is because a part of the heat energy of the air is recovered by the heat exchanger 40, so that the capacity of the intercooler 16 can be reduced accordingly. Even if the flow rate of the air used for heat exchange is changed by the flow rate adjusting valve 50 by passing the air that has passed through the heat exchanger 40 through the intercooler 16, the temperature of the air supplied to the fuel cell stack 2. The change of can be suppressed.

  By the way, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the heat exchanger 40 may be integrated with the current collector plate. The current collector plate has a large heat capacity and thermal conductivity, and is likely to take heat away from the cell 4 at the end. If the heat exchanger 40 is integrated with the current collector plate, the heat exchange efficiency for the cell 4 at the end can be increased. In addition, the number of parts can be reduced.

  The fuel cell system shown in FIG. 1 is a so-called circulation type system that operates while circulating hydrogen, but the present invention is a so-called circulation-less type that operates in a state where it is stopped in the fuel cell stack without circulating hydrogen. It can also be applied to a fuel cell system.

  Finally, a fuel cell system devised in the inventive process and having technical characteristics different from those of the above embodiment will be described. FIG. 2 is a diagram showing the configuration of the fuel cell system. Elements common to the system shown in FIG. 1 among the elements shown in FIG. 2 are denoted by the same reference numerals.

  The system shown in FIG. 2 is technically characterized by warming up the end cell 4 using the air discharged from the fuel cell stack 2. In other words, the heat released from the inner cell 4 having a high temperature is supplied to the cell 4 at the end via the exhaust air and the heat exchanger 40. Specifically, a discharge air introduction passage 62 branched from the air discharge passage 14 is connected to the inlet side of the heat exchanger 40. In the heat exchanger 40, the high-temperature exhaust air taken out from the air exhaust passage 14 by the exhaust air introduction passage 62 is used for heat exchange. The exhaust air introduction passage 62 branches from the air exhaust passage 14 upstream of the pressure regulating valve 20. On the other hand, a return passage 64 for returning exhaust air used for heat exchange to the air discharge passage 14 is connected to the outlet side of the heat exchanger 40. The connection point of the return passage 64 to the air discharge passage 14 is downstream of the humidifier 18. Although omitted in FIG. 2, it is preferable that a flow rate adjusting valve for adjusting the flow rate of the exhaust air introduced into the heat exchanger 40 is provided in the exhaust air introduction passage 62. The opening degree of the flow rate adjusting valve is controlled based on the inlet air temperature and the outlet air temperature of the heat exchanger 40.

  In the case of the configuration shown in FIG. 2, it is considered that the effect is low when the temperature of the entire fuel cell stack 2 is low, such as immediately after a cold start. However, when the temperature of the inner cell 4 becomes high after a while after starting, the same effect as that of the above embodiment can be obtained. Further, according to the configuration shown in FIG. 2, there is an advantage that waste heat from the fuel cell stack 2 can be effectively used.

The following invention can be found from the configuration described above.
A fuel cell stack that generates power by receiving supply of air and fuel gas as an oxidant gas;
A heat exchanger arranged alongside a plurality of cells constituting the fuel cell stack at an end of the fuel cell stack;
An exhaust air introduction passage for introducing air exhausted from the fuel cell stack into the heat exchanger;
A fuel cell system comprising:

It is a figure which shows the structure of the fuel cell system as embodiment of this invention. It is a figure which shows the structure of the fuel cell system devised in the creation process of this invention.

Explanation of symbols

2 Fuel cell stack 4 Cell 6 End plate 10 Air compressor 12 Air supply passage 14 Air discharge passage 16 Intercooler 18 Humidifier 20 Pressure regulating valve 26 Hydrogen supply passage 28 Hydrogen discharge passage 30 Hydrogen tank 32 Hydrogen circulation pump 36 Gas-liquid separator 38 Exhaust valve 40 Heat exchanger 42 Heat exchange air introduction passage 44 Return passages 46, 48 Temperature sensor 50 Flow rate adjustment valve 52 Control device

Claims (9)

A fuel cell stack that generates power by receiving supply of oxidant gas and fuel gas; and
An air compressor for supplying air as an oxidant gas to the fuel cell stack;
A heat exchanger attached to the fuel cell stack, through which air heated by compression by the air compressor is passed;
A fuel cell system comprising:   The fuel cell system according to claim 1, wherein the air that has passed through the heat exchanger is supplied to the fuel cell stack as an oxidant gas.   An air supply path from the air compressor to the fuel cell stack includes a main path that directly connects the air compressor and the fuel cell, a branch from the main path, the heat exchanger, and then the main path again. The fuel cell system according to claim 2, further comprising a sub-passage that joins the passage.   The main passage is provided with a cooler that cools the air that has been compressed by the air compressor and heated, and the sub-passage is branched from the main passage upstream of the cooler and again upstream of the cooler. The fuel cell system according to claim 3, wherein the fuel cell system joins the main passage.   5. A flow rate adjusting means for adjusting a flow rate of air supplied from the air compressor to the fuel cell stack through the auxiliary passage among the air supplied to the fuel cell stack. Fuel cell system.   6. The fuel cell system according to claim 5, wherein the flow rate adjusting means adjusts the flow rate of air passed through the heat exchanger based on the temperature of air at the inlet and outlet of the heat exchanger.   7. The fuel cell system according to claim 1, wherein the heat exchanger is arranged in the fuel cell stack side by side with a plurality of cells constituting the fuel cell stack.   The fuel cell system according to claim 7, wherein the heat exchanger is disposed inside the end plate at an end of the fuel cell stack.   The fuel cell system according to claim 8, wherein the heat exchanger is integrated with a current collector plate provided at an end of the fuel cell stack.

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