JP2002158023A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system with a solid polymer fuel cell enabled to disuse a supplemental device for the electrolyte humidification, to unify the moisture content ratio of the electrolyte, with few power loss caused by disusing the humidification of the electrolyte, and easy to reuse the water generated inside the cell. SOLUTION: The fuel cell system 10 comprises a solid polymer fuel cell 20, a fuel gas supplying means 30 supplying the fuel gas to a fuel electrode of the solid polymer fuel cell 20, and an oxidant gas supplying means 40 supplying the oxidant gas to an air electrode of the solid polymer fuel cell 20. A switching means 46, reversibly switching the flow path of the air to be supplied to solid polymer fuel cell 20, is installed to the oxidant gas supplying means 40. Further, recirculating means 62, 72 and/or trapping means 82, 84 may be installed to the oxidant gas supplying means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system, and more particularly, to a fuel cell system suitable as a portable small power source, a vehicle power source, a cogeneration system, and the like.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell generally has a structure in which a fuel electrode and an air electrode are joined to both sides of a solid polymer electrolyte membrane, and both sides are sandwiched by a separator having a reaction gas flow path formed therein. . In addition, the fuel electrode and the air electrode generally have a two-layer structure of a diffusion layer and a catalyst layer, and the catalyst layer is composed of a composite of a carrier supporting a catalyst and a solid polymer electrolyte. A fuel cell system using a polymer electrolyte fuel cell generally includes a fuel cell stack in which a number of such unit cells are stacked, a fuel gas supply unit that supplies a fuel gas to a fuel electrode,
Oxidizing gas supply means for supplying an oxidizing gas to the air electrode.

When the fuel gas and the oxidizing gas are supplied to the fuel electrode and the air electrode using the fuel gas supplying means and the oxidizing gas supplying means, respectively, the fuel is oxidized to produce water. The change in free energy released at that time can be directly taken out as electric energy via a separator also serving as a current collector. At this time, the solid polymer electrolyte contained in the catalyst layer exchanges protons at the three-phase interface, and the solid polymer electrolyte membrane plays a role of moving protons generated at the fuel electrode to the air electrode side. Therefore,
In order to stably obtain a high output, the electrolyte contained in both the membrane and the electrode is required to have high proton conductivity.

On the other hand, various materials are known for an electrolyte used in a polymer electrolyte fuel cell.
In any case, water is required to develop proton conductivity. Therefore, when the moisture contained in the electrolyte is removed by the continuously supplied reaction gas, the proton conductivity of the electrolyte is reduced, which causes the output of the fuel cell to be reduced. That is, in a fuel cell system using a polymer electrolyte fuel cell, it is necessary to keep the water content of the electrolyte constant in order to stably obtain a high output.

In the conventional fuel cell system, in order to solve this problem, the reaction gas is humidified by using a bubbler, a mist generator, or the like, or the moisture is directly supplied to the reaction gas flow path formed inside the separator. In general, a method of replenishing the electrolyte with water using an auxiliary machine, such as injecting water, is used.

However, the humidification of the electrolyte using the auxiliary equipment includes various components such as a water tank for storing water for humidification, a humidifier, and a condenser for collecting water discharged from the fuel cell. This necessitates a problem that the fuel cell system becomes complicated and large. In particular, when the power generation is high, such as when generating power at a high output density, the electrolyte dries due to the increase in the temperature of the fuel cell, and the resistance of the electrolyte increases extremely. There is a need to. Therefore, in such a case, a large-capacity water tank and its recovery system are required, and the fuel cell system is further complicated and large.

In addition, humidification of the electrolyte using the auxiliary equipment requires extra auxiliary power, which lowers the power generation efficiency of the fuel cell system. Further, when considering application to a vehicle-mounted power source, water may freeze in a water tank or a fuel cell in winter, which may cause a start-up failure or battery failure. Therefore, in a fuel cell system including a polymer electrolyte fuel cell, it is desired to reduce or eliminate humidification of an electrolyte by an auxiliary machine, and various proposals have been made.

For example, Japanese Patent Publication No. Hei 8-500931 discloses an air supply pipe for supplying air to an air electrode of a polymer electrolyte fuel cell and an exhaust gas pipe for discharging exhaust gas from the air electrode through a recirculation path. A fuel cell is disclosed in which a part of exhaust gas discharged from an air electrode is recirculated to an air electrode supply pipe using a gas compressor or an air jet compressor.

[0009] For example, Japanese Patent Application Laid-Open No. 9-266002 discloses an air introduction path for supplying air to an air electrode of a polymer electrolyte fuel cell and an air discharge path for discharging exhaust gas from the air electrode. Further, a fuel cell power generator is disclosed in which a cooling means for condensing water vapor contained in exhaust gas discharged from an air electrode is provided in an air discharge path.

[0010]

In the case of a polymer electrolyte fuel cell, since water is generated on the air electrode side, most of the water inside the fuel cell is discharged from the air electrode side to the outside together with the exhaust gas (off gas). And a part is discharged from the fuel electrode side. Accordingly, when a circulation path is provided particularly on the air electrode side and a part of the water contained in the off-gas is returned to the oxidizing gas (in-gas) supplied to the air electrode using a gas compressor, the amount of discharged water is reduced. In addition, humidification of the electrolyte by the auxiliary equipment can be eliminated.

However, when a gas compressor is used to recirculate a part of the off-gas, there is a problem that the power loss is large. Further, even when the electrolyte is humidified by recirculation of off-gas, the water content of the electrolyte tends to be lower on the supply side of the air electrode and higher on the discharge side. If the water content of the electrolyte is non-uniform depending on the position, the battery reaction also becomes non-uniform, and high output and efficiency cannot be obtained.

In the case where air is used as the oxidizing gas, when the amount of recirculated off-gas increases, the oxygen concentration in the in-gas decreases. Therefore, in order to maintain a constant air stoichiometric ratio, it is necessary to increase the flow rate of the ingas. However, when the flow rate of the ingas is increased, there is a problem that the water content of the electrolyte becomes more uneven, and the output of the fuel cell is reduced.

Further, when the cooling means is provided in the air discharge path, the amount of water discharged from the fuel cell can be minimized. However, in order to return the water obtained by cooling and condensing the water vapor in the exhaust gas to the electrolyte, a separate mechanism is required. Further, even if the water condensed by cooling is vaporized or atomized and supplied to the air supply path, the water content of the electrolyte cannot be made uniform, and a high output cannot be obtained.

An object of the present invention is to eliminate the need for auxiliary equipment to humidify an electrolyte in a fuel cell system having a polymer electrolyte fuel cell. Also,
Another object to be solved by the present invention is to provide a fuel cell system capable of equalizing the water content of the electrolyte, reducing the power loss required for dehumidifying the electrolyte, and easily reusing water generated inside the battery. Is to provide.

[0015]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a polymer electrolyte fuel cell, fuel gas supply means for supplying a fuel gas to a fuel electrode of the polymer electrolyte fuel cell, An oxidizing gas supply unit that supplies an oxidizing gas to an air electrode of the polymer electrolyte fuel cell, wherein the oxidizing gas supply unit and / or the fuel gas supplying unit includes the air electrode. And / or switching means for reversibly switching the direction of the flow of the reaction gas supplied to the fuel electrode.

When the flow direction of the reaction gas is switched at predetermined time intervals, a part of the water vapor contained in the off-gas and water collected in the passages, electrodes, etc. are returned to the fuel cell as it is, and the humidified electrolyte is removed. Reused. Therefore, the amount of water discharged from the fuel cell is reduced, and the humidification of the electrolyte by the auxiliary equipment can be eliminated. In addition, by reversing the direction of the flow of the reaction gas, the water content of the electrolyte is made uniform at the inlet and outlet of the gas. Therefore, the drying of the electrolyte at the inlet and the flooding of the outlet (a state of oxygen supply inhibition due to excess water. )) And make the reaction more homogeneous,
High output and efficiency are obtained. Further, since humidification can be achieved only by switching the flow direction of the reaction gas, power loss can be minimized.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a schematic configuration diagram of a fuel cell system 10 according to the first embodiment of the present invention. In FIG. 1, a fuel cell system 10
Are a fuel cell 20, a fuel gas supply means 30, an air supply means (oxidant gas supply means) 40, and a control unit 5.
0.

In the present embodiment, a polymer electrolyte fuel cell is used as the fuel cell 20. As described above, the solid polymer electrolyte fuel cell has a fuel electrode and an air electrode joined to both surfaces of a solid polymer electrolyte membrane to form a membrane electrode assembly, and a fuel flow path and an air flow path (both in FIG. (Not shown)). Further, the catalyst layer constituting a part of the fuel electrode and the air electrode is composed of a composite of a carrier supporting a catalyst and a solid polymer electrolyte. As the fuel cell 20, a stack in which many unit cells having such a structure are stacked is usually used.

The fuel gas supply means 30 includes a fuel in gas passage 32, a fuel off gas passage 34, a flow rate control valve 36, and a hydrogen supply source 38. One end of the fuel ingas passage 32 is connected to a hydrogen supply source 38, and the other end of the fuel ingas passage 32 is connected to one end of a fuel flow path of the fuel cell 20 (hereinafter, referred to as “A end”). I have. One end of the fuel off-gas passage 34 is connected to the fuel cell 2
The other end of the fuel passage 0 (hereinafter referred to as “B end”).
The other end of the fuel off-gas passage 34 is connected to an exhaust port (not shown).

Further, a flow rate control valve 36 for controlling the flow rate of the fuel supplied from the hydrogen supply source 38 to the fuel cell 20 is provided in the fuel ingas passage 32. The hydrogen supply source 38 may be any of a hydrogen cylinder for supplying pure hydrogen and a reformer for supplying a reformed gas, and is not particularly limited. Further, the fuel off-gas passage 34 may be connected to the fuel-in gas passage 32 to form a circulation circuit.

The air supply means 40 includes a first air passage 42a.
, A second air passage 42b, a third air passage 42c, a fourth air passage 42d, an air pump 44,
And One end of the first air passage 42a is connected to an intake port (not shown) for taking in air, and the other end of the first air passage 42a is connected to the switching means 46. An air pump 44 is further provided in the first air passage 42a.
Is provided so that air as an oxidizing gas is sent into the air flow path of the fuel cell 20.

Further, one end of the second air passage 42b is connected to the switching means 46, and the other end of the second air passage 42b is connected to one end of an air flow passage of the fuel cell 20 (hereinafter referred to as "B end"). .)It is connected to the. Also, the third air passage 42c
Is connected to the other end of the air flow path of the fuel cell 20 (hereinafter referred to as “A end”), and the third air passage 42c
Is connected to the switching means 46. Further, one end of the fourth air passage 42d is connected to the switching means 46,
The other end of the fourth air passage 42d is connected to an exhaust port (not shown).

The switching means 46 is for reversibly switching the direction of the flow of air supplied to the air flow path of the fuel cell 20. That is, the switching unit 46 transfers the air supplied from the first air passage 42a to the second air passage 42b when the air flows from the end B to the end A of the air flow path (indicated by a dotted line in FIG. 1). The air discharged from the end A of the air passage is guided from the third air passage 42 c to the fourth air passage 4.
It has the function of leading to 2d. Further, the switching means 46
Air flows from end A to end B of the air flow path (FIG. 1).
(Indicated by middle and solid lines), the air supplied from the first air passage 42a is guided to the third air passage 42c,
The air discharged from the end is transferred from the second air passage 42b to the fourth air passage 42b.
It has a function of leading to the air passage 42d.

FIG. 2 shows an example of the switching means 46 having such a function. The switching means 46 illustrated in FIG.
It has two three-way valves 48a, 48b. The first air passage 42a is connected to one three-way valve (hereinafter, referred to as "first valve") 48a, and the fourth air passage 42d is connected to the other three-way valve (hereinafter, referred to as "second valve"). This is connected to the valve 48b.) Also,
The second air passage 42b is connected to the first valve 48a,
Further, the second valve 48b is connected via the bypass passage 42f.
Is also connected. Similarly, the third air passage 42c is
The bypass valve 4 is connected to the second valve 48b.
It is also connected to the first valve 48a via 2g.

Therefore, in the switching means 46 having such a structure, the first valve 48a is connected to the second air passage 42b.
When the second valve 48b is switched to the third air passage 42c side, the air supplied from the air pump 44 is supplied to the air flow path B of the fuel cell 20 as shown in FIG.
It can flow from the end to the A end. Conversely, if the first valve 48a is switched to the third air passage 42c and the second valve 48b is switched to the second air passage 42b, FIG.
As shown in (b), air can flow from the end A to the end B of the air flow path of the fuel cell 20.

The control unit 50 controls the fuel cell system 1
0 (for example, the voltage of the fuel cell 20,
Current, output, resistance etc. ), Calculating means (not shown) for calculating the control amount of each device in the system based on the input signal, and calculating the control amount for each device in the system. There is provided a signal transmitting means (not shown) for transmitting to the device. The calculating means is a CPU, RO
M, RAM, etc., and a switching means 4
Various controls for controlling the entire fuel cell system 10, such as a control program for controlling the switching direction and the switching timing of No. 6, and a control program for controlling the fuel flow rate and the air flow rate so as to obtain the required output. The program is stored.

Next, an operation method of the fuel cell system 10 according to the present embodiment will be described. First, when a control signal instructing the fuel cell system 10 to increase or decrease the output of the fuel cell 20 is input, the control unit 50 calculates a fuel flow rate and an air flow rate necessary to obtain a required output. . Next, the opening degree of the flow control valve 36 and the output of the air pump 44 are adjusted so that the calculated fuel flow rate and air flow rate are obtained.

In this case, the fuel electrode in-gas is always supplied from the end A of the fuel flow path, and the fuel electrode off-gas is always discharged from the end B of the fuel flow path. On the other hand, the air electrode ingas is first guided from the first air passage 42a to the switching means 46, and then supplied to one of the A end and the B end of the air flow path according to the switching direction of the switching means 46. You. Also, A
The air electrode off-gas discharged from the other end or the end B is guided to the fourth air passage 42 d via the switching means 46.

The control unit 50 monitors the voltage and resistance of the fuel cell 20 while continuing the operation of the fuel cell 20 in this state. Generally, when electrolyte dry-up occurs, the current for a certain voltage decreases, which appears as an increase in resistance. Therefore, by monitoring at least the voltage and the resistance of the fuel cell 20, it is possible to determine the water-containing state of the electrolyte. Next, when the control unit 50 determines that the water content of the electrolyte estimated from the voltage and the resistance has fallen below a certain threshold value, the switching unit 46 switches the air flow direction to the opposite direction. Thereafter, such feedback control is repeated until the operation of the fuel cell system 10 is stopped.

Next, the operation of the fuel cell system according to this embodiment will be described. In the case of a polymer electrolyte fuel cell, water is generated on the air electrode side by a cell reaction. When protons move to the air electrode side, water molecules also move to the air electrode side by electroosmosis. On the other hand, on the fuel electrode side, water is not generated, and a part of the water on the air electrode side moves to the fuel electrode side by back diffusion.

That is, inside the fuel cell 20, the air electrode side contains more moisture than the fuel electrode side. Therefore, when power is generated while flowing the reaction gas in one direction, most of the water inside the fuel cell is discharged to the outside from the air electrode side together with the off-gas. Since the amount of water discharged is usually larger than the amount of water generated by the battery reaction, if the amount of humidification with respect to the reaction gas is small, the water content of the electrolyte decreases, causing a decrease in output.

On the other hand, the fuel cell system 10 according to the present embodiment is provided with the switching means 46 for reversibly switching the direction of the air flow, so that when the direction of the air flow is reversed, Part of the water contained in the pole off-gas is returned to the fuel cell 20 as it is, and the fuel cell 2
The amount of water discharged from zero decreases. The water returned to the inside of the fuel cell 20 is reused for humidifying the electrolyte as it is, so that the water content of the electrolyte can be maintained at a constant level only by the water generated by the cell reaction. Therefore, power generation can be performed without humidifying the electrolyte using the auxiliary device.

For example, when air flows in one direction from end B to end A of the air flow path, the air is gradually humidified by the moisture in the air flow path. Therefore, the humidity of the air is low on the B end side, and becomes higher toward the A end side. Accordingly, the water content of the electrolyte also tends to increase toward the A-end side, and resistance increases due to drying at the B-end, and flooding due to an increase in moisture tends to occur at the A-end. As described above, when the water content of the electrolyte is non-uniform depending on the position, the battery reaction also becomes non-uniform, and a high output cannot be obtained.

On the other hand, when air is caused to flow from the end B to the end A of the air flow path and then the direction of the air flow is reversed by using the switching means 46, the air having the low humidity flows.
High humidity air flows into the end. Therefore, when the direction of the flow of air is reversibly switched at predetermined time intervals, the water content of the electrolyte membrane becomes uniform, and a high output is obtained.

Further, if the switching direction and the switching timing of the switching means 46 are feedback-controlled while monitoring the operating condition of the fuel cell 20, the water content of the electrolyte can be controlled with high accuracy, and a high output can be obtained stably. Can be Further, since the switching of the direction of the air flow using the switching means 46 does not involve a large pressure loss, the power loss due to non-humidification of the electrolyte can be minimized.

In this embodiment, the switching means 4
Although 6 is provided only on the air electrode side, part of the water is also discharged from the fuel electrode side of the fuel cell 20. Therefore, the switching means 46 may be provided on the fuel electrode side, or may be provided on both the air electrode side and the fuel electrode side.

Next, a fuel cell system according to a second embodiment of the present invention will be described. FIG. 3 shows a schematic configuration diagram of the fuel cell system 12 according to the present embodiment. In FIG. 3, the fuel cell system 12 includes a fuel cell 20
, A fuel gas supply means 30, an air supply means 60, and a control unit 52.

Here, the fuel cell 20 and the fuel gas supply means 30 correspond to the fuel cell system 1 according to the first embodiment.
Since it is the same as 0, the description is omitted. Further, the point that the air supply means 60 includes first to fourth air passages 42a to 42d, an air pump 44 and a switching means 46 is different from the air supply means 4 of the fuel cell system 10 according to the first embodiment.
0, except that the recirculation means 62 is further provided.

The recirculation means 62 includes a recirculation passage 64, a dynamic pressure difference generator 66, and a flow control valve 68. The dynamic differential pressure generator 66 is provided on the first air passage 42a and between the air pump 44 and the switching means 46. The flow control valve 68 is connected to the fourth air passage 42d.
Provided above. Further, the dynamic differential pressure generator 66 and the flow control valve 68 are connected by a recirculation passage 64.

The dynamic differential pressure generator 66 has a function of drawing a part of the air electrode off-gas into the air electrode in-gas by utilizing a dynamic differential pressure based on a difference in flow velocity. FIG. 4 shows an example of the dynamic differential pressure generator 66 having such a function. The dynamic differential pressure generator 66 illustrated in FIG. 4 includes a main body 66a and a nozzle 66b provided therein. Body 66a
Is provided on the first air passage 42a, and a recirculation passage 64 is connected to a side surface of the main body 66a. The nozzle 66b is provided along the direction of the flow of the air electrode ingas, and its tail end is connected to the first air passage 4 on the air pump 44 side.
2a.

The flow control valve 68 is connected to the fourth air passage 42
a part of the air electrode off-gas discharged to
The flow rate of the recirculated off-gas flowing into the recirculation passage 64 can be varied by adjusting the opening of the flow control valve 68.

The control unit 52 includes signal receiving means, arithmetic means, and signal transmitting means, and the arithmetic means stores various control programs for controlling the fuel cell system 12. Is the same as in the first embodiment, except that the arithmetic means further stores a control program for adjusting the opening of the flow control valve 68 in accordance with the water content of the electrolyte. Is different.

Next, the operation of the fuel cell system 12 according to the present embodiment will be described. When air is sent from the air pump 44 to the first air passage 42a, the dynamic differential pressure generator 6
At 6, a dynamic differential pressure is generated. For example, in the case of the dynamic differential pressure generator 66 having the structure shown in FIG. 4, when air supplied from the air pump 44 is jetted from the tip of the nozzle 66b,
A dynamic pressure difference is generated at the tip of the nozzle 66b. Due to this dynamic differential pressure, a part of the air electrode off-gas is drawn into the recirculation passage 64 as a recirculation off-gas, and this recirculation off-gas is
It flows into the main body 66a through the recirculation passage 64.

At this time, if the opening of the flow control valve 68 is adjusted according to the water content of the electrolyte, the amount of recirculated off-gas drawn into the main body 66a can be controlled. Specifically, first, the voltage and resistance of the fuel cell 20 are monitored to determine the water content of the electrolyte. Next, when it is determined that the water content of the electrolyte is too low, the opening degree of the flow control valve 68 may be increased to increase the amount of recirculated off-gas. On the other hand, when it is determined that the water content of the electrolyte is excessive, the opening of the flow control valve 68 may be reduced to reduce the amount of recirculated off-gas.

The fuel cell system 12 according to the present embodiment
Has a switching means 46 in addition to the recirculation means 62, so that part of the water contained in the air electrode off-gas is returned to the fuel cell 20 and reused for humidifying the electrolyte. . Therefore, even if the electrolyte is not humidified by the auxiliary equipment, the water content of the electrolyte is maintained at a certain level,
Power generation can be continued. Further, if the recirculation off-gas amount by the recirculation unit 60 and the switching direction and the switching timing of the switching unit 46 are feedback-controlled based on the operating environment of the fuel cell 20, the fuel cell 2
The amount of water discharged from zero can be more finely controlled.

Further, in addition to the switching of the air flow direction by the switching means 46, the recirculation means 62 humidifies the air electrode ingas, so that the water content of the electrolyte is further uniformed, and the high output is stabilized. can get. Also,
Dynamic differential pressure generator 6 for recirculating air electrode off-gas
6, the structure is simple, and the power loss required for recirculation can be minimized.

In this embodiment, the switching means 4
6 and the recirculation means 62 are provided on the air electrode side, but these means may be provided on the fuel electrode side, or may be provided on both the air electrode and the fuel electrode side.

Next, a fuel cell system according to a third embodiment of the present invention will be described. FIG. 5 shows a schematic configuration diagram of the fuel cell system 14 according to the present embodiment. In FIG. 5, the fuel cell system 14 includes a fuel cell 20
, A fuel gas supply means 30, an air supply means 70, and a control unit 54.

Here, the fuel cell 20 and the fuel gas supply means 30 correspond to the fuel cell system 1 according to the first embodiment.
Since it is the same as 0, the description is omitted. Further, the point that the air supply means 70 includes the first to fourth air passages 42a to 42d, the air pump 44, and the switching means 46 is different from the air supply means 4 of the fuel cell system 10 according to the first embodiment.
0, except that the recirculation means 72 is further provided.

The recirculation means 72 includes a recirculation passage 74, 2
And two variable dynamic differential pressure generators 76 and 78. One variable dynamic differential pressure generator (hereinafter, referred to as “first variable dynamic differential pressure generator”) 76 is provided on the second air passage 42b, and the other variable dynamic differential pressure generator (hereinafter, referred to as “first variable dynamic differential pressure generator”). This is referred to as a "second variable dynamic differential pressure generator.") 78 is the third air passage 42.
c. In addition, the first variable dynamic differential pressure generator 7
The sixth and second dynamic differential pressure generators 78 are connected by a recirculation passage 74.

The first and second variable dynamic differential pressure generators 76 and 78
Has a function of generating a dynamic pressure difference when the air electrode ingas flows therein, and furthermore, has a function of varying the generated dynamic pressure difference. FIG. 6 shows an example of the first variable dynamic differential pressure generator 76 having such a function. The first variable dynamic differential pressure generator 76 illustrated in FIG. 6 includes a main body 76a and a variable nozzle 76b provided therein. The main body 76a
The recirculation passage 74 is provided on the second air passage 42b, and is connected to a side surface of the main body 76a. The variable nozzle 76b is provided along the direction of the flow of the air electrode ingas, and its tail end is connected to the second air passage 42 on the switching unit 46 side.
a. Further, the variable nozzle 76b can change the length of its tip. The second variable dynamic differential pressure generator 78 provided in the third air passage 42c
Also has a similar configuration.

The control unit 54 is provided with a signal receiving means, a calculating means, and a signal transmitting means. The calculating means stores various control programs for controlling the fuel cell system 14. The point is the same as that of the first embodiment, but the arithmetic means further includes first and second points according to the water-containing state of the electrolyte membrane and the direction of the air flow.
Variable nozzles 76b, 78 of variable dynamic pressure difference generators 76, 78
The difference is that a control program for adjusting the length of b is stored.

Next, the operation of the fuel cell system 14 according to the present embodiment will be described. A from the B end of the air flow path
When the air flows toward the end, the first variable dynamic differential pressure generator 76, as shown in FIG.
Extend the tip of the. Also, the second variable dynamic differential pressure generator 78
As shown in FIG. 6B, the tip of the variable nozzle 78b is shortened. In this state, when the in-gas flows into the first variable dynamic differential pressure generator 76, a larger dynamic differential pressure is generated at the tip of the variable nozzle 76a. Therefore, part of the air electrode off-gas is drawn into the recirculation passage 74 as a recirculation off-gas, and the recirculation off-gas flows through the recirculation passage 74 into the main body 76a of the first variable operating pressure generator.

On the other hand, when air flows from the end A to the end B of the air flow path, the second variable dynamic differential pressure generator 78
As shown in FIG. 6A, the tip of the variable nozzle 78a is elongated. The first variable dynamic differential pressure generator 76 shortens the tip of the variable nozzle 76b as shown in FIG. 6B. In this state, when the in-gas flows into the second variable dynamic differential pressure generator 78, a larger dynamic differential pressure is generated at the tip of the variable nozzle 78b. Therefore, a part of the air electrode off-gas is drawn into the recirculation passage 74 as a recirculation off-gas, and the recirculation off-gas flows into the main body 76 a of the second variable dynamic differential pressure generator 78 through the recirculation passage 74.

At this time, when the length of each of the variable nozzles 76b and 78b is adjusted, the generated dynamic differential pressure and the resistance to inflow into the recirculation passage 74 change, and as a result, the amount of recirculated off-gas can be controlled. it can. Specifically, first, the voltage and resistance of the fuel cell 20 are monitored to determine the water content of the electrolyte. Next, when it is determined that the water content of the electrolyte is too low, the dynamic differential pressure generated on the ingas side is large,
And / or the length of each variable nozzle 76b, 78b is adjusted so that the inflow resistance on the off-gas side is reduced. Thereby, the amount of recirculated off-gas can be increased. On the other hand, when it is determined that the water content of the electrolyte is excessive, the dynamic differential pressure generated on the ingas side is small, and / or
Alternatively, the length of each of the variable nozzles 76b and 78b is adjusted so that the inflow resistance on the off-gas side is increased. Thereby, the amount of recirculated off-gas can be reduced.

The fuel cell system 14 according to the present embodiment
Has a switching means 46 in addition to the recirculation means 72, so that a part of the water contained in the air electrode off-gas is returned to the fuel cell 20 and reused for humidifying the electrolyte. You. Therefore, even if the electrolyte is not humidified by the auxiliary equipment, the water content of the electrolyte is maintained at a constant level, and the power generation can be continued. Also, the fuel cell 20
If the recirculation off-gas amount by the recirculation unit 70 and the switching direction and the switching timing of the switching unit 46 are feedback-controlled based on the operating environment of, the amount of water discharged from the fuel cell 20 can be more finely controlled. it can.

Further, in addition to the switching of the direction of the air flow by the switching means 46, the recirculation means 72 humidifies the air electrode ingas, so that the water content of the electrolyte is further uniformed, and the high output is stabilized. can get. Also,
Since the variable dynamic differential pressure generators 76 and 78 are used to recirculate the air electrode off-gas, the configuration is simple, and the power loss required for recirculation can be minimized.

The switching means 46 and the recirculation means 72 may be provided on the fuel electrode side instead of being provided on the air electrode side, and these means may be provided on both the air electrode and the fuel electrode side. Is similar to the fuel cell system 12 according to the second embodiment.

Next, a fuel cell system according to a fourth embodiment of the present invention will be described. FIG. 7 shows a schematic configuration diagram of a fuel cell system 16 according to the present embodiment. 7, the fuel cell system 16 includes a fuel cell 20
, A fuel gas supply means 30, an air supply means 80, and a control unit 56.

Here, the fuel cell 20 and the fuel gas supply means 30 correspond to the fuel cell system 1 according to the first embodiment.
Since it is the same as 0, the description is omitted. Further, the point that the air supply means 80 includes first to fourth air passages 42a to 42d, an air pump 44 and a switching means 46 is different from the air supply means 4 of the fuel cell system 10 according to the first embodiment.
0, except that trap units 82 and 84 are further provided.

The trap means 82 and 84 are provided in passages in which the flow direction of the reaction gas is reversibly switched, that is, in the second air passage 42b and the third air passage 42c. When the air electrode off-gas is flowing into the second air passage 42b by the switching means 46, the trap means 82 traps the moisture in the air electrode off-gas, and the air electrode in-gas flows into the second air passage 42b. In this case, it has a function of releasing trapped moisture into the air electrode ingas. Similarly, the trap unit 84 has a function of trapping moisture in the air electrode off-gas and releasing the trapped moisture into the air electrode in-gas.

As the trap means having such a function, for example, a steam condenser having a heating / cooling means,
A water-absorbing material (for example, a hygroscopic resin, silica gel, or a porous material having nanometer pores) that absorbs and releases moisture according to the humidity and temperature in the atmosphere is a preferred example. In particular, the water-absorbing material is suitable as the trap means 82 and 84 because it can occlude and release moisture with a simple configuration.

The control unit 56 includes a signal receiving means, a calculating means, and a signal transmitting means. The calculating means stores various control programs for controlling the operation of the fuel cell system 16. This is the same as in the first embodiment. Further, a control program for controlling the operation of the trap units 82 and 84 is stored in the arithmetic unit as needed.

Next, the operation of the fuel cell system 16 according to the present embodiment will be described. In the fuel cell system 16 according to the present embodiment, for example, the second air passage 4
When 2b functions as an off-gas passage, the trap unit 82 collects moisture from the air electrode off-gas. On the other hand, when the second air passage 42b functions as an ingas passage, the trap unit 82 releases the trapped moisture to the air electrode ingas. The released moisture is
It is transported to the cathode as it is and reused for humidifying the electrolyte. Trap means 84 provided in the third air passage 42c
The same is true for Therefore, even if humidification by the auxiliary equipment is not performed, the water content of the electrolyte is maintained at a constant level, and power generation can be continued.

Further, in addition to the switching of the direction of the air flow by the switching means 46, the trapping means 82,
Since the air electrode ingas is humidified by 84, the water content of the electrolyte is further uniformed, and a high output is stably obtained.

In the present embodiment, the trap means 82 and 84 are provided at two places of the second air passage 42b and the third air passage 42c, but the trap means is provided only at one of them. Is also good. Further, although the switching means 46 and the trap means 82 and 84 are provided on the air electrode side, they may be provided on the fuel electrode side, or may be provided on both the air electrode side and the fuel electrode side. . Further, the trap means 82 and 84 may be used alone for the fuel cell system provided with the switching means 46, or
You may use together with the recirculation means 62 and 72 mentioned above.

[0067]

EXAMPLE 1 As shown in FIG. 3, a fuel cell system 12 provided with a switching means 46 and a recirculation means 62 on the air electrode side was manufactured, and a steady operation test was performed. The operating conditions are as follows: bipolar humidification, cell temperature: 70 ° C, excess air ratio: 1.
8. Excess hydrogen ratio: 1.2, pressure: 1.2 ata.
The amount of recirculated off-gas was set to be constant at 30%. Further, the direction of the air flow was periodically reversed by the switching means 46 based on the water content of the electrolyte determined from the voltage and resistance of the fuel cell 20. When steady operation was performed under such conditions, 0.7 A / cm ²
At a current density of 0.62 V, the fuel cell 20 operated stably.

(Example 2) A power generation test was performed using the fuel cell system 12 manufactured in Example 1 while changing the cell temperature from 80 ° C to 95 ° C. The operating conditions were bipolar humidification, an excess air ratio of 1.8, an excess hydrogen ratio of 1.2, and a pressure of 1.5 ata. Also, the amount of recirculated off-gas is
While monitoring the output voltage, control was performed so that the excess air ratio of 1.8 was maintained. Further, the direction of the air flow was periodically reversed by the switching means 46 based on the water content of the electrolyte determined from the voltage and resistance of the fuel cell 20. When the operation was performed under such conditions, the amount of recirculated off-gas increased as the cell temperature increased, but the fuel cell 20 operated stably at any temperature.

(Comparative Example 1) The amount of recirculated off gas was set to 0,
A steady operation test was performed under the same conditions as in Example 1 except that the direction of the air flow was not switched by the switching unit 46. Immediately after the operation, the voltage dropped to 0.52 V due to no humidification in both electrodes. After a while, the electrolyte was dried and the operation became impossible.

Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. is there.

For example, in the above embodiment, an example in which air is used as the oxidizing gas has been mainly described, but oxygen may be used as the oxidizing gas. In addition, the method of dehumidifying an electrolyte according to the present invention is particularly suitable for a fuel cell system having a polymer electrolyte fuel cell, but these methods require water management of the electrolyte. The present invention can be similarly applied to a fuel cell system including a fuel cell of the type (for example, a phosphoric acid fuel cell, an alkaline fuel cell, and the like).

[0072]

The fuel cell system according to the present invention is provided with switching means for reversibly switching the direction of the flow of the reaction gas supplied to the polymer electrolyte fuel cell, so that the reaction gas is discharged from the fuel cell. There is an effect that the amount of water is reduced and the humidification of the electrolyte by the auxiliary equipment can be made unnecessary. Also,
By reversing the direction of the flow of the reaction gas, there is an effect that the water content of the electrolyte is made uniform, local flooding and drying are suppressed, and high output and efficiency are obtained. Furthermore, since the electrolyte can be dehumidified only by switching the flow direction of the reaction gas, there is an effect that power loss can be minimized.

When a recirculation means for returning a part of the off-gas discharged from one electrode to the in-gas supplied to the electrode is further provided, the water discharged from the fuel cell is used for humidifying the electrolyte. There is an effect that the electrolyte can be easily reused and dehumidification of the electrolyte is further facilitated.

Further, when at least one of the passages in which the direction of the flow of the reaction gas is reversibly switched is provided with a trap means for trapping moisture in the off-gas and releasing the trapped moisture into the in-gas. Has an effect that water discharged from the fuel cell can be easily and efficiently reused for humidifying the electrolyte, and dehumidification of the electrolyte is further facilitated.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a fuel cell system according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram illustrating an example of a switching unit.

FIG. 3 is a schematic configuration diagram of a fuel cell system according to a second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram illustrating an example of a dynamic differential pressure generator.

FIG. 5 is a schematic configuration diagram of a fuel cell system according to a third embodiment of the present invention.

FIG. 6 is a schematic configuration diagram illustrating an example of a variable dynamic differential pressure generator.

FIG. 7 is a schematic configuration diagram of a fuel cell system according to a fourth embodiment of the present invention.

[Explanation of symbols]

10, 12, 14, 16 fuel cell system 20 fuel cell (polymer electrolyte fuel cell) 30 fuel gas supply means 40, 60, 70, 80 oxidant gas supply means (air supply means) 46 switching means 62, 72 Circulation means 82, 84 Trap means

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takehiko Asaoka 41-cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory Co., Ltd. (72) Inventor Tomo Morimoto Nagakute-cho, Aichi-gun, Aichi 41, Chochu-Yokomichi, Toyota Central Research Laboratory Co., Ltd. (72) Inventor Hiroshi Aoki 41, Nagakute-cho, Aichi-gun, Aichi Prefecture, Oji-cho, Toyota Chuo Research Institute, Inc. (72) Inventor Kazuo Kawahara 41F, No. 41, Chuchu-Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture F-term in Toyota Central R & D Laboratories Co., Ltd. 5H026 AA06 5H027 AA06 BA01 BA13 BA19 BC19 MM03 MM08

Claims (3)

[Claims] 1. A polymer electrolyte fuel cell, fuel gas supply means for supplying a fuel gas to a fuel electrode of the polymer electrolyte fuel cell, and an oxidant gas to an air electrode of the polymer electrolyte fuel cell. A fuel cell system provided with an oxidizing gas supply unit for supplying the oxidizing gas supply unit and / or the fuel gas supplying unit. A fuel cell system comprising switching means for reversibly switching directions. 2. The oxidizing gas supply unit and / or the fuel gas supply unit further include a recirculation unit that returns a part of the off-gas discharged from one electrode to the in-gas supplied to the electrode. The fuel cell system according to claim 1. 3. The method according to claim 1, wherein the oxidizing gas supply unit and / or the fuel gas supply unit trap moisture in the off-gas in at least one of the passages in which the flow direction of the reaction gas is reversibly switched. The fuel cell system according to claim 1, further comprising a trap unit configured to release the moisture into ingas.