JP2003115317A - Stopping method of power generation of fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent damage of a solid polymer electrolyte membrane at the stopping time of power generation of a fuel cell. SOLUTION: In the stopping method of power generation of the fuel cell 1 wherein power generation is carried out by using air supplied by an air compressor 7 and hydrogen supplied by a hydrogen supplying means 13 as reaction gases, at the stopping time of the power generation of the fuel cell 1, air off-gas discharged from the cathode of the fuel cell 1 is recirculated and supplied to the cathode, and the power generation is continued by using residual oxygen in the air off-gas, and when the power generation voltage becomes a prescribed value or less, the power generation is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power generation stopping method for a fuel cell, which uses hydrogen and air as reaction gases to generate power.

[0002]

2. Description of the Related Art In a fuel cell mounted on a fuel cell vehicle, a solid polymer electrolyte membrane composed of, for example, a solid polymer ion exchange membrane is sandwiched between an anode and a cathode from both sides, and a pair of separators is provided outside the membrane. It consists of a stack of multiple cells formed by sandwiching them, and hydrogen gas is supplied to the anode of each cell as fuel gas and air containing oxygen as oxidant gas is supplied to the cathode to generate electricity. There is something. Hereinafter, the fuel gas and the oxidant gas are collectively referred to as a reaction gas. In this fuel cell, the hydrogen ions generated by the catalytic reaction at the anode are
It moves through the solid polymer electrolyte membrane to the cathode, where it causes an electrochemical reaction with oxygen to generate electricity.

In this type of fuel cell, when power generation is stopped, hydrogen gas on the anode side remaining in the fuel cell permeates the solid polymer electrolyte membrane to the cathode side, and oxygen gas in the air on the cathode side or It is known that so-called cross leak occurs in which nitrogen gas permeates the solid polymer electrolyte membrane and moves to the anode side. When this cross leak occurs,
There is a possibility that hydrogen and oxygen react near the solid polymer electrolyte membrane and the solid polymer electrolyte membrane is damaged.

Therefore, in this type of fuel cell, in order to protect the solid polymer electrolyte membrane, an inert gas such as nitrogen gas is supplied to the fuel cell when the power generation is stopped, and hydrogen gas and air in the fuel cell are discharged. Then, contain an inert gas in the anode side and the cathode side, or supply the inert gas before supplying hydrogen gas to the anode side of the fuel cell at the start of power generation, and discharge the residual gas to the anode side,
After that, hydrogen gas is supplied.

[0005]

However, if such a method is adopted, it is necessary to prepare an inert gas source (tank or the like), and a system for supplying the inert gas to the fuel cell. (Pump, piping, control device, etc.) are required. As a result, there is a problem that the entire system of the fuel cell becomes large in size, and it is not suitable for vehicle mounting, which has a limited mounting space. Further, when the remaining amount of the inert gas has decreased, the inert gas must be replenished, which is troublesome. Therefore, the present invention provides a method for stopping power generation of a fuel cell that does not require an inert gas source and can protect the fuel cell during power generation stoppage.

[0006]

In order to solve the above problems, the invention described in claim 1 provides a compressor (for example, an air compressor 7 in an embodiment described later).
Of the fuel cell (for example, the fuel cell 1 in the embodiment to be described later) that generates electric power by using the air supplied by the hydrogen and the hydrogen supply means (for example, the hydrogen supply means 13 in the embodiment to be described later) as the reaction gas. In the power generation stopping method, when the power generation of the fuel cell is stopped, exhaust gas discharged from the cathode of the fuel cell (for example, air off-gas in the embodiments described later) is recirculated by the compressor to be supplied to the cathode and discharged. It is characterized in that power generation is continued by residual oxygen in the gas and power generation is stopped when the power generation voltage becomes equal to or lower than a predetermined value.

With this structure, while the exhaust gas discharged from the cathode of the fuel cell is being recirculated to the cathode to generate electric power, the oxygen remaining in the exhaust gas is reduced and the generated voltage is reduced. When is below a predetermined value,
The oxygen concentration in the exhaust gas becomes extremely low, and it becomes possible to form an atmosphere very close to that in which an inert gas is filled on the cathode side. Therefore, by stopping the power generation at this point, even if a cross leak occurs after the power generation is stopped, there is almost no reaction between hydrogen and oxygen. Further, the inert gas source and the inert gas supply system which have been conventionally required are not required.

The invention described in claim 2 is characterized in that, in the invention described in claim 1, the compressor is driven by electric power obtained by power generation by residual oxygen in the exhaust gas. With this configuration, the electric power obtained by the exhaust gas recirculation power generation is not wasted, and the electric power stored in the storage means such as a battery is not consumed.

According to a third aspect of the present invention, in the first aspect of the invention, the reaction gas supply passage of the fuel cell is shut off from the outside after the power generation is stopped. By configuring in this way, while power generation is stopped,
New oxygen can be prevented from entering the cathode side, and the cathode side can be maintained in a low oxygen concentration state.

According to a fourth aspect of the present invention, in the first aspect of the invention, a dehumidifier (for example, an embodiment described later) provided in a circulation path of the exhaust gas at the time of power generation by residual oxygen in the exhaust gas. The exhaust gas is dehumidified by the dehumidifier 12). With this configuration, it is possible to remove the water produced by the exhaust gas recirculation power generation from the exhaust gas.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a method for stopping power generation of a fuel cell according to the present invention will be described below with reference to the drawings of FIGS. 1 and 2 are schematic configuration diagrams of a fuel cell system mounted on a fuel cell vehicle.

The fuel cell 1 is a solid polymer electrolyte membrane type fuel cell. For example, a solid polymer electrolyte membrane made of, for example, a solid polymer ion exchange membrane is sandwiched between an anode and a cathode from both sides, and a pair of outer sides is provided. It is composed of a stack formed by stacking a plurality of cells sandwiched between separators. In this fuel cell 1, when hydrogen gas is supplied to the anode and air containing oxygen is supplied to the cathode, hydrogen ions generated by the catalytic reaction at the anode pass through the solid polymer electrolyte membrane and move to the cathode. Then, the cathode causes an electrochemical reaction with oxygen to generate power.

The flow of the reaction gas during normal power generation is shown in FIG.
Will be described with reference to. The hydrogen gas is discharged from the hydrogen supply means 13 such as a high-pressure hydrogen tank, reduced in pressure by the fuel supply control valve 2, and then supplied to the anode of each cell of the fuel cell 1 through the hydrogen cutoff valve 3 and the ejector 4. . After this hydrogen gas is used for power generation, unreacted hydrogen gas is discharged from the fuel cell 1 as hydrogen off-gas, sucked through the dehumidifier 5 to the ejector 4, and supplied with hydrogen gas from the hydrogen supply means 13. They are merged and supplied again to the fuel cell 1.

On the other hand, the outside air as air is sucked into the air compressor 7 through the first flow path switching valve 6 and pressurized by the air compressor 7, and then passes through the first air shutoff valve 8 to pass through the fuel cell 1. Is supplied to the cathode of each cell. Part of the oxygen in the air supplied to the cathode is used as an oxidant for power generation, and the air containing unreacted oxygen is discharged from the fuel cell 1 as air off gas (exhaust gas), and the second air cutoff valve 9 and It is released to the atmosphere through the second flow path switching valve 10. The air compressor 2 is normally driven by electric power obtained by the power generation of the fuel cell 1 except at the time of starting. The above is the flow of the reaction gas during normal power generation.

In this fuel cell system, the first flow path switching valve 6 and the second flow path switching valve 10 are connected by an air circulation path 11, and a dehumidifier 12 is installed in the air circulation path 11. The first flow path switching valve 6 opens so as to allow the outside air to flow to the air compressor 7 during normal power generation, and shuts off the air circulation path 11. Further, the second flow path switching valve 10 opens so as to release the air off gas discharged from the fuel cell 1 to the atmosphere during normal power generation, and shuts off the air circulation path 11. Therefore, no gas flows through the air circulation path 11 during normal power generation. In FIG. 1, the air circulation path 11 is shown by a broken line, which means that gas is not flowing.

Next, the power generation stopping process of the fuel cell 1 will be described with reference to the flowchart of FIG. 3, and the flow of the reaction gas at that time will be described with reference to the schematic configuration diagram of FIG. This power generation stop processing is executed by using the power generation stop command as a trigger. First, in step S101, the introduction of outside air is stopped and the recirculation of air off-gas is started. Therefore, the open / closed state of the first flow path switching valve 6 is opened so as to connect the air circulation path 11 and the air compressor 7, the outside air inflow side is shut off, and the open / closed state of the second flow path switching valve 10 is changed to the fuel cell. The air off gas exhausted from No. 1 is opened so as to circulate in the air circulation path 11, and the atmosphere emission side is shut off. By switching the flow path switching valves 6 and 10 in this way, new outside air is no longer supplied to the fuel cell 1, and the air off gas discharged from the cathode of the fuel cell 1 is changed from the fuel cell 1 to the second air cutoff valve. A closed circuit of 9 → second flow path switching valve 10 → dehumidifier 12 → first flow path switching valve 6 → air compressor 7 → first air shutoff valve 8 → fuel cell 1 comes to circulate. Regarding the supply of hydrogen gas, the same state as during normal power generation is maintained.

As described above, even when the air off-gas is circulated through the cathode of the fuel cell 1, the fuel cell 1 continues to generate electricity if oxygen remains in the air off-gas. Hereinafter, the recirculation of the air off gas to generate the fuel cell 1 will be referred to as exhaust gas recirculation power generation. If the exhaust gas recirculation power generation is continued, oxygen in the air off gas is consumed during power generation, and as a result, the oxygen concentration in the air off gas gradually decreases, and the oxygen gas pressure decreases. As the pressure of the air off-gas decreases, the cathode gas pressure at the start of exhaust gas recirculation power generation is set so that the gas pressure of the cathode at the end of exhaust gas recirculation power generation is slightly higher than atmospheric pressure. (For example, 120 to 130 kP
a)).

Next, in step S102, it is determined whether the fuel cell 1 is capable of self-sustaining power generation. Here, the self-sustaining power generation is to drive and control the auxiliary devices necessary for power generation such as the air compressor 7 only by the power generated by the fuel cell 1 itself. Whether or not the self-sustaining power generation is possible can be determined by detecting the total voltage of the fuel cell 1 or each cell voltage, and when these voltages are equal to or higher than a predetermined value, the self-sustaining power generation can be determined. Immediately after the start of the recirculation of the air off gas, that is, immediately after the start of the exhaust gas recirculation power generation, there is usually a sufficient amount of oxygen remaining in the air off gas to enable independent power generation. Further, when the self-sustaining power generation is impossible, it can be determined that the voltage required for the self-sustaining power generation cannot be obtained because the oxygen concentration in the air off gas is extremely low.

The determination result in step S102 is "Y.
If "ES" (independent power generation is possible), step S10
3, the air compressor 7 is driven by the electric power obtained by the exhaust gas recirculation power generation. As a result, the electric power obtained by the exhaust gas recirculation power generation is not wasted, so that the energy can be effectively used, and the electric power stored in the storage means such as the battery is not consumed.

Further, in step S104, the hydrogen gas pressure is controlled according to the residual oxygen gas pressure in the air off gas. The hydrogen gas must be set to the same pressure as the cathode side or slightly higher, but as mentioned above, when exhaust gas recirculation power generation is continued, residual oxygen in the air off gas is consumed and residual oxygen gas This is because the pressure decreases and the pressure of the air off gas decreases, so that the pressure of the hydrogen gas also needs to decrease correspondingly.

When the result of the determination in step S102 is "NO" (independent power generation is impossible), power generation is stopped (step S105). This is because if the self-sustaining power generation is disabled, the oxygen concentration in the air offgas is sufficiently reduced, and it is judged that no problem will occur even if cross leak occurs between the anode and the cathode during the power generation stop. Because. That is, when the oxygen concentration in the air off gas is sufficiently low, a cross leak occurs during power generation stop, hydrogen gas on the anode side moves to the cathode side, or gas on the cathode side moves to the anode side. However, there is almost no reaction between hydrogen and oxygen, and the solid polymer electrolyte membrane is not damaged. That is, it is possible to obtain the same effect as when the cathode is filled with the inert gas.

After this, the process further proceeds to step S106,
The hydrogen shutoff valve 3 and the first and second air shutoff valves 8 and 9 are closed, the reaction gas supply passage of the fuel cell 1 is shut off from the outside and closed, and the power generation stop processing ends. As a result, the fuel cell 1
Since it is possible to prevent new air from entering the cathode side of the fuel cell and keep the cathode side of the fuel cell 1 at an extremely low oxygen concentration,
The protection of the solid polymer electrolyte membrane can be continued.

Since the air off-gas passes through the dehumidifier 12 during the exhaust gas recirculation power generation, the generated water generated by the exhaust gas recirculation power generation can be removed from the air off gas, and the generated water is in the fuel cell 1. Can be prevented from remaining. As a result, the startability when the fuel cell 1 is restarted next is improved.

As described above, according to the power generation stopping method of the fuel cell in this embodiment, even if the inert gas source and the inert gas supply system are not provided, it is possible to fill the cathode side with the inert gas. The solid polymer electrolyte membrane can be protected. Therefore, it is possible to reduce the size and weight of the entire fuel cell system.

[Other Embodiments] The present invention is not limited to the above-described embodiments. For example, in the above-described embodiment, the first and second air cutoff valves 8 and 9 are closed to shut off the air supply passage from the outside in step S106. However, the first flow passage switching valve 6 and the second flow passage switching valve 10
The air supply passage may be blocked from the outside by maintaining the open / closed state of the air off gas in a circulatable state. In this way, the first and second air cutoff valves 8 and 9 are unnecessary.

[0026]

As described above, according to the invention described in claim 1, the exhaust gas recirculation power generation reduces the oxygen concentration in the exhaust gas supplied to the cathode, and when the power generation is stopped, the oxygen concentration is increased to the cathode side. Since it is possible to create an atmosphere very close to that in which an inert gas is filled, even if a cross leak occurs after power generation is stopped, there is almost no reaction between hydrogen and oxygen, and as a result, the solid polymer electrolyte membrane is protected and the fuel The excellent effect that the battery can be protected is exhibited. Further, since the inert gas source and the inert gas supply system which have been conventionally required are not required, there is an effect that the overall system of the fuel cell can be made compact and lightweight.

According to the invention described in claim 2, since the electric power obtained by the exhaust gas recirculation power generation is not wasted, it is possible to effectively use the energy, and the electric power is stored in the electric storage means such as a battery. The effect that it does not have to consume the electric power that is being produced. According to the invention described in claim 3,
While power generation is stopped, new oxygen can be prevented from entering the cathode side, and the cathode side can be maintained in a low oxygen concentration state, so that the solid polymer electrolyte membrane and fuel cell The protection can be effective.

According to the invention described in claim 4, since the generated water generated by the exhaust gas recirculation power generation can be removed from the exhaust gas, it is possible to prevent the generated water from remaining in the fuel cell, There is an effect that the restartability of the fuel cell can be improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a fuel cell system capable of implementing a method for stopping power generation of a fuel cell according to the present invention, showing a flow of a reaction gas during normal power generation.

FIG. 2 is a schematic configuration diagram of the fuel cell system of the embodiment, showing a flow of a reaction gas when power generation is stopped.

FIG. 3 is a flowchart of a power generation stop process.

[Explanation of symbols]

1 fuel cell 7 Air compressor (compressor) 12 Dehumidifier 13 Hydrogen supply means

Continued front page    F-term (reference) 5H026 AA06                 5H027 AA06 BA13 BA19 BC19 KK54                       MM03 MM04 MM08 MM09

Claims (4)

[Claims] 1. A method of stopping power generation of a fuel cell, wherein the air supplied by a compressor and hydrogen supplied by a hydrogen supply means are used as reaction gases to generate power, and when the power generation of the fuel cell is stopped, the fuel cell is discharged from a cathode of the fuel cell. Exhaust gas is recirculated by the compressor to be supplied to the cathode, power generation is continued by residual oxygen in the exhaust gas, and power generation is stopped when the power generation voltage becomes equal to or lower than a predetermined value. How to stop power generation. 2. The method for stopping power generation of a fuel cell according to claim 1, wherein the compressor is driven by electric power obtained by power generation by residual oxygen in the exhaust gas. 3. The reaction gas supply passage of the fuel cell is shut off from the outside after the power generation is stopped.
The method for stopping power generation of a fuel cell according to. 4. The power generation stoppage of the fuel cell according to claim 1, wherein the exhaust gas is dehumidified by a dehumidifier provided in the exhaust gas circulation path during power generation by residual oxygen in the exhaust gas. Method.