JP2002246054A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system which is used under a low-temperature environment, capable of removing water inside a fuel cell in a short time, when operation is stopped. SOLUTION: A cooling water path 40 for circulating cooling water in the fuel cell 10 is provided with cooling parts 42, 43 for cooling cooling water, when normal operation of the fuel cell 10 is performed and a heating part 44 for heating cooling water, when water removing operation is performed; and a flow passage of cooling water is constituted so as to switch to cooling part 42, 43 sides or a heating part 44 side. After normal operation of the fuel cell 10 is ended, prescribed dry air is supplied into an air path 20 and a hydrogen path 30, and the flow passage of cooling water is switched to the heating part 44 side so as to heat the fuel cell 10 up to a prescribed temperature.

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 comprising a fuel cell which generates electric energy by a chemical reaction between hydrogen and oxygen, and is applied to a moving body such as a vehicle, a ship and a portable generator. It is valid.

[0002]

2. Description of the Related Art Conventionally, there has been known a fuel cell system including a fuel cell which generates electric power by utilizing an electrochemical reaction between hydrogen and oxygen (air). For example, in a polymer electrolyte fuel cell that is considered as a driving source for vehicles and the like, 0 ° C.
In the following low-temperature state, there is a problem that moisture existing in the vicinity of the electrode freezes to hinder the diffusion of the reaction gas and that the electric conductivity of the electrolyte membrane decreases.

When the fuel cell is started in such a low temperature environment, the fuel gas is supplied due to clogging of the reaction gas path due to freezing or hindering the progress and arrival of the reaction gas (hydrogen and air) to the electrolyte membrane. However, there is a problem that the electrochemical reaction does not proceed and the fuel cell cannot be started. In addition, blockage of the gas path due to freezing of water condensed in the reaction gas path occurs.

[0004] In order to prevent freezing inside the fuel cell and improve low-temperature startability, it is desirable to remove moisture that freezes in a low-temperature environment from the inside of the fuel cell in advance. To this end, it is conceivable to supply air into the fuel cell to remove moisture in the fuel cell by an air flow.

[0005]

However, when water in the fuel cell is removed by an air flow, heat is taken away by the latent heat of evaporation during the evaporation of water, and the temperature inside the fuel cell decreases. Becomes As a result, there is a problem that the amount of evaporation of the water decreases and it takes time to remove the water from the fuel cell.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a fuel cell system which can be used in a low-temperature environment and can remove moisture inside the fuel cell in a short time when operation is stopped. The purpose is to:

[0007]

According to the first aspect of the present invention, there is provided a fuel cell system including a fuel cell (10) for obtaining electric power by electrochemically reacting hydrogen and oxygen. An air path (20) through which oxygen supplied to the fuel cell (10) passes; and a fuel cell (10).
A hydrogen path (30) through which hydrogen supplied to the fuel cell passes; and a heating means (44) for heating the fuel cell (10). After normal operation of the fuel cell (10) is stopped, the air path (20) and the hydrogen A predetermined dry gas is supplied to the passage (30), and the fuel cell (10) is heated to a predetermined temperature by the heating means (44).

As described above, the fuel cell (1) is simultaneously supplied with the gas.
By heating 0), it is possible to prevent the temperature of the fuel cell from decreasing due to the evaporation of water during the water removal operation. Thereby, the evaporation of the residual moisture inside the fuel cell (10) can be promoted, and the fuel cell (10) can be
It is possible to improve the startability of the fuel cell (10) at a low temperature by removing internal water and avoiding freezing of the fuel cell.

Further, in the invention according to claim 2, the dry gas is air. By using air as described above, moisture can be removed without providing a special gas supply device. Also, the dry air
This can be provided by not humidifying the air that is performed during normal operation.

According to the third aspect of the present invention, the cooling water circulation path (4) for circulating the cooling water through the fuel cell (10).
0) and the cooling water path (40), and the fuel cell (1)
0) during the normal operation of the cooling unit (42, 4) for cooling the cooling water
3), and the heating means is a heating unit (44) provided in parallel or in series with the cooling units (42, 43) in the cooling water path (40) to heat the cooling water, The flow path of the cooling section (42, 43) or the heating section (4)
4) is configured to be switchable to the fuel cell (1).
After the normal operation of 0), when heating the fuel cell (10), the flow path of the cooling water is switched to the heating unit (44) side.

With such a configuration, the fuel cell (10) can be heated with a simple configuration using an existing fuel cell cooling system and adding a heating section (44) to the cooling water.

Further, in the invention according to claim 4, a temperature sensor (12) for detecting the temperature of the fuel cell (10) is provided, and the heating means (44) is used based on the temperature detected by the temperature sensor (12). It is characterized in that the heating temperature of the fuel cell (10) is controlled. Thereby, the temperature of the fuel cell can be maintained at a temperature at which the residual water can be efficiently evaporated within a range that does not destroy the electrolyte membrane or the like of the fuel cell (10).

The reference numerals in parentheses of the above means indicate the correspondence with specific means described in the embodiments described later.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.
A description will be given based on FIG. In this embodiment, the fuel cell system is applied to an electric vehicle (fuel cell vehicle) that runs using a fuel cell as a power source.

FIG. 1 shows the overall configuration of a fuel cell system according to this embodiment. As shown in FIG. 1, the fuel cell system according to the present embodiment includes a fuel cell (FC stack) 10 that generates electric power using an electrochemical reaction between hydrogen and oxygen.
It has. The FC stack 10 is configured to supply electric power to an electric motor (load) 11 for driving the vehicle and electric equipment such as a secondary battery (not shown).

In the FC stack 10, the following electrochemical reaction between hydrogen and oxygen occurs, and electric energy is generated. (Negative electrode side) H ₂ → 2H ⁺ + 2e ⁻ (positive electrode side) 2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O In the present embodiment, a solid polymer electrolyte fuel cell is used as the FC stack 10 and the basic unit is Cells are stacked. Each cell has a configuration in which an electrolyte membrane is sandwiched between a pair of electrodes. Further, the FC stack 10 is provided with a temperature sensor 12 for detecting the temperature of the main body of the FC stack.

The fuel cell system includes an FC stack 10
An air path 20 for supplying air (oxygen) to the oxygen electrode (positive electrode) 10a side and a hydrogen path 30 for supplying hydrogen to the hydrogen electrode (negative electrode) 10b side of the FC stack 10 are provided. The air path 20 is provided with a blower (gas compressor) 21 for air supply for supplying air. Hydrogen is supplied to the hydrogen path 30 from a hydrogen supply device 31.

Due to the electrochemical reaction during power generation, F
It is necessary to keep the electrolyte membrane in the C stack 10 in a wet state containing water. Therefore, during normal operation, the humidifier (not shown) humidifies the air in the air path 20 and the hydrogen in the hydrogen path 30, and the humidified air and hydrogen are supplied to the FC stack 10. Thereby, F
The inside of the C stack 10 operates in a wet state.
On the oxygen electrode 10a side, water is generated by the above-mentioned electrochemical reaction.

At the time of a moisture removal operation described later, the non-humidified dry air and the non-humidified dry hydrogen are supplied to the FC stack 10. It is desirable that these dry gases have as low a humidity as possible in order to remove moisture remaining in the FC stack 10, and it is necessary that the humidity be at least lower than the humidity in the FC stack 10.

At both ends of the air path 20, shut valves 22 and 23 for shutting off the air path 20 are provided. By closing these shut valves 22, 23, the inside of the FC stack 10 and the air path 20 are closed.
The inside can be shut off from the outside air. Similar shut valves 32 and 33 are provided at both ends of the hydrogen path 30.

Further, the air path 20 and the hydrogen path 30
It is connected on the upstream side of the C stack 10. A hydrogen path switching valve 35 is provided at a connection portion in the hydrogen path 30. By switching the hydrogen path switching valve 35, the hydrogen supply device 31 is connected to the hydrogen path 30 during normal operation.
From the air path 20 and the air from the air path 20 to the hydrogen path 30 during the water removal operation.

The FC stack 10 includes the FC stack 10
Moisture sensors 24 and 34 for detecting residual moisture existing in the oxygen electrode 10a and the hydrogen electrode 10b are provided. In the present embodiment, humidity sensors are used as the moisture sensors 24 and 34. The humidity sensors 24, 34
To properly detect the humidity inside the C stack 10, the FC stack 1 at the oxygen electrode 10a and the hydrogen electrode 10b
It is desirable to provide it near the exit 0.

The FC stack 10 generates heat with power generation. Therefore, the fuel cell system includes the FC stack 1
Cooling systems 40 to 45 are provided so as to cool 0 and bring the operating temperature to a suitable temperature (about 80 ° C.) for the electrochemical reaction.

The cooling system is provided with a cooling water path 40 for circulating cooling water (heat medium) through the FC stack 10, a water pump 41 for circulating cooling water, and a radiator 42 having a fan 43. The radiator 42 and the fan 43 constitute a cooling unit.

The heat generated in the FC stack 10 is discharged outside the system by the radiator 42 via the cooling water. With such a cooling system, the cooling amount of the FC stack 10 can be controlled by the flow rate control by the water pump 41 and the air flow rate control by the radiator 42 and the fan 43.

Further, in the cooling system of this embodiment, a heating section (heating means) 44 for heating the cooling water is provided in parallel with the radiator 43. As the heating unit 43, for example, an electric heater, a combustion heater, a catalyst heater, or the like can be used. With such a configuration, the heating amount control of the cooling water by the heating unit 44 and the flow rate control by the water pump 41 can control the heating amount of the FC stack 10.

The flow path of the cooling water is switched between the radiator 43 side and the heating section 44 side by a cooling water switching valve 45.
During normal operation of the FC stack 10, the cooling water switching valve 45
Is switched to the radiator 43 side and the FC stack 10
Is cooled. On the other hand, during the moisture removal operation of the FC stack 10 in the present embodiment, the cooling water switching valve 45 is switched to the heating unit 44 side, and the FC stack 10 is heated.

The fuel cell system of this embodiment is provided with a control unit (ECU) 50 for performing various controls. A required power signal from the load 11, a temperature signal from the temperature sensor 12, a residual moisture content signal from the moisture sensors 24 and 34, and the like are input to the control unit 50. The control unit 50 is configured to output control signals to the secondary battery, the blower 21, the water pump 41, the radiator fan 43, the heating unit 44, the cooling water switching valve 45, and the like.

Next, water removal control in the fuel cell system having the above configuration will be described with reference to FIG. FIG. 2 is a flowchart showing the water removal control of the fuel cell system.

First, after the normal operation is stopped, the FC stack 10
It is determined whether or not moisture removal (moisture purge) is necessary (step S10). To determine whether or not to remove water,
This is performed in consideration of the environmental temperature (outside temperature) at the time of operation stop, seasonal information, and the like. That is, the necessity of the water removal operation is determined based on the condition that the environmental temperature is 0 ° C. or lower, or that the temperature is predicted to decrease in winter or the like.
Naturally, there is no danger of freezing in summer or other conditions, so no moisture operation is required.

When the operation of the FC stack 10 is stopped,
The configuration may be such that the estimated time of the FC stack 10 stop time by the driver is input. This is FC Stack 1
Even if the environmental temperature is below the freezing point at the stop of 0,
This is because the preheating of the FC stack 10 is sufficient, so that the FC stack 10 does not instantaneously fall below the freezing point, and the high temperature is maintained for a while. Therefore, about 10 hours (all day and night)
It is not necessary to remove the residual water at the time of operation stoppage within the stop time.

If it is determined in step S10 that the water removal operation is necessary, the cooling water switching valve 45 is switched to the heating section 44.
Side (step S11). Thereby, the cooling water is heated by the heating unit 44. Note that F
Since the C-stack 10 has already stopped generating power, the cooling water switching valve 45 and the like operate by power supply from the secondary battery.

Next, the hydrogen path switching valve 35 is connected to the air path 20.
Side (step S12), and the blower 21 performs blower control (step S13). Thereby, air is supplied to the air path 20 and the hydrogen path 30. At this time, the air was not humidified, and the oxygen electrode 1 of the FC stack 10 was not humidified.
Dry air is supplied to Oa and the hydrogen electrode 10b. As a result, water present as droplets in the FC stack 10 is blown out of the FC stack 10 by an air flow.

Next, the remaining moisture content in the FC stack 10 is detected by the moisture sensors 24 and 34 (step S14).
It is determined whether the residual water content is smaller than the predetermined amount and is lower than the freezing range (step S15).

When the amount of residual moisture in the FC stack 10 is lower than the freezing range, the shut valves 22 and 2 provided at both ends of the air path 20 and the hydrogen path 30 are used.
3, 32 and 33 are closed (step S16). Thereby, the inside of the FC stack 10, the inside of the air path 20, and the inside of the hydrogen path 30 are cut off from the outside air, and the intrusion of moisture from the outside environment can be prevented.

As a result, if the residual water content in the FC stack 10 exceeds the freezing range, the following step S
The FC stack temperature is controlled in steps 17 to S21, and the FC stack 10 is heated to evaporate and remove the residual moisture.

First, the temperature T of the main body of the FC stack 10 is detected by the temperature sensor 12 (step S17), and it is determined whether or not the FC stack temperature T is higher than the target temperature Tr (step S18). The target temperature Tr is preferably as high as possible to evaporate the water in the FC stack 10. However, if the target temperature Tr is set too high, the physique of the heating unit 44 is increased, and F
The electrolyte membrane inside the C stack 10 is destroyed. Therefore, in order to prevent these problems, the target temperature Tr is set to 80 to
Set to 100 ° C.

If the FC stack temperature T is higher than the target temperature Tr, the cooling water heating amount by the heating unit 44 is set to zero (step S19), and if the FC stack temperature T is lower than the target temperature. Sets the cooling water heating amount by the heating unit 44 to K (Tr-T) [K: proportional constant] (step S20). Next, the circulation amount of the cooling water is controlled by the water pump 41 (step S21). Thereby, the temperature is controlled so that the FC stack temperature T becomes the target temperature Tr. After the above temperature control, the process returns to step S14.

By performing the FC stack temperature control in steps S17 to S21, the inside of the FC stack 10 can be kept at a high temperature without lowering the temperature due to evaporation of water. Thereby, evaporation of the residual water inside the FC stack 10 is promoted. The evaporated residual water is discharged to the outside of the FC stack 10 while being contained in the air supplied from the air path 20 and the hydrogen path 30. At this time, since the dry air is supplied from the air path 20 and the hydrogen path 30, the inside of the FC stack 10 can be efficiently dried.

(Other Embodiments) In the above embodiment, the humidity sensors are used as the moisture sensors 24 and 34 for detecting the amount of residual moisture in the FC stack 10. However, the present invention is not limited to this. By measuring the change in the electric resistance of the electrolyte membrane inside the stack 10, the amount of residual moisture inside the FC stack 10 can also be detected.

Further, it is sufficient that at least a part of the individual cells constituting the FC stack 10 have been subjected to moisture removal. If a part of the cell is dry, power generation can be started by supplying hydrogen and air to the dry part. When power generation is started in a part of the cell, the temperature of the other part can be raised by the heat generated by the power generation, and power can be generated in the entire cell.

In the above embodiment, the dry air is supplied from the air path 20 and the hydrogen path 30 during the water removal operation. However, the present invention is not limited to this, and an arbitrary gas such as nitrogen may be supplied. .

Also, the FC detected in step S16 is used.
The stack temperature T is a temperature at which the electrolyte membrane is broken (for example, 15
When the temperature is equal to or higher than 0 ° C.), the cooling water switching valve 45 may be switched to the radiator side to actively cool the cooling water to cool the FC stack 10.

In the above embodiment, the heating section 44 for heating the cooling water is provided in parallel with the radiator 43. However, the present invention is not limited to this. The heating section 44 is provided in the cooling water path 40 in series with the radiator 43. You may. In this case, in the configuration of the fuel cell system shown in FIG. In the case of such a configuration, the path provided with the heating unit 44 becomes a bypass path for causing the cooling water to bypass the radiator 42. With such a configuration, when performing the water removal control after the end of the normal operation, the cooling water heated by passing through the heating unit 44 passes through the bypass passage and bypasses the radiator 42.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a schematic configuration of a fuel cell system according to the embodiment.

FIG. 2 is a flowchart showing water removal control of the fuel cell system of FIG.

[Explanation of symbols]

10: fuel cell (FC stack), 10a: oxygen electrode, 1
0b: hydrogen electrode, 12: temperature sensor, 20: air path, 2
2, 23 ... shut valve, 30 ... hydrogen path, 32, 3
3 Shut valve, 35 Hydrogen path switching valve, 42, 4
3. Cooling unit, 44 heating unit (heating means), 50 control unit (ECU).

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Haruhiko Kato 1-1-1, Showa-cho, Kariya-shi, Aichi Pref. (72) Inventor Naoto Hotta 1-1-1, Showa-cho, Kariya-shi, Aichi F-term (reference) in Denso Corporation 5H027 AA06 CC04 KK46

Claims (4)

[Claims] 1. A fuel cell system comprising a fuel cell (10) for obtaining electric power by electrochemically reacting hydrogen and oxygen, wherein an air path (20) through which oxygen supplied to the fuel cell (10) passes is provided. ), A hydrogen path (30) through which hydrogen supplied to the fuel cell (10) passes, and heating means (44) for heating the fuel cell (10). After the operation is stopped, a predetermined dry gas is supplied to the air path (20) and the hydrogen path (30), and the fuel cell (10) is heated to a predetermined temperature by the heating means (44). Fuel cell system. 2. The fuel cell system according to claim 1, wherein the dry gas is air. 3. A cooling water circulation path (40) for circulating cooling water through the fuel cell (10); and a cooling water circulation path (40) provided in the cooling water path (40).
0) during the normal operation of the cooling unit (4) for cooling the cooling water.
The heating unit is provided in the cooling water path (40) in parallel or in series with the cooling unit (42, 43), and heats the cooling water. The flow path of the cooling water is configured to be switchable to the cooling unit (42, 43) side or the heating unit (44) side, and after the normal operation of the fuel cell (10), 3. The fuel cell system according to claim 1, wherein when heating the fuel cell, the flow path of the cooling water is switched to the side of the heating unit. 4. 4. A fuel cell (10) comprising a temperature sensor (12) for detecting a temperature of the fuel cell (10), and the heating means (44) based on the temperature detected by the temperature sensor (12). The fuel cell system according to any one of claims 1 to 3, wherein a heating temperature of the fuel cell is controlled.