JPH09312165A - Fuel cell generating device and operating method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the output constant by monitoring the stack temperature of a high molecular solid electrolyte fuel cell and the air manifold temperature, and while controlling these temperature so that a temperature difference between them exists in the predetermined range. SOLUTION: Stack temperature Ts measured by a stack temperature sensor 1 and air manifold temperature Tm measured by an air manifold sensor 2 are input to a CPU 3. The CPU 3 compares the stack temperature Ts with the air manifold temperature Tm, and on the basis of a result of this comparison, the CPU 3 selectively controls operation of a temperature adjusting means such as a blower fan 4 for leading the air to an air supplying manifold, a cooling means 5 for cooling a stack, a heating means 6 for heating an air supplying manifold, and a heating means 7 for heating an air discharge manifold.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a fuel cell power generator,
In particular, the present invention relates to a power generator using a polymer electrolyte fuel cell and an operating method thereof.

[0002]

2. Description of the Related Art In a solid polymer electrolyte fuel cell, an ion conductive film is used as an electrolyte, and hydrogen ions obtained at the fuel electrode of the fuel cell are transferred to the air electrode side in the electrolyte film in the form of protons. Although an electromotive force can be obtained by this, in order to obtain a stable high output, it is important to always keep this electrolyte membrane in an optimally water-containing state.

Therefore, conventionally, fuel gas (hydrogen) or oxidant gas (air or oxygen) is humidified by using a humidifier such as a bubbling device, and the humidified gas is passed through an electrolyte membrane to form an electrolyte. The method of humidifying the membrane is generally adopted.

[0004]

However, during the operation of the fuel cell stack, the temperature T inside the stack is increased.
s (as a temperature representative of the stack, for example, detected by a temperature sensor installed in almost the center cell of the stack)
Is higher than the temperature outside the stack, that is, the temperature Tm inside the gas manifold (for example, detected by a temperature sensor installed on at least one of the oxidant gas discharge side and the supply side manifold), that is, Ts> Tm.

When Ts> Tm, moisture condenses in the gas supply manifold, resulting in insufficient humidification of the electrolyte membrane.
There is a problem that the membrane resistance increases and the battery output decreases.

On the other hand, when the gas is cooled in the gas supply or discharge manifold and water in the gas is condensed to generate water droplets, the condensed water blocks the gas flow path on the electrode and lowers the cell voltage. There was a problem.

[0007] In particular, since water is produced by the cell reaction at the air electrode, the above-mentioned phenomenon is remarkable in the air manifold.

When the operation of the power generator is stopped, the humidification by the supply gas and the water supply to the stack by the water generated by the cell reaction are stopped, so that the stack is dried and the membrane resistance of the electrolyte membrane increases when the operation is restarted. And not enough output is obtained.

Further, since the stack temperature is lowered after the operation is stopped, the supply water or the generated water for humidification may be stagnant in the gas flow passage and block the gas flow passage when the operation is restarted.

Further, when the operation of the power generator is stopped for a long time, the water retention state in the stack depends on the outside air temperature. For example, when the outside air temperature is high, such as in the summer, the water retained in the stack is insufficient due to evaporation, and the electrolyte membrane is in a dry state. Sufficient output cannot be obtained until the state is reached.

On the other hand, when the outside air temperature is low as in winter, excessive moisture may be retained in the gas flow path above the electrode, and it may take time until the stack temperature Ts rises sufficiently after startup. However, there is a possibility that the gas flow path will be blocked during that time.

[0012]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to appropriately and automatically adjust the amount of water in a stack during operation of a polymer solid oxide membrane fuel cell power generator to maintain a constant output. To do.

Another object of the present invention is to maintain an appropriate amount of water in the stack even when the fuel cell power generator is stopped to improve the startability.

That is, according to the present invention, in a power generator using a fuel cell in which an air electrode and a fuel electrode are arranged on both sides of a solid polymer electrolyte membrane, the temperature Ts in the stack of the fuel cell is
And a second temperature measuring means for measuring the temperature Tm in the oxidant gas manifold at the air electrode of the fuel cell, and at least one of the stack temperature Ts and the oxidant gas manifold temperature Tm. The temperature adjusting means for heating or cooling one of them is compared with the stack temperature Ts and the oxidant gas manifold temperature Tm measured by the first and second temperature measuring means, and the temperature adjusting means is operated based on the comparison result. A control unit for controlling the fuel cell power generation device.

The temperature adjusting means preferably includes a stack cooling means for cooling the fuel cell stack and an oxidant gas manifold heating means for heating the oxidant gas manifold.

The present invention also provides a method of operating the fuel cell power generator having the above structure, wherein the stack temperature Ts and the oxidant gas manifold temperature Tm are maintained during operation of the fuel cell power generator. The control means controls the temperature adjusting means so as to maintain the temperature difference within a predetermined range.

When the fuel cell power generator is stopped, the stack temperature Ts is compared with the oxidant gas manifold temperature Tm, and the control means controls the temperature adjusting means based on the comparison result.

[0018]

1 is a diagram showing a control system in a polymer electrolyte fuel cell power generator according to the present invention.

The stack temperature sensor 1 is installed in the cell at the approximate center of the stack to measure the fuel cell stack temperature Ts. The air manifold temperature sensor 2 is installed in the air manifold to measure the temperature Tm in the air manifold.

The stack temperature Ts and the air manifold temperature Tm measured by these temperature sensors 1 and 2 are C
Input to PU3.

The CPU 3 compares the stack temperature Ts with the air manifold temperature Tm, and based on the comparison result,
Temperatures of blower fan 4 for introducing air into the air supply manifold, cooling means 5 for cooling the stack, heating means 6 for heating the air supply manifold, heating means 7 for heating the air discharge manifold, etc. Selectively controlling the operation of the adjusting means.

That is, Ts> Tm is generally satisfied during the operation of the fuel cell. If this state is left, water is condensed in the air manifold whose temperature is lower than that of the stack, and the water on the electrode on the air electrode side is condensed. The gas flow path is blocked and the electrolyte membrane is dried to increase the membrane resistance, resulting in a decrease in output voltage. Therefore, when it is found from the measurement results of the sensors 1 and 2 that Ts> Tm,
The CPU 3 turns on the blower fan 4 and turns on the stack cooling means 5.
Is turned on, the air supply manifold heating means 6 is turned off, and the air discharge manifold heating means 7 is turned on, so that
Let s = Tm. As a result, the amount of condensed water in the air manifold is reduced, the gas flow path on the air electrode side is prevented from being blocked, and the electrolyte membrane is humidified.

If Ts <Tm during operation of the fuel cell, water will be condensed in the stack. A part of the condensed water in the stack is absorbed by the electrolyte membrane to help humidify the electrolyte membrane, but when water is excessively condensed in the stack, the gas flow path on the electrode is blocked. Therefore, from the measurement results of the sensors 1 and 2, Ts
When it is determined that <Tm, the CPU 3 turns on the blower fan 4, turns off the stack cooling means 5, turns on the air supply manifold heating means 6, and turns off the air discharge manifold heating means 7 to actually set. Ts = Tm. This reduces the amount of condensed water in the stack and prevents the gas flow path on the air electrode side from being blocked.

Since the condensed water in the stack is absorbed by the electrolyte membrane to some extent as described above, when Ts <Tm, a temperature difference of up to about 5 ° C. is allowed, but Ts> Tm.
In this case, the condensed water in the manifold has a large adverse effect on the blockage of the gas flow path, so the temperature difference is suppressed to 3 ° C. or less.
During the operation of the fuel cell, the CPU 3 controls Ts and Tm so that they fall within such a temperature difference range.

When the fuel cell is stopped, the continuous stop time is short (for example, about 1 to 2 days and nights), and the temperature of the water held in the stack does not fluctuate greatly as in the spring and autumn. When the outside temperature is high, Ts and Tm are kept within a predetermined temperature difference range (for example, a temperature difference of 3 ° C. or less at 60 to 90 ° C.) during and immediately after the load is cut off during the above operation. Perform the same control as.

When the continuous stop time is a long time such as several days or more, or the outside air temperature is high as in summer, the water retained in the stack is evaporated and the electrolyte membrane is dried even when the operation is stopped for a short time. If the temperature is to be increased, or if it takes time to raise the temperature at startup due to low outside air temperature such as in winter, the following control is performed.

In the summer, even after the blower fan 4 is stopped after the load is cut off, the stack cooling means 5 is operated for a while,
The stack temperature Ts is set to be lower than the air exhaust manifold temperature Tm. As a result, water is condensed in the stack, and the amount of retained water in the stack becomes more than during operation, so that the wet state of the electrolyte membrane is maintained even during the stop period, and the next startup time is shortened.

On the other hand, in winter, the blower fan 4 is provided after the load is cut off.
Is started, the air exhaust manifold heating means 7 is started, and the stack cooling means 5 is turned off. As a result, the temperature Tm of the air exhaust manifold becomes equal to the stack temperature Ts.
Therefore, the water in the gas flow path on the electrode of the fuel cell that is stopped is discharged, and the flow path is blocked by the water in the gas flow path during the temperature rise of the stack at the next startup. Can be prevented.

Any structure may be adopted for the stack cooling means 5, the air supply manifold heating means and the air discharge manifold heating means. For example, the stack cooling unit 5 may be an air cooling unit such as a cooling fan or a water cooling unit using cooling water. Further, the air supply manifold heating means and the air discharge manifold heating means are generally configured as various heaters, but when the fuel cell power generator is mounted on a vehicle, it may be configured to heat with radiator water. It is possible.

FIG. 2 is a schematic diagram showing the structure of a polymer electrolyte fuel cell power generator according to the present invention.
0 is shown as a side view as seen from the air electrode (cathode) side. As is well known, in this fuel cell, a fuel electrode (anode) into which a fuel gas such as hydrogen is introduced is arranged on the side opposite to the air electrode with the polymer solid electrolyte membrane interposed therebetween. In addition, in practice, it is put to practical use as a stack in which a large number of such fuel cells are stacked.

Air as the oxidant gas is the air introduction path 11
Is supplied to the air supply manifold 13 by the blower fan 12, and is supplied to the air electrode.

As is well known, when hydrogen gas is supplied to the fuel electrode of the fuel cell and air is supplied to the air electrode, hydrogen ions move in the form of protons in the solid polymer electrolyte membrane, and the cell reaction takes place. Be seen. At this time, in the air electrode, the supplied oxygen reacts with the transferred hydrogen ions and electrons to generate water.

Therefore, the exhaust gas discharged from the air electrode contains reaction product water (steam) at the air electrode in addition to unreacted oxygen.

This exhaust gas is sent to the air exhaust manifold 14
Is sent to the air exhaust passage 15, but the air exhaust passage is connected to the air introduction passage 11 via the circulation passage 16,
Exhaust gas accompanied by reaction product water can be reintroduced into the air electrode.

That is, an exhaust valve 17 is provided in connection with the circulation path 16, and a certain amount of exhaust gas from the air electrode is discharged out of the system according to the opening degree of the exhaust valve 17, and the remaining amount is It is reintroduced into the air electrode via the circulation path 16 and the air introduction path 11.

By thus re-introducing the exhaust gas containing the reaction product water into the air electrode of the fuel cell 10,
The reaction product water (water vapor) permeates the electrolyte membrane due to the concentration difference and moves to the fuel electrode side, and the water that has moved to the fuel electrode side moves to the air electrode side as electro-osmotic water, and these water moves back and forth. Moisture of the electrolyte membrane is efficiently and averagely carried out by the movement.

The opening of the exhaust valve 17 is determined by the correlation between the output current value of the fuel cell 10 and the temperature of the exhaust gas from the air electrode, and a control means (CPU) for giving the fuel cell 10 an optimum water balance condition. Although controlled by 18, this control is not directly related to the subject matter of the present invention, and a description thereof will be omitted.

In the present invention, as shown, a stack temperature sensor 19 for monitoring the fuel cell stack temperature Ts and an air exhaust manifold temperature sensor 20 for monitoring the air exhaust manifold temperature Tm are provided. Further, a cooling fan 21 as a cooling means for cooling the fuel cell stack, a heater 22 as a heating means for heating the air supply manifold 13,
A heater 23 is provided as a heating means for heating the air exhaust manifold 14.

These cooling fan 21, heater 22 and heater 23 are based on the comparison results of the stack temperature Ts and the air exhaust manifold temperature Tm monitored by the temperature sensors 19 and 20, as described above with reference to FIG. At, the operations are controlled by the CPU 18.

When the fuel cell power generator is configured so that the air discharged from the air electrode is reintroduced into the air electrode through the circulation path 16 as shown in FIG. 2, the air discharge manifold heater 23 heats the air. Since at least a part of the discharged exhaust air is introduced into the air electrode, the means (heater 22) for heating the air supply manifold 13 can be omitted.

It should be noted that the air manifolds 13, 14 and especially the air exhaust manifold 14 may be provided with a moisture absorbent material that absorbs excess water inside. Any material can be used as the hygroscopic material. For example, a fibrous sheet or porous particles are used as the air exhaust manifold 14.
Built in to absorb condensed excess water.

Further, it is preferable that the air supply manifold 13 contains an ion exchange resin in order to purify the air supplied to the fuel cell stack. Since the ion exchange resin generally has a water absorbing property, it can be expected to have an effect of preventing the gas flow passage from being blocked.

[0043]

According to the present invention, in the polymer electrolyte fuel cell stack, the stack temperature and the air manifold temperature are monitored and controlled so that the temperature difference between them is kept within a predetermined range. During operation of the cell, the water content in the stack is kept in the optimum range and thus the output is kept constant.

In particular, since the condensation of water in the air manifold is prevented, the amount of water vapor loss in the exhaust air is reduced, and the exhaust air is reintroduced into the air electrode. It is possible to keep the electrolyte membrane in a constant wet state without the need to provide.

Further, even when the fuel cell is stopped, the next-time startability is improved by controlling so that an appropriate amount of water is retained in the stack. Since such control is performed so as to appropriately adjust the moisture retention amount of the stack according to the outside temperature even in the summer, winter, or long-term stoppage, the start-up time can be greatly shortened.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control system by a polymer electrolyte fuel cell power generator according to the present invention.

FIG. 2 is a schematic diagram showing a schematic configuration of a solid polymer electrolyte fuel cell power generator according to the present invention.

[Explanation of symbols]

 1 Stack Temperature Sensor 2 Air Manifold Temperature Sensor 3 CPU 4 Blower Fan 5 Stack Cooling Means 6 Air Supply Manifold Warming Means 7 Air Discharge Manifold Warming Means 10 Fuel Cell 11 Air Intake Path 12 Blower Fan 13 Air Supply Manifold 14 Air Discharge Manifold 15 Air Discharge Path 16 Circulation Path 17 Exhaust Valve 18 Control Unit (CPU) 19 Stack Temperature Sensor 20 Air Discharge Manifold Temperature Sensor 21 Stack Cooling Fan 22 Air Supply Manifold Heater 23 Air Discharge Manifold Heater

Claims (4)

[Claims] 1. In a power generator using a fuel cell in which an air electrode and a fuel electrode are arranged on both sides of a polymer solid electrolyte membrane, first temperature measuring means for measuring a temperature Ts in a stack of the fuel cell. Second temperature measuring means for measuring the temperature Tm in the oxidant gas manifold at the air electrode of the fuel cell, and temperature adjusting means for heating or cooling at least one of the stack temperature Ts and the oxidant gas manifold temperature Tm. And a control means for comparing the stack temperature Ts and the oxidant gas manifold temperature Tm measured by the first and second temperature measuring means and controlling the operation of the temperature adjusting means based on the comparison result. A fuel cell power generator characterized by comprising. 2. The fuel cell power generation according to claim 1, wherein the temperature adjusting means includes a stack cooling means for cooling the fuel cell stack and an oxidant gas manifold heating means for heating the oxidant gas manifold. apparatus. 3. The method of operating a fuel cell power generator according to claim 1, wherein the temperature difference between the stack temperature Ts and the oxidant gas manifold temperature Tm is maintained within a predetermined range during operation of the fuel cell power generator. A method for operating a fuel cell power generator, wherein the control means controls the temperature adjusting means as described above. 4. The method of operating a fuel cell power generator according to claim 1, wherein the stack temperature Ts and the oxidant gas manifold temperature Tm are compared when the fuel cell power generator is stopped, and based on the comparison result. A method for operating a fuel cell power generator, wherein the control means controls the temperature adjusting means.