JPH05266907A - Differential pressure control of fuel cell - Google Patents

Abstract

PURPOSE:To prevent mixing between anode gas and cathode gas, and to prevent oxidation of anode during an operation stoppage by increasing or reducing the gas pressure of a cathode system compared with the gas pressure of an anode system during normal operation or during the operation stoppage, and by controlling the gas pressure of the cathode system not to exceed the gas pressure in a battery container. CONSTITUTION:An inert gas to which a small amount of oxygen is added for preventing corrosion of cell members is used as a container gas. A reduction gas is used as an anode gas. It is so controlled that a gas pressure Pc of a cathode electrode system will be larger than a gas pressure Pa of an anode system, and that the gas pressure Pc will not exceed a gas pressure Pv in a battery container, during operation. Namely, the pressure in the container 2 is detected by a pressure controller 18 to adjust a container gas outlet side valve 13, and the Pv is thus controlled. The gas pressure in the container 2 as well as of a cathode gas discharge line 7 is detected by a differential pressure controller 19, to adjust a cathode outlet side valve 14, and the Pc is thus controlled. The gas differential pressure between the line 7 and an anode discharge line 8 is detected by a differential pressure controller 20, and an anode gas output side valve 15 is adjusted to control the Pa. Cathode as well as anode gases from lines 4, 5 are stopped during an operation stoppage, satisfying a condition Pc<Pv<Pa.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a differential pressure of a fuel cell such as a molten carbonate type fuel cell.

[0002]

2. Description of the Related Art A conventional fuel cell system in which a gas containing an inert gas as a main component is used as a container gas of a fuel cell, an oxidizing gas is used as a cathode gas, and a reducing gas is used as an anode gas is in operation. In the above, the pressure inside the battery container, the cathode gas pressure, and the anode gas pressure were controlled to be as equal as possible so as not to cause a differential pressure.

[0003]

However, as described above, in the conventional technique, the three pressures of the gas pressure in the battery container, the cathode electrode system gas pressure, and the anode electrode system gas pressure are controlled to be equal. Although the target is set to, the actual operation is performed in a state where a large or small differential pressure is generated between them due to the control performance. In this case, when the cathode gas pressure is higher than the anode gas pressure, if the cathode gas is mixed with the anode gas in a small amount, it is safe to reach the upper explosion limit. The problem is less likely to occur because the range is wide, but conversely, when the anode gas pressure is higher than the cathode gas pressure, the anode gas may mix with the cathode gas. Even if a relatively small amount occurs, there is a problem that the safety range up to the lower explosion limit is narrow and the explosion range is easily reached. In addition, when operating at a pressure difference where the cathode electrode gas pressure or the anode electrode gas pressure is higher than the gas pressure in the battery container, internal substances such as corrosive electrolyte leak into the container. There is a problem that comes.

The present invention is intended to solve the above problems. That is, the present invention, during driving,
Fuel cell difference that eliminates the risk of the anode gas mixing with the cathode gas, reduces the risk of explosion, and prevents internal substances such as corrosive electrolyte inside the cell from leaking into the container. An object of the present invention is to provide a pressure control method. In the case of a molten carbonate fuel cell, during normal operation, the gas inside the container containing a small amount of oxygen to prevent the oxidizing gas on the cathode side and the corrosion of the cell members leaks to the anode side. However, since the anode gas is a reducing gas, there is no possibility that the anode electrode is oxidized and its function is deteriorated or lost. However, during the stop, the gas in the anode is safe and is purged with nitrogen gas to become nitrogen gas and lose its reducing property.
In this state, if the cathode gas containing the remaining oxygen content or the container gas containing oxygen leaks to the anode electrode side, the anode electrode is oxidized and the function as the electrode is deteriorated or lost. There is a point. Once
When the anode electrode is oxidized, even if it is subsequently reduced with a reducing gas, the microscopic structure important for the electrode function is not restored.

[0005]

In order to achieve the above object, the fuel cell differential pressure control method of the present invention uses a gas containing an inert gas as a main component as a container gas of a fuel cell and oxidizing as a cathode gas. In a fuel cell system that uses a reducing gas as the anode gas and a neutral gas, the cathode electrode system gas pressure should not exceed the anode electrode system gas pressure and the cell container gas pressure during normal operation. When the fuel cell is stopped, the cathode gas and the anode gas remaining in the fuel cell are purged with an inert gas, and then the cathode electrode system gas pressure is smaller than the anode electrode system gas pressure, and The control is made so that the gas pressure in the battery container does not become higher than the gas pressure in the battery container.

[0006]

According to the present invention, in the fuel cell system,
During normal operation, the cathode electrode system gas pressure is higher than the anode electrode system gas pressure, so the anode gas does not mix with the cathode gas and there is little risk of explosion. Further, the gas pressure in the battery container is higher than or equal to the cathode electrode gas pressure and higher than the anode electrode gas pressure, so that the highly corrosive electrolyte substance in the battery does not leak into the container. During the stop, the cathode gas and the anode gas remaining in the fuel cell are purged with an inert gas, which is safe.After that, the cathode electrode system gas pressure should be made smaller than the anode electrode system gas pressure. ,
Since the pressure is not higher than the pressure of the container gas, even if the purge is not completely performed and the cathode gas remains, the cathode gas does not enter the anode electrode and the inside of the container containing a small amount of oxygen. The gas does not enter the anode, and the anode is neither oxidized nor deteriorated.

[0007]

FIG. 1 is an explanatory view showing an example of a fuel cell system for carrying out the method of the present invention. In FIG. 1, 1 is a fuel cell body including a cathode electrode C and an anode electrode 2, 2 is a fuel cell container, 3 is a container gas inlet line, 4 is a cathode gas inlet line, 5 is an anode gas inlet line, and 6 is a container gas. A discharge line, 7 is a cathode gas discharge line, 8 is an anode gas discharge line, 9 is an inert gas supply main line, 10 is an inert gas supply first branch line, 11 is an inert gas supply second branch line, and 12 is Container gas inlet valve, 13 is container gas outlet valve, 14 is cathode gas outlet valve used in normal operation, 15 is anode gas outlet valve used in normal operation, 16 is first inlet valve, 17 is first 2 inlet valve, 18 is a pressure controller, 19 is a first differential pressure controller, 20
Is a second differential pressure controller, 21 is a stop signal transmitter, 22 is a purge command signal transmitter, 23 is a timer, 24 is a cathode gas outlet valve used during stop, and 25 is anode gas output used during stop. It is a side valve.

That is, in this embodiment, as the container gas, an inert gas containing a small amount of oxygen for preventing corrosion of the battery member is used. An oxidizing gas is used as the cathode gas. A reducing gas is used as the anode gas.
Then, during operation, control is performed so that the cathode electrode system gas pressure Pc is higher than the anode electrode system gas pressure Pa and not higher than the battery container gas pressure Pv. That is, the control is performed so as to satisfy the expression of Equation 1.

[Equation 1] That is, the gas pressure Pv in the cell container is controlled by detecting the pressure in the fuel cell container 2 with the pressure controller 18 and adjusting the container gas outlet valve 13. As for the cathode electrode system gas pressure Pc, the fuel cell container 2 is controlled by the first differential pressure controller 19.
The gas pressures inside the cathode gas discharge line 7 are detected and the cathode gas outlet valve 14 is adjusted and controlled. Regarding the anode electrode system gas pressure Pa, the second pressure difference controller 20 detects the pressure difference between the gas pressures of the cathode gas discharge line 7 and the anode gas discharge line 8 and adjusts and controls the anode gas outlet valve 15. ..

By controlling in this way, during normal operation, since the cathode electrode system gas pressure Pc is higher than the anode electrode system gas pressure Pa, the anode gas is not mixed with the cathode gas and there is a risk of explosion. Few. The gas pressure Pv in the battery container is the cathode electrode system gas pressure P.
Since it is larger than c and further larger than the anode gas pressure Pa, the substance in the battery does not leak into the container 2.

Next, regarding the stop, first, the cathode gas from the cathode gas inlet line 4 and the anode gas from the anode gas inlet line 5 are stopped, and the first inlet valve 1 is stopped.
6 and the second inlet valve 17 are opened, and the inert gas from the inert gas supply main line 9 is supplied to the cathode electrode system and the anode electrode system to purge the cathode gas and the anode gas in the battery. After that, the valves 14 and 15 are fully closed so that the relationship between the gas pressure Pv in the battery container, the cathode electrode system gas pressure Pc, and the anode electrode system gas pressure Pa satisfies the equation (2). Controlled by 25.

[Equation 2] That is, the cathode electrode system gas pressure Pc is controlled so as to be lower than the anode electrode system gas pressure Pa and not higher than the battery container gas pressure Pv.

Referring to FIG. 1, regarding the stop, a signal is transmitted from the stop signal transmitter 21 to the purge command signal transmitter 22, the first inlet valve 16 and the second inlet valve 17 are fully opened, and the remaining in the battery. The cathode gas and the anode gas are purged, the timer 23 operates the first differential pressure controller 19 and the second differential pressure controller 20 at an appropriate time, and the cathode electrode system gas pressure Pc is the cathode gas outlet side. The valve 24 is adjusted and controlled, and the anode gas pressure Pa is controlled by adjusting the anode gas outlet valve 25.

As described above, it is safe to stop the fuel cell because the cathode gas and the anode gas remaining in the fuel cell are purged with the inert gas.
The cathode electrode system gas pressure Pc is set to the anode electrode system gas pressure Pa.
Since the pressure is made smaller than the pressure Pv of the container gas, the purging is not completed completely.
Even if the cathode gas remains, the cathode gas does not enter the anode electrode, the container gas containing a small amount of oxygen does not enter the anode electrode, and the anode electrode is not oxidized or deteriorated.

[0013]

As described above, according to the present invention,
In the fuel cell system, the cathode electrode system gas pressure is made higher than the anode electrode system gas pressure during normal operation, so that the anode gas does not mix with the cathode gas, and there is little risk of explosion. Further, the gas pressure in the battery container is higher than the cathode electrode system gas pressure and higher than the anode electrode system gas pressure, so that substances such as the electrolyte in the battery do not leak into the container. And while stopped,
It is safe to purge the cathode gas and anode gas remaining in the fuel cell with an inert gas, and after that, make the cathode electrode system gas pressure and container gas pressure lower than the anode electrode system gas pressure, and Since the pressure is not higher than the pressure, even if the purge is not completely performed and the cathode gas remains, the cathode gas does not enter the anode electrode, and the container gas containing a small amount of oxygen does not enter the anode electrode. It does not enter and does not oxidize or deteriorate the anode.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a fuel cell system for carrying out the method of the present invention. 1: Fuel cell main body 2: Fuel cell container 9: Inert gas supply main line 10: Inert gas supply first branch line 11: Inert gas supply second branch line 13: Vessel gas outlet valve 14: Cathode gas outlet Side valve 15: Anode gas outlet valve 16: First inlet valve 17: Second inlet valve 18: Pressure controller 19: First differential pressure controller 20: Second differential pressure controller 24: Cathode gas outlet valve 25 : Anode gas outlet valve

Claims (3)

[Claims] 1. A fuel cell system in which a gas containing an inert gas as a main component is used as a container gas of a fuel cell, an oxidizing gas is used as a cathode gas, and a reducing gas is used as an anode gas, during normal operation. , The cathode electrode system gas pressure is higher than the anode electrode system gas pressure, and
Control so that it does not exceed the gas pressure in the battery container,
During the stop, the cathode gas and the anode gas remaining in the fuel cell are purged with an inert gas, and then,
A fuel cell differential pressure control method, wherein the cathode electrode system gas pressure is controlled to be lower than the anode electrode system gas pressure and not higher than the cell container gas pressure. 2. The cathode gas pressure control during normal operation is performed by a cathode gas outlet valve provided in the cathode gas discharge line, and the anode gas pressure control is performed in the anode gas discharge line. 2. The fuel cell differential pressure control method according to claim 1, wherein the gas outlet valve is used and the control of the gas pressure in the cell container is performed by the container gas outlet valve provided in the container gas discharge line. 3. The inert gas connected to the anode gas inlet line on the cathode side by the first inlet valve provided in the inert gas supply first branch line connected to the cathode gas inlet line during stoppage. The second inlet valve provided in the supply second branch line supplies the inert gas to the anode side, and the cathode gas outlet valve and the anode gas outlet valve, which are used in normal operation, are arranged in parallel, respectively. The side valve and the anode gas outlet valve control the cathode electrode system gas pressure by the former and the anode electrode system gas pressure by the latter, and the gas pressure in the battery container is controlled by the container gas outlet side provided in the container gas discharge line. The fuel cell differential pressure control method according to claim 1, which is performed by using a valve.