JPH0754711B2 - Fuel cell device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel cell device for converting chemical energy of fuel gas into electric energy by an electrochemical reaction.

[Prior art and its problems]

There is a fuel cell as a device that directly converts the chemical energy of the fuel into electric energy by extracting the electric power by reacting the fuel and the oxidant electrochemically.

The specific structure of the first-generation phosphoric acid electrolyte fuel cell will be described below as an example. FIG. 1 (a) shows a schematic view of the power generation unit. Grooves of gas flow paths were provided on both sides of a unitary cell formed by integrating a matrix 4 holding an electrolyte between a pair of opposed gas diffusion electrodes (anode 2 and cathode 3) coated with a catalyst layer 1. A conductive separator 5 is placed, and a fuel gas 6 and an oxidant gas 7 are normally flowed in a direction orthogonal to each other as shown in FIG. Note that FIG. 1 (b) is a plan view of FIG. 1 (a). Since the output of this unit battery is at most 1V, a large number of these unit batteries are stacked for power generation. Tightening bar 8 as shown in FIGS. 2 (a) and 2 (b)
And a fastening rod 9, and manifolds 10a, 10b, 10c, and 10d for gas supply and discharge are attached to the peripheral portion to form a stacked battery (stack).

As for the battery output, the pressure in the supply gas increases the concentration (activity) of the reactive species and promotes the electromotive reaction, so it is better to increase the pressure in the manifold. Since the pressure tightness of the airtight portion is not so large, the stack is housed in the pressure vessel 12, and the pressure difference from the atmospheric pressure is received by the flange portion of the pressure vessel.

Also, the supply pressure of natural gas reformed gas (H ₂ 80% + CO ₂ 20%) as fuel and air as oxidant should be adjusted so that the fuel gas and oxidant gas do not cross-mix through the matrix layer. For example, based on the pressure inside the container, the pressure on the oxidant gas side is kept higher by several cmAg than that on the fuel gas side.

The differential pressure allowed for these supply gases is determined in consideration of the bubble pressure of the matrix layer in the unit cell. By the way, in an actual power plant, the reaction gas is supplied to and discharged from the fuel cell device through a pressure control system including a complicated piping system and a pressure control valve.

It is the electrolyte retention matrix layer that has the lowest pressure resistance among all the paths of these piping systems and the reaction gas path in the fuel cell.
On the other hand, since the gas capacity (dead volume) in the piping system is large and the response speed of the pressure control system is slow, in the case of a sudden accident such as blockage or breakage of the piping system, especially when it is performed near the fuel cell module, Moreover, the matrix layer in the battery was likely to be damaged.

That is, when the pressure of either the fuel gas or the oxidant gas fluctuates rapidly at the moment until the differential pressure control by the pressure control system is performed and bubbles occur in the matrix layer, such irreversible electrolyte layer irreversible Due to deterioration, extensive cross-mixing (crossover) will occur in the electrolyte layer after this accident.

[Object of the Invention]

An object of the present invention is to generate a pressure relief before bubble generation of the matrix layer when a rapid pressure difference variation between supply gases occurs, and to restore the pressure when the pressure control system is activated. The escape mechanism is provided in the fuel cell device to prevent irreversible deterioration of the matrix layer, that is, increase in cross-mixing of the feed gas.

[Summary of the Invention] The present invention provides a separator comprising a unit cell including a pair of opposed gas diffusion electrodes provided adjacent to a gas flow path, and a matrix holding an electrolyte interposed between the gas diffusion electrodes. A fuel cell stack having a plurality of stacked vias is provided with a manifold having a reaction gas supply pipe or a reaction gas discharge pipe for supplying or discharging a reaction gas to the gas flow path, and these are housed in a pressure vessel. In the fuel cell device, a bidirectional pressure relief is generated between the inside of the manifold and the inside of the pressure container so that the differential pressure between the internal pressure of the manifold and the internal pressure of the pressure container becomes a set value. It has a pressure relief mechanism and a connection portion for connecting the pressure relief mechanism to the manifold, and the cross-sectional area of the connection portion is the reaction gas supply pipe or the reaction gas. It is characterized in that it is formed to be larger than the cross-sectional area of the gas discharge pipe.

[Effects of the Invention] By connecting the pressure relief mechanism to the manifold as in the present invention, the pressure in the manifold does not rise or fall below the set value as compared with the pressure in the pressure vessel, and the piping system It is possible to prevent the matrix layer from being destroyed in the unit cell when the internal pressure of the cell is rapidly increased until the pressure control system is restored due to an accident such as blockage or destruction.

Further, by forming the cross-sectional area of the connection portion between the pressure relief mechanism and the manifold to be larger than the cross-sectional area of the reaction gas supply pipe or the reaction gas discharge pipe, the response speed at the time of sudden pressure change becomes faster, and the matrix It is possible to surely generate the pressure relief before the layer bubbles, and it is possible to remarkably improve the reliability of the fuel cell device.

The present invention is not limited to the first generation type, but can be similarly applied to the second generation type molten carbonate fuel cell.
At this time, a molten salt having a eutectic composition of lithium carbonate and potassium carbonate is used as a liquid for liquid sealing.

Example of Invention

 Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 shows an example of the structure of a structure using a relief valve as the pressure relief mechanism 31 as one embodiment of the present invention. Splines 14 and 14 'having a spring constant corresponding to a set reference pressure are placed in a cylindrical cylinder 13 attached to a connecting pipe 11 extending from a manifold 10, and a valve 15 provided with a gas flow path is interposed therebetween. By selecting a spring with an appropriate spring constant, when the pressure inside the manifold 10 rises and approaches the bubble pressure in the matrix, the movable valve 15 moves and the groove 15a and the gas discharge pipe 17 are communicated with each other. Is discharged into the pressure vessel 12. Conversely the manifold
When the pressure in 10 decreases, the inert gas in the pressure vessel 12 flows into the manifold through the gas discharge pipe 17 and the movable valve 15. Such relief valves are, for example, connecting pipes 11a, 11 taken out from the respective manifolds 10a, 10b, 10c, 10d of FIG.
By connecting to b, 11c and 11d, it is possible to prevent the pressure in the manifold from rising or falling above the reference value. That is, it can be kept within the set differential pressure.
Also, there is no gas communication within the set differential pressure.

[Other Embodiments of the Invention]

4 and 5 instead of the spring type relief valve described above.
Bi-directional pressure relief mechanism 31 ′, 31 ″ of liquid sealing mechanism as shown
Can also be used.

FIG. 4 is a sectional view showing the structure of such a valve. The liquid reservoirs 18, 19 having the structure shown in the figure are provided on the upper part of the manifold 10, one end is attached to the manifold 10, and the other end is provided with open curved pipes 29, 30 in the pressure vessel 12. In order to maintain airtightness, 18, 19 are filled with high boiling point oil 20 having an appropriate specific gravity and viscosity, and floats 21, 22 having an appropriate weight, for example, 5-10 g / cm ² are placed there.

Now when the pressure in the manifold rises above the pressure vessel,
The gas flows through the path shown by the solid line A in the figure, lifts the float 21, and is discharged into the pressure vessel 12. Conversely, when the pressure in the manifold falls below the pressure drop of the pressure vessel by a pressure equal to or greater than the set pressure difference, the gas flows through the path indicated by the broken line B in the figure, lifts the float 22, and enters the manifold. When the pressure difference between the pressure inside the manifold and the pressure inside the pressure vessel is maintained at the set pressure, the floats 21 and 22 on both sides are lowered, and the airtightness of the gas between them is maintained.

FIG. 5 shows another example of a bidirectional valve having a similar liquid sealing mechanism.

The manifold 10 is provided with recesses 23, 24 for storing liquid, the high boiling point oil 20 is filled therein, and the floats 25, 26 having an appropriate shape and constant specific gravity are placed therein, and the upper part of the recess is Claws 27 and 28 are attached to prevent flying when the float rises due to pressure increase in the system. When the pressure in the manifold rises above the set value, the float 25 rises and the gas escapes into the pressure vessel. On the contrary, when the pressure in the manifold is lower than the pressure vessel by a set value or more, the float 26 rises and the inert gas in the pressure vessel escapes into the manifold. When the pressure difference between the two is kept constant, the
The pressure drop between the manifold and the pressure vessel is kept constant.

The bidirectional valve described above is simple in structure and has a large gas escape area. Therefore, the response speed at the time of a sudden pressure change is fast, which is advantageous.

Also in the structures shown in FIGS. 3 and 4, the pipe diameter of the portion attached to the manifold is made larger than the pipe diameters of the gas supply and discharge pipes in order to increase the response speed when the pressure changes abruptly. That is, the pipe cross-sectional area of the connecting pipe is formed to be larger than the pipe cross-sectional areas of the gas supply and discharge pipes. According to such a configuration, even if a sudden difference in pressure difference occurs between the supply gases, it becomes possible to surely cause the pressure escape before the foaming of the matrix layer occurs.

In the pressure relief mechanism having the structure of FIG. 5 described above, the number of pressure relief portions is not limited to one, and the weight of floating at each mounting portion may be slightly changed. The oil used for liquid sealing may be solid at room temperature.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a power generation unit of a fuel cell, FIG. 2 is a diagram showing an outline of a fuel cell stack, and FIG. 3 is a sectional view showing an essential part of an embodiment according to the present invention. Figure 4,
FIG. 5 is a sectional view showing another embodiment of the present invention. 10 …… manifold, 1 …… connection pipe, 13 …… cylinder,
14,14 ′ …… Spring, 15 …… Valve, 17 …… Gas discharge pipe, 31 …… Pressure relief mechanism.

Claims (1)

[Claims] 1. A unit cell comprising a pair of opposed gas diffusion electrodes provided adjacent to a gas flow path, and a matrix holding an electrolyte interposed between the gas diffusion electrodes,
A plurality of fuel cell stacks with a separator interposed therebetween is provided with a manifold having a reaction gas supply pipe or a reaction gas discharge pipe for supplying or discharging a reaction gas to the gas flow path, and these are housed in a pressure vessel. In the fuel cell device, a bidirectional pressure relief is generated between the inside of the manifold and the inside of the pressure vessel so that the differential pressure between the internal pressure of the manifold and the internal pressure of the pressure vessel becomes a set value. A pressure relief mechanism for tightening, and a connection portion for connecting the pressure relief mechanism to the manifold, and the cross-sectional area of this connection portion is larger than the cross-sectional area of the reaction gas supply pipe or the reaction gas discharge pipe. A fuel cell device, which is formed to be large.