JPH06196185A - Fuel cell power plant - Google Patents

Abstract

(57) [Abstract] [Purpose] By improving the configuration of the gas flow system in the battery stack, and in particular by preventing the electrolyte from being carried out,
A highly practical fuel cell power plant capable of maintaining high cell characteristics for a long period of time. [Structure] A plurality of battery stacks A and B each including a plurality of unit cells stacked with a separator or a cooling plate interposed therebetween are provided. A gas distribution line (31, A, 33, B, 32) for fuel gas distribution and a gas distribution line (34, A, 36, for oxidant gas distribution) in the cell stacks A and B, respectively.
B, 35). The gas distribution lines of at least two or more battery stacks A and B among the plurality of battery stacks are connected in series. Specifically, the direction of the gas flow is reversed at regular intervals, and the battery stack on the downstream side is operated at a temperature lower than that of the battery stack on the upstream side according to the direction of the gas flow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell power plant, and more particularly to improvement of a gas distribution system.

[0002]

2. Description of the Related Art A fuel cell is known as a device for directly converting the energy of a fuel into electric energy. In this fuel cell, usually, a pair of electrodes are arranged with an electrolyte holding layer sandwiched between them, a fuel gas such as hydrogen is brought into contact with the back surface of one electrode, and an oxidant gas such as oxygen is brought into contact with the back surface of the other electrode. The electrochemical reaction that takes place at this time is utilized to take out electrical energy from the pair of electrodes.

Further, in this fuel cell, the electrolyte retaining layer is formed by impregnating and retaining an electrolyte such as phosphoric acid in a porous matrix substrate made of electrolyte resistant fine particles or a fibrous sheet. This electrolyte holding layer plays a role of ion transfer between the electrodes involved in the electrochemical reaction of the electrodes, and in addition, the fuel gas and the oxidant gas supplied to each electrode are prevented from being mixed with each other so that they are not mixed with each other. It serves to separate the gases from each other.

In the fuel cell having the above-mentioned structure, as long as the fuel gas and the oxidant gas are supplied, the electric energy can be taken out with high conversion efficiency, but in general, one cell ( Since the output voltage of a unit cell is small (about 0.8 V), in a practical machine, a plurality of unit cells are stacked in series to form a battery stack.
Along with the recent increase in power demand, fuel cell power generation plants using two or more cell stacks are being developed and put into practical use.

FIG. 4 is a piping diagram showing an example of the structure of a gas distribution line conventionally proposed for a fuel cell power plant having two or more cell stacks. That is, gas distribution manifolds 1 to 4 and 11 to 14 are provided on the four sides of the two battery stacks A and B arranged side by side on the right and left sides in the drawing, respectively. Then, in the manifolds 3 and 13 located on one side (left side in the drawing) of the battery stacks A and B in the arrangement line direction,
Manifold 1, which is connected to the fuel gas supply pipes 5, 15 and faces the manifolds 3, 13
The fuel gas discharge pipes 6 and 16 are connected to 11, respectively. In addition, the manifolds (2, 4), (1) on both sides facing each other with the arrangement line of the two battery stacks A and B interposed therebetween are provided.
2,14) on the same side of manifolds 4,14,
The oxidant gas supply pipes 7 and 17 are connected to each other, and the oxidant gas discharge pipes 8 and 18 are connected to the manifolds 2 and 12 on the opposite side, respectively.

With such a piping structure, the fuel gas flow 21 supplied to each of the cell stacks A and B is supplied to each of the cell stacks A and B as indicated by an arrow in the figure. Along the arrangement line of, the flow individually from the left side of the figure to the right side of the figure. Further, the oxidant gas flow 22 supplied to each of the battery stacks A and B has a shape that is orthogonal to the arrangement line of the battery stacks A and B for each of the battery stacks A and B, as shown by the arrow in the figure. Then, they will flow in parallel and individually. As shown in FIG. 4, the battery stacks A and B have, for example, about 2
It is assumed to operate at about 00 ° C.

[0007]

By the way, in the conventional fuel cell power generation plant as shown in FIG. 4, when a long-term operation of tens of thousands of hours is performed, the electrolyte inside the unit cell largely disappears, and the battery There arises a problem that the characteristics are significantly deteriorated. This point will be described below.

That is, as described above, the electrolyte holding layer of the fuel cell plays a role of ion transfer between the electrodes accompanying the electrochemical reaction of the electrodes, and in addition to the fuel gas supplied to each electrode and the oxidation. It serves to separate these reaction gases from each other so that the agent gases are not mixed. There is no problem if the pores of this electrolyte holding layer are sufficiently impregnated with electrolyte, but when the amount of impregnated electrolyte decreases, the resistance of ionic conduction increases, and the reaction gas leaks to the counter electrode (crossover). Occurs and the voltage of the unit cell drops significantly. In the worst case, it may cause an explosion. Therefore, maintaining the amount of electrolyte in the matrix layer above a certain level is extremely important for maintaining the high performance of the battery and for ensuring the safe operation of the battery.

However, when the fuel cell is operated,
It is known that the electrolyte inside the battery evaporates and is carried out by the exhaust gas of the fuel gas or the oxidant gas. This is described, for example, in the document “Operating condition dependence of the amount of phosphoric acid carried out in a phosphoric acid electrolyte fuel cell” (Ogami et al., Electrochemical Society Conference 53 times, April 1986). That is, in this document, in a short-term operation of several thousand hours, the amount of electrolyte reduction is not a problem, but in the long-term operation of tens of thousands of hours, the electrolyte inside the unit cell is significantly lost. However, it has been reported that the battery characteristics are significantly deteriorated. In addition, according to the results of the present study conducted by the present inventor, it has been found that when the amount of the electrolyte in the unit cell becomes lower than a certain level, a crossover of the reaction gas occurs and power generation becomes impossible.

FIG. 5 is a graph showing the life test results of the cell stack of the fuel cell power plant shown in FIG.
(A) is the transition of the cell voltage with the passage of operating time,
(B) shows the transition of the internal resistance of the cell with the passage of operating time. As shown in FIG. 5, the internal resistance of the cell is
The cell voltage gradually increases with the lapse of the operating time, and rapidly increases at a certain time, and the cell voltage sharply decreases.

Conventionally, as a method of solving such a problem, a method of reserving the electrolyte inside the stack (internal reserve method), a method of recovering the electrolyte at the reaction gas outlet of the cell (internal recovery method), and after a certain period of operation , A method of replenishing the electrolyte from the outside of the battery stack (external replenishment method) has been proposed. However, the internal reserve method has a problem that the reserve amount is limited, and the internal recovery method and the external replenishment method have a complicated battery structure,
There are problems such as high manufacturing cost and maintenance cost of the cell stack, and as a result, it is difficult to apply these methods to a practical machine of a fuel cell power plant.

The present invention has been proposed in order to solve the problems of the prior art as described above, and its object is to improve the structure of the gas flow system in a battery stack, and in particular,
It is an object of the present invention to provide a highly practical fuel cell power generation plant capable of maintaining high cell characteristics for a long period of time by preventing the electrolyte from being carried out to the outside. More specifically, the purpose is to maintain high battery characteristics over a long period of 40,000 hours or more.

[0013]

According to the present invention, a pair of electrodes having a catalyst layer on a conductive porous substrate are arranged so as to face each other with an electrolyte holding layer interposed therebetween. Fuel gas to the electrode, a unit cell for obtaining electric energy by supplying an oxidant gas to the other electrode, respectively, in a fuel cell power plant having a cell stack configured by stacking a plurality of separators via a cooling plate, This is an improved configuration of the gas distribution system.

That is, the fuel cell power plant of the present invention has a plurality of cell stacks, and each of the plurality of cell stacks has a gas distribution line for fuel gas distribution and a gas distribution line for oxidant gas distribution. Is provided and the gas flow lines of at least two or more battery stacks among the plurality of battery stacks are connected in series. Specifically, a series gas distribution line is configured to be capable of reversing the gas flow direction at regular time intervals, and the plurality of battery stacks are connected to the downstream battery stack according to the gas flow direction. Is operable at a temperature lower than that of the upstream battery stack.

[0015]

The operation of the present invention constructed as described above is as follows. That is, since the gas distribution lines of two or more cell stacks are connected in series, the operating temperature control unit lowers the operating temperature of the fuel cell stack on the downstream side to be lower than the operating temperature on the upstream side, so that the gas distribution is reduced. The electrolyte discharged from the upstream battery stack in the line can be collected by the downstream battery stack, and the electrolyte can be prevented from being discharged to the outside of the battery stack. This is because the vapor pressure of the electrolyte depends on the temperature.

When such an operation is continued, the electrolyte in the battery stack increases in the battery stack on the downstream side of the gas distribution line. Therefore, the gas flow direction control means operates the gas flow direction switching means at regular intervals. Then, by reversing the direction of the gas flow in the gas distribution line of the battery stack, it is possible to prevent the bias of the electrolyte between the plurality of battery stacks. In this case, the fixed time for switching the direction of the gas flow is set sufficiently shorter than the time for which the characteristics of the battery stack on the upstream side deteriorate. Further, in the battery stack on the upstream side of the gas distribution line, the utilization rate of the reaction gas can be reduced, and the secondary effect that the cell characteristics can be improved is also obtained.

[0017]

EXAMPLE A typical example of a fuel cell power plant according to the present invention will be described below with reference to FIG. In this case, FIG. 1 is a piping diagram showing the configuration of the gas distribution line of the fuel cell power plant according to the present invention. The same parts as those in the conventional example shown in FIG. 4 are designated by the same reference numerals and the description thereof will be omitted.

First, as shown in FIG. 1, in the present embodiment, the manifolds located at both ends on the arrangement line of the two battery stacks A and B, that is, the manifold 1 of the battery stack A and the battery stack B. The first and second fuel gas pipes 31 and 32 for supplying and discharging the fuel gas are respectively connected to the manifold 13 of the above, and the inner manifolds facing each other on the arrangement line, that is, the manifold 3 of the battery stack A and the battery Stack B
The manifolds 11 are connected by a first connection pipe 33. In addition, the two battery stacks 11 and 12
Of the manifolds (2, 4), (12, 14) on both sides of the manifold line (2, 4), (12, 14) facing each other across the arrangement line of the first and second sides for supplying and discharging the oxidant gas.
The oxidant gas pipes 34 and 35 are connected to each other, and the manifolds 4 and 14 on the opposite side are connected to each other by a second connection pipe 36.

Then, the first and second fuel gas pipes 31, 3
In No. 2, the fuel gas is supplied to either one of them, and the fuel gas is discharged from the other, and the supply side and the discharge side are switched at predetermined time intervals, whereby the direction of the fuel gas flow is changed. It is configured to reverse. Similarly, the first and second oxidant gas pipes 34, 35
The oxidant gas is supplied to either one of them, and the oxidant gas is discharged from the other, and the supply side and the discharge side are switched at preset constant time intervals. The directions are reversed.

Further, the operating temperatures of the two battery stacks A and B are appropriately set and are individually controllable. Specifically, the operating temperature of the battery stack on the upstream side of the gas flow is set to 200 ° C. and the operating temperature of the battery stack on the downstream side is set to 180 ° C. according to the direction of the gas flow. There is. It should be noted that the predetermined time for switching the supply side and the discharge side of the fuel gas and the oxidant gas and reversing the direction of the gas flow is at least sufficiently longer than the time for which the characteristics of the battery stack on the upstream side deteriorate. It is necessary to set it short, and in this embodiment, it is set to 5000 hours for convenience.

The operation of the fuel cell power plant of the present embodiment constructed as described above is as follows. That is,
For example, when the cell stack A is set to the upstream side of the gas flow for the first 5000 hours, the first fuel gas pipe 31 is set to the supply side, the second fuel gas pipe 32 is set to the discharge side, and the first The oxidant gas pipe 34 is on the supply side, and the second oxidant gas pipe 35 is on the discharge side. By setting the gas distribution line in this way, as shown in FIG. 1, the fuel gas flow 21 is supplied to the first fuel gas pipe 31, the cell stack A,
The first connecting pipe 33, the cell stack B, and the second fuel gas pipe 32 flow in the path, and the oxidant gas flow 22 is the first oxidizing gas pipe 34, the battery stack A, the second connecting pipe 36,
It flows in the path of the battery stack B and the second oxidant gas pipe 35. In this case, the operating temperatures of the two battery stacks A and B are individually controlled, the battery stack A that is the upstream side of the gas flows 21 and 22 operates at 200 ° C., and the battery stack B that is the downstream side is operated. Operate at 180 ° C. Note that FIG. 1 shows the operating states of the battery stacks A and B under this condition.

Then, in the above operating state,
When 5000 hours have elapsed, the upstream side and the downstream side of the two battery stacks A and B are reversed, and at the same time, the operating temperatures of the two battery stacks A and B are reversed. That is, contrary to the operating state described above, the first fuel gas pipe 31 is on the discharge side, the second fuel gas pipe 32 is on the supply side, and
The first oxidant gas pipe 34 is on the discharge side, and the second oxidant gas pipe 35 is on the supply side. By switching the gas distribution lines in this manner, the fuel gas flow 21 is reversed from the above-described operating state, and the second fuel gas pipe 32, the cell stack B, the first connection pipe 33, the cell stack A, the first The oxidant gas flow 22 flows through the path of the fuel gas pipe 31, and the oxidant gas flow 22 is the second oxidant gas pipe 35, the cell stack B, and the second connection pipe 3.
6, the battery stack A and the first oxidant gas pipe 34 flow. Further, the operating temperature of the battery stack B, which is newly on the upstream side of the gas flow, is switched to 200 ° C., and the operating temperature of the battery stack A, which is newly on the downstream side, is switched to 180 ° C.
Then, in such an operating state, further 5000
After a lapse of time, the gas distribution line is switched again to switch to the same operating state as the initial 5000 hours described above.

Further, FIG. 2 is a graph showing the results of the aging characteristic test of the first and second battery stacks A and B in the above long-time operation. (B) shows the transition of the cell voltage, and (b) shows the transition of the internal resistance of the cell with the lapse of operating time. As shown in FIG. 2, in the battery stack on the upstream side of the gas flow, the cell internal resistance gradually increases, whereas in the downstream battery stack, the cell internal resistance is stable. Even if the internal resistance of the cell increases during upstream operation, the internal resistance of the cell gradually decreases by operating by reversing the gas flow. The resistance has dropped to about the initial value. This phenomenon means that the phosphoric acid electrolyte carried out by the battery stack on the upstream side of the gas flow is recovered by the battery stack on the downstream side. Since the vapor partial pressure of phosphoric acid (P ₄ O ₁₀ ) at 180 ° C. is about 10% of the vapor partial pressure at 200 ° C., theoretically, 90% of phosphoric acid carried out from the upstream battery stack is , Can be collected in the battery stack on the downstream side. Further, the larger the operating temperature difference between the battery stacks, the higher the phosphoric acid recovery efficiency.

In the above embodiment, the application to the fuel cell power generation plant having two cell stacks A and B has been described, but the present invention is applicable to the fuel cell power generation plant having three or more cell stacks. Can be similarly applied. For example, with two battery stacks as one set, a plurality of sets of battery stacks can be individually configured with the same gas flow system as in the above embodiment.

The structure of the reaction gas pipe can be freely changed. For example, as shown in FIG. 3, instead of providing an individual manifold at the connection portion between the two battery stacks A and B, a common manifold is provided. A configuration using the manifolds 41 and 42 is possible. When configured in this way, the first and second connection pipes 33, 3 in the above embodiment are provided.
Since 6 is unnecessary and the number of manifolds can be reduced,
The size and simplification of the entire device can be greatly reduced.

Further, the specific constitution such as means for switching the direction of the gas flow and means for controlling the temperature of the battery stack can be freely selected. Further, since the amount of phosphoric acid carried out by the cathode gas is larger than the amount of phosphoric acid carried out by the anode gas, it is possible to provide only the gas pipe of the cathode in series. On the other hand, although the case where phosphoric acid is used as the electrolyte has been described in the above-described examples, the present invention is similarly applicable to the case where an electrolyte other than phosphoric acid is used. Further, those skilled in the art can further propose various embodiments based on the present invention, and those embodiments are also included in the scope of the present invention.

[0027]

As described above, according to the present invention,
By connecting the gas distribution lines of two or more cell stacks in series, it is possible to provide a fuel cell power generation plant capable of maintaining high cell characteristics for a long period of time. Specifically, high battery characteristics can be maintained over a long period of 40,000 hours or more.

[Brief description of drawings]

FIG. 1 is a piping diagram showing the configuration of a gas distribution line in a typical example of a fuel cell power plant according to the present invention.

2A and 2B are graphs showing the results of the aging characteristic test of the cell stack of the fuel cell plant of FIG. 1, in which FIG. 2A is a graph showing the transition of the cell voltage with the passage of operating time, and FIG. 2B is the operating time. The graph which shows the transition of the cell internal resistance with progress of.

FIG. 3 is a piping diagram showing the configuration of a gas distribution line in another embodiment of the fuel cell power plant according to the present invention.

FIG. 4 is a piping diagram showing an example of a configuration of a gas distribution line of a conventional fuel cell power plant.

5 is a graph showing a life test result of a cell stack of the fuel cell power plant of FIG. 4, (a) is a graph showing changes in cell voltage with the passage of operating time, and (b) is operating time. The graph which shows the transition of the cell internal resistance with progress of.

[Explanation of symbols]

 A, B ... Battery stack 1-4, 11-14 ... Manifold 5,15 ... Fuel gas supply pipe 6,16 ... Fuel gas discharge pipe 7,17 ... Oxidant gas supply pipe 8, 18 ... Oxidant gas discharge pipe 21 ... fuel gas flow 22 ... oxidant gas flow 31 ... first fuel gas pipe 32 ... second fuel gas pipe 33 ... first connection pipe 34 ... first oxidant gas pipe 35 ... second oxidant gas pipe 36 ... second 2 connection pipes 41, 42 ... Common manifold

Claims (2)

[Claims] 1. A pair of electrodes having a catalyst layer on a conductive porous substrate are arranged to face each other with an electrolyte holding layer interposed therebetween, and one of the electrodes is provided with fuel gas and the other is provided with fuel gas. In a fuel cell power plant having a cell stack configured by stacking a plurality of unit cells each of which obtains electric energy by supplying an oxidant gas to an electrode, with a separator or a cooling plate, a plurality of the battery stacks are provided. The plurality of battery stacks are respectively provided with a gas distribution line for the fuel gas distribution and a gas distribution line for the oxidant gas distribution, and at least two or more of the plurality of battery stacks are provided. 2. The fuel cell power plant, wherein the gas distribution lines are connected in series. 2. The series gas distribution lines are configured such that the gas flow direction can be reversed at regular time intervals, and the plurality of battery stacks are connected to a downstream battery according to the gas flow direction. The fuel cell power plant according to claim 1, wherein the stack is configured to be operable at a temperature lower than that of the upstream cell stack.