JPH01197969A - Cell structure of molten carbonate fuel cell - Google Patents

Abstract

PURPOSE:To stabilize cell performance by supplying an oxidizing agent gas from the center of a fuel passage, that is from the central part of a cell or the part inclined to the inlet side of a fuel gas from the central part. CONSTITUTION:A fuel gas flows from the side 4 of a cell 1 toward the side 5 through fuel passages 14 to supply the fuel gas to a fuel electrode 11. An oxidizing agent gas flows from sides 2, 3 to an oxidizing agent passages 15, then branched to the sides 4, 5 through oxidizing agent passages 16 to supply the oxidizing agent gas to an oxidizing agent electrode 12. Thereby, electrochemical reaction occurs to generate electric power. Since the heat generated by electrochemical reaction is radiated from the surroundings of the cell 1, the temperature in the central part of the cell 1 tends to be increased. By supplying the oxidizing agent gas which also serves as a cooling medium to the oxidizing agent passages 15 in the center of the cell 1, the oxidizing agent gas cools at first the central part of the cell 1, and the temperature distribution on the reaction surface of the cell 1 is made uniform. Cell performance is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cell structure of a molten carbonate fuel cell using carbonate as an electrolyte.

[Conventional technology]

A bath-fused carbonate fuel cell includes an electrolyte plate containing carbonate,
A fuel electrode and an oxidizer electrode sandwich this, and a concave fuel flow path that supplies fuel gas, which is a reactive gas, to the fuel electrodes arranged on both sides of these 'FjL electrodes. The fuel gas and the oxidant gas are introduced into the cell in a high temperature state where the carbonate is bath melted, and the fuel gas and the oxidant gas are passed through the separator plate. The fuel is supplied to the fuel electrode and the oxidizer electrode through the 1M fuel flow path to cause an electrochemical reaction and generate electricity.

By the way, there are three types of flow directions for supplying the reactant gases, fuel gas and oxidant gas, to the electrodes: cross flow, parallel flow, and counterflow, depending on the shape of the intersection between the fuel gas and oxidant gas. As shown in Fig. 1, the cross flow of the reactant gas is carried out from one surface 2 of the rectangular cell 1 facing the oxidant electrode through the oxidant flow path provided temporarily in a separate section. A method of flowing fuel gas from one side 4 to the other side 5 of different opposing sides through a fuel flow path provided in a separator plate and onto a fuel electrode surface on the back side of an oxidizer electrode. It is. Furthermore, cocurrent flow is a method in which the oxidant gas and fuel gas are flowed into the cell 1 from the side surface 4 to the side surface 5 in the same direction to the oxidizer electrode surface and the fuel electrode surface, as shown in FIG. As shown in Fig. 6, the oxidant gas is supplied to the cell 1 from side 5 to side 4 to the oxidizer electrode surface, and the fuel gas is supplied to the fuel electrode surface from side 4 to side 4 or vertically 1 to 5 in the opposite direction to the flow direction of the fuel gas. This is a method that allows the flow to flow.

In such a 3 fj 4 type flow method, when the cell performs an electrochemical reaction, the temperature distribution on the cell reaction surface 6 is expressed as the temperature distribution on the cell reaction surface 6 using temperature as a parameter in the method using cross flow of reaction gas. In Figure J, in parallel flow, the horizontal axis is the length of the cell reaction surface taken in the flow direction of the reaction gas,
Figure 1 shows temperature on the vertical axis, and in countercurrent flow, the horizontal axis shows the length of the cell reaction surface taken in the flow direction of the reaction gas, and the vertical axis shows temperature? The result will be as shown in the figure below.

The reason why the temperature distribution of the cell reaction surface has such characteristics due to the cross flow, parallel flow, and counter flow of the reaction gas is as follows.

(1) The oxidant gas must be flowed in large quantities to cool the cell. (2) The flow rate of the fuel gas must be small to increase the efficiency of the fuel cell σ). (3) The oxidant electrode is not highly dependent on gas concentration. (4) Fuel 7 has a high dependence on the concentration of the electrode, and even if the carbon dioxide gas and acid system in the cell inlet composition are consumed by the reaction, it will not affect the characteristics much. The characteristics of the gas inlet and outlet vary greatly due to consumption and the generation of water vapor and carbon dioxide scum, and the internal resistance changes due to the difference in characteristics. The reaction progresses in the direction of the current density, and at a constant current density, the part with less polarization becomes a high current density, which balances out the other parts.The heat generated by the load electrical current is proportional to the square of the current (current density), so the heat is generated. Due to the above-mentioned reasons, fuel cells generate electricity with different temperature distributions depending on how the reaction gas flows on the reaction surface of the cell during operation.

[Problem to be solved by the invention]

In fuel cells as well as molten carbonate fuel cells, it is desirable that the temperature difference between the highest and lowest temperature distributions on the cell reaction surface be as small as possible. This has the disadvantage that cell characteristics are poor if the temperature is low, and the life is short if the temperature is high, so the smaller the temperature difference within the cell as possible, the more the desired operating conditions can be secured and the operation will be easier. Good cell characteristics (
This is because a long life can be expected.

However, in the method of flowing the reaction gas as described above, the largest temperature difference on the cell reaction surface is due to the countercurrent flow shown in Figure 9, which is about 250°C, and the smallest is:
The temperature is approximately 150°C due to the parallel flow shown in Figure 8, and the temperature in between is approximately 200°C due to the cross flow shown in Figure 7.
However, there is still a problem that the difference in temperature distribution is large.

An object of the present invention is to provide a cell structure for a molten carbonate fuel cell that can stabilize cell characteristics and prolong its life by reducing the temperature difference in the temperature distribution of the cell reaction surface.

[Means to solve the problem]

In order to solve the above problems, the present invention includes an electrolyte plate containing carbonate, a fuel electrode and an oxidizer electrode sandwiching the electrolyte plate, and a fuel electrode and an oxidizer electrode disposed on both sides of these electrodes to supply fuel gas to the fuel electrode. In the cell, the fuel flow path is connected to the oxidant electrode, and the fuel gas is supplied from one side of the cell to the other side. The oxidant gas is provided so as to flow toward the side surface of the fuel gas, and the oxidant gas flows from a central portion between the opposing side surfaces, or from a portion where the oxidant gas is biased from this portion to the side surface on the inlet side of the fuel gas to the one side surface. and the other side.

[For production]

The cell is heated by the heat generated during the electrochemical reaction due to the supply of reaction gas, but the temperature at the center of the cell reaction surface becomes high due to heat dissipation from the same curve of the cell. Further, since the fuel concentration of the fuel gas is higher on the fuel gas inlet side, the current density is higher, and therefore the temperature is higher on the fuel gas inlet side. Therefore, the oxidant gas, which is also used as a cooling medium, is passed between the sides in the flow direction of the fuel gas, that is, between the sides in the flow direction of the fuel gas, or from this part to the inlet side of the fuel gas. The temperature distribution on the cell reaction surface is made uniform by allowing the fuel gas to flow from a portion that is biased toward the side surface toward both the side surfaces on the inlet side and the outlet side.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is an exploded perspective view showing the cell structure of a molten carbonate fuel cell according to an embodiment of the present invention.

Note that in Figure 1 and Figures 2 and 3, which will be described later,
Components that are the same as those in the conventional example shown in the figures through FIG. In Figure 1, molten carbonate fuel 11! A pond cell 1 includes an electrolyte plate 10 containing carbonate, a fuel electrode 11 and an oxidizer electrode 12 that sandwich the electrolyte plate, and gas-impermeable separate plates 13 disposed on both sides of the electrolyte plate 10.
It is composed of. Here, the separate plate 13 separates the reaction gas according to the present invention from the fuel electrode and the oxidizer! The structure has a flow path for supplying to the poles. That is, separate plate 1
A plurality of concave fuel passages 14 are provided on the surface of the cell 1 in contact with the fuel electrode 11 so that the fuel gas flows from one surface 4 of the cell 1 to the opposite side surface 5. On the surface, there is an oxidant flow path 15 in which the oxidant gas flows in from the side surfaces 2 and 3 across the center of the cell, which is the center of the fuel flow path 14, and the oxidant flow path 15 also branches to flow the fuel gas. A plurality of concave oxidant channels 16 are provided to allow the oxidant to flow toward the 111 surface 4 on the inlet side and the side surface 5 on the outlet side.

Note that the separate plate 13 is provided with a fuel flow path on one side and an oxidizer flow path on the other side, so that when cells are stacked, the separate plate 13 is used as a common separate plate for adjacent cells. :r.

Due to this structure of the cell, during fuel cell operation, the fuel gas flows from the side surface 4 of the cell 1 toward the side surface 5 through the fuel flow path 14 (see FIG. 1), as shown in FIG. Fuel gas is supplied to side 11, - oxidant gas is supplied to sides 2 and 3.
The oxidizer flows into the oxidant flow path 15 (see Figure 1), and further flows through the oxidizer flow path 16 (see Figure 1), splitting toward the side surfaces 4 and 5, and flowing toward the oxidizer electrode. By supplying oxidant gas to the oxidant gas, an electrochemical reaction occurs and electricity is generated.

By the way, the heat generated by the electrochemical reaction is dissipated from the periphery of the cell, so the center of the cell tends to reach a high temperature. Therefore, by first flowing the oxidant gas, which is also a cooling medium, into the oxidant flow path 15 in the center of the cell, the oxidant gas first cools the center of the cell, and the temperature distribution on the reaction surface of the cell is made uniform.

Since the temperature on the fuel gas inlet side tends to be high as described above, the oxidant flow path 15 in FIG. 1 is biased from the center toward the side surface 4 on the fuel gas inlet side, and By making the oxidant gas flow as shown in the figure, the temperature distribution on the cell reaction surface is made uniform.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the oxidizing gas is supplied from the center of the fuel flow path through which the fuel gas flows, that is, from the central part of the cell, or from a part biased from this part toward the fuel gas inlet side. By doing so, the oxidant gas acting as a cooling medium first cools down the high temperature areas of the cell, which equalizes the temperature distribution on the cell reaction surface, which stabilizes the cell characteristics. This has the effect of lengthening the lifespan.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view showing the structure of a cell of a bath molten carbonate fuel cell according to an embodiment of the present invention, FIG. 2 is a flow chart showing the direction of flow of reactant gas into the cell of FIG. 1, and FIG. is a flowchart showing the flow direction of the reactant gas when the oxidant gas inlet is biased towards the fuel gas inlet side in the cell of Fig. 1, and Fig. 4 shows the flow direction of the reactant gas flowing into the cell by cross flow. 5 is a flowchart showing the direction of flow in which the reaction gas flows into the cell in parallel flow, FIG. Figure 8 is a diagram showing the temperature distribution of the cell reaction surface due to alternating current, Figure 8 is a diagram showing the temperature distribution of the cell reaction surface due to parallel flow as shown in Figure 5, and Figure 9 is a diagram showing the temperature distribution of the cell reaction surface due to countercurrent flow as shown in Figure 6. Oxidizing agent 1, 13
: Separate plate, 14: Upper C Le Figure 1 Figure 2 Figure 3 Figure 4 Figure 2 - Father 7Fj ↓ ÷ Figure 7

Claims (1)

[Claims] An electrolyte plate containing carbonate, a fuel electrode and an oxidizer electrode that sandwich this, and arranged on both sides of these electrodes,
In a cell comprising separate plates each having a fuel flow path for supplying fuel gas to a fuel electrode and an oxidizer flow path for supplying a arranging agent gas to an oxidizer electrode, the fuel gas flows through the fuel flow path into the cell. The oxidizing agent flow path is provided so that the oxidizing agent gas flows from one opposing side surface to the other side surface, and the oxidizing agent flow path is provided so that the oxidizing agent gas flows to a central portion between the opposing side surfaces, or from this portion to the side surface on the inlet side of the fuel gas. A cell structure of a molten carbonate fuel cell, characterized in that the cell structure is provided so that the flow flows from the biased portion toward the one side surface and the other side surface.