JPS61148766A - Fused carbonate type fuel cell - Google Patents

Abstract

PURPOSE:To prevent leakage of fuel gas, especially hydrogen gas, and improve the utilization factor of oxidizer gas by supplying oxidizer gas to the main body of a fuel cell through an external manifold and supplying fuel gas through an internal manifold. CONSTITUTION:When fuel gas P reaches an internal manifold pipe 26b on the exhaust side, it is taken into the pipe 26b. Fuel gas P, taken into the pipe 26b, advances downward through a fuel gas exhaust passage C2 and is discharged out of the cell. Meanwhile, when oxidizer gas Q is led through an inlet pipe 35a to an external manifold 34b, oxidizer gas Q advances in a direction running counter to the flow of fuel gas P and is discharged out through the opposing manifold 34b. By means of a wet seal, fuel gas P and oxidizer gas Q are completely separated. Since the two kinds of reaction gas flow in opposite directions, it is possible to even electric current distribution and thereby improve the utilization factor.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to improvements in molten carbonate fuel cells.

[Technical background of the invention and its problems]

In recent years, molten carbonate fuel cells have been developed as next-generation fuel cells. A molten carbonate fuel cell is one in which an electrolyte made of carbonate is brought to a molten state under a to cause an electrode reaction.Compared to other fuel cells such as phosphoric acid type and solid electrolyte type, electrode reactions occur more easily. It has features such as being easy to use, has high heat generation efficiency, and does not require expensive precious metal catalysts.

By the way, in such a molten carbonate fuel cell, the electromotive force obtained by one fuel cell is as low as 1, so in order to construct a power generation plant with a high output, multiple unit cells must be stacked in series to generate the fuel. The battery body must be configured to obtain the summed output of each unit battery. Therefore, this type of fuel cell is constructed as follows.

That is, each unit cell is composed of a pair of porous electrode plates (an anode electrode and a cand electrode) and an electrolyte layer made of an alkali carbonate interposed between them. These unit batteries are stacked with separators in between. The separator has both the function of electrical connection between each unit cell and the function of forming a passage for reaction gas to each electrode plate.

Manifolds with reactive gas distribution and recovery functions are placed on four sides of the fuel cell body. Then, oxidizing gas is supplied to one of these manifolds and fuel gas is supplied to the adjacent manifold, and both gases are made to flow orthogonally to both sides of the unit cell.
At the anode side electrode, the reaction is H2+CO32--*H20+CO2+2e-, and at the cathode side, the reaction is 1/202 +CO
After the reaction 2+2e--+GO3z- is caused and a direct current output is obtained, the gas is discharged from each opposing manifold. A wet seal made of molten carbonate is formed on the peripheral edge of each unit cell to prevent cross-mixing of both of the reaction gases inside the fuel cell main body. Further, a wet seal is also formed between the fuel cell main body and the manifold to prevent leakage of both of the above gases.

However, the fuel cell configured in this manner has the following drawbacks.

That is, in the above configuration, since the fuel gas and the oxidizing gas are made to flow in orthogonal directions, there are large variations in the current density distribution and temperature distribution within the unit cell. For this reason,
This results in a localized decrease in efficiency and a decrease in the overall current density. In addition, if the temperature is uneven in places like this, thermal stress acts on the stacked structure of the fuel cell body, causing creep or deformation of the stack, resulting in leakage of reactant gas. There was a problem. In particular, leakage of hydrogen in the fuel gas became a problem from a cost standpoint.

Further, the fuel cell main body generates heat as well as electric power through the above chemical reaction. If this heat is not removed, the operating temperature range of molten carbonate fuel cells, 600-700°C, will be exceeded, making it impossible to promote effective electrode reactions. However, with the above structure, the four sides of the fuel cell body are covered with manifolds, so the heat removal ability is low, and furthermore, it is difficult to add external cooling means due to the structure. For this reason, the oxidant gas must also be used as a coolant and the oxidant gas must be passed through the interior of the fuel cell body in excess, resulting in a problem that the utilization rate of the oxidant gas is low.

[Purpose of the invention]

The present invention was made in view of these problems, and its purpose is to improve current density distribution inside a unit battery,
It is an object of the present invention to provide a molten carbonate fuel cell that can reduce variations in temperature distribution, effectively prevent leakage of fuel gas, particularly hydrogen, and increase the utilization rate of oxidant gas.

[Summary of the invention]

In the present invention, in order to cause the fuel gas and the oxidant gas to flow counter-currently to each unit cell, rather than in a perpendicular direction, the oxidant gas is supplied to the fuel cell main body by an external manifold, and the fuel gas is supplied by an internal manifold. The fuel is supplied to the fuel cell itself.

That is, the present invention constitutes a fuel cell main body having a stacked structure with a plurality of unit cells and the plurality of unit cells inserted between these unit cells, and a fuel cell body is formed on a surface adjacent to one of the unit cells. forming a gas flow path, forming an oxidizing gas flow path on a surface adjacent to the other unit cell, and extending the fuel gas flow path from a side surface of the fuel cell main body to a peripheral edge of the fuel gas flow path forming surface; a separator provided with a protruding peripheral wall for blocking;
an introduction-side external manifold that is applied to one side of the fuel cell main body and introduces the oxidant gas into the oxidant gas flow path; Penetrating in the stacking direction an exhaust-side external manifold that guides the oxidant gas introduced into the agent gas flow path to the outside, and a position inside the fuel cell main body and near a side surface to which the exhaust-side external manifold is applied. and an inlet-side internal manifold that guides the fuel gas to the fuel gas flow path, and a position inside the fuel cell main body and near the side surface to which the inlet-side external manifold is applied, in the stacking direction, and the fuel gas flow path. It is characterized by being equipped with an internal discharge side manifold that guides the fuel gas introduced into the passageway to the outside.

〔Effect of the invention〕

According to the present invention, since the fuel gas and the oxidant gas flow countercurrently to the unit cell, the current density distribution and temperature distribution within the unit cell can be made uniform. Therefore, deformation and creep due to thermal stress of the fuel cell main body having a stacked structure can be avoided, and leakage of reaction gas can be prevented. In particular, since the fuel gas is supplied through the internal manifold, leakage to the outside or leakage of hydrogen is unlikely to occur.

Also, since an external manifold for fuel gas is not required, one opposing side of the fuel cell body can be used for external cooling of the fuel cell body. Therefore, it is no longer necessary to flow a large amount of oxidizing gas for cooling as in the conventional case, and the utilization rate of the oxidizing gas can be increased.

[Embodiments of the invention]

Hereinafter, a molten carbonate fuel cell according to an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a fuel cell main body which is rectangular in its entirety and has a laminated structure. On this fuel cell main body, a plurality of unit cells 4 are stacked with separators 5 interposed between end plates 3a and 3b. In order to simplify the explanation hereinafter, a pair of opposing surfaces to which an external manifold, which will be described later, is attached on the upper p side of the fuel cell main body will be referred to as A, respectively.

Define the A2 surface and the pair of opposing surfaces adjacent to these as 8.
It is defined as 87 sides.

On the unit cell, as shown in FIG. 2, a pair of porous electrode plates made of a nickel alloy, namely an anode electrode plate 7a.
An electrolyte plate 8 is inserted between the anode electrode plate 7b and the anode electrode plate 7b, and an anode side current collector plate 9a is attached to the anode electrode plate 7a, and a cathode side current collector plate 9b is attached to the cathode electrode plate 7b side. It is configured. The electrolyte plate 8 is made by holding a carbonate electrolyte made of a mixture of lithium carbonate, potassium carbonate, etc. with a ceramic holding material such as lithium aluminate, and the electrolyte plate 8 is formed by holding a carbonate electrolyte made by mixing lithium carbonate, potassium carbonate, etc. with a ceramic holding material such as lithium aluminate. A plurality of through holes 10 are provided at equal intervals in the vicinity. Further, the anode side current collector plate 9a is made of a spongy metal such as nickel, and the cathode side current collector plate 9b is made of a spongy metal such as stainless steel (SLJS316).

The separator 5 is constructed as shown in FIG.

That is, numeral 21 in the figure is a thin plate made of a conductive material and having a through hole 22 for fuel gas flow coaxial with the through hole 10 of the electrolyte layer 8. A
A stepped protrusion 23 is provided to form an oxidizing gas flow path that allows the oxidizing gas to flow from the surface to the A2 surface. This protrusion 23 also supports the cathode-side current collector plate 9b at its stepped portion, and supports the cathode electrode plate 7b at its upper end. On the other hand, at the peripheral edge of the surface of the thin plate 21 facing the anode side current collector plate 9a, there is provided a fuel gas flow that allows the fuel gas to flow from the through hole 22 on the A' side to the through hole 22 on the A side. An annular projecting peripheral wall 24 is provided to form a passageway and to prevent fuel gas from leaking from the side surface of the fuel cell main body 1. This annular projecting peripheral wall 24 has a seventh node side current collector root 9a and an anode electrode plate 7 on its inner peripheral surface.
A notch 25 is formed in the through hole 22 so as to restrict the position of a, but not to obstruct the flow of fuel gas. A plurality of internal manifold pipes 26a for introducing fuel gas are protruded at the positions where the through holes 22 on the side A' of the WI plate 21 are formed, and the through holes 22 on the side A' of the WI plate 21 are formed. A plurality of internal manifold pipes 26b for discharging fuel gas are protruded from the position. The internal manifold tubes 26a and 26b are made of an insulating material such as alumina, and their length is the sum of the thicknesses of the cathode side current collector plate 9b, cathode electrode plate 7b, and electrolyte layer 8. It is set.

On the A and A' faces on the fuel cell main body, there is an external manifold 34a for guiding the oxidant gas through, for example, rectangular annular zirconia felts 33a and 33b that form a wet seal with the molten carbonate.

34b is applied. The external manifold 34a is provided with an oxidant gas Q introduction pipe 35a, and the external manifold 34b is provided with an oxidant gas Q discharge pipe 35.
b is provided.

Furthermore, among the aforementioned end plates 3a and 3b, the end plate 3b located at the lower end in the figure has a fuel gas introduction path 37a that guides the fuel gas P to the internal manifold pipe 26a.
is formed inside the internal manifold pipe 26b.
A fuel gas discharge path 37b is formed inside to guide the fuel gas P discharged from the fuel gas P to the outside. An inlet pipe 38a for guiding the fuel gas P to the fuel gas inlet passage 37a is connected to the end of the end plate 3b on the A' side, and an inlet pipe 38a for guiding the fuel gas P to the A' side is connected to the end of the end plate 3b on the A' side. Road 3
An exhaust pipe 38b is connected to guide exhaust gas from 7b to the outside. Further, a protrusion 39 is provided in the center of the inner surface of the end plate 3b to protrude from the lower surface of the separator 5 in order to separate the introduced gas and the exhaust gas.

This end plate 3b is connected to the separator 5 via a gasket 40.

The assembled state of the fuel cell thus constructed is shown in cross section in FIG.

Now, when the temperature of the fuel cell is raised to a predetermined operating temperature, the electrolyte melts and forms a part between the projecting peripheral wall 24 and the electrolyte layer 8.

A wet seal is established between the internal manifold pipes 26a and 26b and the electrolytic layer 8. In this state, when the fuel gas P is introduced into the through hole 22 of the separator 5 through the introduction pipe 38a and the fuel gas introduction path 37a, the fuel gas P is transferred between the through hole 22 and the inside of the introduction side, as shown in FIG. Manifold pipe 26
The introduction side channel C's extending in the stacking direction formed by A and A advances upward in the figure. In the process of this progress, the fuel gas P is separated and introduced into the anode side current collector plate 9a, and the fuel gas P is separated and introduced into the anode side current collector plate 9a.
Proceed to the left in the diagram. When the fuel gas P reaches the discharge-side internal manifold pipe 26b, it is taken into the discharge-side internal manifold pipe 26b. The fuel gas P taken into the discharge side internal manifold pipe 26b is transferred to the through hole 22.
The fuel gas travels downward in the drawing through a discharge side flow path C2 extending in the stacking direction formed by the fuel gas discharge passage 37b and the discharge side internal manifold pipe 26b, and is discharged to the outside via the fuel gas discharge passage 37b and the discharge pipe 38b. On the other hand, when the oxidizing gas Q is introduced into the manifold 34b through the introduction pipe 35a, the oxidizing gas Q is introduced into the oxidizing gas flow path of the separator 5, and the inside of the cathode side current collector plate 9b is turned into the fuel gas P. The gas flows in a countercurrent direction, that is, to the right in the figure, and is discharged to the outside via the opposing external manifold 34b and discharge pipe 35b. In this way, both gases P
, Q flow through the current collector plates 9a and 9b, respectively, each electrode plate 7a.

At 1b, the electrochemical reaction described above occurs and electrical energy is generated.

According to this embodiment, the space between the fuel gas P and the oxidizing gas Q is completely sealed by the wet seal described above,
In addition, the fuel gas P does not leak to the outside, and in this case, both reaction gases flow countercurrently.
Current density distribution and temperature distribution can be made more uniform compared to conventional methods. Further, in this embodiment, an external cooling means can be added to the 8.8' surface, so that the oxidizing gas can be used effectively.

The effects of this example could also be confirmed through experiments conducted by the present inventors. That is, in the fuel cell of this example, low-8TLJ was used as the fuel gas, air/CO2-70/30 was used as the II agent gas, the inlet gas temperature was 800, the fuel gas utilization rate was 25%, and the average single cell It was operated at a voltage of 0.85V. As a result, the variation in current density is reduced, and the average current density is now 19
While it was 8fflA/m, in this example it was 227
The mA/d was improved by about 15V%.

In addition, in the past, there was a temperature difference of 810K at the inlet of the oxidant gas and 1020K and 210K at the outlet, but in this embodiment, the temperature difference is 810K at the inlet and 980K at the outlet. 170, making it possible to reduce the temperature difference by about 19% compared to conventional methods. Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, the Hayabusa electric plate 9 has a current collecting function as well as diffusing a reactive gas.
Although spongy metal is used for a and 9b, for example, grooves having similar functions may be formed in the separator 5.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a schematic configuration of an ia carbonate fuel cell according to an embodiment of the present invention, FIG. 2 is an exploded perspective view showing the fuel cell main body of the fuel cell, and FIG. 3 is a perspective view showing the fuel cell main body of the fuel cell. FIG. 4 is a perspective view showing the separator of the fuel cell, in which FIG. 4(a) shows the upper surface, FIG. Engineering...Fuel cell main body, 3a, 3b...End plate, 4...Unit cell, 5...Separator, 7a...
... Anode electrode plate, 7b... Cathode electrode plate, 8.
... Electrolyte layer, 9a... Anode side current collector plate, 9b...
- Cathode side current collector plate, 23... Projection, 24... Projection peripheral wall, 26a, 26b... Internal manifold pipe, 3
3a to 33d...zirconia 7x rut, 34a. 34b...External manifold, P...Fuel gas, Q
...oxidant gas. Applicant's agent Patent attorney Takehiko Suzue Figure 2 Figure 3 (a) (b)

Claims (1)

[Claims] A plurality of unit cells and the plurality of unit cells inserted between these unit cells constitute a fuel cell main body having a stacked structure, and a fuel gas flow path is formed on a surface adjacent to one of the unit cells. An oxidant gas flow path is formed on a surface adjacent to the other unit cell, and a projecting peripheral wall is provided at a peripheral edge of the fuel gas flow path forming surface to block the fuel gas flow path from a side surface of the fuel cell main body. an inlet-side external manifold that is applied to one side of the fuel cell main body and introduces the oxidant gas into the oxidant gas flow path; and an introduction side external manifold that is applied to the side opposite to the one side of the fuel cell main body. A discharge-side external manifold that guides the oxidant gas introduced into the oxidant gas flow path to the outside, and a position in the vicinity of a side surface of the fuel cell main body to which the discharge-side external manifold is applied in the stacking direction. an inlet-side internal manifold that penetrates and guides the fuel gas to the fuel gas flow path; and an inlet-side internal manifold that penetrates the fuel cell main body at a position near the side surface to which the inlet-side external manifold is applied in the stacking direction; A molten carbonate fuel cell characterized by comprising an internal discharge side manifold that guides fuel gas introduced into a gas flow path to the outside.