JPH0680591B2 - Molten carbonate fuel cell - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an improvement of a molten carbonate fuel cell using an alkali metal carbonate or an alkaline earth carbonate as an electrolyte.

[Technical background of the invention and its problems]

In recent years, development of a molten carbonate fuel cell using an alkali carbonate as an electrolyte has been advanced. Since the molten carbonate fuel cell can use not only H ₂ but also CO as a fuel and can utilize high exhaust heat, early development as a power generation unit for a high-efficiency power generation plant is desired.

The molten carbonate fuel cell currently under development is
Generally, as shown in FIG. 3, a porous electrode plate made of a corrosion-resistant metal, that is, an anode 2 and a cathode 3 is arranged on both sides of an electrolyte layer 1 made of a mixture of inert inorganic material particles and an alkali carbonate. The battery 4 is configured. These unit batteries 4 have a separator 5 having an electrical connection function between the unit batteries and a function of forming a passage of a reaction gas to each electrode plate.
Are stacked through. Then, by flowing the fuel gas P to the anode 2 side and the oxidant gas Q to the cathode 3 side, respectively, on the anode side, H ₂ + CO ₃ ^2- → CO ₂ + H ₂ O + 2e (1) (CO + H ₂ O → CO ₂ + H ₂ )… (2) and 1 / 2O ₂ + CO ₂ + 2e → CO ₃ ^2- … (3) on the cathode side, and the reaction proceeds to generate electricity. Is continued. It should be noted that in the formula (2), the carbon monoxide supplied as a fuel is not directly subjected to the electrode reaction, but is converted into H ₂ which is the active material of the anode through a conversion reaction,
It is shown that it is subjected to an electrode reaction.

By the way, in order to maintain the high reliability of the fuel cell and to prolong the life of the fuel cell, it is an essential condition that the electrode reaction proceeds uniformly over the entire surface of the electrode. However, in the conventional fuel cell of this type, when supplying the reaction gas to be used in the electromotive reaction, a cross-flow method shown in FIG. 3, a parallel flow method (not shown) in which both gases flow in the same direction, or a reverse direction is used. The counter flow method is adopted, and the results of analysis of reaction rates show that the generated current density near the fuel gas inlet is nearly twice as large as that near the fuel gas inlet. For this reason, electric power is concentrated in about 1/3 from the fuel inlet side,
In addition to uneven consumption of carbonate electrolyte due to reaction, the heat distribution generated by ohmic loss becomes non-uniform, making it difficult to continue stable power generation for a long period of time when a large number of cells are stacked. there were.

[Object of the Invention]

The present invention has been made on the basis of such a problem, and it is a molten carbonate fuel capable of causing the electrode reaction to proceed uniformly over the entire electrode surface and thus maintaining stable power generation for a long period of time. To provide batteries.

[Outline of Invention]

The present invention is intended to make the fuel gas uniform in the fuel electrode by flowing the fuel gas into two flow paths having different paths.

That is, the present invention provides a plurality of unit cells, a plurality of separators that are inserted between these unit cells to form a fuel cell main body having a laminated structure, and supply a fuel gas to each of the unit cells. In order to do so, a fuel gas passage formed on one surface side of each separator, and an oxidant gas formed on the other surface side of each separator to supply an oxidant gas to each unit cell Molten carbonate fuel cell comprising a passage, a fuel gas guide means for allowing a fuel gas to flow through each of the fuel gas passages, and an oxidant gas guide means for causing an oxidant gas to pass through each of the oxidant gas passages In the system, the fuel gas guide means is formed in a stacking direction by a hole provided in a central portion of each of the laminated members forming the fuel cell main body, and is connected to the central portion of each of the fuel gas passages. Of the fuel gas passages formed in the stacking direction by holes provided at both ends of the fuel gas introducing passage and the fuel gas introducing passages of the respective laminated members as boundaries. And an oxidant gas guide means for communicating the fuel gas flowing through each of the fuel gas passages. It is characterized in that it is constituted by an external manifold that allows the oxidant gas to flow through the respective oxidant gas passages in a direction orthogonal to the flow direction.

〔The invention's effect〕

According to the present invention, since the fuel gas is divided into two different flow paths to flow, it is possible to disperse the parts where the generated current density is higher than in the conventional case. In other words, since it is possible to cause a reaction evenly over the entire electrode surface, the consumption of the carbonate electrolyte also progresses uniformly, the heat distribution becomes uniform, and eventually stable power generation is maintained over a long period of time. Can be made.

Example of Invention

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a fuel cell main body 11 is constructed by stacking a plurality of unit cells 12 with separator elements 13 interposed between them so that the entire body has a rectangular shape. For the sake of simplicity, a pair of opposite side surfaces of the fuel cell body 11 to which an external manifold is attached, which will be described later, are defined as A and A ′ surfaces, and the other side surfaces are B and B ′ surfaces. Define.

The unit cell 12 is composed of an electrolyte plate 21, an anode plate 22 arranged on the lower surface of the electrolyte plate 21, and a cathode plate 23 arranged on the upper surface thereof.

The electrolyte plate 21 is, for example, formed by mixing LiAlO ₂ fine powder and K ₂ CO ₃ -Li ₂ O ₃ fine powder into a rectangular shape by hot pressing, and has short sides near both ends in the longitudinal direction. A plurality of holes 21a, 21b for discharging the fuel gas are formed side by side in the same direction, and a plurality of holes 21c for introducing the fuel gas are formed in the same central portion in the short side direction.

The anode plate 22 has, for example, a pore size of 3 to 6 μm and a porosity of 60 to 80.
% Nickel alloy porous body. The cathode plate 23 has, for example, a pore size of 6 to 15 μm and a porosity of 70 to 80.
% Nickel porous body. The anode plate 22 and the cathode plate 23 are each formed in a rectangular shape, and a plurality of holes 22c, 23c arranged in the short side direction corresponding to the central hole 21c of the electrolyte plate 21 are formed in the central portion thereof. ing. Further, a plurality of holes 22a, 22b arranged in the short side direction are formed at both ends in the longitudinal direction of the anode plate 22 at positions corresponding to the holes 21a, 21b at both ends of the electrolyte plate 21, respectively. On the other hand, the cathode plate 23 is formed with a length that does not reach the holes 21a and 21b at both ends of the electrolyte plate 21 in the longitudinal direction.

In the separator element 13, the fuel gas passage forming plate 25 and the punch metal 26 are arranged on the upper surface of the separator plate 24, and the fuel gas passage forming plate 25 and the punch metal 26 are arranged on the lower surface side.
It is configured by disposing a single oxidant gas passage forming plate 27 and a punch metal 28.

The separator plate 24 is formed with a projecting peripheral wall 31 having a step portion 30 at the upper surface peripheral portion thereof, and projecting ridges 33, 34 having step portions 32 at both longitudinal end portions of the lower surface thereof, and further at the center position of the lower surface. The ridge 35 extending in the short side direction is formed. The projecting peripheral wall 31 has a function of sealing the fuel gas introducing space R formed therein from the outside, and the three projecting ridges 33 to 35 are two grooves extending in the short side direction which are oxidant gas flow paths. Form U. The three protrusions 33 to 35 have a plurality of holes at positions corresponding to the holes 21a to 21c of the electrolyte plate 21, respectively.
24a, 24b, 24c are formed.

The fuel gas passage forming plate 25 has a plurality of longitudinally extending grooves 36 for guiding the fuel gas P on the upper surface side thereof, and the holes 25 are formed at positions corresponding to the holes 21a to 21c of the electrolyte plate 21, respectively.
A, 25b, 25c are formed, and the groove 36 in the portion where the holes 25a to 25c are located is communicated in the short side direction to uniformly guide the fuel gas P to each groove.

The punch metal 26 has a plurality of pores for supplying the fuel gas P from the fuel gas passage forming plate 25 to the anode plate 22,
It also has a current collecting function for the anode plate 22. This punch metal
The anode plate 26 has substantially the same shape as the anode plate 22, and is also provided with a plurality of holes 26a, 26b, 26c at both longitudinal end portions and the central portion thereof.

The oxidant gas passage forming plate 27 is formed in a shape that fits into two grooves U formed on the lower surface of the separator plate 24, and is formed on the lower surface side in a direction orthogonal to the groove 36 of the fuel gas passage forming plate 25. A plurality of extending grooves 38 are formed.

The punch metal 28 has a plurality of pores for supplying the oxidant gas Q from the oxidant gas passage forming plate 27 to the cathode plate 23, and also has a current collecting function of the cathode plate 23.

An inorganic tape 40 for sealing the introduced gas is interposed between the protruding strip 35 located at the center of the lower surface of the separator plate 24 and the cathode plate 23. The inorganic tape 40 also has a plurality of holes 40c corresponding to the central hole 21c of the electrolyte plate 21. The inorganic tape 40 is formed, for example, by impregnating a nonwoven fabric with a carbonate.

Such a fuel cell main body 11 is formed as follows. That is, first, the fuel gas passage forming plate 25 is fitted in the fuel gas introducing space R on the upper surface of the separator plate 24, and the punch metal 26 and the anode plate 22 are fitted on the upper surface of the fuel gas passage forming plate 25 so as to be fitted to the step portion 30 of the protruding peripheral wall 31. Wear and. Further, the oxidant gas passage forming plate 27 is fitted into the groove U on the lower surface of the separator plate 24, and the punch metal 28 is fitted to the lower surface thereof so as to be fitted to the step portion 32 of the protrusions 33 and 34.
Are arranged, the inorganic tape 40 is arranged on the tip end surface of the ridge 35, and the cathode plate 23 is arranged on the lower surface thereof. Then, the assembly and the electrolyte plates 21 are alternately laminated. As a result, the holes provided in each member communicate with each other in the stacking direction. The cylindrical space formed by the hole provided in the center of each member serves as the flow path S for introducing the fuel gas P, and the cylindrical space formed in the stacking direction by the holes provided at both longitudinal ends of each member. Serves as a flow path T for discharging the fuel gas P. That is,
An internal manifold is formed in each of these cylindrical spaces.

In the fuel cell main body 11 thus laminated, a small manifold for introducing and discharging the fuel gas P (not shown) is arranged on the lower surface, and a manifold for introducing the oxidant gas Q (not shown) is arranged on the same surface A. An oxidant gas Q exhaust manifold (not shown) is arranged on the A ′ surface.

As shown in FIG. 2, the fuel gas from the small manifold travels upward in the central introduction flow path S in the stacking direction, and is distributed to the grooves 36 of each fuel gas passage forming plate 25 in the middle of this progress. To be done. The fuel gas P introduced into these grooves 36 travels in opposite directions in the first passage extending from the central portion of the fuel cell toward the B surface and the second passage extending from the central portion toward the B ′ surface. In the middle of its progress, it is supplied to the anode plate 22 through the pores of the punch metal 26. The fuel gas P provided for the electromotive reaction advances downward in the exhaust flow paths T at both ends in the stacking direction, and is exhausted to the outside through the small manifold.

On the other hand, the oxidant gas Q from the external manifold flows through the grooves 38 of each oxidant gas passage forming plate 28 in the direction orthogonal to the traveling direction of the fuel gas P. In the middle of this flow, punch metal It is supplied to the cathode plate 23 through 28 pores. The oxidant gas Q provided for the electromotive reaction is discharged to the outside through the manifold on the A'side.

The fuel gas P is prevented from leaking to the outside by a wet seal between the electrolyte plate 21 and the projecting peripheral wall 31 of the separator plate 24 and the ridges 33, 34. Further, the flow path of the oxidant gas Q is a wet seal between the peripheral walls 33, 34 of the separator plate 24 and the electrolyte plate 21, and the melt leached from the inorganic tape 40 and the electrolyte plate 21 to the cathode plate 23. Each is sealed with a carbonate wet seal. As a result, crossover between the oxidant gas Q and the fuel gas P is prevented.

Next, an experimental example actually performed by the present inventor will be described.

The electrolyte plate 21 is a plate having a width of 50 cm, a length of 100 cm and a thickness of 0.15 cm, and is a mixture of LiAlO ₂ , K ₂ CO ₃ and Li ₂ O ₃ in a weight ratio of 40:37:23. About 5% by weight of polyethylene was added to the body, and hot pressing was performed at a temperature of 250 ° C. and a pressure of about 500 tons. The electrolyte plate 21 has a caliber of 2.5 cm at a position 4.5 cm from both ends in the longitudinal direction and at intervals of 11 cm in the short side direction.
Four holes 21a and 21b of cm are formed respectively. Further, four holes 21c having a diameter of 3 cm are formed at 11 cm intervals in the central portion of the electrolyte plate 21 in parallel with the arrangement direction of the four holes 21a and 21b.

Ni-Cr with a pore size of 4-6 μm and a porosity of 75% is used for the anode plate.
A sintered porous body of (10%) alloy having a thickness of 0.4 mm, a width of 46 cm, and a length of 96 cm was used.

The cathode plate 23 has a pore diameter of 8 to 12 μm and a porosity of 70 to 80%.
A Ni porous plate having a size of width 50 cm, length 86 cm, and thickness 0.86 mm was used.

Then, four holes 22a, 22b, 22c, and 23c arranged in the short side direction are also formed in the anode plate 22 and the cathode plate 23.

The separator plate 25 has a thickness of 0.4 mm, a width of 50 cm, and a length of 100 cm.
Using a clad plate of SUS316 / Ni, a protruding peripheral wall 31 of Ni with a thickness of 2 mm and a width of 3 cm is adhered to the peripheral portion of the Ni side surface by welding,
Further, a step having a width of 5 mm and a depth of 0.5 mm was formed inside the protruding peripheral wall 31. On the other hand, on the SUS316 side, thickness at both ends in the longitudinal direction
The ridges 33 and 34 made of SUS316 having a width of 2.5 mm and a width of 70 mm and the ridge 35 made of SUS316 having a thickness of 1.5 mm and a width of 80 mm were welded and fixed to the central portion in the longitudinal direction. The ridges 33 and 34 are 4.5 cm from the outer side
Holes 24a, 2 with a diameter of 2.5 mm at a distance of 11 cm from the center along the line
Forming each 4b, 1mm with a width of 5mm from the inside
Formed a step. In addition, the ridge 35 is 11 cm from the center.
Holes 24c having a diameter of 3 cm were formed at intervals.

The fuel gas passage forming plate 25 has a thickness of 1.5 mm, a width of 44 cm,
Using a 94 cm long Ni plate, groove pitch 5 mm, groove 36 depth 1
mm with the same width of 3 mm.

The punched metal 26 has pores with a diameter of 1 mm that reach 33% of the total area. Thickness 0.2 mm, width 46 cm, length 96 cm.
Ni plate was used.

The punch metal 28 is made of the same material as the punch metal 26, and has two pieces of SUS having a thickness of 0.2 mm, a width of 50 cm, and a length of 39 cm.
A 316 plate was used.

As the inorganic tape 40, a sealing material obtained by impregnating a zirconia non-woven fabric with LiKCO ₃ salt was used.

A stack of 41 kw output is constructed by stacking 10 sets of cells with such members, and the fuel gas P and the oxidant gas Q are supplied as described above, and the fuel utilization rate is 70% and the oxidant gas utilization rate is 50%.
%, Temperature 650 ° C., normal pressure, current density 0.16 A / cm ² For comparison, a conventional parallel flow stack was used as Comparative Example 1 and a conventional cross flow stack was used as Comparative Example 2 under the same conditions as above. The characteristics of each cell at this time are shown in the following table.

As is clear from this result, in this example, the average voltage of each cell was higher than that of the conventional one, and the variation in voltage between cells was also improved.

As described above, according to the present embodiment, the electromotive reaction can be uniformly progressed over the entire electrode by causing the fuel gas P to flow in two systems, and it is possible to prevent the electric power from being concentrated on a specific portion. Therefore, the effects described above can be obtained.

Further, in the above-described embodiment, since the oxidant gas is supplied by the external manifold, the gas flow passage can be made large, and even when a large amount of oxidant gas is flown to cool the fuel cell, the fuel cell It is possible to significantly improve drivability without causing crossover due to pressure loss inside.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the anode plate 22 is on the lower side,
Further, the unit cell 12 is configured by disposing the cathode plate 23 on the upper side, respectively, but even if the fuel cell is assembled by disposing the anode plate 22 on the upper side and the cathode plate on the lower side, the result shown in the above experimental example is shown. Was almost the same.

Further, the fuel gas passage forming plate 25 and the oxidant gas passage forming plate 27
Instead of, for example, Celmet (trade name; Sumitomo Metals)
It was possible to obtain good characteristics by using.

Furthermore, the anode plate 22 is also not limited to the Ni-Cr alloy,
For example, a Ni porous plate treated with Cr may be used. The cathode plate 23 may use a NiO porous plate. Further, the electrolyte plate 21 may be obtained by hot pressing at 460 ° C. and 300 kg / cm ² pressure.

In addition, the cross section of the fuel cell body may also be a square instead of a rectangle, or may be a rectangle whose longitudinal direction is the flow direction of the oxidant gas. Further, the number of holes penetrating the fuel cell body in the stacking direction can be set arbitrarily.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a fuel cell main body according to an embodiment of the present invention with a part cut away, FIG. 2 is a vertical cross-sectional view of the same fuel cell main body, and FIG. 3 is an exploded view of a conventional orthogonal flow fuel cell. It is a perspective view. 1, 21 ... Electrolyte plate, 2 ... Anode, 3 ... Cathode, 4, 12 ...
Unit cells, 5 ... Separator, 11 ... Fuel cell main body, 13 ... Separator element, 22 ... Anode plate, 23 ... Cathode plate, 24 ...
Separator plate, 25 ... Fuel gas passage forming plate, 26, 28 ... Punch metal, 27 ... Oxidizing gas passage forming plate, 40 ... Inorganic tape, P ... Fuel gas, Q ... Oxidizing gas, R ... Fuel gas introducing space, S ... Introduction side flow path, T ... Discharge side flow path.

Claims (1)

[Claims] 1. A plurality of unit cells and a plurality of separators that are interposed between these unit cells to form a fuel cell main body having a laminated structure, and a fuel gas is supplied to each unit cell. A fuel gas passage formed on one surface side of each separator and an oxidant gas passage formed on the other surface side of each separator for supplying an oxidant gas to each unit cell. And a fuel gas guide means for causing a fuel gas to flow through each of the fuel gas passages,
In a molten carbonate fuel cell provided with an oxidant gas guide means for causing an oxidant gas to flow through each of the oxidant gas passages, the fuel gas guide means is a center of each laminated member constituting the fuel cell body The fuel gas introduction passage of one system which is formed in the stacking direction by the holes provided in the section and communicates with the central portion of each of the fuel gas passages and the position of the fuel gas introduction passage of each of the laminated members are defined as boundaries. The fuel gas discharge passages of two systems are formed in the stacking direction by the holes provided at both ends of the fuel gas passage and communicate with the end portions on both sides of the fuel gas passage at the above-mentioned position. The oxidant gas guiding means is configured by an internal manifold, and causes the oxidant gas to flow through the oxidant gas passages in a direction orthogonal to the flow direction of the fuel gas flowing through the fuel gas passages. Molten carbonate fuel cells, characterized by being composed in parts manifold.