JP2004055196A - Oxidant gas feeding mechanism for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To dispense with a compressor and the like for introducing an oxidant gas and to reduce a load of a fuel cell for improving power generation efficiency and lowering a cost. <P>SOLUTION: A power generation cell 5 is constituted by arranging a fuel electrode layer 3 and an oxidant electrode layer 4 on both faces of a solid electrolyte layer 2, and a cell stack 1 is constituted by layering a plurality of power generation cells 5 and separators 8 alternately. A fuel cell module 10 is constituted by arranging the cell stack 1 in a casing body 20 while setting the layering direction horizontally. A supply port 21 for the oxidant gas is arranged in the lower center of the fuel cell module 10 while an exhaust port 22 for a reaction gas is arranged in the upper center. The oxidant gas is let to flow inward by using natural convection in a high temperature environment, and waste gas generated in the cell reaction is discharged from the exhaust port 22. In this way, a compressor and the like for introducing the oxidant gas can be dispensed with, and a load of the fuel cell can be reduced by an equivalent required for the compressor and the like, and consequently, power generation efficiency is improved. The structure is simplified and the cost is lowered when a distributer for distributing the oxidant gas is omitted. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a supply mechanism of a reaction gas in a fuel cell, and more particularly to a supply mechanism of an oxidant gas suitable for being applied to a plate-stacked solid oxide fuel cell.
[0002]
[Prior art]
A solid electrolyte fuel cell with a laminated structure in which a solid electrolyte layer composed of an oxide ion conductor is sandwiched between an air electrode layer (oxidant electrode layer) and a fuel electrode layer is a third-generation fuel cell for power generation. Development is in progress. In a solid oxide fuel cell, oxygen (air) is supplied to the air electrode side, and fuel gas (H ₂ , CO, etc.) is supplied to the fuel electrode side. Both the air electrode and the fuel electrode are porous so that the gas can reach the interface with the solid electrolyte.
[0003]
Oxygen supplied to the air electrode side passes through pores in the air electrode layer and reaches near the interface with the solid electrolyte layer, where electrons are received from the air electrode and converted into oxide ions (O ²⁻ ). Ionized. The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode. The oxide ions that have reached the vicinity of the interface with the fuel electrode react with the fuel gas at this portion to generate a reaction product (H ₂ O, CO _2, etc.), and emit electrons to the fuel electrode.
[0004]
The electrode reaction when hydrogen is used as the fuel is as follows.
Air electrode: 1/2 O ₂ + 2e ⁻ → O ²⁻
The fuel ^{_{electrode: H 2 + O 2- → H}} 2 O + 2e -
Whole: H ₂ + 1 / 2O ₂ → H ₂ O
[0005]
The solid electrolyte layer is a gas impermeable dense structure because it functions as a partition for preventing direct contact between fuel gas and air, as well as a moving medium for oxide ions. This solid electrolyte layer must be composed of a material that has high oxide ion conductivity, is chemically stable under the conditions from the oxidizing atmosphere on the air electrode side to the reducing atmosphere on the fuel electrode side, and is resistant to thermal shock. As a material satisfying such requirements, stabilized zirconia (YSZ) to which yttria is added is generally used.
[0006]
On the other hand, both the air electrode layer (cathode) and the fuel electrode layer (anode), which are electrodes, need to be made of a material having high electron conductivity. Since the air electrode material must be chemically stable in a high-temperature oxidizing atmosphere of about 700 ° C., a metal is inappropriate, and a perovskite-type oxide material having electron conductivity, specifically LaMnO ₃ Alternatively, LaCoO ₃ or a solid solution in which part of La is replaced with Sr, Ca, or the like is generally used. The fuel electrode material is generally a metal such as Ni or Co, or a cermet such as Ni-YSZ or Co-YSZ.
[0007]
Solid oxide fuel cells include a high-temperature operation type that operates at a high temperature of about 1000 ° C. and a low-temperature operation type that operates at a low temperature of about 700 ° C. In a low-temperature operation type solid oxide fuel cell, for example, the thickness of stabilized zirconia (YSZ) to which yttria as an electrolyte is added is reduced to about 10 μm to lower the resistance of the electrolyte, and power is generated as a fuel cell even at a low temperature. Use a modified power generation cell.
[0008]
In a high-temperature solid oxide fuel cell, a ceramic having electronic conductivity such as lanthanum chromite (LaCrO ₃ ) is used as a separator. In a low-temperature operating solid oxide fuel cell, a metal material such as stainless steel is used. Can be used.
[0009]
In addition, three types of structures of a solid oxide fuel cell, a cylindrical type, a monolith type, and a flat plate type, have been proposed. Among these structures, a low-temperature-operating solid oxide fuel cell can use a metal separator, and therefore, a flat plate-type structure that can easily impart a shape to the metal separator is suitable.
[0010]
The stack of the plate-stacked solid oxide fuel cell has a structure in which power generation cells, current collectors, and separators are alternately stacked. A pair of separators sandwich the power generation cell from both sides, one of which is in contact with the air electrode via the air electrode current collector, and the other is in contact with the fuel electrode via the fuel electrode current collector. A sponge-like porous material such as a Ni-based alloy can be used for the fuel electrode current collector, and a similar sponge-like porous material such as an Ag-based alloy can be used for the air electrode current collector. Can be. The sponge-like porous body has a current collecting function, a gas permeating function, a uniform gas diffusing function, a cushioning function, a thermal expansion difference absorbing function, and the like, and is therefore suitable as a multifunctional current collector material.
[0011]
The separator has a function of electrically connecting the power generation cells and supplying a reaction gas to the power generation cells. The separator introduces the fuel gas from the outer peripheral surface of the separator and discharges the fuel gas from the surface of the separator facing the fuel electrode layer. It has a fuel passage and an oxidant passage for introducing an oxidant gas from the outer peripheral surface of the separator and discharging the oxidant gas from the surface of the separator facing the oxidant electrode layer.
[0012]
FIG. 3 shows an example of the configuration of the stack 1, in which a power generation cell 5 in which a fuel electrode layer 3 and an air electrode layer 4 (oxidant electrode layer) are arranged on both surfaces of a solid electrolyte layer 2, and a fuel outside the fuel electrode layer 3. A plurality of pole current collectors 6, a plurality of cathode current collectors 7 (oxidant pole current collectors) outside the cathode layer 4, and a plurality of separators 8 outside the current collectors 6 and 7 are sequentially stacked. Having a structure.
[0013]
The separator has a function of electrically connecting the power generation cells and supplying a reaction gas to the power generation cell 5, and introduces a fuel gas into the inside of the separator 8 from the outer peripheral surface of the separator 8 to form a fuel electrode of the separator. The fuel passage 11 is discharged from substantially the center of the surface facing the current collector, and the oxidizing gas (air) is introduced from the outer peripheral surface of the separator 8 to form the separator 8 facing the air electrode current collector 7. And an oxidizing agent passage 12 that is discharged from a central portion.
[0014]
On one side of the stack 1, a fuel distributor 15 for distributing a fuel gas from the outside through the connecting pipe 13 to the fuel passage 11 of each separator 8 is provided. On the other side, an oxidizing agent passage of each separator 8 is provided. An oxidant distributor 16 for distributing an oxidant gas from the outside through a connection pipe 14 is provided upright along the stacking direction of the power generation cells.
[0015]
[Problems to be solved by the invention]
By the way, in a solid oxide fuel cell, a distributor mechanism as described above is generally used as a method for supplying a reaction gas to each power generation cell (single cell) constituting the stack 1. Had the following problems.
[0016]
That is, in each distributor, a large number of connecting pipes branched from the distributor, and a mechanism for attaching (tightening) these connecting pipes to the separator, matching of the thermal expansion coefficient with other battery components in a high temperature atmosphere of, for example, 1000 ° C. (If the coefficients of thermal expansion are not completely matched, stress will be generated due to the difference in thermal expansion of each member, resulting in deformation and breakage of the joining members, lowering the power generation efficiency.) And the size of the stack itself increases.
[0017]
Separately from this, particularly in the case of a solid oxide fuel cell, an oxidizing gas (air is generally used) is used not only as a reaction gas but also as a cooling gas. Because there was no restriction in terms of quality, there was a tendency to supply as much as possible.
For this reason, conventionally, a high-output auxiliary power device such as a compressor or a blower has been installed so that a sufficient oxidant gas can be supplied (spouted) from the distributor to each power generation cell through a thin oxidant passage. Although the compressed air is caused to flow in, the driving power of such an auxiliary power device uses the electromotive force of the fuel cell, so that unnecessary power consumption is originally increased (for example, 5 to 5 of the electromotive force). 10% is used as the driving power), and accordingly, there is a problem that the efficiency of the power generation system is reduced and a problem that it is necessary to secure a place for installing the auxiliary power device.
[0018]
The present invention has been made in view of such problems, and reduces unnecessary power consumption by supplying an oxidizing gas using natural convection in a high-temperature atmosphere, thereby improving power generation efficiency. It is another object of the present invention to provide an oxidizing gas supply mechanism for a fuel cell which is low in cost by simplifying the configuration.
[0019]
[Means for Solving the Problems]
That is, the present invention according to claim 1 forms a power generation cell by arranging a fuel electrode layer and an oxidant electrode layer on both sides of an electrolyte layer, and alternately stacks a plurality of the power generation cells and separators to form a battery stack. The fuel cell module is constructed by placing the cell stack in a box with the stacking direction being horizontal, and a supply port for an oxidizing gas is provided at a lower central portion of the fuel cell module, and the fuel cell module faces the fuel cell module. An exhaust port for a reaction gas is provided in the upper central portion of the fuel cell module, and an oxidizing gas flows from the supply port using natural convection in a high-temperature atmosphere, and a reaction gas generated by an internal cell reaction is supplied to the oxidizing gas. The gas is discharged from the exhaust port.
In the above configuration, a compressor and a blower for introducing the oxidizing gas into the fuel cell module from the outside are not required, and the load on the fuel cell is reduced correspondingly, so that the power generation efficiency is improved. Further, the distributor mechanism for distributing the oxidizing gas, which is conventionally installed, can be eliminated, and the gas supply mechanism can be simplified and the cost can be reduced.
[0020]
According to a second aspect of the present invention, in the fuel cell oxidizing gas supply mechanism according to the first aspect, a blower fan is provided near the oxidizing gas supply port and / or near the reaction gas exhaust port. It is characterized by having been installed.
By providing a simple electric drive fan, the amount of inflow of the oxidizing gas supplied from the outside into the fuel cell module can be increased, so that the power generation efficiency is improved.
[0021]
According to a third aspect of the present invention, in the fuel cell oxidizing gas supply mechanism according to the first or second aspect, the separator is provided on a surface of the separator in contact with the oxidizing electrode layer. A groove perpendicular to the direction is provided.
Thereby, the oxidizing gas introduced from below the separator through the supply port can easily pass through the entire surface of each power generation cell, and therefore, the utilization rate of the oxidizing gas increases, and the power generation efficiency improves. .
[0022]
According to a fourth aspect of the present invention, there is provided the fuel cell oxidizing gas supply mechanism according to any one of the first to third aspects, wherein the first heat exchange is provided near an outlet of the reaction gas. A second heat exchanger near the supply port of the oxidizing gas, and transferring the heat of the exhaust gas heat-exchanged in the first heat exchanger to the second heat exchanger. Features.
By heating the oxidizing gas supplied into the fuel cell module using the heat of the exhaust gas discharged from the exhaust port as in the above configuration, the natural convection phenomenon of the oxidizing gas becomes active and the battery Since the reaction is activated, the power generation efficiency is improved.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
Here, FIG. 1 is a sectional view showing the internal structure of the fuel cell module according to the present embodiment, and FIG. 2 is a sectional view showing the structure of the separator. In order to simplify the description, in the following description, the same reference numerals are used for the same parts as those in the related art.
[0024]
As shown in FIG. 1, a fuel cell module 10 of the present embodiment constitutes a power generation cell 5 by arranging a fuel electrode layer 3 on one surface of a solid electrolyte layer 2 and an oxidant electrode layer 4 on the other surface. A stack 1 is formed by alternately stacking a plurality of the power generation cells 5 and the separators 8, and the stack 1 is oriented sideways so that the stacking direction of the power generation cells 5 is horizontal. It is installed inside a box 20 composed of: Positive terminals 18 and negative terminals 19 protruding from the separators 8, 8 disposed at the extreme ends of the stack 1 project from both left and right ends of the box 20 so as to face each other.
[0025]
Here, the configuration of the stack 1 is substantially the same as that of the conventional type shown in FIG. 3, but in the present embodiment, the stack 1 does not include the oxidant-side distributor 16 as shown in FIG. There is no oxidant passage 12 as in the prior art. Instead, as shown in FIG. 2, the separator 8 of the present embodiment has a groove that traverses perpendicularly to the laminating direction (that is, is parallel to the fuel passage 11) on the surface where the separator 8 contacts the oxidant electrode layer 4. 9 is provided. The overall shape is a square or circular body having a predetermined thickness.
[0026]
A supply port 21 is provided at a lower central portion of the box 20, and an oxidant gas (air) flows into the box from the outside through a supply pipe 23 connected to the supply port 21. I have. In FIG. 1, one supply port 21 for the oxidizing gas is provided. However, a plurality of supply ports 21 may be provided according to the gas supply amount. Further, an exhaust port 22 is provided at the upper center of the box 20, and a reaction gas (exhaust gas) generated by an internal battery reaction is discharged to the outside through an exhaust pipe 24 connected to the exhaust port 22. It has become.
[0027]
As described above, according to the present invention, the supply of the oxidizing gas using the natural convection in the high-temperature atmosphere is performed so that the oxidizing gas flows from the lower supply port 21 and the reaction gas is discharged from the upper exhaust port 22. In order to make this natural convection phenomenon more efficient, two blowers 17 each of which can be driven with low power are installed near the supply port 21 and near the exhaust port 22 in the case. . Note that these blower fans 17 may be installed near the supply port 21 and the exhaust port 22 outside the box.
[0028]
In the above configuration, the fuel gas (H ₂ ) introduced from the outside is once branched into a plurality of fuel connection pipes 13 by the distributor 15, and from each connection pipe 13 via the fuel passage 11 of the separator 8. The fuel is spouted from the center and supplied to the fuel electrode layer 3 of each power generation cell 5. Then, the water vapor generated by the above-described electrode reaction and a small amount of excess fuel (unreacted gas) are discharged from the outer peripheral portion of the stack 5 into the casing.
[0029]
On the other hand, the oxidizing gas (air) from the outside flows into the case by natural convection due to the high temperature atmosphere from the supply port 21 at the lower part of the case 20, and further in the right and left directions indicated by arrows by the suction force of the blower fan 17. While being diffused, it rises toward the lower center of the stack 1. The oxidizing gas that has reached each of the separators 8 arranged in the vertical direction flows into the gap between the power generation cell 5 and the plurality of grooves 9 (see FIG. 2) provided in the separator 8 and slowly rises through the grooves 9. Then, oxygen ions are formed in the oxidant electrode layer 4, diffuse inside the solid electrolyte, reach the fuel electrode layer 3, and react with the fuel gas.
[0030]
As shown in FIG. 2, by providing grooves 9 uniformly over the entire surface of the separator, the oxidant gas flows evenly over the entire surface of the oxidant electrode layer 4. You can get the output. The oxidant gas after the reaction is discharged out of the stack, reacts with excess fuel (unreacted gas) discharged from the fuel electrode layer 3 and burns around the stack 1, and the high-temperature exhaust gas (CO ₂ ) Is discharged out of the battery together with water vapor (H ₂ O) through an exhaust pipe 24 from an exhaust port 22 in the upper part of the case. Note that, also in this case, the exhaust capability is enhanced by the suction action of the blower fan 17.
[0031]
As described above, by using the blower fan, the inflow amount of the oxidizing gas supplied from the outside into the fuel cell module can be increased, and the introduced oxidizing gas can be diffused evenly in every corner of the case. Thus, the oxidant gas can be effectively used.
In addition, by providing a plurality of upwardly directed grooves 9 in the separator 8, the oxidizing gas introduced from below the separator 8 can evenly and easily pass through the surface of each power generation cell 5, This has the effect of increasing the utilization rate of the oxidizing gas and improving the power generation efficiency.
[0032]
In this embodiment, as shown in FIG. 1, a first heat exchanger 25 is provided near the exhaust port of the upper exhaust pipe 24, and a second heat exchanger is provided near the supply port of the lower supply pipe 23. The first heat exchanger 25 and the second heat exchanger 26 are connected by a duct 27, and the heat of the high-temperature exhaust gas heat-exchanged in the first heat exchanger 25 is converted into a liquid such as a carbonate. The heat is transmitted to the second heat exchanger 26 through the medium, and the oxidant gas passing through the supply pipe 23 is supplied to the housing while being heated by the heat exchange action of the second heat exchanger 26. Has become.
[0033]
By heating the oxidizing gas supplied into the fuel cell module by using the heat of the exhaust gas discharged from the exhaust port 22 as in the above configuration, the natural convection of the oxidizing gas becomes active, and Since the electrode reaction is also activated by the heated oxidizing gas, the power generation efficiency can be improved. In order to improve the heat exchange rate in each heat exchanger, it is preferable to insert a member having excellent air permeability and capable of holding heat, such as a porous metal, inside the supply pipe 23 and the exhaust pipe 24.
[0034]
As described above, in the fuel cell oxidizing gas supply mechanism of the present embodiment, the oxidizing gas is introduced from the outside into the fuel cell module by natural convection, so that the oxidizing gas is conventionally provided for supplying the oxidizing gas. A high-output auxiliary power device, such as a compressor or a blower, for supplying the reaction gas is not required, so that the load on the fuel cell can be reduced and the power generation efficiency can be improved.
Further, since the conventional distributor mechanism for distributing the oxidizing gas can be eliminated, the structure is simplified and the cost is reduced. In addition, in this configuration, the gap between the boxes 20 can be effectively used, so that the volume of the fuel cell module can be reduced and the size of the fuel cell can be reduced.
[0035]
In this embodiment, a solid oxide fuel cell (SOFC) using a solid oxide such as zirconia as an electrolyte has been described. However, the present invention is not limited to this, and power is generated by an electrode reaction between a fuel gas and an oxidizing gas. Any fuel cell may be used, such as a phosphoric acid fuel cell (PAFC) using phosphoric acid as an electrolyte, a molten carbonate fuel cell (MCFC) using a molten carbonate as an electrolyte, or a solid polymer fuel using an ion exchange membrane as an electrolyte. Of course, it can be applied to a battery (PEFC) and the like.
[0036]
【The invention's effect】
As described above, according to the first aspect of the present invention, an oxidizing gas supply port is provided in the lower central portion of the fuel cell module, and the reactant gas is provided in the upper central portion of the fuel cell module opposed thereto. The oxidizing gas flows in from the supply port using natural convection in a high-temperature atmosphere, and the reaction gas generated by the internal battery reaction is exhausted from the exhaust port. It is not necessary to install a high-output auxiliary power device such as a compressor or a blower used for supplying the agent gas, and the load on the fuel cell can be reduced and the power generation efficiency can be improved.
Further, since the conventional distributor mechanism for distributing the oxidizing gas can be eliminated, the structure is simplified, and the miniaturization and cost reduction can be realized together with the elimination of the auxiliary power device.
[0037]
According to the second aspect of the present invention, since the blower fan is installed near the supply port of the oxidizing gas or near the exhaust port of the reaction gas, the oxidizing gas supplied from outside into the fuel cell module is provided. Can be increased, and the introduced oxidizing gas can be diffused evenly in the casing, so that the oxidizing gas can be effectively used and the power generation efficiency is improved.
[0038]
According to the third aspect of the present invention, since a groove perpendicular to the laminating direction is provided on the surface of the separator in contact with the oxidant electrode layer, the oxidant gas introduced from below the separator is supplied to each power generation cell. Can easily and evenly pass through the surface, thereby increasing the utilization rate of the oxidizing gas and improving the power generation efficiency.
[0039]
Further, according to the present invention, the first heat exchanger is provided near the exhaust port, and the second heat exchanger is provided near the oxidant gas supply port, so that the first heat exchange is performed. The heat of the exhaust gas heat-exchanged by the heat exchanger is transmitted to the second heat exchanger to heat the oxidizing gas supplied into the fuel cell module, so that the natural convection of the oxidizing gas becomes more active, In addition, since the electrode reaction is activated by the heated oxidizing gas, the power generation efficiency is improved.
[Brief description of the drawings]
FIG. 1 is a sectional view showing the internal structure of a fuel cell module according to the present invention.
FIG. 2 is a sectional view showing a structure of a separator used in the present invention.
FIG. 3 is an exploded cross-sectional view showing a configuration example of a conventional stack.
[Explanation of symbols]
1 stack 2 electrolyte layer (solid electrolyte layer)
3 Fuel electrode layer 4 Oxidizer electrode layer (Air electrode layer)
5 Power generation cell 8 Separator 9 Groove 10 Fuel cell module 17 Blower fan 20 Box 21 Supply port 22 Exhaust port 25 First heat exchanger 26 Second heat exchanger

Claims (4)

A fuel cell layer and an oxidizer electrode layer are arranged on both sides of the electrolyte layer to form a power generation cell, and a stack is formed by alternately stacking a plurality of the power generation cells and separators, and the stacking direction is horizontal to stack the stack. Installed in a box to form a fuel cell module,
An oxidant gas supply port is provided at a lower central portion of the fuel cell module, and a reaction gas exhaust port is provided at an upper central portion of the fuel cell module opposed thereto.
An oxidizing gas for a fuel cell, wherein an oxidizing gas flows from the supply port using natural convection in a high-temperature atmosphere and a reaction gas generated by an internal battery reaction is discharged from the exhaust port. Supply mechanism. 2. The oxidizing gas supply mechanism for a fuel cell according to claim 1, wherein a blower fan is provided near the oxidizing gas supply port and / or near the reaction gas exhaust port. The fuel cell oxidizing gas supply mechanism according to claim 1, wherein a groove perpendicular to a laminating direction is provided on a surface of the separator in contact with the oxidizing electrode layer. A first heat exchanger is provided near an outlet of the reaction gas, and a second heat exchanger is provided near a supply port of the oxidizing gas. The fuel cell oxidizing gas supply mechanism according to any one of claims 1 to 3, wherein heat is transmitted to the second heat exchanger.

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