JP2004139960A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell that has a preheating mechanism capable of performing efficient preheating. <P>SOLUTION: A stack 1 is constructed by connecting a plurality of generating cells 5 in which a fuel electrode layer 3 is formed on one side of an electrolyte layer 2 and an oxidant electrode layer 4 is formed on another side. By housing this stack 1 in a box body 20, a fuel cell module 10 is constructed. Preheating cavities 15, 16 which become passages of reaction gas (fuel gas, oxidizer gas) is formed inside the box body 20 so as to surround the stack 1, and by receiving the radiation heat from the fuel cell, the gas flowing in the cavity is preheated. Thereby, the heat radiated from the fuel cell is efficiently utilized as preheating energy of the gas, and sufficient preheating can be performed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell, and more particularly, to a mechanism for preheating a reaction gas (fuel gas, oxidizing gas) supplied to a power generation cell.
[0002]
[Prior art]
As the fuel cell, a solid oxide fuel cell (SOFC) is being developed as a third-generation fuel cell for power generation. Three types of solid oxide fuel cells, a cylindrical type, a monolith type, and a flat plate type, have been proposed. In each case, a solid electrolyte composed of an oxide ion conductor is provided with an air electrode (cathode) as an electrode and a fuel. It has a laminated structure sandwiched between a pole (anode). A large number of power generation cells composed of the stacked body are connected via an interconnector (separator) to form a stack, and a gas supply distributor is interposed if necessary. These stacks and distributors are housed in a box made of a heat insulating material, a heat-resistant metal, ceramics or the like to constitute a fuel cell module.
[0003]
In a solid oxide fuel cell, oxygen (air) is supplied to the air electrode side, and fuel gas (H ₂ , CO, CH _4, etc.) is supplied to the fuel electrode side. Both the air electrode and the fuel electrode are porous layers so that the gas can reach the interface with the solid electrolyte.
[0004]
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. The electrons are taken out as electricity to obtain an electromotive force.
[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 and the fuel electrode layer, which are electrodes, need to be made of a material having high electron conductivity. Since the air electrode material must be chemically stable in an oxidizing atmosphere at about 1000 ° C., a metal is inappropriate, and a perovskite-type oxide material having electron conductivity, specifically, LaMnO ₃ or LaCoO ₃ is used. ₃ or a solid solution obtained by substituting a part of La with Sr, Ca or the like is generally used. As a fuel electrode material, a metal such as Ni or Co, or a cermet such as Ni-YSZ or Co-YSZ is generally used.
[0007]
By the way, as described above, the electrochemical reaction in the power generation cell is performed in a high-temperature oxidizing atmosphere of about 1000 ° C. In order to activate the battery reaction at this time, oxygen (air) serving as a reaction gas is used. ) And the fuel gas must be preheated to a required temperature (for example, several hundred degrees Celsius).
[0008]
Conventionally, an air preheating tube or a fuel gas preheating tube is arranged around a box constituting a fuel cell module to preheat an externally introduced gas. These air preheating pipes and fuel gas preheating pipes have, for example, a double pipe structure, and air and fuel gas supplied from the outside are respectively introduced from the inner pipe side of the double pipe, and at the outer pipe side, By passing internal combustion gas discharged to the outside as exhaust gas, low temperature gas passing through the inner pipe is preheated (heat exchange) with high temperature exhaust gas.
The air preheated by the air preheating pipe is supplied to the air electrode side of each power generation cell via the oxidizing gas distributor, and the fuel gas preheated by the fuel gas preheating pipe is supplied to each power generation cell via the fuel gas distributor. It is supplied to the fuel electrode side.
[0009]
[Problems to be solved by the invention]
However, the air preheating pipe and the fuel gas preheating pipe are not sufficiently heat-exchanged in the double-pipe heat exchanger described above, and the heat in the exhaust gas is efficiently absorbed to preheat the gas in the pipe to a high temperature. It was difficult to do. In addition, these double-tube preheating tubes are structurally complicated because they are usually buried in a heat insulating material surrounding the inner periphery of the casing.
[0010]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and uses heat radiated from a stack positively for preheating of a gas, and at the same time, sufficiently secures a preheating area of a gas to perform efficient preheating. It is an object of the present invention to provide a fuel cell having a mechanism.
[0011]
[Means for Solving the Problems]
That is, according to the present invention, a fuel electrode layer is formed on one of the electrolyte layers, and a plurality of power generation cells each having an oxidant electrode layer formed on the other are connected to form a stack. The fuel cell module accommodates the fuel cell module and supplies a gas for reaction to the fuel electrode layer and the oxidant electrode layer from the outside. In the fuel cell, the gas is contained inside the box so as to surround the stack. It is characterized by having a mechanism for forming a cavity serving as a flow path and preheating gas flowing into the cavity by radiant heat from the fuel cell.
In this configuration, since the heat radiated from the fuel cell is used as the preheating energy of the reaction gas (fuel gas, oxidizing gas), sufficient preheating can be performed. Further, the preheating mechanism is simplified as compared with the conventional double pipe structure.
[0012]
According to a second aspect of the present invention, in the fuel cell according to the first aspect, the cavity is formed in one or more layers in an outer circumferential direction of the box, and the gas is formed in an outer circumferential direction. It is characterized by having a structure that is introduced from the layer and flows toward the inner layer.
In this configuration, in the outer peripheral layer, the external side of the fuel cell module can be cooled by heat exchange with the introduced gas, and is preheated by radiant heat from the stack toward the inner layer. In addition, by making the cavities multilayer, the preheating area of the gas (that is, the preheating section) can be increased, and thus sufficient preheating can be performed.
[0013]
According to a third aspect of the present invention, in the fuel cell according to the second aspect, the thickness of the cavity of the outer peripheral layer is set to 30 mm or less.
In this configuration, the linear velocity of the introduced gas flowing in the outermost cavity can be increased, the cooling effect on the outer side of the fuel cell module can be improved, and the heat of the inner layer can be dissipated to the outer side. And the inner layer side can be kept at a high temperature.
[0014]
According to a fourth aspect of the present invention, in the fuel cell according to the third aspect, the thickness of the cavity of the inner layer is twice or more the thickness of the cavity of the outer peripheral layer. I have.
In this configuration, the introduced gas is sufficiently preheated by radiant heat in order to maintain a low linear velocity of the introduced gas flowing in the cavity of the inner layer.
[0015]
According to a fifth aspect of the present invention, in the fuel cell according to any one of the first to fourth aspects, the wall surface of the cavity is subjected to Ag plating by Ni base plating.
For example, by using a heat-resistant metal such as SUS as a wall material for forming a cavity and applying Ag plating to the surface thereof, excellent corrosion resistance (oxidation resistance) is obtained in a high-temperature oxidizing atmosphere, and the life of the preheating mechanism is improved. it can.
[0016]
According to a sixth aspect of the present invention, in the fuel cell according to any one of the first to fifth aspects, a heat insulating layer is provided between the hollow layers. In this configuration, since the heat of the inner layer side can be maintained at a high temperature without being released to the outer layer side, the internal heat energy can be efficiently used and sufficient preheating can be performed.
[0017]
According to a seventh aspect of the present invention, in the fuel cell according to any one of the first to sixth aspects, an exhaust pipe for discharging exhaust gas is installed in the cavity located inside. It is characterized by doing.
In this configuration, since the inside of the cavity can be heated by the radiation heat from the stack and the heat of the exhaust gas, sufficient preheating can be performed. In particular, it is more effective when applied to a cavity for oxidant gas into which cool air flows.
[0018]
According to an eighth aspect of the present invention, in the fuel cell according to any one of the first to seventh aspects, a fuel gas cavity supplied to the fuel electrode layer and a fuel gas supplied to the oxidant electrode layer are provided. And a cavity for the oxidizing gas.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0020]
FIG. 1 shows a first embodiment of a fuel cell module (flat stack type solid oxide fuel cell) to which the present invention is applied.
In a fuel cell module 10 shown in FIG. 1, a fuel electrode layer 3 is arranged on one surface of a solid electrolyte layer 2 and an oxidant electrode layer 4 (air electrode layer) is arranged on the other surface to constitute a power generation cell 5, The stack 1 has a cylindrical configuration in which a plurality of the power generation cells 5 and separators 8 described later are alternately stacked.
[0021]
The separator 8 has a function of supplying a reaction gas to each of the power generation cells 5 at the same time as electrically connecting the power generation cells, and supplying the fuel gas (H ₂ ) from the outer peripheral surface of the separator 8. A fuel passage 6 for introducing and ejecting from the central portion on the fuel electrode layer side; and an oxidizing agent passage 7 for introducing oxidizing gas (air) from the outer peripheral surface of the separator 8 and ejecting from the central portion on the oxidizing electrode layer side. Respectively.
[0022]
On one side of the stack 1, a fuel gas distributor 13 for distributing fuel gas introduced from the outside through the fuel gas connection pipe 11 into the fuel passage 6 of each separator 8 is provided. An oxidizing gas distributor 14 that distributes an oxidizing gas from the outside to the oxidizing passage 7 through the oxidizing gas connecting pipe 12 is provided upright along the stacking direction of the power generation cells 5.
[0023]
The fuel cell module 10 is configured by housing the stack 1 and the distributors 13 and 14 in a box 20 made of a heat-resistant metal (for example, SUS). Further, at the upper and lower ends of the box 20, positive and negative terminals 18 and 19 drawn out from the separators 8, 8 provided at the extreme end of the stack 1 are provided so as to face each other. At the same time, an exhaust pipe 17 protrudes from an upper portion of the box 20, and a reaction gas (exhaust gas) generated by a battery reaction is discharged from an exhaust port 17 a of the exhaust pipe 17 to the outside. .
[0024]
By the way, in the fuel cell module 10 having the above configuration, the gas flow path is provided by providing a partition wall 9a having a heat-resistant metal plate as a base material along the inner wall of the SUS box 20 and in the outer peripheral direction. Is formed. In the present embodiment, the partition walls 9a are provided twice at predetermined intervals to form a two-layer cavity, and further, a partition wall 9b is provided in the vicinity of the center in the vertical direction in the horizontal direction to form the preheating cavity. The upper and lower oxidant gas preheating cavities 15 and the lower fuel gas preheating cavities 16 which are divided into upper and lower parts and which are separated in an airtight manner form a mechanism for preheating a reaction gas introduced from the outside. Make up.
[0025]
The partition walls 9a and the partition walls 9b are made of, for example, a SUS plate having excellent heat resistance and corrosion resistance as a base material, and are coated with Ni plating on their surfaces so as to obtain excellent corrosion resistance (oxidation resistance) in a high-temperature oxidizing atmosphere. Ag plating as a base is applied. Thereby, the life of the preheating mechanism is extended.
[0026]
In the oxidizing gas preheating cavity 15, the outer layer and the inner layer forming the preheating cavity are communicated with each other by the through hole 21 provided in the outer partition wall 9 a, and the oxidizing gas supplied from the oxidizing gas supply port 23 is provided. The gas (air) is supplied to the oxidizing gas distributor 14 through the oxidizing gas supply pipe 25 while flowing from the outer layer toward the inner layer.
On the other hand, in the fuel gas preheating cavity 16, the outer layer and the inner layer of the preheating cavity communicate with each other by the through holes 22 provided in the outer partition wall 9 a, and the fuel gas (H ₂ ) introduced from the fuel gas supply port 24 flows. The fuel gas is supplied to the fuel gas distributor 13 through the fuel gas supply pipe 26 while flowing from the outer layer to the inner layer.
[0027]
In the fuel cell module 10 having the above configuration, the internal temperature of the cell is maintained at a high temperature of 900 to 1000 ° C. for the battery reaction (power generation) in the stack 1, and thus the radiant heat is received and the fuel cell module 10 is provided in the casing. The insides of the fuel gas preheating cavity 16 and the oxidizing gas preheating cavity 15 are also high in temperature.
[0028]
Under such circumstances, the low-temperature fuel gas (H ₂ ) introduced into the fuel gas preheating cavity 16 from the fuel gas supply port 24 flows through the outer layer portion toward the inner layer portion in the direction of the arrow, and flows therethrough. In the process, the gas is supplied to the fuel gas distributor 13 through the fuel gas supply pipe 26 in the inner layer while being heated (preheated) to a predetermined temperature by the high temperature atmosphere in the cavity.
The preheating gas is once filled in the fuel gas distributor 13 and distributed to each of the plurality of fuel gas connection pipes 11, and is discharged from each connection pipe 11 through the fuel passage 6 of the separator 8 from the center thereof. Is supplied to the fuel electrode layer 3 of each power generation cell 5. Then, the water vapor generated by the electrode reaction and a small amount of excess fuel (unreacted gas) are discharged from the outer peripheral portion of the stack 1 into the casing.
[0029]
On the other hand, the low-temperature oxidizing gas (air) introduced into the oxidizing gas preheating cavity 15 from the oxidizing gas supply port 23 flows toward the inner layer portion through the outer layer portion in the direction of the arrow, and in the flowing process, the inside of the hollow portion is formed. After being heated (preheated) to a predetermined temperature by the high-temperature atmosphere, the gas is supplied to the oxidizing gas distributor 14 through the oxidizing gas supply pipe 25 in the inner layer portion.
The preheated air is once filled in the oxidizing gas distributor 14 and distributed to the plurality of oxidizing gas connecting pipes 12, and from each of the connecting pipes 12 via the oxidizing passage 7 of the separator 8 to the central portion thereof. And is supplied to the oxidant electrode layer 4 of each power generation cell 5.
[0030]
Oxygen ions are formed in the oxidant electrode layer 4 and diffuse inside the solid electrolyte to reach the fuel electrode layer 3 and react with the fuel gas. Due to this battery reaction, an electromotive force is generated in the power generation cell 5 (that is, the stack 1), and necessary power is taken out from the positive terminal 18 and the negative terminal 19.
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 ) at that time Is discharged out of the battery together with the water vapor (H ₂ O) through the exhaust pipe 17 on the upper part of the box.
[0031]
As described above, since the present invention uses the radiant heat generated by the power generation of the stack 1 as the preheating energy of the fuel gas and the oxidizing gas, a sufficient preheating mechanism is provided in comparison with the conventional preheating mechanism using only the heat of the exhaust gas. Can be performed, and the battery reaction can be activated to improve the power generation efficiency. In addition, the preheating mechanism can be simplified as compared with the conventional double pipe structure.
[0032]
In addition, since the preheating cavity 16 for fuel gas and the preheating cavity 15 for oxidizing gas have a two-layer structure, a sufficient preheating section for gas can be secured. In particular, in the preheating cavity having the multilayer structure, the outer layer portion performs a cooling function of the external portion of the fuel cell module by heat exchange with a low-temperature gas introduced from the outside, and the preheating is sufficiently performed in a high temperature atmosphere in the inner layer portion. Will be.
[0033]
Further, in the present embodiment, in the preheating mechanism having the above-described configuration, the thickness of the preheating cavities 15 and 16 of the outer layer is reduced to 30 mm or less, and the thickness of the preheating cavities 15 and 16 of the inner layer is More than twice as wide. By narrowing the outer layer side, the linear velocity of the introduced gas flowing in the cavity can be increased, the cooling effect on the outer side of the fuel cell module can be improved, and the heat on the inner layer can be radiated to the outer side. And the inner layer side can be maintained at a high temperature. The thickness of the preheating cavity in the outer peripheral layer depends on the output scale of the fuel cell, and the thickness increases as the size increases. Conversely, a small machine having an output of about 1 kW preferably has a thickness of about 1 mm.
On the other hand, by making the thickness of the preheating cavities 15 and 16 of the inner layer wider than that of the outer peripheral layer, the linear velocity of the introduced gas flowing through the preheating cavity of the inner layer is reduced. It will be sufficiently preheated and supplied to each distributor.
[0034]
Next, FIG. 2 shows a second embodiment of the present invention. The stack 1 of the fuel cell module 10 has exactly the same configuration as that of the first embodiment shown in FIG. 1, but differs in the structure of the preheating mechanism.
[0035]
That is, in the present embodiment, in the preheating cavity 15 for the oxidizing gas and the preheating cavity 16 for the fuel gas, a vacuum portion 27 (vacuum heat insulating layer 27) is provided between the preheating cavities located outside the preheating cavities. The structure is such that heat conduction between adjacent layers (in the case of a two-layer structure, heat conduction from the inner layer to the outer layer) is suppressed.
In the present embodiment, a cavity is formed by the partition walls 9c, 9c having a double structure provided with a predetermined gap, and the inside thereof is evacuated to form a heat insulating layer. In this case, as in the case of the partition walls 9a and the partition walls 9b, the base material is made of SUS, and the surface thereof is plated with Ag with Ni plating as a base. The vacuum heat insulating layer 27 does not allow the heat on the inner layer side to escape to the outer layer side, so that the preheating cavities 15 and 16 can always be kept at a high temperature, and the radiant heat of the fuel cell can be used efficiently.
[0036]
Next, FIG. 3 shows a third embodiment of the present invention. Also in this embodiment, the configuration of the stack 1 is completely the same as the embodiment shown in FIGS. 1 and 2, but the structure of the preheating mechanism is different.
[0037]
That is, in the present embodiment, in the preheating cavity 15 for the oxidizing gas, an exhaust pipe 17 for discharging exhaust gas is installed inside the preheating cavity located inside, and the inside of the cavity heated by radiant heat from the fuel cell is installed. Is further heated by the heat of the exhaust gas. The exhaust port 17a of the exhaust pipe 17 is located at the inner layer end of the oxidizing gas preheating cavity 15, and the exhaust pipe 17 protrudes from the box 20 through the outer layer from the other end of the inner layer. As a result, it covers almost the entire inner layer of the oxidizing gas preheating cavity 15. The hot exhaust gas inside the module exchanges heat with the gas in the inner layer while passing through the exhaust pipe 17.
As a result, the gas can be preheated more reliably, and the heat of the exhaust gas discharged to the outside can be used as preheating energy, so that the energy efficiency of the fuel cell can be further improved.
[0038]
The exhaust pipe 17 can be installed in the fuel gas preheating cavity 16 together with the oxidizing gas preheating cavity 15, but in general, the oxidizing gas (air) is used not only as a chemical reaction gas but also as a module. It is also used for cooling, and since there is a tendency that a large amount of compressed air is supplied from a compressor, a blower or the like installed outside (not shown), the preheating cavity 15 for the oxidizing gas into which such cool air is introduced is used. Installation is more effective.
[0039]
In the above 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 an electric power is generated by an electrode reaction between a fuel gas and an oxidizing gas. Any type of 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 cell using an ion exchange membrane as an electrolyte (PEFC) and the like can of course be applied.
[0040]
Further, the preheating cavities 15 and 16 each serving as a preheating mechanism have a two-layer structure. However, the present invention is not limited to this. The number of layers may be one or two or more. The preheating cavity may be configured so that a suitable preheating temperature is appropriately obtained according to the gas or the like.
[0041]
【The invention's effect】
As described above, according to the present invention, since the cavity serving as the flow path of the reaction gas is formed inside the box, the fuel cell is used as the preheating energy of the reaction gas (fuel gas, oxidizing gas). The heat radiated from the air can be efficiently used, and sufficient preheating can be performed. Further, the preheating section of the gas can be made longer than in the conventional double pipe structure, and the preheating mechanism can be simplified.
[0042]
In addition, since the wall surface of the cavity constituting the preheating mechanism is plated with Ag by Ni base plating, excellent corrosion resistance (oxidation resistance) is obtained in a high-temperature oxidizing atmosphere inside the fuel cell module, and the life of the preheating mechanism is extended. Can be improved.
[Brief description of the drawings]
FIG. 1 is a sectional view showing the internal structure of a fuel cell module according to a first embodiment of the present invention.
FIG. 2 is a sectional view showing the internal structure of a fuel cell module according to a second embodiment of the present invention.
FIG. 3 is a sectional view showing the internal structure of a fuel cell module according to a third embodiment of the present invention.
[Explanation of symbols]
1 stack 2 electrolyte layer (solid electrolyte layer)
REFERENCE SIGNS LIST 3 fuel electrode layer 4 oxidant electrode layer 5 power generation cell 10 fuel cell module 15 oxidant gas preheating cavity 16 fuel gas preheating cavity 17 exhaust pipe 20 box 27 heat insulation layer (vacuum heat insulation layer)

Claims (8)

A fuel electrode layer is formed on one of the electrolyte layers, and a plurality of power generation cells each having an oxidant electrode layer formed on the other are connected to form a stack, and the stack is housed in a box to form a fuel cell module. In a fuel cell for supplying a reaction gas to each of the fuel electrode layer and the oxidant electrode layer,
A fuel having a mechanism for forming a cavity serving as a flow path of the gas inside the box so as to surround the stack, and preheating a gas flowing into the cavity by radiant heat from a fuel cell. battery. The cavity is formed in one or more layers in the outer peripheral direction of the box, and has a structure in which the gas is introduced from the outer peripheral layer and flows toward the inner layer. The fuel cell according to claim 1, wherein 3. The fuel cell according to claim 2, wherein the thickness of the cavity of the outer peripheral layer is set to 30 mm or less. 4. The fuel cell according to claim 3, wherein the thickness of the cavity of the inner layer is twice or more the thickness of the cavity of the outer peripheral layer. The fuel cell according to any one of claims 1 to 4, wherein the wall surface of the cavity is plated with Ag by Ni base plating. The fuel cell according to any one of claims 1 to 5, wherein a heat insulating layer is provided between layers of the cavity. The fuel cell according to any one of claims 1 to 6, wherein an exhaust pipe for exhausting exhaust gas is provided in the cavity located inside. The fuel according to any one of claims 1 to 7, further comprising a cavity for a fuel gas supplied to the fuel electrode layer and a cavity for an oxidant gas supplied to the oxidant electrode layer. battery.

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