JP4513281B2 - Fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell, and more particularly to a preheating mechanism for a reaction gas (fuel gas, oxidant 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 have been proposed: a cylindrical type, a monolith type, and a flat plate type, all of which include an air electrode (cathode) that uses a solid electrolyte made of an oxide ion conductor as an electrode and a fuel. It has a laminated structure sandwiched between the electrode (anode). A large number of power generation cells made of this laminate are connected via an interconnector (separator) to form a stack, and a gas supply distributor is interposed as necessary. These stacks and distributors are housed in a box made of heat insulating material, heat-resistant metal, ceramics, or the like to constitute a fuel cell module.
[0003]
In the 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. The air electrode and the fuel electrode are both porous layers so that the gas can reach the interface with the solid electrolyte.
[0004]
Oxygen supplied to the air electrode side passes through the pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte layer. At this part, it receives electrons from the air electrode and converts them into oxide ions (O ²⁻ ). Ionized. The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode. Oxide ions that have reached the vicinity of the interface with the fuel electrode react with the fuel gas at this portion to generate reaction products (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 moving medium for oxide ions and at the same time functions as a partition for preventing direct contact between the fuel gas and air, and thus has a dense structure that is impermeable to gas. This solid electrolyte layer should have a high oxide ion conductivity, be chemically stable under conditions from the oxidizing atmosphere on the air electrode side to the reducing atmosphere on the fuel electrode side, and be made of a material that is resistant to thermal shock. There is generally used stabilized zirconia (YSZ) to which yttria is added as a material satisfying such requirements.
[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 around 1000 ° C., the metal is unsuitable, and a perovskite oxide material having electron conductivity, specifically LaMnO ₃ or LaCoO ₃ or a solid solution in which a part of La is substituted with Sr, Ca or the like is generally used. Further, as the fuel electrode material, metals such as Ni and Co, or cermets such as Ni—YSZ and Co—YSZ are 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 activated. ) And the fuel gas must be preheated to a required temperature (for example, several hundred degrees C).
[0008]
Conventionally, an air preheating pipe and a fuel gas preheating pipe are arranged around a box constituting the fuel cell module to preheat the introduced gas from the outside. These air preheating pipes and fuel gas preheating pipes have, for example, a double pipe structure and introduce air and fuel gas supplied from the outside from the inner pipe side of the double pipes respectively, By passing the internal combustion gas discharged to the outside as exhaust gas, the low temperature gas passing through the inner pipe is preheated (heat exchange) with the 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 oxidant 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. 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 do not perform sufficient heat exchange in the double pipe structure heat exchanger as described above, and efficiently absorb the heat of the exhaust gas to preheat the gas in the pipe to a high temperature. It was difficult to do. In addition, these double-pipe preheating tubes are usually structurally complicated because they are usually embedded in a heat insulating material that encloses the inner periphery of the box.
[0010]
The present invention has been made in view of the above-described conventional problems, and preheats which can efficiently use the heat radiated from the stack for preheating the gas and ensure a sufficient gas preheating area. It aims at providing the fuel cell provided with the mechanism.
[0011]
[Means for Solving the Problems]
That is, according to the present invention, a stack is formed by connecting a plurality of power generation cells each having a fuel electrode layer formed on one electrolyte layer and an oxidant electrode layer formed on the other, and the stack is formed in a box. housing to constitute a fuel cell module, the fuel cell for supplying a gas for each reaction to the externally fuel electrode layer and the oxidant electrode layer, to surround the stack, the interior of the box-body, the the fuel gas and oxidant gas cavity and the cavity of the oxidizer gas supplied to the oxidant electrode layer for a fuel gas supplied to the fuel electrode layer is formed, to flow into the cavity by the radiation heat from the stack have a mechanism for preheating the, and cavities and cavities of the oxidizer gas, together with the formed two or more layers along the inner wall of each of the box-body, the fuel gas and oxidizer gas periphery for the fuel gas layer Ri is introduced, it is characterized by having a structure that flows toward the inner layer.
In this configuration, since the heat radiated from the fuel cell is used as the preheating energy of the fuel gas and the oxidant gas , sufficient preheating can be performed. Further, the preheating mechanism is simplified as compared with the conventional double pipe structure.
Further, since two or more layers of the cavity for the fuel gas and the cavity for the oxidant gas are formed along the inner wall of the box, the preheating area (that is, the preheating section) of the fuel gas and the oxidant gas is formed. ) Can be increased, so that more sufficient preheating can be performed.
In addition, in this configuration, the outer side of the outer peripheral layer can be cooled by heat exchange with the fuel gas and the oxidant gas, and is preheated by the radiant heat from the stack toward the inner layer. The
[0013]
Further, according to a second aspect of the present invention, in the fuel cell according to the first aspect , the thickness of the cavity of the outer peripheral layer is within 30 mm.
In this configuration, the linear velocity of the introduced gas flowing through the cavity of the outermost layer 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 side can be diffused to the outer side. The inner layer side can be kept at a high temperature.
[0014]
According to a third aspect of the present invention, in the fuel cell according to the first or second aspect , the thickness of the cavity of the inner layer is at least twice the thickness of the cavity of the outer peripheral layer. It is characterized by that.
In this configuration, since the linear velocity of the introduced gas flowing through the cavity of the inner layer is kept low, the introduced gas is sufficiently preheated by radiant heat.
[0015]
According to a fourth aspect of the present invention, in the fuel cell according to any one of the first to third aspects, the hollow wall surface is subjected to Ag plating by Ni base plating.
For example, SUS or other heat-resistant metal is used as the wall material to form the cavity, and Ag plating is applied to the surface to provide excellent corrosion resistance (oxidation resistance) in a high-temperature oxidizing atmosphere, improving the life of the preheating mechanism it can.
[0016]
The present invention according to claim 5 is characterized in that in the fuel cell according to any one of claims 1 to 4 , a heat insulating layer is provided between the layers of the cavities.
In this configuration, the heat on the inner layer side can be kept at a high temperature without escaping to the outer layer side, so that the internal heat energy can be efficiently utilized and sufficient preheating can be performed.
[0017]
According to a sixth aspect of the present invention, in the fuel cell according to any one of the first to fifth aspects, an exhaust pipe for exhausting exhaust gas is installed in the cavity located inside. It is characterized by that.
In this configuration, since the inside of the cavity can be heated by the radiant heat from the stack and the heat of the exhaust gas, sufficient preheating can be performed. In particular, the present invention is more effective when applied to an oxidant gas cavity into which cold air flows.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
[0020]
FIG. 1 shows a first embodiment of a fuel cell module (flat plate solid oxide fuel cell) to which the present invention is applied.
A fuel cell module 10 shown in FIG. 1 includes a fuel electrode layer 3 on one surface of a solid electrolyte layer 2 and an oxidant electrode layer 4 (air electrode layer) on the other surface to form a power generation cell 5. A stack 1 is formed in which a plurality of power generation cells 5 and separators 8 to be described later are alternately stacked to form a cylindrical shape.
[0021]
The separator 8 has a function of supplying a reaction gas to each power generation cell 5 at the same time electrically connecting between the power generation cells, a fuel gas (H ₂₎ from the outer peripheral surface of the separator 8 A fuel passage 6 that is introduced and ejected from the central portion on the fuel electrode layer side; an oxidant passage 7 that introduces oxidant gas (air) from the outer peripheral surface of the separator 8 and ejects the gas from the central portion on the oxidant electrode layer side; Respectively.
[0022]
A fuel gas distributor 13 for distributing fuel gas introduced from the outside through the fuel gas connection pipe 11 to the fuel passage 6 of each separator 8 is provided on one side of the stack 1, and each separator 8 is provided on the other side. The oxidant gas distributors 14 for distributing the oxidant gas from the outside through the oxidant gas connection pipe 12 are erected along the stacking direction of the power generation cells 5.
[0023]
The stack 1, the distributors 13 and 14 and the like are accommodated in a box 20 made of a heat-resistant metal (for example, made of SUS) to constitute a fuel cell module 10.
Further, at the upper and lower ends of the box 20, a positive terminal 18 and a negative terminal 19 drawn out from the separators 8, 8 disposed at the endmost portion of the stack 1 are provided so as to face each other. At the same time, an exhaust pipe 17 protrudes from the upper portion of the box 20, and a reaction gas (exhaust gas) generated by a battery reaction is exhausted from the exhaust port 17a of the exhaust pipe 17 to the outside. .
[0024]
By the way, in the fuel cell module 10 having the above-described configuration, a gas flow path is provided by providing a partition wall 9a using a heat-resistant metal plate as a base material along the inner wall of the SUS box 20 and toward the outer peripheral direction. A preheating cavity is formed. In the present embodiment, the partition walls 9a are doubled at a predetermined interval to form a two-layered cavity, and further, a partition wall 9b is provided in the horizontal direction near the center in the vertical direction to provide the preheating cavity. A reaction gas preheating mechanism introduced from outside is divided into an upper part oxidant gas preheating cavity 15 and a lower part fuel gas preheating cavity 16 which are divided into upper and lower parts and separated into airtight states. It is composed.
[0025]
The partition wall 9a and the partition wall 9b are made of, for example, a SUS plate having excellent heat resistance and corrosion resistance as a base material, and Ni plating is provided on the surface so that excellent corrosion resistance (oxidation resistance) can be obtained in a high temperature oxidizing atmosphere. Ag plating as a base is applied. Thereby, the lifetime improvement of the preheating mechanism is achieved.
[0026]
In the oxidant gas preheating cavity 15, an outer layer and an inner layer that form a preheating cavity are communicated with each other through a through hole 21 provided in the outer partition wall 9 a, and an oxidant introduced from an oxidant gas supply port 23. Gas (air) is supplied to the oxidant gas distributor 14 through the oxidant gas supply pipe 25 while flowing from the outer layer part toward the inner layer part.
On the other hand, in the preheating cavity 16 for fuel gas, the outer layer and the inner layer of the preheating cavity are communicated with each other through the through hole 22 provided in the outer partition wall 9a, and the fuel gas (H ₂ ) introduced from the fuel gas supply port 24 is communicated. The fuel gas is supplied to the fuel gas distributor 13 through the fuel gas supply pipe 26 while flowing from the outer layer portion toward the inner layer portion.
[0027]
In the fuel cell module 10 having the above-described 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, so that the radiant heat is received and provided in the box. The insides of the fuel gas preheating cavity 16 and the oxidant gas preheating cavity 15 are also hot.
[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 circulates in the direction of the arrow toward the inner layer portion through the outer layer portion, and the distribution thereof. In the process, the fuel 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 preheated 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 ejected from the center of each of the connection pipes 11 through the fuel passage 6 of the separator 8. , And supplied to the fuel electrode layer 3 of each power generation cell 5. And the water vapor | steam produced | generated by electrode reaction and a small amount of excess fuel (unreacted gas) are discharged | emitted from the outer peripheral part of the stack 1 in a box.
[0029]
On the other hand, the low-temperature oxidant gas (air) introduced into the oxidant gas preheating cavity 15 from the oxidant gas supply port 23 flows in the direction of the arrow through the outer layer part toward the inner layer part, After being heated (pre-heated) to a predetermined temperature in the high temperature atmosphere, it is supplied to the oxidant gas distributor 14 through the oxidant gas supply pipe 25 in the inner layer portion.
The preheated air is once filled in the oxidant gas distributor 14 and distributed to each of the plurality of oxidant gas connection pipes 12, and the central portion of each of the preheated air passes through the oxidant passages 7 of the separators 8. And is supplied to the oxidant electrode layer 4 of each power generation cell 5.
[0030]
In the oxidant electrode layer 4, oxygen ions are formed, diffuse inside the solid electrolyte, reach the fuel electrode layer 3, and react with the fuel gas. By 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 the 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 water vapor (H ₂ O) through the exhaust pipe 17 at the top of the box.
[0031]
As described above, since the present invention uses the radiant heat generated by the power generation of the stack 1 for the preheating energy of the fuel gas and the oxidant gas, the preheating is sufficient as compared with the conventional preheating mechanism using only the heat of the exhaust gas. The battery reaction can be activated and the power generation efficiency can be improved. In addition, the preheating mechanism can be simplified as compared with the conventional double tube structure.
[0032]
In addition, by providing the fuel gas preheating cavity 16 and the oxidant gas preheating cavity 15 with a two-layer structure, a sufficient gas preheating section can be secured. In particular, in a preheat cavity having a multi-layer structure, the outer layer portion performs a cooling function of the outer appearance portion of the fuel cell module by heat exchange with a low-temperature gas introduced from the outside, and sufficient preheating is performed in a high temperature atmosphere in the inner layer portion. It will be.
[0033]
Further, in the present embodiment, in the preheating mechanism configured as described above, the thickness of the preheating cavities 15 and 16 in the outer peripheral layer is narrowed to within 30 mm, and the thickness of the preheating cavities 15 and 16 in the inner layer is the same as that of the outer peripheral layer. 2 times more 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 side is diffused to the outer side. And the inner layer side can be kept 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. On the other hand, a thickness of about 1 mm is preferable for a small machine with an output of about 1 KW.
On the other hand, by making the thickness of the inner layer preheating cavities 15 and 16 wider than that of the outer peripheral layer, the linear velocity of the introduced gas flowing through the inner layer preheating cavities is reduced. It will be fully 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 the same configuration as that of the first embodiment shown in FIG. 1, but the structure of the preheating mechanism is different.
[0035]
That is, in the present embodiment, in the preheating cavity 15 for the oxidant 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. In this structure, 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 this embodiment, a cavity is formed by the double-structured partition walls 9c, 9c provided with a predetermined gap, and the inside is formed in a vacuum state to form a heat insulating layer. Also in this case, like the partition wall 9a and the partition wall 9b, the base material is made of SUS, and the surface thereof is subjected to Ag plating 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 exactly the same as that of the embodiment shown in FIGS. 1 and 2, but the structure of the preheating mechanism is different.
[0037]
That is, in this embodiment, in the preheating cavity 15 for the oxidant gas, an exhaust pipe 17 for exhaust gas exhaust is installed inside the preheating cavity located inside, and the inside of the cavity heated by the 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 oxidant gas preheating cavity 15. The exhaust pipe 17 projects from the box 20 through the outer layer from the other end of the inner layer. Thus, almost the entire inner layer portion of the preheating cavity 15 for the oxidant gas is covered. 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 preheating of the gas can be performed more reliably, and the heat of the exhaust gas released to the outside can be used as the 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 oxidant gas preheating cavity 15, but in general, the oxidant gas (air) is not only used as a chemical reaction gas but also in the module. It is also used for cooling, and a large amount of compressed air tends to be supplied from an external compressor (not shown), a blower or the like, so that the oxidant gas preheating cavity 15 into which such cold air is introduced is used. It is more effective to install.
[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 the power generation is performed by an electrode reaction between a fuel gas and an oxidant gas. The phosphoric acid fuel cell (PAFC) using phosphoric acid as an electrolyte, the molten carbonate fuel cell (MCFC) using molten carbonate as an electrolyte, or the solid polymer fuel cell using an ion exchange membrane as an electrolyte Of course, it can also be applied to (PEFC).
[0040]
Each of the preheating cavities 15 and 16 serving as a preheating mechanism has a two-layer structure. However, the present invention is not limited to this, and one layer or two or more layers may be used. What is necessary is just to comprise a preheating cavity so that suitable preheating temperature may be suitably obtained according to gas etc.
[0041]
【The invention's effect】
As described above, according to the present invention, since the forming cavity and the cavity of the oxidizer gas supplied to the oxidant electrode layer for a fuel gas supplied to the fuel electrode layer to the inside of a box body, wherein The heat radiated from the fuel cell can be efficiently used as the preheating energy of the fuel gas and the oxidant gas, and sufficient preheating can be performed. Moreover, preheating mechanism than the conventional double-tube structure is also simplified. Furthermore, since two or more layers of the cavity for the fuel gas and the cavity for the oxidant gas are formed along the inner wall of the box, the gas preheating area (that is, the preheating section) can be increased. Since it is possible, more sufficient preheating can be performed. In addition, since the fuel gas and the oxidant gas are introduced from the outer peripheral layer and flow toward the inner layer, the outer appearance of the fuel cell module is exchanged with the introduced gas in the outer peripheral layer. The sides can be cooled and preheated with radiant heat from the stack toward the inner layer.
[0042]
In addition, since the Ag wall is plated on the hollow wall that constitutes the preheating mechanism by Ni base plating, excellent corrosion resistance (oxidation resistance) can be obtained in a high temperature oxidizing atmosphere inside the fuel cell module, and the life of the preheating mechanism can be increased. It can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an internal structure of a fuel cell module according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view showing an internal structure of a fuel cell module according to a second embodiment of the present invention.
FIG. 3 is a cross-sectional view showing an 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)
3 Fuel electrode layer 4 Oxidant electrode layer 5 Power generation cell 10 Fuel cell module 15 Preheating cavity 16 for oxidant gas 17 Preheating cavity 17 for fuel gas Exhaust pipe 20 Box 27 Heat insulation layer (vacuum heat insulation layer)

Claims (6)

A stack is formed by connecting a plurality of power generation cells each having a fuel electrode layer formed on one of the electrolyte layers and an oxidant electrode layer formed on the other side, and the fuel cell module is configured by housing the stack in a box. In the fuel cell for supplying a reaction gas to each of the fuel electrode layer and the oxidant electrode layer,
A cavity for fuel gas to be supplied to the fuel electrode layer and a cavity for oxidant gas to be supplied to the oxidant electrode layer are formed inside the box so as to surround the stack , and radiation from the stack is formed. heat by have a mechanism for preheating the fuel gas and the oxidizing gas flowing into the cavity, and the cavity and the cavity of the oxidant gas for the fuel gas, two layers along an inner wall of each of the box-body A fuel cell having the structure as described above, wherein the fuel gas and the oxidant gas are introduced from the outer peripheral layer and circulate toward the inner layer . 2. The fuel cell according to claim 1, wherein the thickness of the cavity of the outer peripheral layer is within 30 mm . 3. The fuel cell according to claim 1 , wherein the thickness of the cavity of the inner layer is twice or more than the thickness of the cavity of the outer peripheral layer . The fuel cell according to any of claims 1 to 3, characterized in that subjected to Ag plating with Ni base plating on the wall of the cavity. The fuel cell according to any one of claims 1 to 4, wherein a heat insulating layer is provided between the hollow layers . The fuel cell according to any one of claims 1 to 5 , wherein an exhaust pipe for exhaust gas exhaust is installed in the cavity located inside .

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