JP2005203255A - Manifold structure of fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manifold structure of a fuel cell which can homogenize temperature distribution in the direction of laminated layers in a fuel cell stack. <P>SOLUTION: While the fuel cell stack 1 is constituted by laminating alternately power generation cells 5 composed of electrode layers installed on both faces of solid electrolyte layers and separators 8 having reaction gas passages 9, 10 inside, and in the fuel cell which is provided with manifolds 17, 18 for the reaction gas passage that is penetrated through the separator 8 in the thickness direction extending toward the direction of the laminated layers and in which reaction gas is supplied to each electrode layer through the gas passages 9, 10 inside the separator 8 through which the manifolds 17, 18 are communicated, gas introduction pipes 31 to 35 communicated with the prescribed separators 8 are arranged inside the manifolds 17, 18. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a manifold structure for a fuel cell having a structure in which power generation cells and separators are alternately stacked, and more particularly to a manifold structure that is preferable for making the temperature distribution in the stacking direction of a fuel cell stack uniform.

  Solid oxide fuel cells (SOFC) are being developed as third-generation fuel cells for power generation. Currently, three types of solid oxide fuel cells have been proposed: a cylindrical type, a monolith type, and a flat plate type, all of which have a solid electrolyte composed of an oxide ion conductor as an air electrode (cathode) from both sides. It has a laminated structure sandwiched between fuel electrodes (anodes). A fuel cell stack is configured by stacking a plurality of power generation cells composed of this laminate alternately with separators with a fuel electrode current collector and an air electrode current collector interposed therebetween.

As an example, the solid electrolyte layer is composed of stabilized zirconia (YSZ) or the like to which yttria is added, and the fuel electrode layer is composed of a metal such as Ni or Co or a cermet such as Ni-YSZ or Co-YSZ. The air electrode layer is made of LaMnO ₃ , LaCoO ₃ or the like, the fuel electrode current collector is made of a sponge-like porous sintered metal plate such as a Ni-based alloy, and the air electrode current collector is made of an Ag-based alloy or the like. And a separator made of stainless steel or the like.

In the solid oxide fuel cell, an oxidant gas (oxygen) is supplied to the air electrode side and a fuel gas (H ₂ , CO, CH _4, etc.) is supplied to the fuel electrode side as a reaction gas. The air electrode and the fuel electrode are both porous layers so that the gas can reach the interface with the solid electrolyte.
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, electrons are received from the air electrode and ionized to oxide ions (O ²⁻ ). Is done. 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. This electron can be taken out as an electromotive force in an external circuit of another route.

  By the way, the fuel cell includes a gas supply mechanism that distributes the reaction gas introduced from the outside to each of the stacked power generation cells, and an external manifold and an internal manifold are known as such a gas supply mechanism.

The external manifold has a structure in which a reaction gas introduction tube is extended outside the fuel cell stack in the stacking direction, and the tube and each separator communicate with each other through a connection tube. Although the external manifold is structurally simple, the fuel cell stack itself is enlarged, and a high gas sealing property is required for the connecting portion with the connecting pipe. Many internal manifolds are used that extend directly into the fuel stack.
In the case of the internal manifold, the reaction gas is supplied to the corresponding power generation cell through the gas passage of each separator while being distributed at the communication portion with the separator in the process of flowing in the stacking direction in the pipe. Such an internal manifold is disclosed in Patent Document 1 and Patent Document 2.
JP-A-5-307969 JP-A-6-196195

  By the way, in the conventional flat plate type fuel cell stack, the temperature distribution in the stacking direction has a tendency that the temperature in the vicinity of both ends of the fuel cell stack is extremely lower than that in the middle portion as shown by the solid line in FIG. This is because the Joule heat of the power generation cell is more easily dissipated at the end of the fuel cell stack than at the middle stage. A power generation cell having a low temperature has a lower power generation performance because an electrode reaction is not actively performed compared to a power generation cell having a high temperature.

  In a fuel cell stack configured by connecting a plurality of power generation cells in series, if the temperature distribution with both shoulders down in the stacking direction of the fuel cell stack occurs, the power generation performance of the entire fuel cell is the power generation performance of the low temperature part. Due to the limitation, there is a problem that efficient power generation cannot be performed.

  Conventionally, in order to uniformize the temperature distribution in the stacking direction in the fuel cell stack, in the case of an external manifold, measures such as introducing cold air from the central part of the manifold to lower the temperature of the middle stage part of the stack have also been taken. In the case of an internal manifold in which air must be introduced from the end of the manifold due to the structure, such a gas supply method has been difficult to realize.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a fuel cell manifold structure capable of uniforming the temperature distribution in the stacking direction in the fuel cell stack.

  That is, according to the present invention, a fuel cell stack is formed by alternately laminating a plurality of power generation cells configured by arranging electrode layers on both surfaces of a solid electrolyte layer and separators having a reaction gas passage inside. And a reaction gas introduction manifold that extends through the separator in the thickness direction and extends in the stacking direction, and supplies the reaction gas to each electrode layer through the gas passage of the separator that communicates with the manifold. In the fuel cell configured as described above, a gas introduction pipe communicating with a predetermined separator is disposed inside the manifold.

In an internal manifold in which a manifold mechanism is provided directly in a stacked fuel cell stack, a reaction gas (fuel gas, oxidant gas) is introduced from the end of the manifold and is distributed in the process of flowing through the pipe in the stacking direction. The gas flow paths are supplied to the corresponding power generation cells through the gas passages of the separators. Therefore, the upstream / downstream relationship of the reaction gas with respect to the separator is uniquely determined by the introduction position of the reaction gas in the manifold.
In this configuration, a gas introduction pipe is arranged inside the manifold and a multi-tube structure with an outer pipe (manifold itself) and an inner pipe (each gas introduction pipe) is used to directly supply the reaction gas to the desired separator. Therefore, the temperature distribution in the fuel cell stack can be made uniform. Of course, the reaction gas is introduced not only into the inner tube but also into the outer tube.

According to a second aspect of the present invention, there is provided the fuel cell manifold structure according to the first aspect, wherein the oxidant gas manifold is provided with a gas introduction pipe communicating with a separator at a middle stage of the fuel cell stack. It is characterized by introducing cold air into the gas introduction pipe.
In this configuration, since the power generation cells in the middle stage of the fuel cell stack having a relatively high temperature are cooled by the cold air supplied from the gas introduction pipe, the temperature distribution in the stacking direction in the fuel cell stack is made uniform and efficient. Power generation is possible.

According to a third aspect of the present invention, there is provided the fuel cell manifold structure according to the first or second aspect, wherein the oxidant gas manifold includes a separator at an end of the fuel cell stack. A gas introduction pipe that communicates is provided, and hot air is introduced into the gas introduction pipe.
In this configuration, in addition to the operation and effect of the second aspect, the temperature of the power generation cell at the end of the fuel cell stack having a relatively low temperature is raised by the introduction of warm air, so that the temperature distribution of the fuel cell stack is made more uniform. Can be

According to a fourth aspect of the present invention, there is provided the fuel cell manifold structure according to any one of the first to third aspects, wherein the fuel gas manifold communicates with a separator at an end of the fuel cell stack. A gas introduction pipe is disposed, and the fuel gas supply amount to the separator is larger than that of other separators.
In this configuration, in addition to the effect of uniforming the temperature distribution according to the configurations of claims 2 and 3, the power generation cells at the end of the fuel cell stack are electroded by the fuel gas flow rate above the average supplied from the gas introduction pipe. Since the reaction is activated, more efficient power generation can be performed.

According to a fifth aspect of the present invention, in the fuel cell manifold structure according to any one of the first to fourth aspects, a gas flow rate for adjusting a flow rate of the reaction gas in the introduction pipe. An adjustment mechanism is provided.
In this configuration, the temperature distribution can be made more uniform by adjusting the amount of reaction gas flowing through each introduction pipe.

  As described above, according to the present invention, a gas introduction pipe that communicates with a predetermined separator is disposed inside the manifold, cold air is supplied to the middle stage of the fuel cell stack, and hot air is supplied to both ends. Thus, the end portion of the fuel cell stack is heated by hot air, the middle stage portion is cooled by cold air, and the temperature distribution in the stacking direction is made uniform. Thereby, efficient power generation can be performed.

  In addition, since the flow rate of the fuel gas supplied to the power generation cells at both ends of the fuel cell stack is greater than that of other power generation cells, the power generation performance at the end of the fuel cell stack can be prevented from being degraded due to a temperature drop. As a result, more efficient power generation can be performed.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
FIG. 1 shows a configuration of a main part of a flat plate type solid oxide fuel cell, FIG. 2 shows a temperature distribution in the stacking direction of power generation cells in the fuel cell stack, and FIG. 3 shows a manifold used for the fuel cell of the present invention. The structure of the ring is shown.

  As shown in FIG. 1, a fuel cell stack 1 includes a power generation cell 5 configured by disposing a fuel electrode layer and an air electrode layer on both sides of a solid electrolyte layer, and a fuel electrode current collector disposed outside the fuel electrode layer. 6, an air electrode current collector 7 arranged outside the air electrode layer, and a separator 8 arranged outside each current collector 6, 7 constitute a single cell, and this single cell is insulated between A large number of the manifold rings 15 and 16 are stacked. In addition, each element which comprises a single cell can use the same physical property as the past.

  The separator 8 is composed of a square stainless steel plate having a thickness of about several millimeters with an Ag plating treatment for preventing oxidation on the surface, a fuel gas passage 9 through which fuel gas flows, an oxidant gas, and the like. An oxidant gas passage 10 through which (generally air) flows is formed. However, as shown in FIG. 1, only the fuel gas passage 9 is formed in the separator 8 located at the lowermost portion, and only the oxidant gas passage 10 is formed in the separator 8 located at the uppermost portion.

  One end (upstream side) of the fuel gas passage 9 communicates with a fuel gas introduction hole 13 provided on the left side of the separator 8, and the other end (downstream side) of the separator 8 faces the anode current collector 6. To the central gas discharge hole 11. One end (upstream side) of the oxidant gas passage 10 communicates with an oxidant gas introduction hole 14 provided on the right side of the separator 8, and the other end (downstream side) faces the air electrode current collector 7. It communicates with the gas discharge hole 12 in the central part of the separator. Only the oxidant gas introduction hole 14 is formed in the uppermost separator 8, and the oxidant gas introduction hole 14 is opened only on the lower side. The gas introduction holes 13 and 14 other than the uppermost part penetrate the separator 8 in the thickness direction.

  Further, gas supply pipes 24 and 25 for introducing reaction gas supplied from the outside are connected to the lowermost separator 8, and among these, the fuel gas supply pipe 25 to which fuel gas is supplied is An oxidant gas supply pipe 24 that communicates with the fuel gas introduction hole 13 and is supplied with oxidant gas communicates with the oxidant gas introduction hole 14.

  A fuel gas manifold ring 15 is disposed in the upper and lower openings of the fuel gas introduction hole 13, and an oxidant gas manifold ring 16 is disposed in the upper and lower openings of the oxidant gas introduction hole 14. The manifold rings 15 and 16 are connected in the vertical direction (stacking direction) via the gas introduction holes 13 and 14 of the separator 8 to form a fuel gas manifold 17 having a tubular shape. And an oxidant gas manifold 18.

  As shown in FIG. 3, the above-described manifold rings 15 and 16 include a ring-shaped glass layer 19 serving as an insulating / seal layer disposed in the middle portion, and a ring-shaped metal disposed on both surfaces of the glass layer 19. It is comprised by the layers 18 and 18 (stainless steel material).

  In the fuel cell stack 1 configured as described above, the fuel gas and the oxidant gas supplied from the outside via the fuel gas supply pipe 25 and the oxidant gas supply pipe 24 are respectively supplied from the separator 8 at the bottom of the stack to the fuel gas manifold 17. In the process of being introduced into the oxidant gas manifold 18 and flowing in the longitudinally extending manifold, each gas passage 9 of each separator 8 is distributed while being distributed from the gas introduction holes 13 and 14 of each layer (single cell). 10 is supplied to the electrode portion of each power generation cell 5 through 10.

That is, the fuel gas in the fuel gas manifold 17 is introduced into the fuel gas passage 9 from the fuel gas introduction hole 13 of each separator 8 and discharged from the fuel gas discharge hole 11 at the end of the passage to face the fuel electrode current collector. 6, passes through here while diffusing, and reaches the fuel electrode layer of the power generation cell 5.
On the other hand, the oxidant gas in the oxidant gas manifold 18 is introduced from the oxidant gas introduction hole 14 of each separator 8 into the oxidant gas passage 10 and discharged from the oxidant gas discharge hole 12 at the end of the passage to face each other. It is supplied to the air electrode current collector 7, passes through here while diffusing, and reaches the air electrode layer of the power generation cell 5.
Hereinafter, the electrochemical reaction in each single cell is as described in the section of the prior art, and the high-temperature exhaust gas generated by this electrochemical reaction is discharged from the single cell to the outside of the stack through a predetermined exhaust route. The

  By the way, in the present invention, as shown in FIG. 1, a stainless steel gas introduction pipe is further arranged in the vertical direction inside the oxidant gas manifold 18 and the fuel gas manifold 17 so as to form a manifold having a multi-tube structure. Is configured.

In this embodiment, three gas introduction pipes 31 to 33 are arranged inside the oxidant gas manifold 18, and two gas introduction pipes 34 and 35 are arranged inside the fuel gas manifold 17. It is arranged. Each gas introduction pipe is provided with a gas outlet 30 at the end, and the reaction gas introduced into the pipe is jetted toward the openings of the gas passages 9 and 10 facing from the gas outlet 30. It has become.
In the oxidant gas manifold 18, the gas injection port 30 of the gas introduction pipe 31 communicates with the oxidant gas introduction hole 14 of the separator 8 located at the lowermost part of the fuel cell stack 1, and the gas injection pipe 32 gas injection The outlet 30 communicates with the oxidant gas introduction hole 14 of the separator 8 located at the top of the stack, and the gas injection port 30 of the gas introduction pipe 33 further enters the oxidant gas introduction hole 14 of the separator 8 located at the middle stage of the stack. Each is arranged with a predetermined pipe length so as to communicate with each other, and hot air is introduced from the upstream side of the gas introduction pipes 31 and 32, and cold air is introduced from the upstream side of the gas introduction pipe 33. It has become.

  On the other hand, in the fuel gas manifold 17, the gas injection port 30 of the gas introduction pipe 34 communicates with the fuel gas introduction hole 13 of the separator 8 located at the bottom of the fuel cell stack, and the gas injection port 30 of the gas introduction pipe 32 Each is arranged with a predetermined pipe length so as to communicate with the fuel gas introduction hole 13 of the separator 8 located at the top of the stack, and the flow rate of the fuel gas supplied to these gas introduction pipes 34 and 35 is the fuel cell. The flow rate is set to be equal to or higher than the average gas flow rate supplied to the other separators 8 excluding both end portions and the middle step portion of the stack 1.

  As described above, a gas introduction pipe is arranged inside the manifold, and the gas flow is made to be a multiple flow path structure with the manifold itself serving as the outer pipe and each gas introduction pipe serving as the inner pipe. Can be directly supplied to a desired separator. Thereby, the temperature distribution in the stacking direction of the fuel cell stack 1 can be made uniform.

That is, during operation of the fuel cell, in the oxidant gas manifold 18, the temperature of the power generation cells at both ends of the stack, which is relatively low, is increased by the hot air from the gas introduction pipes 31 and 32, and the power generation at the middle stage of the stack is performed. The cell is cooled by cold air from the gas introduction pipe 33. Thereby, the temperature distribution in the stacking direction in the fuel cell stack 1 is made uniform. In this case, the reaction gas flowing in the outer pipe is supplied to the power generation cells 5 other than the both ends and the middle stage of the fuel cell stack 1.
As the warm air, cold air supplied from the outside is used which is heated by heat exchange with high-temperature exhaust heat by a heat exchange mechanism such as a preheating tube inside the fuel cell.

  On the other hand, in the fuel gas manifold 17, the electrode reaction of the power generation cells 5 at the both ends of the stack is more active than the electrode reaction of the power generation cells 5 in the other portions due to the fuel gas supplied from the gas introduction pipes 34, 35. In the power generation cell 5 at the end of the fuel cell stack 1, it is possible to prevent a decrease in power generation performance due to a temperature decrease, and in addition to the effect of uniforming the temperature distribution by the oxidant gas manifold 18 described above, more efficient It becomes possible to generate electricity.

  Further, as shown in FIG. 1, a flow rate adjustment valve 40 for each reaction gas is provided upstream of each gas introduction pipe 31 to 35 to individually adjust the flow rate of the reaction gas flowing through the gas introduction pipes 31 to 35. As a result, the temperature distribution can be made more uniform. In this case, it is preferable to automatically adjust the opening of each gas flow rate adjustment valve 40 by detecting the temperature difference in the stacking direction of the fuel cell stack 1.

FIG. 2 shows the temperature distribution in the stacking direction of the fuel cell stack 1, where the solid line is due to the conventional manifold, and the broken line is due to the manifold of the present invention shown in FIG.
As shown in FIG. 2, in the case of the conventional type, the temperature distribution has a characteristic that the middle part is high, but the high temperature part of the fuel cell stack is cooled and the low temperature part is heated as in the present invention. Thus, the temperature difference between the high temperature part and the low temperature part can be reduced as much as possible, and a substantially uniform temperature distribution can be obtained over the entire region in the stacking direction, thereby improving the efficiency of power generation. In addition, by reducing the temperature of the power generation cell in the high temperature area as shown by the broken line, damage to the power generation cell 5 such as peeling of the fuel electrode layer due to thermal stress can be prevented, and the durability (thermal cycle characteristics) of the fuel cell is improved. improves.

As described above, in the present embodiment, the case where the present invention is applied to both the fuel gas manifold 17 and the oxidant gas manifold 18 has been described. However, even if only the oxidant gas manifold 18 has a multi-tube structure, the temperature distribution. This is extremely effective for the equalization of power and the improvement of power generation efficiency.
Further, the gas introduction pipes 31 and 32 and the introduction pipes 34 and 35 communicating with the separator at the end of the fuel cell stack are each provided with gas outlets 30 at two locations, the upper end and the lower end corresponding to the separator. Of course, it is possible to share with other pipes.

1 is a cross-sectional view showing a configuration of a main part of a flat plate type solid oxide fuel cell to which the present invention is applied. The figure which shows the temperature distribution of the lamination direction of the electric power generation cell in a fuel cell stack. The manifold ring used for the fuel cell of this invention is shown, (a) is a perspective view, (b) is a side view.

Explanation of symbols

1 Fuel cell stack 5 Power generation cell 8 Separator 9, 10 Gas passage (fuel gas passage, oxidant gas passage)
17 Manifold for fuel gas 18 Manifold for oxidant gas 31-35 Gas introduction pipe 40 Gas flow rate adjusting mechanism (gas flow rate adjusting valve)

Claims (5)

A fuel cell stack is formed by alternately laminating a plurality of power generation cells configured with electrode layers on both sides of a solid electrolyte layer and separators having a reaction gas passage inside, and penetrates the separator in the thickness direction. In the fuel cell comprising a reaction gas introduction manifold extending in the stacking direction and configured to supply the reaction gas to each electrode layer through the gas passage of the separator communicated with the manifold,
A fuel cell manifold structure, wherein a gas introduction pipe communicating with a predetermined separator is disposed inside the manifold. 2. The fuel according to claim 1, wherein in the oxidant gas manifold, a gas introduction pipe communicating with a separator in a middle stage of the fuel cell stack is provided, and cold air is introduced into the gas introduction pipe. Battery manifold mechanism. 3. The oxidant gas manifold is provided with a gas introduction pipe communicating with a separator at an end of the fuel cell stack, and hot air is introduced into the gas introduction pipe. A fuel cell manifold structure according to any one of the above. 2. The fuel gas manifold includes a gas introduction pipe communicating with a separator at an end of the fuel cell stack, and the amount of fuel gas supplied to the separator is larger than that of other separators. A fuel cell manifold structure according to any one of claims 1 to 3. The fuel cell manifold structure according to any one of claims 1 to 4, wherein a gas flow rate adjusting mechanism for adjusting a flow rate of the reaction gas is provided in the gas introduction pipe.

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