JP5211621B2 - Fuel cell stack - Google Patents

Description

  The present invention relates to a fuel cell stack in which a plurality of power generation cells and separators arranged in the same plane are alternately stacked, and more particularly to temperature uniformity in the stacking direction of the fuel cell stack.

Conventionally, a power generation cell having a structure in which a solid electrolyte layer made of an oxide ion conductor is sandwiched from both sides by an air electrode layer and a fuel electrode layer has air (oxygen) in the air electrode layer and fuel gas (H _{2 in the} fuel electrode layer). , CO, CH ₄ ), it is known that a power generation reaction occurs between the electrodes and an electromotive force is obtained.

  By the way, in the power generation cell having the above configuration, the electromotive force per unit cell is as small as about 1 V at most. Therefore, normally, a large number of the power generation cells are stacked through a conductive member such as a separator or a current collector to form a stack. By doing so, a substantial battery output is obtained.

  However, in such a flat plate type fuel cell stack, there is a temperature difference between the power generation cells in the stacking direction, and the stack temperature is high in the middle stage of the stack as shown in FIG. It tends to be lower at the stack edge.

This is because the end of the fuel cell stack is more likely to dissipate the Joule heat of the power generation cells to the outside as compared to the middle stage, and in the case of a vertically installed fuel cell stack in which the stacking direction of the stack is vertical, Regarding the temperature of the stack end, the upper stage of the stack is heated by the rising high-temperature exhaust gas, so that the temperature of the upper end is high and the temperature of the lower end is low.
The power generation cell in the low temperature part has an inactive electrode reaction, and thus the internal resistance is large, and the power generation performance is lower than that in the power generation cell in the middle part of the stack, which is the high temperature part.

Thus, if temperature distribution occurs in the stacking direction of the fuel cell stack, the total power generation performance is limited by the power generation performance of the power generation cells located in the low-temperature part, so that efficient power generation cannot be performed. There was. This tendency becomes more prominent as the number of stacks in the stack increases.
In addition, the power generation cell in the high temperature part has good power generation performance, but the components such as the power generation cell and the separator are exposed to a higher temperature than in other parts, and thus there is a problem that they are easily deteriorated and damaged.

For example, Patent Document 1 is disclosed as a technique for equalizing the temperature in the stacking direction of the fuel cell stack. In Patent Document 1, heat release fins are provided in each separator in a stacked state, and the temperature distribution of the fuel cell stack is controlled by improving the thermal radiation of the separator (the stack temperature is lowered by heat dissipation). In the control of the thermal radiation by the heat radiating fins, it was not possible to raise the temperature at the lower end of the stack where the temperature was particularly low.
Therefore, even if the temperature distribution in the stack stacking direction is reduced to some extent by the above technique, the power generation performance of the power generation cell located at the lower end of the stack remains low, and thus the total power generation of the fuel cell stack The performance was never satisfactory.
JP 2004-273140 A

  The present invention has been made in view of the above problems, and an exhaust gas flow path is provided inside the fuel cell stack to distribute the exhaust gas discharged from the power generation cells in the stacking direction of the stack. It is an object of the present invention to provide a highly efficient fuel cell stack in which the temperature in the stack is made uniform so that the temperature in the stack stacking direction is made uniform and the power generation performance of the power generation cells located at the stack end is improved.

  That is, in the fuel cell stack according to claim 1, in the fuel cell stack in which a plurality of power generation cells are arranged in the same plane, and the plurality of power generation cells are stacked with a separator interposed therebetween, An exhaust gas flow path through which the exhaust gas after the power generation reaction flows in the stacking direction is provided, and the gas flow rate on one side in the stacking direction in the exhaust gas flow channel is greater than the gas flow rate on the other side in the stacking direction. It is characterized by.

  The invention according to claim 2 is the fuel cell stack according to claim 1, wherein the power generation cell has a sealless structure that discharges exhaust gas after power generation reaction from the outer periphery, and each separator A gas discharge hole penetrating in the stacking direction is provided in a portion corresponding to the portion surrounded by the plurality of power generation cells, and the exhaust gas flows in the stacking direction through the gas discharge hole.

Further, the invention according to claim 3 is the fuel cell stack according to claim 2, wherein the size of the gas discharge hole of the separator located at the other end in the stacking direction of the stack is set to the gas of the other separator. It is characterized by being made smaller than the discharge hole.
Thereby, in this exhaust gas flow path, the flow of the exhaust gas mainly toward the one side from the other side of the stacking direction of the stack can be generated.

  According to a fourth aspect of the present invention, there is provided the fuel cell stack according to the third aspect, wherein the opening degree of the gas discharge hole of the separator located at the other end in the stacking direction of the stack is adjusted. It is characterized by including a lid mechanism.

  Further, the invention according to claim 5 is the fuel cell stack according to any one of claims 1 to 4, wherein end plates are respectively provided at both ends of the stack, and one end in the stacking direction is provided. A gas discharge port for discharging the exhaust gas in the exhaust gas flow path out of the stack is provided on the end plate of the end portion.

According to the first to fifth aspects of the present invention, the exhaust gas flow path through which the exhaust gas after the power generation reaction flows in the stacking direction is provided inside the stack, and the gas flow rate to one side in the stacking direction of the exhaust gas flow path is set to the other side. Since the amount of gas flowing to the side is larger than that in the stack middle stage, the exhaust gas from the power generation cell circulates in the exhaust gas flow path, so that the heat dissipation of the power generation cell is improved and the stack middle stage The temperature of the stack can be lowered, and at the stack end where the temperature is low, the stack temperature rises due to the heat of the exhaust gas flowing in the stacking direction and the temperature distribution in the stack stacking direction is reduced (soaking). Can do.
In particular, in a vertically installed fuel cell stack, the temperature at the lower end of the stack having the lowest temperature is made higher than the stack average temperature by causing the exhaust gas flow in the exhaust gas channel to flow downward on one side in the stacking direction. It can also be raised. As a result, the power generation performance of the power generation cell at the lower end of the stack is improved, and the overall power generation performance of the fuel cell stack can be improved.
In addition, as described above, the heat diffusibility is improved by the flow of the exhaust gas to the gas discharge hole, and the temperature of the middle stage part of the stack is lowered. Therefore, the durability and reliability of the fuel cell stack can be improved.

According to the invention described in claim 2, since the gas discharge hole is provided in the portion corresponding to the portion surrounded by the plurality of power generation cells of the separator, the exhaust gas discharged from the outer peripheral portion of the power generation cell is used as the power generation cell. The gas flow path can be circulated in the stacking direction of the stack through the gas discharge holes without being retained in the periphery of the stack.
Accordingly, the reaction gas is smoothly supplied to each power generation cell, and the power generation performance of each power generation cell can be improved. In addition, in the middle stage of the stack where the temperature is relatively high, the heat dissipating property of the power generation cell can be improved and the temperature of the middle part of the stack can be lowered, and in the stack end where the temperature is low, the heat of exhaust gas flowing in the stacking direction As a result, the stack temperature rises and the temperature distribution in the stacking direction can be reduced.

According to the invention described in claim 3, since the size of the gas discharge hole of the separator located at the other end in the stacking direction of the stack is made smaller than the gas discharge hole of the other separator, The flow rate of the exhaust gas flowing out to the other side in the stacking direction is reduced, so that a flow of exhaust gas mainly directed to one side in the stacking direction can be generated in the exhaust gas flow path.
Due to the heat of the exhaust gas, in particular, in the vertically installed fuel cell stack, it is possible to raise the temperature at the lower end of the stack, which is the lowest temperature on one side in the stacking direction, from the average temperature of the stack. The power generation performance of the power generation cell at the lower end of the stack is improved, and the overall power generation performance of the fuel cell stack can be improved.

  Further, according to the invention described in claim 4, since the lid mechanism for adjusting the opening degree of the gas discharge hole of the separator located at the other end portion in the stacking direction of the stack is provided, The opening is adjusted according to the state of temperature distribution in the stacking direction (that is, the number of stacks in the stack and the electrical output density), and the amount of gas flowing upward and downward in the stacking direction in the exhaust gas flow path By appropriately adjusting the gas flow rate, the temperature at both ends of the stack can be adjusted in a well-balanced manner, the temperature distribution in the stack stacking direction can be more reliably reduced, and the stack temperature can be equalized.

  Further, according to the invention described in claim 5, since the gas discharge port for discharging the exhaust gas released from the exhaust gas flow path to the outside of the stack is provided on the end plate on one side in the stacking direction, The flow of exhaust gas to one side in the stacking direction becomes smooth, and the temperature at the stack end can be increased efficiently.

Hereinafter, an embodiment of a fuel cell stack according to the present invention will be described with reference to FIGS.
FIG. 1 is a schematic view showing the internal structure of the solid oxide fuel cell stack according to the present embodiment, FIG. 2 is a top view of a lower end plate, and FIG. 3 is a view showing the structure of a separator.

The solid oxide fuel cell stack according to the present embodiment includes a plurality of power generation cells 5 (with a fuel electrode layer 3 and an air electrode layer 4 disposed on both surfaces of a solid electrolyte layer 2 as shown in an enlarged view of the main part of FIG. 5a to 5d), the anode current collector 6 outside the anode layer 3, the cathode current collector 7 outside the cathode layer 4, and the separator 8 outside each collector 6, 7 respectively. It has a structure in which a large number of layers are stacked in order.
Among the constituent elements of the laminate (stack), the solid electrolyte layer 2 is made of stabilized zirconia (YSZ) or the like to which yttria is added, and the fuel electrode layer 3 is made of a metal such as Ni or a cermet such as Ni-YSZ. The air electrode layer 4 is made of LaMnO ₃ or LaCoO ₃ , the fuel electrode current collector 6 is made of a sponge-like porous sintered metal plate such as Ni, and the air electrode current collector 7 is made of Ag. It is comprised with the sponge-like porous sintered metal plate.

  Further, as shown in FIG. 3, the separator 8 is made of a substantially rectangular stainless steel plate having a thickness of several millimeters, and the plurality of power generation cells 5 and the current collectors 6 and 7 outside the power generation cells 5 described above. The separator main body 8a is disposed in the plane direction and the arm portions 8b and 8b are provided so as to extend in the surface direction from the separator main body 8a and support the opposing edge portions of the separator main body 8a at two locations.

In the present embodiment, as indicated by the alternate long and short dash line in FIG. 3, four power generation cells 5 a to 5 d having a circular shape in plan view are arranged on the same plane in vertical and horizontal symmetry at the central portion of the separator body 8 a.
The separator 8 electrically connects the power generation cells 5a to 5d arranged on the same plane via the current collectors 6 and 7, and the power generation cell group (5a to 5d) connected in parallel. ) In series in the stacking direction.
Further, the separator 8 has a function of supplying a fuel gas and air as a reaction gas to each of the power generation cells 5a to 5d, and a fuel gas passage 11 through which the fuel gas flows and air A circulating air flow path 12 is formed. In addition, a fuel introduction port 13 and an air introduction port 14 penetrating in the thickness direction are provided at opposite ends at the end portions of the arm portions 8 b and 8 b, and the fuel introduction port 13 communicates with the fuel gas channel 11. The air inlet 14 communicates with the air flow path 12.

More specifically, as shown in FIG. 3, the air flow path 12 passes through the inside of one arm portion 8 b from the air introduction port 14 to the lower side center portion P <b> 1 of the separator 8, and generates power inward from here. It reaches the central portion P2 of the separator body 8a surrounded by the cells 5a to 5d and branches into a horizontal T-shape at P2, and one (leftward) air flow path 12 is at the intermediate portion P3 between the power generation cells 5a and 5b. At P3, it further branches into a vertical T-shape and communicates with air discharge ports 12a and 12a opened on the separator surfaces corresponding to the central portions of the power generation cells 5a and 5b, respectively.
On the other hand, in P2, the other (right side) air flow path 12 reaches an intermediate portion P4 between the power generation cell 5c and the power generation cell 5d, and further branches in a vertical T-shape at P4 to the center of the power generation cells 5c and 5d, respectively. The air discharge ports 12a and 12a opened on the corresponding separator surfaces communicate with each other.

Further, the fuel gas passage 11 passes from the fuel introduction port 13 through the arm portion 8b different from the above to the intermediate portion P5 between the power generation cell 5c and the power generation cell 5d from the center of the upper side portion of the separator 8, The one (left side) fuel gas flow path 11 reaches the intermediate portion P6 between the power generation cell 5a and the power generation cell 5b along the periphery of the power generation cell 5b, and further branches into a vertical T-shape at P6, The fuel discharge ports 11a and 11a open on the separator surface corresponding to the central portions of the power generation cells 5a and 5b.
On the other hand, the other (right side) fuel gas passage 11 at P5 reaches the intermediate portion P7 between the power generation cell 5c and the power generation cell 5d along the periphery of the power generation cell 5c, and further branches into a horizontal T-shape at P7 to generate power. The fuel discharge ports 11a and 11a opened on the separator surface corresponding to the central portions of the cells 5c and 5d communicate with each other.
The fuel gas flow path 11 is reduced to the power generation cells 5a to 5d by reducing the cross-sectional area every time the gas flow path is branched at the portions P5, P6, and P7 on the separator body 8a. This makes it possible to distribute fuel gas evenly.

  Further, between the power generation cell 5a and the power generation cell 5b and between the power generation cell 5c and the power generation cell 5d, the portion sandwiched between the branch portion P6 of the fuel gas flow path 11 and the branch path P3 of the air flow path 12 In addition, an elongated hole portion 32 penetrating in the thickness direction is formed in a portion sandwiched between the branch portion P5 and the gas discharge hole 31 of the fuel gas flow path 11. Since these hole portions 32 have an effect of improving the heat dissipation of the adjacent portion of the separator, it is possible to reduce the temperature distribution in the separator surface.

By the way, the separator 8 of the present embodiment is notable in that a gas discharge hole 31 for exhaust gas discharge penetrating in the thickness direction is formed in the central portion of each separator 8 corresponding to the portion surrounded by the power generation cells 5a to 5d. It is a point that has been. The gas discharge holes 31 are a total of three through holes formed in a triangular shape or a trapezoidal shape so as to surround the air flow path 12 in the central portion of the separator body 8a. By stacking a large number of separators 8 having these gas discharge holes 31, as shown in FIG. 1, an exhaust gas passage 30 penetrating in the vertical direction is formed at the center of the stack.
In this embodiment, the size of the gas discharge holes 31 of the separator 8 located at the upper end of the stack (the total area of the three through holes described above) is the same as the gas discharge holes 31 of the other separators 8 positioned below. It is set smaller than the size of.

Further, as shown in FIG. 1, a stainless upper end plate 9a and a lower end plate 9b are arranged at both upper and lower ends of the stack with insulating manifold rings 15 and 16 interposed therebetween, and these upper and lower end plates 9a, 9b. Thus, the stack is fastened in the stacking direction.
A round hole 19 is provided in the central portion of the upper end plate 9 a, and a cylindrical weight 20 is placed on the upper surface of the separator 8 at the upper end of the stack through the round hole 19. When the stack is pressed downward by the load from the weight 20, the constituent elements (the power generation cell 5, the current collectors 6 and 7, and the separator 8) are in close contact with each other and are integrally fixed.
A leg 20 a is provided at the bottom of the weight 20, and a space is formed between the lower surface of the weight 20 and the upper surface of the separator 8. Accordingly, the exhaust gas flowing upward in the exhaust gas flow channel 30 is discharged into the space portion from the gas discharge hole 31 of the separator 8 at the upper end of the stack (the upper end portion of the exhaust gas flow channel 30), and flows through the space portion to generate fuel. It is discharged from the side of the battery stack 1.

  In addition, tubular fuel gas manifolds 17 and air manifolds 18 extend in the vertical direction at opposite edges of the stack. These manifolds 17 and 18 are constituted by manifold rings 15 and 16 interposed between the separators 8 in order to connect the fuel inlets 13 and the air inlets 14 of the separators 8 vertically. The gas manifold 17 communicates with the fuel gas flow path 11 via the fuel introduction port 13 of each separator 8 in the stack, and the air manifold 18 communicates with the air flow path 12 via the air introduction port 14 of each separator 8. doing.

As shown in FIGS. 1 and 2, an air pipe 25 for introducing external air is provided on one side of the lower end plate 9 b and in the vicinity of the lower end of the air manifold 18. A fuel gas pipe 24 through which external fuel gas is introduced is provided on the other side of the plate 9 b and in the vicinity of the lower end of the fuel gas manifold 17. The air pipe 25 communicates with the lower end portion of the air manifold 18 via an air passage 23 formed in the lower end plate 9b, and the fuel gas pipe 24 communicates with fuel via a fuel passage 22 formed in the lower end plate 9b. The gas manifold 17 communicates with the lower end portion.
A gas discharge port 21 is provided at the center of the lower end plate 9b for discharging the exhaust gas flowing downward in the exhaust gas flow path 30 to the outside of the stack. Legs 26 are provided on the lower surface of the lower end plate 9b, and a space in which exhaust gas discharged from the gas discharge port 21 can flow is ensured between the leg portions 26 and an installation surface (not shown).

  In the fuel cell stack 1 configured as described above, during operation, air and fuel gas supplied from the outside through the air pipe 25 and the fuel gas pipe 24 are circulated through the air manifold 18 and the fuel gas manifold 17, and these reaction gases are supplied to the separators. 8 are discharged from the fuel inlet 11 and the air outlet 12 through the fuel gas passage 11 and the air passage 12 to the fuel electrode current collector 6 side and the air electrode current collector 7 side. A power generation reaction occurs by diffusing and moving inside these current collectors and being guided to each electrode surface (the fuel electrode layer 3 and the air electrode layer 4) of each power generation cell 5.

Due to this power generation reaction, Joule heat is generated in each power generation cell 5, and the thermal energy is released to the outside through each separator 8. Further, the power generation cell 5 has a sealless structure in which no gas leakage prevention seal is provided on the outer peripheral portion, and the remaining gas (exhaust gas) that has not been consumed in the power generation reaction is discharged from the outer peripheral portion of each power generation cell 5. . Accordingly, in the central portion of the separator 8 surrounded by the plurality of power generation cells 5a to 5d, the exhaust gas discharged from the side portions of the power generation cells 5a to 5d passes through the gas discharge holes 31 of the separators 8 and enters the exhaust gas flow path 30. And flows in the exhaust gas passage 30 in the vertical direction.
The exhaust gas flowing upward in the exhaust gas flow channel 30 is discharged from the gas discharge holes 31 of the uppermost separator 8 at the upper end of the exhaust gas flow channel 30, and the space between the upper surface of the separator 8 and the lower surface of the weight 20. Is distributed outside the stack. On the other hand, the exhaust gas flowing downward is discharged from the gas discharge hole 31 of the lowermost separator 8 at the lower end portion of the exhaust gas flow path 30, and is mainly discharged out of the stack through the gas discharge port 21 of the lower end plate 9b.

  As described above, in the present embodiment, since the gas discharge hole 31 is provided in the central portion of the separator 8 corresponding to the portion surrounded by the four power generation cells 5a to 5d, the gas discharge holes 31 are discharged from the outer peripheral portions of the power generation cells 5a to 5d. Without causing the exhaust gas to stay near the center of the separator 8, the exhaust gas flow path 30 can be circulated in the vertical direction through the gas discharge holes 31.

  As a result, the reaction gas from the outside can be smoothly supplied to each power generation cell 5, and the power generation performance of each power generation cell 5 a to 5 d can be improved. The flow of exhaust gas to the gas discharge hole 31 improves the heat dissipating properties of the power generation cells 5a to 5d and lowers the temperature of the middle stage of the stack. Thermal stress on each component such as the power generation cells 5a to 5d and the separator 8 Therefore, the durability and reliability of the fuel cell stack 1 can be improved, and at the stack end where the temperature is low, the stack temperature is increased by the heat of the exhaust gas flowing up and down to increase the stack stacking direction. Can be reduced (soaking).

In particular, since the size of the gas discharge hole 31 of the separator 8 located at the upper end of the stack is made smaller than that of the other gas discharge holes 31, the flow rate of the exhaust gas passing through the upper end of the exhaust gas flow path 30 is reduced. A downward exhaust gas flow can be generated in the passage 30.
As shown in FIG. 4 (b), the lower end of the stack having the lowest temperature is heated by the heat of the exhaust gas flowing downward, and the temperature of the portion can be raised. The power generation performance of the power generation cells 5a to 5d is improved, and the overall power generation performance of the fuel cell stack 1 can be improved.

  In addition, since the gas discharge port 21 for discharging the exhaust gas discharged from the lower end portion of the exhaust gas flow path 30 to the outside of the stack is provided in the lower end plate 9b, the flow of the exhaust gas downward in the exhaust gas flow path 30 becomes smooth. The temperature at the lower end of the stack can be increased efficiently.

In this case, as shown in FIG. 1, a plate-like lid mechanism 29 that covers the gas discharge hole 31 of the separator 8 located at the upper end of the stack is movably provided so that the opening degree of the gas discharge hole 31 can be adjusted. Is also possible.
By the lid mechanism 29, the opening degree of the gas discharge hole 31 is adjusted according to the state of the temperature distribution in the stack stacking direction (that is, the number of stack stacks and the electrical output density), By appropriately adjusting the gas flow rate and the downward gas flow rate, the temperature at both ends of the stack can be adjusted in a well-balanced manner, and the temperature distribution in the stack stacking direction can be more reliably reduced.

  In the present embodiment, the vertical installation type fuel cell stack 1 has been described. However, the present invention is naturally applicable to a horizontal installation type fuel cell stack in which the stacking direction of the stack is horizontal, in which case The exhaust gas flow path in which the exhaust gas after the power generation reaction flows in the lateral direction is formed inside the stack. Also in the fuel cell stack of this configuration, in the stack middle stage where the temperature is relatively high, the heat dissipation of the power generation cells can be improved and the temperature of the stack middle stage can be lowered, and at the stack end where the temperature becomes lower, The temperature of the stack stack end increases due to the heat of the exhaust gas flowing in the lateral direction, and the temperature distribution in the stack stacking direction can be reduced.

The schematic diagram which shows the internal structure of the solid oxide fuel cell stack concerning this invention. The top view of the lower end board of FIG. The figure which shows the structure of the separator of FIG. The figure which shows the temperature distribution of a stack lamination direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell stack 5 (5a-5d) Power generation cell 8 Separator 9a, 9b End plate 21 Gas discharge port 29 Cover mechanism 30 Exhaust gas flow path 31 Gas discharge hole

Claims (5)

In a fuel cell stack in which a plurality of power generation cells are arranged in the same plane and a plurality of these power generation cells are stacked via separators,
An exhaust gas flow channel through which the exhaust gas after the power generation reaction flows in the stacking direction is provided inside the stack, and the gas flow rate to one side of the stacking direction in the exhaust gas flow channel is the gas flow to the other side of the stacking direction. A fuel cell stack characterized by having more than the amount.   The power generation cell has a sealless structure that discharges the exhaust gas after the power generation reaction from the outer peripheral portion, and the gas discharge penetrates in a portion corresponding to the portion surrounded by the plurality of power generation cells of each separator in the stacking direction. The fuel cell stack according to claim 1, wherein holes are provided, and the exhaust gas flows in the stacking direction through the gas discharge holes.   3. The fuel cell stack according to claim 2, wherein the size of the gas discharge hole of the separator located at the other end in the stacking direction of the stack is made smaller than the gas discharge hole of the other separator.   4. The fuel cell stack according to claim 3, further comprising a lid mechanism for adjusting an opening degree of a gas discharge hole of the separator located at an end portion on the other side in the stacking direction of the stack.   End plates are provided at both ends of the stack, respectively, and gas exhaust ports for exhausting the exhaust gas in the exhaust gas flow path to the outside of the stack are provided on one end plate in the stacking direction. The fuel cell stack according to any one of claims 1 to 4.

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