JP2005353539A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid reduction in power generation efficiency caused by taking heat through a support body to support a cell stack. <P>SOLUTION: A support body 22b supports a cell stack 10 to house it inside a stack container 20. The support body 22b also functions as a gas supplying means to supply fuel gas and oxidation gas to the cell stack 10. Discharge gas with high temperature to be discharged from the cell stack 10 is discharged outside the stack container 20 through gas discharge holes 22e disposed an a bottom plate 22 of the stack container 20. The discharge holes 22e are disposed in plural numbers so as to surround the support body 22b immediately close to the support body 22b. The discharge gas with the high temperature wraps around up to in the vicinity of a center part below the cell stack 10 to effectively and specifically heat a battery reactive area of a battery cell on a lower side. Temperature reduction of the battery cell on the lower side being a stack support side is evaded, and the cell temperature is unified in a cell laminated direction, and then power generation efficiency is enhanced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell that generates electricity by reacting a hydrogen-rich fuel gas with an oxidizing gas.

  One typical fuel cell is a solid oxide fuel cell (SOFC). In this fuel cell, there is a disk-shaped solid electrolyte with an electrode in which an anode electrode layer is formed on one surface of a thin and brittle circular solid electrolyte plate made of yttria-stabilized zirconia and the like, and a cathode electrode layer is formed on the other surface. Used as a battery cell.

  Usually, this battery cell is used as a cell stack formed by stacking a plurality of battery cells in the central axis direction. More specifically, a cylindrical cell stack is formed by stacking disk-shaped interconnectors in the thickness direction so that reaction spaces are formed on both sides of the cell with battery cells in between. And used.

  In operation, hydrogen-rich fuel gas and oxidizing gas such as air are supplied to the center of the cell stack. The fuel gas supplied into the cell stack flows from the inner peripheral portion to the outer peripheral portion in a reaction space on the anode side formed on one surface side of the battery cell. Further, the oxidizing gas flows from the inner peripheral portion to the outer peripheral portion in the cathode-side reaction space formed on the other surface side of the battery cell. This generates electricity.

  In such a fuel cell, high-temperature combustion gas is discharged from the cell stack to the outer peripheral side with power generation. In some cases, unreacted fuel gas is recovered. In this case, high-temperature oxidizing gas is discharged from the cell stack to the outer peripheral side. For this reason, a cell stack is accommodated in the cylindrical stack container which consists of a heat-resistant metal, and discharges high temperature exhaust gas outside through the container (refer patent document 1).

EP13447529A2 specification

  In general, the cell stack is supported in the stack container by supporting the central portion of the cell stack with a support from below, and this support allows fuel gas and oxidizing gas to enter the cell stack. In general, it also serves as a gas supply means.

  According to such a support structure of the cell stack, the retained heat of the cell stack is dissipated to the outside through the lower support. In the case where the support also serves as the gas supply means, the temperature of the support is kept at a low temperature, so that the heat removal downward through the support is further promoted. As a result, the temperature distribution in the axial direction of the stacked cells in the cell stack tends to decrease as the lower cell.

  Here, the plurality of battery cells in the cell stack are also electrically connected in series. FIG. 7 is a graph showing the power generation characteristics of battery cells for four types of operating temperatures of 850 ° C., 800 ° C., 750 ° C., and 700 ° C. A battery cell shows the characteristic that a voltage falls as an electric current increases, and the fall of a voltage becomes so remarkable that the operating temperature of a battery cell falls. As a result, when compared with the current 100%, which is the operating point, when the operating temperature drops from 800 ° C to 750 ° C by 50 ° C, the voltage drops from 0.75V to 0.6V by about 20%, and the operating temperature becomes 750 ° C When the voltage drops from 700 to 700 ° C. by 50 ° C., the voltage drops from 0.6 V to 0.4 V by 30% or more. As the cell temperature decreases as described above, the voltage decrease becomes more significant. As a result, the temperature decrease of the lower cell due to heat removal through the support greatly affects the power generation efficiency of the cell stack.

  The above is the case where the center part of the cell stack is supported from below, but when the center part of the cell stack is supported from above by the support body that also serves as a means for supplying the fuel gas and the oxidizing gas, the support is provided via the upper support body. Lowering the temperature of the upper cell due to heat removal greatly affects the power generation efficiency of the cell stack.

  An object of the present invention is to provide a fuel cell that can effectively avoid a decrease in power generation efficiency due to heat removal via a support.

  In order to achieve the above object, a fuel cell according to the present invention includes a cell stack that is configured by stacking battery cells in a central axis direction, and that is housed in a stack container by supporting a central portion with a support. When the high temperature exhaust gas discharged from the cell stack to the outer peripheral side is discharged out of the stack container, the exhaust gas discharge hole is arranged so that the exhaust gas goes around to the vicinity of the center part on the support side of the cell stack. Is provided near the center of the stack container on the support side.

  In the fuel cell according to the present invention, by devising the position of the exhaust hole for exhaust gas discharged from the cell stack to the outer peripheral side, the exhaust gas goes around to the vicinity of the center portion on the support side of the cell stack. As a result, the battery cell on the support side where heat removal through the support proceeds is forcibly heated with high-temperature exhaust gas and the temperature is raised, so that the cell temperature distribution in the stacking direction is made uniform, and the support side The voltage drop in the battery cell is prevented.

  The support is preferably configured to support the inside as much as possible from the battery reaction region in the cell stack. Thereby, the battery reaction area | region of the battery cell by the side of a support body can be heated more effectively with high temperature waste gas.

  It is preferable that a plurality of the discharge holes are provided on the end plate of the stack container so as to surround the support body in the vicinity of the support body. Thereby, the battery reaction area | region of the battery cell by the side of a support body can be heated more effectively with high temperature exhaust gas.

  It is preferable from the viewpoint of simplification of the structure that the support also serves as a gas supply means for supplying fuel gas and oxidizing gas to the cell stack. When such a configuration is adopted, the temperature of the support is lowered, and heat removal through the support proceeds, but even in this case, a decrease in power generation efficiency is effectively avoided by heating with high-temperature exhaust gas. be able to.

  In the fuel cell of the present invention, the battery cell on the support side where the heat removal through the support proceeds is forced by the high-temperature exhaust gas by devising the position of the exhaust hole for exhaust gas discharged from the cell stack to the outer peripheral side. It is possible to effectively avoid a decrease in power generation efficiency due to heat removal through the support.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a fuel cell showing one embodiment of the present invention, FIG. 2 is a configuration diagram of a cell stack constituting the fuel cell, and FIG. 3 is a two-side view of a battery cell constituting the cell stack, FIG. 4 is a two-side view of an interconnector constituting the cell stack.

  As shown in FIG. 1, the fuel cell of the present embodiment includes a columnar cell stack 10 and a cylindrical stack container 20 that accommodates the cell stack 10. The stack container 20 includes a container main body 21 whose upper surface is closed, and a bottom plate 22 that closes the lower surface opening. The bottom plate 22 also serves as a support member for the cell stack 10.

  As shown in FIG. 2, the cell stack 10 has a predetermined number of disk-shaped interconnectors 11, 11,... Stacked in the axial direction while sandwiching disk-shaped battery cells 12 between adjacent interconnectors. It is comprised by doing. This laminate is sandwiched between an upper end plate 13 and a lower end plate 14. As will be described later, the lower end plate 14 is formed integrally with the bottom plate 22 of the stack container 20.

  The bottom plate 22 of the stack container 20 includes an annular main body 22a that closes the lower surface opening of the container main body 21 of the stack container 20, and a cylindrical support 22b that rises upward from the inner peripheral edge of the main body 22a. . Inside the main body 22a and the support 22b is a gas flow path 22c that supplies air as an oxidizing gas to the cell stack 10. An annular gas passage 22d for supplying fuel gas to the cell stack 10 is formed inside the support 22b.

  The end plate 14 of the cell stack 10 is integrally formed on the upper end side of the support 22c. An air supply hole 15 that communicates with the gas flow path 22 c is provided at the center of the end plate 14, and a plurality of fuel supply holes 16 and 16 that communicate with the gas flow path 22 d surround the air supply hole 15. Is provided. In the main body 22a of the bottom plate 22, a plurality of gas discharge holes 22e and 22e surround the support 22b in order to discharge the high temperature exhaust gas discharged from the cell stack 10 to the outer peripheral side to the outside of the container. It is provided as follows.

  What is important here is that the outer diameter of the support 22 b is designed to be sufficiently smaller than the outer diameter of the end plate 14. Incidentally, the outer diameter of the end plate 14 is the same as the outer diameter of the cell stack 10. More specifically, in the cell stack 10, fuel gas and air are supplied to the inner peripheral portion, and the outer peripheral portion becomes a battery reaction region, but the support 22b is positioned inside the battery reaction region, The outer diameter of the support 22b is set. A plurality of gas discharge holes 22e and 22e are provided so as to surround the support 22b in the immediate vicinity.

  Next, the internal structure of the cell stack 10 will be described with reference to FIGS.

  As described above, in the cell stack 10, a predetermined number of disk-shaped interconnectors 11, 11,... Are stacked in the axial direction with the disk-shaped battery cells 12 sandwiched between adjacent interconnectors. (See FIG. 2). As shown in FIG. 3, in the battery cell 12, an anode electrode layer 12b is formed on one surface of a thin and brittle circular solid electrolyte plate 12a made of yttria-stabilized zirconia, and a cathode electrode layer 12c is formed on the other surface. It is a thin disk. The center portion of the battery cell 12 is provided with a relatively large-diameter first gas hole 12d through which air flows, and a plurality of relatively small-diameter second gas holes 12e, 12e,. One gas hole 12d is provided so as to surround it.

  As shown in FIG. 4, the interconnector 11 is a disk having the same outer diameter as that of the battery cell 12, and is made of a heat-resistant metal such as stainless steel. In the central part of the interconnector 11, a first gas hole 11 a through which air flows is provided corresponding to the first gas hole 12 d of the battery cell 12. The first gas hole 11a has a smaller diameter than the first gas hole 12d of the battery cell 12, and a plurality of support rod through-holes 11b and 12b are formed on the outer periphery of the first gas hole 11a. It is provided so as to be inscribed or located inside thereof. A plurality of second gas holes 11c, 11c,... Through which the fuel gas flows are arranged on the outer peripheral side of the support rod through holes 11b, 12b so as to correspond to the second gas holes 12e, 12e,. Is provided. The inner diameters of the second gas holes 11c, 11c,... Are the same as the inner diameters of the second gas holes 12e, 12e,.

  The surface on the cathode side of the interconnector 11 (the surface facing the cathode electrode layer 12a of the battery cell 12) is shown in FIG. In this surface, in order to prevent the fuel gas flowing through the second gas holes 11c, 11c,... From flowing in, a plurality of annular convex portions 11d, 11d,. Is also provided as a spacer. Further, a large number of small-diameter projections 11e, 11e,... Are provided as spacers on the outer peripheral side of the annular projections 11d, 11d,.

  On the other hand, the surface on the anode side of the interconnector 11 (the surface facing the anode electrode layer 12b of the battery cell 12) is shown in FIG. On this surface, in order to prevent inflow of air flowing through the first gas hole 11a, an annular convex portion 11f surrounding the first gas hole 11a is provided as a spacer. The annular convex portion 11f is provided up to the vicinity of the second gas holes 11c, 11c,... In order to guide the fuel gas flowing out from the second gas holes 11c to the outer peripheral side while meandering. The radial linear ribs 11g and the circumferential arc-shaped ribs 11h are combined to serve as spacers.

  In such a cell stack 10, a predetermined number of disk-shaped interconnectors 11, 11... Are sandwiched between adjacent interconnectors while using a positioning support rod. However, it is assembled by laminating in the axial direction and sandwiching it between the upper and lower end plates 13 and 14.

  That is, in assembling the cell stack 10, a plurality of (in this case, two) support rods 19, 19 made of ceramic are pierced through the support rod through holes 11 b, 12 b of the interconnector 11, thereby interconnectors 11, 11. ..Positioning between. At the same time, another plurality (usually 2 to 3) of support rods are selectively inserted into the second gas holes 11c, 11c,... Of the interconnector 10 and the second gas holes 12e, 12e,. Through the positioning, the interconnectors 11, 11,... And the battery cells 12, 12,. After the stacking of the interconnectors 11, 11... And the battery cells 12, 12..., The former support bars 19 and 19 are left, the latter support bars are pulled out, and the stacked body is tightened in the stacking direction.

  By leaving the former support rods 19 and 19 in the laminated body, misalignment between the interconnectors 11 and 11 is prevented. The support rods 19, 19 are in contact with or located inside the battery cells 12, 12,... And do not directly contribute to the positioning of the battery cells 12, 12,. However, since the interconnectors 11, 11,... And the battery cells 12, 12,... Are pressed by tightening in the stacking direction, the battery cells 12, 12,. Does not shift. For this reason, only the support rods 19, 19 with respect to the interconnectors 11, 11,.

  That is, the positioning is performed without inserting the support rods into the battery cells 12, 12. In other words, even if the battery cell 12 is not provided with a dedicated support rod through hole, the battery cell 12 can be interconnected if the second gas holes 12e, 12e,. 11 is fixed together. The advantage of not forming the support rod through hole in the battery cell 12 is as follows.

  Unlike the interconnector made of a metal plate, the battery cell 12 is made of ceramics, so even if a support rod through-hole is provided, it is difficult to ensure high positional accuracy, and it is not necessarily possible to ensure high positioning accuracy. Not exclusively. Moreover, when a support rod is left in the support rod through-hole of the battery cell 12, there is a risk that the battery cell 12 is damaged due to a difference in thermal expansion. In addition to this, when the support rod through hole is formed between the first gas hole 12d of the battery cell 12 and the second gas holes 12e, 12e,..., The first gas hole 12d needs to be reduced. The area of the battery cell 12 is reduced, and the material cost is increased. By omitting the support rod through hole and enlarging the first gas hole 12d, the material cost can be reduced.

  The assembled cell stack 10 is set in a stack container 20 and completed as a fuel cell. In the completed fuel cell, air is supplied to the center of the cell stack 10 from the gas flow path 22c formed inside the main body 22a and the support 22b. Further, the fuel gas is supplied to the central portion of the cell stack 10 from an annular gas passage 22d formed inside the support 22b.

  The air supplied to the central portion of the cell stack 10 ascends the gas flow path in which the first gas hole 11a of the interconnector 11 and the first gas hole 12d of the battery cell 12 are continuously formed in the axial direction. A space between the cell 10 and the interconnector 11 disposed on the cathode side thereof radiates radially to the outer peripheral side (see FIG. 4A). Further, the fuel gas supplied to the central portion of the cell stack 10 has the second gas holes 11c, 11c,... Of the interconnector 11 and the second gas holes 12e, 12e,. The plurality of formed gas flow paths are raised, and the space between the battery cell 10 and the interconnector 11 disposed on the anode side thereof circulates radially to the outer peripheral side (see FIG. 4B).

  As described above, the fuel gas and the air circulate from the central portion to the outer peripheral portion with the battery cell 12 interposed therebetween, thereby generating power. The fuel gas and air finally undergo a combustion reaction, become a high-temperature combustion gas, and are discharged to the outer peripheral side of the cell stack 10. When recovering unreacted fuel gas, high-temperature air is discharged from the cell stack to the outer peripheral side. The discharged high-temperature exhaust gas is discharged out of the stack container 20 through a plurality of gas discharge holes 22e and 22e provided in the main body 22a of the bottom plate 22.

  Here, a plurality of gas discharge holes 22e and 22e for discharging the exhaust gas to the outside of the container are provided in the main body 22a of the bottom plate 22 so as to surround it in the immediate vicinity of the support 22b. Further, the support 22 b is located inside the battery reaction region formed in the outer peripheral portion outside the center portion of the cell stack 10. As a result, the high-temperature exhaust gas discharged from the cell stack 10 descends in the stack container 20, goes around the battery reaction region in the cell stack 10, and is discharged outside the stack container 20.

  Thereby, the cell stack 10, especially the battery reaction region, is efficiently heated from below by the high temperature exhaust gas. The support 22b that supports the cell stack 10 is also heated together with the lower end plate 14 and the like. As a result, heat removal from the cell stack 10 via the support 22b that supports the cell stack 10 is prevented, and the temperature of the battery cells 12, 12,. Uniform in the stacking direction. Therefore, the power generation efficiency of the cell stack 10 increases.

  In order to confirm the effect of this embodiment, the gas exhaust hole of the exhaust gas discharged from the cell stack 10 was changed. In the first modified example, as shown in FIG. 5A, a plurality of gas discharge holes 22 e are provided at the outer peripheral portion of the main body 22 a of the bottom plate 22, more specifically at the outer peripheral side of the cell stack 10. , 22e ·· are provided. In the second modification, the gas discharge hole 21a is provided in the top plate portion of the main body 21 of the stack container 20, that is, the container end plate on the side opposite to the support. In each case, FIG. 6 shows the temperature distribution in the stacking direction of the battery cells 12, 12,..., More specifically, the temperature distribution at the midpoint in the radial direction of the battery reaction region.

  In the case of the gas discharge structure shown in FIG. 5A, the high-temperature exhaust gas discharged from the cell stack 10 descends in the stack container 20 but does not enter the lower side of the cell stack 10. The cell temperature is below 750 ° C. at the bottom. In the case of the gas discharge structure shown in FIG. 5B, the high temperature exhaust gas discharged from the cell stack 10 rises in the stack container 20, so that the upper temperature of the cell stack 10 exceeds 800 ° C. Then the temperature drops to near 700 ° C. On the other hand, in the case of the fuel cell of the embodiment shown in FIG. 1, although the temperature at the upper part does not increase as in the case of FIG. 5B, the temperature hardly decreases at the lower part, and 770 ° C. or more in the entire stacking direction. Temperature is maintained. As described above, the fact that a small temperature drop affects the power generation efficiency more significantly than the temperature rise (see FIG. 7).

  Therefore, in the fuel cell of this embodiment, high heat generation efficiency is ensured by preventing heat removal via the support 22b that supports the interconnector 10 by using high-temperature exhaust gas.

  The cell reaction region in the cell stack 10 is usually in the range from 0 to the position from the outer periphery to the position of 0.2 to 0.98 when the radius is 1 and expressed by the distance from the outer periphery. The gas discharge holes 22e, 22e,... Are preferably formed within a range of 0.2 to 0.90 in terms of a distance from the outer peripheral edge of the cell stack 10, and within a range of 0.3 to 0.8. Particularly preferred. If the gas discharge holes 22e, 22e,.. If the gas discharge holes 22e, 22e,... Are too close to the inner peripheral side, the support 22b located on the inner side becomes too thin, and there is a risk of hindering mechanical strength and gas supply using this.

  Incidentally, the outer diameter of the support 22b is preferably 0.2 to 0.7 times the outer diameter of the cell stack 10. When the support 22b becomes thicker, the gas discharge holes 22e, 22e,... Move toward the outer peripheral side, and the efficiency of heating the cell stack 10 from below decreases. If the support body 22b becomes thin, it will interfere with the mechanical strength of the support body 22b and the gas supply using this.

  In the above embodiment, the cell stack 10 is supported by a support from below, but the cell stack 10 may be supported by a support from above. In that case, gas discharge holes 22e, 22e,... Are provided around the container end plate on the support body side of the stack container 20, that is, the support body of the top plate portion of the main body 21.

It is a longitudinal cross-sectional view of the fuel cell which shows one Embodiment of this invention. It is a block diagram of the cell stack which comprises the fuel cell. It is a 2nd page figure of the battery cell which comprises the same cell stack, (a) is a top view, (b) is a side view. It is a 2nd page figure of the interconnector which comprises the same cell stack, (a) is a top view, (b) is a bottom view. (A) And (b) is a longitudinal cross-sectional view of the fuel cell which shows a comparative example. It is a graph which shows the temperature distribution in the lamination direction of a battery cell about the Example and comparative example of this invention. It is a graph which shows the influence which cell temperature has on power generation efficiency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cell stack 11 Interconnector 11a 1st gas hole 11b Support rod through-hole 11c 2nd gas hole 12 Battery cell 12d 1st gas hole 12e 2nd gas hole 13,14 End plate 15 Air supply hole 16 Fuel supply hole 19 Support rod 20 Stack container 21 Container body 22 Bottom plate 22a Body 22b Support body 22c, 22d Gas flow path 22e Gas discharge hole

Claims (4)

  It is configured by stacking battery cells in the direction of the central axis, and has a cell stack accommodated in a stack container by being supported by a support at the center, and a high temperature discharged from the cell stack to the outer peripheral side. When exhaust gas is discharged out of the stack container, the exhaust gas exhaust hole is provided in the vicinity of the center part on the support side of the stack container so that the exhaust gas goes around to the vicinity of the center part on the support side of the cell stack. A fuel cell.   The fuel cell according to claim 1, wherein the support also serves as a gas supply unit that supplies fuel gas and oxidizing gas to the cell stack.   The fuel cell according to claim 1, wherein the support supports an inner side from a battery reaction region in the cell stack.   2. The fuel cell according to claim 1, wherein a plurality of the discharge holes are provided in an end plate on the support body side of the stack container so as to surround the support body in the immediate vicinity of the support body.

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