Arrangement for tightening stack of fuel cell elements

Abstract: An arrangement for tightening a stack (S) of fuel cell ele­ ments (I), each cell element (I) including a cathode (2), and anode (3) and a tile (1) sandwiched by the cathode (2) and the anode (3) and the cell elements (I) being piled up one after another with separators (4) being interposed therebetween, comprising: an upper and a lower holder (114, 115) for sandwiching the fuel cell stack (S); an upper and a lower adiabatic material (112, 113) for sandwiching the upper and lower holders (114, 115), and a pressing device (110, 111, 119) for pressing the upper and lower adiabatic materials (112, 113), the upper and lower holders (114, 115) and fuel cell stack (S). The arrangement further includes pressure-adjusting members (118) defined by a hollow body (120, 121) and gas enclosed therein for adjusting the pressure on the fuel cell stack (S) one of which members (118) being interposed between the upper holder (114) and upper adiabatic material (112) and the other member (118) being interposed between the lower holder (115) and lower adiabatic material (113), such that the pressing force of the pressing device (110, 111, 119) is imposed on the fuel cell stack (S) with uniform pressure through the pressure adjusting members (118).

Description: The present invention relates to an arrangement according to the generic part of claim 1 for tightening a stack of fuel cell elements that directly converts chemical energy to electrical energy. An arrangement of this kind is described in JP-A-248368 of 5.11.86. A cell element of a known fuel cell arrangement similar to that described in JP-A-62 256 381 of 9.11.87, in case of a fused carbonate type fuel cell for instance as illustrated in Figure 6 of the accompanying drawings, comprises a cathode (oxide electrode) 2, an anode (fuel electrode) 3 and a tile (a plate of electrolyte) 1 interposed between these electrodes. The cell elements I are stacked one after another with separator plates 4 being interposed therebetween, so as to form a stack S. Oxidising gas OG is supplied to the cathode 2 and fuel gas FG is supplied to the anode 3, whereby power generation occurs. The fuel cell arrangement depicted in Figure 6, which is called an internal manifold type fuel cell arrangement, possesses a plurality of separator plates 4, each plate being provided with convexo-concave gas passages on both faces thereof at central part thereof (indicated like a wave in Figure 6). Oxidizing gas passages 5 and 6 and fuel gas passages 7 and 8 extend penetrating the fuel cell stack S near the periphery thereof. The tiles of fused carbonate serve as wet-sealing means. The stack S also includes a plurality of masking plates 9 disposed between the separators 4 and the tiles 1 for the sake of sealing. The convexo-concave passages and the vertically extending fuel and oxidizing gas passages FG and OG are enclosed and connected to each other by the masking plates 9. The stack S is provided with an upper pressure plate (not shown) and a lower pressure plate (not shown) respectively on the top and the bottom faces thereof, and these pressure plates are pressed by springs, for example, near the periphery thereof as indicated by arrows 50. Meantime, it is known that a uniform contact is required between the tiles 1, the cathode 2, the anode 3 and the separator plate 4, and that the wet-sealing has to be maintained, in order to ensure a proper function of the fuel cell. It is obvious that less pressure is exerted on the central part of the fuel cell as the fuel cell is designed larger if only springs are provided as the stack-tightening device, which only press the periphery of the stack. This would be overcome by employing thicker pressure plates. However, employing thicker pressure plates would lead to an undesired construction: a thicker fuel cell arrangement, and in turn a larger casing for the same. Another prior art arrangement for tightening the fuel cell stack S is illustrated in Figure 7. A lower holder 115, equipped with a heart, is provided on a lower bolster plate 111 of a pressing machine via an heat insulating material 113. Vertical rods 116 extend upward from the lower bolster plate 111 and support an upper bolster plate 110 spanning the vertical rods 116. The upper bolster plate 110 supports an upper holder (114 (a pressure plate) provided with a heater, which is attached to a lower face of an heat insulating member 112 and a cylinder 117 for moving the upper holder. The upper holder 114 is lowered by the cylinder 117 and exerts pressure on the fuel cell stack S between the upper and the lower holders 114 and 115. As the height of the fuel cell stack S decreases during power generation, the cylinder 117 loweres the upper holder 114 so as to keep the tightening pressure unchanged. However, the deflection of the upper and the lower holders 114 and 115 must be low in order to obtain unchanged tightening pressure. For this purpose, the upper and lower holders 114 and 115 as well as the upper and lower bolster plates 110 and 111 have to be designed thicker. Therefore, this prior art arrangement is not suited for a compact system. Similar devices are described in JP-A-58 163 185 of 27.9.83 and in JP-A-58 93 174 of 2.6.83. Another tightening arrangement which uses pneumatic pressure by means of bellows is known from JP-A 62-264570 of 17.11.87. However, this arrangment has to be equipped with very long bellows to respond the reduction of the fuel cell stack in height. The long bellows raise the expense of the entire arrangement. One object of the present invention is to provide a fuel cell stack tightening apparatus that prevents the reduction of the pressure on the central part of the fuel cell stack and presses the fuel cell stack with uniform pressure without employing thicker pressure plates. Another object of the present invention is to provide a compact, inexpensive fuel cell stack tightening apparatus that exerts a uniform pressure on the fuel cell stack without employing thick pressure (bolster) plates and holders and that adjusts the tightening pressure upon shrinkage of the fuel cell stack. These objects are achieved by the features of claim 1. Advantageous further developments are described in the subclaims. According to one aspect of the present invention, there is provided a tightening apparatus used for a fuel cell stack including a plurality of fuel cell elements of anode plates, tiles and cathode plates with separator plates being interposed between the fuel cell elements, which tightening apparatus comprising an upper and lower holder plate for holding the fuel cell stack and an upper and a lower pressure plate for pressing the holders with a pair of thin, hollow plates that include therein porous adiabatic members being interposed between the holder plates and the pressure plates. The upper and lower pressure plates are pressed by springs. As the temperature of the fuel cell stack increases, each thin, hollow plate between the holder plate and the pressure plate expands and exerts pressure against the holder plate and the pressure plate, and in turn the holder plates are pressed toward the fuel cell stack, thereby exerting a uniform pressure on the fuel cell stack. According to another aspect of the present invention, there is provided a tightening apparatus used for a fuel cell stack including a plurality of fuel cell elements of anode plates, tiles and cathode plates with separator plates being interposed between the fuel cell elements, which tightening apparatus comprising an upper and lower holder plate for sandwiching the fuel cell stack, an upper and a lower heat insulator for sandwiching the upper and lower holders and upper and lower pressure (bolster) plates of a spring means for pressing the upper and the lower heat insulator, with an upper and lower expandable member (metallic cushion) being interposed between the upper holder and the upper heat insulator and a lower expandable member (metallic cushion) being interposed between the lower holder and the lower heat insulator. In this arrangement, the pressing force of the spring means is transmitted to the fuel cell stack via the pressure (bolster) plates, the heat insulator, the expandable members (metallic cushions) and the holders. During the pressure transmission, these expandable members (cushions) serve as pressure-adjusting means, i. e., as the expandable members (cushions) are pressed, the reaction forces thereof press the fuel cell stack with a uniform pressure via the holders. Also, the spring means is able to compensate the change of the tightening pressure when the fuel cell stack shrinks during power generation. The invention will now be further described with reference to the drawings in which Figure 1 is a lateral view showing an arrangement for tightening the fuel cell stack according to a first embodiment of the present invention; Figure 2 is a sectional view showing a hollow plate of Figure 1; Figure 3 illustrates how the fuel cell stack is pressed as the fuel cell stack temperature rises; Figure 4 is a schematic view depicting another tightening arrangement for the fuel cell stack according to a second embodiment of the present invention; Figure 5 is a sectional view of an expandable (cushion) member of Figure 4; Figure 6 is a partial sectional view of the fuel cell stack; and Figure 7 schematically illustrates a prior art arrangement for tightening the fuel cell stack. Figure 1 through 3 illustrate a first embodiment of the present invention. A fuel cell stack S, as previously explained with reference to Figure 6, is constituted by plural fuel cell elements, each cell element including a cathode plate, an anode plate and a tile sandwiched by these plates, that are piled up one after another with separator plates being interposed between the cell elements. The stack S, as shown in Figure 1, is disposed between an upper and a lower holder 10 and 11 which are in turn sandwiched by an upper and a lower hollow plate 16 and 16, and an upper and a lower pressure plate 12 and 13. The upper and the lower pressure plates 12 and 13 are connected to each other by rods 14 and 14 at the periphery thereof. A spring 15 is provided between the head 20 of each rod 14 and the upper holder plate 12, so as to press the fuel cell stack S via the upper and the lower holders 10 and 11, and the upper and the lower hollow plates 16 and 16. The hollow plate 16, as illustrated in Figure 2, comprises a sealed hollow body of two disc-shaped, thin plates 17a and 17b which are for example seam welded, and a porous material 18 housed therein. Thus, the hollow plate 16 encloses air. As the fuel cell starts power generation, the stack temperature rises and reaches to approximately 650 degrees C (1202 degrees F). Due to this temperature rise, the internal pressure P of the hollow plate 16 also rises. Then, as shown in Figure 3, the upper thin plate 17a between the upper holder 10 and the upper pressure plate 12 is bent upward, and the lower thin plate 17b between the lower holder 11 and the lower pressure plate 13 is bent downward. While the thin upper and the lower pressure plates 12 and 13 are bent outward as the thin plate 17a of the upper hollow plate and the lower thin plate 17b of the lower hollow plate are, the holders 10 and 11 are pressed against the stack S, so that the adequate tightening pressure is given to the central part of the stack S. Thus, the stack S is tightened with a uniform pressure without employing thicker pressure plates, and in turn a compact fuel cell arrangement can be designed. Although two round plates are utilized to form a hollow body of the hollow plate 16 in the foregoing embodiment, square plates may be utilized instead thereof. Referring now to Figure 4 which depicts a second embodiment of the present invention, the fuel cell stack S is sandwiched by an upper and a lower, heater-equipped holder 114 and 115, an upper and a lower expandable (cushion) member 118 and 118, an upper and a lower heat insulating member 112 and 113, and an upper and a lower pressure (bolster) plate 110 and 111 of a spring means. The expandable (cushion) member 118 consists of a hollow body and a filler medium which inflates the hollow body as shown in Figure 5. The hollow body includes two metallic plates 120 and 121 joined by welding at their periphery, and the filler medium may be gas such as air or liquid such as oil, or combination of the two. The upper and the lower pressure (bolster) plates 110 and 111 are biased toward the fuel cell stack S by the pressing elements 119 provided with compression springs. The biasing force of the pressing elements 119 is transmitted to the stack S via the pressure (bolster) plates 110 and 111, the heat insulating members 112 and 113, the expandable (cushion) members 118 and 118 and the holders 114 and 115. In this case, as the pressing force is imposed on the expandable (metallic cushion) member 118, a reaction force thereof works against the holders 114 and 115 which sandwich the fuel cell stack S, such that a uniform pressure is exerted on the upper and the lower faces of the stack S, namely on the cathode plates, the tiles, the anode plates and the separator plates. Also, even if the fuel cell stack S shrinks during power generation, a uniform pressure on the stack S is maintained since the distance between the upper and the lower pressure (bolster) plates 110 and 111 is automatically reduced by the compression springs of the pressing elements 119. As explained above, the uniform pressure is exerted on the fuel cell stack due to the expandable (cushion) members 118, and the follow-up control relative to the shrinkage of the stack S is ensured by the pressing elements 119. Therefore, it is possible to provide an inexpensive, compact tightening arrangement without employing thicker pressure (bolster) plates or long bellows which are employed by the prior art arrangements. In this particular embodiment, the expandable (cushion) members are disposed between the holders and the heat insulating members. Moreover, the pressing elements may further include the cylinders of Figure 7.

Claims: An arrangement for tightening a stack (S) of fuel cell elements (I), each cell element (I) including a cathode (2), and anode (3) and a tile (1) sandwiched by the cathode (2) and the anode (3) and the cell elements (I) being piled up one after another with separators (4) being interposed therebetween, comprising: an upper and a lower holder (10, 11; 114, 115) for sandwiching said fuel cell stack (S); an upper and a lower pressure plate (12, 13; 110, 111) for sandwiching said upper and lower holders (10, 11; 114, 115); and spring means (14, 15; 119) for pressing said upper and lower pressure plates (12, 13; 110, 111), upper and lower holders (10, 11; 114, 115) an fuel cell stack (S), characterized in that said spring means (14, 15; 119) are arranged outside said holders (10, 11; 114, 115) and fuel cell stack (S) and said arrangement further includes two expandable members (16; 118) for adjusting the pressure on the fuel cell stack (S) one of which expandable members (16; 118) being interposed between said upper holder (10; 114) and upper pressure plate (12; 110) and the other member (16; 118) being interposed between said lower holder (11; 115) and lower pressure plate (13; 111), such that each expandable member (16; 118) expands as said fuel cell stack (S) temperature rises, and exerts a uniform pressure on said upper and lower holders (10, 11; 114, 115) as well as on said fuel cell stack (S), each expandable member being a hollow body the internal pressure of which rises automatically with increasing temperature An arrangement of claim 1, wherein each of said expandable members (16) includes a porous heat insulator (18) therein. An arrangement of claim 1 or 2, wherein each of said expandable members (16) includes a thin, hollow disc plate (17a, 17b). An arrangement of claim 3, wherein said pressure plate (12, 13) has a configuration analogous to said thin, hollow plate (17a, 17b). An arrangement of anyone of the foregoing claims, wherein said spring means (14, 15; 119) includes rods (14) extending between said upper and lower pressure plates (12, 13; 110, 111), and springs (15) mounted on said rods (14) so as to bias the upper pressure plate (12; 110) toward the lower pressure plate (13; 111). An arrangement of anyone of claims 1 to 5, wherein an upper heat insulator (112) is placed between the upper pressure plate (110) and the upper expandable member (118) and a lower heat insulator (113) is placed between the lower pressure plate (111) and the lower expandable member (118). An arrangement of claim 6, wherein each of said expandable members (118) includes a hollow body made by welding two thin, metallic plates (120, 121) and filler gas enclosed therein. An arrangement of claim 7, wherein the hollow body (120, 121) further includes liquid therein. An arrangement of anyone of claims 5 to 8, wherein said compression springs (119) adjust the distance between said upper and lower pressure plates (110, 111) as said fuel cell stack (S) changes its height.

Inventors: HIRATA TETSUYA, HOTTA MINORU, ZAIMA NOBOYUKI, HIRATA, TETSUYA, HOTTA, MINORU, ZAIMA, NOBOYUKI, Zaima, Nobuyuki
Applicants: ISHIKAWAJIMA HARIMA HEAVY IND, ISHIKAWAJIMA-HARIMA HEAVY INDUSTRIES CO., LTD.
Application year: 1989
Main classification: H01M8
IPC codes: H01M8