1. Technical Field
The present invention relates to an arrangement for tightening a stack of fuel cell elements that directly converts chemical energy to electrical energy.
2. Background Art
A cell element of a known fuel cell arrangement, in case of a fused carbonate type fuel cell for instance as illustrated in FIG. 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. Oxidizing gas OG is supplied to the cathode 2 and fuel gas FG is supplied to the anode 3, whereby power generation takes place.
The fuel cell arrangement depicted in FIG. 6, which is called an internal manifold type fuel cell arrangement, possesses a plurality of separator plates 4, each plate being provided with convex-concave gas passages on either face thereof at central part thereof (indicated like a wave in FIG. 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 presser plate (not shown) and a lower presser plate (not shown) respectively on the top and the bottom faces thereof, and these presser plates are pressed by springs, for example, near the periphery thereof as indicated by arrows 50.
Meantime it is known that an uniform contact is required between the tile 1, the cathode 2, the anode 0 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 presser plates. However, employing thicker presser 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 FIG. 7. A lower holder equipped with a heater, 115 is provided on a lower bolster plate of a pressing machine via a adiabatic 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 (a presser plate) provided with a heater, 114 which is attached to a lower face of a adiabatic 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 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 lowers the upper holder 114 so as to keep the tightening pressure unchanged. However, the deflection of the upper and 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 110 have to be designed thicker. Therefore, this prior art arrangement is not suited for a compact system.
Another tightening arrangement which uses air pressure by means of bellows is known in the art. However, this arrangement has to be equipped with very long bellows to respond the reduction of the fuel cell stack in height. The long bellows raises the expense of the entire arrangement.