Flat gasket for a solid oxide fuel cell, arrangement and solid oxide fuel cell with such a flat gasket

Abstract

Flat gasket for sealing between a base plate and a stack of several electrochemical cells of a solid oxide fuel cell, with at least one metallic sealing layer into which sealing elements are embossed, characterized in that the metallic layer has at least one fixing point, wherein the fixing point has a structure that projects from the surface of the metallic layer adjacent to the structure, which forms an outer surface of the flat gasket, and has at least one free edge in the projecting area.

Description

[0001] The present invention relates to a flat gasket for arrangement between a base plate and a stack of electrochemical cells in a solid oxide fuel cell.

[0002] Solid oxide fuel cells are high-temperature fuel cells whose electrolyte consists of a solid ceramic material. Such a fuel cell comprises a stack of electrochemical cells arranged on a base plate. The supply of reactants and the removal of products and unreacted reactants occur through through-holes in the stack of electrochemical cells and the base plate, extending in the direction of the cell stack.

[0003] A seal is therefore required between the base plate and the stack of electrochemical cells to prevent or minimize the leakage of products and reactants through the gap between the base plate and the cell stack.

[0004] Due to the high temperatures at which a solid oxide fuel cell operates, ranging from 600 °C to 1200 °C, achieving a proper seal with conventional gaskets is difficult. Even when using a multilayer gasket (MLS), the significant temperature fluctuations between operating and non-operating phases of the fuel cell result in relative movements between the base plate and the gasket, as well as between the gasket and the cell stack, which impair the sealing effect.

[0005] Conventionally, relative movement is prevented by having studs on the base plate that engage in openings in the seal, thus fixing it in place. However, this solution is structurally complex and expensive.

[0006] Alternatively, in the prior art, the gasket is inserted completely into shallow pockets milled into the base plate. The depth of these pockets must be precisely determined so that the gasket thickness is sufficient but does not exceed the depth of the milled pocket too much. However, this requires high precision in milling the pockets in the base plate as well as very dimensionally accurate, flat gaskets that center themselves within the shallow milled pockets. Furthermore, such flat gaskets inserted into milled pockets are difficult to press firmly between the base plate and the cell stack. This further impairs the sealing effect of the flat gasket.

[0007] The object of the present invention is therefore to provide a flat gasket, an arrangement of a base plate and a cell stack end plate, and a solid oxide fuel cell that can be manufactured cost-effectively with high sealing effect and minimized relative movements between a base plate of the solid oxide fuel cell and the flat gasket.

[0008] This problem is solved by the flat gasket according to claim 1, the arrangement according to claim 9, and the solid oxide fuel cell according to claim 10. Advantageous embodiments of the solutions according to the invention are given in the respective dependent claims.

[0009] The flat gasket according to the invention serves to seal between a base plate and a stack of several electrochemical cells of a solid oxide fuel cell. It has at least one metallic sealing layer into which sealing elements are embossed. Such metallic gaskets are particularly suitable for sealing between two surfaces of two components at high temperatures and high pressures.

[0010] According to the invention, the metallic layer has at least one fixing point. The fixing point has a structure that projects from the surface of the metallic layer adjacent to the structure, which forms an outer surface of the flat gasket. In other words, this structure projects beyond the adjacent surface of the metallic layer in the direction of one of the components between which sealing is to be achieved by means of the flat gasket. The structure has at least one free edge in the projecting area.

[0011] By means of the free edge of this structure, which can, for example, be a tab bent out from the metallic layer, the flat gasket can be positively locked to the adjacent component, in particular the base plate of a solid oxide fuel cell or also to the cell stack or another adjacent component, in at least one direction in the plane of the metallic layer of the flat gasket. It is sufficient if the structure, for example the tab, engages in a recess in the surface of the adjacent component. If the gasket is only locked by a free edge, movements in other directions in the plane of the metallic layer are still possible. By using suitably designed and positioned additional such structures, it is possible according to the invention to lock the flat gasket to the adjacent component in further directions as well.It is always possible, through appropriate design, to create a fit of the flat gasket to the adjacent component with virtually no play or with play in one, several or all directions.

[0012] The solution according to the invention avoids milling a pocket for the entire seal into the adjacent component, for example, a base plate, and thus avoids the accuracy requirements of the milled pocket and the flat seal associated with solutions typically found in the prior art. Furthermore, the design of the flat seal according to the invention allows it to be positioned in the primary force-bearing area between the adjacent components to be sealed against each other, thereby achieving improved sealing. The flat seal is nevertheless able to absorb shear forces between the components without being displaced in an unacceptable manner relative to an adjacent component.

[0013] A structure according to the invention can be provided not only to fix the flat gasket to a (single) adjacent component. Rather, such structures according to the invention can also be provided on both sides of the flat gasket to fix the flat gasket to both components between which the flat gasket is located.

[0014] It is also possible to arrange one or more of the structures according to the invention in the same or different orientations on one or both sides of the flat gasket.

[0015] Solid oxide fuel cells often do not simply have a single stack of electrochemical cells per base plate, but rather two or more stacks can be arranged adjacent to each other on a single base plate. In this case, it is possible to arrange a separate flat gasket according to the invention on the base plate for each stack, or to provide a flat gasket with a continuous metallic layer for two or more of the stacks, or even for all stacks. If several stacks are arranged on a common flat gasket, it is also possible to arrange several of the structures according to the invention on the flat gasket in order to fix the flat gasket in different areas on the base plate or to fix the flat gasket independently on individual or each of the stacks.

[0016] Advantageously, the structure according to the invention can be an embossed or bent structure. This makes it possible to form the structure cost-effectively in the metallic layer using bending or embossing techniques. In particular, the structure can be an embossed bead having a free edge at at least one of its longitudinal ends. It can also have a free edge at both longitudinal ends of the bead, so that the bead is formed as a web extending transversely to the bead direction.

[0017] Advantageously, the bead can be a full bead. However, it can also be designed as a half bead. If the structure is designed as a half bead, which has a free edge at both ends in the direction of the bead's path and also a free edge at one end in the transverse direction to the bead's path, then the half bead forms a flap bent out of the plane of the metallic layer.

[0018] The structure can be – even independently of a previously described possible design as a half-bead – an embossed or bent tab that projects from the metallic layer out of its layer plane and has a free edge at its projecting end.

[0019] Advantageously, the bead, whether as a full bead or as a half bead, has at least in some areas a substantially or completely flat bead roof, wherein the layer plane in the flat area of ​​the bead roof is advantageously substantially or completely parallel to the layer plane of the metallic layer adjacent to the bead.

[0020] Advantageously, the groove can also have, at least in some areas, a substantially or completely rounded groove roof and / or, at least in some areas, a groove roof that tapers to a point, possibly from both sides.

[0021] The present invention also relates to an arrangement comprising a base plate and a stacking end plate arranged on the base plate for a stack of one or more electrochemical cells of a solid oxide fuel cell, wherein the base plate and / or the stacking end plate have at least one recess and a flat gasket according to the invention is arranged between the base plate and the stacking end plate. The flat gasket is arranged with its inventive structure such that its projecting structure engages in the recess.

[0022] If several structures according to the invention project from the plane of the layer towards the adjacent component, base plate or stacking end plate, in the flat gasket, a recess must be provided in the adjacent component for each of the structures, into which the structure can engage. It is possible to provide a separate recess for each of the structures or to provide a common recess for several of the structures. Alternatively, one or more structures can also be fixed to the outer edge of the base plate.

[0023] The invention further relates to a solid oxide fuel cell comprising a base plate, at least one stack of one or more electrochemical cells, and at least one stack end plate, which is arranged at the end of the stack facing the base plate, between the base plate and the stack. The base plate and / or the stack end plate have at least one recess. A flat gasket according to the invention is arranged between the base plate and the stack end plate. The flat gasket is arranged with its inventive structure such that its projecting structure engages in the recess.

[0024] The flat gasket has at least one metallic layer. However, it is also possible for the flat gasket to have several metallic layers. Each of the metallic layers can have the structures according to the invention, but it is essential that—if a structure according to the invention is arranged in one of the inner layers of the flat gasket—the structure must project beyond the adjacent surface of the flat gasket to enable it to engage in a recess in the adjacent component. Preferably, however, the structures according to the invention are located in one or both of the outermost layers of the flat gasket and project beyond the outer surface of the respective layer adjacent to the respective structure in the layer plane.

[0025] The external shape of the flat gasket is in no way restricted; the flat gasket can have smaller external dimensions than one or both adjacent components, particularly the base plate or the stacking end plate, either completely or only partially. However, the flat gasket can also extend beyond the external dimensions of one or both adjacent components, particularly the base plate or the stacking end plate, either completely or only partially. It is also possible to precisely match the external dimensions of the flat gasket to the external dimensions of one or both adjacent components, either completely or only partially.

[0026] One or more of the sealing elements of the flat gasket can be self-contained sealing beads. These can, for example, surround through-openings in the flat gasket or the outer circumferential edge of the flat gasket. The following materials are advantageously used:

[0027] For the flat gasket, spring steel, stainless steel, or a nickel-based alloy are suitable. The use of a nickel-based alloy has the advantage of being particularly well-suited for use at high temperatures. It is also characterized by high creep resistance.

[0028] For the base plate: die-cast, cast steel and stainless steel.

[0029] For the stacking end plate, stainless steel, titanium or high-temperature alloys.

[0030] The following are some examples of flat gaskets, arrangements, and solid oxide fuel cells according to the invention. Identical and similar reference numerals denote identical or similar elements. Therefore, the description of identical reference numerals is not always repeated. In the following examples, required and optional features of the present invention are presented together. However, it is also possible to combine one or more of the optional features of one or more examples without implementing further optional features.

[0031] They show: Fig. 1 an arrangement consisting of a base plate and a flat gasket; Fig. 2 to 5 each section of a flat gasket according to the invention in an arrangement (partial figure A) and independently (partial figure B); and Fig. 6 an arrangement according to the invention of a flat gasket in a solid oxide fuel cell.

[0032] Fig. Figure 1 shows a cross-section and a section around a fixing point 20 of an arrangement of a solid oxide fuel cell 1, wherein the arrangement has a base plate 2 and a flat gasket 10 with, in this example, a metallic layer 11. Electrochemical cells 4 of a cell stack 3 of the fuel cell 1 are in Fig. 6 shown.

[0033] The base plate has a surface 7 facing the flat gasket 10. The flat gasket has a surface 14 facing the base plate 2 and—though not necessarily, in this case—rests directly on the surface 7 of the base plate 2. The flat gasket 10 also has a surface 15 facing away from the base plate 2. Since, in this example, the flat gasket 10 has only one metallic layer 11, surfaces 14 and 15 are also the surfaces of the metallic layer 11. Facing the surface 15 of the flat gasket 10 and the metallic layer 11 is a stacking end plate 8 with a surface 9 facing the flat gasket 10.

[0034] The base plate 2, the seal 10, and the stacking end plate 8 each have a through-hole 5 or 13 and 16 for the passage of a screw 19 as a fastening means to secure the stacking end plate 8 and the seal 10 to the base plate 2. Despite this screw connection, lateral displacements of the seal 10 relative to the base plate 2 occur due to the high temperatures and thus the strong temperature fluctuations in the solid oxide fuel cell 1.

[0035] To limit these lateral displacements and absorb shear forces, the base plate 2 has a flat recess 6 milled into its surface 7 facing the seal 10. The flat seal has a fixing point 20. This fixing point is designed as a web 21, which projects from the surface 14 of the seal 10 facing the base plate 2 towards the base plate 2 and engages in the recess 6. In the cross-section shown, this web 21 is designed as a solid corrugation with a substantially flat, planar corrugation roof. The web 21 is embossed or bent from the plane of the seal 10. It has free edges running parallel to the drawing plane both in front of and behind it, with which the web 21, and thus the seal 10, is positively locked to the base plate 2 in a direction perpendicular to the drawing plane, with or without play.This allows the bridge to absorb shear forces in a direction perpendicular to the plane of the drawing and to prevent excessive displacement of the seal 10 relative to the base plate 2 in this direction.

[0036] However, the web does not fix the seal 10 in a horizontal direction relative to the base plate 2 in the plane of the drawing and allows displacement in this direction. This displacement can be prevented or limited by the arrangement of a further fixing point, which is designed according to the invention. For this purpose, a copy of the fixing point 20 can be arranged at another location on the seal 10 with the web 21 oriented in a different direction relative to the fixing point 6.

[0037] Fig. 2 shows in Fig. 2A an oblique top view with cross-section of the arrangement in Fig. 1 in the excerpt and in Fig. 2B an oblique top view of the metallic layer 11 of the flat gasket 10 without section.

[0038] The fixing point 20 has a web 21, freestanding between two through-openings 23a and 23b, which is designed as a groove 21. The groove 21 extends longitudinally between the two openings 23a and 23b, so that the web forms free edges 22a and 22b as part of the circumferential edge of the openings 23a and 23b, which extend to both sides of the web 21. The groove 21 has a corrugated roof 24, which is essentially flat and, in the installed state of the flat gasket 10 on the base plate 2, runs in the recess 6. The free edges 22a and 22b form stops on the adjacent edges of the recess 6 and therefore limit the displacement of the web 21 and thus of the metallic layer 11 of the flat seal 10 in a form-fitting manner in the direction of the longitudinal extension of the corrugated roof 24.

[0039] Fig. Figure 3 shows similar representations of a fixation point 20 in sub-figures A and B as in the Fig. 2A and Fig. 2B. The metallic layer 11 of the flat gasket 10 is like that in Fig. 2 trained. Unlike Fig. However, in this case, the recess in the base plate 2 is not designed as a flat milled recess 6, but as a through-hole 6 with a round cross-section through the base plate 2. The free edges 22a and 22b of the web 21 now engage positively in the opening 6 of the base plate 2 and secure the metallic layer 11 of the flat gasket 10 in the same way as in Fig. 2.

[0040] Fig. Figure 4 shows similar representations of a fixation point 20 in sub-figures A and B as in the Fig. 2A and Fig. 2B. The recess 6 of the base plate 2 is essentially designed as an essentially rectangular flat milled recess in the surface 7 of the base plate 2 as shown in Fig. 2. Only the corners of the rectangular flat recess are rounded. Unlike Fig. 2 is the jetty 21 in Fig. 4 is not designed as a bead whose bead roof 24 runs perpendicular to the longitudinal extent of the web 21 between the openings 23a and 23b, projects furthest towards the base plate and engages in the recess 6. Rather, the web 21 is designed as a bead whose bead roof 24 runs in the plane of the metallic layer 11 and whose bead roof 24 extends between the attachment points of the web 21 to the metallic layer 11. The free edges 22a and 22b of the web 21, facing the openings 23a and 23b and partially forming the circumferential edges of the openings 23a and 23b, are bent out of the plane of the metallic layer 11 present in adjacent areas and the plane of the corrugated roof 24 in the direction of the surface 7 of the base plate 2. The areas between the corrugated roof 24 and the free edges 22a and 22b thus form, as flanks of the corrugation 21, a tab 25a and 25b respectively, which engage in the recess 6 of the base plate 2.This means that the free edges 22a and 22b also engage in the recess 6 in the surface 7 of the base plate 2 and limit the play of the flat gasket 10 in a form-fitting manner in the direction extending between the two openings 23a and 23b.

[0041] Fig. Figure 5 shows a fixation point similar to the one in Fig. 4. However, the tabs 25a and 25b engage with their corners of the free edges 22a and 22b in a round recess 6 of the base plate 2. Since the recess 6 has a round cross-section for displacement protection in the base plate 2, the free edges 22a and 22b do not touch the walls of the recess 6 along their entire length, but only the corners of the edges 22a' and 22a'', as well as 22b' and 22b'', fix the flat gasket 10. The flat gasket 10 in Fig. 5 is otherwise analogous to the flat gasket 10 in Fig. 4 designed.

[0042] Fig.Figure 6 shows the structure of a solid oxide fuel cell 1 with a base plate 2, a flat gasket 10 according to the invention, a stacking end plate 8, and electrochemical cells 4 forming a cell stack 3. The cell stack 3 is bounded at its upper end by an upper stacking end plate 17. The flat gasket 10 according to the invention includes sealing elements 12a and 12b, which surround the media inlet 26 and the media outlet 27, as well as two fixing points 20a and 20b according to the invention, which engage in recesses 6a and 6b of the base plate 2. The fixing elements 20a and 20b are symbolized here as boxes and, in this example, fix the flat gasket 10 to the base plate 2 against displacement out of the plane of the drawing. The stacking end plate 8 can therefore still move relative to the flat gasket 10 in all directions. Reference sign 1 fuel cell 2 Base plate 3 cell stacks 4 electrochemical cell(s) 5 holes for mounting element 6. Recess in the base plate for anti-displacement protection 7 Surface of the base plate, oriented towards the flat gasket 8 Stacking end plate 9 Surface of the stacking end plate oriented towards the flat gasket 10 flat gaskets 11 metallic layer(s) 12 Sealing element 13 Through-opening of the flat gasket for fastening element 14 Surface of the flat gasket, oriented towards the base plate 15 Surface of the flat gasket, oriented towards the stacking end plate 16 Through opening of the stacking end plate 17 Top stacking end plate 19 Fastening element (screw etc.) 20 fixation point(s) 21 cantilever(s) 22 free edge(s) or their corners 23 exception(s) 24 ribbed roof 25 bead flank(s), tab(s) 26 Media entrance 27 Media outlet

Claims

[1] Flat gasket for sealing between a base plate and a stack of several electrochemical cells of a solid oxide fuel cell, with at least one metallic sealing layer into which sealing elements are embossed, characterized by that the metallic layer has at least one fixing point, wherein the fixing point has a structure which projects from the surface of the metallic layer adjacent to the structure, which forms an outer side of the flat gasket, and has at least one free edge in the projecting region. [2] Flat gasket according to the preceding claim, characterized by that the structure is an embossed or curved structure. [3] Flat gasket according to one of the preceding claims, characterized by that the structure is an embossed bead having a free edge at at least one of its longitudinal ends. [4] Flat gasket according to the preceding claim, characterized by that the bead is a full bead. [5] Flat gasket according to one of claims 3 and 4, characterized by that the bead has, at least in some regions, a substantially or completely flat bead roof, wherein advantageously the layer plane in the flat region of the bead roof is substantially or completely parallel to the layer plane of the metallic layer adjacent to the bead. [6] Flat gasket according to one of claims 3 and 4, characterized by that the bead has, at least in some areas, a substantially or completely rounded bead roof and / or, at least in some areas, a tapered bead roof, optionally on both sides. [7] Flat gasket according to claim 1 or two, characterized by that the structure is an embossed or bent tab which projects from the metallic layer out of its layer plane and has a free edge at its projecting end. [8] Flat gasket according to one of the preceding claims, characterized bythat the metallic layer has several fixing points with structures as described above. [9] Arrangement of a base plate and a stack end plate arranged on the base plate for a stack of one or more electrochemical cells of a solid oxide fuel cell, characterized by that the base plate and / or the stack end plate have at least one recess and a flat seal according to one of claims 1 to 8 is arranged between the base plate and the stack end plate such that its projecting structure engages in the recess. [10] Solid oxide fuel cell with a base plate, at least one stack of one or more electrochemical cells and at least one stack end plate arranged between the base plate and the stack at the end of the stack facing the base plate, characterized bythat the base plate and / or the stack end plate have at least one recess and a flat seal according to one of claims 1 to 8 is arranged between the base plate and the stack end plate such that its projecting structure engages in the recess.

Images