The subject of the invention is a stack of high-temperature fuel cells known as Anode Supported Solid Oxide Fuel Cells (AS SOFCs) or Cathode Supported Solid Oxide Fuel Cells (CS SOFCs) to be used to generate electric power from gas fuels such as hydrogen, synthesis gas, methane, biogas, ethanol and bioethanol, methanol, gasoline and similar hydrocarbons.

Fuel cells are devices converting chemical energy into electric power as a result of electrochemical reaction between fuel supplied to the anode surface and an oxidising gas supplied to cathode after passing through an0 electrolyte membrane conducting oxygen ions towards anode where they are combined with the fuel creating heat energy and electric power. A characteristic feature of the fuel cell is the ability to transform chemical energy directly into electric power in the flameless combustion process. This results in a higher efficiency of the device (45-55%) compared to the5 majority of thermo-mechanical solutions (e.g. 40-42% in gas turbines). In combined heat-and-power generating systems, fuel cells can reach the overall energy efficiency levels as high as up to 90%. Another beneficial feature of using fuel cells as power generators consists in much lower emissions of carbon dioxide, SO ₂ , ΝΟχ, hydrocarbons, carbon oxide and0 solid particles to atmosphere (especially when hydrogen is used as fuel) compared to traditional power plants fired with conventional fossil fuels. Dimensions of fuel cells are small, but they can be combined in modular systems easy to expand at low investment cost. The cells can be operated continuously, consuming fuel and oxidiser in amounts corresponding to the5 electric load, being at the same time resistant to instantaneous overload and load conditions. Easiness of expansion and absence of moving components (no abrasion wear, no vibration, no problems with mechanical strength) result in high reliability of fuel cell-based power sources.

The fuel most commonly used in fuel cells is hydrogen, while research is conducted also on using methane, carbon oxide, and other hydrocarbons as the gas fuels, The oxidiser is oxygen supplied to the device as pure gas or together with atmospheric air. A single fuel cell in the form of a square or circular plate is composed of two electrodes: anode made of Y ₂ O ₃ -stabilised zirconium dioxide/nickel oxide composite and cathode made of a ceramic material with structure of perovskite containing oxides of lanthanum, strontium, cobalt, manganese, and iron, the two electrodes being separated from each other by means of solid electrolyte made of Y ₂ O ₃ -stabilised zirconium oxide in the amount of 3-10% by mole or stabilised with SC ₂ O ₃ , which at high temperatures (650-900°C) is a very good conductor for oxygen anions.

Another well-known battery of fuel cells known also as the cell stack comprises a plurality of heat-resisting metal frames stacked one upon another with individual cells disposed in them and separated from each other by means of inter-connector metal plates conveying electric charge and provided with horizontal grooves allowing the gaseous reagents to reach surfaces of the electrodes. Both metal frames and inter-connector plates are separated from each other by means of insulation separators and provide with vertical ducts supplying reagents to and discharging combustion products from individual cells. Known are also solutions in which instead of grooved interconnecting metal plates, corrugated thin metal plates are disposed directly inside metal frames playing the same role. The electric power is taken from the cell stack via leads connected to stack-binding bolts remaining in contact with the metal plates.

From literature of the subject ("Fabrication of structures anode- supported solid oxide fuel cell by power injection moulding", Journal of Power Sources 2013, p. 35-40) known is a solution in which the anode surface of a round fuel cell has projections allowing the fuel to be supplied to the anode, while electric charge is collected by a mesh connected to electric lead. On the cathode side, solid grooved metal plates are employed provided with metal mesh and current terminals.

Known is a fuel-cell device in the form of a stack of individual cells supplied with a flow of a fuel gas and an oxidiser, in which the fuel stream is directed parallel to individual cells so that each cell is supplied with the same amount of fuel equalling the total fuel flow rate divided by the number of cells, whereas the stream of oxidiser is also directed parallel to individual cells so that each cell is supplied with the same amount of oxidiser. At output of each cell, the component fuel flows and the component oxidiser flows are the same and each of these cells is an electric power generator with the same output voltage and current. However, such cells are characterised with low effectiveness of fuel usage and thus low overall efficiency.

Description of Polish patent No. PL211985B1 reveals a fuel cell converting energy contained in the fuel directly into electric power in the flameless combustion process, where the cell constitutes an assembly of individual cells arranged into a stack where inputs of the cells are connected with fuel ducts and oxidiser ducts. The assembly is characterised in that its oxidiser duct is connected in parallel to many individual cells so that each of them is supplied with one n-th of the oxidiser flow, and the fuel duct supplies individual cells in series, whereas each of the cells is supplied with the whole volume of fuel flow with gradually decreasing share of fuel and increasing share of combustion gases. Cells of the stack are sources of electric power which, at the same value of current, have different voltages and the sum of the generated voltages observed at the output of the cell assembly is higher than this at the output of the known solution described above. This allows to utilise fuel more effectively and obtain higher efficiency, but at higher investment cost.

Another assembly of fuel cells known from description of Polish patent No. 363200 is provided with a manifold with a suitable connection zones for fuel cells, whereas some of these zones have different characteristic properties, including dimensions and arrangement of electric connectors, inlet ports, and outlet ports corresponding to different electric power generation efficiencies of individual cell assemblies. Furthermore, the cell assemblies have also one or more fuel cell stacks, and some of these stacks have different electric power generating efficiencies corresponding to different properties characteristic of individual zones of the manifold and respectively, different arrangements of electric connections, inlet ports, and outlet ports. Characteristic properties of some of these stacks are designed in such a way that only a fuel cell stack with specifically designed output can be added to given zone of said manifold which corresponds to this specific output. Further, a locking plate is used to couple the assembly of fuel cells with such manifold zones in which the placement of any fuel cell stack is undesirable, whereas the design of manifold ducts allows to make connection with the duct tight in case when a specific zone of the manifold is connected neither to the locking plate nor to a fuel cell stack, and further, the design of the manifold ducts eliminates the need to use such locking plates.

The objective of the present invention is to provide a simple and compact design of a stack of high-temperature fuel cells, including those of SOFC type, to generate electric power from the supplied gas fuel such as: hydrogen, synthesis gas, and hydrocarbons, especially methane, biogas, ethanol, bioethanol and methanol, allowing to install one or more such stacks in a thermally insulated modular metal housing equipped with heating coils provided between the stacks and powered in the course of start-up from an external power source. The objective of the invention is also to develop such a design of the stack which will allow to minimise the number of its structural components, fabricate them of inexpensive materials, especially ceramic ones, and with the use of inexpensive processes, and thus reduce significantly the manufacturing cost guaranteeing at the same time high performance of the cell stack.

The essential idea of using high-temperature fuel cells to generate electric power in a stack of fuel cells according to the invention consists in that the cells are arranged into an assembly comprising from several to a dozen or so identical modules containing two fuel cells each arranged in a stack assuming thus the form of a cuboidal solid and with modules bound to each other separably; a heat-resisting metal base on which the assembly of modules is seated; and a heat-resisting metal cover covering the set which is provided with a sleeve port supplying the gas fuel to the inner angle collecting duct and another sleeve port supplying air to the inner angle collecting duct, whereas the heat-resisting metal base is provided with a sleeve port constituting an extension of the inner combustion gas discharge collecting duct, and another sleeve port, constituting an extension of the inner nitrogen discharge collecting duct. Each of the modules composed of two fuel cells consists of a ceramic frame, the central straight-through square-shaped opening of which is given the form of a two-step frame socket, and its lower portion houses a perforated heat-resisting metal cathode plate with U-shaped profile with a double-angle offset on its upper side, inside which a moulded ceramic piece with grooves on both sides is disposed, while over them, on the flat portion of the cathode plate, two single-side grooved fuel cells are situated facing each other with their grooved sides and separated from each other by means of perforated heat- resisting metal anode plate with one of its ends being given the shape of letter "U" and adhering to the double-angle offset of the cathode plate. Moreover, each of the single-side grooved fuel cells is composed of a 0.8- 2.0-mm thick anode layer made of NiO-ZrO ₂ composite stabilised with Y ₂ O ₃ situated on the grooved side of the cell, a 5-15-μm thick layer of solid electrolyte m made of ZrO ₂ stabilised with Y ₂ O ₃ or SC ₂ O ₃ adjacent to the flat surface of the cell, and a 100-250-μm thick cathode layer made of a material with perovskite structure being a mixture of La, Sr, Co, and Fe (LSCF) oxides or La, Sr, and Mn (LSM) oxides, adhering to the cathode layer. It is favourable when the ceramic frame of each of the two-cell modules is provided with two straight-through profiled holes oriented axially with respect to each other on each of the upper surfaces of its shorter sides, namely when one of the sides is provided with the gas fuel-supplying hole and the air-supplying hole, and on the second shorter side it is provided with the nitrogen-discharging hole and the combustion gas-discharging hole, and further the side wall of the gas fuel-supplying hole is connected by means of pinholes supplying said fuel with the upper side wall of the two-step frame socket, side wall of the air-supplying hole is connected by means of air supplying pinholes with lower side wall of said socket, the side wall of the nitrogen discharge hole is connected by means of nitrogen discharging pinholes with the lower side wall of the two-step frame socket, and the side wall of the combustion gas-discharging hole is connected by means of combustion gas discharging pinholes with the upper side wall of the socket It is favourable when the lower element of the perforated U-shaped heat- resisting metal cathode plate remains in contact with the heat-resisting metal base, remaining in turn in contact with two stack-binding bolts insulated in the heat-resisting metal cover, and the upper perforated metal anode plate remains in contact with the heat-resisting metal cover, the latter in turn remaining in contact with the other two stack-binding bolts insulated in the base. It is favourable when the contact surfaces between fuel cells and walls of two-step frame sockets as well as contact surfaces between ceramic frames arranged in a stack are sealed by means of ceramic fibre paper saturated with finely ground glass-ceramic material.

The use of fuel cells with single-side grooved anodes or cathodes in the stack according to the invention allowed to eliminate the necessity to used additional expensive grooved inter-connector metal plates, corrugated plates, or ceramic spacing components necessary to distribute gas fuel over anode surfaces of these cells. Instead, using identical double-socket ceramic frames in modules of the stacks allowed to dispose two fuel cells per frame together with the moulded ceramic piece with grooves on both sides distributing air onto surfaces of two neighbouring cathodes. It further allowed to use perforated metal plates collecting electric charge inside these frames, making the structure compact and significantly simplified.

Further, by using versatile ceramic frames in fuel cells according to the invention, it is possible to manufacture them with the use of inexpensive raw materials and by means on well-known and inexpensive methods such as thermoplastic injection, eliminating at the same time the need to provide additional electrical insulation between cells and the frames, which results in reduction of the overall manufacturing cost of the cell stack. Further merits of the stack according to the invention include also the use of circumferential joints of the groove-tongue type in the design of ceramic frames, metal base, and metal cover, which improves significantly stability and tightness of stacks formed by the modules, while the use of ceramic fibre paper saturated with finely ground glass-ceramic material for sealing the contact surfaces between fuel cells and frames protects the sealings against getting stuck and thus allows to disassembly the components of the stack without the risk of mechanical damage.

The subject of the invention is presented in illustrations showing its example embodiment, of which Fig. 1 shows the electric-power generating stack comprising six modules of high-temperature fuel cells, in the perspective view; Fig. 2— the same cell stack in the top view; Fig. 3— vertical section of the same cell stack vertical section along line A-A; Fig. 4 — vertical section of the same cell stack along line B-B; Fig. 5— vertical section of the same cell stack along line C~C; Fig. 6— vertical section of the same cell stack along line D-D; Fig. 7— vertical section of the same cell stack along line E-E; Fig. 8— ceramic load-bearing frame of the cell stack in the perspective view; Fig. 9— the same ceramic frame in the top view; Fig.10— vertical section of the same ceramic frame along line F-F of Fig. 9; Fig. 11— vertical section of the same ceramic frame along line G-G; Fig. 12— vertical section of the same ceramic frame along line H-H; Fig. 13— vertical section of the same ceramic frame along line J-J; Fig. 14— vertical section of the same ceramic frame along line K-K; Fig. 15— vertical section of the same ceramic frame along line L~L; Fig. 16— moulded ceramic piece with grooves on both sides distributing air over the fuel cell surface as seen from the cathode side in the perspective view; Fig. 17— vertical section of the same moulded ceramic piece along line M-M; Fig. 18— a single fuel cell membrane in the perspective view; Fig. 19— vertical section of the same membrane along line N-N; Fig. 20 — a magnification of the membrane end detail "Z" of Fig. 19; Fig. 21— perforated metal plate collecting electric charge from fuel cell anode surfaces, in the top view; Fig. 22— vertical section of the same perforated plate along line O-O; Fig. 23— perforated metal plate collecting electric charge from fuel cell cathode surfaces, in the top view; Fig. 24— vertical section of the same perforated plate along line P-P; Fig. 25— a complete module of two fuel cells together with air-distributing moulded ceramic pieces disposed in a single ceramic frame, in the top view; Fig. 26— vertical section of the same complete module along line R-R; Fig. 27— vertical section of the same complete module along line S-S; Fig. 28— vertical section of the same complete module along line T-T; and Fig, 29— vertical section of the second variant in the form of a stack of a larger number (a dozen or so) of high-temperature fuel cell modules with the middle portion of the stack between the wavy lines not shown.

An example embodiment of the stack of high-temperature fuel cells for generating electric power from a gas fuel and air shown in Fig. 1 comprises a heat-resisting metal base 1, an assembly 2 composed of six identical complete modules 3 of two fuel cells located in separate ceramic frames 4 seated on said base and arranged in a stack, and a heat-resisting metal cover 5 covering the assembly, whereas all the modules have the form of flat cuboids with rectangular bases and are joined with each other by means of grooves 6 and tongues 7 provided on their circumferential surfaces. Each of the complete two-cell modules 3 is composed of a rectangular ceramic frame 4 with a lower circumferential groove 6 and an upper circumferential tongue 7, said frame having also four circular assembly straight-through holes 8 and 8' in its corners and two straight-through holes in the form of rectangles with shorter sides rounded between the assembly holes provided along both of the two shorter sides of the frame, namely the gas fuel-supplying hole 9, the air- supplying hole 10, the nitrogen-discharging hole 11, and the combustion gas-discharging hole 12. Furthermore, the upper surface 13 of the ceramic frame 4 is provided with a two-step frame socket 15 with different transversal dimensions around the centrally situated straight-through square- shaped opening 14 of said frame, the higher vertical side wall of said socket being connected, via pinholes 16 provide in it, with the fuel-supplying hole 9, one vertical side wall of the square opening 14 situated under said socket being connected, via pinholes 17 made in said wall, with the air-supplying hole 10, the higher side wall of the opposite side of the socket being connected via pinholes 18 with the nitrogen-discharging hole 11, and the vertical side wall of the square-shaped opening 14 situated lower being connected via pinholes 19 provided therein with combustion gas-discharging hole. Further, in the square-shaped straight-through opening 14 of the moulded ceramic piece 4 as well as in the lower two-step frame socket 15, a perforated heat-resisting metal cathode plate 20 with U-shaped profile is disposed, the lower free end of which is provided with a double-angle offset 21, horizontal portion of which adheres to the horizontal side of the lower two-step socket 15, and inside the cathode plate disposed is a square moulded ceramic piece 22 provided with air-distributing grooves 22' on both sides, whereas in the upper higher portion of the frame socket 15 on the upper portion 23 of the cathode plate 20 disposed are two single-side grooved fuel cells 24 of the module 3, facing each other with their grooved sides 25 and separated from each other by means of a perforated heat- resisting metal anode plate 26 with one U-shaped end 27 adhering to the horizontal portion of the double-angle offset 21 of the cathode plate 20. Moreover, surfaces of contact of the fuel cells 24 with surfaces of side walls of the two-step frame sockets 15 provided in ceramic frames 4 as well as surfaces of ceramic frames 4 forming the stack are sealed by means of a high-temperature ceramic fibre paper (not shown in the figures). All the single-side grooved fuel cells 24 have on the their grooved side 25 a 1.2-mm thick anode layer 28 made of NiO-Y-ZrO ₂ (zirconium dioxide stabilised with yttrium oxide) composite constituting a load-bearing layer of the cell, a 5-μm thick solid electrolyte layer 29 made of ZrO ₂ stabilised with Y ₂ O ₃ - adhering to the flat surface of the cell, and a cathode layer (cathode) 30 made of material with perovskite structure constituting a 30-μm thick layer of mixture of La, Sr, Co, and Fe (LCSF) oxides and a 200-μm thick layer of La, Sr, and Mn (LSM) oxides adhering to said cathode layer. The metal cover 5 covering the assembly of complete modules 3 is provided with sleeve port 31 supplying the gas fuel to the angle collecting duct 32 and a sleeve duct 33 supplying air to the angle collecting duct 34, the duct being formed by the modules and the cover, whereas ends of horizontal portions 35 and 35' of the ducts provided in the metal cover 5 are closed by means of metal plugs 36, while vertical segments 37 and 37' of the ducts are extensions of holes 9 and 10, respectively, constituting vertical portions of collecting ducts 32 and 34, respectively. Further, the other holes 11 provided in ceramic frames 4 of the assembly 2 of modules 3 constitute the nitrogen discharge collecting duct 38, extension of which in the metal base 1 is provided with a sti'aight-through hole 39 terminated with a sleeve port 40 planted in said hole, while holes 12 of the frames create the combustion gas discharge collecting duct 41, extension of which in the metal base 1 is provided with a straight-through hole 42 terminated with a sleeve port 43 planted in the latter. Furthermore, the metal base 1, the assembly 2 of five complete modules 3 of two fuel cells 24 sitting on said base, and the metal cover 5 covering said set are bound together by means of four binding bolts 44 and 45, located in corners and inserted into holes 8 and 8' of moulded ceramic pieces 4, in holes 46 provided in the metal base 1 and coaxial with the latter, and in holes 47 provided in the metal cover 5. Moreover, in the lower portion of the metal base 1, the two bolts 45 situated at corners of one of the shorter sides of the assembly 2 bridged together by means of metal plate 48 adjoining flanges of ceramic flanged sleeves 49 planted in the base along extension of holes 8' of the assembly 2 aligned coaxially with respect to each other and bound with heads 50 of the bolts, whereas heads 50' of the other two binding bolts 44 are situated on the opposite side of the assembly 2 and adhere directly to the lower surface of said metal base. Further, upper ends of binding bolts 44 and 45 are inserted in ceramic distance tubes 51 sitting on the upper surface of the metal cover 5, and upper ends of two binding bolts 44 are inserted in ceramic flanged sleeves 52 planted in holes provided in said cover and aligned coaxially with holes 8 of the assembly 2, while flanges 53 of said sleeves support analogous ceramic distance tubes 51 also put onto said bolts, whereas faces of the distance tubes carry helical springs 54 placed onto bolts 44 and 45 are pressed against said tubes by means of annular washers 55 and nuts 56 screwed onto tips of the bolts. Holes 9, 10, 11, and 12 in ceramic frames 4 have the form of a rectangle with rounded shorter sides.

In the second example embodiment shown in Fig. 29, the stack according to the invention is the assembly 2 composed of fifteen identical complete modules 3 comprising two fuel cells each identical to those used in the first example embodiment, whereas the design of the stack provided for single-side grooved fuel cells 24 in which the anode layer 28 was 2-mm thick, the electrolyte layer 29 made of ZrO ₂ but stabilised with SC ₂ O ₃ was 15-μm thick, and the cathode 30 adhering to the latter was 200-μm thick.

In another example embodiment of the stack according to the invention, not shown in the figures, CS SOFC-type cells were used as fuel cells 24 in which the 8-μm thick electrolyte layer 29 was made of zirconium dioxide stabilised with Y ₂ O ₃ ; the single-side grooved cathode 30 was 1.5-mm thick and constituted at the same time the mechanical load-carrying layer; and anode 28 was given the form of flat 150-μm thick layer which resulted in rearrangement of points where fuel gas and air were supplied and combustion gas and nitrogen discharged. Moreover, in this embodiment, ceramic frames provided with oval holes 9, 10, 11 and 12 were used.

The principle of generating electric power by means of a stack of fuel cells according to the invention consists in that the fuel cell stack designed as described above is placed in a chamber-housing made of sheet metal and lined inside with fibrous layer of thermal insulation and equipped with heating coils surrounding the stack, whereas end portions of bolts 44 and 45 protruding outside are provided with electric leads connecting the bolts to a receiver of electric power generated from the gas, not shown in the figures. The gas fuel, preferably hydrogen or a mixture of hydrogen and carbon oxide, such as the synthesis gas, or products obtained by reforming hydrocarbons such as natural gas, biogas, and methanol are supplied under pressure of up to 30 kPa to the fuel port 31 fixed to the heat-resisting metal cover 5 of said stack, from where via horizontal duct 35 the fuel passes to a vertical collecting duct 32, and further via pinholes 16 it gets in between grooves 25 of two anode layers 28 of fuel cells 24, said layers being situated opposite and separated from each other by means of heat-resisting metal anode plate 26 carrying the electric charge. At the same time, the sleeve port 33 planted in the heat-resisting metal cover 5 is supplied with air necessary for the fuel to be combusted. The air, under pressure amounting to 30 kPa, passes via horizontal duct 35' to a vertical collecting duct 34 from where via pinholes 17 it further passes in between double grooves 22' of the moulded ceramic piece 22 distributing the air onto two adjacent flats surfaces of cathodes 30 of the fuel cells 24. At the same time, oxygen contained in the air supplied to surfaces of the cathodes is subject to ionisation by bonding two electrons from the external circuit, while the emerging O ₂ ions, as a result of different partial pressure prevailing on both sides of the cells, migrate via oxygen vacancies in the crystalline structure of the solid electrolyte layer 29 towards anodes 28 where, passing via perforated anode plates 26, they give away two electrons each to the external circuit connected to the power consuming appliance not shown in the figures, whereas the released oxygen atoms are combined with hydrogen and/or carbon oxide molecules creating water vapour and/or carbon dioxide which, through pinholes 19 of each of the ceramic frames 4 oriented diagonally with respect to fuel supplying pinholes 16 pass to combustion gas collecting duct 41 and further via the outlet sleeve port 43 in the metal base 1 outside the device containing the stack according to the invention, whereas nitrogen remaining in the cathode area together with remains of air flows from pinholes 18 of the ceramic frame oriented diagonally with respect to air inlet pinholes 17, from where via the nitrogen collecting duct 38 and the sleeve port 40 of metal base 1 is discharged outside the device.

Further, electric charge originated on both of neighbouring anode layers

28 of the fuel cells 24 is collected by perforated anode plates 26 disposed between pairs of grooved anode-layer carrying surfaces 28 of the two fuel cells 24 and transferred to cathode layers 30 of neighbouring modules 3 by means of perforated metal cathode plates 20 remaining in contact with perforated anode plates 26. By connecting modules 3 set up by two fuel cells 24 in series it is possible to increase the voltage generated by the stack by adding consecutive modules to the stack and increasing their active surface with current kept at constant value. Furthermore, at the bottom of the stack according to the present invention, perforated metal cathode plates 20 remain in contact with metal base 1 of the stack, said base remaining in turn in contact with two stack-binding bolts 44 situated on one of shorter sides of ceramic frames 4 but not insulated from the base, whereas said bolts go through insulating flanged ceramic insulation sleeves 52 planted in metal cover 5 of the stack. Further, in the upper portion of the stack, perforated metal anode plates 26 remain in contact with metal cover 5 and with the other two binding bolts 45 lower ends of which are inserted insulating ceramic distance tubes 49 planted in metal base 1 of the stack and are connected to each other from the bottom by means of steel plate 48. Electric power generated in fuel cells 4 is transferred to suitable receiver by means of electric leads attached to cold upper portions of opposite binding bolts 44 and 45 by means of nuts (nor shown in figures). A single sheet-metal thermally insulated chamber casing equipped with heating coils may house a single stack of fuel cells described as an example embodiment of the invention or a larger number, such as a dozen or so, of such stacks surrounded with or separated by heating coils along their longer sides, with the stacks, depending on the required current-voltage conditions, connected in series or in parallel outside such device. Moreover, in order to improve the overall efficiency, the device can be additionally equipped with nitrogen- air and/or combustion gas-air heat exchangers.

List of designations used in Figures

1— heat-resisting metal base

2— a set of six two-fuel-cell modules

3— module of two fuel cells

4— module ceramic frame

5— heat-resisting metal cover

6— circumferential grooves of ceramic frame, metal base, and metal cover

7— circumferential tongues of ceramic frame, metal base, and metal cover

8— two holes for stack-binding bolts

8'— two holes for stack-binding bolts

9— ceramic frame, fuel supplying rectangular hole with its shorter sides rounded or oval hole

10— ceramic frame, air supplying rectangular hole with shorter sides rounded or oval hole

11— ceramic frame, nitrogen discharging rectangular hole with shorter sides rounded or oval hole

12— ceramic frame, combustion gas-discharging rectangular hole with shorter sides rounded or oval hole

13— ceramic frame, upper surface

14— ceramic frame, central square opening

15— ceramic frame, two-step frame socket

16— pinholes connecting the two-step socket with the fuel-supplying hole

17— pinholes connecting the two-step socket with the air-supplying hole

18— pinholes connecting the two-step socket with the nitrogen-discharging hole

19— pinholes connecting the two-step socket with the combustion gas discharging hole

20— perforated metal cathode plate

21— double-angle offset of the perforated cathode plate

22— moulded ceramic piece with grooves on both sides

22'— grooves on both sides of the moulded ceramic piece

23— upper portion of perforated cathode plate

24— one-sidedly corrugated fuel cell

25— grooves of the single-side grooved cell

26— perforated metal anode plate 27— U-shaped end of perforated anode plate

28— anode layer of the single-side grooved fuel cell

29— solid electrolyte layer of the single-side grooved fuel cell

30— cathode layer of the single-side grooved fuel cell

31— fuel supplying sleeve port in the metal cover

32— fuel supplying angle collecting duct

33— metal cover air supplying sleeve port

34— air supplying angle collecting duct

35— horizontal port of the fuel supplying collecting duct 35'— horizontal port of the air supplying collecting duct

36— metal plugs

37— vertical section of the fuel supplying angle collecting duct 37'— vertical section of the air supplying angle collecting duct

38— nitrogen discharge collecting duct

39— metal base straight-through hole

40— metal base nitrogen discharging sleeve port

41— combustion gas discharge collecting duct

42— metal base straight-through hole

43— metal base combustion gas discharging sleeve port

44— stack binding bolts

45— stack binding bolts

46— metal base bolt holes

47— metal cover bolt holes

48— metal plate bridging the bolts

49— metal base flanged sleeves

50, 50'— heads of stack binding bolts

51— metal cover ceramic distance tubes

52— metal cover flanged ceramic sleeves

53— flanges of the flanged sleeves

54— helical springs

55— nut washers

56— nuts of stack binding bolts