Method of ameliorating temperature distribution of a fuel cell

Abstract: In a fuel cell comprising: cell elements (10), including each an electrolyte plate, an anode plate and a cathode plate, the electrolyte plate being sandwitched by the anode plate and the cathode plate; and separator plates (18) possessing each passages (A1, A2, C1, C2) formed on the front and back faces thereof so as to supply fuel gas to the anode plate of the cell element (10) and to supply gaseous oxidizer to the cathode plate, the cell elements (10) and the separator plates (18) being piled up one after the other, creating plural stages, anode side gas supply means (30a, 32a) for supplying the fuel gas to fuel gas passages (A1, A2) formed on one face of the separator plate (18); cathode side gas supply means (34a, 36a) for supplying the gaseous oxidizer to the oxidizer passages (C1, C2) formed on the other face of the separator plate (18) in a manner such that the oxidizer gas supplied to one separator plate (18) may flow in the direction opposite to the oxidizer gas supplied to adjacent separator plates (18); and heat transfer assisting means (22, 24) formed on the front and back faces of each separator plate (18) so as to assist heat transfer in the direction the separator plates (18) and the cell elements (10) are piled up.

Description: The present invention relates to a method of ameliorating temperature distribution of a fuel cell according to the first part of claim 1. The principle of the fuel cell is as follows: hydrogen of the fuel gas and oxygen of the oxidizer are chemically reacted with each other with use of electrolyte, thereby producing electricity and water. This is the reversal of the electrodialysis of water. Major components of the fuel cell are cell elements, each of which elements includes an electrolyte plate, a porous anode plate and a porous cathode plate, with the electrolyte plate being sandwiched by the anode and the cathode plates. Electricity is generated by supplying the fuel gas to the anode side while supplying the oxidizer to the cathode side. Heretobefore phosphoric acid or fused carbonate is employed as the electrolyte of the fuel cell. Reactions at the anode and the cathode plates, when the fused carbonate is utilized as the electrolyte, are as follows: Cathode: 1/2 O₂ + CO₂ + 2e → CO₃²⁻ Anode: H₂ + CO₃²⁻ → H₂O + CO₂ + 2e⁻ In the conventional fuel cell, the cell elements and the separator plates are piled up alternately, making plural stages, and the fuel gas and the gaseous oxidizer are supplied to each cell element in a manner such that those gases flow along the upper and lower faces of the separator plate from one side of the separator plate to the other side thereof. Meanwhile, since heat is produced upon generation of electricity in the fuel cell, certain measure has to be taken for elimination of such heat. Heat elimination, or cooling can be carried out by certain cooling means, or by continuous supply of fuel gas and oxidizer gas so that the previously supplied fuel gas and oxidizer and the fuel cell system may be cooled by the following gases. Gases introduced in a passage formed within the separator plate cool the cell element by receiving heat from the cell element as well as the separator plate until they reach the exit of the passage. In such a cooling, however, temperature distribution along the cell element face is not gentle, creating considerable temperature difference of as large as three hundred degrees C between the heighest and the lowest temperature points thereof. Such a large undulation in temperature profile along the cell element surface results in nonuniform current density, which in turn leads to deterioration of power generation efficiency of the fuel cell. Also, a sharp inclination in temperature distribution reduces longevity of the cell element and the separator. A fuel cell according to the first part of claim 1 is known from JP-A-62-80 967 and JP-A-63-27 9574. The flow direction of the fuel gas on the one side of the separator plate is the same as the flow direction of the oxidizing gas on the other side of the separator plate. The gas flow direction at one separator plate is opposite to the gas flow direction at the adjacent separator plates. US-A-4 708 916 discloses a fuel cell comprising a stack of cell elements separated by separator plates, wherein the electrodes of the cell elements and the separator plates have openings providing channels for the fuel gas and the oxidizing gas. Further the piled-up cell elements and separator plates are clamped together by holding means. JP-A-62 108 67 discloses a separator element having openings for supplying and discharging air and fuel gas. Recessed or projecting parts departing from the openings or directed to the openings form guiding or distributor means for guiding or distributing the gas flows. An object of the present invention is to provide a method of reducing the ups and downs in the temperature distribution all over the surfaces of the cell elements and the separators and wherein the temperature profile of the cell element may be symmetrical with only small fall and rise. According to one aspect of the present invention there is provided a method of improving the temperature distribution for a fuel cell comprising cell elements, each cell element including an electrolyte plate, an anode plate and a cathode plate, the electrolyte plate being sandwiched by the anode plate and the cathode plate; and separator plates, each separator plate possessing passages formed on the front and back faces thereof so as to supply fuel gas to the anode plate of the cell element and to supply gaseous oxidizer to the cathode plate, the cell elements and the separator plates being piled up one after the other, creating plural stages, anode side gas supply and discharge means, for supplying the fuel gas to fuel gas passages formed on one face of the separator plate, cathode side gas supply and discharge means for supplying the gaseous oxidizer to the oxidizer passages formed on the other face of the separator plate in a manner such that the oxidizer gas supplied to one separator plate may flow in the direction opposite to the oxidizer gas supplied to adjacent separator plates, and heat transfer assisting means formed on the front and back faces of each separator plate so as to assist heat transfer in the direction the separator plates and the cell elements are piled up, wich method is characterized in that the anode side gas supply and discharge means of one separator plate supplies the fuel gas in the direction parallel to the oxidizer gas supplied from the cathode gas supply and discharge means of the next separator plate with respect to one cell element between those separator plates. The objects, aspects and advantages of the present invention will be more fully understood by reference to the following detailed description taken in conjunction with the various figures and appended claims. The drawings form an integral part of the description of the preferred embodiment and are to be read in conjunction therewith. Figure 1 is a perspective view showing a fundamental arrangement of a fuel cell used with the present invention; Figure 2 is a schematic view to explain supply and discharge of the fuel gas and the oxidizer to separator plates which are stacked on cell elements one after the other; Figure 3 is a partial sectional perspective view depicting an entire fuel cell system used with the present invention; Figure 4 is a perspective view depicting the details of the cell elements and the separator plates of Figure 3 as they are stacked one after the other. Figure 5 is a partial enlarged view of the separator plate; Figure 6 is a partical enlarged view to explain the gases fed through the gas passages to the separator plates as the cell elements and the separator plates are stacked; Figure 7 is a diagram showing temperature distribution of the gases flowing along the front and back faces of adjacent separator plates and the cell element with the horizontal axis being a distance measured in the direction the gas flows; Figure 8 is a perspective view illustrating a fundamental construction for assembling of the fuel cell according to another embodiment used with the present invention; and Figure 9 is a partially-cut perspective view of the fuel cell of Figure 8. Figure 10 shows temperature distribution of a conventional fuel cell for comparison with Figure 7. Now referring to Figure 1 of the accompanying drawings, a basic construction of a fuel cell used with the present invention will be described. Reference numeral 10 designates a cell element, which is composed of an electrolyte plate 12 made from fused carbonate, phosphoric acid, or the like, and an anode plate 14 and a cathode plate 16, with the electrolyte plate being located between the anode plate and the cathode plate. Numeral 18 denotes a separator plate through which fuel gas such as hydrogen is supplied to the anode plate 14 and gaseous oxidizer such as air is supplied to the cathode plate 16. The cell elements 10 and the separator plates 18 are piled up one after the other, creating multiple stages as a body 20 of the fuel cell. In piling, each cell element 10 is arranged in a manner such that the cathode plate 16 may become a front face or an upper face while the anode plate 14 a back face or a lower face, and such that fuel gas passages A1 and A2 may be formed between the anode plate 14 and the upper face of the separator plate 18, as indicated by shaded arrows in Figure 1 while oxidizer gas passages C1 and C2 may be formed between the cathode plate 16 and the lower face of the separator 18 as indicated by unshaded arrows C1 and C2. The oxidizer gas passages C1 and C2 are formed such that the oxidizer supplied to one separator plate may flow in the counter direction relative to the oxidizer gas supplied to adjacent separator plates as indicated by C1 and C2. As for one cell element 10, the oxidizer gas and the fuel gas flow in the same direction, which is referred to as "co-flow", as indicated by C2 and A2, or C1 and A1. As for one separator plate 18, the fuel gas supplied to one face thereof flows in the counter direction against the oxidizer gas supplied to the other face thereof as indicated by A1 and C2, or A2 and C1. On the top face as well as the bottom face of each separator plate 18, there are formed near the entrance and the exit of the passage block-like projections or fins22 and 24 which extend parallel to each other in the direction the supplied gases flow, and small semispherical projections 26 therebetween. Among these fins 22 and 24, the outermost fins 22 are made relatively short, and the fins 24 thereinside are spaced from the outermost fins 22 by clearance 28 and made relatively long. These fins 22 and 24 are formed such that they occupy approximately half the separator plate surface from the entrance and exit side, with one-fourth being occupied from each side. Another half of the separator plate surface is occuppied by the small semispherical projections 26 provided between the fins 24. The block-shaped fins 22 and 24 contact with corresponding anode plate 14 and cathode plate 16 of the cell elements 10 as the cell elements 10 and the separator plates 18 are stacked, so that the heat transfer between the anode plate 14 and the cathode plate 16 are improved. So is that between cathode plates of the adjacent cell elements. Referring now to Figure 2, the anode side passages A1 and A2 of adjacent separators 18 are connected to fuel gas supply passages 30a and 32a and fuel gas discharge passages 30b and 32b respectively, while the cathode side passages C1 and C2 are communicated with oxidizer gas supply passages 34a and 36a, and oxidizer gas discharge passages 34b and 36b respectively, so that the fuel gas and the oxidizer gas may flow in the opposite directions along the top face and the bottom face of each separator plate 18 respectively, and that C1 and C2 may be directed in directions opposite to each other. As the fuel gas is fed to the anode plate 14 and the oxidizer gas is fed to the cathode plate 16 of each cell element 10, the gases so fed react with each other via the electrolyte 12, generating electrical energy, as illustrated in Figures 1 and 2. Each cell element 10 and separator plate 18 are electrically connected to each other, whereby superposed electric power can be drawn from the uppermost cathode plate 16 and the lowermost anode plate 14 of the fuel cell body 20. During generation of the electric power, the oxidizer gas is supplied 10 to 20 times as much as the fuel gas. If the oxidizer gas temperature at the entrance of the passage is 550 °C, the same rises to 750 °C, which is very influential to the temperature profile of the cell element. In this particular embodiment, since the oxidizer gas passages C1 and C2 are directed in the opposite direction respectively, and the fins 22 and 24 are provided near the entrances and the exits of those passages, mainly, heat of the oxidizer gas is transmitted in the direction of the piling near the block-like fins 22 and 24. In other words, since these fins 22 and 24 serve to assist the heat transmission between adjacent cell elements 10, particularly between oxidizer gases flowing through C1 and C2, the temperature difference between the entrance and the exit of each cell element 10 is reduced, shaping the temperature distribution curve rather flat in the direction the gases flow in. Figures 3 to 6 illustrate more detailed view of construction of the fuel cell according to the present invention. The cell element 10 and the separator plate 18 are shaped rectangular, as shown in Figure 4. A large number of small openings 40 and 42, which serve as the supply passage 30a, 32a, 34a and 36a, and the discharge passage 30b, 32b, 34b and 36b of Figure 2, are formed with equal intervals within the plate 10 along the both longer lateral sides thereof. The cell element 10 is constituted by sandwitching the electrolyte 12 by the anode plate 14 and the cathode plate 16. The openings 40 for supplying/discharging the gases are formed in the anode plate 14 as well as the cathode plate 16. The pores 42 of the separator plate 18 are provided with distributors 44a and 44b which allow the pores 44a and 44b to communicate with the corresponding passages A1, A2, C1 and C2 so that the fuel gases and the oxidizer may be introduced to the passages A1, A2, C1 and C2 formed on the upper and lower faces of the separator 18. In clearer terms, as illustrated in Figures 5 and 6, if the fuel gases are desired to be supplied to the anode side gas passage A2 of the separator plate 18, an entrance distributor 44a is provided to the fuel gas supply passage 32a, and an exit distributor 44b is provided to the discharge passage 32b. For example when there is provided a four-channel supply/discharge line for the fuel gas and oxidizer, four distributors 44a/44b are provided along the pores 42 on either side of the separator plate 18. Sealing frames 46 for securing tight seal with the cell element 10 are respectively mounted on the upper and lower faces of the separator plate 18, and a punching metal 48 is provided inside the sealing frame 46 such that heat may be transferred well between two adjacent cell elements through the projecting fins 22 and 24 of the separator plate 18 and the punching metal 48 while allowing the supplied gases to pass through the passages. Assemblying of the above described fuel cell system including the cell elements 10 and the separator plates 18, being piled up one after the other, will be explained with Figure 3. On the bottom holder 50, a fuel cell body 20, which is a laminated body of plural cell elements 10 and the separator plates 18, is located, and a top holder 52 is placed on the top face of the laminated body 20. In the bottom and top holders 50 and 52, entrance and exit ports 30A, 32A, 34A, 36A, 30B, 32B, 34B, and 36B are formed, which are respectively connected to the gas supply passage 30a, 32a, 34a, 36a and the discharge passage 30b, 32b, 34b, 36b. To connect these entrance and exit ports to each other, pathes 52a and 52b are formed within the holders 50 and 52. Terminals for taking out electric current, 54 and 56 are also provided to the lower and upper holders 50 and 52. A presser plate 60 is disposed on the upper holder 52 via a bellows 58. Lugs 62 and 64 project from the lower holder 50 and the presser plate 60 respectively at corresponding positions thereof, and each pair of lugs 62 and 64 are joined by a rod 68 and nuts 70. Reinforcement members 72 are integrally provided to the presser plate 60 so as to span every two lugs 64 in the width direction of the fuel cell body. According to the fuel cell constructed in the above manner, when the power generation temperature is set to 650 degrees C, fuel gas, such as hydrogen, of approximately 500 degrees C has to be supplied to the inlet port 30A and 32A. The fuel gas is, for example, hydrogen-rich gas which is obtained by reforming natural gas with steam by a reformer. Oxidant gas of approximately 400 degrees C is fed to the inlets 34A and 36A. The oxidizer gas is supplied preferably between ten and twenty times as much as the fuel gas. Upon power generation, steam and CO₂ are expelled from the fuel gas exit 30B and 32B while residual gases are exhausted from the oxidant gas exit 34B and 36B. Referring now to Figure 7, A1 and A2 indicate fuel gas temperature, C1 and C2 indicate oxidant gas temperature, and I indicates cell element temperature in the direction the respective gases flow. Since the fins 22 and 24 which serve as thermal transfer assisting means are provided near the entrances and the exits of the separator plate, heat propagation between the oxidizer gas flowing through C1 and C2, which is influential to the temperature distribution, is promoted, whereby the undulation of the cell element temperature profile I becomes more gentle, namely the temperature range is reduced to as small as about one hundred degrees C, with symmetrical configuration Figure 10 shows temperature profile of a fuel cell of conventional structure: the cathode side gas C1 and C2 flow in the same direction ("co-flow" type) for comparison with Figure 8. In Figure 10, the gas temperature at the entrance is about 550 °C and that at the exit is about 700 °C, so that the profile has a large undulation of approximately 150 °C. Figure 8 illustrates a basic construction of another embodiment used with the present invention. Major feature of this illustrated embodiment lies in the way the fuel gas and the oxidant gas flow in, i. e., the fuel gas and the oxidant gas flow perpendicularly to each other along the upper face and the lower face of the separator plate 18 respectively. Fundamental structure of the fuel cell of this embodiment is idential to that illustrated in Figure 1 and like numerals are assigned to like components in both figures, so that explanation about those components are omitted. In this particular embodiment the Projecting fins 22 and 24 of the cathode plate 16 are layed in the direction perpendicular to those of the anode 14 so that the passages C1 and C2 on the cathode plate may cross the passages A1 and A2 on the anode plate at right angles. A fuel cell employing the basic structure depicted in Figure 8 is illustrated in Figure 9. The cell element 10 and the separator plate 18 are shaped square respectively, openings 40 and 42 are made along the periphery thereof so as to form the supply and discharge pathes for the fuel gas and oxidant gas. The distributors 44 are formed at the openings 42 for respective pathes of the separator plates 18. Entrance and exit ports for the fuel gas and the oxidant gas, 30A, 32A, 34A, 36A, 30B, 32B, 34B and 36B are respectively provided to the lower holder 50 and the upper holder 52, and therefore the fuel gas and the oxidant gas enter from those entrance ports, flowing through the passages 30a, 32a, 34a, 36a, 30b, 32b, 34b and 36b, and discharged from the exit ports. In this embodiment, although the directions of the fuel gas flow and the oxidant gas flow are orthogonal at two faces of each separator plate 18, the projecting fins 22 and 24 disposed in the gas passages function as the heat transmission assisting means, likewise as mentioned in the foregoing embodiment, thereby improving heat exhange between the fuel gas flowing along one face of the separator and the oxidant gas flowing along the other face thereof. Hence, the temperature profile of the cell element 10 possesses more gentle rise and fall. It is recognized, of course, that those skilled in the art may make various modifications to the preferred embodiments chosed to illustrate the present invention. As one modification the cathode may be attached to the the lower face of the cell element 10 and the anode may be to the upper face thereof.

Claims: A method of improving the temperature distribution of a cell element (10) for a fuel cell comprising: cell elements (10), each cell element (10) including an electrolyte plate (12), an anode plate (14) and a cathode plate (16), the electrolyte plate (12) being sandwiched by the anode plate (14) and the cathode plate (16); and separator plates (18), each separator plate (18) possessing passages (A1, A2, C1, C2) formed on the front and back faces thereof so as to supply fuel gas to the anode plate (14) of the cell element (10) and to supply gaseous oxidizer to the cathode plate (16), the cell elements (10) and the separator plates (18) being piled up one after the other, creating plural stages, anode (14) side gas supply and discharge means (30a, 32a, 30b, 32b) for supplying the fuel gas to fuel gas passages (A1, A2) formed on one face of the separator plate (18); cathode (16) side gas supply and discharge means (34a, 36a, 42a, 44a, 34b, 36b, 42b, 44b) for supplying the gaseous oxidizer to the oxidizer passages (C1, C2) formed on the other face of the separator plate (18) in a manner such that the oxidizer gas supplied to one separator plate (18) may flow in the direction opposite to the oxidizer gas supplied to adjacent separator plates (18); and heat transfer assisting means (22, 24) formed on the front and back faces of each separator plate (18) so as to assist heat transfer in the direction the separator plates (18) and the cell elements (10) are piled up, which method is characterized in that the anode side gas supply and discharge means (30a, 32a, 30b, 32b) of one separator plate (18) supplies the fuel gas in the direction (A2) parallel to the oxidizer gas (C2) supplied from the cathode gas supply and discharge means (34a, 36a, 42a, 44a, 34b, 36b, 42b, 44b) of the next separator plate (18) with respect to one cell element (10) between those separator plates (18, 18). A method according to claim 1, characterized in that the power generation temperature is between 650 and 700°C, and the oxidizer gas is supplied about 10 to 20 times as much as the fuel gas in volume. A method of claim 1 or 2, wherein the electrolyte plate (12) is made from fused carbonate. A method as set forth in one of claims 1 to 3, wherein the fuel gas includes hydrogen, and the oxidizer includes oxygen. A method of any one of foregoing claims, characterized in that a plurality of openings (40, 42) are formed along lateral sides of the cell elements (10) as well as the separator plates (18) in a manner such that these openings (40, 42) form paths (30a, 32a, 34a, 36a, 30b, 32b, 34b, 36b) as the cell elements (10) and the separator plates (18) are stacked, and the fuel gas and the oxidizer gas are supplied and discharged through the paths. A method of claim 5, characterized in that anode side distributors (44a, 44b) are provided in the vicinity of the openings (40a, 42b) which serve as the entrance and the exit of the fuel gas passages (A1, A2) such that the fuel gas enters and exits from the fuel cell element (10) through the anode side distributors (44a, 44b), and cathode side distributors (44a, 44b) are provided in the vicinity of the openings (42a, 42b) which serve as the entrance and the exit of the oxidizer gas passages (C1, C2) such that the oxidizer gas enters and exits from the fuel cell element (10) through the cathode side distributors (44a, 44b).

Inventors: SHIMIZU TORU, SHIOZAWA SHOJI, SHIMIZU, TORU, SHIOZAWA, SHOJI
Applicants: ISHIKAWAJIMA HARIMA HEAVY IND, ISHIKAWAJIMA-HARIMA HEAVY INDUSTRIES CO., LTD.
Application year: 1988
Main classification: H01M8
IPC codes: H01M8, F28F3