JP5426485B2 - Fuel cell stack - Google Patents

Description

  The present invention relates to a fuel cell stack.

  In recent years, fuel cells have attracted attention as power generation means used in next-generation cogeneration systems because high efficiency can be obtained regardless of the size. A fuel cell is a battery that uses a chemical reaction between an oxidant gas such as oxygen and a fuel gas such as hydrogen, and a single cell in which an electrolyte layer is sandwiched between an anode called an air electrode and a cathode called a fuel electrode. A plurality of sheets are overlapped. The electric voltage obtained by a set of cells (single cells) is about 0.7 V, but a desired voltage can be supplied by using a plurality of single cells in an overlapping manner. Such fuel cells include a solid polymer type using a polymer material for the electrolyte layer, and a solid oxide type using an oxide such as ceramics for the electrolyte layer.

  The polymer electrolyte fuel cell has an operating temperature of about 90 ° C. at most, and can be applied to automobiles and household cogeneration systems. On the other hand, the solid oxide fuel cell is characterized by an operating temperature as high as 600 ° C. or higher and a high power generation efficiency of 45% or higher. Therefore, a solid oxide fuel cell with a stack structure in which a plurality of single cells are combined has the advantage that a highly efficient cogeneration system can be constructed by combining turbine power generation, etc. Expected.

  By the way, in order to obtain a practical output in a solid oxide fuel cell, it is necessary to connect a plurality of solid oxide fuel cells (hereinafter referred to as single cells) in series or in parallel. At this time, each unit cell is electrically connected in a state where the fuel gas supplied to the fuel electrode side of each unit cell and the oxidant gas supplied to the air station side are not mixed. Thus, in order to make an electrical connection in a state in which mixing of gases is prevented, a member made of a material that does not transmit gas and has high electrical conductivity is used, such as a separator or an interconnector.

  A practical output can be obtained by forming a cell stack by stacking (stacking) a power generation unit including a solid oxide fuel cell and the interconnector in series. Under an operating temperature of 600 ° C. or higher, the stacked power generation units are displaced due to thermal vibrations or external vibrations, resulting in not only a decrease in power generation output but also damage to the cell stack. Further, a fuel gas is supplied to the fuel electrode side of the cell stack, and a large amount of air is supplied to the air electrode side. For this reason, the inside of the cell stack is in a positive pressure state as compared with the outside, and gas is likely to leak from the manifold portion which is each gas supply passage. For this reason, measures such as applying a load in the vertical direction of the cell stack are taken. To date, a method of fixing and applying a load to the cell stack by tightening a fixing screw at several locations around the cell stack under a constant torque has been provided (for example, see Patent Document 1).

JP 2007-53043 A

  However, even if the screws are tightened under a constant torque, it is very difficult to tighten all the screws to the same degree because they are affected by the state of the seat surface and the coefficient of friction of the screw holes. As a result, when the cell stack is tightened with several screws, there is a high possibility that the cell stack is laterally shifted for each power generation unit, and the cell stack is likely to be damaged.

  The present invention has been made in view of the above-described conventional problems, and the object of the present invention is that the cell stack may be laterally shifted for each power generation unit or the cell stack may be damaged when tightened with screws. There is no fuel cell stack to offer.

  In order to achieve this object, the present invention provides a fuel cell stack in which a cell stack is formed by laminating a power generation unit composed of a fuel cell and an interconnector sandwiching an electrolyte between a fuel electrode and an air electrode. A pressing plate and a lower fixing plate sandwiching the upper and lower ends of the cell stack, an upper fixing plate provided above the pressing plate, a tightening bolt screwed into a central portion of the upper fixing plate, and the lower fixing plate Each of the peripheral portions of the pressing plate and the upper fixing plate, and a plurality of support bolts erected on the peripheral portion of the support plate, and nuts that are screwed to the support bolt and restrict the upward movement of the upper fixing plate. Provided with a plurality of loose insertion holes for loosely inserting the support bolts, and formed at a central portion of the pressing plate that is larger than the diameter of the tightening bolt and a lower end of the tightening bolt abutting on the bolt receiver. In which parts are provided.

  In the present invention according to the present invention, an insulating plate is interposed between the pressing plate and the upper end of the cell stack and between the lower fixing plate and the lower end of the cell stack.

  According to the present invention, in any one of the above inventions, the interconnector is formed of heat-resistant stainless steel, and the support bolt is formed of a material having a smaller thermal expansion coefficient than the interconnector.

  According to the present invention, in any one of the above inventions, the upper fixing plate, the pressing plate, and the lower fixing plate are formed of heat-resistant stainless steel, and the fastening bolt is connected to the upper fixing plate, the pressing plate, and the lower fixing plate. It is formed of a material having a larger thermal expansion coefficient than the plate.

  According to the present invention, since the central portion of the cell stack is pressurized by one tightening bolt, a load can be applied to the cell stack in the vertical direction. For this reason, since the cell stack does not cause a lateral shift for each power generation unit, it is possible to prevent the cell stack from being damaged. In addition, since the screw receiving portion having a diameter larger than the diameter of the fastening bolt is provided at the central portion of the pressing plate, it is possible to accurately apply a load to the central portion of the pressing plate.

  According to one of the inventions, the insulating plate is interposed between the pressing plate and the upper end of the cell stack and between the lower fixing plate and the lower end of the cell stack, so that the cell stack An electrical short circuit can be prevented between the upper part and the lower part.

  According to one of the above inventions, the column bolts standing on the lower fixing plate and inserted in the loose insertion holes of the pressing plate and the upper fixing plate form an interconnector of the cell stack. Since it is made of a material having a smaller thermal expansion coefficient than the heat resistant stainless steel, it is possible to continue to apply a load to the cell stack even at an operating temperature.

  According to one of the inventions described above, the fastening bolt is made of a material having a larger thermal expansion coefficient than the upper fixing plate, the pressing plate, and the lower fixing plate, so that the fastening bolt does not loosen. It becomes possible to continue applying a load to the cell stack.

It is sectional drawing which shows the structure of the fuel electrode support type solid oxide fuel cell of the fuel cell stack concerning this invention. 1 is a conceptual diagram of a fuel cell stack according to the present invention. FIG. 4A is a cross-sectional view showing the configuration of the power generation unit of the fuel cell stack according to the present invention, and FIG. 4B is an enlarged view of a portion III (B) in FIG. 1 is a cross-sectional view showing a structure for applying a load to a cell stack in a fuel cell stack according to the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  A fuel electrode-supported solid oxide fuel cell (hereinafter referred to as a single cell) generally indicated by reference numeral 1 in FIG. 1 is formed from a plate-type oxide by a plate-type fuel electrode 2 and a plate-type air electrode 3. The current collector 4 is sandwiched and the current collecting layer 5 is disposed on the air electrode 3. Examples of the material of the fuel electrode 2 include metals Ni, such as nickel-added yttria-stabilized zirconia (Ni-YSZ), nickel-added samaria-stabilized zirconia (Ni-SSZ), and nickel-added scandia-stabilized zirconia (Ni-ScSZ). There is a mixture with the material constituting the solid electrolyte.

  Examples of the material for the air electrode 3 include lanthanum nickel ferrite (LNF), lanthanum manganate (LSM), lanthanum strontium cobaltite (LSC), lanthanum strontium cobaltite ferrite (LSCF), lanthanum strontium ferrite (LSF), and samarium. There is strontium cobaltite (SSC).

  Examples of the material of the electrolyte 4 include scandia-stabilized zirconia (ScSZ), yttria-stabilized zirconia (YSZ), samaria-stabilized zirconia (SSZ), and cobalt-added lanthanum gallate-based oxide (LSGMC).

  In order to obtain a high power generation output from the single cell 1, as shown in FIG. 3A, the power generation unit 6 is provided by separators 9 and 10 as interconnectors in which the gas flow path 7 and the gas supply pipe 8 are provided. And the cell stack 12 is formed by stacking the power generation units 6 as shown in FIG. At this time, on the surface where the gas flow path 7 of the fuel side separator 9 is disposed, a current collector for improving the electrical connection between the fuel electrode 2 and the fuel electrode side separator 9 as shown in FIG. The body 14 is disposed, and the single cell 1 is disposed thereon. Further, a glass material having a softening point near the operating temperature, such as borosilicate glass, is used as a sealing material 15 in a gap between the fuel electrode side separator 9 and the peripheral portion of the single cell 1. The separators 9 and 10 are made of heat resistant stainless steel.

  Next, with respect to the air electrode 3 side, the air electrode side connecting material 16 made of a paste material is disposed between the current collecting layer 5 and the air electrode side separator 10 so that the current collecting layer 5 and the air electrode side separator 10 are disposed. The electrical connection with can be improved. This paste material is applied on the current collecting layer 5 in advance before the first operation, and the air electrode side separator 10 is disposed thereon, so that a better electrical connection can be obtained in the temperature rising process during the first operation. . Further, a better electrical connection can be obtained by applying pressure to the contact surface between the separators 9 and 10 and the electrodes 2 and 3.

  Furthermore, as shown in FIG. 5A, the insulator 17 is disposed on the seal material 15 to prevent a short circuit between the air electrode side separator 10 and the fuel electrode side separator 9. Examples of the material of the insulator 17 include ceramics that are insulating even at high temperatures such as alumina, and insulating materials such as mica. 16 is an air electrode side connecting material, and 18 is a cell holder.

  Next, a structure for applying a load to the cell stack 12 and fixing the cell stack 12 will be described with reference to FIG.

  In the figure, reference numerals 20 and 21 denote a pressing plate and a lower fixing plate that sandwich the upper and lower ends of the cell stack 12, and between the pressing plate 20 and the upper end of the cell stack 12 and between the lower fixing plate 21 and the lower end of the cell stack 12. Insulating plate 22 is interposed between the two. A loose insertion hole 20a having a diameter larger than the diameter of a support bolt 23 described later is provided at two locations on the peripheral edge of the pressing plate 20, and a lower end of a tightening bolt 26 described later is applied to the center of the upper surface. A circular bolt receiving portion 20b having a diameter larger than the diameter of the contact tightening bolt 26 in a plan view is recessed.

  The column bolt 23 has a thread portion formed in the entire vertical direction, and a lower end portion is screwed into a female screw portion (not shown) of the lower fixing plate 21, and is erected at two positions on the peripheral edge portion of the lower fixing plate 21. ing. The support bolt 23 is formed of a material having a smaller thermal expansion coefficient than the separators 9 and 10 described above. Reference numeral 24 denotes an upper fixing plate provided above the pressing plate 20 so as to face the pressing plate 20, and loose insertion holes 24 a having a diameter larger than the diameter of the column bolt 23 are provided at two positions on the peripheral edge. An internal thread portion 24b into which the fastening bolt 26 is screwed is formed at the center. The pressing plate 20, the lower fixing plate 21, and the upper fixing plate 24 are made of heat resistant stainless steel, and are formed to have a thickness having sufficient rigidity so as not to break when a load is applied to the cell stack 12, as will be described later. Has been.

Reference numerals 25 and 25 denote nuts that are screwed to the support bolts 23, engage with the upper surface of the upper fixing plate 24, and restrict the upward movement of the upper fixing plate 24 when the tightening operation is performed by the tightening bolts 26. It functions as a stopper. A handle 27 is provided at the head of the tightening bolt 26, and the handle 27 is gripped, rotated so as to move the tightening bolt 26 downward, and performing a tightening operation. The pressing plate 20 is pressed downward through the bolt receiving portion 20b with which the lower end is in contact. The fastening bolt 26 is made of a material having a larger thermal expansion coefficient than the pressing plate 20, the lower fixing plate 21, and the upper fixing plate 24 .

  In the plate type solid oxide fuel cell stack 30 configured as described above, when a load is applied to the cell stack 12, the handle 27 is gripped and the tightening bolt 26 is rotated so as to move downward. , Tightening operation. By this tightening operation, the lower end of the tightening bolt 26 comes into contact with the bolt receiving portion 20b of the pressing plate 20, and the pressing plate 20 is pressed downward through the bolt receiving portion 20b. At this time, a load is applied so that the upper fixing plate 24 moves upward due to the reaction force, but since the upward movement is restricted by the nut 25, the upper fixing plate 24 is held in a fixed state.

  In the present invention, since the central portion of the cell stack 12 is pressurized by one fastening bolt 26, a load can be applied to the cell stack 12 in the vertical direction. For this reason, since the cell stack 12 does not cause a lateral shift for each power generation unit 6, it is possible to prevent the cell stack 12 from being damaged. Further, since the screw receiving portion 20b having a diameter larger than the diameter of the tightening bolt 26 is provided at the center portion of the pressing plate 20, it is possible to accurately apply a load to the center portion of the pressing plate 20.

  Further, since the insulating plate 8 is interposed between the pressing plate 20 and the upper end of the cell stack 12 and between the lower fixing plate 21 and the lower end of the cell stack 12, the upper and lower portions of the cell stack 12 are disposed. And can prevent electrical short circuit.

  Further, the support bolts 23 that are erected on the lower fixing plate 21 and are inserted into the loose insertion holes 20 a and 24 a of the pressing plate 20 and the upper fixing plate 24 form the separators 9 and 10 of the cell stack 12. Since it is made of a material having a smaller coefficient of thermal expansion than stainless steel, it is possible to continue to apply a load to the cell stack even at an operating temperature.

Further, since the fastening bolt 26 is formed of a material having a thermal expansion coefficient larger than that of the pressing plate 20, the lower fixing plate 21, and the upper fixing plate 24, a load is continuously applied to the cell stack without the tightening bolt 26 being loosened. It becomes possible.

  Here, in order to evaluate the effect of the solid oxide fuel cell stack according to the present invention, a flat plate fuel in which the air electrode 3 is composed of LNF, the fuel electrode 2 is composed of Ni and SASZ, and the electrolyte 4 is composed of SASZ. A cell stack 12 is produced by laminating 40 stages of power generation units 6 composed of pole-supported solid oxide fuel cells and separators 9 and 10 made of ferritic heat-resistant stainless steel. The power generation characteristics were evaluated.

  One fixed the cell stack using the fixing method of the present invention, and the other was fixed only by bolts arranged in the peripheral portion of the cell stack as described in the prior art.

  Table 1 shows the power generation characteristics at 800 ° C. before and after transportation. When the fixing method of the present invention was used under the same power generation current, fuel utilization rate and oxygen utilization rate conditions, the power generation characteristics were not deteriorated before and after transportation, but the bolts arranged in the peripheral part of the cell stack In the method described in the related art fixed only by the above, a significant decrease in power generation characteristics was confirmed.

  Table 2 shows the results of evaluating the sustainability of the power generation output for 1000 hours with the power generation current, the fuel utilization rate, and the oxygen utilization rate set under certain conditions. As can be seen from Table 2, when the fixing method of the present invention was used, no decrease in the power generation output was observed. From these results, the above-described effects of the present invention were demonstrated.

  In the present embodiment, two support bolts 23 are used, but three or more support bolts may be used if necessary.

  DESCRIPTION OF SYMBOLS 1 ... Fuel electrode support type solid oxide fuel cell (single cell), 2 ... Fuel electrode, 3 ... Air electrode, 4 ... Electrolyte, 6 ... Power generation unit, 9, 10 ... Separator (interconnector), 12 ... Cell Stack, 20 ... Pressing plate, 20a, 24a ... Free insertion hole, 20b ... Bolt receiving portion, 21 ... Lower fixing plate, 22 ... Insulating plate, 23 ... Post bolt, 24 ... Upper fixing plate, 25 ... Nut, 26 ... Tightening Bolts, 30 ... A flat solid oxide fuel cell stack.

Claims (4)

In a fuel cell stack in which a cell stack is formed by laminating a power generation unit composed of a fuel cell and an interconnector sandwiching an electrolyte between a fuel electrode and an air electrode,
A pressing plate and a lower fixing plate sandwiching the upper and lower ends of the cell stack;
An upper fixing plate provided above the pressing plate;
A tightening bolt screwed into the central portion of the upper fixing plate;
A plurality of support bolts erected on the peripheral edge of the lower fixing plate;
A nut that is screwed to the support bolt and restricts the upward movement of the upper fixing plate;
With
A plurality of loose insertion holes for loosely inserting the support bolts are provided in the peripheral portions of the pressing plate and the upper fixing plate,
A fuel cell stack, wherein a bolt receiving portion that is formed to be larger than the diameter of the fastening bolt and is in contact with the lower end of the fastening bolt is provided at the center of the pressing plate. The fuel cell stack according to claim 1, wherein
An insulating plate is interposed between the pressing plate and the upper end of the cell stack and between the lower fixing plate and the lower end of the cell stack, respectively. The fuel cell stack according to claim 1 or 2,
The interconnector is formed of heat resistant stainless steel,
The fuel cell stack, wherein the support bolt is made of a material having a smaller thermal expansion coefficient than the interconnector. The fuel cell stack according to claim 1 or 2,
The upper fixing plate and the pressing plate and the lower fixing plate are formed of heat resistant stainless steel,
The fuel cell stack, wherein the fastening bolt is made of a material having a larger coefficient of thermal expansion than the upper fixing plate, the pressing plate, and the lower fixing plate.

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