JP2009277374A - Solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid oxide fuel cell capable of reducing radiation heat from a conductive member for electric power extraction. <P>SOLUTION: The the solid oxide fuel cell is equipped with air for reaction with a fuel gas in a fuel cell stack; a supply route to supply a fluid of either of water or the fuel gas, in order to steam reform the fuel gas; an output member to take out electric power generated at the fuel cell stack; and a heat exchanger in order to carry out heat exchange between the output member and the fluid. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a solid oxide fuel cell.

Solid oxide fuel cells use solid oxide to generate electric power by reacting fuel gas (combustible gas) with oxygen. Here, a technique for maintaining the thermal uniformity of the fuel cell stack constituting the fuel cell is disclosed (see Patent Document 1). That is, the heat supplied to the fuel cell is heated by heat radiation from the end plate. As a result, heat dissipation from the end plate is reduced, and the thermal uniformity of the fuel cell stack is maintained.
By the way, in order to extract electric power from the fuel cell stack, a conductive member is connected to the fuel cell stack (see Patent Document 2).

JP 2006-179286 A JP 2005-183089 A

Here, it was found that the heat radiation from the conductive member for extracting power was large. In general, the fuel cell stack is stored in a heat insulating container and maintained at a high temperature. For this reason, the conductive member for extracting power is disposed across the high temperature region in the heat insulating container and the low temperature region in the outside, and the amount of heat radiation tends to increase due to the temperature difference.
In view of the above, an object of the present invention is to provide a solid oxide fuel cell capable of reducing heat radiation from a conductive member for extracting power.

  A solid oxide fuel cell according to an aspect of the present invention includes an oxygen ion conductive solid electrolyte body in which a fuel electrode and an air electrode are arranged on both sides, and generates electric power by reaction between fuel gas and oxygen in the air. A fuel cell stack to be generated, a supply path for supplying the fuel cell stack with air for reacting with the fuel gas, water for steam reforming the fuel gas, and any fluid of the fuel gas; An output member for extracting electric power generated in the fuel cell stack, and a heat exchanger for exchanging heat between the output member and the fluid are provided.

  ADVANTAGE OF THE INVENTION According to this invention, the solid oxide fuel cell which can reduce the thermal radiation from the electroconductive member for electric power extraction can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a side view showing a solid oxide fuel cell 100 according to the first embodiment of the present invention. The solid oxide fuel cell 100 is a device that generates power by receiving supply of fuel gas and air. A hydrocarbon fuel such as city gas can be used as the fuel gas. The solid oxide fuel cell 100 includes a fuel cell stack 110, air pipes 121 and 122, conductive output members 131 and 132, a heat exchanger 140, and a heat insulating container 170. In addition, the heat exchanger 140 and the air piping 121 and 122 represent the cut | disconnected cross-sectional state. Also, illustration of fuel gas and exhaust gas piping is omitted.

  The fuel cell stack 110 includes stacked fuel battery cells 111 and end plates 112 and 113. The fuel cell 111 has a plate shape and is a power generation unit. In the present embodiment, the fuel cell stack 110 is charged with more fuel gas than is necessary for power generation, and the surplus fuel gas is combusted inside the fuel cell stack 110. The heat generated by the combustion of the fuel gas in the fuel cell stack 110 and the Joule heat in the fuel cell stack 110 during power generation and the endothermic component such as heat release from the heat insulating container 170 and preheating of the input gas are balanced. As a result, the temperature of the fuel cell stack 110 is kept constant, and the heat independent operation is performed. Details of the fuel cell 111 will be described later.

  The end plates 112 and 113 are made of a plate material excellent in heat resistance and conductivity (for example, a plate material made of stainless steel). The end plates 112 and 113 are holding plates that press the stacked fuel battery cells 111 and are also output terminals for current from the fuel battery stack 110. The fuel cell stack 110 is configured by the fuel cell 111 being fastened and fixed and integrated by fixing members 114 and 115 penetrating the fuel cell stack 110 in the stacking direction via the end plates 112 and 113. The fixing members 114 and 115 are, for example, bolts and nuts screwed to the bolts, and are disposed so as to penetrate through holes formed in the frame portion of the fuel cell stack 110. In the present embodiment, the end plates 112 and 113 are a positive electrode and a negative electrode, respectively.

  The air pipes 121 and 122 are supply paths for supplying air (fluid) for reacting with the fuel gas to the fuel cell stack 110. Air supplied from the air pipe 122 is heated by the heat exchanger 140 and supplied to the fuel cell stack 110 via the air pipe 121.

  The conductive output members 131 and 132 are members for taking out electric power from the fuel cell stack 110. Bar-shaped conductive output members 131 and 132 are connected to the end plates 112 and 113, respectively. The conductive output members 131 and 132 are made of, for example, nickel having excellent heat resistance and conductivity, and function as lead portions for taking out electric power out of the fuel cell stack 110. A screw hole for a female screw is formed on the right side surface of the end plates 112 and 113 (not shown). On the other hand, a threaded portion of a male screw is formed on the outer periphery of the left end portion of the conductive output members 131 and 132 connected to the end plates 112 and 113 (not shown). The end plates 112 and 113 and the conductive output members 131 and 132 are connected by screwing of the male screw and the female screw.

  The heat exchanger 140 enables heat exchange between the air supplied through the air pipe 122 and the conductive output member 131. The heat exchanger 140 has a container 141 and a cavity 142 in the container 141. A conductive output member 131 passes through the heat exchanger 140 and is disposed in the cavity 142. The air supplied through the air pipe 122 is heated by heat radiation from the conductive output member 131 when passing through the cavity 142. By this heat exchange, the heat radiation from the conductive output member 131 is effectively used and is prevented from flowing out. By recovering the heat released from the output extraction portion (conductive output member 131) by the air introduced into the fuel cell stack 110, the heat loss is reduced. As a result, the fuel cell stack 110 can be easily operated by heat.

  FIG. 2 is a perspective view showing a state in which the fuel cell 111 is disassembled. The fuel cell 111 includes a connector plate 41 (41a, 41b), an air electrode frame 42, an insulating frame 43, a separator 44, an air electrode 45, an electrolyte 46, a fuel electrode 47, and a fuel electrode frame 48.

  The connector plates 41 a and 41 b are made of a conductive material such as metal, and a pair is arranged on both sides of the fuel cell 111 in the thickness direction. The connector plate 41 separates the gas flow paths of the fuel cells 111 and ensures conduction in the thickness direction.

  The connector plate 41 disposed between the adjacent fuel cells 111 serves as an interconnector, and separates the adjacent fuel cells 111. The connector plates 41 arranged at both ends in the stacking direction of the fuel cell stack 110 become the end plates 112 and 113.

The electrolyte 46 has a rectangular plate shape, is made of an oxide such as ZrO ₂ , and is fixed to the lower surface of the separator 44. The electrolyte 46 functions as an oxygen ion conductive solid electrolyte body. An air electrode 45 and a fuel electrode 47 are fixed on and under the electrolyte 46. A current collector (not shown) is arranged between the air electrode 45 and the connector plate 41a in order to ensure the conduction.

  An air chamber is formed above the separator 44 by the connector plate 41 a, the air electrode frame 42, and the insulating frame 43. A fuel chamber is formed below the separator 44 by the fuel electrode frame 48 and the connector plate 41b. Fuel gas and air are introduced into the fuel chamber and the air chamber, respectively, and heated to a high temperature (for example, about 700 ° C.), so that the fuel gas and oxygen in the air react via the electrolyte 46, and the air electrode 45, direct current electric energy is generated using the fuel electrode 47 as a positive electrode and a negative electrode, respectively.

  The heat insulating container 170 is a container having heat insulating performance, and stores the fuel cell stack 110. The air pipes 121 and 122 are disposed inside and outside the heat insulating container 170. The conductive output members 131 and 132 are disposed through the heat insulating container 170. In this example, the heat exchanger 140 is disposed across the inside and outside of the heat insulating container 170. On the other hand, it is also possible to arrange the heat exchanger 140 only inside or outside the heat insulating container 170. However, if anything, it is preferable to install the heat exchanger 140 outside the heat insulating container 170. This is because when the heat exchanger 140 is installed inside the heat insulating container 170, the heat in the heat insulating container 170 is absorbed by the heat exchanger 140.

(Second Embodiment)
FIG. 3 is a side view showing a solid oxide fuel cell 200 according to the second embodiment of the present invention. The solid oxide fuel cell 200 includes a fuel cell stack 110, air pipes 221 and 222, conductive output members 131 and 132, a heat exchanger 240, and a heat insulating container 170. The heat exchanger 240 and the air pipes 221 and 222 represent a cut cross-sectional state. Also, illustration of fuel gas and exhaust gas piping is omitted.

The heat exchanger 240 enables heat exchange between the air supplied through the air pipe 222 and the conductive output member 131. The heat exchanger 240 has a container 241 and a cavity 242 in the container 241. A conductive output member 131 passes through the heat exchanger 240 and is disposed in the cavity 242. The air supplied from the air pipe 222 is heated by heat radiation from the conductive output member 131 when passing through the cavity 242. In this embodiment, the container 141 and the cavity 242 are cylindrical, and the conductive output member 131 is disposed along the axis. By disposing the conductive output member 131 on the shaft of the cavity 242, heat radiation from the conductive output member 131 is uniformly transmitted to the air in the cavity 242, and further reduction in heat loss is possible (effectively Heat recovery).
Except for the above points, the solid oxide fuel cell 200 according to the present embodiment is not substantially different from the solid oxide fuel cell 100, and a detailed description thereof will be omitted.

(Third embodiment)
FIG. 4 is a side view showing a solid oxide fuel cell 300 according to the third embodiment of the present invention. The solid oxide fuel cell 300 includes a fuel cell stack 110, air pipes 321 and 322, conductive output members 131 and 132, a heat exchanger 340, and a heat insulating container 170. Illustration of piping for fuel gas and exhaust gas is omitted.

The heat exchanger 340 enables heat exchange between the air supplied through the air pipe 322 and the conductive output member 131. The heat exchanger 340 has an air pipe 341. The air pipe 341 is disposed between the air pipes 321 and 322 and is wound around the conductive output member 131 in a spiral shape. Air passing through the air pipe 341 is heated by heat radiation from the conductive output member 131.
Except for the above points, the solid oxide fuel cell 300 according to the present embodiment is not substantially different from the solid oxide fuel cell 100, and a detailed description thereof will be omitted.

(Comparative example)
FIG. 5 is a side view showing a solid oxide fuel cell 100x according to a comparative example of the present invention. The solid oxide fuel cell 100x includes a fuel cell stack 110, an air pipe 121x, conductive output members 131 and 132, and a heat insulating container 170. That is, the solid oxide fuel cell 100x does not have a heat exchanger, and the air flowing from the air pipe 121x is input to the fuel cell stack 110 as it is.

(Other embodiments)
Embodiments of the present invention are not limited to the above-described embodiments, and can be expanded and modified. The expanded and modified embodiments are also included in the technical scope of the present invention.

1. In the above embodiment, the reaction air in the fuel cell stack 110 is heated by the heat exchangers 140 to 340. It is possible to heat other fluids instead of air. As such a fluid, (1) fuel gas, (2) water for steam reforming the fuel gas, and (3) general-purpose water can be considered.

  If carbon deposits at the fuel electrode 47 of the solid oxide fuel cell 100, the fuel cell stack 110 may be deteriorated or damaged. For this reason, it is desirable to reform the fuel gas (hydrocarbon fuel) and then flow it to the fuel cell stack 110. Fuel gas (for example, hydrocarbon fuel) can be reformed with steam (steam reforming method) to prevent carbon deposition. For this purpose, water for steam reforming is supplied to the solid oxide fuel cell 100. A vaporizer is needed to vaporize the water, and a reformer containing a reforming catalyst is needed to reform the fuel gas. However, it is also possible to perform steam reforming at the fuel electrode of the solid oxide fuel cell. In this case, there is no need to provide a separate reformer. Heat loss from the conductive output member 131 can also be reduced by heating the reforming water using the heat exchangers 140 to 340.

2. In the above embodiment, the heat exchangers 140 to 340 are attached only to the conductive output member 131. On the other hand, the heat exchangers 140 to 340 may be attached only to the conductive output member 132 and to both the conductive output members 131 and 132. It is also possible to heat different fluids with the conductive output members 131 and 132. For example, air and water can be heated by the conductive output members 131 and 132, respectively.

Examples of the present invention will be described below.
Example 1 corresponds to the first embodiment. That is, the output extraction member (conductive output member 131) from the fuel cell stack 110 is assembled so as to penetrate the heat exchanger 140, and the heat from the output extraction member (conductive output member 131) is recovered. However, the heated fluid was general-purpose water. This water can be used, for example, for a bath.

  Example 2 was the same as Example 1 except that the fluid flowing through the heat exchanger 140 was used as water for steam reforming.

  Example 3 was the same as Example 1 except that the fluid flowing through the heat exchanger 140 was air necessary for power generation.

  Example 4 was the same as Example 1 except that the fluid flowing through the heat exchanger 140 was methane as the fuel gas.

  Example 5 corresponds to the second embodiment. That is, the heat exchanger 240 has a double structure, and air or water flows outside.

  Example 6 corresponds to the third embodiment. In other words, the air pipe 341 is spirally wound around the conductive output member 131 and air or water is caused to flow through the air pipe 341.

  In Example 7, there are two heat exchangers. That is, piping was attached to each of the conductive output members 131 and 132, fuel gas was flowed on one side, and air was flowed on the other side.

  Example 8 was the same as Example 7 except that water was passed through one pipe and air was passed through the other pipe.

  Example 9 was the same as Example 7 except that fuel gas (methane) was passed through one pipe and water was passed through the other pipe.

  The comparative example does not have a heat exchanger. That is, no heat exchange function is given to the conductive output members 131 and 132.

  The amount of heat recovered by the heat exchanger was calculated by calculating from the temperature difference just before being introduced to the fuel cell stack 110 and the temperature difference at the time of introduction to the heat exchanger, specific heat, density, and flow rate. The result is shown in FIG.

  In Comparative Example 1, since the heat radiation from the output take-out members (conductive output members 131 and 132) is not recovered, when an output line of about φ15 is used, 15 per unit when the stack temperature is 700 ° C. There is ~ 20W heat dissipation.

  The heat radiation from the conductive output members 131 and 132 is considerably large. When the conductive output member 131 is φ15 mm, the length is 200 mm, and the temperature of the fuel cell stack 110 is 700 ° C., there is about 20 W of heat dissipation per conductive output member 131, 132. When the solid oxide fuel cell 100 has a 1 kW output, the heat self-sustained operation is possible even if the heat dissipation is about 900 W. However, when the load on the solid oxide fuel cell 100 is reduced to 500 W, 200 W, and 100 W, the heat self-sustaining operation is impossible unless the heat radiation is set to 450 W, 180 W, and 90 W or less, respectively. Thus, the heat radiation from the conductive output members 131 and 132 is not a negligible value. By recovering the heat radiation and returning it to the fuel cell stack 110, the thermal self-sustained operation becomes easy even when the power generation is lower.

  Heat is exchanged with water as in the first embodiment, and the water is used, for example, as a pre-stage of a device that generates hot water as cogeneration, so that heat can be used, leading to improvement in overall system efficiency.

  In the second embodiment, the water movement distance is shortened by introducing the heat-exchanged water into the fuel cell stack 110. For this reason, heat loss is small and the recovered heat can be used effectively.

  The same effect as in the second embodiment can be obtained by using air instead of water as in the third embodiment instead of water.

  The same effect as in the second embodiment can be obtained by using a fluid for heat exchange as in the fourth embodiment as a fuel.

  The heat exchanger having a double structure as in the fifth embodiment enables effective heat exchange and reduces heat loss.

  As in the sixth embodiment, a pipe is spirally wound and a fluid for heat exchange is allowed to flow through the pipe, so that heat exchange can be performed more effectively than in the fifth embodiment, and heat loss is reduced. .

  As in Examples 7 to 9, heat loss can be reduced by providing a heat exchange function to both the conductive output members 131 and 132. That is, as in Examples 7 to 9, the two conductive output members 131 and 132 are heated by any two fluids (mediums) out of fuel, air, and water necessary for the fuel cell stack 110. Replacing was the most efficient. In this case, the final recovered heat amount is the sum of the recovered heat amounts of the two media. From this point of view, the combination of water and air in Example 8 was good.

  In Examples 5 and 6, since two media (air and water) are used separately (not using two media at the same time), the final recovered heat quantity is determined for each medium. This is the amount of heat recovered.

1 is a side view showing a solid oxide fuel cell 100 according to a first embodiment of the present invention. It is a perspective view showing the state where fuel cell 111 was disassembled. It is a side view showing the solid oxide fuel cell 200 concerning a 2nd embodiment of the present invention. It is a side view showing the solid oxide fuel cell 300 concerning a 3rd embodiment of the present invention. It is a side view showing the solid oxide fuel cell 100x which concerns on the comparative example of this invention. It is the table | surface which summarized the experimental result.

Explanation of symbols

100 Solid oxide fuel cell 110 Fuel cell stack 111 Fuel cell 112, 113 End plate 114, 115 Fixing member 121, 122 Air piping 131, 132 Conductive output member 140 Heat exchanger 141 Container 142 Cavity 170 Thermal insulation container 41 ( 41a, 41b) Connector plate 42 Air electrode frame 43 Insulating frame 44 Separator 45 Air electrode 46 Electrolyte 47 Fuel electrode 48 Fuel electrode frame

Claims (6)

A fuel cell stack in which an oxygen ion conductive solid electrolyte body with a fuel electrode and an air electrode disposed on both sides is stacked, and generates electric power by the reaction between fuel gas and oxygen in the air;
A supply path for supplying the fuel cell stack with air for reacting with the fuel gas, water for steam reforming the fuel gas, and any fluid of the fuel gas;
An output member for extracting electric power generated in the fuel cell stack;
A heat exchanger for exchanging heat between the output member and the fluid;
A solid oxide fuel cell comprising: The solid oxide fuel cell according to claim 1, wherein the heat exchanger includes a container that surrounds the output member and allows the fluid to pass therethrough. The solid oxide fuel cell according to claim 1, wherein the heat exchanger includes a pipe wound around the output member and allowing the fluid to pass therethrough. The output member has first and second output members corresponding to the positive electrode and the negative electrode,
The solid oxide according to any one of claims 1 to 3, wherein the heat exchanger includes first and second heat exchangers corresponding to the first and second output members, respectively. Fuel cell. 5. The solid oxide fuel cell according to claim 4, wherein fluids exchanged by the first and second heat exchangers are different from each other. The solid oxide fuel cell according to any one of claims 1 to 5, further comprising a heat insulating container covering the fuel cell stack.

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