JP2005129513A - Fuel cell power generation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal reform type fuel cell power generation system achieving a high power generation efficiency by reducing the temperature distribution produced at a power generation part of a cylindrical fuel cell assembly during power generation. <P>SOLUTION: The fuel cell power generation system comprises an assembly of cylindrical fuel cells composed of a porous supporting tube, an air electrode, a solid oxide, a fuel electrode and an inter connector; a heat insulating board disposed around the assembly of the fuel cell; and a metal casing surrounding around the board, and has a fuel flow path for feeding fuel to a fuel electrode. The flow path is composed of a main flow path directly feeding the fuel from a just beneath part of the fuel cell to the fuel electrode of the fuel cell and a bypass fuel flow path, the bypass fuel flow path is disposed between the board and the casing, and a fuel feeding port from the bypass fuel flow path to the assembly is disposed on the board. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell power generation system, and more particularly to a high temperature direct internal reforming fuel cell power generation system.

The cylindrical solid oxide fuel cell is composed of a porous support tube-air electrode-solid oxide-fuel electrode-interconnector. In some cases, the air electrode also serves as a porous support tube. In the fuel cell power generation system, the fuel cell is housed in a fuel cell container. Fuel gas is supplied from the fuel gas line to the fuel electrode outside the fuel cell. An air introduction pipe is inserted inside the fuel battery cell, and an oxidant gas is supplied through the air distributor.
Although hydrogen gas is most preferably used as the fuel gas, it is often introduced by converting a hydrocarbon-based fuel gas such as natural gas or propane gas into a hydrogen-rich gas by a reformer or the like. On the other hand, oxygen gas is most preferably used as the oxidant gas, but air is generally used because of availability problems. When the fuel gas is supplied to the fuel electrode side and the oxidant gas is supplied to the air electrode side in this way, an electrochemical reaction occurs on both sides of the electrolyte to generate electric power, heat, and water. This reaction is the reverse reaction of water electrolysis.

A power generation system using a cylindrical solid oxide fuel cell is usually configured by electrically connecting and collecting tens to hundreds of cells. A conventional internal reforming fuel cell power generation system is shown in FIG. The assembly in which the plurality of cylindrical fuel cells 1 are joined is surrounded by a heat insulating board 2 and further surrounded by a metal casing 3. When the heat insulation is insufficient, the outer side of the metal casing 3 is also surrounded by a heat insulation board and kept warm (not shown). It is desirable to have a mechanism for pressing from the outside in order to maintain electrical contact between the cylindrical fuel cells.
On the other hand, as a feature of a solid oxide fuel cell that is a high-temperature type, it is possible to generate hydrogen directly from hydrocarbons such as city gas and LPG by using the operating temperature to cause a steam reforming reaction in the cell itself. Points are raised. Therefore, it is possible to perform power generation by supplying unreformed or partially reformed gas as fuel gas directly to the cylindrical fuel cell assembly. This method is called an internal reforming method. Since the steam reforming reaction is an endothermic reaction, the heat generated from the battery reaction can be used effectively. Moreover, water (steam) generated by the battery reaction can also be used for the reforming reaction. In FIG. 4, the preheated, unreformed or partially reformed fuel is supplied from the fuel gas inlet 5, and the oxidant gas is supplied from above through the air distributor and the air introduction pipe. (Not shown).

  In an actual power generation state, there is a problem that temperature distribution occurs in the power generation portion of the cylindrical fuel cell assembly, and the cell performance cannot be fully exhibited. Normally, a fuel cell has a temperature range that is optimal for maximizing its performance. For example, in a solid oxide fuel cell using zirconia as an electrolyte, the range is about 900 to 950 ° C. When the temperature is higher than this, the power generation performance is hardly improved. Rather, the cell main body and surrounding materials are damaged by the high temperature, and the power generation performance cannot be sufficiently exhibited at a temperature lower than this. However, when the cells are assembled, it is difficult to control the entire cell within this temperature range. In the cylindrical fuel cell assembly described above, the fuel flow direction and the oxidant gas flow are described based on the fuel flow direction. Although it is greatly influenced by the supply conditions, it is generally low at the fuel inlet and outlet and tends to reach a maximum temperature around the middle.

Particularly in the internal reforming method, the steam reforming reaction proceeds considerably at the fuel inlet of the cylindrical fuel cell assembly, the temperature of the fuel inlet becomes even lower, and the temperature distribution of the power generation part of the cylindrical fuel cell assembly As a countermeasure against this problem, the thickness of the fuel electrode is reduced on the fuel gas inlet side and increased as it approaches the fuel gas outlet, and the electrode reforming performance is lower on the inlet side and on the outlet side. There is an example of making it high (see, for example, Patent Document 1). Although this example is an example of a flat plate fuel cell, it is also applicable to a cylindrical fuel cell. However, manufacturing such a cell has a problem in that the manufacturing process becomes complicated. In addition, there is a problem that difficulty arises even when the cells are stacked due to partial differences in cell thickness.

As another method, there is a method of providing a reaction tube for steam reforming hydrocarbon fuel between the assembled cells (see, for example, Patent Document 2). In this example, the thickness of the tube wall of the reaction tube is adjusted so as to effectively cool the high temperature portion. However, such a method has a problem that the power generation system becomes complicated and large.
JP-A-6-342663 (FIG. 1) JP 2003-115307 A (FIG. 1)

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to lower the temperature of the lower part of the fuel cell in the power generation part of the cylindrical fuel cell assembly in the power generation state of the fuel cell power generation system. This means that the temperature distribution is too high and the cell performance cannot be fully exhibited. When the internal reforming method was adopted, this temperature distribution tended to be larger.

  In order to solve the above problems, in the present invention, an assembly of cylindrical fuel cells composed of a porous support tube-air electrode-solid oxide-fuel electrode-interconnector, and an assembly of the cylindrical fuel cells A fuel cell power generation system comprising a heat insulating board disposed around the body and a metal casing surrounding the heat insulating board, and having a fuel flow path for supplying fuel to the fuel electrode. A main flow path that directly supplies the fuel electrode of the cylindrical fuel battery cell from directly below the fuel battery cell, and a bypass flow path, the bypass fuel flow path is provided between the heat insulation board and the metal casing, A fuel cell power generation system is provided in which a fuel supply port from the bypass fuel flow path to a tubular fuel cell assembly is provided in the heat insulation board. As a result, the lower part of the cell can be prevented from becoming too low, and at the same time, the central part to the upper part of the cell can be cooled to reduce the temperature distribution.

In a preferred aspect of the present invention, in the fuel cell power generation system, the ventilation resistance in the supply port provided in the heat insulation board is made lower than the ventilation resistance of the gas flow path other than the supply port. As a result, more gas that has passed through the bypass fuel flow path can be caused to flow to the high temperature portion of the cell.

In a preferred aspect of the present invention, a gas sealing portion is provided downstream of the supply port of the bypass fuel flow path. The fuel gas that has passed through the bypass fuel flow path can be supplied to the high temperature portion without waste.

In a preferred aspect of the present invention, by narrowing the gap between the heat insulation board and the metal casing downstream from the supply port of the bypass fuel flow path, the fuel gas that has passed through the bypass fuel flow path is efficiently used as a high temperature part. Can supply.

In a preferred embodiment of the present invention, a groove is carved on the outer side of the heat insulation board disposed around the assembly of cylindrical fuel cells, so that a bypass fuel flow path for cooling the high temperature part can be easily formed. .

In a preferred embodiment of the present invention, the position of the supply portion provided on the heat insulation board for supplying a part of the fuel to the fuel cell is in the substantially central portion of the cell, thereby effectively cooling the high temperature portion. Can do. The substantially central portion may be a portion except both ends when the fuel cell assembly is divided into four equal parts in the fuel flow direction.

As is clear from the above description, according to the fuel cell power generation system of the present invention, by providing the bypass fuel flow path and supplying the gas containing unreformed fuel to the high temperature portion of the assembly of cylindrical fuel cells. The temperature distribution in the power generation unit can be reduced, and the efficiency of the power generation system can be increased.

Hereinafter, the present invention will be described more specifically with reference to the drawings.
As shown in FIG. 1, the assembly in which a plurality of cylindrical fuel cells 1 are joined is surrounded by a heat insulating board 2, and the outside thereof is surrounded by a metal casing 3. When the heat insulation is insufficient, the outer side of the metal casing 3 is also surrounded by a heat insulation board and kept warm (not shown). It is desirable to have a mechanism for pressing from the outside in order to maintain electrical contact between the cylindrical fuel cells. From the lower part, unheated or partially reformed fuel preheated from the fuel gas inlet 5 is supplied, and oxidant gas is supplied from the upper part through an air distributor and an air introduction pipe (illustrated). do not do). A part of the fuel gas passes through the gap between the bottom and the side formed by the heat insulating board 2 and the metal casing 3 and the fuel gas bypass passage 6, and after passing through the bottom, is parallel to the fuel passing through the fuel cell assembly. Moving. Then, the fuel cell assembly part enters the fuel cell assembly part from the supply port of the heat insulation board near the position where the temperature of the fuel cell assembly part is the highest. When the range of the high temperature part is wide, the positions of the supply ports may be dispersed. The position of such a supply port is preferably between 1/4 and 3/4 with respect to the fuel flow direction in the power generation portion of the fuel cell assembly, with the fuel inlet of the power generation portion as a base point. Thus, the upward flow in the drawing is stopped by the gas sealing portion 4. The fuel that has entered the fuel cell assembly part in the middle is steam reformed in the high temperature part, and this part is cooled, thereby reducing the overall temperature distribution. This effect is greatest in the cell closest to the heat insulation board, and the effect is spread to the inner cell due to gas diffusion and heat transfer.

  In order to secure a gap between the bottom and the side formed by the heat insulating board 2 and the metal casing 3, a spacer formed of a heat insulating material plate or a metal plate may be inserted in a part of the gap. It is possible to control the flow rate of the bypass fuel gas by the position and width of these spacers. Similarly, in order to secure the gap, a metallic corrugated plate or the like may be inserted in a part or the whole of the gap. These may be used in combination.

  In the example shown in FIG. 1, the gas passage from the fuel gas bypass passage to the fuel cell assembly is a hole formed in the heat insulation board, but a heat insulation board having high gas permeability is installed only in this portion. Also good.

FIG. 2 shows an example of a fuel cell power generation system in which the gap between the heat insulation board 2 and the metal casing 3 is narrowed to stop the bypass fuel flow path, and the metal casing is pressed directly against the heat insulation board. In FIG. 2, the metal casing 3 side is processed to have a step, but the heat insulating board 2 side may have a reverse step, or both methods may be used in combination.
As in the example of FIG. 1, a spacer formed of a heat insulating material plate or a metal plate may be inserted in a part of the gap in order to secure the gap. The flow rate of the bypass fuel gas can be controlled by the position and width of the spacer. Similarly, in order to secure the gap, a metallic corrugated plate or the like may be inserted in a part or the whole of the gap. These may be used in combination.
Alternatively, the groove may be formed by processing the metal casing so that the bypass fuel gas passes through a part between the heat insulating board and the metal casing.

FIG. 3 is an example of a fuel cell power generation system in which the bypass fuel flow path is a groove carved out of the heat insulation board 2 arranged around the assembly of cylindrical fuel cells. In the figure, the groove portion is indicated by a dotted line from the bottom to the side of the heat insulating board 2. The flow rate of the bypass fuel gas can be controlled by the position and depth of the groove.

1 is a diagram schematically illustrating an embodiment of a fuel cell power generation system according to the present invention. FIG. 6 is a diagram schematically showing another embodiment of the fuel cell power generation system of the present invention. FIG. 6 is a diagram schematically showing another embodiment of the fuel cell power generation system of the present invention. It is a figure which briefly shows one Example of the conventional fuel cell power generation system. It is a figure which shows the fuel supply port of the fuel cell power generation system of this invention, and the fuel gas flow of the vicinity schematically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tubular fuel cell 2 Heat insulation board 3 Metal casing 4 Gas sealing part 5 Unreformed or partially reformed fuel gas inlet 6 Unreformed or partially reformed fuel gas bypass flow Road 7 Combustion exhaust gas outlet 8 Fuel supply port 9 Portion with low ventilation resistance 10 Portion with high ventilation resistance 11 Fuel gas 12 Power generation portion

Claims (6)

An assembly of cylindrical fuel cells composed of a porous support tube-air electrode-solid oxide-fuel electrode-interconnector, a heat insulation board arranged around the assembly of the cylindrical fuel cells, and the heat insulation In a fuel cell power generation system comprising a metal casing that surrounds the periphery of the board, and having a fuel flow path for supplying fuel to the fuel electrode,
The flow path consists of a main flow path that directly supplies the fuel electrode of the cylindrical fuel battery cell from directly below the cylindrical fuel battery cell, and a bypass flow path,
The bypass fuel flow path is provided between the heat insulation board and the metal casing, and a fuel supply port from the bypass fuel flow path to the tubular fuel cell assembly is provided in the heat insulation board. Fuel cell power generation system. 2. The fuel cell power generation system according to claim 1, wherein a ventilation resistance in a supply port provided in the heat insulating board is lower than a ventilation resistance of a gas flow path other than the supply port in the fuel cell power generation system. 3. The fuel according to claim 1, wherein a gas sealing portion is provided downstream of the previous-stage supply port of the bypass fuel flow path in order to make the ventilation resistance in the supply port relatively low. Battery power generation system. The gap between the heat insulation board and the metal casing is narrowed downstream of the supply port of the bypass fuel flow path in order to relatively reduce the ventilation resistance in the supply port. The fuel cell power generation system described in 1. 3. The fuel cell power generation system according to claim 1, wherein the bypass fuel flow path is a groove formed on an outside of the heat insulation board. The position of the supply port provided in the heat insulation board for supplying a part of fuel to the fuel cell is substantially in the center with respect to the fuel flow direction of the cylindrical fuel cell assembly. The fuel cell power generation system according to claim 2.

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