JPS63110557A - Operating method for solid electrolyte fuel cell - Google Patents

Abstract

PURPOSE:To enable high-power direct generation by the use of hydrogen carbide like CH4 as fuel by mixing hydrogen carbide group fuel with air in such amount that partial oxidation is required in advance and supplying this mixed fuel to a fuel pole of a solid electrolyte fuel cell, so that internal reforming reaction due to partial oxidation is generated inside a fuel cell. CONSTITUTION:In stead of conventional internal reforming by the use of H2O, hydrogen carbide group fuel like CH4 is mixed with air in such amount that partial oxidation is required in advance, and this mixed fuel is supplied to a fuel pole of SOFC, so that internal reforming reaction due to the partial oxidation is generated in the fuel pole. Reaction formulas are shown in I and II, where the reaction in the formula I is made to advance very quickly by properly selecting the fuel pole and the amount of air addition. Hence, together with obtaining such an effect that a fuel pole low in catalysis can be also used, highpower direct generation can be performed by the use of hydrogen carbide like CH4 as fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of operating a solid electrolyte fuel cell using a hydrocarbon such as methane (CH4) as fuel.

[Prior Art] Power generation systems using solid electrolyte fuel cells are currently under development mainly in the United States, with the goal of putting them into practical use in the late 1990s. Therefore, although there is currently no commercially available system, various systems configurations are being studied, and high thermal efficiency of 50 to 60%, which is not found in conventional power generation systems, is expected.

By the way, for power generation systems using solid electrolyte fuel cells (hereinafter abbreviated as 5OFC), a so-called internal reforming method has been proposed with the main purpose of improving system efficiency and reducing the number of devices, similar to molten carbonate fuel cells. has been done. This is an electrochemical reaction in which the fuel, such as natural gas or hydrocarbon such as propane, reacts with added water vapor to convert it into Co and H2 inside the cell. Once completed, this method will provide the most efficient system possible.

[Problems to be Solved by the Invention] However, there are problems such as selection of a highly catalytic fuel electrode, selection of the amount of steam added to prevent carbon deposition, and control of cell temperature. The make-up amount of added H20 also becomes a problem depending on the installation location of the plant.

The present invention was made in view of the above circumstances, and solves problems such as selecting a highly catalytic fuel electrode, selecting the amount of steam added to prevent carbon precipitation, and controlling cell temperature, and also solves problems such as selecting a highly catalytic fuel electrode, selecting the amount of steam added to prevent carbon precipitation, and controlling cell temperature. The object of the present invention is to provide a method of operating a solid electrolytic fuel cell that can directly generate electricity using hydrocarbons such as CHa as fuel.

[Means for Solving the Problems] The present invention does not involve normal internal reforming using H20, but instead involves pre-mixing a hydrocarbon fuel such as CM with the necessary amount of air to form a 5OFC fuel. The gist is to feed the fuel to the fuel electrode and cause an internal reforming reaction by partial oxidation reaction within the fuel electrode. The reaction formula according to the present invention is the following formula (1
), as shown in equation (2).

C) It +AIRCO+H20...(1) (However,
(No catalyst or fuel electrode catalyst) Conventional reaction formulas are as shown in formula (3) and formula (4).

ClLa + H20-Machisulirishi CO+ 3H2・
...(3) IK [Function] The present inventors have determined that the above formula (1) (method of the present invention) and formula (3) (
The reaction characteristics that can be expressed using conventional methods were investigated in detail.

As a result, if the fuel electrode and the amount of air added are selected appropriately, the formula (1
) was found to proceed extremely rapidly compared to the reaction of formula (3).

[Example] Examples according to the present invention will be described below.

First, the following table shows a comparison between the examples according to the present invention and the conventional method. Prototype 61 type test cell (No.
1 to No. 6), the material of the base tube is porous A No. 203,
Air electrode material: LaCo0s + electrolyte material: Zr
02-'J+o, l'% Y2O3, and the material of the fuel electrode is ■Co (70%) Zr02 cermet, ■N
It was made from three types: i (70%)-Zr02 cermet and ■ nickel oxide. Also, No. 1 to No. of the table,
For 3, the electrolyte, air electrode, and fuel electrode were all formed by thermal spraying, No. 1 was 200 umS No. 2 was 15
0 μm, No. 3 had a film thickness of 100 μm. On the other hand, N
For Nos. 0 and 4 to NO6, only the electrolyte was formed by CVD, and the others were formed by thermal spraying (the film thickness is the same as above).

Furthermore, CH4 was used as the fuel and air was used as the oxidizer.

And in the case of the conventional method, Hz O/CH4 (molar ratio)! :
i1.0, in the case of the method of the present invention (in A I R) 027CH
A power generation test was conducted with a (molar ratio) #0.6, and the differences between the two were investigated.

However, as is clear from the table below, which No.
It was found that in Nos. 1 to 6, the method of the present invention (that is, B in which air was added to the fuel) provided higher output than the conventional method (A). Further, as a result of investigating the outlet gas component concentration, it was found that in the conventional method, the residual concentration of CH4 was high and the internal reforming reaction did not proceed sufficiently. This seems to be because the catalytic performance of the fuel electrode is not sufficient and a higher-performance catalyst or a larger amount of catalyst is required. Furthermore, cell no.
, 5 was used to change the amount of added air using the non-explosion OR method, and a power generation test was conducted. As a result, the 02/CH4 molar ratio was 0.4~
Almost the same output was obtained with 1.3, but the output decreased slightly outside this range. This indicates that there is an appropriate amount of air to be added, and in practice, it is necessary to select an amount of air sufficient for partial oxidation.

That is, the above embodiment has the effects listed below.

■ Since air is used instead of water, fuel electrodes with low catalytic properties can be used, and issues such as selecting the amount of steam added for carbon deposition and controlling cell temperature can be resolved.

■ As shown in the table below, a higher yield can be obtained compared to the conventional method.

■ Direct power generation using hydrocarbons such as CH4 as fuel is possible.

[Effects of the Invention] As detailed above, the present invention has effects such as being able to use fuel electrodes with low catalytic properties, and also enables direct power generation with high output using hydrocarbons such as CH as fuel. Therefore, it is possible to provide a method for operating a solid electrolytic fuel cell that is effective in application to small-sized 5OFC power plants and 5OFC plants where it is difficult to make up reforming steam.

Claims (1)

[Claims] The method is characterized in that a hydrocarbon fuel is mixed in advance with air in an amount necessary for partial oxidation, and then fed to a fuel electrode of a solid electrolyte fuel cell to cause an internal reforming reaction by a partial oxidation reaction within the fuel cell. How to operate a solid electrolyte fuel cell.