Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2000-06-21
2002-11-05
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S010000, C429S010000, C429S010000, C429S006000, C429S006000, C429S006000, C429S006000, C429S006000, C429S006000, C429S064000
Reexamination Certificate
active
06475655
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel cell system for generation of electric energy by reaction between a hydrogen-rich fuel gas and oxygen gas.
2. Description of Related Art
As is widely known, a fuel cell is continuously supplied with a fuel (hydrogen) and an oxidizing agent (oxygen) from outside of the fuel cell when generating electricity. The fuel is supplied to a negative electrode side whereas the oxidizing agent is supplied to a positive electrode side of the cell. The positive electrode and the negative electrode are separated from each other by an electrolytic member. The fuel cell converts chemical energy generated in oxidization of the supplied fuel directly into electric energy, serving as an electric power source.
An operating principle of the fuel cell is as follows: First, the hydrogen supplied as the negative-electrode active agent dissociates into electrons and protons. In order to promote the dissociation, platinum (Pt) for example is used as a catalyzer. After the dissociation, the protons pass the electrolyte of the fuel cell, and react with the supplied oxygen (positive-electrode active agent). The reaction yields water. On the other hand, the electrons resulted from the dissociation moves from the negative electrode to the positive electrode, generating electromotive force between the two electrodes.
The fuel cell directly converts chemical energy into electric energy. In this method, higher conversion efficiency can be expected than in a thermal generation method. For this reason, the fuel cell can be utilized effectively as a power source for a drive motor of an electric car for example. Further, exhaust from the fuel cell is mainly water vapor, which is not toxic like carbon monoxide contained in exhaust from an internal combustion engine.
Normally, the fuel cell does not function by itself as a source of electric supply. In order for the fuel cell to operate, means for supplying hydrogen gas to the fuel cell and other peripheral devices must be deployed. In other words, the fuel cell is part of a fuel cell system further comprising other peripheral devices, and operates within this system. The means for supplying the fuel cell with hydrogen may be pressure feeding from a high-pressure container loaded with hydrogen, or pressure feeding of hydrogen gas obtained by reforming a hydrogen-containing substance. Using the hydrogen gas stored in the high-pressure container can relatively simplify the system, and has a number of other advantages. On the contrary, a very high pressure and a long time are required for charging the container with hydrogen. Another problem is that a specific infrastructure such as a gas charge station network has to be prepared. These problems have been a major hurdle for making practical an electric automobile powered by the fuel cell.
The above problem can be solved by the feeding of hydrogen gas obtained by reforming a hydrogen-containing compound (such as methanol). Publicly known examples of this method include contacting the hydrogen-containing compound with steam, and oxidizing part of the hydrogen-containing compound. In these methods, the reformation of the hydrogen-containing compound leaves carbon dioxide and a trace quantity of carbon monoxide gas. Therefore, the desired hydrogen gas is obtained as a gas mixture containing these carbon dioxide and carbon monoxide gases.
If the platinum is used as the catalyzer for the negative electrode, the carbon monoxide contained in the gas mixture is problematic in the following point: As is widely known, platinum is poisoned by carbon monoxide gas, and gradually deteriorates in its activity. Therefore, if the hydrogen gas is supplied to the fuel cell as the gas mixture containing the carbon monoxide gas, life of the platinum catalyzer is shortened.
The poisoning of the platinum can be eliminated by converting the carbon monoxide gas in the gas mixture into carbon dioxide gas, and then supplying this modified gas mixture to the fuel cell. Generally, a multi-stage conversion method is used in which the carbon monoxide is first oxidized at a high temperature, and then residual carbon monoxide is oxidized at a low temperature.
However, the fuel cell does not consume all of the supplied hydrogen gas for the generation of electricity. Part of the hydrogen gas is discharged out of the fuel cell as non-reacted gas. In an attempt to effectively use this non-reacted hydrogen gas, methods of recycling the discharged gas mixture (containing the non-reacted hydrogen gas and the carbon dioxide gas) from the fuel cell back into the fuel cell are being tried conventionally. However, concentration of the non-reacted hydrogen gas in the recycled gas mixture is lower than in the gas mixture originally supplied to the fuel cell. Therefore, in the method of reforming a hydrogen-containing compound in which obtained hydrogen gas is low in purity, repeated recycling of the gas mixture will enrich gases other than the hydrogen gas (such as carbon dioxide), unjustifiably decreasing energy conversion efficiency.
DISCLOSURE OF THE INVENTION
The present invention is proposed under the circumstances described above. An object of the present invention is to minimize the decrease in energy conversion efficiency of the overall fuel cell system, in a fuel cell system which generates electricity by using a gas mixture discharged from the fuel cell. Another object of the present invention is to provide a fuel cell stack suitably used in the above fuel cell system.
A fuel cell system provided by a first aspect of the present invention comprises a reforming device for producing a hydrogen-rich gas mixture by reforming a hydrogen-containing compound; a fuel cell for generating electromotive force by a reaction between hydrogen and oxygen; and further a hydrogen separating device disposed between the reforming device and the fuel cell. The hydrogen separating device is provided with hydrogen permeating means for obtaining a fuel gas by separating hydrogen gas from the gas mixture.
Preferably, the fuel cell system further comprises circulating means for supplying non-reacted gas discharged from the fuel cell, to the fuel cell as fuel gas.
The hydrogen-containing compound is one of ethanol, methanol, dimethyl ether, propane and natural gas.
The hydrogen permeating means may include a palladium alloy film. The palladium alloy film can be made of an alloy including palladium and at least one metal selected from silver, gold and ruthenium.
The hydrogen permeating means may include solid high-polymer hollow yarn. The solid high-polymer hollow yarn is made of polyimide for example.
The reforming device may include a steam generating portion for vaporization of water by heating, a combusting portion for heating the steam generating portion by burning a predetermined fuel, and a reforming portion for producing the hydrogen-rich gas mixture by reacting steam generated by the steam generating portion with the hydrogen-containing compound. The gas mixture from which hydrogen is separated by the hydrogen separating device can be used by the combusting portion as a fuel.
The fuel cell system may comprise a fuel cell stack including the fuel cell and at least an additional fuel cell laminated on the fuel cell.
A fuel cell system provided by a second aspect of the present invention comprises a plurality of fuel cell stacks each including a plurality of fuel cells in lamination, supply means for supplying a fuel and an oxidizing agent to each of the fuel cell stacks, and operation control means for controlling operation of the fuel cell stacks. The fuel cell stacks are divided into a plurality of groups including at least a first and a second groups, and the operation control means is arranged to operate and stop the fuel cell stacks of the first group independently of the fuel cell stacks of the second group.
Preferably, the operation control means is arranged to operate and stop each of the plurality of fuel cell stacks independently of the other fuel cell stacks.
Preferably,
Abe Masahiro
Asazawa Koichiro
Nakanishi Haruyuki
Tanaka Hirohisa
Yamada Koji
Chaney Carol
Daihatsu Motor Co. Ltd.
Merchant & Gould P,C,
Yuan Dah Wei
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