Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2001-01-12
2003-12-02
Ruthkosky, Mark (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S010000
Reexamination Certificate
active
06656617
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel gas production system that produces hydrogen, which is to be fed to fuel cells, from a raw material containing hydrogen atoms. More specifically the present invention pertains to a fuel gas production system having a hydrogen separation mechanism that separates hydrogen in the course of production.
2. Description of the Related Art
Each of the fuel cells has a hydrogen electrode and an oxygen electrode disposed across an electrolyte layer, which hydrogen ions pass through, and generates an electromotive force through the following reactions proceeding at the respective electrodes:
Hydrogen electrode: H
2
→2H
+
+2e
−
Oxygen electrode: (½)O
2
+2H
+
+2e
−
→H
2
O
A hydrogen-rich fuel gas may be produced by reforming a hydrocarbon compound, such as methanol or natural gas, in a fuel gas production system. The material is decomposed to the hydrogen-rich fuel gas stepwise through plural stages of reactions in the fuel gas production system.
The first stage reaction is called the reforming reaction and is expressed by Equations (1) and (2) given below in the case of a hydrocarbon material
C
n
H
m
+n
H
2
O
→n
CO+(
n+m/
2)H
2
(1)
C
n
H
m
+n/
2O
2
→n
CO+
m/
2H
2
(2)
The second stage reaction utilizes steam to oxidize carbon monoxide produced by the reforming reaction while producing hydrogen. This second stage reaction is called the shift reaction and is expressed by Equation (3) given below:
CO+H
2
O→CO
2
+H
2
(3)
In some cases, the CO oxidation is subsequently performed as the third stage reaction. The CO oxidation selectively oxidizes carbon monoxide that has not been oxidized by the shift reaction but remains. Carbon monoxide contained in the fuel gas may poison the electrodes and interfere with the stable reactions. The shift reaction and the subsequent CO oxidation sufficiently lower the concentration of carbon monoxide, so as to prevent the potential poisoning of the electrodes.
One application utilizes hydrogen separated from the gaseous mixture, which has been produced through the chemical reactions, as the gaseous mixture. The separation of hydrogen enhances the hydrogen partial pressure in the fuel gas and effectively prevents the gaseous mixture from containing any noxious components.
FIG. 36
schematically illustrates the structure of a prior art fuel cells system including a hydrogen separation mechanism. Supplies of a material and water are respectively fed from a material reservoir
200
and a water reservoir
230
to a reformer unit
216
via an evaporator
212
. A reforming reaction proceeds in the reformer unit
216
to produce a gaseous mixture including carbon monoxide. Gaseous hydrogen included in the gaseous mixture permeates a hydrogen separation membrane
218
to a separation unit
220
. For the purpose of efficient separation of hydrogen, a gas for carrying out hydrogen (hereinafter referred to as the purge gas) is introduced into the separation unit
220
. The purge gas used here is steam obtained by evaporating water led from the water reservoir
230
by an evaporator
232
. The separated hydrogen is supplied to fuel cells
228
after removal of the excess water content in a condenser
226
. The gaseous mixture after separation of hydrogen (hereinafter referred to as the residual gas) includes carbon monoxide and remaining hydrogen that has not been separated by the hydrogen separation membrane
218
. The residual gas is discharged to the outside after carbon monoxide and hydrogen included therein are oxidized in a combustion unit
222
.
Any of a variety of condensable gases that have no adverse effects on the fuel cells may be used for the purge gas, in place of steam. A substance that has a small heat of vaporization and is liquid at ordinary temperature is generally suitable for the purge gas.
FIG. 37
is a graph showing the relationship between the heat of vaporization and the boiling point. This is cited from the Chemical Handbook. According to the above conditions, paraffin hydrocarbons, dimethyl ether, and acetic acid are suitable for the purge gas.
The prior art fuel gas production system, however, has several problems discussed below.
The prior art technique has an insufficient production efficiency of hydrogen from the material and a relatively low hydrogen partial pressure in the fuel gas. For example, part of the material is not subjected to any reaction but is discharged to the outside. In the fuel gas production system having the hydrogen separation mechanism, hydrogen remaining in the residual gas is often wasted. The low production efficiency of hydrogen leads to an increase in consumption of the material. This results in raising the operation cost, increasing the required capacity of the material reservoir, and thereby expanding the size of the whole fuel cells system. The low hydrogen partial pressure in the fuel gas results in lowering the efficiency of power generation of the fuel cells and thereby expanding the size of the whole fuel cells system.
The prior art fuel gas production system requires the evaporator and the water reservoir for producing the purge gas. This leads to the size expansion and the complicated structure of the fuel gas production system.
In the prior art fuel gas production system, the flow rate of the purge gas is substantially not regulated. The flow rate of the purge gas affects the separation efficiency of hydrogen and the driving efficiency of the fuel cells. Such effects are especially prominent when the driving conditions of the fuel cells change. The insufficient flow rate of the purge gas may cause an insufficient supply or a delayed supply of the fuel gas and a response delay of the hydrogen output.
From the viewpoint of the environmental protection, the recent requirement is to mount such fuel cells on a vehicle. For this purpose, the lowered driving efficiency and the size expansion of the whole fuel cells system are significant problems.
SUMMARY OF THE INVENTION
The object of the present invention is accordingly to enhance the production efficiency of hydrogen and raise the hydrogen partial pressure in a resulting fuel gas in a fuel gas production system, to enable efficient production of a purge gas, and to appropriately regulate the flow rate of the purge gas to improve the driving efficiency and the response of fuel cells.
At least one of the above and the other related objects is actualized by a first fuel gas production system that produces a hydrogen-rich fuel gas, which is to be supplied to fuel cells, from a raw material. The fuel gas production system includes: a chemical reaction device that produces a gaseous mixture containing hydrogen from the raw material through a plurality of chemical processes; a hydrogen separation mechanism that separates hydrogen from the gaseous mixture in at least one place of the chemical reaction device; and a flow path that feeds both the hydrogen separated by the hydrogen separation mechanism and a residual gas after the separation of hydrogen from the gaseous mixture to the fuel cells, so as to ensure a supply of all hydrogen obtained in all the chemical processes in the chemical reaction device to the fuel cells.
Any of a variety of compounds containing hydrogen atoms, for example, hydrocarbons like gasoline, alcohols, ethers, and aldehydes, may be used for the raw material.
The flow path is arranged to supply both the hydrogen separation by the hydrogen separation mechanism and the residual gas to the fuel cells. This arrangement enables not only the separated hydrogen but the remaining hydrogen, which has not been separated from the gaseous mixture by the hydrogen separation mechanism, to be supplied to the fuel cells. Namely the arrangement of the present invention enables most of the hydrogen produced through the plurality of chemical processes to be supplied to the fuel cells. The separation of hydrogen by the hydrogen separ
Aoyama Satoshi
Iguchi Satoshi
Nakata Toshihide
Sato Hiromichi
Ruthkosky Mark
Toyota Jidosha & Kabushiki Kaisha
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