Fuel cell system

Details Fuel cell system Fuel cell system

2001-10-12

2004-03-02

Ryan, Patrick (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Having magnetic field feature

C429S006000, C429S006000, C429S006000

Reexamination Certificate

active

06699609

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a fuel cell, which supplies fuel gas obtained by reforming hydrocarbon based raw fuel has been reformed to a fuel cell to generate electric power.
DESCRIPTION OF RELATED ARTS
In recent years, due to its cleanness and excellent energy efficiency, a fuel cell (proton exchange membrane type fuel cell) has found attracted as a power source for an electric vehicle or such. The fuel cell can be regarded to as one of a power generator which electrochemically generates power upon supplying fuel gas (hydrogen) for first reactant gas and oxidant gas (air) for second reactant gas.
In a fuel cell powered electric vehicle which carries a fuel cell, mileage of one refueling is required to be as long as possible. For this reason, the fuel cell powered electric vehicle has been developed, which possesses a container for raw fuel liquid such as methanol instead of a hydrogen tank, and the hydrocarbon raw fuel liquid is reformed to produce hydrogen-containing fuel gas to generate power.
Now referring to
FIG. 6
, a conventional fuel cell system FCS' possessing a reformer will be described.
A water/methanol mixed liquid (hereinafter referred to as “raw fuel liquid”), which is raw material stored in a storage tank for the raw fuel liquid is pumped to an evaporator
102
by means of a pump P. It is noted that why the raw fuel liquid comprises a mixed liquid of water and methanol is that hydrogen is produced from water and methanol by a steam reforming reaction, which will be described later on. Subsequently, in the evaporator
102
, the raw fuel liquid is injected from a raw fuel injecting device
102
b
to a body
102
a
of the evaporator, and is evaporated due the heat generated by the catalytic combustion in a catalyst combustor
102
c
. Also, reforming air from an air compressor
104
is supplied to the body
102
a
of the evaporator. Within the body
102
a
of the evaporator, the vapor of the raw fuel liquid and the vapor are heated and mixed with each other to form raw fuel gas, which is supplied to a reactor
103
.
The reactor
103
is composed of a reformer
103
a
and a CO remover
103
b
. A catalyst for an automatic thermal reaction (TAR) is incorporated into the reformer
103
a
, and the reformer
103
a
reforms the raw fuel gas supplied to the reactor
103
(reformer
103
a
) to thereby produce hydrogen-containing fuel gas. In the automatic thermal reaction, the following reactions (1) to (4) takes place to produce hydrogen, carbon dioxide, carbon monoxide (small amount), and water.
(1) Steam Reforming Reaction:
OH
3
OH+H
2
O→H
2
O→3H
2
+CO
2
(2) Oxidation
 OH
3
OH+3/2O
2
→2H
2
O+CO
2
(3) Thermal Decomposition
OH
3
OH→2H
2
+CO
(4) Shift Reaction
CO+H
2
O→H
2
+CO
2
It is noted that the reactions (1) and (3) are endothermic reactions and the reactions (2) and (4) are exothermic reactions.
As a result of these reactions (1) to (4), the fuel gas produced in the reformer
103
a
contains a small amount (approximately 1%) of carbon monoxide. Supplying fuel gas containing carbon to the proton exchange membrane type fuel cell
101
is not preferable, because a platinum catalyst within the fuel cell
101
is poisoned. Consequently, the fuel cell produced in the reformer
103
a
is supplied to the CO remover
103
b
at which CO is converted into CO
2
and is removed. Into the CO remover is supplied air for selective oxidation, and by the catalytic function of a catalyst disposed in the CO remover, CO is selectively oxidized. In front of the CO remover
103
b
, a heat exchanger (not shown) is provided for the purpose of controlling the temperature of the fuel gas within a given level to remove CO in an efficient manner.
In conventional, when the automatic thermal reaction is carried out, the amount of the reforming air to be mixed with the raw fuel gas (the amount of the air to be supplied in the body
102
a
of the evaporator) is set according to the following procedures (1) to (3):
(1) From the demand output from the fuel cell
101
, the demand load from the reformer
103
is set. (2) Based on the demand load, the amount of raw fuel liquid (the injection amount of the raw fuel) to be injected to the body
102
a
of the evaporator is set. (3) Based on the injection amount of the raw fuel, the amount of reforming air required in the reformer
103
a
from a map for the amount of the reforming air.
In order to stabilize the reaction in the reformer
103
a
, the temperature of the evaporator
102
or such is controlled so as to supply the raw fuel gas having a prescribed temperature.
However, the temperature of the raw fuel gas varies depending on the variation in the driving conditions of the fuel cell system FCS' and external factors (such as atmospheric temperature). If the temperature of the raw fuel gas is changed, the temperature of the reforming catalyst is also changed accordingly. Specifically, when the temperature of the raw fuel gas to be supplied to the reformer
103
a
becomes higher, the temperature of the reforming catalyst becomes higher. Conversely, when the temperature of the raw fuel gas becomes lower, the temperature of the reforming catalyst becomes lower. Here, as shown in
FIG. 8
, if the temperature of the reforming catalyst is increased, the concentration of carbon monoxide (CO concentration) contained in the fuel gas produced is increased. If the CO concentration is too increased, CO is removed in the CO remover
103
b
only with an insufficient manner, which possibly has an influence upon the platinum catalyst of the fuel cell
101
. On the other hand, if the temperature of the reforming catalyst becomes lower, the CO concentration in the fuel gas produced becomes smaller, but the total hydrocarbon (THC) concentration would be increased (in which case, the reforming reaction takes place slowly and unreacted raw fuel is passed as it is, together with the raw fuel gas not sufficiently reformed). For this reason, the amount of the hydrogen produced is decreased, changing the fuel ratio for the worse. If the amount of the hydrogen produced is too decreased, the fuel cell
101
cannot generate power any longer. Particularly, in the case where the fuel cell system FCS' is carried on a vehicle like a fuel cell powered vehicle, the driving conditions and the external factors would be severely changed.
SUMMARY OF THE INVENTION
A main object of the present invention is, therefore, to provide a fuel cell system, which can be operated under appropriate conditions by keeping the temperature of the reforming catalyst at a prescribed level, even if the temperature of raw fuel gas is changed.
As a result of serious studies in light of the object described above, it has been found that as shown in
FIG. 9
showing the relation between the temperature of the raw fuel gas to be supplied to the reformer and the amount of the reforming air in the case of keeping the temperature of the reforming catalyst at constant, if the amount (flow amount) of the reforming air to be supplied to the reformer is controlled even when the temperature of the raw fuel gas is changed, the temperature of the reforming catalyst can be kept at a prescribed level, reaching the present invention.
Specifically, the fuel cell system according to the present invention, which attains these and other objects, comprises:
a fuel cell in which first reactant gas and second reactant gas are supplied to generate electricity,
an evaporator for evaporating a raw fuel, which combustor exhaust gas discharged from said fuel cell and makes use of said exhaust gas to evaporate and volatile a raw material for said first reactant gas,
a reformer which reforms the evaporated and volatilized raw fuel vapor by means of a reforming catalyst to produce the first reactant gas, and
an air-introducing device, which introduces air used to be reformed into said evaporator or said reformed in a manner that the flow rate of the air is controlled depending upon the output from the fuel cell and upon the temperature

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