Fuel cell system

Details Fuel cell system Fuel cell system

2001-11-06

2004-12-21

Ryan, Patrick (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000

Reexamination Certificate

active

06833208

ABSTRACT:

BACKGROUND ARTS
1. Field of the Invention
The present invention relates to a reformation type fuel cell system, which reforms a fuel such as methanol into a hydrogen-enriched fuel gas and takes it, and particularly to a fuel cell system suitable as a power source for an electric vehicle.
2. Description of Related Arts
In recent years, various electric vehicles have been developed having a driving motor carried thereon instead of an engine. As one of such types of vehicles, development of a vehicle (hereinafter referred to as “fuel cell electric vehicle”) having a fuel cell system as a power source for the driving motor carried thereon has been sharply made. A so-called reformation type fuel cell system has been known as one of such fuel cell systems.
An example of the reformation type fuel cell system for use in the fuel cell vehicle will be described with reference to
FIG. 7. A
fuel cell system
50
depicted on
FIG. 7
has a fuel cell
51
, in which a hydrogen-enriched gas is supplied to an anode side thereof and air serving as an oxidant gas is supplied to a cathode side thereof to thereby generate electric power. The fuel cell system
50
also has an evaporator
52
which evaporates raw fuel liquid such as water/methanol mixed liquid to form raw fuel gas. To the evaporator
52
is connected a storage tank T for the water/methanol mixed liquid via a pump P, and the raw fuel liquid comprising the water/methanol mixed liquid is supplied to the evaporator
52
by the actuation of the pump P. The raw fuel gas obtained by the evaporation of the raw fuel liquid by means of the evaporator
52
is supplied to a reformer
53
. In the reformer
53
, the raw fuel gas undergoes a catalytic reformation reaction such as an automatic thermal reaction to produce hydrogen enriched fuel gas. The fuel gas produced in the reformer
53
is supplied to a CO remover
54
at which carbon monoxide by-product produced in the course of the reforming reaction, which is harmful for the fuel cell
51
, is removed. The fuel gas from which carbon monoxide is removed by means of the CO remover
54
is then supplied to the anode side of the fuel cell
51
. The fuel cell system
50
also has an air compressor
551
and by means of the air compressor
55
, the air as the oxidant gas is supplied to the cathode side of the fuel cell
51
. The air compressor
55
supplies the air as reforming air required for the reforming reaction (hereinafter referred to as “reforming air”) to the reformer
53
.
In the case where the fuel cell electric vehicle having the fuel cell system
50
carried thereon, which has been stopped, is started, the evaporator
52
, the reformer
53
, and the like are usually cooled. For this reason, in order to exhibit prescribed performances possessed by the evaporator
52
and the reformer
53
, a prescribed degree of heat is required for heating them. For this reason, a combustion burner
56
for starting (hereinafter referred to as “starting combustion burner) which heats the evaporator
52
and a starting combustion burner
57
for heating the reformer
53
are provided on the conventional fuel cell system
50
. After the catalyst layer of the evaporator
52
and the reforming catalyst of the reformer
53
are heated up to prescribed temperatures respectively by means of the combustion burners
56
and
57
for starting, the raw fuel liquid is supplied and the reforming air is supplied in the conventional fuel cell system
50
.
Since the reforming air is directly introduced into the reformer
53
in the conventional fuel cell system
50
, in some cases, the reforming air is not introduced into the reformer
53
in a uniform manner. In this case, differences in the density of the reforming air occurs in the reformer
53
, changing the admixture of the raw fuel gas with the reforming air for the worse, which is apt to cause uneven temperatures on the surfaces of the reforming catalyst provided within the reformer
53
. Typically, the temperature of the reforming catalyst becomes higher at the portion where the reforming air is concentrated, while the temperature of the reforming catalyst becomes lower at the portion where the reforming catalyst is diluted. Specifically, the oxidation represented by the formula (1), which is an exothermic reaction is accelerated on the portion where the reforming air is concentrated, and due to the heat generated at this time, the temperature of the reforming catalyst is increased.
CH
3
OH+3/2O
2
→2H
2
O+CO
2
  (1)
On the other hand, a steam reforming reaction represented by the following formula (2), which is an endothermic reaction, is promoted on the portion where the reforming air is diluted, and the temperature of the reforming catalyst is decreased due to the endothermic reaction.
CH
3
OH+H
2
O→3H
2
+CO
2
  (2)
For this reason, the temperature difference in the reforming catalyst occurs.
FIG. 8
shows the relation between the concentration of carbon monoxide in the fuel gas and the temperature of the reforming catalyst. It can be proven from this figure that if the temperature of the reforming catalyst is low, an amount of the total hydrocarbons (THC) becomes unduly high, meaning that the raw fuel gas is passed through with no or insufficient reformation, and the CO concentration becomes low, while THC is decreased according to the increasing of the temperature of the reforming catalyst and the CO concentration has a tendency to be increased. Consequently, with such uneven temperatures of the surfaces of the reforming catalyst, there arises a problem that the raw fuel gas is passed through with no or insufficient reformation to be unreformed fuel gas on the portion where the temperature of the reforming catalyst is low, while the CO concentration becomes high at which the temperature of the reforming catalyst is high. If the amount of unreformed gas is increased, no sufficient amount of hydrogen can be obtained, considering that the power generation in the fuel cell system
51
sometimes has a trouble. On the other hand, if the CO concentration is high, there is a fear of poisoning the fuel cell system
51
with CO.
In order to solve such a problem as just mentioned, it could be considered that as shown in an ideal line of
FIG. 7
a mixer
58
for mixing the raw fuel gas with the reforming air is separately disposed for the purpose of homogenizing the temperature distribution over the reforming catalyst. However, if such a mixer
58
is disposed, the fuel cell system
50
becomes large-scale, or the pressure loss of the total system becomes large, leading to poor system efficiency.
On the other hand, at the time of starting the conventional fuel cell system
50
, two starting combustion burners, i.e., the starting combustion burner
56
for warming up the evaporator
52
and the starting combustion burner
57
for warming up the reformer
53
, have been utilized. However, the use of many starting combustion burners as described above also leads to enlarge the size of the system, causing the problem of unsuitability for use in the fuel cell system for carrying a vehicle.
SUMMARY OF THE INVENTION
An object of the present invention is, therefore, to provide a fuel cell system which can appropriately mix the fuel gas in the reformer with the reforming air and which can rapidly operate the evaporator and the reformer at the time of starting the fuel cell system without enlarging the total size of the fuel cell system.
According to the present invention, which attains the object described above, there is provided a fuel cell system comprising:
a fuel cell in which fuel gas and oxidant gas are supplied to generate power;
an evaporator which evaporates raw fuel liquid by a combustion heat obtained by combusting exhaust gas exhausted from said fuel cell to provide raw fuel gas; and
a reformer which reforms the raw fuel gas supplied from said evaporator to provide said fuel gas;
said fuel cell system further comprising:
at least one air introduction member which introduces air for use in the reforming reacti

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