Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2001-03-07
2004-02-24
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S010000, C429S006000, C429S006000
Reexamination Certificate
active
06696192
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fuel cell system comprising a water-permeable-type humidifier. For example, this invention relates to the fuel cell system comprising a humidifier which collects water contained in exhaust gas from a fuel cell, which generates power by the chemical reaction of hydrogen and oxygen, and humidifies the gas supplied to a fuel cell. More particularly, this invention relates to technology which is effective in humidifying a fuel cell at start-up and during the operation thereof.
2. Description of the Related Art
For example, in a fuel cell which uses a solid high polymer membrane as an electrolyte membrane, the solid high polymer membrane must be kept saturated by water in order to obtain the functions of a proton-(hydrogen ion-) conductive electrolyte. In view of this, a water-permeable-type humidifier is provided for collecting water in exhaust gas (off gas) from the fuel cell, and using the collected water to humidify supply gas (hydrogen gas and oxygen gas) which is supplied to the fuel cell.
One type of this water-permeable-type humidifier is a hollow fiber membrane water collecting apparatus comprising a hollow fiber membrane which allows water to permeate parallel to the thickness of the membrane, as for example disclosed in Japanese Unexamined Patent Applications, First Publications Nos. Hei 7-71795 and Hei 8-273687.
In the hollow fiber membrane water collecting apparatus, water is collected from one (high humidity side) of the fluids flowing in and out of the hollow fiber membrane, and the other fluid (low humidity side) is humidified by transferring the collected water through the hollow fiber membrane to the other fluid.
FIG. 28
shows a general fuel cell. As shown in
FIG. 28
, a fuel cell
201
comprises a cathode (air electrode) and an anode (fuel electrode) on either side of an electrolyte membrane comprising a solid high polymer membrane
201
c
. A cathode electrode
201
and an anode electrode
201
d
comprise catalysts, and are provided respectively to the two sides. The solid high polymer membrane
201
c
for example comprises a proton exchange membrane of perfluorocarbonsulfonic acid membrane, and functions as a proton-conductive electrolyte when saturated by water. At room temperature there is a low specific resistance of 20 &OHgr;-proton or less. The catalyst in the cathode electrode
201
b
creates oxygen ions from oxygen, and the catalyst in the anode electrode
201
d
creates protons from hydrogen. A cathode side gas passage
201
a
is provided in the outer side of the cathode electrode
201
b
, and allows an air supply As of oxidizing gas to flow through. An anode side gas passage
201
e
is provided in the outer side of the anode electrode
201
d
, and allows a hydrogen supply Hs of fuel gas to flow through. When the air supply As flows along the cathode side gas passage
201
a
and the hydrogen supply Hs flows along the anode side gas passage
201
e
, the effect of the catalyst of the anode electrode
201
d
ionizes the hydrogen, creating protons. The protons move through an electrolyte membrane comprising the solid high polymer membrane
201
c
, and reach the cathode electrode
201
b
. The protons react with the oxygen ions, created from the oxygen of the air supply As by the effect of the catalyst, and thereby create water. The air supply As containing the created water and unused oxygen is exhausted as exhaust air Ae from the cathode side gas passage
201
a
of the fuel cell
201
. On the anode electrode
201
d
, electrons are created when ionizing the hydrogen. These electrons pass through an external load, such as a motor M or the like, and reach the cathode electrode
201
b.
In the fuel cell system comprising the hollow fiber membrane collecting apparatus, the water which is created when the fuel cell is operated, and exhausted therefrom, is collected via the hollow fiber membrane and used as water for humidifying the fuel cell. In cases where the fuel cell system is switched off for a long period of time and the like, the hollow fiber membrane becomes dry, making it impossible to humidify the fuel cell and to start generating power when the fuel cell is started up.
Not only immediately after start-up but also during normal operation (power-generation) of the fuel cell, there are cases where the amount of humidification obtained by the water-permeable-type humidifier is insufficient, depending on the operational status of the fuel cell (e.g. the humidifying capability of the water-permeable-type humidifier and the changes in the amount of humidification required by the fuel cell). In the abovementioned fuel cell system, the water-permeable-type humidifier collects water from the exhaust air and humidifies the air supply by using the collected water. However, in view of the fact that the evaporation rate of water is inversely proportional to pressure at constant temperature, the amount of water required per fixed volume (capacity) changes when the pressure is changed, even when the predetermined dew-point of the air supply to the fuel cell remains the same. As a consequence, the amount of water acquired from the exhaust air of the fuel cell may not be sufficient for humidification.
By way of example, let us compare (a) a high-pressure operating system which comprises a pump upstream in the cathode side gas passage and shifts the air by positive pressure, and (b) a low-pressure operating system which comprises a pump downstream in the cathode side gas passage and shifts the air by negative pressure. The low-pressure operating system of (b) has less pressure loss than the high-pressure operating system of (a), and superior driving force, but has a drawback that it requires a far greater amount of water per constant volume (capacity). For this reason, the humidification amount of the polymer membrane may be insufficient when using only water acquired from exhaust air, particularly in negative pressure operations, and insufficient humidification of the supply gas may lead to poor power generation while the fuel cell is operating. The degree of humidification insufficiency is noticeable greater than in the case of positive pressure operations.
One conceivable solution would be to increase the scale of the water-permeable-type humidifier, but the inevitable increase in pressure loss makes this impractical.
SUMMARY OF THE INVENTION
The present invention has been achieved in order to solve the above problems. It is an object of this invention to provide a fuel cell system which can effectively humidify a fuel cell without excess or insufficiency, both at start-up and during operation of the fuel cell. It is another object of this invention to realize the fuel cell system which can effectively humidify a fuel cell without excess or insufficiency, not only when operating at positive pressure but also when operating at negative pressure, where the humidification is especially likely to become insufficient, and can utilize the economical features of negative-pressure operation.
In order to achieve the above objects, the fuel cell system of this invention comprises a fuel cell (
1
,
101
) which generates power by using a supply of fuel gas and oxidizing gas; a water-permeable-type humidifier (a hollow fiber membrane water collecting apparatus
2
, a water-permeable-type humidifier
123
) which collects water from exhaust gas exhausted from the fuel cell, and humidifies the gas supply to the fuel cell; and an auxiliary humidifier which is provided with a vapor/liquid separator (
3
, a condenser
126
) which separates the water from the exhaust gas, a collected water storage tank (
4
, a reservoir section of a condenser
126
) which stores the separated collected water (
9
), and an injector (
17
,
126
b
) which injects the collected water, stored in the collected water storage tank, to the gas supply or the exhaust gas.
Furthermore, this invention provides a fuel cell system comprises a fuel cell (
1
,
101
) which generates power by using a supply of fuel gas and oxidizing g
Kanai Yasushi
Kobayashi Tomoki
Kurosaki Kouji
Okamoto Hideo
Shimanuki Hiroshi
Lahive & Cockfield LLP
Mercado Julian
Ryan Patrick
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