Note: Descriptions are shown in the official language in which they were submitted.
CA 02588211 2007-05-03
FUEL CELL SYSTEM HAVING UNREACTED GAS DISCHARGE
PIPELINE
FIELD OF THE iNVENTYON
[0001] The present invention rclates to a technique for treating unreacted
gas discharged from a fuel cell stack, and more particularly to a fuel cell
system having unreacted gas discharge pipeline associated with a humidifier.
BACKGROUND OF THE INVENTION
[0002] A fuel cell is a power-generating unit that genera.tes electrical
energy through electrochernical reaction of hydrogen-containing fuel and air.
Since the fuel cell has the advantages of low pollution, high efficiency, and
high energy density, it has been positively researched, developed, and
promoted in many countries. Among others, the proton exchange membrane
fuel cell (1''EMFC) is the most industrially valuable product due to its low
operating temperature, quick activation, and high energy density.
100031 In the fuel cell, hydrogen ions move from the anode to the cathode
to complete the electrochemical reaction. The performance of a fuel cell has
close relation to different operating conditions, such as temperature,
humidity,
hydrogen flow, air #low, etc. Regarding the humidity, it is necessary to keep
a high molecular proton exchange membrane in the fuel cell at proper
operating humidity for the fuel cell to achieve high performance. Meanwhile,
the fuel cell must also be maintained at a proper operating temperature.
[0004J To maintain the fuel cell at proper operating humidity and
temperature, one of the currently adopted ways is to provide the reactant gas
supply pipelines of the fuel cell with a humidifier associated with a cooling
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water system. With this arrangement, cooling water is supplied from the
cooling water system to cool the fuel cell and then discharged from the fuel
cell. The discharged cooling water has a high tetnperatu.re about 60 to 70 C,
and is led to the humidifier to increase the relative humidity and temperature
of
the reactant gas passed through the humidifier before the reactant gas is
supplied to the fuel cell. For example, fresh air or oxygen is sent by an air
blower to the humidifier before being led to the fuel cell via an oxygen inlet
port thereof, so that the air flown into the fuel cell has a proper relative
humidity.
[00051 While the technique of providing a humidifier to regulate the
humidity of the reactant gas for the fuel cell has become matured, there is
not
any technical teachftig or suggestion on using a humidifier to treat the
unreacted gas discharged f'ror.n the fuel cell.
[0006] Another important issue about the fuel cell is the unreacted
hydrogen. discharged from the fuel cell. Unlike the unreactcd oxygen that
can be directly discharged into amloient air, the unreacted hydrogen is highly
dangerous and subject to self-combustion and explosion when a local
concentration of the discharged unrea;;ted hydrogen exceeds 4%. Therefore
proper measures must be taken to treat the unreacted hydrogen discharged from
the fuel cell. In a currently adopted way, the unreacted hydrogen is led back
to the fuel cell and recycled. However, the recycled hydrogen as reactant gas
has reduced purity to possibly cause the poisoning problem. One way to
solve the above put-ity and poisoning problems is to recycle only part of the
discharged unreacted hydrogen. The remaining part of the discharged
unreacted hydrogeti is led to a catalytic converter and treated before being
discharged into ambient air. However, the catalytic converter requires
additional and quite high cost.
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SUMMARY OF THE INVENTION
[0007} A primary object of the present invention is to provide a fuel cell
system having unreacted gas discharge pipeline associated with humidifier, so
that unreacted hydrogen discharged from a:i'uel cell stack is humidified at a
humidifier and the humidified unreacted hydrogen can be safely discharged
into ambient air without causing potential danger.
[0008] Another object of the present invention is to provide a fuel cell
system having an unreacted hydrogen discharge pipeline that replaces the
catalytic converter used in con'1entional fuel cell stack for treating
unreacted
gas, so that the cost for treating the unreacted gas discharged from the fuel
cell
stack can be reduced.
[0009] To fulfill the above objects, the present invention provides a fuel
cell system having unreacted gas discharge pipeline associated with
humidifier.
The fuel cell system comrpises a fuel cell stack and a humidifier. The
humidifier includes an unreacted gas inlet porC connected to an end of an
unreacted hydrogen discharge pipeline, which is connected at the other end to
a
hydrogen outlet port of the fuel cell stack, such that the unreacted bydrogen
discharged from the fuel cell stack via the hydrogen outlet port is led by the
unreacted hydrogen discharge pipeline into the hwnidi#ier. The humidifier
regulates relative humidity and concentration of the unreacted hydrogen led
thereinto, and the humidified uiireacted hydrogen is then discharged from the
humidifier.
[00] 0] With the arrangements of the present invention, reactant gas is
regulated at the hurnidifier to increase the relative humidity and temperature
thereof before being supplied to the fuel cell stack, so that the fuel cell
stack
can be maintained at proper operating humidity and temperature. Moreover,
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a part of the unreacted hydrogen may be led back to the fuel cell stack and
recycled while the other part of the tmreacted hydrogen is led to the
hunaidifier
to be humidified and diluted for safely discharging into ambient air.
Therefore, the present invention enables reduced cost for treating unreacted
gas
discharged from the fuel cell stack.
B1tIEF DESCRIPTION OF THE DRAWINGS
[0011] The structure and the technical means adopted by the present
invention to achieve the above and other objects can be best understood by
referring to the following detailed description of the preferred embodiments
and the accompanying drawings, wherein:
[0012] Fig. 1 is a block diagram of a fuel cell system having unreacted gas
discharge pipeline associated with humidifier according to a first embodiment
of the present invention;
[0013] Fig. 2 is a block diagraln of a fuel cell system having unreacted gas
discharge pipeline associatccy with humidifier according to a second
embodiment of the present invention; and
[0014] Fig. 3 is a block diagram of a fuQl cell system having unreacted gas
discharge pipeline associated with humidifier according to a third embodiment
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] Please refer to Fig. I that is a block diagram of a fuel cell system
having unreacted gas discharge pipeline associated with humidifier 100
according to a first embodiment of the present invention. As shown, the fuel
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cell system 100 includes a fuel cell stack 1, a hydrogen source 2, an oxygen
source 3, an unreacted hydrogen discharge pipeline 4, and a humidifier S.
100161 The fuel cell stack 1 includes a hydrogen inlet port 11. A
hydrogen supplying pipeline 21 is extended between and connected to the
hydrogen source 2 and the hydrogen inlet port 11, so that hydrogen supplied
from the hydrogen source 2 is led into the fuel cell stack 1. via the hydrogen
supplying pipeline 21 and the hydrogen inlet port 11. The fuel cell stack 1
further includes a hydrogen outlet port 12, via wbich unreacted hydrogen in
discharged .f.rom the fuel cell stack 1; an oxygen inlet port 13, via which
oxygen is fed into the fuel cell stack 1; and an oxygen outlet port 14, via
which
unreacted oxygen is discharged from the fuel cell stack 1.
[0017] The unreacted hydrogen discharge pipeline 4 is conneeted at an end
to the hydrogen outlet port 12 for leading the unreacted hydrogen discharged
from the fuel cell stack 1 to the humidifier 5. A pressurizing unit 41, a gas
mixing device 42, and an unreacted hydrogen discharge control unit 43 are
connected to the unreacted hydrogen discharge pipeline 4. The pressurizing
unit 41 applies appropriate pressure to the unreacted hydrogen to thereby
increase a flow rate of the unreacted hydrogen. The unreacted hydrogen and
unreacted oxygen discharged from the fuel cell stack 1 are led to the gas
mixing device 42 to mix with each other thercin. The unreacted hydrogen
discharge control unit 43 controls the volume of unreacted hydrogen to be led
into the gas mixing device 42.
[001$] The huniidifier 5 includes an unreacted gas inlet port 51, to which
the other end of the unreacted hydrogen discharge pipeline 4 is connected, so
that the unreacted hydrogen discharged from the fuel cell stack I is finally
led
to the humidifier 5; a humidified unreacted gas outlet port 52; an oxygen
source inlet port 53 connected to the oxygen source 3 via an oxygen supply
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pipe 31, so that oxygen supplied from the oxygen source 3 is led by the oxygen
supply pipe 31 into the humidifier 5 via the oxygen source inlet port 53 for
humidity regulation; and a humidified oxygen outlet port 54 connected to the
oxygen inlet port 13 of the fuel cell stack 1 via an oxygen supplying pipeline
32, so that oxygen having been humidified in the humidifier 5 is fed into the
fuel cell stack 1 via the oxygen supplying pipelinc 32 and the oxygen inlet
port
13.
[0019] The fuel cell system 100 further includes an unreacted oxygen
discharge pipeline 33 extended between and connected to the oxygen outlet
port 14 of the fuel cell stack 1 and the gas mixing device 42 on the unreacted
hydrogen discharge pipeline 4, so that unreacted oxygen discharged via the
oxygen outlet port 14 is mixed with the discharged unreacted hydrogen in the
gas mixing device 42. The oxygen/hydrogen gas mixture is then led into the
humidifier 5 via the 'unreacted gas inlet port 51.
[0020J The oxygen supplied from the oxygen source 3 is relatively dry.
The relatively dry oxygen from the oxygen source 3 is led into the humidifier
5
via the oxygen supply pipe 31 and regulated to become relatively humid.
The relatively humid oxygen is then led from the humidifier 5 to the fuel cell
stack 1 via the oxygen supplying pipeline 32.
[00211 The humidifier 5 also regulates the humidity of the unreacted
oxygen/hydrogen gas mixture led thereto from the gas rnixing device 42.
The humidified oxygen/hydrogen gas mixture is then discharged via the
humidified urireacted gas outlet port 52,
[0022] By mixing the unreactecl hydrogen with the unreacted oxygen in the
gas mixing device 42, the potentially dangerous unreacted hydrogen may have
a reduced concentration. And, by humidifying the oxygen/hydrogen gas
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mixture in the humidifier 5, the concentration of the unreacted hydrogen is
further reduced even to less than 1% in some practical applications of the
present invention, and the relative humidity of the unreacted hydrogen is also
increased to reduce the potential taazard of hydrogen, allowing the unreacted
hydrogen to be safely discharged into aznYaient air.
[00231 Fig. 2 is a block diagrarn of a fuel cell system having unreaeted gas
discharge pipeline associated vrith httmidifier 200 according to a second
embodiment of the present invention. As can be seen from Fig. 2, the fuel
cell system 200 in the second embodiment is generally structurally similar to
the first embodiment, except for an ul-reacted hydrogen recycling pipeline 44
extended between and connected to the unreacted hydrogen discharge pipeline
4 and the hydrogen supplying pipeline 21.
[00241 W"ith the unreacted hydrogen recycling pipeline 44, a part of the
unreacted hydrogen discharged from the fuel cell stack 1 is led back to the
fuel
cell stack I via the hydrogen supplying pipeline 21 and recycled. The
remaining part of the discharged unreacted hydrogen is still led to the gas
mixing device 42 for mixing with the unreacted oxygen before being led to the
humidifier 5 and discharged into anibient air.
[00251 Please refer to Fig. 3 that is a block diagram of -a fuel cell system
having unreacted gas discharge pipeline associated with humidifier 300
according to a third embodiment of the present invention. As can be seen
from Fig. 3, the fuel cell system 300 in the third embodiment is generally
structurally similar to the fuel ce;ll system 200 in the second embodiment,
except for a water cooliug system 6.
[0026] The water cooling system 6 includes a cooling water unit 61 and a
water pressurizing unit 64. Tne cooling water unit 61 is connected to the fuel
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cell stack 1 via a cooling water supplying pipeline 62, so as to supply low
temperature cooling water to the fuel cell stack 1 to lower the high
temperature
produced by the reaction in the fuel cell stack 1 and thereby maintains the
fuel
cell stack 1 in a normal operatirng state. The low temperature cooling water
having been used to cool and then discharged from the fuel cell stack 1 has a
high temperature. The high ternperature cooling water is led to the
humidifier 5 to serve as a high temperature water source thereof, so as to
increase the humidity and tetxtpera.w.re of the oxygen supplied from the
oxygen
source 3 to the humidifier 5, and the humidity of the oxygen/hydrogen gas
mixture led from the gas mixing device 42 to the humidifier 5. The high
temperature cooling water flowing tl7rough the humidifier 5 is then led via a
cooling water recycling pipeline 63 to the cooling water unit 61 and be cooled
thereat. The water pressurizisig uYlit 64 applies pressure to the cooling
water
in the water cooling system f, so as to increase the flow rate of the cooling
water.
[0027] In the above illustrated embodiments, the unreacted oxygen
discharge pipeline 33 is simply provided to lead the unreacted oxygen to the
gas mixing device 42 for mixing with the unreacted hydrogen and thereby
reduces the concentration of the unr-eacted hydrogen. In practieal application
of the present irivention, the uilreacted oxygen may be directly discharged
from
the fuel cell stack I via the oxygen outlet port 14 into the ambient air,
while the
oxygen for mixing with the unreacted hydrogen in the gas mixing device 42
may be supplied directly from the ag-nbient air by, for example, providing an
additional air inlet port on the gas tdlixing device 42.
[0028] The hydrogen source '1 and the oxygen source 3 are simply
provided to supply reactant gases for the fuel cell stack 1; wherein the
hydrogen source 2 may be a hy=irogen storage alloy or a hydrogen tank, and the
oxygen source 3 may be an oxygen tank or an air blower. However, the
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hydrogen and oxygen sources 2, 3 may also be any other known types of gas
sources.
[0029] The gas mixing device: 42 is simply provided for mixing the
unreacted hydrogen and oxygen. In practical application of the present
invention, the gas mixing device 42 may be a gas mixing chamber, or a
three-way union.
[0030] The unreacted hydrogen discharge control unit 43 is also provided
simply for controlling the flow of the discharged unreacted hydrogen.
Therefore, the unreacted hydrogen Eiischarge control unit 43 may be a throttle
valve, an electromagnetic valve, or any other known types of controlling
units,
so long as these valves and units provide equivalent function and effect.
[0031] In the illustrated embodiments of the present invention, the oxygen
source and the hydrogen source are provided mainly to supply oxygen and
hydrogen needed by the fuel cell stack. Any other known types of oxygen
and hydrogen sources providing ecluivalent function and effect may also be
employed in the present invention. For example, the oxygen source may be
ambient air and a cooperative blower, or a high-pressure oxygen cylinder or
tank; and the hydrogen source may be a high-pressure hydrogen cylinder or
tank, or a hydrogen storage alloy.
100321 While the present invention has been described with reference to
the specific embodiments, the description is illustrative of the invention and
is
not to be construed as limiting the invention. Therefore, various
modifications to the present invention can be made to the preferred
embodiments by those skilled in the art without departing from the true spirit
and scope of the invention as defined by the appended claims.
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