Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
FUEL CELL SYSTEM AND METHOD FOR REDUCING ELECTRODE
DETERIORATION DURING START UP
Technical Field
The present invention relates to a proton exchange
membrane fuel cell system.
Background Art
In general, if hydrogen and oxygen are unevenly
distributed in a fuel electrode of a fuel cell-when the fuel
cell is started, a local potential is generated in a region
where a hydrogen concentration is relatively high and serves
to cause a current flow in a direction opposite to that in a
normal power-generating state in a region where an oxygen
concentration is relatively high. Therefore, an oxidizer
electrode, in particular, quickly deteriorates. In order to
solve this problem, an invention for discharging oxygen that
remains in the fuel electrode and replacing the oxygen with
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hydrogen gas in a short time is disclosed in, for example,
Japanese Unexamined Patent Application Publication No. 2004-
139984 (see page 12 and Fig. 14). According to this
invention, when a fuel cell is started, a control value of a
secondary pressure regulator is set to be higher than a
supply pressure in a normal power-generating state and
hydrogen is supplied to the fuel cell by opening a'hydrogen
supply solenoid valve while driving a hydrogen pump.
Disclosure of Invention
However, according to the start method disclosed in the
above-mentioned publication in which the hydrogen pump is
started first, even when the fuel electrode of the fuel cell
is filled with air (or hydrogen), if the gas composition in
the fuel electrode and a hydrogen circulation path is.uneven,
hydrogen (or air) that remains in the hydrogen circulation
path flows into the fuel electrode immediately after the
operation of the hydrogen pump is started. In addition, it
requires a relatively long time for the hydrogen circulation
pump to accelerate to a predetermined rotational speed after
the hydrogen circulation pump is started. Therefore, it
takes a relatively long time to eliminate the uneven
distribution of hydrogen and oxygen in the fuel electrode,
and accordingly the deterioration of the fuel cell
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progresses.
In order to solve the above-described problem, a fuel
cell system according to one aspect of the present
invention includes an air-replacement-state recognizing
unit for estimating or detecting a state in which hydrogen
and air are unevenly distributed in at least one of a fuel
electrode and a fuel-gas circulation path and a start
control device that selects an order for operating the fuel-
gas circulation pump and supplying the fuel gas upon
starting the fuel cell based on the output of the air-
replacement-state recognizing means. This system can be
used to reduce the period of time in which hydrogen and
oxygen are unevenly distributed in the fuel electrode,
thereby reducing deterioration.
According to the present invention, the timings of
activation of the fuel-gas circulation pump and the supply
of fuel gas are changed on the basis of the air replacement
state and, as a result, deterioration of the fuel cell
caused by uneven distribution of the fuel gas and air in
the fuel electrode caused by air infiltration into the fuel
chamber (the fuel electrode, the fuel-gas circulation path,
and fuel-gas circulating means) is prevented.
The air-replacement-state recognizing means may
comprise a timer for estimating the air replacement state,
or one or more sensors for detecting the oxygen
concentration and/or hydrogen (fuel gas) at a portion of the
fuel-gas circulation path where replacement of the hydrogen
by air is finished first or last after the fuel cell stops,
or any combination thereof.
Thus in one aspect, the present invention provides a
fuel cell system comprising: a fuel cell that includes a
fuel electrode and an oxidizer electrode and an electrolyte
disposed between the fuel electrode and the oxidizer
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electrode, the fuel cell generating electric power when fuel
gas and oxidizing gas are supplied to the fuel electrode and
the oxidizer electrode, respectively; a fuel-gas circulation
path that connects an inlet of the fuel electrode to an
outlet of the fuel electrode, the fuel gas being supplied
through the inlet and discharged from the outlet; a fuel-gas
circulation pump on the fuel-gas circulation path; air-
replacement-state recognizing means that estimates or
detects a state in which hydrogen and air are unevenly
distributed in at least one of the fuel electrode and the
fuel-gas circulation path, wherein the air replacement state
recognizing means comprises a timer for estimating the air
replacement state, or an oxygen concentration sensor and/or
a fuel-gas concentration sensor for detecting the air
replacement state and being disposed at a portion of the
fuel-gas circulation path where replacement of the fuel gas
by air is finished first or last after the fuel cell stops,
or any combination thereof; and a controller that detects a
desire to start the fuel cell, that samples an output of the
air-replacement-state recognizing means after detecting the
desire to start the fuel cell and that selects an order for
operating the fuel-gas circulation pump and supplying the
fuel gas upon starting the fuel cell based on the output of
the air-replacement-state recognizing means.
In another aspect, the present invention provides a
method for starting up a fuel cell system, wherein the fuel
cell system comprises a fuel cell that includes a fuel
electrode, an oxidizer electrode and an electrolyte disposed
between the fuel electrode and the oxidizer electrode, the
fuel cell generating electric power when fuel gas and
oxidizing gas are supplied to the fuel electrode and the
oxidizer electrode, respectively, a fuel-gas circulation
path that connects an inlet of the fuel electrode to an
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outlet of the fuel electrode, the fuel gas being supplied
through the inlet and discharged from the outlet, a fuel-gas
circulation pump provided on the fuel-gas circulation path,
and air-replacement-state-recognizing means that estimates
or detects a state in which hydrogen and air are unevenly
distributed in at least one of the fuel electrode and the
fuel-gas circulation path, wherein the air replacement state
recognizing means comprises a timer for estimating the air
replacement state, or an oxygen concentration sensor and/or
a fuel-gas concentration sensor for detecting the air
replacement state and being disposed at a portion of the
fuel-gas circulation path where replacement of the fuel gas
by air is finished first or last after the fuel cell stops,
or any combination thereof, the method comprising: detecting
a desire to start the fuel cell; estimating or detecting a
state in which hydrogen and air are unevenly distributed in
at least one of the fuel electrode and the fuel-gas
circulation path after detecting the desire to start the
fuel cell and before starting the fuel cell; and selecting
an order for operating the fuel-gas circulation pump and for
activating a fuel gas supply upon starting the fuel cell
based on whether or not it is estimated or detected that
hydrogen and air are unevenly distributed.
In certain embodiments of the above-described fuel cell
system, the controller is configured to operate the fuel-gas
circulation pump after supplying the fuel gas if the output
of the air-replacement-state-recognizing means indicates
that hydrogen and air are unevenly distributed, so as to
reduce the time period in which hydrogen and oxygen are
unevenly distributed in the fuel electrode and reduce
deterioration of the fuel cell.
In certain other embodiments, the above-described fuel
cell system further comprises a shutoff valve disposed
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between an outlet of the fuel-gas circulation pump and an
inlet of a fuel cell body, and in this type of system, if
the output of the air-replacement-state recognizing means
indicates that hydrogen and air are unevenly distributed,
the controller starts operation of the fuel-gas circulation
pump after closing the shutoff valve, and then opens the
shutoff valve and starts the supply of the fuel gas when a
rotational speed of the fuel-gas circulation pump becomes
equal to or more than a predetermined value or when an inner
pressure of the fuel electrode becomes equal to or less than
a predetermined value.
Brief Description of the Drawings
Fig. 1 is a diagram illustrating a fuel cell system.
Fig. 2 is a diagram illustrating a single cell in a
fuel cell.
Fig. 3 is a diagram illustrating an inner state (state
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A) of a fuel chamber.
Fig. 4 is a diagram illustrating another inner state
(state B) of the fuel chamber.
Fig. 5 is a diagram illustrating another inner state
(state C) of the fuel chamber.
Fig. 6 is a flowchart of a process performed in a fuel
cell system according to a first embodiment of the present
invention.
Fig. 7 is a diagram illustrating the fuel cell system
according to the first embodiment of the present invention.
Fig. 8 is a diagram illustrating a fuel cell system
according to a second embodiment of the present invention.
Fig. 9 is a flowchart of a process performed in the
fuel cell system according to the second embodiment of the
present invention.
Fig. 10 is a diagram illustrating a fuel cell system
according to a third embodiment of the present invention.
Fig. 11 is a flowchart of a process performed in the
fuel cell system according to the third embodiment of the
present invention.
Fig. 12 is a diagram illustrating a fuel cell system
according to a fourth embodiment of the present invention.
Fig. 13 is a flowchart of a process performed in the
fuel cell system according to the fourth embodiment of the
present invention.
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Fig. 14 is a diagram illustrating a fuel cell system
according to a fifth embodiment of the present invention.
Fig. 15 is a flowchart of a process performed in the
fuel cell system according to the fifth embodiment of the
present invention.
Fig. 16 is a diagram illustrating a fuel cell system
according to a sixth embodiment of the present invention.
Fig. 17 is a flowchart of a process performed in the
fuel cell system according to the sixth embodiment of the
present invention.
Fig. 18 is a flowchart of a process performed in a fuel
cell system according to a seventh embodiment of the present
invention.
Reference Numerals
1 fuel cell body
la oxidizer electrode
lb fuel electrode
11 air compressor
12 air supply path
13 air-system humidifier
14 air discharge path
15 air pressure regulator
16 air pressure gage
17 hydrogen detector
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21 high-pressure hydrogen tank
22 hydrogen supply path
23 hydrogen pressure regulator
24 hydrogen circulation pump
25 hydrogen-system humidifier
26 hydrogen circulation path
27 hydrogen discharge path
28 hydrogen discharge valve
29 hydrogen pressure gage
31 cooling water pump
32 cooling water circulation path
33 heat exchanger
34 cooling water thermometer
40 load device
41 voltmeter
42 ammeter
43 controller
50 oxygen concentration meter
51 hydrogen concentration meter
52 oxygen concentration meter
53 hydrogen concentration meter
54 hydrogen-circulation-pump discharge shutoff valve
60 timer
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Detailed Description
Next, embodiments of the present invention will be
described in detail with reference to the drawings.
First, the overall structure of a fuel cell system to
which the present invention may be applied will be described
below with reference to Fig. 1, which is a diagram
illustrating the fuel cell system and Fig. 2, which is a
diagram illustrating a single cell in a fuel cell.
Fuel Cell Body
As shown in Fig. 2, a single cell 100 of a fuel cell
includes a membrane-electrode assembly (MEA) 101 including a
solid polymer electrolyte membrane 102, a fuel-electrode
catalyst layer 103 provided on one side of the electrolyte
membrane 102, and an oxidizer-electrode catalyst layer 104
provided on the other side of the electrolyte membrane 102;
a fuel-gas diffusion layer 105 provided on one side of the
MEA 101; an oxidizing-gas diffusion layer 106 provided on
the other side of the MEA 101; and separators 107 and 108.
A fuel-gas path 109 is provided between the separator
107 and the fuel-gas diffusion layer 105 and an oxidizing-
gas path 110 is provided between the separator 108 and the
oxidizing-gas diffusion layer 106. The fuel cell body
includes a plurality of cells similar to the single cell 100.
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Fuel gas (hydrogen) and oxidizing gas (air) are externally
supplied to the fuel cell body and are caused to flow
through the fuel-gas path 109 and the oxidizing-gas path 110,
respectively, so that electric power is generated as a
result of electrochemical reaction.
A fuel cell system to which the present invention may
be applied includes a fuel cell body 1, an air system for
supplying air, a hydrogen system for supplying hydrogen, a
cooling water system for supplying cooling water, and a load
system for extracting the electric power from the fuel cell
body 1.
Air System
The air system includes an air compressor 11 for
sucking in and compressing air, an air-system humidifier 13
for humidifying the air compressed by the air compressor 11
and supplying the humidified air to an oxidizer electrode la,
an air pressure gage 16 for detecting the pressure of the
air supplied to the oxidizer electrode la, and an air
pressure regulator 15 for adjusting the pressure in the
oxidizer electrode la by regulating the air discharged from
the oxidizer electrode la.
The air compressed by the air compressor 11 is supplied
through the air supply path 12 to the air-system humidifier
13, and is humidified. Then, the humidified air is supplied
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to the oxidizer electrode la of the fuel cell body 1, and is
consumed by the electrochemical reaction in the fuel cell
body 1. Then, the exhaust air is caused to flow through the
air discharge path 14= and is discharged from the system
after the pressure adjustment is performed by the air
pressure regulator 15. The pressure of the air supplied to
the oxidizer electrode la is detected by the air pressure
gage 16 disposed at an inlet of the oxidizer electrode la,
and the air pressure regulator 15 is controlled such that
the detected pressure becomes equal to a desired pressure.
The air-system humidifier 13 may include a water vapor
exchange membrane for utilizing moisture included in the
exhaust or may use pure water that is externally supplied.
A hydrogen detector 17 for detecting hydrogen included
in the exhaust air is disposed downstream of the air
pressure regulator 15. Accordingly, hydrogen that enters
through the electrolyte membrane 102 from the fuel electrode
to the oxidizer electrode and hydrogen that leaks from a
sealed portion can be detected.
Hydrogen System
The hydrogen system includes a high-pressure hydrogen
tank 21 that stores hydrogen gas, a hydrogen pressure
regulator 23 for adjusting the pressure of the hydrogen, a
hydrogen-system humidifier 25 for humidifying the hydrogen
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after the pressure thereof is adjusted and supplying the
humidified hydrogen to a fuel electrode ib, a hydrogen
pressure gage 29 for detecting the pressure of the hydrogen
supplied to the fuel electrode ib, a hydrogen circulation
pump 24 and a hydrogen circulation path 26 for circulating
the hydrogen discharged from an outlet of the fuel electrode
lb to an inlet of the fuel electrode lb, and a hydrogen
discharge path 27 and a hydrogen discharge valve 28 for
discharging impurities accumulated in the fuel electrode lb
and the hydrogen circulation path 26 from the system.
The hydrogen supplied from the high-pressure hydrogen
tank 21 flows through the hydrogen supply path 22 via the
hydrogen pressure regulator 23, where the pressure of the
hydrogen is adjusted to a desire pressure, and joins the
discharge hydrogen circulated by the hydrogen circulation
pump 24. Then, the hydrogen is humidified by the hydrogen
system humidifier 25, and is fed to the fuel electrode lb of
the fuel-cell body 1. The pressure of the hydrogen supplied
to the fuel electrode lb is detected by the hydrogen
pressure gage 29 provided at the inlet of the fuel electrode
lb, and the hydrogen pressure regulator 23 is controlled
such that the detected pressure becomes equal to the desired
pressure. After the hydrogen is consumed by the
electrochemical reaction in the fuel cell body 1, the excess
hydrogen is caused to pass through the hydrogen circulation
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path 26 by the hydrogen circulation pump 24 and is used for
power generation again.
On the other hand, nitrogen that enters from the
oxidizer electrode la to the fuel electrode lb during the
operation and impurities included in the high-pressure
hydrogen tank 21 accumulate in the hydrogen system.
Therefore, these impurities are discharged from the system
through the hydrogen discharge path 27 by opening the
hydrogen discharge valve 28.
Cooling Water System
The cooling water system is provided to maintain the
temperature of the fuel cell body 1 at an adequate
temperature by removing heat generated as a result of power
generation performed by the fuel cell body 1. The cooling
water system includes a cooling water pump 31 for
circulating the cooling water, a cooling water circulation
path 32, a heat exchanger 33 for dissipating heat to the
outside of the system, and a cooling water thermometer 34
for detecting the temperature of the cooling water at a
position near a cooling-water outlet of the fuel cell body 1.
The cooling water is pressurized by the cooling water
.pump 31 so as to flow through the fuel cell body 1, and
thereby absorbs heat. Then, the cooling water flows through
the cooling water circulation path 32 to the heat exchanger
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33, where the.heat is discharged to the outside of the
system. Then, the cooling water is caused to flow through
the fuel cell body 1 again by the cooling water pump 31.
The temperature of the cooling water is monitored by the
cooling water thermometer 34 and is adjusted to a
temperature appropriate for the power generation level
provided by the fuel cell body by controlling the amount of
air flow supplied to the heat exchanger 33 by a blower.
Load System
A load device 40 that absorbs the electric power
generated by the fuel cell body 1 functions as, for example,
an inverter for supplying electric power to a vehicle drive
motor in a fuel cell vehicle. A power generation voltage of
the fuel cell body 1 is detected by a voltmeter 41 and a
.current supplied to the load device 40 from the fuel cell
body 1 is detected by an ammeter 42.
Control System
A controller 43 operates as a start control device to
control the overall operation of the fuel cell system
including the fuel cell body 1. The controller 43 includes,
for example, a central processing unit (CPU), a read only
memory (ROM) that stores control programs and control
parameters, a working random access memory (RAM), and a
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microprocessor including an input/output interface.
The controller 43 outputs control signals to the air
compressor 11, the air pressure regulator 15, the hydrogen
pressure regulator 23, the hydrogen discharge valve 28, the
cooling water pump 31, and the load device 40 on the basis
of detected signals obtained from the air pressure gage 16,
the hydrogen pressure gage 29, the cooling water thermometer
34, the voltmeter 41, and the ammeter 42 in order to adjust
the pressure, temperature, the amount of flow, and the load
in the fuel cell body 1.
Next, the state of the fuel chamber (the hydrogen
supply path 22, the hydrogen circulation pump 24, the
hydrogen-system humidifier 25, the fuel electrode lb, and
the hydrogen circulation path 26 that varies in a period
from when the fuel cell system stops to when the fuel cell
system is restarted will be described with reference to Figs.
3, 4, and 5. In the figures, the hydrogen-system humidifier
25 is omitted.
A. Immediately after stoppage
In a period immediately after the stoppage, the fuel
chamber is filled with hydrogen provided before the power
generation was stopped.
B. After an extended time from stoppage (or when air
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replacement occurs)
After a sufficient time from the stoppage, air leaks or
otherwise enters through the MEA 101 from the oxidizer
electrode la to the fuel electrode lb and diffuses into the
fuel chamber so that the fuel chamber becomes filled with
the air. The amount of the original hydrogen that has been
replaced by the infiltrated air is referred to herein as the
air replacement state. The time required for the air to
fill the fuel chamber varies in accordance with the material,
the thickness, the temperature, etc., of the MEA, but is
generally about several hours.
C. Several minutes to several tens of minutes after stoppage
In a relatively short time period after the stoppage,
the air diffuses into the fuel electrode lb, whereas other
portions (the hydrogen circulation pump 24, the hydrogen-
system humidifier 25, and the hydrogen circulation path 26)
remain filled with hydrogen provided in the previous
operation of power generation. Therefore, different from
state B, the air and hydrogen are unevenly distributed in
the fuel chamber. The time period and rate in which the
hydrogen is replaced with air varies in accordance with the
material, the thickness, the temperature, etc., of the MEA,
but is generally about several minutes to several tens of
minutes. Here, the uneven distribution refers to the state
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in which hydrogen and oxygen (or gases having different
hydrogen densities) exist separately within the fuel chamber.
First Embodiment
Next, a fuel cell system according to a first
embodiment of the present invention will be described below.
The structure of'the fuel cell system according to the first
embodiment is similar to that shown in Fig. 1. However, the
controller 43 includes an air-replacement-state estimator
for estimating an air replacement state of the fuel
electrode lb and the hydrogen circulation path 26 when the
fuel cell system is stopped. When the fuel cell system is
started, the controller 43 controls the timings at which the
operation of the hydrogen circulation pump 24 is started and
the hydrogen pressure regulator 23 is opened to start
supplying the fuel gas on the basis of the estimated air
replacement state.
Start Method for First Embodiment
Next, a method for starting the fuel cell system
according to the present embodiment will be described below
with reference to a flowchart shown in Fig. 6. When, for
example, the state of a key switch is changed from Off to On,
the controller 43 detects the change and follows the steps
of the flowchart of Fig. 6 to start the fuel cell system.
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First, in Step 01 ('Step' is hereafter abbreviated as
'S'), it is determined whether or not a time elapsed after
the previous stoppage is within a first predetermined time
by referring to an air replacement state recognizing means
(e.g., a timer 60).
If it is determined that the elapsed time is equal to
or less than the first predetermined time in SOl, that is,
if the result of the determination of S0l is Yes, it is
determined that the fuel chamber is filled with hydrogen
provided in the previous operation of power generation
(state A). Accordingly, it is determined that hydrogen and
oxygen are not unevenly distributed in the fuel electrode lb
and the deterioration will not progress during start up.
Therefore, the process proceeds to S06, where the supply of
hydrogen is started and the hydrogen circulation pump 24 is
activated. Here, the order in which the supply of hydrogen
is started and the hydrogen circulation pump 24 is activated
is not restricted. Accordingly, the supply of hydrogen may
be started and the hydrogen circulation pump 24 may be
activated at the same time. Then, the process proceeds to
S05, where a normal operation routine is performed. The
normal operation routine is a control routine for performing
a normal operation. More specifically, in the normal
operation, the air system, the hydrogen system, the cooling
system, the load system, and the control system are operated
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in accordance with the load requirement of the system. Here,
the uneven distribution refers to the state in which
hydrogen and oxygen (or gases having different hydrogen
densities) exist separately.
If it is determined that the elapsed time is more than
the first predetermined time in S01, that is, if the result
of the determination of SO1 is No, the process proceeds to
S02, where it is determined whether or not the time elapsed
after the previous stoppage is equal to or more than a
second predetermined time by referring to the timer.
If it is determined that the elapsed time is equal to
or more than.the second predetermined time in S02, that is,
if the result of the determination of S02 is Yes, it is
determined that the fuel chamber is filled with air from the
oxidizer electrode la during the stoppage (state B) and the
process proceeds to S03. In S03, first, the hydrogen
circulation pump 24 is activated to generate a negative
pressure at the outlet of (and gas flow through) the fuel
electrode lb, and then the supply of hydrogen gas is started
by executing a hydrogen supply start routine. Therefore,
the time period in which hydrogen and oxygen are unevenly
distributed in the fuel electrode lb is reduced and the
deterioration is reduced. Then, the process proceeds to S05,
where the normal operation routine is performed.
If it is determined that the elapsed time is less than
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the second predetermined time in S02, that is, if the result
of the determination of S02 is No, it is determined that
hydrogen that remains after the previous stoppage of power
generation and air that enters from the oxidizer electrode
la are unevenly distributed in the fuel chamber (state C),
and the process proceeds to S04. In S04, first, the supply
of hydrogen gas is started, and then the hydrogen
circulation pump 24 is started. Therefore, the uneven
distribution of hydrogen and oxygen in the fuel electrode lb,
which would otherwise occur under prior art methods
immediately after the hydrogen circulation pump is activated,
can be avoided and the deterioration can be prevented from
progressing. The process then proceeds to S05, where the
normal operation routine is performed.
The above-described embodiment provides the following
effects:
(1) If it is determined that the fuel electrode lb is
filled with hydrogen (state A), then the normal power
generating operation can be started immediately. Therefore,
the start time can be reduced.
(2) If it is determined that fuel electrode lb is
substantially filled with air (state B), then high-pressure
hydrogen can be supplied and drawn through the fuel
electrode lb in response to a negative pressure generated in
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the fuel electrode lb by the hydrogen circulation pump 24.
Therefore, the time period during which hydrogen and oxygen
are unevenly distributed in the fuel electrode lb can be
reduced and the deterioration of the fuel cell can be
suppressed.
(3) If it is determined that hydrogen that remains
after the previous stoppage of power generation and air that
enters from the oxidizer electrode la are unevenly
distributed in the fuel chamber (state C), then the hydrogen
circulation pump 24 is started after the supply of hydrogen
gas is started. Therefore, the uneven distribution of
hydrogen and oxygen in the fuel electrode lb, which would
otherwise occur using prior art methods immediately after
the hydrogen circulation pump is operated, can be avoided
and the deterioration of the fuel cell can be prevented from
progressing.
Estimation of the air replacement state of the fuel chamber
based on the stop period and correction based on temperature
Next, the first and second predetermined times for
determining the mixed air state of the fuel chamber on'the
basis of the time elapsed after the previous stoppage until
the restart will be described below. To determine these
times, an oxygen concentration sensor or a hydrogen
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concentration sensor is disposed at a certain position in
the fuel chamber of an experimental fuel cell system and a
variation with time in the concentration of oxygen or
hydrogen after the fuel cell system is stopped is
experimentally measured. Then, the first predetermined time
is determined as a time period during which the oxygen
concentration is equal to or less than a predetermined value
(the hydrogen concentration is equal to or more than a
predetermined value) and at which the deterioration does not
progress even when the normal operation routine is started
in the fuel chamber immediately after the fuel cell system
is started.
The second predetermined time is based upon temperature
and is determined as a time period required for the oxygen
concentration to become equal to or more than a
predetermined value (for the hydrogen concentration to
become equal to or less than a predetermined value) at which
the deterioration of the fuel electrode lb does not progress
even when the hydrogen circulation pump 24 is operated first
in the fuel chamber.
The time rate at which the air enters from the oxidizer
electrode la to the fuel electrode lb depends on the
temperature of the fuel cell body 1, and the transmission
speed is increased as the temperature is increased.
Therefore, an experiment of, for example, varying the fuel
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cell temperature detected by the cooling water thermometer
34 and measuring the variation with time in gas
concentration in the fuel chamber is performed and a
correction value (correction coefficient) shown in Fig. 7 is
determined and stored in the controller in advance. The
first and second predetermined times are multiplied by the
correction value so that first and second predetermined
times can be used as more accurate determination thresholds.
Second Embodiment
A fuel cell system according to a second illustrated
embodiment of the present invention will be described below.
Fig. 8 is a system diagram showing the structure according
to the second embodiment. The structure according to the
second embodiment is similar to that shown in Fig. 1 except
an oxygen concentration meter 50 for measuring the oxygen
concentration in the hydrogen circulation pump 24 is
additionally provided as an air replacement state
recognizing means.
Start Method
A method for starting the fuel cell system according to
the second embodiment will be described below with reference
to a flowchart shown in Fig. 9. When, for example, the
state of a key switch is changed from Off to On, the
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controller 43 detects the change and follows the steps of
the flowchart of Fig. 9 to start the fuel cell system.
First, in Sil, a detection value of the oxygen
concentration meter 50 is read and it is determined whether
or not the oxygen concentration in the hydrogen circulation
pump 24 is equal to or more than a predetermined value. If
it is determined that the oxygen concentration is equal to
or more than the predetermined value in S11, that is, if the
result of the determination of S11 is Yes, it is determined
that the fuel chamber is filled with air transmitted from .
the oxidizer electrode la during the stoppage (state B) and
the process proceeds to S12. In S12, first, the hydrogen
circulation pump 24 is started to generate a negative
pressure at the outlet of (and gas flow through) the fuel
electrode lb, and then the supply of fuel gas is started.
Therefore, the time period in which hydrogen and oxygen are
unevenly distributed in the fuel electrode lb is reduced and
the deterioration is suppressed. The process then proceeds
to S14, where the normal operation routine is performed.
If is determined that the oxygen concentration is less
than the predetermined value in S11, that is, if the result
of the determination of S11 is No, it is determined that
hydrogen that remains after the previous stoppage of power
generation and air that enters from the oxidizer electrode
la are unevenly distributed in the fuel chamber (state C) or
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that the fuel chamber is filled with hydrogen provided
before the previous stoppage of power generation (state A),
and the process proceeds to S13.
In S13, first, the supply of hydrogen gas is started,
and then the operation of the hydrogen circulation pump 24
is started. Therefore, the uneven distribution of hydrogen
and oxygen in the fuel electrode lb, which would otherwise
occur under prior methods immediately after the hydrogen
circulation pump is started, can be avoided and the
deterioration of the fuel cell can be prevented from
progressing. Then, the process proceeds to S14, where the
normal operation routine is performed.
The above-described embodiment provides the following
effects:
(1) If it is determined that fuel electrode lb is
filled with air (state B), high-pressure hydrogen can be
supplied after a negative pressure is generated in, and gas
flow resumes, through the fuel electrode lb by operation of
the hydrogen circulation pump 24. Therefore, the time
period during which hydrogen and oxygen are unevenly
distributed in the fuel electrode lb can be reduced and the
deterioration of the fuel cell can be suppressed.
(2) If it is determined that hydrogen provided in the
previous operation of power generation and air that enters
CA 02629627 2008-05-14
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from the oxidizer electrode la are unevenly distributed in
the fuel chamber (state C) or that the fuel chamber lb is
filled with hydrogen (state A), the operation of the
hydrogen circulation pump 24 is started after the supply of
hydrogen gas is started. Therefore, the uneven distribution
of hydrogen and oxygen in the fuel electrode ib, which would
otherwise occur using prior methods immediately after the
hydrogen circulation pump is operated, can be avoided and
the deterioration of the fuel cell can be prevented from
progressing.
State A and state C can be divided from each other on
the basis of the time elapsed after the stoppage, as
described in the first embodiment. Therefore, the start
time may, of course, be reduced by immediately performing
the normal operation routine if it is determined that the
fuel chamber is in state A.
Predetermined value of oxygen concentration
The predetermined value used for the determination
performed in Sli is obtained in advance by experiment and is
set to an oxygen concentration at which the deterioration of
the fuel electrode lb does not progress even when the
hydrogen circulation pump 24 is operated first in the fuel
chamber.
CA 02629627 2008-05-14
25 -
Reason why the oxygen concentration meter is disposed in the
hydrogen circulation pump 24
In the hydrogen circulation pump 24, a gap between a
casing and a rotor is set to be sufficiently small so as to
prevent an internal leakage from an outlet to an inlet
during operation. Therefore, the hydrogen circulation pump
24 cannot be easily filled with air compared to other
portions after stopping, and is last to be filled with air
in the hydrogen circulation system via diffusion.
Third Embodiment
A fuel cell system according to a third illustrated
embodiment of the present invention will be described below.
Fig. 10 is a system diagram showing the structure according
to the third embodiment. The structure according to the
third embodiment is similar to that shown in Fig. 1 except a
hydrogen concentration meter 51 for measuring the hydrogen
concentration in the hydrogen circulation pump 24 is
additionally provided as an air replacement state
recognizing means.
Start Method
A method for starting the fuel cell system according to
the third embodiment will be described below with reference
CA 02629627 2008-05-14
26 -
to a flowchart shown in Fig. 11. When, for example, the
state of a key switch is changed from Off to On, the
controller 43 detects the change and follows the steps of
the flowchart of Fig. 11 to start the fuel cell system.
First, in S21, a detection value of the hydrogen
concentration meter 51 is read and it is determined whether
or not the hydrogen concentration in the hydrogen
circulation pump 24 is equal to or less than a predetermined
value. If it is determined that the hydrogen concentration
is equal to or less than the predetermined value in S21,
that is, if the result of the determination of S21 is Yes,
it is determined that the fuel chamber is filled with air
transmitted from the oxidizer electrode la during the
stoppage (state B) and the process proceeds to S22. In S22,
first, the hydrogen circulation pump 24 is started to
generate a negative pressure at the outlet of the fuel
electrode lb (and gas flow through the fuel electrode lb),
and then the supply of fuel gas is started. Therefore, the
time period in which hydrogen and oxygen are unevenly
distributed in the fuel electrode lb is reduced and
deterioration is suppressed. Then, the process proceeds to
S24, where a normal operation routine is performed.
If is determined that the hydrogen concentration is
more than the predetermined value in 521, that is, if the
result of the determination of S21 is No, it is determined
CA 02629627 2008-05-14
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27 -
that hydrogen that remains after the previous stoppage of
power generation and air that enters from the oxidizer
electrode la are unevenly distributed in the fuel chamber
(state C) or that the fuel chamber is filled with hydrogen
provided before the previous stoppage of power generation
(state A), and the process proceeds to S23.
In S23, first, the supply of hydrogen gas is started,
and then the hydrogen circulation pump 24 is started.
Therefore, the uneven distribution of hydrogen and oxygen in
the fuel electrode lb, which would otherwise occur using
prior art methods immediately after the hydrogen circulation
pump is operated, can be avoided and the deterioration of
the fuel cell is prevented from progressing. Then, the
process proceeds to S24, where the normal operation routine
is performed.
The above-described embodiment provides the following
effects:
(1) If it is determined that fuel electrode lb is
filled with air (state B), high-pressure hydrogen is
supplied after a negative pressure is generated in the fuel
electrode lb (and gas flow resumes through the fuel
electrode lb) by operation of the hydrogen circulation pump
24. Therefore, the time period during which hydrogen and
oxygen are unevenly distributed in the fuel electrode lb is
CA 02629627 2008-05-14
s
28 -
reduced and the deterioration of the fuel cell is suppressed.
(2) If it is determined that hydrogen provided in the
previous operation of power generation and air that enters
from the oxidizer electrode la are unevenly distributed in
the fuel chamber (state C) or that the fuel chamber lb is
filled with hydrogen (state A), the operation of the
hydrogen circulation pump 24 is started after the supply of
hydrogen gas is started. Therefore, the uneven distribution
of hydrogen and oxygen in the fuel electrode ib, which would
otherwise occur using prior art methods immediately after
the hydrogen circulation pump is operated, is avoided and
the deterioration of the fuel cell is prevented from
progressing.
State A and state C can be divided from each other on
the basis of the time elapsed after the stoppage, as
described in the first embodiment. Therefore, the start
time may, of course, be reduced by immediately performing
the normal operation routine if it is determined that the
fuel chamber is in state A.
Predetermined value of hydrogen concentration
The predetermined value used for the determination
performed in S21 is obtained in advance by experiment and is
set to a hydrogen concentration at which the deterioration
of the fuel electrode lb does not progress even when the
CA 02629627 2008-05-14
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hydrogen circulation pump 24 is operated first in the fuel
chamber.
Reason why the hydrogen concentration meter is disposed in
the hydrogen circulation pump 24
In the hydrogen circulation pump 24, a gap between a
casing and a rotor is set to be sufficiently small so as to
prevent an internal leakage from an outlet to an inlet
during the operation. Therefore, the hydrogen circulation
pump 24 cannot be easily filled with air compared to other
portions after stopping, and is last to be filled with air
in the hydrogen circulation system via diffusion.
Fourth Embodiment
Next, a fuel cell system according to a fourth
illustrated embodiment of the present invention will be
described below. Fig. 12 is a system diagram showing the
structure according to the fourth embodiment. The structure
according to the fourth embodiment is similar to that shown
in Fig. 1 except an oxygen concentration meter 52 for
measuring the oxygen concentration is additionally provided
at the outlet of the fuel electrode lb of the fuel cell body
1 as an air replacement state recognizing means.
Start Method
CA 02629627 2008-05-14
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A method for starting the fuel cell system according to
the fourth embodiment will be described below with reference
to a flowchart shown in Fig. 13. When, for example, the
state of a key switch is changed from Off to On, the
controller 43 detects the change and follows the step of the
flowchart of Fig. 13 to start the fuel cell system.
First, in S31, a detection value of the oxygen
concentration meter 52 is read and it is determined whether
or not the oxygen concentration at the outlet of the fuel
cell body 1 is equal to or less than a predetermined value.
If it is determined that the oxygen concentration is equal
to or less than the predetermined value in S31, that is, if
the result of the determination of S31 is Yes, then it is
determined that the fuel chamber is filled with hydrogen
provided before the previous stoppage of power generation
(state A). Accordingly, it is determined that hydrogen and
oxygen are not unevenly distributed in the fuel electrode lb
and the deterioration of the fuel cell will not progress.
Therefore, the process proceeds to S34, where the supply of
hydrogen is started and the hydrogen circulation pump 24 is
activated. Here, the order in which the supply of hydrogen
is started and the hydrogen circulation pump 24 is activated
is not restricted. Accordingly, the supply of hydrogen may
be started and the hydrogen circulation pump 24 may be
activated simultaneously. Then, the process proceeds to S33,
CA 02629627 2008-05-14
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where the normal operation routine is performed.
If it is determined that the oxygen concentration is
more than the first predetermined time in S31, that is, if
the result of the determination at S31 is No, it is
determined that the fuel chamber is filled with air
transmitted from the oxidizer electrode la during the
stoppage (state B) or that hydrogen provided before the
previous stoppage of power generation and air that enters
from the oxidizer electrode la are unevenly distributed in
the fuel chamber (state C), and the process proceeds to S32.
In S32, first, the supply of hydrogen gas is started, and
then hydrogen circulation pump 24 is started. Therefore,
uneven distribution of hydrogen and oxygen can be avoided
and the deterioration of the fuel cell can be prevented from
progressing. Then, the process proceeds to S33, where the
normal operation routine is performed.
The above-described embodiment provides the following
effects:
(1) If it is determined that the fuel electrode lb is
filled with hydrogen (state A), the normal power generating
operation can be started immediately. Therefore, the start
time can be reduced.
(2) If it-is determined that the fuel chamber is filled
CA 02629627 2008-05-14
r
32 -
with air transmitted from the oxidizer electrode la during
the stoppage (state B) or that hydrogen provided in the
previous operation of power generation and air that enters
from the oxidizer electrode la are unevenly distributed in
the fuel chamber (state C), the operation of the hydrogen
circulation pump 24 is started after the supply of hydrogen
gas is started. Therefore, the uneven distribution of
hydrogen and oxygen in the fuel electrode lb, which would
otherwise occur using prior art methods immediately after
the hydrogen circulation pump is operated, can be avoided
and the deterioration of the fuel cell can be prevented from
progressing.
State B and state C can be divided from each other on
the basis of the time elapsed after the stoppage, as
described in the first embodiment. Therefore, the
deterioration of the fuel cell can be suppressed by
operating the hydrogen circulation pump 24 first when it is
determined that the fuel chamber is in state B.
Predetermined value of oxygen concentration
The predetermined value used for the determination
performed in S31 is obtained in advance by experiment and is
set to an oxygen concentration at which the deterioration of
the fuel electrode lb does not progress even when the normal
operation routine is started in the fuel chamber immediately
CA 02629627 2008-05-14
33 -
after the system is started.
Reason why the oxygen concentration meter is disposed at the
outlet of the fuel cell body 1
Since the air enters from the oxidizer electrode la
into the fuel electrode lb during the stoppage, the air
replacement state in the fuel chamber can be detected by
placing the oxygen concentration meter at the outlet of the
fuel cell body 1. The oxygen concentration meter may, of
course, be placed at the inlet of the fuel cell body 1. The
outlet and the inlet of the fuel electrode lb of the fuel
cell body 1 are first to be filled with air in the hydrogen
circulation system except for the inside of the fuel cell,
where it is difficult to set the oxygen concentration meter.
Fifth Embodiment
Next, a fuel cell system according to a fifth
illustrated embodiment of the present invention will be
described below. Fig. 14 is a system diagram showing the
structure according to the fifth embodiment. The structure
according to the fifth embodiment is similar to that shown
in Fig. 1 except a hydrogen concentration meter 53 for
measuring the hydrogen concentration is additionally
provided at an outlet of the fuel electrode lb of the fuel
cell body 1 as an air replacement state recognizing means.
CA 02629627 2008-05-14
s
34 -
Start Method
Next, a method for starting the fuel cell system
according to the present embodiment will be described below
with reference to a flowchart shown in Fig. 15. When, for
example, the state of a key switch is changed from Off to On,
the controller 43 detects the change and follows the steps
of the flowchart of Fig. 15 to start the fuel cell system.
First, in S41, a detection value of the hydrogen
concentration meter 53 is read and it is determined whether
or not the hydrogen concentration at the outlet of the fuel
cell body 1 is equal to or more than a predetermined value.
If it is determined that the hydrogen concentration is equal
to or more than the predetermined value in S41, that is, if
the result of the determination of S41 is Yes, it is
determined that the fuel chamber is filled with hydrogen
provided before the previous stoppage of power generation
(state A). Accordingly, it is determined that hydrogen and
oxygen are not unevenly distributed in the fuel electrode lb
and the deterioration of the fuel cell does not progress.
Therefore, the process proceeds to S44, where the supply of
hydrogen is started and the hydrogen circulation pump 24 is
activated. Here, the order in which the supply of hydrogen
is started and the hydrogen circulation pump 24 is activated
is not restricted. Accordingly, the supply of hydrogen may
CA 02629627 2008-05-14
35 -
be started and the hydrogen circulation pump 24 may be
activated at the same time. Then, the process proceeds to
S43, where a normal operation routine is performed.
If it is determined that the hydrogen concentration is
less than the first predetermined time in S41, that is, if
the result of the determination of S41 is No, then it is
determined that*the fuel chamber is filled with air that
enters from the oxidizer electrode la during the stoppage
(state B) or that hydrogen provided before the previous
stoppage of power generation and air that enters from the
oxidizer electrode la are unevenly distributed in the fuel
chamber (state C), and the process proceeds to S42.
In S42, first, the supply of hydrogen gas is started,
and then the operation of the hydrogen circulation pump 24
is started. Therefore, uneven distribution of hydrogen and
oxygen can be avoided and the deterioration of the fuel cell
can be prevented from progressing. Then, the process
proceeds to S43, where the normal operation routine is
performed.
The above-described embodiment provides the following
effects:
(1) If it is determined that the fuel electrode lb is
filled with hydrogen (state A), the normal power generating
CA 02629627 2008-05-14
36 -
operation can be started immediately. Therefore, the start
time can be reduced.
(2) If it is determined that the fuel chamber is filled
with air transmitted from the oxidizer electrode la during
the stoppage (state B) or that hydrogen provided in the
previous operation of power generation and air that enters
from the oxidizer electrode la are unevenly distributed in
the fuel chamber (state C), the hydrogen circulation pump 24
is started after the supply of hydrogen gas is started.
Therefore, the uneven distribution of hydrogen and oxygen in
the fuel electrode 1b, which would otherwise occur using
prior art methods immediately after the hydrogen circulation
pump is operated, can be avoided and the deterioration of
the fuel cell can be prevented from progressing.
State B and state C can be divided from each other on
the basis of the time elapsed after the stoppage, as
described in the first embodiment. Therefore, the
deterioration of the fuel cell can be suppressed by
operating the hydrogen circulation pump 24 first when it is
determined that the fuel chamber is in state B.
Predetermined value of hydrogen concentration
The predetermined value used for the determination
performed in S41 is determined in advance by experiment and
is set to a hydrogen concentration at which the
CA 02629627 2008-05-14
37 -
deterioration of the fuel electrode lb does not progress
even when the normal operation routine is started in the
fuel chamber immediately after the system is started.
Reason why hydrogen concentration meter is disposed at the
outlet of the fuel cell body 1
Since the air enters from the oxidizer electrode la to
the fuel electrode lb during the stoppage, the air
replacement state in the fuel chamber can be detected by
placing the hydrogen concentration meter at the outlet of
the fuel cell body 1. The hydrogen concentration meter may,
of course, be placed at the inlet of the fuel cell body 1.
The outlet and the inlet of the fuel electrode lb of the
fuel cell body 1 are first to be filled with air in the
hydrogen circulation system except for the inside of the
fuel cell, where it is difficult to set the hydrogen
concentration meter.
Sixth Embodiment
A fuel cell system according to a sixth illustrated
embodiment of the present invention will be described below.
Fig. 16 is a system diagram showing the structure according
to the sixth embodiment. The structure according to the
sixth embodiment is similar to that shown in Fig. 1 except a
hydrogen-circulation-pump discharge shutoff valve 54 is
CA 02629627 2008-05-14
38 -
additionally provided between the outlet of the hydrogen
circulation pump 24 and a junction of the hydrogen supply
path 22 and the hydrogen circulation path 26.
Start Method
Next, a method for starting the fuel cell system
according to the present embodiment will be described below
with reference to a flowchart shown in Fig. 17. When, for
example, the state of a key switch is changed from Off to On,
the controller 43 detects the change and follows the steps
of the flowchart of Fig. 17 to start the fuel cell system.
First, in S51, the hydrogen-circulation-pump discharge
shutoff valve 54 is closed. Then, in S52, the operation of
the hydrogen circulation pump 24 is started. Then, in S53,
the rotational speed of the hydrogen circulation pump 24 is
detected and it is determined whether or not the rotational
speed is equal to or more than a predetermined value (e.g.,
in revolutions per second). If it is determined that the
rotational speed is equal to or less than the predetermined
value in S53, that is, if the result of the determination of
S53 is No, then S53 is repeated until the rotational speed
reaches the predetermined value.
If it is determined that the rotational speed is equal
to or more than the predetermined value in S53, that is, if
the result of the determination of S53 is Yes, then it is
CA 02629627 2008-05-14
- 39 -
determined that a sufficient negative pressure is generated
to cause sufficient gas flow through the fuel electrode lb
and the process proceeds to S54. The negative pressure in
the fuel electrode lb may also be determined on the basis of
pressure detected by the hydrogen pressure gage 29, instead
of the rotational speed of the hydrogen circulation pump 24.
In S54, the hydrogen-circulation-pump discharge shutoff
valve 54 is opened and the process proceeds to S55. In S55,
the supply of hydrogen is started to eliminate the uneven
distribution of hydrogen and oxygen in the fuel electrode lb,
and then the normal operation routine is performed in S56.
According to the above-described sixth illustrated
embodiment, the operation of the hydrogen gas circulation
pump is started after the shutoff valve 54 provided
downstream of the hydrogen circulation pump is closed.
Therefore, if it is determined that hydrogen provided before
the previous stoppage of power generation and air that
enters from the oxidizer electrode la are unevenly
distributed in the fuel chamber (state C), the uneven
distribution of hydrogen and oxygen in the fuel electrode lb,
which would otherwise occur immediately after the hydrogen
circulation pump 24 is activated, can be avoided and the
deterioration of the fuel cell can be prevented from
CA 02629627 2008-05-14
40 -
progressing.
Seventh Embodiment
A fuel cell system according to a seventh embodiment of
the present invention will be described below. The
structure according to the seventh embodiment is similar to
those shown in Figs. 1 and 16 except oxygen concentration
meters and hydrogen concentration meters similar to the
oxygen concentration meters 50 and 52 and the hydrogen
concentration meter 51 and 53, respectively, are
additionally provided in the hydrogen circulation pump 24
and at the outlet of the fuel cell body 1, as in the second
to fourth embodiments.
Start Method
A method for starting the fuel cell system according to
the seventh embodiment will be described below with
reference to a flowchart shown in Fig. 18. When, for
example, the state of a key switch is changed from Off to On,
the controller 43 detects the change and follows the steps
of the flowchart of Fig. 18 to start the fuel cell system.
First, in S61, it is determined whether or not the fuel
chamber is filled with hydrogen that remains after the
previous stoppage of power generation. If it is determined
that the fuel chamber is filled with hydrogen in S61, that
CA 02629627 2008-05-14
41 -
is, if the result of the determination of S62 is Yes, then
it is determined that the fuel chamber is filled with
hydrogen that remains after the previous stoppage of power
generation (state A), that hydrogen and oxygen are not
unevenly distributed in the fuel electrode lb and that the
deterioration of the fuel cell will not progress. Therefore,
the process proceeds to S68 and the normal operation routine
is performed.
If it is determined that the fuel chamber is not filled
with hydrogen in S61, that is, if the result of the
determination of S61 is No, then the process proceeds to S62,
where it is determined whether or not the fuel chamber is
filled with air that enters from the oxidizer electrode la
(state B). If it is determined that the fuel chamber is
filled with air in S62, that is, if the result of the
determination of S62 is Yes, the uneven distribution of
hydrogen and oxygen will not occur in the fuel electrode lb
even in the case where the hydrogen-circulation-pump
discharge shutoff valve 54 is not closed. Therefore, the
routine for closing the hydrogen-circulation-pump discharge
shutoff valve 54 (S63) is skipped and the routine for
operating the hydrogen circulation pump 24 is performed in
S64.
If it is determined that the fuel chamber is not filled
with air in S62, that is, if the result of the determination
CA 02629627 2008-05-14
42 -
of S62 is No, then it is determined that hydrogen provided
in the previous operation of power generation and air that
enters from the oxidizer electrode la are unevenly
distributed in the fuel chamber (state C). Accordingly, the
process proceeds to S63, where the hydrogen-circulation-pump
discharge shutoff valve 54 is closed. S63 to S68 are
similar to S51 to S56 according to the sixth embodiment, and'
explanations thereof are thus omitted.
The above-described embodiment provides the following
effects:
(1) If it is determined that the fuel electrode lb is
filled with hydrogen (state A), the normal power generating
operation can be started immediately. Therefore, the start
time can be reduced.
(2) If it is determined that the fuel electrode lb is
filled with air (state B), the step of closing the hydrogen-
circulation-pump discharge shutoff valve 54 is omitted.
Therefore, the start time can be reduced.
(3) If it is determined that hydrogen provided in the
previous operation of power generation and air transmitted
from the oxidizer electrode la are unevenly distributed in
the fuel chamber (state C), an effect similar to that of the
sixth embodiment can be obtained.
CA 02629627 2012-03-09
-43-
Estimation of the air replacement state in the fuel chamber
In S61 and S62, the air replacement state in the fuel
chamber is estimated on the basis of the time elapsed after
the stoppage and the detection results of the oxygen
concentration meters 50 and 52 and the hydrogen
concentration meters 51 and 53 disposed in the hydrogen
circulation pump 24 and at the outlet of the fuel cell body
1, similar to the first, second, third, fourth, and fifth
embodiments.
In the above-described embodiments, the case in which
the fuel cell system is stopped while the fuel electrode is
in the hydrogen state and the air electrode is in the air
state. However, the effects of the second to seventh
embodiments may also be obtained when the fuel electrode
and the air electrode are stopped in inert gas (the case in
the fuel chamber is not completely filled with the inert
gas and hydrogen remains in the fuel chamber).
A specific embodiment of method and apparatus for
providing a fuel cell system has been described for the
purpose of illustrating the manner in which the invention
is made and used. It should be understood that the
CA 02629627 2012-03-09
-44-
invention is not limited by the specific embodiments
described.
