U.S. patent application number 09/725808 was filed with the patent office on 2001-05-31 for method of starting and stopping methanol reforming apparatus and apparatus for supplying fuel to said apparatus.
Invention is credited to Furuyama, Masataka, Hiramatsu, Yasushi, Isobe, Shoji, Naka, Takahiro, Sumi, Hideaki, Yoneoka, Mikio.
Application Number | 20010002043 09/725808 |
Document ID | / |
Family ID | 27341007 |
Filed Date | 2001-05-31 |
United States Patent
Application |
20010002043 |
Kind Code |
A1 |
Naka, Takahiro ; et
al. |
May 31, 2001 |
Method of starting and stopping methanol reforming apparatus and
apparatus for supplying fuel to said apparatus
Abstract
The present invention presents: (1) a starting method that is
capable of quickly switching to the reforming process after warming
up a catalyst; (2) a fuel supplying apparatus that is capable of
maintaining a stable supply of a mixed water-methanol solution
while preventing water from freezing in a cold climate, and is also
capable of immediately supplying a mixed water-methanol gas that
has a composition which is outside of the high-rate reaction region
during the starting/stopping operation of the reformer when the
control tends to be unstable; (3) a method to quickly cool down a
catalyst layer without causing thermal runaway when stopping the
operation of the methanol reforming apparatus; and (4) a method to
quickly cool down the catalyst layer while preventing thermal
runaway from occurring and removing residual fuel when stopping the
operation of the methanol reforming apparatus. In order to achieve
the objects described above, the methanol reforming apparatus that
generates a hydrogen-rich gas by reacting a mixed gas of water,
methanol and air on a catalyst is supplied with the fuel from a
fuel supplying apparatus comprising a mixed water-methanol solution
tank wherein the molar ratio of water and methanol used for
reforming is controlled to a predetermined value, a mixed
water-methanol solution tank wherein the molar ratio of water and
methanol is controlled to 4.6 or higher, and a switching means that
switches the mixed water-methanol solution tank used as a fuel
source according to the conditions of operation of the methanol
reforming apparatus.
Inventors: |
Naka, Takahiro; (Wako-shi,
JP) ; Sumi, Hideaki; (Wako-shi, JP) ;
Furuyama, Masataka; (Wako-shi, JP) ; Isobe,
Shoji; (Wako-shi, JP) ; Hiramatsu, Yasushi;
(Niigata-shi, JP) ; Yoneoka, Mikio; (Niigata-shi,
JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN, PLLC
1050 Connecticut Avenue, NW
Suite 600
Washington
DC
20036-5339
US
|
Family ID: |
27341007 |
Appl. No.: |
09/725808 |
Filed: |
November 30, 2000 |
Current U.S.
Class: |
252/373 ;
422/5 |
Current CPC
Class: |
C01B 3/323 20130101;
H01M 8/04302 20160201; Y02E 60/50 20130101; H01M 8/04303 20160201;
H01M 8/0618 20130101; H01M 8/0668 20130101; B01B 1/005 20130101;
Y02E 60/10 20130101; H01M 8/04022 20130101; H01M 16/006
20130101 |
Class at
Publication: |
252/373 ;
422/5 |
International
Class: |
A61L 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 1999 |
JP |
11-341442 |
Nov 30, 1999 |
JP |
11-341443 |
Nov 30, 1999 |
JP |
11-341444 |
Claims
What is claimed is:
1. A method of starting a methanol reforming apparatus that
generates a hydrogen-rich gas by reacting a mixed gas of water,
methanol and air on a catalyst, which comprises: controlling the
amounts to be introduced so that the molar ratio of water/methanol
is 4.6 or higher and/or the molar ratio of air/methanol is 1.5 or
lower.
2. A method of starting a methanol reforming apparatus according to
claim 1, wherein a mixed water-methanol gas is introduced
simultaneously with or after the introduction of air.
3. A method of starting a methanol reforming apparatus according to
claim 1 or 2, wherein the amounts to be introduced are controlled
so that the molar ratio of water/methanol falls within a range of
1.0-2.0 at a time when the concentration of air at the inlet of the
catalyst has decreased to 50% by mole or lower.
4. An apparatus for feeding a fuel to a methanol reforming
apparatus that generates a hydrogen-rich gas by reacting a mixed
gas of water, methanol and air on a catalyst, comprising: a mixed
water-methanol solution tank wherein the molar ratio of
water/methanol is controlled to a predetermined value for use in
reforming; a mixed water-methanol solution tank wherein the molar
ratio of water/methanol is controlled to 4.6 or higher; and a
switching means that switches the mixed water-methanol solution
tanks used as a fuel source according to the conditions of
operation of the methanol reforming apparatus.
5. A method of stopping a methanol reforming apparatus that
generates a hydrogen-rich gas by reacting a mixed gas of water,
methanol and air on a catalyst, which comprises: stopping the
introduction of air, changing the molar ratio of water/methanol to
a value higher than that of steady operation, and stopping the
introduction of water and methanol.
6. A method of stopping a methanol reforming apparatus according to
claim 5, wherein the molar ratio is set to 4.6 or higher.
7. A method of stopping a methanol reforming apparatus that
generates a hydrogen-rich gas by reacting a mixed gas of water,
methanol and air on a catalyst, which comprises: stopping the
introduction of air to thereby lower the catalyst temperature
through a steam reforming reaction, stopping the introduction of
water and methanol while the catalyst is still hotter than
100.degree.C., and adjusting the methanol concentration to 18% by
mole or lower.
8. A method of stopping a methanol reforming apparatus according to
claim 7, wherein air is introduced again after bringing the
methanol concentration to 18% by mole or lower, then remaining
water and methanol are evaporated and removed by means of the
oxidization heat of the catalyst.
9. A method of stopping a methanol reforming apparatus according to
claim 8, wherein air at a temperature of 100.degree.C. or lower is
introduced after removing water and methanol by evaporation, and
then the catalyst is cooled down and the gas is purged.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to method of starting and
stopping a methanol reforming apparatus that generates a hydrogen
enriched gas from water and methanol, and an apparatus for
supplying a fuel to said methanol reforming apparatus.
[0003] 2. Description of Related Art
[0004] Fuel cells have been developed as a means for driving
low-pollution vehicles and for supplying electric power to
vehicles.
[0005] Hydrogen in the form of a compressed hydrogen gas or liquid
hydrogen is convenient as the energy source for the fuel cell, but
there are problems regarding the ease of handling. Thus there is a
demand for a hydrogen supply apparatus which is very easy to
handle.
[0006] Recently, technologies for preparing hydrogen enriched gas
by reforming alcohol or hydrocarbons using a catalyst have been
intensively studied and developed, and various catalysts and
reaction apparatuses have been invented.
[0007] An example of the reaction apparatus is a methanol reforming
apparatus (hereinafter referred to as "reformer") 1 shown in FIG.
6. For supplying fuel to the reformer 1, methods are known such as
separately providing a water tank and a methanol tank or separately
providing a mixed water-methanol solution tank 2 and a methanol
tank 3 in order to prevent water from freezing in cold climates, as
disclosed in Japanese Patent Application, First Publication No. Hei
8-91804, wherein water and methanol are delivered from the two
tanks in a liquid state to an evaporator 4 to produce a mixed
water-methanol gas which is then supplied to the reformer 1.
[0008] However, when methanol, which has a low flash point and a
low ignition point, is reformed, particularly when employing the
autothermal reaction process, wherein a partial oxidization
reaction and steam reforming reaction are carried out at the same
time, methanol vapor and air coexist on a catalyst that has a high
temperature, and therefore the reforming process must be carried
out in a strictly controlled system to prevent the reaction from
proceeding at an excessively high rate.
[0009] Specifically, the mixing ratio of water, methanol and air
must not be within a range in which the reaction proceeds at an
excessively high rate (hereinafter this range is referred to as
"high-rate reaction region"), and the amounts of these materials to
be introduced must be strictly controlled.
[0010] Before starting the operation of the reformer, on the other
hand, the reformer must be warmed and particularly the catalyst
layer must be warmed by a heating means until the catalyst becomes
active. Hot air or electric heating have been normally used for
this purpose.
[0011] While water, methanol and air are introduced into the
catalyst after the warm-up operation, it is very difficult to
control the mixing ratio of the three components so as to avoid the
high-rate reaction region. To get around this difficulty, such
measures have been taken in the prior art as changing the order of
introducing the materials, for example, introducing air after water
and methanol have been introduced.
[0012] In practice, such measures involve the problems that it
takes a long time to start the operation or that special means are
required to warm up the catalyst.
[0013] To prevent water from freezing in a cold climate, it is more
advantageous to provide a mixed water-methanol solution tank 2 than
to separately provide a water tank and a methanol tank. Actually,
however, it is a common practice to provide a methanol tank 3 in
addition to the mixed water-methanol solution tank 2 and to control
the mixing ratio using the methanol tank 3 in order to obtain the
desired ratio of water and methanol.
[0014] As a consequence, there was a problem in that a mixed
water-methanol gas having a ratio outside of the high-rate reaction
region cannot be immediately supplied during the starting/stopping
operations of the reformer 1, when the control tends to be
unstable.
[0015] A similar problem can also be expected in the case that a
water tank and a methanol tank are separately provided.
[0016] On the other hand, stopping the operation of the methanol
reforming apparatus, the supplies of water, methanol and air are
stopped and the catalyst layer is cooled. However, if an excessive
amount of air is supplied during the autothermal reaction process,
a partial oxidization reaction proceeds, thus giving rise to the
possibility of an uncontrolled thermal runaway of the catalyst
layer.
[0017] Therefore, when stopping the methanol reforming apparatus,
it is also important to strictly control the mixing ratio of water,
methanol and air so as to avoid the high-rate reaction region.
Particularly, since the operation must be stopped while controlling
the air supply to a proper level, it takes a long time to stop the
operation.
[0018] Also, if water and methanol used as the fuel remain in the
apparatus when restarting a methanol reforming apparatus that has
been stopped, the remaining fuel will deviate the mixing ratio of
water, methanol and air when starting the operation, thus giving
rise to the possibility of thermal runaway of the catalyst.
[0019] Therefore, the operation of stopping the methanol reforming
apparatus must be carried out while paying attention to the mixing
ratio of water, methanol and air, and the fuel must not be allowed
to remain in the apparatus. Thus, the stopping operation takes a
long time and requires a complicated control procedure.
BRIEF SUMMARY OF THE INVENTION
[0020] The present invention has been made in consideration of the
problems described above, and an object thereof is to provide a
starting method that allows it to quickly shift to the reforming
process after warming up the catalyst.
[0021] Another object of the present invention is to provide a fuel
supplying apparatus that is capable of maintaining a stable supply
of mixed water-methanol solution while preventing water from
freezing in a cold climate, and is capable of immediately supplying
mixed water-methanol gas that has composition which does not fall
in the high-rate reaction region during a starting/stopping
operation when the control tends to be unstable.
[0022] Still another object of the present invention is to quickly
cool down a catalyst layer without causing thermal runaway when
stopping a methanol reforming apparatus.
[0023] A further object of the present invention is to quickly cool
down the catalyst layer while preventing thermal runaway from
occurring and removing the remaining fuel when stopping the
operation of the methanol reforming apparatus.
[0024] Method of Starting Methanol Reforming Apparatus
[0025] According to the method of starting the methanol reforming
apparatus of the present invention, in order to achieve the objects
described above, first a catalyst layer (reforming catalyst layer
41 in FIG. 1) is heated to an activation temperature. An external
heat source such as an electric heater may be used or a flow of
heating gas such as air that has been heated to a predetermined
temperature may be used for heating the catalyst layer.
[0026] When the catalyst layer (reforming catalyst layer 41) has
been heated to the predetermined activation temperature, a mixed
water-methanol gas is supplied as the fuel, thereby carrying out
the reforming reaction.
[0027] The reaction can be started smoothly by controlling the
water, methanol and air gas mixture so as to avoid the high-rate
reaction region when introducing the fuel.
[0028] The present inventors have found, from the three-component
mixture phase diagram of water, methanol and air shown in FIG. 2,
that the reaction can be started smoothly without allowing the
reaction to proceed at a high rate by controlling the amount of
mixed gas of water, methanol and air introduced so as to keep the
molar ratio of water/methanol (hereinafter referred to as S/C
ratio) to 4.6 (=82% by mole/18% by mole) or higher, or to keep the
molar ratio of air/methanol (hereinafter referred to as A/C ratio)
to 1.5 (= 60% by mole/40% by mole) or lower. In this drawing, the
hatched portion is the high-rate reaction region.
[0029] The present inventors have also found that, once the
starting operation has been completed, the reaction does not
proceed at a high rate even when the S/C ratio of the mixed
water-methanol gas is changed within a range of 1.0-2.0 after the
air concentration at the inlet of the catalyst layer (reforming
catalyst layer 41) has decreased to 50% by mole or lower.
[0030] Based on the facts described above, the present invention
makes it possible to control the mixed water-methanol gas so as to
avoid the high-rate reaction region when it is introduced into the
apparatus when the oxygen concentration is high immediately after
starting the operation. It is also possible to quickly shift to the
reforming process after the starting operation has been
completed.
[0031] According to the present invention, two tanks are provided
separately: a mixed water-methanol solution tank (27a) wherein the
mixing ratio of water and methanol is controlled to within a range
of S/C ratios (for example, 1.0-2.0) that are used in a normal
reforming process, and a mixed water-methanol solution tank (27b)
wherein mixing ratio of water and methanol is controlled to within
a range of S/C ratios (4.6 or higher) used when starting or
stopping the reforming process.
[0032] The two mixed water-methanol solution tanks (27a, 27b) are
connected with respective liquid transport tubes to an evaporator
(22) that is located in a stage prior to the catalyst layer of the
reformer (23), while the source for supplying the fuel to the
evaporator (22) is switched by means of three way valves (51, 52)
or the like.
[0033] Since the mixed water-methanol solution used in the normal
reforming process is supplied from the mixed water-methanol
solution tank (27a) where the S/C ratio is controlled to within a
range of 1.2-2.0, a mixed water-methanol gas having the ideal molar
ratio can be immediately supplied to the reformer (23) when the
operation shifts from the start-up to the normal reforming
process.
[0034] The S/C ratio can be set to any desired value according to
the characteristics of the reforming catalyst.
[0035] The mixed water-methanol solution used mainly when starting
or stopping the reformer (23) is supplied from the other mixed
water-methanol solution tank (27b) where the S/C ratio is
controlled to 4.6 or higher. Thus the composition of the mixed gas
of water, methanol and air that is supplied to the reformer (23)
does not fall in the high-rate reaction region during the
starting/stopping operation when the control tends to be
unstable.
[0036] This is because, as will be apparent from the
three-component phase diagram of FIG. 2, the danger of falling in
the high-rate reaction region can be avoided regardless of the
mixing conditions as long as the S/C ratio is controlled to 4.6 or
higher.
[0037] While the composition of the fuel departs more from the
high-rate reaction region as the S/C ratio becomes higher, the S/C
ratio is preferably set to 4.6 since the mixing ratio should have a
value that best facilitates the starting and stoping of the
reformer (23).
[0038] The method of starting the methanol reforming apparatus
according to the present invention has the following effects.
[0039] (a) Since the method controls the amount of the mixture of
water, methanol and air that is introduced so that the molar ratio
of water/methanol becomes 4.6 or higher and/or the molar ratio of
air/methanol becomes 1.5 or lower when starting the reformer, the
reaction can be started smoothly with a mixing ratio which is clear
of the high-rate reaction region even at the start of operation
when the oxygen concentration is high.
[0040] (b) Since the mixed water-methanol gas is introduced
simultaneously with or after the introduction of air, the starting
time can be made shorter.
[0041] (c) Since the amount of fuel introduced is controlled so
that the molar ratio of water/methanol is within a range of 1.0-2.0
once the concentration of air at the inlet of the reforming
catalyst has decreased to 50% by mole or lower, changing from the
start-up operation to the reforming operation can be carried out
quickly without falling in the high-rate reaction region.
[0042] (d) A switching means is provided to switch the mixed
water-methanol solution tank to be used as the source of fuel
supply, between the mixed water-methanol solution tank wherein the
molar ratio of water/methanol is controlled to the predetermined
concentration used in the reforming process, and the mixed
water-methanol solution tank wherein the molar ratio of
water/methanol is controlled to 4.6 or higher, in accordance to the
operating conditions of the reformer. Thus a stable supply of the
mixed water-methanol solution is made possible while preventing the
water from freezing in a cold climate.
[0043] Also, a mixed water-methanol gas of a composition that is
outside of the high-rate reaction region can be immediately
supplied during start/stop of the reformer when the control tends
to be unstable.
[0044] First Method of Stopping Methanol Reforming Apparatus
[0045] With the first method to stop the methanol reforming
apparatus according to the present invention, first the
introduction of air is stopped while the introduction of water and
methanol to the catalyst layer (reforming catalyst 41 in FIG. 1) is
continued, to thereby lower the catalyst layer temperature by
making use of the endothermic effect of the methanol steam
reforming reaction.
[0046] The introduction of air may be stopped either quickly by
means of a shut-off valve or gradually by means of a control valve
or the like.
[0047] On the other hand, the catalyst layer temperature can be
lowered quickly by setting the molar ratio of water/methanol, which
is to be continually introduced after stopping the supply of air,
to a molar ratio higher than that of the normal operation (for
example, 1.0-2.0) since this accelerates the methanol steam
reforming reaction, which is an endothermic reaction.
[0048] When the catalyst layer has been cooled down to a
predetermined temperature, the introduction of water and methanol
is stopped.
[0049] If the molar ratio of water/methanol is set to a value
outside of the high-rate reaction region in advance before stopping
the introduction of fuel, the operation can be stopped smoothly
without causing thermal runaway.
[0050] The present inventors have found, from the three-component
mixture phase diagram of water, methanol and air shown in FIG. 2,
that the reaction can be stopped smoothly without allowing the
reaction to proceed at a high rate by controlling the mixing ratio
of water, methanol and air so as to keep the molar ratio of
water/methanol (hereinafter referred to as S/C ratio) at 4.6 (=82%
by mole/18% by mole) or higher. In this drawing, the hatched
portion shows the high-rate reaction region.
[0051] Therefore, in order to stop the process smoothly, it is
preferable to stop the introduction of water and methanol after
switching the S/C ratio to 4.5 or higher.
[0052] The first method of stopping the methanol reforming
apparatus according to the present invention has the following
effects.
[0053] (a) Operation of the methanol reforming apparatus is stopped
by first stopping the introduction of air and then, after changing
the molar ratio of water/methanol to a value higher than that of
normal operation, the introduction of water and methanol is
stopped. As a result, it is made possible to cause the steam
reforming reaction which is an endothermic reaction to proceed
while suppressing the partial oxidization reaction which is an
exothermic reaction, by first stopping the introduction of air and,
moreover, the endothermic reaction can be further accelerated by
the change of the molar ratio of water/methanol that is
subsequently made.
[0054] As a result, the catalyst temperature can be lowered quickly
and the time required to stop the operation can be reduced.
[0055] (b) Since the introduction of water and methanol is stopped
after switching the value of the molar ratio of water/methanol to
4.6 or higher, clear of the high-rate reaction region, when
stopping the methanol reforming apparatus, the process can be
stopped smoothly without causing thermal runaway.
[0056] Second Method of Stopping Methanol Reforming Apparatus
[0057] With the second method to stop the operation of the methanol
reforming apparatus according to the present invention, first the
introduction of air is stopped while the introduction of water and
methanol to the catalyst layer (reforming catalyst 41 in FIG. 1) is
continued, to thereby lower the catalyst layer temperature by
making use of the endothermic effect of the methanol steam
reforming reaction.
[0058] The introduction of air may be stopped either quickly by
means of a shut-off valve or gradually by means of a control valve
or the like.
[0059] When the catalyst layer has been cooled down to a
predetermined temperature, the introduction of water and methanol
is stopped.
[0060] Provided that the operation described above is carried out
while the catalyst layer temperature is 100.degree.C. or higher,
the methanol steam reforming reaction can be effectively continued
by using the residual heat of the catalyst layer.
[0061] Consequently, the cooling of the catalyst layer is
accelerated and the methanol concentration in the mixed gas can be
lowered quickly to 18% by mole or less, which is outside of the
high-rate reaction region.
[0062] The present inventors found, from the three-component
mixture phase diagram of water, methanol and air shown in FIG. 2,
that the reaction does not proceed at a high rate when the methanol
concentration in the mixed gas is 18% by mole or less. In this
drawing, the hatched portion shows the highrate reaction
region.
[0063] Therefore, the water and methanol that remain in the
apparatus (hereinafter sometimes referred to as "residual fuel")
can be evaporated and removed by reintroducing air into the
catalyst layer to oxidize the catalyst and utilizing the
oxidization heat generated thereby, after the methanol
concentration in the mixed gas has decreased to 18% by mole or
less.
[0064] Once the residual fuel has been removed by the operation
described above, the catalyst temperature can be lowered quickly
without causing dew condensation even when cool air at a
temperature lower than 100.degree.C. is introduced into the
catalyst.
[0065] Also because the residual fuel gas, too, is purged from the
apparatus by the cool air, the possibility of the amount of the
mixture of water, methanol and air introduced deviating from the
set value when restarting the operation can be effectively
avoided.
[0066] The second method of stopping the operation of the methanol
reforming apparatus according to the present invention has the
following effects.
[0067] (a) The introduction of water and methanol is stopped while
the catalyst layer temperature is 100.degree.C. or higher after the
introduction of air has been stopped and the catalyst temperature
has decreased due to the steam reforming reaction when stopping the
operation of the methanol reforming apparatus. Thus the methanol
steam reforming reaction can be effectively continued by using the
residual heat of the catalyst layer.
[0068] Consequently, the cooling down of the catalyst layer is
accelerated and the methanol concentration in mixed gas can be
lowered quickly to 18% by mole or less, which is outside of the
high-rate reaction region.
[0069] (b) If air is reintroduced after lowering the methanol
concentration to 18% by mole or less and water and methanol that
remain in the apparatus are evaporated and removed by utilizing the
oxidization heat generated as the catalyst is oxidized, the
possibility of altering the mixing ratio of water, methanol and air
during start-up can be effectively avoided.
[0070] (c) If air at a temperature of 100.degree.C. or lower is
introduced after removing water and methanol by evaporation, the
catalyst temperature can be lowered quickly without causing dew
condensation.
[0071] Also because the introduction of air purges the residual
fuel from the apparatus, the possibility of altering the mixing
ratio can be effectively avoided.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0072] FIG. 1 shows a system for supplying fuel to a fuel cell in
an electric vehicle according to the present invention.
[0073] FIG. 2 is a three-component mixture phase diagram of water,
methanol and air.
[0074] FIG. 3 shows a system for supplying fuel to a fuel cell in
an electric vehicle according to Second Embodiment and Fourth
Embodiment of the present invention.
[0075] FIG. 4 shows a change in the temperature of a catalyst
measured using a test apparatus according to Examples 1 to 3.
[0076] FIG. 5 shows a change in the temperature of a catalyst
measured using a test apparatus according to Examples 4 to 7.
[0077] FIG. 6 shows a system for supplying fuel to a fuel cell in
an electric vehicle according to a conventional example.
DETAILED DESCRPTION OF THE INVENTION
[0078] Preferred embodiments of the present invention will now be
described below with reference to the accompanying drawings.
[0079] First Embodiment
[0080] FIG. 1 shows a system for supplying fuel to a fuel cell in
an electric vehicle, where the reference numeral 10 denotes a fuel
cell.
[0081] The fuel cell 10 generates electricity by using hydrogen and
oxygen that is taken from air as the fuel.
[0082] A hydrogen supply system and an air supply system for the
fuel cell 10 will be described below.
[0083] [Hydrogen Supply System]
[0084] The hydrogen supply system comprises a combustion device 21,
an evaporator 22, a reformer (methanol reforming apparatus) 23, a
CO eliminator 24, a starting heater 25, heat exchangers 26a, 26b,
mixed water-methanol solution tanks 27a, 27b and a methanol tank 28
as major components.
[0085] The combustion device 21 has an electric heater 31 serving
as an ignition device, a combustion catalyst 32 that maintains the
state of combustion and a temperature sensor 33 that monitors the
temperature inside of the apparatus, wherein methanol supplied from
the methanol tank 28 is burned with the air supplied from the air
supply system, thereby generating a combustion gas used to warm up
the evaporator 22 which evaporates the mixed water-methanol
solution that is supplied to the evaporator 22.
[0086] Connected to the combustion device 21 is an off gas tube 34
provided for the purpose of reusing the off gas that includes
hydrogen-rich gas, which is generated in the reformer 23 in the
period from the startup to the normal operation, and unreacted
hydrogen, which is discharged from the fuel cell 10 during
stationary operation, as the fuel for combustion.
[0087] In the evaporator 22, the mixed water-methanol solution that
has been supplied from the mixed water-methanol solution tank 27a
where the S/C ratio is controlled to 1.5 or from the mixed
water-methanol solution tank 27b where the S/C ratio is controlled
to 4.6 is sprayed from a nozzle and evaporated by the combustion
gas supplied from the combustion device 21, thereby generating the
mixed water-methanol gas.
[0088] The evaporator 22 is provided with a temperature sensor 36
for monitoring the temperature inside of the device.
[0089] Installed in the reformer 23 is a reforming catalyst 41
comprising a honeycomb structure of which surface is coated with a
catalyst such as Ni, Ru, Rh, Cu--Zn or the like, so that the mixed
water-methanol gas supplied from the evaporator 22 is brought onto
the reforming catalyst layer 41 to generate hydrogen-rich gas.
[0090] The reforming catalyst layer 41 has an O.sub.2 sensor 42
installed at the inlet thereof, and a temperature sensor 43
installed inside of the reforming catalyst layer 41.
[0091] In the reformer 23, the autothermal reforming reaction takes
place as follows.
CH.sub.3OH+H.sub.2O.fwdarw.3H.sub.2+CO.sub.2 (1)
CH.sub.3OH+20.sub.2.fwdarw.2H.sub.2O+CO.sub.2 (2)
[0092] The reaction scheme (1) represents the steam reforming
reaction by methanol and water that produces the target product of
hydrogen.
[0093] The reaction scheme (1) represents the-reaction of partial
oxidization of methanol that produces heat by oxidization reaction
which provides for the heat needed in the endothermic reaction
represented by reaction scheme (1).
[0094] In the reformer 23, in addition to the reactions represented
by the reaction schemes (1) and (2), a trace amount of carbon
monoxide is generated in an inevitable reaction of methanol
decomposition represented as follows.
CH.sub.3OH.fwdarw.2H.sub.2+CO (3)
[0095] The carbon monoxide deteriorates Pt catalyst provided in the
fuel cell 10 and leads to lower efficiency of power generation and
shortens the service life of the cell, and is therefore removed by
the CO eliminator 24 installed in a latter stage.
[0096] The CO eliminator 24 has a selective oxidization catalyst
layer made by coating the surface of a honeycomb structure with a
catalyst such as Pt or Ru. When hydrogen-rich gas generated by the
reformer 23 is supplied, the carbon monoxide is removed from the
hydrogen-rich gas in the following reaction of selective
oxidization of Co.
2CO+O.sub.2.fwdarw.2CO.sub.2 (4)
[0097] Installed between the reformer 23 and the CO eliminator 24
is the heat exchanger 26a provided for the purpose of cooling down
the hydrogen-rich gas generated by the reformer 23 thereby
protecting the selective oxidization catalyst in the CO eliminator
24 from thermal damage. Similarly installed between the CO
eliminator 24 and he fuel cell 10 is the heat exchanger 26b
provided for the purpose of cooling down the hydrogen-rich gas
supplied from the CO eliminator 24 thereby protecting the Pt
catalyst in the fuel cell 10 from thermal damage.
[0098] Valves 51, . . . , pumps 55, . . . installed in the hydrogen
supply system are controlled by an ECU (Electronic Control Unit)
45.
[0099] The ECU 45 sends command signals to the valves 51, the pumps
55, . . . in accordance to the output signals from the O.sub.2
sensor 42 and the temperature sensor 43 and a stop command, thereby
causing these devices to function.
[0100] The ECU 45 functions also as means for switching the mixed
water-methanol solution tanks 27a, 27b that are used as fuel supply
sources.
[0101] [Air Supply System]
[0102] The air supply system comprises a PCU (power control unit)
61, a drive motor 62, a super charger 63, an inter cooler 64 and
filters 65a, 65b as major components, and supplies air, that is
introduced from the outside, to the fuel cell 10, the combustion
device 21 and the starting heater 25.
[0103] Main function of the PCU 61 is to adjust the output of the
drive motor 62, by regulating the electric power supplied from the
fuel cell 10 and supplies the regulated power to the drive motor
62.
[0104] The super charger 63 compresses the air taken from the
outside through the filter 65a, via a resonator 66.
[0105] The inter cooler 64 is provided for cooling down the air
that has been heated through compression by the super charger 63.
The cooled air passes through the filter 65b, which is installed in
the latter stage of the inter cooler 64, and is supplied to the
fuel cell 10, the combustion device 21 and the starting heater
25.
[0106] Now the method of starting the reformer 23 according to this
embodiment will be described below.
[0107] To start the apparatus in cold state, it is necessary to
warm up the evaporator 22, the reformer 23 and the CO eliminator 24
of the hydrogen supply system. For this reason, the valve 53 is
opened to spray methanol into the combustion device 21 and air that
includes oxygen is supplied from the air supply system to burn the
methanol, while the combustion gas generated thereby is supplied to
evaporator 22 for the warming up thereof.
[0108] Air is supplied also to the starting heater 25, while the
air heated therein is sent to the reformer 23 thereby warming up
the reformer 23 and the CO eliminator 24 installed downstream
thereof.
[0109] When the evaporator 22 has been heated to a temperature high
enough to evaporate the mixed water-methanol solution and the
reformer 23, the reforming catalyst 41 in the CO eliminator 24 and
the selective oxidization catalyst layer have reached the
activation temperature, the valves 53, 54 are closed, while
spraying of methanol into the combustion device 21 and the supply
of air to the starting heater 25 are stopped.
[0110] At this time, the reformer 23 is supplied only with air from
the air supply system.
[0111] The combustion device 21 is also supplied only with air from
the air supply system, while the state of combustion by the
combustion catalyst 32 is maintained.
[0112] Then the valve 51 is opened with the valve 52 is left
closed, while the pump 55 supplies the mixed water-methanol
solution, with the S/C ratio therein being controlled to 4.6, from
the mixed water-methanol solution tank 27b to the evaporator 22, so
that the mixed water-methanol solution is sprayed from the nozzle
into the evaporator 22.
[0113] In the evaporator 22, the mixed water-methanol solution is
evaporated by the combustion gas supplied from the combustion
device 21, thereby generating the mixed water-methanol gas which is
supplied to the reformer 23.
[0114] In the reformer 23, the mixed water-methanol gas is passed
through the reforming catalyst 41 to produce hydrogen-rich gas
through the reactions of the reaction schemes (1) and (2).
[0115] At this time, according to the three-component mixture phase
diagram of water, methanol and air of FIG. 2, smooth startup is
achieved provided that the S/C ratio of the mixed water-methanol
gas is 4.6 which means the mixing ratio is outside of the high-rate
reaction region.
[0116] The reforming process enters the steady state upon lapse of
some time after starting the reformer 23.
[0117] During this transition of the state of operation, it is
necessary to change the S/C ratio from 4.6, which is the value for
starting the operation, to 1.0 to 2.0 which is a range of values
for normal reforming operation.
[0118] Accordingly, the valve 51 is closed and the valve 52 is
opened when the air concentration measured by the 02 sensor 42
installed at the inlet of the reforming catalyst layer 41 has
decreased to 50% by mole or less.
[0119] Then the pump 56 supplies the mixed water-methanol solution
with the S/C ratio controlled to 1.5 from the mixed water-methanol
solution tank 27a to the evaporator 22, so that the mixed
water-methanol solution is sprayed from the nozzle into the
evaporator 22.
[0120] In the evaporator 22, the mixed water-methanol solution is
evaporated by the combustion gas supplied from the combustion
device 21 to generate the mixed water-methanol gas which is
supplied to the reformer 23.
[0121] The hydrogen-rich gas produced in the reformer 23 is cooled
down from about 300.degree.C. to about 100.degree.C. while passing
through the heat exchanger 26a, to be supplied to the CO eliminator
24.
[0122] In the CO eliminator 24, carbon monoxide is removed in the
reaction of the reaction scheme (4) by passing the hydrogen-rich
gas through the selective oxidization catalyst layer.
[0123] The hydrogen-rich gas with CO removed therefrom is cooled
down from about 180.degree.C. to about 80.degree.C. while passing
through the heat exchanger 26b, and then supplied to the fuel cell
10 to be used in power generation.
[0124] On the other hand, the air that has been introduced through
the resonator 66 and the filter 65a into the air supply system is
compressed in the super charger 63 and is then cooled down in the
inter cooler 64, before passing through the filter 65b and supplied
to the fuel cell 10 and the combustion device 21.
[0125] Oxygen included in the air that is supplied to the fuel cell
10 is used, together with hydrogen supplied from the hydrogen
supply system, for power generation.
[0126] The air supplied to the combustion device 21 is used for
generating the combustion gas.
[0127] The off gas that includes the unreacted hydrogen discharged
from the fuel cell 10 is returned to the combustion device 21
through the off gas tube 34, and is reused as the fuel for
combustion.
[0128] Second Embodiment
[0129] Method of starting the reformer 23 according to the second
embodiment of the present invention will be described below with
reference to FIG. 3. Identical components to those shown in FIG. 1
will be assigned with the same reference numerals and description
thereof will be omitted.
[0130] This embodiment is similar to First Embodiment, except for a
part of the hydrogen supply system and a part of the air supply
system which are different from those of First Embodiment.
[0131] The hydrogen supply system has a condenser 71 and an S/C
control tank 72 instead of the mixed water-methanol solution tank
27b where the S/C ratio is controlled to 4.6 shown in FIG. 1.
[0132] The condenser 71 recovers water, that is generated in the
reaction and combustion in the fuel cell 10, from the evaporator
22.
[0133] In the S/C control tank 72, mixed water-methanol solution
(S/C ratio 4.6 or higher) used in start/stop operation is prepared
from the mixed water-methanol solution (S/C ratio 1.5) supplied
from the mixed water-methanol solution tank 27a and the recovered
water supplied from the condenser 71.
[0134] S/C ratio of the liquid in the S/C control tank 72 is
constantly monitored by a methanol sensor 73 of which signal is
sent to the ECU 45.
[0135] The ECU 45 controls the extents of opening of valves 75, 76
according to the signal.
[0136] After the preparation of the mixed water-methanol solution
by the S/C control tank 72 and when the operation is stopped,
excessive recovered water in the condenser 71 is discarded.
[0137] The air supply system has an air supply line 81 connected to
the evaporator 22.
[0138] Accordingly, the evaporator 22 also serves as a heater that
heats the air supplied via the air supply line 81.
[0139] Consequently, in this embodiment, the starting heater 25
shown in FIG. 1 is not necessary since the reformer 23 can be
warmed up by the heated air.
[0140] With the constitution described above, too, the mixed
water-methanol solution tank 27a for the normal reforming process
and the S/C control tank 72 for the start/stop operation can be
switched according to the state of operation of the reformer 23,
and therefore it is made possible to maintain stable supply of
mixed water-methanol solution while preventing water from freezing
in a cold climate, and is capable of immediately supplying mixed
water-methanol gas that has composition outside of the high-rate
reaction region during starting/stopping operation of the reformer
23 when the control tends to be unstable.
[0141] Third Embodiment
[0142] A method of stopping the reformer 23 according to the third
embodiment of the present invention will now be described below
with reference to the system diagram of fuel supply to the fuel
cell of the electric vehicle shown in FIG. 1. Before the
description, an example of steady operation (normal reforming
operation) will be outlined.
[0143] During steady operation, the valve 50 is open so that air
from the air supply system, namely the air that has been introduced
through the resonator 66 and the filter 65a, cooled by the inter
cooler 64 and has passed through the filter 65b, is supplied to the
combustion device 21 and the evaporator 22, the reformer 23, . . .
, that are installed in the latter stage thereof.
[0144] With the valve 51 being closed and the valve 52 open, the
pump 56 supplies the mixed water-methanol solution with the S/C
ratio controlled to 1.5 from the mixed water-methanol solution tank
27a to the evaporator 22, so that the mixed water-methanol solution
is sprayed from the nozzle into the evaporator 22.
[0145] In the evaporator 22, the mixed water-methanol solution is
evaporated by the combustion gas supplied from the combustion
device 21, thereby generating the mixed water-methanol gas which is
supplied to the reformer 23.
[0146] In the reformer 23, the mixed water-methanol gas is passed
through the reforming catalyst 41 to produce hydrogen-rich gas
through the reactions of the reaction schemes (1) and (2).
[0147] The hydrogen-rich gas produced in the reformer 23 is cooled
down from about 300.degree.C. to about 100.degree.C. while passing
through the heat exchanger 26a, to be supplied to the CO eliminator
24.
[0148] In the CO eliminator 24, carbon monoxide is removed in the
reaction of the reaction scheme (4) by passing the hydrogen-rich
gas through the selective oxidization catalyst layer.
[0149] The hydrogen-rich gas with CO removed therefrom is cooled
down from about 180.degree.C. to about 80.degree.C. while passing
through the heat exchanger 26b, and is then supplied to the fuel
cell 10.
[0150] In the fuel cell 10, the hydrogen-rich gas supplied from the
hydrogen supply system and air supplied from the air supply system
are used to generate electricity.
[0151] While the fuel cell 10 discharges the off gas that includes
unreacted hydrogen, the off gas is returned through an off gas tube
to the combustion device 21 and is reused as the fuel of
combustion.
[0152] Now the method to stop the steady operation of the reformer
23 will be described below.
[0153] This reformer stopping method comprises a first step in
which the introduction of air to the reformer 23 is stopped, a
second step in which the S/C ratio of mixed water-methanol gas
supplied to the reformer 23 is changed to a value higher than that
of the steady operation, and a third step in which the introduction
of the mixed water-methanol gas to the reformer 23 is stopped.
[0154] In the first step, the valve 50 that has been open during
the steady operation is closed.
[0155] This shuts off the introduction of air from the air supply
system to the hydrogen supply system, namely to the combustion
device 21 and the evaporator 22, the reformer 23, . . . , that are
installed in the latter stage thereof.
[0156] At this time, since the ratio of air in the mixture
decreases in comparison to water and methanol in the reformer 23,
the endothermic reaction of the reaction scheme (1) proceeds while
the exothermic reaction of the reaction scheme (2) is suppressed.
As a result, the reforming catalyst layer 41 is effectively
cooled.
[0157] In the second step, the valve 52 that has been open during
the steady operation is closed and the valve 51 that has been
closed is opened.
[0158] This causes the pump 55 to supply the mixed water-methanol
solution with the S/C ratio controlled to 4.6 from the mixed
water-methanol solution tank 27b to the evaporator 22, so that the
mixed water-methanol gas generated through evaporation in the
evaporator 22 is supplied to the reformer 23.
[0159] At this time, since the S/C ratio of the mixed
water-methanol gas is set higher than that of the steady operation
(for example, S/C=1.0-2.0), the endothermic reaction of the
reaction scheme (1) is accelerated so that the reforming catalyst
layer 41 is cooled down quickly.
[0160] Last, in the third step, when the reforming catalyst layer
41 is cooled down to a predetermined temperature, the valve 51 that
was opened in the second step is closed.
[0161] This shuts off the supply of the mixed water-methanol
solution from the mixed water-methanol solution tank 27b to the
evaporator 22 and stops the introduction of the mixed
water-methanol gas to the reformer 23.
[0162] At this time, since the S/C ratio is set to a value outside
of the high-rate reaction region (refer to FIG. 2), the process can
be stopped smoothly without causing thermal runaway.
[0163] Fourth Embodiment
[0164] A method of stopping the reformer 23 according to the fourth
embodiment of the present invention will be described below with
reference to FIG. 3, which is also referred to in the second
embodiment.
[0165] The constitution of this embodiment is the seme as that of
the second embodiment.
[0166] With this constitution, the S/C ratio can be changed in the
second step by switching the mixed water-methanol solution tank 27a
for the normal reforming process and the S/C control tank 72 for
the start/stop operation when stopping the operation of the
reformer 23, and therefore it is made possible to immediately
supply the mixed water-methanol gas that has a composition which
does not fall in the high-rate reaction region even when stopping
the operation of the reformer 23 when the control tends to be
unstable. Thus the reforming catalyst layer 41 can be cooled down
smoothly and quickly, without causing thermal runaway of the
reforming catalyst layer 41.
[0167] Fifth Embodiment
[0168] A method of stopping the reformer according to the fifth
embodiment of the present invention will now be described below,
with regard to the reformer 23 in steady reforming operation, with
reference to the system diagram of fuel supply to the fuel cell of
the electric vehicle shown in FIG. 1. In this embodiment, a
methanol sensor not shown in the drawing is provided inside of the
reforming catalyst layer 41 in addition to the temperature sensor
43.
[0169] This reformer stopping method comprises a first step in
which the introduction of air to the reformer 23 is stopped, a
second step in which the introduction of mixed water-methanol gas
to the reformer 23 is stopped, a third step in which air is
introduced again, and a fourth step in which air of a temperature
of 100.degree.C. or lower is introduced.
[0170] In the first step, the valve 50 that has been open during
the steady operation is closed.
[0171] This shuts off the introduction of air from the air supply
system to the hydrogen supply system, namely to the combustion
device 21 and the evaporator 22, the reformer 23, . . . , that are
installed in the latter stage thereof.
[0172] At this time, since the ratio of air in the mixture
decreases in comparison to water and methanol in the reformer 23,
the endothermic reaction of the reaction scheme (1) proceeds while
the exothermic reaction of the reaction scheme (2) is suppressed.
As a result, the reforming catalyst layer 41 is effectively
cooled.
[0173] In the second step, the valve 52 that has been open during
the steady operation is closed while the reforming catalyst layer
41 which is being cooled is still hotter than 100.degree.C.
[0174] Temperature of the reforming catalyst layer 41 is constantly
monitored by a temperature sensor 43 installed therein, and the ECU
45 controls the valve 52 to close according to the signal from the
temperature sensor 43.
[0175] This shuts off the supply of the mixed water-methanol
solution from the mixed water-methanol solution tank 27a to the
evaporator 22 and stops the introduction of the mixed
water-methanol gas to the reformer 23.
[0176] Even after the introduction has been stopped, the steam
reforming reaction is effectively continued by making use of the
residual heat of the reforming catalyst layer 41, thereby
accelerating the cooling of the reforming catalyst layer 41. At the
same time, methanol concentration in the mixed gas quickly
decreases to 18% by mole or lower, clear of the high-rate reaction
region.
[0177] Next in the third step, when methanol concentration has
decreased to 18% by mole or lower, the valve 50 that was closed in
the first step is opened.
[0178] The methanol concentration is monitored by the methanol
sensor installed in the reforming catalyst layer 41, and the ECU 45
controls the valve 50 to open according to the signal from the
methanol sensor.
[0179] This causes air from the air supply system to be introduced
again into the reforming catalyst 41, so that the catalyst is
oxidized and refreshed.
[0180] Water and methanol that remain in the reformer 23, namely
the residual fuel, are evaporated and removed by the oxidization
heat generated when the catalyst is oxidized.
[0181] It is made possible to introduce the air again in the third
step because the methanol concentration is 18% by mole or lower,
clear of the high-rate reaction region.
[0182] Last, in the fourth step, air that has been cooled down to
100.degree.C. or lower while passing through the inter cooler 64 in
the air supply system is introduced into the reforming catalyst
layer 41.
[0183] At this time, since the residual fuel has been effectively
removed in the third step, the catalyst can be cooled down quickly
by the cold air without causing dew condensation.
[0184] Moreover, since the residual fuel gas is purged at the same
time, a trouble such as alteration in the mixing ratio of water,
methanol and air when restarting the operation can be effectively
avoided.
EXAMPLE 1
[0185] Using a test apparatus equipped with a reactor tube made of
quartz having inner diameter of 20 mm that was filled with 9.2 g of
methanol reforming catalyst pellets including Cu, Zn and Al in the
ratio of 1.3:1:0.05, heated air was introduced to the catalyst at a
flow rate of 40 ml/min thereby heating the catalyst to
230.degree.C.
[0186] After making sure that the catalyst has been heated to
230.degree.C., the mixed water-methanol solution of which S/C ratio
was regulated to 1.5 was supplied to the evaporator, and the mixed
water-methanol gas generated therein was supplied to the catalyst
at a flow rate of 1.8 ml/min, while recording the changes in the
catalyst temperature immediately after supplying the gas (plots
.diamond-solid. in FIG. 4).
EXAMPLE 2
[0187] Using the same test apparatus as in Example 1, heated air
was introduced to the catalyst at a flow rate of 40 ml/min to heat
the catalyst to 230.degree.C.
[0188] After stopping the introduction of air and making sure that
the catalyst was heated to 230.degree.C., the mixed water-methanol
solution similar to that of Example 1 was supplied to the
evaporator, and the mixed water-methanol gas generated therein was
supplied to the catalyst at a flow rate of 1.8 ml/min, while
recording the changes in the catalyst temperature immediately after
supplying the gas. Then the introduction of air was resumed at a
flow rate of 40 ml/min while recording the changes in the catalyst
temperature immediately after the introduction (plots .quadrature.
in FIG. 4).
EXAMPLE 3
Present Invention
[0189] Using the same test apparatus as in Example 1, heated air
was introduced to the catalyst at a flow rate of 40 ml/min to heat
the catalyst to 230.degree.C.
[0190] After making sure that the catalyst was heated to
230.degree.C., the mixed water-methanol solution of which S/C ratio
was regulated to 4.6 was supplied to the evaporator, and the mixed
water-methanol gas generated therein was supplied to the catalyst
at a flow rate of 1.8 ml/min, while recording the changes in the
catalyst temperature immediately after supplying the gas (plots
.DELTA. in FIG. 4).
[0191] When the mixed water-methanol gas having a low value of S/C
ratio was supplied to the heated catalyst under the condition of
introducing air as in Example 1, it was confirmed that the catalyst
temperature rose rapidly and it took a long time to stabilize the
reaction, while the danger of thermal runaway increased.
[0192] This is because the exothermic reaction of the reaction
scheme (2) proceeds at a higher rate than the endothermic reaction
of the reaction scheme (1).
[0193] Similarly, when the mixed water-methanol gas having a low
value of S/C ratio was supplied while stopping the introduction of
air as in Example 2, it was confirmed that the catalyst temperature
rose rapidly, although the peak temperature as high as in Example 1
was not reached.
[0194] This is because the exothermic reaction of the reaction
scheme (2) proceeds rapidly as the system already includes air even
when the air is not flowing.
[0195] However, only the endothermic reaction of the reaction
scheme (1) proceeds thereafter because of the lack of air,
resulting in a problem that the catalyst temperature drops
quickly.
[0196] Even when the introduction of air is resumed, the catalyst
temperature rises rapidly, although the peak temperature as high as
in the case of supplying the mixed water-methanol gas is not
reached.
[0197] As described above, unstable condition wherein the
temperature repeatedly fluctuates continues for several minutes in
Example 2.
[0198] In contrast to Examples 1 and 2, when the S/C ratio was set
to a value outside of the high-rate reaction region in the early
stage of introducing the mixed water-methanol gas as in Example 3,
excessive increase in the catalyst temperature and fluctuation of
the temperature could be suppressed and the danger of thermal
runaway could be avoided. Consequently, switching to the mixed
water-methanol solution of the desired value of S/C ratio could be
quickly provided for.
[0199] This is because the endothermic reaction of the reaction
scheme (1) proceeds predominantly over the exothermic reaction of
the reaction scheme (2) due to the supply of water-rich fuel, thus
maintaining the thermal balance.
[0200] The present invention is not limited to the embodiments
described above, and the reforming catalyst 41 may be warmed up by
electric heating instead of air heating.
[0201] As will be apparent from FIG. 2, the process can be started
smoothly outside of the high-rate reaction region similarly to the
above also by controlling the mixing ratio of water, methanol and
air so that the A/C ratio becomes 1.5 or lower.
[0202] This is because lower ratio of oxygen is introduced compared
to methanol, resulting in less amount of heat generated in the
reaction of the reaction scheme (2).
[0203] The S/C ratio may also be controlled to be 4.6 or higher
while the A/C ratio is set to 1.5 or lower, as a matter of
course.
EXAMPLE 4
[0204] Using the same test apparatus as in Example 1, heated air
was introduced to the catalyst at a flow rate of 40 ml/min to heat
the catalyst to 230.degree.C.
[0205] Meanwhile, the mixed water-methanol solution of which S/C
ratio was regulated to 1.5 was supplied to the evaporator.
[0206] The mixed water-methanol gas generated in the evaporator was
supplied to the catalyst at a flow rate of 1.8 ml/min thereby
starting the reforming reaction by the autothermal reaction
method.
[0207] Amount of the air introduced was controlled to keep the
catalyst layer at 230.degree.C. and the reforming reaction was
stabilized.
[0208] Then to stop the process, the supplies of water, methanol
and air were stopped simultaneously while recording the changes in
the catalyst temperature (plots .diamond-solid. in FIG. 5).
EXAMPLE 5
[0209] Using the same test apparatus as in Example 1, the reforming
reaction was started and stabilized in the same procedure as in
Example 4.
[0210] Then to stop the process, first the supplies of water and
methanol were stopped and then the supply of air was stopped, while
recording the changes in the catalyst temperature (plots
.quadrature. in FIG. 5).
EXAMPLE 6
[0211] Using the same test apparatus as in Example 1, the reforming
reaction was started and stabilized in the same procedure as in
Example 4.
[0212] Then to stop the process, first the supply of air was
stopped and then the supplies of water and methanol were stopped,
while recording the changes in the catalyst temperature (plots
.DELTA. in FIG. 5).
EXAMPLE 7
Present Invention
[0213] Using the same test apparatus as in Example 1, the reforming
reaction was started and stabilized in the same procedure as in
Example 4.
[0214] Then to stop the process, first the supply of air was
stopped and then the S/C ratio of water and methanol being supplied
continuously was changed to 4.6, while recording the changes in the
catalyst temperature (plots .largecircle. in FIG. 5).
[0215] In contrast to the case where the supplies of water,
methanol and air were stopped simultaneously and the catalyst layer
was cooled naturally as in Example 4, it was found that stopping
the supplies of water and methanol first as in Example 2 resulted
in excessive heat generation of the residual methanol and sudden
rise in the catalyst layer temperature.
[0216] This is because excessive amount of air was supplied to the
catalyst layer, thus causing the exothermic reaction of the
reaction scheme (2) to proceed at a high rate.
[0217] When the supply of air was stopped first, as in Example 6,
it was found that the catalyst could be cooled down more quickly
than in the case of natural cooling due to the endothermic reaction
accompanying the reforming of steam by water and methanol.
[0218] This is because the endothermic reaction of the reaction
scheme (1) proceeds while the exothermic reaction of the reaction
scheme (2) is suppressed.
[0219] When the S/C ratio of water and methanol was changed to a
value outside of the high-rate reaction region after stopping the
supply of air (or at the same time as the supply of air is stopped)
as in Example 7, it was confirmed that the catalyst could be cooled
down more quickly than in the case of Example 7.
[0220] This is because the endothermic reaction of the reaction
scheme (1) is accelerated further while the exothermic reaction of
the reaction scheme (2) is suppressed due to the supply of
water-rich fuel.
[0221] As is apparent from the comparison of Examples 4 to 7, it is
confirmed that the catalyst can be cooled down smoothly and quickly
without causing thermal runaway, when the operation of the reformer
23 is stopped by first stopping the supply of air, then changing
the S/C ratio of water and methanol to a value outside of the
high-rate reaction region, and last stopping the supplies of water
and methanol.
* * * * *