U.S. patent application number 12/885455 was filed with the patent office on 2011-03-03 for method and arrangement for reforming fuel.
This patent application is currently assigned to AB VOLVO. Invention is credited to Per Ekdunge, Bard Lindstrom, Per Rutquist.
Application Number | 20110053021 12/885455 |
Document ID | / |
Family ID | 34982574 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110053021 |
Kind Code |
A1 |
Lindstrom; Bard ; et
al. |
March 3, 2011 |
METHOD AND ARRANGEMENT FOR REFORMING FUEL
Abstract
A method and an arrangement for reforming a hydrocarbon fuel
such as dimethyl ether (DME), methanol, ethanol, propanol, or any
variants or other oxidized fuels is disclosed for generating
hydrogen especially for supplying a fuel cell. Furthermore, a fuel
cell system is disclosed which includes such an arrangement,
especially for providing power to a stationary or mobile power
consuming unit like especially an auxiliary power unit (APU) for
application in aircraft, ships and vehicles, or as a part of a
hybrid drive or as a sole driving unit for, e.g., a ship or a
vehicle.
Inventors: |
Lindstrom; Bard; (Stockholm,
SE) ; Ekdunge; Per; (Vastra Frolunda, SE) ;
Rutquist; Per; (Goteborg, SE) |
Assignee: |
AB VOLVO
Goteborg
SE
|
Family ID: |
34982574 |
Appl. No.: |
12/885455 |
Filed: |
September 18, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11572325 |
Jan 19, 2007 |
7828863 |
|
|
PCT/EP2005/007861 |
Jul 19, 2005 |
|
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12885455 |
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Current U.S.
Class: |
429/425 ;
422/625 |
Current CPC
Class: |
C01B 2203/1041 20130101;
C01B 2203/047 20130101; H01M 8/04022 20130101; C01B 2203/066
20130101; C01B 2203/0261 20130101; C01B 2203/142 20130101; C01B
2203/148 20130101; H01M 8/04156 20130101; C01B 2203/1023 20130101;
C01B 2203/1604 20130101; C01B 3/323 20130101; C01B 2203/1076
20130101; C01B 2203/0244 20130101; H01M 8/0618 20130101; C01B
2203/82 20130101; Y02E 60/50 20130101; C01B 2203/1011 20130101;
C01B 2203/1223 20130101; C01B 2203/044 20130101; C01B 2203/0844
20130101 |
Class at
Publication: |
429/425 ;
422/625 |
International
Class: |
H01M 8/06 20060101
H01M008/06; B01J 8/00 20060101 B01J008/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2005 |
SE |
SE2004/001142 |
Claims
1. Method for reforming a hydrocarbon fuel for generating hydrogen
especially for operating a fuel cell, comprising a start-up phase
with: a first stage in which the hydrocarbon fuel is reformed in a
fuel reformer by an exothermic catalytic partial oxidation process
(CPO or catalytic POx) to hydrogen; a second stage in which the
generated hydrogen is converted into water steam which is fed back
into the fuel reformer; and a third stage in which an endothermic
catalytic steam reforming process is initiated in the fuel reformer
by the water steam, so that by the combination of exothermic and
the endothermic processes an autothermal fuel reforming process
(ATR) is created; and a steady state operation phase in which the
hydrogen which is generated by the ATR process is fed to the fuel
cell for operating the same.
2. Method according to claim 1, wherein an initial step is
preceeding the first stage, in which hydrocarbon fuel and air is
fed into the fuel reformer as a lean mixture such that the fuel
reformer is catalytically started and heated by an exothermic
reaction.
3. Method according to claim 1, wherein a fourth stage is following
the third stage in which the hydrogen which is generated by the ATR
process is purified prior to supplying it to the fuel cell, by
especially reducing the amount of carbon monoxide.
4. Method according to claim 1, wherein a transition phase is
preceeding the steady state operation in which a portion of the
hydrogen which is generated by the ATR process is supplied to the
fuel cell and another portion is converted into water steam, which
is fed back into the fuel reformer.
5. Method according to claim 1, wherein a catalytic combustion
reactor is used for conducting the second stage and wherein in the
steady state operation, excess hydrogen which is generated by the
fuel cell is supplied to the combustion reactor for catalytically
converting the same into water steam, which is fed as a heat source
to a heat exchanger in which water which is generated by the fuel
cell is evaporated to steam which is fed into the fuel
reformer.
6. Method according to claim 1, in which in the first stage oxygen
is fed into the fuel reformer in the form of ambient air such that
the lambda value of the air to fuel mixture is about 0.1 to
0.7.
7. Method according to claim 2, in which in the initial step oxygen
is fed into the fuel reformer in the form of ambient air such that
the lambda value of the air to fuel mixture is between about 4 and
about 8.
8. Arrangement for reforming a hydrocarbon fuel, especially
according to a method of at least one of claims 1 to 7, for
generating hydrogen especially for operating a fuel cell, wherein
the arrangement comprises: a fuel reformer (1) containing an
oxidation catalyst (1a), for generating hydrogen from supplied fuel
and oxygen; and a catalytic combustion reactor (3), for
catalytically converting hydrogen into water steam; wherein the
fuel reformer (1) and the combustion reactor (3) are connected in a
loop such that by the water steam from the combustion reactor (3)
an autothermal fuel reforming process (ATR) can be created in the
fuel reformer (1).
9. Arrangement according to claim 8, comprising a gas clean-up
reactor (2) between an outlet of the fuel reformer (1) and an inlet
of the combustion reactor (3) for reducing the amount of carbon
monoxide from the product of the fuel reformer (1).
10. Arrangement according to claim 8, comprising a control unit
(1d) for controlling the ratio of air to fuel supplied into the
fuel reformer (1).
11. Arrangement according to claim 8, comprising a control unit
(1d) for controlling inlet valves of the fuel reformer (1) so that
the first stage according to claim 1 and/or the initial step
according to claim 2 is realized.
12. Arrangement according to claim 8, comprising a fuel reformer
(1) which comprises a catalyst (1a) with a multipurpose catalyst
material or at least two one-purpose catalyst materials, for
conducting endothermic steam reforming and exothermic oxidation
processes.
13. Control unit (1d) for controlling an arrangement according to
at least one of claims 8 to 11.
14. Fuel cell system for generating power by means of at least one
fuel cell (4), comprising an arrangement according to at least one
of claims 8 to 11.
15. Fuel cell system according to claim 14, in which hydrogen
generated by the fuel cell (4) is supplied via a separator (7) to
the combustion reactor (3) for generating heat for evaporating
water of the fuel cell.
16. Fuel cell system according to claim 14, in which water
generated by the fuel cell (4) is supplied via a separator (7) into
a vessel (8) for generating steam for feeding the fuel reformer
(1).
17. Computer program comprising computer program code means adapted
to perform a method according to at least one of claims 1 to 7 when
said program is run on a programmable microcomputer.
18. Computer program according to claim 17 adapted to be downloaded
to an arrangement according to claim 8 or a fuel cell system
according to claim 14 or one of its components when run on a
computer which is connected to the interne.
19. Computer program product stored on a computer readable medium,
comprising computer program code means according to claim 17.
Description
[0001] The present application is a divisional of U.S. App.
11/572,325, filed Jan. 19, 2007, which is a U.S. National Stage of
PCT/EP2005/007861, filed Jul. 19, 2005, which claims priority to
SE2004/001142, filed Jul. 19, 2004, all of which are incorporated
by reference.
[0002] The invention relates to a method and arrangement for
reforming a hydrocarbon fuel like for example di-methyl ether
(DME), methanol, ethanol, propanol, or any variants or other
oxidized fuels, for generating hydrogen especially for supplying a
fuel cell. Furthermore, the invention relates to a fuel cell system
comprising such an arrangement, especially for providing power to a
stationary or mobile power consuming unit like especially an
auxiliary power unit (APU) for application in aircraft, ships and
vehicles, or as a part of a hybrid drive or as a sole driving unit
for e.g., for a ship or a vehicle.
[0003] Fuel cell systems are generally considered as highly
feasible solutions especially for providing power to vehicles, and
in particular for eliminating idle operation of heavy-duty
trucks.
[0004] For providing a fuel cell with hydrogen, fuels can be
reformed for generating this hydrogen. Such a reforming process
requires water steam for operating a fuel reformer. For starting-up
the reforming process, the water steam usually has to be generated
from external water which is stored in a water tank. However,
storing water in a water tank on-board a vehicle is not feasible in
cold geographic regions because the water can freeze so that the
system may be damaged as well as considerably slowed down during
the start-up phase.
[0005] US 2001/0038816 discloses a gas generator for generating a
hydrogen rich gas from a water-fuel mixture by catalytic steam
reforming and/or from an oxygen-fuel mixture by partial oxidation,
wherein the generator includes at least one water vessel. The
stored water contains a water-methanol mixture having a mixing
ratio which is effective to ensure adequate frost protection.
However, this might cause difficulties to control and optimize the
reforming process.
[0006] WO 00/70697 discloses a fuel cell system which instead of
separate fuel and water supplies uses an emulsion of fuel and water
which can be formulated to remain in a liquid state at low ambient
operating temperatures. Additives are added to the emulsion in
order to further lower the freezing point. However, this system has
the same disadvantages as the above gas generator and furthermore
requires considerable changes of the whole arrangement.
[0007] It is desirable to provide a method and an arrangement for
reforming fuel to produce hydrogen for a fuel cell, which by simple
measures can be started and operated reliably especially under
ambient temperatures which are below the freezing point of
water.
[0008] It is desirable to provide a method and an arrangement for
reforming fuel which can be started and operated reliably
especially under freezing ambient temperature conditions without
using anti-freezing agents in a water supply.
[0009] One considerable advantage of these solutions is the fact
that no external water supply and no extra water tank which is
filled with water for starting the process so that a considerable
amount of weight is saved. This is especially important in case of
a fuel cell system for mobile applications as e.g., the above
mentioned applications in aircrafts and vehicles, because the water
supply which is required for the steady state operation is
considerably smaller.
[0010] By this, a fuel cell system can be provided which due to its
low weight and the fact that it can be operated under ambient
temperatures which are below the freezing point of water, is
especially suitable for mobile applications as e.g., the above
mentioned applications in aircrafts and vehicles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Further details, features and advantages of the invention
become obvious from the following description of exemplary and
preferred embodiments of the invention with respect to the drawings
in which schematically shows:
[0012] FIG. 1 a block diagram of a first component of an
arrangement according to the invention for presenting an initial
step of a start-up phase of a method according to the
invention;
[0013] FIG. 2 a block diagram of the arrangement for presenting a
first stage of the start-up phase of the method according to the
invention;
[0014] FIG. 3 a block diagram of the arrangement for presenting a
second and a third stage of the start-up phase of the method
according to the invention;
[0015] FIG. 4 a block diagram of the arrangement for presenting a
fourth stage of the start-up phase of the method according to the
invention;
[0016] FIG. 5 a block diagram of a fuel cell system comprising an
arrangement according to the invention for presenting a transition
phase; and
[0017] FIG. 6 a block diagram according to FIG. 5 after termination
of the transition phase and during the steady state of operation
phase of the fuel cell system.
DETAILED DESCRIPTION
[0018] With the method and the arrangement according to the
invention a fuel reforming process which is conducted for supplying
a fuel cell with hydrogen can be started by means of a start-up
phase which needs no extra water from an external water supply.
[0019] Basically, this is accomplished by an arrangement according
to the invention for conducting a start-up phase in which at first
hydrocarbon fuel is converted in a fuel reformer comprising an
oxidation catalyst by an exothermic catalytic partial oxidation
process (CPO or catalytic POx) to hydrogen. The generated hydrogen
is fed to a catalytic combustion reactor, in which the generated
hydrogen is catalytically converted into water steam. The water
steam is fed back into the fuel reformer whereby an endothermic
catalytic steam reforming process is initiated, so that by the
combination of the exothermic and the endothermic process gradually
an autothermal fuel reforming process (ATR, which is also called
autothermic mode and is disclosed e.g., in US 2001/0038816) is
established.
[0020] When this autothermal (ATR) process is stabilized, a part or
all of the generated hydrogen is fed to a fuel cell in which
electricity and water are generated in a known manner, thereby
terminating the start-up phase. The water which is evaporated is
fed back into the fuel reformer so that the fuel cell system is
self-sufficient with respect to the need and the generation of
water steam during the start-up phase as well as during the steady
state operation phase.
[0021] By including the catalytic combustion reactor into the
arrangement that is provided for creating water steam from hydrogen
generated in a partial oxidation process, steam can be generated
directly from the fuel which obviates the need for storing water
needed for the start-up phase of the arrangement for reforming
fuel.
[0022] However, in dependence on the kind of the fuel to be
reformed and its composition and components, not only hydrogen is
generated by the fuel reformer, but also carbon dioxide, carbon
monoxide and fractions of hydrocarbons. While carbon dioxide has
largely no influence on the method, especially carbon monoxide may
decrease the efficiency of the whole fuel cell system and/or may
damage one or more of its components. In order to avoid this, the
gas stream which is generated by the fuel reformer and which
comprises the wanted hydrogen, is purified prior to supplying it to
the fuel cell. For this purpose, the arrangement is provided with a
gas clean-up reactor by which especially the amount of carbon
monoxide is reduced below an allowable threshold value or is
minimized, so that the performance of the fuel cell is not
decreased or shut down by its aggressive chemical properties.
[0023] In the following, this start-up phase shall now be described
in more details with reference to the drawings in which the same
reference signs denote the same or corresponding parts or units.
The drawings each show only the active parts and components of the
arrangement in the related stages and phases. With respect to the
general chemical reactions in connection with fuel reforming, it is
referred to both of the prior art documents mentioned in the
introductory part above which are made by reference to a part of
this disclosure.
[0024] FIG. 1 schematically shows the fuel reformer 1 comprising a
catalyst 1a with one multipurpose catalyst material or at least two
one-purpose catalyst materials, so that the catalyst 1a is usable
for endothermic steam reforming and exothermic oxidation processes.
Further, a first pipe or line 1b for supplying oxygen preferably in
the form of ambient air and a second pipe or line 1c for supplying
a hydrocarbon fuel to be reformed are provided. Finally, a control
unit 1d is provided for closing and partly or totally opening each
one valve within the first and the second line 1b, 1c,
respectively, in order to control the amount of oxygen (air) and
hydrocarbon fuel, respectively, flowing through these lines 1b, 1c
into the fuel reformer 1. In FIGS. 2 to 6 the control unit 1d and
the valves are not shown for reason of simplicity.
[0025] In an initial step preceding a first stage of the start-up
phase, the hydrocarbon fuel and air are fed into the fuel reformer
1 at an air-to-fuel ratio (lambda value) which is considerably
greater than 1 (which usually is called a lean mixture). This value
which is e.g., between about 4 and about 8 and especially between
about 5 and about 7, is chosen in dependence on the kind of fuel
and the kind of the catalyst 1a such that by an excess of oxygen
the fuel reformer 1 is catalytically started and heated by a highly
exothermic reaction (combustion of fuel). During this initial step,
substantially water and carbon dioxide are produced by the fuel
reformer 1.
[0026] Alternatively, the fuel reformer 1 can be started by
igniting the supplied air/fuel mixture e.g., with a spark plug (not
shown). In this case the air-to-fuel ratio can be less lean or more
lean than in the above case.
[0027] When this combustion process is stable (usually after about
1 to 10 seconds), the first stage of the start-up phase begins. In
this first stage the air-to-fuel ratio is reduced by means of the
control unit 1d to a lambda value lower than 1, e.g., about 0.25
(or, as an alternative, about one fifth of the lambda value during
the initial step, however less than 1) which usually is called a
fat mixture, in order to initiate the catalytic partial oxidation
(CPO) of the fuel in the oxidation catalyst 1a (and to ensure that
the allowable temperature limits of the fuel reformer 1 and the
catalyst 1a are not exceeded). The transition between the initial
step and this first stage is performed e.g., at a temperature of
between about 300 and about 500.degree. C. By this, the products
generated by the fuel reformer 1 now change from water and carbon
dioxide (initial step) to hydrogen and carbon dioxide and carbon
monoxide. Due to the kind of the catalyst 1a and the kind of fuel,
there might be small amounts of fractions of the fuel or other
hydrocarbons as well, which are commonly indicated in the drawings
with the letters "HC".
[0028] These products are then fed according to FIG. 2 through a
third line or pipe 5 a via a gas clean-up reactor 2 (which is not
effective as a clean-up reactor at this stage but preferably is
only used for cooling the gas stream) into a catalytic combustion
reactor 3 comprising a catalyst 3 a, into which oxygen, preferably
in the form of ambient air is supplied as well.
[0029] In a second stage of the start-up phase, the hydrogen is now
converted in the catalytic combustion reactor 3 into water steam
which according to FIG. 3 is fed back (together with the carbon
dioxide) via the third line 5a into the fuel reformer 1. An exhaust
valve 15 (first valve) is provided in this line 5 a as an
overpressure protection. (The dotted pipe or line in FIG. 2 between
the outlet of the combustion reactor 2 and the inlet of the fuel
reformer 1 only indicates that in a transition phase between this
second and the following third stage there is only a small amount
of products flowing through this pipe.)
[0030] By distributing the heat dissipation in the process of
converting hydrogen to water or water steam over more than one
catalytic unit, namely both the gas clean-up reactor 2 and the
catalytic combustion reactor 3, the risk of overheating the system
in the start-up phase is reduced.
[0031] As the products from the catalytic combustion reactor 3 are
fed back into the fuel reformer 1 (FIG. 3), an endothermic
catalytic steam reforming process is initiated in the fuel reformer
1 in a third stage, so that together with the above exothermic
catalytic partial oxidation (CPO) process, the chemical reaction in
the fuel reformer 1 gradually changes into an autothermal reforming
(ATR) process. By this, the concentration of the carbon monoxide in
the product of the fuel reformer 1 gradually decreases in
comparison to the product of the first stage, until it reaches a
minimum value when the ATR process is stable. Furthermore,
by-products like fragments of carbon hydrogen (HC) are removed or
at least substantially decreased as well in comparison to the first
stage.
[0032] In a fourth stage according to FIG. 4, which begins when the
ATR process is stabilized, oxygen preferably in the form of ambient
air is now fed into the gas clean-up reactor 2, which comprises a
preferential oxidizer (PrOx) 2a. By passing the hydrogen rich gas
from the fuel reformer 1 through the gas clean-up reactor 2 to the
combustion reactor 3, the gas stream is further purified from
unwanted by-products, especially from carbon monoxide.
[0033] By establishing the AIR process prior to cleaning the
products of the fuel reformer 1 by means of the clean-up reactor 2,
an overload of this reactor 2 with carbon monoxide is prevented
(which might lead to too high temperatures).
[0034] When the level of carbon monoxide and other unwanted
by-products in the gas stream coming out of the gas clean-up
reactor 2 are below an allowable threshold value as mentioned
above, a transition phase is initiated according to FIG. 5 by
partly opening an outlet of a second valve 5 between the clean-up
reactor 2 and the combustion reactor 3 to a fuel cell 4 by means of
the control unit 1d (not shown), whereby the products from the gas
clean-up reactor 2 are now partly supplied to the fuel cell 4 for
generating electric power.
[0035] Excess hydrogen from the fuel cell 4 is fed via a separator
7 to the catalytic combustion reactor 3 for generating water steam
for the fuel reformer 1 from the portion of the product from the
gas clean-up reactor 2 which is not fed to the fuel cell 4 but
directly into the combustion reactor 3.
[0036] Furthermore, steam is also generated from the water that is
generated in the fuel cell 4 by supplying this water via a vessel 8
to a heat exchanger 6. This heat exchanger 6 is supplied with heat
from the water steam which is fed from the catalytic combustion
reactor 3 to the fuel reformer 1, such that the water from the fuel
cell is evaporated in the heat exchanger 6 and provided in the form
of steam to the fuel reformer 1 as well.
[0037] In this transition phase, the more water is generated by the
fuel cell 4 (and is supplied in the form of steam to the fuel
reformer 1), the less water steam is generated by and supplied from
the combustion reactor 3 to the fuel reformer 1. This is
appropriately controlled by controlling the openings of the outlets
of the second valve 5 to the fuel cell 4 and to the combustion
reactor 3, respectively, by means of the control unit 1d (not
shown). Furthermore, the steam supplied from the combustion reactor
3 to the fuel reformer 1 can also be controlled by the second valve
15 by means of the control unit 1d.
[0038] In the steady state operation of the fuel cell system
according to FIG. 6 in which the fuel cell 4 has reached its normal
operating temperature, sufficient water is generated by the fuel
cell 4 so that sufficient steam can be generated by the heat
ex-changer 6 for operating the fuel reformer 1, so that there is no
need any longer for feeding steam from the combustion reactor 3
into the fuel reformer 1.
[0039] In order to realize this, the valve 5 is controlled by the
control unit 1d (not shown) such that all of the products from the
gas clean-up reactor 2 are now fed to the fuel cell 4 alone.
[0040] The catalytic combustion reactor 3 is now used only for
generating and supplying heat to the heat exchanger 6. This is
accomplished by means of excess hydrogen from the fuel cell 4 which
is supplied to and converted in the combustion reactor 3 by oxygen
from ambient air into water steam. This water steam is exclusively
supplied to the heat exchanger 6 in which the heat is used for
evaporating water from the water vessel 8 and generated by the fuel
cell 4 and for supplying the evaporated water to the fuel reformer
1.
[0041] As shown in FIGS. 5 and 6, the separating unit 7 is
connected to the outlet side of the fuel cell 4. The separating
unit 7 separates hydrogen, which is fed into the catalytic
combustion reactor 3, from water which is fed into the vessel 8.
The vessel 8 stores water only during the operation of the fuel
cell system. When the system is shut down, the vessel 8 is
preferably emptied, in order to reduce the risk of system damage
due to freezing at low ambient temperatures. The vessel 8 may be
provided with a valve (not shown) which is controlled by the
control unit 1d (not shown) such that the valve opens when the
system is shut down.
[0042] As indicated above, water is fed from the vessel 8 to the
heat exchanger 6 for the production of steam (if the vessel 8
already contains water). The feeding of steam generated in the
catalytic combustion reactor 3 into the fuel reformer 1 can then
gradually be reduced as the generation of steam from water supplied
from the vessel 8 to the heat exchanger 6 is increased to an amount
that is sufficient for maintaining the autothermal fuel reforming
process (ATR) in the fuel reformer 1.
[0043] The flow control valve 5 may, in order to enable the fuel
cell system to gradually shift from the transition phase to the
steady state operation be designed as a multi outlet port valve
which is capable of controlling the distribution of the inlet flow
among a set of outlets included in the valve 5.
[0044] The fuel reformer 1, the gas clean-up reactor 2, the
catalytic combustion reactor 3 and the fuel cell 4 are conventional
devices well known to a person skilled in the art. The fuel
reformer 1 may for instance be using a carrier made of gamma
alumina in the form of pellets or a wash coat adhered to a
substrate of, for instance, a ceramic monolithe. The carrier may
suitably be coated with oxides of manganese or copper.
[0045] The gas clean-up reactor 2 may e.g., suitably have a carrier
material which is coated with noble metals such as Pt, Ru, Rh and
Pd. The catalytic combustion reactor 3 may e.g., suitably have a
carrier material which is coated with metals such as Pt, Mn and Pd
or other metals. The fuel cell 4 is advantageously a normal or high
temperature PEM type.
[0046] For the operation of the fuel cell system, temperature
sensor elements, means for regulating flow and CO sensors are
preferably used to control the flow through the system and the
supply of fuel and air into the system by means of the control unit
1d.
[0047] Generally, di-methyl ether (DME) and methanol are preferred
for conducting the method, but other oxidized fuels can be used as
well. However, the heavier and longer the molecular chains are, the
more carbon monoxide and the lesser carbon dioxide are produced
which has the effect that the efficiency and performance of the
whole method and arrangement decreases.
* * * * *