U.S. patent application number 10/006875 was filed with the patent office on 2002-07-25 for apparatus and method for heating catalyst for start-up of a compact fuel processor.
Invention is credited to Krause, Curtis L., Martin, Paul, Phan, Jennifer L., Scott, T. Glenn, Stevens, James F..
Application Number | 20020098129 10/006875 |
Document ID | / |
Family ID | 22951014 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020098129 |
Kind Code |
A1 |
Martin, Paul ; et
al. |
July 25, 2002 |
Apparatus and method for heating catalyst for start-up of a compact
fuel processor
Abstract
The present invention specifically relates to the methods and
apparatus for heating a catalyst bed for start-up and for providing
heat to a catalyst bed during transient operation to maintain
desired reaction temperatures. An electrical heating element may
directly or indirectly heat the catalyst. The direct heating of
catalyst is achieved by having direct contact of the heater element
with the catalyst. Indirect heating is achieved by direct heating
of a fluid, such as a process flow, which in turn flows through the
catalyst, thereby transferring heat to the catalyst. Additionally,
indirect heating may be achieved by placing the heating element
within a sheath that is then either in direct contact with the
catalyst or fluid that flows through the catalyst. By these means,
catalyst of many forms may employ this catalyst heater including
pellets, extrudates, spheres, and monoliths. The catalyst heater in
accordance with this invention can be made of any resistive wire,
cartridges, or rods that may be coupled to a power source to
provide the energy to produce the heat.
Inventors: |
Martin, Paul; (Toronto,
CA) ; Scott, T. Glenn; (Houston, TX) ; Phan,
Jennifer L.; (Rosharon, TX) ; Stevens, James F.;
(Katy, TX) ; Krause, Curtis L.; (Houston,
TX) |
Correspondence
Address: |
STEPHEN H. CAGLE
HOWREY, SIMON, ARNOLD & WHITE, LLP
750 BERING DRIVE
HOUSTON
TX
77057
US
|
Family ID: |
22951014 |
Appl. No.: |
10/006875 |
Filed: |
December 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60251226 |
Dec 5, 2000 |
|
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|
Current U.S.
Class: |
422/173 ;
422/168; 422/171; 422/198; 422/199; 422/211; 423/651 |
Current CPC
Class: |
C01B 2203/1205 20130101;
B01J 8/009 20130101; C01B 2203/0866 20130101; C01B 3/48 20130101;
H01M 8/0631 20130101; B01J 2219/182 20130101; B01J 2219/00135
20130101; C01B 2203/0495 20130101; B01J 19/2475 20130101; B01J
2208/00176 20130101; C01B 3/16 20130101; C01B 2203/047 20130101;
C01B 2203/1035 20130101; C01B 2203/1011 20130101; C01B 2203/1604
20130101; B01J 8/0278 20130101; B01J 8/048 20130101; B01J 8/0496
20130101; H01M 8/04037 20130101; C01B 2203/0465 20130101; C01B
2203/0894 20130101; C01B 2203/0244 20130101; B01J 2208/00407
20130101; C01B 3/38 20130101; B01J 2208/00194 20130101; Y02E 60/50
20130101; B01J 19/2485 20130101; C01B 3/386 20130101; C01B
2203/0805 20130101; B01J 2208/00203 20130101; C01B 3/583 20130101;
C01B 2203/147 20130101; H01M 8/04059 20130101; B01J 8/0488
20130101; B01J 2208/00415 20130101; B01J 2219/1944 20130101; C01B
2203/0883 20130101; C01B 2203/142 20130101; H01M 8/04022 20130101;
H01M 8/0612 20130101; C01B 2203/146 20130101; B01J 2219/185
20130101; B01J 8/0492 20130101; B01J 8/067 20130101; C01B 2203/0455
20130101; C01B 2203/1023 20130101; B01J 8/0453 20130101; C01B 3/382
20130101; C01B 2203/066 20130101; C01B 2203/1017 20130101; B01J
2208/00141 20130101; C01B 2203/0288 20130101; C01B 2203/0485
20130101; C01B 2203/0877 20130101; C01B 2203/1082 20130101; B01J
8/0423 20130101; C01B 3/384 20130101; C01B 2203/1235 20130101; C01B
2203/82 20130101; C01B 2203/085 20130101; C01B 2203/1041 20130101;
B01J 2219/00083 20130101; C01B 2203/0283 20130101; C01B 2203/0844
20130101; Y02P 20/52 20151101; B01J 19/0013 20130101; B01J
2208/00716 20130101; C01B 2203/044 20130101; C01B 2203/1276
20130101; C01B 2203/80 20130101; H01M 8/0668 20130101; B01J 8/0285
20130101; B01J 2219/0002 20130101; B01J 2208/025 20130101; B01J
2208/00814 20130101 |
Class at
Publication: |
422/173 ;
423/651; 422/168; 422/171; 422/198; 422/199; 422/211 |
International
Class: |
F01N 003/10; F28D
021/00; B01J 008/02 |
Claims
What is claimed is:
1. A method for heating a catalyst bed for start-up, comprising:
providing a catalyst bed having an upstream face and a downstream
face; providing an electrical heating element positioned along one
face of the catalyst bed; passing a small flow of reactants through
the electrical heating element and catalyst bed; and heating the
electrical heating element to initiate an exothermic reaction at
the face of the catalyst bed, wherein the heat of reaction
propagates throughout the catalyst bed thereby heating the catalyst
bed for start-up.
2. The method of claim 1, wherein the electrical heating element is
positioned along the upstream face of the catalyst bed.
3. The method of claim 1, wherein the electrical heating element is
formed in a spiral design along one face of the catalyst bed.
4. The method of claim 1, wherein the catalyst bed is selected from
the group consisting of pellets, extrudates, spheres, monoliths,
and any combinations thereof.
5. The method of claim 1, wherein the catalyst bed contains
catalyst selected from the group consisting of autothermal
reforming catalysts, partial oxidation catalysts, steam reforming
catalysts, water gas shift catalysts, preferential oxidation
catalysts, anode tailgas oxidation catalysts, and sulfur
absorbents.
6. A reactor module for use in a compact fuel processor,
comprising: a catalyst bed having an upstream face and a downstream
face; and an electrical heating element positioned along the
upstream face of the catalyst bed, the heating element capable of
initiating an exothermic reaction at the upstream face of the
catalyst bed in the presence of a small flow of reactants.
7. The reactor module of claim 6, wherein the electrical heating
element is formed in a spiral design.
8. The reactor module of claim 6, wherein the catalyst bed is
selected from the group consisting of pellets, extrudates, spheres,
monoliths, and any combinations thereof.
9. The reactor module of claim 6, wherein the catalyst bed contains
catalyst selected from the group consisting of autothermal
reforming catalysts, partial oxidation catalysts, steam reforming
catalysts, water gas shift catalysts, preferential oxidation
catalysts, anode tailgas oxidation catalysts, and sulfir
absorbents.
10. A reactor module for use in a compact fuel processor,
comprising: a catalyst bed; a cooling coil positioned substantially
within the catalyst bed for removing excess heat during normal
operation; and an electrical heating element positioned within the
cooling coil, the heating element capable of heating the catalyst
to a desired reaction temperature.
11. The reactor module of claim 10, wherein the catalyst bed is
selected from the group consisting of pellets, extrudates, spheres,
monoliths, and any combinations thereof.
12. The reactor module of claim 10, wherein the catalyst bed
contains catalyst selected from the group consisting of autothermal
reforming catalysts, partial oxidation catalysts, steam reforming
catalysts, water gas shift catalysts, preferential oxidation
catalysts, anode tailgas oxidation catalysts, and sulfur
absorbents.
13. A method for heating a catalyst bed, comprising: providing an
electrical heating element positioned within a cooling coil located
substantially within the catalyst bed; and heating the electrical
heating element thereby heating the catalyst bed to a desired
temperature.
14. The method of claim 13, wherein the desired temperature is the
start-up temperature.
15. The method of claim 13, wherein the desired temperature is the
desired reaction temperature during transient operation.
16. A method for heating a catalyst bed to a desired temperature,
comprising: providing a catalyst bed in communication with an
electrical heating element; and heating the electrical heating
element so as to maintain the desired temperature of the catalyst
bed.
17. The method of claim 16, wherein the desired temperature is the
start-up temperature.
18. The method of claim 16, wherein the desired temperature is the
desired reaction temperature during transient operation.
19. The method of claim 16, wherein the electrical heating element
is weaved through the catalyst bed.
20. The method of claim 16, wherein the catalyst bed is a
monolith.
21. The method of claim 18, wherein the electrical heating element
is wrapped around the monolith.
22. A method for heating a catalyst bed to a desired temperature,
comprising: positioning an electrical heating element upstream of
the catalyst bed; and passing a fluid across the electrical heating
element and through the catalyst bed, wherein the catalyst bed is
heated to the desired temperature.
23. The method of claim 22, wherein the desired temperature is the
start-up temperature.
24. The method of claim 22, wherein the desired temperature is the
desired reaction temperature during transient operation.
Description
BACKGROUND OF THE INVENTION
[0001] Fuel cells provide electricity from chemical
oxidation-reduction reactions and possess significant advantages
over other forms of power generation in terms of cleanliness and
efficiency. Typically, fuel cells employ hydrogen as the fuel and
oxygen as the oxidizing agent. The power generation is proportional
to the consumption rate of the reactants.
[0002] A significant disadvantage which inhibits the wider use of
fuel cells is the lack of a widespread hydrogen infrastructure.
Hydrogen has a relatively low volumetric energy density and is more
difficult to store and transport than the hydrocarbon fuels
currently used in most power generation systems. One way to
overcome this difficulty is the use of reformers to convert the
hydrocarbons to a hydrogen rich gas stream which can be used as a
feed for fuel cells.
[0003] Hydrocarbon-based fuels, such as natural gas, LPG, gasoline,
and diesel, require conversion processes to be used as fuel sources
for most fuel cells. Current art uses multi-step processes
combining an initial conversion process with several clean-up
processes. The initial process is most often steam reforming (SR),
autothermal reforming (ATR), catalytic partial oxidation (CPOX), or
non-catalytic partial oxidation (POX). The clean-up processes are
usually comprised of a combination of desulfurization, high
temperature water-gas shift, low temperature water-gas shift,
selective CO oxidation, or selective CO methanation. Alternative
processes include hydrogen selective membrane reactors and
filters.
[0004] Despite the above work, there remains a need for a simple
unit for converting a hydrocarbon fuel to a hydrogen rich gas
stream for use with a fuel cell. A practical obstacle facing any
solution to this problem is the need to start-up catalyst beds and
maintain desired reaction temperatures during transient operation.
The present invention addresses this need.
SUMMARY OF THE INVENTION
[0005] The present invention specifically relates to the methods
and apparatus for heating a catalyst bed for start-up and for
providing heat to a catalyst bed during transient operation to
maintain desired reaction temperatures. Such methods and apparatus
can be used in a fuel processor so as to make the start-up of the
fuel processor faster and easier. In fuel processors there are
several catalysts that may be used with the present invention,
including but not limited to autothermal reforming catalysts,
partial oxidation catalysts, steam reforming catalysts, water gas
shift catalysts, preferential oxidation catalysts, and sulfur
absorbents, as well as with anode tailgas oxidation catalysts
associated with an adjoining fuel cell.
[0006] As embodied by the present invention an electrical heating
element may directly or indirectly heat the catalyst and thus
rapidly obtain the desired reaction temperature within the catalyst
bed. The direct heating of catalyst is achieved by having direct
contact of the heater element with the catalyst. Indirect heating
is achieved by direct heating of a fluid, such as a process flow,
which in turn flows through the catalyst, thereby transferring heat
to the catalyst. Additionally, indirect heating may be achieved by
placing the heating element within a sheath which is then either in
direct contact with the catalyst or fluid which flows through the
catalyst. As is contemplated within the scope of the present
invention, a wide variety of catalyst forms may employ a catalyst
heater including pellets, extrudates, spheres, and monoliths. In
one illustrative embodiment of the present invention a catalyst
heater in accordance with this invention can be made of any
resistive wire, cartridges, or rods that can be formed as outlined
below. A power source, such as an electric power source, provides
the energy to produce the heat that preheats the catalyst bed.
[0007] One illustrative embodiment of the present invention is a
reactor in a fuel processor that includes a catalyst bed, a cooling
coil positioned within the catalyst bed for removing excess heat
during normal operation, and an electrical heating element
positioned within the cooling coil for heating the catalyst to a
desired reaction temperature during start-up and during transient
operation. Such a preferred and illustrative example is generally
referred to in the present disclosure as sheathed heating.
Important illustrative advantages of this illustrative embodiment
include: the provision of heat to the catalyst for fast and
efficient start-up, the preheating of the hydrocarbon fuel feed to
the fuel processor and it provides assistance to the reactor in
maintaining reaction temperature during transient operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The description is presented with reference to the
accompanying drawings in which:
[0009] FIG. 1 depicts a simple process flow diagram for a fuel
processor.
[0010] FIG. 2 illustrates a compact fuel processor; and
[0011] FIG. 3 illustrates one illustrative embodiment of a face
heater for a catalyst bed.
[0012] FIG. 4 illustrates one illustrative embodiment of weaving a
monolithic catalyst bed with an electrical heating element.
[0013] FIG. 5 illustrates one illustrative embodiment of wrapping a
monolithic catalyst bed with an electrical heating element.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0014] The present invention is generally directed to an apparatus
and method for heating a catalyst bed for start-up and for
providing heat to a catalyst bed during transient operation to
maintain desired reaction temperatures. In a preferred aspect, the
apparatus and method described herein relate to providing heat to
catalyst beds in a compact fuel processor for producing a hydrogen
rich gas stream from a hydrocarbon fuel feed. Hydrogen rich gas
produced from such compact fuel processors will have increasing
importance in the development of fuel cells, including fuel cells
used to power automotive vehicles. However, other possible uses are
contemplated for the apparatus and methods described herein,
including the start-up and reaction temperature maintenance for
exothermic catalyst beds not in fuel processor service.
Accordingly, while the invention is described herein as being used
in conjunction with compact fuel processors and fuel cells, the
scope of the invention is not limited to such use.
[0015] Each of the illustrative embodiments of the present
invention relates to exothermic catalyst beds associated with fuel
processors with hydrocarbon fuel feed being directed through the
fuel processor. The hydrocarbon fuel may be liquid or gas at
ambient conditions as long as it can be vaporized. As used herein
the term "hydrocarbon" includes organic compounds having C--H bonds
which are capable of producing hydrogen from a partial oxidation or
steam reforming reaction. The presence of atoms other than carbon
and hydrogen in the molecular structure of the compound is not
excluded. Thus, suitable fuels for use in the method and apparatus
disclosed herein include, but are not limited to hydrocarbon fuels
such as natural gas, methane, ethane, propane, butane, naphtha,
gasoline, and diesel fuel, and alcohols such as methanol, ethanol,
propanol, and the like.
[0016] The fuel processor feeds include hydrocarbon fuel, oxygen,
and water. The oxygen can be in the form of air, enriched air, or
substantially pure oxygen. The water can be introduced as a liquid
or vapor. The composition percentages of the feed components are
determined by the desired operating conditions, as discussed
below.
[0017] The fuel processor effluent stream includes hydrogen and
carbon dioxide and can also include some water, unconverted
hydrocarbons, carbon monoxide, impurities (e.g. hydrogen sulfide
and ammonia) and inert components (e.g., nitrogen and argon,
especially if air was a component of the feed stream).
[0018] FIG. 1 depicts a general process flow diagram for a fuel
processor. One of skill in the art should appreciate that a certain
amount of progressive order is needed in the flow of the reactants
through the reactors disclosed herein.
[0019] Process step A is an autothermal reforming process in which
two reactions, partial oxidation (formula I, below) and optionally
also steam reforming (formula II, below), are combined to convert
the feed stream F into a synthesis gas containing hydrogen and
carbon monoxide. Formulas I and II are exemplary reaction formulas
wherein methane is considered as the hydrocarbon:
CH.sub.4+1/2O.sub.2.fwdarw.2H.sub.2+CO (I)
CH.sub.4+H.sub.2O.fwdarw.3H.sub.2+CO (II)
[0020] The partial oxidation reaction occurs very quickly to the
complete conversion of oxygen added and produces heat. The steam
reforming reaction occurs slower and consumes heat. A higher
concentration of oxygen in the feed stream favors partial oxidation
whereas a higher concentration of water vapor favors steam
reforming. Therefore, the ratios of oxygen to hydrocarbon and water
to hydrocarbon become characterizing parameters. These ratios
affect the operating temperature and hydrogen yield.
[0021] The operating temperature of the autothermal reforming step
can range from about 550.degree. C. to about 900.degree. C.,
depending on the feed conditions and the catalyst. The invention
uses a catalyst bed of a partial oxidation catalyst with or without
a steam reforming catalyst. The catalyst may be in any form
including pellets, spheres, extrudate, monoliths, and the like.
Partial oxidation catalysts should be well known to those with
skill in the art and are often comprised of noble metals such as
platinum, palladium, rhodium, and/or ruthenium on an alumina
washcoat on a monolith, extrudate, pellet or other support.
Non-noble metals such as nickel or cobalt have been used. Other
washcoats such as titania, zirconia, silica, and magnesia have been
cited in the literature. Many additional materials such as
lanthanum, cerium, and potassium have been cited in the literature
as "promoters" that improve the performance of the partial
oxidation catalyst.
[0022] Steam reforming catalysts should be known to those with
skill in the art and can include nickel with amounts of cobalt or a
noble metal such as platinum, palladium, rhodium, ruthenium, and/or
iridium. The catalyst can be supported, for example, on magnesia,
alumina, silica, zirconia, or magnesium aluminate, singly or in
combination. Alternatively, the steam reforming catalyst can
include nickel, preferably supported on magnesia, alumina, silica,
zirconia, or magnesium aluminate, singly or in combination,
promoted by an alkali metal such as potassium.
[0023] Process step B is a cooling step for cooling the synthesis
gas stream from process step A to a temperature of from about
200.degree. C. to about 600.degree. C., preferably from about
300.degree. C. to about 500.degree. C., and more preferably from
about 375.degree. C. to about 425.degree. C., to optimize the
temperature of the synthesis gas effluent for the next step. This
cooling may be achieved with heat sinks, heat pipes or heat
exchangers depending upon the design specifications and the need to
recover/recycle the heat content of the gas stream. One
illustrative embodiment for step B is the use of a heat exchanger
utilizing feed stream F as the coolant circulated through the heat
exchanger. The heat exchanger can be of any suitable construction
known to those with skill in the art including shell and tube,
plate, spiral, etc. Alternatively, or in addition thereto, cooling
step B may be accomplished by injecting additional feed components
such as fuel, air or water. Water is preferred because of its
ability to absorb a large amount of heat as it is vaporized to
steam. The amounts of added components depend upon the degree of
cooling desired and are readily determined by those with skill in
the art.
[0024] Process step C is a purifying step. One of the main
impurities of the hydrocarbon stream is sulfur, which is converted
by the autothermal reforming step A to hydrogen sulfide. The
processing core used in process step C preferably includes zinc
oxide and/or other material capable of absorbing and converting
hydrogen sulfide, and may include a support (e.g., monolith,
extrudate, pellet etc.). Desulfurization is accomplished by
converting the hydrogen sulfide to water in accordance with the
following reaction formula III:
H.sub.2S+ZnO.fwdarw.H.sub.2O+ZnS (III)
[0025] Other impurities such as chlorides can also be removed. The
reaction is preferably carried out at a temperature of from about
300.degree. C. to about 500.degree. C., and more preferably from
about 375.degree. C. to about 425.degree. C. Zinc oxide is an
effective hydrogen sulfide absorbent over a wide range of
temperatures from about 25.degree. C. to about 700.degree. C. and
affords great flexibility for optimizing the sequence of processing
steps by appropriate selection of operating temperature.
[0026] The effluent stream may then be sent to a mixing step D in
which water is optionally added to the gas stream. The addition of
water lowers the temperature of the reactant stream as it vaporizes
and supplies more water for the water gas shift reaction of process
step E (discussed below). The water vapor and other effluent stream
components are mixed by being passed through a processing core of
inert materials such as ceramic beads or other similar materials
that effectively mix and/or assist in the vaporization of the
water. Alternatively, any additional water can be introduced with
feed, and the mixing step can be repositioned to provide better
mixing of the oxidant gas in the CO oxidation step G disclosed
below.
[0027] Process step E is a water gas shift reaction that converts
carbon monoxide to carbon dioxide in accordance with formula
IV:
H.sub.2O+CO.fwdarw.H.sub.2+CO.sub.2 (IV)
[0028] This is an important step because carbon monoxide, in
addition to being highly toxic to humans, is a poison to fuel
cells. The concentration of carbon monoxide should preferably be
lowered to a level that can be tolerated by fuel cells, typically
below 50 ppm. Generally, the water gas shift reaction can take
place at temperatures of from 150.degree. C. to 600.degree. C.
depending on the catalyst used. Under such conditions, most of the
carbon monoxide in the gas stream is converted in this step.
[0029] Low temperature shift catalysts operate at a range of from
about 150.degree. C. to about 300.degree. C. and include for
example, copper oxide, or copper supported on other transition
metal oxides such as zirconia, zinc supported on transition metal
oxides or refractory supports such as silica, alumina, zirconia,
etc., or a noble metal such as platinum, rhenium, palladium,
rhodium or gold on a suitable support such as silica, alumina,
zirconia, and the like.
[0030] High temperature shift catalysts are preferably operated at
temperatures ranging from about 300.degree. C. to about 600.degree.
C. and can include transition metal oxides such as ferric oxide or
chromic oxide, and optionally including a promoter such as copper
or iron silicide. Also included, as high temperature shift
catalysts are supported noble metals such as supported platinum,
palladium and/or other platinum group members.
[0031] The processing core utilized to carry out this step can
include a packed bed of high temperature or low temperature shift
catalyst such as described above, or a combination of both high
temperature and low temperature shift catalysts. The process should
be operated at any temperature suitable for the water gas shift
reaction, preferably at a temperature of from 150.degree. C. to
about 400.degree. C. depending on the type of catalyst used.
Optionally, a cooling element such as a cooling coil may be
disposed in the processing core of the shift reactor to lower the
reaction temperature within the packed bed of catalyst. Lower
temperatures favor the conversion of carbon monoxide to carbon
dioxide. Also, a purification processing step C can be performed
between high and low shift conversions by providing separate steps
for high temperature and low temperature shift with a
desulfurization module between the high and low temperature shift
steps.
[0032] Process step F is a cooling step performed in one
illustrative embodiment by a heat exchanger. The heat exchanger can
be of any suitable construction including shell and tube, plate,
spiral, etc. Alternatively a heat pipe or other form of heat sink
may be utilized. The goal of the heat exchanger is to reduce the
temperature of the gas stream to produce an effluent having a
temperature preferably in the range of from about 90.degree. C. to
about 150.degree. C.
[0033] Oxygen is added to the process in step F. The oxygen is
consumed by the reactions of process step G described below. The
oxygen can be in the form of air, enriched air, or substantially
pure oxygen. The heat exchanger may by design provide mixing of the
air with the hydrogen rich gas. Alternatively, the illustrative
embodiment of process step D may be used to perform the mixing.
[0034] Process step G is an oxidation step wherein almost all of
the remaining carbon monoxide in the effluent stream is converted
to carbon dioxide. The processing is carried out in the presence of
a catalyst for the oxidation of carbon monoxide and may be in any
suitable form, such as pellets, spheres, monolith, etc. Oxidation
catalysts for carbon monoxide are known and typically include noble
metals (e.g., platinum, palladium) and/or transition metals (e.g.,
iron, chromium, manganese), and/or compounds of noble or transition
metals, particularly oxides. A preferred oxidation catalyst is
platinum on an alumina washcoat. The washcoat may be applied to a
monolith, extrudate, pellet or other support. Additional materials
such as cerium or lanthanum may be added to improve performance.
Many other formulations have been cited in the literature with some
practitioners claiming superior performance from rhodium or alumina
catalysts. Ruthenium, palladium, gold, and other materials have
been cited in the literature as being active for this use.
[0035] Two reactions occur in process step G: the desired oxidation
of carbon monoxide (formula V) and the undesired oxidation of
hydrogen (formula VI) as follows:
CO+1/2O.sub.2.fwdarw.C0.sub.2 (V)
H.sub.2+1/2O.sub.2.fwdarw.H.sub.2O (VI)
[0036] The preferential oxidation of carbon monoxide is favored by
low temperatures. Since both reactions produce heat it may be
advantageous to optionally include a cooling element such as a
cooling coil disposed within the process. The operating temperature
of process is preferably kept in the range of from about 90.degree.
C. to about 150.degree. C. Process step G preferably reduces the
carbon monoxide level to less than 50 ppm, which is a suitable
level for use in fuel cells, but one of skill in the art should
appreciate that the present invention can be adapted to produce a
hydrogen rich product with of higher and lower levels of carbon
monoxide.
[0037] The effluent exiting the fuel processor is a hydrogen rich
gas containing carbon dioxide and other constituents which may be
present such as water, inert components (e.g., nitrogen, argon),
residual hydrocarbon, etc. Product gas may be used as the feed for
a fuel cell or for other applications where a hydrogen rich feed
stream is desired. Optionally, product gas may be sent on to
further processing, for example, to remove the carbon dioxide,
water or other components.
[0038] In one illustrative embodiment of a fuel processor, a
compact fuel processor is of modular construction with individual
modular units, which are separable, rearrangeable, and individually
replaceable. Referring to FIG. 2, the compact fuel processor 100
includes a series of individual modules (110, 120, 130, 140, 150,
160 and 170). The modular units may be used in any orientation,
e.g., vertical or horizontal orientation, and is adapted to be used
in conjunction with a fuel cell such that the hydrogen rich product
gas of the reactor described herein is supplied directly to a fuel
cell as a feed stream. While the modules can have any cross
sectional configuration, such as circular, rectangular, triangular,
etc., a circular cross section is preferred with the fuel processor
100 being of a generally tubular shape.
[0039] Fuel processor 100 as shown in FIG. 2 effects the process
diagrammatically illustrated in FIG. 1. Feed stream F is introduced
through inlet pipe 102 and product gas P is drawn off via outlet
pipe 103. The apparatus 100 includes several modules that may be
stacked to form a modular assembly that can be modified by the
replacement of individual modules. Each module performs a separate
operational function and is generally configured as shown in FIG.
2. Module 110 is the autothermal reforming module corresponding to
process step A of FIG. 1. Module 120 is a cooling step
corresponding to process step B of FIG. 1. In this illustrative
embodiment, heat exchanger 121 is shown as a general heat sink for
Module 120. Module 130 is a purifying module corresponding to
process step C of FIG. 1. Module 140 is an optional mixing step
corresponding to process step D of FIG. 1. Feed nozzle 131 provides
an optional water stream feed to Module 140 to aid in driving the
water gas shift reaction (Equation IV) of Module 150. Module 150 is
a water gas shift module corresponding to process step E of FIG. 1.
Feed nozzle 151 provides a source for oxygen to process gas for the
oxidation reaction (Equation V) of Module 170. Module 150 also
contains a heat exchanger (not shown) positioned within or
surrounding the catalyst bed so as to maintain a desired water gas
shift reaction temperature. Module 160 is a cooling step
corresponding to process step F of FIG. 1. In this illustrative
embodiment, heat exchanger 161 is shown as a general heat sink for
Module 160. Module 170 is an oxidation step corresponding to
process step G of FIG. 1. Module 170 also contains a heat exchanger
(not shown) positioned within or surrounding the catalyst bed so as
to maintain a desired oxidation reaction temperature. One of skill
in the art should appreciate that the process configuration
described in this illustrative embodiment may vary depending on
numerous factors, including but not limited to feedstock quality
and required product quality.
[0040] The present invention specifically relates to the methods
and apparatus for heating a catalyst bed for start-up and for
providing heat to a catalyst bed during transient operation to
maintain desired reaction temperatures. Transient operation
includes but is not limited to hydrocarbon fuel feedstock changes
to the fuel processor, process upsets, changes in catalyst
activity, and increased or decreased volumetric throughput of feed
to the fuel processor. In fuel processors such as the ones
described above, there are several catalysts that may be used with
the present invention, including autothermal reforming catalysts,
partial oxidation catalysts, steam reforming catalysts, water gas
shift catalysts, preferential oxidation catalysts, and sulfur
absorbents. In these exothermic catalyst beds, heating the catalyst
to reaction temperature is important for efficiently starting-up a
fuel processor from a cold start. Because one envisioned use for
compact fuel processors is in automotive vehicles, a solution
utilizing electrical heating elements is desirable. Furthermore,
transient operation is an important issue for ensuring stable
hydrogen rich gas supply for a fuel cell that is fed directly from
a fuel processor.
[0041] In general, an electrical heating element may directly or
indirectly heat the catalyst. The direct heating of catalyst is
achieved by having direct contact of the heater element with the
catalyst. Indirect heating is achieved by direct heating of a
fluid, such as a process flow, which in turn flows through the
catalyst, thereby transferring heat to the catalyst. Additionally,
indirect heating may be achieved by placing the heating element
within a sheath which is then either in direct contact with the
catalyst or fluid which flows through the catalyst. By these means,
catalyst of many forms may employ this catalyst heater including
pellets, extrudates, spheres, and monoliths. The catalyst heater in
accordance with this invention can be made of any resistive wire,
cartridges or rods that can be formed as outlined below. A power
source, such as an electric power source, provides the energy to
produce the heat.
[0042] Referring now to FIG. 3, face heater 300 can be utilized to
provide heat to a catalyst bed face 310. The catalyst bed face is
represented in this illustrative embodiment as one end of a
cylindrically shaped catalyst bed. It will be appreciated by one of
skill in the art that the orientation of the catalyst bed may
either be vertical or horizontal in the present invention. In this
illustrative embodiment, face heater 300 is an electrical heating
element formed in a spiral design along the face of the catalyst
bed, although other illustrative embodiments may be utilized to
provide sufficient heat transfer to the catalyst bed face. By
passing a small flow of reactants through the electrical heating
element and catalyst bed, the exothermic reaction is initiated at
the face of the catalyst bed. The heat provided by the face heater
diffuses through the volume of the catalyst bed and additionally
the heat of reaction produced at the catalyst bed face propagates
throughout the catalyst bed thereby heating the catalyst bed for
start-up. A preferred aspect of this illustrative embodiment is the
use of the face heater 300 on the upstream face of the catalyst bed
(i.e. the face of the catalyst bed that sees the reactor feed) such
that the heat of reaction is carried into the "cold" catalyst to
improve start-up efficiency of the catalyst.
[0043] Referring now to FIG. 4, the electrical heating element 400
is woven through the catalyst bed 410. In this illustrative
embodiment, the electrical heating element is woven through either
a catalyst bed of pellets, extrudates, spheres, etc., or through a
monolithic catalyst structure. The weaving design (such as a coil)
may be designed for optimal heating of the catalyst bed. This
illustrative embodiment provides heating from the inside of the
catalyst outwards. The flowing a fluid through the catalyst during
heating is optional.
[0044] Referring now to FIG. 5, the electrical heating element 500
is wrapped around a monolithic catalyst structure 510. This
provides heating from the outside of the catalyst towards the
center. The flowing a fluid through the catalyst during heating is
optional.
[0045] Another illustrative embodiment includes a reactor in a fuel
processor that includes a catalyst bed, a cooling coil positioned
within the catalyst bed for removing excess heat during normal
operation, and an electrical heating element positioned within the
cooling coil for heating the catalyst to a desired reaction
temperature during start-up and during transient operation. This is
an example of sheathed heating as described above. One of skill in
the art should appreciate that many advantages of this illustrative
embodiment are that it provides heat to the catalyst for fast and
efficient start-up, it preheats the hydrocarbon fuel feed to the
fuel processor which may pass through the cooling coil in a compact
fuel processor design, and it assists the reactor in maintaining
reaction temperature during transient operation.
[0046] While the apparatus, compositions and methods of this
invention have been described in terms of preferred or illustrative
embodiments, it will be apparent to those of skill in the art that
variations may be applied to the process described herein without
departing from the concept and scope of the invention. All such
similar substitutes and modifications apparent to those skilled in
the art are deemed to be within the scope and concept of the
invention as it is set out in the following claims.
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