U.S. patent application number 10/006876 was filed with the patent office on 2002-07-11 for method for reducing the carbon monoxide content of a hydrogen rich gas.
Invention is credited to Krause, Curtis L., Naae, Doug, Stevens, James F..
Application Number | 20020090334 10/006876 |
Document ID | / |
Family ID | 22951014 |
Filed Date | 2002-07-11 |
United States Patent
Application |
20020090334 |
Kind Code |
A1 |
Stevens, James F. ; et
al. |
July 11, 2002 |
Method for reducing the carbon monoxide content of a hydrogen rich
gas
Abstract
A method and apparatus for reducing the carbon monoxide content
of a hydrogen rich gas including a catalyst bed containing an
oxidation catalyst, a porous tube positioned substantially within
the catalyst bed for distributing an oxygen-containing stream
throughout the catalyst bed, and a cooling jacket for maintaining
the reactor operating temperature in a desired range. The porous
tube can be constructed as a sintered stainless steel tube or as an
alumina tube or as any equivalent porous tube that is known to
those of skill in the art to perform the objectives of this method
and apparatus. The porous tube is generally positioned along the
length of the catalyst bed in manner that optimizes dispersion of
the oxygen-containing stream throughout the catalyst bed. The
reactor operating temperature is controlled by a cooling jacket to
from about 90.degree. C. to about 180.degree. C., more preferably
from about 90.degree. C. to about 150.degree. C. The cooling jacket
should contain a circulating coolant that can be water, steam, air,
or the hydrocarbon fuel to the fuel processor.
Inventors: |
Stevens, James F.; (Katy,
TX) ; Krause, Curtis L.; (Houston, TX) ; Naae,
Doug; (Sugar Land, TX) |
Correspondence
Address: |
STEPHEN H. CAGLE
HOWREY, SIMON, ARNOLD & WHITE, LLP
750 BERING DRIVE
HOUSTON
TX
77057
US
|
Family ID: |
22951014 |
Appl. No.: |
10/006876 |
Filed: |
December 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60251226 |
Dec 5, 2000 |
|
|
|
Current U.S.
Class: |
423/247 ;
422/176 |
Current CPC
Class: |
B01J 2208/00176
20130101; B01J 2219/0002 20130101; C01B 2203/0805 20130101; B01J
8/009 20130101; C01B 3/386 20130101; C01B 2203/0244 20130101; C01B
2203/0455 20130101; C01B 2203/0894 20130101; B01J 2219/182
20130101; C01B 3/382 20130101; C01B 2203/1041 20130101; Y02E 60/50
20130101; C01B 2203/0877 20130101; B01J 8/0285 20130101; B01J
19/2485 20130101; B01J 2208/00203 20130101; C01B 2203/147 20130101;
H01M 8/0612 20130101; B01J 2219/00083 20130101; C01B 3/384
20130101; C01B 3/16 20130101; B01J 8/0278 20130101; B01J 8/067
20130101; C01B 2203/1276 20130101; B01J 8/0453 20130101; C01B 3/38
20130101; C01B 2203/0283 20130101; C01B 2203/0844 20130101; H01M
8/0631 20130101; B01J 2208/00194 20130101; C01B 2203/1082 20130101;
C01B 2203/1235 20130101; C01B 2203/0288 20130101; C01B 2203/142
20130101; B01J 19/0013 20130101; B01J 2208/00141 20130101; B01J
2208/00716 20130101; C01B 2203/044 20130101; B01J 2208/00415
20130101; B01J 2219/00135 20130101; Y02P 20/52 20151101; C01B
2203/0866 20130101; H01M 8/04022 20130101; B01J 2208/00407
20130101; C01B 3/583 20130101; C01B 2203/0485 20130101; B01J 8/0488
20130101; B01J 2208/00814 20130101; B01J 2208/025 20130101; C01B
2203/066 20130101; C01B 2203/146 20130101; C01B 2203/1023 20130101;
C01B 2203/1035 20130101; C01B 2203/1604 20130101; B01J 8/0423
20130101; C01B 2203/085 20130101; C01B 2203/1011 20130101; B01J
19/2475 20130101; C01B 2203/047 20130101; C01B 2203/0883 20130101;
B01J 8/048 20130101; B01J 8/0492 20130101; B01J 2219/185 20130101;
C01B 2203/0465 20130101; C01B 2203/1205 20130101; C01B 2203/0495
20130101; H01M 8/0668 20130101; C01B 2203/1017 20130101; B01J
8/0496 20130101; C01B 3/48 20130101; H01M 8/04037 20130101; B01J
2219/1944 20130101; H01M 8/04059 20130101; C01B 2203/80 20130101;
C01B 2203/82 20130101 |
Class at
Publication: |
423/247 ;
422/176 |
International
Class: |
C10K 001/20; F01N
003/08 |
Claims
What is claimed is:
1. A method for reducing the carbon monoxide content of a hydrogen
rich gas, comprising: providing a reactor having a catalyst bed
containing an oxidation catalyst; distributing an oxygen-containing
stream throughout the catalyst bed in the presence of the hydrogen
rich gas and the oxidation catalyst bed; maintaining the reactor
operating temperature in a desired range.
2. The method of claim 1, wherein the reactor has a porous tube
substantially positioned within the catalyst bed for distributing
the oxygen-containing stream throughout the catalyst bed.
3. The method of claim 2, wherein the oxygen-containing stream is
maintained at a higher pressure than the hydrogen rich gas.
4. The method of claim 1, wherein the desired range for the reactor
operating temperature minimizes the oxidation of hydrogen.
5. The method of claim 1, wherein the desired range for the reactor
operating temperature is from about 90.degree. C. to about
180.degree. C.
6. The method of claim 1, wherein the desired range for the reactor
operating temperature is from about 90.degree. C. to about
150.degree. C.
7. The method of claim 1, wherein the reactor has a cooling jacket
for maintaining the reactor operating temperature.
8. The method of claim 7, wherein the cooling jacket contains a
circulating coolant selected from the group consisting of water,
steam, air, and hydrocarbon fuel.
9. An apparatus for selectively reducing the carbon monoxide
content of a hydrogen rich gas, comprising: a catalyst bed
containing an oxidation catalyst; a porous tube positioned
substantially within the catalyst bed for distributing an
oxygen-containing stream throughout the catalyst bed; and a cooling
jacket for maintaining the reactor operating temperature in a
desired range.
10. The apparatus of claim 9, wherein the porous tube is a sintered
stainless steel tube.
11. The apparatus of claim 9, wherein the porous tube is an alumina
tube.
12. The apparatus of claim 9, wherein the porous tube is
substantially positioned along the catalyst bed length.
13. The apparatus of claim 9, wherein the desired range for the
reactor operating temperature is from about 90.degree. C. to about
180.degree. C.
14. The apparatus of claim 9, wherein the desired range for the
reactor operating temperature is from about 90.degree. C. to about
150.degree. C.
15. The apparatus of claim 9, wherein the cooling jacket contains a
circulating coolant selected from the group consisting of water,
steam, air, and hydrocarbon fuel.
16. A reactor module for use in a compact fuel processor for
selectively reducing the carbon monoxide content of a hydrogen rich
gas, comprising: a catalyst bed containing an oxidation catalyst; a
porous tube positioned substantially within the catalyst bed along
the catalyst bed length for distributing an oxygen-containing
stream throughout the catalyst bed; and a cooling jacket
surrounding the catalyst bed for maintaining the reactor operating
temperature in a desired range.
17. The reactor of claim 16, wherein the porous tube is a sintered
stainless steel tube.
18. The reactor of claim 16, wherein the porous tube is an alumina
tube.
19. The reactor of claim 16, wherein the desired range for the
reactor operating temperature is from about 90.degree. C. to about
180.degree. C.
20. The reactor of claim 16, wherein the desired range for the
reactor operating temperature is from about 90.degree. C. to about
150.degree. C.
21. The reactor of claim 16, wherein the cooling jacket contains a
circulating coolant selected from the group consisting of water,
air, and hydrocarbon fuel.
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 multistep 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).
[0004] As a practical matter, the hydrogen rich gas also contains
other chemical species such as nitrogen, hydrogen sulfide, carbon
monoxide, carbon dioxide, and carbonyl sulfide. For many uses, such
as fuel for fuel cells or as feed to an ammonia plant, carbon
monoxide levels must be reduced greatly. Catalyst enhanced
water-gas shift reaction steps are generally used to reduce the
carbon monoxide level to 0.1 to 0.5 mole %. For uses that require
lower concentrations of carbon monoxide, a common practice is to
oxidize the carbon monoxide to carbon dioxide by the addition of
air to the hydrogen rich product gas in the presence of catalysts
that promote the oxidation of carbon monoxide over the oxidation of
hydrogen to water. As commonly practiced this method of removing
carbon monoxide can result in large losses of hydrogen if the heat
produced by the exothermic oxidation process is not removed since
the catalysts used tend to become less specific for carbon monoxide
oxidation as the temperature increases. In addition, if the
temperature is too low, the carbon monoxide can deactivate the
catalyst.
[0005] Despite the above work, there remains a need for a simple
unit for use with a fuel cell--one that can produce hydrogen rich
gas with minimal carbon monoxide impurity.
SUMMARY OF THE INVENTION
[0006] The present invention utilizes a porous distribution tube to
add air for carbon monoxide oxidation throughout the length of a
catalyst bed. By distributing the air injection, hot and cold areas
in the catalyst bed can be avoided, thereby improving the
selectivity of the reactor to carbon monoxide oxidation.
[0007] One illustrative embodiment of the present invention
includes a method and apparatus for reducing the carbon monoxide
content of a hydrogen rich gas having a catalyst bed containing an
oxidation catalyst, a porous tube positioned substantially within
the catalyst bed for distributing an oxygen-containing stream
throughout the catalyst bed, and a cooling jacket for maintaining
the reactor operating temperature in a desired range. The porous
tube can be constructed as a sintered stainless steel tube or as an
alumina tube or as any equivalent porous tube that is known to
those of skill in the art to perform the objectives of this method
and apparatus. The porous tube is positioned along the catalyst bed
length, or may be aligned in any orientation that one of skill in
the art would appreciate to result in optimal dispersion of the
oxygen-containing stream throughout the catalyst bed. In one
illustrative embodiment of the present invention is for the reactor
operating temperature to be controlled by the cooling jacket from
about 90.degree. C. to about 180.degree. C., more preferably from
about 90.degree. C. to about 150.degree. C. The cooling jacket
should contain a circulating coolant that can be water, steam, or
air, or, in one illustrative embodiment, the hydrocarbon fuel feed
to the fuel processor for energy efficiency.
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 an improved apparatus and method for
selectively oxidizing carbon monoxide in accordance with the
present invention
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0011] The present invention is generally directed to an improved
method for reducing the carbon monoxide content of a hydrogen rich
gas stream. In one illustrative embodiment, the present invention
uses a porous distribution tube to add an oxygen-containing stream
for the carbon monoxide oxidation throughout the length of a
catalyst bed instead of one or two fixed injection points as is
currently practiced. By distributing the air injection hot and cold
areas in the catalyst bed can be avoided, thereby improving the
selectivity of the reactor to carbon monoxide oxidation. In one
illustrative embodiment of the present invention, the apparatus and
methods described relate to improved reduction of the carbon
monoxide content of a hydrogen rich gas stream in a compact fuel
processor for feeding a fuel cell. 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. 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.
[0012] The hydrocarbon fuel feed to a fuel processor 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 that 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.
[0013] 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.
[0014] 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).
[0015] 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.
[0016] 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)
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.). Desulfirization 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)
[0022] 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.
[0023] 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.
[0024] 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+C0.sub.2 (IV)
[0025] 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.
[0026] 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.
[0027] High temperature shift catalysts are preferably operated at
temperatures ranging from about 300.degree. 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.
[0028] 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.
[0029] 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.
[0030] 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 embodiment of
process step D may be used to perform the mixing.
[0031] 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.
[0032] 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.CO.sub.2 (V)
H.sub.2+1/2O.sub.2.fwdarw.H.sub.2O (VI)
[0033] 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 higher and lower levels of carbon
monoxide.
[0034] 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.
[0035] In one illustrative embodiment of the above described fuel
processor, a compact fuel processor is of modular construction with
individual modular units, which are separable, rearrangeable, and
individually replaceable.
[0036] The present invention is an improvement to process step G
described above, and utilizes a porous distribution tube to add air
for the carbon monoxide oxidation throughout the catalyst bed
length instead of one or two fixed injection points. By
distributing the air injection hot and cold areas in the catalyst
bed can be avoided.
[0037] Referring to the oxidation reactor 200 in FIG. 2, air A is
injected through a porous tube 210, such as a sintered stainless
steel tube manufactured by the Mott Corporation or an alumina tube
as manufactured by the NGK corporation of Japan. By maintaining the
air supply at a slightly higher pressure than the hydrogen rich gas
feed H, supply air A will enter the chamber containing a carbon
monoxide selective oxidation catalyst 220, such as that
manufactured by the Engelhard Corporation. Upon coming into contact
with the catalyst 220, the oxygen in the air will oxidize carbon
monoxide and hydrogen (according to equations V and VI, above)
causing the catalyst 220 and reactor 200 to warm. By using a
cooling jacket 230 containing water, steam, air, or a cool
hydrocarbon fuel feed stream, reactor 200 can be maintained in the
desired operating temperature range of from about 90.degree. C. to
about 180.degree. C. This oxidation step 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 P with higher and lower levels of carbon
monoxide.
[0038] In view of the above disclosure, one of skill in the art
should understand and appreciate that one illustrative embodiment
of the present invention includes a method and apparatus for
reducing the carbon monoxide content of a hydrogen rich gas. Such
an illustrative embodiment includes a catalyst bed containing an
oxidation catalyst, a porous tube positioned substantially within
the catalyst bed for distributing an oxygen-containing stream
throughout the catalyst bed, and a cooling jacket for maintaining
the reactor operating temperature in a desired range. The porous
tube can be constructed as a sintered stainless steel tube or as an
alumina tube or as any equivalent porous tube that is known to
those of skill in the art to perform the objectives of this method
and apparatus. The porous tube is positioned along the catalyst bed
length, or may be aligned in any orientation that one of skill in
the art would appreciate to result in optimal dispersion of the
oxygen-containing stream throughout the catalyst bed. In one
illustrative embodiment of the present invention is for the reactor
operating temperature to be controlled by the cooling jacket from
about 90.degree. C. to about 180.degree. C., more preferably from
about 90.degree. C. to about 150.degree. C. The cooling jacket
should contain a circulating coolant that can be water, air, or the
hydrocarbon fuel to the fuel processor for energy efficiency
improvements.
[0039] The present invention is intended not only for general
oxidation reactors, but is also a preferred technology selection
for the carbon monoxide oxidation reactors of fuel processors.
Because of the direct feed to a fuel cell, there is a great need to
ensure continuous on-specification hydrogen rich gas produced from
compact fuel processors.
[0040] 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.
* * * * *