U.S. patent application number 10/487579 was filed with the patent office on 2005-04-07 for reformate stream cooler with a catalytic coating for use in a gas generation system.
Invention is credited to Brakonier, Pascal, Corneille, Marcel, Griesmeier, Uwe, Keppeler, Berthold.
Application Number | 20050074377 10/487579 |
Document ID | / |
Family ID | 7697330 |
Filed Date | 2005-04-07 |
United States Patent
Application |
20050074377 |
Kind Code |
A1 |
Brakonier, Pascal ; et
al. |
April 7, 2005 |
Reformate stream cooler with a catalytic coating for use in a gas
generation system
Abstract
A gas generation system comprises a reformer (1) to generate a
hydrogen-containing reformate stream (4), a reformate stream cooler
(2), and a shift stage (3) down-stream of the reformate stream
cooler to purify the reformate stream. The surfaces of the cooler
that come into contact with the reformate stream are coated with a
material that contains at least one catalytically active
constituent. The coating is selected such that it also protects
against corrosion and sooting in the presence of oxidizing,
reducing, and carbon-containing gases. By directly utilizing the
coated reformate stream cooler as a catalytically active reactor
unit, a water-gas shift reaction to reduce the carbon monoxide
concentration takes place to some extent in the cooler prior to the
reformate stream entering the actual shift stage. This enables the
size of subsequent shift stage(s) to be reduced.
Inventors: |
Brakonier, Pascal;
(Koeln-Muelheim, DE) ; Corneille, Marcel;
(Stuttgart, DE) ; Griesmeier, Uwe; (Markdorf,
DE) ; Keppeler, Berthold; (Owen, DE) |
Correspondence
Address: |
SEED INTELLECTUAL PROPERTY LAW GROUP PLLC
701 FIFTH AVE
SUITE 6300
SEATTLE
WA
98104-7092
US
|
Family ID: |
7697330 |
Appl. No.: |
10/487579 |
Filed: |
September 21, 2004 |
PCT Filed: |
August 30, 2002 |
PCT NO: |
PCT/EP02/09708 |
Current U.S.
Class: |
422/198 |
Current CPC
Class: |
C01B 2203/0288 20130101;
C01B 2203/0872 20130101; C01B 2203/1082 20130101; B01J 19/0026
20130101; C01B 2203/1041 20130101; C01B 2203/0205 20130101; C01B
2203/1064 20130101; B01J 19/02 20130101; B01J 12/007 20130101; B01J
2219/0236 20130101; B01J 2219/00247 20130101; C01B 2203/1035
20130101; F28F 19/02 20130101; C01B 2203/1094 20130101; C01B 3/48
20130101 |
Class at
Publication: |
422/198 |
International
Class: |
F28D 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2001 |
DE |
10142794.8 |
Claims
1. A gas generation system comprising: a reformer to generate a
reformate stream, a cooler downstream of the reformer to cool the
reformate stream, and a shift stage downstream of the cooler to
reduce the carbon monoxide concentration in the reformate stream,
wherein surfaces of the cooler that come into contact with the
reformate stream are coated with a cooler coating that is
soot-inhibiting and is catalytically active with respect to the
water-gas shift reaction.
2. The system of claim 1, wherein the composition of the cooler
coating varies along the reformate stream flow path.
3. The system of claim 2, wherein the cooler coating comprises at
least two areas of different composition, which differ with respect
to soot-inhibiting activity, or catalytic activity with respect to
the water-gas shift reaction, or both.
4. The system of any one of claims 1 to 3, wherein the system
further comprises a cooler feed line connecting the reformer to the
cooler and a cooler discharge line connecting the cooler to the
shift stage, and wherein the cooler feed line and the cooler
discharge line are coated with a line coating that is
soot-inhibiting material and is catalytically active with respect
to the water-gas shift reaction.
5. The system of claim 4 wherein the line coating exhibits greater
soot-inhibiting activity and lesser activity with respect to the
water-gas shift reaction than the cooler coating.
6. The system of claim 4 wherein the cooler coating comprises a
first material of the same composition as the line coating, and a
second material that exhibits greater catalytic activity with
respect to the water-gas shift reaction and a lower soot-inhibiting
activity than the material.
7. The system of claim 1, wherein the surfaces of the cooler that
come into contact with the reformate stream are coated with at
least one layer of a base material, wherein the base material is
disposed between the surfaces and the cooler coating, and wherein
the base material comprises a metal-containing substance, selected
from the group consisting of chromium, silicon, aluminum,
magnesium, manganese, titanium, rare earths, compounds of chromium,
silicon, aluminum, magnesium, manganese, titanium and rare earths,
and alloys of chromium, silicon, aluminum, magnesium, manganese,
titanium and rare earths.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to German Application No.
10142794.8, filed Aug. 31, 2001, which priority application is
incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention concerns a reformate stream cooler in which
the surfaces of the cooler that come into contact with the
reformate stream are coated with a catalytically active
material.
[0004] 2. Description of the Related Art
[0005] Gas generation systems comprising a reformer to generate a
reformate stream, a reformate stream cooler, and a downstream shift
stage to purify the reformate stream are used in fuel-cell-powered
motor vehicles to provide the hydrogen that is needed to operate
the fuel cells. In addition to hydrogen, the reforming of
carbon-containing fuels produces by-products such as carbon
monoxide, which must only be present in very small quantities in
proton-exchange membrane (PEM) fuel cells. Accordingly gas
purification upstream of the fuel cell is required. Present
technology for the reduction of the carbon monoxide concentration
in hydrogen-rich streams include the water-gas shift reaction and
the selective oxidation of carbon monoxide in fixed-bed reactors
with suitable selective oxidation catalysts. However, at the
necessarily low operating temperatures, the water-gas shift
reaction Is comparatively slow, so that higher amounts of catalyst
are required, leading to larger shift stages and/or increased costs
due to the higher noble metal content. The selective oxidation
units (for selective oxidation of carbon monoxide) are not able to
handle high carbon monoxide concentrations (>2%).
[0006] Moreover, as for example described in U.S. Pat. No.
5,873,951, the generation of hydrogen from carbon-containing fuels
brings with it the problem of sooting or coking (i.e. the formation
of carbon black or carburization). This problem, also known as
metal dusting corrosion, is encountered where hot carbon
monoxide-containing gas cools on a metal surface and the carbon
monoxide breaks down into carbon and carbon dioxide in the
air-carbon reaction. In this manner carbides are formed in the
metal structure, which leads to the degradation of the material
structure. Metal dusting corrosion not only affects steel, but also
nickel-based materials, for example. The intensity of the corrosion
increases with carbon monoxide partial pressure and the molar
carbon monoxide/carbon dioxide ratio at the metal surface.
[0007] Metal dusting corrosion can be prevented by carrying out the
desired process outside of the critical temperature range for metal
dusting corrosion, or by "bypassing" the critical temperature range
as rapidly as possible. A common method of bypassing the critical
temperature range is quenching the reformate stream by introducing
water into the reformate stream between the reformer and the shift
stage. The disadvantage of this method is that the thermal energy
contained in the reformate stream can not then be utilized
elsewhere, which leads to a significantly lower efficiency.
[0008] To provide a solution to the problem of efficiently reducing
carbon monoxide in a compact system, EP 0 974 393 A2 provides a gas
generation system comprising a reformer, a carbon monoxide shift
reactor, and a catalytic burner. The publication describes that the
fuel gas is conducted in counter-current flow, which allows
efficient cooling of the carbon monoxide shift stage (which shifts
the shift gas balance in the reformate stream towards a lower
carbon monoxide concentration), in a more compact design.
[0009] However, there remains a need for an improved gas generation
system for real-life applications that offers consistent high
performance and reliability over the entire lifetime of the system,
as well as a more compact design.
BRIEF SUMMARY OF THE INVENTION
[0010] A gas generation system comprises a reformer to generate a
hydrogen-containing reformate stream, a reformate stream cooler (or
heat exchanger), and a shift stage downstream of the reformate
cooler to purify the reformate stream. The surfaces of the cooler
that come into contact with the reformate stream are coated with a
material that contains at least one catalytically active
constituent. The coating is selected such that it also protects
against corrosion and sooting in the presence of oxidizing,
reducing, and carbon-containing gases. By directly utilizing the
coated reformate stream cooler as a catalytically active reactor
unit, a water-gas shift reaction to reduce the carbon monoxide
concentration takes place to some extent in the cooler prior to the
reformate stream entering the actual shift stage. This enables the
size of the subsequent shift stage(s) to be reduced, resulting in a
more lightweight and compact gas generation system.
[0011] These and other aspects will be evident upon reference to
the attached Figures and following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a flow diagram for a conventional system for the
reforming of carbon-containing fuels with subsequent gas
purification and water injection.
[0013] FIG. 2 is a flow diagram for an embodiment of the present
system for the reforming of carbon-containing fuels with gas
purification and reformate stream cooling.
DETAILED DESCRIPTION OF THE INVENTION
[0014] In order to be able to reliably operate a gas generation
system, for example in a fuel-cell-powered motor vehicle, the
carbon monoxide concentration in the reformate stream has to be
reduced. Reducing the carbon monoxide concentration also suppresses
or prevents the reaction that is responsible for formation and
deposition of carbon black, which leads to carburization and
consequently to the embrittlement of components. Components that
are at risk include pipes and channels exposed to the carbon
monoxide-containing reformate stream, heat exchangers used to cool
the reformate stream, shift stages, nozzles, and all of the
components connected downstream of the reformer, but upstream of
the fuel cell. Moreover, some of the catalyst material in these
components may be clogged by soot particulates, rendering it
unavailable for the catalytic reaction. The transfer of heat and
materials in heat exchangers and similar components is also
inhibited by the deposits (sooting). Reactors in gas generation
system are typically constructed of high-temperature-resistant
alloys, which provide a long service life. But in a carbon
monoxide-containing reformate stream atmosphere, iron and nickel,
which are constituents of such alloys, exhibit significant
catalytic activity with respect to sooting.
[0015] FIG. 1 shows a conventional method of preventing metal
dusting corrosion. The critical temperature is bypassed by
quenching the reformate stream 4 by introducing water 5 into the
reformate stream between a reformer 1 and a shift stage 3. This
process has the disadvantage that thermal energy contained in the
reformate stream cannot be used to heat other reactant streams.
[0016] To solve this problem, the present gas generation system,
which comprises a reformer 1 to generate a reformate stream 4, a
reformate stream cooler 2, and a shift stage 3 connected downstream
of cooler 2 for reformate stream purification, may be employed. The
surfaces of cooler 2 that come into contact with the reformate
stream 4 are coated with a soot-inhibiting material that is also
catalytically active with respect to the water-gas shift
reaction.
[0017] In order to vary the catalytic activity with respect to the
water-gas shift reaction and/or the soot-inhibiting activity, the
composition of the coating may vary along the flow path. In one
embodiment, the coating contains at least two areas of different
composition in terms of soot-inhibiting activity and/or catalytic
activity with respect to the water-gas shift reaction.
[0018] In another embodiment, cooler 2 comprises a feed line and a
discharge line, connecting reformer 1 with cooler 2 and cooler 2
with the downstream shift stage 3, respectively. The lines are
coated, with a composition that exhibits greater soot-inhibiting
activity and lesser catalytic activity with respect to the
water-gas shift reaction than the coating inside cooler 2.
[0019] In another embodiment, cooler 2 and the feed line and the
discharge line are coated with a material of the same composition,
and cooler 2 is coated with an additional material, selected to
exhibit high catalytic activity with respect to the water-gas shift
reaction and lower soot-inhibiting activity than the common
coating.
[0020] The following references relating to the exhaust
gas/catalytic converter area of internal combustion engines provide
information on chemical substances and/or chemical compounds that
may be used to promote certain reactions, and/or to suppress, or
even prevent, other chemical reactions: WO 00/33408, EP 414 573 B1,
EP 427 493 A2, EP 637 461 A1, WO 93/01130, EP 305 119 B1, EP 428
753 B1, EP 21325 A1, EP 630 289 B1, EP 238 700 B1, U.S. Pat. No.
4,503,162, "Promotion of the Water Gas Shift Reaction by Cesium
Surface", Ind. Eng. Chem. Fundam. 1986, 25, 36-42,
"Reactant-promoted reaction mechanism for Water-Gas Shift Reaction
on RH-doped CeO.sub.2", Journal of Catalysis 141, 71-81 (1993),
"Thermal stability of oxygen storage properties in a mixed
CeO.sub.2-ZrO.sub.2 system", Applied Catalysis B: Environmental 16
(1998) 105-117.
[0021] If, for example, .gamma.-Al.sub.2O.sub.3 is used as catalyst
support material, then the oxygen-ion-conducting support material
is thermally stabilized against surface losses by the addition of
oxides such as ZrO.sub.2 and/or CeO.sub.2. On the other hand, the
addition of a cerium compound to the catalytic material leads to an
Increased activity of the catalytic material for promoting the
water-gas shift reaction and acting as an oxygen storage unit.
[0022] Adding caesium compounds to the coating in the form of
alkaline doping and/or adding further alkali oxides or alkaline
earth oxides and/or metal oxides of the IIb subgroup also increases
the activity of the coating with respect to the water-gas shift
reaction. Caesium compounds that may be used include caesium oxides
or other oxygen-containing compounds that are converted to oxides
at high temperatures, such as carbonate, acetate, and nitrate.
[0023] Vanadium components that may be used in the production of
the catalyst, individually or in the form of mixtures, include
various vanadium oxides or vanadium compounds that are converted to
vanadium oxides when heated in contact with air. Suitable vanadium
oxides include V.sub.2O.sub.5, V.sub.3O.sub.7, V.sub.4O.sub.9, and
V.sub.6O.sub.13, as V.sub.2O.sub.4, and oxides such as
V.sub.2O.sub.3, V.sub.3O.sub.5, V.sub.4O.sub.7, V.sub.5O.sub.9,
V.sub.6O.sub.11, and V.sub.7O.sub.13, with V.sub.2O.sub.5 being
particularly preferred. Vanadium oxides of this type may be
produced, for example, by the thermal decomposition of ammonium
metavanadate (NH.sub.4VO.sub.3), by the heating of mixtures of
V.sub.2O.sub.3 and V.sub.2O.sub.5, or by the reduction of
V.sub.2O.sub.5 with sulphur oxide gas.
[0024] Suitable vanadium compounds that are converted to a vanadium
oxide when heated in contact with air include ammonium
metavanadate, vanadyl sulphate, vanadyl chloride, vanadyl
dichloride dihydrate, vanadyl trichloride, other vanadyl halides,
metavanadic acid, pyrovanadic acid, vanadium hydroxide, vanadyl
acetylacetonate, or vanadyl carboxylates, such as vanadyl oxalate,
with ammonium metavanadate being particularly preferred.
[0025] Oxides, such as V.sub.2O.sub.5 and SiO.sub.2, act as
protective agents against aging of the noble-metal catalyst in the
coating as they are structural promoters, which--on account of
their thermally stabilizing action--inhibit structural changes of
the noblemetal catalyst during manufacturing of the coating and
during operation of the gas generation system. The noble-metal
catalyst may comprise at least a metal, a metal-containing
compound, and/or a metal-containing alloy.
[0026] The catalytically active coating may be applied to cooler 2
using processes known in the art, such as dip-coating, spraying,
doctor blade application, or other application processes. The
coating, as well as being suitable to reduce or prevent the
formation and deposition of carbon black and subsequently the
carburization and embrittlement of the components, may also make it
possible to suppress methanation that takes place as an undesired
secondary reaction. By directly utilizing the coated cooler as a
catalytically active reactor, a water-gas shift reaction to reduce
the carbon monoxide concentration takes place to some extent in
cooler 2 prior to the actual shift stage 3. This results in some
hydrogen production occurring in cooler 2 in addition to the
hydrogen production which occurs in the reformer. This makes it
possible to reduce the size of the subsequent shift stage(s), which
in turn results in a more lightweight and compact gas generation
system. Moreover, the service life of the catalysts employed in the
shift stages is increased.
[0027] The overall efficiency of the system increases, since the
coating of cooler 2 makes it possible to extract a significant
amount of heat from the reformate stream 4. The reaction
temperatures in cooler 2 are typically in the range of 300 to
850.degree. C., preferably between 400 and 700.degree. C. A
reformate stream cooler coated in this manner is able to adjust the
thermodynamic equilibrium with respect to the water-gas shift
reaction suitable for the discharge conditions, such as
temperature, pressure, stoichiometric ratios (water/carbon monoxide
ratios), while at the same time preventing sooting.
[0028] The surfaces of cooler 2 that come into contact with the
reformate stream 4 may be coated with at least one layer of a
further base coating. This base coating is disposed between the
wall of the cooler and the coating layer and comprises at least one
metal, typically chromium, silicon, aluminum, magnesium, manganese,
titanium, rare earths, and/or compounds and/or alloys of these
substances. The base coating or "diffusion coating" may be applied
to cooler 2 in a manner known in the art. Various processes that
are appropriate for corrosion- and wear-resistant high-temperature
composite materials may be employed. Examples of possible processes
include, but are not limited to, build-up welding, thermal spray
processes, such as plasma spraying, vacuum plasma spraying,
plasma-powder surfacing, high-velocity flame spraying, or laser
coating. Other examples can be found in U.S. Pat. No. 5,873,951,
U.S. Pat. No. 6,139,649, U.S. Pat. No. 6,165,286, and U.S. Pat. No.
5,972,429. In addition to the advantages already outlined above,
the diffusion coating of the present system offers excellent
corrosion protection as well as protection against sooting in
oxidizing, reducing, and carbon-containing gases.
[0029] From the foregoing it will be appreciated that, although
specific embodiments of the invention have been described herein
for purposes of illustration, various modifications may be made
without deviating from the spirit and scope of the invention.
Accordingly, the invention is not limited except as by the appended
claims.
* * * * *