U.S. patent application number 09/999069 was filed with the patent office on 2002-06-06 for fuel cell system having two reformation reactors and method for operating same.
Invention is credited to Griesmeier, Uwe.
Application Number | 20020068205 09/999069 |
Document ID | / |
Family ID | 7665378 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020068205 |
Kind Code |
A1 |
Griesmeier, Uwe |
June 6, 2002 |
Fuel cell system having two reformation reactors and method for
operating same
Abstract
A fuel cell system includes a fuel cell unit and a
gas-generating system containing at least one reforming unit for
obtaining a hydrogen-rich reformate from a fuel. It is possible to
supply the reformate at least partly to the anode side of the fuel
cell unit. The system may include a first reforming reactor for
producing a first reformate with a high outlet temperature; a
second reforming reactor for producing a second reformate with a
second outlet temperature which is below the first outlet
temperature; a mixing element for mixing the first reformate with
at least one fuel and located between an outlet of the first
reforming reactor and an inlet of the second reforming reactor. The
second reformate may be supplied to a gas-purification system and
the purified reformate supplied to the fuel cell unit.
Inventors: |
Griesmeier, Uwe; (Markdorf,
DE) |
Correspondence
Address: |
CROWELL & MORING, L.L.P.
P.O. Box 14300
Washington
DC
20044-4300
US
|
Family ID: |
7665378 |
Appl. No.: |
09/999069 |
Filed: |
December 3, 2001 |
Current U.S.
Class: |
429/410 ;
429/423; 429/424; 429/440; 429/444 |
Current CPC
Class: |
B01J 8/04 20130101; B01J
8/06 20130101; C01B 2203/0883 20130101; H01M 8/0662 20130101; H01M
8/0612 20130101; C01B 2203/0233 20130101; B01J 2208/00274 20130101;
C01B 3/323 20130101; C01B 2203/0844 20130101; Y02P 20/52 20151101;
C01B 2203/1223 20130101; C01B 2203/1604 20130101; B01J 2208/00716
20130101; C01B 2203/0283 20130101; B01D 53/00 20130101; Y02E 60/50
20130101; C01B 2203/1064 20130101; C01B 2203/143 20130101; B01J
23/40 20130101; C01B 2203/066 20130101; B01J 2208/00823 20130101;
B01J 2219/00006 20130101; C01B 3/48 20130101; C01B 2203/047
20130101; C01B 2203/1076 20130101; C01B 2203/044 20130101; C01B
2203/141 20130101; C01B 2203/82 20130101; B01J 19/0013 20130101;
C01B 2203/0244 20130101 |
Class at
Publication: |
429/19 ; 429/20;
429/17 |
International
Class: |
H01M 008/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 2000 |
DE |
100 59 674.6 |
Claims
What is claimed is:
1. A fuel cell system, comprising: a fuel cell unit and a
gas-generating system, said gas generating system comprising: a
first reforming reactor for producing a first reformate (R1) with
an outlet temperature (T.sub.1, out); a second reforming reactor
for producing a second reformate (R2) with a second outlet
temperature (T.sub.2, out) that is below the first outlet
temperature (T.sub.1, out); and an device that supplies at least
one fuel to the first reformate (R1) between an outlet of the first
reforming reactor and an inlet of the second reforming reactor.
2. A fuel cell system according to claim 1, wherein the at least
one fuel comprises methanol.
3. A fuel cell system according to claim 1, wherein the device is a
mixing element.
4. A fuel cell system according to claim 1, further comprising a
first heat exchanger upstream from the first reforming reactor.
5. A fuel cell system according to claim 1, wherein the first
reforming reactor is an auto-thermal reactor.
6. A fuel cell system according to claim 1, wherein the second
reforming reactor is an adiabatic reactor.
7. A fuel cell system according to claim 1, further comprising a
gas purification system that can be cooled with waste gas from at
least one of an anode and a cathode of the fuel cell unit.
8. A fuel cell system according to claim 7, wherein the gas
purification system is a one-step system.
9. A fuel cell system according to claim 7, wherein the gas
purification system is a two-step system, comprising: a first
device in which the second reformate can be cooled with waste gas
from the cathode; and a second device in which the second reformate
can be cooled with waste gas from the anode of the fuel cell
unit.
10. A fuel cell system according to claim 1, further comprising a
gas purification system, an afterburner and a first heat exchanger
located downstream from the afterburner, wherein the gas
purification system, the afterburner, and the first heat exchanger
are disposed one after the other in the direction of waste gas flow
from the fuel cell unit.
11. A fuel cell system according to claim 10, further comprising an
expander disposed between the afterburner and the first heat
exchanger.
12. A fuel cell system according to claim 10, further comprising an
expander disposed in the waste gas downstream from the first heat
exchanger.
13. A fuel cell system according to claim 11, wherein the expander
is coupled with a compressor in an air supply for the fuel cell
unit.
14. A fuel cell system according to claim 1, further comprising a
reformate cooling unit disposed downstream from a gas purification
system.
15. A fuel cell system according to claim in 14, wherein the
reformate cooling unit can be cooled by a cooling medium of the
fuel cell unit.
16. A fuel cell system according to claim 1, wherein the first
reforming reactor has a non-selective catalyst and the second
reforming reactor has a selective catalyst.
17. A method for operating a fuel cell system, comprising:
supplying at least one fuel with a first inlet temperature
(T.sub.1, in) to a first reforming reactor; carrying out an
auto-thermal reforming reaction in the first reforming reactor,
wherein the reaction proceeds in thermodynamic equilibrium, thereby
forming a first reformate (R1) with a first outlet temperature
(T.sub.1, out) that is higher than the first inlet temperature
(T.sub.1, in); mixing the first reformate with a fuel having a
lower temperature than the first outlet temperature (T.sub.1, out),
thereby forming a mixture having a second, lower inlet temperature
(T.sub.2, in); and supplying the mixture to a second reforming
reactor in which, under adiabatic conditions, steam reforming and a
hydrogen shift reaction take place, thereby producing a second
reformate (R2) with a second outlet temperature (T.sub.2, out) that
is below the first outlet temperature (T.sub.1, out) of the first
reformate (R1).
18. A method according to claim 17, wherein the at least one fuel
comprises methanol.
19. A method according to claim 17, wherein the fuel having a lower
temperature than the first outlet temperature (T.sub.1, out)
comprises methanol.
20. A method according to claim 17, wherein the second outlet
temperature (T.sub.2, out) of the second reformate (R2) is equal to
the first inlet temperature (T.sub.1, in).
21. A method according to claim 17, wherein the second outlet
temperature (T.sub.2, out) of the second reformate (R2) is less
than the first inlet temperature (T.sub.1, in).
22. A method according to claim 17, wherein the first outlet
temperature (T.sub.1, out) from the first reforming reactor (4) is
between 600.degree. C. and 900.degree. C.
23. A method according to claim 17, wherein the first inlet
temperature (T.sub.1, in) in the first reforming reactor is between
200.degree. C. and 300.degree. C.
24. A method according to claim 17, wherein the second outlet
temperature (T.sub.2, out) of the second reforming reactor is
between 150.degree. C. and 250.degree. C.
25. A method according to claim 17, wherein the second inlet
temperature (T.sub.2, in) in the second reforming reactor is
between 200.degree. C. and 400.degree. C.
Description
[0001] This applications claims the priority of German patent
document 100 59 674.6 filed Dec. 1, 2000, the disclosure of which
is expressly incorporated by reference herein.
BACKGROUND AND SUMMARY OF INVENTION
[0002] The present invention relates to a fuel cell system and to a
method for operating the fuel cell system.
[0003] DE 196 24 435 C1 (U.S. Pat. No. 5,928,614) discloses a
reforming reactor that is used for the steam reforming of methanol.
To stabilize the temperature of the different reactor steps, a
heating device is provided for a middle step, while the steps at
the inlet side and the outlet side are constructed as heat
exchanges. During the methanol reforming reaction, carbon dioxide
is formed, which must be removed from the reformate. In general, it
is difficult to remove the waste heat developed during a customary,
subsequent hydrogen gas shift reaction from the system in order to
ensure a balance, thermal equilibrium that has sufficient
dynamics.
[0004] Pursuant to the present invention, it is possible to work
largely without heat exchange during the reforming and the
subsequent gas purification. The reforming reactors can be
constructed simply and compactly. The manufacturing costs of the
reactors can thus be reduced. The system has fewer components and
the pressure loss in the gas generating system is reduced.
[0005] It is advantageous that the methanol reforming system is
very simple and therefore inexpensive. In the reforming region,
heat exchangers are not required and, instead, adiabatic reactors
can be used. The efficiency is good, especially in low-pressure
systems. The system can, however, also be operated in the
high-pressure range. A portion of the fuel may contain impurities,
since these are broken down in the high-temperature adiabatic
reactor. This leads to a savings in costs, since fuels of a lesser
purity can be used.
[0006] It is to be understood that the aforementioned
distinguishing features and those, which are still to be explained
below, can be used not only in the combination given, but also in
other combinations or by themselves, without leaving the scope of
the present invention.
[0007] Other objects, advantages and novel features of the present
invention will become apparent from the following detailed
description of the present invention when considered in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 shows a diagrammatic representation of a device with
two reforming reactors according to one embodiment of the present
invention;
[0009] FIG. 2 shows a diagrammatic representation of a section from
a fuel cell system according to the present invention; and
[0010] FIG. 3 shows a detail of the reactor arrangement for a cold
starting case.
DETAILED DESCRIPTION OF THE DRAWINGS
[0011] The present invention is suitable particularly for fuel cell
systems that are used in mobile systems.
[0012] In FIG. 2, a diagrammatic representation of an arrangement
in a fuel cell system according to the present invention is shown.
The fuel cell system has a fuel cell unit 1 and a gas generating
system 2. In the gas generating system 2, hydrogen, for operating
the fuel cell system, is obtained from a fuel, preferably an
alcohol such as methanol or an ether, an ester, a hydrocarbon or
the like. In a conventional gas generating system, at least one
reforming unit is provided for attaining a hydrogen-rich reformate
and the reformate can be supplied at least partly to the anode side
of the fuel cell unit. Usually, the reformate is purified in a gas
purifying system to remove undesirable constituents, such as carbon
monoxide.
[0013] As shown in FIG. 1, the fuel cell system has a first
reforming reactor 4 for generating a first reformate R.sub.1 and a
second reforming reactor 7 for generating a second reformate R2. A
first fuel, preferably a mixture of methanol and water as well as
reaction air, is supplied to the inlet 3 of the first reforming
reactor 4. Previously, the mixture is heated with the help of a
heat exchanger 11 to a first inlet temperature T.sub.1, in.
Preferably, this first inlet temperature is between 200.degree. and
300.degree. C.
[0014] The catalyst-containing reforming reactor 4 may be an
auto-thermal reactor with a catalyst, which preferably is not
selective. The constituents supplied undergo reactions, which take
place in accordance with thermodynamic equilibrium, in this
reactor. In addition, the first reforming reactor 4 advisably has a
catalyst that permits such reactions, preferably, a noble metal
catalyst, such as platinum or a mixed catalyst, such as
platinum/ruthenium. A reformate R1 is formed which is in
thermodynamic equilibrium. The temperature of the first reformate
R1 is appreciably above the first inlet temperature T.sub.1, in.
The first outlet temperature T.sub.1, out at the outlet 5 of the
first reforming reactor 4 of 600.degree. to 900.degree. C. is high.
An auto-thermal reactor is understood to be a reactor, which is
operated adiabatically and in which steam reforming of the fuel
takes place simultaneously with a partial oxidation at least of the
fuel in the same reactor.
[0015] The fuel, which is supplied to the first reforming reactor
4, may also contain appreciable amounts of impurities, since the
materials are decomposed reliably at the high temperature level,
which is present.
[0016] The first reformate R1 is supplied to a second reforming
reactor 7 for generating a second reformate R.sub.2. For this
purpose, the first reformate R1 is cooled to a lower temperature in
an element 9, preferably a mixing element, which is between the
outlet 5 of the first reforming reactor 4 and an inlet 6 of the
second reforming reactor 7. This lower temperature corresponds to
the second inlet temperature T.sub.2, in in the second reforming
reactor 7. The second inlet temperature T.sub.2, in in preferably
is below the first outlet temperature T.sub.1, out. For this
purpose, a second fuel, preferably water and methanol, having a
lower temperature T.sub.MeOH, such as ambient temperature, is
admixed in the mixing element 9. In so doing, the fuel or the
mixture of fuels MeOH+H.sub.2O is evaporated and the reformate R2
is cooled. The second inlet temperature T.sub.2, in preferably is
between 200.degree. and 500.degree. C. The temperature can be
adjusted by the amount of fuel, namely MeOH+H.sub.2O, admixed with
the first reformate R1.
[0017] Pursuant to the present invention, the second reforming
reactor 7 is an adiabatic reactor. Such an adiabatic reactor is not
cooled or heated externally, that is, additional heat is neither
supplied from or discharged to the outside, with the exception of
heat that is supplied to or discharged from the reforming reactor 7
by the media themselves, which are to be reacted, or of heat that
is generated or consumed in the reactor by the reactions of the
media, which are to be reacted. The second reforming reactor 7 has
a catalyst that works selectively. In the second, adiabatic
reforming reactor 7, two reactions take place, namely a steam
reforming of the methanol and, simultaneously, a shift reaction,
with which the carbon monoxide content in the medium is reduced. A
copper-containing catalyst, such as Cu--Zn, is a preferred catalyst
for the second reforming reactor 7.
[0018] The reformate R2, leaving at the outlet 8 of the second
reforming reactor 7, has a second outlet temperature T.sub.2, out,
which is below the first outlet temperature T.sub.1, out.
Preferably, this temperature is between 150.degree. and 250.degree.
C.
[0019] Subsequently, the second reformate R2 can be supplied to a
gas purification system 10 and the reformate, purified there, can
be supplied to the anode side of the fuel cell unit 1.
[0020] Preferably, the first inlet temperature T.sub.1, in is
adjusted over the first heat exchanger 11, which is disposed
upstream from the first reforming reactor 4, in that the medium is
tempered there with waste gas from the fuel cell.
[0021] If the first and second reforming reactors 4, 7 are
considered together, the different temperature levels are
practically invisible from the outside. The exchange of the
necessary reaction temperatures takes place within the reforming
region. Moreover, the reforming reactors 4, 7 are not cooled
directly and, instead, are operated adiabatically or
auto-thermally. The first fuel enters the reforming region 4, 7
with a first inlet temperature T.sub.1, in of, for example,
250.degree. C. and a reformate R2 leaves the reforming region 4, 7
as an end product with an, at most, only slightly lower outlet
temperature T.sub.2, out of, for example, 200.degree. C. The
arrangement enables the reactor to be constructed very simply. The
reforming reactors 4, 7 can be constructed, for example, as tubular
reactors, which are filled with a catalyst.
[0022] In FIG. 2, a diagrammatic representation of a fuel cell
system according to the present invention is shown. Comparable
components have been given the reference numbers of FIG. 1.
[0023] Adjoining the reforming region with the reforming reactors
4, 7, there is a gas purification system 10, in which the reformate
R2 is purified by the removal of undesirable residues of carbon
monoxide. The gas-purification system 10 can be constructed as a
one-step system and cooled with the waste gas from the anode and/or
of the cathode of the fuel cell unit 1. The gas purification system
10 can, however, also be constructed as a two-step system, the
first step 12 preferably being cooled with waste gas from the
cathode and the second step 13 being cooled preferably with waste
gas from the anode of the fuel cell unit 1. This is indicated by
broken lines in FIG. 2. Preferably, selective oxidation of carbon
monoxide takes place in the purification step.
[0024] The gas purification system 10, an afterburner 15, and
downstream from the afterburner, the first heat exchanger 11 are
disposed one after the other in the direction of flow in the waste
gas from the fuel cell unit 1.
[0025] The system can be operated at a low pressure, such as 1 to 2
bar, or also at higher operating pressures. For high-pressure
operation, it is advantageous to provide an expander 16 in the
waste gas downstream from the afterburner. In a preferred
arrangement, the expander 16 may be disposed between the
after-burner 15 and the first heat exchanger 11. However, the
temperature load on the expander 16 is high at this place. If a
lower temperature load is desired, the expander can also be
disposed downstream from the first heat exchanger 11.
[0026] The expander 16 may be coupled with a compressor 17 in an
air supply 20 to the fuel cell unit 1.
[0027] A reformate cooling device 19, which can be cooled
preferably by a cooling medium (not shown) of the fuel cell unit 1,
may be disposed in the flowing reformate 18 downstream from the gas
purification system 10.
[0028] In the case of a cold start, it may be advantageous to
supply additional air to the second reforming reactor 7. This is of
benefit when the catalyst material in the second reforming reactor
7 is appropriately robust. It is also possible, in the case of a
cold start, to pass waste gas from the second reforming reactor 7
in a region of the reactor 7, which is constructed as an internal
heat exchanger 7.1 and in which this waste gas generates heat for
heating the reactor 7 by the selective catalytic oxidation of
hydrogen. This is shown in FIG. 3. Moreover, air is added only in
this region 7.1 (not shown). The heat flux dQ/dt from the
integrated, heat-generating starting step 7.1 into the actual
reactor part of the reforming reactor 7 is indicated by an arrow.
The first reformate R1 reaches the first reforming reactor 4 in the
second reforming reactor 7. A portion of the reformate R2, which is
formed there, is passed from a branch part into part 7.1 and
oxidized there. The waste gas 7.1 can be supplied, preferably
downstream from the branch part, to the second reformate R2.
[0029] Although particular embodiments of the present invention
have been illustrated and described, it will be apparent to those
skilled in the art that various changes and modifications can be
made without departing from the spirit of the present invention. It
is therefore intended to encompass within the appended claims all
such changes and modifications that fall within the scope of the
present invention.
* * * * *