U.S. patent application number 10/627145 was filed with the patent office on 2004-08-05 for water vapor transfer device for a fuel cell power plant.
Invention is credited to Brundage, Mark A., Burch, Steven, Forte, Jameson R..
Application Number | 20040151965 10/627145 |
Document ID | / |
Family ID | 25428637 |
Filed Date | 2004-08-05 |
United States Patent
Application |
20040151965 |
Kind Code |
A1 |
Forte, Jameson R. ; et
al. |
August 5, 2004 |
Water vapor transfer device for a fuel cell power plant
Abstract
A fuel cell system that extracts water from the effluent of a
fuel cell for supply to other components of the fuel cell system
that require water. A preferred embodiment is a fuel cell system,
for the production of electricity from hydrogen gas and an oxidant,
comprising: (a) a fuel cell comprising an anode input for a
hydrogen-containing anode supply stream, a cathode input for an
oxidant-containing cathode supply stream, and a cathode output for
cathode effluent comprising water produced by said fuel cell; and
(b) a water transfer device, connected to said fuel cell, that
transfers water from said cathode effluent to said anode supply
stream.
Inventors: |
Forte, Jameson R.;
(Rochester, NY) ; Burch, Steven; (Honeoye Falls,
NY) ; Brundage, Mark A.; (Pittsford, NY) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Family ID: |
25428637 |
Appl. No.: |
10/627145 |
Filed: |
July 25, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10627145 |
Jul 25, 2003 |
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09910331 |
Jul 20, 2001 |
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6630260 |
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Current U.S.
Class: |
429/414 ;
429/425; 429/450 |
Current CPC
Class: |
H01M 8/04119 20130101;
H01M 8/0612 20130101; C01B 2203/0283 20130101; C01B 2203/0838
20130101; C01B 2203/047 20130101; C01B 2203/00 20130101; C01B
2203/0844 20130101; C01B 2203/0866 20130101; C01B 2203/0495
20130101; Y02E 60/50 20130101; C01B 2203/044 20130101; C01B
2203/148 20130101; C01B 2203/066 20130101; C01B 2203/0405 20130101;
C01B 3/48 20130101; C01B 2203/142 20130101; C01B 2203/82 20130101;
C01B 2203/146 20130101; C01B 3/34 20130101; C01B 2203/0244
20130101 |
Class at
Publication: |
429/034 ;
429/019; 429/013 |
International
Class: |
H01M 008/04; H01M
008/06 |
Claims
What is claimed is:
1. A fuel cell system, comprising: (a) a fuel cell comprising an
anode input for a hydrogen-containing anode supply stream, a
cathode input for an oxidant-containing cathode supply stream, an
anode effluent output, and a cathode output for cathode effluent
comprising water produced by said fuel cell; (b) a water transfer
device, comprising (i) a device cathode effluent input connected to
said cathode output, (ii) a device supply stream output connected
to either or both of said fuel cell inputs, and (iii) a
water-transfer membrane; wherein said water transfer device
transfers water from said cathode effluent to either or both of
said supply streams, and wherein the temperature of said cathode
effluent at said device cathode effluent input is not significantly
greater than the temperature of said cathode effluent at said
cathode output; and said temperature at said device input being
sufficient to maintain water in its vapor state and being greater
than its dew point and up to about 10.degree. C. above its dew
point.
2. A fuel cell system according to claim 1, wherein said water
transfer membrane comprises poly acid.
3. A fuel cell system according to claim 1, wherein said anode
supply stream comprises reformate from a hydrocarbon fuel
processor.
4. A fuel cell system according to claim 3, wherein said
hydrocarbon fuel processor comprises an autothermal reformer.
5. A fuel cell system according to claim 1, wherein said water
transfer device transfers water to said cathode supply stream.
6. A fuel cell system, comprising: (a) a fuel cell comprising an
anode input for a hydrogen-containing anode supply stream, a
cathode input for an air supply stream, an anode output for anode
effluent comprising water produced by said fuel cell; and a cathode
output for cathode effluent comprising water produced by said fuel
cell; (b) a compressor having an input for an air stream and an
output connected to said cathode input of the fuel cell stack; and
(c) a water transfer device, comprising (i) a device effluent input
connected to one or both of the outputs of said fuel cell, (ii) a
device supply stream output connected to the input of said
compressor, and (iii) a water-transfer membrane; wherein said water
transfer device transfers water from one or both of said anode
effluent and said cathode effluent outputs to said air stream input
to the compressor; and wherein said cathode effluent has a
temperature at said device input, said temperature being sufficient
to maintain water in its vapor state and being greater than its dew
point and up to about 10.degree. C. above its dew point.
7. A fuel cell system according to claim 6, wherein said water
transfer membrane comprises poly[perfluorosulfonic] acid.
8. A fuel cell system according to claim 6, wherein said anode
supply stream comprises reformate produced by a hydrocarbon fuel
processor.
9. A fuel cell system according to claim 8, wherein said
hydrocarbon fuel processor comprises an autothermal reformer.
10. A method of operating a fuel cell power plant comprising a
reactor for the production of a reformate supply stream using a
reactant stream comprising a reactor oxidant stream and a reactor
hydrocarbon fuel stream, wherein said reformate supply stream
comprises water; and a fuel cell comprising an anode input for said
reformate supply stream, a cathode input for a cathode oxidant
supply stream, an anode output for an anode effluent stream, a
cathode output for an cathode effluent stream, wherein either or
both of said anode effluent and said cathode effluent comprise
water produced by said fuel cell; said method comprising: (a)
transferring water from said reformate supply stream to a one or
both of said reactant streams in a first water transfer device that
has a high pressure side and a low pressure side, by transporting
said one or both of said reactant streams through said low pressure
side, and by transporting said reformate supply stream through said
high pressure side; and (b) transferring water from one or more of
said reaction oxidant stream said reformate supply stream, and said
cathode oxidant supply stream in a second water transfer device
that has a high pressure side and a low pressure side, by
transporting said one or more of said reactor oxidant stream, said
reformate supply stream, and said cathode oxidant supply stream
though said low pressure side, and by transporting one or both of
said effluent streams through said high pressure side.
11. The method of claim 10, wherein each of said water transfer
devices comprises a membrane which comprises
poly[perfluorosulfonic] acid.
12. The method of claim 10, wherein said second water transfer
device transfers water from said cathode effluent to said air
supply stream.
13. The method of claim 10, wherein said second water transfer
device is connected to said reactor through said first water
transfer device, and transfers water to a reactant stream of said
reactor.
14. The method of claim 13, wherein said reactant stream is said
reactor oxidant stream comprising air.
15. The method of claim 14, wherein said air is at a temperature
less than about 50.degree. C.
16. The method of claim 15, wherein said air is at about ambient
temperature.
17. The method of claim 10, wherein said reactor comprises an
autothermal reactor.
18. The method of claim 17, wherein said reactor additionally
comprises a water-gas shift reactor and a preferential oxidation
reactor, and wherein said autothermal reactor produces reformate
which is supplied, in series, to said water-gas shift reactor and
to said preferential oxidation reactor, and wherein said first
water transfer device transfers water from said reformate stream
after said reformate exits said water-gas shift reactor and before
said reformate enters said preferential oxidation reactor.
19. The method of claim 17, wherein said reactor additionally
comprises a water-gas shift reactor and a preferential oxidation
reactor, and wherein said autothermal reactor produces reformate
which is supplied, in series, to said water-gas shift reactor and
to said preferential oxidation reactor, and wherein said first
water transfer device transfers water from said reformate stream
after said reformate exits said preferential oxidation reactor.
20. The method of claim 10, additionally comprising an air moving
device connected to said cathode input, wherein said air supply
stream flows through said air moving device before entering said
cathode input, and wherein said second water transfer device is
connected to the input of said compressor and transfers water to
said air supply stream prior to the entry of said stream into said
air moving device.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 09/910,331 filed on Jul. 20, 2001. The
disclosure of the above application is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to fuel cell power plants for the
production of electricity from the electrochemical reaction of
hydrogen and an oxidant. Preferred plants produce hydrogen from
hydrocarbon fuel. In particular, this invention relates to fuel
cell power plants having a device that transfers water vapor from
the effluent of a fuel cell to components of the power plant that
require water.
[0003] Fuel cells are devices that convert electrochemical energy
from the reaction of reducing and oxidizing chemicals, into
electricity. Fuel cells have been used as a power source in many
applications, and can offer significant benefits over other sources
of electrical energy, such as improved efficiency, reliability,
durability, cost and environmental benefits. In particular,
electric motors powered by fuel cells have been proposed for use in
cars and other vehicles to replace internal combustion engines.
[0004] Fuel cells typically use hydrogen and air as the reducing
and oxidizing materials to produce electrical energy, and water.
The cell generally comprises an anode electrode and a cathode
electrode separated by an electrolyte. Hydrogen is supplied to the
anode electrode, and oxygen (or air) is supplied to the cathode
electrode. The hydrogen gas is separated into electrons and
hydrogen ions (protons) at the anode. The hydrogen ions pass
through the electrolyte to the cathode; the electrons travel to the
cathode through the power circuit (e.g., to a motor). At the
cathode, the hydrogen ions, electrons, and oxygen then combine to
form water. The reactions at the anode and cathode are facilitated
by a catalyst, typically platinum.
[0005] The anode and cathode of the fuel cell are separated by an
electrolyte. There are several types of fuel cells, each
incorporating a different electrolyte system, and each having
advantages that may make them particularly suited to given
commercial applications. One type is the proton exchange membrane
(PEM) fuel cell, which employs a thin polymer membrane that is
permeable to protons but not electrons. PEM fuel cells, in
particular, are well suited for use in vehicles, because they can
provide high power and weigh less than other fuel cell systems.
[0006] The membrane in the PEM fuel cell is part of a membrane
electrode assembly (MEA) having the anode on one face of the
membrane, and the cathode on the opposite face. The membrane is
typically made from an ion exchange resin such as a perfluoronated
sulfonic acid. The MEA is sandwiched between a pair of electrically
conductive elements that serve as current collectors for the anode
and cathode, and contain appropriate channels and/or openings for
distribution of the fuel cell's gaseous reactants over the surfaces
of the respective anode and cathode catalysts.
[0007] The anode and cathode typically comprise finely divided
catalytic particles, supported on carbon particles, and admixed
with a proton conductive resin. The catalytic particles are
typically precious metal particles, such as platinum. Such MEAs
are, accordingly, relatively expensive to manufacture and require
controlled operating conditions in order to prevent degradation of
the membrane and catalysts. These conditions include proper water
management and humidification, and control of catalyst fouling
constituents, such as carbon monoxide. Typical PEM fuel cells and
MEAs are described in U.S. Pat. No. 5,272,017, Swathirajan et al.,
issued Dec. 21, 1993, and U.S. Pat. No. 5,316,871, Swathirajan et
al., issued May 31, 1994.
[0008] The voltage from an individual cell is only about 1 volt.
Accordingly, to meet the higher power requirements of vehicles and
other commercial applications, several cells are combined in
series. This combination is typically arranged in a "stack"
surrounded by an electrically insulating frame that has passages
for directing the flow of the hydrogen and oxygen (air) reactants,
and the water effluent. Because the reaction of oxygen and hydrogen
also produces heat, the fuel cell stack must also be cooled.
Arrangements of multiple cells in a stack are described in U.S.
Pat. No. 5,763,113, Meltser et al., issued Jun. 9, 1998; and U.S.
Pat. No. 6,099,484, Rock, issued Aug. 8, 2000.
[0009] For many applications, it is desirable to use a readily
available hydrocarbon fuel, such as methane (natural gas),
methanol, gasoline, or diesel fuel, as the source of hydrogen for
the fuel cell. Liquid fuels, such as gasoline, are particularly
suited for vehicular applications. Liquid fuels are relatively easy
to store, and there is an existing commercial infrastructure for
their supply. However, hydrocarbon fuels must be dissociated to
release hydrogen gas for fueling the fuel cell. Power plant fuel
processors for providing hydrogen contain one or more reactors or
"reformers" wherein the fuel reacts with steam, and sometimes air,
to yield reaction products comprising primarily hydrogen and carbon
dioxide.
[0010] In general, there are two types of reforming systems: steam
reformers, and autothermal reformers. Each system has operating
characteristics that make it more or less suited to the use of
particular types of fuels and in particular applications. In steam
reformation, a hydrocarbon fuel (typically methane or methanol) and
water (as steam) are reacted to generate hydrogen and carbon
dioxide. This reaction is endothermic, requiring the addition of
heat. In preferred systems, this heat is provided by a combustor
that burns hydrogen that remains unreacted after the reformate
passes through the fuel cell stack.
[0011] In an autothermal reformation process, a hydrocarbon fuel
(typically gasoline), steam and air are supplied to a primary
reactor that performs two reactions. One is a partial oxidation
reaction, where air reacts with the fuel exothermally, and the
other is the endothermic steam reforming reaction (as in steam
reformation). The heat from the exothermic reaction is used in the
endothermic reaction, minimizing the need for an external heat
source.
[0012] A by-product of the reaction, in both steam and autothermal
reforming, is carbon monoxide. Unfortunately, carbon monoxide will
degrade the operation of the fuel cell, particularly PEM fuel
cells. Thus, reactors downstream of the primary reactor are
required to lower the carbon monoxide concentration in the
hydrogen-rich reformate to levels tolerable in the fuel cell stack.
Downstream reactors may include a water/gas shift (WGS) reactor and
a preferential oxidizer (PrOx) reactor. The WGS reactor
catalytically converts carbon dioxide and water to hydrogen and
carbon dioxide. The PrOx reactor selectively oxidizes carbon
monoxide to produce carbon dioxide, using oxygen from air as an
oxidant. Control of air feed to the PrOx reactor is important to
selectively oxidize carbon monoxide, while minimizing the oxidation
of hydrogen to water.
[0013] Fuel cell systems that dissociate a hydrocarbon fuel to
produce a hydrogen-rich reformate for consumption by PEM fuel cells
are well known in the art. Such systems are described in U.S. Pat.
No. 6,077,620, Pettit, issued Jun. 20, 2000; European Patent
Publication 977,293, Skala, et al., published Feb. 2, 2000; and
U.S. Pat. No. 4,650,722, Vanderborgh, et al., issued Mar. 17,
1987.
[0014] The use of hydrocarbon reformate fuel cell systems in cars
and other vehicles presents special concerns. In addition to the
desirability of using readily-available liquid fuels, discussed
above, the reformer and fuel cell systems must be relatively light
in weight, and must be able to operate efficiently under a wide
range of ambient conditions (e.g., under a range of temperatures
and humidity conditions). They should also be able to be started
quickly, so as to produce power within a short time interval after
start-up of the vehicle. Thus, it is desirable to minimize the
amount of heating of reactant components for the reformer. It is
also desirable to minimize the amount of liquid water that must be
handled in the system, particularly to avoid the need to replenish
water within the system.
[0015] As discussed above, there are several components in the
reformate fuel cell system that require water, particularly
including the reformer that requires steam as a reactant, the WGS
reactor, and the fuel cell that requires humidification of the MEA
in order to function properly. A common approach to enhancing water
balance in fuel cell systems is use of condensing heat exchangers
at various points in the system. For example, heat exchangers are
used downstream of the reformer to cool the reformate exhaust to a
temperature at or below its dew point so as to precipitate water.
The water is separated from the gaseous reformate, and stored in a
reservoir. The water is then returned to the reformer where it is
heated to create steam. Heat exchangers are also used to cool the
exhaust stream exiting the cathode of the fuel cell so as to
condense water which is used in humidifying the MEA. The use of
heat exchangers presents issues, however. For example, the water
recovery efficiency of heat exchangers is reduced as the ambient
temperature increases. Large radiators may be required so as to
dissipate the heat of condensation. Moreover, the liquid condensate
produced by the heat exchangers must be vaporized for re-use in the
system, creating an additional energy load and inefficiencies in
the system.
[0016] Attempts to address the water balance needs in fuel cell
systems have been described in the art. See, for example, German
Patent Disclosure 42 01632, Strasser, published Jul. 29, 1993; U.S.
Pat. No. 6,007,931, Fuller et al., issued Dec. 28, 1999; and U.S.
Pat. No. 6,013,385, DuBose, issued Jan. 11, 2000. However, water
management systems among those known in the art do not adequately
address these needs, due to problems such as their inability to
maintain true water balance over a wide range of operating
conditions, mechanical complexity and reliability, increased system
energy requirements, and potential safety issues.
SUMMARY OF THE INVENTION
[0017] The present invention provides a fuel cell system that
extracts water from the effluent of a fuel cell for supply to other
components of the fuel cell system that require water. Accordingly,
the present invention provides a fuel cell system for the
production of electricity from hydrogen and an oxidant,
comprising:
[0018] (a) a fuel cell for the production of electricity using
hydrogen and an oxidant; and
[0019] (b) a water transfer device that transfers water vapor from
the anode or cathode effluent of said fuel cell to other components
of the fuel cell system. A preferred embodiment is a fuel cell
system, for the production of electricity from hydrogen gas and an
oxidant, comprising:
[0020] (a) a fuel cell comprising an anode input for a
hydrogen-containing anode supply stream, a cathode input for an
oxidant-containing cathode supply stream, and a cathode output for
cathode effluent comprising water produced by said fuel cell;
and
[0021] (b) a water transfer device, connected to said fuel cell,
that transfers water from said cathode effluent to said anode
supply stream. Another preferred embodiment is a fuel cell power
plant comprising:
[0022] (a) a reactor for the production of a reformate supply
stream using a reactor oxidant stream and a reactor hydrocarbon
fuel stream, wherein said reformate supply stream comprises
water;
[0023] (b) a first water transfer device that transfers water from
said reformate supply stream to a one or both of said reactant
streams, comprising a water-transfer membrane;
[0024] (c) a fuel cell comprising an anode input for said reformate
supply stream, a cathode input for a cathode oxidant supply stream,
an anode output for an anode effluent stream, a cathode output for
an cathode effluent stream, wherein either or both of said anode
effluent and said cathode effluent comprise water produced by said
fuel cell; and
[0025] (d) a second water transfer device, connected to said fuel
cell, that transfers water from one or both of said effluent
streams to one or more of said oxidant reactant stream, said
reformate supply stream and said cathode oxidant supply stream.
[0026] It has been found that such water transfer devices afford
significant advantages over water management systems known in the
art. In particular, such systems afford advantages maintaining an
overall water balance in the system under a range of operating
conditions, reduced energy requirements, reduced component
complexity and reliability, and enhanced operating safety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a diagram depicting a fuel a fuel cell system of
this invention showing the flow of materials in and out of the fuel
cell and water transfer device.
[0028] FIG. 2 is a diagram of a preferred embodiment of this
invention, comprising a reactor, a water transfer device for
transferring water vapor from the reformate output of the reactor
to the air input of the reactor, a fuel cell, and a water transfer
device for transferring water vapor from the cathode effluent of
the fuel cell to the cathode input of the fuel cell.
[0029] FIG. 3 is a diagram of another preferred embodiment of this
invention, comprising a reactor, a water transfer device for
transferring water vapor from the reformate output of the reactor
to the air input of the reactor, a fuel cell, and a water transfer
device for transferring water vapor from the cathode effluent of
the fuel cell to the anode input of the fuel cell.
[0030] FIG. 4 is a diagram of another preferred embodiment of this
invention, comprising a reactor, a water transfer device for
transferring water vapor from the reformate output of the reactor
to the air input of the reactor, a fuel cell, and a water transfer
device for transferring water vapor from the cathode effluent of
said fuel cell to a splitter, where the water vapor is further
transferred to the air input of the reactor (via the first water
transfer device) and to the cathode and (optionally) the anode
inputs of the fuel cell.
[0031] FIG. 5 depicts a cross sectional view of a water transfer
device among those useful in this invention.
DETAILED DESCRIPTION
[0032] The present invention provides a fuel cell system. As
referred to herein, a "fuel cell system" is an apparatus comprising
a fuel cell and a water transfer device. The water vapor transfer
device transfers water vapor from an effluent of the fuel cell to
another component of the fuel cell system. In a particular
embodiment, as depicted in FIG. 1, the water transfer device (10)
transfers water vapor from a fuel cell (11) effluent stream (12)
that contains oxygen and water, to an input stream (13) of the fuel
cell. Preferably, the water vapor is transferred from the cathode
effluent of the fuel cell. A preferred embodiment of a fuel cell
system also comprises a combustor (14), for burning anode fuel cell
effluent. Also preferably, the fuel cell system is a hydrocarbon
fuel cell plant, embodiments of which are depicted in FIGS. 2, 3
and 4.
[0033] As referred to herein, a "fuel cell" may be a single cell
for the electrochemical creation of electricity, preferably a PEM
fuel cell, using hydrogen and an oxidant or a plurality of cells in
a stack or other configuration that allows series connection of the
cells so as to produce increased voltage. As referred to herein, a
"hydrocarbon fuel cell plant" is an apparatus that comprises a fuel
cell and a hydrocarbon fuel processor for providing hydrogen for
the fuel cell. As referred to herein, a "hydrocarbon fuel
processor" comprises any device that converts a hydrocarbon fuel
into hydrogen. In a preferred embodiment, the hydrocarbon fuel cell
plant is suitable for use in a motor vehicle. In another preferred
embodiment, the hydrocarbon fuel cell plant is suitable for use in
a stationary apparatus, such as an emergency or supplemental power
generator for home or commercial use.
[0034] Preferably, the hydrocarbon fuel processor converts
hydrocarbon fuel, using an oxidant and water, to create a stream of
hydrogen gas. Preferably, the hydrocarbon fuel is any fuel capable
of being reformed to produce hydrogen, including gasoline, diesel
fuel, natural gas, methane, butane, propane, methanol, ethanol, or
mixtures thereof. (As used herein, the word "include," and its
variants, is intended to be non-limiting, such that recitation of
items in a list is not to the exclusion of other like items that
may also be useful in the apparatuses, devices, components,
materials, compositions and methods of this invention.)
[0035] In particular, as depicted in FIGS. 2, 3 and 4, preferred
embodiments of the present invention also provide a power plant
fuel processor comprising a reactor 20, 30 or 40 and a water
transfer device (21) that transfers water vapor from the reformate
produced by the reactor to the input of the reactor. As referred to
herein, "reformate" is the gaseous product or effluent comprising
hydrogen that is produced by a reactor from a hydrocarbon fuel. In
one embodiment, the reformate from the reactor, after passing
through the water transfer device, flows to the fuel cell (11).
Also in the depicted embodiments, the water vapor is transferred to
the reactor as part of the oxidant stream. The transfer may be
directly to the input of the reactor or to a device, such as an air
moving device, which in turn is connected to the input of the
reactor. The water transfer device preferably comprises a
water-transfer membrane.
[0036] Reactor:
[0037] The fuel cell systems of the present invention preferably
comprise a reactor that is capable of converting a hydrocarbon fuel
to hydrogen for use in a fuel cell. Preferred reactors include
steam reforming reactors and autothermal reactors as generally
described in the background, above. Among such reactors useful in
this invention are those known in the art, such as described in the
following documents, all of which are incorporated by reference
herein: U.S. Pat. No. 4,650,722, Vanderborgh, et al., issued Mar.
17, 1987; U.S. Pat. No. 6,077,620, Pettit, issued Jun. 20, 2000;
and U.S. Pat. No. 6,132,689, Skala et al., issued Sep. 22, 1998;
U.S. Pat. No. 6,159,626, Keskula et al., issued Jul. 6, 1999;
European Patent Publication 977,293, Skala, et al., published Feb.
2, 2000; and European Patent Publication 1,066,876, Keskula et al.,
published Jan. 10, 2001.
[0038] The reactor preferably comprises one or more reactors
wherein the hydrocarbon fuel (stream 7) undergoes dissociation in
the presence of water/steam to produce the reformate. In one such
specific embodiment, air is used in a combination partial
oxidation/steam reforming reaction. In this case, one or more of
the reactors also receive an air stream. Each reactor may comprise
one or more sections or reactor beds. A variety of designs are
known and usable. Therefore, the selection and arrangement of
reactors may vary; exemplary fuel reformation reactor(s) and
downstream reactor(s) are further described below.
[0039] In an exemplary autothermal reformation process, gasoline,
water (as steam), and oxygen (air) are reacted in a primary reactor
to generate hydrogen and carbon dioxide as described earlier in the
background. The reactor comprises two sections. One section of the
reactor is primarily a partial oxidation reactor (POX) and the
other section of the reactor is primarily a steam reformer (SR),
although there is some overlap in the type of reactions occurring
in the POX and SR sections. The POX reaction is predominantly
between fuel and air, having the following general reaction
scheme.
C.sub.8H.sub.18+4O.sub.2.fwdarw.8CO+9H.sub.2
[0040] This reaction is facilitated by use of a catalyst and is
exothermic. A preferred POX catalyst comprises one or more noble
metals, Pt, Rh, Pd, Ir, Os, Au, and Ru. Other non-noble metals, or
combination of metals, such as Ni and Co, are also useable. The
reaction in the POX section is preferably fuel-rich. The hot POX
reaction products, along with steam introduced with the fuel, pass
into the SR section where the hydrocarbons react with steam
according to the following general reaction scheme.
C.sub.8H.sub.18+8H.sub.2O.fwdarw.8CO+17H.sub.2
[0041] The steam reforming reaction is endothermic. Heat required
for this endothermic reaction is provided from the heat that is
generated by the exothermic POX reaction and is carried forward
into the SR section by the POX section effluent (thus, the name
"autothermal reactor").
[0042] The primary reformate products from the primary reactor exit
the primary reactor, in one embodiment, and are cooled by a heat
exchanger that transfers heat from the reformate to the air
supplied to the primary reactor. In another preferred embodiment,
this heat transfer is effected by the water transfer device,
without the use of a separate heat exchanger. Hydrogen is produced,
but the gasoline reformation also produces carbon dioxide, water
and carbon monoxide. Carbon monoxide, in particular, may have a
detrimental effect on the catalyst used in the fuel cell stack.
Accordingly, it is preferable to reduce the carbon monoxide content
of the product stream.
[0043] Preferably, then, the fuel processor also comprises one or
more downstream reactors, such as water/gas shift (WGS) reactor and
preferential oxidizer (PrOx) reactor, that are used to convert
carbon monoxide to carbon dioxide. Preferably, the carbon monoxide
is reduced to acceptable levels, preferably below about 20 ppm.
[0044] The shift reactor preferably includes one or more sections
whose carbon monoxide and water are reacted according to the
following general scheme.
CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2
[0045] In one embodiment, there is provided a high temperature
shift section and a low temperature shift section. In one such
specific embodiment, the high temperature shift reactor comprises a
Fe.sub.3O.sub.4/Cr.sub.2O.sub.3 catalyst, and runs at a temperature
of from about 400.degree. C. (752.degree. F.) to about 550.degree.
C. (1022.degree. F.). In the embodiment, the low temperature shift
reactor comprises a CuO/ZnO/Al.sub.2 O.sub.3 catalyst, and runs at
a temperature of from about 200.degree. C. (392.degree. F.) to
about 300.degree. C. (572.degree. F.). Preferably, cooling of the
reformate stream occurs between the high temperature and the low
temperature sections. In other embodiments, the WGS reactor
contains a medium temperature shift reactor running at a
temperature of from about 300.degree. C. (572.degree. F.) to about
400.degree. C. (752.degree. F.), instead of, or in addition to, the
high and low temperature reactors.
[0046] Reformate exiting the shift reactor enters a preferential
oxidation PrOx reactor where it is catalytically reacted with
oxygen through an air supply according to the following general
reaction scheme.
CO+{fraction (1/2)}O.sub.2.fwdarw.CO.sub.2
[0047] This reaction is conducted to consume essentially all of, or
at least most of, the residual carbon monoxide without consuming
excess quantities of hydrogen.
[0048] An air stream supplied to the fuel processor may be used in
one or more of the reactors. For systems with an autothermal
reformer, air is supplied to reactor. The PrOx reactor also
utilizes air to oxidize carbon monoxide to carbon dioxide, using a
noble metal catalyst. Preferably air is supplied from an air moving
device, preferably a compressor. The air may be heated, using one
or more heat exchanger(s), to the desired temperatures for the
primary reactors. In such embodiments, the air for the primary
reactor is preferably supplied at a temperature of at least about
700.degree. C. (1292.degree. F.) depending on operating
conditions.
[0049] In one embodiment, the PrOx hydrogen stream exits the PrOx
reactor and is cooled by heat exchanger to a temperature suitable
for use in a fuel cell. The hydrogen stream is preferably cooled to
a temperature below about 100.degree. C. (212.degree. F.). The
hydrogen stream is then fed into the anode chamber of the fuel
cell, via the water transfer device, as discussed below. At the
same time, oxygen (e.g., air) from an oxidant stream is fed into
the cathode chamber of the fuel cell. Preferably, the air is
compressed, using a compressor. The hydrogen from the reformate
stream and the oxygen from the oxidant stream react in the fuel
cell to produce electricity, in an electrochemical reaction in the
presence of the catalyst. Water is produced as a by-product of the
reaction. Exhaust or effluent from the anode side of the fuel cell
contains some unreacted hydrogen. The exhaust or effluent from the
cathode side of the fuel cell also contains some unreacted
oxygen.
[0050] Some of the reactions that occur in the reactors are
endothermic and so require heat; other reactions are exothermic and
require removal of heat. Typically, the PrOx reactor requires
removal of heat. Depending on the type of reformer, one or more of
the reactions in the primary reactor are endothermic and require
heat be added. This is typically accomplished by preheating one or
more of the fuel, water, and air reactants and/or, for a steam
reforming reactor, by heating the selected reactors. The system
preferably contains heat exchangers to transfer thermal energy from
those parts of the system that generate heat, to those that require
heat.
[0051] The fuel processor optionally comprises a combustor, which
may heat the fuel, air and/or water reactants entering the reactor.
For fuel processors having a steam reforming reactor, the combustor
preferably also heats the reformer, directly or indirectly. In a
preferred steam reforming system, the reactor beds are heated by
the hot exhaust of the combustor. A preferred embodiment comprising
an autothermal reformer does not have a combustor.
[0052] The combustor preferably comprises a chamber with an inlet,
an exhaust, and a catalyst. Preferably, the source of fuel in the
combustor is the unreacted hydrogen in the anode effluent.
Additional fuel may be provided directly to the combustor, as
needed to meet the transient and steady state needs of the fuel
cell apparatus.
[0053] The hydrocarbon fuel and/or anode effluent are reacted in
the catalyst section of the combustor. Oxygen is provided to the
combustor either from the air supply and/or, preferably, the
cathode effluent stream, depending on system operating conditions.
Preferably, the exhaust from the combustor passes through a
regulator and a muffler being released to the atmosphere. In
systems where the reactor is heated by the combustor, enthalpy
equations are used to determine the amount of cathode exhaust air
to be supplied to the combustor so as to provide the heat needed by
the reactors. Any oxygen demand required by the combustor that is
not met by the cathode effluent is preferably supplied by a
compressor in an amount to satisfy the heat and temperature
demanded by the combustor.
[0054] Water for the reactors is preferably provided by the water
transfer device, as further discussed below. However, under certain
situations (such as start-up of the system), additional water may
be needed. This water is preferably obtained from the anode
effluent and cathode effluent, such as using a condenser and a
water separator. Liquid water is then stored in a reservoir. Water
may also be added to the reservoir from external sources.
[0055] Preferably, the various aspects of the operation of the
system are controlled using a suitable microprocessor,
microcontroller, personal computer, etc., which has central
processing unit capable of executing a control program and data
stored in a memory. The controller may be a dedicated controller
specific to any of the components, or implemented in software
stored in a main vehicle electronic control module. Further,
although software based control programs are usable for controlling
system components in various modes of operation as described above,
it will also be understood that the control can also be implemented
in part or whole by dedicated electronic circuitry.
[0056] Fuel Cell:
[0057] The apparatus of the present invention comprises a fuel
cell, which converts electrochemical energy, from the reaction of
reducing and oxidizing chemicals, into electricity. Preferably the
fuel cells used in the present invention use hydrogen and air as
the reducing and oxidizing materials to produce electrical energy,
and water. The cell generally comprises an anode electrode and a
cathode electrode separated by an electrolyte. Hydrogen is supplied
to the anode electrode, and oxygen (or air) is supplied to the
cathode electrode. The hydrogen gas is separated into electrons and
hydrogen ions (protons) at the anode. The hydrogen ions pass
through the electrolyte to the cathode; the electrons travel to the
cathode through the power circuit (e.g., to a motor). At the
cathode, the hydrogen ions, electrons, and oxygen then combine to
form water. The reactions at the anode and cathode are facilitated
by a catalyst, typically platinum.
[0058] A preferred electrolyte is a proton exchange membrane (PEM),
which comprises a thin polymer membrane that is permeable to
protons but not electrons. A preferred membrane material is an ion
exchange resin such as a perfluoronated sulfonic acid. A
particularly preferred membrane material is a perfluoronated
sulfonic acid polymer sold as NAFION3 by the E.I. DuPont de
Nemeours & Co.
[0059] The membrane in the PEM fuel cell is part of a membrane
electrode assembly (MEA) having the anode on one face of the
membrane, and the cathode on the opposite face. The MEA is
sandwiched between a pair of electrically conductive elements that
serve as current collectors for the anode and cathode, and contain
appropriate channels and/or openings for distribution of the fuel
cell's gaseous reactants over the surfaces of the respective anode
and cathode catalysts.
[0060] In one embodiment, the anode and cathode comprise a film
made of finely divided catalytic particles, supported on carbon
particles, and admixed with a proton conductive resin, preferably a
perfluoronated sulfonic acid polymer such as NAFION3. In another
embodiment, the anode and cathode comprise a film made of finely
divided catalytic particles dispersed throughout a
polytetrafluoroethylene (PTFE) binder. The catalytic particles are
typically precious metal particles, such as platinum. Such MEAs
require controlled operating conditions, including humidification,
to facilitate efficient energy production and to prevent
degradation of the membrane and catalysts. Fuel cells among those
useful herein are described in the following documents, all of
which are incorporated by reference herein: U.S. Pat. No.
3,134,697, Niedrach, issued May 26, 1964; U.S. Pat. No. 5,272,017,
Swathirajan et al., issued Dec. 21, 1993, and U.S. Pat. No.
5,316,871, Swathirajan et al., issued May 31, 1994; and Journal of
Power Sources, Volume 29 (1990) pages 367-387.
[0061] Preferably, the fuel cells used in the present invention
comprise a plurality of fuel cells electrically connected in series
for increasing voltage. This combination is preferably arranged in
a "stack" surrounded by an electrically insulating frame. In a
preferred embodiment, individual MEAs are sandwiched between sheets
of porous, gas-permeable, conductive material which press against
the anode and cathode faces of the MEA and serve as (a) the primary
current collectors for the anode and cathode, and (b) mechanical
support for the MEA. The bipolar plates each include flow fields
having a plurality of flow channels formed in the faces of the
plates for distributing fuel and oxidant gases, e.g.,
hydrogen-containing reformate and oxygen (air), to the reactive
faces of the MEAs. Nonconductive gaskets or seals provide a seal
and electrical insulation between the several plates of the fuel
cell stack. Preferred primary current collector sheets comprise
carbon or graphite paper or cloth, fine mesh noble metal screen,
open cell noble metal foams, and similar materials that conduct
current from the electrodes while allowing gas to pass through.
This assembly is referred to as the MEA/primary current collector
assembly herein.
[0062] The MEA/primary current collector assembly is pressed
between a pair of non-porous, electrically conductive plates or
metal sheets which serve as secondary collectors for the current
from the primary current collectors and conducting current between
adjacent cells internally of the stack (i.e., in the case of
bipolar plates) and at the ends of a cell externally of the stack
(i.e., in the case of monopolar plates). The secondary current
collecting plate contains a flow field that distributes the gaseous
reactants, e.g., hydrogen-containing reformate and oxygen (air),
over the surfaces of the anode and cathode. These flow fields
generally include a plurality of lands which engage the primary
current collector and define therebetween a plurality of flow
channels through which the gaseous reactants flow between a supply
header at one end of the channel and an exhaust header at the other
end of the channel. Because the reaction of water and hydrogen also
produces heat, the fuel cell stack must also be cooled.
[0063] An oxidant gas such as oxygen or air is supplied to the
cathode side of the fuel cell stack from a storage tank via
appropriate supply plumbing. Similarly, hydrogen (e.g., essentially
pure, or reformate) is supplied to the anode side of the fuel cell
via appropriate supply plumbing. Exhaust plumbing for both the fuel
and oxidant of the MEAs is also provided for removing
hydrogen-depleted anode gas (herein "anode effluent)" from the
anode flow field and oxygen-depleted water-containing cathode gas
(herein "cathode effluent") from the cathode flow field. Coolant
plumbing and is provided for supplying and exhausting liquid
coolant to the bipolar plates and, as needed. Arrangements of
multiple cells in a stack among those useful herein are described
in U.S. Pat. No. 5,763,113, Meltser et al., issued Jun. 9, 1998;
and U.S. Pat. No. 6,099,484, Rock, issued Aug. 8, 2000.
[0064] Water Transfer Device:
[0065] The present invention also provides a water transfer device
that transfers water vapor from a wet gas stream to a dry gas
stream. The water transfer devices of this invention comprise a
structure comprising a flow path for a primary gas, a flow path for
secondary gas, and a water transfer membrane having a first and
second surface, wherein the first surface of the membrane is in
substantial contact with the flow path for the primary gas, and the
second surface is in substantial contact with the second flow path.
Water vapor in a gas traveling in one flow path (e.g., the first
flow path) is transferred through the membrane to the other flow
path (e.g., the second flow path). A preferred water transfer
device such as the one depicted in FIG. 5, for the transfer of
water vapor between a primary gas and a secondary gas in a fuel
cell system, comprises:
[0066] (a) a primary gas inlet (51);
[0067] (b) a primary gas outlet (52);
[0068] (c) a conduit (53) having an inner void (54) and outer
surface (55), the walls of which comprise a water transfer membrane
material, wherein one end of the conduit is connected to the
primary gas inlet (51), and the other end of the conduit is
connected to the primary gas outlet (52) so as to allow for the
flow of a primary gas through the inner void; and
[0069] (d) a housing (56) which encloses and provides a void space
(57) around at least a portion of the outer surface of said conduit
(53), wherein said housing has a secondary gas inlet (58) and a
secondary gas outlet (59) allowing for the flow of a secondary gas
through said void space (57); wherein secondary gas flowing through
the void space of said housing passes over an outer surface of said
conduit (53), but does not substantially mix with primary gas
flowing through the inner void (54) of said conduit.
[0070] The conduits (53) may be any of a variety of shapes,
including substantially cylindrical tubes, and three dimensional
rectangular (block) passages. Preferably the water transfer device
comprises a plurality of conduits (60), which are connected to a
plenum (61) at the primary gas inlet and a plenum (62) at the
primary gas outlet, so as to allow the flow of primary gas through
all of the conduits. As used herein, the term "connected" refers to
any mechanism which allows the passage of fluid from one point to
another, preferably without substantial loss of fluid. The device
preferably also comprises a mechanism for supporting the conduits
in the housing. Preferably the direction of flow of the primary gas
is in a substantially different, preferably essentially opposite,
direction than the flow of the secondary gas.
[0071] The water transfer membrane material useful herein is any
material that allows the transfer of water vapor from one gas to
another. Preferably, such material selectively allows the transfer
of water vapor, without also allowing the transfer of other gasses.
A preferred water transfer membrane selectively allows the transfer
of water vapor from a stream of primary gas to a stream of
secondary gas, without allowing significant passage (leaking) of
other components from the primary gas stream to the secondary
stream. Preferably, as depicted in FIG. 5, the primary gas is the
wet gas stream, from which water vapor is transferred to the
secondary gas, which is the dry gas stream. Preferably for water
transfer devices that transfer water vapor from reformate to an
input of a reactor, the primary gas is reformate and, preferably,
the secondary gas is air. Preferably, for water transfer devices
that transfer water vapor from a fuel cell effluent to another,
part of the fuel cell system, the primary gas is cathode effluent
and, preferably, the secondary gas is air.
[0072] Preferred water transfer membrane materials useful herein
include those made from poly[perfluorosulfonic] acid, sulfonated
polystyrene, polyethersulfone, sulfonated polyetherketone,
polycarbonates, other sulfonated materials, and mixtures thereof. A
preferred membrane material is comprised of poly[perfluorosulfonic]
acid. A particularly preferred membrane material is sold under the
brand name "NAFION" by the E.I. DuPont de Nemours Company. Tubes
useful herein made of NAFION membrane are and sold under the brand
name "PD SERIES MOISTURE EXCHANGERS" by Perma Pure, Inc.
[0073] Preferably the pressure of the primary gas in the conduit is
from about 50% to about 500%, more preferably from about 100% to
about 300%, more preferably from about 170% to about 270%, of the
pressure of the secondary gas in the housing. Also preferably, the
temperature of the dry gas stream is less than or equal to the
temperature of the wet gas stream. In a preferred embodiment, the
dry gas stream is air, preferably at a temperature less than about
85.degree. C. (185.degree. F.), more preferably less than about
50.degree. C. (122.degree. C.), more preferably less than about
30.degree. C. (86.degree. F.). Preferably the dry gas stream is air
at about ambient temperature and at about ambient pressure.
[0074] Preferably the temperature of the wet gas stream at the
input of the water transfer device, is maintained at a temperature
above the dew point of the gas, so that water does not condense in
the water transfer device. Preferably the temperature of the wet
gas stream at the inlet of the water transfer device is from about
1.degree. C. (1.8.degree. F.) to 10.degree. C. (18.degree. F.),
more preferably from about 1.degree. C. (1.8.degree. F.) to about
5.degree. C. (9.degree. F.), above its dew point.
[0075] Preferably, the water transfer efficiency of the water
transfer device of this invention is at least about 30% preferably
at least about 50%, more preferably at least about 80%, more
preferably at least about 90%. As referred to herein, "water
transfer efficiency" is the ratio of dW.sub.act/dW.sub.max, where
dW.sub.act is the amount of water actually transferred from the dry
gas stream to the wet gas stream, and dW.sub.max is the maximum
amount of water that theoretically could have been transferred. The
amount of water transferred may be determined using conventional
measurements of water content of gaseous streams, known in the art.
The maximum amount of water dW.sub.max is the lesser of the maximum
amount of water that can be absorbed by the dry gas stream (at a
given operating temperature and pressure), and the actual amount of
water in the input wet gas stream.
[0076] A preferred fuel processor embodiment also comprises an air
moving device, such as a compressor or blower for supply of air to
the reactor (e.g., the primary and PrOx reactors). In embodiments
in which the water transfer device humidifies the air for the
reactor, the water transfer device may humidify the air after it
has been compressed (i.e., the device is connected to the output of
the compressor) or, preferably, it may humidify the air before it
compressed (i.e., the device is connected to the input of the
compressor).
[0077] In a preferred embodiment of the invention, as depicted in
FIG. 2, a first water transfer device (21) transfers water vapor
from hydrogen reformate (22, the primary gas flowing through the
water transfer device) made by a reactor (20), containing water as
a by-product of the reformate reactions. The water vapor is
transferred to the air input stream (23), the secondary gas flowing
through the water transfer device) for the reactor. The reactor
(20) comprises a primary reactor (e.g., an autothermal reformer),
preferably in combination with a water/gas shift (WGS) reactor and
a preferential oxidation (PrOx) reactor. Fuel to the reactor is
provided from a fuel tank (24). The reformate (22) is passed
through the water transfer device (21) immediately after exiting
either the WGS or the PrOx reactor. Preferably, the air stream (23)
supplied to the water transfer device is ambient air, at ambient
pressure. The air passes through an air moving device, preferably a
compressor (25) prior to introduction to those components of the
reactor that require air (e.g., the primary reactor and the PrOx
reactor). After passing through the water transfer device, the
reformate (22) is supplied to the anode input of a fuel cell (11),
preferably a fuel cell stack.
[0078] The fuel cell system of the embodiment depicted in FIG. 2
also comprises a second water transfer device (10). The second
water transfer device (10) is connected to the cathode output of
the fuel cell (11) and transfers water vapor from the cathode
effluent (12, the primary gas in the water transfer device) to an
air stream (26, the secondary gas in the water transfer device).
The air stream (26) is supplied to the water transfer device (10)
at ambient temperature and pressure. After humidification, the air
stream is compressed with a compressor (27), and is supplied to the
cathode input of the fuel cell (11). After passing through the
water transfer device (10), the cathode effluent (12), along with
the anode effluent (28) is supplied to a combustor (14).
[0079] Accordingly, a preferred fuel cell system comprises:
[0080] (a) a fuel cell comprising an anode input for a
hydrogen-containing anode supply stream which is preferably
reformate, a cathode input for an oxidant-containing cathode supply
stream, which is preferably air, and a cathode output for a cathode
effluent which comprises water produced by the fuel cell; and
[0081] (b) a water transfer device connected to either or both of
the fuel cell inputs, preferably to the cathode input, wherein the
water transfer device transfers water from the cathode effluent to
either or both of the anode supply stream or the cathode supply
stream.
[0082] More specifically, a preferred fuel cell system
comprises:
[0083] (a) a fuel cell having an anode input for an anode supply
stream, a cathode input for a cathode supply stream, and a cathode
output for cathode effluent that comprises water produced by the
fuel cell; and
[0084] (b) a water transfer device comprising (i) a device cathode
effluent input connected to the cathode output of the fuel cell,
(ii) a device supply stream output connected to one or both of the
inputs of the fuel cell, and (iii) a water-transfer membrane;
[0085] wherein the water transfer device transfers water from the
cathode effluent to one or both of the fuel cell supply streams. A
preferred embodiment of this invention comprises the transfer of
water vapor from the cathode effluent to the cathode supply stream.
Another preferred embodiment comprises the transfer of water vapor
from the cathode effluent to the anode supply stream. Preferably,
the temperature of the cathode effluent at the device input is not
significantly greater than the temperature of the effluent at the
cathode output of the fuel cell. Accordingly, preferably, the
cathode effluent does not pass through a combustor prior to
entering the water transfer device. Also, in another preferred
embodiment, the air output of the water transfer device passes
through an air moving device, preferably a compressor, before
entering the cathode input of the fuel cell.
[0086] In another preferred embodiment of the invention, as
depicted in FIG. 3, a first water transfer device (21) transfers
water from reformate (22) to the air supply (23) for a primary
reactor (30), which comprises an autothermal reactor and a
water-gas shift (WGS) reactor. The reformate (22) is then supplied
to the water transfer device (21). Preferably, the air stream (23)
supplied to the water transfer device is ambient air, at ambient
pressure. After humidification in the water transfer device, the
air is compressed in an air moving device, preferably a compressor
(25) prior to introduction to the primary reactor (30) and a
preferential oxidation (PrOx) reactor (33). After passing through
the water transfer device, the reformate (22) passes through the
PrOx reactor, and is then supplied to the anode input of a fuel
cell (11), preferably a fuel cell stack.
[0087] In this embodiment, the fuel cell system comprises a second
water transfer device (10). The second water transfer device (10)
is connected to the cathode output of the fuel cell (11), and
transfers water vapor from cathode effluent (12) to the reformate
(22) after the reformate exits the PrOx (33). Air (34), as the
oxidant-containing gas, is supplied to the fuel cell from a
compressor (35). After humidification, the reformate (22) is
supplied to the anode input of the fuel cell (11). After passing
through the water transfer device (10), the cathode effluent (12)
is vented to the atmosphere. The anode effluent (28) is supplied to
a hydrogen reservoir (36), which stores or otherwise disposes of
any unreacted hydrogen in the anode effluent. Optionally, the
cathode effluent and anode effluent are supplied to a
combustor.
[0088] Accordingly, a preferred embodiment of this invention is a
fuel cell power plant, comprising:
[0089] (a) a reactor having a reactant input for a reactor oxidant
stream supplied to the reactor, and a reactor reformate output for
a reformate stream produced by the reactor;
[0090] (b) a first water transfer device comprising (i) a first
device reformate input connected to said reactor reformate output,
(ii) a first device reformate output; (iii) a first device oxidant
input; (iv) a first device oxidant output connected to said
reactant input of the reactor; and (v) a water-transfer membrane;
wherein said water transfer device transfers water from the
reformate stream to the reactor oxidant stream;
[0091] (c) a fuel cell comprising an anode input for an anode
reformate supply stream, a cathode input for a cathode oxidant
supply stream, an anode output for an anode effluent; and a cathode
output for a cathode effluent; and
[0092] (d) a second water transfer device comprising (i) a second
device reformate input connected to the first device reformate
output; (ii) a second device reformate output connected to the
anode input of the fuel cell stack; (iii) a second device effluent
input connected to one or both of the effluent outputs of the fuel
cell; (iv) a second device effluent output; and (v) a water
transfer membrane; wherein said second water transfer device
transfers water from one or both of said effluent streams to said
anode reformate supply stream. Preferably, in this embodiment, the
second water transfer device transfers water from the cathode
effluent stream to the reformate supply stream.
[0093] In another preferred embodiment of the invention, as
depicted in FIG. 4, a first water transfer device (21) transfers
water from reformate (22) to the air supply (23) for a reactor
(40). The reactor (40) preferably comprises a primary reactor and a
water-gas shift (WGS) reactor, wherein reformate produced by the
primary reactor flows through the WGS reactor. Preferably the
primary reactor is an autothermal reactor. After exiting the WGS
reactor, the reformate (22) passes through a preferential oxidation
(PrOx) reactor (33), and enters the first water transfer device
(21). After exiting the first water transfer device (21), the
reformate (22) is supplied to the anode of a fuel cell (11),
preferably a fuel cell stack.
[0094] The air stream (41) supplied to the first water transfer
device (21) flows from a second water transfer device (10) through
a splitter (42). After humidification by the first water transfer
device, air is supplied to the primary reactor and the WGS reactor
(40).
[0095] The second water transfer device (10) transfers water from
the cathode effluent (12) of the fuel cell (11) to the air stream
(41) that is supplied to the splitter (42). Air supplied to the
second water transfer device (10) is preferably provided by an air
moving device, preferably a compressor (43). The splitter (42)
diverts a portion of the air stream (41) to the cathode input of
the fuel cell (11), and a portion to the first water transfer
device (21). Optionally, water may also be provided by the splitter
(42) to the anode input of the fuel cell (22). Accordingly, the
second water transfer device (10) provides humidified air to the
stack, and also augments humidification of air supplied to the
primary and WGS reactors (40) through the first water transfer
device (21).
[0096] Also in this embodiment, the anode and cathode effluents
pass through condensor/separators (44 and 45) to extract liquid
water (46) from the anode and cathode effluents. The liquid water
(46) is stored in a water tank (47), for use during start-up of the
reactors (40). Optionally, the cathode effluent (12), after passing
through the second water transfer device (10) is supplied to a
combustor (14), along with anode effluent (28).
[0097] Accordingly, a preferred embodiment of this invention is a
fuel cell power plant, comprising:
[0098] (a) a reactor having a reactant input for a reactor oxidant
stream supplied to the reactor, and a reactor reformate output for
a reformate supply stream produced by the reactor;
[0099] (b) a first water transfer device comprising (i) a first
device reformate input connected to said reactor reformate output,
(ii) a first device reformate output; (iii) a first device oxidant
input for a first oxidant supply stream; (iv) a first device
oxidant output connected to said reactant input of the reactor; and
(v) a water-transfer membrane;
[0100] (c) a fuel cell comprising an anode input for the reformate
supply stream, a cathode input for a cathode oxidant stream, an
anode output for an anode effluent stream; and a cathode output for
a cathode effluent stream; and
[0101] (d) a second water transfer device comprising (i) a second
device cathode effluent input connected to the cathode output of
the fuel cell, (ii) a second device cathode effluent output, (iii)
a second device oxidant input for a second oxidant supply steam,
(iv) a second device oxidant output, connected to said first device
oxidant gas input, and (v) a water transfer membrane; wherein the
first water transfer device transfers water from the reformate
stream to the reactor oxidant stream, and wherein the second water
transfer device transfers water from the cathode effluent to the
first oxidant supply stream and to the cathode oxidant stream.
[0102] The examples and other embodiments described herein are
exemplary and not intended to be limiting in describing the full
scope of apparatuses, devices, components, materials, compositions
and methods of this invention. Equivalent changes, modifications
and variations of specific embodiments, materials, compositions and
methods may be made with substantially similar results.
* * * * *