U.S. patent application number 12/186433 was filed with the patent office on 2008-11-27 for fuel processor for use in a fuel cell system.
This patent application is currently assigned to ULTRACELL CORPORATION. Invention is credited to Jennifer BRANTLEY, Ian W. KAYE, Kenneth NEWELL, Arpad SOMOGYVARI, David SOPCHAK, Jesse THOMPSON.
Application Number | 20080289180 12/186433 |
Document ID | / |
Family ID | 39082629 |
Filed Date | 2008-11-27 |
United States Patent
Application |
20080289180 |
Kind Code |
A1 |
BRANTLEY; Jennifer ; et
al. |
November 27, 2008 |
FUEL PROCESSOR FOR USE IN A FUEL CELL SYSTEM
Abstract
A method for manufacturing a fuel processor may comprise
coupling a plurality of micro-tubes in parallel to form a flow
field tube array, each of the plurality of micro-tubes designed to
receive a fluid flow, depositing a catalyst layer inside each of
the plurality of micro-tubes, and attaching at least one burner to
a first end of the flow field tube array.
Inventors: |
BRANTLEY; Jennifer; (Dublin,
CA) ; NEWELL; Kenneth; (Livermore, CA) ;
SOPCHAK; David; (Oakland, CA) ; KAYE; Ian W.;
(Livermore, CA) ; THOMPSON; Jesse; (Brentwood,
CA) ; SOMOGYVARI; Arpad; (Livermore, CA) |
Correspondence
Address: |
Beyer Law Group LLP
P.O. BOX 1687
Cupertino
CA
95015-1687
US
|
Assignee: |
ULTRACELL CORPORATION
Livermore
CA
|
Family ID: |
39082629 |
Appl. No.: |
12/186433 |
Filed: |
August 5, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11835747 |
Aug 8, 2007 |
|
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12186433 |
|
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60836859 |
Aug 9, 2006 |
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Current U.S.
Class: |
29/890 ;
427/115 |
Current CPC
Class: |
C01B 2203/1023 20130101;
C01B 2203/0827 20130101; C01B 2203/1029 20130101; C01B 2203/1614
20130101; C01B 2203/0233 20130101; C01B 2203/0811 20130101; C01B
2203/0822 20130101; B01J 8/067 20130101; B01J 2208/0053 20130101;
B01J 8/0449 20130101; B01J 2219/00835 20130101; B01J 2219/00869
20130101; B01J 8/0484 20130101; B01J 2208/00504 20130101; B01J
2219/00891 20130101; B01J 8/06 20130101; Y02E 60/50 20130101; B01J
2219/00788 20130101; C01B 2203/1017 20130101; B01J 2208/00672
20130101; B01J 2208/00309 20130101; B01J 8/0496 20130101; C01B
2203/1288 20130101; C01B 3/323 20130101; H01M 8/04022 20130101;
B01J 2219/0086 20130101; B01J 2219/00873 20130101; B01J 8/0492
20130101; Y02P 20/10 20151101; Y02P 70/50 20151101; H01M 8/0631
20130101; C01B 2203/1076 20130101; B01J 19/0093 20130101; C01B
2203/066 20130101; Y10T 29/49345 20150115; B01J 2219/00846
20130101; C01B 2203/1064 20130101; B01J 8/065 20130101; C01B
2203/1223 20130101; B01J 19/2495 20130101 |
Class at
Publication: |
29/890 ;
427/115 |
International
Class: |
B21D 51/16 20060101
B21D051/16; H01M 8/00 20060101 H01M008/00 |
Claims
1. A method for manufacturing a fuel processor, comprising:
coupling a plurality of micro-tubes in parallel to form a flow
field tube array, each of the plurality of micro-tubes designed to
receive a fluid flow; depositing a catalyst layer inside each of
the plurality of micro-tubes; and attaching at least one burner to
a first end of the flow field tube array.
2. The method of claim 1, further comprising positioning at least
one membrane electrode assembly (MEA) adjacent the flow field tube
array.
3. The method of claim 1, wherein the plurality of micro-tubes are
thermally and electrically conductive.
4. The method of claim 1, wherein the coupling further comprises
welding the plurality of micro-tubes in parallel.
5. The method of claim 1, further comprising attaching a reformer
between the burner and the flow field tube array.
6. The method of claim 5, further comprising depositing a catalyst
layer in the reformer.
7. The method of claim 1, further comprising depositing a catalyst
layer in the at least one burner.
8. The method of claim 1, wherein the catalyst layer is a reformer
catalyst layer.
9. The method of claim 1, wherein the depositing further
comprising: trapping the catalyst layer in a macro cage of a
zeolite; and depositing the zeolite inside each of the plurality of
micro-tubes.
10. The method of claim 1, wherein the depositing further comprises
mixing the catalyst layer with the fluid flow.
11. The method of claim 1, wherein the depositing further comprises
etching the catalyst layer inside each of the plurality of
micro-tubes.
12. The method of claim 1, further comprising depositing a second
catalyst layer in the at least one burner.
13. The method of claim 12, wherein the depositing the second
catalyst layer further comprises: depositing an alumina layer on a
thermally conductive substrate; depositing a catalyst layer over
the alumina layer; and reducing the catalyst layer and the alumina
layer.
14. The method of claim 13, wherein the substrate is an aluminum
porous metal or an aluminum metallic sponge.
15. The method of claim 13, wherein the reducing further comprises
depositing a reducing agent gas over the catalyst layer.
16. The method of claim 1, further comprises wash coating a
catalyst layer to at least one wall of the at least one burner.
17. A method for manufacturing a fuel processor, comprising:
forming at least one catalyst layer, comprising: depositing an
alumina layer on a thermally conductive substrate; depositing a
catalyst layer over the alumina layer; and reducing the catalyst
layer and the alumina layer; coupling a plurality of micro-tubes in
parallel to form a flow field tube array, each of the plurality of
micro-tubes designed to receive a fluid flow; placing at least one
of the catalyst layers inside each of the plurality of micro-tubes;
attaching at least one burner to a first end of the flow field tube
array, and placing at least one of the catalyst layers in the at
least one burner.
18. The method of claim 17, wherein the substrate is an aluminum
porous metal or an aluminum metallic sponge.
19. The method of claim 17, further comprising positioning at least
one membrane electrode assembly (MEA) adjacent the flow field tube
array.
20. The method of claim 17, wherein the plurality of micro-tubes
are thermally and electrically conductive.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional Application which claims
priority under 35 U.S.C. .sctn.120 from co-pending U.S. patent
application Ser. No. 11/835,747, filed on Aug. 8, 2007 entitled
"Fuel Processor For Use In A Fuel Cell System", which claims
priority under 35 U.S.C. .sctn.119(e) from U.S. Provisional Patent
Application No. 60/836,859, filed Aug. 9, 2006 both of which are
incorporated by reference herein for all purposes.
FIELD OF THE INVENTION
[0002] The present disclosure relates generally to fuel cell
technology. In particular, the invention relates to a fuel
processor, used in a fuel cell system, to convert a fuel source to
hydrogen.
BACKGROUND OF THE INVENTION
[0003] Commonly, a fuel processor is often designed specifically
for a given fuel cell stack based on the fuel cell's power
performance, size and hydrogen fuel consumption requirements. As
such, it can only be integrated with a given cell stack. The fuel
processor is also a separate device, thermally and fluidically, and
requires substantial fluidic and gaseous manifolding and thermal
insulation, which adds to the fuel cell system volume and mass. In
addition, some fuel cell stack designs rely on a separate device
(such as a stack burner) to assist the stack in achieving operation
temperatures.
[0004] A fuel cell system electrochemically combines hydrogen and
oxygen to produce electrical energy. A reformed hydrogen supply
processes a fuel source to produce hydrogen. The fuel source acts
as a hydrogen carrier. Currently available hydrocarbon fuel sources
include methanol, ethanol, gasoline, propane and natural gas. The
reaction in the fuel processor should be carried out under
controlled temperatures to improve the performance of the processor
by preventing hot and cold spots, efficiently convert the
hydrocarbon fuel source to hydrogen, and preserve the integrity of
the catalyst in the catalytic chamber. Thermal inefficiencies in a
fuel cell system wastes energy and undesirably requires more fuel
to be consumed and carried.
OVERVIEW
[0005] A fuel processor for use in a fuel cell system, may be
formed from a monolith structure wherein the fluid flow directions
in the burner flow chamber and the reformer flow chamber are
directed in the same direction. This allows the fuel processor to
be run under controlled temperatures to improve the performance of
the processor by preventing hot and cold spots, efficiently convert
the hydrocarbon fuel source to hydrogen, and preserve the integrity
of the catalyst in the catalytic chamber.
[0006] In one embodiment, a method for manufacturing a fuel
processor may comprise coupling a plurality of micro-tubes in
parallel to form a flow field tube array, each of the plurality of
micro-tubes designed to receive a fluid flow, depositing a catalyst
layer inside each of the plurality of micro-tubes, and attaching at
least one burner to a first end of the flow field tube array.
[0007] In another embodiment, a method for manufacturing a fuel
processor may comprise forming at least one catalyst layer,
comprising: depositing an alumina layer on a thermally conductive
substrate, depositing a catalyst layer over the alumina layer, and
reducing the catalyst layer and the alumina layer. The method may
further comprise coupling a plurality of micro-tubes in parallel to
form a flow field tube array, each of the plurality of micro-tubes
designed to receive a fluid flow, placing at least one of the
catalyst layers inside each of the plurality of micro-tubes,
attaching at least one burner to a first end of the flow field tube
array, and placing at least one of the catalyst layers in the at
least one burner.
[0008] These and other features will be presented in more detail in
the following detailed description of the invention and the
associated figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The accompanying drawings, which are incorporated into and
constitute a part of this specification, illustrate one or more
example embodiments and, together with the description of example
embodiments, serve to explain the principles and
implementations.
[0010] In the drawings:
[0011] FIGS. 1A and 1B illustrate an example fuel processor.
[0012] FIG. 2 is a flow diagram illustrating an example method for
forming a catalyst for use in a fuel cell system.
[0013] FIGS. 3A-3D illustrate an example flow path for a fuel in a
fuel processor.
[0014] FIG. 4 illustrates an example flow path for a fuel in
another example fuel processor.
[0015] FIGS. 5A-5E illustrate exemplary distributed fuel processors
and methods of manufacturing the distributed fuel processors.
[0016] FIGS. 6A and 6B illustrate an example regenerator.
[0017] FIGS. 7A, 7B, and 7C illustrate other example
recuperators.
[0018] FIG. 8 illustrates an example fuel processor.
[0019] FIGS. 9A and 9B illustrate velocity flows of a fuel through
the fuel processor of FIG. 8 and an alternative embodiment of a
fuel processor, respectively.
[0020] FIGS. 10A, 10B, and 10C illustrate another example fuel
processor.
[0021] FIGS. 11A and 11B illustrate an example fuel cell package
and a schematic operation of the fuel cell package.
DESCRIPTION OF EXAMPLE EMBODIMENTS
[0022] Embodiments are described herein in the context of a fuel
processor for use in a fuel cell system. The following detailed
description is illustrative only and is not intended to be in any
way limiting. Other embodiments will readily suggest themselves to
such skilled persons having the benefit of this disclosure.
Reference will now be made in detail to implementations as
illustrated in the accompanying drawings. The same reference
indicators will be used throughout the drawings and the following
detailed description to refer to the same or like parts.
[0023] In the interest of clarity, not all of the routine features
of the implementations described herein are shown and described. It
will, of course, be appreciated that in the development of any such
actual implementation, numerous implementation-specific decisions
must be made in order to achieve the developer's specific goals,
such as compliance with application- and business-related
constraints, and that these specific goals will vary from one
implementation to another and from one developer to another.
Moreover, it will be appreciated that such a development effort
might be complex and time-consuming, but would nevertheless be a
routine undertaking of engineering for those of ordinary skill in
the art having the benefit of this disclosure.
[0024] Exemplary Fuel Processor
[0025] FIGS. 1A and 1B illustrate an example fuel processor. FIG.
1A illustrates a top perspective view of the fuel processor used in
a fuel cell system. Fuel processor 15 may reform methanol to
produce hydrogen. Fuel processor 15 comprises monolithic structure
100, end plates 182 and 184, end plate 185, reformer 32, heater 30,
boiler 34, boiler 108, recuperator 150 and housing 152 (FIG. 1B).
Although described with respect to methanol consumption for
hydrogen production, it is understood that fuel processors may
consume another fuel source, such as ethanol, gasoline, propane,
and other fuel sources.
[0026] As the term is used herein, `monolithic` refers to a single
and integrated structure that includes at least portions of
multiple components used in fuel processor 15. As shown in FIG. 1B,
a cross-sectional front view of monolithic structure 100 taken
through a mid-plane of fuel processor 15, monolithic structure 100
includes reformer 32, burner 30, boiler 34 and boiler 108.
Monolithic structure 100 also includes associated plumbing inlets
and outlets for reformer 32, burner 30 and boiler 34 disposed on
end plates 182 and 184 and interconnect 200. Monolithic structure
100 comprises a common material 141 that constitutes the structure.
The monolithic structure 100 and common material 141 simplify
manufacture of fuel processor 15. For example, using a metal for
common material 141 allows monolithic structure 100 to be formed by
extrusion. In a specific embodiment, monolithic structure 100 is
consistent in cross sectional dimensions between end plates 182 and
184 and solely comprises copper formed in a single extrusion.
[0027] An interconnect 200 may be disposed at least partially
between the fuel cell and the fuel processor to form a structural
and plumbing intermediary between the two. Interconnect is
described in commonly owned co-pending patent application Ser. No.
11/120,643, entitled "Compact Fuel Cell Package", filed May 2, 2005
which is incorporated by reference for all purposes, and will not
be discussed herein for brevity.
[0028] Housing 152 provides mechanical protection for internal
components of fuel processor 15 such as burner 30 and reformer 32.
Housing 152 also provides separation from the environment external
to processor 15 and includes inlet and outlet ports for gaseous and
liquid communication in and out of fuel processor 15. Housing 152
includes a set of housing walls that at least partially contain a
recuperator 150 and provides external mechanical protection for
components in fuel processor 15. The walls may comprise a suitably
stiff material such as a metal or a rigid polymer, for example.
Recuperator 150 improves thermal heat management for fuel processor
15 by a) allowing incoming air to be pre-heated before entering
burner 30, b) dissipating heat generated by burner 32 into the
incoming air before the heat reaches the outside of housing
152.
[0029] Boiler 34 heats methanol before reformer 32 receives the
methanol. Boiler 34 receives methanol via a fuel source inlet 81 on
interconnect 200, which couples to a methanol supply line 27 (FIG.
11B). Since methanol reforming and hydrogen production via a
catalyst 102 in reformer 32 often requires elevated methanol
temperatures, fuel processor 15 pre-heats the methanol before
receipt by reformer 32 via boiler 34. Boiler 34 is disposed in
proximity to burner 30 to receive heat generated in burner 30. The
heat transfers via conduction through monolithic structure from
burner 30 to boiler 34 and via convection from boiler 34 walls to
the methanol passing therethrough. In one embodiment, boiler 34 is
configured to vaporize liquid methanol. Boiler 34 then passes the
gaseous methanol to reformer 32 for gaseous interaction with
catalyst 102.
[0030] Reformer 32 is configured to receive methanol from boiler
34. Walls 111 in monolithic structure 100 and end walls 113 on end
plates 182 and 184 define dimensions for a reformer chamber 103. In
one embodiment, end plate 182 and/or end plate 184 includes a
channel that routes heated methanol exhausted from boiler 34 into
reformer 32.
[0031] In one embodiment, a reformer includes a multi-pass
arrangement. Reformer 32 includes three multi-pass portions that
process methanol in series: chamber section 32a, chamber section
32b, and chamber section 32c. A reformer chamber 103 then includes
the volume of all three sections 32a-c. Each section traverses the
length of monolithic structure 100 and opens to each other in
series such that sections 32a-c form one continuous path for
gaseous flow. More specifically, heated and gaseous methanol from
boiler 34 a) enters reformer chamber section 32a at an inlet end of
monolithic structure 100 and flows to the other end over catalyst
102 in section 32a, b) then flows into chamber section 32b at the
second end of monolithic structure 100 and flows to the inlet end
over catalyst 102 in section 32b, and c) flows into chamber section
32c at one end of monolithic structure 100 and flows to the other
end over catalyst 102 in the chamber section 32c.
[0032] Reformer 32 includes a catalyst 102 that facilitates the
production of hydrogen. Catalytic combustion provides heat for the
reforming process and lessens emissions. Better heat and mass
transfer improves performance of the reforming process, both with
regard to combustion and steam reforming. Catalyst 102 reacts with
methanol and produces hydrogen gas and carbon dioxide. In one
embodiment, catalyst 102 comprises pellets packed to form a porous
catalyst bed or otherwise suitably filled into the volume of
reformer chamber 103. Pellet diameters ranging from about 50
microns to about 1.5 millimeters are suitable for many
applications. Pellet diameters ranging from about 500 microns to
about 1 millimeter are suitable for use with reformer 32. Pellet
sizes may be varied relative to the cross sectional size of
reformer sections 32a-c, e.g., as the reformer sections increase in
size so does catalyst 102 pellet diameters.
[0033] Pellet sizes and packing may also be varied to control the
pressure drop that occurs through reformer chamber 103. In one
embodiment, pressure drops from about 0.2 to about 2 psi gauge are
suitable between the inlet and outlet of reformer chamber 103.
However, the mass of gaseous material flowing through the reactor
may affect heat transfer. For example, the pressure drop across a
packed catalyst bed may be relatively high and the fans, blowers or
compressors used in the process may limit mass flow through the
catalyst bed. The combustion process may further be limited by the
use of oxygen depleted "air" and require high volumetric flows
through the catalyst bed to provide sufficient oxygen for complete
combustion. The cooling effect of these high flows may be
substantial as the heating and cooling of large volumes of inert
gases may decrease the efficiency of the fuel cell system 10.
[0034] One suitable catalyst 102 may include copper-zinc alloy
(CuZn) coated onto alumina pellets when methanol is used as a
hydrocarbon fuel source 17. Other materials suitable for catalyst
102 include platinum (Pt), palladium (Pd), a platinum/palladium
mix, nickel, and other precious metal catalysts for example. In
another embodiment, catalyst 102 may also comprise catalyst
materials listed herein coated onto a metal sponge or metal foam.
However, some catalysts used for combustion may include a shell of
active material, such Pt or Pd, on an alumina core. The bulk of the
catalyst may consist of the alumina, which may be a relatively poor
thermal conductor. Thus, much of the initial energy produced during
startup of a reformer may be used to heat the alumina and heat
transfer to the alumina limits rapid thermal response of the fuel
cell system 10. Furthermore, some steam reforming catalysts may
also have relatively low thermal conductivity, which further
complicates heat transfer from the catalytic heater. Thus, in
another embodiment, a thermally conductive substrate such as
aluminum in the form of a porous metal or metallic sponge may be
used as the catalyst. The porosity of the metal or sponge, and
consequently the pressure drop, may be controlled to meet fuel
processor and fuel cell system requirements.
[0035] FIG. 2 is a flow diagram illustrating a example method for
forming a catalyst for use in a fuel cell system. The catalyst may
be used in the reformer or burner. A thermally conductive aluminum
porous metal or aluminum metallic sponge substrate may be obtained
at 200. An alumina layer may be deposited on the thermally
conductive substrate at 202. The substrate may be anodized to
deposit the alumina layer. Other methods may also be used, such as
chemical and electrochemical etching.
[0036] An active catalyst may be deposited onto the alumina layer
at 204. The catalyst deposited may be specific for an intended
purpose. For example, chloroplatinic acid may be deposited onto the
alumina layer for use in the burner. The depth of the alumina layer
may be controlled to optimize both adhesion of an active catalyst
and heat transfer to the aluminum. An outer surface of the aluminum
may also be constructed to optimize heat transfer between it and a
reactor wall. Consequently, a large portion of the heat transfer
proceeds via conduction through the substrate.
[0037] The catalyst layer may then be reduced at 206 to remove the
hydrogen or acid before being inserted into the fuel cell system at
208. As stated above, the catalyst may be inserted into the
reformer and/or burner. The substrate may be reduced by any known
method, such as by the introduction of hydrogen gas into the
catalyst layer.
[0038] In another embodiment, a fuel processor may include a
microlith reactor, where the porosity, and consequently the
pressure drop, can be controlled in a manufacturing process. An
example of a microlith reactor may be those made by Precision
Combustion, Inc. of North Haven, Conn. For example, heat transfer
in the reformer may be improved by use of a Raney Copper-Zinc
catalyst. The starting material, a copper-zinc-aluminum
(Cu--Zn--Al) alloy, may be prepared to optimize the Cu:Zn ratio.
The fully extracted catalyst may include a metallic powder while a
partially extracted catalyst may be shaped to maximize contact with
the catalytic burner.
[0039] Use of the porous metal or metallic sponge may improve heat
transfer within the catalyst bed and from the combustion chamber to
the reforming chamber. This promotes a more even temperature
distribution throughout the reactors and allow for more energy
efficient operation. Additionally, a wash coat of the desired metal
catalyst material may be placed onto the walls of the reformer
chamber or the burner chamber to improve heat transfer.
[0040] Referring back to FIGS. 1A and 1B, reformer 32 is configured
to output hydrogen and includes an outlet port 209 that
communicates hydrogen formed in reformer 32 outside of fuel
processor 15. Port 209 is disposed on a wall of end plate 184 and
includes a hole that passes through the wall. Port 209 opens to
hydrogen conduit 204a in interconnect 200, which then forms part of
a hydrogen provision line 39 (FIG. 11B). Line 39 communicates the
hydrogen to the anode of fuel cell 20 for electrical energy
generation.
[0041] Hydrogen production in reformer 32 is slightly endothermic
and draws heat from burner 30. Burner 30 generates heat and is
configured to provide heat to reformer 32. As shown in FIG. 1B,
burner 30 may comprise four burner chambers 105a-d that surround
reformer 32. In one embodiment, burner 30 uses electrical
resistance and electrical energy to produce heat.
[0042] In the embodiment shown, burner 30 employs catalytic
combustion to produce heat. As the term is used herein, a burner
refers to a heater that uses a catalytic heating process to
generate heat. A heater in a fuel processor may alternatively
employ electrical heating, for example. A catalyst 104 disposed in
each burner chamber 105 helps a burner fuel passed through the
chamber generate heat. Burner 30 includes an inlet that receives
methanol 17 from boiler 108 via a channel in one of end plates 182
or 184. In one embodiment, methanol produces heat in burner 30 and
catalyst 104 facilitates the methanol production of heat. In
another embodiment, waste hydrogen from fuel cell 20 produces heat
in the presence of catalyst 104. Suitable burner catalysts 104 may
include platinum or palladium coated onto alumina pellets for
example. Other materials suitable for catalyst 104 include iron,
tin oxide, other noble-metal catalysts, reducible oxides, and
mixtures thereof.
[0043] The pellets that may be packed into burner chamber 105 to
form a porous bed or otherwise suitably filled into the burner
chamber volume. Catalyst 104 pellet sizes may be varied relative to
the cross sectional size of burner chamber 105. Catalyst 104 may
also comprise catalyst materials listed above coated onto a metal
sponge or metal foam as discussed with reference to FIG. 2.
Moreover, catalyst 104 may be wash coated onto the walls of burner
chamber 105.
[0044] Some fuel sources generate additional heat in burner 30, or
generate heat more efficiently, with elevated temperatures. Fuel
processor 15 includes a boiler 108 that heats methanol before
burner 30 receives the fuel source. In this case, boiler 108
receives the methanol via fuel source inlet 85. Boiler 108 is
disposed in proximity to burner 30 to receive heat generated in
burner 30. The heat transfers via conduction through monolithic
structure from burner 30 to boiler 108 and via convection from
boiler 108 walls to the methanol passing therethrough.
[0045] Air including oxygen enters fuel processor 15 via air inlet
port 91. Burner 30 uses the oxygen for catalytic combustion of
methanol. A burner 30 in fuel processor 15 generates heat and
typically operates at an elevated temperature. In one embodiment,
fuel processor 15 comprises a recuperator 150 to improve thermal
management for fuel processor 15. Recuperator 150 at least
partially thermally isolates components internal to housing
152--such as burner 30--and contains heat within fuel processor 15.
Recuperator 150 is configured such that air passing through
recuperator chamber 156 receives heat generated in burner 30.
Recuperator 150 offers thus two functions for fuel processor 15: a)
it permits active cooling of components within fuel processor 15
before the heat reaches an outer portion of the fuel processor, and
b) it pre-heats the air going to burner 30. Air first passes along
the outside of recuperator 150 before passing through apertures in
the recuperator and along the inside of recuperator 150. This heats
the air before receipt by air inlet port 93 of burner 30.
[0046] In one embodiment, as illustrated in FIG. 11B, fuel cell
system or package 10 runs anode exhaust from the fuel cell 20 back
to fuel processor. Line 38 routes unused hydrogen from fuel cell 20
burner inlet 109, which provides the anode exhaust to burner 30 (or
to the regenerator 36 and then to burner inlet 109 and into burner
30). Burner 30 includes a thermal catalyst that reacts with the
unused hydrogen to produce heat. Since hydrogen consumption within
fuel cell 20 is often incomplete and the anode exhaust often
includes unused hydrogen, re-routing the anode exhaust to burner 30
allows fuel cell system 10 to capitalize on unused hydrogen in fuel
cell 20 and increase hydrogen usage and efficiency. Package 10 thus
provides flexibility to use different fuels in a catalytic burner
30. For example, if fuel cell 20 can reliably and efficiently
consume over 90% of the hydrogen in the anode stream, then there
may not be sufficient hydrogen to maintain reformer and boiler
operating temperatures in fuel processor 15. Under this
circumstance, methanol supply is increased to produce additional
heat to maintain the reformer and boiler temperatures.
[0047] Referring now to FIG. 1B, burner inlet 109 traverses
monolithic structure 100 and carries anode exhaust from fuel cell
20 before provision into burner 30. Disposing burner inlet 109
adjacent to a burner chamber 105 also heats the incoming anode
exhaust, which reduces heat transferred to the anode exhaust in the
burner chamber 105.
[0048] Referring back to FIG. 11B, in another embodiment, package
10 runs a heating medium from fuel processor 15 to fuel cell 20 to
provide heat to fuel cell 20. In this case, package 10 includes
plumbing configured to transport the heating medium from fuel
processor 15 to fuel cell 20. As the term is used herein, plumbing
may comprise any tubing, piping and/or channeling that communicates
a gas or liquid from one location to a second location. The
plumbing may also comprise one or more valves, gates or other
devices to facilitate and control flow. Plumbing between burner 30
and fuel cell 20 occurs via interconnect 200.
[0049] In a specific embodiment, line 35 transports heated gases to
fan 37, which moves the heated gases within fuel cell 20 and across
the fuel cell stack and heat transfer appendages. Alternatively,
the plumbing may be configured to transport the heating medium from
burner 30 to one or more heat transfer appendages. In this case,
line 35 may continue through the fuel cell housing and open in the
proximity of one or more heat transfer appendages. A hole in the
fuel cell housing then allows line 35 to pass therethrough or
connect to a port that communicates the gases to plumbing inside
the fuel cell for delivery to the fuel cell stack and heat transfer
appendage. For catalytic heat generation in fuel cell 20, the
plumbing may also transport the heating medium to facilitate
gaseous interaction with the catalyst, such as plumbing delivery to
one or more bulkheads.
[0050] In one embodiment, the heating medium comprises heated gases
exhausted from burner 30. A catalytic burner or electrical
resistance burner operates at elevated temperatures. Cooling air
exhausted from an electric burner or product gases exhausted from a
catalytic burner are often greater than about 100 degrees Celsius
when the gases leaves the fuel processor. For many catalytic
burners, depending on the fuel source employed, the heating medium
is commonly greater than about 200 degrees Celsius when the heating
medium leaves the fuel processor. These heated gases are
transported to the fuel cell for convective heat transfer in the
fuel cell, such as passing the heated gases over one or more heat
transfer appendages 46 for convective heat transfer from the warmer
gases into the cooler heat transfer appendages.
[0051] In another embodiment, burner 30 is a catalytic burner and
the heating medium comprises the fuel source. Catalytic combustion
in burner 30 is often incomplete and the burner exhaust gases
include unused and gaseous methanol. Fuel cell 20 then comprises a
thermal catalyst that facilitates production of heat in the fuel
cell in the presence of methanol. The fuel source is typically
vaporized prior to reaching the burner to facilitate catalytic
combustion. In this case, conduit 35 transports the gaseous and
unused methanol to the thermal catalyst in fuel cell 20. Suitable
methanol catalysts, such as platinum or palladium coated onto
alumina pellets, are also described herein with respect to catalyst
104 in burner 30.
[0052] In one embodiment, the heating medium is transported to the
fuel cell during a start-up period before the fuel cell begins
generating electrical energy, e.g., in response to a request for
electrical energy. Heating a fuel cell in this manner allows fuel
cell component operating temperatures to be reached sooner and
expedites warm-up time needed when initially turning on fuel cell
20. In another embodiment, the heating medium is transported from
the fuel processor to the fuel cell during a period of non-activity
in which the fuel cell does not generate electrical energy and the
component cools. Since many fuel cells require elevated
temperatures for operation and the electrical energy generating
process is exothermic, the fuel cell usually does not require
external heating during electrical energy generation. However, when
electrical energy generation ceases for an extended time and the
component drops below a threshold operating temperature, the
heating medium may then be transported from the fuel processor to
regain the operating temperature and resume electrical energy
generation. This permits operating temperatures in a fuel cell to
be maintained when electrical energy is not being generated by the
fuel cell.
[0053] Although FIGS. 1A and 1B are illustrated with respect to the
reformer and burner, it is anticipated that a fuel cell package may
include other fuel processor designs. Many architectures employ a
planar reformer disposed on top or below to a planar burner.
Micro-channel designs fabricated in silicon commonly employ such
stacked planar architectures may be used. Other fuel processors may
be used that process fuel sources other than methanol. Fuel sources
other than methanol were listed above, and processors for these
fuels are not detailed herein for sake of brevity. Further
description of planar fuel processors suitable for use are included
in commonly owned co-pending patent application Ser. No.
10/877,044, entitled "Annular Fuel Processor And Methods", filed
Jun. 25, 2004 which is incorporated by reference for all
purposes.
[0054] FIGS. 3A-3D illustrate an example flow path for a fuel in a
fuel processor. FIG. 3A is a schematic diagram of a counter-flow
path for fuel used in a fuel processor, such as in the example fuel
processors described herein with reference to FIGS. 1A, 1B, 8, and
10A. Current fuel processors may have fuel flows that are in a
counter-flow orientation as illustrated in FIG. 3A. Fuel in burner
chamber 302 may flow in the direction of arrow A while fuel in the
reformer chamber 304 may flow in the direction of arrow B, which
may be partially counter to the fuel flow in burner chamber 302.
The fuel and air in the burner chamber 302 combusts more at the
beginning 306 of the burner chamber 302, rather than at the end
310, because of the higher concentration of each reactant. The
reaction is an exothermic reaction and the heat released is formed
through the oxidation of the fuel such as hydrogen, methanol,
ethanol, and other fuel sources. This leads to a higher heat
production at the beginning 306 of the burner chamber 302 as
illustrated in FIG. 3A where the hottest areas are represented by
the darker shading. The heat release in the burner chamber 302 may
decrease over its length toward the end 310 of the burner chamber
302, as represented by the lighter shading, and the end or
downstream section 310 of the burner chamber 302 may be primarily
dedicated to cleaning up pre-combustion products such as carbon
monoxide, formaldehyde, and other products.
[0055] The fuel (e.g. methanol and water mixture) in the reformer
chamber 304 may also reform more at the beginning 308 of the
reformer chamber 304 because of a higher concentration of
reactants. However, this is an endothermic reaction and therefore
is a higher heat sink where heat demand is the highest, as
represented by the lighter shading at the beginning 308. As the
reaction completes to form carbon dioxide and water at the end 312
of the reformer chamber 304, the reaction may become partially
exothermic and release some heat, as represented by the darker
shading at end 312.
[0056] Thus, in a counter-flow orientation, the temperature is
slightly higher at the beginning 306 of the burner chamber 302,
which provides more heat to the reformer at the end 312 of the
reformer flow path. This provides more energy to convert any
remaining methanol in the reformer stream at the end of the
reformer flow path.
[0057] FIG. 3B a schematic diagram of a co-flow path for fuel in a
fuel processor, such as the embodiment described herein with
reference to FIGS. 1A, 1B, 8, and 10A. Fuel in burner chamber 302
may flow in the direction of arrow C while fuel in the reformer
chamber 304 may flow in the direction of arrow D, which may be in
the same direction as the fuel flow in burner chamber 302. In this
co-flow configuration, the hottest section 310 of the burner
chamber 302 may be adjacent to the beginning 308 of the reformer
chamber 304 where heat demand is the highest. This co-flow
configuration may result in reduced burner exhaust temperature
and/or reduced heat load in the burner thereby increasing the
efficiency of the fuel processor 15 and the overall electrical
efficiency and energy density of the system 10.
[0058] Thus, by matching the heat production of the burner chamber
302 and the heat load of the reformer chamber 304, the efficiency
of the fuel processor 15 may be improved, and the catalysts in each
chamber 302,304 may be more effectively used. Moreover, by
orienting the flows to be co-flow or in the same direction in the
fuel processor 15, the heat loads may be matched, which may prevent
hot and cold spots that contribute to poor performance of the
system 10.
[0059] FIG. 3C illustrates an example fuel processor and FIG. 3D is
a side view of the fuel processor of FIG. 3C. In use, the fuel for
the reformer may be vaporized in a flow passage in the direction of
arrow E in a boiler 314 of the fuel processor 15. Vaporizing the
fuel way from the reformer chamber 304 may ensure that the
vaporization of fuel does not hinder the heat transfer between the
burner chamber 302 and the reformer chamber 304. Although
illustrated with the use of a boiler 314, this is not intended to
be limiting as the reformer fuel may be vaporized with any external
device, such as an external heat exchanger or recuperator.
[0060] The chambers 302, 304 may be formed in a copper monolith
having a high thermal conductivity, hermetic, and non-porous to
efficiently facilitate heat transfer between the chambers 302, 304.
Other materials such as anodized aluminum, silicon carbide,
stainless steel, ceramic, titanium, and the like may also be
used.
[0061] Once the fuel is vaporized in boiler 314, the fuel may flow
to reformer chamber 304 and flow in the direction of arrow D. Fuel
from burner chamber 302 may flow in direction of arrow C, the same
direction as the reformer fuel flow. The fuel may flow from the
burner chamber 302 to the reformer chamber 304. In this embodiment,
the flow path for each fuel may be in a U-shape. For example, the
fuel flow from the boiler 314 to the reformer chamber 304 may be in
a U-shape. Similarly, the fuel flow from the burner chamber 302 to
the reformer chamber 304 may be in a U-shape. As discussed in
detail below with reference to FIGS. 8, 9A, and 9B, this flow path
provides for a smoother and more efficient fuel flow.
[0062] FIG. 4 illustrates an example flow path for a fuel in
another example fuel processor. The fuel processor 400 may be a
single pass fuel processor whereby the burner fuel flow and the
reformer fuel flow are in the same direction. Although illustrated
in a co-flow orientation, it is not intended to be limiting as the
flow directions of the burner fuel and the reformer fuel may be
partially counter to each other. As illustrated, fuel processor 400
may be used with the manifolds in interconnect 200. Fuel processor
400 may have at least two chambers, a reformer chamber 404 and a
burner chamber 402. The burner chamber 402 may have at least two
flow passages 424 and 426. Ambient air may be received from air
inlets 416, 428 or from regenerator air inlet 414. A regenerator
(not shown) may be used to enclose the fuel processor 400 to
pre-heat the ambient air. Example regenerators are discussed
throughout and will not be discussed herein for brevity.
[0063] Air may enter burner chamber 402 from air inlet 416 and be
directed into burner chamber 424 via openings 430 in the direction
of arrows D. Air in burner chamber 424 may contact catalyst 406a
and be directed to flow passage 426 in the direction of arrow F.
Air may also be directed into burner chamber 426 via air inlet 428
in the direction of arrow E. Air may be directed into the burner
chamber 426 by any known means such as a fan. The air may contact
catalyst 406b and exit the burner chamber 402 at burner exhaust
410.
[0064] The reformer chamber may have at least two flow passages 418
and 420. Flow passage 418 may receive fuel from inlet 422 in the
direction of arrow A. The fuel may contact reformer catalyst 408a
and flow in the direction of arrow B. The fuel may then be directed
to flow into flow passage 420 in the direction of arrow C toward
catalyst 408b and exit at reformer exhaust 412.
[0065] The combustion and reforming reactions in the burner chamber
402 and reformer chamber 404, respectively, may run substantially
parallel to each other and in the same direction as illustrated
with arrows C and F. Thus, the orientation of the fuel flows in the
chambers 402, 404 may match the heat loads in the fuel processor as
discussed above with reference to FIG. 3B. Thus, the co-flow
configuration may result in reduced burner exhaust temperature
and/or reduced heat load in the burner thereby increasing the
efficiency of the fuel processor 400 and the electrical efficiency
and energy density of the system 10.
[0066] FIGS. 5A-5E illustrate exemplary distributed fuel processors
and methods of manufacturing the distributed fuel processors. FIG.
5A illustrates the distributed fuel processor positioned within a
fuel cell stack. In one embodiment, the distributed fuel processor
502 may be positioned directly between membrane electrode
assemblies (MEAs) 504 (e.g., bi-polar plates) of a fuel cell stack
500. In another embodiment, the distributed fuel processor 502 may
be integral with the MEA 504 as illustrated with reference to FIGS.
5C and 5D. The distributed fuel processors 502 may be designed and
configured to deliver hydrogen to the MEA 504. Since the
distributed fuel processors 502 may be integrated directly onto the
periphery of the bi-polar plate, use of the distributed fuel
processors 502 may reduce the complexity, volume and mass
associated with fluidic and gaseous distribution between a fuel
cell and a fuel processor. Having the distributed fuel processor
502 either integrated directly onto the periphery of or integral
with the MEA 504 may result in a substantially smaller and modular
reformed fuel cell system. Moreover, the heat generated by the
distributed fuel processors 502 may provide direct heating of the
fuel cell stack 500 to more quickly and efficiently achieve
operational temperatures for the MEA.
[0067] FIG. 5B illustrates a perspective cross-sectional view of
the distributed fuel processor. The distributed fuel processor 502
may have a burner 506 coupled to the fuel processor first end 508.
The burner 506 may have an inlet (not shown) substantially opposite
an exhaust port 510. The inlet may allow gasses, such as air, to
enter the burner 506 in the direction of arrow A. The inlet and
exhaust port 510 may be an opening in the burner 506.
Alternatively, a tube may be used as the inlet and/or exhaust port
510. Any exhaust gasses may exit the burner 506 at the exhaust port
510 in the direction of arrow D. The burner 506 may have a catalyst
channel therein (not shown) filled with catalyst, such as alumina
beads coated with ultra-fine Platinum powder.
[0068] The fuel processor 502 may have a heat exchanger 512 having
a plurality of parallel micro-tubes 514. The micro-tubes may have
an outer diameter of about 0.5 mm-3 mm. The micro-tubes 514 may be
thermally and electrically conductive and joined parallel along
their outer surface via brazing, laser, ultrasonic, or any other
welding methods. The micro-tubes may then form a flow field tube
array whereby gases may flow between channels 516 formed between
the micro-tubes 514.
[0069] Although not illustrated, a second burner may be positioned
at the second end 520 of the distributed fuel processor 502. In
use, fuel, such as air or a methanol/water mixture, may be flowed
into the burner 506 and second burner through inlet in the
direction of arrow A. Through conductive heating by the burners
506, the fuel is vaporized and enters the micro-tubes 514, such as
in the direction of arrow B. The inside walls of the micro-tubes
514 may be coated with an active reformer catalyst. As such, the
micro-tube 514 array may play a dual role as a flow field and as a
reformer.
[0070] In one embodiment, the reformed catalyst may be deposited
into the micro-tubes by depositing a solution of the active
catalyst into the solution flowing through the micro-tubes. In this
case, an adhesive substrate such as alumina or silica nanoparticles
may be used. In another embodiment, the substrate may be etched
either chemically or electrochemically from an aluminum tube. Such
methods may be used to deposit active steam reforming catalyst. In
yet another embodiment, a spray powder may be milled to sub-micron
particle sizes or prepared as nanoparticles for deposition into the
micro-tubes. In still another embodiment, the active catalyst may
be trapped inside a macro cage of a zeolite and the modified
zeolite may be deposited into the micro-tubes. Other known methods
may also be used to deposit the catalyst in the micro-tubes
514.
[0071] The fuel may react with the reformer catalyst in the
micro-tubes 514 to form reformate. The resulting reformate may exit
the micro-tubes at apertures 522 in the direction of arrow C on
each end of the distributed fuel processor 502. The apertures 522
may be positioned on an anode side such that the hydrogen from the
reformate flows into the anode gas diffusion layer of the MEA.
[0072] FIG. 5C illustrates a top view of a distributed fuel
processor integral with an MEA. In one embodiment, the distributed
fuel processor 550 may be used in a reformed methanol fuel cell
(RMFC). A burner 552 and reformer 554 may be positioned on a
periphery of the MEA or bi-polar plate 558. In a specific
embodiment, the burner 552 may be located on an outermost edge or
at a first side 556 of the MEA 558. The burner may have an inlet
564 and a burner exhaust 566. The inlet 564 may receive gasses in
the direction of arrow B to flow into the burner 552 and burner
exhaust gasses may exit the burner exhaust 566 in the direction of
arrow C. The reformer 554 may be parallel to and positioned between
the burner 552 and MEA 558. This allows the reformer 554 to be
located inboard and adjacent to the burner 552 thereby sharing a
common surface 560 for the purposes of heat transfer from the
burner 552 to the reformer 554. Although illustrated with the
burner 552 and reformer 554 positioned on first side 556, the
position of the burner 552 and reformer 554 is not intended to be
limiting as they may be located on either of the other three sides
of the MEA 558.
[0073] The burner 552 may have a catalyst channel therein (not
shown) filled with catalyst, such as alumina beads coated with
ultra-fine Platinum powder. The reformer 554 may have a reformer
catalyst channel therein (not shown) filled with catalyst, such as
a coarse copper-zinc oxide powder.
[0074] During start-up, the burner 552 may receive a fuel, such as
a methanol/water (MeOH--H.sub.2O) blend, through inlet 564. In one
embodiment, inlet 564 may be a resistive annular heater tube to
vaporize the fuel source upon entry to the burner 552. In another
embodiment, the fuel source may be vaporized by a heater source
separate from the distributed fuel processor 550. When the
vaporized fuel contacts the burner catalyst, heat may be generated
along the length of the burner 552 catalyst channel and
conductively transfer the heat through the shared wall 560 to the
reformer 554 catalyst channel.
[0075] The heat in the reformer 554 will react with the catalyst in
the reformer 554 catalyst channel to produce reformate (Hydrogen
(H.sub.2), Carbon Dioxide (CO.sub.2) and carbon monoxide (CO)). The
reformate may be passed through to the anode gas diffusion layer
574 (FIG. 5D) of the bi-polar plate 558 via reformer outlets 570.
The hydrogen may be catalytically reduced to atomic hydrogen in the
anode gas diffusion layer 574 of the MEA 558 as further discussed
below. Excess or unreacted hydrogen may be collected or diffused at
reformate exhaust 562 and routed via channel 572 to combine with
the air supplied by inlet 564 to burner 552. Reformate exhaust 562
may be positioned opposite the burner 552 and reformer 554. Excess
reformate may thus be exhausted back to the burner 552 and mixed
with the depleted air to sustain the catalytic reaction in the
burner 552 without using additional fuel source, such as the
MeOH-water mixture. Thus, after start-up, the burner 552 heat may
be sustained by the excess (or unreacted) hydrogen from the MEA 558
and air. This provides for a more efficient fuel cell system since
less fuel may be used.
[0076] FIG. 5D is a cross-sectional view of yet another example
distributed fuel processor. In another embodiment, a plurality of
micro-tubes 576, similar to the micro-tubes discussed above with
reference to FIG. 5B, may be integrated with the MEA 558. The
micro-tubes 576 may have an outer diameter between about 0.5 mm-3
mm. The micro-tubes 576 may be thermally and electrically
conductive and joined in parallel along their outer surface via
brazing, laser, ultrasonic welding, or any other welding technique.
The joined micro-tubes 576 may produce a flow-field tube array. A
burner and reformer may be positioned on at least one end of the
flow field tube array.
[0077] FIG. 5E is a flow diagram illustrating a method for
manufacturing a distributed fuel processor. A plurality of
micro-tubes may be attached in parallel to form a flow field tube
array at 580. The micro-tubes may have an outer diameter of about
0.5 mm-3 mm. The micro-tubes may be thermally and electrically
conductive and joined parallel along their outer surface via
brazing, laser, ultrasonic, or any other welding methods. The
micro-tubes may then form a flow field tube array whereby gases may
flow between channels formed between the micro-tubes 514. The flow
field tube array may also act as a heat exchanger since heat from
the burner may be used to heat the incoming fuel.
[0078] Catalyst may be deposited into the micro-tubes at 582. The
catalyst deposited may be reformer catalyst. The reformed catalyst
may be deposited into the micro-tubes by depositing a solution of
the active catalyst into the solution flowing through the
micro-tubes. In this case, an adhesive substrate such as alumina or
silica nanoparticles may be used. In another embodiment, the
substrate may be etched either chemically or electrochemically from
an aluminum tube. Such methods may be used to deposit active steam
reforming catalyst. In yet another embodiment, a spray powder may
be milled to sub-micron particle sizes or prepared as nanoparticles
for deposition into the micro-tubes. In still another embodiment,
the active catalyst may be trapped inside a macro cage of a zeolite
and the modified zeolite may be deposited into the micro-tubes.
Other known methods may also be used to deposit the catalyst in the
micro-tubes.
[0079] A burner may be coupled to each ends of the flow field tube
array at 584. The burner may have a catalyst channel filled with
catalyst, such as alumina beads coated with ultra-fine Platinum
powder. The burner may receive a fuel flow, such as air or a
MeOH--H.sub.2O mixture, via an inlet. The heat generated by the
burner may be used to vaporize the fuel. The vaporized fuel may
then flow into the micro-tubes to form reformate.
[0080] The distributed fuel processor may be positioned between two
MEAs to form a fuel cell stack at 586. If the fuel cell stack is
not completed at 588, additional distributed fuel processor may be
formed by repeating steps 580 through 586.
[0081] FIGS. 6A and 6B illustrate an example regenerator. While
thermal management techniques described herein will now be
described as fuel processor components, those skilled in the art
will recognize that the methods of thermal management may also be
used for general applications. A regenerator 600 may pre-heat a
process gas or liquid before it enters burner 30 (FIG. 1B).
Regenerator 600 may also reduce heat loss from fuel cell 15 by
heating the incoming process liquids or gases before the heat
escapes fuel processor 15. In one sense, regenerator 600 may
regenerate waste heat in fuel processor 15 to improve thermal
management and thermal efficiency of the fuel processor 15.
Specifically, waste heat from burner 30 may be used to pre-heat
incoming air provided to burner 30 to reduce heat transfer to the
air in the burner so more heat transfers to reformer 32. Other
exemplary regenerators are also discussed in patent application
Ser. No. 10/877,044.
[0082] As illustrated in FIG. 1B, fuel processors may have a
regenerator having a gap around the entire fuel processor 15.
However, due to space constraints, this may be too bulky for
smaller compact and portable fuel cell systems. FIG. 6A illustrates
an exemplary regenerator enclosing a fuel processor 15. The bottom
of the regenerator 600 is not shown to illustrate the fuel
processor 15 within the regenerator 600. FIG. 6B is a side
cross-sectional view of the exemplary regenerator of FIG. 6A. The
regenerator 600, may have a plurality of walls 612a, 612b, 612c,
612d, a top wall 614, and a bottom wall 616 (FIG. 6B) thereby
forming an enclosure to enclose the devices of the fuel processor
15. The regenerator 600 may have at least one wall joined or
coupled to the fuel processor 15. In other words, a gap between the
fuel processor 15 and the regenerator 600 may be on at least one
but not all sides around the fuel processor 15. For example, as
illustrated in FIG. 6A, the regenerator chamber 622 includes gaps
on three sides of the fuel processor 15: the bottom 602, right 604,
and left 606 sides. The top 618 of the fuel processor 15 may be
joined to the top wall 614 of the regenerator 600. Within the
regenerator chamber 622, air may flow and be pre-heated before
entering the burner 30.
[0083] Joining at least one wall of the regenerator 600 to the main
body of the fuel processor 15 may reduce the overall volume of a
fuel processor 15, but maintain some gap 622 for pre-heating
incoming air. Additionally, this may allow for less exposure to an
outer surface 608 of the regenerator 600 which may reduce further
heat loss. Moreover, the size of the fuel processor 15 may be
reduced yet efficiency improves by reducing heat losses.
[0084] In one embodiment, the inner surface 610 of walls 612a-d,
614, 616 of the regenerator 600 may include a radiative or
reflective layer of material such as stainless steel, plated
ceramic, plated plastic, or other metals. The radiative layer may
help to reflect radiant heat from the inner surface 610 into
chamber 622. In another embodiment the outer surface 608 of
regenerator 600 may also include a radiative layer to decrease
radiative heat transfer into the outer surface 608. Generally, the
material used in radiative layer may have a lower emissivity than
the material used in regenerator 600. Materials suitable for use as
a radiative layer may be nickel or a ceramic, for example. The
radiative layer may also comprise gold, platinum, silver,
palladium, nickel and the metal may be sputter coated onto the
inner surface 610 and/or outer surface 608. In one embodiment,
radiative layer may have a low heat conductivity such as a ceramic,
for example.
[0085] Regenerator 600 may be configured such that a process gas or
liquid passing through regenerator chamber 622 receives heat
generated in burner 30. The process gas or liquid may include any
reactant used in fuel processor such as oxygen, air, or fuel source
17 (FIG. 11B), for example. In another embodiment, regenerator 600
may include an air inlet port 620 or hole that permits the passage
of air from outside the regenerator 600 into chamber 622. A fan may
be used to provide the air directly to fuel processor 15 and
pressurize the air coming through port 620. Regenerator 600 offers
thus two functions for fuel processor 15: a) it permits active
cooling of components within fuel processor 15 before the heat
reaches an outer portion of the fuel processor, and b) it pre-heats
the air going to burner 30. For the former, air moves through fuel
processor 15 and across walls 154 of regenerator 600 such that the
cooler air absorbs heat from the warmer fuel processor 15
components. Generally, burner 30 may operate at a temperature
greater than about 200 degrees Celsius yet the outer side of the
housing 152 remains less than about 50 degrees Celsius.
[0086] In embodiments for portable applications where fuel
processor 15 occupies a small volume, chamber 622 may be relatively
small and comprise narrow channels and ducts. In some cases, the
height of chamber 622 may be less than 5 millimeters.
[0087] The thermal benefits gained by use of regenerator 600 may
also permit the use of higher temperature burning fuels as a fuel
source for hydrogen production, such as ethanol and gasoline. In
one embodiment, the thermal management benefits gained by use of
regenerator 600 may permit reformer 32 to process methanol at
temperatures well above 100 degrees Celsius and at temperatures
high enough that carbon monoxide production in reformer 32 drops to
an amount such that a preferential oxidizer may not be needed.
[0088] As mentioned above, regenerator 600 may pre-heat the air
going to a burner 30. Burner 30 may rely on catalytic combustion to
produce heat. Oxygen in the air provided to burner 30 may be
consumed as part of the combustion process. Heat generated in the
burner 30 may heat cool incoming air, depending on the temperature
of the air. This heat loss to incoming cool air may reduce the
heating efficiency of burner 30, and may result in a greater
consumption of fuel. To increase the heating efficiency of burner
30, the incoming air may be heated so less heat generated in the
burner passes into the incoming air. In other words, air flow
formed by regenerator 600 may allow waste heat from the burner 30
to pre-heat air before reaching the burner 30, thus acting as a
regenerator for fuel cell 15.
[0089] Regenerator 600 may be formed by various known methods. For
example, walls 612a-d and 614 may be made with a single mold with
bottom wall 616 sealed to walls 612a-d. Depending on the material
chosen for walls 612a-d, 614, 616, the bottom wall 616 may be
sealed to walls 612a-d via any known method, for example, by
laser-welding, ultra-sonic welding, or nuts, bolts, or a
gasket.
[0090] By allowing fuel processor 15 and regenerator 600 to share
at least one wall may improve fuel processor performance by
pre-heating air, lowering heat losses from the fuel processor,
lowering temperature material selection requirements for heater
components, and permit a smaller sized fuel processor.
[0091] FIGS. 7A, 7B, and 7C illustrate other example recuperators
or heat exchangers. A wide variety of recuperators or heat
exchanging devices may be suitable for use herein to transfer heat
from the heating medium in fuel cell system 10 to the incoming
fuel. Descriptions of other exemplary recuperators suitable for use
are included in commonly owned co-pending patent application Ser.
No. 11/314/810, entitled "Heat Efficient Portable Fuel Cell
Systems", filed Dec. 20, 2005, which is incorporated by reference
for all purposes.
[0092] Thermal efficiency may manage heat loss from a fuel cell
system package 10 (FIG. 11B). Many fuel cells and fuel processors
operate at elevated temperatures. The electrochemical reaction
responsible for hydrogen consumption and electrical energy
generation typically requires an elevated temperature. However, the
ambient environment around the fuel cell package may be cooler.
Thus, heat loss from a fuel cell or fuel processor to the ambient
environment decreases efficiency of each device in the package 10
and of the overall fuel cell system 10.
[0093] A recuperator may be located adjacent the fuel processor to
manage heat loss. For example, FIGS. 7A and 7B illustrate a
recuperator 702 positioned above the fuel processor 15. FIG. 7C
illustrates a recuperator 704 positioned below the fuel processor
15. The recuperator 702, 704 may be thermally isolated from the
fuel processor 15 while still being fluidically connected to the
fuel processor 15. Integrating the recuperator 702, 704 above or
below the fuel processor 15 may allow for efficient packaging of a
fuel cell system or package 10.
[0094] Depending on the design of the fuel cell system, the
recuperator may be configured to transfer heat from the hot exhaust
of a burner in the fuel processor to incoming reformer fuel (liquid
or gas). The recuperator may also be configured to transfer heat
from hot reformer gas to the incoming reformer fuel, from the hot
burner exhaust to the incoming burner fuel, or from the hot exhaust
to the cool incoming air. Thus, the configuration of the
recuperator is not intended to be limiting as the recuperator may
be configured to any desired use.
[0095] FIG. 7A illustrates an example recuperator without a cover.
FIG. 7B illustrates the recuperator of FIG. 7A with an example
cover 712 that may be integrated with the fuel cell manifold. In
one embodiment, the recuperator 702 may be located above the fuel
processor 15 with a hot side 706 located near the fuel processor 15
and a cold side 708 located away from the fuel processor 15. The
hot and cold fuels may flow via adjacent channels 710 in a single
monolithic body for the recuperator 702. In one embodiment, the
cold fuels may flow in channels 710b and the hot fuels may flow in
channels 710a. The cold fuel flow may be located furthest away from
the fuel processor 15 to keep outside packaging of the fuel
processor 15 or fuel cell system package 10 cooler. The hot fuel
flow may be located on the surface facing the fuel processor 15 so
that any heat loss may be directed to the fuel processor 15 and
vice versa. This heat transfer interaction may reduce over all
system exhaust temperature and improve system 10 efficiency.
[0096] A separator material between the hot and cold fuel flow
channels 710 may be a thin material made out of a high thermally
conductive material such as copper, aluminum, or another material
with similar thermal characteristics. The monolithic recuperator
702 may be formed through machining, metal-injection molding, or
other metal forming processes.
[0097] Although illustrated with the use of channels, the shape or
design of the recuperator 702 is not intended to be limiting as the
recuperator may be of any shape or design. For example, the
recuperator may be a single planar plate where the cold fuel flow
is on one side (such as the side away from the fuel processor) of
the plate and the hot fuel flow is on the opposite side (such as
the side facing the fuel processor). The planar plate design may be
fabricated through stamping, machining, etching, or other metal
forming processes. Thus, other shapes and designs of the
recuperator may be used as desired.
[0098] As illustrated in FIGS. 7A-7C, the recuperator 702, 704 may
be integrated into a manifold between the fuel processor 15 and the
fuel cell via interconnect 200. The recuperator 702 may fluidly
connect to the corresponding chambers in the fuel processor 15 via
one or more thin walled fluid passages in the interconnect 200 so
as to reduce heat conduction between the fuel processor 15 and the
recuperator 702. Moreover, locating a cold stream chamber in the
recuperator 702, 704 at the interface of the fuel processor 15 and
fuel cell (not shown) may reduce heat loss from the fuel processor
15 to the fuel cell. Thus, any heat loss will flow from the fuel
processor or the fuel cell into the cold stream chamber which may
then flow back into the fuel processor carried by the processed
fluids, such as air or fuel. This reduces the net heat loss for the
fuel cell system and increases efficiency and energy of the fuel
cell system.
[0099] FIG. 7C illustrates the recuperator 704 positioned below the
fuel processor 15, yet in fluid communication with the fuel
processor 15 and fuel cell via interconnect 200. The recuperator
704 may be the same recuperator as described above with reference
to FIGS. 7A and 7B. However, positioning recuperator 704 below fuel
cell 15 may permit the use of a larger sized recuperator 704.
[0100] In one embodiment, insulation may be used to reduce heat
loss from the fuel cell or fuel processor 15. The insulation may
include one or more layers of insulation that are disposed at least
partially between a spacing 714 between the fuel processor 15 and
the recuperator 702, 704. The insulation arrangement reduces heat
transfer from the fuel processor, which in turn reduces heat loss
to the ambient environment. Thus, the insulation arrangement keeps
heat in the fuel cell and increases efficiency for the system 10
components running at elevated temperatures.
[0101] Referring now to FIG. 8, an example fuel processor. Prior
fuel processors include chambers with flow paths that make 90
degree turns, which increased the pressure drop of gasses in the
chambers. The pressure drop creates a higher flow resistance, which
in turn, requires the use of more energy to move the fuel flow.
Furthermore, the pressure drop creates a slower fuel flow velocity,
which does not efficiently use the catalyst beds.
[0102] The fuel processor 800 may have a U-shaped fuel flow path to
improve performance. The U-shaped flow path may provide for a
smoother fuel flow through the fuel processor chambers 802a, 802b
which may reduce pressure drops. The curvature of the U-shape may
vary as illustrated in FIGS. 9B, 10B, and 10C. In one embodiment,
as illustrated in FIG. 8, the curved path may be more gradual for
the outside reformer flow chamber 802b than the inside burner flow
chamber 802a. The use of small catalyst particles and small
chambers may often contribute to pressure drop increases since
smaller catalyst particles may pack together tighter thereby
resulting in smaller and less voids which results in a greater
resistance for the fuel flow. Thus, the gradual curve and slight
turn of the reformer flow chamber 802b and the burner flow chamber
802a may permit the flow path to lengthen in a small package and
therefore may not contribute to further pressure drop increases
even when using small catalyst particles. The chambers 802 may be
formed from any material having a high thermal conductivity and
able to withstand the desired fuel used, such as copper. The
material may also be hermetic, solid, and not porous.
[0103] The geometry of the catalyst chambers 804 may, at least
partially, define the flow paths through the reformer catalyst beds
804b and burner catalyst beds 804a. Previous fuel processors
provided for cutting a metallic center catalyst chamber in the same
direction as the flow path, which only allowed for 90 degree turns
in flow direction. As discussed above, this may result in large
pressure drops. As illustrated in FIG. 8, the catalyst beds 804 may
be cut perpendicular to the flow paths, which allows for the
flexibility in curving each flow path 802 in a U-shape and lower
pressure drops.
[0104] In another embodiment, the catalyst bed may have slots (not
shown), to receive porous metal foam or porous sintered metal, to
hold a catalyst in place and provide diffusion of gases across the
chamber. For example, the burner catalyst bed at the beginning of
the fuel flow may contain an area for copper shots to help transfer
heat to the cold incoming fuel. The copper shot may also help to
diffuse fuel and prevent thermal shock from liquid fuel vaporizing
on the burner catalysts. The copper shots may act like a boiler for
the burner fuel but does not introduce a pressure drop as is often
seen in current boiler tubes. In another example, the slots may
receive the porous metal or metallic sponge as discussed above with
reference to FIG. 2.
[0105] In one embodiment, the reformer flow path may be in a
counter-flow orientation from the burner flow path as illustrated
with arrows A and C. In other words, as air passes through the
reformer chamber 802b, it flows in a direction that at least
partially counters a direction that the air passes through burner
chamber 802a. As discussed above, the temperature is slightly
higher at the beginning of a burner chamber 802a, which provides
more heat to the reformer at the end of its path. This provides
more energy to convert the low concentration of methanol in the
reformer stream at the end of a reformer flow path. In another
embodiment, the reformer flow path and burner flow path may be the
same as illustrated with arrows B and C. Co-flow of the burner flow
path and reformer flow path is further described and discussed in
detail above with reference to FIGS. 3A and 3D.
[0106] FIGS. 9A and 9B illustrate velocity flows of a fuel through
the burner chamber of fuel processor of FIG. 8 and an alternative
embodiment of a fuel processor, respectively. As illustrated in
FIGS. 8 and 9A, the burner flow path 802a is internal to the
reformer flow path 802b and generally follows a similar U-shaped
flow path, but at a smaller radius and with a less gradual turn.
Computational Fluid Dynamics (CFD) simulations were conducted to
determine and/or study the velocity profiles of various flow paths.
FIG. 9A illustrates the CFD simulation of the fuel processor of
FIG. 8. As illustrated, the flow path is not uniform and has a 0
velocity flow (e.g. no movement) at 902. While the velocity of the
flow path does not have to be uniform, a uniform velocity profile
improves catalyst usage and efficacy across the flow path. In other
words, complete and efficient usage of the catalyst occurs when
fuel flows through the catalyst and not when there is no flow, such
as at 902.
[0107] FIG. 9B illustrates an alternative embodiment of a fuel
processor. Use of CFD simulations determined that an extended and
more rounded baffle may provide for a better velocity profile
uniformity. As illustrated, the fuel processor 904 may be designed
to have an extended and rounded baffle 906. Although the velocity
flow has a 0 velocity flow at 908, it is less than that of FIG.
9A.
[0108] FIGS. 10A, 10B, and 10C illustrate another example fuel
processor. Specifically, FIGS. 10A-c illustrate an assembled fuel
processor. FIG. 10A illustrates the various parts of the fuel
processor. The fuel processor 15 may have at least three parts that
include: a bottom plate 1002, an air inlet cover 1004, and a top
plate 1006. Although illustrated with three parts, the number of
parts is not intended to be limiting as the fuel processor may be
assembled without the air inlet cover 1004. Each part may be
fabricated separately using various different methods. For example,
through-cuts may be made via water-jet cutting, laser cutting,
machining, stamping, and/or other metal cutting processes. Any
known method may be used to join each part such as brazing and/or
laser welding which provides for the use of permanent joints to
prevent leaks in the fuel cell system 10.
[0109] The bottom plate 1002 may be shaped with an elongated and
rounded baffle 1016 for a better velocity flow. Insulation material
may be inserted within the thermal well 1030, formed by the
elongated and rounded baffle 1016. The insulation may reduce heat
loss and improve thermal management of fuel processor 15. The
bottom plate may also have a regenerator 1008 similar to the
regenerator discussed with reference to FIG. 6A. The regenerator
1008 may be used to also improve thermal management for fuel
processor 15 by at least partially thermally isolating some
components of the fuel processor 15 and contain heat within the
fuel processor 15. Regenerator 1008 may also pre-heat air, received
from inlet 1028, in regenerator chamber 1010 before it is received
in the burner flow chamber 1012.
[0110] Bottom plate 1002 may have a reformer flow chamber 1014 and
a burner flow chamber 1012. The burner chamber 1012 may receive
fuel from inlets 1026 and/or air inlet port 1034 on air inlet cover
1004. The fuel may then flow out at burner exhaust 1024. As
described in detail above with reference to FIG. 8, the burner flow
chamber 1012 may have catalyst beds 804 positioned perpendicular to
the burner and reformer flow paths.
[0111] In one embodiment, besides the internal flow paths, the fuel
processor may include various inlets to direct external flow of air
that eventually enters burner chamber 1012. Air inlet cover 1004
may have at least one ambient air inlet ramp 1020a, 1020b. The air
inlet ramps 1020a, 1020b may be a stamped piece of stainless steel
that is bent into a predetermined position. However, the air inlet
ramps 120a, b may be made with any other strong material. This air
inlet cover 1004 may direct incoming air through a more tortuous
path that increases the convective heating of the air before
entering the burner chamber 1012 via inlet air port 1034. This may
provide for a more even heat distribution of the air. Air inlet
cover may also have a thermal well opening 1032 to receive
insulation as discussed above. Air inlet cover 1004 may be made of
any strong material such as stainless steel.
[0112] A top plate 1006 may be used to enclose the fuel cell 15.
Top plate may have at least one flow baffle 1022. The flow baffle
1022 may also be used to direct incoming air through a more
tortuous path that increases the convective heating of the air
before entering the burner chamber 1012 via inlet air port 1034.
Although illustrated with a specific layout, the layout of the flow
baffles 1022 is not intended to be limiting as the location of the
flow baffles 1022 may vary based upon the design of the fuel cell
15 and/or top plate 1006.
[0113] FIG. 10B illustrates a top view of the fuel cell and FIG.
10C illustrates a bottom view of the fuel cell. FIGS. 10B and 10C
are illustrated with air inlet covers 1004 coupled to the bottom
plate 1002. As illustrated, air inlet ramps 1020a, 1020b may be
positioned within the regenerator chamber 1010 to direct the
incoming air through a more tortuous path to increase conductive
heating. In use, ambient air enters inlet 1028 and is directed
through regenerator chamber 1010. The air may then be directed on a
path either by the air inlet ramps 1020a, 1020b or flow baffles
1022 on top plate 1006 (FIG. 10A) to pre-heat the air. The
pre-heated air may then be directed into the burner chamber 1012
via inlet air port 1034.
[0114] In one embodiment, at least one thermal sensor may be placed
in the fuel cell 15. FIG. 10C illustrates the use of two thermal
sensors or thermocouple placement bores. One thermal sensor 1036a
may be positioned near the center of the burner 30 and another
sensor 1036b may be positioned near the beginning of the reformer
flow chamber 1014. The sensors may include thermocouple wells, for
example, that are embedded into the structure and removed from the
flow stream so as to avoid requiring added sealing of the reformer
or burner walls.
[0115] The fuel cell above may improve manufacturability, reduce
manufacturing cost, provide better seals, improve catalytic and
fuel processor performance, and lower pressure drops in each
chamber. Additionally, because the pressure drop across the fuel
processor is reduced, the pressure specification for the pumps and
compressors loosens. This allows for choosing a potentially less
expensive, smaller, quieter, and less power intensive pump and/or
compressor.
[0116] Fuel Cell System Overview
[0117] Fuel cell systems that benefit from embodiments described
herein will be described. FIG. 11A illustrates a fuel cell system
10 for producing electrical energy in accordance with one
embodiment. As shown, `reformed` hydrogen system 10 includes a fuel
processor 15 and fuel cell 20, with a fuel storage device 16
coupled to system 10 for fuel provision. System 10 processes a fuel
17 to produce hydrogen for fuel cell 20.
[0118] Storage device, or cartridge, 16 stores a fuel 17, and may
comprise a refillable and/or disposable device. Either design
permits recharging capability for system 10 or an electronics
device using the output electrical power by swapping a depleted
cartridge for one with fuel. A connector on cartridge 16 interfaces
with a mating connector on system 10 or the electronics device to
permit fuel transfer from the cartridge. In a specific embodiment,
cartridge 16 includes a bladder that contains the fuel 17 and
conforms to the volume of fuel in the bladder. An outer rigid
housing of device 16 provides mechanical protection for the
bladder. The bladder and housing permit a wide range of cartridge
sizes with fuel capacities ranging from a few milliliters to
several liters. In one embodiment, the cartridge is vented and
includes a small hole, single direction flow valve, hydrophobic
filter, or other aperture to allow air to enter the fuel cartridge
as fuel 17 is consumed and displaced from the cartridge. In another
specific embodiment, the cartridge includes `smarts`, or a digital
memory used to store information related to usage of device 16.
[0119] A pressure source moves fuel 17 from storage device 16 to
fuel processor 15. In a specific embodiment, a pump in system 10
draws fuel from the storage device. Cartridge 16 may also be
pressurized with a pressure source such as a compressible foam,
spring, or a propellant internal to the housing that pushes on the
bladder (e.g., propane or compressed nitrogen gas). In this case, a
control valve in system 10 regulates fuel flow. Other fuel
cartridge designs suitable for use herein may include a wick that
moves a liquid fuel from within cartridge 16 to a cartridge exit.
If system 10 is load following, then a sensor meters fuel delivery
to processor 15, and a control system in communication with the
sensor regulates the fuel flow rate as determined by a desired
power level output of fuel cell 20.
[0120] Fuel 17 acts as a carrier for hydrogen and can be processed
or manipulated to separate hydrogen. The terms `fuel`, `fuel
source` and `hydrogen fuel source` are interchangeable herein and
all refer to any fluid (liquid or gas) that can be manipulated to
separate hydrogen. Liquid fuels 17 offer high energy densities and
the ability to be readily stored and shipped. Fuel 17 may include
any hydrogen bearing fuel stream, hydrocarbon fuel or other source
of hydrogen such as ammonia. Currently available hydrocarbon fuels
17 suitable for use with system 10 include gasoline, C.sub.1 to
C.sub.4 hydrocarbons, their oxygenated analogues and/or their
combinations, for example. Other fuel sources may be used with
system 10, such as sodium borohydride. Several hydrocarbon and
ammonia products may also be used.
[0121] Fuel 17 may be stored as a fuel mixture. When the fuel
processor 15 comprises a steam reformer, for example, storage
device 16 includes a fuel mixture of a hydrocarbon fuel and water.
Hydrocarbon fuel/water mixtures are frequently represented as a
percentage of fuel in water. In one embodiment, fuel 17 comprises
methanol or ethanol concentrations in water in the range of
1-99.9%. Other liquid fuels such as butane, propane, gasoline,
military grade "JP8", etc. may also be contained in storage device
16 with concentrations in water from 5-100%. In a specific
embodiment, fuel 17 comprises 67% methanol by volume.
[0122] Fuel processor 15 receives methanol 17 and outputs hydrogen.
In one embodiment, a hydrocarbon fuel processor 15 heats and
processes a hydrocarbon fuel 17 in the presence of a catalyst to
produce hydrogen. Fuel processor 15 comprises a reformer, which is
a catalytic device that converts a liquid or gaseous hydrocarbon
fuel 17 into hydrogen and carbon dioxide. As the term is used
herein, reforming refers to the process of producing hydrogen from
a fuel 17. Fuel processor 15 may output either pure hydrogen or a
hydrogen bearing gas stream (also commonly referred to as
`reformate`).
[0123] Various types of reformers are suitable for use in fuel cell
system 10; these include steam reformers, auto thermal reformers
(ATR) and catalytic partial oxidizers (CPOX) for example. A steam
reformer only needs steam and fuel to produce hydrogen. ATR and
CPOX reformers mix air with a fuel/steam mixture. ATR and CPOX
systems reform fuels such as methanol, diesel, regular unleaded
gasoline and other hydrocarbons. In a specific embodiment, storage
device 16 provides methanol 17 to fuel processor 15, which reforms
the methanol at about 280 degrees Celsius or less and allows fuel
cell system 10 usage in low temperature applications.
[0124] Fuel cell 20 electrochemically converts hydrogen and oxygen
to water, generating electrical energy (and sometimes heat) in the
process. Ambient air readily supplies oxygen. A pure or direct
oxygen source may also be used. The water often forms as a vapor,
depending on the temperature of fuel cell 20. For some fuel cells,
the electrochemical reaction may also produce carbon dioxide as a
byproduct.
[0125] In one embodiment, fuel cell 20 is a low volume ion
conductive membrane (PEM) fuel cell suitable for use with portable
applications and consumer electronics. A PEM fuel cell comprises a
MEA that carries out the electrical energy generating an
electrochemical reaction. The MEA includes a hydrogen catalyst, an
oxygen catalyst, and an ion conductive membrane that a) selectively
conducts protons and b) electrically isolates the hydrogen catalyst
from the oxygen catalyst. One suitable MEA is model number Celtec
1000 as provided by BASF--The Chemical Company of Murray Hill, N.J.
A hydrogen gas distribution layer may also be included; it contains
the hydrogen catalyst and allows the diffusion of hydrogen
therethrough. An oxygen gas distribution layer contains the oxygen
catalyst and allows the diffusion of oxygen and hydrogen protons
therethrough. Typically, the ion conductive membrane separates the
hydrogen and oxygen gas distribution layers. In chemical terms, the
anode comprises the hydrogen gas distribution layer and hydrogen
catalyst, while the cathode comprises the oxygen gas distribution
layer and oxygen catalyst.
[0126] In one embodiment, a PEM fuel cell includes a fuel cell
stack having a set of bi-polar plates. In a specific embodiment,
each bi-polar plate is formed from a thin single sheet of metal
that includes channel fields on opposite surfaces of the metal
sheet. Thickness for these plates is typically below about 5
millimeters, and compact fuel cells for portable applications may
employ plates thinner than about 2 millimeters. The single bi-polar
plate thus dually distributes hydrogen and oxygen; one channel
field distributes hydrogen while a channel field on the opposite
surface distributes oxygen. In another embodiment, each bi-polar
plate is formed from multiple layers that include more than one
sheet of metal. Multiple bi-polar plates can be stacked to produce
the `fuel cell stack` in which a membrane electrode assembly is
disposed between each pair of adjacent bi-polar plates. Gaseous
hydrogen distribution to the hydrogen gas distribution layer in the
MEA occurs via a channel field on one plate while oxygen
distribution to the oxygen gas distribution layer in the MES occurs
via a channel field on a second plate on the other surface of the
membrane electrode assembly.
[0127] In electrical terms, the anode includes the hydrogen gas
distribution layer, hydrogen catalyst and a bi-polar plate. The
anode acts as the negative electrode for fuel cell 20 and conducts
electrons that are freed from hydrogen molecules so that they can
be used externally, e.g., to power an external circuit or stored in
a battery. In electrical terms, the cathode includes the oxygen gas
distribution layer, oxygen catalyst and an adjacent bi-polar plate.
The cathode represents the positive electrode for fuel cell 20 and
conducts the electrons back from the external electrical circuit to
the oxygen catalyst, where they can recombine with hydrogen ions
and oxygen to form water.
[0128] In a fuel cell stack, the assembled bi-polar plates are
connected in series to add electrical potential gained in each
layer of the stack. The term `bi-polar` refers electrically to a
bi-polar plate (whether mechanically comprised of one plate or two
plates) sandwiched between two membrane electrode assembly layers.
In a stack where plates are connected in series, a bi-polar plate
acts as both a negative terminal for one adjacent (e.g., above)
membrane electrode assembly and a positive terminal for a second
adjacent (e.g., below) membrane electrode assembly arranged on the
opposite surface of the bi-polar plate.
[0129] In a PEM fuel cell, the hydrogen catalyst separates the
hydrogen into protons and electrons. The ion conductive membrane
blocks the electrons, and electrically isolates the chemical anode
(hydrogen gas distribution layer and hydrogen catalyst) from the
chemical cathode. The ion conductive membrane also selectively
conducts positively charged ions. Electrically, the anode conducts
electrons to a load (electrical energy is produced) or battery
(energy is stored). Meanwhile, protons move through the ion
conductive membrane. The protons and used electrons subsequently
meet on the cathode side, and combine with oxygen to form water.
The oxygen catalyst in the oxygen gas distribution layer
facilitates this reaction. One common oxygen catalyst comprises
platinum powder thinly coated onto a carbon paper or cloth. Many
designs employ a rough and porous catalyst to increase surface area
of the platinum exposed to the hydrogen and oxygen. A fuel cell
suitable for use herein is further described in commonly owned
patent application Ser. No. 11/120,643, entitled "Compact Fuel Cell
Package", which is incorporated by reference in its entirety for
all purposes.
[0130] Since the electrical generation process in fuel cell 20 is
exothermic, fuel cell 20 may implement a thermal management system
to dissipate heat. Fuel cell 20 may also employ a number of
humidification plates (HP) to manage moisture levels in the fuel
cell.
[0131] While system 10 will mainly be discussed with respect to PEM
fuel cells, it is understood that system 10 may be practiced with
other fuel cell architectures. The main difference between fuel
cell architectures is the type of ion conductive membrane used. In
another embodiment, fuel cell 20 is phosphoric acid fuel cell that
employs liquid phosphoric acid for ion exchange. Solid oxide fuel
cells employ a hard, non-porous ceramic compound for ion exchange
and may be suitable for use with embodiments described herein.
Other suitable fuel cell architectures may include alkaline and
molten carbonate fuel cells, for example.
[0132] FIG. 11B illustrates schematic operation for the fuel cell
system 10 of FIG. 11A in accordance with a specific embodiment.
Fuel cell system 10 is included in a portable package 11. In this
case, package 11 includes fuel cell 20, fuel processor 15, and all
other balance-of-plant components except cartridge 16. As the term
is used herein, a fuel cell system package 11 refers to a fuel cell
system that receives a fuel and outputs electrical energy. At a
minimum, this includes a fuel cell and fuel processor. The package
need not include a cover or housing, e.g., in the case where a fuel
cell, or a fuel cell and fuel processor, is included in a battery
bay of a laptop computer. In this case, the portable fuel cell
system package 11 only includes the fuel cell, or fuel cell and
fuel processor, and no housing. The package may include a compact
profile, low volume, or low mass--any of which is useful in any
power application where size is relevant.
[0133] Package 11 is divided into two parts: a) an engine block 12
and b) all other parts and components of system 10 in the portable
package 11 not included in engine block 12. In one embodiment,
engine block 12 includes the core power-producing mechanical
components of system 10. At a minimum, this includes fuel processor
15 and fuel cell 20. It may also include any plumbing configured to
transport fluids between the two. Other system components included
in engine block 12 may include: one or more sensors for fuel
processor 15 and fuel cell 20, a glow plug or electrical heater for
fuel heating in fuel processor during start-up, and/or one or more
cooling components. Engine block 12 may include other system
components.
[0134] Components outside of engine block 12 may include: a body
for the package, connector 23, inlet and outlet plumbing for system
fluids to or from fuel processor 15 or fuel cell 20, one or more
compressors or fans, electronic controls, system pumps and valves,
any system sensors, manifolds, heat exchangers and electrical
interconnects useful for carrying out functionality of fuel cell
system 10.
[0135] In one embodiment, the engine block 12 includes a fuel cell,
a fuel processor, and dedicated mechanical and fluidic connectivity
between the two. The dedicated connectivity may provide a) fluid or
gas communication between the fuel processor and the fuel cell,
and/or b) structural support between the two or for the package. In
one embodiment, an interconnect, which is a separate device
dedicated to interconnecting the two devices, provides much of the
connectivity. In another embodiment, direct and dedicated
connectivity is provided on the fuel cell and/or fuel processor to
interface with the other. For example, a fuel cell may be designed
to interface with a particular fuel processor and includes
dedicated connectivity for that fuel processor. Alternatively, a
fuel processor may be designed to interface with a particular fuel
cell. Assembling the fuel processor and fuel cell together in a
common and substantially enclosed package 11 provides a portable
`black box` device that receives a fuel and outputs electrical
energy.
[0136] In one embodiment, system 10 is sold as a physical engine
block 12 plus specifications for interfacing with the engine block
12. The specifications may include desired cooling rates, airflow
rates, physical sizing, heat capture and release information,
plumbing specifications, fuel inlet parameters such as the fuel
type, mixture and flow rates, etc. This permits engine block 12 to
be sold as a core component employed in a wide variety of devices
determined by the engine block purchaser. Sample devices include:
portable fuel cell systems, consumer electronics components such as
laptop computers, and custom electronics devices.
[0137] Fuel storage device 16 stores methanol or a methanol mixture
as a hydrogen fuel 17. An outlet of storage device 16 includes a
connector 23 that couples to a mating connector on package 11. In a
specific embodiment, connector 23 and mating connector form a quick
connect/disconnect for easy replacement of cartridges 16. The
mating connector communicates methanol 17 into hydrogen fuel line
25, which is internal to package 11.
[0138] Line 25 divides into two lines: a first line 27 that
transports methanol 17 to a burner/heater 30 for fuel processor 15
and a second line 29 that transports methanol 17 for a reformer 32
in fuel processor 15. Lines 25, 27 and 29 may comprise channels
disposed in the fuel processor (e.g., channels in one or more metal
components) and/or tubes leading thereto.
[0139] As the term is used herein, a line refers to one or more
conduits or channels that communicate a fluid (a gas, liquid, or
combination thereof). For example, a line may include a separable
plastic conduit. In a specific embodiment to reduce package size,
the fuel cell and the fuel processor may each include a molded
channel dedicated to the delivering hydrogen from the processor to
the cell. The channeling may be included in a structure for each.
When the fuel cell attaches directly to the fuel processor, the
hydrogen transport line then includes a) channeling in the fuel
processor to deliver hydrogen from a reformer to the connection,
and b) channeling in the fuel cell to deliver the hydrogen from the
connection to a hydrogen intake manifold. An interconnect may also
facilitate connection between the fuel cell and the fuel processor.
The interconnect includes an integrated hydrogen conduit dedicated
to hydrogen transfer from the fuel processor to the fuel cell.
Other plumbing techniques known to those of skill in the art may be
used to transport fluids in a line.
[0140] Flow control is provided on each line 27 and 29. In this
embodiment, separate pumps 21a and 21b are provided for lines 27
and 29, respectively, to pressurize each line separately and
transfer methanol at independent rates, if desired. A model
030SP-S6112 pump as provided by Biochem, NJ is suitable to transmit
liquid methanol on either line in a specific embodiment. A
diaphragm or piezoelectric pump is also suitable for use with
system 10. A flow restriction may also be provided on each line 27
and 29 to facilitate sensor feedback and flow rate control. In
conjunction with suitable control, such as digital control applied
by a processor that implements instructions from stored software,
each pump 21 responds to control signals from the processor and
moves a desired amount of methanol 17 from storage device 16 to
heater 30 and reformer 32 on each line 27 and 29.
[0141] Air source 41 delivers oxygen and air from the ambient room
through line 31 to the cathode in fuel cell 20, where some oxygen
is used in the cathode to generate electricity. Air source 41 may
include a pump, fan, blower, or compressor, for example.
[0142] High operating temperatures in fuel cell 20 also heat the
oxygen and air. In the embodiment shown, the heated oxygen and air
is then transmitted from the fuel cell, via line 33, to a
regenerator 36 (also referred to herein as a `dewar`) of fuel
processor 15, where the air is additionally heated (by escaping
heat from heater 30) before the air enters heater 30. This double
pre-heating increases efficiency of fuel cell system 10 by a)
reducing heat lost to reactants in heater 30 (such as fresh oxygen
that would otherwise be near room temperature when combusted in the
heater), and b) cooling the fuel cell during energy production. In
a specific embodiment, a model BTC compressor as provided by
Hargraves, N.C. is suitable to pressurize oxygen and air for fuel
cell system 10.
[0143] When fuel cell cooling is needed, a fan 37 blows air from
the ambient room over fuel cell 20. Fan 37 may be suitably sized to
move air as desired by the heating requirements of fuel cell 20;
and many vendors known to those of skill in the art provide fans
and blowers suitable for use with package 10.
[0144] Fuel processor 15 is configured to process fuel 17 and
output hydrogen. Fuel processor 15 comprises heater 30, reformer
32, boiler 34, and regenerator 36. Heater 30 (also referred to
herein as a burner when it uses catalytic combustion to generate
heat) includes an inlet that receives methanol 17 from line 27. In
a specific embodiment, the burner includes a catalyst that helps
generate heat from methanol, such as platinum or palladium coated
onto a suitable support or alumina pellets for example.
[0145] In a specific embodiment, heater 30 includes its own boiler
to preheat fuel for the heater. Boiler 34 includes a chamber having
an inlet that receives methanol 17 from line 29. The boiler chamber
is configured to receive heat from heater 30, via heat conduction
through one or more walls between the boiler 34 and heater 30, and
use the heat to boil the methanol passing through the boiler
chamber. The structure of boiler 34 permits heat produced in heater
30 to heat methanol 17 in boiler 34 before reformer 32 receives the
methanol 17. In a specific embodiment, the boiler chamber is sized
to boil methanol before receipt by reformer 32. Boiler 34 includes
an outlet that provides heated methanol 17 to reformer 32.
[0146] Reformer 32 includes an inlet that receives heated methanol
17 from boiler 34. A catalyst in reformer 32 reacts with the
methanol 17 to produce hydrogen and carbon dioxide; this reaction
is endothermic and draws heat from heater 30. A hydrogen outlet of
reformer 32 outputs hydrogen to line 39. In one embodiment, fuel
processor 15 also includes a preferential oxidizer that intercepts
reformer 32 hydrogen exhaust and decreases the amount of carbon
monoxide in the exhaust. The preferential oxidizer employs oxygen
from an air inlet to the preferential oxidizer and a catalyst, such
as ruthenium that is preferential to carbon monoxide over
hydrogen.
[0147] Regenerator 36 pre-heats incoming air before the air enters
heater 30. In one sense, regenerator 36 uses outward traveling
waste heat in fuel processor 15 to increase thermal management and
thermal efficiency of the fuel processor. Specifically, waste heat
from heater 30 pre-heats incoming air provided to heater 30 to
reduce heat transfer to the air within the heater. As a result,
more heat transfers from the heater to reformer 32. The regenerator
also functions as insulation. More specifically, by reducing the
overall amount of heat loss from fuel processor 15, regenerator 36
also reduces heat loss from package 11. This enables a cooler fuel
cell system 10 package.
[0148] In one embodiment, fuel processor 15 includes a monolithic
structure having common walls between the heater 30 and other
chambers in the fuel processor. Fuel processors suitable for use
herein are further described in commonly owned patent application
Ser. No. 10/877,044.
[0149] Line 39 transports hydrogen (or `reformate`) from fuel
processor 15 to fuel cell 20. In a specific embodiment, gaseous
delivery lines 33, 35 and 39 include channels in a metal
interconnect that couples to both fuel processor 15 and fuel cell
20. A hydrogen flow sensor (not shown) may also be added on line 39
to detect and communicate the amount of hydrogen being delivered to
fuel cell 20. In conjunction with the hydrogen flow sensor and
suitable control, such as digital control applied by a processor
that implements instructions from stored software, system 10
regulates hydrogen gas provision to fuel cell 20.
[0150] Fuel cell 20 includes a hydrogen inlet port that receives
hydrogen from line 39 and includes a hydrogen intake manifold that
delivers the gas to one or more bi-polar plates and their hydrogen
distribution channels. An oxygen inlet port of fuel cell 20
receives oxygen from line 31; an oxygen intake manifold receives
the oxygen from the port and delivers the oxygen to one or more
bi-polar plates and their oxygen distribution channels. A cathode
exhaust manifold collects gases from the oxygen distribution
channels and delivers them to a cathode exhaust port and line 33,
or to the ambient room. An anode exhaust manifold 38 collects gases
from the hydrogen distribution channels, and in one embodiment,
delivers the gases to the ambient room.
[0151] In a specific embodiment, and as shown, the anode exhaust is
transferred back to fuel processor 15. In this case, system 10
comprises plumbing 38 that transports unused hydrogen from the
anode exhaust to heater 30. For system 10, heater 30 includes two
inlets: an inlet configured to receive fuel 17 and an inlet
configured to receive hydrogen from line 38. Heater 30 then
includes a thermal catalyst that reacts with the unused hydrogen to
produce heat. Since hydrogen consumption within a PEM fuel cell 20
is often incomplete and the anode exhaust often includes unused
hydrogen, re-routing the anode exhaust to heater 30 allows a fuel
cell system to capitalize on unused hydrogen and increase hydrogen
usage and energy efficiency. The fuel cell system thus provides
flexibility to use different fuels in a catalytic heater 30. For
example, if fuel cell 20 can reliably and efficiently consume over
90% of the hydrogen in the anode stream, then there may not be
sufficient hydrogen to maintain reformer and boiler operating
temperatures in fuel processor 15. Under this circumstance,
methanol supply is increased to produce additional heat to maintain
the reformer and boiler temperatures. In one embodiment, gaseous
delivery in line 38 back to fuel processor 15 relies on pressure at
the exhaust of the anode gas distribution channels, e.g., in the
anode exhaust manifold. In another embodiment, an anode recycling
pump or fan is added to line 38 to pressurize the line and return
unused hydrogen back to fuel processor 15. The unused hydrogen is
then combusted for heat generation.
[0152] In one embodiment, fuel cell 20 includes one or more heat
transfer appendages 46 that permit conductive heat transfer with
internal portions of a fuel cell stack. This may be done for
heating and/or cooling fuel cell 20. In a specific heating
embodiment, exhaust 35 of heater 30 is transported to the one or
more heat transfer appendages 46 during system start-up to expedite
reaching initial elevated operating temperatures in fuel cell 20.
The heat may come from hot exhaust gases or unburned fuel in the
exhaust, which then interacts with a catalyst disposed on or in
proximity with a heat transfer appendage 46. In a specific cooling
embodiment, fan 37 blows cooling air over the one or more heat
transfer appendages 46, which provides dedicated and controllable
cooling of the stack during electrical energy production. Fuel
cells suitable for use herein are further described in commonly
owned patent application Ser. No. 10/877,770, entitled "Micro Fuel
Cell Thermal Management", filed Jun. 25, 2004, which is
incorporated by reference in its entirety for all purposes.
[0153] Heat exchanger 42 transfers heat from fuel cell system 10 to
the inlet fuel 17 before the methanol reaches fuel processor 15.
This increases thermal efficiency for system 10 by preheating the
incoming fuel (to reduce heating of the fuel in heater 30) and
reuses heat that would otherwise be expended from the system. While
system 10 shows heat exchanger 42 heating methanol in line 29 that
carries fuel 17 to the boiler 34 and reformer 32, it is understood
that heat exchanger 42 may be used to heat methanol in line 27 that
carries fuel 17 to burner 30.
[0154] In one embodiment, system 10 increases thermal and overall
efficiency of a portable fuel cell system by using waste heat in
the system to heat incoming reactants such as an incoming fuel or
air. To this end, the embodiment in FIG. 11B includes heat
exchanger, or recuperator, 42.
[0155] Heat exchanger 42 transfers heat from fuel cell system 10 to
the inlet fuel 17 before the methanol reaches fuel processor 15.
This increases thermal efficiency for system 10 by preheating the
incoming fuel (to reduce heating of the fuel in heater 30) and
reuses heat that would otherwise be expended from the system. While
system 10 shows heat exchanger 42 heating methanol in line 29 that
carries fuel 17 to the boiler 34 and reformer 32, it is understood
that heat exchanger 42 may be used to heat methanol in line 27 that
carries fuel 17 to burner 30.
[0156] In addition to the components shown in shown in FIG. 1B,
system 10 may also include other elements such as electronic
controls, additional pumps and valves, added system sensors,
manifolds, heat exchangers and electrical interconnects useful for
carrying out functionality of a fuel cell system 10 that are known
to one of skill in the art and omitted for sake of brevity. FIG. 1B
shows one specific plumbing arrangement for a fuel cell system;
other plumbing arrangements are suitable for use herein. For
example, the heat transfer appendages 46, a heat exchanger and
dewar 36 need not be included. Other alterations to system 10 are
permissible, as one of skill in the art will appreciate.
[0157] System 10 generates direct current (DC) voltage, and is
suitable for use in a wide variety of portable applications. For
example, electrical energy generated by fuel cell 20 may power a
notebook computer 11 or a portable electrical generator 11 carried
by military personnel.
[0158] In one embodiment, system 10 provides portable, or `small`,
fuel cell systems that are configured to output less than 200 watts
of power (net or total). Fuel cell systems of this size are
commonly referred to as `micro fuel cell systems` and are well
suited for use with portable electronics devices. In one
embodiment, the fuel cell is configured to generate from about 1
milliwatt to about 200 Watts. In another embodiment, the fuel cell
generates from about 5 Watts to about 60 Watts. Fuel cell system 10
may be a stand-alone system, which is a single package 11 that
produces power as long as it has access to a) oxygen and b)
hydrogen or a fuel such as a hydrocarbon fuel. One specific
portable fuel cell package produces about 20 Watts or about 45
Watts, depending on the number of cells in a stack for fuel cell
20.
[0159] While the embodiment discussed herein mainly been discussed
so far with respect to a reformed methanol fuel cell (RMFC), the
present invention may also apply to other types of fuel cells, such
as a solid oxide fuel cell (SOFC), a phosphoric acid fuel cell
(PAFC), a direct methanol fuel cell (DMFC), or a direct ethanol
fuel cell (DEFC). In this case, fuel cell 20 includes components
specific to these architectures, as one of skill in the art will
appreciate. A DMFC or DEFC receives and processes a fuel. More
specifically, a DMFC or DEFC receives liquid methanol or ethanol,
respectively, channels the fuel into the fuel cell stack 60 and
processes the liquid fuel to separate hydrogen for electrical
energy generation. For a DMFC, shared flow fields 208 in the flow
field plates 202 distribute liquid methanol instead of hydrogen.
Hydrogen catalyst 126 described above would then comprise a
suitable anode catalyst for separating hydrogen from methanol.
Oxygen catalyst 128 would comprise a suitable cathode catalyst for
processing oxygen or another suitable oxidant used in the DMFC,
such as peroxide. In general, hydrogen catalyst 126 is also
commonly referred to as an anode catalyst in other fuel cell
architectures and may comprise any suitable catalyst that removes
hydrogen for electrical energy generation in a fuel cell, such as
directly from the fuel as in a DMFC. In general, oxygen catalyst
128 may include any catalyst that processes an oxidant in used in
fuel cell 20. The oxidant may include any liquid or gas that
oxidizes the fuel and is not limited to oxygen gas as described
above. An SOFC, PAFC, or molten carbonate fuel cell (MCFC) may also
benefit from inventions described herein, for example. In this
case, fuel cell 20 comprises an anode catalyst 126, cathode
catalyst 128, anode fuel and oxidant according to a specific SOFC,
PAFC, or MCFC design.
[0160] While embodiments and applications of this invention have
been shown and described, it would be apparent to those skilled in
the art having the benefit of this disclosure that many more
modifications than mentioned above are possible without departing
from the inventive concepts herein.
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