U.S. patent application number 10/684168 was filed with the patent office on 2004-04-22 for methods and apparatuses for a pressure driven fuel cell system.
Invention is credited to Gottesfeld, Shimson.
Application Number | 20040076859 10/684168 |
Document ID | / |
Family ID | 25322606 |
Filed Date | 2004-04-22 |
United States Patent
Application |
20040076859 |
Kind Code |
A1 |
Gottesfeld, Shimson |
April 22, 2004 |
Methods and apparatuses for a pressure driven fuel cell system
Abstract
A fuel cell system including a housing defining an anode chamber
and a cathode chamber and including a catalyst, a protonically
conductive, but electronically non-conductive membrane positioned
between the anode chamber and the cathode chamber and a first vent,
a fuel chamber in gaseous communication with the anode chamber via
a first valve, a liquid chamber in gaseous communication with the
anode chamber via a second valve, and a mixing chamber having a
second vent. The mixing chamber is in gaseous communication with
the anode chamber via a third valve and receives fuel from the fuel
chamber through a fuel valve, liquid from the liquid chamber via a
liquid valve, and liquid effluent from the anode chamber via a
liquid effluent valve. The mixing chamber also provides a fuel
mixture to the anode chamber via a fuel mixture valve. Using
effluent gases, the present invention drives fluids between
elements of the fuel cell system.
Inventors: |
Gottesfeld, Shimson;
(Niskayuna, NY) |
Correspondence
Address: |
MINTZ, LEVIN, COHN, FERRIS
GLOVSKY AND POPEO, P.C.
The Chrysler Center
666 Third Avenue
New York
NY
10017
US
|
Family ID: |
25322606 |
Appl. No.: |
10/684168 |
Filed: |
October 10, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10684168 |
Oct 10, 2003 |
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09855982 |
May 15, 2001 |
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6686081 |
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Current U.S.
Class: |
429/446 ;
220/567.2; 429/450; 429/515 |
Current CPC
Class: |
H01M 8/04194 20130101;
Y02E 60/50 20130101; H01M 8/1009 20130101; H01M 8/04186
20130101 |
Class at
Publication: |
429/013 ;
429/034; 220/567.2 |
International
Class: |
H01M 008/04; B65D
088/00; H01M 008/00 |
Claims
1. (Amended) A detachable fuel chamber for a fuel cell system,
comprising an area for holding an amount of fuel, a first port for
gaseous connection with a fuel cell system and a second port for
liquid connection with the fuel cell system. [A fuel cell system
comprising: a housing defining an anode chamber and a cathode
chamber and including a catalyst, a protonically conductive but
electronically non-conductive membrane positioned between said
anode chamber and said cathode chamber and a first vent in said
anode chamber; a fuel chamber in gaseous communication with said
anode chamber via a first valve; a water chamber in gaseous
communication with said anode chamber via a second valve; and a
mixing chamber having a second vent, wherein said mixing chamber is
in gaseous communication with said anode chamber via a third valve,
wherein said mixing chamber receives fuel from said fuel chamber
through a fuel valve, water from said water chamber via a water
valve, and liquid effluent from said anode chamber via a liquid
effluent valve, and said mixing chamber provides a fuel mixture to
said anode chamber via a fuel mixture valve.]
2. (new) A detachable fuel chamber for a fuel cell system,
comprising fuel storage means; gaseous communication means and
liquid communication means.
3. (new) The detachable fuel chamber according to claim 1, wherein
the first port and second port are in communication with the fuel
cell.
4. (new) A method for delivering fuel from a fuel chamber to a fuel
cell comprising: allowing gaseous product from an anode chamber of
a fuel cell system to be introduced to the fuel chamber; creating a
pressure differential between the fuel chamber and a destination
for the fuel; and releasing the pressure in the fuel chamber to the
destination area; and driving fuel contained in the fuel chamber to
the destination area as a result of the release of pressure.
5. (new) The method according to claim 4, wherein the destination
area is an anode chamber of the fuel cell.
6. (new) The method according to claim 4, wherein the destination
area is a mixing chamber of the fuel cell system.
7. (new) A method for driving a fluid in a fuel cell system
comprising: pressurizing a first chamber with gaseous product
produced by an anode chamber of a fuel cell system; creating a
pressure differential between the first chamber and a second
chamber containing a liquid; releasing the pressure contained in
the first chamber into the second chamber; and either driving the
liquid from the second chamber to a destination area; or agitating
the liquid in the second chamber.
8. (new) The method according to claim 7, wherein the released
pressure flows from the first chamber to the second chamber via a
third chamber.
9. (new) A fuel cell system comprising: a housing defining an anode
chamber and a cathode chamber and including a catalyst, a
protonically conductive but electronically non-conductive membrane
positioned between said anode chamber and said cathode chamber and
a vent;
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is directed to methods and apparatuses
for driving fluids in a fuel cell, and more particularly, to
methods and apparatuses for moving fluids, specifically water,
fuel, a fuel mixture and liquid effluent, in a direct methanol fuel
cell system using self-generated pressure differentials.
[0003] 2. Background of the Prior Art
[0004] Substantial research has been dedicated to development of
direct oxidation fuel cell systems, including but not limited to
direct methanol fuel cell systems for use in portable electronics
in recent years. Those skilled in the art will recognize a direct
oxidation fuel cell is one that does not require fuel to be
processed following its introduction into the fuel cell system. For
a direct methanol fuel cell system to operate properly, it is
imperative that the fluids in the system are available to the fuel
cell for the generation of electricity.
[0005] Currently, direct oxidation fuel cell systems, including
direct methanol fuel cell systems (DMFC Systems) are typically
operated in a particular physical orientation in order for the
system to properly operate (e.g., fuel supply, water supply).
However, because many potential applications for DMFC Systems are
operated in a variety of orientations, it is imperative that the
DMFC System be able to operate regardless of its orientation.
[0006] Previous methods of supplying fuel to a fuel cell have
focused on directing the fuel with a pump or series of pumps, as
shown in FIG. 1. Alternatively, pressurized fuel tanks or
cartridges may be used to drive fuel into the system. However,
pumps result in parasitic power loss, and fabrication of
pressurized fuel tanks that will effectively deliver fuel to a
direct methanol fuel cell (DMFC) is cost prohibitive and difficult.
In addition, in a DMFC System that recirculates the unreacted
methanol/water fuel mixture and adds neat methanol to provide
adequate fuel to the system, it is necessary to ensure that the new
methanol is evenly mixed in the mixture prior to introduction into
the anode.
[0007] It is therefore desirable to have a fuel delivery and
mixture maintaining system that does not require that a pump or
other power consuming device be used to manage fluid flow and
composition within the fuel cell system.
SUMMARY OF THE INVENTION
[0008] The present invention provides unique methods and
apparatuses for driving fluids throughout a fuel cell system, and
for mixing fuel and water into a fuel mixture using pressure
differentials produced by an effluent gas. Thus, the present
invention allows for the movement and mixing of fluids in a direct
oxidation fuel cell system without the use of electrically driven
pumps or other electrically driven apparatuses.
[0009] The present invention presents novel apparatuses and methods
to utilize anodically generated CO.sub.2 to maintain and provide a
sufficient flow of methanol and water ultimately to the anode
chamber of a fuel cell. It will be understood by those skilled in
the art that the invention can be used with a variety of fuel cell
configurations, including but not limited to configurations
utilizing a bipolar stack, as well as those that use multiple
Protonically Conductive Membranes assembled in a single plane, or
single-cell Direct Methanol Fuel Cell System designs.
[0010] Accordingly, it is an object of the present invention to
provide a means to ensure that a consistent supply of the fuel
mixture is provided to an anode chamber of a fuel cell to enable
electricity generating reactions to continue
[0011] It is also an object of the present invention to provide
orientation independence for a fuel cell system. That is, the
present invention allows a fuel cell system to operate in any
variety of orientations. In prior art direct oxidation fuel cell
systems, the fuel cell is typically required to remain in a single
position, so that gravity is used to aid in movement of
liquids/gases in the system. Accordingly, the present invention
allows for direct oxidation fuel cell systems to be used in
portable electronics.
[0012] It is yet a further object of the present invention to
provide a fuel cell system to ensure that proper amounts of the
constituents that comprise the fuel mixture are supplied to a
mixing chamber.
[0013] It is another object of the present invention to ensure that
proper flow of the fuel mixture, liquid anode effluent comprised of
unreacted fuel and water, added fuel and/or added water, occurs.
Moreover, the present invention allows for the accelerated and
enhanced mixing of "neat" methanol with the liquid anode effluent
and cathodically generated water.
[0014] In each of the embodiments of the invention, it is important
to note that the fuel may be delivered to the system via a
cartridge (similar to that used in a fountain pen) or through a
tank that may be refilled. It should be further understood that the
valves described in the present invention are preferably
electrically actuated and allow the flow of fluid only when open,
and preferably only in one direction.
[0015] Accordingly, in a first aspect of the present invention, a
fuel cell system includes a housing defining an anode chamber and a
cathode chamber and includes a catalyst, a protonically conductive
(but electronically non-conductive) membrane positioned between the
anode chamber and the cathode chamber and a first vent connecting
said anode chamber with the ambient environment. The catalyst is
preferably applied to the anode and cathode faces of the
protonically conductive membrane. The system also includes a fuel
chamber in gaseous communication with the anode chamber via a first
valve, a water chamber in gaseous communication with the anode
chamber via a second valve, and a mixing chamber having a second
vent. The mixing chamber is in gaseous communication with the anode
chamber via a third valve and receives fuel from the fuel chamber
through a fuel valve, water from said water chamber via a water
valve, and liquid effluent from the anode chamber via a liquid
effluent valve. The mixing chamber also provides a fuel mixture to
the anode chamber via a fuel mixture valve.
[0016] In yet another aspect of the present invention, a method for
moving a liquid between chambers of a fuel cell system includes
sealing off an anode chamber and a first chamber having a liquid
stored therein of a fuel cell system from external pressure
creating a closed sub-system, while allowing an effluent gas
produced in the anode chamber to freely flow between the anode
chamber and the first chamber, and storing a portion of said
effluent gas in the first chamber. A first pressure of the
sub-system increases due to an increasing volume of effluent gas
being produced-in the anode chamber. The method also includes
sealing off the first chamber from the anode chamber, substantially
ceasing the flow of the effluent gas between the anode chamber and
the first chamber, creating a pressure differential between a
second chamber and the first chamber by lowering a second pressure
in the second chamber to a point below the first pressure, opening
a conduit between the first chamber and the second chamber, where,
as a result of the pressure differential, the liquid stored in the
first chamber flows into the second chamber via the second
conduit.
[0017] In the above aspect, the first and second chambers may be
the following:
1 First Chamber Liquid Second Chamber mixing chamber fuel mixture
anode chamber water chamber water mixing chamber fuel chamber fuel
mixing chamber anode chamber liquid effluent mixing chamber
[0018] In yet another aspect of the present invention, a method for
agitating a liquid stored in a first chamber of a fuel cell system
includes sealing off the anode chamber from external pressure,
storing an effluent gas produced in the anode chamber within the
anode chamber, where pressure within the anode chamber increases
over a period of time due to an increasing volume of effluent gas
being produced. The method also includes creating a pressure
differential between the first chamber and the anode chamber by
lowering a first pressure of a first chamber to a point below the
anode pressure, and opening a conduit between the anode chamber and
the first chamber. As a result of the pressure differential,
effluent gas stored in the anode chamber flows into the first
chamber agitating the liquid stored there and is then vented to the
ambient environment.
[0019] The following additional aspects of the present invention,
working in conjunction with the fuel cell system described in the
first aspect, are directed to methods for moving particular fluids
between chambers of the fuel cell system, and are each set out
below:
[0020] A method for moving a fuel and water mixture stored within
the mixing chamber to the anode chamber. This method includes
closing the first vent, the second vent, the first valve, the
second valve, the fuel valve, the fuel mixture valve, the water
valve, and the liquid effluent valve, establishing a closed
sub-system between the anode chamber and the mixing chamber. The
method also includes the steps of opening the third valve allowing
an effluent gas produced in the anode chamber to freely flow
between the anode chamber and the mixing chamber, and storing a
portion of the effluent gas produced in the anode chamber in the
mixing chamber. A volume of the effluent gas establishes a first
pressure within the closed sub-system and the first pressure
becomes increasingly higher as the effluent gas is produced. The
method further includes the steps of closing the third valve to
isolate the mixing chamber from the anode chamber, opening the
first vent to release the first pressure in the anode chamber such
that a second pressure is established within the anode chamber
lower than the first pressure creating a pressure differential
between the mixing chamber and the anode chamber, closing the first
vent, and opening the fuel mixture valve and allowing the fuel
mixture to flow from the mixing chamber into the anode chamber as a
result of the pressure differential.
[0021] A method for moving water stored within the water chamber to
the mixing chamber. The method includes closing the first vent, the
second vent, the first valve, the third valve, the fuel valve, the
fuel mixture valve, the water valve, and the liquid effluent valve,
wherein a closed sub-system is established between the anode
chamber and the water chamber. The method also includes the steps
of opening the second valve allowing an effluent gas produced in
the anode chamber to freely flow between the anode chamber and the
water chamber, and storing a portion of the effluent gas produced
in the anode chamber in the water chamber. A volume of the effluent
gas establishes a first pressure within the closed sub-system, and
the first pressure becomes increasingly higher as the effluent gas
is produced. The second valve is then closed to isolate the water
chamber from the anode chamber, and then the second vent is opened
to lower a second pressure in the mixing chamber below the first
pressure creating a pressure differential between the water chamber
and the mixing chamber. The method further includes the steps of
closing the second vent, opening the water valve and allowing water
to flow from the water chamber into the mixing chamber as a result
of the pressure differential.
[0022] A method for moving fuel stored within the fuel chamber to
the mixing chamber includes closing the first vent, the second
vent, the second valve, the third valve, the fuel valve, the fuel
mixture valve, the water valve, and the liquid effluent valve,
establishing a closed sub-system between the anode chamber and the
water chamber, opening the first valve allowing an effluent gas
produced in the anode chamber to freely flow between the anode
chamber and the fuel chamber and storing a portion of the effluent
gas produced in the anode chamber in the fuel chamber. A volume of
the effluent gas establishes a first pressure within the closed
sub-system which becomes increasingly higher as the effluent gas is
produced. The method further includes the steps of closing the
first valve to isolate the fuel chamber from the anode chamber,
opening the second vent to lower a second pressure below the first
pressure, creating a pressure differential between the fuel chamber
and the mixing chamber, closing the second vent, opening the fuel
valve and allowing fuel to flow from the fuel chamber into the
mixing chamber as a result of the pressure differential.
[0023] A method for moving liquid effluent from the anode chamber
to the mixing chamber includes closing the first vent, the second
vent, the first valve, the second valve, the third valve, the fuel
valve, the fuel mixture valve, the water valve, and the liquid
effluent valve establishing a closed sub-system between the anode
chamber and the liquid chamber, and storing an effluent gas
produced in the anode chamber in the anode chamber. A volume of the
effluent gas establishes a first pressure within the anode chamber
that becomes increasingly higher as the effluent gas is produced.
The method further includes opening the second vent and the
effluent valve allowing an effluent liquid stored in the anode
chamber to flow from the anode chamber into the mixing chamber as a
result of the pressure differential.
[0024] A method for agitating a fuel mixture stored within the
mixing chamber includes closing the first vent, the second vent,
the first valve, the second valve, the third valve, the fuel valve,
the fuel mixture valve, the water valve, and the liquid effluent
valve, wherein a closed sub-system is established between the anode
chamber and the water chamber, and storing an effluent gas produced
in the anode chamber in the anode chamber. A volume of the effluent
gas establishes a first pressure within the anode chamber that
becomes increasingly higher as the effluent gas is produced. The
method further includes the steps of opening the second vent and
the third valve allowing the stored effluent gas to flow from the
anode chamber into the mixing chamber and out the second vent,
where the fuel mixture stored in the mixing chamber is agitated as
a result of the effluent gas flowing into the mixing chamber and
out of the second vent as a result of the pressure
differential.
[0025] In the preceding aspects, pressure may be lowered in a
particular chamber by venting the respective chamber to an
environment having a lower pressure. Thus, such an environment may
include ambient air pressure.
[0026] In yet another aspect of the present invention, a fuel cell
system similar to the first aspect includes a pump in place of the
mixing chamber. Effluent gas is used to move fuel from the fuel
chamber to the pump. Thus, this aspect includes a housing defining
an anode chamber and a cathode chamber and including a catalyst and
a protonically conductive, but electronically non-conductive,
membrane positioned between the anode chamber and the cathode
chamber where the anode chamber includes a first vent, a fuel
chamber in gaseous communication with the anode chamber via a first
valve, a water chamber, and a pump. The pump receives fuel from the
fuel chamber via a fuel valve, water from the water chamber, and
liquid effluent from the anode chamber. The pump provides a fuel
mixture to the anode chamber.
[0027] In yet a further aspect of the present invention, the above
fuel cell system is used with a method for supplying fuel to the
pump and includes closing the fuel valve, opening the first valve
allowing an effluent gas produced in the anode chamber to freely
flow between the anode chamber and the fuel chamber, establishing a
closed sub-system between the anode chamber and the fuel chamber,
and storing a portion of said effluent gas produced in the anode
chamber in the fuel chamber. A volume of the effluent gas
establishes a first pressure within the closed sub-system, with the
first pressure becoming increasingly higher as the effluent gas is
produced and the first pressure is higher than a second pressure of
the pump establishing a pressure differential there between. The
method also includes closing the first valve to isolate the fuel
chamber from the anode chamber, opening the fuel valve and allowing
fuel to flow from the fuel chamber into the pump as a result of the
pressure differential.
[0028] In yet a further aspect of the present invention, a fuel
cell system includes a housing defining an anode chamber and a
cathode chamber and including a catalyst, a protonically conductive
but electronically non-conductive membrane positioned between the
anode chamber and the cathode chamber and a first vent, a first
conduit having a first end for receiving liquid effluent from the
anode chamber and a second end for supplying a fuel mixture
comprised of fuel and/or water, and the liquid effluent to the
anode chamber, and a fuel chamber in gaseous communication with the
anode chamber via a first valve and in communication with the first
conduit via a fuel valve. The water chamber may also be in
communication with the cathode chamber to receive cathodically
generated water within the cathode chamber.
[0029] In yet another aspect of the present invention, a method for
controlling a concentration of fuel in a fuel-water mixture for a
direct oxidation fuel cell system includes determining a first
concentration level of fuel in a fuel-water mixture of an anode
chamber of a direct oxidation fuel cell system and comparing the
first concentration level to a second required concentration level
required for a particular operating condition. Fuel is added to the
fuel-water mixture when the first concentration level is less than
the second required concentration level, under given operating
conditions and water is added to the fuel-water mixture when the
first concentration level is higher than the second required
concentration level under given operating conditions.
[0030] In a related aspect, a system for performing this method
includes a housing defining an anode chamber and a cathode chamber,
with the housing also including a catalyst and a protonically
conductive but electronically non-conductive membrane and the anode
chamber including a fuel-water mixture. The system also includes a
fuel concentration sensor for determining a first concentration
level of fuel in said fuel-water mixture, a fuel chamber for
storage of fuel, where the fuel chamber is in communication with
the liquid-fuel mixture, a water chamber for storage of water,
where the water chamber is in communication with the fuel-water
mixture, and a controller for controlling a first flow of fuel to
the fuel-water mixture, for controlling a second flow of water to
the fuel-water mixture, and including a memory having a look-up
table stored therein. The look-up table includes operating
condition data and associated fuel concentration levels.
[0031] For a better understanding of the above aspects of the
invention, reference is made to the below referenced drawings and
written description following immediately thereafter
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 illustrates a schematic of a prior art fuel cell
system using a pump to supply a fuel mixture to an anode chamber of
a fuel cell system.
[0033] FIG. 2 illustrates a schematic of a fuel cell system where
an effluent gas is used to fully drive liquids throughout the
system according to an embodiment of the present invention.
[0034] FIG. 3 illustrates a schematic of a fuel cell system where
an effluent gas produced in the anode chamber is used to partially
drive liquids in the fuel cell according to an embodiment of the
present invention.
[0035] FIG. 4 illustrates a schematic of a fuel cell system
according to another embodiment of the present invention.
[0036] FIG. 5 illustrates a schematic of a fuel cell according to
another embodiment of the present invention.
[0037] FIG. 6 illustrates a schematic of a fuel cell according to
another embodiment of the present invention.
[0038] FIG. 7 illustrates a schematic of a fuel cell according to
another embodiment of the present invention.
[0039] FIG. 8 illustrates a flexible impermeable diaphragm used
with the embodiments of the presents a schematic of a fuel cell
according to another embodiment of the present invention.
[0040] FIG. 9 illustrates a schematic view of a controller for
controlling the opening and closing of the valves of the fuel cell
system according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] First Embodiment
[0042] As shown in FIG. 2, a direct methanol fuel cell system 2
includes a housing 4 defining an anode chamber 6 and a cathode
chamber 8, a protonically conductive 10 but electronically
non-conductive membrane (Protonically Conductive Membrane) and a
catalyst, a mixing chamber 12, a fuel tank 14, and a water tank 16.
The catalyst may be positioned anywhere within the anode and
cathode chambers, but preferably is applied to one or both faces of
the Protonically Conductive Membrane.
[0043] Gas carrying conduits connect the anode chamber (via conduit
17) to each of the fuel tank (via conduit 18), the water tank (via
conduit 20), and the mixing chamber (via conduit 22). The gas
carrying conduits ferry anodically generated gaseous effluent,
CO.sub.2 in a DMFC System, from the anode chamber to one or more of
the other elements of the fuel cell. Each conduit also includes a
valve to control the flow within a particular conduit. Thus, gas
conduit 17 includes valve 17A, gas conduit 18 includes valve 18A,
gas conduit 20 includes valve 20A, and gas conduit 22 includes
valve 22A. In each embodiment of the invention, a gas separator
(not shown) may be incorporated using methods well known in the
art. Liquid-carrying conduits carry fuel and water from the fuel
tank (via conduit 24) and the water tank (via conduit 26),
respectively, to the mixing chamber. Additional liquid conduits
ferry fuel mixture from the mixing chamber (via conduit 28) to the
anode chamber, and liquid effluent (un-reacted methanol and water)
from the anode chamber to the mixing chamber.
[0044] Each of the liquid carrying conduits also includes a valve
to control the flow therein. Accordingly, conduit 24 includes valve
24A, conduit 26 includes valve 26A, conduit 28 includes valve 28A,
and conduit 30 includes valve 30A.
[0045] The anode chamber, the mixing chamber and the water tank are
each equipped with a vent to the external environment, which can be
opened to allow the pressure within each to be equalized with the
ambient environment.
[0046] In the first embodiment, fluids contained in respective
chambers can be driven to another chamber or stirred, via a
pressure differential developed between the chamber providing the
fluid and the chamber receiving the fluid. Specifically, using
CO.sub.2 gas produced as a result of the anodic oxidation of the
methanol fuel mixture in the anode chamber, pressure can be
increased in the providing chamber above the pressure in the
receiving chamber. The fluid carrying conduit between the two
chambers includes a valve which is opened at an appropriate time to
drive liquid from the providing chamber to the receiving chamber,
once the pressure has reached a predetermined level.
[0047] Accordingly, through the select opening and closing of
respective valves among the elements and chambers of the fuel cell
system according to the first embodiment of the present invention,
in a predetermined sequence, controlled flow of the fluid between
elements is established.
[0048] For example, fluid may be moved to the anode chamber either
directly (from the mixing chamber) or from the fuel and water tanks
through the mixing chamber. In addition, unreacted methanol and
water effluent from the anode chamber may be moved from the anode
chamber to the mixing chamber through the coordinated opening and
closing of the valves. A variety of functions may thus be performed
using this system.
[0049] The following are examples of different functions that may
be performed using the fuel cell system according to the present
invention. Each example specifies the function, actions, and valve
positions to carry our the particular function.
[0050] Each of the following functions occurs during operation of
the fuel cell. Specifically, an electrical load (not shown) is
placed electrically between the anode chamber and cathode chamber
of the fuel cell, thereby establishing a path for electrons
produced in the anode chamber to be transported to the cathode
chamber. Accordingly, in an initial state of the fuel cell, prior
to closing the circuit and connecting the load to the fuel cell,
the anode chamber includes an initial supply of an appropriate
amount of fuel mixture and effluents have not yet been
produced.
[0051] One skilled in the art will appreciate that although the
description for this embodiment includes a first valve 17A (and
associated valve positions) located along the gas carrying conduit
17 adjacent the anode chamber, it is not necessary. The operation
of gas valves located adjacent the other elements render this first
valve redundant, but conceptually allows for more efficient
pressure capture and venting within the system.
[0052] Function 1: Add fuel mixture to anode chamber
[0053] A pressure differential between the mixing chamber and the
anode chamber is established by creating a closed sub-system
comprising the anode chamber, the mixing chamber, and the gas
carrying conduit connecting them. CO.sub.2 generated in the anode
chamber increases and produces a corresponding increase in pressure
in the sub-system. Accordingly, the sub-system is established using
the following valve positions:
2 Valve Positions: Valve Status 17A Open 18A Closed 20A Closed 22A
Open 24A Closed 26A Closed 28A Closed 30A Closed 38A Closed
[0054] Since the anode chamber and the mixing chamber are at the
same pressure, above an initial pressure (which is generally
ambient, atmospheric pressure), the two chambers must be isolated
from one another and the pressure in the anode chamber lowered to
produce the required pressure differential between the two
chambers. Accordingly, valves are positioned in the following
manner:
3 Valve Positions: Valve Status 17A Closed 18A Closed 20A Closed
22A Closed 24A Closed 26A Closed 28A Closed 30A Closed 38A
Closed
[0055] The anode vent is then opened to equalize the pressure
therein with ambient pressure. Thus, since the mixing chamber
remains at the higher pressure, a pressure differential between the
two chambers is established.
[0056] Thus, to move the fluid in the mixing chamber to the anode
chamber, the valves are positioned in the following manner:
4 Valve Positions: Valve Status 17A Closed* 18A Closed 20A Closed
22A Closed* 24A Closed 26A Closed 28A Open 30A Closed 38A Closed
*Valves may remain open, but are preferably closed
[0057] The anode vent may be thereafter closed, or may remain open
during the fluid transfer. However, for a next pressure driven
function to occur, the anode vent must be closed so that the
CO.sub.2 gas may be efficiently used to create a required pressure
differential between the chambers where the fluid transfer will
take place.
[0058] Function 2: Add water to mixing chamber
[0059] A pressure differential between the water chamber and the
mixing chamber is established by creating a closed sub-system
comprising the anode chamber, the water chamber, and the gas
carrying conduit connecting them. CO.sub.2 generated in the anode
chamber increases and produces a corresponding increase in pressure
in the sub-system. Accordingly, the sub-system is established using
the following valve positions:
5 Valve Positions: Valve Status 17A Open 18A Closed 20A Open 22A
Closed 24A Closed 26A Closed 28A Closed 30A Closed 38A Closed
[0060] In order to insure that there is a pressure differential
between the water chamber and the mixing chamber, the vent in the
mixing chamber is opened to equalize the mixing chamber pressure
with ambient pressure. Thereafter, the valves are positioned in the
following manner:
6 Valve Positions: Valve Status 17A Closed 18A Closed 20A Closed
22A Closed 24A Closed 26A Closed 28A Closed 30A Closed 38A
Closed
[0061] Since the water chamber is at a pressure higher than
ambient, it is also therefore higher than the pressure in the
mixing chamber thereby establishing the pressure differential
between the two chambers.
[0062] Thus, to move water from the water chamber to the mixing
chamber, the mixing chamber vent is closed and the valves are
positioned in the following manner:
7 Valve Positions: Valve Status 17A Closed* 18A Closed 20A Closed*
22A Closed 24A Closed 26A Open 28A Closed 30A Closed 38A Closed
*Valves may remain open, but are preferably closed.
[0063] The anode vent may be open after valve 20A has been closed,
or may remain closed. For a next pressure driven function to occur,
however, the anode vent must be closed so that the CO.sub.2 gas may
be efficiently used to create a required pressure differential
between the chambers where the fluid transfer will take place.
[0064] Function 3: Add fuel to mixing chamber.
[0065] A pressure differential between the fuel chamber and the
mixing chamber is established by creating a closed sub-system
comprising the anode chamber, the fuel chamber, and the gas
carrying conduit connecting them. CO.sub.2 generated in the anode
chamber increases and produces a corresponding increase in pressure
in the sub-system. Accordingly, the sub-system is established using
the following valve positions
8 Valve Positions: Valve Status 17A Open 18A Open 20A Closed 22A
Closed 24A Closed 26A Closed 28A Closed 30A Closed 38A Closed
[0066] In order to insure that there is a pressure differential
between the water chamber and the mixing chamber, the vent in the
mixing chamber is opened to equalize the mixing chamber pressure
with ambient pressure. Thereafter, the valves are positioned in the
following manner:
9 Valve Positions: Valve Status 17A Closed 18A Closed 20A Closed
22A Closed 24A Closed 26A Closed 28A Closed 30A Closed 38A
Closed
[0067] Since the fuel chamber is at a pressure higher than ambient,
it is also therefore higher than the pressure in the mixing chamber
thereby establishing the pressure differential between the two
chambers.
[0068] Thus, to move fuel from the fuel chamber to the mixing
chamber, the mixing chamber vent is closed and the valves are
positioned in the following manner:
10 Valve Positions: Valve Status 17A Closed* 18A Closed* 20A Closed
22A Closed 30A Closed 24A Open 26A Closed 28A Open 38A Closed
*Valves may remain open, but are preferably closed.
[0069] The anode vent may be open after valve 18A has been closed,
or may remain closed. For a next pressure driven function to occur,
however, the anode vent must be closed so that the CO.sub.2 gas may
be efficiently used to create a required pressure differential
between the chambers where the fluid transfer will take place.
[0070] Function 4: Move liquid effluent from anode chamber to
mixing chamber.
[0071] A pressure differential between the anode chamber and the
mixing chamber is established by isolating the anode chamber from
the remainder of the system. CO.sub.2 generated in the anode
chamber increases and produces a corresponding increase in
pressure. Accordingly, the anode vent is closed and the valves are
placed in the following positions:
11 Valve Positions: Valve Status 17A Closed 18A Closed 20A Closed
22A Closed 30A Closed 24A Closed 26A Closed 28A Closed 38A
Closed
[0072] In order to insure that there is a pressure differential
between the anode chamber and the mixing chamber, the vent in the
mixing chamber is opened to equalize the mixing chamber pressure
with ambient pressure. Thereafter, the valves are positioned in the
following manner to send liquid effluent to the mixing chamber from
the anode chamber:
12 Valve Positions: Valve Status 17A Closed 18A Closed 20A Closed
22A Closed 24A Closed 26A Closed 28A Closed 30A Open 38A Closed
[0073] Thereafter, the CO.sub.2 generated in the anode chamber may
be vented to the ambient environment, or used to create pressure
differentials within the fuel cell system.
[0074] Function 5: Stir fuel mixture in the mixing chamber.
[0075] A pressure differential between the anode chamber and the
mixing chamber is established by isolating the anode chamber from
the remainder of the system. CO.sub.2 generated in the anode
chamber increases and produces a corresponding increase in
pressure. Accordingly, the anode vent is closed and the valves are
placed in the following positions:
13 Valve Positions: Valve Status 17A Closed 18A Closed 20A Closed
22A Closed 24A Closed 26A Closed 28A Closed 30A Closed 38A
Closed
[0076] In order to insure that there is a pressure differential
between the anode chamber and the mixing chamber, the vent in the
mixing chamber is opened to equalize the mixing chamber pressure
with ambient pressure. Thereafter, the valves are positioned in the
following manner to send CO2 flowing through the mixing chamber
from the anode chamber to the mixing chamber in order to agitate
the fuel-water mixture:
14 Valve Positions: Valve Status 17A Open 18A Closed 20A Closed 22A
Open 24A Closed 26A Closed 28A Closed 30A Closed 38A Closed
[0077] It will be understood to those skilled in the art that it
may require more than one actuation to properly mix the fuel-water
mixture.
[0078] Water generated on the cathode may be moved from the cathode
to the water tank via a wicking agent, and/or by other systems
including use of the system described in associated U.S.
application Ser. No. 09/818,290, filed Mar. 27, 2001, entitled,
METHODS AND APPARATUSES FOR MANAGING EFFLUENT PRODUCTS IN A DIRECT
CONVERSION FUEL CELL SYSTEM (which is commonly owned by the
assignee of the present invention) the entire application of which
is incorporated by reference. Water generated on the cathode may
also be removed to the water tank by other means known to those
skilled in the art, including but not limited to gravity based
systems.
[0079] While it is preferable to implement this embodiment of the
present invention using only valves to control the flow of
CO.sub.2, a flexible impermeable membrane 200 (FIG. 7) may also be
used to prevent the CO.sub.2 from mixing with the various liquids
and bubbling out before creating the necessary pressure
differential.
[0080] The valves of the present invention may be electrically or
mechanically actuated and may be fabricated using a variety of
designs well known to those skilled in the art. Moreover, the fluid
valves are preferably metering valves that may be used to control
the amount of fluid that is released when actuated.
[0081] To coordinate the opening and closing of the valves, a
computer processor and associated supporting and peripheral systems
may be used and programmed to actuate the valves according to the
above functions.
[0082] Second Embodiment
[0083] FIG. 3 illustrates a second embodiment according to the
present invention. Here, a direct methanol fuel cell system
includes a housing 42 defining an anode chamber 44 having a vent 46
and a cathode chamber 48. The system includes a protonically
conductive but electronically non-conductive membrane 50
(Protonically Conductive Membrane), a catalyst, a pump 52, a fuel
tank 54, and a water tank 56. As in the previous embodiment, the
catalyst may be positioned anywhere within the anode and cathode
chambers, but preferably is applied to one or both sides of the
Protonically Conductive Membrane 50.
[0084] It should be understood that the pump includes, but is not
limited to, a passively driven pump as disclosed in U.S. patent
application Ser. No. 09/717,754, filed Dec. 8, 2000, entitled
PASSIVELY PUMPED LIQUID FEED FUEL CELL SYSTEM, which is commonly
owned by the assignee of the present invention, and which is
incorporated by reference herein in its entirety. A gas carrying
conduit 58 connect the anode chamber to the fuel tank.
Liquid-carrying conduits carry fuel and water from the fuel tank
and the water tank via conduits 60 and 62, respectively, to the
pump, fuel mixture from the pump to anode chamber via conduit 64,
and liquid effluent from the anode chamber to the pump via conduit
66. An additional liquid conduit 68 may be included which
transports liquid effluent from the cathode chamber to the water
tank. A valve 60A controls the flow from the fuel tank to the
pump.
[0085] Similar to functions performed by the valves according to
the first invention, this embodiment utilizes CO.sub.2 produced in
the anode chamber to create a pressure differential between the
fuel tank and a pump, so that when the fuel mixture is too lean
(i.e., not enough fuel in the water/fuel mixture), fuel may be
driven to the pump.
[0086] The pump operates to force a fuel mixture into the anode
chamber and for drawing liquid effluent from the anode chamber. A
vent positioned on the pump allows for pressure within the pump to
be equalized with ambient pressure, to insure that an adequate
pressure differential between the fuel tank and the pump is
created.
[0087] Accordingly, pressure is increased in the fuel tank by
closing the anode vent 46, opening valves 58A and 58B, and closing
valve 60A. A pump vent 53 is opened to insure that the pressure
therein is at a lower pressure, i.e., ambient pressure, than that
of the fuel tank.
[0088] When the pressure of the fuel tank reaches an appropriate
level to drive fuel into the pump, and the pump requires the
addition of fuel, valves 58A and 58B are closed (although either
one or both may remain open), the anode vent 46 is opened, the pump
vent 53 is closed, and valve 60A is opened. Fuel is then driven by
the pressure differential to the pump.
[0089] Third Embodiment
[0090] The fuel cell according to the fourth embodiment of the
present invention is substantially similar to the DMFCs described
in the first and second embodiments, except in place of the mixing
chamber, a recirculation conduit 69 is included. Specifically,
liquid effluent from the anode chamber 70 is circulated through the
conduit from one end of the anode chamber to the other end. The
fuel tank 72 provides fuel to the recirculation conduit through a
conduit 74 and 74A fuel valve. Similarly, the water tank supplies
water to the recirculation conduit through a conduit 80 and 80A
water valve.
[0091] Accordingly, fuel and water are provided into the
recirculation conduit as they are needed, so that the fuel
concentration in the fuel mixture remains at a predetermined
amount, or may be adjusted as necessary. Thus a gas conduit 84
delivers effluent gas from the anode chamber 70 to each of the fuel
tank 72 and water tank 78 via conduit 71 and associated valve 71A
and conduit 77 and associated valve 77A, respectively. Effluent
from the cathode chamber 75 may be delivered to the water tank 78
via liquid conduit 79 and valve 79A.
[0092] To move fuel to the recirculation conduit, an anode vent 73
is closed, valves 84A and 71A are opened, and valves 77A, 74A, 80A
and 79A are closed. The increasing volume of CO.sub.2 produced in
the anode chamber increases the pressure of the anode chamber/fuel
tank. When a this pressure reaches a predetermined level, and the
fuel mixture requires more fuel, valves 84A and/or 71A are then
closed and the anode vent is opened to equalize the pressure
therein to ambient pressure, thereby establishing a pressure
differential between the fuel tank and the recirculation
conduit/anode chamber. Thereafter, the anode vent is closed and
valve 74A is opened. The pressure differential drives the fuel from
the fuel tank and into the recirculation conduit.
[0093] The same process is used to deliver water to the fuel
mixture. The anode vent 73 is closed, valves 84A and 77A are
opened, and valves 71A, 74A, 80A and 79A are closed. After the
pressure in the anode chamber/water chamber reaches a predetermined
amount, and the fuel mixture requires more water, valves 84A and/or
77A are closed and the anode vent is opened. Opening the anode
vent, of course, equalizes the pressure therein to ambient,
creating the necessary pressure differential between the water tank
and the anode chamber. The anode vent is then closed, and valve 80A
is opened, driving water into the fuel mixture.
[0094] Fourth Embodiment
[0095] FIG. 5 illustrates a similar design to that of FIG. 4,
except in this case, the system does not include a water tank and
associated conduits and valves. To drive fuel into the
recirculation conduit, the procedure described in association with
FIG. 4 is followed. Additional water, if necessary, may be provided
from the cathode chamber to maintain the proper fuel-water
mixture.
[0096] Fifth Embodiment
[0097] FIG. 6 illustrates yet another alternative design to that of
FIGS. 4 and 5. Specifically, in this embodiment, fuel is supplied
directly into the anode chamber without being diluted, being driven
in the same procedure as that described in association with the
third and fourth embodiments.
[0098] Sixth Embodiment
[0099] FIG. 8 illustrates the sixth embodiment according to the
present invention relating to a method and system for determining
an appropriate level of fuel in a fuel mixture for a DMFC. This
system will be described with reference to the system illustrated
in FIG. 2.
[0100] A fuel concentration sensor 21 (FIG. 9) located within the
system is used to determine a first concentration level of fuel in
the fuel mixture. The fuel tank and the water tank supplies fuel
and water, respectively, to the fuel mixture using the methods
according to the previous embodiments. The fuel cell system, and
specifically the gaseous and liquid valves, and vents are operated
and controlled via a controller 100 as shown in FIG. 9. FIG. 9
illustrates the controller in communication with each one of the
valves and vents of the fuel cell system. The controller also
includes a memory 102 containing a look-up table having data
associated with fuel levels in the fuel mixture for specific
operating parameters. A clock/timer 106 is used to measure time
between obtaining fuel concentration levels. Alternatively, an
electrical meter or other device which measures the electrical
output of the fuel cell system may be used to determine when to
re-measure the fuel concentration level. As shown in FIG. 8, the
system monitors the fuel level in the fuel mixture as well as the
electricity that is being required of the system using a metering
device 104. Accordingly, the system obtains the current fuel
concentration compares (step S1) and it with a fuel level required
for a particular condition using the look-up table (step S2). If
the fuel mixture is too lean, requiring more fuel from the fuel
tank, the system opens/closes the appropriate vents and valves to
drive fuel into the fuel mixture (steps S7, S8). If the fuel
mixture is too rich, requiring more water from the water tank, the
system responses appropriately (steps S4, S5).
[0101] Each time fuel or water is added, a period of time is
pre-programmed to elapse so that the component can adequately mix
with the pre-existing mixture (step S6). Otherwise, the fuel level
sensor might obtain a false reading and supply fuel or water to the
system at an inappropriate time. This would eventually lead to
inefficient operation of the DMFC, potentially resulting in failure
of the fuel cell system.
[0102] One skilled in the art will appreciate that the controller
of FIG. 9 and the method outlined in FIG. 8 may be used with any of
the above-described embodiments of the invention. For simplicity,
the controller was illustrated in communication with the valves and
vents as shown in FIG. 2.
[0103] Having thus presented the present invention in view of the
above described embodiments, various alterations, modifications and
improvements will readily occur to those skilled in the art. Such
alterations, modifications and improvements are intended to be
within the scope and spirit of the invention. Accordingly, the
foregoing description is by way of example only and is not intended
as limiting. The invention's limit is defined only in the following
claims and the equivalents thereto.
* * * * *