Pumps – Motor driven – Fluid motor
Reexamination Certificate
2002-11-19
2004-03-02
Freay, Charles G. (Department: 3746)
Pumps
Motor driven
Fluid motor
C417S394000, C417S395000, C429S006000
Reexamination Certificate
active
06699021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of fuel cells and, more specifically, to a direct methanol fuel cell system in which carbon dioxide generated by the electro-chemical reaction is used to drive a pump which pumps fuel into the system.
2. Background Information
Fuel cells are devices in which an electro-chemical reaction is used to generate electricity. A variety of materials may be suitable for use as a fuel, depending upon the materials chosen for the components of the cell. Organic materials, such as methanol or formaldehyde, are attractive choices for fuels due to their high specific energies.
Fuel cell systems may be divided into “reformer based” (i.e., those in which the fuel is processed in some fashion before it is introduced into the cell) or “direct oxidation” in which the fuel is fed directly into the cell without internal processing. Most currently available fuel cells are of the reformer-based type, and their fuel processing requirement limits their application to relatively large applications relative to direct oxidation systems.
An example of a direct oxidation system is the direct methanol fuel cell system or DMFC. In a DMFC, the electro-chemical reaction at the anode is a conversion of methanol and water to CO
2
, H
+
and e
−
. The hydrogen ions flow through a membrane electrolyte to the cathode, while the free electrons flow through a load which is normally connected between the anode and cathode. The carbon dioxide, which is essentially waste, is separated from the remaining methanol fuel and vented before such fuel is recirculated. At the cathode, oxygen reacts with hydrogen ions and free electrons to form water.
Many DMFC designs rely on a simple gravity feed to draw methanol from a source and introduce it into the anode. Two disadvantages of the gravity feed are that it is difficult to vary the flow of methanol into the fuel cell system in response to changes in demand for power, and operation may be interrupted when the system is moved or oriented such that fuel does not flow smoothly. These are significant disadvantages in applications that have a variable load or which are expected to operate in situations where orientation is variable, such as consumer electronic devices, in which DMFCs may be candidates to replace batteries as the power source. Other DMFC designs rely on motorized pumps to pump the methanol into the cell. However, the use of such pumps may bring intolerable increases in size or weight, and will increase the cost of manufacturing and cost of operation due to the electricity or other energy needed to drive the pump. The parasitic power loss used to drive the pump decreases efficiency and will therefore decrease the operation time of the system, and decrease the effective output of such a system.
SUMMARY OF THE INVENTION
The present invention provides a fuel cell system in which fuel is circulated by a pump driven by a gas produced naturally as part of the electro-chemical reaction. In a preferred embodiment, a fuel cell system is provided in which the methanol fuel is pumped by a pump driven by carbon dioxide generated at the anode. The pump receives methanol fuel from a source and water from a gas separator which separates the effluent from the cathode into water and air. Effluent from the anode is directed through another gas separator which separates methanol and water as liquids from the carbon dioxide gas. The separated liquids and gas are then passed to the fuel pump where the CO
2
is used to drive the pump.
Because the amount of CO
2
generated by the fuel cell is proportional to the power generated and, in turn, the demand for fuel, the fuel pump is self-regulating. That is, as more power is demanded, more CO
2
is produced, which results in the fuel pump delivering more fuel to the cell. Conversely, as power demand decreases, less CO
2
is produced by the fuel cell, which in turn decreases the amount of fuel pumped to the cell. As the CO
2
used to drive the pump is produced naturally as part of the fuel cell's operation, there is no parasitic power loss caused by the pump's operation, and the fuel cell system's operating time is not decreased. In addition, all or most of the components of the system may be fabricated using microelectromechanical system techniques, thus providing a compact, highly integrated system.
REFERENCES:
patent: 2952217 (1960-09-01), Lindbom
patent: 3468713 (1969-09-01), Mueller
patent: 4046956 (1977-09-01), Fanciullo
patent: 4572876 (1986-02-01), Spurrier
patent: 4593534 (1986-06-01), Bloomfield
patent: 4673624 (1987-06-01), Hockaday
patent: 4810597 (1989-03-01), Kumagai et al.
patent: 5523177 (1996-06-01), Kosek et al.
patent: 5573866 (1996-11-01), Van Dine et al.
patent: 5599638 (1997-02-01), Surampudi et al.
patent: 5631099 (1997-05-01), Hockaday
patent: 5723228 (1998-03-01), Okamoto
patent: 5759712 (1998-06-01), Hockaday
patent: 5766786 (1998-06-01), Fleck et al.
patent: 5773162 (1998-06-01), Surampudi et al.
patent: 5795668 (1998-08-01), Banerjee
patent: 5916699 (1999-06-01), Thomas et al.
patent: 5925476 (1999-07-01), Kawatsu
patent: 5945231 (1999-08-01), Narayanan et al.
patent: 5992008 (1999-11-01), Kindler
patent: 6146781 (2000-11-01), Surampudi et al.
patent: 6265093 (2001-07-01), Surampudi et al.
patent: 6296964 (2001-10-01), Ren et al.
patent: 6322917 (2001-11-01), Acker
patent: 6350540 (2002-02-01), Sugita et al.
patent: 6420059 (2002-07-01), Surampudi et al.
patent: 2002/0015872 (2002-02-01), Surampudi et al.
patent: 1114489 (1968-05-01), None
patent: 2010385 (1979-06-01), None
patent: 01 54216 (2001-07-01), None
U.S. patent application Publication No. US 2002/0155341 A1, Published Oct. 24, 2002, by Finkelshtain et al. for a Self-Managing Electrochemical Fuel Cell and Fuel Cell Anode, all pages.
International Search Report for International Application No. PCT/US 01/43417, filed Jun. 11, 2001, all pages.
Ren, Xiaoming et al. Methanol Cross-Over in Direct Methanol Fuel Cells, Electronic and Electrochemical Materials and Devices, MST-11, MS-D429, Los Alamos National Laboratory, NM, all pages.
Fuel Cell, 1992 Fuel Cell Seminar, Program and Abstracts, Nov. 29,—Dec. 2, 1992, Tucson, AZ, pp. 233-236, 461-464.
Maynard, Helen et al., Miniaturized Fuel Cells for Portable Power, Lucent Technologies, 2000.
Sharke, Paul, Pocket-Size PEMs, Mechanical Engineering. Http://www.memagazine.org/contents/current/features/pems/pems.html all pages.
Gottesfeld, Shimshon et al., Polymer Electrolyte Fuel Cells as Potential Power Sources for Portable Electronic Devices, pp. 487-517.
Acker William P.
McNamee George C.
Cesari and McKenna LLP
Freay Charles G.
MTI MicroFuel Cells Inc.
LandOfFree
Passively pumped liquid feed fuel cell system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Passively pumped liquid feed fuel cell system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Passively pumped liquid feed fuel cell system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3256810