Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
1998-07-17
2001-08-21
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S006000, C429S010000, C422S182000
Reexamination Certificate
active
06277508
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to fuel cell power supplies and more particularly to methods and apparatus for improved water management in fuel cell power supplies.
BACKGROUND
Many types of fuel cells are known in the art, such as solid oxide fuel cells, molten carbonate fuel cells, phosphoric acid fuel cells and proton exchange membrane (PEM) fuel cells. Conceptually, the operation of a fuel cell is very simple. An electrolytic medium separates an anode and a cathode, between which electricity is produced when a fuel is introduced to the anode, an oxidizer is introduced to the cathode, and the cell is maintained at the proper temperature. The electrolytic medium allows an ionic species to travel between the cathode and the anode. The reaction products are relatively simple and benign, typically including carbon dioxide and water, thus minimizing environmental concerns. In contrast to other energy sources, such as internal combustion engines, fuel cells are simpler, less noisy, do not pollute, demonstrate high efficiencies, and create electricity directly.
In practice, however, a fuel cell power supply can be relatively complex, as considerable hardware can be required to support the fuel cells, which are typically arranged in an cell stack assembly (CSA). Such hardware can include a thermal management subsystem for maintaining the CSA at the proper operating temperature, a fuel processing subsystem that can include fuel reformers and shift converters for generating a hydrogen fuel from a hydrocarbon fuel, and a water management subsystem for recovering water generated by the operation of the fuel cell(s) to reduce the need for external water. Desulfurization of the fuel is often also required. The various subsystems are often interrelated, for example including heat exchangers, blowdown coolers or condensers for transferring heat and/or water from one subsystem to another.
Water management is particularly important in a Proton Exchange Membrane (PEM) fuel cell power supply. Water generated at the cathode should be removed to avoid flooding the cathode and preventing the oxidant from reacting at the cathode. Furthermore, water is dragged through the membrane by H
+
protons to the cathode, drying out the anode and adding to the water that must be removed from the cathode. Such drying of the anode, or even drying of the cathode due to improper water management, can damage the proton exchange membrane. Accordingly, water is typically added to the fuel input of the anode, and removed from the cathode in controlled manner by exhausting of the cathode external to the system. Other subsystems, such as a fuel reformer, can require water. It is desirable that water use and generation be balanced such that the power supply be self-sufficient and does not require water from an external source. Water balance concerns thus add complexity to PEM fuel cell power supplies.
To date, fuel cells power supplies, such as those based on PEM cells, have not found widespread use, such that their environmental and other benefits can be fully realized, in part because of the complexity and associated cost of existing fuel cell power supplies. Such a situation is far from satisfactory, as environmental and other concerns with the drawbacks of traditional power sources (such as internal combustion engines and coal or oil fired electrical power generation plants) are unlikely to become less pressing.
Accordingly it is an object of the invention to reduce the complexity and/or the cost of fuel cell power supplies.
It is another object of the invention to provide methods and apparatus for improving water management in a PEM fuel cell power supply.
Other objects of the invention will in part be apparent and in part appear hereinafter.
SUMMARY OF THE INVENTION
The present invention achieves these and other objects by providing methods and apparatus for recycling anode exhaust from the anode flow field of a fuel cell power supply. Anode exhaust is provided to a combustion unit, and the combustion exhaust routed to at least one of the cathode flow field and the anode flow field of the supply.
According to one aspect of the invention, a fuel cell power supply for producing electricity from input fuel and oxidizer reactants includes a cell stack assembly (CSA). The CSA includes at least one fuel cell having an anode, a cathode, and an electrolytic medium therebetween. The CSA is adapted for defining an anode flow field for receiving and exposing the anode to the fuel and a cathode flow field for receiving and exposing the cathode to the oxidizer. The CSA is also adapted for providing an exhaust from the anode flow field. The power supply includes a removal means for removing water from the cathode flow field. A combustion unit receives exhaust from the anode flow field to produce a combusted exhaust including water, and the combustion unit fluidly communicates the combusted exhaust to the cathode flow field and/or the anode flow field. The combustion unit can be thermally coupled to a fuel processor for processing the input fuel. Optionally, cathode exhaust from the cathode flow field may also be provided to the combustion unit.
According to another aspect of the invention, a fuel cell power supply for producing electricity from fuel and oxidizer reactants includes a cell stack assembly (CSA) including at least one fuel cell having an anode, a cathode, and an proton exchange membrane (PEM) therebetween. The CSA is adapted for defining an anode flow field for receiving the fuel for exposure to the anode, for providing an exhaust from the anode flow field, and for defining a cathode flow field for receiving oxidizer for exposure to the cathode. The CSA is also adapted for defining a coolant flow field for cooling the CSA and for recovering water internal to the CSA. The power supply also includes a combustion unit for receiving exhaust from the anode flow field to produce a combusted exhaust including water. The combustion unit fluidly communicates with the anode flow field for providing at least a portion of the combusted exhaust to the anode flow field. Alternatively, the combustion unit can be in fluid communication with the cathode flow field for providing at least a portion of the combusted exhaust to the cathode flow field. Optionally, cathode exhaust from the cathode flow field may also be provided to the combustion unit.
In yet a further aspect, the invention provides a method of operating a fuel cell power supply to produce electricity from input fuel and oxidizer reactants where the fuel cell power supply includes a cell stack assembly (CSA) including at least one fuel cell having an anode, a cathode, and an electrolytic medium therebetween. The method includes providing an anode flow field for exposing the anode to the fuel; providing a cathode flow field for exposing the cathode to the oxidizer; delivering at least at portion of anode exhaust from the anode flow field to a combustion unit; combusting the anode exhaust to produce combusted exhaust including water; providing the combusted exhaust to at least one of the anode flow field and the cathode flow field; and removing water from the cathode flow field for use in the fuel cell power supply. Water can be removed from the cathode flow field via internal water recovery. Furthermore, the method can include providing cathode exhaust from the cathode flow field to the combustion unit.
One advantage of the invention is that the condenser typically employed for recovering water from combusted exhaust can be eliminated, of reduced capacity, or operated less frequently, thereby reducing the cost and/or the complexity of the fuel cell power supply or of the operation thereof.
These and other features of the invention are more fully set forth with reference to the following detailed description, and the accompanying drawings.
REFERENCES:
patent: 4826741 (1989-05-01), Aldhart et al.
patent: 5134043 (1992-07-01), Nakazawa
patent: 5441821 (1995-08-01), Merritt et al.
patent: 5635039 (1997-06-01), Cisar et al.
patent: 5753383 (1998-05-01),
Margiott Paul Richard
Reiser Carl Anthony
Yang Deliang
Alejandro R
International Fuel Cells Corporation
Maples John S.
McCormick Paulding & Huber LLP
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