Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2001-05-14
2004-02-03
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S006000, C429S006000
Reexamination Certificate
active
06686079
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to fuel cells, and in one embodiment, to fuel cells that are especially well suited for downhole use in oil and gas wells, and for subsea use in connection with offshore wells. The invention can also be useful for commercial energy generation, powering electric vehicles, and powering other equipment, for example, communication and control equipment located in remote areas away from commercially available power sources.
BACKGROUND OF THE INVENTION
Several types of equipment used downhole in oil and gas wells, or beneath the surface of the sea adjacent to offshore wells, are electrically operated or actuated. Examples of such equipment include certain wireline tools and remote well telemetry equipment. The electrical power required can be provided by connecting the device to a surface power source via electrical cables, or by placing a power source near the site of the device itself. Often it is not practical to use electrical cables running from the surface to the subterranean or subsea site of the electrically-powered device, because of the great distance involved, or because the cables can interfere with the passage of other equipment through the wellbore, and are vulnerable to being damaged during well operations.
Batteries can be used as a local source of power for downhole and subsea electrical devices, but are subject to their own problems. For example, increasing the power and energy generation capacity of a battery generally requires a proportionate increase in the size of the battery, which can present difficulties given the space constraints that exist in wellbores. Also, batteries will typically need to be electrically recharged at some point, thereby often making it necessary to provide some type of recharging equipment in physical proximity to the battery.
Fuel cells make use of an electrochemical reaction involving a fuel and an oxidant in a cell that comprises an anode, cathode, and electrolyte, to generate electricity without also generating the unwanted by-products associated with combustion, while providing relatively higher energy efficiency. Thus, fuel cells potentially have a number of advantages over other power generation or storage means in many applications. The fuel cells of the present invention can be used in a variety of applications. Although the invention is primarily described herein in relation to applications involving subterranean wellbores, it should be understood that the invention can be used in applications other than wellbore applications.
A number of obstacles have hindered the use of fuel cells in downhole and subsea applications. For instance, fuel cells typically include one or more pumps to provide circulation of fuel and/or oxidant in a closed loop through the cell. If such a pump fails downhole, repair or replacement can be extremely expensive, given the need to retrieve the fuel cell to the surface. Further, the operation of the pumps consumes some of the energy produced by the cell, thus reducing the net power yield available to operate an external device. This latter point can be a significant problem in downhole or subsea applications in which a supply of power is needed for an extended period of time, and yet space constraints limit the ability to simply increase the size of the fuel and oxidant reservoirs. Additionally, the reaction product, water vapor, needs to be removed from the fuel cell stack in order to continuously run the fuel cell. Removal of the water downhole and in a subsea environment presents a challenge because the surrounding pressure is higher than that present in a conventional fuel cell placed at surface in an ambient environment and operating in air. Using a pump to expel the water into the high pressure downhole or subsea environment may require a large amount of power making such a system impractical.
VanBerg U.S. Pat. No. 5,202,194 describes a power supply for providing electricity to electrical circuits located downhole in a well. The power supply comprises a fuel cell, which is fed by hydrogen from a pressure container and oxygen from compressed oxygen gas bottles. Pressure regulators are located in the line between the hydrogen container and the fuel cell, and in the line between the oxygen bottles and the fuel cell. A pump is used to eject water from the fuel cell into the wellbore. The need to have a water outflow path from the interior of this fuel cell to its exterior raises potential reliability issues and may be impractical for downhole use.
There is a need for a new fuel cell operation concept and an improved fuel cell apparatus that can provide the electrical power needed to operate various downhole and subsea equipment.
SUMMARY OF THE INVENTION
One embodiment of the present invention relates to a fuel cell that includes a fuel vessel that comprises a source of fuel and an oxidant vessel comprising a source of oxidant. A reaction zone comprises at least one cathode, at least one anode, and electrolyte between each anode and cathode. A closed water vessel is connected to the reaction zone by at least one capillary flow path. The fuel cell also comprises a fuel conduit that connects the fuel vessel and the reaction zone. This fuel conduit comprises a fuel pressure control apparatus adapted to maintain a static pressure of fuel in the reaction zone. The fuel cell further comprises an oxidant conduit that connects the oxidant vessel and the reaction zone, and includes an oxidant pressure control apparatus adapted to maintain a static pressure of oxidant in the reaction zone. In addition, the fuel cell comprises electrical conductors connected to the anode and cathode and adapted to conduct electricity to an external device.
In a fuel cell of certain embodiments of the present invention, there is no need for fuel, oxidant, or water to dynamically flow in a closed loop through the reaction zone. This is because the fuel and oxidant vessels, and the pressure control apparatus, provide a static, elevated pressure in the reaction zone. The closed water vessel receives and stores the water (liquid) produced by the fuel cell reaction, thus eliminating the need to pump the water out of the fuel cell for disposal.
In some embodiments, the fuel cell of the present invention does not include any fuel pump, oxidant pump, or water pump. As mentioned above, such pumps are not required in some embodiments of the present invention. It is also possible that the reaction zone comprise as its only openings for fluid flow at least one aperture connected to the fuel conduit for admitting fuel into the reaction zone, at least one aperture connected to the oxidant conduit for admitting oxidant into the reaction zone, and the capillary flow path (or paths) that connects the reaction zone to the water vessel. The capillary flow path can comprise a tube, thread, conduit or other forms that can transport the produced water from the reaction zone to the water vessel and can be attached to or lying on or otherwise physically touching the membrane surfaces of the reaction zone.
The fuel cell of some embodiments of the present invention is operated with a static pressure in the reaction zone that is high enough to cause any water vapor formed and generated in the fuel cell to condense once the saturation point is reached. Accordingly, the fuel cell must operate at a pressure that is higher than the saturated water vapor pressure for the given application. A “static pressure” in this context is one that varies between the anode and cathode chamber of the fuel cell not more than about 5% in normal operation. Some embodiments of the invention operate with pressures for the reaction zone between about 40-400 psig, more typically about 50-200 psig, depending upon the operating temperature.
In one specific embodiment of the invention, the fuel pressure control apparatus and the oxidant pressure control apparatus are pressure regulator valves. In another specific embodiment of the invention, the water vessel is located within at least one cathode. In other embodiments the wate
Havlinek Kenneth L.
Hensley Donald E.
Zhang Wenlin
Curington Tim
Jeffery Brigitte C.
Kalafut Stephen
Schlumberger Technology Corporation
Williams Morgan & Amerson
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