Pumps – Electrical or getter type – Getter heating – vaporizing – or regeneration
Reexamination Certificate
2000-06-29
2002-02-19
Freay, Charles G. (Department: 3746)
Pumps
Electrical or getter type
Getter heating, vaporizing, or regeneration
C417S199100, C074S572200, C310S074000
Reexamination Certificate
active
06347925
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to flywheel energy storage systems, and more particularly to a flywheel energy storage system that includes a high-speed flywheel assembly, and a plurality of pumps arranged in parallel for reducing windage losses due to gases evolving from the high-speed flywheel assembly.
2. Background
FIG. 1
shows a simplified view of a conventional flywheel energy storage system
100
used for storing kinetic energy. The conventional flywheel system
100
includes a flywheel assembly
104
disposed in a flywheel housing
102
. Such assemblies are run under vacuum, in order to avoid drag on the flywheel. The systems are evacuated with standard vacuum pumps, e.g. turbo pumps, and then sealed, preferably by pinching off and then fusing the end of a copper tube, thus forming an all metal seal, which is impervious even to argon. However, the materials which make up the flywheel system may entrain or evolve substantial quantities of materials which may be released within the system, thus causing a reduction of the vacuum, and drag on the flywheel. To partially deal with that problem, a drag pump
106
is incorporated into the flywheel assembly
104
for pumping gases from the flywheel housing
102
into a separate gas storage chamber
108
. For example,
FIG. 1
includes arrows for indicating a direction of evolved gas flow from the flywheel housing
102
, through helical grooves (not numbered) formed in the drag pump
106
, and then into the gas storage chamber
108
.
Traditionally, flywheel assemblies have been made of metal, e.g., high strength steel. More recently, flywheel assemblies have been fabricated using fiber composite materials, e.g., fiberglass or carbon wound with a resin binder, thereby making flywheel assemblies that are lighter in weight and capable of operating at higher speeds than the traditional metal flywheel assemblies operate. Both the flywheel assemblies that are made of metal and those made of fiber composite materials typically evolve substantial quantities of gases during operation, thereby potentially increasing gas pressure levels inside flywheel housings to unacceptable levels. Such increased pressures can significantly reduce the useful lifetime of flywheel energy storage systems because they generally lead to high windage losses.
For this reason, pumps like the drag pump
106
shown in
FIG. 1
have been used for drawing off evolved gases from flywheel housings. Pumps suitable for this purpose include both turbo-molecular pumps and molecular drag pumps. However, such pumps have drawbacks in that they are typically not designed for pumping evolved gases directly from flywheel housings to the atmosphere.
A common solution to this problem is to provide a mechanical roughing pump (not shown) at the outlet of a drag pump in a flywheel system. Such mechanical roughing pumps are generally capable of exhausting directly to the atmosphere. As a result, the drag pump and the roughing pump may be used in combination for drawing off the evolved gases in the flywheel housing, thereby reducing gas pressure levels in the flywheel housing for optimal flywheel operation. However, mechanical roughing pumps also have drawbacks in that they are usually high in cost and typically require frequent maintenance.
Another solution is to provide a gas storage chamber such as the chamber
108
(see
FIG. 1
) at the outlet of the drag pump. For example, in U.S. Pat. No. 5,462,402 (“the '402 patent”) issued Oct. 31, 1995, to Bakholdin et al., a flywheel energy storage system with an integral molecular pump is disclosed. In accordance with that disclosure, a flywheel assembly used for mobile energy storage incorporates a molecular pump and an internal chamber containing molecular sieves. The molecular pump shares the shaft, bearings, and motor of the flywheel rotor, and maintains the high vacuum desired in the vicinity of the flywheel rotor. The gases, which evolve from the rotor during its operational life, are pumped into the chamber containing the molecular sieves where they are adsorbed.
However, the flywheel energy storage system described in the '402 patent also has some drawbacks. For example, the molecular sieves contained in the internal chamber typically cannot adsorb all of the different types of gases that can evolve from the flywheel rotor during high-speed operation of the flywheel assembly.
Specifically, the evolved gases may include water vapor along with various quantities of hydrocarbons and/or other active gases. Although molecular sieves can, in general, efficiently adsorb, e.g., water vapor, they typically cannot adsorb substantial quantities of hydrocarbons and/or other active gases, especially at temperatures of about 20° C. and above. This is a significant problem because flywheel assemblies operating at high-speed, especially those made of fiber composite materials, arc likely to evolve substantial quantities of active gases. If these gases are not adsorbed by the molecular sieves or otherwise pumped out to the atmosphere, the flywheel system, e.g., the flywheel housing and/or the above-described internal chamber, will likely be subjected to unacceptable gas pressure levels over time, thereby increasing windage losses and significantly limiting the useful lifetime of the flywheel system.
Further, in accordance with the disclosure of the '402 patent, getter materials may be disposed throughout the vacuum housing of the flywheel to absorb trace quantities of gases that are not readily adsorbed by the molecular sieves contained in the internal chamber of the flywheel system.
However, this approach also has some drawbacks. Specifically, as the getter material disposed in the flywheel housing increasingly absorbs the trace quantities of gases, its capacity for further absorbing gases typically degrades. For example, evaporated getter pumps designed for use in flywheel systems typically have limited pumping capacities. As a result, gas pressure surrounding the getter material in the flywheel housing can increase over time, thereby increasing overall gas pressure in the flywheel housing to unacceptable levels.
One way of achieving increased pumping capacity in flywheel systems is to use non-evaporable getter (NEG) pumps, which generally have pumping capacities that are significantly greater than that of evaporated getter pumps. Such NEG pumps typically achieve a maximum capacity for pumping various gases at elevated temperatures, e.g., 250° C. or higher. For example, in U.S. Pat. No. 5,879,134 (“the '134 patent”) issued Mar. 9, 1999, to Lorimer et al., a getter pump for pumping gases in a wafer processing system is disclosed. In accordance with that disclosure, a wafer processing system includes a processing chamber, a low-pressure pump coupled to the processing chamber for pumping gases, a valve mechanism coupling a source of inert gas to the processing chamber, an in situ getter pump disposed within the processing chamber which pumps certain active gases during the flow of the inert gas into the chamber, and a processing mechanism for processing a wafer disposed within the processing chamber. Preferably, the in situ getter pump can be operated at a number of different temperatures to preferentially pump different species of gas at those temperatures. A gas analyzer is used to automatically control the temperature of the getter pump to control the species of gases that are pumped from the chamber.
However, the getter pump for pumping gases described in the '134 patent also has some drawbacks. For example, systems incorporating such getter pumps typically consume significant amounts of power. Although high power consumption might be acceptable in systems such as wafer processing systems, it is generally unacceptable in flywheel energy storage systems.
In addition, as explained above, gases that evolve from high-speed flywheel assemblies typically include water vapor along with lesser quantities of hydrocarbons and/or other active gases. Further, the getter materi
Rathbun Jeremiah I.
Woodard Nathan G.
Beacon Power Corporation
Conlin David G.
Daley, Jr. William J.
Dike, Bronstein, Roberts and Cushman Intellectual Property Pract
Freay Charles G.
LandOfFree
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