Power plants – Motive fluid energized by externally applied heat – Process of power production or system operation
Reexamination Certificate
1999-05-26
2001-02-27
Nguyen, Hoang (Department: 3748)
Power plants
Motive fluid energized by externally applied heat
Process of power production or system operation
C060S657000
Reexamination Certificate
active
06192687
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to uninterruptible power supplies that include a thermal energy source as a back-up energy source. More particularly, the power supplies of the present invention include a material that is heated and maintained at an elevated temperature during standby operations. In the event of a failure of the primary power source, such as utility power, the stored thermal energy is converted into electricity that provides the necessary back-up power until the primary supply comes back on line.
Uninterruptible power supplies (UPS) are well known. Such devices often are used to provide a nominal amount of power for a certain time period so that various pieces of equipment utilizing primary power may be shut down in a relatively normal fashion, rather than the instantaneous shut-down that would occur from a loss of primary power without a backup supply. One known configuration for a UPS is to provide a bank of chemical batteries as a short-term, secondary power source. The batteries often are combined with an emergency generator that provides long-term secondary power.
Chemical batteries suffer from various deficiencies including bulkiness, lack of reliability, limited lifespan (typically requiring replacement every 3-8 years), high maintenance costs and relatively low safety. For example, chemical batteries require relatively constant and complex recharging, depending on the type of batteries involved to insure that the batteries continue to operate efficiently and maintain their full storage capacity. Even well maintained batteries, however, may be unreliable due to a relatively high sensitivity to temperature. Additionally, chemical batteries raise various safety considerations due to the general nature of the large quantities of toxic and caustic chemicals involved. Typical large battery installations often require special venting and air-conditioning systems for the dedicated battery storage rooms.
In view of the foregoing, it is an object is of this invention to provide improved uninterruptible power supplies that provide back-up power from a thermal source of energy.
It is also an object of the present invention to provide improved uninterruptible power supplies that are relatively insensitive to ambient temperature variations while providing back-up power.
It is an additional object of the present invention to provide improved uninterruptible power supplies that have reduced maintenance requirements.
It is a still further object of the present invention to provide improved uninterruptible power supplies that have an essentially unlimited life cycle.
SUMMARY OF THE INVENTION
These and other objects of the invention are accomplished in accordance with the principles of the invention by providing various uninterruptible power supplies that utilize stored thermal energy to provide back-up power. The preferred embodiments include a material that is heated to store energy. That material may be either at least one vessel which stores a liquid that is heated or a solid mass, such as a block of iron, that is heated. The material may be heated utilizing various different methods, such as resistance heating or using a boiler to heat fluid that is circulated in a closed loop from the vessel to the boiler, or resistance heating to heat the solid mass.
When primary power, such as utility power, is present, the primary power may be used to heat a resistor immersed in the fluid within the vessel or a resistor in thermal contact with the solid mass. The resistor then heats the material to keep it at a predetermined temperature, such as between 150 and 300 degrees Celsius for the liquid, or between 150 and 1000 degrees Celsius for the solid. Alternately, in the fluid embodiments, the fluid in the vessel may be circulated through a boiler which may be powered, for example, by fuel from a utility gas line or external fuel tank, or both. Power from the utility also may be used to power a generator as a motor so that it is spinning at all times—this will enable the system to provide almost instantaneous back-up power in the event of a loss of primary power.
The heat engines utilized to drive the generator in the various UPS embodiments of the present invention may be mechanical heat engines, such as a steam engine or Stirling engine. Instead, they may be thermionic or thermoelectric heat engines that generate DC power directly from the stored thermal energy. If a steam engine configuration is utilized, the engine may be a turbine or reciprocating engine without departing from the scope of the invention. One particular type of steam turbine that may be used is an expander wheel that drives a shaft that drives the generator.
In some instances, a fluid, such as water, passes through pipes placed within the vessel. The heated fluid transfers heat to the fluid in the closed loop pipe so that the fluid is heated. It may be preferable for efficiency to heat the fluid above its boiling point so that, for example, water turns into steam, however, persons skilled in the art will appreciate that the principles of the present invention may be practiced without a phase change occurring. The resultant steam is used to drive either the heat engine or a turbine connected to the generator (the expander changes the pressure of the steam from high to low, which drives the turbine). In other instances, the heat from the material may be transferred directly from the vessel or solid mass to the heat engine.
A further advantage of the present invention is realized from the turbine rotor itself, which is constantly rotated when utility power is present by the utility power itself (thus, during stand-by mode, the generator is operated as a motor). Additional improvements in reliability may be provided by utilizing magnetic bearings, preferably active bearings, to alleviate substantially all of the weight from the rotor so that the rotor may spin continuously at high speeds without wear. The rotating heat engine rotor, which may be rotated from about 20-50 k RPM, provides an additional source of stored energy, in this case kinetic energy, that may be used to provide power to the critical load during the period that the heat flow is increased.
Additional advantages of the present invention may be obtained by including a condenser or liquid cooling tank in the water/steam loop. The condenser or cooling tank, if used, cools the steam from the expander wheel into water for re-circulation back into the heating vessel. If a condenser is used, it may also be preferred to utilize a radiator that operates to offload the heat from the condenser. A choice between a conventional condenser and modified condenser that includes a cooling tank is preferably made depending on the desired runtime of the system. For example, if the back-up system is designed for a relatively short duration, such as 15-20 minutes (in which case another back-up power source would likely be used, such as an external diesel engine-generator), the cooling tank configuration may be used. If, on the other hand, the thermal back-up system is designed to run until utility power returns, then it would be preferable to utilize the conventional condenser/radiator combination.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.
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Clifton David B.
Pinkerton Joseph F.
Active Power Inc.
Fish & Neave
Morris Robert W.
Nguyen Hoang
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