Power plants – Utilizing natural heat – Solar
Reexamination Certificate
2000-08-29
2002-10-29
Nguyen, Hoang (Department: 3748)
Power plants
Utilizing natural heat
Solar
C060S039600
Reexamination Certificate
active
06470683
ABSTRACT:
This invention was partially developed with funds provided through Assistance Agreement No. 1425-97-FC-81-30006C provided b the Bureau of Reclamation, U.S. Department of the Interior. The Government may have some rights in this invention.
The present invention relates to a controlled direct drive engine system that can be-applied to pumps and compressors for moving a variety of fluids at high and low pressures and to methods for efficiently pumping fluids using a Modified Brayton cycle or the like power cycles.
Typically, such fluid-moving devices are driven by electric motors, gas turbines, steam turbines, direct-acting steam drive, or conventional Diesel or Otto cycle engines. These pumps and compressors can be of a variety of types, including: crank-driven piston or plunger, rotary screw, or centrifugal. It is generally accepted that the crank-driven pumps and compressors (positive displacement), when driven by conventional reciprocating engines, have the highest fuel-to-fluid efficiency presently available. However, these devices tend to have relatively high maintenance due to the high cycle speeds and pulsating flow—primarily as a result of the mechanical limitations of the crank, and conventional reciprocating engines have high emissions—primarily as a result of being internal combustion. It is also generally accepted that centrifugal pumps and compressors driven by electric motors are the most widely used, which is believed to be primarily due to their smooth output flow and convenience in installation. Moreover, these centrifugal fluid-moving devices are often used even though they inherently have lower fuel-to-fluid efficiency than competing devices and even though the device must be carefully matched to the flow and pressure conditions in the system. Accordingly, solutions have been sought that would overcome these limitations and provide smooth variable flow, low cycle speeds, high fuel-to-fluid efficiency, low emissions, and the capability to efficiently match nearly any flow or pressure condition, up to the ratings of the equipment.
It is known in the art that, when a gas at high temperature and pressure is applied to a piston, the resulting force and velocity can impart energy to another piston to pump a liquid or compress a gas. One version of such a fluid-moving device is known as the direct-acting steam pump, using the Rankine thermodynamic cycle, see
FIG. 1
, which is shown in the Standard Handbook for Mechanical Engineers, Seventh Edition, Page 14-9. There are simplex (single piston assemblies) and duplex (double piston assemblies) versions of these pumps. However, these types of fluid-moving devices have low fuel-to-fluid efficiency, which results from the inability to expand the steam to fairly low pressures and temperatures in order to thus recover more available thermodynamic energy in the steam. This latent energy in the steam is lost when the driving cylinders are vented for the return stroke. Also, because of the thermodynamic characteristic of steam, or other vaporizing liquid that might be used in the Rankine cycle, the pressure ratio from the inlet conditions to the discharge conditions is quite large. This provides another inherent limitation of the direct-acting steam pump.
Furthermore, the direct-acting steam pump has an additional limitation because it normally operates in a “bang-bang” uncontrolled velocity mode. In this bang-bang mode, steam is admitted at the start of the stroke and causes the piston to travel at full velocity until it reaches the end of the stroke—hence the term bang-bang. The inlet pressure of the energy source fluid (steam), and the resistance pressure exerted by the fluid being moved, determines the piston velocity. In addition, the piston velocity that can be achieved may often be limited by pressure drops in the pipes and valves, or it may often be necessary to throttle the steam or the fluid being moved —with such a pressure drop resulting in energy losses. Moreover, these losses will occur even if multiple pistons are actuated in sequence, such as in the case of a duplex configuration.
It should be apparent that what is needed is a controlled direct drive engine system to power pumps and compressors that accomplishes the functions provided by the previously mentioned devices and methods, yet overcomes the shortcomings. It is an object of the present invention to overcome these shortcomings and assure more efficient operation in systems of this type as well as addressing other needs.
In seeking to overcome these shortcomings, it was felt that modern high performance hydraulic power transmission, electronic control, and other techniques that would replace bulky cranks, gearing and housings normally associated with positive displacement energy conversion equipment might aid in finding solutions. The variable displacement capability (and high power density) of hydraulic power was felt to allow the energy conversion process to be optimized in ways that are not usually feasible with conventional positive displacement or rotodynamic energy conversion techniques, and it was felt that this capability could result in a significant improvement in energy utilization effectiveness in addition to improved efficiency. Thus, it was felt that modern hydraulic hydrostatic transmission (HST) technology should be closely examined in this respect.
Conventional hydrostatic transmission equipment includes the variable displacement, over-center, hydraulic hydrostatic pump (HSP) which includes a tiltable swash plate and which may be used to drive a fixed displacement hydraulic hydrostatic motor (HSM). Hydrostatic transmissions of this general type have gained use as variable speed transmissions replacing conventional gear transmissions. Modern agriculture equipment, such as combines and tractors, commonly use these as continuously variable transmissions. The reasons for such use include high power density and the ability to control machine speed precisely with single lever control, while maintaining efficient engine speed. The swash plate angle position of a variable displacement pump can be controlled by a variety of mechanisms, ranging from a simple manual lever control to a sophisticated electronic servo control.
It should be noted that the hydrostatic pump is a reversible device and can also function as a hydraulic motor, when pressure is applied to the ports from another source. This inherent capability further adds to the versatility of the invention, and provides capability for a variety of energy conversion purposes.
Hydrostatic transmission components are presently manufactured in sizes from 5 to 3000 horsepower. One unique characteristic of such a positive displacement hydrostatic transmission component (pump or motor) is that its best-efficiency-point (bep) is quite high over a wide range of sizes (88% to 94%), and its efficiency remains quite high over a wide range of speed, pressure, and power. By comparison, rotodynamic devices (e.g. centrifugal pumps and turbines) have only one bep; their efficiency and system effectiveness can thus dramatically decrease in comparison.
SUMMARY OF THE INVENTION
The present invention accomplishes the functions achieved by the above-mentioned prior art in a unique way, and in a preferred mode thereof, three primary energy transfer functions are accomplished. Energy is first transferred from an energy source fluid using positive displacement. A second energy transfer is then made to a piston that is driving a fluid that is being moved while a hydraulic power device controls the power being transferred to the fluid being moved. Finally, a third transfer of energy is preferably made between piston assemblies that are operating in a complementary fashion through the controlled power device. The controlled power device controls the piston velocity profile, which includes timing sequence, acceleration, velocity, deceleration, stroke distance, and dwell of the stroking pistons, in a prescribed manner. In addition, there is preferably a transfer of energy from a piston assembly having excess available
Childs Willard D.
Dabiri Ali
Fitch Even Tabin & Flannery
Nguyen Hoang
Science Applications International Corporation
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