Power plants – Fluid motor means driven by waste heat or by exhaust energy... – Having fluid motor motive fluid treating – controlling or...
Reexamination Certificate
2002-09-13
2003-11-25
Nguyen, Hoang (Department: 3748)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
Having fluid motor motive fluid treating, controlling or...
C060S616000, C060S614000
Reexamination Certificate
active
06651433
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to improvements in the efficiency of internal combustion engines within combined-cycle power plants.
BRIEF DESCRIPTION OF THE PRIOR ART
Combined-cycle power plants are known and are becoming dominant in the larger engine power industry, particularly in fixed-plant applications. Commonly, these power plants include gas turbine generators exhausting to Rankine cycle steam generating plants and are found in large installations with gas turbine generators rating as high as 390 megawatts with a claimed thermal efficiency of 58% for the combined cycle. Conventional gas turbines consist of a bladed compressor and a bladed expander mounted on the same shaft. The compressor, as distinguished from positive displacement engines, must run at high RPM to pump air at low pressure. The resulting large mass flow of high temperature air requires large heat recovery equipment. Systems of this type generally operate continuously at full load, because both efficiency and torque drop considerably with a reduction of size, speed or load.
The configuration of a screw engine is comparable to that of a gas turbine to the extent that both include a compressor, a combustor, and an expander. Largely for this reason, screw engines are commonly mis-identified as screw turbines when, in fact, they are positive displacement mechanisms comparable to a piston engine. The close clearances of screw engines make them self-cleaning, free of the deposits that build up in the bladed compressor of a gas turbine. Air-fuel ratios can be maintained at optimum levels over the range of operation, so there is no excess air and mass flow. The result is higher exhaust temperatures, permitting the use of smaller heat recovery units. Further, the expander may be equipped with an expansion ratio modulation system, as is commonly known in screw engine applications. Under low load conditions, there could be an over-expansion of the gasses, resulting in a power drag on the unit. A capacity control modulation system results if slots are cut in the first compressor stages. Opening a slide valve vents these stages to the inlet end of the unit to delay compression. Similar slots in the screw expander at the exhaust end give similar early exhaust at low loads.
Combined-cycle power systems are also found in vehicles such as large trucks, locomotives and busses. Regenerative vehicle braking systems have been developed using flywheels, where the braking energy speeds up a flywheel to store energy which is later used to propel the vehicle. The Swedish Cumulo system uses braking energy to pump oil into a chamber at up to 6,000 psi. The pressure energy is then used to accelerate the vehicle. This system requires heavy duty piping and components which reduce the vehicle's payload carrying capacity. Electric drive power systems, generally known as hybrid systems, are also known. An engine drives a generator, which in turn powers the electric drive motor. On braking, computer control changes the drive motor to generator mode and electricity is fed back into a battery grid. This system has a limited amount of energy storage and, when the storage limit is reached, further braking energy is wasted.
Current submarine propulsion systems have unique problems due to the desirability of remaining submerged for long periods of time while retaining the capability of moving at high speeds. At present, the world naval submarine fleet numbers almost seven hundred boats—some of which are nuclear. Nuclear submarines have the ability to submerge and stay under water for weeks or even months. However, they are large, heavy, and very costly to build and operate. They are also designed to meet the Cold War need for difficult-to-detect, deep ocean, strategic nuclear weapons platforms. Because of their size, they are not suitable for the littoral warfare foreseen for the present and near future.
The great majority of the world's submarines have non-nuclear diesel-electric propulsion systems. For the cost of a nuclear submarine, four or more diesel-electric submarines could be built which would be equal to or better in agility, maneuverability, and quietness than nuclear submarines. Since the advent of the submarine, however, designers have been faced with the problem that the conventional non-nuclear submarine required two power systems for propulsion—internal combustion engines for surface use and battery charging, and battery systems when submerged. Diesel-electric submarines must surface (at least to periscope depth) often, depending upon their use of battery power. Surfacing to charge batteries takes time, during which the submarine is most vulnerable to detection.
In order to extend submerged time for diesel-electric submarines, various air-independent propulsion (AIP) systems have been developed. These systems are generally not over three hundred horsepower and commonly only extend the use of the batteries. They could be used directly to provide propulsion power, but only at relatively slow speed. Higher speeds would drain the propulsion batteries, and flank speed would likely drain the batteries within a few hours. Present AIP systems are offered for retrofitting in older boats. To accommodate the system, a plug, equal to the diameter of the hull, must be installed in the submarine. This makes the submarine heavier, longer, and less maneuverable. AIP systems in the prior art include Stirling engines, MESMA systems, fuel cells, and closed cycle diesels.
The Stirling engine is used in the Swedish Kockums design. The design uses two or more Stirling engines, which require a special fuel oil, as well as liquid oxygen (LOX), naphtha for the AIP, and diesel fuel. The French MESMA system uses a simple Rankine cycle, with a high consumption of fuel oil and LOX. The steam pressure generated is approximately 260 psi and the closed combustion pressure is approximately 870 psi, which makes it possible to blow the exhaust overboard at great depth. Both the Swedish and the French systems operate on a closed cycle with continuous combustion. Resulting carbon dioxide (CO
2
) is not detrimental to the combustion process and is used as the working fluid. Other combustion products include water and other non-combustible gasses.
The fuel cell has been touted as the power system of the future, for both vehicle and marine power. It has a number of problems, including high weight/horsepower ratio and high fabrication costs due to utilization of costly materials. Submarines equipped with fuel cells must carry fuel oil for the diesels as well as LOX and hydrogen for the fuel cells. The hazards associated with hydrogen make this a questionable material to be carried on a military vessel. Finally, thermal efficiency at low speeds falls off as speed and power demands increase. Balancing these problems is the absence of exhaust pollution, for the sole fuel cell by-product is pure water.
The addition of any of the above AIP systems makes it possible for a submarine to remain submerged for weeks at a time provided they are operated at 4-5 knots and the main propulsion batteries are not drawn upon. At any higher speed, main batteries must be used, and the submarine may have to surface several times in one day to charge the batteries. These AIP systems add to the length and weight of the submarine in new construction, and in retrofitting an older boat the previously mentioned plug is required. For example, the French MESMA system adds 270 horsepower to the submarine, yet adds 250 tons to its weight and 33 feet to its length. The result includes increased water resistance under speed as well as a reduction in maneuverability.
The closed cycle diesel system is the only proven AIP system that propels the submarine both on the surface and when submerged. The system requires diesel fuel, oil, oxygen and argon for submerged closed-cycle operation.
All of the systems described above except the fuel cell generate carbon dioxide as a by-product. A closed cycle diesel must remove the carbon dioxide from the working fluid because car
Laubscher, Jr. Lawrence E.
Nguyen Hoang
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