Power plants – Motive fluid energized by externally applied heat – Process of power production or system operation
Reexamination Certificate
2000-03-02
2002-03-19
Nguyen, Hoang (Department: 3748)
Power plants
Motive fluid energized by externally applied heat
Process of power production or system operation
C060S670000
Reexamination Certificate
active
06357235
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to power generation cycles, and more specifically to a steam power plant that utilizes a compressor.
2. Description of the Related Art
The first pneumatic transmission dates back to the year 1700, when the French Physicist Denis Papin used the force of a windmill to compress fluid that was then transported through pipes. Approximately one century later, British inventor George Medhurst obtained a patent on a device to propel an engine with compressed fluid, although the first practical implementation of this method is usually attributed to inventor George Law who, in 1865, designed a rock drill in which an air-driven piston activated a hammer. The use of this drill became widely accepted and was used in the perforation of the Mount Cenis tunnel in The Alps, inaugurated in 1871, and in the Hossac in Massachusetts (United States of America), inaugurated in 1875. Another significant breakthrough was the compressed air train break, designed around 1868 by the American inventor, engineer, and industrialist George Westinghouse.
Fluid pumping arose from the need to transport fluid through pipes or channels. This fluid movement is accomplished through energy transfer. The usual means to accomplish fluid flow are: gravity, displacement, centrifugal force, electromagnetic power, movement quantity transfer, mechanical impulse, or a combination of these six basic principles. After gravity, the most common means used at present is centrifugal force.
Discharge of a fluid from a vessel by the total or partial displacement of the vessel's internal volume by a second flow, or through mechanical means, is the principle of operation of many fluid transport systems. This group includes the diaphragm and alternating piston-movement machines, gear and rotating blade-type devices, fluid piston compressors, oval tanks for acid fluid storage, and pneumatic elevators.
When centrifuge force is used, this force is supplied through a pump or a compressor. Although the physical characteristics of the different types of compressors and centrifugal pumps differ widely, their basic function is always the same, that is, the production of kinetic energy through the action of a centrifugal force, and then the partial conversion of this energy into pressure through efficient fluid velocity reduction.
When the fluid involved is a good electrical conductor, as in the case of melted metals, an electromagnetic field can be applied around the fluid conduit, so as to generate a propelling force that will cause the flow to take place.
The deceleration of a fluid to transfer its momentum, or amount of movement, to another fluid is a commonly used principle for corrosive material management, for pumping from inaccessible depths, or for casting.
The mechanical force principle, applied to fluids, is usually combined with another means of creating movement.
a. Compressors
Gaseous fluid pressure is raised by devices called compressors. There are commonly two types of compressors: alternating and centrifugal. Alternating compressors can be divided into the rotating and reciprocating types. These compressors have constant capacity and variable discharge pressures.
Positive displacement rotating compressors use an additional mobile, rotating part activated by a shaft or axle of an engine that can be of different types. Contrary to centrifugal compressors (described below), their flow is not smooth nor pulsation free. There are several types of positive displacement rotating compressors, among them the pipe blower, the rotating spiral, and the water ring types. All have substantially the same performance curve of the reciprocating compressor; that is to say, they have fixed capacity and variable counter-pressure. Rotating compressors are more useful than reciprocating ones for variable speed motor units like steam turbines.
Reciprocating compressors work on the adiabatic principle (there is no heat transfer between the system and the environment) by which gas is introduced in the compressor cylinder(s) through the inlet valves, is retained and compressed inside the cylinder(s)—typically by a piston arrangement, and is discharged through an outlet.
FIG. 1
illustrates a schematic of a typical reciprocating compressor, wherein the gas flow is controlled via a control valve assembly and the compressed outlet gas is delivered to a reservoir for use as needed. These compressors are rarely used as standalone units, except where the process requires intermittent operation.
Reciprocating compressors generate considerable friction between parts like rings and pistons that come in contact with the cylinder walls, the valve springs, and plates or disks that couple with their seats, and between the packing and the connecting rod. All these parts are subject to friction wear, with significant influence on the efficiency of the machine. The motor operation of these compressors is based on either: (1) a connecting rod-crank system; or (2) the gradual pressurization of a fluid activating a piston. There is never a direct, sudden impact applied through reciprocating compressors.
Centrifugal compressors work by applying power from an external source to a shaft that rotates a blade wheel, known as a rotor or impeller, inside a stationary casing, as seen in FIG.
2
. When the impeller blades rotate, pressure is reduced at the impeller's inlet, creating suction. The casing may be equipped with a series of outer curved blades that function as a diffuser, whereby the fluid drawn into the inlet is discharged through the outlet at a higher pressure and at a lower flow rate.
A centrifugal compressor offers the following advantages:
in the 2000 to 200,000 ft
3
/min capacity range, it is considered an economical compressor
because a single unit can be utilized over a wide range of compression ratios;
it offers a considerably wide range of flow with a small load change;
the relatively low friction between components in the compression flow allows long up-times between maintenance down times, as long as the auxiliary lubrication and seal oil systems are properly sized and functioning;
large compressed fluid volumes can be obtained in a relatively small location—this can represent a significant advantage where land is costly; and
it provides a smooth, nonpulsating flow.
Disadvantages of a centrifugal compressor include:
centrifuges are sensitive to the molecular weight of the gas being compressed;
unexpected changes in molecular weight can result in a too high or too low discharge pressure;
very high velocities are required at the impeller ends to produce compression;
a small pressure drop in the system may cause major reductions in the compressor's capacity;
a complex lubricating oil and seal oil system is required.
b. Pumps
Liquid fluid pressure is raised by devices called pumps. The four major fluid pump types are described below:
i. Alternating pumps: These consist of a piston oscillating inside a cylinder equipped with valves to regulate fluid flow to and from the cylinder. These pumps can be single or double-action pumps. In a single-action pump, pumping takes place in only one side of the piston, analogous to a regular impeller pump, and the piston is made to slide up and down the cylinder manually. In a double-action pump, pumping takes place at both sides of the piston, like in electrical or steam boiler feeding pumps used to feed water at high pressure to a water or steam boiler. These pumps may be of one or several stages. Multi-stage alternating pumps have several sequenced cylinders.
ii. Centrifugal pumps: Centrifugal pumps, also called rotating pumps, have a rotating blade rotor or impeller submerged in the fluid. The fluid enters the pump near the rotor axis, and the blades drag it towards their high pressure ends. The rotor also gives the fluid a relatively high velocity that is converted to pressure at the stationary part of the pump, known as the diffuser. In high pressure pumps, several rotors arranged as a series can be used, and diffuser
Cacumen LTDA.
Nguyen Hoang
Streets Jeffrey L.
Streets & Steele
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