Специальность «Эксплуатация судовых энергетических установок»
МЕТОДИЧЕСКИЕ УКАЗАНИЯ III КУРС (6 семестр)
2014/2015 учебный год
I. Практика устной речи:
Main and auxiliary turbines
Turbine Construction
The gas turbines
II. Чтение и устный перевод текстов
Автор: 1. Пивненко Б. А. Английский язык для инженеров-судомехаников: учеб. пособие / Б. А. Пивненко. - Одесса : Студия "Негоциант", 2007. - 352 с.
1. с. 82-83 Steam Turbines;
2. c. 87-89 Turbine Parts;
3. c. 93-94 Reduction Gears and Couplings;
4. c. 98-99 Starting;
5. c. 101 Under Way and Shutting-Down
6. c. 103-104 Vibration.
Практика устной речи
MAIN AND AUXILIARY TURBINES
There are four main types of marine engine: the steam turbine, the gas turbine, the diesel engine and the marine nuclear plant. Each type has its own practical application.
If a vessel is driven by a steam turbine we call her steam-driven ship.
If a ship is driven by a gas turbine she is called a turbine driven vessel.
If a vessel is driven by a nuclear plant she can be called a nuclear-powered ship or ice-breaker.
Steam turbines are used for ship propulsion and for driving many of the auxiliary machinery units associated with the propulsion plant, such as lubricating oil pumps, condensate pumps, feed pumps, circulating pumps, fuel oil pumps, forced draft blowers, and electric generators.
The two principal types of steam turbine ship propulsion plants in use today are the geared-turbine drive and the turbo-electric drive.
In the geared-turbine drive, a reduction gear unit is used as the means for transforming high turbine rpm to a much lower propeller shaft rpm.
In the electric drive, the necessary speed reduction is done electrically. That is, the turbine drives a generator at high rpm; and the generator supplies power to drive an electric propulsion motor, which operates in a low rpm range.
In the geared-turbine drive, the propulsion shaft, which extends from the low speed shaft of the reduction gear to the propeller, is supported and held in alignment by the spring bearings and the stern tube bearings.
The axial thrust, acting on the propulsion shaft as a result of the pushing effect of the propeller, is absorbed in the main thrust bearing. In most ships, the main thrust bearing is located at the forward end of the main shaft, within the reduction gear casing. In some very large ships, however, the main shaft thrust bearing is located farther aft in a machinery space or a shaft alley.
Unlike gear-turbine propulsion plants, which have two ahead turbines and an astern element for propulsion shaft, the turbo-electric drive installations have a single turbine unit for each installed shaft. The propulsion unit includes a turbine, main generator, propulsion motor, a direct current generator for supplying excitation current to the generator and propulsion motor, and a propulsion control board.
The basic distinction between turbines concerns the manner in which the steam causes the turbine rotor to move. When the rotor is moved by a push or impulse from a high velocity jet of steam that strikes the blades mounted on the wheel, the turbine is called an impulse turbine. When the rotor is moved by the force of reaction, the turbine is called a reaction turbine.
Turbine Construction
A turbine consists primarily of a rotor, which carries the blades; a casing, in which the rotor revolves; and nozzles or stationary blading, through which the steam is expanded and directed. In addition, bearings, shaft glands, lubrication equipment, devices for the control of turbine speed, flexible couplings, and in some cases reduction gears are required.
The flanges in the casing are bolted together. Each casing has a steam chest, to receive the incoming steam, and an exhaust connection. Access openings are sometimes provided in the casing to allow the checking of blading clearances. Other opening in the casing include drain connections and opening for pressure gages and relief valves.
Turbine rotors consist of bladed wheel and shaft assemblies. On impulse turbines, an equalising hole is drilled through the rotor to prevent development of a pressure difference between the two sides.
Turbine rotors are supported and kept in position by bearings. The bearings, which serve to maintain the correct radial clearance between the rotor and the casing, are called radial bearings. The bearings which serve to limit the axial, that is longitudinal movement of the rotor are called axial or thrust bearing. Either ball bearings or sleeve bearings may be used as radial bearings on auxiliary turbines.
The shell of the sleeve bearing is lined with babbit, which is a relatively soft metal composed of tin, copper, antimony, and a small amount of lead. The bearing shell is held stationary within the bearing housing by a dowel.
Shaft glands are used at the points where the shaft extends through the casing. Two type of packing are used - labyrinth and carbon packing.
Reduction gears are used to transmit rotary motion from the driving turbine shaft to the shaft of the driven auxiliary.
Many turbine-driven auxiliary units are joined to the turbine by means of a flexible coupling, which compensates very slight misalignment between the driving and the driven shafts. Many different designs of flexible coupling are used.
The speed-regulating governor is used on constant speed machines to maintain a constant speed regardless of the load on the turbine. They are used on generator turbines and on air compressor turbines. The overspeed trip shuts off the steam supply to the turbine, and thus stops the unit, after a predetermined speed has been reached.
The safety device for variable-speed units is called speed-limiting governor. It allows the turbine to operate under all conditions from no-load to overload, up to the speed for which the governor is set, but it does not allow operation in excess of 110 percent of normal operating speed.
The bearings on very small turbines are often of the selfoiling type. These bearings have one or two rings, which hang on the turbine shaft and revolve with it (although at a slower rate). On each revolution, the rings dip into the oil reservoir and carry oil around to the upper part of the bearing shell.
In the pressure lubricating system, the bottom section of the gear casing forms the oil reservoir. The reservoir is filled through an oil filler hole in the top of the casing, and emptied through a drain outlet at the base, of the casing. The shaft, which carries the gear-type oil pump on one end and the governor on the other, is geared to the pump shaft, which is geared to the turbine shaft. The lubricating oil passes through an oil flow sight, a filter, and an oil cooler. Oil is then piped to the bearings on the turbine' shaft, to the governor, and to the worm gear on the pump. The bearings and gear on the oil pump and governor shaft are lubricated by oil, which drains from the governor and passes back into the oil reservoir.
|
1 – steam pipeline 2 – inlet control valve 3 – nozzle chamber 4 – nozzle-box 5 – outlet 6 – stator 7 – blade carrier 8 – casing
|
9 – rotor disc 10 – rotor 11 – journal bearing 13 – thrust bearing 14 – generator rotor 15 – coupling 16 – labyrinth packing 19 – steam bleeding (extraction) |
21 – bearing pedestal 22 – safety governor 23 – main oil pump 24 – centrifugal governor 25 – turning gear 29 – control stage impulse blading |
