29-02-2012, 02:28 PM
STUDY OF STEAM TURBINE
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1.1Introduction
A steam turbine is a heat engine in which the energy of the steam is transformed into kinetic energy by expanding the steam through NOZZLE. This resultant kinetic energy is converted into force by impinging on rings of MOVING BLADES (which deflect the jets of steam) mounted on a rotating element called a ROTOR. A steam turbine may be utilized in process industries, Power plants and for transport.
1.3Theory of Steam Turbines
Steam turbines extract heat from steam and transform it into rotational energy by expanding the steam from high to low pressure, resulting in mechanical work. Small and intermediate-sized steam turbines are used for a wide range of applications, including power generation, drivers for mechanical services. When coupled with gears they can be used to drive fans, reciprocating compressors and other classes of low-speed machinery. The largest turbine applications are generator drives in utility and other central power stations.
1.5 Steam Turbine Classification and Types
Steam turbines are classified according to their fundamental operating
Principles, some of which are:
• Number of stages: single or multi stage
• Number of valves: single or multi valve
• Steam supply: saturated or superheated; single or multi pressure
• Turbine stage design class: impulse or reaction
• Steam exhaust conditions: condensing, non-condensing, automatic extraction, mixed pressure, regenerative extraction or reheat
• Types of driven apparatus: mechanical drive or generator drive
1.6.1 Impulse Turbine
The impulse turbine was one of the basic steam turbines. It involved striking of the blades by a stream or a jet of high pressure steam, which caused the blades of the turbine to rotate. The direction of the jet was perpendicular to the axis of the blade. It was realized that the impulse turbine was not very efficient and required high pressures, which is also quite difficult to maintain. The impulse turbine has nozzles that are fixed to convert the steam to high pressure steam before letting it strike the blades.
