Air or Compressors

Introduction to turbines(Steam & Gas)Lecture # 27-28

Mujahid Mehdi Abro Indus University

Turbine

Turbines An IntroductionA turbine is a rotary mechanical device that extracts energy from a fluid flow and converts it into mechanical energy.

Classification of turbines Classification of turbines based on working fluid:

Hydraulic turbines

Wind turbine

Steam turbines

Gas turbinessteam turbinesWhen the working fluid is steam, turbines are called steam turbines.

INTRODUCTIONA steam turbine is a prime mover in which rotary motion is obtained by the gradual change of momentum of the steam.

WORKINGIn steam turbine the force exerted on the blades is due to the velocity of the steam. Curved blades receive a force or impulse by changing the direction of steam. This action of steam is dynamic. The dynamic pressure of steam rotates the vanes, buckets or blades. These blades are curved in such a way that steam enters upon them without shock. There is some loss of energy by the friction upon the surface of blades.PARTSIn general, the steam turbine essentially consists of two parts.

1) The nozzle: -The nozzle in which the heat energy of high pressure steam is converted in to kinetic energy, so that the steam issues from the nozzle with a very high velocity.

2) The blades: -Which change the direction of steam issuing from the nozzle, so that a force acts on the blades due to change of momentum and propel them.CLASSIFICATION OF STEAM TURBINESi) Impulse turbine ii) Reaction turbine

IMPULSE TURBINEDEFINATION: -It is a turbine which turns by the impulse of steam jet.

IMPULSE: -Here impulse means the action of the jet of steam, impinging on the blades.The steam is first made to flow through the nozzle, then the steam jet impinges on the turbine blades (curved like buckets) and are mounted on the circumference of the wheel. The steam jet after pinging glides over the concave surfaces of the blades and finally leave the turbine by giving it a rotation. Here should be noted that the rotation of rotor is due to the impulsive forces of the steam jets.WORKING

REACTION TURBINEWORKING: -In a reaction turbine the steam enters the wheel under pressure and flows over the blades. The steam while gliding, propels the blades and make them to move.The turbine runner is rotated by the reactive forces of steam jets. The backward motion of the blades is similar to the recoil of the gun.

COMPARISION BETWEEN IMPULSE AND REACTION TURBINE

The idea of gas turbine is oldest one, and improved version is windmill, which was used several centuries back. In order to achieve an efficient working of the turbine the movement of gas (air) is properly controlled and then directed on the blades. The air under pressure is supplied to the turbine by an air compressor, which is run by the turbine itself.GAS TURBINES

CLASSIFICATION OF GAS TURBINESThere are generally two types of gas turbine:

Closed cycle gas turbines

Open cycle gas turbinesCLOSED CYCLE GAS TURBINEClosed cycle gas turbine consists of a compressor, heating chamber, gas turbine that drives the generator and compressor and a cooling chamber.OPEN CYCLE GAS TURBINEThe open cycle gas turbine consists of a compressor, combustion chamber and a gas turbine, which drives the generator, and a compressor.Components of Gas Turbine :

The air compressor and turbine are mounted at either end on a common shaft, with the combustion chamber between them.

Gas turbines are not self starting. A starting motor is used.

The air compressor sucks in air and compresses it, thereby increasing its pressure.

Air compressor:

Combustion chamber:

In the combustion chamber, the compressed air combines with fuel and the resulting mixture is burnt.

The greater the pressure of air, the better the fuel air mixture burns.

Modern gas turbines usually use gaseous fuel, natural gas or gas produced artificially by gasification of a solid fuel.

Turbine:

Hot gases move through a multistage gas turbine.

Like in steam turbine, the gas turbine also has stationary and moving blades.

The shaft of the turbine is coupled to a generator.

20The air obtained from the atmosphere is compressed in an air compressor. The compressed air is then passed in the combustion chamber where it is heated. The hot air is then allowed to flow over the blades, which produces a rotation. During this process the air gets expanded and finally it is exhausted. A major part of power developed is consumed for driving the compressor. The remaining power is utilized for doing some external work.WORKING

Applications of gas turbine:

Drive Pumps, Compressors And High Speed Cars.

Aircraft and ships.

Power generation (used for peak load and as stand-by unit).

COMPARISION BETWEEN GAS AND STEAM TURBINE