5 e 56 presentation 1

7/27/2019 5 e 56 Presentation 1

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POLITEKNIK SEBERANG PERAI

JABATAN KEJURUTERAAN MEKANIKAL

DIPLOMA KEJURUTERAAN MEKANIKAL

LOJI


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POWER PLANT

JL 303

GAS TURBINE POWER PLANT

NAME MATRIK NO

MOHD FAIZ BIN ABD

RAZAK

10 DJL 10 F1039

LAI SUNG HING 10 DJL 10 F1016

RAZNAN BIN ABD RASHID 10 DJL 10 F1012


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Gas turbine:Working principle :

Air is compressed(squeezed) to high pressure

by a fan-like device called the compressor. Then fuel and compressed air are mixed in a

combustion chamber and ignited.

Hot gases are given off, which spin the

turbine wheels.

Most of the turbines power runs the

compressor. Part of it drives the

generator/machinery.


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Gas turbine:Description:

Gas turbines burn fuels such as oil,nature gas and pulverised(powdered)

coal. Instead of using the heat to produce

steam, as in steam turbines, gas turbinesuse the hot gases directly to turn theturbine blades.

Gas turbines have three main parts:i) Air compressorii) Combustion chamber

iii) Turbine


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Gas turbines usually operate on an opencycle, as shown in Figure 1. Fresh air atambient conditions is drawn into thecompressor, where its temperature andpressure are raised. The high-pressure airproceeds into the combustion chamber,

where the fuel is burned at constantpressure.

(2) The resulting high-temperature gasesthen enter the turbine, where they expandto the atmospheric pressure through a rowof nozzle vanes.5 This expansion causesthe turbine blade to spin, which then turns

a shaft inside a magnetic coil. When theshaft is rotating inside the magnetic coil,electrical current is produced. The exhaustgases leaving the turbine in the open cycleare not re-circulated.

Figure 1 An Open Cycle

Gas-Turbine Engine


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The open gas-turbine cycle can bemodeled as a closed cycle as shown inFigure 2 by utilizing the air-standardassumptions. Here the compression andexpansion process remain the same, buta constant-pressure heat-rejectionprocess to the ambient air replaces thecombustion process. The ideal cyclethat the working fluid undergoes in thisclosed loop is the Brayton cycle, whichis made up of four internally reversibleprocesses:

1-2 Isentropic compression (in a

compressor) 2-3 Constant pressure heat addition 3-4 Isentropic expansion (in a turbine) 4-1 Constant pressure heat rejection (2)

Figure 2 A Closed Cycle

Gas-Turbine Engine


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Gas turbine:Air compressor:

The air compressor and turbine are

mounted at either end on a common

horizontal axle(shaft), with thecombustion chamber between them.

Gas turbines are not self starting. A

starting motor initially drives the

compressor till the first combustion of

fuel takes place, later, part of the

turbines power runs the compressor.

The air compressor sucks in air and

compresses it, thereby increasing its

pressure. An Axial-Flow Compressor


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Gas turbine:Combustion chamber: In the combustion chamber, the

compressed air combines with fuel andthe resulting mixture is burnt.

The greater the pressure of air, thebetter the fuel air mixture burns. Modern gas turbines usually use liquid

fuel, but they may also use gaseousfuel, natural gas or gas producedartificially by gasification of a solid

fuel.Note : The combination of air compressor

and combustion chamber is called asgas generator.

A Combustion Chamber Can


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Gas turbine:Turbine:

o The burning gases expand rapidly and rush

into the turbine, where they cause the turbine

wheels to rotate.o Hot gases move through a multistage gas

turbine.

o Like in steam turbine, the gas turbine also

has fixed(stationary) and moving(rotor)

blades.

o The stationary blades guide the moving gases

to the rotor blades and adjust its velocity.

o The shaft of the turbine is coupled to a

generator or machinery to drive it. TURBINE CHAMBER


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Intercooling also involves the use of aheat exchanger. An intercooler is aheat exchangerthat cools compressor gas during thecompression process. For instance, ifthe compressor

consists of a high and a low pressureunit, the intercooler could be mountedbetween them to cool the flow anddecrease the work necessary forcompression in the high pressurecompressor (Fig. 6b). The cooling

fluid could be atmospheric air or water(e.g., sea water in the case of amarine gas turbine). It can be shownthat the output of a gas turbine isincreased with a well-designedintercooler.


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Reheating occurs in the turbine and is a wayto increase turbine work without changingcompressor work or melting the materialsfrom which the turbine is constructed. If agas turbine has a high pressure and a lowpressure turbine at the back end of themachine, a reheater (usually anothercombustor) can be used to"reheat" the flowbetween the two turbines (Fig. 6c).This canincrease efficiency by 1-3%. Reheat in a jetengine is accomplished by adding anafterburner at the turbine exhaust, therebyincreasing thrust, atthe expense of a greatly increased fuel

consumption rate.Figure 6.

5 e 56 presentation 1

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