combustor n turbine

8/13/2019 combustor n turbine

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GAS TURBINEAND

AUXILIARIES


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Simple Gas Turbine Plant


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Purpose of Combustor ?

The primary purpose of

the combustor is to provide

space for the chemical reactionof fuel and air.


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Requirements of a Combustor

The combustor must ensure the

quick start up of the plant. The combustion must take place at

higher efficiency.

Pressure losses/drop should be as

low as possible.


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The hydraulic resistance must be as low as

feasible.

The geometry and arrangement of the

combustor must provide for stability ofcombustion over a wide range of air fuel

ratio, which varies from 40:1 to 200:1. Ignition must be reliable and accomplished

with ease over a wide range of atmospheric

conditions.


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High degree of mixing (Thorough mixing of

air with fuel and as well as with combustion

products)

Carbon deposits should not be formedunder any conditions to enhance the life of

the combustion chamber. Combustion gases going to the turbine

should be cooled adequately so as not to

affect the blades.


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For longer service life, the combustor must

be cooled properly especially in the hottest

portions. The combustor must be simple in design,

safe in operation, and easy and inexpensive

in manufacture.

Combustors of mobile and transportable

gas-turbine plants must have a low- mass

and small dimensions as for as possible.


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Primary Zone

Secondary zone

Tertiary Zone

Combustion Process


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Combustion Process


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Downstream Type Combustion

Chamber


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Combustor Parts

Outer casing. combustion liner. Cross Fire tube

Fuel injection systems

Initial ignition system


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Combustor Parts

Ultra violet flame

detectors Transition pieces


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Tested burner Combustion liner

Secondary air holes

Main burnerAuxiliarycombustor

Air

Fuel


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Annular Gap Igniter Plug


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The intense spark is obtained byexpending a small amount of electric

energy in a very short time.


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Flame Detector UV


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Ignitor plugs

Igniter plugs serve a purpose similar

to the spark plug in a reciprocating engine,although operation of the ignition system

and the igniter plugs is necessary only for a

short period during the engine starting

cycle.


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Major Differences

The elements of gas turbines are made up

of special heat-resistant steels and alloys

and various methods are employed to cool

turbine blades and discs.

The difference between the height of the

first-and last-stage blades in gas turbines is

substantially smaller than that in steam

turbines.


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The worked-out heat drop in a steam

turbine is 3-5 times less than that in a gas

turbine.

The height of blades in the first stages of

gas turbines is greater than in steam

turbines of comparable capacity.


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Disc type rotors

Rotors with Discs without centralborings have a higher strengthespecially during the action ofcentrifugal forces.

Since the discs are manufacturedfrom individual small-size

forging, they can be machinedindependently


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Root fastening slots in the discs

can be made by the most

advanced machining methods.

Disc type rotors


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The high operating temperature effects, Centrifugal tensile stresses due to rotational

speeds of the Order of 8000 to as high as30,000 r.p.m.

Bending stresses due to equivalent impulseload of the gases, which acts at a certaindistance from the fixing of the cantilever

blade. Hot erosive and corrosive effects due to the

high temperature combustion products e.g.CO2and CO with 02.


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Material should possess maximum strength at

high temperature.

High creep strength.

High resistance to corrosion.Endurance against fluctuating bending stresses.Maximum erosion resistance.Structural stability when exposed to varying

temperatures.


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.Castability or forgability.Weldability, if welding is used in themanufacture.Machinability.

Absence of embrittlement in the service.


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Advantages of Steam Cooling

It keeps the gas temperature higher than

the air cooled gas turbine.

While cooling it picks up the heat which is

used in the steam turbine.

It reduce the compressor discharge air

thereby allowing more flow to combustor.

Open loop air cooled Closed loop


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p p

nozzle

p

steam cooling


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Equiaxed

l lli bl d

Directionally

lidifi d


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polycrystalline bladessolidified


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A modern turbine blade alloy is complex in

that it contains up to ten significant alloying

elements, but its microstructure is verysimple.


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combustor n turbine