5 Gas Turbine_Turbine and Exhaust System

8/2/2019 5 Gas Turbine_Turbine and Exhaust System

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Dr. Walid Abdelghaffar


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Dr. W al id Abde lghaf f a rGas Turbine-Turbine and Exhaust System

Turbine

The information inthis presentationfocuses on the last

two sections of thegas turbine engine,the turbine and theexhaust sections.


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The turbine provides the power for the compressors) and the mechThe turbine provides the power for the compressors) and the mechanical output.anical output.The power is produced by extracting energy from the hot gases reThe power is produced by extracting energy from the hot gases released from theleased from the

combustion chambers and expanding them to a lower pressure and tcombustion chambers and expanding them to a lower pressure and temperature.emperature.

High stresses are involved in this process. Since the turbine opHigh stresses are involved in this process. Since the turbine operates at high speederates at high speed

it is exposed to large centrifugal forces. The gas enters the tuit is exposed to large centrifugal forces. The gas enters the turbine at a very highrbine at a very high

temperature which also causing stress.temperature which also causing stress.

The turbine blades are fitted to the turbine discs,

mostly by means of fir-tree RootsAxial flow turbine

The TurbineThe Turbine


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The turbine normally consists of several stages. Each stage consists of a row ofstationary guide vanes followed by a row of rotor blades. The guide vanes are fixedto the turbine casing and the rotor blades are fitted to turbine discs. The rotating

blades are fixed to the disc using a special technique called fir-tree roots.

Function PrincipleFunction Principle

The hot gases are expanded in the convergent passageThe hot gases are expanded in the convergent passagebetween the guide vanes andbetween the guide vanes and

the turbine blades. Pressure energy is converted into kineticthe turbine blades. Pressure energy is converted into kineticenergy and the gasesenergy and the gases

are accelerated. At the same time the gas is spinning andare accelerated. At the same time the gas is spinning and

swirling in direction ofswirling in direction ofthe turbine blades. The turbine blades force the gases tothe turbine blades. The turbine blades force the gases todeflect and as the passagedeflect and as the passage

is convergent the gases are further expanded. On impact withis convergent the gases are further expanded. On impact withthe turbine bladesthe turbine blades

and during the subsequent reaction through the passage,and during the subsequent reaction through the passage,

energy is absorbed. Thisenergy is absorbed. Thisenergy causes the turbine to rotate and provides the power forenergy causes the turbine to rotate and provides the power fordriving the turbinedriving the turbine

shaft. The guide vanes in the following stage expand the gasesshaft. The guide vanes in the following stage expand the gasesfurther and directfurther and direct

them to the next row of blades.them to the next row of blades.

The gas-flow

through the turbine

Axial Flow Turbine Design


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Like the compressor

section, the turbine sectionconsists of two majorcomponents:

the stator or turbinenozzles

the rotor or turbine wheel

Turbine: Component s


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Stators & Rotors

The stators and the rotors

of the turbine andcompressor sections aresimilar in their construction.

The primary dif ference isthe angle at which thevanes, nozzles, and bladesare positioned.

Their positioning is critical

to efficient engineoperation.

Turbine : Components


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Components: Turbine Nozzle

The turbine nozzle vanes have twopurposes:

prepare the combustion gases for

driving the turbine rotor

deflect the combustion gases in thedirection of the turbine rotation

To accomplish this, the shape andposition of the turbine nozzle vanes formpassages for expanding gas flow.

Turbine Nozzle


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These passages:

change the direction of gas flow

increase gas velocity

reduce pressure and temperature of

the gas

Turbine Nozzle


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Component s: Turbine Rotor

The energy of the gases leaving the

first row of turbine nozzle vanesencounters the next major componentof the turbine section, the rotor orturbine wheel.

The purpose of the turbine rotor is toextract mechanical energy to operatethe compressor, accessories, and load.

The turbine rotor consists of thefollowing:

shaft blades or buckets disk

Turbine Rotor


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Component s: Turbine RotorBlades

The blades of the turbine wheel aremounted to the disk in the same manner ascompressor blades are mounted to the rotor,by either fir-tree, bulb, or dove-tail typeroots.

This blades and disk assembly is attached tothe shaft.

As the turbine wheel rotates it transfers energy to the shaft, which is connectedto the compressor, the accessories, and/or the load.The turbine section may be either single stage or multistage.When the turbine has more than one stage, nozzle vanes are installed between

each stage.

Turbine Rotor Blades


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Each set of stator vanesforms a nozzle vane

assembly for the followingturbine wheel.

Exit guide vanes straightenthe gas flow as it enters theexhaust section.

Nozzle Vane Assembly


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Hot, expanding gases from eachburner (or combustion chamber)flow through a transition duct toturbine nozzle vanes.

The nozzle vanes direct theexpanding gases into the turbinesection.

As you recall, the components ofthe compressor section convertenergy by increasing the airflowpressure.

Turbine: Operat ion


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In contrast, the components of

the turbine section convertenergy by reducing thepressure of the flowing gases.

Pressure is changed to velocityby the shape and position ofboth the turbine stator vanesand the rotor blades.

Turbine: Operation


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Operat ion: Gas Flow

The shape of the vanes causes an

increase in velocity as the gasespass between the vanes.

As the gases flow into the first set

of vanes, the gases acceleratebecause the space between thevanes is converging (a funnel effectsimilar to the first half of the venturitube).

As Bernoul li' s principle st ates:

an increase in velocity causes adecrease in pressure

Turbine: Operat ion


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Operat ion: Gas Flow

The gases leaving the nozzle vanes reachtheir maximum velocity just before they hitthe first-stage turbine, causing it to rotate.

The shape of the rotor blades alsoaccelerates the gases.

At this point, the gases still have enough

energy to do work.

The turbine blades redirect the hot gasesinto the second row of nozzle vanes.

Turbine: Operat ion


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The gases are again accelerated between

the nozzles.

The second set of nozzles generates

additional gas velocity just before the hotgases impinge on (hit) the second set of

rotor blades.

Turbine: Operat ion


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The process continues through eachstage of the turbine section.

Exit vanes reduce turbulence beforethe gases enter the exhaust section.This reduces backpressure on theturbine section.

Approximately two-thirds of the total

energy available for work in a gasturbine is used to turn thecompressor.

Turbine: Operat ion


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The remaining energy available for workis used to drive the load.

Turbine: Operat ion

Movie on: Gas turbine performance compressorMovie on: Gas turbine performance compressor


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Movie on: Gas turbine performance, compressorMovie on: Gas turbine performance, compressor

rotor and turbine rotor assemblyrotor and turbine rotor assembly

T bi bl d


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Turbine blades

-Turbine blades work at

high temperatures, requiring

advanced materials andcooling design.

- The parts exposed to the

hot gas are subjected to :

Corrosion

Steady forces causing creep

Vibratory forces causingfatigue

Thermal gradients causing

thermal fatigue

T bi Bl d D i


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Turbine Blade Design

The common and necessary things that must follow it in Design ofTurbine blades include:

The turbine blade design should comply with the following rules:

Multiple circular arc airfoils.

Clear separation of functions. Free expansion for every part.

No stress raisers and no notches.

Minimal thermal stress, (Thermal barrier

coating ) Ease of manufacture, e.g. by precision

casting.

Minimum machining of high-temperature

alloys.

Minimum cost.

T bi Bl d D i


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To analyze isolated airfoils in incompressible orcompressible flows for turbine blade:

1- Drag and moment coefficient versus angle of attack2- Surface pressure coefficient

3- Velocity

4-Mach number

5-Temperature

6-Vortex panel

7-Computing the overall lift for rectangular & tapered

Turbine Blade Design

C l f Th T bi Bl d


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Control of The Turbine Blade

To improve the turbine work and preventing possible

where do theTurbine sentryproblems install

following:

Improve operating efficiency.

Prevent premature damage.

Prevent blade failures in utility combustion turbines.


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Turbine Sent ry

Turbine sentry FunctionsCombustion turbine blade temperature analysisCan provide the operator a large amount of information


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Maj or Mat e r ia l Used in Gas Tu r b in e


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Tu r b in e Blade Mat e r ia l


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Tu r b in e Blade Mat e r ia l

Tu r b in e Vane Mat e r ia l


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Tu r b in e Vane Mat e r ia l

Com bu st o r Mat er i al


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Com bu st o r Mat er i al

Selection of Material


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Selection of Material

In blade material we study about theimportant following things :

1- corrosion resistance.

2- high-temperature strength.3- cast ability.

The Development of Turbine Materials


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1-TITANIUM ALLOYS.Advantages

high strength

low density .

exceptional resistanceto corrosion.

It has lower thermal conductivity

and thermal expansion than steel

or nickel base alloys.2-NICKEL BASE ALLOYS.Advantages

outstanding strength and oxidation resistance

over the temperature range encountered.

it has a fully austenitic face centered cubic (FCC)

3- MDSC-7M.single crystal super alloys

Tit anium blade

The Development of Turbine Materials

Turbine Cooling


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g

Cooling methods such as :

( 1 ) Film cooling.

( 2 ) Impingement.

( 3 ) Convective.

( 4 ) Transpiration.

General film cooling technique.

General impingement cooling technique.

( 1 ) ( 2 )


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( 3 )

General convection cooling technique

( 4 )

Transpiration cooling technique

Methods of Cooling


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Methods of Cooling

When considering turbine cooling, one must first decide what fluid will beused as a coolant.( 1 ) Air is the most logical choice as a coolant, since it is readily available. It

can be extracted (bled) from the compressor, ducted to the turbine blade(stator or rotor), and used as a coolant.( 2 ) Another choice of coolant is a liquid coolant such as water.

Turbine Cooling Techniques Using Air as Coolant :( 1 ) Film cooling technique.

(2) Impingement cooling technique.

(3) Convection cooling technique.

(4) Vane cooling technique.

(5) Transpiration cooling technique.

Liq id Cooled T rbine


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Water

CooledCopper Chill

Liquid-Cooled Turbine Blades :A more effective way of cooling turbine

blades is to use a liquid coolant. A liquidcoolant has a much higher specific heat

and provides the opportunity forevaporative cooling .

This method may be considered onlyfor use in stationary power plants or otheron-ground applications

Liquid-Cooled Turbine

liquid-cooled turbine blade

Advantages and disadvantages air and liquid asl


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coolant

For liquid coolant :

( 1 ) Liquid-cooling is thus a good solution to a difficultproblem, but sometimes it is even difficult to move enough

liquid coolant to keep a part cool, it may boil, expand to agas.

( 2 ) Liquid-cooling makes it easier to maintain each part of the engineat a given temperature in normal operation.

( 3 ) Liquid-coolant makes corrosion in turbine blades.

( 4 ) Liquid-coolant sometimes not avaliable in some places.

( 5 ) Liquid-coolant haver than air - coolant.


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Turbine Blades Problems


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Fig . ( 1) an over-heated turbine blade

Fig . (2) turbine blade coating corrosion

In blade material we study aboutthe important following things :

( 1 ) corrosion resistance:

the corrosion happen when the bladesoperating in wear conditions, shown infigure (1).

( 2 ) high-temperature strength :

high temperature strength happenwhen the turbine blades operating inhigh temperature conditions, shown infigure ( 2 )

Turbine rotor


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Turbine rotor

Turbine rotor


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Turbine rotor


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Turbine rotor


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Sect i on a l Dr aw in g


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Guide Blade

Carrier

Casing

Rotor

Blades

Tu r b ine Man u f act u r i ng


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Blades

Blad es: Raw Mat er i a l


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Blades: Man u fact u r in g


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Blades: Di f f e r en t Ty p es


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Rotor

Rot o r : Fo r g in g


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Rot o r : Tu r n i n g com p let ed


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Rot o r : Read y f or Blad in g


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Ro t o r : Co m p let e Assem b ly


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Rot o r : Com p le t e


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Rot o r : Ba lan cin g


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W o r k s h o p


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Guide Blade Carrier

Blad e Car r ie r : Cast in g


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Blade Car r ie r : Pr e -Tu r n ed


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Blad e Car r ie r : Gu id e Blad e Rin g s


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Blade Car r ie r : Blade Assem b ly


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Blade car r ie r : Blade Assem bly


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Gu ide-Blade Car r i er ( com p let e)


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Valves

Em er gency St op Val ve: Cast i ng


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Em er g en cy St o p - Valv e


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Valve Body

Control Device

Con t r o l Valv e + Ser vo ( m ou n t ed )


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Control Device

Valve

ServoValve Body

Con t r o l Valv es

Valve-Chest


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Valve-Spindle



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Turbine Casing


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Casin g : Man u fact u r in g


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Casing : Com p let e Mach in ed


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Casing : Com p let e Mach in ed


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Casin g : D im en sion Ch eck


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St at o r Par t s: Dim ension Check


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Tu r b in e: Fina l Measu r em en t s


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Transport

Tr anspor t : Ou t o f Fact o r y


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Tr a n sp o r t : Sh i p Lo ad in g


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ATP: Nozzle Ch est


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Exhaust Section: Purpose


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When the gas exit the turbinesection they enter the last section ofthe gas turbine, the exhaust section.

The exhaust section is locateddirectly behind the turbine section of

the engine.

The purpose of the exhaust sectionis to discharge the spent gases to

the atmosphere.

The exhaust section usuallyconsists of the following

Exhaust Section: Components


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gcomponents:

outer housing inner housing struts plenum

These components act as a

diffuser, to reduce theturbulence and velocity ofexhaust gases

The outer housing isfastened to the rear flange of


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gthe turbine section.

The inner housing isconnected to the outerhousing by struts and maybe fitted with a cone to helpin the diffusion process.

Struts also straighten theexhaust flow.

Exhaust Sect ion:


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Exhaust Sect ion:Components

The inner housing may contain the gasturbine rear bearing assembly andoverspeed trip device.

The outer housing flange is used toconnect the exhaust collector or plenumto the gas turbine exhaust section.

The diffusion process occurs in theexhaust section as the volume isincreased.

As the exhaust gases pass through the

Exhaust section: Operation


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g p gexhaust section components:

the velocity is decreased the pressure remains relativelyconstant the turbulence is reduced

The exhaust gases enter theatmosphere from the exhaust plenum.

Because exhaust gas temperatures normally exceed 700F, externalareas are covered with insulation or guards to protect personnel and toprevent fire.


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Dr. Walid Abdelghaffar

5 Gas Turbine_Turbine and Exhaust System

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