design consideration of gas turbine

7/29/2019 Design Consideration Of Gas Turbine

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DISCUSSION ONGAS TURBINE DESIGN

CONSIDERATION

Completed by :Mohammad Ibnul Hossain

Executive Engineer (Operation)Tongi 80(105) MW GT Power Station

Bangladesh Power Development BoardE-mail : [email protected]


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Efficiency

Reliability

Thermal consideration

Corrosion

Wear

FrictionUtility

Cost

Safety

Weight

Noise

Strength

Shape

Size

Flexibility

Cost

Control

Stiffness

Surface Finish

Environment

Maintenance

Volume


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The Brayton CycleThe Brayton cycle consists of two adiabatic work transfers and twoconstant pressure heat transfer heat processes .

From State 1 to State 2 the gas undergoes an isentropic,adiabatic compression. This process increases the temperature,

pressure, and density of the gas.

T= 15C

T= 1268C

T= 1110C

T= 365C


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Static pressure(Ps )The force per unit area exerted on the walls of a container by astationary fluid. tire pressure

Impact pressure (Pi) is the force per unit area exerted by fluids in motionthe pressureexerted on one's hand held outside a moving cars window

Pt = Ps + PiPart (a) illustrates the measurement of static pressure. Static pressure will not take intoaccount the velocity of the air.

Part (b) illustrates the measurement of total pressure, which accounts forboth static pressure and the pressure due to the moving fluid (impact pressure).


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Here { E + or }

v (velocity) Eg P & T pressure and temperature.Here , v ( small inlet to a larger outlet ) (Pi)

Here , { E + or } , So , Pt

As , Pt = Ps + Pi , So , Ps

Pt Ps

So , Pt , so T ( Charls and Boyls Law)


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DIVERGENT DUCT :


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DIVERGENT DUCT :

Velocity

Pressure

Temperature


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BLADE VANE

Axial flow compressor,P current stage > P previous stage [ incrementally]What a single stage of compressor consistsof ?A set of rotor blades attached to a rotatingdisk . Flow area between rotor blade isslightly divergent .

followed by stator vanes attached to astationary ring.Flow area between compressor vanes is alsodivergent than blade .What is done by the blade ?

convert mechanical energy into gaseousenergy. ( Here , energy is added) .What happens?Pi So Pt and

slight Ps for divergence

Pt

Ps

v


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What is done in Stator Vane ?

slow the air divergent duct shape,

BLADE VANE

Here { E + or }

v (velocity) Eg P & T pressure and

temperature.

Here , v ( small inlet to a larger outlet )

(Pi)

Here , { E + or } ,

So , Pt

As , Pt = Ps + Pi ,

So ,

Pt Ps

Pt

Ps

v


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Variable Inlet Guide Vane

IGV


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Condition IGV opening

Startup - 2850 34

2850- Loading 57

Loading increases >> exhausttemperature increase

IGV opening increase

At Base Load to keep the

exhaust temp. from 570 C84

At Peak Load to keep the

exhaust temp. not beyond to C + C

84


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Compressor


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inlet guide vanes,The axial-flow compressor section

consists of the compressor rotor and the

inclosing casing.the 17 stages of rotor and stator blading,

the exit guide vanes.

Compressor


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Variable Inlet Guide Vanes

(IGVs)IGVs are used to control the airflow

through the compressor, in turn controllingthe airflow through the entire machine.

The IGVs modulate during the start-up andacceleration of the gas turbine to ratedspeed, loading & unloading of the

generator and deceleration of the gasturbine during shutdown.


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Compressor Structure

Inlet Guide Vane


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Compressor cylinder

Compressor cylinder has 3 parts:

Forward casing ;

After casing

compressor outlet casing.


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Forward casing After casing


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Discharge casing



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Compressor outlet casing



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compressor structure

Compressor vane: IGV, stationary blade and EGV (Exhaust Guide vane)

IGV

EGV

StationaryBlade


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Stationary Blade (lower half of the Cylinder )

P bl O d i O ti f th C d


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Problems Occur during Operation of the Compressor and

Its solution by design consideration

Problem :Stalling and Surging during lower speed .

Remedy :

The inlet guide vanes are incorporated . It limits the

amount of air flowing through the compressor andprevents stalling .

Provisions for bleeding air from the compressor areprovided at one or more stages. This prevent both stalling

and Surging.


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Compressor moving blade


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compressor rotor

Compressor rotor is a drumstructure with 17 impellers(including a half shaft).17impeller panels are tightly pulledby 16 long bolt pull rods to beintegrated.



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Working Principle :air is confined to the space between the

rotor and stator blading >>>>compressed instages by a series of alternate rotating(rotor) and stationary (stator) airfoil shaped

blades.

The rotor blades supply the force needed tocompress the air in each stage and the statorblades guide the air so that it enters in thefollowing rotor stage at the proper angle.


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The compressed air exits through the compressordischarge casing to the combustion chambers.

Air is extracted from the compressor for turbinecooling, for bearing sealing, and during start-up

for pulsation control.

P bl O d i O ti f th C


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Problems Occur during Operation of the Compressorand Its solution by design consideration :

Problem :

Air has the natural tendency to flow toward low-pressurezones. If air were allowed to flow "backward" into the lowerpressure zones, the efficiency of the compressor would

decrease tremendously as the energy used to increase the

pressure of the air was wasted.

Remedy :

seals are incorporated at the base of Each row of vanes to

prevent air leakage.

The tip clearances of the rotating blades are also kept at a

minimum by the use ofcoating on the inner surface of the

compressor case.


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The MS5001N and P, the MS7001A and B, and the

MS9001B are essentially the same

GROWTH OF PRESSURE RATIO OF GAS TURBINE


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What is achieved ?

Reliability


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What is achieved ?Performance

Reliability

Some Initiative to improve performance of Compressor and


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Some Initiative to improve performance of Compressor and

Implementation by design consideration ( Improving Design)

Goal :

Increase the Pressure Ratio.

Increase the Air Flow .

How It is Implemented ? Increase the Diameter of the inlet-stage. No. of stages are added.

What Result We get ?

Model - MS5000 - pressure ratio 6.78MS5001N -compressor operated at a pressure

ratio of 9.8. and Now we get more the 10 in the

frame-9 Machine.


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What is achieved ?

More Efficiency

To improve performance of Compressor and Implemented


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To improve performance of Compressor and Implemented

by design consideration ( Improving Design) :

Goal :To provide higher firing temperature at reduced loadfor regenerative-cycle and combined-cycle applications.

Implemented by :

The fixed inlet guide vane was replaced with a variableguide vane


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What is achieved ?Flexibility

of Operation


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.

GROWTH OF AIR FLOW OF GAS TURBINE

Lists some of the parameters of these axial compressors.


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p pBy starting with an efficient, reliable design and improving this design in agradual manner, improved overall compressor performance has been achievedwithout sacrificing reliability or mechanical integrity.

Objective of How it is done ? & How it is Figure Goal


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jDesignconsideration

incorporated ?g

Achieved

optimizingcompressor

wheel materialcharacteristics,cost, andserviceconditions

This type of constructionreduces weighs reduction ,

minimizes acceleration duringstart-up.

The disks are assembled witha number of axial tie-bolts,with the bolt-circle diameter

selected to produce adynamically stiff rotor andgood torque transmission.Weight loss+ StiffnessEnsuresV critical > V running .Axial clearance is providedbetween wheel rims to allowthermal expansion during start-up.

Weightreduction ,

stiffnessthermalconsiderationCostServicecondition

Objective of How it is done ? & How it is Figure Goal


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Objective ofDesignconsideration

How it is done ? & How it isincorporated ?

Figure GoalAchieved

Using Right

QualityMaterial inlastcompressorstage tocompensate

thetemperaturerise ,minimizethermalstress duringstart-up ,shut-down,

Higher-strength material (CrMoV)

(Chromium Molybdenum steels- 0.5 to5% Cr and 0.5 to 1.5% Mo with smalladditions of vanadium)used in the last compressor stage. high-temperature strength aftertesting stringent process controls and

ultrasonic inspection procedure.wheel life of 30 years at base load.designed for may thousands ofstarts and shut-down.Remainder of the compressor wheelsare made of three basic grades ofsteel, CrMo, NiCrMo, and NiCrMoVthe principal alloyingelements. Processing of these alloysproduces abalance of desired material

properties includingtensile strength and fracture

strength

thermal stressLife span

Objective of How it is done ? & How Figure Goal


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Designconsideration

it isincorporated ?

Achieved

Using RightQuality

Material in lastcompressorstage toproduces abalance ofdesired

materialpropertiesincludingtensilestrength andfracture

toughness.

CrMo,NiCrMo, and NiCrMoV

Materials are used .optimization of thesematerial has resultedin a 35% improvementin fracture toughness

strengthfracture

toughness.

The Brayton Cycle


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The Brayton CycleThe Brayton cycle consists of two adiabatic work transfers and twoconstant pressure heat transfer heat processes (Figure 3).

From State 2 to State 3, heat is added at constant pressure. For a gas-turbine, heat is added through a combustion process.

The combustor of a gas turbine is the device that accepts both


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The combustor of a gas turbine is the device that accepts bothhighly compressed air from the compressor and fuel from a fuelsupply so that continuous combustion can take place.

Fuel

High compressed air

This raises the temperature of the working gases to a very highlevel. This combustion must take place with a minimum ofpressure drop and emission production. The very hightemperature gases flow from the combustor to the first stage

turbine nozzles.


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Combustion Chamber Design :

Most Simple :

Fuel Injector

Impractical-f the excessive pressure loss resulting from

combust on at high velocities.Pressure loss from combustion the air velocity squared.

Velocity too high to establish stable combustion . Even

if ignited initially , the flame will be carried downstream

and cant be sustain without continuous i nition.


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Adding Baffle :

Flame stabilization zone (Eddy region)baffle

To secure flame at low velocity regionis achieved by installing baffle which will further generate

eddy region behind baffle and allow sufficient time for fuel to

completely combust.At that place, flame will stabilize and gives us continuous

ignition.


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Adding Swirl :

strong vortex is produced using swirl vanes around fuel nozzle xwill create low pressure region. Due to this pressure difference, airstarts moving towards it from radial holes around liner. With thismovement, flame start propagating up to some extent and will form arecirculation zone which stabilizes flame.

combustor air enters in the chamber through rings. and producerecirculation zone which further stabilizes flame for

complete combustion.

Dilution zone

Vortex

PrimaryZone

Swirl
http://www.bestinnovativesource.com/wp-content/uploads/2013/02/Flame-stabilization-region-created-by-swirl-vanes.jpg


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So we have ,

Combustion takes place in the primary zone of the Combustor .

Primary air = of total airflow) is used to support the combustionprocess.

The remaining air, referred to as secondary or dilution air, is admitted

into the liners in a controlled manner.


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The secondary air

controls the flame pattern,cools the liner walls,

dilutes the temperature of the core gasses,

This cooling air is critical,as the flame temperature is above 1930C which is

higher than the metals in the engine can endure.

Important


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Important

fuel nozzles and combustion liners control the burning and

mixing of fuel and air under all conditions to avoid excesstemperatures reaching the turbine or combustion cases.Maximum combustion section outlet temperature (turbine

inlet temperature) in this engine is about 1070C

Ab t th t bili ti f fl


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About the stabilization of flame,

air velocity plays a vital role. To understand this effect, we will

take the help of following graph

the velocity of air range of burnable mixture

For the stabilization of flame,the size of baffle is also important.Flow velocity in the Flow velocity in the combustion chamber ismaintained below blowout limit so that combustion chamber can

support wide range of fuel to air ratios.
http://www.bestinnovativesource.com/wp-content/uploads/2013/02/Range-of-burnable-fuel-to-air-ratios-versus-combustion-chamber-gas-velocity.jpg


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Combustion Chamber

Cross-

firetube

Secondary

Flamedetector

Primary

FlameDetector


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Some notable arrangements in combustionChamber:

a)Primary Flame Detector in the Chamber 1,2,3,14b)Secondary Flame Detector in the chamber 1,2,3,14c) Primary , Secondary and Tertiary Fuel Connection

clock wise direction from manifold .


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Introduction of combustion chamber structure


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TRASTION PIECE


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FLOW SLEEVE


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Cap-liner


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Primary Nozzle


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Primary Nozzle


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Secondary and Tertiary Nozzle


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Secondary and Tertiary Nozzle

TertiaryNozzle

Tertiary

Nozzle


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The number of combustors


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the machine airflow by thepressure ratio Example

the MS9001E uses 14 combustors

compared to 10 on the MS7001E

becausethe 9E airflow is 1.44 times as

large To improve performance of Combustion Chamber and Implementedby design consideration ( Improving Design) :


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y g ( p g g )

Goal :

a) Improve High Temperature Strength .

b) Reduction Thermal Gradient.

In the Liner Section

Implementation :

Improvement in the liner Construction and using bettermaterial .Example :

In Model MS7001FA liner is 30% thicker and 210 mm (8.4

in.) and Using Hastelloy-X material and addition of HS-188in the aft 278 mm (11.1 in.) portion and the application of

thermal barrier coating to the internal surface.

To improve performance of Combustion Chamber and Implementedby design consideration ( Improving Design) :


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y g ( p g g )

Goal :

a) Improve High Temperature Strength .

b) Reduction Thermal Gradient.

In the Transition Piece Section

Implementation :

Improvement in the Transition Piece Construction andusing better material .Example :

Nimonic 263, was introduced into service for transition

pieces. This material is a precipitation-strengthened, nickel-base alloy with higher strength capability than Hastelloy-X.

Since the early 1980s, Thermal Barrier Coatings (TBCs) have

been applied to the transition pieces.


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What is achieved ?

ReliabilityHigh Temperature Strength

Reduction Thermal Gradient.IN LINER

andTransition Piece



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y g p g g

Goal :

a) Reduction of Combustion noise .

b) Reduction Wear .In the Liner Section

Implementation

Incorporating More No. Nozzle instead of One with waterInjection system.Example :

MS7001E design to accommodate six fuel nozzles

instead of one with water injection forNOx control (Discuss Later)



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y g p g g

Goal :

Reduction Wear .

In the Transition Piece

ImplementationTo increase the wear resistance of some transition piecesin the aft end Cobalt-base hard coatings applied by thermal

spray improve the wear life of sealing components by more

than four times.


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Goal :Reliability in Ignition Process

IMPLEMENTATION :

a)Using Two sparking Plug .b)Using Two Flame Detector .

c) Using Cross Fire Tubes .


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What is achieved ?

ReliabilityIn

Ignition System



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Goal :Completely burn of the residual fuel.

Implementation:

By allowing air jets in the combustion chamber for properStoichiometric air fuel mixture .Combustor length must be sufficient to provide for flame

stabilization. combustion. and mixing with dilution air. The

typical value of the length-to-diameter ratio for linersranges from three to six.


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What is Stoichiometric Ratio ?

The Stoichiometric ratio is the

perfect ideal fuel ratio where thechemical mixing proportion iscorrect.

When burned all fuel and air isconsumed without any excess left

over


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What is achieved ?

Fuel Economy



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Goal :

To remove NOx from the combustion.

What is NOx ?

NO and NO2, collectively called NOx.

Why Removal of NOx ?

It is bad for the environment and bad for the health.Must below 100 ppm in the combustion product .

Where it is produced ?

2 sources of NOx emissions .1. NOx is generated by the fixation of atmospheric nitrogen in the

flame. This is called thermal NOx.2. Other NOx are also generated by the conversion of a fraction of

any nitrogen chemically bound in the fuel (called fuel-bound

nitrogen or FBN).

Thermal NOx


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Is an exponential function of the (T)

temperature of the flame a linear function of time (t)

To Minimize the NOx we have to designthe combustion chamber

Where

The combustion temperature must belowthe NOx producing Temp.

And

The combustion process takes lesser time .

The combustion chamber Which is used for dln system


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The combustion chamber Which is used for dln system


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What is achieved ?

EnvironmentFriendly

Machine

Some Design Factors must be done in designing combustion chamber


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Wobbe Number :

Wobbe Number is an indicator of the characteristics and stability of

the combustion process.

Here , LHV Lower Heating Value of fuel ,Sp. GR Specific GravityTamb Ambient Temperature

the wobbe Number can cause the Flame to burn closer to the liner.

Decreasing the wobbe Number can cause pulsations in the

combustor.



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:

Pressure drop.

100 fps (30mps), 4%

80fps (24mps), 2.5%:

70fps (21 mps), 2%:

50fps (15mps), 1%.



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The heat-release the fuel-to-air ratio

The heat-release the combustor pressure.

The heat-release = ( Combustor capacity)

The Brayton Cycle

From State 3 to State 4 the gas passes through an adiabaticisentropic turbine which decreases the temperature and pressure of

the gas

Static pressure(Ps )The force per unit area exerted on the walls of a container by astationary fluid. tire pressure


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Impact pressure (Pi) is the force per unit area exerted by fluids in motionthe pressureexerted on one's hand held outside a moving cars window

Pt = Ps + PiPart (a) illustrates the measurement of static pressure. Static pressure will not take intoaccount the velocity of the air.

Part (b) illustrates the measurement of total pressure, which accounts forboth static pressure and the pressure due to the moving fluid (impact pressure).

Convergent Duct


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Velocity

Pressure

Temperature


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Pt PiA static pressure decrease is seen as air flows through a convergent duct and goesthrough expansion. A temperature drop is associated with any expansion process.

Here { E + or }

Here , v (large inlet to a smaller outlet )

(Pi)

Here , { E + or } So , Pt

As , Pt = Ps + Pi So , Ps

Axial flow compressor,P current stage > P previous stage [ incrementally]


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BLADE VANE

What a single stage of compressor consistsof ?A set of rotor blades attached to a rotating

disk . Flow area between rotor blade isslightly divergent .

followed by stator vanes attached to a

stationary ring.Flow area between compressor vanes is alsodivergent than blade .What is done by the blade ?

convert mechanical energy into gaseousenergy. ( Here , energy is added) .What happens?Pi So Pt andslight Ps for divergence

Pt

Ps

v

Vane /Nozzle

nozzles convert the gaseous heat andpressure energy into higher velocity gas flow(Pi)


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NozzleBlade

Pt

Ps

v

Vane Blade

(Pi)

In addition to accelerating the gas,the vanes "turn" the flow to direct it into therotor blades at the optimum angle.

As the mass of the high velocity gas flows

across the turbine blades, the gaseous energyis converted to mechanical energy.

Velocity, temperature, and pressure of the gas

are sacrificed in order to rotate the turbine togenerate shaft power

f b


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Types of Gas Turbine :

1.Impulse

2.Reaction


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P1 P2

V1 V2

Here ,P1 > P2

v1> v2Velocity-v, pressure-P


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If Pressure decreases

Velocity increases

Kinetic Energy increases

RMP increases


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Change in pressure is done :

1) By Convergent Nozzle .

2) By Convergent Blade.


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In Turbine ( Gas or Steam) :

has ConvergentNozzle system and uniform blade

system .Reaction Turbine has Convergent

Blade system and uniform nozzle

system

Impulse Turbine nozzle and blading

arrangement


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arrangement

Conver-gent

Guidevan

Here :

P1 >P2V2> V1

Moving BladeFixed Blade

ConstantArea

MovingBlade

P1P2

V1 V2

Impulse Turbine in Action


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Reaction Turbine nozzle and blading arrangement


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ConstantAreaGuidevane

Conver-gentNozzle

Here

P1 > P2V2> V1

Fixed BladeMovingBlade

P1

P2

V1 V2

Reaction Turbine in Action


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A reaction turbine is moved by two main


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A reaction turbine is moved by two mainforces:

1. There is expansion of steam is there ,pressure is decreasing so there isincrease in kinetic energy by increasingvelocity .

2. the push or impulse of the gasimpinging upon the blades


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Impulse Turbine create large

amounts of Tangential thrust

Reaction turbines create largeamounts of axial thrust, and so

require the use

So the combination of impulse


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So the combination of impulse -

reaction turbineis widely used .

Impulse Reaction Turbinereduces both the tangential

and axial stressTo the Rotor

Impulse Reaction Blade


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Impulse Reaction Blade

The fixed blades are set in a reversed mannercompared to the moving blades,

Schematic drawing of major components of gas turbine


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Gas TurbineAuxiliaries

Air InletSystem CompressorSection

ExhaustSystemTurbineSection

CombustionSection

AirInlet

Compressor TurbineSection

CombustionSection

ExhaustSection


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To improve performance of Turbine and Implementedby designconsideration ( Improving Design) :

Goal :


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Goal :

To improve the Higher firing temperature .How it is Implemented ?

Improved nozzle and bucket material .

The air-cooling of this hardware.

Simultaneous development in alloy corrosion and

oxidation resistance and bucket surface protection

systems have played a significant role in supportingfiring temperature increases.


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What is achieved ?

More Efficiency

To improve performance of Turbine and Implementedby designconsideration ( Improving Design) :

Goal :


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Goal :

To make Vibration Free Bucket at all speed of theturbine and Making Thermal Isolation .How it is Implemented ?

The long-shank bucket and the bucket tip shroud is

introduced.

How it works ?

Damping is introduced near the bucket mid span .


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Damping is introduced near the bucket mid span .

The shank has a second important advantage in providing aneffective thermal isolation between the gas path and theturbine wheel dovetail.


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What is achieved ?

Reliability inOperation

ByVibration Control

Problems Occur during Operation of the Turbine and Its solution bydesign consideration :

Creep/Rupture


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Creep/Rupture

How it is overcome


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A creep strain criterion is chosen to avoid creep cracking.


Th l F ti


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Thermal Fatigue

It is due to the temperature gradient for the cooling of the hightemperature Component of gas turbine in both transient and steady-State operation , such as Vane in fig .


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Cant be eliminated, but their impact can bemitigated by judicious design and careful operation.


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What is achieved ?Thermal

Consideration


Corrosion


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Co os o

The use of Ni-base super alloys as turbine blades in an actual end-use atmosphere produces deterioration of material properties.This deterioration can result from erosion or corrosionErosion results from hard particles impinging on the turbine bladeand removing material from the blade surface.

Corrosion is described as hot corrosion and sulfidation processes.Hot corrosion is an accelerated oxidation of alloys caused by thedeposition of Na2SO4. Oxidation results from the ingestion of salts

in the engine and sulfur from the combustion of fuel.

Sulfidation corrosion is considered a form of hot corrosion in whichthe residue that contains alkaline sulfates. Corrosion causesdeterioration of blade materials and reduces component life.

Remedy :

Pl ti h i l i id diff i t ti


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Platinum-chromium-aluminide diffusion-type coatings

developedPt-Cr-Al coating

developed

Combination of IN-738 and Pt- Cr-Aldeveloped

vacuum plasma spray coatings are overlay-typecoatingsdeveloped


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What is achieved ?Corrosion

Control


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ThankYou

design consideration of gas turbine

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