173623205-steam-turbine-ppt (1).pdf

8/20/2019 173623205-Steam-Turbine-PPT (1).pdf

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STEAM TURBINE

Dr. K.C. Yadav, Head,

Training & Development


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Learning Agenda Expansion of steam and work done

Description of the nozzle angles (α), blade angles (β) andsurface roughness (µ) and their impact on turbine

performance Velocity vector diagrams and estimation of turbine stage

output and efficiency

Purpose, principle, classification, construction andfunctioning of steam turbine

Physical significance of turbo-supervisory parameters

Performance of steam turbine


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Purpose of Steam Turbine

Steam turbine is prime-mover for electric power generation,

which converts heat energy of steam to mechanical energy

of Steam Turbine Rotor.

This mechanical energy is utilized to spin rotor (magnet) of

the electricity generator to produce electric power.


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Steam Expansion Steam expands, whenever it is subjected either to lower

pressure or to a higher temperature.

It is considered to be free expansion when the expanding

boundary is free from any resistance from the surrounding.Though the free expansion has no engineering application but

it provides enough guidelines to the designers of steam

turbines/engine to properly deal with steam operating

parameter to avoid any possibility of free expansion.

Expanding steam (thermodynamic System) does work onsurrounding irrespective of its being a solid, liquid or gas

separated by well defined boundary.

Expansion of steam in turbine is facilitated to do work on

turbine blades mounted on the freely rotating shaft.


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Principle of Steam TurbineWhen steam is allowed to expand through anozzle, then its heat is converted to kinetic energy

of steam itself, which in turn converts into kineticenergy (mechanical energy) of Turbine Rotor through the impact (impulse) or in an other way,when it expands through Turbine Rotor Blades

without any change in its velocity then its heat isconverted directly in to kinetic energy (mechanicalenergy) of Turbine Rotor through reaction of steam expansion against the blades.


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Types of Steam Turbine Impulse Turbine (DR = 0)

Reaction Turbine (DR = 1)

Impulse - Reaction Turbine (DR > 0 &


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Impulse Turbine Velocity compounded

Pressure compounded

Pressure - Velocity compounded


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Reaction TurbineExpanding steam has to be accommodated in moving

blades without any change in velocity by suitably

increasing the space in the blade down stream, which isvery difficult and hence no steam turbine is constructed to

be pure reaction turbine.


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Impulse - Reaction TurbineExpanding steam does work on surrounding blade

surface by virtue of its volume change and at the same

time incremental velocity of steam stream also doessignificant work on moving blades by impaction.


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Turbine Blade


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Vector Diagram


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Multistage Turbine Blade Arrangement


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Multistage Turbine Blade Arrangement


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3


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Stationary Diaphragm


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Components of Steam Turbine Foundation (TG & Pillar)

Base plate / sole plate

Bearing pedestal / pedestal plate

CasingSingle / double (Inner or outer casing) / Triple casing

Barrel type or axially spilt (bottom or top flange)

Body liners and stationary diaphragm

Rotor

Inbuilt (solid), key & shrunk fit and welded

Moving diaphragm

Studs and nuts


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Components of Steam Turbine HP, IP & LP turbine.

Bearings.

Shaft sealing .

Stop & control valves.

Turbine control system.

Turbine monitoring system.

Turbine oil system.

Turbine turning gear


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TG Foundation


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*


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IP Cylinder of a

500 MW Unit


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Barrel Type HP Turbine


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Hydraulic Turning Gear The function of the hydraulic turning gear is

to rotate the shaft system at sufficient speed

before start-up and after shutdown in order to avoid irregular heating up or cooling down

and also to avoid any distortion of the

turbine rotors. The hydraulic turning gear is

situated at the front end of the HP turbinefront bearing pedestal.


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Hydraulic Turning Gear


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Mechanical Barring Gear The turbo- generator is equipped with a

mechanical barring gear, which enables

the combined shaft system to be

rotated manually in the event of a

failure of the normal hydraulic turning

gear. It is located at IP-LP pedestal(Brg No-3).


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Mechanical Barring Gear


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Low Pressure TurbineOuter casing ,upper half

Outer shel l , upper hal f Inner shel l , upper hal f

Inner shell, lower half Outer shell, lower half

Outer casing, lower half

STEAM FLOW


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Fixed Points of a 250 MW Turbine

Casing Expansion:

HP Turbine outer Casing expands towards frontPedestal.

IP Turbine Casing expands towards Generator side. LP Turbine outer casing expands towards both ends

from center.

Rotor Expansion:

HP Rotor towards front Bearing.

IP Rotor towards Generator side.

LPT Rotor towards Generator.


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Casing ExpansionThe bearing pedestals are anchored to the foundation bymeans of anchor bolts and are fixed in position. The HP

and IP turbines rest with their lateral support horns on the

bearing pedestals at the turbine centerline level. The HPand IP casings are connected with the bearing pedestals

by casing guides which establish the centerline alignment

of the turbine casings. The axial position of HP and IP

casings is fixed at the HP-IP pedestal. Hence, when there

is a temperature rise, the outer casings of the HP turbineexpand from their fixed points towards Front pedestal.

Casing of IP Turbine expand from its fixed point towards

the generator.


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Casing ExpansionThe LP Turbine outer casing is held in placeaxially, at centre area of longitudinal girder by

means of fitted keys. Free lateral expansion isallowed. Centering of LP outer casing is providedby guides which run in recesses in the foundationcross beam. Axial movement of the casings isunrestrained. LP Casing expands from its fixed

point at front end, towards the generator at centrearea of longitudinal girder by means of fittedkeys. Free lateral expansion is allowed.


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Rotor ExpansionThe thrust bearing is housed in the rear bearing pedestal

of the HP turbine. The HP turbine rotor expands from the

thrust bearing towards the front bearing pedestal of theHP turbine and the IP turbine rotor from the thrust bearing

towards the generator. The LP turbine rotor is displaced

towards the generator by the expansion of the shaft

assembly, originating from the thrust bearing.


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Turbo Supervisory Parameters

Over all expansion

Axial shift

Differential expansion

Eccentricity

Vibration


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Performance of Steam Turbine THR = [(Qms*Hms – Qfw*hfw) + Qrh*(Hhrh – Hcrh)]/P

P = PGen.Ter. – (Pexc + Pmin)

ηta = 3600/THR = ηt*ηg*ηc

ηt = Wt/Hise

ηg = MW/Wt

ηc = Hise /[(Qms*Hms – Qfw*hfw) + Qrh*(Hhrh – Hcrh)] or

ηc = [Qms*(Hms –Hcrh)+Qrh*(Hhrh – Hexh)–Sum(qb*Hb)] /[(Qms*Hms –Qfw*hfw)+Qrh*(Hhrh –Hcrh)]


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Enthalpy Drop Across the TurbineHPT

Qms*(Hms-H7) + (Qms-q7)*(H7-Hcrh)

IPT

+ Qrh*(Hhrh-H5) + (Qrh-q5-qd)*(H5-H4)+ (Qrh-q4-q5-qd)*(H4-H3)

+ (Qrh-q3-q4-q5-qd)*(H3-H2)

LPT

+ (Qrh-q2-q3-q4-q5-qd)*(H2-H1)+ (Qrh-q1-q2-q3-q4-q5-qd)*(H1-Hexh)


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Velocity Vector Diagram forPure Impulse Turbine

β1α1 β2α2

β1α1

β2

α2


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Blade Performance of Pure Impulse Turbine

Wo = C2 Cos α2 (clockwise tangential component)

Wi = C1 Cos α1 (anticlockwise tangential component)

R2 < R1 & R2 = µ*R1

For smooth surface µ = 1 & R2 = R1

P = [Wi - (-Wo)]*u = [C2 Cos α2 + C1 Cos α1]*u

C2 Cos α2 = R2 Cos β2 –u = R1 Cos β1 –u

or C2 Cos α2 = C1 Cos α1 - u – u = C1 Cos α1 – 2u

P = [C1 Cos α1 + C1 Cos α1 – 2u]*u = 2*u*[C1 Cos α1 – u]

ηb = 2*P/C1**2 = 4*[(u/C1)*Cos α1 – (u/C1)**2]


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Velocity VectorDiagram for Impulse-

Reaction Turbine

β1α1 β2α2

β1 α1

β2α2


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Work Done in Imp-Reaction Steam Turbine


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Deduction of C2 & R1 in terms of R2 & C1


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Stage Efficiency


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Internal Losses


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Thank you

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