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Steam Turbines:
Classification
constructional details
By
Mahendra chikhale
Engineer (M) PHS
Condition Monitoring Cell
Rashtriya Chemicals Fertilizers Ltd
Chembur , Mumbai
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What is Turbine?
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Fundamentals
Steam turbine is power producing d
Steam turbine is a device which cothermal/heat energy of steam frommechanical energy of rotational tothe output shaft and in turn the pow
Steam turbines are utilized to driveof equipment types of numerous sizspeeds in just about every industry sincluding power generation , pulp, paper , steel, chemical , oil and gas
industries.
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History
De Laval, Parsons and Curtis devethe concept for the steam turbine1880s
Modern steam turbines use essen
same concept but many detailedimprovements have been made iintervening years mainly to improvturbine efficiency.
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Principles of operation
The motive power in a steam turbine is obthe rate of change in momentum of a high
of steam impinging on a curved blade whirotate.
The steam from the boiler is expanded in resulting into a high velocity jet. This jet of
impinges on the moving blades, mounted Here it undergoes a change of direction o
which in turn change in momentum and thforce.
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Simple arrangement of a Turbine
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Principle ofoperation
Impulseturbine
Reactionturbine
Impulse
reactionturbine
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Impulse principle
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Impulse turbine
In impulse turbine, the drop in psteam takes place only in nozzle
moving blades.
This is obtained by making the bpassage of constant cross-sectio
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Reaction principle
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Reaction turbine
The drop in pressure takes place in fixed
well as moving blades.
The pressure drop suffered by steam whthrough the moving blades causes a furthgeneration of kinetic energy within these
giving rise to reaction and add to the propwhich is applied through the rotor to the t
The blade passage cross-sectional area (converging type).
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Reaction stages
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Impulse-Reaction turbine
Utilizes the principle of impulse and rea
There are a number of rows of moving battached to the rotor and an equal numbblades attached to the casing.
The fixed blades are set in a reversed m
compared to the moving blades, and actDue to the row of fixed blades at the en
instead of nozzles, steam is admitted forcircumference and hence there is an all-complete admission.
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Nozzle & bucket Arrangements
For Impulse & Reaction Turbine
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Why compounding/multi staging
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Why compounding/multi-staging
In steam engines, it is difficult to obtain fast rotatioturbines have a great difficulty to run at slower sp
For example: Steam expanding from 10.34 bar to
through diverging nozzle will attain velocity of 1.2Therefore, an impulse type turbine wheel of 12 inc
diameter will rotate in the proximity of 35,000 rpm
This impulse wheel would soar to over 75,000 rpmwould suddenly drop.
The reaction type turbine wheel of the same diamwould actually run in the proximity of 69,000 to 75
These speeds are too high for all practical purpos
Rotational speeds are reduced by velocity comppressure compounding.
It is for this reason that multi staging is almost alw
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Blading/compounding
Pressurecompounded velocitycompounded
pressureveloc
compou
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Pressure compounded impulse
Splitting up of the whole pressure drop fsteam chest pressure to the condenser pa series of smaller pressure drops acrossstages of impulse turbine.
The nozzles are fitted into a diaphragm lcasing. This diaphragm separates one wchamber from another.
All rotors are mounted on the same shafblades are attached on the rotor.
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Pressure compounding
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Velocity compounded impulse t
Velocity drop is arranged in many through many moving rows of blad
of a single row of moving blades.
It consists of a nozzle or a set of n
rows of moving blades attached to
the wheel and rows of fixed blades
to the casing.
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Pressure Velocity Compounding
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Pressure-Velocity Compounding
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No ofstages
Singlestage
Multistage
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Single stage turbine
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multi stage turbine
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Exhaustconditions
Back
pressure Type
Extraction
type
Condensin
Type
B k P St T bi
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Steam exits the turbine at a higher pressure that the at
Back Pressure Steam Turbin
Figure: Back pressure steam turbine
Advantages:
-Simple config
-Low capital co
-Low need of c
-High total effi
Disadvantage
-Larger steam-Electrical load
be matched
Fuel
BoilerTurbine
Process
HP Steam
Condensate
LP
Steam
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Steam obtained by from an intermedia
Remaining steam is
Relatively high cap
lower total efficienc
Control of electrica
independent of the
Extraction Condensing Steam Turbin
Boiler Turbine
Process
HP Steam
LP Steam
Condensate
Condenser
Fuel
Figure: Extraction condensing steam turbine
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All steam is exhaust
very high capital cos
total efficiency
Control of electrical
independent of therm
Extraction Condensing Steam Turbin
Boiler Turbine
HP Steam
Condensate
Condenser
Fuel
Figure: condensing steam turbine
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Si l li d t bi
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Single cylinder turbine
multi cylinder turbine
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multi cylinder turbine
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Flow of
steam
Single flow Compoundflow
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Bi flow turbine
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Bi flow turbine
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Arrangementof cylinders
Tandemarrangement
Crossarrangement
In tandem compound arrangement the rotor
of the cylinder make one common shaft thatgenerator. The rotors may be coupled togeth
Cross compound machines avoid long shaftsenable fewer LP turbines if LP turbine shafts ardifferent speeds.
Two cylinder Tandem arrangement
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Cylinder 2Cylinder 1
Steam IN
Steam OUT
Two cylinder Tandem arrangement
Steam IN Cross cylinder arrangement
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Cylinder 2
Generator 2
Generato
Steam IN
Steam OUT
y g
Cylinder 4Cylinder 3
Cylinder 1
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Why multi-cylinder arrangement
The limit of a single-cylinder turbine is aMW.
Multi-cylinder designs are used in large
e.g. one high pressure (HP) turbine, on
intermediate pressure (IP) turbine and
pressure (LP) turbines.
The IP and LP turbines are usually doub
Schematic Diagram
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g
Turbine components
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Turbine components
Turbine balding : Stationary blades , Mblades
RotorTurning Gear/Barring gear
Casing
Steam Valves
Journal bearing
Thrust bearing
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Turbine rotor
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Turbine rotor
Types of rotors
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Types of rotors
Disc type rotors Drum type r
Types of Rotor
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Types of Rotor
St T bi bl di
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Steam Turbine blading
Rows of stationary balding and Rows of Rotating baldin
Stationary balding- nozzles , vanes , partitions and stati
balding (Diaphragms) Rotating balding buckets , blades and rotating blading
Turbine balding different shapes either impulse bladireaction blading.
Impulse balding are U shaped
Reaction blading aerofile shape
Impulse turbine utilized in high pressure section
Reaction blading utilized in the lower pressure section
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Steam Turbine balding
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Regardless of balding type blade tips may have integral shrouds which ablades
Blade root Attachment
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f l d h
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Types of Blade root Attachment
Dovetail root
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Dovetail root
Internal tree root
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Internal T root
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Bulbous root
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Bulbous root
Straddle tree root
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Shrouding
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Types of shrouding
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shrouding
Rivettedshroud
IntegralShroud
Lash
Integral shroud
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Riveted shroud
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Riveted types
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Lashing type shrouding
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rivetedlashinIntegral
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Turning Gear
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Turbine Sealing
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Interstate sealingShaft sealing
interstate sealing
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g
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shaft sealing
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Turbine seal types
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Carbon rings
Labyrinth seal
Stuffing box
principle
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Simple Labyrinth seal
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Labyrinth seal
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Carbon Seal rings
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Stuffing box
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Turbine casing
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Double casing Single casin
principle
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Journal bearing types
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Lobe bearings
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Tilting pads journal bearing
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Thrust bearing
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Babbitt
faced collar bearingsTilting pads
Tapered land bearing
Rolling contact (roller or ball) bearing
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A fluid film thrust bearing
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T
BS
Antifriction Thrust bearing
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The Babbitt face of a tapered land thrust bearing has
fixed pads divided by radial slots. The leading edge o
sector is tapered, allowing an oil wedge to build up and
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secto s tape ed, a o g a o edge to bu d up a d
thrust between the collar and pad
Balancing Drum To contract axial thrust steam is admitted to a dummy( balance )
piston chamber at the low pressure end of the rotor.
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Balancing Drum arrangement
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governor
Control valveStop valve
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turbineGovernor
Speed sensor
Steam IN
Steam OUT
Set point
Power supply
Turbine Valves
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The stop valve
The Control valve
Steam stop valve
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Important to any turbine is the ability to start and stop the ma
normal (controlled) and emergency conditions. For steam tuable to shut off the steam supply quickly & reliably is required
This is normally accomplished by either main steam (MS) stopand throttle (T&T) valves which are usually installed in the inlesteam turbine or on the turbine shell.
Ventilator valvefunction of ventilator valve is to prevent the turbinoverheating during a turbine trip or shutdown.
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ventilator valve
Stop valve
turbine G
conde
turbine
Emergency blow-down valve
Emergency blow-down valve is used to prevent oveduring load rejection.
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turbine
Emergency blow-down valve
Stop valve
conde
turbine
g j
Drain valves
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Turbine drain valves is used to remove moisture
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Trouble shooting of steam
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Corrosion/Erosion
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Broken blades
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summery
looseness
L li
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Loose coupling
Excessive clearanceof bearings
Loose coupling joint
summery
operation Salt deposition
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Salt deposition
Steam quality
Improper inter-stage sealing
Broken nozzles
Over-speeding due to governorproblem
Salt deposition
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summery
Bearing Lack of lubrication
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gfailure
Lack of lubrication
Poor oil grade
Dirt Contaminated oil
Moisture contamination
Residual magnetism
Design flaws
Bearing failure due tooverheating
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Contaminated oil erosion
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Shaft Grounding Locations
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Oil whirl and oil whip
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Oil whirl
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Probe sensing areas
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Probe surfacing area should be properly demagnetized
Combined total electrical & mechanical run out does not expercent of the maximum allowable peak to peak value or
Which ever is greater
For radial vibration probe 0.25 mils
For axila position probes- 0.5 mil
Why steam quality is important?
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Steam Purity Why ?
Impurities can cause damage to turbicomponents by - corrosion, stress corrocorrosion fatigue, erosion-corrosion.
Deposition can cause thermodynamlosses, lower efficiency, upsetting of pdistributions, clogging of seals andclearances
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