A brief Presentation to Steam turbine

8/17/2019 A brief Presentation to Steam turbine

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Prepared by: Mohammad Shoeb Siddiqui

Senior Shift SupervisorSaba Power Company

Cell # +92 321 4598293


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What is Steam Turbine? A Steam Turbine is a device that extracts Thermal

Energy from pressurized Steam and uses it todo Mechanical Energy on a rotating output shaft.

Steam Turbine is device where Kinetic Energy(Heat) converted into Mechanical Energy (in shapeof rotation).

Turbine is an Engine that converts Energy of Fluidinto Mechanical energy & The steam turbine issteam driven rotary engine.

This Presentation is base on basic of Steam Turbine& 134 MW Toshiba Steam Turbine.

Prepared byMohammad Shoeb SiddiquiSenior Shift Supervisor


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In order to better understand turbine operation, Four BasicClassifications are discussed. Type of Steam Flow &

Division of Steam Flow, describes the flow of steam inrelation to the axis of the rotor. indicates whether thesteam flows in just one direction or if it flows in more thanone direction. Way of Energy Conversion & Type ofBlading, Reaction, Impulse and Impulse & ReactionCombine. identifies the blading as either impulse blading

or reaction blading. Type of Compounding & Cylinderarrangement refers to the use of blading which causes aseries of pressure drops, a series of velocity drops, or acombination of the two. (number of cylinders; whethersingle, tandem or cross-compound in design) ExhaustingCondition & Number of Stages is determined by whether

the turbine exhausts into its own condenser or whether itexhausts into another piping system.

Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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1. Type of Steam FlowTurbines may be classifiedaccording to the direction ofsteam flow in relation to theturbine wheel or drum

- Axial.

- Radial.

- Mixed

- Tangential Or Helical.

- Reentry



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Radial Flow:

A turbine may also be

constructed so that thesteam flow is in a radial

direction, either toward or

away from the axis. In

figure illustrates an

impulse, radial

flow, auxiliary turbine such

as may be used as a pump

drive.

The radial turbine is not nor

mally

the preferred choice for

electricity generation and is

usually only employed for

small output applicationsPrepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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Axial Flow:

The great majority of

turbines, especially thoseof high power, are axial

flow. In such turbines the

steam flows in a direction

or directions parallel to the

axis of the wheel or rotor.

The axial flow type of turbi

ne is the most preferred for

electricity generation as

several cylinders can be

easily coupled together to

achieve a turbine with agreater output.

.Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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Reverse Flow

In some modern turbine designs the

steam flows through part of the highpressure (HP) cylinder and then is

reversed to flow in the oppositedirection through the remainder of the

HP cylinder. The benefits of this

arrangement are:

outer casing joint flanges and boltsexperience much lower steam

conditions than with the one directiondesign

reduction or elimination of axial

(parallel to shaft) thrust created withinthe cylinder

lower steam pressure that the outer

casing shaft glands have toaccommodate

A simplified diagram of a reverse flow highpressure cylinder is shown in Figure Prepared by

MohammadShoeb SiddiquiSenior Shift Supervisor


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2. Way of Energy Conversion & Types of Blading

- Impulse turbines

- Reaction turbines

- Impulse & Reaction Combine



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By Types of Blading :

The heat energy contained within the steam that

passes through a turbine must be converted

into mechanical energy. How this is achieved

depends on the shape of the turbine blades. The

two basic blade designs are:

1. Impulse

2. Reaction



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Impulse:Impulse blades work on the principle

of high pressure steam striking orhitting against the moving blades.

The principle of a simple impulse

turbine is shown in Figure.

Impulse blades are usually

symmetrical and have an entrance

and exit angle of approximately 200.They are generally installed in the

higher pressure sections of the

turbine where the specific volume of

steam is low and requires much

smaller flow areas than that at lower

pressures. The impulse blades are

short and have a constant cross

section.



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Reaction:The principle of a pure reaction turbine

is that all the energy contained within the

steam is converted to mechanicalenergy by reaction of the jet of steam asit expands through the blades of the rotor.

A simple reaction turbine is shown inFigure. The rotor is forced to rotate as the

expanding steam exhausts the rotor arm

nozzles.

In a reaction turbine the steam expands when passing across the fixed blades

and incurs a pressure drop and anincrease in velocity. When passing

across the moving blades the steam

incurs both a pressure drop and adecrease in velocity

A section of reaction type blading isshown in Figure



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Impulse stage

Whole pressure drop innozzle (whole enthalpydrop is changed intokinetic energy in thenozzle)

Reaction stagePressure drop both instationary blades and inrotary blades (enthalpydrop changed intokinetic energy both in

stationary blades and inthe moving blades inrotor) Prepared by



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An impulse stage consists ofstationary blades forming

nozzles through which thesteam expands, increasingvelocity as a result ofdecreasing pressure. Thesteam then strikes the rotatingblades and performs work on

them, which in turn decreasesthe velocity (kinetic energy) ofthe steam. The stream thenpasses through another set ofstationary blades which turn itback to the original direction

and increases the velocityagain though nozzle action.



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In Reaction Turbine both themoving blades and the non-moving blades designed to actlike nozzles. As steam passesthrough the non-movingblades, no work is extracted.Pressure will decrease and

velocity will increase as steampasses through these non-moving blades. In the movingblades work is extracted. Eventhough the moving blades aredesigned to act likenozzles, velocity and pressure

will decrease due to workbeing extracted from thesteam.



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This utilizes the principle of

impulse and reaction. It isshown diagrammatically :

There are a number of rows ofmoving blades attached to therotor and an equal number offixed blades attached to the

casing. The fixed blades are setin a reversed manner comparedto the moving blades, and act asnozzles. Due to the row of fixedblades at the entrance, instead ofnozzles, steam is admitted for

the whole circumference andhence there is an all-round orcomplete admission. Prepared by



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Compounding of Impulse Turbine

This is done to reduce the rotational speed of the

impulse turbine to practical limits. (A rotor speedof 30,000 rpm is possible, which is pretty high forpractical uses.)

Compounding is achieved by using more than oneset of nozzles, blades, rotors, in a series, keyed toa common shaft; so that either the steam pressure

or the jet velocity is absorbed by the turbine instages.

Three main types of compounded impulse turbinesare:

a) Pressure compounded,

b) velocity compounded and

c) pressure and velocity compounded impulse turbines.



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When the velocity energy produced

by one set of fixed nozzles is unable

to be efficiently converted into

rotational motion by one set of

moving blades then it is common to

install a series of blades as shown in

Figure. This arrangement is known

as velocity compounding.

Velocity drop is arranged in many

small drops through many movingrows of blades instead of a single

row of moving blades.

It consists of a nozzle or a set of

nozzles and rows of moving blades

attached to the rotor or the wheel and

rows of fixed blades attached to thecasing.



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This is a combination of

pressure-velocity compounding.

Most modern turbines have acombination of pressure and

velocity compounding. This type

of arrangement provides a

smaller, shorter and cheaper

turbine; but has a slight

efficiency trade off.Turbines using this

arrangement are often referred

to as CURTIS turbines after the

inventor. Individual pressure

stages (each with two or more

velocity stages) are sometimescalled CURTIS stages.



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This setup of a nozzlefollowed by a set of movingblades, non

-moving

blades, and moving bladesmakes up a single Curtisstage. After steam exits thenozzle there are no further

pressure drops.However, across both setsof moving blades there is avelocity drop. This causesthe Curtis stage to beclassified as velocity

compounded blading.



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Turbines can be arranged either single cylinder or multi-stage in design.

The multi-stage can be either velocity, pressure or velocity

-pressure

compounded (discussed as earlier.

Single cylinder construction or Single Flow TurbineSingle cylinder turbines have only one cylinder casing(although may be is

multiple sections). Steam enters at the high pressure section of the turbine

and passes through the turbine to the low pressure end of the turbine then

exhausts to the condenser. Figure shows a single cylinder turbine with a

high, intermediate and low pressure section contained within the one

cylinder casing.



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Tandem construction or Compound Flow Turbine

Dictated by practical design and manufacturers considerations modern

turbines are manufactured in multiple sections also called cylinders.

Greater output and efficiency can be achieved by coupling a number ofindividual cylinders together in what is referred to as tandem (on one

axis).

Tandem compound

Large electric power generating turbines commonly have a highpressure casing, which receives superheated steam directly from the

boiler or steam generator. The high pressure turbine may then exhaustto an intermediate pressure turbine, or may pass back to a reheatsection in the boiler before passing to a reheat intermediate pressureturbine. The reheat turbine may then exhaust to one or more lowpressure casings, which are usually two exhaust flow turbines, with thelow pressure steam entering the middle of the turbine and flowing in

opposite directions toward two exhaust end before passing into thecondenser. When the turbine casings are arranged on a single shaft, theturbine is said to be tandem compounded.



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Tandem construction or Compound Flow Turbine

A tandem two cylinder turbine with a single flow high pressure (HP) cylinder and a

double flow low pressure (LP)cylinder is shown in Figure.



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Tandem Three Cylinder Turbine

It has a double flow LP cylinder with an IP cylinder arranged so that the

steam flow through it is in the opposite direction to the HP cylinder. This

design also greatly reduces the axial thrust on the rotor.

Tandem three cylinder turbine is shown in Figure as under:



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Tandem Cross-Compounding Turbine

In cross compound turbines, the high-

pressure, exhaust passes over to

intermediate or low pressure casings which

are mounted on separate shafts. The two

shafts may drive separate loads, or may be

geared together to a single load.

In some larger overseas installations that

operate at 60 hertz (frequency) the use of

cross-compounding is some times employed.

Cross-compounding is where the HP and IP

cylinders are mounted on one shaft drivingone alternator while the LP cylinders are

mounted on a separate shaft driving another

alternator. This is done so as the LP cylinder

with its large diameter blading can be

operated at a greatly reduced speed thus

reducing the centrifugal force.

Tandem cross-compounding turbine is

shown in Figure:Prepared byMohammad Shoeb SiddiquiSenior Shift Supervisor


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T d f li d bi i h fl


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Tandem four cylinder turbine with reverse flow

The final turbine arrangement that is becoming increasingly popular is

the “Tandem four cylinder turbine with reverse flow HP cylinder, double

flow IP and twin double flow LP cylinders”. This arrangement is shownin Figure:



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04. Number of Stages

- Single stage

- Multi-stage



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i l bi


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In an impulse turbine,

the stage is a set of

moving blades behind

the nozzle. In a

reaction turbine, each

row of blades is calleda "stage." A single

Curtis stage may

consist of two or more

rows of moving blades.


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5. Exhaust Conditions

- Condensing

- Extraction

- Back-pressure



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By steam supply and exhaust conditions:

Condensing

Extraction, (Automatic or controlled )

Non-condensing (back pressure),

Mixed pressure (where there are two or more

steam sources at different pressures), Reheat (where steam is extracted at an

intermediate stage, reheated in the boiler, and re-admitted at a lower turbine stage).



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Condensing


The condensing turbine processesresult in maximum power and electrical

generation efficiency from the steam

supply and boiler fuel. The power output

of condensing turbines is sensitive to

ambient conditions.

The cooling water condenses the steam

turbine exhaust steam in the condensercreating the condenser vacuum. As a

small amount of air leaks into the

system when it is below atmospheric

pressure, a relatively small compressor

(Vacuum pump) or Air Ejector System

removes non-condensable gases from

the condenser.


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Extraction


In an extraction turbine, steam is withdrawn fromone or more stages, at one or more

pressures, for heating, plant process, or feed

water heater needs. They are often called"bleeder turbines.“The steam extraction pressure may or may notbe automatically regulated. Regulated extraction

permits more steam to flow through the turbine to

generate additional electricity during periods oflow thermal demand by the CHP system. In utility

type steam turbines, there may be several

extraction points, each at a different pressurecorresponding to a different temperature. The

facility’s specific needs for steam and power over

time determine the extent to which steam in anextraction turbine is extracted for use in the

process.


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Back-pressure


Figure shows the non-

condensing turbine (also

referred to as a back-

pressure turbine) exhausts its

entire flow of steam to theindustrial process or facility

steam mains at conditions

close to the process heat

requirements.


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4. Rotational

Speed- Regular- Low-speed

- High-speed

5. Inlet steampressure

- High pressure(p>6,5MPa)

- Intermediatepressure(2,5MPa


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8 Application


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8. Application

- Power station- Industrial- Transport



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In actual practice, not all of the energy in the


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p , gysteam is converted to useful work. Lossescommon to all turbines are described

below:

Loss of working substance. Loss of steamalong the shaft through the shaft glands wherethe shaft penetrates the casing.

Work loss. Loss due to mechanical frictionbetween moving parts.

Throttling loss. Wherever there is a reductionin steam pressure without a corresponding

production of work, such as in a throttle valve.



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Leaving loss. The kinetic energy of the steam leavingthe last stage blading This leaving loss can be


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the last stage blading. This leaving loss can beminimized by lightly loading the last stage blading by

increasing the annular exhaust area of the turbine. Thisis often optimized through economic studies.

Windage loss. This is caused by fluid friction as theturbine wheel and blades rotate through thesurrounding steam.

Friction loss as the steam passes through nozzles andblading.

Diaphragm packing loss as the steam passes from onestage to another through the diaphragm packing.

Tip leakage loss in reaction turbines as steam passes

over the tips of the blades without doing any useful work.Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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Rankine cycle with superheat


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Rankine cycle with superheatProcess 1-2: The working fluid is

pumped from low to high pressure.Process 2-3: The high pressure liquidenters a boiler where it is heated atconstant pressure by an external heatsource to become a dry saturated vapor.Process 3-3': The vapour is superheated.

Process 3-4 and 3'-4': The dry saturatedvapor expands through a turbine,generating power. This decreases thetemperature and pressure of the vapor,and some condensation may occur.Process 4-1: The wet vapor then enters a

condenser where it is condensed at aconstant pressure to become a saturatedliquid.



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Foundation IV (Intercept Valve)


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Rotor or Shaft

Cylinder or Casing

Blades

Diaphragm

Steam Chest

Coupling

Bearings

Labyrinth Seal

Front Pedestal

TSI

D

-EHC (Governor)

MSV (Main Steam Stop Valve)

CV(Control Valve)

IV (Intercept Valve)

CRV (Combined Reheat Valve)

Turbine Turning Gear

Turbine Bypass & Drains

Atmospheric ReliefDiaphragm (Rupture Disk)

Lube Oil System EHC Oil System

Gland Steam System

Condenser

Steam Jet Ejector

Vacuum BreakerPrepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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F (B ) S t th t t t d


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Frame (Base): Supports the stator, rotor and

governor pedestal.

Shell: Consists cylinder, casing, nozzles, steamchest & bearing.

Rotor: Consists of low, intermediate, and high

pressure stage blades, and possible stub shaft (s)

for governor pedestal components, thrustbearing, journal bearings, turning gear & mainlube oil system.

Governor Pedestal: Consists of the EHC oilsystem, turbine speed governor, and protective

devicesPrepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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An multistage steam turbines are

manufactured with solid forgedrotor construction. Rotors areprecisely machined from solid alloysteel forgings. An integrally forgedrotor provides increased reliabilityparticularly for high speedapplications.

The complete rotor assembly isdynamically balanced at operatingspeed and over speed tested in avacuum bunker to ensure safety inoperation. High speed balancingcan also reduce residual stresses

and the effects of blade seating.Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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The casings of turbine cylinders are

of simple construction to minimize any

distortion due to temperature changes.

They are constructed in two halves (top and

bottom) along a horizontal joint so that the

cylinder is easily opened for inspection andmaintenance. With the top cylinder casing

removed the rotor can also be easily

withdrawn with out interfering with the

alignment of the bearings.


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Most turbines constructed today either have a


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Most turbines constructed today either have a

double or partial double casing on the high pressure(HP) and intermediate pressure (IP) cylinders. This

arrangement subjects the outer casing joint

flanges, bolts and outer casing glands to lower

steam condition. This also makes it possible for

reverse flow within the cylinder and greatly reducesfabrication thickness as pressure within the cylinder

is distributed across two casings instead of one. This

reduced wall thickness also enables the cylinder to

respond more rapidly to changes in steam

temperature due to the reduced thermal mass.


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Th hi h d f th t bi i


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The high-pressure end of the turbine is

supported by the steam end bearing housing which is flexibly mounted to allow for axialexpansion caused by temperature changes.The exhaust casing is centerline supported onpedestals that maintain perfect unit alignment

while permitting lateral expansion. Covers onboth the steam end and exhaust end bearinghousings and seal housings may be liftedindependently of the main casing to provideready access to such items as the bearings,

control components and seals.Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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Atmosphere Relief Diaphragm


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HP Turbine Casing IP Turbine Casing

LP Turbine Casing

HP Turbine Casing

CV

CV



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One method of joining the top


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One method of joining the top

and bottom halves of thecylinder casing is by usingflanges with machined holes.Bolts or studs are insertion intothese machined holes to holdthe top and bottom halvestogether.

To prevent leakage from the joint between the top flange andthe bottom flange the joint facesare accurately machined. Atypical bolted flange joint isshown in Figure.



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Another method of joining


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Another method of joining

the top and bottom cylinderflanges is by clamps boltedradially around the outer ofthe cylinder. The outer facesof the flanges are made

wedge-shaped so that the

tighter the clamps are pulledthe greater the pressure onthe joint faces. This methodof joining top and bottomcasings is shown in Figure.



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Blade design is extremely important in attaining


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Blade design is extremely important in attaining

high turbine reliability and efficiency. A largeselection of efficient blade profiles have beendeveloped and proven by extensive field serviceallowing for optimal blade selection for allconditions of service. Blades are milled fromstainless steel within strict specifications for properstrength, damping and corrosion resistantproperties.

Disk profiles are designed to minimize centrifugalstresses, thermal gradient and blade loading at thedisk rims.



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Rotary Blades


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09HP Turbine Blades

07 IP Turbine Blades

05 LP Turbine Blades


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Partitions between pressure stages in a

t bi ' i ll d di h Th


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turbine's casing are called diaphragms. Theyhold the vane-shaped nozzles and sealsbetween the stages. Usually labyrinth-typeseals are used. One-half of the diaphragm isfitted into the top of the casing, the other halfinto the bottom.

Nozzle rings and diaphragms are specifically

designed and fabricated to handle thepressure, temperature and volume of the

steam, the size of the turbine and the required

pressure drop across the stage. The nozzles

used in the first stage nozzle ring are cut from

stainless steel. Steam passages are then

precision milled into these nozzle blocks

before they are welded together to form the

nozzle ring. Prepared by



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The nozzles in the intermediatepressure stages are formed fromprofiled stainless steel nozzle sectionsand inner and outer bands These are

Steam Turbine Components And Relative Equipments


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and inner and outer bands. These arethen welded to a circular center sectionand to an outer ring then precisionmachined.

The low-pressure diaphragms in

condensing turbines are made bycasting the stainless nozzle sectionsdirectly into high

-strength cast iron. This

design includes a moisture catchingprovision around the circumference which collects released moisture andremoves it from the steam passage.Additional features such as windageshields and inter

-stage drains are used

as required by stage conditions tominimize erosion. All diaphragms are

horizontally split for easy removal andalignment adjustment.

Mohammad Shoeb SiddiquiSenior Shift Supervisor


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Various root fixing shapes have been

developed for turbine blading to suit


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p g

both construction requirements andconditions under which turbines

operate. The most popular types of

blade root fixing available are:

Grooves

Straddle

Rivet


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Straddle construction

Straddle construction is where the

blade root fits over the machining on


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g

the outer periphery of the rotor wheelor disc. An example of straddle fir

-tree

blade root construction is shown in

Figure A. while the disc peripheral

machining is shown in Figure B.

Once again with this type ofconstruction the blade roots are

installed through the closing blade

window slid around the circumference

of the disc into position, then the lastblade inserted is doweled in the closing

blade window location.


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Rivet construction

Rivet construction is where the blade root

either inserts into a groove or straddles the

disc and all blades are doweled into position.


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Peripheral blade fixing

On larger blading where the blade length is

relatively long a system of lacing wire or

shroud rings are installed to give the blading

additional support and reduce

vibration. The lacing wire is installed a small

distance from the outer ends of the blades while the shoud rings are fitted to tangs on

the outer edges of the blades and secured by

peening the tangs. A section of blading

showing the installation of the lacing wire is

shown in Figure A while a section of blading

showing shroud ring installation is shown inFigure B.


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Steam chest: The steamchest, located on the



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forward, upper half of theHP turbine casing, housesthe throttle valve assembly.This is the area of theturbine where main steamfirst enters the main engine.The throttle valve assemblyregulates the amount ofsteam entering the turbine.After passing through thethrottle valve, steam entersthe nozzle block.



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With multi-cylinder turbines it is necessary to have

some method of connecting individual cylinder rotors.



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It is also a requirement to connect the turbine to thealternator rotor. To achieve these connections we

use a device known as a coupling. These couplings

must be capable of transmitting heavy loads and in

some turbines are required to accommodate for axial

expansion and contraction.

The types of couplings generally employed in power

plants are:

Flexible coupling

Solid shaft couplingPrepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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Flexible couplings

Where axial shaft movement is required a flexible



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coupling is employed and these are either:

1. Sliding claw (or tooth)

2. Flexible connection (between the two flanges)

With both of the above flexible couplings it is

necessary to have a separate thrust bearing for

each shaft to maintain the same relative position

between rotor and cylinder casing.



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Flexible connection coupling

Flexible connections such as the bibby coupling are constructed in twohalves. Each half is shrunk onto their

respective shaft and secured with keys



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respective shaft and secured with keysor driven pins. The halves aremachined with groves parallel ornearly parallel to that of the alignmentof the shaft. Flexible spring steel gridsare inserted into these machinedgroves and held in place with an outercover. This type of coupling is effective

in allowing axial expansion andcontraction along with the ability totolerate minor misalignment. A bibby coupling is shown in Figure.

The flexible couplings just mentionedare by no means the only flexiblecouplings available but they are thepreferred choice for high load

applications.Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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Solid shaft coupling

When shaft movement is notrequired it is usual to install a

solid type coupling Two flanges



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solid type coupling. Two flangesare installed onto theirrespective shafts and then thetwo flanges are bolted togetherto form a solid joint as shown inFigure A.

Often teeth are machined on theouter rim of these couplings andused as a point for barring theturbine shaft. (more aboutbarring the turbine later). FigureB shows a solid shaft coupling

with a barring gear fitted Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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Turbine Bearings

Journal Bearing:

The turbine rotors are

supported by two journalbearings Both the No 1


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supported by two journalbearings. Both the No.1and No.2 bearings areof a double

-tilting pad

type. The bearing metalis divided into six pads

which are self-aligned. Acenter adjustment of

these bearings caneasily be made withshimmed pads.



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A labyrinth seal is a typeof mechanical seal that

provides a tortuous path tohelp prevent leakage An



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provides a tortuous path tohelp prevent leakage. Anexample of such a seal issometimes found withinan axle's bearing to helpprevent the leakage of the oil

lubricating the bearing.A labyrinth seal may becomposed ofmany grooves that presstightly inside another axle, orinside a hole, so that the fluid

has to pass through a longand difficult path to escape. Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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Labyrinth seals are utilized asend gland seals and also inter

-

stage seals. Stationary labyrinth

seals are standard for all



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seals are standard for allmultistage turbines and groovesare machined on the rotating partto improve the sealing effect. Theleakage steam from the outerglands is generally condensed by

the gland condenser. Someleakage steam from theintermediate section of the steamend gland seals can be

withdrawn and utilized by re-

injecting it into the low-pressure

stage or low-

pressure steamline. Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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Toothed- wheel for speed sensors

The turbine rotating speed issensed by the magnetic pickups

FRONT STANDARD & TSISteam Turbine Components And Relative Equipments


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g psensed by the magnetic pickupsfaced to the toothed

- wheel (96

teeth) installed on the control rotor.The pulse signal is produced wheneach tooth passes the pickups. Thefrequency signals from two (2)

pickups are converted into digitalvalue proportional to the turbinespeed through F/D (Frequency toDigital) converters.

Other three (3) sensors are located

around toothed- wheel. These

sensors are used for trip detector. Prepared by



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The electromagnetic pickup use forspeed detector is fixed facing thetooth face of the speed detectinggear connected directly to the rotor

end of

the turbine. (Inside of

frontstandard) The turbine speed can be

FRONT STANDARD & TSISteam Turbine Components And Relative Equipments


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) pdetected as the sine wave frequencysignal in proportion to the turbinespeed. This frequency signal isconverted to an digital signal bymeans of the F/D converter tobecome a feedback signal to the

speed control circuit.Over speed detector also makefrequency signal in proportion to theturbine speed. They face to tooth

-

wheel on control rotor. Pickup isused eddy current type. Clearancebetween sensor face and tooth faceis different from electromagnetic

pickup type.Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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Principles Of Governing

During operation of a Turbine Generator Unit

STEAM TURBINE SPEED CONTROL


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During operation of a Turbine-Generator Unit

the Load carried by the Generator may vary

over time. In order to respond to changing

System Load demands the amount of steam

directed to the Turbine must be varied inproportion to each demand.

The function of a governor is to provide rapid

automatic response to load variations.


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STEAM TURBINE SPEED CONTROL


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System Features

Application:

D-EHC system can be applied to control, protection and monitoring of steamturbines for various type of power plants including conventional fossil-fired

power plants, combined cycle plants, co-generation plants, and atomic powerplants.



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Powerful and reliable controllers:

High-speed control with state-of-the-art microprocessor based control system

Distributed and hierarchical architecture consists of;System controller, Master controller, Programmable logic device,

Valve interface

Normal Operation:

During Normal Operation, the main stop valves, intermediate stop valves

and intercept valves are wide open. Operation of the T-G is under the control

of the Electro-Hydraulic Control (EHC) System. The EHC System iscomprised of three basic subsystems: the speed control unit, the load control

unit, and the flow control unit. The normal function of the EHC System is togenerate the position signals for the four main stop valves, four main control

valves, and intermediate stop valves and intercept valves. Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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The main stop valve is locatedin the main steam piping

between the boiler and theoutlet piping to turbine controlvalve chest in turbine casing


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valve chest in turbine casing.The main stop valve has oneinlet and two identical outletpipe connections. Outlet pipesare welded directory.

The primary function of themain stop valves is to quicklyshut off the steam flow to theturbine under emergencyconditions such as failure of thecontrol valves to close on lossof load.



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Two combined reheatvalves are provided, onein each hot reheat line.Supplying reheat steam tothe turbine. As the nameimplies The combined


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implies. The combinedvalve is actually two valve.The intercept valve andthe reheat stop

valve, incorporated in onevalve casing. Althoughthey utilize a commonvalve casing, these valvesprovide entirely different

functions. Prepared byMohammadShoeb SiddiquiSenior Shift Supervisor


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The motor driven turning gear

is mounted on the turbine

bearing cap, adjacent to the

turbine-generator coupling soas to mesh with a bull gear

Turning Gear

Driven Motor

Turning Gear

Driven Chain


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(spacer disk gear type). Which

is bolted between the turbine-

generator coupling faces.

The primary function of the

turning gear is to rotate theturbine

-generator shaft slowly

and continuously during

shutdown periods when rotor

temperature changes occur.

Turning Gear

Turning Gear Oil Supply



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When the turbine is shutdown, cooling of its inner

elements is continues for many hours. If the rotor

is allowed to remain stationary during this coolingperiod, distortion begins almost immediately. This


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p g y

distortion is caused by the flow of hot vapors to

the upper part of the turbine casing, resulting in

the upper half of the turbine being at a higher

temperature than the lower half. The parts do notreturn to their normal position until the turbine has

cooled to the point where both the upper and

lower halves are at approximately the same

temperature.


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Water induction can happen at any time;however the most common situations are

during transients such as start up, shut

down and load changes. In figure

illustrates the percentage of times variousevents contribute to water induction for aconventional steam cycle It is interesting


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conventional steam cycle. It is interesting

that only 18 percent of water induction

incidents occur when the unit is at load.

Turbine drains are necessary to avoidslugging nozzles and blades inside the

turbine with condensate on start-up; thiscan break these components from impact.

The blades were designed to handle

steam, not water.

Turbine casing drains remove thecondensate from the turbine casing during

warm-up, securing, maneuvering and other

low flow conditions. Prepared byMohammad Shoeb SiddiquiSenior Shift Supervisor


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The atmospheric relief diaphragm is a safety feature which protects the exhaust hood and condenseragainst excessive steam pressure in case thecondenser water for any reason is lost.

The device consists of hard rolled silver bearing



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The device consists of hard rolled silver bearingcopper sheet of sufficient area to pass full throttlesteam flow at a safe protective pressure. In normaloperation of the turbine with proper vacuum

conditions, the diaphragm is dished inward againstthe supporting grid by atmospheric pressure shouldthe vacuum conditions fail for any reason and theinternal exhaust hood pressure raise to approximately5 psig, it would force the diaphragm outward againstthe cutting knife. The diaphragm would be cut free asa disk relieving the exhaust pressure to atmosphere.



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FunctionThe function of lubrication is to interpose a film of

lubricant such as grease or oil between the movingsurfaces in a bearing.



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g

Lubrication reduces friction, minimizes

wear, provides cooling and excludes water and

contaminants from bearing components. The

protection of rotating heavy machinery depends

greatly on the effective operation and supervision of

lubricating oil systems and bearings.



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Establishment of Oil Film

Oil lubricated bearings rely on the physical separation

of the two bearing surfaces by a thin film or wedge of

oil. In order to establish and maintain this oil film thefollowing conditions must be established.


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1) There must be relative motion between the two beari

ng surfaces to build up sufficient pressure within the oil

to prevent the film breaking down.

2) There must be an uninterrupted supplyof oil available to the bearing.

3) The bearing surfaces must not be parallel and need

a narrow angle between them. This is to enable the oil

to be shaped into a thin wedge tapering off in the

direction of the motion


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Oil Film Dynamics

1). With the shaft at rest the journal lies in the

bottom of the bearing. The weight of the shaft

tends to squeeze the oil out of the bearing so

that metal to metal contact occurs


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that metal to metal contact occurs.

2). As the shaft commences to rotate the first

action of the journal is to climb up the bearing

wall until it begins to slip and some metal to

metal contact occurs.

3) As the shaft continues to increase in speed

the oil is dragged around by virtue of viscosity

until it forms a thin oil wedge. it's


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The purpose of the

gland steam system

is to reduce steam

leakage to aminimum and toprevent air ingress.


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p gOr

Function of the gland

sealing system falls

into two categories:• Seal the turbine

glands under all

operating conditions

• Extract leak-off steam

from the turbine

glands.


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Steam leakage leads to the requirement for

increased make up; this increases the load on

the feed and boiler water treatment chemicalsand to a deterioration of the working

environment surrounding the power plant


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environment surrounding the power plant.

Air ingress leads to a loss of vacuum and hence

reduction in plant efficiency, and causesproblems of thermal stressing around the gland

as well as increases oxygen content of the

exhaust steam.


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Gland Steam CondenserThe gland steam condenser is cooled by the

condensate extracted from the main condenser and soacting as a feed heater. The gland steam often shares

its condenser with the air ejector reducing the cost of


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j g

having two units.

A fan is fitted to induce a flow through the system

without incurring a negative pressure in the finalpocket as this would allow the ingress of air. This is

ensured by the fitting on valves to the exhaust line

from the glands so enabling the back pressure to be

set.


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A surface condenser is a

commonly used term for a water-

cooled shell and tube heat

exchanger installed on the

exhaust steam from a steam

turbine in thermal powerstations. These condensers are heat

exchangers which convert steam


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from its gaseous to its liquid state at

a pressure below atmospheric

pressure. Where cooling water is in

short supply, an air-cooled

condenser is often used. An air-

cooled condenser is however

significantly more expensive and

cannot achieve as low a steam

turbine exhaust pressure as a water-

cooled surface condenser.


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The purpose of a Vacuum Breaker Valve is to quickly

allow air into the vacuum space of the condenser and

low pressure turbine exhaust hood. The vacuumbreaker valve is usually located on the steam turbine

or the condenser shell/transition.

A b k l i i ll bl b


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A vacuum breaker valve is typically operable by a

controller responsive to losses of load on the steam

turbine.Once opened, the vacuum breaker valve will allow air

into the steam space to quickly reduce the existing

vacuum and hence reduce the acceleration of the

steam turbine upon loss of load by the generator.


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(1) Emergency trip pushbutton in control room

(2) Boiler Trip, Turbine trip

(3) Low condenser vacuum

(4) Low lube oil pressure

(5) LP turbine exhaust hood high temperature

(6) Thrust bearing wear

(7) Emergency trip at front standard


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( ) g y p

(8) Low hydraulic fluid pressure

(9) Loss of EHC

(10) Excessive turbine shaft vibration(11) Loss of two speed signals

- either Normal Speed Control or

Emergency Over speed Trip

(12) Over Speed Trip 1

(13) Over Speed Trip 2



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A brief Presentation to Steam turbine

Documents

Transcript of A brief Presentation to Steam turbine