final mannual ppe

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MERCHANT POLYTECHNIC, BASNA

OBJECTIVE: TO STUDY ABOUT ELEMENT OF POWER PANTS

LEARNIG:

TYPE OF POWER PLANT BASIC ELEMENTS OF POWER PLANTS

INTRODUCTION :

Basically power plant is an energy transformation unit. In general the

meanings of the words powerplant & power station are same. But logicallythere is big difference.This differencecan easilyund erstood by definitions.

a) Power pla nt :

Powerplant is an arrangement of various appratus in which continuously

electrical/mechanical power is gained in bulk as output by utilisation of

givenform of energy as inputand distributedto variousconsumers.

b) PowerStation:

Powerstation is complex unit where numb ers ofpower plants are usually

located to generate mechanical and/or electrical power in

bulk,continuously and from where it is transmitted to various consumers.

So, the object in design and operation of powerplant (station) is to

generate electricalpowersafely, efficientlyand economically.

TYPES OF POWERPLANTS:

1. Accordingto type of Energy Sources:

a) ThermalPowerPlant

I. Steam PowerPlant

II. D iesel PowerPlant

III. Gas TurbinePowerPlant

b ) Hydel PowerPlant

c) Nuclear Power Plant

d) SolarPowerPlant

e) Wind energy Power Plant

f) Tidal Power Plant

g) GeothermalPowerPlant

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STUDY OF BASIC ELEMENTS OF VARIOUS POWER PLANTS

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2. Accordingto Load:

a) Ba se LoadPowerPlant

b) PeakLoadPowerPlant

3. Accordingto types of Utilization:

a) Standby Powerplant.

b) Emergency PowerPlant.

c) Total Energy PowerPlant.

d) Nursery PowerPlant.

e) Pum p Storage PowerPlant.

f) Mobile Power Plant

4. Accordingto capacityand Ownership:

a) Central Power Plant

b) CaptivePowerPlant

5. Accordingto location:

a) Peat Head Power Plant

b) Loadcenter PowerPlant

BASICELEMENTS OF VARIOUSPOWERPLANTS:

I. Basic elements of Steam PowerPlant:

a) Steam Generator

b) St eam Turbine

c) St eam Condenser

d) Feed Pump

e) Alternator(Generator)

II. Basic elements of Diesel PowerPlant:

a) Diesel Engine

b) Alternator(Generator)

III . Basicelements of Gas TurbinePowerPlant:

a) Compressor

b) Combustion Chamber

c) Gas Turbine

d) Alternator(Generator)

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IV. Basicelements ofNuclearPowerPlant:

a) Atomic Reactor

b) St eam Turbine

c) St eam Condenser

d) Feedpumpe) Alternator(Generator)

Here some of thebasicelements of steam powerplantisexplainedin detail:

Steam Generator(Boiler):

A thermal power plant using steam as a working substance works

basically on the Rankine cycle. Steam of desired quality and quantity is

generated in the boiler(Steam generator).The Steam generator is a complex

combination of economiser, evaporator, superheater, reheater and air

preheater. In add ition, it has various auxiliaries like furnaces, stokers,pulverising

systems,burners; fans, stacks and ash handling equipements. Mordern

powerplantsteam generators are essentially of two basictypes.

1. Sub CriticalSteam Generator:

Sub Critical steam generator operates below 225 bar,usually about130 bar to 180bar.

2. SuperCriticalSteam Generator:

Supercriticalsteam generator operates above 225bar.

La Moun t, Benson ,Loeffler,Schmidt-Hartmann ,Velox,sterlling,BHEL

are some of high pressure steam generator used in mordern steam

powerplants.

Steam Turbine:

A Steam turbine is a prime mover which continuously converts the energy

of high pressure,high temp erature steam supplied by a steam generator,into

shaft wor k and the low temp erature steam exhausted to a condenser.Thia

energy conversionessentiallyoccurs in two steps.

1) The high pressure,high temp erature steam first expands in nozzles

and comes out at a hogh velocity.

2) The high velocity jets of steam coming out of nozzle,imping on the

blades mounted on a whee l,get deflected by an angle and suffer a

loss of momentum,which is absorbed by the rotating whee l inproducingtorque.

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Thereare mainly two types of turbines:

1. Impulseturbine:

In this type of turbine,all pressure drop of steam occure in the

nozzles and there is no pressure drop as steam flows through the

passa ge between two blades.

2. ReactionTurbine:

In reaction turbinepressure drop occures both in the nozzles or the

fixed row of blades,aswell as in the movingrow ofblades.

Steam Condenser:

The exhuast steam from turbine is condensed at constant pressure in a

condenser to recover the high quality of feed water for reuse in the cycle.There

are two objects of usinga condenserin a steam plant.

1) To reduce the turbine exhaust pressure so as to increase the

specific output of turbine.

2) To recoverhigh quality feed water in the form of condensate and

feed itback to the steam generator withoutany furth ertreatment.

Thereare two broad classes of condenser:

1. DirectContact Type Condenser (Jet condenser):

Where the condensate and cooling water directly mix and comes

out as a singlestream.

2. Su rface Condenser:

Which are indirect heat exchanger,where the two fluids do not

come in the direct contact and the heat released by the

condensation of steam is transfered through the walls of the tubes

in to the cooling water continouslycirculating insidethem.

Feed P ump:

Feed pump s are used to supply feed wa ter to the steam generator at

required rate and pressure.For small capacity,low pressure steam generator

reciprocating pum ps a re utilized as feed pum p and for high capacity,high

pressure steam gen erators generally multistage centrifugalpumps are utilized

as feedpumps.

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Alternator(Generator):

The alternator (El ectric generator) is the most importantpart of

the powerplant as all other un

its in the power p

lant are

i

nstalled for the

purpose of driving alternator.

The principle of electromagnetic induction is used for the generation of electric

power with the help of generator.All modern typed of alternating current

generators are essentially of a fixed stator and revolving rotor.The stator core

carries three phase winding in which alternating emf is induced when the shaft

of the rotor is revolved with the help of the prime mover.The rotor is carrying

field magnet and coils which provide the magnetic flux of the machine.The field

is excited by a direct current brough t in to the field circuit by means of two

rotorslip-rings and set ofbrushes ridingon them.

The magnitude of the induced voltage in the single phase of the statorwinding

depends upon the strengt h of the magnatic field,the speed of rotation and

numb erof statorcoils in series.

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OBJECTIVE: STUDY OF VARIOUS CIRCUITS OF MORDERN THERMAL

POWER PLANT

LEARNING:

COAL AND ASH HANDLING CIRCUIT

AIR AND GAS CIRCUIT

FEED WATER AND STEAM CIRCUIT

CONDENSER COOLING WATER CIRCUIT

STEAM TURBINE LUBRICATION CIRCUIT

INTRODUCTION:

A thermal powerplant, using steam as working medium, works

basicallyon Rankine cycle. Steamis generated in a boiler & expanded In the a

boiler & expanded in the prime mover& then condensed in condenser and feed

back in to the boiler. However ,inpractice, there are num erous modificationsand

improvements in this cyc le with the aim of achieving safety, economy and

higher

efficiency.

Forachieving easiness in operation and better control over various

processes, th e whole sys tem of modern power station is divided in following

maincircuits,

Coal and ash handlingcircuit. Air and gas circuit. Feed wa ter and steam circuit. Condenser cooling water circuit. Steamturbine lubricationcircuit.

Coal and ash handli ng circuit:

Coal in various forms is used as main fuel for steam powerstation,so

careful consideration should be given to coal and ash handling circuit

while designingpowerstation.

A hug e quantity of of coa

l (about 50% to 60% of the tota

l operat

ing

cost is invested in fuel purchasing) is required for large power station

and huge quantity of ash is produced also.

Coal handling and ash disposal sys tems are designedaccording to types

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STUDY OF VARIOUS CIRCUITS OF MORDERN THERMAL POWER

PLANT

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& quantity of coalconsumptionand ash production.

In coal handling system generally unloading,primary preparation,metal

separation,transfer,final preparation,weighing and other required

functionsare done.

Coal recevei

ng: Fi

rst coa

l r

ecei

ved by

su

itab

le tran

sportat

i

onsystem(like sea,river,rail or road) is un loaded by appopriate mechanism like

tower crane,grab buckets,car shaker ,rotarycar dampers,wagon

tripplers,selfunloadingboats etc.

Storage: Then coal is stored in coal yard either in open heaps or in

bunkers.generally 10% of annu al coal consumption quantity is stored in

coal yardfor achiving continuous coal availability to boiler furnaces and

economy.

Apporoximately25% land ofpowerstationis utilisedforcoalyard.

Figure : COAL & ASH HANDLINGSYSTEM

Crushing:Before feeding coal to the combustion chamber some

processes like primary crushing,metalremoval,drying,weighing,pulverizing and screening are done in suitable

equipements.

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Pulverising: Pulverising is the process of making powder of coal of

required size to chieve rapid combustion rate and easiness in supp lying

coalto theboilerfurnace.

Screening: It is done to pass only the required size of coal to the

combustion chamb er the larger size particles is recycled forpulverising

again.

Combustion: The pulverized coal is fed to the boiler furnace with the

help of primary air flow,where combustion of coal takes place.Thet will

giveash as byproduct.

Ash collection & disposal : Heavy ash is collected in the ash pit and is

disposed off to suitable site by mechanical or hydraulic system. Where

as fly ash which travels with the flue gases,is coolected by suitable

method and disposed off with the bottom ash.If the power station is

located near sea ao river,the ash is dispossed off in the water.But in the

land stations ash is usually dispossed off by auction of the contractorsfor use in building construction, road construction, industrial

process ing, etc.

AIRAND GAS CIRCUIT:

Necess ity of Air: Air is necessa ry to appritiate and complete combustion

of any type of fuel.In coal fired sys tem air also works as lifting agent of

pulverizedcoaland carries itto the furnace frompulverizer.

Figure : Air and gas circuit

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Supply of Air: Airsupp lied to the combustion chamb er of the boiler either

through F.D or I.D. fan orby usingboth.These fans are used to increase

the pressure of airto achieveproperdraft.This forced air is admittedin to

air preheater,where it is heated with the help of exhuast gases.This

heated air is then sent to the boilerfurnace forcombustion of fuel. Gas path: The gases, generated du e to combustion, carryheat withit. This

heat energy is absorbed in various parts like wa ter walls, evaporating

coils,drum,super heater, reheater, economiser and air preheater,

when these gases pass es f rom those parts. Then the hot gases go to the

dust collector,where flying ash is collected by suitable method and finally

they

are dischargedto the atmosphereby chimneyat sufficientheight.

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FEED WATERAND STEAM CIRCUIT:

Initially for the first cyc le the total circuit is filled with the wa ter after

proper wa ter treatment and for next incoming cycles the required quantity

of make up wa ter is added in to feed wa ter and steam circuit to

componsate the working medium loss.

Figure:Feed water and steam circuit steam generated in the steam generator with the help of combustion of

fuel is admitted to super heater to superheat the steam up to required

temperature.

Then this superheated s team is introduced in to turbine where it is

expanded up to certainpressure and then further steam is carried out and

it is then admitted in to reheater to reheat up to certain temerature withthe help of flue gases.Then tiis reheated steam is further steam is

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expanded in to turbine up to condenserpressure.Then the exhaust steam

from the turbine is condensed in to the condenser and then condensate

formed is stored in to the hot well.

To avoiderosion of turbinebladesduringexpansion of steam in to turbine

stages some amount of steam is carried out from the turbine as bleedsteam.Here in this figure steam is bleeded in to two steps from two

different stages of the turbine.One is higher pressure stage and second is

lowerpressure stage.

The accumulated condensate of hot well is pump ed by condensate pump

in to the low pressure feed wa ter heater ,where condensate and bleed

steam from lower pressure stage are mixed to recover heat energy from

bleedsteam.

Then this mixture of feed water is mixed withbleed steam from high

pressure stage.Then this feed water is carried to the economiser,where

temerature of the wa ter is increased with the help of heat energy of flue

gases.After recovering heat energy from the fule gases in to economiser

the heated feed wa ter enters back in to the steam generator.

CONDENSERCOOLINGWATERCIRCUIT:

Steam coming out from steam turbine is condensed in condenserwith thehelp of cooling water.The latent heat of the steam is absorbed by

condenser cooling water and thus the temperature of cooling water

increases.

Figure:Condensercoo ling wa ter circuit

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To reuse this wa teragain and again for coolingpurp ose,the cooling water

is coo led down with the help of atmospheric air in to cooling tower,coo ling

pond, spray pond orcooling canal.

Figure shows conden ser cooling water circuit.Hot water coming out from

condenser is taken in to cooling tower and coo led with the atmospheric

airand then collectedin to water pond of cooling tower. The circulatingpump supp lies this coo ler wa ter back to the condenser.To

condensa te evaporation loss of water,required quantity of make up water

is added to the circuit in the basin of cooling tower after doing required

wa tertreatment. STEAM TURBINELUBRICATION CIRCUIT:

Steam turbine is important comp onent of steam plants running

continuously at high speed.To reduce friction of its rubbing compenents

like main bearing,thrust bearing and gearbox,lubrication sys tem is

provided.

Figure:Steam turbine lubrication circuit

Due to continuous hogh speed,high temerature and steam,rapid oxidation

and water mixing with lubrication oil are mainproblems of the lubrication

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sys tem.S o to prevent oxidation proper anti-oxidant agent is added to the

lubrication oil,and to prevent emulsion special construction of lubrication

sys tem is adopted,whichprevent mixing of steam and lubricatingoil.

Figure shows simple steam turbine lubrication circuit.Pump-1 pumps

lubricating oil from oil sump (tank) to the coo ler,where oil is coo led down

to maintain proper lubricating properties and then this oil is pumped byturbinedrivenpum p to the distributor.

Distributor supplies lubricating oil at regulated pressure in sufficient

qaun tity to various rubb ing comp onenets like bearing,control relay and

gearbox. Lubricating oil,coming out from those

components,carries impurities and heat energy.So this oil is purified

in oil cleaner and then supp liedback to the oil tank.

During starting,stopp ing and abnormal conditions,auxiliary lubricating

pum p supplies lubricating oil to the distributor.Vapour extractor is

provided in to lubricating oil tank to remove oil vapour and gases formed

due to dehydration of lubricatingoil.

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OBJECTIVE: TO STUDY OF HIGH PRESSURE BOILERS.

LEARNING: TYPES OF BOILERS

La-Mont Boiler

Benson Boiler

Leflore Boiler

Schmidt-Harman Boiler

INTRODUCTION:

To increase the efficiency of thermal (steam) powerplant and to reduce the

cost of electricityproduction utilization of highpressure, high temperature

steam is necessa ry due to this reason, demand forhigh pressure boilers has

increased.

The high pressure and heavy dut y boilers are those s team generators, which

produce steam in the range of 30 to 650 tones per hour with a pressure

range from 60 to Supercrtitical pressure and maximum steam temperatureof about 540 C.

SPEICIALFEATURES OF HIGHPRE SSURE BOILERS:

High pressure boilers have some special features over low and medium

pressure boilers like forced circulation, small tubes, lack of drums,

pressurizedcombustion,

Multiple tub e circuits, comp actness and low weight . Some of these features

are discussed below:

Methodof wa ter circulation :

In high pressure boilers the water circulation is maintained by forced

circulation with the help of pump . The forced circulation of wa ter inside the

tubes causes increased rate of heat transfer. It also helps to reduce tube

diameter and hence provision of more numb er of water tubes in given space

is poss ible. It also helps to reduce scale formation inside the tubes due to

higherwa tervelocity.

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STUDY OF HIGH PRESSURE BOILERS

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Increased area ofHeating:

The heat transfer area in high pressure boilers considerably increases due to

adoption of more numb er of tub es of smaller diameter and due to

costruction of water walls .

Imp roved Heating Method:

1. High steam generation rate can be poss ible due to high steam generating

pressure (above critical pressure ). This is poss iblebecause no latentheat is needed

to Evaporatethe water.

2. High steam generating rate can be poss ible by direct mixing of

superheated steam Tofeed wa ter.

3. With the help of high gas and wa tervelocity high heat transfer rate

can be achieved.4. Due to adoption ofpulverizing firing sys tem high heat release can

beposs ible.

TYPES OF HIGHPRESSU RE BOILERS:

A wide variety of highpressure boilers are available. Some comm on high

pressureboilersare as under

(A) La-Mont Boiler(B) Benson Boiler

(C) LefloreBoiler

(D) Schmidt-HarmanBoiler

La-MontBoiler:

A forced circulation boiler was first introduced in 192 5 by La- Mont. Thearrangement Of water circulation and different components of La-Mont

boiler is shown in figure:

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The feed wa ter from hot-well is supp lied to a storing and separating drumthough the economizer. The most of the sensible heat is supp lied to the

feed water in economizer .A Centrifugalpump circulates the waterequal

to 8 to 10 timesthe weight of steam generated.

This water is circulated through the evaporator and the part of the waterevapor ated is Separated in the separator drum .the large quantity ofwa tercirculatedprevents the tub es frombeingoverheated. The steam, separated in the drum, is further pass ed through the superheater and finally supp liedto theprimemover.

This boilers has been built to generate 45 to 50 ton s of superheatedsteam at pressure of 12 0 atom. And at a temp eratures of 500 C

BensonBoilers:

Benson in 1922 argued that if the boiler pressure was raised to

critical pressure (225 Atm), the steam and wa ter have the same density and

there for the dangerofbubblecan be eliminated.

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The arrangement ofbenson boilercomp onents is shown in figure.

The wa ter after pass ing through economizer enters into the radiant

evaporator , where majority of the Wa ter is converted into steam .the

remaining water is evapor ated in the final (convective) evapor ated by

absorbingthe heat of hot gases by convection. the saturated highpressure

Steam at 225 atm. Is further pass es through the super heater and goes to

primemover in superheated condition.

Major difficulty of salt deposition is experienced in the convictive

evaporators, where all remaining wa ter converted into steam. To avoid this

difficulty, the boiler (convective Evaporator) is normally flashed out after

every 4000 working hours to remove the salt

The maximum workingpressure obtained in Benson boiler is 5000 atm. With

150 tons per hour s team generationcapacity.

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LoefflerBoiler:

The major difficulty experienced in La-Montboiler is the deposition of salt

and Sediment on the inner surface of the water tube s .this difficulty was

solved in Loeffer- boiler by preventing the flow of water in to the boiler

tubes.

In loefferboiler most of the steam is generated outside of the boiler tubes

from the feed wa ter usingpart of superheated steam coming out from the

boiler.The arrangement of the different comp onents and wa ter and

steam circulationare shown in figure.

The feed pum p draws the wa ter through economizer and delivers it into the

Evaporator drum . about 65% to of the steam coming out of sup er heater

is passed through the evapor ator drum is or der to evapor ate the feed

wa tercomingfrom economizer.

The steam circulating pump draws the saturated steam from the

evaporator drum and is pass ed through the radiant super heater and then

convective super heater about 35 % of the steam coming out from the

super heater is supplied to the H.P. turbine.

The steam comi

ngout from H.P. turbi

ne

ispass ed through re-heater

be

fore

supp lying to L.P. turbine. The nozzles which distributes the super heated

steam throug h out the wa terin to the eva porator drum are of special

designand avoidprimingand noise.

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Loefflerboiler with generating capacity of 100 tons per hour and operating

at 140 bar are alreadycomm iss ioned .

Schmidt HartmannBoiler:

The arrangement of the boiler comp onents is as per Fig. the operation of

theboiler is similarto an electrictransformer.

In the primary circuit the steam at 100 atm is produced from distilled

water . The generated steam is pass ed through a submerged

gheatingp coil which is located in an evapor ater drums of secondary

circuit. With heat transfer rate of 2500 Kcal/ sq.m hr.C Is generated in

the evapor ator drum of secondary circuit.

The steam produce in the evapor ator drum impure water is further

pass ed through the super heater and then supp lied to the prime mover.

The highpressure c ondensate forme d in the submerged heating coil is

circulated through a low pressure feed heater on its way to raise the

feed wa ter temp . to saturation temp. therefore, only latent heat is

supp liedin the evaporatordrum.

Natural circulation is used in the primary circuit and this is sufficient to

aff ect the desired rate of heat transfer and to overcome the thermo

siphon head of about 2m to 10m in normal circumstances, thereplenishment of distilled water in the primary circuit is not required as

every care is taken in design and construction to prevent the leakage

but as a safeguard against leakage . a pressure gauge a nd safety

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valveare fittedin the circuit.

OBJECTIVE: TO STUDY OF BOILER FURNACES

LEARNING:

CLASSIFICATION OF FURNACES

HAND FIRED FURNACE

STUDY OF BOILER FURNACES

SPREADER TYPRE TOKER FURNACESINGLE RETOER FURNACE

PULVERIZED FUEL FIRING FURNACE

CYCLONE FURNACE

FLUIDIZED BED FURNACE

INTRODUCTION:

At the heart of foss il-fueled power plant operation is the combustion

process. Through the combustion process, modern powe r plants burn fuel to

release the energy that generates steam energy that ultimately is transformed

in to electricity. So combustion or conversion of fuel in to useable energy

mu st be carefully controlled and managed. Only the heat released that is

successfully captured by the steam is useful for generating power. Hence the

ability of steam generator to successfully transfer energy from the fuel to

steam is driven by the combustionprocess.

Theoretically combustion can be defined as the rapid comical reaction of

oxygen with the combustible elements of a fuel practically from enginee ring

point of view combustion can be defined as the chemical un ion of the fuel

combustible and the oxygen of air controlled at a rate that products useful

heat energy.

Furnace provides closed space for combustion of fuel for controlled and

efficient combustion of fuel within a f urnace following basic criteria must be

satisfied:

1. Adequatequantity of air(oxygen) supp liedto the fuel.

2. Oxygen and fuel thoroughlymixed.

3. Fuel airmixturemaintainedat or above the ignitiontemperature.

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STUDY OF BOILER FURNACES

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4. Furnace volume large enough to give the mixture time for complete

combustion.

5. Continuousreliable ignition.

6. Satisfactoryhighflametemperature.

7. Minimumpressure loss.

8. Proper ash collectionand disposal.

Considering above criteria furnace should provide following facilities for

controllingefficientcombustion of fuel.

1. It providesfacility ofbu rners for proper mixing of airand fuel.

2. It is capable for generating flue gases at required temp erature at

requiredrate.

3. It prevents heat losses to surroundings by wa terwalls, refractory layerand radiantsuper heater orevaporator.

4. Provided properbuffles to divert flue gases in proper manner with

minimumpressure loss.

5. Give qui ck response by adjusting combustion rate against change of

load.

Hence furnace designdepends on parameters like,

. Types and quantity of fuel.

Types of firing.

Steam qualityand generationrate.

Gr ate area.

Flame length.

Ashfusiontemperature.

Temperatureand flow rate of air.

Flue gases path and types ofbuffles.

Generally in modern s team (Thermal) powerplants inner layer of furnace

wall is provided with a layer of refractory material like fire clay, silica, alumina

kreoline,etc. To prevent heat loss to the surrounding by reflecting back the

radiant heat energy inside the refractory layer wa ter (working medium).Tubes

are arranged in such a way that they form a wall as a known as water wall

which absorbs maximum amount of radiant heat librated from the combustion

of fuel.

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CLASSIFICATION OF FURNACES:

According to method of firing for various types of fuel furnace can be

classifiedin following manner:

Since today coal in its various forms is widely utilized in steam (thermal) power

plants. Some of the solid fuel firing furnaces is discussed in detailhere.

Hand fired furnace:

These types of furnace a re utilized formedium and low capacity boilers in which

coal is fed by shovel on the grate surface. This is the simplest method of solid

bed firing but can not be used in modern powerplants due to lower combustion

efficiency and poor response againstfluctuating load. Travelinggrate or chin grate stoker:

The chain grate stokerconsists of an end less chain made from cast iron

links or bars which forms a supp ort f or the fuel bed . The chain travels over two

sprocket whee ls one at the front and other at the rear of the furnace the front

sprocket is connected to variablespeed drivemechanism.

The coal is fed by gravity from a hopper located in front of the stoker.

The depth of fuel on the grate is regulated by hand adjusted gate. The speed of

the grate varies at the rate at which the coal fed to the furnace. The

combustion controls automatically regulates the speed of the grate to maintain

the required steam rate. The ash containing a small amoun t combustible

materia

lis carr

ied over the rear and of the stoker and depos

ited in the ash p

it.

Chain grate stokers are best suited for non-caking, high-volatile and high ash

coals. The bar grate stokers are burn lignite and small size anthracite coal

successfully.

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Sp reader consist of rapidly rotating shaft carrying blades to provide un iform

distribution of the coal over the grate .A wide variety and poor quality coal can

be burnt efficiently withthis type of stoker.

Single retort/Multiretort s stokerfurnace:

This is und er feed stoker furnace, in which coal is feed from und er meath the

fire and moves gradually upwa rds. The primary air is supp lied just below the

level at which combustion takes place. In this types of furnace fuel is placed in

large hopper on the front of the furnace and then it is further fed by

reciprocating ram or screw conveyer in to the bottom of the horizontal through.

The air is supplied through the tuyeres provided along the upp er edge of thegrate. The ash and clinkers are collected on the ash plate provided with dumping

arrangenment. the coal feeding capacity of a single retort stokervaries from 100

to 200 0 kg/hr.

The increase of capacity in the under feed can not be obtained simply by

bui lding large single retort stoker due to inability to obtained even airdistribution from the sides of retorts.Multi retort stokers are generally used for

increasingtheburningcapacity of the furnace.

Pulverized fuel firing furnace:

In a pulverized fuel firing furnaces the coal is redu ced to a finepowder with

the help of grinding mill and then proje cted in to the combustion chamberwith

he help of hot air current. The amount of air required (Secondary air) to

complete the combustion is supplied separately to the combustion chamber . Theresulting turbulence in the combustion chamb er helps for un iform mixing of fuel

and air.The amount of airused to carry the coal isknown as primaryair.

The efficiency of pulverized fuel firing furnace mostly depend s up on the size of

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the powder, abili ty of the bu rners to produ ce un iform mixing of coal and air and

turbulencewithin the furnace.

Generally pulverize fuel firing furnace can be classified according to

arrangement ofbu rners like:

1) Longflame(U-flame)furnace.

2) Sh or t flame(turbulence)furnace.

3) Tangentialburnerfurnace.

In pulverized fuel firing furnace wide variety and low grade coal can burnt

easily. It gives fast response to load changes. Moreover the sys tem is perfectly

free f rom clinkers and slugg ing troubles. Large amount s of heat release are

poss ible and with such rate of heat generation each boiler can generate as large

as 200 0 tons of steam perhour.

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Cyclonefurnace:

The cyclone furnace is a new method of burning coal particles in suspension.

Basically this furnace was designed to burn crushed low grade bituminous coal

that normallyhas highcontent of low fusingtemp erature ash.

The cyclone furnace is a horizontal cylinder of water-coo led construction.The

insidepart of the cyclone cylinder is lined with chrome ore.The horizontal axis

of the cylinder is slightly deflected towa rds the boiler main furnace and the

cylinder is equipped with a single scroll type inlet at one end a nd a gas

discharge throat in to the boilermainfurnace at the otherend.

The c rushed coal of 6mm maximum size is blown tangentially in to a cylinder of

cyclone furnace w ith primary air at outlet end .which creates strong and high

turbulent vor tex. As the coal with air moves from the front to the rear,

secondary air is introduced tangentially to complete the combustion. Extremely

high heat liberation rate and the use ofpreheated air cause high temperature

(200 00C) in the cyclone. The fuel supplied is quickly consumed and liberated

ash forms a molten film flowing over inner wall of the cylinder. The molten ash

flows to an appropriate disposal system as the horizontal axis of burner is

tilted.

The cyclone furnace givesbest results with low grade fuels and high silica ratio

(80%).

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Fl uidi zed bed furnace:

To reduce SO2 not NOX formation, this type of furnace designed was suggested

in 1950 , w hich is alsoknown as pressurizedfluidized bed combustionfurnace.

In this type of furnace crushed coa

lof 6 to 20 mm s

ize w

ith

lime stone and ash

is spreaded over grate surface to form fuel bed.High velocity air is supplied

from the bot tom of grates,which acts as rising agent and levitates the fuel-

limestone mixture.Turbulence created thus helps for suspension firing of

fuel.Temperature of about 8000c to 900

0c is achieved due to boiler size and to

achievehighheat transferrate.

The SO2 formed due to combustion is absorbed by limestone and due to low

temp erature NOX formation also reduces. Thus pollutants in the exhaust gases

reduce greatly,du e to thisfurnace.

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OBJECTIVE: TO STUDY OF COAL AND ASH HANDLING SYSTEM.

LEARNING:

COAL HANDLING SYSTEM

IN PLANT COAL HANDLING SYSTEM

OUT PLANT HANDLING SYSTEM

ASH HANDLING SYSTEM

INTRODUCTION

The coal and ash handling fac ility is the life line of a coal fired power

station. Modern station have a high coal demand because of ever increasing

power demand and economic advantage of a single fuel handling facility sewing

a multi unitpowerstation. Thus this facility have had to become more flexible ,

more reliable & capable of handling larger amoun t of materials in less time thaneverbefore.

Coal and ash handling fac ilities normally require large ground areas &proper

conveying systems to elevate the material from sys tem. Planning & designing

of coal and ash handling facilities depend upon fuelburning rate, plant location

coal source & transportation, environmental conditions, types & properties of

coal, capacity of unloading systems, storage & preparation facilities, drying

facilities, weighing systems capacity & dust collection systems capacity etc.

Proper coordination between all above fac ilities required to balance the plant

supp lywiththeplantconsumption.

The coalhandlingsystem of modern powerstationis dividedin to two parts

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STUDY OF COAL AND ASH HANDLING SYSTEMS OF MORDERN POWER

STATION

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1. Outplanthandlingsystem.

2. Inplantcoalhandlingsystem.

Out pla nt handli ng system:

The coal from the coal mines to the powerstation is transported by out-plant

coal handling systems like sea, rail or road transportations. The supply of coal

by road is limited to a small capacitypowerplant & this method of handling

coal does not suit with modern power station. So following means of

t ransportationsare adopted for modern powerstation.

Transportationof coal by sea orriver:If the powerstation is located on the bank of river or near the sea shore , it is

often economical to transport the coal by ships or barges. Various un loading

sys tems like clamshell back ed unloader, continuous bucket ladder un loader,

vertica

lscrew un

loader,are ut

ilized to un

load the coa

lfrom sh

ips or barges. The

un loaded coal is either sent to storage yard ordirectly to the conveyersystem.

The loading & unloading of huge amount of coal to the ships &barges are the

majorproblemswith thistype of transportation.

Transportationof coal by rail:Railway is the most important means of coal trasportation for interior power

stations. A railway siding line is takento the power station & coal is delivered to

the storage yard,whichis c

loseto thepo

int of consumpt

ion.

Railcars are built to two basic designs to un load (1) the bottom dump car and

(2)th e top dum p car.Bottom dum p car utilies door s at the car bottom for

un loading,while the top dump car is un loaded by turning the car overby rotary

car dump ers (wa ggon trippers).

To minimise the time fortransportation,loading & unloading,un it train system is

adopted,in which the train moves continuously round the c lock along the

circular track.A circular track,known as Merry Go Round system,is arranged

between coalfield &powerstation.

Transportationof coal by rope- ways:When the distance of coal mines to the powerstation to less than 10 kms,the

ropeway is utilised to trasport the coal.This system supplies the coal

continuouslyfrom coalminesto the powerstation.

Transportationof coal by overland conveyers:When the coal mines are adjacent to the power station ,over load conveyers

like belt conveyor is utilised to supply the coal to the powerstation.Overland

conveyors comm only move material up to 16 km from the mines.Several types

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of conveyor sys tems allow the beltto convey materialaruond a horizontalcurve

& alsocompletelyenclosethe materialwithin the belt.

Transportationof coal by pipeline:

Pipeline of coal slurry fromremote mines to strategically locatedpower station

is capable

of tranporti

ng conti

nuousl

y verylarg

e quant

ity of coa

lsl

urry with

less time.Slurry preparation system,pumping system and recovery sys tem are

three maincomp onenets of this type of trasportationsystem.

Homogeneous slurry by mixing crushed coal & water is made in to preparation

system.The formed slurry is then pumped in to the pipe line.Coal is dewatered

& recovered for use in recovery system.The recovery sys tem includes slurry

receiving tank,dewatering plant,drying sys tem and storage bunkers.the

dewatered& dried caol generally contains 9 to 10% of surface moisture as

furtherdrying is uneconomical.

STOKEOUT,RECLAIM AND OUT- PLANT STORAGE SYSTEMS:

After receiving coal from out-plant handling system,coal is stored in storage

area ofplant site.Stoke out is the term for method & equipements used to palce

in the s torage area.Reclaim is the term for method & equipement used to

retrieve the coal from the storage area.St orage is the area where the coal is

held from the time it is received to the time it is required for plant

consumption.Car shkers,rotary car dampers,un loading towers & bridges,self

un loadingboats,lift,trucks,cranes &buckets are utilised to un load the coal from

outplantcoalhandlingsystem.

The coal is stored in storage area which includesboth active & reserve coal

storage.Coalfrom an active coalstorage is utilisedforconsumptionwithin short

time.to avoid use of mobile equipement to transfer coal from active storage,this

storage space is kept near to the point of app lication.The reserve coal storage

is a long term storage that provides an emergency supp lyof coal for any

unavilabledelay in coalsupply.

The coal is stored by following methods to reduce the chance of oxidation &

combustion(1)stoking the coal in heaps (2)under wa ter storage(3)covered

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storage(4)bunkers.Faction like available ground area,risk of combustion,losses

on storage,cost of storage & handling local weather conditions,daily

consumption&supplycondition influencethe storage facility.

IN-PLANT COAL HANDLINGSYSTEM:

From storage space coal is transfered to the firing equipement through various

equipement like crusher,sizers,dryers,magnetic seperators,weighingequipements,storage bun kers & pulverising mills depending upon the firing

sys tem utilised.Transfer of coal from sys tem to system is done by various

equipement like grab bucket conveyors,bu cket elevators belt conveyors,screw

conveyors,flight coneyors & skip hoists.These equipement are discussed inbrief

as under.

1. Grab bucket conveyor:

When other alternative equipement are not poss ible to use,grab bucketconveyor is utilised to transfer coal with the help of crane or tower.Figure

shows the construction of grab bucket conveyor in which vertical movement of

bucket is carried out with the help crane & the crane moves horizontally on

trackprovidedfor the same.

2. Bucket elevator:

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For vertical movement of coal,bucket elevatora are used in which loading is

done at bottom & discharging is done at the top.Buckets are fixed to a chain

which moves over two whee ls as shown in figure.The bucket elevators are

classifiedaccording to mannerof dischargeas non-continuous & continuous.

3. Belt conveyors:

This is very suitable means of tranferring large quantity oa caol over large

distance.It can elevate coal up to 200

to the horizontal & convey up to 400

meters,with ava rage speed ao belt ranging from 60 to 100m/min.Belt conveyor

consists of endless belt made of rubb er ,canvas orbalata runn ing over a pair of

end pulleys & suppor ted by series of rollers known as idlers,provided at regular

intervals.

4. Sc rew conveyors:

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It consists of an endless helioid screw rotating in a trough.The movement of

screw drive the coa

l from one end to the other & d

ischarge at any s

i

utable

point as shown in figure.Screw conveyors are w ell suited for small applications

where space is limited.

5. Flig ht conveyors:

When filling of numb er of storage bins situated under the conveyor is

required,this type of conveyor is utilised.It consists of a series of scrape rs or

flightsbolted to one or two endless chain moving on chain whee ls at two ends

as shown in figure.The scraper moves inside a truogh of cast-iron orstee l.Coal

is also carried forward during the movement & discharged at required point

through suitableopening in the trough bottom.

6. Skop hoist:

For movement of coal for medium size plant hoist is the simplest device.It

consists of a bucket movingbetween guides with the powerof a cable received

round sheaves & drums which turn thruogh electric drive.The cable is provided

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for elevatating the bucket.The bucket can be provided with referance to its

centerof gravity.A curve guide is located at the dampingpoint near the top of

the hoist way& engages a roller in each side of the bucket pulling it in to

dumpingposition.

ASH HANDLINGSYSTEM:

High quantity of ash is generated from largepower stations.Thus hundreds of

tons of ash may have to be handeled every day in largepowerstation.Handling

of ash includes its removals from the furnace,loading on conveyors& delivery to

the dumpingsite.

Following methods are adopted for ash handlingin powerstations:

Manualhandling. Mechanicalhandling. Steam jet systems. Pnumetic-conveyorsystem. Hydraulic orgravitysystem.

Same mechanical handling equipements,utilised for coal handling can be

utilised for ash hopper is fed.The app lication of this system is limited to small &

mediumcapacitypowerstation.

Steam jet systems:

This system utilizesjets of high pressure steam to convey ash in which ash

from hopper is fed.The app ilication of this is limited to small & medium capacity

powerstation.

Pnu metic-c onveyorsystem:

This system has been developed for handling abrasive as well as fine dusty

materialssuch as fly-ash & soot.

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As shown in figure,the ash and dust from all dischargepoint is picked up by

highvelocityairsteam createdby an exhauster.Thecollectedash of ash hopperis

crushed in crusher & carried away by the air is seperated in primary &

secondary s eparators & is collected in ash hopper as shown in figure.The

separated clean air is removed to atmosphere through top of the secondary

separator and ash collectedin hopper is disposed off by some suitablemethod.

Hydraulic or gravity system:

The hydraulic ash handling system carries the ash with the flow of wa ter with

high velocity through channel & finally dump ed to the sump.The ash is

separated from wa ter when it reaches to the sump.The separated wa teris used

againwhile the ash collectedin the sump is sent out through carriages.

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OBJRCTIVE: TO STUDY GOVERNING SYSTEM OF STEAM TURBINE.

LEARNING:

MAINCOMPONENTS OF STEAM TURBINE

GOVERINGSYSTEM OF STEAM TURBINE

Nozz le controlGoverning. Thrott leGoverning. Bypass Governing. Thrott leand nozzlecontrolGoverning. Thrott leand bypass Governing.INTRODUCTION:

Steam turbine is a primemover used in steam powerplant and nuclear

powerplant. Insteam turbinesteam energy is converted in to resolvingmotion of

the shaft of the rotor i.e. thermal energy is converte d in to mechanical

energy. Thereare mainly two types of steam turbines:

ImpulseturbineImpu

lse-React

ionturb

ine.

In a Impulse turbine, steam coming through nozzle impinge on the tip of

the blades, mounted on the rotor of the turbine. Blade changes direction of

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STUDY OF GOVERNING SYSTEMS OF STEAM TURBINE.

POWER STATION.

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steam flow without changing pressure of steam. Due to change in momentu m

resultant motiveforce is created, whichrotates turbineshaft.

e.g. De-laval,Curtisand RateauTurbine.

In a reaction turbine,velocity of the steam coming thruogh nozzle increases

relative to rotating disc of the turbine.As a result reaction force created which

rotates discand shaft.Shaftrotates oppositeto jet . e.g. Parson turbine.

MAINCOMPONENTS OF STEAM TURBINE:

Following are the maincomp onents of the turbine:

1) Nozzle

2) Bladesand vane

3) Rotor

4) Ro torshaft

5) Casing

6) Shaft glands

7) Bearings

8) Servomotor

9) Governor

10) Lubricationsystem.

GOVERINGSYSTEM OF STEAM TURBINE:

The actual consumption of electricalpower at a particular time is known

asload.(E

lectr

ica

l load).The outpu t of the turb

ine mu st be adjusted

according to load,as electrical cannot be stored.Electricalenergy is

generated according to load demand otherwise it is wasted resulting in

loss.Load changes according to powerconsumption.During variation of load

it is necessa ry to run turbine at constant speed.The control of output of

turbine according to variation in load is known as governing of turbineand it

is done by governingsys tem orGovernor.

The mainfunct

ions of the Go vernorare: It regulatesshaftspeed of the turbine It regulatessteam pressure in automaticextractionunit.

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The frequency of the outpu t (electricalpower)of the turbine mu st be kept

constant at 50 cycles/secin india.

Go vernor regulates opening of turbine inlet valve or bypass valve according

to change in load.For operating valves servomotor is used.Primary elements

of mechanical,centrifugal or hydraulic type are necessa ry to maintain

sensitivity e.g. flyball type centrifugal arrangement is primary element.Such

element operates servomotor through pivot valve which provides necessary

motiveforce to operate pivotvalve.

METHODS OF STEAM TURBINEGOVERNING:

Following are the methods used forgoverning of steam turbine. Nozz le controlGoverning. Thrott leGoverning. Bypass Governing. Thrott leand nozzlecontrolGoverning.Thrott

leand bypass Govern

ing.

Nozz le control Governing:

In this method of control,the steam supp lied to the different nozzle groups is

controlled by uncovering as many steam passa ges as are necessa ry to meet

the laod by poppet valves.An arrangement often used forlarge steam power

plants is shown in figure.The numb er of nozzlessupplying the steam to the

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turbine are divided in to groups as N1, N2 and N3 and the supp ly to these

nozzles is controlled by valves V1, V2 and V3.In this way steam flow can be

changed as loadchanges.

This method is used in Impulse or Impulse reaction turbines.It cannot used

formultistage turbines.

Thrott leGoverning:

It is a qualitative governing system.The arrangement of this

governingis shown in fig.

The quantity of steam entering in to the turbine is dreduced by the

thrott ling of the steam.The throttling is achieved with the help of double of

double heat balanced value which is operated by a centrifugal governor

through the servo-mechanism.The effort of thr governor may not be

sufficient to move the valve against the piston in big un its.Therefore an oiloperated relay in incorporated in the circuit to magnify the small force

produced by the governor to operate the valve.

Let the piston of the governor(position of pilot piston and relay piston)is

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shown in figure. Corresponding to the full load on the turbine and runn ing at

full speed.If the load on the turbine is reduced,the turbine will start to rotate

at speed greater that full load speed as the energy supp lied is same.An

increased speed of the turbine shaft causes the governorsleeve to move

upwa rd and this causes to move the pilot piston upwards.The upwa rd motion

of the pilot piston allows the highpressure oil to enter on the top side of the

relaycylinder to come out through pilot cylinder.

The downward motion of the relay piston partly closes the thrott le valve

causing the reduction in steam supply.The reserve operation takes place

when the loadon the turbine increses.

The thrott le governing is simple in operation but thermodynamically

insufficient as the available heat drop is reduced in the irreversible thrott ling

process.

By pass Governing:

It is used in multistage impulse turbine to have full admission in to high

pressure stages to reduce thepartialadmiss ion losses.

The arrangement ofby-pass governing is shown in fig.Forhigh loads (higher

than 80% full load) a by-pass line is provided for the steam from the first

stage nozzlebox in to the latter stage as shown in fig. The by pass steam is

automatically controlled by the lift of the valve.Theby-pass valve rremains

und er the cotrol of speed governor for all lodswithin itsrange.

NOTE:

In practice combination of thrott le governing and nozzle control

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governingorcombination of throttlegoverningand by-pass governing is

used.

In reaction turbine where full admiss ion is required nozzle cotrol

governingsystem can not used be used hance combination of throttle

and by-pass governingsystem is used.

Nozzle controlgoverningcan not be used withby-pass governing.

There is a higherhaet drop in nozzlecontrolgoverningso it is not

suitableforhighpressure impulseturbine.

Higherlossesin nozzlecontrolgovernibgdue to lesseradmiss ion. In throttlegoverning lossesare less due to low admissionand there is

low leatdrop.

OBJECTIVE: STUDY OF CONTROL SYSTEM OF STEAM POWER PLANTS.

LEARNING: CLASSIFICATION CONTROL SYSTEM

INTODUCTION

The powerplant supp lies electrical power to various consumers.Load on

the powerplant varies moment to moment according to consumers demand &

this effects on various parameters of different equipments.To generate

electrical power of constant f requency (50 HZ),turbine speed should be kept

constant.So operations of various equipements must be properly coordinated to

meet the demand of constant turbine speed & electricity generation process

mu st be regulated to meet the design condition.The palant control system

provides the necessary too ls to enable proper regulation & co ordination of

plantoperationforreliable & efficientelectricitygeneration.

CLASSIFICATION OF CONTROL SYSTEM USED IN STEAM

(THERMAL)POWERPALNT:Steam power plant is a complx combination of various sytem.Various control

sys tem ranging from manual control sys tem to automatic control sys tem are

utilised for reliable,safe& economic generation of electrical power.In mordern

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STUDY OF CONTROL SYSTEM OF STEAM POWER PLANTS

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powerplant,general the controlsys tems are classifiedas following:

1) According to logic of control mechanism.

a) Open loop controlsystem

b) Closedloop controlsystem.

2) Accordingto location of controlsystem.

a) Areacontrolsystem

b) Centralisedcontrolsytem

3) Accord

i

ngto the type

of controlact

i

ona) On-offcontrolsystems.(Digitalcontrolsystem)

b) Modulatingcontrolsystems(Analogcontrolsystem)

a) Op en loop contro l system:

In this type of control sys tem after sensing variation in particular

parameter,corrective action is done by the control system.But actual result of

corrective action is fed back to the control sys tem.So accurate controlling is

onlyposs iblewhen conditionis as good as the calibrationcondition.

b) Closedloop contro l system:

In this type of control system after sensing variation in particular

parameter,corrective action is done by control system & then the actual result

of corrective action are fed back to control sys tem for proper further corrective

action.This type of sys tem is mostly utilised in mordern powerplants due to its

accuracy.

c) Areacontrol system:

In this type of control sys tem operation of powerplant is divided in to various

segments & separate control sys tem is provided for each segment. It means

that there is separate control roo m for each segment.This type of control

sys tem is economical & simple in operation bu t coorination between various

segments is difficult.

d) Centralisedcontro l sytem:

Now a days this type of control sys tem is mostly adopted due to automations &

easiness in gathering informations.A central roo m is established from where

whole operation of powerpalnt is being controlled.This type of control system

requires less man power& proper coordination with different areas is achieved

withoutdelay.

e) On-off contro l systems.(Digitalcontro l system):

This type of control sys tem is known as digital control,binary control,discrete

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control,sequential control or motor interlocks.The control sys tem produces

either a start (running) comm and or a stop command & controlled equipment

reacts to comm and with two distinct outcomes either start or stop No

intermediatestate existsbetween the runn ing & the stop states.

In power plantapp lications, the equipementcontrolled by this controlaction can

be dividedin to follo wing major categories. Motor driven rotating equipments

like pumps, fans, compressors & conveyors.

Motoroperated shut off valves & dampers.

Solenoidoperated equipementsuch as pnumaticshut off valves.The control action may be initiated by manually by operator comm and or

automatically by the sys tem based on the intelligence received from the

process.

f) Modulatingcontrol systems(Analogcontro l system):

This control sys tem is known as analog control,continuous control or close loop

control.Modulating control produces outpu t signal with a magnitude that varies

smoothlyfrom one valueto another.

The most important application of modulating control in the powerplant are in

the area of boiler control & other app lication involve controlling

pressure,temperature,level & flow variables in the turbine cycles & plantauxiliarysystem.

Following are the parameters controlled by modulatingcontrolsystem. Firing rate control Loaddemand controlBulverisercoaland air flow control Secondary airflow control Furnace draft control

Superheat&reheat steam temp. Control Feed wa ter flow control Sup erheater bypass & start-up system control Cooling water flow control Feed wa ter heater levelcontrol Boiler feed pump recirculationcontrol BASICELEMENTS OF CONTROL SYSTEM:

Any controlsys tem requiresthreebasicelements

(1) Primaryelement

(2) Relaying element &

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(3) Powerelement

1. Prima ry element:

Primary elements of control sys tem do functions like monitering,measuring &

indicating of various parameters of power plant like

pressure,temperature,speed,flow rate etc.It senses the deviation from given

input value ofparameter&produces a signal forcontrol sys tem, eg., change

inpressure is sensed by pressure gu age manometer,change in temerature is

sensedby thermometers,thermocouplesorby pyrometers.

2. Re layi ng element:

Signal sensed by primary element for any deviation in particular

parameter is converted in controlling impulse & sent to controlling device

(control point) by relaying element of control system.The signal istransferred by various sys tems like mechanical,pnumatic,hydraulic,electrical

orelectronicssystem.

3. Powerelement:

Power elementprovide sufficient motive force to operate controlling system

as per signal received from relaying element of the control system.So

proper control action can be activated.generally electric,motor,hydraulic

pump,pnumaticcompressors are utilizedas powerelement. Re quirement of contro l system:Power plant is a complex combination of various systems,which runs

continuously to generate electrical power as per consumersdemand.Controlling the operations of such system efficiently,safely &

economically within short time is the prime criteria to achieve proper

coordination among such sys tems.So control of any power plant mustsatisfy

following requirement.

1) Sensitivity: Sensitivity of control system is the ability to sense the

minimum deviation in given value of parameter or input

signal.This depends on primary element of control system whichmonitorsthe inputsignal.

2) Sp eed of response:

It is the s peed to convert input signal in to out put signal.In

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otherwards,it is the time taken to take corrective action after

sensing any deviation in particularparameter.Generally it depends

on relyingelement of controlsystem.

3) Stability:

It is the ability to produce specific ouppu t signal for specific input

signal value at any time. In otherwords,it is the ability to produce

same correctiveactionfor same deviationin inpitsignalevery time.

4) Power:

It is the ability to activate corrective action according to change in

inputsignals.

5) Ruggedness:

It is the ability to control sys tem to operate properly in any

situation.

Main contro l system of steam powerplant:Feed wa ter control system,combustion control sys tem,steam temerature

control system,fuel & air flow control system,draft control system,condenser

cooling water control sys tem,etc are the main control systems of steam

powerplant.

Feed wa ter contro l system:

This sys tem controls the wa ter level in drum within specified specified

range.The specified level of water is known as set level.As the steam

consumption increases,water level in the drum decreases.At that time

control sys tem gives comm and to fill waterby feed pump to maintain water

level within specific range.Various types of control sys tems like thermo-

hydraulic system,regulator system,pneumatic system,electric sys tem,etc are

utilisedfor feed wa tercontrolsystem.

Three basic parameters like drum wa ter level,steam generation rate & feed

wa ter flow arte are taken as primary elements by feed wa ter control

system.Depending upon number ofprimary element selected from above,the

sys tem is classifiedas:

a) Single element feed wa ter control system:

b) Doubl e element feed wa ter control system:

c) Triple elementfeed wa tercontrolsystem:

Combustioncontrol system:

Higher combustion rate is required to satisfy high steam demand & low

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combustion rate is required to satisfy low steam demand.Three basic

parameters like steam pressure,fuel flow arte & air flow rate are monitored

by combustion control sys tem & control signal to fuel supp ly controller,air

supp ly controller,damper position controller & draft controller,are given to

controlcombustionarte of fuel.

Steam temerature contro l system:

The steam temerature is controlled by regulating heat given to the

superheaterby various methods orby spraying water flow in to superheated

steam.The temerature control sys tem a single element control system that

measures the steam outlet temerature & comp are it to a set values.The

controller outpu t provides corrective action to maintain temerature of steam

to a set value.

Condenserscooling wa ter flow contro l system:

The cooling water supp lies cooling water to the condenser& various

coo lers.The cooling wa ter sys tem employs a set of cooling water pump s that

supp ly water to the equipements via a wa tersupp ly header.The return water

is supp liedback to the pump s suction through a return header.Control valve

is installed between two headers with wa ter bypass line.The control system

controls the position of control valve to regulate water flow rate within

specifiedrange.

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OBJECTIVE: TO STUDY OF DIESEL POWER PLANT.

LEARNING : WORKING OF DIESEL POWER PLANT.

STARTING SYSTEM

INTEC AND EXAUST SYSTEM

FUEL STORAGE SYSTEM

ENGINE COOLING SYSTEM

INTRODUCTION:Due to high thermal efficiency,qui ck starting,minimum standby

loss,low initial cost,mobility,multi-fuel ability and full flanged

developement,the diesel engine powerplant,in range of 2 MW to 50 MW,is

utilized generally as peak load powerplant,mobile powerplant,standby power

plant,emergency power plant,nursery station,starting station and even as

centralpowerstationforelectricpowergeneration.

The diesel engines,used for electric power generation,are more reliable for

long period,but rapid developement of other sources foe electric powergeneration and pollution problems have made diesel engine powerplants to

disappear as thier generation cost was considerably high.So now a day,use of

large capacity dieselengine power plants is limited for undeveloped

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STUDY OF DIESEL ENGINE POWER PLANTS

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and remote area of the coun try.But small and medium capacity diesel

engine power plants are widely utilized as emergency power plants in

public,industrial and institutional locations like

hospitals,factories,cinema halls,shopping center s,etc. In absence of main

gridpower.

DIESELENGINEPOWERPLANT:The schematic diagram of diesel engine powerplant is shown in figure.The

essentialcomponents of dieselenginepowerplantare as under.

1) The Diesel Engine: This is the main compn ents of the plant which

developespower. Generallyengine is coupled directly to the

generator.Dieselenginemay be a four stroke or a two stroke engine.

2) Engine Air Intake System:This system supp lies required quantity of

pure airat requiredpressure and temerature forcombustion of fuel.

3) Exhaust Gas System:Gases coming out from cylinders,after combustion

of fuel,arecarriedout inproper manner in to atmosphere by thissystem.

4) Fue l Stor age and Supply System: Thissys tem store s sufficient quantity

of fuel and supplies itto the engineas perloadvariation.

5) Cooling System: Thissys tem keeps the temperature ofvarious

comp onenets of dieselengine in proper range by cooling effect.

6) Lubrication System: This sys tem provides lubricating oil to various

runn ingcomp onenets of the engineto redu ce the friction.

7) Start ing System: This sys tem helps to start the diesel engine from cold

condition.

8) Governing System: This sys tem maintains the speed of the diesel engine

constant irrespective of load on the plant.This is done generally by

varyingfuel supp lyto the engineaccording to load.

ExplanationofVariousSystems of Di esel PowerPlant:When diesel engine is utilised for electric power generation,the diesel

engine is generally coupled directly with generator by grid coupling.For

generation of electric power of constant frequency,engine speed must remain

constant.So following sys tems of diesel engine power plant are designed

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according to the main considerations like plant capacity,type and period of

use,working condition,etc.here the various sys tems of diesel engine power

plantare discussed in details.

EngineAirIntaleSystem:

Diesel engine generally requires 4 to 8 m3/kwh of air mass flow rate.The

main function of air intake sys tem is to provide sufficient quantity of air ofrequired purity at required pressure and temerature.Beside that,according to

necss ity,followingfunctionsare doneby air intakesystem.

i.Purify the air

ii.Reducenoisepollution

iii.Done superchargingto increaseenginecapacity

iv.Increase air temerature to redu ce misfiring of fuel in cold climates

v.Done effectivescavenging in two stroke engines

Thus, according to above various functions,air intake system consists of air

filter,silencer,supercharger/turbocharger,heat exchanger,intake manifold and

piping system.

ExhaustGas System:

Exhaust gas sys tem does following two oppositefunctions.

1) Discharging exhaust gases to atmosphere by providing minimumpressure

loss.

2) Re duce noisepollution.xhaust gas system is designed in such a way that

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proper satisfactions to both the above functions are achieved.Besides thatfollowing functions are also doneby the exhaust system.

i. Discharge exhausts gas at proper height to prevent accumulation of

pollutants in working zone.

ii. To pu t off the sparks created in exhaust gasesby sparkarrester.

iii. Keep isolate the engine from vibrationsarisesdue to flow of exhaust gases.

iv. Give haet energy to driveturbocharger or to other haet recovery system.

Figure shows schematic diagram of exhaust gas sys tem of diesel engine

powerplant.It consists of exhaust manifold,silencer,piping connection and

heat recovery system,etc

Fuel stor age and supply system:

The fuel supply and stor age sys tem generally depend on the type of fuel,size

of theplantand type of engineused,etc.

The fuel supplysystem generallyclassifiedas:

1) Simple suction type system:

In a simple suction type sys tem,th e fuel oil is taken by suction pumpdriven by engines from service tank located above the engine level.Such

pum p delivers constant volume of fuel;therefore,an overflow line is

required bqck to the tank.This sys tem is used for small capacity

engines.

2) Transfertype:

In the transfer type sys tem,th e motor driven pump takes the fuel oil

from main stor age tank and supp

ly to the day stor age tank as shown

in

figure.This system is generally utilised for medium size or large size

powerplants.

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The location of main stor age tank above ground orbelow depends upon local

conditions.The over ground tanks have the advantage of detecting the fuel oil

leakage easily,low maintainance and easy cleaning.On the other hand,under

groun d tanks have the advantage of reduced fire hazards and use of ground

space.

The heating requ

irement depend s up on the local climatic cond

itions and

viscosity of the fuel oil.If the heating is required,then it is generally done in

the main storage tankby passing the hot jack et water through a coil dipped

in the storage tank.

The fuel oil,which is tranfered to the daily consumption tank,which is located

well above the engine levelflows by gravityto the enginepumps.

Enginecooling system:

Due to combustion of fuel and friction developed bet ween moving surfaces,the

temerature of comp onents of dieselenginebecome high. So for three main

purposes,the cooling sys tema re requiredin dieselenginepowerplant.

i. To prevent over heating of various components

ii. To preventburning of lubrication oil film and

iii. To prevent thermal stress developed due to uneven temerature

distribution.

Generally,water cooling system is adopted in diesel engine powerplant.Proper

cooling of engine is absolutely necessa ry to extend life of the plant.Therefore

exit temerature of cooling water must be controlled.If it is too low,lubrication

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oil will not spread properly and wearing of moving surfac es takes place.If it is

too high,the lubricating oil burns.Therefore,the maximum exit temerature of

the water is limitedto 700

C.

A common water cooling sys tem used in dieselpowerplant is shown in figure.

The cooling water is soften in water treatment plant to control the scaling in

different parts of the sys tem and also chlorinated to prevent growth of

algae.Generally,thequantity of cooling water requiredis 35 to 60 lit/kwh.

As the circulation of water in the cooling sys tem is concerned,th ese are

di

vi

ded

in to a

sing

lecircu

itand doub

lecircu

itsystem asshown in

figur

e.

The single cuircuit sys tem may be subjected to corrosion in the cylinder

jack ets because of dissolved gases in the cooling water.The double circuit

sys tem largely eliminates internal jacket corrosion,but the corrosion may

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existin tht raw water circuit.

Lubricatingsystem:

The lubricating system of diesel engine does functions like lubrication,coo ling

cleaning,sealing and noise reduction.The life of the engine,the overall

efficiency of the plant and poss ible continuous service of the plant are

dependent on the effectiveness of the lubricatingsystem.

Lubricatingsystem of dieselenginepowerplantworks in two parts:

1. lubricatingsystem insidethe dieselengine.

2. lubricatingsystem outsidethe dieselengine.

Generally,splash lubrication system outside the diesel engine provides flow of

sufficient lubricating oil to the diesel engine and purify the lubricating oil.It

consists of storage tank,oil filter,oil heating/cooling system,oil pumps,control

valves,etc. As shown in figure. Cooling is done by oil coo lerbefore supp lying

the lubricating oil to the engine to maintainproper lubricatingproper ty of the

oil and heating is done by heater before supp lying the lubricating oil to the oil

cleaningsys tem to redu ce viscisity of the oil.

Lubricating oil consumption is nearly 3 lit/1000 kwh gen erated at full load

condition.Thus,lubricating oil consumption is nearl 1% of the fuel oil

consumption.

Starting system:

It is difficult to s tart even smallest diesel engine by hand cracking as the

compress ion ratio is high.Therefore some mechanical sys tem mu st be used to

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start the engine. Generally, compressed air, electric motor and auxiliary petrol

engines are used for starting purpose. Compressed airsystem is comm only

used in dieselenginepowerplant.

Airstarting sys tem uses valve arrangement to admit pressurised air about 20

atm. To a few of the cylinders,making them to act as reciprocating air motorto turn the engine shaft.Admitt ing fuel oil to the remaining engine cylinder

helpsthe engineto start inder itsown power.

During the normalworking of theplant, thepower from the main shaft is used

to drive the compressor, which accumulates air in to the accumulators. Once

the accumulators indicate the rated pressure, th e comp ressoris automatically

disconnectedfrom the powershaft.

Forautomatic starting sys tem, th e ordinary air starting equipments are

arranged to open in the corre ct sequ ence and close when the engine starts

runn ing. The automatic starting system is also used to prime the lubricating oil

sys tema nd to start the automatic flow of the cooling water also.

Governing system:

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The governing of diesel engine is done by varying the quantity of fuel supplied

to the engine.Generally,constantstroke withvariablesuctionorvariablebypass

method is used to control the quantity of fuel supp lied according to

load.Centrifugalgovernor as shown in figureIs used.

Efficient governing sys tem controls speed of the engine by changing fuel

supp ly according to load,from no load condition to full load condition without

huantingwithhighsensitivityand stability.

OBJECTIVE: TO STUDY GAS TURBINE POWER PLANT

LEARNING: WORKING OF GAS TURBINE CYCLE

ELEMENTS OF GAS TURBINE CYCLE

IMPROVEMENT IN GAS TURBINE CYCLE

APPLICATION OF GAS TURBINE CYCLE

55

STUDY OF GAS TURBINE POWER PLANTS

9

DATE: / /


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MERCHANT POLYTECHNIC, BASNA INTRODUCTION:A gas turbine is a rotary machine,similar inprinciple to a steam turbine.It

consists of main comp onents,a compressor, a combustion chamb er and a

turbine.The air afterbeing,compressed in to comp ressor ,is heated eitherby

directlyburning fuel in it orby burning fuel externally in a heat exchanger.The

heated air with or withoutproducts of combustion is wxpanded in a turbine

resulting in work outpu t,a substantialpart about two third of which is used to

drive the compressor.Rest,about one third,is available as useful work output.

The gas turbine is the most direct in converting heat in to usable mechanical

energy,i.e. the rotary motion.The steam turbine introduces an intermediate

fluid,so the products of combustion do not act directly on the mechanism

creating motion.Piston engines ini tially convert heat in to linear motion which

mu st be transmitted through a crankshaft to produce usable shaft

power.But,the gas turbine,in its simplest form, conver ts thermal energy in to

shaftpowerwithno

intermed

iateheat ormechan

ica

lred

irect

ion.EssentialGas TurbineComponents:

1) Compressor:

The key to successful gas turbine operation is an efficient compressor.All

comp ressors in gas turbine app lications are of axial flow or centrifugal flow

or a combination of these two flows. Figure shows the constructions & flow

patterns of variousdynamiccompressors.

In the centrifugal flow compressor tha air is imparted a high velocity and

pressure rise by a row of moving blades,i.e. impeller.The increase in kinetic

energy is converted in to further pressure rise by a diffuser.Single stage

centrifugal compressors are capable of producingpressure ratio of about

4:1.But,they have large frontal area.Multi-stage centrifugal comp ressors are

capable ofproducingpressure ratio of about 14 -16 with 15-400 m3/min.flow

rate. Due to high frontal area and less engine length,these types of

compressors are utilised in small industrial gas turbine power plants.

Centrifugal compressors are cpable to give high efficiency of compress ion

with large mass flow rate range and have litt le effect on efficiency of dust

particles in the working medium,i.e.air.

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In the axial flow compressor, blades on the rotor have aerofoil shapes to

provide optimum air flow transmiss ion. Moving blades draw in

entering air,speed it up and force it in to following stationary vanes. These

are shaped to form diffusers; those converts the kinetic energy of moving air

to staticpressure.For one stage of axial flow comp ressor , p ressure ratio up

to 2:1 is

obtained and for mu

lti stage of ax

ia

lflow compressor,10kg/cm

2

pressurewith 150 -3000 m

3/min. or more mass flow rate.Axial flow comp ressors have

small frontal area and large air handling capacities,but due to this type of

compressors, engine length increases but frontal area reduces comp are to

centrifugalcompressors.

Axial flow compressors are able to give nearly constant mass flow rate with

large pressure ratio range. But they have shor t opening range for maximum

efficiency.For this reason and due to aerofoil blades,they are utilised in

aviationfield and largecapacitypowerplants.

The mixed flow comp ressors combine the advantages ofboth centrifugal and

axial flow compressors.

Proper type of comp ressor is selected considering capacity of un it,dust

particles in the working medium,enginesize,pressureration,cost,etc.

2. ComustionChamber(Combuster):

For efficient combustion,the combustor or combustion chamb er must

ass ure low pressure loss,minimum carbon formation,proper mixing of fuel

and air,positive ignition und er all atmospheric conditions,flame stability,with

un iformoutlettemerature and highcombustionefficiency.

A wide numb er of configurations are used for combustion chamber

depending upon the gas turbine engine and its applications to meet the

specific requirements.Thethree maintypes are:

a) Tubular or can type

b) Annulartype

c) Tubo-annularorcan-annulartype.57


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For all these,the design is such that less than a third of the total volume of

air entering the combu storis permitted to mix with the fuel,the reminder isused forcoo ling.The ratio of total air to fual varies among engine types from

40 to 80 parts of airby weightto one of fuel.

Figureshows the constructions of tubulartype combustionchamber.

2 Turbine:

This comp onent is an energy converter,tranferring energy of high

temerature,high pressure gases in to shaft output.Gas turbine follow impulse

and reaction designs,terms, which describe the blading arrangement.The

distinction depends upon how the pressure drop at each stage is divided.If

the entire drop takes place across the fixed blades and none across the

moving blades,it is an impulse stage.If the drop takes place in the moving

blades,aswell as in the fixedblades,it is reactionstage.

The gas turbine mu st work with high inlet

temerature.manu fracturers continuously strive to build turbine that can be

acc omodate higher temp erature either through new designs or through new

bladematerials.

IMPROVEMENTSIN SIMPLEGAS TURBINECYCLES:

The efficiency and the specific work output of the simp

le gas turb

ine are

quite low. Therefore, following modifications are necessa ry in three main

processes of the cycle, i.e.compress ion, heatsupplyand expansion.

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Gas turbine cycle wi th regeneration:

The regenerative cyc le was designed to make use of exhaust heat.The

regenerator receives hot turbine exhaust gases at 5 and rejects at

6.Compressed air pass es through the un it in a counter-flow direction and

picks up heat from turbine exhaust gases,then the heated air leaves the

regenerator at 3 and pass es in to the combuster.Hotter air in the combustor

needs less fuel to reach maximum temerature before flowing in to the

turbine.Thus,thermal efficiecy can be improved,generally exceeding 30%

againstdrawback ofpressure losses in regenerator.

II .Gasturbine cycle wi th intercoo ling:

Intercoo ling is used for decreasing the work done on the compressor.The

total compress ion is divided in to a numb er of stages and working fluid is

withdrawnand coo ledbetween stages as shown in figure.

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Intercoo ling gives more net work per kilogram of working fluid,allowing a

smallerturbineplantfor the same output.

III . Gas turbine cycle wi th reheating:

Another method of increasing the net work out-p ut of the cyc le is to use

reheating to increase turbine work.The total expansion is divided in to a

numb er of stages and the working fluid is withdrawn and reheated in seperate

combustionchamber between stages as shown in figure.

Reheating gives more net work per kilogram of working fluid with little

increase in the plantsize.

Closedcycle gas turbine:

In the closed cyc le gas turbine ,the air is heated in an air heaterby

burning fuel externally.The hot air expands in the turbine and then coo led in a

precoo ler and supp lied back to the compressor.The same working fluid

circulatesover and again in the system.

Due to closed cyc le gas turbine,poss ibility of using highpressure through out

the cyc le and gases other than air having more desirable thermal properties is

incresed.Besides advantages of the smaller plant and efficient control,the

closed cyc le also avoid erosion of the blades and oth erditrimental effects due

to products of combustion.

Auxiliariessystems of gas turbi ne powerplant:

Following auxiliary sys tems are utilised for better performance and safety of

the gas turbinepowerplant.

start ing system: Gas turbine is not self-starting prime mover.Diesel

engine or electric motor is utilised to start the gas turbine up to 25%

speed of its normal runn ing speed.After achieving stable flame condition

in combustion chamb er at this speed,the speed of the gas turbine starts

to increase and at

final mannual ppe

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