1

INTRODUCTION Due to high rate of increasing population day by day, widening gap between

power demand and its availability was one the basic reason for envisaging the G.N.D.T.P.

for the state of Punjab. The other factors favoring the installation of the thermal power

station were low initial cost and comparatively less gestation period as compared to hydro

electric generating stations. The foundation stone of G.N.D.T.P. at bathinda was laid on 19th

November 1969, the auspicious occasion of 500th

birth anniversary of great Guru Nanak Dev

Ji.

The historic town of bathinda was selected for this first and prestigious thermal

project of the state due to its good railway connections for fast transportations of coal,

availability of canal water and proximity to load center.

The total installed capacity of the power station 440MW with four units of 110MW

each. The first unit of the plant was commissioned in September, 1974. Subsequently second,

third and fourth units started generation in September 1975, March 1978, January 1979

respectively. The power available from this plant gives spin to the wheels of industry and

agricultural pumping sets.

Guru Nanak Dev Thermal Power Plant is a coal-based plant. The requirement of coal

for four units based on specific fuel consumption of 0.60 kg / kwh . The conveying and

crushing system will have the same capacity as that of the unloading system. The coal comes

in as large pieces. This coal is fed to primary crushers, which reduce the size of coal pieces

from 400mm to 150mm. Then the coal is sent to secondary crusher through forward

conveyors where it is crushed from 150mm to 200mm as required at the mills. Then the coal

is sent to boilers with the help of primary fans. The coal is burnt in the boiler. Boiler includes

the pipes carrying water through them; heat produced from the combustion of coal is used to

convert water in pipes into stThis steam generated used to run the turbine.

The basic requirements are:-

♣ Fuel (coal)

♣ Boiler

♣ Steam turbine

♣ Generator

♣ Ash handling system

2

Thermodynamics is the main subject of Thermal Engineering. It deals with the

behavior of gases and vapors, when they are subjected to varying temperatures and pressure.

In a thermal power plant, heat energy of the steam is converted to mechanical energy of the

turbine, which is further converted to electrical energy with the help of a generator. The

simple circuit of thermal plant can be drawn as below:-

\

Fig 2.1

Some of the definitions dealing with the thermodynamics are as below:-

GAS:- A gas is the name given to the state of any substance of which the evaporation from

the liquid state is complete. For example Hydrogen, Oxygen and air etc.

VAPOUR:-A vapor may be defined as a partially evaporated liquid and consists of the pure

gas state along with particles of liquid in suspension. It does not behave in the same way as

the gas, as the substance is further liable to the evaporation. The laws of gases do not apply

to vapors. When a vapor becomes completely evaporated, it is said to be dry and any further

heating of a dry vapor is termed as super heating. Once a vapor is superheated it is approx.

behaves as a gas.

HEATING OF A GAS:- A gas may be heated while either its volume is kept constant or its

pressure is kept constant, when the volume is kept constant, the temperature, pressure will

increase as the heat is supplied to a gas. But there will be no work done by the gas as there is

no change in volume. But when the gas is heated at constant pressure then the volume

increases and some work is done by the gas in expanding.

BASICS OF THERMAL

POWER PLANT

3

Work = pressure x change in volume

INTERNAL ENERGY OF GAS:- The internal energy of a gas is the heat energy stored in

the gas. It is quantity of heat. If the quantity of steam is applied to a gas, the temperature of

gas may increase or its volume may increase thus doing external work or it may do both, the

result will depend upon certain set of conditions under which heat is supplied to gas. If this

heating is accompanied by a rise of temperature, the gas will increase its internal energy.

This means that some of the heat supplied has been stored in gas in the form of heat energy.

Thus producing the rise of temperature the gas will have increased its internal energy. This

means that some of the heat supplied has been stored in the form of heat energy, remaining is

given out by gas as the form of external work as gas increased its volume. The increase in

heat energy stored in the gas due to rise of temperature is called the increase of internal

energy.

LAW OF CONSERVATION OF ENERGY:-

Total heat supplied to a gas must be equal to the increase of internal energy plus any

external work done by the gas in expanding.

H = total heat supplied to gas

E = increase in internal energy

W = external work done by gas

Then H = W + E

ISOTHERMAL EXPANSION:- Heat can be supplied to a gas keeping its temperature

constant. In this case the gas will expand doing external work equal to the amount of heat

supplied. This type of expansion is called Isothermal Expansion.

ADIABATIC EXPANSION:- When a gas expands, doing external work in such a manner

that no heat is supplied or rejected during the expansion. Such an expansion is called

adiabatic expansion.

ENTHALPY :-The total heat of substance is known as its enthalpy.

BASIC TYPE OF STEAM POWER PLANT :- The conversion of heat energy of organic

or nuclear fuel into mechanical energy with the aid of steam is carried out in steam power

plant. A diagrammatic view of the simplest steam power plant is shown on next page :-

4

Fig 2.2

The initial state of the working body is assumed to be water, which at a certain

temperature is compressed by the pump BFP and is fed into boiler ‘B’ through economizer

‘E’. In the Boiler water is heated at constant pressure process (4-5), to its Boiling point.

When the vaporization takes place in the same boiler process (5-6), since dry saturated steam

is rarely used in power plants, it is superheated to the required temperature in superheated

state.

The steam which is superheated through a pipe flows to steam turbine ‘T’. Where it

undergoes adiabatic expansion producing some external work (process 1-2). To have the

steam produce more work, its pressure at the turbine outlet must be as low as possible. For

this purpose steam from turbine is exhausted to a special apparatus condenser ‘C’, in which

the pressure of below atmosphere (vacuum) is created. In the condenser latent heat of

vaporization is removed from the steam with the aid of cooling water and the steam

condenses into liquid (the process of condensation 2-3) at a constant pressure and

temperature. Then this cycle is reheated. The basic cycle of the steam power plant

considered above is called the Rankine cycle.

ηR = H1 – H2

H1 – Hw

where

ηR = Rankine efficiency

H1 = enthalpy of steam at turbine inlet

H2 = enthalpy of steam at turbine outlet

Hw = enthalpy of condensate

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METHODS OF INCREASING EFFICIENCY:-

Raising the initial steam pressure:- By increasing the initial pressure at turbine inlet, the

enthalpy drop (H1 –H2) can be increased. Thereby increase in thermal efficiency of Rankine

cycle. However it must be mentioned that an increase in the initial steam pressure results in

increase in the wetness of the steam at the end of expansion. The drops of liquid of steam can

appearing in the steam at the last stage of the turbine cause erosion of blades and reduce

overall efficiency of turbine.

In order to avoid this increase in steam wetness above the tolerated value, an increased

temperature of the superheated steam as well as reheating may be employed.

REHEATING:-

Fig2.3

Reheating:- Reheating consists of subjecting steam to repeated super heating, after it

has expanded in the first cylinder of the turbine, at originally constant pressure in the

reheaters to original temperature, then the steam is directed into the second cylinder of the

turbine T2, where the steam expands and goes to the condenser. Reheating increases dryness

fraction of steam. It also results in the thermal efficiency of the cycle.

Raising the temperature of superheating:- By raising the temperature of superheated

steam at constant pressure, the heat drop (H1-H2) increases. As a result efficiency increases.

Increasing the temperature of superheated steam also increases the dryness factor. In modern

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steam power plants the temperature of superheating is limited. By the heat resistant

properties of the metal used.

Increasing the vacuum at condenser or reducing pressure at final:- A reduction in the

final pressure increases the heat drop (H1-H2) which results in the increase in the thermal

efficiency of the cycle.

Regenerative feed heat cycle:- In this system, the steam is fed from the turbine at certain

points during its expansion and is utilized for preheating the feed water supplied to the boiler.

At certain sections of turbine a small quantity of wet steam is drawn from the turbine. This

steam is circulated around the feed water pipe leading from the hot well to boiler. The

relatively cold water causes this steam to condensate. The heat thus lost by the steam being is

transferred to the feed water; the condensed steam then drains into the hot well.

The net effect of this process is to supply the boiler with hotter water while a small

amount of work is lost by the turbine. There is a slight increase in efficiency due to this

process, but there efficiency depends upon following factors:-

� Steam pressure

� Degree of superheat in steam

� Reheat/nonreheat

� Vacuum in condenser

� Regenerative/ non regenerative cycle

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PROJECT AREA:-

Power plant 238 acres

Ash disposal 845

Lake 180

Residential colony 285

Marshalling yard 256

Total area 1804

TOTAL COST: - Rs. 115 crores

STATION CAPACITY: - four units of 110MW.each

BOILER:-

Manufacturers B.H.E.L

Maximum continuous rating (M.C.R.) 375T/hr.

Superheater outlet pressure 139kg/cm²

Reheater outlet pressure 33.8 kg/cm²

Final superheater/reheater temperature 540°C

Feed water temperature 240°C

Efficiency 86%

Coal consumption per day per unit 1400 tones (Approximate)

STEAM TURBINE:-

Manufacturers B.H.E.L.

Rated output 110MW.

Rated speed 3000 r.p.m.

Number of cylinders three

Rated pressure 130kg/ cm²

Rated temperature 535°C

Condenser vacuum 0.9 kg/cm²

GENERATOR:-

Manufacturers B.H.E.L.

PLANT SALIENT

FEATURES

THE PLANT

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Rated output (Unit- 1 & 2) 125000KV

(Unit -3 & 4)137000KVa

Generator voltage 11000 volts

Rated phase current (unit –1 & 2) 6560 Amps.

(unit –3 & 4) 7220 Amp

Generator cooling hydrogen

BOILER FEED PUMPS

Number per unit two of 100% duty each

Type centrifugal

Rated discharge 445 T/hr.

Discharge head 1960 MWC .

Speed 4500 r.p.m.

CIRCULATING WATER PUMPS:-

Numbers for two units five of 50% duty each

Type mixed flow

Discharge head 24 MWC.

COOLING TOWERS:-

Numbers four

Water cooled 18000 T/hr.

Cooling range 10°C

Height 120/12 1metres

COAL PULVERISING MILLS:-

Numbers three per unit

Type drum-ball

Rated output 27 T/hr.

Coal bunkers 16 per unit

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RATING OF 6.6 KV AUXILLIARY MOTORS:-

Coal mill 630 KW

Vapour fan 320 KW

C.W. Fan 800/746 KW

Coal crusher 520 KW

Primary air fan 320 KW

Forced draught fan 320 KW

Boiler feed pump 3500 KW

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Coal received from collieries in the rail wagon is mechanically unloaded by

Wagon Tippler and carried by belt Conveyor System Boiler Raw Coal Bunkers after

crushing in the coal crusher. The crushed coal when not required for Raw Coal Bunker is

carried to the coal storage area through belt conveyor. The raw coal feeder regulates the

quantity of coal from coal bunker to the coal mill, where the coal is pulverized to a fine

powder. The pulverized coal is then sucked by the vapour fan and finally stored in

pulverized coal bunkers. The pulverized coal is then pushed to boiler furnace with the help

of hot air steam supplied by primary air fan. The coal being in pulverized state gets burnt

immediately in the boiler furnace, which is comprised of water tube wall all around through

which water circulates. The water gets converted into steam by heat released by the

combustion of fuel in the furnace. The air required for the combustion if coal is supplied by

forced draught fan. This air is however heated by the outgoing flue gases in the air heaters

before entering the furnace.

The products of combustion in the furnace are the flue gases and the ash. About 20%

of the ash falls in the bottom ash hopper of the boiler and is periodically removed

mechanically. The remaining ash carried by the flue gases, is separated in the electrostatic

precipitators and further disposed off in the ash damping area. The cleaner flue gases are let

off to atmosphere through the chimney by induced draught fan.

The chemically treated water running through the water walls of boiler furnace gets

evaporated at high temperature into steam by absorption of furnace heat. The steam is further

heated in the super heater. The dry steam at high temperature is then led to the turbine

comprising of three cylinders. The thermal energy of this steam is utilized in turbine for

rotating its shaft at high speed. The steam discharged from high pressure (H.P.) turbine is

returned to boiler reheater for heating it once again before passing it into the medium

pressure (M.P.) turbine. The steam is then let to the coupled to turbine shaft is the rotor of

the generator, which produces electricity. The power pumped into power grid system

through the generator transformer by stepping up the voltage.

WORKING OF

THERMAL PLANT

11

Fig4.3

12

The steam after doing the useful work in turbine is condensed to water in the

condenser for recycling in the boiler. The water is pumped to deaerator from the condenser

by the condensate extraction pumps after being heated in the low pressure heater (L.P.H)

from the deaerator, a hot water storage tank. The boiler feed pump discharge feed water to

boiler at the economizer by the hot flue gases leaving the boiler, before entering the boiler

drum to which the water walls and super heater of boiler are connected.

The condenser is having a large number of brass tubes through which the cold water

is circulated continuously for condensing the steam passing out sides the surface of the brass

tubes, which has discharged down by circulating it through the cooling tower shell. The

natural draught of cold air is created in the cooling tower, cools the water fall in the sump

and is then recirculated by circulating water pumps to the condenser.

GENERAL LAYOUT OF THERMAL POWER PLANT

The general layout mainly consists of four circuits:-

1) Coal and ash circuit.

2) Air and gas circuit.

3) Feed water and steam flow circuit.

4) Cooling water circuit.

Thermal power plant using steam as working fluid basically works upon the principle

of Rankine cycle. Steam is generated from water in boiler, expanded in prime mover and

then condensed in condenser and again fed into the boiler.

1) Coal and Ash circuit: - In this circuit the coal from storage is fed to boiler through coal

handling equipment for generation of steam. Ash produced due to combustion of coal is

removed to ash storage through ash handling system. Coal fed to boiler is first dried by

hot air to remove moisture and to increase the combustion rate.

2) Air and gas circuit: - Air is supplied to the combustion chamber of the boiler either

through induced draught fan or forced draught fan or both. The dust is removed from air

through filters before supplying to the combustion chamber. The exhaust gases carrying

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sufficient amount of heat and ash are passed through air pre-heater , where exhaust heat

of gas is removed before exhausting the gases to atmosphere through chimney.

3) Feed water and steam circuit: - The steam generated in boiler is fed to steam prime

mover to convert heat of steam into mechanical work. This steam coming out of prime

mover is condensed and then fed to boiler with the help of a pump. The condensate is

heated in feed heaters using steam trapped from different points of turbine.

Some of the steam and water is lost passing through different components of

system. Therefore feed water is supplied from external source to compensate this loss.

The feed water supplied from external source to compensate this loss. The feed water

supplied from external source is passed through purifying plant to reduce the dissolved

salts to an acceptable level. This purification is necessary to avoid the sealing of the

boiler tubes.

4) Cooling water circuit: - The quantity of cooling water required to condense

the steam is considerably large and this steam i.e. condensed steam is fed to boiler. The

cooling water is taken from canal.

The different types of systems and components, which are used in thermal power

plant are listed below :-

a) Coal handling system

b) Ash and dust handling system

c) Draught

d) High pressure boiler

e) Prime mover

f) Condenser and cooling water

g) Compressors

h) Feed water purification plant

i) Different components used as economizer, superheater, feed heater etc. to

increase the thermal efficiency of the plant.

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BOILER FEED PUMP:-

As the heart is to human body, so is the boiler feed pump to the steam power plant. It is

used for recycling feed water into the boiler at a high pressure for reconversion into steam.

Two nos. 100% duty, barrel design, horizontal, centrifugal multistage feed pumps with

hydraulic coupling are provided for each unit. This is the largest auxiliary of the power plant

driven by 3500 KW electric motor.

The capacity of each boiler at GURU NANAK DEV THERMAL PLANT is 375

tones/hr. The pump which supplies feed water to the boiler is named as boiler feed pump.

This is the largest auxiliary in the unit with 100% capacity which takes suction of feed water

from feed water tank and supplies to the boiler drum after preheating the same in HP-1, HP-2

and economizer. The delivery capacity of each boiler feed pump is 445 tones/hr. to meet

better requirements corresponding to the various loads, to control steam temperature, boiler

make up water etc. The detailed particulars checking of protections and inter locks, starting

permission etc. are as below:-

Particulars of BFP and its main motor:-

� BOILER FEED PUMP: - The 110 MW turboset is provided with two boiler feed

pumps, each of 100% of total quantity. It is of barrel design and is of horizontal

arrangement, driven by an electric motor through a hydraulic coupling.

Type 200 KHI

No. of stages 6

Delivery capacity 445 t/hr.

Feed water temperature 158°C

Speed 4500 rpm

Pressure at suction 8.30 kg/cm²

Stuffing box mechanical seal

Lubrication of pump by oil under pressure And motor bearing

supplied by hydraulic coupling

Consumption of cooling water 230 L/min.

WATER TREATMENT PLANT:-

The water before it can be used in the boiler has to be chemically treated, since untreated

water results in scale formation in the boiler tubes especially at high pressure and

GENERAL

DESCRIPTION

15

temperatures. The water is demineralised by Ion Exchange Process. The water treatment

plant has production capacity of 1800 Tones per day for meeting the make-up water

requirement of the power station.

COAL MILL:-

Coal Mill pulverizes the raw coal into a fine powder before it is burnt in the boiler furnace.

The pulverizing of coal is achieved with the impact of falling steel balls, weighing 52.5

tonnes, contained in the mill drum rotating at a slow speed of 17.5 r.p.m. The raw coal is

dried, before pulverizing, with inert hot flue gases tapped from the boiler. Three coal mills

each with a pulverizing capacity of 27 T/hr. are provided for one unit.

INDUCED DRAUGHT FAN:-

Two nos. axial flow Induced Draught Fans are provided for each unit to exhaust ash laden

flue gases from boiler furnace through dust extraction equipment and to chimney. The fan is

driven by an electric motor through a flexible coupling and is equipped with remote

controlled regulating vanes to balance draught conditions in the furnace. The fan is designed

to handle hot flue gases with a small percentage of abrasive particles in suspension.

CONTROL ROOM:-

The control room is the operational nerve center of the power plant. The performance of all

the equipments of the plant is constantly monitored here with the help of sophisticated

instrumentation and controllers. Any adverse deviation in the parameters of various systems

is immediately indicated by visual and audio warning and suitable corrective action is taken,

accordingly. The control room is air conditioned to maintain the desired temperature for

proper functioning of the instruments.

SWITCH YARD:-

Electricity generated at 11 KV by the turbo-set is stepped-up by unit transformers to 132/220

KV for further transmission through high tension lines to Maur, Muktsar, Malout, N.F.L.,

Sangrur and Ludhiana. Transmission of power to grid is controlled through 7 nos. 220 KV

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and 15 nos. 132 KV. Air Blast Circuit Breakers along with their associated protective

systems.

WAGON TIPPLER:-

The coal received from the collieries, in more than 100 rail wagons a day, is unloaded

mechanically by two nos. wagon tipplers out of which one serves as a standby. Each loaded

wagon is emptied by tippling it in the underground coal hopper from where the coal is

carried by conveyor to the crusher house. Arrangements have been provided for weighing

each rail wagon before and after tippling. Each tippler is capable of unloading 6-8 rail

wagons of 55 tonnes capacity in an hour.

CRUSHER HOUSE:-

Coal unloaded by the wagon tippler is carried to crusher house through conveyors for

crushing. Two nos. hammer type coal crushers are provided, which can crush coal to a size

of 10 mm. The crushed coal is then supplied to Boiler Raw Coal Bunkers. The surplus coal is

carried to coal storage area by series of conveyors. Crushing of coal is an essential

requirement for its optimum pulverizing and safe storage.

COOLING TOWERS:-

Cooling Towers of the power plant are the land mark of the Bathinda City even for a far

distance of 8-10 kilometers. One cooling tower is provided for each unit for cooling 18000

tones of water per hour by 10°C. cooling towers are massive Ferro-concrete structure having

hyperbolic profile creating natural draught of air responsible for achieving the cooling effect.

Cooling tower is as high as 40 storey building.

BOILER:-

It is a single drum, balanced draught, natural circulation, reheat type, vertical combustion

chamber consists of seamless steel tubes on all its sides through which water circulates and is

converted into steam with the combustion of fuel. The temperature inside the furnace where

the fuel is burnt is of the order of 1500°C. The entire boiler structure is of 42meter height.

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BOILER CHIMNEY:-

The flues from the boiler, after removal of ash in the precipitators, are let off to atmosphere

through boiler chimney, a tall Ferro-concrete structure standing as high as the historic Qutab

Minar. Four chimneys, one for each unit, are installed. The chimney is lined with fire bricks

for protection of ferro-concrete against hot flue gases. A protective coating of acid resistant

paint is applied outside on its top 10 meters.

CIRCULATING WATER PUMP:-

Two nos. of circulating water pumps provided for each unit, circulate water at the rate of

17200 T/hr. in a closed cycle comprising of Turbine Condenser and Cooling Tower. An

additional Circulating Water Pump provided serves by for two units. The water requirement

for bearing cooling of all the plant auxiliaries is also catered by these pumps.

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TURBINE SECTION

Turbine

Turbine is a prime mover for the Generator in the power plant. In steam turbine, the potential

energy of steam is transformed into kinetic energy and later in its turn is transformed into the

mechanical energy of the rotation of the turbine shaft. The common types of turbines are:-

���� IMPULSE TURBINE:- In this type of turbine, steam expands in the nozzles

and its pressure does not alter as it moves over the blades.

� REACTION TURBINE:- In this type of turbine, the steam expands

continuously as it passes over the blades and thus there is a gradual fall in

pressure during expans

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Fig 7.1

Different types ofsteam turbines are used in Thermal Power Plant but the ones which are

used at G.N.D.T.P. are categorized as follows:-

Sr. No. Type of Turbine Turbines at G.N.D.T.P.

1 Horizontal/Vertical Horizontal

2 Single/Multi-cylinder Multi-cylinder (3-cylinder)

3 Impulse/Reaction Impulse

4 Condensing/Non-condensing Condensing

5. Reheat/Non-reheat Reheat

6 Regenerative/Non- Regenerative With bypass (ST-1)

7 With bypass/Without bypass Without bypass (ST-2)

MAIN TECHNICAL DATA

a) The basic parameters:

Rated output measured at Terminal of the generator. 110.000KW

Economical output. 95.000KW

Rated speed. 3.000RPM

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Rated temp. of stearn just before the stop valve. 535°C

Max Temp. of steam before the stop valve. 545°C

Rated pressure of steam before the MP casing. 31.63°C

Max. pressure of steam before the MP casing 35°C

Rated temp. of steam before the MP casing. 535°C

Max. temp. of steam before the MP casing. 545°C

b) System of turbine:

4 Governing valves +2 interceptor valves HP cylinder- 2 Row Curtis wheel +8 moving

wheels.

Wt. Of HP rotor approx. 5,500 Kg.

MP cylinder - 12 Moving wheels.

Wt. Of MP rotor. Approx. 11,000 Kg.

LP cylinder - 4 Moving wheels of double flow design.

Wt. Of MP rotor approx. 24,000 Kg.

Direction of the turbine rotation - To the right, when looking at the turbine from the front

bearing pedestal.

TURBINE ASSEMBLY WITH LOWER CASING

Fig 7.2

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TURBINE ACCESSORIES AND AUXILIARIES:

The following are turbine accessories and auxiliaries:

1. Surface condensers.

2. Steam jet air ejector

3. LP and HP heaters.

4. Chimney steam condenser.

5. Gland stearn condenser.

6. Oil purifier of centrifuge.

7. Clean oil pumps with clean oil tank.

8. Dirty oil pumps with dirty oil tank.

9. Auxiliary oil pump with aux. Oil tank.

10. Starting oil pumps.

11. Emergency oil pumps (AC and DC).

12. Jacking oil pumping.

13. Bearing or turning gear.

1. SURFACE CONDENSERS

Two no. surface condensers are used for condensing the steam which has worked in

the turbine. The coolant for condensing the steam is circulating water, which is inside the

condenser brass tubes, and steam is outside.

TECHNICAL DATA OF EACH CONDENSER:

Cooling area 3330 m2

No. of brass tube 6000

Circulating water required for each condenser 7500T/Hr.

Circulating water required for both condense r2x7500T/Hr. 15000T/Hr.

Allowable difference between inlet & outlet C.W. water 10°C Temp.

Vacuum in the condenser 0.90 Kg/cm2

22

2. STEAM JET AIR EJECTORS

Starting ejector or hogger is used for quick evacuation of the turbo set during starting

whereas main steam jet air ejector (Duplex Type) is used to maintain the vacuum in the

condenser. Steam Jet Air Ejector works on the principle of venture with steam working

media to eject air from the condenser.

3. STEAM HEATERS

In regenerative system there is a stream of 5 LP heater, one desecrator and 2 HP

heaters. All LP and HP heaters are of surface type i.e. condensate of feed water is inside the

heaters tubes and steam extractions are outside the heater tubes in the heater shells. LP

heaters are of single flow type whereas HP heaters are of double flow type i.e. feed water is

flowing twice through the HP heaters in order to extract total HP latent heat and super heat

of steam going into HP heaters, desecrator is a contact type heater in which steam and

condensate come in direct contact with each other.

Details of Steam Extraction:

Steam into HP heater NO. 2 is from cold reheat line.

Steam into HP heater NO.1 is from MP turbine, LPH- 4 LPH- 5 is from MP casing at

differently steam pressures and temperatures.

4. CHIMNEY STEAM AND GLAND STEAM CONDENSERS

There are the additional two heater stages provided in the regeneration system of the

turbine for heating the condensate flowing through it. Steam leak offs from the turbine a

gland is used for heating the condensate in these heaters.

5. STARTING OIL PUMPS AND ARRING GEAR

S.O.P supply necessary turbine oil during starting of the turbine and up to turbine

speed of 2930 RPM till the main oil pump mounted on the turbine rotor at the HP extension.

takes manually in order to provide lub. Oil for turbo set.

Emergency pumps (AC & DC) are meant to start on auto when turbine trips and lub.

Oil pressure falls in order to provide lubrication of turbine and generator bearings.

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6. JACKING OIL PUMP AND ARRING GEAR

Jacking oil pump is used in order to lift the turbine rotor before it is put on barring

gear jacking oil pump takes suction from the turbine lub. Oil system and provide a thin film

of oil for lifting the rotor. Barring gear motor used to rotate the turbine rotor at 62 RPM after

engaging the rotor with the gear during starting and stopping of the turbine.

7. CIRCULATING WATER PUMPS

Two nos. circulating water pumps provide for each unit circulate water @17200

tonnes per hour in a closer cycle comprising of turbine condenser and cooling tower. An

additional circulating water pump provide, serves as a stand by for two units. The water

requirement for bearingcooling of all plant auxiliaries is also catered by these pumps.

(II) STEAM JET AIR EJECTOR

Starting ejector is used for quick evacuation of the turbo set during starting whereas main

steam jet air ejector is used to maintain Vacuum in the condenser. It works on the principle

of ‘VENTURI’ with steam working media to eject air from the condenser.

(III) LP AND HP HEATERS

In regenerative system there is a steam of 5 LP heaters, one Deaereator, 2 HP heaters. All LP

and HP heaters are of surface type i.e. condensate or feed water is inside the heater tubes in

the heater shells. L.P. heaters are of single flow whereas HP heaters are of double flow type.

Deaereator is contact type heater in which steam and condensate come in direct contact.

(IV, V) CHIMNEY STEAM AND GLAND STEAM CODENSER: - There are additional

two heating stages provided in the regeneration system of the turbine for heating the

condense flowing through it steam leaks off from the turbine glands is used for heating the

condensate in these heaters.

(VI, VII, VIII, IX, X) VARIOUS OIL PUMPS

Centrifuge is an oil purifier used to remove moisture and other impurities from the turbine

oil. Maximum allowable moisture content in the turbine oil is 0.2%. In case the oil level of

24

the main oil tank is to be made up then either oil can transferred from clean oil tank to main

oil tank with centrifuge or from dirty oil tank to main oil tank with centrifuge.

(XI) STARTING OIL PUMPS AND EMERGENCY OIL PUMPS

Starting oil pumps supply the necessary turbine oil during starting of the turbine and upto

turbine speed of 2930 rpm till the main oil pump mounted on the turbine rotor at the HP

extension takes manually in order to provide lubrication oil for the turbo set. Emergency oil

pumps are meant to start on auto, when turbine trips and lubrication oil pressure falls in order

to provide lubrication to the turbine and generator bearings.

MAIN TECHNICAL DATA ABOUT TURBINE

a) The Basic Parameters

• Rated output measured at terminal of the generator. 110,000KW

• Economical output. 95,000KW

• Rated speed 3,000 RPM

• Rated temp. Of steam just before the stop valve. 535°C

• Max temp. Of steam before the stop valve 545°C

• Rated pressure of steam before the MP casing 31.63 atm

• Max. Pressure of steam before the MP casing 35 atm

• Rated temp. Of steam before the MP casing 535°C

• Max. Temp. of steam before the MP casing 545°C

•

(a) System of turbine:

Governing valves 2 interceptor valves

HP cylinder 2 Row Curtis wheel +8 moving wheels.

Wt. of HP rotor is approx. 5,5000kg.

MP cylinder 12 moving wheels.

Wt. Of MP rotor is approx. 11,000kg

LP cylinder 4 Moving wheels of double flow design.

Wt. of MP rotor is approx. 24,000.

Direction of the

25

FUNCTION AND TYPES OF STEAM TURBINE

FUNCTION OF STEAM TURBINE

Steam turbine is a from of heat engine in which the available heat energy in from of

steam is converted into kinetic energy, to rotate the turbine rotor, by expansion of steam in a

suitable shaped nozzle, the pressure on the blades causing rotary motion is purely dynamical

and is due solely to the change of momentum of the steam jet during its passage through

these blades.

TYPES OF STEAM TURBINE

The steam turbines are broadly classified into three groups depending on the

conditions of operations of the steam on the rotor blades.

1) Impulse Type

This is again subdivided into:-

a) Simple Impulse

b) Compound Impulse

(Pressure, Velocity and Pressure & Velocity compounded)

c) Combined Impulse

2) Reaction Type

This is again grouped into:-

a) Axial Flow

b) Radial flow

c) Mixed flow

3) Impulse reaction Type

Fig 7.3

26

IMPULSE TURBINES

In an impulse turbine the potential energy in the steam due to pressure and superheat is

converted into kinetic energy in the form of weight and velocity by expanding it in suitably

shaped nozzles. The whole of the expansion takes place in the fixed nozzles. The steam

pressure at the inlet and outlet edges of the rotor blades are equal as there is no expansion in

the rotor bicycles. The steam impinges on the wheel I blades causing the wheels to rotate.

The expansion is carried out in stages referred to as “Pressure, Stages the commonest type of

impulse turbine is the Delaval turbine.

REACTION TURBINE

In the type of turbines the steam expands in both the stationary and moving blades.

So, the steam pressure, at inlet to the moving blades is greater than the exit pressure. The

term” reactions” is strictly not correct as no turbine practice works on pure reaction principle.

The action on the balding is both impulse an “reaction”.

The steam turbine installed is a 3 cylinder,(HP , IP and LP r condensing, reheat cycle

type with 8 non~regulated extractions for regenerative heating pf the boiler feed water. The

cross section through a typical 110 MV steam turbine.

The high-pressure turbine is made of two horizontally split concentric casings. The

inner casing is placed inside the, outer casing so as to permit the expansion of the casing at

all directions. The main steam from the boiler is admitted into the HP turbine through t-{O

quick clashing~) t09 valves.(HPQCV)and four nos of Governing va1VBs. These v81ves are

operated hydraulically and they operate on increase / decrease of secondary oil pressure. In

the HP turbine, steam expands in a two row Curtis stage called the impulse stage and further

in 8 stages of fixed and moving blades” Labyrinth type seals are provided for the HP turbine

at both front and II rear ends and CRH steam or 11 at PRDS steam is used for sealing glands.

The medium pressure part of the turbine is a horizontally divided casing. The guide

wheels are partly mounted in the casing in carriers and directly in the casing. The steam after

HP turbine enters the reheater, gets heated to 540°C and returns to the MP, turbine through

27

MPOCSV and interceptor valves steam entering the MP part flow through 12 fixed and

moving blades and taken to the low pressure turbine through the two corrosive pipes.

The MPQCSV and IVs are also operated Hydraulically.

MEDIUM PRESSURE TURBINE

Fig 7.4

The low pressure turbine is split horizontally into three parts and all the parts are connected

by vertical flanges. The extreme parts of the L.P. turbine are connected rigidly with surface

condensers mounted on sturdy spring supports. The steam entering the L.P. casing flows in

both directions through 4 stages and finally exhausted into the condenser. The middle part of

the L.P. casing houses tube nests of first and second low pressure heaters for heating the

condensate.

The flanges of H.P., M.P. casings are designed to be heated by steam during the

starting up to turbine generator. By heating of the flanges, the differences in temperature

between the cylindrical portion of the casing, flanges and the connecting bolts are reduced

hence limiting the additional stresses on the bottles. The very important criteria for starting

and rate of loading the machine is the difference between the temperature of the steam

admitted in and that of the internals of the turbine. For the purpose of measuring the

temperature of the casing and the steam transfer piping there monopoles are provided at

appropriate points.

28

The turbine is the prime mover for the generator in the power plant Different types of steam

turbines used in thermal power plants, but the ones. Which are used at G.N.D.T. P. are

categorized as follows

S.No. Type of Turbine Turbine at GNDP at

1. Horizontal/vertical Horizontal

2 . Single/multi cylinder

Multicylinder

3. Condensing/non condensing condensing

4. Reheat/ non-reheat Reheat

5. Regenerative/non

regenerative

Regenerative

6. With by pas/without by pass with by pass (stage-1)

Without by pass (stage-2)

BASIC WORKING OF TURBINE

First of all the turbine is run on gear motor with the help of exciter. At that time

steam is kept on recirculating with the help of by pass valve. When the pressure of steam is

increased to on optimum level and turbine acquires a particular rpm then steam is introduced

in the H.P. (high-pressure) cylinder first. The temperature of steam at entrance is 540°C and

pressure is about 139 Kg/cm2. After doing its work on the H.P. Turbine, the steam is taken

out for reheating rated temperature of steam at reheater inlet is 360°C. The temperature of

steam is increased up to 535°C in the boiler shell and steam is again introduced in M.P

(Medium pressure) turbine. After M.P.turbine, the steam is passed on to L.P. (Low-pressure)

turbine. This process helps the turbine to reach the speed of 3000 rpm. After L.P. turbine, the

steam is condensed in condenser, build below the turbine unit. The condenser contains a

number of brass tubes through which cooling out from L.P. turbine it comes in contact with

colder brass tubes then steam get transformed into water. This water get collected in HOT

WELL just below the condenser. From here the hot water is again pumped with the help of

condensate pumps. The cooling water is used to condense steam gets heated up and is cooled

29

by falling from cooling tower. This completes the processing of steam through turbine and

condenser.

4. STEAM CYCLE

The design of the power cycle based on the modern concept, where a unit consists of a steam

generator with its independent firing system tied to the steam generation. The steam

generator is designed for maximum continuous rating of 375-tonnes/hr. and steam Pressure

of 139-kg/cm2 at temperature of 540°C respectively. The steam generator is designed to

supply to a single reheat type condensing steam turbine with a 8 non regulated extraction

points of steam for heading the condensate and feed water. The steam cycle can be classified

into the following three divisions: -

(a) Main steam

(b) Reheat steam

(c) extraction steam

(a) MAIN STEAM

Saturated steam from the steam generator drum is led to the super heater bank to heat if up to

540°C saturated steam from the drum is led to the ceiling super hearter (between SHH1 and

SHH2) from ceiling super steam goes to convection

30

Super heater (between SHH2 and SHH3) the first regulated infection for at temperature takes

place after convection super heater (between SHH9 and SHH10). Before entry to final super

heater the steam is again at temperature by regulated injection. The steam is coming out from

the final super heater normally at a pressure of 139 kg/cm2 at a temperature of 540

oC. This

steam is feed to the control valve. In each of the two live steam lines there is one turbine side

main steam stop valve and one high pressure quick closing valve along with two control

valves.

(b) EXTRACTION STEAM

Steam for heating of the condenser and the feed steam is extracted from 8 non regulated

extraction points from the turbine. Heating is carried out in five stages of L.P. heaters, one

deareating heater and in two H.P. heaters extraction 1, 2, 3, is taken from L.P. turbine.

Extraction 4, 5, 6 and 7 are taken from M.P. turbine. Extraction 8 is obtained from C.R.H.

line first and second stage of heating is done by two sets of twin low-pressure heaters

mounted directly in the L.P. casing of the turbine. Extraction 3, 4 and 5 are connected to the

deaereating heater placed above feed water storage tank 7th

and 8th

extraction steam is fed to

the vertical H.P. heaters respectively.

31

(C) REHEAT STEAM

Exit steam from the H.P. turbine is taken back to the reheater section of the steam generating

unit. Reheating is done in two stages both by flue gas and by super heated steam. The steam

to be reheated is first pass through the triple-heated exchanger, where super heated steam is

used as the heating media. The steam is finally reheated in final reheaters (RHH3) RHH4

and RHH5) suspended in the horizontal pass of the furnace. Reheat steam at a normal

pressure of 36.4 kg/cm2 at a temperature of 540°C respectively is fed to the M.P. cylinder by

two hot reheat steam pipes through strainers and combined stop and interceptor valves. In

each of the cold reheat steam lines from H.P. cylinder a non-return valve is operated by oil

pressure is provided.

5. Turbine Accessories and Auxiliaries

I. Surface condenser.

II. Steam jet air ejector

III. LP and HP heaters.

IV. Chimney steam condenser.

V. Gland steam condenser.

VI. Oil purifier or centrifuge.

VII. Clean oil pump with clean oil tank

VIII. Dirty oil pump with clean oil tank.

IX. Auxiliary oil pump with auxiliary oil tank

X. Starting oil pump.

XI. Emergency oil pump.

(I) SURFACE CONDENSER

Two surface condensers are used for condensing the steam which has worked in the turbine.

The coolant for condensing the steam is circulating water which is inside the condenser brass

tubes and steam is outside.

Technical data of Condenser

• Cooling Area 3300 msq.

• Number of brass tubes 6000

• Circulating water required 7500 tonnes/hr.

• Vacuum in the condenser 0.90 kg/cm sq.

32

Fig.7.5 surface condenser

HIGH PRESSURE TURBINE

INTRODUCTION

HP turbine or high-pressure turbine is a single flow turbine. The heated steam enters

from one side and expands in one direction before exhaust. The main steam lines to HP

turbine are shown in figure. The super heated steam flow from boiler enters the turbine in the

direction shown in figures. This line is known as HRH lines. The HP turbine has a throttle

control valve. Steams on expansion again go to boiler from the turbine via CRH line. The

properties of steam when it enters are as:

1. Pressure at inlet :142 Kg/cm2

2. Temperature at inlet :540 C

3. Conditions of steam :Superheated

DESIGN

HP turbine casing is designed as a barrel type casing without axial joint.

An axially split guide blade carriers is arranged in the barrel type casing. The barrel type

casing has neither an axial nor a radial flange. This prevents mass accumulation with high

thermal stresses. The almost perfect rotational symmetry permits moderate wall thickness of

nearly equal strength at all the sections. The inner casing is axially split and kinematically

33

supported. As the pressure difference across the wall of inner casing confines to below

horizontal flange and connection bolts can be kept small. Barrel type casing is preferred due

to following reasons:

� Rotational symmetry.

� Remain constant in shape and leak proof during quick change in temperature.

INNER CASING

The guide blade carrier is attached in the horizontal and

vertical plane in the barrel type casing so that it can freely expand rapidly in all direction and

axially from a fixed when heating up while maintaining concentricity relative to the turbine

rotor. On the admission side four projections of guide blades carrier and on the exhaust side

two projections fitted into corresponding grooves in the barrel type casing.

34

INTERMEDIATE PRESSURE TURBINE

INTRODUCTION The IP turbine is double flow type turbine. This turbine is after the HP

turbine. IP turbine has two inlets at center and four exhausts, two at each end. Similar to HP

turbine, IP turbine has moving as well as stationary blades. IP turbine has 20 stages. This is

also a reaction type turbine. Constructional features are as follows:

1. Pressure at inlet : 38 Kg/cm2

2. Temperature at inlet :345 C

DOUBLE SHELL CONSTRUCTION

The casing IP turbine is split horizontally and is of double shell construction. A

double flow inner casing is supported in outer casing. Steam from the HP turbine after

reheating enters the inner casing from above and below through two inlet nozzles flanged to

the mid section of the outer casing. This arrangement provides opposed double flow in the

two sections and compensates axial thrust. The center flow prevents the steam inlet

temperature form affecting the support brackets and bearing sections.

INLET AND EXTRACTION NOZZLES

The angle sealing ring forms the connection of the inlet and extraction nozzles

with the inner casing. One leg of the angle ring at such a connection bears against the back of

the collar of the threaded ring in the inner casing, while the other fits into an annular groove

in the inlet nozzle. The Threaded ring is fitted in such a way that the short leg of the angle

sealing ring can slide freely between the collar of the threaded ring and the inner casing. The

steam pressure prevailing on the inside forces the sealing ring against the face of the inner

casing. The tolerances of the annular grooves in the inlet nozzle (7) are dimensioned to allow

the long legs of the annular rings to slide in the groove. The angle rings are flexibly

expanded by the pressure on the inside and their outer areas forced against the annular

grooves to provide the desired sealing affect.While providing a light seal, this arrangement

35

permits the inner casing to move freely in all direction. The inlet nozzle and the extraction

nozzle are bolted to the outer casing.

IP TURBINE BLADING

The IP turbine blading consists of several drum stages. All the stages are reaction stages with

50%. The stationary and moving blade of the front stage is provided with T-root. Their cover

plates are machined in integral with the blades and provides a continues shroud after

insertion.

The moving and stationary are inserted into appropriately shaped grooves in the

shaft or inner casing and bottom caulked with caulking material. The insertion slot in the

shaft is closed by a locking blade which is either by taper pins or grub screws. Special end

blades which lock with the horizontal joint are used at the horizontal joints of the inner

casing. Grub screws which are inserted from the joint secure the stationary blades in the

grooves.

The rear stages have stationary with the hook type roots, which are secured in

annular grooves in the inner casing by filler pieces. The shrouds of these blades are riveted to

the blades in sections. The moving blades of these have design as those of the front stages.

Fig 7.6. Intermediate turbine

36

LOW PRESURE TURBINE

CONSTRUCTION

The LP turbine casing consists of a double flow unit and has a triple shell welded

casing. The outer casing consists of front and rear walls, the later longitudinal support being

and the upper part. The front and the rear walls, as well as the correction areas of the upper

part are reinforced by means of the circular box beams. The outer casing supported by the

ends of the longitudinal beams on the bare plates of the foundation.

1. Pressure at inlet : 35 Kg/cm2

2. Temperature at inlet :540 C

3. Conditions of steam :Superheated

STEAM INLET

Steam inlet to the LP turbine from the IP turbine flows into the inner

casing from both sides through inlet nozzles before the LP blading. Expansion joints are

installed in the steam piping to prevent any undesirable deformation of the casing due to

thermal expansion of the steam piping.

INNER CASING

The double flow inner casing, which is of double shell construction,

consists of the outer shell and the inner shell. The inner shell is attached in outer shell with

the provision for free thermal movement. Stationary blading is carried by the inner shell. The

stationary blade row segments of the LP stages are bolted to the outer shell of the inner

casing.

37

DRUM BLADING

The drum blading of the double flow LP turbine is of reaction type.

The stationary blades are located in the inner shell of the inner casing and from the inlet

group of blading of the LP turbine. The LP exhaust stages following these blades are

described in detail in a separate section.

The stationery blades of the first stage have T-roots,. They are fitted in the inner casing in

grooves of corresponding design where they are secured by caulking material. The remaining

stationary blades, which have hook-type roots, are secured in their grooves by means of filter

pieces. Special locking blades are used at the horizontal joint, secured by means of grub

screws.

The moving blades have T-roots, which are inserted into grooves of corresponding design in

the LP turbine shaft and secured by caulking material. The insertion slot is closed by means

of a locking blade, which is attached to adjacent blades by means of taper pins.

All T-roots blades have integral shroud, which upon installation, form a continuous

shroud. The blades with hook-type roots have riveted shrouds. Inorder to keep the

blade tip losses low, replaceable sealing strips are caulked into the inner casing and the

turbine shaft.

38

LOW PRESSURE HEATER

INTRODUCTION There are shell and tube type of heat exchanger with heating

steam on shell side and condensate on tube side. These are used to take the advantage of the

access steam in turbines. Some portion of superheated steam at different points is extracted.

This steam is made to flow in LPH. Here the condensate water coming from Drain Cooler

takes the heat and passes to dearator. There are three heaters LPH 1, LPH 2, and LPH 3.

The condensate first comes in LPH 1, then in LPH 2, and at last in LPH 3.

� TEMPERATURE AT INLET LPH 1 : 50 C

� TEMPERATURE AT INLET LPH 2 : 60 C

� TEMPERATURE AT INLET LPH 3 : 85 C

� TEMPERATURE AT OTULET LPH 3 : 120 C

After the LPH 3, the heated water goes to dearator.

The main parts of LPH are given below:

• SHELL

• TUBE SYSTEM

• WATER SYSTEM.

These parts are described below

SHELL

The shell is of cylindrical construction with dished end welded at bottom and

having a flange at the upper end for assembly of tube system and water box. The shell is

provided with a suitable steam inlet and drain connection along with other nozzle

connections to accommodate various fittings.

39

TUBE SYSTEM

Tube system consists of U-shaped brass tubes (90/10 Cu-Ni ) which have been

fixed in he tube holes, at both ends, by rolling. Tube system have been provided rollers to

facilitate its withdraw. Tube plate is of mid steel and is secured to the water box and shell

flange by means of nuts and bolts.

WATER BOX

Water box is a fabricated shell having on one end for fixing with the tube plate and

shell and the other end is enclosed by dished end. Partition plates have been provided for

making the heater four-pass on water side. Suitable nozzle have been provided for inlet and

outlet.

40

HIGH PRESSURE HEATER

INTRODUCTION

The high pressure feed water heaters are employed to increase the overall

efficiency of the regenerative cycle by heating the feed water by the steam extracted from the

suitable stages of turbine .the feed water passes through the U-tubes and the steam/drain

passes over the tubes. /these heaters are located on the discharge side oil feed pump and use

superheated steam for heating the feed water .the heaters are therefore subjected to very high

pressure and temperatures. There are two High Pressure Heaters HPH 5, HPH 6.

WORKING OF HPH

The high-pressure heater consists of following three zones:

1) DESUPERHEATING ZONE:

The steam first enters the desuperheating zone and

looses its superheat to the feed water. The steam enters into this section and flows over the

tubes through specially designed disc and baffles.

This reduces the pressure drop on steam side and increases the efficiency of the heater disc

and baffles are provided to regulate the steam flow for efficient heat transfer and prevention

of tube viberations.

`

2) CONDENSING ZONE

slightly superheated steam coming out of desuperhating

zone condenses in condensing zone giving its sensible and latent heat to the feed water

41

flowing through the tubes. This zone is provided with specially designed baffles to prevent

tube viberations and for efficient heat transfer.

3 ) DRAIN COOLING ZONE:

Condensed steam I.e., drain from condensing zone passes over the tubes in drain

cooling zone and finally goes out of the heater and is sent to lower stage heater. In this zone

segmental baffles have been provided for efficient heat transfer and for prevention of

vibration. Flow of feed water is counter to drain flow direction feed water flows through the

tubes and then to condensing zone and finally to D.S. zone. Feed water after leaving the

lower stage heater goes to top H.P.heater and from there to boiler.

42

TURBO-GENERATOR (T.G.)

INTRODUCTION: The generator is directly coupled to the turbine shaft, converts

mechanical energy of turbine shaft into electrical energy. It consists of two electrical

windings. One is mounted on the turbine shaft, rotating with it, and is called the rotor. The

other is arranged as a shroud around the rotor, fixed to the floor, and is called stator. The

relative motion of rotor and stator generates the electricity. The generator, which is hydrogen,

cooled produces electricity at 15,750Volt.

The T-G is two pole type with cylindrical rotor (Non -Salient Pole type) using direct water

cooling of stator winding, including phases connecting bus bar, terminal bushing and direct

hydrogen cooling of rotor winding. The stator frame is of pressure –resistant and gas tight

construction with 4 horizontal coolers in the frame itself forming part of ventilation and

closed cooling circuit.

GENERATOR CAPABILITY

The generator is capable of delivering 247MVA continuously at 15.75KV terminal voltage,

9050 Amps stator current and 3.5Kg/Cm2 hydrogen pressure with cold gas temperature not

exceeding 44degrree Celsius and distillate temperature at inlet of stator winding not

exceeding 45 degree celicsus. Output of the generator at the various lagging and leading

power factors at rated hydrogen pressure are as per the generator capability curve given.

Characteristics (O.C.C, S.C.C) and v-curves of the generator are shown on the diagrams.

HYDROGEN COOLER:

The turbo-generator has been provided with four Nos. gas coolers mounted longitudinally in

side stator body for cooling of hot gas, thus taking away the heat looses generated by rotor

winding, stator core and wind age losses. The gas cooler is a shell and tube heat exchanger

consisting of cooling tubes with coiled copper wire around them to increase the surface area

of cooling. Cooling water flows through the tubes while hydrogen flowing across coolers

comes into contact with external surface of cooling tubes. Heat removed from hydrogen is

dissipated through cooling water.

43

AUXILIARIES

SEAL OIL SUPPLY SYSTEM

The shaft seals are supplied with seal oil from a separate circuit, which consists to

the following principal component Vacuum Tank, AC seal oil pumps 1&2, DC seal

oil pump, Vacuum pump, oil coolers, and Seal oil filters, Intermediate oil tank.

A vacuum tank pump keeps the seal oil in the vacuum tank under vacuum and largely

extracts the gas absorbed by the oil while passing through the hydrogen and air atmospheres.

The seal oil is drawn from the vacuum tank and delivered to the shaft seals via a cooler and

filter. In the event of a failure of seal oil pump1. Seal oil pump 2. Automatically takes over

the seal oil supply. Upon failure of seal oil pump2, the standby DC seal oil pump is

automatically takes over the oil supply to the shaft seals.

GAS SUPPLY SYSTEM

The gas system has the following functions:

• To provide means for safely putting H2 into or taking it out of the machine.

• To maintain gas pressure in the machine at the desired value.

• To indicate to the operator at all tomes the condition of gas in the machine, its

pressure and purity.

• To dry the gas in the machine and remove any water vapour which may get into it

from the seal oil.

The gas system essentially comprises the following equipments

• H2 and CO2 cylinders

• Pressure reducers

• CO2 vaporizer

• Gas drier

• Humidity Monitors

• Purity measuring instruments.

Hydrogen is admitted to the generator through a perforated pipe header extending

along the length of the casing at the top. To prevent formation of an explosive mixture in the

generator casing during filling and removing the hydrogen. The air or hydrogen in the casing

44

is first removed with carbon dioxide respectively. The latter is introduced through CO2 feed

pipe, and the air or hydrogen in the casing is discharged to atmosphere through the hydrogen

feed line. The hydrogen driers, services to dry the gas inside the generator.

STATOR WATER COOLING SYSTEM

The water for cooling the stator winding, phase connection and bushing is circulated in a

closed circuit. To ensure uninterrupted generator operation 100% capacity pumps sets are

provided. In the event of a failure of one pump the standby pump is immediately cut in by

automatic starting equipment.

The stator water supply systems essentially comprise the following components:

• Expansion Tank

• Stator Water Pump A&B

• Stator Water Cooler A&B

• Stator Water Filter A&B

The operating pump draws the water from the expansion tank. The water after

passing through water coolers, filters enter the winding and returns back to the expansion

tank.

START UP OF GENERATOR

Prior to start up, it should be ascertained that the following auxiliaries are in operation and

will continue to remain in service.

• Seal oil system

• Gas System

• Stator water system

• Secondary cooling water system

Prior to startup, all the connections should be rechecked. This applies to the piping as

well as to cabling. When checking the cabling, special attention should be paid to testing the

metering and signal cables. All alarm systems should be checked. All temperature

measuring points should also be checked . This applies to the local as well as remote reading

thermometers.

SHUT DOWN OF GENERATOR

When shutting down the generator all excitation should be removed by the time speed

45

reaches to 2000rpm. If this is not done the field winding temperature will rise to lack

ventilation since rate of gas circulation is proportional to speed.

CONDENSATE AND BOILER FEED SYSTEM

The steam after doing the useful work in the turbine is exhausted into the condensers

where it is condensed by the cooling water (circulating water) flowing through a network of

tubes. After condensation, the condensate is collected in the hot wells of the condensers.

From the hot wells, the condensate is handled by the condensate extraction pumps and is

taken back to the closed loop system. Condensate pump delivers the condensate into the

deaerator through the main ejectors, chimney steam condenser, gland steam condenser and

low-pressure heaters. There are three number of condensate extraction pumps of vertical

turbine type installed for the above purpose. The pump capacity of 160 T/hr and develops

215 MWC head. Under normal conditions of operation of the unit (including full load

condition) two pumps are required to be kept in service while the third is a standby.

The condensate tapped off from the condensate extraction pumps discharge header is

utilized for the following services:-

1. Sealing of valves in the vacuum system. Condensate booster pump stuffing box

sealing.

2. L.P. gland sealing de-super heaters.

3. de-super heaters in the chimney steam condenser.

4. Cooler in the TG-exhaust.

5. Dilution of phosphate and hydrazine solutions.

The make up to the closed cycle is added at the condenser hot well by means of the

make up water pumps. There are 5 numbers D.M. transfer pumps installed which take their

suction from a D.M. water storage tank.

The condensate entering the desecrator under goes desecration process in which all

the dissolved gases in the condensate are removed to a greater extent and the desecrated

water is collected in the feed water tank which is an integral part of the deaerator. The feed

water tank is installed at a sufficiently higher elevation to provide a positive suction to the

boiler feed pumps.

46

The flow path of feed water is schematically shown in fig. The boiler feed pumps

(locted in the ground floor of the turbine hall) take their suction from the feed water tank and

deliver the feed water into the boiler drum through high pressure heater, feed control station

and economizer.

Two Nos. of boiler feed pump each of capacity- 445 /hr (8180 1 pm) developing 178

atm. head is installed. Out of two pumps, one pump is required to be kept in service while

the other one is a standby.

The feed control station consists of three branches of feed lines- a low load line

meant for up to 20% MCR and other two lines meant for 100% MCR conditions. (Out of the

two 100% MCR lines, one will be service while other is a standby).

The feed water for the de-super heaters of the SH and RH is tapped off before the

feed control station. Provisions are made to use the condensate booster pump for initial

filling of the boiler drum.

PROTECTIONS AND INTERLOCKS

The main turbine trip relay (TTX) energizes the turbine and trips the turbine under

the following conditions:-

1. Under frequency protection.

2. Generator shut-down energization.

3. Remote trip (P.B).

4. Generator distance relay actuation.

5. Generator negative sequence.

6. Generator transformer ground.

7. Generator loss of excitation.

8. Boiler master trip.

9. L.P.G. heater no.1 level high.(left or right: 775mm).

10. L.P. heater no. 2 level high (left or right: 775mm).

11. Axial shift thrust bearing high: (± 0.65mm).

12. Hydro mechanical protection axial shift very high: (±0.85mm).

13. Primary governing oil pressure high: (3.05atm.).

14. Bearing oil pressure very low: (0.8atm.).

47

15. Main oil pump discharge very low: (7 atm.).

16. Exhaust pressure very high: (0.5 atm.).

EXPLANATION OF TURBINE SYSTEM :-

First of all the steam is generated in the steam generator i.e. boiler. From second pass

of the boiler the steam is generated at 530°C and at a pressure of 110 kg/cm2 enters the high

pressure turbine. The steam works i.e. expands along the rows of blades and the prime mover

i.e. turbine starts moving. After working in the high pressure turbine the steam again enters

the second pass of the boiler for reheat. All the turbines are coupled to a single rotor. The

high pressure turbine is of reaction turbine, horizontal type multicylinder. In reaction turbine

the steam expands continuously as it passes over the rows of blades and thus there is gradual

fall in pressure during expansion.

The steam from high pressure turbine enters the second pass of boiler for reheat at

30kg/cm2 at 360°C. After reheating the steam again enters the medium pressure turbine at 28

kg/cm2 . The temperature of the steam entering the medium pressure turbine is 530°C. After

working the steam leaves the medium pressure turbine is of impulse type. In impulse

turbines steam expands in the nozzles and its pressure does not alter as it moves over the

blades. So the pressure of the steam entering the MP and leaving MP remains 28kg/cm2.

With in the casing of the MP. Number of tappings namely 4,5,6,7 are made for low pressure

heaters. Tapping number six is the dummy tapping.

Tapping number 5 from the MP turbine goes to the LP turbine goes to the heater NO.

2. The condensate of all the three LPHs goes to the deaerator. Tapping no.7 from MP turbine

goes to high pressure heater no.2, HPH no.1 gets connestion from the cold reheat from the

high pressure turbine. The condensate of the high pressure heaters goes to the economizer.

The outlet temperature of condensate from HPH is 240°C. From the deaerator after deaerator

the condensate through boiler feed pump goes to HPHs from where this enters to economizer.

48

From the MP turbine the steam enters the LP turbine. After working, the steam enters

the condenser, four LPHs are also placed within the casing of the LP turbine. The condensate

from these heaters through a single pipe enters the ejector, fromwhere the condensate enters

the chimney steam condenser and then to the gland steam condenser through which the

condensate enters the HPHs and then goes to economizer. The steam leaves the LP turbine at

-0.90 kg/cm2 i.e. it works under vacuum.

The work of the ejector is to create vacuum. The condensate from the ejector enters

the main steam to the condenser. After condensation the condensate entersthe condensate

enters the well of the condenser which is at 45°C. One tapping from the well goes to the

ejector. a level of the water is maintained in the well. The condensate from the gland steam

condenser and chimney steam condenser enters the water well.

With in the medium pressure turbine a dummy tapping is there. The steam enters this

turbine at 530°C from two sides. The pressure of steam is 28

The cold reheat from the HP turbine enters the second pass of the boiler. The turbine

speed is controlled by electro-hydraulic governing device, from where governing is done.

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CONSTRUCTION OF TURBINE :-

The turbine is a tandem compound machine with HP, IP and LP parts. The HP part is

single flow cylinder and IP and LP parts are double flow cylinders. The individual turbine

rotors and the governor rotors are connected by rigid couplings.

In designing the supports for the turbine on the foundation, attention is given to the

expansion and contraction of the machine during thermal cycling. Excessive stresses would

be caused in the components if the thermal expansion or contraction were restricted in any

way. The method of attachments were restricted in any way. The method of attachments of

the machine components and their coupling together are also decisive factors in determining

the magnitude of the relative axial expansion between the rotor system and turbine casing.

CASING EXPANSION:-

The front and rear bearing housing of the HP turbine can slide on their base plates in

an axial direction. Any lateral movement perpendicular to the machine axis is prevented by

fitted keys. The bearing housings are connected to the HP and IP turbine casing by guides

which ensures that the turbine casing maintain the central position while at the same time

allowing axial movement. Thus the origin of the cumulative expansion of the casing is at the

front bearing housing of the IP turbine.

ROTOR EXPANSION:-

The thrust bearing is in corporated in the rear bearing housing of the HP turbine.

Since this bearing housing is free to slide on the base plate. The shafting system moves with

it. Seen from this point both the rotors and casing of the HP turbine expand towards the front

bearing housing of the HP turbine. The rotor and casing of the IP turbine expand towards the

generator in a similar manner.

DIFFERENTIAL EXPANSION:-

Differential expansion between the rotor and casing results from the difference

between the casing expansion. Originally from the bearing housing behind the IP turbine.

CONSTRUCTION OF TURBINE (HP) :-

Casing :- Barrel type without axial joint. An axially split guide blade carrier is arranged in

the barrel type casing suitable for quick start up and loads.

Blading :-The HP turbine blading consists of several stages. All the stages are reaction stages

with 50%.

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FOR IP TURBINE:-

Casing :- The casing of IP turbine is split horizontally and is of double shell construction.

Casing :- The LP turbine casing consists of a double flow unit and has a triple shell welded

casing. The turbine has a hydraulic speed governor MAX46BY00l and electro-hydraulic

turbine controller. The hydraulic speed governor adjusts main control values MAA10 +

20AA002 and MAB10 + 20AA00l by way of hydraulic convertor.

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BOILER

Boiler section

The steam generating unit is designed to meet the nominal requirements of

110MW turbo generator set. The unit is designed for a maximum continuous rating of 375

tones/hr. at a pressure of 139kg/cm2 and a steam temperature of 5400°C. the reheated steam

flows at MCR 32H tones/hr. at the feed water temp at MCR is 2400°C. The unit is a balance

draught dry bottom; single drum natural circulation, vertical water tube type, construction

with skin casing and a single reheat system. The furnace is arranged for dry ash discharge

and is fitted with burners located at the four corners. Each corner burner comprises coal,

vapour oil and secondary air compartments. The unit is provided with three ball mills and

arranged to operate with intermediate cool powder bunker. The steam super heater consists

of 4 stages Viz. Ceiling, convection, platen and final superheated. The ceiling super heated

forms the roof of the furnace and horizontal pass and finishes as the rear wall of the second

pass. The convection super heated is made up of horizontal banks located in the second pass.

While the platens are located at the furnace exit, the portion above the furnace nose encloses

52

the final superheated reheater are in two stages, first stage is the triflux heat exchangers

located in the second pass, which absorbs heat from superheated steam as well as from the

flue gases. The second stage is exit reheater located in the horizontal pass as pendant tubular

loops.

(a) The flue gas for drying the cool in the mills is tapped off after the triflux heat exchangers.

The damper located in the hot flue gases pipe leading to mill controls the quantity. Control

the circulating vapour of the mill entry effect temperature control.

Immediately after the triflux heat exchanger, the air heaters and economizers are located.

The air heater is in 2 stages.

(b) The hot air for combustion from air heater stage 2 is led into the common wind box

located on the sided of the furnace. 4 cool air mixed pipes from pulverized coal bounders are

connected to 4 cool burners’ nozzle at the corners. There will be totally 16 coal nozzles. 4

located in each corner. Oil guns will be located in the secondary air nozzle for coal burning.

The turn down ratio of the guns will be so selected that it will be possible to use them also

for pulverized fuels flame stabilization while operating under load below the control point.

(c) Take into consideration the high % age of ash and the relatively poor quality of coal due

regards has been paid to wide pitching the tubes and to the gas velocity across the heating

surface areas. In order to insure reliable and continuous operation sample sot blowing

equipment is provided. There are short retractable steam root blowers provide at the top of

furnace fully retractable rotary type blowers are located for cleaning of the secondary super

heater and final heater partly retractable steam blowers are arranged for the horizontal

reheater and super heaters in the second pass. The steam root blowers are electrically

operated.

(d) Root blowing nozzles using blow down from boilers drum are provide for the cleaning of

areas around the burners nozzles zone for dislodging of slag boulder if any in the bottom ash

hopper in the furnace.

(e) Two FD fans are provided per boiler. The FD fans are of the axial type driven by constant

speed motor. The regulation of quantity and pressure is done by inlet vane control. The flue

gases are sucked through the mechanical and electrostatic precipitators by I.D. fans and

delivered into the chimney. Two I.D. fans are provided for each boiler and they are of the

axial type driven by constant speed motors. Inlet vane control effects the capacity change

53

with reference to load. Both the I.D. and FD fans have been dimensioned taking into account

the minimum margins of 15% on volume and 32% on pressure.

Specification

• Manufacturer B.H.E.L

• Maximum continuous rating 375tones/hr.

• Super heater outlet pressure 139kg /cm2

• Reheater outlet pressure 33.8 kg/cm2

• Final super heater temperature 540 deg.c

• Feed water temperature 240deg.c

• Efficiency 86% (stage-1)

• Coal consumption per day 1500 tones

54

Fig 11.1

The G.N.D.T.P. units are primarily coal-fired units and the coal consumption at

maximum continuous rating (M.C.R.) per unit is about 58 T/Hr. the coal used at G.N.D.T.P.

is of bituminous and sub-bituminous type and this is received from some collieries of M.P.

and Bihar. The designed composition of coal is as below:-

� Type Bituminous Coal

� Net calorific value 4300 kcal/kg

� Moisture content in coal 10%

� Ash content 30%

� Volatile matter in combustibles 24%

� Grind ability index 50 Hard Groove

The coal handling plant at G.N.D.T.P. has been supplied and erected by M/s Elecon

Engineering Company Limited, Vallabh Vidya Nagar, Gugarat. Coal is transported from the

coal mines to the plant site by Railways. Generally, the raw coal comes by railway wagons

of either eight wheels weighing about 75 to 80 tones each or four wheels weighing about 35

to 40 tones each. The loaded wagon rake is brought by railways main line loco and left on

COAL HANDLING PLANT

(CHP)

55

one of the loaded wagon tracks in the power station marshalling yard. The main line loco

escapes through the engine track. The station marshalling yard is provided with 8 tracks. The

arrangement of the tracks in the marshalling yard is as follows:-

DESTINATION NO. OF TRACKS

Loaded wagons receiving tracks Four

Empty wagon standing tracks Three

Engine escape tracks One

UNLOADING OF COAL:-

In order to unload coal from the wagons, two Roadside Tipplers of Elecon make are

provided. Each is capable of unloading 12 open type of wagons per hour. Normally one

tippler will be in operation while the other will be standby. The loaded wagons are brought

to the tippler side by the loco shunters. Then with the help of inhaul beetle one wagon is

brought on the tippler table. The wagon is then tilted upside down and emptied in the hopper

down below. The emptied wagon comes back to the tippler table and the outhaul beetle

handles the empty wagons on the discharge side of the tippler. The tippler is equipped with

the integral weighbridge machine. This machine consists of a set of weighing levers centrally

disposed relative to tippler. The rail platform rests on the weighing girders and free from rest

of the tippler when the wagon is being weighed. After weighing the loaded wagons is tipped

and returned empty to the weighing girders and again weighed. Thus the difference of the

gross weight and the tare weight gives the weight of the wagon contents. The tipplers are run

by motors of 80 H.P. each through gears only.

Fig11.2 WAGON TIPPLER

56

The tippler is designed to work on the following cycle of operation:-

Tipping 90 seconds

Pause 5-12 seconds

Return 90 seconds

Weighing 30 seconds

Total 215-222 seconds

Allowing 85 seconds for wagon changing it will be seen that 12 eight-wheel wagons

or 24 four-wheel wagons per hours can be tipped. However since the coal carrying capacity

is 500 tones per hour load of 12 wagons comes to 8 to 9 per hour.

DUST TRAPPING SYSTEM:-

The tippler is also provided with the dust trapping systems by which the dust

nuisance will be minimized. As the tippler rotates, a normally closed hopper valve opens

automatically and the discharged material passes through it into the hopper with its dust-

setting chamber, there is an air valve of large area, which opens, simultaneously with the

hopper valve. The object of this air valve is to blow back through the hopper valve into the

tipping chamber, which must occur if, the settling chamber were closed, it being

remembered that a large wagon contains some 240 cubic feet of material and that this

volume of dust air would be forced back at each tip if the hopper chamber were a “closed

bottle”. The air valve and the hopper valve are shut immediately on reversal of the tippler

and are kept shut at all times except during the actual discharge. The hopper valve is

operated by a motor of 10 H.P., 415 Volts and the air valve is operated by electro-hydraulic

thruster. Inlet valve consists of large number of plates sliding under the wagon tippler grating.

Coal in the wagon tippler hopper forms the heap and as such obstructs the movement of

sliding valve and damaging the plates. The inlet and outlet valves have therefore been

bypassed.

The unloaded material falls into the wagon tippler hopper (common to both tipplers)

having a capacity of 210 tones. The hopper has been provided with a grating of 300mm X

300mm size at the top so as to large size boulders getting into the coal stream. There is also a

provision of unloading the wagons manually into the MANUALLY UNLOADED HOPPER

57

of 110 tones capacity. Manually unloading will be restored to while unloading coal from sick

wagons or closed wagons.

MAGNETIC PULLEYS:-

On belt conveyor no. 4A and 4B, there have been provided high intensity

electromagnetic pulleys for separating out tramp iron particles/pieces from the main stream

of coal conveying. D.C. supply for the magnet is taken on 415 volt, 3 phase, 50 cycles A.C.

supply system.

In addition to above high intensity suspension type electromagnets have also been

provided on belt conveyors 4A and 4B for separating out tramp iron pieces/particles.

RECLAIMING:-

If the receipt of coal on any day more than the requirement of the boilers, the

balanced material will be stocked via conveyor 7Aand 7B and through telescopic chute fitted

at the end of the conveyor. At the end of the chute one tele level switch is provided, which

automatically lifts the telescopic chute to a predetermined height every time. The tele level

switch is actuated by the coal pile. When the telescopic chute reaches maximum height

during operation, which will be cut off by limit, switch and stop the conveying system.

When the pile under the telescopic chute is cleared, the telescopic chute can be

independently lower manually by push buttons.

There are five bulldozers to spread and compact the coal pile. Bulldozers of Bharat Earth

Movers Limited Make are fitted with 250 H.P. diesel engines. Each bulldozer is able to

spread the crushed coal at the rate of 250 tones/hr. over a load distance of 60m the coal can

be stacked to a height of 6m the stockpile stores coal for about 45 days for four units with an

annual load factor of 0.66.

Whenever coal is to be reclaimed the bulldozers are employed to push the coal in the

reclaim hopper having a capacity of 110 tones. The coal from the reclaim hopper is fed either

9A or 9B belt conveyor through vibratory feeders 8A and 8B.

58

CRUSHER HOUSE:-

The crusher house accommodates the discharge ends of the conveyor 4A, 4B

receiving ends of conveyor 5A, 5B and conveyor 7A and 7B, two crushers, vibrating feeders

and necessary chute work. There are two crushers each driven by 700H.P. electric motor, 3

phase, 50 cycles and 6.6 kV supply. The maximum size of the crushed coal is 10mm. The

capacity of each crusher is 500 tones/hr. one crusher works at a time and the other is standby.

From the crusher the coal can be fed either to the conveyors 5A, 5B or 7A, 7B by adjusting

the flap provided for this purpose. There is built in arrangement of bypassing the crusher by

which the coal can be fed directly to the conveyors bypassing crusher.

Fig. 11.3

CONVEYER BELT AND CRUSHER HOUSE

59

Spending Our six week of training in Guru Nanak Dev Thermal Plant,

Bathinda, We concluded that this is a very excellent industry of its own type. They have

achieved milestones in the field of power generation. They guide well to every person in the

industry i.e. trainees or any worker. We had an opportunity to work in various sections

namely switch gear, Boiler section, Turbine section, EM-2 CELL etc. while attending

various equipments and machines. We had got an endeverous knowledge about the handling

of coal, various processes involved like unloading, belting, crushing and firing of coal. The

other machines related to my field that we got familiar with boiler, turbine, compressors,

condenser etc. We found that there existed a big gap between the working in an institute

workshop and that in the industry. Above all the knowledge about the production of

electricity from steam helped me a lot to discover and sort out my problems in my mind

related to the steam turbine, their manufacture, their capacity, their angle of blades and their

manufacturing. The training that We had undergone in this industry will definitely help me

to apply theoretical knowledge to the practical situation with confidence.

CONCLUSION

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REFERENCES

1. MANUAL OF NANAK DEV THERMAL PLANT, BATHINDA.

2. Thermal Engineering , R.S khurmi & J.K Gupta

3. www.wikipedia. com

4. A textbook of power plant engineering: - Er. R.K.RAJPUT