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NTPC

NTPC Limited (formerly national thermal power corporation) is the largest power

generating company in India. It is an Indian public sector company listed on the

Bombay stock exchange although at present the government of India holds 89.5% of its

equity. It was founded on November 7, 1975. It started work on its first thermal power

project in 1976 at Singrauli in Uttar Pradesh.

NTPC’s core business is engineering, construction and operation of power

generating plants and providing consultancy to power utilities in India and abroad.

NTPC is the largest thermal power generating company in the country, with 17

coal based power stations. The company has a coal based installed capacity of 33,675

MW. Every fourth home in India is lit by NTPC. 241.139 BU of electricity was

produced by its stations in the financial year 2014-15. It is ranked 431th in the Forbes

Global 2000 for 2015. The net profit after tax on march 2013-14 was INR 10975 crores

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BRIEF HISTORY

The company was founded in November 1975 as "National Thermal Power Corporation Private Limited". It started work on its first thermal power project in 1976 at Singrauli in Uttar Pradesh. In the same year, its name was changed to "National Thermal Power Corporation Limited". In 1983, NTPC began commercial operations (of selling power) and earned profits of INR 4.5 crores in FY 1982-83. In the year 1997, Government of India conferred it with "Navratna" status. In the same year it achieved a milestone of generation of 100 billion units of electricity in a year. In 1998, it commissioned its first naptha-based plant at Kayamkulam with a capacity of 350 MW. In 1999, its plant in Dadri, which had the highest plant load factor (PLF) in India of 96%, was certified with ISO-14001.

BTPS

Badarpur Thermal Power Station

Badarpur Thermal Power Station is located at Badarpur area in NCT Delhi.

The power plant is one of the coal based power plants of NTPC. BTPS was planned by

CWPC (Central Water and Power Commission) which was bifurcated later on into

Central Electrical Authority (CEA) and Central Water Commission during 1960’s to

cater the growing needs of power of Delhi. The area was selected which was out of the

city limits of that time and near the Agra canal for its water requirements. The area was

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full of the stones of Aravali hills. The coal requirements of the plants with jharia

(Dhanbad) coal mines through nearby Tughlakabad railway station.

At the time only 3 units of 100 MW were planned and the work was given to

public sector company Bharat Heavy Electronics Ltd. (BHEL). Ministry of power

provided Rs 66 crores to CEA for the construction of 1st stage of Power House which

comprised of 3 units of 100 MW each, link canal from Agra canal and discharge canal

to Agra canal, Ash-disposal area, Water treatment plant and Residential area

subsequently. 2 more units were planned with a capacity of 210 MW each taking a full

capacity of 720 MW at the cost of Rs 170 crores. The land was acquired in 1967 and the

work was started. Thereafter 1st unit of 100 MW was synchronized on 23rd September,

1973. It was transferred from ministry of power to the NTPC in March 1978.

It was originally conceived to provide power to neighbouring states of Haryana,

Punjab, Jammu and Kashmir, U.P., Rajasthan, and Delhi. But since year 1987 Delhi has

become its sole beneficiary. It is one of the oldest plants in operation. Its 100 MW units

capacity have been reduced to 95 MW. Units 1-2-3 have indirectly fired boiler, while

Units 4-5 i.e. 210 MW units have directly fired boiler. All the turbines are of Russian

Design. Both turbine and boilers have been supplied by BHEL. The boiler of Stage-I i.e.

Unit 1, 2 and 3 are of Czech Design. The boilers of Unit 4 and 5 are designed by

combustion engineering (USA).

BTPS has also attained ISO: 9001 and ISO: 14001 for environment management

systems. BTPS has planted many thousand trees in its area for environmental control.

BTPS (705 MW)

Approved capacity 705 MW

Installed capacity 705 MW

Location New Delhi

Coal source Jharia coal mines (Dhanbad)

Water source Yamuna (Agra canal)

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Beneficiary state Delhi

Unit size 3 X 95 MW , 2 X 210 MW

Unit commissioned Unit 1 (95 MW) → 1973-74

Unit 2 (95 MW) → 1974-75

Unit 3 (95 MW) → 1975-76

Unit 4 (210 MW) → 1978-79

Unit 5 (210 MW) → 1981-82

THERMAL POWER PLANT

A power station (also referred to as power plants or generating station) is an

industrial facility for the generation of electric power. Power plant is also used to refer

to the engine in the ships, aircraft and other large vehicles. Some prefer to use the term

energy centre because it more accurately describes what the plants do, which is the

conversion of other forms of energy like chemical energy, gravitational potential energy

or heat energy into electric energy. However, power plant is the most common term in

U.S., while elsewhere power station and power plant are both widely used, power

station prevailing in many commonwealth countries and especially in United Kingdom.

In thermal power stations, mechanical power is produced by a heat engine, which

transforms thermal energy often from combustion of fuel into rotational energy. Most

thermal power station produce steam and these are sometimes called steam power

station. A thermal power station is a power plant in which the prime

mover is steam driven. Water is heated, turns into steam and spins a steam

turbine which drives an electrical generator. After it passes through the turbine, the

steam is condensed in a condenser and recycled to where it was heated. The greatest

variation in the design of thermal power stations is due to the different fossil

fuel resources generally used to heat the water. Certain thermal power plants also are

designed to produce heat energy for industrial purposes of district heating,

or desalination of water, in addition to generating electrical power. Globally, fossil

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fuelled thermal power plants produce a large part of man-made CO2 emissions to the

atmosphere, and efforts to reduce these are varied and widespread.

About 80% of all electric power is generated by use of steam turbine. Not all

thermal energy can be transformed to mechanical power, according to second law of

thermodynamics. Therefore, there is always a heat loss to the environment. If this loss is

employed as useful heat, for industrial processes or district heat, the power plant is

referred to as cogeneration power plant or CHP (combined heat power) plant. In

countries, where district heating is common, there are dedicated heat plants called

heatonly boiler stations. An important class of power station in the Middle East uses

byproduct heat for desalination of water.

Constituents of Thermal Power Plant :-

Cooling tower

Cooling water pump

Transmission line (3-phase)

Step-up transformer (3-phase)

Electrical generator (3-phase)

Low pressure steam turbine

Condensate pump

Surface condenser

Intermediate pressure steam turbine

Steam control valve

High pressure steam turbine

Deaerator

Feed water heater

Boiler steam drum

Superheater

Forced draft fan

reheater

Combustion air intake

Induced draft fan

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Power Generation

COAL TO ELECTRICITY

The basic steps in the generation of electricity from coal involves following steps:

Coal to steam

Steam to mechanical power

Mechanical power to electrical power

COAL BOILER STEAM TURBINE Chemical energy Thermal energy Mechanical energy

DIFFERENT LOADS GENERATOR Light energy or other required energy Electrical

energy

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CHP (COAL HANDALING DEPARTMENT) OR (COAL CYCLE) From Jharia mines Railway wagon

Magnetic separator BTPS wagon tripper

Crusher house Coal stock yard

RC feeder RC bunker

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Bowl mill Furnace

In a conventional thermal power station, a fuel is used to heat water, which gives off

steam at high pressure. This in turn drives turbines to create electricity. At the heart of a

power station is a generator, a rotating machine that converts mechanical energy into

electrical energy by creating a relative motion between the magnetic field and the

conductor. The energy source harnessed to turn the generator varies widely. It depends

chiefly on which fuels are easily available and on the type of technology used.

Basic Power Plant Cycle

A thermal (steam) plant uses a dual (vapour + liquid) phase cycle.

It is a closed cycle to enable the working fluid (water) to be used again and

again.

The cycle made use of is “Rankine cycle”, modified to include super heating of

steam, regeneration feed water heating and reheating of steam.

The average temperature at which heat is added to the working fluid can be

increased by preheating the feed water before it enters the boiler. For this, a part

of steam is extracted at some intermediate stage during expansion in the turbine.

The rest of the steam expands in the turbine to the condenser pressure. The

steam thus extracted is mixed with feed water coming from the hot well. The

system of abstracting heat from any point in the turbine and subsequently using

it for heating feed water is called Bleeding. This process is called regenerative

heating.

In reheat cycle, the expansion of the stem is carried out in two or more stages.

After partial expansion to an intermediate pressure in the high pressure turbine,

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the steam is withdrawn and reheated to the original temperature at constant

pressure and then returned on to the low pressure turbine and further expanded

to the condenser pressure. The reheat cycle reduces the moisture content at the

low pressure exhaust. It also increases the output, though at the cost of

additional consumption of heat required for reheat cycle.

Reheat cycle is as follows:-

Process 1-2 → Reversible adiabatic pumping of condensate water from pressure P1 to

boiler pressure P2.

Process 2-3 → Heating of water at constant pressure.

Process 3-4 → Isentropic expansion of steam before reheating.

Process 4-5 → Reheating of steam at constant pressure.

Process 5-6 → Isentropic expansion of steam after reheating.

Process 6-1→ Extraction of latent heat in condenser.

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Regenerative cycle with reheating

PLANT LAYOUT

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BMD

( Boiler Maintenance Department )

Boiler and its Components

A boiler is a closed vessel in which the heat produced by the combustion of fuel

is transferred to water for its conversion into steam of the desired temperature and

pressure. The steam produced may be supplied to the turbine for power generation. The

steam generating boiler has to produce steam at the highest purity, pressure and

temperature required for the steam turbine that drives the electrical generator.

The boiler used is manufactured by BHEL of 210 MW.

Specifications of the boiler

1. Main Boiler (at 100% load)

Evaporation 700 tons/hr

Feed water temperature 247 °C

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Feed water leaving economizer 276 °C

2. Steam Temperature

Drum 341°C

Super heater outlet 540°C

Reheat inlet 332°C

Reheat outlet 540°C

3. Steam Pressure

Drum design 158.20 kgf/cm2

Drum operating 149.70 kgf/cm2

Super heater outlet 137.00 kgf/cm2

Reheat inlet 26.35 kgf/cm2

Reheat outlet 24.50 kgf/cm2

4. Fuel

a) Coal

Fixed carbon 38 %

Volatile matter 26 %

Moisture 8 %

Grindability 50 HGI

High Heat 4860 kcal/kg

b) Oil

Calorific value of fuel oil 10000 kcal/kg

Sulphur 4.5 % w/w

Moisture 1 % w/w

Flash point 66°C

Main Parts Of The Boiler

1. Boiler Drum

Its main function is to separate steam from water. The boiler drum is a cylindrical

pressure vessel with hemispherical ends in which the water level is maintained at 10”

below the centre of the drum. The wet steam enters in the drum through the water wall

of boiler. The drum consists of baffles and thin fine sieves through which wet steam

passes. The baffles provided number of plates in downward direction. The wet steam

passes through these baffles and after that it passes through thin sieves at the top of the

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drum. The water droplets in the steam fall down through baffles and sieves. The pure

steam passes to root panels. Now, the steam is sent to the super heaters while the

saturated liquid water is again circulated through the down-comers and then

subsequently through the risers till all the water in the drum turns into steam and passes

to the next stage of heating that is superheating. The drum houses all equipments used

for purification of steam after being separated from water. These equipments are known

as ‘drum internals’.

Material – Carbon steel I.D. – 1676 mm

Weight – 123 tonnes O.D. – 1942 mm

Length – 15700 mm Temperature – 342 °C

Pressure – 150.7 kg/cm2

2. Furnace

A boiler furnace is the main part of the boiler in which coal or fuel is burnt and

produce a lot of heat and flue gases to convert the water into steam.

First the pulverized coal is fed to the furnace through a pump. The air and oil are

fed to the furnace through FD fan and oil guns. When the temperature required for self

burning of the coal is reached a lot of heat and flue gases are produced. The water

contained inside the water tubes turns into steam. The furnace is open at the bottom to

allow ash/clinkers to fall freely into the furnace bottom ash hopper (through a ‘furnace

throat’), and at the top of its rear wall, above the arch, to allow hot gases to enter the

rear gas pass.

Height – 43.979 m

Length – 13.868 m

Width – 10.592 m

Volume – 5210 m3

3. Economizer

The function of an economizer in a steam-generating unit is to absorb heat from

the flue gases and add this as sensible heat to the feed water before the feed water enters

the evaporative circuit of the boiler. This additional heating surface in the path of the

feed water increases the efficiency of the steam generating cycle, saving in fuel

consumption. It is arranged between feed pumps and boiler drum.

The temperature before entering the economizer is 240 °C.

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The temperature after leaving the economizer is 280 °C.

4. Downcomers

Down comers provide a passage for water from the boiler drum to bottom ring

header. From bottom ring header the water goes to water walls for heat absorption and

conversion into steam heating .To achieve the circulation of water into water wall Boiler

circulation pumps are provided in down comers.

5. Water walls

Water walls are the necessary elements of the boiler. They serve as the means of

heating and evaporating the feed water supplied to the boiler from the economizers via

boiler drum and down comers.

In large boilers, water walls completely cover the interior surfaces of the furnace

providing practically complete elimination of exposed refractory surface. They usually

consist of vertical tubes membrane and are connected at the top and at the bottom to

headers. These tubes receive water from the boiler drum by means of down comers

connected between drum and water walls lower header. Water walls absorb 50 percent

of the heat released by the combustion of fuel in the furnace, which is utilized for

evaporation of feed water. The mixture of water and steam is discharged from the top of

the water walls into the upper wall header and then passes through riser tubes to the

steam drum.

6. Riser tubes

A riser is a tube through which the mixture of water and steam pass from an

upper water wall header to the steam drum.

7. Superheater

The steam generated by the boiler is usually wet because it is in direct contact with

water. So, in order to increase the dryness fraction of the exiting steam we get it

superheated, a device known as superheater has to be incorporated in the boiler. This is

because if the dryness fraction is low, as is the case with saturated steam, the presence

of moisture can cause corrosion of the blades of the turbine. Super heated steam also has

several merits such as increased working capacity, ability to increase the plant

efficiency, lesser erosion and etc.

The function of the superheater system, is to accept dry saturated steam from the

steam drum and to supply superheated steam at the specified final temperature of

540°C, by means of a series of heat transfer surfaces arranged within the boiler gas

passes.

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The dry saturated steam from the boiler drum flows inside the superheater tubes and the

hot flue gases flows over the tubes and in this way its temperature is increased at the

same pressure.

The super heater consists of three sections classified as Low temperature super

heater (LTSH), Radiant Pendent super heater (RPSH) and Platen super heaters (PLSH)

after which the steam is sent through the Main Steam (MS) piping for driving the

turbine. The outlet temperature & pressure of the steam coming out from the super

heater is 540° C & 157 kg/cm2.

8. Reheater

A reheater is a device that is incorporated in the upper arch of the boiler near the

gooseneck in the path of the outgoing flue gases. As the name indicates, it reheats the

outlet steam from the HP turbine and thus increasing its temperature up to the desired

value.

The reheater steam from the HP turbine exhaust and supply hot reheat steam at

the specified outlet steam temperature of 540°C by means of heat transfer surfaces

arranged within the boiler gas passes. The reheater consists of 2 heating coils which

finally raise the temperature of the steam to the required level.

Steam from the HP turbine exhaust enters the reheater system through two parallel

mounted spray water desuperheaters liners located in the cold reheat pipe work, then

passes through reheater, increasing the temperature as it travels through it. Reheater

outlet temperature is controlled by raising or lowering the angle of burner tilt. When this

reheated steam enters the IP turbine, the net efficiency of the cycle is increased.

9. Air Preheaters

Air Pre heater is a heat transferring device in which air temperature is raised by

transferring heat from flue gases. The purpose of the air pre heater is to recover the heat

from the boiler flue gas which increases the thermal efficiency of the boiler by reducing

the useful heat lost in the flue gas. As a consequence, the flue gases are also sent to the

chimney at a lower temperature and results in increasing the boiler efficiency. For every

20 °C drop in flue gas exit temperature, the boiler efficiency increases by about 1%.

10. Electrostatic Precipitator (ESP)

An Electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate

device that removes particles from a flowing gas (such as air) using the force of an

induced electrostatic charge. The ash content in the Indian coal is of the order of 30% to

40%. When coal is fired in the boiler, ashes are liberated and about 80% of ash is

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carried along with the flue gases. If this ash is allowed to atmosphere, it is hazardous to

health. So, it became necessary to incorporate an electrostatic precipitator in the path of

the flue gases going in the atmosphere. The electrostatic precipitators are preferred to

mechanical precipitators because they are capable of precipitating particles from sub

micron to large sizes of particles. The efficiency of the modern ESP’s is of the order of

99.9%.

The electrostatic precipitator consists of a large chamber, which comprises of

parallel rows of sheet type collecting electrodes suspended from the precipitator casing

with wire type discharge electrodes arranged mid-way between them. At the inlet of the

chamber, gas distributor screens for uniform distribution of the gases in the chamber,

are provided.

The collectors are connected to earth at positive polarity while the discharge

electrodes are connected to a high voltage dc supply at negative polarity. When dust-

laden gas flows between the electrodes, the corona discharge causes the dust particles to

become charged, the particles then being attracted towards and, eventually, deposited on

the collector electrodes.

This dust falls as the collecting electrodes are continuously rapped through a

rapping system and is collected into the pyramid type hoppers, located beneath each

collecting electrodes, from where it is removed by the ash handling system.

11. Scraper conveyer

Scraper conveyor is used for removing ash from the combustion chamber. It is

mounted at the bottom of the furnace where ash is collected after burning the coal. It is

generally used for removing heavy dust.

12. Clinker grinder

It is an apparatus which is connected with scraper conveyer for the purpose of

removing ash from the boiler. The heavy long ash pieces are crushed in the clinker

grinder so that they can easily flow out of the boiler.

Milling System

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Coal Bunker

These are in-process storage silos used for storing crushed coal coming from the

coal handling plant through conveyor belts.

There are six coalbunkers supplying coal to each mill and are located at top of the

mills to aid in gravity feeding of the coal. Each bunker can store coal, which can be

used for 12hrs.

Coal Feeder

Coal feeders are used to regulate the flow of coal from bunker to the pulveriser.

Each mill is provided with a drag link chain feeder to transport raw coal from the

bunker to the inlet chute, leading to mill at a desired rate. The principle of operation of

coal feeder is that coal flows from the bunker into the chain feeder via feed hopper and

is conveyed to the mill, when the feeder is in the operation, the conveyor chain drag a

fixed head of coal towards the driven ends of the feeder. At the end of the carrying

plates the coal falls through the conveyor onto the bottom plate, where it is picked up by

the returning flight bars and dragged back along the feeder to fall into the mill.

RC Feeder specifications :-

S NO. DESCRIPTION VALUE

1. Number 3 per boiler

2. Type Chain type

3. Speed 3.2 to 9.2 rpm

4. Capacity 13 to 40 tons per hr

MOTOR

S NO. DESCRIPTION VALUE

1. Rating 7.5 kw

2. Speed 1430 rpm

3. Voltage 415

Pulveriser Mill :-

These mills pulverize coal to desired fineness to be fed to the furnace for

combustion. The main structure of the pulverisering mill is fabricated from mild steel in

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three cylindrical sections, the bottom section (the mill housing support )which support

the entire unit and encloses the mill drive gear unit, a center section (the mill

housing)that contains the rotary grinding element and upper section (the classifier

housing )comprising an accommodate the gas loading cylinders of the mill loading

gear .A platform around the upper section provide an access to an inspection door and to

the top of the mill routine maintenance and is served by detachable ladder .

The grinding element comprises of 3 rotatory rollers.

The raw coal enter the mill through inlet and fall into the grinding zones ,where

rotating bottom grinding and transport coal through the grinding element into the

primary air stream .The primary air enters through the inlet duct in the mill while goes

to the furnace from four outlet ducts at the top of the mill.

The ground fuel particle are picked up by the primary air stream after it is passed

through the throat plates and carried upwards towards the classifier .The larger particle

are initially carried upwards by the air stream and circulate over the upper grinding ring

before falling back into the grinding zone by virtue of their weight .The coal /air

mixture then passes into the classifier ,where any remaining oversize particle are

separated out and fall down to the return skirt until their commutative weight is

sufficient to deflect the flaps and return them into the grinding zone .

Heavy material such as pyrites and tramp iron which has passed through grinding

zone without being pulverized is carried around throat plate and discharged through a

counter balance relief gate into the space below the yoke.

Classifier

It is equipment which serves separation of fine pulverized coal particles medium

from coarse medium. The pulverized coal along with the carrying medium strikes the

impact plate through the lower part. Large particles are then transferred to the ball mill.

Cyclone Separators

It separates the pulverized coal from carrying medium. The mixture of pulverized

coal vapour caters the cyclone separators tangentially in the upper part of the separator.

Due to decrease in the velocity the centrifugal action, the pulverized coal separated from

the vapour &falls down to the lower epical part.

The Turnigate

It serves to transport pulverized coal from cyclone separators to pulverized coal

bunker or to worm conveyors. There are 4 turnigates per boiler.

Worm Conveyor

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It is equipment used to distribute the pulverized coal from bunker of one system

to bunker of other system. It can be operated in both directions.

TYPES OF FAN

A fan is a device by which the air is made to flow at required velocity and

pressure in a defined path imparting K.E of its impellers to air/flue gases. This pressure

boost is used to create a draught in the air and flue gas system. Fans mainly perform two

functions:

i. They supply air required for combustion in the furnace with required pressure & flow.

ii. They evacuate the product of combustion i.e. flue gases into the atmosphere via

chimney.

Forced Draft Fan

The forced draught fan system sucks air directly from the atmosphere. It is

provided to supply secondary air required for pulverized coal combustion in the furnace,

air for fuel oil combustion and over fire air to minimize Nox production. The air from

fan discharges into a hot air crossover duct via a main air heater. This duct extends

around to each side of the boiler furnace to form two secondary air to burners ducts. At

the sides of the furnace, each duct split to supply air to two corners.

Primary Air Fan

The primary air fan supplies heated air to the coal mills known as primary air, to

give dry and pulverized coal to the furnace for efficient combustion. There are two P.A

fans per boiler. The fan impeller is a double inlet, centrifugal wheel with backward

curved plate blades.

The air from each fan discharges into a hot air crossover duct via a steam air heater.

This duct extends around to each side of the boiler to supply the hot air to mills duct,

both of which are branched to supply hot air to four coal mills.

Induced Draft Fan

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The induced draught fan system comprises of three centrifugal double inlet fans

per boiler, two operating and one standby. Each fan unit consists of a backward curved

plate bladed impeller, which is driven by an electric motor through a variable speed

hydraulic coupling. The I.D fan serves the purpose of evacuating the products of

combustion or the flue gases in the atmosphere via chimney. The flue gases after being

cleaned in the precipitators is directed towards the atmosphere through the chimney.

PAM

( Plant Auxiliary Maintenance )

PAM stands for plant auxiliary maintenance. It is not heart of plant but

responsible for working of plant heart systems like boiler and turbine by providing

water for steam generation which is blood of thermal power plants.

The auxiliaries that come under PAM are:-

Control Structure Pump House (CSPH)

Water Treatment Plant (WTP)

Ash Handling System

Compressed Air Handling System

Cooling Towers

Central Repair Shop (CRS)

Control Structure Pump House

The CSPH at BTPS supplies the water for processes and service requirements.

Service water is required in the following purposes:

Sealing of furnace bottom and ESP hoppers

Water for ash flushing and ash sluicing

Water for fire fighting and mill fans

Sealing of ash pumps, coal crusher coupling cooling, hydrogen plant and station

compressors.

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1. CRW Pumps :-

BTPS employs 3 nos. of Clarified water pump, 3500m³/h. It Provide raw water to

water treatment plant for clarified water and Demineralize water.

2. HP Pump :-

BTPS employs 6 nos. of high pressure pumps HP-1 to 4 -500 m³/h and HP 5&6-

400 m³/h. They are 5 stages pumps. These are vertical types. They are used for cooling

of turbines, boiler and washing of ash in the boilers.

3. LP Pump :-

BTPS employs 3 nos. of Low Pressure pump. They supply water for ash slurry

preparation and cooling machines other than turbines.

4. FS Pump :-

BTPS employs 2 nos. of Fire Screen pump. These pumps are used to supply water

for firefighting system, as service water in boiler area and for cleaning of vertical

screens.

5. DEDS Pump :-

DEDS stands for Dust Extraction And Dust Suspension System. Clarified water

after generator gas cooling is supplied by 3 vertical pump and 1 centrifugal pump for

spraying water in coal yard form preventing auto ignition of coal and to TWS pumps for

TWS cleaning.

6. TWS Pump :-

Travelling water screen pumps are used for boosting pressure of DEDS pumps

discharge.

Water Treatment Plant

The availability of suitable supply of water both for cooling purpose and for

boiler feed make up is one of the basic requirements of a thermal power plant. The

water treatment plant is meeting this requirement. The water which is used in the boiler

must be in very pure form to avoid corrosion of boiler tubes, scale formation on the

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inside surfaces of various parts and to avoid silica carry over to turbine corrosion of

tubes leads to its failure and this reduces boiler reliability, scale formation leads to

resistance to heat transfer and overheating of tube metal and gets deposited on the

relatively cold portion of turbine and creates resistance to steam flow efficiency of

turbine. As the working pressure and temperature of boiler goes high with unit size

increasing, the requirement of very pure water becomes more stringent. Therefore, the

main objective of water treatment plant is to remove all impurities from the water being

sent to boiler in order that the steam generated shall be pure and boiler can give

uninterrupted services.

Water treatment process which is generally made up of two sections:

a) Pre-treatment section

b) Demineralization section

Pre-treatment section

Pre-treatment plant removes the suspended solids such as clay, silt, organic and

inorganic matter, plants and other microscopic organism. The turbidity may be taken as

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of two types of suspended solids in water. Firstly, the separable solids and secondly the

non separable solids (colloids). The coarse components, such as sand, silt etc, can be

removed from the water by simple sedimentation. Finer particles however, will not

settle in any reasonable time and must be flocculated to produce the large

particles which are settling able. Long term ability to remain suspended in water is

basically a function of both size and specific gravity. The  settling  rate  of  the

colloidal  and finely divided (approximately 001 to 1 micron) suspended matter is so

slow that removing them from water by plain sedimentation is tank shaving

ordinary dimensions is impossible.  Settling velocity of finely divided and collide

particles under gravity also are so small that ordinary sedimentation is not possible. It is

necessary, therefore, to use procedures which agglomerate the small particles into

larger aggregates, which have practical settling velocities. The term "Coagulation" and

“flocculation” have been used in discriminately to describe process of turbidity removal.

"Coagulation" means to bring together the suspended particles. The process describes

the effect produced by the addition of a chemical Al (SP) g to a colloidal

dispersion resulting in particle destabilization by a reduction of force tending to keep

particles apart. Rapid mixing is important at this stage to obtain.  Uniform dispersion of

the chemical and  to increase  opportunity  for  particles  to particle

contact. This operation is done by flash mixer in the c1ariflocculator. Second stage of

formation of settle able particles from destabilized  colloidal sized  particles  is termed a

"flocculation". Here coagulated particles grow in size by attaching to each other. In

contrast to coagulation where the primary force is electrostatic  or 

intrinsic, "flocculation" occurs by chemical bridging. Flocculation is obtained by gentle

and prolonged mixing which converts the sub microscopic coagulated particle into

discrete, visible & suspended particles. At this stage particles are large  enough  to 

settle rapidly under the influence of gravity anomaly be removed.

Demineralization

The requirement of power plant is totally demineralised water thus; the water

should not contain any dissolved impurities or minerals. The minerals and elements

commonly present in the water are CaCO3, CaCl2, CaHCO3, MgCl2 and phosphorous

etc. for the removal of dissolved impurities filtered water is taken to demineralised tank.

There are five such tanks:-

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a) Activated carbon filter

b) Cation exchanger

c) Degasifier

d) Anion exchanger

e) Mixed bed

1. Activated carbon filter

To neutralize chlorine in water, the water is passed through activated carbon

filter. It consists of a capsule shaped tower, which is about 5 m high and contains a bed

of activated coal. The chlorine gets collected in the bed in HCl form. After sometime

the chlorine bed gets exhausted. For regeneration the inlet and outlet valves are closed

and back washing of the bed is doe by passing water at high pressure in opposite

direction and the HCl is washed away in drain. The regeneration is necessary after 16

hours.

2. Cation exchanger

In the cation exchanger the cation present in water such as Ca2+, Mg2+, Al3+,

Na2+ and K+ are removed. In cation battery there is sand like resin, which is granular in

formbut sands is lighter than the resin material. The composition of resin is supplier

company basically it is polystyrene sulphorate. The resin is in RH for. Positive ion

reacts with resin free water is removed and hydrogen is replaced. Capacity of resins 850

ton in the power station and 50 ton/hr. Thus, regeneration is necessary after every 16

hours. For regeneration inlet and outlet of valves of water is closed and 5% HCl

solution is added in the cation exchanger and regeneration is allowed for 55 minutes. On

addition of HCl, CaCl2 and etc are formed and are reached by back washing by feeding

high pressure from bottom.

3. Degasifier

In this carbon dioxide dissolved in water is removed. In the degasifiers the partial

pressure of the CO2 is decreased to zero and thus CO2 escapes into the atmosphere.

Thus, the degasifier works on the principal of henry’s law of partial pressure.

4. Anion exchanger

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The anion resin is basically the amines technically the anion resin used in the

anion exchanger is namely as DAN IP. After sometimes the anion battery gets

exhausted and has to be regenerated. Life of battery is 15-16 hrs, having maximum

capacity of 700 tonnes. The regeneration is done by adding 5 % set of NAOH to the

resin for 30 min. approximately.

5. Mixed bed

Before feeding into the boiler the water should be totally free from minerals. The

water is finally passed through the mixed bed filled in a battery. The composition of

mixed bed is not fixed. It contains both cation exchange resin and anion exchange resin.

Regeneration process of battery carried out in the following way:

I. Back washing

II. Regeneration of anion battery

III. Regeneration of cation battery

IV. Again rinse the battery

V. Again final rinsing of particle like HCl and NAOH

VI. Final mixing is done by passing compressed air into the bed

Finally after all this process, demineralise water of PH-7 and silica content

0.02% and conductivity 0.1 is obtained. The demineralise water produced by

water treatment plant is stored in tanks.

Compressor House

Compressor house is source of compressed air for plant. Compressed air as name

implies having pressure above atmospheric pressure and used to operate many crucial

functions.

Compressed air in plant used in two forms.

Plant Air

Instrumental Air

Plant air also known as service air is used as service air for cleaning different

locations. It may be somewhat impure and contains moisture, oil particles, etc. It is used

in general purposes in plant. These are:

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Sand blasting of turbine blades

Filter cleaning of main oil tank

Light oil atomization in igniters gun

Opening of gates of 210 MW unit for mixing of hot primary air

In 210 MW units there are certain pneumatic machines which require extremely

pure compressed air free from any moisture or oil content. These include motors of air

pre heater and certain valve operation. Thus, instrumental air is used in pneumatic

instruments.

Different compressors used at Plant:-

a) Station Air Compressor: All three station air compressors are reciprocating

type. Compressed air is used mainly in stage 1.

b) Instrument Air Compressor: There are two instrument air compressors B&C.

Compressed air after compressor is goes through air drying Unit A & B. Air

Drying Unit Consist of heaters and Silica gel and perform the function of air

drying.

c) Plant Air Compressor: There are three plant air compressors A, B, C.

Compressed air of plant air compressor is used mainly as service air and used for

cleaning purpose.

d) Denso Air Compressor: There are four denso air compressors A, B; C & D.

Denso air compressor air is used mainly in Bowl mills of Unit 4&5.

The compressors used in the compressor house are of horizontal type, double

acting and two cylinder type. The high pressure and low pressure cylinders. But they are

connected to a common lead.

Ash Handling System

1. Bottom ash handling system

In the bottom ash system the ash discharged from the furnace bottom is collected

in two water compounded scraper through installed below bottom ash hoppers. The ash

is continuously transported by means of the scraper chain conveyor onto the respective

clinker grinders which reduce the lump sizes to the required fineness and the crushed

clinkers falls into sluice channel where high pressure water jets have been fitted at

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suitable locations convey the mixture of ash and water through the system of sluice

channel and into the air slurry pumps for outward disposal by ash slurry pumps.

2. Fly ash handling system

Fly ash is captured and removed from the flue gas by electrostatic precipitators or

fabric bag filters (or sometimes both) located at the outlet of the furnace and before the

induced draft fan. The fly ash is periodically removed from the collection hoppers

below the precipitators. Generally, the fly ash is pneumatically transported to storage

silos for subsequent transport by trucks or railroad cars.

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Cooling Towers

A cooling tower is a steel or concrete hyperbolic structure having a reservoir at

the bottom for storage of cool water. Warm water is lead to the top. The water drops

falling from the top come in contact with the air loses heat to the air and gets cooled.

There are three cooling towers in BTPS. Cooling Towers fulfill the scarcity of

water and is that component which transform open cycle power plant to closed cycle.

Cooling Towers are nothing more than heat exchanger. In cooling towers, heat

exchange process take place where cooling medium is environmental air and interaction

of hot water with environmental air brings down temperature of hot water to

environmental temperature.

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TMD

(Turbine Maintenance Department)

Turbine Classification:

1. Impulse Turbine

In Impulse Turbine steam expands in fixed nozzles. The high velocity steam from

nozzles does work on moving blades which causes the shaft to rotate. The essential

features of impulse turbine are that all pressure drops occur at nozzles and not on

blades. A simple impulse turbine is not very efficient because it does not fully use the

velocity of the steam. Many impulse turbines are velocity compounded. This means

they have two or more sets of moving blades in each stage.

2. Reaction Turbine:

In this type of turbine pressure is reduced at both fixed& moving blades. Both

fixed& moving blades act as nozzles. Work is done by the impulse effect of steam due

to reversals of direction of high velocity steam. The expansion of steam takes place on

moving blades. A reaction turbine uses the "kickback" force of the steam as it leaves the

moving blades and fixed blades have the same shape and act like nozzles. Thus, steam

expands, loses pressure and increases in velocity as it passes through both sets of blades.

All reaction turbines are pressure-compounded turbines.

3. Compounded Turbines

Several problems occur if energy of steam is converted in single step & so

compounding is done. Following are the types of compounded turbine:

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Velocity Compounded Turbine

Like simple turbine it has only one set of nozzle &entire steam pressure drop

takes place there. The kinetic energy of steam fully on the nozzles is utilized in moving

blades. The role of fixed blades is to change the direction of steam jet & to guide it.

Pressure Compounded Turbine

This is basically a no. of single impulse turbines in series or on the same shaft.

The exhaust of first turbine enters the nozzle of the next turbine. Total pressure drop of

steam does not take on first nozzle ring but divided equally on all of them.

Pressure Velocity Compounded Turbine

It is just the combination of the two compounding has the advantages of allowing

bigger pressure drops in each stage &so fewer stages are necessary. Here for given

pressure drop the turbine will be shorter length but diameter will be increased.

Operating Principles

A steam turbines two main parts are the cylinder and the rotor. As the steam

passes through the fixed blades or nozzles it expands and its velocity increases. The

high-velocity jet of steam strikes the first set of moving blades. The kinetic energy of

the steam changes into mechanical energy, causing the shaft to rotate. The steam then

enters the next set of fixed blades and strikes the next row of moving blades. As the

steam flows through the turbine, its pressure and temperature decreases, while its

volume increases. The decrease in pressure and temperature occurs as the steam

transmits .energy to the shaft and performs work. After passing through the last turbine

stage, the steam exhausts into the condenser or process steam system. The kinetic

energy of the steam changes into mechanical erringly through the impact (impulse) or

reaction of the steam against the blades.

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Steam Cycle

Condenser

L P Turbine

I P Turbine

Reaheater

H P Turbine

Main Steam Line

Final Super Heater

Platen Super Heater

Low Temperature Super Heater

From boiler drum

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Condensate Cycle

Daerator Tank

L.P.H. 4

L.P.H. 3

L.P.H. 2

Gland Steam Cooler 2

L.P.H. 1

Gland Steam Cooler 1

Ejector

Condensate Pump

Hot Well

Condenser

From LP turbine

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Feed Water Cycle

Low Temperature Super Heater

Boiler Drum

Water Walls

Down Comers

Boiler Drum

Economiser

Feed Water Line

H.P. heaters 1, 2, 3 (240 ° C)

Boiler Feed Pump150 kg/cm2

Boiler Feed Pump (booster pump)10 kg/cm2

Deaerator tank

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Turbine and its auxiliaries

Main Turbine

The 210MW turbine is a tandem compounded type machine comprising of H.P.

& I.P. cylinders. The H.P. turbine comprises of 12 stages the I.P. turbine has 11 stages

& the L.P. has four stages of double flow. The H.P. & I.P. turbine rotor are rigidly

compounded & the I.P. & the I.P. rotor by lens type semi flexible coupling. All the three

rotors are aligned on five bearings of which the bearing no.2 is combined with thrust

bearing. The main superheated steam branches off into two streams from the boiler and

passes through the emergency stop valve and control valve before entering, the

governing wheel chamber of the H.P. turbine. After expanding in the 12 stages in the

H.P. turbine the steam returned in the boiler for reheating. The reheated steam from the

boiler enter I.P. turbine via interceptor valves and control valves and after expanding

enters the L.P. turbine stage via 2 numbers of cross over pipes. In the L.P. stage the

steam expands in axially opposite direction to counteract the trust and enters the

condenser placed directly below the L.P. turbine. The cooling water flowing throughout

the condenser tubes condenses the steam and the condensate collected in the hot well of

the condenser. The condensate collected is pumped by means of 3*50% duty

condensate pumps through L.P. heaters to deaerator from where the boiler feed pump

delivers the water to boiler through H.P. heaters thus forming a closed cycle.

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HP Turbine

HP turbine is a single flow design with twelve stages of blading .Each stage comprises

stationary and moving blades which are positioned into the rotor mounted on the

diaphragms directs steam into the rotor mounted on the moving blades. H.P. turbine is

double shell construction comprising inner and outer casing. H.P steam enters the H.P.

turbine inner casing through vertical inlet connection are mounted on the top and

bottom outer casing .The steam directed through the diaphragm expands through the

rotor blades and diaphragm towards the fronts of the cylinder. The steam exhausts

through the two branches in the bottom half casing and returns to the boiler to be

reheated to increase the temperature of the steam to 540°C so that the efficiency of

Rankine Cycle increases.

I.P. Turbine

Intermediate pressure turbine is a double flow design with eleven stage of blading on

either side of central steam inlet. Each stage comprises stationary and moving blades

which are positioned so that the stationary blades mounted on diaphragm, directs the

steam into the rotor mounted moving blades. Turbine is double shell construction inner

casing , two diaphragm carries the ring , and outer casing .The first 4 stage of each flow

are located within the inner casing and remaining stage within the diaphragm carries the

ring .The inner casing, diaphragm carrier ring and outer casing are made in halves

bolted together in the horizontal centre.

L.P. Turbine

LP turbine is of double flow design incorporating eight stages in each of its front and

rear flow paths. Each stage consists of number of stationary blades incorporating in the

diaphragm located in the casing and a set of rotating blades mounted on a rotor disc. A

spray water system design to operate automatically ,ensure that excessive temperature

are not produced in the exhaust flow during prolonged operation at low turbine load

/low condenser vacuum.

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Turbine Casing

1. H P Turbine Casing

Outer casing: a barrel-type without axial or radial flange

Barrel-type casing suitable for quick startup and loading.

The inner casing- cylindrically, axially split.

The inner casing is attached in the horizontal and vertical planes in the barrel

casing so that it can freely expand radially in all the directions and axially

from a fixed point (HP- inlet side).

2. I P Turbine Casing

The casing of the IP turbine is split horizontally and is of double-shell

construction.

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Both are axially split and a double flow inner casing is supported in the outer

casing and carries the guide blades.

Provides opposed double flow in the two blade sections and compensates

axial thrust.

Steam after reheating enters the inner casing from Top & Bottom.

3. L P Turbine Casing

The L P turbine casing consists of a double flow unit and has a triple shell

welded casing.

The shells are axially split and of rigid welded construction.

The inner shell taking the first rows of guide blades is attached kinematically

in the middle shell.

Independent of the outer shell, the middle shell, is supported at four points on

longitudinal beams.

Steam admitted to the L P turbine from the IP turbine flows into the inner

casing from both sides.

Blades

Most costly element of the turbine.

Blades fixed in stationary part are called guide blades/ nozzles and those fitted

inmoving part are called rotating/working blades.

Blades have three main parts:

o Aerofoil: working part.

o Root

o Shrouds

Shroud are used to prevent steam leakage and guide steam to next set of moving

blades.

Vacuum System

The comprises of

Condenser

Ejectors

Condensate Water Feed Pumps (CW pumps)

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Condenser

There are two condensers entered to the two exhausters of the LP turbine. These are

surface type condensers with two pass arrangement. Cooling water pumped into each

condenser by a vertical CW pump through the inlet pipe. Water enters the inlet chamber

of the front water box, passes horizontally through the brass tubes to the water box at

the other end, takes a turn, passes through the upper cluster of tubes and reaches the

outlet chamber in the front water box. From there, cooling water leaves the condenser

through the outlet pipe and discharged into the discharge duct. Steam exhausted from

the LP turbine washing the outside of the condenser tubes losses its latent heat to the

cooling water in the steam side of the condenser. This condensate collects in the hot

well, welded to the bottom of the condensers.

Ejectors

There are two 100% capacity ejectors of the steam eject type. The purpose of the ejector

is to evacuate air and other non-condensing gases from the condensers and thus

maintain the vacuum in the condensers. A 3 stage ejector using steam from the

deaerator with 11 ata header as the working medium is employed. In addition to the

main ejectors there is a single starting ejector which is used for initial pulling of vacuum

up to 500mm of Hg. It consists of nozzle through which the working steam expands; the

throat of the nozzle is connected to the air pipe from the condenser.

40

C.W. pumps

The pumps which supply the cooling water to the condensers are called circulating

water pumps. There are two such pumps for each unit with requisite capacity. These

pumps are normally vertical, wet pit, mixed flow type, designed for continuous heavy

duty; suitable for water drawn through an open gravity intake channel terminating in

twin-closed ducts running parallel to the main building. The fluid through the suction

bow/eye provided with stream lined guide vanes, whose function is to prevent pre-whirl

and impart hydraulically correct flow to the liquid. The propeller, in turn, imparts

motion to the fluid. The purpose of the discharge bowl provided with streamlined

diffuser vanes, is to direct the flow of water into the discharge column. Bulk

requirement of water is used in thermal plants for the purpose of cooling the steam in

condensers. The requirement of water for this purpose is of the order of 1.5-to2.0

cusecs/MW of installation where sufficient water is available once through system is

used.

Condensate System

Condensate pumps: 3 per unit of 50% capacity each located near condenser hot

well.

L P Heater: Normally 4 in number with no.1 located at the upper part of the

condenser and nos. 2, 3 & 4 around 4m level.

Deaerator: one per unit at 18 m level.

Condensate Pumps

The function of these pumps is to pumps out the condensate to the desecrator through

ejectors, gland steam cooler, and L.P. heaters. These pumps have four stages and since

the suction is at a negative pressure, special arrangements have been made

for providing sealing. This pump is rated generally for 160m3 hr. at a pressure of 13.2 k

Kg/cm2.

L.P. Heaters

Turbine has been provided with non-controlled extractions which  are  utilized  for

heating  the condensate, from turbine bleed steam. There are 410w pressure heaters in

which the last four extractions are used. L.P. Heater-1 has two parts LPH-1Aand LPH-

41

1B located in the upper parts of condenser A and condenser B respectively. These are of

horizontal type with shell and tube construction. L.P.H. 2, 3 and 4 are of similar

construction and they are mounted in a row at 4 m level. They are of vertical

construction with brass tubes the ends of which are expanded into tube plate. The

condensate flows in the "U" tubes in four passes and extraction steam washes the

outside of the tubes. Condensate passes thru' these four L.P. heaters in

succession. These heaters are equipped with necessary safety valves in the steam space

level indicator for visual level indication of heating steam condensate pressure vacuum

gauges for measurement of steam pressure etc.

Deaerator

A Deaerator is a boiler feed device for air removal and used to remove dissolved gases

(an alternate would be the use of water treatment chemicals) from boiler feed water to

make it noncorrosive. A deaerator is an open type feed water heater. A dearator

typically includes a vertical domed deaeration section as the deaeration boiler feed

water tank. A steam generating boiler requires that the circulating steam, condensate,

and feed water should be devoid of dissolved gases, particularly corrosive ones and

dissolved or suspended solids. The gases will give rise to corrosion of the metal. The

solids will deposit on the heating surfaces giving rise to localized heating and tube

ruptures due to overheating. Under some conditions it may give rise to stress corrosion

cracking. Deaerator at 38 level and pressure must be controlled by adjusting control

valves the level by regulating condensate flow and the pressure by regulating steam

flow. If operated properly, most deaerators will guarantee that oxygen in the deaerated

water will not exceed 7 ppb by weight (0.005 cm3/L).

Feed Water System

Boiler feed pump: Three per unit of 50% capacity each located in the µ0 meter

level in the T bay.

High pressure heaters: Normally three in number and are situated in the TG

bay.

Drip pumps: generally two in number of 100% capacity each situated beneath

the LP heaters.

42

Turbine Lubricating Oil System: This consists of the Main Oil Pump (MOP),

Starting Oil Pump (SOP), AC standby oil pumps and emergency DC Oil Pump

and Jacking Oil Pump (JOP). (one each per unit)

Boiler feed pump

This pump is horizontal and of barrel design driven by an Electric Motor through a

hydraulic coupling. All the bearings of pump and motor are forced lubricated by a

suitable oil lubricating system with adequate protection to trip the pump if the

lubrication oil pressure falls below a preset value. The high pressure boiler feed pump is

a very expensive machine which calls for a very careful operation and skilled

maintenance. Operating staff must be able to find out the causes of defect at the very

beginning, which can be easily removed without endangering the operator of the power

plant and also without the expensive dismantling of the high pressure feed pump.

Function: The water with the given operating temperature should flow continuously to

the pump under a certain minimum pressure. It passes through the suction branch into

the intake spiral and from there; it is directed to the first impeller. After leaving the

impeller it passes through the distributing passages of the diffuser and thereby gets a

certain pressure rise and at the same time it flows over to the guide vanes to the inlet of

the next impeller. This will repeat from one stage to the other till it passes through the

last impeller and the end diffuser. Thus the feed water reaching into the discharge space

develops the necessary operating pressure.

Booster pump

Each boiler feed pump is provided with a booster pump in its suction line which is

driven by the main motor of the boiler feed pump. One of the major damages which

may occur to a boiler feed pump is from cavitation or vapour bounding at the pump

suction due to suction failure. Cavitation will occur when the suction pressure of the

pump at the pump section is equal or very near to the vapour pressure of the liquid to be

pumped at a particular feed water temperature. By the use of booster pump in the main

pump suction line, always there will be positive suction pressure which will remove the

possibility of cavitation. Therefore all the feed pumps are provided with a main shaft

driven booster pump in its suction line for obtaining a definite positive suction pressure.

43

High Pressure Heaters

These are regenerative feed water heaters operating at high pressure and located by the

side of the turbine. These are generally vertical type and turbine bleed steam pipes are

connected to them. HP heaters are connected in series on feed waterside and by such

arrangement, the feed water, after feed pump enters the HP heaters. The steam is

supplied to these heaters form the bleed point of the turbine through motor operated

valves. These heaters have a group bypass protection on the feed waterside. In the event

of tube rupture in any of the HPH and the level of the condensate rising to dangerous

level, the group protection device diverts automatically the feed water directly to the

boiler, thus bypassing all the three HP heaters.

Turbine Governing System

The turbine has an electro-hydraulic governing system. An electric system measures and

controls speed and output, and operate the control valves hydraulically in conjunction

with an electro-hydraulic converter. The electro-hydraulic governing system permits

run-up control of the turbine up to the rated speed and keeps speed swings following

sudden load shedding low. The linear-output characteristic can be very closely set even

during operation.

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Conclusion

As an undergraduate student of IIT Delhi, I would like to say that this training

program is an excellent opportunity for anyone to get to the ground level and experience

the things that we would have never gained through going straight into a job. I am

grateful to IIT Delhi and NTPC Badarpur for giving me this wonderful opportunity. The

industrial training has provide an opportunity to students to identify, observe and

practice the application of engineering in the real industry. It is not only to get

experience on technical practices but also to observe management practices and to

interact with fellow workers. It is as important to work with the staff as it is with

complicated machines. The training provides a great insight to working conditions in a

place like a thermal plant which can be sometimes quite uncomfortable. I also learnt the

way of work in an organization, the importance of being punctual and maximum

commitment, and the importance of team spirit. The training program having several

destinations was a lot more useful than staying at one place throughout the whole one

month. I can make the conclusion that NTPC Badarpur is an appropriate place for

students to do their industrial training as I have acquired a lot of knowledge in this

enriching experience at NTPC Badarpur.