THERMAL POWER GENERATION , NTPC - DADRI

1. KRISHNA INSTITUTE OF ENGINEERING & TECHNOLOGY
GHAZIABAD
SUMMER TRAINING PROJECT REPORT
On
POWER GENERATION OF COAL BASED THERMAL POWER
PLANT
At
NATIONAL THERMAL POWER CORPORATION
LIMITED
Session: 2014-2015
Submitted by:
HARSH KUMAR (1202940074)
B.Tech, 4th
yr., Mechanical Engineering
10 July – 6 August, 2015

2. ACKNOWLEDGEMENT
The successful completion of project work requires efforts of several
intellectual minds. Working with NTPC DADRI has been a great learning
experience for which I would like to thank everybody who has been instrumental in
the completion of my project work.
I wish to express my deep sense of gratitude to my Guide, Mr. Rampal
Singh (DGM-BMD), for his able guidance and useful suggestions, which helped
me in completing the project work, in time.
I would like to give a special thanks to Mr. Ashish Kumar (DGM) and
Mr. Bhaskar Singh Palia for providing me the opportunity to do summer training
at NTPC DADRI.
Thanking You,
HARSH KUMAR

3. COMPANY PROFILE
NTPC Limited (also known as National Thermal Power Corporation
Limited) is an Indian Central Public Sector Undertaking (CPSU) under the Ministry
of Power, Government of India, engaged in the business of generation of electricity
and allied activities. It is a company incorporated under the Companies Act 1956
and a "Government Company" within the meaning of the act. The headquarters of
the company is situated at New Delhi. NTPC's core business is generation and sale
of electricity to state-owned power distribution companies and State Electricity
Boards in India. The company also undertakes consultancy and turnkey project
contracts that involve engineering, project management, construction management
and operation and management of power plants. The company has also ventured into
oil and gas exploration and coal mining activities. It is the largest power company
in India with an electric power generating capacity of 45,548 MW. Although the
company has approx. 18% of the total national capacity it contributes to over 27%
of total power generation due to its focus on operating its power plants at higher
efficiency levels (approx. 83% against the national PLF rate of 78%).
It was founded by Government of India in 1975, which now holds 70% of
its equity shares on 13 May 2015 (after divestment of its stake in 2004, 2010, 2013,
and 2015). In May 2010, NTPC was conferred Maharatna status by the Union
Government of India. It is ranked 431st
in in the Forbes Global 2000 for 2015.

4. NTPC Installed Capacity
Present installed capacity of NTPC is 45,548 MW (including 6,196 MW
through JVs) comprising of 41 NTPC Stations (18 Coal based stations, 7 combined
cycle gas/liquid fuel based stations, 1 Hydro based station), 7 Joint Venture stations
(6 coal based and one gas based) and 8 renewable energy projects.
S.No. NO. OF PLANTS CAPACITY (MW)
NTPC Owned
Coal 18 34,425
Gas/Liquid Fuel 7 4,017
Hydro 1 800
Renewable energy projects 8 110
Total 34 39,352
Owned By JVs
Coal & Gas 7 6,196
Total 41 45,548

5. NTPC Dadri Plant
NTPC Dadri is a unique power plant of NTPC group which has both coal based
thermal plant and gas based thermal plant of 1820 MW and 817 MW respectively
and 5 MW solar plant totaling 2642 MW.
1.Coal based
The coal for the power plant is sourced from Piparwar Mines, Jharkhand.
Source of water for the power plant is Upper Ganga Canal.
Stage
Unit
Number
Installed Capacity
(MW)
Date of Commissioning
1st
1 210 1991 October
2 210 1992 December
3 210 1993 March
4 210 1994 March
2nd
5 490 2010 January
6 490 2010 July
Total Six 1820

6. 2. Gas based
The gas for the power plant is sourced from GAIL HBJ Pipeline, it also supports
HSD as alternate fuel. Source of water for the power plant is Upper Ganga Canal.
Stage
Unit
Number
Installed Capacity
(MW)
Date of
Commissioning
GT / ST
1st
1 130.19 1992 March GT
2 130.19 1992 May GT
3 130.19 1992 June GT
4 130.19 1992 November GT
5 154.51 1993 February ST
6 154.51 1993 March ST
Total Six 829.78
3. Solar plant
The total project capital cost is put at Rs. 48.59 crore. Wipro limited has designed
the project over 27 acres of land within the premises of existing NTPC Dadri plant.
GRAND TOTAL CAPACITY OF NTPC DADRI = 2642 MW

7. COMPANY’S VISION AND MISSION
Vision:
To be the world’s largest and best power producer, powering India’s growth.
Mission:
Develop and provide reliable power, related products and services at competitive
prices, integrating multiple energy sources with innovative and ecofriendly
technologies and contribute to society.
Core Values – BE COMMITTED
• B- Business Ethics
• E- Environmentally & Economically Sustainable
• C- Customer Focus
• O- Organisational & Professional Pride
• M- Mutual Respect & Trust
• M- Motivating Self & others
• I- Innovation & Speed
• T- Total Quality for Excellence
• T- Transparent & Respected Organisation
• E- Enterprising
• D- Devoted

8. LAYOUT OF A TYPICAL COAL FIRED THERMAL POWER
STATION
Following are the basic components of a coal fired thermal power station :-
1. Coal stockpile
2. Coal conveyer
3. Work shop
4. Coal hopper
5. Pulverized fuel mill
6. Boiler
7. Flue gas cleaning
8. Stack
9. Steam turbine
10. Generator
11. Transformer
12. Steam condenser
13. Cooling unit
14. Electrical grid

9. BASIC WORKING OF A THERMAL POWER PLANT
Fig. Coal fired thermal power plant
Firstly, water is taken into the boiler from a water source. The boiler is
heated with the help of coal. The increase in temperature helps in the transformation
of water into steam. The steam generated in the boiler is sent through a steam turbine.
The turbine has blades that rotate when high velocity steam flows across them. This
rotation of turbine blades is used to generate electricity. A generator is connected to
the steam turbine. When the turbine turns, electricity is generated and given as output
by the generator, which is then supplied to the consumers through high-voltage
power lines.
 The coal is brought and crushed to powder. This is feed to boiler for producing
heat .
 In Boiler the water is converted to steam.
 In Superheater the moisture content is removed from the steam and that
steam is called super heated steam.
 The superheated steam rotates the shaft of the High Pressure(HP) turbine.
 The exhausted steam is sent to Reheater and the steam then rotates the
Intermediate Pressure (IP) turbine.

10.  The steam from the IP Turbine is then feed to Low Pressure(LP) turbine.
 The turbine shaft is connected to the Generator, which produces electric
power.
 The steam expanded in turbine is condensed in a Condenser to be feed into
the boiler again.
BASIC POWER PLANT CYCLE
The basic principle of the working of a thermal power plant is quite simple.
The fuel used in the plant is burned in the boiler, and the heat thus generated is used
to boil water which is circulated through several tubes, and the steam that is
generated is then used to drive a turbine, which in turn is coupled with a generator,
which then produces electricity.
The working of the coal based plant is based upon a modified Rankine
cycle. The Rankine cycle is represented most commonly on a temperature-entropy
diagram. The topmost point is known as Critical point.

11. MAJOR SUB-SYSTEMS OF A POWER PLANT
1.COAL HANDLING PLANT (C.H.P.) :-
Coal Handling Plant is the place where processing of raw coal occurs
before it is transferred to the bunkers. CHP enhances the calorific value of coal and
makes its transportation cost lower and easier. The coal is provided by the Deepika
mines under the S.E.C.L, with the help of a dedicated merry-go-round (MGR).When
the coal is supplied at the CHP, the coal is moved along the track hopper towards
the crusher, where the lumps of coal are crushed into 20 mm sized particles, from
where they may be stored in the stack-yard, or sent to the bunkers before being fed
into the boilers.
Salient Features of CHP Stage-I :
• Conveyor Capacity – 2000/2600MTPH
• Conveyor Width – 1600 mm
• Paddle Feeder cap- 1500MTPH
• Crusher Capacity- 1250MTPH
• SR Capacity-2000mtph
• Inter Connection Between ST-1&ST-2
PLC Based Operation

12. Salient Features of CHP Stage-II :
• Conveyor Capacity – 2600 MTPH
• Conveyor Width - 1800 mm
• Conveyor Speed – 3.2 m/sec
• Paddle Feeder capacity- 1950 MTPH
• VGF Capacity – 1625 MTPH
• Crusher Capacity – 1625 MTPH
• STACKER /RECLAIMER Capacity- 2600MTPH
• CCTV compatible to integrated FIRE ALARM SYSTEM
• PLC Based Operation
• Lifts at Crusher House & TP19
• Inter Connection between ST-1&ST-2
MILL:-
The coal particles are ground into finer sized granules. The coal which is
stored in the bunker is sent into the mill, which is primarily a ball type, in which a
drum contains a ball, and when the drum rotates the ball also does, and this causes
the coal particles caught in between to be ground.
After grinding, the coal is then passed through a desired size of mesh, so that
any coal particle not properly ground is not allowed through. Then the coal is forced
by a blast of air coming from the primary air fans to enter the boiler. Coal is fed to
the mills from the bunkers via the raw coal feeders.
Another type of mill is the ball and race mill, in which the coal passes between
the rotating elements again and again until it has been pulverized to the desired
degree of fineness. However, there is greater wear in this mill as compared to other

13. pulverizers. There are 10 mills located adjacent to the furnace. These mills pulverise
coal to the desired fineness to be fed to the furnace for combustion. Capacity of 1
mill is 62.9 tonnes/hr.
Factors affecting bowl mill performance:-
• Size of raw coal
• Raw coal grindability
• Raw coal moisture content
• Pulverized fuel fineness
• Mill internals wear and poor quality of raw coals.
Mill drive system mainly consists of three components namely mill motor,
mill coupling and mill gear box. Mill coupling comprises of Bibby coupling (present
on the motor side) and gear coupling (present on the gear box side). In a bowl mill,
the major grinding element grinding roll is conical in shape and is three in number
per mill.

14. INTERIOR OF BOWL MILL
2. WATER TREATMENT PLANT:
Since water is the basic requirement for the production of the working
substance, it is necessary to have an arrangement to provide water which is not
contaminated by unwanted materials. For this a water treatment unit is provided
which receives water from a source, then demineralizes it and finally after further
treatment, is fed into a boiler feed pump. This is a unit which consumes relatively
low power compared to other units in a power plant. Some of the systems involved
in the treatment of water are de-mineralization plant, raw water pump house,
clarification plant and many others. The type of water used is different for different
purposes.
The process of cooling requires raw water, whereas steam formation, and
many other major processes require de-mineralized water. De-mineralization plants
consist of cation, anion and mixed bed exchangers. The final water from this stage
consists of hydrogen ions and hydroxyl ions which is the chemical composition of
pure water.
3.BOILER:
A boiler is the central component of a power plant, and it is the unit where
the steam required for driving the turbine is generated. The heat absorbing parts
subject to internal pressure in a boiler are called as pressure parts. The main pressure
parts in a boiler are Drums, Water walls, Super heaters, Re heaters, Economisers and
valves & fittings. The Drum, Down comers, water wall headers and water walls
forms the circulation system and cover the furnace zone. The components of Boiler
and their functions are as follows :-

15. a) Boiler Drum : The drum provides the necessary space for locating the steam
separating equipment for separation of steam from mixture of steam and water. It
also serves as a reservoir for the supply of water to circulation system to avoid
possible starvation during operation. The drum is filled with water coming from the
economizer, from where it is brought down with the help of down-comer tubes,
entering the bottom ring headers. From there they enter the riser, which carries the
water (which now is a liquid-vapor mixture), back to the drum. Now, the steam is
sent to be superheated.
For a 660 MW plant, the boiler does not employ any drum; instead the water and
steam go directly into the super heater.
Drum is located at 78 m elevation in the boiler front. Water enters the drum from the
bottom via three ECO links. Drum has connections for Chemical dozing, Emergency
drain, Continuous blow down & sample cooler tapping. Total 5 no. of vents and 6
no of safety valves, 3 on each side are provided on the drum. Total 18 MTM
thermocouples, 6 no of level transmitters, 3 pressure transmitters and 3 pressure
indicators are provided on the drum. There are 2 no of Electronic Water Level
Indicators (EWLI) and 1 no of Direct Water Level Gauge (DWLG) provided on each
side of the drum.
b) Economiser : The economizer is a tube-shaped structure which contains water
from the boiler
feed pump. This water is heated up by the hot flue gases which pass through the
economizer layout, which then enters the drum. The economizer is usually placed

16. below the second pass of the boiler. As the flue gases are being constantly produced
due to the combustion of coal, the water in the economizer is being continuously
being heated up, resulting in the formation of steam to a partial extent. Feedwater
(FW) from Feed Regulating Station (FRS) with parameters P=200.2 ksc, T=255.2 C
travels to Economiser inlet header located at Elevation 44.2m through ECO feed
line. ECO feed line connects to the ECO inlet header at the right side of boiler
backpass. One NRV and motorised ECO stop valve is provided in the ECO feed line
just before it connects to the ECO inlet header. One no of drain is also provided in
the ECO feed line just after the ECO stop valve. The drain is connected to the water
wall (WW) drain header located at „0‟ meter. One no of ECO recirculation line is
provided after the ECO stop valve which connects to the rear ring header.
ECO inlet header:- It is arranged parallel to the drum at the bottom of backpass
middle at the elevation 44.2m. One no of drain is provided in the header. The drain
is connected to the WW drain header.192 x 3 loose tubes connect the ECO inlet
header to the ECO lower assembly.
ECO outlet header:- Located at the Elevation 57.5m, it is arranged parallel to the
drum in backpass. Two links from ECO outlet header project out from back pass
side walls and join again at the boiler front at 66.5m elevation. From this junction
three pipes carry feed water to the drum.
c) CC Pumps:- Six no. of Downcomers carry feedwater(FW) from drum to suction
manifold of
CC Pumps located at 29.5m elevation. 3 no. of suction spool pieces carry FW from
suction manifold to the 3 no. of CC Pumps located at 23.3m elevation. The pumps
are of double discharge type. Parameters at the pump: P=197.4 ksc, 359.1 C and
flow/pump= 3135 cu.m/hr. Connections to the pump include HP fill and purge lines,
LP coolant lines. Inter tie line connecting discharges of all pumps. One equalising
line from the center pump suction connects to the intertie line.
Two no of coolers are also provided: HP Fill and Purge Cooler and LP Cooler for
motor.
Source of HP fill & Purge is from 1. Feed line (for periodic use) 2. From
Condensate system (low pressure fill source).
Source of LP coolant supply: 1. Normal supply 2. From Emergency tank
d) Bottom Ring Header:- The 6 no. of CC pump discharge lines carry FW to the
bottom ring
header located at 10.6m. Ring header is provided with one no of blow off line from
front ring header which is connected to the IBD Tank. One no of drain is also
provided from the rear ring header which is connected to the WW drain header. ECO
recirculation line also connects to the rear ring header.

17. e) Water walls:- 331 tubes each from front & rear ring headers form the front, rear
and corner
water walls. There are 25 tubes in each corner wall & 281 tubes in front and rear
water walls each. Front water wall is integral with the corners 1 & 4 and rear wall is
integral with the corners 2 & 3. Each side water wall (Left & Right) has 224 tubes.
All water wall tubes are rifled from inside except the „S‟ panel tubes. Total no of
tubes originating from Bottom ring header = 331x2 + 224x2 = 1110.
In a 500 MW unit, the water walls are of the vertical type, and have rifled tubing
while in 600 MW, the water walls are spiral type and have smooth tubing.
f) De-aerator: A de-aerator is a device that is widely used for the removal of air
and other dissolved gases from the feedwater to steam-generating boilers.
There are two basic types of deaerators, the tray-type and the spray-type

18. g) Super-Heaters: Super-heaters are used to raise the steam temperature above
the saturation temperature by absorbing heat from flue gas to increase the cycle
efficiency.
Super heating takes place in three stages. In the first stage, the steam is
sent to a simple super heater, known as the low temperature super heater, after which
the second stage consists of several divisional panels. The final stage involves
further heating in a Platen super heater, after which the steam is released for driving
the turbine. After the HP stage of the turbine the steam is re-heated and then again
released.
Superheating is done to increase the dryness fraction of the exiting steam.
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 so on. It is also of interest to know that while
the super heater increases the temperature of the steam, it does not change the
pressure. There are different stages of superheaters besides the sidewalls and
extended sidewalls. The first stage consists of LTSH(low temperature superheater),
which is conventional mixed type with upper & lower banks above the economiser
assembly in rear pass. The other is Divisional Panel Superheater which is hanging
above in the first pass of the boiler above the furnace. The third stage is the Platen
Superheater from where the steam goes into the HP turbine through the main steam
line. The outlet temperature & pressure of the steam coming out from the superheater
is 540 degrees Celsius & 157 kg/cm2
.
4. TURBINES :
The turbine employed in a thermal power plant is a steam turbine. The initial
steam is admitted ahead of the blading via two main stop and control valve
combinations. The turbine unit of any thermal power plant is not a single stage
operation, rather it consists of three stages:
High Pressure Turbine Stage (HPT Stage): This stage takes place immediately
after the Platen super heater stage. This is the first stage of the turbine operation. Its
outer casing is of a barrel type and has neither a radial nor an axial flange. The inner
casing is axially split and supported so as to be free to move in response to thermal
expansion.

19. Intermediate Pressure Turbine Stage (IPT Stage): After the HPT stage, the steam
gets saturated and, consequently, gets cooled. It is, therefore, first sent back to the
boiler unit to be reheated, after which it is sent to the IPT stage. Its section is of
double flow construction with horizontally split casings.
Low Pressure Turbine Stage (LPT Stage): After the IPT, the steam gets cooled to
an intermediate extent, thus directly entering the LPT, where it gets saturated. Its
casing is of the three-shell design. After this stage the water enters the condenser,
which is connected to a condensate extraction pump.
A turbine assembly consists of a rotor assembly on whose circumference is attached
a series of vanes, a bearing assembly to support the shaft, a metallic casing
surrounding the blades, nozzle, rotor etc, a governor to control the speed and a
lubrication system.
The shaft of the turbine is connected to the generator. The purpose of the generator
is to convert the mechanical shaft energy it receives from the turbine into electrical
energy. Steam turbine driven AC synchronous generators (alternators) are of two or
four pole designs. These are three phase machines offering economic advantages in
generation and transmission. Large generators have cylindrical rotors with minimum
heat dissipation surface and so they have forced ventilation to remove the heat. Such
generators generally use an enclosed system with air or hydrogen coolant. The gas
picks up the heat from the generator and gives it up to the circulating water in the
heat exchanger.
Every turbine, except the LPT, has a stop valve and a regulating valve attached to it.
The stop valve is used to stop the flow of steam, whenever required, whereas the
regulating valve is also a kind of a flow controlling device. Each turbine also has an
inlet and an outlet pipe for the steam to enter and exit, respectively. Between the
HPT-IPT combine and the IPT-LPT combine is attached a bearing assembly. It is
constructed using a cross around pipe.
After the steam leaves the turbine, it enters the condenser . The condenser is meant
to receive the steam from the turbine, condense it and to maintain a pressure at the
exhaust lower than the atmospheric pressure. The condenser is an important unit and
some of the auxiliaries required for it to function properly are the cooling water
supply pump, the condensate extraction pump, feed water pump and the air removal
pump.

20. Fig. Schematic diagram of turbine
5. ASH HANDLING & DISPOSAL:

21. There are two types of ash handling methods: dry ash handling and wet ash handling.
Dry ash handling is carried out by storing the ash deposited in large pits, whereas in
the wet ash handling method, the ash is deposited into large reservoirs or ponds.
1.Wet mode:--Ash evacuated from ESP hoppers through vacuum pumps & fed to
wetting head (vacuum system) and collector tank units where ash is mixed with
water & resultant slurry is discharged to slurry trenches.
2.Dry mode:--Ash evacuated from ESP hoppers through vacuum pumps & collected
in Buffer hoppers & Air lock tank, is transported to storage silo by compressed air
(pressure conveying system) through pressure conveying pipe lines.
Components of wet fly ash system
1. ESP hopper
2. Plate valve for isolation .
3. Material Handling Valve (MHV)
4. Piping up to wetting head
5. Wetting head
6. Air washer
7. Vacuum pump
Auxiliaries in a power plant
1) PA FANS: The primary air fans are used to carry the pulverized coal particles
from the mills to the boiler. They are also used to maintain the coal-air
temperature. The specifications of the PA fan used at the plant under
investigation are: axial flow, double stage, reaction fan.
The PA fan circuit consists of:
a) Primary air path through cold air duct
b) Air pre-heater
c) Hot air duct
d) Mills

22. The model no. of the PA fan used at NTPC Sipat is AP2 20/12, where A refers
to the fact that it is an axial flow fan, P refers to the fan being progressive, 2 refers
to the fan involving two stages, and the numbers 20 and 12 refer to the distances in
decimeters from the centre of the shaft to the tip of the impeller and the base of the
impeller, respectively. A PA fan uses 0.72% of plant load for a 500 MW plant.
2) FD FANS: The forced draft fans, also known as the secondary air fans are used
to provide the secondary air required for combustion, and to maintain the wind
box differential pressure. Specifications of the FD fans are: axial flow, single
stage, impulse fan.
The FD fan circuit consists of:
a) Secondary air path through cold air duct
b) Air pre-heater
c) Hot air duct
d) Wind box
The model no. of the FD fan used at NTPC Sipat is AP1 26/16, where the
nomenclature has been described above. FD fans use 0.36% of plant load for a 500
MW plant.
3) ID FANS: An induced fan circuit consists of
a) Flue gas through water walls
b) Super heater
c) Re-heater
d) Platen super heater
e) Low temperature super heater
f) Air pre-heater
g) Electrostatic precipitator

23. The main purpose of an ID fan is to suck the flue gas through all the above mentioned
equipments and to maintain the furnace pressure. ID fans use 1.41% of plant load
for a 500 MW plant.
4) SCANNER AIR FAN: Scanner air fan is used to provide air to the scanner. For
a tangentially fired boiler, the vital thing is to maintain a stable ball of flame at
the centre. A scanner is used to detect the flame, to see whether it is proper and
stable. The fan is used to provide air to the scanner, and it is a crucial component
which prevents the boiler from tripping
5) SEAL AIR FAN: The seal air fan is used near the mill to prevent the loss of any
heat from the coal which is in a pulverized state and to protect the bearings from
coal particle deposition.
6) AIR PRE-HEATERS: Air pre-heaters are used to take heat from the flue gases
and transfer it to the incoming air. They are of two types:
a) Regenerative
b) Recuperative
The APH used at NTPC DADRI is a Ljungstrom regenerative type APH. A
regenerative type air preheater absorbs waste heat from flue gas and transfers this
heat to the incoming cold air by means of continuously rotating heat transfer
elements of specially formed metal sheets. A bi-sector APH preheats the combustion
air. Thousands of these high efficiency elements are spaced and compactly arranged
within sector shaped compartments of a radially divided cylindrical shell called the
rotor. The housing surrounding the rotor is provided with duct connections at both
ends, and is adequately sealed by radial and axial sealing members forming an air
passage through one half of the APH and a gas passage through the other.
As the rotor slowly revolves the elements alternately pass through the air and gas
passages; heat is absorbed by the element surfaces passing through the hot gas

24. stream, then as the same surfaces pass through the air stream, they release the heat
to increase the temperature of the combustion of process air.
A single APH is divided into 4 parts: 2 PAPHs and 2 SAPHs. The P and S refer to
primary and secondary respectively. Each part is divided into two slots, one slot
carrying the primary/secondary air, and the other slot carrying the hot flue gases
coming from the 2nd
pass of the boiler. The PAPH is connected to the mills, whereas
the SAPH is connected to a wind box.
7) ELECTROSTATIC PRECIPITATORS: They are used to separate the ash
particles from the flue gases. In this the flue gas is allowed into the ESP, where there
are several metallic plates
placed at a certain distance
from each other. When
these gases enter, a very
high potential difference is
applied, which causes the
gas particles to ionize and
stick to the plates, whereas
the ash particles fall down
and are collected in a
hopper attached to the
bottom of the ESP. The flue
gas is allowed to cool down and is then released to the ID fan to be sent to the
chimney. Indian coal contains about 30% of ash. The hourly consumption of coal of
a 200 MW unit is about 110 tons. With this, the hourly production of ash will be 33
tons. If such large amount of ash is discharge in atmosphere, it will create heavy air
pollution thereby resulting health hazards. Hence it is necessary to precipitate dust
and ash of the flue gases. Precipitation of ash has another advantage too. It protects
the wear and erosion of ID fan. To achieve the above objectives, Electrostatic
Precipitator (ESP) is used. As they are efficient in precipitating particle form
submicron to large size they are preferred to mechanical precipitation.
Construction
An ESP has series of collecting and emitting electrons in a chamber
collecting electrodes are steel plates while emitting electrodes are thin wire of
2.5mm diameter and helical form. Entire ESP is a hanging structure hence the
electrodes are hung on shock bars in an alternative manner. It has a series of rapping
hammer mounted on a single shaft device by a motor with the help of a gear box at
a speed of 1.2 rpm. At the inlet of the chamber there are distributor screens that

25. distributes the gas uniformly throughout the chamber. There are transformer and
rectifiers located at the roof of chamber. Hopper and flushing system form the base
of chamber.
Working
Flue gases enter the chamber through distributor screen and get uniformly
distributed. High voltage of about 40 to 70 KV form the transformer is fed to
rectifier. Here ac is converted to dc. The negative polarity of this dc is applied across
the emitting electrode while the positive polarity is applied across the collecting
electrodes. This high voltage produces corona effect negative (–ve) ions from
emitting electrode move to collecting electrode. During their motion, they collide
with ash particles and transfer their charge. On gaining this charge, ash particles too
move to collecting electrode and stock to them. Similar is the case with positive
(+ve) ions that moves in opposite direction. The rapping hammers hit the shock bars
periodically and dislodge the collected dust from it. This dust fall into hopper and
passes to flushing system. Here it is mixed with water to form slurry which is passed
to AHP.
Efficiency of ESP is approximately 99.8%.
Theory of Precipitation
Electrostatic precipitation removes particles from the exhaust gas stream of
Boiler combustion process. Six activities typically take place:
 Ionization - Charging of particles
 Migration - Transporting the charged particles to the collecting surfaces
 Collection - Precipitation of the charged particles onto the collecting
surfaces
 Charge Dissipation - Neutralizing the charged particles on the collecting
surfaces
 Particle Dislodging - Removing the particles from the collecting surface
to the hopper
 Particle Removal - Conveying the particles from the hopper to a
disposal point
The ash produced on the combustion of coal is collected by ESP. This ash is
now required to be disposed off. This purpose of ash disposal is solved by Ash
Handling Plant (AHP).

26. 8) CONDENSATE EXTRACTION PUMP: The condensate extraction pump
(CEP) is a centrifugal, vertical pump, consisting of the pump body, the can, the
distributor housing and the driver lantern. A rising main of length depending upon
NPSH available, is also provided. The pump body is arranged vertically in the can
and is attached to the distributor body with the rising main. The rotor is guided in
bearings lubricated by the fluid pumped, is suspended from the support bearing,
which is located in the bearing pedestal in the driver lantern. The shaft exit in the
driver lantern is sealed off by one packed stuffing box.
Casing
It is split on right to the shaft and consists of suction rings and 4 no. of guide
vane housing. Casing components are bolted together and sealed off from one
another by 'O' rings. For internal sealing of individual stages, the casing components
are provided with exchangeable casing wear rings in the arc of impeller necks. In
each guide vane casing, a bearing bush is installed to guide the shaft of pump.
Rotor
The pump impellers are radially fixed on the shaft by keys. The impellers are
fixed in position axially by the bearing sleeves and are attached to the shaft by means
of impeller nut. Impellers are single entry type, semi-axial and hydraulically
balanced by means of balance holes in the shroud and throttle sections at suction and
discharge side. A thrust bearing located in the motor stool absorbs residual axial
thrusts.
Bearings
In each guide vane housing the shaft is guided by a plain bearing. These
bearings do not absorb any axial forces. Pump bearings consist of bearing sleeve,
rotating with the shaft and bearing bush, mounted in guide vane housing. The
intermediate shaft is guided in bearing spider and shaft sleeve. The arrangement of
bearing corresponds to the bearings of pump shaft. They are lubricated by
condensate itself. A combined thrust and radial bearing is installed as support
bearing to absorb residual thrust. Axial load is transmitted to the distributor casing
via the thrust bearing plate, the thrust bearing and bearing housing. A radial bearing
attached to the bearing is installed in an enclosed housing and is splash lubricated
by oil filled in the enclosure. Built-in cooling coils in the bath and cooling water
control oil temperature.
9) BOILER FEED PUMP: The auxiliary component which consumes the
maximum amount of power earmarked for such purposes is the boiler feed pump.
At NTPC Sipat, the auxiliaries consume about 7% of the plant load. The boiler feed
pump is used to feed water to the boiler, as the name suggests, through the

27. economizer. The BFP is fed from the CEP and the water source. The BFP is of two
types
a) TDBFP: turbo-driven boiler feed pump.
b) MDBFP: motor driven boiler feed pump.
The boiler feed pump is fed water from the condensate extraction pump. The
condensate extraction pump collects the condensate from the condenser. Then the
condensate is further cooled by being sent into the gland steam coolers, after which
it is sent into the BFP.
10) COOLING TOWERS: Cooling towers are used to remove the heat from the
condensers. In this cooling water is discharged to the condenser with the help of a
cooling water pump (CW pump). This water enters the condenser through several
tubes. Steam entering the condenser from the turbine after expansion further loses
heat and condenses, while the water circulating inside the tube gains heat and goes
back to the cooling tower. Inside the tower is a cooling fan which takes the heat from
this batch of water, which is then sent back again for the cycle to be repeated. It is
hence known as a regenerating cycle.
Cooling towers are eveporative coolers used for cooling water. Cooling
tower uses the concept of evaporation of water to reject heat from processes such
by cooling the circulaing water used in oil refineries, chemical plants, power
plants, etc. Smaller towers are normally factory built while larger ones are
constructed on site. The primary use of large, industrial cooling tower system is to
remove the heat by circulating the hot water used by the plants
The absorbed heat is rejected to the atmosphere by the evaporation of
some of the cooling water in mechanical forced – draft or induced draft towers or
in natural draft hyperbolic shaped cooling towers as seen at most nuclear power
plants.
4 Nos Induced draft cooling towers with 10 fans each tower are installed at
NTPC Dadri for the above said pupose.

28. 11) WIND BOX: These act as distributing media for supplying secondary/excess air
to the furnace for combustion. These are generally located on the left and and
right sides of the furnace while facing the chimney.
12) IGNITER FAN: Igniter fans which are 2 per boiler are used to supply air for
cooling Igniters & combustion of igniter air fuel mixture.
13) CHIMNEY: These are tall RCC structures with single & multiple flues. Here,
for I & II we have 1 chimney, for unit III there is 1 chimney & for units IV & V
there is 1 chimney. So number of chimneys is 5 and the height of each is 275
metres.
14) COAL BUNKER: These are in process storage used for storing crushed coal
from the coal handling system. Generally, these are made up of welded steel
plates. Normally, these are located on top of mills to aid in gravity feeding of
coal. There are 10 such bunkers corresponding to each mill.
15) REHEATER: The function of reheater is to reheat the steam coming out from
the high pressure turbine to a temperature of 540 degrees Celsius. It is composed
of two sections: the rear pendant section is located above the furnace arc & the
front pendant section is located between the rear water hanger tubes & the Platen
superheater section.
16) BURNERS: There are total 20 pulverised coal burners for the boiler present here,
& 10 of the burners provided in each side at every elevation named as
A,B,C,D,E,F,G,H,J,K. There are oil burners present in every elevation to fire the
fuel oil (LDO & HFO) during light up.

29. REFERENCE
1. www.ntpc.co.in/index.php?option=com_content&id=312&Itemid.
2. en.wikipedia.org/wiki/NTPC_Dadri
3. wikimapia.org › India › Uttar Pradesh › Dadri
4. articles.economictimes.indiatimes.com › Collections › Solar Plant
5. www.ndtv.com › Topic
6. www.business-standard.com/.../no-shortage-of-coal-supply-to-ntpc-sdad.
7. globalenergyobservatory.org/geoid/4562
8. ntpc.co.in/index.php?option=com_content&id=28&Itemid=41