Summer Training Project Report
SUBMITTED BY:EMAM RAZA (1002940032)
(B. TECH MECH. ENGG.)
Department of Mechanical Engineering
KIET School of Engineering & Technology
Ghaziabad-Meerut Highway (NH-58)
Uttar Pradesh, INDIA
Declaration by StuDent
I hereby declare that work entitled “summer training project
report”, submitted towards completion of vocational training
after 3nd year of B. Tech (Mechanical Engineering) at Krishna
Institute of Engineering And Technology, Ghaziabad.
Comprises of my original work pursued under the supervision
of Guides at NTPC (DADRI).
Name: - Emam Raza
Roll No: - 1002940032
B. Tech (7th Semester)
“It is not possible to prepare a project report without the assistance &
encouragement of other people. This one is certainly no exception.”
On the very outset of this report, I would like to extend my sincere and
heartfelt obligation towards all the personages who have helped me in this
endeavor. Without their active guidance, help, cooperation and
encouragement, I would not have made head way in the project. First and
foremost, I would like to express my sincere gratitude to my project guide,
Shri R.K Shinha.
I was privileged to experience a sustained enthusiastic and involved interest
from his side. This fuelled my enthusiasm even further and encouraged me
to boldly step into what was a totally dark and unexplored expanse before
me. He always fuelled my thoughts to think broad and out of the box.
I would also like to thank Mr. Shrishir Sriwastv who, instead of his busy
schedule, always guided me in right direction to head and also helped in
understanding the all component of modified rankine cycle.
I would like to thank Employee development Centre for organizing and
permitting the Vocational training program for us.
POWER SECTOR IN INDIA
Power sector plays a very vital role in overall economic growth of any country. For Indian
perspective, the power sector needs to grow at the rate of at least 12% to maintain the present
GDP growth of about 8%. As per the Ministry of Power report, the per capita consumption of
electricity is expected to grow to 1000 kWh / year by the year 2012 which during the year 2004
– 2005 was 606 kWh/year. To meet the per capita consumption of 1000 kWh/year by the year
2012 the capacity augmentation requirement is about 1,00,000 MW. Presently there is a
significant gap between the demand and supply of power. The energy deficit is about 8.3% and
the power shortage during the peak demand is about 12.5%.
NATIONAL THERMAL POWER CORPORATION LIMITED
NTPC Limited is the largest power generation company in India. Forbes Global 2000 for 2009
ranked it 317th in the world. It is an Indian public sector company listed on the Bombay Stock
Exchange although at present the Government of India holds 84.5% of its equity. With a current
generating capacity of 32,694 MW, NTPC has embarked on plans to become a 75,000 MW
company by 2017. It was founded on November 7, 1975 with 100% ownership of the Central
government. In 1997, Government of India granted NTPC status of “Navratna‟ being one of the
nine jewels of India, enhancing the powers to the Board of Directors. NTPC became a
Maharatna company in May, 2010, one of the only four companies to be awarded this status.
NTPC‟s core business is engineering, construction and operation of power generating plants and
providing consultancy to power utilities in India and abroad.
The total installed capacity of NTPC in India is as follows at present:
NO. OF PLANTS
Owned By JVs
Coal & Gas 5
NTPC has been operating its plants at high efficiency levels. Although the company has 18.10%
of the total national capacity, it contributes 28.60% of total power generation due to its focus on
NTPC-Dadri,Vidyut Nagar-201 008,Dist.
Gautambudhnagar, Uttar Pradesh
Distt. Gautam Budh Nagar, Uttar Pradesh
HBJ Pipe line/ 3 MMSCMD (APM Gas)
Alternate Fuel: HSD
Upper Ganga Canal
Rs.960.35 crores (02.11.94)
4 GTX 130.19 MW + 2 STX 154.51 MW
GT-I- 130.19 MW May 1992
GT II- 130.19 MW June1992
GT III-130.19 MW August1992
GT IV-130.19 MW December1992
ST-I- 154.51 MW August 1996
ST-II- 154.51 MW April 1997
National Capital Power Station (NCPS) Or NTPC Dadri, is the power project to meet the power
demand of National capital region. It has a huge coal-fired thermal power plant and a gas-fired
plant and has a small township located in Uttar Pradesh, India for its employees. It is located
in Gautam Budh Nagar district of Uttar Pradesh about 25 km from Ghaziabad and about 25 km
fromDadri. It is nearly 48 km from New Delhi towards Hapur. The township has an area of about
500 acres over all. NTPC Dadri is a branch of National Thermal Power Corporation, which is a
public sector now. It is located 12 km from Nai Abad
NTPC Dadri plant and township are property of ntpc ltd and were built around 1988-1990. The
township is surrounded by boundary walls from all sides for secutiry reasons. The neighbouring
villages which provide it with milk vegetables etc. Though the township has self sufficient
markets inside it, residents usually go to Ghaziabad or Delhi for extra shopping. NTPC Dadri has
two shopping centers( old, new ) which caters to the need of employees and their families as well
as other people, and the Silver Jubilee Park (formerly known as Central Park), a fountain park in
front of new market and numerous small parks for children and employees for recreation. It also
has a helipad for landing of small helicopter (though not well maintained). There is a
MAHARANA PRATAP sports stadium inside the campus which is equipped with floodlights for
day/night domestic tournaments
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
the critical point.
Typical diagram of a thermal power plant :1. Cooling tower
2. Cooling water pump
10. Steam Control valve 19. Superheater
11. High pressure steam turbine 20. Forced draught
3. transmission line (3-phase) 12. Deaerator
4. Step-up transformer (3phase)
5. Electrical generator (3phase)
6. Low pressure steam
13. Feedwater heater
22. Combustion air intake
14. Coal conveyor
15. Coal hopper
24. Air preheater
7. Condensate pump
16. Coal pulverizer
8. Surface condenser
17. Boiler steam drum
26. Induced draught (draft)
9. Intermediate pressure
18. Bottom ash hopper
27. Flue gas stack
MAJOR SUB-SYSTEMS OF A POWER PLANT: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
Inter Connection Between ST-1&ST-2
PLC Based Operation
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
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
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 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
• Pulverised 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
INTERIOR OF BOWL MILL
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 stageconsists of hydrogen ions and hydroxyl ions which is the chemical composition of pure
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 :-
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.
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 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
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.
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:
The tray-type (also called the cascade-type) includes a vertical domed deaeration
section mounted on top of a horizontal cylindrical vessel which serves as the deaerated
boiler feedwater storage tank. The spray-type consists only of a horizontal (or vertical)
cylindrical vessel which serves as both the deaeration section and the boiler feedwater
F) 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.
5) 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 th ree
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.
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
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.
6) ASH HANDLING AND DISPOSAL: 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
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.
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:
Primary air path through cold air duct
Hot air duct
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.
1) ID FANS: An induced fan circuit consists of
a) Flue gas through water walls
b) Super heater
d) Platen super heater
e) Low temperature super heater
f) Air pre-heater
g) Electrostatic precipitator
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
1) 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
2) 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.
3) AIR PRE-HEATERS: Air pre-heaters are used to take heat from the flue gases and transfer it to
incoming air. They are of two types:
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 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.
4) 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.
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
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.
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
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).
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.
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.
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, semiaxial 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.
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, thethrust 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 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
sipat for the above said pupose.
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.
BOILER maintenance department
A boiler is a heat exchanger in which the working fluid water is heated. The heated or vaporized
fluid exits the boiler for use in various processes or heating applications. The boiler used in NTPC
is Controlled Cirulation with Rifle Tubing Radiant Reheat Dry Bottom Top Supported .
Conversion of Water to Steam Evolves in three stages:
Heating the water from cold condition to boiling point or saturation temperature – Sensible Heat
Water boils at saturation temperature to produce steam – Latent Heat Addition.
Heating steam from saturation temperature to higher temperature called Superheating to increase
the power plant output and efficiency
In a tangential firing system the coal is pulverized in coal mills and is carried by primary air to
the furnace through coal pipes. The mills are usually a constant airflow mill and have a specific
output in mass of coal ground depending on coal properties like hardness, moisture, and fineness
which affect the mill output. In direct tangential firing systems, the pulverized coal from the coal
mills is directly taken to the furnace. Coal properties such as FC/VM (Fixed Carbon / Volatile
Matter), particle size, oxygen, calorific value of the coal, reactivity, and ash content seem to be
the most important variables for pulverised coal combustion in tangentially fired boilers, and
they are highly inter-related. The total quantity of coal to be pulverized for a specified size of
boiler at a designed efficiency will depend on the calorific value of coal. As the ash content in
coal goes up, the calorific value per unit mass of coal comes down. This increases the mass of
coal to be prepared, which in turn increases the number of mills or elevations needed in a
tangential firing system. The secondary air required for combustion is sent into the furnace
through a windbox housing the coal nozzles, oil guns, and the secondary air nozzles. Behind the
coal nozzles there are fuel-air dampers which are used for keeping the flame front away from the
coal nozzles by at least one meter from the tip. This is required to prevent the coal nozzle tips
from getting burnt due to radiation from coal flame. The flame front is predominantly affected
by the volatile matter in coal and the fuel air damper is modulated for controlling the flame
front. As the fuel air dampers are opened, more secondary air goes through this damper and
physically pushes the flame front away. However, when the flame front is already away from the
nozzle tip, the fuel air damper needs to be closed fully.
Understanding the quality of flame in any boiler furnace is very important to tune the boiler to
the optimal level of performance. The aspects of combustion tuning involve looking at the
boiler furnace and making sure the quality of flame is acceptable and good. The gas and oil
fired boilers do not pose much problem in establishing a good flame in furnace. The available
instruments like flame scanners, CO monitors and Oxygen indicators, along with the exit gas
temperature, give a good indication to perceive if the quality of the flame is good. In coal fired
boilers and mainly in tangential fired boilers, the furnace acts as a single burner, so it is required
to look at the flame and understand the quality of the flame.
SALIENT FEATURES OF 500 MW BOILER
Some important features of 500 MW Boiler are listed as :
CONTROLLED CIRCULATION SYSTEM
This is achieved by three numbers of glandless pump and wet motor installed in the downcomer
line after the suction manifold. These pump motor assemblies have single suction and double
discharge introduction of these pumps in the boiler system have led to the designing of a furnace
with lesser diameter tubes and high parameters operating characteristics.
The advantages of the controlled circulation boiler over natural circulation boiler are given below:
Uniform drum cooling and heating. In controlled circulation boilers this is possible
because of arrangement of relief tubes inlets to the drum and the internal baffles of the
drum from both sides. The internal base plates are arranged in such a way that it guides
the steam water mixture from the relief tubes as in controlled circulation boiler does not
exist in natural circulation (NC) boiler because in that case the relief required to be taken
over the drum and fed from both sides. This shall increase the pressure losses in the riser
tubes and also the hot static head requirement for start up. Since the available head in NC
Boiler is very less; efforts are always made to reduce the pressure loss and improve the
circulation. Second reason is to commence flow in the riser tubes immediately after light
up hot static head is kept as minimum as possible.
Better cleaning of boiler:
For effective acid washing, the acid has to be kept at certain temperature uniformly through the
This is possible with the assistance of controlled circulation.
· Uniform expansion of pressure part and lower metal temperature:
This means lesser thermal stresses on the tubes. Because of controlled circulation, lower
diameter tubes are used, which result in high mass flow rate thereby preventing departure from
nucleate boiling (DNB) maintains a lower metal temperature.
along the whole circumference of the drum. The drum is therefore uniformly heated and cooled.
Whereas in Natural Circulation Boiler, the arrangement of relief tubes and baffleplates is only on
side of the drum and this imposes a constraint on uniform heating of drum. Similar
arrangement of relief
USE OF RIFLE TUBES FOR FURNACE CONSTRUCTION
This is one of the extraordinary features of 500 MW capacity boilers. Because of the excessive
heat release in the burner zone of the furnace, the metal tubes constituting the furnace at that
zone are exposed to the maximum temperature. This being a water-cooled furnace, the steam
water mixture inside the tubes should effectively carry the heat from the burner zone of the
In this zone, the tubes have an internally cut spiral like a rifle bore so that when water flows
through the tubes, due to hot static heat, it takes a screwed path and attains a certain degree of
spin by which the watness of the tube is always maintained. This prevents the tubes form
departure from Nucleate boiling under all operating condition of the boiler and increases the
OVER FIRE AIR SYSTEM FOR NOX (OXIDES OF NITROGEN) CONTROL
Industrial growth in the recent years has necessitated the need to have a cleaner and pollution
free atmosphere, by controlling the production of industrial wastes with the application of
improved technology. Power plants are the major sources of the industrial pollution by virture of
the stanch emission in the atmosphere. These emissions contain mostly gases and dust particles,
which have ill effect on the ecological system. In the 500 MW capacity boiler design, this aspect
has been given due importance and certain technical improvements have been incorporated.
These are tilting tangential firing and over fire air system. Tangential firing helps in keeping the
temperature of the furnace low so that NOX emission is reduced considerably. In addition to the
above the over fire air is provided which is used as combustion process adjustment technically
for keeping the furnace temperature low and thereby low Nox formation.
Each corner of the burner windbox is provided with two numbers of separate over fire air
compartments, kept one above the other and the over fire air is admitted tangentially into the
BOILER WATER CIRCULATION PUMPS
Each Boiler Water Circulation pump consists of a single stage centrifugal pump on a wet stator
induction motor mounted within a common pressure vessel. The vessel consists of three main
parts a pump casing, motor housing and motor covers. The motor is suspended beneath pump
casing and is filled with boiler water at full system pressure. No seal exists between the pump
and motor, but provision is made to thermally isolate the pump from the motor in the following
Thermal Conduction. To minimise heat conduction, a simple restriction in the form of
thermal neck is provided.
Hot Water Diffusion. To minimise diffusion of boiler water, a narrow annulus surrounds the
rotor shaft, between the hot and cold regions. A baffle ring restricts solids entering the annulus.
Motor Cooling. The motor cavity is maintained at a low temperature by a heat exchanger
and a closed loop water circulation system, thus extracting the heat conducted form the pump.
In addition, this water circulates through the stator and rotor bearings extracting the heat
generated in the windings and also provide bearing lubrication. An internal filter is incorporated in
the circulation system.
In emergency conditions, if low-pressure coolant to the heat exchanger fails, or is
inadequate to cope with heat flow from pump case, a cold purge can be applied to the bottom of
the motor to limit the temperature rise.
The pump comprises a single suction and dual discharge branch casing. The case is welded into
the boiler system pipework at the suction and discharge branches with the suction upper most.
Within the pump cavity rotates a key driven, fully shrouded, mixed flow type impeller,
mounted on the end of the extended motor shaft. Renewable wear rings are fitted to both the
impeller and pump case. The impeller wear ring is the harder component to prevent galling.
The motor is a squirrel cage, wet stator, induction motor, the stator, wound with a special
watertight insulated cable. The phase joints and lead connections are also moulded in an
insulated material. The motor is joined to the pump casing by a pressure tight flange joint and a
motor cover completes the pressure tight shell.
Boiler Fittings And Accessories:
Safety Valve: It is used to relieve pressure and prevent possible explosion of a boiler.
Water Level Indicators: They show the operator the level of fluid in the boiler, also known as a
sight glass, water gauge or water column is provided.
Bottom Blowdown Valves: They provide a means for removing solid particulates that condense
and lie on the bottom of a boiler. As the name implies, this valve is usually located directly on
the bottom of the boiler, and is occasionally opened to use the pressure in the boiler to push these
Continuous Blowdown Valve: This allows a small quantity of water to escape continuously. Its
purpose is to prevent the water in the boiler becoming saturated with dissolved salts. Saturation
would lead to foaming and cause water droplets to be carried over with the steam - a condition
known as priming. Blowdown is also often used to monitor the chemistry of the boiler water.
Flash Tank: High pressure blowdown enters this vessel where the steam can 'flash' safely and be
used in a low-pressure system or be vented to atmosphere while the ambient pressure blowdown
flows to drain.
Automatic Blowdown/Continuous Heat Recovery System : This system allows the boiler to
blowdown only when makeup water is flowing to the boiler, thereby transferring the maximum
amount of heat possible from the blowdown to the makeup water. No flash tank is generally
needed as the blowdown discharged is close to the temperature of the makeup water.
Hand holes: They are steel plates installed in openings in "header" to allow for inspections &
installation of tubes and inspection of internal surfaces.
Steam Drum Internals: A series of screen, scrubber & cans (cyclone separators).
Low- Water Cutoff: It is a mechanical means (usually a float switch) that is used to turn off the
burner or shut off fuel to the boiler to prevent it from running once the water goes below a certain
point. If a boiler is "dry-fired" (burned without water in it) it can cause rupture or catastrophic
Surface Blowdown Line: It provides a means for removing foam or other lightweight
noncondensible substances that tend to float on top of the water inside the boiler.
Circulating Pump: It is designed to circulate water back to the boiler after it has expelled some
of its heat.
Feedwater Vheck Valve or Clack Valve : A non-return stop valve in the feedwater line. This
may be fitted to the side of the boiler, just below the water level, or to the top of the boiler.
Top Feed: A check valve (clack valve) in the feedwater line, mounted on top of the boiler. It is
intended to reduce the nuisance of limescale. It does not prevent limescale formation but causes
the limescale to be precipitated in a powdery form which is easily washed out of the boiler.
Desuperheater Tubes or Bundles: A series of tubes or bundles of tubes in the water drum or the
steam drum designed to cool superheated steam. Thus is to supply auxiliary equipment that
doesn't need, or may be damaged by, dry steam.
Chemical Injection Line: A connection to add chemicals for controlling feedwater pH.
A steam turbine is a mechanical device that extracts steam energy from pressurized steam, &
converts it into useful mechanical work. The simplest turbines have one moving part, a rotor
assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the
blades react to the flow, so that they move and impart rotational energy to the rotor.
TYPES OF TURBINE:
IMPULSE TURBINE: These turbines change the direction of flow of a high velocity fluid or
gas jet. The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic
energy. There is no pressure change of the fluid or gas in the turbine rotor blades (the moving
blades), as in the case of a steam or gas turbine, all the pressure drop takes place in the stationary
blades (the nozzles). Before reaching the turbine, the fluid's pressure head is changed to velocity
head by accelerating the fluid with a nozzle. Pelton wheels and de Laval turbines use this
process exclusively. Impulse turbines do not require a pressure casement around the rotor since
the fluid jet is created by the nozzle prior to reaching the blading on the rotor. Newton's second
law describes the transfer of energy for impulse turbines.
REACTION TURBINE: These turbines develop torque by reacting to the gas or fluid's
pressure or mass. The pressure of the gas or fluid changes as it passes through the turbine rotor
blades. A pressure casement is needed to contain the working fluid as it acts on the turbine
stage(s) or the turbine must be fully immersed in the fluid flow (such as with wind turbines). The
casing contains and directs the working fluid and, for water turbines, maintains the suction
imparted by the draft tube. Francis turbines and most steam turbines use this concept. For
compressible working fluids, multiple turbine stages are usually used to harness the expanding
gas efficiently. Newton's third law describes the transfer of energy for reaction turbines.
These are non-moving parts covering the pedestal containing fixed blades. Casing should be
towards expansion of turbine.
HP Turbine Casing:
Outer Casing- Barrel Type without axial or radial flange.
Barrel-type casing (suitable for quick startup & loading) Inner Casing- Cylindrical,
The inner casing is attached in the horizontal & vertical planes in the barrel casing so that
it can freely expand radially in all directions & axially from a fixed point.
IP TURBINE CASING:
Three Shell Design
All Casings Axially Split
Exhaust Hood Spray Arrangement
Inner casing carrying first 6 rows of shrouded guide blade
Middle casing carrying the last 2 stage free standing blades
LP TURBINE CASING:
The LP 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
Independent of the outer shell, is supported at four points on longitudinal beams.
Steam admitted to the LP turbine from the IP turbine flows into the inner casing from
LOSSES DURING MAINTAINANCE OF PLANT OPERATION &
1) SURFACE ROUGHNESS: It increases friction & resistance. It can be due to Chemical
deposits, Solid particle damage, Corrosion Pitting & Water erosion. As a thumb rule, surface
roughness of about 0.05 mm can lead to a decrease in efficiency of 4%.
2) LEAKAGE LOSS:
Turbine end Gland Leakages
About 2 - 7.5 kW is lost per stage if clearances are increased by 0.025 mm depending
upon LP or HP stage.
3) WETNESS LOSS:
Drag Loss: Due to difference in the velocities of the steam & water particles, water
particles lag behind & can even take different trajectory leading to losses.
• Sudden condensation can create shock disturbances & hence losses.
About 1% wetness leads to 1% loss in stage efficiency.
4) OFF DESIGN LOSSES:
Losses resulting due to turbine not operating with design terminal conditions.
Change in Main Steam pressure & temperature.
Change in HRH pressure & temperature.
Condenser Back Pressure
Convergent-Divergent nozzles are more prone to Off Design losses then Convergent
nozzles as shock formation is not there in convergent nozzles.
5) PARTIAL ADMISSION LOSSES:
In Impulse turbines, the controlling stage is fed with means of nozzle boxes, the
control valves of which open or close sequentially.
• At some partial load some nozzle boxes can be partially open / Completely closed.
Shock formation takes place as rotor blades at some time are full of steam & at some
other moment, devoid of steam leading to considerable losses.
6) LOSS DUE TO EROSION OF LP LAST STAGE BLADES:
Erosion of the last stage blades leads to considerable loss of energy. Also, It is the
least efficient stage.
Erosion in the 10% length of the blade leads to decrease in 0.1% of efficiency.
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