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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
9
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
23
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.
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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-
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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.
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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.
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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.