report on power plant

1. INTRODUCTION
The Farakka Super Thermal Power Station (F.S.T.P.S) spread across over
4000 odd acres with the townships scattered in the two districts of
Murshidabad & Malda is a 1600MW plant(200x3+500x2).The foundation
stone was laid on 29.12.81 by late Smt. Indira Gandhi. Its first unit was
synchronized on 1/1/1986 and its last (fifth) unit on 07/03/1994.SIXTH unit
500 MW is under erection by M/S BHEL
The source of coal is the nearby Rajmahal coalfields in Bihar and
water is obtained from the Farakka feeder canal. The plant supplies power to
West Bengal as well as the neighboring states .
FARAKKA SUPER THERMAL POWER PROJECT
- AN OVERVIEW
LOCATION: - STATE : - WEST BENGAL
DISTRICT : - MURSHIDABAD
SOURCES OF RAW MATERIAL : -
COAL - RAJMAHAL COAL FIELD, JHARKHAND
WATER- FARAKKA FEEDER CANAL.
GOVT. APROVAL OF STAGE I [ 3*200MW ] MARCH ‘79
THE PROJECT :- STAGE II [ 2*500MW ] SEPTEMPER’89
CAPACITY : - 1600MW STAGE I 3*200 MW
STAGE II 2*500 MW
PROJECT COST: - STAGE I [ 3*200MW ]
STAGE II [ 2*500MW ] Rs.3184.22
Crores
TOTAL AREA: - PLANT 2129 Acres
ASH POND 1894 Acres 4398 Acres
TOWNSHIP 375 Acres
TOTAL MANPOWER : - 1750 (31-03-2002)
POWER BENEFICIARY STATE AND ITS DISTRIBUTION:-
W.B - 33.12 BIHAR - 18.25
ORISSA - 14.69 D.V.C - 6.50

2. SIKKIM- 0.99 JHARKHAND- 2.61
OTHER REGION- 23.92
MANUFACTURE OF THE MAJOR EQUIPTMENTS:-
STAGE I BOILER – BHEL Maker, CORNER FIRED TYPE
TURBINE & GENERATOR – BHEL MAKE
COOLING SYSTEM – OPEN CYCLE.
STAGE II BOILER – Ansaldo Italy front & rear fired type .
TURBINE & GENERATOR – BHEL MAKE
COOLING SYSTEM – OPEN CYCLE.
Coal to Electricity …. Basics
In a thermal power plant, the thermal energy of the
superheated steam is used to drive the generator which in turn produces
electricity. The superheated steam is produced from any fossil fuel like coal,
crude oil etc. Since coal is available in plenty and in cheap, we use coal as
the primary fuel in the thermal power plants. The coal is pulverized, grinded
and powdered before it is used in the boiler. The pulverization of coal
increases the surface area of the coal which helps in the smooth combustion
Coal
Chemical
Energy
(Coal)
Super Heated
Steam
Pollutants
Thermal
Energy
(Steam)
Turbine
Torque
Heat Lo ss
in
Co ndenser
Mechani
cal
Energy
Electrical
Energy
Alternating current in
Stator
Mech.
Energy Lo ssASH
Heat
Loss
Elec.
Energy Lo ss

3. of the coal. The coal is feed to the boiler where it is fired to produce heat.
Initially, a small quantity of crude oil is used for the purpose. The water is
passed through the pipes fitted in the walls of the boiler. The water is heated
to produce steam, which is further reheated to produce superheated steam.
The superheated steam at an exceedingly high temp and pressure drives the
turbine. The turbine rotates following which the generator which is coupled
to the turbine also rotates producing electricity.
Thus, the chemical energy of the coal is
utilized to produce steam. The thermal energy of the steam is converted to
the mechanical energy of the rotating turbines which is converted to the
electrical energy in the generator.
COAL HANDLING PLANT(CHP)
For a pulverized coal-fired boiler, the coal is transported from the nearby
Lalmatia mines via the Merry-Go-Round (MGR) system. It is then handled at the CHP
(Coal handling Plant) and supplied to the main plant at about 20mm size. From there
through coal Bunkers, coal feeders and mills (for pulverization) it is supplied to the
burners through a piping system. Heated air, called primary air, is passed through the
pulverizers to pick up the fine particles of coal and carry them to the furnace.
COAL UNLOADING :
 At NTPC end, Coal is unloaded in the Track hoppers.
 Track Hopper, normally of 200-250m length.
 After placing the wagons on the hopper, electrical pulse is given to the
pneumatic device for opening the bottom doors.
 Coal rushes down due to its own weight.
 When the track hopper is empty, it takes only 20 seconds for unloading
one wagon i.e. 60 Tons.
 This coal falls on a ‘T’ table, over which a paddle feeder runs and pushes
the coal on to a conveyor.
COAL HANDLING SYSTEM EQUIPMENT :
 Plough feeder/ paddle feeder
 vibrating screen
 Crushers,
 Conveyor belt,

4.  Idlers,
 Pulleys,
 Drive Unit,
 Take-ups,
 Skirt board,
 Scrapper,
 Stacker-cum-reclaimer,
 Magnetic separators,
 Motorized tripper.
COAL-HANDLING SYSTEM:
 Coal handling system is the arrangement for transferring of coal from coal-
wagons to coal-bunker or coal stock yard.
 It also provide arrangement for separation of material impurities, crushing of
coals, Coal sampling etc.
 In the coal handling system of NTPC stations, three coal paths are normally
available
Path A - direct conveying of coal from track hopper to boiler bunkers.
Path B - from track hopper to stockyard
Path C - from stockyard to boiler bunkers.
The storage facilities at the stockyards have been provided only for crushed coal.
COAL-HANDLING PROCESS:
From the track hopper 200mm coal is transferred to the conveyor via paddle
feeder and finally sent to the crusher house.
In the Crusher House the vibrating screen sends the coal having size of less than
20mm to belt feeder through the bypass chute bypassing the crusher and sends the coal of
more than 20mm size to the crusher.
Farakka Borhait Pokhra
Lalmatia

5. STEAM GENERATION
BOILING STEAMGENERATION
Boiling & consequent steam generation is a quite familiar process. In brief , as
we began to heat water, it goes on absorbing heat at constant pressure and is
evident by rise in the temp. A stage reaches when water begins to boil and there
is no rise in temp., at this stage steam is formed, whichcontinues to be so at the
same temp. unless and until pressure changes. The first stage of heat has ;dueto
the latent heat. Thus, thermodynamically speaking, boiling may be considered a
special case of adding heat to the working substance in a constant-pressure,
constant temp. process.
.
As the pressure rises ,latent heat decreases and a stage is reached at (221.06
bar ), when thelatent heat become zero, this pressure began termed as critical
pressure. .Further , once the steam is formed & does not have any traces of
water i.e. is dry & saturated ,we keep the pressure constant while heat is being
added, the temperature of steam will begin to rise, theheat expended being
known as superheat.As the working pressure rises, the specific weight of the
water goes on decreasing while that of steam goes on rising till at critical
pressure it becomes equal both for steam and water .
.Because of specific weight, differential between water & steam at a given
pressure, there existsa different head, which ever a pretty long range of pressure
provides a good means for circulation during steam generation. Depending upon
working pressure i.e. below critical , the steam generatorsare designated as
subcritical or super-critical.Whereas, for a greater part of the range in subcritical
pressure it is possible to have naturalcirculation during evaporation, but above
supercritical pressure circulation is forced one. In the highersubcritical pressure
range also due to the reason of economy, forced or assisted circulation may
beemployed.
CIRCULATION SYSTEMS :
GENERAL
Modern boilers may be with or without the drum. The boilers working below the
sub-criticalpressure are generally provided with drums, or a small separating
vessel (high pressure nearing critical) in its place irrespective of the type of the
type of circulation employed. The drum-acts as reservoir forwater & saturated
steam and also provides means and arrangements for separation and purification

6. of steam. The term circulation generally with drum type of boilers applies to the
movement of fluid fromthe drum to the combustion zone and back to the drum.
The feed water to the drum in any case reachesthe drum from the boiler feed
pump via the economizer, the drum - less boilers work above criticalpressures &
there is straight transformation to steam without passing through the boiling
stageinvolving latent heat of evaporation. Some designs in this type of boilers
provide a small mixing or separating vessel which deals with the water drops
particularly during starting.It is essential to provide an adequate flow of water and
/or of water steam mixture for anefficient transfer of heat from furnace to the
working fluid and to prevent 'burn outs'. This isirrespective of the mode of
circulation being used.
TYPES OF BOILER CIRCULATION SYSTEMS :
The boiler circulation systems have been designated in different ways by the
variousmanufacturers. Of course they are similar as for as basic principles are
concerned and differ in minordetails and nomenclature. The various classification
in vogue are given below
.
1 SOME DESIGNERS HAVE THE FOLLOWING CLASSIFICATIONS FOR
TYPES OF CIRCULATIONS :
a) Natural circulation:- In this type, no external pumping device is
used for the movement of thefluid. The difference in densities in
contents of fluids in downcomers from the drum and risers in
thefurnace is used to effect the movement of fluids. This type of
circulation is employed in most of theutility boilers and in fact in
India excepting one unit at Trombay power station all boilers work
onnatural circulation.
b) Positive circulation ::- In this type , use of pumps is made for
movement of fluid through thecombustion zone or complete heat
transfer circuits. This type of circulation is further divided into
.I) Assisted circulation : The term is generally used in case of boilers
having drums and working below critical pressures. Circulating water pumps are
used in between the bottom headers of downcomers and risers to overcome
frictional losses and the consequent movement of water and watersteam
mixture.500 Mw BHEL boiler in NTPC Farakka has this type of circulation where
CC pump is used in downcomers.
II)Forced circulation :
:- This term is generally used for movement of fluid in boilers working above
critical pressures. These boilers are of 'Once-through' type. The pump forces
movement of fluidthrough all the heating zones viz. Economizers , tubes in

7. combustion zones and superheaters. A smallseparating or mixing vessel may be
provided for removal of moisture from steam and pumping back tothe circuit.
CIRCULATION RATIO :
It is essential to maintain a certain amount of flow of water to the steam
generatingcircuits in commensurate with the amount of steam generated from
them, in order to prevent `Burn-outs' and `On-load Corrosion'. The ratio by weight
of the water fed to the steam-generating circuits tothe steam actually generated
(Kg water : Kg steam ) is called `Circulation Ratio'. Taking circuit shownin Fig. 1.8
as an example for a unit period of time 5 kg water is admitted to risers (which will
getconverted into mixture of water and steam during its passage through the
furnace) and 1 kg of steam istaken out of the drum, the value of circulation ratio
will be five. The remaining 4 Kg of water will berecirculated in the system. To

8. compensate for 1 Kg. Of steam taken out, 1 Kg. Of water will have to beadded to
the drum, which will enter the risers alongwith the water under recirculation.
INTRODUCTION OF BOILER AT NTPC FARAKKA:
The 200 MW unit boilers (3 Nos.) are Natural Circulation, Dry bottom,
Single drum, Tangentially fired, Balanced draft, Radiant reheat type direct
corner fired pulverized coal system.
The description of these technical terms is –
(a) Natural Circulation – The flow of water & steam within the boiler
circuit is called Circulation. If circulation is caused by density difference
(without assistance of any pump), the boiler is said to have natural
circulation.
(b) Dry Bottom – In a dry-bottom furnace, ash or slag is removed in the
solid or dry state. The exit temperature of gases leaving the furnaces must
be below the ash fusion temperature.
(c) Single Drum –There is only one drum i.e. steam drum in boiler
circuit. There is no mud drum (also called water drum) in our unit.
(d) Tangentially Fired & Direct corner fired –In tangential fired boilers
with corner burners, flame jets directed tangentially to an imaginary
circle 1-2.5 m in diameter in the furnace center. Both fuel & air are
projected horizontally from the corners of the furnace along lines tangent
to a vertical cylinder (Imaginary) at the center of the furnace. Intensive
mixing occurs where the stream meet. A rotating motion, similar to that
of cyclone, is imparted to the flame body, which spreads out & fills the
furnace area.
This arrangement helps in avoiding clinkering of water walls due to intense
thermal loading near those walls in Corner Firing with Encountering Flame
Jets burner arrangement.

9. (e) Balanced Draft –In balance draft (draught) the pressure in furnace is
slightly negative gauge pressure to ensure that any leakage would be
inward.
(f) Radiant reheat type – In our boiler reheater is placed in the radiant
zone of the furnace near the rear water wall to absorb heat by radiation.
(g) Pulverized coal system -In pulverized coal system, coal is first
ground to dust like size in a mill & powdered coal is then carried in a
stream of air (PA) to be fed through burners into the furnace.
In fossil-fueled power plants,steam generator refers to a furnace that burns
the fossil fuel to boil water to generate steam. The steam generating boiler
has to produce steam at the high purity, pressure and temperature required

10. Schematic Diagram of 200 MW Boiler

11. for the steam turbine that drives the electrical generator. A fossil fuel steam
generator includes an economizer, a steam drum, and the furnace with its
steam generating tubes and superheater coils. Necessary safety valves are
located at suitable points to avoid excessive boiler pressure. The air and flue
gas path equipment include: forced draft (FD) fan, air preheater (APH),
boiler furnace, induced draft (ID) fan, fly ash collectors (electrostatic
precipitator or baghouse) and the flue gas stack..
For units over about 200 MW capacity, redundancy of key components is
provided by installing duplicates of the FD fan, APH, fly ash collectors and
ID fan with isolating dampers. On some units of about 60 MW, two boilers
per unit may instead be provided.
Boiler furnace and Steam drum
Once water inside the boiler or steam generator, the process of adding the
latent heat of vaporization or enthalpy is underway. The boiler transfers
energy to the water by the chemical reaction of burning some type of fuel.
The water enters the boiler through a section in the convection pass called
the economizer.
From the economizer it passes to the steam drum. Once the water enters the
steam drum it goes down the downcomers to the lower inlet waterwall
headers. From the inlet headers the water rises through the waterwalls(due to
density difference) and is eventually turned into steam due to the heat being
generated by the burners located on the front and rear waterwalls (typically).
As the water is turned into steam/vapor in the waterwalls, the steam/vapor
once again enters the steam drum. The steam/vapor is passed through a
series of steam and water separators and then dryers inside the steam drum.
The steam separators and dryers remove water droplets from the steam and
the cycle through the waterwalls is repeated. This process is known as
natural circulation.
The boiler furnace auxiliary equipment includes coal feed nozzles and
igniter guns, soot blowers, water lancing and observation ports (in the

12. furnace walls) for observation of the furnace interior. Furnace explosions
due to any accumulation of combustible gases after a trip-out are avoided by
flushing out such gases from the combustion zone before igniting the coal.
The steam drum (as well as the superheater coils and headers) have air vents
and drains needed for initial startup. The steam drum has internal devices
that removes moisture from the wet steam entering the drum from the steam
generating tubes. The dry steam then flows into the superheater coils.
Superheater
Fossil fuel power plants can have a superheater and/or reheater section in
the steam generating furnace. In a fossil fuel plant, after the steam is
conditioned by the drying equipment inside the steam drum, it is piped
from the upper drum area into tubes inside an area of the furnace
known as the superheater, which has an elaborate set up of tubing
where the steam vapor picks up more energy from hot flue gases
outside the tubing and its temperature is now superheated above the
saturation temperature. The superheated steam is then piped through
the main steam lines to the valves before the high pressure turbine.
Reheater
Power plant furnaces may have a reheater section containing tubes heated by
hot flue gases outside the tubes. Exhaust steam from the high pressure
turbine is rerouted to go inside the reheater tubes to pickup more energy to
go drive intermediate or lower pressure turbines.
Fuel preparation system
In coal-fired power stations, the raw feed coal from the coal storage area is
first crushed into small pieces and then conveyed to the coal feed hoppers at
the boilers. The coal is next pulverized into a very fine powder. The
pulverizers may be ball mills, rotating drum grinders, or other types of
grinders.
Some power stations burn fuel oil rather than coal. The oil must kept warm
(above its pour point) in the fuel oil storage tanks to prevent the oil from
congealing and becoming unpumpable. The oil is usually heated to about
100°C before being pumped through the furnace fuel oil spray nozzles.
Boilers in some power stations use processed natural gas as their main fuel.
Other power stations may use processed natural gas as auxiliary fuel in the

13. event that their main fuel supply (coal or oil) is interrupted. In such cases,
separate gas burners are provided on the boiler furnaces.
Air path
External fans are provided to give sufficient air for combustion. The forced
draft fan takes air from the atmosphere and, first warming it in the air
preheater for better combustion, injects it via the air nozzles on the furnace
wall.
The induced draft fan assists the FD fan by drawing out combustible gases
from the furnace, maintaining a slightly negative pressure in the furnace to
avoid backfiring through any opening. At the furnace outlet, and before the
furnace gases are handled by the ID fan, fine dust carried by the outlet gases
is removed to avoid atmospheric pollution. This is an environmental
limitation prescribed by law, and additionally minimizes erosion of the ID
fan.
Auxiliary systems
ASH HANDLING
Fly ash collection
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 or bag filters.
Generally, the fly ash is pneumatically transported to storage silos for
subsequent transport by trucks or railroad cars.
Bottom ash collection and disposal
At the bottom of the furnace, there is a hopper for collection of bottom ash.
This hopper is always filled with water to quench the ash and clinkers falling
down from the furnace. Some arrangement is included to crush the clinkers
and for conveying the crushed clinkers and bottom ash to a storage site.
Boiler make-up water treatment plant and storage
Since there is continuous withdrawal of steam and continuous return of
condensate to the boiler, losses due to blowdown and leakages have to be
made up to maintain a desired water level in the boiler steam drum. For this,

14. continuous make-up water is added to the boiler water system. Impurities in
the raw water input to the plant generally consist of calcium and magnesium
salts which impart hardness to the water. Hardness in the make-up water to
the boiler will form deposits on the tube water surfaces which will lead to
overheating and failure of the tubes. Thus, the salts have to be removed from
the water, and that is done by a water demineralising treatment plant (DM).
A DM plant generally consists of cation, anion, and mixed bed exchangers.
Any ions in the final water from this process consist essentially of hydrogen
ions and hydroxide ions, which recombine to form pure water. Very pure
DM water becomes highly corrosive once it absorbs oxygen from the
atmosphere because of its very high affinity for oxygen.
The capacity of the DM plant is dictated by the type and quantity of salts in
the raw water input. However, some storage is essential as the DM plant
may be down for maintenance. For this purpose, a storage tank is installed
from which DM water is continuously withdrawn for boiler make-up. The
storage tank for DM water is made from materials not affected by corrosive
water, such as PVC. The piping and valves are generally of stainless steel.
Sometimes, a steam blanketing arrangement or stainless steel doughnut float
is provided on top of the water in the tank to avoid contact with air. DM
water make-up is generally added at the steam space of the
surfaccondenser(i.e., the vacuum side). This arrangement not only sprays the
water but also DM water gets deaerated, with the dissolved gases being
removed by an air ejector attached to the condenser.
ELECTROSTATIC PRECIPITATOR
It is a device which captures the dust particles from the flue gas thereby reducing
the chimney emission.
Precipitators function by electrostatically charging the dust particles in the gas
stream. The charged particles are then attracted to and deposited on plates or
other collection devices. When enough dust has accumulated, the collectors are
shaken to dislodge the dust, causing it to fall with the force of gravity to hoppers
below. The dust is then removed by a conveyor system for disposal or recycling .

15. TYPICAL SPECIFICATIONS FOR A 200MW UNITS
NUMBER OF PASS PER BOILER 4
NUMBER OF FIELD IN EACH PASS 6
EFFICIENCY 99.9%
PRESSURE DROP 20 mmWC
GAS FLOW RATE 312.7 Cu.m/sec
INLET TEMPERATURE 136 DEGREE
VELOCITY OF GAS AT ELECTRODE 0.839 m/sec
TOTAL TREATMENT TIME 32.18 SEC
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

16.  Particle Removal - Conveying the particles from the hopper to a disposal
point
Components of ESP
• Discharge Electrodes
• Power Components
• Precipitator Controls
• Rapping Systems
• Purge Air Systems
• Flue Gas Conditioning
• Emitting Electrodes
• Collecting Electrodes
• High Voltage Equipment
• Rapping Mechanism
• Hoppers
• Heaters
• ALI
• Gas Distribution Screen
• Segregating Gates