This Project Report has been prepared in fulfilment of Industrial Training to be carried
out in third year of our four year B.TECH course. For preparing the Project Report, we
have visited Mejia Thermal Power Station under Damodar Valley Corporation during
the suggested duration for the period of 21 days, to avail the necessary information.
The blend of learning and knowledge acquired during our practical studies at the
company is presented in this Project Report.
The rationale behind visiting the power plant and preparing the Project Report is to
study the mechanical overview, electrical overview, various cycles and processes (viz.
Steam Generation, Turbo Generation and Balance of Plant) of power generation and
details of control and instrumentation required in thermal power plant.
We have carried out this training under well experienced and highly qualified engineers
of MTPS, DVC of various departments’ viz. Mechanical, Electrical, Chemical and Control
& Instrumentation depts. We have taken the opportunity to explore the Electrical
Department, its use, necessity in power plant and maintenance of various instruments
used for monitoring and controlling the numerous processes of power generation. We
have tried our best to cover all the aspects of the power plant and their brief detailing in
this project report.
All the above mentioned topics will be presented in the following pages of this report.
The main aim to carry out this training is to familiarize ourselves with the real industrial
scenario, so that we can relate with our engineering studies.
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I take this opportunity to express my profound gratitude and deep regards to Mr. P.K.
Dubey for his exemplary guidance, monitoring and constant encouragement
throughout the course of this thesis. The blessing, help and guidance given by him time
to time shall carry me a long way in the journey of life on which I am about to embark.
I also take this opportunity to express a deep sense of gratitude to Mejia Thermal
Power Station, DVC, for their cordial support, valuable information and guidance, which
helped me in completing this task through various stages.
I am also thankful to the Director (HRD), the Chief Engineer and Project Head, Mr. G.
Nandesu (Asstt. Manager HR) for providing me opportunity to carry out my vocational
training in MTPS.
I am obliged to staff members of Mejia Thermal Power Station, DVC for the valuable
information provided by them in their respective fields. I am grateful for their
cooperation during the period of my assignment.
Lastly, I thank almighty, my parents, brother, sisters and friends for their constant
encouragement without which this assignment would not be possible.
Signature of the Trainee
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Table of Contents Page No.
Damodar Valley Corporation 5
Basic needs and overview of a power plant 7
Mejia Thermal power station 9
MTPS Unit Overview 11
Coal Handling Plant 12
Coal Mill 15
Furnace and Boiler 17
Steam Turbine 20
Introduction to Water Treatment 23
Pre Treatment of Water 24
DM Plant Treatment 25
Waste Water Treatment 26
Steam/Water Circuit of MTPS 27
Components of Steam/Water Cycle 29
Cooling Towers 32
Air and Flue Gas Path 33
Electrostatic Precipitators 35
Ash Handling Plant 40
Electrical System Overview 43
Excitation System 44
Control and Instrumentation 50
Automatic Voltage Regulator 53
AC and DC Power Flow in MTPS 55
Frequency Control 60
Voltage Control 61
National Grid 62
Central Load Dispatch 63
DVC: Transmission and Distribution Network 65
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Electricity generation is the process of generating electric power from sources of
energy. Electricity is most often generated at a power station by
electromechanical generators, primarily driven by heat engines fuelled by
chemical combustion or nuclear fission but also by other means such as the kinetic
energy of flowing water and wind. There are many other technologies that can be and
are used to generate electricity such as solar photovoltaic and geothermal power.
In Indian subcontinent the abundance of coal leads to establishment of thermal
power stations and governing bodies namely DVC, NTPC, TATA power acts as pioneers
in the generation of electricity.
Damodar Valley Corporation
Damodar Valley Corporation was established on 7th July 1947.It is the
most reputed company in the eastern zone of India. DVC is established on the
To foster integrated development of Damodar Valley Command Area and achieve
par excellence in its multifaceted activities of control of floods, provision of irrigation,
generation, transmission and distribution of electrical energy and also soil conservation,
unified tourism, fisheries, socio-economic & health development of villages within a
radius of 10 KM of its projects.
To establish DVC as one of the largest power majors of Eastern India while
discharging the responsibilities of its other projects adequately.
In order to achieve this goal against the backdrop of the competitive market
scenario in the power sector, the objective of the Corporation has been redefined.
Entrusted with the responsibilities of providing the vital input power for industrial
growth in the resource rich Damodar Valley region, DVC has been practically operating
as a pioneer, using latest available technologies to supply bulk power at reasonable
rates to the major industries.
DVC has maintained its lead role in the eastern region by adopting itself to the
challenges of time and technology during the course of last 64 years. DVC has been
generating and transmitting power since 1953 and has succeeded not only in meeting
the needs of consumers but has also helped to increase the demand of power which
itself is an index of development.
Therefore, DVC, a legacy to the people of India, emerged as a culmination of
attempts made over a whole century to control the wild and erratic Damodar river. The
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river spans over an area of 25,000 km2 covering the states of Bihar (now Jharkhand) &
With the time DVC developed and expanded its infrastructure, seven thermal
power stations with a capacity of 8910MW, three hydroelectric power stations with a
capacity of 147 MW. Presently DVC has more than 60 substations and receiving stations
more than 5500-circuit km of transmission and distribution lines.DVC has also four
dams, a barrage and a network of canals that play effective role in water management.
The construction of check dams, development of forests and farms and upland and
wasteland treatment developed by DVC play a vital role in eco conservation.
Thermal Power Stations:
Sr.No. Plant State Installed Capacity
1 Bokaro Thermal Power Station B Jharkhand 630
2 Chandrapura Jharkhand 1140
3 Durgapur Thermal Power Station West Bengal 350
4 Mejia Thermal Power Station West Bengal 2340
5 Koderma Stage-1 Jharkhand 1000
6 Durgapur Steel Thermal Power West Bengal 1000
7 Raghunathpur phase-1 Thermal West Bengal 1200
Total : 8,910
Hydel Power Station:
Sl. No. Plant State Installed
Capacity in MW
1 Maithon Dam Jharkhand 63.2
2 Panchet Dam Jharkhand 80
Total : 147.2
Joint Venture Stations:
Sl. No. Sl. No. State Installed
Capacity in MW
1 Bokaro Power Supply Corporation Jharkhand 302
2 Maithon Power Limited Jharkhand 1050
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Basic Needs and Overview of a Thermal Power Pl ant
The idea that STEAM has potential energy and can be converted into kinetic energy was
given by famous scientist, Sir. James Watt. This idea became the governing principal of
many mechanical processes and finally led to the success of Thermal Power Energy. The
need of establishing a Thermal Power Plant came to engineers by the realization of the
fact that Hydel Power could be utilized only for certain period of time in a year. This
section will give the basic requirements for Thermal Power Plant.
SITE REQUIREMENT: - The basic requirements of thermal power plant is determined
by the type, size and other specifications of the plant. It is required to know the
immediate capacity of the power plant after construction and the extension of
capacity in the future, to determine the area required for construction of the plant.
The basic things that are taken into consideration are <1>Station Building
<2> Coal Store
<4>Switch yard compound
<5>Surrounding areas and
GEOLOGY: - The geology of the site should be cost effective and the subsoil must be
able to with stand huge load of foundation.
WATER REQUIREMENT: - Water is required in power plant for two basic needs, first is
for steam generation and second is for cooling purpose. Thermal Power Plant
requires huge volume of water, nearly of about 3 to 4 Tons/hr/MW only for steam
generation. So site of plant must also have reliable and huge water sources located
near to it.
COAL: - Coal is the prime requirement of any thermal power plant, it is the main
source of fuel as it is most economic and residue of coal after combustion is also
used by many industries like cement industries, so the plant must have reliable
sources of coal and regular supply in huge amount like 20,000 Tons per week.
TRANSPORT: - It is one of the another vital factor of the plant as huge burden lies on
transportation in daily basis because of huge need of coal, furnace oil, hydrochloric
acid and other chemical products along with mechanical products.
DISPOSAL OF EFFLUENTS: - Due to heavy rate of coal combustion residual volume is
also high. The main residual product is ash. The plant must have facilities like ash
pond to dispose them safely without harming the environment.
TRANSMISSION: -The plant area must have route available for transmission over
head cables to the nearest grid lines or load points which will be capable of
accepting the generated power output of the power station.
CLIMATIC CONDITION : - The tropical climate is best for erection of thermal power
plant, because areas having high humidity and fluctuating temperature lead to dew
point and condensation which as a result damages the electrical machines and
corrodes the insulation and over head cables.
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PROXIMITY OF AIRFIELDS:- The airfields must be studied properly to avoid mishaps as
the chimney height ranges from 500 to 600 fts and boiler housing is of 200 fts in
PERSONNEL REQUIREMENTS: - To run a plant smoothly requirement of skilled and
unskilled personnel is very important. So recruitment of workers and skilled
personnel should be made carefully and in adequate amount.
AMENITIES: -Some considerations like availability of hospital, educational institutes
and other facilities must be taken into account.
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Mejia Thermal Power Station
Mejia Thermal Power Station also known as MTPS is located in the
outskirts of Raniganj in Bankura District. It is one of the 5 Thermal
Power Stations of Damodar Valley Corporation in the state of
West Bengal. The total power plant campus area is surrounded by
boundary walls and is basically divided into two major parts,
first the Power Plant area itself and the second is the Colony area
for the residence and other facilities for MTPS employees.
Technical Specification of MTPS long with Specialities
1) Total number of Units: -
4*210 MW with Static Generators
2*250 MW with Brush less Type Generators
2*500 MW with Brush less Type Generators
2) Total Energy Generation: -2340 MW
3) Source of Water: - Damodar River
4) Sources of Coal: -
B.C.C.L and E.C.L, also imported from Indonesia
5) Required Water Consumption: -
6) Approximate coal requirement: - 73, 00,000
Tons/annum at 75% PLF (Plant Load Factor)
7) Ash Deposited per annum: - 1.30 million Tons /annum
SPECIALITIES OF MEJIA THERMAL POWER PLANT:
The plant is designed and engineered by both Bharat Heavy Electricals Ltd (BHEL)
and Damodar Valley Corporation.
Pipelines of 17km long and 1473mm in diameter spiral welded MS pipes laid to
transport river water from upstream of Durgapur barrage by pump sets of 500KV
pump motor set.
Rail cum Road Bridge across Damodar River near Raniganj Station.
2KM Merry Go Round Railway System.
20mtr high RCC multiple flue stack.
Direct ignition of pulverized coal introduced for reduction in consumption of fuel
Ball and Tube type Mills for more mill rejects and less maintenance cost.
Boiler of 200ft height and four corner firing system for better combustion.
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All major and hazardous systems like Steam Generation and Turbo Generation
section are incorporated with FSSS (Furnace Safety Supervisory System) for
Other logic systems like EAST and ATRS are also incorporated.
Water treatment Plants along with two artificial water reservoirs and Two
Demineralization Plants loaded with PLC system.
Chimney height up to 600fts for less pollution.
The plant is loaded with latest technology sensor, transducers and transmitters
for more accurate analyzing of various processes.
All the units are loaded with intelligent smart microprocessor based systems
known to be DCS systems provided by KELTRON, SIEMENS and MAX-DNA for
Station Service Transformers of 6.6KV step-down type are also available for
better distribution of power inside the plant for various requirements.
Switchyard with individual step-up generator transformers of ONAN/ANOF/AFOF
cooling Transformers of 220KV for supply to national grid, along with other safety
Details of MTPS Generating Units
Gen. Name of Original Present Year of Special Features
Unit Manufacturers capacity capacity commissioning
Boiler TG (MW) (MW)
1 BHEL BHEL 210 210 March , 1996 DIPC Boilers with zero
2 BHEL BHEL 210 210 March, 1998 reject tube mills.
3 BHEL BHEL 210 210 September, 1999
4 BHEL BHEL 210 210 February, 2005
5 BHEL BHEL 250 250 February, 2008
6 BHEL BHEL 250 250 2009
7 BHEL BHEL 500 500 2010
8 BHEL BHEL 500 500 2010
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Coal Handling Plant
Coal: The Black Diamond
Coal is the basic and the oldest raw material used on large scale throughout the world.
Throughout history, coal has been a useful resource. It is primarily burned for the
production of electricity and/or heat, and is also used for industrial purposes, such as
refining metals. A fossil fuel, coal forms when dead plant matter is converted into peat,
which in turn is converted into lignite, then sub-bituminous coal, after that bituminous
coal, and lastly anthracite. This involves biological and geological processes that take
place over a long period.
Coal Handling Plant
In a coal based thermal power plant, the initial process in the power generation is “Coal
Handling”. Coal is extracted from the ground by coal mining, either underground by
shaft mining, or at ground level by open pit mining extraction. The huge amount of coal
is usually supplied through railways. A railway siding line is taken into the power station
and the coal is delivered in the storage yard. The coal is unloaded from the point of
delivery by means of wagon tippler. It is rack and pinion type. The coal is taken from the
unloading site to dead storage by belt conveyors. The belt delivers the coal to 0m level
to the pent house and further moves to transfer point 8.
The transfer points are used to transfer coal to
the next belt. The belt elevates the coal to
breaker house. It consists of a rotary machine,
which rotates the coal and separates the light
dust from it through the action of gravity and
transfer this dust to reject bin house through
The belt further elevates the coal to the transfer
point 7 and it reaches the crusher through belt.
In the crusher a high-speed 3-phase induction
motor is used to crush the coal to a size of 50mm
so as to be suitable for milling system. Coal rises
from crusher house and reaches the dead
storage by passing through transfer point 8.
Stages in Coal Handling plant
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Ultimate Analysis of Coal
Carbon : 49.63%
Hydrogen : 3.66%
Sulphur : 0.47%
Nitrogen : 0.91%
Oxygen : 6.4%
Moisture : 5.0%
Ash : 34.0%
Total : 100%
Operation of a Coal Handling Plant
The purpose of the Coal handling plant in a thermal power plant is to process raw
coal & insure against their regular supply of coal which is dependent on many
players in the supply chain.
The function of a CHP is to receive process, store, and feed the Coal bunkers
consistently over the entire life of the Power plant.
Coal is received from mines in the form of lumps, the sizes varying from 100mm to
350mm, in two types of wagons through Rail; BOBR meaning Bogie Open Bottom
Rapid discharge & BOXN meaning Bogie Open High Sided Side discharge Wagon
BOBR wagons are unloaded in Track Hoppers & BOXN Wagons are unloaded by
Coal is then supplied to the crusher house through Roller screens or Vibrating
feeders to sieve the coal before feeding to the crusher; 20% of the coal that is
received is already <20mm size so this is separated & only larger lumps are fed to the
The crusher breaks the lumps to sizes <20mm which is the input size to the coal
The crushed coal is fed to the conveyors in the crusher house through Belt feeders;
Coal is either directly fed to the coal bunkers or to the Stacker/Reclaimers for
stocking when the bunkers are full.
The stacking is done to insulate the plant against the erratic supply of coal;
CERC allows stocking of1½months stock of coal for Pithead plants.
In case of non-receipt of wagons the coal from the stockpile is reclaimed through the
Stacker/Reclaimers & fed to the coal Bunkers.
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To increase redundancy certain Plants also have Emergency reclaim Hoppers near
the Crushed coal Stock pile where the dozers are used to feed coal to the bunkers
when the Reclaimers breakdown.
Coal is conveyed by means of conveyor Belts in the coal handling plant.
Components of a Coal Handling Plant
1. Stockpile: Stockpiles provide surge capacity to various parts of the CHP. Coal is
delivered with large variations in production rate of tonnes per hour (tph). A
stockpile is used to allow the washplant to be fed coal at lower, constant rate.
A simple stockpile is formed by machinery dumping coal into a pile, either from
dump trucks, pushed into heaps with bulldozers or from conveyor booms. Taller and
wider stockpiles reduce the land area required to store a set tonnage of coal. Larger
coal stockpiles have a reduced rate of heat loss, leading to a higher risk of
2. Stack: Travelling, luffing boom stackers that straddle a feed conveyor are commonly
used to create coal stockpiles.
3. Reclaimer: High-capacity stockpiles are
commonly reclaimed using bucket-wheel
reclaimers. These can achieve very high
rates. Tunnel conveyors can be fed by a
continuous slot hopper or bunker beneath
the stockpile to reclaim material. Front-end
loaders and bulldozers can be used to push
the coal into feeders. Sometimes front-end
loaders are the only means of reclaiming coal
from the stockpile. This has a low up-front
capital cost, but much higher operating costs,
measured in dollars per tonne handled. Reclaimer pouring coal into stack
4. Crush House: After hand picking foreign material, coal is transported to the Crush
house by conveyor belts where it is crushed to small pieces of
about 20 mm diameter. The crushed coal is then transported
to the store yard. Coal is transported to bowl mills by coal
5. Tipplers: Coal from the coal wagons is unloaded in the coal
handling plant. This unloading is done by the “Tipplers”. This
coal is transported up to the raw coal bunkers with the help
of conveyor belts.
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6. Pull chord switch: A series of such switches are arranged in series at a 1m
distance on the side of conveyor belt. The power supply to rotor of the conveyor belt
is established only if all switches in series are connected.
7. Vibrating feeder: The coal stored in a huge hub is collected on the belt through
vibrations created by the vibrating feeder.
8. Flap gates: These are used to channelize the route of coal through another belt in
case the former is broken or unhealthy. The flap gates open let the coal pass and if
closed stop its movement.
9. Magnetic separator: These are used to separate the ferrous impurities from the
10. Metal detector: This are detect the presence of any ferrous and non-ferrous
metal in the coal and sends a signal to a relay which closes to seize the movement of
belt until the metal is removed. It basically consists of a transmitter and a receiver.
The transmitter consists of a high frequency oscillator, which produces oscillations
of 1500 Hz at 15V. The receiver receives this frequency signal. If there is any
presence of metal in the coal then this frequency is disturbed and a tripping signal is
send to relay to stop the conveyor belt.
11. Belt weightier: It is used to keep an account of the tension on the belt carrying
coal and is moves accordingly to release tension on the belt.
12. Reclaim hopper: Reclaimation is a process of taking coal from the dead storage
for preparation or further feeding to reclaim hoppers. This is accomplished by belt
A pulveriser or grinder is a mechanical device for the grinding of many different types of
materials. For example, they are used to pulverize coal for combustion in the steam-
generating furnaces of thermal power plants.
The MILL consists of FEEDER, MILL for
pulverization of coal (BALL & TUBE TYPE MILL) and
CLASSIFIER. The stacked coal in the bunker is
dropped to the feeder automatically; the feeder is
housed with a conveyor belt system with motors
and pulleys. The feeder actually governs the
amount of coal to be transferred to the ball & tube
mill for pulverizing. The flow of coal is maintained
by the speed/rpm of the conveyor belt of the
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feeder. The coal from the bunker drops to the feeder s conveyor belt at a constant
rate determined by the bunker level, in this condition higher the rpm of the conveyor
belt greater will be the rate of volume of the coal transferred to the mill. In the same
way if the rpm is lower then lesser will be the volume of coal transferred to the mill.
Thus the coal from the feeder is transported to the mill where the pulverization takes
place. Here the ball & tube method is utilized for pulverizing of coal to 20micron
diameter size. This type of mill consists of
arrangement of iron alloy balls inside a MTPS Unit 3: Coal Mill
tube like structure that is rotated by its Specification
auxiliaries. The coal is fed to the tube at
its two ends where it is crushed to the Ball Tube Mill: (3Nos.-CM # 2AB, 3AB, 3EF)
above mentioned size, these pulverized Capacity: 77 Tonne/Hour
coal is taken back from the mill to the Power Rating: 2.25MW
classifier. In case of ball and tube type
Primary Air Fan: (3Nos.-PA FAN # 2AB,
mills, there are 3 mill units; out of which 2 3AB, 3EF)
must be running and 1 for standby while Type: NDV20H
the unit is running on load. The classifier Capacity: 65.9 m /sec
Total Head Developed: 806 mmWC
consists of strainers; the primary air brings Power Rating: 850KW
the coal from the mill to the classifier
where the pulverized coal is passed
through strainers. The strainers allow 80%
(approx.) of the coal to pass from 200 mesh and rest is fed back to the mill for further
pulverization. Here the primary air is utilized to maintain the temperature of the coal up
to 80 C-90 C for better combustion. The classifier has 4 outlets and each ball and
tube type mills have 6 such classifier (2for each mill unit). The coal from each outlets of
a classifier goes to each of the 4 corners of the furnace; therefore coal from each
outlets of all the 6 classifier goes to all the 24 elevations (A-B-C-D-E-F of each corner) of
furnace in all. All transport of coal from mill to the furnace is done by the primary air
produced by PA fans.
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Furnace and Boiler
What is Boiler?
A boiler is a closed vessel in which water or other fluid is heated. The heated or
vaporized fluid exits the boiler for use in various processes or heating
applications, including boiler-based power generation, cooking, and sanitation.
Here in MTPS, the boiler is a rectangular furnace about 50 feet (15 m) on a side and 130
feet (40 m) tall. Its walls are made of a web of high pressure steel tubes about 2.3
inches (58 mm) in diameter.
Types of Boiler:
Fire Tube Boiler:
In fire tube boiler, hot gases pass through the tubes
and boiler feed water in the shell side is converted
into steam. Fire tube boilers are generally used for
relatively small steam capacities and low to medium
steam pressures. As a guideline, fire tube boilers are
competitive for steam rates up to 12,000 kg/hour
and pressures up to 18 kg/cm2. Fire tube boilers are
Fire tube Boiler
available for operation with oil, gas or solid fuels. For
economic reasons, most fire tube boilers are nowadays of “packaged” construction (i.e.
manufacturers shop erected) for all fuels.
Water Tube Boiler:
In water tube boiler, boiler feed water flows through the
tubes and enters the boiler drum. The circulated water is
heated by the combustion gases and converted into steam at
the vapour space in the drum. These boilers are selected
when the steam demand as well as steam pressure
requirements are high as in the case of process cum power
boiler / power boilers.
Most modern water boiler tube designs are within the
capacity range 4,500 – 120,000 kg/hour of steam, at very high
pressures. Many water tube boilers nowadays are of
“packaged” construction if oil and /or gas are to be used as
fuel. Solid fuel fired water tube designs are available but
packaged designs are less common. Water tube Boiler
The features of water tube boilers are:
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Forced, induced and balanced draft provisions help to improve combustion
Less tolerance for water quality calls for water treatment plant.
Higher thermal efficiency shifts are possible
Note: In MTPS Water tube Boilers are incorporated.
A furnace is a device used for heating. The name derives
from Latin fornax, oven.
The boiler furnace auxiliary equipment includes coal feed
nozzles and igniter guns, soot blowers, water lancing and
observation ports (in the 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 coal is ground (pulverized) to a fine powder, so that less than 2% is +300 micro
meter (μm) and 70-75% is below 75 microns, for a bituminous coal. It should be noted
that too fine a powder is wasteful of grinding mill power. On the other hand, too coarse
a powder does not burn completely in the combustion chamber and results in higher
The pulverized coal is blown with part of the combustion air into the boiler plant
through a series of burner nozzles. Secondary and tertiary air may also be added.
Combustion takes place at temperatures from 1300-1700°C, depending largely on coal
grade. Particle residence time in the boiler is typically 2 to 5 seconds, and the particles
must be small enough for complete combustion to have taken place during this time.
This system has many advantages such as ability to fire varying quality of coal, quick
responses to changes in load, use of high pre-heat air temperatures etc.
One of the most popular systems for firing pulverized coal is the tangential firing using
four burners corner to corner to create a fireball at the center of the furnace.
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 to the downside the steam drum. The steam
separators and dryers remove water droplets from the steam and the cycle through the
water walls is repeated. This process is known as natural circulation.
Pulverized coal is air-blown into the furnace from fuel nozzles at the four corners and it
rapidly burns, forming a large fireball at the center. The thermal radiation of the fireball
heats the water that circulates through the boiler tubes near the boiler perimeter. The
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water circulation rate in the boiler is three to four times the throughput and is typically
driven by pumps. As the water in the boiler circulates it absorbs heat and changes into
steam at 700 °F (370 °C) and 3,200 psi (22,000 kPa). It is separated from the water
inside a drum at the top of the furnace. The saturated steam is introduced
into superheat pendant tubes that hang in the hottest part of the combustion gases as
they exit the furnace. Here the steam is superheated to 1,000 °F (540 °C) to prepare it
for the turbine.
Boiler is the main section where the steam is produced by coal combustion. Boiler
consists of boiler drum, water walls, wind box, heaters. The boiler
has 13 elevations named as AA-A-AB-B-BC-C-CD-D-DE-E-EF-F-FF. Coal
is inserted into the boiler from A-B-C-D-E-F elevations. BC is used for
insertion of Heavy Oil and Light Oil after atomization with steam and
air respectively. DF is used for insertion of oil i.e. only heavy oil. Both
the elevations have Oil Gun mounted for insertion of oil in proper
ratio into the boiler. Liquid fuel (viz. Heavy Oil and Light Oil) is used
for initial light up process. Other elevations are used to insert
secondary air from wind box. The furnace is divided into two
sections named as first pass and second pass separated by Goose
Neck. The combustion takes place in the first pass and the heating of
steam through super heaters takes place in
the second pass.
Boiler Drum: -
Boiler Drum is the part of boiler where the
dematerialized water is stored and is
inserted into the boiler. It is also houses the
steam that is formed in the boiler. Water
stored in the drum comes down to the top
of the boiler and forms a Water Ring which
is then inserted into the boiler through the
water walls. Water Walls are basically tubes
along the walls of the furnace, it is here
where the water is converted into steam at
1300C and then the produced steam is taken
back to the boiler drum. The drum has a propeller that rotates at high speed and makes
the steam and water separated due to centrifugal force. The pressure of boiler drum is
150kg/sq.cm and must be always maintained. Water in the drum comes from feed
control station via economizer.
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Mechanical Construction of Turbine Assembly
The 200/210 MW turbine installed in MTPS is of condensing-tandem-compound, three
cylinder, horizontal, disc and diaphragm, reheat type with nozzle governing and
regenerative system of feedwater heating and
is directly coupled with the A.C generator.
TURBINE CASING: - The turbine assembly
comprises of three types of casing.
1) High Pressure Casing
2) Intermediate Pressure Casing
3) Low Pressure Casing
OTHER TURBINE COMPONENTS: -
ROTOR: - The rotor is basically the main
rotating part of the turbine which is also
called the shaft and is attached with the
rotor of the A.C generator via coupling.
Rotor is basically divided into 3 categories
and they are as follows: - Cross section of a turbine
a) HIGH PRESSURE ROTOR: - This is basically made of single Cr-Mo-V steel forged
with internal disc attached to T-shoot fastening designed especially for
stabilizing the HPT and preventing the axial shift.
b) INTERMEDIATE PRESSURE ROTOR: - This is made from high creep resisting Cr-
Mo-V steel forging and the shrunk fit disc are machined from nickel-steel
forging. This basically adjusts the frequency of the blades.
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c) LOW PRESSURE ROTOR: - This is made from the above mention alloy used in
IP Rotors; blades are secured to the respective disc by riveted fork root
fastening. Wires are provided in all stages of this to adjust the frequency of the
BLADES: - Blades are single most costly element fitted in the turbine. Blades fitted in
the stationary part are called guide blades and those fitted in the rotor are called
moving or working blades. Blades are of basically three types, they are as follows: -
a) Cylindrical ( constant profile) blade
b) Tapered cylindrical blade
c) Twisted and varying profile blade.
SEALING GLANDS: - To eliminate the possibility of steam leakage to the atmosphere
from the inlet and the exhaust end of the cylinder, labyrinth glands of the radial
clearance type are provided which provide a trouble free frictionless sealing
EMERGENCY STOP VALVES AND CONTROL VALVES: - Turbine is equipped with
emergency stop valves to cut off steam supply and with control valve regulate steam
supply. Emergency stop valves are provided in main stream line and control valves
are provided in the hot reheat line.
COUPLING: - Since the rotor is made in small parts due to forging limitations and
other technological and economic reasons, the couplings are required between any
two rotors. The coupling permits angular misalignment, transmits axial thrust and
ensures axial location.
BEARING: - Journal bearing are manufactured in two halves and usually consist of
bearing body faced with anti-friction tin based habiting to decrease coefficient of
friction. Bearings are usually force lubricated and have provision for admission of
Thrust bearing is normally Mitchell type and is usually combined with a journal
bearing, housed in spherically machined steel shell. The bearing between HP
and IP rotor is of this type. The rest is of journal type.
BARRING GEAR: - The barring gear is mounted on the L.P rear bearing cover to mesh
with spur gear L.P rotor rear coupling. The primary function of the barring gear is to
rotate the rotor of the turbo generator slowly and continuously during the start-up
and shut sown process when the temperature of the rotor changes.
TURBINE LUBRICATION OIL SYSTEM: - The LUB-OIL system of turbine comprises of
a) MAIN OIL PUMP: - It is mounted on the front bearing pedestal and coupled
through gear coupling to the rotor. When the turbine is running at its normal
Page | 21
speed of 3000rpmthen the oil to the governing system (at 20 kg/sq.cm) and to
the lubrication system (at 1 kg/sq.cm) is supplied by this pump.
b) STARTING OIL PUMP: - It is a multi-staged centrifugal oil pump driven by A.C
powered electric motor. It provides the oil requirement for starting up and
stopping of the turbine. It provides oil to the governing system and to the
lubrication system until the turbine is running at speed lower than 2800rpm.
c) STANDBY OIL PUMP: - This is a centrifugal pump driven by A.C motor. It runs for
initial10 minutes at the starting to remove air from the governing system and
fill up oil to it.
d) EMERGENCY OIL PUMP: - This is a centrifugal pump driven by D.C motor. This
pump is foreseen as a backup oil pump to A.C oil pumps. This pump
automatically cuts in when the A.C power fails in the power station.
e) JACKING OIL PUMP: - This pump enables the complete rotor assembly to be raised
upor to be floated in the bearing assembly during the start-up and shut down
process of the process. Thus this prevents the damage to the bearings when the
shaft is too low for hydrodynamic lubrication to take place. JOP sucks and
delivers oil to the journal bearings at 120kg/sq.cm for lifting of the rotor.
f) OIL COOLERS: - The oil of governing and lubrication system is cooled in the oil
coolers by the circulating water. There are five such coolers, 4 are for
continuous operation and 1for standby.
Specification of Turbine
U #1 to U #4
Mega Watt : 210
R.P.M. : 3000
Steam Pressure : 150 Kg/cm2 (Abs)
Steam Temperature : 535 C
Reheat Steam : 535 C
Make : BHEL
U #5 & U #6
Mega Watt : 250
R.P.M. : 3000
Steam Pressure : 150 Kg/cm2 (Abs)
Steam Temperature : 537 C
Reheat Steam : 537 C
Make : BHEL
Page | 22
Introduction of Water Treatment in Thermal
In Thermal power plants, plenty of water is needed for generation of electricity.
Now question is for what purpose we need water here?
There are two purposes:
1. As a Working Fluid
2. As Cooling water
Water which is used as a working fluid needs some treatment.
Reasons to choose Water as a Working Fluid:
• It is only common substance available & exists in 3 states (Ice, water, steam)at
• Having high specific heat mean heat carrying capacity is high.
• Having low specific volume than air.
• Low Cost
• High Availability
But water is universal solvent; it dissolves many gases, salts, metals etc. so no source of
water is pure.
Water contamination depends upon source of water.
There are 3 sources of water mainly;
1. Surface Water
2. Ground Water
3. Recycled Water
Impurities in Water
Impurities present in water are grouped into 4 categories:
1) Suspended Matter –
• Mean any matter floating or suspended nature in water
2) Dissolved Salts –
• Ca, Mg, K, Chlorates, Sulphates, Silicates etc.
3) Dissolved Gases –
• Oxygen, Carbon di oxide, Ammonia etc.
Page | 23
A 210 MW unit typically requires 30,000 to 33,000 m3/h of water. A large part of this
water is used for condenser cooling and a small quantity is used for boiler feed makeup
and other uses.
Total Water Management in Mejia Thermal Power station consists of:
1. Pre Treatment of Water
2. Treatment of water for boiler feed
3. Treatment of water for condenser cooling
4. Treatment of wastewater for disposal or recovery of water for reuse.
1. Pre Treatment of Water:
Aerator: Aerators are various devices used for aeration, or mixing air with another
substance, like water. It also converts turbulent water flow into laminar water flow.
Coagulation & Flocculation Basin: One of the first steps in a conventional water
purification process is the addition of chemicals to assist in the removal of particles
suspended in water. Particles can be inorganic such as clay and silt or organic such
as algae, bacteria, viruses, protozoa and natural organic matter. Inorganic and
organic particles contribute to the turbidity and colour of water.
The addition of inorganic coagulants such as aluminium sulphate (or alum) or iron
(III) salts such as iron(III) chloride cause several simultaneous chemical and physical
interactions on and among the particles. Within seconds, negative charges on the
particles are neutralized by inorganic coagulants. Also within seconds, metal
hydroxide precipitates of the aluminium and iron (III) ions begin to form. These
precipitates combine into larger particles under natural processes such as Brownian
motion and through induced mixing which is sometimes referred to as flocculation.
The term most often used for the amorphous metal hydroxides is “floc.” Large,
amorphous aluminium and iron (III) hydroxides adsorb and enmesh particles in
suspension and facilitate the removal of particles by subsequent processes of
sedimentation and filtration.
Clarifiers: Waters exiting the flocculation basin may enter the sedimentation basin,
also called a clarifier or settling basin. It is a large tank with low water velocities,
allowing floc to settle to the bottom. The sedimentation basin is best located close
to the flocculation basin so the transit between the two processes does not permit
settlement or floc break up. Sedimentation basins may be rectangular, where water
flows from end to end or circular where flow is from the centre outward.
Sedimentation basin outflow is typically over a weir so only a thin top layer of
water—that furthest from the sludge—exits.
Gravitation Filter: The most common type of filter is a rapid sand filter(gravity
filter). Water moves vertically through sand which often has a layer of activated
carbon or anthracite coal above the sand. The top layer removes organic
compounds, which contribute to taste and odour. The space between sand
particles is larger than the smallest suspended particles, so simple filtration is not
Page | 24
enough. Most particles pass through surface layers but are trapped in pore spaces
or adhere to sand particles.
To clean the filter, water is passed quickly upward through the filter, opposite the
normal direction (called back flushing or backwashing) to remove embedded
2. Treatment of water for boiler feed:
Boiler feed water treatment for high pressure boilers are almost standard. Raw
water is clarified and filtered for removal of un-dissolved impurities and demineralised
for removal of dissolved salts. Dissolved oxygen is removed in a thermal de-aerator.
Residual dissolved oxygen is removed by hydrazine.
DM Plant: 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
surface condenser (i.e., the vacuum side). This arrangement not only sprays the
water but also DM water gets de-aerated, with the dissolved gases being removed
by a de-aerator through an ejector attached to the condenser.
Page | 25
Presence of silica in boiler feed water is harmful as silica tends to volatilize along
with steam and get deposited as glassy and hard deposits on the turbine blades. It
has been established that concentrations of silica in excess of 0.03 mg/l invariably
causes problems in turbine operation. Suitable lower silica level should be
maintained boiler water to maintain silica less than 0.02 mg/l in steam leaving the
Silica in water is present mostly as reactive or dissolved silica. In surface waters, a
small quantity of non-reactive silica (in colloidal dimensions) may also be present
during parts of the year especially during the monsoon. A DM plant removes reactive
silica almost completely, to less than 0.005 mg/l. However, non-reactive silica is not
removed and finds its way into the boiler drum where it gets converted into reactive
silica under the operating conditions of high pressure and temperature. The station
chemists usually overcome this problem by having increased blow-downs during
3. Treatment off wastewater and its disposal or recovery and
reuse off water:
Water is a scarce resource and Thermal Power stations are today being compelled to
minimise consumption of water to the extent possible. It is possible to recover and
reuse water from most of the waste streams generated in a thermal power station. The
main waste streams are:
· Gravity filter backwash water
· Wastewater generated from the DM plant
· Ash pond overflows water
· Boiler blow down and turbine drains.
· Recovery of water from treated sewage
Page | 26
Steam/Water Circuit of Power Plant (MTPS):
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; this is known as a Rankin cycle.
This section deals with supplying of steam generated from the boiler to the turbines and
to handle the outgoing steam from the turbine by cooling it to form water in the
condenser so that it can be reused in the boiler plus making good any losses due to
WATER PATH: -
Water comes from the water reservoir to the demineralization plant (DM Plant) for
removal of all minerals present in normal water for making it non-conductive and
increasing the efficiency of the overall system. After DM plant water goes to the boiler
drum via condenser and the feed control station.
STEAM GENERATION PROCESS: -
Water from the boiler drum comes down to the top of the boiler and forms a ring head
and finally goes to the boiler through the water walls. The boiler/furnace is lit up by four
corner firing technique; this produces a ball of fire and reaches a temperature of 1200
C. This as a result converts the water in the water walls into steam at high pressure. This
steam is sent back to the boiler drum where it is separated from the water with the help
of high speed propeller. The steam is taken to the super heaters via water pipes where
it is converted to superheated steam for total moisture removal. After super-heaters
the steam divides into two ducts called Main Steam Left (L) and Main Steam Right(R)
and finally reaches the turbines.
Page | 27
TURBINES are form of engine and hence it requires suitable fluid for working, a
source of high grade energy and a sink of low grade energy, the fluid when flows
through the turbine the energy content of it is continuously extracted and converted
into its useful mechanical work. The turbines used in thermal power plants are of
STEAM GAS type which uses the heat energy of the steam for its working. Turbine Cycle
is the most vital part of the overall process; this is where the mechanical energy of the
steam is converted to electrical energy via turbine assembly. The turbine assembly
comprises of three turbines named as High Pressure Turbine (HPT), Intermediate
Pressure Turbine (IPT) and the Low Pressure turbine (LPT).
The steam that is generated in the SG section comes to the HPT through main
steam lines via control valves. The steam when strikes the HPT have 540 C at
150kg/sq.cm pressure. This high pressure superheated steam rotates the turbine, the
speed of the turbines is controlled by the controlling the amount of steam through
control valves. Generally only 3%-4% steam is enough to rotate the turbine at3000rpm
at no load but at full load condition 100% steam is required to rotate the turbine at
3000rpm, because to produce power at 50Hz frequency the rpm required is 3000. The
HPT is a single head chamber type of turbine.
Page | 28
One part of the exhaust steam from HPT is taken to re-heaters through cold
reheat line (CRH line) which are again of mechanical type; for restoring the superheated
properties of the steam for further use. The reheated steam is brought back to the IPT
via HRH (hot reheat steam) line. And the other part of the exhaust steam is taken to the
HP heaters (i.e. to HPH-6)
The reheated steam is mechanical energy is utilized by the IPT which is a double
head chamber type turbine, where steam enters from the top-mid section of the
turbine and leaves the turbine from the front and back section. The exhaust of IPT is
divided into 3 parts, one goes for the HP heaters (HPH-5), another goes to the de-
aerator and the last part goes to the LPT.
The exhaust steam of the LPT Is divided into 4 parts, 3 of them goes for the Low
Pressure Heaters (LPH-1, LPH-2, LPH-3) for heating the condensate, and the last part
goes to the condenser for the steam condensation process and regeneration of water.
The condensation is done to minimize the production of DM water to make the process
cost effective. The steam is converted to water and extracted by CEP from the
condenser and transported to Gland Sealing Coolers (GSC) via Ejectors (EJE). The GSC
cools the sealing of the ducts; the condensate is taken to the LPH from the GSC for
heating at lower pressure to increase the enthalpy of the water for better efficiency.
Water after LPH reaches the de-aerator where the oxygen is removed from it and is
taken to the BFPs, the BFPs increases the pressure of the water up to 160kg/sq.cm and
sends it the high pressure heaters (HPH-5 & HPH-6). HPH increases the temperature of
the water once more and transfers it to the Economizer, in economizer the temperature
of water is again increased by the flue gas and is finally is transported to the steam
generation process via the Feed Control Station
SOME IMPORTANT COMPONENT OF STEAM/WATER CYCLE:
A fossil fuel steam generator includes an economizer, a steam drum, and the furnace
with its steam generating tubes and super-heater coils. Necessary safety valves are
located at suitable points to avoid excessive boiler pressure.
De-aerator: Typically, the condensate plus the makeup water then flows through a
de-aerator that removes dissolved air from the water, further purifying and reducing
its corrosiveness. The water may be dosed following this point with hydrazine, a
chemical that removes the remaining oxygen in the water to below 5 parts per
Page | 29
Courtesy SIEMENS OS220EA, C&I, MTPS, DVC
Condenser: The condenser condenses the steam from the exhaust of the turbine
into liquid to allow it to be pumped. If the condenser can be made cooler, the
pressure of the exhaust steam is reduced and efficiency of the cycle increases. The
surface condenser is a shell and tube heat exchanger in which cooling water is
circulated through the tubes.
The exhaust steam from the low pressure turbine enters the shell where it is cooled
and converted to condensate (water) by flowing over the tubes as shown in the
For best efficiency, the temperature in the condenser must be kept as low as
practical in order to achieve the lowest possible pressure in the condensing steam.
Page | 30
Typically the cooling water
causes the steam to condense at
a temperature of about 35 °C (95
°F) and that creates an absolute
pressure in the condenser of
about 2–7 kPa (0.59–2.1 in Hg),
i.e. a vacuum of about −95 kPa
(−28.1 in Hg) relative to
atmospheric pressure. The large
decrease in volume that occurs
when water vapour condenses to
liquid creates the low vacuum that helps pull steam through and increase the
efficiency of the turbines.
The condenser generally uses either circulating cooling water from a cooling tower
to reject waste heat to the atmosphere, or once-through water from a river, lake or
ocean. The cooling water used to condense the steam in the condenser returns to its
source without having been changed other than having been warmed.
The lower portion of condenser where the condensed water stored known as
Economizers: These are heat exchange devices that heat fluids, usually water, up to
but not normally beyond the boiling point of that fluid. Economizers are so named
because they can make use of the enthalpy in fluid streams that are hot, but not hot
enough to be used in a boiler, thereby recovering more useful enthalpy and
improving the boiler's efficiency. They are a device fitted to a boiler which saves
energy by using the exhaust gases from the boiler to preheat the feed.
GSC: Gland steam condenser is meant for condensing the steam which was used for
sealing the LABYRINTH GLAND and reusing it in cycle.
Low Pressure Heater: A Heater is located between the condensate pomp and either
of the boiler feed pump. It normally extracts steam from low pressure turbine.
High Pressure Heater: A heater located downstream of boiler feed pump. Typically,
the tube side design pressure is at least 100Kg/cm2, and the steam source is the high
[The heating process by means of extraction of steam is referred to as being
Page | 31
Cooling Towers :
The condensate (water) formed in the condenser after condensation is initially at high
temperature. This hot water is passed to cooling towers. It is a tower- or building-like
device in which atmospheric air (the heat receiver) circulates in direct or indirect
contact with warmer water (the heat source) and the water is thereby cooled (see
illustration). A cooling tower may serve as the heat sink in a conventional
thermodynamic process, such as refrigeration or steam power generation, and when it
is convenient or desirable to make final heat rejection to atmospheric air. Water, acting
as the heat-transfer fluid, gives up heat to atmospheric air, and thus cooled, is
recirculate through the system, affording economical operation of the process.
With respect to drawing air through the tower, there are three types of cooling towers:
Natural draft — Utilizes buoyancy via a tall chimney. Warm, moist air naturally rises due
to the density differential compared to
the dry, cooler outside air. Warm moist
air is less dense than drier air at the
same pressure. This moist air buoyancy
produces an upwards current of air
through the tower.
Induced draft — A mechanical draft
tower with a fan at the discharge (at
the top) which pulls air up through the
tower. The fan induces hot moist air
out the discharge. This produces low
entering and high exiting air velocities, reducing the possibility of recirculation in which
discharged air flows back into the air intake. This fan/fin arrangement is also known as
Forced draft — A mechanical draft tower with a blower type fan at the intake. The fan
forces air into the tower, creating high entering and low exiting air velocities. The low
exiting velocity is much more susceptible to recirculation. With the fan on the air intake,
the fan is more susceptible to complications due to freezing conditions. Another
disadvantage is that a forced draft design typically requires more motor horsepower
than an equivalent induced draft design. The benefit of the forced draft design is its
ability to work with high static pressure. Such setups can be installed in more-confined
spaces and even in some indoor situations. This fan/fill geometry is also known as blow-
Page | 32
Air and Flue Gas Path
In fossil-fuelled power plants, water is taken to the boiler or steam generator where
coal is burnt. The boiler transfers heat energy to the water in form of latent heat of
vaporization or enthalpy by the chemical reaction of burning coal. External fans, such as
PA fans and FD fans, are provided to give sufficient air for combustion. The air and flue
gas path equipment include: forced draft (FD) fan, air preheater (APH), boiler furnace,
induced draft (ID) fan, fly ash collectors (ESP or electrostatic precipitator), flue gas stack,
etc. External fans re provided to give sufficient air for combustion.
INDUCED DRAFT (ID) FAN: -
FD & ID Fan
This fan is used to create negative pressure in the 3 Phase Asynchronous Motor
furnace, i.e. furnace pressure is lower than the Make : BHEL
Connection : Y
atmospheric pressure, as a result of which the fire Type : S. Cage
ball inside the furnace cannot come out of the Insul. Class : F
Frequency : 50Hz
furnace. ID fan also drives the flue gas throughout
its path and above processes and finally ejects it
out of the chimney. It sucks air from inside the furnace and ejects it to the atmosphere.
Mechanically ID fan consists of one 3-phase asynchronous type motor, a hydro coupling
unit for coupling rotor shaft of the motor and the rotor shaft of the fan, scoop unit, a
pair of journal bearings and lubrication oil system. It is the only fan which have hydro
coupling because this gives more accurate control to its speed for maintaining the
negative pressure more precisely since controlling of negative pressure is the most vital
factor in any thermal power unit. The lube-oil system has two motors out of which one
remains standby; for maintaining perfect pressure of lubrication throughout the ID fan
assembly. The second motor automatically starts up when the oil pressure drops below
a certain level; this motor increases the oil pressure in the system. Water cools down
the oil flowing in the tubes inside the coolers. There are three ID Fans in each unit of
thermal power plant, named as ID-A, ID-B, ID-C.
FORCE DRAFT (FD) FAN : Forced Draft (FD) fans purpose is to provide a positive
pressure to a system. This basic concept is used in a wide variety of industries but the
term FD Fans is most often found in the boiler industry. Fans for boilers force ambient
air into the boiler, typically through a preheater to
increase overall boiler efficiency. Inlet or outlet dampers
are used to control and maintain the system pressure.
The outlet of the FD fan divides into 5 ways; 2 goes to
the air-preheater, and remaining 3 goes to the PA fan
supplying cold air. Mechanically FD fans consist of one 3-
Page | 33
phase asynchronous type motor, a pair of journal bearings and lube-oil system. Unlike
ID fan these fans have direct coupling of rotor shaft of the motor and rotor shaft of the
fan. The lube-oil system is designed same as ID fans. There are 2 FD fans in a single unit.
THE SYNCHRONIZATION OF ID-FAN AND FD-FAN IS VERY IMPORTANT AS THESE TWO FANS COMBINELY
BALANCE THE PLANT. WHEN WORKING TOGETHER IT IS CALLED BALACED DRAFT.
PRIMARY AIR FAN/PA FAN:-
Primary air fan is used for mixing of cold air of FD fan outlet and hot air of air-preheater
outlet. The main function of this is to transport the pulverized coal from the mill to the
furnace via classifier. Mixing of hot and
cold air is necessary because it is needed
to maintain the temperature of the
pulverized coal from 80⁰C-90⁰C for better
transport of coal and better combustion
in the furnace. Mechanically the
construction of PA fan is same as FD fans
along with the lube-oil system. There are
3 PA fans in a single mill of ball and tube
SCANNER AIR FAN / SC FAN/SA FAN:-
The scanner air fans are relatively smaller in size and consume low power as compared
to the above mentioned fans. These are simple motor operated fans that suck air from
atmosphere and utilize it to cool the flame scanners (explained in C&I section later)
inside the furnace.
The flue gas produced as a result of combustion of fossil fuel in the furnace is taken to
the air-preheater. The air-preheater is used to heat up the atmospheric air to make hot
air used for combustion and transport of coal dust from mill to furnace; which is called
secondary air. This heater has a unique process of heating, it has a shaft attached to a
rotating wheel type structure (like turbine but arrangement of blades are different).
Atmospheric air sucked by FD fans passes through one side of the rotating shaft and the
hot flue gas passes through another side. This way heat of the flue gas gets transferred
to the atmospheric air and it gets heated. There are two air-preheaters named as AH-A
and AH-B. These heaters can be found beside the boiler in the burner floor.
A chimney is a structure which provides ventilation for hot flue gases or smoke from a
boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically
vertical, or as near as possible to vertical, to ensure that the gases flow smoothly,
drawing air into the combustion in what is known as the stack, or chimney, effect.
Page | 34
An electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate collection
device that removes particles from a flowing gas (such as air) using the force of an
induced electrostatic charge. Electrostatic precipitators are highly efficient filtration
devices that minimally impede the flow of gases through the device, and can easily
remove fine particulate matter such as dust and smoke from the air stream. In contrast
to wet scrubbers which apply energy directly to the flowing fluid medium, an ESP
applies energy only to the particulate matter being collected and therefore is very
efficient in its consumption of energy (in the form of electricity).
PRINCIPLE OF ESP:
In the electrostatic precipitator the
particles are removed from the gas
stream by utilizing electrical force .A
charged particle in the electrical field
experiences a force proportional to
the size of the charge and to the
The precipitation process therefore
A method of charging the
A means of establishing an
electrical field and
A method of removing the collected particles.
An industrial ESP includes a large number of discharge electrodes. Pirated wires and
rows of collecting electrodes plates forming passage through which the gas flows with
High voltage is applied to the discharge electrodes resulting in the high electric field
near the wire and an associated corona producing gas ions .The ions collide with and
held by, the dust particles and this in turn become electrically charged the particles
moved towards the grounded collecting electrode plates from which the accumulated
dust is dislodged by rapping the dust falls to the bottom of the precipitator casing from
which it is removed by different methods.
PARTS OF THE PRECIPITATORS:
The various parts of the precipitators are divided to two groups. Mechanical system
comprising of casing, hoppers, gas distribution system, collecting and emitting system,
rapping mechanisms, stair ways and galleries.
Page | 35
Electrical system comprising of transformer-rectifier units, electronic controllers
auxiliary control panels, safety interlocks and field devices.
1. MECHANICAL SYSTEM:
A. Precipitator casing:
casing is an all welded
of prefabricated wall and
the roof panels. The
casing is provided with
inspection doors for
entry into the chamber.
The doors are of heavy
machined surfaces to
ensure a gas tight seal.
The roof carries the
transformers etc. The casing rests on supports, which allow for free thermal expansion
of the casing during operation. Galleries and stairways are provided on the sides of the
casing for easy access to rapping motors, inspection doors, transformers.
The hoppers are adequately sized to hold the ash, Baffle plates are provided in
each hopper to avoid gas sneak age. An inspection door is provided on each hopper.
Thermostatically controlled heating elements are arranged at the bottom portion to the
hopper to ensure free flow of ash. The precipitator casing is an all welded construction,
consisting of prefabricated
C. Gas distribution systems:
The performance of the precipitator depends on even distribution of gas over the
entire cross section of the field. Guide vanes, splitters and screens and screens are
provided in the inlet funnel to direct the flue gas evenly over the entire cross section of
D. Collecting Electrode System:
The collecting plates are made of 1.5mm cold rolled milled steel plate and shaped
in one piece by roll forming .The collecting electrode has unique profile designed to give
rigidity and to contain the dust in a quiescent zone free from re-entrainment .The
400mm collecting plates are provided with hooks to their top edge for suspension .The
hooks engage the slots of the supporting angles 750mm collecting plates in a row are
held in position by a shock bar at the bottom. The shock bars are spaced by guides.
Page | 36
E. Emitting Electrode System:
The most essential part of the precipitator is emitting electrode system.4
insulators support this. The frames for holding the emitting electrodes are located
centrally between collecting electrode curtains. The entire discharge frames are welded
to form rigid bars
F) Rapping Systems:
Rapping systems are provided for collecting and emitting electrodes. Geared
motors drive these rappers. The rapping system employs tumbling hammers, which are
mounted on the horizontal shaft. As the shaft rotates slowly the hammers tumble on
the shaft will clean the entire field. The rapper programmer decides the rapping
frequency. The tumbling hammers disposition and the periodicity of rapping are
selected in such a way that less than 2% of the collecting area is rapped at any instant.
This avoids re-entrainment of dust and puffing at the stack. The rapping shaft from the
gear motor drive by a shaft insulator. The space around the shaft insulator is
continuously heated to avoid condensation.
G) Insulator Housing:
The support insulators, supporting the emitting electrodes housed in insulator
housings. The HVDC connection is taken through a bushing insulator mounted on the
insulator housing wall.
In order to avoid the condensation on the support insulators, each insulator is provided
with one electrical heating element. Heating elements of one pass are controlled by
2) ELECTRICAL SYSTEM:
A) High Voltage Transformer Rectifier (H.V.R) with electronic controller (E.C)
The transformer rectifier
supplies the power for
particulate charging and
collection. The basic
function of the E.C is to
feed precipitator with
maximum power input
under constant current
regulation. So, thereby
any flash over between
collecting and emitting
electrodes, the E.C will
sense the flash over and
quickly react by bringing
the input voltage ton
zero and blocking it for a
Page | 37
specific period. After the ionized gases are cleared and the dielectric strength restored,
the control will quickly bring back the power to the present value and raise it to the
original non-sparking level. Thus the E.C ensures adequate power input to the
precipitator while reckoning the electrical disturbances within the precipitator.
Regulated ac power from E.C is fed to the primary of the transformer, which is stepped
up and rectified to give a full wave power output. The transformer rectifier is mounted
on the roof of the precipitator while the E.C is located in an air-conditioned control
B) Auxiliary control panel (A.C.P)
The A.C.P controls the power supply to the EP auxiliary i.e. rapping motors and
heating element dampers etc. The complete A.C.P. is of modular type with individual
modules for each feeder. Each module houses the power and control circuits with
meters, push buttons, switches and indicating lamps.
Following are the modules for the outgoing feeders
Hopper heaters for each field
Support insulator heaters
Shaft insulator heaters
Collecting electrode rapping motor for each field
The program control circuit for the sequence and timing of operation for rapping
motors is included in the A.C.P.
For continuous operation of the rapping motors, the programmer can be bypassed
through a switch. Thermal overload relay is provided for overload protection to the
rapping motors. Local push buttons are available for tripping the motors to meet the
exigencies and for maintenance purposes.
Ammeters with selector switches to indicate line currents of motors and heating
element feeders are provided. Indicating lamps are provided “main supply on”,
“overload trip”, “local push button activated”, “space meter on”, and “control supply
Potential free contacts are provided for remote indication for rapping motor trip due to
C) Safety Interlock:
A safety interlock system is incorporated to prevent accidental contact with live
parts of the precipitator and enable energisation only when the ESP is boxed up. The
interlock system covers all the inspection doors of casing, insulator housing and
Warning: familiarity with this system may felon the operating personnel bypass the
interlock. As this would defend the very purpose of the interlocking system, such a
temptation should be resisted and the sequence of operation at every stage should be
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D) Disconnecting switch:
Each field is provided with one disconnecting switch for isolation of emitting system
from the associated transformer .In the on position the emitting system is connected to
the transformer and in the OFF position it is grounded.
ESP in MTPS:
ESPs continue to be excellent devices for control of many industrial particulate
emissions, including smoke from electricity-generating utilities (coal and oil fired), salt
cake collection from black liquor boilers in pulp mills, and catalyst collection from
fluidized bed catalytic cracker units in oil refineries to name a few. These devices treat
gas volumes from several hundred thousand ACFM to 2.5 million ACFM (1,180 m³/s) in
the largest coal-fired boiler applications. For a coal-fired boiler the collection is usually
performed downstream of the air preheater at about 160 °C (320 deg.F) which provides
optimal resistivity of the coal-ash particles. For some difficult applications with low-
sulphur fuel hot-end units have been built operating above 371 °C (700 deg.F).
The flue gas after passing through the air-preheaters comes down to lower temperature
that is feasible for releasing into the atmosphere, but one vital job remains still left out,
i.e. to remove the carbon content of the gas so that it does not harm the atmosphere.
This job is done by ESP, the flue gas after air-preheater comes
to the ESP unit. ESP actually works on the principal of
CORONA DISCHARGE EFFECT ; the ESP unit houses two
electrode plates called emitting plate and collecting plate.
The emitting plate is supplied with a very high DC negative
potential (in order of**), this results into ionizing of air
molecules surrounding the emitting plate which is called
corona effect. The collecting plate is grounded and a positive
potential develops on it, as a result when the flue gas pass
through between them the
carbon particles are
attracted to the collecting
plates. The collecting Inside ESP, MTPS
plates are attached to hopper
where the ashes get deposited by hammering action
on the collecting plate. For a 210MW unit 24 such
hoppers are present in each ESP; these hoppers have
mechanical transport system for proper disposal of
ash. For better corona effect the emitting plate is
made corrugated because this way more air
molecules get ionized as corona discharge points are
more in number in corrugated plate.
Exciter Transformer of ESP, MTPS
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Ash Handling Plant
What is Ash?
Ash is the residue remaining after the coal is incinerated.
What is Ash Handling?
Ash handling refers to the method of collection, conveying, interim storage and
load out of various types of ash residue left over from solid fuel combustion processes.
Why Ash Handling System is required?
In Thermal Power Plant’s coal is generally used as fuel and hence the ash is produced
as the by-product of Combustion. Ash generated in power plant is about 30-40% of
total coal consumption and hence the system is required to handle Ash for its proper
utilization or disposal.
CHALLENGES OF ASH HANDLING:-
Indian coal presents high ash content generally which tends to be inconsistent.
Design of the system has to adequately cover anticipated variations and be capable
of handling the worst scenario.
System has to be environmentally friendly.
System has to be reliable with least maintenance problem.
System has to be energy efficient.
Ash terminology in power plants:-
Fly Ash ( Around 80% is the value of fly ash generated)
Bottom ash (Bottom ash is 20% of the ash generated in coal based power
What is fly ash?
Ash generated in the ESP which got carried out with the flue gas is generally
called Fly ash. It also consists of Air pre heater ash & Economiser ash (it is about 2
% of the total ash content).
What is bottom ash?
Ash generated below furnace of the steam generator is called the bottom ash.
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Volume of ash and properties
The ash handling system handles the ash by bottom ash handling system, coarse ash
handling system, fly ash handling system, ash disposal system up to the ash disposal
area and water recovery system from ash pond and Bottom ash overflow. Description is
A. Bottom Ash Handling System
Bottom ash resulting from the combustion of coal in the boiler shall fall into the over
ground, refractory lined, water impounded, maintained level, double V-Section type/ W
type steel- fabricated bottom ash hopper having a hold up volume to store bottom ash
and economizer ash of maximum allowable condition with the rate specified. The slurry
formed shall be transported to slurry sump through pipes.
C. Air Pre Heater ash handling system
Ash generated from APH hoppers shall be evacuated once in a shift by vacuum
conveying system connected with the ESP hopper vacuum conveying system.
D. Fly Ash Handling System
Fly ash is considered to be collected in ESP Hoppers. Fly ashes from ESP hoppers,
extracted by Vacuum Pumps, fly up to Intermediate Surge Hopper cum Bag Filter for
further Dry Conveying to fly ash silo.
Under each surge hopper ash vessels shall be connected with Oil free screw compressor
for conveying the fly ash from Intermediate Surge Hopper to silo. Total fly ash
generated from each unit will be conveyed through streams operating simultaneously
and in parallel.
E. Ash Slurry Disposal System
Bottom Ash slurry, Fly ash slurry and the Coarse Ash slurry shall be pumped from the
common ash slurry sump up to the dyke area which is located at a distance from Slurry
i) Commercial utilization of ash in: iii)Energy Efficient
–Cement additives. iv)High reliability
–Brick plants. v)Long Plant Life
–Road making, etc. vi)Least maintenance
ii) Saving of water - vii)Environment concern
a precious commodity.
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ELECTRICAL SYSTEM OVERVIEW
ELECTRICAL SYSTEM OF A THERMAL POWER PLANT BASICALLY CONSISTS OF THE
POWER DISTRIDUTION SYSTEM
The transformation of mechanical energy into electrical energy is carried out by
generator. The A.C generator or alternator is based on the principal of
electromagnetic induction and generally consists of a stationary part called stator
and a rotating part called rotor. The stator houses the armature windings and the
rotor houses the field windings. A D.C voltage is applied to the field winding in the
rotor through slip rings, when the rotor is rotated, the lines of magnetic flux is cut
through the stator windings. This as a result produces an induced e.m.f
(electromotive force) in the stator winding which is tapped out as output. The
magnitude of this output is determined by the following equation:-
E = 4.44/O f N volts
Where E = e.m.f. induced;
O =Strength of magnetic field in Weber;
f= Frequency in cycles per second or in hertz;
N = Number of turns in the winding of the stator;
Again, f = P n/120;
Where P = Number of poles;
n = revolutions per second of the rotor.
From the above expression it is clear that for the same frequency number of poles
increases with decrease in speed and vice versa. Therefore low speed hydro turbine
drives generators have 14to 20poles where as for high speed steam turbine driven
generators have 2 poles.
Rotor: Rotor is the most difficult part to construct; it revolves at a speed of
3000rpm. The massive non-uniform shaft subjected to a multiplicity of differential
stresses must operate in oil lubricated sleeve bearings supported by a structure
mounted on foundations all of which poses complex dynamic behaviour peculiar to
them. It is also an electromagnet and to give it the necessary magnetic strength the
Page | 42
windings must carry a fairly high current. The rotor is a cast steel ingot and it is further
forged and machined. Very often a hole bored through the centre of the rotor axially
from one end to the other for inspection. Slots are then machined for windings and
Rotor winding: Silver bearing copper is used for the winding with mica as insulation
between conductors. A mechanically strong insulator such as micanite is used for lining
the slots. For cooling purpose slots and holes are provided for circulation of cooling gas.
The wedges the windings when the centrifugal force developed due to high speed
rotation tries to lift the windings. The two ends of the winding are connected to slip
rings made of forged steel and mounted on insulated sleeves.
Stator: The major part of the stator frame is the stator core, it comprises of inner
and outer frame. The stator core is built up of a large number of punching or section of
thin steel plates. The use of cold rolled grain-oriented steel can contribute to reduction
of stator core.
Stator windings: Each stator conductor must be capable of carrying the rated
current without overheating. The insulation must be sufficient to prevent leakage
current flowing between the phases to earth. Windings for the stator are made up from
copper strips wound with insulated tape switch is impregnated with varnish, dried
under vacuum and hot pressed to form a solid insulation bar. In 210MW generators the
windings are made up of copper tubes through which water is circulated for cooling
Generator Cooling and Sealing System
1) HYDROGEN COOLING SYSTEM: Hydrogen is used as cooling medium in large
capacity generators in view of its high heat carrying capacity and low density. But in
view of its explosive mixture with oxygen, proper arrangement for filling, purging
and maintaining its purity inside the generator have to be made. Also in order to
prevent escape of hydrogen from the generator casing, shaft sealing system is used
to provide oil sealing. The system is capable of performing the following functions:-
a) Filling in and purging of hydrogen safely.
b) Maintaining the gas pressure inside the machine at the desired value all the time.
c) Provide indication of pressure, temperature and purity of hydrogen.
d) Indication of liquid level inside the generator.
2) Generator Sealing System: Seals are employed to prevent leakage of
hydrogen from the stator at the point of rotor exit. A continuous film between the
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rotor collar and the seal liner is maintained by means of oil at the pressure which is
about above the casing hydrogen gas pressure. The thrust pad is held against the collar
of rotor by means of thrust oil pressure, which is regulated in relation to the hydrogen
pressure and provides the positive maintenance of the oil film thickness. The shaft
sealing system contains the following components.
a) A.C oil pump.
b) D.C oil pump.
c) Oil injector.
d) Differential Pressure Regulator
e) Damper tank.
1) STATIC EXCITATION:
Alternator terminal voltage is used here.
SCR- based controlled rectifier is supplied is supplied from alternator output
through step down transformer.
SCR gate signal are derived from alternator output through CT & PT.
Rectifier output voltage is fed to the alternator field winding.
To generate the alternator output, it is run at rated speed with its field supplied
from a separate D.C supply bank.
This scheme is less expensive & requires little maintenance.
Excitation energy depends on alternator speed.
2) BRUSHLESS EXCITATION:
Main shaft of prime movers drives pilot exciter, main exciter & the main
Pilot exciter is a permanent magnet alternator.
Pilot exciter feeds 3-phase power to main exciter.
Main exciter supplies A.C power to silicon diode bridge rectifier through hollow
shaft which feeds the D.C to the field of main alternator.
SCR gate signals are derived from alternator output through CT & PT.
This scheme is mainly employed in turbo alternators.
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Specification of Generators
PARAMETERS UNIT-1 UNIT-2 UNIT-3 UNIT-4 UNIT-5 UNIT-6
Maker BHEL BHEL BHEL BHEL BHEL BHEL
Kw 210000 210000 210000 210000 250000 250000
P.F 0.85 Lag 0.85 Lag 0.85 Lag 0.85 Lag 0.85 Lag 0.85 Lag
KVA 247000 247000 247000 247000 294100 294100
Stator Volts- Volts- Volts- Volts- Volts- Volts-
15750 15750 15750 15750 15750 16500
Amps- Amps- Amps- Amps- Amps- Amps-
9050 9050 9050 9054 10781 10291
Rotor Volts- 310 Volts- Volts- Volts- Volts- Volts-
Amps- 310 310 256 292 292
2600 Amps- Amps- Amps- Amps- Amps-
2600 2600 2088 2395 2395
R.P.M. 3000 3000 3000 3000 3000 3000
Hz 50 50 50 50 50 50
Phase 3 3 3 3 3 3
Connection YY YY YY YY YY YY
Coolant Hydrogen Hydrogen Hydrogen Hydrogen Hydrogen Hydrogen
& water & water & water
Gas pressure 3.5 BAR(G) 3.5 3.5 2 BAR(G) 3 BAR(G) 3 BAR(G)
Insulation B B B F F F
Year of 1994 1994 1992- 2004 2006 2006
It is a static device which transfers electric powers from one circuit to the other
without any change in frequency, but with a change in voltage and corresponding
current levels also.
Here the transformers used are to transfer electric power from 15.75KV to 220KV
or 400KVthat are provided to the national grid.
The step-up generator transformers are of ONAN/ANOF/AFOF cooling type.
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Neutral Grounding Transformer(NGT):
The NGT is used to prevent the generator from earth faults.
It comprises of primary winding and secondary winding, the secondary
winding is connected with a high value resistance. Whenever earth fault arises
heavy current flows to the primary winding and as a result an e.m.f is induced
in the secondary.
The voltage drop across the resistance is sensed by the NGT relay and it
actuates to actuate the Generator Circuit Breaker (GCB) and thus the
generator is tripped.
Limited Earth-Fault Earthling System: Generators and other apparatus
installed at higher voltage levels are exposed to much greater fault energy…
in the order of thousands of MVA. Earth-fault currents could damage iron
structures in generators, motors, and transformers, so that they can't be
repaired, but instead must be replaced… at great cost! Hence, some method
of current limiting, like NGT (Neutral Grounding Transformer) or NGR (Neutral
Grounding Resistor) is beneficial.
Power Transformers enhances the productivity as well as maximizes the
capacity level of the high power supply equipments.
These are ultimate for the regular power without any cut off. They are used
for control high voltage and frequency for the different systems.
Power transformers having the following standards:
They can assist three phases.
There ratings are up to 2000 KVA.
Copper and aluminium winding material is used in this.
Applicable Standards are IS, IEC, ANSI, JIS, etc.
It is sufficient for primary as well as secondary voltage.
High voltage auto-transformers represent an important component of bulk
transmission systems and are used to transform voltage from one level to
These auto-transformers are critical for regional load supply, inter-regional
load transfers and for certain generator/load connections.
Major or catastrophic failures to this equipment can have severe
consequences to electric utilities in terms of increased operating costs and
customer load losses.
To minimize the impact of this type of failures, utilities may carry some spare
units to guard against such events. These spare units are going to cost utilities
money (utility cost) to purchase, to store and to maintain and utilities should
try to strike the right balance between the utility cost and the risk cost (if
spare units are not there).
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Advantages of Autotransformers:
1. Its efficiency is more when compared with the conventional one.
2. Its size is relatively very smaller.
3. Voltage regulation of autotransformer is much better.
4. Lower cost.
5. Low requirements of excitation current.
6. Less copper is used in its design and construction.
7. In conventional transformer the voltage step up or step down value is fixed
while in autotransformer, we can vary the output voltage as per out requirements
and can smoothly increase or decrease its value as per our requirement.
1. Used in both Synchronous Motor and Induction Motor.
2. Used in electrical apparatus testing labs since the voltage can be smoothly and
3. They find application as boosters in AC feeders to increase the voltage levels.
Generating Transformer (GT):
This is a type of Power Transformer where the LV winding is connected to the
generator through the bus duct and HV winding to the transmission system. In
addition to the features of Power Transformer, our Generator Transformer is
designed to withstand over voltage caused by sudden load throw off from the
generator. It is built as a single or three phase unit and located in power stations.
Normally generating voltage is 15.75KV from generator. If we want to transmit
that power to 220 KV busbar. This voltage must be stepped up, otherwise if we
transmit at same voltage level as generation voltages that is associated with high
transmission loss so the transformer which is used at generator terminal for
stepping up the voltage is called Generating transformer.
Specification of GT
MVA HV- 150/200/250
VOLTS HV- 245 KV
LV- 15.75 KV
RATED CURRENT HV- 151/482/602
TYPE OF COOLING OFAF/ONAF
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