EE, 4th year
GURU NANAK INSTITUTE OF TECHNOLOGY
Thermal Power Plant
2.Overview of Mejia Thermal Power Plant
3.Power plant layout
4.Main and Auxiliary Equipment
A Thermal Power Plant converts the heat energy of coal into
electrical energy. Coal is burnt in a boiler which converts water
into steam. The expansion of steam in turbine produces
mechanical power which drives the alternator coupled to the
turbine.Thermal Power Plants contribute maximum to the
generation of Power for any country . Thermal Power Plants
constitute 75.43% of the total installed captive and non-captive
power generation in India . In thermal generating stations coal,
oil, natural gas etc. are employed as primary sources of energy.
Overview of MTPS
Damodar Valley Corporation was established on 7th July 1948.
The MTPS under the DVC is the second largest thermal plant in West Bengal.
It has the capacity of 2340 MW with 4 units of 210 MW each, 2 units of 250 MW
each & 2 units of 500 MW each.
With the introduction of another two units of 500 MW that is in construction it will be the
largest in West Bengal.
Mejia Thermal Power Station is located in the outskirts of Raniganj in Bankura District.
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
Diagram of a typical coal-fired thermal power
Main and Auxiliary Equipments
1. Coal handling plant
2. Pulverizing plant
3. Draft fans
5. Ash handling plant
8. Cooling towers and ponds
9. Feed water heater
11. Superheater and Reheater
12. Air preheater
Coal handling plant
•The function of coal handling plant is automatic feeding of coal to the boiler furnace.
• A thermal power plant burns enormous amounts of coal.
•A 200MW plant may require around 2000 tons of coal daily
In modern thermal power plant , coal is
pulverised i.e. ground to dust like size and
carried to the furnace in a stream of hot air.
Pulverising is a means of exposing a large
surface area to the action of oxygen and
consequently helping combustion.
Pulverising mills are further classified as:
1. Contact mill
2. Ball mill
3. Impact mill
ASH HANDLING PLANT
The percentage of ash in coal is 5% in good
quality coal & about 40% in poor quality coal.
Power plants generally use poor quality of
coal , thus amount of ash produced by it is
A modern 1000MW plant produces about
4800 tons of ash daily.
The stations use some conveyor
arrangement to carry ash to dump sites.
Boiler is an enclosed vessel in which water is
heated and circulated until the water is
turned in to steam at the required pressure.
Coal is burned inside the combustion
chamber of boiler. The products of
combustion are nothing but gases. These
gases which are at high temperature
vaporize the water inside the boiler to
Boilers are classified as:
1. Fire tube boilers
2. Water tube boilers
• The steam produced in the boiler goes
to the steam drum and is then piped
through the primary, platen and final
super-heaters where it reaches the outlet
temperature of 560 C and 160 ksc
• At this point in the process they have
now turned the water into a very
powerful source of energy
• This rotates the turbine to which
generator is on the other end
• From rotating generator electricity is
Some of the heat of superheated
steam is used to rotate the
turbine where it loses some of its
energy. The steam after reheating
is used to rotate the second
steam turbine where the heat is
converted to mechanical energy.
This mechanical energy is used to
run the alternator, which is
coupled to turbine , there by
generating electrical energy.
Steam after rotating steam turbine comes to condenser. Condenser refers
here to the shell and tube heat exchanger (or surface condenser) installed
at the outlet of every steam turbine in Thermal power stations of utility
The purpose is to condense the outlet (or exhaust) steam from steam
turbine to obtain maximum efficiency and also to get the condensed
steam in the form of pure water, otherwise known as condensate, back to
steam generator or (boiler) as boiler feed water.
Condensers are classified as:
i)Jet condensers or contact condensers,
Primary Air Fan
• Air to blow the coal from the mill to the
boiler, called the primary air, is supplied
by a large fan driven by a variable
• When mixed with a stream of air the
powdered coal behaves more like a gas
than a solid
• Primary air does two jobs – heating the
coal powder and secondly lifting it into
the furnace through pipelines
Forced Draught (FD) Fan
• Each unit shall have two forced
• The fans draw warm air from the top
of the boiler house through large air
heaters becoming the primary and
secondary air used for the boiler
• The air heater warms the incoming
air by transferring heat energy from
the outgoing flue gases
Air Pre-Heater (APH)
• The air heaters use the remaining
heat energy in the flue gas to heat up
the combustion air for the boiler
• Efficiency is increased by using this
heat that would otherwise go up the
chimney. The air temperature leaving
the air heaters is at 300 C
• The air heaters use the remaining
heat energy and efficiency is
increased by using this heat that
would otherwise go up the chimney
Induced Draught (ID) Fan
• Two induced draught fans draw
gases out of the boiler
• The gas has already passed
through the air heaters and
precipitators before it has reached
• The heat from the flue gases or
smoke is used in the air heaters to
heat up the primary and secondary
• The chimney is 275 meters' high and
50,000 tonnes of reinforced concrete were
used to make it
• It consists of flues each of which serve
typically two or three boilers (two units)
• Each boiler has 4 passes with 7 fields each
containing high voltage electrodes
• These attract the dust or ash from the flue gases
• At regular intervals the electrodes are rapped with
motor-driven hammers and the PFA falls into
• In a year 1,000 MW station may generate 1.5
million ton of ash
• This is one of the ways to clean up the flue gases
or smoke sent up the chimney
• Secondly this ash is used by construction industry
for use in building materials (bricks !!, Cement
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
Types Of Cooling Tower-
1. Wet cooling tower
2. Dry cooling tower
Flue gases coming out of the boiler carry
lot of heat. Function of economizer is to
recover some of the heat from the heat
carried away in the flue gases up the
chimney and utilize for heating the feed
water to the boiler.
It is placed in the passage of flue gases in
between the exit from the boiler and the
entry to the chimney.
The use of economizer results in saving
in coal consumption, increase in
steaming rate and high boiler efficiency
but needs extra investment and increase
in maintenance costs and floor area
required for the plant.
A steam turbine is a device that
extracts thermal energy from
pressurized steam and uses it to
do mechanical work on a rotating
The steam turbine is a form
of heat engine that derives much
of its improvement in
thermodynamic efficiency from
the use of multiple stages in the
expansion of the steam, which
results in a closer approach to the
ideal reversible expansion process.
An alternator is an electromechanical device that converts mechanical
energy to alternating current electrical energy. Most alternators use a
rotating magnetic field. Different geometries - such as a linear alternator
for use with sterling engines - are also occasionally used. In principle, any
AC generator can be called an alternator, but usually the word refers to
small rotating machines driven by automotive and other internal
It is a device that transfers electric energy
from one alternating-current circuit to
one or more other circuits, either
increasing (stepping up) or reducing
(stepping down) the voltage.
Transformers act through
electromagnetic induction; current in
the primary coil induces current in the
secondary coil. The secondary voltage is
calculated by multiplying the primary
voltage by the ratio of the number of
turns in the secondary coil to that in the
Placed where switching operation of power distribution is performed.
Air insulated switch yard of 220KV-400KV are used.
Main Components of Switch Yard:
These are used for automatic switching during normal or abnormal conditions .
Manufacturer ABB Limited
Type of Circuit Breaker SF6
Rated Voltage 245 KV
Under Site Condition of 40 0C
Under Site Condition of 50 0C
Rated Frequency 50 Hz
These are used to disconnect transmission line under no-load condition for safety,
isolation and maintenance.
Rated current for site conditions 2000 A
Rated Voltage 245 KV
Rated Frequency 50 Hz
Operating time of Isolator Less than 12 sec.
These are used to discharge lightning over voltages and switching over voltages to earth.
Manufacturer Crompton Greaves Ltd, Nasik
Model No. ZLA X 25 C
Ref. Standard IEC 99 – 4. 1991
Rated Frequency 50 Hz
Max. Leakage Current 5 mA
The conductors to which several incoming and outgoing
lines are connected.
They are made up of Cu & Al,
The incoming and outgoing cables are provided for
These are used to step-down currents for measurement, control &
Current transformers are used extensively for measuring current
and monitoring the operation of the power grid.
VT measure voltage and this parameter used for protection of
For high voltage CVT (capacitive voltage transformer) is used
instead of VT and capacitors play divider role.
We can also use these capacitors for PLC system.
Stepwise Operation of Thermal Power Plant
1) First the pulverized coal is burnt into the furnace of boiler.
2) High pressure steam is produced in the boiler.
3) This steam is then passed through the super heater, where it further heated up.
4) This supper heated steam is then entered into a turbine at high speed.
5) In turbine this steam force rotates the turbine blades that means here in the turbine
the stored potential energy of the high pressured steam is converted into mechanical
6) After rotating the turbine blades, the steam has lost its high pressure, passes out of
turbine blades and enters into a condenser.
7) in the condenser the cold water is circulated with help of pump which condenses the
low pressure wet steam.
8) This condensed water is then further supplied to low pressure water heater where the
low pressure steam increases the temperature of this feed water; it is then again heated
in a high pressure heater where the high pressure of steam is used for heating.
9) The turbine in thermal power station acts as a prime mover of the alternator.
Efficiency of Thermal Power Station or Plant
The overall efficiency of a thermal power station or plant varies from 20% to 26%
and it depends upon plant capacity.