COAL BASED THERMALCOAL BASED THERMAL
POWER PLANTPOWER PLANT
A thermal power station is a power plant in which the prime mover is
steam driven. Water when heated turns into steam which drives a steam
After passing through the turbine, the steam is condensed in a condenser
and recycled to where it was heated. [Rankine cycle]
Coal is used as a fuel to heat water in a coal based thermal power
Thermal Power PlantThermal Power Plant
Stage 1: Conversion of Chemical energy of coal to heat energy
Stage 2: Conversion of heat energy to mechanical energy of
Stage 3: Conversion of mechanical energy to rotational energy
of turbine which drives generator.
Stage 4: Rotational energy to electrical energy based on
Faraday’s Law of electromagnetic induction.
Energy ConversionsEnergy Conversions
1. Coal Handling Plant
2. Boiler and its auxiliaries
3. Turbine and its auxiliaries
4. Condenser and Cooling Tower
5. Ash Handling Plant
6. Electrical Equipments
Major Components of Coal Based
Thermal Power Plants
Major Components of Coal Based
Thermal Power Plants
• A coal handling plant is the area of the thermal power
plant where the raw coal is brought from the coal mines
and is processed into a form that can fed into the boiler.
1. Transportation System
2. Coal Crusher
3. Coal Storage Area
Coal Handling SystemCoal Handling System
The transportation system is the various methods through which the
raw coal is brought into the plant
The usual system is through trains but many other methods are
followed . some of the methods are as follows :
Merry go round: in this in spite of following the conventional
method of trumpling the railway wagon upside down the wagons are
provided with a door at the bottom from which the wagons are
emptied on an under ground conveyor belt which take the coal to the
crusher house .
Other methods for coal transportation are as follows:
• Transportation through ships is done when the power plant is situated
near the sea area.
• When the power plant is situated near the coal mine the coal is directly fed
into the plant through conveyers.
• Some times road transportation is used cut in very rare cases because it is
unable to supply the amount needed for undisturbed power generation.
• Sometimes the coal is also transported by pipelines. This is method is said
to be more efficient as it is not affected by the traffic and weather
• Once the coal is in plant it has to undergo some preparatory
processes before being fed into the boiler
• First the coal goes to the crusher house where the coal is
crushed manually into a size of about 20mm .This coal is then
passed further some part of it is fed into the plant while the
other is stored.
• Generally most of the power plants store a coal for the use of
20 days this is known as dead storage.
• The coal is then is passed through vibrator which separates
the 20 mm sized coal from larger one. This 20 mm coal is
then fed into the raw coal bunker from where it goes to the
coal mill .The rate of feeding of coal is controlled by raw coal
• The coal mill pulverizes the coal i.e. it crushes the coal into a
tiny sized particles which are similar to that of talcum powder.
It is done to avoid incomplete combustion of
• Boiler is a container into which water can be
fed and steam can be taken out at desired
pressure, temperature and flow
• It is rectangular in cross section and wall made
of tubes hence all four walls are made of
tubes which contain water
Firing in boiler
• Corner fired boilers are used now days and in
these all nozzles face downwards and burning
takes place in the coal firing wall called fire
• Economiser is there to improve the efficiency
of boiler by extracting heat from flue gases to
heat water and send it to boiler drum.
Advantages of Economiser
Advantages of Economiser include
• Fuel economy: - used to save fuel and increase
overall efficiency of boiler plant.
• Reducing size of boiler: - as the feed water is
preheated in the economiser and enter boiler
tube at elevated temperature. The heat
transfer area required for evaporation
• The heat carried out with the flue gases
coming out of economiser are further utilized
for preheating the air before supplying to the
• Raising the temperature of steam after part of
the energy is extracted from it in the steam
turbine called re-heating of steam which
increases the cycle efficiency.
• This reheating is done in the boiler, which
supplies super heated steam to the turbine
itself at the heating surfaces called Reheaters
• Steam turbine is used as a prime mover
• It is a 3 cylinder turbine
• Condensers are heat exchangers which convert steam from
its gaseous to its liquid state at a pressure below atmospheric
• Two types: i) Air Cooled ii) Water Cooled
• Convert the turbine exhaust steam into pure water so that it
may be reused in the steam generator or boiler as boiler feed
Boiler Feed Pump
• It is a pressure raising device.
• Pumps feed water to Economiser.
• BFP is the biggest auxiliary equipment after Boiler and Turbine.
• It consumes about 4 to 5 % of total Electricity Generation.
• NPSH avoids formation of water vapour in the Impeller.
(6 - Stage)
• It is a heat rejection device.
• A small portion of the water being cooled is being
evaporate into a moving air stream to provide
significant cooling to the rest of that water stream.
• For 200MW plant 600m3
/hr water is evaporated.
• Categorization by air-to-water flow
Types of Cooling Towers
• Natural Draft Cooling
Tower: which utilizes
buoyancy via a tall
• Mechanized Draft Cooling
Tower: which uses power
driven fan motors to force
or draw air through the
Types of Mechanized Draft
• Forced draft system: A mechanical draft
tower with a blower type fan at the intake.
• Induced draft system: A mechanical draft
tower with a fan at the discharge which pulls
air through tower.
• Balanced draft system: In this system both FD
fan and ID fan are provided.
Ash Handling System
• Ash handling refers to the
method of collection,
conveying, interim storage
and load out of various
types of ash residue left over
from coal combustion
• Indian coal has high content
of ash. Out of which:
– 20% is Bottom Ash
– 80% is Fly Ash.
Types of Ash Handling
• Bottom Ash - At the bottom of the furnace, there is a
hopper for collection of bottom ash. This hopper is always
filled with water to quench the ash and clinkers falling
down from the furnace. This ash is then passed through
Clinker Grinder or Scrapper convertor.
• Fly ash - is captured and removed from the flue gas by ESP
or fabric bag filters located at the outlet of the furnace and
before the ID fan.
• Fly Ash Handling is done as:
a)Dry Fly Ash Handling: i)Evacuated ii)Pressurized
b) Wet Fly Ash Handling
• Excitation System
• Cooling System
Advantages of Coal Based Power Plant
• They can respond to rapidly changing loads without
• A portion of the steam generated can be used as a
process steam in different industries
• Steam engines and turbines can work under 25 % of
• Fuel used is cheaper
• Cheaper in production cost in comparison with that
of diesel power stations.
Disadvantages of Coal Based Power Plant
• Maintenance and operating costs are high
• Long time required for erection and putting into
• A large quantity of water is required
• Great difficulty experienced in coal handling
• Presence of troubles due to smoke and heat in
• Unavailability of good quality coal
• Maximum of heat energy lost
• Problem of ash removing.
• Supercritical steam parameters results in
higher efficiencies – above 45%.
• The supercritical coal based units have faster
starting time and load changes and are more
suitable for daily start up/shut down
Advantages of Supercritical
• Reduced fuel costs due to improved plant efficiency
• Significant reduction in CO2 emissions
• Much reduced NOx, SOx and particulate emissions
• Excellent availability, comparable with that of an
existing sub-critical plant
• Plant costs comparable with sub-critical technology
and less than other clean coal technologies
• Compatible with biomass co-firing
• Can be fully integrated with appropriate CO2 capture
Ultra Mega Power Projects (UMPPs)
• Development of Ultra Mega Power Projects (UMPPs)
has been identified as a thrust area. These are very
large sized projects, approximately 4000 MW each
involving an estimated investment of about Rs.
16,000 crore .
• Ultra Mega Power Projects would use Super Critical
technology with a view to achieve higher levels of
fuel efficiency, which results in saving of fuel and
lower green-house gas emissions.
Ultra Mega Power Projects(cont..)
• These projects will meet the power needs of a number
of States/ distribution companies located in these
States, and are being developed on a Build, Own, and
Operate (BOO) basis
• Flexibility in unit size subject to adoption of specified
minimum Supercritical parameters
• Integrated power project with dedicated captive coal
blocks for pithead projects
• Coastal projects to use imported coal
Mixing Solar with Coal to Cut Costs
• A new strategy that could reduce coal plant
emissions and cut the cost of solar power.
• In the new project, because parabolic troughs
don't generate sufficiently high temperatures,
the heat they produce won't be fed directly into
• Instead, it will be used to preheat water that
will be fed into the coal plant's boilers, where
coal is burned to turn the water into steam.