A coal-fired power plant operates on the Rankine thermodynamic cycle. Coal is pulverized and burned in a boiler to produce high pressure steam, which spins turbines connected to generators to produce electricity. The steam is then condensed in a condenser and returned to the boiler to repeat the cycle. Coal-fired power plants have low capital costs but low efficiency around 35-42% and contribute significantly to air pollution and global warming.

1.  Electricity is the only form of energy which is
easy to produce, easy to transport, easy to use
and easy to control. So, it is mostly the terminal
form of energy for transmission and
distribution. Electricity consumption per capita
is the index of the living standard of people of
a place or country. Electricity in bulk quantities
is produced in power plants.

2.  Power plant engineering deals with the study
of energy, its sources and utilization of energy
for power generation. The power is generated
by prime movers (example Hydraulic turbines,
steam turbines, diesel engines). Large amount
of power is generated using prime movers in a
site or layout called power plants, where all the
equipments and machineries required for
power generation is located.

3.  The following are a few types of power plants -
1. Hydro-Electric power plant.
2. Steam engine power plant.
3. Gas, Diesel and petrol engine power plant.
4. Steam Turbine power plant.
5. Gas Turbine power plant.
6. Combined Gas and Steam turbines power plant.
7. Rankine Organic power plant.
8. Binary Vapor cycle power plant.
9. Nuclear power plant.
10. Solar energy power plant.
And so on…

4.  Low capital cost
 Reliability of supply power
 Low maintenance cost
 High efficiency
 Reserve capacity

5.  Almost two third of electricity requirement of the
world is fulfilled by thermal power plants (or thermal
power stations). In these power stations, steam is
produced by burning some fossil fuel (e.g. coal) and
then used to run a steam turbine. Thus, a thermal
power station may sometimes called as a Steam Power
Station. After the steam passes through the steam
turbine, it is condensed in a condenser and again fed
back into the boiler to become steam. This is known
as ranking cycle. This article explains how electricity is
generated in thermal power plants. As majority of
thermal power plants use coal as their primary fuel,
this article is focused on a coal fired thermal power
plant.

7.  Combustion, a chemical reaction between
substances, usually including oxygen and
usually accompanied by the generation
of heat and light in the form of flame.
 The rate or speed at which the reactants
combine is high, in part because of the nature
of the chemical reaction itself and in part
because more energy is generated than can
escape into the surrounding medium, with the
result that the temperature of the reactants is
raised to accelerate the reaction even more.

8.  The purpose of combustion is to produce heat
which is radiated from the combustion zone or
carried away by the gaseous products of
combustion.

9.  The power plant which is used to generate
electricity by the use of steam turbine. The
major components of these power plants
are boiler, steam turbine, condenser, and water
feed pump.

10.  A steam power plant consists of a boiler, steam
turbine and generator, and other auxiliaries.
The boiler generates steam at high pressure
and high temperature. The steam
turbine converts the heat energy of steam into
mechanical energy. The generator then
converts the mechanical energy into electric
power.

12.  A coal-fired power station or coal power
plant is a thermal power station which
burns coal to generate electricity. Coal-fired
power stations generate a third of the world's
electricity but cause hundreds of thousands of
early deaths each year, mainly from air
pollution.

14.  Coal: In a coal based thermal power plant, coal is
transported from coal mines to the generating station.
Generally, bituminous coal or brown coal is used as fuel.
The coal is stored in either 'dead storage' or in 'live storage'.
Dead storage is generally 40 days backup coal storage which
is used when coal supply is unavailable. Live storage is a
raw coal bunker in boiler house. The coal is cleaned in a
magnetic cleaner to filter out if any iron particles are present
which may cause wear and tear in the equipment. The coal
from live storage is first crushed in small particles and then
taken into pulverizer to make it in powdered form. Fine
powdered coal undergoes complete combustion, and thus
pulverized coal improves efficiency of the boiler. The ash
produced after the combustion of coal is taken out of the
boiler furnace and then properly disposed. Periodic removal
of ash from the boiler furnace is necessary for the proper
combustion.

15.  Boiler: The mixture of pulverized coal and air
(usually preheated air) is taken into boiler and
then burnt in the combustion zone. On ignition of
fuel a large fireball is formed at the center of the
boiler and large amount of heat energy is radiated
from it. The heat energy is utilized to convert the
water into steam at high temperature and pressure.
Steel tubes run along the boiler walls in which
water is converted in steam. The flue gases from
the boiler make their way through superheater,
economizer, air preheater and finally get
exhausted to the atmosphere from the chimney.

16.  Superheater: The superheater tubes are hanged
at the hottest part of the boiler. The saturated
steam produced in the boiler tubes is
superheated to about 540 °C in the superheater.
The superheated high pressure steam is then
fed to the steam turbine.

17.  Economizer: An economizer is essentially a
feed water heater which heats the water before
supplying to the boiler.
 Air pre-heater: The primary air fan takes air
from the atmosphere and it is then warmed in
the air pre-heater. Pre-heated air is injected
with coal in the boiler. The advantage of pre-
heating the air is that it improves the coal
combustion.

18.  Steam turbine: High pressure super heated
steam is fed to the steam turbine which causes
turbine blades to rotate. Energy in the steam is
converted into mechanical energy in the steam
turbine which acts as the prime mover. The
pressure and temperature of the steam falls to a
lower value and it expands in volume as it
passes through the turbine. The expanded low
pressure steam is exhausted in the condenser.

19.  Condenser: The exhausted steam is condensed in
the condenser by means of cold water circulation.
Here, the steam loses it's pressure as well as
temperature and it is converted back into water.
Condensing is essential because, compressing a
fluid which is in gaseous state requires a huge
amount of energy with respect to the energy
required in compressing liquid. Thus, condensing
increases efficiency of the cycle.

20.  Generator: The steam turbine is coupled to an
alternator. When the turbine rotates the
alternator, electrical energy is generated. This
generated electrical voltage is then stepped up
with the help of a transformer and then
transmitted where it is to be utilized.

21.  Feed water pump: The condensed water is
again fed to the boiler by a feed water pump.
Some water may be lost during the cycle,
which is suitably supplied from an external
water source.

22.  Cooling Tower: It is a tower which contains
cold water. Cold water is circulates to the
condenser for the cooling of the residual steam
from the turbine.

23.  Chimney: It is used to release the hot burnt
gases or smoke from the furnace to the
environment at appropriate height. The height
of the tower is very high such that it can easily
throw the smoke and exhaust gases at the
appropriate height. And it cannot affect the
population living near the steam power plant.
 Ash Storage: It is used to store the ash after
the burning of the coal.

24.  The pulverised coal is fed into the boiler where the
pulverised coal is burnt into the furnace
 Due to heat from the furnace, the water present in
the boiler drum changes to the high pressure
steam.
 From the boiler this high pressure steam is passed
to the super heater where it is again heated up to
its dryness.
 After that this super heated steam strikes the
turbine blades with a high speed and the turbine
blades starts rotating to at high speed. Here the
stored potential energy of the steam is gets
converted into mechanical energy.

25.  A generator is coupled with the turbine rotor. As the
turbine rotates, the generator also rotate with same
speed and mechanical energy of the turbine gets
converted into electrical energy.
 Steam after hitting the turbines blades lost its most of
the energy and leaves the turbine with low pressure
steam.
 This low pressure steam enters into the condenser.
Cold water circulates in the condenser from the cooling
tower. Here the low pressure wet steam is converted
into water.
 After that condensed water with the feed water passed
to the economiser where it gets heated up by the
superheater. And finally the feed water enters into the
boiler by a feed water pump to repeat the cycle.

26.  The burnt flue gases from the furnace passes
through the superheater, economiser and air
pre-heater. This heat of the flue gases is used to
heat the steam in the super heater to its
dryness, to heat feed water in the economiser
before entering into the boiler and to heat air
form the atmosphere in the air pre-heater
before it enters into the furnace.
 The ash from the furnace is transported to ash
handling plant and finally to the ash storage.

27.  The power plant that operates on coal
constitutes almost 41% of the world’s electricity
generation.
 It is the modified Rankine thermodynamic
cycle on which the coal-fired power plant
operates.
 The overall efficiency of the coal power plant
ranges from 32% to 42%. And this is calculated
by the superheat pressures and superheat and
reheat temperatures of steam.

28.  Most of the large power plants that operates at
steam pressures of 170 bar,570 ℃ superheat
and 570 ℃ reheat steam temperatures can achieve
the efficiency ranges from 35% to 38%.
 The efficiency of the super critical power plants
operating at 220 bar steam pressure, 600/600
℃ superheat/reheat temperatures can achieve is
42%.
 The efficiency in the range of 45 to 48% can be
achieved by the ultra-super critical power plants
operating at 300 bar pressure, 600/600 ℃
superheat/reheat steam temperatures.

29.  Supply of fuel: The steam power plant should be located
near the coal mines so that transportation cost of fuel is
minimum. However, if such a plant is to be installed at a
place where coal is not available, then care should be taken
that adequate facilities exist for the transportation of coal.
 Availability of water: As huge amount of water is required
for the condenser, therefore, such a plant should be located
on the bank of a river or near a canal to ensure the
continuous supply of water.
 Transportation facilities: A modern steam power
plant often requires the transportation of material and
machinery. Therefore, adequate transportation facilities
must exist i.e., the plant should be well connected to other
parts of the country by rail, road. etc.

30.  Cost and type of land: The steam power station should be
located at a place where land is cheap and further extension,
if necessary, is possible. Moreover, the bearing capacity of
the ground should be adequate so that heavy equipment
could be installed.
 Nearness to load centres: In order to reduce the
transmission cost, the plant should be located near the
centre of the load. This is particularly important if dc supply
system is adopted. However, if ac the supply system is
adopted, this factor becomes relatively less important. It is
because ac power can be transmitted at high voltages with
consequently reduced transmission cost. Therefore, it is
possible to install the plant away from the load centres,
provided other conditions are favourable.

31.  Distance from populated area: As huge
amount of coal is burnt in a steam power
station, therefore, smoke and fumes pollute the
surrounding area. This necessitates that the
plant should be located at a considerable
distance from the populated areas.

32.  As compared with the power generating plant, it
has a low initial cost and hence economical.
 Less land area is required as compared with the
hydro power plant.
 Coal is used as fuel and the cost of coal is cheaper
than petrol and diesel fuel. So the power
generation cost is economical.
 This power plant has easy maintenance cost.
 Steam power plant can be installed in any area
where water sources and transportation facility are
easily available.

33.  The running cost of the steam power plant is
comparatively high because of fuel, maintenance,
etc
 If we talk about the overall efficiency of the steam
power plant then it is about 35 % to 41% which is
low.
 Due to the release of burnt gases of coal or fuel, it
contributes to global warming to a larger extent.
 The heated water that is thrown in the rivers,
ponds etc puts an adverse effect on the living
organism and disturbs the ecology.