Layout of Steam Power Plant
Essential Requirement of SPP
Selection of Site
Layout and units of modern SPP
Coal and Ash handling System
Air and gas circuit
Accessories used in SPP
Steam Turbine and Steam Turbine Generator
Cooling ponds and cooling towers
History of Steam Power plant
Existing and Upcoming thermal power plants in India
Advantages and Disadvantages of SPP
A Steam 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 electric 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 Rankine cycle.
Some thermal power plants also deliver heat energy for industrial
purposes, for district heating, or for desalination of water as well as
delivering electrical power.
A large part of human CO2 emissions comes from fossil fuelled thermal
power plants; efforts to reduce these outputs are various and widespread.
Minimum capital cost
Minimum operation and maintenance cost
Capacity to meet peak load effectively
Minimum loss of energy in transmission
Low cost of energy supplied to the consumers
Reserve capacity to meet future demands
Availability of raw material
Nature of land
Cost of land
Availability of water
Ash disposal facilities
Availability of labour
Size of plant
Coal and ash handling circuit- Coal arrives at the storage yard and after
necessary handling, passes on to the furnaces through the fuel feeding device. Ash
resulting from combustion of coal collects at the back of the boiler removed
through ash handling system.
Air and gas circuit- Air taken from atmosphere by forced induced draught fan
and passes on to the furnace through the air preheater heated by flue gases which
passes to the chimney via the preheater. Flue gases are then passes through
Precipitator, Economizer and air preheater before being exhausted to the
Feed water and steam flow circuit- Condensate leaving the condenser is
first heated in a closed feed water heater through extracted steam from the lowest
pressure extraction point of the turbine. It then passes through the deaerator and a
few more water heaters before going in to the boiler through economizer.
Cooling water circuit- To keep maintain the low pressure in condenser. It
may be taken from natural gas, lake or sea of may be some water circulate over
Coal Delivery :- From the supply points the coal may be delivered to power
station through rail, road, river or sea.
Unloading:- Coal delivered by truck directly may dump the coal to outdoor
storage. If transported by sea unloading equipment like portable conveyors, coal
accelerators etc. are used.
Preparation:- if coal delivered in form of lumps the coal preparation carried by:
1. breakers 4. dryers
2. crushers 5. magnetic separators
Transfer:- Transfer means handling of coal between the unloading point and the
final storage point from where it discharge to the firing equipment. Belt Conveyor is
very suitable means of transporting large quantities of coal over large distance.
1.Inclination at which coal can be elevated- 20˚
2. Average Speed of Belt Conveyor – 60 – 100 meter per minute
3.Load carrying capacity – 50 –100 tonnes/hour and it can easily transfer
through 400m. It is used in medium and large power plants.
Storage of coal :- Storage of coal gives protection against the in interruption of
coal supplies when there is delay in transportation of coal. There should be no
standing water in storage area, Fire fighting equipment should be available, it
should be protected against wind erosion.
Inplant Handling:- it refer to coal handling between final storage and the firing
equipment . It includes the equipment such as belt conveyors, screw conveyors,
Bucket elevators to transfer the coal. Weigh lorries, hoopers and automatic scales
used to record the quantity of coal delivered to furnace.
Weighing and Measuring:- To weigh the quantity of coal following equipment
are used –
1. Weigh Bridge 2. Belt Scale
3. Weigh Lorry 4. Automatic Scale
Furnace Firing:- Since the source of heat is the combustion of fuel, a working
unit must have equipment necessary to receive the fuel and air in proportion as per
the boiler steam demand, mix, ignite, and perform other combustion duties such as
distillation of volatile from coal prior to ignition.
* Method of furnace firing depends upon the type of fuels and in SPP mainly the
Bituminous Coal is used as fuel because it is one of the best coal type contains
no moisture, easy to crack and ash contents are very low. Volatile matter on dry
ash free basis range from between 10% and 14% to 40% and over. Calorific
Value of Bituminous coal is 6000 kcal/kg.
* Furnace Firing with coal as fuel is done by three methods:
1. Stroker firing- A Stroker is a power operated fuel feeding mechanism.
2. Pulverized Fuel Firing- In this coal is reduced into fine powder with the
help of grinding mill and then projected into combustion chamber with the
help of hot air current .
Boilers burning pulverized coal generates approx. 80% fly ash and 20% bottom ash.
Bottom ash particles are collected under the furnace in a water-filled ash hooper. Fly
ash is collected in dust collector with either electrostatic precipitator or a baghouse.
Handling of ash includes:-
1. its removal from the furnace.
2. loading on the conveyors and delivery to the fill or dump where it can b disposed
of by sale or otherwise.
Three major factors should be considered for ash disposal as it is very dangerous for
living organism as well as environment :-
1. Plant Site
2. Fuel Source
3. Environmental Regulation
Mechanical handling system- This system is generally employed for low
capacity coal fired power plant. Hot ash from boiler furnace is made to fall over
belt conveyor after cooling through water then transported to an ash bunker
through the belt conveyor.
Hydraulic System- In this system ash is carried with the flow of water with
high velocity through a channel and finally dumped in the sump.
Pneumatic System- This system can handle abrasive ash as well as fine dusty
material such as fly ash and soot. The exhauster at the discharge creates a high
velocity stream which picks up ash and dust and then these are carried in the
Steam Jet System- In this case steam at sufficiently high velocity is passed
through a pipe carrying dry solid materials of considerable size. A jet of high
Pressure steam is passed in the direction of ash travel through a conveying pipe in
which the ash from the boiler ash Hooper is fed. The ash is disposed into the ash
The constituents of fly ash are- SiO2(30-60%), Al2O3(15-30%), unburnt carbon
upto 30%, CaO(1-7%), MgO & SO3 in small amounts. In fly ash the carbon
content should be small & silicon content should be high as possible.
Disposal :- It is disposed in two ways
1. Dry System- Fly ash is transferred into a bunker pneumatically.
2. Wet System- Fly ash is mixed with water and sluiced to the settling ponds or
dumping area near the plant.
1. It is used in concrete as an add mixture or in-part replacement of cement, fine
2. Fly ash and binder in the form of lime are mixed by auto claving and blocks
are form which are light in weight. These blocks have low thermal
conductivity and stable against temperature.
Air is taken in from atmosphere through the action of a forced or induced draught
fan and passes on the furnace through the air preheater, where it has been heated
by the heat of flue gases which pass to the chimney via the pre heater
It consist mainly of chimney draught & steam jet draught
The small pressure difference which causes flow of gases to take place is termed as
Draught may be classified as
1.Natural or chimney draught:-
The chimney is a boiler installation that produces a draught where by the air & gas
are forced through the fuel bed. It carries the products of combustion to such a hide
before discharging them that they will not injurious to surroundings
Artificial draughts are used to produced total static draught varrying from 30-350
mm of water column. It may be a mechanical or steam jet draught
A blower or a fan is installed near the base of boiler to forced the air through the cool
bed & other passages through the furnace, economiser etc. It is a possitive pressure
This draught is usually used when the economiser and air preheater are incorporated in
the system. It is similar to natural draught
It is a combination of forced & induced draught system. The forced draught
overcomes the resistance in the air preheater & chain grate stoker while the induced
draught fan overcome draught losses through boiler economiser
6.Steam jet draught:-
Steam jet is directed into the smoke box near the stack, the air is induced through the
fuels, the grate & ash pit to the smoke box
A boiler is defined as the closed vessel in which steam is produced from water by
combustion of fuel
Classification of boilers:-
1.Horizontal, vertical or inclined
2.Fire tube & water tube
3.Externally fired & internally fired
4.Forced circulation & natural circulation
5.High pressure & low pressure boiler
6.Stationary & portable
1.The working pressure & quality of steam required
2.Steam generation rate
3.Floor area available
4.Accessibility for repair and inspection
5.Comparative initial cost
7.The fuel & water available
8.Operating & maintainance cost
They are the auxiliary plants required for steam boilers for their proper operation
and further increase of their efficiency
It is a pump which is used to deliver feed water to the boiler. They are of two types :
1. Reciprocating pumps
2. Rotary pumps
It is desirable that the quantity of water supplied should be atleast equal to that
evaporated and supplied to the engine.
It has a function to feed water into the boiler . It is commonly employed for
large capacity high pressure boiler . It is used where the space is not available
for the installation of a feed pump.
In an injector the water is delivered to the boiler by steam pressure. The kinetic
energy of steam is used to increase the pressure and velocity of feed water.
It is a device in which the waste heat of the flue gases is utilized for heating
the feed water. They are of two types
1. Independent type:-
It is installed in chamber apart from the boiler setting. The chamber is
situated at the passage of the flow of the flue gases from the boiler .
2. Integral type :-
It is the part of boiler heating surface and is installed within the boiler
Its function is to increase the temperature of air before it enters the furnace. It is
generally placed after the economizer so the flue gases pass through the
economizer and then to the air pre heater . Pre heated air accelerates the
combustion and facilitate burning of coal. There are three types of air preheater
The function is to increase the temperature of the steam above its saturation point.
Superheated steam has following advantages:
Steam consumption is reduced
Losses due to condensation are reduced
Erosion of turbine blade is eliminated
Efficiency of SPP is increased
They are of two types:-
Feed water heating with steam at low pressure then boiler pressure usually
raises overall plant efficiency.
Feed water heater may be classified as follows :-
1. Open or Contact heaters-
- Tray Type
- Jet Type
2. Closed or surface heater
They are used to give a supply of pure water as a make up feed for the boilers.
Raw water is evaporated by using extracted steam and the condensed to give
distilled and pure feed water. They are of two types:
1. Film type evaporator
2. Submerged type evaporator
The steam turbine is a prime mover in which the potential energy of the steam is
transformed into kinetic energy and latter in its turn is transformed into the
mechanical energy of rotation of the turbine shaft.
Classification of steam turbines:-
According to action of steam –
3. Combination of impulse and reaction
According to no. of pressure stages –
1. Single stage turbine
2. Multistage impulse and reaction turbines
According to direction of steam flow-
1. Axial turbine
2. Radial turbine
According to no. of cylinder –
1. Single cylinder turbine
2. Double cylinder turbine
3. Three cylinder turbine
4. Four cylinder turbine
According to the method of governing-
1. Turbine with throttle governing
2. Turbine with nozzle governing
3. Turbine with bypass governing
According to heat drop process-
1. Condensing turbine with generator
2. Back pressure turbine
3. Low pressure turbines
4. Topping turbines
According to steam condition at inlet to turbine –
1. Low pressure turbine (1.2 – 2 ata)
2. Medium pressure (upto 40 ata)
3. High Pressure (above 40ata)
4. Turbines of supercritical pressure (above 225 ata)
According to their usage in industry –
1. Stationary turbines with constant speed of rotation
2. Stationary steam turbine
3. Non Stationary turbines with variable speed
The turbine generator consists of a series of steam turbines interconnected to each
other and a generator on a common shaft. There is a high pressure turbine at one
end, followed by an intermediate pressure turbine, two low pressure turbines, and
As steam moves through the system and loses pressure and thermal energy it
expands in volume, requiring increasing diameter and longer blades at each
succeeding stage to extract the remaining energy.
Superheated steam from the boiler is delivered through 14–16-inch (360–410 mm)
diameter piping to the high pressure turbine where it falls in pressure to 600 psi
(4.1 MPa) and to 600 °F (320 °C) in temperature through the stage. It exits via
24–26-inch (610–660 mm) diameter cold reheat lines and passes back into the
boiler where the steam is reheated in special reheat pendant tubes back to 1,000
°F (500 °C).
The hot reheat steam is conducted to the intermediate pressure turbine where it
falls in both temperature and pressure and exits directly to the long-bladed low
pressure turbines and finally exits to the condenser.
The generator, 30 feet (9 m) long and 12 feet (3.7 m) in diameter, contains a
stationary stator and a spinning rotor, each containing miles of heavy
copper conductor—no permanent magnets here. In operation it generates up to
21,000 amperes at 24,000 volts AC (504 MWe) as it spins at either 3,000 or
3,600 rpm, synchronized to the power grid. The rotor spins in a sealed chamber
cooled with hydrogen gas, selected because it has the highest known heat
transfer coefficient of any gas and for its low viscosity which
reduces windage losses.
This system requires special handling during start up, with air in the chamber
first displaced by carbon dioxide before filling with hydrogen. This ensures that
the highly explosive hydrogen–oxygen environment is not created.
The power grid frequency is 60 Hz across North America and 50 Hz
in Europe, Oceania, Asia (Korea and parts of Japan are notable exceptions) and
parts of Africa.
The electricity flows to a distribution yard where transformers step the voltage
up to 115, 230, 500 or 765 kV AC as needed for transmission to its destination.
It is a device in which steam condenses and heat released by steam is absorbed by
water. It serves the following purposes:
It maintains a very low back pressure on the exhaust side of the piston of the
steam engine or turbine. The steam expands to a greater extend resulting in
increase in available heat energy.
It supplies to the boiler pure and hot feed water.
Jet Condensers :- The exhaust steam and water come in direct contact with each
other and temperature of the condensate is same as that of cooling water leaving
the condenser. These condensers are of three types:
1. Parallel Flow Type
2. Counter Flow Type
3. Ejector Type.
Surface Condensers:- The exhaust steam and water do not come in to direct
contact. The steam passes over the outer surface of tubes through which a supply
of cooling water is maintained. They may b single pass or double pass. Surface
condensers are classified on the direction of flow of condensate .
1. Down Flow Type
2. Central Flow Type
3. Inverted Flow Type
4. Regenerative Type
5. Evaporative Type
The condenser transfer the latent heat of the exhaust steam to water exposed to the
atmosphere. This water is called circulating or cooling water . The requirement of
cooling water is large as 5-8kg/kWh. This means a 1000 MW station will require
about 100 thousand tonnes of circulating water per day even with the use og
The cooling water supply is made by following types:
1.River or sea
In SPP the hot water from condenser is cooled in cooling tower so that it can be
reused in condenser for condensation of steam. In cooling tower water is made to
trickle down drop by drop so that it comes in contact with the air moving in the
opposite direction. As a result of this some water is evaporated and is taken away
with air. In evaporation the heat is taken away from the bulk of water, which is
Classification of cooling tower
Natural Draught Cooling Tower :- The hot water from the condensers is
pumped to the nozzle situated near the bottom. The air enters the Cooling Tower
from the air openings provided near the base, rises upward and takes up the heat
of the falling water.
Mechanical Draught Cooling Tower :- In these towers the draught of air for
cooling the tower is produced mechanically by means of propeller fans. They are
of two types-
1. Forced Draught
2. Induced Draught
Reciprocating steam engines have been used for mechanical power sources since
the 18th Century, with notable improvements being made by James Watt.
The very first commercial central electrical generating stations in the Pearl Street
Station, New York and the Holborn Viaduct power station, London, in 1882, also
used reciprocating steam engines. The development of the steam turbine allowed
larger and more efficient central generating stations to be built.
By 1892 it was considered as an alternative to reciprocating engines. Turbines
offered higher speeds, more compact machinery, and stable speed regulation
allowing for parallel synchronous operation of generators on a common bus.
Turbines entirely replaced reciprocating engines in large central stations after
about 1905. The largest reciprocating engine-generator sets ever built were
completed in 1901 for the Manhattan Elevated Railway. Each of seventeen units
weighed about 500 tons and was rated 6000 kilowatts; a contemporary turbine-set
of similar rating would have weighed about 20% as much.
Name Location Units Capacity (MW)
Madhya Pradesh 6X210, 4X500 3260
Orissa 6 X 500 3000
Maharashtra 10 X 270 2700
Andhra Pradesh 3X200, 4X500 2600
Maharashtra 4 X 210, 3X500 2340
Sr. No. Name of Plant Location Capacity (MW)
1. Sangam power Generation
Allahabad, U.P 2 X 660
2. M.P Power Generation Co
Satpura, M.P 2 X 250
3. V. S Lignite Power Ltd. Bikaner,
1 X 35
4. Hindalco Industries Ltd. U.P 999.7
5. Durgapur Projects Ltd. West Bengal 2 X 250
NTPC Limited (formerly National Thermal Power Corporation) is the
largest state-owned power generating company in India. Forbes Global 2000 for
2010 ranked it 341th in the world.
It is an Indian public sector company listed on the Bombay Stock
Exchange although at present the Government of India holds 84.5% (after
divestment the stake by Indian government on 19th October, 2009) of its equity.
With a current generating capacity of 34894 MW, NTPC has embarked on plans
to become a 75,000 MW company by 2017.
It was founded on November 7, 1975.
The total installed capacity of the company is 34894 MW (including JVs) with
15 coal based and 7 gas based stations, located across the country.
Although the company has 18.79% of the total national capacity it contributes
28.60% of total power generation due to its focus on high efficiency.
Rapid response to changing load.
A portion of steam generated can be used as a process steam in different
Can be located conveniently near the load center, hence transmission cost are
Steam engines and turbines can work under 25% of overload continuously.
Fuel used is cheaper and easily available.
Less space required in comparison to HPP.
Cheap Production and cheap initial cost as compare to diesel power station.
Maintenance and operating costs are high.
The cost of plant increases with increase in temperature and pressure.
Long time required for erection and putting into action.
A large quantity of water is required.
Great difficulty experienced in coal handling.
The plant efficiency decreases rapidly below 75% load.
Presence of troubles due to smoke and heat in the plant.
Sector Hydro Thermal Nuclear Total
Central 3455 7574 880 4909
State 5814.7 4933 - 10747.7
Private 550 17038.5 - 17588.5
Total 9819.7 29545.5 880 40245.2
Continuous deterioration in performance of thermal power stations had been
observed during early 80's. Therefore, Renovation and Modernisation
Schemes(R&M Schemes) were drawn and executed for improving the
performance of existing thermal power stations.
Pollution control measures in these power stations being a capital-intensive
activity, it accounted for major portion-around 40% of Rs. 12 Billion kept
for R&M schemes under phase-I.
During phase-I, 163 units of 34 thermal power stations were covered. As a
result of R&M schemes these achieved 10,000 million units of additional
generation per annum against the target of 7000 million units.
Encouraged by the results achieved, R&M phase-II programme is presently
under progress. Total estimated cost of these works is Rs. 24 Billion.
Most of the Electricity Boards or other generating agencies are facing
financial constraints to carry out R&M activities. Therefore, this area
has to be taken on priority to arrange financial assistance.
Several organizations have carried out Energy audits of thermal power
plants with a view to suggest measures to improve their operational
efficiency and to identify areas having wasteful use of energy.
Steps have been suggested to reduce energy losses and their
implementation is being monitored vigorously.
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