steam power plant
Electrical Engineering Department.
BABA HIRA SINGH BHATTAL INSTITUTE OF
ENGINEERING AND TECHNOLOGY LEHRAGAGA-
148031 DISTT.SANGRUR (Pb.)
Essentials of Steam Power Plant Equipment
A steam power plant must have following equipment :
(a) A furnace to burn the fuel.
(b) Steam generator or boiler containing water.
Heat generated in the furnace is utilized to
convert water into steam.
(c) Main power unit such as an engine or
turbine to use the heat energy of steam and
(d) Piping system to convey steam and water.
The flow sheet of a thermal power plant
consists of the following four main circuits :
(a) Feed water and steam flow circuit.
(b) Coal and ash circuit.
(c) Air and gas circuit.
(d) Cooling water circuit.
A steam power plant using steam as working
substance works basically on Rankine cycle.
Steam is generated in a boiler, expanded in the
prime mover and condensed in the condenser
and fed into the boiler again.
The different types of components used in steam
(a) High pressure boiler.
(b) Prime mover .
(c) Condensers and cooling towers .
(d) Coal handling system .
(e) Ash and dust handling system .
(f) Draught system .
(g) Feed water purification plant .
(h) Pumping system .
(i) Air preheater, economizer, super heater, feed
Types of steam Generators
Horizontal vertical or inclined.
Fire tube or water tube.
Externally fired or internally fired.
Forced circulation and natural circulation.
High pressure or low pressure boiler.
The partial pressure pressure of each
constituent is that pressure which the gas
would exert if it occupied alone that volume
occupied by the mixture at the same
Factors that should be considered while
selecting the boiler
Working pressure and quality of steam
Steam generation rate.
Floor area available.
The portable load factor.
Properties of good steam generators
It should be absolutely reliable.
It should occupy minimum space.
It should be light in weight.
Capable of quick starting.
Erection of boiler should be simple.
Steam Power Plants are also Classified as;
Central stations; the electrical energy available from
these stations is meant for sale to the consumers who
wish to purchase it.
Industrial/ captive power stations; this type of
power station is run by the manufacturing company for
its own use and its output is not available for general
Jet condenser; low manufacturing cost. Low
upkeeps, requires small floor space and more
auxiliary power required.
surface condenser; high manufacturing
cost. high upkeeps, requires large floor space and
less auxiliary power required.
Feed water heating improves overall plant
Quantity of steam produced by the boiler is
Thermal stress due to cold water entering the
boiler drum are avoided.
Chance of boiler corrosion are decrease.
Dust collectors are Classified as;
Mechanical dust collectors;
Spray type, packed type and impingement type.
(b) Dry type.
Gravitational separators, cyclone separators,
electrical dust collectors;
Rod type and plate type.
DIFFERENT TYPES OF BOILERS USED IN
STEAM POWER PLANTS
horizontal, vertical or inclined.
fire tube and water tube .
Externally or internally fired.
Forced or natural circulation.
High pressure or low pressure.
Stationary or portable.
Single-tube and multi-tube.
Steam Turbine Power Plant
(Boiler / Furnace)
Schematic arrangement of equipment of a
steam power station.
Coal received in coal storage yard of power
station is transferred in the furnace by coal
handling unit. Heat produced due to burning of
coal is utilized in converting water contained in
boiler drum into steam at suitable pressure and
temperature. The steam generated is passed
through the superheater.
Superheated steam then flows through the
turbine. After doing work in the turbine the
pressure of steam is reduced. Steam leaving
the turbine passes through the condenser
which is maintained the low pressure of
steam at the exhaust of turbine.
Steam pressure in the condenser depends upon
flow rate and temperature of cooling water and
on effectiveness of air removal equipment.
Water circulating through the condenser may be
taken from the various sources such as river, lake
or sea. If sufficient quantity of water is not
available the hot water coming out of the
condenser may be cooled in cooling towers and
circulated again through the condenser.
Bled steam taken from the turbine at suitable
extraction points is sent to low pressure and high
pressure water heaters.
Air taken from the atmosphere is first
passed through the air pre-heater, where it is
heated by flue gases. The hot air then passes
through the furnace.
The flue gases after passing over boiler and
superheater tubes, flow through the dust
collector and then through economiser, air
pre-heater and finally they are exhausted to
the atmosphere through the chimney.
Disadvantage of steam power plant
Maintenance and operating cost are high.
Long time required for erection and putting into
Large quantity of water is required.
Great difficulty experienced in coal handling .
Efficiency decreases rapidly below about 75
The superheater consists of a superheater
header and superheater elements. Steam from
the main steam pipe arrives at the saturated
steam chamber of the superheater header and is
fed into the superheater elements.
Superheated steam arrives back at the
superheated steam chamber of the superheater
header and is fed into the steam pipe to the
cylinders. Superheated steam is more expansive.
Advantages of superheated steam
Capacity to do work is increased without
increasing its pressure.
High temperature of super heated steam
results in an increase in thermal efficiency.
Heat losses due to condensation of stem on
cylinder walls are avoided to a great extent.
Does not produce corrosion effect on
It is a heating device.
It is used to raise temp of steam at const
It removes even last traces of moisture.
The function of reheater is similar to the
superheater in that it serves to elevate the
steam temperature. Primary steam is supplied
to the high pressure turbine.
After passing through the high pressure
turbine, the steam is returned to the steam
generator for reheating (in a reheater) after
which it is sent to the low pressure turbine. A
second reheat cycle may also be provided.
The fuel used in thermal power plants causes
soot and this is deposited on the boiler tubes,
economizer tubes, air pre heaters, etc.
This drastically reduces the amount of heat
transfer of the heat exchangers. Soot blowers
control the formation of soot and reduce its
The types of soot blowers are fixed type, which
may be further classified into lane type and
mass type depending upon the type of spray and
The use of a condenser in a power plant is to
improve the efficiency of the power plant by
decreasing the exhaust pressure of the steam
Another advantage of the condenser is that the
steam condensed may be recovered to provide a
source of good pure feed water to the boiler and
reduce the water softening capacity to a
considerable extent. A condenser is one of the
essential components of a power plant.
Functions of Condensers
The main purposes of the condenser are to
condense the exhaust steam from the turbine
for reuse in the cycle and to maximize turbine
efficiency by maintaining proper vacuum.
As the operating pressure of the condenser is
lowered (vacuum is increased), the enthalpy
drop of the expanding steam in the turbine will
also increase. This will increase the amount of
available work from the turbine (electrical
The importance of the cooling tower is felt
when the cooling water from the condenser has
to be cooled.
The cooling water after condensing the steam
becomes hot and it has to be cooled as it
belongs to a closed system. The Cooling towers
do the job of decreasing the temperature of the
cooling water after condensing the steam in the
Cooling Towers have one function :
Remove heat from the water discharged
from the condenser so that the water can be
discharged to the river or re-circulated and
A cooling tower extracts heat from water by
evaporation. In an evaporative cooling
tower, a small portion of the water being
cooled is allowed to evaporate into a moving
air stream to provide significant cooling to
the rest of that water stream.
Cooling Towers are commonly used to
provide lower than ambient water
temperatures and are more cost effective and
energy efficient than most other alternatives.
The smallest cooling towers are structured for
only a few litres of water per minute while the
largest cooling towers may handle upwards of
thousands of litres per minute. The pipes are
obviously much larger to accommodate this
much water in the larger towers and can
range up to 12 inches in diameter.
Advantages of regenerative cycle
Improve overall plant efficiency.
Protect boiler corrosion.
Avoid the thermal stresses due to cold water
entering the boiler .
Increased the quantity of steam produced by
Function of economizer
To extract a part of heat from the fuel gas
coming out of the boiler.
To use heat for heating feed water to the
To increases the efficiency of boiler.
The economizer is a feed water heater,
deriving heat from the flue gases. The
justifiable cost of the economizer depends on
the total gain in efficiency. In turn this
depends on the flue gas temperature leaving
the boiler and the feed water inlet
The flue gases coming out of the economizer
is used to preheat the air before supplying it
to the combustion chamber. An increase in
air temperature of 20 degrees can be
achieved by this method. The pre heated air
is used for combustion and also to dry the
crushed coal before pulverizing.
Advantages of mechanical handling
Less labour required.
Operation is easy and smooth.
Economical for large capacity plant.
Losses in transport are minimised.
Steam Turbine Power Plant
R. Shanthini 15
According to the
2nd Law of Thermodynamics
when heat is converted into work,
part of the heat energy must be wasted
Diesel engine 10 - 30 7 – 22
Gas Turbine 50 - 100 36 – 78
Steam Turbine 200 - 800 120 – 560
Combined (ST & GT) 300 - 600 150 – 380
Nuclear (BWR & PWR) 500 - 1100 330 – 760
How can We Increase the Efficiency of the
Rankine cycle efficiency can be increased by
increasing average temperature at which
heat is transferred to the working fluid in
the boiler or decreasing the average
temperature at which heat is rejected from
the working fluid in the condenser. That is,
the average fluid temperature should be as
high as possible during heat addition and as
low as possible during heat rejection.
The three ways by which efficiency of the
Rankine cycle can be increased are :
(a) Lowering the condenser pressure.
(b) Superheating the steam to high
(c) Increasing the boiler pressure.
• The thermal efficiency of the Rankine cycle
can be increased by increasing the average
temperature at which heat is added to the
working fluid and/or by decreasing the
average temperature at which heat is
rejected to the cooling medium. The average
temperature during heat rejection can be
decreased by lowering the turbine exit
Consequently, the condenser pressure of most
vapor power plants is well below the
atmospheric pressure. The average
temperature during heat addition can be
increased by raising the boiler pressure or by
superheating the fluid to high temperatures.
There is a limit to the degree of superheating,
however, since the fluid temperature is not
allowed to exceed a metallurgically safe value.
• Superheating has the added advantage of
decreasing the moisture content of the steam at
the turbine exit. Lowering the exhaust pressure
or raising the boiler pressure, however, increases
the moisture content. To take advantage of the
improved efficiencies at higher boiler pressures
and lower condenser pressures, steam is usually
reheated after expanding partially in the high-pressure
This is done by extracting the steam after
partial extraction in the high-pressure
turbine, sending it back to the boiler where
it is reheated at constant pressure, and
returning it to the low-pressure turbine for
complete expansion to the condenser
The average temperature during the reheat
process, and thus the thermal efficiency of
the cycle, can be increased by increasing the
number of expansion and reheat stages. As
the number of stages is increased, the
expansion and reheat processes approach an
isothermal process at maximum
temperature. Reheating also decreases the
moisture content at the turbine exit.
• Another way of increasing the thermal
efficiency of the Rankine cycle is by
regeneration. During a regeneration process,
liquid water (feed water) leaving the pump
is heated by some steam bled off the turbine
at some intermediate pressure in devices
called feed water heaters.
The two streams are mixed in open feed
water heaters, and the mixture leaves
as a saturated liquid at the heater
pressure. In closed feed water heaters,
heat is transferred from the steam to
the feed water without mixing.
• The production of more than one useful
form of energy (such as process heat and
electric power) from the same energy source
is called cogeneration. Cogeneration plants
produce electric power while meeting the
process heat requirements of certain
This way, more of the energy
transferred to the fluid in the boiler
is utilized for a useful purpose. The
faction of energy that is used for
either process heat or power
generation is called the utilization
factor of the cogeneration plant.
• The overall thermal efficiency of a power
plant can be increased by using binary
cycles or combined cycles. A binary cycle
is composed of two separate cycles, one at
high temperatures (topping cycle) and the
other at relatively low temperatures.
The most common combined cycle is the gas-steam
combined cycle where a gas-turbine
cycle operates at the high-temperature range
and a steam-turbine cycle at the low-temperature
range. Steam is heated by the
high-temperature exhaust gases leaving the
gas turbine. Combined cycles have a higher
thermal efficiency than the steam- or gas-turbine
cycles operating alone.
Selection of plant site
The selection of plant site for thermal power
plant compared with hydro-power plant is
more difficult as it involves number of
factors to be considered for its economic
A few important factors to be considered for
the selection of thermal power plants.
Selection of plant site
AVAILABILITY OF COAL.
Huge quantity of coal is required for
large thermal plants.
ASH DISPOSAL FACILITIES.
NATURE OF LAND.
AVAILABILITY OF WATER.
Selection of plant site
AVAILABILITY OF LABOUR.
SIZE OF THE PLANT.
Nowadays, the environment protection has
become a crucial problem and the
authorities are requested to set increasingly
more stringent limits , one of which is the
emissions from the industrial plants of solid
particulate and other gaseous pollutants.
ABOUT ELECTROSTATIC PRECIPITATOR
What is ESP
Electrostatic precipitator (ESP) is a widely
used device in so many different domains
to remove the pollutant particulates,
especially in industrial plants.
HOW ESP WORKS
Main process of ESP
Generally, the processes of
electrostatic precipitator are known as
three main stages: particle charging,
transport and collection.
PROCESS OF Particle charging
Particle charging is the first and
foremost beginning in processes.
As the voltage applied on precipitator
reach threshold value, the space inside
divided into ionization region and drift
The electric field magnitude around the
negative electrode is so strong that the
electrons escape from molecule.
Under the influence of electric field, the positive
ions move towards the corona, while the
negative ions and electrons towards the
In the moving way, under the influence of
electric field, negative ions cohere and charge the
particles, make the particles be forced towards
As soon as the particles reach the plate,
they will be neutralized and packed by
the succeeded ones subsequently. The
continuous process happens, as a result,
particles are collected on the collecting
What is a Boiler?
• Vessel that heats water to become hot water
• At atmospheric pressure water volume
increases 1,600 times
• Hot water or steam used to transfer heat to a
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.
A boiler should fulfill the following requirements
(a)Safety : The boiler should be safe under
(b) Accessibility : The various parts of the
boiler should be accessible for repair and
(c) Capacity : The boiler should be capable of
supplying steam according to the requirements.
(d) Efficiency : To permit efficient operation, the boiler
should be able to absorb a maximum amount of heat
produced due to burning of fuel in the furnace.
(e) It should be simple in construction and its
maintenance cost should be low.
(f) Its initial cost should be low.
(g) The boiler should have no joints exposed to flames.
(h) The boiler should be capable of quick starting and
EXHAUST GAS VENT
Figure: Schematic overview of a boiler room
Types of Boilers
What Type of Boilers Are There?
1. Fire Tube Boiler
2. Water Tube Boiler
3. Packaged Boiler
4. Fluidized Bed (FBC) Boiler
5. Stoker Fired Boiler
6. Pulverized Fuel Boiler
7. Waste Heat Boiler
8. Thermic Fluid Heater (not a boiler!)
The boilers can be classified according to the
According to flow of water and hot
(a) Water tube
(b) Fire tube.
Type of Boilers
1. Fire Tube Boiler
• Relatively small steam
capacities (12,000 kg/hour)
• Low to medium steam
pressures (18 kg/cm2)
• Operates with oil, gas or solid
Type of Boilers
2. Water Tube Boiler
• Used for high steam demand
and pressure requirements
• Capacity range of 4,500 –
• Combustion efficiency
enhanced by induced draft
• Lower tolerance for water
quality and needs water
3. Packaged Boiler
• Comes in complete package
• High heat transfer
• Faster evaporation
• Good convective heat
• Good combustion efficiency
• High thermal efficiency
• Classified based on number of
Working of power plant
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 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
(371 °C) and 3,200 psi
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 lower inlet water wall headers.
From the inlet headers the water rises
through the water walls and is eventually
turned into steam due to the heat being
generated by the burners located on the
front and rear water walls (typically). As
the water is turned into steam/vapor in the
water walls, the steam/vapor once again
enters the steam drum.
The steam/vapor is passed through a series of
steam and water separators and then dryers
inside 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.
Fossil fuel power plants can have a super
heater and/or re-heater section in the steam
generating furnace. In a fossil fuel plant,
after the steam is conditioned by the drying
equipment inside the steam drum, it is piped
from the upper drum area into tubes inside
an area of the furnace known as the super
which has an elaborate set up of tubing where
the steam vapor picks up more energy from
hot flue gases outside the tubing and its
temperature is now superheated above the
saturation temperature. The superheated
steam is then piped through the main steam
lines to the valves before the high pressure
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
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
Since the condenser temperature can almost
always be kept significantly below 100 °C
where the vapor pressure of water is much
less than atmospheric pressure, the condenser
generally works under vacuum. Thus leaks
of non-condensible air into the closed loop
must be prevented.
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 condenser tubes are made of brass
or stainless steel to resist corrosion
from either side. Nevertheless they may
become internally fouled during operation
by bacteria or algae in the cooling water or
by mineral scaling, all of which inhibit heat
transfer and reduce thermodynamic
Many plants include an automatic
cleaning system that circulates sponge
rubber balls through the tubes to scrub
them clean without the need to take the
Power plant furnaces may have a re heater
section containing tubes heated by hot flue
gases outside the tubes. Exhaust steam from
the high pressure turbine is rerouted to go
inside the re heater tubes to pickup more
energy to go drive intermediate or lower
Main pollutants from a power system
Non –toxic dust
Soot (fly ash)
Pollution can be define as the contamination of soil,
air and water with undesirable amount of material and
Acid rain; the rain which contain acid as its
constituents, brings all the acid down from high
above the environment.
Contaminant; it is the another name of
pollution. It is undesirable substances which
may be physical, chemical or biological.
Pollutant; these are undesirable substances
present in the environment these can be NO2,
SO2, CO2,smoke,salt, bacteria.
Bad effects of thermal pollution
Lot of heat is injected into biosphere from
thermal power plant, through exhaust gases
and waste water. The major problem is the
effect of discharge of large quantity of
heated wasted water into natural water
basins. Hot water raises the temperature
and disturbs the natural ecological balance
Advantages of combined operation of plants
Greater reliability of supply to the consumers.
Avoid complete shut down.
The overall cost of energy per unit of an
interconnected system is less.
There is a more effective use of transmission
Less capital investment required.
Less expenses on supervision, operation and
Due to limited generating capacity diesel
power stations is not suitable for base load
Nuclear power stations is not suitable for
peak load plants.
Incremental rate curve shows that as
output power increases, cost of plant