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UNIT-1
THERMAL POWER STATIONS
Introduction
➢ Thermal energy is the major source of power generation in India
...
India has large deposit of coal
(about 170 billion tonnes), 5th largest in world
...

In Steam power plants, the heat of combustion of fossil fuels is utilized by the boilers
to raise steam at high pressure and temperature
...

Steam turbines or steam engines used in steam power plants not only act as prime
movers but also as drives for auxiliary equipment, such as pumps, stokers fans etc
...

The steam for process purposes is extracted from a certain section of turbine and the
remaining steam is allowed to expand in the turbine
...

Thermal stations can be private industrial plants and central station
...

▪

It requires less land as compared to hydro power plant
...
e
...


▪

The cost of generation is lesser than that of diesel power plants
...
This is one of
the causes of global warming
...


▪

Requires long time for errection and put into action
...


▪

Requirement of water in huge quantity
...


Selection of site for thermal power plant
•

Nearness to the load centre: The power plant should be as near as possible to the load
centre to the centre of load
...
This
factor is most important when Dc supply system is adopted
...


•

Water resources: For the construction and operating of power plant large volumes of
water are required for the following reasons
(i)

To raise the steam in boiler
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(iv)

For drinking purposes
...
Therefore
having enough water supplies in defined vicinity can be a factor in the selection of the site
...
Since the
government policy is to use the only low grade coal with 30 to 40 % ash content for power
generation purposes, the steam power plants should be located near the coal mines to avoid
the transport of coal & ash
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Eg: For 2000MW plant, the land requirement may be of the order of 200-250 acres
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Land should be available for future extension
...
g near railway station
...


•

Ash Disposal: Ash is the main waste product of the steam power plant and with low
grade coal, it may be 3
...
It may be purchased by building contractors, or it can be used
for brick making near the plant site
...
In case of site located near a river,sea or lake ash can be
dumped into it
...
Such a pollution
due to smoke is dangerous for the people living around the area
...


Major Components of a Thermal Power Plant
•

Coal Handling Plant

•

Pulverizing Plant

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Draft or Draught fan

•

Boiler

•

Ash Handling Plant

•

Turbine and Generator

•

Condenser

•

Cooling Tower And Ponds

•

Feed Water Heater

•

Economiser

•

Super heater and Reheater

•

Air pre heater

•

Alternator with Exciter

•

Protection and control equipment

•

Instrumentation

BOILER
❖ A boiler (or steam generator) is a closed vessel in which water, under pressure , is
converted into steam
...
e
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❖ Major types of boilers are: (i) fire tube boiler and (ii) water tube boiler
❖ Generally water tube boilers are used for electric power stations
...


•

Depending on whether the tube is vertical or horizontal the fire tube boiler is divided
into two types
1
...
Horizontal tube boiler

•

A fire tube boiler is simple ,compact and rugged in construction
...


•

Water being more and circulation being poor they cannot meet quickly to changes in steam
demand
...
5 kg/cm2 with a capacity of 15,000kg of
steam per hour
...


•

In the event of a sudden and major tube failure
...


•

Fire tube boilers use is therefore limited to low cost small size and low pressure plants
...


•

Water tube boiler are classified as
1
...
Horizontal tube boiler
3
...


•

For Central steam power plants large capacity of water tube boilers are used
...


•

The boiler drum contains both steam and water, the former being trapped from the top of
the drum where the highest concentration of dry steam exists
...


•

For this purpose the heat of the combustion gases from the furnace is utilized
...
The additional heat provide more energy to the turbine hence power out put


•

•

is more
...
However ,convention
superheaters are more commonly used
...
The function of the reaheater is
to superheat the partly expanded steam from the turbine, this ensure that the steam remain



dry through the last stage of the turbine
...



Feed Water Heaters: These heaters are used to heat the feed water by means of blend steam
before it is supplied to the boiler
...

•

Feed Water heating improve overall efficiency
...


•

Thermal stresses due to cold water entering the boiler drum are avoided
...


•

Some other impurities carried by steam and condensate, due to corrosion in boiler
and condenser, are precipitated outside the boiler
...
An increase of about 20% in boiler efficiency is achieved by providing both


•

economizer and air pre-heaters
...
The feed water from the high pressure heaters enters the
economizer and picks up heat from the flue gases after the low temperature super



heater
...


•

For pressure of 70 Kg/cm2 or more economizer becomes a necessity
...


•

Feed water flows through the tubes and the flue gases outside the tubes across them
...


•

The temperature of the feed water entering the economizer should be high enough so
that moister from the flue gases does not condense on the economizer tubes
...


•

Air preheaters may be of following types:
➢ Plate type
➢ Tubular type
➢ Regenerative type

•

Cooling of flue gases by 200increase the efficiency of the plant by 1%
...


•

Air preheaters should have high thermal efficiency, reliability of operation, less
maintance charges, should occupy small space, should be reasonable in initial cost and
should be accessible
...


Figure : Air Preheater

STEAM TURBINES
•
•
•

Steam entering from a small opening attains a very high velocity
...

The difference in initial and final heat content represent the heat energy to be converted to
kinetic energy
...
The moving blades are
mounted on the shaft and fixed blades are fixed to the casing of the turbine
...
The P
...
E
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➢ The direction of steam flow changes without changing its pressure
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Reaction Turbine:
➢ Reaction turbine have no nozzles
...
The moving blades are mounted on shaft, while fixed blades are fixed in
casing of turbine
...

➢ As steam passes over moving blades, the steam expands and imparts energy,resulting
in reduction in pressure and velocity of steam
...
Generally
multistage turbines are used
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P steam after doing work in the H
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P stage
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Compounding of steam turbines:
Single stage turbines are of low efficiency
...


Figure : Steam Turbines

CONDENSERS
The function of the condenser is to condense the steam exiting the turbine
...

Two types of condensers are used
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Steam and water do not mix
...
cooling water temperature at outlet
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Condensate recovered is fed back to the boiler
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Low initial cost

High initial cost
...
Condensate is not wasted so pumping power is
less
...

➢ In particular, dissolved oxygen in boiler feedwaters will cause serious corrosion damage
in steam systems by attaching to the walls of metal piping and other metallic equipment
and forming oxides (rust)
...
the tray-type an
2
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➢ The spray-type consists only of a horizontal (or vertical) cylindrical vessel which serves
as both the deaeration section and the boiler feedwater storage tank
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•

Water is led into the plants by means of circulating water pumps and after passing
through the condenser is discharged back into the river
...


•

In such cases ponds and cooling towers are used where the water loses heat to the
atmosphere
...


•

the basic idea of an ESP:
❖ Charging
❖ collecting
...


•

we impart a negative charge to all the particles in a gas stream in ESP
...


•

The negatively charged particle would migrate to the grounded collection plate and
be captured
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The dust layer
would accumulate until we removed it
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❖ tubular type ESP
❖ plate type ESP

•

The method of charging
❖ single-stage ESP
❖ two-stage ESP

•

The temperature of operation
❖ cold-side ESP
❖ hot-side ESP

•

The method of particle removal from collection surfaces
❖ wet ESP
❖ Dry ESP



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