Thermal Power Plant Project Report

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Detailed Project report of thermal power plant

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1.1 Introduction
A thermal power plant is an industrial facility for the generation of electric power. It
is also termed as energy centre because it more accurately describes what the plants do,
which is the conversion of other forms of energy like chemical energy, heat energy into
electrical energy.
Energy exists in various forms i.e. mechanical, thermal, electrical etc... One form of
energy can be converted into other by the use of suitable arrangements. Out of all these forms
of energy, electrical energy is preferred due to the following advantages:





Can be easily transported from one place to another.
Losses in transport are minimum.
Can be easily subdivided.
Economical in use.
Easily converted into other forms of energy.

Power is primarily associated with mechanical work and electrical energy. Therefore,
power can be defined as the rate of flow of energy and can state that a power plant is a unit
for production and delivery of a flow of mechanical and electrical energy. In common usages,
a machine or assemblage of equipments that produce and delivers a flow of mechanical or
electrical energy is power plant.
A thermal power station is a power plant in which the prime mover is steam driven.
Water is heated, converted into steam and spins a steam turbine which drives an electrical
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 Rankine Cycle. The greatest variation in the
design of thermal power station is due to the different fossil fuel resources generally used to
heat the water. Certain thermal power plants are also designed to produce heat energy for
industrial purposes district heating or desalination of water, in addition to generating
electrical power. Globally, fossil fuelled thermal power plant produce a large part of manmade CO2 emission to the atmosphere, and efforts to reduce these are many, varied and
widespread.
Commercial electric utility power stations are most usually constructed on a very
large scale and designed for continuous operation. Electric power plants typically use three
phase or individual phase electric generators to produce Alternating Current (AC) electric
power at a frequency of 50Hz (hertz, which is an AC sine wave per second).

1.2 Concept of Thermal Power Station
Thermal power plant converts energy rich fuel into electricity and heat. Possible fuels
include coal, natural gas, petroleum products, agricultural waste and domestic waste. Other
sources of fuel include landfill gas and bio gases. In some plants renewal fuels such as biogas
are co-fired with coal.

1

Coal and lignite accounted for about 57% of India’s installed capacity. However,
wind energy depends upon wind speed, and hydropower energy on water level, thermal
power plant accounts for over 65% of India’s generated electricity, India’s electricity sector
consumes about 80% of the coal product in the county.
India expects that its projected rapid growth in electricity generation over the next
couple of decades is expected to be largely met by thermal power plant.

Fig.1.1 Total Installed Power Generation Capacity in India

1.3 History of Thermal Power Plant
The initially developed reciprocating steam engine has been used to produce
mechanical power since the 18th century, with notable improvements being made by James
Watt. When the first commercially developed central electrical power stations were
established in 1882 at Pearl Street in New York and Holborn viaduct power station in
London, reciprocating steam engines were used. The development of steam turbine in 1884
provided large and more efficient machine designs for central generating stations. By 1892
the turbine was considered a better 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. After about 1905, turbines entirely
replaced reciprocating engines in large central power stations.
The largest reciprocating steam engine-generator sets ever built were completed in
1901 for the Manhattan Elevated Railway. Each of seventeen units weighed about 500tonnes
and was rated 6000kilowatts; a contemporary turbine set of similar rating would have
weighed about 20% as much.
2

2.1 Introduction
A steam power plant converts the chemical energy of the fossil fuels (Coal, Oil and
Gas) into mechanical/electrical energy. This is achieved by raising the steam in the boilers,
expanding it through the turbines and coupling the turbines to the generator which convert
mechanical energy to electrical energy.

Fig.2.1 Production of Electricity by Steam Power Plant.
The following two purposes can be served by a steam power plant:



To produce electric power.
To produce steam for industrial purposes besides producing electrical power.

The steam may be used for varying industries such as textiles, food manufacturing,
paper mills, sugar mills and refineries etc.

2.2 General Layout of Thermal Power Plant
The general layout of a thermal power plant consists of mainly four circuits. The four
main circuits are:
1.
2.
3.
4.

Coal and ash circuit.
Air and gas circuit.
Feed water and steam flow circuit.
Cooling water circuit.

3

Fig.2.2 Layout of Thermal Power Plant.
A thermal power station using steam as working fluid basically works on the Rankine
cycle. Steam is generated in a boiler, expanded in the prime mover and condensed in
condenser and fed into the boiler again with the help of pump. However, in actual practice,
there are numerous modifications and improvements in the cycle with the aim of affecting
heat economy and to increase the thermal efficiency of the plant.
1. Coal and ash circuit. In this circuit, the coal from the storage is fed to the boiler
through coal handling equipment for the generation of steam. Ash produced due to
combustion of coal is removed to ash storage through ash-handling system.
2. Air and gas circuit. Air is supplied to the combustion chamber of the boiler either
through F.D or I.D fan or by using both. The dust from the air is removed before
supplying to the combustion chamber. The exhaust gases carrying sufficient quantity
of heat and ash are passed through the air-heater where the exhaust heat of the gases is
given to the air and then it is passed through the dust collectors where most of the dust
is removed before exhausting the gases to the atmosphere through the chimney.
3. Feed water and steam circuit. The steam generated in the boiler is fed to the steam
prime mover to develop the power. The steam coming out of prime mover is
condensed in the condenser and then fed to the boiler with the help of pump. The
condensate is heated in the feed-heaters using the steam tapped from different points
of the turbine. The feed heaters may be of mixed type or indirect heating type. Some
4

of the steam and water is lost passing through different components of the system;
therefore, feed water is supplied from external source to compensate this loss. The
feed water supplied from external source is passed through the purifying plant to
reduce the dissolved salts to an acceptable level. The purification is necessary to avoid
the scaling of the boiler tubes.
4. Cooling water circuit. The quantity of cooling water required to condensate the
steam is considerably large and it is taken either from lake, river or sea. The cooling
water is taken from the upper side of the river; it is passed through the condenser and
discharged to the lower side of the river. Such system of cooling water supply is
possible if adequate cooling water is available throughout the year. This system is
known as open system. When adequate water is not available, then the water coming
out from the condenser is either cooled in the cooling pond or cooling tower. The
cooling is affected by partly evaporating the water. This evaporative loss is nearly 2 to
5% of the cooling water circulated in the system. To compensate the evaporative loss,
the water from the river is continuously supplied. When the cooling water coming out
of the condenser is cooled again and supplied to the condenser, then the system is
known as closed system. When the water coming out of the condenser is discharged
to river downward side directly, the system is known as open system.

2.3 Working Principle of Thermal Power Plant
A thermal power station works on the basic principle that heat liberated by burning
fuel is converted into mechanical work by means of a suitable working fluid. The mechanical
work is converted into electric energy by the help of generators.
Steam is generated in the boiler of the thermal power plant using the heat of the fuel
burned in the combustion chamber. The steam generated is passed through steam turbine
where part of its thermal energy is converted into mechanical energy which is further used for
generating electric power. The steam coming out of the steam-turbine is condensed in the
condenser and the condensate is supplied back to the boiler with the help of the feed pump
and the cycle is repeated.
The function of the boiler is to generate the steam. The function of the condenser is to
condensate the steam coming out of steam turbine at low pressure. The function of the steam
turbine is to convert part of heat energy of steam into mechanical energy. The function of
pump is to raise the pressure of the condensate from the condenser pressure (0.015 bars) to
boiler pressure (8 bars). The other components like economiser, superheater are used in the
primary circuit to increase the overall efficiency of the thermal power plant.

5

Fig.2.3 Rankine Cycle.
The working fluid in a Rankine cycle follows a closed loop and is reused constantly.
The water vapour with condensed droplets often seen billowing from power stations is
created by the cooling systems (not directly from the closed-loop Rankine power cycle) and
represents the means for (low temperature) waste heat to exit the system, allowing for the
addition of (higher temperature) heat that can then be converted to useful work. This 'exhaust'
heat is represented by the "Qout" flowing out of the lower side of the cycle. By condensing the
working steam vapour to a liquid the pressure at the turbine outlet is lowered and the energy
required by the feed pump consumes only 1% to 3% of the turbine output power and these
factors contribute to a higher efficiency for the cycle.

Fig.2.4 T-S Diagram of a Rankine Cycle.
6

The different processes of the Rankine cycle are described below:
1. The point‘d’ represents the water at condenser pressure p2 and corresponding
saturation temperature T2. The process ‘de’ represents the adiabatic compression of
water by the pump from condenser pressure to boiler pressure. There is slight rise in
temperature of water during the compression process.
2. During the process ‘ea’ and ‘ab’, heat is supplied by the boiler to the water to convert
into steam. The process ‘ea’ represents the supply of heat at constant pressure till the
saturation temperature of water is reached corresponding to boiler pressure. The
process ‘ab’ represents the addition of heat to the water at constant pressure till the
water completely converts into steam. The final condition of steam may be wet, dry
saturated or super heated depending upon the quantity of heat supplied by the boiler.
3. The process ‘bc’ represents the isentropic expansion of steam in the prime mover.
During this expansion process, external work is developed and the pressure of steam
falls from p1 to p2 and its temperature will be T2.
4. The process ‘cd’ represents the condensation of steam coming out from the prime
mover in the condenser. During the condensation of steam, the pressure is constant
and there is only change of phase from steam to water as the latent heat of steam is
carried by circulating water in the condenser. Again the process ‘de’ represents the
adiabatic compression of water by the pump from the pressure p2 to p1 and the cycle is
repeated.
Let
hb = enthalpy of steam per kg at point ‘b’
hc = enthalpy of steam per kg at point ‘c’
vw = specific volume of water at point 1 or 2 as there is much change in
specific volume during this process
hfe = enthalpy of water per kg at point ‘e’
hfa = enthalpy of water per kg at point ‘a’
hfd = enthalpy of water per kg at point ‘d’
Total heat supplied by the boiler per kg of steam generated
= hb - hfe
= hb – (hfd + wp)
Where wp is the work done by the pump per kg of water supplied.
Work done per kg of steam in the prime mover
= hb - hc
Work done by the pump per kg of water supplied to the boiler
wp = [vf2 (p1 – p2)] J/kg where p is in N/m2
where vf2 is the specific volume of saturated water at pressure p2.
7

Net work available per kg of water
= (hb – hc) – vfa



= (hb – hc) – wp
The Rankine efficiency of the cycle is given by
ɳr =
= [(hb – hc) – wp] / [hb – (hfd + wp)]
The pump work is always neglected for all practical purpose as it is very small
compared with other heat quantities.
ɳr = (h3-h4) / (h3-hf4) as wp is zero.

8

3.1 Selection of Fuel
1. Solid Fuel
It is not so simple to suggest the general trend of suitability of coals for steam
generation. The firing qualities of coal are very important when combustion equipment is
being considered.
The slower burning coal of low volatile content generated high-bed temperature and
therefore requires forced draught. The high fuel bed temperature may damage the grate unless
it is protected by adequate ash.
The fast burning coals of high volatile content require large combustion chambers for
the combustion of the volatiles. Such coals are more suitable for meeting sudden demand for
steam because the liberation of combustible volatile gas burns rapidly than the solid fuel on
the grate.
The most important factors which are considered for the selection of coal are the
sizing, caking, swelling properties and ash fusion temperature. The sulphur content in the
coal also carries considerable importance in most of the cases.
Electro-static preceptors work (ESP) better with high sulphur coal because of
improved resistivity of the flue gases. However, for other systems, a little SO2 can raise the
acid DPT dramatically and this raise can retard the corrosive effects on the equipments.
The larger size coal should be used when the draught is low and some moisture
percentage must be essentially maintained if the percentage of fineness of coal is high. The
use of anthracite coal as fuel requires forced draught furnaces incorporating means for
admitting steam to cool the fire bars and hardened clinker.
2. Liquid Fuel
The liquid fuel is used in thermal power plants to generate the steam instead of coal as
it offers many advantages over coal as listed below:
1) Excess air required for complete combustion is less as uniform mixing of fuel
and air is possible.
2) The storage and handling is much easier compared with coal.
3) The changes in load can be met easily and rapidly.
4) There is no problem of ash disposal.
5) The system is very clean.
6) The operational labour required is less and therefore overheads are
considerably less.
All the commercially used liquid fuels are furnished by petroleum and its by-products.
The petroleum or the crude oil consists of 83-87% carbon, 10.14% hydrogen and various
percentages of sulphur, nitrogen, oxygen and metallic derivatives.
9

The fuel oils used for industrial or domestic purposes are obtained by refining the
crude oil. The refining process separates and recombines the hydro-carbons into specialised
products like gasoline, fuel oil, etc. The distillation process is generally used to separate into
different groups of fuel. The typical fractions from light to heavy are naptha, gasoline,
kerosene and gas oil and the remainder is heavy fuel oil which is commonly used for steam
generation.
Constituent Carbon
Percentage 84

Hydrogen
Sulphur
Oxygen
22
2
1
Table.3.1 Fuel Oil Analysis.

Nitrogen
0.5

Moisture
3.5

The important properties of liquid fuel considered are specific heat, viscosity, pour
points, flash point, volatility, carbon residue, heating value, ash, moisture, sediments and
sulphur.
The pour point indicates the case of handling the oil flow through the lowest
temperature at which the oil will flow under specified conditions.
The viscosity is the measure of resistance to the oil flow through the pipes and
nozzles. This affects the cost of pumping the fuel. The viscosity of the fuel oil is generally
determined by standard viscometer.
The flash point of fuel oil decides the safety of fuel and it is also an indication of ease
of ignition.
The percentage of sulphur should be as minimum as possible as it results in the
corrosion of different parts in the plants and reduces the life.
For better combustion of fuel, the moisture and sediments must be as small as
possible. The ash content in the fuel oil is not very important in steam power plant.
As the fuel oil contains more percentage of hydrogen as compared to coal, therefore,
the moisture carried by the gas per kg on fuel burned is considerably more. This results in
overall lower combustion efficiency of the plant as compared to coal burning.
The use of oil for steam generation has no scope in India due to limited resources of
oil which are badly needed for industrial and transport purposes.
3. Gaseous Fuel
The gaseous fuel may be either natural or manufactured. The manufactured gas is
costly, therefore, only natural gas is used for steam generation.
The natural gas generally comes out of gas wells and petroleum wells. It contains
60.95% of methane with small amounts of other hydrocarbons such as ethane, napthene and
aromatic, CO2 and nitrogen. The natural gas is carried through pipes to distances which are
hundreds of kilometres from the source.

10

The natural gas is colourless, odourless and non-poisonous. Its C.V. lies between
25000kJ to 50,000 kJ/m3 according to percentage of methane in gas.
The various manufactured gases are coal gas, coke oven gas, blast furnace gas, water
gas and producer gas. The coal gas and coke oven gas are produced by carbonizing high
volatile bituminous coal. The blast furnace gas is produced as by-product from blast furnace
used in steel industry. The water gas is produced by passing steam and air through a bed of
incandescent carbon.
The gaseous fuels have all the advantages of oil fuels except ease of storage. The
major disadvantage of using natural gas as fuel is that the power plant must be located near
the natural gas field otherwise transportation and cost of transportation play an important part
in selecting the fuel for thermal power plant.

3.2 Coal Handling, Storage & Feeding
The coals from the coal mines to the power station are transported by sea or river or
rail or road. The supply of coal by road is limited to a small capacity power plant and this
mode of handling the coal does not play much important part in modern capacity power plant.
a) Transportation by Sea or River. If the power plant is situated on the bank of river or
near the sea shore, it is often economical to transport the coal by ships. The coal
brought by the ships is unloaded mechanically by cranes at the site of the power plant.
The unloaded coal form the ship is either sent to storage yard or directly to the
conveyer system which carries coal directly to the combustion chamber hopper.
b) Transportation by Rail. The transportation of coal by rail is the most important
means of transportation in common use. The coal supply to Indian power plants is
mainly by rail as unfortunately river transportation is not available. This mode of
transport plays very important role for power stations which are located interior. A
railway siding line is taken to the power station and coal is either delivered to the
storage yard or close to the point of consumption.
c) Transportation by Ropeways. This is very efficient method of transporting the coal
from the mine to the power station. This is particularly used when the distance
between the mine and power station is less than 10 kilometres. The major advantage
of this system is, it supplies the cola continuously and free from workers’ strike which
is common with rail transport.
d) Transportation by Road. The transportation of coal by road is used only for small
capacity plants. The major advantage of road transport is that the coal can be carried
directly into the power house upto the point of consumption. This is better system for
small capacity plants as traffic restrictions are comparatively less.
The selection of proper method of coal supply from the coal mines to the power stations
depends upon the system capacity in tonnes per hour, location of the plant with respect to rail
or water facilities available and location of available outside storage and overhead coal
bunkers.

11

e) Transportation of Coal by Pipeline. The power demand throughout the world is
increasing quite faster and coal is going to be the only fuel to run the thermal plants as
liquid fuel prices are escalating day by day. In India it is expected that the power
demand will be doubled by the end of the century and it is physically impossible for
the railway to haul the required coal to the coming-up power plants.
Transportation of coal by pipeline is considered most speedy method among all available.
Pipe lining of coal slurries from remote mines to strategically located generating plants shows
great promise for future development.
The pipeline coal transport system offers many advantages as listed below:
i.
ii.
iii.
iv.
v.
vi.
vii.
viii.
ix.
x.

It is a continuous transport system unaffected by the climate and weather.
It is capable of transporting very large quantities of coal.
It has high degree of reliability and safety as the moving machines are limited to the
stationary pumping and boosting stations.
It is easy to carry the pipeline through difficult terrain like hills, valleys and swamps
compared with other modes of transport.
Man-power required is low and maintenance charges are also low.
Loss of coal during transport due to theft totally eliminated.
Requirement of large areas as in the case of railway system for site dumping and
storage is eliminated.
It produces the least environmental disturbance as noise and dust problem and traffic
congestion is drastically reduced.
It provides simplicity in installation and increased safety in operation.
The impact of inflation on the operating cost is less than other modes of transport.

Some of the disadvantages of the system are listed below:
i.
ii.
iii.

It requires large quantity of water as 1 kg of coal requires one kg of water.
Preparation of coal at the pumping terminal as well as dewatering and recovery of the
coal at the delivery terminal requires high capital and operating cost.
Consumer must be able to use coal with added surface moisture (10%). This also
results in some loss in the useful heat of coal.

3.3 Storage of Coal at Plant Site
The purpose of coal storage is twofold. First, fuel storage is an insurance against
complete shutdown of a power plant occurring from failure of normal supplies. Second, the
storage permits choice of the date of purchase allowing the management to take advantage of
seasonal market condition. Storage of coal protects the plant failure in case of coal strikes,
failure of the transportation system and general coal storages.
The storage of coal is undesirable, because it costs more as there is risk of
spontaneous combustion, possibility of loss and deterioration during storage, interest on
capital cost of coal laying dormant, cost of insurance, handling cost required by storage and
12

reclamation, cost of area required, cost required to protect the stored coal from deterioration
and many others. With all this disadvantages of coal storage, it is more important to public
service stations as light and power have become vital and essential in every day domestic and
industrial life.
To store the coal containing high sulphur is more troublesome because local heating
further aggravates the reaction between sulphur, air and water causing rapid deterioration of
coal and increases the chances of spontaneous combustion. Lower rank coals (lignite and
bituminous) have a higher tendency to ignite spontaneously compared with high rank coals
(anthracite and graphite).
The coal is stored by using one of the following methods to reduce the chances of
oxidation and combustion:
1. Stocking the Coal in Heaps. The ground used for stocking should be dry and level.
Generally concrete floored are is used to prevent the flow of air from the bottom. The
coal is piled at height of 10m to 12m. During storage of coal in heaps, the coal should
be compacted in layer of 15 to 30 cm in thickness by means of bulldozers and rubbertired scrapers. This effectively prevents the sir circulation in the interior of the pile.
Another method of removing the heat of oxidation is, the air is allowed to move through
the layers evenly so that the heat of reaction is carried away and the temperature of coal is
maintained below the combustion temperature (70˚C.).
2. Under-Water Storage. The possibility of slow oxidation and spontaneous
combustion can be completely eliminated by storing the coal under water. The dock
basins can be used for storage of coal under water.
The following points should be kept in mind during selecting the site for storage and
piling.
i.
ii.
iii.
iv.
v.
vi.
vii.
viii.
ix.
x.
xi.

The storage area should be free from standing water.
The artificial drainage in the storage area should be provided if well drained
area is not available.
The storage area should be cleared of all foreign matter such as wood, paper,
rags, waste oil or materials having a low ignition temperature.
The storage site should be selected in such a way that the handling cost is
minimum.
The piles should be built-up in successive layers and as far as possible
compact.
The piles should be dressed to prevent rain from penetrating into pile.
Alternate wetting and drying of coal are undesirable.
Storage on hot bright days should be avoided.
A provision for temperature check at different point should be made.
A conical piling should be avoided.
A fire fighting equipment should be easily available at the storage site.
13

4.1 Introduction
Steam is mainly required for power generation, process heating and space heating
purposes. The capacity of the boilers used for power generation is considerably large
compared with other boilers.
Due to the requirement of high efficiency, the steam for power generation is produced
at high pressures and in very large quantities. They are very large in size and are of individual
design depending on the type of fuel used.
A steam generator popularly known as boiler is a closed vessel made of high quality
steel in which steam is generated from water by the application of heat. The water receives
heat from the hot gases through the heating surface of the boiler. The hot gases are formed by
burning fuel, may be coal, oil or gas. Heating surface of the boiler is that part of the boiler
which is exposed to hot gases on one side and water or steam on the other side. The steam
which is collected over the water surface is taken from the boiler through super heater and
then suitable pipes to turbine. Usually boilers are coal or oil fired.
According to American Society of Mechanical Engineers (A.S.M.E.) a ‘steam
generating unit’ is defined as:
“A combination of apparatus for producing, furnishing or recovering heat together
with the apparatus for transferring the heat so made available to the fluid being heated and
vaporised”.
The steam generated is employed for the following purposes:
i.
ii.
iii.

For generating power in steam engines or steam turbines.
In the textile industries for sizing and bleaching etc. and many other industries
like sugar mills; chemical industries.
For heating the building in cold weather and for producing hot water for hot
water supply.

The primary requirements of boiler are:
i.
ii.

The water must be contained safely.
The steam must be safely delivered in desired condition.

4.2 Classification of Boiler
The boilers may be classified as follows:
1. Horizontal, Vertical or Inclined
If the axis of the boiler is horizontal, the boiler is called as horizontal, if the axis is
vertical, it is called vertical boiler and of the axis is inclined it is known as inclined boiler.
The parts of a horizontal boiler can be inspected and repaired easily but it occupies more
spaces. The vertical boiler occupies less floor area.
14

Fig.4.1 Horizontal Boiler.
2. Fire Tube And Water Tube
In the fire tube boilers, the hot gases are inside the tubes and the water surrounds the
tubes. Examples: Cochran, Lancashire and Locomotive boilers.
In the water tube boilers, the water is inside the tube and hot gases surround them.
Examples: Babcock and Wilcox, Stirling boiler etc.

Fig.4.2 Fire Tube Boiler.
3. Externally Fired And Internally Fired
The boiler is known as externally fired if the fire is outside the boiler shell. Examples:
Babcock and Wilcox, Stirling boiler.
In case of internally fired boilers, the furnace is located inside the boiler shell. Example:
Cochran, Lancashire boiler etc.

Fig.4.3 Externally Fired Boiler.

15

4. Forced Circulation And Natural Circulation
In forced circulation type boilers, the circulation of water is done by a forced pump.
Examples: Velox, Lamont, Benson boiler etc.
In natural circulation type boilers, circulation of water in the boiler takes place due to
natural convention currents produced by the application of heat. Examples: Lancashire,
Babcock and Wilcox boiler etc.

Fig.4.4 Forced Circulation and Natural Circulation Boiler.
5. High Pressure And Low Pressure Boiler
The boiler which produce steam at a pressure of 80 bar and above are called high pressure
boiler. Examples: Babcock and Wilcox, Velox, Lamont, Benson boilers.
The boilers which can produce steam at a pressure below 80 bars are called low pressure
boilers. Examples: Cochran, Cornish, Lancashire and locomotive boilers.
6. Single Tube And Multi-Tube Boiler
The fire tube boilers are classified as single tube and multi-tube boilers, depending upon
whether the fire tube is one or more than one. The examples of former type are Cornish,
simple vertical boiler and rest of the boilers are multi-tube boilers.

Fig.4.5 Single Tube Boiler.

16

4.3 Selection of a Boiler
The following factors should be considered while selecting a boiler:
i.
ii.
iii.
iv.
v.
vi.
vii.
viii.

The working pressure and quality of steam required.
Steam generation rate.
Floor area available.
Accessibility for repair and inspection.
Comparative initial cost.
The probable load factor.
The fuel and water available.
Operating and maintenance cost.

4.4 Performance of Boiler
Evaporative Capacity
Performance of boiler is expressed in terms of evaporative capacity which is defined
as the amount of water evaporated or steam produced in kg per hour.
Boiler Efficiency
Boiler efficiency is the ratio of heat actually utilised in generation of steam to the heat
supplied by the fuel in the same period.
i.e., boiler efficiency = [ma (h - hf1)]/C
Where, ma = mass of water actually evaporated into steam per kg of fuel at the
working pressure,
h = enthalpy of steam per kg under the generating condition,
hf1 = specific enthalpy of water at a given feed temperature, and
C = calorific value of fuel in kJ/kg.
If the boiler, economiser, and superheater are considered as a single unit, then the boiler
efficiency is termed as overall efficiency of the boiler plant.

4.5 Boiler Mountings
4.5.1 Introduction
Different fittings and devices necessary for the operation and safety of a boiler are
known as boiler mountings. The safety valve, water level indicator, and the fusible plug are
the devices used for safety operation of the boiler. The pressure gauge, feed check valve,
blow-off cock and steam stop valve fall under the category of fittings and these are essential
for the operation of the boiler.

17

4.5.2 Safety Valve
When there is a sudden drop in steam requirements, the steam pressure in the boiler
will increase. The main function of a safety valve is to prevent under such a condition, an
increase in the steam pressure in the boiler exceeding a predetermined, maximum pressure for
which the boiler is designed. This is automatically done by opening of the valve and
discharging the steam to the atmosphere as soon as the pressure inside the boiler increases
above the predetermined value. The safety valves are directly placed on the top of the boiler
shell.
Spring Loaded Safety Valve
This type of safety valve is commonly used now-a-days for stationary as well as
mobile boilers. It is loaded with spring instead of weights. The spring is made from a square
steel rod in helical form.
Spring loaded safety valve consists of two valves, each of which is placed over a
valve seat fixed over a branch pipe. The two branch pipes are connected to a common block
which is fixed on the shell of the boiler. The lever has two pivots each of which is placed
over each respective valve. The lever is attached with a spring at its middle which pulls the
lever in downward direction. The lower end of the spring is attached to the back. Thus the
vales are held tight to their sates by the spring force.

Fig.4.6 Safety Valve.
These valves are fitted against the spring when the steam pressure is greater than the
working pressure and allows the steam to escape from the boiler till the pressure in the boiler
reaches its working pressure. The lever has an extension which projects into the driver’s
cabin. The driver can release the pressure if required just by raising the lever. The lever is
connected loosely by a link to the block. This limits the valve opening and prevents the lever
blowing off in case of spring failure.
18

4.5.3 Water Level Indicator
It is an important fitting which indicates water level inside the boiler to the observer.
Usually two water level indicators are fitted in front of the boiler. The water indicator shows
the level or water in the boiler drum and warns the operator if by chance the water level goes
below a fixed mark, so that corrective action may be taken in time to avoid any accident.
4.5.4 Pressure Gauge
A pressure gauge is used to measure the pressure of steam inside the boiler. The
commonly used pressure gauge is known as Bourdon type pressure gauge. It consists of an
elastic metallic type of elliptical cross-section and is bent in the form of circular arc. One end
of the tube is fixed and connected to the steam space of the boiler and other end is connected
to a sector wheel through a link. The sector remains in mesh with a pinion fixed on a spindle
to read the pressure on a dial gauge.

Fig.4.7 Pressure Gauge.
When high pressure steam enters the elliptical tube, the tube section tries to become
circular which causes the other end of the tube to move outward. The movement of the closed
end of the tube is transmitted and magnified by the link and sector. The magnitude of the
movement is indicated by the pointer on the dial.
4.5.5 Fusible Plug
The main objective of the fusible plug is to put off the fire in the furnace of the boiler
when the water level in the boiler falls below an unsafe level and thus avoids the explosion
which may take place due to overheating of the tubes and shell. This plug is generally fitted
over the crown of the furnace or over the combustion chamber.

Fig.4.8 Fusible Plug.

19

Under normal water level condition in the boiler, this plug is covered with water
which keeps the temperature of the fusible metal below its melting point. But when the water
level in the boiler falls low enough to uncover the plug; the fusible metal between the plug
quickly melts and drops out. The opening so made allows the steam to rush the water into the
furnace and extinguish the fire. The steam rushing out puts out the fire and gives warning that
the crown of the furnace is in danger of being overheated.
4.5.6 Feed Check Valve
The function of the feed check valve is to allow the supply of water to the boiler at
high pressure continuously and to prevent the back flow of water from the boiler when pump
pressure is less than boiler pressure or when pump fails.

Fig.4.9 Feed Check Valve.
It is fitted to the shell slightly below the normal water level of the boiler. The lift of
the non-return valve is regulated by the end position of the spindle which is attached with the
hand wheel. The spindle can be moved upward or downward with the help of hand wheel as
the upper portion of the spindle is screwed to a nut.
At normal working condition, the non-return valve is lifted due to the pressure of
water from the pump and the water is fed to the boiler. But when the pump pressure falls
below boiler pressure or if the pump stops, non-return valve is closed automatically due to the
pressure of the steam from the boiler and prevents the escape of water form the boiler.
4.5.7 Blow-Off Cock
The blow-off cock used for dual functions:
1. To empty the boiler when necessary for cleaning, repair and inspection.
2. To discharge the mud and sediments carried with the feed water and accumulated at
the bottom of the boiler.

20

By periodic blow-off, the salt concentration in the boiler is also reduced. Even with a
small amount of dissolved salt, over a period of time, due to the evaporation of water, the salt
accumulates in the boiler, raising the salt concentration.
It is fitted to the lowest part of the boiler either directly with the boiler shell or to a pip[e
connected with the boiler.

Fig.4.10 Blow-Off Cock.
It consists of a conical plug fitted accurately into a smaller casing. The plug has a
rectangular opening which may be brought with the line of the passage of the casing by
rotating the plug. This causes the water to be discharged from the boiler. The discharging of
water may be stopped by rotating the plug again.
The blow-off cock should be operated only when the boiler is on if the sediments are to
be removed. This is because; the sediments are forced out quickly due to the high steam
pressure in the boiler.
4.5.8 Steam Stop Valve
It is the largest valve on the steam boiler and usually fitted to the highest part of the
boiler shell. The function of the stop valve is to regulate the flow of steam from the boiler to
the turbine as per requirement and shut off the steam flow when not required.

Fig.4.11 Steam Stop Valve.
21

The main body is made of cast steel. The valve, valve seat and the nut through which
the valve spindle works, are made of brass for smooth working. The spindle is passed through
a gland to prevent the leakage of steam. The spindle is rotated by means of hand wheel. Due
to the rotation of hand wheel, the valve may move up or down and it may close or open the
passage fully or partially for the flow of the steam.

4.6 Boiler Accessories
4.6.1 Introduction
Accessories are the auxiliary plants required for steam boilers for their proper
operation and for the increase of their efficiency. Water feeding equipments, air-preheater,
economisers and super heaters are some of the essential accessories of the boiler.
In the present age of costly fuel, it has become necessary to conserve the fuel by
utilizing the wasted energy to the atmosphere. This is done in all modern power plants by
incorporating economiser and air preheater. By increasing the temperature of feed water
passing through the economiser using waste heat of gas, the quantity of heat given per kg of
steam generated in the boiler is reduced. Similarly, the temperature of air is also increased by
passing through the air preheater using remaining waste energy of the gases. The preheated
air increases the combustion efficiency in the furnace and reduces the fuel loss. In both
equipments, the quantity of fuel is reduced by extracting the heat from the exhaust gases.
The common equipments used in thermal power plants to increase the thermal
efficiency are economisers, and air pre-heaters. The heat carried with the flue gases is partly
recovered in air-preheater and economiser and reduces the fuel supplied to the boiler. The
preheating of air with gases increases the combustion efficiency and reduces the fuel
consumption.
The adoption of one or both equipments depends upon the economical justification. It
is also equally essential to maintain the performance of these equipments by preventing
corrosion and fouling from inside and outside; otherwise the gain from these equipments
reduces rapidly with respect to time. The corrosion is generally prevented by using proper
materials for the equipments and controlling the flue gas temperature to avoid the
condensation of corrosive gases carried by the exhaust gases.
4.6.2 Economisers
An economiser is a device used for heating the feed water by means of flue gases
from boiler. The economiser usually extracts the waste heat of the chimney gases to preheat
the water before it is fed into the boiler.
A boiler producing between 10 to 100tonnes of steam per hour and operating at 30%
or more loads should be evaluated for possible retrofitting with an economiser. The cost
benefits depend upon the boiler size; type of fuel used and exhausts gas temperature. It has
been estimated that about 1% fuel can cost can be saved for every 6˚C rise in temperature of

22

Fig.4.12 Return Bend Economiser.
the boiler feed water. Saving upto maximum 20% can be achieved by incorporating
economiser where boiler operates very effectively.

Fig.4.13 Flue Gas Temperature Entering The Economiser On Fuel Saving.
When more heat is available, that can be used in increasing the sensible heat of the
feed water or pass it through an air heater. However, in most economisers, the feed water is
not heated higher than to within 25˚C of the temperature corresponding to the saturation
temperature of steam in the boiler thus preventing steam formation in the economiser.
A water temperature of 85˚C in the hot well is the maximum at which the feed pump
works satisfactorily, as there is slight negative pressure on the suction side of the pump. At
temperature over 85˚C, steam bubbles begin to form and the boiler feed pump will not be
able to pump steam and water flow stops. Therefore, the feed water is pumped through and
heated in the economiser. Since it is on the pressure side of the pump, the water can be heated
to a much higher temperature than the hot well temperature. The maximum temperature to
which water can be heated in the economiser is 25˚C below steam forming temperature in the
boiler. The following table gives the maximum temperature for varying pressures and the
possible fuel savings for different hot well temperatures.

23

Pressure in the
boiler in
(Kgf/cm2)

8
13
18

Saturation temp. in
the boiler in (˚C)

174.5
194.1
208.8

Max
economiser
outlet temp.
in ( ˚C)

149.5
169
183

Percentage fuel saving using
economiser with different hot well
temperature.

45˚C

65˚C

85˚C

17
20
23

14
17
19

10
14
16

Table.4.1 Maximum Pressure for Varying Pressures and the Possible Fuel Savings for
Different Hot Well Temperatures.
Design Requirement for an Economiser. The design requirements must satisfy the
following conditions:








The heat transfer surface should be minimum.
It must be able to extract maximum possible heat from exhaust gases.
The height of the tube banks should be minimum so the cleaning on load can
be done effectively.
The gas side pressure loss should be minimum to reduce the running expenses
of I.D. fans.
There must be uniform water flow to avoid the steam formation in the
economiser. The pressure loss of water side must be also minimum to reduce
the running expenses of the pump.
There must be connection from steam and water drum to the economiser inlet
header, to permit the free circulation of water around the economiser to
prevent the overheating and boiling during the period when there is no feedflow during early pressure rising stages.

Types of Economisers. Basically there are two types of economisers:
1) Plain Tube Economiser. Plain tube types are generally used under natural draught
condition. The tubes are made of cast iron to resist corrosive action of the flue gases
and their ends are pressed into top and bottom headers.
An economiser consists of a group of these cast iron tubes located in the main flue
between the boiler and the chimney. The waste flue gases flow outside the economiser
tubes and heat is transferred to the feed water flowing inside the tubes. The external
surfaces of the tubes are continuously cleaned by soot scrapers moving up and down.
2) Gilled Tube Type Economiser. A reduction in economiser size together with
increase in heat transmission can be obtained by casting rectangular gills on the bare
tube walls. Cast iron gilled tube economiser can be used upto 50bar working pressure
and such economisers are indigenously available. At higher pressure steel tubes are
used instead of cast-iron gilled sleeves are shrunk to them.

24

Corrosion of Economiser and Its Prevention. The corrosion and its prevention are very
important for safe and efficient working of the economiser. Internal and external corrosion
are the primary enemies of an economiser and dissolved O2 and CO2 are the major culprits.
A properly designed deaerator, combined with water treatment plant, virtually eliminates
internal corrosion in the economiser tubes. Deaeration removes 95% dissolved O2 and CO2
from the feed water. Vigorous steam scrubbing with chemical assist should follow deaeration
to ensure complete O2 removal and corrosion control.
CO2 forms carbonic acid (H2CO3) when it dissolves in water. This compound is unstable
and ionizes into H2 ion (H+) and bicarbonate radical (H CO3-). The H CO3- further ionizes to
form the H+ ion and carbonate ion (CO3 -). The H2CO3 is the only one that exerts gas
pressure; therefore, CO2 must be removed by deaeration at low pH levels.
NH3 gas forms NH4 OH (ammonium hydroxide) upon dissolving in water. NH4 OH
ionizes to form NH4+ and OH- ions. Therefore, NH4 OH is responsible for exerting gas
pressure and it must be removed by deaeration at higher pH.
The pH value of water passing through the economiser should be maintained between 8
and 9 to reduce its effect of acid. CO2 removal is achieved at low pH and NH3 removal is
achieved at high pH, therefore complete degasification of flow containing combination of
two is very difficult to achieve through deaeration alone.
Advantages of Economiser. There are several indirect advantages obtained by installing an
economiser with a boiler plant as listed below:
1) The feeding of the boiler with water at a temperature near the boiling point
reduces the temperature differences in the boiler, prevents the formation of
stagnation pockets of the cold water and thus reduces greatly the thermal stress
created in the pressure part of the boiler and the boiler and promotes better
internal circulation.
2) When the feed water is not as pure as it should be, the temporary hardness is
deposited on the inside of the economiser tubes and while this necessitates
internal cleaning of the economiser, the evil is not as great as internal cleaning
of the boiler.
3) Due to the reduction in the combustion rate of the furnace, the boiler will be
more efficient and the actual fuel saving will be greater than the theoretically
calculated.
4) The flow of flue gases over the economiser tubes acts indirectly as a grit
arrester and large portion of the soot and fly-ash is deposited on the tubes and
scraped off into the soot chamber. This reduces the omission of soot and flyash.

25

4.6.3 Air Preheater
Air preheater, recovers some portion of the waste heat of the flue gases. Air supplied
to the combustion chamber is preheated by using the heat in the waste flue gases. Airs
preheater is placed after the economiser and before the gases enter the chimney.
The heat carried with the flue gases coming out of the economiser is further utilised
for preheating the air before supplying to the combustion chamber. It has been found that an
increase of 20˚C in the air temperature increases the boiler efficiency by 1%.
The air heater is not only considered in terms of boiler efficiency in modern power
plants, but also as a necessary equipment for supply of hot air for drying the coal in
pulverised fuel systems to facilitates grinding and satisfactory combustion of fuel in the
furnace.
The use of preheater is much economical when used with pulverised fuel boilers
because the temperature of flue gases going out is sufficiently large and high air temperature
is always desirable for better combustion.
Air heaters are usually installed on steam generators that burn solid fuels but rarely on
gas or oil fired units. By contrast, economisers are specified for most boilers burning liquid or
gas or coal whether or not an air heater is provided.
The principal benefits of preheating the air are:
I.
II.
III.
IV.
V.

Improved combustion.
Successful use of low grade fuel.
Increased thermal efficiency.
Saving in fuel consumption.
Increased steam generation capacity of the boiler.

The air preheater are generally divided into two groups as recuperative and
regenerative type.
The recuperative heaters continuously transfer the heat from hot gases to cold air. The
regenerative heater alternately gets heated and cooled by hot gases and cold air. Unlike the
recuperative type, the regenerative is discontinuous in action and operates on cycle. In rotary
regenerative type, the cyclic action applies to the heating and cooling of an individual
element of the surface but the flowing steam of air receives heat continuously.
The two recuperative types of heat-exchangers which are commonly used for airheating are described below:
Tubular Air-Heater. The flue gases flow through the tubes and air is passed over the
outer surface of the tubes. The horizontal baffles are provided to increase time of contact
which will help for higher heat transfer. The steel tubes 3 to 10 m in height and 6 to 8 cm in
diameter are commonly used.

26

Fig 4.14 Tubular Air-Heater.
Plate Type Air-Heater. It consists of rectangular flat plates spaced from 1.5 to 2.5
cm apart leaving alternate air and gas passage. This type of air-heater is not used in modern
installation as it is more expensive both as to flat cost and maintenance cost compared with
tubular air-heaters.
Regenerative Heat Exchangers. The transfer of heat from hot gases to cold air is
divided into two stages. In the first stage, the heat of the hot gases flowing through the heat
exchanger is transferred to the packing of the heater and it is accumulated in the packing and
the hot gases are cooled to sufficiently low temperature before exhaust to atmosphere. This
stage is referred to as ‘Heating period’. In the second stage, the cold air is passed through the
hot packing where the heat is accumulated and the heat from the packing is transferred to the
cold air. This stage is known as ‘Cooling period’.
4.6.4 Superheater
The function of the superheater in the thermal power plant is to remove the last traces
of moisture (1 to 2%) from the saturated steam coming out of boiler and to increase its
temperature sufficiently above saturation temperature. The superheating raises overall cycle
efficiency as well as avoids too much condensation in the last stages of the turbine which
avoids the blade erosion.
The heat of combustion gases from furnace is utilised for the removal of moisture
from steam and to superheat the steam. Super heaters usually have several tube circuits in
parallel with one or more return bends, connected between headers.

27

Fig.4.15 Superheater.
Superheated steam has the following advantages:
I.
II.
III.
IV.

Steam consumption of the turbine is reduced.
Losses due to condensation in the cylinder and the steam pipe are reduced.
Erosion of turbine blade is reduced.
Efficiency of the steam plant is increased.

Types of Superheater
There are two types of super heaters:
1. Convective superheater
2. Radiant superheater
Convective superheater makes use of heat in flue gases whereas a radiant superheater
is placed in the furnace and a wall tube receives heat from the burning fuels through radiant
process. The radiant type of superheater is generally used where a high amount of superheat
temperature is required.
Heat from the hot gases to the vapour in the superheater is transferred at high
temperatures. Therefore primary section of superheater is arranged in counter flow and
secondary section in parallel flow to reduce the temperature stressing of the tube wall. The
metal used for superheat tubes must have high temperature strength, high creep strength and
high resistance to oxidation as superheater tubes get rougher service than water wall of the
modern boilers. Carbon steels (510˚C) and chromium-molybdenum alloys (650˚C) are
commonly used for superheater tubes.
The superheater tubes are subjected to corrosion when they are exposed to oxidising
and reducing conditions alternately. This destroys the protective oxide film and exposes the
metal surface open to further corrosion. The alkali deposits formed also have corrosion effect
28

on steel depending upon its temperature and composition. Low chromium ferritic steels
confer some corrosion resistance but marked resistance is obtained by the use of austenitic
alloys.
4.6.5 Steam Separator
The steam available from a boiler may be wet, dry; or superheated; but in many cases
there will be loss of heat from it during its passage through the steam pipe from the boiler to
the engine tending to produce wetness. The use of wet steam in an engine or turbine is
uneconomical besides involving some risk; hence it is usual to need to separate any water that
may be present from the steam before the latter enters the engine. This is accomplished by the
use of a steam separator. Thus the function of a steam separator is to remove the entrained
water particles from the steam conveyed to the steam turbine.

Fig 4.16 Steam Separator.

29

5.1 Introduction
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. The turbine shaft, directly or with the help of a
reduction gearing, is connected with the driven mechanism. Depending on the type of the
driven mechanism a steam turbine may be utilised in most diverse fields of industry, for
power generation.
The steam turbines are mainly divided into two groups as:
a) Impulse turbine
b) Reaction turbine
In both types of turbine, first the heat energy of the steam at high pressure is
converted into kinetic energy passing through the nozzles. The turbines are classified as
impulse or reaction according to the action of high velocity steam used to develop the power.
In impulse turbine, the steam coming out at a very high velocity through the fixed
nozzles impinges on the blades fixed on the periphery of a rotor. The blades change the
direction of the steam flow without changing its pressure. The resulting motive force (due to
the change in momentum) gives the rotation to the turbine shaft.

Fig 5.1 Impulse and Reaction Turbine.
In the reaction turbine, the high pressure steam from the boiler is passed through the
nozzles. When the steam comes out through this nozzles the velocity of the steam increases
relative to the rotating disc. The resulting reaction force of the steam on nozzle gives the
30

rotating motion to the disc and the shaft. The shaft rotates in the opposite direction to the
direction of the steam jet.
In an impulse reaction turbine, the steam expands both in fixed and moving blades
continuously as the steam passes over them. Therefore, the pressure drop occurs gradually
and continuously over both moving and fixed blades.

5.2 Compounding of Steam Turbine
If the entire pressure drop from boiler pressure to condenser pressure is carried out in
single stage nozzle, then the velocity of the steam entering into the turbine could be very high
of the order of 1500 m/sec. The turbine rotor velocity will be very high, of the order of
30,000 r.p.m as it is directly proportional to the steam entering velocity. Such high R.P.M. of
the turbine rotor is not useful for practical purpose and a reduction gear is necessary between
the turbine and external equipment driven by the turbine. There is also danger of structural
failure of the blade due to excessive centrifugal stresses. Therefore the velocity of the blades
is limited to 400 m/sec.
The velocity of the steam at the exit of the turbine is sufficiently high when single
stage blades are used. This gives a considerable loss of kinetic energy (about 10 to 12%). The
above-mentioned difficulties associated with the single stage turbine can be solved by
compound. The combinations of stages are known as compounding. The different methods of
compounding are:
1. Velocity Compounding
2. Pressure Compounding
3. Pressure And Velocity Compounding
1. Velocity Compounding. There is only one set of nozzles and two or more rows of
moving blades. There is also a row of fixed blades in between the moving blades. The
function of fixed blade is only to direct the steam coming out from first moving row
to next moving row. The heat energy drop takes place only in the nozzle at the first
stage and it converts into kinetic energy. The kinetic energy of the steam gained in the
nozzles is successively used by the rows of moving blades and finally exhausted from
the last row of the blades on the turbine rotor. The function of the fixed blades is
merely to turn the steam into the direction required for entry into the next row of rotor
blades without altering pressure and velocity of the steam. A turbine working on this
principle is known as velocity compounded impulse turbine.
2. Pressure Compounding. A number of simple impulse turbine sets arranged in series
is known as pressure compounding. In this arrangement, the turbine is provided with
one row of fixed blades at the entry of each row of moving blades. The total pressure
drop of the steam does not take place in a single stage nozzle but is divided equally in
all the rows of fixed blades which work as nozzles.

31

Fig.5.2 Pressure Compounded Steam Turbine.
3. Pressure and Velocity Compounding. This compounding is a combination of
pressure and velocity compounding. The total pressure drop of the steam from boiler
to condenser pressure is divided into a number of stages as done in pressure
compounding and velocity obtained in each stage is also compounded. This
arrangement requires less stages and compact turbine can be designed for a given
pressure drop. This compounding has an advantage of pressure compounding to
provide higher pressure drop in each stage and hence less number of stages and an
advantage of velocity compounding to reduce the velocity of each blade row.

Fig.5.3 Velocity and Pressure Compounded Steam Turbine.
32

Advantages and Disadvantages of Velocity Compounding
Advantages:
1.
2.
3.
4.

It requires less number (2 to 3 only) of stages, therefore initial cost is less.
The space required is less.
The system is easy to operate and more reliable.
The turbine housing need not be made strong as pressure in the housing is
considerably less because the total pressure falls in the nozzle only.

Disadvantages:
1. The friction losses are too larger due to the high velocity of steam.
2. The maximum blade efficiency and efficiency range decreases with an increase in
number of stages.
3. The power developed in each successive blade row decreases with an increase in
number of rows, even though all the rows require same space, material and initial
cost. Therefore all the stages are not economically used. Velocity compounded steam
turbines are generally used as drives for centrifugal compressors, centrifugal pumps,
and small generators and feed pumps of high capacity power plants.

5.3 Losses in Steam Turbine
The causes for the energy losses in steam turbines are listed below:
1. Residual Velocity Loss. The steam leaves the turbine with some absolute velocity.
The energy loss due to absolute exit velocity of steam is equivalent to Vaex2/2gJ kJ/kg,
where Vaex is absolute velocity of steam leaving the turbine.
The residual velocity loss is 10to 12% in a single stage impulse turbine. This loss is
reduced by using the multistage.
2. Loss Due To Friction and Turbulence. Friction loss occurs in nozzles, turbine
blades and between the steam and rotating discs. The friction loss in the nozzle is
taken into account with introducing factor ‘nozzle efficiency’. The loss due to friction
and turbulence is about 10%.
3. Leakage Loss. The leakage of steam occurs at the points mentioned below:
a) Between the turbine shaft and bearing.
b) Between the shaft and stationary diaphragms carrying nozzle in case of
reaction turbine.
c) Leakage at the blade tips in the glands.
d) Leakage of steam through the glands.
The total leakage loss is about 1 to 2%.
4. Loss Due To Mechanical Friction. The loss due to friction between the shaft and
bearing comes under this category. Some loss also occurs in regulating the valves.
This friction loss can be reduced with the help of an efficient lubricating system.

33

5. Radiation Loss. The heat is lost from the turbine to the surroundings as its
temperature is higher than atmospheric temperature. Usually the turbines are highly
insulated to reduce this loss. The loss due to radiation is always negligible.
6. Loss Due To Moisture. The steam contains water particles passing through the lower
stages of the turbine as it becomes wet. The velocity of the water particles is less than
the steam and therefore the water particles have to be dragged along with the steam
and consequently part of the K.E. of the steam is lost.

5.4 Governing of Steam Turbine
The main function of the governing is to maintain the speed constant irrespective of
load on the turbine. The different methods which are commonly used for governing the steam
turbines are listed below:
1.
2.
3.
4.
5.
1.

Throttle Governing.
Nozzle Control Governing.
By-Pass Governing.
Combination of Throttle and Nozzle Governing.
Combination of Throttle and By-Pass Governing.
Throttle Governing. The quantity of steam entering into the turbine is reduced by the
throttling of the steam. The throttling is achieved with the help of double heat
balanced valve which is operated by a centrifugal governor through the servomechanism. The effort of the governor may not be sufficient to move the valve
against the piston in big units. Therefore an oil operated relay is incorporated in the
circuit to magnify the small force produced by the governor to operate the valve.

Fig.5.4 Throttle Governing.
2. Nozzle Control Governing. In this method of control, the steam supplied to the
different nozzle groups is controlled by uncovering as many steam passages as
necessary to meet the load by poppet valves.
An arrangement often used for large steam power plants is shown in fig. The numbers
of nozzles supplying the steam to the turbine are divided into three groups and the
supply to these nozzles is controlled by the three valves.
34

Fig.5.5 Nozzle Control Governing.
3. By-Pass Governing. More than one stage is used for high pressure impulse turbine to
reduce the diameter of the wheel. The nozzle control governing cannot be used for
multi stage impulse turbine due to small heat drop in first stage. It is also desirable in
multistage impulse turbine to have full admission into high pressure stages to reduce
the partial admission losses. In such cases by-pass governing is generally employed.

Fig 5.6 By-Pass Governing.

5.5 Turbine Troubles
The following troubles may occur during the running of turbines which may cause the
damage to the turbines:
1) Loss of blade shrouding.
2) Damage of the seal.
3) Failure of a bearing or whipping of shaft because of improper lubricating-oil
pressure; temperature or viscosity.
35

Sudden increase in the vibration of the turbine is the most usual indication of any
trouble caused during running of the turbine.

5.6 Blade Materials for Turbines
The creep phenomenon is the main criteria in selection of blade material especially
for high temperature region. 1% Cr-Mo-V alloy and stainless steels having 12% Cr are
widely used. Austenite alloys are preferred for still higher temperature.
Blades of L.P. stage, though, at the low temperature end have to withstand the effect
of corrosion and erosion due to water droplets (0.25mm), about 10-12% stainless iron is
commonly used. New materials such as titanium, plastics reinforced with carbon having a
lower specific weight and higher strengths are also considered as they have high tensile
strength (70 kgf/mm2).

5.7 ALTERNATOR
5.7.1 Introduction
The alternator is universally used in automotive applications. It converts mechanical
energy into electrical energy, by electro-magnetic induction.
In a simple version, a bar magnet rotates in an iron yoke which concentrates the
magnetic field. A coil of wire is wound around the stem of the yoke. As the magnet turns,
voltage is induced in the coil, producing a current flow. When the North Pole is up, and South
is down, voltage is induced in the coil, producing current flow in one direction.

Fig.5.7 Alternator.
As the magnet rotates, and the position of the poles reverses, the polarity of the
voltage reverses too, and as a result, so does the direction of current flow. Current that
36

changes direction in this way is called alternating current, or AC. The change in direction
occurs once for every complete revolution of the magnet.
5.7.2 Theory of Operation
Alternators generate electricity by the same principle as DC generators. When
magnetic field lines cut across a conductor, a current is induced in the conductor. In general,
an alternator has a stationary part (stator) and a rotating part (rotor). The stator contains
windings of conductors and the rotor contains a moving magnetic field. The field cuts across
the conductors, generating an electrical current, as the mechanical input causes the rotor to
turn.

Fig.5.8 Alternator Working Principle.
The rotor magnetic field may be produced by induction (in a "brushless" generator),
by permanent magnets, or by a rotor winding energized with direct current through slip rings
and brushes. Automotive alternators invariably use brushes and slip rings, which allows
control of the alternator generated voltage by varying the current in the rotor field winding.
Permanent magnet machines avoid the loss due to magnetizing current in the rotor but are
restricted in size owing to the cost of the magnet material. Since the permanent magnet field
is constant, the terminal voltage varies directly with the speed of the generator. Brushless AC
generators are usually larger machines than those used in automotive applications.
5.7.3 Alternator Protection
An alternator is an important aspect of a power plant's electrical system. Any kind of
obstacle in its performance can mar the working of the power plant's overall electrical
system. It is for this reason that it requires adequate protection systems to prevent any kind of
hindrance to the power plant's functionality.
The main types of protection system are:
1. Over Current Protection
2. Reverse Power Protection
Over Current Protection. Every alternator has an over current protection. With the
help of this trip, the alternator and distribution system can be protected from various faults

37

but the main thing to be considered in this method is to maintain power to the distribution
system till the time the alternator trips on any other protection devices.
For this reason, the protection device has been designed in such a way that in case the over
current is not high enough, a time delay provided by an inverse definite minimum time
(IDMT) relay occurs, which prevents the alternator from tripping in case the over current
values reduces back to normal within the IDMT characteristics. But in case of a major fault
such as short circuit, the alternator will trip instantaneously without any delay, protecting all
devices on the distribution system. Overload of alternator is caused either due to increased
switchboard load or serious fault causing very high current flow.
If sudden over load occurs then, the load is reduced with the help of preferential trips
which removes non essential load such as of air conditioning, ventilation fans etc., from the
switchboard. These preferential trips are operated by relays which are set to about 110% of
the normal full load of alternator.
Reverse Power Protection. There is not much difference between an alternator and
electric motors from the engineer's perspective. They are both based on similar principles. So
just imagine what would happen if an alternator suddenly would act as a motor. This is only
possible in systems where two or more generators are running in parallel,
Hence this type of protection system is used only if there is more than one alternator
on board a ship. The system is designed in such a way that it will release the breaker and
prevent motoring of alternator if a reversal of power occurs. This protection device is also
used to prevent damage to the prime mover, which might be stopped due to some fault.
Though it is extremely difficult to detect reverse current with an alternating current system,
reverse power can be detected and protection can be provided by reverse power relay.

38

6.1 Introduction
A steam condenser is a device or an appliance in which steam condenses and heat
released by steam is absorbed by water. The use of condenser in the power plant improves the
efficiency of the power plant by decreasing the exhaust pressure of the steam below
atmosphere. 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 reduces the water
softening plant capacity to a considerable extent.
The maximum possible thermal efficiency of a power system is given by (T1 – T2)/T1
where T1 and T2 are the supply and exhaust temperatures. This expansion of efficiency shows
that the efficiency increases with an increase in temperature T1 and with the decrease in
temperature T2. The maximum value of temperature T1 of the steam supplied to a steam
prime-mover is limited by the material consideration. The temperature T2 can be reduced if
the exhaust of the steam prime mover takes place below the atmospheric pressure. This is
because; there is definite relation between the steam temperature and pressure. Low exhaust
pressure means low exhaust temperature. The steam cannot be exhausted to atmosphere if it
is expanded in the turbine below atmospheric pressure. Under this condition, the steam is
made to exhaust in a vessel known as condenser where the pressure inside is maintained
below the atmospheric pressure by condensing the steam with the circulation of the cold
water.
A closed vessel in which steam is condensed by abstracting heat from steam and the
pressure is maintained below atmospheric pressure is known as condenser. The efficiency of
the steam plant is considerably increased by the use of condenser.

6.2 Advantages of Condenser
The advantages obtained by incorporating a condenser in the steam power plant are
listed below:
1. The condensed steam from the condenser is used as feed water for boiler. Using
the condensate as feed for boiler reduces the cost of power generation as the
condensate is supplied at higher temperature to the boiler and it reduces the
capacity of the feed water cleaning system.
2. The efficiency of the plant increases as the enthalpy drop increases by increasing
the vacuum in the condenser.
The specific steam consumption of the plant also decreases as the available
enthalpy drop or work developed per kg of steam increases with decrease in back
pressure by using condenser.
3. The deposition of salt in the boiler is prevented with the use of condensate instead
of using the feed water from outer source with contained salt. The deposition of
salt in boiler shell also reduces the boiler efficiency. This is particularly important
in marine steam power plant.

39

The use of condenser in steam power plant reduces the overall cost of generation
by increasing the thermal efficiency of the power plant.
The efficient condenser plant must be capable of producing and maintaining a
high vacuum with the quality of cooling water available and should be designed to
operate for the prolonged periods without trouble.
The desirable features of good condensing plant are:
i.
Minimum quantity of circulating water.
ii. Minimum cooling surface area per KW capacity.
iii. Minimum auxiliary power.
iv.
Maximum area of condensed per m2 of surface area.
The effect of low vacuum is very pronounced. The efficiency of the power plant
depends to a greater extent on the pressure at the exhaust than the high pressure condition of
the steam at inlet.

6.3 Types of Steam Condenser
The condensers are mainly classified as mixing type or jet condenser and non-mixing
type or surface condenser.
In mixing type condensers, the exhaust steam form prime mover and cooling water
come in direct contact with each other and steam condenses in water directly. The
temperature of the condensate (condensed steam + cooling water) is same as that of cooling
water leaving the condenser. The condensate coming out from the mixing type condenser
cannot be used as feed to the boiler as it is not free form salt and pollutant. These type of
condenser are generally preferred where the good quality water are feed to the boiler are
easily available in ample quantity. Mixing condenser is seldom used in modern power plants.
In non-mixing type of condenser, steam and cooling water do not come in direct
contact with each other. The cooling water passes through the number of tubes attached to
condenser shell and steam surrounds the tubes. These type of condensers are universally used
in all high capacity modern steam power plants as the condensate coming out from the
condenser is used as feed for the boiler.
A. Mixing or Jet Type of Condenser. The jet condensers are mainly divided as parallel
flow and counter flow jet condenser.
In parallel flow condensers, the steam and cooling water flow in same direction where
as the flow in opposite direction in counter flow condenser.
Mixing type condenser is mainly classified into three categories depending upon the
arrangement used for the removal of condensate as low level, high level and ejector
condenser.
B. Non-Mixing Type or Surface Condenser. In this type of condenser, the cooling
tower and exhaust steam do not come in direct contact with each other as in case of jet
condenser. This is generally used where large quantity of inferior water is available
and better quality of feed water to the boiler must be used most economically.
40

Surface condenser consists of a cast iron air-tight cylindrical shell closed at each end.
A number of water tubes are fixed in the tube plates which are located between each
cover head and shell.
The exhaust steam from the prime mover enters at the top of the condenser and
surrounds the condenser tubes through which cooling water is circulated under force. The
steam gets condensed as it comes in contact with cold surface of the tubes. The cooling water
flows in one direction through the first set of the tubes situated in the lower half of condenser
and returns in the opposite direction through the second set of the tubes situated in the upper
half of the condenser. The cooling water comes out from the condenser is discharged into the
river or pond. The condensed steam is taken out form the condenser by a separate extraction
pump and air is removed by an air pump.

Fig.6.1 Surface Condenser.
6.3.1 Requirements of Surface Condenser. The requirements of an ideal surface
condenser used for power plants are listed below.
1. The steam should be evenly distributed over the whole cooling surface of the
condenser vessel with minimum pressure loss.
2. There should not be under cooling of condensate. To achieve this, the quantity
of cooling water circulated should be so regulated that the temperature of the
steam corresponding to the steam pressure in the condenser.
3. The water should be passed through the tubes and steam must surround the
tubes from outside. This helps to prevent the deposition of dirt on the outer
surface of the tubes.
4. There should not be air-leakage at all in the condenser as it destroys the
vacuum in the condenser and reduces the work done per kg of steam. The
presence of air also reduces the heat transfer rates in the condenser very
rapidly.

41

6.3.2 Advantages of Surface Condenser
The advantages of surface condenser are listed below:
1. A high vacuum can be attained in the surface condenser providing a high thermal
efficiency.
2. The condensate can be directly used as boiler feed water. This is very important in
any large power plant.
3. Any kind of cooling water can be used in the condenser as it does not directly
contact with steam.
The limitations of this type are:
1. The surface condenser is bulky and therefore requires more space.
2. Its capital, running and maintenance costs are considerably greater than that of jet
condenser.
C. Evaporative Condenser. These condensers are more preferable acute shortage of
cooling water exits. The arrangement of the condenser is shown in fig. Water is
sprayed through the nozzles over the pipe carrying exhaust steam and forms a thin
film over it. The air is drawn over the surface of the coil with the help of induced fan
as shown in fig. The air passing over the coil carries the water from the surface of
condenser coil in the form of vapour. The latent heat required from the evaporation of
water vapour is taken from the water film formed on the condenser coil enter the
temperature of the water field and this helps for heat transfer from steam to the water.
This mode of heat transfer reduces the cooling water requirement of the condenser to
10% of the requirement of the surface condenser. The water particle carried with air
due to high velocity of air is removed with the help of eliminator. The makeup water
is supplied from outside source.

Fig.6.2 Evaporative Condenser.
42

The quantity of water sprayed over the condenser coil should be just sufficient to keep
the condenser coil thoroughly wetted. The water flow rate higher than this will only increase
the power requirement of water pump without increasing the condenser capacity. This type of
condenser works better in dry weather compared with wet weather as the water vapour
carrying capacity of dry air is higher than wet air at the same temperature.
The arrangement of this type of condenser is simple and cheap in first cost. It does not
require large quantity of water therefore needs a small capacity cooling water pump. The
vacuum maintained in this condenser is not as high as in surface condensers therefore the
work done per kg of steam is less with this condenser compared with surface condenser.
These condensers are generally preferred for small power plants and where there is acute
shortage of cooling water.

6.4 Corrosion and Scale Formation in Condenser Tubes and Their Prevention
The efficiency of the condenser tube depends upon maintenance of heat transfer
surface cleanliness, adjustment of water flow of best economy and reduction of air-leakage to
a minimum. The importance of water flow and prevention of air leakage are already
discussed. The success of heat transfer with minimum power consumption for a long time
mostly depends upon the clean lines of the condenser tubes. The corrosion and scale
formation are the common phenomenon in condenser tube during operation due to the action
of chemical compounds and deposited collected on the tube surface carried with the water.
The life of the tubes is also reduced due to erosion which ids the effect of abrasive materials
(like sand) carried with cooling water.
In the average condenser installation on a river or lake, provision must be made for
cleaning the condenser tubes. The fouling of tubes occurs because of algae, organic matter,
leaves or other floating debris. Grills and screens removes most of the floating debris, even
the small particle will eventually accumulate on the tubes and reduces the heat transfer. It is
also desirable to clean the condenser while it is under load. A single pass condenser during
working condition can be cleaned by using back-washing. A valve arrangement is generally
provided for back-washing purpose.
With the most waters, there is general tendency for algae growth to build up on the
tube surface. Algae growth is considerably more rapid under warm water conditions therefore
summer periods are of the greatest trouble from this source in North American power plants.
The algae often serve as a binder for mud or scale and if algae deposits are removed or
controlled, other deposits are also minimised as well.
In closed type cooling system, where the cooling water is concentrated by
evaporation, the possibility of scale formation is more if the water is not chemically treated
Two general methods of treatment are used for condenser tubes cleaning. First is the
sterilization of the heat exchange surface of the condenser. This sterilization can be

43

accomplished by a number of commercially available compounds as copper sulphate,
chlorine, chlorinated phenols or mercurials.

6.5 Material for Steam Condenser
The application of stainless steel tubing for surface condenser is approximately 30
years old. The major growth of this application has occurred in past two decade only.
Originally these materials were only considered for highly corrosion environments or areas
exposed to severe erosion. The cost of stainless steel tubes and available heat transfer data, a
decade ago, restricted there used to the really difficult problems areas. Since that time, a
number of important advances have been achieved which have permitted a more use of these
materials for condenser application.
The determination of the overall heat transfer properties of stainless steel condenser
tubes in the early 1960 led to more extensive use of these materials. The popular types are
304 (72% iron, 19% chromium, 9% nickel) and 316. 304 are used in cooling water
environment with low chloride concentrations and 316 are used for sea water environments.
In case of stainless steel tubes, the fouling is due to the formation of deposits from the
cooling water only but the fouling of the brass is caused by deposits and corrosion of the
inside tube surface also.
The overall corrosion resistance of stainless steel, 304 type is excellent for condenser
tube service both the interior and exterior surface resist the formation of corrosion product
which has an important influence on the heat transfer characteristics of the tubes. It offers
excellent erosion and corrosion resistance in fresh water, immunity to NH3 and sulphide
attack and the elimination of potentially troublesome copper ions in feed water.

44

7.1 Introduction
The cooling water system is one of the most important systems of power plant and its
availability predominantly decides the plant site. The high cost of water makes it necessary to
use cooling towers for water cooled condenser.
The main steam condenser performs the dual function of removing this rejected
energy from the plant cycle and keeping the turbine back pressure at the lowest possible
level. The rejected energy must be returned to the atmosphere. The condenser does this by
transferring the latent heat of the exhaust steam to water exposed to the atmosphere. This
water is called circulating or cooling water. The cooling water requirement in an open system
is about 50times the flow of the steam to the condenser.
In power plants the hot water from condenser is cooled in cooling tower, so it can be
reused in condenser for condensation of steam. In a 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 thus cooled.
Factors affecting cooling of water in a cooling tower are:
1.
2.
3.
4.
5.
6.
7.
8.

Temperature of air.
Humidity of air.
Temperature of hot air.
Size and height of tower.
Velocity of air entering tower.
Accessibility of air to all parts of tower.
Degree of uniformly in descending water.
Arrangement of plates in tower.

7.2 Classification of Cooling Tower
The cooling towers may classified as follows:
1. Natural Draught Cooling Tower
2. Mechanical Draught Cooling Tower
(i)
Forced Draught Cooling Tower
(ii)
Induced Draught Cooling Tower
1. Natural Draught Cooling Tower. In this type of tower, the hot water from the
condenser is pumped to the troughs and nozzles situated near the bottom. Troughs
spray the water falls in the form of droplets into a pond situated at the bottom of the
tower. The air enters the cooling tower from air openings provided near the base, rises
upward and takes up the heat of falling water.

45

Fig.7.1 Natural Draught Cooling Tower.
Natural draught cooling tower has the following advantages:
I.
II.
III.
IV.

Low operating and maintenance cost.
It gives more or less trouble free operation.
Considerable less ground area required.
The enlarged top of the tower allows water to fall out of suspension.

The main drawbacks of this tower are:
I.
II.

High initial cost.
Its performance varies with the seasonal changes in dry bulb temperature and relative
humidity of air.
2. Mechanical Draught Cooling Tower. In these towers the draught of air for cooling
the tower is produced mechanically by means of propeller fans. These towers are
usually built in cells or units, the capacity depending upon the number of cells used.

Fig.7.2 Forced Draught Cooling Tower.
46

It is similar to natural draught tower as far as interior construction is concerned, but
the sides of the tower are closed from an air and water tight structure, except for fan opening
at the base for the inlet of fresh air, and the outlet at the top for the exit of air and vapour.
There are hoods at the base projecting from the main portion of the tower where the fans are
placed for forcing the air, into the tower.
Forced Draught Cooling Tower
Advantages:
1.
2.
3.
4.

More efficient (than induced draught).
No problem of fan blade erosion (as it handles dry air only).
More safe.
The vibration and noise are minimum.

Disadvantages:
1. The fan size is limited to 4 meters.
2. Power requirement high (approximately double that of induced draught system for the
same capacity).
3. In the cold weather, ice is formed on nearly equipments and buildings or in the fan
housing itself. The frost in the fan outlet can break the fan blades.

Fig.7.3 Induced Draught Cooling Tower.
Induced Draught Cooling Tower
Advantages:
1. The coldest water comes in contact with the driest air and warmest water comes in
contact with the most humid air.
2. In this tower, the recirculation is seldom a problem
47

3. Lower first cost.
4. Less space required.
5. This tower is capable of cooling through a wide range.
Disadvantages:
1. The air velocities through the packing are unevenly distributed and it has very little
movement near the walls and centre of the tower.
2. Higher H.P. motor is required to drive the fan comparatively. This is due to the fact
that the static pressure loss is higher as restricted are at base tends to choke off the
flow of higher velocity air.

7.3 Maintenance of Cooling Tower
The regular maintenance of cooling tower is very essential to achieve the desired
cooling and to reduce the depreciation cost. The maintenance of cooling tower includes the
following:
1.
2.
3.
4.

The fan, motor housing should be inspected from time to time.
Motor bearing should be greased and gearbox oiled.
At least once in a year motor’s gear boxes should be checked for structural weakness.
The water spraying nozzles should be inspected regularly for clogging.

48

8.1 Boiler Used in Project
A boiler is a closed vessel made of high quality steel in which steam is generated form
water by the application of heat. The water receives heat from the hot gases through the
heating surface of the boiler. The hot gases are formed by burning fuel which is gas. The
boiler used is simple horizontal boiler.
The particulars (dimensions, capacity etc.) relating to this boiler is given below:
Diameter of drum

.............

15.2 c.m.

Length

.............

38 c.m.

Size of super heater tubes

.............

6.5 c.m.

Size of economiser tubes

.............

6.5 c.m.

Working pressure

.............

11 bar (max.)

Efficiency

.............

60 to 70%

Fig.8.1 Simple Horizontal Boiler.
It consists of a longitudinal drum, the greater portion of which is full of water and
remaining is the steam space. On the lower side of the boiler, burner is provided to supply the
heat of combustion of gas.
When the heat is supplied to the boiler, lower surface of the boiler comes in contact
with the hot gases at higher temperature. So the water from this portion rises in the upper
direction due to decreased density and passed into the upper section. Here the steam and
water are separated and the steam being lighter is collected in the upper part of the drum. The
circulation of water is maintained by convective currents and is known as natural circulation.
A superheater is placed between the furnace and the boiler drum. The hot gases are
passed over the superheater tubes and the steam is passed through the super heater and
becomes super heated steam. The steam is taken into the super heater from the steam space of
49

the drum through a copper tube through the pressure gauge valve. The super heated steam
coming out of the super heater is supplied through steam pipe to the steam turbine.
At the lower portion of the boiler a drain nut is provided to remove the mud or water
when the boiler is not in use.
The entire boiler is hung by means of metallic straps of mild steel supported on pillars. The
various mountings used in the boiler are pressure gauge, safety valve, main stop valve, super
heater, and economiser.

8.2 Turbine Used in Project
The steam turbine is a prime mover in which enthalpy of steam is first converted into
kinetic-energy in nozzles or blade passages. The high velocity steam impinges on the curved
blades which change the flow direction of steam causes a force to be exerted on the blades
fixed on a rotor and power is developed due to the rotation of these blades.
The technical specification of turbine is given below:
Diameter of blade

............

Speed

............

Rotational direction

............

Anti-Clockwise

Number of blades

............

5

Blade material

............

Aluminium

Fig.8.2 Blade of Steam Turbine.
The type of turbine blade used is impulse turbine. It is coupled to the shaft of the
electric generator. The blade is covered by the casing. The super heated steam coming out
from the super heater strikes the turbine blade which changes the flow direction of steam
causes a force to be exerted on the blades. As the blade is fixed to the rotor mechanical power
is developed.
50

Fig.8.3 Working Model of Steam Power Plant

51

8.3 Alternator Used in Project
The alternator is universally used in automotive applications. It converts mechanical
energy into electrical energy, by electro-magnetic induction.
In a simple version, a bar magnet rotates in an iron yoke which concentrates the
magnetic field. A coil of wire is wound around the stem of the yoke. As the magnet turns,
voltage is induced in the coil, producing a current flow. When the North Pole is up, and South
is down, voltage is induced in the coil, producing current flow in one direction. As the
magnet rotates, and the position of the poles reverses, the polarity of the voltage reverses too,
and as a result, so does the direction of current flow. Current that changes direction in this
way is called alternating current, or AC. The change in direction occurs once for every
complete revolution of the magnet.
Technical specification of alternator:
Voltage

……….

12 volt

Current

……….

0.13 amp

Fig.8.4 Alternator.
The alternator is coupled to the shaft of the turbine. As the shaft of the turbine rotates
the alternator also rotates and cuts magnetic lines of forces due to which an emf is induced in
the conductor. The magnitude of this induced emf is directly proportional to the rate of
change of flux. This emf will cause a direct current (D.C.) to flow in the conductor circuit.
In the project 12 V D.C. is generated. This 12 V D.C. is supplied to a storage device
which is known as battery. The type of battery used here in this project is rechargeable type
battery. Battery stores the energy generated from the generator (Alternator).

52

Technical specification of battery used:
Voltage

……….

12.5 volt

Current

……….

7.2 AH

An inverter circuit is connected to the battery which converts the D.C. (Direct
Current) stored in the battery to A.C. (Alternating Current). This current is used supplied for
use.

8.4 Condenser Used in Project
A closed vessel in which steam is condensed by abstracting heat from steam and the
pressure is maintained below atmospheric pressure is known as condenser. The efficiency of
the steam plant is considerably increased by the use of condenser. 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 reduces the water softening plant capacity to a considerable
extent.

Fig.8.5 Surface Condenser.
The type of condenser used is surface condenser type. It consists of a shell which is of
cylindrical shape. It has cover plates at the ends and furnished with two parallel copper tubes.
The cooling water enters the shell at the lower half section and after travelling through the
upper half section comes out through the outlet. The exhaust steam after working in the
turbine enters from the top of the condenser and flows down over the tubes and gets
condensed and is finally removed from the lower side of the shell.

53

8.5 Cooling Tower Used in Project
In power plants the hot water from condenser is cooled in cooling tower, so it can be
reused in condenser for condensation of steam. In a 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 thus cooled.

Fig.8.6 Cooling Tower.
The type of cooling tower used is forced draught. In these towers the draught of air
for cooling the tower is produced mechanically by means of propeller fans. The sides of the
tower are closed from an air and water tight structure, except for fan opening at the base for
the inlet of fresh air, and the outlet at the top for the exit of air and vapour.
The hot water from the condenser is sprinkled from the top of the cooling tower
through the nozzles. The sprinkled water particles flows through the fills and air is supplied
by the mechanical fans from the lower side of the tower. The cooled water collected at the
lower portion of the cooling tower is again pumped to the condenser by the help of a
submersible pump. This forms a closed cycle of operation.
Technical specification of fans and submersible pump used:
FAN:
Fan dimension

……….

120 × 120 × 25 mm

Fan speed

……….

2000 RPM

Fan weight

……….

116 g

Blade diameter

……….

120 mm

SUBMERSIBLE PUMP:
Operating voltage

……….

165 - 250 V
54

Frequency

……….

50 Hz

Input power

……….

18 watt

Delivery head

……….

1.65 m

Output

……….

1800 Litre/hr

8.6 Feed Pump Used in Project
A boiler feed water pump is a specific type of pump used to pump feed water into
a steam boiler. The water may be freshly supplied or returning condensate produced as a
result of the condensation of the steam produced by the boiler. These pumps are normally
high pressure units that take suction from a condensate return system and can be of the
centrifugal pump type or positive displacement type.

Fig.8.7 Feed Water Pump.
The type of pump used is submersible type centrifugal pump. The pump is placed in a
container. Condensate water is collected in the container and pumped to the boiler by the help
of the submersible centrifugal pump. There is only one limitation of the use of pump that the
pump can only operate when the boiler is in off condition. This is due to the fact that the
boiler pressure is much higher than the pump working pressure and pump cannot feed the
condensate to higher pressure region.
Technical specification of pump used:
Operating voltage

……….

165 - 250 V

Frequency

……….

50 Hz

Input power

……….

18 watt

Delivery head

……….

1.8 m

Output

……….

1100 Litre/hr

55

9.1 Calculation
Condition of steam inlet to turbine is 5 bar and 143˚C.
Outlet from turbine and inlet to condenser is 0.08 bar and 39˚C.
Outlet from condenser and inlet to pump is 0.07 bar and 32˚C.
From steam table,
At 5 bar,
h1 = 2748.7 kJ/kg
S1 = 6.8213 kJ/kg.K
At 0.08 bar,
hf2 = 173.88 kJ/kg
hfg2 = 2403.1 kJ/kg
In turbine entropy remains constant
S1 = S2
S1 = Sf2 + x2.Sfg2
⇒ 6.8213 = 0.6079 + x2.7.5994

⇒ 6.8213 – 0.6079 = x2.7.5994
⇒ x2 = 0.8176
h2 = hf2 + x2.hfg2
= 173.88 + (0.8176 × 2401.3)
= 2138.65 kJ/kg
At 0.07 bar,
hf3 = 146.68 kJ/kg
Total input to pump is 18 J/sec.
Mass flow rate of pump = 1100 litre/hr
= 0.305 kg/sec.
18 J/sec = 0.305 × (hf4 – hf3)
⇒ 18/0.305 = hf4 – 146.68
56

⇒ hf4 = 205.69 kJ/kg
Thermal efficiency of the plat
ɳth = (h1 – h2) / (h1 – hf4)
= (2748.7 – 2138.65) / (2748.7 – 205.69)
= 610.05 / 2543.01
= 0.2399 ×100 %
= 23.99 %
ɳth ≈ 24 %

57

9.2 Thermal Power Plants in India
Thermal power is the "largest" source of power in India. There are different types
of Thermal power plants based on the fuel used to generate the steam such as coal, gas, diesel
etc. About 65% of electricity consumed in India is generated by thermal power plants.
Coal
More than 51% of India's commercial energy demand is met through the country's
vast coal reserves. Public sector undertaking NTPC and several other state level power
generating companies are engaged in operating coal based Thermal Power Plants. Apart
from NTPC and other state level operators, some private companies are also operating the
power plants. As on July 31, 2010, and as per the Central Electricity Authority the total
installed capacity of Coal or Lignite based power plants in India are 87,093.38 MW. Some
list of currently operating coal based thermal power plants in India are:
Singrauli Uttar Pradesh

2000MW

Korba Chhattisgarh

2100MW

Ramagundam Andhra Pradesh

2600MW

Vindhyachala Madhya Pradesh

3260MW

NCTPP Dadri Uttar Pradesh

2310MW

Talcher Orissa

3000MW

Udupi power corporation Karnataka

1250MW

RTPC Raichur Karnataka

1720MW

JSW Bellary Karnataka

600MW

Vedanta Orissa

2400MW

CTPS Maharashtra

2340MW

Jindal Chhattisgarh

1000MW

58

Fig.9.1 Thermal Power Plants In India

59

Gas or Liquid based
As per the Central Electricity Authority the total installed capacity of gas based power
plants in India is 14,398.57 MW. This accounts for 10% of the total installed capacity.
GAIL is the main source of fuel for most of these plants. Here is some list of presently
operating plants.
Diesel Based
As per the Central Electricity Authority the total installed capacity of Diesel based
power plants in India is 1,199.75 MW. Normally the diesel based power plants are either
operated from remote locations or operated to cater peak load demands.

9.3 Thermal Efficiency of Power Plant
Coal the primary energy source consists mainly of Carbon. During the combustion
process the Carbon in the coal combines with Oxygen in the air to produce Carbon dioxide
producing heat. The high heating value, the energy available in the coal, is in the range of
10,500 kJ/kg to 27,000 kJ/kg.
For example, consider a coal with a high heating value of 20,000 kJ/kg. Theoretically
this is equivalent to 5.56 kwhr of electrical energy. Can we get all of this as electric power?
No. In practice the effective conversion is only around one third of the theoretically possible
value.
Why is it so?
The first process of energy conversion is the combustion where the potential energy in
coal is converted to heat energy. The efficiency of this conversion is around 90 %. Why?





Due to practical limitations in heat transfer, all the heat produced by combustion is
not transferred to the water; some is lost to the atmosphere as hot gases.
The coal contains moisture. Also coal contains a small percent of Hydrogen, which
also gets converted to moisture during combustion. In the furnace, moisture vaporizes
taking Latent heat from the combustion heat and exits the boiler along with the hot
gases.
Improper combustion of coal, hot ash discharged from the boiler and radiation are
some of the other losses.

The second stage of conversion is the thermodynamic stage. The heat from combustion is
transferred to the water to produce steam. The energy of the steam is converted to mechanical
rotation of the turbine. The steam is then condensed to water and pumped back into the boiler
for re-use. This stage works on the principle of the Rankine cycle. For plants operating with
steam at subcritical pressures (less than 221 bar) and steam temperatures of 570 °C, the

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Rankine cycle efficiency is around 43 %. For the state of the art plants running at greater than
supercritical pressure and steam temperatures near to 600 °C, the efficiency is around 47 %.
Why is it so low?





The steam is condensed for re-use. During this process the latent heat of condensation
is lost to the cooling water. This is the major loss and is almost 40 % of the energy
input.
Losses in the turbine blades and exit losses at turbine end are some of the other losses.
The Rankine cycle efficiency is dictated by the maximum temperature of steam that
can be admitted into the turbine. Due to metallurgical constraints steam temperatures
are at present limited to slightly more than 600 °C.

The third stage converts the mechanical rotation to electricity in a generator. Copper,
magnetic and mechanical losses account for 5 % loss in the Generator. Another 3 % is lost in
the step-up transformer which makes the power ready for transmission to the consumer.
To operate the power plant it is required to run various auxiliary equipment like
pulverizes fans, pumps and precipitators. The power to operate these auxiliaries has to come
from the power plant itself. For large power plants around 6 % of the generator output is used
for internal consumption. This brings the overall efficiency of the power plant to around 33.5
%. This means we get only 1.9 kwhr of electrical energy from one kg of coal instead of the
5.56 kwhr that is theoretically available in the coal.
The efficiency or inefficiency of power plants is something that we have to live with for
the present till technology finds a way out.

9.4 ADVANTAGES AND DISADVANTAGES OF THERMAL POWER PLANT
Advantages of Thermal Power Plant
1. The fuel used is quite cheap.
2. Less initial cost as compared to other generating plants.
3. It can be installed at any place irrespective of the existence of coal. The coal can be
transported to the site of the plant by rail or road.
4. It requires less space as compared to Hydro power plants.
5. Cost of generation is less than that of diesel power plants.
6. This plants can be quickly installed and commissioned and can be loaded when
compare to hydroelectric power plant.
7. It can meet sudden changes in the load without much difficulty controlling operation
to increase steam generation.
8. Coal is less costly than diesel.
9. Maintenance and lubrication cost is lower.

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Disadvantages of Thermal Power Plant
1. It pollutes the atmosphere due to production of large amount of smoke and fumes.
2. It is costlier in running cost as compared to Hydro electric plants.
3. Well, stations always take up room for the environment which could be cultivated for
the use of growing food etc. which is a great disadvantage is our day and age, as food
is necessary to live.
4. However, this could create more jobs for a lot of people thus increasing in a good way
our current economic situation which by is failing miserably.
5. Over all capital investment is very high on account of turbines, condensers, boilers reheaters etc. maintenance cost is also high on lubrication, fuel handling, fuel
processing.
6. It requires comparatively more space and more skilled operating staff as the
operations are complex and required precise execution
7. A large number of circuits makes the design complex
8. Starting of a thermal power plant takes fairly long time as the boiler operation and
steam generation process are not rapid and instantaneous

9.6 CONCLUSION
Though Thermal power energy has so many advantages, the main disadvantage is
thermla pollution. Water mainly gets polluted using thermal energy. The automobile industry,
textile industry, thermal power plant, nuclear power plant release hot water to the water
bodies.
Thermal power plants are goods that produce electricity. Morever, these plants are
important to customers and are presumed to have a service life of greater then twenty years.
Accordingly, the reliability of a power plants is considered most important, followed by aftersales service and then economic efficiency.
As demand for electrical power increases throught the world, various plants intend to
continue to strive to supply power plants that provide reliability, high performance and low
price in accordance with the need of customers.

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REFERENCES
1. http://en.wikipedia.org/wiki/Thermal_power_station
2. http://en.wikipedia.org/wiki/Electricity_sector_in_India#Thermal_power
3. http://en.wikipedia.org/wiki/Rankine_cycle
4. http://en.wikipedia.org/wiki/Boiler
5. http://en.wikipedia.org/wiki/Power_station
6. http://en.wikipedia.org/wiki/Water-tube_boiler
7. http://en.wikipedia.org/wiki/Surface_condenser
8. http://en.wikipedia.org/wiki/Cooling_tower_system
9. http://www.brighthubengineering.com/marine-engines-machinery/42651-marinealternators-protection-systems-used-on-board-ships/
10. http://indianpowersector.com/home/power-station/thermal-power-plant/
11. Babcock & Wilcox Co. (2005). Steam: Its Generation and Use (41st edition
ed.).ISBN 0-9634570-0-4.
12. Dr. R.K. Rajput, Power Plant Engineering
Laxmi publication (P) Ltd, 2007.
13. Arora, Domkundwar, A course in Power Plant Engineering
Dhanpat Rai & Co., 2008.
14. Domkundwar, Kothandaraman, A course in Thermal Engineering
Dhanpat Rai & Co., 2010.

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