A PRACTICAL TRAINING REPORT ON SURATGARH SUPER THERMAL POWER STATION Submitted in partial fulfillment for the award of the degree of BACHELOR OF TECHNOLOGY (Rajasthan Technical University, Kota) IN Electrical Engineering SESSION (2013-2014) SUBMITTED TO: SUBMITTED BY: 1
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A PRACTICAL TRAINING REPORT
ON
SURATGARH SUPER THERMAL POWER STATION
Submitted in partial fulfillment for the award of the degree of
BACHELOR OF TECHNOLOGY (Rajasthan Technical University, Kota) IN
Electrical Engineering
SESSION (2013-2014)
SUBMITTED TO: SUBMITTED BY: Mr. Hemant Kaushik Manish SahuElectrical Engineering E.E. – 7th
Sem 10EMEEE023
DEPARTMENT OF ELECTRICAL ENGINEERINGMARUDHAR ENGINEERING COLLEGE
NH-11, RAISAR, BIKANER
1
AKNOWLEDGEMENT
This is opportunity to express my heartfelt words for the people who were part
of this training in numerous ways, people who gave me unending support right
from beginning of the training.
I am grateful to Training In charge Mr. Hemant Kaushik for giving
guidelines to make the project successful.
I want to give sincere thanks to the Principal, Dr. R.P.S. Jakhar for his
valuable support.
I extend my thanks to Dr. Javed Khan Bhutto Head of the Department for his
cooperation and guidance.
Yours Sincerely,
Manish Sahu
Contents
2
ABSTRACT 1
3
Chpater-1 INTRODUCTION 2-31.1 Suratgarh Super Therml Power Station 21.2 Installed Capacity 3
Chapter-2 SELECTION OF SITE FOR THERMAL POWER PLANTS 4-52.1 Supply of Water 42.2 Requirement of Land 42.3 Labour Supplies 42.4 Transportation Facility 52.5 Ash Disposal 52.6 Distance from the Populated area 52.7 Near of the Load Centre 5
Chapter-4 FUEL HANDLING AND FEED WATER 19-214.1 Fuel Handling 194.2 Feed Water 20
Chapter-5 ASH HANDLING AND DROUGHT SYSTEM 22-235.1 Ash Handling 225.2 Dust Collection 225.3 Draught System 23
Chapter-6 STEAM POWER PLANT CONTROLS 24Chapter-7 THERMAL POWER PLANT AUXILIARIES 25-28
7.1 Boiler make-up water treatment plant and storage
25
7.2 Fuel preparation system 267.3 Barring gear 267.4 Oil system 267.5 Generator cooling 277.6 Generator high-voltage system 277.7 Monitoring and alarm system 28
Chapter-8 MAJOR EQUIPMENT IN POWER PLANT 29-388.1 Power Transformers 298.2 Voltage Regulators 298.3 Bus-Bars 298.4 Reactors 308.5 Insulators 308.6 Switchgears 318.7 Switches 32
4
8.8 Protective Equipment 328.9 Protective Relays 348.10 Current Transformers 348.11 Potential Transformers 348.12 Lightning Arresters 358.13 Earthing of Power System 368.14 Control Room 38
Chapter-9 EFFICIENCY AND SUPERCRITICAL TECHNOLOGY 39-409.1 Efficiency of Thermal Power Plants 399.2 Advantages of Thermal Power Plants 399.3 Disadvantages of Thermal Power Plants 409.4 Super Critical Technology 40
Chapter-10 Reference 41
Table of FiguresFig. No Title of Figure Page No.
1 Thermal Power Plant Layout 62 Boiler 83 Internal Structure of Boiler 94 Super Heater 115 Condenser 146 Internal Structure of Feed Water Heater 167 Side View of Cooling Tower 178 Internal Structure of Cooling Tower 179 Types of Insulators 3110 Control Room of Thermal Power Plant 38
Table of TablesTable No. Title of Table Page No.
1 Installed Capacity of SSTPS 32 Efficiency of Installed Plant Capacity 39
5
ABSTRACT
The Suratgarh Super Critical Thermal Power Station is an electricity production project that
is maintained by the Rajasthan Rajya Vidhyut Nigam Limited. It is Rajasthan’s foremost
super thermal power station.
This station has been successful in controlling pollution and maintaining balance of
atmospheric emissions in the environment. The Union Ministry of Power has awarded this
power station with the Golden Shield Award.
The resinous project of Rajasthan, the Super Thermal Power Station, and Suratgarh is
situated near village Thukrana about 27 km. from Suratgarh city in Sriganganagar district.
The site was considered an ideal location for setting up a thermal power station due to
availability of land, water, transmission line and cheap labour.
Suratgarh Super Thermal Power Station has reached such dizzying heights of success that
its sixth unit. In this unit, maximum capacity on coal firing was attained in less than 10
hours and the phenomenal completion of the project in less than two years is a
groundbreaking achievement for the nation. Besides the philanthropic organization also has
a social conscience. The organization plants nearly 3.5 Lakhs saplings every year, digs up
dykes and water bodies and monitors the effusion of effluent materials and ambient air
quality in order to check the pollution level.
6
Chapter 1
INTRODUCTION
1.1 Suratgarh Super Thermal Power StationSTPS is situated near village Thukrana about 27Km south east of Suratgarh town is Shri
Ganaganager Distt. Suratgarh was considered an ideal location for setting up a thermal
power station in the state having regards to the availability of land, water, transmission
network proximity to broad gauge railway and being an important load centre for north-
west Rajasthan. Water and coal required in a large amount. Coal is received here from coal-
fields of MP areas through railways and water is received from INDIRA GANDHI
CANAL. The supply of coal is from MP, Jharkhand by rail. About 18000 tonne coal
required per day for whole unit and each unit consumes 150tonnes coal per day. About 2x3
km2 area covered by plant and approximately 1800 employees works in a plant including
chief engineer to labour. The supply electricity to the northern Rajasthan, Ratangarh,
Bikaner, Ganganagar.
The techno-economic clearance for the prefect was issued by CEA in June1991. The
planning commission accorded investment sanction for the project in Nov. 1991 for a total
estimated cost of Rs. 1253.31 Crores on prices prevailing in Sept.1990. The updated cost of
the project is estimates at Rs. 2300 Crores of including IDC.
Unit 1st of STPS was commissioned on coal firing on 4.10.1998 and commercial
operation of the unit was declared from 1.2.1999. The unit was dedicated to the
Nation by Hon’ble Chief Minister of Rajasthan Shri Ashok Gehlot on 3.10.1999.
The foundation stone for Unit 3rd and 4th STPS stage-II was laid by Hon’ble Chief
Minister of Rajasthan Shri Ashok Gehlot on 3.10.1999.
250MW Unit of STPS was commissioned on 28.3.2000 and was put on commercial
operation from 16.7.2000. It saved Rs. 80 Crores due to early start of generation.
The Unit was dedicated to the Nation by Hon’ble Dy. Leader of Opposition, Lok-
Sabha Smt. Sonia Gandhi on 13.10.2000.
7
The foundation stone 250MW Unit 5th under STPS stage-III was laid by Hon’ble
Union Minister of Power Shri Suresh P.Prabhu on 12.2.2001.
250MW Unit 3rd of STPS was commissioned on oil 29.10.2001 and was put on
commercial from 15.1.2002. The unit was dedicated to the Nation by Hon’ble Dy.
Leader of Opposition, Lok Sabha Shri Shivraj V.Patil on 17.3.2002.
250MW Unit 4th of STPS was commissioned on oil 25.3.2002 and has been put on
commercial operation from 31.7.2002. The unit was dedicated to the Nation by
Hon’ble Leader of Opposition, RajyaSabha Dr. Manmohan Singh on 10.8.2002.
With the commissioning of Unit 4th of 250MW at STPS it became FRIST SUPER
THERMAL POWER STATION OF RAJASTHAN.
650MW Unit 5th & Unit 6th of STPS was commissioned on oil 25.3.2002 and has
been put on commercial operation from 31.7.2002. The unit was dedicated to the
Nation by Hon’ble Leader of Opposition, RajyaSabha Dr. Manmohan Singh on
10.8.2002. With the commissioning of Unit 4th of 250MW at STPS it became
FRIST SUPER CRITICAL THERMAL POWER STATION OF RAJASTHAN.
1.2 Installed CapacityFollowing is the unit wise capacity of the plant:
Table1. Installed Capacity of SSTPS
Stage
Unit Numbe
r
Installed Capacity (MW)
Date of Commissionin
gStatus
Stage I
1 250 May, 1998 Running
Stage I
2 250 March, 2000 Running
Stage II
3 250 October, 2001 Running
Stage II
4 250 March, 2002 Running
Stage 5 250 June, 2003 Running
8
Stage
Unit Numbe
r
Installed Capacity (MW)
Date of Commissionin
gStatus
III
Stage IV
6 250 March, 2009 Running
Stage V
7 650 2011Work in progress
Stage V
8 650 2011Work in progress
Chapter 2
SELECTION OF SITE FOR THERMAL POWER
PLANTS
The following factor should be considered while selecting a site for a steam power plant for
economical and efficient generation:-
2.1 Supply of WaterA large quantity of water is required in steam power plants. It is required:
i. It raises the steam in the boiler.
ii. For cooling purposes such as in condensers.
iii. As a carrying medium such as in disposal of ash.
iv. For drinking purposes.
The efficiency of direct cooled plant is about 0.5% higher than that of the plant in which
cooling towers are used. This means a saving of about Rs. 7.5 Lakhs per year in fuel cost for
a 2000 MW station.
Huge amounts of coal is required for raising the steam (20,000 tonnes per day for a 2,000
MWs ). Since the Government policy is to use only low grade coal with 30 to 40% ash
content for the power generation purpose, the steam power plant should be located near the
coal mines to avoid the transport of coal and ash.
9
2.2 Requirement of LandThe land is required not only for setting up of the plant but also for other purposes such as
staff colonies, coal storage, ash disposal etc. Cost o land adds to the final cost of plant. So it
should be available at a reasonable cost. Land should be good bearing capacity since it has
to withstand about 7Kg./Sq. Cm. Moreover, land should be reasonably level. It should not
be low lying.
As the cost of the land adds up to the final cost of the plant, it should be available at a
reasonable price. Land should be also available for future extension.
2.3 Labour Supplies Skilled and unskilled labourers should be available at reasonable rates near the site of power
plant.
2.4 Transportation FacilityThe land and rail connections should be proper and capable of taking heavy and over
dimensioned loads of machines etc. To carry coal, oil etc. Which are daily requirements,
we need these transport linkages.
The facilities must be available for transportation of heavy equipment and fuels e.g. near
railway station
2.5 Ash DisposalAsh is the main waste product of the steam power plant. Hence some suitable means for
disposal of ash should be applied. Ash can be purchased by building contractors, cements
manufacturers or it can be sued for brick making near the plant site. Otherwise wasteland
should be available near the plant site for disposal of ash.
2.6 Distances from the Populated AreaSince most of the modern generating stations employ pulverized fuel residues and fumes
from them are quite harmful. Therefore the site for the plant should be away from the
populate area.
The factors to be considered while selecting a site for a steam power plant for the efficient
generation are:
10
2.7 Nearness of the load centre The power plant should ne as near as possible to the centre of load so that the transmission
cost and losses are minimum. This factor is most important when dc supply system is
adopted.
Chapter 3
PLANT FAMILIARIZATION
11
Fig.1 Thermal Power Plant Layout
3.1 TURBINE
3.1.1 Introduction The steam turbines and their auxiliaries installed have been manufactured by BHEL. The
turbines are three cylinders, compound 3000 rpm, double flow exhaust type reheat units
with initial parameters of 13 Kg/cm2. And five low pressure heaters are fed. The high
pressure cylinder comprises of two curt is wheels as a regulation stage. Intermediate
pressure cylinders comprise of twelve stages and each of the double flow section of the L.P.
cylinder consists of four stages.
3.1.2 OperationThere are two live steam lines connecting the boiler to the turbine. The superheated steam
enters the H.P. turbine and strikes its blades hence heat energy of steam is converted into
mechanical energy. The steam from H.P. turbine is reheated in reheaters and reheated steam
is sent to L.P. turbine through hot steam lines. Here second stage of energy conversion is
takes place. Then steam is sent to L.P. turbine from where it is ejected by vacuum ejectors
and condensed. Here are low cold reheaters and two hot reheat lines connecting the reheater
and turbine. In each of the two steam lines one electrically operated isolating valve, one
water separator and one quick closing stop valve are mounted. The direction of revolution
of turbine is clockwise when looking at turbine from front bearing pedestal. For the oil
lubrication of bearings and for governing, the main oil pump driven shaft is assembled into
the front bearing pedestal of turbine itself.
3.1.3 Components of Turbine
3.1.3.1 Casing or Cylinders:
A casing is essentially a pressure vessel which must be capable of withstanding the
maximum working pressure and temperature that can be produced within it. The working
pressure aspects demand thicker and thicker casing and the temperature aspects demand
thinner and thinner casings.
12
i. H.P Turbine Casing: The principal parts of the HP turbine casing are and axially
split inner shell, enclosing the rotor and outer shell of a barrel-type construction.
The barrel type of cylinder construction ensures symmetry of the wall thickness
around the axis of rotation and hence the wall thickness itself is relatively less
than that used in other type of construction.
ii. I.P. Turbine Casing: The IP turbine is split axially and is of single shell design.
The outer casing accommodates a double flow inner casing. The steam coming
from the re-heater is passed into the inner casing via admission branches which
are symmetrically arranged in the top and bottom halves of the outer casing.
iii. L.P Turbine Casing: The LP turbine is of double flow type. The casing is of
triple shell, fabricated construction. The outer casing consists of the front an drear
end walls, two longitudinal girders and a top cover. The inner shell of the inner
casing acts as the guide blade carriers for the initial stages of the turbine. The
guide blade carriers of the LP stage groups are so designed that, together with the
inner casing, they form annular ducts which are used for extractions.
3.2 BoilerThe boiler is installed in STPS are made by BHEL. Each of the boilers are single drum,
tangential fired water tube naturally circulated over hanged, balanced draft, dry bottom
reheat type and is designed for pulverizing coal firing with a max. Continuous steam output
of 375 Hour/hour at 138 Kg/cm2 pressure and 540℃ temperature. The thermal efficiency
of each boiler at MCR is 86.8%. Four number of bowl mills have been installed for each
boiler. Oil burners are provided for initial start up and stabilization of low load. Two E.S.P.
(One for each boiler) is arranged to handle flue gases from the respective boilers. The gases
from E.S.P. are discharged through 180 meters high chimney. I.D. fan and a motor is
provided near the chimney to induce the flue gases. The boiler is provided with a balanced
draft consisting of tow forced draft fans and two induced draft fans. Flue gases are utilized
to heat the secondary air for combustion tin the tubular type air heaters installed in the
13
boilers. Since the boiler furnace is maintained at t negative pressure, to avoid atmospheric
air entering the furnace a hydraulic pressure is maintained at the furnace bottom. The water
filled in the stainless steel seal through the hydraulic seal between the furnace ash hoppers
and the water wall ring heater. Adequate clearance is also provided for the downward
expansion of the furnace. Ash is formed by the result of burning of coal inside furnace. A
small quantity of ash is collected in the bottom ash hopper and considerable amount of ash
is collected in the E.S.P. and magnetic separator hopper.
This collected ash is extract and disposed off in as slurry from in the ash disposal arc.
For the central steam power plants o large capacity water tube are used. Water tube boilers
essentially consist of drums and tubes. The tubes are always external to drum. In
comparison to fire tube boilers, the drum in such boilers do not contain any tubular heating
surface, so they can be built in smaller diameters and consequently they will withstand high
pressure. The water tube boilers have got following advantages over the fire tube boilers.
The selection of the size and type of boiler depends upon –
14
Fig.3 Internal Structure of Boiler
i. The output required in terms of amount of steam per hour, operating temperature
and pressure.
ii. Availability of fuel and water.
iii. The probable load factor.
iv. Initial costs, maintenance costs, labour costs
v. Space requirement and availability.
3.3 Boiler Furnaces
A boiler furnace is a chamber in which fuel is burnt to liberate the heat energy. It provides
support and enclosures for the combustion equipments. The boiler furnace walls are made
of refractory materials such as fire clay, silica, kaolin etc. Such materials have the property
of resisting change of shape, weight or physical properties at high temperatures. The
construction of boiler furnace varies from plain refractory walls to completely water cooled
walls, depending upon characteristics of fuel used and ash produced, firing method, nature
of load demand, combustion space required, excess air used, operating temperature, initial
and operating costs.
The plain refractory walls are suitable for small plants where the furnace temperature may
not be high. For larger plants, where the furnace temperature is quite high, refractory walls
are made hollow and air is circulated through hollow space to keep the temperature of the
furnace walls low.
The recent development is to use water walls. Water walls are built of tubes of diameters
ranging from 25mm to 100mm variously spaced with or without fins or studs and bare or
with different thickness of mouldable refractory on the inner face. Heat transfer rates run
from 0.5x106 to 104x106 Kilo-calories per cubic metre of surface. To meet these
requirements of heat transmission, circulation on the water side must be adequate obtained
by convection or by pumps. This type is suitable for pulverised fuel fired boilers and high
steaming rates can be maintained.
3.4 Super-heater and Re-heaterA Super-heater is a device which removes the last traces of moisture from the saturated
steam leaving the boiler tubes and also increases its temperature above the saturation
temperature. For this purpose, the heat of combustion gases from the furnace is utilised.
Super-heaters consists of groups of tubes made of steel (carbon steel for steam temperature
up to 950℉ , carbon-molybdenum steel for steam temperatue of 1,050℉ and stainless steel
15
for steam temperature of 1,200℉) with an outside diameter ranging from 25mm to 64mm.
The super-heater tubes are heated by the heat of combustion gases during their passage from
the furnace to the chimney.
Super-heaters are classified into two parts.
3.4.1 Radiant Super-Heater:- It is located in the furnace between the furnace
water-walls and absorbs heat from the burning fuel through radiation. It has two main
disadvantages firstly, owing to high furnace temperature; it may get overhead and therefore,
requires a careful design. Secondly it gives drooping characteristics i.e. the temperature of
superheat falls with the increase in steam output, because with the increases in steam output
and radiant heat transfer being a function of furnace temperature increases slowly with
steam flow or the steam temperature falls.
Fig.4 Super Heater
3.4.2 Convection Super-Heater:- It is located well back in the boiler tube bank,
receives its heat entirely from fuel gases through convection. It gives rising characteristics
i.e. the temperature of superheat increases with the increase in steam output because with
the increase in steam output both gas flow over the super-heater tubes and steam flow
within the tubes increase with causes increase in the rate of heat transfer and mean
temperature difference. Convection super-heaters are more commonly used.
16
The function of the re-heater is to re-superheat the partly expanded steam from the turbine.
This is done so that the steam remains dry as far as possible through the last stage of the
turbine. Modern plants have re-heaters as well as super-heaters in the same gas passage of
the boiler. They can also be of combination type using both radiant and convective heating.
3.5 Economiser When the combustion gases leave the boiler after giving most of their heat to water tubes,
super-heater tubes and reheater tubes, they still possess lot of heat which if not recovered y
means of some devices, would go waste. Economiser and air pre-heater are such devices
which recover the heat from the flue gases on their way to chimney and raise the
temperature of feed water and air supplied for combustion respectively.
Economiser raises boiler efficiency (by10-12%), causes saving in fuel consumption and
reduces temperature stresses in boiler joints because of higher temperature of feed water,
but involves extra cost of installation, maintenance and regular cleaning and additional
requirement of space. Economiser tubes are made of steel either smooth or covered with
fins to increase the heat transfer surface area. The tubes can be arranged in parallel
continuous loops welded to and running between a pair of water headers or in return bend
design with horizontal tubes connected at their ends by welded or gasketed return bends
outside the gas path. The feed water flow through the tubes and the flue gases outside the
tubes across them. The heat transfer from flue gases to feed water is by convection. The
feed water should be sufficiently pure not to cause forming of scales and cause internal
corrosion and under boiler pressure. The temperature of feed water entering the economiser
should be high enough so that moisture from the flue gases does not condense on the
economiser tubes, which may absorb S02 and CO2 from the flue gases and form acid to
corrode the tubes. The temperature of the feed water entering the economiser is usually kept
above 84℃. In a modern economiser, the temperature of feed water is raised from about
247℃ to 276℃.
3.6 AirpreheaterAirpreheaters are employed to recover the heat from the flue gases leaving the economiser
and heat the incoming air required for combustion. This raises the temperature of the
furnace gases, improves combustions rates and efficiency, and lowers the stack temperature,
thus improving the overall efficiency of the boiler. It has been found that a drop of 20-22c
17
in the fuel gas temperature increases the boiler efficiency by about 1%. An air pre-heater
should have high thermal efficiency, reliability of operation, less maintenance charges,
should occupy small space, should be reasonable in initial cost and should be accessible.
Airpreheater are two types –
3.6.1 Recuperative Airpreheater: - These types of airpreheater are continuous in
action while the regenerative type is discontinuous in action and operates on cycle. In
recuperative type of heaters, the two fluids ate separated by heat transfer surface, one fluid
flowing constantly on one side and the other fluid on the other side of the surface. In the
recuperative type of heaters, the rate of heat transfer is low, space occupied in large and
cleaning of surface is difficult. The plate type recuperative heater consists of rectangular flat
plates spaced from 12.5mm to 25mm apart, leaving alternate air and gas passages.
3.6.2 Regenerative Airpreheater: - It consists of a rotor made up of corrugated
elements. The rotor is placed in a drum which has been divided into two compartments, air
and gas compartments. To avoid leakage from one compartment to the other seals are
provided. The rotor rotates at a very slow speed of 3-4rpm. As the rotor rotates, it
alternately passes through flue gases and air zones. The rotor elements are heated by the
flue gases in their zone and transfer this heat to air when they are in air zone.
3.7 CondenserSteam, after expansion through the prime mover, goes through the condenser which
condenses the exhaust steam and also removes air and other non-condensable gases from
steam while passing through them. The recovery of exhaust steam in the condenser reduces
the make-up feed water that must be added to the system, from 100% when exhausted to
atmosphere, to about 1-5% and thereby reduces considerably the capacity of water treatment
plant. The exhaust pressure may be lowered from the standard atmospheric pressure to
about 25mm of Hg absolute and thereby permitting expansion of steam, in the prime mover,
to a very low pressure and increasing plant efficiency operation.
Any leakage of air into the condenser destroys the vacuum and causes
i. An increase in the condenser pressure which limits the useful heat drop in the
prime mover.
18
ii. A lowering of the partial pressure of the steam and of the saturation
temperature along with it. This means that the latent heat increases and there-
fore, more cooling water is required.
Fig.5 Condenser
3.8 EvaporatorEvaporators ate employed for supplying pure water as make-up feed water in steam power
plants. In an evaporator raw water is evaporated by using extracted steam and the vapours
so produced may vex condensed to give a supply of distilled or pure feed water. These
vapours can be condensed in feed water heaters by the fee water or in separate evaporator
condensers using teed water as the cooling medium.
19
There are two main types of evaporators-
3.8.1 Film or Flash Type Evaporator: - In this kind of evaporators, there are
tubes or coils through which the steam is passed. Raw water is sprayed by means of nozzles
on the surface of these tubes and some of the raw water will be converted into vapours.
These vapours ate collected from the evaporator and are condensed to give pure and
distilled water for boilers.
3.8.2 Submerged Type Evaporator: - In this kind of evaporators, the tubes
through which the steam is passed are submerged in raw water. The vapours rising from the
raw water are collected and condensed to provide a supply of pure make-up feed water.
Because of continuous operation of raw water, concentration of impurities goes on
increasing, so periodic blowing down of raw water is essential. Scales formed on the surface
of the tubes will retard the heat transfer rate and so its removed is very necessary. This is
removed by draining the raw water from the shell and then spraying the tubes with cold
water while the tubes are kept hot by flow of steam through them. The scale is cracked off
and is washed away by the spray.
3.9 Feed Water HeaterThese heaters are used to heat the feed water by means of bled steam before it is
supplied to the boiler. Necessity of heating feed water before feeding it back to the boiler
arises due to the following reasons:
i. Overall power plant efficiency is improved.
ii. Thermal stresses due to cold water entering the drum of boiler are avoided.
iii. There is an increase in the quantity of steam produced by the boiler.
iv. The dissolved oxygen and carbon dioxide which would otherwise cause boiler
corrosion are removed in the feed water heaters.
v. Some other impurities carried by steam and condensate, due to corrosion in the
boiler and condenser, ate precipitated outside the boiler.
Feed water heaters are two types:
3.9.1 Open or Contact Heaters :- These are usually constructed to remove non-
condensable gases from water and steam along with raising the feed water temperature.
Such heaters are also called the deaerator. The amount of gas dissolved in water depends
20
upon its temperature. This decreases sharply with the increasing temperatures and falls to
almost zero at the boiling point. Such feed water heaters are used in small power plants.
3.9.2 Closed or Surface Heaters :- These heaters consist of closed shell in which
there are tubes or coils through which either steam or water is circulated. Usually, the water
is circulated through the tubes and the steam and water may flow either in the same
direction or in opposite directions. Such heaters may be the temperature of steam. For
maintaining a high overall heat transfer for the heater, the water velocity should be high but
pumping costs limit the velocity to about 1-2.5m/s.
Fig.6 Internal Structure of Feed Water Heater
3.10 Cooling TowersA cooling tower is a wooden or metallic rectangular structure inside of which is packed with
baffling devices. The hot water is led to the tower top and falls down through the tower and
is broken into small particles while passing over the baffling devices. Air enters the tower
from the bottom and flows upward. The air vaporises a small percentages of water, thereby
cooling the remaining water. The air gets heated and leaves the tower at the top. The cooled
water falls down into a tank below the tower from where into small droplets, the drought
provided by the tower and the large evaporating surface help to cool water very quickly
practically during the time while it is descending. Although eliminators are provided at the
21
top of the tower to prevent escape of water particles with air but even then there is a loss of
water to the extent of around 5% and this loss has to made up by water drawn from well or
any other source. Air can be circulated in cooling towers through draught.
Fig.7 Side View of Cooling Tower
Fig.8 Internal Structure of Cooling Tower
22
3.11 Turbo AlternatorIn a central power station, the system turbine and alternator are directly coupled to avoid
transmission losses. Turbo-alternators are high speed machines (3,000 or 5,000RPM) for 50
Hz systems. These machines have horizontal configurations and smooth cylindrical (or non
salient pole) type field structure wound usually for 2 or 4 poles. To reduce the peripheral
speed (maximum peripheral speed should not exceed 175 m/s) the diameter of the rotor is
kept small and axial length is increased. The ratio of diameter to axial length ranges from
1/3 to ½.
Due to high peripheral speed, the rotating part of the turbo-alternator is subjected to high
mechanical stresses. As a result the rotor of large turbo-alternator is normally built from
solid steel forging. Chromium-nickel-steel or special chrome-nickel-molybdenum steel is
used for rotors of turbo-alternators. The coils are held in place by steel or bronze wedges
and the coil ends are fastened by metal rings. Normally two-third of the rotor is slotted for
the field winding and one-third is left without slots so as to form the pole faces. 500 MW
units generally use hollow stator conductor. The short-circuit ratio is 0.4 to 0.6
The non-salient field structure used in turbo-alternators has the following special features:
i. They are of smaller diameter (maximum 1m in 2-pole machine) and of very long
axial length.
ii. Robust construction and noiseless operation.
iii. Less windage (air-resistance) loss.
iv. Better in dynamic balancing.
v. High operating speed (3,000 or 1,500).
vi. Nearly sinusoidal flux distribution around the periphery, and therefore, gives a better
emf waveform than obtainable with salient pole field structure.
vii. There is no need of providing damper windings (except in special cases to assist in
synchronising) because the solid field poles themselves act as efficient dampers.
.
23
Chapter 4
FUEL HANDLING AND FEED WATER4.1 Fuel Handling Coal can be handled manually or mechanically. Mechanical adopted as it is reliable,
expeditious and economical. Owing to large quantity of coal required to be handled every
day, mechanical handling has become absolutely necessary.
The main required of a coal handling plant are reliability, soundness and simplicity
requiring a minimum of operatives and minimum of maintenance. Besides, the plant should
be able to deliver the required quantity of coal at destination during peak hours.
4.1.1 Transportation or Delivery of CoalThere are three ways of transporting coal from coal mines to the site of power plant i.e. by
sea or river, by road and by rail. If the power plant is situated on the bank of a river or near
the sea-shore, it is often economical to transport coal in boats or barges, unload
mechanically by cranes or grab buckets and place in the storage yard or directly to the
conveyor system to be carried to the power plant. Transportation by road is possible for
small and medium size plants only. The chief advantage of this system is possibility of
carrying coal directly into the power house up to the point of consumption. Moreover due to
less traffic restrictions it is considered better system in comparison to rail transport.
Transportation of coal by rail, particularly for station located interior, is still the most
important mean of transportation in common use.
4.1.2 Methods of Coal HandlingIrrespective of the method of transportation of coal adopted, the coal has to be carried to the
boiler stokers or the coal preparation plant in the case of pulverised fuel firing. The various
stages in coal handling are:
4.1.2.1Unloading Stage:- The coal is unloaded from the point of delivery by means of
i. coal shakers or coal accelerators
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ii. rotary car dumpers or wagon tipplers and
iii. grab buckets
The choice equipment will depended upon the method of transportation adopted. The main
equipment employed for taking the coal from the unloading site to the dead storage are belt