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VOCATIONAL TRAINING PROJECT
REPORT
15/05/2012 - 09/06/2012
DEEPAK KUSHWAHA
BTech Mechanical Engineering
Motilal Nehru National Institute Of Technology,
Allahabad.
CONTENTS
1. Introduction to the company
a.About the company
b.Vision
c.Strategies
d.Evolution
2.Introduction to the project
3.Project report
a.Introduction
b.Steam boiler
c.Steam turbine
d.Turbine generator
INTRODUCTION TO
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THE COMPANYAbout the CompanyVision
Strategies
Evolution
ABOUT THE COMPANYNTPC, the largest power Company in India, was setup in 1975 to acceleratepower developmentin the country. It is among the worlds largest and most efficient power
generation companies. In Forbes list of Worlds 2000 Largest Companies for
the year 2007, NTPC occupies 411th place.
NTPC has installed capacity of 29,394 MW. It has 15 coal based power stations
(23,395 MW), 7 gas based power stations (3,955 MW) and 4 power stations inJoint Ventures (1,794 MW). The company has power generating facilities in all
major regions of the country. It plans to be a 75,000 MW company by 2017.
NTPC has gone beyond the thermal power generation. It has diversified into
hydro power, coal mining,power equipment manufacturing, oil & gasexploration, power trading & distribution.
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NTPC is now in the entire power value
chain and is poised to become an Integrated Power Major.
NTPC's share on 31 Mar 2008 in the total installed capacity of the country was
19.1% and it contributed 28.50% of the total power generation of the countryduring 2007-08. NTPC has setnew benchmarks for the power industry both in the area of power plant
construction and operations.
With its experience and expertise in the power sector, NTPC is extending
consultancy services to various organizations in the power business. It provides
consultancy in the area of powerplant constructions and power generation to companies in India and abroad.
In November 2004, NTPC came out with its Initial Public Offering (IPO)
consisting of 5.25% as fresh issue and 5.25% as offer for sale by Government of
India. NTPC thus became a listed company with Government holding 89.5% of
the equity share capital and rest held by Institutional Investors and Public. The
issue was a resounding success. NTPC is among the
largest five companies in India in terms of market capitalization.
Recognizing its excellent performance and vast potential, Government of the
India has identified NTPC as one of the jewels of Public Sector 'Navratnas'- a
potential global giant. Inspired by its glorious past and vibrant present, NTPC is
well on its way to realize its vision of being "A world
class integrated power major, powering India's growth, with increasing global
presence".
VISION
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A world class integrated power major, powering India's growth with increasing
global presence.
Develop and provide reliable power related products and services at competitive
prices,integrating multiple energy resources with innovative & Eco-friendlytechnologies and
contribution to the society
Core Values - BCOMIT
Business ethics
Customer Focus
Organizational & Professional PrideMutual Respect & Trust
Innovation & Speed
Total Quality for Excellence
STRATEGIES1.Sustainable development .
2.Maintain sector leadership position through expansion
3.Further enhance fuel security
4.Exploit new business opportunities.
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5.Technology initiatives.
6.Nurturing human resources.
INTRODUCTION TO
THERMAL POWER
PLANTIntroductionClassification
Functioning
INTRODUCTION
Power Station (also referred to as generating station or power plant) is an
industrial facility for the generation of electric power. Power plant is also used
to refer to the engine in ships, aircraft and other large vehicles. Some prefer touse the term energy center because it more accurately describes what the plants
do, which is the conversion of other forms of energy, like chemical energy,
gravitational potential energy or heat energy into electrical energy. However,
power plant is the most common term in the U.S., while elsewhere power
station and power plant are both widely used, power station prevailing in manyCommonwealth countries and especially in the United Kingdom.
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At the center of nearly all power stations is a generator, a rotating machine thatconverts
mechanical energy into electrical energy by creating relative motion between a
magnetic field and a conductor. The energy source harnessed to turn the
generator varies widely. It depends chiefly on what fuels are easily available
and the types of technology that the power company has access to.In thermal power stations, mechanical power is produced by a heat engine,
which transforms thermal energy, often from combustion of a fuel, into
rotational energy. Most thermal power stations produce steam, and these are
sometimes called steam power stations. About 80% of all electric power is
generated by use of steam turbines. Not all thermal energy can be transformedto mechanical power, according to the second law of thermodynamics.
Therefore, there is always heat lost to the environment. If this loss is employed
as useful heat, for industrial processes or district heating, the power plant is
referred to as a cogeneration power plant or CHP (combined heat-and-power)plant. In countries where district heating is common, there are dedicated heat
plants called heat-only boiler stations. An important class of power stations in
the Middle East uses byproduct heat for desalination of water.
CLASSIFICATION
By fuel
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generator.
il fuelled power plants may also use a steam turbine generator or in the
case of
natural gas fired plants may use a combustion turbine.
waste from sugar cane,
municipal solid
waste, landfill methane, or other forms of biomass.
-cost, although
low-energy density,fuel.trated enough to
use for
power generation, usually in a steam boiler and turbine.
By prime mover
by expanding
steam to turn the blades of a turbine. Almost all large non-hydro plants use thissystem.
operate the
turbine. Natural-gas fuelled turbine plants can start rapidly and so are used to
supply"peak" energy during periods of high demand, though at higher cost than base-
loaded
plants. These may be comparatively small units, and sometimes completely
unmanned,
being remotely operated. This type was pioneered by the UK, Prince town beingthe
world's first, commissioned in 1959.
ne fired by natural gas, and a
steam boilerand steam turbine which use the exhaust gas from the gas turbine to produce
electricity.
This greatly increases the overall efficiency of the plant, and many new baseload power
plants are combined cycle plants fired by natural gas.
isolated
communities and are frequently used for small cogeneration plants. Hospitals,
office
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buildings, industrial plants, and other critical facilities also use them to provide
backup
power in case of a power outage. These are usually fuelled by diesel oil, heavy
oil,
natural gas and landfill gas.
engines are low
cost solutions for using opportunity fuels, such as landfill gas, digester gas from
water
treatment plants and waste gas from oil production.
FUNCTIONING
Functioning of thermal power plant:
In a thermal power plant, one of coal, oil or natural gas is used to heat the boiler
to convert the water into steam. The steam is used to turn a turbine, which isconnected to a generator. When the turbine turns, electricity is generated and
given as output by the generator, which is then supplied to the consumers
through high-voltage power lines.
Detailed process of power generation in athermal power plant:
1)Water intake:Firstly, water is taken into the boiler through a water source. If water is
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available in a plenty in the region, then the source is an open pond or river. If
water is scarce, then it is recycled and the same water is used over and over
again.
2) Boiler heating: The boiler is heated with the help of oil, coal or natural gas.A furnace is used to heat the fuel and supply the heat produced to the boiler.The increase in temperature helps in the transformation of water into steam.
3) Steam Turbine: The steam generated in the boiler is sent through a steam
turbine. The turbine has blades that rotate when high velocity steam flows
across them. This rotation of turbine blades is used to generate electricity.
4) Generator: A generator is connected to the steam turbine. When the turbine
rotates, the generator produces electricity which is then passed on to the power
distribution systems.
5) Special mountings: There is some other equipment like the economizer and
air pre-heater.An economizer uses the heat from the exhaust gases to heat the
feed water. An air pre-heater heats the air sent into the combustion chamber to
improve the efficiency of the combustion process.
6) Ash collection system: There is a separate residue and ash collection system
in place to collect all the waste materials from the combustion process and to
prevent them from escaping into the atmosphere.Apart from this, there are various other monitoring systems and instruments in
place to keep track of the functioning of all the devices. This prevents any
hazards from taking place in the plant.
PROJECT REPORT
Introduction
Steam Generator or Boiler
Steam Turbine
Electric Generator
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IntroductionThe operating performance of NTPC has been considerably above the national
average. The availability factor for coal stations has increased from 85.03 % in
1997-98 to 90.09 % in 2006-07, which compares favourably with internationalstandards. The PLF has increased from 75.2% in 1997-98 to 89.4% during the
year 2006-07 which is the highest since the inception of NTPC.
steam is produced and used to spin a turbine that operates
a generator. Water is heated, turns into steam and spins a steam turbine whichdrives an
electrical generator. After it passes through the turbine, the steam is condensed
in a condenser; this is known as a Rankine cycle. Shown here is a diagram of a
conventional thermal power plant, which uses coal, oil, or natural gas as fuel to
boil water to produce the steam. The electricity generated at the plant is sent toconsumers through high-voltage power lines.
There are basically three main units of a thermal power plant:
1. Steam Generator or Boiler
2. Steam Turbine
3. Electric Generator
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Coal is conveyed (14) from an external stack and ground to a very fine powder
by large metal spheres in the pulverised fuel mill (16). There it is mixed with
preheated air (24) driven by the forced draught fan (20). The hot air-fuel
mixture is forced at high pressure into the boiler where it rapidly ignites. Water
of a high purity flows vertically up the tube-lined walls of the boiler, where itturns into steam, and is passed to the boiler drum, where steam is separatedfrom any remaining water. The steam passes through a manifold in the roof of
the drum into the pendant superheater (19) where its temperature and pressure
increase rapidly to around 200 bar and 540C, sufficient to make the tube walls
glow a dull red. The steam is piped to the high pressure turbine (11), the first of
a three-stage turbine process. A steam governor valve (10) allows for bothmanual control of the turbine and automatic set-point following. The steam is
exhausted from the high pressure turbine, and reduced in both pressure and
temperature, is returned to the
boiler reheater (21). The reheated steam is then passed to the intermediate
pressure turbine (9), and from there passed directly to the low pressure turbine
set (6). The exiting steam, now a little above its boiling point, is brought into
thermal contact with cold water (pumped in from the cooling tower) in the
condensor (8), where it condenses rapidly back into water, creating near
vacuum-like conditions inside the condensor chest. The condensed water is then
passed by a feed pump (7) through a deaerator (12), and pre-warmed, first in a
feed heater (13) powered by steam drawn from the high pressure set, and then in
the economiser (23), before being returned to the boiler drum. The cooling
water from the condensor is sprayed inside a cooling tower (1), creating ahighly visible plume of water vapor, before being pumped back to the
condensor (8) in cooling water cycle.
The three turbine sets are sometimes coupled on the same shaft as the three-
phase electrical generator (5) which generates an intermediate level voltage(typically 20-25 kV). This is stepped up by the unit transformer (4) to a voltage
more suitable for transmission (typically 250-500 kV) and is sent out onto the
three-phase transmission system (3).
Exhaust gas from the boiler is drawn by the induced draft fan (26) through an
electrostatic precipitator (25) and is then vented through the chimney stack (27).
Steam Generator or Boiler
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The boiler is a rectangular furnace about 50 ft (15 m) on a side and 130 ft (40
m) tall. Its walls are made of a web of high pressure steel tubes about 2.3 inches
(60 mm) in diameter.
Pulverized coal is air-blown into the furnace from fuel nozzles at the four
corners and it rapidly burns, forming a large fireball at the center. The thermal
radiation of the fireball heats the water that circulates through the boiler tubesnear the boiler perimeter. The water circulation rate in the boiler is three to four
times the throughput and is typically driven by pumps. As the water in the
boiler circulates it absorbs heat and changes into steam at 700 F (370 C) and
3,200 psi (22.1 MPa). It is separated from the water inside a drum at the top ofthe furnace. The saturated steam is introduced into superheat pendant tubes that
hang in the hottest part of the combustion gases as they exit the furnace. Here
the steam is superheated to 1,000 F (540 C) to prepare it for the turbine.
The steam generating boiler has to produce steam at the high purity, pressure
and temperature required for the steam turbine that drives the electricalgenerator. The generator includes the economizer, the steam drum, the chemical
dosing equipment, and the furnace with its steam generating tubes and the
superheater coils. Necessary safety valves are located at suitable points to avoid
excessive boiler pressure. The air and flue gas path equipment include: forced
draft (FD) fan, air preheater (APH), boiler furnace, induced draft (ID) fan, fly
ash collectors (electrostatic precipitator or baghouse) and the flue gas stack.
For units over about 210 MW capacity, redundancy of key components is
provided by installing duplicates of the FD fan, APH, fly ash collectors and ID
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fan with isolating dampers. On some units of about 60 MW, two boilers per unit
may instead be provided.
Boiler Furnace and Steam Drum
Once water inside the boiler or steam generator, the process of adding the latent
heat of
vaporization or enthalpy is underway. The boiler transfers energy to the water
by the chemical reaction of burning some type of fuel.The water enters the boiler through a section in the convection pass called the
economizer. From the economizer it passes to the steam drum. Once the water
enters the steam drum it goes down the down comers to the lower inlet water
wall headers. From the inlet headers the water rises through the water walls and
is eventually turned into steam due to the heat being generated by the burnerslocated on the front and rear water walls (typically). As the water is turned into
steam/vapor in the water walls, the steam/vapor once again enters the steamdrum.
The steam/vapor is passed through a series of steam and water separators andthen dryers inside the steam drum. The steam separators and dryers remove the
water droplets from the steam and the cycle through the water walls is repeated.
This process is known as natural circulation.
The boiler furnace auxiliary equipment includes coal feed nozzles and igniter
guns, soot
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blowers, water lancing and observation ports (in the furnace walls) for
observation of the
furnace interior. Furnace explosions due to any accumulation of combustible
gases after a tripout are avoided by flushing out such gases from the combustion
zone before igniting the coal.The steam drum (as well as the superheater coils and headers) have air ventsand drains needed for initial startup. The steam drum has an internal device that
removes moisture from the wet steam entering the drum from the steam
generating tubes. The dry steam then flows into the superheater coils.
Geothermal plants need no boiler since they use naturally occurring steam
sources. Heat exchangers may be used where the geothermal steam is verycorrosive or contains excessive suspended solids. Nuclear plants also boil water
to raise steam, either directly passing the working steam through the reactor or
else using an intermediate heat exchanger.
Fuel Preparation System
In coal-fired power stations, the raw feed coal from the coal storage area is first
crushed into small pieces and then conveyed to the coal feed hoppers at theboilers. The coal is next pulverized into a very fine powder. The pulverizers
may be ball mills, rotating drum grinders, or other types of grinders.
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Some power stations burn fuel oil rather than coal. The oil must kept warm
(above its pour point) in the fuel oil storage tanks to prevent the oil from
congealing and becoming unpumpable.
The oil is usually heated to about 100C before being pumped through the
furnace fuel oil spray nozzles.
Boilers in some power stations use processed natural gas as their main fuel.
Other power stations may use processed natural gas as auxiliary fuel in the
event that their main fuel supply (coal or oil) is interrupted. In such cases,
separate gas burners are provided on the boiler furnaces.
Fuel Firing System and Igniter System
From the pulverized coal bin, coal is blown by hot air through the furnace coalburners at an angle which imparts a swirling motion to the powdered coal to
enhance mixing of the coal powder with the incoming preheated combustion airand thus to enhance the combustion.
To provide sufficient combustion temperature in the furnace before igniting the
powdered coal, the furnace temperature is raised by first burning some light fuel
oil or processed natural gas (by using auxiliary burners and igniters provide for
that purpose).
Air Path
External fans are provided to give sufficient air for combustion. The forced
draft fan takes air from the atmosphere and, first warming it in the air preheaterfor better combustion, injects it via the air nozzles on the furnace wall.
The induced draft fan assists the FD fan by drawing out combustible gases from
the furnace,maintaining a slightly negative pressure in the furnace to avoid
backfiring through any opening.
At the furnace outlet, and before the furnace gases are handled by the ID fan,
fine dust carried by the outlet gases is removed to avoid atmospheric pollution.
This is an environmental limitation prescribed by law, and additionallyminimizes erosion of the ID fan.
Auxiliary Systems
Fly Ash Collection
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Fly ash is captured and removed from the flue gas by electrostatic precipitators
or fabric bag filters (or sometimes both) located at the outlet of the furnace and
before the induced draft fan.The fly ash is periodically removed from the collection hoppers below the
precipitators or bag filters. Generally, the fly ash is pneumatically transported tostorage silos for subsequent transport by trucks or railroad cars.
Bottom Ash Collection and Disposal
At the bottom of every boiler, a hopper has been provided for collection of the
bottom ash from the bottom of the furnace. This hopper is always filled with
water to quench the ash and clinkers falling down from the furnace. Some
arrangement is included to crush the clinkers and for conveying the crushedclinkers and bottom ash to a storage site.
Boiler Make-up Water Treatment Plant and Storage
Since there is continuous withdrawal of steam and continuous return of
condensate to the boiler,losses due to blow-down and leakages have to be made
up for so as to maintain the desired water level in the boiler steam drum. Forthis, continuous make-up water is added to the boiler water system. The
impurities in the raw water input to the plant generally consist of calcium and
magnesium salts which impart hardness to the water. Hardness in the make-up
water to the boiler will form deposits on the tube water surfaces which will lead
to overheating and failure of the tubes. Thus, the salts have to be removed from
the water and that is done by a water demineralising treatment plant
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DM :-A DM plant generally consists of cation, anion and mixed bed exchangers. The
final water from this process consists essentially of hydrogen ions and
hydroxide ions which is the chemical composition of pure water. The DM
water, being very pure, becomes highly corrosive once it absorbs oxygen fromthe atmosphere because of its very high affinity for oxygen absorption.The capacity of the DM plant is dictated by the type and quantity of salts in the
raw water input. However, some storage is essential as the DM plant may be
down for maintenance. For this purpose, a storage tank is installed from which
DM water is continuously withdrawn for boiler make-up. The storage tank for
DM water is made from materials not affected by corrosive water, such as PVC.The piping and valves are generally of stainless steel. Sometimes, a steam
blanketing arrangement or stainless steel doughnut float is provided on top of
the water in the tank to avoid contact with atmospheric air. DM water make-up
is generally added at the steam space of the surface condenser (i.e., the vacuum
side). This arrangement not only sprays the
water but also DM water gets deaerated, with the dissolved gases being
removed by the ejector of the condenser itself.
Steam Turbine
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Steam turbines are used in all of our major coal fired power stations to drive thegenerators or alternators, which produce electricity. The turbines themselves are
driven by steam generated in 'Boilers' or 'Steam Generators' as they are
sometimes called.
Energy in the steam after it leaves the boiler is converted into rotational energyas it passes through the turbine. The turbine normally consists of several stages
with each stage consisting of a stationary blade (or nozzle) and a rotating blade.
Stationary blades convert the potential energy of the steam (temperature and
pressure) into kinetic energy (velocity) and direct the flow onto the rotating
blades. The rotating blades convert the kinetic energy into forces, caused bypressure drop, which results in the rotation of the turbine shaft. The turbine
shaft is connected to a generator, which produces the electrical energy. The
rotational speed is 3000 rpm for Indian System (50 Hz) systems and 3600 for
American (60 Hz) systems. In a typical larger power stations, the steam turbines
are split into three separate stages, the first being the High Pressure (HP), the
second the Intermediate Pressure (IP) and the third the Low Pressure (LP) stage,
where high, intermediate and low describe the pressure of the steam.After the steam has passed through the HP stage, it is returned to the boiler to be
re-heated to its original temperature although the pressure remains greatly
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reduced. The reheated steam then passes through the IP stage and finally to the
LP stage of the turbine.
A distinction is made between "impulse" and "reaction" turbine designs based
on the relative pressure drop across the stage. There are two measures for
pressure drop, the pressure ratio and the percent reaction. Pressure ratio is thepressure at the stage exit divided by the pressure at the stage entrance. Reactionis the percentage isentropic enthalpy drop across the rotating blade or bucket
compared to the total stage enthalpy drop. Some manufacturers utilise percent
pressure drop across stage to define reaction.
Steam turbines can be configured in many different ways. Several IP or LP
stages can be incorporated into the one steam turbine. A single shaft or several
shafts coupled together may be used. Either way, the principles are the same for
all steam turbines. The configuration is decided by the use to which the steam
turbine is put, co-generation or pure electricity production. For cogeneration,
the steam pressure is highest when used as process steam and at a lower
pressure when used for the secondary function of electricity production.
Nozzles and Blades
Steam enthalpy is converted into rotational energy as it passes through a turbine
stage. A turbine stage consists of a stationary blade (or nozzle) and a rotating
blade (or bucket). Stationary blades convert the potential energy of the steam(temperature and pressure) into kinetic energy (velocity) and direct the flow
onto the rotating blades. The rotating blades convert the kinetic energy into
impulse and reaction forces caused by pressure drop, which results in therotation of the turbine shaft or rotor.
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Steam turbines are machines which must be designed, manufactured and
maintained to high tolerances so that the design power output and availability is
obtained. They are subject to a number of damage mechanisms, with two of the
most important being:
Erosion due to Moisture: -The presence of water droplets in the last stages of aturbine causes erosion to the blades. This has led to the imposition of an
allowable limit of about 12% wetness in the exhaust steam;
Solid Particle Erosion: -The entrainment of erosive materials from the boiler in
the steam causes wear to the turbine blades.
Cogeneration Cycles
In cogeneration cycles, steam is typically generated at a higher temperature andpressure than required for a particular industrial process. The steam is expanded
through a turbine to produce electricity and the resulting extractions at the
discharge are at the temperature and pressure required by the process.
Turbines can be condensing or non-condensing design typically with large mass
flows and comparably low output. Traditionally, pressures were 6.21 MPa and
below with temperatures 441o C or lower, although the trend towards higherlevels of each continues.There are now a considerable number of co-generation
steam turbines with initial steam pressures in the 8.63 to 10 MPa range and
steam temperatures of 482 to 510o C.Bearings and Lubrication
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Two types of bearings are used to support and locate the rotors of steam
turbines:
rbine rotors. A
journal bearing consists of two half-cylinders that enclose the shaft and are
internally lined with Babbitt, a metal alloy usually consisting of tin, copper andantimony; and
aring is made up
of a series of Babbitt lined pads that run against a locating disk attached to the
turbine rotor.
High-pressure oil is injected into the bearings to provide lubrication. The oil is
carefullyfiltered to remove solid particles. Specially designed centrifuges remove any
water from the oil.
Shaft Seals
The shaft seal on a turbine rotor consist of a series of ridges and groves around
the rotor and its housing which present a long, tortuous path for any steam
leaking through the seal. The seal therefore does not prevent the steam from
leaking, merely reduces the leakage to a minimum.The leaking steam is collected and returned to a low-pressure part of the steam
circuit.
Turning Gear
Large steam turbines are equipped with "turning gear" to slowly rotate the
turbines after they have been shut down and while they are cooling. This evens
out the temperature distribution around the turbines and prevents bowing of the
rotors.
Vibration
The balancing of the large rotating steam turbines is a critical component inensuring the reliable operation of the plant. Most large steam turbines havesensors installed to measure the movement of the shafts in their bearings. This
condition monitoring can identify many potential problems and allows the
repair of the turbine to be planned before the problems become serious.
Electric Generator
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The steam turbine-driven generators have auxiliary systems enabling them to
work satisfactorily and safely. The steam turbine generator being rotating
equipment generally has a heavy, large diameter shaft. The shaft therefore
requires not only supports but also has to be kept in position while running. To
minimize the frictional resistance to the rotation, the shaft has a number of
bearings. The bearing shells, in which the shaft rotates, are lined with a lowfriction material like Babbitt metal. Oil lubrication is provided to further reduce
the friction between shaft and bearing surface and to limit the heat generated.
Barring Gear (or Turning Gear)
Barring gear is the term used for the mechanism provided for rotation of the
turbine generator shaft at a very low speed (about one revolution per minute)after unit stoppages for any reason. Once the unit is "tripped" (i.e., the turbine
steam inlet valve is closed), the turbine starts slowing or "coasting down".
When it stops completely, there is a tendency for the turbine shaft to deflect orbend if allowed to remain in one position too long. This deflection is because
the heat inside the turbine casing tends to concentrate in the top half of the
casing, thus making the top half portion of the shaft hotter than the bottom half.The shaft therefore warps or bends by millionths of inches, only detectable by
monitoring eccentricity meters.
But this small amount of shaft deflection would be enough to cause vibrations
and damage the entire steam turbine generator unit when it is restarted.
Therefore, the shaft is not permitted to come to a complete stop by a mechanism
known as "turning gear" or "barring gear" that automatically takes over to rotatethe unit at a preset low speed.
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If the unit is shut down for major maintenance, then the barring gear must be
kept in service until the temperatures of the casings and bearings are sufficiently
low.
Condenser
The surface condenser is a shell and tube heat exchanger in which cooling water
is circulated through the tubes. The exhaust steam from the low pressure turbine
enters the shell where it is cooled and converted to condensate (water) by
flowing over the tubes as shown in the adjacent diagram. Such condensers use
steam ejectors or rotary motor-driven exhausters for continuous removal of air
and gases from the steam side to maintain vacuum.
A Typical Water Cooled Condenser
For best efficiency, the temperature in the condenser must be kept as low as
practical in order to achieve the lowest possible pressure in the condensing
steam. Since the condenser temperature can almost always be kept significantly
below 100 oC where the vapor pressure of water is much less than atmospheric
pressure, the condenser generally works under vacuum. Thus leaks of
noncondensible air into the closed loop must be prevented. Plants operating inhot climates may have to reduce output if their source of condenser cooling
water becomes warmer; unfortunately this usually coincides with periods of
high electrical demand for air conditioning.
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The condenser generally uses either circulating cooling water from a cooling
tower to reject waste heat to the atmosphere, or once-through water from a
river, lake or ocean.
Feedwater Heater
In the case of a conventional steam-electric power plant utilizing a drum boiler,
the surface condenser removes the latent heat of vaporization from the steam as
it changes states from vapour to liquid. The heat content (btu) in the steam is
referred to as Enthalpy. The condensate pump then pumps the condensate waterthrough a feedwater heater. The feedwater heating equipment then raises the
temperature of the water by utilizing extraction steam A Rankine cycle with a
two-stage steam turbine and a single feedwater heater.
from various stages of the turbine.A Rankine cycle with a two-stage steam turbine and a single feedwater heater
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Preheating the feedwater reduces the irreversibilities involved in steam
generation and therefore improves the thermodynamic efficiency of the
system.[9] This reduces plant operating costs and also helps to avoid thermal
shock to the boiler metal when the feedwater is introduced back into the steam
cycle.
Superheater
As the steam is conditioned by the drying equipment inside the drum, it is piped
from the upper drum area into an elaborate set up of tubing in different areas of
the boiler. The areas known as superheater and reheater. The steam vapor picks
up energy and its temperature is now superheated above the saturation
temperature. The superheated steam is then piped through the main steam lines
to the valves of the high pressure turbine.
Deaerator
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A steam generating boiler requires that the boiler feed water should be devoid
of air and other dissolved gases, particularly corrosive ones, in order to avoid
corrosion of the metal.Generally, power stations use a deaerator to provide for
the removal of air and other dissolved gases from the boiler feedwater. A
deaerator typically includes a vertical, domed deaeration section mounted ontop of a horizontal cylindrical vessel which serves as the deaerated boiler
feedwater storage tank.
There are many different designs for a deaerator and the designs will vary from
one
manufacturer to another. The adjacent diagram depicts a typical conventional
trayed deaerator. If operated properly, most deaerator manufacturers will
guarantee that oxygen in the deaerated
water will not exceed 7 ppb by weight (0.005 cm3/L).
Auxiliary Systems
Oil System
An auxiliary oil system pump is used to supply oil at the start-up of the steam
turbine generator. It supplies the hydraulic oil system required for steam
turbine's main inlet steam stop valve, the governing control valves, the bearing
and seal oil systems, the relevant hydraulic relays and other mechanisms.At a preset speed of the turbine during start-ups, a pump driven by the turbine
main shaft takes over the functions of the auxiliary system.
Generator Heat Dissipation
The electricity generator requires cooling to dissipate the heat that it generates.
While small units may be cooled by air drawn through filters at the inlet, larger
units generally require special cooling arrangements. Hydrogen gas cooling, in
an oil-sealed casing, is used because it has the highest known heat transfercoefficient of any gas and for its low viscosity which reduces windage losses.This system requires special handling during start-up, with air in the chamber
first displaced by carbon dioxide before filling with hydrogen. This ensures that
the highly flammable hydrogen does not mix with oxygen in the air.
The hydrogen pressure inside the casing is maintained slightly higher than
atmospheric pressure to avoid outside air ingress. The hydrogen must be sealed
against outward leakage where the shaft emerges from the casing. Mechanical
seals around the shaft are installed with a very small annular gap to avoid
rubbing between the shaft and the seals. Seal oil is used to prevent the hydrogengas leakage to atmosphere.
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The generator also uses water cooling. Since the generator coils are at a
potential of about 15.75kV and water is conductive, an insulating barrier such as
Teflon is used to interconnect the water line and the generator high voltage
windings. Demineralized water of low conductivity is used.
Generator High Voltage System
The generator voltage ranges from 10.5 kV in smaller units to 15.75 kV in
larger units. The generator high voltage leads are normally large aluminumchannels because of their high current as compared to the cables used in smaller
machines. They are enclosed in well-grounded aluminum bus ducts and are
supported on suitable insulators. The generator high voltage channels are
connected to step-up transformers for connecting to a high voltage electrical
substation (of the order of 220 kV) for further transmission by the local powergrid.
The necessary protection and metering devices are included for the high voltageleads. Thus, the steam turbine generator and the transformer form one unit. In
smaller units, generating at 10.5kV, a breaker is provided to connect it to a
common 10.5 kV bus system.
Other Systems
Monitoring and Alarm system
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Most of the power plants operational controls are automatic. However, at
times, manual
intervention may be required. Thus, the plant is provided with monitors andalarm systems that alert the plant operators when certain operating parameters
are seriously deviating from their normal range.
Battery Supplied Emergency Lighting & Communication
A central battery system consisting of lead acid cell units is provided to supply
emergency electric power, when needed, to essential items such as the power
plant's control systems, communication systems, turbine lube oil pumps, and
emergency lighting. This is essential for a safe, damage-free shutdown of theunits in an emergency situation.
DEEPAK KUSHWAHA
9956620375
mailto:[email protected]:[email protected]:[email protected]