project report deepak kushwaha.docx

7/30/2019 project report DEEPAK KUSHWAHA.docx

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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

[email protected]

9956620375
mailto:[email protected]:[email protected]:[email protected]

project report deepak kushwaha.docx

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