42584029 Abhinav Training Report

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SUMMER TRAINING REPORT

5th July to 14th August

Submitted By:-

Abhishek.B.Tech. 3rd year

Roll no. 0709740003


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This is to certify that Abhishek student of 2007-2011 Batch of

Mechanical branch in 3rd Year of has successfully completed hisindustrial training atBadarpur Thermal Power Station- NTPC, New

Delhi for six weeks from 5th July to 14th August 2010. He has

completed the whole training as per the training report submitted by

him.

Training In-charge

Badarpur Thermal Power Station

NTPC, Badarpur New

Delhi.


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Table of Contents

1. Acknowledgement

2. About the Company

3. Thermal Power Plant

Introduction

Operation

Functioning

4. Electricity Generation Process

5. PAM

6. TMD


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Acknowledgement

With profound respect and gratitude, I take the opportunity to conveymy thanks to NTPC Badarpur Management . I express gratitude to the

Program Manager and other faculty members of Mechanical

Engineering Department for providing this opportunity to undergo

industrial training at National Thermal Power Corporation, Badarpur,

New Delhi.

I do extend my heartfelt thanks to Ms. Rachna Singh Bhalfor providingme this opportunity to be a part of this esteemed organization.

I am extremely grateful to Mr. G.D.Sharma, Superintendent of Im-Plant

Training at BTPS-NTPC, Badarpur for his guidance during whole

training.

I am extremely grateful to all the technical staff of BTPS-NTPC for theirco-operation and guidance that helped me a lot during the course of

training. I have learnt a lot working under them and I will always be

indebted of them for this value addition in me.

Finally, I am indebted to all whosoever have contributed in this report

work and friendly stay at Badarpur Thermal Power Station, Badarpur,

New Delhi.


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About The Company

CORPORATE VISIONA world class integrated power major, powering India's

growth with increasing global presence.

CORE VALUES

BCOMITB- Business ethics

C- Customer focus

O- Organizational & professional pride

M- Mutual respect & trust

I- Innovation & speed

T- Total quality for excellence


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Mission

Develop and provide reliable power related products andservices at competitive prices, integrating multiple energy

resources with innovative & Eco-friendly technologies and

contribution to the society.


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A Graphical Overview


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JOURNEY OF NTPC

NTPC was set up in 1975 with 100% ownership by

the Government of India. In the last 30 years, NTPChas grown into the largest power utility in India.

In 1997, Government of India granted NTPC status of

Navratna being one of the nine jewels of India,

enhancing the powers to the Board of Directors.

NTPC became a listed company with majority

Government ownership of 89.5%.

NTPC becomes third largest by Market Capitalization

of listed companies

The company rechristened as NTPC Limited in line

with its changing business portfolio and transforms

itself from a thermal power utility to an integrated

power utility.

National Thermal Power Corporation is the largestpower generation company in India. Forbes Global

2000 for 2008 ranked it 411th in the world.

1975

1997

2005

2004

2008


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National Thermal Power Corporation is the largest

power generation company in India. Forbes Global

2000 for 2008 ranked it 317th in the world.

NTPC has also set up a plan to achieve a target of

50,000 MW generation capacity.

NTPC has embarked on plans to become a 75,000MW company by 2017.

NTPC is the largest power utility in India, accounting for about 20% of

Indias installed capacity.

2009

2017

2012


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NTPC Limited , Badarpur

Installed capacity : 720 MWDerated Capacity : 705 MW

Location : New Delhi

Coal Source : Jharia Coal Fields

Water Source : Agra Canal

Beneficiary States : Delhi

Unit Sizes : 3X95 MW2X210 MW

Units Commissioned : Unit I- 95 MW - July1973

Unit II- 95 MWAugust 1974

Unit III- 95 MWMarch 1975

Unit IV - 210 MWDecember 1978

Unit V - 210 MWDecember 1981


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THEMAL POWER PLANT

Introduction

Classification

Functioning


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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 to use the term energy center because it more accurately

describes what the plants do, which is the conversion of other forms ofenergy, 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 many Commonwealth countries

and especially in the United Kingdom.


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A coal-fired Thermal Power Plant

At the center of nearly all power stations is a generator, a rotating

machine that converts 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 transformed to mechanical power, according to the second

law of thermodynamics. Therefore, there is always heat lost to theenvironment. 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 by-product heat for desalination of

water.


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F UNCTIONING

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 aturbine, which is connected 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.

Process of a Thermal Power Plant


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OPERATION

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 international

standards. 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.

Operation Room of Power Plant

In Badarpur Thermal Power Station, steam is produced and used to spin a turbine

that operates a generator. Water is heated, turns into steam and spins a steamturbine which drives an electrical generator. After it passes through the turbine, the

steam is condensed in a condenser; this is known as a Rankine cycle. The

electricity generated at the plant is sent to consumers through high-voltage power

lines.


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The Badarpur Thermal Power Plant has Steam Turbine-Driven Generators which

has a collective capacity of 705MW.

The fuel being used is Coal which is supplied from the Jharia Coal Field in

Jharkhand.

Water supply is given from the Agra Canal.

Table: Capacity of Badarpur Thermal Power Station, (BTPS) New Delhi

There are basically three main units of a thermal power plant:

1. Steam Generator or Boiler

2. Steam Turbine

3. Electric Generator

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 it turns into

steam, and is passed to the boiler drum, where steam is separated from any

remaining water. The steam passes through a manifold in the roof of the drum into

the pendant super heater (19) where its temperature and pressure increase rapidlyto around 200 bar and 540C,


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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 both manual 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 condenser (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 a highly visible plume of water vapour, before being

pumped back to the condensor (8) in cooling water cycle. The three turbine sets aresometimes 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

220-250 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).


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Steam Generator/ Boiler

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

tubes near 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 (22.1MPa). It is separated from the water inside a drum at the top of the

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 steamgenerating boiler has to produce steam at the high purity, pressure and temperature

required for the steam turbine that drives the electrical generator. 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.

Schematic diagram of a coal-fired power plant steam generator


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Boiler Fur nace 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 burners located on the front and rear water walls (typically). As the water is

turned into steam/vapour in the water walls, the steam/vapour once again enters the

steam drum.

External view of a boiler

The steam/vapour is passed through a series of steam and water separators and then

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 equipmentincludes coal feed nozzles and igniter guns, soot 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

vents and drains needed for initial start-up. The steam drum has an internal device


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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 very corrosive 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 the boilers.

The coal is next pulverized into a very fine powder. The pulverisers may be ballmills, rotating drum grinders, or other types of grinders. 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 coal

burners at an angle which imparts a swirling motion to the powdered coal to

enhance mixing of the coal powder with the incoming preheated combustion air

and 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).


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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 (DM).

Ash Handling System at Badarpur Thermal Power Station, New Delhi

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 from the atmosphere

because of its very high affinity for oxygen absorption. The capacity of the DMplant 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


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A 95 MW Generator at BTPS, New Delhi

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 or bend 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 thetop 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 rotate

the unit at a preset low speed. 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 CondenserFor 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

C where the vapour pressure of water is much less than atmospheric pressure,

the condenser generally works under vacuum. Thus leaks of noncondensible air


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into the closed loop must be prevented. Plants operating in hot 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. 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.

A typical water cooled condensor

Feedwater Heater

A Rankine cycle with a two-stage steam turbine and a single feedwater heater. Inthe 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 water through a

feedwater heater. The feedwater heating equipment then raises the temperature of

the water by utilizing extraction steam from various stages of the turbine.


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Preheating the feedwater reduces the irreversibilitys 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.


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A Rankine cycle with a 2-stage steam turbine and a single feedwater

heater

Superheater

As the steam is conditioned by the drying equipment inside the drum, it is pipedfrom 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 vapour 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

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 on top of a

horizontal cylindrical vessel which serves as the deaerated boiler feedwater storage

tank.


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Boiler Feed Water DeaeratorThere 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 guaranteethat 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 oilsystems, 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 anoil-sealed casing, is used because it has the highest known heat transfer coefficient

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 hydrogen gas leakage to atmosphere. 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. Demineralised

water of low conductivity is used.


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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 aluminum channels

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 power grid. The necessary protection

and metering devices are included for the high voltage leads. 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.

ELECTRICITY GENERATION PROCESS

(A BASIC OVERVIEW)

HOW ELECTRICITY IS GENERATED?

Thermal power station burns fuel and uses the resultant heat to raise steam which

drives the TURBO GENERATOR. The fuel may be fossil(coal,oil,natural gas) or

it may be fissionable, whichever fuel is used, the objective is same to convert the

mechanical energy into electricity by rotating a magnet inside a set of winding.

COAL TO STAEM

Its other raw materials are air and water. The coal brought to the station by trains

or by other means, travels handling plant by conveyer belts, travels from

pulverizing mills, which grind it as fine as the face powder of size upto 20 microns.


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The finely produced coal mixed with preheated air is then blown into the boiler by

a fan called primary air fan where it burns more like a gas than as a solid, in the

conventional domestic or industrial grate, with additional amount of air, called

secondary air supply, by forced draft fan.

As coal is ground so finally the resultant ash is also a fine powder. Some of it binds

together to form pumps, which falls into ash pits at the bottom of the furnace. The

water-quenched ash from the bottom is conveyed to pits for subsequent disposal or

sale. Most of ash, still in fine partical form is carried out of boilers to the

precipitator as dust, where electrodes charged with high voltage electricity trap it.

The dust is then conveyed to water to disposal area or to bunker for sale while the

clean flue gases are passed on through IP fans to be discharged through chimneys.

The heat released from the coal has been absorbed by the many kilometers tubingwhich line the boiler walls. Inside the tubes the boiler feed water, which is

transformed by heat into staemat high temperature and pressure.. The steam

superheated in further tubes (superheaters) passes to turbine where it is discharged

through the nozzle on the turbine blades. Just as the energy of wind turns the sail of

the windmill, the energy of steam striking the blade makes the turbine rotate.

Coupled to the end of the turbine is the rotor of the generator. The rotor is housed

inside the stator having heavy coils of the bars in which electricity is produced

through the movement of magnetic field created by the rotor. Electricity passes

from stator windings to step-up transformer which increases its voltage so that itcan be transmited efficiently over lines of grid.

The staem which has given up its heat energy is cahnged back into water in a

condenser so that it is ready for re-use. The condenser contains many kilometers of

tubing through which cold water is constantly pumped. The staem passing around

the tubes looses heat.Thus it is rapidly changed back into water.

But, the two lots of water, that is, the boiler feed and cooling water must never

mix. Cooling water is drawn from river- bed, but the boiler feed water must beabsolutely pure, far purer than the water we drink(de-mineralized water),

otherwise it may damage the boiler tubes.


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My summer training of 4 weeks (5th July 24th August ) has been

scheduled as follows:

CHP ( Coal Handling Plant ) --- 1week

PAM ( Plant Auxiliary Maintenance ) --- 2 week

TMD ( Turbine Maintenance Deptt. ) --- 1 weeks


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Coal Handling Plant

Coal is delivered by highway truck, rail, barge or collier ship. Some plants are even

built near coal mines and coal is delivered by conveyors. A large coal train called a

"unit train" may be a kilometres (over a mile) long, containing 60 cars with 100

tons of coal in each one, for a total load of 6,000 tons. A large plant under full load

requires at least one coal delivery this size every day. Plants may get as many as

three to five trains a day, especially in "peak season", during the summer months

when power consumption is high. A large thermal power plant such as the

Badarpur Thermal Power Station, New Delhi stores several million tons of coal for

use when there is no wagon supply.


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Coal Handling Plant Layout

Modern unloaders use rotary dump devices, which eliminate problems with coalfreezing in bottom dump cars. The unloader includes a train positioner arm that

pulls the entire train to position each car over a coal hopper. The dumper clamps an

individual car against a platform that swivels the car upside down to dump the

coal. Swivelling couplers enable the entire operation to occur while the cars are

still coupled together. Unloading a unit train takes about three hours.


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Shorter trains may use railcars with an "air-dump", which relies on air pressure

from the engine plus a "hot shoe" on each car. This "hot shoe" when it comes into

contact with a "hot rail" at the unloading trestle, shoots an electric charge through

the air dump apparatus and causes the doors on the bottom of the car to open,

dumping the coal through the opening in the trestle. Unloading one of these trains

takes anywhere from an hour to an hour and a half. Older unloaders may still use

manually operated bottom-dump rail cars and a "shaker" attached to dump the coal.

Generating stations adjacent to a mine may receive coal by conveyor belt or

massive diesel electric-drive trucks.

Coal is prepared for use by crushing the rough coal to pieces less than 2 inches (50mm) in size. The coal is then transported from the storage yard to in-plant storage

silos by rubberized conveyor belts at rates up to 4,000 tons/hour. In plants that

burn pulverized coal, silos feed coal pulverisers (coal mill) that take the larger 2

inch pieces grind them into the consistency of face powder, classify them, and

mixes them with primary combustion air which transports the coal to the furnace

and preheats the coal to drive off excess moisture content. In plants that do not


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burn pulverized coal, the larger 2 inch pieces may be directly fed into the silos

which then feed the cyclone burners, a specific kind of combust or that can

efficiently burn larger pieces of fuel.

Run-Of-Mine (ROM) Coal

The coal delivered from the mine that reports to the Coal Handling Plant is called

Run-of-mine, or ROM, coal. This is the raw material for the CHP, and consists of

coal, rocks, middlings, minerals and contamination. Contamination is usually

introduced by the mining process and may include machine parts, used

consumables and parts of ground engaging tools. ROM coal can have a large

variability of moisture and maximum particle size.

Coal Handling

Coal needs to be stored at various stages of the preparation process, and conveyed

around the CHP facilities. Coal handling is part of the larger field of bulk material

handling, and is a complex and vital part of the CHP.

Stockpiles

Stockpiles provide surge capacity to various parts of the CHP. ROM coal is

delivered with large variations in production rate of tonnes per hour (tph). A ROM

stockpile is used to allow the wash plant to be fed coal at lower, constant rate.

Coal Handling Division of BTPS, New Delhi


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A simple stockpile is formed by machinery dumping coal into a pile, either from

dump trucks, pushed into heaps with bulldozers or from conveyor booms. More

controlled stockpiles are formed using stackers to form piles along the length of a

conveyor, and reclaimers to retrieve the coal when required for product loading,etc. Taller and wider stockpiles reduce the land area required to store a set tonnage

of coal. Larger coal stockpiles have a reduced rate of heat lost, leading to a higher

risk of spontaneous combustion.

Stacking

Travelling, lugging boom stackers that straddle a feed conveyor are commonly

used to create coal stockpiles. Stackers are nominally rated in tph (tonnes per hour)

for capacity and normally travel on a rail between stockpiles in the stockyard. Astacker can usually move in at least two directions typically: horizontally along the

rail and vertically by luffing its boom. Luffing of the boom minimises dust by

reducing the height that the coal needs to fall to the top of the stockpile. The boom

is luffed upwards as the stockpile height grows.


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Wagon Tripler at Badarpur Thermal Power Station, New Delhi

Some stackers are able to rotate by slewing the boom. This allows a single stacker

to form two stockpiles, one on either side of the conveyor. Stackers are used to

stack into different patterns, such as cone stacking and chevron stacking. Stackingin a single cone tends to cause size segregation, with coarser material moving out

towards the base. Raw cone ply stacking is when additional cones are added next

to the first cone. Chevron stacking is when the stacker travels along the length of

the stockpile adding layer upon layer of material. Stackers and Reclaimers were

originally manually controlled manned machines with no remote control. Modern

machines are typically semi-automatic or fully automated, with parameters

remotely set.

Reclaiming

Tunnel conveyors can be fed by a continuous slot hopper or bunker beneath the

stockpile to reclaim material. Front-end loaders and bulldozers can be used to push

the coal into feeders. Sometimes front-end loaders are the only means of

reclaiming coal from the stockpile. This has a low up-front capital cost, but much

higher operating costs, measured in dollars per tonne handled.


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Coal Storage Area of the Badarpur Thermal Power Station, New Delhi

High-capacity stockpiles are commonly reclaimed using bucket-wheel reclaimers.These can achieve very high rates.

Coal Sampling

Sampling of coal is an important part of the process control in the CHP. A grab

sample is a one off sample of the coal at a point in the process stream, and tends

not to be very representative. A routine sample is taken at a set frequency, either

over a period of time or per shipment.

Screening


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Screens are used to group process particles into ranges by size. These size ranges

are also called grades. Dewatering screens are used to remove water from the

product. Screens can be static, or mechanically vibrated. Screen decks can be made

from different materials such as high tensile steel, stainless steel, or polyethylene.

Screening and Separation Unit of Coal Handling Division

Magnetic Separation

Magnetic separators shall be used in coal conveying systems to separate tramp iron

(including steel) from the coal. Basically, two types are available. One type

incorporates permanent or electromagnets into the head pulley of a belt conveyor.

The tramp iron clings to the belt as it goes around the pulley drum and falls off into

a collection hopper or trough after the point at which coal is charged from the belt.

The other type consists of permanent or electromagnets incorporated into a belt


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Advantages of Pulverized Coal Pulverized coal is used for large capacity plants.

It is easier to adapt to fluctuating load as there are no limitations on the

combustion capacity. Coal with higher ash percentage cannot be used without pulverizing because of

the problem of large amount ash deposition after combustion.

Increased thermal efficiency is obtained through pulverization.

The use of secondary air in the combustion chamber along with the powered coal

helps in creating turbulence and therefore uniform mixing of the coal and the air

during combustion.

Greater surface area of coal per unit mass of coal allows faster combustion as

more coal is exposed to heat and combustion.

The combustion process is almost free from clinker and slag formation.

The boiler can be easily started from cold condition in case of emergency. Practically no ash handling problem.

The furnace volume required is less as the turbulence caused aids in complete

combustion of the coal with minimum travel of the particles.

The pulverized coal is passed from the pulverizer to the boiler by means of the

primary air that is used not only to dry the coal but also to heat is as it goes into the

boiler. The secondary air is used to provide the necessary air required for complete

combustion. The primary air may vary anywhere from 10% to the entire air

depending on the design of the boiler. The coal is sent into the boiler through

burners. A very important and widely used type of burner arrangement is theTangential Firing arrangement.

Tangential Burners

The tangential burners are arranged such that they discharge the fuel air mixture

tangentially to an imaginary circle in the center of the furnace. The swirling action

produces sufficient turbulence in the furnace to complete the combustion in a short

period of time and avoid the necessity of producing high turbulence at the burner

itself. High heat release rates are possible with this method of firing. The burners

are placed at the four corners of the furnace. At the Badarpur Thermal Power

Station five sets of such burners are placed one above the other to form six firing

zones. These burners are constructed with tips that can be angled through a small

vertical arc. By adjusting the angle of the burners the position of the fire ball can

be adjusted so as to raise or lower the position of the turbulent combustion region.

When the burners are tilted downward the furnace gets filled completely with the


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flame and the furnace exit gas temperature gets reduced. When the burners are

tiled upward the furnace exit gas temperature increases. A difference of

100 degrees can be achieved by tilting the burners.

AshHandling

The ever increasing capacities of boiler units together with their ability to use low

grade high ash content coal have been responsible for the development of modern

day ash handling systems. The widely used ash handling systems are

1. Mechanical Handling System

2. Hydraulic System

3. Pneumatic System

4. Steam Jet System

The Hydraulic Ash handling system is used at the Badarpur Thermal Power

Station.

Ash Handling System of a Thermal Power Plant

Hydraulic Ash Handling System

The hydraulic system carried the ash with the flow of water with high velocity

through a channel and finally dumps into a sump. The hydraulic system is divided


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into a low velocity and high velocity system. In the low velocity system the ash

from the boilers falls into a stream of water flowing into the sump. The ash is

carried along with the water and they are separated at the sump. In the high

velocity system a jet of water is sprayed to quench the hot ash. Two other jets force

the ash into a trough in which they are washed away by the water into the sump,

where they are separated. The molten slag formed in the pulverized fuel system

can also be quenched and washed by using the high velocity system. The

advantages of this system are that its clean, large ash handling capacity,

considerable distance can be traversed, absence of working parts in contact with

ash.

42584029 Abhinav Training Report

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