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NTPC SUMMER TRAINING REPORT 2013

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    Submitted by:

    Sanket Kinage

    B.Tech. 2nd Year

    VT0733

    IIT Jodhpur

    Summer Training Report

    20th May to 15thJune 2013

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    ACKNOWLEDGEMENT

    With profound respect and gratitude, I take the opportunityto convey my thanks to complete the training here.

    I do extend my heartfelt thanks to Ms. Rachna Singh Bhal

    for providing me this opportunity to be a part of this esteemed

    organization.

    I am extremely grateful to all the technical staff of BTPS /

    NTPC for their co-operation and guidance that has 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.

    SANKET KINAGE

    IIT JODHPUR

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    INDEX

    OVERVIEW ABOUT NTPC

    VISION AND MISSION

    ABOUT BTPS

    NEED OF THERMAL POWER STATION

    HOW COAL PRODUCES ELECTRICITY?

    RANKINE CYCLE

    BOILER MAINTENANCE DEPARTMENT

    PLANT AUXILIARY MAINTENANCE

    TURBINE MAINTENANCE DEPARTMENT

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    OVERVIEW

    Indias largest power company, NTPC was set up in 1975 toaccelerate power development in India. NTPC is emerging as a

    diversified power major with presence in the entire value chain

    of the power generation business. Apart from powergeneration, which is the mainstay of the company, NTPC has

    already ventured into consultancy, power trading, ash

    utilization and coal mining. NTPC ranked 337th in the 2012,

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    Forbes Global 2000ranking of the Worlds biggest companies.NTPC became a Maharatna company in May, 2010, one of theonly four companies to be awarded this status.

    The total installed capacity of the company is 41,184 MW(including JVs) with 16 coal based and 7 gas based stations,

    located across the country. In addition under JVs, 7 stations are

    coal based & another station uses naphtha/LNG as fuel and 2

    renewable energy projects. The company has set a target tohave an installed power generating capacity of1, 28,000 MWby the year 2032. The capacity will have a diversified fuel mixcomprising 56% coal, 16% Gas, 11% Nuclear and 17%

    Renewable Energy Sources(RES) including hydro. By 2032,

    non-fossil fuel based generation capacity shall make up nearly

    28% of NTPCs portfolio.

    NTPC has been operating its plants at high efficiency levels.

    Although the company has 17.75% of the total nationalcapacity, it contributes 27.40% of total power generation dueto its focus on high efficiency.

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    In October 2004, NTPC launched 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 listedcompany in November 2004 with the Government holding

    89.5% of the equity share capital. In February 2010, the

    Shareholding of Government of India was reduced from 89.5%

    to 84.5% through Further Public Offer. The rest is held by

    Institutional Investors and the Public.

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    VISION AND MISSION

    VISIONTo be the worlds largest and best power producer,

    powering Indiasgrowth.

    MISSIONDevelop and provide reliable power, related products

    and services at competitive prices, integrating multipleenergy sources with innovative and eco-friendly

    technologies and contribute to society.

    COREVALUESo

    BE COMMITED

    B Business EthicsE Environmentally & Economically SustainableC Customer FocusO Organizational & Professional PrideM Mutual Respect & TrustM Motivating Self & othersI Innovation & Speed

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    T Total Quality for ExcellenceT Transparent & Respected OrganizationE EnterprisingD Devoted

    ABOUT BTPS

    Badarpur Thermal Power Station is located at Badarpur area inNCT Delhi. The Badarpur Thermal Power Station has aninstalled capacity of705 MW. It is situated in south east cornerof Delhi on Mathura Road near Faridabad. It was the first

    central sector power plant conceived in India, in 1965. It wasoriginally conceived to provide power to neighboring states of

    Haryana, Punjab, Jammu and Kashmir, U.P., Rajasthan, andDelhi. But since year 1987 Delhi has become its solebeneficiary. It was owned and conceived by Central Electric

    Authority. Its construction was started in year 1968, and theFirst unit was commissioned in 26July 1973. The coal for theplant is derived from the Jharia Coal Fields. This wasconstructed under ownership of Central Electric Authority,

    later it was transferred to NTPC.

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    It supplies power to Delhi city. It is one of the oldest plant in

    operation. Its 100 MW units capacity have been reduced to 95MW. These units have indirectly fired boiler, while 210 MWunits have directly fired boiler. All the turbines are of Russian

    Design. Both turbine and boilers have been supplied by BHEL.

    The boiler of Stage-I units are of Czech design. The boilers of

    Unit 4 and 5 are designed by combustion engineering (USA).

    The instrumentation of the stage I units and unit 4 are of The

    Russian design. Instrumentation of unit5 is provided by M/S

    Instrumentation Ltd. Kota, is of Kent design.

    Installed capacity

    StageUnit

    Number

    Installed Capacity

    (MW)

    Date of

    Commissioning

    Status

    First 1 95 July, 1973 Running

    First 2 95 August, 1974 Running

    First 3 95 March, 1975 Running

    Second 4 210 December, 1978 Running

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    StageUnit

    Number

    Installed Capacity

    (MW)

    Date of

    CommissioningStatus

    Second 5 210 December, 1981Running

    NEED OF THERMAL POWER STATION

    Scarcity of water resources: Water resources are notabundantly available and are geographically unevenly

    distributed. Thus hydro power plants cannot be installed with

    ease and are limited to certain locations.

    Widely available alternate flues: Many alternate fuels such as

    coal, diesel, nuclear fuels, geo-thermal energy sources, solar-

    energy, and biomass fuels can be used to generate power using

    steam cycles.

    Maintenance and lubrication cost is lower: Once installed,

    these require less maintenance costs and on repairs.

    Lubrication is not a major problem compared to hydro power

    plant.

    Coal is abundant: Coal is available in excess quantities in Indiaand is rich form of energy available at relatively lower cost.

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    Working fluid remains within the system, and need not be

    replaced every time thus simplifies the process.

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    HOW COAL POWER PLANTS PRODUCE ELECTRICITY

    The conversion from coal to electricity takes place in three stages.

    STAGE 1:

    The first conversion of energy takes place in the

    boiler. Coal is burnt in the boiler furnace to produce

    heat. Carbon in the coal and Oxygen in the air

    combine to produce Carbon Dioxide and heat.

    STAGE 2:The second stage is the thermodynamic process. The

    heat from combustion of the coal boils water in the

    boiler to produce steam. In modern power plant, boilers

    produce steam at a high pressure and temperature. The

    steam is then piped to a turbine. The high pressure steam

    impinges and expands across a number of sets of blades in

    the turbine. The impulse and the thrust created rotates the

    turbine. The steam is then condensed to water and

    pumped back into the boiler to repeat to the cycle. This

    cycle in ideal case is known as Rankine cycle.

    STAGE 3:

    In the third stage, rotation of the turbine rotates the

    generator rotor to produce electricity based of Faradays

    Principle of electromagnetic induction.

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    RANKINE CYCLE

    The Rankine cycle is an idealized thermodynamic cycle of

    a heat engine that converts heat into mechanical work.

    The heat is supplied externally to a closed loop, which

    usually uses water as the working fluid. The Rankine

    cycle, in the form of steam engines generates about 90% of

    all electric power used throughout the world.

    GENERAL LAYOUT OF THE FOUR MAIN DEVICES

    USED IN THE RANKINE CYCLE

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    THERE ARE FOUR PROCESSES IN THE RANKINE CYCLE.

    Process 1-2: The working fluid is pumped from low to highpressure. As the fluid is a liquid at this stage the pumprequires little input energy.

    Process 2-3: The high pressure liquid enters a boiler where itis heated at constant pressure by an external heat source to

    become a dry saturated vapor. The input energy required

    can be easily calculated using steam tables.

    Process 3-4: The dry saturated vapor expands through aturbine, generating power. This decreases the temperature

    and pressure of the vapor, and some condensation may

    occur. The output in this process can be easily calculated

    using the Enthalpy-entropy chart or the steam tables. Ideally

    this process is isentropic i.e. entropy of steam doesnt changeduring this process, but in actual case there is increase in

    entropy of steam due to irreversibility and hence work

    extracted from turbine is less than the work in ideal case.

    Process 4-1: The wet vapor then enters a condenser where itis condensed at a constant pressure to become saturated

    liquid.

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    POWER PLANT CYCLE OR REAL RANKINE CYCLE

    In a real power plant cycle (the name 'Rankine' cycle used

    only for the ideal cycle), the compression by the pump andthe expansion in the turbine arenot isentropic. In otherwords, these processes are non-reversible and entropy is

    increased during the two processes. This somewhat

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    increases the power required by the pump and decreases

    the power generated by the turbine.

    Isentropic efficiency of the Turbine is defined as the ratio

    of the work extracted out of turbine to the ideal workconsidering isentropic process.

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    GENERAL LAYOUT OF STEAM POWER PLANT

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    BOILER MAINTENANCE DEPARTMENT

    Boiler and Its Description

    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 centre. 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.

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    Boiler Side of the Badarpur Thermal Power Station,

    New Delhi

    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

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    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.

    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 fan with isolating dampers. On

    some units of about 60 MW, two boilers per unit may instead be

    provided.

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    Schematic diagram of a coal-fired power plant steam

    generator

    Specifications of the boiler

    1.Main Boiler (AT 100% LOAD):i. Evaporation 700 tons/hr

    ii. Feed water temperature 247C

    iii. Feed water leaving economizer 276C

    2.Steam Temperature:

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    i. Drum 341Cii. Super heater outlet 540C

    iii. Reheat inlet 332Civ. Reheat outlet 540C

    3.Steam Pressure:

    i. Drum design 158. 20

    kg/cm2ii. Drum operating 149.70

    kg/cm2iii. Super heater outlet 137.00

    kg/cm2iv. Reheat inlet 26.35 kg/cm2v. Reheat outlet 24.50 kg/cm2

    4.Fuel Specifications

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    A) Coali. Fixed Carbon 38%

    ii. Volatile Matter 26%

    iii. Moisture 8.0%

    iv. Ash 28%

    v. Grind ability 55HGI

    vi. High Heat 4860 Kcal/Kg

    vii. Coal size to Mill 20 mm

    B)Oili. Low Heat value 10000 kcal/kg

    ii. Sulphur 4.5% w/w

    iii. Moisture 1% w/w

    iv. Flash point 660

    C.

    v. Viscosity 1500 redwood at 37.80

    C.

    vi. Sp. Weight 0.98 at 380

    C.

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    5.Heat Balance

    i. Dry gas loss 4.63%

    ii. Carbon loss 2%

    iii. Radiation loss 0.26%

    iv. Unaccounted loss 1.5%

    v. H2

    in air and H2O in fuel 4.9%

    vi. Total loss 13.3%

    vii. Efficiency 86.7%

    AUXILIARIES OF THE BOILER

    1.Furnace Furnace is primary part of boiler where the chemical

    energy of the fuel is converted to thermal energy by

    combustion. Furnace is designed for efficient and complete

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    combustion. Major factors that assist for efficient

    combustion are amount of fuel inside the furnace and

    turbulence, which causes rapid mixing between fuel and

    air. In modern boilers, water furnaces are used.

    2.Boiler drum Drum is of fusion-welded design with welded

    hemispherical dished ends. It is provided with stubs for

    welding all the connecting tubes, i.e. downcomers, risers,

    pipes, saturated steam outlet. The function of steam drum

    internals is to separate the water from the steam generated

    in the furnace walls and to reduce the dissolved solid

    contents of the steam below the prescribed limit of 1 ppm

    and also take care of the sudden change of steam demand

    for boiler.

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    The secondary stage of two opposite banks of closely spaced

    thin corrugated sheets, which direct the steam and force the

    remaining entertained water against the corrugated plates.

    Since the velocity is relatively low this water does not get

    picked up again but runs down the plates and off the second

    stage of the two steam outlets.

    From the secondary separators the steam flows upwards to

    the series of screen dryers, extending in layers across the

    length of the drum. These screens perform the final stage of

    the separation.

    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

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    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.

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    External View of an Industrial Boiler at BTPS, New

    Delhi

    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.

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    The boiler furnace auxiliary equipment includes 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 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.

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    Nuclear plants also boil water to raise steam, either directly

    passing the working steam through the reactor or else using

    an intermediate heat exchanger.

    3.Water walls Water flows to the water walls from the boiler drum by

    natural circulation. The front and the two side water walls

    constitute the main evaporation surface, absorbing the bulk

    of radiant heat of the fuel burnt in the chamber. The front

    and rear walls are bent at the lower ends to form a water-

    cooled slag hopper. The upper part of the chamber is

    narrowed to achieve perfect mixing of combustion gases.

    The water wall tubes are connected to headers at the top

    and bottom. The rear water wall tubes at the top are

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    grounded in four rows at a wider pitch forming g the grid

    tubes.

    4.Reheater Reheater is used to raise the temperature of steam from

    which a part of energy has been extracted in highpressure

    turbine. This is another method of increasing the cycle

    efficiency. Reheating requires additional equipment i.e.

    heating surface connecting boiler and turbine pipe safety

    equipment like safety valve, non return valves, isolating

    valves, high pressure feed pump, etc: Reheater is composed

    of two sections namely the front and the rear pendant

    section, which is located above the furnace arc between

    water-cooled, screen wall tubes and rear wall tubes.

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    Tubes of a reheater

    5.Superheater Whatever type of boiler is used, steam will leave the water

    at its surface and pass into the steam space. Steam formed

    above the water surface in a shell boiler is always saturated

    and become superheated in the boiler shell, as it is

    constantly. If superheated steam is required, the saturated

    steam must pass through a superheater. This is simply a

    heat exchanger where additional heat is added to the steam.

    In water-tube boilers, the superheater may be an additional

    pendant suspended in the furnace area where the hot gases

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    will provide the degree of superheat required. In other

    cases, for example in CHP schemes where the gas turbine

    exhaust gases are relatively cool, a separately fired

    superheater may be needed to provide the additional heat.

    6.Economizer The function of an economizer in a steam-generating unit

    is to absorb heat from the flue gases and add as a sensible

    heat to the feed water before the water enters the

    evaporation circuit of the boiler. Earlier economizer were introduced mainly to recover the

    heat available in the flue gases that leaves the boiler and

    provision of this addition heating surface increases the

    efficiency of steam generators. In the modern boilers used

    for power generation feed water heaters were used to

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    increase the efficiency of turbine unit and feed water

    temperature.

    An economizer

    Use of economizer or air heater or both is decided by the

    total economy that will result in flexibility in operation,

    maintenance and selection of firing system and other

    related equipment. Modern medium and high capacity

    boilers are used both as economizers and air heaters. In low

    capacity, air heaters may alone be selected.

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    Stop valves and non-return valves may be incorporated to

    keep circulation in economizer into steam drum when

    there is fire in the furnace but not feed flow. Tube elements

    composing the unit are built up into banks and these are

    connected to inlet and outlet headers.

    7.Air preheater Air preheater absorbs waste heat from the flue gases and

    transfers this heat to incoming cold air, by means of

    continuously rotating heat transfer element of specially

    formed metal plates. Thousands of these high efficiency

    elements are spaced and compactly arranged within 12

    sections. Sloped compartments of a radially divided

    cylindrical shell called the rotor. The housing surrounding

    the rotor is provided with duct connecting both the ends

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    and is adequately scaled by radial and circumferential

    scaling.

    An air preheater

    Special sealing arrangements are provided in the provided

    in the air preheater to prevent the leakage between the air

    and gas sides. Adjustable plates are also used to help the

    sealing arrangements and prevent the leakage as expansion

    occurs. The air preheater heating surface elements are

    provided with two types of cleaning devices, soot blowers

    to clean normal devices and washing devices to clean the

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    element when soot blowing alone cannot keep the element

    clean.

    8.Pulverizer

    A pulverizer is a mechanical device for the grinding of

    many types of materials. For example, they are used to

    pulverize coal for combustion in the steam-generating

    furnaces of the fossil fuel power plants.

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    A PulverizerTypes of Pulverizer

    i. Ball and Tube millsA ball mill is a pulverizer that consists of a horizontal

    cylinder, up to three diameters in length, containing a

    charge of tumbling or cascading steel balls, pebbles or steel

    rods.

    A tube mill is a revolving cylinder of up to five diameters in

    length used for finer pulverization of ore, rock and other

    such materials; the materials mixed with water is fed into

    the chamber from one end, and passes out the other end as

    slime.

    ii. Bowl millIt uses tires to crush coal. It is of two types; a deep bowl mill

    and the shallow bowl mill.

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    An external view of a Coal Pulverizer

    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.

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    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.

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    The furnace volume required is less as the turbulence

    caused aids in complete combustion of the coal with

    minimum travel of the particles.

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    PLANT AUXILIARY MAINTENANCE

    1. Water circulation system

    Theory of CirculationWater must flow through the heat absorption surface of the

    boiler in order that it be evaporated into steam. In drum type

    units (natural and controlled circulation), the water is circulated

    from the drum through the generating circuits and then back to

    the drum where the steam is separated and directed to the super

    heater. The water leaves the drum through the down corners at

    a temperature slightly below the saturation temperature. The

    flow through the furnace wall is at saturation temperature. Heat

    absorbed in water wall is latent heat of vaporization creating a

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    mixture of steam and water. The ratio of the weight of the water

    to the weight of the steam in the mixture leaving the heat

    absorption surface is called circulation ratio.

    Types of Boiler Circulating System

    i. Natural circulation system

    ii. Controlled circulation systemiii. Combined circulation system

    i. Natural Circulation SystemWater delivered to steam generator from feed water is at a

    temperature well below the saturation value corresponding to

    that pressure. Entering first the economizer, it is heated to about

    30-40

    C below saturation temperature. From economizer thewater enters the drum and thus joins the circulation system.

    Water entering the drum flows through the down corner and

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    enters ring heater at the bottom. In the water walls, a part of the

    water is converted to steam and the mixture flows back to the

    drum. In the drum, the steam is separated, and sent to

    superheater for superheating and then sent to the high-pressure

    turbine. Remaining water mixes with the incoming water from

    the economizer and the cycle is repeated.As the pressure increases, the difference in density between

    water and steam reduces. Thus the hydrostatic head available

    will not be able to overcome the frictional resistance for a flow

    corresponding to the minimum requirement of cooling of water

    wall tubes. Therefore natural circulation is limited to the boiler

    with drum operating pressure around 175 kg/ cm2.

    ii. Controlled Circulation System

    Beyond 80 kg/ cm2 of pressure, circulation is to be assisted with

    mechanical pumps to overcome the frictional losses. To regulate

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    the flow through various tubes, orifices plates are used. This

    system is applicable in the high sub-critical regions (200 kg/

    cm2).

    2. Ash handling plant

    The widely used ash handling systems are:i. Mechanical Handling System

    ii. Hydraulic System

    iii. Pneumatic System

    iv. Steam Jet System

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    Ash Handling System at Badarpur Thermal Power

    Station, New Delhi

    The Hydraulic Ash handling system is used at the Badarpur

    Thermal Power Station.

    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 into a low velocity and high

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    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.

    Fly Ash Collection

    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

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    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 to storage silos for subsequent

    transport by trucks or railroad cars.

    Bottom Ash Collection and DisposalAt 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 crushed clinkers and

    bottom ash to a storage site.

    3. Water treatment plant

    As the types of boiler are not alike their working pressure and

    operating conditions vary and so do the types and methods of

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    water treatment. Water treatment plants used in thermal power

    plants used in thermal power plants are designed to process the

    raw water to water with a very low content of dissolved solids

    known as demineralized water. No doubt, this plant has to be

    engineered very carefully keeping in view the type of raw water

    to the thermal plant, its treatment costs and overall economics.

    A water treatment plant

    The type of demineralization process chosen for a power station

    depends on three main factors:

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    i. The quality of the raw water.

    ii. The degree of de-ionization i.e. treated water quality.

    iii. Selectivity of resins.

    Water treatment process is generally made up of two sections:

    Pretreatment section.

    Demineralization section

    Pretreatment SectionPretreatment plant removes the suspended solids such as clay,

    silt, organic and inorganic matter, plants and other microscopic

    organism. The turbidity may be taken as two types of suspended

    solid in water; firstly, the separable solids and secondly the non-

    separable solids (colloids). The coarse components, such as sand,

    silt, etc: can be removed from the water by simple sedimentation.

    Finer particles, however, will not settle in any reasonable time

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    and must be flocculated to produce the large particles, which are

    settle able. Long term ability to remain suspended in water is

    basically a function of both size and specific gravity.DemineralizationThis filter water is now used for demineralizing purpose and is

    fed to cation exchanger bed, but enroute being first

    dechlorinated, which is either done by passing through activated

    carbon filter or injecting along the flow of water, an equivalent

    amount of sodium sulphite through some stroke pumps. The

    residual chlorine, which is maintained in clarification plant to

    remove organic matter from raw water, is now detrimental to

    action resin and must be eliminated before its entry to this bed.

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    A demineralization tank

    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 DM plant is dictated by the type

    and quantity of salts in the raw water input. However, some

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    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.

    4. Draught system

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    A natural draught system

    Induced Draft SystemIn this system, the air is admitted to natural pressure difference

    and the flue gases are taken out by means of Induced Draught

    (I.D.) fans and the furnace is maintained under vacuum.

    An induced draught system

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    Balanced Draught SystemHere a set of Induced and Forced Draft Fans are utilized in

    maintaining a vacuum in the furnace. Normally all the power

    stations utilize this draft system.

    5. Industrial fans

    ID FanThe induced Draft Fans are generally of Axial-Impulse Type.

    Impeller nominal diameter is of the order of 2500 mm. The fan

    consists of the following sub-assemblies:

    Suction Chamber

    Inlet Vane Control

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    Impeller

    Outlet Guide Vane Assembly

    An ID fan

    FD FanThe fan, normally of the same type as ID Fan, consists of the

    following components:

    Silencer

    Inlet Bend

    Fan Housing

    Impeller with blades and setting mechanism

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    An FD fan

    The centrifugal and setting forces of the blades are taken up by

    the blade bearings. The blade shafts are placed in combined

    radial and axial anti-friction bearings, which are sealed off to

    the outside. The angle of incidence of the blades may be adjusted

    during operation. The characteristic pressure volume curves of

    the fan may be changed in a large range without essentially

    modifying the efficiency. The fan can then be easily adapted to

    changing operating conditions.

    The rotor is accommodated in cylindrical roller bearings and an

    inclined ball bearing at the drive side absorbs the axial thrust.

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    Lubrication and cooling these bearings is assured by a combined

    oil level and circulating lubrication system.

    Primary Air FanPA Fan if flange-mounted design, single stage suction, NDFV

    type, backward curved bladed radial fan operating on the

    principle of energy transformation due to centrifugal forces.

    Some amount of the velocity energy is converted to pressure

    energy in the spiral casing. The fan is driven at a constant speed

    and varying the angle of the inlet vane control controls the flow.

    The special feature of the fan is that is provided with inlet guide

    vane control with a positive and precise link mechanism.

    It is robust in construction for higher peripheral speed so as to

    have unit sizes. Fan can develop high pressures at low and

    medium volumes and can handle hot-air laden with dust

    particles.

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    Primary air fan

    6. Compressor house

    Instrument air is required for operating various dampers,

    burner tilting, devices, diaphragm valves, etc: in the 210 MW

    units. Station air meets the general requirement of the power

    station such as light oil atomizing air, for cleaning filters and for

    various maintenance works. The control air compressors and

    station air compressors have been housed separately with

    separate receivers and supply headers and their tapping.

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    A compressor house

    Instrument Air SystemControl air compressors have been installed for supplying

    moisture free dry air required for instrument used. The output

    from the compressors is fed to air receivers via return valves.From the receiver air passed through the dryers to the main

    instrument airline, which runs along with the boiler house and

    turbine house of 210 MW units. Adequate numbers of tapping

    have been provided all over the area.

    Air-Drying Unit

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    A 95 MW Generator at BTPS, New Delhi

    CompoundingSeveral problems occur if energy of steam is converted in single

    step and so compounding is done. Following are the type of

    compounded turbine:

    i. Velocity Compounded TurbineLike simple turbine it has only one set of nozzles and

    entire steam pressure drop takes place there. The kinetic

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    MAIN TURBINE

    The 210MW turbine is a cylinder tandem compounded type

    machine comprising of H.P. and I.P and L.P cylinders. The H.P.

    turbine comprises of 12 stages the I.P turbine has 11 stages and

    the L.P has four stages of double flow. The H.P and I.P. turbine

    rotor are rigidly compounded and the I.P. and L.P rotor by lens

    type semi flexible coupling. All the 3 rotors are aligned on five

    bearings of which the bearing number is combined with thrust

    bearing.

    The main superheated steam branches off into two streams from

    the boiler and passes through the emergency stop valve and

    control valve before entering the governing wheel chamber of

    the H.P. Turbine. After expanding in the 12 stages in the H.P.

    turbine then steam is returned in the boiler for reheating.

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    The reheated steam from boiler enters I.P. turbine via the

    interceptor valves and control valves and after expanding enters

    the L.P stage via 2 numbers of cross over pipes.

    In the L.P. stage the steam expands in axially opposed direction

    to counteract the thrust and enters the condenser placed directly

    below the L.P. turbine. The cooling water flowing through the

    condenser tubes condenses the steam and the condensate the

    collected in the hot well of the condenser.

    The condensate collected the pumped by means of 3x50% duty

    condensate pumps through L.P heaters to deaerator from where

    the boiler feed pump delivers the water to the boiler through H.P.

    heaters thus forming a closed cycle.

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    divided at the horizontal centerline. Its halves are bolted together

    for easy access. The cylinder contains fixed blades, vanes and

    nozzles that direct steam into the moving blades carried by the

    rotor. Each fixed blade set is mounted in diaphragms located in

    front of each disc on the rotor, or directly in the casing. A disc

    and diaphragm pair a turbine stage. Steam turbines can have

    many stages. A rotor is a rotating shaft that carries the moving

    blades on the outer edges of either discs or drums. The blades

    rotate as the rotor revolves. The rotor of a large steam turbine

    consists of large, intermediate and low-pressure sections.

    In a multiple-stage turbine, steam at a high pressure and high

    temperature enters the first row of fixed blades or nozzles

    through an inlet valve/valves. As the steam passes through the

    fixed blades or nozzles, it expands and its velocity increases. The

    high velocity jet of stream strikes the first set of moving blades.

    The kinetic energy of the steam changes into mechanical energy,

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    causing the shaft to rotate. The steam that enters the next set of

    fixed blades strikes the next row of moving blades.

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    As the steam flows through the turbine, its pressure and

    temperature decreases while its volume increases. The decrease

    in pressure and temperature occurs as the steam transmits

    energy to the shaft and performs work. After passing through

    the last turbine stage, the steam exhausts into the condenser or

    process steam system.

    The kinetic energy of the steam changes into mechanical energy

    through the impact (impulse) or reaction of the steam against

    the blades. An impulse turbine uses the impact force of the steam

    jet on the blades to turn the shaft. Steam expands as it passes

    through thee nozzles, where its pressure drops and its velocity

    increases. As the steam flows through the moving blades, its

    pressure remains the same, but its velocity decreases. The steam

    does not expand as it flows through the moving blades.

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    STEAM CYCLE

    The thermal (steam) power plant uses a dual (vapor+liquid)

    phase cycle. It is a closed cycle to enable the working fluid

    (water) to be used again and again. The cycle used is Rankine

    cycle modified to include superheating of steam, regenerative

    feed water heating and reheating of steam.

    MAIN TURBINE

    The 210 MW turbine is a tandem compounded type machine

    comprising of H.P. and I.P. cylinders. The H.P. turbines comprise

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    of 12 stages, I.P. turbine has 11 stages and the L.P. turbine has 4

    stages of double flow.

    The H.P. and I.P. turbine rotors are rigidly compounded and the

    L.P. motor by the lens type semi flexible coupling. All the three

    rotors are aligned on five bearings of which the bearing no. 2 is

    combined with the thrust bearing

    The main superheated steam branches off into two streams from

    the boiler and passes through the emergency stop valve and

    control valve before entering the governing wheel chamber of

    the H.P. turbine. After expanding in the 12 stages in the H.P.

    turbine the steam is returned in boiler for reheating.

    The reheated steam for the boiler enters the I.P> turbine via the

    interceptor valves and control valves and after expanding enters

    the L.P. turbine stage via 2 nos of cross-over pipes.

    In the L.P. stage the steam expands in axially opposite direction

    to counteract the trust and enters the condensers placed below

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    the L.P. turbine. The cooling water flowing throughout the

    condenser tubes condenses the steam and the condensate

    collected in the hot well of the condenser.

    The condensate collected is pumped by means of 3*50% duty

    condensate pumps through L.P. heaters to deaerator from where

    the boiler feed pump delivers the water to boiler through H.P.

    heaters thus forming a close cycle.

    The Main Turbine

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    TURBINE CYCLE

    Fresh steam from the boiler is supplied to the turbine through

    the emergency stop valve. From the stop valves steam is supplied

    to control valves situated in H.P. cylinders on the front bearing

    end. After expansion through 12 stages at the H.P. cylinder,

    steam flows back to the boiler for reheating steam and reheated

    steam from the boiler cover to the intermediate pressure turbine

    through two interceptor valves and four control valves mounted

    on I.P. turbine.

    After flowing through I.P. turbine steam enters the middle part

    of the L.P. turbine through cross-over pipes. In L.P. turbine the

    exhaust steam condenses in the surface condensers welded

    directly to the exhaust part of L.P. turbine.

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    from deaerator through a collection where pressure of steam is

    regulated.

    From the condenser, condensate is pumped with the help of

    3*50% capacity condensate pumps to deaerator through the

    low-pressure regenerative equipments.

    Feed water is pumped from deaerator to the boiler through the

    H.P. heaters by means of 3*50% capacity feed pumps connected

    before the H.P. heaters.

    SPECIFICATIONS OF THE TURBINE

    Type: Tandem compound 3 cylinder reheated type. Rated power:210 MW. Number of stages:12 in H.P., 11 in I.P. and 4*2 in L.P.

    cylinder.

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    Rated steam pressure:130 kg /sq. cm before entering thestop valve.

    Rated steam temperature:535C after reheating at inlet. Steam flow: 670T / hr. H.P. turbine exhaust pressure: 27 kg /sq. cm., 327C Condenser back pressure:0.09 kg /sq. cm. Type of governing:nozzle governing. Number of bearing:5 excluding generator and exciter.

    Lubrication Oil: turbine oil 14 of IOC. Gland steam pressure:1.03 to 1.05 kg /sq. cm (Abs) Critical speed:1585, 1881, 2017. Ejector steam parameter:4.5 kg /sq. cm. Condenser cooling water pressure: 1.0 to 1.1 kg /sq.

    cm.

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    Condenser cooling water temperature:27000 cu. M/hr.

    Number of extraction lines for regenerative heatingof feed water: seven.

    TURBINE COMPONENTS

    Casing.

    Rotor.

    Blades.

    Sealing system.

    Stop & control valves.

    Couplings and bearings.

    Barring gear.

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    TURBINE CASINGS

    HP Turbine Casings Outer casing: a barrel-type without axial or radial flange.

    Barrel-type casing suitable for quick startup and loading.

    The inner casing- cylindrically, axially split.

    The inner casing is attached in the horizontal and vertical

    planes in the barrel casing so that it can freely expand

    radially in all the directions and axially from a fixed point

    (HP- inlet side).

    IP Turbine Casing: The casing of the IP turbine is split horizontally and is of

    double-shell construction.

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    Both are axially split and a double flow inner casing is

    supported in the outer casing and carries the guide blades.

    Provides opposed double flow in the two blade sections and

    compensates axial thrust.

    Steam after reheating enters the inner casing from Top &

    Bottom.

    LP Turbine Casing: The LP turbine casing consists of a double flow unit and has

    a triple shell welded casing. The shells are axially split and of rigid welded construction.

    The inner shell taking the first rows of guide blades is

    attached kinematically in the middle shell.

    Independent of the outer shell, the middle shell, is

    supported at four points on longitudinal beams.

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    In all the stages lashing wires are provided to adjust the

    frequency of blades. In the last two rows, satellite strips are

    provided at the leading edges of the blades to protect them

    against wet-steam erosion.

    BLADES Most costly element of the turbine.

    Blades fixed in stationary part are called guide blades/

    nozzles and those fitted in moving part are called

    rotating/working blades.

    Blades have three main parts:

    oAerofoil: working part.

    oRoot.

    oShrouds.

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    Shroud are used to prevent steam leakage and guide steam

    to next set of moving blades.

    VACUUM SYSTEMThis comprises of:

    Condenser: 2 for 200 MW unit at the exhaust of LPturbine.

    Ejectors:One starting and two main ejectors connected tothe condenser locared near the turbine.

    C.W. Pumps: Normally two per unit of 50% capacity.

    CONDENSERThere are two condensers entered to the two exhausters of the

    L.P. turbine. These are surface-type condensers with two pass

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    valves in the steam space level indicator for visual level

    indication of heating steam condensate pressure vacuum gauges

    for measurement of steam pressure, etc.

    DeaeratorThe presence of certain gases, principally oxygen, carbon

    dioxide and ammonia, dissolved in water is generally considered

    harmful because of their corrosive attack on metals, particularly

    at elevated temperatures. One of the most important factors in

    the prevention of internal corrosion in modern boilers and

    associated plant therefore, is that the boiler feed water should be

    free as far as possible from all dissolved gases especially oxygen.

    This is achieved by embodying into the boiler feed system a

    deaerating unit, whose function is to remove the dissolved gases

    from the feed water by mechanical means. Particularly the unit

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    lubricating system with adequate protection to trip the pump if

    the lubrication oil pressure falls below a preset value.

    The high pressure boiler feed pump is a very expensive machine

    which calls for a very careful operation and skilled maintenance.

    Operating staff must be able to find out the causes of defect at

    the very beginning, which can be easily removed without

    endangering the operator of the power plant and also without

    the expensive dismantling of the high pressure feed pump.

    Function

    The water with the given operating temperature should flow

    continuously to the pump under a certain minimum pressure. It

    passes through the suction branch into the intake spiral and

    from there; it is directed to the first impeller. After leaving the

    impeller it passes through the distributing passages of the

    diffuser and thereby gets a certain pressure rise and at the same

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    suction pressure which will remove the possibility of cavitation.

    Therefore all the feed pumps are provided with a main shaft

    driven booster pump in its suction line for obtaining a definite

    positive suction pressure.

    Lubricating Pressure

    All the bearings of boiler feed pump, pump motor and hydraulic

    coupling are force lubricated. The feed pump consists of two

    radial sleeve bearings and one thrust bearing. The thrust bearing

    is located at the free end of the pump.

    High Pressure Heaters

    These are regenerative feed waters heaters operating at high

    pressure and located by the side of turbine. These are generally

    vertical type and turbine based steam pipes are connected to

    them.

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    HP heaters are connected in series on feed waterside and by such

    arrangement, the feed water, after feed pump enters the HP

    heaters. The steam is supplied to these heaters to form the bleed

    point of the turbine through motor operated valves. These

    heaters have a group bypass protection on the feed waterside.

    In the event of tube rupture in any of the HPH and the level of

    condensate rising to dangerous level, the group protection

    devices divert automatically the feed water directly to boiler,

    thus bypassing all the 3 H.P. heaters.

    An HP heater

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