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    SUBMITTED BY: ALOK KUMARBRANCH: MECHANICAL ENGG.(BE 2nd YR. )

    COLLEGE OF TECHNOLOGY & ENGG,UDAIPUR MPUAT UNIVERSITYUDAIPUR(RAJASTHAN)

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    ACKNOWLEDGEMENT

    I would like to thankN.T.PC. BADARPURfor providing me agolden opportunity to work with them . The support and theenvironment provided to me during my project was morethan what anyone would have expected.

    I am very grateful to Mr. MAN MOHAN SINGH(DY.

    MANAGER) who granted me the opportunity of working as asummer trainee at mechanical Division.

    I would also like to thanks Mrs RACHNA BHAL (H.R.) ,Mr. G.D SHARMA(TRAINING COORDINATOR) and myinstructors ofB.M.D.,P.A.M., T.M.D. and divisions withoutthem I would not be able to perform such a delightful job.

    And at last I would like to thanks all the people

    involve in the training who helped me in accomplishing it insuch a wonderful way.

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    PREFACE

    NTPC is one of the most important industry for producingthe electricity.Every 3rd ball in india is glown by NTPC. Thereare various divisions in NTPC for various branches likemechanical division, electrical division etc. The main

    objective of preparing this report has been to present theoperations of BMD, PAM, TMD of mechanical division in alogical, innovative and lucide manner. The basic theorypresented in this report has been evolved out of simple andreadily understood principles. A sincere effort has beenmade to maintain physical concepts in various operations.

    An effort has been made to give a balancedpresentation of this report with the help of figures, differenttypes of data and related suitable theories as well asconcepts.

    Eventually, again I would like to thank BTPS.

    ALOK KUMARBE 2ND YEAR

    Email:[email protected]

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    * CONTENTS

    *

    ABOUT N.T.P.C

    (NATIONAL THERMAL POWERCORPORATION)

    INTRODUCTION

    VISION, MISSION AND CORE VALUES

    POWER PLANT OPERATIONS OPERATIONAL PERFORMANCES

    CAPACITY

    COAL STATION

    GAS STATION

    CAPTIVE POWER PLANT

    POWER STATIONS IN INDIA

    ABOUT B.T.P.S(BADARPUR THERMAL POWER STATION)

    INTRODUCTION

    TRASFORMATION OF ENERGY

    COAL CYCLE

    COAL TO ELECTRICITY

    BASIC POWER PLANT CYCLE

    ABOUT BMD(BOILER MAINTENANCE DEPARTMENT)

    BOILER DESCRIPTION

    FEED WATER & CONDENSATE CYCLE COMBUSTION PRINCIPLE(TRIPLE TS)

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    FURNACE & THEIR TYPE

    BASICS OF FAN & DRAFT SYSTEM

    PULVERISER(COAL IN TO PULVERISED COALOUT )

    BOILER AUXILIARIES AND MOUNTINGS

    ABOUT PAM(PLANT AUXILIARY MAINTENANCE

    DEPARTMENT) THEORY OF CIRCULATION OF WATER

    ASH HANDLING PLANT

    CSP HOUSE

    WATER TREATMENT PLANT

    ABOUT TMD

    (TURBINE MAINTENANCE DEPARTMENT)

    STEAM TURBINE THEORY

    STEAM CYCLE

    TURBINE CLASSIFICATION TURBINE CYCLE

    DESCRIPTION OF MAIN TURBINE

    TURBINE AUXILLIARIES AN THEIRARRANGEMENT

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    http://en.wikipedia.org/wiki/Image:Ntpc.jpg
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    Type Public

    Founded 1975Headquarters Delhi,India

    Key peopleR S Sharma, Chairman& Managing Director

    Industry Electricity generation

    Products Electricity

    RevenueINR 261 billion (2006)

    or USD 5.91 billionNet income

    INR 5.8 billion (2006)or USD 131 million

    Employees 23867 (2006)

    Website http://www.ntpc.co.in

    BRIEFING NTPC

    National Thermal Power Corporation is the largest powergeneration company in India. Forbes Global 2000 for 2008

    ranked it 411th in the world. It is an Indianpublic sectorcompany

    listed on the Bombay Stock Exchange although at present the

    Government of India holds 89.5% of its equity. NTPC was

    established as a public sector power utility by Government of

    http://en.wikipedia.org/wiki/Category:Types_of_companieshttp://en.wikipedia.org/wiki/Public_companyhttp://en.wikipedia.org/wiki/1975http://en.wikipedia.org/wiki/Delhihttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Industryhttp://en.wikipedia.org/wiki/Electricity_generationhttp://en.wikipedia.org/wiki/Product_(business)http://en.wikipedia.org/wiki/Revenuehttp://en.wikipedia.org/wiki/Rs.http://en.wikipedia.org/wiki/2006http://en.wikipedia.org/wiki/USDhttp://en.wikipedia.org/wiki/Net_incomehttp://en.wikipedia.org/wiki/Rs.http://en.wikipedia.org/wiki/2006http://en.wikipedia.org/wiki/USDhttp://en.wikipedia.org/wiki/Employmenthttp://en.wikipedia.org/wiki/2006http://en.wikipedia.org/wiki/Websitehttp://www.ntpc.co.in/http://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Forbes_Global_2000http://en.wikipedia.org/wiki/Public_sectorhttp://en.wikipedia.org/wiki/Bombay_Stock_Exchangehttp://en.wikipedia.org/wiki/Image:Ntpc.jpghttp://en.wikipedia.org/wiki/Category:Types_of_companieshttp://en.wikipedia.org/wiki/Public_companyhttp://en.wikipedia.org/wiki/1975http://en.wikipedia.org/wiki/Delhihttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Industryhttp://en.wikipedia.org/wiki/Electricity_generationhttp://en.wikipedia.org/wiki/Product_(business)http://en.wikipedia.org/wiki/Revenuehttp://en.wikipedia.org/wiki/Rs.http://en.wikipedia.org/wiki/2006http://en.wikipedia.org/wiki/USDhttp://en.wikipedia.org/wiki/Net_incomehttp://en.wikipedia.org/wiki/Rs.http://en.wikipedia.org/wiki/2006http://en.wikipedia.org/wiki/USDhttp://en.wikipedia.org/wiki/Employmenthttp://en.wikipedia.org/wiki/2006http://en.wikipedia.org/wiki/Websitehttp://www.ntpc.co.in/http://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Forbes_Global_2000http://en.wikipedia.org/wiki/Public_sectorhttp://en.wikipedia.org/wiki/Bombay_Stock_Exchange
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    India on November 7, 1975. The reason NTPC was created was to

    bridge the huge electricity supply-demand gap and the State

    Electricity Boards were not able to cope up with the situation. True

    to the expectation, it played a key role in the development of the

    sector, lighting every fourth bulb in the country, become the largestpower utility of India, Sixth largest thermal power generator in the

    World and the Second most efficient utility in terms of capacity

    utilization. Rightly, NTPC has set for itself the Vision statement

    To be one of the worlds largest and best power utilities,

    powering Indias growth.

    Vision

    To be a catalyst in development of wholesale power market in India enabling

    trading operation.

    Mission

    Provide good value to potential sellers and develop commercial arrangements . Enable NTPC to maintain optimal generation level through mutually beneficial trading.

    Provide viable alternatives to buyers for meeting their demands.

    Plan and establish a Power Exchange at National Level using state-of-the-art technology

    Our Core Values (BCOMIT)

    Business Ethics

    Customer Focus

    Organizational & Professional Pride

    Mutual Respect and Trust

    Innovation & Speed

    Total Quality for Excellence

    INSTALLED CAPACITY

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    NTPC Owned

    15 COAL Based Plants 23,395 MW

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    07 GAS/LIQ. FUEL Based Plants 3,955MW

    Owned by JVCs

    3 Coal Based JVC Plants 314* MW (* Captive Power

    Plant under JV with SAIL)

    GRAND TOTAL

    27,904 MW

    COAL STATIONS

    Total - 22,895 MW

    # Power Plant StateCommissioned

    Capacity (MW)

    1 Singrauli Uttar Pradesh 2,000

    2 Korba Chattishgarh 2,100

    4 Farakka West Bengal 1,600

    5 VindhyachalMadhya

    Pradesh3,260

    6 Rihand Uttar Pradesh 2,000

    http://en.wikipedia.org/wiki/Singraulihttp://en.wikipedia.org/wiki/Uttar_Pradeshhttp://en.wikipedia.org/wiki/Korba%2C_Chhattisgarhhttp://en.wikipedia.org/wiki/West_Bengalhttp://en.wikipedia.org/wiki/Singraulihttp://en.wikipedia.org/wiki/Uttar_Pradeshhttp://en.wikipedia.org/wiki/Korba%2C_Chhattisgarhhttp://en.wikipedia.org/wiki/West_Bengal
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    7 Kahalgaon Bihar 1340

    8 NCTPPDadri Uttar Pradesh 840

    9Talcher

    KanihaOrissa 3000

    10 Unchahar Utter Pradesh 1050

    11Talcher

    AngulOrissa 460

    12 Simhadri AndhraPradesh 1,000

    13 Tanda Uttar Pradesh 440

    14 Badarpur Delhi 705

    15 Sipat-II Chattishgarh 500

    GAS/LIQ. FUEL STATIONS

    http://en.wikipedia.org/wiki/Biharhttp://en.wikipedia.org/wiki/Orissahttp://en.wikipedia.org/wiki/Biharhttp://en.wikipedia.org/wiki/Orissa
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    Total - 3955 MW

    #Power Plant State Commissioned Capacity (MW)

    1

    6Anta Rajasthan 413

    1

    7Auraiya Uttar Pradesh 652

    1

    8Kawas Gujrat 645

    1

    9Dadri Uttar Pradesh 817

    2

    0Jhanor-Gandhar Gujrat 648

    2

    1 Kayamkulam Kerala 350

    2

    2Faridabad Haryana 430

    http://en.wikipedia.org/wiki/Rajasthanhttp://en.wikipedia.org/wiki/Uttar_Pradeshhttp://en.wikipedia.org/wiki/Gujrathttp://en.wikipedia.org/wiki/Keralahttp://en.wikipedia.org/wiki/Rajasthanhttp://en.wikipedia.org/wiki/Uttar_Pradeshhttp://en.wikipedia.org/wiki/Gujrathttp://en.wikipedia.org/wiki/Kerala
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    CAPATIVE POWER PLANT UNDER JV WITH SAIL& GAIL

    Total - 1054 MW

    # Power Plant StateCommissioned Capacity

    (MW)

    23

    Durgapur West Bengal 120

    2

    4Rourkela Orissa 120

    2

    5 Bhilai Chattishgarh 74

    2

    6

    Ratnagiri Gas Power

    Plant LimitedMaharashtra 740

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    CAPACITY ADDITION

    Additional capacity under implementation in 10'thFive Year Plan (2002-2007)

    # Power Plant StateCapacity

    (MW)

    Projected

    Commissioning

    Date

    1 Unchahar Stage-3Uttar

    Pradesh210 Sept 2006

    2Kahalgaon Phase-2

    (Stage-1) Unit-5Bihar 500 Nov 2006

    3Vindhyachal Stage-3

    Unit-9

    Madhya

    Pradesh500 July 2006

    4Kahalgaon Phase-2

    (Stage-2) Unit-7Bihar 500 Mar 2007

    5Kahalgaon Phase-2

    (Stage-1) Unit-6Bihar 500 May 2007

    6 Sipat Stage-2 Unit-1 Chattishgarh 500 Jun 2007

    http://en.wikipedia.org/wiki/Five-Year_Plans_of_Indiahttp://en.wikipedia.org/wiki/Five-Year_Plans_of_India
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    7Bhilai (JV with SAIL)

    Unit-1Chattishgarh 250 Jul 2007

    8Vindhyachal Stage-3

    Unit-10

    Madhya

    Pradesh500 Mar 2007

    9Bhilai (JV with SAIL)

    Unit-2Chattishgarh 250 Oct 2007

    1

    0 Sipat Stage-2 Unit-2 Chattishgarh 500 Dec 2007

    Total4710

    MW

    UPCOMING/FUTURE PROJECTS

    In November 2007, NTPC signed a joint venture withIndian Railways to set up a 1,000 Mega Watt (MW) power plant in

    Nabinagar in Bihar. The JV would be called Bharatiya Rail Bijlee

    Company.

    http://en.wikipedia.org/wiki/Indian_Railwayshttp://en.wikipedia.org/wiki/Indian_Railways
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    NTPC POWER STATIONS IN INDIA

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    DESCRIPTIONN OF BTPS

    (BADARPUR THERMAL POWER STATION)

    Address: Badarpur,New Delhi 110 044

    Telephone: (STD-011) - 26949523

    Fax: 26949532

    Email:

    Installed Capacity 720 MW

    Derated Capacity 705 MW

    Location New DelhiCoal Source Jharia Coal Fields

    Water Source Agra Canal

    Beneficiary States Delhi

    Unit Sizes

    3X95 MW

    2X210 MW

    Units Commissioned

    Unit I- 95 MW - July 1973

    Unit II- 95 MW August 1974Unit III- 95 MW March 1975

    Unit IV - 210 MW December 1978

    Unit V - 210 MW - December 1981

    Transfer of BTPS to

    NTPC

    Ownership of BTPS was transferred to

    NTPC with effect from 01.06.2006

    through GOIs Gazette Notification.

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    COAL TO ELECTRICITY TRANSFORMATION OF ENERGY

    COAL BOILER STEAM TURBINEChemical energy Thermal energy Mechanical energy

    DIFFERENT LOADS GENERATORLight energy or other required energy Electrical energy

    CHP(COAL HANDALING DEPARTMENT)

    OR(COAL CYCLE)

    From Jharia mines

    Railway wagon

    BTPS wagon tripper

    Magnetic separator

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    Crusher house

    Coal stock yard

    RC bunker

    RC feeder

    Bowl mill

    Furnace Basic Power Plant Cycle

    The thermal (steam) power plant uses a dual(vapour + liquid) phase cycle. It is a closed cycle to enablethe working fluid (water) to be used again and again. Thecycle used is "Rankine Cycle" modified to include superheating of steam, regenerative feed water heating and

    reheating of steam.

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    On large turbines, it becomes economical toincrease the cycle efficiency by using reheat, which is a wayof partially overcoming temperature limitations. Byreturning partially expanded steam, to a reheat, the averagetemperature at which heat is added, is increased and, byexpanding this reheated steam to the remaining stages of theturbine, the exhaust wetness is considerably less than itwould otherwise be conversely, if the maximum tolerablewetness is allowed, the initial pressure of the steam can beappreciably increased.

    Coal to Steam

    Coal from the coal wagons is unloaded in the coalhandling plant. This Coal is transported up to the raw coalbunkers with the help of belt conveyors. Coal is transportedto Bowl Mills by Coal feeders The coal is pulverized in the

    Bowl Mill, where it is ground to a powder form. The millconsists of a round metallic table on which coal particles fall.This table is rotated with the help of a motor. There are threelarge steel rollers which are spaced 120" apart. When there isno coal, these rollers does not rotate but when the coal is fedto the table it packs up between roller and the table and this

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    forces the rollers to rotate. Coal is crushed by the crushingaction between the rollers and rotating table. This crushedcoal is taken away to the furnace through coal pipes with thehelp of hot and cold air mixture from P.A. Fan.

    Water from the boiler feed pump passes througheconomizer and reaches the boiler drum. Water from thedrum passes through down comers and goes to bottom ringheader. Water from the bottom ring header is divided to all

    the four sides of the furnace. Due to heat and- the densitydifference the water rises up in the water wall tubes . "Wateris partly converted to steam 'as it rises up in the furnace. Thissteam and water mixture is again taken to the boiler drumwhere the steam is separated from water. Water follows thesame path while the steam is sent to superheaters for

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    superheating. The superheaters are located inside thefurnace and the steam is superheated (540"C) and finally itgoes to turbine.Steam to mechanical Power

    From the boiler, a steam pipe conveys steam to theturbine through a stop valve (which can be used to. shut offsteam in an emergency) and through control valves thatautomatically regulate the supply of steam to the turbinewhere it passes through a ring of stationary blades fixed tothe cylinder wall. These act as nozzles and direct the steaminto a second ring of moving blades mounted on a disc

    which rotates the blades and its passage of some heat energyis changed into mechanichal energy.

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    The turbine shaft usually rotates at 3,000revolutions per minute. This speed is determined by thefrequency of the electrical system used in this country and isthe speed at which a 2- pole generator must be driven togenerate alternating current at a frequency of 50 cycles persecond.

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    BOILER

    DESCRIPTION:

    A boiler is a closed vessel in which waterorotherfluid is heated. The heated or vaporized fluid exits the boiler

    for use in various processes or heating applications

    Construction of boilers is mainly of

    steel, stainless steel, and wrought iron. In live steam models,

    copperorbrass is often used. Historically copper was often used

    for fireboxes (particularly for steam locomotives), because of its

    http://en.wikipedia.org/wiki/Pressure_vesselhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Mild_steelhttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Wrought_ironhttp://en.wikipedia.org/wiki/Live_steamhttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Brasshttp://en.wikipedia.org/wiki/Fireboxhttp://en.wikipedia.org/wiki/Steam_locomotivehttp://en.wikipedia.org/wiki/Pressure_vesselhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Fluidhttp://en.wikipedia.org/wiki/Mild_steelhttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Wrought_ironhttp://en.wikipedia.org/wiki/Live_steamhttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Brasshttp://en.wikipedia.org/wiki/Fireboxhttp://en.wikipedia.org/wiki/Steam_locomotive
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    better thermal conductivity. The price of copper now makes this

    impractical.

    Cast iron is used for domestic water heaters. Although

    these are usually termed "boilers", their purpose is to produce hot

    water, not steam, and so they run at low pressure and try to avoidactual boiling. The brittleness of cast iron makes it impractical for

    steam pressure vessels.

    The steam generating boiler has to produce steam at

    the high purity, pressure and temperature required for the steam

    turbine that drives the electrical generator. The boiler includes the

    economizer, the steam drum, the chemical dosing equipment, and

    http://en.wikipedia.org/wiki/Cast_ironhttp://en.wikipedia.org/wiki/Cast_iron
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    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 precipitatororbaghouse) and the flue gas stack.[1][2]

    [3]

    Schematic diagram of typical coal-fired power plant steam generator highlighting the

    air preheater (APH) location.

    MAIN BOILER: AT 100% LOAD

    Evaporation 700t/hr

    Feed watertemperature 247C

    Feed waterleaving economizer 276C

    http://en.wikipedia.org/wiki/Furnacehttp://en.wikipedia.org/wiki/Flue_gashttp://en.wikipedia.org/wiki/Centrifugal_fanhttp://en.wikipedia.org/wiki/Air_preheaterhttp://en.wikipedia.org/wiki/Electrostatic_precipitatorhttp://en.wikipedia.org/wiki/Dust_collector#Fabric_filtershttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Thermal_power_station#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Thermal_power_station#cite_note-Babcock-1%23cite_note-Babcock-1http://en.wikipedia.org/wiki/Thermal_power_station#cite_note-Elliott-2%23cite_note-Elliott-2http://en.wikipedia.org/wiki/Image:Steam_Generator.pnghttp://en.wikipedia.org/wiki/Image:Steam_Generator.pnghttp://en.wikipedia.org/wiki/Image:Steam_Generator.pnghttp://en.wikipedia.org/wiki/Furnacehttp://en.wikipedia.org/wiki/Flue_gashttp://en.wikipedia.org/wiki/Centrifugal_fanhttp://en.wikipedia.org/wiki/Air_preheaterhttp://en.wikipedia.org/wiki/Electrostatic_precipitatorhttp://en.wikipedia.org/wiki/Dust_collector#Fabric_filtershttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Thermal_power_station#cite_note-0%23cite_note-0http://en.wikipedia.org/wiki/Thermal_power_station#cite_note-Babcock-1%23cite_note-Babcock-1http://en.wikipedia.org/wiki/Thermal_power_station#cite_note-Elliott-2%23cite_note-Elliott-2
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    STEAM TEMPERATURE:

    Drum 341C

    Super heater outlet 540C

    Reheat inlet 332C

    Reheat outlet 540C

    STEAM PRESSURE:

    Drum design 158.20 kg/cm2

    Drum operating 149.70 kg/cm2

    Super heater outlet 137.00 kg/cm2

    Reheat inlet 26.35 kg/cm2

    Reheat outlet 24.50 kg/cm2

    FUEL:

    COAL DESIGN WORST

    Fixed carbon 38% 25%

    Volatile matter 26% 25%

    Moisture 8% 9%

    Grindability 50% Hardgrove 45% Hardgrove

    OIL:

    Calorific value of fuel oil 10,000 kcal/kg

    Sulphur content 4.5% W/W

    Moisture content 1.1% W/W

    Flash point 66C

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    FEED WATER CYCLE

    Deaerator

    Boiler feed pump

    H.P. Heater-1

    H.P.Heater-2

    H.P. Heater-3

    Feed water line

    Economiser

    Boiler drum

    Downcomer

    Water walls

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    Condensate Cycle

    From low pressure turbine

    Condenser

    Condensate pump

    Ejector

    Gland steam cooler

    GSC2

    LPH2

    LPH3

    LPH4

    Deareator

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    Principles of Combustion

    The primary function of oil and coal burning systems the

    process of steam generation is to provide controlled efficientconversation of the chemical energy of the fuel into heat energy

    which is then transferred to the heat absorbing surfaces of the

    steam generator. The combustion elements of a fuel consist of

    carbon, hydrogen and usually a small amount of sulphur. When

    combustion is properly completed the exhaust gases will contain,

    carbon dioxide,. water vapour, sulphur dioxide and a large volume

    of Nitrogen, Combustion is brought about by combining carbon

    and hydrogen or hydrocarbons with the oxygen in air. Whencarbon burns completely, it results in the formation of a gas known

    as carbon dioxide. When carbon burns incompletely it forms

    carbon monoxide.

    The following factors in efficient combustion areusually referred to as "The three Ts

    Time:

    It will take a definite time to heat the fuel to its ignition

    temperature and having ignited, it will also take time to bum.

    Consequently sufficient time must be allowed for complete

    combustion of the fuel to take place in the chamber.

    Temperature:

    A fuel will not burn until it has reached its

    ignition temperature. The speed at which this Temperature will be

    reached is increased by preheating the combustion air. The

    temperature of the flame of the burning fuel may vary with the

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    quantity of air used. Too much combustion air will lower the flame

    temperature and may cause unstable ignition.

    Turbulence:

    Turbulence is introduced to achieve a rapid

    relative motion between the air and the fuel particles. It is found

    that this produces a quick propagation of the flame and its rapid

    spread throughout the fuel/air mixture in the combustion chamber.

    Combustion efficiency: It varies with individual different grades of

    fuel within each boiler. The idea to be aimed at is the correct

    quantity of air together with good mixing of fuel and air to obtain

    the maximum heat release.

    Maximum combustion efficiency depends on

    Design of the boiler.

    Fuel used.

    Skill in obtaining combustion with the minimum amount of

    excess air.

    FURNACE

    INTRODUCTION:

    Furnace is primary part of boiler where the

    chemical energy of fuel is converted to thermal energy by

    combustion. Furnace is designed for efficient and complete

    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-cooled

    furnaces are used.

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    TYPES OF FURNACE

    P.F. FIRED DRY BOTTOM FURNACE:

    The tall rectangular radiant type furnace has now become afeature of modern dry bottom P.F. boiler. Indorsed height not only

    facilitates adequate natural circulation but also aids reduction of

    furnace exit gas temperature and hence less soot deposit in

    superheaters and reheaters. SLAG TYPE FURNACE:

    Furnace of this type normally has two parts. Primary

    furnace is used for very high rate of combustion. Provision is tomake molten slag and crush the granular form for easy disposal. As

    the ash has to flow from the primary furnace, coal having low

    melting temperature can only be used. To obtain high temperature

    inside the primary surface that will facilitate the easy flow of ash,

    very small but highly rated design is needed for primary furnace

    hence maintenance is needed.

    OIL FIRED BOILER FURNACE:

    Normally about 65% of furnace volume is enough for an

    oil-fired boiler as compared to the corresponding P.F. fired boiler.

    Oil-fired furnace is generally closed at the bottom, as there is no

    need to remove slag as in case of P.F. fired boiler. The bottom part

    will have small amount of slope to prevent film boiler building in

    the bottom tubes.

    If boiler has to design for both P.F. as well as oil, the

    furnace has to be designed for coal, as otherwise higher heatloading with P.F. will cause slogging and high furnace exit gas

    temperature.

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    SPECIFICATIONS

    FURNACE

    Width 13.868 m

    Depth 10.592 m

    Height 42.797 m

    Volume 5210 m3

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    BOILER DRUM

    Drum is of fusion-welded design with welded hemi-

    spherical dished ends. It is provided with stubs for welding all theconnecting 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 opposed 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 runsdown 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 separation.

    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 walls tubes are

    connected to headers at the top and bottom. The rear water walls

    tubes at the top are grounded in four rows at a wider pitch forming

    the grid tubes.

    REHEATER

    Reheater is used to raise the temperature of

    steam from which a part of energy has been extracted in high-

    pressure turbine. This is another method of increasing the cycle

    efficiency. Reheating srequires additional equipment I.e. Heatingsurface connecting boiler and turbine pipe safety equipment like

    safety valve, non-return valve, isolating valves, high pressure feed

    pump, etc. Reheater is composed to two sections namely front and

    rear pendant section which is located above the furnace arch

    between water-cooled screen wall tubes and rear wall hanger tubes.

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    Super heaters

    Whatever type of boiler is used, steam will

    leave the water at its surface and pass into the steam space. Steamformed above the water surface in a shell boiler is always saturated

    and cannot become superheated in the boiler shell, as it is

    constantly in contact with the water surface.

    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 saturated steam.

    In water-tube boilers, the superheater may be

    an additional pendant suspended in the furnace area where the hot

    gases will provide the degree of superheat required (see Figure

    3.4.4). 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.

    Fig. A water tube boiler with a super heater

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    If accurate control of the degree of superheat is

    required, as would be the case if the steam is to be used to drive

    turbines, then an attemperator (desuperheater) is fitted. This is a

    device installed after the superheater, which injects water into the

    superheated steam to reduce its temperature.

    ECONOMISER

    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 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 increase the efficiency of turbine unit

    and feed-water temperature.

    LOCATION AND MAINTENANCE:

    It is usual to locate economizer ahead of air

    heater. Counter flow arrangement is normally selected so that

    heating surface requirement is kept minimum for the same

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    temperature drop in flue gas. Water flow is from bottom to top so

    that steam if any formed during the heat transfer can move along

    with water and the lock up steam which will cause overheating and

    failure of economizer tube.

    Manholes and adequate spacing between thebanks of tubes are provided for inspection and maintenance works.

    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 ofspecially 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 and is adequately scaled by radial and

    circumferential scaling. Air Preheater consists of:

    Connecting plates

    Housing

    Rotor

    Heating surface elements

    Bearings

    Sector plates and Sealing arrangement

    SPECIFICATIONS

    Number of air preheater per unit 2

    Heater size 27-VI-(T)-74 casing

    Approx heating surface 19000 m2 each

    Rotor drive motor 15 H.P.

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    Speed reduction ratio 110:1

    Approx oil capacity 13 Gallons

    Solenoid Value 110 V, A.C.

    Basics of Fans

    The air we need for combustion in the furnace and the flue gas that

    we must evacuate would not possible without using fans. A fan iscapable of imparting energy to the air/gas in the form of a boost in

    pressure. We overcome the losses through the system by means of

    this pressure boost. The boost is dependent on density for a given

    fan at a given speed. The higher the temperature, the lower is the

    boost. Fan performance (Max. capability) is represented as volume

    vs. pressure boost.

    The basic information needed to select a fan is:

    Air or Gas flow (Kg/hr).

    Density (function of temperature and pressure).

    System, resistance (losses).

    Classification of FansIn boiler practice, we meet the following types of fans.

    Axial fans

    Centrifugal (Radial) fansAxial FansIn this type the movement of air or gas is parallel to its exit of

    rotation. These fans are better suited to low resistance applications.

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    The axial flow fan uses the screw like action of a multiplied

    rotating shaft, or propeller, to move air or gas in a straight through

    path.

    Centrifugal Fan

    This fan moves gas or air perpendicular to

    the axis of rotation. There are advantages when the air must be

    moved in a system where the frictional resistance is relatively high.

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    The blade wheel whirls air centrifugally between each pair of

    blades and forces it out peripherally at high velocity and high static

    pressure. More air is sucked in at the eye of the impeller. As the air

    leaves the revolving blade tips, part of its velocity is converted into

    additional static pressure by scroll shaped housing.

    There are three types of blades.

    Backward curved blades.

    Forward curved blades.

    Radial blades.

    Draft SystemBefore a detailed study of industrial fans it is in the fitness of

    things to understand the various draft systems maintained by those

    fans.

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    The terms draft denotes the difference

    between the atmospheric pressure and the pressure existing in the

    furnace.

    Depending upon the draft used, we have

    Natural Draft

    Induced Draft

    Forced Draft

    Balanced Draft System

    Natural Draft

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    In natural draft units the pressure

    differentials are obtained have constructing tall chimneys so that

    vacuum is' created in the furnace Due to small pressure difference,

    air is admitted into the furnace.

    Induced Draft

    In this system the air is admitted to natural

    pressure difference and the flue gases are taken out by means of

    induced Draft fans and the furnace is maintained under vacuum.Forced Draft

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    A set of forced draft fans are made use of forsupplying air to the furnace and so the furnace is pressurized. The

    flue gases are taken out due to the pressure difference between the

    furnace and the atmosphere.

    Balance Draft

    Here a set of Induced and Forced Draft

    Fans are utilized in maintaining a vacuuming the furnace.

    Normally all the power stations utilize this draft system.

    Industrial Fans

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    I.D. Fan

    The 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

    Impeller

    Outlet Guide Vane Assembly

    The outlet guides are fixed in between the

    case of the diffuser and the casing. These guide vanes serve to

    direct the flow axially and to stabilize the draft-flow caused in the

    impeller. These outlet blades are removable type from outside.

    During operation of the fan itself these blades can be replaced one

    by one.

    Periodically the outlet blades can be removed one at a time to find

    out the extent of wear on the blade. If excessive wear is noticed the

    blade can be replaced by a new blade.F.D Fan

    The fan, normally of the same type as ID Fan, consists of the

    following components:

    * Silencer

    * Inlet bend

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    * Fan housing

    * Impeller with blades and setting mechanism

    * Guide wheel casing with guide vanes and diffuser.

    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 antifriction 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 aninclined ball bearing at the drive side adsorbs the axial thrust.

    Lubrication and cooling these bearings is assured by a combined

    oil level and circulating lubrication system.

    Primary Air FanP.A. ran 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 amountof the velocity energy is converted to pressure energy in the spiral

    casing. The fan is driven at a constant speed and the flow is

    controlled by varying the angle of the inlet vane control. The

    Special feature of the fan is that is provided with inlet guide vane

    control with a positive and precise link mechanism.

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    PulverizerA pulverizer is a mechanical device for the grinding of many

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

    pulverize coal for combustion in the steam-generating furnaces of

    fossil fuel power plants.

    Fig. PULVERIZER

    http://en.wikipedia.org/wiki/Coalhttp://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Furnaceshttp://en.wikipedia.org/wiki/Fossil_fuel_power_planthttp://en.wikipedia.org/wiki/Coalhttp://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Furnaceshttp://en.wikipedia.org/wiki/Fossil_fuel_power_plant
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    Types of Pulverizers

    Ball and Tube Mills

    A ball mill is a pulverizer that consists of a

    horizontal rotating cylinder, up to three diameters in length,

    containing a charge of tumbling or cascading steel balls, pebbles,

    or rods.

    A tube mill is a revolving cylinder of up to five

    diameters in length used for fine pulverization of ore, rock, and

    other such materials; the material, mixed with water, is fed into the

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

    Ring and Ball Mill

    This type of mill consists of two rings separated

    by a series of large balls. The lower ring rotates, while the upper

    ring presses down on the balls via a set of spring and adjuster

    assemblies. The material to be pulverized is introduced into the

    center or side of the pulverizer (depending on the design) and is

    ground as the lower ring rotates causing the balls to orbit between

    the upper and lower rings. The pulverized material is carried out of

    the mill by the flow of air moving through it. The size of the

    pulverized particles released from the grinding section of the mill

    is determined by a classifer separator.

    MPS Mill

    Similar to the Ring and Ball Mill, this mill useslarge "tires" to crush the coal. These are usually found in utility

    plants.

    Bowl Mill

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    Similar to the MPS mill, it also uses tires to crush coal. There are

    two types, a deep bowl mill, and a shallow bowl mill.Advantage of pulverized coal

    Efficient utilization of cheap and low grade coal

    Flexibility to meet fluctuating load

    Elevation of bending loser Boiler Fittings and Mountings Safety valve

    A safety valve is a valve mechanism for the automatic

    release of a gas from a boiler, pressure vessel, or other system

    when the pressure or temperature exceeds preset limits. It is part of

    a bigger set named Pressure Safety Valves (PSV) or Pressure

    Relief Valves (PRV). The other parts of the set are named reliefvalves, safety relief valves, pilot-operated safety relief valves, low

    pressure safety valves, vacuum pressure safety valves.

    Function and design

    Fig. Boiler safety valve

    Boiler stop valves

    http://en.wikipedia.org/wiki/Valvehttp://en.wikipedia.org/wiki/Boilerhttp://en.wikipedia.org/wiki/Pressure_vesselhttp://en.wikipedia.org/wiki/Systemhttp://en.wikipedia.org/w/index.php?title=Pressure_Safety_Valve&action=edit&redlink=1http://en.wikipedia.org/wiki/Pressure_Relief_Valvehttp://en.wikipedia.org/wiki/Pressure_Relief_Valvehttp://en.wikipedia.org/wiki/Relief_valvehttp://en.wikipedia.org/wiki/Relief_valvehttp://en.wikipedia.org/wiki/Valvehttp://en.wikipedia.org/wiki/Boilerhttp://en.wikipedia.org/wiki/Pressure_vesselhttp://en.wikipedia.org/wiki/Systemhttp://en.wikipedia.org/w/index.php?title=Pressure_Safety_Valve&action=edit&redlink=1http://en.wikipedia.org/wiki/Pressure_Relief_Valvehttp://en.wikipedia.org/wiki/Pressure_Relief_Valvehttp://en.wikipedia.org/wiki/Relief_valvehttp://en.wikipedia.org/wiki/Relief_valve
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    A steam boiler must be fitted with a stop

    valve (also known as a crown valve) which isolates the steam

    boiler and its pressure from the process or plant. It is generally an

    angle pattern globe valve of the screw-down variety

    Fig: Boiler stop valve

    The stop valve is not designed as a

    throttling valve, and should be fully open or closed. It should

    always be opened slowly to prevent any sudden rise in downstream

    pressure and associated waterhammer, and to help restrict the fall

    in boiler pressure and any possible associated priming.

    Feedwater check valves

    The feedwater check valve is

    installed in the boiler feedwater line between the feedpump and

    boiler. A boiler feed stop valve is fitted at the boiler shell.

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    other pressure containers such as blowdown vessels, and will

    usually have smaller dials as shown in Figure

    Fig: Typical pressure gauge with ring siphon

    Gauge glasses and fittings

    All steam boilers are fitted with at leastone water level indicator, but those with a rating of 100 kW or

    more should be fitted with two indicators. The indicators are

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    usually referred to as gauge glasses complying with BS 3463.

    Fig. Gauge glass and fittings

    A gauge glass shows the current level of

    water in the boiler, regardless of the boiler's operating conditions.

    Gauge glasses should be installed so that their lowest reading will

    show the water level at 50 mm above the point where overheating

    will occur. They should also be fitted with a protector around

    them, but this should not hinder visibility of the water level.

    Gauge glasses are prone to damage from a number of sources, suchas corrosion from the chemicals in boiler water, and erosion during

    blow down, particularly at the steam end. Any sign of corrosion or

    erosion indicates that a new glass is required.

    When testing the gauge glass steam

    connection, the water cock should be closed. When testing the

    gauge glass water connections, the steam cock pipe should be

    closed.

    Gauge glass guards

    The gauge glass guard should be kept

    clean. When the guard is being cleaned in place, or removed for

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    cleaning, the gauge should be temporarily shut-off.

    Make sure there is a satisfactory water

    level before shutting off the gauge and take care not to touch or

    knock the gauge glass. After cleaning, and when the guard hasbeen replaced, the gauge should be tested and the cocks set in the

    correct position.Coal Bunker

    These are in process storage silos used for

    storing crushed coal from the coal handling system. Generally,

    these are made up of welded steel plates.' Normally, there are six

    such bunkers supplying coal of the corresponding mills. These arelocated on top of the mills so as to aid in gravity feeding of coal.

    Coal FeederEach mill is provided with a drag link chain/ rotary/ gravimetric

    feeder to transport raw coal from the bunker to the inlet chute,

    leading to mill at a desired rate.MillsThere are six mill (25% capacity each), for every 200 .MW unit,

    located adjacent to the furnace at '0' M level. These mills pulverize

    coal to the desired fineness to be fed to the furnace for combustion.Electrostatic precipitator

    These are generally two plate type located

    between boiler and the crr1imney. The precipitator is arranged for

    horizontal gas flow and is constructed with welded steel casi

    **************************

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    WATER CIRCULATION SYSTEM

    Theory of circulation

    Water 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 comers

    at a temperature slightly below the saturation temperature. The

    flow through the furnace wall is at saturation temperature. Heatabsorbed in water wall is latent heat of vaporization creating a

    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

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    Types of boiler circulating system:

    Natural circulation system

    Controlled circulation system

    Combines circulation system

    Natural circulation system

    Water delivered to steam generator from

    feed heater is at a temperature well below the saturation value

    corresponding to that pressure. Entering first the economizer it isheated to about 30-40C below saturation temperature. From

    economizer the water enters the drum and thus joins the circulation

    system. Water entering the drum flows through the down comer

    and 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 super heater

    for super heating and then sent to the high pressure turbine.

    Remaining water mixes with the incoming water from theeconomizer and the cycle is repeated.

    The circulation in this case takes place on

    the thermo-siphon principle. The dowm comers contain relatively

    cold water whereas the riser tubes contain a steam water mixture.

    Circulation takes place at such a rate that the driving force and the

    frictional resistance in water walls are balanced.

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    As the pressure increases, the difference in density between waterand 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/cm.

    Controlled circulation system

    Beyond 80 kg/cm of pressure, circulationis to be assisted with mechanical pumps to overcome the frictional

    losses. To regulate the flow through various tubes, orifice plates

    are used. This system is applicable in the high sub-critical regions

    (200 kg/cm).

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    Combined circulation system

    Beyond the critical pressure, phase

    transformation is absent, and hence once through system is

    adopted. However, it has been found that even at super critical

    pressure, it is advantageous to recirculate the water through the

    furnace tubes and simplifies the start up procedure. A typical

    operating pressure for such a system is 260 kg/cm.

    ASH HANDLING PLANT

    The ash produced in the boiler is transported

    to ash dump area by means of sluicing type hydraulic ash handling

    system, which consists of Bottom ash system, Ash water system

    and Ash slurry system.

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    Bottom ash system

    In the bottom ash system the ashdischarged from the furnace bottom is collected in two water

    compounded scraper through installed below bottom ash hoppers.

    The ash is continuously transported by means of the scraper chain

    conveyor onto the respective clinker grinders which reduce the

    lump sizes to the required fineness. The crushed ash from the

    bottom ash hopper from where the ash slurry is further transported

    to operation, the bottom ash can be discharged directly into the

    sluice channel through the bifurcating chute bypass the grinder.The position of the flap gate in the bifurcating chute bypasses the

    grinder. The position of the flap gate in the bifurcating chute is to

    be manually changed.

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    Fly ash system

    The flushing apparatus are provided underE.P. hoppers (40 No.s), economizer hoppers (4 No.s), air pre

    heaters (2 No.s), and stack hoppers (4 No.s),. The fly ash gets

    mixed with flushing water and the resulting slurry drops into the

    ash sluice channel. Low pressure water is applied through the

    nozzle directing tangentially to the section of pipe to create

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    turbulence and proper mixing of ash with water. For the

    maintenance of flushing apparatus plate valve is provided between

    apparatus and connecting tube.

    Ash water system

    High pressure water required for bottom ash

    hopper quenching nozzles, bottom ash hopper spraying, clinker

    grinder sealing scraper bars, cleaning nozzles, bottom ash hopper

    seal through flushing, economizer hopper flushing nozzles and

    sluicing trench jetting nozzles is tapped from the high pressure

    water ring mainly provided in the plant area.

    Low pressure water required for bottom ash

    hopper seal through make up, scraper conveyor make up, flushing

    apparatus jetting nozzles for all fly ash hoppers excepting

    economizer hoppers, is trapped from low pressure water rings

    mainly provided in the plant area.

    Ash slurry system

    Bottom ash and fly ash slurry of the system

    is sluiced upto ash pump along the channel with the acid of high

    pressure water jets located at suitable intervals along the channel.

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    Slurry pump suction line consisting of reducing elbow with drain

    valve, reducer and butterfly valve and portion of slurry pumpdelivery line consisting of butterfly valve, pipe & fitting has also

    been provided.

    CHPH

    (CONTROL STRUCTURE PUMP HOUSE)

    The control system has following pumps:-

    Chlorine pump-2(for chlorination of water) HP pump-6(for boiling of water)

    LP pump-3(for EP pump house)

    Fire pump-(incase of fire breakdown)

    TWS pump-3(for screening of water)

    CRW pump-3(supply water for water treatment)

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    This house is known as control house because amount of water to

    be supplied for treatment is controlled from this house with the

    help of these pumps. Generally 2 CRW pumps out of 3pumps

    remains open.similarly,1 FS ,2 LP,4 HP,1 TWS pumps remainsopen. If more water is needed then others pumps are opened.

    WATER TREATMENT PLANT

    As the types of boiler are not alike their

    working pressure and operating conditions vary and so do the typesand methods of water treatment. Water treatment plants used in

    thermal power plants are designed to process the raw water to

    water with vary lowin dissolved solids known as "dematerializedwater". 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

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    Actually, the type of demineralization processchosen for a power station depends on three main

    factors:

    The quality of the raw water.

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

    Selectivity of resins.

    Water treatment process which is generally made up of two

    sections:

    Pretreatment section

    Demineralization section

    Pretreatment section

    Pretreatment plant removes the suspended

    solids such as clay, silt, organic and inorganic matter, plants and

    other microscopic organism. The turbidity may be taken as of two

    types of suspended solids 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 waterby simple sedimentation. Finer particles however, will not settle in

    any reasonable time 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. The settling rate of the colloidal and finely divided

    (approximately 001 to 1 micron) suspended matter is so slow that

    removing them from water by plain sedimentation is tank shaving

    ordinary dimensions is impossible. Settling velocity of finelydivided and collide particles under gravity also are so small that

    ordinary sedimentation is not possible. It is necessary, therefore, to

    use procedures which agglomerate the small particles into larger

    aggregates, which have practical settling velocities. The term

    "Coagulation" and "flocculation" have been used indiscriminately

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    to describe process of turbidity removal. "Coagulation" means to

    bring together the suspended particles. The process describes the

    effect produced by the addition of a chemical Al (SP) g to a

    colloidal dispersion resulting in particle destabilization by a

    reduction of force tending to keep particles apart. Rapid mixing isimportant at this stage to obtain. Uniform dispersion of the

    chemical and to increase opportunity for particles to particle

    contact. This operation is done by flash mixer in the

    c1ariflocculator. Second stage of formation of settle able particles

    from destabilized colloidal sized particles is termed a

    "flocculation". Here coagulated particles grow in size by attaching

    to each other. In contrast to coagulation where the primary force is

    electrostatic or intrinsic, "flocculation" occurs by chemicalbridging. Flocculation is obtained by gentle and prolonged mixing

    which converts the submicroscopic coagulated particle into

    discrete, visible & suspended particles. At this stage particles are

    large enough to settle rapidly under the influence of gravity

    anomaly be removed.

    If pretreatment of the water is not done efficiently then

    consequences are as follows:

    Si02 may escape with water which will increase the anionloading.

    Organic matter may escape which may cause organic fouling

    in the anion exchanger beds. In the 'pre-treatment plant

    chlorine addition provision is normally made to combat

    organic contamination.

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    us see, what happens actually in each bed when water is passed

    from one to another.

    Resins, which are built on synthetic matrix

    of a styrene divinely benzene copolymer, are manufactured in such

    a way that these have the ability to, exchange one ion for another,hold it temporarily in chemical combination and give it to a strong

    electrolytic solution. Suitable treatment is also given to them in

    such a way that a particular resin absorbs only a particular group of

    ions. Resins, when absorbing and releasing cationic portion of

    dissolved salts, is called cation, exchanger resin and when

    removing anionic portion is called anion exchanger resin. preset

    trend is of employing 'strongly acidic cation exchanger resin and

    strongly basic anion exchanger resin in a DM Plant of modernthermal power station. We may see that the chemically active

    group in a cationic resin is SOx-H (normally represented by RH)

    and in an anionic resin the active group is either tertiary amine or

    quaternary ammonium group (normally the resin is represented by

    ROH). The reaction of exchange may be further represented as

    below

    Cation Resin

    RH + Na ------------------------- RNa + H2SO4

    K K HCl

    Mg Mg

    Ca Ca HNO3

    In the Resin in RemovedForm of in H2CO3 indegasser

    Salts form tower

    Anion Resin

    ROH + H2SO4 ------------------ RSO4 + H2O

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    HCl Cl

    HNO3 NO3

    Mineral acid Resins in exhausted

    Obtain from cation formexchanger

    The water from the ex-cation contains

    carbonic acid also sufficiently, which is very weak acid difficult to

    be removed by strongly basic anion resin and causing hindrance to

    remove silicate ions from the bed. It is therefore a usual practice to

    remove carbonic acid before it is led to anion exchanger bed. The

    ex-cation water is trickled in fine streams from top of a tall towerpacked with, rasching rings, and compressed air is passed from the

    bottom. Carbonic acid breaks into C03 and water mechanically

    (Henry's Law) with the carbon dioxide escaping into the

    atmosphere. The water is accumulated in suitable storage tank

    below the tower, called degassed water dump from where the same

    is led to anion exchanger bed, using acid resistant pump.

    The ex-anion water is fed to the mixed bedexchanger containing both cationic resin and anionic resin. This

    bed not only takes care of sodium slip from cation but also silica

    slip from anion exchanger very effectively. The final output from

    the mixed bed is Exira-ordinarily pure water having less than

    0.2/Mho conductivity 7.0 and silica content less than 0.02 pm. Any

    deviation from the above quality means that the resins in mixed

    bed are exhausted and need regeneration, regeneration of the

    mixed bed first calls for suitable, back washing and settling, so that

    the two types of resins are seperated from each other. Lighter anion

    resin rises to the top and the heavier cation resin settles to the

    bottom. Both the resins are then regenerated separately with alkali

    and acid, rinsed to the desired value and air mixed, to mix the resin

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    again thoroughly. It is then put to final rinsing till the desired

    quality is obtained.

    It may be mentioned here that there are two types of

    strongly basic anion exchanger. Type II resins are slightly less

    basic than type I, but have higher regeneration efficiency than typeI. Again as type II resins are unable to remove silica effectively,

    type I resins also have to be used for the purpose. As such, the

    general condition so far prevailing in India, is to employ type II

    resin in anion exchangers bed and type I resin in mixed bed (for

    the anionic portion).

    It is also a general convention to regenerate the

    above two resins under through fare system i.e. the caustic soda

    entering into mixed bed for regeneration, of type I anion resin, isutilized to regenerate type II resin in anion exchanger bed. The

    content of utilizing the above resin and mode of regeneration is

    now days being switched over from the economy to a higher cost

    so as to have more stringent quality control of the final D.M.

    Water.Internal Treatment

    This final D.M effluent is then either led to

    hot well of the condenser directly as make up to boilers, or being

    stored in D.M. Water storage tanks first and then pumped for make

    up purpose to boiler feed.

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    As the D.M. Water has a good affinity to

    absorb carbon dioxide and oxygen, and both are extremely harmful

    to metal surfaces for their destruction like corrosion, these have to

    be removed before it is fed to boiler. This is being done indesecrator. Still the residual oxygen which is remaining in the

    water is neutralized by a suitable doze of hydrazine, at the point

    after desecrator. To have further minimum corrosion, the pH of

    feed water is to be maintained at around 9.0 for which purpose

    ammonia in suitable doze is added to this make up water at a point

    along with hydrazine as stated above.

    **********************

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    STEAM TURBINE THEORY

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    Operating Principles

    A steam turbine's two main parts are the cylinder andthe rotor.As the steam passes through the fixed blades or nozzles it

    expands and its velocity increases. The high-velocity jet of steam

    strikes the first set of moving blades. The kinetic energy of the

    steam changes into mechanical energy, causing the shaft to rotate.

    The steam then enters the next set of fixed blades and strikes the

    next row of moving blades.

    As the steam flows through the turbine, its pressure and

    temperature decreases, while its volume increases. The decrease inpressure 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.

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    The kinetic energy of the steam changes into

    mechanical erringly through the impact (impulse) or reaction of the

    steam against the blades.

    STEAM CYCLEThe thermal (steam) power plant uses a dual (vapour +

    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 super heating of steam, regenerative

    feed water heating and reheating of steam.

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    On large turbines, it becomes economic to increase the

    cycle efficiency by using reheat, which is a way of partially

    overcoming temperature limitations. By returning partially

    expanded steam to a reheat, the average temperature at which heat

    is added is increased and by expanding this reheated steam to theremaining stages of the turbine, the exhaust wetness is

    considerably less than it would otherwise be conversely, if the

    maximum tolerable wetness is allowed, the initial pressure of the

    steam can be appreciably increased.

    TURBINE CLASSIFICATION

    Impulse Turbine:In Impulse Turbine steam expands in fixed nozzles.

    The high velocity steam from nozzles does work on moving blades

    which causes the shaft to rotate. The essential features of impulse

    turbine are that all pressure drops occur at nozzles and not on

    blades.

    A simple impulse turbine is not very efficient because it does

    not fully use the velocity of the steam. Many impulse turbines are

    velocity compounded. This means they have two or more sets ofmoving blades in each stage.

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    Reaction Turbine:

    In this type of turbine pressure is reduced at both fixed

    & moving blades. Both fixed& moving blades act as nozzles.

    Work done by the impulse effect of steam due to reversals ofdirection of high velocity steam. The expansion of steam takes

    place on moving blades.

    A reaction turbine uses the "kickback" force of the

    steam as it leaves the moving blades and fixed blades have the

    same shape and act like nozzles. Thus, steam expands, loses

    pressure and increases in velocity as it passes through both sets of

    blades. All reaction turbines are pressure-compounded turbines.

    Compounding:

    Several problems occur if energy of steam is converted

    in single step & so compounding is done. Following are the typesof compounded turbine:

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    Velocity Compounded Turbine

    Like simple turbine it has only one set of nozzle &

    entire steam pressure drop takes place there. The kinetic energy of

    steam fully on the nozzles is utilized in moving blades. The role of

    fixed blades is to change the direction of steam jet & to guide it.

    Pressure Compounded Turbine

    This is basically a no. of single impulse turbines in

    series or on the same shaft.

    The exhaust of first turbine enters the nozzle of the next turbine.

    Total pressure drop of steam does not take on first nozzle ring but

    divided equally on all of them.

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    Pressure Velocity Compounded Turbine

    It is just the combination of the two compounding has

    the advantages of allowing bigger pressure drops in each stage &

    so fewer stages are necessary. Here for given pressure drop the

    turbine will be shorter length but diameter will be increased.

    Steam turbines may be classified into different categories

    depending on their construction, the process by which heat dropis achieved, the initial and final conditions of steam used and

    their industrial usage.

    According to the direction of steam flow

    Axial turbines

    Radial turbines

    According to the number of cylinder

    Single - cylinder turbines.

    Double- cylinder turbines.

    Three-Cylinder turbines.

    Four-Cylinder turbines.

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    Multi - Cylinder turbines

    According to the steam conditions at inlet toturbines

    Low-pressure turbines Medium -pressure turbines

    High-pressure

    Turbines of very high pressures

    Turbines of supercritical pressures

    According to their usage in industry

    Turbines with constant speed of rotation primarily used for

    driving alternators. Steam turbines with variable speed meant for driving turbo

    blowers, air circulators, pumps etc.

    Turbines with variable speed: Turbines of this type are usually

    employed in steamers, ships and railway locomotives (turbo

    locomotives)

    Main Turbine

    The 210MW turbine is a tandem compounded type

    machine comprising of H.P. & I.P. cylinders. The H.P. turbine

    comprises of 12 stages the I.P. turbine has 11 stages & the L.P. has

    four stages of double flow. The H.P. & I.P. turbine rotor are rigidly

    compounded & the I.P. & the I.P. rotor by lens type semi flexible

    coupling. All the three rotors are aligned on five bearings of which

    the bearing no.2 is combined with thrust bearing.

    The main superheated steam branches off into twostreams 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 returned in the boiler for reheating.

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

    interceptor valves and control valves and after expanding enters

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

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

    direction to counteract the trust and enters the condenser placed

    directly below 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 closed cycle.

    TURBINE CYCLEFresh steam from boiler is supplied to the turbine

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

    supplied to control valves situated on H.P. cylinders on the front

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

    steam flows back to boiler for reheating and reheated steam from

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    the boiler cover to the intermediate pressure turbine trough two

    interceptor valves and four control valves mounted on the I.P.

    turbine.

    After flowing trough I.P. turbine steam enters the middlepart 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.

    The selection of extraction points and cold reheat pressure

    has been done with a view to achieve the highest efficiency. These

    are two extractions from H.P. turbine, four from I.P. turbine and

    one from L.P. turbine. Steam at 1.10 to 1.03 g/sq cm Abs is

    supplied for the gland sealing. Steam for this purpose is obtained

    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.

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    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.

    DESCRIPTION OF MAIN TURBINEMain Components of Turbine:

    Emergency Stop Valve

    Steam from the boiler is supplied to the turbine through

    two emergency stop valves. The emergency stop valve operated by

    hydraulic servomotor shuts off steam supply to the turbine whenthe turbo set is tripped. The emergency stop valves connected to

    the four control valves through four flexible loop pipes of

    Chromium-Molybdenum-Vanadium steel.

    H.P. Cylinder

    It is made of creep resisting Cr-Mo-V steel casting

    made of two halves joined at the horizontal plane.

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    The horizontal joint is secured with the help of studs

    and nuts made of high creep resisting Cr-Mo-V steel forgings. To

    ensure H.P. tightness the studs are tightened by heat to a

    predetermined temperature with the help of electric heater.

    H.P. Rotor

    The H.P. rotor has discs integrally forged with the shafts

    and is mechanical forming single Cr-Mo-V steel forging. A special

    process to prevent abnormal rotor deflection thermally stabilizes

    the rotor forging.

    L.P. Rotor

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    It consists of shrunk fit discs on a shaft. The shaft is a

    forging of Cr-Mo-V steel while the discs are of high strength Ni

    steel forging.

    The H.P. rotor is connected by rigid couplings whole the

    I.P. rotor and L.P. rotor are connected by semi-flexible lens typecoupling. The rotors are dynamically balanced to a very precise

    degree.

    Turbine Bearings

    The three turbine rotors are supported on fine bearings.

    The second bearing from pedestal side is a combined radial thrust

    bearing while all others are journal bearings.

    Thrust Bearings

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    It is Mitchell type with bearing surface distributed over

    a number of bearing surfaces. They are pivoted in housing on the

    side of I.P. rotor thrust collar.

    During operation on oil film is forced between pads

    and thrust collar and there is a no metal-to-metal contact. A second

    ring of pads on opposite side of thrust collar takes the axial thrust

    as may occur under abnormal conditions.

    L.P. Heaters

    Turbine is provided with non-controlled extractions which

    are utilized for heating the condensate from turbine bleeding

    system. There are four L.P. heaters. They are equipped with

    necessary safety valves in steam space level indicator for visual

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    level indication of heated steam. Condensate pressure vaccum

    gauges are present for measurement of steam pressure.

    Gland Steam Cooler

    Gland steam cooler has been provided to suck and cool

    the air steam mixture from the gland seats. It employs a small

    ejector for which the working medium is steam of low parameters,

    which can be taken either from the deaerator or auxiliary source.

    The pressure and temperature of this steam should of this steam is

    retrieved to the fullest possible extent as the gland steam cooler is

    also interposed in the condensate heating cycle thereby improving

    overall efficiency of the cycle.

    TURBINE AUXILLARIECondensate Pumps

    The function of these pumps is to pumps out thecondensate to the desecrator through ejectors, gland steam cooler,

    and L.P. heaters. These pumps have four stages and since the

    suction is at a negative pressure, special arrangements have been

    made for providing sealing. This pump is rated generally for

    160m3 hr. at a pressure 13.2 Kg/cm2.

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    L.P. Heaters

    Turbine has been provided with non-controlled

    extractions which are utilized for heating the condensate, fromturbine bleed steam. There are 410w pressure heaters in which the

    last four extractions are used. L.P. Heater-1 has two parts LPH-1A

    and LPH-1B located in the upper parts of condenser A and

    condenser B respectively. These are of horizontal type with shell

    and tube construction. L.P.H. 2, 3 and 4 are of similar construction

    and they are mounted in a row at 5M level. They are of vertical

    construction with brass tubes the ends of which are expanded into

    tube plate. The condensate flows in the "U" tubes in four passesand extraction steam washes the outside of the tubes. Condensate

    passes thru' these four L.P. heaters in succession. These heaters

    are equipped with necessary safety valves in the steam space level

    indicator for visual level indication of heating steam condensate

    pressure vacuum gauges for measurement of steam pressure etc

    Feed Water System

    The main equipments coming under this system are

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    Boiler Feed Pump: Three per unit of 50% capaCity each

    located in the '0' meter level in the TG bay.

    High Pressure Heaters: Normally three in number and are

    situated in the TG bay.

    Drip Pumps: Generally two in number of 100% capacity eachsituated beneath the LP heaters.

    Turbine Lubricating Oil System: This consists of Main Oil

    Pump (MOP) Starting Oil Pump (SOP), AC standby oil pumps

    and emergency DC' oil pump and Jacking Oil Pump (JOP) (one

    each per unit).Boiler Feed Pumps

    This pump is horizontal and of barrel design driven byan Electric motor through a hydraulic coupling. All the bearings of

    pump and motor are forced lubricated by a suitable oil 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 very expensive

    machine which calls for a very careful operation and skilled

    maintenance. The safety in operation and efficiency of the feed

    pump depends largely on the reliable operation and 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.

    The feed pump consists of pump barrel, into which is

    mounted the inside stator together with rotor. The hydraulic part is

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    enclosed by the high pressure cover along with the balancing

    device. The suction side of the barrel and the space in the high

    pressure cover behind the balancing device are enclosed by the low

    pressure covers along with the stuffing box casings. The brackets

    of the radial bearing of the suction side and radial and thrustbearing of the discharge side are fixed to the low pressure covers.

    The entire pumps are mounted on a foundation frame. The

    hydraulic coupling and two claws coupling with coupling guards

    are also delivered along with the pump. Water cooling and oil

    lubricating are provided with their accessories.

    Turbine Driven Boiler Feed Pump

    The single cylinder turbine is of the axial flow type.

    The live steam flows through the emergency stop valve and then

    through the main Control Valves 5 nos. (Nozzle governing). These

    valves regulate the steam supply through the turbine in accordance

    with load requirements. The control valves are actuated by a lift

    bar which is raised or lowered via a lever system by the relay

    cylinder mounted on the turbine casing.

    The journal bearings supporting the turbine shaft arearranged in the two bearing blocks. The front end -bearing block

    also houses the thrust bearing, which locates the turbine shaft and

    takes up "the axial forces.

    There are 14 stages of reaction balding. The balancing

    piston is provided at the. Steam admission side to compensate the

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    axial thrust to the maximum extent. Since the axial thrust varies

    with the load, the residual thrust is taken up by the thrust bearing.

    The leak off from the balancing piston is connected back to the

    turbine after 9th stage.The turbine is provided with hydraulic and

    electro-hydraulic governing system. A primary oil pump is used asa speed sensor for hydraulic governing and shall Probes are used as

    a speed sensor for electro hydraulic governing.

    Whenever steam is drawn from the cold reheat line or

    auxiliary supply, steam flow is controlled by auxiliary control

    valve. During this period the main control valves (4 nos.) will

    remain fully opened and the bypass valve across it will remain

    closed. (Bypass remains closed for a short period when change,

    over from IP steam to CRH takes place).The steam exhaust for the BFP- Turbine is connected to

    the main condenser and the turbine glands are sealed by gland

    steam.

    High Pressure Heaters

    These are regenerative feed water heaters operating at

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

    generally vertical type and turbine bleed steam pipes are connected

    to them.

    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 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 f tube rupture in any of the HPH and the level of the

    condensate rising to dangerous level, the group protection devicediverts automatically the feed water directly to boiler, thus

    bypassing all the 3 H.P. heaters.

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    Following fittings are generally provided on the HP heaters

    Gauge glass for indicating the drain level.

    Pressure gauge with three way cock.

    Air Vent cock.

    Safety valve shell side.

    Seal pot.

    Isolating valves.

    High level alarm switch.

    Speed Governor

    It is directly coupled to the turbine rotor through

    coupling and has been designed to maintain automatically the

    speed of the turbo set. It is located with the front pedestals.

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    Load Limiter

    Turbine is equipped with the load limiter used in special

    cases to limit the opening of valves by speed governor.

    Purpose: To limit the load rising beyond the set point, can bevaried over the entire load range.

    Turbine Oil Lubricating System

    This consists of main oil pump, starting oil pump emergency

    D.C. oil pump and each per unit.

    TYPES OF VALVES USED AND MAINTAINED IN TMD

    Gate Valve

    Regulating Valve

    Non-Return Valve

    Safety Valve

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    Valves are made of cast iron, cast steel, carbon steel,alloy steel.

    Cast iron valves: 0-150 deg Cel temperature (used for water

    lines).

    Carbon steel valves: 150-425 deg Cel temperature (used for

    water/steam lines).

    Alloy steel valves: 425-535 deg Cel temperature (used for

    steam lines).

    *************************

    Thanks

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