dvc mejia report

8/16/2019 DVC Mejia Report

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Training Report

1.1. 2013 Training Report onMejia Thermal Power Station Pintu Khan Asansol Engineering

College 1/22/20132.2. Copyright NoticeCopyright © 2012 by AECAll rights reserved. No part of this

publication may be reproduced, distributed, ortransmitted in any form or by any means,

including photocopying, recording, or otherelectronic or mechanical methods, without the

prior written permission of thepublisher, except in the case of brief quotations embodied

in critical reviews and certainother non-commercial uses permitted by copyright law. Page

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3.3. PrefaceThis Project Report has been prepared in fulfilment of Industrial Training to be

carriedout in third year of our four year B.TECH course. For preparing the Project Report,

wehave visited Mejia Thermal Power Station under Damodar Valley Corporation

duringthe suggested duration for the period of 21 days, to avail the necessaryinformation.The blend of learning and knowledge acquired during our practical studies at

thecompany is presented in this Project Report.The rationale behind visiting the power

plant and preparing the Project Report is tostudy the mechanical overview, electrical

overview, various cycles and processes (viz.Steam Generation, Turbo Generation and

Balance of Plant) of power generation anddetails of control and instrumentation required

in thermal power plant.We have carried out this training under well experienced and

highly qualified engineersof MTPS, DVC of various departments’ viz. Mechanical,

Electrical, Chemical and Control& Instrumentation depts. We have taken the opportunity

to explore the ElectricalDepartment, its use, necessity in power plant and maintenance of

various instrumentsused for monitoring and controlling the numerous processes of powergeneration. Wehave tried our best to cover all the aspects of the power plant and their

brief detailing inthis project report.All the above mentioned topics will be presented in the

following pages of this report.The main aim to carry out this training is to familiarize

ourselves with the real industrialscenario, so that we can relate with our engineering

studies. Page | 2

4.4. AcknowledgementI take this opportunity to express my profound gratitude and deep

regards to Mr. P.K.Dubey for his exemplary guidance, monitoring and constant

encouragementthroughout the course of this thesis. The blessing, help and guidance

given by him timeto time shall carry me a long way in the journey of life on which I am

about to embark.I also take this opportunity to express a deep sense of gratitude to MejiaThermalPower Station, DVC, for their cordial support, valuable information and guidance,

whichhelped me in completing this task through various stages.I am also thankful to the

Director (HRD), the Chief Engineer and Project Head, Mr. G.Nandesu (Asstt. Manager

HR) for providing me opportunity to carry out my vocationaltraining in MTPS. I am obliged

to staff members of Mejia Thermal Power Station, DVC for the valuableinformation

provided by them in their respective fields. I am grateful for theircooperation during the

period of my assignment.Lastly, I thank almighty, my parents, brother, sisters and friends

for their constantencouragement without which this assignment would not be possible.

Signature of the Trainee Page | 3

5.5. Table of Contents Page No. Introduction 5• Damodar Valley Corporation 5• Basicneeds and overview of a power plant 7• Mejia Thermal power station 9• MTPS Unit

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Overview 11♣ Coal Handling Plant 12♣ Coal Mill 15♣ Furnace and Boiler 17♣ Steam

Turbine 20♣ Introduction to Water Treatment 23• Pre Treatment of Water 24• DM Plant

Treatment 25• Waste Water Treatment 26♣ Steam/Water Circuit of MTPS 27•

Components of Steam/Water Cycle 29♣ Cooling Towers 32♣ Air and Flue Gas Path 33♣

Electrostatic Precipitators 35♣ Ash Handling Plant 40♣ Electrical System Overview 43•

Generator 43• Excitation System 44• Transformers 45• Control and Instrumentation 50

• Automatic Voltage Regulator 53• AC and DC Power Flow in MTPS 55• Switchyard 56

• Frequency Control 60• Voltage Control 61♣ National Grid 62♣ Central Load Dispatch

63♣ DVC: Transmission and Distribution Network 65♣ Conclusion 67♣ Bibliography 68

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6.6. INTRODUCTION Electricity generation is the process of generating electric power

from sources ofenergy. Electricity is most often generated at a power station

byelectromechanical generators, primarily driven by heat engines fuelled bychemical

combustion or nuclear fission but also by other means such as the kineticenergy of

flowing water and wind. There are many other technologies that can be andare used togenerate electricity such as solar photovoltaic and geothermal power. In Indian

subcontinent the abundance of coal leads to establishment of thermalpower stations and

governing bodies namely DVC, NTPC, TATA power acts as pioneersin the generation of

electricity.Damodar Valley Corporation Damodar Valley Corporation was established on

7th July 1947.It is themost reputed company in the eastern zone of India. DVC is

established on theDamodar River.Vision: To foster integrated development of Damodar

Valley Command Area and achievepar excellence in its multifaceted activities of control of

floods, provision of irrigation,generation, transmission and distribution of electrical energy

and also soil conservation,unified tourism, fisheries, socio-economic & health

development of villages within aradius of 10 KM of its projects. To establish DVC as oneof the largest power majors of Eastern India whiledischarging the responsibilities of its

other projects adequately. In order to achieve this goal against the backdrop of the

competitive marketscenario in the power sector, the objective of the Corporation has

been redefined.Generation: Entrusted with the responsibilities of providing the vital input

power for industrialgrowth in the resource rich Damodar Valley region, DVC has been

practically operatingas a pioneer, using latest available technologies to supply bulk power

at reasonablerates to the major industries. DVC has maintained its lead role in the

eastern region by adopting itself to thechallenges of time and technology during the

course of last 64 years. DVC has beengenerating and transmitting power since 1953 and

has succeeded not only in meetingthe needs of consumers but has also helped toincrease the demand of power whichitself is an index of development. Therefore, DVC, a

legacy to the people of India, emerged as a culmination ofattempts made over a whole

century to control the wild and erratic Damodar river. The Page | 5

7.7. river spans over an area of 25,000 km2 covering the states of Bihar (now Jharkhand)

&West Bengal.Infrastructure: With the time DVC developed and expanded its

infrastructure, seven thermalpower stations with a capacity of 8910MW, three

hydroelectric power stations with acapacity of 147 MW. Presently DVC has more than 60

substations and receiving stationsmore than 5500-circuit km of transmission and

distribution lines.DVC has also fourdams, a barrage and a network of canals that play

effective role in water management.The construction of check dams, development offorests and farms and upland andwasteland treatment developed by DVC play a vital role

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in eco conservation.Thermal Power Stations: Sr.No. Plant State Installed Capacity in MW

1 Bokaro Thermal Power Station B Jharkhand 630 2 Chandrapura Jharkhand 1140 3

Durgapur Thermal Power Station West Bengal 350 4 Mejia Thermal Power Station West

Bengal 2340 5 Koderma Stage-1 Jharkhand 1000 6 Durgapur Steel Thermal Power West

Bengal 1000 Station 7 Raghunathpur phase-1 Thermal West Bengal 1200 Power Station

Total : 8,910Hydel Power Station: Sl. No. Plant State Installed Capacity in MW 1 Maithon

Dam Jharkhand 63.2 2 Panchet Dam Jharkhand 80 Total : 147.2Joint Venture Stations:

Sl. No. Sl. No. State Installed Capacity in MW 1 Bokaro Power Supply Corporation

Jharkhand 302 Limited(BPSCL) 2 Maithon Power Limited Jharkhand 1050 Total: 1352

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8.8. Basic Needs and Overview of a Thermal Power Pl antThe idea that STEAM has

potential energy and can be converted into kinetic energy wasgiven by famous scientist,

Sir. James Watt. This idea became the governing principal ofmany mechanical processes

and finally led to the success of Thermal Power Energy. Theneed of establishing a

Thermal Power Plant came to engineers by the realization of thefact that Hydel Powercould be utilized only for certain period of time in a year. Thissection will give the basic

requirements for Thermal Power Plant. SITE REQUIREMENT: - The basic requirements

of thermal power plant is determined by the type, size and other specifications of the

plant. It is required to know the immediate capacity of the power plant after construction

and the extension of capacity in the future, to determine the area required for construction

of the plant. The basic things that are taken into consideration are Station Building

Coal Store Cooling Towers Switch yard compound Surrounding areas

and approaching. GEOLOGY: - The geology of the site should be cost effective and the

subsoil must be able to with stand huge load of foundation. WATER REQUIREMENT: -

Water is required in power plant for two basic needs, first is for steam generation andsecond is for cooling purpose. Thermal Power Plant requires huge volume of water,

nearly of about 3 to 4 Tons/hr/MW only for steam generation. So site of plant must also

have reliable and huge water sources located near to it. COAL: - Coal is the prime

requirement of any thermal power plant, it is the main source of fuel as it is most

economic and residue of coal after combustion is also used by many industries like

cement industries, so the plant must have reliable sources of coal and regular supply in

huge amount like 20,000 Tons per week. TRANSPORT: - It is one of the another vital

factor of the plant as huge burden lies on transportation in daily basis because of huge

need of coal, furnace oil, hydrochloric acid and other chemical products along with

mechanical products. DISPOSAL OF EFFLUENTS: - Due to heavy rate of coalcombustion residual volume is also high. The main residual product is ash. The plant

must have facilities like ash pond to dispose them safely without harming the

environment. TRANSMISSION: -The plant area must have route available for

transmission over head cables to the nearest grid lines or load points which will be

capable of accepting the generated power output of the power station. CLIMATIC

CONDITION : - The tropical climate is best for erection of thermal power plant, because

areas having high humidity and fluctuating temperature lead to dew point and

condensation which as a result damages the electrical machines and corrodes the

insulation and over head cables. Page | 7

9.9. PROXIMITY OF AIRFIELDS:- The airfields must be studied properly to avoidmishaps as the chimney height ranges from 500 to 600 fts and boiler housing is of 200 fts

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in general. PERSONNEL REQUIREMENTS: - To run a plant smoothly requirement of

skilled and unskilled personnel is very important. So recruitment of workers and skilled

personnel should be made carefully and in adequate amount. AMENITIES: -Some

considerations like availability of hospital, educational institutes and other facilities must

be taken into account. Page | 8

10.10. Mejia Thermal Power StationMejia Thermal Power Station also known as MTPS is

located in theoutskirts of Raniganj in Bankura District. It is one of the 5 ThermalPower

Stations of Damodar Valley Corporation in the state ofWest Bengal. The total power plant

campus area is surrounded byboundary walls and is basically divided into two major

parts,first the Power Plant area itself and the second is the Colony areafor the residence

and other facilities for MTPS employees.Technical Specification of MTPS long with

SpecialitiesInstalled capacities:1) Total number of Units: - 4*210 MW with Static

Generators 2*250 MW with Brush less Type Generators 2*500 MW with Brush less Type

Generators2) Total Energy Generation: -2340 MW3) Source of Water: - Damodar River4)

Sources of Coal: -B.C.C.L and E.C.L, also imported from Indonesia5) Required WaterConsumption: -6) Approximate coal requirement: - 73, 00,000Tons/annum at 75% PLF

(Plant Load Factor)7) Ash Deposited per annum: - 1.30 million Tons

/annumSPECIALITIES OF MEJIA THERMAL POWER PLANT: The plant is designed

and engineered by both Bharat Heavy Electricals Ltd (BHEL) and Damodar Valley

Corporation. Pipelines of 17km long and 1473mm in diameter spiral welded MS pipes

laid to transport river water from upstream of Durgapur barrage by pump sets of 500KV

pump motor set. Rail cum Road Bridge across Damodar River near Raniganj Station.

2KM Merry Go Round Railway System. 20mtr high RCC multiple flue stack. Direct

ignition of pulverized coal introduced for reduction in consumption of fuel oil. Ball and

Tube type Mills for more mill rejects and less maintenance cost. Boiler of 200ft heightand four corner firing system for better combustion. Page | 9

11.11. All major and hazardous systems like Steam Generation and Turbo Generation

section are incorporated with FSSS (Furnace Safety Supervisory System) for better

safety. Other logic systems like EAST and ATRS are also incorporated. Water

treatment Plants along with two artificial water reservoirs and Two Demineralization

Plants loaded with PLC system. Chimney height up to 600fts for less pollution. The

plant is loaded with latest technology sensor, transducers and transmitters for more

accurate analyzing of various processes. All the units are loaded with intelligent smart

microprocessor based systems known to be DCS systems provided by KELTRON,

SIEMENS and MAX-DNA for process control. Station Service Transformers of 6.6KVstep-down type are also available for better distribution of power inside the plant for

various requirements. Switchyard with individual step-up generator transformers of

ONAN/ANOF/AFOF cooling Transformers of 220KV for supply to national grid, along with

other safety instruments. Details of MTPS Generating UnitsGen. Name of Original

Present Year of Special FeaturesUnit Manufacturers capacity capacity commissioning

Boiler TG (MW) (MW) 1 BHEL BHEL 210 210 March , 1996 DIPC Boilers with zero 2

BHEL BHEL 210 210 March, 1998 reject tube mills. 3 BHEL BHEL 210 210 September,

1999 4 BHEL BHEL 210 210 February, 2005 5 BHEL BHEL 250 250 February, 2008 6

BHEL BHEL 250 250 2009 7 BHEL BHEL 500 500 2010 8 BHEL BHEL 500 500 2010

Page | 1012.12. TPS Unit Overview Page | 11

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13.13. Coal Handling PlantCoal: The Black DiamondCoal is the basic and the oldest raw

material used on large scale throughout the world.Throughout history, coal has been a

useful resource. It is primarily burned for theproduction of electricity and/or heat, and is

also used for industrial purposes, such asrefining metals. A fossil fuel, coal forms when

dead plant matter is converted into peat,which in turn is converted into lignite, then sub-

bituminous coal, after that bituminouscoal, and lastly anthracite. This involves biological

and geological processes that takeplace over a long period.Coal Handling PlantIn a coal

based thermal power plant, the initial process in the power generation is “CoalHandling”.

Coal is extracted from the ground by coal mining, either underground byshaft mining, or

at ground level by open pit mining extraction. The huge amount of coalis usually supplied

through railways. A railway siding line is taken into the power stationand the coal is

delivered in the storage yard. The coal is unloaded from the point ofdelivery by means of

wagon tippler. It is rack and pinion type. The coal is taken from theunloading site to dead

storage by belt conveyors. The belt delivers the coal to 0m levelto the pent house and

further moves to transfer point 8.The transfer points are used to transfer coal tothe nextbelt. The belt elevates the coal tobreaker house. It consists of a rotary machine,which

rotates the coal and separates the lightdust from it through the action of gravity

andtransfer this dust to reject bin house throughbelt.The belt further elevates the coal to

the transferpoint 7 and it reaches the crusher through belt.In the crusher a high-speed 3-

phase inductionmotor is used to crush the coal to a size of 50mmso as to be suitable for

milling system. Coal risesfrom crusher house and reaches the deadstorage by passing

through transfer point 8. Stages in Coal Handling plant Page | 12

14.14. Ultimate Analysis of CoalCarbon : 49.63%Hydrogen : 3.66%Sulphur :

0.47%Nitrogen : 0.91%Oxygen : 6.4%Moisture : 5.0%Ash : 34.0%Total : 100%Operation

of a Coal Handling Plant The purpose of the Coal handling plant in a thermal powerplant is to process raw coal & insure against their regular supply of coal which is

dependent on many players in the supply chain. The function of a CHP is to receive

process, store, and feed the Coal bunkers consistently over the entire life of the Power

plant. Coal is received from mines in the form of lumps, the sizes varying from 100mm

to 350mm, in two types of wagons through Rail; BOBR meaning Bogie Open Bottom

Rapid discharge & BOXN meaning Bogie Open High Sided Side discharge Wagon

BOBR wagons are unloaded in Track Hoppers & BOXN Wagons are unloaded by Wagon

tipplers. Coal is then supplied to the crusher house through Roller screens or Vibrating

feeders to sieve the coal before feeding to the crusher; 20% of the coal that is received is

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surge capacity to various parts of the CHP. Coal is delivered with large variations in

production rate of tonnes per hour (tph). A stockpile is used to allow the washplant to be

fed coal at lower, constant rate. A simple stockpile is formed by machinery dumping coal

into a pile, either from dump trucks, pushed into heaps with bulldozers or from conveyor

booms. Taller and wider stockpiles reduce the land area required to store a set tonnage

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

spontaneous combustion.2. Stack: Travelling, luffing boom stackers that straddle a feed

conveyor are commonly used to create coal stockpiles.3. Reclaimer: High-capacity

stockpiles are commonly reclaimed using bucket-wheel reclaimers. These can achieve

very high rates. Tunnel conveyors can be fed by a continuous slot hopper or bunker

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

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

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

operating costs, measured in dollars per tonne handled. Reclaimer pouring coal into

stack4. Crush House: After hand picking foreign material, coal is transported to the Crushhouse by conveyor belts where it is crushed to small pieces of about 20 mm diameter.

The crushed coal is then transported to the store yard. Coal is transported to bowl mills

by coal feeders.5. Tipplers: Coal from the coal wagons is unloaded in the coal handling

plant. This unloading is done by the “Tipplers”. This coal is transported up to the raw coal

bunkers with the help of conveyor belts. Crusher Page | 14

16.16. 6. Pull chord switch: A series of such switches are arranged in series at a 1m

distance on the side of conveyor belt. The power supply to rotor of the conveyor belt is

established only if all switches in series are connected.7. Vibrating feeder: The coal

stored in a huge hub is collected on the belt through vibrations created by the vibrating

feeder.8. Flap gates: These are used to channelize the route of coal through another beltin case the former is broken or unhealthy. The flap gates open let the coal pass and if

closed stop its movement.9. Magnetic separator: These are used to separate the ferrous

impurities from the coal.10. Metal detector: This are detect the presence of any ferrous

and non-ferrous metal in the coal and sends a signal to a relay which closes to seize the

movement of belt until the metal is removed. It basically consists of a transmitter and a

receiver. The transmitter consists of a high frequency oscillator, which produces

oscillations of 1500 Hz at 15V. The receiver receives this frequency signal. If there is any

presence of metal in the coal then this frequency is disturbed and a tripping signal is send

to relay to stop the conveyor belt.11. Belt weightier: It is used to keep an account of the

tension on the belt carrying coal and is moves accordingly to release tension on thebelt.12. Reclaim hopper: Reclaimation is a process of taking coal from the dead storage

for preparation or further feeding to reclaim hoppers. This is accomplished by belt

conveyors.Coal MillA pulveriser or grinder is a mechanical device for the grinding of many

different types ofmaterials. For example, they are used to pulverize coal for combustion in

the steam-generating furnaces of thermal power plants.The MILL consists of FEEDER,

MILL forpulverization of coal (BALL & TUBE TYPE MILL) andCLASSIFIER. The stacked

coal in the bunker isdropped to the feeder automatically; the feeder ishoused with a

conveyor belt system with motorsand pulleys. The feeder actually governs theamount of

coal to be transferred to the ball & tubemill for pulverizing. The flow of coal is

maintainedby the speed/rpm of the conveyor belt of the Page | 15

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17.17. feeder. The coal from the bunker drops to the feeder s conveyor belt at a constantrate

determined by the bunker level, in this condition higher the rpm of the conveyorbelt

greater will be the rate of volume of the coal transferred to the mill. In the sameway if the

rpm is lower then lesser will be the volume of coal transferred to the mill.Thus the coal

from the feeder is transported to the mill where the pulverization takesplace. Here the ball

& tube method is utilized for pulverizing of coal to 20microndiameter size. This type of mill

consists ofarrangement of iron alloy balls inside a MTPS Unit 3: Coal Milltube like

structure that is rotated by its Specificationauxiliaries. The coal is fed to the tube atits two

ends where it is crushed to the Ball Tube Mill: (3Nos.-CM # 2AB, 3AB, 3EF) Type:

BBD4760above mentioned size, these pulverized Capacity: 77 Tonne/Hourcoal is taken

back from the mill to the Power Rating: 2.25MWclassifier. In case of ball and tube type

Primary Air Fan: (3Nos.-PA FAN # 2AB,mills, there are 3 mill units; out of which 2 3AB,

3EF)must be running and 1 for standby while Type: NDV20H 3the unit is running on load.

The classifier Capacity: 65.9 m /sec Total Head Developed: 806 mmWCconsists of

strainers; the primary air brings Power Rating: 850KWthe coal from the mill to theclassifierwhere the pulverized coal is passedthrough strainers. The strainers allow 80%

(approx.) of the coal to pass from 200 mesh and rest is fed back to the mill for

furtherpulverization. Here the primary air is utilized to maintain the temperature of the

coal upto 80 C-90 C for better combustion. The classifier has 4 outlets and each ball

andtube type mills have 6 such classifier (2for each mill unit). The coal from each outlets

ofa classifier goes to each of the 4 corners of the furnace; therefore coal from eachoutlets

of all the 6 classifier goes to all the 24 elevations (A-B-C-D-E-F of each corner) offurnace

in all. All transport of coal from mill to the furnace is done by the primary airproduced by

PA fans. Page | 16

18.18. Furnace and Boiler♣ What is Boiler?A boiler is a closed vessel in which water orother fluid is heated. The heated orvaporized fluid exits the boiler for use in various

processes or heatingapplications, including boiler-based power generation, cooking, and

sanitation.Here in MTPS, the boiler is a rectangular furnace about 50 feet (15 m) on a

side and 130feet (40 m) tall. Its walls are made of a web of high pressure steel tubes

about 2.3inches (58 mm) in diameter.Types of Boiler:Fire Tube Boiler:In fire tube boiler,

hot gases pass through the tubesand boiler feed water in the shell side is convertedinto

steam. Fire tube boilers are generally used forrelatively small steam capacities and low to

mediumsteam pressures. As a guideline, fire tube boilers arecompetitive for steam rates

up to 12,000 kg/hourand pressures up to 18 kg/cm2. Fire tube boilers are Fire tube

Boileravailable for operation with oil, gas or solid fuels. Foreconomic reasons, most firetube boilers are nowadays of “packaged” construction (i.e.manufacturers shop erected)

for all fuels.Water Tube Boiler:In water tube boiler, boiler feed water flows through

thetubes and enters the boiler drum. The circulated water isheated by the combustion

gases and converted into steam atthe vapour space in the drum. These boilers are

selectedwhen the steam demand as well as steam pressurerequirements are high as in

the case of process cum powerboiler / power boilers.Most modern water boiler tube

designs are within thecapacity range 4,500 – 120,000 kg/hour of steam, at very

highpressures. Many water tube boilers nowadays are of“packaged” construction if oil

and /or gas are to be used asfuel. Solid fuel fired water tube designs are available

butpackaged designs are less common. Water tube BoilerThe features of water tubeboilers are: Page | 17



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19.19. Forced, induced and balanced draft provisions help to improve combustion

efficiency. Less tolerance for water quality calls for water treatment plant. Higher

thermal efficiency shifts are possibleNote: In MTPS Water tube Boilers are

incorporated.Furnace:A furnace is a device used for heating. The name derivesfrom Latin

fornax, oven.The boiler furnace auxiliary equipment includes coal feednozzles and igniter

guns, soot blowers, water lancing andobservation ports (in the furnace walls) for

observation ofthe furnace interior. Furnace explosions due to anyaccumulation of

combustible gases after a trip-out are avoided by flushing out suchgases from the

combustion zone before igniting the coal.The coal is ground (pulverized) to a fine powder,

so that less than 2% is +300 micrometer (μm) and 70-75% is below 75 microns, for a

bituminous coal. It should be notedthat too fine a powder is wasteful of grinding mill

power. On the other hand, too coarsea powder does not burn completely in the

combustion chamber and results in higherun-burnt losses.The pulverized coal is blown

with part of the combustion air into the boiler plantthrough a series of burner nozzles.

Secondary and tertiary air may also be added.Combustion takes place at temperaturesfrom 1300-1700°C, depending largely on coalgrade. Particle residence time in the boiler

is typically 2 to 5 seconds, and the particlesmust be small enough for complete

combustion to have taken place during this time.This system has many advantages such

as ability to fire varying quality of coal, quickresponses to changes in load, use of high

pre-heat air temperatures etc.One of the most popular systems for firing pulverized coal

is the tangential firing usingfour burners corner to corner to create a fireball at the center

of the furnace.Boiler Operation:The water enters the boiler through a section in the

convection pass calledthe economizer. From the economizer it passes to the steam

drum. Once the waterenters the steam drum it goes down to the downside the steam

drum. The steamseparators and dryers remove water droplets from the steam and thecycle through thewater walls is repeated. This process is known as natural

circulation.Pulverized coal is air-blown into the furnace from fuel nozzles at the four

corners and itrapidly burns, forming a large fireball at the center. The thermal radiation of

the fireballheats the water that circulates through the boiler tubes near the boiler

perimeter. The Page | 18

20.20. water circulation rate in the boiler is three to four times the throughput and is

typicallydriven by pumps. As the water in the boiler circulates it absorbs heat and

changes intosteam at 700 °F (370 °C) and 3,200 psi (22,000 kPa). It is separated from

the waterinside a drum at the top of the furnace. The saturated steam is introducedinto

superheat pendant tubes that hang in the hottest part of the combustion gases astheyexit the furnace. Here the steam is superheated to 1,000 °F (540 °C) to prepare itfor the

turbine.Boiler is the main section where the steam is produced by coal combustion.

Boilerconsists of boiler drum, water walls, wind box, heaters. The boilerhas 13 elevations

named as AA-A-AB-B-BC-C-CD-D-DE-E-EF-F-FF. Coalis inserted into the boiler from A-

B-C-D-E-F elevations. BC is used forinsertion of Heavy Oil and Light Oil after atomization

with steam andair respectively. DF is used for insertion of oil i.e. only heavy oil. Boththe

elevations have Oil Gun mounted for insertion of oil in properratio into the boiler. Liquid

fuel (viz. Heavy Oil and Light Oil) is usedfor initial light up process. Other elevations are

used to insertsecondary air from wind box. The furnace is divided into twosections

named as first pass and second pass separated by GooseNeck. The combustion takesplace in the first pass and the heating ofsteam through super heaters takes place inthe

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second pass.Boiler Drum: -Boiler Drum is the part of boiler where thedematerialized

water is stored and isinserted into the boiler. It is also houses thesteam that is formed in

the boiler. Waterstored in the drum comes down to the topof the boiler and forms a Water

Ring whichis then inserted into the boiler through thewater walls. Water Walls are

basically tubesalong the walls of the furnace, it is herewhere the water is converted into

steam at1300°C and then the produced steam is takenback to the boiler drum. The drum

has a propeller that rotates at high speed and makesthe steam and water separated due

to centrifugal force. The pressure of boiler drum is150kg/sq.cm and must be always

maintained. Water in the drum comes from feedcontrol station via economizer. Page | 19

21.21. Steam Turbine Mechanical Construction of Turbine AssemblyThe 200/210 MW

turbine installed in MTPS is of condensing-tandem-compound, threecylinder, horizontal,

disc and diaphragm, reheat type with nozzle governing andregenerative system of

feedwater heating andis directly coupled with the A.C generator.TURBINE CASING: -

The turbine assemblycomprises of three types of casing. 1) High Pressure Casing 2)

Intermediate Pressure Casing 3) Low Pressure CasingOTHER TURBINECOMPONENTS: -♣ ROTOR: - The rotor is basically the main rotating part of the turbine

which is also called the shaft and is attached with the rotor of the A.C generator via

coupling. Rotor is basically divided into 3 categories and they are as follows: - Cross

section of a turbine a) HIGH PRESSURE ROTOR: - This is basically made of single Cr-

Mo-V steel forged with internal disc attached to T-shoot fastening designed especially for

stabilizing the HPT and preventing the axial shift. b) INTERMEDIATE PRESSURE

ROTOR: - This is made from high creep resisting Cr- Mo-V steel forging and the shrunk fit

disc are machined from nickel-steel forging. This basically adjusts the frequency of the

blades. Page | 20

22.22. c) LOW PRESSURE ROTOR: - This is made from the above mention alloy used in IPRotors; blades are secured to the respective disc by riveted fork root fastening. Wires are

provided in all stages of this to adjust the frequency of the blades.♣ BLADES: - Blades

are single most costly element fitted in the turbine. Blades fitted in the stationary part are

called guide blades and those fitted in the rotor are called moving or working blades.

Blades are of basically three types, they are as follows: - a) Cylindrical ( constant profile)

blade b) Tapered cylindrical blade c) Twisted and varying profile blade.♣ SEALING

GLANDS: - To eliminate the possibility of steam leakage to the atmosphere from the inlet

and the exhaust end of the cylinder, labyrinth glands of the radial clearance type are

provided which provide a trouble free frictionless sealing .♣ EMERGENCY STOP

VALVES AND CONTROL VALVES: - Turbine is equipped with emergency stop valves tocut off steam supply and with control valve regulate steam supply. Emergency stop valves

are provided in main stream line and control valves are provided in the hot reheat line.♣

COUPLING: - Since the rotor is made in small parts due to forging limitations and other

technological and economic reasons, the couplings are required between any two rotors.

The coupling permits angular misalignment, transmits axial thrust and ensures axial

location.♣ BEARING: - Journal bearing are manufactured in two halves and usually

consist of bearing body faced with anti-friction tin based habiting to decrease coefficient

of friction. Bearings are usually force lubricated and have provision for admission of

jacking oil. Thrust bearing is normally Mitchell type and is usually combined with a journal

bearing, housed in spherically machined steel shell. The bearing between HP and IProtor is of this type. The rest is of journal type.♣ BARRING GEAR: - The barring gear is



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mounted on the L.P rear bearing cover to mesh with spur gear L.P rotor rear coupling.

The primary function of the barring gear is to rotate the rotor of the turbo generator slowly

and continuously during the start-up and shut sown process when the temperature of the

rotor changes.♣ TURBINE LUBRICATION OIL SYSTEM: - The LUB-OIL system of

turbine comprises of following category. a) MAIN OIL PUMP: - It is mounted on the front

bearing pedestal and coupled through gear coupling to the rotor. When the turbine is

running at its normal Page | 21

23.23. speed of 3000rpmthen the oil to the governing system (at 20 kg/sq.cm) and to the

lubrication system (at 1 kg/sq.cm) is supplied by this pump. b) STARTING OIL PUMP: - It

is a multi-staged centrifugal oil pump driven by A.C powered electric motor. It provides

the oil requirement for starting up and stopping of the turbine. It provides oil to the

governing system and to the lubrication system until the turbine is running at speed lower

than 2800rpm. c) STANDBY OIL PUMP: - This is a centrifugal pump driven by A.C motor.

It runs for initial10 minutes at the starting to remove air from the governing system and fill

up oil to it. d) EMERGENCY OIL PUMP: - This is a centrifugal pump driven by D.C motor.This pump is foreseen as a backup oil pump to A.C oil pumps. This pump automatically

cuts in when the A.C power fails in the power station. e) JACKING OIL PUMP: - This

pump enables the complete rotor assembly to be raised upor to be floated in the bearing

assembly during the start-up and shut down process of the process. Thus this prevents

the damage to the bearings when the shaft is too low for hydrodynamic lubrication to take

place. JOP sucks and delivers oil to the journal bearings at 120kg/sq.cm for lifting of the

rotor. f) OIL COOLERS: - The oil of governing and lubrication system is cooled in the oil

coolers by the circulating water. There are five such coolers, 4 are for continuous

operation and 1for standby. Specification of Turbine (LPT)U #1 to U #4Mega Watt :

210R.P.M. : 3000Steam Pressure : 150 Kg/cm2 (Abs)Steam Temperature : 535°CReheatSteam : 535°CMake : BHELU #5 & U #6Mega Watt : 250R.P.M. : 3000Steam Pressure :

150 Kg/cm2 (Abs)Steam Temperature : 537°CReheat Steam : 537°CMake : BHEL Page

| 22

24.24. Introduction of Water Treatment in ThermalPower PlantsIn Thermal power plants,

plenty of water is needed for generation of electricity.Now question is for what purpose

we need water here?There are two purposes:1. As a Working Fluid2. As Cooling

waterWater which is used as a working fluid needs some treatment.Reasons to choose

Water as a Working Fluid: • It is only common substance available & exists in 3 states

(Ice, water, steam)at normal temperature. • Having high specific heat mean heat carrying

capacity is high. • Having low specific volume than air. • Low Cost • High Availability •Non-reactiveBut water is universal solvent; it dissolves many gases, salts, metals etc. so

no source ofwater is pure.Water contamination depends upon source of water.There are

3 sources of water mainly;1. Surface Water2. Ground Water3. Recycled WaterImpurities

in WaterImpurities present in water are grouped into 4 categories: 1) Suspended Matter –

• Mean any matter floating or suspended nature in water • Microorganisms • Grits2)

Dissolved Salts –• Ca, Mg, K, Chlorates, Sulphates, Silicates etc.3) Dissolved Gases –•

Oxygen, Carbon di oxide, Ammonia etc. Page | 23

25.25. 4) SilicaA 210 MW unit typically requires 30,000 to 33,000 m3/h of water. A large part

of thiswater is used for condenser cooling and a small quantity is used for boiler feed

makeupand other uses.Total Water Management in Mejia Thermal Power station consistsof:1. Pre Treatment of Water2. Treatment of water for boiler feed3. Treatment of water for

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condenser cooling4. Treatment of wastewater for disposal or recovery of water for

reuse.1. Pre Treatment of Water:• Aerator: Aerators are various devices used for

aeration, or mixing air with another substance, like water. It also converts turbulent water

flow into laminar water flow.• Coagulation & Flocculation Basin: One of the first steps in a

conventional water purification process is the addition of chemicals to assist in the

removal of particles suspended in water. Particles can be inorganic such as clay and silt

or organic such as algae, bacteria, viruses, protozoa and natural organic matter.

Inorganic and organic particles contribute to the turbidity and colour of water. The

addition of inorganic coagulants such as aluminium sulphate (or alum) or iron (III) salts

such as iron(III) chloride cause several simultaneous chemical and physical interactions

on and among the particles. Within seconds, negative charges on the particles are

neutralized by inorganic coagulants. Also within seconds, metal hydroxide precipitates of

the aluminium and iron (III) ions begin to form. These precipitates combine into larger

particles under natural processes such as Brownian motion and through induced mixing

which is sometimes referred to as flocculation. The term most often used for theamorphous metal hydroxides is “floc.” Large, amorphous aluminium and iron (III)

hydroxides adsorb and enmesh particles in suspension and facilitate the removal of

particles by subsequent processes of sedimentation and filtration.• Clarifiers: Waters

exiting the flocculation basin may enter the sedimentation basin, also called a clarifier or

settling basin. It is a large tank with low water velocities, allowing floc to settle to the

bottom. The sedimentation basin is best located close to the flocculation basin so the

transit between the two processes does not permit settlement or floc break up.

Sedimentation basins may be rectangular, where water flows from end to end or circular

where flow is from the centre outward. Sedimentation basin outflow is typically over a

weir so only a thin top layer of water—that furthest from the sludge—exits.• GravitationFilter: The most common type of filter is a rapid sand filter(gravity filter). Water moves

vertically through sand which often has a layer of activated carbon or anthracite coal

above the sand. The top layer removes organic compounds, which contribute to taste and

odour. The space between sand particles is larger than the smallest suspended particles,

so simple filtration is not Page | 24

26.26. enough. Most particles pass through surface layers but are trapped in pore spaces or

adhere to sand particles. To clean the filter, water is passed quickly upward through the

filter, opposite the normal direction (called back flushing or backwashing) to remove

embedded particles.2. Treatment of water for boiler feed: Boiler feed water treatment for

high pressure boilers are almost standard. Rawwater is clarified and filtered for removalof un-dissolved impurities and demineralisedfor removal of dissolved salts. Dissolved

oxygen is removed in a thermal de-aerator.Residual dissolved oxygen is removed by

hydrazine.¬ DM Plant: A DM plant generally consists of cation, anion, and mixed bed

exchangers. Any ions in the final water from this process consist essentially of hydrogen

ions and hydroxide ions, which recombine to form pure water. Very pure DM water

becomes highly corrosive once it absorbs oxygen from the atmosphere because of its

very high affinity for oxygen. The capacity of the DM plant is dictated by the type and

quantity of salts in the raw water input. However, some storage is essential as the DM

plant may be down for maintenance. For this purpose, a storage tank is installed from

which DM water is continuously withdrawn for boiler make-up. The storage tank for DMwater is made from materials not affected by corrosive water, such as PVC. The piping



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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 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 de-aerated, with the dissolved gases being removed by a de-aerator

through an ejector attached to the condenser. Normal Water Treatm ent Page | 25

27.27. ¬ Presence of silica in boiler feed water is harmful as silica tends to volatilize along

with steam and get deposited as glassy and hard deposits on the turbine blades. It has

been established that concentrations of silica in excess of 0.03 mg/l invariably causes

problems in turbine operation. Suitable lower silica level should be maintained boiler

water to maintain silica less than 0.02 mg/l in steam leaving the drum.¬ Silica in water is

present mostly as reactive or dissolved silica. In surface waters, a small quantity of non-

reactive silica (in colloidal dimensions) may also be present during parts of the year

especially during the monsoon. A DM plant removes reactive silica almost completely, to

less than 0.005 mg/l. However, non-reactive silica is not removed and finds its way intothe boiler drum where it gets converted into reactive silica under the operating conditions

of high pressure and temperature. The station chemists usually overcome this problem by

having increased blow-downs during these periods. 3. Treatment off wastewater and its

disposal or recovery and reuse off water: Water is a scarce resource and Thermal Power

stations are today being compelled tominimise consumption of water to the extent

possible. It is possible to recover andreuse water from most of the waste streams

generated in a thermal power station. Themain waste streams are: · Gravity filter

backwash water · Wastewater generated from the DM plant · Ash pond overflows water ·

Boiler blow down and turbine drains. · Recovery of water from treated sewage Page | 26

28.28. Steam/Water Circuit of Power Plant (MTPS):A thermal power station is a power plantin which the prime mover is steam driven.Water is heated, turns into steam and spins a

steam turbine which drives an electricalgenerator. After it passes through the turbine, the

steam is condensed in a condenserand recycled to where it was heated; this is known as

a Rankin cycle.This section deals with supplying of steam generated from the boiler to

the turbines andto handle the outgoing steam from the turbine by cooling it to form water

in thecondenser so that it can be reused in the boiler plus making good any losses due

toevaporation etc.WATER PATH: -Water comes from the water reservoir to the

demineralization plant (DM Plant) forremoval of all minerals present in normal water for

making it non-conductive andincreasing the efficiency of the overall system. After DM

plant water goes to the boilerdrum via condenser and the feed control station. STEAMGENERATION PROCESS: -Water from the boiler drum comes down to the top of the

boiler and forms a ring headand finally goes to the boiler through the water walls. The

boiler/furnace is lit up by fourcorner firing technique; this produces a ball of fire and

reaches a temperature of 1200C. This as a result converts the water in the water walls

into steam at high pressure. Thissteam is sent back to the boiler drum where it is

separated from the water with the helpof high speed propeller. The steam is taken to the

super heaters via water pipes whereit is converted to superheated steam for total

moisture removal. After super-heatersthe steam divides into two ducts called Main Steam

Left (L) and Main Steam Right(R)and finally reaches the turbines. Page | 27

29.29. TURBINES are form of engine and hence it requires suitable fluid for working,asource of high grade energy and a sink of low grade energy, the fluid when flowsthrough

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the turbine the energy content of it is continuously extracted and convertedinto its useful

mechanical work. The turbines used in thermal power plants are ofSTEAM GAS type

which uses the heat energy of the steam for its working. Turbine Cycleis the most vital

part of the overall process; this is where the mechanical energy of thesteam is converted

to electrical energy via turbine assembly. The turbine assemblycomprises of three

turbines named as High Pressure Turbine (HPT), IntermediatePressure Turbine (IPT) and

the Low Pressure turbine (LPT). The steam that is generated in the SG section comes to

the HPT through mainsteam lines via control valves. The steam when strikes the HPT

have 540 C at150kg/sq.cm pressure. This high pressure superheated steam rotates the

turbine, thespeed of the turbines is controlled by the controlling the amount of steam

throughcontrol valves. Generally only 3%-4% steam is enough to rotate the turbine

at3000rpmat no load but at full load condition 100% steam is required to rotate the

turbine at3000rpm, because to produce power at 50Hz frequency the rpm required is

3000. TheHPT is a single head chamber type of turbine. Page | 28

30.30. One part of the exhaust steam from HPT is taken to re-heaters through coldreheatline (CRH line) which are again of mechanical type; for restoring the

superheatedproperties of the steam for further use. The reheated steam is brought back

to the IPTvia HRH (hot reheat steam) line. And the other part of the exhaust steam is

taken to theHP heaters (i.e. to HPH-6) The reheated steam is mechanical energy is

utilized by the IPT which is a doublehead chamber type turbine, where steam enters from

the top-mid section of theturbine and leaves the turbine from the front and back section.

The exhaust of IPT isdivided into 3 parts, one goes for the HP heaters (HPH-5), another

goes to the de-aerator and the last part goes to the LPT. The exhaust steam of the LPT Is

divided into 4 parts, 3 of them goes for the LowPressure Heaters (LPH-1, LPH-2, LPH-3)

for heating the condensate, and the last partgoes to the condenser for the steamcondensation process and regeneration of water.The condensation is done to minimize

the production of DM water to make the processcost effective. The steam is converted to

water and extracted by CEP from thecondenser and transported to Gland Sealing

Coolers (GSC) via Ejectors (EJE). The GSCcools the sealing of the ducts; the

condensate is taken to the LPH from the GSC forheating at lower pressure to increase

the enthalpy of the water for better efficiency.Water after LPH reaches the de-aerator

where the oxygen is removed from it and istaken to the BFPs, the BFPs increases the

pressure of the water up to 160kg/sq.cm andsends it the high pressure heaters (HPH-5 &

HPH-6). HPH increases the temperature ofthe water once more and transfers it to the

Economizer, in economizer the temperatureof water is again increased by the flue gasand is finally is transported to the steamgeneration process via the Feed Control

StationSOME IMPORTANT COMPONENT OF STEAM/WATER CYCLE:A fossil fuel

steam generator includes an economizer, a steam drum, and the furnacewith its steam

generating tubes and super-heater coils. Necessary safety valves arelocated at suitable

points to avoid excessive boiler pressure. De-aerator: Typically, the condensate plus the

makeup water then flows through a de-aerator that removes dissolved air from the water,

further purifying and reducing its corrosiveness. The water may be dosed following this

point with hydrazine, a chemical that removes the remaining oxygen in the water to below

5 parts per billion (ppb) Page | 29

31.31. CONDENSATE SYSTEM Courtesy SIEMENS OS220EA, C&I, MTPS, DVC Condenser: The condenser condenses the steam from the exhaust of the turbine into



14/23

liquid to allow it to be pumped. If the condenser can be made cooler, the pressure of the

exhaust steam is reduced and efficiency of the cycle increases. The surface condenser is

a shell and tube heat exchanger in which cooling water is circulated through the tubes.

The exhaust steam from the low pressure turbine enters the shell where it is cooled and

converted to condensate (water) by flowing over the tubes as shown in the adjacent

diagram. For best efficiency, the temperature in the condenser must be kept as low as

practical in order to achieve the lowest possible pressure in the condensing steam. Page |

30

32.32. Typically the cooling water causes the steam to condense at a temperature of about

35 °C (95 °F) and that creates an absolute pressure in the condenser of about 2–7 kPa

(0.59–2.1 in Hg), i.e. a vacuum of about −95 kPa (−28.1 in Hg) relative to atmospheric

pressure. The large decrease in volume that occurs when water vapour condenses to

liquid creates the low vacuum that helps pull steam through and increase the efficiency of

the turbines. The condenser generally uses either circulating cooling water from a cooling

tower to reject waste heat to the atmosphere, or once-through water from a river, lake orocean. The cooling water used to condense the steam in the condenser returns to its

source without having been changed other than having been warmed. The lower portion

of condenser where the condensed water stored known as Hotwell. Economizers: These

are heat exchange devices that heat fluids, usually water, up to but not normally beyond

the boiling point of that fluid. Economizers are so named because they can make use of

the enthalpy in fluid streams that are hot, but not hot enough to be used in a boiler,

thereby recovering more useful enthalpy and improving the boilers efficiency. They are a

device fitted to a boiler which saves energy by using the exhaust gases from the boiler to

preheat the feed. GSC: Gland steam condenser is meant for condensing the steam

which was used for sealing the LABYRINTH GLAND and reusing it in cycle. LowPressure Heater: A Heater is located between the condensate pomp and either of the

boiler feed pump. It normally extracts steam from low pressure turbine. High Pressure

Heater: A heater located downstream of boiler feed pump. Typically, the tube side design

pressure is at least 100Kg/cm2, and the steam source is the high pressure turbine. [The

heating process by means of extraction of steam is referred to as being regenerative.

Page | 31

33.33. Cooling Towers :The condensate (water) formed in the condenser after condensation

is initially at hightemperature. This hot water is passed to cooling towers. It is a tower- or

building-likedevice in which atmospheric air (the heat receiver) circulates in direct or

indirectcontact with warmer water (the heat source) and the water is thereby cooled(seeillustration). A cooling tower may serve as the heat sink in a

conventionalthermodynamic process, such as refrigeration or steam power generation,

and when itis convenient or desirable to make final heat rejection to atmospheric air.

Water, actingas the heat-transfer fluid, gives up heat to atmospheric air, and thus cooled,

isrecirculate through the system, affording economical operation of the process.With

respect to drawing air through the tower, there are three types of cooling towers:Natural

draft — Utilizes buoyancy via a tall chimney. Warm, moist air naturally rises dueto the

density differential compared tothe dry, cooler outside air. Warm moistair is less dense

than drier air at thesame pressure. This moist air buoyancyproduces an upwards current

of airthrough the tower.Induced draft — A mechanical drafttower with a fan at thedischarge (atthe top) which pulls air up through thetower. The fan induces hot moist airout



15/23


16/23

IMPORTANT AS THESE TWO FANS COMBINELYBALANCE THE PLANT. WHEN

WORKING TOGETHER IT IS CALLED BALACED DRAFT.PRIMARY AIR FAN/PA FAN:-

Primary air fan is used for mixing of cold air of FD fan outlet and hot air of air-

preheateroutlet. The main function of this is to transport the pulverized coal from the mill

to thefurnace via classifier. Mixing of hot andcold air is necessary because it is neededto

maintain the temperature of thepulverized coal from 80C-90C for bettertransport of coal⁰ ⁰

and better combustionin the furnace. Mechanically theconstruction of PA fan is same as

FD fansalong with the lube-oil system. There are3 PA fans in a single mill of ball and

tubetype.SCANNER AIR FAN / SC FAN/SA FAN:-The scanner air fans are relatively

smaller in size and consume low power as comparedto the above mentioned fans. These

are simple motor operated fans that suck air fromatmosphere and utilize it to cool the

flame scanners (explained in C&I section later)inside the furnace.AIR-PREHEATER: -The

flue gas produced as a result of combustion of fossil fuel in the furnace is taken tothe air-

preheater. The air-preheater is used to heat up the atmospheric air to make hotair used

for combustion and transport of coal dust from mill to furnace; which is calledsecondaryair. This heater has a unique process of heating, it has a shaft attached to arotating

wheel type structure (like turbine but arrangement of blades are different).Atmospheric air

sucked by FD fans passes through one side of the rotating shaft and thehot flue gas

passes through another side. This way heat of the flue gas gets transferredto the

atmospheric air and it gets heated. There are two air-preheaters named as AH-Aand AH-

B. These heaters can be found beside the boiler in the burner floor.CHIMNEY:-A chimney

is a structure which provides ventilation for hot flue gases or smoke from aboiler, stove,

furnace or fireplace to the outside atmosphere. Chimneys are typicallyvertical, or as near

as possible to vertical, to ensure that the gases flow smoothly,drawing air into the

combustion in what is known as the stack, or chimney, effect. Page | 3436.36. Electrostatic PrecipitatorsAn electrostatic precipitator (ESP) or electrostatic air

cleaner is a particulate collectiondevice that removes particles from a flowing gas (such

as air) using the force of aninduced electrostatic charge. Electrostatic precipitators are

highly efficient filtrationdevices that minimally impede the flow of gases through the

device, and can easilyremove fine particulate matter such as dust and smoke from the air

stream. In contrastto wet scrubbers which apply energy directly to the flowing fluid

medium, an ESPapplies energy only to the particulate matter being collected and

therefore is veryefficient in its consumption of energy (in the form of

electricity).PRINCIPLE OF ESP:In the electrostatic precipitator theparticles are removed

from the gasstream by utilizing electrical force .Acharged particle in the electricalfieldexperiences a force proportional tothe size of the charge and to thestrength.The

precipitation process thereforerequires.• A method of charging the particles electrically.•

A means of establishing an electrical field and• A method of removing the collected

particles. An industrial ESP includes a large number of discharge electrodes. Pirated

wires androws of collecting electrodes plates forming passage through which the gas

flows withvelocity.High voltage is applied to the discharge electrodes resulting in the high

electric fieldnear the wire and an associated corona producing gas ions .The ions collide

with andheld by, the dust particles and this in turn become electrically charged the

particlesmoved towards the grounded collecting electrode plates from which the

accumulateddust is dislodged by rapping the dust falls to the bottom of the precipitatorcasing fromwhich it is removed by different methods.PARTS OF THE



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PRECIPITATORS:The various parts of the precipitators are divided to two groups.

Mechanical systemcomprising of casing, hoppers, gas distribution system, collecting and

emitting system,rapping mechanisms, stair ways and galleries. Page | 35

37.37. Electrical system comprising of transformer-rectifier units, electronic

controllersauxiliary control panels, safety interlocks and field devices. 1. MECHANICAL

SYSTEM:A. Precipitator casing: The precipitatorcasing is an all weldedconstruction,

consistingof prefabricated wall andthe roof panels. Thecasing is provided withinspection

doors forentry into the chamber.The doors are of heavyconstruction withmachined

surfaces toensure a gas tight seal.The roof carries theprecipitator internals,insulator

housing,transformers etc. The casing rests on supports, which allow for free thermal

expansionof the casing during operation. Galleries and stairways are provided on the

sides of thecasing for easy access to rapping motors, inspection doors, transformers.B.

Hoppers: The hoppers are adequately sized to hold the ash, Baffle plates are provided

ineach hopper to avoid gas sneak age. An inspection door is provided on each

hopper.Thermostatically controlled heating elements are arranged at the bottom portionto thehopper to ensure free flow of ash. The precipitator casing is an all welded

construction,consisting of prefabricatedC. Gas distribution systems: The performance of

the precipitator depends on even distribution of gas over theentire cross section of the

field. Guide vanes, splitters and screens and screens areprovided in the inlet funnel to

direct the flue gas evenly over the entire cross section ofthe ESP.D. Collecting Electrode

System: The collecting plates are made of 1.5mm cold rolled milled steel plate and

shapedin one piece by roll forming .The collecting electrode has unique profile designed

to giverigidity and to contain the dust in a quiescent zone free from re-entrainment

.The400mm collecting plates are provided with hooks to their top edge for suspension

.Thehooks engage the slots of the supporting angles 750mm collecting plates in a rowareheld in position by a shock bar at the bottom. The shock bars are spaced by guides.

Page | 36

38.38. E. Emitting Electrode System: The most essential part of the precipitator is emitting

electrode system.4insulators support this. The frames for holding the emitting electrodes

are locatedcentrally between collecting electrode curtains. The entire discharge frames

are weldedto form rigid barsF) Rapping Systems: Rapping systems are provided for

collecting and emitting electrodes. Gearedmotors drive these rappers. The rapping

system employs tumbling hammers, which aremounted on the horizontal shaft. As the

shaft rotates slowly the hammers tumble onthe shaft will clean the entire field. The rapper

programmer decides the rappingfrequency. The tumbling hammers disposition and theperiodicity of rapping areselected in such a way that less than 2% of the collecting area is

rapped at any instant.This avoids re-entrainment of dust and puffing at the stack. The

rapping shaft from thegear motor drive by a shaft insulator. The space around the shaft

insulator iscontinuously heated to avoid condensation.G) Insulator Housing: The support

insulators, supporting the emitting electrodes housed in insulatorhousings. The HVDC

connection is taken through a bushing insulator mounted on theinsulator housing wall.In

order to avoid the condensation on the support insulators, each insulator is providedwith

one electrical heating element. Heating elements of one pass are controlled byone

thermostat.2) ELECTRICAL SYSTEM:A) High Voltage Transformer Rectifier (H.V.R) with

electronic controller (E.C)The transformer rectifiersupplies the power forparticulatecharging andcollection. The basicfunction of the E.C is tofeed precipitator withmaximum



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remove the carbon content of the gas so that it does not harm the atmosphere. This job is

done by ESP, the flue gas after air-preheater comes to the ESP unit. ESP actually works

on the principal of CORONA DISCHARGE EFFECT ; the ESP unit houses two electrode

plates called emitting plate and collecting plate. The emitting plate is supplied with a very

high DC negative potential (in order of**), this results into ionizing of air molecules

surrounding the emitting plate which is called corona effect. The collecting plate is

grounded and a positive potential develops on it, as a result when the flue gas pass

through between them the carbon particles are attracted to the collecting plates. The

collecting Inside ESP, MTPS plates are attached to hopper where the ashes get

deposited by hammering action on the collecting plate. For a 210MW unit 24 such

hoppers are present in each ESP; these hoppers have mechanical transport system for

proper disposal of ash. For better corona effect the emitting plate is made corrugated

because this way more air molecules get ionized as corona discharge points are more in

number in corrugated plate.Exciter Transformer of ESP, MTPS Page | 39

41.41. Ash Handling Plant• What is Ash? Ash is the residue remaining after the coal isincinerated.• What is Ash Handling? Ash handling refers to the method of collection,

conveying, interim storage andload out of various types of ash residue left over from solid

fuel combustion processes.• Why Ash Handling System is required? In Thermal Power

Plant’s coal is generally used as fuel and hence the ash is produced as the by-product of

Combustion. Ash generated in power plant is about 30-40% of total coal consumption

and hence the system is required to handle Ash for its proper utilization or disposal.•

CHALLENGES OF ASH HANDLING:- Indian coal presents high ash content generally

which tends to be inconsistent. Design of the system has to adequately cover anticipated

variations and be capable of handling the worst scenario. System has to be

environmentally friendly. System has to be reliable with least maintenance problem. System has to be energy efficient.• Ash terminology in power plants:- Fly Ash ( Around

80% is the value of fly ash generated) Bottom ash (Bottom ash is 20% of the ash

generated in coal based power stations.)• What is fly ash? Ash generated in the ESP

which got carried out with the flue gas is generally called Fly ash. It also consists of Air

pre heater ash & Economiser ash (it is about 2 % of the total ash content).• What is

bottom ash? Ash generated below furnace of the steam generator is called the bottom

ash. Page | 40

42.42. Volume of ash and propertiesThe ash handling system handles the ash by bottom

ash handling system, coarse ashhandling system, fly ash handling system, ash disposal

system up to the ash disposalarea and water recovery system from ash pond and Bottomash overflow. Description isas follows:A. Bottom Ash Handling SystemBottom ash

resulting from the combustion of coal in the boiler shall fall into the overground, refractory

lined, water impounded, maintained level, double V-Section type/ Wtype steel- fabricated

bottom ash hopper having a hold up volume to store bottom ashand economizer ash of

maximum allowable condition with the rate specified. The slurryformed shall be

transported to slurry sump through pipes.C. Air Pre Heater ash handling systemAsh

generated from APH hoppers shall be evacuated once in a shift by vacuumconveying

system connected with the ESP hopper vacuum conveying system.D. Fly Ash Handling

SystemFly ash is considered to be collected in ESP Hoppers. Fly ashes from ESP

hoppers,extracted by Vacuum Pumps, fly up to Intermediate Surge Hopper cum BagFilter forfurther Dry Conveying to fly ash silo.Under each surge hopper ash vessels shall



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be connected with Oil free screw compressorfor conveying the fly ash from Intermediate

Surge Hopper to silo. Total fly ashgenerated from each unit will be conveyed through

streams operating simultaneouslyand in parallel.E. Ash Slurry Disposal SystemBottom

Ash slurry, Fly ash slurry and the Coarse Ash slurry shall be pumped from thecommon

ash slurry sump up to the dyke area which is located at a distance from Slurrypump

house.• ADVANTAGES:- i) Commercial utilization of ash in: iii)Energy Efficient –Cement

additives. iv)High reliability –Brick plants. v)Long Plant Life –Road making, etc. vi)Least

maintenance ii) Saving of water - vii)Environment concern a precious commodity. Page |

41

43.43. ELECTRICAL SYSTEM OVERVIEWELECTRICAL SYSTEM OF A THERMAL

POWER PLANT BASICALLY CONSISTS OF THEFOLLOWING PARTS:- GENERATOR

SWITCHYARD POWER DISTRIDUTION SYSTEM GENERATOR The transformation

of mechanical energy into electrical energy is carried out by generator. The A.C generator

or alternator is based on the principal of electromagnetic induction and generally consists

of a stationary part called stator and a rotating part called rotor. The stator houses thearmature windings and the rotor houses the field windings. A D.C voltage is applied to the

field winding in the rotor through slip rings, when the rotor is rotated, the lines of magnetic

flux is cut through the stator windings. This as a result produces an induced e.m.f

(electromotive force) in the stator winding which is tapped out as output. The magnitude

of this output is determined by the following equation:- E = 4.44/O f N voltsWhere E =

e.m.f. induced; O =Strength of magnetic field in Weber; f= Frequency in cycles per

second or in hertz; N = Number of turns in the winding of the stator;Again, f = P

n/120;Where P = Number of poles; n = revolutions per second of the rotor.From the

above expression it is clear that for the same frequency number of polesincreases with

decrease in speed and vice versa. Therefore low speed hydro turbinedrives generatorshave 14to 20poles where as for high speed steam turbine drivengenerators have 2

poles.Generator Components Rotor: Rotor is the most difficult part to construct; it

revolves at a speed of 3000rpm. The massive non-uniform shaft subjected to a

multiplicity of differential stresses must operate in oil lubricated sleeve bearings

supported by a structure mounted on foundations all of which poses complex dynamic

behaviour peculiar to them. It is also an electromagnet and to give it the necessary

magnetic strength the Page | 42

44.44. windings must carry a fairly high current. The rotor is a cast steel ingot and it is further

forged and machined. Very often a hole bored through the centre of the rotor axially from

one end to the other for inspection. Slots are then machined for windings andventilation.Rotor winding: Silver bearing copper is used for the winding with mica as

insulationbetween conductors. A mechanically strong insulator such as micanite is used

for liningthe slots. For cooling purpose slots and holes are provided for circulation of

cooling gas.The wedges the windings when the centrifugal force developed due to high

speedrotation tries to lift the windings. The two ends of the winding are connected to

sliprings made of forged steel and mounted on insulated sleeves.Stator: The major part of

the stator frame is the stator core, it comprises of innerand outer frame. The stator core is

built up of a large number of punching or section ofthin steel plates. The use of cold

rolled grain-oriented steel can contribute to reductionof stator core.Stator windings: Each

stator conductor must be capable of carrying the ratedcurrent without overheating. Theinsulation must be sufficient to prevent leakagecurrent flowing between the phases to



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earth. Windings for the stator are made up fromcopper strips wound with insulated tape

switch is impregnated with varnish, driedunder vacuum and hot pressed to form a solid

insulation bar. In 210MW generators thewindings are made up of copper tubes through

which water is circulated for coolingpurpose.Generator Cooling and Sealing System1)

HYDROGEN COOLING SYSTEM: Hydrogen is used as cooling medium in large capacity

generators in view of its high heat carrying capacity and low density. But in view of its

explosive mixture with oxygen, proper arrangement for filling, purging and maintaining its

purity inside the generator have to be made. Also in order to prevent escape of hydrogen

from the generator casing, shaft sealing system is used to provide oil sealing. The system

is capable of performing the following functions:-a) Filling in and purging of hydrogen

safely.b) Maintaining the gas pressure inside the machine at the desired value all the

time.c) Provide indication of pressure, temperature and purity of hydrogen.d) Indication of

liquid level inside the generator.2) Generator Sealing System: Seals are employed to

prevent leakage ofhydrogen from the stator at the point of rotor exit. A continuous film

between the Page | 4345.45. rotor collar and the seal liner is maintained by means of oil at the pressure which

isabout above the casing hydrogen gas pressure. The thrust pad is held against the

collarof rotor by means of thrust oil pressure, which is regulated in relation to the

hydrogenpressure and provides the positive maintenance of the oil film thickness. The

shaftsealing system contains the following components.a) A.C oil pump.b) D.C oil

pump.c) Oil injector.d) Differential Pressure Regulatore) Damper tank.Excitation System1)

STATIC EXCITATION:• Alternator terminal voltage is used here.• SCR- based controlled

rectifier is supplied is supplied from alternator output through step down transformer.•

SCR gate signal are derived from alternator output through CT & PT.• Rectifier output

voltage is fed to the alternator field winding.• To generate the alternator output, it is runat rated speed with its field supplied from a separate D.C supply bank.• This scheme is

less expensive & requires little maintenance.• Excitation energy depends on alternator

speed.2) BRUSHLESS EXCITATION:• Main shaft of prime movers drives pilot exciter,

main exciter & the main alternator.• Pilot exciter is a permanent magnet alternator.• Pilot

exciter feeds 3-phase power to main exciter.• Main exciter supplies A.C power to silicon

diode bridge rectifier through hollow shaft which feeds the D.C to the field of main

alternator.• SCR gate signals are derived from alternator out

dvc mejia report

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