A REPORT OF THE VOCATIONALTRAINING

atMEJIA THERMAL POWER STATION

P.O. MEJIA, DIST. BANKURAWEST BENGAL-722183

OFDAMODAR VALLEY CORPORATION

(D.V.C.)

ACKNOWLEDGEMENT

The dissertation has been prepared based on the vocational trainingundergone in a highly esteemed organisation of Eastern region, a pioneer inGeneration Transmission & Distribution of power, one of the most technicallyadvanced & largest thermal power stations in India , the Mejia ThermalPower Station (M.T.P.S), under DVC.I would like to express my heartfelt gratitude to the authorities of MejiaThermal Power Station for providing us such anopportunity to undergo training in the thermal power plant of DVC, MTPS.I would also like to thank the Engineers, highly experienced without whomsuch type of concept building in respect of thermal power plant would nothave been possible. Some of them are:1) Mr. Parimal Kumar Dubey2) G Nandesu

INTRODUCTION

Damodar Valley Corporation was established on 7th July 1948.It is the most reputed company in the eastern zone of India. DVC in established on the Damodar River. It alsoconsists of the Durgapur Thermal Power Plant in Durgapur. The MTPS under the DVC is the second largest thermal plant in West Bengal. Mejia Thermal Power Station also known as MTPS is located in the outskirts of Raniganj in Bankura District. It is one of the 5 Thermal Power Stations of Damodar Valley Corporation in the state of West Bengal. The total power plant campus area is surrounded by boundary walls and is basically divided into two major parts, first the Power Plant area itself and the second is the Colony area for the residence and other facilities for MTPSs; employees.

TECHNICAL SPECIFICATION OF MTPS

• INSTALLED CAPACITY: -• 1) Total number of Units : - 4 X 210 MW(unit 1 to 4) with Brush Type

Generators, 2 X 250• MW(unit 5 and 6) with Brush less Type Generators, 2*500 MW(unit 7 and

8) Generators.• 2) Total Energy Generation: - 2340 MW• 3) Source of Water: - Damodar River• 4) Sources of Coal: - B.C.C.L and E.C.L, also imported from Indonesia

In a Thermal Power generating unit, combustion of fossil fuel (coal, oil natural gas) in Boiler generates heat energy. This heat energy transforms water stea at high pressure and temperature. This steam is utilised to generate mechanical energy in a Turbine. This mechanical energy, in turn is converted into electrical energy with thehelp of an Alternator coupled with the Turbine. The production of electric energy utilising heat energy is known as thermal power generation.

The heat energy changes into mechanical energy following the principle of Rankine reheat-regenerative cycle and this mechanical energy transforms into electrical energy based on Faraday’s laws of electromagnetic induction.

OVERVIEW OF A THERMAL POWER PLANT

1. Cooling tower. 2. Cooling water pump. 3. Transmission line (3-phase). 4. Unit transformer (3-phase). 5. Electric generator (3-phase). 6. Low pressure turbine. 7. Condensate extraction pump.8. Condenser. 9. Intermediate pressure turbine. 10. Steam governor valve. 11. High pressureturbine. 12. De-aerator. 13. Feed heater. 14. Coal conveyor. 15. Coal hopper. 16. Pulverised fuelmill. 17. Boiler drums. 18. Ash hopper. 19. Super heater. 20. Forced draught fan. 21. Re-heater.22. Air intake. 23. Economiser. 24. Air pre heater. 25. Precipitator. 26. Induced draught fan. 27.Chimney Stack.

MECHANICAL OPERATION

COAL HANDLING PLANT

Generally most of the thermal power plants uses low grades bituminous coal. Theconveyer belt system transports the coal from the coal storage area to the coal mill. Now the FHP(Fuel Handling Plant) department is responsible for converting the coal converting it into fine granular dust by grinding process. The coal from the coal bunkers.Coal is the principal energy source because of its large deposits and availability. Coal can be recovered from different mining techniques like:-

• shallow seams by removing the over burnt expose the coal seam

• underground mining.

The coal handling plant is used to store, transport and distribute coal which comesfrom the mine. The coal is delivered either through a conveyor belt system or by railor road transport. The bulk storage of coal at the power station is important for thecontinues supply of fuel. Usually the stockpiles are divided into three maincategories.• live storage• emergency storage• long term compacted stockpile.The figure below shows the schematic representation of the coal handling plant.Firstly the coal gets deposited into the track hopper from the wagon and then via thepaddle feeder it goes to the conveyer belt#1A. Secondly via the transfer port the coalgoes to another conveyer belt#2B and then to the crusher house. The coal after beingcrushed goes to the stacker via the conveyer belt#3 for being stacked or reclaimedand finally to the desired unit. ILMS is the inline magnetic separator where all themagnetic particles associated with coal get separated.

COAL HANDLING PLANT PROCEDURE

WATER TREATMENT PLANTRaw water supply:Raw water received at the thermal power plant is passed through Water Treatment Plantto separate suspended impurities and dissolved gases including organic substance and

then through De-mineralised Plant to separate soluble impurities.Deaeration:In this process, the raw water is sprayed over cascade aerator in which water flowsdownwards over many steps in the form of thin waterfalls. Cascading increases surface

area water to facilitate easy separation of dissolved undesirable gases (like hydrogen sulphide, ammonia, volatile organic compound etc.) or to help in oxygenation of mainly ferrous ions in presence of atmospheri oxygen to ferric ions.

Coagulation:Coagulation takes place in clariflocculator. Coagulant destabilises suspendedsolids and agglomerates them into heavier floc, which is separated out throughsedimentation. Prime chemicals used for coagulation are alum, poly-aluminium chloride(PAC).Filtration:Filters remove coarse suspended matter and remaining floc or sludge aftercoagulation and also reduce the chlorine demand of the water.

Chlorination:Neutral organic matter is very heterogeneous i.e. it contains many classes of highmolecular weight organic compounds. Humic substances constitute a major portion ofthe dissolved organic carbon from surface waters. They are complex mixtures of organic compounds with relatively unknown structures and chemical composition

DM (Demineralised Water) PlantIn De-mineralised Plant, the filter water of Water Treatment Plant is passedthrough the pressure sand filter (PSF) to reduce turbidity and then throughactivated charcoal filter (ACF) to adsorb the residual chlorine and iron in filter water

BOILER SYSTEMWorking principle of Boiler (Steam Generator): In Boiler, steam is generated from

demineralized water by the addition of heat. The heat added has two parts: sensible heat and latent heat. The sensible heat raises the temperature and pressure of water as well as steam. The latent heat converts water into steam (phase change). This conversion is also known as boiling of water, which is dependent on pressure and corresponding temperature. Thermodynamically, boiling is a process of heat addition to water at constant pressure & temperature. The quantity of latent heat decreases with increase in pressure of water and it becomes zero at 221.06 bars. This pressure is termed as critical pressure. The steam generators are designated as sub-critical or super critical based on its working pressure as below critical or above critical pressure. The steam, thus formed is dry & saturated. Further, addition of heat raises the temperature and pressure of steam, which is known as superheated steam. The differential specific weight between steam and water provides the driving force for natural circulation during the steam generation process. This driving force considerably reduces at pressure around 175 Kg/cm2 and is not able to overcome the frictional resistance of its flow path. For this, forced or assisted circulation is employed at higher sub-critical pressure range due to the reason of economy. But, at supercritical pressures and above, circulation is forced one (such boiler is called once through boiler).

Important parts of Boiler & their functions:

Economizer: Feed water enters into the boiler through economizer. Its function is to recover residual heat of flue gas before leaving boiler to preheat feed water prior to its

entryinto boiler drum The drum water is passed through down-comers for Circulation through the water wall for absorbing heat from furnace. The economizerrecirculation line connects down-comer with the economizer inlet header through an isolating valve and a non-return valve to protect economizer tubes from overheating caused by steam entrapment and starvation. This is done to ensure circulation of water through the tubes during initial lighting up of boiler, when there is no feed water flow through economizer.

Drum:Boiler drum is located outside the furnace region or flue gas path. This stores certain

amount of water and separates steam from steam-water mixture. The minimum drum water level is always maintained so as to prevent formation of vortex and to protect water wall tubes (especially its corner tubes) from steam entrapment / starvation due to higher circulation ratio of boiler.

Superheater: Superheaters (SH) are meant for elevating the steam temperature above the saturation

temperature in phases; so that maximum work can be extracted from high energy (enthalpy) steam and after expansion in Turbine, the dryness fraction does not reach below 80%, for avoiding Turbine blade erosion/damage and attaining maximum Turbine internal efficiency. Steam from Boiler Drum passes through primary superheater placed in the convective zone of the furnace, then through platen superheater placed in the radiant zone of furnace and thereafter, through final superheater placed in the convective zone. The superheated steam at requisite pressure and temperature is taken out of boiler to rotate turbo-generator

Reheater: In order to improve the cycle efficiency, HP turbine exhaust steam is taken back to

boiler to increase temperature by reheating process. The steam is passed through Reheater, placed in between final superheater bank of tubes & platen SH and finally taken out of boiler to extract work out of it in the IP and LP turbine.

De-superheater (Attemperator): Though superheaters are designed to maintain requisite steam temperature, it is necessary

to use de-superheater to control steam temperature. Feed water, generally taken before feed water control station, is used for de-superheating steam to control its temperature at desired level.

Technical data of the Boiler

ASH HANDLING PLANTA large quantity of ash is, produced in steam power plants using coal.Ash produced in about 10 to 20% of the total coal burnt in the furnace. Handling ofash is a problem because ash coming out of the furnace is too hot, it is dusty andirritating to handle and is accompanied by some poisonous gases. It is desirable toquench the ash before handling due to following reasons:1. Quenching reduces the temperature of ash.2. It reduces the corrosive action of ash.3. Ash forms clinkers by fusing in large lumps and by quenching clinkers willdisintegrate.4. Quenching reduces the dust accompanying the ash.Fly ash is collected with an electrostatic precipitator(ESP)

ELECTROSTAIC PRECIPITATOR

The principal components of an ESP are 2 sets of electrodes insulated from each other. First set of rows are electrically grounded vertical plates called collecting electrodes while the second set consists of wires called discharge electrodes. the negatively charged fly ash particles are driven towards the collecting plate and the positive ions travel to the negatively charged wire electrodes. Collected particulate matter is removed from the collecting plates by a mechanical hammer scrapping system.

BOILER AUXILIARIES

Induced draft fan (ID fan): Induced draft represents the system where air or products of combustion are driven out after combustion at boiler furnace by maintaining them at a progressively increasing sub atmospheric pressure. This is achieved with the help of induced draft fan and stack. Induced draft fan is forward curved centrifugal (radial) fan and sucks the fly-ash laden gas of temperature around 125°C out of the furnace to throw it into stack (chimney). The fan is connected with driving motor through hydro-coupling or with variable frequency drive (VFD) motor to keep desired fan speed.

Forced draft fan (FD fan):

Forced draft represents flow of air or products of combustion at a pressure above atmosphere. The air for combustion is carried under forced draft conditions and the fan used for this purpose is called Forced Draft (FD) fan. It is axial type fan and is used to take air from atmosphere at ambient temperature to supply air for combustion, which takes entry to boiler through wind box. In all units except Durgapur TPS Unit #4, this fan also supplies hot /cold air to the coal mills.

Primary air fan (PA fan) or Exhauster fan:

Coal mill or pulveriser:Most efficient way of utilizing coal for steam generation is to burn it in pulverisedform. The coal is pulverized in coal mill or pulveriser to fineness such that 70-80%passes through a 200 mesh sieve. The factors that affect the operation of the mill orreduce the mill output are:• Grindability of coal: Harder coal (i.e. coal having lower hard-grove index (H.G.I.))• reduces mill output and vice versa.• Moisture content of coal: More the moisture content in coal, lesser will be the• mill output & vice versa.• Fineness of output: Higher fineness of coal output reduces mill capacity• Size of coal input: Larger size of raw coal fed to the mill reduces mill output.• Wear of grinding elements: More wear and tear of grinding elements reduces

the• output from mill.• Size of coal input: Larger size of raw coal fed to the mill reduces mill output.• Wear of grinding elements: More wear and tear of grinding elements reduces

the• output from mill.

STEAM TURBINE

A steam turbine is a prime mover which continuously converts the energy of highpressure, high temperature steam supplied by the boiler into shaft work with lowpressure, low temperature steam exhausted to a condenser.

Cooling towerCooling towers cool the warm water discharged from the condenser and feed the

cooled water backto the condenser. They thus reduce the cooling water demand in the power plants. Wet coolingtowers could be mechanically draught or natural draught. In M.T.P.S the cooling towers are I.D.type for units 1-6 and natural draught for units 7&8.

CHIMNEYA chimney may be considered as a cylindrical hollow tower made of bricks or steel. In MTPS the chimneys of eight units are made of bricks. Chimneys are used to release the exhaust gases(coming from the furnace of the boiler)high up in the atmosphere. So, the height of the chimneys are made high.19

CONCLUSIONThe practical experience that I have gathered during the overview training oflarge thermal power plant having a large capacity of 2340 MW for Unit# I toVIII in three weeks will be very useful as a stepping stone in building brightprofessional career in future life. It gave me large spectrum to utilize thetheoretical knowledge and to put it into practice. The trouble shootingactivities in operation and decision making in case of crisis made me moreconfident to work in the industrial atmosphere.Moreover, this overview training has also given a self realization & hands-onexperience in developing the personality, interpersonal relationship with theprofessional executives, staffs and to develop the leadership ability in industrydealing with workers of all categories.I would like to thank everybody who has been a part of this project, withoutwhom this project would never be completed with such ease.