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BADARPUR THERMAL POWER STATIONBadarpur, New Delhi-110044

SUMMER TRAINING REPORTTO STUDY VARIOUS OPERATIONS OF THERMAL POWER PLANT

SUBMITTED BY:PULKIT KHANDURI12109059( Me 7 th semester) NIT JalandharNATIONAL THERMAL POWER PLANTPREFACEI feel honored while presenting this report of my work in BADARPUR THERMAL POWER PLANT for the period of 6 weeks Industrial training. This report has all the details about this power plant and our training experiences. This report contains all the details of various sections of power plant and work performance.

I have tried to keep report as simple as possible and illustrative not leaving any information. We also took the help of NTPC resources.PULKIT KHANDURIACKNOWLEDGEMENTIn this era of global energy we need a great balance between theoretical and practical knowledge. In this respect the vocational training is a great boon for the engineering aspirants. It gives us a great chance to come in line with the actual problems going on in the industries and getting a chance to work with the engineers and learn how to tackle every situation.

I am thankful to the staff of the BTPS for their time and effort and their willingness in shearing there valuable experiences. I would like to my sincere thanks to Mr. Man Mohan Sing for giving me opportunity to learn with this esteemed organization. I would like express my deep sense of gratitude to the operators and technician of thermal power plant (BMD, PAM, & TMD) department for their guidance, continuous encouragement and valuable suggestion.PULKIT KHANDURITable of contentsDescripation

Introduction

Coal to electricity

Principle of combustion

Boiler drum

Air preheater

Basic of fans

Draft system

Pulverizer

Boiler fitting and mountings

Coal feeder

Water circulation system

Ash handling plant

Water treatment plant

Introduction Turbine and classificationNTPC LTD.The year 1975 witnessed the birth of an organization that went on to achieve great feats in performances in sector that was until then, characterized largely by lack of investment, severe supply shortages and operational practices that made the commercial viability of the sector unsustainable. NTPC symbolized hope of the country suffering from crippling power black ours the Government of India, which was trying to put an ailing economy back on tract and the world bank, which was supporting the country in many development initiatives. Thus, NTPC was created not only to redraw the power map of India but also excel in its performance and set benchmarks for others to follow. It succeeded on both counts.

Today with an installed capacity of 43,019 MW, NTPC contributes one fourth of the nationals Power generation, with only one fifth of Indias total installed capacity. An ISO 9001:2000 Certified company, it is worlds 10th largest power generation in the world, 3rd largest in Asia. NTPC is first independent Power Producer in the world. Also it is 337th largest company in the world

It is one of the largest Indian companies in terms of market cap. The corporation recorded a generation of 233.28 billion units in 2012-2013; through 17 coals based, 7gas based power plants, 7 solar based plant spread all over the country and also has 7 plant in joint venture rated as of the sixth best companies to work for in India it has developed into a multi location and multi fuel company over the past three decades.PLANTS DETAILS

The main plant equipment of these units was supplied by M/S. BHEL. The boiler of stage-1 (3X100MW) units is of CZECHOSOLOVAKIAN design and that of 210 MW units are of COMBUSTION ENGINEERING design. The Turbo alternators, supplied by M/S BHEL, are of RUSSIAN deign and Control & Instrumentation foe Stage-1 (3X95MW ) and Stage ll units are mostly of Russian design and for Stage-lll are of KENT design and supplied by M/S instrumentation Ltd., Kota.

Power is evacuated from BTPS by 10 circuits of 220KV network of Delhi through northern grid. The coal supply is through Railways from the linked mines of Bharat Coking Coal Ltd. (BCCL ) and Central Coalfields Ltd. (CCL ) situated in Jharkhand. Water for cooling requirement is receiving from Agra Irrigation Canal. The station is provided with cooling tower to operate on closed cycle period during the monsoon period. The plant became operational on 26th July, 1973.

The transfer of Badarpur Thermal power station built by the central electricity Authority, for management by NTPC on April 1 1978 for the next ten years was an important landmark in the history of the company. Badarpur threw up numerous challenges and opportunities. Though the performance asCOAL TO ELECTRICITYTRANSFORMATION OF ENERGY COALBOILERSTEAM TURBINEDIFFERENT LOADSGENERATORCHPORCOAL CYCLEFROM JHARIA MINES RAILWAY WAGON BTPS WAGON TRIPPERMAGNETIC SEPARATOR CRUSHER HOUSECOAL STOCK YARD RC BUNKERRC FEEDER BOWL MILL FURNACEBASIC POWER PLANT CYCLE

The thermal (steam) power plant uses a dual (vapor + liquid) phase cycle. It is a closed cycle to enable the working fluid (water) to be used again and again. The cycle used is "Rankin Cycle" modified to include superheating of steam, regenerative feed water heating and reheating of steam.On large turbines, it becomes economical 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 the remaining 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.

Coal to Steam

Coal from the coal wagons is unloaded in the coal handling plant. This Coal is transported up to the raw coal bunkers with the help of belt conveyors. Coal is transported to Bowl Mills by Coal feeders the coal is pulverized in the Bowl Mill, where it is ground to a powder form. The mill consists of a round metallic table on which coal particles fall. This table is rotated with the help of a motor. There are three large steel rollers which are spaced 120" apart. When there is no coal, these rollers does not rotate but when the coal is fed to the table it packs up between roller and the table and this forces the rollers torotate. Coal is crushed by the crushing action between the rollers and rotating table. This crushed coal is taken away to the furnace through coal pipes with the help of hot and cold air mixture from P.A. Fan.Water from the boiler feed pump passes through economizer and reaches the boiler drum. Water from the drum passes through down comers and goes to bottom ringleader. Water from the bottom ring header is divided to althea four sides of the furnace. Due to heat and- the density difference the water rises up in the water wall tubes. "Waterish partly converted to steam 'as it rises up in the furnace. This steam and water mixture is again taken to the boiler drum where the steam is separated from water. Water follows the same path while the steam is sent to super heaters for superheating. The super heaters are located inside the furnace and the steam is superheated (540"C) and finally it goes to turbine.

Steam to mechanical Power

From the boiler, a steam pipe conveys steam to the turbine through a stop valve (which can be used to. shut off steam in an emergency) and through control valves that automatically regulate the supply of steam to the turbine where it passes through a ring of stationary blades fixed tithe cylinder wall. These act as nozzles and direct the steam into a second ring of moving blades mounted on a disc which rotates the blades and its passage of some heat energy is changed into mechanical energy.The turbine shaft usually rotates at 3,000revolutions per minute. This speed is determined by the frequency of the electrical system used in this country and is the speed at which a 2- pole generator must be driven to generate alternating current at a frequency of 50 cycles per second.

BOILER MANTENANCE DEPARTMENTSpecificationsMain boilerEvaporationFeed water temperatureFeed water leaving economizerat 100% load 700t/hr 247C276CSTEAM TEMPERATURE:DrumSuper heater outletReheat inletReheat outlet341C540C332C540CSTEAM PRESSURE:Drum designDrum operatingSuper heater outletReheat inletReheat outlet158.20 kg/cm2149.70 kg/cm2137.00 kg/cm226.35 kg/cm224.50 kg/cm2FUEL: COALFixed carbonVolatile matterMoistureGrind abilityDESIGN 38%26%8%50% HardgraveWORST 25%25%9%45% HardgraveOIL:Calorific value of fuel oilSulphur contentMoisture contentFlash point10,000 kcal/kg4.5% W/W1.1% W/W66Feed water cycleCONDENSATE CYCLEDEAERATORFROM LOW PRESSURE TURBINEBOILER FEED PUMPCONDENSERH P HEATER-1HOT WELLH P HEATER-2CONDENATE PUMPH P HEATER-3EJECTORFEED WATER LINELPH1ECONOMISERGLAND STEAM COOLERBOILER DRUMGSC2DEAERATORDOWN COMERSLPH2UPRISERSLPH3BOILER DRUMLHP4Principles of CombustionThe primary function of oil and coal burning systems the process of steam generation is to provide controlled efficient conversation 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 sculpture. 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. When carbon 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 are usually 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 breach is increased by preheating the combustion air. The temperature of the flame of the burning fuel may vary with the 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 onDesign of the boiler.Fuel used.Skill in obtaining combustion with the minimum amount of excess air

INTRODUCTION of furnaceFurnace 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.

TYPES OF FURNACE

P.F. FIRED DRY BOTTOM FURNACE:The tall rectangular radiant type furnace has now become feature of modern dry bottom P.F. boiler. Indorsed height not only facilitates adequate natural circulation but also aids reduction of furnace exitgas temperature and hence less soot deposit insuperheaters 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 to make 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 heat loading with P.F. will cause slogging and high furnace exit gas temperature.BOILER DRUM

Drum is of fusion-welded design with welded hemi-spherical dished ends. It is provided with stubs for welding all the connecting tubes i.e. down comers, 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.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 rundown 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

Reheated 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 requires additional equipment I.e. Heating surface 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 tube.SUPER HEATER

Whatever type of boiler is used, steam will leave the water at its surface and pass into the steam space.Steam formed above the water surface in a shell boiler is always saturated and cannot become superheated in the boiler shell, as it inconstantly in contact with the water surface.

If superheated steam is required, the saturated steam must pass through a superheated. This is simply a heat exchanger where additional heat is added to the saturated steam.

N water-tube boilers, the superheated may be an additional pendant suspended in the furnace area where the hot gases will provide the degree of superheat required (see Figure3.4.4). In other cases, for example in CHP schemes where the gas turbine exhaust gases are relatively cool, a separately firedsuperheater may be needed to provide the additional heat.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 advice installed after the superheated, 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.

ECONOMISERLOCATION AND MAINTENACE

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 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 the banks of tubes are provided for inspection and maintenance works.AIR PREHEATER

Air preheated absorbs waste heat from the flue gases and transfers this heat to incoming cold air, by means of continuously rotating heat transfer element of specially formed metal plates. Thousands of these high efficiency elements are spaced and compactly arranged within 12 sections. Sloped compartments of a radically 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 platesHousingRotorHeating surface elementsBearingsSector plates and Sealing arrangement

SPECIFICATIONS227-VI-(T)-74 casinge a c hNumber of air preheated per unitHeater sizeA p p r o xh e a t i n gs u r f a c eRotor drive motor 15 H.PS p e e d r e d u c t i o n r a t i oA p p r o xo i lc a p a c i t yS o l e n o i d V a l u e1 9 0 0 0m 2

1 1 0 : 11 3G a l l o n s 1 1 0 V , A . CB A S I C S O F F A N S

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 escapable 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 volumes. 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 Fans

In boiler practice, we meet the following types of fans.

Axial fans

Centrifugal (Radial) fans

In this type the movement of air or gas is parallel to its exit of rotation. These fans are better suited to low resistance applications.

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.AXIAL FANThere 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.the atmospheric pressure and theThe terms draft denotes the difference between pressure existing in the furnace.Depending upon the draft used, we have

Natural DraftInduced DraftForced DraftBalanced Draft SystemNATURAL DRAFT

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 DRAFTIn this system the air is admitted to natural pressure difference and the flue gasesare taken out by meansof induced Draft fans and the under vacuum.furnaceismaintained FORCED DRAFTA set of forced draft fans are made use of for supplying 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.

BALANCED DRAFTin maintaininga vacuuming theHere a set of Induced and Forced Draft Fans are utilized furnace. Normally all the power stations utilize this draft system.INDUSTRAIL FANThe induced Draft Fans are generally of Axial -Impulse Type. Impeller nominal diameter is of the order of 2500 mm.The fan consists of the following sub-assembliesSuction ChamberInlet Vane ControlImpellerOutlet Guide Vane Assembly

The outlet guides are fixed in between thec a e o f t h e d i f f u s e r a n d t h e c a s i n g . T h e s e g u i d e v a n e s s e r v e t o direct the flow axially and to stabilize the draft-flow caused in the i m p e l l e r . T h e s e o u t l e t b l a d e s a r e r e m o v a b l e t y p e f r o m o u t s i d e . 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.

FD FANI D F a n ,c o n s i s t so f t h e followingT h e f a n , n o r m a l l y o f t h e s a m e t y p e a s components:

Silencer

Inlet bend

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 an inclined 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 FAN

P.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 amount of 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.

PULVERIZERA pulverize 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.

.Types of Pulverizes

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, another 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 MillThis 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 Millis determined by a classifier separator.

MPS MillSimilar to the Ring and Ball Mill, this mill uses large "tires" to crush the coal. These are usually found in utility plants.

Bowl MillSimilar 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 coalEfficient utilization of cheap and low grade coalFlexibility to meet fluctuating loadElevation of bending loserBOILER 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 (PSV) or Pressure Relief Valves (PRV). The other parts of the set are named relief valves, safety relief valves, pilot-operated safety relief valves, low pressure safety valves, vacuum pressure safety valves.

FUNCTION AND DESIGNBOILER STOP VALVESA 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 varietyThe 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 water hammer, and to help restrict the fall in boiler pressure and any possible associated priming.

FEED WATER CHECK VALVES

The feed water check valve is installed in the boiler feed water line between the feed pump and boiler. A boiler feed stop valve is fitted at the boiler shell.Boiler check valveThe check valve includes a spring equivalent to the head of water in the elevated feed tank when there is no pressure in the boiler. This prevents the boiler being flooded by the static head from the boiler feed tank.

PRESSURE GAUGE

All boilers must be fitted with at least one pressure indicator. The usual type is a simple pressure gauge constructed to BS 1780 Part 2 - Class One. The dial should be at least 150 mm in diameter and of the Bourdon tube type, it should be marked to indicate the normal working pressure and the maximum permissible working pressure / design pressure.

Pressure gauges are connected to the steam space of the boiler and usually have a ring type siphon tube which fills with condensed steam and protects the dial mechanism from high temperatures

Pressure gauges may be fitted to other pressure containers such as blow down vessels, and will usually have smaller dials as shown in FigureGAUGE GLASSES AND FITTINGS

All steam boilers are fitted with at least one water level indicator, but those with a rating of 100 kW or more should be fitted with two indicators. The indicators are usually referred to as gauge glasses complying with BS 3463.GAUGE GLASS GUARDS

The gauge glass guard should be kept clean. When the guard is being cleaned in place, or removed for 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 has been 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 are located 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.

Mills

There 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 precipitatorThese 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 case

************************************************************WATER CIRCULATION SYSTEM

Theory of circulation

Water must flow through the heat absorption surface of the boiler in order that it is 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 comer sat a temperature slightly below the saturation temperature. The flow through the furnace wall is at saturation temperature. Heat absorbed in water wall is latent heat of vaporization creating admixture of steam and water. The ratio of the weight of the water tithe weight of the steam in the mixture leaving the heat absorption surface is calledTypes of boiler circulating system:

Natural circulation systemControlled circulation systemCombines circulation systemNatural 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 is heated 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 the economizer and the cycle is repeated.

The circulation in this case takes place on the thermo-siphon principle. The down 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.

As the pressure increases, the difference in density between water and steam reduces. Thus the hydrostatic head available will not be able to overcome the frictional resistance for a flow corresponding to the minimum requirement of cooling of water wall tubes. Therefore natural circulation is limited to the boiler with drum operating pressure around 175 kg/cm.Controlled circulation system

Beyond 80 kg/cm of pressure, circulation is 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).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 recalculate 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.BOTTOM ASH SYSTEM

In the bottom ash system the ash discharged 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 is 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.The flushing apparatus are provided under E.P. hoppers (40 Nos), economizer hoppers (4 Nos), air repeaters (2 Nos), and stack hoppers (4 Nos), 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 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 systemic sluiced up to ash pump along the channel with the acidathigh pressure water jets suitableintervals alongof locatedthe channel.Slurry pump suction line consisting of reducing elbow with drain valve, reducer and butterfly valve and portion of slurry pump delivery 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-(in case of fire breakdown)

TWS pump-3(for screening of water)

CRW pump-3(supply water for water treatment)

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 3pumpsremains open.similarly, 1 FS, 2 LP, 4 HP, 1 TWS pumps remain open. 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 types and methods of water treatment. Water treatment plants used in thermal power plants are designed to process the raw water to water with very low in dissolved solids known as "dematerialized water". No doubt, this plant has to be engineered very carefully keeping in view the type of raw water to the thermal plant, its treatment costs and overall economic.for a power station depends on threeActually, the type of demineralization process chosen 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 sectionDemineralization section PRETREATMENT SECTION

Pretreatment plant removes the suspended solids such as clay, silt, organic and inorganic matter, plants another 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). Thecoarsecomponents, such as sand, silt etc, can be removed from the water by simple sedimentation. Finer particles however, will not settle in any reasonable time and must be flocculated to produce the large particles which are settling 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 finely divided 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

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 colloidal dispersion resulting in particle destabilization by a reduction of force tending to keep particles apart. Rapid mixing is important 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 thec1ariflocculator. 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 chemical bridging. 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 anion loading.

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.

Action loading may unnecessary increase due to addition of Ca(OH)2 in excess of calculated amount for raising the pH of the water for maximum floe formation and also AKOrDgmayN precipitate out. If less than calculated amount of Ca (OH) 2 is added, proper pH flocculation will not beobtained and silica escape to demineralization section will occur, thereby increasing load on anion bed.

DEMINERALIZATION

This filter water is now used for dematerializing purpose and is fed to cation exchanger bed, butenroute being first dechlorinated, which is either done by passing through activated carbon filter or injecting along the flow of water, an equivalent amount of sodium sulphite through some stroke pumps. The residual chlorine which is- maintained in clarification plant to remove organic matter from raw water is now detrimental to action resin and must be eliminated before its entry to this bed.

Normally, the typical scheme of demineralization up to the .mark against average surface water is three bed systems with a provision of removing gaseous carbon dioxide from water before feeding to Anion Exchanger. Now, let 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 manufacturedin 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 modern thermal 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 ResinRH+NaKMgCaRNaKCa+H2SO4HCl HNO3(In the form of salts)(Resin in H2CO3 form)(Removed in degasser tower)Anion Resin

ROH+ H2SO4RSO4+ H2O

HCl ClHNO3 NO3Mineral acid Resins in exhausted Obtain from cation form exchanger

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 tower packed with, ranching 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 bed exchanger 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 than0.2/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 separated 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 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 type I. 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 I 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, is utilized to regeneratetype 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 makeup purpose to boiler feed.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 in desecrator. 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.

STEM TURBINEOPERATING PRINICIPLES

A steam turbines two main parts are the cylinder and the 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 in pressure and temperature occurs as the steam transmits .energy to theshaft and performs work. After passing through the last turbine stage, the steam exhausts into the condenser or process steam system.The kinetic energy of the steam changes into mechanical erringly through the impact (impulse) or reaction of the steam against the blades.

STEAM CYCLE

The 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 "RankineCycle" modified to include super heating of steam, regenerative feed water heating and reheating of steamOn to usi ove ret reh whi exp re exh tha iflarge turbines, it becomes economic increase the cycle efficiency by ng reheat, which is a way of partially rcoming temperature limitations. By urning partially expanded steam to a eat, the average temperature at ch heat is added is increased and by anding this reheated steam to the maining stages of the turbine, the aust wetness is considerably less n it would otherwise be conversely, the maximum tolerable wetness isallowed, 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 of moving blades in each stage.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 of direction 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 types of compounded turbine:

VELOCITY COMPOUND 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.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 drop is achieved, the initial and final conditions of steam used and their industrial usage.According to the direction of steam flow

Axial turbines

Radial turbinesAccording to the number of cylinder

Single - cylinder turbines.

Double- cylinder turbines.

Three-Cylinder turbines.

Four-Cylinder turbines

Multi - Cylinder turbinesAccording to the steam conditions at inlet to turbines

Low-pressure turbines

Medium -pressure turbines

High-pressure

Turbines of very high pressuresTurbines 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 usuallyemployed 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. TheH.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 two streams from the boiler and passes through the emergency stop valve and control valve before entering, the governing wheel chamber of the H.P.turbine. After expanding in the 12 stages in the H.P. turbine the steam returned in the boiler for reheating

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 a n d t h e 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 CYCLE

Fresh 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 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 middle part of the L.P. turbine through cross over pipes. In L.P. turbine the exhaust steam condenses in the surface condensers welded directly to the exhaust part of L.P. turbine

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.

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 TURBINE

MAIN COMPONENTS OF TURBINEEMERGENCY STOP VALVESteam 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 when the turbo set is tripped. The emergency stop valves connected to the four control valves through four flexible loop pipes of Chromium-Molybdenum-Vanadium steel.

HP ROTORThe 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.

LP ROTORIt 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 BEARINGSThe 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

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.

LP HEATERSTurbine 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 level indication of heated steam. Condensate pressure vaccum gauges are present for measurement of steam pressure.

Turbine has been provided with non-controlled extractions which are utilized for heating the condensate, from turbine bleed steam. There are 410w pressure heaters in which the last four extractions are used. L.P. Heater-1 has two parts LPH-1Aand 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 passes and 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.GLAND STEAM COOLERGland 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 AUXILIARIE

CONDENSATE PUMPS

The function of these pumps is to pumps out the condensate 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.

FEED WATER SYSTEMThe main equipments coming under this system are

Boiler Feed Pump: Three per unit of 50% capacity each located in the '0' meter level in the TGbay.

High Pressure Heaters: Normally three in number and are situated in the TG bay.

Drip Pumps: Generally two in number of 100% capacity each situated 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).Objective of training

To gain maximum knowledge about the practical work.

To see employee the practical work

To see department of company and also the work system of another department

To understand the problem faced by the employees

To understand the relative working of the plant and its departments