training report(ntpc) (2)

7/30/2019 Training Report(Ntpc) (2)

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INDUSTRIAL TRAINING REPORT ON

NTPC, BADARPUR

Submitted By:- RUPAK KUMARMechanical(3rd year)


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Department of Mechanical Engineering G.L BAJAJ Institute of Technology & MANAGEMENT, GreaterNoida.


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ACKNOWLEDGEMENT

I express my sincere thanks to the engineers and electrical maintenance persons for theguidance and support that they provided during my training period of May-June 2012.

I would like to thank Mr.G.D SHARMA sir for giving me opportunity to take training in esteemorganization of NTPC Badarpur.

I would like to specially convey my heartily thanks to Mr. P.K Prabhakar of BMD, Mr. Gaurav

Goel at the PAM section, and Mr.S.K Garg at the TMD section and many other employees ofNTPC for devoting their time to give me on-site presentations.


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Rupak kumar

ME-1001940048

G.L BAJAJ INSTITUTE OF TECHNOLOGY & MANAGEMENTGREATER NOIDA


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TO WHOM IT MAY CONCERN

I hereby certify that Rupak Kumar Roll.1019240048 of G.L BAJAJ INSTITUTE OF TECHNOLOGY & MANAGEMENTGREATER NOIDA has undergone 27 days industrial training from 28th may to 23rd June 2012 at our organization to fulfill therequirements for the award of degree of B.Tech in Mechanincal. He works on Power Plant Overview project during the training underthe supervision of Mr. G. D. Sharma. During his tenure with us we found him sincere and hard working.We wish him a great success in the future.


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Signature of the Student

CONTENTS

History of power development in India Thermal power development in India Thermal power station and its CLASSIFICATION COAL TO ELECTRICITY NTPC Performance POWER STATIONS in INDIA BTPS Introduction


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Steam Generator or Boiler

Boiler Furnace and Steam Drum

Fuel Preparation System Fuel Firing System and Igniter System Steam Turbine Coal Handling Plant Generator Transformer

History of power development in India:

India is one of the youngest and yet the largest domestic republic in the world, having an area of 1.27 million square miles with apopulation of around 1000 millions there are 5.76 lakhs villages in India and cover a population of about 70% of total population .Thehistory of power development in India dates back to 1897 when 200 kW hydro station was first commissioned at Darjeeling. In


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early years, most of the electricity supplies were privately owned and it catered to the needs of towns and cities. The majority of the

earlier power stations comprised of diesel generating sets. The first steam station was commissioned in Calcutta in 1899 with atotal installed capacity of 1000 kW. During the first two decades of the twentieth century, steam power stations at Kanpur, Madras

and Calcutta of 2170 kW, 9000 kW, 15000 kW capacities respectively, were commissioned. Similarly, hydro-plants of 4500 kW atSivasamud in Karnataka in 1902, 3000 kW at Mohara in J&K in 1907, 500 kW at Shimla in Himachal Pradesh in 1911 1550 kW atGokak falls in 1914 and 40000 kW at Tata hydro(Mumbai) in 1915 were installed. By the end of 1940, the total installed capacityrose to 1208 MW. The installed capacities in utilities by march 1951 was 1710 MW comprising hydro 560 MW, thermal 1000 MWand diesel 150 MW. The installed capacity in self-generating non-utilities was 590 MW.Efforts for organizing the power supply in industry in a rational manner began only after independence. Planned power developmentin a systematic manner began in 1951 with the launching of the first 5 year plan. During the first plan (1951-56), the installedgenerating capacity increased by 1100 MW bringing the total capacity to 3400 MW at the end of the plan . During the five yearsperiod covered by the plan, the generation increased from 7514 KWh to 11872 million KWh. In the second plan period theinvestment made in the power sector was three times the investment made in the preceding plan. The total generation rose to 20123

million KWh during this period. The first 220 kV line was commissioned in during this period. Third five year plan wascharacterized by two important developments. The first was the recognition of the importance of rural electrification as a key toinfrastructure for economic development. The second was the development of the importance of the interconnecting power stations sothat the available generating capacities could be pooled and used for the best advantage. This logically led to the demarcation of thecountry, for system operation purposes into five regions, namely, northern region (U.P, Haryana, Punjab, Rajasthan, HimachalPradesh , and JK); western region(M.P, Gujarat, Maharashtra, Goa, Daman and Diu); southern region (A.P, Karnataka, T.N,Pondicherry and Kerala); eastern region(Bihar, Orissa, West Bengal) and North Eastern region(Assam, Meghalaya, Tripura,Arunachal Pradesh, Nagaland, Manipur and Mizoram) and establishment of Regional Electricity Board in each of these five regions.The growth of power generation during various five year plans has been 10.5 %( first plan), 4.9 %( second plan), 14.3 %( third plan)and 6.9 %( fourth plan). This shows that the power industry in the country has been facing serious problems at the end of fourth plan

due to shortfall in achievement of targets. This was due to lack of proper maintenance of plants leading to sub-optimum utilization ofinstalled capacity, organizational weakness and scarcity of funds. Since the beginning of fifth five year plan, a concentrated effort hasbeen made to reorganize the scenario for more effective performance.One of the major developments in this sector is the thermal power generation which is still our main feeding source for the power weneed.

Thermal power generation can be achieved in various following ways:


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Coal Di esel Gas Nuclear

Though other sources of power development are available, power production by using coal as fuel is most common in India. It is

cheapest and most reliable form of energy till date due to the vast reserve of coal fields available in India as well as in other

countries from where it can be easily imported.

Thermal power development in India:

The known resources of coal in India is assumed to be 81,000 million tones which are fairly localized in four states West Bengal,Bihar, M.P and Andhra Pradesh. Most of the resources are inferior quality (non cooking type). The limited resource for higher gradecooking coal to the mines of Bihar and West Bengal are conserved for metallurgical industries. The present day annual production ofcoal is 90 million tones (as per data available in 1978) of which thermal stations consume about 30 million tones which is low gradecoal with high ash content (as high as 40%).

Presently, India imports coal from Australia which stands at $489 million in 1993-94. According to new guidelines prescribed byministry of environment, all coal based power plants with an installed capacity of 500 MW or more will be granted environmentalclearance only when the plants have a linkage with mines which supply washed coal.

Thermal power station and its CLASSIFICATION:

In thermal power stations, mechanical power is produced by aheat engine, which transformsthermal energy, often fromcombustionof afuel, into rotational energy. Most thermal power stations produce steam, and these are sometimes called steam power stations.About 86% of all electric power is generated by use of steam turbines. Not all thermal energy can be transformed to mechanical
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power, according to thesecond law of thermodynamics. Therefore, there is always heat lost to the environment. If this loss isemployed as useful heat, for industrial processes ordistrict heating, the power plant is referred to as acogenerationpower plant orCHP (combined heat-and-power) plant. In countries where district heating is common, there are dedicated heat plants called heat-only

boiler stations. An important class of power stations in the Middle East uses byproduct heat fordesalinationof water.

Classification:

CHP plant in Warsaw, Poland

Geothermal power station in the Philippines
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Coal Power Station in Tampa FL

Thermal power plants are classified by the type of fuel and the type of prime mover installed.

By fuel

Nuclear power plantsuse anuclear reactor's heat to operate asteam turbinegenerator. Fossil fuelled power plantsmay also use a steam turbine generator or in the case ofnatural gasfired plants may use acombustion

turbine.

Geothermal powerplants use steam extracted from hot underground rocks. Renewable energyplants may be fuelled bywaste from sugar cane,municipal solid waste, landfillmethane, or other forms of

biomass.

In integratedsteel mills,blast furnaceexhaust gas is a low-cost, although low-energy-density, fuel. Waste heat from industrial processesis occasionally concentrated enough to use for power generation, usually in a steam boiler and

turbine.

By prime mover

Steam turbineplants use the dynamic pressure generated by expanding steam to turn the blades of a turbine. Gas turbineplants use the dynamic pressure from flowing gases to directly operate the turbine. Natural-gas fuelled turbine plants can

start rapidly and so are used to supply "peak" energy during periods of high demand, though at higher cost than base-loaded plants.
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Combined cycleplants have both a gas turbine fired by natural gas, and a steam boiler and steam turbine which use the exhaust gasfrom the gas turbine to produce electricity. This greatly increases the overall efficiency of the plant, and most new baseload power

plants are combined cycle plants fired by natural gas.

Internal combustionReciprocating enginesare used to provide power for isolated communities and are frequently used for smallcogeneration plants. Hospitals, office buildings, industrial plants, and other critical facilities also use them to provide backup power in

case of a power outage. These are usually fuelled by diesel oil, heavy oil, natural gas and landfill gas.

Microturbines,Stirling engineand internal combustion reciprocating engines are low cost solutions for using opportunity fuels, suchas landfill gas, digester gas from water treatment plants and waste gas from oil production.

Cooling towers

Coal power plantin China with a hyperbolic cooling tower

Because of the fundamental limits to thermodynamic efficiency of anyheat engine, all thermal power plants produce waste heat as a

byproduct of the useful electrical energy produced. Natural draft wetcooling towersat nuclear power plants and at some large thermalpower plants are large hyperbolicchimney-like structures (as seen in the image at the left) that release the waste heat to the ambient

atmosphere by the evaporation of water (lower left image).
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A Marley mechanical induced-draft cooling tower

However, the mechanical induced-draft or forced-draft wet cooling towers (as seen in the image to the right) in many large thermal

power plants,petroleum refineries,petrochemical plants,geothermal,biomassandwaste to energy plantsusefansto provide air

movement upward through down coming water and are not hyperbolic chimney-like structures. The induced or forced-draft cooling

towers are rectangular, box-like structures filled with a material that enhances the contacting of the up flowing air and the down

flowing water. In desert areas a dry cooling tower or radiator may be necessary, since the cost of make-up water for evaporativecooling would be prohibitive. These have lower efficiency and higher energy consumption in fans than a wet, evaporative cooling

tower.

Where economically and environmentally possible, electric companies prefer to use cooling water from the ocean, or a lake or river,

or a cooling pond, instead of a cooling tower. This type of cooling can save the cost of a cooling tower and may have lower energy

costs for pumping cooling water through the plant'sheat exchangers. However, the waste heat can cause the temperature of the water

to rise detectably. Power plants using natural bodies of water for cooling must be designed to prevent intake of organisms into the

cooling cycle. A further environmental impact would be organisms that adapt to the warmer plant water and may be injured if the

plant shuts down in cold weather.
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Evaporation of water" at Ratcliffe Power Plant, UK

Other sources of energyOther power stations use the energy fromwaveortidalmotion,wind,sunlightor the energy of falling water,hydroelectricity. These

types of energy sources are calledrenewable energy.

HydroelectricityHydroelectricity impounds areservoirof water and releases it through one or morewater turbinesto generate electricity.

Pumped storage

Apumped storagehydroelectric power plant is a net consumer of energy but decreases the price of electricity. Water is pumped to a

high reservoir during the night when the demand, and price, for electricity is low. During hours of peak demand, when the price of
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electricity is high, the stored water is released to produce electric power. Some pumped storage plants are actually not net consumers

of electricity because they release some of the water from the lower reservoir downstream, either continuously or in bursts.

Solar

A control room of a modern power station

A solarphotovoltaicpower plant converts sunlight into electrical energy, which may needconversiontoalternating currentfortransmission to users. This type of plant does not use rotating machines for energy conversion. Solar thermal electric plants are

another type of solar power plant. They direct sunlight using either parabolic troughs orheliostats. Parabolic troughs direct sunlight

onto a pipe containing a heat transfer fluid, such as oil, which is then used to boil water, which turns the generator. The central tower

type of power plant uses hundreds or thousands of mirrors, depending on size, to direct sunlight onto a receiver on top of a tower.

Again, the heat is used to produce steam to turn turbines. There is yet another type of solar thermal electric plant. The sunlight strikes

the bottom of the pond, warming the lowest layer which is prevented from rising by a salt gradient. A Rankine cycle engine exploits

the temperature difference in the power station layers to produce electricity. Not many solar thermal electric plants have been built.

Most of them can be found in the Mojave Desert, although Sandia National Laboratory, Israel and Spain have also built a few plants.

WindWind turbinescan be used to generate electricity in areas with strong, steady winds. Many different designs have been used in the

past, but almost all modern turbines being produced today use the Dutch six-bladed, upwind design. Grid-connected wind turbines

now being built are much larger than the units installed during the 1970s, and so produce power more cheaply and reliably than earlier
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models. With larger turbines (on the order of one megawatt), the blades move more slowly than older, smaller, units, which makes

them less visually distracting and safer for airborne animals. However, the old turbines can still be seen at some wind farms,

particularly atAltamont Pass.

COAL TO ELECTRICITY

Coal from the coal wagons is unloaded in the coal handling plant. This coal is up to the raw coalbunkers with the help of belt

conveyers. Coal is transported to the 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.

These are three large rollers, which are spaced 120 degree apart.

When there is no coal, these rollers do not rotate but when coal is fed to the table it packs up between roller and the table and thisforces the roller to rotate. Coal is crushed by the crushing action between rollers and the 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. This fan takes atmospheric air, a part

of which is sent to air pre-heaters for heating while a part goes directly to the mill for temperature control. Atmospheric air from

F.D. fan is heated in the air heaters and sent to the furnace as combustion air.

Water from boiler feed pump passes through economizer and reaches the boiler drum. Water from the drum passes through down

comers and goes to bottom ring header. Water from the bottom ring header is divided to all the four sides of the furnace. Due to

heat and density difference the water rises up in the water wall tubes. Water is partly converted to steam as it rises up in the

furnace. This steam and water mixture is again taken to the boilers drum where the steam is separated from the water. Water

follows the same path while the steam is sent to super heaters for superheating. The super heaters are located inside the furnaceand the steam is superheated (540 deg C) finally it goes to turbine.

A flue gas from the furnace is extracted from the induced draft fan, which maintains balance draft in the furnace with forced draft

fans. These flue gases emits their heat energy to various super heaters in the pant house and finally passes through air pre-heaters

and goes to electrostatic precipitator where the ash particles are extracted. Electrostatic precipitator consists of metal plates which

are electrically charged. Ash particles are attracted on to these plates, so that they do not pass through the chimney, to pollute the
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atmosphere. A regular mechanical hammer causes the accumulation of ash to fall to the bottom of the precipitator where they are

collected in a hopper for disposal. This ash is mixed with water to form slurry and is pumped to ash pond.

The steam from the boiler is conveyed to the turbine through the steam pipes and through stop valve and control valve that

automatically regulate the supply of steam to the turbine. Stop valves and control valves are located in a steam chest and governordriven from the main turbine shaft operates the control valves to regulate the amount used.

Steam from the control valves enters the high-pressure cylinder of the turbine, where it passes through the ring of blades fixed to

the cylinder wall. These act as nozzles and direct the steam into a second ring of moving blades mounted on the disc secured to the

turbine shaft. The second ring turns the shaft as a result of the force of the steam. The stationary and moving blades together

constitute a stage of a turbine and in practice many stages are necessary, so that the cylinder contains a number of rings of

stationary blades with rings of moving blades arranged between them. The steam passes though each stage in turn until it reaches

the end of the high-pressure cylinder and in its passage some of its heat energy is changed in to mechanical energy. The steam

leaving the high-pressure cylinder goes back to the boiler for reheating and returns by a further pipe to the intermediate pressure

cylinder. Here it passes through another series of stationary and moving blades. Finally the steam is taken to the low pressure

cylinders, each of which it enters at the center flowing outwards in the opposite directions through the rows of turbines bla desan

arrangement known as double flow-to extremities of the cylinder as the steam gives up its heat energy to drive the turbine its

temperature and pressure falls and it expands, because of this expansion the blades are much larger and longer towards the low

pressure ends of the turbine.

The turbine shaft usually rotates at 3000rpm.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 /sec. When

as much as energy as possible has been extracted from the steam it is exhausted directly to the condenser. This runs the length of

the low pressure part of the turbine and may be beneath on either side of it the condenser consist of a large vessel containing some

20000 tubes each about 25mm in diameter cold water from the river, estuary, sea or cooling tower is circulated through these tubes

and as the steam from the turbine passes round them it is rapidly condensed into water condensate. Because water has a muchsmaller comparative volume than steam, a vacuum is created in the condenser. This allows the steam to reduce down to pressure

below that of the normal atmosphere and more energy can be utilized.

From the condenser, the condensate is pumped through low-pressure heaters by the extraction pumps after which its pressure is

raised to boiler pressure by the boiler feed pump. It is passed through further feed heaters to the economizer and the boiler for the

reconversion into steam.


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A power station generating 2000000 KW of electricity requires about 227500 cubic meter of water an hour for cooling purpose. Here

cooling towers are used, about 1/100 part of the cooling water evaporates and a certain amount is returned to its source to carry

away any impurities that collects most of it is however recirculated.

RANKINE CYCLE:The thermodynamic cycle on which the steam (or thermal) power plant is operated is modified ranking cycle. A simple ranking cycle

consists of four processes: reversible constant pressure heat addition; reversible adiabatic expansion; reversible constant pressure

heat rejection; reversible adiabatic compression.

REGENERATIVE CYCLE:

The sample plant cycle illustrated with symbols, lines, and process units in this diagram is more complex than any previousexamples. Note the two independent closed heaters at points (b) and (d). The other units in this cycle have their conventionalroles in the generation of power from a working fluid. On the lower half of the diagram is the temperature-entropy (TS)diagram resulting from examination of the ideal process. The stages of regeneration actually shift the water among differentsaturation lines, permitting an increase in temperatureand therefore increases in both the maximum power output andthermal efficiency of the designwithout unduly altering entropy. Instead of boiling water at the low pressure pL or even atintermediate pressures pj or pi, the phase change occurs at the highest possible pressure, pH , available for the design. Sinceturbines operate most effectively and most efficiently when a large pressure drop is established, a plant employing regenerationof this type will be able to produce more power per unit of original energy resource and mass of water.

Regeneration basically means "generation again" or "repeat generation." As the heavy black line on the process flowdiagram on the left shows, water is partially condensed between points (d) and (a), but then prior to arrival at the boiler

for another heating stage, the working fluid enters the turbine again in order to extract all possible useful energy from the

water and vapor. A thermal power plant works on a modified ranking cycle that is a combination of reheat and

regenerative. So there is also a low and high pressure turbine for reheat purposes and heaters (L.P. and H.P.) for

regenerative purposes.


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Some of the vital parts of the power plant are as follows:

Boilers Electrostatic precipitators(ESP) Conveyors Draught systems Economizers Super heaters Desuperheaters Cooling towers Pumps Turbines Furnace Pulverizing plant

Basic conceptsIn a fossil fuel power plant the chemical energy stored in fossil fuels such as coal, fuel oil, natural gas oroil shale is converted

successively into thermal energy, mechanical energy and, finally, electrical energy for continuous use and distribution across a wide

geographic area. Almost all large fossil fuel power plants are steam-electric power plants, except forgas turbines and utility-sized

reciprocating engines that may run on natural gas ordiesel.

The burning of fossil fuel is summarized in the following chemical reaction:

and the simple word equation for this chemical reaction is:

All fossil fuels generate carbon dioxide, when combusted. Chemical side reactions also take place, generating, among others, sulfur

dioxide (predominantly in coal) and oxides ofnitrogen. Each fossil fuel power plant is a highly complex, custom-designed system.

Present construction costs, as of 2004, run to US$1,300 perkilowatt, or $650 million for a 500 MWe unit. Multiple generating units

may be built at a single site for more efficient use ofland, natural resources and labor.
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NTPC PerformanceThe operating performance of NTPC has been considerably above the national average. The availability factor for coal stations has

increased from 78.21% in 1985-86 to 88.54% in 2000-01, which compares favorably with international standards. The PLF has

increased from 70% in 1992-93 to 81.8% during the year 2000-01.

However, for regions other than Eastern Region which has power evacuation constraints due to low system demand, a PLF of 88.6%was achieved during this year. Over eight years, employee productivity has increased almost threefold as measured by the ratio of

turnover to number of employees.


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It may be seen from the table below that while the installed capacity has increased by 49.36% in the last eight years, the employeestrength went up by only 10.2%. This includes employees of Orissa State Electricity Board who had to be absorbed in NTPCconsequent upon the take over of 460 MW Talcher Power Station from the Orissa Government on 3-6-1995 and 440 MW Tanda

Thermal Power Project from U. P. Government on 15-01-2000.

Description Unit 92-93 2000-01 % of increase

Installed capacity MW 13,054 19,497 49.36

Generation MUs 66,113 1,30,154 96.87

No. of employees No. 21,797 24,012 10.2

Generation/employee MUs 3.03 5.42 83.1

Turnover/employee Rs.(Lakhs) 20.74 80.04 385.9

Description Unit 92-93 2000-01 % of increase

Installed capacity MW 13,054 19,497 49.36

Generation MUs 66,113 1,30,154 96.87

No. of employees No. 21,797 24,012 10.2

Generation/employee MUs 3.03 5.42 83.1

Turnover/employee Rs. Lakh 20.74 80.04 385.9

For the year 2000-01, NTPC's Dadri Coal & Singrauli Station recorded a PLF of 93.6% which was the highest in the country.


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NTPC:

1. Stands for National Thermal Power Station.2. 6th leading company in India.3. Core business includes- engineering, construction & operation of power plants.4. Also provides Consultancy service in India & abroad.5. Owns 14 coal based plants, 7 fuel based plants.6. Total installed capacity(all over INDIA)24,600 MegaWatts.

The development of power in the country was achieved through State Electricity Boards (SEBS) during the first three decades afterindependence. The outlay for power during viii-plan was Rs.34270 crores against Rs.393 crores during the first plan period. Theoutlay for power remained 19-20% during all plan periods out of total outlay.With significance achievements since independence, power shortage has persisted because the demand has always been outstrippingthe supply. This was because, financial resources were not available to the extent required to create the necessary power supply

capacity.Due to shortage of power in different regions and imbalance power generation, and non availability of inter-regional grids, it wasdecided to install generation capacity in central sector. Two central companies, the National Thermal Power Corporation (NTPC est.in 1975 Nov.) and the National Hydroelectric Corporation (NHPC) were setup in 1975 and NEEPC (North Eastern Electric PowerCorporation) to serve north eastern region thus was considered a major stride in the establishment of an integrated grid at the nationallevel through inter-connection of national grids. A third central generation company, the Nuclear Power Corporation (NPC) has beenformed to develop nuclear power potential.


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round rail transportation system, data acquisition system, & micro processor based distributed control system, satellite communicationand computerization.The NTPC energized the following 400 kV transmission lines during 1984-85.

1.

Bihar-Koradi -273 km2. Muradnagar-Panipat-86 km3. Hyderabad-Nagarjun Sagar- 150 km

The transmission system associated with Rihand super thermal power station (3000 MW) includes construction of 910 km of highvoltage direct current (HVDC) line. The HVDC technology in transmission is being introduced in the country for the first time byNTPC.To combat the acute power shortage in the south, the NTPC has planned to shift focus to the southern states, where the mismatchbetween demand and supply is quite alarming.The bulwork of NTPC in the south would be 2100 MW Ramagundam super thermal power station (226 km) from Hyderabad which isto be upgraded to 2600 MW making it the countrys largest single thermal power station. The other southern projects of the NTPC are

only in the conceptual stage now. The states where the projects are planned are Andhra Pradesh, Tamil Nadu and Karnataka.Kayamkulam power project of 1300 MW in Kerela, gas based station using naphtha in the beginning and switch over to natural gaslater, 500 MW station in Karnataka, the expansion of Tuticorin thermal power station and power station at Cuddalore in Tamil Naduare in the future plan of NTPC.The NTPC has planned to add over 5000 MW in IX-plan period where these projects will involve an investment of Rs.16000 crores attodays priceThe NTPC has installed 16085 MW generating capacity during last two decades and navigated from construction to operation stage.The corporation operates presently 11-coal based and five-gas based combined cycle plants including Bharat Aluminium CaptivePower Project and Badarpur in Delhi.The power projects of NTPC generated 79093 million units which is 23% of the total generation of the country during 1994-95. Thecorporation netted profit in the same year was rs.1112 crores.For the next 8 years (1995-2003), NTPC has chalked out an ambitious capacity additional program of 10,000 MW by installingseveral coal and gas based power plants. This will take the total installed capacity of NTPC to more than 25000 MW (20%, 25% oftotal national capacity).The future development program includes the second stage Vindhyachal thermal power station in M.P where first stage where 1260MW already under operation. The work on expansion of the Unchaher stage two of 420 MW plant in U.P has also been under takenwith the completion of second stage Unchaher capacity will go up to 840 MW. Rihand expansion in U.P will add a capacity if another1000 MW. Expansions of the Talcher super thermal project in Orissa will add another 2000 MW. Also, the expansion of the Kawas,


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Anta, and Auraiya gas projects located in Gujarat, Rajasthan and U.P are in the pipeline. Work on the Kayamkulam project of 400MW capacity in Kerela is expected to start soon. The cabinet committee on economic affairs has cleared this project with estimatedcost of Rs.1310 crores (aug. 1995). The first gas turbine has been made ready by the middle of 1998. The whole project will be

supplied to Kerela in view of heavy power shortage in the state. The 400 MW gas project at Faridabad is yet to be cleared by thepublic investment bureau (PIB). The A.P government has allocated two projects to NTPC, 1000 MW thermal project at Simhadri nearVizag and a 650 MW naphtha based Hyderabad Metro power project near Hyderabad.Recognizing and anticipating the emerging scenario in the power sector with particular reference to private sector participation, NTPCis seeking alliance with companies having complimentary strength. After successful joint venture with a private company for settingup 208 MW unit in A.P, a MoU has also been concluded with Bombay suburban electricity services to take up construction, erectionand project management activities in power sector as joint ventures.For an environment friendly growth, NTPC has developed a comprehensive action plan. Keeping in view, the environmentalregulation and need to utilize the ash effectively, an ash utilization division has been formed. During the year 1994-95, about 1.8 MTof ash has been utilized for various productive purposes. Agreements have already been signed with a couple of parties for making

bricks and other various products from fly ash.NTPC is also executing transmission lines and substation packages in Nepal and Dubai. Recently an order has been secured from theTanzanian govt. for the preparation of feasibility and project reports for a power station.The story of NTPC is the story of three powerful and successful decades of excellence in power generation. In a short span of twodecades, NTPC has installed 16085 MW, contributing 23% of the total power generating capacity of the country, lighting one-fifth ofthe nation. Another outstanding feature is. Plant load factor during 1994-95 was 0.766. it employs 22500 people with a net profit ofRs.1125 crores in 1994-95.

NTPCs role in development of gas based power station:

The NTPC has already executed or in the stage of executing 4 gas based combined cycle projects. Out of four, Anta, Auriya haveachieved their phased operational capacity. The other two at Kawas and Dadri are at different stages of completion.Seventh plan period witnessed the introduction of gas based power generation. First gas based unit was commissioned in 1989.NTPC has established itself as a pioneer in setting up and operating combined cycle gas based plants. This is going to be beneficial tothe nation as substantial power generation is anticipated through gas based plants. With the recent indication of increasing availability


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of natural gas in the country, gas based power plants offer growth opportunities. NTPC has taken up to install gas based plants atGandhar (650 MW), Faridabad (800 MW), Dadri (1200 MW), Anta (430 MW), Godavari (800 MW) and Tripura (500 MW). Thecommissioning of NTPCs gas based units not only marked heralding of the era of gas based combined cycle plant but also created

history in terms of shortening the generation period.The recent discoveries of gas reserves in the country have come at a very opportune time and would help to bridge the gap betweenenergy supply and demand over the shorter time horizon.It is unfortunate that the country has gas reserves of 1200 billion cubic meters. But the govt. is yet to firm up its policy on use ofnatural gas for power generation on long term basis. But in view of the advantages of gas based generation, it is anticipated that powergeneration based on gas would continue to increase in the next decade and beyond.

Mission

1) Make available reliable and quality power in increasingly large quantities at appropriate tariffs, and ensure timely realization

of revenues.

2) Speedily plan and implement power projects, with contemporary technologies.

3) Implement strategic diversifications in the areas of R&M, Hydro, LNG and non-conventional and eco-friendly fuels and explore

new areas like transmission, information technology etc.

4) Promote consultancy and make prudent acquisitions.


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5) Continuously develop competent human resources to match world standards

Be a responsible corporate citizen with thrust on environment protection, rehabilitation and ash utilization

Objectives

In pursuance of the vision & mission, the following would be the Corporate Objectives of NTPC:

1) To add generating capacity within prescribed time and cost;2) To expand consultancy operations and to participate in ventures abroad;

3) To diversify in Hydro and Non-Conventional Energy Sources Power Generation;

4) To diversify into power related businesses to ensure integrated development of energy sector in India.

Performance Leadership

To achieve continuous performance improvement in the areas of project implementation, plant operation and maintenance,

generation efficiency etc. and to acquire and sustain internationally comparable standards in these areas with good business

ethics and values

Human Resources Development


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1) To develop a learning Organization having knowledge-based competitive edge.

2) To create a culture of team building, empowerment and accountability to convert knowledge into productive action with

speed, creativity and flexibility.

Financial Soundness

1) To maintain and improve the financial soundness of NTPC by managing the financial resources in accordance with the best

commercial utility practices.

2) To develop appropriate commercial polices which ensure remunerative tariffs and minimum receivables.

Technology Leadership

To acquire, assimilate and adopt reliable, efficient and cost-effective technologies and to disseminate knowledge to other

constituents of the power sector in the country.

CORE VALUES (Commitments)

Customer focus Organizational pride Mutual respect and trust Initiative and speed Total quality


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NTPC Limited

Type Public

Founded 1975
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Headquarters Delhi,India

Key people

Mr. T. Sankaralingam,

Chairman & ManagingDirector

Industry Power Generation

Products Electricity

RevenueINR261 billion (2006) or

USD5.91 billion

Net incomeINR5.8 billion (2006) or

USD131 millionEmployees 23867 (2006)

POWER STATIONS in INDIA:
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BTPS

1. Stands for Badarpur Thermal Power Station.2. Total installed capacity705 MW in 5 units

- 3 units: 95 MW each

- 2 units: 205 MW each

3. Main Operating Divisions consists of-Electrical Maintenance Division

-Operations

-Control & Instrumentation

Unit Capacity Year

Unit-I 95 MW 1973-74

Unit-II 95 MW 1974-75


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Unit-III 95 MW 1974-75

Unit-IV 210 MW 1978-79

Unit-V 210 MW 1981-82

The Management of the Centrally owned Badarpur Thermal Power Station was handed over to NTPC on April 15, 1978.

Introduction

The operating performance of NTPC has been considerably above the national average. The availability factor for coal stations has

increased from 85.03 % in 1997-98 to 90.09 % in 2006- 07, which compares favourably with international standards. The PLF has

increased from 75.2% in 1997-98 to 89.4% during the year 2006-07 which is the highest since the inception of NTPC.


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Operation Room of Power Plant

In a Badarpur Thermal Power Station, steam is produced and used to spin a turbine that operates a generator. Water is heated, turnsinto steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in

a condenser; this is known as a Rankine cycle. Shown here is a diagram of a conventional thermal power plant, which uses coal, oil, ornatural gas as fuel to boil water to produce the steam. The electricity generated at the plant is sent to consumers through high-voltagepower lines.

The Badarpur Thermal Power Plant has Steam Turbine-Driven Generators which has a collective capacity of 705MW. The fuel beingused is Coal which is supplied from the Jharia Coal Field in Jharkhand. Water supply is given from the Agra Canal.


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There are basically three main units of a thermal power plant

1. Steam Generator or Boiler

2. Steam Turbine3. Electric Generator

We have discussed about the processes of electrical generation further. A complete detailed description of the three units is given

further.

Typical Diagram of a Coal based Thermal Power Plant


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Coal is conveyed (14) from an external stack and ground to a very fine powder by large metal spheres in the pulverised fuel mill (16).

There it is mixed with preheated air (24) driven by the forced draught fan (20). The hot air-fuel mixture is forced at high pressure intothe boiler where it rapidly ignites. Water of a high purity flows vertically up the tube-lined walls of the boiler, where it turns into

steam, and is passed to the boiler drum, where steam is separated from any remaining water. The steam passes through a manifold in

the roof of the drum into the pendant superheater (19) where its temperature and pressure increase rapidly to around 200 bar and

540C, sufficient to make the tube walls glow a dull red. The steam is piped to the high pressure turbine (11), the first of a three-stage

turbine process. A steam governor valve (10) allows for both manual control of the turbine and automatic set-point following. The

steam is exhausted from the high pressure turbine, and reduced in both pressure and temperature, is returned to the boiler reheater

(21). The reheated steam is then passed to the intermediate pressure turbine (9), and from there passed directly to the low pressure

turbine set (6). The exiting steam, now a little above its boiling point, is brought into thermal contact with cold water (pumped in from

the cooling tower) in the condensor (8), where it condenses rapidly back into water, creating near vacuum-like conditions inside the

condensor chest. The condensed water is then passed by a feed pump (7) through a deaerator (12), and pre-warmed, first in a feed

heater (13) powered by steam drawn from the high pressure set, and then in the economiser (23), before being returned to the boiler

drum. The cooling water from the condensor is sprayed inside a cooling tower (1), creating a highly visible plume of water vapor,

before being pumped back to the condensor (8) in cooling water cycle.

The three turbine sets are sometimes coupled on the same shaft as the three-phase electrical generator (5) which generates an

intermediate level voltage (typically 20-25 kV). This is stepped up by the unit transformer (4) to a voltage more suitable fortransmission (typically 250-500 kV) and is sent out onto the three-phase transmission system (3).Exhaust gas from the boiler is drawn

by the induced draft fan (26) through an electrostatic precipitator (25) and is then vented through the chimney stack (27)


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Steam Generator or Boiler

The boiler is a rectangular furnace about 50 ft (15 m) on a side and 130 ft (40 m) tall. Its wallsare made of a web of high pressure steel tubes about 2.3 inches (60 mm) in diameter.

Pulverized coal is air-blown into the furnace from fuel nozzles at the four corners and it rapidly burns, forming a large fireball at the

center. The thermal radiation of the fireball heats the water that circulates through the boiler tubes near the boiler perimeter. The water

circulation rate in the boiler is three to four times the throughput and is typically driven by pumps. As the water in the boiler circulates

it absorbs heat and changes into steam at 700 F (370 C) and 3,200 psi (22.1 MPa). It is separated from the water inside a drum at the

top of the furnace. The saturated steam is introduced into superheat pendant tubes that hang in the hottest part of the combustion gases

as they exit the furnace. Here the steam is superheated to 1,000 F (540 C) to prepare it for the turbine.

The steam generating boiler has to produce steam at the high purity, pressure and temperature required for the steam turbine that

drives the electrical generator. The generator includes the economizer, the steam drum, the chemical dosing equipment, and the

furnace with its steam generating tubes and the superheater coils. Necessary safety valves are located at suitable points to avoid

excessive boiler pressure. The air and flue gas path equipment include: forced draft (FD) fan, air preheater (APH), boiler furnace,

induced draft (ID) fan, fly ash collectors (electrostatic precipitator or baghouse) and the flue gas stack.Schematic diagram of a coal-fired power plant steam generator


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For units over about 210 MW capacity, redundancy of key components is provided by installing duplicates of the FD fan, APH, flyash collectors and ID fan with isolating dampers. On some units of about 60 MW, two boilers per unit may instead be provided.

Boiler Furnace and Steam Drum

Once water inside the boiler or steam generator, the process of adding the latent heat of vaporization or enthalpy is underway. Theboiler transfers energy to the water by the chemical reaction of burning some type of fuel.


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The water enters the boiler through a section in the convection pass called the economizer. From the economizer it passes to the steamdrum. Once the water enters the steam drum it goes down the down comers to the lower inlet water wall headers. From the inletheaders the water rises through the water walls and is eventually turned into steam due to the heat being generated by the burnerslocated on the front and rear water walls (typically). As the water is turned into steam/vapor in the water walls, the steam/vapor onceagain enters the steam drum.


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External View of an Industrial Boiler at Badarpur Thermal Power Station, New Delhi

The steam/vapor is passed through a series of steam and water separators and then dryers inside the steam drum. The steam separatorsand dryers remove the water droplets from the steam and the cycle through the water walls is repeated. This process is known asnatural circulation.

The boiler furnace auxiliary equipment includes coal feed nozzles and igniter guns, soot blowers, water lancing and observation ports(in the furnace walls) for observation of the furnace interior. Furnace explosions due to any accumulation of combustible gases after atrip- out are avoided by flushing out such gases from the combustion zone before igniting the coal.

The steam drum (as well as the superheater coils and headers) have air vents and drains needed for initial startup. The steam drum hasan internal device that removes moisture from the wet steam entering the drum from the steam generating tubes. The dry steam thenflows into the superheater coils.

Geothermal plants need no boiler since they use naturally occurring steam sources. Heat exchangers may be used where thegeothermal steam is very corrosive or contains excessive suspended solids. Nuclear plants also boil water to raise steam, eitherdirectly passing the working steam through the reactor or else using an intermediate heat exchanger.

Fuel Preparation System

In coal-fired power stations, the raw feed coal from the coal storage area is first crushed into small pieces and then conveyed to thecoal feed hoppers at the boilers. The coal is next pulverized into a very fine powder. The pulverizers may be ball mills, rotating drumgrinders, or other types of grinders.

Some power stations burn fuel oil rather than coal. The oil must kept warm (above its pour point) in the fuel oil storage tanks toprevent the oil from congealing and becoming unpumpable. The oil is usually heated to about 100C before being pumped through thefurnace fuel oil spray nozzles.


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Boiler Side of the Badarpur Thermal Power Station, New Delhi

Boilers in some power stations use processed natural gas as their main fuel. Other power stations may use processed natural gas asauxiliary fuel in the event that their main fuel supply (coal or oil) is interrupted. In such cases, separate gas burners are provided on theboiler furnaces.

Fuel Firing System and Igniter System

From the pulverized coal bin, coal is blown by hot air through the furnace coal burners at an angle which imparts a swirling motion to

the powdered coal to enhance mixing of the coal powder with the incoming preheated combustion air and thus to enhance thecombustion.

To provide sufficient combustion temperature in the furnace before igniting the powdered coal, the furnace temperature is raised byfirst burning some light fuel oil or processed natural gas (by using auxiliary burners and igniters provide for that purpose).


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Air Path

External fans are provided to give sufficient air for combustion. The forced draft fan takes air from the atmosphere and, first warming

it in the air preheater for better combustion, injects it via the air nozzles on the furnace wall.

The induced draft fan assists the FD fan by drawing out combustible gases from the furnace, maintaining a slightly negative pressurein the furnace to avoid backfiring through any opening. At the furnace outlet, and before the furnace gases are handled by the ID fan,fine dust carried by the outlet gases is removed to avoid atmospheric pollution. This is an environmental limitation prescribed by law,and additionally minimizes erosion of the ID fan.

Auxiliary Systems

Fly Ash Collection

Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag filters (or sometimes both) located at theoutlet of the furnace and before the induced draft fan. The fly ash is periodically removed from the collection hoppers below theprecipitators or bag filters. Generally, the fly ash is pneumatically transported to storage silos for subsequent transport by trucks orrailroad cars.

Bottom Ash Collection and Disposal

At the bottom of every boiler, a hopper has been provided for collection of the bottom ash from the bottom of the furnace. This hopperis always filled with water to quench the ash and clinkers falling down from the furnace. Some arrangement is included to crush the

clinkers and for conveying the crushed clinkers and bottom ash to a storage site.

Boiler Make-up Water Treatment Plant and Storage

Since there is continuous withdrawal of steam and continuous return of condensate to the boiler, losses due to blow-down andleakages have to be made up for so as to maintain the desired water level in the boiler steam drum. For this, continuous make-up water


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is added to the boiler water system. The impurities in the raw water input to the plant generally consist of calcium and magnesiumsalts which impart hardness to the water. Hardness in the make-up water to the boiler will form deposits on the tube water surfaceswhich will lead to overheating and failure of the tubes. Thus, the salts have to be removed from the water and that is done by a waterdemineralising treatment plant (DM).

Ash Handling System at Badarpur Thermal Power Station, New DelhiA DM plant generally consists of cation, anion and mixed bed exchangers. The final water from this process consists essentially ofhydrogen ions and hydroxide ions which is the chemical composition of pure water. The DM water, being very pure, becomes highlycorrosive once it absorbs oxygen from the atmosphere because of its very high affinity for oxygen absorption.


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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 asthe DM plant may be down for maintenance. For this purpose, a storage tank is installed from which DM water is continuouslywithdrawn for boiler make-up. The storage tank for DM water is made from materials not affected by corrosive water, such as PVC.The piping and valves are generally of stainless steel. Sometimes, a steam blanketing arrangement or stainless steel doughnut float isprovided on top of the water in the tank to avoid contact with atmospheric air. DM water make-up is generally added at the steamspace of the surface condenser (i.e., the vacuum side). This arrangement not only sprays the water but also DM water gets deaerated,with the dissolved gases being removed by the ejector of the condenser itself.

Steam Turbine

Steam turbines are used in all of our major coal fired power stations to drive the generators or alternators, which produce electricity.The turbines themselves are driven by steam generated in 'Boilers' or 'Steam Generators' as they are sometimes called.

Energy in the steam after it leaves the boiler is converted into rotational energy as it passes through the turbine. The turbine normallyconsists of several stages with each stage consisting of a stationary blade (or nozzle) and a rotating blade. Stationary blades convertthe potential energy of the steam (temperature and pressure) into kinetic energy (velocity) and direct the flow onto the rotating blades.The rotating blades convert the kinetic energy into forces, caused by pressure drop, which results in the rotation of the turbine shaft.The turbine shaft is connected to a generator, which produces the electrical energy. The rotational speed is 3000 rpm for IndianSystem (50 Hz) systems and 3600 for American (60 Hz) systems.


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In a typical larger power stations, the steam turbines are split into three separate stages, the first being the High Pressure (HP), the

second the Intermediate Pressure (IP) and the third the Low Pressure (LP) stage, where high, intermediate and low describe the

pressure of the steam.

After the steam has passed through the HP stage, it is returned to the boiler to be re-heated to its original temperature although the

pressure remains greatly reduced. The reheated steam then passes through the IP stage and finally to the LP stage of the turbine.


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A distinction is made between "impulse" and "reaction" turbine designs based on the relative pressure drop across the stage. There are

two measures for pressure drop, the pressure ratio and the percent reaction. Pressure ratio is the pressure at the stage exit divided by

the pressure at the stage entrance. Reaction is the percentage isentropic enthalpy drop across the rotating blade or bucket compared to

the total stage enthalpy drop. Some manufacturers utilise percent pressure drop across stage to define reaction.

Steam turbines can be configured in many different ways. Several IP or LP stages can be incorporated into the one steam turbine. A

single shaft or several shafts coupled together may be used. Either way, the principles are the same for all steam turbines. The

configuration is decided by the use to which the steam turbine is put, co-generation or pure electricity production. For cogeneration,

the steam pressure is highest when used as process steam and at a lower pressure when used for the secondary function of electricity

production.


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kinetic energy (velocity) and direct the flow onto the rotating blades. The rotating blades convert the kinetic energy into impulse and

reaction forces caused by pressure drop, which results in the rotation of the turbine shaft or rotor.

Steam turbines are machines which must be designed, manufactured and maintained to high tolerances so that the design power output

and availability is obtained. They are subject to a number of damage mechanisms, with two of the most important being:

Erosion due to Moisture: - The presence of water droplets in the last stages of a turbine causes erosion to the blades. This has led to

the imposition of an allowable limit of about 12% wetness in the exhaust steam;Solid Particle Erosion: - The entrainment of erosive materials from the boiler in the steamcauses wear to the turbine blades.

Cogeneration Cycles

In cogeneration cycles, steam is typically generated at a higher temperature and pressure than required for a particular industrialprocess. The steam is expanded through a turbine to produce electricity and the resulting extractions at the discharge are at the

temperature and pressure required by the process. Turbines can be condensing or non-condensing design typically with large mass

flows and comparably low output. Traditionally, pressures were 6.21 MPa and below with temperatures 441 C or lower, although the

trend towards higher levels of each continues. There are now a considerable number of co-generation steam turbines with initial steam

pressures in the 8.63 to 10 MPa range and steam temperatures of 482 to 510 C.


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Bearings and Lubrication

Two types of bearings are used to support and locate the rotors of steam turbines:

Journal bearings are used to support the weight of the turbine rotors. A journal bearing consists of two half-cylinders that enclose theshaft and are internally lined with Babbitt, a metal alloy usually consisting of tin, copper and antimony; and Thrust bearings axiallylocate the turbine rotors. A thrust bearing is made up of a series of Babbitt lined pads that run against a locating disk attached to the

turbine rotor. High-pressure oil is injected into the bearings to provide lubrication. The oil is carefully filtered to remove solidparticles. Specially designed centrifuges remove any water from the oil.

Shaft Seals


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The shaft seal on a turbine rotor consist of a series of ridges and groves around the rotor and its housing which present a long, tortuous

path for any steam leaking through the seal. The seal therefore does not prevent the steam from leaking, merely reduces the leakage to

a minimum. The leaking steam is collected and returned to a low-pressure part of the steam circuit.

Turning Gear

Large steam turbines are equipped with "turning gear" to slowly rotate the turbines after they have been shut down and while they arecooling. This evens out the temperature distribution around the turbines and prevents bowing of the rotors.

Vibration

The balancing of the large rotating steam turbines is a critical component in ensuring the reliable operation of the plant. Most largesteam turbines have sensors installed to measure the movement of the shafts in their bearings. This condition monitoring can identifymany potential problems and allows the repair of the turbine to be planned before the problems become serious

Condenser

The surface condenser is a shell and tube heat exchanger in which cooling water is circulated through the tubes. The exhaust steamfrom 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. Such condensers use steam ejectors or rotary motor-driven exhausters for continuous removal of airand gases from the steam side to maintain vacuum.


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A Typical Water Cooled Condenser

For best efficiency, the temperature in the condenser must be kept as low as practical in order to achieve the lowest possible pressurein the condensing steam. Since the condenser temperature can almost always be kept significantly below 100oC where the vapor

pressure of water is much less than atmospheric pressure, the condenser generally works under vacuum. Thus leaks of non-condensible air into the closed loop must be prevented. Plants operating in hot climates may have to reduce output if their source ofcondenser cooling water becomes warmer; unfortunately this usually coincides with periods of high electrical demand for airconditioning.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 or ocean.


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Feedwater Heater

A Rankine cycle with a two-stage steam turbine and a single feedwater heater. In the case of a conventional steam-electric power

plant utilizing a drum boiler, the surface condenser removes the latent heat of vaporization from the steam as it changes states fromvapour to liquid. The heat content (btu) in the steam is referred to as Enthalpy. The condensate pump then pumps the condensate waterthrough a feedwater heater. The feedwater heating equipment then raises the temperature of the water by utilizing extraction steamfrom various stages of the turbine.


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A Rankine cycle with a two-stage steam turbine and a single feedwater heater


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Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic

efficiency of the system.[9] This reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when the

feedwater is introduced back into the steam cycle.

DeaeratorA steam generating boiler requires that the boiler feed water should be devoid of air and otherdissolved gases, particularly corrosive ones, in order to avoid corrosion of the metal. Generally, power stations use a deaerator toprovide for the removal of air and other dissolved gases from the boiler feedwater. A deaerator typically includes a vertical, domeddeaeration section mounted on top of a horizontal cylindrical vessel which serves as the deaerated boiler feedwater storage tank.


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Boiler Feed Water Deaerator (with vertical, domed aeration section and horizontal water storage section)

There are many different designs for a deaerator and the designs will vary from one manufacturer to another. The adjacent diagramdepicts a typical conventional trayed deaerator. If operated properly, most deaerator manufacturers will guarantee that oxygen in thedeaerated water will not exceed 7 ppb by weight (0.005 cm/L).


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Auxiliary SystemsOil System

An auxiliary oil system pump is used to supply oil at the start-up of the steam turbine generator. It supplies the hydraulic oil systemrequired for steam turbine's main inlet steam stop valve, the governing control valves, the bearing and seal oil systems, the relevanthydraulic relays and other mechanisms.At a preset speed of the turbine during start-ups, a pump driven by the turbine main shaft takesover the functions of the auxiliary system.

Generator Heat Dissipation

The electricity generator requires cooling to dissipate the heat that it generates. While small units may be cooled by air drawn throughfilters at the inlet, larger units generally require special cooling arrangements. Hydrogen gas cooling, in an oil-sealed casing, is usedbecause it has the highest known heat transfer coefficient of any gas and for its low viscosity which reduces windage losses. Thissystem requires special handling during start-up, with air in the chamber first displaced by carbon dioxide before filling withhydrogen. This ensures that the highly flammable hydrogen does not mix with oxygen in the air.

The hydrogen pressure inside the casing is maintained slightly higher than atmospheric pressure to avoid outside air ingress. Thehydrogen must be sealed against outward leakage where the shaft emerges from the casing. Mechanical seals around the shaft areinstalled with a very small annular gap to avoid rubbing between the shaft and the seals. Seal oil is used to prevent the hydrogen gasleakage to atmosphere. The generator also uses water cooling. Since the generator coils are at a potential of about 15.75 kV and wateris conductive, an insulating barrier such as Teflon is used to interconnect the water line and the generator high voltage windings.Demineralized water of low conductivity is used.

Generator High Voltage System


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The generator voltage ranges from 10.5 kV in smaller units to 15.75 kV in larger units. The generator high voltage leads are normallylarge aluminum channels because of their high current as compared to the cables used in smaller machines. They are enclosed in well-grounded aluminum bus ducts and are supported on suitable insulators. The generator high voltage channels are connected to step-uptransformers for connecting to a high voltage electrical substation (of the order of 220 kV) for further transmission by the local power

grid.

The necessary protection and metering devices are included for the high voltage leads. Thus, the steam turbine generator and thetransformer form one unit. In smaller units, generating at 10.5 kV, a breaker is provided to connect it to a common 10.5 kV bussystem.

Coal Handling Plant

Coal is delivered by highway truck, rail, barge or collier ship. Some plants are even built near coal mines and coal is delivered byconveyors. A large coal train called a "unit train" may be a kilometers (over a mile) long, containing 60 cars with 100 tons of coal ineach one, for a total load of 6,000 tons. A large plant under full load requires at least one coal delivery this size every day. Plants mayget as many as three to five trains a day, especially in "peak season", during the summer months when power consumption is high. Alarge thermal power plant such as the Badarpur Thermal PowerStation, New Delhi stores several million tons of coal for use when there is no wagon supply.


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Modern unloaders use rotary dump devices, which eliminate problems with coal freezing in bottom dump cars. The unloader includesa train positioner arm that pulls the entire train to position each car over a coal hopper. The dumper clamps an individual car against aplatform that swivels the car upside down to dump the coal. Swiveling couplers enable the entire operation to occur while the cars arestill coupled together. Unloading a unit train takes about

three hours. Shorter trains may use railcars with an "air-dump", which relies on air pressure from the engine plus a "hot shoe" on eachcar. This "hot shoe" when it comes into contact with a "hot rail" at the unloading trestle, shoots an electric charge through the air dumpapparatus and causes the doors on the bottom of the car to open, dumping the coal through the opening in the trestle. Unloading one ofthese trains takes anywhere from an hour to an hour and a half. Older unloaders may still use manually operated bottom-dump rail carsand a "shaker" attached to dump the coal. Generating stations adjacent to a mine may receive coal by conveyor belt or massive diesel-electric-drive trucks.


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Layout of Coal Handling Plant at Badarpur Thermal Power Station, New Delhi

Coal is prepared for use by crushing the rough coal to pieces less than 2 inches (50 mm) in size. The coal is then transported from thestorage yard to in-plant storage silos by rubberized conveyor belts at rates up to 4,000 tons/hour.In plants that burn pulverized coal, silos feed coal pulverizers (coal mill) that take the larger 2 inch pieces grind them into theconsistency of face powder, classify them, and mixes them with primary combustion air which transports the coal to the furnace and


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preheats the coal to drive off excess moisture content. In plants that do not burn pulverized coal, the larger 2 inch pieces may bedirectly fed into the silos which then feed the cyclone burners, a specific kind of combustor that can efficiently burn larger pieces offuel.

Run-Of-Mine (ROM) Coal

The coal delivered from the mine that reports to the Coal Handling Plant is called Run-of-mine, or ROM, coal. This is the raw materialfor the CHP, and consists of coal, rocks, middlings, minerals and contamination. Contamination is usually introduced by the miningprocess and may include machine parts, used consumables and parts of ground engaging tools. ROM coal can have a large variabilityof moisture and maximum particle size.

Coal Handling

Coal needs to be stored at various stages of the preparation process, and conveyed around the CHP facilities. Coal handling is part ofthe larger field of bulk material handling, and is a complex and vital part of the CHP.

Stockpiles

Stockpiles provide surge capacity to various parts of the CHP. ROM coal is delivered with large variations in production rate of tonnesper hour (tph). A ROM stockpile is used to allow the washplant to be fed coal at lower, constant rate.


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Coal Handling Division of Badarpur Thermal Power Station, New Delhi

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. More controlled stockpiles are formed using stackers to form piles alongthe length of a conveyor, and reclaimers to retrieve thecoal when required for product loading, etc. 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 lost, leading to a higher risk of spontaneous combustion.

Stacking

Travelling, lugging boom stackers that straddle a feed conveyor are commonly used to create coal stockpiles. Stackers are nominallyrated in tph (tonnes per hour) for capacity and normally travel on a rail between stockpiles in the stockyard. A stacker can usually

move in at least two directions typically: horizontally along the rail and vertically by luffing its boom. Luffing of the boom minimisesdust by reducing the height that the coal needs to fall to the top of the stockpile. The boom is luffed upwards as the stockpile heightgrows.


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Wagon Tripler at Badarpur Thermal Power Station, New Delhi

Some stackers are able to rotate by slewing the boom. This allows a single stacker to form twostockpiles, one on either side of the conveyor.


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Stackers are used to stack into different patterns, such as cone stacking and chevron stacking. Stacking in a single cone tends to causesize segregation, with coarser material moving out towards the base. Raw cone ply stacking is when additional cones are added next tothe first cone. Chevron stacking is when the stacker travels along the length of the stockpile adding layer upon layer of material.

Stackers and Reclaimers were originally manually controlled manned machines with no remote control. Modern machines aretypically semi-automatic or fully automated, with parameters remotely set.

Reclaiming

Tunnel conveyors can be fed by a continuous slot hopper or bunker beneath the stockpile to reclaim material. Front-end loaders andbulldozers can be used to push the coal into feeders. Sometimes front-end loaders are the only means of reclaiming coal from thestockpile. This has a low up-front capital cost, but much higher operating costs, measured in dollars per tonne handled.


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Coal Storage Area of the Badarpur Thermal Power Station, New Delhi

Coal Sampling


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Sampling of coal is an important part of the process control in the CHP. A grab sample is a one- off sample of the coal at a point in theprocess stream, and tends not to be very representative. A routine sample is taken at a set frequency, either over a period of time or pershipment.

Screening

Screens are used to group process particles into ranges by size. These size ranges are also called grades. Dewatering screens are usedto remove water from the product. Screens can be static, or mechanically vibrated. Screen decks can be made from different materialssuch as high tensile steel, stainless steel, or polyethelene.


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Screening and Separation Unit of Coal Handling Division of a Thermal Power Plant.

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