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Page | 2
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With respectful regards, I take the opportunity to convey my thanks to the management of Badarpur thermal power station division of National Thermal Power Corporation for giving me the opportunity to complete my summer training here.
I do extend my heartfelt thanks to Mrs. Rachna Singh Bahal for providing me this opportunity to be a part of this esteemed organization.
I am extremely grateful to all the technical staff of BTPS / NTPC for their co-operation and guidance that has helped me a lot during the course of training. I have learnt a lot working under them and I will always be indebted of them for this value addition in me.
I would also like to thank the training incharge of G.B.P.E.C, Delhi and all the faculty members of Mechanical Engineering Department for their effort of constant co- operation, which have been a significant factor in the accomplishment of my industrial training.
NITIN JAIN
G. B.P.E.C. (NEW DELHI)
Page | 3
TTrraaiinniinngg aatt BBTTPPSS I was appointed to do 27 days training at this esteemed organization from 13th May 2011 to 7th July 2011. In these 27 days I was assigned to visit various division of the plant which were
Boiler maintenance division ‐I (BMD‐I)
Boiler maintenance division ‐II (BMD‐ II)
Boiler maintenance division ‐III (BMD‐ III)
Plant auxiliary maintenance division (PAM)
Turbine maintenance division (TMD)
This 27 Days training was a very educational adventure for me. It was really amazing to see the plant by myself and learn how electricity, which is one of our daily requirements of life, is produced. This report has been made by self‐experience at BTPS. The material in this report has been gathered from my textbooks, senior student report, and trainer manual provided by training department. The specification & principles are at learned by me from the employee of each division of BTPS.
Page | 4
CCCOOONNNTTTEEENNNTTT
A). THE COMPANY
Installed Capacity
Project Profile
BADARPUR THERMAL POWER STATION
Thermal power plant
B). BOILER MAINTENANCE DIVISION
Main Boiler ‐ Boiler Fundamentals
Boilers, their classification and types
Categorization of Boilers
Main boiler
Main parts of boiler
• Boiler drum • Furnace • Combustion chamber • Scraper conveyor • Clinker grinder • Economizer • Super heater • Air preheater
Pulversing mill • Contact mill • Ball mill • Bowl mill
Page | 5
Fuel firing
• Coal • Oil • High pressure air
High pressure safety valve
ESP (Electrostatic Precipitator)
Up‐gradation & Retrofitting of Pollution Control Systems
Resources Conservation
C). PLANT AUXILIARY MAINTENANCE DIVISION
Compressor house
Gas compressor
• Centrifugal compressor • Diagonal or mixed – flow compressor • Axial flow compressor • Reciprocating compressor • Rotary screw compressor • Diaphragm compressor
Four main types of compressors used at the BTPS
• Densvevor Compressors • Plant compressors • Instrument compressors • Blast air compressors
Staged compression
Prime movers
Control structure pump house
Ash handling
WTP and geo miller
• W.T.P.‐I&II • Geomiller • Clarifloculator
Page | 6
• Mixed bed exchanger Important Specifications
The cooling tower
D). TURBINE MAINTENANCE DIVISION
Main turbine
• Types of turbine • Casing or shaft arrangement • Principle of operation and design • Operation and maintenance • Speed regulation
C.W. booster pump
Condenser
Valve
• Types/Designations • Valve parts • Body and bonnet • Ports • Disc/rotor/valve member • Seat • Stem • Bonnet • Spring • Valve balls
Material of valve
Operative type
Sealing material
Condensate pump group
Boiler feed pump
Page | 7
TTTHHHEEE CCCOOOMMMPPPAAANNNYYY
NTPC Limited (formerly National Thermal Power Corporation) was founded on November 7, 1975. Today it is the largest state‐owned power generating company in India. It is an Indian public sector company listed on the Bombay Stock Exchange although at present the Government of India holds 84.5% (after divestment the stake by Indian government on 19th October, 2009) of its equity.
In November 2004, NTPC came out with its Initial Public Offering (IPO) consisting of 5.25% as fresh issue and 5.25% as offer for sale by Government of India. NTPC thus became a listed company with Government holding 89.5% of the equity share capital and rest held by Institutional Investors and Public. The issue was a resounding success. NTPC is among the largest five companies in India in terms of market capitalization.
Page | 8
In Forbes list of World’s 2000 Largest Companies for the year 2010, NTPC occupies 341th place. The Company has power generating facilities in all major regions of the country. The total installed capacity of the company is 34894 MW (including JVs) with 15 coal based (25,815MW) and 7 gas based (3995MW) stations, located across the country. In addition under JVs, 5 stations are coal based & another station uses naphtha/LNG as fuel. It is among the world’s largest and most efficient power generation companies. NTPC has embarked on plans to become a 75,000 MW company by 2017.
NTPC has gone beyond the thermal power generation. It has diversified into hydro power, coal mining, power equipment manufacturing, oil & gas exploration, power trading & distribution. NTPC is now in the entire power value chain and is poised to become an Integrated Power Major.
NTPC's share on 31 Mar 2008 in the total installed capacity of the country was 19.1% and it contributed 28.50% of the total power generation of the country during 2007‐08. NTPC has set new benchmarks for the power industry both in the area of power plant construction and operations. With its experience and expertise in the power sector, NTPC is extending consultancy services to various organisations in the power business. It provides consultancy in the area of power plant constructions and power generation to companies in India and abroad. Recognising its excellent performance and vast potential, Government of the India has identified NTPC as one of the jewels of Public Sector 'Navratnas'‐ a potential global giant. Inspired by its glorious past and vibrant present, NTPC is well on its way to realise its vision of being "A world class integrated power major, powering India's growth, with increasing global presence".
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IIINNNSSSTTTAAALLLLLLEEEDDD CCCAAAPPPAAACCCIIITTTYYY
An overview
NO. OF PLANTS CAPACITY (MW)
NTPC Owned
Coal 15 27,535
Gas/Liquid Fuel 7 3,955
Total 22 31,490
Owned By JVs
Coal & Gas 6 3,364
Total 28 34,854
Regional Spread of Generating Facilities
REGION COAL GAS TOTAL
Northern 8,015 2,312 10,327
Western 7,520 1,293 8,813
Southern 4,100 350 4,450
Eastern 7,900 - 7,900
JVs 1,424 1,940 3,364
Total 28,959 5,895 34,854
Page | 10
PPPRRROOOJJJEEECCCTTT PPPRRROOOFFFIIILLLEEE
Coal Based Power Stations
COAL BASED(Owned by
NTPC) STATE COMMISSIONED CAPACITY(MW)
1. Singrauli Uttar Pradesh 2,000
2. Korba Chhattisgarh 2,600
3. Ramagundam Andhra Pradesh 2,600
4. Farakka West Bengal 2,100
5. Vindhyachal Madhya Pradesh 3,260
6. Rihand Uttar Pradesh 2,000
7. Kahalgaon Bihar 2,340
8. NCTPP, Dadri Uttar Pradesh 1,820
9. Talcher Kaniha Orissa 3,000
10. Feroze Gandhi, Unchahar
Uttar Pradesh 1,050
11. Talcher Thermal Orissa 460
12. Simhadri Andhra Pradesh 1,500
13. Tanda Uttar Pradesh 440
14. Badarpur Delhi 705
15. Sipat Chhattisgarh 1,660
Total 27,535
Page | 11
Coal Based Joint Ventures:
COAL BASED (Owned by JVs)
STATE COMMISSIONED
CAPACITY
1. Durgapur West Bengal 120
2. Rourkela Orissa 120
3. Bhilai Chhattisgarh 574
4. Kanti Bihar 110
5.IGSTPP, Jhajjar
Haryana 500
Total 1,424
Gas/Liq. Fuel Based Power Stations
GAS BASED
(Owned by NTPC) STATE
COMMISSIONED CAPACITY(MW)
1. Anta Rajasthan 413
2. Auraiya Uttar Pradesh 652
3. Kawas Gujarat 645
4. Dadri Uttar Pradesh 817
5. Jhanor-Gandhar Gujarat 648
6. Rajiv Gandhi CCPP Kayamkulam Kerala 350
7. Faridabad Haryana 430
Total 3,955
Gas Based Joint Ventures:
COAL BASED (Owned by JVs) STATE COMMISSIONED CAPACITY
1. RGPPL Maharashtra 1940
Total 1940
Page | 12
BBBAAADDDAAARRRPPPUUURRR TTTHHHEEERRRMMMAAALLL PPPOOOWWWEEERRR SSSTTTAAATTTIIIOOONNN
The Badarpur thermal power Station was planned by CWPC‐ Central Water & Power Commission which was bifurcated later on into Central Electricity Authority (CEA) under Ministry of Power and Central Water Commission ‐ during sixties to cater the growing needs of power of Delhi. The area was selected which was out of city limits at that time and near the AGRA CANAL for its water requirements. The area was full of stones of ARAVALl HILLS. Coal requirements of plant were tied up with JHARIA / DHANBAD coal mines through nearby Tuglakabad railway station.
At that time, only three units of 95MW were planned and the work was given to Public Sector Company namely BHARAT HEAVY ELECTRICAL LIMITED (BHEL). Ministry of Power provided Rs.66 crores to CEA for the construction of first stage of power house which comprised three units of 95 MW, link canal from Agra Canal, & discharge canal to Agra Canal, Coal Handling Plant, Ash Handling Plant, Ash Disposal area, Water Treatment Plant and residential area. Subsequently, two more units were planned with a capacity of 210 MW each taking full capacity to 705 MW at the cost of Rs.170 crores. Out of this 705MW, 65MW is consumed by the plant itself and rest 640MW is transmitted to grid so that it can be distributed to the consumers. The power generated was to be utilized by the main beneficiary Delhi and the adjoining area like Haryana, D.P. & Rajasthan.
The land was acquired in 1967 and work started thereafter. First unit of 95MW was synchronized on 23rd September 1973.
Power generated is utilised by the beneficiary states through agreements of purchase with NTPC. As CEA was having only one Power house namely BTPS, it was decided by the Ministry of Power to hand over BTPS to NTPC in March 1978 on contract basis. BTPS has scaled many records of plant load factor (PLF) during last decade and also received many rewards from Ministry of Power for attaining highest PLF, lowest oil consumption. BTPS also attained ISO 9002 & ISO 14001 for Environment Management System. BTPS has planted many thousand trees in its area for environment control.
Thermal power plant
Thermal power plant converts the heat energy of coal to electrical energy. Coal is burnt in a boiler which converts water into steam. The expansion of steam in turbine produces mechanical power which drives the alternator. Thus the main equipment in the thermal power plant consists of boiler, steam turbine and alternator. To achieve efficient conversion of heat energy into electrical energy a variety of auxiliary equipment are needed.
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BBBAAASSSIIICCC PPPRRRIIINNNCCCIIIPPPLLLEEE
The basic raw materials required for the plants are coal, air and water. The coal is brought to the station by trains from Bihar, A.P, Orissa and M.P. coal is unloaded from the wagon by the help of wagon tipplers. Then coal is transferred from coal handing plant by conveyor belt to the coal bunkers, from where it is fed to the pulverising mills, which grind it as fine as face power. The finally powered coal mixed with pre‐heated air is then blown into the boiler by a fan called Primary Air Fan, where it burns, more like a gas then as a solid in the conventional domestic or industrial grate, with additional amount of air called secondary air supplied by a Force Draft Fan. As the coal has been ground so finely, the resultant ash is also a fine powder. Some of it binds together to form lumps which fall into the ash pits at the bottom of the furnace. The water quenched ash from the bottom of the furnace is conveyed to pits for subsequent disposal or sale. Most of the ash, still in the fine particle form is carried out of the boiler to the precipitators as dust, where it is trapped by electrodes changed with high voltage electricity. The dust is then conveyed by water to disposal areas or to bunkers for sale. While the cleaned flue gasses pass on through I.D. Fan to be discharged up the chimney. The steam which has given up its heat energy is changed back into water in a condenser so that it is ready for re‐use. The condenser contains many kilometers of tubing through which cold water is constantly pumped.
Coupled to the end of the turbine is the rotor of the generator, a large cylindrical magnet ‐ so that when the turbine rotates the rotor turns with it, the rotor housed inside the stator having heavy coils of cooper bars in which electricity is produced through the movement of the magnetic field created by the rotor. The electricity passes from the stator windings to the step‐up that it can be transmitted efficiently over the power line of the grid.
Meanwhile the heat released from the coal has been absorbed by many kilometers of tubing which line the boiler walls. Inside the tubes is the boiler feed water which is transformed by the heat into steam at high pressure and temperature. The steam, super heated in further tube (Super Heater) passes to the turbine, where it is discharged through nozzles on the turbine blades. Just as the energy of the wind turns the sails of the wind‐mill, so the energy of steam, striking the blades, makes the turbine rotate. Looses heat and is rapidly changed back to water. But the two lots of water (i.e. boiler feed water and cooling water) must never mix. The cooling water is drawn from the river/sea, but the boiler feed water must be absolutely pure, far purer than the water, which we drink. Indeed the chemistry at a power station is largely chemistry of water.
Why bother to change the steam from the turbine back into water if it has to be heated up again immediately?
The answer lies in the law of physics, which states that the boiling point of water is directly proportional to pressure. The lower the pressure, the lower the temperature at which water boils.
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The turbine designed wants as low boiling point as possible because we can only utilize the energy from steam ‐ when the steam changes back to water we can get no more work out of it. So a condenser is required by which rapidly changing the steam back into water creates a vacuum. The vacuum results in a much lower boiling point which, in turn, means we can continue getting work out of the steam wet below 100 C at which it would normally change into water.
To condense the large quantities to steam, huge and continuous volume of cooling water is essential. In most of the power station, the same water is to be used over and over again. So the heat which the water extracts from the steam in the condenser is removed by pumping the water out to the cooling towers. The cooling towers are simple concrete shells acting as huge chimneys creating a draught (nature mechanically assisted by fans) of air, the water is sprayed out at top of the towers and as it falls into the pond beneath it is cooled by the upward draught of air. The cold water in the pond is then recalculated by pumps to the condensers, inevitably, however, some of the water is drawn upward as a vapors by the draught and it is this water which forms the familiar while clouds which emerge from the towers seen sometimes.
The Badarpur Thermal Power Plant works on MMMOOODDDIIIFFFIIIEEEDDD RRRAAANNNKKKIIINNNEEE CCCYYYCCCLLLEEE. It is a cycle that converts heat into work. The heat is supplied externally to a closed loop, which usually uses water.
Process 1‐2 represents the admission of high pressure steam into the engine cylinder, process 2‐3 is the reversible adiabatic expansion of steam in the cylinder and process 3‐4 is the exhaust of steam into condenser. Net work done is represented by the area 1‐ 2‐3‐4‐1. Observe that the area 3‐6‐5 is very small and in order to obtain this small work, the cylinder volume must be increased from v6 to v3.This makes cylinder very bulky. For this reason, the expansion process is terminated at point 5. So that indicator diagram becomes 1‐2‐5‐6‐4. The work lost is small but there is large saving in cylinder volume. Process 5‐6 represents the release of steam into the condenser, thus causing the cylinder pressure to drop from P5 to P6. Process 6‐4 is the exhaust of steam at constant pressure. Cycle 1‐2‐5‐6‐4 is called as the “modified Rankine cycle”.
Page | 15
BBBMMMDDD
BBBOOOIIILLLEEERRR MMMAAAIIINNNTTTEEENNNAAANNNCCCEEE DDDEEEPPPAAARRRTTTMMMEEENNNTTT
Page | 16
Main Boiler - Boiler Fundamentals:
The objective of this chapter is to acquaint the readers with the basics of combustion, Theory, types and classification of boilers and an overview of the arrangement of various Boiler accessories.
PRINCIPLES OF COMBUSTION:
The primary function of oil and coal burning systems in 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 sulphur. When combustion is properly completed the exhaust gases will contain, carbon dioxide, water vapour, sulphur dioxide and a large volume of Nitrogen, combining carbon and hydrogen or hydrocarbons with the oxygen in air brings about Combustion. When carbon burns completely, it results in the formation of a gas known as carbon dioxide. When carbon burns incompletely it forms carbon monoxide.
Composition of air: the supply of oxygen for combustion is obtained from air. This is as important as the supply of fuel. The average composition of air is
79% nitrogen and 21% oxygen by volume
77% nitrogen and 23% oxygen by weight
Nitrogen does not burn but passes through the combustion chamber to the chimney unchanged excepting its temperature.
Ignition: Fuel must be ignited before it can burn. Raising the temperature of the fuel to its ignition temperature brings about combustion. This temperature varies with different fuels.
Excess air: The amount of air required to burn any fuel can be calculated if the amount of the elements present in the fuel are known. This amount of air is known as the theoretical air. In practice this quantity is not sufficient to ensure complete combustion and extra air has to be supplied. This extra air is known as excess air.
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The loss of combustibles and sunburn gas loss reduces as excess air is added reach maximum and any further additions of excess air beyond this stage, the boiler losses increase. Thus there is one and only one quantity of excess air, which will give the lowest combustion loss. The value of excess air needed depends upon the fuel used, the type of firing etc.
The following factors in efficient combustion are usually referred to as "The three T's”:
Time: It will take a definite time to heat the fuel to its ignition temperature and having ignited, it will also take time to burn. 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. Preheating the combustion air increases the speed at which this Temperature will be reached. 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 on
• Design of the boiler
• Fuel used
• Skill in obtaining combustion with the minimum amount of excess air.
Thermal efficiency of a boiler is measured by the amount of heat transferred to the water in the boiler by each Kg of fuel used and is expressed as a percentage of the total heat energy in one Kg. of fuel. The thermal efficiency is dependent on the factors governing efficient combustion.
Boilers, their classification and types:
Boiler is a device for generating steam for power, processing or heating purposes.
Boiler is designed to transmit heat from an external combustion source (usually fuel combustion to a fluid) contained within the boiler itself.
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The heat‐generating unit includes a furnace in which the fuel is burned. With the advantage of water‐cooled furnace walls, super heaters, air heaters and economizers, the term steam generator was evolved as a better description of the apparatus.
Boilers maybe classified on the basis of any of the following characteristics:
• Use • Pressure • Materials • Size • Tube Content • Tube Shape and position • Firing • Heat Source • Fuel • Fluid • Circulations • Furnace position • Furnace type • General shape • Trade name • Special features.
Use: The characteristics of the boiler vary according to the nature of service performed.
Customarily boiler is called either stationary or mobile. Large units used primarily for electric power generation are known as control station steam generator or utility plants.
Pressure: To provide safety control over construction features, all boilers must be constructed in accordance with the Boiler codes, which differentiates boiler as per their characteristics.
Materials: Selection of construction materials is controlled by boiler code material specifications. Power boilers are usually constructed of special steels.
Size: Rating code for boiler standardize the size and ratings of boilers based on heating surfaces. The same is verified by performance tests.
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Tube Contents: In addition to ordinary shell type of boiler, there are two general steel boiler classifications, the fire tube and water tube boilers. Fire tube boiler is boilers with straight tubes that are surrounded by water and through which the products of combustion pass. Water tube boilers are those, in which the tubes themselves contain steam or water, the heat being applied to the outside surface.
Firing: The boiler may be a fired or unfired pressure vessel. In fired boilers, the heat applied is a product of fuel combustion. A non‐fired boiler has a heat source other than combustion.
Heat Source: The heat may be derived from (1) the combustion of fuel (2) the hot gasses of other chemical reactions (3) the utilization of nuclear energy.
Fuel: Boilers are often designated with respect to the fuel burned.
Fluid: The general concept of a boiler is that of a vessel to generate steam. A few utilities plants have installed mercury boilers.
Circulation: The majority of boilers operate with natural circulation. Some utilize positive circulation in which the operative fluid may be forced 'once through' or controlled with partial circulation.
Furnace Position: The boiler is an external combustion device in which the combustion takes place outside the region of boiling water. The relative location of the furnace to the boiler is indicated by the description of the furnace as being internally or externally fired.
The furnace is internally fired if the furnace region is completely surrounded by water cooled surfaces. The furnace is externally fired if the furnace is auxiliary to the boiler.
Furnace type: The boiler may be described in terms of the furnace type.
General Shape: During the evaluation of the boiler as a heat producer, many new shapes and designs have appeared and these are widely recognized in the trade.
Trade Name: Many manufacturers coin their own name for each boiler and these names come into common usage as being descriptive of the boiler.
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Special features: some times the type of boiler like differential firing and Tangential firing are described.
Categorization of Boilers:
Boilers are generally categorized as follows:
• Steel boilers
• Fire Tube type
• Water tube type
• Horizontal Straight tube
MAIN BOILER
A boiler is a closed vessel in which the heat produced by the combustion of fuel is transferred to water for its conversation into steam of the desired temperature & pressure.
The steam produced may be supplied to turbine for power generation.
The boiler is generally used for power production are two types:‐
1. Corner boiler
2. Front fire boiler
The boiler mainly has natural circulation of gases, steam and other things. They contain vertical membrane water. The pulverized fuel which is being used in the furnace is fixed tangentially. They consume approximately 700 ton.\hr of coal of about 1370kg\cm2 of pressure having temperature of 540оc
The boiler used is manufactured by BHEL of 210MW. The first pass of the boiler has a combustion chamber enclosed with water walls of fusion welded construction on all four sides. In addition there are four water platens to increase the radiant heating surface.
Beside this platen super heater reheater sections are also suspended in the furnace combustion chamber. The first pass is a high heat zone since the fuel is burn in this pass.
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The second pass is surrounded by steam cooled walls on all four sides as well as roof of the boiler. A horizontal super heater, an economiser & two air heaters are located in the second pass.
MAIN PARTS OF THE BOILER
BOILER DRUM
Its main function is to separate steam from water. It is a circular vessel in which water level is maintained at 10" below the centre of the drum. The wet steam enters in the drum through the water wall of boiler.
The drum consists of baffles and thin fine sieves trough which wet steam passes. The baffles provided number of plates in downward slope direction. The wet steam first passes trough these baffles and after that it passes through thin sieves at the top of drum.
The water droplets in the steam fall down through baffles and sieves. The pure steam passes to root panels.
The water in drum is attached with down comer and risers. The water in the boiler is fed through the down comers.
Weight ‐ 123 tonnes
Length ‐ l5700mm
Inner diameter ‐ l676mm
Outer diameter ‐ 1942mm
Material ‐ carbon steel
Pressure ‐ l50.7g\cm2
Temp ‐ 342оc
Page | 22
FURNACE
It is the main part of the boiler where the fuel or coal is burnt and produce lots of heat and flue gases to convert the water into steam.
Height ‐ 42.797m
Length ‐ l3.868m
Width ‐ 10.592m
Volume ‐ 52l0m3
To start the production unit, firstly pulverised coal is fed to the furnace through a pump.
For fuel burning, ignition temperature and pressure are also necessary. The burning of coal completely and raise the temperature to an approximately level. Initially air and oil are also fed to it through F.D. fan and oil gun respectively. Then when the temperature is reached to the required level coal starts burning and produces lots of heat and flue gases. The water tube flowing inside the boiler containing water turns into wet steam. It is a water tube boiler.
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COMBUSTION CHAMBER
It is made of seamless steel tubes and walls are joined by fusion weld. Walls on all sides are rectangular in cross section. The space between the water walls tubes is of fusion welded to form a complete gas tight seal. These are four platen water walls in the combustion chamber to increase the heating surface. The front and bottom walls slope down toward the centre of furnace to form inclined sides of the bottom. Ash from the furnace is discharged through the bottom opening into bottom ash hopper.
SCRAPER CONVEYOR
The scraper conveyor is used for two functions:
• Remove ash from the combustion chamber
• Provide ceiling to boiler
The scraper conveyer is mounted at the bottom of furnace where ash is collected after burning the coal and removes from the boiler. Scraper conveyer is generally used for removing heavy dust.
Capacity 20 tonnes\hr
Body ‐ mild steel.
Liners sail yard
Scraper ms
CLINKER GRINDER
It is an apparatus which is connected with scraper conveyer for the purpose of removing ash from the boiler. The heavy long ash pieces are crushed in the clinker grinder so that they can be easily flow out from the boiler.
ECONOMISER
It is used for utilize the heat of flue gases since for improving the temperature of feed water so that the efficiency of the boiler is increased.
The flue gas when leaves the boiler its temperature is higher then the temperature of feed water so the waste heat of flue gases can be utilized. It is mounted at the second pass of the boiler. It is arranged between the feed pump and drums.
The temperature before entering the economiser is 240 degree centigrade.
The temperature after discharging the economiser is 280 degree centigrade.
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SUPER HEATER
It is an apparatus which is used to increase the efficiency of boiler the super heater used are generally four types:‐
1. Sealing SH
2. Lower temperature SH
3. Radiant SH
4. Final SH
The function of super heater is to convert the wet steam into dry steam. The wet steam from the boiler is entered into the low temperature super heater and then into radiant super heater and then finally into final super heater and passed to main steam line.
AIR PRE HEATER
The Air pre heater is used in the boiler for improving efficiency and transferring heat from flue gas to secondary air and primary air. The air entering the boiler furnace is at a low temperature as compared to the temperature of exhaust flue gases. The air is heated by the heat carried away by the flue gases and going as a waste through chimney. It is situated between the economiser and the chimney.
The plant efficiency is increase by the air prehearter. It is mounted on the 2nd pass. The APH are used are tabular APH. In the tabular tube, the air passes down outside the tubes and the flue gases through the tubes before going to ID fan at the base of the chimney.
PULVERISING MILL 1. CONTACT MILL It has stationary and power driven rotating elements having a rolling action with respect to each other. Coal is made to pass trough these elements again and again till it is pulverized. Hot air is circulated which takes away the fine particle to the burner. 2. BALL MILL A large cylinder or drum partly filled with various sized ball is used in this mill, the cylinder is rotated at approximately 17 to 20 rpm while coal is continuously fed into it, hot air enters the cylinders dries the coal during pulverization and carries pulverized coal to burner. 3. BOWL MILL In the bowl mill, crushed coal is pulverized and further dried by hot primary air. A portion of primary air from P.A. fan discharges is heated from this type sector.
Page | 25
FUEL FIRING
There are mainly three components which are used in fuel firing:‐
1. Pulverised coal
2. High pressure air
3. Oil
COAL
The coal has various varieties. The coal which is used out they should have high calorific value, produce maximum heat produce less ash and pollution on burning easily available, low cost etc. these features are available in bituminous coal, which is used in the plant. It has about 90‐95% carbon and its caloric value varies between 3600‐4200. Coal is brought in large pieces, so in first stage the coal is finally crushed so that it burns completely.
Then it is sent the furnace through conveyor belt. In the furnace the coal burns and produces steam. The ash which gets collected in the scraper is removed time to time with the help of water. Its main function is to produce lot of heat so ass to convert water into steam.
OIL
Oil is supplied with the help of oil gun to coal so that the coal can be easily burn.
HIGH PRESSURE AIR
High pressure air is introduced into the furnace so that the coal can be reached at ignited temperature. The high pressure air from fan is introduced to the furnace through F.D fan.
The successfully working of an oil firing equipment depends on the following:‐
I. The correct design of control flow.
2. The design of combustion chamber.
3. The design of the economiser which must be able to reduce the fuel to a finally divided stay.
HIGH PRESSURE SAFTY VALVE
It is a device which comes into operation when the pressure in the boiler exceeds the working pressure. It discharges some of the steam automatically out of the boiler and brings the pressure down to the normal working limit. There are many type of valves but the valve used is spring loaded
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safety valve. In this valve the valve rest on its seat under the action of spring. The valve is fitted on the drum. When steam pressure exceeds the normal working limit, these valves are lifted from their seats allowing passage for steam to escape out till the pressure falls below the specified limit after which the valve again rest on the seal. It is made up of C.I.
ESP (ELECTROSTATIC PRECIPITATOR)
When coal is burnt in the boiler ash is liberated and carried along with flue gases if these ashes are exhausted to the atmosphere. It will create pollution resulting in health hazard. Hence it is necessary to precipitate the dust from the flue gases and in this process is ESP finds place in the power plant. In 21OMw 11OT of coal burns per hour and if coal contents 30% ash then ash carried along with flue gases will be 33Tonns\hr.
ADVANTAGES
1. Higher efficiency
2. Minimum cost
3. Low maintenance
4. Large volume of ash particle
5. Creates less pollution
DISADVANTAGES
1. High initial cost
2. Loss of efficiency when flow is above the desired rate
3. Unpredictable efficiency
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UPGRADATION & RETROFITTING OF POLLUTION CONTROL SYSTEMS: In order to keep pace with the changing norms and ensure compliance with statutory requirements in the field of pollution control, NTPC keeps an open mind for Renovation and Modernization (R & M) and Retrofitting and Up gradation of pollution monitoring and control facilities in its existing stations. It is important to mention that such modifications/retrofit programs not only helped in betterment of environment but also in resource conservation.
High efficiency Electro‐Static Precipitators (ESPs) of the order of 99.5% and above have been provided at NTPC stations for control of stack particulate emissions. However, the ESPs of a number of stations were built prior to the promulgation of the Environment (Protection) Act, 1986 and notification of emission control standards under this Act. Remedial measures have already been taken up and implemented to improve the efficiency of the existing ESPs at various NTPC stations. ESP performance enhancement programme by adopting advanced micro‐processor based Electrostatic Precipitator Management System (EPMS) was installed at its power stations at Singrauli, Ramagundam, Korba, Farakka, Rihand, Vindhyachal and Unchahar. Additional ESPs were retrofitted in the older power stations, namely at Badarpur and Talcher Thermal. As a result of the above retrofits, the emission of Suspended Particulate Matter (SPM) has been brought down appreciably at the above stations and is maintained within the present statutory limit of 150 mg/Nm3. In new projects, the ESPs have been designed for a maximum permissible outlet dust emission of 50 mg/Nm3 to meet the likely stringent emission norms in the near future.
RESOURCES CONSERVATION
With better awareness and appreciation towards ecology and environment, the organization is continually looking for innovative and cost effective solutions to conserve natural resources and reduce wastes. Some of the measures include:
• Reduction in land requirements for main plant and ash disposal areas in newer units. • Capacity addition in old plants, within existing land. • Reduction in water requirement for main plant and ash disposal areas through recycle and
reuse of water. • Efficient use of Fuel (Coal, Natural gas and Fuel oil) and • Reduction in fuel requirement through more efficient combustion and adoption of state‐of‐
the‐art technologies such as super critical boilers
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• COMPRESSOR HOUSE • CONTROL STRUCTURE PUMP HOUSE • ASH PUMP HOUSE • WTP • COOLING TOWER
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GAS COMPRESSOR
A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.
Centrifugal compressors
Centrifugal compressors use a rotating disk or impeller in a shaped housing to force the gas to the rim of the impeller, increasing the velocity of the gas. A diffuser (divergent duct) section converts the velocity energy to pressure energy. They are primarily used for continuous, stationary service in industries such as oil refineries, chemical and petrochemical plants and natural gas processing plants. Their application can be from 100 hp (75 kW) to thousands of horsepower. With multiple staging, they can achieve extremely high output pressures greater than 10,000 psi (69 MPa).
Diagonal or mixed‐flow compressors
Diagonal or mixed‐flow compressors are similar to centrifugal compressors, but have a radial and axial velocity component at the exit from the rotor. The diffuser is often used to turn diagonal flow to the axial direction. The diagonal compressor has a lower diameter diffuser than the equivalent centrifugal compressor.
Axial‐flow compressors
Axial‐flow compressors are dynamic rotating compressors that use arrays of fan‐like aerofoils to progressively compress the working fluid. They are used where there is a requirement for a high flows or a compact design.
The arrays of aerofoils are set in rows, usually as pairs: one rotating and one stationary. The rotating aerofoils, also known as blades or rotors, accelerate the fluid. The stationary aerofoils, also known as a stators or vanes, turn and decelerate the fluid; preparing and redirecting the flow for the rotor
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blades of the next stage. Axial compressors are almost always multi‐staged, with the cross‐sectional area of the gas passage diminishing along the compressor to maintain an optimum axial Mach number. Beyond about 5 stages or a 4:1 design pressure ratio, variable geometry is normally used to improve operation.
Axial compressors can have high efficiencies; around 90% polytropic at their design conditions. However, they are relatively expensive, requiring a large number of components, tight tolerances and high quality materials. Axial‐flow compressors can be found in medium to large gas turbine engines, in natural gas pumping stations, and within certain chemical plants.
Reciprocating compressors
Reciprocating compressors use pistons driven by a crankshaft. They can be either stationary or portable, can be single or multi‐staged, and can be driven by electric motors or internal combustion engines. Small reciprocating compressors from 5 to 30 horsepower (hp) are commonly seen in automotive applications and are typically for intermittent duty. Larger reciprocating compressors up to 1000 hp are still commonly found in large industrial applications, but their numbers are declining as they are replaced by various other types of compressors. Discharge pressures can range from low pressure to very high pressure (>5000 psi or 35 MPa). In certain applications, such as air compression, multi‐stage double‐acting compressors are said to be the most efficient compressors available, and are typically larger, noisier, and more costly than comparable rotary units.
Rotary screw compressors
Rotary screw compressors use two meshed rotating positive‐displacement helical screws to force the gas into a smaller space. These are usually used for continuous operation in commercial and industrial applications and may be either stationary or portable. Their application can be from 3 hp (2.24 kW) to over 500 hp (375 kW) and from low pressure to very high pressure (>1200 psi or 8.3 MPa). They are commonly seen with roadside repair crews powering air‐tools. This type is also used for many automobile engine superchargers because it is easily matched to the induction capacity of a piston Engine
Diaphragm compressors
A diaphragm compressor (also known as a membrane compressor) is a variant of the conventional reciprocating compressor. The compression of gas occurs by the movement of a flexible membrane, instead of an intake element. The back and forth movement of the membrane is driven by a rod and a crankshaft mechanism. Only the membrane and the compressor box come in touch with the gas being compressed.
There are four main types of compressors used at the Badarpur Thermal Power Station.
These are as follows: ‐
Densvevor Compressors: ‐
It is the most important compressor used at B.T.P.S. These are four in number. One Densveyor compressor is connected with each mill. It provides the primary as well as secondary air to the plant.
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These compressors are automatically operated. It carries the coal directly from the mills to the furnace. These compressors work under a maximum pressure of 8kgf.
Plant compressors: ‐
These compressors are two in number. Plant compressors are moisture type compressors.
These are mainly used for washing the ash formed in the furnace and disposing them off.
These compressors work under a maximum pressure of 8kgf.
Instrument compressors:‐
These are dry type compressors. These are used to operate different instruments. These compressors are three in number. These also work under a maximum pressure of 8kgf.
Blast air compressors: ‐
These compressors are smaller in size and are not as important as the other three types of compressors. The coal in the RC (raw coal) bunkers sometimes sticks to the surface of the bunkers due to moisture content in the coal. In such cases, blast air compressors are used to detach the coal from the surface of the RC (raw coal) bunkers.
TEMPERATURE
Compression of a gas naturally increases its temperature.
In an attempt to model the compression of gas, there are two theoretical relationships between temperature and pressure in a volume of gas undergoing compression. Although neither of them model the real world exactly, each can be useful for analysis. A third method measures real‐world results:
Isothermal ‐ This model assumes that the compressed gas remains at a constant temperature throughout the compression or expansion process. In this cycle, internal energy is removed from the system as heat at the same rate that it is added by the mechanical work of compression. Isothermal compression or expansion more closely models real life when the compressor has a large heat exchanging surface, a small gas volume, or a long time scale (i.e., a small power level). Compressors that utilize inter‐stage cooling between compression stages come closest to achieving perfect isothermal compression. However, with practical devices perfect isothermal compression is not attainable. For example, unless you have an infinite number of compression stages with corresponding intercoolers, you will never achieve perfect isothermal compression.
Adiabatic ‐ This model assumes that no energy (heat) is transferred to or from the gas during the compression, and all supplied work is added to the internal energy of the gas, resulting in increases of temperature and pressure. Theoretical temperature rise is T2 = T1∙Rc
(k‐1)/k, with T1 and T2 in degrees Rankine or kelvins, and k = ratio of specific heats (approximately 1.4 for air). R is the compression
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ratio; being the absolute outlet pressure divided by the absolute inlet pressure. The rise in air and temperature ratio means compression does not follow a simple pressure to volume ratio. This is less efficient, but quick. Adiabatic compression or expansion more closely model real life when a compressor has good insulation, a large gas volume, or a short time scale (i.e., a high power level). In practice there will always be a certain amount of heat flow out of the compressed gas. Thus, making a perfect adiabatic compressor would require perfect heat insulation of all parts of the machine. For example, even a bicycle tire pump's metal tube becomes hot as you compress the air to fill a tire.
Polytropic ‐ This model takes into account both a rise in temperature in the gas as well as some loss of energy (heat) to the compressor's components. This assumes that heat may enter or leave the system, and that input shaft work can appear as both increased pressure (usually useful work) and increased temperature above adiabatic (usually losses due to cycle efficiency). Compression efficiency is then the ratio of temperature rise at theoretical 100 percent (adiabatic) vs. actual (polytropic).
In the case of the fire piston and the heat pump, people desire temperature change, and compressing gas is only a means to that end.
STAGED COMPRESSION
Since compression generates heat, the compressed gas is to be cooled between stages making the compression less adiabatic and more isothermal. The inter‐stage coolers cause condensation meaning water separators with drain valves are present. In the case of small reciprocating compressors, the compressor flywheel may drive a cooling fan that directs ambient air across the intercooler of a two or more stage compressor.
Because of mechanical limitations and to increase efficiency, most compressors utilize staged compression, usually with intercooling between stages. In the case of centrifugal compressors, commercial designs currently do not exceed more than a 3.5 to 1 ratio in any one stage. Because rotary screw compressors can make use of cooling lubricant to remove the heat of compression, they very often exceed a 9 to 1 ratio. For instance, in a typical diving compressor the air is compressed in three stages. If each stage has a compression ratio of 7 to 1, the compressor can output 343 times atmospheric pressure (7 x 7 x 7 = 343 Atmospheres).
PRIME MOVERS
There are many options for the "prime mover" or motor which powers the compressor: gas turbines power the axial and centrifugal flow compressors that are part of jet engines. steam turbines or water turbines are possible for large compressors, electric motors are cheap and quiet for static compressors. Small motors suitable for domestic electrical supplies use single phase alternating current. Larger motors can only be used where an industrial electrical three phase alternating current supply is available. Diesel engines or petrol engines are suitable for portable compressors and support compressors used as superchargers from their own crankshaft power. They use exhaust gas energy to power turbochargers
Page | 33
CONTORL STRUCTURE PUMP HOUSE
The CSPH is just located near the entrance of BTPS at the left side of the way, the basic work of CSPH is to treat the raw water coming from the lake, this water is first treated in CSPH and then delivered to the other units such as WTP cooling tower ESP etc.
The water is received from lake is totally dirty and full of hard and thick impurities. The water is first screened of using the screen wash pump rotating continuously consisting of filter.
THE CSPH HAS FOLLOWING PUMPS:‐
S.NO. Name Number of pump in BTPS
Operating pressure
Use
1. CRW (clarify raw water pump)
3 1 kg To clarify raw water
2. FS (fire screening) 2 6 kg Fire fighting 3. HP (high pressure pumps) 6 6‐7 kg 2 used for cooling
turbine water, 3 for disposal of ash from ESP and 1 for pressuring low pressure pump
4. TWS (traveling water screening)
7 7 kg For screening of traveling water
5. LP (low pressure pumps) 3 2 – 2.5 kg For EP pump house 6. Chlorine pumps 2 For chlorination of water
ASH HANDLING
Ash utilization is one of the key concerns at NTPC. The Ash Utilization Division, set up in 1991, strives to derive maximum usage from the vast quantities of ash produced at its coal‐based stations. The division proactively formulates policy, plans and programme for ash utilization. It further monitors the progress in these areas and works at developing new fields of ash utilization.
Pumps used for ash handling:
S.NO. PUMP LUBRICANT CAPACITY 1. 1 Servo 57/68 oil 1000 m3/hr 2. 2 Servo 40 oil 1300 m3/hr 3. 3 Servo 40 oil 1300 m3/hr 4. 4 Servo 40 oil 1300 m3/hr
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The quality of ash produced conforms to the requirements of IS 3812. The fly ash generated at NTPC stations is ideal for use in cement, concrete, concrete products, cellular concrete, lightweight aggregates, bricks/blocks/tiles etc. This is attributed to its very low loss on ignition value. To facilitate availability of dry ash to end‐users all new units of NTPC are provided with the facility of dry ash collection system. Partial dry ash collection systems have also been set up at the existing stations where these facilities did not exist earlier. Augmentation of these systems to 100% capacity is presently in progress. As the emphasis on gainful utilization of ash grew, the usage over the years also increased. From 0.3 million tonnes in 1991‐1992, the level of utilization during 2006‐07 stood at over 20.76 million tonnes.
The various channels of ash utilization currently include use by a number of Cement, Asbestos‐Cement products & Concrete manufacturing Industries, Land Development, Roads & Embankments, Ash Dyke Raising, and Building Products. Area wise break‐up of utilization for the year 2006‐07 is as under:
Area of Utilization Quantity (in Million Tons)
Land Development 7.51
Cement & Concrete 7.40
Roads/Embankments 1.76
Ash Dyke Raising 2.69
Bricks 0.15
Mine Filling 0.61
Others 0.64
Total 20.76
NTPC has adopted user friendly policy guidelines on ash utilisation. These include actions identified for:
• Ash Collection & Storage System • Facilities & Incentives to users • Direct Department Activities • Administrative & Financial aspects.
In order to motivate entrepreneurs to come forward with ash utilisation schemes, NTPC offers several facilities and incentives. These include free issue of all types of ash viz. Dry Fly Ash / Pond Ash / Bottom Ash & infrastructure facilities, wherever feasible. Necessary help and assistance is also
Page | 35
offered to facilitate procurement of land, supply of electricity etc. from Govt. Authorities. Necessary techno‐managerial assistance is given wherever considered necessary. Besides NTPC uses only ash based bricks & portland pozzolana cement (FAPPC) in most of its construction activities. FAPPC (as per IS 1489 Part‐1) and Fly Ash Bricks (as per IS 12894) have been included in our standard specifications. Demonstration projects are taken up in area of Agriculture, Building materials, Mine filling etc.
NTPC continually strives to evolve innovative and diverse means of ash utilization to further broaden the scope. Prominent among the methods devised so far are:
• Dry Fly ash Extraction Systems • Use in cement & concrete • Use in Ash based products including setting up of • Ash Technology Park • Land Development/Wasteland Development, Roads & Embankments, Raising ash dykes' • Mine filling / Stowing • Agriculture
NTPC, Ash Utilization Division has brought out a booklet titled 'NTPC Guide for Users of Coal Ash' for distribution amongst prospective entrepreneurs and users of ash. It covers salient information about NTPC's power stations, facilities offered for setting up of ash based industry, statistics about ash production and its quality, brief write‐up about various technologies available for utilization of ash, list of equipment manufacturers, technology suppliers, agencies who may be approached for setting up the projects etc.
WTP AND GEO MILLER:
W.T.P.-I&II
The availability of suitable supply of water both for cooling purposes and for boiler feed make a in one of the basic requirement of the power station the water treatment plant is meeting this requirement the water which is used in the boiler circuit must be in very pure form to avoid corrosion of boiler tube scale formation on the inside surface of various parts and to avoid silica carryover to turbine corrosion tunes leads to its failure and this reduces boiler reliability scale formation leads to resistance to heat transfer and over hearting of the tube metal and thus causes frequent shut downs. Silica caries over from boiler gets deposited on relatively cold portion of turbine and create resistance to stream flow thrust reducing efficiency of turbine as the working pressure and temperature of boiler goes high with unit size increasing the requirement of very pure water becomes even more stringent therefore the main object of the WTP is to remove impurities of water being sent to boiler in order that the steam generated is pure and boiler can give an uninterrupted surface.
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GEOMILLER
The name given to this unit is because 'geo miller' named company built it and started it.
Its main function is to make water pure and clean.
The raw water coming from CRW goes into the tank where alum and chlorine are added to it. With the help of chlorine and alum all the mud and dust settles down and clean water is taken from above. From there it goes to two separate tanks and from there 7 pumps 4 of 100Mw and 3 of 21OMw power takes the water to various sections such as WTP‐I & II etc.
CLARIFLOCULA TOR
To the chlorinated raw water chemical are added in the form of solution and through violet turbulence chemical are adequately mixed in a flash mixer tank the water is then lead to central chamber of clarifloculator having rotatory type of arrangement here with slow motor given to water the newly formed flew is repeatedly brought into impact with other flow particles and they attack themselves together in large masses which settles quickly the water is then allowed slowly to come in other chamber the also has slow rotating arrangement
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MIXED BED EXCHANGER
The water from the cation exchangers enters the final treatment unit for removing the traces of impurities remaining in the anion treated water ~e mixed exchanger is milled steel rubber lines pressure vessels externally fitted with manual and pneumatic valve the internal includes and inlet water distributor, caustic soda distributor for the regeneration of anion resins.
Specifications:‐
1). CLARIFLOCULATOR
Dimension ‐ 13715 mm diameter
Metal construction‐ RCC
Flow rate ‐ 200m3/hr
2). ALUM DISSOLVER TANK
1500 mm diameter x 1500 mm deep
Metal of construction‐ ms
3). ALUM SERVICE TANK
1370 mm diameter X 120 deep
Metal of construction‐ MS
4).CATION EXCHANGER
4 numbers
Dimension ‐ 1676 mm diameter
Material of construction ‐ ms
Qty. ‐ 30% HCL
Minimum flow ‐ 10m3/hr
Maximum flow ‐ 35m3/hr
Page | 38
5).ANION EXCHANGER
4 numbers
Dimension ‐ 1676 diameter
Material of construction ‐ MS
Minimum flow ‐ 10m3/hr
Maximum flow ‐ 35m3/hr
Net flow rate ‐ 25m3/hr
6).MIX BED EXCHANGER
4 numbers
Quantity ‐ 30% HCL + 30caustic soda
Dimension ‐ 762 diameter
Material of construction ‐ ms
Minimum flow ‐ 2m3/hr
Maximum flow ‐ 26.8m3/hr
THE COOLING TOWER
CIRCULATING WATER SYSTEM AND COOLING TOWER
The circulating water is use for the condenser to condense the exhaust steam form the turbine since sum change of state takes place therefore the vacuum is crated inside the condenser for the degree of vacuum will depend upon the extent of cooling and thus on the quantity of circulating water and its temperature it is therefore desirable that this water should be of low temp. when the water is obtained from the lake, canal, river etc the requirement may be about 59 gallons per hour per kilo watt of the plant this sis sum what high for cooling water system the cooling effect in the cooling tower depends upon the wet bulb temperature of the atmosphere and addition of 10 % capacity of tower may be required during summer cooling tower are used lager size stations there is a
Page | 39
temperature to favour cooling tower even for the medium size station due to the other advantages is that closed approach the wet bulb temp is permissible through these.
The cooling tower is wooden steel concrete structure inside which is provided with an arrangement of wooden check or work perforated trays etc at the bottom is a reservoir for storage of cooled water warm water is fed to the tower on the top and is allowed to pass into these sheet through trace while airflows form the bottom of tower to top there is a good contact of air and water with the result of that the latter is cooled and fills in the reservoir air passing out at the top to prevent the escape of water particles drift eliminator are simple construction are made of few rows of blades places inclined to each other and provide a zig zag path of air system the moisture its deposited on the blades and falls back in the tank.
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MAIN TURBINE
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into useful mechanical work.
It has almost completely replaced the reciprocating piston steam engine (invented by Thomas Newcomen and greatly improved by James Watt) primarily because of its greater thermal efficiency and higher power‐to‐weight ratio. Also, because the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator; about 80% of all electric generation in the world is by use of steam turbines. — it doesn't require a linkage mechanism to convert reciprocating to rotary motion. The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency through the use of multiple stages in the expansion of the steam (as opposed to the one stage in the Watt engine), which results in a closer approach to the ideal reversible process.
Types
Steam turbines are made in a variety of sizes ranging from small 1 hp (0.75 kW) units (rare) used as mechanical drives for pumps, compressors and other shaft driven equipment, to 2,000,000 hp (1,500,000 kW) turbines used to generate electricity. There are several classifications for modern steam turbines.
Steam Supply and Exhaust Conditions
These types include condensing, no condensing, reheat, extraction and induction.
Noncondensing or backpressure turbines are most widely used for process steam applications. The exhaust pressure is controlled by a regulating valve to suit the needs of the process steam pressure. These are commonly found at refineries, district heating units, pulp and paper plants, and desalination facilities where large amounts of low pressure process steam are available.
Condensing turbines are most commonly found in electrical power plants. These turbines exhaust steam in a partially condensed state, typically of a quality near 90%, at a pressure well below atmospheric to a condenser.
Reheat turbines are also used almost exclusively in electrical power plants. In a reheat turbine, steam flow exits from a high pressure section of the turbine and is returned to the boiler where additional superheat is added. The steam then goes back into an intermediate pressure section of the turbine and continues its expansion.
Extracting type turbines are common in all applications. In an extracting type turbine, steam is released from various stages of the turbine, and used for industrial process needs or sent to boiler feed water heaters to improve overall cycle efficiency. Extraction flows may be controlled with a valve, or left uncontrolled. Induction turbines introduce low pressure steam at an intermediate stage to produce additional power.
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Page | 43
Impulse Turbines
An impulse turbine has fixed nozzles that orient the steam flow into high speed jets. These jets contain significant kinetic energy, which the rotor blades, shaped like buckets, convert into shaft rotation as the steam jet changes direction. A pressure drop occurs across only the stationary blades, with a net increase in steam velocity across the stage.
As the steam flows through the nozzle its pressure falls from steam chest pressure to condenser pressure (or atmosphere pressure). Due to this relatively higher ratio of expansion of steam in the nozzle the steam leaves the nozzle with a very high velocity. The steam leaving the moving blades is a large portion of the maximum velocity of the steam when leaving the nozzle. The loss of energy due to this higher exit velocity is commonly called the "carry over velocity" or "leaving loss".
Reaction Turbines
In the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor. Steam is directed onto the rotor by the fixed vanes of the stator. It leaves the stator as a jet that fills the entire circumference of the rotor. The steam then changes direction and increases its speed relative to the speed of the blades. A pressure drop occurs across both the stator and the rotor, with steam accelerating through the stator and decelerating through the rotor, with no net change in steam velocity across the stage but with a decrease in both pressure and temperature, reflecting the work performed in the driving of the rotor.
Operation and Maintenance
When warming up a steam turbine for use, the main steam stop valves (after the boiler) have a bypass line to allow superheated steam to slowly bypass the valve and proceed to heat up the lines in the system along with the steam turbine. Also a turning gear is engaged when there is no steam to the turbine to slowly rotate the turbine to ensure even heating to prevent uneven expansion. After first rotating the turbine by the turning gear, allowing time for the rotor to assume a straight plane (no bowing), then the turning gear is disengaged and steam is admitted to the turbine, first to the astern blades then to the ahead blades slowly rotating the turbine at 10 to 15 RPM to slowly warm the turbine.
Problems with turbines are now rare and maintenance requirements are relatively small. Any imbalance of the rotor can lead to vibration, which in extreme cases can lead to a blade letting go and punching straight through the casing. It is, however, essential that the turbine be turned with dry steam. If water gets into the steam and is blasted onto the blades (moisture carryover) rapid impingement and erosion of the blades can occur, possibly leading to imbalance and catastrophic failure. Also, water entering the blades will likely result in the destruction of the thrust bearing for the turbine shaft. To prevent this, along with controls and baffles in the boilers to ensure high quality steam, condensate drains are installed in the steam piping leading to the turbine.
Speed regulation
The control of a turbine with a governor is essential, as turbines need to be run up slowly, to prevent damage while some applications (such as the generation of alternating current electricity) require precise speed control. Uncontrolled acceleration of the turbine rotor can lead to an overspeed trip, which causes the nozzle valves that control the flow of steam to the turbine to close. If this fails then
Page | 44
the turbine may continue accelerating until it breaks apart, often spectacularly. Turbines are expensive to make, requiring precision manufacture and special quality materials.
The turbines used in BTPS are like as shown in figure:
• It have 31 stages • HP and IP are single side forced • LP is double side forced • HP have 12 stages, 12 moving and 12 fixed blades • IP have 11 stages, 11 moving and 11 fixed blades • LP have 4 stages, 8 moving and 8 fixed blades
The complete turbine assembly is mounted on foundation frames pedestals and sale plate is designed that the component are free to expand or control utilizes correct alignment is maintained during start up shut down and through the working temperature range.
In 210Mw the pressure is 120kg/cm2 and rotates at 3000rpm. Rated quantity of circulating water through condenser is 27000 cubic meter/hr.
The high super heated steam is passes on the blades of turbine, so that it rotates very high speed and produces the power with the attachment of turbine. The generator which is connected with the turbine is rotates with the rotation of turbine and produced electricity.
In working of turbine first MS ‐4, MS‐5, MS‐6, MS‐3 valves are opened then ESV (emergency steam valve) situated at right or left is opened. Then steam is entered in HPT.
The turbine has a governing system consists of main oil pump (MOP) for supplying the oil to turbine. During the operation the oil becomes dirty. For purifying the oil 12 filter are maintained. In which 6 has thick sieves and another 6 has thin sieves. The dirty oil first passed in thick sieves and then passed to thin sieves. The oil is provided in the main oil tank which contains 28000 litre oil.
Page | 45
When steam entered in the turbine control valve 1,2,3,4 are opens. Rotor of turbine is placed between the pads, the fire pads are at the top of rotor and another fire is at the bottom of rotor. When steam passed the turbine some steam are rejected. The rejected steam are collected in intermediate cylinder and passed to condenser for reheating, so that once again high pressure steam is entered in the furnace. The trust bearing are placed in the middle of turbine. During the operation some steam are leakages. The leakage steam are collected in gland steam cooler and passed to LPH to HP to economiser to super heater to boiler drum for making pure steam.
The internal temp of the turbine is 360C.
When the turbine shut down it should ensured that the rotor is not suddenly stopped instantly or in other words it should not be stopped at high speed. Since when the rotor is stopped suddenly the high pressure steam forced on the blades of turbine and damages it.
So when the rotor is stopped its temp is about 80'C. This is done with the help of bearing gear. Then the turbine shut down a lever on bearing gear is down on right side. A 30KW three face induction motor running at 730r.p.m. forms the main driving force of bearing gear which gives the slow rotation of the turbine rotor.
C.W. BOOSTER PUMP
Cooling water booster is used for cooling form turbine to boiler. It has single and single discharge. The pressure of CW booster pump is 3 to 4Kg/Cm2. The CW booster pump provides the raw water from turbine to boiler for cooling the plant. It takes the water from
CW pumps and provides the plant.
In 100 MW booster pump has a double suction and single discharge. It means two way of inlet water and one way of outlet water. It discharge pressure is very between 1.5 to
2Kg/cm2
CONDENSER
A condenser involves the transformation of water vapor to liquid by mechanical means. Although water is one of the most of versatile liquids on earth, it can be difficult to isolate water going from one phase to another. Thus, condensers are devices involved in the dehumidification of air. There are generally three methods to dehumidify air; absorption of water vapor by a liquid solution, adsorbent materials (silica gel or activated alumina), and shell and tube convection.
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In BTPS the type of condenser used is a simple shell and tube condenser.
The condenser used in 210 mw unit has
• 17,000 pipes • Inner diameter of 26mm • Outer diameter of 27mm • And are 10m long
The condenser used in 95mw unit has
• 14,800 pipes • Inner diameter 26mm • Outer diameter 27mm • And are 10m long
VALVE
A valve is a device that regulates the flow of materials (gases, fluidized solids, slurries, or liquids) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but usually are discussed separately.
Types/Designations
Valves can be categorized into the following design types and although there are hundreds of variations they all fit into these basic types:
• Gate • Plug • Globe • Check • Butterfly • Diaphragm • Ball • SOLENOID • NEEDLE • HYDRAULIC
Also the valves can be classified as:
• Conventional Valve • Severe Service Valve
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Valve parts
Body and Bonnet
The main part of the valve consists of the valve body and bonnet. These two parts form the vessel or casing that holds the fluid going through the valve. Valve bodies are usually metallic. Brass, bronze, cast or ductile iron, steel, alloy steels and stainless steels are very common. Plastic bodies are used for relatively low pressures and temperatures. PVC, PP, PVDF and glass‐reinforced nylon are common plastics used for valve bodies.
Ports
Integral to the valve body are the passages that allow flow into and out of the valve. These are called ports. These ports are obstructed or opened up by the valve member or disc to control the fluid flow. Valves with two or three ports are the most common, while valves with multiple ports (up to 20) are used in special applications. Nearly all valves are built with some means of connection at the ports. These include Threads (male or female); BSP or NPT are most common. Compression fittings, to suit tube s/s or copper. Glue or cement application (especially for plastic) almost always a socket type connection (not a butt) Flanges ANSI, BS, DIN, or JIS. (US, British, European, Japanese standards) Welding either Socket type or Butt type welds.
Disc / Rotor / Valve Member
Inside the valve body, flow through the valve may be partly or fully blocked by an object called a disc or valve member. Although valve discs of some kinds of valves are traditionally disc‐shaped, discs can come in various shapes. Although the valve body remains stationary within the fluid system, the disc in the valve is movable so it can control flow. A round type of disc with fluid pathway(s) inside which can be rotated to direct flow between certain ports is usually called a ball. Ball valves are valves which use spherical rotors, except for the interior fluid passageways. Plug valves use cylindrical or conically tapered rotors called plugs. Other round shapes for rotors are possible too in rotor valves, as long as the rotor can be turned inside the valve body. However not all round or spherical discs are rotors; for example, a ball check valve uses the ball to block reverse flow, but is not a rotor because operating the valve does not involve rotation of the ball.
Seat
The valve seat is the interior surface in the body which contacts or could contact the disc to form a seal which should be leak‐tight when the valve is shut. If the disc moves linearly as the valve is controlled, the disc comes into contact with the seat when the valve is shut. When the valve has a rotor, the seat is always in contact with the rotor, but the surface area of contact on the rotor changes as the rotor is turned. If the disc swings on a hinge, as in a swing check valve, it contacts the seat to shut the valve and stop flow. In all the above cases, the seat remains stationary while the disc or rotor moves. The body and the seat could both come in one piece of solid material, or the seat could be a separate piece attached or fixed to the inside of the valve body, depending on the valve design.
Seats can be integral to the valve body, that is "hard" metal or plastic. Nearly all metal seated valves leak, even though some leaks are extremely small.
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"Soft" seats can be fitted to the valve body and made of materials such as PTFE or various elastomers such as NBR, EPDM, and FKM. Each of these soft materials is limited by temperature (rough maximum temperatures are listed below)
NBR 80 °C
EPDM 120 °C
FKM 170 °C
PTFE 200 °C
The advantage of soft seats is that they are more likely to offer 100% tight shutoff when valve is closed.
There are advantages of hard seated Valves as well in applications where there is heavy erosion due to the material flowing from the pipes then the metal seated valves are preferred over soft seated valves.
Metal seated Valves have longer life as well.
Gate Valves, Globe Valves, Check Valves are usually hard seated Valves and Butterfly Valves, Ball Valves, Plug Valves, Diaphragm Valves are Usually soft seated Valves.
Though there are some special cases where we do have hard seated Butterfly Valves and Hard seated Ball Valves as well.
Stem
The stem is a rod or similar piece spanning the inside and the outside of the valve, transmitting motion to control the internal disc or rotor from outside the valve. Inside the valve, the rod is joined to or contacts the disc/rotor. Outside the valve the stem is attached to a handle or another controlling device. Between inside and outside, the stem typically goes through a valve bonnet if there is one. In some cases, the stem and the disc can be combined in one piece, or the stem and the handle are combined in one piece.
The motion transmitted by the stem can be a linear push or pull motion, a rotating motion, or some combination of these. A valve with a rotor would be controlled by turning the stem. The valve and stem can be threaded such that the stem can be screwed into or out of the valve by turning it in one direction or the other, thus moving the disc back or forth inside the body. Packing is often used between the stem and the bonnet to seal fluid inside the valve in spite of turning of the stem. Some valves have no external control and do not need a stem; for example, most check valves. Check valves are valves which allow flow in one direction, but block flow in the opposite direction. Some refer to them as one‐way valves.
Valves whose disc is between the seat and the stem and where the stem moves in a direction into the valve to shut it are normally‐seated (also called 'front seated'). Valves whose seat is between the disc and the stem and where the stem moves in a direction out of the valve to shut it are reverse‐seated (also called 'back seated'). These terms do not apply to valves with no stem nor to valves using rotors.
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Bonnet
A bonnet acts as a cover on the valve body. It is commonly semi‐permanently screwed into the valve body. During manufacture of the valve, the internal parts are put into the body and then the bonnet is attached to hold everything together inside. To access internal parts of a valve, a user would take off the bonnet, usually for maintenance. Many valves do not have bonnets; for example, plug valves usually do not have bonnets.
Spring
Many valves have a spring for spring‐loading, to normally shift the disc into some position by default but allow control to reposition the disc. Relief valves commonly use a spring to keep the valve shut, but allow excessive pressure to force the valve open against the spring‐loading. Typical spring materials include carbon steel (often cad plated), 304 Series stainless steels and for high temperature applications Inconel X750. Springs can be typical 'coil' types or 'bellville" washer stacks or even bimetallic elements which exert a spring force on temperature change.
Valve balls
A valve ball is also used for severe duty, high‐pressure, high‐tolerance applications. They are typically made of stainless steel, titanium, Stellite, Hastelloy, brass, or nickel. They can also be made of different types of plastic, such as ABS, PVC, PP or PVDF.
Material of valve:
• Cast iron • Brass • Bronze • Gun metal • Carbon steel • Cast steel • Alloy steel • Some small parts are made up of stainless steel.
Operative type
• Hand operated valve • Electrically operated valve • Hydraulic or pneumatically controlled valve •
Sealing material
• Gas cut sheet Non‐metallic (fiber, asbestos, graphite and grease) Metallic (a composite is formed using non‐metallic material as stated above and wires)
• Gland packing Rope (circular or rectangular cross section, metallic or non‐metallic)
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CONDENSATE PUMP GROUP
Its main function is to take water from condenser and supply to diameter.
Condensate pump has mainly 2 types of pumps i.e. 95Mw & 210Mw
100 MW
• It has 2 shafts • It has 4 stages • It has 4 impeller, 3 impeller made of brass and 1 impeller‐made of mild steel. • It has a diffuser to keep the pressure constant.
210MW
• It has 2 shafts • It has 8 stages • It has 8 impeller out of which 2 impeller is for emergency leak pump. • It has barrel coupling
BOILER FEED PUMP
B.F.P. takes water from dieter & provides it to boiler drum passing through H.P heater.
Suction pressure of 100mw ‐ 8kg/cm2
Suction pressure of 210mw ‐ 12kg/cm2
Recharge pressure of 100mw ‐ 150kg/cm2
Recharge pressure of 210mw‐ 150‐200kg/cm2
R.P.M. of 100mw ‐ 3000
R.P.M.of210mw ‐ 4000 or more
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In 100MW motor is directly coupled whereas in 210MW motor & pump are coupled with a hydraulic gear box.
Inside discharge rate, there is a balancing chamber inside the pump which is used to keep the balance of rotor or the pump. The pressure of balancing leads off is outside the pressure of section of the feed pump. After balancing leak off the feed water which is left behind then goes to the seal water cooler from estaping box through pumping. In seal water cooler circular coil is made which is fed by hot water & the remaining cooler is filled with cold water & the water in the coil also becomes cool. Balancing chamber is made of two discs one is bearing disc and the other is balancing disc. The bearing disc is fitted to the body and the balancing disc to the rotating with same speed.