Summer Training Training Project Project Report On Coal-Fired Steam Power Plants
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NATIONAL THERMAL THERMAL POWER CORPORATION CORPORATION SIPAT (CHhATTISG (CHhATTISGARH) ARH) (SUBMITTED TOWARDS COMPLETION OF VOCATIONAL TRAINING AT NTPC SIPAT)
Under the guidance of ::-
Submitted by:-
Shri U.R.Verma
Dinesh Kumar
DGM, Boiler Maintenance Maintenanc e
Mechanical Engg.(4th sem)
Department
I.I.T.Kharagpur
Declaration Declaration by Student I hereby declare that work entitled “Summer training project report”, submitted towards completion of vocational training after 2nd year of B.Tech (Mechanical Engineering) at Indian Institute of Technology Kharagpur comprises of my original work pursued under the supervision of Guides at N TPC Si . Si pat The results embodied in this report have not been submitted to any other Institute or University for the fulfillment of any other curriculum.
Name:- Dinesh Kumar Roll No:- 10ME10016 B.tech (4th Semester) I.I.T. Kharagpur West Bengal
This is to certify that Mr. Dinesh Kumar of Indian Institute of Technology Kharagpur has undergone Vocational training from 21/05/2012 to 18/06/2012 at National Thermal Power Corporation, Sipat in the Boiler Maintenance Department and has made the project under my guidance.
Project Guide
Shri U.R.Verma Deputy General Manager Boiler Maintenance department
Acknowledgement “It is not possible to prepare a project report without the assistance & encouragement of other people. This one is certainly no exception.”
On the very outset of this report, I would like to extend my sincere and heartfelt obligation towards all the personages who have helped me in this endeavor. Without their active guidance, help, cooperation and encouragement, I would not have made head way in the project. First and foremost, I would like to express my sincere gratitude to my project guide, Shri U.R.Verma . I was privileged to experience a sustained enthusiastic and involved interest from his side. This fuelled my enthusiasm even further and encouraged me to boldly step into what was a totally dark and unexplored expanse before me. He always fuelled my thoughts to think broad and out of the box. I would also like to thank Mr. Dibtendu Mandal who, instead of his busy schedule, always guided me in right direction to head and also helped in understanding the Rotary parts of Boiler. Last but not least, I would like to thank Mr. Girish Choudhary and Mr. Rishabh Kapoor for teaching and helping me in every sphere of rotary and pressure parts respectively. I would like to thank Employee development Centre for organizing and permitting the Vocational training program for us.
Thanking you, Dinesh Kumar
POWER SECTOR IN INDIA Power sector plays a very vital role in overall eco nomic growth of any country. For Indian perspective, the power sector needs to grow at the rate of at least least 12% to maintain the present GDP growth of about 8%. As per the Ministry of Power report, the per capita co nsumption of electricity electricity is expected to grow to 1000 kWh / year by the year 2012 which during the year 2004 – 2004 – 2005 2005 was 606 kWh/year. To meet the t he per capita consumption of 1000 kWh/year by the year 2012 the capacity augmentation requirement requ irement is about 1,00,000 MW. Presently there is a significant gap between the demand and supply of power. The energy deficit de ficit is about 8.3% and the power po wer shortage during the peak demand is about 12.5%.
NATIONAL THERMAL POWER CORPORATION LIMITED th
NTPC Limited is the largest power generation company in India. Fo rbes Global 2000 for 2009 ranked it 317 in the world. It is an Indian public sector company listed on the Bombay Stock Exchange E xchange although at present the Government of India holds 84.5% of its equity. With a current generating capacity of 32,694 MW, NTPC has embarked on plans to become a 75,000 MW company by 2017. It was founded on November 7, 197 5 with 100% ownership of the Central government. In 1997, Government Government of India granted NTPC status of “Navratna‟ being one of the nine jewels of India, enhancing the powers to the Board of Directors. Directors. NTPC became a Maharatna company in May, May, 2010, one of the only four companies to be awarded this this status.|~|
NTPC‟s core business core business is engineering, engineering, construction and operation of power generating plants and providing consultancy to power utilities in India and abroad. The total installed capacity of NTPC in India is as follows follows at present:
NO. OF PLANTS
NTPC Owned Coal Gas/Liquid Fuel Total Owned By JVs Coal & Gas Total
CAPACITY (MW)
15 7 22
25,375 3,955 29,330
5 27
3,364 32,694
NTPC has been operating its plants at high efficiency levels. levels. Although the company has 18.10% of the total national capacity, it co ntributes 28.60% of total power generation due to its focus on high e fficiency.
Location
:
22 Km from Bilaspur, CG
Capacity
:
3 X 660 MW Stage-I and
2 X 500 MW Stage-II
Water Source
:
From Hasdeo right bank canal
Coal Mines
:
Dipika Mines of SECL Korba.
Coal Transport
:
By dedicated MGR (42 Kms)
Highlights: * Super Critical Technology first time in India *765 KV Transmission System first time in India *100 Mtr. wide peripheral green belt around the pro ject *Submerged ash dyke *State-of-the-art Technology for Environmental Management NTPC Sipat Super Thermal Power Project is a cynosure of power generation generation in India. It is a priceless gem of mineral rich state of Chhattisgarh. Chhattisgarh. Being in the vicinity of Bilaspur, the second largest city of Chhattisgarh Chhattisgarh and at the vertex of transport arteries adds to its majestic aura. Total installed capacity of the Sipat Super Thermal Power Project is 2980 MW (Stage I -660 X 3 & Stage II-500 X 2 MW). Plant‟s water requirement is catered by Hasdeo right bank cana l. It gets coal supply supply from Dipika mines of SECL, Korba. The co al is transport via dedicated MGR system of total length 42 km. Sipat Super Thermal Power Project has many acco lades to its credits. Being a pioneer of Super Critical Technology in India and transmission system of 766 kV for the first time in India are the most unique att ributes. Addressing this most pressing need of the hour, i.e. o ur environment, Sipat Project has 100 meter wide peripheral green belt, submerged ash dykes and state-of-the art technology for environment management.|~|
The basic principle of the working of a thermal power plant is quite simple. The fuel used in the plant is burned in the boiler, and the heat thus generated is used to boil water which is circulated through several tubes, and the steam that is generated is then used to drive a turbine, which in turn is coupled with a generator, which then produces electricity. The working of the coal based plant is based upon a modified Rankine cycle . The Rankine cycle is represented most commonly on a temperature-entropy diagram. The topmost point is known as the critical point.
Typical diagram of a thermal power plant :1. Cooling tower
10. Steam Control valve
2. Cooling water pump
11. High pressure steam turbine 20. Forced draught (draft) fan
3. transmission line (3-phase)
12. Deaerator
21. Reheater
4. Step-up transformer (3-phase)
13. Feedwater heater
22. Combustion air intake
5. Electrical generator (3-phase)
14. Coal conveyor
23. Economiser
6. Low pressure steam turbine
15. Coal hopper
24. Air preheater
7. Condensate pump
16. Coal pulverizer
25. Precipitator
8. Surface condenser
17. Boiler steam drum
26. Induced draught (draft) fan
18. Bottom ash hopper
27. Flue gas stack
9. Intermediate pressure steam turbine
1)
19. Superheater
COAL HANDLING PLANT (C.H.P):- Coal Handling Plant is the place where processing of raw
coal occurs before it is transferred to the bunkers. CHP enhances the calorific value of coal and makes its transportation cost lower and easier. The coal is provided by the Deepika mines under the S.E.C.L, with the help of a dedicated merry-go-round (MGR).When (MGR).When the coal is supplied at the CHP, the coal is moved along the track hopper towards the crusher, where the lumps of coal are crushed into 20 mm sized particles, from where they may be stored in the stack-yard, or sent to the bunkers before being fed into the boilers bo ilers..
Salient Features of CHP Stage-I : •
Conveyor Capacity – Capacity – 2000/2600MTPH 2000/2600MTPH
•
Conveyor Width – Width – 1600 1600 mm
•
Paddle Feeder cap- 1500MTPH
•
Crusher Capacity- 1250MTPH
•
SR Capacity-2000mtph • •
Inter Connection Between ST-1&ST-2 PLC Based Operation
Salient Features of CHP Stage-II : •
Conveyor Capacity – Capacity – 2600 2600 MTPH
•
Conveyor Width - 1800 mm
•
Conveyor Speed – Speed – 3.2 3.2 m/sec
•
Paddle Feeder capacity- 1950 MTPH
•
VGF Capacity – Capacity – 1625 1625 MTPH
•
Crusher Capacity – Capacity – 1625 1625 MTPH
•
STACKER /RECLAIMER Capacity- 2600MTPH
•
CCTV compatible to integrated FIRE ALARM
•
PLC Based Operation
•
Lifts at Crusher House & TP19
•
Inter Connection between ST-1&ST-2
SYSTEM
2) MILL:
The coal particles are ground into finer sized granules. The coal which is stored in the bunker is
sent into the mill, which is primarily a ball type, in which a drum contains a ball, and when the drum rotates the ball also does, and this causes the coal particles caught in between to be ground. After grinding, the coal is then passed through a desired size of mesh, so that any coal particle not properly ground is not allowed through. Then the coal is forced by a blast of air coming from the primary air fans to enter the boiler. Coal is fed to the t he mills from from the bunkers via v ia the raw coal feeders. Another type of mill is the ball and race mill, in which the coal passes between the rotating elements again and again until it has been pulverized to the desired degree of fineness. However, there is greater wear in this mill as compared to other pulverizers. There are 10 mills located adjacent to the furnace. These mills pulverise coal to the desired fineness to be fed to t he furnace for combustion. Capacity of 1 mill is 62.9 tonnes/hr.
Factors affecting bowl mill performance:
Size of raw coal
Raw coal grindability
Raw coal moisture content
Pulverised fuel fineness
Mill internals wear and poor quality of raw co als.
Mill drive system mainly consists of three components namely mill motor, mill coupling and mill gear box. Mill coupling comprises of Bibby coupling (present on the motor side) and gear coupling (present on the gear box side). In a bowl mill, the major grinding element grinding roll is conical in shape and is three in number per mill
INTERIOR OF BOWL MILL 3) WATER TREATMENT PLANT:
Since water is the basic requirement for the production of the
working substance, it is necessary to have an arrangement to provide water which is not contaminated by unwanted materials. For this a water treatment unit is provided which receives water from a source, then demineralizes it and finally after further treatment, is fed into a boiler feed pump. This is a unit which consumes relatively low power compared to other units in a power plant. Some of the systems involved in the treatment of water are de-mineralization plant, raw water pump house, clarification plant and many others. The type of water used is different for different purposes. The process of cooling requires raw water, whereas steam formation, and many other major processes require de -mineralized water. De-mineralization plants consist of cation, anion and mixed bed exchangers. The final water from this stage consists of hydrogen ions and hydroxyl ions w hich is the chemical composition of pure water. wat er.
4) BOILER:
A boiler is the central component of a power plant, and it is the unit where the steam
required for driving the turbine is generated. The heat absorbing parts subject to internal pressure in a boiler are called as pressure parts. The main pressure parts in a boiler are Drums, Water walls, Super heaters, Re heaters, Economisers and valves & fittings. The Drum, Down comers, water wall headers and water walls forms the circulation system and cover the furnace zone. The components of Boiler and their functions are as follows :-
a)Boiler Drum: The drum provides the necessary space for locating the steam separating equipment for separation of steam from mixture of steam and water. It also serves as a reservoir for the supply o f water
to circulation system to avoid possible starvation during operation. The drum is filled with water coming from the economizer, from where it is brought down with the help of down-comer tubes, entering the bottom ring headers. From there they enter the t he riser, which carries carr ies the water (which now is a liquid-vapor mixture), back to the drum. Now, the t he steam is sent to be superheated. For a 660 MW plant, the boiler does not employ any drum; instead the water and steam go directly into the super heater. Drum is located at 78 m elevation in the boiler front. Water enters the drum from the bottom via three ECO links. Drum has connections for Chemical dozing, Emergency drain, Continuous blow down & sample cooler tapping. Total 5 no. of vents and 6 no of safety valves, 3 on each side are provided on the drum. Total 18 MTM thermocouples, 6 no of level transmitters, 3 pressure transmitters and 3 pressure indicators are provided on the drum. There are 2 no of Electronic Water Level Indicators (EWLI) and 1 no of Direct Water Level Gauge (DWLG) provided on each side of the drum.
b) Economiser:
The economizer is a tube-shaped structure which contains water from the boiler feed
pump. This water is heated up by the hot flue gases which pass through the economizer layout, which then enters the drum. The economizer is usually placed below the second pass of the boiler. As the flue gases are being constantly produced due to the combustion of coal, the water in the economizer is being continuously being heated heat ed up, resulting in the formation of steam to a partial extent. Feedwater (FW) from Feed Regulating Station (FRS) with parameters P=200.2 ksc, T=255.2 C travels to Economiser inlet header located at Elevation 44.2m through ECO feed line. ECO feed line connects to the ECO inlet header at the right side of boiler backpass. One NRV and a nd motorised moto rised ECO sto p valve is provided in the ECO feed line just before it connects to the ECO inlet header. One no of drain is also provided in the ECO feed line just after the ECO stop valve. The drain is connected to the water wall (WW) drain header located at „0‟ meter. One no of ECO recirculation line is provided after the ECO stop valve which w hich connects to the rear ring header. ECO in let heade header: r: - It is arranged parallel to the drum at the bottom of backpass middle at the elevation 44.2m.
One no of drain is provided in the header. The drain is connected to the WW drain header.192 x 3 loose tubes connect the ECO inlet header to t he ECO lower assembly. ECO outl et heade header: r: - Located at the Elevation 57.5m, it is arranged parallel to the drum in backpass. Two
links from ECO outlet header project out from back pass side walls and join again at the boiler front at 66.5m elevation. From this junction three pipes carry feed water to the drum.
c) CC Pumps:-
Six no. of Downcomers carry feedwater(FW) from drum to suction manifold of CC
Pumps located at 29.5m elevation. 3 no. of suction spool pieces carry FW from suction manifold to the 3 no. of CC Pumps located at 23.3m elevation. The pumps are of double discharge type. Parameters at the pump: P=197.4 ksc, 359.1 C and flow/pump= 3135 cu.m/hr. Connections to the pump include HP fill and purge lines, LP coolant lines. Inter tie line connecting discharges of all pumps. One equalising line from the center pump suction connects to the intertie line. Two no of coolers are also provided: HP Fill and Purge Cooler and LP Co oler for motor. Source of HP fill & Purge is from 1. Feed line (for periodic use) 2. From Condensate system (low pressure fill source). Source of LP coolant supply: 1. Normal supply 2. From Emergency tank
d) Bottom Ring Header :- The 6 no. of CC pump discharge lines carry FW to the bottom ring header located at 10.6m. Ring header is provided with one no of blow off line from front ring header which is connected to the IBD Tank. One no of drain is also provided from the rear ring header which is connected to the WW drain header. ECO recirculation line also co nnects to the rear ring header.
e) Water walls:- 331
tubes each from front & rear ring headers form the front, rear and corner water
walls. There are 25 tubes in each corner wall & 281 tubes in front and rear water walls each. Front water wall is integral with the corners 1 & 4 and rear wall is integral with the corners 2 & 3. Each side water wall (Left & Right) has 224 tubes. All water wall tubes are rifled from inside except the „S‟ panel tubes. Total no of tubes originating from Bottom ring header = 331x2 + 224x2 = 1110. In a 500 MW unit, the water walls are of the vertical type, and have rifled tubing while in 600 MW, the water walls are spiral type and have smooth tub ing.
F) De-aerator : A de-aerator is a device that is widely used for the removal of air and other dissolved gases from the feedwater to steam-generating bo ilers.
There are two basic types of deaerators, the t he tray-type and the spray-type: spray-t ype: The tray-type (also called the cascade-type) includes a vertical domed deaeration section mounted on top of a horizontal cylindrical vessel which serves as the deaerat ed boiler feedwater storage tank. The spray-type consists only of a horizontal (or vertical) cylindrical vessel which serves as both the deaeration section and the bo iler feedwater storage tank.
G) Super-Heaters:
Super-heaters are used to raise the steam temperature above the saturation
temperature by absorbing heat from flue gas to increase the cycle efficiency. Super heating takes place in three stages. In the first stage, the steam is sent to a simple super heater, known as the low temperature super heater, after which the second stage consists of several divisional panels. The final stage involves further heating in a Platen super heater, after which the steam is released for driving the turbine. After the HP stage of the turbine the steam is re -heated and then again aga in released. Superheating is done to increase the dryness fraction of the exiting steam. This is because if the dryness fraction is low, as is the case with saturated steam, the presence of moisture can cause corrosion of the blades of the turbine. Super heated steam also has several merits such as increased working capacity, ability to increase the plant efficiency, lesser erosion and so on. o n. It is also of o f interest to know that while the super heater increases the temperature of the steam, it does not change the pressure. There are different stages of superheaters besides the sidewalls and extended sidewalls. The first stage consists of LTSH(low temperature superheater), which is conventional mixed type with upper & lower banks above the economiser assembly in rear pass. The other is Divisional Panel Superheater which is hanging above in the first pass of the boiler above the furnace. The third stage is the Platen Superheater from where the steam goes into the HP turbine through the main steam line. The outlet temperature & pressure of the steam coming out from the superheater is 540 degrees Celsius & 157 2
kg/cm .
5) TURBINES
: The turbine employed employed in a thermal power plant is a steam turbine. The initial steam is
admitted ahead of the blading via two main stop and control valve combinations. The turbine unit of any thermal power plant is not a single stage operation, o peration, rather it consists of three stages: High Pressure Turbine Stage (HPT Stage): This stage takes place immediately after the Platen super heater stage. This is the first stage of the turbine operation. Its outer casing is of a barrel type and has neither a radial nor an axial flange. The inner casing is axially split and supported so as to be free to move in response to thermal expansion. Intermediate Pressure Turbine Stage (IPT Stage): After the HPT stage, the steam gets saturated and, consequently, gets cooled. It is, therefore, first first sent back t o the boiler unit to be reheated, after which it is sent to the IPT stage. Its section is of double flow co nstruction nstruction with w ith horizontally split split casings. Low Pressure Turbine Stage (LPT Stage): After the IPT, the steam gets cooled to an intermediate extent, thus directly entering the LPT, where it gets saturated. Its casing is of the three-shell design. After this stage the water enters the condenser, which is connected to a condensate extraction pump.
A turbine assembly consists of a rotor assembly on whose circumference is attached a series of vanes, a bearing assembly to support the shaft, a metallic casing surrounding the blades, nozzle, rotor etc, a governor to control the speed and a lubrication system. The shaft of the turbine is connected to the generator. The purpose of the generator is to convert the mechanical shaft energy it receives from the turbine into electrical energy. Steam turbine driven AC synchronous generators (alternators) are of two or four pole designs. These are three phase machines offering economic advantages in generation and transmission. Large generators have cylindrical rotors with minimum
heat dissipation surface and so they have forced ventilation to remove the heat. Such generators generally use an enclosed system with air or hydrogen coolant. The gas picks up the heat from the generator and gives it up to the circulating water in the heat exchanger. Every turbine, except the LPT, has a stop valve and a regulating valve attached to it. The stop valve is used to stop the flow of steam, whenever required, whereas the regulating valve is also a kind of a flow controlling device. Each turbine also has an inlet and an outlet pipe for the steam to enter and exit, respectively. Between the HPT-IPT combine and the IPT-LPT combine is attached a bearing assembly. It is constructed using a cross around pipe. After the steam leaves the turbine, it enters the condenser . The condenser is meant to receive the steam from the turbine, condense it and to maintain a pressure at the exhaust lower than the atmospheric pressure. The condenser is an important unit and some of the auxiliaries required for it to function properly are the cooling water supply pump, the condensate extraction pump, feed water pump and the air removal pump.
6) ASH HANDLING AND DISPOSAL:
There are two types of ash handling methods: dry ash
handling and wet ash handling. Dry ash handling is carried out by storing the ash deposited in large pits, whereas in the wet ash handling method, the ash is deposited into large reservoirs or ponds.
1. Wet mode:--Ash evacuated from ESP hoppers through vacuum pumps & fed to wetting head (vacuu m system) and collector tank units where ash is mixed with water & resultant slurry is discharged to slurry trenches. 2. Dry mode:--Ash evacuated from ESP hoppers through vacuum pumps & collected in Buffer hoppers & Air lock tank, is transported to storage silo by compressed air (pressure conveying system) through pressure conveying pipe lines. Components of wet fly ash system 1. ESP hopper 2. Plate valve for isolation . 3. Material Handling Valve (MHV) 4. Piping up to wetting head 5. Wetting head 6. Air washer 7. Vacuum pump
Auxiliaries in a power plant 1) PA FANS: The primary air fans are used to carry the pulverized coal particles from the mills to the boiler. They are also used to maintain the coal-air coa l-air temperature. The specifications of o f the PA P A fan used at the plant under investigation are: axial flow, do uble stage, reaction fan.
The PA fan circuit consists co nsists of: a) Primary air path through cold air duct b) Air pre-heater c) Hot air duct d) Mills The model no. of the PA fan used at NTPC Sipat is AP2 20/12, where A refers to the fact that it is an axial flow fan, P refers to the fan being progressive, 2 refers to the fan involving two stages, and the numbers 20 and 12 refer to the distances in decimeters from the centre of the shaft to the tip of the impeller and the base of the impeller, respectively. A PA fan uses 0.72% of plant load for a 500 MW plant. 2) FD FANS : The forced draft fans, also known as the secondary air fans are used to provide the secondary air required for combustion, and to maintain the wind box differential pressure. Specifications of the FD fans are: axial axia l flow, single stage, impulse fan.
The FD fan circuit consists of: a) Secondary air path through cold air duct b) Air pre-heater c) Hot air duct d) Wind box The model no. of the FD fan used at NTPC Sipat is AP1 26/16, where the nomenclature has been described above. FD fans use 0.36% of plant load for a 500 MW plant.
3) ID FANS: An induced fan circuit consists of a) Flue gas through water walls b) Super heater c) Re-heater d) Platen super heater e) Low temperature super heater
f) Air pre-heater g) Electrostatic precipitator The main purpose of an ID fan is to suck the flue gas through throug h all the above mentioned equipments and to maintain the furnace pressure. ID fans use 1.41% of plant load for a 500 MW plant. plant . fired 4) SCANNER AIR FAN : Scanner air fan is used to provide air to t he scanner. For a tangent ially fired boiler, the vital thing is to maintain maintain a stable ball of flame at the centre. A scanner is used to detect the flame, to see whether it is proper and stable. stab le. The fan is used to provide air to the t he scanner, and it is a crucial component which prevents t he boiler from tripping 5) SEAL AIR FAN: The seal air fan is used near the t he mill to prevent the loss of any heat from the coal which is in a pulverized state and to protect the bearings from coal particle deposition.
6) AIR PRE-HEATERS: Air pre-heaters are used to take heat from the flue gases and transfer it to the incoming air. They are of two types: a)
Regenerative
b)
Recuperative
The APH used at NTPC Sipat is a Ljungstrom regenerative type APH. A regenerative type air preheater absorbs waste heat from flue gas and transfers this heat to the incoming cold air by means of continuously rotating heat transfer elements of specially formed metal sheets. A bi-sector APH preheats the combustion air. Thousands of these high efficiency elements are spaced and compactly arranged within sector shaped compartments of a radially divided c ylindrical shell called the rotor. The housing surrounding the rotor is provided with duct connections at both ends, and is adequately sealed by radial and axial sealing members forming an air passage through one half of the APH and a gas passage through the other. As the rotor slowly revolves the elements alternately pass through the air and gas passages; heat is absorbed by the element surfaces passing through the hot gas stream, then as the same surfaces pass through the air stream, they release the heat to increase the temperature of the combustion of process air. A single APH is divided into 4 parts: 2 PAPHs and 2 SAPHs. The P and S refer to primary and secondary respectively. Each part is divided into two slots, slots, one slot carrying carrying the primary/secondary pr imary/secondary air, nd and the other slot carrying the hot flue gases coming from the 2 pass of the boiler. The PAPH is connected to the t he mills, mills, whereas the SAPH is connected to a wind box.
7) ELECTROSTATIC PRECIPITATORS : They are used to separate the ash particles from the flue gases. In this the flue gas is allowed into the ESP, where there are several metallic plates placed at a certain distance from each other. When these gases enter, a very high potential difference is applied, which causes the gas particles to t o ionize and stick to the plates, whereas the ash particles fall down and are collected in a hopper attached to the bottom of the ESP. The flue gas is allowed to cool down and is then released to the ID fan to be sent to the chimney.
Indian coal contains about 30% of ash. The hourly consumption of coal of a 200 MW unit is about 110 11 0 tons. With this, the hourly production of ash will be 33 3 3 tons. If such large amount amou nt of ash is discharge in atmosphere, it will create heavy air pollution thereby resulting health hazards. Hence it is necessary to precipitate dust and ash of the flue gases. Precipitation of ash has another advantage too. It protects the wear and erosion of ID fan. To achieve the above objectives, Electrostatic Precipitator (ESP) is used. As they are efficient in precipitating particle form submicron to large size they are preferred to mechanical precipitation. Construction An ESP has series of collecting and emitting electrons in a chamber collecting electrodes are steel plates while emitting electrodes are thin wire of 2.5mm diameter and helical form. Entire ESP is a hanging structure hence the electrodes are hung on shock bars in an alternative manner. It has a series of rapping hammer mounted on a single shaft device by a motor with the help of a gear box at a speed of 1.2 rpm. At the inlet of the chamber there are distributor screens that distributes the gas uniformly throughout the chamber. There are transformer and rectifiers located at the roof roo f of chamber. Hopper and flushing system form the base of chamber. Working: Flue gases enter the chamber through distributor screen and get uniformly distributed. High voltage of about 40 to 70 KV form the transformer is fed to rectifier. Here ac is converted to dc. The negative
polarity of this dc is applied across the emitting electrode while the positive polarity is applied across the collecting electrodes. This high voltage produces corona effect negative (–ve) ions from emitting electrode move to collecting electrode. During their motion, they collide with ash particles and transfer their charge. On gaining this charge, ash particles too move to collecting electrode and stock to them. Similar is the case with positive (+ve) ions that moves mo ves in opposite direction. The rapping hammers hit the shock bars periodically and dislodge the collected dust from it. This dust fall into hopper and passes to flushing system. Here it is mixed with water to form slurry which is passed to AHP. Efficiency of ESP is approximately 99.8%. Theory of Precipitation Electrostatic precipitation removes particles from the exhaust gas stream of Boiler combustion process. Six activities typically take place:
Ionization - Charging of particles
Migration - Transporting the charged particles to the collecting surfaces
Collection - Precipitation of the charged particles onto the collecting surfaces
Charge Dissipation Dissipation - Neutralizing the charged particles on the collecting surfaces
Particle Dislodging - Removing the particles from the collecting surface to the hopper
Particle Removal - Conveying the particles from the hopper to a disposal point
The ash produced on the th e combustion of coal is collected by ESP. This ash is now required to be disposed off. This purpose of ash disposal is solved by Ash Handling Plant (AHP).
8) CONDENSATE EXTRACTION PUMP : The condensate extraction pump (CEP) is a centrifugal, vertical pump, consisting of the pu mp body, the can, the distributor housing and the dr iver lantern. A rising main of length depending upon NPSH available, is also provided. The pump body is arranged vertically in the can and is attached att ached to the distributor body with the t he rising main. The rotor is guided in bearings lubricated by the fluid pumped, is suspended from the support bearing, which is located in the bear ing pedestal in the driver lantern. The shaft exit in the driver lantern is sealed off by one packed stuffing box.
Casing It is split on right to the shaft and consists of suction rings and 4 no. of guide vane housing. Casing components are bolted together and sealed off o ff from one another by 'O' rings. For internal sealing of individual stages, the casing components are provided with w ith exchangeable casing wear rings in the arc o f impeller necks. In each guide vane casing, a bearing bush is installed to guide the shaft of pu mp.
Rotor The pump impellers are radially fixed on the shaft by k eys. The impellers are fixed in position axially by the bearing sleeves and are attached to the shaft by means of impeller nut. Impellers are single single entry type, semiaxial and hydraulically balanced by means of balance holes ho les in the shroud and throttle sections at suction and discharge side. A thrust bearing located in the motor stool absorbs residual axial thrusts.
Bearings In each guide vane housing the shaft is guided by a plain bearing. These bearings do not absorb any axial forces. Pump bearings consist of bearing sleeve, rotating with the shaft and bearing bush, mounted in guide vane housing. The intermediate shaft is guided in bear ing spider and shaft sleeve. The arrangement of bearing corresponds to the bearings of pump shaft. They T hey are lubricated by condensate itself. itself. A combined co mbined thrust and radial bearing is installed as support bearing to absorb residual thrust. Axial load load is transmitted to the distributor casing via the thrust bearing plate, thethrust bearing and bearing housing. A rad ial bearing attached to the bearing is installed in an enc losed housing and is splash lubricated by oil o il filled filled in the enclosure. Built-in cooling coils in the bath and cooling water control oil temperature. 9) BOILER FEED PUMP: The auxiliary component which consumes the maximum amount of power earmarked for such purposes is the boiler feed pump. At NTPC Sipat, the auxiliaries consume about 7% of the plant load. The boiler feed pump is used to feed water to the boiler, as the name suggests, through the economizer. The BFP is fed from the CEP and the th e water source. The BFP is of two types
a) TDBFP: turbo-driven boiler feed pump. b) MDBFP: motor driven boiler feed pump. The boiler feed pump is fed water from the condensate extraction pump. The condensate extraction pump collects the condensate from the condenser. Then the condensate is further cooled by being sent into the gland steam coolers, after which it is sent into the BFP. 10) COOLING TOWERS : Cooling towers are used to remove the heat from the condensers. In this
cooling water is discharged to the condenser with the help of a cooling water pump (CW pump). This water enters the condenser through several tubes. Steam entering the condenser from the turbine after expansion further loses heat and condenses, while the water circulating inside the tube gains heat and goes back to the cooling tower. Inside the tower is a cooling fan which takes the heat from this batch of water, which is then sent back again for the cycle to be repeated. It is hence known as a regenerating cycle. Cooling towers are eveporative coolers used for cooling cool ing water. Cooling tower uses the concept of evaporation of water to reject heat from processes such by cooling the circulaing water used in oil refineries, chemical plants, power plants, etc. Smaller towers are normally factory buil t while larger ones are constructed on site. The primary use of large, industrial cooling tower system is to remove the heat by circulating the hot water used by the plants The absorbed heat is rejected to the atmosphere atmo sphere by the evaporation of some of the cooling water in mechanical forced – draft or induced draft towers or in natural draft hyperbolic shaped cooling towers as seen at most nuclear power plants. 4 Nos Induced draft cooling towers with 10 fans each tower are installed at NTPC sipat for the above said pupose.
11) WIND BOX : These act as distributing media for supplying secondary/excess air to the furnace for combustion. These are generally located on the left and and right sides of the furnace while facing the chimney.
12) IGNITER FAN: Igniter fans which are 2 per boiler are used to supply air for cooling Igniters & combustion of igniter air fuel mixture.
13) CHIMNEY: These are tall RCC structures with single & multiple flues. Here, for I & II we have 1 chimney, for unit III there is 1 chimney & for units IV & V there is 1 chimney. So number of chimneys is 5 and the height of each is 275 metres.
14) COAL BUNKER: These are in process storage used for storing crushed coal from the coal handling system. Generally, these are made up of welded steel plates. Normally, these are located on top of mills to aid in gravity feeding o f coal. There are 10 such bunkers corresponding to each mill.
15) REHEATER : The function of reheater is to reheat the steam coming out from the high pressure turbine to a temperature of 540 degrees Celsius. It is composed of two sections: sections: the rear pendant section is located above the furnace arc & the front pendant section is located between the rear water hanger tubes & the P laten superheater section.
16) BURNERS: There are total 20 pulverised coal burners for the boiler present here, & 10 of the burners provided pro vided in each eac h side at every elevation named as A,B,C,D,E,F,G,H,J,K. There are oil burners present in every elevation to fire the fuel oil (LDO & HFO) during light up. |~|
A boiler is a heat exchanger in which the working fluid water is heated. The heated or o r vaporized fluid exits the boiler for use in various processes or heating heating applications. The boiler used in NTPC is Controlled Cirulation with Rifle Tubing Radiant Reheat Dry Bottom Top Supported. Conversion of Water to Steam Evolves in three stages: boiling point po int or saturation temperature – temperature – Sensible Sensible Heat Heating the water from cold condition to boiling Addition. Water boils at saturation temperature to produce steam – steam – Latent Latent Heat Addition. Heating steam from saturation temperature to higher temperature called Superheating to increase the power plant output and efficiency
540 C, 255 Ksc
568 C, 47 Ksc
492 C, 260 Ksc
457 C, 49 Ksc
FUR ROOF
ECO HGR
I/L HDR
O/L HDR
HRH LINE MS LINE
411 C, 277Ksc
411 C, 275 Ksc
SEPARATOR
S T
FINAL SH FINAL
O
LTRH
RH
R A G
DIV PANELS SH
PLATEN SH
E T
VERTICAL WW
A
G LPT C O
c s K 9 4 , C 5 0 3
N LPT
K
IPT HPT
N D E
ECO JUNCTION HDR
ECONOMISER
N S E R
ECO I/L
FEED WATER
BWRP
290 C, 302 KSC
FUR LOWER HDR
FRS
In a tangential firing system the coal is pulverized in co al mills and is carried by primary air to the furnace through coal pipes. The mills are usually a co nstant airflow airflow mill and have a specific output in mass of coal ground depending on coal co al properties like hardness, moisture, and fineness which affect the mill output. In direct tangential firing systems, the pulverized coal from the coal mills is directly taken to t he furnace. Coal properties such as FC/VM (Fixed Carbon / Vo latile latile Matter), particle size, oxygen, calorific value of the coal, co al, reactivity, and ash content seem to be the most important variables for pulverised coal combustion in tangent ially fired boilers, and they are highly inter-related. The total quantity of coal to be pulverized for for a specified sp ecified size of boiler at a designed efficiency will depend on t he calorific value of coal. As the ash content in coal goes up, the calorific value per unit mass of coal comes co mes down. This increases the mass of coal to be prepared, which in turn increases the number of mills or elevations needed in a t angential firing system. The secondary air required for combustion is sent into the furnace through a windbox housing the coal nozz les, oil guns, and the secondary air nozzles. Behind the coal coa l nozzles there are fuel-air dampers which are used for keeping the flame front away from the coal nozzles by at least one meter from the tip. This is required to prevent the co al nozzle tips from getting burnt due to radiation from coal coa l flame. The flame front is predominantly affected b y the volatile matter in coal and the fuel air damper is modulated for controlling the flame front. As the fuel air dampers are o pened, more secondary air goes through this t his damper and physically pushes the flame front away. Ho wever, when the flame front is already away from the nozzle tip, the fuel air damper needs to be closed c losed fully.
Understanding the quality of flame in any boiler bo iler furnace is very important to tune the boiler to t he optimal level of performance. The aspects of combustion tuning involve looking at the boiler bo iler furnace and making sure the quality of flame is acceptable and good. go od. The gas and oil fired bo ilers do not pose much problem in establishing a good flame in furnace. The T he available instruments like flame scanners, CO monitors and Oxyg en indicators, along with the exit gas temperature, give g ive a good indication to perceive if the qua lity lity of the flame is good. In coal fired boilers and mainly in tangential tangent ial fired fired boilers, bo ilers, the furnace acts as a single burner, so it is required to look at the flame and understand the t he quality of the flame.
SALIENT FEATURES OF 500 MW BOILER Some important features of 500 MW Boiler are listed as : CONTROLLED CIRCULATION SYSTEM This is achieved by three numbers of o f glandless pump and wet motor installed installed in the downcomer d owncomer line after the suction manifold. These pump motor assemblies have single suct ion and double discharge introduction of these pumps in the boiler system have led to the designing of a furnace with lesser lesser diameter tubes and high parameters operating characteristics. characteristics. The advantages of the co ntrolled ntrolled circulation boiler bo iler over natural circulation boiler are given below: Uniform drum cooling and heating. In controlled co ntrolled circulation boilers this is possible because of arrangement of relief tubes inlets to the drum and the internal baffles of the drum from both sides. The internal base plates are arranged in such suc h a way that it guides the steam water mixture from the relief tubes along the whole circumference of o f the drum. The drum is therefore there fore uniformly heated and cooled. Whereas in Natural Circulation Boiler, the arrangement of relief tubes and baffleplates is only on o ne
side of the drum and this imposes a constraint co nstraint on uniform heating of drum. Simil S imilar ar arrangement of o f relief as in controlled circulation boiler does not exist in natural circulation (NC) boiler because in that case the relief required to be t aken over the drum and fed from both bot h sides. This shall increase the pressure losses in the riser riser tubes and also the hot static head requirement for start up. Since the available head in NC Boiler is very less; efforts are always made to reduce the pressure loss and improve the circulation. Second reason is to commence flow flow in the riser tubes immediately after light up hot static head is kept as minimum as possible. po ssible. Better cleaning of boiler: For effective acid washing, the acid has to be kept at certain temperature unif u niformly ormly through the t he system. This is possible with the assistance of controlled circulation. · Uniform expansion of pressure part and lower metal temperature: This means lesser thermal stresses on the tubes. Because of controlled c irculation, lower diameter tubes are used, which result in high mass flow rate thereby preventing departure from nucleate boiling (DNB) maintains a lower metal temperature.
USE OF RIFLE TUBES FOR FURNACE CONSTRUCTION
This is one of the extraordinary features of 500 MW capacity boilers. Because of the excessive e xcessive heat release in the burner zone of the furnace, the metal tubes constituting the furnace at that zone are exposed expo sed to the maximum temperature. This being a water-cooled furnace, t he steam water mixture inside the tubes should effectively carry the heat from the burner zone zo ne of the furnace. In this zone, the tubes have a n internally cut spiral like a rifle bore so that when water flows through the tubes, due to hot static heat, it takes a screwed path and attains att ains a certain degree of spin by which wh ich the watness of the tube is always maintained. This prevents the tubes form departure from Nucleate boiling under all operat ing condition of the boiler and increases the c irculation ratio. OVER FIRE AIR SYSTEM FOR NOX (OXIDES OF NITROGEN) CONTROL
Industrial growth in the recent years has necessitated the need to have a cleaner and pollution free atmosphere, by controlling the production of industrial wastes wastes with the application of improved technology. Power plants are the major sources of the industrial pollution by virture of the stanch e mission mission in the atmosphere. These emissions contain mostly gases and dust particles, which have ill effect o n the ecological eco logical system. system. In the 500 MW capacity boiler design, this aspect has been g iven due importance and certain technical improvements have been incorporated. These are tilting tangential firing and over fire air air system. Tangential firing helps in keeping the temperature of the furnace low so that NOX emission emission is reduced considerably. In addition add ition to the above the over fire air is provided which is used as co mbustion process adjustment technically for keep ing the furnace temperature low and thereby low Nox No x formation. Each corner of the burner windbox is provided with two numbers of separate over fire air compartments, kept one above the other ot her and the over fire air is admitted tangentially t angentially into the furnace.
Each Boiler Water Circulation pump consists of a single stage centrifugal pump on a wet stator induction motor mounted within a common pressure vessel. The vessel consists of three main parts a pump casing, motor housing and motor covers. The motor is suspended beneath pump casing and is filled with boiler water at full system pressure. No seal exists between between the pump pump and motor, motor, but provision is made to thermally isolate the pump pump from the motor motor in the following respect: respect: Thermal Conduction. To minimise heat conduction, a simple restriction in the form of thermal neck is provided. Hot Water Diffusion. To minimise diffusion of boiler water, a narrow annulus surrounds the rotor shaft, between the hot and cold regions. A baffle ring restricts solids entering the annulus. Motor Cooling. The motor cavity is maintained at a low temperature by a heat exchanger and a closed loop water circulation system, thus extracting the heat conducted form the pump.
In addition, this water circulates through the stator and rotor bearings extracting the heat generated in the windings and also provide bearing lubrication. An internal filter is incorporated in the circulation system. In emergency conditions, if low-pressure coolant to the heat exchanger fails, or is inadequate to cope with heat flow from pump case, a cold purge can be applied to the bottom of the motor to limit the temperature rise.
Pump The pump comprises a single suction and dual discharge branch casing. The case is welded into the boiler system pipework at the suction suction and discharge branches branches with the suction suction upper most. most. Within Within the pump cavity cavity rotates rotates a key driven, driven, fully shrouded, mixed flow type impeller, mounted on the end of the extended motor shaft. Renewable wear rings are fitted to both the impeller and pump case. The impeller wear ring is the harder component to prevent galling.
Motor The motor is a squirrel cage, wet stator, induction motor, the stator, wound with a special watertight insulated cable. The phase joints joints and lead connections connections are also moulded in an insulated insulated material. material. The motor motor is joined to the pump pump casing by a pressure tight tight flange joint and a motor cover cover completes completes the pressure tight tight shell.
Safety Valve : It is used to relieve pressure and prevent pre vent possible explosion of a boiler. bo iler. Water Level Indicators : They show t he operator the level of fluid in the boiler, also known as a sight
glass, water gauge or water column is provided. Bottom Blowdown Valves : They provide a means for removing solid particulates that condense and
lie on the bottom of a boiler. As the name implies, this valve is usually located directly on the bottom of the boiler, and is occasionally opened to use the pressure in the boiler b oiler to push these particulates out. Continuous Blowdown Valve : This allows a small quantity of water to escape continuously. Its
purpose is to prevent the water in the boiler becoming saturated with with dissolved salts. Saturation would lead to foaming and cause water droplets to be carried over with the steam - a condition known as priming. Blowdown is also often used to monitor the chemistry of the boiler water. Flash Tank : High pressure blowdown enters this vessel where the steam can 'flash' safely and be used
in a low-pressure system or be vented to atmosphere while the ambient pressure blowdown flows to drain. Automatic Blowdown/Continuous Heat Recovery System : This system allows the boiler to
blowdown only when makeup water is flowing to the boiler, thereby transferring transferring the maximum amount of heat possible from the blowdown to the makeup water. No flash tank is generally needed as the blowdown discharged is close to the temperature of the makeup water. installed in openings in "header" to allow for inspections & Hand holes: They are steel plates installed installation of tubes and inspection of internal surfaces. Steam Drum Internals : A series of screen, scrubber & cans (cyclone separators). Low- Water Cutoff : It is a mechanical means (usually a float switch) that is used to turn off the
burner or shut off fuel to the boiler to prevent prevent it from running once the water goes below a certain point. If a boiler is "dry-fired" "dry-fired" (burned without water in it) it can cause rupture or catastrophic failure.
Surface Blowdown Line : It provides a means for removing foam or other lightweight non-
condensible substances that tend to float on to p of the water inside the boiler. Circulating Pump : It is designed to circulate water back to the boiler after it has expelled so me of its
heat. Feedwater Vheck Valve or Clack Valve : A non-return stop valve in the feedwater line. This may be
fitted to the side of the boiler, bo iler, just below the water level, or to the top o f the boiler. Top Feed: A check valve va lve (clack valve) in the feedwater line, line, mounted o n top of the boiler. It is
intended to reduce the t he nuisance of limescale. It does not prevent limescale limescale formation but causes the limescale to be precipitated in a powdery po wdery form which is easily washed out o ut of the boiler. Desuperheater Tubes or Bundles : A series of tubes or bundles of o f tubes in the water drum or the
steam drum designed to cool superheated steam. Thus is to supply auxiliary equipment that doesn't need, or may be damaged da maged by, dry steam. connection to add chemicals for controlling controlling feedwater pH. Chemical Injection Line : A connection
A steam turbine is a mechanical device that extracts steam energy from pressurized steam, & converts it into useful mechanical work. The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and impart rotational energy to the rotor .
TYPES OF TURBINE:
IMPULSE TURBINE: These turbines change the direction of flow of a high velocity fluid or gas jet. The resulting impulse spins the turbine and leaves the fluid flow with diminished diminished kinetic energy. There is no pressure change of the fluid or gas in the turbine rotor blades (the ( the moving blades), as in the case of a steam or gas turbine, all the pressure drop takes place in the stationary blades (the no zzles). Before reaching the turbine, the fluid's pressure fluid's pressure head is head is changed to velocity head by head by accelerating the fluid with a nozzle nozzle.. Pelton wheels and de Laval turbines use this process exclusively. Impulse turbines t urbines do not require a pressure casement around the rotor since the fluid jet is created by the nozzle prior to reaching the blading on the rotor. Newton's rotor. Newton's second law describes the transfer of energy for impulse turbines.
torque by by reacting to the gas or fluid's pressure or REACTION TURBINE: These turbines develop torque mass. The pressure of the gas or fluid changes as it passes through the turbine rotor blades. A pressure casement is needed to contain the working fluid as it acts on the turbine stage(s) or the turbine must be fully immersed in the fluid flow (such as with wind turbines). The casing contains and directs the working fluid and, for water turbines, maintains the suction imparted by the draft tube. Francis turbines and most steam turbines use this concept. For compressible working fluids, multiple turbine stages are usually used to harness the expanding e xpanding gas efficiently. Newton's efficiently. Newton's third law describes the transfer of energy for reaction turbines. t urbines.
TURBINE COMPONENTS TURBINE CASING : These are non-moving parts covering cover ing the pedestal containing fixed blades. Casing should be to wards expansion of turbine.
HP Turbine Casing: Outer Casing- Barrel Type without axial or radial flange.
qu ick startup & loading) Barrel-type casing (suitable for quick Inner Casing- Cylindrical, Axially split.
The inner casing is attached in the horizontal & vertical planes in the barrel casing so that it can freely
expand radially in all directions & axially from a fixed po int.
IP TURBINE CASING: Three Shell Design All Casings Axially Split Exhaust Hood Spray Arrangement Inner casing carrying first 6 rows of shrouded guide blade Middle casing carrying the last 2 stage free standing blades
LP TURBINE CASING: co nsists of a double flow unit and has a triple shell welded casing. The LP Turbine casing consists The shells are axially split and of rigid welded construction. The inner shell taking the first rows of guide blades, is attached kinematically in the middle shell.
shell, is supported support ed at four points on o n longitudinal beams. Independent of the outer shell, t urbine from the IP turbine flows flows into the inner casing from both sides. Steam admitted to the LP turbine
1) SURFACE ROUGHNESS:
It increases friction friction & resistance. It can be due to Chemical deposits, Solid particle damage, Corrosion Pitting & Water erosion. As a thumb ru le, surface roughness of about 0.05 mm can lead to a decrease in efficiency of 4%.
2) LEAKAGE LOSS:
Interstage Leakage Turbine end Gland Leakages About 2 - 7.5 kW is lost per stage if clearances are increased by 0.025 mm depending upon LP or HP stage.
3) WETNESS LOSS:
Drag Loss: Due to difference in the velocities of the steam & water particles, water particles particles lag behind & can even take different trajectory leading to losses. Sudden condensation can create shock disturbances & hence losses. About 1% wetness leads to 1% loss in stage efficiency.
4) OFF DESIGN LOSSES:
Losses resulting due to turbine not operatin op erating g with design terminal conditions. co nditions. Change in Main Steam Stea m pressure & temperature.
Change in HRH pressure & temperature.
Condenser Back Pressure
Convergent-Divergent nozzles are more prone to O ff Design losses then Convergent nozzles as shock formation is not there in convergent nozzles.
5) PARTIAL ADMISSION LOSSES:
In Impulse turbines, the controlling stage is fed with means of nozzle boxes, t he control valves of which open or close c lose sequentially. sequentially.
At some partial load some nozzle boxes can be partially open / Completely Co mpletely closed. closed.
Shock formation takes place as rotor blades at some time are full of steam & at some other moment, devoid of steam leading to considerable losses.
6) LOSS DUE TO EROSION OF LP LAST STAGE BLADES:
Erosion of the last stage blades leads to considerable loss loss of energy. e nergy. Also, It is the least efficient stage. Erosion in the 10% length of the blade leads to decrease in 0.1% of efficiency. |~|
