ritesh final project
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1 PROJECT REPORT ON: --------------------------------------------------------- THERMAL POWER PRODUCING PLANT AND ANALYSIS ON VIBRATION OF FANS BY: RITESH PANDEY, B-TECH (MECHANICAL),
Transcript of ritesh final project
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PROJECT REPORT ON:
---------------------------------------------------------
THERMAL POWER PRODUCING PLANT AND
ANALYSIS ON VIBRATION OF FANS
BY:
RITESH PANDEY,
B-TECH (MECHANICAL),
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AMITY UNIVERSITY.
Acknowledgements
First of all, I would like to express my sincere gratitude to Mr. Pradeep Mahapatra, AGM, SEL, Jharsuguda for giving me this project and providing me with constant support and invaluable guidance throughout the duration of the project. I would also like to thank Mr. Sunil Shrivastava, Head-Learning and Development, VAL, Jharsuguda for giving me an opportunity to work at VAL-J. I am highly grateful to Mr. Nikunj Nihar, Assistant Manager, SEL, Jharsuguda and Shrikant Srivastava, Associate Manager, SEL, Jharsuguda for guiding our field visits and helping with our project at each stage.
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A special vote of thanks to my fellow summer
intern, Vishal Kr. Patel. For helping and providing
me support during the internship.
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Introduction:
Vedanta Aluminium Limited (VAL) is an associate company of the London Stock
Exchange listed. VAL is a leading producer of metallurgical grade alumina and other aluminium products, which cater to a wide spectrum of industries.
The IPP is a power generation plant, with the main fuel as coal. It is spread across 570 acres. It has 4 units producing 600MW each.
So total power generated:
4*600=2400MW
7.2% of the total power produced is utilized within the plant for self-consumption.
The required coal is imported from Australia, Indonesia and from MCL, Talcher
and Lakhanpura Open Coal Mines.
Jharsuguda is also the site of the 2400 MW Independent Power Plant being set up
by group company Sterlite Energy Ltd to meet the growing demand for power from both urban and rural consumers.
It supplies Power to Orissa Power Generation Company Ltd (OPGCL) and Power Grid Corporation of India (PGCI).
It is one of the leading power producing units with latest and efficient equipments.
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The electricity produced by the Principle of a Rankine Cycle.
This cycle helps in increasing the Boiler efficiency.
A Thermal Power Station is a power plant in which the prime mover (TURBINE)
is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is
condensed in a condenser and recycled to where it was heated, this is known as a Rankine cycle. Energy conversion from heat energy to mechanical energy
(Turbine) to electrical energy (Generator) takes place.
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COAL HANDLING PLANT (C.H.P) It is the part of IPP that deals all the processes right from the import of the coal to
the feeding of coal to the bunker.
Coal handling system in thermal power plant, usually means the technique or the procedure by which conveying of coal from loading and unloading outside the
factory to boiler, coal storage is possible. Because of the large number of machinery and equipment involved, we can sort as we used it, the important part
includes unloading coal, coal yard, transport and accessory equipment, are collectively called coal handling mechanical.
The input of C.H.P is coal of various sizes and output is coal of 30mm size.
There are 2 ways by which coal is delivered to C.H.P
By road- Trucks and Dumpers.
By tracks- Rake (BOBRN & BOXN)
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Trucks and dumpers are unloaded in truck tippler and BOBRN in track hopper and BOXN in wagon tippler.
The coal suppliers are:
Here 5 types of coal are used. These are classified according to their GCV
(Grossed Calorific Value), these are given below:
• Imported type coal -> 5500-6000Kcal/kg
• Linkage type coal -> 2700-3200Kcal/kg
• LOCM -> 2500-2800Kcal/kg
• Washer -> 2800-3100Kcal/kg
• E-Auction -> 2400-2600Kcal/kg
• Australia.
• Indonesia.Imported
coal
• MCL, Talcher.
• Lakhanpura open coal mines.
local coal
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TRUCK TIPPLER: In this section of C.H.P trucks and dumpers are unloaded.
The specification of the tripling platform:
Length: 8.5m
Width: 3.2m
Depth: 2.1m (below platform)
Capacity: 40 ton
Tripling angle: 0-55ᵒ
Hydraulic pump pressure:
500 kg
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Safety instruments:
There are 6 hydraulic cylinders
2- Re-track
2- Tripling platform
2- Hook chains
Lubricating system for the above hydraulic system:
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Working Principle:
The truck or the dumper is brought to the platform; the re-track guides the rear
wheels of the truck during the tripling procedure, the hook chains are then attached to the front axial of the truck so that the truck doesn’t troop inside the hopper.
Once the truck is ready for tripling the operator signals and then the platform is
inclined to an angle of 50⁰-55⁰ and the coal is unloaded. The tripling is done with a
hydraulic pump which is manually operated.
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If coal more than the size of the grill is obtained then the coal is manually drilled, hammered and crushed to the required size and then dropped into the hopper.
The coal is further passed on with the help of apron feeder and dribble conveyer to the crusher.
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Inside skit- 1660mm
Inside skit liner- 1640mm
Speed- 15m/min
Material depth- 1300mm
Chain- grawler type, 215.9
GEAR BOX:
Helical Gear Ratio- 40:1
SPEN Gearing Spur ratio- 4.68:1
Geared Coupling
Take up manually operated screw.
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MOTOR SPECIFICATION:
15 KW, 28.3 Amps at 40⁰C
N.L Current- 14.1 Amp
Weight- 208Kg
The coal dust or small size coal that troops down is carried in a dribble conveyer
Capacity- 60 TPH
Pulley C/C dist.-14650mm
Belt speed- 0.5m/sec
There is a scrapper on the opening of the chute or at the tail end of the dribble
conveyer for the removal of the wet coal that sticks to the conveyer. Failing which the belt may be damaged or there would be improper functioning of the conveyer. The coal is then passed to the crusher for decreasing the size of the coal.
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CRUSHER:
The crusher type used in TT is a single roller crusher which has grinding teeth with the help of which the coal is crushed. The coal feed size of the crusher is 500mm-
1000mm (approx.) and the output size of the crusher is 300mm with an effic iency of about 80%.
The crusher capacity is 250 TPH. It is run by a motor of following specification:
180 HP
1485 rpm
TEFC Squirrel cage induction motor.
The motor runs a single roller crusher which grinds the coal and reduces its size to 300mm.
The crusher needs high maintenance depending upon the running of the system as the teeth face high wear and tear and the grinding edges blunt down. So it is
regularly checked so that the system works smoothly and efficiently.
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The crushed coal of size <300mm is then passed on to the conveyer belt 5 and further to the main crusher.
WAGON TIPPLER
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The major parts of a wagon tippler are:
Side arm charger.
Tripling platform.
End disc.
Clamps.
DS system.
Drive Unit.
Side Arm Charger: This unit is used for bringing the wagon on the tripling platform and then moving it
out from the platform after the engine drops the wagons at their respective position.
Tripling Platform: This is the platform where the wagon is brought for unloading purpose. There is a weighing gauge with the help of which the weight of the wagon is determined with
the coal and then after unloading again the weight is noted to find out the amount of coal unloaded from an individual wagon.
End Disc: A pair of end rings with gear sectors mounted on the periphery will be driven by two pinions fixed on the line shaft driven through a suitable drive unit. Each of end
rings is trunnion mounted for the purpose of rotation. These end rings are built in the form of semi circle by a suitably designed plate structure.
Clamps: The wagon tippler is equipped with six hydraulically-operated steel clamping arms moving through the hydraulic cylinder. All the clamps are designed to more into position as the wagon tippler begins to rotate, and they clamp on the top of the
wagon at a pre-determined angle and hold the wagon firmly until it returns to its normal resting position.
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DS System: This is a dust suppressing system. When the wagon is unloaded and the coal falls on the hopper there is a release of a vast amount of dust, so in order to minimize
the dust there are water sprinklers that help in suppressing the dust. This system is manually operated as per the requirement.
Drive Unit: The drive unit is either electromechanical or hydraulic. The electromechanical drive consists of an electric motor coupled with a speed reduction gear box and
brake mounted on the input shaft of the gear box. A hydraulic drive consists of a power pack with electric motor and a hydraulic motor coupled with a helical gear
box. The brake is built into the hydraulic motor, and an external hydraulic thruster brake is mounted on the input shaft of the gear box.
Guide Wheel: It is a devise that keeps the side arm charger on track and bear the jerk or pressure while pulling or pushing of wagons.
WORKING PRINCIPLE:
In the tippling operation, loaded wagon is placed on the wagon tippler platform and wagon tippler rotation starts. The clamping system holds the wagon in place as its rotated. The clamping system
is having six vertical clamps, which are operated by oil pressure and clamps holds the wagon from the top. In the process of discharge, rotation is start from 40º and
continues up to max angle of 150º, so as to discharge the material into the hopper. After process of discharge, the return cycle starts and the empty wagon with
platform comes to the rest position.
The wagon tippler is operated by a hydraulic system for the tripling purpose. The clams, the inclination of the platform are operated by hydraulic system by a drive
unit which is located on any one side of the wagon tippler.
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The specification of the motor used for the movement of the side arm charger is:
Weight- 910 Kg Re-lubricating interval D/N- 3000/6000 hrs
Grease- UNIREXN3
V Conn. Hz KW HP Rpm Amp
415 Δ 50 110 150 1485 190
There are 3 hydraulic pumps of 190 bar pressure.
1- Forward movement. 1- Reverse movement.
1- Movement of the boom.
There is a limit switch to control the height of the boom, sometimes we need to lower the boom or increase its height, so after reaching the extreme positions the
operator comes to know with the help of the censor.
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The specification of the clamping motor is as follows:
Ambient temp.- 50⁰C
Eff. - 93.80 Weight- 610 Kg
Re-lubricating interval D/N: 6000/6100 hrs Grease: UNIREXN3
V Conn. Hz KW HP rpm Amp.
415 Δ 50 75 100 1475 132
+/- 10% +/- 5%
There is another motor for the movement of end disc. The gear box of end disc is
located below it.
The specification of the motor is as follows:
V Conn. Hz KW rpm Amp
415 Δ 50 132 1485 287
Weight – 960 Kg
Amb. - 45⁰C
Eff. – 95.50%
Re-lubrication interval D/L : 3000/3500 hrs Grease – 10 C SERVO PLEX LL3 or Equivalent 4 Complex
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After the coal is stocked in the hopper, it follows the same path to that of the truck tippler i.e. it is carried by an apron feeder and then by a dribble conveyer to the
crusher. The specifications of the apron drive motor:
3φ squirrel cage induction motor.
Duty- S1
Insulation class- F Grease Quantity- 112
DE Brg- N321 NDE Brg- 6321
Pf V KW HP Amp Rpm Eff. Hz
.85 415 132 175 229 987 94.51 50
Gear box- 38.4:1 P1
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The specification of the motor that drives the dribble conveyer:
V KW Hz PF Amp Min-1
415 55 50 0.80 99.9 1450
CRUSHER:
The crusher used in WT is same as that used in TT. It is a single roller crusher which has grinding teeth with the help of which the coal is crushed. The coal feed
size of the crusher is 770mm-800mm (approx.) and the output size of the crusher is 300mm with an efficiency of about 80%.
It is run by the motor of following specification:
3φ AC Induction Motor
V KW Hz PF Amp Eff. Rpm Amb.
6600 225 50 0.86 240 96% 1490 50⁰C
Lubrication- GREASE SHELL ALVANIA-3
Weight- 2600 Kg G.D2 – 35 Kg m2
Conn. – Δ Frame – DC315F800
The size of the output coal from the crusher is approximately equal to 300mm. The
coal from wagon tippler is then passed on to the main crusher through conveyer belt 1.
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In the Track Hopper BOBRN i.e. Bottom Opening Bottom Releasing wagons are unloaded.
Hopper is 250m long and 7.5m wide with 4500 ton capacity.
The grill size of the track hopper is 300mm X 300mm. The coal more than the size of the grill doesn’t fall directly into the hopper; it is
drilled, hammered and then transformed into coal of required size. Then the coal is stored in the hopper. No DS system is required in track hopper as it is
underground and the amount of dust generated is comparatively very less.
The coal received through bottom opening bottom release (BOBR) wagon rakes is unloaded in underground R.C.C. track hopper. Paddle feeders are employed under
track hopper to scoop the coal and feeding onto underground reclaim conveyors. Belt weigh scales are provided on these conveyors for measurement of coal flow
rate.
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PADDLE FEEDER: In recent times Paddle Feeders have been very successfully used in Coal Handling
Plants and other installations all over the world. Especially, for the extraction of loose materials from Bottom Discharge Wagon System.
Only the bulk material in the angle of repose is discharged from the bunker table and onto a conveying system underneath, such as a belt conveyor. This bunker arrangement is used for free-flowing bulk material because new material will
freely flow downward to replace material which has previously been discharged. As the material flows through the gate, its angle of repose will stop the flow of
material. For cohesive and difficult flowing bulks materials, the Discharge Paddle not only
discharges from the angle of repose, but it deeply penetrates the bulk material. The degree of penetration of the Discharge Paddle depends upon the flow-ability
of the bulk material, i.e., the internal friction of the material. The penetration must be sufficient so that the bridges formed by the bulk material are continuously
destroyed during discharge by the vertical pressure head of material above. Activation of the bunker content becomes greater yet by the back and forth motion
of the Discharge Wheel along the bunker table. This effect of activation is more intensive the more often the Discharge Wheel travels back and forth during discharging.
The throat of the bunker table depends on the size bulk material and should, in general, be three to five times larger than the maximum lump size.
There are 2 paddle feeders that cover the entire length of the hopper for discharge
of coal. In case, if one of the paddle feeders is not working than 1 paddle feeder is designed in such a way that it can alone cover up the entire length. There is a limit
switch which guides each of the paddle feeders to the centre. Hence, the entire length of the hopper is covered by 2 paddle feeders in full working condition.
There are 2 censors installed that guide the paddle feeder in forward as well as in
backward direction. There are 2 electric motors. One of the motor is used for rotating the arm that helps in movement of coal from the hopper to the belt and the
other motor drives the paddle feeder in forward and backward direction.
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I.L.M.S. It stands for In Line Magnetic Separator. It is a device that separates the foreign
material that comes with the coal like steel rods, iron balls, etc. this foreign material that come along with the bulk material may damage the conveyer belts,
scrappers and if it passes through the scrapper in any case then it may block the chute or it can also damage the crusher.
Inline / Cross Belt magnetic separator consists of a magnet with a belt conveyer around it. Functionally it is the same as the suspension magnet except in this case
the tramp iron/ ferrous particles are separated and simultaneously knocked off from the magnet and the conveyer line. Hence it is generally called the Self cleaning
magnet.
No man power is required during the operation of the magnet and after the magnet has been operated.
Coal then passes on to the screamer.
SCREAMER:
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The screamer has 12 LT motors arranged at a distance of 30mm between each motor.
It has 2 CHUTES for following purpose:-
The coal of size 0-30mm is dispersed to the buffer drum.
The coal of size 31-300mm is passed to the crusher for crushing.
CRUSHER:
It has a rotor shaft mounted on a Suspension Bar that has four row of alternate
tooth hammer and ring hammer arrangement with a gap of 30mm.
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Specification of drive motor:
3φSq. Cage induction Motor 710 KW
11KV 50Hz
50.8 Amp RATED SPEED- 596 rpm
AMB Temp. - 40⁰C
WEIGHT- 9900 Kg Connection- Y
Cosφ= 0.78
BUFFER DRUM:
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STACKER AND RECLAIMER:
BOOM:
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Used for both stacking and reclaiming.
Can rotate 180⁰ from its normal by slew mechanism.
Boom luffing arrangement for up and down movement of the boom. It can
move down to 11.8⁰ and upward to 8⁰. Operated by a separate control panel not by PLC.
BUCKET:
STRECHABLE DEVICE: USED FOR FOLLOWING PURPOSES:
To determine whether to receive coal from 4A or 4B or both.
Whether to directly send it to bunker or to send it to yard.
Used for stacking and reclaiming.
PULSE CLOTH BAG CATCHER:
It is situated on opening of the chutes.
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It extracts dust aroused by the discharge of coal.
It has collector bags inside which sticks the dust in it. Then the air is filtered
out and the dust is vibrated off. It pulses once in 10sec.
15KW, Filter Area- 130m², Rated coined vol.- 1300m³/h, Resistance from
equipment- 1200Pa, Efficiency of Dust Catcher- 99.9%.
CONVEYER SYSTEM:- A conveyor belt (or belt conveyor) consists of two or more pulleys, with a continuous loop of material - the conveyor belt - that rotates about them. One or
both of the pulleys are powered, moving the belt and the material on the belt forward. The powered pulley is called the drive pulley while the unpowered pulley
is called the idler. There are two main industrial classes of belt conveyors; those in general material handling such as those moving boxes along inside a factory and
bulk material handling such as those used to transport industrial and agricultural materials, such as grain, coal, ores, etc. generally in outdoor locations. For keeping
proper tension in the belt, a counter weight is hanged by pulley system. Belt capacity is 3000 ton/hr. Belt conveyor speed is maintained at 3.31 m/s.
Conveyor safety devices in CHP:-
Pull chord:
Pull cord switch is mounted on the walkway side of the conveyor belt,
preferably at about every 20-25 meters. When the rope is pulled from any side, the switch gets operated. Unless and until the handle is reset to normal
position manually, the switch remains in operated condition. Pull Rope switch All the Pull Cord Switches installed along an individual belt are electrically wired in series and connected to the control station by a two core
cable. Therefore actuation of any one of these Pull Cord Switches will stop the concerned conveyor until the particular switch is manually reset.
Belt Sway:
For normal running of the belt with acceptable swaying, the belt-sway switch is generally mounted on both sides and near the edge of the conveyor
belt. A is generally mounted on the both sides and near the edge of the conveyor belt. A small clearance is allowed between contact roller and the
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belt edge to allow the normal running of the belt with acceptable swaying. When swaying exceeds normal limit, the belt edge pushes the contact roller,
which drives the switch and operates the contacts. The switch reset automatically when the belt resumes normal running.
Zero Speed Switch:
The basic principle of speed monitor is comparison of pulses received from sensor with standard pulses. The unit consists of two parts: CONTROL
UNIT and “SENSOR PROBE”. The sensor is to be installed with its sensing face in close proximity of rotating object. On this object, flags are to be
fixed. The sensor produces strong electromagnetic waves, which get disturbed by the flags, giving rise to corresponding pulses. These pulses are fed to the control unit where they are compared with standard pulses to sense
the speed.
Local Stop push button
Interlock system
IDLERS:
Carrying idler.
Returning idler.
Carrying adjustable idler.
Returning adjustable idler.
Bed idler.
Angular idler.
Impact idler.
Adjustable idlers are kept at a distance of 4m approx from each other.
Impact idlers are installed on the conveyer belt below the opening of the
discharge chute to take the pressure of the discharge and to prevent the
damage caused to the conveyer belt.
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STACKING CYCLE
0A/B /C/D→1A→2A→Roller screen A/C→ Crusher A/C→ Buffer
drum→3A→4A→5A→Boom Conv.
0A/B /C/D→1B→2B→Roller screen B/D→ Crusher B/D→ Buffer
drum→3B→4B→5A→Boom Conv.
0A/B /C/D→1A→2A→Roller screen A/C→ Crusher A/C→ Buffer
drum→3A→4A→6A→5B→Boom Conv.
0A/B /C/D→1B→2B→Roller screen B/D→ Crusher B/D→ Buffer drum→3B→4B→6B→5B→Boom Conv.
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SCRAPERS: Scrappers are of various types like:
Primary Scrapper.
Secondary Scrapper.
V-shaped Scrapper.
Diagonal Scrapper.
All the above scrappers are installed in different areas of CHP depending upon
their use. Like V –shaped scrapper are used in bunker area for feeding the coal into the bunker from 2 feeding chutes, diagonal scrapper are used in the area where the
coal is to be discharged in an angle and where there is only 1 discharge chute.
FEEDERS:
Model F55
Accuracy Grade 1
Capacity 105 t/h
Power 8 KW
Belt width 1000mm
Power supply 415 V 50 Hz
Serial No. 6L080454
Date of manufacture 2008/6
Company SAIMO TECHNOLOGY
Feeders serve the job of transporting the coal from the bunker to the mill with the help of a chain belt and a Clean Out Conveyer. The coal in the chain belt
sometimes fall inside the feeder, the job of clean out conveyer is to clean this coal dust and drop it inside the mill.
The specifications of the motors that drive the above belts is as follows:
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PARAMETERS MAIN FEEDER MOTOR (specifications)
COC MOTOR (specification)
TYPE DV112M4 DT90L4
r/min 1420 1410
V 240Δ /415Y 240Δ /415Y
A 14.6/8.4 5.9/3.45
cosφ 0.84 0.78
Power 4 KW 1.5KW
Duty S1 S1
PARAMETERS
MAIN FEEDER MOTOR GEAR-BOX
COC MOTOR GEAR-BOX
Type SA77PV112M4 SA67 DT9024
ne 1420rpm 1410rpm
I 41.07 85.83
oil Shell Omala 680/5.8L Shell Omala 680/2.9L
ma 960 Nm 600 Nm
na 35 rpm 16 rpm
IM M4A M4A
THE MILL:
The mill installed in Vedanta is a BBD 4772 DOUBLE INLET DOUBLE
OUTLET TUBE MILL. It is 72m in length and 47 m in diameter. The input coal
size of mill is 30 mm and the output coal size is 80 microns. Pinion teeth – 25nos.
Bull Gear teeth – 225nos. Speed ratio between Bull Gear and Pinion - 225/25 =9
Speed ratio of Reducer Gear Box – 993/139=7.1
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The grinding media used in the mill is grinding balls which are also known as
chromium balls generally called chromium steel because chromium is in maximum
percentage that is 14 %.
Others material used are
Nickel
Silicon
Manganese
Carbon
The mill is run by 2 motors main motor and slow motor. Slow motor is used when
the mill is to be rotated at a slow speed initially.
Main Motor
Power 2500KW
V 11
rpm 993rpm
A 164
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Slow Motor
Power 22 KW
V 415V DC 110V
rpm 1470rpm
A 38.5
Torque 220 Nm
Weight 215 Kg
The rpm of the mill is 15.3 so a speed reducer or a sun and planet gear speed reducing system is installed which is lubricated by a device of following
specification:
JET LUBRICATION
DEVICE
Oil Pressure 0.63 Mpa
Air Pressure 0.63 Mpa
Nozzle No. 5
Jet Range 200mm
Before the mill starts working, the sides of the mill are sealed by an air layer that is provided by sealed air fan which provides a pressure of 14 kg.
BOILER:
A BOILER is a device for generating steam. It consists of two principal parts: the
furnace, which provides heat, usually by burning a fuel, and the boiler proper, a
device in which the heat changes water into steam. A steam engine is driven by
steam generated under pressure in a boiler. The amount of steam that can be
generated per hour depends upon the rate of combustion of the fuel in the furnace
and upon the efficiency of heat transfer to the boiler proper. Since the rate of
combustion of the fuel in a furnace is largely dependent upon the quantity of air
available, i.e., upon the draft, a sufficient supply of air is an important
consideration in boiler construction. In some large installations the incoming air is
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preheated by the waste heat of the flue gases, and in order to increase the speed of
combustion a forced draft (air at higher than atmospheric pressure) is often used.
Two types of boilers are most common—fire-tube boilers, containing long steel
tubes through which the hot gases from the furnace pass and around which the
water to be changed to steam circulates, and water-tube boilers, in which the
conditions are reversed. Water is changed to steam in these continuous circuits and
also is super-heated in transit. This additional heating of the steam increases the
efficiency of the power-generating cycle.
There are 4 boilers in Independent Power Plant (IPP) at VEDANTA
ALUMINIUM LIMITED, Jharsuguda, which produces superheated steam at a
temperature of about 540 °C and 17.5Mpa pressure. This super-heated steam is
used to rotate the prime move (turbine) to produce electricity from generator.
SCHEMATIC DIAGRAM OF COAL FEED BOILER:
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Make - Harbin boiler, China
TYPE: -
Subcritical reheat, Single furnace, Pulverized fuel, water tube, forced/assisted
circulation, tangential fire, balance draft.
Length x Width = 17.448m x 18.542m
Height of boiler = 90m
Boiler Drum level = 70m
Chimney height = 275m
Conversion of Water to Steam evolves in three stages.
• Heating the water from cold condition to boiling point or saturation temperature –
(sensible heat addition).
• Water boils at saturation temperature to produce steam – (Latent heat addition.)
•Heating steam from saturation temperature to higher temperature called
Superheating to increase the power plant output and efficiency.
WATER CYCLE:
1. BOILER FEED 2. PUMP 3. HP HEATERS
4. FRS (Feed Regulating Station) 5. ECONOMISER
6. BOILER DRUM 7. DOWNCOMER
8. HEADER 9. BOILER CIRCULATION PUMP
10. BOTTOM RING HEADER 11. WATER TUBE
12. BOILER DRUM
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STEAM CYCLE:
1. BOILER DRUM 2. Low Temperature Super Heater
3. Divisional Super heater 4. Platen Super heater
5. Final Super Heater 6. Main Steam Pipe
7. HP TURBINE 8. COLD REHEAT LINE
9. REHEATER 10. HOT REHEAT PIPE
11. IP TURBINE 12. CROSS OVER P
13. LP TURBINE(2 Nos)
FLUE GAS CYCLE:
1. FURNACE 2. ECONOMISER 3. Air Pre-Heater
4. ELECTROSTATIC PRECIPITATOR 5. FABRIC FILTER
6. ID FAN 7. CHIMNEY
BOILER DRUM: Internal dia-1778mm
Wall thickness –
Top half 182mm
Bottom half 153mm
Normal water level – below the drum centre line is 229mm
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Boiler drum has:
Cyclone separator (112nos)
Single separator output - 18.11 tons/hr. Use: It separates the steam from water.
DRIER (148Nos)
Use: Remove the moisture content from steam.
BLOW DOWN (2types)
1. Continuous blow down (CBD)
2. Intermediate blow down (IBD)
Down comers- 6nos.
Pipe diameter × wall thickness-406×34 in mm
Steam output from boiler – 1800tons/hr.
BOILER CIRCULATION PUMP (BCW PUMP): This pump is installed at 26m height in boiler front side. It is a vertical type centrifugal pump which has suction (of saturated water at 3500C) from boiler
drum.
Suction Pressure-19.1MPa
Discharge Presure-19.6MPa
Pump type – LUVAC 2*350-500/1
Nominal bore of pump nozzle: Suction nozzle (diameter – 427.25mm) Discharge nozzle (diameter – 303mm)
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ECONOMISER:
Economiser is one type of heat exchanger, in which Feed water (i.e. Boiler feed
pump discharge water) collects heat from flue gas. Feed water flows though tubes. It is installed in the second pass in the boiler. Feed water inlet temperature in
Economizer is 1800C and outlet temperature is 3500C. There is a piping between Bottom ring header and economizer which is called economizer recirculation line. When the feed water flow is not sufficient in economizer in initial boiler starting,
water comes from bottom ring header to economizer by this recirculation line to prevent economizer tubes.
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AIR PRE-HEATER (APH): It receives heat from flue gas and transfers it to the primary air and secondary air
coming from PA fan and FD fan. In each boiler 2 numbers of APH are installed. Here tri-sector APH (L jungstrom APH) are used which have three sections as shown in figure below. The APH rotates at 1rpm.
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APH Main technical specifications: There are 3numbers of heating element layer in APH which are collect heat from
Flue gas and release it to primary and secondary air.
PRIMARY AIR PATH:
BURNER:
A Boiler has 4nos. of burner in each corner of boiler first pass. In Each burner there are 18 nos. of dampers (or pneumatic actuators) of coal, oil and air and there
arrangement is shown below:
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Therefore each boiler has total 24 coal lines, 16 oil lines and 32 air lines and each
burner has 6 coal lines, 4 oil lines and 8 air lines. In burner there are 3 nos. of igniters and flame scanners. Air lines cannot be seen on the boiler because they are
interconnecting with wind box (A chamber in two side of boiler storing secondary air for proper combustion) from boiler inside.
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SOOT BLOWERS: Types of soot blowers:
Short soot blower(SRSB) – 88Nos
Long soot blower(LRSB) – 32Nos
Helical soot blower(HRSB) – 8Nos
APH soot blower – 2Nos
Use:
Soot blower is used for removing soot from boiler pressure parts and APH providing steam from platen super heater with temperature 350˚C and pressure
1MPa. SRSB are in the first pass of boiler which removes soot from water walls, LRSB and HRSB are in first pass and second pass of boiler upper side respectively.
FANS: Types of fans:
Primary Air Fan (2nos.)
Forced Draft Fan (2nos.)
Induced Draft Fan (2nos.)
Seal Air Fan (2nos.)
Scanner Air Fan (2nos.)
PRIMARY AIR FAN (AXIAL TYPE FAN): It is a variable moving blade type axial flow fan. PA Fan takes its suction from the atmosphere and the air is discharged into two directions. First, hot PA which is
passed though APH and Second, Cold PA which is directly send to coal mill. In PA fan flow is controlled by the method Blade Pitch Control which is Air flow in
fan is controlled by fan blade angle changing. Hot PA is used for remove moisture content from coal inside the mill. Cold PA is
used for feeding of coal into the burner which restricts self-combustion of coal. Before entering mill, cold PA and hot PA are mixed to maintain standard operating
temperature (mill outlet temperature is700C).
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PA Fan Motor Specifications:
Power - 3300KW Voltage – 11kv
Speed – 1493rpm Current – 181amp
FORCED DRAFT FAN (AXIAL TYPE FAN): FD fan takes its suction from the atmosphere and discharges to the APH. From APH the secondary air goes to the Wind box in furnace. In PA fan flow control is
Blade Pitch Control in which Air flow in fan is controlled by fan blade angle changing. FD fan supply secondary air to furnace for proper combustion.
FD Fan Motor Specifications:
Power – 1176kw Voltage – 11kv
Speed – 993rpm Current – 94amp
INDUCED DRAFT FAN (AXIAL TYPE FAN): ID Fan sucks the flue gas from Fabric filter and throws out flue gas to the
atmosphere through the chimney. Flow control of ID fan by Inlet Guide Vane (IGV).
ID Fan Motor Specifications:
Power – 6000kw Voltage – 11kv
Speed – 747 rpm Current – 369amp
SEAL AIR FAN (RADIAL TYPE FAN): Seal air fan is used for sealing of Coal mill, as it prevents the entering of dust particle into the system. It takes its suction from cold PA.
SA Fan Motor Specifications: Power – 250kw
Voltage – 11kv Speed – 1490rpm
Current – 16.6amp
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TURBINE:
Turbine is a rotary engine that extracts energy from a fluid flow and converts it
into useful 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.
Steam turbines usually have a casing around the blades that contains and controls
the working fluid.
Modern steam turbines frequently employ both reaction and impulse in the same
unit, typically varying the degree of reaction and impulse from the blade root to its periphery.
In Power Plant the turbine Shaft is coupled to the Alternator shaft in which the
rotational energy is then converted into electrical energy.
SPECIFICATIONS:
Make - Don Fang, CHINA Rotation speed-3000 rpm
Steam input at HP turbine 17MPa and 5400C Steam input at IP turbine 3.5MPa and 3500C
TYPE: sub-critical, primary reheating, single shaft, three cylinder and condensing type.
HP Turbine – Impulse-Reaction type (1No)
IP Turbine – Reaction type (1No)
LP Turbine – Reaction type (2Nos)
Stages:-
HP Turbine – 1(Impulse) + 8(Reaction) = 9 stages
IP Turbine -5 stages
LP Turbine - 2*7=14 stages in each turbine
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EXTRACTIONS: Eight steam extractions are designed, which supply 3 HP heaters, 1 de-aerator and 4 LP heaters.
1st extraction to HPH 1 -> HP turbine 6th stage
2nd extraction to HPH 2 -> HP exhaust/CRH line
3rd extraction to HPH 3 -> IP turbine 2nd stage
4th extraction to DEARATOR and CRH -> IP turbine 5th stage
5th extraction to LPH 5 -> LP turbine 2nd stage
6th extraction to LPH 6 -> LP turbine 3rd stage
7th extraction to LPH 7A/7B -> LP turbine 4th stage
8th extraction to 8A/8B -> LP turbine 5th stage
CONDENSATION PATH: HP TURBINE – High Pressure Turbine
IP TURBINE – Intermediate Pressure Turbine
LP TURBINE – Low Pressure Turbine
CEP – Condensate Extraction Pump
CPU – Condensate Polishing Unit
GSC – Gland Steam Condenser
LPH – Low Pressure Heater
HPH – High Pressure Heater
FRS – Feed Regulating Station
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The Turbine Shaft has 10nos. of bearings for holding it. Among these 9nos. are
Journal bearings and one is thrust bearing. The superheated steam from boiler is expanded in HP turbine. After expansion the steam is reheated in re-heater for further expansion the steam goes into IP Turbine
and through cross over pipes it goes to LP Turbine.
CONDENSER:
It is one type of heat exchanger. The extracted steam from LP turbine is condensate in condenser by cooling water is placed below the LP turbine. There are around
forty thousand tubes in the condenser by which water is carried to the cooling tower where the cycle water is naturally cooled.
Specifications:
Type – Double shell, double back-pressure, single stroke (in terms of each shell)
Cooling Area – 40,000 m2 Design outlet Cooling Water Temperature – 35.3˚C (max. 38˚C) Condenser design pressure – 10.2kPa
Condensate Water Temperature – 46.5˚C Cooling Medium – Fresh water
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Cooling Towers:
It utilizes natural flow and buoyancy of the air so as to remove the heat via the tall
chimney like cooling towers.
Specifications:
Type-Natural Draft Cooling Tower (NDCT) No of cooling tower – 1x 4(1 per unit)
Height – 150.1m Cooling Area – 9000 m2 Dia.
Of the tower at the bottom – 110 m Tower throat diameter – 66.50 m Of the tower top -71.176 m
Hot Well:
The condensate water from condenser is stored in Hot well.
CEP: It is a single stage, vertical centrifugal pump. These pumps are provided for
extracting condensed Water from hot well.
Specifications:
Flow – 1639/1784 (max.) tons/hr. Inlet water pressure – 2.9/3.9 (max) MPa Efficiency – 84%
Speed – 1480rpm
CPU:
In CPU, 3 nos. of mixed bed chambers are used. Here chemical dosing of the condensate water is carried out by adding chemicals like hydrazine (N2H4) and
ammonia (NH3). N2H4 is used for Oxygen removal and NH3 is used for increasing the pH value.
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GSC:
In the initial stage the turbines are in vacuum state. To prevent the atmospheric air inflow, labyrinth glands are provided at the turbine inlet. Leak off steam from
turbine gland is utilized for heating the condensed water which is coming from CPU. The steam is then vented out in the atmosphere.
FRS:
This includes a non-returnable valve (NRV), which maintains the direction of flow
of feed water from HP heaters to Economiser. Two more valves maintain the amount of flow. It also includes 30% bypass line regulated by a valve.
DE-AERATOR:- It is used for removing Oxygen from water. The principle
followed is Henry’s solubility law, according to which solubility is inversely proportional to temperature.
Specifications: Design pressure – 1.23MPa
Working pressure – 1.083MPa Design temperature – 300˚C
Working temperature – 356.9˚C Rated inlet water temperature – 185.6˚C
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LP HEATERS:
HP HEATERS:
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MOTOR DRIVEN BOILER FEED PUMP (MDBFP): This pump is used during initial start-up of the unit when sufficient steam to drive
the TDBFP is unavailable. It is also used when 1 TDBFP is under maintenance. Power consumption of MDBFP is 11.6MW. A fluid coupling is used to control the feed water flow.
Specifications:
Type – horizontal centrifugal pump No. of stages - 5
Rated flow – 1155m³/hr.
Rated speed – 5873rpm Inlet water pressure – 2.38MPa Inlet temperature – 179.9˚C Necessary
NPSH – 58.4m
Motor specifications: Power – 11.6MW
Voltage – 11KV Speed – 1490rpm
TURBINE DRIVEN BOILER FEED PUMP (2NOS.): Turbine driven boiler feed pump (TDBFP) increases the pressure from 1.2MPa to
20MPa. This type of feed pump is preferred as there is no power consumption by the motor. In normal operating conditions, both TDBFPs run while MDBFP is
switched off.
Specifications: Type – single cylinder, single flow, impulse, condensing type Steam source – steam extraction no.4
No. of stages – 7 Rated power – 12000KW
Maximum working speed – 6000rpm Exhaust pressure – 11.9KPa
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BOOSTER PUMP (3nos.):
Boiler feed pump (BFP) is unable to suck low pressure water (2kg/cm2), so Booster pump is used to increase the pressure up to 12kg/cm2. Booster pump
supplies BFP sufficient NPSH (Net Positive Suction Head). Specifications:
Type – single stage, double extraction, horizontal type, centrifugal pump
Flow – 1198.5 m³/hr.
Water temperature – 179.9˚C
Speed – 1490rpm Shaft power – 518KW
Inlet pressure – 1.19MPa
DEMINERALIZE WATER PLANT & WATER
TREATMENT SYSTEM
DM Water:- Water without minerals like calcium, magnesium, carbonates, chlorides, silica etc.
is known as De-mineralized water.
Why DM Plant required?
• To prevent scaling, corrosion and erosion of Water and steam pipes and
tubes.
• To avoid deposition and erosion over turbine blade.
• To ensure the better utilization of heat energy and improve efficiency.
Pre-treatment of water (PT Plant):- • The water entering DM plant should be free from suspended colloidal
particles and Impurities which are removed in the PT PLANT.
• The suspended and colloidal particles are removed in clarifiers.
• In clarifiers, coagulation and dosing processes are done and are called as Poly Aluminium Chloride (PAC) and Poly Acrylic Amyl (PAM).
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PAC: - It helps in neutralization of charges of suspended and colloidal particles
and after neutralization they come in contact with each other and make a flux of
95% suspended and colloidal particle, so repulsion occurs between them.
PAM: - It helps to combine the smaller particles i.e. flux to form bigger size i.e.
heavier ones and settle down as sludge. It helps in decreasing turbidity of water.
Turbidity less than 10 is considered very good quality for use in the DM plant.
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Pre-water Treatment Procedure:-
Chemical Dosing In PAC:-
Raw water
Coagulation Treatment (PAC and PAM dosing)
Clarification Treatment
(adding coagulating agent to the reaction)
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Factors Affecting Coagulation Treatment:-
Water temperature (350C)
pH of water (6.5-7.5)
Chemical dosage
Foreign material in raw water
PAC electric agitator tank
PAC container
PAC dosing & metering pump (3 NOS.)
Mechanical accelerator clarification
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Flow Chart of Water System:-
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Reserviour
Raw water tank
Raw water pump (5 nos.)
Mechanical clarification pond (6 nos.)
Water basin (4 nos.)
compressive pump (4 nos.)
DM plant
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SOURCE OF RAW WATER: Raw water is received from Hirakud Dam at a pressure of 8kg/cm2 and its capacity
is 2800m3/hr.
RESERVOIR:
There are two reservoirs and their capacities are 2.4lakhs m3 and 1.9lakh m3 respectively.
RAW WATER TANK:
Water comes from reservoir through gravity valves (2nos). Its capacity is 1000m3.
CLARIFIERS:
Water comes from water tank to the reservoir through raw water pumps
(6nos.). Each having a capacity of 1330m3.
Before water coming to the clarifier chemical dosing is done (PAC and
PAM).
WATER BASIN: There are three numbers of water basins are present.
• Circulation water basin
• Service water basin
• Five fish pump basin
COMPRESSIVE PUMPS:
There are four nos. of pumps. • CW make-up water pump – 3nos.
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• Service water pump – 3nos.
• APH back wash pumps – 2nos.
• Potable water pump – 2nos.
Then the service water goes to DM Plant.
DM Plant:-
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RAW WATER STORAGE TANK: Capacity – 500m3
RAW WATER PUMP: Capacity – 283m3/hr.
MECHANICAL FILTER: Diameter – 3224mm Flow rate – 58m3/hr.
Filter cloth – 800mm
Use:- Removes turbidity.
ACTIVATED CARBON FILTER: Diameter – 3224mm Flow rate – 58m3/hr.
Temperature – 0 to 500C Height – 2000mm
Use:- Remove odour (de-chlorination).
STRONG ACID CAT ION: Diameter – 3024mm Height – 3000mm
Flow rate – 283m3/hr. Dilute - HCL Use: - Removes hardness.
DEGASIFIER (DE-CARBONATOR): Diameter – 2824mm
Height – 1600mm Capacity – 15m3
Flow rate – 283m3/hr.
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Use: - CO2 removal.
INTERMEDIATE PUMP: Capacity – 283m3/hr.
STRONG BASE ANION: Height – 3750mm Pressure –0.75mpa
Flow rate – 283m3/hr. Dilute - NaOH
Use:- Remove CO2, Cl2, SO4-2 & Sio2.
MIXED BED: Diameter – 3024mm
Temperature – 500C Flow rate – 283m3/hr
Dilute – NAOH & HCL
DM WATER STORAGE TANK: Diameter – 18000mm Capacity – 2400m3
Height-10446mm
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ASH HANDLING PLANT (AHP):
This system carries out the vital function of disposing the ash generated in the whole process. It has following components:- Bottom Ash Handling – slurry pumping system
Fly Ash Handling – pressurized pneumatic conveying system
Ash Disposal – high concentration slurry disposal (HCSD) system
Water Recovery System – water consumption reduced by reutilization of
bottom ash water
TYPES OF ASH:
Bottom Ash – it is collected from the furnace bottom. It generally constitutes 20% of the total ash generated.
Fly Ash – it is collected from the hoppers of ESP, FF, APH and Economiser. This constitutes rest 80% of the ash generated.
CAPACITY OF AHP:
Capacity of ash handling plant – 8820 tons/day/2 units Total coal consumption – 10500 tons/day/unit Ash % in design coal – 42%
Ash generated – 4410 tons/day/unit
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General Flow Diagram in Ash Handling Plant:-
BAH-BOTTOM ASH HANDLING
SCC- submerged scraper chain conveyor
CG- Clinker Grinder
ART- Agitator Retention Tank
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BOTTOM ASH HANDLING:-
In this the bottom ash collected from furnace bottom is carried over by the SCC to slag crusher and CG where the size of particles is reduced to less than .036mm.
This slurry is fed into the slurry pond from where the Bottom Ash slurry pumps transfer the slurry into the Dewatering bins for further disposal. Dewatering bin
receives slurry from the Bottom Ash pump and filling process starts. In filling the slurry is allowed to settle for 12 hours. Then a physical check is carried out to ensure 80% filling of ash. The overflow water is sent to the settling tank, which
has settling plates. The overflow water is then sent to the ash water pond where the ash particles are present in negligible amount (in the order of 20ppm). This
water is then reused. Decanting process starts once 80% filling is completed. There are two decanters- centre decanter and side decanter through which water
flows while ash settles in the dewatering bin. De-ashing is carried out by sending the collected ash to the ART by means of conveyor belt. Both decanting and de-
ashing are carried out for 12 hours in each dewatering bin.
Specifications:-
Dewatering bin capacity – 1350 m3
Dewatering bin height – 14m
High efficiency settling tank capacity – 1110 m3
Ash water pond capacity – 1110 m3
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FLY ASH HANDLING:
Fly ash is collected from the hoppers of ESP, FF, APH and Economiser. Then they are brought to the transfer silo by compressed air followed by terminal silo. This
is disposed in three ways – wet ash unloading, dry ash unloading and HCSD system. At first the ash is sent to Ash mixer, using screw conveyors, where LP water is mixed with ash to maintain the ash: water ratio of 40:60. Then this slurry
is sent to the ART. Wet ash and dry ash are disposed off in trucks while HCS is disposed using GEHO pump.
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In ART both bottom ash and fly ash are mixed and they form a mixture to be
disposed which is known as High Concentration Slurry which has very low consumption of water content compared to lean slurry disposal system. This HCSD
system has a ratio of 60% ash and 40 % water. Of this 60% of ash, we are disposing in ratio of 80:20 (bottom ash and fly ash respectively). After this slurry is
sucked by GEHO pump in presence of a suction strainer and then the slurry is disposed in the ash pond.
MAJOR COMPONENTS IN ASH HANDLING SYSTEM: Dewatering bins (3nos.)
Settling tank (1no.)
Ash water tank (1no.)
Transfer silo (2nos.)
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Terminal silo (2nos.)
Agitator Retention Tank (3nos.)
GEHO pump suction Strainer (6nos.)
HP pump (3nos.)
LP pump (2nos.)
Charge pump (3nos.)
GEHO pump (3nos.)
Sewage pump (2nos.)
HP/SLURRY PUMP:-
Motor power – 90kw Discharge – 143m3/hr.
Current – 150amp Speed – 1480rpm
Frequency – 50Hz
Use:- HP water pump is used for flushing and conveying. Flushing of strainers is
necessary as the ash particles stuck on the mesh have to be removed.
LP PUMP:-
Motor power – 185kw Voltage – 415v
Current – 317amp Power factor – 0.86
Speed - 990rpm Frequency – 50Hz
Use: - LP pump is used for mixing ash and water.
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SEWAGE PUMP:- Motor power – 37kw
Voltage – 415/720v Speed – 1475rpm Frequency – 50Hz
Use:- Sewage pump is used for slurry conveying.
CHARGE PUMP:
Discharge – 320m3/hr. Suction pressure – 6kg/cm2
Use:- GEHO pump takes suction from charge pump. A strainer with meshing is provided which prevents particles greater than 6 microns from entering the GEHO pump
GEHO PUMP (PLUNGER TYPE PUMP): Motor power – 1218kw
Discharge – 26.3 to 263m3/hr. Pressure – 16000KPa Speed – 5.7 to 57rpm
Use: To reduce the use of water and conveying slurry to the ash pond.
VERTICAL SLURRY PUMP: Motor power – 15kw Discharge –40m3/hr.
Speed – 2053rpm
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SWITCHYARD AND GENERATOR
SUBSTATION LAYOUT:- It is important regarding the design aspect. It determines the location and spacing
of equipment, bay width and length, layout of the cable trenches, and roads. SEL has a 400KV substation. It has 18 bays in the old switch yard and 6 bays in the new
switchyard. Here the bus is extended to the new switchyard. The switchyard bus bar is connected to 12nos. of 1-Ø generating transformers. It has a two bus-bar
system from which power is extended to other grids. The main parts of a substation are:
Transformers
Circuit breakers
Isolators
Potential transformers
Insulator and fittings
Lightning protection
Coupling capacitor and wave trap
Instrument transformers (current transformers)
Design of earthing
Protection schemes and interlocks
Auxiliary facilities
TRANSFORMERS: The transformers are used according to the requirement i.e. step up or step down. In this switch yard there are 12nos. of generating transformers, 2nos. of station
transformers and 2nos. of interconnecting transformers.
Generating transformers: The generating transformers are used to step up the
generated voltage (22KV) to 400KV.
Rated Power: 250000/250000KVA Rated Voltage:
(420/√3)±2*2.25%)/22KV
Station Transformer: These transformers are used to provide power to the plant from the bus-bar. It is rated as 400KV/11KV Rated Power:
80000/50000/50000±26700KVA Rated Voltage: (420±610*1.25%)/11.5-11.5KV
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CIRCUIT BREAKERS: Circuit breakers are on-load switching devices used to connect or disconnect a circuit. They are designed keeping in view, the intended voltage application,
location of installation and design characteristics. In the switch yard SF6 circuit breakers are used.
ISOLATORS: These are off load switching devices basically used to isolate a part of the switch yard. It is of three types single break, double break and pantograph isolator.
POTENTIAL TRANSFORMERS:
These are transformers used to step down voltages for metering purposes. The voltage is stepped down to a value which can be measured by voltmeter of lower range.
INSULATOR AND FITTINGS: Insulation accounts for a major part. Insulators are used to maintain gap between
the structures and the conductors. They also provide mechanical support to the conductors.
LIGHTNING PROTECTION: Lightning conductors and arrestors are used for providing protection against
lightning. When lightning strikes, it follows the low resistance path to ground which is provided by the conductors which in turn are grounded.
COUPLING CAPACITOR AND WAVE TRAP: These are used to facilitate Power Line Career Communication (PLCC) which can
be used to facilitate communication along the transmission lines.
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INSTRUMENT TRANSFORMERS (CURRENT
TRANSFORMERS):
These are used to step down current to a measurable limit .They are also coupled with differential relays to provide fault protection.
DESIGN OF EARTHING:
System Earthing: To restrict live conductor potential with respect to earth
1. Safe guards the insulation of system
2. Operates protective devices under single phase and earth fault condition
Equipment Earthing: To maintain the non current carrying parts at earth
potential. Safe guards for human & animal from shock hazard and also operate protective devices when fault to earth occurs
AUXILIARY FACILITIES:
These include illumination and ac/dc supply, transformer oil handling system, compressed air system, service bay and fire extinguishers
GENERATOR SPECIFICATION
Type totally enclosed, self-ventilated,
forced lubrication water-hydrogen
cooling, cylinder rotor,
synchronous AC non salient pole
generator.
Model QFSN-600-22F
Power (rated/maximum) (600MW/640MW)
Capacity (rated/maximum) (706 MVA)
Terminal voltage 22KV
Rated current 18525A
Power factor 0.85(LOG)
Short circuit ratio No less than 0.5
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Efficiency ≥98.5% (at 600mw,0.8 logging
power factor )
Rated hydrogen
pressure/maximum hydrogen
pressure
0.45MPa/0.5MPa
NO. of poles 2
NO. of phase 3
Speed 3000 rpm
Frequency 50Hz
Cooling mode Stator winding:-direct cooling,
stator rotor iron core and rotor
winding :direct hydrogen cooling
Insulation class Stator winding :class F
Rotor winding : class F
Unbalance load capability 8% (continuous) I22.t (maximum
transient value): 10
Stator cooling water inlet
temperature
45°c
Stator cooling water outlet
temperature
≤85°C
Hydrogen temperature after
cooling
48°c
Hot hydrogen temperature ≤68°c
Cooler water inlet temperature Maximum 33°c for hydrogen
cooler and stator water cooling
Stator winding temperature limit ≤120°c inter layer temperature
difference (maximum value-
average value )≤12°c
Rotor winding temperature limit ≤115°c
Temperature limit of the structure
on stator end
≤120°c
Stator core temperature limit ≤120°c
Collector ring temperature limit ≤120°c
Hydrogen purity ≥98%
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Hydrogen purity consumption ≤14m³/day
Hydrogen cooler capacity When one hydrogen cooler is
shaped the generator could run at
least 80% of rating without over
heating
Hydrogen capacity 86 m³
Electrical conductivity 0.5-15µS/cm
Stator enclose type double layer enclose
Rated voltage of the rotor 431v
Rated current of the rotor 4727 A
No-load voltage of the rotor 95V
No-load current of the rotor 788A
Excitation mode Self-shunt excitation on static
silicon controlled end
Generated noise level At 1m from generator enclosure
≤90 dB (absolute)
Manufacturer DONGFANG ELECTRICAL
MACHINE CO.LTD.
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Project on fans vibration analysis.
Basically at Vedanta there are two types of fans
1) Centrifugal fan ( shield air fans)
2) Axial fan (ID fan FD fan )
Generally there are three types of fan
1) Centrifugal fans.
2) Axial fans.
Fans at Vedanta
1) PA fan.
2) FD fan.
3) ID fan.
4) Shield air fan.
5) Scanner.
PA fan: - Stands for primary air fan it takes air from the atmosphere and give to
APH (air pre-heater) it takes heat from the flue gas and heat up the air and this
heated air goes into mill to provide proper passage or say guide the way for the
coal dust to exit from the mill and also remove moisture from the coal dust.
FD fan: - Stands for forced draft fan it takes air from atmosphere provided the air
to the boiler for combustion of the coal in it.
ID fan: - Induced draft fan helps for taking out the waste gas from the boiler and
release out it from chimney.
SCANNER:- Scanner air fans are small fans ( Both AC & DC) for supplying
cooling air to scanner head. Scanner heads are placed near the fuel nozzle of every
elevation to monitor the fireball of the furnace. For AC motor driven fans the
suction is taken from FD discharge and for DC motor driven fans
( only for emergency suction is taken from atmosphere.) Complete sets of dampers
suction & discharge are attached on the ducts as per requirement. This fans are
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located rear side of the boiler operating floor and do not need any civil foundation.
It is mounted on structural items and standard erection procedure can be adopted.
Seal air fan: - Seal Air Fan basically functions as booster fan taking suction from primary air fan discharge (cold primary air before AH-A&B) boosting up the air
pressure and supplying seal air to various sealing points of Bowl Mills.
Fan and blower selection depends on the volume flow rate, pressure, type of
material handled, space limitations, and efficiency. Fan efficiencies differ from in Table 1.1.
Fans fall into two general categories: centrifugal flow and axial flow. In centrifugal flow, airflow changes direction twice - once when entering and
second when leaving (forward curved, backward curved or inclined, radial) (see Figure 1.1).
In axial flow, air enters and leaves the fan with no change in direction (propeller, tube axial, vane axial) (see Figure 1.2).
Fan efficiency table:- Table no (1.1)
Type of fan Peak efficiency range
Centrifugal fan
Air foil, backward curve/inclined 79-83
Modified radial 72-79
Radial 69-75
Pressure blower 58-68
Forward curved 60-65
Axial fan
Vain axial 78-85
Tube axial 67-72
Propeller 45-50
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Figure (1.1):- Centrifugal fan
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Figure (1.2):- Axial fan
Centrifugal Fan: - Type The major types of centrifugal fan are: - radial, forward curved and backward curved (see Figure 1.3).
Radial fans are industrial workhorses because of their high static pressures (up to
1400 mm WC) and ability to handle heavily contaminated airstreams. Because of their simple design, radial fans are well suited for high temperatures and medium
blade tip speeds.
Forward-curved fans are used in clean environments and operate at lower temperatures. They are well suited for low tip speed and high-airflow work - they
are best suited for moving large volumes of air against relatively low pressures.
Backward-inclined fans are more efficient than forward-curved fans. Backward-inclined fans reach their peak power consumption and then power demand drops off well within their useable airflow range. Backward-inclined fans are known as
"non-overloading" because changes in static pressure do not overload the motor.
Paddle blade (radial
blade)
Forward curve (multi vane) Backward curve
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Figure (1.3) Type of centrifugal fan
Axial Flow Fan: Types The major types of axial flow fans are: tube axial, vane axial and propeller (see Figure 1.4)
Tube axial fans have a wheel inside a cylindrical housing, with close clearance
between blade and housing to improve airflow efficiency. The wheel turn faster than propeller fans, enabling operation under high-pressures 250 – 400 mm WC.
The efficiency is up to 65%.
Vane axial fans are similar to tube-axial but with addition of guide vanes that improve efficiency by directing and straightening the flow. As a result, they have a
higher static pressure with less dependence on the duct static pressure. Such fans are used generally for pressures up to 500 mm WC. Vane-axial are typically the
most energy-efficient fans available and should be used whenever possible.
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Propeller fans usually run at low speeds and moderate temperatures. They experience a large change in airflow with small changes in static pressure. They
handle large volumes of air at low pressure or free delivery. Propeller fans are often used indoors as exhaust fans. Outdoor applications include air-cooled
condensers and cooling towers. Efficiency is low – approximately 50% or less.
Tube axial Vein axial Propeller
Figure (1.4) Types of axial fan
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Common Blower Types:-
Blowers can achieve much higher pressures than fans, as high as 1.20 kg/cm2.
They are also used to produce negative pressures for industrial vacuum systems. Major types are: centrifugal blower and positive-displacement blower.
Centrifugal blowers look more like centrifugal pumps than fans. The impeller is typically gear-driven and rotates as fast as 15,000 rpm. In multi-stage blowers, air
is accelerated as it passes through each impeller. In single-stage blower, air does not take many turns and hence it is more efficient.
Centrifugal blowers typically operate against pressures of 0.35 to 0.70 kg/cm2, but can achieve higher pressures. One characteristic is that airflow tends to drop
drastically as system pressure increases, which can be a disadvantage in material conveying systems that depend on a steady air volume. Because of this, they are
most often used in applications that are not prone to clogging. Positive-displacement blowers have rotors, which "trap" air and push it through
housing. Positive-displacement blowers provide a constant volume of air even if the system pressure varies. They are especially suitable for applications prone to clogging, since they can produce enough pressure-Typically up to 1.25 kg/cm2 - to
blow clogged materials free. They turn much slower than centrifugal blowers (e.g. 3,600 rpm), and are often belt driven to facilitate speed changes.
Fan Performance Evaluation and Efficient System Operation
System Characteristics:-
The term "system resistance" is used when referring to the static pressure. The system resistance is the sum of static pressure losses in the system. The system
resistance is a function of the configuration of ducts, pickups, elbows and the pressure drops across equipment-for example back filter or cyclone. The system
resistance varies with the square of the volume of air flowing through the system. For a given volume of air, the fan in a system with narrow ducts and multiple short
radius elbows is going to have to work harder to overcome a greater system resistance than it would in a system with larger ducts and a minimum number of
long radius turns. Long narrow ducts with many bends and twists will require more energy to pull the air through them. Consequently, for a given fan speed, the fan will be able to pull less air through
this system than through a short system with no elbows. Thus, the system
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resistance increases substantially as the volume of air flowing through the system increases; square of air flow.
Conversely, resistance decreases as flow decreases. To determine what volume the fan will produce, it is therefore necessary to know the system resistance
characteristics. In existing systems, the system resistance can be measured. In systems that have
been designed, but not built, the system resistance must be calculated. Typically a system resistance curve (see Figure 1.5) is generated with for various flow rates on
the x-axis and the associated resistance on the y-axis.
Figure (1.5) System resistance curve
Fan Characteristics:-
Fan characteristics can be represented in form of fan curve(s). The fan curve is a performance curve for the particular fan under a specific set of conditions. The fan
curve is a graphical representation of a number of inter-related parameters. Typically a curve will be developed for a given set of conditions usually including: fan volume, system static pressure, fan speed, and rake horsepower required to
drive the fan under the stated conditions. Some fan curves will also include an efficiency curve so that a system designer will know where on that curve the fan
will be operating under the chosen conditions (see Figure 1.6). In the many curves shown in the Figure, the curve static pressure (SP) vs. flow is especially important.
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The intersection of the system curve and the static pressure curve defines the operating point. When the system resistance changes, the operating point also
changes. Once the operating point is fixed, the power required could be found by following a vertical line hat passes through the operating point to an intersection
with the power (BHP) curve. A horizontal line drawn through the intersection with the power curve will lead to the required power on the right vertical axis. In the
depicted curves, the fan efficiency curve is also presented.
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88
Figure (1.6) Fan characteristics curve by the manufacturer
System Characteristics and Fan Curves:-
In any fan system, the resistance to air flow (pressure) increases when the flow of air is increased. As mentioned before, it varies as the square of the flow. The pressure required by a system over a range of flows can be determined and a
"system performance curve" can be developed (shown as SC) (see Figure 1.7). This system curve can then be plotted on the fan curve to show the fan's actual
operating point at "A" where the two curves (N1 and SC1) intersect. This operating point is at air flow Q1 delivered against pressure P1
A fan operates along a performance given by the manufacturer for a particular fan speed. (The fan performance chart shows performance curves for a series of fan
speeds.) At fan speed N1, the fan will operate along the N1 performance curve as shown in (Figure 1.7). The fan's actual operating point on this curve will depend on
the system resistance; fan's operating point at "A" is flow (Q1) against pressure (P1).
Two methods can be used to reduce air flow from Q1 to Q2
First method is to restrict the air flow by partially closing a damper in the
system. This action causes a new system performance curve (SC2) where the required pressure is greater for any given air flow. The fan will now operate
at "B" to provide the reduced air flow Q2 against higher pressure P2.
Second method to reduce air flow is by reducing the speed from N1 to N2, keeping the damper fully open. The fan would operate at "C" to provide the
same Q2 air flow, but at a lower pressure P3. Thus, reducing the fan speed is a much more efficient method to decrease airflow since less power is
required and less energy is consumed.
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Figure (1.7) System curve
Fan Laws:-
The fans operate under a predictable set of laws concerning speed, power and pressure. A change in speed (RPM) of any fan will predictably change the pressure
rise and power necessary to operate it at the new RPM.
Fan Design and Selection Criteria:-
Precise determination of air-flow and required outlet pressure are most important in proper selection of fan type and size. The air-flow required depends on the
process requirements; normally determined from heat transfer \ rates or combustion air or flue gas quantity to be handled. System pressure requirement is
usually more difficult to compute or predict. Detailed analysis should be carried out to determine pressure drop across the length, bends, contractions and
expansions in the ducting system, pressure drop across filters, drop in branch lines, etc. These pressure drops should be added to any fixed pressure required by the
process (in the case of ventilation fans there is no fixed pressure requirement). Frequently, a very conservative approach is adopted allocating large safety
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margins, resulting in over-sized fans which operate at flow rates much below their design values and, consequently, at very poor efficiency.
Fan Design and Selection Criteria:-
Precise determination of air-flow and required outlet pressure are most important
in proper selection of fan type and size. The air-flow required depends on the process requirements; normally determined from heat transfer rates, or combustion
air or flue gas quantity to be handled. System pressure requirement is usually more difficult to compute or predict.
Detailed analysis should be carried out to determine pressure drop across the length, bends, contractions and expansions in the ducting system, pressure drop
across filters, drop in branch lines, etc. These pressure drops should be added to any fixed pressure required by the process (in the case of ventilation fans there is
no fixed pressure requirement). Frequently, a very conservative approach is adopted allocating large safety margins, resulting in over-sized fans which operate
at flow rates much below their design values and, consequently, at very poor efficiency.
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Once the system flow and pressure requirements are determined, the fan and impeller type are then selected. For best results, values should be obtained from the
manufacturer for specific fans and impellers. The choice of fan type for a given application depends on the magnitudes of
required flow and static pressure. For a given fan type, the selection of the appropriate impeller depends additionally on rotational speed. Speed of operation
varies with the application. High speed small units are generally more economical because of their higher hydraulic efficiency and relatively low cost. However, at
low pressure ratios, large, low-speed units are preferable.
Fan Performance and Efficiency:-
Typical static pressures and power requirements for different types of fans are given in the Figure (1.8).
Figure (1.8) Fan static pressure and pwer reqiurment for different fan
Fan performance characteristics and efficiency differ based on fan and impeller
type (See Figure 1.9). In the case of centrifugal fans, the hub to- tip ratios (ratio of inner-to-outer impeller diameter) the tip angles (angle at which forward or backward curved blades are curved at the blade tip - at the base the blades are
always oriented in the direction of flow), and the blade width determine the pressure developed by the fan.
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Forward curved fans have large hub-to tip ratios compared to backward curved fans and produce lower pressure.
Radial fans can be made with different heel-to-tip ratios to produce different pressures.
Figure (1.9) Fan performance characteristics based on fans/impellers
At both design and off-design points, backward-curved fans provide the most
stable operation. Also, the power required by most backward –curved fans will decrease at flow
higher than design values. A similar effect can be obtained by using inlet guide vanes instead of replacing the impeller with different tip angles. Radial fans are
simple in construction and are preferable for high-pressure applications. Forward curved fans, however, are less efficient than backward curved fans and
power rises continuously with flow. Thus, they are generally more expensive to operate despite their lower first cost.
Among centrifugal fan designs, aerofoil designs provide the highest efficiency (up to 10% Higher than backward curved blades), but their use is limited to clean, dust-free air.
Axial-flow fans produce lower pressure than centrifugal fans, and exhibit a dip in pressure before reaching the peak pressure point. Axial-flow fans equipped with
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adjustable / variable pitch blades are also available to meet varying flow requirements.
Propeller-type fans are capable of high-flow rates at low pressures. Tube-axial fans have medium pressure, high flow capability and are not equipped with guide
vanes. Vane-axial fans are equipped with inlet or outlet guide vanes, and are characterized
by high pressure, medium flow-rate capabilities. Performance is also dependant on the fan enclosure and duct design. Spiral housing
designs with inducers, diffusers are more efficient as compared to square housings. Density of inlet air is another important consideration, since it affects both volume
flow-rate and capacity of the fan to develop pressure. Inlet and outlet conditions (whirl and turbulence created by grills, dampers, etc.) can significantly alter fan
performance curves from that provided by the manufacturer (which are developed under controlled conditions). Bends and elbows in the inlet or outlet ducting can
change the velocity of air, thereby changing fan characteristics (the pressure drop in these elements is attributed to the system resistance). All these factors, termed as System Effect Factors, should, therefore, be carefully evaluated during fan
selection since they would modify the fan performance curve. Centrifugal fans are suitable for low to moderate flow at high pressures, while
axial-flow fans are suitable for low to high flows at low pressures. Centrifugal fans are generally more expensive than axial fans. Fan prices vary widely based on the
impeller type and the mounting (direct-or-belt-coupled, wall-or-duct-mounted). Among centrifugal fans, aerofoil and backward-curved blade designs tend to be
somewhat more expensive than forward-curved blade designs and will typically provide more favourable economics on a lifecycle basis. Reliable cost comparisons
are difficult since costs vary with a number of application-specific factors. A careful technical and economic evaluation of available options is important in
identifying the fan that will minimize lifecycle costs in any specific application.
Safety margin:-
The choice of safety margin also affects the efficient operation of the fan. In all cases where the fan requirement is linked to the process/other equipment, the safety margin is to be decided, based on the discussions with the process
equipment supplier. In general, the safety margin can be 5% over the maximum requirement on flow rate. In the case of boilers, the induced draft (ID) fan can be
designed with a safety margin of 20% on volume and 30% on head. The forced draft (FD) fans and primary air (PA) fans do not require any safety margins.
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However, safety margins of 10 % on volume and 20% on pressure are maintained for FD and PA fans
Some pointers on fan specification:-
The right specification of the parameters of the fan at the initial stage, is pre-
requisite for choosing the appropriate and energy efficient fan.
The user should specify following information to fan manufacturer to enable
right selection:
Design operating point of the fan – volume and pressure
Normal operating point – volume and pressure
Maximum continuous rating
Low load operation - This is particularly essential for units, which in the
initial few years may operate at lower capacities, with plans for up gradation
at a later stage. The initial low load and the later higher load operational requirements need to be specified clearly, so that, the manufacturer can
supplies a fan which can meet both the requirements, with different sizes of impeller.
Ambient temperature – The ambient temperatures, both the minimum and maximum, are to be specified to the supplier. This affects the choice of the
material of construction of the impeller.
The maximum temperature of the gas at the fan during upset conditions
should be specified to the supplier. This will enable choice of the right
material of the required creep strength.
Density of gas at different temperatures at fan outlet
Composition of the gas – This is very important for choosing the material of
construction of the fan.
Dust concentration and nature of dust – The dust concentration and the
nature of dust (E.g. bagasse – soft dust, coal – hard dust) should be clearly specified.
The proposed control mechanisms that are going to be used for controlling
the fan.
The operating frequency varies from plant-to-plant, depending on the source
of power supply. Since this has a direct effect on the speed of the fan, the frequency prevailing or being maintained in the plant also needs to be
specified to the supplier.
Altitude of the plant
The choice of speed of the fan can be best left to fan manufacturer. This will
enable him to design the fan of the highest possible efficiency. However, if
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the plant has some preferred speeds on account of any operational need, the same can be communicated to the fan supplier.
Installation of Fan:-
The installation of fan and mechanical maintenance of the fan also plays a critical role in the efficiency of the fan. The following clearances (typical values) should
be maintained for the efficient operation of the impeller.
Impeller Inlet Seal Clearances:- • Axial overlap –5 to 10 mm for 1 metre plus dia impeller
• Radial clearance –1 to 2 mm for 1 metre plus dia impeller • Back plate clearance –20 to 30 mm for 1 metre plus dia impeller
• Labyrinth seal clearance –0.5 to 1.5 mm
The inlet damper positioning is also to be checked regularly so that the "full open" and "full close" conditions are satisfied. The fan user should get all the details of
the mechanical clearances from the supplier at the time of installation. As these should be strictly adhered to, for efficient operation of the fan, and a checklist should be prepared on these clearances. A check on these clearances should be
done after every maintenance, so that efficient operation of the fan is ensured on a continuous basis.
System Resistance Change:-
The system resistance has a major role in determining the performance and
efficiency of a fan. The system resistance also changes depending on the process. For example, the formation of the coatings / erosion of the lining in the ducts,
changes the system resistance marginally. In some cases, the change of equipment (e.g. Replacement of Multi-cyclones with ESP /
Installation of low pressure drop cyclones in cement industry) duct modifications drastically shift the operating point, resulting in lower efficiency. In such cases, to
maintain the efficiency as before, the fan has to be changed. Hence, the system resistance has to be periodically checked, more so when
modifications are introduced and action taken accordingly, for efficient operation of the fan.
Flow Control Strategies:-
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Typically, once a fan system is designed and installed, the fan operates at a constant speed. There may be occasions when a speed change is desirable, i.e., when adding a new run of duct that requires an increase in air flow (volume)
through the fan. There are also instances when the fan is oversized and flow reductions are required. Various ways to achieve change in flow are: pulley
change, damper control, inlet guide vane control, variable speed drive and series and parallel operation of fans.
Pulley Change:-
When a fan volume change is required on a permanent basis, and the existing fan
can handle the change in capacity, the volume change can be achieved with a speed is with a pulley change. For this, the fan must be driven by a motor through a v-
belt system. The fan speed can be increased or decreased with a change in the drive pulley or the driven pulley or in some cases, both pulleys. As shown in the Figure
(2.0), a higher sized fan operating with damper control was downsized by reducing the motor (drive) pulley size from 8" to 6". The power reduction was 15 kW.
Figure (2.0) Pulley change
Damper Controls:-
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Some fans are designed with damper controls (see Figure 5.11). Dampers can be located at inlet or outlet. Dampers provide a means of changing air volume by
adding or removing system resistance. This resistance forces the fan to move up or down along its characteristic curve, generating more or less air without changing
fan speed. However, dampers provide a limited amount of adjustment, and they are not particularly energy efficient.
Figure (2.1) Damper change
Inlet Guide Vanes:- Inlet guide vanes are another mechanism that can be used to meet variable air
demand (see Figure 2.2). Guide vanes are curved sections that lay against the inlet of the fan when they are open. When they are closed, they extend out into the air
stream. As they are closed, guide vanes pre-swirl the air entering the fan housing. This changes the angle at which the air is presented to the fan blades, which, in turn, changes the characteristics of the fan curve. Guide vanes are energy efficient
for modest flow reductions – from 100 percent flow to about 80 percent. Below 80 percent flow, energy efficiency drops sharply.
Axial-flow fans can be equipped with variable pitch blades, which can be hydraulically or pneumatically controlled to change blade pitch, while the fan is at
stationary. Variable-pitch blades modify the fan characteristics substantially and thereby provide dramatically higher energy efficiency than the other options
discussed thus far.
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Figure (2.2) Inlet guide vain
Variable Speed Drives:-
Although, variable speed drives are expensive, they provide almost infinite variability in speed control. Variable speed operation involves reducing the speed
of the fan to meet reduced flow requirements. Fan performance can be predicted at different speeds using the fan laws. Since power input to the fan changes as the
cube of the flow, this will usually be the most efficient form of capacity control. However, variable speed control may not be economical for systems, which have
infrequent flow variations. When considering variable speed drive, the efficiency of the control system (fluid coupling, eddy-current, VFD, etc.) should be accounted
for, in the analysis of power consumption.
Series and Parallel Operation:-
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Parallel operation of fans is another useful form of capacity control. Fans in parallel can be additionally equipped with dampers, variable inlet vanes, variable-
pitch blades, or speed controls to provide a high degree of flexibility and reliability. Combining fans in series or parallel can achieve the desired airflow
without greatly increasing the system package size or fan diameter. Parallel operation is defined as having two or more fans blowing together side by side. The
performance of two fans in parallel will result in doubling the volume flow, but only at free delivery. As Figure 5.13 shows, when a system curve is overlaid on the
parallel performance curves, the higher the system resistance, the less increase in flow results with parallel fan operation. Thus, this type of application should only
be used when the fans can operate in a low resistance almost in a free delivery condition.
Series operation can be defined as using multiple fans in a push-pull arrangement.
By staging two fans in series, the static pressure capability at a given airflow can be increased, but again, not to double at every flow point, as the above Figure displays. In series operation, the best results are achieved in systems with high
resistances. In both series and parallel operation, particularly with multiple fans certain areas of the combined performance curve will be unstable and should be
avoided. This instability is unpredictable and is a function of the fan and motor construction and the operating point.
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Figure (2.3) Series and parallel operation
Factors to be considered in the selection of flow control methods:-
Comparison of various volume control methods with respect to power consumption (%) required power is shown in Figure 5.14.
All methods of capacity control mentioned above have turn-down ratios (ratio of maximum–to–minimum flow rate) determined by the amount of leakage (slip)
through the control elements. For example, even with dampers fully closed, the flow may not be zero due to leakage through the damper. In the case of variable-
speed drives the turn-down ratio is limited by the control system. In many cases, the minimum possible flow will be determined by the characteristics of the fan
itself. Stable operation of a fan requires that it operate in a region where the system curve has a positive slope and the fan curve has a negative slope. The range of operation and the time duration at each operating point also serves as a guide to
selection of the most suitable capacity control system. Outlet damper control due to its simplicity, ease of operation, and low investment cost, is the most prevalent
form of capacity control. However, it is the most inefficient of all methods and is
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best suited for situations where only small, infrequent changes are required (for example, minor process variations due to seasonal changes. The economic
advantage of one method over the other is determined by the time duration over which the fan operates at different operating points. The frequency of flow change
is another important determinant. For systems requiring frequent flow control, damper adjustment may not be convenient. Indeed, in many plants, dampers are
not easily accessible and are left at some intermediate position to avoid frequent control.
Figure (2.4) Comparison: - various volume control method
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Fan Performance Assessment The fans are tested for field performance by measurement of flow, head, and temperature on the fan side and electrical motor kW input on the motor side.
Air flow measurement Static pressure
Static pressure is the potential energy put into the system by the fan. It is given up to friction in the ducts and at the duct inlet as it is converted to velocity pressure.
At the inlet to the duct, the static pressure produces an area of low pressure (see Figure 2.5).
Velocity pressure Velocity pressure is the pressure along the line of the flow that results from the air
flowing through the duct. The velocity pressure is used to calculate air velocity. Total pressure Total pressure is the sum of the static and velocity pressure. Velocity pressure and
static pressure can change as the air flows though different size ducts, accelerating and decelerating the velocity. The total pressure stays constant, changing only with
friction losses. The illustration that follows shows how the total pressure changes in a system. The fan flow is measured using pitot-tube manometer combination or
a flow sensor (differential pressure instrument) or an accurate anemometer. Care needs to be taken regarding number of traverse points, straight length section
(to avoid turbulent flow regimes of measurement) upstream and downstream of measurement location. The measurements can be on the suction or discharge side
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of the fan and preferably both where feasible
Figure (2.5) static Total pressure
Measurement by Pitot tube:- The Figure (2.6) shows how velocity pressure is measured using a pitot tube and a
manometer. Total pressure is measured using the inner tube of pitot tube and static pressure is measured using the outer tube of pitot tube. When the inner and outer
tube ends are connected to a manometer, we get the velocity pressure. For measuring low velocities, it is preferable to use an inclined tube manometer instead
of U tube manometer.
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Figure (2.6) velocity measurement using pitot tube
Measurements and Calculations
Velocity pressure/velocity calculation:-
When measuring velocity pressure the duct diameter (or the circumference from which to calculate the diameter) should be measured as well. This will allow us to
calculate the velocity and the volume of air in the duct. In most cases, velocity must be measured at several places in the same system. The velocity pressure varies across the duct. Friction slows the air near the duct walls, so the
Velocity is greater in the centre of the duct. The velocity is affected by changes in the ducting configuration such as bends and curves. The best place to take
measurements is in a section of duct that is straight for at least 3–5 diameters after any elbows, branch entries or duct size changes To determine the average velocity,
it is necessary to take a number of velocity pressure readings across the cross-section of the duct. The velocity should be calculated for each velocity pressure
reading, and the average of the velocities should be used. Do not average the velocity pressure; average the velocities. For round ducts over 6 inches diameter,
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the following locations will give areas of equal concentric area (see Figure 2.7). For best results, one set of readings should be taken in one direction and another
set at a 90 ° angle to the first. For square ducts, the readings can be taken in 16 equally spaced areas. If it is impossible to traverse the duct, an approximate
average velocity can be calculated by measuring the velocity pressure in the centre of the duct and calculating the velocity. This value is reduced to an approximate
average by multiplying by 0 .9.
Figure (2.7) traverse point for circular duct
Now coming to the various problems which arise in fans.
There are many reasons for the defect following are some of them (1) Bearing defect (2) Erosion
(3) Corrosion (4) Vibration
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Bearing defect:-
To be able to monitor bearings is the reason that most vibration analysis programs are started. Ninety per cent of bearing failures can be predicted months before
hand. There are still approximately 10 per cent of bearing failures that are abrupt and unforeseen. Being able to predict the 90 per cent majority is a good enough
reason to invest in a bearing monitoring program for many companies. However, if this is the only use of the vibration instrumentation, then it is underutilized.
There are very few “bad” bearings coming out of bearing factories. The state of
quality control at these facilities is of the highest calibre of any manufactured goods. Bearings fail for several reasons, the least of which is a manufactured-in
defect. All bearings have some defects, and they are graded accordingly. It is only a matter of degree of defects that separates’ out the highest –quality bearings from the lowest quality ones. The presence of these defects is not the primary cause of
bearing failure. The primary causes of bearing failures are:
1. Contamination, including moisture (Some sources claim that 40 per cent of
bearing failures are caused by contamination. This is Certainly believable based on my field experience.)
2. Overstress
3. Lack of lubrication
4. Defects created after manufacturing
Bearings typically achieve only about 10 per cent of their rated life. Tests of bearing life under laboratory conditions yield lives of 100 to 1000 years. Clearly,
the design and manufacturing do not present deficiencies that limit their life. So why don’t bearings under service conditions achieve those running times? The
answer is that in the laboratory, there is no contamination of dirt or water, there is little imbalance or misalignment to cause overstress, the lubrication is the best,
and the bearing is handled as if it wear a delicate instrument, which it is. Under service conditions, these factors are not all optimum as they wear during the
laboratory tests. The test prove that long life is achievable with same care.
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Erosion:-
One of the most common damage mechanism associated with power plant is fan failures due to erosion, which is responsible for serious and costly maintenance.
The rate of erosion depends on suspended particle / fly ash in the flue gas.
Effect of blade type on erosion resistance and efficiency:-
Blade Type Typical max static
efficiency
Tolerance to erosion
environment
Radial 70 High
Radial tip 80 Medium to high
Backward inclined solid 85 Medium
Air foil 90 Low
Resistance to Erosion:- The rate of erosion experienced by fan used in harsh application is often
controlled by the use of repairable liners, replaceable liners or renewable liners. Reducing fan speed and selecting a fan blade type that is more resistance to
erosion will slow down the abrasive wall thinning experienced by fan unit surface.
Abrasion resistance impeller:- Fans that operate in flue gas, such as induced draft fans for coal fired boilers
are required to be resistance to abrasion by ash in the flue gas.
Corrosion:- The following list is the most common type of corrosion problem found in
thermal power plant. (1) Erosion corrosion:-
Erosion corrosion is a degradation of material surface due to mechanical action,
often by impinging liquid, abrasion by slurry, particles suspended in fast flowing
liquid or gas, bubbles or droplets, cavitation, etc. The mechanism can be described as follows:-
mechanical erosion of the material, or protective (or passive) oxide layer on its surface,
Enhanced corrosion of the material, if the corrosion rate of the material depends on the thickness of the oxide layer.
(2) Crevice corrosion & Galvanic corrosion:-
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Fan body is made from the CORTEN steel, Table 1, and the working surfaces of the blades are covered by wear plates 4666 CDP (4666 DP 0503) produced by
CASTOLIN Co., attached to the blades by spot arc welding, Fig 2 and 3, Table 2. The deposit of 4666 CDP is produced by SSA surfacing process using CASTOLIN
TeroMatec 4666 self-shielded wire. Deposit thickness is 3,0 [mm] and its structure is hypereutectic high chromium cast iron alloy containing complex carboborides
and carbides, shown in Fig. 3. The base material of 4666 CDP is S235JRG2 carbon steel of thickness 5,0 [mm], Table 1 [1, 2].
During fumes suction operation the fan blades are subjected very strong wear phenomena of erosion corrosion (mechanical erosion degradation augmented by
corrosion) which result in very strong wear of the centre part of the blade, Fig. 1a. Fumes produced during steel milling process ventilated by the suction system are
polluted by water leakage from furnace cooling system. Water presence in fumes as a pollutant is the main source of atmospheric and galvanic corrosion which
strongly augments fumes’ erosion wear phenomenon. Atmospheric corrosion of fan blades is greatly accelerated by water (moisture) in fumes. The surface of the wear plate is attacked by atmospheric corrosion and as the result products of the
corrosion in the form of oxides (rust) and sulphates are constantly produced on the fan blades wears plate’s surfaces and the surface of CORTEN steel fan body.
Products of atmospheric corrosion are not erosion resistant in comparison to high chromium cast iron alloy deposit of the wear plates of blades, so these products are
rapidly removed from the deposit surface what strongly accelerates fan blades wear [3, 4].
In the same time galvanic corrosion takes place because of difference in the chemical composition and the structure of deposit and carbon steel base material of
4666 CDP and CORTEN steel fan body, shown in Fig. 3, Table 1 and 2. Less noble - anodic carbon steel base material of 4666 CDP and CORTEN steel fan
body ( - 0,6 [V] to – 0,7[V] – standard potential) then cathodic high chromium base cast iron alloy of 4666 CDP deposit ( - 0,45 [V] to -0,50 [V]) are attacked to greater degree. As a result the 4666 CDP base material and CORTEN steel of the
fan body are strongly dissolute and form ions which migrate from anodic areas of carbon steels on the surface into the electrolyte. Additionally galvanic corrosion
initiates strong crevice corrosion in the area of fusion zone between deposit and base material of 4666 CDP, in the bottom area of the residual stresses cracks of the
deposit, shown in Fig 2, which later continues as stress corrosion cracking. On the other hand due to very complex hypereutectic ledeburite structure of 4666 CDP
deposit of ferritic matrix containing carboborides and chromium and niobium carbides of different potential in galvanic series, stress corrosion cracks are
initiated as the synergistic interaction between mechanical (welding) stresses in the deposit and a galvanic corrosion on the surface of deposit deposit of ferritic matrix
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containing carboborides and chromium and niobium carbides of different potential in galvanic series, stress corrosion cracks are initiated as the synergistic interaction
between mechanical (welding) stresses in the deposit and a galvanic corrosion on the surface of deposit.
Table1:-
The chemical composition (wt-%) of CORTEN steel and S235JRG2 steel
Elements C Mn Si Cr Cu P S
CORTNE 0.10-0.15
0.25-0.55
0.25-0.60
0.5-1.5 0.25-0.50
Max 0.04
Max 0.05
S235JRG2 0.17 1.4 - - - Max
0.045
Max
0.045
Table 2.
Classification, chemical composition and hardness of the deposit of fan blades wear plates - 4666 DP 0503
Figure 1. a) - a view of the fan of steel mill fumes suction system. Fan blades are
covered by the wear plates 4666 CDP attached to the fan body by arc spot welding, b) - a view of worn centre part of the fan blade.
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CONCLUSIONS 1. Basic compounds of the products of atmospheric corrosion of 4666 CDP deposit
are Mn3O4, Fe2O3 and Cr5O12 oxides and FeS troilite as a result of water pollution of fumes.
2. Basic compounds of the products of atmospheric corrosion of 4666 CDP deposit are Mn3O4 and Fe2O3 oxides and FeS troilite as a result of water pollution of
fumes. 3. Visual and metallographic examination have proved that the main reason of very
strong wear of the middle part of the fan blades is fumes erosion phenomenon greatly accelerated by water pollution of fumes. Water pollution is the source of
very strong atmospheric corrosion and galvanic corrosion of 4666 CDP and CORTEN steel fan body.
4. Galvanic corrosion induced strong crevice corrosion and stress corrosion cracking of the 4666 CDP.
Here is some other corrosion which are responsible for damage in fans blades and effect the efficiency of the fans.
(3) Pitting (4) General corrosion
(5) Differential oxygenation (6) Biological corrosion
(7) Intergranual corrosion
Vibration:-
Possible reason as to why vibration occurs in fan units are listed below (1) Improper balancing
(2) Loss component (3) Worn/damage/cracking of fan part (4) Improper lubrication
(5) Improper clearance of moving part (6) Excitation of resonant frequency
(7) Corrosion/erosion high/low cycle fatigue effect (8) Misalignments
(9) Bent shaft (10) Improper design or deteriorated foundation
(11) Build-up of material in rotor
Following are the main cause for vibration in fans:-
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Ever since centrifugal fans have been manufactured they have been subject to vibration related problems. These problems range from simple unbalance
conditions caused by mass variations on the fan rotor to much more complex issues related to shaft alignment, bearing fatigue, or resonance issues. In many cases
excessive vibration levels in fans lead to unplanned, forced outages to perform maintenance.
Once to this stage, these outages are necessary to maintain safety. However, most
often, they are costly both from a maintenance and lost production standpoint. Standards have been set as to what are acceptable vibration levels for
corresponding operating speeds.
Other sources that outline acceptable balance and vibration levels for fans include ANSI/AMCA 204-96, Balance Quality and Vibration Levels for Fans? And ISO
14694:2003, Industrial Fans, Specifications for Balance Quality and Vibration Levels.
Shaft Misalignment
Proper alignment between a drive motor shaft and a fan shaft is an important step that needs to be properly addressed during new fan installation or if a shaft/rotor
assembly is replaced. Misalignment between a drive motor shaft and fan shaft typically results in a 1X and 2X harmonic component of vibration. Often times, misalignment conditions will also lead to excessive levels of axial vibration. Since
most fans are not equipped with axial vibration probes this is often not detected unless the 2X vibration component exists. Misalignment can be caused by careless
installation of new equipment, but is more commonly caused by bent shafts or improperly seated bearings. Misalignment should be able to be detected prior to
start-up of a fan by using a dial or laser alignment system to verify proper alignment between the drive motor shaft and fan shaft. However, a bent fan shaft
may not be detected by the alignment system, which may allow the above symptoms to persist.
Importance of shaft alignment:-
The objective of optimized shaft alignment is to increase the operating life span of
rotating machinery. To achieve this goal, components that are the most likely to
fail must be made to operate within their acceptable design limits. While misalignment has no measurable effect on motor efficiency, correct shaft
alignment ensures the smooth, efficient transmission of power from the motor to
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the driven equipment. Incorrect alignment occurs when the centrelines of the
motor and the driven equipment shafts are not in line with each other.
Misalignment produces excessive vibration, noise, coupling, and bearing
temperature increases, and premature bearing, coupling, or shaft failure.
Types of Alignment
Ideal Alignment Parallel Misalignment
Angular Misalignment There are three types of motor misalignment: • Angular misalignment occurs when the motor is set at an angle to the driven
equipment. If the centrelines of the motor and the driven equipment shafts
were to be extended, they would cross each other, rather than superimpose or
run along a common centreline. The “gap” or difference in slope of the motor
shaft when compared with the slope of the stationary machine shaft can have
horizontal misalignment, vertical misalignment, or both. Angular
misalignment, in particular can cause severe damage to the driven equipment
and the motor. • Parallel misalignment occurs when the two shaft centrelines are parallel, but
not in the same line. There are two planes of parallel misalignment as shafts
may be offset horizontally (displaced to the left or right), vertically (positioned
at different elevations), or both. • Combination misalignment occurs when the motor shaft suffers from
angular misalignment in addition to parallel misalignment. •
Couplings:-
Larger motors are usually directly coupled to their loads with rigid or flexible couplings.
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Rigid couplings do not compensate for any motor-to-driven-equipment
misalignment, while flexible couplings tolerate small amounts of misalignment.
Flexible couplings also can reduce vibration transmitted from one piece of
equipment to another, and some can insulate the driven equipment shaft against
stray electrical currents. Even flexible couplings have alignment requirements,
defined in the instruction sheet for the coupling.
However, it is a mistake to rely on coupling flexibility for excessive
misalignment, because flexing of the coupling and of the shaft will exert forces
on the motor and driven-equipment bearings. These forces may result in
premature bearing, seal, or coupling failures, shaft breaking or cracking, and
excessive radial and axial vibrations. Secondary effects include loosening of
foundation bolts, and loose or broken coupling bolts. Operating life is shortened
when shafts are misaligned.
Alignment Tolerances:-
No industry standard on alignment exists. Proper shaft alignment is especially critical when the motor is operated at high speeds. Standard industry norms for
alignment tolerances are cited in Table 1 Table 1. Shaft Alignment Tolerances for Direct-Coupled Shafts
Parallel Offset (mils)
Angular Misalignment
(mils per inch)
Motor Speed
Short Flex Couplings
Spacer Couplings
(RPM)
Excellent Acceptable Excellent Acceptable
900 3.0 6.0 1.2 2.0
1,200 2.5 4.0 0.9 1.5
1,800 2.0 3.0 0.6 1.0
3,600 1.0 1.5 0.3 0.5
In practice, proper alignment is difficult to achieve without using alignment
equipment such as dial indicators or laser alignment tools. The proper shaft
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alignment procedure is to secure the driven equipment first because moving a
pump, for example, would stress the connecting piping. Next, install the
coupling to the driven equipment. The motor should then be moved into proper
alignment and joined to the coupling.
After the equipment has operated long enough to become temperature
stabilized, shut it down and immediately recheck alignment. Due to thermal
growth, machines that are aligned in the “cold” propagating condition are
almost always out of alignment when operating temperatures are attained.
Many equipment manufacturers publish thermal offset values so the alignment
technician can correct for thermal growth during the initial alignment process.
Resonance
Resonance problems are often twofold on large fan assemblies. The first
component that has to be addressed is critical speeds. Critical speed mapping is typically a task that is addressed during new fan design. Most fans are designed to
operate below first critical speed. The factors in avoiding critical speed in fan design are overall rotating mass, span between bearings, and necessary operating speed to produce the required airflow. If a fan operates above first critical speed
then careful attention has to be paid to vibration levels as the fan accelerates up to operating speed and, more importantly, coasts down to a stop from operating
speed. Excessive levels of vibration while passing through a critical speed can lead to severe damage to bearings, seals, and other related equipment. The second
factor, structural resonance, can be much more challenging to predict. Every structure has a natural frequency at which it will resonate. If a fan operates at a
structural resonance point that is not corrected it can also lead to component failures. Structural resonance can occur at 1X operating speed or at a harmonic
frequency (2X, 3X, etc.). Structural resonance will vary depending on operating speed and can be easily identified by performing a signature plot mapping
vibration amplitude, versus frequency, versus rotational speed.
Mechanically Loose Connections
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Looseness in any mechanical connection between bearing caps, bearing pedestals, or foundations can cause excessive vibration levels or amplify an already existing
unbalance problem. In most cases, a mechanically loose connection will yield harmonic levels of vibration (2X, 3X, etc.) and may also yield sub-harmonic levels
of vibration (X/2, X/3, etc.). Vibration caused by mechanically loose connections is often misdiagnosed
due to the presence of sub-harmonic vibration levels. A second type of vibration caused by mechanically loose connections can take
place if there is looseness in the connection between the fan rotor and fan shaft. In many cases this will induce an extremely high unbalance related vibration level
that is not necessarily at 1X operating speed. This type of vibration can be very difficult to determine, but easily corrected if found. In most cases, properly
designed interference fits between the rotor hub and fan shaft can be implemented to avoid this condition.
Cracked Shafts or Rotors
Crack propagation in either a fan shaft or rotor can lead to one of the most dreaded
failure modes in any type of rotating equipment. If undetected, a crack in a shaft or rotor can eventually lead to catastrophic failure of the fan. Early crack detection
can take place if vibration trending and analysis takes place on a piece of equipment. The common symptoms of a crack propagating in a fan are both an
emergence and growth of a 2X component of vibration along with a change in the phase and amplitude of the 1X vibration component.
Rotor Mass Unbalance
Rotor mass unbalance is the most common cause of excessive vibration in most
rotating equipment and fans. The primary symptom of rotor mass unbalance is a high 1X vibration level. Rotor mass variation leading to an unbalanced condition is
typically caused by four primary factors.
1. Variations in manufacturing can lead to unevenly distributed mass in the fan rotor.
2. Exposure to high air stream temperatures
can cause uneven growth of the fan rotor.
3. Deterioration of the fan rotor caused
by either high speed particle collisions….”
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______________ __ __________ ____________ _____ _____ ____
There are various method and procedure by which we can ensure the problem and also reduce the chances of failure.
Condition monitoring:-
Condition monitoring is an advance technology to determine equipment’s condition and potential and also predicts failures.
It includes technology such as the following:-
(1) Vibration measurement and analysis
(2) Oil analysis (3) Non-destructive examination (NDF)
(4) Infrared thermography (5) Motor current analysis
In order to increase the efficiency of fans at power plant is to use VFD at PA, FD,
ID fans.
VFD: - VARIABLE FREQUENCY DRIVES
Variable frequency drives (VFD) are becoming more common place and more
widely used in applications. They are capable of varying the output speed of a
motor without the need for mechanical pulleys, thus reducing the number of
mechanical components and overall maintenance. But the biggest advantage that a
VFD has is the ability to save the user money through its inherit nature to save
energy by consuming only the power that’s needed. The main question now is,
How does a VFD accomplish this? The simple answer to this question is power conversion.
A VFD is similar to the motor to which it’s attached, they both convert power to a
usable form. In the case of an induction motor, the electrical power supplied to it is
converted to mechanical power through the rotation of the motor’s rotor and the
torque that it produces through motor slip. A VFD, on the other hand, will convert
its incoming power, a fixed voltage and frequency, to a variable voltage and
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frequency. This same concept is also the basis to vary the speed of the motor without the need of adjustable pulleys or gearing changes.
As VFD usage in HVAC applications has increased, fans, pumps, air handlers, and chillier can benefit from speed control. Variable frequency drives provide the
following advantages: • energy savings
• low motor starting current • reduction of thermal and mechanical
stresses on motors and belts during starts
• simple installation
• high power factor • lower KVA
Understanding the basis for these benefits will allow engineers and operators to apply VFDs with confidence and achieve the greatest operational savings.
So far we have discussed about various problems arising at fans and there
treatment through installing an electrical circuit that is VFD. But there are many sensors and monitoring system for prediction of various problems which are very much useful as well as essential.
Firstly we will say why we need a monitoring system:-
Many new power plants that have supercritical technology are coming up in India. There are several challenges for maintenance and instrumentation engineers to
keep a high uptime. At the same time, there is a large population of old power plants in the country and there is need to upgrade these with new technology and
products, to monitor key machines and plan actions in advance before they break down.
Twenty years ago, power plants were shut down frequently for maintenance. But now it is imperative to monitor these plants to increase the uptime to 95%. It is
essential to monitor these critical machines for increasing their efficiency and reliability. Hence real time vibration monitoring is the key to reduce frequent
failures of machinery.
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Here is a common overview of a power plant which needs VSM (vibration monitoring system)
A typical layout of a power plant which explains where
Vibration Monitoring is required and how critical is each
machine if there is shut down, is shown in the below figure.
Power Plants are categorized into –
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This solution is cost effective as maintenance can be planned without influencing the total availability of the plant. Condition characteristics of the machine such as
bearing damage, unbalance, alignment or cavitation’s enable a differentiated evaluation of mechanical stress which will keep all on track for when to have the
shut down and the process is on-going without any manual interruption. Hence we will be able to protect the equipment from expensive consequential costs.
The machines can be taken for maintenance, without dismantling, just by knowing the health of the machine which is possible by online monitoring. Implementing
predictive maintenance leads to a substantial increase in productivity of up to (35%). Preventing unpredicted shutdowns on one hand and anticipating corrective
operations on the other can be carried out under the best conditions.
Knowledge of the root cause of the malfunctioning of the machine can help
expedite the actions that are needed to be taken instead of shutting down the whole system. This is nothing but predictive maintenance for prediction of the health of
the machine. Here the performance level is decided with the help of the reports taken at intervals. There is rapid notification and fast error detection. Diagnostics feature give the root cause of the failure of machinery.
Details of Vibration Measurement Parameters:-
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Radial Vibration
Radial vibration measures the radial motion of the rotating shaft relative to the
case. This measurement gives the first indication of a fault, such as unbalance, misalignment, cracked shaft, oil whirl or other dynamic instabilities. Vibration
Measurements can be made in a single plane or a two plane (X-Y) arrangement where the sensors are 90 degrees apart and perpendicular to the shaft.
Eddy current probes are usually installed in a hole drilled through the bearing cap and is held in place by either a bracket or a probe holder.
Absolute Shaft Vibration
Absolute shaft vibration is a measure of the shaft’s motion relative to free space. The measurement is typically applied when the rotating assembly is five or more
times heavier than the case of the machine. Absolute shaft motion is proportional to the vector addition of the casing absolute motion and the shaft relative motion.
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Casing Vibration (Absolute Bearing Vibration):-
This is the vibration measurement to measure vibration on bearing housing by
using contact type sensors mounted with the help of mounting pad / studs. These are mounted 90 degree apart from each other. Typically piezo-velocity &
accelerometer sensors are used.
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Casing Expansion:-
Steam temperature varies greatly between start up, operation, and shutdown. Shell
expansion is a measurement of how much the turbine’s case expands from its fixed point outward as it is heated. Continuous indication of shell thermal growth allows
the operator to manage the amount of shell distortion as the load is increased or decreased. This thermal growth of the case from its fixed point outward is
measured by the Linear Variable Differential Transformer (LVDT) plunger fixed to the case.
Differential Expansion:- Differential Expansion (DE) is the difference between the thermal growth of the rotor compared to the case. It provides the operator continuous indication of the critical clearances between the expanding rotor and blades with respect to the expanding shell or casing.
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Differential expansion monitoring is critical during a turbine "cold” start-up. The rotor is fixed axially by the thrust bearing. This thrust bearing moves as the case expands - thus the need to monitor the difference in thermal expansion. Ideally, differential expansion should indicate zero change in the gap relationship between the two surfaces
Thrust Position (Axial Measurement):-
Axial position (thrust) is a measurement of the relative position of the thrust collar to the thrust bearing. Measurement may be made in both the active and inactive
thrust directions. Measurements taken outside of the thrust bearing area (greater than 12 inches) are generally affected by the rotor’s thermal expansion and an
increase in the required dynamic measurement range. This measurement is typically referred to as rotor axial) position.
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Eccentricity Measurement:-
Eccentricity is a measurement of the amount of sag or bow in a rotor. After an extended shutdown, the shaft will bow if heated unevenly. Prior to startup, the
rotor is placed on turning gear and slow-rolled, allowing the shaft to straighten to within acceptable limits – the turbine is not brought up to speed until eccentricity is
within limits. Excessive eccentricity could cause rubs and damage to the seals. Eccentricity measurement may also provide indication of a bent shaft.
Phase Measurement:-
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Phase is defined as the angle between a reference mark (usually a keyway on the shaft) and the heavy spot on the rotor. Phase measurement is required for accurate
balancing of any rotor. It also provides an indication of shaft cracks, misalignment, mass loss (such as throwing a blade), and other faults.
Fans with HT Motors:- Other critical machines in power plants are fans used for ventilation and industrial
process requirements. Induced Draft Fans (ID Fans) and Forced Draft Fans (FD Fans) are used to control air flow through the stack, maximizing the efficiency of
the boiler. Gas Recirculation Fans collect unburned gas and send it back to be burned again,
reducing the particulates that are emitted to the air. As in vibration terms fans contributes to the maximum. The motor shaft is coupled to the fan through the
coupling (plume block), can be fluid coupling.
Induced Draft Fans (ID)
Forced Draft Fans (FD)
Primary Air Fans (PA)
Details of Vibration Monitoring System in Power Plants:- A. Sensors Used for Vibration Monitoring:-
The types of sensors that provide vibration information are well known. The three principal vibration sensor or monitor types are displacement, velocity, and accelerometer. The displacement transducer is an eddy current device, the velocity
transducer is often a spring held magnet moving through a coil of wire, and the accelerometer is a piezoelectric device
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Somewhat similar to ultrasonic transducers. The following information briefly describes how these transducers work, where they work best, and what kind of
results they provide.
Non-Contact type displacement sensors are non-contact devices measuring the gap between the plant equipment and the fixed sensor. It is usually mounted 380-2,030
μm (15-80 milli-in.) from the part to be observed. The coil in the eddy current device is usually a pancake coil in the end of a cylindrical tube that can be
mounted close to the moving part. Excitation is very high frequency, about 240,000 Hz, for detection of small gap
changes (as low as 1 μm i.e. 40 milliin.) at 0.5 MHz. This sensor measures
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vibration as horizontal or vertical motion (requiring two different mountings of one sensor or two sensors). The best measurements are at low frequencies of vibration
of the part, below 1,000 Hz, where signals as large as 4,000 mV/μm (100 mV/milli-in.) can be obtained. Since the signal can be large, very low amplitude
displacements or vibrations can be measured. Displacement sensors work well for applications such as shaft motion and clearance measurements.
Piezo Velocity Sensors (give velocity output) work well over a very wide range of frequencies (1 to 20,000 Hz). They work best for high frequencies where
acceleration is large. Examples are the passage of turbine blades, which may be one hundred times the shaft rotation, or the meshing of gears or ball/roller
bearings, which may be many times the shaft rotations per minute. Other advantages include their small size, lightweight, good temperature stability, and
moderate price. Accelerometers develop a voltage from a piezoelectric crystal that has a mass
mounted upon it. A quartz crystal is frequently used. When the mass fixed to the crystal vibrates from the motion of the device upon which the sensor is attached, the crystal generates a voltage proportional to the force applied by the mass as it
vibrates with the machinery. While no external excitation is required for the sensor to produce its voltage signal, the signal is small (self-generated) and requires a
preamplifier. The preamp is often in the sensor case so the connecting cable must carry preamp power to the sensor as well as the signal from it. The accelerometer
is the workhorse of vibration sensors because they offer such a wide range of working frequencies plus the other advantages given above.
API-670 Monitoring System Details:-
For Vibration Monitoring System there is a global standard API 670 Fifth Edition – Machinery Protection System. For plant maintenance, it is useful to have a
uniform system such as API 670 Compliance Vibration Sensors, 19” Rack Based Monitoring System and required relay outputs, 4-20 mA outputs, DCS Interface
and 02 Raw Buffer Signal output for further integration.
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CA/CV Series Velocity Sensor and Accelerometers:-
• Multi-purpose and intrinsically safe Accelerometers. Available in both top
and side connectors, or with top and side exit integral cables. • High temperature, low frequency and Piezo velocity transducers. Available
in both top and side connector versions.
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Conclusion:-
By monitoring the performance of the critical machines and
secondary critical machines we can predictive shutdown of the plant instead of frequent planned shutdowns. The root causes of
machinery failure can be known by using the Vibration
monitoring System. Lead to increase in the reliability of the system machinery. Reduction of manual intervention that is
erroneous. Will eventually increase the plant uptime to 95% overall.
Installation of VFD leads in following benefits:-
• Energy savings • Low motor starting current
• Reduction of thermal and mechanical • Stresses on motors and belts during starts
• Simple installation
• High power factor • Lower KVA (NOTE: KVA = Volts x Amps x 1.732).
