INDUCED DRAFT FAN
RITESH KUMAR CONSTRUCTION , M6K221 MECHANICAL ENGGINEER
Reference : shaft alignment hand book", john piotrowski.
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DRAFT SYSTEM
Supply air for combustion Remove air from furnace Transporting pulverized coal to furnace Maintain speed for heat transfer
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DRAFT SYSTEM
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TYPES OF FANS
Axial fan
Fluid comes axially . Get compressed while
Centrifugal fan
Fluid comes axially. Get compressed because of
moving axial. Move out axially.
centrifugal action. Comes out of fan radially.
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CENRIFUGAL FANS
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ERECTION OF INDUCED DRAFT FANS
Blue matching
Erection of packer plates Primary alignment Secondary alignments Inlet cone erection Erection of casing
Blue matching of machine foot , wedge plates and packer plates is done
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Leveling device
Packer plate
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Erection of packer plate
Elevation
Flatness
Co planarity positioning
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Master level
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Installation of induced draft fan
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Result of improper installation
Lose of production
Premature failure of machine components Loss of energy
To insure ,before alignment some primary checks are done
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Preliminary checks
Coupling half runout
Soft footing Bearing
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Runout check
Runout standards
Shaft speed Maximum runout 0.13 mm
0-1800 rpm
1800-3600 rpm
0.08 mm
3600+ rpm
0.05 mm
Maximum times these standards are provided by manufacturer
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Ways of detecting soft foot
Dial indicator shims
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Checking procedure
Dial indicator
First tight the bolt Place dial indicator Loose bolts See dial show less then 0.06
shims
Check gap between foot and
mm.
pedestal by shims at four sides of foot. They should come same other wise soft footing is there.
Repeat this for all foots
Eliminating soft footing is most time consuming and skilled job. Machines on maximum occasion have vibration problem due soft footing This is very much a trial and error method because every time you need to put shims as per calculation and check for soft footing till you eliminating.
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Example of soft footing
This condition is outcome of
bad blue matching, leveling and complaining of packers
Reasons of soft footing
Insufficient contact between machine foot and pedestal. Noncoplanarity foot or pedestal .
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Alignment basics
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Types of misalignments
Measured in mm
Measured in degree of angle
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Calculation of angular misalignment
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Alignment methods
Face to Rim method Reverse indicator method
There other method to align shafts but these are predominantly used. Reverse indicator method is more accurate then Face to Rim method.
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Face to Rim method
Advantage of Face to Rim method above reverse indicator method , it can be used for alignment when rotating both shaft is not possible
Both shafts are moving so facial reading is going to be effected. To overcome ,we are using two extra dial indicator .
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Set of readings
Making compensation for shaft movement is important .
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Other arrangement used in Face to Rim method
Axial reading = A1- A2/2
Why compensation is this?
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Dimension required
Accuracy of Face to Rim method depends on diameter at which facial reading is taken.
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How to align
Electrical machines have magnetic center , so motor shaft first
needs to be positioned to it magnetic center , only then alignment is done. With above mentioned formula calculate position of Driver and Driven machine inboard and outboard foots. Find out movement of inboard and outboard foots to make shafts collinear and coplanar. This can easily be done by using graph paper Individuals do it on hit and trial basis but by using above process can be done in less time.
Magnetic center of electric machines is specified by manufacturer 25
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Interpretation of dial reading in 3-D view
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Example
Page 361
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Reverse indicator method
Same process of finding movement of Drive and Driven machine inboard and outboard foot to align shafts we follow here.
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Why to rotate both shaft
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Alignment specification
Most of time provided by manufacturer
Depends on coupling ,speed and power.
NTPC allowable tolerance Parallel misalignment
Output of rotor in KW Coupling Speed rpm
Below 400 (mm) 400-1000 (mm) Over 1000 (mm)
Angular misalignment
Output of rotor in KW Coupling Speed rpm
Below 400 (mm) 400-1000 (mm) Over 1000 (mm)
2500-4000
0.01 0.025 0.04 0-01 0.015
0.02 0.04 0.06 0.02 0.03
0.03 0.06 0.10 0.03 0.04 Rigid coupling Flexible coupling
2500-4000
1300-2500 Below 1300 2500-4000 Below 2500
0.02
0.06 0.08 0.02 0.03
0.03
0.07 0.10 0.03 0.04
0.04
0.10 0.15 0.04 0.05
Flexible coupling
1300-2500 Below 1300
Rigid coupling
2500-4000
Below 2500
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OPERATION PROBLEM
Part load Fluctuating weather
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FLOW CONTROLING
Dampers
Inlet vane Hydraulic variable speed coupling Variable frequency drive
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Inlet vane
Damper
Inlet control valve is also controlled by motor actuators
Actuator
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Mechanical comparison
Speed (flow) 100 % 90% 80% 70% 60% Hours 400 800 4000 2000 800 Load KW 933 680 477 320 201 Fluid coupling KWh 439,000 725,000 2,935,000 1,143,000 350,000 Variable speed coupling 439,000 648,000 2,229,000 780,000 201,000
Annual KWh
Annual energy cost Maintenance costs Total annual costs Capital costs Total five year cost Total ten year cost
5,559,000
$279,600 $20,000 $299,600 $235,000 $1,733,000 $3,231,000
4,367,000
$218,350 $10,000 $228,350 $295,000 $1,436,000 $2,578,000
Cost summary
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The application considered above is an induced draft fan
Horse power 1250 hp. Cost of energy is $0.05.
Reference :
Fan drive system efficiencies", Universal Dynamics Limited, ADAM CREERY .
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THANK YOU
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