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PROBLEMS FACED & ACTION TAKEN
E R O S I O NProblem :
High pressure air mixes with ash and leaks to low pressure sideleads to erosion of static seals, radial seals etc.
Action Taken :
Reverse rotation of APH ( Gas to SA to PA )
Additional layer of by-pass seal near sector plate.
Kao-wool packing carried out at the inboard sector plates,static seals and ASP TO SP seal.
Seal thickness increased (1.6 mm to 2.5 mm)
Seal tabs introduced in Axial & Radial seals.
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PROBLEMS FACED & ACTION TAKEN
Problem :
High Leakage of Air to Gas path
Action Taken :
1. Double sealing arrangement introduced in Khaperkheda,Simhadri & Talcher projects etc.
2. PG tests conducted in various R&M projects and resultsfound
encouraging.2. Before PG tests, APHs are attended for seal adjustments,
issued Technical Directive regarding Leakage & necessaryoperations.
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PROBLEMS FACED & ACTION TAKEN
F I R EDuring start up with oil firing, impropercombustion may result in the accumulation ofcondensed oil vapours and un burnt carbon onAir preheater surfaces by carry over from
furnace.PREVENTIVE
Soot blower should be in operation.
Fire sensing device ( Thermocouples ) to be
commissioned.Oil carry over detector to be commissioned andmonitored during oil firing.
Heat rate of firing should be controlled.
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PROBLEMS FACED & ACTION TAKEN
BEARING FAILURESOil contamination
Starvation of oil
Mis-alignment
Lack of maintenanceHigher operating oil
temperature
Foreign materials in
bearing
Action Taken:
Technical directive
issued.
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PROBLEMS FACED & ACTION TAKEN
PROBLEMS IN DRIVE UNIT ASSY ;
Over running clutch failure:Over heating
Sealed bearings
No oil circulation
Action Taken:
New design evolved eliminating
Overrunning clutches in main
and stand by electric drives.
Vibration of drive unit:Misalignment.
Failure of bearings in motor,
gear box etc
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PROBLEMS FACED & ACTION TAKEN
CLEANING DEVICE ASSY :
Drive unit failure
Chandrapur unit-7 SAPH failed due to closure of
soot blower drain valve.
- The drain valve to be kept crack open
- Technical directive issued.Nozzle erosion
- Parking position to be at inboard end.
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PROBLEMS FACED & ACTION TAKEN
FIRE SENSING DEVICE ASSY :
Failure of Thermocouples:
Design changed to individual thermocouples.
Failure of scanners:
Local Temperature scanners eliminated anddirectly connected to DDCMIS for betteroperation from Khaperkheda project onwards.
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OPERATION PROBLEMS
HIGHER PRESSURE DROP ACROSS APH
1. Choking of heating elements
2. Higher flows
3. Eroded/damaged heating elements -obstructs flow path.
4. Improper steam parameters and
eroded nozzles and steam pipes.
5. Low cold end average temperature.
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OPERATION PROBLEMS
HIGH GAS LEAVING TEMPERATURES
1. More gas flow with high inlet temperature
temp.2. Less air flow and high inlet temp.
3. Choking of SCAPH less air flow
4. Choking of heating elements
5. Erosion & corrosion of heating elements
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OPERATION PROBLEMS
CHOKING OF HEATING ELEMENTS :1. Improper evacuation of economiser hopper.
2. Corrosion of heating elements
3. Boiler slagging
4. Improper drying of heating elements after waterwashing.
5. Excess air operation.
6. Leak in SCAPH and water washing & deluge line,soot blower passing etc.
7. Frequent water washing of heating elements andimproper drying.
8. Proper exit gas temperature with respect to % ofsulphur in fuel.
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TROUBLE SHOOTING
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Sl. FAULT PROBABLE CAUSES REMEDY
01 Excessive leak
between gas and air
side
Damaged / worn out
seals.
- Due to high gas
inlet temp. Less air
flow.
Inspect all seals and
adjust or replace if
necessary.
02. Excessive noise
from rotor
Warped rotor due to
excessive
expansion.
Foreign object in
rotor.
Bad bearings
Reduce boiler load
or admit more cold
air.
Stop rotor and
visually inspect it
Replace Bearings.
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03. Rotor does not turn Defective drive unit
Foreign object in
rotor
Ensure power is
available to drive
unit
Check pinion gear
and pin rack.
Inspect rotor and
remove any foreign
object.
04 Drive unit
overheats
Inadequate
lubrication in drive
unit.
Pinion gear and pin
rack meshing too
hard due to
expansion
Hard rubbing seals
Bad bearings in gear
reducer.
Lubricate drive unit
components
Adjust drive unit to
proper clearances.
Adjust seals *
Change the
bearings.
* Slight overheating due to hard rubbing seals may be relieved when the Air preheater
reaches normal running temperature or after the seals have worn in properly.
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05 Noisy Bearings Inadequate
lubrication
Check that oil is
flowing through
Flow indicator and
check oil line, if
necessary
06 Oil temperature too
high
Insufficient cooling
Improper oil
viscosity being used.
Absorption of
radiation heat due to
improper insulation.
Check that
adequate water flow
is going into oil
cooler
Replace oil with
proper type of oil.
Insulate properly.
07. Circulating oil
foamy
Air leak into the oil
system
Check for an air leak
on the suction side
of the oil system.
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08. Low oil level Leak in oil system Locate and arrest the leak.
09. Soot blower
not
functioning
Power failure
Swivel header travel
incorrect.
Incorrect steampressure
Check electrical connection.
Check the speed reducermoveable parts for binding.
Adjust travel of nozzle pipe.
Ensure adequate steam
supply is available.
Check DA head valve.
10. Excessive
pressure
drop through
gas & air
sides
Badly fouled heating
elements.
- due to improper
combustion.
Excessive plugging.
Thinned down and
damaged elements
Operate soot blower and
check soot blower steam for
proper pr. and temperature.
Investigate & remeditate the
cause. If soot blower is noteffective, heater can be
isolated and water washed
off load (in worst case),
remove the basket and clean
them outside. Rectify and
replace the element baskets.
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11. Variation
(periodic
kick) in the
main driveammeter
current
Excessive rubbing
of some seals.
Faulty bearings
Locate faulty seals and
replace.
Rectify or replace thebearings.
12. Abnormalincrease in
the
temperature
Starting up of fireinside the Air
preheater
Immediately isolate airheater and check for fire
and admit large quantity
of water. CO2 foam,
steam should not be
used.
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13. Increase in
gas outlet
temp. and
steady fall
of air outlet
temp.
Air preheater
stalled.
Heating elements
plugged
Isolate Air pre heater
and check for troubles
in the drive system.
Clean heating
elements.
14. Excessive
pressure
build up by
Lub oilpump.
Oil filter chocked Clean or replace the
cartridge.
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IMPROVEMENTS REQUIRED - INSTALLATION
1. Storage of APH components.
2. Maintenance of stored components.
3. Support bearing - oil contamination.
4. Improper locking of shim type sector plate adjusters.
5. Welding of drive panel before final alignment
6. Insulation of primary centre section sector plate adjusters.
7. Ensure free movement of hot end sector plates after staticseal welding to avoid guide bearing failures.
8. Check the main drive motor alignment with gear box andcorrect if necessary before trial operation.
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IMPROVEMENTS REQUIRED - COMMISSIONING
Before light up: Commission Cleaning device assy, oil carryover probe, fire sensing device, RSA & wash pipe assy.
Maintain gas outlet tempr is same in both APHs (with in 10 C )
If one APH is used out of two, the other APH should be kept inrotation or should be blanked properly to avoid fire.
Ash accumulation over guide bearing assy, soot blower assy &
LOPs must be avoided.
Ensure clean dry air to Air motor without moisture. Keep the airmotor in working condition by operating 5 minutes in a day.
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IMPROVEMENTS REQUIRED - COMMISSIONING
1. Lub oil pumps should not be started when the lub oiltemperature is less than 40 c to avoid pump oil sealfailure.
1. Water washing is to be done during shutdown when the gasinlet temperature is 100 c. Do not water wash APH justbefore light up since proper drying is not possible which maylead to more unburnt deposition which in turn cause APHfire.
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IMPORTANT INSTRUCTIONS - DO'S
1. Plan in advance the sequence of erection.
2. Keep the necessary tools and tackles ready before start of erection.3. Contact the Airpreheater engineering / BAP / Ranipet if any deviation
or rectification is to be made.
4. Apply rust preventive oil to protect components from rusting due to
long storage and bad weather.
5. Store the heating elements covered with tarpaulin and ensure cover
sheets even after installation into the rotor.6. Maintain the required accuracy in erection, which leads for a
satisfactory operation.
7. Tighten bolts to the required torque.
8. Fill the bearings with specified oil or equivalent even during erection.
9. Rotate the Airpreheater in the correct direction of rotation.
10. Keep a record of the readings in the check sheets which shall be
despatched for the reference of Airpreheater Engineering / BAP /
Ranipet.
11. Seal weld outside and inside for rotor housing panels, connecting
plates (hot and cold) to housing panels, connecting plates (hot and
cold) to air and gas ducts.
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IMPORTANT INSTRUCTIONS - DON'TS
1. Do not mix up items belonging to different Airpreheaters.2. Do not use shop lugs for lifting components / assemblies.
3. Do not support rotor on hot end connecting plate while lifting.
4. Do not carry out the bearing assemblies in open, dusty
atmosphere.
5. Do not spoil the seal leaf by standing on them, by any otherexternal load or interference with foreign material or by wrong
direction of rotation.
6. Do not allow any foreign particle such as electrode bits, slag
wool etc enter into heat transfer elements during erection.
7. Do not carry out final welds before final alignments, checks etc.8. Do not spoil the seal straight edge during trail run.
9. Do not start Airpreheater without filling with specified lubricants
during erection check up.
10. Do not operate air motor without filter lubricator during trial run.
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DAILY CHECK
Oil levels in :
Support bearing, Guide bearing, Main drive gear reducer &
Air line lubricator
For any unusual noise in:
Rotor , Rotor main drive bearings, Drive motor, Main gear reducer,
Cleaning device during operation & Oil circulation systems
For cleanliness near:Rotor drive unit, Rotor main bearings,
Cleaning device & Oil circulation system
Instruments for proper working:
Bearing lube oil thermometers, Bearing lube oil pressure gauges ,
Thermocouples if provided in bearings for alarm or remote
indication. Air inlet and outlet, gas inlet and outlet temperature
measuring instruments. Manometers for measuring pressure drop
across air preheater for gas and air flows.
The condition of cold end elements