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Slide 1
Basically a Heat Exchanger
Heat Transfer takes place from Flue Gas to AirReduces heat rejection to AtmosphereHelps in better Combustion StabilityIncreases boiler efficiency200C drop in flue gas temp results in 1% efficiencyincrease
Hot Primary air for drying the Coal and Transportation
1
Types of Air Preheaters
Recuperative
Re-Generative
Static Construction
Rotary Construction
Tri-SectorBi-Sector
Tubular Type
Rothemuhf
Plate Type
Matrix Element Stationary
Ljungstrom Type
Matrix Element Rotary
Absorbs waste heat from flue gas and transfers to cold air (Primary & Secondary)
Continuously rotating heat transfer elements
Formed by metal sheets in matrix form and placed in modules
For Sizes 24.5 to 27 : 12 Sector Compartment For Sizes 28 to 33: 24 Sector Compartment
Rotor
A radially divided open ended cylinder
Contains the heating surface elements
Centre shaft of the rotor is known as post
Diaphragm Plates extend outward from post
Diaphragm plates divide the rotor into 12 or 24 sectors that are divided into Compartments
Compartments are further packed with heating element baskets.
Hot end baskets
First layer of heating element from hot end sideMade of 24/22 gauge (0.5/0.8 mm) carbon steelNotches run parallel with the rotor axisProvide the correct spacing between the sheetsHeight of the baskets is 850 mm
Hot Intermediate end baskets
Second layer of heating element from hot end sideMade of 24/22 gauge (0.5/0.8 mm) carbon steelHeight of the baskets is 650 mm
Mostly similar to hot end baskets
Cold end baskets
Last layer of heating element from hot end sideMade of 22/18 gauge steel
Height of the baskets is 500 mm
Cold end baskets are arranged for removal through thebasket removal door in the housing.
Hot end baskets are arranged for removal through thehot end ducts.
With the introduction of semi- modular design, side removal ofbaskets is possible for both hot and cold end
DU PROFILE
Leakage of the higher pressure air to the lower pressure flue gasthrough the clearances between the rotor seals and the sector plates
Air to gas leakage increases with time, to more than twice theimmediate post overhaul level.
Increases with increase in differential pressure of two fluids
Effect of Seal Leakage
If seal leakage at Hot end increases
Air outlet temperature decreases
FD fan Power Consumption increases ID fan Power Consumption increases
If seal leakage at Cold end increases
FD fan Power Consumption increasesID fan Power Consumption increases
Entrained Air Leakage
This is mainly entrapped air in between the heatingelements
Direct Leakage
This is mainly due to the differential pressure between thetwo fluids.
Increase in seal clearances at hot condition.Erosion of seals.
Improper seal setting
Radial Seals
located along the edges of the diaphragm plates and bearagainst the sector plates
Housed under Centre sections
Axial Seals
located axially in line with the outer edge of diaphragm platesand bear against the axial seal plates
Mounted in the housing pedestals.
By Pass Seals
located on the housing around the periphery of the rotor andbear against the T-bar attached to the periphery of the rotor.
SEALING SYSTEM: -
It is noted that nearly
LEAKAGE PATH
80-85% leakage isfrom Radial Seal
10-15% through By-Pass Seal
5-10% through Axial
DRIVE ARRANGEMENT :
The drive mechanism consists of
Two electric motors connected to a gear reduction unit throughoverrunning clutch and fluid coupling driving a pinion gear.
The pinion gear meshes with a pin rack on the rotor which allows therotor to rotate at a low speed.
Provision of Air Motor is also given for any failure of electric drive units.
Rotor Drive Assembly
(Down Shaft Design)
1. High Speed Coupling
2. Drive Motor (Main)
3. Pin Rack
4. Rotor Housing.
5. Support Bracket
6. Pinion
7. Pinion Cover
8. Speed Reducer
9. Air Motor (Auxiliary)
Fire Sensing Devices (IRDS)
Provides alarm indication in case of fire in the APH
Greatly save the equipment from mechanical damaged byfire. Meant for washing of heating surface elements.
Rotor Stoppage Alarm
Device fitted to the rotor shaft.
Provides alarm indication in case of rotor stoppage.
Air Preheater Trouble Shooting
Air Preheater Seal Leakage
Higher pressure differential between the air and gas streamsthan the design value.
Improper installation of APH components.Improper seal setting.
Wear / Erosion of seals.
Erosion
Leakage of ash laden air
High differential pressure between air and gas streamsExcessive velocities through the leaks
High ash coals
can be reduced by modifying the static seals, staticspool, ceramic wool packing, selection of seal material
Air Preheater Trouble Shooting
It can be reduced by
modifying the static seals,
ceramic wool packing,
selection of seal material etc.
Corrosion
Cold end heating elements are the most affected.Mainly severe in oil fired boilers.
To avoid corrosion:
a. Complete combustion of fuel oil to be ensured.
b. Soot blowing at regular intervals to be done.
c. Maintaining minimum cold end average temperature.
d. Heating elements to be dried properly after water washing.
e. Oil quality to be ensured.
Air Preheater Trouble Shooting
Higher Pressure Drop across APH
Increases ID/FD/PA fan power consumption
Occurs due to plugging / chocking of heating elements.
To avoid higher pressure drop.
Frequent cleaning of heating elements with soot blowers.Proper evacuation of ash from economizer hoppers.Proper drying of heating elements after water washing.
Pre Start Checks
Support bearing/Guide bearing lube oil pumps are running andlube oil coolers are Charged.
Bearing temperature is Not High (less than 60oC).
Electrical supply to APH motor is Available.
Ensure that Isolating valves of air motor (s) are Open.
Also Ensure that bypass valves of air motor solenoids areClosed.
Air motors lube oil level is Adequate.
Service air pressure is Adequate (> 5 Kg/cm2).
APH Starting Procedure
When both APH are off
Start air motors of both the APH.
Observe for Air motor(s) on indication to appear on panel.Isolating dampers of APHs start opening.
Start air pre heater electrical motor.
Breaker Closed indication should appear on panel.Associated air motor stops.
Starting current shoots up and comes down to normal loadcurrent.
Isolating dampers of the air heater remain open.
Isolating dampers of the other air heater, not inservice, start closing if its air motor is not on.Instruct the local operator to check, locally for anyabnormal sound from bearings/seals.
There should be no abnormal hunting in air heateramperes meter reading.
There should be no abnormal sound from air pre-heater seals or bearings.
Bearing temperatures must be within the normalrange (65 0C -75 0C).
APH Starting Procedure
When one APH is running
Start air motor of second APH if it is not running.
Observe for Air motor(s) on indication to appear onpanel.
Isolating dampers of APH start opening.Start air pre heater electrical motor.
Breaker Closed indication should appear on panel.Associated air motor stops.
Starting current shoots up and comes down to normalload current.
There should be no abnormal hunting in air heater amperesmeter reading.
There should be no abnormal sound from air pre-heater sealsor bearings.
Bearing temperatures must be within the normal range (65 0C
-75 0C).
APH Shut Down Procedure
Check for running of Corresponding ID & FD Fans.Unload associated ID/FD fans, gradually.
The other pair of ID/FD fans (if running) starts loading up onauto.
Stop the associated FD fan. Maintain desired oxygenpercentage.
Furnace total airflow indication drops slightly. Reduce firing ifrequired.
Stop the associated ID fan.
Furnace pressure increases slightly. Maintain furnace draftbetween -5 to - 10 mm wcl.
Stop air heater electrical motor.
With a few seconds time delay, the isolating dampers of the airheater are closed.