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.