om raph bhel

AIR PREHEATER

----------------------------------------------------------------------------------------------------- - 2 - OPERATION & MAINTENANCE MANUAL

The copyright on all documents, drawings and other instruments are the property ofBharat Heavy Electricals Limited. Those shall not be used without their expresswritten permission in any form or part thereof for any other purposes than for whichthis publication is sent to the receiver.

2004PUBLICATION NO. BAP::062004

ISSUED BYO & M SECTION

ENGINEERING AND DEVELOPMENT CENTREBHARAT HEAVY ELECTRICALS LIMITED

RANIPET - INDIA

AIR PREHEATER


F O R E W A R D

This Operation and maintenance Manual is a comprehensive manual covering the

various types of Air preheaters designed, manufactured and supplied by Bharat

Heavy Electricals Limited, Boiler Auxiliaries plant, Ranipet-Tamilnadu. This covers Bi-

sector and Tri-sector modular types of Air preheaters.

Care shall be taken to refer the relevant portions of this manual for Operation &

Maintenance as per the type of Air preheater supplied along with the contract

drawings supplied.

Every possible care has been taken to ensure that the contents are accurate. It

must be recognised that no amount of written instructions can replace intelligent

thinking and reasoning on the part of the operating personnel particularly when

coping up with the individual site conditions. However, should further information

be desired, or should particular problems arise which are not covered sufficiently in

this manual, please refer the matter to EDC/APH, BHEL, Ranipet- 632 406.

Tamilnadu.

BHARAT HEAVY ELECTRICALS LIMITED

BOILER AUXILIARIES PLANT

RANIPET - 632 406.

TAMILNADU

INDIA

AIR PREHEATER


C O N T E N T S

Sl. Description Page No.

01. How the Ljungstrom Air preheater works 05

02. Heating Elements 08

03. Rotor bearings 10

04. Oil Circulation System 16

05. Rotor Drive System 22

06. Rotor Seals 31

07. Cleaning Device 42

08. Water washing of Air preheater 45

09. Lubrication 50

10. Instructions for placing APH in Service 59

11. Pre-commissioning checks 65

12. Checks during operation 72

13. Air preheater fires 76

14. Rotor Stoppage alarm. 78

15. Trouble shooting 81

16. Maintenance 83

17. List of Recommended spares 91

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01. HOW THE REGENERATIVE AIR PREHEATER WORKS

The Ljungstrom Regenerative Air preheater absorbs waste

heat from flue gas and transfers this heat to incoming cold air

by means of continuously rotating heat transfer elements of

specially formed metal sheets. Bi-sector Air preheater preheats

the combustion air (FIGURE-1). Tri-sector air preheater

preheats the secondary air for combustion and also primary air

which is required to preheat & carry pulverised fuel to the

burners (FIGURE-2). Thousands of these high efficiency

elements are spaced and compactly arranged with in

twelve/twenty four sector shaped compartments for heater

sizes from 24.5 to 27.5 and twenty four sector shaped

compartments for heater sizes from 28 to 36, of a radially

divided cylindrical shell called the rotor. The housing

surrounding the rotor is provided with duct connections at

both the ends, and is adequately sealed by radial and axial

sealing members – forming an air passage through one half of

the Air preheater and a gas passage through the other.

As the rotor slowly revolves the mass of the elements

alternately pass through the air and gas passages; heat is

absorbed by the element surfaces passing through the hot gas

stream; then, as the same surfaces are carried through the air

stream, they release the stored up heat thus increasing the

temperature of the incoming combustion or process air.

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EXPLODED VIEW OF MODULAR BI-SECTOR AIRPREHEATER

FIGURE-1

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EXPLODED VIEW OF MODULAR TRI–SECTOR AIRPREHEATER

FIGURE-2

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2.0 HEATING ELEMENTS

2.1 HEATING ELEMENTS

The heating element is a compact arrangement of formed metal sheets contained inthe rotor in two or more layers (FIGURE-3). The basketed element at the cold end,where air is admitted and flue gases are discharged, can be removed through anaccess door in the Air preheater housing without disturbing sealing members of thepreheater components. When one edge of the cold end element has thinned toapproximately one third of its original thickness, the basket can be reversed forextended element life. Similarly, when the top edge of the hot end elements closeto the rotor periphery have eroded resulting in loss of height by 50 mm, the basketscan be reversed. The type of element and the material used are listed in theGeneral specification sheet provided for each contract ( FIGURE-4).

2.2 CLEANING

Special care should be taken to see that the heating element remains free fromdeposit build up, particularly during start up periods. If there is going to be anextended period of time before the Unit is erected, the heating elements should beapplied with one of the following rust preventive oil, once in six months, to retardrusting.

RP102 of Indian Oil Corporation Ltd.Rustop 173 of Hindustan Petroleum corporation Ltd.Rusgard P 214 of Plastipeel Chemicals & Plastic, Thane

A pressure pump, garden type, pneumatic spray gun of 5 to 10 litres capacity issuitable to apply anti rust oil with good penetration.

2.3 MAINTENANCE

During operation of heater, the condition of cold end heating elements can beobserved through a glass faced observation port provided. A vapour proof light toilluminate the inside of duct is also mounted near the port. If cleaning is necessary,operate the on-load cleaner. On every sufficiently long outage, Inspect heatingelements for corrosion, erosion, mechanical damages, chocking, etc., and, if needed,clean / rectify / replace.

2.4 SPARES

It is advisable to have one set of cold end elements and hot end outer row elementsas spares. Other elements can be ordered in advance before the plannedreplacement. Proper storage and refurbishing of spare elements are necessary toavoid rusting and accumulation of dust.

AIR PREHEATER


HEATING ELEMENT BASKETS

FIGURE-3

----------------------------------------------------------------------------------------

HEATING ELEMENT PROFILES

DOUBLE UNDULATED PROFILE

NN

NOTCHED FLAT PROFILE

FIGURE-4

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3.0 ROTOR BEARINGS

3.1 VERTICAL PREHEATERS

A thrust bearing supports the complete rotor. Support bearing assy has two types1.Hanging design (FIGURE-5) 2. Integral design (FIGURE-6). The load istransmitted to the thrust bearing by a trunnion, bolted to the lower end of the rotorpost or by an extension to the rotor post. To guide the upper end of the rotor, aguide trunnion is bolted to the face of the rotor post. A radial guide bearingassembly maintains the position of this trunnion. FIGURE-8 Both the support andguide bearings are lubricated with an oil bath.

3.2 JACKING PROCEDURE FOR REMOVAL OF SUPPORT BEARING

HEATERSIZE

BEARINGSERIES

CAPACITYOF JACK

NO.OFJACKS

REQUIRED24.5-25.5 225 30 4

24.5 -27 290-335 50 4

27.5-33 450-700 100 4

29-34 850-1150 150 4

3.3 For heaters where external hanging type support baring is providedFIGURE-7

• Refer drawing ' Jacking Procedure'• Ensure enough clearance between a) Pin rack bottom bar and pinion bottom

face; and b) hot end T- bar and sector plate.• Remove water shield and cold end air seal cover.• Remove the support trunnion bolt locking bars and grind the heads of the

bolts smoothly.• Remove the bearing housing bolt locking bars.• Remove the bearing housing cover and rotor stoppage alarm band• Place the jacking beams on jack stands.• Place the hydraulic jacks on the beam ( two on each beam as shown in

figure ) and position the jacks on the beam so that they line up with thetrunnion bolts. Depending upon the height of the jacks. It may benecessary to provide packer pieces between jacking beams and bottom ofjacks.

• Elevate the jacks uniformly by a common pump until jack rams contact thetrunnion. Raise the jacks to an additional height of 6 mm to relieve thebearing off the load.

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• Insert support blocks between the jacking beams and trunnion surfacessurrounding the trunnion bolts with four pipes and packer pieces, whichhave been supplied under Items per contract. Release the jacks carefully,allowing the rotor to rest on the support pipes slowly.

• It should be noted that a single hydraulic pump activates all the four jackswith a common distributor.

• The bearing housing can then be lowered for further works.

3.4 For Air preheaters which have internal type support bearing ( i.e. where bearing housing is held inside the cold end centre section ) FIGURE-7

• Refer drawing ' Jacking Procedure'

• Check for enough clearance between a) Pin rack bottom rack bar and pinionbottom surface b) Hot end T-bar and sector plate.

• Unscrew the bolt and remove sections from trunnion spool for access to endof rotor post.

• Position the jacks on jack supports so that, when elevated, they wouldcontact the rotor post headers.

• Remove the bearing housing cover.

• Raise the rotor, by using the jacks, approximately by 6mm and lock the jacksby using lock nuts if provided or provide packers below the support pipes.

• Remove the four hold-down bolts of the support bearing housing.

• Raise the support bearing housing by 4 to 5 mm with the help of four jackingbolts.

• Remove the shims beneath the housing and lower the housing slowly with thehelp of jacking bolts so that it sits on the support pad.

• The housing can then be pulled out for further works.

NOTE : WHILE REMOVING BEARING HOUSING FROM CENTRE SECTION, CARESHOULD BE TAKEN SO THAT THE BEARING PARTS DO NOT GET DAMAGED.

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SUPPORT BEARING ASSEMBLY – HANGING TYPE

FIGURE-5

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SUPPORT BEARING ASSEMBLY – INTEGRAL TYPE

FIGURE-6

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FIGURE-7

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GUIDE BEARING ASSY WITH MODIFIED TRACKING ARRGT

FIGURE-8

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4.0 OIL CIRCULATION SYSTEM

4.1 DESCRIPTION

The oil circulation system is designed to supply the bearing with a bath ofcontinuously cleaned oil at proper viscosity. To accomplish this, the bearing oil iscirculated by means of a motor driven pump through an external filtering system.The system components are a pump, motor, thermometer, pressure gauge coolerand filters. A thermostat may be used to limit the operation of the system totemperature, which will not overload the pump or motor as a result of high oilviscosity. The schematic diagram shows the path, which the oil takes as it, passesthrough this system (FIGURE-9). Oil is drawn from bearing housing by the pumpinto the filter and back to the bearing housing. For support bearing scheme referfig. FIGURE-10.

4.2 CHOICE OF LUBRICANT

Select proper lubricating oil for guide and support bearings in accordance with thelubrication chart. The oil selected must have a minimum viscosity of 1000 SSU atthe maximum operating temperature. Set the thermostat to 40 ºC for support& guide bearing to start the lub oil system. The corresponding alarm setpoints of RTD is 70º for both support and guide bearings.

4.3 OPERATION

In certain locations where oil is subjected to cold ambient temperature, starting thepump should be delayed until the oil temperature has risen to 40°C sufficiently tolower the viscosity to a point where it can be moved without undue loading of thepump. Running the pump less than 40°C would lead to pump oil sealfailure. While starting the system, all valves should be kept wide open. The reliefvalve opens automatically to reduce pump load when the oil pressure is more.FIGURE-11.

The dipstick in the bearing housing should be removed and inspected for signs offoaming. If foaming is evident test all pipe joints, valve packing glands and pumppacking glands for possible air leakage. Any leak, particularly in the suction side ofthe system will cause foaming of oil and possible overflowing of the sealing tube inthe guide bearing. A shut down of the oil circulation unit for a nominal duration, suchas when changing the filter cartridges, is not critical, however, operation should berestored as soon as possible.

4.4 MAINTENANCE

The pump discharge pressure will gradually increase as fouling of the filterprogresses. Filter cartridges should be replaced (or cleaned if found good) when theoil at normal operating viscosity indicates a pressure gauge reading of approximately1 kg/sq. cm higher than normal; or it can be done once in six months as a routinework.

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Check the oil level in the bearing housing periodically. Any sign of foaming may alsobe observed during routine inspections.

4.5 REFILLING THE SYSTEM If the oil has been drained from the bearing housing, the circulation system shouldbe refilled as follows;

• Add oil through the dipstick hole until the maximum oil level mark on the dipstickis reached.

• Start the oil pump. This will drain oil from the housing to fill oil lines, filter andpump thus purging air from the system. Prime the pump if it does not deliver oilafter operating for one minute.

• Shut the system down, allowing oil level to stabilise. Refill the bearing housingto the indicated level. Start oil pump once again. Allow the system to operatefor several minutes before shutting it down for another oil level reading.

• Repeat the above procedure until proper oil level is obtained and all signs of theair have been eliminated.

CAUTION : DO NOT OVER FILL THE SYSTEM. AN EXCESSIVE HIGH OILLEVEL MAY CAUSE LEAKS IN THE BEARING HOUSING SEALS, WHICH MAYLEAD TO FIRE.

4.6 REPLACEMENT OF FILTER CARTRIDGES

• Replace (or clean) the filter cartridge once in 6 months.

• After changing / cleaning the cartridge, open the valves on each side of the filter.Loosen the vent plug at the inlet connection of the filter allowing air to flow outand the unit to fill with oil. Tighten the vent plug when oil starts coming throughthe vent hole.

• Add oil to the system to bring oil level back to the level mark in the housingdipstick. The quantity of oil to be refilled in the housing will be approximatelythe same as the amount removed through the filter drain plug.

• Run the system for a few minutes to purge any remaining air from the system;then check the dipstick reading and add oil if necessary.

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4.7 MAINTENANCE OF ROTOR BEARING

Bearing area has to be kept clean always. Check that the insulation is proper in thisarea to avoid heat radiation to bearing and ambient cooling air circulation is notobstructed. Check oil level in every shift

CAUTION:

Guide bearing oil level should be checked only with the oil circulation systemswitched off. When the system is in operation, the level might be lower than thenormal due to the portion of oil bearing in circulation. If oil is added to bring backthe level under this condition and when the circulation system is stopped, thecirculating oil might rush back to the bearing housing and the level would go upbeyond the permitted value resulting in leakage of oil through the sealing tubepacking. This is a fire hazard. Oil circulation can be stopped under normalcircumstances for brief periods (say 15 minutes) for checking oil level without illeffects. Periodically oil levels in the bearings are to be checked by removing theoverflow plugs provided in the housing to make sure that the dipstick indications arecorrect. While filling oil through dipstick assembly, the viscous oil may take sometime to reach the bearing housing. Hence, oil level should be checked only afterensuring that the filled up oil has reached the bearing housing. Otherwise it willlead to false indication of oil level.

4.8 SPARES

One set of motor bearings may be held for a multiple or single unit installation.Gaskets and packing are required for each heater. Extreme care is required in storageof the bearing against rusting. For oil circulation system, one assembled pumping unitcomplete with motor, coupling, etc., for each system must be kept in addition toindividual spare part kits for the various components. A good number of filterelements, coolers and a set of pressure gauges, thermometers and thermostats areessential.

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SCHEME FOR GUIDE BEARING LUB OIL CIRCULATION

SYSTEM WITH STAND BY

FIGURE-9

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SCHEME FOR SUPPORT BEARING LUB OIL CIRCULATION

SYSTEM WITH STAND BY

FIGURE-10

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LUB OIL CIRCULATION UNIT

FIGURE - 11

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5.0 ROTOR DRIVE SYSTEM

5.1 DESCRIPTION

The driving force for turning the rotor is applied at its periphery. A pinion attachedto the low speed shaft of a power driven speed reducer engages a pin rack mountedon the rotor shell. Operation and maintenance instructions for the motor, speedreducer and couplings are described in the respective manufacturer catalogues. For upshaft design ref fig FIGURE-12 and for down shaft design ref fig. FIGURE-13.

5.2 AUXILIARY DRIVE

The auxiliary drive ensures the continued operation of the preheater even if power tothe electric motor is interrupted. Generally Air motor is used for the auxiliary drive.In certain installations, electric motor ( either AC or DC ) is provided as an auxiliarydrive upon specific requirement of the customer.

The auxiliary drive motor may also be used to control the speed of the rotor duringwater washing of the heating surface. The gear box is furnished with an auxiliaryhigh speed shaft extension, thus permitting the installation of the auxiliary drivemotor at any time. A lubricator is furnished with all air motor drive for installationin the air line. Ensure clean dry compressed air with required pressure intothe Air motor to avoid jamming / failure. (FIGURE-17).

CAUTION: AIR MOTOR SHOULD NOT BE OPERATED WITHOUT THELUBRICTOR. BOILER LOAD NEED NOT BE REDUCED WHEN THE AIRPREHEATER IS IN OPERATION WITH AUXILIARY DRIVE MOTOR.

5.3 MAINTENANCE

The drive unit has to be kept clean. Insulation in heater casing around this area hasto be maintained in sound condition to avoid heat radiation and consequentoverheating of components. Oil level in the reducer and the air line lubricator to airmotor to be checked at every shift. All the mounting fasteners are to be checkedperiodically for tightness. Any unusual noise or vibration needs immediate attention.The solenoid value in the air line is to be checked for proper functioning. Air linefilter to be cleaned/replaced if found necessary. Run Air motor for two minutesdaily to keep it fit for operation.

5.4 SPARES

One number in each of fluid coupling, air motor, speed reducer, overrunning clutchmay be kept for multiple unit installation in addition to individual spare parts kit.

Sufficient number of coupling spring elements, taper lock bush, packing and gasketsets are required. Parts have to be carefully stored and refurbished to avoid rusting.

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5.4.1 OVER-RUNNING CLUTCH COUPLING

The installation of the over–running clutch is not a difficult procedure, but one whichrequires care to assure proper operation.

To assemble the clutch coupling on the reducer auxiliary high speed shaft extension,heat the clutch in a clean oil bath and push on. FIGURE-14

CAUTION: DO NOT DRIVE ON BY ANY SHOCK METHOD SUCH ASHAMMERING BEFORE INSTALLING THE COVER, CHECK THE OIL SEALMAKING SURE THAT THE SEALING LIP IS TOWARDS THE INSIDE OF THEREDUCER.

NOTE : (1) APPLICABLE FOR FALK REDUCERS

The over-running clutch coupling requires no lubrication before installation. Onceassembled on the reducer, it becomes an integral part of the unit, picking up oilsplashed by the gears, which provides proper lubrication.

NOTE : (2) REDUCERS OTHER THAN FALK MAKE :

As recommended by the manufacturer-refer O&M catalogue of manufactures.

5.5 TAPER LOCK BUSHING WITH ADAPTER (For up – shaft ) FIGURE-15

5.5.1 TO INSTALL

• Remove bushing if unit is already assembled. Carefully clean the taperedsurfaces, shaft bore and outside of bushing, bore of hub or adopter sleeve.Remove any oil, lacquer or dirt. Remove any burr, which may be formed on theend of the shaft or end of bushing. Place bushing in hub or adopter.

• Oil the threads and under – head of cap screws. Place screws loosely in holes asshown in the diagram.

• Make sure bushing is free in hub or adopter sleeve. Slip assembly on to shaftand located in position desired.

• Tightened screws alternately and evenly until all are pulled up very tightly andwrench upto 17 kgm

• Hammer against large end of bushing using hammer and block or sleeve of softmetal such as brass to avoid damage. Screws can now be turned a little moreusing the specified torque wrench.

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• Repeat this alternate hammering and screw re tightening until the specifiedtorque wrench no longer turns the screws after hammering. Screws must bekept tight at all times. Fill other holes with grease to exclude dirt.

5.5.2 TO REMOVE

• Remove all screws. Oil the threads and under-head of cap screws.• Insert screws in holes shown blocked in diagram. Note that one screw is left

over and is not used in this loosening operation.• Tightened screws alternately until bushing is loosened in hub or adopter

sleeve.

5.7 QD BUSH / WORTHING TON HUB FIGURE-16

5.7.1 TO INSTALL

• Clean the hub of the pinion and the taper bush thoroughly.• Insert the pinion on to the drive shaft and centre it. The pinion can be

supported by wooden blocks.• Keep the taper bush in between the pinion and the shaft.• Raise the hub on to the shaft using a jack until the specific dimension

between the hub flange surface and the shaft bottom face is achieved.• Now, with the help of the 4 screws, which are to be applied with anti-seize

thread coating compound, fasten the hub and the pinion. The screws are tobe tightened to a torque of 58 kgm ( 56 to 59 kgm )

• In case the distance between the hub bottom flange and the bottom surfaceof the shaft is more/less than the required value, the hub is to be withdrawnand reassembled.

• After final assembly, lock the key with the help of the grub screw.

5.7.2 TO REMOVE

• Support the pinion with the help of wooden blocks suitably.• Remove the four holding bolts.• Fix two bolts in the two threaded jacking holes and tighten the bolts so that

the taper bush comes out freely.

WORTHINGTON HUB IS GIVEN IN CERTAIN INSTALLTION INSTEAD OF TAPERLOCK BUSH. (FOR ASSEMBLY PROCEDURE REFER TO THE ROTORASSEMBLY DRAWING)

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MAIN DRIVE ASSY - UPSHAFT

FIGURE-12

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FIGURE-13

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FIGURE-14

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TAPER LOCK BUSH

FIGURE-15

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FIGURE-16

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SCHEME OF AIR SUPPLY TO AIR MOTR

FIGURE-17

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6.0 ROTOR SEALS

6.1 DESCRIPTION

Seals are provided at both the ends of the Air preheater to minimise leakagebetween the air side and gas side. The hot and cold end radial seals are attached toeach diaphragm of the rotor and are set at a specified clearance from the sectorplates which separate the gas and air streams. Axial seals were provided tominimise the leakage axially. Axial seals would rub against the axial seal plates inhot condition to minimise leakage of air to gas side. Seals provided at the rotor postare set to operate with minimum clearance with respect to the horizontal sealingsurface of the sector plate. The circumferential / by pass seals provide sealingbetween the periphery of the rotor and the connecting plate / housing. All sealsmay be adjusted to necessary clearances. Information regarding the types of sealsprovided for the Air preheater have been given separately.

6.2 MAINTENANCE

During every sufficiently long outage, inspect all seals for mechanical damage,erosion, etc., and if necessary replace/rectify. When seals are replaced, observeproper setting dimensions. Check the seal fixing fasteners for tightness and properlocking.

NOTE : SETTING VALUES GIVEN IN THE CHART ARE FOR FULL LOADOPERATNG CONDITIONS ONLY. AT PART LOAD OPERATIONS ANDDEVIATIONS FROM THE ABOVE VALUES WILL LEAD TO MORE LEAKAGE.

6.3 SPARES

One set of complete seals, holding strips and fasteners for each heater is essentialas they are likely to get damaged due to erosion and mechanical rubbing.

6.4 SEAL INSTALLATIONS

6.4.1 RADIAL SEALS ( FIGURE-18 )Setting of straight edge: Bolt the aluminium finger tabs or gauges in radial seal boltholes, one in the inboard and the other in the outboard of the diaphragm. Set eachone to sector plate in accordance with the seal setting chart, with feeler gauges.Then, rotate the finger tabs to straight edge and set straight edge to gauges.Attachthe seal straight edge to the support channels welded inside the connecting plate.Install the radial seals to the leading edges of the rotor diaphragms. In the hot end,leave the seals loose and push them down towards the element for additional sectorplate clearance. In the cold end of the V and VI heaters, move the seals up wardselements and hold them with the help, of two end bolts temporarily so as to clear thesector plates. Set the straight edge to clearances from sector plates in accordancewith the seal clearance chart.

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Set one seal so that each section touches across the full length of the straight edge.Turn the rotor and check this first seal clearance across the sector plates. Ifclearance is not correct, reset the straight edge to correct clearance then set theremaining seals.

NOTE: WHEN FIXING NEW SEAL LEAVES, IF IT IS OVERLAPPING AT THEJOINT, GRIND THE EXCESS MATERIAL OF THE SEAL LEAVES, DO NOTGAS CUT. SEALING TAPS ARE TO BE WELDED AS PER DRAWING.

6.4.2 AXIAL SEAL INSTALLATION FIGURE-19

Set axial seal straight edge to support channels located inside rotor housing with 5mm gap to the high point of T bar. Straight edge to be vertical to the plumb.FIGURE-20 Fix seals and adjust to the straight edge and tighten fasteners. Axial sealplate to sector plate seals ref fig FIGURE-21

NOTE: THE AXIAL SEAL PLATES ARE TO BE ADJUSTED AS PER THE SEALCLEARANCE MENTIONED IN THE SEAL CLEARANCE CHART.

6.4.3 BYPASS SEAL INSTALLATION FIGURE-22

By pass seals are provided with a number of slots to bend them easily. They mustbe installed in pairs with staggering of their slots to avoid leakage of gas / air. Theends ( near sector plates) can be fitted with three layers of by pass sealleaves. Every leaf fixed near the sector plates should be held atleast by two boltsand the overlapping of two seal leaves is to suit the direction of rotation of therotor. Maintain clearances as per the seal setting chart.

6.4.4 ROTOR POST SEAL INSTALLATION FIGURE-22

It will seldom be necessary to replace rotor post seals. If the occasion should arisethey are installed in the same way as the existing seal.

6.5 STATIC SEALS – LARGE AIR PREHEATERS FIGURE-23

6.5.1 DESCRIPTION

The sealing system in the large Air preheaters is provided with adjustable sectorplates and axial seal plates to effect higher sealing efficiency in conjunction with therotor seals. They are attached to connecting plate centre sections and main pedestalsby means of adjusters to position them in line with the rotor planes. As there arerelative movements between sector plates and their carrying structures, gaps areprovided between them. These gaps are closed by means of static seals to avoidleakage.

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6.5.2 MAINTENANCE

Static seals may be subjected to erosion in the long run. If large holes are allowedto be formed, excessive leakage of air may result. Periodically these have to becarefully inspected and repaired.

The static sealing area near hot end trunnion is of vital importance with regard toerosion. The inboard adjusters (tracking rods) of hot end sector plate located in thisarea have to be checked for erosion periodically.

In tracking spool type arrangement care should be taken to weld the static seals asper the drawing with respect to spool in the inboard of rotor, in order to avoid theprevention of tracking, which will lead to guide bearing damage and damage to theguide bearing seating plate in the centre section.

NOTE : FIGURE-24 & FIGURE-25

The Air preheater seals are initially set for certain predicted gas and airflow & temperature condition. During the initial seal settings, a certainnumber of aluminium finger tabs are also fixed along with the seals.

The tabs are set slightly higher than the respective seals so that they arepermitted to rub with the sealing surfaces (i.e.) sector plates and axial sealplates) and wear out to the correct height depending upon the actualthermal expansion occurring inside the Air preheater.

Once the boiler reaches its MCR capacity with specified fuel and after a fewhundred hours of operation at that load it is necessary to shut down the Airpreheater and inspect the seals for wear and tear.

The seals are to be reset to the height of the finger tabs for proper leakagecontrol. If the seals and the tabs are at the same level, the seals are to beleft as it is and no further adjustment is required. The seals are to be resetduring each annual overhauling to the required levels if required. Onlyafter doing the resetting performance test on Air preheater can beconducted.

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RADIAL SEAL INSTALLATION – MODULAR ROTOR

FIGURE-18

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AXIAL SEAL

FIGURE-19

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AXIAL SEAL ASSEMBLY

FIGURE-20

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AXIAL SEAL PLATE TO SECTOR PLATE SEAL

FIGURE-21

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FIGURE-22

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FIGURE-23

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AIRPREHEATER SEAL CLEARANCE VALUES

SEAL CLEARANCE VALUES:

HOT END COLD END

RADIAL SEALS INOARD OUTBOARD

(C ) = 0.0 to 1.0 MM(D ) = 0.0 to 1.0 MM

(A) = 0.0 to 1.0 MM(B) = MM

AXIAL SEALS (G) = MM (H) = MMBY PASS SEALS (M) = MM (N) = MM

FIGURE-24

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AIRPREHEATER SEAL CLEARANCE VALUES

SEAL CLEARANCE VALUES:

HOT END COLD END

RADIAL SEALS INOARD OUTBOARD

(C ) = 0.0 to 1.0 MM(D ) = 0.0 to 1.0 MM

(A) = 0.0 to 1.0 MM(B) = MM

AXIAL SEALS (G) = MM (H) = MMBY PASS SEALS (M) = MM (N) = MM

FIGURE-25

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7.0 CLEANING DEVICE

SINGLE NOZZLE OR TWIN NOZZLE

Cleaning device is provided at the cold end gas side to remove soot deposits on theheating elements. From the past experience, it is seen that hot end elements areclean due to erosive action of the fly ash and do not need cleaning.

The cleaning device consists of an electric motor coupled to a gear driven crankmechanism, which oscillates the swivel header carrying the nozzle pipe or pipes. Thecleaning medium is conveyed through the swivel header unit respective nozzle pipe,to the nozzle at the end. A rotary joint in the supply line permits free motion of theswivel header while connected to the source of supply.

The arc traversed by the nozzle and the rotation of the rotor subjects the entire areaof the rotor to the action of the cleaning jet. If steam is used, drain connections arerecommended in the steam piping layout for removing condensate from the pipingsystem while the device is idle and just before it is placed in operation.

The steam supply line to cleaning device has to be supported in such a way to avoidaxial and side thrust being applied on to the rotary swivel joint. If care is not takenin this regard heavy leak may occur in this joint.

If the cleaning device is installed in hot end also, it will be operated depending onthe requirement, i.e., when the pressure drop across Air preheater is more.

Ensure the drain connections are properly maintained and no condensate isleft in the pipe line. Keep the drain valve crack open.

7.1 SPARES ( POWER DRIVEN CLEANING DEVICE )

One fully assembled unit may be kept for multiple units installations, in addition tospare part kits for individual components like motor, speed reducer, couplings, wormgear box, etc. A set of nozzles is also required.

7.2 OPERATING INSTRUCTIONS (AIR OR STEAM)

7.2.1 FREQUENCY OF CLEANING

During early operation of the Air preheater it is extremely important that thecleaning device be operated in accordance with the procedure described in thesection ‘ Air preheater operation’ under ‘ placing the Air preheater in operation’.The frequency of cleaning will be determined by the rate of deposit accumulation onthe heating element. For cleaning procedures when the preheater is coming out ofservice, refer to the SHUTTING DOWN AND STAND BY instructions in the section ‘Air preheater Operations’.

AIR PREHEATER


7.3 PRESSURE REQUIREMENTS

For normal operation the recommended steam pressure is 14kg/cm2 at 150ºCsuper heat for steam and 6.4 kg/sq.cm for compressed air, with the inlet valvewide open. Effective cleaning action will not be obtained if pressure is too low.Steam pressure should not exceed 17 kg/sq.cm and air pressure should not exceed14 kg/sq.cm. Excessive pressure for an extended period may damage rotor sealsand heating surface. The steam pressure is to be controlled by DA head valueprovided. If DA head valve is not provided, the orifice plate has to be installed.

7.3.1 OPERATION FOR AIR OR STEAM

A complete blowing cycle consists of a single pass over the heating element startingat diagram position ‘A’ and travelling as shown in sketch. When nozzle reachesposition ‘B’ it will oscillate back to starting position ‘A’ without blowing. To clean theheating surface properly, every effort should be made to provide dry air or steam.

Before admitting steam to the cleaning device nozzle, drain the supply linesthoroughly to assure complete removal of wet steam and condensate from linesahead of the cleaning device. Definite rules cannot be stated on the amount of timeor frequency of cleaning required to clean the heating surface thoroughly becausethe rate of deposit accumulation varies with different fuels and operating conditions.Observe the conditions of the heating surface regularly and be guide accordingly.If the Air preheater is equipped with a combination-cleaning device using air orsteam and water, see separate instructions for water washing.

7.4 MAINTENANCE INSTRUCTIONS FOR THE AIR PREHEATER POWEROPERATED CLEANING DEVICE AND PIPING

Maintenance of the cleaning device consists of checking valves for leaking seats,examining nozzle pipe and nozzle for corrosion/erosion, removing sediment andscale from the nozzle pipe and lubricate the speed reducer, drive motor and swiveljoint.

Give immediate attention to the valves if there is evidence of leak. A leak maycontribute to rapid deterioration and corrosion of the nozzle pipe and nozzle. It mayalso result in corrosion and plugging of the heating surface.Inspect the nozzle periodically and remove any accumulation of sediment and scalein the piping to assure an adequate supply of cleaning medium to the nozzle at therequired pressure. Note if excessive wear of the nozzle has developed. A badlyworn nozzle may reduce cleaning efficiency.

Check the orifice plate in the supply line, if provided, to avoid excessive pressuredue to erosion of the orifice. Too much pressure may damage rotor seals andheating surface. Lubricate the speed reducer and drive motor regularly inaccordance with the manufacturer’s instructions indicated on the equipment. Referalso the section ‘ Lubrication’.

AIR PREHEATER


The worm gear housing is packed with grease at the factory and no furtherattention is required. However, if for some reason the lubricant is lost or it isnecessary to add lubricant, a good grade of grease as given in the lubrication chartis recommended. (Grease nipple provided in worm gear housing)

7.4.1 SOOT BLOWING – DRAIN CONNECTIONS

Do not connect drains from the cleaning device to a closed drainage system. A freedrain will prevent water and condensate from entering the Air preheater due to aback – flow from a closed drainage system. A free drain also serves to indicateleaking valves. Install the drain outlets so that the operator may observe thedischarge. Make every effort to provide dry system or air for cleaning the Airpreheater heating surface.

7.4.2 CLEANING DEVICE – SETTING OF NOZZLE SWEEP

i) Remove key from lever throw arm to speed reducer shaft andleave lever arm to turn free on shaft.

ii) On large device units disengage coupling between speed reducer andworm gear drive, and freewheel the nozzle pipe and linkage by using awrench on the lock nut of the gear drive shaft located underneath thedrive base.

iii) Set lever arm and connecting link arm in a straight line by looseninglever clamp.

iv) By hand with lever clamp loose swing nozzle inside heater to approx.50 mm from duct wall say point ‘A’ Tighten up lever clamp and swingnozzle to full extent of sweep, say, towards point ‘B’

v) Measure distance left from nozzle to duct wall at point ‘B’ and keepinglever arm and connecting link in a straight line ( jack knifed) at thisend of sweep, loosen lever clamp and move nozzle one half thedistance remaining to duct wall, point ‘B

vi) Tighten up lever again and by means of the eccentric pin are secured,move nozzle to proper clearance from duct wall at point ‘B’ and lockeccentric pin.

vii) Making sure both lever clamp and eccentric pin are secured, movenozzle back to opposite duct wall point ‘A’ and make minoradjustments by using the lever clamp and eccentric pin.

viii) The accepted setting is with the steam blast from the nozzle coveringthe entire element surface but not blowing directly onto the by pass orcircumferrential seals.

AIR PREHEATER


8.0 WATER WASHING OF AIR PREHEATER

8.1 GENERAL

In cases when residual deposit accumulations cannot be removed readily by sootblowing, it sometimes becomes necessary to water wash the heating surfaces tomaintain acceptable draft losses through the Air preheater. In some instances, thismay be required more frequently than during the scheduled boiler outages. Mostdeposit accumulations forming on the air preheater heat transfer surface are highlysoluble in water and, therefore, are easily removed by washing provided a sufficientquantity of water is used.

8.2 WASHING DEVICE

Washing devices are located at both the hot and cold ends of the Air preheater andthey should be operated simultaneously to provide effective removal of the deposit.The stationary multi-nozzle water devices consist of a straight pipe with (15° Sprayangle) flat spray nozzles spaced to distribute the wash water evenly over the heatingsurface. Washing pipes are located on the gas side. Refer to the suggested schemeof connections.and must be kept open and free of deposit throughout the washperiod in order to prevent water build-up in the ductwork and to ensure. FIGURE-26

CAUTION: CHECK WHETHER THE STRAINERS ARE INSTALLED AT THE ENTRYOF WASHING PIPES TO PREVENT ANY DEBRIS THAT WOULD CLOG THENOZZLES.

8.3 WATER SOURCE

Fresh water is ordinarily used for washing Air preheaters. The most commonly usedsources of water for washing Air preheaters are rivers, lakes and ponds althoughwell water and house service water are also used extensively. No restriction isplaced on the water source except that it be free of any debris that would tend tofoul the pumps, clog water washing device nozzles or plug the heating element gaspassages.

8.4 DRAINAGE

Adequate drainage facilities are of vital importance for washing the Air preheater.They must be provided on the side of the Air preheater where washing is beingcarried out. If possible, drains should be provided on both sides of the Unit. This isnecessary because some wash water will be carried over from the source to theopposite side of the Air preheater. The drain plugs must be opened prior to washingproper disposal of the washing effluent.

AIR PREHEATER


8.5 FREQUENCY OF WASHING

Frequency of washing is an unpredictable factor, depending upon such variables asthey quality of the fuel burnt, nature and amount of deposit, boiler operatingconditions, dryness of soot blowing medium, etc. If a regular soot-blowing scheduleusing a dry cleaning medium is followed, it is ordinarily not necessary to wash theAir preheater except during regular outages. At times it may be desirable to washthe Air preheater with the boiler in service in order to maintain boiler loadavailability. In these cases washing may be undertaken either on a predeterminedschedule established by actual operating experience with the unit involved, or on aspecified increase in pressure differential across the Air preheater.

Consequently, the actual washing operations may be carried out under any one ofthe following conditions:

i) Out of service; and ii) In-service – isolated.

i) OUT OF SERVICE WASHING

Out of service preheater washing is accomplished when the boiler is shut down for anormal scheduled inspection or for repair work. Out of service washing affords thebest possible opportunity for close control of the washing operation and for makinga thorough inspection of the heating surface both during and after washing.

Best results can be obtained by washing when the gas inlet temperatureattains 100 °C. The air preheater may be washed at any time after the boiler hasbeen shut down. The rotor can be turned at normal speed during the operation.However, if it is necessary to restrict the discharge of wash water to one side of theair preheater, the auxiliary drive may be employed to reduce the rotor speed. Afterthe drainage system has been checked to see that no obstructions exist, watershould be admitted to both the hot and cold end devices. The heat transfer surfaceshould be inspected periodically throughout the washing cycle. When it is observedthat the heating surface has been thoroughly cleaned, the unit should be allowed tocompletely dry before it is put back into service.

If incomplete washing, resulting due to use of insufficient quantity of water or dueto lack of time to completely wash all the deposits from heating surface, is done theresidue can adhere to the element. Experience shows that this type of depositbecomes backed on the heating surface and it is extremely difficult to remove later.Such deposits tend to encourage further deposit build-up on the heating surface atan accelerated rate.

ii) IN SERVICE – ISOLATED WASHING

In service- isolated washing ( isolated washing) consists of washing one Airpreheater in a two or more Air preheaters installation. The procedure of reducingboiler load and isolating one Air preheater by closing the dampers and shutting downassociated fans while the boiler remains on line.

AIR PREHEATER


The other Air preheater(s) and fan(s) continue in operation. For this type ofwashing, close the gas inlet damper of Air preheater and the damper after thehopper below the Air preheater in the Gas side ( before EP). The damper after therespective ID fan must also be closed. On the air side, the damper at the air outletand air inlet must be closed to totally isolate the Air prehater for washing.

The actual washing procedure closely resembles that for ‘out of service’ washing.The isolated rotor can be run at normal rotor speed during the washing operationunless it is necessary to restrict the wash water discharge as much as possible toone side of the unit. In this case, the rotor speed can be reduced by means of theauxiliary drive unit. It should be ascertained that the drainage system is free of anyobstruction prior to admitting water to the washing devices. Whenever possible, thewash water should be shut off periodically during the washing operation. Visualinspection of the heating surface should then be made to determine its degree ofcleanliness. Washing should be continued until such time as inspection of thesurface reveals that it is clean. If inspection of the heating element is not possible,observation and chemical testing of the washing effluent may obtain some indicationof its condition. When the washing effluent appears to be clear and a chemical testindicates a pH of approximately 7, it can generally be assured that the Air preheateris clean. Caution should be exercised when using chemical testing as a cleanlinessindicator. Such a test will not reveal the presence of insoluble material on theheating surfaces. Consequently, erroneous conclusions can be drawn as to Airpreheater cleanliness if sole reliance is placed on a chemical test. After the isolatedAPH is completely washed and dried, the procedure is reversed allowing all gas andair to flow through the clean heater while the other unit is isolated and is washed inthe same manner. The ‘isolated’ method of washing Air preheaters has been foundto produce excellent results both from the standpoint of cleanliness and timerequirement. APH washed by this procedure can be cleaned in four to sixteen hours.

8.6 DELUGE PIPES

They are identical to wash pipes and are fitted optionally to dump water on heatingelements during Air preheater fire. In case of fire, water through the wash pipesshould also be admitted in addition to Deluge pipes to quench the fire effectively.FIGURE-27

8.7 MAINTENANCE OF WASHING AND DELUGE PIPES

On outages, inspect the nozzles for pluggage. Periodically, the strainers fitted in theinlets of these pipes have to be opened and the gaskets are to be cleaned. Checkfor leaks in the system and rectify.

8.8 DRYING OF HEATING ELEMENTS

The heating elements are to be dried immediately after water washingthoroughly. If not done immediately, water will react with atmosphere andoxidisation will start and heating elements plugging will occur and maylead to APH fire.

AIR PREHEATER


FIGURE-26

AIR PREHEATER


FIGURE-27

AIR PREHEATER


9.0 LUBRICATION

9.1 ROTOR SUPPORT BEARING

The rotor support bearing of the Ljungstrom Air preheater may be lubricated by oneof the two methods. It may be either bath lubricated, or lubricated by means of acombined bath and forced circulation and filtering system. Certain installationsrequire inclusion of a cooler in the circulating system.

The choice of lubricant will depend on the expected maximum operating temperatureof the support bearing. This, in turn will depend upon the type of lubricating andcooling system, and upon conditions surrounding the support bearing. Experienceindicates that the following maximum temperatures may be expected.

9.2 Expected maximum operating temperatures

BATH LUBRICATIONCOOLER BY

TYPE OF AIRPREHEATER

WATER AIR

OIL CIRCULATIONSYSTEM WITH ORWITHOUT COOLER

VI HEATER (NOTE-1) 95°C 70°C 60°CV – HEATER 60°C 50° -H- HOT SIDE 95°C 70° 60°CH- COLD SIDE 60°C 50° -ALL OTHERS - 50°C

NOTE (1) : Operating temperatures exceeding 80°C are not recommended.Supplemental air-cooling or added insulation of adjacent structure and ductwork, orcombinations of both, will be effective. The lubricating oil used may be either an FPtype of lubricant with lead napthenate additive, or a straight mineral oil.

NOTE (2) : If operating temperature is above 70°C, the oil supplier should beconsulted as to the effect of such temperature on an FP lubricant of hismanufacture.

The oil selected for the support bearing will also be suitable for the Guide bearing.Lubricants for installations equipped with oil circulating systems should haveviscosity’s no higher than needed for the maximum temperature expected (60°C).Otherwise, the oil circulating pump may be overloaded when the temperature of thelubricant is low, such as would possibly be obtaining during starting up periods.

9.3 OIL CIRCULATION SYSTEM

FHP MOTORS:

After every six months of operation, the bearings and housings should be thoroughlycleaned and packed with new grease. For the type of grease, refer lubrication chart.

AIR PREHEATER


NOTE :

All Air preheater support and guide bearings are bath lubricated regardless ofwhether or not a circulating system is provided. The purpose of the circulatingsystem is for viscosity control and filtering of the oil. Loss of oil circulating systemis not an emergency situation that requires shut down of the equipment.

9.4 ROTOR DRIVE COMPONENTS

9.4.1 DRIVE REDUCTION GEAR- VISCOSITY RECOMMENDATIONS:

In this type of reducer, the lubricant is picked up from the sump at the bottom ofthe case by the rotating gear and thrown in such a manner as to distribute an amplesupply of oil to all gears and oil lubricated bearings.

If the oil is permitted to thin out to the extent that it loses a considerable portion ofits protective and lubricating value, premature wear may follow. Therefore, heavieroils are used to offset the effects of high temperatures.

The lubrication plate attached to the housing lists the viscosity recommendation forthree different ambient temperature ranges. The ambient temperature is thesurrounding room temperature and can vary. It should be remembered that somereducers might operate under varying temperature conditions and that specialconsiderations must be given to these applications.

Likewise, for low temperatures, a lighter oil is recommended because it is absolutelynecessary that the oil be free to circulate at all times. The pour point of the oilshould be less than the minimum external temperature encountered. With theambient temperature known, the proper viscosity of the lubricant may be determinedfrom the lubrication chart.

LUBRICATION

Fill to indicated oil level with mineral oil of recommended grade, pour point must beless than the minimum temperature. Drain and flush – once in 6 months. Re greaselow speed shaft bearings – upper and lower, once in 6 months. At frequent intervals– carefully check the oil level. If too low, add enough oil to restore to proper level.Do not fill above mark indicated, as leakage or undue heating may result.

LUBRICANT SPECIFICATIONS

The lubricating oil used must meet the following specifications:

i) High quality, well refined petroleum oil.ii) Non-corrosive to gears, ball, roller or sleeve bearings and free from

grit and abrasives.iii) Good de-foaming properties and good resistance to oxidation.iv) Straight mineral type.

AIR PREHEATER


Normally, spring element type flexible couplings and gear type couplings incombination with fluid couplings are lubricated once in a year

GREASE LUBRICATIED BEARINGS:

There are two lubrication plates attached to the reducer housing, which refer to thegrease lubricated upper and lower low speed bearings. These bearings are greasedat the factory and they should be lubricated whenever the oil is changed or once in6/12 months. For these bearings, use a good grade of no.3 ball and roller bearinggrease. The grease should be made of high grade sodium soap and a refinedmineral oil. It must be chemically neutral and free from graphite or fillers.

9.4.2 OVERRUNNING CLUTCH COUPLING:

The over running clutch coupling fitted in Falk gear boxes requires no lubricationbefore installation. When assembled on the reducer, it becomes an integral part ofthe unit, oil supply for the coupling which provides proper lubrication. For othermake gear boxes refer O&M catalogue of the manufacture of coupling.

9.4.3 MAIN AND AUXILIARY DRIVE COUPLINGS

Normally, spring element type flexible couplings and gear type couplings incombination with fluid couplings are used. Once in a year or even earlier they haveto be re-lubricated.

9.4.4 AIR MOTOR

When installing a new air motor, pour liberal quantity of clean, light oil into the airinlet ( SAE 10 or 10W, or a good 150 viscosity oil). For intermittent service withtemporary hook up, lubricate motor before and after use.

NOTE: USE FOG TYPE LUBRICATION AND FILTERS ON PERMANENTINSTALLATIONS AND INCORPORATE IT IN THE LINE NEAR THE MOTOR.USE PIPE SIZE EQUIVALENT TO AIR INLET.

GEAR CASE

Check for proper amount of lubricant before using and at frequent intervals when inconstant use. If motor is used only occasionally for cleaning cycles, re-lubricateevery six months. The gear case should be kept 2/3 full of the recommendedgrease.

RECOMMENDED LUBRICANTS

Oil – use SAE 10 or 10 W, or a good grade, clean 150 viscosity oil. Grease – use aball bearing grease containing an oil having a viscosity of 180 to 500 SSU at 40°C, aworked penetration of 190 to 310 at 25°C (ASTM method) with a melting point ofnot less than 135 °C.

AIR PREHEATER


AIR MOTOR SUPPLY LINE OIL FOG LUBRICATOR LUBRICATION

Normal operating temperature 15°C to 50°C. In the majority of applications using oilfog lubrication, we recommend using a high quality lubricating oil of approximately150 to 200 SSU at 40°C. For extreme temperature conditions, select an oil having ahigh viscosity index. Compounded oils containing graphites, soap, filters, etc., arenot recommended.

OPERATION

In starting lubricator, close the needle valve completely. After the air is turned on,open the needle valve and adjust for the desired number of drops per minute.Usually 3 to 5 drops per minute are sufficient.

9.5 CLEANING DEVICE COMPONENTS FRACTIONAL HP MOTOR ( Fig.28)

After every six months of operation, the bearings and housings should be thoroughlycleaned and packed with new grease. For the type of grease refer lubrication chart.

SPEED REDUCTION GEAR UNIT

The use of high grade non-corrosive oil is recommended as lubricant. FIGURE-29

WORM GEAR HOUSING ( CLEANING DEVICE UNIT)

The worm gear housing is packed with a good grade of industrial grease at thefactory. If addition or renewal of the lubricant is required, it is recommended thatthe type of industrial grease indicated in the lubrication chart or a similar product beused.

SWIVEL JOINT (BARCO)

Lubrication Pellets shall be used if provision is made in swivel joint assy. FIGURE-30

SLEEVE BEARINGS ( CLEANING DEVICE SWIVEL ASSY )

On K,S and R types of Air preheaters up to size 21.5, no lubrication is required. OnAir preheaters of sizes 22 and above, sleeve bearings require lubrication. Refer tothe lubrication chart. For proper maintenance, sleeve bearings should be periodicallylubricated, preferably during operation of the cleaning device.

It is recommended that the bearings be taken apart and thoroughly cleaned andrelubricated once in 6 month.

AIR PREHEATER


FIGURE-28

AIR PREHEATER


FIGURE-29

AIR PREHEATER


RECOMMENDED SWIVEL JOINT AND CLEANING

DEVICE PIPING SUPPORT

FIGURE-30

AIR PREHEATER


RECOMMENDED LUBRICATION CHART 24.5 - 27.5 VIM

SL EQUIPMENTDESCRIPTION IOC HPC BP QTY/

APHFre. OfChange

01 Main Drive Elec.Motor Brgs. Servogem 3 Lithon 3 MP Grease 3 0.4 Kg 6 Month

02 Fluid Coupling Servo prime 46 Turbinal 46 Bharat turbol46 4.5 lts Yearly

03 Main drivereducera) Gear case

b) Bearings

Servomesh SP220Servogem 3

Parathan EP220Lithon 3

Amocam 220

Bharat MP 3

90 lts

0.3 kg

6 month

6 month

04 Air motor :a) Couplingsb) Gear casec) Bearingsd) Compressed

air line

Servogem 3Gear oil SAE90Servogem 3Servo sys 32

Lithon 3 -Lithon 3Enklo 32

MP grease 3 -MP grease 3Actuma t oil10w

1 kg0.5 lt0.25kg0.5 lt

Yearly6 monthYearlyRegular

05 Support Bearing Servocyl C-680 Cyndol TC-680 Bharat Engol

J-680 90 lts 6 month

06 Guide Bearing Servocyl C-680

Cyndol TC-680

Bharat EngolJ-680 45 lts 6 month

07 Lub Oil Pump &Motor bearings

Servogem 3 Lithon 3 MP Grease 3 0.5 kg 6 month

08 Cleaning Device.

a) Motorbearings &worm gearreducer

b) Two stageworm gearbox

c) Sleevebearing

Servogem 3

Servomesh SP460

Servogem HTXX

Lithon 3

Gear oil ST140

---

MP grease 3

Spirol 140 EP

---

2 kg

1 Lit

0.2 kg

6 month

6 month

6 month

Note: Check Oil Level After Stopping Of Lub Oil Systems.Caution: Over Filling Of Oil In Guide Bearing Assembly May Cause AirPreheater Fire.

AIR PREHEATER


RECOMMENDED LUBRICATION CHART - 30 / 30.5 VIM

SL EQUIPMENTDESCRIPTION IOC HPC BP QTY/

APHFre. OfChange

01 Main Drive Elec.Motor Brgs. Servogem 3 Lithon 3 MP Grease 3 0.4 Kg 6 Month

02 Fluid Coupling Servo prime 46 Turbinal 46 Bharat turbol46 6.8 lts Yearly

03 Main drivereducer

a)Gear case

b)Bearings

Servomesh SP220Servogem 3

Parathan EP220Lithon 3

Amocam 220

Bharat MP 3

130lts

0.3 kg

6 month

6 month

04 Air motor :a)Couplingsb)Gear casec)Bearingsd)Comp.air line

Servogem 3Gearoil SAE 90Servogem 3Servo sys 32

Lithon 3 -Lithon 3Enklo 32

MP grease 3 -MP grease 3Actumatoil10w

1 kg0.5 lt0.25kg0.5 lt

Yearly6 monthYearlyRegular

05 Support Bearing Servocyl C-680 Cyndol TC-680 Bharat Engol

J-680 130 lts 6 month

06 Guide Bearing Servocyl C-680

Cyndol TC-680

Bharat EngolJ-680 50 lts 6 month

07 Lub Oil Pump &Motor bearings

Servogem 3 Lithon 3 MP Grease 3 0.5 kg 6 month

08 Cleaning Device.

a)Motor bearings& worm gearreducer

b)Two stageworm gear box

c) SleeveBearing

Servogem 3

Servomesh SP460

Servogem HTXX

Lithon 3

Gear oil ST140

---

MP grease 3

Spirol 140 EP

---

1 kg

1 Lit

0.2 kg

6 month

6 month

6 month

Note: Check Oil Level After Stopping Of Lub Oil Systems.Caution: Over Filling Of Oil In Guide Bearing Assembly May Cause Air

Preheater Fire.

AIR PREHEATER


10.0 INSTRUCTIONS FOR PLACING THE

AIR PREHEATER IN SERVICE

10.1 COLD RUNNING TEST CHECK LIST

The decision as to whether or not the Air preheater is ready for service isdetermined by a complete inspection before starting the Unit.

10.1.1 ROTOR INSPECTION

Inspect both ends of the rotor thoroughly before starting. Turn the rotor throughone complete revolution with the hand crank or air motor prior to starting with theelectric motor. Any foreign material lying within the rotor housing may interferewith rotation or damage rotor seals.

10.1.2 CLEANING DEVICE

Check to see that the long axis of the nozzle mouth is properly positioned with therespect to the centerline of the nozzle arm ( Air preheater's oscillating arm cleaner).Refer to the section on cleaning devices for this information. Operate cleaner to besure that no interference exists with the travel of the cleaning device nozzle and thatthe heating element surface is fully covered by action of the cleaning jet. (Seespecific instructions mentioned in the cleaning device section of this manual).

10.1.3 OIL LEVEL

Examine oil level indicators to assure that sufficient oil is provided in all bearinghousings and speed reducers. In order to avoid overflow of oil, do not fill above theindicated levels. (Refer to individual lubrication recommendations for the variouscomponents described in the Lubrication section of this manual).

10.1.4 ROTOR ROATION

Check the high speed shaft of the drive motor to be sure that it turns in thedirection indicated by the arrow attached to the rotor drive unit. Incorrect rotationwill seriously damage rotor seals. If the rotor drive unit is equipped with anauxiliary air motor, check for proper rotation and be sure that the air line lubricatoris functioning properly.

AIR PREHEATER


10.1.5 ROTOR SEALS

Inspect all rotor seals for possible damage and make certain that clearances for allseals confirm the dimensions given in the seal setting chart included in the rotorseals section of this manual.

10.1.6 ELECTRICAL CIRCUITS

Check all electrical circuits serving the equipment to assure that they are connectedproperly and protected with thermal relays or fuses.

10.1.7 OIL CIRCULATING UNIT

Inspect all components of the oil circulating and filtering system serving the rotorbearings. See separate instructions covering the operation and maintenance of thesystem in the ROTOR BEARING section of this manual.

10.1.8 COOLING SYSTEM

If water cooling is required, be sure that sufficient water is available to supplybearing jackets, coolers and other water cooled members.same time as the forcedand induced draft fans.

10.9 COLD RUN

After checking the above points, run the rotor for one hour at normal speed. Thiscold running period should indicate if further adjustments are required.

10.1.10 MOTOR TEMPERATURE

If the motor generates excessive heat, check the amount of current being used, thenturn off the power and investigate the cause for overload. Under normal conditions,motor temperature should remain constant after the first fifteen minutes ofoperation. A slight overload on the drive motor can be due to hard rubbing rotorseals. This condition can relieve itself when the preheater reaches normaloperatingtemperatures, or after the seals have 'worn in' properly. Seal noise is notnecessarily an indication of trouble. After making all necessary adjustments, test runthe preheater again to ensure smooth operation.

AIR PREHEATER


10.2.0 STARTING INSTRUCTIONS

Before lighting off, the Air preheater drive should be started at the damper first andfollow with the gas damper. If two or more Air preheaters are provided, the rotors ofall units should be started in motion, even if only one unit is subjected to air andgas flow and the others have air and gas dampened off. As each remainingpreheater is required in the plant operation. Open the air damper first and followwith the gas damper.This sequence will prevent the rotor from overheating andfreezing in position due to excessive thermal expansion.

Note the rate of increase in the temperature of the drive motor. Overheating may bedue to insufficient clearance of the rotor seals. If the overload is not heavy and thecapacity of thermal relays or fuses is not exceeded, the seals will gradually 'wear in',thus relieving the overload. Readjustment of hard rubbing rotor seals is necessaryonly if the motor overload is excessive.

Rotor expansion in preheaters equipped with a gear rack or pin rack and pinion drivemay cause these drive members to mesh too hard. Shifting the drive unit canregulate depth of tooth engagement. Check grease and oil supplies of all partsrequiring lubrication. Refer to specific instructions covering oil circulating systemsand lubrication recommendations.

10.2.1 LIGHT UP - GASEOUS FUELS

There has been evidence of fame instability during start-up on gaseous fuels. Whenthe Air preheater is started with the fans at light-off, it is possible, depending onoperating conditions, that entrained products and/or free moisture carried by the airpreheater rotor to the combustion air stream might contribute to this instability. Werecommend, therefore, that specific startup instructions stipulated by our Boilerdesign group or Field engineering services group should be followed.

In those cases where instructions provide for keeping the Air preheater out ofservice during light-off, no permanent damage will occur to the Air preheater withgas temperatures up to 200°C. Some difficulty may occur in starting the Airpreheater at the higher gastemperatures. The degree of difficulty will, of course,vary with individual Air preheaters, depending on seal setting and condition. Noseditious difficulty should be found in starting the Air preheater at gas temperaturesof 200°C or less.

10.2.2 LIGHT-UP : OIL FUEL

It is essential that careful attention be given to combustion conditions during initialfiring of a cold furnace or restarting after a hot stand-by. Improper combustion mayresult in the accumulation of condensed oil vapours and unburnt carbon on Airpreheater surfaces by carry-over from the furnace during these critical stages.

AIR PREHEATER


If combustible, the deposits may ignite under certain conditions resulting in damageto the Air preheater heating elements and structure.

IMPROPER COMBUSTION CAN BE CAUSED BY:• In adequate atomization due to low oil temperature and/or improper oil

pressure or atomizer pressure.• Fouling or atomizer components with solid or gummy debris.• Improper combustion air distribution.• Difference in Fuel oil flow from the various burners.• Igniter oil leakage.

10.3.0 RECOMMENDATIONS

REFER TO GENERAL FIELD ENGINEERING SERVICES MANUAL FORDETAILED START-UP INSTRUCTIONS

It is essential that the operators observe the flame, the exit of the furnace sectioncontinuously and the stack, periodically during initial firing of a cold furnace orrestarting after a hot stand-by.

The flame should be stable without flashing back to the burner up or blowing furtherinto the furnace. If a white smoke observed leaving the flame, or a black or whitesmoke leaving the stack, burner adjustment should be checked immediately.

Start the Air preheater at the same time, the FD fans are started. Accumulation ofdeposits on the heating element must be prevented, as their ignition would result ina destructive fire. The cold end soot blower should be used during start-up tocontrol the rate of normal deposit (non-combustible) buildup. The soot blowingequipment will aid in the removal of limited types of instructions as indicated in thesection entitled "cleaning the Air preheater during start-up".The soot blower shouldnot be relief on, to remove combustible deposits from the heating surface at anydepth in the element pack. If the deposit is a baked on varnish type, then evenwater washing may not be effective in its removal.

A means should be provided for positive identification of combustibles entering theAir preheater. We have a water cooled lance located in the gas duct leading from theeconomizer outlet to the Air preheater inlet. This lance would be maintained at atemperature of 90°C or below which would cause any oil vapour in the fuel gasstream to condense. The lance would be withdrawn from the duct by an operatorevery 15 minutes such that condensed oil could be observed and corrections inburner settings made.

A close watch should be maintained on the four terminal temperatures of the Airpreheater ( Gas inlet, Gas outlet, Air inlet and Air outlet). Any unusual increase inone of or more of these temperatures should be investigated immediately. Refer todetailed instruction relative to possible fires in Air preheaters.

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Strict adherence to the recommendations outlined in 'Light Up - Oil fuel' and thoseinstructions issued by our Boiler design group relative to start-up will reduce thepossibility of combustible deposits accumulating on the air preheater heatingsurface.

10.4 STAND-BY AND HOT START-UP

Follow instructions as indicated under ' Light-Up - Oil fuel'. Keep the Air preheateroperating at all times that the boiler is on stand-by bottled-up.

10.4.1 FOR CYCLING UNITS ONLY

The Air preheater seals have been set to accommodate a bottled-up temperature of315°C within the preheater.

10.5 SHUTTING DOWN

When taking the boiler out of service, use the soot blowing equipment to removeany deposits, which may have accumulated on the heating surface. Keep the fanrunning during the cleaning operating. Keep the rotor turning until the gas inlettemperature at the preheater inlet drops below 200°C.

10.6 CLEANING THE AIR PREHEATERS DURING START-UP

When compressed air is the blowing medium, it should be made available for thecleaning device and used at frequent intervals - at least every four hours after thefires are lighted, until stable combustion conditions exists in the furnace.Satisfactory conditions usually prevail after 24 hours of continuous firing.

If steam is the blowing medium, it should be used as soon as pressure at the boilerbeing fired has raised sufficiently to provide the required steam pressure at thecleaning device. In the event that the firing period to reach this pressure exceedsfour hours, it is recommended that a temporary steam of station Air supply may beconnected to the cleaning device. Steam should be provided at a minimum of 10kg/sq.cm, or compressed air at a minimum of about 6 kg/sq.cm. Under nocircumstances should the pressure of the temporary steam supply be allowed toexceed normal cleaning device blowing pressures, as this could result in severedamage to the rotor seals and heating element. Do not bypass the cleaning deviceorifice plate once this pressure is reached. Clean at frequent intervals - at leastevery four hours after the fires are lighted, until stable combustion conditions existin the furnace.

The following will apply only when the unit is operated other than as a cycling unitand the air preheater seals have been set for contract temperature conditions.

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10.7 EXCESSIVE SEAL WEAR

The Air preheater seals and sealing surfaces are positioned to provide best leakagecontrol at design load. The following operating conditions will result in excessiveseal wear, thus higher leakage during normal operation:-

• Gas temperatures entering the preheater in excess of the design point.• Reduced Air flow through the heater. The degree of seal wear increases as

the air flow approaches zero. Whenever there is gas flow through the heater,air flow should be maintained.

• Bottled-up conditions with no air flow or gas flow, but with heat maintained inthe boiler and air heater or heaters.

• Lower than design rotor speeds while operating the air preheater on anauxiliary drive can cause seal wear which will take place at rotor speeds lessthan 1/8 rpm. The degree of seal wear increases as the rotor speeddecreases. An exception to this is during on - steam washing of the heater.See instructions for on-stream washing procedure if this method of washing isused.

• Operation of the Air preheater before its being insulated.• Rotor trip-out may occur if the seal drag is such as to overload the drive

motor.

Gas temperatures of 200°C or less entering the Air preheater will cause noproblems with regard to excessive seal wear.

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11. PRE-COMMISSIONING CHECKS

11.1 GENERAL

• Cleanliness of the entire plant is a vital one. All the erection debris, dust,rags, etc., must be thoroughly cleaned before proceeding to anything on theheaters.

• Check gas inlet, gas outlet, air inlet and air outlet to air preheater to findwhether expansion bellows are provided and temporary shipping braces ofsuch bellows are provided and temporary shipping braces of such bellows areremoved and ready for operation. Duct weights should not bear uponpreheater flanges.

• Check whether the preheater is insulated properly. Special attention isnecessary in the area near guide bearing. All connecting ducts, centresection, etc., must be reliably insulated to avoid heat transmission to bearing.

• Check all the flue gas and air dampers provided at the air preheater terminalsare in operating condition and connected to drives. Verify through inspectionopenings the dampers are fully closing and opening.

• Check all the instrument connected at the air preheater terminals to measurepressure, temperature, oxygen, etc., are in working condition.

• Check for the tapping points for the local measurements.

• Check Air preheater support pedestals are free to expand ( nothing obstructstheir movement)

• Check all the electricals wiring to the preheater installation are properly madeand required supply voltages are available at terminals.

• Check compressed air piping to emergency pneumatic drive is in order. Air atrequired pressure must be available. Make sure moisture trap is fitted in theline.

• Check steam supply to the air preheater soot blower is connected properlyand insulated. Pressure and temperature of steam should confirm to therequired parameters.

• Make sure that either a temporary steam or compressed air connection ismade to the soot blower during start-up till the main steam supply isavailable.

• Check water washing manifolds are connected to the piping system properly.Water at the required pressure and quantity must be available. Check thedrainage facility also.

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• Check cooling water system is connected to the guide bearing oil cooler andsupply is established.

• Check for the space and lifting arrangements for the removal and replacementof elements and bearings.

• Check platforms, ladders, structural stub, etc., are not obstructing thermalexpansion of casing in all directions.

• Check aluminium finger tabs set installed after seals are set to thespecification.

• Check canopy provided for oil circulation system. Guide bearing and ALCS (IF applicable at customer's cost to safeguard the equipment from fly ash andwater).

11.2 ROTOR DRIVE

• Check all mounting bolts are satisfactorily tightened and locked.

• Check up lubrication of :-

Main drive electric motor bearingsMain drive couplingGear reducerAir motor couplingAir line lubricatorCam clutch box ( if applicable)

• If the unit is provided with a fluid coupling, check correct grade of oil in thecorrect quantity is filled up.

• Check up oil level in the lubricator in the compressed air line and clean the airline filter.

• Check up the pinion air seal to see carbon rings in proper position.

• Check the connections of Electric motor and Air motor for correct direction ofrotation properly.

• Check and clean if necessary the filter cartridges.

11.3 SUPPORT BEARING AND OIL CIRCULATION

• Check support bearing mounting bolts are tightened to the specified torqueand locked.

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• Check bearing is filled with proper grade of oil to the required level. Oil levelis to be checked with dipstick.

• Check for oil leakage in the piping around drain plugs, thermocoupleconnections, etc.

• Check bearing cover is properly secured with sealing compound and glandpacking are installed.

• Check air seal cover is fitted with proper clearances.

• Check water shield is secured to trunnion correctly.

• Check whether oil circulation system is connected to bearing properly.

• Check pressure gauge and thermometer are in working conditions.

• Check the setting of relief valve is not tampered.

• Check bearing is filled with proper grade of oil to the required level.

• Check the oil level marking in dipstick after running the oil Check thermostatis wired to the oil circulation motor controls

11.4 GUIDE BEARING AND OIL CIRCULATION SYSTEM

• Check whether locking cap bolts and bearing housing mounting bolts aretightened to the specified torque and locked.

• Circulation system for five minutes.

• Check for oil leakage in the piping around drain plugs, thermocoupleconnections, etc.

• Check bearing cover is properly secured and land packing are installed, bothat top and at flange. Check motor for correct direction of rotation.

• Check air seal cover is fitted with proper clearances around trunnion

• Check thermostat is wired to the oil circulation motor controls Check hot endtracking arrangements are mounted properly and the system is free to move.Mark to observe movement.

• Check gland packing of tracking rods for proper installation.

• Check bearing air breather is not clogged and free from dirt.

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• Check whether oil circulation system is connected to bearing properly.

• Check pressure gauge and thermometer are in working condition.

• Check the setting of relief valve is not tampered.

• Check thermostat is wired to the oil circulation motor controls properly.

• Check and clan if necessary the filter cartridges.

11.5 POWER DRIVEN CLEANING DEVICE

• Check all the mounting bolts are tightened fully.

• Check lubrication of a)motor, b) reducer, c) journal.

• Clean the unit and check the swivel is free to rotate and pipe anchored sourcenear to swivel.

• Check the swing of cleaning device is adjusted as per the instructions in thechapter 'cleaning device'.

11.6 OBSERVATION PORT AND LIGHT ASSEMBLY

• Check whether the light assembly and observation port are in position andwired.

• Check the port glass is clear and not damaged and tight.

11.7 SECTOR PLATE ADJUSTERS

• Check adjuster nuts are fully tightened and locked to specification.

11.8 AXIAL SEAL PLATE ADJUSTERS

• Check lock nuts are fully tightened.

• Check cover is installed with sealing compound to protect adjusters from dust.

11.9 AXIAL SEAL PLATE TO SECTOR PLATE SEALS - PLATE TYPE

• Check proper seating of these seals and adjust if necessary. Whenever sectorplate levelling is disturbed/corrected, this should also be adjusted suitably.

11.10 SPRING LOADED BY PASS SEAL BARS ( if provided )

• Check for correct tightness of the holding bolts and adjust if necessary

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11.11 TRIAL RUN

11.11.1 GENERAL

• Before proceeding to conduct trial runs, make sure all pre-commissioningchecks have been made thoroughly.

• Inspect the Air preheater for cleanliness and nothing obstructs the movementof rotor or any other rotating equipment.

• Make sure all personnel are away from the rotating parts. Safety is veryimportant.

• Check the direction of rotation of rotor.

11.11.2 CLEANING DEVICE

• Make sure the cleaning device linkages are not binding and the motor is freeto rotate.

• Disconnect the limit switch wiring.

• Start and run the motor for about two hours.

• During the run, check the following:

• The travel of blower nozzle is correct as prescribed.

• The nozzle travels at the specified height from the elements and nointerfering with seals.

• The motor is running freely and not getting heated up excessively.

• No unusual sound in the gear reducers and no heating up of them.

• Limit switches are operated by the cams smoothly.

• No rubbing or grinding or thumping noises in the linkages.,

• After completion of trial run, include the connection for limit switches andcheck:

• The parking switch is able to stop the motor in the limiting position of thenozzle (i.e. end of the cycle). The steam admission valve of Air preheater sootblower is actuated at the beginning with the start of the motor and at the endof forward cycle.

• Check for any steam leakage especially through the lapping joint.

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11.11.3 OIL CIRCULATION SYSTEM FOR SUPPORT AND GUIDE BEARINGS

• Open the suction and delivery valves.

• Measure ambient temperature. If it is more than the thermostat setting, theoil pump motor must be running as soon as supply is given. If it is less, donot attempt to run the motor as the oil is highly viscous and it is notadvisable to run the pump.

• Check the pump is running in the proper direction and continue to run forabout eight hours.

• Check oil pressure is normal.

• Check for oil leakage in the entire system

• Operate the handle of self-cleaning filter, if provided, to make sure it worksfreely.

• Check oil flow.

• Check whether the relief valve pressure is set to the required.

11.11.4 ROTOR DRIVE

• Check for correct direction of motor rotation and run it for eight hours.

• Check electric motor for unusual noise, heating up of bearings and motor andnote the load current.

• Check fluid coupling for noise, temperature and heating up of bearings.

• Lub oil level may go down during the unit is under operation

• Check oil level after stopping of lub oil unit

• Check Bibby couplings/gear couplings for adequacy of lubrication.

• Check gear reducer for noise, temperature, oil level and heating up ofbearings.

• Check pin rack drive for knocking, rubbing noise. Etc. due to misalignment.

• Run air motor after switching off electric motor for about two hours and checkfor unusual nose. Lubrication ( gear noise) - lubricator, filter and checkoperation of solenoid valve.

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• Check air motor coupling for lubrication and proper running.

• Check pinion seal for breakage - replace and adjust, if necessary

• Check for lose mounting bolts and retighten if necessary

• Check for vibration of all rotating parts.

11.11.5 MAIN BEARINGS

• Check oil level and unusual noise, if any during the rotation of rotor.

• Check bearing housing seal for any rubbing of trunnion with seal ring andcorrect, if necessary.

• Tighten all loose bolts.

• Check air seal cover is free from touching trunnions and to be corrected ifnecessary. Otherwise, a groove will be formed in the trunnion owing torubbing.

• Check for hot end tracking by raising and lowering the hot end sector platein-board end.

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12.0 CHECKS DURING OPERATION

12.1 DAILY CHECK

i) Oil levels in

a) Support bearing

b) Guide bearing

c) Main drive gear reducer

d) Air line lubricator

ii) For any unusual noise in

a) Rotor

b) Rotor main drive bearings

c) Drive motor and gear reducer

d) Cleaning device during operation

e) Oil circulation system.

iii) For cleanliness near

a) Rotor drive unit

b) Rotor main bearings

c) Cleaning device

d) Oil circulation system

iv) Instruments for proper working

a) Bearing lube oil thermometers

b) Thermocouples if provided in bearings for alarm or remote Bearing

lube oil pressure gauges

c) indication.

d) Air inlet and outlet, gas inlet and outlet temperature measuring

instruments.

e) Manometers for measuring pressure drops across air preheater for

gas and air flows.

v) The condition of cold end elements through observation Port by switching on the inspection lights.

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12.2 WEEKLY CHECK

FOR OIL LEAKS

• Around bearing oil drain plugs, instruments connections etc

• In oil piping

• In threaded connections in oil circulation systems

Attention: Any leak found in the hot end bearing is to be rectifiedimmediately as this may cause fire break - out due to high ambienttemperature in this region.

• Around main drive gear reducer drain plugs, dipstick connections, etc.,

• Start and run air motor for a minute

• Check working of lubrication.

• Give a few turns for the self-cleaning filters if provided in the circulationsystem

• Check the operation of solenoid valve.

12.3 MONTHLY CHECK

• Check the linkage of power drive cleaning device (PDCD) from binding.

• Check trunnions are running from rubbing with packing rings and bearingcovers.

• Check gland packing and adjust if necessary.

• Check pinion air seal whether carbon rings/packing rings are ok.

• Check hot end sector plate and adjuster and hot end tracking linkages areworking properly.

• Check cold end sector plates for looseness, tighten if necessary.

12.4 HALF YEARLY CHECK

• Check lubrication of all items and change lubricants as per schedule.

• Examine all the seals of air preheaters for wear and tear; if necessaryreadjust.

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• Check the cleanliness of the element baskets; if necessary water wash theheater

• Thoroughly clean the areas around drive units, bearing, oil circulation system,power driven cleaning device, etc., for dirt, oil etc.

• Check the lubrication filter cartridges for choking and clean / replace thecartridges.

12.5 ANNUAL OVERHAUL

• Clean up first the entire heater before proceeding with any maintenance workon the Air preheater

• Carefully examine the condition of heating element and replace, if necessary.Check cold end gratings for erosion and repair, if necessary.

• Repeat half-yearly inspection.

• Replace gland packing.

• Open inspection cover on bearings and inspect the condition of bearings.

NOTE : WHILE DRAINING THE OLD OIL FROM THE BEARINGS,CAREFULLY EXAMIN FOR ANY METALLIC FRAGMENTS /CONTAMINATION.

a) Examine trunnion bolts.

b) Examine rotor post to diaphragm welds at the trunnion ends.

c) Open pinion cover. Examine pinion and pin rack for wear and tear and properengagement.

d) Pack all electric motor bearing with fresh grease. ( Refer manufacturer'sinstruction in O&M manual)

e) Change gear reducer oil and inspect the old oil for metal fragments.

f) Open inspection covers to examine the condition of gears, pinions andbearings.

g) Lubricate all couplings grid / gear type.

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h) Change oil in the fluid coupling

i) Change the oil seals in the oil pump, if necessary.

j) Check the calibration of all instruments.

k) Examine oil line for dents, cracks, damages, etc.

l) Cleaning device gear boxes to be examined.

m) Steam blowing nozzles to be checked

s) Water washing nozzles to be inspected and cleaned, if necessary.

t) Carefully examine for corrosion at the cold end. If corrosion has damaged the cold end, the basket can be reversed and installed

u) Examine tube braces for erosion.

v) Check all static seals for erosion replace or repair if necessary.

w) Examine hot end sector plate in-board support plate and adjuster linksFor erosion – repair if necessary.

x) Inspect all adjuster mechanisms of sector plates and axial seal plates for correct positioning and locking.

y) Check axial seal plate to sector plate seals for erosion and replace if necessary.

z) Check oil carry over detector for any erosion, if necessary rework it.

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13.0 AIR PREHEATER FIRES

Air preheater fires are rare. A fire may occur during cold start up on oil or start-upfollowing hot stand-by because of poor combustion of the oil fuel. The impropercombustion results in unburnt or partially burnt oil condensing and depositing on theair preheater element surface. As the temperature entering the air preheaterincreases, this deposit is baked to a hard varnish-like material. These deposits canignite as temperature increases to 315-370 °C range.

This ignition usually starts in a small area of the deposit. During the early stages ofdeposit generated is carried away from the area of its origin. Downstream mixing ofthe fluids further minimises any external effect. Most of the heat generated isabsorbed by the metal heat transfer element nearby. The actual temperature buildup during this period is relatively slow. If the condition can be detected at thattime, the amount of water required to reduce the temperatures quickly to below theignition temperature, is much less.

If this ignited deposit remains undetected it will continue to generate heat until themetal heat transfer element reaches 730 to 765 °C. At this point, metal may ignitewith temperatures reaching 1650 °C and higher in a matter of minutes.

Metal fires are self-sustaining and would require more water than is normallyavailable to drop the temperature to a reasonable level. It should be noted that CO2,

Halon and other extinguishing agents are ineffective under these circumstances.

13.1 FIRE SENSING DEVICE

INTRODUCTION

The primary purpose of this accessory to the Air preheater is to detect small areas (hot spots ) of hot metal surfaces within the rotating heating element.

TYPES OF HOT SPOT DETECTORS

THERMOCOUPLES:

Even though it is strong enough to withstand the environment, slow in response toshort duration temperature changes.

ULTRA VIOLET DETECTOR

It requires visible flame for detection and hence not suitable for our purpose

INFRA RED SYSTEM

It is easily adaptable to present day requirements. For our Air preheater wegenerally use thermocouple and infrared system only.

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REQUIREMENT OF A FIRE DETECTOR

• Rapid response time

• Ability to discern metal temperature not more than 150°C above the maximum

• heating element metal temperature under normal operating conditions.

• Ability to detect small fires that are deep within the heating element pack.

• High reliability

• Ease of installation on existing as well as new Air preheaters

• Simplicity of maintenance and servicing.

• Ability to provide signal for operating personnel and ability to monitor theentire rotating structure.

13 . 2 THERMOCOUPLE FIRE DETECTOR - PRINCIPLE OF OPERATION

A Thermocouple is a device that converts thermal energy directly into anelectric voltage where a temp gradient exists between the two end junction ofa pair of dissimilar metal wires. This may be applied at any temperature upto1200 °C for base metals and 1500°C for noble metals. Base metal couples aremade from Chromel-Alumel wire for temperature upto 1200°C.

This system detects a fire situation by sensing an undue temperature rise inthe air and gas flow streams. It consists of a set of thermocouples locatedstrategically in the air preheater flow streams and a scanner device, whichmeasures, at set intervals, the temperature of each thermocouple andcompares with its set point. In case of a measured value being more thanthe set point, an alarm contact is closed to inform the operator about apossible fire situation demanding immediate attention.

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14.0 ROTOR STOPPAGE ALARM

14 . 1 INTRODUCTION:

Rotor stoppage alarm is a device, which is used to give a signal when the rotor isstopped without our control.

It is not advisable to allow the rotor to be stopped when high temperature gases areflowing through it as this may cause unequal expansion and pose problems forrestarting the rotor. To indicate the slowing down of the rotor, the rotor stoppagealarm is fitted;

S.NO REASONS FOR ROTORSTOPPING

REMEDIAL MEASURE

1. Big foreign materials jammedin between the rotor andsector plate

Thoroughly cleaning the Air preheaterafter erection & maintenance. Replacingof eroded duct pipes

2. Main drive failure Proper maintenance of main drive.3. Auxiliary drive failure Solenoid valve is not in good condition

and it fails operate the air motor.4. Service beam can fail on the

rotor due to erosion.Service beam should be removed when itis not in use.

PRINCIPLE OF OPERATION:

This consists mainly of control unit, vane operated limit switch and vanes which aremounted on the trunnion. If the vanes fail to pass under the limit switch within theset-time interval, a relay is closed in the control unit to give an alarm in the controlpanel to warn the operator that the rotor is slowing/stopped. FIGURE-31

• GENERAL DESCRIPTION:

It consists of two solid state time relays and one single pole double throw (ferrousmetal operated) magnetic proximity switch. These relays and associated terminalsare mounted in a Nema enclosure for location by the customer. The relays are ofthe delay on de-energisation type. The magnetic switch is mounted just adjacent tothe rotor and activated by the steel vane(s). FIGURE-32

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FIGURE-31

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FIGURE-32

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15.0 TROUBLE SHOOTING

This section contains trouble-shooting procedures that will assist maintenancepersonnel. Each fault that is likely to occur is listed along with suggested remedies.When any fault occurs which does not have a logical remedy, the manufacturershould be consulted.

S.NO FAULT CAUSES REMEDY01 Excessive leak betn

.gas & air sideLeaking seals Inspect all seals and adjust

or replace if necessary.02. Excessive noise

from rotorWarped rotor due toexcessive expansion.Foreign object inrotor.Bad bearings

Reduce boiler load oradmit more cold air.Stop rotor and visuallyinspect itReplace bearings.

03. Rotor does not turn Defective drive unit

Foreign object inrotor

Ensure power is availableto drive unitCheck pinion gear and pinrack for binding.Inspect rotor and removeany foreign object.

04 Drive unit overheats Inadequatelubrication in driveunit.Pinion gear and pinrack meshing toohard due toexpansionHard rubbing sealsBad bearings in gearreducer.

Lubricate drive unitcomponents

Adjust drive unit to properclearancess.

Adjust seals *Change the bearings.

05 Noisy Bearings Inadequatelubrication

Check that oil is flowingthrough the sight glass andcheck oil line up, ifnecessary

06 Oil temperature toohigh

Insufficient cooling

Improper oilviscosity being used.Absorption ofradiation heat due toimproper insulation.

Check that adequate waterflow is going into oilcoolerReplace oil with propertype of oil.Insulate properly.

07. Circulating oilfoamy

Air leak into the oilsystem

Check for an air leak onthe suction side of the oilsystem.

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S.NO FAULT CAUSES REMEDY

08. Low oil level Leak in oil system Locate and arrest the leak.09. Soot blower not

functioningPower failure

Swivel header travelincorrect.Incorrect steampressure

Check electricalconnection.Check the speed reducermoveable parts for binding.Adjust travel of nozzlepipe.Ensure adequate steamsupply is available.Check nozzle pipe for badnozzles.

10. Excessive pressuredrop

Badly fouledAirpreheater.

Excessive plugging.

Thinned down anddamaged elements

Operate soot blower andcheck soot blower steamfor proper pressure andtemperature.If soot blower is noteffective, heater can beisolated and water washedoff load(in worst case), remove thebasket and clean themoutside.Rectify and replace theelement baskets.

11. Variation (periodickick) in the maindrive ammetercurrent

Excessive rubbing ofsome seals.Faulty bearings

Locate faulty seals andreplace.Rectify or replace thebearings.

12. Abnormal increasein the temperatures

Starting up of fireinside the Airpreheater

Immediately isolate airheater and check for fireand admit large quantity ofwater

13. Increase in gasoutlet temperatureand steady fall of airoutlet temperatures.

Air preheater stalled.

Heating elementsplugged

Isolate Air pre heater andcheck for troubles in thedrive system.Clean heating elements.

14. Excessive pressurebuild up by Lub oilpump.

Oil filter chocked Clean or replace thecartridge.

• Slight overheating due to hard rubbing seals may be relieved when the Airpreheater reaches normal running temperature or after the seals have worn inproperly.

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16.0 MAINTENANCE16.1 GENERAL

This section contains the procedures necessary to maintain the Air preheaters inproper order. For further maintenance information, the manufacturer's publicationshould be used.

16.2 PRECAUTIONS

The following precautions should be observed before and after maintenance onthe Air preheaters.

16.2.1 PRECAUTIONS BEFORE MAINTENANCE

• Obtain a work permit.• Ensure that the Air preheater is electrically isolated and will remain isolated

while maintenance is being performed.• Open inspection and access doors from the ducts to ensure adequate

ventilation.• Check for poisonous gases.• Ensure that the Air preheater is adequately cooled down.• Ensure that the supplies to the soot blowers and water washing devices are

shut off and will remain off.• A check must be kept on the oil temperature in the bearing housing when the

Air preheater is running with no oil circulation.• Check air inlet dampers are closed in secondary and primary sides.

16.2.2 PRECAUTIONS AFTER MAINTENANCE

• Ensure that all tools and extraneous equipment are removed from the Airpreheater.

• Check that any components, which have been serviced are properly re-lubricated.

• Rotate the rotor slowly by Air motor for one complete revolution to provefreeness of rotation.

• Secure all access and inspection doors.• Ensure all electrical power is restored.

16.3 LUBRICATION

• Proper lubrication of moving parts is essential for optimum equipmentperformance. For the lubrication schedule for the Air preheaters, refer toLubrication chart.

• Ensure that the supplies to the soot blowers and water washing devices areavailable.

• Open air inlet dampers in primary & secondary sides.• Return work permit.

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16.4 INSPECTION FOR WEAR, CORROSION & CHOCKING

During Air preheater outages the following components should be inspected forexcessive wear or corrosion.

1) The heating element surfaces should be examined for excessivecorrosions/erosion or deposits that have resisted removal by soot blowing. Twopeople should perform element inspection, one passing a lamp across one end ofthe elements. When necessary, wash the elements and renew any badly pluggedones.

An increased pressure drop across the air preheater is an indication of elementchoking, erosion or corrosion, which may have been caused by any of the followingreasons:-

• Condensation on the elements when starting up from cold or during bankedconditions due to faulty isolating dampers.

• Operating below the minimum combined temperature.

• Excessive moisture during normal operation. Possibly due to leaky sootblower valves or the forced draught fan drawing in very moist air.

Check gratings at cold end for erosion / corrosion during every annual over-haulingand carry out necessary repair/replacement so that the cold end heating elementswill not fall down.

2) SEALING ARRANGEMENTS

The condition of the seals should be checked as well as the sealing surfaces. Anyexcessively worn seals should be replaced and any defective sealing should berectified. The eroded static seals at inboard and outboard of sector plates & centresection are to be closed by welding suitable plates at HE & CE.

3) DRIVE UNIT GEAR TOOTH

The drive unit gear teeth should be checked for undue wear or scuffing which maybe caused by the gears meshing too hard due to rotor expansion. The gears shouldbe set to the correct clearances to correct this situation.

4) DRIVE UNIT AUTOMATIC CLUTCH ( IF APPLICABLE )

The drive unit automatic clutch friction linings should be checked for wear andreplaced when necessary. When replacing coupling shoes, ensure leading shoerotation is used. Also, the condition of the clutch drum should be checked forscoring.

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5) SOOT BLOWER AND WASHING DEVICE NOZZLES

The nozzles of the soot blowers and washing devices should be checked forcorrosion, scale deposits and leaks which should be rectified as soon as possible.

6) SOOT BLOWER MOVEABLE LINKAGES

Soot blower movable linkages should be checked for excessive wear or bindingwhich should be rectified as soon as possible.

16.5 ELEMENT WASHING

No specific schedule can be laid down for water washing since this operation canonly be instigated by the operator following an examination of the heating surfaceelements. When water washing is required, the following procedure should befollowed.

Normally water at a temperature of 70 to 80° has been found to be most effectivefor water washing but lower temperature may be used. Washing will beaccomplished more quickly and efficiently if the operation is carried out before theair preheater is allowed to cool off, i.e. when the gas inlet temperature is around100°C

Washing should be carried out as soon as the air preheater comes off load.Alternatively, the elements can be removed and washed external to the airpreheater. Also, the addition of soda ash to the washing water increases theefficiency of water washing.

Once water washing is started, it should be continued until the elements whichbakes hard when the air preheater returns on load.

The following procedure should be followed to wash the elements:

• Shut the isolating dampers.• Stop the rotor.• When the Air preheater is cool enough, inspect the elements to determine if

washing is necessary.• Start the rotor auxiliary air motor ensuring that all personnel are away.• Add soda ash to the washing water until it has a PH of 11.• Operate the washing device until the effluent draining from the elements has

a PH of 7 (ie neutral)

NOTE :

Ensure effluent is draining properly. Place the Air preheater in operation using the normal start-up procedure.

AIR PREHEATER


16.5 ACID CLEANING PROCEDURE:

This procedure uses an inhibitor to prevent acid from attacking carbon steel. Thisprocedure calls for removal of baskets from Air preheater and subsequent carefulhandling of the baskets during the time consuming dipping process. Hence, it shouldbe well planned out in advance before work is taken up.

MATERIALS REQUIRED:

01 Caustic NAOH 10 % caustic solution W/V. In this solution it isrecommended to add wetting agent like Teepol orLissapol by 0.1 % V/V. Heat to 80 to 95 °C

02 Acid 10 % Muriatic acid with inhibitor. Muriatic acid isnothing but hydrochloric acid V/V. For inhibitor rodine213 or 213 special is easily available in our country. 0.`1to 0.15 % V/V concentration can be used. Heat to 65°C

03 Passivator 1 % W/V that is for 1000 litres of passivator solution. 10kg of composite chemicals consisting of 2.5 kg di-sodiumphosphate, 2.5 kg of monosodium phosphate and 5 kg ofsodium nitrate can be used.

Three tanks - one each for Caustic, acid and passivator.

PROCEDURE:

• Place element in caustic solution for one hour.• Rinse the elements with water to assure a complete wash.• Place the elements in acid solution for one hour• Place the elements in caustic solution, remove and allow excess to drip off.• Place the elements in passivator solution for one and half hour.

CAUTION:

Personnel involved in the acid cleaning procedure should exercise extreme caution.Al the safety precautions including those outlined by the chemical manufactures ofthe products used should be strictly adhered to.

AIR PREHEATER


16.6 ELEMENT LOADING AND REPLACEMENT

The heating surface elements are packed in reversible containers( baskets ) tofacilitate removal during maintenance. When an inspection reveals that one end ofthe elements is thin or that erosion has started, the containers should be removedfrom the rotor and replaced upside down.

1. Removing Cold end baskets

• Remove CE basket removal door from housing panel as well as from the rotorsegment.

• Withdraw the cold end baskets.• Either replace the baskets upside down, or replace with new baskets.• Place the covers and into the rotor.• Continue this procedure for the remaining sectors.

NOTE :When removing the baskets completely remove the baskets from diametricallyopposite sectors to prevent excess unbalance of the rotor.

2. REMOVING HOT END BASKTS:

• Open the HE basket removal door provided in the Gas Inlet / Air outlet duct.• Remove the radial seals• Remove the hot end baskets through basket removal door.• Either replace the baskets upside down, or replace with new baskets.• Continue this procedure for the remaining rotors.

NOTE:When removing the baskets completely, remove the baskets from diametricallyopposite sectors to prevent excess unbalance of the rotor.

16.8 SEAL REPLACEMENT AND SETTING

The air preheater seals should be set to run just clear of the sealing surface duringnormal operation. They should be replaced when excessive leakage occurs betweenthe air and gas sides. When replacing seals they should be set to the correctclearances.

16.9 DRIVE UNIT MAINTENANCE

Maintenance on the drive unit consists of providing proper lubrication and removingthe unit for maintenance. The procedure to remove the unit is outlined below:

• Disconnect electrical and air supplies.• Remove hold down bolts from air motor.• Disconnect air motor coupling and remove air motor.

AIR PREHEATER


• Remove air motor bracket.• Remove pinion cover.• Remove holding down bolts from electric motor.• Disconnect electric motor coupling, remove electric motor and its bracket.• Remove holding down bolts from gearbox.• Slide the gearbox on to a temporary stand with the help of slings.

NOTE:When replacing drive unit, correct pinion gear and pin rack clearance must bemaintained.

16.10 OIL CIRCULATING SYSTEM MAINTENANCE

Maintenance of the oil circulating system consists of filling the system with oil,replacing the filter cartridge, cleaning the oil cooler, and removing the pump unit formaintenance.

i) FILLING OIL CIRCULATING SYSTEM

• Fill each bearing housing by adding oil through the dipstick opening until therequired level is reached .

• Start the oil pump

• Stop the pump and add oil as necessary to the bearing housing until therequired oil level is reached.

• Continue to start and stop the pump and adding oil until all air is purged formthe system and oil levels in the bearing housings are at the proper level.

ii) REPLACING THE FILTER CARTRIDGE

• Stop the oil pump

• Remove the nut holding the filter container in place.

• Remove the old filter from the container and replace with a new filterelement.

• Reassemble the filter replacing the gasket if necessary.

• Start the oil pump.

AIR PREHEATER


iii) CLEANING OIL COOLER

• Stop oil pump.

• Stop cooling water supply

• Disconnect water inlet and outlet pipes.

• Remove the nuts securing the water jacket to the end covers.

• Clean any scale or deposits from the water jacket

• Reassemble the oil cooler

• Start oil pump.

16.11 SOOT BLOWER MAINTENANCE

Maintenance of the soot blowers consists of inspecting the valves for leaking seals,examining the nozzles for corrosion, removing scale and sediment from the nozzlesand adjusting the nozzle pipe. The two adjustments provided for the soot blowernozzle pipe centering adjustment.

16.12 WASHING DEVICE MAINTENANCE

Maintenance on the washing devices consists of inspecting the valves for leakingseals, examining the nozzles for corrosion and removing any scale or sediment fromthe nozzles.

16.13 SEALANTS, THREAD LUBRICANT AND COATING COMPOUNDS FOR AIR PREHEATER COMPONENTS ASSEMBLY.

16.13.1 HIGH TEMPERATURE THREAD LUBRICANT

There are a number of bolts which require to be tightened to a specified torque,further they are subjected to high temperature during operating causing them toseize making it extremely difficult of their removal if needed. A special lubricant isapplied to the bolt threads and contact surface of the bolt head to acquire propertorque during tightening and also to serve as a anti seize medium duringtemperature service. Typical example : Trunnion bolt, support bearing mountingbolt, Sector plate and axial seal adjusters, axial seal plate to sector plate sealadjusters.

Name of Lubricant: Molycote, Mahomoly antiseize thread lubricant.

AIR PREHEATER


16.13.2 THREAD COATING COMPOUND

A number of threaded fasteners, which may require removal at a later date, areexposed to the gases and ambient air. The exposure of the fasteners to suchadverse environment may result in corrosion and possibly the fastener may bedamaged permanently. Removal also may be very difficult. Such fasteners arecoated with a special compound which protects them during service and enableseasy removal of them.

Typical example: Rotor basket door cover bolts; bearing housing adjustment bolts.

Name of compounds: Felpro 5A, Molysulf thread coating compound.

16.13.2 SEALING COMPOUND

There are certain joints made of rough surfaces (fabricated or cast) which are to besealed by suitable agent to avoid leakage of air and dust. A sealing by suitableagent to avoid leakage of air and dust. A sealing compound is provided for thispurpose which has to be applied to such mating surfaces. Typical example ; Underair sealing covers in trunnions and drive pinion.

Name of the compounds: Armcote & Molysulf dust tight joints sealant and thinner.A suitable thinner is also provided to remove the excess compound.

16.13.3 GASKET COMPOUND

At the joints of machined surfaces normally gaskets are used. For large surfaces abead of the gasket compound is applied and the surfaces are tightened. Thecompound dries and forms a leak proof gasket type layers which is pliable forremoval. This can be applied to even threaded joints. Example : Bearing housingcover, water shield, sealing tube, etc.

Compounds : Felpro- 51169 & GS-2

16.13.4 SEALING TAPE:

To make threaded joints leak proof Teflon tape is provided. They can be wound onthe male thread to a suitable thickness and screwed on to make a liquid tightconnection.

NOTE: Locations for the application of the above mentioned items are clearlyindicated in the drawings: Some of the compounds have low shelf-life

16.14.0 The Air preheater seals shall have to be readjusted replaced / rectified if required before the PG test of the Boiler.

AIR PREHEATER


17.0 LIST OF RECOMMENDED SPARESThe list is given simply as an aid to the selection of spare parts. The responsibilityof selecting any additional any part rests solely with the user.

Sl PGMA DESCRIPTION UNIT Qty/Aph01 52-010 Pin rack Set 102 52-013 Radial seals ( Hot & Colds) Set 103 52-013 Post seals (Hot & Cold ends) Set 104 52-024 Cold end basketed heating elements Set 105 52-047 Kao-wool packing 1"x4"x25" No. 306 52-047 Static seal assembly Set 107 52-054 Axial seals Set 108 52-055 By-pass seals Set 109 52-100 Bearings and gears for speed reducer Set 110 52-100 Oil seals for drive speed reducer Set 111 52-100 Gaskets for drive speed reducer Set 112 52-100 Over running clutch assembly No. 113 52-100 Carbon ring with tension spring Set 114 52-100 Coupling assembly for electric motor side No. 115 52-100 Coupling for auxiliary motor side No. 116 52-100 Filter & Lubricator Set 117 52-100 Speed reducer No. 118 52-100 Pinion No. 119 52-100 Solenoid valve No. 120 52-100 Air motor No. 121 52-100 Spare kit for Air motor No. 122 52-217 Spare kit for Rotor stoppage alarm Set 123 52-261 Guide bearing & lock nut - Spherical roller No. 124 52-262 Support bearing – Thrust roller No. 125 52-271 Rubber spider for Lovejoy coupling No. 226 52-271 G. brg lub oil pump No. 127 52-271 Oil seal for lub oil pump No. 128 52-271 Lub oil filter cartridge No. 229 52-271 Temperature gauge No. 130 52-271 Pressure gauge No. 131 52-272 Rubber spider for love joy coupling No. 232 52-272 G. brg lub oil pump No. 133 52-272 Oil seal for lub oil pump No. 134 52-272 Lub oil filter cartridge No. 235 52-272 Temperature gauge No. 136 52-301/302 Nozzles Set 237 52-326 Nozzle No. 238 52-329 Rubber spider for Love joy coupling No. 239 52-329 Bearings - double reduction speed reducer Set 140 52-329 Oil seals - double reduction speed reducer Set 141 52-329 Self lubricating bushes - worm gear reducer Set 142 52-329 Sleeve bearings No. 143 52-360 Spare kit for Fire Sensing device Set 1

om raph bhel

Documents

temporary

sector shaped

diametrically

lub oil systems

sufficiently

axial seal

axial seal

worm gear