Best Practices in

Erection & Commissioning

Product : Air preheaters

AIR PREHEATER APPLICATIONSUtility BoilersIndustrial BoilersCFBC boilersFertilizer plants - Ammonia Reformer furnaceCement plants - Gas cooling in Kiln and Clinker Refinery furnacesFlue gas desulphurization plant - Gas to Gas Heater

AIR PREHEATER Air preheater is an heat recovery unit used in the last stage in boiler.

It is a heat exchanger that absorbs waste heat from exit flue gas in boiler and transfers the heat to the incoming cold air.

In utility boilers it is used to heat the air required for combustion purpose as well as dry & transport coal.

ADVANTAGES OF USING AIR PREHEATER IN A BOILERThe efficiency of boiler increased by 1 % for every 20C drop in flue gas temperature.Saves as much as 15% on fuel costs.Enables efficient burning of lower grade fuels.Permits faster load variation. Preheats air for coal drying and transporting the pulverised coal to burners.Reduced flue gas volume leads to size reduction in pollution control equipment.

BHEL introduced Ljungstrom Airpreheaters in the early seventies through a technical licensing agreement with M/s CE-APCO, USA. So far we have supplied over 600 Airpreheaters and for capacity ranges up to 500 MW utility boilers.

Best Practices - ErectionStorage of APH components are to be improved to avoid- Rework / damage (Housing panels)- Reduce erection time ( T-bars )- Meet quality at first time ( All Seals )

Maintenance of stored components- Frequent inspection of components ( Bearing assemblies)- Necessary preservation for components at regular intervals. ( Heating elements)

Handling of components with- Utmost care - Proper lifting tools and tackles- Safety

Best Practices ErectionAlways ensure proper storage and handling of components Air preheater can be fast erected if a proper sequence of erection followed.Extra care taken during erection will ensure trouble free operation.Refer to Air preheater Engineering / BHEL / Ranipet for any doubts / deviations in the drgs / Erection manuals.Ensure all erection welding is done by a qualified welder.Check all components for defects, damages and dimensional deviations before erection and correct them.Tonnage and quality of erection should go hand in hand.Inspect all weld joints for defects and rectify them to avoid leakage of air and seepage of water.Overlooking of minor details of drawings will lead to major rework.Never erect a damaged component Ensure proper earthing to rotor while doing any welding in rotor.

Best Practices - Erection

Plan in advance the sequence of erection.Apply rust preventive oil to protect components from rusting due to long storage and bad weather.Store the heating elements covered with tarpaulin and ensure cover sheets even after installation into the rotor and remove before light-up.Maintain the required accuracy in erection, which leads for a satisfactory operation.Tighten bolts to the required torque.Fill the bearings with specified oil or equivalent even during erection.Rotate the Air preheater in the correct direction of rotation.Keep a record of the readings in the check sheets which shall be despatched for the reference of Air preheater Engineering / BAP / Ranipet. Seal weld outside and inside for rotor housing panels, connecting plates (hot and cold) to housing panels, connecting plates (hot and cold) to air and gas ducts.

Best Practices - Erection Do not mix up items belonging to different Air preheatersDo not use shop lugs for lifting components / assembliesDo not support rotor on hot end connecting plate while liftingDo not carry out the bearing assemblies in open, dusty atmosphereDo not spoil the seal leaf by standing on them, by any other external load or interference with foreign material or by wrong direction of rotationDo not allow any foreign particle such as electrode bits, slag wool etc enter into heat transfer elements during erectionDo not carry out final welds before final alignments, checks etc.Do not spoil the seal straight edge during trail runDo not start Air preheater without filling with specified lubricants during erection check upDo not operate air motor without filter lubricator during trial run

Best Practices - Commissioning - Commission Cleaning device assy, Oil carry over probe, Fire sensing device, Rotor Stop alarm and Wash & Deluge pipe assy before first light-up. - If one APH is used out of two, the other APH should be kept in rotation or should be blanked properly to avoid fire. - Ash accumulation over guide bearing assy, soot blower assy & LOPs must be avoided. - Ensure Proper evacuation of Economiser ash to avoid choking of heating elements.Ensure clean dry air to Air motor without moisture. Keep the air motor in working condition by operating 5 minutes in a day.- Complete Insulation for Air preheater before light up.

Recent problems

Sl.ProblemCauseRemedy 01.High DP across APHBasket protection sheet (4 out of 12) were not removed.Basket protection sheets removed and problem resolved.02APH not rotating with stand by motorDrive unit assemblies found interchanged between A & BDrive unit supplier visited site and corrected. 03Support bearing jammed (kingsbury)Welding burrs & foreign materials found in housingBearing serviced and problem resolved.04High DP across APHNo evacuation of ash from economiser hopperBaskets cleaning 05Rotor jammedNo evacuation of ash from economiser hopperAsh removed and rotor made free to rotate.06Frequent failure of support bearings Improper tightness of trunnion boltsBolts tightened. 07Guide bearing failedImproper tightening of cap bolts over trunnionCorrective and preventive action taken.

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