BOILER OPERATIONOBJECTIVESProduction of steam at desired parameters and purityProtection of pressure parts from corrosion, overheating, thermal stresses etcPrevention of furnace explosions

BOILER OPERATIONDIFFERENT PHASESSTART UP PROCEDURESCold startHot startCARE DURING NORMAL RUNNINGLoad changesRoutine checksOPERATION UNDER ABNORMAL CONDITIONSSHUTDOWN PROCEDURESTo coldTo hot stand by

BOILER COLD STARTMAJOR ACTIVITIESPre checksBoiler fillingStarting draught systemCharging steam to scaphBoiler purgingLight up with oil (L.D.O.)Switching over to H.F.O.firingRaising the parametersSwitching over to P.F. firingLoading the boiler

PRE CHECKS FOR BOILER LIGHTUPCHECK AND ENSURE THATAll systems to be started are free from man and material and all work permits/line clears are returned.Local drum level indicator is in service.Furnace temperature probe is available for serviceAll soot blowers are in retracted conditionSafety valves gags/test plugs are removed.

PRE CHECKS FOR BOILER LIGHTUP CHECK AND ENSURE THATImpulse safety valve/e.m.r. valve is in service position and its isolating valve is open.All drives of valves and dampers are in perfect condition and operetable from control desk. All control and interlock circuits are in healthy condition.Bottom ash hopper and seal trough are filled with water and adequate water supply is available

PRE CHECKS FOR BOILER LIGHTUP CHECK AND ENSURE THATAll ash hoppers are emptied and E.S.P.is cleaned and ready for operation.All sy.air dampers and burner tilt are freely operating and burner tilt is in horizontal position.All oil guns and spark plug assemblies are cleaned.All boiler,super heater,re heater drains and vents are in start up position.

PRE CHECKS FOR BOILER LIGHTUPCHECK AND ENSURE THATAll de super heater spray control valves are in closed condition and available for service.Fire fighting system is ready.Adequate fuel oil quantity is stored.Raw coal bunkers are filled.D.M. water tank is filled.

PRE CHECKS FOR BOILER LIGHTUPCHECK AND ENSURE THATBearing cooling water system is started.Compressed air from instrument air and service air compressors are available and air pressures are adequate.

BOILER FILLINGAll vent valves on feed line, economiser,drum,headers and m.s.line are kept open.All drain and blow down valves are kept closed.Do not fill the water above the boiling point.Do not fill with excessive cold water.If possible fill with water 100c above boiler metal to avoid temp. stresses

BOILER FILLINGOpen and close gauge glass cocks and drains on the water column to make sure that these connections are unobstructed and free.Fill till free jet of water comes out through economiser vent and drum vents.Bring down level in drum to normal by draining after closing economiser vent.

STARTING DRAUGHT SYSTEMLineup lub.oil system of all fans and air heaters and take them into serviceLineup flue gas pathLineup air pathStart air heater AStart air heater BStart one I.D. fanStart corresponding F.D. fanRaise load on I.D.&F.D. to maintain 30% of full load air flow through Boiler and necessary furnace draughtStart scanner air fanDraught system ready for light up

STARTING DRAUGHT SYSTEM

LINE UP FLUEGAS PATHEnsure all man hole doors are closedEnsure ESP hoppers are sealedEnsure sufficient flow through furnace water sealEstablish power supply to all flue gas path dampersEstablish power supply to all flue gas path instrumentsClose suction and discharge dampers of both I.D.fansKeep I.D.fan control devices in minimum positionKeep open flue gas inlet and outlet dampers to both air heaters

LINEUP AIR PATHEnsure all air path man hole doors are closed Establish power supply to all air path dampersEstablish power supply to all air path instrumentsClose discharge dampers of both F.D.fansKeep F.D.fan control devices in minimum positionKeep open sy.air inlet and outlet dampers to both air heaters

STARTING AIR HEATERS

Check support bearing and guide bearing lub. oil systems are in service.Check air and flue gas paths are lined up.Check air heater water wash lines are closed.Check service air supply to air heater is available.Establish electric supply to air heater motor.Start the motor.Observe whether motor current is normal.Observe for rubbing/abnormal noise at local.Open water inlet and outlet valves in lub. oil systems.Start second air heater as above

BOILER PURGINGCHECK THE FOLLOWING PURGE PERMISSIVES ARE SATISFIEDA.C.& D.C.power supply to F.S.S.S.is availableDrum level is normal.Atleast one I.D.fan and one F.D.fan are in serviceMinimum 30% of full load airflow is maintained.All oil trip valves and nozzle valves are proven closedAll auxiliary air dampers are modulating to maintain adequate windbox to furnace differential pressureAll pulverisers and feeders are offAll hot air gates are closed and cold air dampers are less than 5% open.All flame scanners sense no flame. No boiler trip command is present

BOILER PURGINGSatisfy purge permissivesGive purge start commandPurge on indicationcomesPurge complete indication comes

LIGHTOIL FIRINGOpen ignitor oil trip valveOpen light oil trip valveSelect light oil firing in AB elevationEnsure elevation permissivesStart one pair of oil gunsStart second pair of oil gunsCheck 3 out of 4 L.O. guns are proven on in timed sequence

ON LIGHTUP WITH LIGHT OILEnsure adequate light oil / atomising air pressureCheck boiler expansion is freeControl firing rate in such away that steaming starts only after 45 minutesKeep economiser re circulation valve openWhen drum pressure reaches 2 kg/cm2close drum vents Control firing rate according to start up curve and FOT not exceeding 5400cStart closing S.H. vents and drains except start up ventIncrease steam pressureWarm up main steam lines

HEAVY OIL FIRINGEnsure auxiliary steam lines are chargedEnsure atomising steam lines are chargedEnsure H.O.system is started through re circulation SCAPHcorresponding to F.D.in service is chargedOpen H.O. trip valveEnsure CD elevation permissivesStart one pair of CD elevation gunsStart second pairEnsure minimum 3 out of 4 corners are proven onChange over to H.O. firing in AB elevation

HEAVY OIL FIRINGControl firing rate as per start up curveClose R.H.vents and drainsPull vacuum in condenserTake HP/LP by pass into serviceClose start up ventMaintain drum level by intermittently feedingStart feeding through low load FCV if drum level continue to recedeClose economiser re circulation valveMonitor boiler expansionEnsure F.G. temp. after A.H.above acid dew point by regulating steam to SCAPHRaise steam to rolling parametersTurbine rolled,synchronised

TO S.H.ATTEMPERATIONTO S.H.ATTEMPERATIONFEED WATER FROMH.P.HEATERTOECO.DRAINDRAINDRAINDRAINDRAINDRAINDRAINDRAINDRAINF.C.V.FEED REGULATING STATION

PREPARATION FOR COAL FIRINGCheck boiler water qualityMaintain boiler water pH through phosphate dozing Ensure silica level and TDS are in permissible levelsStart scrapper conveyor and slag crusherCheck E.S.P. rapping mechanism in serviceStart one P.A.fanStart seal air fanKeep S.H/R.H spray control system ready

STARTING COAL FIRINGEnsure mill ready permissives for mill AMake ignition energy availableto mill AStart mill AOpen hot air gateStart R.C.feeder AIncrease feeder speed graduallyMaintain drum levelMaintain furnace draughtSwitch on E.S.P.hopper heatersControl firing rate according to start up curve

STARTING COAL FIRINGPrepare for starting mill B when first mill is loaded to 50%Start mill B in same way as mill AStart R.C.feeder B and equalise loading in both feedersControl firing rate by reducing oil firing rateChange over to 100% F.C.V. when low load feed control valve is more than 80% openIncrease air flow proportional to boiler load when load crosses 30%Control S.H. temp.by attemperation and R.H.temp.by burner tiltingGradually increase boiler load

WHEN BOILER LOAD APPROCHES 50%Start second I.D.fanEqualise loading on both i.d.fansStart second F.D.fanEqualise loading on both F.D.fansTake SCAPH of second F.D.into serviceEnsure adequate wind box to furnace differential pressure is maintainedStart second P.A.fanEqualise load on both P.A.fans

GOING TO FULL LOADStart third mill when first two mills are loaded to 80%Start third R.C.feederEqualise loading on all three millsStart fourth mill when first three mills are loaded to 80%Start fourth R.C.feeder Equalise loading on all four millsIncrease boiler loading to full load

ON NEARING FULL LOADFeed control valve can be put on autoS.H/R.H steam temp. control on autoFurnace draught control on autoE.S.P. fields are chargedOil firing can be stopped when boiler load is more than 6o% and more than two mills are in service at minimum 50% loading and atleast two adjacent mills are in serviceSteam to SCAPH s cut off when flue gas outlet temperature more than 1500c

ROUTINE CHECKSMake a round of boiler to inspectFlame condition/ stabilityPressure parts for leakageLeakage in air/flue gas pathsRunning auxiliaries for abnormal noise vibration,high bearing temp. etc.Maintain hourly log. Identify deviations and take corrective actions

ROUTINE CHECKSCompare unit operating parameters with predicted readings.Any deviation should be reasoned and correctedCompare local instruments reading with remote instruments once a day.Any discrepancy to be correctedMaintain feed water,steam qualityEnsure flow of sampling water is maintainedAnalyse F.G. through orsat apparatus once a dayCheck fineness of p.f.

ROUTINE CHECKSCheck pr.drop of F.G.,feed water temp before and after economiser, steam temp at various stages of S.H., metal temp. of S.H. and R.H.Carry out soot blowing as and when requiredCarry out soot blowing of A.H. once in a shiftEnsure no choking in bunkersMaintain mill parametersEmpty the bunker if the mill is taken for long shut downEnsure satisfactory operation of slag conveyors slag crushers,fly ash system

ROUTINE CHECKSControl R.H. temp. by burner tiltLoad pulverisers only to 80%Keep clean ignitor spark plugs,atomisers.Maintain H.O.and atomising steam temp.and pr.Parallel running fans are loaded equallyChange over to stand by equipment of following aux. once a weekSeal air fanHydrazine pumpCoal millsLub.oil pumps

BOILER SHUT DOWN PROCEDUREReversal of light up procedureTake all controls on manual modeBy pass Turbine trip on Temp. protectionReduce speed of running R.C feeders graduallyEnsure the firing rate is decreased in such a way that the rate of saturated steam temp drop at boiler drum is not exceeding the limits prescribed in the shut down curve (830 C per Hr ) all the time till the boiler is shut down

BOILER SHUT DOWN PROCEDUREMaintain drum level and furnace draughtTake oil support at the adjacent elevation to the top coal elevation in serviceTrip the top elevation R.C.feeder when its speed nears to minimumShare the load on other feedersRun the mill corresponding to the feeder tripped for some more time till it is cleared of coalStop the mill and isolate it

BOILER SHUT DOWN PROCEDUREReduce load further by reducing speed of feeders, tripping the feeder after taking oil support etc.When the load drops below 50% stop one F.D.fan, one I.D.fan Ensure the tripped fans suction and discharge dampers are fully closed Reduce load further by reducing speed of feeders, tripping the feeder after taking oil support etc

BOILER SHUT DOWN PROCEDUREWhen the load drops below 30%Change over to low load feed control valveEnsure the wind box to furnace Diff. Pr. is changed to low set pointMaintain air flow to the boiler at 30 to 40% of full load air flow on further reduction of load On further reduction of firing rate in the above manner at one stage the boiler will be running only with oil guns

BOILER SHUT DOWN PROCEDUREWhen the load drops below 10% trip the boiler through protectionEnsure all the oil valves are fully closedCarry out boiler purgingDo not stop the air heaters till the gas inlet temperature drops to 1000C Carry out cooling of the boiler on the method desired

COOLING THE BOILER ON SHUT DOWNMETHODS OF COOLINGNATURAL COOLINGFORCED COOLINGBOX UPBOILER IS COOLEDInternallyExternallyBy Radiation

NATURAL COOLING

On tripping of the boiler bring the drum level to very high level and stop feedingAfter purging stop F.D.and I.D.fansAll the dampers in air and flue gas path remain in open positionStart up vent in open positionInternal cooling takes place due to circulation of water inside tubesTop up water in drum when the level recedes

NATURAL COOLING

External cooling takes place by the air flow due to natural draught effect which is at a slow rateAlso cooled by radiationWhen the pressure drops to 5kg/cm2 open the S.H.,R.H. vents When the pressure drops to 2kg/cm2 open the drum ventsNatural cooling will take more time

FORCED COOLING

On tripping of the boiler bring the drum level to very high level and stop feedingAfter purging do not stop F.D.and I.D.fansAdjust air flow according to the cooling rate desiredEnsure the saturated steam temperature drop is not more than 830C per hour

FORCED COOLING

Start up vent in open positionInternal cooling takes place due to circulation of water inside tubesTop up water in drum when the level recedesExternal cooling takes place by the air flow at a faster rate according to air flow rateAlso cooled by radiation

FORCED COOLING

When the pressure drops to 5kg/cm2 open the S.H.,R.H.ventsWhen the pressure drops to 2kg/cm2 open the drum ventsBoiler will be cooled at a faster rate in forced coolingNot healthy for boiler as it induces stresses in boiler tubesUsed only in emergencies

BOX UPOn tripping of the boiler bring the drum level to very high level and stop feedingAfter purging stop F.D.and I.D.fansKeep all the vents and drains including start up vent in closed conditionAs such there will not be any circulation and so no internal coolingKeep all dampers in air and flue gas path in closed conditionAs such there will not be any air flow through boiler and so no external cooling

BOX UPCooling can be only through radiationHeat inside the boiler can be retained for more time Adopted for keeping the boiler ready for hot start up on shut down