M. Syed Amirsha Hakani, B.E.

Precommissioning activities:Air and gas tight testChemical cleaningThermal flow testSteam blowingSafety valve settingClean air flow test of pulverisersTesting of protection and interlockCalibration of instruments

*AIR & GAS TIGHTNESS TEST

Gas Tightness Test:To detect the source of leakages in the system, before applying the insulation. Before this test ensure access doors, observation ports and other openings are to be closed securely.Run F.D fan and open all dampers in air & flue gas path except I.D fan discharge damper. Pressurize the flue gas path to 50mm of W.C. The furnace pr. should be 100mm of W.C.

* Air Tightness Test:

Run F.D fan keeping all dampers in air path open except dampers in wind box.System is pressurized to 100mm of W.C.Bubble test method (or) candle flame method are carried out to detect leakages and rectified.

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water washing DM rinse alkali boil out soda ash washing rinsing (or) water flushing passivation

preservation acid washing DM rinse

citric acid rinse

CHEMICAL CLEANING OF THE BOILER ( only for drainable portion)

Chemical cleaning1. Alkali boil out 2. Acid cleaning1. Alkali boil outRemove sand loose mill scale during erectionSodium sulphite added to reduce o2 corrosion ,sodium nitrate to prevent caustic embrittlementBoilout process followed by hot and cold water flushing Boiler filled with water to normal level chemicals added through man hole door in drum, ensure natural circulationFiring rate minimum, check uniform expansion while raising pressure to 1/5 times operating pressureEvery 2 to 4 hrs drains in ring header blow down for 2 min after putting out fireProcess terminated oil content reduces to 1ppmBoiler boxed up for slow cooling

Acid Cleaning:

For low pressure boilers ( < 60kg/cm2) alkali boil out alone is adequate. Two methods of acid cleaning are:Soaking method internal surfaces of the boiler are soaked in inhibited acid for 4 to 6 hrs after firing the unit to raise the temp. Circulation method inhibited acid is under circulation for 4 to 5 hrs by acid circulation pump. Temp. is maintained by adding steam from external source in dissolving tank.*

Passivation coating:Coating (protection layer) created after acid cleaning. This magnetic coating is done to avoid corrosion of material surface.Passivation is done at 250C & 40 kg/cm2 with adequate Hydrazine as prime chemical.This passivation coating (magnetic coating) is called Anti corrosive Layer.*

STEAM BLOWINGTo remove mill-scales, welding slag, debris or foreign material left in SH, RH and steam piping.It is to create momentum equal to (or) preferably greater than that during normal operation.1. Continuous Blowing Method constant purge steam rate is maintained by firing the unit for few mins.*

2. Puffing method thermal shock is created to dislodge scales from internal surfaces. Fire is quenched & pr. is allowed to decay durig steam blowing.Boiler is filled upto NWL with D.M water & steam pressure is raised to 40 atmosphere and firing discontinued.Valves in steam line are opened, venting out steam to atmosphere at velocity greater than normal.When Pr. drops to 25 atmosphere, the valves are closed & firing restarted to raise pr. again for next blow.*

Thermal flow test:Thermal flow test is done to detect passage obstruction in WW,ECO,SHchoked tube is identified with help of thermal flow meter using principle the rate of cooling of heated tube depend upon fluid flow inside the tubeMeasure Time taken for heated tube to drop 10 c temp Flow maintained a minimum velocity of 0.1 m/sec

Safety Valve Floating:To ensure the availability of safety valves for pressure release in times of necessity & adequacy of venting system.Gradually raise the boiler pr. at lower rate (93C/hr).All safety valves are to be gagged (arrested) except the testing valve.Hand pop the valve at lower pr. (i.e.) 10% below the set pressure.Raise the pressure to set pressure and put off the fire.Ensure proper operation of safety valve to release excess pr

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*BOILER START-UP:Cold Start-up below 150C Metal temp. of Warm Start-up 150C to 350C H.P turbine Hot Start-up greater than 350C casing in regular zone

BOILER COLD START UP SEQUENCE 1. Boiler filling using BFP Keep all vents and drains and ECO recirculation valves in open ECO, WW,Drum vents and drain valves closed

Fill the dearator with dm water using BFPOpen hydrazine dosing valve in BF suction lineTurn on FW heating system Run BFP on recirculationCrack open BFP discharge valve bypass valve and slowly charge FW line Open low load feed control valve charge line upto ecoOpen BFP discharge valve and close bypass valveMaintain moderate feeding 40 t/hr add make up water when level goes downDrum metal temp rise rate must be less than 110cEnsure BFP recirculation valve opens when flow is reduced to 100 t/hrBoiler is filled up

Draft system starting:Line up APH guide and support bearing oil circulating systemLine up flue gas pathLine up secondary air pathTake both APH in serviceStart one ID fanStart one FD fanStart ignitor air fanStart scanner air fanStart second ID fan (equalise load on both)Start second FD fan (equalise load on both)Stablise furnace draftPut furnace draft on auto

APH STARTINGI/L and O/L dampers in the gas path, secondary air path, primary air path are in full open conditions.One Electric Motor and one Air Motor have been providedSump oil temp of support/guide bearing of AH is < 600C.Impulse shall be given for closing of the I/L and O/L dampers of other AH which is OFF

Starting ID Fan:ID Fan outlet gates closed , inlet regulating damper minimumClose inlet and outlet gates of second fanFan 2 started following the same procedure

Starting FD Fan:ID Fan A or B is ONFan regulating vane in the min position& O/L damper closed

Starting of Warm up OIL(W.O) & Heavy fuel oil(H.O) GunsPermisiveIgniter trip valve open No boiler trip commandAir flow b/w 30 to 40 % of full load air flowBurner tilt in Horizondal position

Igniter start (oil supply pr 13 kg/cm2)1st Igniter ON , corner 1,3 if flame not proved trip valve closes after 10 sec25 sec later corner 2,4 started

W.O gun start( oil supply pr 4.5 kg/cm2, oil/air dp 1 to 1.5 kg/cm2)Light oil gun advances to firing position,open atomising air trip valve then light oil trip valve

H.O gun start (oil pr 7.5 kg/cm2 , oil/steam dp 1 to 1.5 kg/cm2, Heavy oil temp above 100 c)HO is placed in place of LO, atomising steam in place of airigniters removed -min 2 out of 4 flame scanner proven igniters removed -3 out of 4 guns open

Pulveriser Start up:Permisive Pulveriser discharge valve open Seal air valve open.cold air shut off gate openPulveriser outlet temp less than 90 cFeed inlet gate openPrimary air adequatePulveriser start ( start push button)Coal flow proven by coal flow detector within 5 sec after feeder start 15 sec after feeder is started , feeder is put on auto, fuel air damper is openWhen min 2 feeders are I operation for 50 sec ,oil gun of that elevation can be withdrawn

Start up sequence:

sequenceM.S prM.S tempLoadW.O5 kg/cm2195 cH.O6 kg/cm2275 cCoal 1st mill65 kg/cm2430 c30 MW 2nd mill105 kg/cm2500 c70 MW 3rd mill120 kg/cm2530 c120 MW 4th mill130 kg/cm2540 cFull load

Boiler purging and light upFurnace purge 30% airflow for 5minStart ignitor 1,3 then 2,4Warm up oil firing (L.O)When boiler starts steaming (40 45 min) throttle S.H vents and drains ,control FOT 538 cWhen drum pr raises 2 kg/cm2 close drum vents ,keep CBD fully open Ensure M.S line drain is opened ,close RH vents and drain before vacuum raising

Heavy oil firing Check HO recirculation pr heater tracing,Check atomising steam is chargedTake SCAPH corresponding to running FD fanTake HP and LP bypass when condenser vacuum is 540 mm hg ensure BFP and condensate pumps in serviceAfter synchronisation check furnace probe is retracted at FOT 540 c

Pulveriser operationStart scraper conveyor and slag crusher,Maintain cold end temp using SCAP, check CBD openStart one pa fanCharge ESP fieldsMake SH , RH spray system ready Close eco recirculation valves ,sh header drainstake main feed control valve in service isolate low load valve

Start 1st mill preferably lowest ,put mill outlet 65 -75 c and flow on auto , Increase load in generator as boiler output increases

Start 2nd mill when first mill is loaded to 80 % check mill air temp 75-80 c Ensure HP heaters in service at MS pr 105 kg/cm2

Start 2nd ID fan Start 2nd FD fan Start 2nd PA fan Start 2nd condensate pump and boiler feed pumpDearator pr raised to 6 kg /cm2

Start 3rd mill increase load on generator Put MS and RH steam temp ,BFP, main feed control valve, both ID, FD fan on auto

Start 4th mill Flame support HO guns can be removed once boiler loading is 60%SCAPH can be cut out or put in autoIncrease load on generator check boiler parameters Drum pr 145 kg/cm2 , Feed water temp 245 cMS pr 138 kg/cm2 temp 540 c RH steam pr 24 kg/cm temp 540 c Check MS temp low trip interlock comes in service when MS temp 520 c

*Boiler Shut Down Procedure (From Normal Operating to Cooling the Boiler)Gradually reduce the load by reducing firing rate. Allow boiler pr & temp drop, acceptable to turbine limitation.Introduce Supporting fuel when load is reduced Remove mill one by one from top in stages after emptying feeder and bowl.Change operation from auto mode to manual control at appropriate condition.Operate soot blowers at part load. Operation of APH soot blowers is very essential.

*Saturation temperature drop rate should not exceed the limit (83C / hr)When air flow reaches 30 % of MCR, keep it constant.Close DESH isolation valves in SH & RH system.Open start up vent and RH vent before shutting down steam to turbine. Take out oil burners after scavenging. Kill the fire & purging for 5 mins with 30% air flow. Stop PA fan, seal air fan & ignitor fan.Open other vents and drains of SH outlet & RH outlet atmosphere. Pressure reduction rate should not exceed the limit. HP & LP by pass can be kept in service.

*Stop FD,ID fan, and APH when flue gas temperature is 200CStill keep scanner fans in service.Continue feed water so that drum water level is maintained to NWL.Open drum vents to allow drum pressure decayed to about 2kg/cm2.Boiler can be drained if necessary when water temperature reduced to 85C.Shut down F.D, I.D & scanner fans.Boiler pressure parts are to be preserved during long shut down to avoid corrosion.Boiler preservation method has to be followed.

Emergency operation

High/low furnace prHigh/low Drum levelFlame failure at an elevationOne Fan tripsOne Feeder tripsOne Mill tripsCoal Hang up in millWater tube leakageRH SH Eco tube failureMaster fuel tripFurnace explosion