trial cleaning of fouled aph baskets of # 5 2013 presentations/day-2 at pmi...trial chemical...

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  • TRIALCHEMICALCLEANINGOFFOULEDAPHBASKETS

    Dr.Abhay KumarSahay,AGM(CCOS)

    Bijay Manjul,AGM(Operation)Kahalgaon

  • AIR PRE HEATER

    Boiler has three inputs

    1. WATER

    2. COAL

    3. AIR

    Steam generator

    Burner

    Seco

    ndar

    y ai

    r

    Air preheater

    FD-Fans

    Excess Air

    Electricprecipitator

    Intermed. Fly-ash bunker

    Fly ash

    Flue gasCoal bunker

    Coal mill

    Pul

    veri

    zed

    fuel

    Prim

    ary

    air

    2

  • 3710C

    1430C380C

    3220C

    Air enters to the Boiler & exits from the Boiler through APH.

    This is LUNGS of the Boiler.

    3

    Though it cost only 2%of total cost of boiler but transfer 20% of total heatfed to the boiler.

  • The purpose of air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by using the useful heat which would be lost in the flue gas.

    4

  • 1% improvement in boiler efficiency is realized for each 20C increase in boiler inlet air temperature

    1% improvement in boiler efficiency

    = 1% improvement in heat rate= 24 K Cal / KW Heat gain

    20C +1%Efficiency5

  • Air heater fouling is usually in the form of plugging of the element channels by deposits of:

    Fly Ash Sulfur (and Sulfuric Acid)Other Corrosion and Flow limiting Deposits

    An increase in pressure differential across the air heater is directly related to the degree of fouling

    6

  • An increase in pressure differentials across the air heater can cause:

    Increase in Fan Amps/Aux. PowerDecrease in Mw OutputReduced Boiler EfficiencyIncreased Heat RateIncreased CO2 Emissions

    7

  • Severe fouling of fin tube surfaces in steam coil air preheaters

    Severe Fouling of element channels in rotary air preheaters

    8

  • AN INSIGHT INTO COLD END DEPOSITPrecipitation fouling: Precipitation of dissolved substances on lowering of temp.Chemical reaction fouling: Deposits formed due to chemical reaction.Particulate fouling: Deposition of impurities from gas stream & reduction of heat transfer, increase in pr drop.Corrosion fouling: Heat transfer surface reacts itself.Deposition of Al2O3, Fe2O3, SiO2 particulates, sulfur, sodium, vanadium & chlorine from oil.Dew point condensation of Na2SO4, K2SO4, P2O5, Na2CO3, NaCl.

    9

  • AIR PRE HEATER COLD END GAS SIDE DEPOSIT

    SO3 (H2SO4) in Flue gas ppmS + O2 = SO2, 2SO2 + O2 = 2SO3

    Excess air increases dew point of flue gas from designed 1290C. Below dew point temp free sulphuric acid appear and dissolve calcium and depositing calcium sulphate retarding heat transfer. Calcium sulphate can not be removed by water or acid cleaning. 10

  • Common methods for cleaning of air preheater elements include;

    High pressure water jettingSaturated/superheated steamCompressed air

    The most common method is high pressure water jetting

    11

  • The amount of wastewater produced during cleaning can exceed 17500 M3.Removing one waste at the cost of generating another waste Tenacious deposits & sulphate scales cannot be removed by present methods of cleaning.Even in a freshly cleaned Air Preheater air temp does not go beyond 2600C to 2800C.Reducing Mill outlet temp threatening moisture separation in P.F.Pipe.

    12

  • ComparisonbetweenHPhydrojetcleaningversuschemicalcleaningHydrojetcleaning

    Oilonbasketsurfaceremains Duetocrisscrossgeometryof

    themessofbasket,waterentersatoneangleandleavesthebasketatanotherangleleadingtotaperformationofthedepositsratherthancompleteremoval

    Metalloss/damageofthebasketsduemechanicalrubbing

    hugeamountofwaterrequiredandcleaningnoteffective

    Beinghardsiliceousdeposits,,longercleaningtime(1012hrsperbasket)requiredwithproportionatelabour cost

    Toocumbersome,

    Chemicalcleaning Effectiveremovalofalldeposits

    includingoilwithsimultaneousprotectionofthemetalasthechemicalsincludinginhibitorsarecarefullyselectedforthisspecificlotofbasketsexactlyinthesimilarmannerasweusuallydoforpostoperationalchemicalcleaningofboilerswhichhasbeenanestablishedpracticeinNTPCsofar.

    Totalcleaningtimeisreducedby50%andsoisthelabour cost

    Qualityofcleaningwithdueprotectionofthebasemetalisfarsuperiorascomparedtothatofwaterjetcleaning.

  • TRIALCHEMICALCLEANINGOFFOULEDAPHBASKETS

  • DuringoperationtheAirPreHeaterBasketbecamefouledwithoil,grease,dustandcarbonaceousmatter.Depositsofthesematerialshasaffectedaffecttheperformanceofthesystem.

    Compositionofthedeposit: Acidinsoluble Ca PO4 Oil

  • InitiallyHPwaterjettinghasbeentriedonthesefouledbaskets.Butissueswithwaterjetcleaningare: Toocumbersome, timetaking(810hrsperbasket) hugeamountofwaterrequiredandcleaningnoteffective. Particularlyoilonthebasketsurfaceremainswhichisapotentialproblemwhenthebasketswillbeputbackintoservice.Inviewofabove,achemicalcleaninghasbeenattempted.

  • BasicMechanismonwhichthischemicalcompositionworksTheAirPreheatersBasketareimmersedinabathcontainingCompositechemicals.BycontinuousAiragitationintheliquiditcreatesmicroscopicvacuumbubbles,whichimplodeforcefullyontothesurfacethatistobecleaned.Thisphenomenoniscalledcavitation.

  • Thisenergyproducesapowerfulcleaningeffectthatisabletoremovestubborncontamination,eveninspacesthatarehardtoreach,drasticallyshorteningthecleaningtime.Thencompositechemicalspenetratesthedepositsdissolvingoilymatterandlooseninginsolublesolids,sothattheycanbeeasilyremovedbyagitating.

  • TheCleaninghasbeenenvisagedbyusingeco friendlyreadilyavailablechemicalswithappropriatecleaningperformance.1.Atemporarytankofsuitablecapacityhasbeen

    preparedtoimmersetheAPHBASKETwithairheader,waterlineanddrainpointconnection.

    2.WATERFLUSHING:BeforeimmersingtheAPHBasket,flushwithplentyofwatertoremoveallloose ,deposits,dirt,dust,etc.Thiscanbecarriedouttothedurationof15minutesanddrainthedirtywater.

  • PROCEDUREFORCHEMICALCLEANINGOFonenooffouledAPHBASKET.Compositechemicalconsistmixtureof(a)1kgofFormicacid(85%Purity)Commercialgrade,(b)2KgPhosphoricacid(85%purity)commercialgrade,(c)500mlCorrosioninhibitor,and(d)3KgWettingagentandDispersant Fillupthetank

    withfreshwater.NowaddthecompositechemicalcleaningCompound intheratioof1:10(i.e.)onepartofchemicaland10partsofwater Allowforsoakingtothedurationof4Hrs.CompressedAirpurgingshouldbegiventhroughoutprocessperiod.

    Theratioofthecleaningchemicalandalsotheprocesstimeofsoakingmayincreasedordecreaseddependingupontheextentofdeposit.

    Draintheentiresolution.

  • WATERWASH: Fillupthetankwithfreshwaterandcarryoutthemassflushing.

    RemoveAirPreHeaterBasketfromtheTankandflushwithwaterifrequired.

    ApplyHighpressurecleaningtoremovethelooseneddislodgeddepositfromthesystem.

  • Seeingisbelieving!!

  • Fouled basket inside the tank

  • After putting the chemicals inside the tank with air blowing

  • Continuous air scouring in progress

  • Soaking step nearing completion

  • Basket taken out of tank after completion of soaking period

  • First we tried with fire water

  • Flushing with fire water in progress

  • Jet piping got ready

  • Flushing with HP jet pipe in progress

  • Flushing with HP jet pipe in progress

  • Flushing with HP jet pipe in progress

  • After flushing Cleaned basket resembling very closely to new one

  • Even side plates are thoroughly cleaned

  • More than 95 % of the mesh has been cleaned effectively

  • Before cleaningAfter cleaning

  • Before cleaning After cleaning

  • Costcomparison

    Approx.CostNewAPHbasketisRs 60000/Perbasket.OncereclaimedthereisarealisticprospectofasavingsofRs 58000perbasketandletussayforasetof100basketsofoneAPH,ittranslatesintoadirectsavingsofRs 5800000/besidesotherassociatedbenefits.Withafleetsizeof100(+)ofthermalunits,thereisagreatopportunityofsavings!!

    CostofinhousechemicalcleaningofonebasketisApprx.2000/

    Timetakenisapprox.5hrs(4hrssoaking+1hrsflushing)*.

    *(Thiscanbeoptimizedwithsimultaneouscleaningusingabiggertank)Sinceitisproposedtobeainhouseactivity,thereforeworthtrying.

  • But we have to keep in mind the following :Cleaning of each set of baskets shall be taken up on case to case basis, as the chemical composition needs to be formulated based on the deposit material on the target baskets.

    Conclusion :We plan to go for one more trial cleaning of affected basket forone of our stations for finalizing the structured procedure of this cleaning method . And of course,

    Most important point is support from all concerned !!

  • TRIAL CHEMICAL CLEANING OF FOULED APH BASKETS Dr. Abhay Kumar Sahay, AGM(CC-OS) Bijay Manjul, AGComparison between HP hydro jet cleaning versus chemical cleaning TRIAL CHEMICAL CLEANING OF FOULED APH BASKETS During operation the Air Pre Heater Basket became fouled with oil, grease, dust and carbonaceous matter. Deposits of these ma Initially HP water jetting has been tried on these fouled baskets. But issues with water jet cleaning are :- Too cumbersomeBasic Mechanism on which this chemical composition worksThe Air Pre heaters Basket are immersed in a bath containing ComposiThis energy produces a powerful cleaning effect that is able to remove stubborn contamination, even in spaces that are hard toThe Cleaning has been envisaged by using eco- friendly readily available chemicals with appropriate cleaning performance.1. PROCEDURE FOR CHEMICAL CLEANING OF one no of fouled APH BASKET . Composite ch