High Temperature Corrosion Phenomena in Waste to ??2014-04-17High‐Temperature Corrosion Phenomena in Waste‐to‐Energy Boilers ... The low carbon steel SA178A had the worst corrosion resistance among all alloys tested. ... Conclusion

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  • HighTemperatureCorrosionPhenomenain

    WastetoEnergyBoilers

    ShangHsiuLee

    Submittedinpartialfulfilmentofthe

    Requirementsforthedegree

    ofDoctorofPhilosophy

    intheGraduateSchoolofArtsandSciences

    ColumbiaUniversity2009

  • 2009

    ShangHsiuLee

    AllRightsReserved

  • Abstract

    HighTemperatureCorrosionPhenomenainWastetoEnergyBoilers

    ShangHsiuLee

    WastetoEnergy (WTE) technology is an essential part of sustainable waste

    management.Itgenerateselectricitybycombustingmunicipalsolidwaste(MSW)under

    controlledconditions.Thereareover600WTE facilitiesgloballycombustingover170

    million tons ofMSW annually. However, high temperature corrosion of boiler tubes

    remainsanoperationalandeconomicproblemfortheWTEindustry.

    PastresearchworkconcentratedonreducingcorrosioninWTEboilerseitherby

    improving the process conditions in the boiler, or by developing alloys that can

    withstand better the relatively high chlorine concentration in the combustion gases

    (400600ppmHCl).

    ThisresearchexaminedthecorrosionmechanismsinWTEboilersbyconducting

    laboratorytestsunderconditionsthatsimulatedtheWTEenvironment.Thecontrolling

    variablesinthetestswerebasedontheanalysisofdataprovidedbyoverfiftyU.S.WTE

    facilitiesinresponsetoacorrosionsurveythatwasdistributedbytheWastetoEnergy

    ResearchandTechnologyCouncil,anacademicindustryorganizationheadquarteredat

    ColumbaUniversity.This studyalsoexplored the feasibilityofanovelprocedure that

    aimedtoreducingthehydrogenchlorideconcentrationinthecombustiongasesflowing

    throughtheboiler.

  • The research effort included (1) an indepth analysis of the survey on high

    temperaturecorrosion; (2) laboratory tests that, for the first timesimulated the large

    temperature gradients encountered across the wall of WTE heat exchanging metal

    surfacesandclarifiedthemechanismandkineticsofchlorineinducedcorrosionandthe

    effectofhydrogen chloride gas concentrationson corrosion rates; and (3) laboratory

    testson the sequestrationof chlorine in theWTEprocessgas bymeansof injecting

    chemicalsintothefurnace.

    Thecorrosionsurveyshowedthatthemostcommonwaterwalltubingwaslow

    carbon steel SA178A (>99%Fe) claddedwith Inconel 625 (58%Ni2023%Cr810%Mo)

    applied. Lowcarbon, intermediatechromealloysSA213T11 (Fe1.05%Cr0.08%C)and

    T22(Fe2.21%Cr0.1%C)weremostlyusedassuperheatertubing.

    In the experimental corrosion tests, the stainless steel alloy NSSER4 (Fe

    17.3%Cr13.1%Ni2.5%Si) that is produced by a Japanese company showed excellent

    corrosionresistance.AlthoughNSSER4isnotavailableintheU.S.steelindustrynow,it

    ishighly recommended for superheater tubingwherehighermetal temperatures are

    required.The lowcarbon, intermediatechrome steel SA213T11exhibitedacceptable

    corrosionresistanceatmetaltemperaturesupto540oC.The lowcarbonsteelSA178A

    hadtheworstcorrosionresistanceamongallalloystested.

    Increasing the HCl concentration in the synthetic gas flow through the

    experimentalapparatus increased the corrosion ratesof test coupons.TheHCleffect

    was amplified with increasing metal temperature. In addition, the presence of HCl

    promotedtheformationofsulfatesaltsandincreasedthecorrosion.Theresultsofthe

  • chemicalratetestshowedthattheoverallreactionprocessofalloySA178Aduringthe

    100hour test followed theparabolic timedependencewhichwasoften found inhigh

    temperatureoxidations.TheoverallapparentactivationenergyofalloySA178Awithin

    the 100hour test was 178kJ/mol which was determined from multiple tests. The

    calculatedactivationenergyofalloySA178Aafterasingle100hourtestwas149kJ/mol,

    whichwasclosetoitsoverallactivationenergyshowingthatthe100hoursofexposure

    wassuitableforthecorrosiontest.Fromthecomparisonofactivationenergiesofthree

    testmaterials, itwas inferred that thecorrosionof the lowcarbonsteel,SA178Awas

    more kinetically controlled while the stainless steel, NSSER4 was more diffusion

    controlled.

    Theinjectionofcalciumhydroxideslurrydroplets,inordertoreactwithHCl/Cl2

    and thus lower theeffective chlorine concentration in the gas,was shown to reduce

    appreciablythecorrosionrateofthemetalcouponsinthetestchamber.Theobserved

    reduction of overallmass loss ranged from 0.318% for three differentmetal alloys.

    Theseacceleratedcorrosiontestswereconductedatmetaltemperaturesof700oC,that

    isappreciablyhigherthanthetemperaturegradienttests(450580oC).Evenunderthese

    conditions the stainless steelalloy,NSSER4,exhibitedvastly superiorperformance to

    thesteelalloysthatarecommonlyused intheWTE industry. Itsoverallmass lossper

    surfaceareawas64timeslowerthanSA178Aand70timeslowerthanSA213T11.

  • i

    TableofContents

    Page

    TableofContents.................................................................................................................i

    ListofFigures......................................................................................................................iv

    ListofTables........................................................................................................................x

    Acknowledgements.............................................................................................................xi

    1. Introduction....................................................................................................................1

    1.1.IndustrialSignificance..............................................................................................1

    1.1.1.WastetoEnergyTechnologies.........................................................................2

    1.1.2.HighTemperatureCorrosioninWastetoEnergyFacilities.............................4

    1.2.ResearchObjectivesandScope...............................................................................7

    2.HighTemperatureCorrosionMechanisms....................................................................9

    2.1.PrincipalsMechanismsandCorrosionFactors........................................................9

    2.2.CorrosionKinetics..................................................................................................14

    2.2.1.RateEquationsofMetalOxidation[8,16].....................................................14

    2.3.CurrentMethodsofProtection.............................................................................17

    3. CorrosionSurveyandAnalysis.....................................................................................24

  • ii

    3.1.CorrosionQuestionnaire........................................................................................24

    3.2.ResultsandAnalysis...............................................................................................25

    4. ExperimentalSection....................................................................................................42

    4.1.OverviewoftheExperimentalWork.....................................................................42

    4.2.ExperimentalProcedureandApparatus...............................................................43

    4.2.1.TestMaterialsandSamplePreparations........................................................44

    4.2.2.ApparatusofCorrosionTests.........................................................................47

    4.2.3.ApparatusofHCl/Cl2SequestrationTests......................................................50

    4.2.4.PostTestAnalysis............................................................................................54

    5. ExperimentResultsandDiscussion..............................................................................56

    5.1.CorrosionKineticTests..........................................................................................56

    5.1.1.TestBackground.............................................................................................56

    5.1.2.ResultsandDiscussion....................................................................................58

    5.1.3.Conclusion.......................................................................................................63

    5.2.ChlorineInducedCorrosionMechanisms..............................................................64

    5.2.1.TestBackground.............................................................................................64

    5.2.2.Results.............................................................................................................64

  • iii

    5.2.3.Discussion.......................................................................................................74

    5.2.4.Conclusions.....................................................................................................76

    5.3.EffectsofHydrogenChlorideGasConcentrationsonCorrosionRatesof

    CommercialTubeAlloysunderSimulatedEnvironmentofWTEFacilities..................78

    5.3.1.TestBackground.............................................................................................78

    5.3.2.ResultsandDiscussion....................................................................................79

    5.3.3.Conclusions...................................................................................................110

    5.4.PreliminaryResultsofHCl/Cl2SequestrationTests.............................................111

    5.4.1.TestBackground...........................................................................................111

    5.4.2.ExperimentalMatrix.....................................................................................116

    5.4.3.ResultsandD