Co-firing of coal and biomass fuel blends

Co-firingofcoalandbiomassfuelblendsM.Sami,K.Annamalai*,M.Wooldridge1DepartmentofMechanicalEngineering,TexasA&MUniversity,CollegeStation,TX77843-3123,USAReceived4August1999;accepted6June2000AbstractThispaperreviewsliteratureonco-firingofcoalwithbiomassfuels.Here,thetermbiomassincludesorganicmatterproducedasaresultofphotosynthesisaswellasmunicipal,industrialandanimalwastematerial.Briefsummariesofthebasicconceptsinvolvedinthecombustionofcoalandbiomassfuelsarepresented.Differentclassesofco-firingmethodsareidentified.Experimentalresultsforalargevarietyoffuelblendsandconditionsarepresented.Numericalstudiesarealsodiscussed.Biomassandcoalblendcombustionisapromisingcombustiontechnology;however,significantdevelopmentworkisrequiredbeforelarge-scaleimplementationcanberealized.Issuesrelatedtosuccessfulimplementationofcoalbiomassblendcombustionareidentified.q2001PublishedbyElsevierScienceLtd.Keywords:Co-firing;Coal;Biomass;Emissions;RenewableenergyContents1.Introduction..................................................................1722.Fundamentalcombustionissues....................................................1782.1.Materialandcombustioncharacteristicsofcoal....................................1782.2.Pyrolysis................................................................1792.3.Volatilesoxidation.........................................................1792.4.Charreactions.............................................................1792.5.Homogeneousreactions......................................................1802.6.Ignition.................................................................1802.7.Charcombustion...........................................................1812.8.Pollutantemissions.........................................................1823.Biomassfuel..................................................................1833.1.Pyrolysis................................................................1863.2.Ignition.................................................................1873.3.Charcombustion...........................................................1873.4.Foulingissuesinbiomasscombustion...........................................1893.5.Summarycomparisonofcoalandbiomasscombustion...............................1914.Co-firingofblends.............................................................1914.1.Blendcombustionefficiency..................................................1924.2.Classesofco-firing.........................................................1924.3.Coalandagriculturalresidues.................................................1934.4.CoalandRDF.............................................................195ProgressinEnergyandCombustionScience27(2001)171–214PERGAMONwww.elsevier.com/locate/pecs0360-1285/01/$-seefrontmatterq2001PublishedbyElsevierScienceLtd.PII:S0360-1285(00)00020-4*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](K.Annamalai).1Currentaddress:MechanicalEngineeringandAppliedMechanicsDepartment,UniversityofMichigan,AnnArbor,MI48109-2125,USA.4.5.Coalandanimalwaste......................................................2004.6.Combustionmodelingforcoalbiomassblends.....................................2034.7.Foulingissuesinco-firing....................................................2085.Issuesandopportunities..........................................................2096.Conclusions..................................................................211Acknowledgements................................................................212References......................................................................2121.IntroductionThecombustionoffossilfuelsprovidesalmost85%oftheenergyrequirementintheUnitedStates[1].In1997,theUSelectricalpowerutilitiesconsumed,87%ofthenearly1.1billiontonsofcoalproduced[1].Duetothelargecoalreserves,theUnitedStatesreliesheavilyoncoalforelectricitygeneration.Coalwasusedtoprovide51%ofthetotalpowergenerationintheUnitedStatesin1995andisprojectedtoprovide49%in2020[1].Hence,coalwillcontinuetobethedominantfuelforuseinelectricityproductionintheUnitedStatesfortheforesee-ablefuture.Assuch,theairpollutionemissionsaccom-panyingthecoalcombustionaresignificant.Amongthesepollutantsareoxidesofsulfur(SOx)andnitrogen(NOx),whichleadtoacidrainandozonedepletion.Inaddition,greenhousegasemissions(CO2,CH4,etc.)havebecomeaglobalconcern.Duetoconcernsoverpublichealthandtheenvironment,federalregulationsregardingtheemissionofairpollutantshavebecomeparticularlydemanding.TheEPANewSourcePerformanceStandards(NSPS)passedin1990requirea50%reductionofemissionsthatleadtoacidrain(i.e.NOxandSO2).Thepreviousstandardwas520gSO2/GJthermal(1.2lb/MBtu),whereGJthermalisthethermalenergyfromfuelcombustion.Thecurrentstandardis260gSO2/GJthermal(0.6lb/MBtu).InSwedenandinsomeportionsoftheUnitedStates,thestandardsareevenmoresevere,limitingemissionsto50gSO2/GJthermal(0.115lb/MBtu).Asadirectresultoftheseregulations,almost50%reductioninSO2fromutilityboilershasbeenachievedduringth