combustion and incineration processes

COMBUSTIONANDINCINERATIONPROCESSESThird Edition,Revised andExpandedWalter R. NiessenNlessenConsultantsS.P.Andover,MassachusettsM A R C E LEZDEKKERMARCELDEK K ER, I NC.NEW Y O RK B AS ELMarcel Dekker, Inc., and the author make no warranty with regard to the accompanying software, itsaccuracy, oritssuitabilityforanypurposeotherthanasdescribedinthepreface. Thissoftwareislicensedsolelyonanas is basis. Theonlywarrantymadewithrespect totheaccompanyingsoftwareisthat thediskettemediumonwhichthesoftwareisrecordedisfreeof defects. MarcelDekker, Inc., will replaceadiskette found tobe defectiveif such defectis not attributable to misusebythepurchaserorhisagent. Thedefectivediskettemustbereturnedwithinten(10)daysto:CustomerServiceMarcelDekker, Inc.P. O. Box5005CimarronRoadMonticello, NY12701(914)796-1919ISBN:0-8247-0629-3Thisbookisprintedonacid-freepaper.HeadquartersMarcelDekker, Inc.270MadisonAvenue,NewYork, NY10016tel:212-696-9000;fax:212-685-4540EasternHemisphereDistributionMarcelDekkerAGHutgasse4, Postfach812,CH-4001Basel, Switzerlandtel:41-61-261-8482;fax:41-61-261-8896WorldWideWebhttp:==www.dekker.comThepublisheroffersdiscountsonthisbookwhenorderedinbulkquantities.Formoreinformation,writetoSpecialSales=ProfessionalMarketingattheheadquartersaddressabove.Copyright # 2002byMarcelDekker, Inc. AllRightsReserved.Neither thisbooknor anypart maybereproducedor transmittedinanyformor byanymeans,electronicormechanical,includingphotocopying,microlming,andrecording,orbyanyinforma-tionstorageandretrievalsystem, withoutpermissioninwritingfromthepublisher.Currentprinting(lastdigit):10987654321PRINTEDINTHEUNITEDSTATESOF AMERICA1. Toxic Metal Chemistry in Marine Environments, Muhammad Sadiq2. Handbook of Polymer Degradation, editedby S. Halim Hamid, MohamedB.Amin, and Ali G. Maadhah3. Unit Processes in Drinking Water Treatment, Willy J. Masschelein4. Groundwater Contamination and Analysis at Hazardous Waste Sites, editedby Suzanne Lesage and Richard E. Jackson5. Plastics WasteManagement: Disposal, Recycling, andReuse, edited byNabil Mustafa6. HazardousWasteSiteSoil Remediation: Theoryand Application of Inno-vative Technologies, edited by David J. Wilson and Ann N. Clarke7. Process Engineering for Pollution Control and Waste Minimization, edited byDonald L. Wise and Debra J. Trantolo8. Remediation of Hazardous Waste Contaminated Soils, editedby DonaldL.Wise and Debra J. Trantolo9. Water Contaminationand Health: Integrationof Exposure Assessment,Toxicology, and Risk Assessment, edited by Rhoda G. M. Wang10. Pollution Controlin Fertilizer Production, editedbyCharlesA. HodgeandNeculai N. Popovici11. Groundwater Contamination and Control, edited by Uri Zoller12. Toxic Properties of Pesticides, Nicholas P. Cheremisinoff and John A. King13. Combustion and Incineration Processes: Applications in EnvironmentalEngineering, Second Edition, Revised and Expanded, Walter R. Niessen14. Hazardous Chemicals in the Polymer Industry, Nicholas P. Cheremisinoff15. Handbook of Highly Toxic MaterialsHandling and Management,editedbyStanley S. Grossel and Daniel A. Crow16. Separation Processes in Waste Minimization, Robert B. Long17. Handbook of Pollution and Hazardous Materials Compliance: A Sourcebookfor Environmental Managers, Nicholas P. Cheremisinoff and Nadelyn Graffia18. Biosolids Treatment and Management, Mark J. Girovich19. Biological Wastewater Treatment: Second Edition, Revised and Expanded, C.P. Leslie Grady, Jr., Glen T. Daigger, and Henry C. Lim20. SeparationMethods for Waste andEnvironmental Applications, Jack S.Watson21. Handbook of Polymer Degradation: Second Edition, Revised and Expanded,S. Halim Hamid22. Bioremediation of Contaminated Soils, editedbyDonaldL. Wise, DebraJ.Trantolo, Edward J. Cichon, Hilary I. Inyang, and Ulrich Stottmeister23. Remediation Engineering of Contaminated Soils, editedby DonaldL. Wise,Debra J. Trantolo, Edward J. Cichon, Hilary I. Inyang, and Ulrich Stottmeister24. Handbook of Pollution Prevention Practices, Nicholas P. Cheremisinoff25. Combustion and Incineration Processes: Third Edition, Revised andExpanded, Walter R. NiessenAdditional Volumes in PreparationTomywife, DorothyAnne,whocontinuestoselesslyandunreservedlysupportmeinthisandallmyotherpersonalandprofessionalendeavorsPrefacetotheThirdEditionThe third edition of Combustion and Incineration Processes incorporates technologyupdatesandadditionaldetailoncombustionandairpollutioncontrol,processevaluation,design,andoperationsfromthe1990s.Also,thescopehasbeenexpandedtoinclude:(1)additional details andgraphics regardingthe designandoperational characteristics ofmunicipalwasteincinerationsystemsandnumerousrenementsinair pollutioncontrol,(2)theemergingalternativesusingrefusegasicationtechnology, (3)lower-temperaturethermalprocessingappliedtosoilremediation,and(4)plasmatechnologiesasappliedtohazardouswastes. Theaccompanyingdisketteoffersadditionalcomputertools.The1990sweredifcult forincineration-basedwastemanagement technologiesinthe United States. New plant construction slowed or stopped because of the anxiety of thepublic, fanned at times by political rhetoric, about the health effects of air emissions. Issuesincludedafocusonemissionsof air toxics(heavymetalsandaspectrumoforganiccompounds); softening in the selling price of electricity generatedin waste-to-energyplants; reduced pressure on land disposal as recycling programs emerged; and the openingof several newlandllsandsomedepressioninlandllingcosts. Also, thedecadesawgreat attention paid to the potential hazards ofincinerator ash materials (few hazards weredemonstrated, however). Thesefactorsreducedthecompetitivepressuresthat supportedburgeoningincineratorgrowthofthepreviousdecade.Chapters 13and14of this book, most importantly, give testimonytothegreatconcern that has been expressed about air emissions frommetal waste combustion(MWC). Thisconcernhasofteninvolvedstrongadversarial responsebyindividualsinpotential host communities that slowed or ultimately blocked the installation of newfacilitiesandgreatlyexpandedtherequireddepthof analysisandintensiedregulatoryagencyscrutinyintheair permittingprocess. Further, theconcernmanifesteditself inmore and more stringent air emission regulations that drove system designers toincorporatecostlyprocesscontrol features andtoinstall elaborateandexpensivetrainsofback-end airpollution controlequipment.A comparative analysis suggeststhat MWCsaresubjecttomoreexactingregulationsthanmanyotheremissionsources[506]. Thisisnot tosaythat environmental improvementsarewithout merit, but inthis instancethehighercoststothetaxpayersand=orthedogmaticeliminationofausefuloptionforsolidwastemanagementmaynotbejustiedbytheactualbenetsrealized.The situation inEurope has been quite different. Manyof the countries of theEuropean Community have passed legislation that greatly restricts the quantity and qualityofmaterialsconsignedtolandlls.InGermany,forexample,theClosedCycleEconomyLaw(reningtheWasteActof1986)raisedenergyrecoveryfromwasteincinerationtoalevelequaltothatofmaterialsrecyclinginthehierarchyofpreferenceinwastemanage-mentalternatives. Further,theirTechnicalDirective forResidualWasteseverelyrestrictedthelossonignitionof wastedestinedfor landll tolessthan5%andthetotal organiccarbon to less than 3%. These combined factors make incineration almost a requirement. Itmust be said, however, that Europeanair emissionrequirements are equal toor morestringent thantheircounterpartsintheUnitedStatesand, therefore, theincreaseduseofincinerationwillcomeataveryhighcost.Theincinerationcommunityhas respondedwell tothesetechnical, political, andeconomic challenges. Over the past 40 years, incineration technology, and its embodimentinprocessingplants, hasmovedfromitsprimitiveearlydaysasabonreinaboxtosophisticated,energyrecoverycombustionsystemswitheffectiveprocesscontrolcappedwith broad-spectrum andhighly efcientairpollutioncontrolsystemscapable ofmeetingstringentemissionstandards.Andimprovementsandenhancementscontinuetobemade.This bookhelpsengineersandscientists workinginthischallengingandcomplex eldtocontinuetheevolutionofthisfascinating, interdisciplinarytechnology.WalterR. NiessenPrefacetotheSecondEditionThesecondeditionofCombustionandIncinerationProcesseswaspreparedasanupdateandasasubstantialextensionoftherstedition. However,theunderlyingphilosophyofthe rst edition has been retained: a focus on the fundamentals of incineration andcombustionprocessesratherthanonspecicequipment.Therehave beenmanytechnicaladvancesinthe15yearssincethisbookrstappeared.Theapplicationofincinerationtothehazardouswasteareahasrequirednewlevelsofprocesscontrolandbetterandmorereliablecombustionperformance.Thereisnowaprofoundandpervasiveimpactofstateandfederal environmental regulations andguidelines ondesignandoperation. Conse-quently, air pollutant emission issues have assumed a dominant position in shaping systemcongurationandcost.The topics concerned with basic waste combustion processes (atomization, chemicalkineticsof pyrolysisandoxidation, mixing, etc.) havebeenexpanded. Applicationsarepresentedrelevant tohazardouswastesandtheirincinerationsystems. Analysismethodsand discussions of key design parameters for several additional incinerator types(especially forthose burning sludges, liquids, and gases) have been signicantly enlarged.Thesectionofthebookdealingwithtechniquesforwastedataanalysisandwastecharacterizationhas beensubstantiallyexpanded. This reects the stronginuence ofwastecompositionontheincinerationprocessandtheincreasedregulatoryattentionpaidto emissions of toxic, carcinogenic, and otherwise environmentally signicant traceelementsandcompoundsfoundinwastes(theairtoxics).The rst edition of Combustion and Incineration Processes focused on theincinerationof municipal solidwastes. Then, resourcerecovery(energyrecovery) wasemergingastheonlyincinerationconcept, whichmadeeconomicsenseforlargeplants.Ination had greatly increased capital and operating costs. An offset fromelectricalrevenuehadbecomecritical toviability. Technologythat fedas-receivedrefusetothefurnace (mass burn) was competing for attention with facilities that rst processed waste toarefuse-derivedfuel(RDF). Still, astheresearchsupportingthetextforthersteditionwasprepared, fewfacilitiesofeithertypewereoperatingintheUnitedStates. Datawasscant andmuchwastobelearned. Thistechnologyhasmaturedsincethen.TheCleanAir Act hadbeenlongpassedby1978andits provisions werefullyimplementedregardingthecontrol of municipal incinerators. However, onlytotal parti-culate emissions were regulated. Investigators in The Netherlands had reported thepresence of dioxin in the collected particulate of their local refuse incinerators; acidgas, heavy metal, or NOxcontrols were not incorporated into any municipal plant.However, overthepast 15years, regulatoryactions( publichearings, permits, approvals,mandateddesignandoperatingguidelines, etc.) haveassumeda dominant role inthedesign, cost, performance objectives, and implementation schedules of incinerationfacilities. Consequently, additional andupdatedmethodologiesarepresentedtoestimatepollutant emission rates. Also (but modestly and in keeping with the primary focus on theincinerationsystem), adiscussionofairpollutioncontroltechnologyhasbeenincluded.Theattentionofthepublicandthepoliticalandregulatoryestablishmentswerejustbeginningtofocusonhazardouswastes. TheResourceConservationandRecoveryAct(RCRA), whichmandatedthestructuredandrigorousmanagement ofhazardouswastes,was new. Its full scopeandrequirements werestill uncertain. PublicLaw96-510, theComprehensiveEnvironmental Response, Compensation, andLiabilityAct (CERCLA),better known as the Super-Fund Act, dealing with abandoned hazardous waste sites, hadnotyetbeenwritten.ThechallengestoincinerationofRCRAandCERCLAapplicationsare signicant. Emission mitigation using both sophisticated combustion control and back-endcontrolequipmentisofgreat interesttobothregulatorsandthepublic.I wouldliketoacknowledgethesupport givenbyCampDresser &McKeeInc.(CDM) in underwriting the preparation of many of the graphics incorporated in this editionand for their forbearance during the many months of manuscript preparation andrenement. I thankthemanyclients for whomI haveworkedover theyears for theircondence and, importantly, for their support as together we addressed theirproblems andlearnedmoreof incinerationtechnology. Finally, Iwant tothankthemanycolleaguesIhaveworkedwithover the yearsbothinside andoutside myemployers rm. Theirprofessionalsupportandhelphavebeenaconstant sourceofstimulation.WalterR. NiessenPrefacetotheFirstEditionPuricationbyreisanancientconcept,itsapplicationsnotedintheearliestchaptersofrecorded history. The art and the technology of combustion (incineration) and pyrolysis asappliedtoenvironmental engineeringproblemsdrawsonthisexperience, aswell astheresultsofsophisticatedcontemporaryresearch.Tomanyengineers,however,combustionsystems still hold an unnecessary mystery, pose unnecessary questions, and generateunnecessary mental barriers to their full exploitation as tools to solve tough problems. Thisbookwaswritteninanearnestattempttothinthecloudsofmystery,answermanyofthequestions (those for which answers are available), and provide a clearer way for theengineer toanalyze, evaluate, anddesignsolutionstoenvironmental problemsbasedoncombustion.Thebookdescribescombustionandcombustionsystemsfromaprocessviewpointinanattempttodevelopfundamentalunderstandingratherthanpresentsimplisticdesignequationsor nomographs. Inlargepart, thisapproachwasselectedbecausecombustionsystems are complex and not readily susceptible to cook-book design methods.Consequently, considerablespaceisdevotedtothebasics: describingthechemical andphysicalprocesseswhichcontrolsystembehavior.In an effort to make the book as comprehensive as possible, a large number of topicshavebeendealtwith.Specialistsinparticulareldsmayperhapsfeelthatthesubjectsinwhich they are interested have received inadequate treatment. This may be resolved in partbyexploringthenotedreferences, anactivityalsorecommendedtothenewcomertotheeld.Thepublicationofthisbookappearstimelysincecurrent trendsinenvironmentalawareness and regulatory controls will prompt increases in the use of combustiontechnologyas the preferredor onlysolution. Inlight of escalatingconstructioncosts,thesoaringexpenseanddiminishingavailabilityoffossil fuelsusedasauxiliaryenergysources (or the growing value of recovered energy), and the ever more stringent regulatoryinsistence on high performance regarding combustion efciency and=or air pollutantemissions, theblackboxapproachisincreasinglyunacceptabletothedesignerandtotheprospectiveowner.This book was prepared to meet the needs of many: students; educators; researchers;practicing civil, sanitary, mechanical, and chemical engineers; and the owners andoperators of combustion systems of all typesbut particularly those dealing withenvironmental problems. To serve this diverse audience, considerable effort has beenexpendedtoprovidereferencedata, correlations, numerical examples, andother aidstofullerunderstandinganduse.Last (but of the greatest signicance to me, personally), the book was writtenbecause I ndthe study andapplication of combustion tobe anexcitingandmind-stretchingexperience:everfascinatinginitsblendofpredictabilitywithsurprise(thoughsometimes, thesurprisesarecruel intheir impact). Combustionprocessesareandwillcontinue to be useful resources in solving many of the pressing environmental problems ofmodern civilization. I sincerely hope that my efforts to share both contemporarycombustiontechnologyandmysenseofexcitementintheeldwillassist inrespondingtotheseproblems.In the preparation of this book, I have drawn from a broad spectrum of the publishedliteratureandonthethoughts,insights,andeffortsofcolleagueswithwhomIhavebeenassociatedthroughout myprofessional career. I amparticularlygrateful for the manycontributions of mypast associates at Arthur D. Little, Inc. andat the MassachusettsInstitute of Technology, whose inspiration and perspiration contributed greatly to thesubstance of the book. Also, the many discussions and exchanges with my fellow membersof theIncinerator Division(nowtheSolidWasteProcessingDivision) of theAmericanSocietyofMechanicalEngineershavebeenofgreat value.I must specically acknowledge Professor Hoyt C. Hottel of MITwho introduced metocombustionandinspiredmewithhis brilliance, Mr. Robert E. Zinnof ADLwhopatientlycoachedandtaughtmeasIenteredtheeldofincineration,andProfessorAdelF. Sarom of MITwhose technical insights and personal encouragement have been a majorforceinmyprofessionalgrowth.I wouldliketoacknowledgethesupport givenbyRoyF. WestonInc. andCampDresser&McKeeInc.inunderwritingthetypingofthetextdraftsandthepreparationofthe art work. Particularly, I would thank Louise Miller, Bonnie Anderson, and JoanBuckley, whostruggledthroughthemanypages of handwrittentext andequations inproducingthedraft.WalterR. NiessenContentsPrefacetotheThirdEditionPrefacetotheSecondEditionPrefacetotheFirst Edition1. Introduction2. StoichiometryI. UnitsandFundamentalRelationshipsA. UnitsB. GasLawsC. EnergyII. SystemsAnalysisA. GeneralApproachB. AnalysesIII. Material BalancesA. BalancesBasedonFuelAnalysisB. BalancesBasedonFlueGasAnalysisC. Cross-CheckingBetweenFuelandFlueGasAnalysisIV. EnergyBalancesV. EquilibriumVI. CombustionKineticsA. IntroductiontoKineticsB. KineticsofCarbonMonoxideOxidationC. KineticsofSootOxidationD. KineticsofWastePyrolysisandOxidation3. SelectedTopicsonCombustionProcessesI. GaseousCombustionA. ThePremixed(Bunsen)LaminarFlameB. TheDiffusionFlameII. LiquidCombustionA. PoolBurningB. DropletBurningIII. SolidCombustionA. ThermalDecompositionB. ParticleBurningProcessesC. MassBurningProcesses4. WasteCharacterizationI. GeneralA. ChemistryB. HeatofCombustionC. AshFusionCharacteristicsD. SmokingTendencyII. SolidWasteA. SolidWasteCompositionB. SolidWastePropertiesIII. BiologicalWastewaterSludgeA. SludgeCompositionB. SludgeProperties5. CombustionSystemEnclosuresandHeatRecoveryI. EnclosuresA. RefractoryEnclosureSystemsB. Water-CooledEnclosuresandHeatRecoverySystemsII. HeatTransferA. ConductionB. ConvectionC. RadiationD. HeatTransferImplicationsinDesignIII. SlaggingandFouling6. FluidFlowConsiderationsinIncineratorApplicationsI. DrivenFlowA. JetFlowB. SwirlingFlowsII. InducedFlowA. JetRecirculationB. BuoyancyIII. MixingandResidenceTimeA. FundamentalDistributionRelationshipsB. CommonDistributionFunctionsC. FailureModesD. ResidenceTimeScenarios7. MaterialsPreparationandHandlingI. SolidWastesA. GeneralB. PitandCraneHandlingofSolidWastesC. SizeReductionofMunicipalSolidWastesD. ConveyingofSolidWastesE. SizeClassicationandScreeningF. FerrousMetalSeparationII. SludgeHandlingA. GeneralB. SludgePumpinginPipes8. IncinerationSystemsforMunicipalSolidWastesI. PerformanceObjectivesA. ThroughputandRefuseHeatContentB. TheFiringDiagram:TheOverallProcessEnvelopeC. PlantAvailabilityII. SiteDesignConsiderationsA. SiteGradingB. SiteDrainageC. SiteTrafcandRoadConsiderationsIII. CollectionandDeliveryofRefuseIV. RefuseHandlingandStorageA. TippingFloor-BasedWasteStorageandReclaimSystemsB. PitandCrane-BasedWasteStorageandReclaimSystemsC. BinStorageandReclaimSystemsforRDFV. SizeControlandSalvageVI. IncineratorFeedSystemsA. FeedSystemsforFloorDumpReceiptandStorageB. FeedSystemsforPitandCraneReceiptandStorageSystemsVII. GratesandHearthsA. StationaryHearthB. RotaryKilnC. StationaryGratesD. MechanicalGrates:BatchOperationsE. MechanicalGrates:ContinuousOperationsF. OConnerRotaryCombustor(Kiln)G. FluidBedSystemsVIII. IncineratorFurnaceEnclosuresA. RefractoryEnclosuresB. OtherEnclosure-RelatedDesignConsiderationsIX. EnergyMarketsandEnergyRecoveryA. MarketSizeB. MarketTypeC. MarketReliabilityD. RevenueReliabilityX. CombustionAirA. UnderreAirB. OverreAirC. SecondaryAirD. CombustionAirFansE. AirPreheatXI. AshRemovalandHandlingA. OverviewofAshProblemsB. AshPropertiesC. BottomAshD. SiftingsE. FlyAshF. MaterialsRecoveryfromAshXII. FlueGasConditioningA. CoolingbyWaterEvaporationB. CoolingbyAirDilutionC. CoolingbyHeatWithdrawalD. SteamPlumesXIII. EnvironmentalPollutionControlA. AirPollutionB. WaterPollutionC. NoisePollutionXIV. InducedDraftFanA. FanTypesB. InletandOutletConnectionsC. FanControlXV. IncineratorStacksXVI. Refuse-DerivedFuelSystemsA. RDFProcessingB. RDFCombustionSystemsXVII. InstrumentationandControlA. InstrumentationandControlSystemDesignApproachB. ProcessMeasurementsandFieldInstrumentsC. ControlSystemLevelsD. GeneralControlPhilosophyE. PortableInstrumentsF. SummaryXVIII. OperationsA. MassBurnIncinerationB. RDFIncineration9. IncinerationSystemsforSludgeWastesI. Multiple-HearthFurnace(MHF)SystemsA. ProcessCharacteristicsB. ProcessRelationshipsII. FluidBedSystemsA. ProcessCharacteristicsB. ProcessRelationships(OxidizingMode)C. OperatingCharacteristicsD. GeneralEnvironmentalConsiderationsIII. SlaggingCombustionSystemsforBiologicalSludgeA. KubotaSystemB. ItohTakumaSystem10. IncinerationSystemsforLiquidandGaseousWastesI. LiquidWasteIncineratorsA. LiquidStorageB. AtomizationC. IgnitionTilesD. CombustionSpaceE. IncineratorTypesII. IncineratorsforGases(Afterburners)A. EnergyConservationImpactsonAfterburnerDesignB. CurrentAfterburnerEngineeringTechnologyC. AfterburnerSystemsD. PotentialApplicationsIII. OperationsandSafety11. IncinerationSystemsforHazardousWastesI. GeneralA. ReceivingandStorageSystemsB. FiringSystemsC. ControlSystemsD. RefractoryE. AirPollutionControlforHazardousWasteIncineratorsF. EvaluationTestsandPOHCSelectionII. RotaryKilnSystemsA. SludgeIncinerationApplicationsB. SolidWasteIncinerationApplicationsIII. CirculatingFluidBedA. CFBHydrodynamicsIV. ThermalDesorptionA. SoilParametersB. ThermalDesorptionSystemsC. OperatingParametersD. RemediationPerformanceV. PlasmaTechnology12. OtherIncinerationSystemsforSolidWastesI. MultipleChamber(HearthorFixedGrate)II. MultipleChamber(MovingGrate)III. ModularStarvedAirIV. OpenPitTypeV. Conical(Tepee)TypeVI. GasicationProcessesforMSWA. GeneralB. GasicationofanRDFbyPartialCombustionC. GasicationofanRDFbyPyrolysisandSteamReforming(Battelle)D. GasicationofRawMSWbyPyrolysis13. AirPollutionAspectsofIncinerationProcessesI. AirPollutantsfromCombustionProcessesA. ParticulateMatterB. CombustibleSolids, Liquids, andGasesC. GaseousPollutantsRelatedtoFuelChemistryD. NitrogenOxidesII. AirToxicsA. MetalEmissionRatesB. EmissionsofOrganicCompounds14. AirPollutionControlforIncinerationSystemsI. EquipmentOptionsforIncineratorAirPollutionControlA. SettlingChambersB. CyclonesandInertialCollectorsC. WetScrubbersD. ElectrostaticPrecipitatorsE. FabricFilter(Baghouse)F. AbsorbersG. SpecializedAbatementTechnologyII. ControlStrategiesforIncineratorAirPollutionControlA. AirPollutionControlthroughProcessOptimizationB. ControlSelectionsforIncineratorTypesC. Continuous-EmissionMonitoringD. AirPollutionControltoAchieveAir-QualityObjectives15. ApproachestoIncineratorSelectionandDesignI. CharacterizetheWasteII. LayOuttheSysteminBlocksIII. EstablishPerformanceObjectivesIV. DevelopHeatandMaterial BalancesV. DevelopIncineratorEnvelopeVI. EvaluateIncineratorDynamicsVII. DeveloptheDesignsofAuxiliaryEquipmentVIII. DevelopIncineratorEconomicsA. GeneralIX. BuildandOperateAppendicesA. Symbols:APartial ListB. ConversionFactorsC. PeriodicTableofElementsD. CombustionPropertiesofCoal, Oil, NaturalGas, andOtherMaterialsE. PyrometricConeEquivalentF. Spreadsheet TemplatesforUseinHeat andMaterial BalanceCalculationsA. Heat andMaterial BalanceSpreadsheetsB. Heat ofCombustionCalculator:HCOMB.xlsC. MoistureCorrectioninRefuseAnalyses:Moisture.xlsD. EquilibriumConstant Estimation:Equil.xlsE. Steam.exeProgramG. ThermalStabilityIndicesNotesandReferences1IntroductionFormanywastes,combustion(incineration)isan attractive ornecessary elementof wastemanagement.Occasionally,asfortheincinerationof fumesoressentiallyash-freeliquidsor solids, combustion processes may properly be called disposal. For most solids and manyliquids, incineration is only a processing step. Liquid or solid residues remain forsubsequentdisposal.Incinerationofwastesoffersthefollowingpotentialadvantages:1. Volume reduction: important for bulky solids or wastes with a high combustibleand=ormoisturecontent.2. Detoxication:especiallyforcombustiblecarcinogens,pathologicallycontami-natedmaterial, toxicorganiccompounds, or biologicallyactivematerialsthatwouldaffectsewagetreatmentplants.3. Environmental impact mitigation: especiallyfor organicmaterials that wouldleach from landlls or create odor nuisances. In addition, the impact of the CO2greenhousegasgeneratedinincineratingsolidwasteislessthanthatofthemethane(CH4)andCO2generatedinlandllingoperations. Also, becauseofstrict air pollution emission requirements applicable to municipal refuseincinerators,thecriteriapollutantairemissionsperkilowattofpowerproducedaresignicantlyless thanthat generatedbythecoal- andoil-burningutilityplantswhoseelectricityisreplacedbywaste-to-energyfacilities(506).4. Regulatory compliance: applicable to fumes containing odorous or photo-reactive organic compounds, carbon monoxide, volatile organic compounds(VOCs), or other combustiblematerialssubject toregulatoryemissionlimita-tions.5. Energyrecovery: important whenlargequantities of wasteareavailableandreliablemarketsforby-productfuel, steam, orelectricityarenearby.6. Stabilization in landlls: biodegradation of organic material in a landll leads tosubsidenceandgasformationthatdisruptscellcappingstructures.Destructionofwasteorganicmattereliminatesthisproblem.Incinerationalsoformsoxidesorglassy,sinteredresiduesthatareinsoluble(nonleaching).7. Sanitation: destructionof pathogenicorganismspresentingahazardtopublichealth.These advantages have justied development of a varietyof incineration systems, ofwidely different complexity and function to meet the needs of municipalities andcommercialandindustrial rmsandinstitutions.Operatingcountertotheseadvantagesarethefollowingdisadvantagesofincinera-tion:1. Cost: usually, incineration is a costly waste processing step, both in initialinvestmentandinoperation.2. Operatingproblems: variabilityinwastecompositionandtheseverityof theincineratorenvironmentresultinmanypractical waste-handlingproblems, highmaintenancerequirements, andequipmentunreliability.3. Stafngproblems:thelowstatusoftenaccordedtowastedisposalcanmakeitdifculttoobtainandretainqualiedsupervisoryandoperatingstaff.Becauseof theaggressiveandunforgivingnatureof theincinerationprocess, stafngweaknesses can lead to adverse impacts on system availability and maintenanceexpense.4. Secondaryenvironmentalimpacts:Airemissions:manywastecombustionsystemsresultinthepresenceofodors,sulfur dioxide, hydrogen chloride, carbon monoxide, carcinogenic poly-nuclear hydrocarbons, nitrogenoxides, yashandparticulatefumes, andother toxicor noxiousmaterialsintheuegases. Control of emissionstoverylowlevelshasbeenshowntobewithinthecapabilityof modernairpollutioncontroltechnology.Waterborneemissions: water usedinwet scrubber-typeair pollutioncontroloften becomes highly acidic. Scrubber blowdown and wastewater fromresidue quenching may contain high levels of dissolved solids, abrasivesuspendedsolids, biological andchemical oxygendemand, heavymetals,and pathogenic organisms. As for the air pollutants, control of thesepollutants can be readily effected to discharge standards using availabletechnology.Residue impacts:residuedisposal (y ash and bottomash) presents a variety ofaesthetic, water pollution, andworker health-relatedproblems that requireattentioninsystemdesignandoperation.5. Publicsectorreaction:fewincineratorsareinstalledwithoutarousingconcern,close scrutiny, and, at times, hostilityor profoundpolicyconicts fromthepublic, environmental actiongroups, andlocal, state, andfederal regulatoryagencies.6. Technical risk: process analysis of combustors is verydifcult. Changes inwastecharacterarecommonduetoseasonal variationsinmunicipal wasteorproduct changesinindustrial waste. Theseandother factorscontributetotheriskthatanewincineratormaynotworkasenvisionedor,inextremecases,atall. In most cases, the shortfall in performance is realized as higher thanexpectedmaintenanceexpense,reducedsystemavailability,and=ordiminishedcapacity.Generally,changesinwastecharacterinvalidateperformanceguaran-teesgivenbyequipmentvendors.Withallthesedisadvantages, incinerationhaspersistedasanimportantconceptinwastemanagement. About 16%of the municipal solid waste and wastewater sludge wasincineratedintheUnitedStatesinthemid-1990s.Overtheyears,therateofconstructionofnewincinerationunitshasvariedgreatly. Keyfactorsinslowingconstructionincludehigh interest rates, cost escalation fromchanges in air pollution control regulations,recessioninuencesonmunicipal budgets, andsurgesinanti-incinerationpressurefromthe advocates of recycling. However, increasingconcernover leachate, odor, andgasgeneration and control in waste landlls (with consequent impacts on their availability andcost), regulatory and policy limitations on the landlling of combustible hazardous wastes,and increases in the value of energy suggest a continuing role ofincineration in the future,particularlyinEurope.Combustionprocesses are complicated. Ananalytical descriptionof combustionsystembehaviorrequiresconsiderationof1. Chemical reactionkineticsandequilibriumundernonisothermal, nonhomoge-neous, unsteadyconditions2. Fluidmechanics innonisothermal, nonhomogeneous, reactingmixtures withheat releasewhichcaninvolvelaminar, transitionandturbulent, plug, recircu-lating, andswirlingowswithingeometricallycomplexenclosures3. Heat transfer byconduction, convection, andradiationbetweengasvolumes,liquids, andsolidswithhighheat releaseratesand(withboilersystems)highheatwithdrawalratesInincinerationapplications,thiscomplexityisoftenincreasedbyfrequent,unpredictableshifts in fuel composition that result in changes in heat release rate and combustioncharacteristics(ignitiontemperature, air requirement, etc.). Compoundingtheseprocess-relatedfacets of waste combustionarethepractical designandoperatingproblems inmaterials handling, corrosion, odor, vector and vermin control, residue disposal, associatedairandwaterpollutioncontrol,andmyriadsocial,political,andregulatorypressuresandconstraints.With these technical challenges facing the waste disposal technologist, it is a wonderthatthestate-of-the-art has advancedbeyondsimple,batch-fed,refractoryhearthsystems.Indeed, incineration technology is still regarded by many as an art, too complex tounderstand.Theoriginsofsuchtechnicalpessimismhavearisenfrommanyfactsandpracticalrealities:1. Waste management has seldom represented a large enough business opportunityto support extensive internal or sponsored research by equipment vendors,universities, orresearchinstitutions.2. Municipal governments and most industries have had neither budgets norinclinationtofundextensiveanalysiseffortsaspartofthedesignprocess.3. As a high-temperature process carried out in relatively large equipment,incinerationresearchisdifcultandcostly.4. Thetechnicalresponsibilityforwastedisposalhasusuallybeengiventormsandindividualsskilledinthecivil andsanitaryengineeringdisciplines, eldswhere high-temperature, reacting, mixing, radiating (etc.) processes are not partofthestandardcurriculum.Such pessimismis extreme. To be sure, the physical situation is complex, but, drawing onthe extensive scientic and engineering literature in conventional combustion, theproblemscanbemadetractable. Thepractical realitythat pencil andpaper areever somuch cheaper than concrete and steel is an important support to the argument foraggressiveexploitationofthepowerofengineeringanalysis.The remainder of this volume attempts to bring a measure of structure andunderstanding to those wishing to analyze, design, and operate incineration systems.Although the result cannot be expected to answer all questions and anticipate all problems,it will give the student orpracticing engineer the quantitative and qualitative guidance andunderstandingtocopewiththisimportantsectorofenvironmentalcontrolengineering.The analytical methods and computational tools used draw heavily on the disciplinesofchemicaland,toalesserextent,mechanicalengineering.Asmanyreadersmaynotbefamiliarwiththetermsandconceptsinvolved,theearlychaptersreviewthefundamentalanalysis methodsof process engineering. Combustionandpyrolysis processes arethendiscussed, followed by a quantitative and qualitative review of the heat and uid mechanicsaspectsofcombustionsystems.Building on the basic framework of combustion technology, combustion-basedwaste disposal is then introduced: waste characterization, incinerator systems, designprinciples, andcalculations.2StoichiometryStoichiometry isthedisciplineof tracking matter(particularly theelements,partitioned inaccord with the laws of chemical combining weights and proportions) and energy (in all itsforms) in either batch or continuous processes. Sincethese quantitiesare conserved in thecourseofanyprocess, theengineercanapplytheprincipleofconservationtofollowthecourseofcombustionandowprocessesandtocomputeairrequirements,owvolumes,andvelocities, temperatures, andother useful quantities. Asarenement, theengineershouldacknowledgethefact that somereactionsandheat transfer processessometimesstopshortofcompletionbecauseofequilibriumlimitations.Also,forsomesituations,thechemicalreactionratemaylimitthedegreeofcompleteness, especiallywhensystemresidencetimeisshortortemperaturesarelow.I. UNITSANDFUNDAMENTALRELATIONSHIPSA. UnitsIn analyzing combustion problems, it is advantageous to use the molecular (atomic) weightexpressedinkilograms(thekilogrammol or kilogramatom) astheunit quantity. Thisadvantagederivesfromthefactsthat onemolecular (atomic) weight of anycompound(element) containsthesamenumber of molecules(atoms) andthat eachmol of gas, atstandardpressureandtemperature, occupiesthesamevolumeifthegasesareideal.Theconcept of anideal gas arises inthecourseof thermodynamicanalysis anddescribes agas for whichintermolecular attractions arenegligiblysmall, inwhichtheactual volumeof themoleculesissmall incomparisonwiththespacetheyinhabit andwhereintermolecularcollisionsareperfectlyelastic.B. GasLaws1. ThePerfectGasLawThebehaviorofidealgasesisdescribedbyEq. (1a), theperfectgaslaw:PV nRT 1aInthisrelationshipPistheabsolutepressureofthegas, Vitsvolume, nthenumberofmols of gas, R the universal gas constant, and Tthe absolute temperature. Note that 273.15mustbeaddedtotheCelsiustemperatureand459.69totheFahrenheittemperatureto gettheabsolutetemperatureindegreesKelvin(

K)ordegreesRankine(

R), respectively.Theperfectgaslawwasdevelopedfromasimpliedmodelofthekineticbehaviorof molecules. The relationship becomes inaccurate at very lowtemperatures, at highpressures, andinothercircumstanceswhenintermolecularforcesbecomesignicant. Intheanalysisofcombustionsystemsatelevatedtemperaturesandatatmosphericpressure,theassumptionof idealgasbehaviorissound.ThesamevalueoftheuniversalgasconstantRisusedforallgases. Caremustbegiven to assure compatibility of the units of Rwith those used for P; V; n, and T.CommonlyusedvaluesofRaregiveninTable1.Inthemechanicalengineeringliterature,oneoftenndsagaslawinuse wherethenumerical value of the gas constant (say, R0) is specic to the gas under consideration. Thegas constant in such relationships is usually found to be the universal gas constant dividedby the molecular weight of the compound. In this formulation of the gas law, the weight wratherthanthenumberofmolsofgasisused:PV wR0T 1bEXAMPLE 1. Ten thousand kg=day of a spent absorbent containing 92% carbon, 6%ash, and2%moistureistobeburnedcompletelytogeneratecarbondioxideforprocessuse. The exit temperature of the incinerator is 1000

C. How many kilogram mols and howmany kilograms of CO2will be formed per minute? How many cubic meters per minute atapressureof1.04atm?One must rst determine the number of kilogramatoms per minute of carbon(atomicweight 12.01)owinginthewastefeed:0:92 10;000=12:01 24 60 0:532 kg atoms=minTable1 ValuesoftheUniversalGasConstantRforIdealGasesPressure Volume Mols Temperature GasconstantEnergy P V n T R atm m3kg mol

K 0:08205m3atmkg mol K kPa m3kg mol

K 8:3137kPa m3kg mol Kkcal kg mol

K 1:9872kcalkg mol Kjoules(abs) g mol

K 8:3144joulesg mol Kft-lb psia ft3lb mol

R 1545:0ft lblb mol RBtu lb mol

R 1:9872Btulb mol R atm ft3lb mol

R 0:7302ft3atmlb mol RNoting that with complete combustion each atom of carbon yields one molecule of carbondioxide, the generation rate of CO2is 0.532 kg mol=min. The weight owof CO2(molecularweight 44.01)willbe(0.532)(44.01) 23.4kg=minofCO2.Thetempera-ture(

K)is1000 273:15 1273:15, andfromEq. 1.V nRTP0:532 0:08206 1273:151:04 53:4 m3=min CO2In combustion calculations, one commonly knows the number of mols and the temperatureandneedstocomputethevolume. For thesecalculations, it isconvenient toobtaintheanswerbyadjustingaunit volumeat aspeciedstandardconditiontotheconditionsofinterest. For such calculations one can use the gas laws expressed in terms of the volume of1kgorlbmol ofanideal gasat thestandardconditionsof0

Cor273:15

K(32

For492

R) and 1 atm. The molecular volume is 22:4 m3(359:3 ft3). If we denote the molecularvolumeas V0, andthe pressure andtemperature at standardconditions as P0andT0,respectively,thegaslawthenyields:V n V0P0PTT02whereP0andT0maybeexpressedinanyconsistentabsoluteunits.Forexample,thegasvolumefromtheprecedingexamplecouldbecalculatedasV 0:532 22:4 1:001:041273:15273:15 53:41 m3=min CO2Daltonslaw(1801)ofpartial pressuresisanotheruseful identityderivedfromtheidealgas law. Daltons law states that the total pressure of a mixture of gases is equal to the sumof the partial pressures of the constituent gases, where the partial pressure is dened as thepressureeachgaswouldexertifitaloneoccupiedthevolumeofthemixtureatthesametemperature. For a perfect gas, Daltons lawequates thevolumepercent withthemolpercent andthepartialpressure:Volume percent 100 mol fraction 100partial pressuretotal pressure3EXAMPLE2. Fluegasesfromcombustionof14.34 kgofgraphite(essentially,purecarbon)withoxygenareatatemperatureof1000

Candapressureof1.04 atm.Whatisthevolumeinm3oftheCO2formed?Whatisitsdensity?V 14:3412:0122:4 1:01:041000 273:15273:15 119:87 m3For eachmol of CO2formed, themass is 12.01 32.00, or 44.01 kg(seeTable1inAppendixCforatomicweights). ThegasdensityundertheseconditionsisrCO244:1222:4 1:01:041000 273:15273:15 0:438 kg=m3EXAMPLE3. Thecarbonmonoxide(CO) concentrationinauegasstreamwith10%moistureat 500

Cand1.05 atmismeasuredat 88.86partspermillionbyvolume.Doesthismeettheregulatorylimitof100 mgpernormalcubicmeter(Nm3),establishedby the regulation as being a dry basis at 0

C and 1.0 atm? Adjustment to the temperature orpressureconditionsoftheregulatorylimitdoesnotchangethemolfractionofCOinthegas. TheCOconcentrationcorrespondingtotheregulatorylimit underdryconditionsiscalculatedas(88.86)(1.0 0.1), or79.97partspermillion, dryvolume(ppmdv).The volume of one kilogrammolof anygas at 0

Cand 1.0 atmis22.4 m3. For CO,withamolecularweightof28.01,themassofonemolis28:01 106mg.Therefore,themassconcentrationofCOintheuegasesisgivenbyCO 79:97 10628:01 10622:4 100:0 mg=Nm32. StandardConditionsThroughoutthepublishedliterature,inregulatorylanguage,inindustrialdatasheets,etc.,onefrequentlyndsreferencestothetermstandardconditions. Whilethewordsimplystandardization, itshouldbecautionedthatthemeaningisnotatallconsistent.Forexample, owcalculationsbyU.S. fanmanufacturersandtheU.S. natural gasindustry are referenced to 60

F 15:6

C), and 1 atm (29.92 in Hg or 14:7 lb=in:2absolute).The manufacturedgas industryuses 60

F, saturatedwithwater vapor at 30 in. of Hgabsolute, formarketingbut60

Fdryat1 atmforcombustioncalculations.Other important appearances of thetermstandardconditions arefoundinthecalculationsandreportsassociatedwithpermitsforatmosphericdischarges.Thestandardconditions in which to report stack gas ows in the United States are often based on 20

C(68

F)and1 atm.Thereferencestatesusedtospecifyandreporttheconcentrationof pollutantsinairpollutionregulationsandpermitsoftengenerateanothersetofstandardconditions.IntheUnited States, this may involve the calculation of volume in standard cubic feet (scf) at areference temperature of 32

Fand 1 atm. In Europe, the metric equivalent (0

Cand1.0 atm)isusedtocharacterizethenormalcubicmeter,orNm3.Forparticulatematterandtheconcentrationsofgaseouspollutants, thereferencevolumeiscommonlyfurthercorrectedtoaspeciedconcentrationofoxygen(usually7%O2intheUnitedStatesbut11%O2inEuropeandAsia)orcarbondioxide(usually12%CO2)bythemathematicaladdition=subtractionofoxygenandnitrogenintheproportionsfoundinair.As an alternative to specifying the oxygen or carbon dioxide concentration atstandardconditions,someagenciescallforadjustmenttoa speciedpercent excess air(thecombustionair suppliedinexcessofthetheoretical air requirement expressedasapercentage of the theoretical air). Further correction may be required to express theconcentrationonadrybasis.Inmostrealsituations,thegastemperature,pressure,andstateofdrynessarequitedifferent from the standard conditions requested. In these circumstances, the perfect gaslawanditsextensions(e.g., Daltonslaw)areusedtomakethecorrections.EXAMPLE4. Asampleweight of 76 mgof particulatematter is collectedinthecourseof sampling 2.35 actualm3of ue gas at 68

C and 1.03 atm. The ue gas contains12.5%moisture. AnOrsat (drybasis) analysisof thegasesshows10.03%oxygenand10.20%carbondioxide.Theairpollutioncodeemissionlimitis60 mg=Nm3correctedto7%oxygen.Theemissioncodedenesnormalcubicmeter(Nm3)as0

Cand1.0 atm.Isthesourceinconformancewiththecode?What ifthecodereferencedacorrectionto12%carbondioxide?Orto50%excessair?CorrectthegasvolumetoreferencetemperatureandpressureusingEq. (2).V 2:35273:15 0:0273:15 68:0 1:001:03 1:827 m3wetCorrectgasvolumetodrybasis.corrected volume 1:8271:00 0:125 1:598 Nm3dryCalculategasvolumeanddustconcentrationatreferenceO2concentration.CO221:0 measured %O221:0 reference %O2Thegasvolumeat7%O2iscalculatedwiththecorrectionfactorCO2.CO221:0 10:0321:0 7:04HereCO2 0:784, andthecorrectedgasvolumeis1:5980:784 1:252 Nm37% O2Theparticulateconcentrationis, then,76=1:252 60:7 mg=Nm3at 7% O2fails the emission codeCalculatedustconcentrationatreferenceCO2concentration.Thegasvolumeat12%CO2iscalculatedwiththecorrectionfactorCCO2.CCO2measured % CO2reference % CO210:212:005Therefore, CCO2 0:85, andthecorrectedvolumeis1:5980:85 1:358 Nm312% CO2Theparticulateconcentrationis, then,76=1:358 56:0 mg=Nm3at 12% CO2passes the emission codeCalculatedust concentrationatreferenceexcessair.By difference, the nitrogen concentration (dry) 100:00 10:2 10:03 79:77%. Acorrection factor (CF50) may be developed that adjusts the gasvolumefromaninitial conditionwithO2, N2, andCOvolume(mol) percentoxygen, nitrogen, and carbon monoxide (dry basis), respectively, to the gasvolume at 50% excess air. The accuracy of the factor dependson theassumptionofnegligiblenitrogencontentforthefuel.CF50 21:1 1:5 O20:75 CO 0:132 N221:16Here, CF50 0:786, andthecorrectedvolumeis1:5980:786 1:256 Nm3at 50% excess airTheparticulateconcentrationis, then,76=1:256 60:5 mg=Nm3at 50% excess air fails the requirementC. EnergyInthis chapter, the basic unit of heat energywill be the kilogramcalorie (kcal): thequantityof heat necessarytoraise the temperature of 1 kgof water 1

C. The BritishThermal Unit (Btu), the energy required to raise the temperature of 1 lb of water 1

F, is thecomparable energy quantity in English units. Commonly used conversion factors are1 kcal 4186.8joulesor3.968Btu;1kcal=kg 1.8 Btu=lb;1Btu 1055.1joules,and1 Btu=lb 2326joules=kg. (SeealsoAppendixB.)1. HeatofReactionThe heat of reactionis denedas the net enthalpychange resultingfroma chemicalreaction. Theenergyeffect canbenetenergyrelease(anexothermicreaction)orenergyabsorption (an endothermic reaction). The heat of reaction may be calculated as thedifference in the heat of formation (DH298) between products and reactants. Heat offormation (tabulated in many handbooks) is the heat effectwhen the compound is formedfromits constituent elements intheir standardstates (usually298:15

K, at 1 atm). Forexample:C graphite O2 gas !CO2 gas DH298 94:03 kcalH2 gas 12O2 gas !H2O liquid DH298 68:30 kcal12H2 gas 12I2 solid !HI gas DH298 5:95 kcalHeat is givenoff bythe rst two(exothermic) reactions. Byconvention, the heat offormationfor exothermic reactions is negative. Inthe formationof gaseous hydrogeniodide(HI) fromits elements, thereactionabsorbs energy(endothermic) andDH298ispositive. Note, however, that in some of the older thermochemical literature, thisconventionisreversed.It isimportant tonotethat, bydenition, theheat offormationoftheelementsintheirstandardstatesiszero.Usefulheatof formation values(expressedinkcal=grammolat25

C)includethoselistedinthefollowingtable:Substance DH298Substance DH298CO2g94:03 COg26:4H2OI68:3 C2H6l23:4SO2g70:2 CH3OHl60:0NH3g11:0 C2H5OHl66:2HClg22:06 CHCl3l31:5For the special case where the reaction ofinterest is oxidation at elevated temperatures, werefer totheheat effect astheheat of combustion. Theheat of combustionfor carbon-hydrogen- andoxygen-basedfuels andwastestreams is, clearly, thereleaseof energywhenthesubstance(s) reactscompletelywithoxygentoformCO2andH2O. Thisheatrelease may be calculated as the difference between the heats of formation of the productsandreactants.TheheatofcombustionforcompoundscontainingN,S,Cl, P,etc.,maybecalculated similarly, but the results may be unreliable due to the uncertainty in the speciccompoundsformed.EXAMPLE 5. Using the heat of formation (DHf) data given above, calculate the heatofcombustion(DHc)ofethylalcohol(C2H5OH)andchloroform(CHCl3).Ethylalcoholburnsasfollows:C2H5OH 3O2 !2CO23H2ODHc DHf products DHf reactants 294:03 368:3 166:2 30:0 326:76 kcal pergram molecularweight GMWForamolecularweightof46, thiscorrespondsto 7:1035 kcal pergram 7103:5 kcal=kg 12;786 Btu=lbChloroformmayburn(a) CHCl332O2 !CO212H2O 32Cl2or(b) CHCl3O2 !CO2HCl Cl2Forreaction(a), DHc 96:68 kcal=GMWForreaction(b), DHc 84:59 kcal=GMWLiteraturevalue: DHc 89:20 kcal=GMWA valuefortheheat ofcombustionofthefeedmaterial isoftenneededwhileanalyzingcombustionsystems. Forthecompletecombustionofmethane, thereactionisCH4g 2O2g !CO2g 2H2O l 212;950 kcalThisshowsthat1 kgmolofmethaneisoxidizedby2 kgmolofoxygen toform1 kgmolof carbon dioxide and 2 kg mol of water; 212,950 kcal of heat are released. The subscriptsg, l, and s denote the gaseous, liquid, and solid states of reactants or products, respectively.Apressureof1 atmandaninitial andnal temperatureofthereactantsandproductsof298.15 K(20

C)isassumed, unlessotherwiseindicated.The heat of combustion given in this manner (with the water condensed) is known asthehigherheatingvalue(HHV).TheHHV isthecommonwaytoreportsuchdataintheU.S.andBritishliterature.Clearly,however,inarealfurnace,thesensible heatcontentofthe ue gases will be lowerthan would be suggested by the HHV by an amount of energyequivalent tothelatent heat of vaporizationof thewater (10,507 kcal=kgmol at 25

C).Thiscorrespondsto21,014 kcal=kgmol of methane. Thus, theso-calledlowerheatingvalue(LHV)correspondstoCH4g 2O2g !CO2g 2H2Og 191;936 kcalTheLHVistheenergyreleasevaluecommonlyreportedintheliteratureofcontinentalEuropeandAsia.Forafuelwithadrybasishydrogencontentof%H2(expressedasapercent), theHHV andLHV(drybasis)arerelatedbyLHV HHV 94:315 %H2 forLHV; HHV in Btu=lb and 7aLHV HHV 52:397 %H2 forLHV; HHV in kcal=kg 7bEXAMPLE6. TheChineseliteraturereportstheheatingvalueofamunicipalrefusefromtheBeijingareaas1800 kcal=kg(asred). Themoisturecontent ofthewastewas37%, and the hydrogen content of the waste (on a dry basis) was 3.69%. How do these datasuggestthattheheatingvalueoftheChinesewastecompareswithwasteburnedinNewYorkCity, whichisoftenreportedtohaveaheatingvalueofabout6300 Btu=lb?As is common in such problems, there is ambiguity in the basis (wet or dry and LHVor HHV) of the two heating values. Most likely, the Chinese are reporting an LHVand theNew York heatingvalueisan HHV.A quickreview of thedatain Chapter4 suggeststhatmostU.S.refusehasanas-red(wetbasis)heatingvaluebetween4500and5500Btu=lb(2500to3050 kcal=kg), sotheNewYorknumberisprobablyonadrybasis. Assumingthesereferenceconditions.ThedrybasisLHV oftheChinesewasteisLHV 18001 0:37 2857 kcal=kgThedrybasisHHV oftheChinesewasteisHHV 2857 52:397 3:69 3050 kcal=kg or5491 Btu=lbTherefore, theChinese wastehasabout85% oftheheatingvalueoftheNew Yorkrefuse.Also,onemightspeculatethattheNewYorkrefuseisabout2025%moisture,sotheas-red(wetbasis)heatingvalueisabout70%ofthatfortheNewYorkwaste.This example problem vividly illustrates the difculties and consequent uncertaintiesintheresultsthatariseduetoincompletespecicationoftheintendedbasisforphysicaland thermochemical properties. This emphasizes the importance of making the basis clearin professional publications, instructions to laboratories, specications for equipmentvendors, andsoforth.2. SensibleHeatofGasesIn analyzing combustion systems it is often necessary to calculate the sensible heat content(enthalpy) of gases at elevated temperatures or to determine the change in enthalpybetween two temperatures. To make such calculations, one can draw on the approximationthat Mcp, the molal specic heat at constant pressure (in units of kcal=kg mol

C which is,incidentally, numerically identical to Btu=lb mol

F), is a function of temperature only andasymptoticallyapproaches avalue Mc

pas thepressure approaches zero. The enthalpychange(Dh)betweentemperaturelimitsT1andT2isthengivenbyDh T2T1McopdTkcal=kg mol 8ThiscalculationmaybecarriedoutusingananalyticalrelationshipforMc

pasafunctionoftemperature.ConstantsforsuchrelationshipsaregiveninTable2forseveralcommongases. Alternatively, one can use a graphical presentation of the average molal heatcapacitybetweenareferencetemperatureof 15

C(60

F) andtheabscissatemperature(Fig. 1). Theaveragemolalheatcapacityiscalculatedandusedasfollows:Mc0p;av T15Mc0pdTT 159Dh nMc0p;avT 15 kcal 10EXAMPLE 7. What is the sensible heat content of 68 kg of carbon dioxide at 1200

Crelativeto15

C?Howmuchheat must beremovedtodropthetemperatureto300

C?First,determinethenumberofmolsofCO268=44 1.55mols.FromTable2,theheatcontentat1200

Cisgivenby:Dh 1:551200159:00 7:183 103T 2:475 106T2dt 1:55 9T 7:183 103T222:475 106T33 !120015 22;340 kcalTable2 ConstantsinMolal Heat Capacity Mcop Relation-shipwithTemperature Mcop a bT CT2aCompound a b cH26.92 0:153 1030:279 106O26.95 2:326 1030:770 106N26.77 1:631 1030:345 106Air 6.81 1:777 1030:434 106CO 6.79 1:840 1030:459 106CO29.00 7:183 1032:475 106H2O 7.76 3:096 1030:343 106NO 6.83 2:102 1030:612 106SO29.29 9:334 1036:38 106HCl 6.45 1:975 1030:547 106HBr 6.85 1:041 1030:158 106Cl28.23 2:389 1030:065 106Br28.66 0:780 1030:356 106CH48.00 15:695 1034:300 106A similar calculation for an upper limit of 300

C yields 4370 kcal and a net heat extractionof22,340 4370 17,970kcal. Alternatively, usingFig. 1, theheatcontentat1200

Cis:1:5512:31200 15 22;600 kcalandat300

C, is1:5510:1300 15 4460 kcalFigure 1 Average molal heat capacity between 15

C and upper temperature (Btu=lb mol, Kcal=kgmol). (Courtesy, ProfessorH.C. Hottel, ChemicalEngineeringDepartment, M.I.T.)Theapproximateheatlossbetween1200

and300

Cis18,140kcal.3. SensibleHeatofSolidsKopps rule [Eq. (11)] (432) can be used to estimate the molar heat capacity (Mcp) of solidcompounds. KoppsrulestatesthatMcp 6n kcal=kg mol C 11wherenequalsthetotalnumberofatomsinthemolecule.Building on Kopps rule, Hurst and Harrison (433) developed an estimationrelationshipfortheMcpofpurecompoundsat25

C:Mcp Pni1NiDEikcal=kg mol C 12wherenisthenumberofdifferentatomicelementsinthecompound,Niisthenumberofatomicelementsiinthecompound,and DEiisthe valuefromTable3fortheithelement.Voskoboinikov(391)developedafunctionalrelationshipbetweentheheatcapacityofslagsCp(incal=gram C)andthetemperatureT

C)givenasfollows.Fortemperaturesfrom20

to1350

C:Cp 0:169 0:201 103T 0:277 106T20:139 109T30:17 104T1 CaO=S 12awhere S is the sum of the dry basis mass percentages SiO2Al2O3FeOMgO MnO.Fortemperaturesfrom1350

to1600

C:Cp 0:15 102T 0:478 106T20:876 0:0161 CaO=S 12bFor many inorganic compounds (e.g., ash), a mean heat capacity of 0.2 to 0.3 kcal=kg

C isareasonableassumption.Table3 AtomicElementContributionstoHurstandHarrisonRelationshipElement DEiElement DEiElement DEiC 2.602 Ba 7.733 Mo 7.033H 1.806 Be 2.979 Na 6.257O 3.206 Ca 6.749 Ni 6.082N 4.477 Co 6.142 Pb 7.549S 2.953 Cu 6.431 Si 4.061F 6.250 Fe 6.947 Sr 6.787Cl 5.898 Hg 6.658 Ti 6.508Br 6.059 K 6.876 V 7.014I 6.042 Li 5.554 W 7.375Al 4.317 Mg 5.421 Zr 6.407B 2.413 Mn 6.704 Allother 6.3624. LatentHeatThechangeinstateofelementsandcompounds,forexample,fromsolid(s)toliquid(l),or fromliquid(l) togas(g), isaccompaniedbyaheat effect: thelatent heat offusion,sublimation, or vaporization for the state changes (s)!(l), (s)!(g), and (l)!(g),respectively.Latentheateffectsinmanyindustrialprocessesarenegligible.Forexample,the heat of vaporization of fuel oil is usually neglected in combustion calculations.Particularly for incinerator design calculations involving wastes or fuels with a highhydrogen content and=or high moisture content, latent heat effects are very signicant. Forreference, severallatentheatvaluesaregiveninTable4.5. DecompositionandIonizationCombustionandincinerationsystems oftenexperience temperatures highenoughthatsomecompoundsdecomposeintoseveral simpler fragments. Thedecompositionisnotnecessarily associated with oxidation reactions and often reects the breakage of chemicalor ionic bonds inthe compounds purelyunder the inuence of heat. These reactionsinclude thermal degradation reactions of organic compounds, thermal decompositionreactionsof inorganiccompounds, andionization.Thethermaldegradationoforganiccompoundsisacommonandimportantstepinthe combustionprocess. Degradationcaninvolvesimple ruptureof bonds inducedbyelevated temperature (pyrolysis). This is, often, an endothermic reaction. In some physicalsituations(starvedairincineration), partial oxidationtakesplace, generatingheat thattriggerspyrolysisreactionsinpartofthecombustiblematerial.Dependingonthebalancebetween pyrolytic and oxidative reactions, the overall heat effect can be either endothermicor exothermic. This important class of decomposition reactions is covered in detailelsewhereinthisbook.Thermal degradation of inorganic compounds can introduce important energyeffectsinsomecombustionandincinerationprocesses. Also, thedecompositionprocessmay involve the shift of all or a portion of the mass of the compound to another phase. Anindustrially important example of such a reaction is the decomposition of calciumcarbonate(limestone)toformlime(solidcalciumoxide)andcarbondioxide(agas).Table4 LatentHeatEffectsforChangesinStateofCommonMaterialsLatentheatof indicatedstatechangeTemperatureMaterial Statechange

C (kcal=kg) (kcal=kg mol) (Btu=lb)Water Fusion 0 80 1435 144Water Vaporization 100 540 9712 971Acetone Vaporization 56 125 7221 224Benzene Vaporization 80 94 7355 170i-Butylalcohol Vaporization 107 138 12,420 248n-Decane Vaporizatioin 160 60 8548 108Methanol Vaporization 65 263 12,614 473Turpentine Vaporization 156 69 9330 123Zinc Fusion 419 28 1839 51In reviewing published data on the decomposition temperature of chemicalcompounds, onemust recognizethat decompositiondoes not suddenlytakeplaceat adiscretetemperature, but, infact, is occurringtosomedegreeat all temperatures. Thedegreeandrateofdecompositionareoftenstronglytemperature-dependent.Atanygiventemperature, the concentration(chemical activity) of the reactants and products tendstowardor achievesaspecicrelationshiponetoanother asdenedbytheequilibriumconstant(discussedinSectionV ofthischapter).Taking limestone decomposition as an example, at any instant of time somemolecules of calcium carbonate are breaking apart, releasing gaseous CO2. Also, however,CO2from the environment is reacting with calcium oxide in the solid matrix to reform thecalciumcarbonate. The equilibriumpartial pressure of CO2over the solid and thedecompositionratearefunctionsoftemperature.Asthetemperatureincreases,thepartialpressure of CO2increases. The approximate decomposition temperatures in Table 5correspondtoapartialpressureof1 atmofthepertinentgaseousproduct.At veryhightemperatures (>2500

C), other classes of decompositionreactionsoccur: thethermal breakdownofpolyatomicgases(e.g., O2andN2intoatomicoxygenandnitrogen)and,atstillhighertemperatures,ionization.Thesereactionsareconnedtotheveryhighest temperatureoperations. However, theycanhavesignicance(throughtheirstronglyendothermicheat effect)inaffectingthepeaktemperatureattainedandongas composition for ames of pure fuels under stoichiometric conditions or withsignicant air preheat or oxygenenrichment. Inincinerationsituations whenmoisture,excessair,orotherfactorstendtofavorloweroperatingtemperatures,thesereactionsareusually unimportant. As for the decomposition reactions, the course of dissociationreactions as the temperature changes is described by equilibriumrelationships. ThedissociationcharacteristicsofatmosphericgasesarepresentedinTable6.6. KineticandPotential EnergyInconcept,afractionoftheheatofcombustioninfuelsandwastescanbeconvertedintokinetic (velocity) and potential (pressure or elevation) energy. Clearly, such a conversion isessential totheoperationof rocket engines, gas turbines, andother highlyspecializedcombustors. Forthe facilitiesofimportance in this book, these energy terms are generallyunimportant.Table5 DecompositionTemperaturesofSelectedCompounds(

C)Material Solid Gaseous TemperatureCaCO3CaO CO2897CaSO4-2H2O CaSO4-0.5H2O 1.5H2O 128CaSO4-0.5H2O CaSO40.5H2O 163Ca(OH)2CaO H2O 580Al(OH)3-nH2O 2H2O 300Fe(OH)3-nH2O 1.5H2O 500Fe2(SO4)3Fe2O33SO3480NaHCO3NaOH CO2270Na2CO3Na2O CO222457. HeatLossesUsually, the largest energy losses from a combustion system are the sensible heat (dry gasloss) and latent heat (moisture loss) of the ue gases. The sensible heat loss is scaled by thestackgastemperature.Latentlossesincludetheheatofevaporationofliquidwaterinthefeed plus that of the water formed by oxidation of feed and fuel hydrogen. These losses areunavoidable, but theymaybeminimized. Drygaslossisreducedthroughtheuseofaneconomizer and=or air heater inenergyrecoverysystemstoextract thelargest possiblequantity of useful heat from theue gases before discharge. Moisture loss can be reducedthrough the removal of excess water from the feed (e.g., the dewatering of sewage sludge).Asecondcategoryof heat loss isassociatedwiththefuel energythat leavesthesystem as unburned combustible in solid residues and as fuel gases (CO, CH4, H2, etc.) inthestackgas.Unburnedcombustibleoftenresultsfromlowtemperaturesinzonesofthecombustor.Toachieverapidandcompleteburnout,hightemperaturesandtheassociatedhighoxidationreactionratesarenecessary. Excessivemoistureinthefeedmaypreventattainment of thesetemperatures. Also, rapidcoolingthatquenches combustionreac-tions mayoccur due toin-leakage of air (trampair inltration) or bythe passage ofcombustion gas over heat-absorbing surfaces (cold, wet feed in countercurrent owsystems, boiler-tubesurfaces, etc.).Also, combustible may not be completely oxidized because of air supply decienciesor ineffective mixing. Inadequate mixing leads, for example, to the appearance ofunburned hydrocarbons and carbon monoxide in the off-gas froma rotary kiln. Thebuoyancy-stabilized, stratiedowintheseunitsoftenresultsinhightemperaturesandoxygen deciency at thetop of thekiln and abundantoxygen at much lowertemperaturesowingalongthebottomofthekiln.Acombination of the lowtemperature and the air insufciency mechanisms isresponsible for the incomplete burnout of massive combustible such as stumps, mattresses,orthickbooksandfortheincompleteburningoflargemetal objects. Inthesecases, theslowdiffusionofheatandoxygenthroughthickashorcharlayersresultsinincompleteoxidationbeforetotalquenchingofcombustionintheresiduedischargesystem.The third cause of unburned combustible is (often inadvertent)short transit times inthe combustor. Examples of this mechanisminclude the material that falls, unburned,throughthegratesofamassburnincineratorortheunburnedpaperfragmentsswepttooquicklyoutofarefuse-derivedfuel(RDF)incineratorbytherisingcombustiongases.Table6 DissociationBehaviorofSelectedMoleculesTemperature % HeateffectReaction

C Dissociation (kcal=mol)O2 $2 O 2725 5.950 117,500N2 $2 N 3950 5.000 H2 $2 H 2200 6.500 102,200H2O $H20:5 O21750 0.370 68,3902200 4.100CO2 $CO 0:5 O21120 0.014 68,0001540 0.4002200 13.500Radiation loss is the expression used to describe the third major heat loss: leakage ofheat intothe surroundings byall modes of heat transfer. Radiationlosses increase inproportion to the exposed area of hot surfaces and may be reduced by the use ofinsulation.Since heat loss is area-dependent, theheat loss (expressedas percentageof total heatrelease)generallyincreasesasthetotalheatreleaseratedecreases. TheAmericanBoilerManufacturersAssociationdevelopedadimensional algorithm[Eq. (13)]withwhichtoestimateheatlossesfromboilersandsimilarcombustors(180). Theheatlossestimateisconservative(high)forlargefurnaces:radiation loss 3:6737C HR CFOP 0:6303ekWtype13wherefortheradiationlosscalculatedinkcal=hr(orBtu=hr):C constant:1.0forkcal=hr(0.252forBtu=hr)HR designtotalenergyinput(fuel wasteheatofcombustion airpreheat)inkcal=hr(orBtu=hr)FOP operatingfactor(actualHRasdecimalpercentofdesignHR)k constantdependentonthemethodofwallcoolingandequaltoWallcoolingmethod kNotcooled 0.0Air-cooled 0.0013926Water-cooled 0.0028768Wtype decimalfractionoffurnaceorboilerwallthatisair-orwater-cooledII. SYSTEMSANALYSISA. GeneralApproach1. BasicDataThebasicinformationusedintheanalysisofcombustionsystemscanincludetabulatedthermochemical data, the results of several varieties of laboratory and eld analyses(concerning fuel, waste, residue, gases in the system), and basic rate data (usually, the owratesof feed, ue gases,etc.).Guidingtheuse ofthesedataarefundamentalrelationshipsthat prescribe the combining proportions in molecules (e.g., two atoms of oxygen with oneofcarboninonemoleculeofcarbondioxide)andthosethatindicatethecourseandheateffectofchemicalreactions.2. BasisofComputationTobeclearandaccurateincombustoranalysis,itisimportanttospecicallyidentifythesystem being analyzed. This should be the rst step in setting down the detailed statementof the problem. In this chapter, the term basis is used. In the course of prolonged analyses,it may appear useful to shift bases. Often, however, the advantages are offset by the lack ofaone-to-onerelationshipbetweenintermediateandnalresults.Astherststep,therefore,theanalystshouldchooseandwritedownthereferencebasis:agivenweightofthefeedmaterial(e.g.,100 kgofwaste)oranelement,oraunittime of operation.Thelatterisusually equivalentto a weight,however,and in generaltheweightbasisispreferred.3. AssumptionsRegardingCombustionChemistryMostincineratedwastescontaintheelementsC,H,O,N,S,andCl.ManycontainP,Br,manymetals, andunspeciedinerts.Incarryingoutmaterial balancecalculations, theanalyst must assumethedispositionoftheseelementsinthecombustorefuent streams(gaseous,liquid,andsolid).Incompletemixing,equilibriumconsiderations,limitationsinheat transferor reactiontime, andotherfactorsmakereal efuentschemicallycomplexand of uncertain composition. However, for use as a basis for material and energybalances, the following assumptions are generally valid for the bulk ow composition in atypicaloxidizingcombustionenvironment:Elemental or organic carbon O2 !CO2. In real systems, a fraction of the carbonisincompletely oxidized. Itappearsas unburned combustible or char in the solidresidue, ashydrocarbons, andasCOintheefuentgases.Dependingontemperature, inorganic (carbonate or bicarbonate) carbonmaybereleasedasCO2bydissociationormayremainintheash.Elementalororganichydrogen O2 !H2O(butseechlorine, below).Dependingontemperature, hydrogenappearinginwaterofhydrationmayormaynotbereleased.Hydrogen appearing in inorganic compounds can leave in a variety of forms,dependingontemperature(e.g., 2NaOH !Na2O H2O.Oxygen associated with the nonmetallic elements C, H, P, S, or Nin organiccompounds or with metals is assumed to behave as O2in air viz. reacting to formoxides(orremainingastheoxide).Oxygen associated with carbonates, phosphates, etc., can leave in a variety of forms,dependingontemperature.NitrogenusuallyleavesasN2(plustracesofNO,NO2).Reducedorganicor inorganicsulfuror elemental sulfur O2 !SO2. AfractionwillbefurtheroxidizedtoSO3.Oxidizedorganicsulfur(e.g., sulfonates) !SO2and=orSO3.Dependingontemperature, oxidizedinorganicsulfur(SO4 ,SO3 )maybereleasedasSO2orSO3(e.g., CaSO4 !CaO SO3.Organicphosphorus(e.g., insomepesticides) ! O2 !P2O5.Dependingontemperature,inorganicphosphorus(e.g.,phosphates)mayleaveinavarietyofforms.Organicchlorineorbromineisusuallyapreferredoxidizingagentforhydrogen !HCl, HBr(HBrmay !H2Br2).Inorganic chlorine and bromine (chlorides and bromides) are generally stable,althoughoxy-halogens(e.g., chlorates, hypochlorites) degradetochloridesandoxygen,water, etc.Metalsinthewaste(e.g., ironandsteel, aluminum, copper, zinc) will, ultimately,become fully oxidized. However, incomplete burning (say, 25%to 75%) iscommonduetothelowrateofsurfaceoxidationandlimitedfurnaceresidencetime.4. ApproachtoComputationAlthough the skilled analyst may elect to skip one or more steps because of limited data orlackofutility, thefollowingsequenceofstepsisstronglyrecommended:1. Sketch a ow sheet. Indicate all ows of heat and material, includingrecirculationstreams. Documentallbasicdataonthesketch,includingspecialfeaturesofanalyticaldataandheateffects.2. Select a basis andannotate the sketchtoshowall knownows of heat ormaterialrelativetothatbasis.3. Applymaterial,elemental, andcomponentbalances.Recognizethattheuseofaverage valuesforquantitiesandcharacteristicsisnecessarybutthatvariationsfromtheaveragearemost likelythenormrather thantheexception. Explorealternativeassumptions.4. Useenergybalances. Here, too, explorealternativeassumptions.5. Applyknownequilibriumrelationships.6. Applyknownreactionraterelationships.7. Reviewthe previous steps, incorporating the renements fromsubsequentstagesintothesimpler, earlierwork.B. AnalysesUnlike more convention combustors, incineration systems are often charged with materialswherethecompositionvarieswidelyovertimeandthat arehighlycomplexmixturesofwastestreams, off-specicationproducts, plant trash, andsoforth. Theanalysisofthesewastesmustoftenbeacompromise.In residential wasteincineration,forexample, what isa shoe?Is it(1)a shoe (i.e.,awastecategoryeasilyidentiedbyuntrainedeldpersonnel)?(2) 0.5 kgintheleatherandrubbercategory?(3)0.2 kgleather, 0.18 kgrubber, 0.02 kgironnails, etc.?(4)8%moisture, 71%combustible, 21%residue, heating value of 3800 kcal=kg? (5) Thecompositionas givenbyultimate analysis? or (6) Properties as givenbya proximateanalysis?(7)Anonhazardouswasteconstituent?Thesearethequestionswasteengineersmustponderas they impingeupontheadequatenessoftheirdesign,theneed forrigorousdetail (inconsiderationof feedvariability), and, importantly, thesamplingandanalysisbudgetallocation.ThenaldecisionshouldbebasedontheimpactoferrorsonRegulatoryandpermitdenitions:hazardousornonhazardousdesignationsMaterialshandling:bulkdensity,storability,explosionandrehazard,etc.Fanrequirements:combustionairanddraftfansHeat releaserate:persquaremeter, percubicmeterofthecombustorMaterials problems: refractoryor reside boiler-tube attack, corrosion in tanks,pipes,orstoragebins, etc.Secondaryenvironmental problems:air, water,andresidue-relatedpollutionProcesseconomics:heatrecoveryrate, laborrequirements, utilityusage, etc.There are no simplerulesin thismatter. Judgmentsare necessary on a case-by-casebasis.Thetechniquesdescribedbelow,however,givetheanalysttoolstoexploremanyoftheseeffects on paper. The cost is much lower than detailed eld testing and laboratory analysisandfarlessthanisincurredafteranincinerationfurnacehasbeeninstalledandfailstooperatesatisfactorily.The data generatedfor the evaluationof waste streams present problems totheanalyst. Theproblembeginswiththelargelyuncontrollablecharacteristicsof thewastegenerators,theunusualnatureofthewasteitself,andimperfectionsintheeldsamplingprocess. Thesedifcultiesmakeitproblematical tosecurepropersamples, toadequatelypreserveandreducethegross samples fromtheeldtotherelativelysmall quantitiessubmittedtothelaboratory,andtoconductthephysicalorchemicalanalysesthemselves.One of the rst problems of concern is the need for a representative sample.Domestic waste compositionhas beenshowntovarybetweenurbanandrural areas;between different economic and cultural groups; from month to month through the year; indifferent geographic, political, andclimatological areas. Thereisaprofoundvariationinthe quantities andcharacteristics of wastes generatedbydifferent industries andevenbetweendifferentprocessalternativesformanufactureofthesameproduct.Thisinherentvariabilityinthebasicwastecompositionisonlythestartingpointinillustratingthedifcultyinsecuringasample(ultimatelyinthe1-to50-gramsize)thatproperly reects the chemistry, heating value, and other signicant characteristics ofaveragewaste.Wastestreamsoftenincludeconstituentsthatarerelativelymassiveandhard to subdivide (e.g., tree stumps, automobile engine blocks). Other constituents may bevolatile or biodegrade on standing. If trace elements or compounds are important, a singlewaste item (e.g., an automobile battery affecting the lead content of the waste) may be therepositoryofalmost all ofthematerial of interest inmanytonsofwaste. If theitemisincluded,thewasteistypical"; ifnot, theanalysisisfaulty.Concern should also be given to the reported moisture level to ensure that it typiesthe material as-red. Often wastes are supplied to the laboratory after air drying. This iseither because the sampling team decided (without consultation) that such a step would begoodorbecauseinsufcient attentionwasgiventomoisturelossduringandafterthewastewassampled.Notuncommonly,a wastesamplemaynotberepresentativebecausethesampling team wanted to give the best they could nd or because they did not wishto handle some undesirable (e.g., decaying garbage) or awkward (e.g., a large pallet) wastecomponents.Letusleavethistopicwithaninjunctiontotheengineer:Knowthedetailsof thesamplingmethodology, thesampleconditioningprotocols, andthelaboratoryanalysisandreportingmethodsbeforetrustingthedata.Several types of wasteanalysis areavailabletocontributetocombustionsystemstudies.Theyarebrieyreviewedhere.Thedifferentanalyticalprotocolscharacterizethewastematerialsfromdifferentperspectivestomeetdifferentappraisalobjectives.1. WasteComponentAnalysisFor manywastestreams, anacceptableanduseful analysisisobtainedbyweighingthewasteafterseparationintovisuallydenablecomponents. Formunicipalsolidwaste, thecomponentcategoriesoftenincludenewsprint,corrugatedcardboard,otherpaper,foodwaste,yardwaste,aluminum,metal(excluding aluminum),glass,leather,rubber,textiles,plastics,andmiscellaneous.Theuseofthesewastecategorieshasobviousadvantagesintheseparationstep. Further, theweights ineachcategoryareoftenuseful inassessingrecyclingprocesses andinmonitoringtrends inwaste sources andcomposition. ThisanalysismethodologyandtaxonomyisdiscussedingreaterdetailinChapter4.2. ProximateAnalysisThe balance between moisture, combustible, and ash content, and the volatilizationcharacteristicsof thecombustiblefractionat hightemperaturesareimportant propertiesaffecting combustor design. Quantitative knowledge of these properties gives considerableinsightintothenatureofthepyrolysisandcombustionprocessesforsludge,solidwaste,andconventionalfuels.Asimpleandrelativelylow-costlaboratorytestthatreportstheseproperties is called the proximate analysis (1). The procedure includes the following steps:1. Heatonehourat104

to110

C. Reportweightlossasmoisture.2. Igniteinacoveredcrucibleforsevenminutesat 950

Candreport theweightloss(combinedwater,hydrogen,andtheportionofthecarboninitiallypresentasorconvertedtovolatilehydrocarbons)asvolatilematter.3. Ignite in an open crucible at 725

C to constant weight and report weight loss asxedcarbon.4. Reporttheresidualmassasash.Itshould be recognizedthat the valuereportedas moisture includes not only free waterbut also, inadvertently, any organic compounds (e.g., solvent) with signicant vaporpressure at 110

C. The value for volatile matter includes organic compounds driven offorpyrolyzedbut mayalsoincludewaterdrivenofffromhydroxidesorhydrates. Fixedcarbon includes the weight of carbon left behind as a char, but the value may be reducedbyweightgaininthecruciblefromoxidationofmetals.Inthecivilsanitaryengineeringliterature concerning sewage treatment plant sludge incineration, volatile matter data areoftentreatedas thoughtheywere equivalent tocombustible matter. For wastewatertreatment sludge containing many hydroxides and hydrated organic and inorganiccompounds, thisisincorrect. It isnot surprising, therefore, that onendsawider thanreasonablerangeinthereportedheatingvalueofsludgevolatilematter.3. UltimateAnalysisFor fuels the term ultimate analysis refers to an analysis routine that reports moisture (lossinweight, forsolidfuelsat 105

C), combinedwater(equivalent totheoxygen), andthecontent of several elements. Carbon, availableor net hydrogen(hydrogenother thaninmoisture and combined water), oxygen, total sulfur, nitrogen, and ash are alwaysreported. Oxygen is generally determined by difference, and thus both the value forpercentoxygenandthecombinedwatervaluemaybeinerror.Incalculationsrelatingtowastedisposal systems, itmaybeappropriatetorequestanalyses for chlorine and for environmentally signicant elements (such as arsenic,beryllium, cadmium, chromium, nickel, and lead) and for other elements that couldinuence the combustion process or would be important to air pollution or waterpollutionassessments. Ingeneral, several different samplesareusedtogeneratethetotal analysisreport. Particularlyfor wasteanalysis, therefore, somenumerical inconsistenciesshouldnotbeunexpected.Asfortheproximateanalysis,thetestingmethodcanproduceuncertainresultsforseveral analysiscategories.The weightreportedasash willbechangedby oxidation ofmetalsin thesample,by releaseof carbondioxidefromcarbonates,bylossof waterfromhydrates or easily decomposed hydroxides, by oxidation of suldes, and by other reactions.Also, volatile organic compounds (e.g., solvent) can be lost in the drying step, thusremovingaportionofthefuelchemistryfromthesample.4. Thermochemical AnalysisThe heat of combustion of wastes is, clearly, important information in incineration systemanalysis. However, one must be cautious in accepting even the mean of a series oflaboratoryvalues(notingthat abombcalorimeter usesonlyabout 1 gof sample) whenthereareproblemsinobtainingarepresentativesample(seebelow). Forbothmunicipaland industrial incineration systems, the analyst must also recognize that within thehardwarelifetimewasteheat content will almost inevitablychange: yeartoyear, seasontoseason, and, evendaytoday. Thisstronglysuggeststheimportanceofevaluatingtheimpact of wastevariationonsystemtemperatures, energyrecovery, etc. Further, suchlikelyvariabilityraiseslegitimatequestionsregardingthecost-effectivenessofextensivesamplingandanalysisprogramstodevelopthistypeofwastepropertyinformation.5. Special AnalysisAcompetent fuels laboratoryoffers other analysis routines that canprovide essentialinformationforcertaintypesofcombustorsorprocessrequirements.The forms of sulfur analysis breaks down the total sulfur content of the material intothreecategories:organic, sulde(pyritic),andsulfate.Theorganic andsulde sulfurformswilloxidizeinanincinerationenvironment,thuscontributingtothestoichiometricoxygen requirement. Oxidation produces SO2and SO3(acid gases) that often havesignicance in airpollution permits. Sulfate sulfur is already fully oxidized and, barringdissociation at very high temperatures, will not contribute to acid gas emissions orconsumealkali inascrubbingsystem.Atestforformsofchlorineprovidesasimilarsegregationbetweenorganicallyandinorganicallyboundchlorineinwastes. Chlorineis averyimportant element inwastecombustion. Organicchlorine[e.g., inpolyvinyl chloride(PVC) andother halogenatedpolymers or pesticides] is almost quantitativelyconvertedbycombustionprocesses toHCl: anacidgasof signicanceinmanystateandfederal air pollutionregulations, animportant contributor to corrosion problems in boilers, scrubbers, and fans, and aconsumer of alkali inscrubbers. Inorganicchlorine(e.g., NaCl) isrelativelybenignbutcontributestoproblemswithrefractoryattack, submicronfumegeneration, etc. Sinceallbut a few inorganic chlorides are water soluble and few organic chloride compounds showanysignicant solubility, leachingandquanticationof thesolublechlorineionintheleachateprovidesasimpleandusefuldifferentiationbetweenthesetwotypesofchlorinecompounds.Anashanalysisisanotherspecialanalysis.Theashanalysisreportsthecontentofthemineral residueastheoxidesof theprincipal ashcations. Atypical ashanalysisisreported as the percent (dry basis) of SiO2, Al2O3, TiO2, Fe2O3, CaO, MgO, P2O5, Na2O,andK2O.AsdiscussedintheRefractoriessectionofChapter5,thebalancebetweentheacidicandbasicoxidesintheashisimportantinsettingashmeltingtemperaturesandininuencingcorrosiveattackofrefractory(uxing).The ash fusion temperature under oxidizingand reducing conditions is anotherimportant test that providesverypractical information. Inthistest (ASTMStandardD-1857), a sample of the material is ashed. The mineral ash is then pressed into a cone shapeand placed in a mufe furnace on a tilted ceramic plate. The furnace temperature is rampedupatasetratewhiletheconeisobserved.Fourtemperaturesarenoted:Initial deformation temperature (IDT), where the tip of the cone just showsdeformationSofteningtemperature(ST), wheretheconeis slumpedsuchthat theheight andwidthoftheashmassareequalHemispherical temperature (HT), where the mass is uid but, due to surface tension,hasahemisphericalshapewiththeheightequal toone-halfofthewidthFluidtemperature (FT), where the molten ash viscosity is very low and the materialowsdowntheplatewithathicknessnotgreaterthan1=16thin(0.15 cm).Inreducingatmospheres, theSTisoftenidentiedwiththefusiontemperatureoftheslag.In combustors such as the uid bed furnace that depend on maintaining dry (non-sticky)ashconditions, theIDTintheashfusiontemperaturedeterminationisaguideinsetting the upper limit to the operating temperature. Similarly, the IDT is a useful guide insetting the maximum temperature where y-ash laden furnace gases should enter a boiler-tube bank to avoid slag buildup on the tubes. For other furnaces and operatingrequirements, the fusion temperature is also useful both in the designand feasibilitystageandinproblem-solvingsituations.The ash fusion test can be conducted underboth oxidizing and reducing conditions.Bothhaveutilityinanticipatingorunderstandingslagbuildupproblems. Althoughmostcombustors are oxidizing overall, almost any combustor has some oxygen-decient zones.Suchzonesincludethepyrolyzing=gasifyingmassonrefuseincineratorgratesorsludgeincinerator hearths and regions in other furnaces where the local air supply is overwhelmedby the available combustible matter. This can be very important since the fusioncharacteristicsof ashcanchangedramaticallyastheenvironment shiftsfromoxidizingtoreducing. This is particularlytrue for ashes containinglarge amounts of iron. Thereduction of Fe2O3to FeO involves a change in behavior of the iron oxide from an acidicoxidetoabasicoxidethatoftenleadstoalowerinitialdeformationtemperature.Anumber of other useful physical properties may merit determination. Theseincludemeltingpoint (toassessthepotential forwastestomelt at incinerationtempera-turesandrunthroughopeningsingrates), viscosity(important inatomizationof liquidwastes), andashpoint (important inassessingsafetyproblemsandakeyparameterinsomeregulatorydenitionsofhazardouscombustiblewastes).Finally, the design of materials handling systems can benet from data such as angleof repose (for bins and belt conveyors), particle size and density (for pneumaticconveyors), andthelike.6. Regulatory=ProcessDenitionsBeyond the materials tests noted above, it may be appropriate to conduct severalspecialized tests or develop waste characterizations to make specic distinctions thataffect thepermit requirementsofthecombustionsystemorthat broadlycharacterizethewasteasaguideinbasiccombustionprocessselection.The permit-generated characterizations are specied in the relevant regulations (e.g.,theUSEPAhazardouswasteregulations).Suchcharacterizationsincludewastechemistryor industrial process source that might denote the presence of carcinogens or toxicsubstances,hazardousphysicalproperties(e.g.,lowashpointorcorrosivity),hazardousbiological properties (e.g., the presence of pathogenic organisms), or the presence of high-orlow-levelradioactivematerials.Process characterizations includedesignationas sewagesludge, ofcetrash,domesticwaste, or cafeteria wastewhichaidin broadincineration conceptselection.7. DataAnalysisIt is not the purpose or within the scope of this book to address in detail methodologies forthestatistical analysis of wastedata. However, fromthediscussionthat introducedtheanalysis topic, it is tobeexpectedthat theanalyst will beconfrontedwithsubstantialscatter inthereportedlaboratoryvaluesfor wasteproperties. Thus, it isappropriatetoincludesomediscussionofdataanalysisandaveragingmethods.In general,the analysis of waste data seeksan estimate of the weightedaverage (themean) of important waste parameters and some measure of their variability. Beforestatistical parameters can be estimated for the data, the basic distribution pattern of the datamustbeknown.Thedistributiontypedeneshowthemean,the variance,etc.,shouldbecalculated.Familiarity,simplicityofcalculation,andconvenienceusuallysuggestthatthenormal distributionanditscomputational methodswill beapplied. However, for wastedata, the log normal distribution (where the logarithms of the data rather than the data itselfarenormallydistributed)isoftenfoundtotthedataaswellasorbetterthanthenormaldistribution. Consequently, abrief summaryandcomparisonof thetwocomputationalmethodswillbepresented.Themost commonlyusedmeasuresofcentral tendencyarethemean, themedian,and the mode. The mean is the weighted average of the values. The median is the value thatdivides a data set so that one-half of the items are equal to or greater than and one-half arelessthanthevalue. Themodeisthemost observedvaluearoundwhichtheitemsintheseriestendtoconcentrate. Thereisnobest measureof central tendency. Sometimeseventhedeterminationofthesemeasuresforaset ofdataisentirelyimpropersincethedata maybelongtomore thanone population. Further, the data maynot represent ameaningful set. What does the value 56.5 signify as the arithmetic mean of the four gures2, 5, 103, and 116? Note also that expressing the mean as 56.5 rather than as ftyish hasimbued the value with an unwarranted aura of accuracy: far beyond its true worth.Statistical analysis of data to test the signicance of trends, groupings, and other inferencesisoftenmerited.Inany event, theanalystof wastemanagementsystemsisfrequentlypresentedwithdatasetsthatcanbesignicanttothedesignorpermittingofincinerationsystems.Suchquantitiesastheheat content, theconcentrationoftoxicelementsorcompounds, orthemoisture and combustible contents have profound signicancein systemdesign. One ruleshouldbekeptinmind, however, inusingthevaluesderivedfromanalyzingsuchdata:Averageisthevalueof acritical parameterthat isneverobservedinpractice. Otherdenitionsincludetypical,assumedvalue,anddesignbasis.Thisdenition,thoughtongueincheek,shouldbetakentoheart.Wastepropertiesareinherentlyvariable.Thus,theanalystisstronglyencouragedtoexploretheimpactofvariations fromtheaverage onsystembehavior. What-if? calculations toevaluatesystem response to alternative property values are recommended. Fortunately, theincineratoritself isoftenaneffectiveaveragingdevice.Itssize,theinventoryofmaterialbeing processed at any one time, the large thermal inertia of the tons of refractorycomprisingtheincineratorchambersallacttosmoothoutmomentaryvariation.a. Probabilistic Models. As noted above, there are two probabilistic models (ordistributions) oftenapplicabletowastedatathat varycontinuously: thenormal andthelognormaldistributions.Thearithmeticcalculationsassociatedwiththenormaldistribu-tionareeasier toimplement andaregenerallyappropriatefor bulkproperties suchasheatingvalue, percent moisture, andthelike. Thecalculationsassumingthelognormaldistributionaremoredifcult but areusuallysuperior inaccuracyfor tracecomponentanalysesandotherpropertiesthathovernearzero.The general shape of the normal and log normal distributions is shown in Fig. 2. Forthenormaldistribution,themean,median,andmodeareallcoincident.Thisprovidesthecomfort thatthevalueusedforthemeanfallsinthemidstofalltheobservationsand,indeed,isthemostobserved value.Forthelognormalcase,themean,median,andmodedifferand themeancan be signicantlyhigherthaneitherthemedianorthemode,whereourintuitivefeelforthedatasaysthecentralvalueshouldbe.The ShapiroWilk test for normality is generally preferable for application to sets ofdata and to the logarithms of the data sets. The KolmogorovSmirnov test fornormality ismore common for this purpose, but the ShapiroWilk test should be considered for samplesizes smaller than 50. Both the test statistic and the level of signicance should becomputed for each formof the data (base and logarithm) to select the probabilityFigure2 Normalandlognormaldistribution.distributionthatbesttsthesituation.A5%level ofsignicanceisareasonablecriteriontodeterminewhetherthedataarenormal (orlognormal). Ifthelevel ofsignicanceisequaltoorgreaterthan5%,thenthehypothesisthatthedataarenormal(orlognormal)cannotberejected.b. Statistical Calculations. Once a probabilistic model has been selected, the mean,variance (square of the standard deviation), and other statistical quantities can begenerated. For convenience, theformulasfor thekeystatisticsaresummarizedhereforthenormal andlognormal cases. Additionaldiscussionsrelatedtoparticlesizedistribu-tionsarepresentedinSectionI.AofChapter13.Thereaderisstronglyrecommendedtorefertomorecomprehensivetextsonthesematters(e.g., 181,182).MEANANDVARIANCE. For normal distributions, the population mean (M) andvariance(S2)areestimatedbyEqs. (14)and(15).M 1n0Pn0i1xi14S21n01Pn0i1xiM215For log normal distributions, the mean (m) and variance (s2) of the logarithms arecalculatedfromthetransformeddatayi loge xiasfollows:m 1n0Pn0i1yi16s21n01Pn0i1yim217Severalusefulmeasuresfromlognormalstatisticsareasfollows:population mean: mln expm 0:5s2 18population variance: s2ln exps2 1exp2m s2 19median at: x expm 20mode at: x expm s2 21lowerquartile at: x expm 0:67s 22upperquartile at: x expm 0:67s 23Often, theresults of laboratoryanalysis of wastematerials for elementsor compoundspresent inlowconcentrations arereportedas nondetect or belowdetectionlimit.Here, limitationsoftheanalytical protocolsorthesensitivityoftheapparatusproduceanull or indeterminate response in detecting the material of interest. That does not mean thatthe correct value is zero. Nor should one, necessarily, be driven to consider thenondetect limit as the effective concentration for the material. For the log normaldistribution case, an elegant analysis (181) supports the development of an unbiasedestimator of themeanandvariancefromadataset withn0sampleswithdiscretedatavalues and n total samples. The unbiased estimator of the population mean and variance intheunitsoftheobservationsforsuchincompletedata sets(midands2id,respectively)isgivenbyEqs. (24) and (25). These relationships make use of a Bessel function PnopresentedinEq.(26)thatisthesumofaninniteseriesbutcanbeeasilyandaccuratelyestimatedfromtherst vetermsorsousingapersonal computerspreadsheet orhandcalculator.mid n0nexpm Pno12s2 !24s2id n0nexp2m Pno2s2 n01n 1 Pnon02n01s2 !25Pnot 1 n01n0t n013n202!n01t2n015n303!n01n03t3. . . 26Notethatforthespecialcaseswheren0isequaltozero,themeanandvariancearezero.Forn0equalto1andforthedatavaluex1, thefollowingequationsapply:mid x1=n and s2id x21=n8. DataCostData are not cheap. In planning a data collection programsupporting the design ofincineration design, the analyst must carefully consider the number of samples required forrepresentativenessandthescopeandsophisticationofthedatatobegenerated. Thesescalarstranslateintothecost andtimeframefor datacollectionandmust bebalancedagainst theutilityoftheinformationthusgained. Thereisnosimplerulewithwhichtostrike this balance. One must recognize, for example, that changes in the composition of awaste streamover the useful life of anincinerator often place great demands ontheexibilityof asystemtoaccommodatethechange. Theseyear-to-year changesmaybemuchmoreprofoundthantheplus-and-minus accuracy of datathat characterizethepresentwaste. Theremay,therefore, beconsiderablemeritinlimitingthedatacollectioneffort infavor of moreexhaustiveengineeringanalysistoexploretheconsequencesofchange.III. MATERIALBALANCESA materialbalance isa quantitative expression ofthe law of conservation of matter:Whatgoesincomesout(unlessitstaysbehind).input output accumulation 26Thisexpressionisalwaystrueforelementsowingthroughcombustionsystems(exceptfor minor deviationsintheunusual casewhereradioactivematerialsareinvolved). It isoften not true for compounds participating in combustion reactions. Because of itsfundamental character andintrinsiccredibility, thematerial balanceis oneof themostusefultoo