COMBUSTION ANDINCINERATIONPROCESSESThird Edition, Revised and ExpandedWalter R. NiessenNlessen Consultants S.P.Andover, MassachusettsM A R C E LEZD E K K E RMARCEL DEK 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, or its suitability for any purpose other than as described in the preface. This software islicensed solely on an as is basis. The only warranty made with respect to the accompanyingsoftware is that the diskette medium on which the software is recorded is free of defects. MarcelDekker, Inc., will replace a diskette found to be defective if such defect is not attributable to misuseby the purchaser or his agent. The defective diskette must be returned within ten (10) days to:Customer ServiceMarcel Dekker, Inc.P. O. Box 5005Cimarron RoadMonticello, NY 12701(914) 796-1919ISBN: 0-8247-0629-3This book is printed on acid-free paper.HeadquartersMarcel Dekker, Inc.270 Madison Avenue, New York, NY 10016tel: 212-696-9000; fax: 212-685-4540Eastern Hemisphere DistributionMarcel Dekker AGHutgasse 4, Postfach 812, CH-4001 Basel, Switzerlandtel: 41-61-261-8482; fax: 41-61-261-8896World Wide Webhttp:==www.dekker.comThe publisher offers discounts on this book when ordered in bulk quantities. For more information,write to Special Sales=Professional Marketing at the headquarters address above.Copyright # 2002 by Marcel Dekker, Inc. All Rights Reserved.Neither this book nor any part may be reproduced or transmitted in any form or by any means,electronic or mechanical, including photocopying, microlming, and recording, or by any informa-tion storage and retrieval system, without permission in writing from the publisher.Current printing (last digit):10 9 8 7 6 5 4 3 2 1PRINTED IN THE UNITED STATES OF AMERICA1. Toxic Metal Chemistry in Marine Environments, Muhammad Sadiq2. Handbook of Polymer Degradation, edited by S. Halim Hamid, Mohamed B.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 Waste Management: Disposal, Recycling, and Reuse, edited byNabil Mustafa6. Hazardous Waste Site Soil Remediation: Theory and 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, edited by Donald L.Wise and Debra J. Trantolo9. Water Contamination and Health: Integration of Exposure Assessment,Toxicology, and Risk Assessment, edited by Rhoda G. M. Wang10. Pollution Control in Fertilizer Production, edited by Charles A. Hodge andNeculai 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 Materials Handling and Management, edited byStanley 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. Separation Methods for Waste and Environmental Applications, Jack S.Watson21. Handbook of Polymer Degradation: Second Edition, Revised and Expanded,S. Halim Hamid22. Bioremediation of Contaminated Soils, edited by Donald L. Wise, Debra J.Trantolo, Edward J. Cichon, Hilary I. Inyang, and Ulrich Stottmeister23. Remediation Engineering of Contaminated Soils, edited by Donald L. 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 PreparationTomy wife, Dorothy Anne,who continues to selessly and unreservedly support me in this andall my other personal and professional endeavorsPreface to the Third EditionThe third edition of Combustion and Incineration Processes incorporates technologyupdates and additional detail on combustion and air pollution control, process evaluation,design, and operations from the 1990s. Also, the scope has been expanded to include: (1)additional details and graphics regarding the design and operational characteristics ofmunicipal waste incineration systems and numerous renements in air pollution control,(2) the emerging alternatives using refuse gasication technology, (3) lower-temperaturethermal processing applied to soil remediation, and (4) plasma technologies as applied tohazardous wastes. The accompanying diskette offers additional computer tools.The 1990s were difcult for incineration-based waste management technologies inthe 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. Issuesincluded a focus on emissions of air toxics (heavy metals and a spectrum of organiccompounds); softening in the selling price of electricity generated in waste-to-energyplants; reduced pressure on land disposal as recycling programs emerged; and the openingof several new landlls and some depression in landlling costs. Also, the decade sawgreat attention paid to the potential hazards of incinerator ash materials (few hazards weredemonstrated, however). These factors reduced the competitive pressures that supportedburgeoning incinerator growth of the previous decade.Chapters 13 and 14 of this book, most importantly, give testimony to the greatconcern that has been expressed about air emissions from metal waste combustion(MWC). This concern has often involved strong adversarial response by individuals inpotential host communities that slowed or ultimately blocked the installation of newfacilities and greatly expanded the required depth of analysis and intensied regulatoryagency scrutiny in the air permitting process. Further, the concern manifested itself inmore and more stringent air emission regulations that drove system designers toincorporate costly process control features and to install elaborate and expensive trainsof back-end air pollution control equipment. A comparative analysis suggests that MWCsare subject to more exacting regulations than many other emission sources [506]. This isnot to say that environmental improvements are without merit, but in this instance thehigher costs to the taxpayers and=or the dogmatic elimination of a useful option for solidwaste management may not be justied by the actual benets realized.The situation in Europe has been quite different. Many of the countries of theEuropean Community have passed legislation that greatly restricts the quantity and qualityof materials consigned to landlls. In Germany, for example, the Closed Cycle EconomyLaw (rening the Waste Act of 1986) raised energy recovery from waste incineration to alevel equal to that of materials recycling in the hierarchy of preference in waste manage-ment alternatives. Further, their Technical Directive for Residual Waste severely restrictedthe loss on ignition of waste destined for landll to less than 5% and the total organiccarbon to less than 3%. These combined factors make incineration almost a requirement. Itmust be said, however, that European air emission requirements are equal to or morestringent than their counterparts in the United States and, therefore, the increased use ofincineration will come at a very high cost.The incineration community has responded well to these technical, political, andeconomic challenges. Over the past 40 years, incineration technology, and its embodimentin processing plants, has moved from its primitive early days as a bonre in a box tosophisticated, energy recovery combustion systems with effective process control cappedwith broad-spectrum and highly efcient air pollution control systems capable of meetingstringent emission standards. And improvements and enhancements continue to be made.This book helps engineers and scientists working in this challenging and complex eld tocontinue the evolution of this fascinating, interdisciplinary technology.Walter R. NiessenPreface to the Second EditionThe second edition of Combustion and Incineration Processes was prepared as an updateand as a substantial extension of the rst edition. However, the underlying philosophy ofthe rst edition has been retained: a focus on the fundamentals of incineration andcombustion processes rather than on specic equipment. There have been many technicaladvances in the 15 years since this book rst appeared. The application of incineration tothe hazardous waste area has required new levels of process control and better and morereliable combustion performance. There is now a profound and pervasive impact of stateand federal environmental regulations and guidelines on design and operation. Conse-quently, air pollutant emission issues have assumed a dominant position in shaping systemconguration and cost.The topics concerned with basic waste combustion processes (atomization, chemicalkinetics of pyrolysis and oxidation, mixing, etc.) have been expanded. Applications arepresented relevant to hazardous wastes and their incineration systems. Analysis methodsand discussions of key design parameters for several additional incinerator types(especially for those burning sludges, liquids, and gases) have been signicantly enlarged.The section of the book dealing with techniques for waste data analysis and wastecharacterization has been substantially expanded. This reects the strong inuence ofwaste composition on the incineration process and the increased regulatory attention paidto emissions of toxic, carcinogenic, and otherwise environmentally signicant traceelements and compounds found in wastes (the air toxics).The rst edition of Combustion and Incineration Processes focused on theincineration of municipal solid wastes. Then, resource recovery (energy recovery) wasemerging as the only incineration concept, which made economic sense for large plants.Ination had greatly increased capital and operating costs. An offset from electricalrevenue had become critical to viability. Technology that fed as-received refuse to thefurnace (mass burn) was competing for attention with facilities that rst processed waste toa refuse-derived fuel (RDF). Still, as the research supporting the text for the rst editionwas prepared, few facilities of either type were operating in the United States. Data wasscant and much was to be learned. This technology has matured since then.The Clean Air Act had been long passed by 1978 and its provisions were fullyimplemented regarding the control of municipal incinerators. However, only total 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 NOx controls were not incorporated into any municipal plant.However, over the past 15 years, regulatory actions ( public hearings, permits, approvals,mandated design and operating guidelines, etc.) have assumed a dominant role in thedesign, cost, performance objectives, and implementation schedules of incinerationfacilities. Consequently, additional and updated methodologies are presented to estimatepollutant emission rates. Also (but modestly and in keeping with the primary focus on theincineration system), a discussion of air pollution control technology has been included.The attention of the public and the political and regulatory establishments were justbeginning to focus on hazardous wastes. The Resource Conservation and Recovery Act(RCRA), which mandated the structured and rigorous management of hazardous wastes,was new. Its full scope and requirements were still uncertain. Public Law 96-510, theComprehensive Environmental Response, Compensation, and Liability Act (CERCLA),better known as the Super-Fund Act, dealing with abandoned hazardous waste sites, hadnot yet been written. The challenges to incineration of RCRA and CERCLA applicationsare signicant. Emission mitigation using both sophisticated combustion control and back-end control equipment is of great interest to both regulators and the public.I would like to acknowledge the support given by Camp Dresser & McKee Inc.(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 thank the many clients for whom I have worked over the years for theircondence and, importantly, for their support as together we addressed their problems andlearned more of incineration technology. Finally, I want to thank the many colleagues Ihave worked with over the yearsboth inside and outside my employers rm. Theirprofessional support and help have been a constant source of stimulation.Walter R. NiessenPreface to the First EditionPurication by re is an ancient concept, its applications noted in the earliest chapters ofrecorded history. The art and the technology of combustion (incineration) and pyrolysis asapplied to environmental engineering problems draws on this experience, as well as theresults of sophisticated contemporary research. To many engineers, however, combustionsystems still hold an unnecessary mystery, pose unnecessary questions, and generateunnecessary mental barriers to their full exploitation as tools to solve tough problems. Thisbook was written in an earnest attempt to thin the clouds of mystery, answer many of thequestions (those for which answers are available), and provide a clearer way for theengineer to analyze, evaluate, and design solutions to environmental problems based oncombustion.The book describes combustion and combustion systems from a process viewpointin an attempt to develop fundamental understanding rather than present simplistic designequations or nomographs. In large part, this approach was selected because combustionsystems are complex and not readily susceptible to cook-book design methods.Consequently, considerable space is devoted to the basics: describing the chemical andphysical processes which control system behavior.In an effort to make the book as comprehensive as possible, a large number of topicshave been dealt with. Specialists in particular elds may perhaps feel that the subjects inwhich they are interested have received inadequate treatment. This may be resolved in partby exploring the noted references, an activity also recommended to the newcomer to theeld.The publication of this book appears timely since current trends in environmentalawareness and regulatory controls will prompt increases in the use of combustiontechnology as the preferred or only solution. In light of escalating construction costs,the soaring expense and diminishing availability of fossil fuels used as auxiliary energysources (or the growing value of recovered energy), and the ever more stringent regulatoryinsistence on high performance regarding combustion efciency and=or air pollutantemissions, the black box approach is increasingly unacceptable to the designer and tothe prospective owner.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 beenexpended to provide reference data, correlations, numerical examples, and other aids tofuller understanding and use.Last (but of the greatest signicance to me, personally), the book was writtenbecause I nd the study and application of combustion to be an exciting and mind-stretching experience: ever fascinating in its blend of predictability with surprise (thoughsometimes, the surprises are cruel in their impact). Combustion processes are and willcontinue to be useful resources in solving many of the pressing environmental problems ofmodern civilization. I sincerely hope that my efforts to share both contemporarycombustion technology and my sense of excitement in the eld will assist in respondingto these problems.In the preparation of this book, I have drawn from a broad spectrum of the publishedliterature and on the thoughts, insights, and efforts of colleagues with whom I have beenassociated throughout my professional career. I am particularly grateful for the manycontributions of my past associates at Arthur D. Little, Inc. and at 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 the Incinerator Division (now the Solid Waste Processing Division) of the AmericanSociety of Mechanical Engineers have been of great value.I must specically acknowledge Professor Hoyt C. Hottel of MITwho introduced meto combustion and inspired me with his brilliance, Mr. Robert E. Zinn of ADL whopatiently coached and taught me as I entered the eld of incineration, and Professor AdelF. Sarom of MITwhose technical insights and personal encouragement have been a majorforce in my professional growth.I would like to acknowledge the support given by Roy F. Weston Inc. and CampDresser & McKee Inc. in underwriting the typing of the text drafts and the preparation ofthe art work. Particularly, I would thank Louise Miller, Bonnie Anderson, and JoanBuckley, who struggled through the many pages of handwritten text and equations inproducing the draft.Walter R. NiessenContentsPreface to the Third EditionPreface to the Second EditionPreface to the First Edition1. Introduction2. StoichiometryI. Units and Fundamental RelationshipsA. UnitsB. Gas LawsC. EnergyII. Systems AnalysisA. General ApproachB. AnalysesIII. Material BalancesA. Balances Based on Fuel AnalysisB. Balances Based on Flue Gas AnalysisC. Cross-Checking Between Fuel and Flue Gas AnalysisIV. Energy BalancesV. EquilibriumVI. Combustion KineticsA. Introduction to KineticsB. Kinetics of Carbon Monoxide OxidationC. Kinetics of Soot OxidationD. Kinetics of Waste Pyrolysis and Oxidation3. Selected Topics on Combustion ProcessesI. Gaseous CombustionA. The Premixed (Bunsen) Laminar FlameB. The Diffusion FlameII. Liquid CombustionA. Pool BurningB. Droplet BurningIII. Solid CombustionA. Thermal DecompositionB. Particle Burning ProcessesC. Mass Burning Processes4. Waste CharacterizationI. GeneralA. ChemistryB. Heat of CombustionC. Ash Fusion CharacteristicsD. Smoking TendencyII. Solid WasteA. Solid Waste CompositionB. Solid Waste PropertiesIII. Biological Wastewater SludgeA. Sludge CompositionB. Sludge Properties5. Combustion System Enclosures and Heat RecoveryI. EnclosuresA. Refractory Enclosure SystemsB. Water-Cooled Enclosures and Heat Recovery SystemsII. Heat TransferA. ConductionB. ConvectionC. RadiationD. Heat Transfer Implications in DesignIII. Slagging and Fouling6. Fluid Flow Considerations in Incinerator ApplicationsI. Driven FlowA. Jet FlowB. Swirling FlowsII. Induced FlowA. Jet RecirculationB. BuoyancyIII. Mixing and Residence TimeA. Fundamental Distribution RelationshipsB. Common Distribution FunctionsC. Failure ModesD. Residence Time Scenarios7. Materials Preparation and HandlingI. Solid WastesA. GeneralB. Pit and Crane Handling of Solid WastesC. Size Reduction of Municipal Solid WastesD. Conveying of Solid WastesE. Size Classication and ScreeningF. Ferrous Metal SeparationII. Sludge HandlingA. GeneralB. Sludge Pumping in Pipes8. Incineration Systems for Municipal Solid WastesI. Performance ObjectivesA. Throughput and Refuse Heat ContentB. The Firing Diagram: The Overall Process EnvelopeC. Plant AvailabilityII. Site Design ConsiderationsA. Site GradingB. Site DrainageC. Site Trafc and Road ConsiderationsIII. Collection and Delivery of RefuseIV. Refuse Handling and StorageA. Tipping Floor-Based Waste Storage and Reclaim SystemsB. Pit and Crane-Based Waste Storage and Reclaim SystemsC. Bin Storage and Reclaim Systems for RDFV. Size Control and SalvageVI. Incinerator Feed SystemsA. Feed Systems for Floor Dump Receipt and StorageB. Feed Systems for Pit and Crane Receipt and Storage SystemsVII. Grates and HearthsA. Stationary HearthB. Rotary KilnC. Stationary GratesD. Mechanical Grates: Batch OperationsE. Mechanical Grates: Continuous OperationsF. OConner Rotary Combustor (Kiln)G. Fluid Bed SystemsVIII. Incinerator Furnace EnclosuresA. Refractory EnclosuresB. Other Enclosure-Related Design ConsiderationsIX. Energy Markets and Energy RecoveryA. Market SizeB. Market TypeC. Market ReliabilityD. Revenue ReliabilityX. Combustion AirA. Underre AirB. Overre AirC. Secondary AirD. Combustion Air FansE. Air PreheatXI. Ash Removal and HandlingA. Overview of Ash ProblemsB. Ash PropertiesC. Bottom AshD. SiftingsE. Fly AshF. Materials Recovery from AshXII. Flue Gas ConditioningA. Cooling by Water EvaporationB. Cooling by Air DilutionC. Cooling by Heat WithdrawalD. Steam PlumesXIII. Environmental Pollution ControlA. Air PollutionB. Water PollutionC. Noise PollutionXIV. Induced Draft FanA. Fan TypesB. Inlet and Outlet ConnectionsC. Fan ControlXV. Incinerator StacksXVI. Refuse-Derived Fuel SystemsA. RDF ProcessingB. RDF Combustion SystemsXVII. Instrumentation and ControlA. Instrumentation and Control System Design ApproachB. Process Measurements and Field InstrumentsC. Control System LevelsD. General Control PhilosophyE. Portable InstrumentsF. SummaryXVIII. OperationsA. Mass Burn IncinerationB. RDF Incineration9. Incineration Systems for Sludge WastesI. Multiple-Hearth Furnace (MHF) SystemsA. Process CharacteristicsB. Process RelationshipsII. Fluid Bed SystemsA. Process CharacteristicsB. Process Relationships (Oxidizing Mode)C. Operating CharacteristicsD. General Environmental ConsiderationsIII. Slagging Combustion Systems for Biological SludgeA. Kubota SystemB. Itoh Takuma System10. Incineration Systems for Liquid and Gaseous WastesI. Liquid Waste IncineratorsA. Liquid StorageB. AtomizationC. Ignition TilesD. Combustion SpaceE. Incinerator TypesII. Incinerators for Gases (Afterburners)A. Energy Conservation Impacts on Afterburner DesignB. Current Afterburner Engineering TechnologyC. Afterburner SystemsD. Potential ApplicationsIII. Operations and Safety11. Incineration Systems for Hazardous WastesI. GeneralA. Receiving and Storage SystemsB. Firing SystemsC. Control SystemsD. RefractoryE. Air Pollution Control for Hazardous Waste IncineratorsF. Evaluation Tests and POHC SelectionII. Rotary Kiln SystemsA. Sludge Incineration ApplicationsB. Solid Waste Incineration ApplicationsIII. Circulating Fluid BedA. CFB HydrodynamicsIV. Thermal DesorptionA. Soil ParametersB. Thermal Desorption SystemsC. Operating ParametersD. Remediation PerformanceV. Plasma Technology12. Other Incineration Systems for Solid WastesI. Multiple Chamber (Hearth or Fixed Grate)II. Multiple Chamber (Moving Grate)III. Modular Starved AirIV. Open Pit TypeV. Conical (Tepee) TypeVI. Gasication Processes for MSWA. GeneralB. Gasication of an RDF by Partial CombustionC. Gasication of an RDF by Pyrolysis and Steam Reforming(Battelle)D. Gasication of Raw MSW by Pyrolysis13. Air Pollution Aspects of Incineration ProcessesI. Air Pollutants from Combustion ProcessesA. Particulate MatterB. Combustible Solids, Liquids, and GasesC. Gaseous Pollutants Related to Fuel ChemistryD. Nitrogen OxidesII. Air ToxicsA. Metal Emission RatesB. Emissions of Organic Compounds14. Air Pollution Control for Incineration SystemsI. Equipment Options for Incinerator Air Pollution ControlA. Settling ChambersB. Cyclones and Inertial CollectorsC. Wet ScrubbersD. Electrostatic PrecipitatorsE. Fabric Filter (Baghouse)F. AbsorbersG. Specialized Abatement TechnologyII. Control Strategies for Incinerator Air Pollution ControlA. Air Pollution Control through Process OptimizationB. Control Selections for Incinerator TypesC. Continuous-Emission MonitoringD. Air Pollution Control to Achieve Air-Quality Objectives15. Approaches to Incinerator Selection and DesignI. Characterize the WasteII. Lay Out the System in BlocksIII. Establish Performance ObjectivesIV. Develop Heat and Material BalancesV. Develop Incinerator EnvelopeVI. Evaluate Incinerator DynamicsVII. Develop the Designs of Auxiliary EquipmentVIII. Develop Incinerator EconomicsA. GeneralIX. Build and OperateAppendicesA. Symbols: A Partial ListB. Conversion FactorsC. Periodic Table of ElementsD. Combustion Properties of Coal, Oil, Natural Gas, and OtherMaterialsE. Pyrometric Cone EquivalentF. Spreadsheet Templates for Use in Heat and Material BalanceCalculationsA. Heat and Material Balance SpreadsheetsB. Heat of Combustion Calculator: HCOMB.xlsC. Moisture Correction in Refuse Analyses: Moisture.xlsD. Equilibrium Constant Estimation: Equil.xlsE. Steam.exe ProgramG. Thermal Stability IndicesNotes and References1IntroductionFor many wastes, combustion (incineration) is an attractive or necessary element of wastemanagement. Occasionally, as for the incineration of fumes or essentially ash-free liquidsor solids, combustion processes may properly be called disposal. For most solids and manyliquids, incineration is only a processing step. Liquid or solid residues remain forsubsequent disposal.Incineration of wastes offers the following potential advantages:1. Volume reduction: important for bulky solids or wastes with a high combustibleand=or moisture content.2. Detoxication: especially for combustible carcinogens, pathologically contami-nated material, toxic organic compounds, or biologically active materials thatwould affect sewage treatment plants.3. Environmental impact mitigation: especially for organic materials that wouldleach from landlls or create odor nuisances. In addition, the impact of the CO2greenhouse gas generated in incinerating solid waste is less than that of themethane (CH4) and CO2 generated in landlling operations. Also, because ofstrict air pollution emission requirements applicable to municipal refuseincinerators, the criteria pollutant air emissions per kilowatt of power producedare signicantly less than that generated by the coal- and oil-burning utilityplants whose electricity is replaced by waste-to-energy facilities (506).4. Regulatory compliance: applicable to fumes containing odorous or photo-reactive organic compounds, carbon monoxide, volatile organic compounds(VOCs), or other combustible materials subject to regulatory emission limita-tions.5. Energy recovery: important when large quantities of waste are available andreliable markets for by-product fuel, steam, or electricity are nearby.6. Stabilization in landlls: biodegradation of organic material in a landll leads tosubsidence and gas formation that disrupts cell capping structures. Destructionof waste organic matter eliminates this problem. Incineration also forms oxidesor glassy, sintered residues that are insoluble (nonleaching).7. Sanitation: destruction of pathogenic organisms presenting a hazard to publichealth.These advantages have justied development of a variety of incineration systems, ofwidely different complexity and function to meet the needs of municipalities andcommercial and industrial rms and institutions.Operating counter to these advantages are the following disadvantages of incinera-tion:1. Cost: usually, incineration is a costly waste processing step, both in initialinvestment and in operation.2. Operating problems: variability in waste composition and the severity of theincinerator environment result in many practical waste-handling problems, highmaintenance requirements, and equipment unreliability.3. Stafng problems: the low status often accorded to waste disposal can make itdifcult to obtain and retain qualied supervisory and operating staff. Becauseof the aggressive and unforgiving nature of the incineration process, stafngweaknesses can lead to adverse impacts on system availability and maintenanceexpense.4. Secondary environmental impacts:Air emissions: many waste combustion systems result in the presence of odors,sulfur dioxide, hydrogen chloride, carbon monoxide, carcinogenic poly-nuclear hydrocarbons, nitrogen oxides, y ash and particulate fumes, andother toxic or noxious materials in the ue gases. Control of emissions tovery low levels has been shown to be within the capability of modern airpollution control technology.Waterborne emissions: water used in wet scrubber-type air pollution controloften becomes highly acidic. Scrubber blowdown and wastewater fromresidue quenching may contain high levels of dissolved solids, abrasivesuspended solids, biological and chemical oxygen demand, heavy metals,and pathogenic organisms. As for the air pollutants, control of thesepollutants can be readily effected to discharge standards using availabletechnology.Residue impacts: residue disposal (y ash and bottom ash) presents a variety ofaesthetic, water pollution, and worker health-related problems that requireattention in system design and operation.5. Public sector reaction: few incinerators are installed without arousing concern,close scrutiny, and, at times, hostility or profound policy conicts from thepublic, environmental action groups, and local, state, and federal regulatoryagencies.6. Technical risk: process analysis of combustors is very difcult. Changes inwaste character are common due to seasonal variations in municipal waste orproduct changes in industrial waste. These and other factors contribute to therisk that a new incinerator may not work as envisioned or, in extreme cases, atall. In most cases, the shortfall in performance is realized as higher thanexpected maintenance expense, reduced system availability, and=or diminishedcapacity. Generally, changes in waste character invalidate performance guaran-tees given by equipment vendors.With all these disadvantages, incineration has persisted as an important concept in wastemanagement. About 16% of the municipal solid waste and wastewater sludge wasincinerated in the United States in the mid-1990s. Over the years, the rate of constructionof new incineration units has varied greatly. Key factors in slowing construction includehigh interest rates, cost escalation from changes in air pollution control regulations,recession inuences on municipal budgets, and surges in anti-incineration pressure fromthe advocates of recycling. However, increasing concern over leachate, odor, and gasgeneration 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 of incineration in the future,particularly in Europe.Combustion processes are complicated. An analytical description of combustionsystem behavior requires consideration of1. Chemical reaction kinetics and equilibrium under nonisothermal, nonhomoge-neous, unsteady conditions2. Fluid mechanics in nonisothermal, nonhomogeneous, reacting mixtures withheat release which can involve laminar, transition and turbulent, plug, recircu-lating, and swirling ows within geometrically complex enclosures3. Heat transfer by conduction, convection, and radiation between gas volumes,liquids, and solids with high heat release rates and (with boiler systems) highheat withdrawal ratesIn incineration applications, this complexity is often increased by frequent, unpredictableshifts in fuel composition that result in changes in heat release rate and combustioncharacteristics (ignition temperature, air requirement, etc.). Compounding these process-related facets of waste combustion are the practical design and operating problems inmaterials handling, corrosion, odor, vector and vermin control, residue disposal, associatedair and water pollution control, and myriad social, political, and regulatory pressures andconstraints.With these technical challenges facing the waste disposal technologist, it is a wonderthat the state-of-the-art has advanced beyond simple, batch-fed, refractory hearth systems.Indeed, incineration technology is still regarded by many as an art, too complex tounderstand.The origins of such technical pessimism have arisen from many facts and practicalrealities:1. Waste management has seldom represented a large enough business opportunityto support extensive internal or sponsored research by equipment vendors,universities, or research institutions.2. Municipal governments and most industries have had neither budgets norinclination to fund extensive analysis efforts as part of the design process.3. As a high-temperature process carried out in relatively large equipment,incineration research is difcult and costly.4. The technical responsibility for waste disposal has usually been given to rmsand individuals skilled in the civil and sanitary engineering disciplines, eldswhere high-temperature, reacting, mixing, radiating (etc.) processes are not partof the standard curriculum.Such pessimism is extreme. To be sure, the physical situation is complex, but, drawing onthe extensive scientic and engineering literature in conventional combustion, theproblems can be made tractable. The practical reality that pencil and paper are ever somuch cheaper than concrete and steel is an important support to the argument foraggressive exploitation of the power of engineering analysis.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 or practicing engineer the quantitative and qualitative guidance andunderstanding to cope with this important sector of environmental control engineering.The analytical methods and computational tools used draw heavily on the disciplinesof chemical and, to a lesser extent, mechanical engineering. As many readers may not befamiliar with the terms and concepts involved, the early chapters review the fundamentalanalysis methods of process engineering. Combustion and pyrolysis processes are thendiscussed, followed by a quantitative and qualitative review of the heat and uid mechanicsaspects of combustion systems.Building on the basic framework of combustion technology, combustion-basedwaste disposal is then introduced: waste characterization, incinerator systems, designprinciples, and calculations.2StoichiometryStoichiometry is the discipline of tracking matter (particularly the elements, partitioned inaccord with the laws of chemical combining weights and proportions) and energy (in all itsforms) in either batch or continuous processes. Since these quantities are conserved in thecourse of any process, the engineer can apply the principle of conservation to follow thecourse of combustion and ow processes and to compute air requirements, ow volumes,and velocities, temperatures, and other useful quantities. As a renement, the engineershould acknowledge the fact that some reactions and heat transfer processes sometimesstop short of completion because of equilibrium limitations. Also, for some situations,the chemical reaction rate may limit the degree of completeness, especially when systemresidence time is short or temperatures are low.I. UNITS AND FUNDAMENTAL RELATIONSHIPSA. UnitsIn analyzing combustion problems, it is advantageous to use the molecular (atomic) weightexpressed in kilograms (the kilogram mol or kilogram atom) as the unit quantity. Thisadvantage derives from the facts that one molecular (atomic) weight of any compound(element) contains the same number of molecules (atoms) and that each mol of gas, atstandard pressure and temperature, occupies the same volume if the gases are ideal.The concept of an ideal gas arises in the course of thermodynamic analysis anddescribes a gas for which intermolecular attractions are negligibly small, in which theactual volume of the molecules is small in comparison with the space they inhabit andwhere intermolecular collisions are perfectly elastic.B. Gas Laws1. The Perfect Gas LawThe behavior of ideal gases is described by Eq. (1a), the perfect gas law:PV nRT 1aIn this relationship P is the absolute pressure of the gas, V its volume, n the number ofmols of gas, R the universal gas constant, and T the absolute temperature. Note that 273.15must be added to the Celsius temperature and 459.69 to the Fahrenheit temperature to getthe absolute temperature in degrees Kelvin (

K) or degrees Rankine (

R), respectively.The perfect gas law was developed from a simplied model of the kinetic behaviorof molecules. The relationship becomes inaccurate at very low temperatures, at highpressures, and in other circumstances when intermolecular forces become signicant. Inthe analysis of combustion systems at elevated temperatures and at atmospheric pressure,the assumption of ideal gas behavior is sound.The same value of the universal gas constant R is used for all gases. Care must begiven to assure compatibility of the units of R with those used for P; V; n, and T.Commonly used values of R are given in Table 1.In the mechanical engineering literature, one often nds a gas law in use where thenumerical 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 wrather than the number of mols of gas is used:PV wR0T 1bEXAMPLE 1. Ten thousand kg=day of a spent absorbent containing 92% carbon, 6%ash, and 2% moisture is to be burned completely to generate carbon dioxide for processuse. The exit temperature of the incinerator is 1000

C. How many kilogram mols and howmany kilograms of CO2 will be formed per minute? How many cubic meters per minute ata pressure of 1.04 atm?One must rst determine the number of kilogram atoms per minute of carbon(atomic weight 12.01) owing in the waste feed:0:92 10;000=12:01 24 60 0:532 kg atoms=minTable 1 Values of the Universal Gas Constant R for Ideal GasesPressure Volume Mols Temperature Gas constantEnergy P V n T R atm m3kg mol K 0:08205 m3atmkg mol K kPa m3kg mol K 8:3137 kPa m3kg mol Kkcal kg mol K 1:9872 kcalkg mol Kjoules (abs) g mol K 8:3144 joulesg mol Kft-lb psia ft3lb mol R 1545:0 ft lblb mol RBtu lb mol R 1:9872 Btulb mol R atm ft3lb mol R 0:7302 ft3atmlb mol RNoting that with complete combustion each atom of carbon yields one molecule of carbondioxide, the generation rate of CO2 is 0.532 kg mol=min. The weight ow of CO2(molecular weight 44.01) will be (0.532)(44.01) 23.4 kg=min of CO2. The tempera-ture (

K) is 1000 273:15 1273:15, and from Eq. 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 temperatureand needs to compute the volume. For these calculations, it is convenient to obtain theanswer by adjusting a unit volume at a specied standard condition to the conditions ofinterest. For such calculations one can use the gas laws expressed in terms of the volume of1 kg or lb mol of an ideal gas at the standard conditions of 0

C or 273:15

K (32

F or492

R) and 1 atm. The molecular volume is 22:4 m3(359:3 ft3). If we denote the molecularvolume as V0, and the pressure and temperature at standard conditions as P0 and T0,respectively, the gas law then yields:V n V0P0P TT02where P0 and T0 may be expressed in any consistent absolute units. For example, the gasvolume from the preceding example could be calculated asV 0:532 22:4 1:001:041273:15273:15 53:41 m3=min CO2Daltons law (1801) of partial pressures is another useful identity derived from the idealgas 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 thepressure each gas would exert if it alone occupied the volume of the mixture at the sametemperature. For a perfect gas, Daltons law equates the volume percent with the molpercent and the partial pressure:Volume percent 100 mol fraction 100 partial pressuretotal pressure 3EXAMPLE 2. Flue gases from combustion of 14.34 kg of graphite (essentially, purecarbon) with oxygen are at a temperature of 1000

C and a pressure of 1.04 atm. What isthe volume in m3of the CO2 formed? What is its density?V 14:3412:0122:4 1:01:041000 273:15273:15 119:87 m3For each mol of CO2 formed, the mass is 12.01 32.00, or 44.01 kg (see Table 1 inAppendix C for atomic weights). The gas density under these conditions isrCO2 44:1222:4 1:01:041000 273:15273:15 0:438 kg=m3EXAMPLE 3. The carbon monoxide (CO) concentration in a ue gas stream with10% moisture at 500

C and 1.05 atm is measured at 88.86 parts per million by volume.Does this meet the regulatory limit of 100 mg per normal cubic meter (Nm3), establishedby the regulation as being a dry basis at 0

C and 1.0 atm? Adjustment to the temperature orpressure conditions of the regulatory limit does not change the mol fraction of CO in thegas. The CO concentration corresponding to the regulatory limit under dry conditions iscalculated as (88.86)(1.0 0.1), or 79.97 parts per million, dry volume (ppmdv).The volume of one kilogram mol of any gas at 0

C and 1.0 atm is 22.4 m3. For CO,with a molecular weight of 28.01, the mass of one mol is 28:01 106mg. Therefore, themass concentration of CO in the ue gases is given byCO 79:97 10628:01 10622:4 100:0 mg=Nm32. Standard ConditionsThroughout the published literature, in regulatory language, in industrial data sheets, etc.,one frequently nds references to the term standard conditions. While the words implystandardization, it should be cautioned that the meaning is not at all consistent.For example, ow calculations by U.S. fan manufacturers and the U.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 manufactured gas industry uses 60

F, saturated with water vapor at 30 in. of Hgabsolute, for marketing but 60

F dry at 1 atm for combustion calculations.Other important appearances of the term standard conditions are found in thecalculations and reports associated with permits for atmospheric discharges. The standardconditions in which to report stack gas ows in the United States are often based on 20

C(68

F) and 1 atm.The reference states used to specify and report the concentration of pollutants in airpollution regulations and permits often generate another set of standard conditions. In theUnited States, this may involve the calculation of volume in standard cubic feet (scf) at areference temperature of 32

F and 1 atm. In Europe, the metric equivalent (0

C and1.0 atm) is used to characterize the normal cubic meter, or Nm3. For particulate matterand the concentrations of gaseous pollutants, the reference volume is commonly furthercorrected to a specied concentration of oxygen (usually 7% O2 in the United States but11% O2 in Europe and Asia) or carbon dioxide (usually 12% CO2) by the mathematicaladdition=subtraction of oxygen and nitrogen in the proportions found in air.As an alternative to specifying the oxygen or carbon dioxide concentration atstandard conditions, some agencies call for adjustment to a specied percent excess air(the combustion air supplied in excess of the theoretical air requirement expressed as apercentage of the theoretical air). Further correction may be required to express theconcentration on a dry basis.In most real situations, the gas temperature, pressure, and state of dryness are quitedifferent from the standard conditions requested. In these circumstances, the perfect gaslaw and its extensions (e.g., Daltons law) are used to make the corrections.EXAMPLE 4. A sample weight of 76 mg of particulate matter is collected in thecourse of sampling 2.35 actual m3of ue gas at 68

C and 1.03 atm. The ue gas contains12.5% moisture. An Orsat (dry basis) analysis of the gases shows 10.03% oxygen and10.20% carbon dioxide. The air pollution code emission limit is 60 mg=Nm3corrected to7% oxygen. The emission code denes normal cubic meter (Nm3) as 0

C and 1.0 atm.Is the source in conformance with the code? What if the code referenced a correction to12% carbon dioxide? Or to 50% excess air?Correct the gas volume to reference temperature and pressure using Eq. (2).V 2:35 273:15 0:0273:15 68:0 1:001:03 1:827 m3wetCorrect gas volume to dry basis.corrected volume 1:8271:00 0:125 1:598 Nm3dryCalculate gas volume and dust concentration at reference O2 concentration.CO221:0 measured %O221:0 reference %O2The gas volume at 7% O2 is calculated with the correction factor CO2.CO221:0 10:0321:0 7:0 4Here CO2 0:784, and the corrected gas volume is1:5980:784 1:252 Nm37% O2The particulate concentration is, then,76=1:252 60:7 mg=Nm3at 7% O2 fails the emission codeCalculate dust concentration at reference CO2 concentration.The gas volume at 12% CO2 is calculated with the correction factor CCO2.CCO2measured % CO2reference % CO2 10:212:005Therefore, CCO2 0:85, and the corrected volume is1:5980:85 1:358 Nm312% CO2The particulate concentration is, then,76=1:358 56:0 mg=Nm3at 12% CO2 passes the emission codeCalculate dust concentration at reference excess air.By difference, the nitrogen concentration (dry) 100:00 10:2 10:03 79:77%. A correction factor (CF50) may be developed that adjusts the gasvolume from an initial condition with O2, N2, and CO volume (mol) percentoxygen, nitrogen, and carbon monoxide (dry basis), respectively, to the gasvolume at 50% excess air. The accuracy of the factor depends on the assumptionof negligible nitrogen content for the fuel.CF50 21:1 1:5 O20:75 CO 0:132 N221:1 6Here, CF50 0:786, and the corrected volume is1:5980:786 1:256 Nm3at 50% excess airThe particulate concentration is, then,76=1:256 60:5 mg=Nm3at 50% excess air fails the requirementC. EnergyIn this chapter, the basic unit of heat energy will be the kilogram calorie (kcal): thequantity of heat necessary to raise the temperature of 1 kg of 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 4186.8 joules or 3.968 Btu; 1 kcal=kg 1.8 Btu=lb; 1 Btu 1055.1 joules, and1 Btu=lb 2326 joules=kg. (See also Appendix B.)1. Heat of ReactionThe heat of reaction is dened as the net enthalpy change resulting from a chemicalreaction. The energy effect can be net energy release (an exothermic reaction) or energyabsorption (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 effect when the compound is formedfrom its constituent elements in their standard states (usually 298:15

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 given off by the rst two (exothermic) reactions. By convention, the heat offormation for exothermic reactions is negative. In the formation of gaseous hydrogeniodide (HI) from its elements, the reaction absorbs energy (endothermic) and DH298 ispositive. Note, however, that in some of the older thermochemical literature, thisconvention is reversed.It is important to note that, by denition, the heat of formation of the elements intheir standard states is zero. Useful heat of formation values (expressed in kcal=gram molat 25

C) include those listed in the following table:Substance DH298 Substance DH298CO2g 94:03 COg 26:4H2OI 68:3 C2H6l 23:4SO2g 70:2 CH3OHl 60:0NH3g 11:0 C2H5OHl 66:2HClg 22:06 CHCl3l 31:5For the special case where the reaction of interest is oxidation at elevated temperatures, werefer to the heat effect as the heat of combustion. The heat of combustion for carbon-hydrogen- and oxygen-based fuels and waste streams is, clearly, the release of energywhen the substance(s) reacts completely with oxygen to form CO2 and H2O. This heatrelease may be calculated as the difference between the heats of formation of the productsand reactants. The heat of combustion for compounds containing N, S, Cl, P, etc., may becalculated similarly, but the results may be unreliable due to the uncertainty in the speciccompounds formed.EXAMPLE 5. Using the heat of formation (DHf) data given above, calculate the heatof combustion (DHc) of ethyl alcohol (C2H5OH) and chloroform (CHCl3).Ethyl alcohol burns as follows:C2H5OH 3O2 !2CO23H2ODHc DHf products DHf reactants 294:03 368:3 166:2 30:0 326:76 kcal per gram molecular weight GMWFor a molecular weight of 46, this corresponds to 7:1035 kcal per gram 7103:5 kcal=kg 12;786 Btu=lbChloroform may burn(a) CHCl332O2 !CO212H2O 32Cl2 or(b) CHCl3O2 !CO2HCl Cl2For reaction (a), DHc 96:68 kcal=GMWFor reaction (b), DHc 84:59 kcal=GMWLiterature value: DHc 89:20 kcal=GMWA value for the heat of combustion of the feed material is often needed while analyzingcombustion systems. For the complete combustion of methane, the reaction isCH4g 2O2g !CO2g 2H2O l 212;950 kcalThis shows that 1 kg mol of methane is oxidized by 2 kg mol of oxygen to form 1 kg molof 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.A pressure of 1 atm and an initial and nal temperature of the reactants and products of298.15 K (20

C ) is assumed, unless otherwise indicated.The heat of combustion given in this manner (with the water condensed) is known asthe higher heating value (HHV). The HHV is the common way to report such data in theU.S. and British literature. Clearly, however, in a real furnace, the sensible heat content ofthe ue gases will be lower than would be suggested by the HHV by an amount of energyequivalent to the latent heat of vaporization of the water (10,507 kcal=kg mol at 25

C).This corresponds to 21,014 kcal=kg mol of methane. Thus, the so-called lower heatingvalue (LHV) corresponds toCH4g 2O2g !CO2g 2H2Og 191;936 kcalThe LHV is the energy release value commonly reported in the literature of continentalEurope and Asia.For a fuel with a dry basis hydrogen content of %H2 (expressed as a percent), theHHV and LHV (dry basis) are related byLHV HHV 94:315 %H2 for LHV; HHV in Btu=lb and 7aLHV HHV 52:397 %H2 for LHV; HHV in kcal=kg 7bEXAMPLE 6. The Chinese literature reports the heating value of a municipal refusefrom the Beijing area as 1800 kcal=kg (as red). The moisture content of the waste was37%, and the hydrogen content of the waste (on a dry basis) was 3.69%. How do these datasuggest that the heating value of the Chinese waste compares with waste burned in NewYork City, which is often reported to have a heating value of about 6300 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 heating value is an HHV. A quick review of the data in Chapter 4 suggests thatmost U.S. refuse has an as-red (wet basis) heating value between 4500 and 5500 Btu=lb(2500 to 3050 kcal=kg), so the New York number is probably on a dry basis. Assumingthese reference conditions.The dry basis LHV of the Chinese waste isLHV 18001 0:37 2857 kcal=kgThe dry basis HHV of the Chinese waste isHHV 2857 52:397 3:69 3050 kcal=kg or 5491 Btu=lbTherefore, the Chinese waste has about 85% of the heating value of the New York refuse.Also, one might speculate that the New York refuse is about 2025% moisture, so the as-red (wet basis) heating value is about 70% of that for the New York waste.This example problem vividly illustrates the difculties and consequent uncertaintiesin the results that arise due to incomplete specication of the intended basis for physicaland thermochemical properties. This emphasizes the importance of making the basis clearin professional publications, instructions to laboratories, specications for equipmentvendors, and so forth.2. Sensible Heat of GasesIn 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 andasymptotically approaches a value Mc

p as the pressure approaches zero. The enthalpychange (Dh) between temperature limits T1 and T2 is then given byDh T2T1Mcop dT kcal=kg mol 8This calculation may be carried out using an analytical relationship for Mc

p as a functionof temperature. Constants for such relationships are given in Table 2 for several commongases. Alternatively, one can use a graphical presentation of the average molal heatcapacity between a reference temperature of 15

C (60

F) and the abscissa temperature(Fig. 1). The average molal heat capacity is calculated and used as follows:Mc0p;av T15Mc0p dTT 15 9Dh nMc0p;avT 15 kcal 10EXAMPLE 7. What is the sensible heat content of 68 kg of carbon dioxide at 1200

Crelative to 15

C? How much heat must be removed to drop the temperature to 300

C?First, determine the number of mols of CO268=44 1.55 mols. From Table 2, the heatcontent at 1200

C is given by:Dh 1:551200159:00 7:183 103T 2:475 106T2dt 1:55 9T 7:183 103T22 2:475 106T33 !120015 22;340 kcalTable 2 Constants in Molal Heat Capacity Mcop Relation-ship with Temperature Mcop a bT CT2aCompound a b cH2 6.92 0:153 1030:279 106O2 6.95 2:326 1030:770 106N2 6.77 1:631 1030:345 106Air 6.81 1:777 1030:434 106CO 6.79 1:840 1030:459 106CO2 9.00 7:183 1032:475 106H2O 7.76 3:096 1030:343 106NO 6.83 2:102 1030:612 106SO2 9.29 9:334 1036:38 106HCl 6.45 1:975 1030:547 106HBr 6.85 1:041 1030:158 106Cl2 8.23 2:389 1030:065 106Br2 8.66 0:780 1030:356 106CH4 8.00 15:695 1034:300 106A similar calculation for an upper limit of 300

C yields 4370 kcal and a net heat extractionof 22,340 4370 17,970 kcal. Alternatively, using Fig. 1, the heat content at 1200

Cis:1:5512:31200 15 22;600 kcaland at 300

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

C and upper temperature (Btu=lb mol, Kcal=kgmol). (Courtesy, Professor H.C. Hottel, Chemical Engineering Department, M.I.T.)The approximate heat loss between 1200

and 300

C is 18,140 kcal.3. Sensible Heat of SolidsKopps rule [Eq. (11)] (432) can be used to estimate the molar heat capacity (Mcp) of solidcompounds. Kopps rule states thatMcp 6n kcal=kg mol C 11where n equals the total number of atoms in the molecule.Building on Kopps rule, Hurst and Harrison (433) developed an estimationrelationship for the Mcp of pure compounds at 25

C:Mcp Pni1NiDEi kcal=kg mol C 12where n is the number of different atomic elements in the compound, Ni is the number ofatomic elements i in the compound, and DEi is the value from Table 3 for the ith element.Voskoboinikov (391) developed a functional relationship between the heat capacityof slags Cp (in cal=gram C) and the temperature T

C) given as follows.For temperatures from 20

to 1350

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.For temperatures from 1350

to 1600

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 isa reasonable assumption.Table 3 Atomic Element Contributions to Hurst and Harrison RelationshipElement DEi Element DEi Element 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 All other 6.3624. Latent HeatThe change in state of elements and compounds, for example, from solid (s) to liquid (l),or from liquid (l) to gas (g), is accompanied by a heat effect: the latent heat of fusion,sublimation, or vaporization for the state changes (s)!(l), (s)!(g), and (l)!(g),respectively. Latent heat effects in many industrial processes are negligible. For example,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, several latent heat values are given in Table 4.5. Decomposition and IonizationCombustion and incineration systems often experience temperatures high enough thatsome compounds decompose into several simpler fragments. The decomposition is notnecessarily associated with oxidation reactions and often reects the breakage of chemicalor ionic bonds in the compounds purely under the inuence of heat. These reactionsinclude thermal degradation reactions of organic compounds, thermal decompositionreactions of inorganic compounds, and ionization.The thermal degradation of organic compounds is a common and important step inthe combustion process. Degradation can involve simple rupture of bonds induced byelevated temperature (pyrolysis). This is, often, an endothermic reaction. In some physicalsituations (starved air incineration), partial oxidation takes place, generating heat thattriggers pyrolysis reactions in part of the combustible material. Depending on the balancebetween pyrolytic and oxidative reactions, the overall heat effect can be either endothermicor exothermic. This important class of decomposition reactions is covered in detailelsewhere in this book.Thermal degradation of inorganic compounds can introduce important energyeffects in some combustion and incineration processes. Also, the decomposition processmay 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) to form lime (solid calcium oxide) and carbon dioxide (a gas).Table 4 Latent Heat Effects for Changes in State of Common MaterialsLatent heat of indicated state changeTemperatureMaterial State change

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-Butyl alcohol 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, one must recognize that decomposition does not suddenly take place at adiscrete temperature, but, in fact, is occurring to some degree at all temperatures. Thedegree and rate of decomposition are often strongly temperature-dependent. At any giventemperature, the concentration (chemical activity) of the reactants and products tendstoward or achieves a specic relationship one to another as dened by the equilibriumconstant (discussed in Section V of this chapter).Taking limestone decomposition as an example, at any instant of time somemolecules of calcium carbonate are breaking apart, releasing gaseous CO2. Also, however,CO2 from the environment is reacting with calcium oxide in the solid matrix to reform thecalcium carbonate. The equilibrium partial pressure of CO2 over the solid and thedecomposition rate are functions of temperature. As the temperature increases, the partialpressure of CO2 increases. The approximate decomposition temperatures in Table 5correspond to a partial pressure of 1 atm of the pertinent gaseous product.At very high temperatures (>2500

C), other classes of decomposition reactionsoccur: the thermal breakdown of polyatomic gases (e.g., O2 and N2 into atomic oxygenand nitrogen) and, at still higher temperatures, ionization. These reactions are conned tothe very highest temperature operations. However, they can have signicance (throughtheir strongly endothermic heat effect) in affecting the peak temperature attained and ongas composition for ames of pure fuels under stoichiometric conditions or withsignicant air preheat or oxygen enrichment. In incineration situations when moisture,excess air, or other factors tend to favor lower operating temperatures, these reactions areusually unimportant. As for the decomposition reactions, the course of dissociationreactions as the temperature changes is described by equilibrium relationships. Thedissociation characteristics of atmospheric gases are presented in Table 6.6. Kinetic and Potential EnergyIn concept, a fraction of the heat of combustion in fuels and wastes can be converted intokinetic (velocity) and potential (pressure or elevation) energy. Clearly, such a conversion isessential to the operation of rocket engines, gas turbines, and other highly specializedcombustors. For the facilities of importance in this book, these energy terms are generallyunimportant.Table 5 Decomposition Temperatures of Selected Compounds (

C)Material Solid Gaseous TemperatureCaCO3 CaO CO2 897CaSO4-2 H2O CaSO4-0.5H2O 1.5 H2O 128CaSO4-0.5 H2O CaSO4 0.5 H2O 163Ca(OH)2 CaO H2O 580Al(OH)3-n H2O 2 H2O 300Fe(OH)3-n H2O 1.5 H2O 500Fe2(SO4)3 Fe2O3 3 SO3 480NaHCO3 NaOH CO2 270Na2CO3 Na2O CO2 22457. Heat LossesUsually, 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 thestack gas temperature. Latent losses include the heat of evaporation of liquid water in thefeed plus that of the water formed by oxidation of feed and fuel hydrogen. These losses areunavoidable, but they may be minimized. Dry gas loss is reduced through the use of aneconomizer and=or air heater in energy recovery systems to extract the largest possiblequantity of useful heat from the ue gases before discharge. Moisture loss can be reducedthrough the removal of excess water from the feed (e.g., the dewatering of sewage sludge).A second category of heat loss is associated with the fuel energy that leaves thesystem as unburned combustible in solid residues and as fuel gases (CO, CH4, H2, etc.) inthe stack gas. Unburned combustible often results from low temperatures in zones of thecombustor. To achieve rapid and complete burnout, high temperatures and the associatedhigh oxidation reaction rates are necessary. Excessive moisture in the feed may preventattainment of these temperatures. Also, rapid cooling thatquenches combustion reac-tions may occur due to in-leakage of air (tramp air inltration) or by the passage ofcombustion gas over heat-absorbing surfaces (cold, wet feed in countercurrent owsystems, boiler-tube surfaces, 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 from a rotary kiln. Thebuoyancy-stabilized, stratied ow in these units often results in high temperatures andoxygen deciency at the top of the kiln and abundant oxygen at much lower temperaturesowing along the bottom of the kiln.A combination of the low temperature and the air insufciency mechanisms isresponsible for the incomplete burnout of massive combustible such as stumps, mattresses,or thick books and for the incomplete burning of large metal objects. In these cases, theslow diffusion of heat and oxygen through thick ash or char layers results in incompleteoxidation before total quenching of combustion in the residue discharge system.The third cause of unburned combustible is (often inadvertent) short transit times inthe combustor. Examples of this mechanism include the material that falls, unburned,through the grates of a mass burn incinerator or the unburned paper fragments swept tooquickly out of a refuse-derived fuel (RDF) incinerator by the rising combustion gases.Table 6 Dissociation Behavior of Selected MoleculesTemperature % Heat effectReaction

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 O2 1750 0.370 68,3902200 4.100CO2 $CO 0:5 O2 1120 0.014 68,0001540 0.4002200 13.500Radiation loss is the expression used to describe the third major heat loss: leakage ofheat into the surroundings by all modes of heat transfer. Radiation losses increase inproportion to the exposed area of hot surfaces and may be reduced by the use of insulation.Since heat loss is area-dependent, the heat loss (expressed as percentage of total heatrelease) generally increases as the total heat release rate decreases. The American BoilerManufacturers Association developed a dimensional algorithm [Eq. (13)] with which toestimate heat losses from boilers and similar combustors (180). The heat loss estimate isconservative (high) for large furnaces:radiation loss 3:6737C HR CFOP 0:6303ekWtype13where for the radiation loss calculated in kcal=hr (or Btu=hr):C constant: 1.0 for kcal=hr (0.252 for Btu=hr)HR design total energy input (fuel waste heat of combustion air preheat) inkcal=hr (or Btu=hr)FOP operating factor (actual HR as decimal percent of design HR)k constant dependent on the method of wall cooling and equal toWall cooling method kNot cooled 0.0Air-cooled 0.0013926Water-cooled 0.0028768Wtype decimal fraction of furnace or boiler wall that is air- or water-cooledII. SYSTEMS ANALYSISA. General Approach1. Basic DataThe basic information used in the analysis of combustion systems can include tabulatedthermochemical 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 owrates of feed, ue gases, etc.). Guiding the use of these data are fundamental relationshipsthat prescribe the combining proportions in molecules (e.g., two atoms of oxygen with oneof carbon in one molecule of carbon dioxide) and those that indicate the course and heateffect of chemical reactions.2. Basis of ComputationTo be clear and accurate in combustor analysis, it is important to specically identify thesystem 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 ofa one-to-one relationship between intermediate and nal results.As the rst step, therefore, the analyst should choose and write down the referencebasis: a given weight of the feed material (e.g., 100 kg of waste) or an element, or a unittime of operation. The latter is usually equivalent to a weight, however, and in general theweight basis is preferred.3. Assumptions Regarding Combustion ChemistryMost incinerated wastes contain the elements C, H, O, N, S, and Cl. Many contain P, Br,many metals, and unspecied inerts. In carrying out material balance calculations, theanalyst must assume the disposition of these elements in the combustor efuent streams(gaseous, liquid, and solid). Incomplete mixing, equilibrium considerations, limitations inheat transfer or reaction time, and other factors make real efuents chemically complexand 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 atypical oxidizing combustion environment:Elemental or organic carbon O2 !CO2. In real systems, a fraction of the carbonis incompletely oxidized. It appears as unburned combustible or char in the solidresidue, as hydrocarbons, and as CO in the efuent gases.Depending on temperature, inorganic (carbonate or bicarbonate) carbon may bereleased as CO2 by dissociation or may remain in the ash.Elemental or organic hydrogen O2 !H2O (but see chlorine, below).Depending on temperature, hydrogen appearing in water of hydration may or maynot be released.Hydrogen appearing in inorganic compounds can leave in a variety of forms,depending on temperature (e.g., 2NaOH !Na2O H2O.Oxygen associated with the nonmetallic elements C, H, P, S, or N in organiccompounds or with metals is assumed to behave as O2 in air viz. reacting to formoxides (or remaining as the oxide).Oxygen associated with carbonates, phosphates, etc., can leave in a variety of forms,depending on temperature.Nitrogen usually leaves as N2 (plus traces of NO, NO2).Reduced organic or inorganic sulfur or elemental sulfur O2 !SO2. A fractionwill be further oxidized to SO3.Oxidized organic sulfur (e.g., sulfonates) !SO2 and=or SO3.Depending on temperature, oxidized inorganic sulfur (SO4 , SO3 ) may be releasedas SO2 or SO3 (e.g., CaSO4 !CaO SO3.Organic phosphorus (e.g., in some pesticides) ! O2 !P2O5.Depending on temperature, inorganic phosphorus (e.g., phosphates) may leave in avariety of forms.Organic chlorine or bromine is usually a preferred oxidizing agent for hydrogen !HCl, HBr ( HBr may !H2Br2).Inorganic chlorine and bromine (chlorides and bromides) are generally stable,although oxy-halogens (e.g., chlorates, hypochlorites) degrade to chlorides andoxygen, water, etc.Metals in the waste (e.g., iron and steel, aluminum, copper, zinc) will, ultimately,become fully oxidized. However, incomplete burning (say, 25% to 75%) iscommon due to the low rate of surface oxidation and limited furnace residencetime.4. Approach to ComputationAlthough the skilled analyst may elect to skip one or more steps because of limited data orlack of utility, the following sequence of steps is strongly recommended:1. Sketch a ow sheet. Indicate all ows of heat and material, includingrecirculation streams. Document all basic data on the sketch, including specialfeatures of analytical data and heat effects.2. Select a basis and annotate the sketch to show all known ows of heat ormaterial relative to that basis.3. Apply material, elemental, and component balances. Recognize that the use ofaverage values for quantities and characteristics is necessary but that variationsfrom the average are most likely the norm rather than the exception. Explorealternative assumptions.4. Use energy balances. Here, too, explore alternative assumptions.5. Apply known equilibrium relationships.6. Apply known reaction rate relationships.7. Review the previous steps, incorporating the renements from subsequentstages into the simpler, earlier work.B. AnalysesUnlike more convention combustors, incineration systems are often charged with materialswhere the composition varies widely over time and that are highly complex mixtures ofwaste streams, off-specication products, plant trash, and so forth. The analysis of thesewastes must often be a compromise.In residential waste incineration, for example, what is a shoe? Is it (1) a shoe (i.e., awaste category easily identied by untrained eld personnel)? (2) 0.5 kg in the leatherand rubber category? (3) 0.2 kg leather, 0.18 kg rubber, 0.02 kg iron nails, etc.? (4) 8%moisture, 71% combustible, 21% residue, heating value of 3800 kcal=kg? (5) Thecomposition as given by ultimate analysis? or (6) Properties as given by a proximateanalysis? (7) A nonhazardous waste constituent? These are the questions waste engineersmust ponder as they impinge upon the adequateness of their design, the need for rigorousdetail (in consideration of feed variability), and, importantly, the sampling and analysisbudget allocation.The nal decision should be based on the impact of errors onRegulatory and permit denitions: hazardous or nonhazardous designationsMaterials handling: bulk density, storability, explosion and re hazard, etc.Fan requirements: combustion air and draft fansHeat release rate: per square meter, per cubic meter of the combustorMaterials problems: refractory or reside boiler-tube attack, corrosion in tanks,pipes, or storage bins, etc.Secondary environmental problems: air, water, and residue-related pollutionProcess economics: heat recovery rate, labor requirements, utility usage, etc.There are no simple rules in this matter. Judgments are necessary on a case-by-case basis.The techniques described below, however, give the analyst tools to explore many of theseeffects on paper. The cost is much lower than detailed eld testing and laboratory analysisand far less than is incurred after an incineration furnace has been installed and fails tooperate satisfactorily.The data generated for the evaluation of waste streams present problems to theanalyst. The problem begins with the largely uncontrollable characteristics of the wastegenerators, the unusual nature of the waste itself, and imperfections in the eld samplingprocess. These difculties make it problematical to secure proper samples, to adequatelypreserve and reduce the gross samples from the eld to the relatively small quantitiessubmitted to the laboratory, and to conduct the physical or chemical analyses themselves.One of the rst problems of concern is the need for a representative sample.Domestic waste composition has been shown to vary between urban and rural areas;between different economic and cultural groups; from month to month through the year; indifferent geographic, political, and climatological areas. There is a profound variation inthe quantities and characteristics of wastes generated by different industries and evenbetween different process alternatives for manufacture of the same product.This inherent variability in the basic waste composition is only the starting point inillustrating the difculty in securing a sample (ultimately in the 1- to 50-gram size) thatproperly reects the chemistry, heating value, and other signicant characteristics ofaverage waste. Waste streams often include constituents that are relatively massive andhard 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 therepository of almost all of the material of interest in many tons of waste. If the item isincluded, the waste is typical"; if not, the analysis is faulty.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 begood or because insufcient attention was given to moisture loss during and after thewaste was sampled. Not uncommonly, a waste sample may not be representative becausethe sampling 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.Let us leave this topic with an injunction to the engineer:Know the details of the sampling methodology, the sample conditioning protocols, and thelaboratory analysis and reporting methods before trusting the data.Several types of waste analysis are available to contribute to combustion systemstudies. They are briey reviewed here. The different analytical protocols characterize thewaste materials from different perspectives to meet different appraisal objectives.1. Waste Component AnalysisFor many waste streams, an acceptable and useful analysis is obtained by weighing thewaste after separation into visually denable components. For municipal solid waste, thecomponent categories often include newsprint, corrugated cardboard, other paper, foodwaste, yard waste, aluminum, metal (excluding aluminum), glass, leather, rubber, textiles,plastics, and miscellaneous. The use of these waste categories has obvious advantages inthe separation step. Further, the weights in each category are often useful in assessingrecycling processes and in monitoring trends in waste sources and composition. Thisanalysis methodology and taxonomy is discussed in greater detail in Chapter 4.2. Proximate AnalysisThe balance between moisture, combustible, and ash content, and the volatilizationcharacteristics of the combustible fraction at high temperatures are important propertiesaffecting combustor design. Quantitative knowledge of these properties gives considerableinsight into the nature of the pyrolysis and combustion processes for sludge, solid waste,and conventional fuels. A simple and relatively low-cost laboratory test that reports theseproperties is called the proximate analysis (1). The procedure includes the following steps:1. Heat one hour at 104

to 110

C. Report weight loss as moisture.2. Ignite in a covered crucible for seven minutes at 950

C and report the weightloss (combined water, hydrogen, and the portion of the carbon initially presentas or converted to volatile hydrocarbons) as volatile matter.3. Ignite in an open crucible at 725

C to constant weight and report weight loss asxed carbon.4. Report the residual mass as ash.It should be recognized that the value reported as 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 offor pyrolyzed but may also include water driven off from hydroxides or hydrates. Fixedcarbon includes the weight of carbon left behind as a char, but the value may be reducedby weight gain in the crucible from oxidation of metals. In the civilsanitary engineeringliterature concerning sewage treatment plant sludge incineration, volatile matter data areoften treated as though they were equivalent to combustible matter. For wastewatertrea