Industrial burners handbook c baukal

1386_HalfTitlePage 7/21/03 10:52 AM Page 1

2003 by CRC PreIndustrialBurners

H A N D B O O Kss LLC

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2003 by CRC PreDUSTRIAL COMBUSTION SERIESEdited by Charles E. Baukal, Jr.

PUBLISHED TITLES

omputational Fluid Dynamics in Industrial CombustionCharles E. Baukal, Jr., Vladimir Y. Gershtein, and Xianming Li

Heat Transfer in Industrial CombustionCharles E. Baukal, Jr.

The Industrial Combustion HandbookCharles E. Baukal, Jr.

The John Zink Combustion HandbookCharles E. Baukal, Jr.

Oxygen-Enhanced CombustionCharles E. Baukal, Jr.ss LLC

1386_TitlePage 7/21/03 10:51 AM Page 1

2003 by CRC PreCRC PR ESSBoca Raton London New York Washington, D.C.

E D I T E D B Y

Charles E. Baukal, Jr.

IndustrialBurners

H A N D B O O Kss LLC

This book contapermission, and reliable data andor for the conseq

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All rights reserveclients, may be gCenter, 222 RosISBN 0-8493-13a photocopy lice

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No claim to original U.S. Government worksInternational Standard Book Number 0-8493-1386-4

Library of Congress Card Number 2003051466Printed in the United States of America 1 2 3 4 5 6 7 8 9 0

Printed on acid-free paper

Library of Congress Cataloging-in-Publication Data

al burners handbook / edited by Charles E. Baukal, Jr.p. cm.

ncludes bibliographical references and index.SBN 0-8493-1386-4 (alk. paper). HeatingEquipment and suppliesHandbooks, manuals, etc. 2. Combustion

neeringHandbook, manuals, etc. I. Baukal, Charles E.

.I517 20033dc21 2003051466ss LLC

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2003 by CRC Prece

cuses specically on industrial burners. This book should be of interest to anyone with the eld of industrial combustion. This includes burner designers, researchers,

rnace designers, government regulators, and funding agencies. It can also serve as ak for those teaching and studying combustion. The book covers a wide range of burnerin a broad array of applications in the metals, minerals, incineration, hydrocarbon/l, and power generation industries. The authors represent a number of prominenters and have hundreds of years of combined experience with industrial burners. is organized in three sections. Section I deals with the basics of combustion inlications. It includes ve general chapters on heat transfer, uid ow, combustion,

r modeling. These chapters are written from the narrow scope of how they apply toion II concerns burner fundamentals. It includes ve chapters on the topics of burner burner noise, burner controls, burner testing, and burner physical modeling. Section 11 specic burner designs, including chapters on high-velocity burners, regenerativeal radiation burners, radiant tube burners, radiant wall burners, natural-draft burners,

s for single-burner applications, boiler burners for multi-burner applications, ductxy/fuel burners, and oxy/fuel burners. very few books that consider burners used in industrial applications. Combustiontain little if anything on practical combustion equipment such as burners. There are that consider industrial burners in differing levels of detail. The North Americanandbook (two volumes: Vol. 1, 3rd edition, 1986; Vol. 2, 3rd edition, 1997; publishedrican Manufacturing Co.) has been the industry standard since the 1950s and discusses of practical combustion systems, including burners. However, it does not go inton burners, nor does it cover the range of burner types that are considered here. Anotheronger in print, but considers industrial burners, is entitled Combustion Engineeringization (3rd edition, E&FN Spon, 1992, edited by J.R. Conforth, and sponsored byn the U.K.). It has two detailed and generously illustrated chapters on burners, butocuses on natural gas applications. The Industrial Heating Equipment Associationmprised of most of the U.S. industrial burner manufacturers. The IHEA publishes a Combustion Technology Manual (5th edition, IHEA, 1994), which contains several on industrial burners.ny book of this type, there are some topics that are not covered and some that aretensively. Because the vast majority of industrial applications use gaseous fuels, thatf this book, with limited discussion of liquid fuels and no discussion of solid fuels.ncerns atmospheric-pressure combustion, which is the predominant type used in

re are some burner designs that are not considered, particularly those intended formited applications.any book of this type, there are sure to be author preferences and biases, but theairly extensive and comprehensive. There are also generous discussions of manystrial applications to help the reader better understand the requirements for differents. Particularly because of the increasing emphasis on the environment, the design ofal burners continues to change and improve to reduce pollutant emissions. Whilener design and development is a dynamic area of continuing research, the principlesre are expected to be applicable well into the foreseeable future.ss LLC

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2003 by CRC Pret the Editor

aukal, Jr., Ph.D., P.E., is the Director of the R&D Test Center, the John Zink Institute,nd Flare R&D for the John Zink Co., LLC (Tulsa, OK) which is a leading supplierombustion equipment in the chemical, petrochemical, and power generation industries.y worked for 13 years at Air Products and Chemicals, Inc. (Allentown, PA) in theen-enhanced combustion and rapid gas quenching in the ferrous and nonferrous metals, waste incineration industries. He has also worked for Marsden, Inc. (Pennsauken,er, printing, and textile industries and Selas Corp. (Dresher, PA) in the metals industry,ea of industrial combustion equipment. He has more than 20 years of experience inindustrial combustion, pollution, and heat transfer and has authored more than 70n those areas. He is the editor of the books Oxygen-Enhanced Combustion, Compu- Dynamics in Industrial Combustion, and The John Zink Combustion Handbook, thebook Heat Transfer in Industrial Combustion, and the general editor of the Industrialeries, all with CRC Press (Boca Raton, FL).Ph.D. in mechanical engineering from the University of Pennsylvania (Philadelphia),.S. in mechanical engineering from Drexel University (Philadelphia), an M.A. in

ies from Dallas Theological Studies (Dallas, TX), and is working on an M.B.A. fromy of Tulsa (Tulsa, OK). He is a licensed Professional Engineer in the state of Penn-ertied Diplomate Environmental Engineer (DEE), and a Qualied Environmental(QEP). He has been an adjunct instructor at several colleges, is an expert witness inmbustion, has nine U.S. patents, and is a member of several Whos Who compilations.er of the American Society of Mechanical Engineers, the Air and Waste Managementhe Combustion Institute, the American Society of Safety Engineers, and several honorss LLC

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2003 by CRC Preowledgments

l would like to thank his wife Beth and his daughters Christine, Caitlyn, and Courtneynce and help during the writing of this book. He would also like to thank the goodithout whom this would not have been possible.nino dedicates his work to Jesus the Christ, his wife Judy, and their three children,

Nathanael J., and Jamie D. edge would like to express thanks to his wife Nancy, who always encourages him toe can be. Additionally, he is thankful to his Lord and Savior, Jesus Christ, for every for his vocation as a mechanical engineer.

Lincoln once said Everything I am, I owe to my angel mother. Joseph Smith gratefully acknowledge his family, friends, and associates for the part they have had life. He expresses his thanks to Dr. Chuck Baukal for his encouragement and example to contribute to the scientic literature, and to the publisher for supporting this effort.

presses deepest gratitude to his wife, Eileen, and his children. They have made life

ava thanks Olivier Charon, his former manager who was the rst contact for this work.s to Bernard Labegorre who is the major pusher to perform this work. Also thanks

amuner and Bertrand Leroux for data collection.lnikov would like to dedicate his work to the memory of his teachers in low-NOxnd boiler elds J.B. Zeldovich, V.V. Pomerantsev, N.V. Koznetsov, and A.D.

Webster would like to thank his wife Sharon for all her love, support, and encourage-ss LLC

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2003 by CRC Preributors

Abe is a Combustion and Process Control Specialist at The North American Manu-pany, Ltd., Cleveland, OH, where he has worked with combustion controls for 30

ngineering and sales/marketing capacity. He is a frequent lecturer on combustionorth American Combustion and Controls Seminars and at the Industrial Heatingssociations annual Safety Standards Seminar for Industrial Furnaces and Ovens.sman, Ph.D., is a Senior Development Engineer at the John Zink Company, LLCHe has more than 10 years of experience as a research and product developmenthe company, and has a Ph.D. in mechanical engineering from the University of Tulsa. U.S. patents, and has authored several publications. He has taught undergraduatechanical engineering at the University of Tulsa. Honors include Kappa Mu Epsilon

l Society and Sigma Xi Research Society. G. Claxton is a Senior Principal Engineer in the Burner Process Engineering Groupink Company, LLC (Tulsa, OK). He has a B.S. in Mechanical Engineering from the Tulsa and has worked for the John Zink Co. in the eld of industrial burners andquipment since 1974. He has co-authored a number papers and presentations coveringcombustion equipment, and combustion-generated emissions, and is co-holder ofustion-related patents.olannino, P.E., is the Director of Engineering and Design at the John Zink Company,OK) and a chemical engineer. He has more than 15 years of experience in therts and over 20 publications to his credit. He is listed in Whos Who in Science andnd Whos Who in California. Joseph is a member of the American Chemical Societye American Statistical Association (ASA).redge, Ph.D., currently works as a combustion and modeling engineer at the Johny, and is involved in both computational and physical uid ow modeling of burnersmponents. He previously worked for more than 5 years at the Lehigh Universityrch Center. He has worked on optimizing combustion on coal and natural gas red

he past 9 years. He worked on a project team as a primary developer of software forptimization of coal-red boilers. He is well experienced in computational uidsell as physical uids modeling. He has a number of publications related to modeling

t components, power plant emissions reductions, and performance improvements. He in mechanical engineering from the University of Tennessee, and is a member of theciety of Mechanical Engineers and The Combustion Institute.d Fleil, Ph.D., is the Acoustics Engineer of John Zink Company, LLC (Tulsa, OK).D. in mechanical engineering from a co-supervisory program between Ain Shamsd MIT. His areas of expertise are uid dynamics, combustion instability, and noiseas more than 20 publications on Active Control of Combustion Instability in IEEE,cience and Technology, and Combustion and Flame journals. He is listed in Whos

ica, Whos Who in Science and Engineering, Lexington Whos Who, and The NationalSpace Exploration Wall of Honor. He is a member of the ASME and AIAA.rd is a Senior Engineer, Instrumentation and Control Systems, at the John ZinkC (Tulsa, OK). He has worked in the eld of control and facilities design for 40 years. in physics. For many years he has conducted company training classes for control technicians. He has received numerous awards for innovative control system designss career, including the General Electric Nuclear Energy Divisions Outstanding Engi-d. Technical society memberships have included the Pacic Association of Generalss LLC

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2003 by CRC Pretists and Engineers (PAGESE), the Instrument Society of America (ISA), the Americanechanical Engineers (ASME), and the National Fire Protection Association (NFPA).uarco is the Combustion Specialist for the TODD Combustion Group of John Zink

joined John Zink in September of 1993 as a utility project engineer. In 1995, he added&D Engineer to his portfolio. In 1998, he assumed the responsibility of heading upical modeling effort, focusing on streamlining the modeling process, while generatingities for business and product development. John has authored papers on several

opics, including eld results of low-NOx combustion in several utility boilers, ultra-burners, eld results of gas-coal co-ring, physical modeling, and other NOx reductionr boilers. He is also one of the contributing authors of The John Zink Combustionhn received both a bachelors and masters degree in mechanical engineering from the Connecticut, as well as an MBA from the University of New Haven.t Hayes is a combustion engineer at the John Zink Company LLC (Tulsa, OK). Hers degree in mechanical engineering from Brigham Young University and has workedf combustion and thermal sciences for 7 years. He is the author or co-author of moreications in the elds of combustion and heat transfer and two patents pending.

ixson joined the CD adapco group in January 2003 as an engineer of CDa-acces, a subsidiary of adapco. Before joining CD adapco, Hixson worked as a CFD engineerink Company (Tulsa, OK).. Jayakaran (Jay Karan) is a director in the Technology & Commercial Development

John Zink Company LLC (Tulsa, OK). He has worked in the elds of combustion,ls, and power for 17 years, with responsibilities in R&D, plant operations, and engi-as an M.S. in mechanical engineering from Texas Tech University. He has authored

ical articles and papers, and has several patents pending.Sho) Kobayashi, Ph.D., is a Corporate Fellow at Praxair, Inc. (Danbury, CT). He hasygen combustion systems and processes for glass, steel, aluminum, petrochemical,and other industries for 27 years, and has authored or co-authored more than 40 U.S.ver 50 technical papers. He has a B.S. in aeronautical engineering from the University M.S. and Ph.D. degrees in mechanical engineering from the Massachusetts Institutey.Kodesh, P.E., is a controls engineer at John Zink Company (Tulsa, OK). He has more of experience as a process design and controls engineer. He has a Masters degreel engineering from Oklahoma State University.g is a project manager at The North American Manufacturing Company, Ltd., Cleve-

e has an associates degree in mechanical technology from Cuyahoga Communityorth American since 1978, he has worked in project and systems engineering and

with regenerative burner systems as a specialty. He is co-holder of several combustion-s.allen, P.E., is an account manager at the John Zink Company LLC (Tulsa, OK). He the eld of combustion for 11 years. He graduated from the University of Tulsa in

ds a B.S. in mechanical engineering.Lorra, Ph.D., started working for John Zink Co. LLC as a CFD engineer in 1999g his Ph.D. (Dr.-Ing.) at Ruhr-Universitaet (Bochum, Germany). He worked atnstitut (Essen, Germany), a well-known and established research facility, for 9 years.perience in NOx reduction techniques, especially reburning technology. During hiserme Institut, he developed his own CFD code for the calculation of turbulent reacting

ng chemistry with the laminar amelet-libraries. Parts of his research have beennternational conferences and are published in Gaswaerme-International.cas is a product manager at The North American Manufacturing Company, Ltd.,H. He has a B.S. in mechanical engineering from Cleveland State University and hasorth American in the eld of industrial burners and combustion systems since 1994,ss LLC

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2003 by CRC Preresponsibility for the companys direct-red regenerative burner line. He is co-holderr a diaphragm-actuated cycle valve.Miller is a research and design engineer at The North American Manufacturing., Cleveland, OH. He has a B.S. in mechanical engineering technology from Clevelandity and has worked for North American on burner product design and developmente is co-holder of several combustion-related patents.by is Vice President for The North American Manufacturing Company, Ltd., Cleve-

s career spans over 35 years in the industrial combustion eld, where he has workeddustrial areas of the world. Formerly the managing director of Hotwork Developmentnd, he operated reGen Systems Inc. in the U.S. until 1986 when he joined Northe has authored and co-authored numerous papers and presentations on combustionstems, and applications, and is co-holder of several combustion-related patents.. Quinn is manager of market development at The North American Manufacturing., Cleveland, OH. For over 20 years he has worked in various development, engineering,pacities with lead responsibilities for custom burner designs and their applications. Heed papers and presentations for the Industrial Heating Equipment Association and is co-ral combustion-related patents. He is a graduate of Cleveland State Universitys Fenngineering and has a B.S. in mechanical engineering and combustion application.ertson is manager of research and development at The North American Manufacturing., Cleveland, OH, where he has, for over 18 years, worked in the eld of fundamental

combustion. He has co-authored papers and taught classes in applied combustion North American Manufacturing and the Center for Professional Advancement. He is Case Western Reserve University and has a B.S. and an M.S. in uid and thermalis co-holder of several combustion-related patents.. Smith joined the CD adapco group in January 2003 as president of CDa-acces, a subsidiary of adapco. CDa-acces main goal is to establish StarCD, adapcos CFD-ring software, as the premier tool to help solve problems with turbulent reacting ow

ue to the hydrocarbon and chemical process industries. Josephs expertise includesncineration, pulverized-coal combustion/gasication, fumed metal-oxides production,g, all with a special emphasis on reaction engineering. Before joining CD adapco,d as director of are technology and computational uid dynamics for the John Zink has taught at Tennessee Technological University, the University of Michigan, andy of IllinoisUrbana/Champaign. He currently serves as an adjunct professor andlahoma State University and the University of Tulsa. Joseph has also consulted for

emical Company, Destec Energy Systems, Southern Company Services, and severallds six patents, and has authored more than 30 published articles and more than 40

apers. He is an active member of AIChE and has served as chair of both the Tulsahigan Sections of AIChE. He has also served as national chair of the Student Chapterse is also a member of Sigma-Xi and Tau Beta Pi. He received B.S., M.S., and Ph.D.

emical engineering from Brigham Young University.M. Smith is the President and CEO of Marsden, Inc., a leading manufacturer of high-o-pollution gas thermal radiation emitters. He studied mechanical/industrial engineer-xel Institute of Technology (Philadelphia, PA) and business management at Rutgersamden, NJ). He worked at TRW, Philco-Ford, and HRB Singer as an industrial

senior industrial engineer over a 10-year period before joining a manufacturers rm as a sales engineer. He rst became a business owner when he purchased thes representative rm in 1972. In 1976, he applied for the rst of over 50 grantedoreign Letters Patent on various embodiments of gas thermal radiation emitters. Heden, Inc. in 1976 to manufacture and market worldwide the unique Marsden Infraredr. Smith has taught national TAPPI courses and has had articles published in variousnals and magazines.ss LLC

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He has over the applicatiochemical engthe University

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2003 by CRC PreL. Somers is a senior process engineer at the John Zink Company, LLC (Tulsa, OK).30 years of experience in combustion and process design, with the past 15 years inn and design of duct burners for HRSG supplementary ring. He has an M.S. inineering from the University of Oklahoma and a B.S. in chemical engineering from of Tulsa.ava, Ph.D., is an engineer at Air Liquide (France) in the R&D Combustion Divisionsible for burner conception, design, and development. He has expertise in combustionl processes. He previously worked as an engineer in the Burner Division of the Steinpany. He has a Ph.D. from Universit Paul Sabatier (Toulouse, France), and hasers on the use of oxy/fuel combustion in the glass and metals industries.

ulnikov, Ph.D., is a senior research engineer for the John Zink Company, LLC/Toddroup (Shelton, CT). He has developed low-emission combustion technologies, low-

and other equipment for gas/oil red utility and industrial boilers. He holds 49 patentsstion/boiler eld, and has published more than 100 technical papers, including fouralso a contributing author to The John Zink Combustion Handbook. Venizelos, Ph.D., has been actively involved in the combustion eld for the last

, including working for two burner companies, John Zink Company, LLC and Zeeco,ed his Ph.D. in mechanical engineering from Louisiana State University. Dr. Venizelos

d basic scientic research work, industrial technology research and development, andesign engineering. He has experience in premixed and lean-premixed combustion,bustion systems, and laser and optical combustion diagnostics, as well as numerical

e has authored several peer-reviewed technical papers, government technical reports,cles, and patent applications.T. Waibel, Ph.D., is a Senior Principal Engineer in the Burner Process EngineeringJohn Zink Company, LLC (Tulsa, OK). He works in the eld of burner design andand has a doctorate in fuel science from the Pennsylvania State University. He haser 70 technical papers, publications, and presentations. Dr. Waibel has been thethe American Flame Research Committee since 1995. Webster is the director of power systems at the John Zink Company, LLC. He has eld of industrial combustion for 10 years and is a licensed professional mechanicalalifornia. He holds a B.S. degree in mechanical engineering from San Jose State

d a Master of Engineering degree from the University of Wisconsin. He has authored publications on combustion and emissions reduction.ss LLC

Table

Section I

Industrial C

Chapter 1

Charles E. B

Chapter 2

Charles E. B

Chapter 3

Wes Bussmanand R. Rober

Chapter 4

Joseph Colan

Chapter 5

Joseph D. Smand Tom Eldr

Section II

Burner Fund

Chapter 6

Charles E. B

Chapter 7

Mahmoud Fland Wes Buss

Chapter 8

Joe Gifford a

Chapter 9

Jeffrey Lewal


2003 by CRC Pre of Contents

ombustion Basics

Introduction

aukal, Jr., Ph.D., P.E.

Heat Transfer


Fluid Flow

, Ph.D., Demetris Venizelos, Ph.D.,t Hayes

Combustion Basics

nino, P.E.

CFD in Burner Development

ith, Michael Lorra, Ph.D., Eric M. Hixson,edge, Ph.D.

amentals

Heat Transfer from Burners


Burner Noise

eil, Ph.D., Jay Karan,man, Ph.D.

Combustion Controls

nd Zachary Kodesh, P.E.

Burner Testing

len, P.E. and Charles E. Baukal, Jr., Ph.D., P.E.ss LLC

Chapter 10

Burner Physical Modeling

John P. Guar

Section III

Burner Desi

Chapter 11

Tom Robertso

Chapter12

Russ Lang, B

Chapter 13

Thomas M. S

Chapter 14

Dennis E. Qu

Chapter 15

Demetris Ven

Chapter 16

Charles E. B

Chapter 17

Lev Tsirulnik

Chapter 18

Lev Tsirulnik

Chapter 19

Stephen L. So

Chapter 20

Charles E. B

Chapter 21

Hisashi Koba


2003 by CRC Preco and Tom Eldredge, Ph.D.

gns

High-Velocity Burners

n, Todd A. Miller, and John Newby

Regenerative Burners

ruce B. Abe, Clive Lucas, and John Newby

Thermal Radiation Burners

mith and Charles E. Baukal, Jr., Ph.D., P.E.

Radiant Tube Burners

inn and John Newby

Radiant Wall Burners

izelos, Ph.D., R. Robert Hayes, and Wes Bussman, Ph.D.

Natural-Draft Burners


Burners for Industrial Boilers

ov, Ph.D., John Guarco, and Timothy Webster

Multi-Burner Boiler Applications

ov, Ph.D., John Guarco, and Timothy Webster

Duct Burners

mers

Air-Oxy/Fuel Burners


Oxy-Fuel Burners

yashi, Ph.D. and Rmi Tsiava, Ph.D.ss LLC

Section IV

Appendices

Appendix A

Appendix B

Appendix C


2003 by CRC PreCommon Conversions

Design Data

Material Propertiesss LLC

Sect

Indus

1386_SectDiv_I.fm Page 1 Tuesday, October 7, 2003 11:10 AM

2003 by CRC Preion I

trial Combustion Basicsss LLC

1

Introduction

Charles E. Baukal, Jr., Ph.D., P.E.

CONTENTS

1.1 Industrial Combustion 1.2 Industrial Combustion Applications

1.2.1 Metals Production1.2.2 Minerals Production 1.2.3 Chemicals Production1.2.4 Waste Incineration1.2.5 Industrial Boilers and Power Generation1.2.6 Drying

1.3 Combustion System Components 1.4 Burner Design Factors

1.4.1 Fuel 1.4.2 Oxidizer 1.4.3 Gas Recirculation

1.5 General Burner Classifications1.5.1 Mixing Type 1.5.2 Fuel Type 1.5.3 Oxidizer Type 1.5.4 Draft Type1.5.5 Heating Type1.5.6 Burner Geometry

1.6 Burner Components1.7 Combustors

1.7.1 Design Considerations1.7.1.1 Load Handling1.7.1.2 Temperature1.7.1.3 Heat Recovery

1.7.2 General Classifications1.7.2.1 Load Processing Method1.7.2.2 Heating Type1.7.2.3 Geometry1.7.2.4 Heat Recuperation

1.8 Heat Load 1.8.1 Opaque Materials1.8.2 Transparent Materials

1.9 Heat Recovery Devices 1.9.1 Recuperators1.9.2 Regenerators

1.10 ConclusionsReferences

1386_C01.fm Page 3 Monday, September 15, 2003 9:34 PM


4

Industrial Burners Handbook

1.1 INDUSTRIAL COMBUSTION

The field of industrial combustion is very broad and touches, directly or indirectly, nearly all aspectsof our lives. The electronic devices we use are generally powered by fossil-fuel-fired power plants.The cars we drive use internal combustion engines. The planes we fly in use jet-fuel-poweredturbine engines. Most of the materials we use have been made through some type of heating process.While this book is concerned specifically with industrial combustion, all of the above combustionprocesses share many features in common.

Industrial combustion is complicated by many factors. First, the science of combustion is stilldeveloping and has a long way to go until we have a complete understanding of it so it can bebetter applied and controlled. While fire has been with us since the beginning of time, much remainsto be learned about it. The science of combustion combines heat transfer, thermodynamics, chemicalkinetics, and multi-phase turbulent fluid flow, to name a few areas of physics. Therefore, the studyof industrial combustion is interdisciplinary by necessity.

Combustion has been the foundation of worldwide industrial development for the past 200years.

1

Industry relies heavily on the combustion process as shown in Table 1.1. The major usesfor combustion in industry are shown in Table 1.2. Hewitt et al. (1994) have listed some of thecommon heating applications used in industry, as shown in Table 1.3.

2

Typical industrial combustionapplications can also be characterized by their temperature ranges as shown in Figure 1.1. As canbe seen in Figure 1.2, the demand for energy is expected to continue to rapidly increase. Most ofthe energy (88%) is produced by the combustion of fossil fuels such as oil, natural gas, and coal.According to the U.S. Dept. of Energy, the demand in the industrial sector is projected to increaseby 0.8% per year to the year 2020.

3

As shown in Figure 1.3, three elements are required to sustain combustion processes: fuel,oxidizer, and an ignition source (usually in the form of heat). Industrial combustion is defined hereas the rapid oxidation of hydrocarbon fuels to generate large quantities of energy for use in industrialheating and melting processes. Industrial fuels can be solids (e.g., coal), liquids (e.g., oil), or gases(e.g., natural gas). The fuels are commonly oxidized by atmospheric air (which is approximately21% O

2

by volume) although it is possible in certain applications to have an oxidizer (sometimesreferred to as an oxidant or comburent) containing less than 21% O

2

(e.g., turbine exhaustgas

4

) or more than 21% O

2

(e.g., oxy/fuel combustion

5

). The fuel and oxidizer are typically mixedin a device referred to as a burner, which is discussed in more detail below and is the subject ofthis book. An industrial heating process can have one or many burners, depending on the specificapplication and heating requirements.

Many theoretical books have been written on the subject of combustion, but they have little ifany discussion of industrial combustion processes.

611

Edwards (1974) has written a brief chapteron applications, including both stationary (boilers and incinerators primarily) and mobile sources

TABLE 1.1The Importance of Combustion in Industry

% Total Energy From (at the point of use)

Industry Steam Heat Combustion

Petroleum refining 29.6 62.6 92.2Forest products 84.4 6.0 90.4Steel 22.6 67.0 89.6Chemicals 49.9 32.7 82.6Glass 4.8 75.2 80.0Metal casting 2.4 67.2 69.6Aluminum 1.3 17.6 18.9

Source:

U.S. Dept. of Energy.

1



Introduction

5

TABLE 1.2Major Process Heating Operations

Metal MeltingSteel makingIron and steel meltingNonferrous melting

Metal HeatingSteel soaking, reheat, ladle preheatingForgingNonferrous heating

Metal Heat TreatingAnnealingStress reliefTemperingSolution heat treatingAgingPrecipitation hardening

Curing and FormingGlass annealing, tempering, formingPlastics fabricationGypsum production

Fluid HeatingOil and natural gas productionChemical/petroleum feedstock preheatingDistillation, visbreaking, hydrotreating, hydrocracking, delayed coking

BondingSintering, brazing

DryingSurface film dryingRubber, plastic, wood, glass products dryingCoal dryingFood processingAnimal food processing

CalciningCement, lime, soda ashAlumina, gypsum

Clay FiringStructural productsRefractories

AgglomerationIron, lead, zinc

SmeltingIron, copper, lead

Nonmetallic Materials MeltingGlass

Other HeatingOre roastingTextile manufacturingFood productionAluminum anode baking

Source:


1



6


(primarily internal combustion engines).

12

Barnard and Bradley (1985) have a brief chapter onindustrial applications.

13

A book by Turns (1996), which is designed for undergraduate and graduatecombustion courses, contains more discussions of practical combustion equipment than most similarbooks.

14

There have also been many books written on the more practical aspects of combustion. Griswolds(1946) book has a substantial treatment of the theory of combustion, but is also very practicallyoriented and includes chapters on gas burners, oil burners, stokers and pulverized-coal burners,heat transfer, furnace refractories, tube heaters, process furnaces, and kilns.

15

Stambuleanus (1976)book on industrial combustion has information on actual furnaces and on aerospace applications,particularly rockets.

16

There is much data in the book on flame lengths, flame shapes, velocityprofiles, species concentrations, liquid and solid fuel combustion, with a limited amount ofinformation on heat transfer. A book on industrial combustion has significant discussions on flamechemistry, but little on pollution from flames.

17

Keatings (1993) book on applied combustion isaimed at engines and has no treatment of industrial combustion processes.

18

A book by Bormanand Ragland (1998) attempts to bridge the gap between the theoretical and practical books oncombustion.

19

However, the book has little discussion of the types of industrial applications con-sidered here. Even handbooks on combustion applications have little if anything on industrialcombustion systems.

2024

1.2 INDUSTRIAL COMBUSTION APPLICATIONS

Burners are a key component in industrial combustion applications. An understanding of theseapplications is necessary when selecting the proper burner design. Some of the more commonburner designs are considered in this book. The uses of each burner type in specific applicationsare discussed in relevant chapters. Some of the most common industrial applications are brieflydiscussed next. Note that not every type of industrial burner is considered in this book as there arenumerous special designs for specific applications.

1.2.1 M

ETALS

P

RODUCTION

Metals are used in nearly all aspects of our lives and play a very important role in society. The useof metals has been around for thousands of years. There are two predominant classifications ofmetals: ferrous (iron-bearing) and nonferrous (e.g., aluminum, copper, and lead). Ferrous metalproduction is often high temperature because of higher metal melting points compared to non-ferrous metals. Many metal production processes are done in batch, compared to most otherindustrial combustion processes considered here which are typically continuous. Another fairlyunique aspect of metal production is the very high use of recycled materials. This often lends itself

TABLE 1.3Examples of Processes in the Process Industries Requiring Industrial Combustion

Process Industry Examples of Processes Using Heat

Steel making Smelting of ores, melting, annealingChemicals Chemical reactions, pyrolysis, dryingNonmetallic minerals (bricks, glass, cement and other refractories)

Firing, kilning, drying, calcining, melting, forming

Metal manufacture (iron and steel, and nonferrous metals) Blast furnaces and cupolas, soaking and heat treatment,melting, sintering, annealing

Paper and printing Drying

Adapted from Reference 3.



Intro

du

ction

7FIGURE 1.1

Temperature ranges of common industrial combustion applications. (Courtesy of Werner Dahm, 1998.)

1386_C01.fm

Page 7 Monday, Septem

ber 15, 2003 9:34 PM


8


to batch production because of the somewhat unknown composition of the incoming scrap materialsthat may contain trace impurities that could be very detrimental to the final product if not removed.The metals are typically melted in some type of vessel and then sampled to determine the chemistryso that the appropriate chemicals can be either added or removed to achieve the desired grade ofmaterial. Another unique aspect of the metals industry is that transfer vessels are preheated priorto the introduction of molten metals into the vessel to minimize the thermal shock to the refractory.Figure 1.4 shows an example of preheating a transfer ladle.

Because metals melt at higher temperatures, higher intensity burners are often used in theseapplications. This includes, for example, oxygen-enhanced combustion

25,26

and air preheating toincrease the flame temperatures and metal melting capability. These higher intensity burners havethe potential to produce high pollutant emissions, so burner design is important to minimizethese emissions.

Another somewhat unique aspect of metals production is that supplemental heating may berequired to reheat the metals for further processing. For example, ingots might be produced inone location and then transported to another location to be made into the desired shape (e.g.,wheel castings are often made from remelting aluminum ingots or sows). While this process canbe economically efficient, it is energy and pollutant inefficient due to the additional heating.Burners are used in the original melting process as well as in the reheating process. This issomething that has begun to attract more attention in recent years, where the entire life cycle ofa product is considered rather than just its unit cost and initial energy requirements. For example,aluminum has a low life-cycle cost compared to many other metals because of its high recycle

FIGURE 1.2

Historical and projected world energy consumption. (

Source:


3

)

FIGURE 1.3

Combustion triangle.

5

1970 1980 1990 2000 2010 2020

50

40

30

20

10

0

Year

Quad

rillio

n Bt

u

History ProjectionsPetroleum

Natural gas

Coal

Nonhydrorenewablesand otherNuclear Hydro

Fuel Oxygen

Source of Ignition



Introduction

9

ratio. While the energy consumption to make aluminum from raw ore is fairly high, remeltingscrap aluminum takes only a fraction of that energy, which also means less overall pollution.Burners commonly used in the metals industry include high-velocity burners (Chapter 11), regen-erative burners (Chapter 12), radiant tube burners (Chapter 14), air-oxy/fuel burners (Chapter 20),and oxy/fuel burners (Chapter 21).

1.2.2 M

INERALS

P

RODUCTION

Some common minerals processes include the production of glass, cement, bricks, refractories, andceramics. These are typically high-temperature heating and melting applications that require asignificant amount of energy per unit of production. They also tend to have fairly high pollutantemissions as a result of the high temperatures and unit energy requirements. Most mineral appli-cations are continuous processes, but there is a wide range of combustors. Large glass furnaces aretypically of rectangular shape and have multiple burners. On the other hand, cement kilns are longrefractory-lined rotating cylinders that are slightly inclined so that the materials flow graduallydownhill (see Figure 1.5). A typical cement plant is shown in Figure 1.6.

Many

minerals applications employ some type of heat recovery in the

form of air preheatingto improve energy efficiency. However, the heat recovery typically significantly increases NOxemissions. While recycling of used glass (referred to as cullet) is practiced in some applications,there is generally must less recycling in the minerals industry compared to the metals industry.Some burners used in minerals applications include regenerative burners (Chapter 12), air-oxy/fuelburners (Chapter 20), and oxy/fuel burners (Chapter 21).

1.2.3 C

HEMICALS

P

RODUCTION

This is a very broad classification that encompasses many different types of production processesthat have been loosely sub-categorized into chemicals (organic and inorganic) and petrochemicals(organic) applications. A typical refinery is shown in Figure 1.7. There is some overlap in terms

FIGURE 1.4

Ladle preheater.

Ladle

Firewall

Ladle Seal



10


FIGURE 1.5

Counter-current rotary cement kiln schematic.

FIGURE 1.6

Cement plant.

FIGURE 1.7

Refinery.

FeedMaterials

ProcessedClinker

To Off GasTreatment

Burner



Introduction

11

of the types of heating equipment used where many of the incoming feed materials are in liquidform (e.g., crude oil) that are processed in heaters with tubes running inside them. These aregenerally lower temperature applications (

12


FIGURE 1.9

Municipal waste incinerator.

FIGURE 1.10

Schematic of municipal solid waste incinerator.

TO STEAM GENERATOR& BAG HOUSE

MOVINGGRATE

ASH & METAL

COMBUSTION AIR

FEEDHOPPER



Introduction

13

of a municipal solid waste incinerator. The waste may be very wet after a rain storm, which mayput a huge extra heat load on the incinerator. In some locations where waste materials are separatedfor recycling, the waste actually fed into the incinerator may have a much higher heating valuecompared to other incinerators where there is no separation of the waste.

A complicating factor with incinerators is that the end product (e.g., the noncombustible waste)must also be disposed of, which means that one of the goals of most incineration processes is toproduce minimal waste output. Because of waste material variability, other pollutants can begenerated that are not normally associated with industrial combustion processes. An example isthe burning of plastics, which can produce dioxins and furans. The types of incinerators can varygreatly, depending on a variety of factors. In some cases, waste materials to be destroyed can befed through the burners. This is particularly true of waste hydrocarbon liquids. Some of the burnersused in incineration include air-oxy/fuel (Chapter 20) and oxy/fuel (Chapter 21).

1.2.5 I

NDUSTRIAL

B

OILERS

AND

P

OWER

G

ENERATION

Boilers are used for a variety of purposes in an assortment of applications. Common uses includeproducing hot water or steam for heating, producing steam for use within a plant such as atomizingoil for oil-fired burners, and producing steam to generate power in large power plants. Applicationsrange from small single-burner uses in hospitals, schools, and small businesses, up to large multi-burner boilers in power plants. The burners used in boilers are typically regulated because of theirproliferation and widespread use in applications involving the general public. The burners arenormally required to have a full complement of safety controls to ensure safe operation. Theseburners are often highly regulated to minimize pollutant emissions, particularly in large powerplants because of the size of the source. The types of burners used in smaller single-burner boilerapplications are considered in Chapter 17. Boiler burners used in larger applications requiringmultiple burners are considered in Chapter 18.

A special category of burners sometimes used in large power generating plants with gasturbines are called duct burners (see Figure 1.11). A schematic of the typical location of ductburners downstream of the turbine is shown in Figure 1.12. These burners are unique becausethey use the combustion products from a turbine as their combustion air. The turbine exhaustgas (TEG) is at an elevated temperature and contains significant quantities of carbon dioxideand water, which are the products of the upstream combustion process. The TEG is also at adepleted oxygen level, so duct burners are designed to operate under these conditions. They aretreated in detail in Chapter 19.

1.2.6 D

RYING

Burners are used in a wide variety of lower-temperature drying applications to remove water fromproducts that was added during the manufacturing process. These are lower-temperature applicationsthat include paper manufacturing, printing and publishing, textile manufacturing, and food processing.Drying is defined as a process in which a wet solid is heated or contacted with a hot gas stream,causing some or all of the liquid wetting the solid to evaporate.

27

Kudra and Mujumdar (2002)have written a new book

28

on advanced drying technologies that covers a wide range of industries.One example is the drying of paper produced from a wet slurry. A typical paper mill is shown inFigure 1.13.

In many drying processes, moisture is removed from webs that may be traveling at high speeds.Radiant heating is often used to supplement steam-heated cylinders or high-velocity hot air dryers.

29

The radiant heaters are either electric or fired with a fuel gas such as natural gas. Thermal radiationburners used in many of these applications are discussed in Chapter 13.



14


1.3 COMBUSTION SYSTEM COMPONENTS

There are six components that may be important in industrial combustion processes (see Figure 1.14).One component is the burner, which combusts the fuel with an oxidizer to release heat. Anothercomponent is the load itself, which can greatly affect how the heat is transferred from the flame. Inmost cases, the flame and the load are located inside a combustor, which may be a furnace, heater,or dryer and constitutes the third component in the system. In some cases, there may be some type

FIGURE 1.11

Duct burner flame. (Courtesy of John Zink Co., LLC.

36

)

FIGURE 1.12

Duct burner process schematic. (Courtesy of John Zink Co., LLC.

36

)

Gas Turbine

Duct Burner

Steam Generator

Stack

Steam Drums



Introduction

15

FIGURE 1.13

Paper mill.

FIGURE 1.14

Schematic of an industrial combustion process.

LoadBurner

Combustion Air

Heat Exchanger

CombustionAir Blower

ExhaustFan

Furnace

Flue Gases

Fuel

Pollution ControlSystem

To Atmosphere

Flow ControlSystem



16


of heat recovery device to increase the thermal efficiency of the overall combustion system, which isthe fourth component of the system. The fifth component is the flow control system used to meterthe fuel and the oxidant to the burners. The sixth and final component is the air pollution controlsystem used to minimize the pollutants emitted from the exhaust stack into the atmosphere. Variousaspects of these components are discussed in more detail in other sections of the book.

1.4 BURNER DESIGN FACTORS

The burner is the device used to combust the fuel with an oxidizer to convert the chemical energyin the fuel to thermal energy. A given combustion system may have a single burner or many burners,depending on the size and type of the application. For example, in a rotary kiln, a single burner islocated in the center of the wall on one end of a cylindrically shaped furnace (see Figure 1.15).The heat from the burner radiates in all directions and is efficiently absorbed by the load. However,the cylindrical geometry has some limitations concerning size and load type, which make its uselimited to certain applications such as melting scrap aluminum or producing cement clinker. Amore common combustion system has multiple burners in a rectangular geometry (see Figure 1.16).This type of system is generally more difficult to analyze because of the multiplicity of heat sourcesand because of the interactions between the flames and their associated products of combustion.

There are many factors that go into the design of a burner. This section briefly considers someof the important factors that are taken into account for a particular type of burner. These factorsaffect things such as heat transfer and pollutant emissions. There have been many changes in thetraditional designs used in burners, primarily because of the recent interest in reducing pollutantemissions. In the past, the burner designer was primarily concerned with efficiently combustingthe fuel and transferring the energy to a heat load. New and increasingly more stringent environ-mental regulations have added the requirement to consider the pollutant emissions produced by theburner. In many cases, reducing pollutant emissions and maximizing combustion efficiency are atodds with each other. For example, a well-accepted technique for reducing NOx emissions is knownas staging, where the primary flame zone is deficient in either fuel or oxidizer.

30

The balance offuel or oxidizer can be injected into the burner in a secondary flame zone or, in a more extreme

FIGURE 1.15

Rotary kiln with single burner.

29

RotaryFurnace

Burnerfuel

air



Introduction

17

case, can be injected somewhere else in the combustion chamber. Staging reduces the peak tem-peratures in the primary flame zone and also alters the chemistry in a way that reduces NOxemissions because fuel-rich or fuel-lean zones are less conducive to NOx formation than near-stoichiometric zones. Figure 1.17 shows how the NOx emissions are affected by the exhaust producttemperature. Because thermal NOx is exponentially dependent on the gas temperature, even smallreductions in the peak flame temperature can dramatically reduce NOx emissions. However, lowerflame temperatures often reduce the radiant heat transfer from the flame because radiation is

FIGURE 1.16

Plan view of multiple burners in a glass furnace.

29

FIGURE 1.17

NOx as a function of gas temperature.

29

Burner Firing

Burner Off Burner Off Burner Off

Burner Firing Burner Firing

Glass Batch

0 400 800 1200 1600 2000 2400 2800 3200 36000

20

40

60

80

100

120

140

160

180

200

0

20

40

60

80

100

120

140

160

180

200

Gas Temperature (K)500 1000 1500 2000

Spec

ies

Conc

entra

tion

(ppmv

w)

Spec

ies

Conc

entra

tion

(ppmv

w)

Gas Temperature (F)



18


dependent on the fourth power of the absolute temperature of the gases. Another potential problemwith staging is that it may increase CO emissions, which is an indication of incomplete combustionand reduced combustion efficiency. However, it is also possible that staged combustion can producesoot in the flame, which can increase flame radiation. The actual impact of staging on the heattransfer from the flame is highly dependent on the actual burner design.

In the past, the challenge for the burner designer was often to maximize the mixing betweenthe fuel and the oxidizer to ensure complete combustion, especially if the fuel was difficult to burn,as in the case of low heating value fuels such as waste liquid fuels or process gases from chemicalsproduction. Now, the burner designer must balance the mixing of the fuel and the oxidizer tomaximize combustion efficiency while simultaneously minimizing all types of pollutant emissions.This is no easy task as, for example, NOx and CO emissions often go in opposite directions, asshown in Figure 1.18. When CO is low, NOx may be high and vice versa. Modern burners must beenvironmentally friendly, while simultaneously efficiently transferring heat to the load.

Many types of burner designs exist due to the wide variety of fuels, oxidizers, combustionchamber geometries, environmental regulations, thermal input sizes, and heat transfer requirements(including flame temperature, flame momentum, and heat distribution). Some of these design factorsare briefly considered here. Other important design factors, such as heat transfer (Chapter 6), noise(Chapter 7), and controls (Chapter 8), are discussed elsewhere in the book. Some of the tools usedto optimize burner design include computational fluid dynamic modeling (Chapter 5), testing(Chapter 9), and physical modeling (Chapter 10).

1.4.1 F

UEL

Depending on many factors, certain types of fuels may be preferred for certain geographic locationsdue to cost and availability considerations. Gaseous fuels, particularly natural gas, are commonly usedin most industrial heating applications in the United States. In Europe, natural gas is also commonlyused along with light fuel oil. In Asia and South America, heavy fuel oils are generally preferredalthough the use of gaseous fuels is on the rise. Fuels also vary depending on the application. Forexample, in incineration processes, waste fuels are commonly used either by themselves or with other

FIGURE 1.18

NOx and CO as a function of stoichiometry.

29

Equivalence Ratio0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Equivalence Ratio0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

CO C

once

ntra

tion

(Vol.

%)

0123456789

10111213

NO

Con

cent

ratio

n (pp

mvw)

0

500

1000

1500

2000

2500

3000

3500

CO (Vol. %)NO (ppmvw)



Introduction

19

fuels such as natural gas. In the petrochemical industry, fuel gases often consist of a blend of severalfuels, including gases such as hydrogen, methane, propane, butane, and propylene.

The fuel choice has an important influence on the heat transfer from a flame. In general, solidfuels (e.g., coal) and liquid fuels l(e.g., oil) produce very luminous flames that contain soot particlesthat radiate like blackbodies to the heat load. Gaseous fuels such as natural gas often producenonluminous flames because they burn so cleanly and completely without producing soot particles.A fuel such as hydrogen is completely nonluminous as there is no carbon available to produce anysoot. In cases where highly radiant flames are required, a luminous flame is preferred. In cases whereconvection heat transfer is preferred, a nonluminous flame may be preferred in an effort to minimizethe possibility of contaminating the heat load with soot particles from a luminous flame. Where naturalgas is the preferred fuel and highly radiant flames are desired, new technologies are being developedto produce more luminous flames. These include pyrolyzing the fuel in a partial oxidation process,

31

using a plasma to produce soot in the fuel,

32

and generally controlling the mixing of the fuel andoxidizer to produce fuel-rich flame zones that generate soot particles.

33

Therefore, the fuel itself hasa significant impact on the heat transfer mechanisms between the flame and the load. In most cases,the fuel choice is dictated by the customer as part of the specifications for the system and is notchosen by the burner designer. The designer must make the best of whatever fuel has been selected.In most cases, the burner design is optimized based on the choice for the fuel.

The fuel also has a large impact on pollutant emissions. For example, gaseous fuels generallycontain little or no sulfur so SOx emissions are usually small. However, heavy oils often containsignificant quantities of sulfur and therefore SOx emissions are of concern and need to be controlled.Another example is particulate emissions. Gaseous fuels generally burn very cleanly and producenegligible particulates. However, heavy liquid oil fuels can generate high levels of particulate emis-sions. Therefore, burner design is important in minimizing pollutant emissions, depending on the fuel.

In some cases, the burner may have more than one type of fuel. An example is shown inFigure 1.19.

34

Dual-fuel burners are typically designed to operate on either gaseous or liquid fuels.These burners are used where the customer may need to switch between a gaseous fuel (e.g., naturalgas) and a liquid fuel (e.g., oil), usually for economic reasons. These burners normally operate onone fuel or the other, and occasionally on both fuels simultaneously. Another application in which

FIGURE 1.19

Dual fuel burner. (Courtesy of John Zink Co., LLC.

36

)

Tertiary Air

Staged air is mixedwith the combustionproducts from theprimary zone,which lowers thepeak flametemperature.

Sub-stoichiometricconditions in primaryzone increase theamount of reducingagents (H2 and CO).

Oil Gun

Primary Air

Secondary Air



20


multiple fuels might be used is in waste incineration. One method of disposing of waste liquidscontaminated with hydrocarbons is to combust them by direct injection through a burner. The wasteliquids are fed through the burner, which is powered by a traditional fuel such as natural gas or oil.The waste liquids often have very low heating values and are difficult to combust without auxiliaryfuel. This further complicates the burner design, where the waste liquid must be vaporized andcombusted concurrently with the normal fuel used in the burner.

1.4.2 O

XIDIZER

The predominant oxidizer used in most industrial heating processes is atmospheric air. This canpresent challenges in some applications where highly accurate control is required due to the dailyvariations in the barometric pressure and humidity of ambient air. The combustion air is sometimespreheated and sometimes blended with some of the combustion products, which is usually referredto as flue gas recirculation (FlGR). In certain cases, preheated air is used to increase the overallthermal efficiency of a process. FlGR is often used to both increase thermal efficiency and to reduceNOx emissions. The thermal efficiency is increased by capturing some of the energy in the exhaustgases that are used to preheat the incoming combustion oxidizer. NOx emissions may also bereduced because the peak flame temperatures are reduced, which can reduce the NOx emissions,which are highly temperature dependent. There are also many high-temperature combustion pro-cesses that use an oxidizer containing a higher proportion of oxygen than the 21% (by volume)found in normal atmospheric air. This is referred to as oxygen-enhanced combustion (OEC) andhas many benefits, including increased productivity and thermal efficiency while reducing theexhaust gas volume and pollutant emissions.

5

A simplified global chemical reaction for the stoichi-ometric combustion of methane with air is given as follows:

CH

4 + 2O2 + 7.52N2 CO2 + 2H2O + 7.52N2, trace species (1.1)This compares to the same reaction where the oxidizer is pure O2 instead of air:

CH4 + 2O2 CO2 + 2H2O + trace species (1.2)The volume of exhaust gases is significantly reduced by the elimination of N2. In general, a

stoichiometric oxygen-enhanced methane combustion process can be represented by:

CH4 + 2O2 + xN2 CO2 + 2H2O + xN2 + trace species (1.3)

where 0 x 7.52, depending on the oxidizer. The N2 contained in air acts as a ballast that mayinhibit the combustion process and have negative consequences. The benefits of using oxygen-enhanced combustion must be weighed against the added cost of the oxidizer, which in the caseof air is essentially free except for the minor cost of the air handling equipment and power for theblower. The use of a higher-purity oxidizer has many consequences with regard to heat transferfrom the flame and pollutant emissions generated. These are considered elsewhere in the book.Oxygen-enhanced combustion is considered in more detail in Chapters 20 and 21.

1.4.3 GAS RECIRCULATION

A common technique used in combustion systems is to design the burner to induce furnacegases to be drawn into the burner to dilute the flame, usually referred to as furnace gasrecirculation (FuGR). Although the furnace gases are hot, they are still much cooler than theflame itself. This dilution may accomplish several purposes. One is to minimize NOx emissionsby reducing the peak temperatures in the flame, as in FlGR (see Figure 1.20). However, furnacegas recirculation may be preferred to FlGR because no external high-temperature ductwork or



Introduction 21

fans are needed to bring the product gases into the flame zone. Another reason to use furnacegas recirculation may be to increase the convective heating from the flame because of the addedgas volume and momentum. An example of flue gas recirculation into the burner is given inFigure 1.20.35 A specific type of burner incorporating furnace gas recirculation is called aregenerative burner (see Chapter 12).

1.5 GENERAL BURNER CLASSIFICATIONS

There are numerous ways to classify burners. Some common ones are discussed below, with a briefconsideration as to how burner performance is impacted.

1.5.1 MIXING TYPE

One common method for classifying burners is according to how the fuel and the oxidizer aremixed. In premixed burners, shown in the diagram in Figure 1.21 and schematically in Figure 1.22,the fuel and the oxidizer are completely mixed before combustion begins. Thermal radiation burners(Chapter 13) and radiant wall burners (Chapter 15) usually are of the premixed type. Premixedburners often produce shorter and more intense flames, as compared to diffusion flames. This canproduce high-temperature regions in the flame, leading to nonuniform heating of the load andhigher NOx emissions, although this is very dependent on the specific design. However, in flameimpingement heating, premixed burners are useful because the higher temperatures and shorterflames can enhance the heating rates.

In diffusion-mixed burners, shown schematically in Figure 1.23, the fuel and the oxidizer remainseparated and unmixed prior to combustion, which begins where the oxidizer/fuel mixture is withinthe flammability range (assuming the temperature is high enough for ignition). Oxygen/fuel burners(see Chapter 21) are usually diffusion burners, primarily for safety reasons, to prevent flashback

FIGURE 1.20 Schematic of flue gas recirculation.29

FIGURE 1.21 Diagram of a premixed burner.29

CombustorBurner

Fuel

RecirculatedCombustion Products

Air ID Fan

To Atmosphere

FUEL

AIR



22 Industrial Burners Handbook

and explosion in a potentially dangerous system. Diffusion gas burners are sometimes referred toas raw gas burners, as the fuel gas exits the burner essentially intact with no oxidant mixed withit. Diffusion burners typically have longer flames than premixed burners, do not have as hightemperature a hot spot, and usually have a more uniform temperature and heat flux distribution.They may also have lower NOx emissions although, again, this is design dependent.

It is also possible to have partially premixed burners, shown schematically in Figure 1.24 andFigure 1.25, where a portion of the fuel is mixed with the oxidizer prior to exiting the burner. This isoften done for stability and safety reasons, wherein the partial premixing helps anchor the flame, while

FIGURE 1.22 Schematic of a premixed burner. (Courtesy of John Zink Co., LLC.36)

FIGURE 1.23 Schematic of a diffusion-mixed burner.29

Secondary air

Primary air

Pilot

Gas

FUELAIR

AIR



Introduction 23

not fully premixing lessens the chance for flashback. This type of burner often has a flame length andtemperature and heat flux distribution that is between the fully premixed and diffusion flames.

Another burner classification based on mixing is known as staging: staged air and staged fuel.A staged air burner is shown in the diagram in Figure 1.26 and schematically in Figure 1.27. Astaged fuel burner is shown in the diagram in Figure 1.28 and schematically in Figure 1.29.Secondary and sometimes tertiary injectors in the burner are used to inject a portion of the fueland/or the oxidizer into the flame, downstream of the root of the flame. Staging is often done tocontrol heat transfer, produce longer flames, and reduce pollutant emissions such as NOx. Theselonger flames typically have a lower peak flame temperature and more uniform heat flux distributionthan nonstaged flames. However, an additional challenge is that multiple longer flames mightinteract with each other and produce unpredictable consequences compared to single shorter flames.

FIGURE 1.24 Partially premixed burner (Courtesy of John Zink Co., LLC).

FIGURE 1.25 Schematic of a partially premixed burner.29

FUEL

FUEL

AIR

AIR

AIR




1.5.2 FUEL TYPE

Burners can also be classified according to fuel type. Gaseous fuel burners are the predominanttype used in most of the applications considered here. In general, natural gas is the predominantgaseous fuel used because of its low cost and availability. However, a wide range of gaseous fuelsare used in, for example, the chemicals industry.36 These fuels contain multiple components suchas methane, hydrogen, propane, nitrogen, and carbon dioxide and are sometimes referred to asrefinery fuel gases. Figure 1.30 shows an example of a typical nonluminous gaseous flame from aburner used in the petrochemical industry. Gaseous fuels are among the easiest to control becauseno vaporization is required, as is the case for liquid and solid fuels. They are also often simpler tocontrol to minimize pollution emissions because they are more easily staged compared to liquidand solid fuels. Table 1.4 shows typical data for the combustion of common hydrocarbons.

FIGURE 1.26 Diagram of a staged-air burner.29

FIGURE 1.27 Schematic of a staged-air process. (Courtesy of John Zink Co., LLC.36)

FIGURE 1.28 Diagram of a staged fuel burner.29

FUELAIR

AIRFUEL

AIR

OIL GUN

REGEN TILE

GAS PILOT

PRIMARY AIR CONTROL

GAS RISERS (FORCOMBINATION FIRING)

SECONDARY AIR CONTROL

TERTIARY AIR CONTROL

GAS RISER MANIFOLD(FOR COMBINATION FIRING)

AIR INLETPLENUM

FUELAIR

AIRFUEL

FUEL



Introduction 25

FIGURE 1.29 Schematic of a staged fuel burner.29

FIGURE 1.30 Typical nonluminous flame. (Courtesy of John Zink Co., LLC.36)

PRIMARY GAS NOZZLE FLAME HOLDER

BURNER TILE

AIR PLENUM

SECONDARYGAS NOZZLE

AIR REGISTER

AIR REGISTERHANDLE



26In

du

strial Bu

rners H

and

bo

ok

TABLE 1.4Combustion Data for Common Hydrocarbons2

Hydrocarbon FormulaHigher Heating Value,

Vapor (Btu/lbm)Theor. Air/FuelRatio, by mass

Max. FlameSpeed (ft/s)

Adiabatic FlameTemp., in Air (F)

Ignition Temp., in Air (F)

Flash Point (F)

Flammability Limits, in Air (% by volume)

Paraffins or AlkanesMethane CH4 23875 17.195 1.1 3484 1301 (gas) 5.0 15.0Ethane C2H6 22323 15.899 1.3 3540 9681166 (gas) 3.0 12.5Propane C3H8 21669 15.246 1.3 3573 871 (gas) 2.1 10.1n-Butane C4H10 21321 14.984 1.2 3583 761 76 1.86 8.41Iso-Butane C4H10 21271 14.984 1.2 3583 864 117 1.80 8.44n-Pentane C5H12 21095 15.323 1.3 4050 588

Introduction 27

Liquid fuel burners are used in some limited applications, but are more prevalent in certainareas of the world such as South America. No. 2 and no. 6 oil are the most commonly used liquidfuels. Waste liquid fuels are also used in incineration processes. One of the specific challenges ofusing oils is vaporizing the liquid into small enough droplets to burn completely. Improper atom-ization produces high unburned hydrocarbon emissions and reduces fuel efficiency. Steam andcompressed air are commonly used to atomize liquid fuels. The atomization requirements oftenreduce the options for modifying the burner design to reduce pollutant emissions. Another challengeis that liquid fuel oils often contain impurities such as nitrogen and sulfur that produce pollutionemissions. In the case of fuel-bound nitrogen, so-called fuel NOx emissions increase. In the caseof sulfur, essentially all of the sulfur in a liquid fuel converts to SOx emissions.

Solid fuels are not commonly used in most industrial combustion applications. The mostcommon solid fuels are coal and coke. Coal is used in power generation and coke is used in someprimary metals production processes. However, neither is considered a traditional industrial com-bustion process and therefore is not considered here. Another type of pseudo solid fuel is sludgethat is processed in incinerators. Solid fuels also often contain impurities such as nitrogen andsulfur that can significantly increase pollutant emissions. Some solid fuels may also containhazardous chemicals that can produce carcinogenic pollution emissions. Because solid fuels arenot used frequently in the applications considered, they are only discussed in those specific cases.

There are some applications that require the burner to be able to fire on a gaseous fuel suchas natural gas, a liquid fuel such as fuel oil, or both simultaneously. This is generally due to theeconomics of the fuel costs. In some locations, a more favorable fuel cost rate can be obtained, forexample, on natural gas, if the supply can be interrupted with sufficient notice. The backup fuel istypically fuel oil. These dual-fuel burners have special challenges because of significant differencesin the design of gaseous and liquid burners.

1.5.3 OXIDIZER TYPE

Burners and flames are often classified according to the type of oxidizer that is used. The majorityof industrial burners use air for combustion. In many of the higher-temperature heating and meltingapplications, such as glass production, the oxidizer is pure oxygen. These burner types are discussedin Chapter 21. In other applications, the oxidizer is a combination of air and oxygen, often referredto as oxygen-enriched air combustion. These burner types are discussed in Chapter 20.

Figure 1.31 shows a schematic of an air/fuel burner, which is the most commonly used typein industrial combustion applications. In most cases, the combustion is supplied by a fan or blower,although there are many applications in the petrochemical industry where natural-draft burners arecommonly used (see Chapter 16). There are numerous variations of air/fuel burners and these arediscussed throughout this book.

FIGURE 1.31 Schematic of an air/fuel burner.29

AIR

FUEL




Figure 1.32 shows a method of using OEC and commonly referred to as an oxy/fuel burner.In nearly all cases, the fuel and the oxygen remain separated inside the burner. They do not mixuntil reaching the outlet of the burner. This is commonly referred to as a nozzle-mix burner, whichproduces a diffusion flame. For safety reasons, there is no premixing of the gases. Because of theextremely high reactivity of pure O2, there is the potential for an explosion if the gases are premixed.In this method, high-purity O2 (>90% O2 by volume) is used to combust the fuel. As discussedlater, there are several ways of generating the O2. In an oxy/fuel system, the actual purity of theoxidizer will depend on which method has been chosen to generate the O2. As shown later, oxy/fuelcombustion has the greatest potential for improving a process, but it also may have the highestoperating cost.

Figure 1.33 shows an air/fuel process in which the air is enriched with O2. This can bereferred to as low-level O2 enrichment, or premix enrichment. Many conventional air/fuel burnerscan be adapted for this technology.37 The O2 is injected into the incoming combustion air supply,usually through a diffuser to ensure adequate mixing. This is usually an inexpensive retrofit thatcan provide substantial benefits. Typically, the added O2 will shorten and intensify the flame.However, there may be some concern if too much O2 is added to a burner designed for air/fuel.The flame shape may become unacceptably short. The higher flame temperature may damagethe burner or burner block. The air piping may need to be modified for safety reasons to handlehigher levels of O2.

FIGURE 1.32 Schematic of an oxy/fuel burner.5

FIGURE 1.33 Schematic of an air-oxy/fuel burner.5

OXYGEN

FUEL

AIR

OXYGEN

FUEL



Introduction 29

1.5.4 DRAFT TYPE

Most industrial burners are known as forced-draft burners. This means that the oxidizer is suppliedto the burner under pressure. For example, in a forced-draft air burner, the air used for combustionis supplied to the burner by a blower. In natural-draft burners (see Chapter 16), the air used forcombustion is induced into the burner by the negative draft produced in the combustor and bythe motive force of the incoming fuel, which may be at a significant pressure. A schematic isshown in Figure 1.34 and an example is shown in Figure 1.35. In this type of burner, the pressuredrop and combustor stack height are critical in producing enough suction to induce sufficientcombustion air into the burners. This type of burner is commonly used in the chemical andpetrochemical industries in fluid heaters. The main consequence of the draft type on burnerperformance is that the natural-draft flames are usually longer than the forced-draft flames sothat the heat flux from the flame is distributed over a longer distance and the peak temperaturein the flame is often lower.

1.5.5 HEATING TYPE

Burners are often classified as to whether they are of the direct (see Figure 1.36) or indirect heatingtype (see Figure 1.37). In direct heating, there is no intermediate heat exchange surface betweenthe flame and the load. In indirect heating, such as radiant tube burners (see Chapter 8), there isan intermediate surface between the flame and the load. This is usually done because the combustionproducts cannot come in contact with the load because of possible contamination.

Radiation heat transfer (see Chapter 2) from the flame to the product is the primary mode usedin many industrial combustion systems (see Chapter 6). There are a variety of burner designs thatrely primarily on this mechanism. Thermal radiation burners are discussed in Chapter 13. Radianttube burners are discussed in Chapter 14. Radiant wall burners are discussed in Chapter 15. Otherburner designs discussed throughout this book also use thermal radiation as the primary heat transfermechanism.

FIGURE 1.34 Schematic of a natural-draft burner. (Courtesy of John Zink Co., LLC.36)

PilotGas Gun

AirInlet

Burner Tile

FlameStabilizer

Heater Floor




Forced convection (see Chapter 2) is the other predominant mechanism for transferring heatfrom flames to a load. For example, high-velocity burners are considered in Chapter 11. These areparticularly useful in applications where primarily radiant heating may overheat the surface withmuch less energy getting inside the load. An example would be heating a pile of scrap metal.Highly radiant heating could melt the outside of the pile and cause excessive oxidation, leading to

FIGURE 1.35 Photo of a natural-draft burner. (Courtesy of John Zink Co., LLC.29)

FIGURE 1.36 Direct fired process.

FIGURE 1.37 Indirect fired process.

BurnerLoad

Load

MuffleBurner



Introduction 31

high metal yield losses. Convective heating can penetrate inside the load to cause more uniformheating. In certain applications, high-velocity burners may not be preferred because the materialsbeing heated may contain fine particles that can easily become airborne. An example is glassmanufacturing, where the incoming batch materials contain fine powders.

1.5.6 BURNER GEOMETRY

There are two primary shapes for the outlet nozzle of industrial burners: round or rectangular.Figure 1.38 shows identical heaters with the same number of burners but with different burnershapes: round flame and flat flame. These are briefly considered next.

Round flames are the predominant shape used in industry. Most of the burners discussed inthis book are predominantly round. This is often due to the lower cost of making round shapescompared to making rectangular shapes. It is also often due to the burner tile; round shapes generallyrequire less maintenance compared to rectangular tiles, which have corners that are more susceptibleto cracking. Another reason may be due to more preferred flow patterns inside round burner plenumscompared to rectangular shapes.

Rectangular shapes are sometimes preferred in certain applications, depending on the geometryof the combustor and the load. Burners with a fairly high aspect ratio (length to width) are sometimesreferred to as flat flame burners because the flame shape appears to be flat. One example is inethylene cracking furnaces where flat-shaped burners fire up along a refractory wall to heat thewall to radiate to tubes opposite that wall. Another example is in glass furnaces where flat-shapedflames fire over the molten glass; these flat shapes often give better flame coverage, more uniformheating, and better thermal efficiency.

1.6 BURNER COMPONENTS

There are several important components briefly considered here that impact the burner design.The ignition system is an important component in the burner system to ensure safe and reliable

operation. The ignition system is often built into the burner, but in some cases it may be separate

FIGURE 1.38 Round (a) and rectangular (b) burner shapes in identical combustors.

Burner

Burner

Burner

Burner

Burner

Burner

(a) (b)




from the burner. The system may be fully automatic or completely manual. Different types ofignitors are available. In many cases, a pilot is used to ignite the main flame. This may be continuousor interruptible, depending on the system design. The pilot may be permanent or removable, andmay be ignited by something like a spark-ignitor or by an external torch. Pilots require a separatefuel supply and are typically premixed.

Plenums are used to homogenize the incoming gas flows to evenly distribute them to the outletof the burner. This is important to ensure proper operation of the burner over the entire range ofoperating conditions, especially at turndown. These gases may include combustion air, premixedfuel and air, or partially premixed fuel and air. If the plenum is too large, then the flows may beunevenly distributed across the burner nozzle outlet. If the plenum is too small, then the pressuredrop through the plenum may be excessive.

The burner tile, sometimes referred to as a block or quarl, is an important component becauseit helps shape the flame and protects the internal parts from overheating. In the majority of designs,the burner tile is made of some type of ceramic that often contains alumina and silica, dependingon the temperature requirements. The burner tile can also play an important role in the ignitionand fluid dynamics of the combustion process. The tile may have bluff body components thatenhance flame stability. There may be holes through the tile to enhance mixing of furnace gaseswith the gases fed into the burner. Advances in ceramics and manufacturing processes have led toincreasingly more complicated burner tiles.

Controls refer not to the control equipment for the flows coming to the burner, but to controlsthat may be on the burner. For example, there is often a damper built into natural-draft burners(see Chapter 16) to control the incoming air flow and the furnace draft. Other controls on a burnermay be for adjusting the distribution of fuels or air throughout the burner. For example, if a burnerhas multiple fuel injectors, particularly for fuel staging, controls on the burner can be used tocontrol how much fuel goes to each injector. Chapter 8 has a detailed discussion of the controlsleading up to the burner.

The flame safety system is critical to the safe operation of the combustion system. This mayinclude some type of flame scanner or flame rod to ensure that either the burner or the pilot isoperating. These are connected to the fuel supply system so that the fuel flow will be stopped ifthe flame goes out to prevent a possible explosion for unignited fuel gases contacting a hot surfacesomewhere in the combustor. This is also discussed in Chapter 8.

1.7 COMBUSTORS

This section briefly introduces the combustors that are commonly used in industrial heating andmelting applications.

1.7.1 DESIGN CONSIDERATIONS

There are many important factors that must be considered when designing a combustor. This sectiononly briefly considers a few of those factors and how they might influence the heat transfer in thesystem.

1.7.1.1 Load Handling

A primary consideration for any combustor is the type of material that will be processed. Thevarious types of loads are