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Industrial and Process Furnaces This page intentionally left blank Industrial and Process Furnaces Principles, Design and Operation Peter Mullinger Associate Professor, School of Chemical Engineering University of Adelaide, South Australia Barrie Jenkins Consulting Engineer, High Wycombe, Bucks, UK...

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Industrial and Process Furnaces

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Industrial and Process Furnaces Principles, Design and Operation

Peter Mullinger Associate Professor, School of Chemical Engineering University of Adelaide, South Australia

Barrie Jenkins Consulting Engineer, High Wycombe, Bucks, UK

AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Butterworth-Heinemann is an imprint of Elsevier

Butterworth-Heinemann is an imprint of Elsevier Linacre House, Jordan Hill, Oxford OX2 8DP, UK 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA First edition 2008 Copyright © 2008 Elsevier Ltd. All rights reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK; phone: (44) (0) 1865 843830; fax: (44) (0) 1865 853333; email: [email protected]. Alternatively you can submit your request online by visiting the Elsevier web site at http://elsevier.com/locate/permissions, and selecting Obtaining permission to use Elsevier material Notice No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloguing in Publication Data A catalogue record for this book is available from the Library of Congress ISBN: 978-0-7506-8692-1 For information on all Butterworth-Heinemann publications visit our web site at http://books.elsevier.com Typeset by Charon Tec Ltd (A Macmillan Company), Chennai, India www.charontec.com Printed and bound in Hungary 08 09 10 11 12 10 9 8 7 6 5 4 3 2 1

To the late Frank David Moles, who showed us a better way of thinking about furnaces, especially those where the product is directly heated by the flame.

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Contents

Foreword Preface Acknowledgements List of Figures List of Tables

xvii xix xxi xxiii xxxi

Chapter 1 Introduction 1.1 What is a furnace? 1.1.1 Furnace outline 1.1.2 Furnace classification 1.1.3 Principle objectives of furnace designers and operators 1.2 Where are furnaces used? Brief review of current furnace applications and technology 1.2.1 Ceramics, brick making and pottery 1.2.2 Cement and lime 1.2.3 Glass making 1.2.4 Metal ore smelting 1.2.5 Metal refining 1.2.6 Flash and fluid bed furnaces 1.2.7 Metal physical processing 1.2.8 Incinerators and resource recovery furnaces 1.2.9 Furnaces with reducing atmospheres 1.2.10 Oil refining and petrochemical furnaces 1.3 Drivers for improved efficiency 1.4 Concluding remarks References

1 3 4 5 5 7 7 8 11 13 16 18 20 24 24 25 28 29 29

Chapter 2 The combustion process 2.1 Simple combustion chemistry 2.1.1 The complete oxidation of carbon 2.1.2 The complete oxidation of hydrogen 2.1.3 The incomplete oxidation of carbon 2.1.4 The oxidation of carbon monoxide 2.2 Combustion calculations 2.3 Chemical reaction kinetics 2.3.1 Types of reactions 2.3.2 Reaction rate theory

31 32 32 32 33 33 33 36 37 38

viii Contents 2.3.3 Reaction rate behaviour 2.3.4 Burning droplets and particles 2.4 The physics of combustion 2.4.1 The role of primary air 2.4.2 The role of swirl flows 2.4.3 Turbulence in jets 2.4.4 Secondary flow aerodynamics 2.4.5 Effect of excess air on fuel consumption 2.4.6 Multiple burner installations Nomenclature References

40 43 47 50 56 57 59 61 62 63 64

Chapter 3 Fuels for furnaces 3.1 Gaseous fuels 3.1.1 Properties of natural gas 3.1.2 Manufactured gas 3.1.3 Wobbe number or index 3.1.4 Flammability limits Calculation of the flammable limits for mixtures of gases Influence of temperature and pressure on the limits 3.1.5 Flame radiation from gaseous fuels 3.2 Liquid fuels 3.3 Solid fuels 3.3.1 Ash 3.4 Waste fuels 3.5 Choice of fuel 3.5.1 Furnace performance Heat transfer Furnace atmosphere Flexibility of operation Effect of ash Refractory life Fuel cost and security of supply Fuel handling system capital and running costs 3.6 Safety 3.7 Emissions Nomenclature References Solid fuel bibliography

67 69 69 69 71 72

Chapter 4 An introduction to heat transfer in furnaces 4.1 Conduction 4.1.1 Steady state conduction

89 90 91

72 73 75 75 77 79 79 80 81 81 83 83 84 84 85 85 86 86 86 87 88

Contents

ix

4.1.2 Transient conduction Analytical approach Numerical approach 4.2 Convection 4.2.1 Dimensional analysis 4.2.2 Application to convective heat transfer 4.2.3 Evaluating convective heat transfer coefficients 4.2.4 High temperature convective heat transfer 4.3 Radiation 4.3.1 Physical basics of radiative exchange 4.3.2 Emissivity and absorptivity 4.3.3 View factors Equivalent grey surface 4.3.4 Mean beam length 4.4 Electrical heating 4.4.1 Resistance heating Direct resistance heating Indirect resistance heating 4.4.2 Arc heating Electrode devices Electrodeless devices 4.4.3 Induction heating 4.4.4 Dielectric heating 4.4.5 Infrared heating Nomenclature References Appendix 4A Tables of emissivity data

93 93 96 100 101 102 104 108 113 114 117 121 126 127 128 128 129 129 129 130 131 132 133 133 134 136 137

Chapter 5 Flames and burners for furnaces 5.1 Types of flame 5.1.1 Premixed flames 5.1.2 Turbulent jet diffusion flames 5.1.3 Heterogeneous combustion Atomisation of liquid fuels and pulverisation of coal The importance of drop and particle size 5.2 Function of a burner and basics of burner design 5.2.1 The essential importance of heat flux profiles 5.2.2 Flame stabilisation 5.3 Gas burners 5.3.1 Premixed burners Effect of excess air (mixture ratio) on flame temperature Radiant wall burners Use of premix burners in low NOx applications Safety issues with premix burners Size limitations

141 142 143 145 145 146 148 152 154 155 158 158 160 161 162 162 165

x Contents 5.3.2 Turbulent jet diffusion burners 5.3.3 Precessing jet diffusion burners 5.4 Oil burners 5.4.1 Turndown 5.4.2 Atomisers Pressure jet atomisers Twin fluid atomisers 5.5 Pulverised coal burners 5.6 Furnace aerodynamics Burner and furnace air flow patterns 5.6.1 Single burner systems Package burner installations Rotary kilns and driers, etc. 5.6.2 Multiple burner systems 5.6.3 Combustion air duct design 5.6.4 Common windbox and plenum design 5.7 Combustion system scaling 5.7.1 Example of combustion system scaling 5.8 Furnace noise 5.8.1 Combustion roar 5.8.2 Nozzle and turbulent jet noise 5.8.3 Fan noise 5.8.4 Pipe and valve noise 5.8.5 Furnace noise attenuation 5.8.6 Combustion driven oscillations Nomenclature References

165 167 168 171 172 173 176 179 182 184 184 185 185 186 188 192 193 194 196 198 198 199 199 200 201 204 205

Chapter 6 Combustion and heat transfer modelling 6.1 Physical modelling 6.1.1 Thring-Newby parameter 6.1.2 Craya-Curtet parameter 6.1.3 Becker throttle factor 6.1.4 Curtet number 6.1.5 Relationship between scaling parameters 6.1.6 Determining the required model flows 6.1.7 Applying the scaling parameter 6.1.8 Applying a post-measurement correction 6.2 Mathematical modelling 6.2.1 Simple well-stirred furnace models 6.2.2 Long furnace models 6.2.3 Two- and three-dimensional zone models 6.2.4 Computational fluid dynamics models Gridding of CFD models Convergence of CFD models 6.2.5 Particle drag in combustion systems

209 211 214 214 215 215 216 216 216 217 217 219 227 229 233 235 237 237

Contents

xi

6.3 Application of modelling to furnace design Nomenclature References

238 239 241

Chapter 7 Fuel handling systems 7.1 Gas valve trains 7.1.1 Safety shutoff systems Double block and bleed Leak testing and proving 7.2 Fuel oil handling systems 7.2.1 Storage, pumping and heating 7.2.2 Oil valve trains 7.3 Pulverised coal handling and firing systems 7.3.1 Raw coal bunkers and feeders 7.3.2 Coal grinding and drying Coal drying characteristics 7.3.3 Coal mills Ball mills Vertical spindle mills High speed mills 7.3.4 Coal mill grinding capacity Coal fineness Coal dryness 7.3.5 Pulverised coal grinding and firing systems Direct and indirect firing systems Direct firing Semi-direct firing Indirect firing Semi-indirect firing 7.3.6 Coal system drying capacity 7.3.7 Coal firing system fans 7.3.8 Fine coal storage 7.3.9 Fine coal feeding and conveying Volumetric feeders Mass flow feeders 7.3.10 Pulverised coal conveying 7.4 Waste fuel handling 7.4.1 Waste gas fuel handling 7.4.2 Waste liquid fuel handling 7.4.3 Solids waste fuel handling Size distribution 7.4.4 Environmental benefits and health hazards of waste fuel utilisation Nomenclature References Applicable codes and standards

243 244 245 246 246 246 247 249 251 252 253 253 254 255 257 258 260 261 262 262 262 263 263 263 263 266 270 271 274 275 276 278 280 281 282 282 282 283 284 284 285

xii Contents Chapter 8 Furnace control and safety 287 8.1 Process control 288 8.1.1 Basic furnace control strategies 289 Control of product temperature 289 Fuzzy logic and rule-based systems 290 8.2 Furnace instrumentation 290 8.2.1 Temperature measurement 290 8.2.2 Heat input measurement 295 Flow measurement of liquid and gaseous fuels 295 Calorific value measurement 296 Solid fuels 296 8.2.3 Determination of excess air 297 8.3 Flue gas analysis 300 8.3.1 Extractive gas sampling systems and analysers 302 Sample probe installation 302 Cold gas extractive systems 305 Hot wet gas extractive systems 305 Dilution extractive systems 306 8.3.2 In-situ systems 306 Dust monitors 307 Oxygen analysers 308 Cross-duct analysers 309 8.4 Combustion control 312 8.5 Ensuring furnace safety 313 8.5.1 Risk factors in furnace operation 313 8.5.2 Furnace start-up 314 Critical time for ignition during furnace start-up 316 8.5.3 Operation with insufficient combustion air 317 Corrective action for unintentional sub-stoichiometric operation 318 8.5.4 Flame quenching 318 8.5.5 Eliminating ignition sources 319 8.6 Burner management systems 319 8.6.1 Safety requirements for burner management systems 320 8.6.2 False trips 322 8.6.3 Achieving acceptable safety standards with programmable logic controller burner management systems 323 8.6.4 Choosing an appropriate safety integrity level 324 8.6.5 Determining the safety integrity level of the BMS system 326 8.6.6 Flame detectors 329 Nomenclature 332 References 332 Certification and testing organisations 333 Chapter 9 Furnace efficiency 9.1 Furnace performance charts 9.2 Mass and energy balances

335 338 341

Contents

xiii

9.2.1 On-site measurement Flue gas sampling and analysis Calibration and errors in plant instrumentation 9.2.2 Constructing mass and energy balances 9.3 Energy conversion 9.3.1 Low and high grade heat 9.3.2 Exergy and pinch point analysis 9.4 Heat recovery equipment 9.4.1 Recuperative heat exchangers 9.4.2 Regenerative heat exchangers 9.4.3 General heat exchanger design procedure 9.5 Identifying efficiency improvements Nomenclature References

342 344 345 346 358 360 362 363 364 366 368 369 372 372

Chapter 10 Emissions and environmental impact 10.1 Formation of carbon monoxide 10.2 Formation of nitrogen oxides 10.2.1 Thermal NOx formation 10.2.2 Fuel NOx formation 10.2.3 Prompt NOx formation 10.2.4 NOx modelling 10.3 Formation of sulphur oxides 10.4 Formation of intermediate combustion products 10.4.1 Volatile organic compounds (VOCs) 10.4.2 Polycyclic aromatic hydrocarbons (PAH) 10.4.3 PCBs, dioxins and furans 10.5 Particulate emissions 10.5.1 Formation of soot 10.5.2 Formation and composition of fuel ash 10.5.3 Non-combustible volatile cycles 10.6 Environmental control of emissions 10.6.1 Prevention and abatement of emissions Pre-flame control In-flame control End-of-pipe control 10.6.2 Dispersion modelling References

375 377 378 379 381 382 384 385 386 386 386 387 390 390 393 394 396 397 397 399 405 408 409

Chapter 11 Furnace construction and materials 11.1 Basic performance requirements of the furnace structure 11.2 Basic construction methods 11.2.1 Brick lining 11.2.2 Monolithic linings Castable refractory

413 414 415 417 419 419

xiv Contents Traditional installation of castable refractory Installation of castable refractory by gunning Drying and curing of cast and gunned refractory Mouldable and rammable refractories 11.2.3 Furnace steelwork 11.2.4 Furnace roof construction 11.2.5 Furnace cooling systems 11.3 Practical engineering considerations in the use of refractories 11.4 Ceramic refractory materials 11.4.1 Testing of refractories 11.4.2 Properties and uses of refractories Silica and siliceous refractories Alumina and aluminous refractories Chromite/magnesite/alumina refractories Dolomite refractories Zircon and zirconia refractories Carbon refractories Insulating refractories 11.5 Heat resisting and refractory metals 11.5.1 Effect of elevated temperature on metal properties 11.5.2 High temperature alloys Service temperature Intergranular corrosion Proprietary high nickel alloys 11.6 Practical engineering considerations in the use of high temperature metals 11.7 Concluding remarks References Selection of relevant standards Advisory organisations Appendix 11A General properties of selected refractory materials

420 421 423 424 425 426 428 431 433 434 435 435 435 436 437 437 438 438 438 439 441 442 442 443

Chapter 12 Furnace design methods 12.1 Introduction 12.1.1 Design constraints 12.1.2 Cost of design changes 12.2 Conceptual design 12.2.1 Process functions Straight-through furnace system Separation furnace system Combining furnace with downstream separation Combining and separation furnace system 12.2.2 Defining the physical and chemical changes 12.2.3 Preliminary mass and energy balances

455 456 458 459 459 460 464 464 464 464 464 466

443 444 445 445 446 447

Contents 12.2.4

xv

Reliability of available process knowledge Existing processes New processes and pilot plants 12.2.5 Effect of upstream and downstream processes 12.2.6 Fuel choice Fuel chemical compatibility with the process Heat transfer compatibility with the process 12.2.7 Potential for heat recovery and choice of equipment Estimating the potential for heat recovery from hot product Estimating the potential for heat recovery from hot flue gas Estimating the potential for heat recovery from shell losses or cooling water Economic considerations 12.3 Furnace sizing Slab heating furnace design Oil heating furnace design Aggregate processing furnace 12.4 Burner selection 12.5 Detailed analysis and validation of the furnace design 12.6 Furnace instrumentation and controls Nomenclature References

466 467 467 468 469 470 472 474

Author index Subject index

507 511

475 476 478 479 479 487 489 492 496 500 501 503 504

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Foreword

Furnaces have been used by humans for thousands of years and yet, beyond the basic chemical reactions and heat release calculations, engineers rarely have any formal training in relation to furnace design, combustion and their integration into industrial processes. It is therefore not surprising that the solution to issues of emissions, throughput and performance related problems have relied heavily on trial and error and experience. Within industry in general equipment would be more successful designed using the principals outlined in this book rather than relying on correlations and scale up factors that have little, or no scientific basis to support them. In the early 1970s the authors set themselves the goal of applying more scientific methods to burner design than were currently used. This led to the realisation that heat release from flames needed to be closely matched to the process requirements and that this was intimately related to the design of the furnace itself. Now, more than ever before, the need to reduce ongoing energy costs and greenhouse gas emissions requires decisions to be made on the basis of knowledge rather than guesswork and past experience. This book, being one of only a few ever published on the subject, highlights the applicable science which can be used to take much of the guesswork out of furnace design. This book also emphasises the importance of ensuring that individual pieces of equipment are appropriate for the whole process and not simply selected on the basis of capacity or lowest capital cost. Alcoa’s alumina refineries operate a range of processes and equipment including boilers, rotary kilns, gas suspension alumina calciners and regenerative thermal oxidisers and, like many other industries, have needed to address emissions, throughput, performance and safety issues without a clear understanding of the science and underlying design basis. This makes it difficult to undertake reliable root cause analysis when problems occur. In the early 1980s I was a mechanical engineer in Alcoa’s Equipment Development Group. I had insufficient knowledge of, and certainly little experience with, combustion processes and was faced with having to address throughput and emissions related issues with alumina calciners. Fortunately I met the authors of this book, Peter Mullinger and Barrie Jenkins, and was delighted to discover that a scientific approach to furnace design is possible and methods are available to investigate and optimise many aspects of the combustion and associated processes. It was highlighted through physical modelling of the flow patterns and acid alkali modelling of the combustion process mixing that both the throughput and emissions could be significantly improved by simply relocating fuel injection points. These modifications proved to be effective and have now been employed on all applicable alumina calciners at Alcoa’s refineries around the world saving otherwise significant capital expenditure with potentially ineffective outcomes.

xviii Foreword Since those early days the science as described in this book has been employed over a wide range of process issues, from the design of new equipment and in the solution of problems with existing equipment, positively impacting on performance and reliability. More recently there has been a major application in relation to the design of safety systems. In particular the application of CFD modelling has highlighted to me that CFD doesn’t replace the need for a deep understanding of the science of combustion and furnace heat transfer processes as there are many traps for the unwary and the uninformed. Whether you are engaged in modelling, design of original equipment or equipment upgrades or operation of combustion and furnace heat transfer processes, this book provides much of the essential understanding required for success. Greg Mills Senior Consultant – Calcination Technology Delivery Group Alcoa World Alumina

Preface

This book has been more than 20 years in gestation; its lineage can be traced back to Barrie’s lecturing at the University of Surrey in the late 1970s and early 1980s and Peter’s first combustion course, provided internally to Rugby Cement’s engineers in 1981. We are not at...