Combustion Engineering, Second - Kenneth W. Ragland (1) (1) PDF

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S ECOND E DITION Combustion Engineering Kenneth W. Ragland Kenneth M. Bryden S ECOND E DITION Combustion Engineering S ECOND E DITION Combustion Engineering Kenneth W. Ragland Kenneth M. Bryden Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business ...

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Combustion Engineering, Second Kenneth W. Ragland (1) (1) Raphael Antwi

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S ECOND E DITION

Combustion Engineering

Kenneth W. Ragland Kenneth M. Bryden

S ECOND E DITION

Combustion Engineering

S ECOND E DITION

Combustion Engineering Kenneth W. Ragland Kenneth M. Bryden

Boca Raton London New York

CRC Press is an imprint of the Taylor & Francis Group, an informa business

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2011 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Version Date: 20110829 International Standard Book Number-13: 978-1-4665-0001-3 (eBook - PDF) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright. com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

To our wives Nancy and Kristy

Contents Preface to Second Edition ...................................................................................... xiii Preface to First Edition ............................................................................................ xv Acknowledgments ..................................................................................................xvii Authors ....................................................................................................................xix Nomenclature and Abbreviations............................................................................xxi Chapter 1

Introduction to Combustion Engineering .............................................1 1.1 The Nature of Combustion ........................................................1 1.2 Combustion Emissions .............................................................. 3 1.3 Global Climate Change .............................................................4 1.4 Sustainability ............................................................................. 6 1.5 World Energy Production .......................................................... 6 1.6 Structure of the Book ................................................................ 7 References ............................................................................................ 8

SECTION I Basic Concepts Chapter 2

Fuels ................................................................................................... 11 2.1

Gaseous Fuels .......................................................................... 11 2.1.1 Characterization of Gaseous Fuels............................. 13 2.2 Liquid Fuels ............................................................................. 15 2.2.1 Molecular Structure.................................................... 16 2.2.2 Characterization of Liquid Fuels ................................ 18 2.2.3 Liquid Fuel Types ....................................................... 22 2.3 Solid Fuels ...............................................................................24 2.3.1 Biomass ...................................................................... 27 2.3.2 Peat ............................................................................. 29 2.3.3 Coal ............................................................................ 30 2.3.4 Refuse-Derived Fuels ................................................. 32 2.3.5 Characterization of Solid Fuels .................................. 33 2.4 Problems .................................................................................. 37 References .......................................................................................... 39 Chapter 3

Thermodynamics of Combustion ....................................................... 41 3.1 3.2 3.3

Review of First Law Concepts................................................. 41 Properties of Mixtures.............................................................44 Combustion Stoichiometry ...................................................... 48 vii

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Contents

3.4

Chemical Energy ..................................................................... 59 3.4.1 Heat of Reaction ......................................................... 59 3.4.2 Heat of Formation and Absolute Enthalpy .................64 3.5 Chemical Equilibrium .............................................................66 3.5.1 Chemical Equilibrium Criterion ................................ 67 3.5.2 Properties of Combustion Products............................80 3.6 Adiabatic Flame Temperature ................................................. 81 3.7 Problems .................................................................................. 86 References ..........................................................................................90 Chapter 4

Chemical Kinetics of Combustion ..................................................... 91 4.1 4.2 4.3 4.4

Elementary Reactions .............................................................. 91 Chain Reactions.......................................................................97 Global Reactions.................................................................... 102 Nitric Oxide Kinetics ............................................................ 108 4.4.1 Prompt NO and Fuel-Bound NO .............................. 115 4.5 Reactions at a Solid Surface .................................................. 116 4.6 Problems ................................................................................ 118 References ........................................................................................ 120

SECTION II Chapter 5

Combustion of Gaseous and Vaporized Fuels

Flames .............................................................................................. 125 5.1

Laminar Premixed Flames .................................................... 125 5.1.1 Effect of Stoichiometry on Laminar Flame Speed .. 126 5.1.2 Effect of Temperature and Pressure on Laminar Flame Speed ............................................................. 130 5.1.3 Stabilization of Premixed Flames ............................ 132 5.2 Laminar Flame Theory ......................................................... 133 5.2.1 Laminar Flame Differential Equations .................... 137 5.2.2 Simplified Laminar Flame Model ............................ 139 5.3 Turbulent Premixed Flames .................................................. 144 5.3.1 Turbulence Parameters, Length Scales, and Time Scales ........................................................................ 145 5.3.2 Turbulent Flame Types ............................................. 147 5.4 Explosion Limits.................................................................... 150 5.5 Diffusion Flames ................................................................... 152 5.5.1 Free Jet Flames ......................................................... 153 5.5.2 Concentric Jet Flames .............................................. 155 5.5.3 Concentric Jet Flame with Bluff Body..................... 157 5.6 Problems ................................................................................ 159 References ........................................................................................ 160

ix

Contents

Chapter 6

Gas-Fired Furnaces and Boilers ....................................................... 163 6.1

Energy Balance and Efficiency ............................................. 163 6.1.1 Furnace and Boiler Efficiency .................................. 167 6.2 Fuel Substitution .................................................................... 170 6.3 Residential Gas Burners ........................................................ 172 6.4 Industrial Gas Burners .......................................................... 174 6.5 Utility Gas Burners................................................................ 176 6.6 Low Swirl Gas Burners ......................................................... 178 6.7 Problems ................................................................................ 180 References ........................................................................................ 181 Chapter 7

Premixed-Charge Engine Combustion ............................................ 183 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9

Introduction to the Spark Ignition Engine ............................. 183 Engine Efficiency .................................................................. 186 One-Zone Model of Combustion in a Piston-Cylinder ......... 188 Two-Zone Model of Combustion in a Piston-Cylinder ......... 193 In-Cylinder Flame Structure ................................................. 197 Combustion Chamber Design................................................ 199 Emission Controls..................................................................200 Ethanol Considerations .......................................................... 203 Review of Terminology for Premixed Gas, Four-Stroke Engines ..................................................................................204 7.10 Problems ...............................................................................206 References ........................................................................................ 210 Chapter 8

Detonation of Gaseous Mixtures...................................................... 213 8.1 8.2 8.3

Transition to Detonation ........................................................ 213 Steady-State Detonations ...................................................... 214 One-Dimensional Model for Propagation Velocity, Pressure, and Temperature Rise across a Detonation ........... 220 8.4 Maintained and Pulse Detonations........................................ 227 8.5 Problems ................................................................................ 230 References ........................................................................................ 231

SECTION III Chapter 9

Combustion of Liquid Fuels

Spray Formation and Droplet Behavior ........................................... 235 9.1 9.2 9.3

Spray Formation .................................................................... 236 Droplet Size Distributions ..................................................... 239 Fuel Injectors ......................................................................... 243 9.3.1 Steady Flow Injectors ............................................... 243

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Contents

9.3.2 Intermittent Injectors ...............................................248 9.4 Vaporization of Single Droplets ............................................ 258 9.5 Problems ................................................................................ 261 References ........................................................................................ 262 Chapter 10 Oil-Fired Furnace Combustion ........................................................ 265 10.1 Oil-Fired Systems .................................................................. 265 10.2 Spray Combustion in Furnaces and Boilers .......................... 269 10.3 Plug Flow Model of a Uniform Field of Droplets ................. 274 10.4 Emissions from Oil-Fired Furnaces and Boilers ................... 279 10.5 Problems ................................................................................284 References ........................................................................................ 285 Chapter 11 Gas Turbine Spray Combustion........................................................ 287 11.1 Gas Turbine Operating Parameters ....................................... 287 11.2 Combustor Design ................................................................. 291 11.2.1 Ignition ..................................................................... 295 11.2.2 Flame Stabilization .................................................. 296 11.2.3 A Specific Combustor Design .................................. 297 11.3 Combustion Rate ...................................................................300 11.4 Liner Heat Transfer ...............................................................308 11.5 Low Emissions Combustors .................................................. 310 11.6 Problems ................................................................................ 313 References ........................................................................................ 314 Chapter 12 Diesel Engine Combustion ............................................................... 317 12.1 12.2 12.3 12.4 12.5 12.6

Introduction to Diesel Engine Combustion .......................... 317 Combustion Chamber Geometry and Flow Patterns............. 318 Fuel Injection ......................................................................... 320 Ignition Delay ........................................................................ 321 One-Zone Model and Rate of Combustion............................ 324 Engine Emissions .................................................................. 327 12.6.1 Diesel Engine Emission Standards .......................... 331 12.7 Diesel Engine Improvements ................................................ 332 12.8 Problems ................................................................................ 334 References ........................................................................................ 335 Chapter 13 Detonation of Liquid and Gaseous Mixtures ................................... 339 13.1 Detonation of Liquid Fuel Sprays ..........................................340 13.1.1 Droplet Breakup .......................................................340 13.1.2 Spray Detonations .................................................... 343 13.2 Detonation of Liquid Fuel Layers .......................................... 347 13.3 Problems ................................................................................ 350 References ........................................................................................ 351

xi

Contents

SECTION IV

Combustion of Solid Fuels

Chapter 14 Solid Fuel Combustion Mechanisms ................................................ 355 14.1 Drying of Solid Fuels ............................................................ 355 14.1.1 Drying of Small Particles ......................................... 356 14.1.2 Drying of Larger Particles........................................ 361 14.2 Devolatilization of Solid Fuels .............................................. 363 14.3 Char Combustion ................................................................... 368 14.3.1 Char Burnout ........................................................... 372 14.3.2 Char Surface Temperature ....................................... 375 14.4 Ash Formation ....................................................................... 377 14.5 Problems ................................................................................ 377 References ........................................................................................ 378 Chapter 15 Fixed Bed Combustion ..................................................................... 381 15.1 Biomass Cookstoves .............................................................. 381 15.2 Space Heating Stoves Using Logs ......................................... 386 15.3 Grate Burning Systems for Heat and Power .......................... 387 15.3.1 Traveling Grate Spreader Stokers............................. 388 15.3.2 Vibrating Grate Spreader Stokers ............................ 389 15.4 Combustion Efficiency and Boiler Efficiency ....................... 391 15.5 Emissions from Grate Burning Systems ............................... 393 15.6 Modeling Combustion of Solid Fuels on a Grate ................. 396 15.6.1 Modeling Fixed-Bed Char Combustion ................... 396 15.6.2 Modeling Fixed-Bed Combustion of Biomass ......... 401 15.7 Problems ................................................................................405 References ........................................................................................408 Chapter 16 Suspension Burning.......................................................................... 411 16.1 Pulverized Coal Burning Systems ......................................... 411 16.1.1 Location of Fuel and Air Nozzles ............................ 413 16.1.2 Furnace Design......................................................... 416 16.2 Pulverized Coal Combustion ................................................. 418 16.2.1 Isothermal Plug Flow of Pulverized Coal ................ 419 16.2.2 Non-Isothermal Plug Flow of Pulverized Char Suspension ................................................................ 425 16.3 Behavior of Ash ..................................................................... 429 16.4 Emissions from Pulverized Coal Boilers .............................. 430 16.5 Carbon Dioxide Capture and Sequestration .......................... 431 16.6 Biomass-Fired Boilers ........................................................... 435 16.7 Problems ................................................................................ 436 References ........................................................................................ 438

xii

Contents

Chapter 17 Fluidized Bed Combustion ............................................................... 441 17.1 Fluidization Fundamentals .................................................... 442 17.1.1 Pressure Drop across the Bed ................................. 445 17.1.2 Minimum Fluidization Velocity ...............................446 17.1.3 Single Particle Terminal Velocity ............................ 447 17.1.4 Bubbling Beds .....................................................