Combustion and Pollution Control in Heating Systems

Transcription

1 Combustion and Pollution Control in Heating Systems

2 v. I. Hanby Combustion and Pollution Control in Heating Systems With 44 Figures Springer-Verlag London Berlin Heidelberg New York Paris Tokyo Hong Kong Barcelona Budapest

3 Victor Ian Hanby, BSc, PhD, CEng, MInstE, MCmSE Department of Civil Engineering, University of Technology, Loughborough, Leicestershire LEII 3TU, UK ISBN-13:978-3-S4G DOl: 10.l007/ e-isbn-13: British Library Cataloguing in Publication Data Hanby, V.I. Combustion and Pollution Control in Heating Systems I. Title ISBN-13: Library of Congress Cataloging-in-Publication Data Hanby, V. I. (Victor Ian), Combustion and pollution control in heating systems 1 V.I. Hanby. p. em. Includes bibliographical references and index. ISBN-13: I. Heating-Equipment and supplies. 2. Hydrocarbons-Combustion. 3. Flue gases-purification. I. Title. TH7345.H dc20 CIP Apart from any fair dealing for the putposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers. Springer-Verlag London Limited 1994 The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. Typeset by Richard Powell Editorial and Production Services, Basingstoke, Hants, RG224TX. 69/ Printed on acid-free paper

4 Preface Combustion is very much an interdisciplinary topic, drawing together elements of chemistry, fluid mechanics and heat transfer. It is an ingredient in many undergraduate degree programmes, ranging from a pivotal role in fuel science through to a component part of courses in chemical, process and building services engineering. For many students in those disciplines where combustion in heating plant is an important part of their studies, there are often problems in coming to grips with the basic principles underlying the combustion of hydrocarbon fuels. In particular, the concepts of chemical and related thermodynamic changes can prove difficult to assimilate. The scientific literature dealing with combustion tends to be rather polarised, with a wealth of literature aimed at the specialist reader, but at a basic level the fundamentals of this important process are often treated rather tersely in textbooks on thermodynamics. The objective of this book is to provide an introduction to the basic principles of the combustion of hydrocarbon fuels in heating plant for buildings and industrial processes. In those chapters where practice in problem solving can make a positive contribution to understanding, some numerical problems have been included. Acknowledging the ever-widening use of computers in technical education, a number of algorithms which can be easily coded up for solving numerical problems have been incorporated in the text. These can prove particularly useful in, for example, the calculation of certain fluid properties, either for use in hand calculation or for incorporation into larger programs. It would be wholly inappropriate to leave out some discussion of the properties of hydrocarbon fuels and the equipment in which they are burned, but this has been deliberately confmed to an outline treatment in Chapters 7, 8 and 9. There are many sources of information dealing with the practical aspects of combustion equipment, and reference is made in the text to a selection of appropriate books and guides to current practice. Barrow-upon-Soar, 1994 V.l. Hanby

5 Contents 1 The Combustion of Hydrocarbon Fuels Introduction The Combustion Process The Complete Combustion Reaction Quantification of the Combustion Reaction 4 :1 Stoichiometric Calculations Applications of the Combustion Equation Combustion Air Requirements - Gaseous Fuels Flue Gas Composition - Gaseous Fuels Combustion Air Requirements - Solid and Liquid Fuels Combustion Products - Solid and Liquid Fuels Practical Significance of the Flue Gas Composition Sub-stoichiometric Combustion Problems 20 3 Heat Release in Combustion Introduction Constant-pressure Combustion Enthalpy of a Mixture of Gases Enthalpy of Combustion Constant-volume Combustion Internal Energy of Combustion Relationship between Ml 2S and ~ U 2 S Calorific Values List of Symbols Problems 34

6 viii CONTENTS 4 Flame Temperature Energy Balance on a System Adiabatic Flame Temperature Specific Heats of Gases Calculation Algorithm Calculated Adiabatic Flame Temperatures References List of Symbols Problems 46 5 Equilibrium Composition of Flames Introduction Chemical Equilibrium Calculation of the Equilibrium Composition Dissociated Flame Temperature Dissociation with Hydrocarbon Fuels References List of Symbols 59 6 Efficiency of Combustion Plant Plant Efficiency Direct Detennination of Efficiency Inferential Measurement of Efficiency Efficiency and Flue Gas Temperature Flue Gas Dew Point Efficiency of a Condensing Boiler References List of Symbols Problems 76 7 Gaseous Fuels Introduction Natural Gas Town Gas (Coal Gas) Liquefied Petroleum Gas (LPG) Combustion of Gaseous Fuels Flammability Limits Burning Velocity Wobbe Number Gas Burners Diffusion Burners Premixed Burners References 87

7 CONTENTS Ix 7.8 List of Symbols 8 Liquid Fuels 8.1 Occurrence and Processing 8.2 Properties of Oil Fuels 8.3 Combustion of Liquid Fuels 8.4 Pressure Jet Burners 8.5 Rotary Cup Burners 8.6 Twin-fluid Atomisers 8.7 Storage of Liquid Fuels 8.8 References 9 Solid Fuels 9.1 Introduction 9.2 Coal Classification 9.3 Coal Properties 9.4 Coal Combustion 9.5 Coal Storage and Handling 9.6 References 10 Emissions from Combustion Plant 10.1 Environmental Considerations 10.2 The Greenhouse Effect 10.3 Carbon Dioxide Emissions 10.4 Carbon Monoxide 10.5 Oxides of Nitrogen Atmospheric Nitrogen Fuel-bound Nitrogen NO x Levels Low-NO x Burner Design 10.6 Oxides of Sulphur The SOx Problem Sulphur Trioxide Formation Flue Gas Desulphurisation 10.7 Particulate Emissions Solid Formation in Combustion Soot Formation Cenosphere Formation Acid Smut Formation Ash 10.8 List of Symbols 10.9 References 11 Flues and Chimneys

8 x CONTENTS 11.1 Functions of the Flue System 11.2 Chimney Heat Transfer Heat Transfer Mechanism U-value ofa Chimney Temperature Distribution in a Chimney 11.3 Pressure Loss Chimney Draught Flow Resistance 11.4 Chimney Location 11.5 List of Symbols 11.6 References Index