"MODULE TITLE:HEAT TRANSFER AND COMBUSTION TOPIC TITLE:COMBUSTION PROCESSES LESSON 1:COMBUSTION OF FUELS HTC - 4 - 1 © Teesside University 2011Published by Teesside University Open Learning (Engineering) School of Science & Engineering Teesside University Tees Valley, UK TS1 3BA +44 (0)1642 342740 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 permission of the Copyright owner. This book is sold subject to the condition that it shall not, by way of trade or otherwise, be lent, re-sold, hired out or otherwise circulated without the publisher's prior consent in any form of binding or cover other than that in which it ispublished and without a similar condition including this condition being imposed on the subsequent purchaser. 1 ________________________________________________________________________________________ INTRODUCTION ________________________________________________________________________________________ The combustion of fuels is an important aspect of heat transfer.The process is the major source of heat used on most chemical plants either to directly heat up other materials or in the production of steam which is then distributed around the site and used to provide heat (and/or power). In this lesson we will look at the combustion of several fuels and use the concept of mass and energy balance, which you may have covered already in the module entitled Mass and Energy Balance, to determine: • air:fuel ratios for good combustion• composition of combustion products. Much of this lesson will have been covered within the Mass and Energy Balance module so this should be partly revision. ________________________________________________________________________________________ YOUR AIMS ________________________________________________________________________________________ At the end of this lesson you should be able to: • write balanced equations for the combustion of selected fuels • understand the terms theoretical air, excess air and air:fuel ratio• use material balances to determine– the composition of fuels containing carbon and hydrogen only – the % excess air – air:fuel ratios by relative mass and relative volume. Teesside University Open Learning © Teesside University 2011 (Engineering)2 ________________________________________________________________________________________ STUDY ADVICE ________________________________________________________________________________________ You should have already studied similar material when doing the Mass and Energy Balance module.If you have, then this lesson will act as a form of revision.It will not be covered in the detail that it was in Mass and Energy balance and you may wish to refer to material in that unit if you do not understand this lesson. If you have not studied the Mass and Energy Balance module, the work is explained in sufficient detail to answer the questions that will be asked in the Tutor Marked Assignment. You will need to understand some basic chemistry involving chemical formulae, atomic and molecular mass and balancing chemical equations.If you have trouble understanding these parts of the lesson, you will need to refer to text books and/or your tutor for further details. You will need a calculator to answer some of the questions. Teesside University Open Learning © Teesside University 2011 (Engineering)3 ________________________________________________________________________________________ COMBUSTION OF FUELS ________________________________________________________________________________________ A fuel is defined by the Cambridge Dictionary as "a substance which is used to provide heat or power, usually by being burned: wood, coal, oil, petrol, natural gas are all different kinds of fuel that are burnt to produce heat.Plutonium and uranium are different kinds of fuel used in nuclear reactors to produce heat and power by reactions which do not involve being burnt". We will only be concerned with those fuels that are burnt to produce heat and power.To burn a fuel requires three 'ingredients', the fuel itself, oxygen (or, more commonly, air which contains approximately 21% oxygen by volume) and a source of ignition.Some fuels (mainly gaseous ones) when mixed with sufficient oxygen are easily ignited by a spark and then burn very easily releasing a constant supply of heat, whilst others (mainly solid fuels, e.g. coal) even when mixed with sufficient oxygen have to be exposed to a high temperature before they burn and then release heat energy, often in a very variable manner. Without any one of the three ingredients – fuel, oxygen (air) and ignition – combustion will not occur and heat will not be released.In addition, a shortage of oxygen will create less efficient combustion of the fuel and poor heat release. In industry, it is important that the supply of heat is controlled and predictable. To this end, it is necessary to determine how much oxygen is theoretically required to completely burn the fuel and in some cases how much extra oxygen is required to ensure that the fuel is burnt efficiently. Teesside University Open Learning © Teesside University 2011 (Engineering)"