Size Reduction of Divided Solids
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Size Reduction of Divided Solids, part of the Industrial Equipment for Chemical Engineering set, presents a practical guide for choosing devices and flow and rate parameters in the size reduction of divided solids. The size reducing principles are presented, with their application to plant products used as examples, also taking into account the influences of heat and humidity.
The author also provides the methods needed for understanding the equipment used in applied thermodynamics to encourage students and engineers to self build the programs they need. Chapters are complemented with appendices that provide additional information and associated references.
- Includes the empirical laws governing overflow and underflow of a bulk solid
- Provides characteristics of bulk solids
- Presents a practical guide for choosing devices and flow and rate parameters in the size reduction of divided solids
Jean-Paul Duroudier
Jean-Paul Duroudier is an engineer from Ecole centrale de Paris, France. He has devoted his professional life to the study of materials in chemical engineering.
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Size Reduction of Divided Solids - Jean-Paul Duroudier
Size Reduction of Divided Solids
Jean-Paul Duroudier
Industrial Equipment for Chemical Engineering Set
coordinated by
Jean-Paul Duroudier
Table of Contents
Cover image
Title page
Dedication
Copyright
Preface
1: Grinding: Principles and Theories
Abstract
1.1 Grinding
1.2 Empirical laws governing overflow and underflow of a bulk solid
1.3 Physics of fragmentation
1.4 Grinding: a unit operation
1.5 Distribution of residence times (continuous grinding)
1.6 Solving mill and grinding circuit equations
2: Grinding Energy
Abstract
2.1 Power and yields
2.2 Bond’s energy index: ball or rod mills
3: Ball and Rod Mills
Abstract
3.1 Introduction
3.2 Ball size
3.3 Operation parameters
3.4 Flow in the mill
3.5 The selection matrix
3.6 Wearing of a mill’s internal surfaces
3.7 Rod mills
4: Crushers and Grinders Except Ball Mills and Rod Mills
Abstract
4.1 Crushers
4.2 Shock equipment
4.3 Roller crushers and mills
4.4 Track crushers and mills
4.5 Autogenous mill
4.6 The bead mill for ultrafines (micronizer)
4.7 Other equipment for ultrafines
4.8 Dispersers (in a liquid)
5: Choice in Comminution Equipment: Mechanical Plant Processing
Abstract
5.1 Characteristics of divided solids
5.2 Machine selection
5.3 Processing plants – the plant cell
5.4 Mechanical preparation of plants
Appendix 1: Mohs Scale
Appendix 2: Real Density of Loose Bulk Solids (kg.m−3)
A2.1 Plant products
A2.2 Natural inorganic products
A2.3 Manufactured products
Bibliography
Index
Dedication
There are no such things as applied sciences, only applications of science.
Louis Pasteur (11 September 1871)
Dedicated to my wife, Anne, without whose unwavering support, none of this would have been possible.
Copyright
First published 2016 in Great Britain and the United States by ISTE Press Ltd and Elsevier Ltd
Apart from any fair dealing for the purposes 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 and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:
ISTE Press Ltd
27-37 St George’s Road
London SW19 4EU
UK
www.iste.co.uk
Elsevier Ltd
The Boulevard, Langford Lane
Kidlington, Oxford, OX5 1GB
UK
www.elsevier.com
Notices
Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.
Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.
To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability 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.
For information on all our publications visit our website at http://store.elsevier.com/
© ISTE Press Ltd 2016
The rights of Jean-Paul Duroudier to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.
British Library Cataloguing-in-Publication Data
A CIP record for this book is available from the British Library
Library of Congress Cataloging in Publication Data
A catalog record for this book is available from the Library of Congress
ISBN 978-1-78548-185-7
Printed and bound in the UK and US
Preface
The observation is often made that, in creating a chemical installation, the time spent on the recipient where the reaction takes place (the reactor) accounts for no more than 5% of the total time spent on the project. This series of books deals with the remaining 95% (with the exception of oil-fired furnaces).
It is conceivable that humans will never understand all the truths of the world. What is certain, though, is that we can and indeed must understand what we and other humans have done and created, and, in particular, the tools we have designed.
Even two thousand years ago, the saying existed: faber fit fabricando
, which, loosely translated, means: "c’est en forgeant que l’on devient forgeron" (a popular French adage: one becomes a smith by smithing), or, still more freely translated into English, practice makes perfect
. The artisan
(faber) of the 21st Century is really the engineer who devises or describes models of thought. It is precisely that which this series of books investigates, the author having long combined industrial practice and reflection about world research.
Scientific and technical research in the 20th century was characterized by a veritable explosion of results. Undeniably, some of the techniques discussed herein date back a very long way (for instance, the mixture of water and ethanol has been being distilled for over a millennium). Today, though, computers are needed to simulate the operation of the atmospheric distillation column of an oil refinery. The laws used may be simple statistical correlations but, sometimes, simple reasoning is enough to account for a phenomenon.
Since our very beginnings on this planet, humans have had to deal with the four primordial elements
as they were known in the ancient world: earth, water, air and fire (and a fifth: aether). Today, we speak of gases, liquids, minerals and vegetables, and finally energy.
The unit operation expressing the behavior of matter are described in thirteen volumes.
It would be pointless, as popular wisdom has it, to try to reinvent the wheel
– i.e. go through prior results. Indeed, we well know that all human reflection is based on memory, and it has been said for centuries that every generation is standing on the shoulders of the previous one.
Therefore, exploiting numerous references taken from all over the world, this series of books describes the operation, the advantages, the drawbacks and, especially, the choices needing to be made for the various pieces of equipment used in tens of elementary operations in industry. It presents simple calculations but also sophisticated logics which will help businesses avoid lengthy and costly testing and trial-and-error.
Herein, readers will find the methods needed for the understanding the machinery, even if, sometimes, we must not shy away from complicated calculations. Fortunately, engineers are trained in computer science, and highly-accurate machines are available on the market, which enables the operator or designer to, themselves, build the programs they need. Indeed, we have to be careful in using commercial programs with obscure internal logic which are not necessarily well suited to the problem at hand.
The copies of all the publications used in this book were provided by the Institut National d’Information Scientifique et Technique at Vandœuvre-lès-Nancy.
The books published in France can be consulted at the Bibliothèque Nationale de France; those from elsewhere are available at the British Library in London.
In the in-chapter bibliographies, the name of the author is specified so as to give each researcher his/her due. By consulting these works, readers may gain more in-depth knowledge about each subject if he/she so desires. In a reflection of today’s multilingual world, the references to which this series points are in German, French and English.
The problems of optimization of costs have not been touched upon. However, when armed with a good knowledge of the devices’ operating parameters, there is no problem with using the method of steepest descent so as to minimize the sum of the investment and operating expenditure.
1
Grinding: Principles and Theories
Abstract
Chemistry uses bulk solids with average particle sizes ranging from 1 mm to 100 μm (fine), including particle sizes less than 20 μm (ultrafines).
Keywords
Cracking; Distribution (or breaking) matrix; Fragmentation; Grinding; Harris distribution; Heterogeneous rocks; Law for underflow; Pinch roll grinding; Residence times; Zero-order grinding
1.1 Grinding
1.1.1 Introduction
Chemistry uses bulk solids with average particle sizes ranging from 1 mm to 100 μm (fine), including particle sizes less than 20 μm (ultrafines).
For fibrous or plastic materials, splitting or shredding is used. However, for classic bulk solids (minerals, crystals, etc.), pressure or collisions are used and shearing is used less often.
Grinding equipment includes:
– a storage hopper for the bulk solid to be processed;
– a feed system using a screw conveyor, a conveyor belt or a vibrating conveyor;
– a comminution device;
– a classifier which generally uses a centrifugal force balanced by air (or water) friction;
– air decontamination equipment (usually dust extraction) and a fan for its removal.
Hixon [HIX 91] reviews different possible processes.
The wearing down of grinding surfaces requires part replacements (for example, plates and millstones).
The shape of the output obtained is important. As such, the gravel’s shape must be compact, that is, its three dimensions must be similar.
The average size of pigmented powders determines its color.
Wet grinding (after dispersion in a liquid) could lead to the flocculation of particles smaller than 10 μm.
Humidity greater than 50% (on-wet) liberates grains and improves their grinding.
The impact of temperature could be eliminated in the following ways, if it is too high:
– mix crushed ice into the feed system;
– cool the device with liquid nitrogen.
The risk of explosion could be eliminated by operating in a neutral atmosphere (CO2, N2, washed combustion gases).
1.1.2 Grain size
The size of the feed has the following order of magnitude:
The reduction ratio is:
The ratio R has a magnitude of 6 for a crusher and could reach up to 400 for a fluid energy mill.
The specifications imposed on the mill often have two limits. For example:
– there must be more than 80% of the mass that is less than 0.3 mm;
– there must be less than 5% of the mass that is less than 0.05 mm.
The fines produced (dry dust and wet pulp viscosity) are:
– very large with grinding track mills;
– much less with roller mills;
– non-existent with shredders (sugar cane) and splitting equipment.
1.1.3 Output granulometry
We will often call the granulometry
of a bulk solid the distribution of particle sizes by mass.
If mi is the mass remaining on the screen i, we can study the variation in mi in comparison with its size xj, which is the frequency distribution. The cumulative distribution, versus xj, looks at variations in the underflow P (see section 1.4.1):
The average size of the output obtained from a comminution process is linked to the type of the process used.
Table 1.1
Average size of