Processing of Particulate Solids

383 Pages·1997·12.84 MB·English

by  Jonathan Seville

Processing of Particulate Solids
Powder Technology Series
EDITED BY
BRIAN SCARLETT and GENJI JIMBO
Delft University of Technology Chuba Powtech Plaza Lab
The Netherlands Japan
Many materials exist in the form of a disperse system, for example
powders, pastes, slurries, emulsions and aerosols. The study of such systems
necessarily arises in many technologies but may alternatively be regarded as
a separate subject which is concerned with the manufacture,
characterization and manipulation of such systems. Chapman & Hall were
one of the first publishers to recognize the basic importance of the subject,
going on to instigate this series of books. The series does not aspire to
define and confine the subject without duplication, but rather to provide a
good home for any book which has a contribution to make to the record of
both the theory and the application of the subject. We hope that all
engineers and scientists who concern themselves with disperse systems will
use these books and that those who become expert will contribute further to
the series.
Particle Size Measurement
Terence Allen
5th edn, hardback (0412753502), 2 volume set, 552 and 272 pages
Chemistry of Powder Production
Yasuo Arai
Hardback (041239540 1), 292 pages
Particle Size Analysis
Claus Bernhardt
Translated by H. Finken
Hardback (0412558807), 428 pages
Particle Classification
K. Heiskanen
Hardback (0412493004), 330 pages
Powder Surface Area and Porosity
S. Lowell and Joan E. Shields
3rd edn, hardback (0412 39690 4), 256 pages
Pneumatic Conveying of Solids
G.E. Klinzing, R.D. Marcus, F. Rizk and L.S. Leung
2nd edn, hardback (0412724405), 624 pages
Principles of Flow in Disperse Systems
O. Molerus
Hardback (0412406306), 314 pages
Processing of Particulate Solids
J.P.K. Seville, U. Tiiziin and R. Clift
Hardback (0751403768), 384 pages
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Processing of
Particulate Solids
Jonathan Seville
Professor of Chemical Engineering
School of Chemical Engineering
University of Birmingham, UK
Ugur Tuzun
Professor of Process Engineering
Department of Chemical and Process Engineering
University of Surrey
Guildford, UK
and
Roland Clift
Professor of Environmental Technology
Centre for Environmental Strategy
University of Surrey
Guildford, UK
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First edition 1997
© 1997 Chapman & Hall
Typeset in 10112pt Times by Cambrian Typesetters, Frimley, Surrey
ISBN-13:978-94-010-7152-9 elSBN:978-94-009-1459-9
DOI:I0.I0071978-94-009-1459-9
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Library of Congress Catalog Card Number: 96-83857
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Contents
Preface xi
1 Particle characterisation 1
1.1 Particle size distributions 1
1.1.1 Definitions 1
1.1.2 Methods of presenting size data 3
1.1.3 Averages 7
1.1.4 Weighted distributions 9
1.1.5 Model distribution functions 16
1.2 Particle size measurement 18
1.2.1 Particle size 18
1.2.2 Particle shape 21
1.2.3 Sampling 26
1.2.4 Methods of particle size measurement 30
1.3 Nomenclature 48
A1 Derivation and properties of the log-normal distribution 49
References 52
2 Particles in fluids 53
2.1 Single particles 53
2.1.1 Fluid-particle drag 53
2.1.2 Fluid motion 56
2.1.3 Free fall or rise 59
2.1.4 Non-continuum effects 76
2.2 Unsteady motion of single particles 79
2.2.1 Drag in unsteady motion 79
2.2.2 Acceleration 80
2.2.3 Curvilinear motion 81
2.3 Assemblages of particles 85
2.3.1 Settling and particulate fluidisation 85
2.3.2 Flow through packed beds 86
2.4 Flow of particlelfluid mixtures in pipes 87
2.4.1 Continuity 88
2.4.2 Momentum balance 91
viii Contents
2.4.3 Mechanical energy balance 95
2.5 Nomenclature 96
References 98
3 Particle mechanics 99
3.1 Interparticle forces 99
3.1.1 van der Waals forces 99
3.1.2 Liquid bridge forces 109
3.1.3 Electrostatic forces 120
3.1.4 Comparison of the magnitude of interparticle forces 123
3.2 Effects of interparticle forces at contacts 125
3.2.1 Contact mechanics 125
3.2.2 Assembly mechanics 127
3.3 Friction at a single contact 132
3.4 Impact and rebound of particles 135
3.4.1 The coefficient of restitution 137
3.4.2 The effect ofliquid layers 140
3.5 Nomenclature 142
References 143
4 Characterisation of bulk mechanical properties 145
4.1 Introduction 145
4.2 Empirical measurements of coefficients of friction 146
4.3 Angles of friction of cohesionless materials 148
4.4 Angles offriction of cohesive materials 151
4.5 Characterisation of 'flowability' of cohesive powders
(Jenike design method) 157
4.5.1 Material flow function (FF) 158
4.5.2 Jenike's hopper flow factor (ff) 159
4.5.3 Jenike's minimum critical outlet span for flow 159
4.6 Equations of stress equilibrium in bulk solids 160
4.7 Bulk failure criterion 163
4.8 Description of bulk solids stress states 165
4.9 Bulk solids flow rules 167
4.10 Empirical measurements of compressibility of bulk solids 168
4.11 Nomenclature 171
References 172
5 Assembly mechanics 174
5.1 Introduction 174
5.2 Assembly modelling of wall friction in a flowing particulate bed 174
5.2.1 Normal stress and dilatancy 176
5.3 The distinct element method 179
5.3.1 General features 179
Contents ix
5.3.2 History and current applications 180
5.3.3 Methodology 182
5.3.4 Forces 187
5.3.5 Particle size and shape 190
5.3.6 Stress analysis 193
5.4 Nomenclature 196
A5 Frictional forces 197
A5.1 Frictional forces 197
A5.2 Single contacts 198
A5.3 Particle assemblies 198
References 199
6 Fluid-particle systems 201
6.1 Hydraulic and pneumatic conveying 201
6.1.1 Differences and similarities 201
6.1.2 Hydraulic transport 205
6.1.3 Pneumatic transport 221.
6.2 Fluidisation 226
6.2.1 Types offluidisation behaviour 227
6.2.2 General description of group behaviour 233
6.2.3 Criteria for group boundaries 236
6.2.4 Temperature and pressure effects 239
6.2.5 Defluidisation and cohesive effects 240
6.2.6 Bubbling fluidised beds 242
6.2.7 Agglomeration 250
6.3 Nomenclature 257
References 258
7 Gas/solid separation 261
7.1 Gas and particle properties 261
7.2 Inertial separators 263
7.2.1 Introduction 263
7.2.2 Analysis of cyclone performance 267
7.2.3 Effects of solid loading 272
7.2.4 Effects of temperature and pressure 273
7.2.5 Concluding remarks 274
7.3 Filtration 274
7.3.1 General features of filtration behaviour 274
7.3.2 Depth filtration 277
7.3.3 Barrierfiltration 285
7.3.4 Concluding remarks 294
7.4 Nomenclature 294
References 295
x Contents
8 Storage and discharge of particulate bulk solids 298
8.1 Introduction 298
8.1.1 General design considerations for 'process' silos 299
8.1.2 Design considerations for large storage silos 301
8.2 Flow regimes in bins and hoppers 302
8.2.1 Mass flow versus funnel flow 302
8.2.2 Other possible flow regimes 306
8.2.3 Choice of flow regime 306
8.3 Velocity distributions in bins and hoppers 308
8.3.1 Steady-state flow fields for 'free-flowing' materials 308
8.3.2 Transient flow fields of 'free-flowing' materials 326
8.4 Discharge rates from bins and hoppers 330
8.4.1 Introduction 330
8.4.2 Early empirical work and discharge rate correlations 331
8.4.3 Theoretical predictions of mass flow rate 337
8.4.4 Effect of interstitial pressure gradients 343
8.5 Stress distributions in bins and hoppers 348
8.5.1 Introduction 348
8.5.2 Approximate analysis: the method of differential slices 350
8.5.3 More realistic analysis of the stresses at the wall 356
8.5 .4 Janssen-Walker analysis in other hopper geometries 358
8.5.5 Walters' switch stress analysis 361
8.6 Nomenclature 363
References 364
Index 369