Applications of Fluidization to Food Processing

258 Pages·2007·3.051 MB·English

by  Peter Smith

Applications of Fluidization to
Food Processing
http://avaxho.me/blogs/ChrisRedfield
Applications of Fluidization
to Food Processing
P. G. Smith
University of Lincoln
UK
Blackwell
Science
© 2007 by Peter G. Smith
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First published 2007
ISBN: 978-0-6320-6456-4
Library of Congress Cataloging-in-Publication Data
Smith, P.G.
Applications of fluidization to food processing / P.G. Smith. – 1st ed.
p. cm.
Includes bibliographical references and index.
ISBN-13: 978-0-632-06456-4 (hardback : alk. paper)
ISBN-10: 0-632-06456-0 (hardback : alk. paper)
1. Fluidization. 2. Fluid dynamics. 3. Food industry and trade. I. Title.
TP156.F65S65 2007
664′.024–dc22
2006102874
A catalogue record for this title is available from the British Library
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For Liz, Alexis, Imogen and Verity
Contents
Preface xii
Glossary xv
Part One: Fundamentals of Fluidization 1
1 A Description of Fluidized Bed Behaviour 3
An introduction to fluidization 3
Industrial applications of fluidization 7
Applications of fluidization in the food industry 8
Gas-solid fluidized bed behaviour 9
Influence of gas velocity 9
Geldart’s classification 11
Bubbles and particle movement 13
Bubble formation at the distributor 13
Bubble growth and bubble shape 13
Minimum bubbling velocity 16
Bubble rise velocity 17
Particle movement due to bubble motion 18
Distributor plate design 20
Characterisation of particulate solids 22
Particle size distribution 22
Mean particle size 24
Particle shape 26
Bulk particle properties 27
Terminal falling velocity and particle drag coefficient 28
Minimum fluidizing velocity in aggregative fluidization 31
Voidage and pressure drop at incipient fluidization 32
Carman-Kozeny equation 32
Ergun equation 35
Minimum fluidizing velocityas a function of terminal
falling velocity 37
Semi-empirical correlations 39
Experimental measurement 40
viii Contents
Fluidized bed behaviour at high gas velocities 40
Slugging 40
Turbulent fluidization and fast fluidization 42
Elutriation and entrainment 42
Other types of fluidization 45
Spouted beds 45
Centrifugal fluidization 47
Particulate fluidization 48
Nomenclature 50
References 52
2 Characteristics of Aggregative Fluidization 55
Heat transfer 55
Correlations for heat transfer coefficients 55
Bed-surface heat transfer 56
Gas-particle heat transfer 57
Gas-particle heattransfer coefficient 58
Mass transfer 61
Correlations for mass transfer coefficients 61
Gas-particle mass transfer 62
Mixing 64
Introduction 64
Mechanisms of solids mixing 65
Mixing in fluidized beds 66
Vertical mixing of solids: the dispersion model 66
Rate of mixing 68
Mixing and segregation of dissimilar particles 68
Mechanisms 68
Patterns of particle segregation 70
Examples of fluidized bed segregation 73
Nomenclature 73
References 75
Part Two: Applications 77
3 Freezing 79
Low-temperature preservation of foods 79
Introduction 79
Industrial freezing equipment 80
Fluidized bed freezing 81
Capacity of fluidized bed freezers 84
Freezing rate and freezing point of foods 87
Prediction of freezing time 89
Contents ix
Design of fluidized bed freezers 92
Introduction 92
Heat transfer in fluidized bed freezers 92
Mixing, dispersion and residence time 103
Applications of fluidized bed freezing 105
Nomenclature 108
References 110
4 Drying 113
Introduction 113
Principles of drying 115
Water activity 115
Effect of water activity on microbial growth 116
Effect of drying on food structure 117
Isotherms and equilibrium 117
Drying kinetics 119
Classification of driers 121
Fluidized bed drying 122
Material and energy balances 122
The well-mixed drier 124
The plug flow drier 127
Variations in fluidized bed drier design 129
Other fluidized bed drying techniques 130
Vibro-fluidization 130
Mechanical agitation 131
Centrifugal fluidization 132
Spouted bed drying 132
Microwave drying 133
Nomenclature 134
References 135
5 Granulation 139
Granulation and particle growth 139
Particle-particle bonding 142
Bonding mechanisms 142
Growth mechanisms in granulation 144
Fluidized bed granulation 145
Introduction 145
Principles of operation of fluidized bed granulation 146
Material and energy balances 149
Batch and continuous operation: population balance 150
Bed quenching 151
Effect of variables on growth 153
Rate and volumeof feed 153
x Contents
Nozzle position and atomising air rate 154
Bed temperature 155
Fluidizing gas velocity 155
Particle size 157
Binder properties 157
Fluidized bed granulation growth models 159
Layered growth model 159
Agglomeration model 161
A theory of fluidized bed granulation 163
Particle growth mechanisms in fluidized bed
granulation 163
Fluidizing gas velocity and particle mixing 164
Binder properties 164
The balance between granulation and fluidization 165
Factors leading to bed quenching 166
An overall mechanism 166
Food applications of fluidized bed granulation 169
Instantising 169
Encapsulation and coating 171
Other applications 174
Spouted bed granulation 176
Nomenclature 177
References 179
6 Gas-Solid Fluidized Bed Fermentation 185
Principles of fluidized bed fermentation 185
Fermentation ofglucose by Saccharomyces cerevisiae 187
Metabolism 187
Production of cell mass and ethanol yield 188
Factors affecting ethanol production 189
Glucose concentration 189
Gaseous environment 190
Ethanol inhibition 191
Temperature 191
pH 192
Moisture content 192
Mass transport limitations 192
Fluidized bed fermentation systems 193
Basic fluidization considerations 193
Anaerobic ethanol production 194
Aerobic ethanol production 195
Agglomeration, quenching and the glucose sink 196
The work of Hayes (1998) 198
A description of the experimental system 198
Contents xi
Dry quenching experiments 201
Ethanol production withgrated pellets 202
Ethanol production withextruded pellets 203
A model for fluidized bed fermentation 206
Material and energy balances 206
Ethanol-water vapour-liquid equilibria 210
The model of Beck and Bauer (1989) 210
The model of Hayes (1998) 212
Modelling the time course ofethanol production 213
Comparison of models with experimental data 215
Conclusion 216
Nomenclature 219
References 220
7 Other Applicationsof Fluidization 224
Introduction 224
Gas-solid fluidization 224
Blanching 224
Roasting 226
Explosion puffing 227
Sterilisation 228
Disinfestation of wheat 229
Freeze drying 230
Liquid-solid fluidization 231
Bioreactions 231
Sterilisation 233
Ultrafiltration and reverse osmosis 234
Other applications 235
References 235
Index 239