Unit operations of particulate solids : theory and practice

492 Pages·2012·8.94 MB·English

by  Enrique Ortega-Rivas

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Boca Raton London New York
CRC Press is an imprint of the
Taylor & Francis Group, an informa business
Unit Operations of
Particulate Solids
Theory and Practice
Enrique Ortega-Rivas
Boca Raton London New York
CRC Press is an imprint of the
Taylor & Francis Group, an informa business
This page intentionally left blank
Boca Raton London New York
CRC Press is an imprint of the
Taylor & Francis Group, an informa business
CRC Press
Taylor & Francis Group
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Boca Raton, FL 33487-2742
© 2012 by Taylor & Francis Group, LLC
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Printed in the United States of America on acid-free paper
Version Date: 20110608
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Contents
Preface ...................................................................................................................xiii
Author ..................................................................................................................xvii
Part I Characterization of Particulate Systems
and Relation to Storage and Conveying
1 Introduction .....................................................................................................3
1.1 Definitions of Unit Operations ............................................................3
1.2 Powder and Particle Technology ........................................................6
1.3 The Solid State: Main Distinctive Properties ....................................7
1.3.1 Primary Properties ..................................................................8
1.3.1.1 Particle Size and Shape ............................................9
1.3.1.2 Particle Density.......................................................18
1.3.2 Packing Properties .................................................................23
1.3.2.1 Bulk Density ............................................................23
1.3.2.2 Other Packing Properties ......................................26
References .......................................................................................................29
2 Bulk Solids: Properties and Characterization ........................................31
2.1 Introductory Aspects ..........................................................................31
2.2 Classification of Powders ...................................................................32
2.2.1 Jenike’s Classification ............................................................33
2.2.2 Geldart’s Classification..........................................................34
2.3 Sampling...............................................................................................37
2.4 Failure Properties ................................................................................48
2.4.1 Introduction ............................................................................48
2.4.2 Description of Failure Properties ........................................50
2.4.3 Experimental Determinations .............................................50
2.4.4 Other Important Properties ..................................................61
2.5 Laboratory Exercise: Determination of Some
Failure Properties of Powders ...........................................................65
2.5.1 Introduction ............................................................................65
2.5.2 Instrument and Materials .....................................................66
2.5.3 Shear Tester Operation ..........................................................66
2.5.4 Calculations and Report .......................................................67
2.6 Particle Size Analysis .........................................................................67
2.6.1 Introduction ............................................................................67
2.6.2 Definitions of Characteristic Linear Dimension ...............68
2.6.3 Types of Distributions ...........................................................68
v
vi Contents
2.6.4 Measures of Central Tendency.............................................69
2.6.5 Presentation of Data ..............................................................71
2.6.6 Laboratory Techniques for Size Measurement ..................76
2.6.6.1 Microscopy ..............................................................77
2.6.6.2 Screening .................................................................77
2.6.6.3 Sedimentation .........................................................81
2.6.6.4 Centrifugation.........................................................82
2.6.6.5 Light Diffraction .....................................................85
2.6.6.6 Particle Counters ....................................................85
2.6.6.7 Online Measurement Techniques ........................86
2.7 Laboratory Exercise: Particle Size Analysis by
Different Methods ...............................................................................89
2.7.1 Introduction ............................................................................89
2.7.2 Materials and Instruments ...................................................90
2.7.3 Accessories ..............................................................................90
2.7.4 Microscopy Method ...............................................................91
2.7.4.1 Introduction ............................................................91
2.7.4.2 Slide Preparation ....................................................91
2.7.4.3 Measurement of Particle Size ...............................91
2.7.4.4 Procedure ................................................................91
2.7.4.5 Calculations and Report ........................................92
2.7.5 Screening Method ..................................................................92
2.7.5.1 Introduction ............................................................92
2.7.5.2 Choice of Sieves ......................................................92
2.7.5.3 Procedure ................................................................93
2.7.5.4 Calculations and Report ........................................93
2.7.6 Sedimentation Method..........................................................93
2.7.6.1 Introduction ............................................................93
2.7.6.2 Preparation of Sample ...........................................94
2.7.6.3 Procedure ................................................................94
2.7.6.4 Calculations and Report ........................................94
2.7.7 Instrumental Method ............................................................95
2.7.7.1 Introduction ............................................................95
2.7.7.2 Procedure ................................................................95
2.7.7.3 Calculations and Report ........................................95
References .......................................................................................................97
3 Storage and Conveying of Bulk Solids ..................................................101
3.1 Introduction: Storage Alternatives .................................................101
3.2 Outdoors Storage ...............................................................................101
3.3 Confined Storage ...............................................................................102
3.3.1 General Considerations .......................................................103
3.3.2 Types of Silos ........................................................................104
3.3.3 Wall Stresses in Axisymmetrical Bins ..............................108
3.3.4 Wall Stresses in Other Types of Vessels ...........................112
Contents vii
3.3.5 Natural Discharge from Silos ............................................112
3.3.5.1 Flow Theories ........................................................113
3.3.5.2 Hopper Opening for Coarse Bulk Solids ..........116
3.3.5.3 Hopper Opening for Fine Bulk Solids ..............120
3.3.6 Assisted Discharge ..............................................................123
3.3.6.1 Types of Discharge ...............................................123
3.3.6.2 Passive Devices .....................................................123
3.3.6.3 Active Devices ......................................................123
3.3.7 Feeders for Discharge Control ...........................................127
3.3.7.1 Feeders Description .............................................127
3.3.7.2 Charge and Power Calculations .........................128
3.3.7.3 Discharge Control in Feeders .............................130
3.3.8 Other Design Factors ...........................................................130
3.4 Laboratory Exercise: Evaluation of Wall Loads in Silos ..............134
3.4.1 Introduction ..........................................................................134
3.4.2 Equipment and Materials ...................................................134
3.4.3 Instruments and Apparatuses ...........................................134
3.4.4 Procedure ..............................................................................134
3.4.5 Calculations and Report .....................................................135
3.5 Bulk Solids Conveying .....................................................................135
3.5.1 Introduction ..........................................................................135
3.5.2 Belt Conveyors ......................................................................136
3.5.3 Chain Conveyors ..................................................................143
3.5.3.1 Scraper and Apron Conveyors ...........................145
3.5.3.2 Bucket Elevators ...................................................148
3.5.4 Screw Conveyors ..................................................................151
3.5.5 Pneumatic Conveying .........................................................155
3.5.5.1 Introduction: Types of Conveyors ......................155
3.5.5.2 Dense-Phase Systems ..........................................157
3.5.5.3 Dilute-Phase Systems ...........................................159
3.5.5.4 Design and Selection of
Dilute-Phase Systems ...........................................163
3.6 Laboratory Exercise: Pneumatic Conveying
Characteristics of Different Granules ............................................171
3.6.1 Introduction ..........................................................................171
3.6.2 Equipment and Materials ...................................................171
3.6.3 Procedure ..............................................................................171
3.6.4 Calculations and Report .....................................................172
References .....................................................................................................173
Part II Bulk Solids Processing
4 Size Reduction .............................................................................................179
4.1 Fundamental Principles of Comminution .....................................179
viii Contents
4.1.1 Introductory Aspects...........................................................179
4.1.2 Forces Involved in Size Reduction.....................................180
4.1.3 Properties of Comminuted Materials ...............................181
4.2 Energy Requirements in Comminution ........................................182
4.2.1 Rittniger’s Law .....................................................................183
4.2.2 Kick’s Law .............................................................................183
4.2.3 Bond’s Law and Work Index ..............................................184
4.3 Size Reduction Equipment ...............................................................184
4.3.1 Classification .........................................................................184
4.3.2 Characteristics ......................................................................184
4.3.2.1 Crushers .................................................................185
4.3.2.2 Rollers Mills ..........................................................188
4.3.2.3 Hammer Mills ......................................................189
4.3.2.4 Disc Attrition Mills ..............................................189
4.3.2.5 Tumbling Mills .....................................................191
4.3.2.6 Other Types of Mills ............................................192
4.3.3 Operation of Equipment .....................................................195
4.4 Criteria for Selecting Size Reduction Processes ...........................200
4.4.1 Characteristics of Raw Materials .......................................201
4.4.2 Feeding and Discharge Control .........................................201
4.4.3 Moisture ................................................................................202
4.4.4 Heat Generation and Removal ...........................................202
4.4.5 Summary of Criteria and Main Applications ..................203
4.5 Laboratory Exercise: Determination of
Reduction Relations Using a Hammer Mill ..................................204
4.5.1 Introduction ..........................................................................204
4.5.2 Equipment and Materials ...................................................204
4.5.3 Instruments...........................................................................205
4.5.4 Screen Analysis ....................................................................205
4.5.5 Operation of the Hammer Mill ..........................................205
4.5.6 Calculations and Report .....................................................205
References .....................................................................................................206
5 Size Enlargement ........................................................................................207
5.1 Introduction: Agglomeration Processes ........................................207
5.2 Aggregation Fundamentals: Strength of Agglomerates .............207
5.3 Agglomeration Methods ..................................................................212
5.3.1 Tumbling Agglomeration ...................................................212
5.3.2 Pressure Agglomeration: Compaction ..............................214
5.3.3 Equipment Operation Variables ........................................216
5.4 Selection Criteria for Agglomeration Methods.............................219
5.4.1 Raw Materials Characteristics ...........................................219
5.4.2 Product Properties ...............................................................221
5.4.3 Technique Options...............................................................221
5.5 Design Aspects of Agglomeration Processes ................................222
Contents ix
5.6 Applications .......................................................................................224
5.7 Laboratory Exercise: Comparing Methods for
Tumbling Agglomeration of Powders ............................................224
5.7.1 Introduction ..........................................................................224
5.7.2 Equipment and Materials ...................................................225
5.7.3 Instruments...........................................................................225
5.7.4 Measurement of Particle Size Distributions ....................225
5.7.5 Operation of the Drum Agglomerator ..............................225
5.7.6 Operation of the Pan (Disc) Agglomerator .......................225
5.7.7 Friability Test ........................................................................226
5.7.8 Calculations and Report .....................................................226
References .....................................................................................................226
6 Mixing ...........................................................................................................229
6.1 Introduction .......................................................................................229
6.2 Blending Mechanisms ......................................................................230
6.3 Statistical Approach of Mixing Processes .....................................231
6.3.1 Sampling ...............................................................................232
6.3.2 Blending Quality:
Mixing Indexes and Mixing Rate ......................................233
6.4 Mixing Equipment ............................................................................239
6.4.1 Tumbling Mixers ..................................................................239
6.4.2 Horizontal Trough Mixers ..................................................240
6.4.3 Vertical Screw Mixers ..........................................................241
6.5 Design and Selection Factors ...........................................................241
6.6 Laboratory Exercise: Determination of Blending
Indices for Different Tumbling Mixers ..........................................244
6.6.1 Introduction ..........................................................................244
6.6.2 Equipment and Materials ...................................................244
6.6.3 Instruments or Apparatuses ..............................................244
6.6.4 Operation of the Mixers ......................................................245
6.6.5 Calculations and Report .....................................................245
References .....................................................................................................246
7 Fluidization ..................................................................................................249
7.1 Theoretical Fundamentals ...............................................................249
7.1.1 Bulk Density and Porosity of Beds ....................................250
7.1.2 Fluid Flow through Solids Beds ........................................250
7.1.3 Mechanism of Fluidization:
Aggregative and Particulate ...............................................251
7.2 Fluidized Regimes ............................................................................253
7.2.1 Pressure Drop–Velocity Relationship ...............................254
7.2.2 Incipient Fluidization and
Minimum Fluidizing Velocity ...........................................256
7.2.3 Heterogeneous Fluidization: Bubbling .............................261