Introduction to particle technologyPDF电子书下载

1 Single Particles in a Fluid 1

1.1 Motion of Solid Particles in a Fluid 1

1.2 Particles Falling Under Gravity Through a Fluid 3

1.3 Non-spherical Particles 5

1.4 Effect of Boundaries on Terminal Velocity 5

1.5 Further Reading 7

1.6 Worked Examples 7

Exercises 17

2 Multiple Particle Systems 19

2.1 Settling of a Suspension of Particles 19

2.2 Batch Settling 21

2.2.1 Settling Flux as a Function of Suspension Concentration 21

2.2.2 Sharp Interfaces in Sedimentation 23

2.2.3 The Batch Settling Test 24

2.2.4 Relationship between the Height-Time Curve and the Flux Plot 26

2.3 Continuous Settling 29

2.3.1 Settling of a Suspension in a Flowing Fluid 29

2.3.2 A Real Thickener（with Upflow and Downflow Sections） 31

2.3.3 Critically Loading Thickener 32

2.3.4 Underloaded Thickener 33

2.3.5 Overloaded Thickener 33

2.3.6 Alternative Form of Total Flux Point 34

2.4 Worked examples 35

Exercises 47

3 Particle Size Analysis 55

3.1 Introduction 55

3.2 Describing the Size of a Single Particle 55

3.3 Description of Populations of Particles 58

3.4 Conversion Between Distributions 60

3.5 Describing the Population by a Single Number 60

3.6 Equivalence of Means 62

3.7 Common Methods of Displaying Size Distributions 64

3.7.1 Arithmetic-normal Distributions 64

3.7.2 Log-normal Distribution 65

3.8 Methods of Particle Size Measurement 66

3.8.1 Sieving 66

3.8.2 Microscopy 66

3.8.3 Sedimentation 66

3.8.4 Permeametry 68

3.8.5 Electrozone Sensing 68

3.8.6 Laser Diffraction 69

3.9 Sampling 70

3.10 Worked Examples 70

Exercises 79

4 Fluid Flow Through a Packed Bed of Particles 81

4.1 Pressure Drop-flow Relationship 81

4.1.1 Laminar Flow 81

4.1.2 Turbulent Flow 83

4.1.3 General Equation for Turbulent and Laminar Flow 83

4.1.4 Non-spherical Particles 84

4.2 Filtration 85

4.2.1 Introduction 85

4.2.2 Incompressible Cake 85

4.2.3 Including the Resistance of the Filter Medium 86

4.2.4 Washing the Cake 87

4.2.5 Compressible Cake 88

4.3 Further Reading 89

4.4 Worked Examples 89

Exercises 93

5 Fluidization 97

5.1 Fundamentals 97

5.2 Relevant Powder and Particle Properties 100

5.3 Bubbling and Non-bubbling Fluidization 101

5.4 Classification of Powders 102

5.5 Expansion of a Fluidized Bed 107

5.5.1 Non-bubbling Fluidization 107

5.5.2 Bubbling Fluidization 108

5.6 Entrainment 110

5.7 Heat Transfer in Fluidized Beds 115

5.7.1 Gas-Particle Heat Transfer 115

5.7.2 Bed-Surface Heat Transfer 116

5.8 Application of Fluidized Beds 119

5.8.1 Physical Processes 119

5.8.2 Chemical Processes 120

5.9 A Simple Model for the Bubbling Fluidized Bed Reactor 122

5.10 Some Practical Considerations 127

5.10.1 Gas Distributor 127

5.10.2 Loss of Fluidizing Gas 127

5.10.3 Erosion 128

5.10.4 Loss of Fines 128

5.10.5 Cyclones 128

5.10.6 Solids Feeders 129

5.11 Worked Examples 129

Exercises 134

6 Pneumatic Transport and Standpipes 139

6.1 Pneumatic Transport 139

6.1.1 Dilute Phase and Dense Phase Transport 140

6.1.2 The Choking Velocity in Vertical Transport 140

6.1.3 The Saltation Velocity in Horizontal Transport 142

6.1.4 Fundamentals 143

6.1.5 Design for Dilute Phase Transport 147

6.1.6 Dense Phase Transport 152

6.1.7 Matching the System to the Powder 158

6.2 Standpipes 159

6.2.1 Standpipes in Packed flow 160

6.2.2 Standpipes in Fluidized Bed Flow 160

6.2.3 Pressure Balances During Standpipe Operation 163

6.3 Further Reading 166

6.4 Worked Examples 166

Exercises 172

7 Separation of Particles from a Gas：Gas Cyclones 175

7.1 Gas Cyclones-description 176

7.2 Flow Characteristics 177

7.3 Efficiency of Separation 177

7.3.1 Total Efficiency and Grade Efficiency 177

7.3.2 Simple Theoretical Analysis for the Gas Cyclone Separator 178

7.3.3 Cyclones Grade Efficiency in Practice 181

7.4 Scale-up of Cyclones 181

7.5 Range of Operation 182

7.6 Some Practical Design and Operation Details 185

7.6.1 Effect of Dust Loading on Efficiency 185

7.6.2 Cyclone Types 185

7.6.3 Abrasion 185

7.6.4 Attrition of Solids 186

7.6.5 Blockages 186

7.6.6 Discharge Hoppers and Diplegs 186

7.6.7 Cyclones in Series 187

7.6.8 Cyclones in Parallel 187

7.7 Worked Examples 187

Exercises 191

8 Storage and Flow of Powders-Hopper Design 193

8.1 Introduction 193

8.2 Mass Flow and Core Flow 193

8.3 The Design Philosophy 196

8.3.1 Flow-No Flow Criterion 197

8.3.2 The Hopper Flow factor ff 197

8.3.3 Unconfined Yield Stress，σy 197

8.3.4 Powder Flow Function 198

8.3.5 Critical Conditions for Flow 198

8.3.6 Critical Outlet Dimension 199

8.3.7 Summary 200

8.4 Shear Cell Tests 200

8.5 Analysis of shear cell test results 202

8.5.1 Mohr’s Circle-in Brief 202

8.5.2 Application of Mohr’s Circle to Analysis of the Yield Locus 202

8.5.3 Determination of σy and σc 203

8.5.4 Determination of δ from Shear Cell Tests 204

8.5.5 The Kinematic Angle of Friction Between Powder and Hopper Wall 205

8.5.6 Determination of the Hopper Flow Factor 206

8.6 Summary of Design Procedure 209

8.7 Discharge Aids 210

8.8 Pressure on the Base of a Tall Cylindrical Bin 210

8.9 Mass Flow Rates 213

8.10 Conclusions 213

8.11 Worked Examples 214

Exercises 217

9 Mixing and Segregation 223

9.1 Introduction 223

9.2 Types of Mixture 223

9.3 Segregation 224

9.3.1 Causes and Consequences of Segregation 224

9.3.2 Mechanisms of Segregation 225

9.4 Reduction of Segregation 229

9.5 Equipment of Particulate Mixing 230

9.5.1 Mechanisms of Mixing 230

9.5.2 Types of Mixer 230

9.6 Assessing the Mixture 232

9.6.1 Quality of a Mixture 232

9.6.2 Sampling 232

9.6.3 Statistics Relevant to Mixing 232

9.7 Worked Examples 235

Exercises 239

10 Particle Size Reduction 241

10.1 Introduction 241

10.2 Particle Fracture Mechanisms 241

10.3 Model Predicting Energy Requirement and Product Size Distribution 245

10.3.1 Energy Requirement 245

10.3.2 Prediction of the Product Size Distribution 249

10.4 Types of Comminution Equipment 250

10.4.1 Factors Affecting Choice of Machine 250

10.4.2 Stressing Mechanisms 251

10.4.3 Particle Size 256

10.4.4 Material Properties 257

10.4.5 Carrier medium 258

10.4.6 Mode of operation 258

10.4.7 Combination with Other Operations 258

10.4.8 Types of Milling Circuit 259

10.5 Worked Examples 260

Exercises 263

11 Size Enlargement 267

11.1 Introduction 267

11.2 Interparticle Forces 268

11.2.1 Van der Waals Forces 268

11.2.2 Forces due to Absorbed Liquid Layers 268

11.2.3 Forces due to Liquid Bridges 268

11.2.4 Electrostatic Forces 269

11.2.5 Solid Bridges 270

11.2.6 Comparison and Interaction between Forces 270

11.3 Granulation 271

11.3.1 Introduction 271

11.3.2 Granulations Rate Processes 271

11.3.3 Simulation of the Granulation Process 275

11.3.4 Granulation Equipment 279

12 Fire and Explosion Hazards of Fine Powders 283

12.1 Introduction 283

12.2 Combustion Fundamentals 284

12.2.1 Flames 284

12.2.2 Explosions and Detonations 284

12.2.3 Ignition，Ignition Energy，Ignition Temperature-a Simple Analysis 284

12.2.4 Flammability Limits 287

12.3 Combustion in Dust Clouds 289

12.3.1 Fundamentals Specific to Dust Cloud Explosions 289

12.3.2 Characteristics of Dust Explosions 289

12.3.3 Apparatus for Determination of Dust Explosion Characteristics 290

12.3.4 Application of the Test Results 292

12.4 Control of the Hazard 293

12.4.1 Introduction 293

12.4.2 Ignition Sources 294

12.4.3 Venting 295

12.4.4 Suppression 296

12.4.5 Inerting 296

12.4.6 Minimise Dust Cloud Formation 296

12.4.7 Containment 296

12.5 Worked Examples 297

Exercises 299

Notation 301

References 309

Index 315