Pneumatic Conveying of Solids (eBook)

Pneumatic Conveying 
 
1 
Preface to the First Edition 5
Preface to the Second Edition 7
Preface to the Third Edition 9
Foreword 11
Nomenclature 13
Contents 
19 
1 An Overview of Pneumatic Conveying Systemsand Performance 31
1.1 Introduction 31
1.2 Why Pneumatic Conveying? 31
1.2.1 Advantages of a Pneumatic Conveying System 32
1.2.2 Disadvantages of a Pneumatic Conveying System 32
1.3 What Can Be Conveyed? 33
1.4 What Constitutes a Pneumatic Conveying System? 36
1.4.1 The Prime Mover 36
1.4.2 Feeding, Mixing and Acceleration Zone 37
1.4.3 The Conveying Zone 38
1.4.4 Gas–Solids Separation Zone 38
1.5 Modes of Pneumatic Conveying 38
1.5.1 Dilute Phase 39
1.5.2 Dense Phase 40
1.6 Basic Pneumatic Conveying Systems 40
1.6.1 Positive Pressure System 40
1.6.2 Negative Pressure Systems 41
1.6.3 Combined Negative–Positive Pressure Systems 42
1.6.4 Closed Loop System 43
1.7 Further Classification Techniques 43
1.7.1 Classification by Pressure of Operation 43
1.7.2 Classification by Solid Feeder Type 44
1.8 Description and Operation of a Pneumatic Conveying System 44
1.8.1 State Diagram 44
1.8.2 Vertical and Horizontal Flow 46
1.8.3 Vacuum and Positive Pressure Systems 46
1.9 Putting It All Together 48
1.9.1 Feeding and Acceleration of Solids 48
1.9.2 Factors Contributing to Pressure Losses (Chapters4–6) 48
1.9.3 Coarse and Fine Particle Suspensions 49
1.9.4 Horizontal Movement Through Pipe: Bed Formation 50
1.9.5 Bend Flow (Chapter4) 51
1.9.6 Stepped Piping Systems 53
1.9.7 Wear in Pneumatic Conveying Systems 53
1.9.8 Gas–Solids Separation 53
1.9.9 Safety 53
1.10 An Overview 53
1.11 Some Useful Conversion Factors 55
References 62
2 Single Phase Flow in Pneumatic Conveying Systems 64
2.1 Introduction 64
2.2 Definitions 64
2.2.1 Free Air 64
2.2.2 Standard Temperature and Pressure (STP) 65
2.2.3 Standard Reference Conditions (SRC) 65
2.2.4 Free Air Delivered (FAD) 66
2.3 Perfect Gas Laws 66
2.4 Drying of Compressed Air 66
2.5 The Compression Process 67
2.5.1 Isothermal Compression 68
2.5.2 Adiabatic Compression 69
2.5.3 Temperature Rise During Adiabatic Compression 70
2.5.4 Power Requirements 71
2.6 Gas Flow Through Pipes 73
2.6.1 Types of Flow 73
2.6.2 Pipe Roughness 75
2.6.3 General Pressure Drop Formula 75
2.6.4 Resistance Due To Pipe Fittings 77
2.7 Illustrative Examples 78
References 83
3 Fluid and Particle Dynamics 84
3.1 Introduction 84
3.2 Law of Continuity 84
3.3 Drag on a Particle 85
3.3.1 The Standard Drag Coefficient Curve 85
3.3.2 Effect of Shape on Drag 87
3.3.3 Effect of Fluid Turbulence 88
3.3.4 Effect of Voidage/Solid Concentration 89
3.3.5 Effect of Acceleration 92
3.3.6 Miscellaneous Other Effects 93
3.4 Equations for Calculation of Relevant Properties 95
3.4.1 Air Velocity 95
3.4.2 Terminal Velocity for a Particle 95
3.4.2.1 Worked Examples on Free Fall Velocity 98
3.4.3 Pressure Drop Through a Packed Bed 99
3.4.4 Minimum Fluidization Velocity 101
3.4.5 Relationship Between vmf and wfo 103
3.5 Fluidization Characteristics of Powders 104
References 107
4 Fundamentals 110
4.1 Introduction 110
4.2 Forces Acting on a Single Particle in an Air Stream 110
4.3 Particle Size 111
4.4 Shape 114
4.5 Dynamic Equations 116
4.6 Terminal Velocity 118
4.7 Single Particle Acceleration 119
4.8 Centrifugal Flow 120
4.9 Slip Velocity in a Gravitational Field 121
4.10 Multiple Particle Systems 121
4.11 Voidage and Slip Velocity 124
4.12 Frictional Representations 127
4.13 Acceleration and Development Regions 129
4.14 Particle Distribution in Pneumatic Conveying 131
4.15 Compressibility Effect Not Negligible 132
4.16 Speed of Sound in Gas–Solid Transport 135
4.17 Gas–Solid Flow with Varying Cross-Sectional Area 137
4.18 Branching Arrangements 139
4.19 Bend Analysis 140
4.20 Downward Sloping Particle Flow 145
4.21 Dense Phase Transport 146
4.22 Estimation of Pressure Drop in Slugging DensePhase Conveying 149
4.22.1 Analogy Between Slugging Conveying and Slugging Fluidization 149
4.22.2 Pressure Drop Estimation in Slugging Conveying 151
4.23 Estimation of Pressure Drop in Non-slugging Dense Phase Conveying 152
4.23.1 Model of Yerushalmi and Cankurt 153
4.23.2 Annular Flow Model of Nakamura and Capes 155
4.24 Plug Flows 156
4.25 Inclined Conveying 165
4.26 Simulations 166
4.27 Worked Examples 168
References 180
5 Flow Regimes in Vertical and Horizontal Conveying 183
5.1 Introduction 183
5.2 Choking Versus Non-choking System in Vertical Flow 187
5.2.1 The Choking Phenomenon 187
5.2.2 Choking Versus Non-choking 188
5.2.2.1 Analysis of Yousfi and Gau [8] 188
5.2.2.2 Analysis of Yang [11] 189
5.2.2.3 Analysis of Smith [9] 190
5.2.2.4 Analysis of Matsen [19] 192
5.2.2.5 Choking Versus Non-choking – A Summary 194
5.3 Choking System in Vertical Flow 195
5.3.1 Prediction of Choking Velocity 195
5.3.1.1 Equations of Barth and Gunther 198
5.3.1.2 Equation of Zenz and Othmer 199
5.3.1.3 Equation of Doig and Roper 199
5.3.1.4 Equation of Rose and Duckworth 199
5.3.1.5 Equation of Leung et al. 199
5.3.1.6 Equation of Yousfi and Gau 200
5.3.1.7 Equation of Knowlton and Bachovchin 201
5.3.1.8 Equations of Yang 201
5.3.1.9 Equations of Punwani et al. 201
5.3.1.10 Selection of Choking Velocity Correlations 202
5.3.1.11 Bi, Grace and Zhu Analysis 202
5.3.2 Transition from Dense Phase Conveying to Packed Bed Conveying 203
5.3.3 A Quantitative Flow Regime Diagram in Vertical Flow 203
5.4 Non-choking System in Vertical Flow 205
5.5 Particle Segregation in Vertical Pneumatic Transport 207
5.5.1 Equations for Predicting Segregation 207
5.6 Saltation and Pick-Up in Horizontal Conveying 208
5.6.1 Theoretical Considerations 208
5.6.2 Saltation Velocity Correlations 209
5.6.2.1 Equation of Rizk 210
5.6.2.2 Equations of Matsumoto et al. 210
5.6.2.3 Equation of Thomas 211
5.6.2.4 Cabrejos and Klinzing 212
5.6.2.5 A Summary 213
5.6.3 A Quantitative Flow Regime Diagram for Horizontal Flow 213
5.6.4 Pick-Up Velocities 214
5.6.5 Interrelationship Between Saltation and Pick-Up Velocities 215
5.6.6 Superficial Velocities in Particle-Fluid Systems Leading to a Generalized Presentation 215
5.7 Circulating Fluid Beds 218
References 218
6 Principles of Pneumatic Conveying 221
6.1 Introduction: Putting It All Together 221
6.2 The State Diagram Revisited 221
6.2.1 Modes of Pneumatic Conveying 222
6.2.2 The General State Diagram and the Normalized State Diagram 222
6.2.3 The Dimensionless State Diagram 224
6.2.4 General Phase Diagram for Fine Particles 225
6.2.5 Diagram of State 227
6.2.6 The Dimensionless Pressure Minimum Curve 229
6.2.7 Verification of Fr Relationship 230
6.2.8 The Relationship Between the Performance Characteristics of the Prime Mover and Product Flow Characteristics 231
6.3 Methods for Scaling Up 234
6.3.1 Geometric Similarity 235
6.3.2 Dynamic Similarity 235
6.3.3 Flow Similarity 236
6.4 Use of Theoretical Models and Definitions 237
6.4.1 Compilation of Power Balance 237
6.4.2 Aerodynamic Force or Drag 238
6.4.3 Forces of Impact and Friction 239
6.4.4 Effect of Gravity in a Horizontal Pipe 240
6.4.5 Power Balance 241
6.5 Additional Pressure Drop Factor (Z) 241
6.6 Pressure Drop 243
6.6.1 Horizontal Conveyance 244
6.6.2 Vertical Conveyance 245
6.6.3 Compressibility of Air 245
6.6.4 Pressure Drop in a Gas–Solid Mixture 247
6.6.5 Pressure Drop Due to Acceleration 247
6.6.6 Pressure Drop Due to Height Z 248
6.6.7 Boundary Conditions for Calculations 248
6.6.8 Comprehensive Pressure Drop Equation 248
6.7 Some Important Functional Relationships 250
6.7.1 Introduction 250
6.7.2 Relationship of z to Fr and 250
6.7.3 Interpretation of Z and 250
6.7.4 Solid/Gas Velocity Ratio c/v 250
6.7.5 The Determination of Particle Velocity (c) and Voidage () 250
6.7.6 Sequence to be Followed to Obtain the Impact and Friction Factor Z 256
6.8 Sequence to be Followed to Obtain the System Pressure Loss (p) 257
References 263
7 Feeding of Pneumatic Conveying Systems 264
7.1 Introduction and Overall Design Philosophy 264
7.2 Classification of Feeding Systems 265
7.2.1 Pressure Characteristics 265
7.2.2 Classification in Terms of System Requirements 265
7.3 Feeder Selection Criteria 265
7.4 Low-Pressure Feeding Devices 266
7.4.1 The Venturi Feeder 267
7.4.2 Negative Pressure Feeding Devices 268
7.4.2.1 Vacuum Nozzles 268
7.4.2.2 Stationary Vacuum Feeding Devices 270
7.4.3 Rotary Airlocks 272
7.4.3.1 Introduction and Description 272
7.4.3.2 Leakage Through a Rotary Airlock 273
7.4.3.3 Feeding Efficiency of a Rotary Airlock 277
7.4.3.4 Valve Configurations 278
7.4.3.5 Rotor Configurations 282
7.4.3.6 Casing Configurations 283
7.4.3.7 Valve Arrangements 284
7.4.4 Combined Negative Pressure/Positive Pressure System 285
7.5 Medium-Pressure Feeding Systems 286
7.5.1 The Fluid–Solids Pump 286
7.5.2 The Mohno Powder Pump 288
7.5.3 The Waeschle High-Pressure Rotary Valve 290
7.5.4 Vertical Lift Pump (Air Lift) 290
7.5.5 Double Gate Lock Feeding Device 295
7.6 High-Pressure Feeding Devices 296
7.6.1 Description of Blow Vessel 296
7.6.2 Blow Vessel Operation 296
7.6.3 Discharge Characteristics of a Blow Vessel 298
7.6.4 Factors Influencing Blow Vessel Performance 301
7.6.5 Blow Vessel Configuration 304
7.6.5.1 Continuous Discharge 304
7.6.5.2 Solids Flow Control 306
7.6.5.3 Gas Supply Configurations 308
7.6.5.4 Mass Flow Nozzles 311
7.6.6 Low-Velocity and Plug Conveying Systems 314
7.6.6.1 Introduction 314
7.6.6.2 Fluidization/Turbulence Systems 315
7.6.6.3 Plug Forming Systems 318
7.6.6.4 Plug Destroying Systems 322
7.6.6.5 Some General Comments on Low-Velocity Systems 323
7.6.6.6 Natural Plug Formation 324
7.6.6.7 Extruded Flow 324
7.6.6.8 Extremely Low-Velocity Conveying (Vibration-Induced Pneumatic Conveying) 325
7.6.6.9 Fluidized Mode Conveying 326
7.6.6.10 Influence of the Dense Phase on the Pipeline 326
7.7 Conclusions 327
References 327
8 Flow in Standpipes and Gravity Conveyors 330
8.1 Introduction: Standpipes and Gravity Conveyors 330
8.2 Classification of Standpipe Systems 330
8.2.1 The Simple Standpipe 332
8.2.2 System with Top and Bottom Terminal Pressure as Independent Parameters 332
8.2.3 System with Top Terminal Pressure as Independent Parameter 333
8.2.4 System with Top and Bottom Terminal Pressure and Solid Rate as Independent Parameters 333
8.2.5 Summary of Classification 335
8.3 Classification of Flow Modes in a Standpipe 335
8.3.1 Non-fluidized Flow 335
8.3.2 Fluidized Flow 336
8.3.3 Summary of Flow Modes 337
8.4 Equations Pertaining to Each Flow Mode 338
8.4.1 Non-fluidized Flow 338
8.4.2 Fluidized Flow 339
8.5 Flow Through a Valve 340
8.5.1 Flow Through a Slide Valve 340
8.5.1.1 Fluidized Flow 340
8.5.1.2 Non-fluidized Flow 341
8.5.2 Flow Through Non-mechanical Valves 342
8.6 Stability of Standpipe Flow 344
8.6.1 Flooding Instability 344
8.6.2 Multiple Steady States and Bifurcation Instability 345
8.6.3 Ledinegg Type Instability 346
8.6.4 Stability Analysis of Rangachari and Jackson 346
8.6.5 A Summary of Instability 346
8.7 Analysis of Industrial Standpipes: Case Studies 346
8.7.1 Underflow Standpipe 347
8.7.2 Overflow Standpipe 349
8.7.3 Summary of Case Studies 350
8.8 Gravity Conveyors 350
8.8.1 Introduction 350
8.8.2 Design Procedure 351
8.8.2.1 Operating Gas Velocity, v 351
8.8.2.2 Width of Conveyer, b 352
8.8.2.3 Height of Fluidized Layer, Z 353
8.8.2.4 Specification of Air Requirement 353
8.8.2.5 Angle of Inclination 354
8.8.2.6 Other Considerations 355
8.8.3 A Worked Example 355
References 356
9 An Overview of High-Pressure Systems Including Long-Distance and Dense Phase Pneumatic Conveying Systems 358
9.1 Introduction 358
9.2 High-Pressure Systems 359
9.3 High-Pressure Conveying 359
9.4 Dense Phase Flow Classification 360
9.5 A Description of Plug Flow and the Relationships Between Plug Flow and Material Characteristics 360
9.6 System Selection and Product Characteristics 364
9.7 Dense Phase System Design 366
9.8 Long-Distance Pneumatic Conveying and Pressure Loss Minimization 369
9.8.1 Introduction 369
9.8.2 Design Considerations: Critical Length 372
9.8.3 Design Considerations: Stepped Pipe 374
9.8.4 Design Considerations: Pipe Length/Pipe Diameter Ratio 376
9.8.5 Design Considerations: Influence of Pipe Diameter Enlargements 377
9.8.6 Optimum Stepping Arrangement and a Flow Economizer 378
9.9 Conclusions 380
References 380
10 Gas–Solids Separation 383
10.1 Introduction 383
10.2 Selection Criteria 384
10.3 Cyclone Separators: Theory of the Separation of Particles in the Centrifugal Field 386
10.3.1 Separation in Depositing Chambers 386
10.3.2 Separation in a Centrifugal Field 389
10.3.3 Setting Velocity in a Centrifugal Field 391
10.3.4 Associated Pressure Losses 392
10.3.4.1 Modified Method for Calculating the Pressure Drop 397
10.3.5 Graphical Estimation of Cyclone Geometry 398
10.3.5.1 Barth's Simplified Assumptions for Calculating vti/vi 403
10.3.5.2 Muschelknautz's Modifications Taking the Mass Load Ratio into Consideration 404
10.3.6 Proven Cyclone Geometries and Configurations 409
10.3.6.1 Entrance Geometry 409
10.3.6.2 Special Cyclone Configurations 409
10.3.6.3 Gas Outlet Tube and Cyclone Length, Knowlton, 409
10.4 Fabric Filters 411
10.4.1 Introduction 411
10.4.2 Modes of Operation 411
10.4.3 Fabric Filter Sizing 414
10.4.4 Construction of Fabric Filter Units 416
10.4.5 Bag Cleaning Techniques 417
10.4.6 Cartridge Filters 420
10.4.7 Arrangement of Filter Housing 420
10.4.8 Dust Explosions and Earthing of Filters 424
10.4.9 Extremely Low Emission Filters 424
10.5 Cleaning by Sound 425
10.6 Conclusions 426
References 426
11 Some Comments on: The Flow Behaviour of Solids from Silos Wear in Pneumatic Conveying Systems
11.1 Introduction 427
11.2 The Flow of Solids from Bins 428
11.2.1 Introduction 428
11.2.2 Common Flow Problems from a Silo Bin 428
11.2.3 Characteristic Flow of Granular and Powdered Products from a Storage Bin 428
11.2.4 Factors Influencing the Flow of Solids from a Bin 430
11.2.5 Stress Distribution in a Silo 431
11.2.6 Experimental Methods for Measuring the Flow Characteristics of Bulk Solid Materials 432
11.2.6.1 Introduction 432
11.2.6.2 The Jenike Shear Cell 433
11.2.7 The Jenike Flow Categorization Technique 434
11.2.8 The Jenike Design Theory 434
11.2.8.1 Results from Shear Cell Analysis 434
11.2.8.2 Flow Factor, ff 435
11.3 Flow Aid Devices for Silos and Hoppers 438
11.3.1 Introduction 438
11.3.2 Types of Flow Aid Devices 439
11.3.2.1 Fluidization 439
11.3.2.2 Air Assisted Flow Aid Devices 440
11.3.2.3 Vibration 442
11.3.2.4 Hopper Liners 444
11.3.2.5 Mechanical Assistance 445
11.4 Wear in Pneumatic Conveying Systems 445
11.4.1 Introduction 445
11.4.2 The Erosion Mechanism 446
11.4.3 Experimental Investigations on the Influence of Impact Angle and Surface Material 447
11.4.4 Surface Ripples 447
11.4.5 Influence of Particle Size 448
11.4.6 Influence of Particle Velocity 448
11.4.7 Effect of Particle Hardness 450
11.4.8 Effect of Solids Loading 451
11.4.9 Particle–Wall Interactions 451
11.4.10 Depth of Penetration 455
11.4.11 Evaluation of Wear-Resistant Materials 455
11.4.12 Minimizing Wear 455
11.4.13 Interpretation of Results from Wear Studies 458
11.4.14 Some Novel Bend Designs 459
11.4.14.1 Bends for Erosive Products 459
11.4.14.2 Bends Reducing Angel Hair – Bend 460
11.5 Attrition of Particles in Pipelines 462
11.5.1 Mechanism 462
11.5.2 Types of Attrition 462
11.5.3 Material Parameters 462
11.5.4 Attrition as a Function of Conveying Parameters 462
11.5.5 Influence of Systems Technology 463
11.5.6 Avoidance and Reduction of Attrition 464
11.6 Simulation and Particle–Wall Interactions 467
11.7 Ancillary Equipment 467
11.7.1 Introduction 467
11.7.2 Valves 469
11.7.2.1 Non-return Valves 469
11.7.2.2 Butterfly Valves 469
11.7.2.3 Ball Valves 471
11.7.2.4 Pinch Valves 472
11.7.2.5 Iris Valves 472
11.7.2.6 Diverter Valves 473
11.7.2.7 Dome Valves 474
11.7.2.8 Slide Valves 475
11.7.2.9 Disk Valves 475
11.7.3 Rigid Piping and Pipe Couplings 475
11.7.4 Flexible Piping 480
11.8 Conclusions 481
References 481
12 Control of Pneumatic Transport 484
12.1 Basic Material Flow and Control Theory 484
12.2 Transport Lags 486
12.3 Analysis of Gas–Solid Flow by Transfer Functions 487
12.4 Stability of Pneumatic Transfer Systems 489
12.5 Air Control Systems for Pneumatic Conveying Systems 490
12.6 Stability Analysis with Taylor Series Linearization 491
12.7 Linear Stability Analysis: Jackson Approach 493
12.8 Stability via the Liapunov Analysis 495
12.9 Artificial Intelligence and Solids Processing 497
References 499
13 Instrumentation 500
13.1 Standard Instrumentation 501
13.2 Transducers 501
13.3 Cross-Correlation Procedures 503
13.4 A Coriolis Force Meter 504
13.5 Dielectric Meter 505
13.6 Load Cells 509
13.7 Particle Tagging 510
13.8 Electrostatic Based Meters 511
13.9 Acoustic Measurements 514
13.10 Screw Conveyors 516
13.11 Light Measuring Devices 517
13.12 Other Techniques for Particle Velocities 519
13.12.1 Microwave Meter 520
13.13 Instrumentation for Industrial Applications 522
13.13.1 Introduction 522
13.13.2 Bulk Material Flow Detector 523
13.13.3 Bulk Solids Impact Flowmeter 524
13.13.4 Mass Flow Measurement of Pneumatically Conveyed Solids 526
13.13.5 Level Detection 531
13.13.6 Nuclear Level Measurement and Detection 533
13.13.7 Pressure Drop Flowmeter 535
13.13.8 High-Temperature Velocity Meter 536
13.13.9 Pressure Fluctuations in Pneumatic Conveying: A Source of Information 537
13.14 Advances in Instrumentation 538
13.14.1 Tomography 538
13.14.2 Electromagnetic Field Applications 539
References 539
14 System Design and Worked Examples 541
14.1 Introduction 541
14.2 Moisture Content in Air 541
14.3 The Design of Industrial Vacuum Systems 544
14.3.1 Introduction 544
14.3.2 Design Philosophy 544
14.3.3 Design Procedure 545
14.4 Dilute Phase Pneumatic Conveying System Design (Method 1) 552
14.4.1 Introduction 552
14.4.2 The Problem 553
14.4.3 Experimental Observations 553
14.4.4 Estimation of Pipe Diameter 554
14.4.5 Estimation of the Pressure Drop 554
14.4.6 Rotary Valve Leakage 559
14.4.7 Selection of Cyclone 560
14.5 Dilute Phase Pneumatic Conveying System Design (Method 2) 560
14.5.1 Introduction 560
14.5.2 The Problem 561
14.5.3 The Solution 561
14.6 Dilute Phase Pneumatic Conveying System Design (Method 3) 566
14.6.1 Introduction 566
14.6.2 The Problem 567
14.6.3 The Solution 568
14.7 Dense Phase Pneumatic Conveying System Design 572
14.7.1 Introduction 572
14.7.2 The Problem 572
14.7.3 The Solution 572
14.8 Cost of Pneumatic Conveying 576
14.9 Design Considerations 577
14.10 Gas–Solid Flow Examples 577
14.11 Conclusions 584
References 584
Index 585