Drying in the Process Industry

1 Introduction 1

2 Drying as Part of the Overall Process 9

2.1 Residual Moisture / 9

2.2 Optimization of the Dewatering Step / 10

2.3 Process Changes to Simplify Drying / 10

2.4 Combination of Drying and Other Process Steps / 12

2.5 Nonthermal Drying / 15

2.6 Process Changes to Avoid Drying / 17

2.7 No Drying / 19

3 Procedures for Choosing a Dryer 21

3.1 Selection Schemes / 21

3.2 Processing Liquids, Slurries, and Pastes / 31

3.3 Special Drying Techniques / 33

3.4 Some Additional Comments / 34

3.5 Testing on Small-Scale Dryers / 37

3.6 Examples of Dryer Selection / 38

4 Convective Drying 41

4.1 Common Aspects of Continuous Convective Dryers / 42

4.2 Saturated Water Vapor Pressure / 43

4.3 Wet-Bulb Temperature / 44

4.4 Adiabatic Saturation Temperature / 46

4.5 Humidity Chart / 47

4.6 Water–Material Interactions / 49

4.7 Drying with an Auxiliary Material / 52

4.8 Gas Velocities / 54

4.9 Heat Losses / 55

4.10 Electrical Energy Consumption / 57

4.11 Miscellaneous Aspects / 59

4.12 Material Balance (kg·h−1) / 61

4.13 Heat Balance (kJ·h−1) / 61

4.14 Specific Heat of Solids / 63

4.15 Gas Flows and Fan Power / 64

4.16 Direct Heating of Drying Air / 65

5 Continuous Fluid-Bed Drying 67

5.1 General Description / 67

5.2 Fluidization Theory / 70

5.3 Drying Theory for Rectangular Dryers / 76

5.4 Removal of Bound Moisture from a Product in a Rectangular Dryer / 88

5.5 Circular Fluid-Bed Dryers / 90

6 Continuous Direct-Heat Rotary Drying 99

6.1 General Description / 99

6.2 Design Methods / 103

7 Flash Drying 117

7.1 General Description / 117

7.2 Design Methods / 120

7.3 Drying in Seconds / 122

7.4 Application of the Design Methods / 126

8 Spray Drying 133

8.1 General Description / 133

8.2 Single-Fluid Nozzle / 138

8.3 Rotary Atomizer / 143

8.4 Pneumatic Nozzle / 145

8.5 Product Quality / 149

8.6 Heat of Crystallization / 153

8.7 Product Recovery / 154

8.8 Product Transportation / 154

8.9 Design Methods / 155

9 Miscellaneous Continuous Convective Dryers and Convective Batch Dryers 163

9.1 Conveyor Dryers / 164

9.2 Wyssmont Turbo-Dryer / 169

9.3 Nara Media Slurry Dryer / 170

9.4 Anhydro Spin Flash Dryer / 172

9.5 Hazemag Rapid Dryer / 174

9.6 Combined Milling and Drying System / 176

9.7 Batch Fluid-Bed Dryer / 178

9.8 Atmospheric Tray Dryer / 182

9.9 Centrifuge–Dryer / 184

10 Atmospheric Contact Dryers 189

10.1 Plate Dryers / 189

10.2 Mildly Agitated Contact Dryers (Paddle Dryers) / 193

10.3 Vigorously Agitated Contact Dryers / 198

10.4 Vertical Thin-Film Dryers / 202

10.5 Drum Dryers / 204

10.6 Steam-Tube Dryers / 208

10.7 Spiral Conveyor Dryers / 212

10.8 Agitated Atmospheric Batch Dryers / 213

11 Vacuum Drying 217

11.1 Vacuum Drying / 219

11.2 Freeze-Drying / 232

11.3 Vacuum Pumps / 242

12 Steam Drying 251

12.1 Sugar Beet Pulp Dryer / 252

12.2 GEA Exergy Barr–Rosin Dryer / 255

12.3 Advantages of Continuous Steam Drying / 257

12.4 Disadvantages of Continuous Steam Drying / 257

12.5 Additional Remarks Concerning Continuous Steam Drying / 258

12.6 Eirich Evactherm Dryer / 258

13 Radiation Drying 263

13.1 Dielectric Drying / 264

13.2 Infrared Drying / 278

14 Product Quality and Safeguarding Drying 289

14.1 Product Quality / 289

14.2 Safeguarding Drying / 291

15 Continuous Moisture-Measurement Methods, Dryer Process Control, and Energy Recovery 313

15.1 Continuous Moisture-Measurement Methods for Solids / 313

15.2 Continuous Moisture-Measurement Methods for Gases / 321

15.3 Dryer Process Control / 327

15.4 Energy Recovery / 335

16 Gas–Solid Separation Methods 339

16.1 Cyclones / 340

16.2 Fabric Filters / 343

16.3 Scrubbers / 346

16.4 Electrostatic Precipitators / 349

17 Dryer Feeding Equipment 357

17.1 Fluid-Bed Dryers / 358

17.2 Direct-Heat Rotary Dryers / 360

17.3 Flash Dryers / 360

17.4 Spray Dryers / 361

17.5 Conveyor Dryers / 361

17.6 Hazemag Rapid Dryer / 363

17.7 Anhydro Spin Flash Dryer / 365

17.8 Plate Dryers / 365

17.9 Vigorously Agitated Contact Dryers / 365

17.10 Vertical Thin-Film and Drum Dryers / 365

Notation 369

Index 377