Drying in the Process Industry

A comprehensive approach to selecting and understanding drying equipment for chemical and mechanical engineers

A detailed reference of interest for engineers and energy specialists working in the process industry field, Drying in the Process Industry investigates the current state of the art of today's industrial drying practices, examines the factors influencing drying's high costs in both equipment and energy consumption, and summarizes key elements for keeping drying operations under budget and performing at peak capacity safely while respecting the environment. Extensive coverage of dryer basics as well as essential procedures concerning the selection of industrial dryers?such as how to gather results of relevant laboratory measurements, carry out small-scale tests, and correctly size equipment?help to inform readers on criteria for generating scalable specifications that greatly assist buying decisions.

Drying in the Process Industry:

• Takes a practical approach to drying equipment, from an author with four decades in the industry
• Describes a diverse array of drying equipment (convective, like flash, spray, fluid-bed, and rotary; contact, like paddle and steam; radiation) from an engineer's perspective
• Provides quick and ready access to drying technologies with references to more detailed literature
• Treats drying in the context of the entire production process

True of all process facilities where drying plays an important role, such as those in the chemical, pharmaceutical, plastics, and food industries, the purchase of improper industrial drying equipment can significantly affect a manufacturer's economic bottom line. With the guidance offered in this book, engineers will be able to confidently choose industrial drying equipment that increases profits, runs efficiently, and optimally suits their needs.

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