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Modern Drying Technology, Volume 4: Energy Savings

ISBN: 978-3-527-31559-8
376 pages
December 2011
Modern Drying Technology, Volume 4: Energy Savings (3527315594) cover image


The five-volume series provides a comprehensive overview of all important aspects of drying technology like computational tools at different scales (Volume 1), modern experimental and analytical techniques (Volume 2), product quality and formulation (Volume 3), energy savings (Volume 4) and process intensification (Volume 5).

Based on high-level cutting-edge results contributed by internationally recognized experts in the various treated fields, this book series is the ultimate reference in the area of industrial drying. Located at the intersection of the two main approaches in modern chemical engineering, product engineering and process systems engineering, the series aims at bringing theory into practice in order to improve the quality of high-value dried products, save energy, and cut the costs of drying processes.

Volume 4 deals with the reduction of energy demand in various drying processes and areas, highlighting the following topics: Energy analysis of dryers, efficient solid-liquid separation techniques, osmotic dehydration, heat pump assisted drying, zeolite usage, solar drying, drying and heat treatment for solid wood and other biomass sources, and sludge thermal processing.


Other Volumes and Sets:

Volume 1 - Modern Drying Technology, Computational Tools at Different Scales

Volume 1: Diverse model types for the drying of products and the design of drying processes (short-cut methods, homogenized, pore network, and continuous thermo-mechanical approaches) are treated, along with computational fluid dynamics, population balances, and process systems simulation tools. Emphasis is put on scale transitions.


Volume 2 - Modern Drying Technology: Experimental Techniques

Volume 2: Comprises experimental methods used in various industries and in research in order to design and control drying processes, measure moisture and moisture distributions, characterize particulate material and the internal micro-structure of dried products, and investigate the behavior of particle systems in drying equipment. Key topics include acoustic levitation, near-infrared spectral imaging, magnetic resonance imaging, X-ray tomography, and positron emission tracking.


Volume 3 - Modern Drying Technology: Product Quality and Formulation

Volume 3: Discusses how desired properties of foods, biomaterials, active pharmaceutical ingredients, and fragile aerogels can be preserved during drying, and how spray drying and spray fluidized bed processes can be used for particle formation and formulation. Methods for monitoring product quality, such as process analytical technology, and modeling tools, such as Monte Carlo simulations, discrete particle modeling and neural networks, are presented with real examples from industry and academia.


Volume 5 - Process Intensification

Volume 5: Dedicated to process intensification by more efficient distribution and flow of the drying medium, foaming, controlled freezing, and the application of superheated steam, infrared radiation, microwaves, power ultrasound and pulsed electric fields. Process efficiency is treated in conjunction with the quality of sensitive products, such as foods, for a variety of hybrid and combined drying processes.


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Also available in electronic formats.

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Table of Contents

Series Preface XI

Preface of Volume 4 XV

List of Contributors XIX

Recommended Notation XXIII

EFCE Working Party on Drying; Address List XXIX

1 Fundamentals of Energy Analysis of Dryers 1
Ian C. Kemp

1.1 Introduction 1

1.2 Energy in Industrial Drying 2

1.3 Fundamentals of Dryer Energy Usage 3

1.3.1 Evaporation Load 3

1.3.2 Dryer Energy Supply 4

1.3.3 Evaluation of Energy Inefficiencies and Losses: Example 5 Dryer Thermal Inefficiencies 6 Inefficiencies in the Utility (Heat Supply) System 8 Other Energy Demands 13

1.3.4 Energy Cost and Environmental Impact 14 Primary Energy Use 14 Energy Costs 14 Carbon Dioxide Emissions and Carbon Footprint 15

1.4 Setting Targets for Energy Reduction 16

1.4.1 Energy Targets 16

1.4.2 Pinch Analysis 17 Basic Principles 17 Application of Pinch Analysis to Dryers 19 The Appropriate Placement Principle Applied to Dryers 21 Pinch Analysis and Utility Systems 24

1.4.3 Drying in the Context of the Overall Process 25

1.5 Classification of Energy Reduction Methods 26

1.5.1 Reducing the Heater Duty of a Convective Dryer 28

1.5.2 Direct Reduction of Dryer Heat Duty 29 Reducing the Inherent Heat Requirement for Drying 29 Altering Operating Conditions to Improve Dryer Efficiency 30

1.5.3 Heat Recovery and Heat Exchange 31 Heat Exchange Within the Dryer 31 Heat Exchange with Other Processes 32

1.5.4 Alternative Utility Supply Systems 32 Low Cost utilities 33 Improving Energy Supply System Efficiency 33 Combined Heat and Power 34 Heat Pumps 36

1.6 Case Study 37

1.6.1 Process Description and Dryer Options 37

1.6.2 Analysis of Dryer Energy Consumption 38

1.6.3 Utility Systems and CHP 42

1.7 Conclusions 43

References 45

2 Mechanical Solid–Liquid Separation Processes and Techniques 47
Harald Anlauf

2.1 Introduction and Overview 47

2.2 Density Separation Processes 51

2.2.1 Froth Flotation 51

2.2.2 Sedimentation 54

2.3 Filtration 61

2.3.1 Cake Filtration 61

2.3.2 Sieving and Blocking Filtration 72

2.3.3 Crossflow Micro- and Ultra-Filtration 73

2.3.4 Depth and Precoat Filtration 75

2.4 Enhancement of Separation Processes by Additional Electric or Magnetic Forces 80

2.5 Mechanical/Thermal Hybrid Processes 83

2.6 Important Aspects of Efficient Solid–Liquid Separation Processes 85

2.6.1 Mode of Apparatus Operation 85

2.6.2 Combination of Separation Apparatuses 87

2.6.3 Suspension Pre-Treatment Methods to Improve Separation Conditions 91

2.7 Conclusions 94

References 95

3 Energy Considerations in Osmotic Dehydration 99
Hosahalli S. Ramaswamy and Yetenayet Bekele Tola

3.1 Scope 99

3.2 Introduction 100

3.3 Mass Transfer Kinetics 101

3.3.1 Pretreatments 101

3.3.2 Product 102

3.3.3 Osmotic Solution 103

3.3.4 Treatment Conditions 103

3.4 Modeling of Osmotic Dehydration 104

3.5 Osmotic Dehydration – Two Major Issues 105

3.5.1 Quality Issues 105

3.5.2 Energy Issues 106 Osmo-Convective Drying 107 Osmo-Freeze Drying 109 Osmo-Microwave Drying 111 Osmotic-Vacuum Drying 113

3.6 Conclusions 114

References 116

4 Heat Pump Assisted Drying Technology – Overview with Focus on Energy, Environment and Product Quality 121
Sachin V. Jangam and Arun S. Mujumdar

4.1 Introduction 121

4.2 Heat Pump Drying System – Fundamentals 122

4.2.1 Heat Pump 122

4.2.2 Refrigerants 125

4.2.3 Heat Pump Dryer 127

4.2.4 Advantages and Limitations of the Heat Pump Dryer 130

4.3 Various Configurations/Layout of a HPD 131

4.4 Heat Pumps – Diverse Options and Advances 132

4.4.1 Multi-Stage Heat Pump 132

4.4.2 Cascade Heat Pump System 133

4.4.3 Use of Heat Pipe 134

4.4.4 Chemical Heat Pump (CHP) 135

4.4.5 Absorption Refrigeration Cycle 138

4.5 Miscellaneous Heat Pump Drying Systems 140

4.5.1 Solar-Assisted Heat Pump Drying 140

4.5.2 Infrared-Assisted Heat Pump Dryer 143

4.5.3 Microwave-Assisted Heat Pump Drying 143

4.5.4 Time-Varying Drying Conditions and Multi-Mode Heat Pump Drying 145

4.5.5 Heat Pump Assisted Spray Drying 147

4.5.6 Modified Atmosphere Heat Pump Drying 148

4.5.7 Atmospheric Freeze Drying Using Heat Pump 149

4.6 Applications of Heat Pump Drying 150

4.6.1 Food and Agricultural Products 150

4.6.2 Drying of Wood/Timber 150

4.6.3 Drying of Pharmaceutical/Biological Products 152

4.7 Sizing of Heat Pump Dryer Components 153

4.8 Future Research and Development Needs in Heat Pump Drying 156

References 158

5 Zeolites for Reducing Drying Energy Usage 163
Antonius J. B. van Boxtel, Moniek A. Boon, Henk C. van Deventer, and Paul J. Th. Bussmann

5.1 Introduction 163

5.2 Zeolite as an Adsorption Material 164

5.2.1 Zeolite 164

5.2.2 Comparing the Main Sorption Properties of Zeolite with other Adsorbents 166

5.3 Using Zeolites in Drying Systems 168

5.3.1 Drying Systems 168

5.3.2 Direct Contact Drying 169

5.3.3 Air Dehumidification 170

5.4 Energy Efficiency and Heat Recovery 173

5.4.1 Defining Energy Efficiency 173

5.4.2 Energy Recovery for a Single-Stage System 174

5.4.3 Energy Recovery in a Multi-Stage System 176

5.4.4 Energy Recovery with Superheated Steam 178

5.5 Realization of Adsorption Dryer Systems 180

5.5.1 Adsorption Dryer Systems for Zeolite 180

5.5.2 Adsorption Wheel Versus Packed Bed 181

5.5.3 Zeolite Mechanical Strength 182

5.5.4 Long Term Capacity of Zeolite 183

5.5.5 Zeolite Adsorption Wheel 183

5.6 Cases 185

5.6.1 Zeolite-Assisted Drying in the Dairy Industry 185

5.6.2 Zeolite-Assisted Manure and Sludge Drying 189

5.6.3 Direct Contact Drying of Seeds with Zeolites 191

5.7 Economic Considerations 193

5.8 Perspectives 195

References 196

6 Solar Drying 199
Joachim Müller and Werner Mühlbauer

6.1 Introduction 199

6.2 Solar Radiation 200

6.3 Solar Air Heaters 204

6.4 Design and Function of Solar Dryers 210

6.4.1 Classification of Solar Dryers 210

6.4.2 Solar Dryers with Natural Convection for Direct Solar Drying 212

6.4.3 Solar Dryers with Natural Convection for Indirect Drying 213

6.4.4 Solar Dryers with Forced Convection for Direct Drying 214

6.4.5 Solar Dryers with Forced Convection for Indirect Drying 218

6.4.6 Dryers with Roof-Integrated Solar Air Heaters 223

6.5 Solar Drying Kinetics 226

6.5.1 Empirical Drying Curves in Solar Drying 226

6.5.2 Equilibrium Model for Solar Drying Kinetics 227

6.6 Control Strategies for Solar Dryers 231

6.6.1 Airflow Management During the Night 231

6.6.2 Recirculation of Drying Air 232

6.6.3 Back-Up Heating Systems 232

6.7 Economic Feasibility of Solar Drying 234

6.7.1 Drying of Timber in Brazil 235

6.7.2 Drying of Tobacco in Brazil 237

6.8 Conclusions and Outlook 239

References 242

7 Energy Issues of Drying and Heat Treatment for Solid Wood and Other Biomass Sources 245
Patrick Perré, Giana Almeida, and Julien Colin

7.1 Introduction 245

7.2 Wood and Biomass as a Source of Renewable Material and Energy 245

7.3 Energy Consumption and Energy Savings in the Drying of Solid Wood 254

7.3.1 Kiln-Drying of Solid Wood: A Real Challenge 254

7.3.2 The Conventional Drying of Wood 258 The Design of Conventional Kilns 258 Drying Time and Energy Efficiency 259

7.3.3 Theoretical Evaluation of the Kiln Efficiency 263

7.3.4 Two Case Studies of Kiln Efficiency 266

7.3.5 Rules for Saving Energy 269 Energy Savings in Conventional Kilns 269 Energy Saving by Alternative Technologies 270

7.4 Preconditioning of Biomass as a Source of Energy: Drying and Heat Treatment 271

7.4.1 Importance of Biomass Drying as a Preconditioning Step 271 Dryers for Biomass 273 Numerical Approach to the Continuous Drying ofWoody Biomass 276

7.4.2 Interest of Heat Treatment as a Preconditioning Step 281

7.5 Conclusions 287

References 289

8 Efficient Sludge Thermal Processing: From Drying to Thermal Valorization 295
Patricia Arlabosse, Jean-Henry Ferrasse, Didier Lecomte, Michel Crine, Yohann Dumont, and Angélique Léonard

8.1 Introduction to the Sludge Context 295

8.1.1 Origin, Production and Valorization Issues 295

8.1.2 Sludge: A Complex Material 297

8.1.3 Useful Properties for Energy Valorization 299

8.2 Sludge Drying Technologies 300

8.2.1 General Remarks 300

8.2.2 Convective Drying Methods and Dryer Types 301

8.2.3 Indirect Contact Drying Methods and Dryer Types 305 Rotor Design and Operation of the Drying Process 306 Drying Performances 308

8.2.4 Solar Drying and Dryer Types 310

8.2.5 Combined and Hybrid Drying 311

8.2.6 Sludge Frying, an Alternative to Conventional Drying 311 Heat and Mass Transfer During Fry-Drying 312 Energy and Environmental Aspects 313

8.2.7 Pathogen Reduction 314

8.3 Energy Efficiency of Sludge Drying Processes 315

8.3.1 Specific Heat Consumption of Sludge Dryers 315

8.3.2 Towards the Reduction of Energy Consumption Associated with Sludge Drying 316

8.3.3 Case Studies 316

8.4 Thermal Valorization of Sewage Sludge 318

8.4.1 General Description of the Thermal Processes Available for Sewage Sludge 318

8.4.2 Desired Water Content for Thermal Processes 319

8.4.3 Including a Drying Step Before Thermal Valorization 320

8.5 Energy Efficiency of Thermal Valorization Routes 321

8.5.1 Importance of Dryer Efficiency 321

8.5.2 Combining Sludge Drying and Thermal Valorization by Integrating on Site 322

8.6 Conclusions 324

References 325

Index 331

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Author Information

Professor Dr. Ing. Evangelos Tsotsas born 1959, Thessaloniki/Greece; PhD: 1985, Karlsruhe/Germany; Habilitation: 1990, Karlsruhe; till 1994: The Dow Chemical Company; since 1994: Professor of Thermal Process Engineering at Otto-von-Guericke-University Magdeburg; 1998-2002: Dean of the Faculty of Process and Systems Engineering; elected German Research Council (DFG) reviewer, member of the selection committee of the Alexander von Humboldt Foundation, the European Multiphase Systems Institute, and the International Center of Heat and Mass Transfer; Chairman of Working Parties on Drying of the EFCE and GVC; 2002: Award for innovation in drying research.

Professor Arun S. Mujumdar; PhD McGill University, Montreal; Professor of Chemical Engineering, McGill University, until July 2000; Visiting Professor at numerous universities; Honorary Professor of five universities in China; President and Principal Consultant, Exergex Corp., Canada 1989-2000; consultant for over 60 companies; authored 2 books and over 60 book chapters, edited or co-edited over 50 books and journals; published more than 300 research papers, presented over 200 conference papers; external reviewer for various research councils; founder, chair or member of organizing panels for numerous major international conferences; elected Fellow of American Society of Mechanical Engineers, Chemical Institute of Canada and Inst. Chem. Eng. (India); member of AIChE, CPPA, Sigma Xi; awarded Senior Fellowship by Japan Society for Promotion of Science (1988 and 1996), Innovation in Drying Award, IDS '86, MIT, The Procter & Gamble Award for Excellence in Drying Research (1998); named Distinguished Scientists of the 20th Century, International Man of the Year by International Biographical Institute, Cambridge (1999); listed in 1000 World Leaders of Influence by the American Biographical Institute, Raleigh, USA (2000).
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“All in all, the book covers a wide range of strategies for energy savings that may be embraced in various drying applications for a broad range of substances. This book covers the state-of-the-art methods and ideas for energy savings in all aspects related to drying technology, from fundamentals to applications. These innovative ideas can be adopted and implemented by engineers and developers who are active in the field of drying technology.”  (Drying Technology, 1 May 2014)

"This five-volume series provides a comprehensive overview of all important aspects of modern drying technology, concentrating on the transfer of cutting-edge research results to industrial use." (ETDE Energy Database, 2012)


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