Hydrodynamics of Gas-Liquid Reactors: Normal Operation and Upset Conditions

The design of chemical reactors and their safety are as critical to the success of a chemical process as the actual chemistry taking place within the reactor. This book provides a comprehensive overview of the practical aspects of multiphase reactor design and operation with an emphasis on safety and clean technology. It considers not only standard operation conditions, but also the problems of runaway reaction conditions and protection against ensuing over-pressure. Hydrodynamics of Multiphase Reactors addresses both practical and theoretical aspects of this topic. Initial chapters discuss various different types of gas/liquid reactors from a practical viewpoint, and later chapters focus on the modelling of multiphase systems and computational methods for reactor design and problem solving. The material is written by experts in their specific fields and will include chapters on the following topics: Multiphase flow, Bubble columns, Sparged stirred vessels, Macroscale modelling, Microscale modelling, Runaway conditions, Behaviour of vessel contents, Choked flow, Measurement techniques.

Table of Contents:
List of Figures xi List of Tables xix Preface xxi Nomenclature xxiii 1. Introduction 1 Part One 2. Bubble Columns 5 2.1 Introduction 6 2.2 Types of Bubble Columns 6 2.3 Introduction of Gas 7 2.3.1 Methodology of Gas Injection 8 2.3.2 Bubble Formation and Size Change 11 2.3.3 Bubble Movement 16 2.3.3.1 Bubble Shape 16 2.3.3.2 Bubble Motion 17 2.3.3.3 Bubble Velocity 17 2.3.3.4 Effect of Multiple Bubbles 21 2.3.4 Void Fraction Prediction 22 2.3.5 Detailed Behaviour of the Flow 33 2.3.6 Gas-Liquid Mass Transfer 37 2.3.7 Design of Gas Introduction Arrangement 41 2.3.8 Worked Example 42 2.4 Disengagement of Liquid from Gas 43 2.4.1 Mechanisms of Drop Formation 43 2.4.2 Drop Capture 44 2.4.3 Wave Plate Mist Eliminators 47 2.4.4 Mesh Mist Eliminators 51 Questions 54 References 56 3. Sparged Stirred Vessels 61 3.1 Introduction 62 3.2 Flow Regimes 63 3.3 Variations 65 3.4 Spargers 65 3.5 Impellers 67 3.5.1 Disc Turbines 67 3.5.2 Pitched Blade Turbines 69 3.5.3 Hydrofoil Impellers 69 3.5.4 Multiple Impellers 72 3.6 Baffles 72 3.7 Power Requirements 73 3.7.1 Single Impellers 73 3.7.2 Multiple Impellers 75 3.7.3 Single-Phase Power 76 3.8 Gas Fraction 77 3.9 Mass Transfer 79 3.9.1 Bubble Size 79 3.9.2 Interfacial Area 80 3.9.3 Mass Transfer 81 3.10 Mixing Times 84 Questions 85 References 87 4. Thin Film Reactors 91 4.1 Introduction 91 4.2 Falling Film Reactors 92 4.2.1 Film Thickness 96 4.2.2 Interfacial Waves 99 4.2.3 Heat and Mass Transfer 102 4.3 Rotating Disc Reactors 105 4.3.1 Film Thickness 105 4.3.2 Interfacial Waves 107 4.3.3 Mass Transfer 108 4.4 Two-Phase Tubular Reactors 109 4.5 Monolith Reactors 113 4.5.1 Micro-Channels 115 4.5.2 Flow Phenomena in Micro-Channels 115 4.5.3 Numerical Modelling 117 Questions 119 References 120 5. Macroscale Modelling 125 5.1 Introduction 126 5.2 Eulerian Multiphase Flow Model 128 5.2.1 Definition 128 5.2.2 Transport Equations 128 5.2.2.1 Continuity Equation 129 5.2.2.2 Momentum Equation 129 5.2.2.3 Energy Equation 130 5.2.3 Interfacial Forces 130 5.2.3.1 Drag Force 130 5.2.3.2 Lift Force 132 5.2.3.3 Virtual Mass Force 132 5.2.3.4 Turbulent Drag Force 133 5.2.3.5 Basset Force 133 5.2.3.6 Wall Lubrication Force 133 5.2.4 Turbulence Models 134 5.2.5 Case Study – Cylindrical Bubble Column 135 5.2.6 Homogenous and Mixture Modelling 135 5.2.6.1 General Formulation 136 5.2.6.2 Mixture Model 137 5.3 Poly-Dispersed Flows 139 5.3.1 Methods of Moments 139 5.3.1.1 Breakup Model 140 5.3.1.2 Coalescence Model 141 5.3.2 Case Study – Hibiki’s Bubble Column 142 5.3.2.1 Numerical Solution Method 142 5.3.2.2 Results and Discussion 142 5.3.2.3 Summary of Case Study 148 5.4 Gassed Stirred Vessels 149 5.4.1 Impeller Model 149 5.4.2 Multiple Reference Frame 150 5.4.3 Multiple Impellers 150 5.5 Summary 154 Questions 155 References 156 6. Mesoscale Modelling Using the Lattice Boltzmann Method 159 6.1 Introduction 159 6.2 Lattice Boltzmann Method and the Advantages 161 6.3 Numerical Simulation of Single-Phase Flow and Heat Transfer 163 6.3.1 LBM Model 164 6.3.2 Treatment for a Curved Boundary 166 6.3.3 Numerical Simulation and Results 167 6.4 Numerical Simulation of Two-Phase Flow 169 6.4.1 Two-Phase Lattice Boltzmann Model 169 6.4.2 Vortices Merging in a Two-Phase Spatially Growing Mixing Layer 175 6.4.3 Viscous Fingering Phenomena of Immiscible Two-Fluid Displacement 176 6.4.4 Bubbles/Drops Flow Behaviour 178 6.4.4.1 LBM Method 178 6.4.4.2 Correction of Pressure 181 6.4.4.3 Boundary Treatment 181 6.4.4.4 Results of Two Rising Bubbles Coalescence 183 6.4.4.5 Results of Droplet Spreading on Partial Wetting Surface 185 References 187 Part Two 7. Upset Conditions 193 7.1 Introduction 193 7.2 Active Relief Methods 194 7.3 Passive Relief Methods 195 References 199 8. Behaviour of Vessel Contents and Outflow Calculations 201 8.1 Introduction 201 8.1.1 Physics of Venting Processes 201 8.1.2 Typical Reactions 202 8.1.3 Trends and Observations 203 8.1.4 Summary of Observations and Measurements of the Level Swell Process 210 8.2 Modelling of the Level Swell Process 212 8.3 Vent Sizing and Vent Performance Calculations 216 8.4 Computer Codes for Level Swell and Venting Calculations 220 8.5 Obtaining Necessary Data 222 8.6 Performance of Models and Codes 226 Appendix 8.A 228 Appendix 8.B 230 Questions 233 References 235 9. Choked Flow 237 9.1 Introduction 237 9.2 Single-Phase Flow 239 9.3 Two-Phase Flow 241 9.4 Effect of Vent Pipework 250 Questions 255 References 256 Part Three 10. Measurement Techniques 259 10.1 Bubble Columns 260 10.1.1 Gas Hold-Up 260 10.1.2 Local Probes: Conductance or Refraction Index 261 10.1.2.1 Gas Fraction 261 10.1.2.2 Bubble Size and Velocity 263 10.1.3 Wire Mesh Sensors 264 10.1.4 Photographic Techniques 266 10.1.5 Laser Doppler Anemometry (LDA) 267 10.1.6 Particle Image Velocimetry (PIV) 268 10.1.7 Electrical Tomography Methods (ECT and ERT) 269 10.1.8 c and X-Ray Tomography 273 10.1.9 CARPT and PEPT 277 10.1.10 Acoustic Methods 279 10.1.11 Mass Transfer Coefficient 281 10.2 Sparged Stirred Tanks 283 10.2.1 Power Draw 283 10.2.1.1 Strain Gauges 284 10.2.1.2 Measurement of Motor Power 285 10.2.1.3 Modified Rheometer Method 285 10.2.2 Velocity Field 285 10.2.3 Void Fraction 286 10.2.4 Mixing Time 286 10.2.5 Mass Transfer Coefficient 288 10.3 Falling Film Reactors 290 10.3.1 Film Thickness 290 10.3.2 Heat and Mass Transfer 296 Questions 300 References 302 Index 307

About the Author :
Professor Barry Azzopardi is based in the School of Chemical and Environmental Engineering at the University of Nottingham. Barry is responsible for multiphase flow research , with particular focus on phase separation in reaction vessels, drop size measurement in complex systems, demisting, gas cleaning and flow in aero-engine bearing chambers. He has over 70 technical publications. Professor Robert Mudde is based in the Department of Multiscale Physics in the Faculty of Applied Science, Delft University of Technology, The Netherlands. His research interests include bubbly flows, advanced experiments in multiphase flows and multiphase hydrodynamics. He has authored more than 50 refereed journal papers and is an associate editor of the International Journal of Multiphase Flow. S. Lo, CD Adapco, (Computational Engineering Company, London) H. Morvan, Mechanical, Manufacturing and Materials Engineering, University of Nottingham Y.Y. Yan, Associate Professor, School of the Built Environment, University of Nottingham Donglin Zhao, Chemical and Environmental Engineering, University of Nottingham