Chapter 8: Fractionators and Absorbers

8.1 Introduction 6
8.1.1 Fractionation and Absorber related references 6
8.2 Distillation fundamentals 6
8.2.1 Process Design Software 6
8.2.2 Hydraulic Design 6
8.2.3 Distillation 6
8.2.4 Relative Volatility (?) 7
8.3 Process Design 10
8.4 Selection of Trays and Packing 11
8.4.1 Packings versus Trays 11
8.4.2 Packed towers 12
8.4.3 Trayed Towers 12
8.4.4 Tray and Packing characteristics 13
8.5 Design of Trayed Columns 14
8.5.1 Noteworthy Point 15
8.6 The Design of a Distillation Column 16
8.6.1 Selection of Key Components in Feed 17
8.6.1.1 Relative volatility of binary liquid mixtures 17
8.6.1.2 Relative volatility of multi-component mixtures 18
8.6.1.3 Effect of temperature or pressure on relative volatility 18
8.6.2 Understanding the Nature of Chemical Constituents 20
8.6.3 Establishing the design basis of distillation 20
8.6.4 Selection of operating pressure of column 21
8.7 Binary Fractionation 25
8.7.1 Nomenclature and Subscripts 25
8.7.2 Tools for Distillation Analysis 26
8.7.3 Envelope Technique 26
8.7.3.1 Binary Distillation Material Balances 27
8.8. Equilibrium 29
8.8.1 Concept 29
8.8.2 Equilibrium Line Equations 30
8.8.3 Non-Ideal Systems 31
8.9 McCabe-Thiele Diagram 32
8.9.1 Introduction 32
8.9.2 Equilibrium Curve 33
8.9.3 Operating Lines 33
8.9.4 Physical Meaning of Points on McCabe-Thiele 34
8.9.4.1 Feed Conditions 35
8.9.4.2 Feed Tray 36
8.9.5 Minimum Reflux/Infinite Trays 38
8.10 Ruheman-Ponchon-Savarit Graphical Method 39
8.10.1 Distillation in Enriching Section of Tower 40
8.10.2 Distillation in Stripping Section of Tower 41
8.10.2.1 Rectifying section 42
8.10.2.2 Stripping section 43
8.11 Analytical Techniques 46
8.11.1 Minimum Reflux/Infinite Trays 46
8.11.2 Minimum Trays/Total Reflux 47
8.11.3 Feed Tray 47
8.11.4 Design Reflux and Trays 49
8.12 Tray Efficiency 50
8.13 Multi-Component Distillation Design 50
8.13.1 Introduction 50
8.13.2 Shortcut Method in Multicomponent Distillation 51
8.13.3 Rigorous Multicomponent Distillation Methods 52
8.13.4 Columns Sequencing Approach for Multicomponent distillation 53
8.13.5 Tray-To-Tray Calculation Approach for Multicomponent Distillation 54
8.13.5.1 Minimum Reflux and Trays 55
8.13.5.2 Design Parameters 56
8.13.5.3 Tray–to–Tray Calculation 60
8.13.5.4 Constant Molal Overflow Procedure 62
8.13.5.5 Procedure with Heat Balance 62
8.14 Absorption and Stripping 64
8.15 Absorbers and Strippers – Simplified Kremser Approach 78
8.15.1 Absorber or stripper with components in lean oil or stripping gas 79
8.16 Efficiency 82
8.17 Designing a Column 83
8.18 Tray Sizing 84
8.18.1 Preliminary Diameter Estimate 85
8.18.2 Tray Spacing 85
8.18.3 Number of Passes 86
8.18.4 Swaging of Towers 86
8.19 Steam Distillation 87
8.20 Column Internal Design Guidelines 93
8.20.1 Selecting the Controlling Case 94
8.20.2 Tray Count and Tower Layout 95
8.20.3 Types of trays 95
8.20.3.1 Overview of Choice of Column Internals 96
8.20.4 Hydraulic Parameters 105
8.20.4.1 Jet Flooding 106
8.20.4.2 Downcomer Backup 107
8.20.5 Geometric Parameters 111
8.20.5.1 Tray Configurations 111
8.20.5.2 One Pass Tray 112
8.20.5.3 Two Pass Tray 113
8.20.5.4 Three Pass Trays 114
8.20.5.5 Four Pass Tray 115
8.20.5.6 Discussion on Tray Configurations 117
8.20.5.7 Tray Action 118
8.20.5.8 Weir Height, Length, Type and Swept Back Weirs 118
8.20.6 Important Formulae Used in Sieve and Valve Trays Design 126
8.20.6.1 Downcomer Backup – Clear Liquid 126
8.20.6.2 Aerated Downcomer Backup 126
8.20.6.3 Total Tray or Wet Tray Pressure Drop 126
8.20.6.4 Weir Crest 127
8.20.6.5 Head Loss under Downcomer 127
8.20.6.6 Throw over Weir 128
8.20.6.7 Anti-Jump Baffles 128
8.20.6.8 Zf and Zh 128
8.20.6.9 Special Considerations for Four-Pass Tray Designs 128
8.20.7 Feed and Draw for Trayed Towers 129
8.20.7.1 Nozzle Sizing 129
8.20.7.2 Reboilers and Bottom Compartments 164
8.20.7.2.1 Reboiler Types 164
8.20.8 Tower Bottom Arrangements 168
8.20.8.1 Flow classifications 168
8.20.8.2 Reboiler Compartments 174
8.20.9 Other Topics 214
8.21 Tray Efficiencies and Turndown 222
8.21.1 Tray Efficiencies 222
8.21.2 Murphree Efficiency 222
8.21.3 Overall Efficiency 223
8.21.4 Derating (‘system’) factors 227
8.21.5 Turndown 229
8.21.6 Tray hydraulic design procedure and guidelines 230
8.21.7 Tips on Balancing Trays 231
8.22 Flow regimes 231
8.22.1 Stability Limits 232
8.23 Tower System Design Pressure, Temperature Determination 235
8.23.1 Approach to Determining Design Pressure & Temperature 236
8.24 Packed Columns 237
8.24.1 Design of Packed Columns 237
8.24.2 Packed Tower Sizing Strategy 244
8.24.3 Example of Bid Evaluation Report for Packed Tower 244
8.25 Tower Packings 250
8.25.1 Random Packings 250
8.25.2 Structured Packings 256
8.25.3 Grid Packings 258
8.25.4 Packing Selection 259
8.25.5 Packing Hydraulics 261
8.25.5.1 Minimum Wetting Rates 261
8.25.5.2 Loading and Flooding 262
8.25.5.3 Pressure Drop 263
8.25.5.4 Liquid Holdup 265
8.25.5.5 Minimum Vapor Rate 266
8.25.5.6 Foaming and Safety Factor 266
8.25.5.7 Other Considerations 266
8.25.5.8 Material and Thickness of Packings 267
8.25.6 Random Packing Efficiency 267
8.25.6.1 Concepts of Packing Efficiency 267
8.25.6.2 Procedure of Random Packing Efficiency Estimate 269
8.25.6.3 Data of Packing Efficiency 269
8.25.6.4 F.R.I. Models for Random Packing Efficiency 272
8.25.6.5 Rules-of-Thumb 274
8.25.6.6 Design Considerations of Random Packing HETP 275
8.25.6.7 Structured Packing Efficiency 276
8.25.6.8 Data of Structured Packing Efficiencies 278
8.25.6.9 Rules of Thumb for HETP for structured packing 278
8.25.6.10 Factors Affecting HETP of Structured Packings 281
8.25.6.11 General Considerations of Structured Packing HETP 282
8.25.6.12 General Considerations of Structured Packing HETP 283
8.26 Liquid Distribution 283
8.26.1 Liquid Distribution and Redistribution 283
8.26.2 Liquid Distribution Quality 284
8.26.3 Types of Liquid Distributors 287
8.26.3.1 Liquid Distributor Selection 290
8.26.3.2 Tower Arrangement for Liquid Distribution Devices 299
8.26.3.3 Liquid Distributor Models from Major Vendors 301
8.26.3.4 Liquid Distributor Assessment 302
8.26.3.5 Distributors for Structured and Grid Packings 304
8.26.3.6 Testing of Liquid Distributors 304
8.26.3.7 Feed Devices 307
8.26.3.7 Intermediate Liquid Draw-Off 309
8.26.4 Draw Nozzle Sizing 313
8.26.5 Support Plates 317
8.27 Datasheet Preparation 320
8.27.1 Column Datasheets 320
8.28 Specialized Services 323
8.29 Distillation Examples 324
8.30 Go-By Column Data Sheets and Tray Data Sheets 388
8.31 References 396

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