Chapter 8: Fractionators and Absorbers

8.1Introduction6
8.1.1Fractionation and Absorber related references6
8.2Distillation fundamentals6
8.2.1Process Design Software6
8.2.2Hydraulic Design6
8.2.3Distillation6
8.2.4Relative Volatility (?)7
8.3Process Design10
8.4Selection of Trays and Packing11
8.4.1Packings versus Trays11
8.4.2Packed towers12
8.4.3Trayed Towers12
8.4.4Tray and Packing characteristics13
8.5Design of Trayed Columns14
8.5.1Noteworthy Point15
8.6The Design of a Distillation Column16
8.6.1Selection of Key Components in Feed17
8.6.1.1Relative volatility of binary liquid mixtures17
8.6.1.2Relative volatility of multi-component mixtures18
8.6.1.3Effect of temperature or pressure on relative volatility18
8.6.2Understanding the Nature of Chemical Constituents20
8.6.3Establishing the design basis of distillation20
8.6.4Selection of operating pressure of column21
8.7Binary Fractionation25
8.7.1Nomenclature and Subscripts25
8.7.2Tools for Distillation Analysis26
8.7.3Envelope Technique26
8.7.3.1Binary Distillation Material Balances27
8.8.Equilibrium29
8.8.1Concept29
8.8.2Equilibrium Line Equations30
8.8.3Non-Ideal Systems31
8.9McCabe-Thiele Diagram32
8.9.1Introduction32
8.9.2Equilibrium Curve33
8.9.3Operating Lines33
8.9.4Physical Meaning of Points on McCabe-Thiele34
8.9.4.1Feed Conditions35
8.9.4.2Feed Tray36
8.9.5Minimum Reflux/Infinite Trays38
8.10Ruheman-Ponchon-Savarit Graphical Method39
8.10.1Distillation in Enriching Section of Tower40
8.10.2Distillation in Stripping Section of Tower41
8.10.2.1Rectifying section42
8.10.2.2Stripping section43
8.11Analytical Techniques46
8.11.1Minimum Reflux/Infinite Trays46
8.11.2Minimum Trays/Total Reflux47
8.11.3Feed Tray47
8.11.4Design Reflux and Trays49
8.12Tray Efficiency50
8.13Multi-Component Distillation Design50
8.13.1Introduction50
8.13.2Shortcut Method in Multicomponent Distillation51
8.13.3Rigorous Multicomponent Distillation Methods52
8.13.4Columns Sequencing Approach for Multicomponent distillation53
8.13.5Tray-To-Tray Calculation Approach for Multicomponent Distillation54
8.13.5.1Minimum Reflux and Trays55
8.13.5.2Design Parameters56
8.13.5.3Tray–to–Tray Calculation60
8.13.5.4Constant Molal Overflow Procedure62
8.13.5.5Procedure with Heat Balance62
8.14Absorption and Stripping64
8.15Absorbers and Strippers – Simplified Kremser Approach78
8.15.1Absorber or stripper with components in lean oil or stripping gas79
8.16Efficiency82
8.17Designing a Column83
8.18Tray Sizing84
8.18.1Preliminary Diameter Estimate85
8.18.2Tray Spacing85
8.18.3Number of Passes86
8.18.4Swaging of Towers86
8.19Steam Distillation87
8.20Column Internal Design Guidelines93
8.20.1Selecting the Controlling Case94
8.20.2Tray Count and Tower Layout95
8.20.3Types of trays95
8.20.3.1Overview of Choice of Column Internals96
8.20.4Hydraulic Parameters105
8.20.4.1Jet Flooding106
8.20.4.2Downcomer Backup107
8.20.5Geometric Parameters111
8.20.5.1Tray Configurations111
8.20.5.2One Pass Tray112
8.20.5.3Two Pass Tray113
8.20.5.4Three Pass Trays114
8.20.5.5Four Pass Tray115
8.20.5.6Discussion on Tray Configurations117
8.20.5.7Tray Action118
8.20.5.8Weir Height, Length, Type and Swept Back Weirs118
8.20.6Important Formulae Used in Sieve and Valve Trays Design126
8.20.6.1Downcomer Backup – Clear Liquid126
8.20.6.2Aerated Downcomer Backup126
8.20.6.3Total Tray or Wet Tray Pressure Drop126
8.20.6.4Weir Crest127
8.20.6.5Head Loss under Downcomer127
8.20.6.6Throw over Weir128
8.20.6.7Anti-Jump Baffles128
8.20.6.8Zf and Zh128
8.20.6.9Special Considerations for Four-Pass Tray Designs128
8.20.7Feed and Draw for Trayed Towers129
8.20.7.1Nozzle Sizing129
8.20.7.2Reboilers and Bottom Compartments164
8.20.7.2.1Reboiler Types164
8.20.8Tower Bottom Arrangements168
8.20.8.1Flow classifications168
8.20.8.2Reboiler Compartments174
8.20.9Other Topics214
8.21Tray Efficiencies and Turndown222
8.21.1Tray Efficiencies222
8.21.2Murphree Efficiency222
8.21.3Overall Efficiency223
8.21.4Derating (‘system’) factors227
8.21.5Turndown229
8.21.6Tray hydraulic design procedure and guidelines230
8.21.7Tips on Balancing Trays231
8.22Flow regimes231
8.22.1Stability Limits232
8.23Tower System Design Pressure, Temperature Determination235
8.23.1Approach to Determining Design Pressure & Temperature236
8.24Packed Columns237
8.24.1Design of Packed Columns237
8.24.2Packed Tower Sizing Strategy244
8.24.3Example of Bid Evaluation Report for Packed Tower244
8.25Tower Packings250
8.25.1Random Packings250
8.25.2Structured Packings256
8.25.3Grid Packings258
8.25.4Packing Selection259
8.25.5Packing Hydraulics261
8.25.5.1Minimum Wetting Rates261
8.25.5.2Loading and Flooding262
8.25.5.3Pressure Drop263
8.25.5.4Liquid Holdup265
8.25.5.5Minimum Vapor Rate266
8.25.5.6Foaming and Safety Factor266
8.25.5.7Other Considerations266
8.25.5.8Material and Thickness of Packings267
8.25.6Random Packing Efficiency267
8.25.6.1Concepts of Packing Efficiency267
8.25.6.2Procedure of Random Packing Efficiency Estimate269
8.25.6.3Data of Packing Efficiency269
8.25.6.4F.R.I. Models for Random Packing Efficiency272
8.25.6.5Rules-of-Thumb274
8.25.6.6Design Considerations of Random Packing HETP275
8.25.6.7Structured Packing Efficiency276
8.25.6.8Data of Structured Packing Efficiencies278
8.25.6.9Rules of Thumb for HETP for structured packing278
8.25.6.10Factors Affecting HETP of Structured Packings281
8.25.6.11General Considerations of Structured Packing HETP282
8.25.6.12General Considerations of Structured Packing HETP283
8.26Liquid Distribution283
8.26.1Liquid Distribution and Redistribution283
8.26.2Liquid Distribution Quality284
8.26.3Types of Liquid Distributors287
8.26.3.1Liquid Distributor Selection290
8.26.3.2Tower Arrangement for Liquid Distribution Devices299
8.26.3.3Liquid Distributor Models from Major Vendors301
8.26.3.4Liquid Distributor Assessment302
8.26.3.5Distributors for Structured and Grid Packings304
8.26.3.6Testing of Liquid Distributors304
8.26.3.7Feed Devices307
8.26.3.7Intermediate Liquid Draw-Off309
8.26.4Draw Nozzle Sizing313
8.26.5Support Plates317
8.27Datasheet Preparation320
8.27.1Column Datasheets320
8.28Specialized Services323
8.29Distillation Examples324
8.30Go-By Column Data Sheets and Tray Data Sheets388
8.31References396