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Heat Effects in Gas Absorption 14-15

Overview 14-15

Effects of Operating Variables 14-16

Equipment Considerations 14-16

Classical Isothermal Design Method 14-16

Classical Adiabatic Design Method 14-17

Rigorous Design Methods 14-17

Direct Comparison of Design Methods 14-17

Example 5: Packed Absorber, Acetone into Water 14-17

Example 6: Solvent Rate for Absorption 14-17

Multicomponent Systems 14-18

Example 7: Multicomponent Absorption, Dilute Case 14-18

Graphical Design Methods for Dilute Systems 14-18

Algebraic Design Method for Dilute Systems 14-19

Example 8: Multicomponent Absorption, Concentrated Case 14-19

Absorption with Chemical Reaction 14-20

Introduction 14-20

Recommended Overall Design Strategy 14-20

Dominant Effects in Absorption with Chemical Reaction 14-20

Applicability of Physical Design Methods 14-22

Traditional Design Method 14-22

Scaling Up from Laboratory Data 14-23

Rigorous Computer-Based Absorber Design 14-24

Development of Thermodynamic Model for Physical and Chemical Equilibrium 14-25

Adoption and Use of Modeling Framework 14-25

Parameterization of Mass Transfer and Kinetic Models 14-25

Deployment of Rigorous Model for Process

Optimization and Equipment Design 14-25

Use of Literature for Specific Systems 14-26

EQUIPMENT FOR DISTILLATION AND GAS ABSORPTION: TRAY COLUMNS

Definitions 14-26

Tray Area Definitions 14-26

Vapor and Liquid Load Definitions 14-27

Flow Regimes on Trays 14-27

Primary Tray Considerations 14-29

Number of Passes 14-29

Tray Spacing 14-29

Outlet Weir 14-29

Downcomers 14-29

Clearance under the Downcomer 14-31

Hole Sizes 14-31

Fractional Hole Area 14-31

Multipass Balancing 14-32

Tray Capacity Enhancement 14-32

Truncated Downcomers/Forward Push Trays 14-32

High Top to Bottom Downcomer Area and

Forward Push 14-34

Large Number of Truncated Downcomers 14-34

Radial Trays 14-34

Centrifugal Force Deentrainment 14-34

Other Tray Types 14-34

Bubble-Cap Trays 14-34

Dual-Flow Trays 14-34

Baffle Trays 14-34

Flooding 14-36

Entrainment (Jet) Flooding 14-36

Spray Entrainment Flooding Prediction 14-36

Example 9: Flooding of a Distillation Tray 14-38

System Limit (Ultimate Capacity) 14-38

Downcomer Backup Flooding 14-38

Downcomer Choke Flooding 14-39

Derating ("System") Factors 14-40

Entrainment 14-40

Effect of Gas Velocity 14-40

Effect of Liquid Rate 14-40

Effect of Other Variables 14-40

Entrainment Prediction 14-41

Example 10: Entrainment Effect on Tray Efficiency 14-42

Pressure Drop 14-42

Example 11: Pressure Drop, Sieve Tray 14-44

Loss under Downcomer 14-44

Other Hydraulic Limits 14-44

Weeping 14-44

Dumping 14-46

Turndown 14-47

Vapor Channeling 14-47

Transition between Flow Regimes 14-47

Froth-Spray 14-47

Froth-Emulsion 14-48

Valve Trays 14-48

Tray Efficiency 14-48

Definitions 14-48

Fundamentals 14-48

Factors Affecting Tray Efficiency 14-49

Obtaining Tray Efficiency 14-50

Rigorous Testing 14-50

Scale-up from an Existing Commercial Column 14-50

Scale-up from Existing Commercial Column to

Different Process Conditions 14-50

Experience Factors 14-50

Scale-up from a Pilot or Bench-Scale Column 14-51

Empirical Efficiency Prediction 14-52

Theoretical Efficiency Prediction 14-53

Example 12: Estimating Tray Efficiency 14-53

EQUIPMENT FOR DISTILLATION AND GAS ABSORPTION: PACKED COLUMNS

Packing Objectives 14-53

Random Packings 14-53

Structured Packings 14-54

Packed-Column Flood and Pressure Drop 14-55

Flood-Point Definition 14-56

Flood and Pressure Drop Prediction 14-57

Pressure Drop 14-59

Example 13: Packed-Column Pressure Drop 14-62

Packing Efficiency 14-63

HETP vs. Fundamental Mass Transfer 14-63

Factors Affecting HETP: An Overview 14-63

HETP Prediction 14-63

Underwetting 14-67

Effect of Lambda 14-67

Pressure 14-67

Physical Properties 14-67

Errors in VLE 14-68

Comparison of Various Packing Efficiencies for Absorption and Stripping 14-68

Summary 14-69

Maldistribution and Its Effects on Packing Efficiency 14-69

Modeling and Prediction 14-69

Implications of Maldistribution to Packing Design Practice 14-70

Packed-Tower Scale-up 14-72

Diameter 14-72

Height 14-72

Loadings 14-73

Wetting 14-73

Underwetting 14-73

Preflooding 14-73

Sampling 14-73

Aging 14-73

Distributors 14-73

Liquid Distributors 14-73

Flashing Feed and Vapor Distributors 14-76

Other Packing Considerations 14-76

Liquid Holdup 14-76

Minimum Wetting Rate 14-79

Two Liquid Phases 14-79

High Viscosity and Surface Tension 14-80

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