Preface xvii
List of Abbreviations xxi
Nomenclature List xxi
1. Introduction 1
1.1 Definitions 1
1.2 Gas Markets, Gas Applications and Feedstock 3
1.3 Sizes 3
1.4 Units 4
1.5 Ambient Conditions 7
1.6 Objective of This Book 7
1.7 Example Problems 7
1.7.1 Synthesis Gas Plant 8
1.7.2 Natural Gas Treatment 9
1.7.3 Natural Gas Treatment for LNG 9
1.7.4 Flue Gas CO2 Capture from a CCGT Power Plant 9
1.7.5 Flue Gas CO2 Capture from a Coal Based Power Plant 11
1.7.6 CO2 Removal from Biogas 11
1.7.7 CO2 Removal from Landfill Gas 12
1.7.8 Summarising Plant Sizes Just Considered 12
References 13
2. Gas Treating in General 15
2.1 Introduction 15
2.2 Process Categories 16
2.2.1 Absorption 16
2.2.2 Adsorption 17
2.2.3 Cryogenics 19
2.2.4 LNG Trains 30
2.2.5 Membranes 36
2.3 Sulfur Removal 37
2.3.1 Scavengers 38
2.3.2 Adsorption 39
2.3.3 Direct Oxidation–Liquid Redox Processes 39
2.3.4 Claus Plants 41
2.3.5 Novelties 43
2.4 Absorption Process 43
References 45
3. Rate of Mass Transfer 49
3.1 Introduction 49
3.2 The Rate Equation 50
3.3 Co-absorption and/or Simultaneous Desorption 51
3.4 Convection and Diffusion 51
3.5 Heat Balance 51
3.6 Axially along the Column 52
3.7 Flowsheet Simulators 52
3.8 Rate versus Equilibrium Approaches 53
Further Reading 53
4. Chemistry in Acid Gas Treating 55
4.1 Introduction 55
4.2 ‘Chemistry’ 57
4.3 Acid Character of CO2 and H2S 63
4.4 The H2S Chemistry with any Alkanolamine 65
4.5 Chemistry of CO2 with Primary and Secondary Alkanolamines 65
4.5.1 Zwitterion Mechanism 66
4.5.2 Termolecular Mechanism of Crooks and Donnellan 67
4.5.3 Australian Approach 69
4.5.4 Older Representations 70
4.6 The Chemistry of Tertiary Amines 72
4.7 Chemistry of the Minor Sulfur Containing Gases 73
4.7.1 The COS Chemistry 74
4.7.2 Chemistry of CS2 76
4.7.3 Chemistry of Mercaptans (RSH) 77
4.8 Sterically Hindered Amines 78
4.9 Hot Carbonate Absorbent Systems 80
4.10 Simultaneous Absorption of H2S and CO2 82
4.11 Reaction Mechanisms and Activators–Final Words 82
4.12 Review Questions, Problems and Challenges 82
References 83
5. Physical Chemistry Topics 87
5.1 Introduction 87
5.2 Discussion of Solvents 87
5.3 Acid–Base Considerations 90
5.3.1 Arrhenius, Bronsted and Lewis 90
5.3.2 Weak and Strong Acids and Bases 91
5.3.3 pH 91
5.3.4 Strength of Acids and Bases 92
5.3.5 Titration 93
5.3.6 Buffer Action in the NaOH or KOH Based CO2 Absorbents 96
5.4 The Amine–CO2 Buffer System 98
5.5 Gas Solubilities, Henry’s and Raoult’s Laws 100
5.5.1 Henry’s Law 101
5.5.2 Gas Solubilities 103
5.5.3 Raoult’s Law 104
5.6 Solubilities of Solids 105
5.7 N2O Analogy 105
5.8 Partial Molar Properties and Representation 106
5.9 Hydration and Hydrolysis 107
5.10 Solvation 107
References 108
6. Diffusion 111
6.1 Dilute Mixtures 111
6.2 Concentrated Mixtures 114
6.3 Values of Diffusion Coefficients 116
6.3.1 Gas Phase Values 117
6.3.2 Liquid Phase Values 119
6.4 Interacting Species 121
6.5 Interaction with Surfaces 122
6.6 Multicomponent Situations 122
6.7 Examples 122
6.7.1 Gaseous CO2 –CH4 122
6.7.2 Gaseous H2O–CH4 123
6.7.3 Liquid Phase Diffusion of H2O in TEG 124
References 125
Further Reading 126
7. Absorption Column Mass Transfer Analysis 127
7.1 Introduction 127
7.2 The Column 128
7.3 The Flux Equations 128
7.4 The Overall Mass Transfer Coefficients and the Interface 129
7.4.1 Overall Gas Side Mass Transfer Coefficient 130
7.4.2 Overall Liquid Side Mass Transfer Coefficient 131
7.5 Control Volumes, Mass and Energy – Balances 132
7.5.1 The Relation between Gas and Liquid Concentrations 132
7.5.2 Height of Column Based on Gas Side Analysis 134
7.5.3 Height of Column Based on Liquid Side Analysis 134
7.6 Analytical Solution and Its Limitations 135
7.7 The NTU–HTU Concept 137
7.8 Operating and Equilibrium Lines – A Graphical Representation 138
7.9 Other Concentration Units 139
7.10 Concentrated Mixtures and Simultaneous Absorption 140
7.11 Liquid or Gas Side Control? A Few Pointers 143
7.12 The Equilibrium Stage Alternative Approach 144
7.13 Co-absorption in a Defined Column 145
7.14 Numerical Examples 146
7.14.1 Ammonia Train CO2 Removal with Sepasolv, NTUs 146
7.14.2 Ammonia Train CO2 Removal with Selexol, NTUs 148
7.14.3 Ammonia Train CO2 Removal with Selexol, NTUs by Numerical Integration 149
References 151
8. Column Hardware 153
8.1 Introduction 153
8.2 Packings 154
8.2.1 Types of Random Packings 155
8.2.2 Types of Structured Packings 157
8.2.3 Fluid Flow Design for Packings 157
8.2.4 Operational Considerations 162
8.3 Packing Auxiliaries 162
8.3.1 Liquid Distributors 162
8.3.2 Liquid Redistributors 163
8.3.3 Packing Support 164
8.3.4 Hold-Down Plate 165
8.4 Tray Columns and Trays 165
8.4.1 Types of Trays 167
8.4.2 Functional Parts of a Tray Column 167
8.4.3 Capacities and Limitations 168
8.4.4 Flow Regimes on Trays 169
8.4.5 Tray Column Efficiencies 170
8.5 Spray Columns 170
8.6 Demisters 170
8.6.1 Knitted Wire Mesh Pads 172
8.6.2 Vanes or Chevrons 172
8.7 Examples 173
8.7.1 The Sepasolv Example from Chapter 7 173
8.7.2 The Selexol Example from Chapter 7 174
8.7.3 Natural Gas Treating Example 175
8.7.4 Example, Flue Gas from CCGT 176
References 178
Further Reading 179
9. Rotating Packed Beds 181
9.1 Introduction 181
9.2 Flooding and Pressure Drop 183
9.3 Fluid Flow 184
9.4 Mass Transfer Correlations 184
9.5 Application to Gas Treating 187
9.5.1 Absorption 188
9.5.2 Desorption 188
9.6 Other Salient Points 189
9.7 Challenges Associated with Rotating Packed Beds 189
References 189
10. Mass Transfer Models 193
10.1 The Film Model 193
10.2 Penetration Theory 195
10.3 Surface Renewal Theory 197
10.4 Boundary Layer Theory 198
10.5 Eddy Diffusion, ‘Film-Penetration’ and More 198
References 199
11. Correlations for Mass Transfer Coefficients 201
11.1 Introduction 201
11.2 Packings: Generic Considerations 201
11.3 Random Packings 202
11.4 Structured Packings 206
11.5 Packed Column Correlations 206
11.6 Tray Columns 211
11.7 Examples 212
11.7.1 Treatment of Natural Gas for CO2 Content 212
11.7.2 Atmospheric Flue Gas CO2 Capture 213
11.7.3 Treatment of Natural Gas for H2 O Content 214
11.7.4 Comparison of Correlations 215
References 218
Further Reading 221
12. Chemistry and Mass Transfer 223
12.1 Background 223
12.2 Equilibrium or Kinetics 223
12.3 Diffusion with Chemical Reaction 225
12.4 Reaction Regimes Related to Mass Transfer 226
12.4.1 Absorption with Slow Reaction 226
12.4.2 Fast First Order Irreversible Reaction 227
12.4.3 Instantaneous Irreversible Reaction 230
12.4.4 Instantaneous Reversible Reaction 234
12.4.5 Second Order Irreversible Reaction 242
12.5 Enhancement Factors 243
12.5.1 Transition from Slow to Fast Reaction 245
12.6 Arbitrary, Reversible Reactions and/or Parallel Reactions 246
12.7 Software 247
12.8 Numerical Examples 248
12.8.1 Natural Gas Problem with MEA 248
12.8.2 Flue Gas Problem 250
12.8.3 Natural Gas Problem Revisited with MDEA 251
References 253
Further Reading 254
13. Selective Absorption of H2S 255
13.1 Background 255
13.2 Theoretical Discussion of Rate Based Selectivity 256
13.3 What Fundamental Information is Available in the Literature? 258
13.3.1 Equilibrium Data 258
13.3.2 Rate and Selectivity Research Data 259
13.4 Process Options and Industrial Practice 260
13.5 Key Design Points 262
13.6 Process Intensification 262
13.7 Numerical Example 262
References 264
14. Gas Dehydration 267
14.1 Background 267
14.2 Dehydration Options 268
14.3 Glycol Based Processes 269
14.4 Contaminants and Countermeasures 273
14.5 Operational Problems 274
14.6 TEG Equilibrium Data 274
14.7 Hydrate Inhibition in Pipelines 276
14.8 Determination of Water 276
14.9 Example Problems 277
14.9.1 Example 1: Check for Hydrate Potential 277
14.9.2 Example 2: TEG and Water Balance 277
14.9.3 Example 3: Tower Diameter 279
14.9.4 Example 4: Mass Transfer Resistances 279
References 280
15. Experimental Techniques 283
15.1 Introduction 283
15.2 Experimental Design 283
15.3 Laminar Jet 285
15.3.1 Background 285
15.3.2 Principle and Experimental Layout 286
15.3.3 Mathematics and Practicalities 287
15.3.4 Past Users 288
15.4 Wetted Wall 289
15.4.1 Background 289
15.4.2 Mathematics and Practicalities 290
15.4.3 Past Users 290
15.5 Single Sphere 291
15.5.1 Background 291
15.5.2 Principle and Experimental Layout 291
15.5.3 Mathematics and Practicalities 293
15.5.4 Past Users 293
15.6 Stirred Cell 293
15.6.1 Background 293
15.6.2 Principle and Experimental Layout 293
15.6.3 Mathematics and Practicalities 294
15.6.4 Past Users 295
15.7 Stopped Flow 295
15.7.1 Background 295
15.7.2 Principle and Experimental Layout 295
15.7.3 Mathematics and Practicalities 297
15.7.4 Past Users 297
15.8 Other Mass Transfer Methods Less Used 298
15.8.1 Rapid Mixing 298
15.8.2 Rotating Drum 298
15.8.3 Moving Band 298
15.8.4 Kinetic Measurement Techniques Summarised 298
15.9 Other Techniques in Gas–Liquid Mass Transfer 300
15.10 Equilibrium Measurements 300
15.10.1 Physical Solubilities 300
15.10.2 Chemical Solubilities 301
15.11 Data Interpretation and Sub-Models 303
References 303
16. Absorption Equilibria 307
16.1 Introduction 307
16.2 Fundamental Relations 308
16.3 Literature Data Reported 311
16.4 Danckwerts–McNeil 312
16.5 Kent–Eisenberg 313
16.6 Deshmukh–Mather 313
16.7 Electrolyte NRTL (Austgen–Bishnoi–Chen–Rochelle) 314
16.8 Li–Mather 314
16.9 Extended UNIQUAC 315
16.10 EoS – SAFT 315
16.11 Other Models 316
References 316
17. Desorption 319
17.1 Introduction 319
17.2 Chemistry of Desorption 322
17.2.1 Zwitterion Based Analysis 323
17.2.2 Crooks–Donnellan 323
17.2.3 Alternative Mechanisms 323
17.2.4 For Tertiary Amines 324
17.2.5 H2S Desorption 324
17.3 Kinetics of Reaction 324
17.4 Bubbling Desorption 325
17.5 Desorption Process Analysis and Modelling 327
17.6 Unconventional Approaches to Desorption 328
References 329
18. Heat Exchangers 333
18.1 Introduction 333
18.2 Reboiler 333
18.2.1 Introduction 333
18.2.2 Heat Media 333
18.2.3 Kettle Reboiler Design 334
18.2.4 Reboiler Specifics 336
18.2.5 Alternatives to Kettle Reboiler 336
18.3 Desorber Overhead Condenser 337
18.3.1 Introduction 337
18.3.2 The Reflux System 337
18.3.3 The Condenser Design 337
18.3.4 Alternatives 338
18.4 Economiser or Lean/Rich Heat Exchanger 338
18.4.1 Introduction 338
18.4.2 Design Considerations 339
18.5 Amine Cooler 341
18.6 Water Wash Circulation Cooler 341
18.7 Heat Exchanger Alternatives 341
References 342
Further Reading 343
19. Solution Management 345
19.1 Introduction 345
19.2 Contaminant Problem 346
19.3 Feed Gas Pretreatment 346
19.4 Rich Absorbent Flash 348
19.5 Filter 348
19.5.1 Active Carbon Filter 349
19.5.2 Mechanical Filter 350
19.6 Reclaiming 351
19.6.1 Traditional Reclaiming 351
19.6.2 Ion Exchange Reclaiming 352
19.6.3 Electrodialysis Reclaiming 353
19.7 Chemicals to Combat Foaming 353
19.8 Corrosion Inhibitors 355
19.9 Waste Handling 355
19.10 Solution Containment 355
19.11 Water Balance 355
19.12 Cleaning the Plant Equipment 356
19.13 Final Words on Solution Management 356
References 356
20. Absorption–Desorption Cycle 359
20.1 The Cycle and the Dimensioning Specifications 359
20.2 Alternative Cycle Variations 362
20.3 Other Limitations 364
20.4 Matching Process and Treating Demands 365
20.5 Solution Management 366
20.6 Flowsheet Variations to Save Desorption Energy 368
References 369
21. Degradation 371
21.1 Introduction to Degradation 371
21.2 Carbamate Polymerisation 372
21.3 Thermal Degradation 372
21.4 Oxidative Degradation 373
21.5 Corrosion and Degradation 373
21.6 The Effect of Heat Stable Salts (HSSs) 373
21.7 SOx and NOx in Feed Gas 373
21.8 Nitrosamines 374
21.9 Concluding Remarks 374
References 374
22. Materials, Corrosion, Inhibitors 375
22.1 Introduction 375
22.2 Corrosion Basics 376
22.3 Gas Phase 377
22.4 Protective Layers and What Makes Them Break Down (Chemistry) 378
22.5 Fluid Velocities and Corrosion 378
22.6 Stress Induced Corrosion 379
22.7 Effect of Heat Stable Salts (HSS) 379
22.8 Inhibitors 379
22.9 Problem Areas, Observations and Mitigation Actions 380
References 380
23. Technological Fronts 383
23.1 Historical Background 383
23.2 Fundamental Understanding and Absorbent Trends 384
23.3 Natural Gas Treating 385
23.4 Syngas Treating 385
23.5 Flue Gas Treating 386
23.6 Where Are We Heading? 386
References 387
24. Flue Gas Treating 389
24.1 Introduction 389
24.2 Pressure Drop and Size Issues 390
24.3 Absorbent Degradation 390
24.4 Treated Gas as Effluent 390
24.5 CO2 Export Specification 391
24.6 Energy Implications 391
24.7 Cost Issues 392
24.8 The Greenhouse Gas Problem 394
24.8.1 Global Warming and Increased Level of CO2 394
24.8.2 Geological Storage 395
24.8.3 Transport of CO2 395
24.8.4 Political Challenges 395
References 396
Web Sites 396
25. Natural Gas Treating (and Syngas) 397
25.1 Introduction 397
25.2 Gas Export Specification 398
25.3 Natural Gas Contaminants and Foaming 398
25.4 Hydrogen Sulfide 399
25.5 Regeneration by Flash 399
25.6 Choice of Absorbents 399
Further Reading 400
26. Treating in Various Situations 401
26.1 Introduction and Environmental Perspective 401
26.2 End of Pipe Solutions 401
26.3 Sulfur Dioxide 402
26.4 Nitrogen Oxides 402
26.5 Dusts and Aerosols 403
26.6 New Challenges 403
Index 405
