Gas Treating

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, Brønsted 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