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Gas Treating: Absorption Theory and Practice

Gas Treating: Absorption Theory and Practice

Dag Eimer

ISBN: 978-1-118-87773-9

Nov 2014

440 pages

In Stock

$155.00

Description

Gas Treating: Absorption Theory and Practice provides an introduction to the treatment of natural gas, synthesis gas and flue gas, addressing why it is necessary and the challenges involved. The book concentrates in particular on the absorption–desorption process and mass transfer coupled with chemical reaction.

Following a general introduction to gas treatment, the chemistry of CO2, H2S and amine systems is described, and selected topics from physical chemistry with relevance to gas treating are presented. Thereafter the absorption process is discussed in detail, column hardware is explained and the traditional mass transfer model mechanisms are presented together with mass transfer correlations. This is followed by the central point of the text in which mass transfer is combined with chemical reaction, highlighting the associated possibilities and problems. Experimental techniques, data analysis and modelling are covered, and the book concludes with a discussion on various process elements which are important in the absorption–desorption process, but are often neglected in its treatment. These include heat exchange, solution management, process flowsheet variations, choice of materials and degradation of absorbents. The text is rounded off with an overview of the current state of research in this field and a discussion of real-world applications.

This book is a practical introduction to gas treating for practicing process engineers and chemical engineers working on purification technologies and gas treatment, in particular, those working on CO2 abatement processes, as well as post-graduate students in process engineering, chemical engineering and chemistry.

Preface xvii

List of Abbreviations xxi

Nomenclature List xxv

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 H2O 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