Distillation Diagnostics: An Engineer's Guidebook

Thorough guide on how to use various diagnostic techniques to troubleshoot problems in distillation columns Distillation Diagnostics familiarizes the reader with the multitude of tools available for diagnosing distillation and absorption tower problems and provides the reader with application guidelines derived from 40+ years of real-world experiences of the author. The book describes the capabilities, strengths and limitations of each tool, provides guidance on how to apply these tools to get the most insight and to test theories and ideas, shares the experience of how to correctly interpret the results provided by each technique, and guides the reader to a multitude of additional testing that they can perform to bring them closer to a correct diagnosis and an effective fix. Each technique is illustrated with real case studies and an extensive “dos and don’ts” list. Written by a global authority on distillation diagnostics and troubleshooting known as ‘The Tower Doctor’ by many in the field, Distillation Diagnostics includes information on: Possible solutions to the growing distillation failure rate despite the tremendous recent advances in distillation technologies Time-tested tools and techniques for correctly diagnosing distillation problems to provide simple low-cost fixes instead of unnecessary wasteful solutions, thus eliminating waste and dramatically reducing CAPEX, energy consumption and carbon footprint Combining the various diagnostic techniques to discard wrong theories and narrow in on the correct root cause and proper solution for various tower malfunctions Diagnosing flooding, foaming, plugging, weeping, maldistribution, channeling, distributor and collector overflows, low efficiencies, feeds and draws bottlenecks, assembly mishaps, tower internals damage, high base level issues, reactions in towers, contaminants, internal and external leaks, startup and/or shutdown difficulties Correctly interpreting gamma scan, thermal scan, and pressure drop data Getting the most out of testing techniques such as gamma scanning, neutron backscatter, wall temperature surveys, pressure drop measurements, column testing, sketching points of transition, collecting data for simulations, conducting mass and energy balances, analyzing operating charts, and in-situ water testing Turnaround tower inspections: what to look for Advanced gamma scanning and thermal scanning techniques and when to apply The “doctor and patient” troubleshooting strategy, which often constitutes the most effective, most systematic, and least expensive course of action Things to remember when formulating and testing theories, such as the balance between theory, data, the laws of physics, and chemistry Distillation Diagnostics is a timely, essential reference on the subject for plant managers and operators, production and startup supervisors, and chemical, process, and design engineers.

Table of Contents:
Preface xv List of Acronyms xix Acknowledgments xxi 1. Troubleshooting Steps 1 1.1 Causes of Column Malfunctions 2 1.2 Column Troubleshooting – a Case History 4 1.3 Strategy for Troubleshooting Distillation Problems 6 1.4 Dos and Don’ts for Formulating and Testing Theories 12 1.5 Learning to Troubleshoot 17 1.6 Classification of Column Problems 18 2. Troubleshooting for Flood 21 2.1 Flooding: The Most Common Tower Throughput Limitation 21 2.2 Flood Mechanisms in Tray and Packed Towers 22 2.3 Flood and Flood Mechanism Determination: Hydraulic Analysis 25 2.4 Operating Window (or Stability) Diagrams 27 2.5 Flood Point Determination: Field Testing 29 2.6 Flood Point Determination in The Field: The Symptoms 31 2.7 Flood Mechanism Determination: Vapor and Liquid Sensitivity Tests 43 2.7.1 Extension of Vapor/Liquid Sensitivity Tests to Complex Fractionators 44 2.8 Gaining Insight into The Cause of Flood From dP Versus Vapor Rate Plots 46 2.9 Diagnosing Floods that Give Small dP or No dP Rise 51 2.9.1 Flood Diagnosis in a Chemical Vacuum Tower with no dP Rise 53 2.9.2 Flood Diagnosis in Packed Pumparound (PA) Beds 54 2.10 Foam Flooding Symptoms and Testing 55 2.11 Downcomer Unsealing Floods at Low Liquid Loads 64 2.12 Channeling-Induced Premature Floods at High Liquid Loads 66 2.13 Floods by High Base Level or Entrainment From the Tower Base 67 2.14 Troubleshooting Intermediate Component Accumulation 71 2.15 Troubleshooting Liquid Side Draw Bottlenecks 74 2.16 Twelve Useful Rules of Thumb 77 3. Efficiency Testing and Separation Troubleshooting 81 3.1 Efficiency Testing for Troubleshooting 81 3.1.1 Purpose and Strategy of Efficiency Testing for Troubleshooting 81 3.1.2 Planning and Execution of Efficiency Testing for Troubleshooting 83 3.1.3 Preparations for Efficiency Testing 85 3.1.4 Last-Minute Preparations 97 3.1.5 The Test Day(s) 100 3.1.6 Processing the Results 100 3.1.7 Determining Hydraulic Loads 113 3.1.8 Hennigan’s Rules 115 3.2 Diagnosing Poor Separation 116 3.2.1 Troubleshoot for Process Leaks 116 3.2.2 Troubleshoot for Tray Weeping 120 3.2.3 Diagnosing Side Draw Liquid Starvation 122 3.2.4 Diagnosing Once-Through Reboiler Liquid Starvation 124 3.2.5 Troubleshoot for Liquid in Vapor Side Draws 125 3.2.6 Troubleshoot for Missing or Damaged Trays or Packing 125 3.2.7 Poor Material Balance Control Produces High Impurities 127 3.2.8 Limitations on Reflux or Reboil Generation 128 3.2.9 Control Instability Increases Impurities 129 3.2.10 Impurities and Contaminants Affecting Azeotroping and Product Purities 129 3.2.11 Absorption of Sparingly Soluble Gases Affecting Product Purity and Downstream Venting 130 3.2.12 Reactions and Contaminants Can Affect Product Purity 130 4. Diagnosing Packed Tower Maldistribution 135 4.1 Diagnosing Packing Maldistribution: an Overview 135 4.2 Expected Packing HETPS 137 4.3 Small-Scale Versus Large-Scale Maldistribution: Do They Equally Raise Hetp? 137 4.4 By How Much does Maldistribution Reduce Packing Efficiency? 138 4.5 Diagnosing Packing and Distributor Plugging 141 4.6 Troubleshooting for Distributor, Collector, and Parting Box Overflows 145 4.6.1 Overflows and Their Impact 145 4.6.2 Overflows in Distributors, Redistributors, and Parting Boxes 145 4.6.3 Overflows in Collectors 148 4.6.4 Overflows due to Plugging, Foaming, Impingement 150 4.7 Troubleshooting Maldistribution at Turndown 150 4.8 Troubleshooting Distributor Out-of-Levelness 151 4.9 Troubleshooting Distributor Feeds 153 4.10 Evaluation of Distributor Irrigation Quality 154 4.11 Troubleshooting for Vapor Maldistribution 158 4.12 Vapor Maldistribution in The Feed Zone to Refinery Vacuum Towers 161 4.13 Troubleshooting Flashing Feeds Entry 164 4.14 Troubleshooting Notched Distributors 167 4.15 Troubleshooting Spray Nozzle Distributors 169 4.16 Distributor Water Tests 173 4.16.1 Gravity Distributor Water Tests in the Supplier Shop 173 4.16.2 Gravity Distributor Water Tests In situ 175 5. Qualitative Gamma Scans Troubleshooting: The Basic Diagnostics Workhorse 179 5.1 Gamma-Ray Absorption 179 5.2 Qualitative Gamma Scans 180 5.2.1 What Do Qualitative Gamma Scans Show in Tray Towers 181 5.2.2 Entrainment versus Weeping 184 5.2.3 What Do Qualitative Gamma Scans Show in Packed Towers 185 5.2.4 Stationary Monitoring (“Time Studies”) 190 5.2.5 What is in the Tower Inlet/Outlet Pipes? 191 5.3 Gamma Scans Pitfalls and Watchouts 191 5.4 Gamma Scan Shortcuts: Cost Versus Benefits 195 5.4.1 Dry (Empty Column) Scans: Yes or No? 195 5.4.2 Initial Operation Scans (Often Referred to as Baseline Scans): Yes or No? 196 5.4.3 Changed Conditions Monitoring Scans 196 5.4.4 Performing Downcomer Scans: Yes or No? 196 5.4.5 Can We Learn More about the Bottleneck? 197 5.4.6 Would Our Proposed Modification Solve the Problem? 197 5.5 Some Applications of Qualitative Gamma Scans 197 5.5.1 Distinguishing Fact from Interpretation 197 5.5.2 Is the Flood a Jet Flood? 199 5.5.3 Diagnosing the Correct Flood Mechanism and Arriving at the Effective Fix 199 5.5.4 Does the Tower Flood Occur at the Expected Location? 202 5.5.5 Foaming or Not Foaming? 204 5.5.6 Insights into Fouling Patterns/Shortcuts Lead to Misinterpretations 209 5.5.7 Multipass Trays Maldistribution 211 5.5.8 Fouling-Induced Maldistribution in 2-Pass Trays 212 5.5.9 Weeping/Dense Liquid/Missing Trays 214 5.5.10 Plugging, Flood, and Fouling Monitoring in a Packed Bed 216 5.5.11 More Plugging and Flooding in a Packed Bed 221 5.5.12 Flood due to Crushed or Damaged Random Packings 221 5.5.13 Missing Random Packings 223 5.5.14 Displaced and Damaged Structured Packings 225 5.5.15 Flooding Induces Channeling in Deep Vacuum Packed Tower 225 5.5.16 Distributor Overflow and Maldistribution 228 5.5.17 Overflow, Entrainment, and Maldistribution from Flashing Feed Distributor 230 5.5.18 Tower Overfill due to Excessive Pressure Drop in Kettle Reboiler Piping 231 5.5.19 Is a Collector (or Chimney Tray) Overflowing? Does this Initiate Flooding? 233 5.5.20 Damaged or Dry Trays? 233 6. Advanced Radioactive Techniques for Distillation Troubleshooting 237 6.1 Quantitative Multi-Chordal Tray Gamma Scans Analysis 237 6.1.1 Harrison’s Method for Froth Height and Flood Determination 238 6.1.2 Application of Harrison’s Method Prevents Unnecessary Shutdown 241 6.1.3 Entrainment Index 243 6.1.4 Kistergrams and their Application 244 6.1.5 Froth (or Spray) Density and Liquid Head Determination 246 6.1.6 Quantitative Analysis for High-Capacity Trays with Truncated Downcomers 248 6.1.7 Scan Chord Selection 251 6.2 Quantitative Analysis of Packing Gamma Scans 256 6.2.1 Packed Tower Quantitative Analysis Techniques 256 6.2.2 Flooding at the Bottom or Missing Packing Tower at the Top? 258 6.2.3 Dense Grid or Flooding/Coking in a Wash Bed? 259 6.2.4 Good or Bad Distribution Quality? 260 6.3 Neutron Backscatter Techniques Application 261 6.3.1 Detecting Flood and Seal Loss in Downcomers 263 6.3.2 Distinguishing Dry from Full Downcomers 264 6.3.3 Detecting Maldistribution in a Kettle Reboiler 264 6.4 CAT Scans 266 6.4.1 Identifying Unexpected Flashing in Reflux Distributor 268 6.4.2 Diagnosing Unexpected Parting Box Overflow 269 6.4.3 Monitoring Coking in a Refinery Vacuum Tower 269 6.5 Tracer Techniques 273 6.5.1 Measuring Flow Rates, Internal Leaks, and Spray Entrainment in Refinery Vacuum Tower 274 6.5.2 Observing Downward Vapor Flow in Packed Bed 275 6.5.3 Quantitative Determination of Entrainment from a Kettle Reboiler 277 6.6 Slant Scanning 280 6.7 Useful Case Histories Literature 283 6.7.1 Qualitative Gamma Scans of Trays 283 6.7.2 Qualitative Gamma Scans of Packings 284 6.7.3 Gamma Scans of Points of Transition and Inlet and Outlet Lines 284 6.7.4 Quantitative Gamma Scans of Trays 284 6.7.5 Quantitative Gamma Scans of Packings 285 6.7.6 Neutron Backscatter 285 6.7.7 CAT Scans 285 6.7.8 Tracer Technique 285 7. Thermal and Energy Troubleshooting 287 7.1 Wall Temperature Surveys 287 7.1.1 Dos and Don’ts for Temperature Surveys 288 7.1.2 Diagnosing Internals Damage 291 7.1.3 Diagnosing Packing Maldistribution 293 7.1.4 Time Study for Diagnosing the Nature of Instability 296 7.1.5 Diagnosing an Unexpected Second Liquid Phase 301 7.1.6 Diagnosing Poor Mixing in a Packing Distributor 304 7.1.7 Diagnosing Flashing in a Packing Distributor 305 7.1.8 Identifying Various Boiling Regions in a Kettle Reboiler 307 7.1.9 Identifying Plugging Zone in a Ladder Pipe Distributor 308 7.1.10 Identifying Uneven Quench Distribution in a Bottom Sump 309 7.1.11 Identifying Flood 309 7.2 Thermal Camera (Thermography) Applications 310 7.2.1 Dos and Don’ts for Thermal Camera Imaging 310 7.2.2 Diagnosing Packing Maldistribution 312 7.2.3 Diagnosing Vapor or Liquid Maldistribution in Insulated Towers 312 7.2.4 H 2 S Amine Absorber Temperature Profile, Foam, and Flooding 314 7.2.5 Temperature Bulges in CO 2 Amine Absorbers 316 7.2.6 Excessive Liquid Levels 318 7.2.7 Diagnosing a Flood due to Bottom Baffle Malfunction 318 7.2.8 Diagnosing a Damaged Draw Pan 321 7.2.9 Liquid Levels in Condensers and Reflux Drums 322 7.2.10 Troubleshooting Condensers and Reboilers 322 7.2.11 Thermal Video Diagnoses Cause of Pressure Instability 327 7.3 Energy Balance Troubleshooting 329 7.3.1 Energy Balance Application for Correctly Validating Simulations and Correctly Diagnosing Tower Problems 329 7.3.2 Energy Balance Troubleshooting to Detect Internal Leaks 332 7.3.3 Energy Balance Troubleshooting to Eliminate Overflows or Leaks in the Upper Parts of Chimneys 335 7.3.4 Energy Balance Troubleshooting of a Two-Compartment Chimney Tray 337 7.3.5 Leaks from Heat Exchangers: The Role of Mass and Energy Balance in their Troubleshooting 338 8. Point of Transition Troubleshooting: You Do Not Need an Expert, You Need a Sketch 343 8.1 Guidelines for Points of Transition Sketches 343 8.2 Flashing Feed Entry Causing a 12-Year Bottleneck 344 8.2.1 Upward Component of Flashing Feed Entry Causes Damage and Flooding 346 8.3 Feed Maldistribution to 4-Pass Trays Causing Poor Separation 347 8.4 Feed Pipes Blocking Liquid Entrance to Downcomers 349 8.5 Draw Sump Blocking Liquid Entrance to Downcomers 350 8.6 Unsealed Downcomers or Overflow Pipes Can Lead to Premature Flood 351 8.7 Excessive Downcomer Submergence Can Lead to Premature Flood 353 8.8 “Leak-Proof” Chimney Trays in an FCC Main Fractionator 354 8.9 More “Leak-Proof” Chimney Trays 355 8.10 Hydraulic Gradients Generating Chimney Tray Overflows 358 8.11 Look for the Possibility of a System Limit Setting In 359 8.12 Vapor Maldistribution at the Tower Base and Chimney Tray 362 8.13 Entrainment from a Gallery Flashing Feed Distributor 364 8.14 Vapor Impinging on Liquid at the Tower Base 365 8.15 More Vapor Impinging on Liquid at the Tower Base 366 8.16 V-Baffles Produce Unexpected Flow Pattern at the Tower Base 368 8.17 Baffling Tower Base Baffles 370 8.18 Liquid Maldistribution at a Feed or a Product Draw 372 8.19 Poor Solvent/Reflux Mixing Gives Poor Separation in Extractive Distillation (ED) Tower 376 8.20 Two Seemingly Well-Designed Pieces May Not Work Well When Combined 378 8.21 Another Two Seemingly Well-Designed Pieces that Did Not Work Well When Combined 380 8.22 Liquid Maldistribution of Internal Reflux Below a Side Draw 381 8.23 Would You Believe this was a Real Troubleshooting Assignment? 381 9. Making the Most of Field Data to Analyze Events and Test Theories 383 9.1 Event Timing Analysis 383 9.1.1 General Application Guidelines for Event Timing Analysis 383 9.1.2 Diagnosing the Unexpected Cause of Off-Spec Product 384 9.1.3 Diagnosing Reboiler Surging 386 9.1.4 Loss of Condensate Seal in a Demethanizer Reboiler 387 9.1.5 Figuring out Hot Vapor Bypass (HVB) Instability 388 9.1.6 Can Multiple Steady States Occur in a Reboiler System? 392 9.1.7 Can a Plugged Packing Distributor Generate Two Steady States? 395 9.1.8 What Caused Tray Damage in Refinery Atmospheric Crude Fractionator? 397 9.1.9 Event timing Analysis of Startup Instability Leads to Improved Startups 401 9.2 Field Testing 404 9.2.1 General Application Guidelines for Field Testing 404 9.2.2 Narrowing Down from 12 Theories to the Root Cause 405 9.2.3 Making Sense of Plant Data and Operation Experience in a Packed Tower 407 9.2.4 Downcomer Unsealing: A Correct Diagnosis Brings a Correct Cure 409 9.2.5 Well-Targeted Field Testing Brings a Correct Diagnosis and an Unexpected Simple Solution 413 9.2.6 Field Testing Brings a Correct Diagnosis where Engineering Analysis Failed 419 9.2.7 Operating Team Observations and Field Testing Brings a Correct Diagnosis where Engineering Analysis Failed 421 9.2.8 Lessons Learnt from Packed Tower History and Testing 422 10. Troubleshooting by Inspection 425 10.1 Safety Precautions for Work Inside The Column 426 10.2 Troubleshooting Starts with Preventive Practices During Installation 427 10.2.1 Preinstallation Dos and Don’ts for Tray Columns 427 10.2.2 Preinstallation Dos and Don’ts for Packed Towers 429 10.2.3 Removal of Existing Trays and Packings 432 10.2.4 Tray Installation 433 10.2.5 Dry versus Wet Random Packing Installation 435 10.2.6 Dos and Don’ts for Random Packing Installation 436 10.2.7 Dos and Don’ts for Structured Packing Installation 438 10.2.8 Some Considerations for Towers Out of Service for a Time 442 10.3 Tower Inspection: What to Look For 442 10.3.1 Strategy 442 10.3.2 Should the Tower be Entered at the Turnaround? 444 10.3.3 Inspector’s Checklist 445 10.3.4 Packing Distributor Checks 449 10.3.5 Packing Assembly Checks – Existing Columns 454 10.3.6 Untightened Nuts, Bolts, Clamps, and Downcomer Panel Assembly 455 10.3.7 Tray Assembly 457 10.3.8 Feeds/Draws Obstruction, Misorientation, and Poor Assembly 472 10.3.9 Cleanliness of Internals 481 10.3.10 Final Inspection 482 10.3.11 Externals Inspection 484 References 487 Index 513