AVOIDING FRACTIONATION PITFALLS

Vapor-liquid equilibrium (VLE): key concepts and simulation traps. Should we believe the simulation? Issues with close-boilers and non-idealities: why some heavy components go up while the simulation thinks they go down. VLE data: to trust or not to trust? Are distillation trays ideal stages? Reflux stages relationship. Multi-component distillation: composition profiles, side draws, accumulation, and cycling problems. What you need to watch out for.

TROUBLESHOOTING DISTILLATION SIMULATIONS

Does your simulation reflect the real world? How poor simulation leads to incorrect problem diagnosis. What validation checks are needed? How far should we go? Sensitivity analysis and graphics for simulation troubleshooting: useful hints.

TRAY HYDRAULICS & LIMITS

Visualization of vapor-liquid dispersions on trays, flooding, entrainment, weeping, dumping. Flood mechanisms: jet (entrainment), system limit, downcomer backup, downcomer choke. Which one limits your tower capacity? Common tray types: sieve, moving valve, fixed valve, sheds: pros and cons. Which works well in fouling applications? Small holes, valves: benefits and traps. Flood: what causes it, what affects it, and how predicted. Are the predictions reliable? Tray efficiency: are simulation predictions reliable? Can it be enhanced by tray modification?

TROUBLESHOOTING TRAY TOWERS

Gamma scans: application for diagnosing flood, missing and damaged trays, foaming, and downcomer flooding. How to combine gamma scans with process checks to get the most out of the scans: the four keys to success. Do gamma scans ever lie? Flooding and foaming symptoms: high dP’s, reduced bottoms, others. Which can be trusted? Liquid and vapor sensitivity field tests: identifying the correct flood mechanism. Downcomer unsealing and tray dryout: when would they affect your tower and how prevented.

TROUBLESHOOTING PACKED TOWERS

Rules of thumb for flood pressure drop and packing efficiency. Simulation hydraulic calculations: to trust or not to trust? Grid gamma scanning for detecting maldistribution, damage, distributor malfunction, distributor and collector overflow. Distributor overflow: DEATH for packed beds. Some do’s and don’ts for distributors. Can poor distributor feeding bottleneck towers? Circumferential surface temperature surveys: how to conduct, what to avoid, and the hidden secrets they reveal.

DEBOTTLENECKING

State-of-the-art trays & packings: strengths and weaknesses. Factors that favor trays and factors that favor packings. The pressure drop bonanza: why packings win in non-fouling vacuum services and in compressor suction. Pitfalls unique to structured packings: high pressure application, oxidation, shutdown fires. High-capacity trays (e.g. Superfrac, VG Plus, MD): principles, tricks, and traps. Do they really give 30% more capacity than conventionals?

DISTILLATION CONTROL

Assembling control loops into an overall scheme: what works, which is better, what causes instability, and what impairs efficiency. The 3 most common causes of control assembly failure: no material balance control, fighting between temperature controllers, and level control on a small stream. Tips for avoiding problems. Can controls affect revamp success? Best temperature control location: is there a reliable method for finding? How can a temperature controller be fooled? Reboiler, condenser, and pressure controls: which loops work and which misbehave. How dead pockets in vapor overhead lines interfere with controls. Understanding hot vapor bypasses: why some work while others don’t. Control systems that did not work.

AVOIDING TOWER MALFUNCTIONS

The 20 most common causes of distillation malfunctions: what trouble should we look for and prevent. Points of transition (feeds, draws, tower base): why these are some of the worst tower bottlenecks: how diagnosed and remedied. High tower base levels: how Your answer to increasing operating efficiency, reducing costs, and promoting trouble-free column operations they induce premature flood, even tray/packing damage, and how you can prevent. Instrument issues at the tower base: what to watch out for. Tray/packing damage: pressure surges due to water entering a tower full of hot oil or insoluble organics, other sources of tray damage and ways to avoid. Some commissioning and startup watchouts: pre-startup inspection, blinding and unblinding, reverse flow, steam-water operation, washing, rapid pressuring/depressuring, drawing vacuum, introducing liquid. Liquid outlets: choking in sidedraw rundown lines and how it restricts tower capacity. Why must self-venting flow be assured in the presence of entrained vapor? Siphon formation.

Case studies

These operating experiences will be scattered throughout to illustrate the key principles and to distinguish good from bad practices.

OPTIONAL HALF DAY SESSION
SPECIAL REFINERY CONSIDERATIONS

(Begins Immediately After Lunch On The Last Day)

Overlaps, gaps, cut points: how they reflect separation quality. Functions of various sections of refinery fractionators: fractionation, pumparound, wash, stripping. Which sections are prone to damage, coking, salting out and which are generally well-behaved. Why preflash drums are used and what are their issues. Pumparound (PA) duty: how does it affect the tower? Shifting duty between PA’s: can maximizing PA destabilize a tower? Vacuum crude towers: how much wash keeps packing wet? True vs. measured overflash. Can tall or efficient wash beds impair capacity or lead to coking? Mass and heat balance troubleshooting: drawing the correct envelopes. Leak/overflow detection: the symptom of low temperature while making more heavy distillate. Checking sprays: plugged? broken? Simple tests that teach a lot.

HENRY Z. KISTER is a leading global distillation expert with over 25 years of vast expertise in all phases of distillation, including troubleshooting, operation, design, start-up, and control. As a director of fractionation technology at Fluor, he designs, revamps and advises on distillation processes, equipment, and controls for the chemical, petrochemical and oil industries. He is also extensively involved in field consulting, start-up and troubleshooting. He is Fluor’s representative on the Fractionation Research Inc. (FRI) Advisory Committee and serves on FRI’s Design Practices Committee.

Before joining Fluor in 1999, he was Brown & Root’s staff consultant on fractionation. He provided clients for over 17 years with designs, debottlenecks, troubleshooting expertise and field assistance on fractionation and absorption technology. Before that, he was with FRI, where he specialized in fractionator hydraulics. Prior to that, he was with ICI Australia Ltd., where his duties included startup supervision, operation, debottlenecking, process and hydraulic design, troubleshooting, and commissioning of several distillation systems.

He is the author of over 140 technical articles on distillation, and two textbooks titled, Distillation Operation and Distillation Design both published by McGraw-Hill. He is also the author of the textbook, Distillation Troubleshooting, published by Wiley.

Henry Kister has conducted over 550 “Practical Distillation Technology” programs for major corporations in the U.S., Canada and overseas.