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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
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.
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Veröffentlichungsjahr: 2024
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Table of Contents
Cover
Table of Contents
Title Page
Copyright
Dedication
Preface
List of Acronyms
Acknowledgments
Chapter 1: Troubleshooting Steps
1.1 CAUSES OF COLUMN MALFUNCTIONS
1.2 COLUMN TROUBLESHOOTING – A CASE HISTORY
1.3 STRATEGY FOR TROUBLESHOOTING DISTILLATION PROBLEMS
1.4 DOS AND DON’TS FOR FORMULATING AND TESTING THEORIES
1.5 LEARNING TO TROUBLESHOOT
1.6 CLASSIFICATION OF COLUMN PROBLEMS
NOTE
Chapter 2: Troubleshooting for Flood
2.1 FLOODING: THE MOST COMMON TOWER THROUGHPUT LIMITATION
2.2 FLOOD MECHANISMS IN TRAY AND PACKED TOWERS
2.3 FLOOD AND FLOOD MECHANISM DETERMINATION: HYDRAULIC ANALYSIS
2.4 OPERATING WINDOW (OR STABILITY) DIAGRAMS
2.5 FLOOD POINT DETERMINATION: FIELD TESTING
2.6 FLOOD POINT DETERMINATION IN THE FIELD: THE SYMPTOMS
2.7 FLOOD MECHANISM DETERMINATION: VAPOR AND LIQUID SENSITIVITY TESTS
2.8 GAINING INSIGHT INTO THE CAUSE OF FLOOD FROM P VERSUS VAPOR RATE PLOTS
2.9 DIAGNOSING FLOODS THAT GIVE SMALL P OR NO P RISE
2.10 FOAM FLOODING SYMPTOMS AND TESTING
2.11 DOWNCOMER UNSEALING FLOODS AT LOW LIQUID LOADS
2.12 CHANNELING-INDUCED PREMATURE FLOODS AT HIGH LIQUID LOADS
2.13 FLOODS BY HIGH BASE LEVEL OR ENTRAINMENT FROM THE TOWER BASE
2.14 TROUBLESHOOTING INTERMEDIATE COMPONENT ACCUMULATION
2.15 TROUBLESHOOTING LIQUID SIDE DRAW BOTTLENECKS
2.16 TWELVE USEFUL RULES OF THUMB
Chapter 3: Efficiency Testing and Separation Troubleshooting
3.1 EFFICIENCY TESTING FOR TROUBLESHOOTING
3.2 DIAGNOSING POOR SEPARATION
Chapter 4: Diagnosing Packed Tower Maldistribution
4.1 DIAGNOSING PACKING MALDISTRIBUTION: AN OVERVIEW
4.2 EXPECTED PACKING HETPS
4.3 SMALL-SCALE VERSUS LARGE-SCALE MALDISTRIBUTION: DO THEY EQUALLY RAISE HETP?
4.4 BY HOW MUCH DOES MALDISTRIBUTION REDUCE PACKING EFFICIENCY?
4.5 DIAGNOSING PACKING AND DISTRIBUTOR PLUGGING
4.6 TROUBLESHOOTING FOR DISTRIBUTOR, COLLECTOR, AND PARTING BOX OVERFLOWS
4.7 TROUBLESHOOTING MALDISTRIBUTION AT TURNDOWN
4.8 TROUBLESHOOTING DISTRIBUTOR OUT-OF-LEVELNESS
4.9 TROUBLESHOOTING DISTRIBUTOR FEEDS
4.10 EVALUATION OF DISTRIBUTOR IRRIGATION QUALITY
4.11 TROUBLESHOOTING FOR VAPOR MALDISTRIBUTION
4.12 VAPOR MALDISTRIBUTION IN THE FEED ZONE TO REFINERY VACUUM TOWERS
4.13 TROUBLESHOOTING FLASHING FEEDS ENTRY
4.14 TROUBLESHOOTING NOTCHED DISTRIBUTORS
4.15 TROUBLESHOOTING SPRAY NOZZLE DISTRIBUTORS
4.16 DISTRIBUTOR WATER TESTS
Chapter 5: Qualitative Gamma Scans Troubleshooting: The Basic Diagnostics Workhorse
5.1 GAMMA-RAY ABSORPTION
5.2 QUALITATIVE GAMMA SCANS
5.3 GAMMA SCANS PITFALLS AND WATCHOUTS
5.4 GAMMA SCAN SHORTCUTS: COST VERSUS BENEFITS
5.5 SOME APPLICATIONS OF QUALITATIVE GAMMA SCANS
Chapter 6: Advanced Radioactive Techniques for Distillation Troubleshooting
6.1 QUANTITATIVE MULTI-CHORDAL TRAY GAMMA SCANS ANALYSIS
6.2 QUANTITATIVE ANALYSIS OF PACKING GAMMA SCANS
6.3 NEUTRON BACKSCATTER TECHNIQUES APPLICATION
6.4 CAT SCANS
6.5 TRACER TECHNIQUES
6.6 SLANT SCANNING
6.7 USEFUL CASE HISTORIES LITERATURE
Chapter 7: Thermal and Energy Troubleshooting
7.1 WALL TEMPERATURE SURVEYS
7.2 THERMAL CAMERA (THERMOGRAPHY) APPLICATIONS
7.3 ENERGY BALANCE TROUBLESHOOTING
Chapter 8: Point of Transition Troubleshooting: You Do Not Need an Expert, You Need a Sketch
8.1 GUIDELINES FOR POINTS OF TRANSITION SKETCHES
8.2 FLASHING FEED ENTRY CAUSING A 12-YEAR BOTTLENECK
8.3 FEED MALDISTRIBUTION TO 4-PASS TRAYS CAUSING POOR SEPARATION
8.4 FEED PIPES BLOCKING LIQUID ENTRANCE TO DOWNCOMERS
8.5 DRAW SUMP BLOCKING LIQUID ENTRANCE TO DOWNCOMERS
8.6 UNSEALED DOWNCOMERS OR OVERFLOW PIPES CAN LEAD TO PREMATURE FLOOD
8.7 EXCESSIVE DOWNCOMER SUBMERGENCE CAN LEAD TO PREMATURE FLOOD
8.8 “LEAK-PROOF” CHIMNEY TRAYS IN AN FCC MAIN FRACTIONATOR
8.9 MORE “LEAK-PROOF” CHIMNEY TRAYS
8.10 HYDRAULIC GRADIENTS GENERATING CHIMNEY TRAY OVERFLOWS
8.11 LOOK FOR THE POSSIBILITY OF A SYSTEM LIMIT SETTING IN
8.12 VAPOR MALDISTRIBUTION AT THE TOWER BASE AND CHIMNEY TRAY
8.13 ENTRAINMENT FROM A GALLERY FLASHING FEED DISTRIBUTOR
8.14 VAPOR IMPINGING ON LIQUID AT THE TOWER BASE
8.15 MORE VAPOR IMPINGING ON LIQUID AT THE TOWER BASE
8.16 V-BAFFLES PRODUCE UNEXPECTED FLOW PATTERN AT THE TOWER BASE
8.17 BAFFLING TOWER BASE BAFFLES
8.18 LIQUID MALDISTRIBUTION AT A FEED OR A PRODUCT DRAW
8.19 POOR SOLVENT/REFLUX MIXING GIVES POOR SEPARATION IN EXTRACTIVE DISTILLATION (ED) TOWER
8.20 TWO SEEMINGLY WELL-DESIGNED PIECES MAY NOT WORK WELL WHEN COMBINED
8.21 ANOTHER TWO SEEMINGLY WELL-DESIGNED PIECES THAT DID NOT WORK WELL WHEN COMBINED
8.22 LIQUID MALDISTRIBUTION OF INTERNAL REFLUX BELOW A SIDE DRAW (275)
8.23 WOULD YOU BELIEVE THIS WAS A REAL TROUBLESHOOTING ASSIGNMENT?
Chapter 9: Making the Most of Field Data to Analyze Events and Test Theories
9.1 EVENT TIMING ANALYSIS
9.2 FIELD TESTING
Chapter 10: Troubleshooting by Inspection
10.1 SAFETY PRECAUTIONS FOR WORK INSIDE THE COLUMN
10.2 TROUBLESHOOTING STARTS WITH PREVENTIVE PRACTICES DURING INSTALLATION
10.3 TOWER INSPECTION: WHAT TO LOOK FOR
References
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Most common causes of column malfunctions. (From Kister, H. Z., Tr...
Chapter 2
Table 2.1 Demethanizer hydraulic analysis that diagnosed tower problem. (Fro...
Chapter 3
Table 3.1 Data collection summary for a C
3
stripper tower.
Table 3.2 Checklist for troubleshooting nonclosure of material, component, a...
Table 3.3 Internal flow rates from tower simulation. (From Kister, H. Z., “P...
Chapter 5
Table 5.1 Hydraulic calculations.
Table 5.2 Hydraulic calculations.
Chapter 9
Table 9.1 Tests of shutting the kero drawoff (243).
Chapter 10
Table 10.1 Maximum acceptable tray ring width left in a tower retrofitted fr...
Table 10.2 Assembly Mishaps (198).
Table 10.3 Column inspection checklist.
List of Illustrations
Chapter 1
Figure 1.1 Column troubleshooting case history. (a) Hot oil from the fractio...
Chapter 2
Figure 2.1 Unflooded and Flooded Tray (a) Unflooded, froth height about 12 i...
Figure 2.2 Downcomer backup in heads of clear liquid. (Copyright © FRI. Repr...
Figure 2.3 Example of a Tray Operating Window Diagram, showing the hard limi...
Figure 2.4 Distillation tower with reflux on flow control and temperature co...
Figure 2.5 Plots of pressure drop versus vapor flow rate for tray column....
Figure 2.6 Typical pressure drop versus vapor flow rate for packed tower....
Figure 2.7 Pressure drop profile obtained with high-speed multichannel strip...
Figure 2.8 Pressure drop measurement locations in one complex tower (the upp...
Figure 2.9 Pressure drop fluctuations due to foam-flooding of a chemical tow...
Figure 2.10 Bottom level and Tray 10 temperature fluctuations upon incipient...
Figure 2.11 Typical distillation column overhead systems (a) reflux drum lev...
Figure 2.12 Typical refinery fractionator distillation column overhead with ...
Figure 2.13 Overall tray efficiency, four foot ID tower, at total reflux, il...
Figure 2.14 Flooded and unflooded tower temperature profiles. The flooded tr...
Figure 2.15 Liquid and vapor sensitivity test in a refinery fractionator (a)...
Figure 2.16 Application of plots of pressure drop versus vapor flow rate to ...
Figure 2.17 Use of dP logs to diagnose tower problems (a) plugged downcomer,...
Figure 2.18 Application of plots of pressure drop versus vapor flow rate to ...
Figure 2.19 Application of pressure drop versus vapor flow rate plot to trac...
Figure 2.20 Application of pressure drop versus vapor flow rate plot to a to...
Figure 2.21 Application of plots of pressure drop versus vapor flow rate to ...
Figure 2.22 Typical operating charts for flood near the top of a tower (a) m...
Figure 2.23 Pressure drop versus gas rate data collected over two months for...
Figure 2.24 Data analysis to diagnose flood in a packed deep vacuum tower (a...
Figure 2.25 Foam in Structured Packing.
Figure 2.26 Symptoms of foaming (a) a typical differential pressure chart, i...
Figure 2.27 Reflux entry into towers with foaming systems (a) dropping the r...
Figure 2.28 Testing for foam (a) an apparatus for dispersing gas through a s...
Figure 2.29 Foaming tests, antifoams screened and tested and a suitable one ...
Figure 2.30 Inlet contamination foaming in an amine absorber (a) lean amine ...
Figure 2.31 Flow Patterns on trays (a) froth regime (liquid phase is continu...
Figure 2.32 Downcomer Unsealing Flood in the spray regime (a) vapor distribu...
Figure 2.33 Vapor cross flow channeling (VCFC) on trays.
Figure 2.34 (a) Liquid level above reboiler return, but level instrument fai...
Figure 2.35 Practices to be avoided. Each of these can lead to premature flo...
Figure 2.36 Minor high-boiling impurity in the feed, 2 ppm, that forms a het...
Figure 2.37 Side draw-off arrangements (a) likely to initiate flooding at ex...
Figure 2.38 Examples of liquid draws from a chimney tray. The residence time...
Figure 2.39 The O’Connel plot for tray efficiency.
Chapter 3
Figure 3.1 Relatively small amount of intermediate component can build up to...
Figure 3.2 Ultrasonic flow meter installed too close to pipe fittings.
Figure 3.3 Flag sheet comparing measured test data (red) with simulated valu...
Figure 3.4 Direct effect of errors in relative volatility on errors in tray ...
Figure 3.5 Indirect effects of errors in relative volatility on the value ca...
Figure 3.6 Feed entry simulation with two feeds. (a) Incorrect, as flash dru...
Figure 3.7 Temperature and concentration profile in an ethylbenzene–styrene ...
Figure 3.8 Efficiency sensitivity checks, stripping section of a depentanize...
Figure 3.9 As minimum reflux is approached, the column efficiency cannot be ...
Figure 3.10 Invaluable checks of the validity and sensitivity of efficiency ...
Figure 3.11 Comparing simulated TBP to test data for side products HVGO, slo...
Figure 3.12 A sketch leads to the correct internal flow rates from the tower...
Figure 3.13 C
2
splitter tower, showing the d
P
bypass.
Figure 3.14 C
4
splitter tower, showing the connections to the storage tanks....
Figure 3.15 Typical amine absorber–regenerator scheme.
Figure 3.16 Starving a liquid draw. (a) Draw starved when weeping exceeds th...
Figure 3.17 Once-through thermosiphon arrangements. (a) Trapout. (b) Chimney...
Figure 3.18 A vapor side draw (two nozzles in four-pass trays) that experien...
Figure 3.19 A control system violating the material balance control principl...
Figure 3.20 Nitrogen absorbed by the liquid in a newly added debutanizer fee...
Chapter 4
Figure 4.1 Two common types of packing liquid distributors (a) an orifice pa...
Figure 4.2 Effect of irrigation quality on packing efficiency. (a) Case hist...
Figure 4.3 Lockett and Billingham’s model for efficiency loss due to maldist...
Figure 4.4 Samples of a tower feed stream (1, 2, and 3), showing coloration....
Figure 4.5 Wall perforations in a trough distributor. The distributor liquid...
Figure 4.6 Packing distributor overflow as photographed during in-situ water...
Figure 4.7 A Liquid overflow in a water test of a model parting box.
Figure 4.8 A water test of a sparger-fed model parting box shows significant...
Figure 4.9 A recommended correlation for self-venting flow.
Figure 4.10 Effect of maldistribution on packing efficiency at turndown.
Figure 4.11 Effect of simulated tilt on packing efficiency.
Figure 4.12 Reflux parting box fed by 70°F subcooled liquid via a central pi...
Figure 4.13 Application of the Moore and Rukovena method for distributor qua...
Figure 4.14 Application of the Moore and Rukovena method to justify distribu...
Figure 4.15 Application of the Moore and Rukovena method to trough distribut...
Figure 4.16 Application of the Perry et al. method using three concentric zo...
Figure 4.17 Inlet vapor jet traveling through a vapor-distributing device (a...
Figure 4.18 Application of computational fluid dynamics to analyze vapor dis...
Figure 4.19 Vertical (“
y
”) velocity profile provided by a CFD analysis of a ...
Figure 4.20 CFD simulation of FCC main fractionator inlet (a) a schematic sh...
Figure 4.21 Bad practices of flashing feed entering liquid distributor parti...
Figure 4.22 A typical gallery distributor design.
Figure 4.23 A notched trough distributor with
Y
notches.
Figure 4.24 Terms used for flow through notches (a) rectangular notch, Eqs. ...
Figure 4.25 Problems experienced with notched trough distributors (a) flow d...
Figure 4.26 Watermarks on a notched trough distributor showing liquid issuin...
Figure 4.27 Water testing of a spray distributor.
Figure 4.28 Spray footprints diagram. (a) Terms used in Eq. (4.10); (b) spra...
Figure 4.29 Distributor water test finds plugged nozzle.
Figure 4.30 Problems uncovered by water testing (a) angled drip tubes were d...
Chapter 5
Figure 5.1 Good gamma scanning practices, shown in reference to 2-pass trays...
Figure 5.2 Illustrative gamma scans, depicting various types of column irreg...
Figure 5.3 A gamma scan illustrating typical evaluation of active areas of t...
Figure 5.4 An active area gamma scan illustrating (a) entrainment and (b) we...
Figure 5.5 Active area gamma scans as the tower rates are raised and the fro...
Figure 5.6 Gamma scanning chords used in packed towers. (a) Grid scan, recom...
Figure 5.7 A packed tower gamma scan, illustrating excellent liquid distribu...
Figure 5.8 A single-chord gamma scan of a bed of fourth-generation metal ran...
Figure 5.9 A single-chord gamma scan of the distributor in the 4 ft ID test ...
Figure 5.10 Bad downcomer gamma scanning practices, not recommended, shown i...
Figure 5.11 An active area gamma scan, illustrating normal operation in the ...
Figure 5.12 Stabilizer unflooded active area scan and center downcomer scan ...
Figure 5.13 Overlay of center downcomer scans under flooded and unflooded co...
Figure 5.14 Debutanizer tray active area gamma scans. The blue (dashed) scan...
Figure 5.15 Debutanizer feed entry arrangement that caused tower and gas pla...
Figure 5.16 An active area gamma scan illustrating foaming in an amine conta...
Figure 5.17 (a) Gamma scans show foaming on active areas and in downcomers. ...
Figure 5.18 Scans of two side downcomers reveal very different behavior for ...
Figure 5.19 Scan chords passing through progressively shorter lengths while ...
Figure 5.20 Gamma scans exploring multipass maldistribution. (a) Scan chords...
Figure 5.21 Active area gamma scans under “flooded” (dashed scans) and “norm...
Figure 5.22 An active area gamma scan, illustrating missing trays, weeping a...
Figure 5.23 Gamma scans of atmospheric tower wash bed. (a) Plugged and sever...
Figure 5.24 Gamma scans of the atmospheric tower wash bed in Figure 5.23 ove...
Figure 5.25 Plugging-induced flooding at the top packed bed of a chemical to...
Figure 5.26 Flood due to crushed random packing. (a) Shortly after returning...
Figure 5.27 Gamma scans indicate the top and middle beds appeared to be in p...
Figure 5.28 Packing displacement in refinery vacuum tower. (a) Wash bed. (b)...
Figure 5.29 Gamma scans of vacuum tower. (a) C-factor of 0.3 ft/s, good dist...
Figure 5.30 Grid scan of stripping tower showing significant liquid maldistr...
Figure 5.31 Frothing and entrainment from flashing-feed distributor. The mai...
Figure 5.32 Gamma scan showing high bottoms liquid level generating flood th...
Figure 5.33 Gamma scan showing liquid level reaching or almost reaching the ...
Figure 5.34 Gamma scans of wash section. (a) At normal operating liquid rate...
Chapter 6
Figure 6.1 Parallel chords used for multi-chordal quantitative gamma scan an...
Figure 6.2 Harrison’s analysis method for spray (or froth) height determinat...
Figure 6.3 Application of Harrison’s method for spray (or froth) height dete...
Figure 6.4 Qualitative gamma scan of the bottom 30 trays in the tower discus...
Figure 6.5 Spray ratios derived from the spray heights determined by Harriso...
Figure 6.6 Kistergrams showing froth heights and entrainment profiles along ...
Figure 6.7 Froth density determination. Froth density profiles obtained from...
Figure 6.8 Scans of the simulator containing multi-downcomer trays rotated 9...
Figure 6.9 Overlay of downcomer and active area scans of multiple downcomer ...
Figure 6.10 Downcomer scans of multiple downcomer trays with truncated downc...
Figure 6.11 Active area scan of multiple downcomer trays with truncated down...
Figure 6.12 Scans of a tower containing high-capacity sieve trays with multi...
Figure 6.13 Packed tower liquid holdup variation with superficial liquid vel...
Figure 6.14 (a) Initial gamma scan results from small-diameter column. (b) G...
Figure 6.15 (a) Initial gamma scan results from crude vacuum tower showing b...
Figure 6.16 (a) Initial gamma scan results showing what appears to be maldis...
Figure 6.17 A typical neutron backscatter device along with an illustrative ...
Figure 6.18 Liquid heights (inches) measured by neutron backscatter along th...
Figure 6.19 Application of neutron backscatter scans to troubleshoot downcom...
Figure 6.20 Neutron backscatter downcomer scans identify the plugged and dry...
Figure 6.21 Neutron backscatter of the kettle reboiler shows heavy entrainme...
Figure 6.22 Source and detector placement in CAT scans. For clarity, only th...
Figure 6.23 A CAT scan through the upper packed bed under upset conditions. ...
Figure 6.24 A CAT scan near the top of the bed, with the chords of a grid sc...
Figure 6.25 Refinery vacuum tower wash bed CAT scan. (a) Baseline scan, imme...
Figure 6.26 Vacuum tower wash bed densities measured by CAT scans. Density r...
Figure 6.27 Vacuum tower wash bed true overflash (net reflux leaving the bot...
Figure 6.28 Lower sections of the refinery vacuum tower that were investigat...
Figure 6.29 Top bed of LNG plant packed tower that was investigated using a ...
Figure 6.30 Tracer detector readings on the southeast (a) and northwest (b) ...
Figure 6.31 Detector response to a nonvolatile tracer injection at the kettl...
Figure 6.32 Plan and elevation of slanted scan.
Figure 6.33 Scans of a two-pass tray in an empty 10 ft ID Sulzer training to...
Figure 6.34 Slanted scan of an empty 12.5 ft ID FCC main fractionator tower ...
Chapter 7
Figure 7.1 Circumferential temperature survey for packed towers.
Figure 7.2 (a) Refinery vacuum tower that experienced wash bed packing damag...
Figure 7.3 Atmospheric crude tower in Section 7.1.3. Temperatures shown are ...
Figure 7.4 Temperature survey in the TPA bed (a) showing the bed top, middle...
Figure 7.5 TPA bed gamma scans, showing liquid bias on the northeast. In the...
Figure 7.6 The refinery crude tower experiencing instability.
Figure 7.7 Steady-state temperature survey of the refinery crude tower exper...
Figure 7.8 Temperature survey time studies of the stove oil draw temperature...
Figure 7.9 Root cause of the instability.
Figure 7.10 Crude tower stove oil draw modifications (boldface indicates mod...
Figure 7.11 Temperature profiles showing two liquid phases in the tower. (a)...
Figure 7.12 Temperature survey of the top 15 trays above the feed showing a ...
Figure 7.13 Debutanizer reflux drum with water removal boot in the case 3 in...
Figure 7.14 Top section of the FCC main fractionator that experienced separa...
Figure 7.15 Temperature survey of the top bed of the chemical tower that was...
Figure 7.16 Temperature survey of a kettle reboiler shows that the inlet reg...
Figure 7.17 Temperature survey showing a hot spot in the northwest quadrant....
Figure 7.18 Temperature survey showing poor mixing of quench liquid in the b...
Figure 7.19 Thermal scans of two acid gas scrubbers operating in parallel. (...
Figure 7.20 Two situations where removing a strip of insulation and shooting...
Figure 7.21 Thermal scans of an amine absorber: (a) normal operation; tray l...
Figure 7.22 Thermal scans of an amine absorber: (a) normal operation; tray l...
Figure 7.23 Thermal scan of an amine absorber compared with a temperature pr...
Figure 7.24 Thermal scan of an amine absorber compared with a temperature pr...
Figure 7.25 Amine absorber temperature profiles from a rate-based simulation...
Figure 7.26 Thermal scans of the bottom sump of an amine absorber that exper...
Figure 7.27 Design flows and temperatures at a tower base (non-bold print), ...
Figure 7.28 Thermal scans of the light diesel draw pipe to check whether the...
Figure 7.29 Thermal scan of a partially flooded overhead condenser, showing ...
Figure 7.30 Reflux drum in a hot vapor bypass system. Note the very distinct...
Figure 7.31 Plugged tubes in air condenser. Yellow shows hot tubes, and purp...
Figure 7.32 Air condenser thermal survey. (a) Tower overhead scheme. (b) The...
Figure 7.33 Right: thermal scans of the channelhead of a horizontal thermosi...
Figure 7.34 Troubleshooting by thermal videos. (a) Overhead system of a hydr...
Figure 7.35 Energy balance troubleshooting that completely changed diagnosis...
Figure 7.36 Top section of the refinery vacuum tower in Section 7.3.2.
Figure 7.37 Leakage from an LVGO collector tray logged against time.
Figure 7.38 Bottom section of the FCC main fractionator that experienced sep...
Figure 7.39 Jet fuel draw tray having a hot and a cold compartment. (a) Chim...
Figure 7.40 Hydrotreater fractionator with three feeds and two feed-bottoms ...
Chapter 8
Figure 8.1 Olefins plant demethanizer bottleneck. (a) Process scheme, showin...
Figure 8.2 Maldistributed feed arrangement to 4-pass trays.
Figure 8.3 Feed pipe blocking entrance to downcomer.
Figure 8.4 Another feed pipe blocking entrance to downcomer.
Figure 8.5 Draw boxes choking downcomer entrance. (a) Draw box restricting t...
Figure 8.6 Floods due to unsealed downcomers or downpipes. (a) Downcomer uns...
Figure 8.7 Downcomer submergence in chimney tray or sump liquid can bring ab...
Figure 8.8 “Leak-proof” total draw chimney tray. (a) Initial design; (b) exp...
Figure 8.9 Liquid getting past another “leak-proof” chimney tray. (a) Bottom...
Figure 8.10 Liquid getting past yet another “leak-proof” chimney tray. Liqui...
Figure 8.11 Overflow due to hydraulic gradients on chimney trays. (a) High h...
Figure 8.12 System limit troubleshooting at points of transition. (a) Premat...
Figure 8.13 Maldistribution of vapor feed. (a) Center downcomer causes vapor...
Figure 8.14 Tower experiencing instability initiating at the gallery distrib...
Figure 8.15 Downward deflection of reboiler return causes instability in a d...
Figure 8.16 Downward deflection of reboiler return or vapor feed. (a) Causes...
Figure 8.17 V-baffles produce unexpected flow pattern at tower base. (a) At ...
Figure 8.18 Preferential baffle arrangements for bottom sumps.
Figure 8.19 Preferential baffle arrangement that worked poorly.
Figure 8.20 Debutanizer bottom sump baffle. (a) Before modification; (b) mod...
Figure 8.21 Flow obstruction causes liquid maldistribution and poor separati...
Figure 8.22 Long edges of long chimneys obstruct liquid movement toward adja...
Figure 8.23 Collector that experienced excessive hydraulic gradients, causin...
Figure 8.24 Poor mixing of feed and reflux in a tower, showing reflux liquid...
Figure 8.25 Poor mixing of cooled slurry feed and volatile liquid from tray ...
Figure 8.26 Poor mixing of solvent and reflux in ED tower. (a) Reflux enteri...
Figure 8.27 Poor mixing of solvent and reflux in ED tower, showing reflux li...
Figure 8.28 Two seemingly well-designed pieces combine to make an arrangemen...
Figure 8.29 Another two seemingly well-designed pieces combine to make an ar...
Figure 8.30 Maldistribution of internal reflux below a side draw.
Figure 8.31 One sketch shows it all – vapor feed blowing liquid onto wall ca...
Chapter 9
Figure 9.1 Operating charts of a high liquid level damage incident (a) final...
Figure 9.2 Reboiler surge incident (a) Operating charts; (b) raising bottom ...
Figure 9.3 Reboiler seal loss incident (a) Demethanizer using reboiler heate...
Figure 9.4 Hot vapor bypass control scheme. (from Kister, H. Z., “Practical ...
Figure 9.5 Operating charts of a hot vapor bypass upset event.
Figure 9.6 Deethanizer stripper reboiler circuits.
Figure 9.7 Process data for initial operation of stripper reboiler circuits....
Figure 9.8 Atmospheric crude fractionator and the kero side stripper that ex...
Figure 9.9 Kero stripper two steady states (a) Bottoms level operating chart...
Figure 9.10 Atmospheric crude fractionator that experienced startup damage....
Figure 9.11 One of the severely damaged trays above the feed of a crude frac...
Figure 9.12 Operating charts for pressure surge (a) tower pressure; (b) feed...
Figure 9.13 Simplified scheme of a typical ethylene fractionator, showing th...
Figure 9.14 Ethylene fractionator transition to total reflux (a) Levels (b) ...
Figure 9.15 Chemical tower that experienced salt plugging (a) the tower (b) ...
Figure 9.16 Atmospheric crude tower wash section (a) Initial (b) after first...
Figure 9.17 Revamp of the lower section of the crude tower in Section 9.2.5,...
Figure 9.18 Diesel draw revamp modifications.
Figure 9.19 How the excursion caused entrainment.
Figure 9.20 Liquid side draw to intercooler that initiated premature flood (...
Figure 9.21 Liquid entry piping arrangements of top and bottom pumparound re...
Figure 9.22 In-situ water test of chemical tower (a) visual observation, sho...
Chapter 10
Figure 10.1 Samples of ceramic saddles fresh from shipment. (a) Chipped sadd...
Figure 10.2 Random packing installation techniques. (a) Recommended wet pack...
Figure 10.3 Installation of structured packing elements. (a) Fitting the ele...
Figure 10.4 Some steps in good practice of structured packings installation....
Figure 10.5 Partial cleaning of trays is trouble.
Figure 10.6
ZIP
LEVEL
®
PRO-2000 altimeter.
Figure 10.7 Flawed orientation of distributor pipes. (a) Feed pipe installed...
Figure 10.8 Flaws picked by distributor inspections. (a) Plugged spray nozzl...
Figure 10.9 Looking for problems in the packings. (a) Fouled and slightly co...
Figure 10.10 Downcomer gaps that cause leakage will reduce tray efficiency....
Figure 10.11 Downcomer inspection checks. (a) Bulging downcomer. (b) Downcom...
Figure 10.12 Missing and damaged gaskets (a) on a tray support ring (b) in a...
Figure 10.13 Miscellaneous fastening issues. (a) Nuts and bolts incorrectly ...
Figure 10.14 Cracks in tray active areas. (a) Due to misalignment of tray pa...
Figure 10.15 Checks of layout of fixed valves. (a) Directional round fixed v...
Figure 10.16 Plugging (a–c), under-deposit corrosion (c) and cracks (d) on t...
Figure 10.17 Scenes from inspections of moving valve trays. (a) Missing valv...
Figure 10.18 Inspections of downcomer clearances. (a) Template for inserting...
Figure 10.19 Outlet weir installation issues. (a) Weir displaced and pushed ...
Figure 10.20 Misplaced inlet weirs. (a) Incorrectly installed on feed tray, ...
Figure 10.21 Anything missing?
Figure 10.22 Clearances to be checked for a typical bottom seal pan arrangem...
Figure 10.23 Incorrectly installed downcomer causes premature flooding. (a) ...
Figure 10.24 Checking seal pan condition and integrity. (a) Fouled. (b) Corr...
Figure 10.25 Some odd features. (a) Obstruction at the downcomer exit. (b) T...
Figure 10.26 Incorrectly installed froth initiators on specialty trays. (a) ...
Figure 10.27 Inspection pinpoints incorrect materials of construction: (a) w...
Figure 10.28 Some dimensions that should be inspected and their typical inst...
Figure 10.29 Orientation of a bottoms drawoff. (a) Correctly installed (liqu...
Figure 10.30 Watermarks reveal unexpected phenomena. (a) A 7-ft vortex in th...
Figure 10.31 Some pipe distributor issues identified by inspection. (a) Feed...
Figure 10.32 Practices to be avoided in bottom feed arrangements.
Figure 10.33 Looking for obstruction to liquid flow toward the draw nozzle. ...
Figure 10.34 Chimney tray with well-mounted hats. Liquid collected between t...
Figure 10.35 Lower level tap installed behind an angle iron intended to keep...
Figure 10.36 Water testing a reboiler draw pan shows massive leaks from the ...
Figure 10.37 Deformed mesh taken from a Y-strainer which would allow solids ...
Guide
Cover
Table of Contents
Title Page
Copyright
Dedication
Preface
List of Acronyms
Acknowledgments
Begin Reading
References
Index
End User License Agreement
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Distillation Diagnostics
An Engineer’s Guidebook
Henry Z. Kister
Fluor Corporation, USA
Copyright © 2025 by the American Institute of Chemical Engineers, Inc. All rights reserved.A Joint Publication of the American Institute of Chemical Engineers and John Wiley & Sons, Inc.
Published by John Wiley & Sons, Inc., Hoboken, New Jersey.Published simultaneously in Canada.
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Library of Congress Cataloging-in-Publication Data:
Names: Kister, Henry Z., author. | John Wiley & Sons, publisher.Title: Distillation diagnostics : an engineer's guidebook / Henry Z Kister.
Description: Hoboken, New Jersey : Wiley, [2025] | Includes index.
Identifiers: LCCN 2024023262 (print) | LCCN 2024023263 (ebook) | ISBN 9781119640110 (hardback) | ISBN 9781119640158 (adobe pdf) | ISBN 9781119640127 (epub)
Subjects: LCSH: Distillation. | Distillation apparatus–Maintenance and repair.
Classification: LCC TP156.D5 K557 2025 (print) | LCC TP156.D5 (ebook) | DDC 665.5/32–dc23/eng/20240604
LC record available at https://lccn.loc.gov/2024023262
LC ebook record available at https://lccn.loc.gov/2024023263
Cover Design: Wiley
To my son, Abraham, and my daughter, Helen, who have been my love, blessings, and the lighthouses illuminating my path
Preface
For over a century, distillation, the “king of separations,” has been by far the most common separation technique in refineries, petrochemical, chemical, and natural gas plants and will remain the prominent separation technique in the foreseeable future. Every chemical process has a reaction section and a separation section, with distillation usually dominating the latter. Three percent of the world’s energy is tied in distillation. The dominance of distillation stems from its low capital compared to other techniques, scaling up well, and not introducing an extra agent that requires removal later.
The past half-century has seen tremendous advances in distillation technology. High-speed computers revolutionized the design, control, and operation of distillation towers. Invention and innovation in tower internals enhanced tower capacity and efficiency beyond previously conceived limits. Despite all these advances, the distillation failure rate has been on the rise and growing.
The great progress has not bypassed the distillation troubleshooting tools. Reliable pressure drop measurements, gamma scans, laser-guided pyrometers, and thermal cameras are tools that not-so-long-ago troubleshooters would only dream of. But again, despite this great progress, the ability of engineers to effectively diagnose and solve plant problems appears to be on the decline.
Why are we losing the problem-solving war? Despite the prominence of distillation in industry, academics prefer to focus on more trendy “cool” fields. The Chemical Processing editorial from March 2018 decries the lack of practical research on distillation in chemical engineering departments. In industry, mergers, cost-cuts, and the pandemic have retired most of the experienced troubleshooters and thinly spread the others. The literature offers little to bridge the experience gap. In the era of information explosion, databases, and computerized searches, finding the appropriate information in due time has become like finding a needle in an ever-growing haystack. To locate a useful reference, one needs to click away a huge volume of wayward leads.
The result is that distillation diagnostics is becoming a lost art. Engineers are given little practical guidance on how to correctly apply and get the most out of the diagnostic tools, so the tools are utilized sparsely and only on a very basic level. Problems are left undiagnosed or misdiagnosed. Solutions based on misdiagnoses are doomed to fail. Lacking a proper diagnosis, some engineers turn to so-called experts and end up being sold a bill of goods or sledge hammers to crack nuts. It is not uncommon to see an expensive new tower solving a problem that can be solved by replacing a faulty feed pipe for nickels and dimes.
The trend away from diagnosis could not have come at a worse time. We are being alarmed by adverse climate and environmental changes, are recognizing the importance of saving our planet, and are striving for a cleaner tomorrow. The engineering community is engaged in developing new technologies for reducing the carbon footprint, aspiring to “zero carbon” energy transition, carbon capture, and replacement of fossil fuels by renewables. Unfortunately, many of these technologies require massive new equipment and additional energy usage, neither of which helps achieve the prescribed goals of reducing carbon footprints.
One simple technology is being forgotten: correct diagnostics. In his book Process Engineering for a Small Planet (Wiley, 2010), Norman Lieberman demonstrates how poor troubleshooting and wasteful practices guzzle energy, generate carbon dioxide, and waste the earth’s precious resources. In Chapter 1 of his book, Lieberman describes a case in which a correct diagnosis would have led to modifying trays and downcomers in a fractionator, and adding mist injection to the overhead compressor, which could have circumvented erecting a giant new fractionator with a new oversized overhead compressor. Just the energy usage due to the compressor oversizing was estimated to waste the amount of crude oil that 400 families use daily. Fabricating the new steelwork and structures consumed additional immense amounts of energy and emitted tons of carbon dioxide, all of which were unnecessary.
In another example (Chapter 2), four uninstalled tray manways induced the escape of a large quantity of diesel in the bottom of a crude fractionator. To vaporize it took 40 MM Btu/h, which is equivalent to the fuel consumption of a quarter of a million 400 horsepower motor cars driving around the clock. Lieberman diagnosed the problem and recommended re-installing the manways, but the implemented solution was to build a new larger heater, wasting not only energy but also concrete, steel, nickel, and chromium needed for the heater and its tubes, the mining and production of which only adds to the carbon footprint. Lieberman presents a book full of similar experiences.
This book builds up on Lieberman’s initiative with a multitude of distillation examples. In one (Chapter 8), a packed stripper was erected to turn a wastewater stream into cooling water makeup. The entering wastewater poured above the oversized hats of the liquid distributor. In the little space between the hats, the vapor sped up and carried the liquid over. Two different consultants studied the problem. The first offered an incorrect diagnosis and a failed fix. The second performed an extensive simulation study, incorrectly concluding that a larger-diameter tower was needed. The plant gave up and junked the tower, with the water still going to the sewer. Good troubleshooting and hat or feed pipe modifications costing nickels and dimes would have saved precious water, reduced sewage, and prevented turning a good tower into scrap metal.
My previous book, Distillation Troubleshooting, focused on case studies and the lessons learned. This book goes further, providing the tools to correctly diagnose and solve operating problems, avoid the wasteful practices, and make the most of existing equipment. It travels through the multitude of invaluable tools available for diagnosing tower problems, providing application guidelines derived from the school of hard knocks. The book describes what each tool can and cannot do, provides insight into how different ideas and theories can be tested using these tools, shares the experience of how to correctly interpret the results provided by each technique, and guides troubleshooters to a multitude of additional tests that they can perform to get closer to a correct diagnosis and an effective fix. The only other place where its information is available is in the heads of experienced troubleshooters.
The techniques are illustrated with real case studies from my experience of 45 years as well as from the experiences of many of my colleagues and those presented in the literature. Every technique is accompanied with an extensive list of “do and don’ts” based on the author’s and industry’s experience. This guidance can make the difference between success and failure, and between good and bad results.
The case studies and lessons learned are described to the best of the author’s and the contributors’ knowledge and in good faith, but may not always correctly reflect the problems and solutions. Many times I thought I had the answer, only to be humbled by a new light or another experience later. The experiences and lessons in this book are not meant to be followed blindly. They are meant to be stories told in good faith and to the best of knowledge and understanding of the author or contributors, which hopefully give troubleshooters ideas to think about. We welcome any comments that either affirm or challenge our perception or understanding.
If an incident that happened in your plant is described, you may notice that some details could have changed. Sometimes, this was done to make it more difficult to tell where the incident occurred. At times, it was done to simplify the story without affecting the key lessons. Sometimes, it happened long ago and memories of some details faded away. Sometimes, and most likely, this incident did not happen in your plant at all. Another plant had a similar incident.
The book emphasizes the “do-it-yourself” approach. It endeavors to place the tools and good application guides in the practitioner’s hands, eliminating reliance on the so-called experts. People who attend my seminar classes come out with knowledge on how to apply the tools and express concern about forgetting this knowledge over the years. They express wishes to have a book like this so they can refresh their memories in the future. This is that book. It is my hope that the book will lead the readers to correct diagnostics and effective fixes to tower problems, and to trouble-free operation.
If you can successfully solve only one problem using the techniques in this book, the savings to your company will be enough to pay for thousands of copies of the book. But far beyond the savings, you will be taking a step in the right direction of saving our small planet and ushering in a cleaner tomorrow.
HENRY Z. KISTER
May 2024
List of Acronyms
AIChE
American Institute of Chemical Engineers
AGO
Atmospheric gas oil
API
American Petroleum Institute
ASTM
American Society for Testing and Materials
ATB
Atmospheric tower bottoms
BPA
Bottom pumparound
BPD
Barrels per day
BPH
Barrels per hour
BPSD
Barrels per stream day
BTM
Bottom
CAT
Computer aided tomography
CFD
Computational fluid dynamics
COND
Condensate
COT
Coil outlet temperature
COV
Coefficient of variation
CW
Cooling water
dP
Differential pressure (pressure drop)
ED
Extractive distillation
FCC
Fluid catalytic cracking
FI
Flow indicator
FRI
Fractionation Research Inc (or Institute)
FRN
Full range naphtha
HAZOP
Hazard and operability analysis
HCO
Heavy cycle oil
HCU
Hydrocracker Unit
HETP
Height equivalent to a theoretical plate
HF
Hydrogen fluoride
HN
Heavy naphtha
HP
High pressure
HSE
Health, Safety, and Environment
HVB
Hot vapor bypass
HVGO
Heavy vacuum gas oil
ID
Internal diameter
IPA
Intermediate pumparound
IR
Infrared
LCO
Light cycle oil
LED
Light Emitting Diode
LI
Level indicator
LN
Light naphtha
LNG
Liquefied natural gas
LV
Liquid volume
LVGO
Light vacuum gas oil
MBPD
Thousand BPD
MCB
Main Column Bottoms
MDEA
Methyldiethanol amine
MEA
Monoethanol amine
MP
Medium pressure
MPA
Mid pumparound
MRI
Magnetic resonance imaging
MSCFH
Standard cubic feet per hour × 1000
OSHA
The Occupational Safety and Health Administration
OVHD
Overhead
P&ID
Process and instrumentation diagram
PA
Pumparound
PFD
Process flow diagram
PI
Pressure indicator
PPR
Polypropylene return
STM
Steam
TAR
Turnaround
TI
Temperature indicator
TPA
Top pumparound
TRC
Temperature recorder/controller
VCFC
Vapor crossflow channeling
VLE
Vapor–liquid equilibrium
VLLE
Vapor–liquid-liquid equilibrium
VTB
Vacuum tower bottoms
Acknowledgments
Many of the experiences and case histories reported in this book have been invaluable contributions from colleagues and friends who kindly and enthusiastically supported this book. Many of the contributors elected to remain anonymous. Kind thanks are due to all contributors, you have done a magnificent service to our beloved science of distillation and to the industry. Special thanks to those whose names do not appear in print. To those behind-the-scenes friends, the author extends special appreciation and gratitude.
Writing this book required breaking away from everyday work and family demands. Special thanks are due to Fluor Corporation, particularly to my supervisors, Curt Graham, Maureen Price, Jeff Scherffius, Jennifer Foelske, and Bill Parente, for their backing, support, and encouragement of this book-writing endeavor, going to great lengths to make it happen. Warmhearted gratitude to my wife Susana for her love, dedication, and devotion to our family, guiding our children to walk in G-d's path and do the right thing, and encouraging them to excellence.
Recognition is due to my mentors who, over the years, encouraged my work; immensely contributed to my achievements; and taught me much about distillation and engineering: to my life-long mentor, Dr. Walter Stupin, who warmly mentored and encouraged my work, throughout my career at C F Braun and later at Fluor, being a ceaseless source of inspiration behind my books and technical achievements, and who taught me a lot of what I know about distillation; Curt Graham and Paul Walker, Fluor, whose warm encouragement, guidance, and support were the perfect motivators for professional excellence and achievement; Professor Ian Doig, University of NSW, who inspired me over the years, showed me the practical side of distillation, and guided me over a crisis early in my career; Professor James Fair, distillation guru, University of Texas, who warmly encouraged my books and distillation work; Reno Zack, who enthusiastically encouraged and inspired my achievements throughout my career at C F Braun; Dick Harris and Trevor Whalley, who taught me about practical distillation and encouraged my work and professional pursuits at ICI Australia. Thanks are due to my colleagues Garry Jacobs and Carlos Trompiz (Fluor), Ron Olsson (Celanese), Daryl Hanson (Valero), Christine Long (Chevron), and troubleshooting guru Norman Lieberman, all of whom taught me a lot by sharing their vast experiences and expertise. The list could go on, and I express special thanks to all who encouraged, inspired, and contributed to my work over the years. Much of my mentors’ and colleagues’ teachings found its way to the following pages.
Special thanks are due to my mother, Dr. Helen Kister, and my father, Dr. John Kister, may their memories be blessed, who dedicated their lives to me, guided me to do things right, enthusiastically supported my work throughout my life, and have been there for me every moment of the day. Their prayers have remained with me even after they left this world. Thanks also for always encouraging me to excel and teaching me to diagnose and critically evaluate problems.
Special thanks are due to Tracerco, in particular to the dedication of Margaret Bletsch and Lowell Pless, who contributed wonderful expertise, experiences, and images for the radioactive troubleshooting sections of this book and assisted me in fitting them to the audience.
Chapter 1Troubleshooting Steps
“In our industry we have many more troublemakers than troubleshooters”
—(Professor Zarko Olujic, presentation to AIChE)
Troubleshooting, revamping, and eliminating waste offer huge benefits in reducing capital investment, downtime, carbon dioxide emissions, and energy consumption. Unfortunately, the attention paid to this resource in the energy-transition era has been too little to reflect its tremendous potential.
A multitude of examples in Norman Lieberman’s book Process Engineering for a Small Planet (287) demonstrate how poor troubleshooting leads to wasteful practices that guzzle energy, increase the carbon footprint, and deplete the earth’s precious resources. The chemical process industry (CPI) has been paying dearly for downtime, lost production, substandard product quality, raw material problems, safety and environmental issues, and excessive energy consumption due to ineffective troubleshooting of abnormal situations (16). In 1997, a consortium estimated that the annual loss for the CPI due to ineffective abnormal situation management was US $10 billion (16).
Correct diagnosis is at the heart of problem identification and implementing a correct, cost-effective solution. An incorrect diagnosis breeds ineffective solutions that prolong the agony and escalate the costs. This chapter focuses on the systematic diagnostic steps. The following chapters will describe the multitude of techniques that have been found effective for diagnosing distillation problems.
A well-known sales axiom states that 20% of the customers bring in 80% of the business. A sales strategy tailored for this axiom concentrates the effort on these 20% without neglecting the others. Distillation diagnostics follow an analogous axiom. A person engaged in diagnosing column problems must develop a good understanding of the factors that cause the vast majority of column malfunctions and the techniques available for narrowing in on their root causes. While a good knowledge and understanding of the broader field of distillation is beneficial, the diagnosis often requires only a shallow knowledge of this broader field.
It is well accepted that diagnosing problems is a primary job function of operating engineers, supervisors, and process operators. Far too few realize that distillation diagnostics start at the design phase. Any designer wishing to achieve a trouble-free column design and operation must be as familiar with diagnostic techniques, many of which are applicable during the design (and more so at the revamp) phase.
Expansive surveys of the causes of column malfunctions were described in previous studies (196, 198, 201). Abundant resources are available to distinguish good from poor practices and to avoid and overcome troublesome design and operations (e.g., 192, 285, 286, 293). What is often missing is the connect. How does one link field observations with the known tower malfunctions in order to develop an effective remedy? This book is all about the link: translating field observations into diagnoses and cures.
Following a brief survey of the primary causes of tower malfunctions, this chapter looks at the basic diagnostic: the systematic strategy for diagnosing distillation problems and the dos and don’ts for formulating and testing theories. Finally, it reviews the techniques for testing these theories and for focusing on the most likely root cause.
1.1 CAUSES OF COLUMN MALFUNCTIONS
Close to 1500 case histories of malfunctioning columns were extracted from the literature and abstracted in Ref. 201. Most of these malfunctions were analyzed in Ref. 198 and classified according to their principal causes. A summary of the common causes of column malfunctions is provided in Table 1.1. If one assumes that these case histories make up a representative sample, then the analysis presented below has statistical significance. Accordingly, Table 1.1 can provide a useful guide to the factors most likely to cause column malfunctions and can direct troubleshooters toward the most likely problem areas.
The general guidelines in Table 1.1 often do not apply to a specific column or even plant. For instance, foaming is not high up in the table; however, in amine absorbers, it is a very common trouble spot. The author therefore warns against blindly applying these guidelines in any specific situation.
The total number of cases in each category is shown in the column headed “Cases.” The other three columns show the split of these cases according to industry categories, namely refining, chemicals, and olefins/gas plants.
An analysis of Table 1.1 suggests the following:
Plugging, tower base, tower internals damage, instrument and control problems, startup and/or shutdown difficulties, points of transition (tower base, packing distributors, intermediate draws, feeds), and assembly mishaps are the major causes of column malfunctions. They make up nearly two-thirds of the reported incidents. Familiarity with these problems, therefore, constitutes the “bread and butter” of distillation and absorption troubleshooters.
Primary design is a very wide topic, encompassing vapor–liquid equilibrium, stage-to-stage calculations, reflux-stages relationship, unique features of multicomponent distillation, tray and packing capacities and efficiencies, scale-up, column diameter and height determination, type of tray, and size and material of packing. This topic represents most of our distillation know-how and occupies the bulk of most of the distillation texts (e.g.,
34
,
193
,
299
,
451
,
492
). While this topic is paramount for designing and optimizing distillation columns, it plays only a minor role in operations and troubleshooting in distillation. As shown in
Table 1.1
, only one column malfunction among fourteen is incurred in the primary design. The actual figure is probably higher for a first-of-its-kind separation, but lower for an established separation. Due to the bulkiness of this topic and its low likelihood to cause malfunctions, and due to the excellent coverage that the topic receives in several texts (e.g.,
34
,
193
,
299
,
451
,
492
), it is only lightly touched upon in this book.
The above statements must not be interpreted to suggest that troubleshooters need not be familiar with the primary design. Quite the contrary. A good troubleshooter must have a solid understanding of primary design because it provides the foundation of distillation know-how. However, the above statements do suggest that in general, when troubleshooters examine the primary design for the cause of a column malfunction, they have less than one chance out of ten of finding it there.
Table 1.1 Most common causes of column malfunctions. (From Kister, H. Z., Transactions of the Institution of Chemical Engineers, 81, Part A, p. 5, January 2003. Reprinted Courtesy of the Institution of Chemical Engineers in the UK.)
No.
Cause
Total cases
Refinery cases
Chemical cases
Olefins/gas cases
1
Plugging, coking
121
68
32
16
2
Tower base and reboiler return
103
51
22
11
3
Tower internals damage (excluding explosion, fire, implosion)
84
35
33
6
4
Abnormal operation incidents (startup, shutdown, commissioning)
84
35
31
12
5
Assembly mishaps
75
23
16
11
6
Packing liquid distributors
74
18
40
6
7
Intermediate draws (including chimney trays)
68
50
10
3
8
Misleading measurements
64
31
9
13
9
Reboilers
62
28
13
15
10
Chemical explosions
53
11
34
9
11
Foaming
51
19
11
15
12
Simulations
47
13
28
6
13
Leaks
41
13
19
7
14
Composition control difficulties
33
11
17
5
15
Condensers that did not work
31
14
13
2
16
Control assembly
29
7
14
7
17
Pressure and condenser controls
29
18
3
2
18
Overpressure relief
24
10
7
2
19
Feed inlets to tray towers
18
11
3
3
20
Fires (excluding explosions)
18
11
3
4
21
Intermediate component accumulation
17
6
4
7
22
Chemicals release to the atmosphere
17
6
10
1
23
Subcooling problems
16
8
5
1
24
Low liquid loads in tray towers
14
6
2
3
25
Reboiler and preheater controls
14
6
–
5
26
Two liquid phases
13
3
9
1
27
Heat integration issues
13
5
2
6
28
Poor packing efficiency (excluding maldistribution/support/hold-down)
12
4
3
2
29
Troublesome tray layouts
12
5
2
–
30
Tray weep
11
6
1
3
31
Packing supports and hold-downs
11
4
2
2
1.2 COLUMN TROUBLESHOOTING – A CASE HISTORY
In Sections 1.3 and 1.4, the systematic approach recommended for diagnosing distillation problems is presented. The recommended sequence of steps is illustrated with reference to the case history described below.1
