Fractionation Design and Operations Reference

Troubleshooting

Module from the Fractionation Design and Operations Reference curriculum.

FRACTIONATION TROUBLESHOOTING · Troubleshooting Decision Matrix

Problem	Symptoms	Column ΔP	Tray Temperatures	Likely Cause	Diagnostic	Corrective Action
Flooding (jet)	Poor separation, liquid carryover in overhead	HIGH — sudden increase	Compressed T profile	Vapor rate too high for tray design	Check rates vs. design, inspect trays	Reduce feed/throughput, check for plugging
Flooding (downcomer)	Similar to jet flood, level instability	HIGH — gradual increase	Compressed in flood zone	Liquid rate exceeds downcomer capacity	Check liquid rates, DC backup calculation	Reduce liquid load, increase DC area (revamp)
Weeping	Poor separation at low rates, low efficiency	LOW	Spread T profile (poor separation)	Vapor rate below weep point	Reduce rate and observe ΔP	Increase throughput, use valve trays
Foaming	Erratic ΔP swings, level instability	FLUCTUATING — high average	Erratic temperature swings	Surface-active contaminants, fine solids	Anti-foam injection test, feed analysis	Add anti-foam, identify and remove contaminant
Entrainment	Product contamination, loss of separation	Normal to slightly high	Normal to slightly compressed	High vapor velocity, damaged demisters	Check overhead product for heavy components	Reduce throughput, check mist eliminators
Damaged trays	Sudden loss of separation, changed ΔP profile	Changed from baseline	Changed from baseline	Corrosion, mechanical damage, surge	Gamma scan, neutron backscatter	Repair at turnaround, inspect damage pattern
Plugged trays	High ΔP, reduced capacity	HIGH — localized	Abnormal profile in plugged zone	Solids, polymer, coke, salt deposits	Gamma scan, ΔP profile by section	Clean at turnaround, address root cause
Reboiler fouling	Declining separation, increasing reboiler ΔT	LOW (insufficient vapor)	Low bottom temperatures	Fouling reduces heat transfer	Check reboiler ΔT and duty trend	Clean reboiler, address fouling mechanism
Condenser fouling	Pressure increase, loss of condensing	Normal column ΔP	Top temperature rising with pressure	Fouling on cooling side of condenser	Check outlet temp, CW flow, ΔP	Clean condenser, inspect tubes
Tray damage (collapsed)	ΔP drops suddenly, separation lost	VERY LOW in damaged zone	Loss of temperature profile	Pressure surge, vacuum event, corrosion	Gamma scan shows liquid bypassing trays	Replace trays at turnaround
Gamma Scanning — Column Diagnostic Tool
Gamma scanning is the primary diagnostic tool for evaluating column internals without entry. Principle: • Radioactive source (Cs-137 or Co-60) on one side of column • Detector on opposite side measures radiation intensity • Liquid absorbs more radiation than vapor • Scan vertically to map liquid/vapor distribution on each tray What It Shows: • Active froth height on each tray → liquid level, flooding indication • Damaged or missing trays → sudden density change • Flooded trays → high density above normal • Plugged trays → high density, no clear liquid/vapor interface • Weeping trays → low froth height • Downcomer backup level Limitations: • Static snapshot (doesn't show dynamic behavior) • Column must be operating at the conditions of interest • Cannot distinguish between internal types of damage • Requires radiation safety controls and trained technicians Neutron Backscatter: alternative technique for liquid detection inside vessels/columns • Single-sided measurement (no access needed on opposite side) • Good for locating liquid levels and liquid hold-up

Source: Fractionation_Design_Ops_Reference_v1.xlsx · Sheet: Troubleshooting

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