TL;DR

Column flooding causes purity loss and pressure drop spike. Reduce vapor or liquid rate to below the flood point, then diagnose the root cause.

What you might see

column differential pressure rising sharply
overhead product purity dropping
bottoms product contaminated with lights
liquid backup visible in downcomer

Likely causes

Tap to mark as ruled out

Vapor rate above the design flood point for the installed packing or tray
Liquid rate above downcomer capacity causing backup and weeping
Feed composition changed causing increased internal vapor/liquid ratio
Packing fouled with solids reducing open area and increasing resistance

Required tools

Differential pressure recorder or transmitter log
Process sample bottles
Lab GC or analyzer

Safety first

Distillation columns processing pharma intermediates or solvents operate under pressure and contain flammable or toxic materials. Do not enter the column without a vessel entry permit and gas detection.
Pressure relief devices on the column must be functional before reducing reboiler duty. Do not bypass or block the relief path.
Hot process fluids are present. Wear appropriate chemical and thermal PPE during sampling.

Procedure

7 steps · ~30 min

1
Log the column differential pressure and compare to the normal operating range.[1]
2
Reduce the reboiler duty or the feed rate by 10 to 15 percent. Watch for differential pressure to decrease.[1]
3
Sample the overhead and bottoms products to confirm the purity impact.
4
Check the feed composition against the design basis. An off-spec feed with excess lights can increase internal vapor load.
5
Review the reflux ratio against the design value. High reflux increases liquid load and can push the column past the downcomer capacity.
6
If the column continues to flood after reducing rates, plan an inspection during the next shutdown for packing fouling or damage.
7
Document the flood point operating conditions for comparison against previous stable operation. This establishes whether capacity has degraded.

Sources

Koch-Glitsch (internals) Koch-Glitsch FLEXIPAC / IMTP / Provalve Distillation Column general technical documentation, Koch-Glitsch (internals)
Koch-Glitsch FLEXIPAC / IMTP / Provalve distillation column general flooding and capacity procedures (general)

More guides for Koch-Glitsch (internals) Koch-Glitsch FLEXIPAC / IMTP / Provalve

How to diagnose packing fouling on a Koch-Glitsch FLEXIPAC / IMTP distillation column

A slow rise in differential pressure over months indicates packing fouling. Track the trend, plan an inspection at the next turnaround, and consider a column wash before opening.

~30 min7 steps

How to diagnose valve tray weeping on a Koch-Glitsch Provalve distillation column

Tray weeping happens when vapor flow is too low to prevent liquid from draining through the tray. Increase vapor load or inspect for damaged valve caps at the next shutdown.