Replacing random packing in an existing tower requires more than matching the old packing size. Hydraulic capacity, pressure drop, flooding margin, bed height, distributor performance, support structure, and material compatibility must all be rechecked.

Existing packing can be reused after shutdown when its geometry, mechanical strength, surface condition, and material integrity remain suitable for the next operating cycle. The decision should also consider future operating conditions and the economic risk of another unplanned shutdown.

Liquid droplets entering catalyst beds can wet surfaces, carry catalyst poisons, leave salt or hydrocarbon deposits, increase bed pressure drop, and create gas maldistribution. Upstream mist separation should therefore be matched to the specific catalyst's contamination tolerance.

Mist eliminator capacity is not one universal velocity. Re-entrainment, liquid-handling, allowable pressure drop, and outlet carryover can each become the governing limit, and fouling can shift those limits during operation.

Downstream duct deposit patterns can reveal whether mist carryover is uniform or concentrated near a specific demister edge, module, or flow path. Deposit location, elbow impact, chemistry, and module mapping can provide valuable troubleshooting evidence.