Frequent start-stop operation introduces repeated wetting, drainage, thermal cycling, idle corrosion, packing movement, and distributor fouling that may not matter in continuous service. Retrofit should therefore optimize the tower for cycle durability and predictable startup rather than only steady-state design conditions.

After a tower is relined, replacement internals should be designed around the finished lined diameter, actual support interfaces, nozzle projections, and installation clearances. The smaller diameter should also be checked hydraulically because it increases gas velocity and can reduce operating margin.

An out-of-round packed tower should be measured at the actual internal elevations and in multiple directions before replacement internals are fabricated. Structured packing, distributors, support grids, collectors, and mist eliminators should be designed around real vessel geometry with controlled installation tolerance rather than nominal diameter alone.

When an upstream knockout separator fails and sends a liquid slug into a packed absorber, the lower bed can experience temporary flooding, packing movement, high support loads, contamination, and severe demister carryover. The investigation should include the upstream separator, transient pressure-drop history, lower-bed condition, support and restraint, and the chemical nature of the carried-over liquid.

When one packed scrubber serves alternating chemical campaigns, residual liquid from the previous service can react with the next campaign and create precipitates, corrosion, or blocked distributor openings. Drainability, residual holdup, flushing sequence, packing cleanability, material compatibility, and changeover frequency should be included in the design basis.