Polymer deposits that harden during shutdown require a retrofit focused on draining, flushing before curing, open packing geometry, cleaning access, and elimination of stagnant pockets. The shutdown chemistry can be more important than the normal operating condition.

Shutdown crystallization can foul a packed tower even when continuous operation is clean. Retrofit should address salt solubility, pre-shutdown flushing, drainage, distributor plugging, packing openness, support cleaning, and procedures that prevent concentrated liquid from drying inside the tower.

Reducing product cross-contamination between campaigns requires attention to residual liquid in packing, distributors, collectors, feed piping, and low points. Retrofit should improve drainability and flushing while maintaining the hydraulic function required during normal production.

Unknown legacy tower-internal materials should be investigated through historical records, appropriate material verification, condition inspection, and new process-compatibility review. Critical components should not be reused based solely on visual assumptions, and the retrofit should create a reliable material record for the future.

When the bottom sump becomes the capacity bottleneck, retrofit should evaluate total liquid balance, outlet nozzle, control valve, downstream piping, working volume, solids accumulation, gas-inlet interaction, and clearance below the packing support. Higher-capacity packing cannot solve insufficient liquid removal from the tower bottom.