Compare tray columns and packed columns for distillation.

Tray columns use horizontal plates with bubble caps, sieve holes, or valves for vapor-liquid contact; they handle high liquid rates, are easier to clean, and provide predictable performance. Packed columns use random or structured packing for continuous contact; they offer lower pressure drop, higher efficiency, and are preferred for vacuum distillation and corrosive services. Packed columns are more economical for diameters under 1m, while trays suit larger columns.