What caused tower malfunctions in the last 50 years?

Nine hundred case histories of malfunctioning towers reported over the last 50 years,were surveyed and analyzed. Our analysis shows rapid growth in the number of malfunctions with no signs of decline. Plugging, especially of tray active areas, packing and distributors, tops the malfunctions list. Coking (refinery towers only), scale and corrosion, and precipitation were the most common causes. The tower base comes second, where liquid level rising above the reboiler inlet caused premature flood and even internals damage. Attention to level measurement and kettle reboiler pressure balance are key preventive measures. Next follow tower internals damage, abnormal operation incidents (startup, shutdown, commissioning), assembly mishaps, packing liquid distributors, intermediate draws, misleading measurements, reboilers, and explosions. Tray design and tower simulation, two topics that receive much attention in the literature, are not high up on the malfunction list. The survey teaches numerous lessons on each of the malfunctions which are invaluable for achieving trouble-free design and operation of distillation towers.