An Investigation of Premature Flooding in a Distillation Column

Surprising observations regarding flooding in the upper fractionation trays of an atmospheric crude-petroleum distillation column are investigated In industial distillation processes, flooding is an abnormal, but relatively common, process condition in which liquid accumulates in the column. The accumulation may be caused by excessive upward vapor flow, which results in massive entrainment, or by a restriction in the downcomers, impeding liquid downflow in the column. Flooding usually results in dramatically reduced separation efficiency, excessive pressure drops and sometimes instability. In many cases, the situation leading to flooding is complicated. Here, the authors present findings from an investigation of flooding in a distillation column at a petroleum refinery that revealed some surprising observations involving the loss of valve floats from the column trays.   Crude tower flooding The investigation centered on an atmospheric crude tower that experienced severe corrosion in the top pumparound (TPA) and upper fractionation trays. The likely cause of the corrosion was the entry of small quantities of water, which hydrolyzed chlorides, forming HCl that caused extensive corrosion and damage to the 410 stainless-steel…