Design and control of distillation columns with inert venting

Abstract

The feed streams in many distillation columns contain small amounts of very light components that must be removed in the overhead system. To avoid having to operate at the high pressures or low temperatures required to totally condense the distillate, a small vapor vent stream is removed from the top of the reflux drum. This paper considers the economic and controllability issues involved in the design and control of these inert venting systems. An important engineering trade-off between product losses in the vent and energy consumption leads to an optimum operating pressure, which varies with the concentration of inert in the feed.