Distillate−Bottoms Control of Middle-Vessel Distillation Columns

Abstract

The performance of a middle-vessel distillation column subject to distillate−bottoms (DB) control configurations is analyzed. DB-controlled columns, where the distillate flow rate is manipulated to control the distillate composition and the bottoms flow rate is manipulated to control the bottoms composition, have been labeled as inoperable for continuous distillation. In this paper, two DB-control configurations for a middle-vessel column (MVC) are shown to overcome the deficiencies commonly associated with DB control. In the first configuration, the feed flow rate from the middle vessel is fixed and the flow rate of the heating medium controls the sump level. In the second “on-demand” configuration, the feed flow rate from the middle vessel is manipulated to control the sump level. To demonstrate the effectiveness of these configurations, the distillation of a near-ideal binary mixture is examined.