New distributed-action control strategy with simultaneous heating and cooling in trays of a pilot-scale diabatic distillation column

Abstract

In order to minimize operation transient times, a new distributed control strategy was performed in a distillation unit. Acting simultaneously by heating in tray 11 (stripping section), and cooling in tray 3 (rectifying section) of a distillation column, the control strategy was implemented using Aspen Hysys® with experimental validation. The new distributed control strategy showed a reduction of 0.32h (19min) in the transient time when a negative disturbance in the feed temperature was applied (−14°C), and 0.37h (22min) when a positive disturbance in the feed temperature was applied (+14°C), compared to conventional control. Variations in internal flow rates, as well as temperatures and compositions, were punctual (just where there is control action) and did not affect the steady-state after the disturbance rejection, when compared to conventional control. Distributed-action approach reduced heat amount transferred in the reboiler and reflux flow rate, due to the association with the heat added/removed in trays, evidencing the soft distribution of the control action along the entire column height. Thus, this new distributed control strategy with simultaneous corrective action between top and bottom of the distillation unit allows a significant reduction in transient times, improving plant productivity.