Dynamic simulation and control of a distillation column

Abstract

Distillation columns are highly coupled and non-linear, and have major impact on the utilities consumption and product quality. By proper design of controls, product variability can be minimized, and facilities can be operated in stable manner thus avoiding unnecessary trips. Hence, selection of proper controls for distillation columns is both challenging and critical. This study deals with the composition control of distillation columns by using rigorous simulators along with an industrial depropaniser as an example. Effect of control structures, ratioing to feed flow rate, level controllers tuning, turn-down operation, and feed tray location on column performance is studied thoroughly; both single-ended and dual-ended composition controls are considered. The control performance is evaluated for step disturbance in feed flow rate and feed composition, as well as sinusoidal disturbance in feed composition. It has been observed that rigorous evaluation through simulation and understanding of these factors can improve the selection and design of control structure for columns.