Eliminating the vapor split in dividing wall columns through controllable double liquid-only side-stream distillation configuration

Abstract

The liquid-only transfer streams are sometimes preferred to replace the thermal coupling stream in distillation at similar energy efficiency for easier controllability. However, the dynamic controllability and practical control structures for such distillation configurations with liquid-only side-stream are still lacking. In search of a solution, this work investigates the dynamic performance of a double liquid-only side-stream process, which has the most complex structure but the lowest energy consumption among all possible liquid-only type ternary distillation configurations. With the aid of composition measurements, the control performances are generally well in case of adding feedforward controllers. Besides, the structure with only temperature controllers is also tested. On the occurrence of ±10% throughput and feed composition disturbances, the process is well-controlled with tiny product purity deviations. However, when the disturbances increase to ±20%, large offsets appear in some cases. To improve the effectiveness of the inferential control scheme, a modified structure with one internal composition controller is finally proposed to handle ±20% step changes. Overall, this work verifies well the easy controlling nature of the liquid transfer stream. The result of the work encourages the promotion of liquid-only side-stream configurations, as a competitive substitute of the well-known Petlyuk column or dividing wall column, for both academic and industrial purposes.