Design and operation of dividing-wall distillation columns. 2. Process dynamics and operation

• Dynamics and controllability of DWDCs with over-design are studied.
• Three performance indexes are used to quantify open-loop controllability.
• Disturbance rejection and set-point tracking are chosen to inspect closed-loop behaviors.
• DWDCs with and without over-design are compared.
• Over-design through the adjustment of the number of stages appears benefits to DWDC.

In the first paper of this series, it was demonstrated that the black-hole problem of dividing-wall distillation columns (DWDCs) could effectively be diminished through over-design in terms of careful adjustment of the number of stages. Because the over-design serves to coordinate the relationship between the prefractionator and main distillation column involved, it yields frequently favorable effect to process dynamics and controllability and this represents essentially an additional advantage of such process modifications to diminish the black-hole problem. The three example systems studied in the first paper of this series are again employed to ascertain the anticipation. The DWDCs with and without the over-design are strictly compared in terms of open- and closed-loop controllability studies. It is found that the over-design helps to coordinate the interaction between the prefractionator and main distillation column involved and leads consequently to improved process dynamics and capabilities in disturbance rejection and set-point tracking. The outcome confirms again the necessity of diminishing the black-hole problem in the synthesis and design of the DWDCs. Though the interpretation is gained from the three example systems studied, it should be considered to be of general significance to the design and operation of the DWDCs.