Employing feed splitting to eliminate the black-hole problem of dividing-wall distillation columns

Because of the intensive material and thermal coupling within dividing-wall distillation columns (DWDCs), the so-called black-hole (BH) problem may occur and arouse consequently uncertainties to control simultaneously the primary component compositions in the top, intermediate, and bottom products and the composition ratio between the rest components in the intermediate product. The elimination of the BH problem is attempted through the adoption of feed splitting in this work, and a systematic procedure is derived to achieve the purpose. Because feed splitting augments the decision variables for process synthesis and design, it could be used effectively to refine the relationship between the prefractionator and main distillation column involved and lead to the elimination of the BH problem. The design and operation of a DWDC fractionating an equi-molar mixture of ethanol, propanol, and butanol are examined to evaluate the systematic procedure proposed. Both open and closed-loop controllability assessments demonstrate that feed splitting can serve as an effective means to eliminate the BH problem. The resultant DWDC with the elimination of the BH problem is even found to exhibit improved process dynamics and controllability when three specifications have been given, respectively, to the primary components of its three products. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd.