Design And Operating Feasible Region Of Dividing-Wall Distillation Columns

Distillation serves as the most commonly used separation techniques in petrochemical, it can achieve the purification of materials. However, this process is based on consuming large amounts of energy. Various scholars devote themselves to improve the thermodynamic efficiency of the distillation process for a long time. The Petlyuk distillation column, which is proposed by the Soviet Union scholars, is the most famous one among them. It is made up of two conventional distillation columns and one of them saves the condenser and reboiler. The coupling of the two columns is accomplished by the interlinking four streams. These advantages make the Petlyuk distillation column has considerably low requirement on capital investment as well as operating cost. Other researchers then put forward the dividing-wall distillation column (DWDC), which is consisted of a conventional distillation column with one vertical wall in it. As a form of the fully thermally coupled distillation column, it also inherits all the advantages of the Petlyuk distillation column.Although the DWDC has its own advantages, the existence of large numbers of design and operating variables pose great concerns to the synthesis and control of the DWDC than the conventional distillation column. For a DWDC with three product specifications (i.e., the main compositions on its top, intermediate, and bottom products, respectively), owing to the complex interactions between the prefractionator and the main distillation column involved, it is usually infeasible to enhance substantially the composition of the intermediate product from its nominal operating condition and this confines terribly the flexibility and operability of the DWDC. The issue reflects an inherent drawback of the DWDC. In terms of its formation mechanism, the group termed it as the black-hole problem in the current work.In this paper, an attempt is made to diminish the black-hole problem through over-design with the adjustment of the number of stages in each section of the DWDC. The philosophy is an effective way to balance the interactions between the prefractionator and the main distillation column involved during process synthesis and design, and it expands the flexibility and operability of the DWDC. Three illustrative examples (i.e., the separations of hypothetical components, A, B, and C, benzene, toluene, and o-xylene, and ethanol, propanol, and butanol) are used to evaluate the feasibility and effectiveness of the proposed philosophy. The results demonstrate that the black-hole problem can be effectively diminished in terms of careful adjustments of the number of stages in each section of the DWDC. The proposed philosophy represents a novel way to balance process design and process flexibility and is considered to be of general significance to the design and operation of the DWDC.