Modeling/Simulation of the Dividing Wall Column by Using the Rigorous Model

Abstract

Dividing wall column (DWC) is an atypical distillation column with an internal, vertical WE partition wall that effectively accommodates two conventional distillation columns into one to improve the thermodynamic efficiency. In previous studies, different equivalent models by combining conventional columns are adopted to approximate the DWC modeling, which may not well describe the integration of the DWC; moreover, the computational cost increases when multiple columns are implemented to represent one DWC. In this paper, a rigorous mathematical model is proposed based on the mass balance, the energy and phase equilibrium of the DWC, where decision variables and state variables are equally treated. The model was developed in the general process modeling system (gPROMS). Based on the rigorous model, the influences of liquid split ratio and vapor split ratio are discussed, and it is shown that the heat duty is sensitive to changes on the liquid and vapor split ratio. Inappropriate liquid and vapor split ratio will increase the mixing effects at both ends of the dividing wall, and adversely affect the thermodynamic efficiency. Hence, the degree of mixing is defined to characterize the column efficiency. Furthermore, the middle component split ratio at the top of the pre-fractionator has an optimal point for better energy saving with certain liquid and vapor split ratios, and can be used as an indicator for the energy performance. Finally, the model was tested and validated against literature data by using the ternary benzene–toluene–xylene mixture system as a case study.

Regions of Optimality for Separation System Synthesis Using Rigorous Modeling, Stochastic Optimization, and Column Stacking

“…Since constructing such diagrams requires the design of each alternative at numerous different values of the feed composition and other variables, most engineers have used shortcut design methods such as assuming constant relative volatility and constant molar overflow and using the vapor rate or total energy consumption as an objective function. − Furthermore, when comparing alternatives to the conventional direct and indirect sequences, most authors reported that DWCs provide cost savings. − However, most do not considered the possibility of stacking the two conventional columns, i.e., adjusting the column pressures so that direct heat transfer between the condenser of one column and the reboiler of the other column is possible. − …”

Process Simulation of the Separation of Aqueous Acetonitrile Solution by Pressure Swing Distillation

“…For increasingly complex industrial technologies, Gao and Dai [26][27][28] proposed the fault detection and diagnosis (FDD) and data-driven approaches in the modeling, control, and optimization of complex industrial systems. Many design variables are involved in the chemical distillation industry, so commercial software, such as Aspen Plus, can better design, optimize, and control the distillation process [29,30]. Aspen Plus (Aspen Tech, Bedford, MA, USA) is a large-scale general process simulation system for plant design, steady-state design, and dynamic simulation.…”