An Improved Shortcut Design Method of Divided Wall Columns Exemplified by a Liquefied Petroleum Gas Process

Abstract

Designing a sustainable and economical distillation system is a big global challenge in the industrial chemical field. To address this issue, one of most promising solutions is the so-called dividing wall columns addressed in this work, which not only can cut energy cost but also use limited installation space. An improved shortcut design approach is developed in this work to provide accurate models for each section of dividing wall columns; meanwhile Underwood’s and Gilliland’s equations are employed to determine minimum reflux ratio and total number of stages in different column sections in terms of corresponding design specifications and operating conditions. This proposed approach has been applied to separations of mixtures of hydrocarbons and alcohol with different values on the ease of separation index. To test its effectiveness, the preliminary design parameters obtained through the improved proposed shortcut method are further validated by a rigorous simulation in Aspen HYSYS. Furthermore, the results indicate that this method could provide much more accuracy of average interconnecting stream composition of the prefractionator and main column than those of other methods. In practice, this method has been applied to a case of liquefied petroleum gas (LPG) separation with three targeted products in an industrial liquefied petroleum gas plant. The applications and efficiency of the shortcut method in this study lay a theoretical foundation for designing the separation of ideal mixtures involving dividing wall columns.

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. − …”

Energy-Saving Optimal Design and Effective Control of Heat Integration-Extractive Dividing Wall Column for Separating Heterogeneous Mixture Methanol/Toluene/Water with Multiazeotropes

“… − , However, conventional ED has a relatively low thermodynamic efficiency, and the high quality energy input is required in the reboiler to perform the separation task. − , Furthermore, the increasing awareness of the energy crisis has made process intensification a promising trend for energy savings strategies in chemical engineering. Therefore, a separation technology, called “dividing-wall columns or DWCs”, separation configuration was proposed and could be applied in the separation of multicomponent or nonideal azeotrope mixtures and have significant advantages than conventional distillation. − ,, …”

“…Therefore, a separation technology, called "dividing-wall columns or DWCs", separation configuration was proposed and could be applied in the separation of multicomponent or nonideal azeotrope mixtures and have significant advantages than conventional distillation. [10][11][12][13]29,30 The divided-wall at the top of the DWC configuration divides the column into two rectifying sections and a shared stripping section, and the dividing-wall is often implemented in the extractive separation denoted as extractive dividing-wall column (EDWC) for separating an azeotropic mixture (see Figure 2a). 14−20 A thermodynamically equivalent process of the EDWC in Aspen Plus is demonstrated in Figure 2b.…”

Remixing Analysis of Four‐Product Dividing‐Wall Columns

“…It could separate three or four pure fractions in a single shell . The short‐cut and rigorous simulation , optimization , control , and implementation have been well studied. In a standard arrangement of a three‐product DWC, the light component and the heavy component have a direct increasing or decreasing trend in the prefractionator and the main column.…”