A new shortcut design method and economic analysis of divided wall columns
Journal
Industrial and Engineering Chemistry Research
Journal Volume
50
Journal Issue
15
Pages
9221-9235
Date Issued
2011
Author(s)
Abstract
Divided wall columns (DWCs) can save energy and capital costs compared with traditional distillation columns; however, the design of DWCs is more difficult because there are more degrees of freedom. This paper describes a novel short-cut method that can be used to rapidly determine near-optimal values of important design parameters, including the reflux ratio, number of stages in all sections, and split liquid and vapor ratios for the three most common types of DWCs. The method is based on the development of a rational and efficient net flow model and the application of the methods of Fenske, Underwood, and Gilliland and the Kirkbride equation. The method is applied to two real systems, and the results are compared with results from rigorous simulations and optimization. The results show that the shortcut method leads to a process similar to a feasible actual process, and the total annual cost (TAC) based on the design method is close to the minimum (optimum) total annual cost. The results also show that the method also provides good initial values for rigorous optimization. The method is also applied to a fictitious process consisting of three components with constant relative volatilities, for different values of the ease of separation index (ESI), overall split difficulty, and feed composition. The results indicate that the method works well for a variety of process conditions and that the minimum vapor flow rate is a good surrogate for the total cost of process operation. ? 2011 American Chemical Society.
Type
journal article