Optimal design and control of three simplified sargent four-product dividing-wall columns

Abstract

Sargent columns have been shown to reduce energy consumption significantly for chemical separations with four product streams. However, the number of vapor splits needed to operate the system poses operational concerns. As a result, simplified configurations have been investigated to reduce vapor splits. This study aims to examine the economic design followed by dynamic performance analysis of three simplified alternative configurations, i.e., s-2-3-4, 2-2-4, and 2-3-3, to the Sargent column, for the separation of a Benzene-Toluene-Xylene (BTX) mixture. The designs were obtained through rigorous simulations in AspenPlus, linked to an optimization code using genetic algorithms in Matlab. The optimization problem considers the total annual cost (TAC) minimization. Optimal designs of the simplified alternatives are economically attractive, with 26 to 33% savings in TAC over the conventional sequence. The dynamic performance of simplified DWCs was studied through temperature-only PID control schemes in a multi-loop framework. The results show that simplified dividing wall columns (DWCs) provide suitable performance without considering vapor splits as manipulated inputs. Small variations from nominal product specifications (<0.25 mole%) were observed after the throughput and composition feed disturbances were imposed. Thus, this work demonstrates that the studied simplified DWC alternatives are attractive options for industrial implementation.