Energy efficient control of a BTX dividing-wall column

Dividing-wall column (DWC) is considered nowadays the new champion in distillation, as it can bring substantial reduction in the capital invested as well as savings in the operating costs. This work presents the simulation results of energy efficient control and dynamics of a dividing-wall column (DWC). In order to allow a fair comparison of the results with previously published references, the case-study considered here is the industrially relevant ternary separation of the mixture benzene-toluene-xylene (BTX) in a DWC. Rigorous simulations were carried out in Aspen Plus and Aspen Dynamics. Several conventional control structures based on PID control loops (DB/LSV, DV/LSB, LB/DSV, LV/DSB) were used as a control basis. These control structures were enhanced by adding an extra loop controlling the heavy component composition in the top of the prefractionator, by using the liquid split as an additional manipulated variable, thus implicitly achieving minimization of energy requirements. The results of the dynamic simulations show relatively short settling times and low overshooting especially for the DB/LSV and LB/DSV control structures. Moreover, the energy efficient control proposed in this work allows the operation of DWC with minimum energy requirements or maximum purity of products.