Evaluation of ratio control schemes in a two-temperature control structure for a methyl acetate reactive distillation column

A two-temperature control structure for a methyl acetate reactive distillation (RD) column, originally proposed by [Roat, S.D., Downs, J.J., Vogel, E.F. and Doss, E.J., 1986, Integration of rigorous dynamic modeling and control system synthesis for distillation columns, in Chemical Process Control CPC III, Morari, M. and McAvoy, T.J. (eds.) (Elsevier, New York.)], is modified to incorporate ratio controllers in three different configurations between the column inputs. Closed loop results for these three configurations, namely, acetic acid feed in ratio with the methanol feed, methanol feed in ratio with the acetic acid feed and the two fresh feeds in ratio with the reboiler duty (through-put manipulator) show that the control performance for load disturbances does not improve and may deteriorate when the two fresh feeds are fed in ratio (acetic acid to methanol or methanol to acetic acid). The deterioration in performance is attributed to input multiplicity and unfavourable dynamic interaction between the control loops. Tighter product purity control is achieved for a through-put change when the two feeds are fed in ratio with the reboiler duty, the through-put manipulator. It is also shown that an alternative design that avoids input multiplicity exhibits better control performance. The results highlight the need for considering the non-linear effects in column and control system design for RD processes.