Comparison of two types of two-temperature control structures for reactive distillation columns

The purpose of this paper is to compare the effectiveness of two different types of two-temperature control structures for reactive distillation columns. The first was a structure proposed by Roat et al. (Roat, S.; Downs, J.; Vogel, E.; Doss, J. Integration of rigorous dynamic modeling and control system synthesis for distillation columns. Chemical Process Control; CPC III; Elsevier: Amsterdam, The Netherlands, 1986) almost 2 decades ago in which two tray temperatures in the column are controlled by manipulating two fresh feed streams. The second was recently proposed by Yu and co-workers (Yu, C. C. Private communication, 2004) in which two tray temperatures are controlled by manipulating one of the fresh feed streams and vapor boilup. The second fresh feed stream is flow controlled. We discuss the issues of the selection of the fresh feed stream to be manipulated and the importance of the tuning procedure for the two interacting temperature controllers. Both an ideal reaction system and the methyl acetate system are studied. The effectiveness and robustness of these control structures are compared in the face of disturbances in the production rate and fresh feed compositions. One of the main conclusions is that the selection of the manipulated fresh feed stream in the second structure has an important role in the stability of the system. Sequential tuning of the interacting temperature controllers is sometimes necessary.