Thesis (M.Eng.)--Chulalongkorn University, 2008

Design a process control structure for a complex process, such as the process having material or energy recycle, is a complicate task. The design control loop would effect the operation significantly. This thesis describes the plantwide control structure design procedure base on general problem that are "what variables should be control" and "How to design the control configuration", the Hydrodealkylation process (HDA) for case study; hence, we present the "Fixture point theorem" to select appropriate the set of controlled variables from a large number of candidate output. The fixture point control theorem states that the most disturbed points must be satisfactorily controlled by giving them consideration before other controlled variables. The maximum (scaled) gain is used to selecting and paring controlled variables with manipulated variables. In this study, the set of first rank of controlled variables is the same as Luyben (1998). We selected three set of controlled variables (second and third rank from fixture point) and five control structures were designed and compared. In order to illustrate the dynamic behaviors of the control structures when economic disturbance load occur such as change in methane composition in fresh feed gas and quencher outlet temperature. The performance of designed control structures were presented in IAE value and compared with reference structure. The designed structures are fast response and the most effective on compared with reference structure1 (Araujo et al, 2006) and same reference structure 2 (Luyben, 1998).