Thesis (M.Eng.)--Chulalongkorn University, 2007

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 presents a plantwide control design procedure base on basic idea of self-optimizing control to select controlled variables which when kept constant lead to minimum economic loss. The maximum scaled gain is used to selecting and paring controlled variables with manipulated variables. This presented-method is elementary and effective. In the study, three control structures were designed and compared. In order to illustrate the dynamic behaviors of the control structures in reaction section of HDA plant when economic disturbance load occur such as change in toluene flowrates, methane composition in fresh gas feed and disturbance load hot stream were made. All of control structures can operate to achieve the objective and within process constraints. The performance of designed control structures were presented in IAE value and compared with reference structure. The designed structures are faster response than reference structure. The benzene products of designed structures (6.25%) are smaller deviation from steady state than reference structure (6.85%). Thence, the designed structures were studied about variation of heat exchanger duty to cost and dynamic performance of structure. Disturbance load cold stream, disturbance load hot stream and fresh toluene feed flowrates were made for study dynamic response. The large heat exchanger is lower utility cost than the small heat exchanger. The good structure can handle disturbance of large heat exchanger which small furnace duty