ADAPTIVE-CONTROL OF MULTIPLE-FRACTION BATCH DISTILLATION FOR TRACKINGOPTIMAL A-PRIORI POLICIES

Unlike one-fraction batch distillation using constant distillate compo sition control, a priori policies are to be tracked with control syste ms designed to realize the optimal operation of multiple-fraction batc h distillation. Adaptive control is proposed to carry out this task. B ased on a detailed model, characteristics of batch distillation contro l are analysed and a proper system is designed for an existing multico mponent/multiple-fraction batch column. Besides tracking the optimal r eflux ratio profile, the maximum vapour load must be maintained during the batch to realize the optimal operation of multiple-fraction batch distillation. In addition, a changing temperature profile of the cond enser should be followed to reduce the operating energy with a possibl y minimum subcooling. Recursive least square estimation (RLSE) with a variable forgetting factor is applied to the on-line identification of the plant to follow the changing dynamics of the process. Generalized predictive control (GPC) is successfully used to track the predefined policies. Moreover, we show that it is difficult to control the proce ss satisfactorily over the whole batch time by PID controllers with fi xed parameters.