The concept of the optimal synthesis of dynamic process systems with uncertain parameters is introduced. A structure parameter approach is used to theoretically derive the necessary condition for the optimal performance system structure, and an effective algorithm for implementing the synthesis method is presented. The results are applied to the optimal synthesis of a reactor-separator system for the dynamic start-up of two reaction systems.
SCOPESignificant progress has been made in the past few years on the synthesis of chemical process systems. The determination of the optimal type and design of processing units, as well as their optimal interconnections within a process flowsheet, can now be done with some success by many synthesis techniques. A good description of the useful techniques has been given by Hendry, Rudd, and Seader (1973), and a latest review of the state of the art of process synthesis can be found in a report by Mah (1975).One serious limitation with most recent studies of process synthesis is that they are mainly concerned with the synthesis of steady state process systems. A wide variety of important chemical process operations, such as the start-up or shutdown of equipment, the batch or semibatch operation of processing units, etc., however, fall into the category of dynamic process systems. Furthermore, a large number of recent studies in chemical engineering have shown that certain types of processing units, such as the parametric pumping and the cycling zone absorption, etc., can give better performance by periodic (dynamic) operations. Therefore, it is of practical interest in many situations to consider the problems of dynamics and control at the stage of process synthesis (Mah, 1975;Henley and Motard, 1972) rather than merely synthesizing the process by assuming a steady state operation and then compensating the effect of dynamics by means of control after the synthesis is completed. Unfortunately, except for the recent studies by the authors (Nishida and Ichikawa, 1975; Nishida, Liu, and Ichikawa, 1975a), this important aspect of including the dynamics and control considerations in the process synthesis problem has been neglected in the literature. Another important aspect of process synthesis which has not been given sufficient attention is the effect of uncertainty in process parameters. In the literature, only the optimal synthesis of steady state process systems with uncertainty has been studied recently (Nishida, Tazaki, and Ichikawa, 1974).The objective of this work is to extend the recent results on the optimal synthesis of dynamic process systems (Nishida and Ichikawa, 1975; Nishida, Liu, and Ichikawa, 1975n) to include the effect of process parameter uncertainty. The problem considered may be stated briefly as: "Given the process dynamics, how to synthesize the process flow sheet and to specify the process design and control variables subject to the uncertainty in process parameters so as to achieve an optimal dynamic operation of the process?" The approach taken is to co...