Studies in process synthesis-I. Branch and bound strategy with list techniques for the synthesis of separation schemes

The synthesis of a good flowsheet for a multicomponent separation problem constitutes a formidable task even for a small scale problem. The number of alternate, feasible separator sequences increases rapidly as the number of components in the mixture and the number of allowed separation methods increase. Some methods to select a sequence are almost purely heuristic to permit rapid screening among the alternatives without a guarantee of optimality. Another is based on dynamic programming and for special problems can in principle locate the best sequence, but it is notably time consuming. This paper uses primal and dual bounds in a branch and bound strategy to develop a procedure for locating a small number of nearly optimal separation sequences; furthermore, the optimal sequence must be among those found. Restrictions necessary for the dynamic programming approach can be relaxed (serial structure, high product purity), and in principle the method should generally be significantly faster. Two examples illustrate the approach.