PRELIMINARY SCREENING-PROCEDURE FOR THE MINLP SYNTHESIS OF PROCESS SYSTEMS .2. HEAT-EXCHANGER NETWORKS

The objective of this paper is to present an implementation of the preliminary screening procedure for the MINLP synthesis of heat exchanger networks, based on the MINLP model by Yee and Grossmann, and utilizing as the aggregated model an MILP reformulation of the transshipment model. It is shown that the MILP reformulation of the transshipment model can be derived mathematically as an aggregation of the MINLP model. Several important aspects that enhance the preliminary screening are the following: First, the generation of the superstructure, as originally proposed, is modified in a preliminary analysis step. The resulting modified superstructure is shown to require no more, and generally fewer units than the original superstructure. Secondly, the transshipment model incorporates the aggregated area cost as an optimization variable, yielding a tight lower bound to the global optimal solution and better cost estimates of alternative solutions. Numerical examples are presented to show: (1) the extent to which the size of the original MINLP problem can be reduced, and thus the computational efficiency enhanced; (2) the robustness of the solution improved through the elimination of poor alternatives; and (3) the value of the global optimal solution of the reduced MINLP bounded.