A rigorous disjunctive optimization model for simultaneous flowsheet optimization and heat integration

This paper presents a new model for heat integration that overcomes difficulties experienced either with direct integration approaches, or with the Duran and Grossmann (1986) model when handling isothermal streams. The proposed model uses logic disjunctions to explicitly model the relative placement of streams for various potential pinch locations, and explicitly considers the non-isothermal and isothermal streams as separate cases. It is shown that the proposed model can be reformulated as a large but tight MINLP problem, even thought uses big-M constraints. It is also shown that the MINLP model can be reduced to a MILP problem when dealing only with isothermal streams. Several examples with up to 12 streams are shown, and the performance of the model compared to that of Duran and Grossmann's (1986). (C) 1998 Published by Elsevier Science Ltd. All rights reserved.