Unified Heat Exchanger Network Synthesis via a Stageless Superstructure

The existing mathematical programming-based methods for simultaneous heat exchanger network synthesis (HENS) have used either match-centric or stage-centric superstructures. Most works over the past four decades have primarily used various modifications of essentially two superstructures whose configurational limitations are well established. We revisit a novel, promising, but unsuccessful, exchanger-centric superstructure proposed by Huang and Karimi (Chem. Eng. Sci. 2013, 98, 231-245). We modify the superstructure and the associated mixed-integer nonlinear programming formulation substantially, and develop an efficient algorithm for its solution. The superstructure simply assumes a pool of two-stream exchangers, to which hot and cold streams are assigned. Given a sufficiently large pool, it embeds all possible heat exchanger network (HEN) configurations (in contrast to previous superstructures) including repeated matches, cross flows, bypasses, etc., and allows multiple utilities. The novel HEN configurations obtained for three case studies and improvements in their total annual costs highlight the advantages of the proposed superstructure and model.