Area and capital cost targets for heat exchanger network synthesis with constrained matches and unequal heat transfer coefficients

Abstract

A pair of “transshipment” nonlinear programs (NLP) are formulated to calculate the area and capital cost targets for heat exchanger network (HEN) synthesis with unequal heat transfer coefficients and different capital cost laws (for different materials of construction, pressure ratings, etc.) when there are constraints on the number of matches (exchangers), forbidden matches and required matches with specified areas (for revamp synthesis). With these NLPs, the trade-off between area and number of units can be evaluated before synthesis. In addition to the targets themselves, solution of the area and capital cost targeting NLPs yield: (1) temperature profiles (much like the composite temperature—enthalpy curves) providing a model for the “ideal” profiles in a HEN achieving the area or capital cost target and corresponding utility target; and (2) a proper selection of stream matches and their heat loads to minimize area (or capital cost). These matches and heat loads provide an excellent starting point for synthesis of HENs achieving (within a few percent) the area and capital cost targets with the same number of exchangers in the HEN as matches in the NLP solution (e.g. corresponding to the units target).