Targeting of heat integrated water allocation networks by one-step MILP formulation

Abstract

Heat integrated water allocation networks (HIWAN) is a system where water and energy are highly interconnected. Well arranged nexus between water allocation networks and heat exchanger networks would reduce the water and energy consumption significantly. The aim of this study is to develop a novel mathematical programming model for targeting minimum simplified total annual cost of HIWAN. A new transshipment type of heat exchanger networks (HEN) representation is proposed, with features of stream splitting, stream by-pass, non-isothermal mixing, and isothermal mixing. Constraints are added to follow up on the flowrate consistency when stream splitting or mixing happens. Furthermore, a new formulation is presented to count heat exchanger units. The proposed model is formulated as a mixed-integer linear programming (MILP) problem. It is much easier to get feasible solutions than mixed-integer non-linear programming (MINLP) problems, especially for large-scale problems. Three examples including an industrial example and a large-scale case are solved by the proposed model. It is shown that the proposed model is suitable for the synthesis of HIWAN, and more importantly, the obtained results are better than literature records.