Simultaneous optimization of water and energy within integrated water networks

Abstract

This contribution presents the synthesis of heat-integrated water-using and wastewater treatment networks (HIWTNs). The superstructure proposed includes process water-using units, wastewater treatment (regeneration) units, and heat exchangers (HEs) as well as all the new opportunities for water and heat integration within the overall network. A two-step solution strategy is proposed for the subsequent solving of two nonlinear models and the identifying of a set of good locally optimal solutions. The targeting model is solved during the first synthesis step thus minimising the operating cost of the network and providing an initialisation, as well as good upper-bounds for freshwater and utilities consumption for the second model. The objective of the second synthesis step is to synthesise HIWTNs simultaneously by minimising total annual cost (TAC). This research was an extension of our previous works and a follow-up on our recent studies, where we addressed the synthesis problems of HIWTNs but now using a different superstructure (e.g. multiple choices mixing and the splitting of streams allowing for additional heat integration within the overall network) and a more efficient solution strategy from the point of generating of multiple solutions. We solved two literature and two newly introduced examples in order to demonstrate the applicability of the proposed strategy. Improvements in the results were achieved using the studied literature examples of HIWTNs.