Design water allocation network with minimum freshwater and energy consumption

In this paper, water minimization as well as energy minimization is taken into account at the same time. Some new concepts are put forward, such as substream, favorable substream, favorable water network and favorable water system. Because of the complexity of coupling water system with energy system, the problem is divided into two steps. First, the optimal water allocation networks are obtained. Since the result may be not unique, those optimal water networks that are favorable to heat integration should be selected. In the selection, choosing those favorable water networks to perform subsequent heat integration. Second, the heat exchanger network of the selected optimal water network is constructed. If the selected network can satisfy the demands of the favorable water network, the determined minimum utilities can guarantee global optimality. Considering the particularity of heat integration on favorable water network, a method to design heat exchanger network on favorable water network is introduced in this paper.