In order to take full advantage of regeneration process to reduce fresh water consumption and avoid the accumulation of trace contaminants, regeneration reuse and regeneration recycle should be distinctive. A stepwise optimal design for water network is developed to simplify solution procedures for the formulated MINLP problem. In this paper, a feasible water reuse network framework is generated. Some heuristic rules from water reuse network are used to guide the placement of regeneration process. Then the outlet stream of regeneration process is considered as new water source. Regeneration reuse network structure is obtained through an iterative optimal procedure by taking the insights from reuse water network structure. Furthermore, regeneration recycle is only utilized to eliminate fresh water usage for processes in which regeneration reuse is impossible. Compared with the results obtained by relevant researches for the same example, the present method not only provides an appropriate regeneration reuse water network with minimum fresh water and regenerated water flow rate but also suggests a water network involving regeneration recycle with minimum recycle water flow rate. The design can utilize reuse, regeneration reuse and regeneration recycle step by step with minor water network structure change to achieve better flexibility. It can satisfy different demands for new plants and modernization of existing plants.
