A cost effective minimum water network model for intra and interplant system

This paper presents a mathematical model for a cost effective minimum water network for intra and interplant involving multiple contaminants for a set of process plants. A generic mixed integer non-linear programming (MINLP) model has been developed based on water network superstructure to targets and design minimum water network for retrofit design. The model includes all levels of the water management hierarchy (i.e. source elimination, source reduction, direct reuse/ outsourcing of external water, regeneration reuse and fresh water) and is set to achieve a payback period criteria set by the designer to ensure cost effectiveness of the solution. The approach is illustrated by using an inter-plant case study involving a semiconductor and a chlor-alkali plant. The results show that the new freshwater and wastewater targets are 14.99 t/hr and 2.94 t/hr respectively with capital cost of USD 276,900 and payback period of 3 years. This represents a 54.90% increment in freshwater reduction as compared to Handani et al [1] and Wan Alwi et al [2].