Synthesis of Water Allocation Network in Process Industries

For many water-intensive process industries, process integration approaches can reduce both freshwater consumption and effluent generation by water reuse/recycle. Based on Source/Sink representation, this paper presents a mathematical programming model for the synthesis of water allocation network (WAN) to achieve the minimum water targets. Discharged water from each unit as well as the fresh feed is considered as water sources, whereas units that accept water are considered as sinks. The method combines water-using processes with water treatment operations into a single network. Embedding all the network configurations of source-sink matches, the model is formulated as a linear programming (LP) with flow rate and concentration constraints, which is then optimized by using commercial software Lingo v.9. Finally, a case study of a paper mill is implemented to show the effectiveness of the model. An 18% reduction of freshwater usage and optimal WAN are obtained.