On the optimality conditions of water utilization systems in process plants with single contaminants

This paper introduces necessary conditions of optimality for water-using networks in refineries and process plants. These necessary conditions correspond to the optimal water allocation planning (WAP) problem that considers wastewater reuse on the basis of a single contaminant and where the objective is to minimize the total water intake. The conditions under which degenerate solutions are possible are also identified. Examples are discussed.