Simultaneous Energy and Water Optimization in Multiple-Contaminant Systems with Flowrate Changes Consideration

In this paper, a new systematic design methodology has been developed for thes imultaneous energy and water minimization in multiple-contaminant systems that also feature maximum re-use of water. In addition to allowing re-use of water in multiple-contaminant systems, issues about heat losses and flowrate changes inside unit operations have also been incorporated in this new design method. To implement such a design, two new design aspects are introduced; new method for “Non-isothermal Mixing” point identification and new “Separate System” generation. The first aspect involves “non-isothermal mixing”, which enables direct heat recovery between water streams, and therefore allows the reduction of the number of heat transfer units. The other aspect is the generation of “separate system “in heat exchanger network design. The flexibility of mixing and splitting of water streams allows separate systems to be created as a cost-effective series of heat-exchanger units between freshwater and wastewater streams. The new design aspects have been illustrated with two examples.