Sequential approach for water-and-heat exchanger network design

Abstract

A water network (WN) is designed to reduce the amount of freshwater usage in industrial processes by reuse, recycle and regeneration methods. Source is indicated as waste stream from industrial process. Sink is indicated as the feed stream of process that usually requires freshwater categorized as fixed-flow rate problem. The way to reduce freshwater required from sink is by maximizing source reuse. Mathematical programming by the general algebraic modeling system (GAMS) is used to simultaneously identify the minimum amounts of freshwater needed and design an optimal network. Mixed integer linear programming (MILP) is used to design an optimal WN where the objective is to minimize the amount of freshwater and wastewater with a minimum number of reuse, freshwater and wastewater streams. WN with regeneration unit and treating unit is studied to futher reduce freshwater consumption. The water-and-heat exchanger network (WHEN) is designed to reduce both freshwater consumption and heat and cold utilities in fixed- flowrate process with desired temperature using mixed integer nonlinear programming (MINLP). consists of mass balance for WN and heat balance for the heat exchanger network (HEN). The sequential step design, has two-step and four- step calculation procedures. Both two calculation methods are compared with based process consumption and other scenarios. WHEN by four-step calculation procedure give a best designed result by lowest total annual cost.