Optimization of Direct Recycle Networks with the Simultaneous Consideration of Property, Mass, and Thermal Effects

Abstract

There is a growing need to develop systematic and cost-effective design strategies for direct recycle strategies that lead to the reduction in the consumption of fresh materials and in the discharge of waste streams. Traditionally, most of the previous research efforts in the area of designing direct-recycle networks have considered the chemical composition as the basis for process constraints. However, there are many design problems that are not component-based; instead, they are property-based (e.g., pH, density, viscosity, chemical oxygen demand (COD), basic oxygen demand (BOD), toxicity). Additionally, thermal constraints (e.g., stream temperature) may be required to identify acceptable recycles. In this work, we introduce a novel approach to the design of recycle networks that allows the simultaneous consideration of mass, thermal, and property constraints. Furthermore, the devised approach also accounts for the heat of mixing and for the interdependence of properties. An optimization formulation is developed to embed all potential configurations of interest and to model the mass, thermal, and property characteristics of the targeted streams and units. Solution strategies are developed to identify stream allocation and targets for minimum fresh usage and waste discharge. A case study is solved to illustrate the concept of the proposed approach and its computational aspects.