Issues in the modeling and design of material recycling systems

Interest in recycling has surged in recent years due to increasing primary material costs, environmental concerns over material production and disposal, and laws in many countries designed to improve material recycling rates. In response, recycling systems are becoming more complex as increasing material recovery is required from products with complicated material mixtures such as WEEE (Waste Electric and Electronic Equipment) and ELVs (End-of-Life Vehicles). To increase separation system performance and to process complex material mixtures, separation systems are typically organized as highly integrated multi-stage systems. In spite of their cost, the problem of estimating the performance and designing multi-stage separation systems has rarely been tackled from a systems engineering perspective, resulting in poor integration and sub-optimal configuration of industrial multi-stage separation systems. This paper presents a new approach to modeling and analyzing the performance in terms of recovery and grade of multi-stage material separation systems. Individual comminution and separation processes are modeled and integrated into a separation network model that can be studied with analytical techniques. This model can be used to evaluate the performance of multi-stage separation systems under varying operating conditions, supporting decisions related to system configurations. Several basic examples demonstrate the utility of this model for design purposes. Furthermore, several open research challenges in this new research area are highlighted.