Simultaneous synthesis of waste interception and material reuse networks: Problem reformulation for global optimization

Abstract

Recycling and reuse of materials are among the most important pollution prevention strategies. In many cases, direct recycling/reuse of process and waste streams may not be feasible because of the intolerable levels of contaminants that can be detrimental to the process performance or can build up to unacceptable levels. Therefore, interception may be used to selectively remove pollutants from the process streams using separation devices or interceptors. In this work, we develop a systematic procedure for the simultaneous synthesis of material reuse and interception networks. A structural representation of the solution alternatives is first presented using a source-interception-sink framework. Then, a generally applicable mathematical formulation is developed. Because of the nonconvexities associated with the general mathematical program, we invoke a number of simplifying assumptions to facilitate reformulation of the problem into a linear program. The concepts of source substreams and interceptor decomposition were used to facilitate the problem reformulation. Additionally, the tasks of assessing interceptor performance and cost were transformed into presynthesis calculations that can be conducted a priori without compromising the accuracy of the models. The problem reformulation yields a linear program that can be solved globally. A case study is solved to illustrate the developed procedure.