Global optimization for the synthesis of property-based recycle and reuse networks including environmental constraints

This paper presents a new formulation and a mathematical programming model for the direct recycle and reuse of mass exchange networks considering simultaneously process and environmental constraints. The model is based on mass and property integration. The properties constrained by the sinks include composition, density, viscosity, pH, and reflectivity, whereas the environmental constraints include the composition for hazardous materials, toxicity, chemical oxygen demand, color, and odor. The model eliminates most of the nonlinearities of the system, and the bilinear terms that remain are handled with a relaxation approach that yields a global optimal solution. The model minimizes the total annual cost that includes the cost of fresh sources and the annualized cost for property interceptors. Two examples are presented to show the effectiveness of the proposed model. The results show that even for a large size problem, the computation effort is relatively small as a result of the linearization procedure.