Global optimization of wastewater integration networks for processes with multiple contaminants

Abstract

A formulation for the global optimization of recycle and reuse mass integration networks is presented. In addition to direct recycle, the model includes adding in-plant interceptors and terminal treatment systems. The model also considers wastewater streams with multiple contaminants. Because of the nonlinear and nonconvex nature of the optimization model, a two-tier approach is proposed along with a simplifying superstructure. First, a presynthesis problem is solved to identify the performance and cost of interceptors with specific tasks. Next, a representation that avoids the mixing of different streams in the treatment system is formulated. As a result, linear relationships on the mass balances are obtained, which implies that the model can be solved for global optimality. An application to a real case study of a refinery system is carried out. When compared to the original system and to the results provided by an integration based on a simple direct recycle strategy, the results show that significant reductions in fresh sources consumption and waste generated can be achieved with the application of the proposed integration framework. © 2011 American Institute of Chemical Engineers Environ Prog, 2011