Life Cycle Optimization for Sustainable Operations in a Petrochemical Complex

Abstract

This paper addresses the optimal operation of a petrochemical complex under economic and environmental criteria. The site mathematical model includes linear and nonlinear simplified models for single plants to calculate site production taking into account main operating variables, intermittent deliveries and inventory variable profiles. The objective function considers the maximization of total profit and the minimization of environmental impact, subject to constraints on mass balances, bounds on product demands, equipment capacities and intermediate and final product storage tanks limitations. The environmental objective is measured with the global warming potential (GWP) and Eco-indicator 99 metrics according to the life cycle assessment procedures. The resulting mixed integer nonlinear programming (MINLP) models have been implemented in GAMS. The bi-criteria MINLP model is solved with the e-constraint method. The resulting pareto-optimal curve shows the tradeoff between the economic and environmental aspects to pursuit a sustainable operation of an existing integrated petrochemical complex. The optimal solution shows that polyethylene plants have the best environmental and economic performances in the entire complex. As compared to current situation, optimization results show that the petrochemical complex can satisfy product demands while improving the environmental behavior by decreasing greenhouse gases emissions in almost 26 %, from 1,018 to 750.42 kt CO2-eq/y.