Optimal Design of Chemical Processes for Multiple Economic and Environmental Objectives

Optimal Design of Chemical Processes for Multiple Economic and Environmental Objectives 

Elaine Su-Qin Lee, Gade Pandu Rangaiah and Naveen Agrawal Department of Chemical Biomolecular Engineering National University of Singapore, 

For process optimization with respect to several economic criteria such as net present worth, payback period and operating cost, the classical Williams and Otto (WO) process and an industrial low-density polyethylene (LDPE) plant are considered. Results show that either single optimal solution or Pareto-optimal solutions are possible for process design problems depending on the objectives and model equations. Subsequently, industrial ecosystems are studied for optimization with respect to both economic and environmental objectives. Economic objective is important as companies are inherently profit-driven, and there is often a tradeoff between profit and environmental impact. Pareto-optimal fronts were successfully obtained for the 6-plant industrial ecosystem optimized for multiple objectives by NSGA-ll-aJG. The study and results reported in this chapter show the need and potential for optimization of processes for multiple economic and environmental objectives. 

Keywords Economic criteria, Enviromnental criteria, MOO, Williams and Otto Process, Low-density polyethylene plant. Industrial ecosystems. 

Multi-objective optimization (MOO) has attracted considerable attention from researchers in chemical engineering, particularly in the past decade. Reported MOO studies have mainly used criteria such as selectivity, yield, productivity and/or energy consumed see Chapter 2 for the chemical engineering applications studied since 2000 and the objectives used in them. However, profit, an important criterion in any commercial operation, was not used in many of these studies. Apart from the simple profit, several economic criteria such as payback period (PBP), net present worth or value (NPW or NPV) and internal rate of return (IRR) are popular for evaluating projects in industrial practice. Edgar et al. (2001) compared the pros and cons of these three profitability criteria. Studies by Huskies (1997) and Pintaric and Kravanja (2006), show that optimal solutions of chemical processes are dependent on the economic objective selected. This indicates the conflicting nature of some, if not all, economic objectives, which means MOO is probably required even if one is interested in only the profitability criteria. 

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