(494d) Efficient Computational Strategies for Multi-Objective Optimization of Multiperiod Waste Management in Chemical Sites

Waste minimization, material recovery and utilities rationalization have been traditionally dealt as integral parts at the design stage of process plants [1,2]. However, once the production process is established, the management of the generated wastes and its coordination with the production processes and utilities systems have a crucial role in the optimal plant resources allocation from an economic and environmental point of view [3].

In industrial practice, many facilities have centralized waste treatment plants, given that these plants provide a service for the whole chemical complex. Such centralized treatment services have a limited flexibility in their operating conditions, and must deal with a large variety of effluents, which differ in chemical features, mass flow and production time. Thus, the treatment plants have resource requirements, such as steam or electricity, and result in treated wastes which must comply with existing regulations, and may even have added value, such as recovered solvent or heat valuable streams. Hence, it is necessary to account for the production facilities and the waste management plants from an integrative perspective considering production planning, operation and resource management.

This work presents a multi-period waste management multi-objective optimization, considering economic and environmental issues. The specific behavior of the considered waste management treatments is included in the optimization problem as black-box models based on practical industrial practice [4,5,6] and computing utility requirements and emissions. To achieve more realistic solutions, the estimation of waste treatment costs and environmental impacts has been explicitly added to the assessment scheme, as well as the constraints of the operating conditions in the treatment units and the fulfillment of environmental regulations for water and air emissions.  This system was applied to an industrial based case study and used to analyze the waste mixing potential.

Two main strategies are proposed to tackle the problem, namely a metaheuristic approach [7] and a rigorous mathematical problem formulation. The performance of both strategies is compared in terms of solution quality and computational complexity with the final aim of finding an efficient methodology for posing the heat and waste management integration problem.

References

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[2]          Chakraborty, A.; Linninger, A. A. Plant-Wide Waste Management. 1. Synthesis and Multiobjective Design. Industrial & Engineering Chemistry Research, 2002, 41, 4591-4604

[3]          Melnyk, S. A.; Sroufe, R. P.; Montabon, F. L.; Hinds, T. J. Green MRP: identifying the material and environmental impacts of production schedules. International Journal of Production Research, 2001, 39, 1559-1573

[4]          Seyler, C.; Hofstetter, T. B. & Hungerbuhler, K. Life cycle inventory for thermal treatment of waste solvent from chemical industry: a multi-input allocation model. Journal of Cleaner Production, 2005, 13, 1211-1224  

[5]          Koehler, A.; Hellweg, S.; Recan, E.; Hungerbuehler, K. Input-dependent life-cycle inventory model of industrial wastewater-treatment processes in the chemical sector. Environmental Science & Technology, 2007, 41, 5515-5522  

[6]          Capello, C.; Hellweg, S.; Badertscher, B.;  Hungerbuhler, K. Life-cycle inventory of waste solvent distillation: Statistical analysis of empirical data. Environmental Science & Technology, 2005, 39, 5885-5892

[7]          Rerat, C.; Papadokonstantakis, S.; Hungerbuhler, K. Integrated liquid waste management in batch chemical industry based on multi-objective optimization. Journal of Air and Waste Management Association. Submitted for publication