Life cycle assessment and its application to process selection, design and optimisation

As the pressures on the chemical and process industries to improve their environmental performance are increasing, the need to move away from narrow system de®nitions and concepts in environmental system management is becoming more apparent. Life Cycle Assessment (LCA) is gaining wider acceptance as a method that enables quanti®cation of environmental interventions and evaluation of the improvement options throughout the life cycle of a process, product or activity. Historically, LCA has mainly been applied to products; however, recent literature suggests that it can assist in identifying more sustainable options in process selection, design and optimisation. This paper reviews some of these newly emerging applications of LCA. A number of case studies indicate that process selection must be based on considerations of the environment as a whole, including indirect releases, consumption of raw materials and waste disposal. This approach goes beyond the present practice of choosing Best Practicable Environmental Option (BPEO), by which it is possible to reduce the environmental impacts directly from the plant, but to increase them elsewhere in the life cycle. These issues are discussed and demonstrated by the examples of end-of-pipe abatement techniques for SO2, NOx and VOCs and processes for the production of liquid CO2 and O2. The integration of LCA into the early stages of process design and optimisation is also reviewed and discussed. The approach is outlined and illustrated with real case studies related to the mineral and chemical industries. It is shown that a newly emerging Life Cycle Process Design (LCPD) tool offers a potential for technological innovation in process concept and structure through the selection of best material and process alternatives over the whole life cycle. The literature also suggests that LCA coupled with multi-objective optimisation (MO) provides a robust framework for process design by simultaneously optimising on environmental, technical, economic and other criteria. Pareto-optimum solutions obtained in MO provide a number of options for improved design and operation throughout the whole life cycle. This approach therefore provides a potentially powerful decision making tool which may help to identify more sustainable solutions in the process industries. # 1999 Elsevier Science S.A. All rights reserved.