The multi-objective framework presented in this example helps to identify choices for the designer among the different economic and environmental objectives considered. In this case, we suggest that especially good designs will be those that have (a) higher profit and lower environmental impacts, (b) lower environmental impacts at the expense of small profit loss, (c) higher profit at the expense of slightly higher environmental impacts, and (d) lower environmental impacts for some categories at the expense of slightly higher environmental impacts in others. It is then a value judgment by the decision maker(s) to determine which design among these is the most appropriate.
The analysis presented thus far has been deterministic, relationships between the system design and economic and environmental performance are assumed to be known and modeled with certainty. In reality major uncertainties are usually present, and these can have a significant effect on the results. Methods for addressing uncertainty in process simulation, design and optimization are considered in the following section, as the next major challenge to implementing efficient, environmentally conscious process design.
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