Use of extended exergy analysis to evaluate the environmental performance of machining processes

Traditional applications of exergy analysis have focused upon the optimization of energy use in thermal and chemical processes. This paper introduces a form of exergy analysis in which the methodology is extended to consider the characteristics of material flows in a process as well. This new form of analysis, termed extended exergy analysis (EEA), is shown to be particularly useful in valuating the environmental performance of industrial processes. EEA differs from traditional theory in its requirement that all ground states be defined such that they are environmentally acceptable. Environmental acceptability can be determined using a number of health, occupational and ecological criteria. By integrating biological considerations into the existing physical definition, EEA provides manufacturers and regulators alike with relevant information regarding the costs of achieving environmentally benign production. These costs are valued consistently for both raw material and energy inputs and product and residual outputs, affording degrees of transparency and objectivity not present in other valuation methodologies. Application of the technique to a case study involving the machining of aluminium is developed.