Introducing exergy analysis in life cycle assessment: A case study

Life Cycle Assessment (LCA) is a methodology for assessing the potential environmental aspects associated with a product or service along its life cycle. However, in the case of energy technologies, it is suggested that the LCA of a product encompasses also further aspects other than environmental aspects and primary energy calculations. In particular, to optimize the reduction of raw materials during the whole life cycle, it is important to introduce the assessment of the irreversibility, applying the exergy analysis. In this paper, an integrated approach of exergy analysis and LCA is proposed, developing the Life-cycle quality index able to suggest potential exergy inefficiencies and the Life Cycle irreversibility index that helps the comparison of processes and products having the same functional unit. In addition, the paper introduces a new dimensionless index, the Technology Obsolescence index, to quantify the technological obsolescence of the energy system examined, merging the energy performance and the material, used both with the same units to achieve a design optimization. The indices proposed are applied to the whole life cycle of a biomass boiler. The results identify that hotspots can be traced in the use stage of the real biomass boiler, where the potential recoverable exergy has an incidence of 17.4% on the total exergy destroyed. Also, in the manufacturing stage, the cooking process produces the highest irreversibilities of the production stage.