Sustainability assessment of biomass resource utilization based on production of entropy – Case study of a bioethanol concept

Increasing interest for use of biomass both for biofuels and materials replacing fossil resources gives increasing reason to make sure that we optimally use available bioresources. Biomass resources should preferably be converted to a maximum of beneficial products with a minimum of harm to the environment. From the second law of thermodynamics we might conclude that the most efficient, and therefore perhaps the most sustainable, utilization of available resources should be the one generating the least amount of entropy. The purpose of this study is to investigate if the entropy production of a process could be used for performance assessment of biomass conversion processes and to explore its implications as a possible aggregated measure for sustainability assessment of such processes. The investigated methodology includes calculation of entropy generation due to both material and energy dispersal and also due to mixing effect of emissions in the environment. The methodology is tested in a case study of the Integrated Biomass Utilization System (IBUS) in Denmark and its different process routes for bioethanol production with several co-products. The impact of energy integrating the IBUS plant with a coal power plant is also assessed to investigate how the assessment outcome is changed by such system changes. The entropy assessment results are compared with an evaluation using traditional LCA methodology. The results from the case study highlight the importance of well integrated and well optimized systems for utilization of biomass. The correlation between the results of entropy generation and weighted environmental load in this case suggest that entropy generation as assessment tool is worth further exploration.