A case study for Life Cycle Assessment (LCA) as an energy decision-making tool: The production of fuel ethanol from various feedstocks

摘要

Life Cycle Analysis (LCA) considers the key environmental impacts for the entire life cycle of alternative products or processes in order to select the best alternative. An ideal LCA would be an expensive and time-consuming process because any product or process typically involves many interacting systems and a considerable amount of data must be analyzed for each system. Practical LCA methods approximate the results of an ideal analysis by setting limited analysis boundaries and by accepting some uncertainty in the data values for the systems considered. However, there is no consensus in the LCA field on the correct method of selecting boundaries or on the treatment of data set uncertainty. This paper demonstrates a new method of selecting system boundaries for LCA studies and presents a brief discussion on applying Monte Carlo Analysis to treat the uncertainty questions in LCA. These techniques are demonstrated using an LCA which compares ethanol fuel produced from three different biological feedstocks. The methodology applied and the results presented by this work will be of primary interest to LCA practitioners and the ethanol industry. Alternative automotive fuels are of significant interest to industries and governments worldwide as concern over the emissions of greenhouse gases rises. Combustion of transportation fuels is the single largest source of greenhouse gas emissions in Canada. Additional concerns of fuel production and use include emissions of ground-level ozone precursors and acid-forming emissions. Ethanol, used as a fuel additive or as neat fuel, is an alternative to conventional gasoline. However, as this work shows, the numerous feedstocks used in producing ethanol differ greatly with respect to their life cycle environmental performance. The paper compares the environmental effects of producing ethanol in Canada using three potential feedstocks: corn, wheat, and poplar trees. The results show corn ethanol to produce 700 kg CO_2 equivalents per 1000 liters of ethanol produced, wheat ethanol to result in 760 kg of CO_2 equivalents, and ethanol from poplar trees through a strong acid process to emit 860 kg of CO_2. The relative importance of production, transportation, processing and combustion is compared for each ethanol feedstock.