(551a) Life Cycle Assessment of the Production of Transportation Fuels From Sweet Sorghum
A life cycle assessment (LCA) is presented that evaluates the environmental impacts of an ethanol production system using sweet sorghum as the biomass feedstock. The process includes a modified forage chopper that cuts the sweet sorghum stalk down to six to eight inch billets, a stationary roller press to extract the juice, a fermentation process to convert the cellulose to ethanol, and a distillation column and molecular sieve to produce anhydrous ethanol. A process simulation was developed using Aspen Plus® to model the distillation process and for evaluating different process options. Several harvesting options are considered, and their impacts on the LCA are assessed. Processing options include: 1) extract the juice on site and transport it to a facility that completes the processing, 2) ferment the juice on site and transport the unprocessed ethanol to a location where the distillation process is performed, and 3) perform the distillation on site and transport the ethanol to a molecular sieve site to produce the anhydrous ethanol. A cradle to gate LCA will be presented that evaluates the environmental impacts from growing the crop to the production of anhydrous ethanol. A cradle to grave LCA will also be presented that includes the end use of the ethanol (transportation fuel). The functional unit for the cradle to gate is 1 MJ of equivalent energy and for the cradle to grave the functional unit is 100 miles. The environmental impacts of this process are compared to that of the production of ethanol from corn and the production of gasoline from crude oil. Inventory data for the system are collected and used to calculate a Life Cycle Impact Assessment (LCIA) using the IMPACT 2002+ framework. Eight impact categories are evaluated: Human toxicity, Respiratory effects, Ozone layer depletion, Terrestrial Eco toxicity, Terrestrial acidification/nutrification, Land occupation, Global Warming, and non-renewable energy. The results of this LCA will facilitate a comparative study to be done on the environmental impacts of the three processes.
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