(695e) Understanding the Uncertainties in Environmental Life Cycle Energy and Carbon Analysis for Biofuel from Forest Residue in the United States
In this work, a cradle-to-gate life-cycle energy and carbon analysis was developed for producing biofuels from pine residues through fast pyrolysis in the Southern U.S.. The system included three life-cycle stages: biomass production, transportation, and biorefinery. The Life Cycle Inventory data were collected either from simulation models (e.g., LobDSS4 for pine growth, Aspen Plus for biorefining) or from literature. The uncertain parameters that might have large impacts on the results were identified through literature review and sensitivity analysis. In biomass production stage, most of those parameters identified are related to pine production or forest management methods, such as thinning schedule, rotation length, or forest operations. In biomass conversion stage, uncertain parameters are mostly related to feedstock quality (i.e. carbon content, ash content, and moisture content) that has large impacts on the mass and energy balance. Quantitative information of those parameters was collected from literature and statistically analyzed to generate the probability density functions that were used as inputs to the Monte Carlo Simulation (MCS). MCS is a widely accepted tool that helps understand the effects of uncertainties or variations and has been largely used in LCA studies.5 The results were used to quantify the impacts of variations on life cycle primary energy consumptions and Greenhouse Gas (GHG) emissions. Different counterfactual scenarios were developed to understand the tradeoffs and potential environmental benefits of turning forest residue into biofuels. Preliminary results showed that the parameters that were related to the residue production such as planting strategies, rotation length, and thinning schedule were critical to the results of life-cycle GHG emissions. For the life cycle primary energy consumption, parameters related to biorefinery were the main contributors to the variations of the results.
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