Parametric Models of Greenhouse Gas Emissions for Coal- and Biomass- to-Liquid Facilities

摘要

The US Air Force is currently assessing the use of Fischer-Tropsch (FT) fuels, blended with conventional jet fuel, as aircraft fuel. However, a potential barrier to the use of FT fuels is the greenhouse gas emissions associated with their manufacture. Emerging guidelines for procurement of fuels place limits on the life cycle greenhouse gas emissions for fuels purchased by the US federal government. Since life cycle greenhouse gas emission estimates depend on inputs and emissions along the entire manufacturing chain, and depend on the fates of co-products of manufacturing processes, they are not directly measurable and must be estimated using models. This work examines the sensitivity of greenhouse gas emission estimates for Fischer-Tropsch (FT) fuels to FT processing conditions and to the assumptions made in the life cycle emission modeling. Overall, the greenhouse gas footprints for FT fuels were most sensitive to the choice of catalyst in the FT reactor, the internal recycling of synthesis gas and heavy ends, the use of biomass as a feedstock rather than coal, and the carbon number distribution of liquid hydrocarbons from the FT reactor. Life cycle assessment methodological choices (i.e., allocation methods) also had a significant impact on the estimated greenhouse gas footprint. These sensitivities were often coupled, with the sensitivity of process conditions depending on the allocation choices. Collectively, these results suggest that potential fuel suppliers will need to document both the details of process configurations and their emission estimation methodologies to obtain precise greenhouse gas emission estimates.