Impacts of feedstock quality on bio-oil production - economics and life cycle implications

Selection of a biomass feedstock has implications for both financial and environmental life cycle burdens associated with a specific conversion process. This work used a combination of experimental data and engineering process simulations to predict the implications of using low cost, high ash feedstocks relative to higher cost, low ash feedstocks through a pyrolysis-based fuel production process. This study examined the impact of variations in the chemical composition of different biomass feedstocks on the final biofuel product. The pyrolysis coversion process was simulated in Aspen Plus®, integrated with a FORTRAN subroutine that contained an empirical model based on bench scale data, that predicted pyrolysis product yield as function of carbon and ash content in biomass.  Model showed that the biomass feedstocks that provided the highest biofuel yield were a clean hardwood and switchgrass with ~180 l/bdton of biomass, while loblolly pine produced 173 l/bdton and bark, the feedstock with the highest ash content, only yielded 147 l/bdton. The energy and mass flows provided by the process model were then used to estimate the life cycle implications of these alternative feedstocks. This analysis showed that the feedstock costs and the yeild of the final fuel product dominated the financial and environmental impacts of the overall process.