(309f) Dynamic Life-Cycle Analysis of Fast Pyrolysis Conversion: Implications on Strategies to Manage Feedstock Variability and Improve Sustainability

Pyrolysis conversion is a main contributor to the GHG emissions for biofuels produced from fast pyrolysis. Feedstock composition and reaction temperature are important parameters of the conversion unit operation as they affect the yields of bio-oil, char, and gaseous products from fast pyrolysis. In this case study, we used the fluidized bed reactor experimental data to examine the impacts of feedstock properties and pyrolysis temperature on greenhouse gas (GHG) emissions of the conversion unit operation. We evaluated the trade-off between the main- and co-product, i.e., hydrocarbon fuels and surplus electricity, and its impact on the conversion GHG emissions. We also compared biorefinery-level GHG emissions reduction at different pyrolysis temperatures as a function of various feedstock properties to quantify the GHG emission reduction potential relative to petroleum fuel production and electricity generation at power plants. Results suggested that conversion GHG emissions increase as ash and lignin contents increase at all investigated temperatures (500 ^oC, 525 ^oC, and 550 ^oC). A trade-off between the organics yield and biochar and off-gas yields as a function of feedstock attributes such as ash content and the pyrolysis temperatures is observed, which influences the conversion GHG emissions. Biorefinery-level GHG emission reduction results show that for a low-ash feedstock, a lower pyrolysis temperature benefits greater biorefinery-level GHG emission reductions, while for a high-ash feedstock, a higher pyrolysis temperature benefits greater biorefinery-level GHG reduction. Biorefinery-level GHG emission reduction could vary from 0.35 to 0.42 tonne per tonne of feedstock converted to biofuels, depending on feedstock attributes and pyrolysis temperatures, which translates to $3 - $14 per ton of feedstock converted with a current carbon credit of $195/tonne of GHG reduction under California’s Low Carbon Fuel Standard. Such results shed light on how the biorefinery can adjust the operating strategy based on the feedstock properties to achieve better sustainability and at the same time maximize its overall carbon credit, which could also help lowering the fuel MFSP.