Assessment of the greenhouse gas emission footprint of a biorefinery over its life cycle

Abstract

Expanding the product portfolio of a biorefinery has the potential to improve the economics of the biorefinery as it not only increases revenue but also improves valuable feedstock use. Such process improvement, however, results in added complexity, energy consumption, and emissions. This study evaluated the energy consumption and greenhouse gas (GHG) emissions of an integrated multi-product biorefinery from a life cycle perspective. Six pathways were assessed in which the by-products of fast pyrolysis – biochar and non-condensable gases (NCGs) – were upgraded to produce ethanol and hydrogen, in addition to bio-oil. The six pathways include six corresponding biorefinery configurations. The configurations differ by NCG application and the kind of fuel used to supplement process heat demand. The GHG emissions intensity of the assessed pathways is between 13.54 and 43.13 gCO2eq/MJ. Our assessment shows a higher GHG emissions intensity in the assessed pathways than the base pathway, in which only bio-oil is produced. Generally, the emission intensities of biorefinery products are lower than when these products are produced from fossil sources but higher than when produced from dedicated bioenergy technologies. Also, when the products are put into an end-use application, like power generation, bio-oil shows lower life cycle GHG emissions compared to conventional fossil-based power plants. When the transportation of the products to the power plant is considered, the life cycle GHG emissions of hydrogen are higher than from the conventional generation methods. Sensitivity analyses show that reducing the feedstock moisture content and increasing ethanol titer can provide significant emission reduction potential. Outside the boundaries of the biorefineries, feedstock transportation also has an impact on the overall emissions.