Framework for consequential life cycle assessment of pyrolysis biorefineries: A case study for the conversion of primary forestry residues

In an endeavor towards GHG neutrality, alternatives to fossil carbon resources are explored, such as the use of biomass carbon. Pyrolysis, a thermochemical process that can convert residual biomasses into liquid (bio-oil), solid (biochar) and gaseous (non-condensable gases) products is gaining increased attention, as it both supplies alternatives to fossil carbon while potentially inducing so-called negative emissions through the biochar. Yet, the pyrolysis technical and environmental performance is heavily dependent upon process operational parameters and biomass types. In the perspective of national strategic bioeconomy planning, this study presents an easily replicable consequential life cycle assessment (LCA) framework to quantify the environmental performance of a pyrolysis biorefinery where process conditions are documented, and boundaries expanded to consider the current use of the residual biomass. Results obtained from this method are intended to provide insights for evidence-based decision making towards investments in the low fossil carbon future. The proposed LCA framework was applied to a national case study for the use of primary forestry residues (PFR). Results showed that as compared to the reference scenario in which PFR are left on soil to decay, pyrolysing PFR to biocrude oil, wood vinegar, biochar and gas presents trade-offs in six out of the 16 impact categories studied. These results highlighted that the biomass feedstock supply, the pyrolysis technology, the co-products yields, properties and uses, as well as the choice of marginal technologies have an influence on the environmental performance of pyrolysis biorefineries.