Integration of a drying and pyrolysis system in a green biorefinery: biochar product quality and impacts on the overall energy balance and climate footprint

Green biorefineries can support the reduction of soybeans imports to Europe, by producing protein-rich animal feed from alternative feedstock such as perennial grass and legume species. Once the protein-rich green juice is extracted, a fiber-rich pulp is left as a residue. This work investigates the thermochemical processing of the pulp via pyrolysis as an option to improve the energy balance and climate footprint of a green biorefinery, by producing non-fossil energy and a high-value biochar product. Laboratory-scale pyrolysis and biochar activation were carried out on pulp samples obtained from different perennial species, different pressing method, and maturity at harvest. The results highlighted the importance of the activation stage to obtain a porous biochar, potentially suitable as animal feed additive. The effects on the overall energy balance and climate impact of the system following the integration of pulp drying and pyrolysis, plus a possible activation step for the biochar, were evaluated with a techno-environmental assessment. The pulp sample composition had only limited influence on the climate impact potentials identified. In all cases, it was found that the integration of a combined drying-pyrolysis-activation system in the green biorefinery may provide substantial additional climate benefits but also that the magnitude of these is strongly dependent on the substitution use-value of the energy products.