Thermochemical evaluation of biochars properties from Portuguese agro-forestry residues for solid fuel applications

This study provides a high-quality comparative characterization of biochars derived from regionally significant Portuguese feedstocks: hazelnut shell, pine, pinecone, oak pruning waste, and swine manure. All feedstocks were subjected to pyrolysis at 450 °C to evaluate their potential as solid fuels. The results demonstrate the clear superiority of woody-based biochars for energy applications, with hazelnut shell biochar exhibiting the highest fixed carbon (up to 82.89%) and the highest lower heating value (up to 31.64 MJ/kg). In contrast, swine manure biochar proved unsuitable as a standalone fuel due to its extremely high ash content (48.34%). A notable preliminary finding, based on a single case study, was the significant improvement in carbon content in a slow-cooled hazelnut sample, suggesting that post-pyrolysis conditions are not chemically inert and offer a promising avenue for future research in biochar optimization. This work highlights a hierarchical valorisation model for local biomass, classifying feedstocks for optimal use in premium fuel production, general energy applications, or soil amendment based on their distinct thermochemical properties.