Comparative life cycle energy and greenhouse gas footprints of dry and wet torrefaction processes of various biomass feedstocks

Abstract This study compares the life cycle energy consumption and greenhouse gas (GHG) emissions of electricity generation from bio-coals produced from various biomass feedstocks via dry torrefaction (DT) and wet torrefaction (WT) processes. Wheat straw, pine woodchips, grape pomace, manure and algae are the main feedstocks evaluated. The energy consumption and the associated GHG emissions at each life cycle stage were calculated. The main stages included are in-field preparation, feedstocks transportation to torrefaction plant, torrefaction process, bio-coal transportation to power plant, and power plant operations. The results show that all pathways are competitive with coal-based electricity in terms of GHG emissions except pathways with algae as feedstock and manure biochar-based electricity generation. Among the pathways, electricity generation from pine woodchips biochar appears to be the best option, with an 88% GHG emissions reduction compared to coal-derived electricity, followed by grape pomace hydrochar with an 85% emission reduction. Electricity generation from wheat straw biochar, grape pomace hydrochar, and pine woodchips biochar lead to the highest net energy ratios (NERs) of 4.19, 4.08, and 3.58, respectively. The developed information is novel and can be used for investment decisions and policy formulation around the world.