Advances in solid biofuels production through torrefaction: Potential biomass, types of torrefaction and reactors, influencing process parameters and future opportunities – A review

Biomass is a versatile, renewable, sustainable feedstock that could be used to produce solid, liquid, and gaseous energy sources. Most feedstocks are subjected to suitable pretreatment to attain enhanced biomass-derived energy with appropriate quality. In this regard, torrefaction is a new thermochemical biomass pretreatment process that addresses the key constraints of biomass, such as heterogeneity, lower bulk density, lower energy density, hygroscopic behavior and fibrous nature. Torrefaction is performed at 200-300 oC in an inert environment at atmospheric pressure, producing high-quality solid biomass products with more hydrophobic, grindable, energy-dense, and less volatiles used for energy generation. Torrefied biomass is employed effectively in co-firing power plants, pushed as a charcoal substitute, and utilized instead of coal in metallurgical processes. This review provides a thorough analysis of current advances in different biomass torrefaction technologies, essential processes affecting parameters, characteristics of terrified biomass, and future opportunities of this technology for sustainable energy generation.