Biomass upgrading by torrefaction for the production of biofuels: A review

An overview of the research on biomass upgrading by torrefaction for the production of biofuels is presented. Torrefaction is a thermal conversion method of biomass in the low temperature range of 200–300 °C. Biomass is pre-treated to produce a high quality solid biofuel that can be used for combustion and gasification. In this review the characteristics of torrefaction are described and a short history of torrefaction is given. Torrefaction is based on the removal of oxygen from biomass which aims to produce a fuel with increased energy density by decomposing the reactive hemicellulose fraction. Different reaction conditions (temperature, inert gas, reaction time) and biomass resources lead to various solid, liquid and gaseous products. A short overview of the different mass and energy balances is presented. Finally, the technology options and the most promising torrefaction applications and their economic potential are described.