Biofuels and Bioenergy

Development of renewable energy is considered as an effective countermeasure for natural resource sustainability and climate change mitigation. Currently, bioenergy accounts for the largest share in the development and utilization of renewable energy and has been extensively applied in heat and power generation as well as residential and transport sectors. Biomass can be transformed into gas or liquid fuels via a variety of methods such as gasification, pyrolysis, anaerobic digestion, fermentation and transesterification. It can also be utilized as a solid fuel and burned directly for heat and power generation. However, raw biomass possesses a number of disadvantages such as hygroscopic and biodegradable nature, high moisture content, low calorific value, large volume or low bulk density and nonhomogeneity. These characteristics result in a low conversion efficiency as well as difficulty in the collection, grinding, storage and transportation of biomass. Torrefaction is a promising technology to upgrade biomass for solid fuel production. After undergoing torrefaction, the aforementioned properties of biomass are improved to a great extent and close to those of coal. Figure-1 provides a summary to illustrate the impact of torrefaction on the properties of biomass. Consequently, torrefied biomass can be used as an alternative to coal consumed in industry. This article addresses the important issues in basic research of torrefaction, especially in the impact of torrefaction on the property variation of biomass. The potential applications of torrefied biomass in industry such as combustion, gasification, ironmaking, pyrolysis and liquefaction will also be illustrated.