Bioenergy and biofuel production from biomass using thermochemical conversions technologies—a review

Biofuel and bioenergy production from diverse biomass sources using thermochemical technologies over the last decades has been investigated. The thermochemical conversion pathways comprise dry processes (i.e., torrefaction, combustion, gasification, and pyrolysis), and wet processes (i.e., liquefaction, supercritical water gasification, and hydrothermal carbonisation). It has been found that the thermochemical processes can convert diverse biomass feedstocks to produce bioenergy sources such as direct heat energy, as well as solid, liquid and gaseous biofuels for instance biochar, bio-oil and syngas. However, some of these processes have limitations that impede their large-scale utilisation such low energy efficiency, high costs, and generation of harmful chemicals that cause environmental concerns. Efforts are being made extensively to improve the conversion technologies in order to reduce or solve these problems for energy efficiency improvement. In this review, the emerging developments in the thermochemical techniques for producing biofuel and bioenergy from biomass are presented and evaluated in terms of their technological concepts and projections for implementation. It is suggested that an integration of torrefaction or hydrothermal carbonisation with combustion and/or gasification may optimise biomass energy use efficiency, enhance product quality, and minimise the formation of noxious compounds.