Densification of raw and torrefied biomass: A review

Densification and torrefaction are potential technologies to valorize lignocellulosic residues into cleaner and sustainable alternative energy carriers for domestic, institutional, commercial and industrial thermal energy applications. Therefore, this review paper has focused on sources of lignocellulosic biomass for energy production. Furthermore, the processes involved in production of raw and torrefied briquettes/pellets have been discussed. Additionally, the physicomechanical, emissions and combustion properties of raw and torrefied briquettes produced from lignocellulosic residues have been presented. Also, the economics of briquetting lignocellulosic biomass materials have also been reviewed. The quality of densified solid biomass fuels from lignocellulosic residues was found to dependent on the feedstock and pretreatment conditions. Additionally, torrefaction and densification have been reported to upgrade the energy properties of loose biomass materials, as potential alternative fuel to firewood and charcoal. Finally, the economic profitability of densification projects has been found to be dependent on the availability of feedstocks, technology used and market potential of the product.