Solid Biofuel Preparation from Eucalyptus Bark by Hydrothermal Treatment and Pelletization: Fuel Properties, Combustion Behavior and Ash Slagging Tendency

Eucalyptus bark (EB) is a promising biomass to replace fossil fuels, but its ash content is high and the energy density is particularly low. In this paper, it was proposed to upgrade EB to prepare solid biofuel by mild hydrothermal treatment (HTT) and pelletization. It was found that HTT could effectively remove troubling elements like Na, K, Zn, Mn, S, Cl, and P in EB. The remaining ashes tend to form higher melting point compounds, whose softening temperature (ST) and flow temperature (FT) increased from 1326 °C to 1399 °C and from 1348 °C to 1425 °C, respectively. The higher heating value of EB increased from 16.32 to 17.68 MJ/Kg after HTT. The density, volume expansion, compressive strength, and durability of the bio-pellet fuel after HTT were all superior to raw EB. HTT and pelletization is a promising method to prepare solid biofuel from EB.