Biomass torrefaction is a thermal process, which is similar to a mild form of pyrolysis at temperatures ranging from 250 to 320 °C to produce energy densified solid fuel. The torrefied biomass is almost equivalent to coal and is termed as bio-coal.
During torrefaction, highly volatile fraction of biomass including moisture and hemicellulose are released as vapors, providing energy enriched solid fuel, which is hydrophobic and brittle.
Bio-coal can be produced from palm kernel shell (PKS) at an optimum temperature of about 300°C with residence time of 15 min and nitrogen gas flow rate of 200 mL/min. Yield of such process results into 73% of bio-coal with calorific value of 24.5 MJ/kg (5856 kcal/kg) with the overall thermal yield of 94%.
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