Densification of torrefied Pinus radiata sawdust as a solid biofuel: Effect of key variables on the durability and hydrophobicity of briquettes

Abstract

The integration of torrefaction and densification is a promising method to produce solid biofuels with high durability, hydrophobicity and energy density if suitable operating conditions are achieved. Variables including the torrefaction temperature, moisture content, briquetting pressure, briquetting time have been optimized based on durability and water resistance tests. Compared with torrefaction at 280 °C for 10 min, torrefaction at 300 °C for 6 min was preferred as it could achieve similar energy recovery (85.7%) with higher heating value (22.35 MJ/kg) using less torrefaction time. A moisture content of torrefied sawdust at 8–10% and a densification pressure at higher than 38 MPa were optimal to make briquettes with higher durability as suggested by drop and tumble tests, while the briquetting holding time had shown no significant difference. Briquettes made of the torrefied sawdust (300 °C for 6 min) with 10% of moisture content showed the highest water resistance as indicated by the moisture absorption test. In general, rapid torrefaction at 300 °C for 6 min with subsequent densification with 10% moisture content and 38 MPa densification pressure is recommended to produce a solid biofuel from radiata pine sawdust with volumetric energy density (17.2 MJ/L) close to sub-bituminous coal.