Drying characteristics and equilibrium moisture content of steam-treated Douglas fir (Pseudotsuga menziesii L.)

Douglas fir (Pseudotsuga menziesii L.) particles were exposed to high pressure saturated steam (200 and 220 °C for 5 and 10 min) to improve the durability and hydrophobicity of pellets produced from them. Depending on treatment severity, the moisture content of the particles increased from 10% to 36% (wet basis). Douglas fir particles steam-treated at 220 °C for 10 min had the fastest drying rate of 0.014 min−1. The equilibrium moisture content (EMC) of steam-treated samples decreased with increasing steam temperature and treatment time. The Giggnheim–Anderson–deBoer (GAB) equilibrium model gave a good fit with the equilibrium data with R2 = 0.99. The adsorption rate of untreated pellets exposed to humid air (30 °C, 90% RH) for 72 h was 0.0152 min−1 while that of steam-treated pellets ranged from 0.0125 to 0.0135 min−1 without a clear trend with steam treatment severity. These findings are critical to develop durable and less hygroscopic pellets.