Torrefaction of Spruce, Beech, and Oak Pellets in Order t o Improve Calorific Value

Native spruce, beech, and oak pellets were treated by torrefaction. The torrefaction was performed without oxygen, in an electric oven, at temperatures of 170 degrees C, 190 degrees C, and 210 degrees C and treatment periods of 1, 2, and 3 h. The results showed an increase in the calorific value of the pellets by raising the parameters of the treatment regime (temperature and duration), achieving maximum values of 18.93 MJ/kg in the case of beech pellets for 3 h and 190 degrees C, 18.97 MJ/kg for the roughest regime with 3 h and 210 degrees C in the case of spruce pellets, and 18.84 MJ/kg in the case of oak pellets with 3 h and 190 degrees C. The torrefaction process for beech and oak must be stopped at 190 degrees C and 3 hours, becoming ineffective after these values of the treatment regime. The shear strength of the pellets were decreased slightly (10 to 15%) by the torrefaction treatment, but ash content slightly increased from 17.7% for spruce pellets to 29.1% for beech pellets. The results suggest that direct torrefaction of native pellets is possible without the use of nitrogen, i.e., by turning off the oxygen intake in the torrefaction oven, with good results for increasing the calorific value with 8.7% for beech pellets, 7.5% for spruce pellets, and 7.9% for oak pellets.