Impact of Torrefaction on Woody Biomass Properties

In this work, Norway spruce stem wood, stump and bark were torrefied in a tubular reactor. The effects of feedstock type and torrefaction process parameters such as torrefaction temperature and residence time on the grindability and chemical properties of the torrefied biomass samples were investigated. In comparison to torrefaction temperature, torrefaction residence time had smaller effects on the grindability of stem wood and stump. For raw bark, much less grinding energy is required compared to those for raw stem wood and stump. Torrefaction has minor effects on grindability of the bark. The cellulose contents of stem wood and stump were reduced slightly at a torrefaction temperature of 275 °C. On the contrary, the cellulose content of the torrefied bark drastically decreased already at a torrefaction temperature of 275 °C, with only trace amounts left in the 300 °C torrefied products.