Effect of Steam Explosion and Torrefaction Treatments of Wood Chips on the Heating Value of Pellets

Abstract

The surplus of wood chips from sawmills is increasing due to the reduction in the demand for newsprint paper. Thus, this study aims to promote the use of wood chips for bioenergy by producing high-quality pellets. More specifically, this project aimed to evaluate the impact of various heat treatment approaches on the heating value of wood pellets made from black spruce (BS), jack pine (JP) and balsam fir (BF). The studied heat treatments were steam explosion and torrefaction. The resulting energy pellets were characterized in terms of density, high heat value (HHV) and durability. The heat treatment improved pellet HHV. Regardless of the type of wood, the HHV of torrefied pellets is significantly higher (27.6–31.1 MJ/kg) compared to steam exploded pellets (21.9–22.7 MJ/kg) and untreated pellets (18–19 MJ/kg). However, as a result of the deterioration of the hydroxyl groups due to torrefaction, the durability of the torrefied pellets is low compared to that of the steam-exploded pellets. Irrespective of the treatment used, JP pellets, with a maximum of 98.9%, had the best durability.