Effect of Fiber Orientation on Compression and Frictional Properties of Sawdust Particles in Fuel Pellet Production

The increasing production of wood pellets has increased the importance of optimizing the raw materials. The pelletizing process is affected by differences in the raw materials, but knowledge of which of the wood's properties that cause these differences is limited. The present study investigates the effect of fiber orientation in the raw material particles of sawdusts from European beech (Fagus sylvatica L.) Quaking aspen (Populus tremula L.) and Scots pine (Pinus sylvestris L.) on their pelletizing properties. Sawdusts with the fibers oriented along the plane of the particles (longitudinal fiber orientation) and across the plane of the particles (transverse fiber orientation), respectively, were prepared, and the effect was quantified by measuring the compression and frictional properties of the sawdust in single-pellet productions, along with measuring the pellet strength. The results showed that sawdust with transverse fiber orientation required less energy to compress, and to press through the die, while producing pellets with the same or higher strength, compared to the longitudinal fiber orientation. Also, the frictional properties of pellets made from beech and aspen with longitudinal fiber orientations were significantly higher than pine, although no significant difference in friction was shown between species, when the pellets were made with transverse fiber orientation in the particles. The study shows that in the preparation of raw materials for wood pellet production, a transverse fiber orientation in the particles should be preferred to optimize the production capacity and minimize the energy consumption of the pellet mills. In addition, the study shows that the fiber orientation must be considered when analyzing the pelletizing properties of sawdust.