Quality of Pellets Obtained from Whole Trees Harvested from Plantations, Coppice Forests and Regular Thinnings

Abstract

Woody biomass represents a sustainable type of fuel that is marketed directly as firewood or pre-treated by grinding, drying and compressing. Densified biomass fuels provide benefits in transport, storage and handling, and wood pellets in particular are one of the most commercially attractive products. With this in mind, the objective of the presented research was to evaluate the quality of various pellets obtained from different tree parts of five species (and various age): Eucalyptus spp., Fagus sylavtica L., Pinus eldarica Medw., Pinus radiata D.Don, and Robinia pseudoacacia L. In all the analysed cases, the wooden material was harvested according to the whole tree system (WTS), with their branches and leaves. The samples were chipped, refined by a shredder and dried. Pelletisation was finally carried out using a 4 kW Bianco line (Cuneo, Italy) pelletiser. Physical and chemical analyses were undertaken to determine the quality of the pellets as an energy source. Results of this classification showed that the best pellets, mostly due to better mechanical properties, were from plantation trees of Eucalyptus spp. (6- and 3-year-old) and from thinnings of Fagus sylavtica L. (70-year-old), whereas the least attractive types were made from 18-year-old, coppice Eucalyptus spp. and 3-year-old Robinia pseudoacacia L. Regarding the classification developed within this study, all the pellet types were found to be classifiable as none exceeded the toxic content limit. In terms of the influence of the species, management system and stem age on pellet quality, this study showed the presence of a link between cycle duration and pellet quality, with increasing stem age resulting in better pellet characteristics.