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.

A Comparison of the Qualitative Characteristics of Pellets Made from Different Types of Raw Materials

“…Monedero et al [45] indicate a certain difficulty in complying with the threshold of 600 kg m 3 for species like poplar and pine, confirming what emerged in this study. A possible explanation of the general low bulk density level achieved can be found in the fact that in this study, the raw material applied was characterized by the presence of branches and, in some cases, leaves, thus material that is less prone to palletization in comparison to the pure sawdust that is applied at the commercial level [46].…”

Eco-Efficiency of Pellet Production from Dedicated Poplar Plantations

“…The main objective of the new European measure on renewable energy, which modifies the previous Red II Directive [6], is to achieve, by 2030, a percentage of energy coming from renewable sources equal to 42.5% (compared to the previous 32%) of the overall energy mix of the European Union. In the context of reducing the concentration of greenhouse gases in the atmosphere, the use of woody biomass as a resource for energy production becomes a key option due to the neutrality of its CO 2 life cycle [2,[7][8][9]. Remembering also that the use of renewable energy leads to a reduction in energy costs determined by fossil fuels [10].…”

“…The pellet, therefore, comes in a cylindrical form with a diameter of 6-8 mm and an average length of 10-12 mm, which is easy to package and use [24,25]. The starting woody material can be represented by residues from wood processing (sawdust), by wood chips obtained from residues of treetops and forest branches, or even materials derived from the use of dedicated energy systems (SRC) or by residues of agroforestry pruning [9,18,[26][27][28][29]. Naturally, the transition from raw wood material to pellets involves a production process consisting of several steps that necessarily increases the cost of the finished product.…”

Quality of the Pellets Obtained with Wood and Cutting Residues of Stone Pine (Pinus pinea L.)

“…Scots pine (Pinus syslvestris L.) wood, either alone [14][15][16][17][18][19][20] or mixed with other species, such as Norway spruce (Picea abies (L.) H. Karst) [21][22][23][24][25] or beech (Fagus sylvatica L.) [26], has been extensively studied. Other pine species have also been assessed, such as Monterey pine (Pinus radiata D. Don) [27,28]; Eldar pine (Pinus eldarica Medw) [27]; Aleppo pine (Pinus halepensis Mill.) [29]; maritime pine (Pinus pinaster Ait.)…”