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

With the aim of extending the production of renewable energy from lignocellulosic materials by improving their energy characteristics, the authors have started a series of experimental activities that involve a densification process of the wood material and a subsequent quantitative and qualitative characterization of the different pellets produced. The research activity was focused on different types of pellets obtained using biomass deriving from dedicated energy crops (medium rotation forestry), pruning residues of agricultural crops, thinning interventions in planted forests, and, lastly, residues from the maintenance of urban greenery. Among the 15 parameters that were investigated, 9 (length, diameter, fusibility, As, Cr, Cu, Pb, Ni, and Zn) were within the limits set by current legislation for all the analyzed pellets. The same was not detected for the remaining 6 parameters (bulk density, heating value, ash, N, durability, and cadmium), the value of which did not reach the quality requirements established by the standards. The biomass obtained from medium rotation forestry plants (MRF) and forest residues turned out to be the best source of material to be used to produce pellets. Within these two groups, the best results were found for eucalypt, except for the heating value. Pellets from MRF also showed interesting values of durability and nitrogen content (classes A1 vs. A2).