Valorising Agricultural Residues through Pelletisation

The agricultural sector and its related production chains are good sources of residual biomass. Olive and vineyard pruning residues are present in high quantities in Italy. The limited bulk and energy densities of these biomass materials affect the harvesting and logistic costs, limiting energy and environmental sustainability. Pelletisation is the most efficient process for increasing bulk and energy densities. This study evaluates the pelletisation process of olive and vineyard prunings, pure, or blended with variable quantities of spruce sawdust. A 15 kW pelletisation system was chosen, in line with production at the farm level. The most important quality parameters of the produced agripellets were analyzed. The results of this investigation suggest that blending could valorize other biomass materials less suitable for pelletisation and reach the pellet quality required by Italian technical standards. The addition of pruning residues to spruce sawdust leads to an improvement in durability. Spruce sawdust pellets have a durability value of 78.4%. Adding 20% of olive prunings (S80O20) increases this value to 92.2, while adding 20% vineyard prunings (S80V20) increases this value up to 90.3. The addition of 20% of pruning residues significantly increased the length and decreased fines.