Abstract

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.

Highlights

  • Agricultural Residues throughThe agricultural sector and its related production chains are sources of a high amount of residual biomass, representing a significant feedstock for the bioenergy sector and potentially for the bio-based industry

  • Data on the quality of the residual biomass materials and agripellets produced are reported in the following paragraphs

  • The addition of pruning residues significantly improves the durability (D) of all the pellet blends. These biomass materials are suitable for pelletisation and the produced agripellets have good mechanical properties

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Summary

Introduction

Agricultural Residues throughThe agricultural sector and its related production chains are sources of a high amount of residual biomass, representing a significant feedstock for the bioenergy sector and potentially for the bio-based industry. The Italian agency ENEA estimated a yearly availability (excluding the zootechnical sector) of around 25 Mt dry matter (d.m.) of residual biomass from agriculture and forestry, corresponding to about 10 million tons of equivalent (Mtoe) thermal energy [1]. More than 5 Mt are constituted of tree prunings. These estimates were confirmed in 2013 by the results of the Extravalore Project [2], funded by the MiPAAF. The same authors quantified 30% of the available solid biomass as corresponding to 1.53 Mt d.m./year and 660 ktoe of thermal energy. Statistics show that over 60% of the available tree pruning comes from vine and olive cultivations, justifying several authors’ interest in the energetic valorisation of this biomass material [3,4,5,6,7,8]

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