Physical and chemical characteristics of renewable fuel obtained from pruning residues

Wood residues generated from orchard maintenance operations represent a serious disposal problem, as well as a valuable opportunity for the bioenergy sector. However, their widespread use as renewable fuel is hindered by uncertainty about crucial quality issues, such as: ash content, ash melting behavior and chemical composition. This paper investigates the main physical and chemical characteristics of pruning residues generated by five of the most common European orchard crops: vine, olive, apple, pear and hazelnut. The results of the analyses are contrasted with the quality specifications set by EU standard UNI EN 14961-1 2010 for forest residues, in the absence of a standard specifically designed for orchard pruning residues. All tested orchard residues biomasses fulfill set specifications, and they also present similar characteristics in terms of ash content, size distribution and heating value. However, the chemical composition of pear and vine residues may raise some concern, due to the high content of nitrogen of the former, and to the high ash, sulfur and chlorine content of the latter. Olive and hazelnut pruning residues seem the most suitable for direct combustion, probably because the origin crops are cultivated less intensively and receive smaller chemical inputs.