Apple pruning residues: Potential for burning in boiler systems and pellet production

Residues from management activities of fruit growing can be an important source of biomass for energy generation. The aim of this study was to determine the potential use of apple pruning residues for energy generation as process steam or power energy. To this end, branches from the pruning of commercial apple orchards have been evaluated in the Santa Catarina State, Brazil. To compare with the traditional biomass used for energetic purposes, particles of Pinus sp. from the industrial timber processing have also been analysed. Homogeneous pellets of the two types of biomass were produced, and three more mixes containing the two raw materials were made. Pellets have been evaluated according to their physical and energetic properties. The results have been compared to the ISO 17,225-2 Standard. Apple pruning residues have the potential for energy generation in boilers, that is, for the production of process steam and electric power. Their potential can vary from 12,649.54 MWh y⁻¹ to 115,442.44 MWh y⁻¹. The physical and energetic properties varied between the analysed residues, except the gross calorific value (19.69 MJ kg⁻¹ for pine wood particles and 20.27 MJ kg⁻¹ for apple pruning). Comparing with the pine wood (87 kg m⁻³), the apple pruning (141 kg m⁻³) has a higher amount of biomass per unit volume processed for energy and less residence time in the burning systems (17.54% fixed carbon for apple pruning and 18.91% fixed carbon for pine wood). However, it generates more wastes (ashes) after burning (3.25% for apple pruning and 0.46% for pine wood). The pellets’ energy density increased by 3.35 times the energy density of the apple pruning particles after pelletizing. The homogeneous apple pruning pellets can only be applied to industrial use (I3), mainly because of its high ash content (2.27%). The pine wood with apple pruning mix used for pellet production reduces the ash content and increases the bulk density and energy density, which improves the quality of the pellets.