Physical quality and surface hydration properties of wood based pellets blended with waste vegetable oil

To satisfy the demand of reducing extensive usage of wood as a raw material for pellets production, application of alternative raw materials, particularly residues, is necessary. The purpose of this paper is, therefore, to study feasibility of alternative wood pellets with addition of waste vegetable oil and to examine how the oil affects pellet's physical quality, surface properties and pelleting process. Furthermore, a novel approach for estimation hydrophobic properties of biomass pellets was presented. Pellet surface hydrophobicity and water drop absorption rate were assessed by measuring contact angle along time. Oil addition was 2.2% and 5.8% based on dry solids. Pellets were produced by single pellet press method under four compacting pressures (75, 150, 225 and 300 MPa) at three pelleting temperatures (60, 120 and 180 °C). The results show that oil addition significantly increases energy content in wood pellets (p < 0.05). Energy content was increased from 19.69 MJ/kg (control) to 20.05 MJ/kg (2.2% of oil) and 20.64 MJ/kg (5.8% of oil). Strength of pellets, as well as sawdust compressibility, was reduced when adding oil. The oil caused lower friction on the pellet-die wall contact area.