Elemental composition of raw and torrefied pellets made from pine and pine-eucalyptus blends

Debarked Pinus radiata wood was blended with debarked Eucalyptus nitens wood in three different proportions: 100% pine (100P), 90% pine-10% eucalyptus (90P/10E) and 60% pine-40% eucalyptus (60P/40E). The pellets were torrefied in dry and non-oxidative conditions at different temperatures (210, 240, 270 and 300 °C) and residence times (40 and 60 min) to enhance the energy properties and determine the elemental composition (18 elements). For raw pellets, the concentrations of Na, K, Zn, B and Cl increased significantly with the proportion of eucalyptus wood, with Cl levels being 60% higher in the 60P/40E than in the 100P pellets. The concentrations of most elements (C, Mg, Al, P, Ca, Fe, Cu) tended to increase (+35% for C, +200–250% for the others) with torrefaction severity, independently of the mixture. Decreases in H and O concentrations were also independent of the mixture. Torrefaction decreased the Cl content by 63–77%, which compensated for the high levels in mixtures with eucalyptus. Increases in the high heating value (by as much as 37%) with torrefaction occurred in parallel with an increase in carbon content and a decrease in the atomic H:C and O:C ratios, particularly in the 260 to 300 °C transition. Torrefaction compensated for the negative effect of the inclusion of eucalyptus, with the alkali index remaining at a relatively safe maximum value of 0.10 kg GJ−1. •Cl and K concentrations increased with the proportion of eucalyptus in the pellets.•Cl decreased by 66–77% with torrefaction severity.•The concentrations of most elements increased with torrefaction severity.•ISO 17225-8 was used to evaluate torrefied pellets.•Debarked eucalyptus can potentially substitute up to 40% of debarked pine.