Estimating biochar yield per hectare from logging residues in Eucalyptus globulus stands

Abstract

Eucalyptus globulus is widely cultivated for wood production due to its high fiber quality and pulp yield. However, large amounts of residual biomass are generated during harvesting, posing disposal challenges. Converting these residues into value-added products is required. One promising approach is the biochar production using pyrolysis. This study assessed the potential biochar yield from logging residues in Eucalyptus globulus stands. The residual biomass harvested was quantified based on the number of logging residue compacted bales (CRLs). A set of equations were fitted to calculate the residual biomass harvested in stands depending on their quality. Pyrolysis tests of residue components (leaves, bark, and branches) were conducted using a response surface methodology (RSM). Additionally, per-hectare revenues from biochar sales via pyrolysis were compared to those from electricity sales via residue combustion. The results showed that the number of CRLs and the volume of debarked wood (m3) ratio was around 0.5, being the collection process efficiency 0.69 ± 0.09. There was a positive correlation between the harvested residual biomass and quality stand, with a difference of 61 t ha-1 between the thighest and lowest quality stands. The highest biochar yields in order were leaves > bark > branches. The peak value was 61.27 % at 300 ◦C and 0.1 L min⁻¹ N₂ flow. The RSM analysis indicated temperature, the square of N2 flow and the square of temperature as significant factors (p < 0.05). The biochar yield of the total residue ranged from 49.1 % at 300 °C to 27.94 % at 600 ◦C. Under optimal pyrolysis conditions, the estimated biochar yield per hectare ranged from 46.8 to 17.3 t ha-1, depending on quality stands. Revenue per hectare from the sale of biochar accounted for 60 % of the revenue from the sale of electricity.