Long-term storage and fuel quality of residual Eucalyptus globulus biomass

Abstract

Maximum energy demand (winter) and logging residue availability (spring and summer) occur at different times promnting the necessity of storage. Our aim was to analyse the effects of storage on baled logging residues from Eucalyptus globulus over a period of storage (TSt) by measuring the moisture content (MC), net calorific value (NCV), and ash content, and by determining dry matter losses (DML) and the usable energy content of the residues. These analyses were performed six out 6 times over the course of 18 months for each component of the residues (leaves, branches and bark). The analysed samples were placed in different positions within stacks of cylindrical bales: 1) centrally placed and 2) surface (open-air). MC decreased during the first 3 months of storage in all samples. From this point onwards, the surface samples’ MC varied significantly throughout the storage time (TSt) because of precipitation influence, whereas it remained stable in the centrally placed samples. Significant differences in NCV (wet basis) were observed in the surface samples with respect to storage time, whereas in the centrally placed samples, these differences were not significant after 3 months of storage. Differences between surface and centrally placed samples for a given TSt were more pronounced during periods of higher precipitation, reaching a value of 4.52 MJ kg−1 after 6 months of storage. The influence of extractive content in the residues was reflected in the NCV (on a dry basis), which varied slightly with TSt, peaking at 3 months with values of 17.60 and 18.34 MJ kg−1, for the surface and centrally placed samples, respectively. The ash content of the surface samples increased significantly (p < 0.05) with storage time, whereas the centrally placed samples did not exhibit this trend. The highest values were recorded in the following order: bark > leaves > branches. The maximum values obtained were 4.2% and 3.7% for the surface and centrally placed samples after 18 months of storage respectively. DMLs increased with storage time, reaching 16.5% and 4.9% for the surface and centrally placed samples after 18 months of storage, respectively. The usable energy content increased during the first 3 months, indicating a positive influence of storage time on the fuel quality. The shape of the top row of bales in a stack could help reduce rainwater penetration, resulting in a higher proportion of internal residues and therefore improving usable energy content.