Effects of sieve size and assortment on wood fuel quality during chipping operations

摘要

Primary residual forest biomass is an important source of energy in Sweden. The fuel quality of this biomass depends on several factors including its moisture content, ash content, and particle size distribution. For optimal combustion, the fuel should have a low content of fine particles. The objective of this study was to compare these quality metrics for five common fuel assortments produced with a drum chipper operated using two different sieve sizes (standard large). Sieve size had no significant effect on any of the studied fuel quality metrics. On average, 37-63 of the fuel's dry mass was distributed in particles of 16-31.5 mm. Because logging residues (tops and branches) contain relatively little stem wood, the average fine particle (<3.15 mm) content of the fuel produced by their chipping was around 10 greater than that of the other studied assortments. Moreover, the ash content of these fines was 2-3 times greater than that of the fines from other assortments. For all assortments, theash content decreased rapidly with increasing particle size, levelling out at 1.14 for particles of 16-31.5 mm. The average ash contents of the five assortments ranged from 0.84-2.98. For all assortments, and logging residues in particular, the fuel quality could be significantly increased by screening out fine particles. However, the economic value of such screening depends heavily on the costs of the refining process and the value/utility of the separated fine particles, which should therefore be investigated further.