Pellet blends of poplar and pine sawdust: Effects of material composition, additive, moisture content and compression die on pellet quality

Abstract

Wood pellet for non-industrial use were prepared from poplar, with and without two additive dosages (1 and 2wt.% d.b.) and from three blends of poplar and pine by a pilot-scale pelletizer. The effect of material composition, additive, moisture content at the inlet die and compression die on the pelletization process and on the pellet quality was studied. The chemical and physical properties of the pellets produced were determined in order to classify the pellets in different categories according to EN 14961-2. The results showed an improvement on pellet processing and physical properties of poplar pellets when 2wt.% d.b. of lignosufonate additive was used but also some deterioration on their chemical properties because of an increase of ash and sulfur content in the pellet. Besides, an improvement in the process was also observed when biomass with high moisture content at the inlet die was used. The optimum operational conditions for the blends were as follows: compression die of 21mm and moisture content at the inlet die around 30wt.% d.b. for blends with poplar content up to 45% and 19mm and 15% for poplar with and without additive. Blends could be classified as ENPlus A2 when the poplar percentage on the blends was between 45 and 25wt.% d.b. and ENPlus A1 when poplar percentage was less than 5wt.% d.b. No classification was possible when only poplar was used regardless the addition of lignosulfonate.