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

• Pelletization of poplar and pine blends was optimized regarding various parameters.
• Effect of material composition, additive, moisture and compression on pellet quality was tested.
• The use of poplar/pine blends allows increasing the poplar pellet quality.
• Lignosulfonate additive improves the pelletization process of poplar.
• Increasing pine content requires high compression die to reach highest quality.

Wood pellet for non-industrial use were prepared from poplar, with and without two additive dosages (1 and 2 wt.% 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 2 wt.% 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 21 mm and moisture content at the inlet die around 30 wt.% d.b. for blends with poplar content up to 45% and 19 mm 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 25 wt.% d.b. and ENPlus A1 when poplar percentage was less than 5 wt.% d.b. No classification was possible when only poplar was used regardless the addition of lignosulfonate.