Influence of wood pellets properties on their grinding performance

This study investigates the influence of wood pellet properties on the grindability of pellets in a lab-scale disc mill. The pellet properties investigated included wood type, moisture content, internal pellet particle size distribution, particle density, and durability. Two pellet qualities for industrial use (designated I1 and I2 as per ISO 17225-2:2014) and two types of semi-industrial pellets (beech and pine) were used and grinding was performed on as-received and oven-dried pellets. The grinding performance was assessed by measuring the grinding energy and analyzing the changes in particle morphology (size and shape) with respect to the internal pellet particle morphology. Von Rittinger’s comminution law was used to characterize the pellet grindability. Drying pellets increased their brittleness and improved their grindability, resulting in both grinding energy savings and a higher milled product fineness, and the impact of drying was larger for industrial pellets. Beech pellets had a better grindability (kWh mm t-1 dry wood) than pine pellets (kWh mm t-1 dry wood). The moisture content of pellets did not influence the shape of the milled particles in terms of circularity and elongation ratio. The study also showed that the proposed disc mill has the potential to quickly determine the relative grindability characteristics of various pellet qualities.