Physical properties of wood pellets exposed to liquid water

Abstract

Wood pellets have become a renewable substitute for coal in heat and power generation facilities. However, the hygroscopic nature of wood pellets is a long-standing problem in handling this product. Pellets may become wet during loading and unloading if a rain incident happens. In this research, three types of commercial wood pellets were exposed to liquid water. The durability, density, and porosity of pellets before and after wetting were measured. The commercial pellets were residential hardwood, residential softwood, and industrial softwood pellets. Predetermined volumes of water were added to increase the moisture contents of pellets to several levels ranging from 1.5 to 30% wet mass basis (wb). Exposure to liquid water caused localized swelling of pellets which dislodged particles from the surface of pellets. The data showed when moisture content (m.c.) increased to 10% wb, the pellet durability dropped from 99.5% to 97.5%. A slight increase in bulk density from an initial 690 kg/m3 was observed for pellets at 6–7% m.c (wb). The bulk density decreased to 500 kg/m3 when the adsorbed moisture was at 15% wb.