Mechanical material properties effect on pelletization
The relation between the mechanical properties of input materials and the smoothness of material flow from a storage bin, cohesion variability of the compressed powder mixtures, and pelletization process were studied. Three material types were examined: Pyrolysis char from biomass – spruce wood (Picea abies L.), compost and spruce sawdust. Increased input material compressibility and cohesion affected the resulting durability and hardness of the pellets. Additional important material parameters affecting the pelletization process and final pellet quality include flowability and wall friction angle: Pellet durability and hardness increases with decreasing flowability (shift to the cohesive materials mode) and wall angle of the incoming materials. Those parameters are taken into account when designing conveyors. Application of the Quality by Design (QbD) approach to the prediction of behaviour in the pelletization process is outlined. The feasibility of inferring acceptable pelletization process behaviour from the mechanical-physical properties of the input materials is demonstrated.