Impact-based pulverisation of dried and screened Norway spruce (Picea abies) sawdust in an oscillatory ball mill

Abstract

Abstract This study investigates the impact-based pulverisation of dried and screened Norway spruce (Picea abies) sawdust into a median particle size range of less than 100 μm in an oscillatory ball mill. Pulverisation is studied by considering the effects of impact energy, the number of impact events and the amount of feed on the size and shape properties of the pulverised wood. The impact energy is treated as the kinetic energy of the grinding ball and the impact event is considered as a period during which the grinding ball travels from one end-wall of the grinding jar to the other. Given a certain number of impact events, the use of higher impact energy lowers the particle sizes of the wood particles until a minimum size is attained. The minimum value for the median particle size is found between 13 μm and 20 μm. In the pulverisation, the aspect ratios of the wood particles decrease with the use of a higher impact energy and larger number of end-wall collisions. Within a certain range, the changes in the size and shape properties can be predicted from the total impact energy available for the pulverisation when the energy efficiency of the pulverisation remains constant. The energy efficiency of the pulverisation process can be affected by varying the amount of the feed. The pulverisation of dried Norway spruce sawdust from a median size range of 1 mm and 2 mm down to a median size below 100 μm is accomplished with the specific energy consumption of 0.36 kJ/g (100 kWh/t); reduction to a median size below 20 μm is accomplished with the specific energy consumption of 1.4 kJ/g (380 kWh/t).