Wood powder production with a novel milling technology : analysis of specific energy consumption and of the product’s bulk properties

Abstract: The interest for lignocellulose biomass has grown strongly in the last decades due to its potential to substitute fossil fuels. Pre-processing of biomass is of-ten needed to enable utilization of its full potential. A common pre-processing step is milling where the biomass is fractionated into wood powder usable for e.g. wood powder combustion. There are a number of problematic factors affecting the utilization of wood powder, such as blockings and bridging, as a result of low density and elongated and irregular particle shapes. The aim with this study was to, for a novel milling technology, determine and evaluate the specific energy consumption, wood powder bulk- and flow properties together with a comparison of the results from a hammer mill. This study was carried out by milling of logs and collecting data from wood powder samples. Data from a log mill and a hammer mill’s energy consump-tion, wood powder density and wood powder flowability was collected. The results show that the log mill consumed least energy, when the blade rotation speed was low in combination with high moisture content and high feeding speed. The wood powder’s tapped densities had an interval of 190-320 kg/m3 respectively 150-260 kg/m3 for the loose density. The Hausner ra-tio had an interval of 1.22-1.32, indicating a good to medium-good flowability. The conclusions are that the log mill’s specific energy consumption de-creases with increasing moisture content, increasing moisture content de-creases the tapped- and loose density and that the Hausner ratio is showing promising results.