Energy consumption of two-stage fine grinding of Douglas-fir wood

Fine wood powders have advantages over traditional coarse wood particles for various emerging applications. However, an efcient system to produce fne wood powders has not been well established. We investigated the comminution capability and efciency of a two-stage grinding system consisting of a hammer mill circuit and an rotor impact mill circuit to convert wood feedstocks into fne powders. Air-dried forest harvest residuals were comminuted by the hammer mill circuit to three intermediate product sizes with geometric mean particle sizes of 1618, 669, and 316 μm. These intermediate products were then pulverized into fne wood powders with median particle sizes ranging from 35 to 250 μm. The specifc energy consumption increased with the decrease of median particle sizes, with a transition at around 100 μm after which the energy consumption increased exponentially. This large-scale grinding trial provides the reliable energy consumption data for design and process economic analysis of mechanical biomass preprocessing.