Analysis of size reduction data from applying knife mill to assess the grindability index for woody biomass

Wood chips must undergo a crucial step of size reduction to attain suitable particle sizes for downstream processing to biofuel and bioenergy production. The ISO technical committee 238 is developing a grinding index method for cellulosic biomass. Wood chips are typically ground to particle sizes below 2 mm. We ground beech wood chips in a knife mill at varying feed rate with screen aperture size of 0.5 to 4 mm to understand the effect of feed rate on the energy consumption and the product particle size. Rittinger's and Holmes equations were fitted to the specific grinding energy data and were equally well suited to describe the energy consumption pattern. When increasing feed rate from 0.2 to 1.4 g/s while grinding on a screen aperture size of 4 mm, specific grinding energy decreased from 500 J/g to 150 J/g and the mean particle size increased from 0.79 mm to 1.02 mm.