Effects of multi-stage milling method on the energy consumption of comminuting forest residuals

This study has evaluated the comminution energy reduction efficiency of a multi-stage milling method and established a mathematical model for estimating the specific energy consumption as a function of moisture content and particle size change. A Bliss hammer mill was employed to grind the feedstock targeting at two final screen sizes of 0.84 and 0.69 mm. For the target screen size of 0.84 mm, the single-stage, two-stage, and three-stage milling process were employed. Whereas, the single-stage, two-stage, and four-stage milling process were employed for the 0.69-mm target screen size. Four moisture content levels were employed, i.e. 6 %, 12 %, 18 %, and 28 %. While the final particle sizes and distributions were similar independent of the intermediate stages, the results showed that the single-stage milling consumed 43 % more energy than the three-stage grinding process. Also, multi-stage milling runs more stable in grinding high-moisture content materials. In addition, a mathematical model based on Bond’s comminution law was established to predict the specific energy consumption with the moisture content and the particle sizes before and after grinding.