Energy consumption of two-stage fine grinding of Douglas-fir wood
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Fine wood powders have advantages over traditional coarse wood particles for various emerging applications. However, an efficient system to produce fine wood powders has not been well established. We investigated the comminution capability and efficiency of a two-stage grinding system consisting of a hammer mill circuit and an rotor impact mill circuit to convert wood feedstocks into fine 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 fine wood powders with median particle sizes ranging from 35 to 250 µm. The specific 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.
KeywordsCoarse grinding Fine grinding Rotor impact mill Hammer mill Energy consumption Size reduction
We thank Jinxue Jiang, Yalan Liu, Lanxing Du, Yu Fu, Vincent McIntyre, John Barth, and Kelly Welsch for collecting the grinding data and size analysis for the hammer mill grinding; Marc Cavaliere, Assistant Manager of Hosokawa Micron Powder Systems for the rotor impact mill grinding trials; and Dane Camenzind for drawing the ACM schematic diagram. The authors gratefully acknowledge the Northwest Advanced Renewables Alliance (NARA), supported by the Agriculture and Food Research Initiative Competitive Grant No. 2011-68005-30416 from the USDA National Institute of Food and Agriculture, for funding the most part of this work, and the Joint Center for Aerospace Technology Innovation of Washington State for funding a part of this work.
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