Pathway Comparison of Comminution Energy Consumption from Wet Wood Chips to Dry Sub-mm Particles

Abstract. This study compared multiple pathways to produce small (0.8mm GMD) wood particles from fuel-grade Douglas fir chips. Six pathways were selected representing two industry-standard hammermill pathways plus four that included rotary shearing of green chips before drying and final hammermilling. We found that drying time is reduced proportionally to the magnitude of particle size reduction prior to drying. Raw chips took an average of 24 minutes to dry from 40% to 7% MC (wb). Size reduction to 2-3mm reduced the drying time to less than 5 minutes. It was shown that flowability increases proportional to the amount of size reduction delivered via rotary shear comminution. Rotary shearing to 2-3mm before drying and hammer-milling substantially improved flowability. A combination of 1^st stage comminution using the Forest Concepts rotary shear system followed by drying and 2^nd stage fine processing with hammermill is an effective way to produce flowable dry sub-mm feedstocks from wet wood chips.