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Abstract: Knowing the effect of mill operating factors on biomass size reduction would be useful for predicting or adjusting particle size distributions that affect supply chain efficiency and biomass-to-fuel conversion processes. Wheat straw (Triticum aestivum L.) particle size distributions generated by a knife mill were determined for integral classifying screen sizes from 12.7 to 50.8 mm, operating frequencies from 4.17 to 8.33 Hz, and mass input rates from 2 to 9 kg min−1. Particle distributions were obtained with standardized sieves for forage analysis that included horizontal sieving motion with machined-aluminum sieves of thickness proportional to sieve opening dimensions to reduce inadvertent particle spearing through sieve openings. Several analytical descriptors were examined to mathematically represent the range of particle sizes in the distributions. Screen size and feed rate directly influenced particle size, whereas operating frequency had a weak indirect relation with particle size. The Rosin-Rammler equation adequately fit the knife-milled wheat straw particle size distribution data (R 2 > 0.982). Mass relative span was >1, which indicated a wide distribution of particle sizes. Uniformity coefficient was <4.0 for 12.7 and 19.0 mm screens, which indicated particles of relatively uniform size. Knife mill chopping of wheat straw produced fine-skewed mesokurtic particles with 12.7–25.4 mm screens and strongly fine-skewed mesokurtic particles with 50.8 mm screen. Other size related parameters, such as, geometric mean length, Rosin-Rammler size parameter, median length, effective length, and size guide number, were well predicted as a function of knife mill screen size, feed rate, and mill frequency. Results showed the relative effects of knife mill operating factors to produce particular particle sizes of wheat straw. [Copyright &y& Elsevier]

Abstract: Biomass particle size impacts handling, storage, conversion, and dust control systems. Switchgrass (Panicum virgatum L.) particle size distributions created by a knife mill were determined for integral classifying screen sizes from 12.7 to 50.8mm, operating speeds from 250 to 500rpm, and mass input rates from 2 to 11kg/min. Particle distributions were classified with standardized sieves for forage analysis that included horizontal sieving motion with machined-aluminum sieves of thickness proportional to sieve opening dimensions. Then, a wide range of analytical descriptors were examined to mathematically represent the range of particle sizes in the distributions. Correlation coefficient of geometric mean length with knife mill screen size, feed rate, and speed were 0.872, 0.349, and 0.037, respectively. Hence, knife mill screen size largely determined particle size of switchgrass chop. Feed rate had an unexpected influence on particle size, though to a lesser degree than screen size. The Rosin–Rammler function fit the chopped switchgrass size distribution data with an R 2 >0.982. Mass relative span was greater than 1, which indicated a wide distribution of particle sizes. Uniformity coefficient was more than 4.0, which indicated a large assortment of particles and also represented a well-graded particle size distribution. Knife mill chopping of switchgrass produced ‘strongly fine skewed mesokurtic’ particles with 12.7–25.4mm screens and ‘fine skewed mesokurtic’ particles with 50.8mm screen. Results of this extensive analysis of particle sizes can be applied to selection of knife mill operating parameters to produce a particular size of switchgrass chop, and will serve as a guide for relations among the various analytic descriptors of biomass particle distributions. [Copyright &y& Elsevier]