Significance of Particle Size in Biomass Logistics

As part of preparing biomass for conversion into biofuels, biomass is ground through mills such as hammer mill and knife mill.  The ground biomass are fed into conversion vessels and/or stored through hoppers that are often attached to storage vessels. The flow of biomass out the hopper without disruption is currently a major bottleneck. Ratholing and arching are the two flow problems associated with discharge of ground particulates from storage containers. 

When ground, biomass particle size has log-normal distribution. This means that the number of smaller particles is considerably larger than the number of larger particles in ground biomass samples. Several studies in literature have shown that particle size may play critical role in flowability of ground material. Therefore our goal is to quantify the effect of particle size on the flowability of ground biomass.

This was achieved by grinding loblolly pine wood chips through 1/8” screen and fractionating the ground biomass into six sizes (between 0.25 mm and 4.17 mm). A Brookfield powder flow tester was then used to measure the flow properties (angle of internal friction, angle of wall friction, and cohesive strength). 

The flow index that was calculated from the values of these flow properties indicate that the ability of ground biomass to flow reduced with decrease in particle size.

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