Biomass Flowability The bane of biomass feedstock engineers James Dooley, P.E. oor feedstock flowability was identified by the U.S. Department of Energy’s Bioenergy Technologies Office and by the USDA as one of the critical issues limiting success in the emerging bioecono-my. Traditional analytical and laboratory flowability metrics are proving to be of little use for designers of hoppers, feed-ers, mixers, and other essential processing equipment. Even with advanced modeling tools, the performance of biomass hoppers and feeders is rarely successful on the first try. The best designers and builders have decades of experience and a junkyard full of lessons learned. Major scale-up and start-up problems at cellulosic biore-fineries and biomass processing facilities are being traced to feedstocks with poor flowability. Augers stall, drive motors burn out, hoppers bridge, mixers plug—the litany goes on and on. Many of the agricultural and biological engineers who are designing facilities for the advanced bioeconomy have a back-ground in grain handling, and they dream of a time when bio-mass feedstocks might flow like corn, wheat, rice, or marbles. Unfortunately, ground corn stalks and shredded poplar trees behave more like matted cat fur than marbles. It’s a running joke in my company that we have never designed and built a biomass feed hopper that worked with-out many artisanal modifications and iterations. If we build a hopper, we have to add a platform for a human assistant, who uses a big stick to keep things flowing. There are two solutions to the problem of flowability. One is to preprocess fibrous biomass materials into particle forms that have better flow prop-erties and less propensity to interlock. The other solution is to quantify the physical prop-erties of available biomass feedstocks in engi-neering science terms and develop better analytical models to enable design of equip-ment and handling systems that actually work. This article is a summary of current research in biomass flowability. AE50 Award, operates in tandem with optimized screening to produce feedstocks that have low aspect ratios, uniform cross-sections, and low compressibility—all of which improve flowability. This machine system and knife mills from other manufacturers are gaining market share. However, although new comminution methods can improve flowability, the best materials produced by these innovations are still mar-ginally flowable compared to corn and small grains. Idaho National Laboratory (INL) has been working on technologies that blend biomass materials into pelletized “uniform format feedstocks” that can be handled like conven-tional fuel pellets. This approach deals with flowability at the biomass source and at depots close to the source. Biorefineries can then use material handling technologies from the established wood pellet industry. Although the INL approach greatly reduces downstream issues, those who convert raw biomass and wood chips to densified pellets still face the flowability problem. ASABE Fellow Shahab Sokhansanj at the University of British Columbia and team members at the Oak Ridge National Laboratory in Tennessee are studying the interactions of bio-mass grinding and flowability characteristics. In particular, they seek to understand the relationships between particle size, shape, and flow properties. ASABE member Amit Kumar and associates at the University of Alberta in Edmonton have been developing workable methods for transporting biomass feedstocks in P Making biomass flowable ASABE member David Lanning at Forest Concepts is leading an effort funded by the Bioenergy Technologies Office of the U.S. Department of Energy to design biomass com-minution and screening equipment that pro-duces flowable feedstocks. The Crumbler ® rotary shear machine, which received a 2016 4 May/June 2017 RESOURCE Flowable 2 mm poplar wood feedstock from Forest Concepts’ Crumbler ® rotary shear machine (left) compared to non-flowable and clumpy material produced by a hammer mill (right) . Photos by Forest Concepts.