The renewable energy industry relies on double screw pyrolyzers to convert cellulosic biomass into bio-oil. Bio-oil can then be converted into synthetic gasoline, diesel, and other transportation fuels, or can be converted into biobased chemicals for a wide range of purposes. One of the processes by which bio-oil is produced in industry today is through fast pyrolysis, the fast thermal decomposition of organic material in the absence of oxygen. One type of pyrolyzer, a double screw pyrolyzer, features two intermeshing screws encased in a reactor which mechanically conveys and mixes the biomass and heat carrier media. The mixing effectiveness of the two materials in the pyrolyzer is directly correlated to the bio-oil yield—the better the mixing, the higher the yields. This study investigates the effects of particle size and density on mixing effectiveness. Using glass beads as simulated heat carrier media and various organic particles as biomass, a cold-flow double screw mixer with 360° of optical access and full sampling capabilities was used to collect mixing data. Advanced optical visualization and composition analysis paired with statistical methods were used to evaluate the effects of varying the biomass particle size and density and varying the heat carrier particle size. A previous study [1] investigated operating condition variations when mixing red oak chips (500 μm –6350 μm, 1.47 g/cc) with glass beads (300 μm –500 μm, 2.53 g/cc). This study replicates selective operating conditions of the previous study while changing either the biomass media or the heat carrier media. The new biomass/heat carrier pairs tested were as follows: 1) red oak chips (300 μm –710 μm, 1.53 g/cc) and glass beads (300 μm –500 μm, 2.53 g/cc); 2) corn stover (300 μm –710 μm, 1.37 g/cc) and glass beads (300 μm –500 μm, 2.53 g/cc); 3) cork (300 μm –710 μm, 0.87 g/cc) and glass beads (300 μm –500 μm, 2.53 g/cc); 4) red oak chips (500 μm –6350 μm, 1.47 g/cc) and glass beads (800 μm –1000 μm, 2.53 g/cc). Both qualitative and quantitative analysis indicated that reducing the biomass particle size disrupts the material flow and reduces mixing effectiveness for counter-rotating up pumping screw rotation orientations; however, for counter-rotating down pumping screw rotation orientations, reducing biomass particle size noticeably increased mixing effectiveness. For all screw rotation orientations, a reduction in biomass particle density showed a decrease in mixing effectiveness. Lastly, an increase in heat carrier media particle size showed both increases and decreases in mixing effectiveness depending on operating condition.

REFERENCES
[1] Kingston, T.A., and Heindel, T.J., “Granular Mixing Optimization and the Influence of Operating Conditions in a Double Screw Mixer,” Powder Technology, 266: 144-155, 2014.