Terminal Velocity Determinations for Component Separation Biomas

Biomass processors require a technology that will separate node and internode segments to enhance the end product or to reduce production cost. Separation techniques that segregate by particle density and aerodynamic differences use terminal velocity properties as exemplified by classifiers and cyclones.

A fabricated vertical wind tunnel for determining terminal velocity had a velocity range from 3.0 to 9.5 m/s. Velocity variations between highest and lowest readings across the outlet was a maximum of about 20% at a given air velocity. Comparisons of measured terminal velocity to values calculated using Mohsenin (Mohsenin, N.N. 1970. Physical Properties of Plant and Animal Materials. New York, N.Y.: Gordon & Breach Science Publ.) equations showed them to be similar, provided the equation for spherical particles was used. Measures of particle density for the node and internode samples differed by about 52.6% for wheat, and from 39.3 to 61.9% for switchgrass, and from 0.4 to 27.6% for corn rind, and between 40.1 to 81.9% for corn pith. These density differences form a basis for separating these biomass components, and should affect terminal velocities as predicted by the Mohsenin equations.

Switchgrass with a high moisture content (52% wet basis, w. b.) cut into 0.6 cm length segments had greater terminal velocity differences (~ 62.5%) between node and internode sections than did longer-length switchgrass groups of 1.3 cm and 2.5 cm with either low (15% w. b.) or high moisture content. In the low moisture level particles, the 2.5 cm lengths proved to have the least difference (~ 30.0%). Corn pith with a high moisture (43% w. b.) had a greater node and internode terminal velocity difference (~ 141.5%) than did the corn rind. For all three species, except for wet corn rinds, the terminal velocity of nodes and internodes differed significantly (P < .0001).

Terminal velocity data determined in this study helps to fill a void in the limited published values of biomass. These data are required to design and engineer improved systems for maximizing the use and value of biomass feedstocks. Results provide a defined physical property difference in biomass segments to accommodate effective separation of plant anatomical components.