Length-sensitive screening of elongated biomass particles in a pilot-scale orbital screen: Experiments, shape-resolved discrete element method simulations, and surrogate modeling

Mechanical screening of elongated biomass is not solely governed by aperture size: particles may be narrow enough to pass yet long enough to cause bridging, blockage, or unstable transport. This study evaluated length-sensitive separation of milled miscanthus in a pilot-scale Forest Concepts Orbital Screen using an experiment-informed framework integrating physical screening tests, 3D particle-shape characterization, shape-resolved discrete element method (DEM) simulations, and machine-learning surrogate modeling. In experiments, all feed particles passed a 12.7-mm sieve-shaker reference, whereas 9.21% of recovered material was retained on the Orbital Screen upper deck as the over-length/oversize stream, demonstrating length-sensitive retention beyond conventional sieve classification. However, elongated particles with lengths up to 20.9 mm also entered the on-spec stream, indicating incomplete partitioning. DEM simulations clarified this behavior by isolating particle width and length in monodisperse cases. For a representative 1.2 × 2.4 × 19.2 mm particle, the passage fraction was 58.5% in the 12.7-mm Orbital Screen upper-deck model, compared with 98.2% in the same-aperture sieve-shaker reference. Surrogate maps showed a broader probabilistic passage-retention transition zone in the Orbital Screen (39.27% of width-length space) than in the sieve-shaker reference (13.98%). Particle-scale analysis linked this broader transition mainly to orientation dynamics: particles in the Orbital Screen remained nearly flat, whereas those in the confined sieve-shaker reference more often adopted upright, passage-prone orientations. These results show that length-sensitive biomass screening depends on particle geometry, deck configuration, and transient orientation, providing a basis for improving over-length rejection while preserving on-spec recovery.