Segregation Mechanism and Step Height Optimisation of Rice Husk and Brown Rice Mixtures on a Stepped Chute for Enhanced Pneumatic Separation

Pneumatic separation is essential in paddy processing, but poor pre-segregation of rice husk–brown rice mixtures causes rice husk retention and brown rice loss. A stepped feeding chute was proposed in this study to enhance the gravity-driven segregation of rice husk–brown rice mixtures before pneumatic separation. The discrete element method was used to simulate particle motion under different step heights and analyze the effects of step height on particle bed porosity, vertical displacement difference, and motion trajectories. Results showed that segregation was governed by the coupled effects of density and surface-roughness differences: brown rice tended to percolate downward, whereas rice husks tended to interlock and remain in the upper layer. The degree of separation first increased and then decreased with increasing step height, owing to the combined influence of porosity-induced changes in vertical displacement difference and impact-induced trajectory fluctuations that promoted remixing. An optimal step height of 13 mm, approximately 1.86 times the brown rice kernel length, reduced rice husk retention by more than 30% and brown rice loss by more than 40%. This design provides an effective approach to improving pneumatic separation. It may also guide the design of segregation-enhanced conveying systems for heterogeneous particulate food materials.