Separation enhancement of 6-1 mm fine coal in a compound dry separator under stepped air distribution

In compound dry separation systems, conventional uniform air distribution is inadequate for fine coal (6–1 mm) because aerodynamic drag induces excessive entrainment and interlayer mixing, thereby reducing separation accuracy. This study investigates the vibration energy distribution across the separating deck and designs three stepped air distribution plates to address this issue. The results reveal a gradient distribution of vibration energy: high intensity in the separation zone, moderate intensity in the stripping zone, and low intensity in the gangue discharge zone. Among the three plates, Plate #2 performs best. Its high inlet air velocity rapidly disperses the feed bed, its moderate middle airflow ensures effective density stratification, and its low outlet velocity suppresses the entrainment of light products. In contrast, Plate #1 causes flow disturbance and material accumulation, while Plate #3 provides insufficient fluidization. Particle motion analysis indicates that coal – gangue separation originates from velocity differences, with high-density particles migrating faster than their low-density counterparts. However, as particle size decreases from 6 mm to 1 mm, this velocity difference diminishes, weakening the separation efficiency for fine particles. Stepped air distribution enables precise airflow allocation, which effectively improves fluidization and stratification. This work offers theoretical and technical support for optimizing compound dry separators for fine coal beneficiation.