Design and DDPM evaluation of a composite gas–solid separation structure for a coal-powder storage bin

Fine coal-dust carryover in the exhaust of a hydraulic-support column-pit coal-sludge cleaning machine operating under negative-pressure suction is mitigated by integrating a compact rectification–expansion–bending gas–solid separation structure into a space-limited storage bin to promote upper venting and lower settling. Three-dimensional simulations are performed using the Realizable k – ε turbulence model with near-wall functions for the gas phase. Particles are tracked with a dense discrete phase model (DDPM); the kinetic theory of granular flow (KTGF) is enabled in dense regions to represent inter-particle collisions. An empty bin (EB) and a composite bin (CB) are compared at inlet velocities of 10–40 m/s for 10/50/100 µm particles with a mass flow rate of 100 g/s. Separation efficiency, mass-weighted mean residence time, 100 s outlet carryover mass, and total inlet–outlet pressure drop are evaluated. CB suppresses high-momentum jets, enlarges low-velocity settling zones in the expansion chamber, and induces secondary flows in the bending passage, enhancing gravitational settling, inertial impaction, and wall capture. Across the investigated range, CB increases residence time by up to 2.5× and reduces the 100 s carryover mass of particles ≤ 50 µm by 25–62%, while the maximum pressure drop is 4.28 kPa, below the fan limit of 6.6 kPa. These results support parameter selection for compact in-bin dust-control designs without external collectors.