Weakening characteristics of arc-shaped plug on elbow erosion in coal pneumatic conveying

Pneumatic conveying is an important way for clean and efficient transportation of granular materials. However, the elbow erosion has long restricted the application of pneumatic conveying technology in the field of coal industry. The elbow shape is one of the important factors affecting the erosion. Therefore, a blind elbow with arc-shaped plug structure suitable for coal transportation was proposed. Firstly, the pneumatic conveying experiments of 7−11 mm coal particles were carried out in the DN50 pipeline system. The airflow velocity was 20 m/s, the gas supply pressure was maintained at 0.4 MPa, the arc angles of the arc-shaped plug were 10°, 20°, 30° and 40°, and the dimensionless heights were 0.4,0.6,0.8 and 1.0, respectively. The erosion distribution and maximum erosion depth of the elbow were measured by confocal three-dimensional profilometer. Secondly, the numerical model was established by Eulerian-Lagrangian bilateral coupling computational fluid dynamics and discrete element method (CFD-DEM), and the scientificity of the model was verified by numerical simulation and experimental measurement of the maximum erosion depth. Finally, the weakening characteristics of arc-shaped plug on elbow erosion were studied from the erosion distribution, the peak erosion and collision energy loss, and the optimal structural parameter criterion of the arc-shaped plug weakening wear was deduced. The results show that the arc angle was the main influencing factor for the arc-shaped plug to weaken the elbow erosion. When the arc angle was less than 20°, the plug could not contain all the radiation areas of the erosion center, and when the arc angle exceeded 40°, the plug bottom was difficult to be completely covered by the particles. Under the above two conditions, the weakening effect of the arc-shaped plug on the elbow erosion was limited. The peak erosion and its growth rate of the blind elbow with arc-shaped plug were lower than those of the ordinary elbow. When the arc angle was 30° and the dimensionless height was 0.8, the erosion center was dispersed to multiple positions on the side wall to avoid concentrated impact, and the peak erosion was 25.1% of that of the ordinary elbow. The change of the collision energy loss of the arc angle with respect to the dimensionless height included one lifting section and two gentle sections. The two critical points represented the height at which the particles began to cover the plug bottom and formed a stable accumulation. The research results were conducive to solving the long-standing problem of elbow erosion, providing a theoretical basis for the industrial application of coal pneumatic conveying, and could be extended to other mineral particle conveying fields.