The hydraulic conveying of coarse particles in pipelines: Flow characteristics and the critical non-deposition velocity

The hydraulic conveying of coarse solid particles in pipelines plays a critical role in the design and operation of the deep-sea mining. In this study, the computational fluid dynamics–discrete element method is employed to investigate this problem numerically, based on which theoretical analyses are carried out. Numerical simulation of hydraulic lifting in the vertical pipeline reveals key characteristics of particle motions, and uncovers the effects of the feed concentration, conveying fluid speed, and particle size on the performance of lifting. The results also show the particle distribution characteristics in the vertical pipeline and the typical phenomenon of velocity fluctuation, which may induce pressure pulsations affecting operational safety and potentially accelerate pipeline erosion in practical engineering scenarios. Additionally, in terms of the horizontal pipeline, a similarity rule is derived based on the dimensional analysis theory, with which a new formula of the critical non-deposition velocity is established. This formula allows quantitative estimation of the critical non-deposition velocity from the particle size, the pipeline diameter, and parameters of the conveying fluid. Compared with existing empirical formulations, the present formula shows better consistency with experimental data and applicability in a broader range of flow parameters. This study provides theoretical support and possesses reference values to the engineering design and optimization of hydraulic transport in deep-sea mining, such as improving conveying efficiency and reducing energy consumption.