The effect of particle concentration on the reflux performance of the lifting pumps

The lifting pump is a critical component in deep-sea mining systems, yet its operation carries the risk of emergency shutdowns due to malfunctions or power outages. Such abrupt shutdowns can cause blockages due to the settling of mineral particles during the shutdown period, which can ultimately prevent the system from restarting and resuming normal operation. To investigate the impact of particle concentration on the reflux performance of lifting pumps, a coupled Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) numerical simulation approach was employed to analyze the influence of particle concentration on reflux characteristics during pump shutdown. The study revealed that during the reflux process of lifting pumps, particles predominantly accumulated at the impeller of the primary stage pump, while in the secondary stage pump, particle aggregation mainly occurred in the guide vane and impeller regions. With increasing particle concentration, the particle distribution within both pump stages became significantly denser, resulting in impeded liquid-phase reflux and subsequent flow obstruction phenomena. The particle distribution range subsequently expanded into the flow channels of both impellers and guide vanes. Elevated particle concentrations induced increased populations of low-velocity or stationary particles, resulting in reduced average velocity and diminished reflux efficiency. During particle reflux, the total collision frequency increased progressively with particle concentration. When the volumetric particle concentration reached critical thresholds, particle collision counts exhibited a linear growth trend, failing to reach a stabilized phase. Furthermore, increased particle concentrations led to a statistically significant dominance of inter-particle collisions, with a corresponding marked reduction in particle–pump wall interactions.