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The deep‐sea six‐stage centrifugal pump is an essential power source of the lifting system that conveys slurry containing coarse particles. Emergency failure of the electric system can easily lead to pump blockage because of slurry reflux. The reflux movement of particles in a six‐stage pump under emergency power failure is investigated using the verified computation fluid dynamics and discrete element method (CFD‐DEM) simulation. The JKR contact model is used to perform particle simulation. Simultaneously, shaped particles are added to realistically simulate the reflux characteristics under deep‐sea mining conditions. The effect of particle size, shape, and size distribution in the reflux is investigated. The blockage behavior of the particles during reflux and the blockage mechanism is clarified. Particles with less shape and size below 30 mm are more conducive to safe slurry transportation. The experimental results verify the credibility of the CFD‐DEM simulation results. [ABSTRACT FROM AUTHOR]

The multistage centrifugal pump is the critical component of mineral resources lifting in deep-sea mining. The reflux of nodules in the lifting pipe caused by the emergency pump stop can easily cause the pump to clog. In this paper, coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM co-simulations) are used to clarify the solid-liquid two-phase flow in two-stage centrifugal pumps under different particle sizes (10–20, 20–30, 30–40, 40–50 mm) with constant particle concentration. The movement and accumulation behaviour of particles in different flow fields (pipeline to pump, the first to the second pump stage) is investigated. Meanwhile, the effect of particle size and particle reflux velocity on the blockage of the flow channel in the pump was investigated. Particle accumulation in the pump was observed to determine the key factors affecting the pump's reflux capacity. The residual mass of particles in the pump at different particle sizes was counted. Simultaneously, the percentage of residual mass of 10–20 mm particles in the pump was compared between the experiment and the simulation with an acceptable tolerance of within 10%. In addition, pressure changes in the blockage-prone section were also investigated. A comparison between experiments and simulations verifies the consistency of the trend on the pump inlet pressure when clogged with 50 mm particles. It was found that larger particles in the range of 10–30 mm can better ensure the pump's reflux performance. [ABSTRACT FROM AUTHOR]

Six-stage centrifugal pumps are used in deep-sea mining lifting systems and are required to convey slurry containing coarse particles. A six-stage centrifugal pump suitable for operation in a natural mining system was manufactured. High-flow and full-scaled slurry conveying experiments at a 5% and 9% volume concentration of particles was carried out at a large modified test site with artificial nodules. CFD-DEM simulations were carried out to obtain slurry transport characteristic curves, particle transport and distribution characteristics, where the simulation method was validated by the experiment data. A clarified two-stage pump can be used instead of a multi-stage pump for simplified simulation calculations with acceptable accuracy. Local agglomeration of particles caused by backflow was found at the outlet of the diffuser, and such agglomeration decreased with increasing flow rates. It was found that particles are transported non-uniformly, particles transport in diffusers in strands. Particles are transported in a pulse-like mode within the pump, with the latter stage showing similar particle characteristics to those transported in the previous pump stage. [ABSTRACT FROM AUTHOR]

The ore collection mechanism of seafloor massive sulfide has not been paid enough attention. In order to achieve collection efficiency, it is necessary to study the ore collection mechanism. Aiming at the ore collection model of the 'KTII' deep-sea mining vehicle, this paper carried out the analysis of the flow field characteristics of the coupled collection, the swirling flow collection and the negative pressure suction flow collection, and the role of each power source in the ore collection process. Finally, the relationship between swirling flow and negative pressure suction flow in the ore collection process is summarized, and the ore collection mechanism is analyzed. The results show that the rotation of the mining head will produce swirling flow, triggering the "inward winding effect", which can ensnare the ground surface fluid into the virtual cutting rotary cavity. The negative pressure suction flow of the collecting hard pipe can suction the liquid in the small-scale range of the throat surface. However, swirling flow and negative pressure suction flow both have advantages and disadvantages in collecting and the two power sources are complementary and inseparable. The research results of this paper have certain guiding significance for the engineering practice of deep-sea mining. • The flow field characteristics of complex collection coupled with swirling flow and suction flow are analyzed. • The function and relationship of swirling flow and suction flow in the ore collection process are analyzed. • The coupling ore collection process and mechanism of swirling flow and negative pressure suction flow are clarified. [ABSTRACT FROM AUTHOR]

In order to solve the problem of low reliability of research results caused by the lack of simulated materials for seafloor massive sulfide (SMS) in laboratory breaking research, this paper proposes a convenient and fast preparation scheme for simulated rocks with Seafloor massive sulfide, using a mixture of cement and gypsum as the binder and natural graded river sand as the filler. At the same time, using this preparation scheme, large blocks of rock were prepared, and then standard cylindrical specimens were prepared through random sampling, core drilling, and other operations. Through density experiment, uniaxial compression experiment, and triaxial compression experiment, six physical and mechanical property parameters of the cylindrical specimen, including density, uniaxial compressive strength, elastic modulus, Poisson's ratio, cohesive force, and internal friction angle, were measured. On this basis, the feasibility and convenience of the proposed preparation method were further demonstrated through comparative analysis. The research content of this article is of great significance for the study of fragmentation experiments and the construction of deep-sea breaking theory. • A convenient and fast preparation scheme for simulated rocks with Seafloor massive sulfide is proposed. • The physical and mechanical property parameters of simulated rocks are measured by experiments. • The feasibility and convenience of the proposed preparation scheme are demonstrated through comparative analysis. [ABSTRACT FROM AUTHOR]