An Experimental Investigation of the Behavior of Single-Particle Breakage on Polymetallic Nodules

Underwater mining systems for mining polymetallic nodules use various transport systems through submersible pumps that can span across subsea platforms (i.e., flexible risers and subsea structures), despite the role of concentration of the medium, shape, and size of the particle and conduit. The crushing unit determines the particle's shape and size, which plays a vital role in transportation (slurry ores) in the subsea environment. The National Institute of Ocean Technology is currently working on a flexible riser transport system. The collected nodules vary in size, and the majority of the nodules are nearly spherical/spheroid in shape with sizes ranging from 3 to 7 cm (Vineesh et al., 2009). The planned vertical slurry transport pipe/flexible hose has an internal diameter of 10 cm for better handling, favorable flow rate, and peak pressure capabilities. The collected nodules are fragmented using a crusher to less than 3 cm (1/3 of the hose inner diameter) to form narrow particle size distribution to prevent layering of the different particle sizes and plug formation by the larger particles during vertical slurry transport. Impact tests were conducted with actual wet nodules of various sizes, using different striker shapes in a drop weight tester to assess the size of the crusher, design the impact surfaces, and estimate the power required. The tests were conducted in submerged conditions to assess the actual load and breakage results. The objective was to maintain low crusher power and have minimal fragmentation to the desired sizes. Single-particle breakage tests were conducted on irregular polymetallic nodules using customized drop-weight impact equipment and a uniaxial compression testing machine to analyze the effect of shape and size on the specific comminution energy (SCE) of three different particle sizes (i.e., 4‐5 cm, 5‐ 6 cm, 6‐7 cm). Furthermore, to understand the deformation behavior of the nodules, experiments are performed with different types of strikers (i.e., hemisphere, conical, and flat). The breakage behavior of ore particles with different particle arrangements and SCE were studied in the tests. Experimental studies indicate that the shape of particles significantly affected the impact-loading mode and the breakage progress. With the increase in the size of particles, the SCE for wet particles decreases for a fixed fraction of particles. Regulating the input power of the crushing machinery and optimizing the crushing technology, considering the influence of particle shape and size, can reduce the SCE consumption and improve energy efficiency. Results reveal that the shape of the striker has a pronounced effect on the SCE in dry, wet, and submerged water test conditions. Compared to wet particles, submerged water conditions show a noticeable increase in SCE consumption due to the associated drag inside water conditions. Our results develop reference data sets required to understand the fragmentation of particles due to intricate crushing and transporting in a submerged environment.

Particle Distribution and Motion in Six-Stage Centrifugal Pump by Means of Slurry Experiment and CFD-DEM Simulation

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.

Experimental Investigation of Large Particle Slurry Transport in Vertically Oscillating Pipe for Subsea Mining

For subsea mining, it is important to predict the pressure loss in oscillating pipes for the safe and reliable operation of ore lifting as well as the design of lifting system. In the present paper, the authors focused on the internal flow in vertical lifting pipe oscillating in the axial direction and carried out slurry transport experiment to investigate the effects of pipe oscillation on the pressure loss. The spherical alumina beads and glass beads were used as the solid particles in the experiment, and the oscillating periods and amplitudes of pipe model as well as the solid concentrations and the mean slurry velocities were varied. The time-averaged components of hydraulic gradient calculated by the prediction method for the steady flow proposed in the past by the authors agreed well with the experimental ones. As for the fluctuating components of hydraulic gradient, the calculation results using a homogeneous mixture model were compared with the experimental data. The comparison result indicated that the homogeneous mixture model would be applicable to the prediction of pressure loss in the vertical pipe oscillating in the axial direction.

The geometric axial surface profiles of granular flows in rotating drums

SYNOPSIS A mechanistic description of axial segregation in rotating drum flows remains an open question. Consequently, optimal mixing of grinding balls and rocks for efficient breakage, maximum production of fines, and slurry transport is seldom achieved. Experimental and numerical studies of granular mixtures in rotating drums identify alternating axial bands that eventually coarsen in the long-term limit. Most models of axial segregation are limited to binary mixtures and cannot always predict the logarithmic coarsening effects observed experimentally. A key missing factor is a robust description of the axial free surface profile that is valid across a wide range of flow regimes. We present a practical model of the axial free surface profile by linking it to readily-derived geometric features of the cross-sectional S-shaped free surface profile. A parametric study shows good agreement with experimental measurements reported in the literature and heuristically valid trends. Keywords: rotating drum, granular flow, axial profile, comminution, mixing, segregation.

Research of Particle Motion in a Two-Stage Slurry Transport Pump for Deep-Ocean Mining by the CFD-DEM Method

The slurry transport pump is the key equipment of deep-ocean mining systems. The motion law of coarse particles in the pump is not clear enough. In this paper, a hydraulic model of a laboratory-scale two-stage slurry transport pump is constructed, and the motion characteristics of coarse particles in the pump are numerically studied by using the computational fluid dynamics–discrete element method (CFD-DEM) method. The performance curve of the pump is obtained by experimental measurement, and the reliability of the calculated results is verified. Due to the application of the amplification flow rate design method, the optimum efficiency point of the pump is shifted to the large flow rate condition. Differences in particle swarm within two stages are compared. The position distribution, velocity variation and trajectory of particles in the impeller and bowl diffuser are studied in detail. The velocity of particles leaving the impeller depends on whether they collide with the impeller blade. The motion of particles in the bowl diffuser is divided into three periods. Collision between particles and blades in the bowl diffuser not only leads to energy loss but also gradually transforms the circumferential velocity of particles into axial velocity in the second period. This work can provide a reference for the study of wear and blockage prevention of slurry transport pumps.

Experimental Investigation of Large Particle Slurry Transport in Vertical Pipes With Pulsating Flow

For subsea mining, it is important to predict the pressure loss in oscillating pipes with pulsating flow for the safe and reliable operation of ore lifting. In the present paper, the authors focused on the pulsating internal flow in static vertical pipe and carried out slurry transport experiment to investigate the effects of flow fluctuation on the pressure loss. The alumina beads and glass beads were used as the solid particles in the experiment, and the fluctuating periods and amplitudes of pulsating water flow were varied. The time-averaged pressure losses calculated by the prediction method for the steady flow proposed in the past by the authors agreed well with the experimental ones. As for the fluctuating component of pressure loss, the calculation results using the quasi-steady expression of a mixture model were compared with the experimental data. The calculated results were different from experimental ones for alumina beads of which densities are almost same as those of the ores of Seafloor Massive Sulfides. It suggests that the expression is insufficient to predict the pressure loss for heavy solid particles. The calculated ones, however, provided those in the safety side. On the other hand, the calculated results for light solid particles such as glass beads agreed well with the experimental ones. It means that the expression would be applicable to the prediction of pressure loss for the mining of manganese nodules which are lighter than the ores of Seafloor Massive Sulfides.