Experimental Verification of Clogging within Vertical Transport Systems for the Deep Sea Mining Industry

This report concerns the experimental validation of recent numerical predictions of pipe blockage during the vertical hydraulic transport of ore for the deep sea mining industry. A hydraulic circuit, incorporating an 8.5 m riser pipe of 99.4 mm inner diameter, was built to identify and quantify the dominant transport mechanisms during conveying, merging and passing of two batches of solids. Experiments were conducted with single batches and various combinations of two batches, including two types of sand (0.39 mm and 1.05 mm), two types of gravel (6.34 mm and 11.20 mm) and Polystyrene granulate (2.80 mm). Experiments indicated a decreasing influence of axial dispersion for an increasing particle size and particle density. By measurement data analysis, it is proven that axial dispersion is negligible for coarser solids, implying a larger risk of concentration peaks during transport compared to recent numerical calculations which assumed Taylor dispersion. Experiments with two merging batches revealed the ability for sand to merge and pass the gravel, whereas polystyrene merges and fuses with the gravel leading to pipe blockage. This discrepancy is thought to originate from a specific solids diameter ratio between both batches. A relation is suggested between the occurrence of pipe blockage and Terzaghi’s filter rules. The report concludes that the volume fraction of solids can rise significantly during the merging process and that for certain solids combinations, the merging process can lead to blockage of the riser.Offshore and Dredging EngineeringMaritime and Transport TechnologyMechanical, Maritime and Materials Engineerin