The presentation will describe the developments to analyze mining slurries in spooled risers and the benefitsof this knowledge in de the design process of spooled risers.Current technology in deep sea mining applications dictates that the slurry produced by the seabed miningtool is transported using a flexible riser to the vertical riser inlet. The vertical riser, similar to oil & gas risers,is a series of steel pipes which transports the mineral slurry from the seabed to the mining support vessel.New developments in riser technology enable flexible hoses to be used for applications in water depths up to500 meters.In this application, a single riser using flexible hoses is used for transporting the slurry from the SeafloorMining Tool (SMT) to the Mining Support Vessel (MS). The advantages are (ⅰ) that the flexible riser can belaunched and recovered by spooling it on a drum installed on the mining support vessel and (ⅱ) can cater forvarying water depths.In the section of flexible hoses spooled on the drum, the slurry behaves differently from what might beexpected. The paper starts with a description and consequences of the phenomena that occur in elbows andin the spooled hoses at the entrance of the spool. Followed by the development of the slurry to a newstratification regime along the first part of the spooled hoses and finally the phenomena which occurthereafter. The envelope of slurry conditions (concentration, particle size distribution and velocity) have animpact on the dynamic pressure losses in the spooled hoses.Insight into the slurry behaviour is obtained using 3D CFD simulations. Verification is performed withinformation retrieved from literature. To represent better the slurry behaviour a pressure ratio, R_(pressure), isintroduced, which is the local pressure gradient in the spool divided by the pressure gradient of a straightpipe. When the total pressure ratio is calculated over a typical length of a design configuration, like an elbowor complete turn, this figure can be compared with other results found in lecture. The envelope of this figurealong its design length is even more important. The changes can be related to changes in mixture behaviour.The new insights not only explain why some slurries show the secondary flow of Dean and others don’t, butalso why some slurry mixtures show lower dynamic pressure losses compared to slurry in a straight pipe.From a practical point of view construction parameters as the spooled riser diameter to drum ratio andconsequences of alignment in the horizontal or vertical position are discussed.Using the 3D-CFD simulations has improved insight in the behaviour of typical mining slurry mixtures in largediameter spooled risers and can be used to control the slurry mixtures in spooled risers. Additionally thedevelopment of suitable internal liners for flexible slurry risers will gain from these models.
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