Stability of vertical hydraulic transport processes for deep ocean mining

Abstract

Vertical hydraulic transport systems for deep ocean mining have lengths up to a few kilometers from seafloor to sea surface. Typical ratios of particle diameter d over riser diameter D   are d/D=O(10⁻¹)d/D=O(10−1), and the feeding of the riser is irregular. These conditions make the vertical transport operation susceptible to propagating density waves which is detrimental for the transport process. There is however few experience with hydraulic transport on this scale. We adopt a continuum description of the transport process and use stability analysis theory from the field of fluidization technology. We indicate the similarities and differences between fluidization and vertical hydraulic transport to show that the theory can be extended to transport conditions as well. We demonstrate the applicability of the theory with a fluidization experiment using particles having d/D≤0.26d/D≤0.26, which is an extension of the d/Dd/D range in classic hindered settling theory. Our transport experiment with similar particles shows differences with the fluidization experiments, indicating that flow stability in vertical transport might actually improve compared to fluidization.