Test Set-Up for Irregular Vertical Hydraulic Transport in Deep Ocean Mining

Abstract

The mining of scarce minerals from the sea-floor at the depths of several kilometers and bringing them to a processing plant at the ocean surface requires new techniques. Seafloor Massive Sulphide (SMS) deposits are known to have an extremely rich mineral content, and are considered technically-economically-environmentally feasible to explore. Vertical hydraulic transport is the link between the sea-floor mining and the maritime vessel where the first processing stage will take place. Clogging of any part of the vertical transport system is an absolute disaster. Fine particles are conveyed faster than coarse particles. High concentrations of fines cannot bypass high concentrations of coarse particles, hence these particle fractions accumulate, potentially blocking the pipe. Fundamental research into yet unexplored physics is necessary. Besides numerical flow simulations, it is necessary to conducted experiments on the transport over large vertical distances. Such tests aim to investigate the dynamic development of density waves consisting of different particle diameters and clogging phenomenon thereof. Different particle size fractions have to be followed in real time as they overtake each other, and change their shape, merge and segregate. It is however impossible to back-scale the prototype riser to a one-pass laboratory test set-up, but the process can be simulated by repeated flow through an asymmetric vertical pipe loop, where slurry flow in the upward leg represent vertical hoist conditions and the slurry is returned quickly via the downward leg. The particle accumulation process is allowed to take place in the upward leg whereas in the downward leg the restoring process is nearly neutralized. The development of accumulations in time (= distance traveled to the ocean surface) can be followed upon multiple passes of the solids batches through the upward leg. The novelty of the described testing method is that the essentials of fundamental processes occurring in long vertical stretches are quantified in a specially designed laboratory setup. Via subsequent implementation of the results in a numerical flow simulation, reliable transport scenarios can be delineated.