Nodule degradation

The vertical hydraulic transport of manganese nodules from seafloor to sea surface over several kilometers requires multiple centrifugal pumps. The transport process causes the particles to degrade, e.g. they get smaller along the way due to different mechanisms. For the design of post-processing equipment like dewatering plants, it is important to know the properties of the slurry leaving the VTS. Modelling of the degradation process is an essential part in this design exercise.

The transport process gives rise to particle degradation by three mechanisms: impact with pump impellers and pipework, abrasion with the riser pipe and inter-particle collisions.

The hypothesis in Blue Nodules is that particle degradation due to impact is the dominant mechanism. Research efforts thus far comprise experiments with full scale and smaller scale centrifugal pumps, and establishing a theoretical framework to judge on the results of the experiments.

Blue Nodules concept: subsea mining tool with centrifugal pump, flexible jumper hose, VTS with multiple booster stations

Scaled experiments with the Nodule Cracker Tool. The pump has been submerged in a pressure tank to assess the influence of large water depths on particle degradation. Photos by NIOZ