Reduction of Energy Consumption When Using a Grab for Deep-Sea Mining Operations

摘要

Recent developments for deep-sea mining have shown multiple scenarios of gaining mineral deposits ofrnSeafloor Massive Sulfides (SMS). One of the problems for these scenarios is the overall large energyrnconsumption of processing rock material which are a technological challenge and are increasing productionrncosts. This paper compares two methods for deep-sea rock excavation on their energy consumption,rnbased on rudimentary calculations.rnThe best known scenario for gaining mineral deposits from the seabed is to excavate rock materialsrnwith a crown or drum cutter and pump the fluidized crushed materials to the vessel at the surface. Thisrnprocess requires high cutting forces deep-sea due to the hyperbaric effect at large water depths, whenrncutting with full cavitation. This high energy consuming process therefore requires a considerable amountrnof subsea installed power.rnAn alternative scenario is to use a hydraulic grab for excavating mineral deposits and not crush all thernmaterials entirely subsea. Using a grab would be very beneficial in rough terrains and unstable seafloorrnconditions, compared to track-driven vehicles typically used for crown or drum cutters. Also specificrncutting forces are much lower when using a grab, because it is not cutting at full cavitation in hyperbaricrnconditions. However the main advantage is to keep most of the rock intact which allows the material tornbe crushed at the surface. Mechanically uplifting large pieces of rock therefore could have the advantagernthat most of the required power can be installed at the surface, rather than subsea for the traditionallyrnproposed hydraulic pumping systems. The rock can then be further crushed under atmospheric pressurernat the surface, avoiding the hyperbaric effect. The combination of using a grab and further crushing atrnatmospheric conditions is more energy efficient and therefore requires substantially less installed subsearnpower.rnUsing rudimentary calculations, a great reduction of energy consumption is found for using a grabrncompared to typically used crown or drum cutters. Substantially less subsea installed power is requiredrnfor excavating the mineral deposits with a grab. Although additional crushing needs to be done at thernsurface, the overall required installed power for using a grab still can be much less than fully subsearnexcavating and crushing.