Multi-Task Type Vertical Transport System Using Air-Lift Pump for Mineral and Energy Resources in Deep Sea - A Numerical Analysis on the System for Shallow-Type Methane Hydrate -

Methane hydrate (hereafter, "MH") is expected as an alternative energy resource to traditional fossil fuels.Further, rare-earth elements-rich mud, polymetallic nodules, cobalt-rich crust, and seafloor hydrothermal deposits are highly attractive mineral resources for exploration and development.These are located in the seabed of Japan's Exclusive Economic Zone.A multitask-type vertical transport system using an air-lift pump is proposed as a common system to transport these mineral and energy resources from the seabed in deep sea.The authors conducted a numerical analysis in the previous study for a shallow-type MH production system using a gas-lift pump, adopting the one-dimensional drift-flux model, and a numerical model for phase change, to examine the multi-phase flow characteristics, and predict the performance of practical ones.In this study, air is used instead of methane gas to apply the system for transporting MH as well as mineral resources.A new scheme, called "the multi gas-phase scheme", is developed and devised in the program to account for flows of both air and methane gas in the lifting pipe.The numerical results of 0 MPa(G) back pressure, 273.15K(0 ) temperature explained the system's flow characteristics in practical operation well, compared with those of 0.2 MPa(G) back pressure, 283.15K(10 ) in the previous study.The MH production rate: 6912t/d, volume concentration of MH: 14.4 -11.3 %, slurry flux: 4.85 -6.18 m/s, power requirement: 1019 -1995 kW are predicted under the dimensions; length and water depth of lifting pipe: 940 and 900 m, water depth at air injection point: 300 m, pipe diameter below and above air injection point: 0.4 and 0.5 m, respectively, and