Numerical Simulation on Gas–Liquid–Solid Three-Phase Flow by Gas-Lift Pumping System for Deep Sea Mining

Abstract Subsea minerals have been found in the deep water within Japan’s exclusive economic zone. However, the development of subsea minerals has not reached the commercialization stage because many technical issues still need to be solved. The gas-lift pumping system is one of the promising methods for subsea minerals transport. Since internal flow in pipes becomes three-phase flow for the gas-lift pumping systems, flow assurance for three-phase flow is important to design the systems for subsea minerals production. It is necessary to figure out the liquid and solid flow rates for principal dimensions of the assumed production systems for designing and operating them. Thus, we simulated gas-liquid two-phase and gas-liquid-solid three-phase flows on the gas-lift pumping systems based on one dimensional drift flux model with reference to the previous studies, and compared the calculated results with the experimental data obtained from the previous studies. The comparison showed that the calculated transient liquid flow rates were consistent with experimental data in gas-liquid two-phase flows for the pipe of 0.026 m in internal diameter. The comparison also showed that the calculated steady liquid flow rates were consistent with the experimental data in gas-liquid-solid three-phase flows for the pipes of 0.026 m and 0.3 m. Since calculated results were generally consistent with experimental data, we could simulate gas-liquid-solid three-phase flows by the present methods. Then, we simulated the three-phase flow for the assumed actual production systems and investigated the effect of the mass flow rate of gas and the water depth of gas injection on lifting efficiency. The lifting efficiency decreased as the mass flow rate of gas increased and increased as the gas injection point approached the sea surface.