Study of Gas-Lift Method for Carbon-Dioxide Disposal into the Ocean

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The feasibility of a disposal system of gaseous CO_2 into the ocean proposed by Kajishima and Saito to mitigate global warming has been established in this project. The main part of this system, GLAD (Gas-Lift Advanced Dissolution) system, is an inverse-J pipeline set in the sea at a depth of 200-400m. Co_2 bubbles injected into the pipe form a buoyant plume and dissolve into the seawater as they rise. This dense solution is released from the other side of the pipe. To develop a numerical method to supplement the practical design by the performance prediction, the flow field has been investigated experimentally as well as numerically.A vertical pipe with a length of 7m set in the National Institute for Resources and Environment was used to measure the basic characteristics of the GLAD system. An optical fiber prove was developed to measure the motion and scale of bubbles. The accuracy was examined in a small water tank. Basic data of the system such as CO_2 dissolution rate, the lifted water rate and the volumetric fraction of bubbles have been obtained. On the other hand, a numerical method including a simple CO_2 dissolution model and an efficient numerical scheme was proposed to simulate a gas-liquid two-phase flow concerning to in the GLAD system. The gas-lift effect by air or CO_2 bubbles was reasonably reproduced in our simulation. The discrete-bubble method was also developed to reduce the numerical error and a reasonable agreement in comparison with experimental data was obtained. In addition, a new method for the direct numerical simulation of two-phase turbulence has been proposed for a basic study of microscopic structure of interaction between CO_2 bubbles and turbulent flow of seawater.