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

该项目确定了Kajishima和Saito为缓解全球变暖而提出的向海洋排放气态二氧化碳的系统的可行性。该系统的主体是GREAD(Gas-Lift Advanced Dissolation)系统，它是一条安装在200-400m水深的反J管线。注入管道的二氧化碳气泡形成一股浮力羽流，并在上升时溶解在海水中。这种稠密的溶液从管道的另一边释放出来。为了开发一种通过性能预测来辅助实际设计的数值方法，对GREAD系统的流场进行了实验和数值研究，并利用国家资源环境研究所设置的7m长的垂直管道对GREAD系统的基本特性进行了测量。研制了一种用于测量气泡运动和尺度的光纤测试仪。准确度在一个小水箱中进行了检验。得到了该体系的CO_2溶解速率、提水速率和气泡体积分数等基本数据。另一方面，提出了一种包括简单的CO2溶解模型和有效的数值格式的数值方法来模拟GRAID系统中涉及到的气液两相流动。我们的模拟合理地再现了空气或二氧化碳气泡的气举效应。为了减小数值误差，还发展了离散气泡法，并与实验数据进行了比较，得到了较为合理的结果。此外，为进一步研究CO2气泡与海水湍流相互作用的微观结构，提出了一种直接数值模拟两相湍流的新方法。

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.