Research for the formation and stability of CO_2 hydrate in deep sea

本文以液态CO_2为研究对象，对CO_2在3000m深度的深海高压低温下的物理行为进行了理论和实验研究。同时，针对CO_2和CO_2水合物的饱和输送和注入，对深海CO_2注入系统进行了研究，提出了新型精密装置的概念设计。直接与海水接触的CO_2会扩散到海水中或在CO_2/水界面形成水合物。在压力容器中，在深海中产生压力和温度，然后在液态CO_2和水的界面上观察到以下事实：(1)瞬间形成水合物膜，但生长非常缓慢(2)通过搅拌界面来加速水合物的形成(3)通过使压力或温度从平衡条件崩溃而迅速溶解水合物，同时伴随着温度的快速下降(4)水合物一旦形成，除非施加电流剪切力，否则是非常稳定的。在一个50-300atm的压力容器中，利用本研究开发的CFD程序分析了CO_2浓度分布随时间的变化，计算了分子在水中的扩散、界面传质和CO_2溶液密度变化的三个主要系数。对利用低温液态CO_2的电厂进行了基础研究。进一步的研究方向：(1)水合物变化的更大范围的追求；(2)气体中CO_2的扩散；(3)考虑液态CO_2颗粒上的扩散和水合物。

Theoretical and experimental studies have been carried out on the physical behavior of CO_2 under the high pressure and low temperature corresponding to the deep ocean of 3000m depth level focusing on the liquid CO_2. Simultaneously the studies of the injection system of CO_2 into the deep ocean result in the conceptual design of new sophisticated devices aiming at a satble transfer and injection of CO_2 and CO_2 hydrate. CO_2 directly contacting with sea water will be diffused into sea water or hydrate will be formed at the interface of CO_2/water. In this study a pressure and temperature in the deep sea was produced in the pressure vessel then the following facts were observed at the interface of liquid CO_2 and water (1) Instant formation of hydrate film but very slow growth of it (2) Asseleration of formation by stirring the interface (3) Prompt dissolution of hydrate by collapsing a pressure or temperature from an equilibrium conditions accompanying a rapid temperature decrease (4) Hydrate once formed is very stable unless current shear force is imposed. In a pressure vessel of 50-300atm containing liquid CO_2 and water, three principal coefficients of molecular diffusion in water, mass transfer at interface and density change of CO_2 solution have been calculated by using the CFD program developed for this research analyzing the change of CO_2 concentration distribution with time. Basic research of power plant utilizing the low temperature of liquid CO_2 has also been carried out. Further research in future of (1) Longer range pursuit of hydrate change (2) Diffusion from gas CO_2 (3) Diffusion and hydrate on a particle of liquid CO_2 are kept in mind.