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

以液态CO_2为研究对象，对3000m深度的深海对应的高压低温条件下CO_2的物理行为进行了理论和实验研究。同时，对深海CO_2注入系统的研究，为实现CO_2和CO_2水合物的稳定输送和注入提供了新型精密装置的概念设计。与海水直接接触的CO_2会扩散到海水中或在CO_2/水界面形成水合物。在深海压力容器中产生压力和温度，然后在液态CO_2和水的界面上观察到以下事实：(1)水合物膜立即形成，但生长缓慢；(2)通过搅拌界面形成的结合力；(3)从平衡条件下的压力或温度崩溃，水合物迅速溶解，同时温度迅速下降；(4)水合物一旦形成，除非有电流，否则非常稳定施加剪切力。利用为分析CO_2浓度随时间分布的变化而开发的CFD程序，计算了50 ~ 300atm含CO_2和水的压力容器中分子在水中的扩散系数、界面传质系数和CO_2溶液密度变化的三个主要系数。同时，还开展了利用液态co2低温发电的基础研究。今后的进一步研究(1)水合物变化的更远距离追求(2)气体CO_2的扩散(3)液体CO_2在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.