Study On The Preparation Of Gas Hydrate In Transfer Of Multiphase Flow

Natural gas is a clean energy and conducive to environmental protection and sustainable development of economy. Transportation of natural gas as Natural Gas Hydrate (NGH) has great advantages and more promising prospects to the liquefied natural gas and pipeline transportation. The key point of storing and transporting natural gas as natural gas hydrate technique is the preparation of NGH. This thesis mainly focuses on the study on the multiphase transfer process in process of NGH preparation.1,Through repeated experiments, it is found that:the preparation of NGH is a crystallization process and generally the operating must be in the super-cooling regions so that the crystallization would be smooth and continuous. However the super-cooling should not be much greater, otherwise the system will generate too much crystal per unit time to block the equipment or icing within the pipeline, which will lead great change to the heat transfer, i.e. haste makes waste. Thence, the refrigerant temperature can not be much lower. Under the general laws of crystallization, it's preferred that the refrigerant temperature should be about 5℃lower than the equilibrium temperature of NGH-water system.2,In the preparation of natural gas hydrate, there may exist four different contact interfaces for gas, water and tube wall. Based on heat transfer analyses on these surfaces, the results show that there is evidently dissimilarity with the heat transfer in different interfaces. When the heat transfer interface is of water-metal under the experimental conditions, the main heat resistance of the process is on the inner tube wall. When the heat transfer interface is of ice-metal, and the ice is thin, the heat transfer does not change obviously, but if the thickness of ice exceeds 1 mm, the heat transfer descends evidently. When the heat transfer interface is of natural gas hydrate-metal, it is similar to ice-metal interfaces. When the heat transfer interface is of natural gas-metal, the heat transfer descends sharply and the preparation of natural gas hydrate can not resume.3,By carefully analyses of heat transfer on different interfaces, it is found that the key factor in preparing natural gas hydrate is to maintain an effective heat transfer. Only by keeping the reactant inside the tube renewed incessantly and removing the heat promptly, the preparation process can be efficient. The fluid flow over the heat transfer interface imposes great affects on the preparation of natural gas hydrate.4,With Ansys Flotran CFD module, the multiphase transfer process in the reaction unit is simulated, which shows that the distribution of gases and liquids inside a tube with smooth inner face is similar to that of experiment. It is clarified that the gas fraction is too high in the region near to the tube wall, which is bad for the reaction to NGH. It's highly demanded that the structure of the inner wall of the tube be improved, so that less or even no gas can be accumulated near the inner wall of the reaction tube...