Study On The Hydrate Formation And Dissociation On A Micro-Scale

Hydrates are widely distributed around the world and have a large amount of resources.They are considered as the most promising new energy sources in the 21 st century.Hydrates are mainly distributed in permafrost and deep-sea sediments.Permafrost and submarine sediments have high porosity so they are all considered as pore systems.For the study of hydrates in permafrost layers and sediments,most of them are concentrated in macro-reactors filled with porous media,and there are less directly involved in the formation and dissociation of hydrates in pores.In this paper,the formation and dissociation process of hydrates in micro-pores are taken as the research objectives.The phase behavior microscopic experimental platform for gas-water-hydrate system is designed to study the formation and dissociation process of gas hydrates and cyclopentane hydrates in micro-pores.The content is divided into the following sections:(1)The effect of pore size on the thermodynamic condition for the formation of hydrates was examined.The equilibrium conditions of ethane and carbon dioxide gas hydrates were measured in 500 ?m and 1000 ?m size micro-channel.The results show that the smaller size of the micro-channel,the temperature required for the formation is lower and the pressure is higher.(2)The effect of temperature and time of dissociation on the memory effect of ethane hydrate were studied.The experimental results show that the higher temperature and the longer time of dissolution,the memory effect of hydrate is obviously dissipated and needs lower temperature to form again.(3)Hydrate formation process at the water-gas interface and the bubble surface were observed.In the presence of hydrates memory effect,the hydrate growth is caused by the floating crystallites touching the phase interface.With the center of contact point,hydrates grow laterally along the interface and grow thicker in the aqueous phase.The growth rate in the aqueous phase strongly depends on the degree of supercooling of the system.(4)Cyclopentane hydrate formation and dissociation process were observed.After cooling,the solid at the cyclopentane-water interface is in a convex form towards the cyclopentane phase.As the temperature increases,the solid phase appeares loose and convex is gradually covered up.The arc of light between cyclopentane and water gradually appeares.When the temperature drops again,hydrate is generated at the cyclopentane-water interface,the hydrate crystal is first generated at the cyclopentanewater-wall surface.The crystal gradually grows up and slowly slides to the tip of the light arc,which cause that hydrate grows along the interface and covers the entire interface and grows to the cyclopentane phase.The growth rate in the cyclopentane phase is affected by the degree of undercooling.(5)The vdW-P model was improved to apply it to the calculation of hydrate phase equilibrium in micro-pores.There is a certain deviation between the calculated value of the model and the experimental value,but the overall agreement is good.It is also necessary to further infer and calculate the relevant formulas and model parameters in the model to improve the model accuracy.