Study On Formation And Decomposition Process Of Mixed Gas Hydrate

Natural gas hydrate(combustible ice)is a kind of new energy,which is widely concerned because of its wide distribution and less pollution.In addition,the environmental problems caused by the disorderly decomposition of natural gas hydrate and its important role in the global carbon cycle have also attracted much attention.The combustible ice is found in the South Poseidon Fox Sea area and the permafrost region of Qilian Mountain.May 18,2017,the first Test of sea ice was carried out.It speeds up the commercial application of gas hydrate.Generally speaking,people's understanding of the combustible ice is far from enough.We still need to strengthen the formation,decomposition and other aspects of basic research of flammable ice.The basic parameters in the process of formation and decomposition of combustible ice are of great significance to the exploration of combustible ice and the application of natural gas storage and transportation.So far,the basic research on the formation and decomposition kinetic characteristics of methane hydrate,which is the most common object molecute in nature is more in-depth,and many scholars at home and abroad have made considerable achievements in the dynamic model of single component hydrate nucleation and the relationship between induction time and environmental conditions such as temperature and pressure.However,relative research on complex gas hydrate is scarce,while the gas components of combustible ice in nature are often mixed with a variety of gas components.This research is based on the visual reactor,which is designed and manufactured for mixed gas hydrate.First,the formation and decomposition process of mixed gas hydrate was carried out by controlling temperature,pressure and stirring speed.At the same time,the macroscopic observation of this process is carried out using this experimental device.Then,with the aid of the Nuclear Magnetic Resonance(NMR)imaging system,the microscopic research on the image of the mixed gas hydrate formation-decomposition process is carried out.Finally,the synthetic mixed gas hydrate is identified by the X-ray diffraction(XRD)technique.Accordingly,the results of this experiment are as follows:(1)The parameters such as stirring speed,pressure and reaction temperature could affecte the formation kinetic of mixed gas hydrate.Stirring,higher initial pressure and lower formation temperature could get shorter induction time of the multiple gas hydrate formation.In addition,higher decomposition temperature and lower decomposition pressure of mixed gas hydrate cause the faster the decomposition rate.(2)Using the visualization reactor could observe of the formation process of the mixed gas hydrate,it is found that the process is the same as that of methane hydrate,there are "wall climbing effect",and there is "armor effect" without stirring.Using NMR imaging could observe microscopic decomposition process of mixed gas hydrate,it is found that the decomposition of mixed gas hydrate is similar to the process of ice melting,and the hydrate at the edge of solid-liquid is decomposed first and gradually expands to the middle.There is no self-protection effect in the decomposition process of mixed gas hydrate.(3)In the end,we optimized the parameters of powder XRD instrument,and established the method of powder XRD to test the crystal structure of natural gas hydrate.Then it was applied to test the crystal structure of mixed gas hydrate sample.The results show that 8 groups of synthetic mixed gas hydrate samples belong to the cubic crystal system,the space groups are Fd3 m,the structures are II,and the lattice parameters are between 17.03 ?-17.25 ?.The study is conducive to understand the accumulation regularity of the mixed gas hydrate.It is vital to avoid the adverse effects on the environment during its exploitation and utilization.