Investigation On Hydrate Exploitation By In-situ Thermal Stimulation Under The Energy Separation Effect Reinforced By A New Structure Vortex Tube

Natural gas hydrate is known as the green and clean strategic energy with the most promising development prospects in the 21 st century,which has attracted widespread attention from domestic and international scholars.Up to now,five countries,China,Russia,the United States,Canada,and Japan,have conducted on-site test production of natural gas hydrates using methods such as thermal stimulation,depressurization,and replacement.The results of the test show that the current hydrate mining methods have disadvantages such as large thermal losses,rapid production decline,and high environmental risks.Therefore,it is urgent to carry out technological innovation on the basis of the original mining method and develop more efficient and safe hydrate mining technology.As a kind of energy separation device with simple structure and high performance,the vortex tube has been widely concerned by scholars since it was put forward,and it is widely used in the industrial field.In this paper,the energy separation effect of the vortex tube is innovatively introduced into the hydrate mining operation.After the optimal structure of the vortex tube is determined,the hydrate generation and decomposition experimental system designed independently is used to analyze the hydrate decomposition characteristics under the energy separation effect of the vortex tube.Experimental research and numerical simulation are both carried out.In this paper,the influence of the structural parameters of the vortex generator(number of nozzles,shrinkage ratio,cold orifice angle and material)on the performance of the vortex tube is studied through experiments,and the energy separation efficiency of the vortex tube is strengthened.The results show that increasing the inlet pressure and the number of nozzles can increase the cooling capacity,heating capacity and exergy efficiency.The cooling capacity and heating capacity will first increase and then decrease with the increase of the cold orifice angle.When the cold orifice angle of the vortex generator is 2°,its exergy efficiency is the highest.In addition,the reduction of the thermal conductivity of the vortex generator material is beneficial to improve the energy separation performance.In addition,the influence of inlet pressure and number of nozzles on temperature stagnation point is more significant than that of cold orifice plate angle and material.The resin material vortex generator with 6 nozzles,1 shrink ratio and 2° cold orifice angle possess the best energy separation performance,and the highest exergy efficiency can reach about 0.5.In this paper,the temperature field of the vortex tube is investigated by using the standard k-ε model by numerical simulation.The energy separation effect mechanism of the vortex tube is obtained through the analysis of the simulation results.The energy separation is caused by the work and heat transmission between the inner and outer fluids.The tangential work transfer is dominant in the entire energy transmission process.In addition,after analyzing the numerical simulation results,it is found that adding a vortex stopper inside the working tube can effectively enhance energy separation performance of vortex tube,and the six-blade vortex stopper can achieve the best thermal stimulation effect.In this paper,the self-designed experimental equipment is used to study the hydrate formation and decomposition characteristics,and the influence of different parameters on the hydrate decomposition effect is investigated.The results show that the energy separation effect of the vortex tube greatly promotes the hydrate decomposition process.In a porous media system with a smaller particle size,the decomposition rate,gas production and other mining parameters are better.The higher inlet pressure of the vortex tube promotes the formation of hydrates,and the gas production can be increased by about 27.71% after the inlet pressure of vortex tube is increased.When the optimized structure of vortex tube is adopted,the decomposition rate of hydrate is effectively increased by the vortex tube.The maximum gas production rate is about 1.6 L/min,and the total gas production can be increased by about 11.14%.