Experimental Study On Formation Characteristics Of Coal-Bed Methane In THF System

Coalbed methane(CBM),as a conventional clean energy source,wasabundant reserves.With the rapid development of China’s economy,the demand for the proportion of energy structure,carbon emissions and other issues had gradually increased.However,due to the limitation of extraction technology,geological occurrence and other reasons,many of the coalbed methane extracted underground can not reach the utilization concentration and directly empty,resulting in a great waste of resources.In recent years,in order to improve China’s energy structure and protect "green water and green mountains",projects such as replacing coal with gas and oil with gas are being promoted.Coalbed methane,like green energy such as natural gas and shale gas,will play an important role in China’s energy strategy if it can be reasonably exploited.Based on gas hydrate technology,methane in coalbed methane can be separated,purified,stored and transported,which has great application prospects in development of coalbed methane in the future.However,problems such as slow formation rate and low methane recovery are often encountered in the hydrate formation of coalbed methane.In order to solve these problems,the THF promoter with 5.56 mol%was used to carry out the formation process of coalbed methane hydrate in tubular reactor with different saturation,initial pressure gradient and porous media system.The P-T characteristics,gas consumption,gas absorption rate and gas storage capacity in the process of methane hydrate were analyzed emphatically.The main conclusions are as follows:(1)Tetrahydrofuran(THF)has excellent promotion effect.5.56 mol%THF greatly reduced the phase equilibrium pressure during the formation of methane hydrate and improved the temperature and pressure conditions of hydration reaction.(2)Under different saturation,the kinetic parameters of coalbed methane hydrate formation have different characteristics.As the saturation of THF solution in the reactor increases gradually,the gas consumption,gas consumption rate and gas storage capacity in the reactor first increase and then decrease.In the THF reaction system with saturation of 37.5%,the hydrate formation of methane in coal-bed gas is the best and the gas storage capacity is the highest.At this time,the gas-liquid ratio in the reactor is 0.07.(3)The experimental results of methane hydrate formation under different initial pressures showed that the pressure driving force can significantly affect the formation rate and methane gas storage in the process of methane hydration.The higher the pressure driving force is,the faster the formation rate of methane hydrate in coalbed methane is,the more methane gasis consumed,and the higher the recovery rate of methane is after the formation of methane hydrate.(4)Compared with the pure THF solution system,the reactor filled with 5A zeolite and SBA-15 mesoporous molecular sieve carriers provides a larger gas-liquid contact area in the hydration process,which enhances the formation process of methane hydrate.Compared with 5A zeolite,the powder SBA-15 zeolite has very high specific surface area and good interface.In the process of coal bed methane hydration reaction,the gas storage capacity is better and the methane storage rate is higher.(5)In the process of coalbed methane hydrate formation,the gas consumption rate in the reactor is the fastest in the rapid generation stage,which is about 10 times of the slow growth stage,and the gas consumption rate in the slow growth stage appears a quiet period.This is because the hydrate film formed in the early stage covers the gas-liquid interface,which affects the gas-liquid mass transfer efficiency in the process of hydrate formation.In the later stage of hydrate formation,the pressure in the system is low and the driving force of hydrate reaction is small,which slows down the formation and growth rate of methane hydrate nuclei.