| CBM is a kind of hydrocarbon gas that is stored in the coalbed with methane(CH4)as its main component.It is mainly adsorbed on the surface of coal matrix particles,partially free of coal pores or dissolved in coal water,and is a kind of high-quality clean energy.Although China has abundant reserves of CBM resources,the technology for the development and utilization of CBM has been limited,which has led to a large number of low-concentration CBM resources that can only be disposed of by venting to the atmosphere.This has not only caused a large amount of energy waste,but also caused serious environmental pollution and improvement of the utilization efficiency of low-concentration coalbed methane have become an urgent problem in the energy sector.Gas hydrate purification of low-concentration CBM is an important approach to achieve efficient utilization of CBM at low concentrations,which has received more and more attention.However,the gas hydrate purification of low-concentration coalbed methane is still in the experimental research stage.Problems such as long crystallization time,low methane recovery and separation factor,and low reaction rate are still the key to the engineering application of this method.In view of the above-mentioned key issues,this article has carried out relevant experimental research on the purification of low-concentration CBM by gas hydrate method.The main research work includes:(1)To solve the problems of low efficiency and poor efficiency in gas hydrate formation and separation of low concentration coalbed methane,the nano-graphite fluid was used as an additive for the hydrate separation of low concentration coalbed methane.The effects of nano-graphite fluids on the gas separation and methane recovery,methane separation factor,induction time and other important separation and purification parameters during the reaction were mainly studied.Firstly,the effects of nano-graphite fluids prepared by adding nano-graphite(GNP)in tetrahydrofuran(THF)+ sodium dodecyl sulfate(SDS)solution system on the purification of low-concentration CBM were investigated.The study found that the addition of GNP in the THF + SDS system compared to the CH4 recovery and separation factor has greatly improved,CH4 recovery rate increased from 33.7% to 49.6%,CH4 separation factor from 2.8 to 6.6.At the same time,the induction time is reduced compared to the previous system,and the gas consumption increases(mol of gas/mol of water).The separation and purification parameters have been improved,and the separation and purification effect has become better(2)Due to the better promotion effect of nano-graphite,a further experimental study was conducted on the above conclusions to study the kinetics experiments for purification of CBM with different mass fractions of GNP solutions(0.1 wt%,0.5 wt%,1 wt%,3 wt%).In terms of impact,their average methane recovery rates were 39.7%,49.6%,40.1%,and 38.9%,respectively;the average methane separation factors were 2.9,6.6,3.8,and 3.4,respectively;the average induction time was 6 min,5.5 min,6.2 min,8.3,respectively.Min.Based on the above separation and purification parameters,it can be concluded that a mass fraction of 0.5% by weight of GNP solution is best for separating and purifying low-methane CBM.(3)The dynamic characteristics of the gas hydrate separation of low concentration CBM in different experimental systems were analyzed and evaluated.This study compares the experimental results of various systems(CP,THF,THF+SDS,TBAB,coal particles,emulsified oil,etc.)and compares the effect of separation and purification of different additives.The parameters such as methane recovery rate,separation factor,and induction time of the GNP+THF+SDS system are greatly improved compared to the conditions of CP,THF,THF+SDS,TBAB,coal particles,and emulsified oil.At present,the methane recovery rate and separation factor are the highest under a mass fraction of 0.5 wt% of GNP solution.(4)On this basis,the microscopic growth process of hydrate in GNP solution system with a mass fraction of 0.5% by weight was observed with a high-pressure visual microscope.The study found that in the system,natural gas hydrates grow from the bottom to the top of the reactor wall,and the hydrates form needles.Then,the hydrates rapidly grow at the gas-liquid contact surface,and then gradually diffuse into the solution and grow inside the solution.As the reaction progressed,a large amount of hydrate crystals appeared.The microscopic photographs of these massive hydrate formations also confirmed from the side that the nano-graphite fluid greatly promotes the purification of low-concentration coalbed methane by the hydrate method.The observation of the hydrate growth condition by the high-pressure visual microscopy system revealed the microscopic growth process of the hydrate,which laid a solid foundation for the further study of the microscopic study of hydrate formation. |
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