Study On The Effect And Its Difference Of Displacement Methane In Coal By Different Adsorption Capability Gas

In order to study the difference in the methane displacment effect of coal with different gases with adsorption capacities,a single-component gas such as CH₄,CO₂,N₂ and He were selected.Under the conditions of isobaric diffusion and high-pressure injection,a gas-bearing coal multi gas replacement device was used to perform replacement experiments to obtain the gas replacement laws,replacement rates,and replacement efficiency characteristics of coal for different adsorption capabilities,and the effect of replacing gas with different adsorption capacity on CH₄ in coal was analyzed.First,the content of the single gas CH₄,CO₂,N₂,He adsorbed by coal at 8 pressure points was measured in the laboratory.Based on the experimental data obtained,isothermal adsorption curves of different gases under the same conditions were drawn.The adsorption rules of CO₂,CH₄ and N₂ are approximately in accordance with the Langmuir isotherm adsorption equation,while the value of He adsorption of coal is positive or negative,but the laws do not fit the model at all.Under the same conditions,the amount of CO₂/CH₄/N₂ gas adsorbed by coal increases rapidly with the increase of pressure,and then stabilizes;while the value of He adsorption of coal is positive,negative,and almost close to 0,showing almost no Adsorption,therefore,it is obtained that the order of the adsorption amount of coal to gas with different adsorption capacity is CO₂>CH₄>N₂>He.Based on the experimental results of single-component gas adsorption on anthracite,six groups of different CH₄ pre-adsorption equilibrium pressures were set,and the effect of gas with different adsorption capacity on CH₄ substitution in coal was analyzed.Under the two conditions of equal pressure diffusion and high pressure injection,the same amount of replacement source gas is injected respectively.The experimental results show that under both conditions,as the replacement pressure of the replacement source gas increases,the amount of CH₄ replacement gradually increases during CO₂ replacement.when N₂ or He is replaced,the amount of CH₄ replacement gradually decreases.Under the conditions of equal pressure diffusion and high pressure injection,as the gas adsorption capacity is enhanced,the CH₄ replacement rate and the gas replacement efficiency are gradually increased.For the same gas,under the condition of equal pressure diffusion,the replacement rate of CH₄ increases with the increase of gas replacement pressure,and the replacement efficiency of each gas decreases with the increase of gas replacement pressure;Under high-pressure injection conditions,when CO₂ is injected,the CH₄ replacement rate and CO₂ replacement efficiency both increase.While N₂ and He replacement are performed,the CH₄ replacement rate,N₂ replacement efficiency,and He replacement efficiency appear to decrease trend.A comparative analysis of the displacement effect under the two injection modes of equal pressure diffusion and high-pressure injection shows that,during the CO₂ injection,the equal pressure diffusion displacement has a higher effect in the low-pressure stage.This advantage gradually turns into that high pressure injection is better than isobaric diffusion;When N₂ and He are replaced,the effect of isobaric diffusion replacement is always better than that of high-pressure injection,and this advantage becomes more obvious as the equilibrium pressure increases.