Experimental Research On Coal Adsorption Isotherm Of Binary Gases Of CH₄,CO₂ And N₂

Since the beginning of the 21st century,carbon emissions have become an important factor affecting a country's international status,economic development and ecological balance,as well as a key factor determining the country's future energy development prospects.At present,there are two main ways to reduce greenhouse gas emissions.One is to improve the utilization efficiency of fossil energy and adopt some clean energy;the other is to collect CO₂and store the carbon dioxide in some suitable geological units and strata.Coal is a porous medium with a complex pore structure.At present,due to the complex geological conditions of coal seams,the mining rate of coalbed methane is low.If CO₂geological storage can be carried out in coal seams,it can not only store CO₂,but also improve the recovery rate of CH₄in coal seams.This paper takes the Permian coal seam in the eastern part of Hedong coalfield as the research object.According to the experimental requirements,the adsorption isotherm is designed by ourselves,and the isotherm adsorption experiments are carried out on coal samples of three different coal ranks.The adsorption capacity of CH₄,N₂and CO₂is calculated through the conservation of mass and the ideal gas equation of state.The compressibility factor is considered in the calculation of the adsorption capacity,and the equation of state of the ideal gas is corrected.At the same time,the adsorption capacity of the binary mixture of CH₄,N₂and CO₂with the mixing ratio of 70%,50%,and 30%is measured and gas chromatographic analysis.After relevant calculation and analysis,the absolute adsorption capacity of the sample under different equilibrium pressures is obtained.Then,this paper uses Freundlich,Langmuir and other common 6 kinds of isotherm adsorption models to perform fitting analysis on the data obtained from the experiment,and the fitting accuracy Both are relatively high,which proves that the experimental data is relatively reasonable.Then using the diffusion theory of porous media to calculate the number of adsorption layers of different gases at different equilibrium pressures,it is found that the gas is not simply a single layer adsorption.After a certain pressure is exceeded,the number of adsorption layers increases with the increase of pressure.At the same time,the surface diffusion coefficients of the three samples for CH₄,N₂and CO₂are obtained through diffusion theory,and it is found that the surface diffusion coefficient increases with the increase of equilibrium pressure.Finally,the diffusion coefficient is corrected by introducing the pressure-related single-layer coverage?,so that the calculation result of the diffusion coefficient is more reasonable.Finally,according to the adsorption kinetic data obtained from the experiment,the permeability of the three samples to CH4 during the stepwise pressurization process was obtained by using the osmotic adsorption theory.It was found that the permeability gradually decreased with the increase of the equilibrium pressure.According to the calculated permeability The obtained relevant parameters study the relationship between equilibrium pressure and permeability,viscosity coefficient and compressibility.Finally,by defining the pressure sensitivity coefficient of methane adsorption,the relationship between the pressure sensitivity coefficient of methane adsorption and permeability is studied,and it is found that the greater the sensitivity coefficient of methane adsorption pressure,the greater the permeability.