The Temperature Effect On The Methane And CO₂ Adsorption Capacities Of Different Degrees Of Deterioration Of Coals

Coalbed methane(CBM)is one of the most important unconventional natural gas resources and its main component is methane.Carbon dioxide is a greenhouse gas that causes global warming.Sealing the carbon dioxide in the coal seam can not only reduce the carbon dioxide in the atmosphere,but also replace the coalbed methane in the coal seam.The sorption capacity of coal is influenced by temperature,coal rank,mineral composition,moisture content and other factors.The effect of temperature on coal adsorption of methane and carbon dioxide is particularly significant.In the study,we chose the Daxing coal seam(DX),Kongzhuang coal seam(KZ),and Jiulishan coal seam(JLS)as experimental samples,and experimentally measured the methane and carbon dioxide sorption capacity at various temperatures for three coal samples.Coal samples of different particle sizes were obtained with the equipment of pulverize and coal sample screen.Then industrial analysis and determination of vitrines reflectance were carried out to obtain basic properties of coal samples.Combining the mercury injection experiment and the liquid nitrogen adsorption experiment,the pore structures of the three coal samples DX,KZ,and JLS were analyzed.The total pore volume of DX coal sample is 0.0607 mL/g,the total pore volume of KZ coal sample is 0.0388 m L/g,and the total pore volume of JLS coal sample is 0.0475 m L/g.The specific surface area of DX coal sample is 11.5 m~2/g,the specific surface area of KZ coal sample is 2.5 m~2/g,and the specific surface area of JLS coal sample is 3.4 m~2/g.The microporous of DX coal sample are more developed,and small holes,middle holes,large holes are not developed.The microporous of DX and KZ coal samples are more developed.The middle holes,large holes are not developed.The adsorption capacity of DX,KZ,JLS coal samples for methane and carbon dioxide was experimentally measured form 283.15 K to 353.15 K.The adsorption isotherms were plotted for various temperatures according to experimental data,which were in line with Langmuir equation.The adsorption amount of each coal sample for methane and carbon dioxide rapidly increases at first.Then it remains constant at every temperature.Among the three coal samples,the adsorption capacity for methane and carbon dioxide in descending order is DX,JLS and KZ under the condition of the same temperature and pressure.The Langmuir volume and Langmuir pressure were estimated according to the adsorption isotherms.The Langmuir volume continuously decreases form 283.15 K to 333.15 K,then remains somewhat constant for the temperature of 333.15 K,343.15 K,353.15 K.The change trend of Langmuir pressure is slowly increasing with increasing temperature.According to the experimental data,we plotted the methane and carbon dioxide adsorption capacities versus the temperature for each injection pressure from 0.5 MPa to 4 MPa.When the temperature of the experiment is lower than the critical temperature of T,the adsorption amount decreases linearly with increasing temperature;When the temperature of the experiment is higher than the critical temperature T,the adsorption amount is basically stable and the change is not obvious.The process of coal adsorption of methane and carbon dioxide is a physical adsorption process.And the physical process is exothermic.Based on the experimental data,the coverage curves of the methane and carbon dioxide versus pressure were plotted.And it rapidly increases at beginning,then remains constant.We also plotted the methane and carbon dioxide coverage curves versus the temperature.With the temperature increasing,the adsorption coverage first slows down slowly and then tends to smooth.