Pore property and its impact on the coalbed methane adsorption of anthracite from Zhu-Zang syncline, Guizhou Province

T Based on the result from the mercury intrusion analyses and low temperature nitrogen adsorption/desorption, the property of pore system of anthracite in Zhu-Zang syncline was analyzed systematically. Combined with isothermal adsorption test, the effect of pore structure on adsorption characteristics had been discussed. The research show that pores in the samples are dominated by micro-pores and the specific surface area mainly comes from the micro-pores. There is a hysteresis loop between the mercury intrusion and extrusion curves and the hysteresis loop did not close when the imposed pressure was reduced back to ambient. The hysteresis behavior and entrapment of mercury can be explained by the pore shielding effect. The result of mercury intrusion is higher than low temperature nitrogen adsorption/desorption due to entire difference in the experimental principles. Langmuir equation was used to characterize the adsorption characteristics of anthracite. The average value of Langmuir volume was 36.70 m³/t, the average value of Langmuir pressure was 3.23 MPa. Langmuir volume and Langmuir pressure increased with the micro-pore surface area and the efficiency of mercury ejection. Additionally, Langmuir pressure seems to be quite sensitive to micro-pore structure. An increase in closed pore leads higher Langmuir pressure.