Effect of degassing temperature on nitrogen adsorption of three rank coals

Low temperature nitrogen adsorption experiment is an important method to study the pore of a coal reservoir. The pore structure of coal can be characterized by the experimental data. The results of lowtemperature nitrogen adsorption experiment are affected by some factors such as sample particle size,degassing temperature,and degassing time. Among these factors,the degassing temperature and degassing time are greatly affected by the nature of the sample and are not easy to be controlled. In order to study the effect of degassing temperature on the results of the lowtemperature nitrogen adsorption experiment,three kinds of coal samples with different metamorphic degrees were used for the lowtemperature nitrogen adsorption experiment,including the medium metamorphic bituminous coal of Beisu mine,the high metamorphic bituminous coal of Malan Mine and the anthracite of Xinjing Mine. The same degassing treatment time was used in the experiment,the time length was 2 hours,and the degassing treatment temperatures were 105,120,135，150 ℃ respectively. By analyzing the parameters such as mass change rate,adsorption isotherm,adsorption capacity,porevolume,porespecific surface area and average pore diameter of three ranking coal samples under the same degassing time and different degassing temperatures,it is found that the experimental results of coal samples with different coal ranks also change when the degassing temperature changes. Also,it is found that the main factors affecting the experimental results of coal pore structure are water and volatile in coal when changing the degassing temperature. With the increase in degassing temperature,the experimental results are gradually weakened by water and enhanced by volatile matter. Under the same degassing time and degassing temperature,the higher the degree of coal metamorphism,the less the influence of water on the experimental results. When the degassing time is 2 hours,the degassing temperature of the coal sample is recommended to be 135 ℃. Low metamorphic coal is more sensitive to temperature because of its high volatile content. Whether it follows the same law needs to be further studied.