Experimental investigation on adsorption characteristics of in coal gas mixture from coal self-heated under different temperatures

The pore structure of coal provides a place for pyrolytic gases from coal storage and movement. The study of the gases movement in coal pore is of significance to the accurate assessment of internal fire risk. The mixture of gases released from the coal self-heating process can move in its pore and be adsorbed by coal. A set of self-designed experimental device is used to study the multi-component gases mixture released during the self-heating process of coal and the flow in the pore of coal particles. The results show that ①the concentration of various gases at the outlet of the reactor can be determined by the characteristics of coal self-heating. Under different temperatures,the concentrations of carbon monoxide and carbon dioxide are the highest,nearly 9%,and the concentration of acetylene is the lowest,less than 100 mg/m³. ②With the different experimental temperatures,the concentration of each component of the gases mixture released from coal changes accordingly. The concentrations of most components in the gases mixture from coal oxidation and pyrolysis are increased with the increase of temperature,while the concentrations of ethane,propane and hydrogen vary irregularly with the temperature. ③In the experiment of gases adsorption in coal,the adsorption of each gas can be determined by the ratio of the concentration of each gas at the entrance and exit of the adsorption column. Gases with a lower critical temperature (such as CO,H₂) are not easily adsorbed in coal. The critical temperature (31.3℃ and 32.8℃,respectively) of ethane and carbon dioxide is close,while the concentrations at the inlet and outlet of carbon dioxide and ethylene are 5%~10% lower than that of ethane because the small molecule gases(below 0.4 nm) are easier to penetrate into the micro porosity of coal,which adsorptions are more likely to happen,and large molecules (such as ethane,propane) cannot infiltrate the coal micropore. Some gases such as ethylene,propylene and acetylene,which have an unstable multiple bond between two carbon atoms (1 α bond and 1 π bond)can help the gases react with the surface of the coal to form new bonds. This indicates that the gases with a high proportion of unsaturated hydrocarbons (such as C₃H₆,C₂H₂) are adsorbed more likely,and it is also related to the nature of the chemical bonds of the gas molecules. In addition,it can be ascertained that the adsorption characteristics of various gases in coal are closely related not only to the physical and chemical properties of gases,but also to the coal properties.