Research on the Low-Temperature Oxygen Consumption and Low-Oxygen Gas Emission Law in Goaf of Ultrathick Coal Seams.

Low-oxygen (oxygen concentration below 18.5%) phenomena often occur in the top coal caving working face of ultrathick coal seams, posing a serious threat to the safety of workers. The characteristics of oxygen consumption and gas production at low-constant temperature and the corresponding functional group evolution of residual coal in goaf were studied by temperature-programmed and infrared spectrum experiments. The influence of different factors on the emission of low-oxygen gases was studied through numerical calculation. The results show that low-temperature oxygen consumption and gas production occurred when the coal was about 40 °C. When the temperature was constant, the oxygen consumption and gas production rate increased with the extension of time. In the early stage of coal oxidation, the aliphatic C-H components were attacked by oxygen molecules and reacted with them. The asymmetric methyl and methylene groups were more likely to oxidize and produce carbonyl compounds. With the increase of nitrogen injection, the overall width of the oxidation zone (oxygen concentration was defined as 10-18%) narrowed, and the range of the oxidation zone moved forward from the depth of the goaf. The oxygen concentration in the air return corner decreased gradually, and the low-oxygen area in the air return corner expanded gradually. The distance between the low-oxygen area of the working face and the air intake corner was gradually shortened. With the increase of air intake, the width of the oxidation zone increased and moved to the depth of goaf, and the degree of low oxygen in the air return corner increased. The research results are of great significance for the understanding and prevention of the low-oxygen phenomenon in ultrathick coal seams.