Changes on the low-temperature oxidation characteristics of coal after CO2 adsorption: A case study

Abstract

Coal spontaneous combustion is a natural hazard during mining. In China, the longwall gob area is the main places that are prone to coal spontaneous combustion due to excessive residual coal in the gob and severe air leakage during underground mine ventilation. Injecting CO2 into gob has many advantages to prevent fire disaster. However the characteristics of coal low-temperature oxidation after CO2 injection were rarely studied. In this paper, a temperature programmed test system was adopted to simulate coal spontaneous combustion at low-temperature stage before and after CO2 adsorption. Compositions and concentrations of gases produced by coal samples from Yiyuan mine in China at different temperatures were analyzed. It is found that with the increase of the temperature, the gas concentration of CO2 generated from coal before CO2 absorption, expressed the trend of exponential growth. While the CO2 concentration after CO2 absorption, showed the distribution of “V” type on the whole, that is, the CO2 concentration firstly dropped to the minimum value and then rose up gradually. Before reaching to the temperature corresponding to the minimum concentration of CO2, the CO2 concentration was significantly higher comparing with that before CO2 absorption. While over that temperature, with the temperature increasing, the CO2 concentration was obviously lower than that before CO2 absorption. During the heating oxidation of coal, the gas concentrations of CO and C2H4 showed the increasing tendency with the temperature increasing. However, the initial temperature of CO and C2H4 detected firstly during the coal oxidation process after CO2 absorption was obviously lower than that before CO2 absorption, what's more, the concentrations of CO and C2H4 were also obviously lower than that before CO2 absorption at the same temperature, showing an obvious “hysteresis” phenomenon of inhibiting coal oxidation. The experimental results provided the basis of a method to control the spontaneous combustion of residual coal by injecting CO2 into the gob. The field test showed that the index gas concentration of CO was reduced sharply and coal spontaneous combustion in the gob was controlled effectively.