Study on aging characteristics and failure mechanism of CO2 absorbents for optical interference methane detector in underground coal mines

After a mine fire or gas explosion, accurate detection of methane concentration is critical for disaster relief decisions. However, high-concentration CO2 from fires causes measurement deviations in optical interference methane detectors, as the CO2 absorption capacity of soda lime absorbent degrades over time. To investigate factors affecting detection accuracy in underground coal mine disaster areas, a simulation system was built to test soda lime's CO2 absorption under varied conditions. This revealed its time-dependent performance characteristics, failure mechanism, and enabled the establishment of a methane concentration correction model for CO2-rich atmospheres. The results show that soda lime's effective CO2 absorption cycles are negatively correlated with CO2 concentration. With CO2 concentrations of 5 %, 10 %, 15 %, 20.99 %, 27.18 %, and 32.09 % in the gas mixture, the effective absorption cycles are 20, 18, 12, 8, 5, and 3 times, respectively. The CO2 absorption time-efficiency curves exhibit an "S"-shaped nonlinear pattern under different concentrations and flow rates. Higher CO2 concentrations and gas flow rates increase absorption per unit time, shorten the high-efficiency duration, accelerate saturation/failure, and reduce the effective absorption time. Therefore, adjusting soda lime dosage and optimizing sampling flow rates are key to improving detection accuracy in high-CO2 environments.