Abstract:
Addressing the low utilization and massive venting of low-concentration methane (LCM) in coal mines (< 8%), which results in energy waste and greenhouse effect. Fe−Co/Al
2O
3 bimetallic porous media catalyst loaded with Fe
2O
3 and Co
3O
4 as dual active components was prepared using ultrasonic-assisted impregnation method to investigate the combustion performance of LCM. The effects of excess air ratio
φa and flow rate
f on combustion characteristics were examined, and long-term combustion stability was tested. The results indicated that the Fe and Co in Fe−Co/Al
2O
3 synergistically engaged in CH
4 catalytic reaction. Fe
3+ and Co
3+ were partially reduced to Fe
2+ and Co
2+ species, and the formation of CoFe
2O
4 spinel structure improved thermal stability and resistance to sintering of the catalyst, enabling it to maintain good catalytic activity during high-temperature lean combustion. CH
4 oxidation reaction followed the MvK mechanism, in which lattice oxygen participated in the cleavage and activation of the C—H bond in CH
4, with its consumption forming oxygen vacancies. Adsorbed oxygen dynamically replenished lattice oxygen to maintain the migration and cycling of oxygen species, while further promoting the oxidation of intermediates. Excess air ratio and flow rate significantly influenced temperature distribution and flame migration, low excess air ratio or low flow rate tended to cause combustion flashback, whereas high excess ratio or high flow rate could lead to the risk of blow off. The thermal buffering effect generated by the gradient pore structure of the porous media, combined with the sustained heat release of the catalytic reaction, alleviated temperature fluctuation and enhanced flame stability. Within the range of
φa = 2.44—2.56 and
f = 50—65 L/min, the flame was anchored in the middle of the burner, the combustion temperature was maintained above 800 ℃, and NO
x emissions were extremely low. At
φa = 2.56, the preheating zone temperature remained around 220 ℃ even after 72 h of combustion, and the CH
4 conversion approached 100% throughout the process, confirming that the coupling of gradient porous media and catalytic reaction significantly improved lean-burn performance and stability. This study provides a novel insights and technical support for the clean and efficient utilization of coal mine LCM.