Experimental and kinetic study on the catalytic effect of AAEMs on coal char combustion under O2/CO2 atmospheres

The oxy-fuel combustion technology has attracted widespread attention because of its relatively low-cost and large-scale CO2 capture. During the oxy-fuel combustion process, the low diffusivity of O2 in CO2 brings several difficulties on coal char combustion due to N2 replacement with CO2. Catalytic combustion by adding alkali and alkaline earth metals (AAEMs) is an effective way to improve the coal char combustion performance. In this work, the catalytic effects of AAEMs on coal char combustion characteristics under different conditions were studied. Besides, the kinetic parameters of char combustion were obtained by Kissinger-Akahira-Sunose, Starink, and Flynn-Wall-Ozawa methods. Results showed that compared with other AAEMs (Na, Ca, and Mg), K showed better catalytic effects on ignition, burnout, and comprehensive combustion characteristics of coal char. The promotion effect of K on the combustion performance was gradually saturated when addition ratios exceeded 1 wt%. At low O2 concentrations or heating rates, K exhibited a strong catalytic effect on coal char combustion. Besides, K could accelerate the decrease in activation energy (Ea) of coal char combustion as char conversion (alpha) increased. When alpha was 0.9, the reduced effect of K on the Ea value was 13%. These results are expected to provide new insights into the improvement of coal char oxy-fuel combustion catalyzed by AAEMs.