Surface CO/CO2 ratio of char combustion measured by thermogravimetry and differential scanning calorimetry

Char combustion is the main stage in the coal-burning process. The CO/CO2 ratio near the surface of a char particle is an important physical quantity that determines the temperature of the particle and that can also help explore the mechanism of char combustion. In this paper, we propose an innovative method, i.e., thermogravimetry and differential scanning calorimetry, to explore the char combustion products from the perspective of heat release, and then we investigated the effect of combustion conditions on the CO/CO2 ratio. It was found that the CO/CO2 ratio first increased and then decreased with temperature from 600 °C to 900 °C, which confirmed the combined effect of both heterogeneous and homogeneous reactions on surface products. Further, by studying the transient products of char combustion, we observed that the CO/CO2 ratio showed a decreasing trend with the reaction processing at higher temperature, which might be due to the change of the carbon-oxygen reaction pathway. In addition, it was suggested that the main effect of oxygen concentration was on the homogeneous reaction, which will affect the relative value of the CO/CO2 ratio but hardly change the variation trend.