Investigation on coal pyrolysis in CO₂ atmosphere

Considerable studies have been reported on the coal pyrolysis process and the formation of SO2 and NOx processors such as H 2S, COS, SO2, HCN, and NH3 in inert atmospheres. Similar studies in CO₂ atmosphere also need to be accomplished for better understanding of the combustion characteristics and the SO2/NOx formation mechanism of oxy-fuel combustion, which is one of the most important technologies for CO₂ capture. In this study, thermogravimetry coupled with Fourier Transform Infrared (TG-FTIR) analysis was employed to measure the volatile yield and gas evolution features during coal pyrolysis process in CO₂ atmosphere. Results show that replacing N₂ with CO₂ does not influence the starting temperature of volatile release but seems to enhance the volatile releasing rate even at 480°C. At about 760°C, CO₂ prevents the calcite from decomposing. In CO₂ atmosphere, the volatile yield increases as the temperature increases and decreases as the heating rate increases. COS is monitored during coal pyrolysis in CO₂ atmosphere while there are only H₂S and SO 2 formed in N₂ atmosphere. The CO₂ is most likely formed by the reaction between CO₂ and H₂S. No NH3 was monitored in this study. In CO₂ atmosphere, the gasification of char elevates the conversion of char-N to HCN. The HCN yield increases as the temperature increases and decreases as the heating rate increases.