Release characteristics of AAEMs and physicochemical structural evolution of char during rapid coal pyrolysis

Rapid pyrolysis experiment of Zhundong coal was conducted in a high-frequency furnace to investigate release characteristics of alkali and alkaline earth metals (AAEMs) and its correlation with changes of physical and chemical properties of char. Residence time and atmosphere during pyrolysis were important process parameters that affected the migration characteristics of AAEMs and physicochemical structural evolution of char. Experimental results show that the release of AAEMs in coal char increases over time. The maximum release rate of Na, Mg and Ca is 61.05%, 64.47%, and 44.01%, respectively. Promoting effect of CO₂ on release of Na mainly occurs in the initial stage of rapid pyrolysis, nevertheless the promoting effect on release of Mg and Ca mainly is in the middle and late stage. CO₂ accelerates release of AAEMs by promoting release of volatiles, facilitating decomposition of oxygen-containing functional groups and aliphatic functional groups, and promoting formation of cracks on surface of coal char.