Effect of heat treatment temperature and atmosphere on physiochemical properties and oxidation behaviour of a Chinese lignite

This work investigates how heat treatment temperature and atmosphere would affect the physicochemical properties and oxidation behaviour of Zhundong lignite (ZD). Samples of ZD were firstly heated at 150–400 °C in either N 2 or simulated flue gas (FG) atmosphere, which were then analysed to obtain their mass losses, elemental composition, oxygen-containing functional groups (OCFGs) and water re-adsorption capacities. Results showed that the dried ZD subjecting to N 2 atmosphere had a mass loss of 9.90 mass%–10.95 mass% at 150–250 °C, but further increased to 25.17 mass% at 400 °C, leading to an increase in C/O ratios from 2.49 to 4.70 as treatment temperature increased. FTIR analysis revealed that OCFGs including hydroxyl, carboxyl, carbonyl and ether bond decreased as heat treatment temperature increased, which also deceased the water re-absorption capacity of heat-treated ZDs. While it is heated in FG, the mass loss of ZDs at temperatures below 300 °C was roughly equivalent to those in N 2 , but was less than those at 350–400 °C, due to the incorporation of O along with increased OCFGs peak intensities at these temperatures. This also allowed for the re-absorption of more moisture than those samples treated in N 2 . In addition, the combustion reactivity of the heat-treated ZDs was enhanced and the combustion process turned into higher temperature zone with increasing treatment temperature, suggesting that the variation in physicochemical properties of heat-treated ZDs also affected their oxidation behaviour.