Release and transformation characteristics of Na/Ca/S compounds of Zhundong coal during combustion/CO2 gasification

Abstract Zhundong (ZD) coal from northwest China is a high quality steam coal with reserves of more than 390 billion tons. However, the utilization of ZD coal is limited due to the high content of alkali and alkaline earth metals. This study aimed at revealing the release and transformation mechanism of Na/Ca/S compounds during combustion/gasification of ZD coal. The results demonstrate that Na was primarily influenced by temperature, mostly releases at 600–800 °C. The transformation of Ca compounds was affected by both temperature and atmosphere. The high temperature of the combustion process could accelerate the decomposition of CaCO 3 and CaSO 4 , and the high content of CO 2 during gasification prolonged the decomposition of CaCO 3 . The transformation of S was primarily influenced by atmosphere. SO 2 could react with CaO and form CaSO 4 during the combustion process. While S compounds were mainly released as S (g) and H 2 S (g) during gasification process. There was a significant interaction among Na/Ca/S compounds during combustion, original CaSO 4 in coal could adsorb Na compounds with SO 2 at 600–800 °C and then reacted with aluminosilicates, by this reaction, Na could be fixed above 1000 °C.