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 CaCO3 and CaSO4, and the high content of CO2 during gasification prolonged the decomposition of CaCO3. The transformation of S was primarily influenced by atmosphere. SO2 could react with CaO and form CaSO4 during the combustion process. While S compounds were mainly released as S (g) and H2S (g) during gasification process. There was a significant interaction among Na/Ca/S compounds during combustion, original CaSO4 in coal could adsorb Na compounds with SO2 at 600–800 °C and then reacted with aluminosilicates, by this reaction, Na could be fixed above 1000 °C.