CaS Oxidation by Reaction with CO2 and H2O

Abstract

Calcium sulfide is an undesirable product from both FBC and topping cycle gasifiers. Unfortunately, its direct oxidation in a FBC environment is made difficult due to the fact that unreacted CaS is protected from further reaction with O2 by formation of a CaSO4 shell. In previous work it was often implied that oxidation of CaS occurred solely by reaction with O2. However, this study shows that CO2 can be an effective oxidant for CaS at temperatures above 600 °C. Furthermore, it appears that the principal gas-phase products are SO2 and CO, and direct attempts to measure COS using mass spectrometry suggest that its formation is negligible. Somewhat surprisingly, SO2/CO molar ratios are in the range of 0.4 to 0.5, which is problematic, if the dominant reaction is CaS + 3CO2 CaO + 3CO + SO2, unless CO2 is reacting to form elemental carbon, which appears unlikely, or side reactions occur, leading to a variety of gaseous products. These results also suggest that CO itself has no significant part in the oxidatio...