| 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 thatunreacted CaS is protected from further reaction with O2 by formation of a CaSO4 shell. Inprevious 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 above600 °C. Furthermore, it appears that the principal gas-phase products are SO2 and CO, anddirect 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 formelemental carbon, which appears unlikely, or side reactions occur, leading to a variety of gaseousproducts. These results also suggest that CO itself has no significant part in the oxidation processat least up to 850 °C or more. Reaction with H2O also begins above 600 °C, but it is a much lesseffective oxidant, and experiments with CO2/H2O further support the idea that CO2 is the moreimportant oxidant and might be used to destroy CaS from topping cycle gasifiers.
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