Role of water vapor in oxidative decomposition of calcium sulfide

CaS formed from the CaO sorbent during desulfurization in coal gasifiers has to be converted to CaSO4 before disposal. CaS is mainly decomposed to CaO and SO2 by O2 and then CaO is converted to CaSO4 by SO2 and O2. The role of H2O in the oxidative decomposition of CaS with O2 was studied using reagent grade CaS and H218O. The following results were obtained: (1) there is a synergistic effect of H2O and O2 on the oxidative decomposition of CaS to CaO and SO2; (2) H2O reacts with CaS to form CaO, SO2 and H2 in the absence of O2; (3) the oxidative decomposition of CaS to CaO and SO2 occurs stepwise; (4) H2O directly reacts with CaS in the presence of O2; (5) H2O plays an important role in the oxidative decomposition of CaS even if the O2 concentration is high.