During coal gasification, the removal of H2S from the hot product gases using limestone generates calcium sulfide, a potentially hazardous chemical requiring treatment before disposal. One approach is to convert the CaS to CaSO4via oxidation in a topping cycle pressurized fluidized bed combustion. In this work, the oxidation behavior of sulfided limestone particles was examined under the conditions of pressurized fluidized bed combustion using a pressurized thermogravimetric analyzer. Experiments were conducted ensuring that the partial pressure of CO2in the reaction gas mixtures exceeded the equilibrium pressure for CaCO3calcination. The effects of total pressure, O2partial pressure and temperature were examined to determine their influence on the conversion of CaS to CaSO4and on the amount of CaCO3formed during the oxidation process. The total pressure was shown to have only a relatively weak influence on the degree of conversion to sulfate, in spite of the fact that the conversion of CaS to CaSO4increased to a certain extent with increasing pressure at a constant oxygen volume fraction. However, over the 0.1-2.0 MPa range, temperature had a strong influence on the CaS oxidation, its effect being more pronounced at lower pressures. Furthermore, the reaction of CaS with CO2occurred above 550 °C and the solid product was primarily CaCO3.
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