Oxidation of sulfided limestone under the conditions of pressurized fluidized bed combustion

Abstract

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 CaSO4 via oxidation in a topping cycle pressurized fluidized bed combustion (PFBC). In this work, the oxidation behavior of sulfided limestone particles was examined under PFBC conditions using a pressurized thermogravimetric analyzer. Experiments were conducted ensuring that the partial pressure of CO2 in the reaction gas mixtures exceeded the equilibrium pressure for CaCO3 calcination. The effects of total pressure, O2 partial pressure and temperature were examined to determine their influence on the conversion of CaS to CaSO4 and on the amount of CaCO3 formed 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 CaSO4 increased 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 CO2 occurred above 550 °C and the solid product was primarily CaCO3.