Effect of CaCO₃ on the Phase Evolution in Simultaneous Removal of SO₂ and NO₂ by Calcium Hydroxide

This study mainly focuses on investigating the effect of in situ-generated CaCO3 on simultaneous SO2 and NO2 removal, clarifying the competitive mechanism of CO2, SO2, and NO2 with absorbent Ca(OH)2 in the removal process. The experiments were carried out by the precarbonated absorbent, whose contents were mainly Ca(OH)2 and CaCO3. The results of the DFT calculation showed that the molecular adsorption energies of CO2, NO2, and SO2 on the surface of Ca(OH)2 were −3.42, −1.28, and −1.16 eV, respectively, and the adsorption order on the surface of Ca(OH)2 was CO2 > NO2 > SO2 under the sintering flue gas condition. The phase evolution was elucidated by morphology and composition analysis of the removal products. In the process of simultaneous removal of SO2 and NO2, CO2 first reacted with absorbent Ca(OH)2 to reach equilibrium. The generated CaCO3 covered the surface of the absorbent, which weakens the activity of the absorbent. At the later stage of the removal process, the activity of Ca(OH)2 decreased. The in situ-generated CaCO3 participated in SO2 and NO2 removal reactions, while the removal effect was lower than that of Ca(OH)2.