The effect of SO2 on CaO capture selenium in the flue gas: Density functional theory and experimental study

Abstract

• SO 2 inhibits CaO capture selenium by surface inhibition. • SO 2 promotes CaO capture selenium through gaseous selenium conversion. • SeO 2 was hardly adsorbed by the sulfide product CaSO 4 from CaO. • The intensity of CaO capture selenium species is: Se > SeO > SeO 2 . In this work, the mechanism of SO 2 on CaO capture selenium was deeply investigated combined density functional theory (DFT) with adsorption experiments. The fixed-bed experiments result showed that SO 2 inhibited CaO capture selenium from 0 to 1000 while promoted in the range of 1000–2000 ppm, and CaSeO 3 was the primary adsorption product at 850 °C. Freundlich equation accurately predicted the adsorption capacity of CaSO 4 for SeO 2 with the concentration from 0 to 800 ppm, indicating weak adsorption activities for SeO 2 . Furthermore, the SO 2 and selenium oxides adsorption mechanism was studied by DFT. It demonstrated that SO 2 and SeO 2 were adsorbed on CaO (0 0 1) surface involved chemical adsorption with oxygen atoms as adsorption sites, which led to the competition of SO 2 and SeO 2 for adsorption sites on the CaO surface. SO 2 adsorbed on the CaO surface inhibited the activity of neighboring adsorption sites for SeO 2 . Moreover, compared with SeO 2 , SeO and Se 0 reduced by SO 2 were more beneficial adsorbed by CaO, the conversion of SeO 2 to selenium and SeO was firstly proposed in selenium adsorption. In detail, SO 2 promoted CaO capture selenium through homogeneous selenium conversion. Finally, it was identified that the CaSO 4 (0 0 1) surface was inert for selenium adsorption in the flue gas, indicating CaO transition to CaSO 4 inhibited selenium adsorption.