Effect of inorganic particulates on the condensation behavior of lead and zinc vapors upon flue gas cooling

This study aims to clarify the influence of particulates on the fate of Pb and Zn compound vapors upon flue gas cooling. Incineration of Pb and Zn-loaded model compounds has been separately carried out in a lab-scale quartz reactor. Three oxides of Fe₂O₃, Al₂O₃ and CaO as inorganic particulates were placed individually in flue gas cooling section to mimic pre-existing particulates in flue gas and examine their impact on the fate of Pb and Zn compound vapors. The effect of gaseous components including HCl, SO₂ and H₂O on the heterogeneous condensation of Pb and Zn compound vapors on particulates grains has also been clarified. The presence of particulates in flue gas exerted remarkable influence on the fate of Pb and Zn compound vapors. Pb compound vapor was found being captured by Al₂O₃ as Pb-Al-O at the temperature above 823 K through chemical reaction, regardless flue gas composition. Zn preferentially transformed into ZnFe₂O₄, ZnAl₂O₄ and ZnO, respectively on the presence of Fe₂O₃, Al ₂O₃ and CaO above 823 K. The presence of SO₂ inhibited the chemical reactions of Pb and Zn vapors with particulates. Such an inhibitory effect was however compensated by the introduction of steam to flue gas. The presence of particulates in flue gas promoted the condensation of Pb and Zn compound vapors at higher temperature in comparison to the blank conditions, through heterogeneous nucleation, which in turn offset the effect of super-cooling. Moreover, the formation of sulfate was increased since the presence of particulates in flue gas triggered the condensation of sulfates vapors at high temperature and then reduced its partial pressure in flue gas, facilitating the sulfation reaction. Adjusting the concentrations of SO ₂ and H₂O in flue gas can prevent the formation of chloride of Pb and Zn, which is notorious for its toxicity and corrosion propensity during solid waste incineration.