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

Abstract

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 823K through chemical reaction, regardless flue gas composition. Zn preferentially transformed into ZnFe2O4, ZnAl2O4 and ZnO, respectively on the presence of Fe2O3, Al2O3 and CaO above 823K. 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 SO2 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.