Emission characteristics of PM, heavy metals, and dioxins in flue gases from sintering machines with wet and semi-dry flue gas desulfurization systems.

Abstract

In iron and steel industry, sintering process releases large amount and different kinds of pollutants. Most sintering plants had applied the dust removal system and the flue gas desulfurization (FGD) system for exhaust treatment in China. Previous studies of FGD systems were focused on the removal of air pollutants from coal-fired boiler, rather than in the iron ore sintering process. In this study, PM, heavy metals, and dioxins were sampled at a China typical sintering plant with both wet and semi-dry FGDs. The results showed that the PM removal efficiencies of the wet and semi-dry FGDs were 29.44% and 22.28%, respectively. The size distributions of PM were at the range of 0.7~4.7 μm in the inlet flue gases of both FGDs. The overall removal efficiencies of heavy metals were above 65%. In both outlet flue gases, Pb as the most elements accounted for 93.33% of total at the wet FGD, while Pb, Cr, and Zn accounted for 76.34% at the semi-dry FGD. The proportions of gaseous heavy metals in the inlets of both FGDs were improved than those in the outlets. Furthermore, the total emission amounts of dioxins in both inlets and outlets of the flue gases were 0.0385 ng-TEQ/m3 and 0.0248 ng-TEQ/m3 at the wet FGD and 0.0078 ng-TEQ/m3 and 0.0050 ng-TEQ/m3 at the semi-dry FGD, respectively. The overall removal efficiencies of dioxins were all above 35%. The polychlorinated dibenzofurans (PCDFs) ratio in the dioxins lightly increased from 84.46 to 88.80% through wet FGD, while it decreased from 80.83 to 44.35% in semi-dry FGD.