Search

• Inorganic trace pollutants are studied in a coal-fired power station in China. • The aqueous (NH 4) 2 SO 4 slurry (pH 3.2) is enriched in inorganic trace pollutants. • NH 3 -FGD performance for the retention efficiency of trace pollutants is questioned. • Acidic conditions of the aqueous (NH 4) 2 SO 4 slurry could lead to low FGD efficiencies. • Operating conditions may affect Hg fate across the PCC-SCR-ESP-NH 3 -FGD. The behaviour and speciation of inorganic trace pollutants were studied in a 270 MWh coal-fired power station equipped with denitrification (DeNOx)-based selective catalytic reduction (SCR), electrostatic precipitators (ESP) and ammonia flue gas desulphurisation (NH 3 -FGD) controls. The aqueous (NH 4) 2 SO 4 slurry (pH 3.2) showed remarkably high concentrations of SO 4 2−, Cl−, Fe, NH 4 +, PO 4 3−, and F− and was substantially enriched in multiple trace pollutants, e.g. Mn, Ni, Zn, and As, which can be ascribed to the diffusion of gaseous pollutants released during combustion and to the partial dissolution of fly ash (FA) particles entrained in the flue gas FGD. These processes were favoured by the iteration of the FGD water re-circulation cycles within the scrubber. Three major unresolved performance issues remain for the NH 3 -FGD with respect to the retention efficiency of major and trace pollutants: (i) the high concentration of soluble salts and major and minor trace elements in the aqueous (NH 4) 2 SO 4 slurry could lead to entrainment of droplets and particles with the outgoing (OUT)-FGD gas; (ii) the ionic strength, as a result of the high concentration of the elements associated with soluble salts and major and minor elements, could lead to diminishing diffusivity of gaseous pollutants into the aqueous phase, where these are supposed to dissolve; and (iii) the acidic conditions of the aqueous (NH 4) 2 SO 4 slurry, caused by Fe-hydrolysis, could lead to low FGD efficiencies. Operating conditions at this power station affect Hg partitioning and fate across the PCC-SCR-ESP-NH 3- FGD. [ABSTRACT FROM AUTHOR]