High mercury emission (both forms: Hg0 and Hg2+) from the wet scrubber in a full-scale lignite-fired power plant

Abstract

The paper describes and discusses the results of research on mercury behaviour, especially its high emission, in both forms: elemental (Hg-0) and oxidised (Hg2+) from the wet flue gas desulphurisation scrubber (WFGD) in a lignite-fired power plant located in central Europe. The presented results involve the collection of lignite power plant samples (liquid, solid, gas) and different laboratory chemical analyses to try to understand the mechanism of mercury re-emission from the wet flue gas desulfurization system. It was noted that 67-80% of the total inlet mercury concentration left the WFGD scrubber. Moreover, the oxidised form of mercury was the main emitted form (about 60-70% of the total mercury concentration). The results show that mercury was found in very high concentration (10 mu g/g) (range: ppm) in the WFGD solid by-products, whereas the liquid phase contained only 1 mu g//l (range: ppb). Considering literature reports and presented data from the investigated power station, we believe that iron (Fe), which occurs in very high concentrations in solid WFGD samples (1.81% wt. Fe) and lignite (up to 20 g/kg Fe) is mainly responsible for disrupting the mercury absorption in the scrubber, the partitioning of the mercury between phases and leads to its reemission. Moreover, we believe also that a relatively high iodine ion concentration (130 mg/l) in the limestone slurry leads to mercury emission in its oxidised form, mainly as Hgl(2), which is highly volatile. Other minor components from limestone dissolution such as Mn, Al and Mg may additionally enhance that "complex" mercury behaviour.