The interactions of Hg with other flue gas components are of
complex nature. Due to the high temperatures in the combustion
chamber, the thermodynamic equilibrium of reactions of Hg is
shifted to its elemental form (Hg0
). With decreasing temperature
and affected by the flue gas composition, gaseous Hg0 undergoes
oxidation to divalent mercury (Hg2+) by hydrogen halides. For typical
coal derived flue gases, HCl is the dominant hydrogen halide,
thus mainly HgCl2 is formed. If HBr concentration of the flue gas
is increased by the use of additives, HgBr2 concentration increases
accordingly. The heterogeneous oxidation of Hg0 is catalyzed by
high-dust SCR DeNOx systems, resulting in higher shares of HgCl2
and/or HgBr2 [6]. A certain fraction of mercury is bound to particulate
matter (Hgp
), due to sorption on the surface of ash particles or
injected dry sorbents. While gaseous Hg0 is considered not to be
affected by conventional flue gas cleaning systems, Hgp is removed
by particle filters [7]. Due to the high solubility of HgCl2 and HgBr2
in water, wet scrubbers offer the possible side benefit of removing
HgCl2 and HgBr2 from the flue gas efficiently. Results of numerous
investigations from lab- to full-scale demonstrate that the wet flue
gas desulfurization (FGD) process is able to remove water soluble
Hg compounds from flue gas at high efficiency [8,9]. The desired
final sink of mercury within this co-removal strategy is the sludge
of the FGD waste water treatment.