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The article provides an overview of the mercury control technologies aimed at lessening the mercury emissions from coal-fired electric utility boilers in the U.S. The author stressed that mercury emissions from anthropogenic emission sources posed a global threat that needs to be subsided. In response, the U.S. Environmental Protection Agency proclaimed the Clean Air Mercury Rule to permanently cap and abridge emissions of mercury from coal-fired power plants. Another regulation promulgated is the Clean Air Interstate Rule, which compels further reduction of sulphur dioxide and nitrogen oxides from these power plants. Among the control technologies stressed include flue-gas desulfurization and limestone forced- oxidation.

Mercury speciation in combustion-generated flue gas was modeled using a detailed chemical mechanism consisting of 60 reactions and 21 species. This speciation model accounts for the chlorination and oxidation of key flue-gas components, including elemental mercury (Hg[sup0]). Results indicated that the performance of the model is very sensitive to temperature. Starting with pure HCl, for lower reactor temperatures (less than ∼630 °C), the model produced only trace amounts of atomic and molecular chlorine (Cl and Cl[sub2]), leading to a drastic underprediction of Hg chlorination compared with experimental data. For higher reactor temperatures, model predictions were in good accord with experimental data. For conditions that produce an excess of Cl and Cl[sub2] relative to Hg, chlorination of Hg is determined by the competing influences of the initiation step, Hg + Cl = HgCl, and the Cl recombination reaction, 2Cl = Cl[sub2]. If the Cl recombination reaction is faster, Hg chlorination will eventually be dictated by the slower pathway Hg + Cl[sub2] = HgCl[sub2]. [ABSTRACT FROM AUTHOR]