Open AccessREDUCTION OF INHERENT MERCURY EMISSIONS IN PC COMBUSTION
Author(s) -
John C. Kramlich,
Rebecca N Sliger,
David J Going
Publication year - 1999
Language(s) - English
Resource type - Reports
DOI - 10.2172/775020
Subject(s) - mercury (programming language) , oxidizing agent , chemistry , combustion , chlorine , elemental mercury , limiting , environmental chemistry , char , organic chemistry , computer science , flue gas , mechanical engineering , engineering , programming language
Mercury emission compliance presents one of the major potential challenges raised by the 1990 Clean Air Act Amendments. Simple ways of controlling emissions have not been identified. The variability in the field data suggest that inherent mercury emissions may be reduced if the source of this inherent capture can be identified and controlled. The key mechanisms appear to involve the oxidation of mercury to Hg{sup 2}, generally producing the more reactive HgCl{sub 2}, followed by its capture by certain components of the fly ash or char, or in the air pollution control equipment. This research focuses on identifying the rate-limiting steps associated with the oxidation step. Work in this reporting period focused on testing of the kinetic mechanism reported in the previous semiannual report, and the interpretation of data (both ours and literature). This model yields good qualitative agreement with the data and indicates that mercury oxidation occurs during the thermal quench of the combustion gases. The model also suggests that atomic chlorine is the key oxidizing species. The oxidation is limited to a temperature window between 700-400 C that is defined by the overlap of (1) a region of significant superequilibrium Cl concentration, and (2) a region where oxidized mercury is favored by equilibrium. Above 700 C reverse reactions effectively limit oxidized mercury concentrations. Below 400 C, atomic chlorine concentrations are too low to support further oxidation. The implication of these results are that homogeneous oxidation is governed primarily by (1) HCl concentration, (2) quench rate, and (3) background gas composition. Work conducted under the present grant has been the subject of one journal paper that was accepted for publication during the reporting period (Sliger et al., 1999)