This paper develops and evaluates an elementary reaction mechanism for homogeneous Hg0 oxidation that accounts for major interactions among Cl-species and other pollutants in coal-derived exhausts. Most importantly, interactions among NO and Cl-species were found to exert a strong and previously unrecognized impact on homogeneous Hg0 oxidation under some but not all conditions. The proposed oxidation mechanism is subjected to quantitative evaluations against all the available laboratory datasets that characterize homogeneous Hg0 oxidation when HCl is the primary chlorinated species. The simulations depict the reported extents of oxidation for broad ranges of HCl and temperature within useful quantitative tolerances without any heuristic parameter adjustments. The predicted pool of Cl-atoms was found to be governed by the chemistries of moist CO oxidation, Cl-species transformations, and NO production. However, an artificial initiation scheme was needed to depict the temperature dependence observed in one set of literature data. This indicates that either the kinetic mechanisms are incomplete or that heterogeneous initiation came into play under these test conditions. The evaluations further show that Hg oxidation is primarily through a Cl atom recycle process, with Cl and Cl2 concentrations both playing an important role. Oxygen weakly promotes homogeneous Hg oxidation, whereas moisture is a stronger inhibitor. NO can promote or inhibit homogeneous Hg oxidation, depending on its concentration. In the presence of NO, extents of Hg oxidation increased for progressively faster quenching. Conversely, without NO, extents of oxidation diminished for faster quenching.

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= 0.65) for the densest fraction. This degree of aromatic carbon substitution for the inertinite fraction reveals that the aromatic structure is not highly condensed.A comparison of the aromatic to aliphatic proton ratio determined by FTIR and NMR for the density fractions can be used to observe the change in infrared extinction coefficient ratio for aromatic and aliphatic C-H bonds. At low density the ratio is approximately 7 but falls to a value of about 1.5 for the densest fractions.

This paper introduces a predictive mechanism for elemental mercury (Hg 0 ) oxidation on selective catalytic reduction (SCR) catalysts in coal-fired utility gas cleaning systems, given the ammonia (NH 3 )/nitric oxide (NO) ratio and concentrations of Hg 0 and HCl at the monolith inlet, the monolith pitch and channel shape, and the SCR temperature and space velocity. A simple premise connects the established mechanism for catalytic NO reduction to the Hg 0 oxidation behavior on SCRs: that hydrochloric acid (HCl) competes for surface sites with NH 3 and that Hg 0 contacts these chlorinated sites either from the gas phase or as a weakly adsorbed species. This mechanism explicitly accounts for the inhibition of Hg 0 oxidation by NH 3 , so that the monolith sustains two chemically distinct regions. In the inlet region, strong NH 3 adsorption minimizes the coverage of chlorinated surface sites, so NO reduction inhibits Hg 0 oxidation. But once NH 3 has been consumed, the Hg 0 oxidation rate rapidly accelerates, even while the HCl concentration in the gas phase is uniform. Factors that shorten the length of the NO reduction region, such as smaller channel pitches and converting from square to circular channels, and factors that enhance surface chlorination, such as higher inlet HCl concentrations and lower NH 3 /NO ratios, promote Hg 0 oxidation. This mechanism accurately interprets the reported tendencies for greater extents of Hg 0 oxidation on honeycomb monoliths with smaller channel pitches and hotter temperatures and the tendency for lower extents of Hg 0 oxidation for hotter temperatures on plate monoliths. The mechanism also depicts the inhibition of Hg 0 oxidation by NH 3 for NH 3 /NO ratios from zero to 0.9. Perhaps most important for practical applications, the mechanism reproduces the reported extents of Hg 0 oxidation on a single catalyst for four coals that generated HCl concentrations from 8 to 241 ppm, which covers the entire range encountered in the U.S. utility industry. Similar performance is also demonstrated for full-scale SCRs with diverse coal types and operating conditions.

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The proposed mercury (Hg) oxidation mechanism consists of a 168-step gas phase mechanism that accounts for interaction among all important flue gas species and a heterogeneous oxidation mechanism on unburned carbon (UBC) particles, similar to established chemistry for dioxin production under comparable conditions. The mechanism was incorporated into a gas cleaning system simulator to predict the proportions of elemental and oxidized Hg species in the flue gases, given relevant coal properties (C/H/O/N/S/Cl/Hg), flue gas composition (O2, H2O, HCl), emissions (NO(X), SO(X), CO), the recovery of fly ash, fly ash loss-on-ignition (LOI), and a thermal history. Predictions are validated without parameter adjustments against datasets from lab-scale and from pilot-scale coal furnaces at 1 and 29 MWt. Collectively, the evaluations cover 16 coals representing ranks from sub-bituminous through high-volatile bituminous, including cases with Cl2 and CaCl2 injection. The predictions are, therefore, validated over virtually the entire domain of Cl-species concentrations and UBC levels of commercial interest. Additional predictions identify the most important operating conditions in the furnace and gas cleaning system, including stoichiometric ratio, NO(X), LOI, and residence time, as well as the most important coal properties, including coal-Cl.