Kinetic modeling of gas-phase mercury oxidation by halides in combustion effluents: The importance of NOx

Document Type

Conference Proceeding

Publication Date

12-1-2010

Abstract

Emissions of mercury from electricity generation and incineration plants have become one of the major environmental control problems that these plants are facing because of the toxicity of mercury. The conversion of mercury from its elemental form to the oxidized form allows the reduction of mercury emissions by current collection methods. In this work, an elementary reaction mechanism is developed for modeling mercury conversion to mercury halides and is used to study the influence of the NOx in this system. Thermochemical properties and kinetic parameters have been calculated for Hg and Halogen - NOx species using B3LYP and CBS-QB3 methods. An elementary reaction mechanism is constructed with use of chemical activation analysis for association and addition reactions with quantum RRK analysis for k(E) and Master Equation analysis for fall-off. Results indicate that the presence of NO decreases the oxidation of mercury by chlorine, because: (i.)NO is a stronger competitor for Cl - the initial NOx-Halogen atom bond is stronger than the Hg-Halogen atom bonds, (ii.) there are several, exothermic, catalytic cycles for loss of Cl atom, (iii.) HCl is less reactive with OH than HBr for loss, abstraction of the H (regeneration of halogen atom). Similar catalytic cycles for loss of Br atom occur, but the overall thermochemistry is less favorable to HBr. Therefore, mercury conversion with Br present is obtained, even at higher NO concentrations.

Identifier

78751474111 (Scopus)

ISBN

[9780816910656]

Publication Title

Aiche Annual Meeting Conference Proceedings

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