Kinetic Modeling of Gas-Phase Mercury Oxidation by Chlorine and Bromine In Combustion Effluents During Oxy-Combustion

Monday, October 17, 2011: 3:40 PM
101 F (Minneapolis Convention Center)
Itsaso Auzmendi-Murua, Chemical, Biological, and Pharmaceutical Engineering, New Jersey Institute of Technology, Newark, NJ and Joseph W. Bozzelli, New Jersey Institute of Technology, Newark, NJ

Around 29 Gt of CO2 are emitted annually worldwide. The main sources of these emissions are transportation and electricity-generating plants, which use coal and fuel combustion. Since CO2 capturing techniques are still expensive, in order to reduce CO2 emissions from fuel combustion, oxy-combustion has been proposed as a solution, with the aim of obtaining combustion flue gases with higher concentrations of CO2 that are easier to remove. The implementation of oxy-combustion affects the speciation of the rest of the combustion products, including the speciation of mercury. Different techniques have been proposed for the control of mercury emissions, due to its high toxicity. In this work, the addition of halogens (chlorine and bromine) to the flue gases have been studied in order to oxidize mercury from its elemental form to oxidized form – HgX2.  As these mercury halides are water soluble, it is feasible to capture the HgX using conventional air pollution control devices. An elementary reaction mechanism has been developed for modeling the oxidation of mercury by the addition of halides, in both regular combustion and oxy-combustion conditions. Thermochemical properties and kinetic parameters have been calculated for Hg and Halogen – NOx species using B3LYP and CBS-QB3 methods. The elementary reaction mechanism has been 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 NOx inhibits Hg oxidation by chlorine addition, through several catalytic cycles for loss of Cl.  As for bromine addition, similar catalytic cycles are observed, but in this case, the overall thermochemistry favours more mercury oxidation. Therefore, results show that during oxy-combustion conditions, Hg oxidation is enhanced, since flue gases contain lower concentrations of NOx.

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See more of this Session: Fundamentals of Environmental Process and Reaction Engineering
See more of this Group/Topical: Environmental Division