Impact of NO and so₂ on measurement of mercury speciation in a wet chemical conditioning system

The impacts of NO and SO₂ on speciated mercury measurements from a wet chemical conditioning system were investigated. A reactor previously used to elucidate the impact of chlorine on mercury oxidation in combustion products was used. NO injected directly into the KCl impinger of the conditioning system was shown to reduce mercury oxidation by 44% at concentration of 500 ppmv NO and 200 ppmv Cl exactly matching results where the NO was injected into the reactor burner at the same concentration. SO₂ was shown to essentially eliminate apparent oxidation at concentrations of 300 ppmv SO ₂ and 200 ppmv Cl when injected into the KCl impinger. The effect of NO and SO₂ on mercury oxidation were also predicted using a detailed kinetic model for the reactor conditions of interest. Model results confirm the observed inhibition does not occur as homogeneous oxidation in the reactor. Reduction of Hg²⁺ in the KCl solution of the wet-chemical conditioning system by SO₂ and NO is likely responsible and is being reported as reduction of oxidation. Due to this measurement bias, the effects of NO and SO₂ can not be elucidated using a mercury analysis system of this type. Further investigation is required to determine the nature and impact of this oxidation-reduction chemistry in the KCl solution.