Kinetics of low-temperature homogeneous SO 3 formation for use in flue gas conditioning for improved electrostatic precipitator performance

Abstract

This paper presents the results of an investigation into the kinetics of homogeneous SO 3 formation used as an alternative to external SO 3 injection for reducing fly ash resistivity. While homogenous SO 2 to SO 3 conversion has been previously studied, primarily for boiler corrosion control, little data exist for low gas temperatures. This work was based on recent studies demonstrating that hydrocarbon flames introduced in relatively low temperature gas streams could provide sufficient O atoms to promote the formation of SO 3 from existing SO 2 . For this study, a premixed natural gas flame was used to promote the conversion of SO 2 to SO 3 in a drop tube furnace with free stream gas temperatures ranging from 450 to 1000 K. SO 2 and SO 3 concentration measurements via wet chemistry and gas chromatography, coupled with numeric modeling of reactions and species concentrations, indicated that lower free stream temperatures reduce the maximum conversion percentage of SO 2 to SO 3 while extending the duration of elevated SO 3 concentration. In addition, the effects of SO 2 and excess O 2 on this conversion process were explored to understand potential ramifications on practical systems. Finally, calculated kinetic parameters of the assumed conversion mechanisms indicate both a greater rate coefficient for H-atom-based decomposition of SO 3 than previously reported and a possible temperature dependence in the collisional dissociation of SO 3 . Other kinetic parameters were in general agreement with studies conducted at higher temperatures.