Modelling electric discharge chemistry

The chemistry occurring in an electric discharge was modelled to predict how it would be influenced by discharge conditions. The discharge was characterized by a calculated Boltzmann electron-energy distribution, from which rate constants for electron-molecule processes in air were determined. These rate constants were used in a chemical kinetics calculation that also included reactions between neutral molecules, ions, free radicals and electronically excited species. The model describes how the discharge chemistry was influenced by humidity, electric field, electron number density, and concentrations of key reagents identified in the study. The use of an electric discharge to destroy airborne contaminant molecules was appraised, the targeted contaminants being CF₂Cl₂, HCN, and SO₂. The modelling results indicate that an electric discharge should be able to remove HCN and CF₂Cl₂ effectively, especially if the discharge conditions have been optimized. Effective destruction is achieved with a moderate electric field (over 1 × 10^-15 V·cm²), a substantial electron number density (over 1 × 10¹² cm^-3), and the presence of H₂O in the process air. The residence time in the discharge was also shown to be important in contaminant destruction. An attempt was made to explain the results of the electric discharge abatement of SO₂, a component of a simulated flue-gas mixture. Results from the model indicate that the discharge parameters that increase the concentration of hydroxyl radical also increase the rate of decomposition of SO₂. An objective of the study was to explain the apparent enhancement of SO₂ destruction by the presence of a small amount of NO₂. It was thought that a likely explanation would be the stabilization of HOSO₂, an important intermediate in the oxidation of SO₂ by NO₂.