Theoretical analysis of removal of oxides of sulphur and nitrogen in pulsed operation of electrostatic precipitators

摘要

An investigation has been made of the various plasma chemistry reactions that occur in the corona discharge of an electrostatic precipitator operating in a typical flue gas. Calculations have been made of the rate coefficients for electron dissociation of the principal gaseous components, namely, nitrogen, oxygen and water vapor as functions of electric field. In addition, calculations have been made of the rates of ionisation and attachment and also the rates of excitation of the principal excited states. The calculations indicate that sulphur dioxide is removed principally by reactions with OH radicals to produce sulphuric acid, while nitrogen oxides are removed principally by reduction via the N radical to molecular nitrogen. However, for these reactions to occur, values of E/N of 70 Td or more are necessary, which is higher than the E/N of 30 Td at which electrical breakdown normally occurs; E is electric field strength and N is the gas number density. Approximate calculations indicate that, for an E/N of 100 Td, voltage pulses of width less than 1 /spl mu/s need to be applied to avoid breakdown. It is also shown that small quantities of nitrous oxide are produced and that the presence of water vapor has a significant effect on the plasma chemistry and increases the breakdown voltage.