CONTROL OF NOX BY POSITIVE AND NEGATIVE PULSED CORONA DISCHARGES

The pulse-induced plasma chemical process (PPCP) is a novel means of processing with great potential in various applications including the removal of No, SO2, HCI, and Hg vapor and other gaseous pollutants from combustion gases, the composition of new gaseous and solid substances, the production of ultrafine particulate materials, the treatment of surfaces, etc. Under normal pressures, the PPCP can raise the electron temperature for production of active chemical species, such as OH radical, O, O3, O−, O2*, etc., without raising the ion temperature; this had been possible only by high-frequency glow discharge under low pressure. A reliable nanosecond-pulse high-voltage generator has been developed enabling continuous operation necessary to establish the PPCP as an industrial device. As one R&D program series, an investigation of the DeNox and DeSOx of combustion gas by PPCP was conducted, confirming that DeNOx is possible by both positive and negative pulsings and DeSOx only by positive pulsing. NO is oxidized by PPCP to NO2, which is removed again by PPCP. The reaction speed by PPCP with positive pulsing is more than one order of magnitude higher than that by negative pulsing applicable to electrostatic precipitators. The reaction speed is greatly enhanced by raising the peak field intensity, which requires the use of a very sharp pulse. The speed is also enhanced by raising pulse frequency, lowering the gas temperature, and using sharp corona wires. The oxidation of NO and removal of NO2 can proceed without O2 and moisture, but it is greatly enhanced by them. The addition of NH3 also enhances NO2 removal, possibly by its NO2-scavenging effect from the gas phase, while it does not enhance NO oxidation. The combination of PPCP with the electron beam DeNOx and DeSOx does not produce a nonlinear enhancing effect other than the independent effect of PPCP alone. © 1990 IEEE