A system for repetitive pulsed corona plasmas, with ecological applications

A depollution system for gases, using the repetitive pulsed corona plasmas, is described. The main sub-systems are: High-voltage repetitive pulser; treatment chamber; gas flow circuit; gas analyzer. The high-voltage repetitive pulser discharges a capacitor in the primary of a pulse transformer. The high-voltage switch is a thyratron. Many construction manners were tested for the pulse transformer. High-voltage pulses with 25-100 ns rise-time have been obtained. The rise-time value depends of the winding connection structure, and also of the transformer ratio (1:2, or 1:3). For greater voltage amplitudes, a circuit with two thyratrons and two pulse transformers is used. The two pulse transformers have series connected secondaries. Taking into account a 15 kV as a maximum anode voltage for each of the two thyratrons, pulses of up to 90 kV amplitude is applied on the treatment chamber. The width of the high-voltage pulses depends of the discharging capacitor value, which is increased in 5 nF steps. With 10-25 nF, the pulses half-width is in the hundreds of nano-seconds range. The repetition frequency is raised up to 1000 Hz. For the treatment chamber, coaxial geometries are tested. With electro-chemical sensors, the gas analyzer (K.M9106 - Kane Intnl. Ltd. - England) can measure concentrations of NO, NO/sub 2/, NO/sub X/, SO/sub 2/, CO, O/sub 2/, and the gas temperature also. In the first stage of experiments, corona current pulses have been analysed, for each treatment chamber and for different discharge conditions. The voltage pulses have 25 - 30 kV amplitude, and the corresponding corona current pulses are of 30 - 80 A amplitude and 40 - 70 ns half-width. The energy dissipation by corona effect is of 20 - 85 mJ per pulse. These results are for dry/humid air streams (2-3 1/min). Afterwards, [(N/sub 2/ + NO + SO/sub 2/) + (O/sub 2/)] gas mixtures is used. We hope to find new ways to improve the energetic efficiency of the pulsed corona plasmas in the field of this ec- logical application.