NOx removal process using pulsed discharge plasma

Nonequilibrium plasma can be used to promote chemical reactions that reduce the emission of gaseous pollutants, such as NO_x, produced by coal-burning power plants or by diesel engines. Laboratory experiments were carried out to study the decrease of NO_x in simulated flue gases (initial concentration of NO: 200-800 ppm, O₂ : 10%, N₂-balance gas) by means of a pulsed discharge plasma generated in a cylinder type reactor (outer electrode: 20-mm diameter). A rotating spark gap provided square wave high-voltages up to 25-kV, at a frequency of 250 Hz, to corona electrodes of 0.1-, 3.3-, and 6.4-mm diameter. The tests were performed at various temperatures (ambient to 220°C) and constant residence time (0.6 s). The removal performance depended on the size of the discharge electrode and was better at room temperature. The addition of C₂H₄ significantly enhanced the removal performance, concentration of NO_x decreased from 800 ppm to 300 ppm in the discharge. The by-products of this process were analyzed using infrared spectroscopy. No traces of toxic gases could be detected