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 to 800 ppms, O ₂: 10%; N₂ was the balance gas) by means of a pulsed-discharge plasma generated in a cylinder-type reactor (outer electrode; 20 mm diameter). A rotary 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; the 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