Nanosecond pulsed power application to nitrogen oxides treatment with coaxial reactors

Nitrogen oxides (NOx) are one of the air pollutants that cause acid rain. Although utilization of catalysts is a typical established method of treatment to remove NOx, the catalyst is expensive so that the total cost of treatment is high. The efficient treatments using pulsed power, which utilize the pulse streamer discharges, have been studied. We have brought the nanosecond pulsed power to the NOx treatment. More efficient treatment is expected with the high electric fields with a nanosecond pulse width. In using the nanosecond pulsed power, the issue of design and modification of reactors configuration becomes important. Coaxial reactors consisting of wire-cylinder electrodes are adopted here and three types of electrical connecting methods between a generator and reactor chambers and gas tubing methods were investigated. The deposited energy density of 150 J/L yielded approximately 100% NO removal ratio for initial NO gas of 100 ppm. The three types of electrical connections were parallel, straight and serial. The parallel and straight connections yielded a higher removal ratio and efficiency in this experiment. Distribution of voltage in the reactors affects the removal ratio and efficiency since the production and development of streamer discharges depends of the amplitude of voltage. While propagating voltage pulses will decay in the reactors, reflections of voltage pulse at the open end of the reactors multiply the voltage distribution. Although impedance matching between the pulsed power generator and the reactors should be important, a multiplication of the transparent voltage pulse into the reactors by mismatching may improve the treatment.