Pulsed Discharge Plasma for Pollution Control

Abstract

Air pollution caused by emission of a pollutant produced by a variety of sources must be substantially reduced as mandated by recent national legislations and international agreements. In recent years, several techniques have been used to remove pollutants from air, with various degrees of success. Nonthermal plasmas, in which the mean energy of electrons is substantially higher than that of the ions and the neutrals, offer a major advantage in reducing the energy requirements to remove the pollutants [1], [2]. The application of a short-duration pulsed power to a gaseous gap at an atmospheric pressure results in the production of nonthermal plasma. Acid rain is partly produced by emissions of nitrogen oxides such as nitric oxide (NO) and nitrogen dioxide (NO2) originating from fossil fuels burning in thermal power stations, motor vehicles, and other industrial processes such as steel production and chemical plants [3]-[8]. Nonthermal plasmas for removal of NOX have been produced using an electron beam [9], [10], a dielectric barrier discharge [6], [11], and a pulsed corona discharge [8], [12][24] at various energy effectiveness. Nevertheless, energy loss occurs in each plasma processing system which cannot be neglected. For an electron beam system, it has been reported that only 26% of the input energy can be transferred to the plasma due to losses in the vacuum interface [25]. In a dielectric barrier discharge system, the input energy is largely consumed by the dielectric barrier and gas heating and cooling. Consequently, only 20% of the primary energy is transmitted into the plasma [26]. In a pulsed discharge, the input energy is mainly consumed in the pulse forming circuit, and the impedance mismatching between the generator and discharge electrode gap results in further energy loss. Approximately 30% of primary energy can be transmitted into the plasma [27]. In order to improve the energy efficiency of plasma processing system, the effect of the pulse duration on NO removal concentration was studied. The results showed the pulse duration of the applied voltage has a strong influence on the energy efficiency of the removal of pollutants [28], [29], shorter pulse duration is required to reach cost effective NO removal. Consequently, a detailed understanding of the development of streamer discharge using very short duration pulses is important for practical applications. Here it should be noted that NO2 can be converted to ammonium nitrate (NH4NO3) by adding ammonia (NH3) into the treatment gas, and NH4NO3 can be used to make fertilizer. Therefore, the major discussion is focused on removal of NO. The mechanism of NO removal is resulted from the plasma enhanced chemical reactions. The energy input into the discharge resulted in a 12