Production of ammonia-derived radicals in a dielectric barrier discharge and their injection for denitrification

Abstract

Atmospheric pressure dielectric barrier discharges (DBDs) have been widely studied for nitric oxide (NO) reduction in flue gases. In particular applying the DBD to generate activated species externally and mix them with the flue gas in a second step is favoured due to its potential energy efficiency and no generation of corrosive acids.In the present work ammonia-derived radicals were generated using an atmospheric pressure Ar/NH3 DBD and subsequently injected into an exhaust chamber where a synthetic flue gas of an NO/N2 mixture was fed for demonstration of NO reduction. Optical emission and laser diode absorption spectroscopy was employed for detection of NH and NH2 in the discharge respectively, while ultraviolet absorption and Fourier transform infrared spectroscopy was used for detection of nitrogen oxides, ammonia, ammonia-derived radicals, and other products after mixing the plasma activated gas with the synthetic flue gas.Although NH and NH2 radicals were observed in the discharge, due to their short lifetimes it is unlikely that they would be simply transported, mixed with the flue gas and react with NO to form N2. On the other hand, hydrazine (N2H4), which is a stable ammonia-derived radical, was observed in the exhaust gas from the Ar/NH3 DBD. It is indicated that the hydrazine is transported into the exhaust chamber, thermally decomposed to NH2, and the efficient NO reduction can be carried out at temperatures of more than 800 K.