Low-temperature SNCR technology for controlling NO_x emission

An innovative technology for removing NO_x through the generation of amidogen (NH₂) and imidogen (NH) free radicals via dielectric barrier discharges (DBD) was demonstrated in this study. A laboratory-scale experimental system was designed and constructed to evaluate the effectiveness of removing NO_x from simulated flue gas at temperatures much lower than traditional SNCR process. Dielectric barrier discharges (DBD) coupled with NH₃ injection was applied to generate NH and NH₂ radicals which could reduce NO_x molecules to form N₂ and H₂O. Dependence of NO removal efficiency on relevant operating parameters including applied voltage, inlet gas composition, inlet gas temperature and power input were also determined. Experimental results indicated that the NO_x reduction efficiency was limited by the concentration of NH_i radicals. Experimental results also showed that as high as 60% of NO_x was removed by NH_i radicals generated with DBD process at room temperature. The influence of oxygen content in the gas stream on NO reduction was not significant, reflecting the characteristics of selective reduction of NO in this process. At lower applied voltages (<17 kV), increasing temperature enhanced the effectiveness for NO removal. On the other hand, the temperature effect was not significant at higher applied voltages (>17 kV). In addition, the spectrums of Fourier transform infrared spectroscopy confirmed that the byproducts detected during reduction process included N₂, H₂O and trace of N₂O. These results indicate that the conventional SNCR process can be operated at temperatures around 100 with the aid of DBD technology.