Nitrogen Fixation as NOx Enabled by a Three-Level Coupled Rotating Electrodes Air Plasma at Atmospheric Pressure

In this paper, a three-level coupled rotating electrodes air plasma at atmospheric pressure is developed for evaluation of nitrogen fixation. Factors influencing the NOx production rate and energy cost, including airflow rate, the input H2O concentration, blade numbers at each rotating electrode and rotating speed, are examined. Air flow rates prove to have no effect on the rotational temperature of N2 337.1 nm and the emission intensities of N2+ and N2, but specific energy input (SEI) and species’ residence time can be shorter with higher air flow rates, resulting in lower NOx concentration and energy cost. The addition of H2O also has a positive effect on both NOx concentration and energy cost. Optical emission spectrum (OES) shows that air + H2O plasma has stronger 336 nm (NH) and 309 nm (OH) emission lines than air plasma, suggests NH and OH are the key species in NOx enhancement. The most energy efficient conditions are found at airflow rate of 15 l min−1, 12% H2O concentration, with 4 blades on each rotating speed. Under these conditions, the lowest energy cost is observed to be 165 GJ/tN.