Absorption of nitrogen oxides into sodium hydroxide solution in a rotating packed bed with preoxidation by ozone

Abstract

This study employed a rotating packed bed (RPB) to enhance the absorption performance of nitrogen oxides (NOx) into sodium hydroxide (NaOH) solution with the preoxidation of NO by ozone. The absorption performance of NOx was evaluated in terms of its removal efficiency (η) from a gas stream under various operating conditions including O3/NOx molar ratio (MR), rotation speed of the RPB (N), liquid flow rate (L), NaOH concentration (CNaOH), inlet NOx concentration (CNOx), and using time (t). Also, the corresponding effect of adding oxidants (NaClO, H2O2, and KMnO4) and a reductant (CO(NH2)2) into the NaOH solution on NOx removal efficiency was investigated. Results indicated that preoxidation of NO by O3 significantly improved NOx removal efficiency and the removal efficiency increased with increasing O3/NOx molar ratio, NaOH concentration, and liquid flow rate but decreased with increase in inlet NOx concentration and using time. Additionally, NOx removal efficiency first increased and then decreased with increasing rotation speed of the RPB. Both the oxidation and reduction additives enhanced NOx removal efficiency, and the order of enhancement was found to be KMnO4 > H2O2 > CO(NH2)2 > NaClO. These results further indicate that the hydrolysis reactions of NOx are the rate-determining steps in the NOx absorption process and, thus, the main factors hindering NOx removal during the wet scrubbing process. This work demonstrates that RPB has great potential for removal of NOx by a wet scrubbing process in view of the small size of the RPB, low temperature, and the short gas retention time of 0.27 s applied in this work.