Simultaneous Removal of NO and SO2 with a Novel Oxidation-Absorption Process Based on Air Microbubble Water System

Abstract

Microbubbles (MBs) can spontaneously generate hydroxyl radicals (·OH) with high oxidizing capacity. In this study, a novel oxidation-absorption process based on a microbubble system in the indirect removal mode was proposed for the simultaneous removal of nitric oxide (NO) and sulfur dioxide (SO2). In this process, an air microbubble water system (AMBW) was produced by a microbubble generator (MBG) inhaling air and tap water and injected into an oxidation-absorption column reactor by the MBG, meanwhile the mixed gas composed of NO and SO2 passed through a micron-sized gas distributor at the bottom of the reactor and flowed into the AMBW. Important parameters including initial pH and temperature of tap water, operation time, NO concentration, SO2 concentration, and NaCl concentration were assessed to investigate the feasibility of the AMBW for the simultaneous removal of NO and SO2. The results showed that ·OH generated from the collapsed MBs played a critical role in the removal and the simultaneous removal of NO and SO2 was successfully achieved with the AMBW. Even with only tap water used as the absorbent, the removal efficiencies of NO and SO2 reached 92.7% and above 99%, respectively, when the experiment conditions were initial water pH 11.5, initial water temperature 298 K, 600 ppm NO, and 3,000 ppm SO2. Compared with the microbubble system in the direct removal mode, this new system is more suitable for the treatment of flue gases with low NO concentration and high volume. Moreover, this novel process should have a good prospect of industrial application in the flue gas treatment due to its high efficiencies of desulfurization and denitration and some advantages such as low usage cost of the reagents, simple system, and small occupation space.