NO3 reduction for flue gas cleaning using wet-type plasma reactor
ABSTRACT Fundamental characteristics of the flue gas cleaning for NOx using the wet-type plasma reactor has been evaluated, with attention being laid on concentration of nitrate and ammonium ions in the liquid. The wet-type plasma reactor was a wire-cylinder, driven by square wave high voltage pulse. A thin liquid film was maintained on the inner wall of the reactor. In this reactor, discharge plasma oxidizes NO to NO2, and NO2 is dissolved into the liquid as HNO3. Continuous absorption induces saturation and acidification of the liquid, inhibiting the absorption of NOx. Effect of the NH3 addition for enhancement of NOx removal has been experimentally confirmed. The NH3 addition was effective for NO oxidation as well as NOx absorption into the liquid, resulting in the increasing of NO2- and NO3+ concentration in the liquid. With the presence of Fe ions in liquid exposed to the discharge plasma, reduction can be made from NO3- to NH4+ through the oxidation of Fe2+ to Fe3+. The reductive reaction enhances the absorption of NOx. These results suggest the possibility of the continuous operation of the wet-type plasma reactor for NOx removal without excess acidification of the absorbing water, nor feeding additives.