NO3 reduction for flue gas cleaning using wet-type plasma reactor

Abstract

Fundamental characteristics of the flue gas cleaning for NO_x 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 NO_x. Effect of the NH₃ addition for enhancement of NO_x removal has been experimentally confirmed. The NH₃ addition was effective for NO oxidation as well as NO_x 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 NO_x. These results suggest the possibility of the continuous operation of the wet-type plasma reactor for NO_x removal without excess acidification of the absorbing water, nor feeding additives.