The Role of Ammonium‐Sulfur Aerosols on Nitrogen Oxides Removal by Pulsed Corona Enhanced Wet Electrostatics Precipitation with Ammonia and Ozone Injection

Abstract

AbstractThe removal of nitrogen oxides (NO and NO2) has been investigated in a bench‐scale pulsed‐corona enhanced wet electrostatic precipitator (wESP). The 70 Hz pulsed voltage is applied up to 60 kV. Simulated flue gases with NOx concentration up to 1200 pp m have been used to determine the feasibility of NOx removal in the wESP. NO must be oxidized to NO2 before any removal takes place. NOx removal efficiency increased with gas residence time, inlet NO concentration and applied corona power. In the air stream with 10 seconds gas residence time, up to 20% of 1000 pp m NO (22% of NOx) was removed at a 20 watt pulsed corona. The amount of in‐situ ozone was not enough to be considered as a major NOx removal mechanism in this wESP. Ozone injection improved the NOx removal for both the corona and non‐corona cases by oxidizing NO. With 300 pp m of ozone, the removal of 750 pp m NO was increased from 18% to 50% by oxidation, but total NOx removal was improved only to 25%.However, very high NOx removals were measured in simulated flue gas that contained ammonia, sulfur dioxide and ozone. For instance, in a 3% oxygen, 11% CO2 simulated flue gas with 800 pp m NO and 70% relative humidity at 8.6 sec of gas residence time, 30 kV corona discharge, the removal efficiency of NO was only 5%. Injecting NH3 only (NH3/NOx ratio 1) at 32 watts corona power, NO removal was increased to 10%. With the co‐presence of 2400 pp m SO2, 200 pp m ozone injection (no ammonia) increased NO removal to 36% by oxidation, but total NOxremoval only to 17%. After co‐injecting 312 pp m ozone and 2900 pp m NH3 (stoichiometry ratio 0.53), total N0X removal was increased to 79%. It was determined that the ammonium salt aerosols produced from the reaction of ammonia and sulfur dioxide enhanced the NOx removal substantially. The significance of this catalyzing effect by the in‐situ ammonium salt aerosols is addressed in this paper.