Enhanced effect of in-situ generated ammonium salts aerosols on the removal of NO_x from simulated flue gas

The combined removal of sulfur dioxide (SO₂, up to 3000 ppm) and nitrogen oxides (NO and NO₂, up to 1200 ppm) has been investigated in a bench-scale pulsed-corona enhanced wet electrostatic precipitator (wESP) with the optional infection of ammonia and/or ozone. The reaction of ammonia with SO₂ produces submicron aerosols under certain conditions. Experiments have shown the feasibility of combined SO₂ and NO_x removal from simulated flue gases by the action of these in-situ generated aerosols. The mechanisms for NO_x removal include oxidation of NO to NO₂ and subsequent absorption of NO₂ into the water wall of the wESP. The results have shown that injecting NH₃ (NH₃/NO_x molar ratio 1) resulted in NO_x removal of ∼13% in a simulated combustion flue gas. Injecting 200 ppm ozone (no ammonia) increased NO conversion to 35% by oxidation, but total NO_x removal increased to only 17%. Without the formation of ammonium salts aerosols (e.g., without SO₂ in the gas), co-injection of ammonia and ozone increased NO conversion to 60% and NO_x removal to 40%. However, high NO_x removals were measured in simulated flue gas that contained NH₃, SO₂, and ozone. The total NO_x removal efficiency was 79% when the ammonium salts aerosols were formed in the presence of 2400 ppm SO₂, 312 ppm O₃, and 2900 ppm NH₃. The energy efficiency of collection improved by ∼250% for SO₂ removal and more than 4700% for NO_x removal under these conditions. It was determined that the ammonium salts aerosols produced from the reaction of ammonia and sulfur dioxide substantially enhanced total NO_x removal.