Removal of sulfur dioxide using absorbent synthesized from coal fly ash: Role of oxygen and nitrogen oxide in the desulfurization reaction

Removal of SO₂ from flue gas by the absorbent synthesized from coal fly ash and calcium oxide was studied under different reaction conditions to elucidate the effect of the coexistence of NO and O₂ in the flue gas. The presence of O₂ and NO in the flue gas was found to be necessary to produce sulfate salts instead of sulfite salts as the final product of the desulfurization reaction. The roles of O₂ and NO were postulated as an oxidizing agent to oxidize SO₂ to SO₃, which then reacts with the absorbent. NO itself is not an oxidizing agent, but with the presence of O₂, it can be oxidized to NO₂ which acts as an oxidizing agent. It was also found that NO₂ (from NO) is a better oxidizing agent compared to O₂ in oxidizing SO₂ to SO₃.