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 (SO42-) salts instead of sulfite (SO32-) 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.