Effect of Replacing the Hearth Layer Used in the Sintering Process on the Reduction of NO and SO₂

Nitrogen oxide (NO) and sulfur dioxide (SO₂) are the major environmental pollutants generated from the steel industry. The sintering process of iron ores accounts for more than 40 and 70 pct of the total emission of NO and SO₂ from the steel industry. The current study aims to clarify the effects of the hearth layer used in the sinter bed on the reduction of NO and SO₂. It was attempted to examine the potential of several materials in reducing NO and SO₂ such as the hearth layer commonly applied in the steel plants, reagent-grade FeO, mill-scale, reagent-grade CaO, and calcined dolomite. The fractional reduction of NO (\({\eta }_{\text{NO}}\)) was directly proportional to the FeO content in the materials. The effects of experimental variables such as temperature, specimen arrangement, and oxygen addition to inlet gas mixture on the fractional reduction of NO (\({\eta }_{\text{NO}}\)) were evaluated. In case the sample was placed perpendicular to the flow of gas at high temperatures, the reduction of NO (\({\eta }_{\text{NO}}\)) was improved. However, the increase of oxygen in the inlet gas decreased the reduction of NO. Reagent-grade FeO and mill-scale were effective at 423 K (150 °C) for reducing NO in coal combustion, while reagent-grade CaO and calcined dolomite facilitate the reduction of SO₂ at 773 K (500 °C). Based on the results, it was suggested to replace the hearth layer in the sinter bed with mill-scale in the low-temperature zone and calcined dolomite in the high-temperature zone, which would provide the best reduction ratio of NO and SO₂.