Nitrogen monoxide reduction by carbon monoxide to combustion control with calcium ferrite redox in iron ore sintering

• Published in: Fuel (Guildford) 2023-04, Vol.337, p.127172, Article 127172
• Main Authors: Dai, Mengbo, Gu, Baoshu, Ma, Xuxu, Chun, Tiejun
• Format: Article
• Language: English
• Subjects: Calcium ferrite; Combustion control; Iron ore sintering; Nitrogen monoxide reduction by carbon monoxide; Redox cycle
• ISSN: 0016-2361
• DOI: 10.1016/j.fuel.2022.127172

[Display omitted] •CO gas and NO gas are switched back and forth over calcium ferrite at 1000℃.•Calcium ferrite redox cycle in catalytic NO reduction by CO.•CO and NO compete for adsorption on calcium ferrite.•Calcium ferrite and its reduction products both function. Steel industry nitrogen oxides (NOx) emission requirements are getting increasingly rigorous. Calcium ferrite around coal or coke fines controls the combustion of nitrogen monoxide (NO) reduction by carbon monoxide (CO) in an iron ore sintering bed. This control lacked mechanistic research. A hypothesis that it belongs to the redox mechanism. In an atmosphere of a combustion boundary layer with 13500 ppm CO and 450 ppm NO at 1000 °C, the transient-response method was used to investigate the effects of CO and NO on the calcium ferrite (CaFe2O4). The activity of CaFe2O4 and its reduction products in NO reduction was examined. The results show that CaFe2O4 features strong basic sites with NO storage capacity of 158.8 μmol/g⋅catalyst at high temperatures to promote the competitive adsorption of CO and NO. The CaFe2O4 reduction path by CO, which is not affected by NO, is CaFe2O4 → Fe-FeO- dicalcium ferrite(Ca2Fe2O5) → Fe-CaO. The reduced calcium ferrites have a catalytic effect of 100 % NO removal and display more pores. After CaFe2O4 reduction, the Fe-CaO oxidation path by NO is Fe-CaO → Fe3O4-Ca2Fe2O5 → CaFe2O4. Ca2Fe2O5 redox is also involved in the redox cycle that Ca2Fe2O5 → Fe-CaO by CO and then Fe-CaO → Ca2Fe2O5 by NO. A strategy of Fe-CaO around fuels is proposed to further improve the combustion control by expanding the reducing layer in the atmosphere and generating more Ca2Fe2O5.