Removal of NO by methane over iron in simulated flue gas with SO2

• Effect of SO2 on NO reduction by CH4 over iron was investigated.
• Metallic iron could simultaneously reduce almost 100% of NO and SO2 above 700 °C.
• SO2 had little influence on NO reduction.
• NO reduction was higher than 95% above 850 °C.

The effect of SO2 on NO reduction by methane over iron and/or iron oxides was experimentally investigated at 300–1000 °C in a tubular flow reactor. NO reduction efficiencies vs temperature were presented at typical conditions and the reaction product scales were analyzed by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) methods. In N2 atmosphere with 0.01–0.04% SO2, iron simultaneously reduced 100% of NO and SO2 above 700 °C. In simulated flue gas atmosphere with 0.01–0.04% SO2, NO reduction efficiency was higher than 95% and 98% when the temperature was above 850 °C and 950 °C respectively at fuel rich conditions. The influence of SO2 on NO reduction was insignificant. In a continuous test in simulated flue gas containing 0.02% SO2, 0.05% NO, 16.8% CO2, 2.0% O2, experimental data demonstrated that more than 95% of NO was reduced by 1.13% methane over iron at 1000 °C over 100 h. The mechanism for the reaction of SO2 with Fe and CH4 was discussed. When iron was exposed to the flue gas mixtures of NO/SO2/CH4, iron reacted with both NO and SO2 and the reaction product was a mixture of Fe2O3/Fe3O4/FeO and FeS. CH4 reduced the iron oxides to iron, at the same time CH4 reacted with SO2 to produce elemental sulfur and H2S. Then H2S reacted with iron/iron oxides to form FeS.

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