Experimental and kinetics study on SO3 catalytic formation by Fe2O3 in oxy-combustion

Abstract Sulfur trioxide (SO 3 ) is corrosive and environmentally harmful. Under oxy-combustion mode, the formation of SO 3 is aggravated due to flue gas recirculation, and should be more concerned than that under traditional air-combustion mode. In this paper, the catalytic formation of SO 3 by iron oxide (Fe 2 O 3 ) under oxy-combustion mode was experimentally studied in a fixed-bed reactor, and effects of temperature (300–900 °C), atmosphere, catalyst particle size, SO 2 , O 2 , and H 2 O concentrations were discussed. Results show that Fe 2 O 3 promotes SO 3 formation, and the yield of SO 3 reaches a maximum at 700 °C under both air- and oxy-combustion modes. Increasing O 2 concentration in a range of 5–20% promotes the catalytic formation of SO 3 , whose effect is restricted at a higher O 2 concentration. Both increases of SO 2 concentration in a range of 500–3000 ppm and steam concentration in a range of 0–20% decrease the SO 3 yield. A significant effect of Fe 2 O 3 particle size on SO 3 catalytic formation is observed. When the particle size decreases from 50-75 μm to 10–25 μm, the inflection temperature shifts from 700 °C to 600 °C, while the maximum SO 3 yield increases by 33%. Kinetics analysis results show that in this case, the catalytic conversion from SO 2 to SO 3 by Fe 2 O 3 has an apparent activation energy E a of 18.9 kJ/mol and a pre-exponential factor A of 5.2 × 10 −5 . At 700 °C and with Fe 2 O 3 particle size of 50–75 μm, the global reaction orders of SO 2 and O 2 for SO 3 formation are 0.71 and 0.13, respectively.