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

Abstract

Sulfur trioxide (SO3) is corrosive and environmentally harmful. Under oxy-combustion mode, the formation of SO3 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 SO3 by iron oxide (Fe2O3) under oxy-combustion mode was experimentally studied in a fixed-bed reactor, and effects of temperature (300–900 °C), atmosphere, catalyst particle size, SO2, O2, and H2O concentrations were discussed. Results show that Fe2O3 promotes SO3 formation, and the yield of SO3 reaches a maximum at 700 °C under both air- and oxy-combustion modes. Increasing O2 concentration in a range of 5–20% promotes the catalytic formation of SO3, whose effect is restricted at a higher O2 concentration. Both increases of SO2 concentration in a range of 500–3000 ppm and steam concentration in a range of 0–20% decrease the SO3 yield. A significant effect of Fe2O3 particle size on SO3 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 SO3 yield increases by 33%. Kinetics analysis results show that in this case, the catalytic conversion from SO2 to SO3 by Fe2O3 has an apparent activation energy Ea of 18.9 kJ/mol and a pre-exponential factor A of 5.2 × 10−5. At 700 °C and with Fe2O3 particle size of 50–75 μm, the global reaction orders of SO2 and O2 for SO3 formation are 0.71 and 0.13, respectively.