Kinetics of the Reaction of Hydrated Lime with SO2 at Low Temperatures: Effects of the Presence of CO2, O2, and NOx

Abstract

The effects of the presence of CO2, O2, and NOx in the flue gas on the kinetics of the sulfation of hydrated lime at low temperatures were studied using a differential fixed-bed reactor. When O2 and NOx were not present together the reaction kinetics was about the same as that under gas mixtures containing SO2, H2O, and N2 only. When both O2 and NOx were present, sulfation of hydrated lime was greatly enhanced, forming a large amount of calcium sulfate in addition to calcium sulfite. Sulfation of hydrated lime was well described by the surface coverage model, despite the gas-phase conditions being different. Relative humidity is the major factor affecting the reaction, and its effect was more marked when both O2 and NOx were present. The kinetic model equations obtained in this work can be used to describe the sulfation of hydrated lime in the low-temperature dry and semidry flue gas desulfurization processes with or without an upstream NOx removal unit.