Study and Kinetic Modeling of Direct Sulfation of Iranian Limestones by Sulfur Dioxide at High CO2 Partial Pressure

The direct sulfation of three high purity Iranian limestones and one precipitated calcium carbonate from different sources, containing more than 97 % CaCO3, were studied in a specially designed fixed bed reactor under atmospheric pressure, in the presence of excess CO2 to prevent decomposition of CaCO3. Experiments were carried out over a range of particle sizes from 1.6-2.5  mm at four temperatures (750, 800, 850, 900 °C), and SO2 concentration of 2400 ppm. The particle size and temperature showed a dominant influence on the variation of conversion with time. The results of experiments show that the Shrinking Unreacted Core Model can beused to predict the behavior of sulfation of limestone. This simple model reveals that the reaction rate is the controlling step. The parameter of model, chemical rate constant (Ks), was obtained as: Ks = 0.1 exp (-6.2/RT)  cm/s. Model predictions are in good agreement with expeimental data.