Kinetics of the Sulfation of Ca(OH)2 at Low Temperatures

Hydrated lime [Ca(OH)2] is frequently used as a sorbent in the spray-drying flue gas desulfurization (FGD) and injection/humidification FGD processes to remove SO2 from the flue gas. In the present study, the kinetics of the reaction of Ca(OH)2 with SO2 has been studied by using a differential reactor and a gas mixture of N2, SO2, and H2O under the conditions of 0−80% relative humidity, 60−90 °C, and 1000−5000 ppm SO2. The reaction ceased before 1 h, and Ca(OH)2 was incompletely converted. The relative humidity of the gas significantly affected the initial reaction rate and the maximum conversion of Ca(OH)2. The temperature and SO2 concentration had mild effects on the reaction. The sulfation of Ca(OH)2 was well described by the asymptotic equation, which is obtained by assuming that the rate was controlled by the chemical reaction occurring on the water-adsorbed sorbent surface and by considering the surface coverage by the product. The results of this study are useful to the design and efficient operation of the processes using hydrated lime to remove SO2 from the flue gas.