Experimental Investigation of the SO₂ Abatement Capacity of South African Calcium-Based Materials

One of the most important steps in the wet limestone-gypsum flue gas desulphurization (WFGD) process is CaCO₃ dissolution, which provides the dissolved alkalinity necessary for SO₂ absorption. Accurately evaluating the CaCO₃ dissolution rate is important in the design and efficient operation of WFGD plants. In the present work, the dissolution of limestone from different sources in South Africa has been studied in a pH-stat apparatus under conditions similar to those encountered in wet FGD processes. The influence of various parameters such as the reaction temperature (30 ≤ T ≤ 70°C), CaCO₃ particle size (25 ≤ dp ≤ 63μm), solution acidity (4 ≤ pH ≤ 6), and chemical composition were studied in order to determine the kinetics of CaCO₃ dissolution. The results obtained indicate that the dissolution rate increased with a decrease in particle size and an increase in temperature. The dissolution curves were evaluated in order to test the shrinking core model for fluid–solid systems. The analysis indicated that the dissolution of CaCO₃ was controlled by chemical reaction, i.e. 1 − (1 − X)^1/3 = kt.