STUDY OF THE DIRECT SULFATION OF LIMESTONE PARTICLES AT HIGH CO2 PARTIAL PRESSURES

The reaction between sulfur dioxide and limestone particles at high CO 2 partial pressures (CaCO3 + SO2 + 1/2O2 --> CaSO4 + CO2), is investig ated by using thermogravimetric analysis under isothermal conditions. A raw limestone is used. Different ranges of particles size, between 2 0 and 850 mum, and temperatures from 750-degrees-C to 900-degrees-C, a re used in this study. By analyzing the dependence or time on fraction al conversion, according to the shrinking core model, it is concluded that diffusion through the product layer is the controlling step for t his reaction. The relationship between product layer diffusivity and t emperature is given by D(e) = 0.0086 exp(- 146,500/RT), m2/s. The natu re of the diffusion process and the mechanism of the reaction is discu ssed. By using the calculated rate parameters, the experimental conver sion-time dependence is predicted.