SO2 reaction with Ca(OH), at medium temperatures (300-425°C):: Kinetic behaviour

The study of the reaction between Ca(OH)(2) and SO2 has been performed in the medium temperature range (300-450 degrees C) under controlled dehydration conditions. The largest SO2 capture has been found at 450 degrees C, 0.64 mol SO2 mol Ca-1, and no influence of the water vapour pressure on the sorbent utilization has been observed. The investigation of the internal porous structure of Ca(OH)2 and sulphated products was carried out, showing a strong decrease in the pore volume of the mesopore region and BET surface area. The kinetics of Ca(OH)2 sulphation is characterized by a dramatic decrease of the reaction rate with the sorbent conversion; a review of exponential models let us consider a general exponential equation that accounts for the decrease in the reaction rate. The reaction is first-order with respect to the SO2 partial pressure in the studied range (1200-11,000 ppmv) and a strong influence of CO2 in the reaction rate has been found. The kinetic model r(s) = ky(1-x)exp {- [gamma(0)/RT . exp (D/T) + b (C-co2/C-so2)]x} and parameters, y(0) = 3 cal mol(-1) D = 5719 K, k = 7.07 x 10(-2) mol m(-2) min(-1) and b = 1.3 allows a good description of the experimental breakthrough curves obtained in an integral sand-bed reactor. (C) 1998 Elsevier Science Ltd. All rights reserved.