SO2 REACTION WITH CA(OH), AT MEDIUM TEMPERATURES (300-425-DEGREES-C) - KINETIC-BEHAVIOR

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 investigat ion 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 sulphati on is characterized by a dramatic decrease of the reaction rate with t he sorbent conversion; a review of exponential models let us consider a general exponential equation that accounts for the decrease in the r eaction rate. The reaction is first-order with respect to the SO2 part ial pressure in the studied range (1200-11,000 ppmv) and a strong infl uence 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 p arameters, 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 br eakthrough curves obtained in an integral sand-bed reactor. (C) 1998 E lsevier Science Ltd. All rights reserved.