Reaction between limestone and SO2 under conditions alternating between oxidizing and reducing. The effect of short cycle times

Sulfur capture by limestone under periodically changing oxidizing and reduc ing conditions was investigated in a quartz reactor. To simulate conditions experienced by limestone particles in fluidized bed combustion, short peri ods of oxidizing and reducing conditions were used. Total cycle times (time under oxidizing conditions + time under reducing conditions) between 2 and 24 s were used. Furthermore, three different fractions of time under reduc ing conditions were tested: 50, 33, and 25%. The degree of conversion of Ca O to CaSO4 under these conditions is very dependent on both total cycle tim e and fraction of time under reducing conditions. For a fraction of time un der reducing conditions of 50%, a minimum in the conversion (1.9%) versus t he total cycle time was found at 8 s. For shorter cycle times a dramatic im provement: of the conversion was obtained, e.g,, 14.2% for 6 s. These high conversion values were also 50% higher compared to those obtained for the s ame Limestone Sulfated under totally oxidizing conditions. When the fractio ns of time under reducing conditions were 33 and 25%, alternating condition s have a positive effect on the conversion compared to that obtained under oxidizing conditions for all cycle times.