Reaction between Limestone and SO2 under Conditions Alternating between Oxidizing and Reducing. The Effect of Short Cycle Times

Abstract

Sulfur capture by limestone under periodically changing oxidizing and reducing conditions was investigated in a quartz reactor. To simulate conditions experienced by limestone particles in fluidized bed combustion, short, periods 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 reducing conditions were e tested: 50, 33, and 25%. The degree of conversion of CaO to CaSO 4 under these conditions is very dependent on both total cycle time and fraction of time under reducing conditions. For a fraction of time under reducing conditions of 50%, a minimum in the conversion (1.9%) versus the total cycle time was found at 8 s. For shorter cycle times a dramatic improvement 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 same limestone sulfated under totally oxidizing conditions. When the fractions of time under reducing conditions were 33 and 25%, alternating conditions have a positive effect on the conversion compared to that obtained under oxidizing conditions for all cycle times.