Reaction between limestone and SO2 under conditions alternating between oxidising and reducing. The effect of the SO2 concentration

Sulphur capture by limestone was investigated in a quartz reactor under per iodically alternating oxidising and reducing conditions, in order to simula te the environment in a fluidised-bed combustor. The influence of the SO2 c oncentration was studied. The lower SO2 concentration was, however, compens ated for by longer test periods; thus the product [SO2] x (total test perio d) was constant. The inlet SO2 concentration was varied between 100 and 150 0 ppm and the total test periods were 2 to 30 h. Total cycle times (oxidisi ng + reducing time period) from 2 to 720 s were used. For cycle times short er than similar to 6 s, the conversion to CaSO4 hardly changed with the inl et SO2 concentration. Furthermore, alternating conditions gave higher conve rsions than under totally oxidising conditions. For long cycle times, howev er, the conversion sharply decreased with a decrease of the SO2 concentrati on and, for low SO2 concentrations, the conversion under alternating condit ions was smaller than under oxidising conditions.