Limestone Calcination with CO ₂ Capture (II): Decomposition in CO ₂/Steam and CO ₂/N ₂ Atmospheres

Decomposition of limestone particles (0.25−0.5 mm) in a steam dilution atmosphere (20−100% steam in CO 2) was investigated by using a continuously operating fluidized bed reactor for CO 2 capture. The decomposition conversion of limestone increased as the steam dilution percentage in the CO 2 supply gas increased. At a bed temperature of 1193 K, the conversions were 72% without dilution (100% CO 2) and 98% with 60% steam dilution. The decomposition conversions obtained with steam dilution and N 2 dilution differed significantly, and this result is explained in terms of the difference between the heat transfer to particle in steam and N 2 dilution atmosphere. The reactivities of the CaO produced from limestone decomposition with steam dilution and without dilution (100% CO 2) were tested by means of hydration and carbonation reactions. In the hydration test, the time required for complete conversion [CaO → Ca(OH) 2] of the CaO produced by steam dilution was approximately half that required for the CaO produced without dilution. In the carbonation test, carbonation conversion (CaO → CaCO 3) of the CaO produced by steam dilution was approximately 70%, whereas the conversion was approximately 40% for the CaO produced without dilution.