The effect of SO2 on limestone attrition during fluidized bed calcium looping cycles for CO2 capture

Attrition of six different limestones was studied during calcium looping cycles for CO2 capture in a lab-scale fluidized bed apparatus. The tests were carried out under realistic conditions representative of a process with calcination in an oxy-firing environment. The focus of the activity was to investigate the effect of the presence of SO2 both in the calcination and in the carbonation stages. Batch experiments under alternating calcination-carbonation conditions were carried out with two SO2 concentration levels. Experiments without SO2 were also performed, for comparison. Attrition processes were characterized by following the modifications of bed sorbent particle size distribution and the elutriation rates of fines throughout conversion over repeated cycles. Results showed that the presence of a high SO2concentration significantly depressed the sorbent CO2 capture capacity, most likely because of the formation of an impervious CaSO4 layer on the surface of the particles. Under a lower SO2 concentration level, the effect on CO2 capture capacity was less important. In both conditions, the extent of limestone attrition was only slightly influenced by the presence of SO2. The analysis of the particle size distribution of the bed material over repeated calcination/carbonation cycles indicated that particle fragmentation was always limited.