Limestone attrition during fluidized bed calcium looping cycles for CO2 capture.

Attrition of a limestone during calcium looping cycles for CO2 capture was studied in a lab-scale fluidized bed apparatus. Batch experiments under alternating calcination-carbonation conditions were carried out to investigate the effect of chemical reactions and temperature changes on the attrition propensity of the sorbent particles. 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. Different bed temperatures and CO2 inlet concentrations were tested in the experiments. Results show that relatively large attrition rates were experienced by the sorbent particles only during the first cycle. From the second cycle on the attrition rate progressively declines, also during the calcination stage where the softer CaO is produced. It is inferred that the combined chemical-thermal treatment affects the particle structure making it increasingly hard. At the same time the CO2 capture capacity decays toward an asymptotic level, possibly related to the very same structural modifications. Bed temperature and CO2 concentration both appear to influence the sorbent behavior in the tests.