Attrition of Limestone During Fluidized Bed Calcium Looping Cycles for CO₂ Capture

Abstract

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 during the calcination stage 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. The bed temperature and CO₂ concentration both appear to influence the sorbent behavior in the tests.

Keywords:

• Attrition
• Calcium looping
• Fluidized bed
• Limestone

ACKNOWLEDGMENTS

This work has been carried out in the framework of the European Commission—Research Fund for Coal and Steel Contract no. RFCR-CT-2010-00013 (CAL-MOD). This work was also supported by the “MSE-CNR Accordo di Programma per l'Attività di Ricerca di Sistema, project: Carbone Pulito-CO₂ Capture.” The experimental support of Ms. Simona Venditto is gratefully acknowledged.

Notes

Published as part of the Seventh Mediterranean Combustion Symposium Special Issue with Guest Editors Federico Beretta, Nevin Selçuk, Mohy S. Mansour, and Andrea D'Anna.