Modified lime-based pellet sorbents for high-temperature CO2 capture: Reactivity and attrition behavior

Modified lime-based pellets have been developed as potential regenerable high-temperature CO2 sorbents using calcium aluminate cement binders to enhance pellet strength. A mechanical pelletizer was used for granulation of the powdered materials, namely quick lime and hydrated lime, produced from Graymont limestone with the addition of spray water. The CO2 carrying capacity of both the pellet sorbents and the parent limestone was tested in a thermogravimetric analyzer (TGA) at 800 °C with repeated calcination/carbonation cycles. It was found that the CO2 carrying capacity of the pelletized sorbent was higher than that of the parent limestone, and the stability over multiple cycles was improved when cement was added to the pellets. The attrition resistance of these pellets was examined using a bubbling fluidized bed (50 mm ID). The particle size distribution (PSD) of both the calcined pellets and limestone was determined before and after 2 h attrition tests which were performed using air as the fluidizing gas at room temperature and at 800 °C. The results of attrition tests showed that after fluidization for 2 h, particle size distribution changed such that the average particle diameter (d50) of the sample always decreased, but for the pellet sorbents, high-temperature fluidization did not result in significantly more pronounced attrition.