Effect of Repeated Steam Hydration Reactivation on CaO-Based Sorbents for CO2 Capture

Samples of natural limestone and commercial calcium carbonate were subjected to successive calcination and carbonation reactions in a TGA and to repeated activity restoration by steam hydration. Steam hydration of spent lime, followed by heating in CO2, was shown to be an effective method for repeatedly restoring high CO2 capture activity to spent lime during a large number of CO2 capture cycles. Steam hydration was also shown to reduce the decay rate of the CO2 capture activity by increasing the rate of carbonation in the diffusion controlled regime. Repeated hydration-carbonation-calcination cycles led to a considerable expansion of the particles through the formation of large vesicles, likely to lead to high attrition levels when applied in fluidized beds. Based on SEM observation of the particles during hydration-carbonation-calcination cycling, a model was proposed for their progressive weakening. It was concluded that strategies to reduce this weakening must limit the growth of the cracks in the crystal as they are cycled repeatedly.