Effect of steam hydration on reactivity and strength of cement‐supported calcium sorbents for CO 2 capture

Steam hydration was used to reactivate spent cement‐supported CO 2 sorbent pellets for recycle. The effect of steam hydration on the reactivity of sorbents was investigated in a bubbling fluidized reactor. A specially designed impact apparatus was developed to evaluate the strength of the reactivated pellets as well as determine the effect of ‘superheating’. It was found that the reactivity of synthetic pellets was elevated significantly over that of raw limestone after steam hydration. The CaO conversion of spent pellets increased from 0.113 to 0.419 after hydration, whereas that of spent limestone ranged from 0.089 to 0.278. The CaO conversions of hydrated samples calcined under different conditions achieved the identical level, proportional to the degree of hydration. As expected, the mechanical strength of synthetic pellets declined severely after reactivation. Large cracks emerged on hydrated limestone as seen in scanning electron microscope images. By contrast, similar cracks were not observed for synthetic pellets after hydration, although hydration did produce higher porosity than seen with limestone and an increased surface area, which enhanced CO 2 capacity and was associated with an increase in strength loss. The breakage rate of superheated, steam‐reactivated limestone‐derived pellets was about half that of hydrated samples. This demonstrates that superheating treatment (which allows the annealing of stacking faults and mechanical strain produced by hydration) could enhance the strength of hydrated pellets. This work demonstrated that combining steam hydration with superheating can both reactivate the spent synthetic pellets and reduce strength decay associated with the hydration process. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.