Effect of steam hydration on reactivity and strength of cement‐supported calcium sorbents for CO₂ capture

Abstract

Steam hydration was used to reactivate spent cement‐supported CO2 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 CO2 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.

Catalytic Toluene Reforming with In Situ CO2 Capture via an Iron–Calcium Hybrid Absorbent for Promoted Hydrogen Production

“…The reason was that reduced H 2 O concentration was not beneficial for toluene reforming, CH 4 reforming, and WGS reactions. In addition, lower H 2 O/C led to higher CO 2 yield which could be attributed to weakened reactivation of CaO by steam hydration for CO 2 capture …”

“…3) Decreased H 2 O/C (Case 8) resulted in larger amount of deposited coke due to weakened water gas reaction. As for CO 2 absorption, lower H 2 O/C was unfavorable to promote carbonation reactivity of CaO via steam hydration, whereas enhanced coke deposition would occupy more CaO active sites for carbonation. Consequently, the amount of captured CO 2 declined at lower H 2 O/C.…”

Mechanism of steam‐declined sulfation and steam‐enhanced carbonation by DFT calculations

“…The CO 2 uptake capacity will significantly decrease even if the SO 2 content is low. On the other hand, both experimental study and theoretical calculation have explained how steam addition improves the carbonation process . Using an Italian limestone in a laboratory‐scale fluidized bed reactor, Coppola et al .…”

Increasing Porosity of Molded Calcium‐Based Sorbents by Glucose Templating for Cyclic CO2 Capture

“…However, these sorbents are fine powders and the preparation processes are relatively time‐consuming. Pelletization is a simple, but effective method to strengthen the sorbents' attrition resistance, i.e., to pelletize the powders to target size . A variety of granulation technologies have been proposed to prepare the tough molded sorbents, such as extrusion with cement addition , , and pelletization with binder tempering , .…”

“…Pelletization is a simple, but effective method to strengthen the sorbents' attrition resistance, i.e., to pelletize the powders to target size . A variety of granulation technologies have been proposed to prepare the tough molded sorbents, such as extrusion with cement addition , , and pelletization with binder tempering , . However, the cyclic CO 2 capture capacities of the pellets were lower than their original powders because densification derived from the extrusion process was inferior for the CO 2 effusion into the sorbents, also the cements and other binders could not react with CO 2 .…”