Steam Hydration of Calcium Oxide for Solid Sorbent Based CO2 Capture: Effects of Sintering and Fluidized Bed Reactor Behavior

Abstract

This study reports on the hydration characteristics in the three-step carbonation–calcination reaction (CCR) process with intermediate steam hydration. Specifically, experimental results of sorbent reactivation in a fluidized bed steam hydration reactor are presented along with the effect of the operating gas velocity (Ug) and different calcination conditions on the hydration reaction. The enhancing effect of increasing Ug on the hydration rate is evident but limited with a threshold at 0.3 m/s, above which the bulk phase mass transfer effects are less significant. The highest hydration conversion of 83% is achieved in 30 min at the highest Ug of 0.5 m/s. However, increasing Ug also yields lower steam utilization during hydration; thus an optimal operating condition with respect to both the solid and steam conversions shall be determined via an overall process analysis. In addition, the parametric effect of different calcination conditions, specifically, the calcination temperature, time, and reactor type, on the hydration reaction mechanism is investigated. The sorbent reactivity and morphology is characterized using thermogravimetric and Brunauer–Emmett–Teller analysis as well as scanning electron microscopy imaging. Sorbents produced at lower calcination temperatures and in a reactor with sufficient mixing exhibit a larger surface area and pore volume, and superior reactivity. The effect of calcination time, within the scope of this study, is not as significant. Lastly, sorbent reactivity toward steam hydration depends strongly on its surface kinetics but not to the same extent as carbonation. The hydration and carbonation reactions are compared using a modified Jander’s equation, [1– (1 – ∝)1/3]N = Kt.