Insight into the deactivation mechanism of CaO-based CO2 sorbent under in-situ coal combustion

Calcium Looping technology is one of the most promising post-combustion CO2 capture technologies. However, the fine CaO-based sorbents are prone to elutriate in the fluidized-bed reactors. The in-situ combustion of coal in the calciner will greatly affect the performance of the regenerated CaO. In this work, extrusion-spheronization method was adopted to prepare limestone-based pellets to mitigate the issue of elutriation. To clearly elucidate the deactivation mechanism of CaO-based sorbents under in-situ coal combustion, the CaO-based sorbents mixed with raw, ammonium acetate-washed, HCl/HF acid-washed coal were conducted respectively. The CaO-based sorbent pre-calcined under in-situ ammonium acetate-washing and HCL/HF acid-washing coal combustion is superior to that pre-calcined under in-situ raw coal combustion for cyclic CO2 capture. The elimination of the low-melting alkali metals (i.e., Na, K) and residual coal ash contributes to the improved cyclic CO2 capture performance of CaO-based sorbent. Moreover, the adverse effect of in-situ coal combustion on limestone-based pellet is less serious than that on limestone powder due to the outer layer of the pellet protecting the active CaO inside from contamination by in-situ coal combustion. Furthermore, the cellulose-modified, limestone-based sorbent pellet exhibits quite prominent advantage on cyclic CO2 capture performance, particularly in the case of pre-calcination under the condition of in-situ coal combustion.