Deactivation features of CaO-based sorbents during coal-assisted calcination under fluidization states

Coal combustion is a typical heat source for regenerating CaO-based CO₂ sorbents in Calcium Looping (CaL) systems. Nevertheless, the mechanisms underlying coal combustion’s impact on CaO-based sorbents within fluidized bed calciners, as well as the extent of this impact, remain unclear. In this work, calcination of CaO-based sorbent pellets was carried out using coal combustion as the heat source in a fluidized-bed reactor, and the deactivation mechanisms of the sorbent pellets were explored in detail. The results reveal that sorbent pellet deactivation is significantly accelerated not only by the high temperatures from combustion heat but also by the interaction between coal-derived elements and CaO. Notably, due to enhanced gas–solid mass transfer, SO₂ released during coal combustion has a more pronounced effect on the sorbents compared to coal ash-derived Al/Si impurities. Furthermore, with the increase in fuel particle size, the impact of the fuel on the sorbent exhibits a trend of first increasing and then decreasing. The results of multi-cycle testing demonstrate that the CO₂ sorption capacity of inert stabilizer-supported sorbents decreases progressively, falling to less than 0.1 g/g after 9 cycles of calcination via coal combustion. The performance degradation is mainly due to thermal sintering-induced pore occlusion, sulfation, and ash permeation—factors that collectively render coal combustion a non-ideal heat source for CaL systems, given its failure to guarantee effective CO₂ capture or continuous system operation.