Analysis of the performance of Air Pollution Control residues as CO₂ sorbents in the calcium looping process

Air Pollution Control (APC) residues deriving from acid gas (HCl, HF, SO₂) removal processes are typically disposed of in hazardous waste landfills. This study explores the potential reuse of these residues as alternative CO₂ sorbents in the Calcium Looping process, leveraging their content of unreacted lime. APC residues originating from different industrial sources (waste-to-energy, ceramic, and glass plants) were subjected to multiple carbonation-calcination cycles and benchmarked against a reference hydrated lime. The observed performance was linked to the morphological and compositional variability of the residues. Ceramic APC residues exhibited an inverse correlation between CO₂ uptake and the presence of stable fluorinated and sulfated phases. The monotonic decline in CO₂ carrying capacity upon cycling was ascribed to sintering. Waste-to-energy residues displayed a more complex cyclic behavior, associated with the melting of chlorinated phases under calcination conditions and the consequent rearrangement of product layers on sorbent particles. Despite their lower performance compared to virgin hydrated lime, APC residues achieved up to 140 mg CO₂/g sorbent after 10 cycles.