Calcium looping for post-combustion CO₂ capture using sorbents derived from incineration ashes

A method was developed to capture carbon dioxide (CO₂) from waste gas streams using ash-derived sorbents via the calcium looping process. The captured CO₂ can be subsequently sequestered in geological formations or utilised to produce fuels and chemicals. This study explored the potential of using waste as a resource and valorised into effective sorbent materials to perform a carbon capture, storage and utilisation (CCSU) technique known as calcium looping (CaL). The characterisation and functionalisation of waste ash materials procured from waste-to-energy plants (WTE) serve to pioneer a novel approach, converting existing waste liabilities into a potential urban mining source of calcium for commercially ready (TRL 9) CCSU applications. This new source will advance climate mitigation goals, close the waste loop, and align well with circular economy principles. Incineration ashes are known to contain rich and complex compositions of minerals, which can be exploited for valorisation in many applications. One of the known elements commonly found in incineration ash is calcium, a potential source for sorbents used in calcium looping. Valorisation of ash materials also alleviate landfilling and proposes new avenues for potential sustainable construction materials. With the development of a novel systematic protocol, various types of incineration and gasification ashes from waste treatment facilities were identified. Each identified ash material was treated optimally. By employing appropriate physical and chemical modifications, Ca-containing ashes were converted into Ca-rich ash-derived sorbent particles for CO₂ capture. Thermogravimetric Analysis testing over 20 isothermal carbonation-calcination cycles showed that fly ashes obtained from incineration and gasification processes exhibited uptake capacities comparable to limestone, up to 442 mg/g for APC and 327 mg/g for GFA. In the hot fluidised bed testing, GFA showed high cyclic stability (97%) under high 60% CO₂ conditions.