Calcium looping (CaL), or the regenerative calcium cycle (RCC), is a second-generation carbon capture technology. It is the most developed form of carbonate looping, where a metal (M) is reversibly reacted between its carbonate form (MCO3) and its oxide form (MO) to separate carbon dioxide from other gases coming from either power generation or an industrial plant. In the calcium looping process, the two species are calcium carbonate (CaCO3) and calcium oxide (CaO). The captured carbon dioxide can then be transported to a storage site, used in enhanced oil recovery or used as a chemical feedstock. Calcium oxide is often referred to as the sorbent. Calcium looping is being developed as it is a more efficient, less toxic alternative to current post-combustion capture processes such as amine scrubbing. It also has interesting potential for integration with the cement industry. Basic concept CaCO3 ←→ CaO + CO2 ΔH = +178 kJ/mol There are two main steps in CaL: Calcination: Solid calcium carbonate is fed into a calciner, where it is heated to 850-950 °C to cause it to thermally decompose into gaseous carbon dioxide and solid calcium oxide (CaO). The almost-pure stream of CO2 is then removed and purified so that it is suitable for storage or use. This is the 'forward' reaction in the equation above. Carbonation: The solid CaO is removed from the calciner and fed into the carbonator. It is cooled to approximately 650 °C and is brought into contact with a flue gas containing a low to medium concentration of CO2. The CaO and CO2 react to form CaCO3, thus reducing the CO2 concentration in the flue gas to a level suitable for emission to the atmosphere. This is the 'backward' reaction in the equation above. Note that carbonation is calcination in reverse. Whilst the process can be theoretically performed an infinite number of times, the calcium oxide sorbent degrades as it is cycled. For this reason, it is necessary to remove (purge) some of the sorbent from the system and replace it with fresh sorbent (often in the carbonate form). The size of the purge stream compared with the amount of sorbent going round the cycle affects the process considerably. Background In the Ca-looping process, a CaO-based sorbent, typically derived from limestone, reacts via the reversible reaction described in Equation () and is repeatedly cycled between two vessels. The forward, endothermic step is called calcination while