CO ₂ Capture System by Calcium Looping with Steam-Enhanced Calcination

The decarbonization of hard-to-abate industrial sectors requires cost-effective CO2 capture technologies capable of delivering high-purity CO2 streams. This work presents the experimental evaluation of a novel packed-bed calcium looping process, CaL, incorporating steam-enhanced calcination to facilitate such objective. The concept exploits the thermal energy released during the exothermic carbonation of CaO to drive subsequent calcination via a rapid CO2 partial-pressure swing induced by steam injection. This approach enables autothermal operation and produces nearly pure CO2 after water condensation. Laboratory-scale tests were conducted in a 1.2-m-long (ID = 50 mm) fixed-bed reactor using lime from a natural limestone as the CaO sorbent. Maximum gas flow rates of up to 35 lN/min were introduced in the packed bed, corresponding to maximum gas hourly space velocities (GHSV) of approximately 3200 h–1 and minimum gas residence times slightly above 1 s. Successive carbonation–calcination cycles demonstrated CO2 capture efficiencies above 95% for feed gases containing 15–40 vol % CO2, with outlet streams during calcination composed of virtually 100% CO2 (dry basis). The maximum temperature reached during the carbonation stages was 835 °C, dictated by the thermodynamic equilibrium at the highest CO2 concentration tested. The extent of sorbent calcination conversion varied between 25 and 100%, depending on the initial calcination temperature and the stage duration. Temperature profiles confirmed that heat stored during carbonation is sufficient to sustain rapid calcination, while integration of brief chemical looping combustion stages within the bed provides additional thermal control and can balance heat losses and gas preheating requirements.