CO2 capture from air via CaO-carbonation using a solar-driven fluidized bed reactor—Effect of temperature and water vapor concentration

A two-step thermochemical cyclic process to capture CO2 from atmospheric air via consecutive CaO-carbonation CaCO3-calcination reactions is investigated using concentrated solar energy. A kinetic analysis of the carbonation of CaO with dry and moist air containing 500 ppm CO2 is performed in a fluidized bed solar reactor with particles directly exposed to high-flux thermal irradiation. The CO2 removal capacity was examined in the temperature range 290–390 °C and water vapor concentration range 0–17%. Complete CO2 removal was achieved from a continuous flow of moist air at 390 °C and residence times of less than 1.5 s, while the extent of CaO-carbonation was almost doubled by the addition of water vapor. Kinetic models that account for consecutive chemically and diffusion-controlled regimes were applied to describe the carbonation rate with dry air, limited initially through interface reactions and later through reactant penetration across the layer of CaCO3 until reaching the unreacted core. In contrast, a chemically-controlled rate law was applied to describe the augmented carbonation rate with moist air, which proceeded through the formation of an interface of water and/or OH ions at the solid surface not covered by CaCO3. The corresponding reaction orders and Arrhenius rate constants were determined by fitting to the experimental data.