CO 2 capture from air via CaO-carbonation using a solar-driven fluidized bed reactor—Effect of temperature and water vapor concentration

Abstract

A two-step thermochemical cyclic process to capture CO 2 from atmospheric air via consecutive CaO-carbonation CaCO 3-calcination reactions is investigated using concentrated solar energy. A kinetic analysis of the carbonation of CaO with dry and moist air containing 500 ppm CO 2 is performed in a fluidized bed solar reactor with particles directly exposed to high-flux thermal irradiation. The CO 2 removal capacity was examined in the temperature range 290–390 °C and water vapor concentration range 0–17%. Complete CO 2 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 CaCO 3 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 CaCO 3. The corresponding reaction orders and Arrhenius rate constants were determined by fitting to the experimental data.