CO2 capture using hydrated lime: A study on the role of water evaporation

The construction industry generates 38% of Europe's total waste, highlighting the need for improved sustainability. This study proposes a mathematical model, implemented in COMSOL Multiphysics 6.2, which incorporates the three primary phenomena occurring during the carbonation of hydrated lime: chemical reaction, diffusion, and water evaporation. Water plays a crucial role in this process, and this work highlights its influence by incorporating rigorous water balances. During carbonation, most of the water in the system evaporates due to the exothermic nature of the reaction. However, a portion of the water becomes physically adsorbed onto the material and remains non-evaporable. A linear equation correlating the evaporation ratio with the total carbon content during the carbonation process is provided. Additionally, the influence of liquid water saturation is considered in both the reaction kinetics and the diffusion phenomena. Experimental results for total carbon uptake and the mass of evaporated water are presented and compared with model predictions, elucidating the effects of the initial water-to-solid ratio and carbon dioxide flow rates. An optimization of initial water-to-solid ratios is provided, achieving an optimal value of 0.3 for the carbonation of hydrated lime. In conclusion, this study contributes to a deeper understanding of CO2 capture through mineral carbonation, supporting efforts to enhance sustainability in the construction sector.