More Efficient and Lower Energy-Intensive Process for Direct Air Capture

Abstract All direct air capture (DAC) technologies utilize either chemical sorbents or physical sorbents for removing CO₂ from the atmospheric air. These technologies tend to be energy-intensive due to the low concentration of CO₂ in the air (typically around a few hundred ppm), necessitating the processing of a large volume of air to capture significant quantities of CO₂. In this study, a DAC plant employing an aqueous basic solution to capture approximately one megaton of CO₂ yearly is considered to tackle this challenge. The study proposes a practical solution to enhance the process efficiency and reduce energy intensity. An experimental study using a packed tower shows that the CO₂ absorption rate into the water increases with the elevation of the CO₂ concentration in the input stream. This increase in the absorption rate is more pronounced at lower concentrations. The findings indicate that reducing the input air stream by 40% and recycling a thin stream (approximately 16%) of captured CO₂ into the input air stream can boost plant efficiency by 30% and decrease the required fan energy by at least 40%. This study demonstrates that the DAC process can be optimized, resulting in a levelized cost per ton of captured CO₂ of less than $87.