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.