Prediction of CO2capture performance of a direct air capture unit under representative atmospheric flow conditions using large eddy simulation

Abstract

The removal of carbon dioxide (CO2) from the atmosphere using direct air capture (DAC) is crucial in achieving the net-zero emissions target and combating global warming. We develop a new numerical model that predicts the performance of DAC units under representative atmospheric flow conditions which captures the interaction between these units and the instantaneous flow fields. A new boundary condition for the CO2concentration associated with the CO2-depleted exit plume was developed. This boundary condition dynamically calculates the time-varying fraction of CO2removed from the air (capture rate) and the total mass of CO2captured by the system per unit time (capture amount). We have also conducted experiments in a lab-scale DAC unit at different inlet air velocities. The experiment showed that both the CO2capture rate and the capture amount depend on the unit’s inlet airflow velocity. Specifically, the CO2capture rate decreases with an increase in unit inlet airflow velocity, while the CO2capture amount increases. These data were used to validate our computational fluid dynamics analysis using a large eddy simulation (LES) approach. After validating the new boundary condition model with experimental data in still air, the LES simulations were extended to include the interaction of atmospheric boundary layer wind with individual DAC units. The CO2capture rate and capture amount are almost constant in still air, whilst they strongly fluctuate for wind speeds above 7 m/s. The amplitude of these fluctuations grows with increasing wind velocity. The LES results showed that when the wind velocity increased, both the CO2capture rate and the overall mean CO2capture amount of an individual DAC unit were reduced. In strong winds of 9 m/s, the total CO2mass removal was reduced by up to 7.5 % ± 6.5 % over one year. The new boundary condition model can more accurately predict the overall CO2capture characteristics of large-scale DAC plants in complex real environmental conditions.