Large eddy simulation of CO2 direct air capture units in different atmospheric boundary layer wind profiles

Direct air capture of CO₂ (DAC) is one of the promising technologies for removing CO₂ from the atmosphere and combating global warming. This study explores the effect of wind velocity on the atmospheric dispersion of CO₂-depleted air released from the outlet of DAC units. This is an important consideration in determining the optimum design and location of DAC units in a large-scale CO₂ capture plant and ultimately the overall land footprint requirement. We considered a crosswind cooling tower as a single DAC absorption unit. Following its validation with field-scale and lab-scale experimental data as well as direct numerical simulation (DNS) data, the large eddy simulation (LES) technique was used to simulate the interaction between the longitudinal atmospheric boundary layer wind and the vertical plume of CO₂-depleted air exiting the DAC unit. The behaviour of the DAC-wind flow regime depends on the velocity ratio of the DAC vertical flow and the longitudinal wind velocity (R_U) which can be divided into three DAC-wind flow regimes: $R_U\gg 1$, $R_U\approx 1$, and $R_U\ll 1$. As the wind velocity increases, the CO₂-depleted air is mixed faster with the free-stream atmospheric flow. Some CO₂-depleted air re-enters the unit through the leeward inlet at moderate and high wind velocities. Using the LES results, practical statistical relationships were developed for CO₂-depleted plume concentration as a function of distance downwind of a DAC unit for different DAC-wind flow regimes. The findings of this study provide insights into the impact of wind on DAC unit performance and the optimal distance required between the units in a large-scale DAC plant.