Spray–gas counterflow interactions in an absorber column

Abstract

Reducing COQ emissions is essential for meeting global climate targets. Capture technologies, widely used to reduce CO2, must be carefully optimized to balance efficiency with sustainability. Spray columns provide large interfacial area and can enhance absorption performance, yet their successful deployment requires minimizing drawbacks such as solvent losses or added operational complexity. To achieve this, it is necessary to fully understand the behavior of the key system components, with the atomizer being of primary importance. Its performance can be strongly influenced by the interaction with an ambient counterflow. In this study twin-fluid effervescent, hollow-cone and full-cone pressure swirl atomizers were investigated under the counterflow conditions. A vertical wind tunnel was used to simulate the counterflow with gas velocities ranging from 0 to 1 m/s. The gas flow was seeded with a water mist, generated by an ultrasonic atomizer, so that the velocity of the continuous gas-flow and discrete droplet phase could be resolved. Simultaneous velocity and droplet size measurements were performed using a 1D Phase Doppler anemometer (PDA) at various axial positions ranging from 0 mm (the atomizer tip position) to 600 mm downstream. Experimental data were compared with numerical results (Ansys Fluent 2024 R2) and analytical solutions. The gas flow field within the spray region was resolved, highlighting the significant influence of liquid-wall interactions. Liquid velocity and the superficial counterflow velocity are the primary parameters controlling spray behavior. Higher liquid velocities lead to increased counterflow velocities in the spray region, which yields an overestimation in the prediction of the entrained droplet sizes. The simulation predicted gas flow velocity adequately and captured key flow field trends across all atomizer types. However, larger deviations were observed for effervescent atomizers, likely due to their complex two-phase flow and primary breakup mechanisms. Counterflow velocity maldistribution was associated with pressure losses, while gas entrainment into the spray accounted for only 0.3% of the total counterflow gas flow rate, suggesting that influence of spray/counterflow mixing on mass transfer in the spray region is minimal.