CO2 absorption in pilot-scale multi-nozzle spray towers: CFD and experimental study of flow and mass transfer dynamics

This study presents a comprehensive investigation into CO 2 absorption in a pilot-scale, multi-nozzle spray tower operating under industrial conditions. Through the integration of pilot-scale experimentation and reactive CFD modeling, this work advances the quantitative understanding of coupled hydrodynamic behavior and mass transfer phenomena in conditions representative of full-scale operations. A modular carbon capture unit was built and deployed at a Swedish waste-to-energy facility to experimentally investigate gas–liquid flow behavior and CO 2 absorption performance using a 15 wt% NaOH solution as the absorbent. The experimental data provided the basis for validating a reactive Euler–Lagrange multiphase CFD model, which elucidated gas–liquid interactions, including droplet dispersion, turbulent flow structures, mixing, and interphase mass transfer. Sensitivity analyses across a range of gas (50–200 m 3 /h) and liquid flow rates demonstrate how operating conditions influence droplet trajectories, residence time, and CO 2 absorption efficiency. Flow segmentation identifies two distinct zones where turbulence and recirculation enhance mixing and mass transfer, with side gas inlet configurations providing more effective radial mixing compared to axial inlet designs. Results demonstrate that tuning the liquid-to-gas (L/G) ratio, droplet characteristics, and gas inlet design significantly influences CO 2 capture, offering practical guidance for the next generation of spray-based carbon capture systems. The study investigated L/G ratios ranging from 2.3 to 7.0 kg/kg and examined the effects of droplet sizes between 200 and 3000 μm, observing that droplets predominantly in the lower size range exhibited improved dispersion and extended residence times, which are favorable for effective CO 2 absorption. The findings provide a direct basis for optimizing hydrodynamics and scaling spray tower absorbers for effective CO 2 capture in real-world systems. • Coupled experimental-CFD study of pilot-scale CO 2 capture in a multi-nozzle spray tower under industrial operating conditions. • Quantified the impact of gas/liquid flow rates on droplet dynamics, mass transfer, and absorption efficiency. • Investigated droplet transport behavior and solvent-phase dispersion using an Euler–Lagrange reactive multiphase model. • Characterized turbulent spray dynamics affecting CO 2 capture efficiency. • Quantified performance differences between side- and axial-inlet gas configurations, revealing key design sensitivities. • Identified key hydrodynamic and mass transfer parameters critical for scaling up spray tower absorbers to industrial applications.