Abstract To improve the process and performance of CO2 capture with ammonia by chemical absorption, a vortex flow-based multistage spray reactor was designed to evaluate the enhancement effect for post-combustion CO2 capture with ammonia. The process intensification analysis based on flow patterns from a CFD (computational fluid dynamics) simulation indicated that the vortex flow presented multi-dimensional velocities including a V-shaped tangential velocity profile and non-uniform axial velocity profile, which resulted in enhancement of gas–liquid contact, mixing, mass transfer, and reaction compared to non-vortex flow. Furthermore, the CO2 capture characteristics were examined at varied operating parameters. It was found that the capture efficiency E increased with increasing ammonia concentration and liquid flow rate but decreased with increasing CO2 inlet concentration and gas flow rate. Meanwhile, the overall gas phase mass transfer coefficient Kga increased with increasing ammonia concentration, liquid flow rate, and gas flow rates but decreased with increasing CO2 inlet concentration. Within the measured range, the E and Kga varied from 72.05 to 86.72% and 0.31–0.49 × 10−3 kmol/m3 kPa s, respectively. Importantly, vortex flow presents relative enhancements of 7–15% in E and 18–33% in Kga compared with non-vortex flow depending on the operating parameters.