Effect of diffuser on condensing flow in nozzles for carbon capture

Previous work investigated the possibility of using Laval nozzles for carbon capture. However, the rapid expansion in nozzles changes the pressure energy to kinetic energy, which resulted in low pressure at the nozzle exit. To reuse this energy, a diffuser is installed at the end of the nozzle. Therefore, a model is established to describe the CO₂ condensing flow in flue gas, and the influence of diffuser and flue gas saturation on the carbon capture is analyzed by CFD. The results show that Wilson point moves upstream by increasing the saturation degree of flue gas. When the saturation increases from 0.19 to 0.24, the limit saturation required for condensation decreases by 0.21, and the liquid CO₂ content and droplet size increase by 36.4% and 81.5%, respectively. If a diffuser with a smaller expansion angle or length wants to achieve the same carbon capture effect as a diffuser with a larger expansion angle or length, the pressure energy should be paid. On the contrary, under the premise of the same pressure loss ratio, the diffuser with smaller expansion angle or length has poor carbon capture effect.