Experimental Research And Numerical Simulation Of Ammonia-Based CO₂ Absorption In A Spray Column

capture and storage technology is an important approach to reduce CO₂ emissions. Because of its high CO₂ removal efficiency, large absorptive capacity, weak tendency to degradation and its low cost, ammonia-based CO₂ capture technique has become a promising means among various CO₂ removal approaches, despite the problem of secondary pollution caused by ammonia volatilization.This paper designed and built a spray column, and performed the ammonia-based CO₂ capture experiments on it. The effects of the operating parameters ?such as ammonia concentration, aqueous ammonia flow rate, flue gas flow rate, CO₂ concentration, temperature and nozzle combination etc.? on the CO₂ removal efficiency, ammonia slip and the ammonia volatilization amount per mole CO₂ removal have been studied. The results show that CO₂ removal efficiency can be up to 93% utilizing the spray column. The increase of the ammonia concentration and aqueous ammonia flow rate can significantly improve CO₂ removal efficiency, but also make a significant increase in ammonia slip. However, when the ammonia concentration increases, the ammonia volatilization amount per mole CO₂ removal significantly increase; when the aqueous ammonia flow rate increases, the ammonia volatilization amount per mole CO₂ removal hardly increase. The increase of the inlet flue gas flow rate and the CO₂ concentration will reduce ammonia slip and the ammonia volatilization amount per mole CO₂ removal, but also make the CO₂ removal efficiency decrease. When aqueous ammonia temperature is lower than 35?, the temperature of aqueous ammonia and flue gas have little effect on the CO₂ removal efficiency and ammonia slip. Furthermore, according to the experiment data, the effect of the above parameters on the volumetric overall mass-transfer coefficient is also analyzed, and its correlation with ammonia molar concentration, flow flux of aqueous ammonia and flue gas flow flux is obtained by fitting curves.Besides, a coupled model incorporated two-phase flow, heat and mass transfer was established based on the two-film theory to model the ammonia-based CO₂ absorption process in the spray column. Numerical simulations were conducted to predict the flow field, temperature field, pressure field and CO₂ concentration field in the spray column. And compared to the experimental data, the comprehensive CFD model was validated. Numerical studies show that, the influence of local gas velocity on local CO₂ absorption rate is the result of combination of local turbulence and local liquid-gas ratio. The atomizing nozzle angle should be 40 degree for this model. With the increase of the liquid droplet size and spray velocity, the CO₂ removal efficiency and the volumetric overall mass-transfer coefficient gradually reduce. That is the result of the reduction of the effective mass-transfer area in unit volume caused by the reduction of the liquid droplet retention time. And the increase of column height can improve the CO₂ removal efficiency and the volumetric overall mass-transfer coefficient due to the extension of the residence time of flue gas. Finally, through orthogonal experimental design method, the order of experiment factors affecting CO₂ removal efficiency were achieved:ammonia concentration> aqueous ammonia flow rate> flue gas flow rate>CO₂ concentration> aqueous ammonia temperature> flue gas temperature.