Modeling and analysis of CO2 capture by aqueous ammonia + piperazine blended solution in a spray column

Abstract

Chemical scrubbing using NH3/PZ solution is a promising pathway for mitigating CO2 emission from fossil-fuel combustion. Herein, we developed an advanced model that can predict CO2 absorption using the blended solvent in a spray column. The model was established in the computational fluid dynamics framework coupled with the properties of the blended solvent. The blended properties were evaluated using the linear combination of each single solvent. The established model was also verified by our previous experimental results. The deviations were found to be within ±15%. Further case studies revealed crucial characteristics of the scrubbing process. Due to the entrainment effect, intensive back-mixing behavior was observed in the gas flow. Energy analysis showed that the heat for water warming-up and evaporation mainly comes from the heat released by the CO2 absorption. The profiles of the gaseous species demonstrated that gaseous concentrations of NH3 and H2O vapor quickly approached their equilibrium values, whereas gaseous CO2 concentration exhibited different variation trends along the column. We also found that the gas-side mass-transfer coefficient was two orders of magnitude greater than the liquid-side. Moreover, the spatial separation of the maximum mass-transfer coefficients and the driving force led to a low CO2 absorption rate. The comparisons of the upward and downward spraying schemes indicated that the upward spraying can mitigate the spatial separation and increase droplet residence time and volume fraction, significantly improving the CO2 removal efficiency from 48.2% to 55.9%.