Modeling and simulation of the combined removal of SO2 and CO2 by aqueous ammonia

Abstract

The combined removal of SO2 and CO2 using aqueous ammonia has many advantages over the conventional processes, such as the ability to capture multiple pollutants, the low cost of absorbent, high CO2 loading capacity, and the capacity to regenerate solvent at low temperature. In this paper, a closed-loop CO2 absorption-desorption process integrated with packed column flue gas desulfurization system was investigated. The CO2 absorption was modeled using the rigorous rate-based RateFrac model in Aspen Plus, whereas the SO2 column and CO2 stripper were modeled based on the RadFrac equilibrium model. The thermodynamic properties of the components were estimated with the Electrolyte NRTL model. The model was coupled with chemical equilibrium and kinetic reactions of the NH3-CO2-H2O and NH3-SO2-H2O system. The predicted results of temperature profile, variation in CO2 concentration along the column, SO2 removal efficiency, and CO2 separation rates agreed with published experimental results. To optimize the operating conditions, the impacts of performance parameters are investigated including flue gas temperature, concentration of CO2 and SO2 in flue gases, and the temperatures of the lean solution and ammoniated water. Furthermore, the performance efficiency of the stripper column is analyzed in terms of reboiler heat duty and CO2 regeneration rate, for the stripper operating pressure range of 2-20 bar and the stripper inlet temperature range of 60-105 degrees C. The results show that the suggested model is an adequate approach for the combined removal of CO2 and SO2 from the stack gases. (C) 2014 Society of Chemical Industry and John Wiley & Sons, Ltd