Experimental study and rate-based modeling on combined CO2 and SO2 absorption using aqueous NH3 in packed column

Abstract

Combined CO2 and SO2 absorption performance in a new combined capture process was evaluated in this work by experimental study using a lab-scale packed column system and a developed rate-based model in Aspen Plus. The combined absorption experiments were carried out to identify the impact of several key operating parameters, including flue gas SO2 and CO2 concentrations, CO2 and SO2 loadings, the absorption temperature, and the L/G ratio, on CO2 absorption and NH3 volatilization. Experimental results indicated that ≥85% CO2 absorption efficiency was achieved in 5wt% aqueous NH3 solvent containing lean CO2 loading at 0.2mol CO2/mol NH3 (C/N) and SO2 loading at 0.1mol SO2/mol NH3 (S/N). The rate-based model was developed using the electrolyte-NRTL method and the RateFrac module in Aspen Plus, and validated as compared to the present experimental results. The modeling results showed that the SO2 loading provided the similar effect on the CO2 mass transfer, the absorption efficiency and the heat of CO2 absorption as compared to the CO2 loading, however, the SO2 loading resulted in lower NH3 volatilization compared to CO2 loading. The lean CO2 loading and the solvent flow rate dynamic adjustment approaches in association with the lean NH3 solvent splitting process were studied to analyze the potential coordination of the combined absorption process and the sulfite treatment system. Maintaining 85% CO2 capture efficiency was possible when SO2 loading was increased from 0.1 to 0.2S/N by reducing the lean CO2 loading from 0.2 to 0.088C/N or increasing the solvent flow rate from 8 to 14.1L/h. The time window for the SO2 treatment by the precipitation process was increased with the increasing split ratio of the lean NH3 solvent splitting process that was associated with the dynamic adjustment approaches. In the present study, the discussion of the combined absorption experiments using the CO2 and SO2 loaded NH3 solvent, the developed rate-based model, and the operation strategies provided valuable contributions to the advancement of the combined CO2 and SO2 capture process.