Thermodynamic modeling of NH3-CO2-SO2-K2SO4-H2O system for combined CO2 and SO2 capture using aqueous NH3

Abstract

A new application of aqueous NH3 based post-combustion CO2 and SO2 combined capture process was proposed to simultaneously capture CO2 and SO2, and remove sulfite by solid (K2SO4) precipitation method. The thermodynamic model of the NH3-CO2-SO2-K2SO4-H2O system for the combined CO2 and SO2 capture process was developed and validated in this work to analyze the heat of CO2 and SO2 absorption in the NH3-CO2-SO2-H2O system, and the K2SO4 precipitation characteristics in the NH3-CO2-SO2-K2SO4-H2O system. The average heat of CO2 absorption in the NH3-CO2-H2O system at 40°C is around −73kJ/mol CO2 in 2.5wt% NH3 with CO2 loading between 0.2 and 0.5 C/N. The average heat of SO2 absorption in the NH3-SO2-H2O system at 40°C is around −120kJ/mol SO2 in 2.5wt% NH3 with SO2 loading between 0 and 0.5S/N. The average heat of CO2 absorption in the NH3-CO2-SO2-H2O system at 40°C is 77, 68, and 58kJ/mol CO2 in 2.5wt% NH3 with CO2 loading between 0.2 and 0.5 C/N, when SO2 loading is 0, 0.1, 0.2S/N, respectively. The solubility of K2SO4 increases with temperature, CO2 and SO2 loadings, but decreases with NH3 concentration in the CO2 and SO2 loaded aqueous NH3. The thermodynamic evaluation indicates that the combined CO2 and SO2 capture process could employ the typical absorption/regeneration process to simultaneously capture CO2 and SO2 in an absorber, thermally desorb CO2 in a stripper, and feasibly remove sulfite (oxidized to sulfate) content by precipitating K2SO4 from the lean NH3 solvent after the lean/rich heat exchanger.