Predicting solvent degradation in absorption–based CO2 capture from industrial flue gases

Abstract

This work aims to predict solvent degradation rates in absorption-based CO2 capture processes using a 30 wt% aqueous monoethanolamine (MEA) solvent. A degradation model for MEA is developed and used to predict solvent degradation in full-scale capture processes. Mass transfer resistances and the solubility of O2 are considered to obtain a generalized and consistent degradation model. Degradation is evaluated for the capture process for flue gases with typical industrial compositions; a natural gas-fired power plant, a waste-to-energy plant, a coal-fired– power plant, and a cement plant. The impact of process modifications, such as absorber intercooling, dissolved O2 removal, a reduction in solvent residence times, and increased stripper pressures on degradation is evaluated.

The predicted degradation rate in the capture processes is approximately 90 to 150 g MEA/ton CO2 captured, and the composition of the flue gas was found to have a significant influence on the distribution of degradation throughout the process. Modifications to the process can significantly affect the overall degradation rate. Both absorber intercooling and removal of dissolved O2 may reduce the overall degradation by up to 40%, depending on the composition of the flue gas. A reduction in solvent residence times or pressure in the stripper has limited effects on the degradation in the case of MEA, because of the amine’s relatively low stability towards oxidative degradation. However, these process modifications look promising for more stable solvents.