Corrosion of Carbon Steel in MDEA-Based CO2 Capture Plants Under Regenerator Conditions: Effects of O2 and Heat-Stable Salts

The corrosion behavior of carbon steel UNS K02600 in 50 wt% methyldiethanolamine solutions was investigated in the back-ground of the carbon dioxide (CO2) capture process in fossil fuel-fired power plants for the purpose of carbon capture and storage. A series of experiments was conducted under regenerator conditions (120°C) with different combinations of CO2 loading (0.3 mol/mol and 0.05 mol/mol), O2, and heat-stable salts (including sulfate, formate, and N,N-bis[2-hydroxyethyl] glycine). The corrosion behavior of carbon steel was investigated using electrochemical techniques (open circuit potential, linear polarization resistance, and potentiodynamic polarization), surface analytical techniques (scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction), and weight-loss methods. The results showed that the corrosion rate of carbon steel initially decreased and then stabilized with time in CO2-loaded methyldiethanolamine solution due to the formation of an iron carbonate (FeCO3) layer, with the exception of methyldiethanolamine/CO2/O2/heat-stable salts, which exhibited a low CO2 loading (0.05 mol/mol). It was found that the presence of HSS significantly accelerated the corrosion process at low CO2 loading, whereas the effect of oxygen on the corrosion rate was not significant at low CO2 loading. The formation mechanism of the FeCO3 layer, which is a key issue in the control of corrosion in these environments, was discussed.