Corrosion of Carbon Steel in MDEA-Based CO₂ Capture Plant under Regenerator Condition: Effect of O₂ and HSS

The corrosion behavior of carbon steel UNS K02600 in 50 wt. % methyldiethanolamine (MDEA) solutions was investigated, under the background of the CO₂ capture process in fossil fuel-fired power plants for the carbon capture and storage (CCS) purpose. Series of experiments were conducted under regenerator conditions (120°C) with different combinations of CO₂ loading, O₂ and heat stable salts (HSS, including sulfate, formate, and N,N-bis(2-hydroxyethyl)glycine). The corrosion behavior of carbon steel was investigated by using electrochemical techniques (open corrosion 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 method. Results showed that the corrosion rate of carbon steel initially decreased and then stabilized with time in CO₂-loaded MDEA solution due to the formation of FeCO₃ layer except for the case of MDEA/CO₂/O₂/HSS with 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 FeCO₃ layer was discussed, which is a key issue to control corrosion in this environment.