Predictive Model of Thermodynamic Properties and CO₂ Corrosion of Carbon Steels in CCS Environments

Abstract

A thermodynamic model (U-Cal model) is proposed to predict the fugacity and water content in the CO₂-rich phase (gas or supercritical fluid), and the CO₂ solubility and pH in aqueous solutions in a CO₂ capture and storage environment, i.e., a CO₂ environment in a supercritical state. The values predicted by the U-Cal model agree well with measured values. The water content in the CO₂-rich phase increases to 1–10 g/L as a result of the mutual dissolution of CO₂ and H₂O. The increase in the solubility of CO₂ in aqueous solution and the decrease in the pH with increasing pressure are small. The CO₂ corrosion behavior of carbon steel is discussed to use the U-Cal model. In iron dissolution-dominant CO₂ corrosion in an aqueous solution with carbon steel, the corrosion rate can be understood as a function of the pH. In FeCO₃ formation-dominant CO₂ corrosion, it is considered that the corrosion progresses as FeCO₃ dissolves to supersaturation and then FeCO₃ precipitates on the surface of the material. The FeCO₃ precipitation behavior is predicted from the crystal growth rate equation. Corrosion of carbon steel in the CO₂-rich phase involves similar mechanisms to corrosion in an aqueous solution; however, the corrosion rate is lower.

 

This Paper was Originally Published in Japanese in Zairyo-to-Kankyo 72 (2023) 131–141.

CO₂ corrosion understanding of carbon steel in CO₂ capture and storage environments by applying the U-Cal model.