Carbon capture and storage (CCS) is regarded as one of the main alternatives for the reduction of anthropologic CO2 emissions. In the CCS process, CO2 from power plants and from other large CO2 point sources are captured and transported at dense (liquid or supercritical) conditions after which it is injected into storage sites. Accurately predicting internal corrosion rates in high-pressure CO2 environments is critical to the design and operation of pipelines used for CCS systems. In water-containing dense phase CO2 environments, corrosion rate increases in conjunction with humidity, typically reaching a critical humidity, beyond which corrosion rates become particularly high. The presence of impurities in the CO2 stream influence the solubility of water and hence the humidity and corrosivity of the CO2 stream. If the CO2 stream is under saturated and below a particular humidity level, then there can be significant cost saving on CCS projects, as this enables carbon steel pipelines to be used with confidence.
The purpose of this work is to develop models to calculate corrosion rates of CO2 systems with under-saturated water conditions in presence and absence of impurities. These models depend on the solubility of water in the CO2 rich phase at saturated conditions. A modified Peng-Robinson equation of state (EoS), E-PPR78 (Jaubert and Mutelet (2004)), available in literature is modified to match water solubility in the CO2 phase for CO2 systems in the presence and absence of impurities at both supercritical conditions and on both sides of the two phase-region.