Water Content of CO₂ rich Mixtures: Measurements and Modeling using the Cubic-Plus-Association Equation of State

Natural gas is well known as the cleanest fossil fuel. However, it is estimated that more than 40% of the remaining conventional natural gas reserves are deemed to be acidic, i.e., containing significant quantities of CO2 and H2S. As the global consumption of natural gas is expected to steadily grow, the demand will be met by sources such as sour/acid gas fields. In some specific applications that require cryogenic processes (LNG, NGL recovery), this issue is commonly addressed upstream of the gas dehydration unit, so that the gas is already sweet when arriving at the drying section. In the other cases, the effect of the acidic species on the gas water content is often not properly accounted for, even though an accurate appraisal of the water content is paramount for the sizing of dehydration units.
In this contribution, the water contents of the ternary system CO2 + CH4 + H2O were determined for various CO2 to CH4 ratios. New experimental data were obtained using a Tuneable Diode Laser Spectroscopy (TDLS) setup, with an accuracy of +/- 1%. The Soave-Redlich-Kwong and the Peng Robinson equations of state combined with the Cubic-Plus Association were used to estimate water content on CO2 rich gas mixtures.