Predicting Possible Effects of H2S Impurity on CO2 Transportation and Geological Storage

For CO2 geological storage, permitting impurities, such as H2S, in CO2 streams can lead to a great potential for capital and energy savings for CO2 capture and separation, but it also increases costs and risk management for transportation and storage. To evaluate the cost benefits, using a recently developed model (Ji, X.; Zhu, C. Geochim. Cosmochim. Acta 2012, 91, 40-59), this study predicts phase equilibria and thermodynamic properties of the system H2S-CO2-H2O-NaCl under transportation and storage conditions and discusses potential effects of H2S on transportation and storage. The prediction shows that inclusion of H2S in CO2 streams may lead to two-phase flow. For H2S-CO2 mixtures, at a given temperature, the bubble and dew pressures decrease with increasing H2S content, while the mass density increases at low pressures and decreases at high pressures. For the CO2-H2S-H2O system, the total gas solubility increases while the mass density of the aqueous solution with dissolved gas decreases. For the CO2-H2S-H2O-NaCl system, at a given temperature, pressure and NaCl concentration, the solubility of the gas mixture in aqueous phase increases with increasing H2S content and then decreases, while the mass density of aqueous solution decreases and may be lower than the mass density of the solution without gas dissolution.