Application of Liquid State Models for the Time Efficient Phase Equilibrium Calculation of Supercritical CO2 and H2O at High Temperatures and Pressures

There are numerous models available to compute phase equilibrium composition of supercritical CO₂ and H₂O at high temperatures and pressures. In this paper a different approach is proposed where liquid state models (LSM) are used following liquid–liquid equilibrium (LLE) flash calculation in order to obtain phase compositions (solubility of CO₂ in the H₂O rich phase and that of H₂O in the CO₂ rich phase). Four LSM (two two-parameter models UNIQUAC and LSG, and two three-parameter models NRTL and GEM-RS) are investigated. The original forms of these models are inappropriate to represent the literature values; the binary interaction parameters are related with both pressure and temperature. These modified versions are suitable to generate phase composition values within 2–7 % deviation. Further investigations show that the LLE calculation is more time efficient than vapor–liquid equilibrium computation, meaning our approach can save computational expense for the numerical simulation of CO₂ flows in a reservoir. Comparison of the time efficiency of these LSM models with respect to other equations of state is given.