Activity Coefficient Models for Calculations of Supercritical CO2 and H2O at High Temperatures and Pressures

Abstract

There are numerous models available to compute phase equilibrium compositions of supercritical CO2 and H2O at high temperatures and pressures. In this monograph, a different approach is developed where, activity coefficient models (ACM) are used, following fully LLE (liquid-liquid equilibrium) flash type computational methods, in order to obtain phase compositions (solubility of CO2 in the H2O-rich phase and that of H2O in the CO2-rich phase). Four ACM models (two two-parameter UNIQUAC and LSG, and two three-parameter NRTL and GEMRS) are investigated. Since the original forms of these models are inadequate to represent the literature values, the binary interaction parameters have been related with both pressure and temperature. These modified versions are able to regenerate the phase composition values within 2-7% deviations. Further investigations also show that LLE calculations are more time-efficient than VLE computations, meaning our approach can save computational expenses for the numerical simulations of CO2 flow in reservoirs. Comparisons of time efficiency of these ACM models with respect to Redlich-Kwong and Span-Wagner equations of state are shown.