Thermodynamic modeling of sour gas mixture (CH4/C3H8/H2S) hydrate formation in the presence of thermodynamic inhibitors mono ethylene glycol, NaCl, and CaCl2 using the ion pair concept

Abstract

Thermodynamic modeling of hydrate equilibrium conditions for sour gas mixture (CH4/C3H8/H2S) in the presence of pure water and thermodynamic inhibitor(s) (MEG, NaCl, and CaCl2) was investigated in this study. Hydrate and vapor phases were evaluated using the van der Waals and Plattueew model, and the Peng-Robinson EoS along with the classic van der Waals mixing rule, respectively. As a different approach, by combining non-synonymous salt ions and forming ion pairs, they can be considered as molecular species. So ion pair concept was used to investigate liquid phase and calculate water activity coefficient in this phase. For short-range and long-range forces, the NRTL molecular model and the Pitzer-Debye-Hückel equation was used, respectively. The results of experimental data in the previous work were compared with the results of the proposed model and PVTsim Nova 3.0 software, and it was discovered that they have an acceptable agreement together. The average deviation in pressure (AARDP %) related to the model is 0.36% to 4.34% and 3.41% to 5.68% related to the software.