PREDICTION OF GAS HYDRATE FORMATION CONDITIONS IN THE ABSENCE OF FREE WATER WITH FLASH CALCULATION

Gas hydrate formation is undesired in gas processing and distribution. Gas hydrates may form, even no liquid phase present in the system. When the water content of gas mixture is less than the water content of saturated gas, at low temperatures and high pressures, hydrate is formed and gas-hydrate equilibrium is established. Hydrate formation in the presence of liquid water, is addressed in many of papers and well modeled but there is little information about gas hydrate in the absence of liquid water. Therefore, it is important to have a thermodynamic model that correctly predicts gas hydrate formation without an aqueous phase. In this paper, the Michelsen’s flash algorithm is applied. The method used to calculate fugacity of hydrate composition, enables the fugacities of all of the components of the hydrate phase, including water, to be calculated as functions of temperature, pressure and composition. The model has been applied to a series of phase equilibrium calculations. This approach provides hydrate composition, vapor composition and hydrate phase fraction. Also, the stability of structures is examined by minimizing Gibbs free energy. Binary interaction coefficients for calculating vapor composition used in the Peng-Robinson equation of state, obtained by fitting the results to experimental data.