The Effect Of Gas Components And Thermodynamic Inhibitors On Hydrate Phase Equilibrium

The exploitation and application of gas hydrate are based on the study of the phase equilibrium of hydrates.The gas can be collected after the hydrate dissociated by changing the stable environment conditions.The thermodynamic inhibitors are always used to prevent the hydrate blocking the gas pipeline,because the formation conditions of the hydrate can be changed by adding thermodynamic inhibitors.It is the key for hydrates exploitation and application to understand the phase equilibrium conditions of gas hydrate and then control the formation and decomposition conditions of hydrates.In this paper,the van der Waals-Platteeuw model is used to predict the phase equilibrium of gas hydrate,and the program is compiled with the software platform of Matlab.On this basis,the effects of mole fraction of gas and thermodynamic inhibitors on the phase equilibrium of hydrates are studied.According to the mole fraction of gases,the phase equilibria of two component?CH₄-C₂H₆?CH₄-C₃H₈?CH₄-CO₂ and CH₄-H₂S?gas hydrates in pure water system were studied.The phase equilibria of single component gases?CH₄?C₂H₆?CO₂ and H₂S?in CH₃OH and NaCl systems with different mass fractions were studied for thermodynamic inhibitors.According to the combined effects of gas mole fraction and thermodynamic inhibitors,the phase equilibria of two component?CH₄-C₂H₆?gas hydrates under different mass fraction of CH₃OH and NaCl were studied respectively.The results show that:CH₄ and C₂H₆,C₃H₈ and H₂S respectively when mixed hydrate phase equilibrium pressure increases with the mole fraction of CH₄ increases,and when the molar fraction of CH₄ were greater than 70%,90%and 70%,corresponding to the binary gas hydrate phase equilibrium pressure increases with the mole fraction of CH4 and CH4-CO2increased.Hydrate phase equilibrium pressure uniformly increases with the mole fraction of CH4 is increased.With the increase of the mass fraction of the thermodynamic inhibitors,the equilibrium pressure of the hydrate phase increases gradually.In addition,the temperature has an obvious effect on the inhibition effect of the thermodynamic inhibitors.In general,when the temperature is greater than 273K,the inhibition effect of the inhibitors on the hydrate is more obvious.There are mainly 3 factors that influence the phase equilibrium of CH₄-C₂H₆hydrate under the condition of thermodynamic inhibitor:the mass fraction of inhibitor,the mole fraction of gas components and the phase equilibrium temperature.And under different conditions,the main factors that affect the phase equilibrium of hydrate are different.In the CH₄-C₂H₆ hydrate,when the CH₄ molar fraction is between 30%-70%,the change of CH₄mole fraction will hardly affect the phase equilibrium of hydrate.The main factors that influence the phase equilibrium of the hydrate are temperature and thermodynamics inhibitors.When the mole fraction of CH₄ is greater than 70%and less than 30%,the thermodynamic equilibrium,the mole fraction of gas components and the phase equilibrium temperature will affect the phase equilibrium pressure of gas hydrate.