Analysis of the Techniques for Measuring the Equilibrium Conditions of Gas Hydrates Formation

The factors affecting the experimental determination of the conditions of gas hydrates phase equilibria in various systems using the stepwise heating and constant-rate heating procedures in the GHA350 stirring autoclave or the RCS6 rocking cells were analyzed. It was found that more reliable results are obtained with the GHA350 autoclave, which gives more intense agitation of the fluids. The stepwise heating method is a priori a more reliable way for determination of the equilibrium conditions of hydrate formation suitable for any system. However, its use requires a greater expenditure of time. With the alternative method of heating at a constant rate of 0.1-1 deg/h it is possible to reduce the length of a single measurement considerably. Anyway, if it is used to obtain reliable experimental data it is necessary to select a heating rate in line with the mixing efficiency of the employed apparatus, the type of system being investigated, and other factors. For most systems the results of measuring the hydrate equilibrium temperatures by the stepwise method and by continuous heating at 0.1 deg/h using the GHA350 autoclave agree within the experimental error limits. Greater discrepancy between the results of the two methods is observed for gas hydrates in concentrated salt solutions that have high viscosity at low temperatures (below –25°C).