REVISITING THE HAMMERSCHMIDT EQUATION: EFFECT OF OPERATING CONDITIONS ON THE SELECTION OF THE HAMMERSCHMIDT CONSTANT

摘要

Gas hydrates represent an operational hazard causing issues related to lost production and safety. For more than 80 years, the Hammerschmidt equation has been in use to help predict the effect of thermodynamic hydrate inhibitors. While more sophisticated tools are available, the Hammerschmidt equation remains popular for its balance of accuracy with simplicity. Values for the Hammerschmidt constant reported in the literature often vary between sources or are given as a range. In reviewing the literature, there is little discussion or explanation as to the source of this variation. At first inspection, one might assume that this range in the value of the constant is due to an uncertainty. However, upon further investigation, this does not appear to be completely the case. Hydrate equilibrium curves with various levels of inhibitor were compared with the predicted Hammerschmidt curves using different values for the constant. It was readily observed that the varying values for the Hammerschmidt constant are a function of the operating (pressure and temperature) conditions. In this way, one value for the constant is valid for low pressures while a second value is valid at high pressures. As pressure increases, there is a distinct transition from one value of the Hammerschmidt constant to another. This transition is more pronounced as the inhibitor concentration increases. A comparison of Hammerschmidt constants was performed for various inhibitors and operating conditions. The valid Hammerschmidt constants for low pressure and high pressure are shown along with a method to incorporate the transition between the constants. This approach can be applied to maintain the simplicity of the Hammerschmidt approach while improving the accuracy of the hydrate curve predictions over the potential operating range.