M.L. Huber, E.W. Lemmon, and R.T Jacobsen
For submission to Proceedings of the AGA 2000 Operations Conference, May 2000, Denver, Colorado
In this work we discuss a mixture model explicit in Helmholtz energy and its application to natural gas mixtures. The model is valid for a wide range of fluids and compositions. It covers all liquid, gas and supercritical states, and may be used to calculate all thermodynamic fluid properties (PVT, speed of sound, isochoric heat capacity, isobaric heat capacity, etc.) in addition to locating fluid phase boundaries. We show comparisons of a preliminary version of the model with experimental compressibility factor data and with the AGA-8 model in its range of validity for multi-component mixtures containing typical components of natural gas, including mixtures with hydrogen. In general, the estimated uncertainty of calculated density is 0.1% from 250 to 350 K in the gas phase, 0.2% for density elsewhere, 0.1% for the speed of sound below 10 MPa, 0.5% for the speed of sound above 10 MPa, and 1.5% for heat capacities.