Influence of Composition on the Thermophysical Properties of LNG

The saturated liquid density deviations were compared using the PR, RSK (Advanced), AGA8, and GERG2008 EoSes. The bubble pressure deviations, saturated liquid densities, isobaric specific heat capacities, and enthalpy of vaporization were compared using the PR, RSK (Advanced) and GERG2008 EoSes. The GERG2008 EoS was used to analyse the effect of nitrogen and heavy alkanes on the thermophysical properties of LNG mixtures. Experimental density data was used to compare the accuracy of the Revised Klosek-McKinley method and the GERG2008 EoS.

When tested with experimental data, the overall results showed that the GERG2008 and AGA8 EoSes predicted densities of LNG similarly. The PR EoS accuracy was dependent on the composition of the LNG mixture, predicting densities more accurately when components are gaseous at ambient conditions, while the RSK (Advanced) EoS predicted densities poorly. The GERG2008 EoS predicted bubble pressure and isobaric specific heat capacities more accurately that the other EoSes. Its accuracy of predicting bubble pressure is dependent on the concentration of methane, isobutane, and n-butane in the LNG mixture.

As the nitrogen concentration increased in the LNG mixture the bubble temperature and isobaric specific heat capacity decreased. The saturated liquid density increased non-linearly with increase in nitrogen concentration, while the latent heat of vaporization was dependent on the concentration of nitrogen and methane in the mixture. As heavy alkane concentration increased, the isobaric specific heat capacity decreased, but the latent heat of vaporization and density increased. For a particular LNG composition, as bubble temperature increased, the density and latent heat of vaporization decreased but the isobaric specific heat capacity increased. The presence of nitrogen in the LNG mixture had the opposite effect on the latent heat of vaporization for a particular LNG composition.

The Revised Klosek-McKinley method predicted density more accurately than the GERG2008 EoS, except when the LNG mixtures contain no nitrogen and the heaviest components were isopentane and n-pentane.