Comparing different methods for prediction of liquefied natural gas densities

The densities of several liquefied natural gas (LNG) mixtures and pure methane using different equations of state and correlations have been predicted and compared with the experimental values. The equations of state were Peng-Robinson (PR), Soave-Redlich-Kwong (SRK), Usdin-McAuliffe (UM), Volume Translated SRK (VT SRK), Nasrifar-Moshfeghian (NM) and modified Nasrifar-Moshfeghian (MNM). The correlations were Racket-Spencer-Danner (RSD), Hankinson-Thompson (HT), Nasrifar-Moshfeghian (NML), and simplified Nasrifar-Moshfeghian (S-NML). It has been attempted to choose the most popular EoSs and correlations with the highest accuracy for predicting the density of LNG mixtures. For the systems under study, the NM EoS had the least average absolute deviation of liquid density among the equations of state evaluated, and the NML correlation predicted the LNG liquid density more accurately than the other liquid density correlations. The accuracy of this method for prediction of methane liquid density is also as good as that of RSD's and HT's. Moreover, using the NM EoS, density as a function of temperature and pressure for the whole phase envelope has been plotted. Results, especially near the critical point, show good compatibility between the bubble and dew point densities. The predicted values of methane vapor and liquid density/specific volume up to near the critical point based on these equations of state are also given. No fitting or adjustable parameters were used for any of the EoSs or correlations.