A new Peng-Robinson modification to enhance dew point estimations of natural gases

Abstract

Equations of state (EOSs) are widely used in calculations such as those involving reservoir simulation, process simulation, gas processing and transportation of natural gas. Predicting the phase envelope, specifically the dew points of natural gas, is among the important roles of EOSs. In this study, a modification is proposed to improve the predictions of dew point properties by the Peng-Robinson (PR) EOS, where the attraction parameter has been modified by a new empirical-based coefficient which is a function of reduced pressure, reduced temperature and critical density. In order to validate the modification, results are presented for four major properties of dew points consisting of the cricondentherm, cricondenbar, dew point temperature and dew point pressure. Furthermore, the performances of the original PR, Soave-Redlich-Kwong (SRK), Schmidt-Wenzel (SW) and GERG-2008 EOSs have been compared to predict the above four properties with respect to the experimental data. Having similar qualitative trends for the four properties, the results show that the modification of this study gives better predictions of the dew point curves, followed by the GERG EOS, which was developed particularly for processed natural gases. The SRK and SW EOSs have comparatively similar results and the PR EOS has the largest deviations.