Prediction of the Condensation Behavior of Natural Gas:  A Comparative Study of the Peng−Robinson and the Simplified-Perturbed-Hard-Chain Theory Equations of State

Abstract

For the prediction of the condensation behavior of natural gas, one has to select an equation of state (EoS) which will be accurate in the temperature and pressure range of interest (10 < P/bar < 70 bar and 250 < T/K < 310). Another requirement of the selected EoS is that it easily can be adapted to a characterization procedure for the heavy-end fraction. For that purpose, two equations were tested: the Peng−Robinson (PR), which is one of the most applied cubic EoS, and the simplified-perturbed-hard-chain theory (SPHCT) equation, which is one of the simplest EoS based on sound statistical mechanical principles. In the underlying study, their predictive capabilities for the prediction of saturated vapor pressures of pure compounds and vapor/liquid equilibrium pressures for binary mixtures are compared. Only components present in natural gas are considered. In addition, new pure-component parameters for the SPHCT EoS for n-alkanes are evaluated. Also a method to find the characteristic energy for non-n-alkane molecules is proposed in this study. This study revealed that the PR EoS predicts more accurately the liquid phase composition, whereas the SPHCT EoS is superior for the gas phase prediction, especially for asymmetric binary mixtures. It was concluded that, with respect to the purpose of this study, both EoS, when used with optimum binary interaction parameters, have an equivalent descriptive accuracy. Therefore, the simpler PR EoS was preferred to describe natural gas mixtures.

Prediction of High‐Pressure Phase Equilibria using Cubic EOS: What Can Be Learned?

“…In contrast to that, the VLE of the methane-alkane systems at higher temperatures is extremely important from a practical point of view (Voulgaris et al, 1998). Both the PSRK and C4EOS models are similarly accurate in predicting the data ( Figure 10).…”

Modeling Mutual Solubility of n-alkanes and CO2 Using SAFT Equation of State

“…25 However, a careful examination of vapor pressure data 5 showed that with a good approximation a methyl-or ethyl-branched alkane (carbon number n C ) behaves thermodynamically as a shorter linear alkane (carbon number n′ C < n C ). The equivalent carbon number n′ C is defined in the same spirit as in the work of Voulgaris et al 26 It is calculated by interpolating the plot of n-alkane normal boiling point vs carbon number using the normal boiling point of the branched alkane. The value of n′ C determined by this method is generally noninteger.…”

Calculation of Phase Equilibrium of Natural Gases with the Peng-Robinson and PC-SAFT Equations of State

“…Voulgaris et al (1998) compare the performance of the Peng-Robinson (Peng and Robinson, 1976) and SimplifiedPerturbed-Hard-Chain Theory (Kim et al, 1986) EOS in predictions of the condensation behavior of natural gases. Bolland (2005, 2006) (Gross and Sadowski, 2001) in the evaluation of thermodynamic properties of synthetic natural gas mixtures.…”