L. F. Baladão Journal of Engineering Research and Application www.ijera.com ISSN : 2248-9622, Vol. 8, Issue 8 (Part -III) Aug 2018, pp 25-34 www.ijera.com DOI: 10.9790/9622-0808032534 25 | Page Comparison of the GERG-2008 and Peng-Robinson Equations of State for Natural Gas Mixtures L. F. Baladão*, R. P. Soares**, P. R. B. Fernandes*** * (Virtual Laboratory for Properties Prediction, Chemical Engineering Department, Federal University of Rio Grande do Sul, Brazil ** (Virtual Laboratory for Properties Prediction, Chemical Engineering Department, Federal University of Rio Grande do Sul, Brazil *** (Group of Integration, Modeling, Simulation and Optimization of Processes, Chemical Engineering Department, Federal University of Rio Grande do Sul, Brazil Corresponding author : L. F. Baladão ABSTRACT This work compares two equations of state applicable to natural gas mixtures, namely the GERG-2008 equation of state (EoS), which was proposed as a high-accuracy reference model, and the traditional Peng-Robinson (PR) EoS. This comparison is done in terms of the accuracy of calculated properties such as pressure and density with respect to experimental data from the literature, as well as in vapor-liquid equilibria (VLE) calculations. It was found that the GERG-2008 EoS gives better results in comparison with PR for the calculation of density and pressure, generating deviations in the range from 0.1 to 1%. For the VLE calculations, the accuracy of GERG- 2008 was slightly better than PR. However, this accuracy is accompanied with increased mathematical complexity, resulting in increased computational time: 2 to 6 times higher. This is due to the fact that the calculation of molar density of GERG-2008 requires an iterative calculation step for the liquid and vapor phases, which makes the resolution of the VLE calculation slower. Keywords - Equation of state, GERG-2008, Natural gas, Multiparametric Equation, Peng-Robinson --------------------------------------------------------------------------------------------------------------------------------------- DATE OF SUBMISSION:16-08-2018 DATE OF ACCEPTANCE: 30-08-2018 --------------------------------------------------------------------------------------------------------------------------------------------------- I. INTRODUCTION The increasing global energy demand associated with environmental concerns has boosted the search for energy sources cleaner than petroleum and coal. Natural gas, despite being a non-renewable fuel, is now well stablished in the global energy market due to recent discoveries and exploitation of unconventional sources. In addition, among the most used non-renewables, natural gas causes the least environmental impact. Therefore, accurate calculations of thermodynamic properties for natural gas and other mixtures formed by its components are of great importance for basic engineering. Examples for this are processing, transport, and storage of liquefied natural gas. During the 70’s, empirical multiparametric equations of state became available and were employed as reliable sources of thermodynamic property data in scientific and engineering applications. The development of such equations continued over the past 20 years. For the thermodynamic properties of mixtures, Helmholtz energy models based on multi- fluid approaches were introduced to obtain high accuracy. As a consequence, appropriate software tools became available, thus increasing the impact of precise empirical models property in practical applications [1]. The GERG-2008 EoS [2] was developed as an extension of the GERG-2004 equation of state [3] in order to constitute a reference model for natural gas and its mixtures. Both equations have the same mathematical formalism, differing only by the number of terms [2]. The GERG-2008 EoS is valid for all mixtures consisting of 21 components of natural gas (Table 1) in any arbitrary combination or concentration. The calculation of the thermodynamic properties of multicomponent mixtures by GERG- 2008 EoS is based on equations developed for binary mixtures, covering a total of 210 pairs of substances. In this study, the accuracy of the GERG- 2008 EoS was evaluated in property calculation (either pressure or molar density) for binary and multicomponent mixtures with respect to experimental data from literature. The results were compared for reference with the standard Peng- Robinson EoS [4]. Moreover, the accuracy in vapor- liquid-equilibria (VLE) computations for 12 binary mixtures was comparatively assessed for both EoS. RESEARCH ARTICLE OPEN ACCESS