A GERG (Groupe EurQpeen de Recherches Gazieres) equation of state (EOS) is presented to calculate the compressibility factor of natural gases. The equation, which does not require detailed gas analysis, can predict the compressibility factor when three of the four following gas properties are known: the gross calorific value, the relative density, and the mole fractions of N 2 and CO 2 , The new equation, known as the SGERG-88 vi rial equation, is based on ideas presented in an earlier study. The new equation, however, applies to wider ranges oftemperature and pressure and can be applied to gases containing hydrogen if the mole fraction of the hydrogen is known. The equation was tested on natural gases purchased, transported, and marketed by the European gas companies. Excellent agreement between computed and experimental compressibility factors was found. This difference is, in most cases (94 % of the data points), less than 0.1 % in the temperature range of 265 to 335 K and for pressures up to 12 MPa.
The European Gas Research Group (GERG, Groupe Europeen de Recherches Gazieres) performed an extensive research project involving the measurement of compressibility factors of pure gases and binary mixtures and of natural gases in the temperature range of 265 to 335 K and at pressures up to 12 MPa. These pure gas and binary mixture data, together with high-quality data from the literature, were used to develop the GERG virial equation for the accurate prediction of the compressibility factor of natural gas (multicomponent) mixtures. Pressure, temperature, and a 13-component composition are used as input data. Eighty-four sets of experimental natural gas data made up of more than 4,000 data points were used to validate the GERG virial equation of state (EOS). The target accuracy of the GERG virial equation is ±0.1 %. A comparison of experimental and predicted compressibility factors shows that this target was achieved. The average root-mean-square (RMS) error for the differences between the experimental and the predicted compressibility factors is 0.06% for pressures up to 12 MPa. Even in the high-pressure range between 8 and 12 MPa, the RMS error is only 0.07%.
In recent years, many problems of elemental sulfur deposits
in
natural gas transmission line systems have been noted. These problems
occur very often immediately downstream of a pressure reduction facility.
To prevent the apparition of solid sulfur deposits causing security
and maintenance problems it is imperative to determine sulfur solubility
in natural gas at pressures and temperatures corresponding to transport
conditions. In a previous work (Serin et al. J. Supercrit.
Fluids
2010, 53, 12–16),
an original experimental apparatus was designed, and experimental
saturation values of carbon dioxide in sulfur were obtained. The protocol
principle is schematically divided into three steps: saturation, trapping,
and quantification. In this work, experimental sulfur solubility in
methane was measured and compared to available studies at 363.15 K
in the pressure range from (4 to 25) MPa. This paper presents these
measurements and the improvements of the trapping and quantification
steps that have been made to get these solubility data.
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