The GERG-2004 wide-range equation of state for natural gases and other mixtures

A wide-range equation of state for the thermodynamic properties of natural gases and other multi-component (and binary) mixtures was developed. The new formulation, adopted by GERG in 2004 and called GERG-2004 equation of state or GERG-2004 for short, is a fundamental equation explicit in the Helmholtz free energy as a function of density, temperature, and composition. The mixture model uses accurate equations of state for the 18 specified natural gas components along with functions that take into account the mixture behaviour. GERG-2004 covers wide ranges of temperature, pressure, and composition and is valid in the gas phase, the liquid phase, the supercritical region, and for vapour-liquid equilibrium states. The equation achieves a high accuracy in the calculation of thermodynamic properties for a broad variety of mixtures. The wide range of validity enables the use of GERG-2004 in both standard and advanced technical applications for natural gases and related mixtures. This includes, e.g. pipeline transport, natural gas storage, improved and integrated processes with liquefied natural gas, the design of separation processes as encountered in natural gas processing, and future applications with natural gas mixtures enriched with hydrogen. (orig.)