A new equation of state for the thermodynamic properties of natural gases, similar gases, and other mixtures, the GERG-2008 equation of state, had been implemented in our products. GERG-2008 is explicit in the Helmholtz free energy as a function of density, temperature, and composition. It provides a robust new algorithm suitable for dry gas and as opposed to AGA-8 also for wet gas and liquids, e.g. LNG.
The equation is based on 21 natural gas components: methane, nitrogen, carbon dioxide, ethane, propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, hydrogen, oxygen, carbon monoxide, water, hydrogen sulfide, helium, and argon. These components are identical to the AGA-8 algorithm.
Over the entire composition range, GERG-2008 covers the gas phase, liquid phase, supercritical region, and vapor–liquid equilibrium states for mixtures of these components.
The normal range of validity of GERG-2008 includes temperatures from (90 to 450) K and pressures up to 35 MPa where the most accurate experimental data of the thermal and caloric properties are represented to within their accuracy.
The extended validity range reaches from (60 to 700) K and up to 70 MPa. The given numerical information (including all of the sophisticated derivatives) enables the use of GERG-2008 for all of the various technical applications.
Examples are processing, transportation through pipelines or by shipping, storage and liquefaction of natural gas, and processes to separate gas components. Comparisons with other equations of state, for example, AGA8-DC92 and Peng–Robinson equation (P-R), show that GERG-2008 is robust and accurate (0.1% for both dry and wet gases).
Another big advantage is that there is no limitation of the composition so it can be used for pure gases as well. Because of its CPU consuming calculations (10 x AGA-8) it requires a calculation powerhouse such as the Flow-X series to have it implemented in a flow computer.
The Flow-X supports the GERG 2008 gas calculation. Flow-Xpert and eXLerate software also support the flash and liquid calculations.