Accurate Predictions of the Effect of Hydrogen Composition on the Thermodynamics and Transport Properties of Natural Gas

This work demonstrates the need for accurate thermodynamic models to reliably quantify changes in the thermophysical properties of natural gas when blended with hydrogen. For this purpose, a systematic evaluation was carried out on the predictive accuracy of three well-known models, the Peng-Robinson equation of state (EoS), the multiparameter empirical GERG-2008 model, and the molecular-based polar soft-SAFT EoS, in describing the thermodynamic behavior of mixtures of hydrogen with commonly found components in natural gas. Deviations between the calculated properties and experimental data for phase equilibria, critical loci, second-order derivative properties and viscosities are used to determine the accuracy of the models, with polar soft-SAFT performing either equally or better than the other two examined models. The evaluation for the effect of H2 content on the properties of methane, simulated as natural gas at conditions for transportation, reveals higher changes in blend density and speed of sound with increasing H2 content within 5% change per 5 mol % H2 added, while viscosity is the least affected property, changing by 0.4% for every 5 mol % H2.