Speed of sound data, derived perfect-gas heat capacities, and acoustic virial coefficients of a calibration standard natural gas mixture and a low-calorific H2-enriched mixture

This work aims to address the technical aspects related to the thermodynamic characterization of natural gas mixtures blended with hydrogen for the introduction of alternative energy sources within the Powerto-Gas framework. For that purpose, new experimental speed of sound data are presented in the pressure range between (0.1 up to 13) MPa and at temperatures of (260, 273.16, 300, 325, and 350) K for two mixtures qualified as primary calibration standards: a 11 component synthetic natural gas mixture (11 M), and another low-calorific H-2-enriched natural gas mixture with a nominal molar percentage x(H2) = 3%. Measurements have been gathered using a spherical acoustic resonator with an experimental expanded (k = 2) uncertainty better than 200 parts in 10(6) (0.02%) in the speed of sound. The heat capacity ratio as perfect-gas gamma(pg), the molar heat capacity as perfect-gas C-p,m(pg), and the second beta(a) and third gamma(a) acoustic virial coefficients are derived from the speed of sound values. All the results are compared with the reference mixture models for natural gas-like mixtures, the AGA8-DC92 EoS and the GERG-2008 EoS, with special attention to the impact of hydrogen on those properties. Data are found to be mostly consistent within the model uncertainty in the 11 M synthetic mixture as expected, but for the hydrogen-enriched mixture in the limit of the model uncertainty at the highest measuring pressures. (C) 2021 Elsevier Ltd.

Automated summary

This study investigates the thermodynamic characterization of natural gas mixtures blended with hydrogen. The experimental data reveals the impact of hydrogen on properties such as speed of sound, heat capacity ratio, and molar heat capacity, compared with reference mixture models. Results show consistency within model uncertainty, with hydrogen-enriched mixtures approaching the limit of uncertainty at high pressures.