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Thermodynamics of LNG
(2020)
Densities of eight gravimetrically prepared ternary and quaternary gas mixtures consisting of methane, ethane, propane, and partially nitrogen were investigated along the four isotherms of –250, –230, –210, and –190 °F at pressures of 350, 500, 650, and 1000 psig using a cryogenic single-sinker densimeter. The experimental densities were compared to densities calculated by various models, namely the EOS-LNG fundamental Helmholtz equation of state, the COSTALD correlation, the Lee-Kessler-Plöcker equation of state, and the Peng-Robinson equation of state. The best performance was shown by the EOS-LNG equation of state which is capable of predicting the liquid densities within the specified uncertainty of the model of 0.05 %. The other models, however, showed significant differences that disqualify for calculation within the p,T-region investigated of the gas mixtures.
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 Power-to-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 H2-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 106 (0.02 %) in the speed of sound. The heat capacity ratio as perfect-gas gammapg, the molar heat capacity as perfect-gas Cp,m pg, and the second betaa and third gammaa 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.
The decarbonization of the energy sector is driving the interest in hydrogen as an energy-storage medium. A practical alternative to transport and distribute H2 is using the existing infrastructure for natural gas. The GERG-2008 equation of state currently serves as the ISO standard (ISO 20765-2) for the calculation of thermodynamic properties of natural gas, but H2 appears only as a secondary component.
The availability of consolidated data for mixtures with H2 available at the time of its constitution was very limited. The experimental characterization of the thermodynamic behavior of mixtures of H2 with the main components of natural gas is thus of great relevance to validate and improve the GERG-2008 equation of state for its use with H2-enriched natural gas.
Continuing our study on (CO2 + O2) mixtures, this work reports new experimental (p, rho, T) data for two oxygen-rich mixtures with mole fractions x(O2) = (0.50 and 0.75) mol·mol−1, in the temperature range T = (250–375) K and pressure range p = (0.5–20) MPa, using a single-sinker densimeter. Experimental density data were compared to two well-established equation-of-state models: EOS-CG and GERG-2008. In the p, T-range investigated, the EOS-CG gave a better reproduction for the equimolar mixture (x(O2) = 0.5), whereas the GERG-2008 performed significantly better for the oxygen-rich mixture (x(O2) = 0.75). The EOS-CG generally overestimates the density, while the GERG-2008 underestimates it. This complete set of new experimental data, together with previous measurements, is used to calculate the virial coefficients B(T, x) and C(T, x), as well as the second interaction virial coefficient B12(T) for the (CO2+ O2) system.
On the way to a low carbon economy mixtures containing carbon dioxide become increasingly important. Processing of such gas mixtures requires reliable thermodynamic models that can accurately describe the state of matter over an extended range. Mixtures with oxygen for example, are frequently encountered in carbon capture and storage (CCS) processes.
This work reports new experimental (p, rho, T) data at T = (250 to 375 K) and up to a maximum pressure pmax = 20 MPa for five binary (CO2 + O2) mixtures which cover the entire composition range.