Accurate Predictions of the Effect of Hydrogen Composition on the Thermodynamics and Transport Properties of Natural Gas (original) (raw)
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Thermodynamic behavior of hydrogen/natural gas mixtures
PROCEEDINGS OF THE ANNUAL CONVENTION GAS PROCESSORS ASSOCIATION, 1995
The process gas of ethylene plants and methyl-tertiary butyl ether plants is normally a hydrogen/methane mixture. The molecular weight of the gas in such processes ranges from 3.5 to 14. Thermodynamic behavior of hydrogen/methane mixture has been and is being researched extensively. The gas dynamic design of turboexpanders which are extensively utilized in such plants depends on the equations of state of the process gas. Optimum performance of the turboexpander and associated equipment demands accurate thermodynamic properties for a wide range of process gas conditions. The existing equations of state, i.e. Benedict-Webb-Rubin (BW R), Soave-Redlich-Kwang and Peng-Robinson have some practical limitations. The equations of state developed by the University of Illinois also have only a limited range of applications. By using the various equations of state, especially in the vapor-liquid equilibrium region, this paper shows that predictions by the various models are not the same and that they also differ from actual field results. The field data collected for hydrogen / methane mixtures are in the range of 100°F to -200°F containing some polar components i.e. H2S and CO2. In this paper, the authors compare performance of several equations of state with the field performance of many expander units.
Journal of Petroleum Science and Engineering, 2006
In this contribution, 10 equations of state (EoSs) are used to predict the thermo-physical properties of natural gas mixtures. One of the EoSs is proposed in this work. This EoS is obtained by matching the critical fugacity coefficient of the EoS to the critical fugacity coefficient of methane. Special attention is given to the supercritical behavior of methane as it is the major component of natural gas mixtures and almost always supercritical at reservoir and surface conditions. As a result, the proposed EoS accurately predicts the supercritical fugacity of methane for wide ranges of temperature and pressure. Using the van der Waals mixing rules with zero binary interaction parameters, the proposed EoS predicts the compressibility factors and speeds of sound data of natural gas mixtures with best accuracy among the other EoSs. The average absolute error was found to be 0.47% for predicting the compressibility factors and 0.70% for the speeds of sound data. The proposed EoS was also used to predict thermal and equilibrium properties. For predicting isobaric heat capacity, Joule-Thomson coefficient, dew points and flash yields of natural gas mixtures, the predictive accuracy of the EoS is comparable to the predictive accuracy of the Redlich-Kwong-Soave (RKS) EoS or one of its variants. For predicting saturated liquid density of LNG mixtures, however, the accuracy of predictions is between the RKS and Peng-Robinson (PR) EoSs.
Comparison of the GERG-2008 and Peng-Robinson Equations of State for Natural Gas Mixtures
This work compares two equations of state applicable to natural gas mixtures, namely the GERG-2008 equation of state (EoS), which was proposed as a high-accuracy reference model, and the traditional Peng-Robinson (PR) EoS. This comparison is done in terms of the accuracy of calculated properties such as pressure and density with respect to experimental data from the literature, as well as in vapor-liquid equilibria (VLE) calculations. It was found that the GERG-2008 EoS gives better results in comparison with PR for the calculation of density and pressure, generating deviations in the range from 0.1 to 1%. For the VLE calculations, the accuracy of GERG-2008 was slightly better than PR. However, this accuracy is accompanied with increased mathematical complexity, resulting in increased computational time: 2 to 6 times higher. This is due to the fact that the calculation of molar density of GERG-2008 requires an iterative calculation step for the liquid and vapor phases, which makes the resolution of the VLE calculation slower.
Development of a thermodynamic model for hydrogen and hydrogen containing mixtures
Fluid Phase Equilibria, 2014
Based on Virial Equation of State (V-EOS), a thermodynamic model was developed in this study. The applicability and performance of proposed modified-Virial EOS (mV-EOS) were assessed for calculation of thermodynamic properties of hydrogen and then extended to the hydrogen containing mixtures. For comparison purpose, a number of cubic equations of state were used. Four statistical parameters were defined as goodness criteria which can be regarded as Objective Functions (OF) introduced to optimization method i.e. Black Hole Method (BH). According to obtained results, the model was able to predict the studied thermodynamic properties with desirable accuracy.
Russian Journal of Applied Chemistry, 2013
Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) was employed for predicting thermodynamic properties of natural gas mixture. Thermodynamic properties like density, isobaric and isochoric heat capacity, enthalpy, entropy, and internal energy were calculated with the PC-SAFT. Results are validated against experimental data for natural gas and mixtures similar to natural gas. The validation show that the Average Absolute Deviation (AAD) for density is 1.10% for binary mixture and 1.08% for mixtures similar to natural gas. Also AAD value for enthalpy is 1.42%, for internal energy, 0.77, for entropy, 0.43, for isochoric heat capacity, 1.26%, and for isobaric heat capacity, 2.66%. Results show PC-SAFT to be able to predict all the thermodynamics properties of natural gas and mixtures similar to natural gas with high accuracy in a wide range of temperature and pressure.
Eleven equations of state are employed to predict the vapor pressures, liquid and vapor densities, liquid and vapor heat capacities, and vaporization enthalpies and entropies of normal hydrogen along the coexistence curve. The volumetric and thermal properties of gaseous hydrogen together with the speeds of sound, Joule–Thomson coefficients and inversion curves for wide ranges of temperature and pressure are predicted as well. The results are compared with experimental data and the recommended values of standard thermodynamic tables. The best equations of state in predicting the properties of hydrogen (saturated and supercritical) are introduced and reported.
Numerical procedures for natural gas accurate thermodynamic properties calculation
Journal of Engineering Thermophysics, 2012
Natural gas (NG) is a mixture of 21 elements and widely used in the industries and domestics. Knowledge of its thermodynamic properties is essential for designing appropriate process and equipments. In this study, the detailed numerical procedures for computing most thermodynamic properties of natural gas are discussed based on the AGA8 equation of state (EOS) and thermodynamics relationships. To validate the procedures, the numerical values are compared with available measured values. The validations show that the average absolute percent deviation (AAPD) for density calculations is 0.0831%, for heat capacity at the constant pressure is 0.87%, for heat capacity at the constant volume is 1.13%, for Joule-Thomson coefficient is 1.93%, for speed of sound is 0.133%, and for enthalpy is 1.06%. Furthermore, in this work, the new procedures are presented for computing the entropy and internal energy. Due to lack of experimental data for these properties, the validation is done for pure methane. The validation shows that AAPD is 0.078% and 0.0133% for internal energy and entropy, respectively.
2022
Hydrogen (H 2) has emerged as a viable solution for energy storage of renewable sources, supplying off-seasonal demand. Hydrogen contamination due to undesired mixing with other fluids during operations is a significant problem. Water contamination is a regular occurrence; therefore, an accurate prediction of H 2-water thermodynamics is crucial for the design of efficient storage and water removal processes. In thermodynamic modeling, the Peng-Robinson (PR) and Soave Redlich-Kwong (SRK) equations of state (EoSs) are widely applied. However, both EoSs fail to predict the vapor-liquid equilibrium (VLE) accurately for H 2-blend mixtures with or without fine-tuning binary interaction parameters due to the polarity of the components. This work investigates the accuracy of two advanced EoSs: the Schwartzentruber and Renon modified Redlich-Kwong cubic EoS (SR-RK) and perturbed-chain statistical associating fluid theory (SAFT) in predicting VLE and solubility properties of H 2 and water. The SR-RK involves the introduction of polar parameters and a volume translation term. The proposed workflow is based on optimizing the binary interaction coefficients using regression against experimental data that cover a wide range of pressure (0.34 to 101.23 MPa), temperature (273.2 to 588.7 K), and H 2 mole fraction (0.0004 to 0.9670) values. A flash liberation model is developed to calculate the H 2 solubility and water vaporization at different temperature and pressure conditions. The model captures the influence of H 2-gas (CO 2) impurity on VLE. The results agreed well with the experimental data, demonstrating the model's capability of predicting the VLE of hydrogen-water mixtures for a broad range of pressures and temperatures. Optimized coefficients of binary interaction parameters for both EoSs are provided. The sensitivity analysis indicates an increase in H 2 solubility with temperature and pressure and a decrease in water vaporization. Moreover, the work demonstrates the capability of SR-RK in modeling the influence of gas impurity (i.e., H 2-CO 2 mixture) on the H 2 solubility and water vaporization, indicating a significant influence over a wide range of H 2-CO 2 mixtures. Increasing the CO 2 ratio from 20% to 80% exhibited almost the opposite behavior of H 2 solubility compared to the pure hydrogen feed solubility. Finally, the work emphasizes the critical selection of proper EoSs for calculating thermodynamic properties and the solubility of gaseous H 2 and water vaporization for the efficient design of H 2 storage and fuel cells.
GERG Project: Wide-range reference equation of state for natural gases
GAS UND …, 2003
A group of European gas companies, GERG, supported the development of a new equation of state for the thermodynamic properties of natural gases covering the gas and liquid region including the vapour-liquid phase equilibrium. The new equation, GERG02, was developed on the basis of a multi-fluid approximation using pure substance equations for each component and experimental data for binary mixtures only. Therefore, the representation of multicomponent mixture data is predictive. The results calculated with the new equation for thermal and caloric properties of natural gas mixtures show substantial improvements in comparison to the AGA8-DC92 and the GERG88 equation, which are known to be the current internationally accepted standard for density or compression factor calculations at pipeline conditions (see ISO 12213-part 2 and 3, 1997). The new reference equation allows high accuracy calculations for thermal and caloric properties in the homogeneous region (gas, liquid and supercritical) and also enables calculations for the vapour-liquid equilibrium. The reference equation can be used as a database or reference for technical applications and processes with natural gases, LNG, LPG, natural gas vehicles and hythane mixtures.
Thermodynamic properties of the methane-ethane systen
Fluid Phase Equilibria, 1992
Our recently completed wide-ranging correlations for the tbermophysical properties of methane and ethane fluids have enabled us to improve the extended corresponding states calculations for the properties of the binary mixtures. The pure fluid equations are based on the analytic Schmidt-Wagner equation of state and give improved results in the general region of the critical point. We use these pure fluid equations (and a reference fluid for which an equivalent equation is known) to calculate properties and compare with experimental PVT data, isochoric heat capacities, and sound speeds of binary mixtures of methane and ethane. We also examine the properties at the vaporliquid boundary and compare the representation from the classical extended corresponding states calculations with quantities derived from a scaling theory model. The shape of the binary mixture phase boundary is improved with this model, however our new representation of the single phase properties provides only a slight improvement over models based on modified Benedict-Webb-Rubin pure fluid equations of state.