52 results found
Kim D, Al Ghafri SZS, Yang X, et al., 2021, High Pressure Thermal Conductivity Measurements of Ternary (Methane + Propane + Heptane) Mixtures with a Transient Hot-Wire Apparatus, International Journal of Thermophysics, Vol: 42, ISSN: 0195-928X
The prediction of thermophysical properties for hydrocarbon mixtures at high pressures, and conditions near the phase boundary or critical point is challenging. However, natural gas processing applications have an increasing need for reliable property predictions at such conditions. In this work, thermal conductivity measurements of three ternary mixtures (methane + propane with heptane at concentration up to 15 mol%) were carried out with a transient hot-wire apparatus. Measurements of the three ternary mixtures were conducted over the temperature range from (199.1 to 424.2) K and the pressure range between (10.41 and 31.55) MPa at single phase conditions with a relative combined expanded uncertainty (k = 2) between 0.015 and 0.056. The measured values were compared to predictions made with the extended corresponding states (ECS) model and SUPERTRAPP model implemented in the software packages REFPROP 10 and MultiFlash 6.2, respectively. The relative deviations of the measured thermal conductivities from the model predictions were (− 5.7 to + 2.4) % for the ECS model and (− 21.1 to − 0.6) % for the SUPERTRAPP model. This indicates the latter, older model should not be used to estimate natural gas thermal conductivities, particularly at high pressure conditions, while the ECS model is capable of representing the data within their uncertainty with no parameter tuning required.
Al Ghafri SZS, Akhfash M, Hughes TJ, et al., 2021, High pressure viscosity measurements of ternary (methane + propane + heptane) mixtures, Fuel Processing Technology, Vol: 223, ISSN: 0378-3820
Prediction of thermophysical properties for natural gas mixtures close to the mixture's critical point and cricondenbar (the maximum pressure at which two fluid phases can co-exist) is challenging but important as often natural gas processes operate close to these conditions. Here we present a comprehensive study of the viscosity of (CH4 + C3H8 + C7H16) mixtures with heptane fractions up to 15 mol%. Accurate measurements of saturated-phase and compressed-fluid (single phase) viscosities, at temperatures from 200 K to 423 K and pressures up to 35 MPa, are presented. The collected data were compared with the prediction of the extended corresponding states (ECS) model, with relative deviations spanning between (−20 to 11) % from the model. Additionally, pure component parameters needed for the residual entropy scaling (RES) model were fit to literature data and then applied predictively to mixtures viscosity without any additional fit parameters. The relative deviation of the measured viscosities from values calculated with the RES model is generally within 15%. This work demonstrates that no current model satisfactorily predict mixtures viscosity, and that high quality experimental data are needed to anchor the methods used to design and optimize natural gas processing.
Al Ghafri SZS, Jiao F, Hughes TJ, et al., 2021, Natural gas density measurements and the impact of accuracy on process design, Fuel, Vol: 304, ISSN: 0016-2361
The liquefaction of natural gas is an energy intensive process, requiring at least 5% of the energy associated with methane's lower heating value. Key to estimating and optimizing these energy requirements are process simulations which rely upon calculated thermophysical properties of the natural gas. In particular, the prediction of thermophysical properties of natural gas mixtures at pressure-temperature conditions close to the mixture's critical point or cricondenbar is challenging but important as often natural gas processes operate close to these conditions. In this work, we present a comprehensive study of two natural gas related systems: (CH4 + C3H8 + CO2) and (CH4 + C3H8 + C7H16) with n-heptane fractions up to 15 mol%. High accuracy measurements of densities, at temperatures from 200 K to 423 K and pressures up to 35 MPa are presented. The extensive experimental data collected for these mixtures were compared with the GERG-2008 equation of state, as implemented in the NIST software REFPROP. The relative deviations of the measured densities from those calculated using the GERG-2008 model range between (−2 to 4)% for all mixtures, presenting a systematic dependent on mixture density and n-heptane content. Finally, a case study is presented that probes the impact of the accuracy of density on the pinch point in a simulated LNG heat exchanger. An uncertainty in the density of 1% is shown to cause significant 30% reduction in the minimum approach temperature difference, suggesting that accurate thermophysical property calculations are key to reducing over-design of processing plant.
Xiao X, Al Ghafri SZS, Rowland D, et al., 2021, Isobaric heat capacity measurements of natural gas model mixtures (methane + n-heptane) and (propane + n-heptane) by differential scanning calorimetry at temperatures from 313 K to 422 K and pressures up to 31 MPa, Fuel, Vol: 296, ISSN: 0016-2361
Heat capacities of pure methane (1), propane (2) and n-heptane (3), and binary mixtures of (methane or propane + n-heptane) at n-heptane mole fractions of (0.070 to 0.750), were measured at temperatures (313 to 42) K and pressures (6.00 to 31.10) MPa using a Tian-Calvet-type differential scanning calorimeter with a combined standard uncertainty of (2.20 to 2.68) % (k = 1). The results for pure methane, propane and n-heptane agreed within 2% of the values calculated from reference equations of state (EOS). In contrast, for the two sets of mixtures measured above their cricondenbars, averaged absolute deviations of 4.6%, 3.7% and 1.2% were observed between the measured cp values and those predicted by the GERG-2008, Peng-Robinson (PR) and SAFT-γ Mie EOS, respectively. The divergences of cp from model calculations for the binary mixtures near the critical region were also investigated. The root mean square (r.m.s.) deviations of the measured heat capacities from those calculated using the GERG-2008, PR, and SAFT-γ Mie exhibited relatively large but similar values of 7.1%, 7.4% and 7.2% for [0.850 CH4 + 0.150 n-C7H16] and 9.1%, 6.9% and 8.0% for [0.930 C3H8 + 0.070 n-C7H16]. This work reveals that the SAFT-γ Mie EOS can adequately describe most heat capacity data above the cricondenbar, while none of the models provide reliable predictions near the critical region.
Siahvashi A, Al Ghafri SZS, Graham BF, et al., 2021, Experimental study of impurity freeze-out in ternary methane + ethane + benzene mixtures with applications to LNG production, Journal of Natural Gas Science and Engineering, Vol: 90, ISSN: 1875-5100
The freeze-out of impurities in LNG production can pose significant operational risks and lead to costly blockage-induced plant shutdowns. Study of ternary and higher-order mixtures, which are more analogous to LNG, present the critical tests of thermodynamic models in terms of their utility and predictive accuracy. In this work, a visual CryoSolids apparatus was upgraded to allow analytical measurements of solvent composition in multi-component systems where a solid phase is present at equilibrium. The analytical system, which included a ROLSI sampling valve and capillary together with a gas chromatograph, was successfully commissioned and used to measure melting temperatures and solvent compositions of a ternary mixture containing methane, ethane, and benzene at temperatures down to 125 K and pressures up to 6 MPa. The effect on the solubility of benzene by adding ethane to the solvent was investigated by varying the ethane mole fraction from 0 to 0.96. The resulting temperature at which benzene melted into the liquid solvent decreased from 246 K at 4.7 MPa to 125 K at 5.7 MPa. The comparison of results with the ThermoFAST model showed that it could describe the new data with a deviation less than 1 K for ethane liquid phase mole fractions from 0 < xC2< 0.5, which increased to less than 4 K for 0.85 < xC2< 0.97. This result indicates that ThermoFAST satisfactorily represents SFE conditions in LNG mixtures of industrial relevance but needs improvement to cover wider ranges of composition.
Al Ghafri SZS, Perez F, Heum Park K, et al., 2021, Advanced boil-off gas studies for liquefied natural gas, Applied Thermal Engineering, Vol: 189, ISSN: 1359-4311
Current methods of estimating boil-off gas (BOG) rates for large-scale liquefied natural gas (LNG) storage tanks are largely empirical and based on limited available experimental data. More accurate models would be extremely valuable for estimating the potential for excessive BOG generation during LNG storage and transportation scenarios as well as providing critical inputs into the design of BOG re-liquefaction systems. This study reports a series of experiments that have been conducted for LNG-like binary mixtures of methane and ethane to measure the BOG production and resultant pressure change under various industrially relevant conditions. Experimental data and observations made in this work are compared with both the available literature and with the predictions of a new non-equilibrium model that uses the GERG-2008 equation of state to calculate relevant LNG and BOG properties. The data reveal three distinct stages of BOG evolution, here labelled as self-pressurisation, transient, and homogenous. It is observed that, in the self-pressurisation stage, the thickness of a thermally stratified layer adjacent to the liquid–vapor interface increases with time. The transient stage is defined to commence when the system reaches the specified relief pressure and the homogeneous stage is reached upon the effective elimination of thermal stratification in the LNG. Good agreement exists between this new model and the experimental and literature data acquired during the self-pressurisation and homogeneous stages. In the transient stage, the model does not accurately quantify the BOG rate indicating a need to incorporate the effects liquid thermal stratification in future model development.
Perez F, Al Ghafri SZS, Gallagher L, et al., 2021, Measurements of boil-off gas and strati fi cation in cryogenic liquid nitrogen with implications for the storage and transport of lique fi ed natural gas, ENERGY, Vol: 222, ISSN: 0360-5442
Xiao X, Oakley J, Al Ghafri SZS, et al., 2021, Isobaric heat capacities of a methane (1) + propane (2) mixture by differential scanning calorimetry at near-critical and supercritical conditions, FUEL, Vol: 289, ISSN: 0016-2361
Xiao X, Rowland D, Al Ghafri SZS, et al., 2021, Wide-Ranging Reference Correlations for Dilute Gas Transport Properties Based on Ab Initio Calculations and Viscosity Ratio Measurements (vol 49, 013101, 2020), JOURNAL OF PHYSICAL AND CHEMICAL REFERENCE DATA, Vol: 50, ISSN: 0047-2689
Siahvashi A, Al Ghafri SZS, Yang X, et al., 2021, Avoiding costly LNG plant freeze-out-induced shutdowns: Measurement and modelling for neopentane solubility at LNG conditions, ENERGY, Vol: 217, ISSN: 0360-5442
Oakley J, Xiao X, Al Ghafri SZS, et al., 2021, High-Pressure Melting Temperature Measurements in Mixtures Relevant to Liquefied Natural Gas Production and Comparisons with Model Predictions, Journal of Chemical and Engineering Data, ISSN: 0021-9568
Accurate melting point data were measured for hydrocarbon mixtures analogous to natural gas under high pressure at cryogenic temperatures using a customized differential scanning calorimeter. New melting temperatures are reported for two [methane (C1) + n-heptane (C7)] binary mixtures, two [methane + propane (C3) + n-heptane] ternary mixtures, and three multicomponent mixtures containing methane + ethane (C2) + propane + butane (C4) with a solute of either benzene (CBz) or para-xylene (Cp-xyl). These measurements were performed over temperatures ranging from 137.82 to 302.18 K and pressures between 11.12 and 34.5 MPa. The binary mixture results were consistent with the literature data, and comparisons with the predictions of models implemented in Multiflash and ThermoFAST software packages showed deviations ΔT = Tmeas - Tcalc around +5 and +3 K, respectively. Similar results were obtained for the ternary mixtures. For the multicomponent mixture containing benzene, the deviation for the model implemented in Multiflash increased to +9.4 K, while it remained at around +3 K for the model implemented in ThermoFAST. However, for the multicomponent with para-xylene, the melting temperature deviations for the Multiflash and ThermoFAST models both increased significantly to +21.5 and +13.7 K, respectively. The results suggest that for well-characterized multicomponent mixtures containing components that have been well studied, the models implemented in ThermoFAST can adequately predict the melting temperatures at high pressure. Nonetheless, improvements are still in need for mixtures containing freeze-out components such as para-xylene that have not yet been studied sufficiently.
Sadaghiani MS, Arami-Niya A, Marsh B, et al., 2021, Vapor-Liquid Equilibria for Carbon Dioxide + 3,3,3-Trifluoropropene Binary Mixtures at Temperatures between (288 and 348) K, Journal of Chemical and Engineering Data, ISSN: 0021-9568
Accurate property data for mixtures of hydrofluoroolefins with refrigerants like CO2 are needed by industry to design safe and efficient refrigeration systems that employ low global warming potential working fluids. However, data available for these mixtures, particularly at conditions of vapor-liquid-equilibrium (VLE), are limited. In this work, the VLE of CO2 and HFO-1243zf binary mixtures was measured along five isotherms at temperatures between (288 and 348) K and pressures between (0.68 and 7.69) MPa. The new VLE data are compared with the predictions of a Helmholtz free energy model that utilizes GERG-2008 mixing rules. Adjusting the model's binary interaction parameters (BIPs) to force agreement with the new measurements reduced the root-mean-square deviation (RMSD) of the data from the model by 45% relative to the default BIPs. Additionally, the data were compared with predictions from the Peng-Robinson advanced equation of state (PRA-EOS) with a one-fluid mixing rule and a fixed binary interaction parameter which was subsequently tuned to the experimental data. The tuned PRA-EOS could represent the experimental CO2 mole fractions with an RMSD of 0.012, which is more than 2 times larger than the average experimental uncertainty, while the RMSD of the tuned Helmholtz free energy model from the experimental data was 0.009. The accurate data and improved model presented in this work will aid the development of environmentally friendly refrigerant mixtures.
Kim D, Yang X, Arami-Niya A, et al., 2020, Thermal conductivity measurements of refrigerant mixtures containing hydrofluorocarbons (HFC-32, HFC-125, HFC-134a), hydrofluoroolefins (HFO-1234yf), and carbon dioxide (CO2), JOURNAL OF CHEMICAL THERMODYNAMICS, Vol: 151, ISSN: 0021-9614
Souza LFS, Ghafri SZSA, Fandiño O, et al., 2020, Vapor-liquid equilibria, solid-vapor-liquid equilibria and H2S partition coefficient in (CO2 + CH4) at temperatures between (203.96 and 303.15) K at pressures up to 9 MPa, Fluid Phase Equilibria, Vol: 522, Pages: 1-13, ISSN: 0378-3812
Vapor-liquid equilibrium (VLE) measurements of the (CO2 + CH4) system are reported along seven isotherms at temperatures varying from just above the triple point to just below the critical point of CO2 at pressures from the vapor pressure of pure CO2 to approximately 9 MPa, including near-critical states. From these data, the critical locus has been determined and correlated over its entire length. The VLE data are correlated with the Peng-Robinson equation of state (PR-EoS), using a temperature-dependent binary interaction parameter, and also compared with the predictions of the GERG-2008 equation of state. The former represents the phase compositions across all isotherms with a root-mean-square mole-fraction deviation of S = 0.0075 while, for the latter, S = 0.0126. Measurements of the three-phase solid-vapor-liquid equilibrium (SVLE) line are reported at temperatures from approximately (204 to 216) K and a new correlation is developed which is valid from 145 K to the triple point of CO2. Additionally, we report the partitioning of trace levels of H2S between coexisting liquid and vapor phases of the (CO2 + CH4) system and compare the results with the predictions of the PR-EoS.
Arami-Niya A, Xiao X, Al Ghafri SZS, et al., 2020, Measurement and modelling of the thermodynamic properties of carbon dioxide mixtures with HFO-1234yf, HFC-125, HFC-134a, and HFC-32: vapour-liquid equilibrium, density, and heat capacity, INTERNATIONAL JOURNAL OF REFRIGERATION, Vol: 118, Pages: 514-528, ISSN: 0140-7007
Yang X, Arami-Niya A, Xiao X, et al., 2020, Viscosity Measurements of Binary and Multicomponent Refrigerant Mixtures Containing HFC-32, HFC-125, HFC-134a, HFO-1234yf, and CO2, JOURNAL OF CHEMICAL AND ENGINEERING DATA, Vol: 65, Pages: 4252-4262, ISSN: 0021-9568
Siahvashi A, Al Ghafri SZS, May EF, 2020, Solid-fluid equilibrium measurements of benzene in methane and implications for freeze-out at LNG conditions, FLUID PHASE EQUILIBRIA, Vol: 519, ISSN: 0378-3812
Al Habsi SSA, Al Ghafri SZS, Bamagain R, et al., 2020, Experimental and modelling study of the phase behavior of (methyl propanoate + carbon dioxide) at temperatures between (298.15 and 423.15) K and pressures up to 20 MPa, Fluid Phase Equilibria, Vol: 519, Pages: 1-8, ISSN: 0378-3812
In this work, we report phase equilibrium measurements on the system (methyl propanoate + carbon dioxide) carried out with a high-pressure quasi-static-analytical apparatus. The measurements were made along six isotherms at temperatures from (298.15 to 423.15) K and at pressures up to the critical pressure at each temperature. Vapor-liquid equilibrium (VLE) data obtained for the mixture have been compared with the predictions of the Statistical Associating Fluid Theory coupled with the Mie potential and a group-contribution approach for the functional group interaction parameters (SAFT-γ Mie). The group interaction parameters in SAFT-γ Mie for the COO–CO2 interaction have been revised in this work by fitting to our experimental VLE data. After tuning, the SAFT model was found to be in good agreement with the measured data for both the liquid and vapor phases. Additionally, the data were compared with the predictions of the Peng-Robinson equation of state (PR-EoS) with one-fluid mixing rules and a temperature-independent binary parameter. This model fitted the VLE data well, except in the critical region. The present work is expected to contribute to optimization of biodiesel production processes.
Al Ghafri SZS, Hughes TJ, Perez F, et al., 2020, Phase equilibrium studies of high-pressure natural gas mixtures with toluene for LNG applications, FLUID PHASE EQUILIBRIA, Vol: 518, ISSN: 0378-3812
Jiao F, Al Ghafri SZS, Hughes TJ, et al., 2020, Extended calibration of a vibrating tube densimeter and new reference density data for a methane-propane mixture at temperatures from (203 to 423) K and pressures to 35 MPa, JOURNAL OF MOLECULAR LIQUIDS, Vol: 310, ISSN: 0167-7322
Xiao X, Rowland D, Al Ghafri SZS, et al., 2020, Wide-Ranging Reference Correlations for Dilute Gas Transport Properties Based on Ab Initio Calculations and Viscosity Ratio Measurements (vol 49, 029901, 2019), JOURNAL OF PHYSICAL AND CHEMICAL REFERENCE DATA, Vol: 49, ISSN: 0047-2689
Xiao X, Rowland D, Al Ghafri SZS, et al., 2020, Wide-Ranging Reference Correlations for Dilute Gas Transport Properties Based on Ab Initio Calculations and Viscosity Ratio Measurements, JOURNAL OF PHYSICAL AND CHEMICAL REFERENCE DATA, Vol: 49, ISSN: 0047-2689
Mylona SK, Yang X, Hughes TJ, et al., 2020, High-Pressure Thermal Conductivity Measurements of a (Methane plus Propane) Mixture with a Transient Hot-Wire Apparatus, JOURNAL OF CHEMICAL AND ENGINEERING DATA, Vol: 65, Pages: 906-915, ISSN: 0021-9568
Sanchez-Vicente Y, Tay WJ, Al Ghafri SZ, et al., 2020, Density and phase behavior of the CO2 + methylbenzene system in wide ranges of temperatures and pressures, Industrial & Engineering Chemistry Research, Vol: 59, Pages: 7224-7237, ISSN: 0888-5885
Knowledge of the thermophysical properties of CO2-hydrocarbon mixtures over extended ranges of temperature and pressure is crucial in the design and operation of many carbon capture and utilization processes. In this paper, we report phase behavior, saturated-phase densities, and compressed-liquid densities of CO2 + methylbenzene at temperatures between 283 K and 473 K and at pressures up to 65 MPa over the full composition range. The saturated-phase densities were correlated by a recently developed empirical equation with an absolute average relative deviation (ΔAARD) of ∼0.5%. The compressed-fluid densities were also correlated using an empirical equation with an ΔAARD value of 0.3%. The new data have been compared with the predictions of two equations of state: the predictive Peng–Robinson (PPR-78) equation of state and the SAFT-γ Mie equation of state. In both of these models, binary parameters are estimated using functional group contributions. Both models provided satisfactory representation of the vapor–liquid equilibrium and saturated-phase-density data, but the accuracy decreased in the prediction of the compressed-liquid densities where the ΔAARD was ∼2%. The isothermal compressibility and isobaric expansivity are also reported here and were predicted better with SAFT-γ Mie than with PPR-78. Overall, the comparisons showed that SAFT-γ Mie performs somewhat better than PPR-78, but the results suggest that further refinement of the SAFT-γ Mie parameter table are required.
Arami-Niya A, Rufford TE, Dresp G, et al., 2019, Measurements of helium adsorption on natural clinoptilolite at temperatures from (123.15 to 423.15) K and pressures up to 35 MPa, SEPARATION AND PURIFICATION TECHNOLOGY, Vol: 223, Pages: 1-9, ISSN: 1383-5866
Al Ghafri SZS, McKenna A, Czubinski FF, et al., 2019, Viscosity of (CH4 + C3H8 + CO2 + N-2) mixtures at temperatures between (243 and 423) K and pressures between (1 and 28) MPa: Experiment and theory, FUEL, Vol: 251, Pages: 447-457, ISSN: 0016-2361
Al Ghafri SZS, Matabishi EA, Trusler JPM, et al., 2019, Speed of sound and derived thermodynamic properties of para-xylene at temperatures between (306 and 448)K and at pressures up to 66 MPa, Journal of Chemical Thermodynamics, Vol: 135, Pages: 369-381, ISSN: 0021-9614
The speed of sound in p-xylene has been measured at temperatures ranging from (306 to 447) K and at pressures from just above saturation to 66 MPa. Measurements were performed using a new double-path pulse-echo instrument, fabricated from Invar 36, that was designed for ease of assembly and calibration as well as robust operation. The cell’s path length was calibrated with water at a single state point against the IAPWS-95 equation of state, with path length corrections for temperature and pressure calculated using material-property data. Validation measurements on water over the range of experimental conditions investigated resulted in deviations from IAPWS-95 smaller than the equation’s relative uncertainty of 0.1 %. The expanded relative uncertainty of the measurements over the reported ranges of pressure and temperature varied from (0.023 to 0.104) % at 95 % confidence. The measured data for p-xylene were compared with the Helmholtz equation of state (EOS) of Zhou et al., which is stated to have a relative uncertainty in sound-speed of 0.3 % in the liquid region. Relative deviations between experiment and the EOS of up to 1 % were observed, especially at high temperatures and low pressures, indicating that the current Helmholtz model should be revised using the new experimental data. Additionally, density, isobaric specific heat capacity, and other thermodynamic properties of p-xylene were derived from the speed-of-sound data by thermodynamic integration; these results expand upon the available literature data and are generally in good agreement with the current Helmholtz EOS. The relative expanded uncertainties for liquid density and isobaric specific heat capacity in this work are estimated to be 0.2 % and 1 %, respectively, equivalent to the uncertainty of the EOS.
Siahvashi A, Al Ghafri SZS, Hughes TJ, et al., 2019, Solubility of p-xylene in methane and ethane and implications for freeze-out at LNG conditions, EXPERIMENTAL THERMAL AND FLUID SCIENCE, Vol: 105, Pages: 47-57, ISSN: 0894-1777
Al Ghafri S, Maitland GC, Trusler JPM, 2019, Densities of aqueous MgCl2(aq), CaCl2(aq), KI(aq), NaCl(aq), KCl(aq), AICl(3) (aq), and (0.964 NaCl + 0.136 KCI)(aq) at temperatures between (283 and 472) K, pressures up to 68.5 MPa, and molalities up to 6 mol.kg(-1) (vol 57, pg 1288, 2012), Journal of Chemical and Engineering Data, Vol: 64, Pages: 2912-2912, ISSN: 0021-9568
Al Ghafri SZ, Trusler JPM, 2019, Phase equilibria of (Methylbenzene + Carbon dioxide + Methane) at elevated pressure: Experiment and modelling, Journal of Supercritical Fluids, Vol: 145, Pages: 1-9, ISSN: 0896-8446
Phase equilibria in the ternary mixture (C7H8 + CO2 + CH4) were measured at temperatures of (323.15, 373.15 and 423.15) K and pressures up to 31 MPa by means of a synthetic method in which both bubble- and dew-points were measured. The results were compared with calculations based on the SAFT-γ Mie and the Predictive Peng-Robinson (PPR-78) equations of state, both of which use group-contribution approaches for parameters estimations. At low pressures, good agreement was observed with both models but this deteriorated with increasing pressure and, in the critical region, both models over-predict the pressure. The deviations are more pronounced at the highest methane content in the ternary system and at the lowest temperature. SAFT-γ Mie is shown to generally give better agreement with experiment than PPR-78. The current work suggests that the interaction parameters between CH4 and one or more of the functional groups in methylbenzene require further refinement.
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