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In alcohol-containing systems, the association of polar molecules significantly influences the calculation of water activity, leading to substantial deviations from ideal solution behavior. This makes it challenging for traditional hydrate formation condition models to accurately predict hydrate formation temperatures and pressures. To address this issue, we propose a novel unified thermodynamic framework based on the Parrish-Prausnitz (P-P) model and the Cubic-Plus-Association (CPA) equation of state (EoS) for calculating the hydrate formation condition in systems containing gas/water/alcohol, by using the advantages of the CPA EoS to characterize the association interaction of polar molecules. In addition, we utilize experimental data to model the molecular association in alcohol-containing systems and conduct regression analysis for binary interaction coefficients among alcohol, water, and gas. Multiple sets of experimental data on component fractions and hydrate formation conditions for methane-alcohol-water systems are used for validation. The proposed model shows an average relative error of 1.17–6.42% for predicting alcohol/methane component fractions in the liquid phase and 1.93–4.78% for predicting hydrate formation conditions in alcohol-containing systems. Compared to traditional models, this model demonstrates a significant improvement in accuracy and performs well in predicting hydrate formation conditions in alcohol-containing systems. [ABSTRACT FROM AUTHOR]

In order to realize the safe transportation of liquefied ethane pipeline in the Oilfield of China, it is necessary to fully study the process of pipeline replacement, operation and shutdown. The accurate calculation of physical property parameters and critical parameters is the basis of studying the gas-liquid two-phase flow and heat and mass transfer process of liquefied ethane in the pipeline. In this paper, different equations of states (EOSs) were used to predict the physical properties (such as density, dew point and dynamic viscosity) of ethane or ethane mixture, and the predicted results were compared with the corresponding experimental data from the literature. The prediction performance of different EOSs were evaluated by using two evaluation indicators, including average absolute deviation (AAD) and average relative deviation (ARD). The results showed that the PR-Peneloux EOS has the best performance for predicting the density of CH4-C2H6-N2 mixture with an ARD value of 4.46%; for predicting the dew point, the BWRS EOS exhibits the superior performance with an ARD value of 0.58%; and for predicting dynamic viscosity, the SuperTRAPP formula has the smallest calculation error, with an ARD value of 1.33%. Considering the comparison results of the calculation accuracy of density, dew point and dynamic viscosity of ethane or ethane mixture by using different EOSs, PR-Peneloux EOS was recommended to calculate the phase characteristics in the process of ethane pipeline replacement operation. The phase characteristics of ethane for pipeline transport in the oilfield of China were obtained. The critical temperature is 32.79℃ and the critical pressure is 4.97 MPa. [ABSTRACT FROM AUTHOR]

Gas solubility in water under hydrate-liquid water (H-L w ) two-phase equilibrium is the foundation of gas hydrate kinetic study. It is significant for the simulation of multiphase pipeline flow, the stability and amount evaluation of natural gas hydrate resources in deep water as well as gas storage and separation. In the current work, thermodynamic models were established by combining van der Waals-Platteeuw theory with PR, VPT and TB equations of state separately, named as Model VPR, VVPT and VTB, to predict methane solubility in water under H-L w equilibrium. The Henry’s law was also included for comparison. Available experimental data in literature were collected to test the applicability of these equations of state. In order to improve the predicting accuracy, binary interaction parameters in the asymmetric contribution term of non-density-dependent (NDD) mixing rules were modified. Good agreements between predicted and experimental data were obtained by Model VVPT with the modified NDD mixing rules. [ABSTRACT FROM AUTHOR]

Peng-Robinson equation of state (PR EoS) is a reliable and widely used cubic EoS to predict natural gases thermodynamic properties. However, large deviations between the calculated compressibility factor values and the realistic values are observed when it is applied to the high volume CO 2 -content natural gas. In order to enhance its applicability, a new correction parameter associated with three-parameters (the reduced temperature T r , reduced pressure P r and CO 2 volume content) is introduced into the attractive term of PR EoS by fitting the deviations between 267 groups of experimental compressibility factors and corresponding calculation values. The results reveal that the average absolute deviation between experimental data and predicted compressibility factors from the improved PR EoS is 2.708% when the pressures range from 3 MPa to 15 MPa, temperatures range from 263.15 K to 313.15 K and CO 2 volume contents range from 9.84% to 100%. The deviation is reduced by 9.61% when compared to that of the original PR EoS. The results also demonstrate that this improved PR EoS has better performance than PRSV, PRTwu BWRS EoSs, and is essentially comparable in predictability to PC-SAFT EoS. [ABSTRACT FROM AUTHOR]

To improve the compressibility factor prediction of CO 2 -content natural gas, this short communication proposes a new combinational Stewart-Burkhardt-Voo (SBV) + Prausnitz-Gunn (PG) mixing rule for the Lee-Kesler equation of state. The rule suggests using SBV and PG mixing rules for the pseudocritical temperature and pressure computations, respectively, when the reduced temperature is higher than one and the reduced pressure is higher than five; otherwise, the pseudocritical temperature and pressure is calculated according to SBV mixing rule. Comparisons between experimental and calculation data show that the maximum average relative deviation is 1.56% when the mole fraction of CO 2 is less than 50%. [ABSTRACT FROM AUTHOR]

Recently, a PRμ viscosity model was developed by Fan et al. It is applicable to both the liquid and gas hydrocarbons, but some large deviations might be obtained when applied to some multi-component mixtures. This short communication proposes an improvement method to enhance the accuracy of this model. The method replaces the universal critical compressibility factor in the original model with each component's real critical compressibility factor. The experimental viscosity data of pure methane, pure propane and thirteen light liquid hydrocarbon mixtures were adopted to validate the improved model. The results show the improved model is suitable to both the light hydrocarbon liquids and gases with satisfactory accuracy. The average ARD of the PRμ model was enhanced 4.78% when applied to thirteen hydrocarbon mixtures. Additionally, when applied to five complicated Qatari synthetic natural gas mixtures, the improved PRμ model is essentially comparable in predictability to five other viscosity prediction models. [ABSTRACT FROM AUTHOR]

The gas compressibility factor as an essential thermodynamic parameter is often used to analyze PVT behavior in natural gas engineering. To accurately predicate it for various gas condensates, a data base containing 916 data sets covering a wide range of experimental conditions is employed to establish and test the prediction model based on a three-parameter cubic equation of state (EoS). The presented model which based on EPT EoS combines with Elliott-Daubert binary interaction coefficients correlation, Ahmed et al. splitting and Hosseinifar-Jamshidi characterization methods is superior to conventional empirical correlations with three mixing rules and two-parameter EoSs as SRK, PR, PRSV and MPR2. Statistical error analysis shows that it outperforms empirical correlations with average absolute relative errors of 1.45% and coefficient of determination of 0.989. At pressure and temperature up to 95.04 MPa and 429.3 K, respectively, the model also outperforms two-parameter EoSs with average absolute relative errors of 1.65% and coefficient of determination of 0.992. The presented model is efficient and practical for predicting the compressibility factor of gas condensate. Four three-parameter EoSs are evaluated at different temperatures and pressures. Three BIC determining methods are compared for various gas condensates. Six characterization methods for pseudo components are optimized. A new method is proposed for gas condensate at a wide range of pressure conditions. The accuracy of the method is better than applied empirical correlations and EoSs. [ABSTRACT FROM AUTHOR]

Knowledge of critical points is important to determine the phase behavior of a mixture. This work proposes a reliable and accurate method in order to locate the liquid-vapor critical point of a given mixture. The theoretical model is developed from the rigorous definition of critical points, based on the SRK equation of state (SRK EoS) or alternatively, on the PR EoS. In order to solve the resulting system of $$C+2$$ nonlinear equations, an improved method is introduced into an existing Newton-Raphson algorithm, which can calculate all the variables simultaneously in each iteration step. The improvements mainly focus on the derivatives of the Jacobian matrix, on the convergence criteria, and on the damping coefficient. As a result, all equations and related conditions required for the computation of the scheme are illustrated in this paper. Finally, experimental data for the critical points of 44 mixtures are adopted in order to validate the method. For the SRK EoS, average absolute errors of the predicted critical-pressure and critical-temperature values are 123.82 kPa and 3.11 K, respectively, whereas the commercial software package Calsep PVTSIM's prediction errors are 131.02 kPa and 3.24 K. For the PR EoS, the two above mentioned average absolute errors are 129.32 kPa and 2.45 K, while the PVTSIM's errors are 137.24 kPa and 2.55 K, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Lee-Kesler (LK) Equation of State (EoS) is the most accurate enthalpy model for gases. The pressures at some condensate gas well heads are higher than 70 MPa. Accurate calculating the compressibility factors of the high pressure gas is essential to the enthalpy calculation of LK EoS. The basic parameters of the LK EoS are the reduced pressure and temperature which should be calculated based on mixing rules. This work researches the API, Plocker and Knapp, Lee and Kesler mixing rules, the combinations composed of Prausnitz and Gunn high pressure mixing rule and the above three rules. Comparisons of 11 experimental and calculated compressibility factors show the API mixing rule is the most accurate one when the pressure is lower than 20 MPa. Comparisons of 31 experimental and calculated compressibilityfactors show the API+PG mixing rule combination is the most accurate when the pressure ranges from 24 to 90.5 MPa, and the maximum relative deviation is less than 2%. [Copyright &y& Elsevier]

The co-existence of gas, water, and monoethylene glycol (MEG) is common in produced fluids of high-pressure gas wells. Accurate predictions on the temperature changes during the choking process are essential for the design and operation of the choke valve. This paper presents an efficient multiphase isenthalpic flash method based on the cubic-plus-association equation of state (CPA EOS) to calculate the choke temperatures. In comparison with the traditional isenthalpic flash algorithm, this new method accounts for the self- and cross-association between polar water and MEG molecules, yielding more accurate enthalpy calculation results and multiphase component distributions for fluids containing water and MEG. The proposed model is validated by field test data with pressures from 8.68 MPa to 119.3 MPa. The average absolute deviations between the calculated choke temperatures and measured values are less than 1.6 °C even for vapor-liquid-aqueous three-phase mixtures at various pressures. Moreover, case studies show that accounting for the association between polar water/MEG molecules contributes to accurate predictions on choke temperatures. At high pressures, the CPA EOS tends to give higher choke temperatures in comparison with those calculated based on the traditional SRK-Peneloux EOS. In contrast, the CPA EOS tends to yield lower temperatures at low pressures. • A multiphase isenthalpic-flash model is proposed to predict choke temperatures. • Prediction results are validated with production data up to 119.3 MPa. • Results based on the CPA and SRK-based EOS are compared. • The effects of water and glycol contents on choke temperatures are discussed. • The polar molecule association is not negligible for predicting choke temperatures. [ABSTRACT FROM AUTHOR]

A new methodology was proposed for predicting the multiphase behavior of a supercritical CO 2 –heavy oil–water–solvent system during supercritical CO 2 extraction. The cubic-plus-association equation of state (CPA EoS) was used to model the hydrogen bond association between asphaltene and water and to develop a nine-step characterization method for asphaltene-containing oil. Results showed that the proposed method could represent phase behavior for three equilibrium phases: the vapor phase and high-density and low-density liquid phases. The absolute average relative deviation between the predicted and experimental phase boundary pressures was 3.6–11.8%, smaller than those (7.0–20.8%) calculated using Soave–Redlich–Kwong EoS with Huron–Vidal mixing rules. Moreover, case studies on appropriate extraction conditions showed that the extraction pressure increased with increasing molecular weight and critical pressure of each pseudocomponent. Increasing extraction pressure for H 2 O-containing systems was beneficial for improving extraction efficiency. [Display omitted] • A new heavy oil characterization method was applied to phase behavior calculation. • Hydrogen bond association between polar components was considered. • Satisfactory accuracy and generality are demonstrated in phase behavior prediction. • High-density oils were extracted at higher pressures than low-density oils. • Increasing pressure for water-containing system was beneficial for extraction. [ABSTRACT FROM AUTHOR]

The Joule-Thomson characteristics of hydrogen-blended natural gas (HBNG) differ from those of natural gas for the differences in properties, deserving a profound study. We foremost analyzed the effects of hydrogen on the properties of HBNG using the Soave-Benedict-Webb-Rubin (BWRS) equation of state (EOS) owing to its lowest deviation among the concerned EOSs. Based on BWRS EOS, the fundamental differential equation, and the isenthalpic equation, we developed a thermodynamic model to evaluate the effects of hydrogen on the isenthalpic curve, Joule-Thomson coefficient (JTC), and Joule-Thomson inversion curve (JTIC) of HBNG within the hydrogen mole fraction (x -H 2) range of 30%. The average absolute relative deviation (AARD) for the isenthalpic curve of the N 2 -H 2 mixture and the JTC of natural gas is 0.02% and 1.62%. We mainly discussed how hydrogen affects the isenthalpic curve, JTC, and JTIC of HBNG. The isenthalpic curve of the CH 4 -H 2 mixture and HBNG rise in a descending gradient with increasing x -H 2. Compared to natural gas, the JTC of HBNG decreases (about 48% when x -H 2 is 30%) and negatively correlates to x -H 2 , pressure, and temperature in a nonlinear function. The JTC is more sensitive to the x -H 2 at higher temperatures and lower pressures. The blended hydrogen narrows the positive effect region of HBNG but does not turn the positive effect into a negative one within the x -H 2 range of 30%. When x -H 2 increases from 0% to 30%, the maximum inversion pressure and corresponding temperature drop at a rate of 0.227 MPa/ x -H 2 % (roughly linear) and 4.9385 K/ x -H 2 % (linear), respectively. • The effects of hydrogen on the isenthalpic curve weaken with increasing x -H 2. • Compared to natural gas, the JTC of HBNG decreases and negatively correlates to x -H 2 , pressure, and temperature in a nonlinear function. • The JTC of HBNG is more sensitive to the x -H 2 at higher temperatures and lower pressures. • Hydrogen narrows the positive effect region of HBNG but does not turn the positive effect to negative within x -H 2 of 30%. [ABSTRACT FROM AUTHOR]

The coexistence of acid gas/water/alcohol/electrolyte mixtures is common during the gas production process. Traditional methods have difficulty accurately predicting hydrate formation temperatures and pressures because of complicated molecular and ionic interactions in such mixture components. Based on the electrolyte Cubic-Plus-Association (e-CPA) equation of state (EoS) and the Parrish-Prausnitz model, this paper proposed a unified thermodynamic model to describe the multiple interactions of acid gas/water/alcohol/electrolyte components on gas, liquid, and hydrate phases by using the advantages of the e-CPA EoS to characterize the hydrogen bond association, solvation, ion electrostatic interaction, and ionic solvation. This work has achieved an accurate and flexible way to compute the hydrate formation conditions with or without acid gases, alcohols, and electrolytes. A total of 281 groups of experimental data at pressures from 0.068 MPa to 186.2 MPa are applied to validate this model. The results show that the average relative deviations (ARDs) of predicted temperatures and pressures are 0.13% and 6.52%, respectively. For nonelectrolyte systems, the ARD between the experimental and calculated hydrate formation temperatures is 0.19%, which is reduced by 0.24% and 0.34% in comparison with traditional Soave–Redlich–Kwong and Peng–Robinson EoSs. For mixtures containing alcohol and/or electrolytes, the ARD of predicted hydrate temperatures is 0.12%. Particularly, for harsh systems with ultrahigh pressure (186.2 MPa), the sour gas content of 24.52 mol%, MeOH concentration of 50% by mass, and salinity of 31% by mass, the deviations are less than 2.2 K. More cases demonstrate the performance and synergistic effect of alcohol and electrolytes in inhibiting hydrate formation. • A unified thermodynamic model based on the Parrish-Prausnitz model/CPA EoS/e-CPA EoS is presented. • Hydrogen bond association, solvation, ion electrostatic interaction, and ionic solvation are considered. • The results based on the P–P/CPA EoS/e-CPA EoS and based SRK/PR models are compared. • Satisfactory accuracy and generality are demonstrated in wide region and complex systems. • The performance and synergistic effect of sodium chloride and monoethylene glycol are shown. [ABSTRACT FROM AUTHOR]