Phase Envelope Research Articles

Saturation point and phase envelope calculation for reactive systems based on the RAND formulation

The equilibrium calculation of a reactive mixture under the phase-fraction specification, including saturation point calculation and phase envelope calculation, is desirable for the relevant process analysis and simulation. We developed the saturation RAND formulation and the corresponding algorithms for these phase-fraction specification problems. Two types of phase fraction were distinguished: the component-based one and the element-based one, which led to different constraint equations in the formulation. We further introduced element-based partition coefficients to cross the critical point of a reactive mixture in the phase envelope construction. In addition, the general formulation for reactive mixtures can be reduced and used for calculating simpler non-reactive mixtures. We illustrated the robustness and efficiency of our algorithms using four examples: Pxy diagrams for CO2-NaCl brine, a solid–liquid Tx diagram for MgCl2-water, a PT phase envelope for a reactive mixture with the alkene hydration reaction, and a PT phase envelope for a non-reactive hydrocarbon mixture.

Numerical Simulation of the Minimum Insulation Thickness to Thermally Design a Subsea Pipeline Carrying an Oil and Gas Flow

This paper considered an existing subsea pipeline transporting an oil and gas flow, and proposed to find the best thermal insulating material and the required thickness of insulation necessary to meet an output temperature of 40℃ and a pressure of 2.4MPa so as to avoid flow assurance issues. MATLAB and PIPESIM software were employed to run the simulations of the temperature and pressure profiles along the considered pipeline. Data used for the simulations were obtained from open literature. Results obtained from our simulations in MATLAB are validated using PIPESIM software, measured values and prediction model from literature. The temperature model was then used to thermally design an insulation thickness for the 50 km long pipeline using three insulating materials which are: black aerogel, polyurethane and calcium silicate. Results from the analysis showed that the black Aerogel material with a critical thickness of 10.16 cm is most effective to satisfy the criterion design. The effect of the selected insulating material was also investigated on the phase envelop. Results shows that for proper insulation thickness the flowing fluid temperature can be maintained at a temperature above which no flow assurance issues can be observed.

Vapour-liquid equilibria (VLE) and gas hydrate phase equilibria predictions using the cubic-plus association equation of state: CSMGem extension to association EoS model

Inaccurate predictions of the vapour-liquid equilibria of polar gas hydrate formers and organic inhibitors can lead to erroneous hydrate phase equilibrium predictions for these associating components. In this work, parameters of the cubic plus association equation of state (CPA-EoS) were optimized for associating components by simultaneous minimization of absolute errors of saturated liquid densities and vapour pressures compared to experimental data. Model prediction accuracies were compared with experimental data after optimizing binary interaction parameters. The proposed association equation of state (based on CPA-EoS) was employed to predict vapour-liquid equilibria of water/N2/H2+non-associating hydrate formers. Water was modelled using a 4C association scheme, i.e., comprising two proton donor and acceptor sites on each water molecule, which has been used previously (Chapman, 1989; Hammerschmidt, 1934; Kontogeorgis, 2006a; Tsivintzelis, 2010; Tsivintzelis et al., 2014; Wichterle and Kobayashi, 1972; Williams and Katz, 1954). For model development and validation, phase envelopes were predicted and validated with experimental solubility data for several systems. Furthermore, the CPA-EoS was also coupled with the Colorado School of Mines Gibbs Energy Minimization (CSMGem) algorithm for hydrate phase equilibria predictions. The predictions were in close agreement with experimental hydrate phase equilibria measurements.

Evaluation the effect of the ambient temperature on the liquid petroleum gas transportation pipeline

Abstract Liquefied petroleum gas (LPG) plays a major role in worldwide energy consumption as a clean source of energy with low greenhouse gases emission. LPG transportation is exhibited through networks of pipelines, maritime, and tracks. LPG transmission using pipeline is environmentally friendly owing to the low greenhouse gases emission and low energy requirements. This work is a comprehensive evaluation of transportation petroleum gas in liquid state and compressible liquid state concerning LPG density, temperature and pressure, flow velocity, and pump energy consumption under the impact of different ambient temperatures. Inevitably, the pipeline surface exchanges heat between LPG and surrounding soil owing to the temperature difference and change in elevation. To prevent phase change, it is important to pay attention for several parameters such as ambient temperature, thermal conductivity of pipeline materials, soil type, and change in elevation for safe, reliable, and economic transportation. Transporting LPG at high pressure requests smaller pipeline size and consumes less energy for pumps due to its higher density. Also, LPG transportation under moderate or low pressure is more likely exposed to phase change, thus more thermal insulation and pressure boosting stations required to maintain the phase envelope. The models developed in this work aim to advance the existing knowledge and serve as a guide for efficient design by underling the importance of the mentioned parameters.

Solid–liquid–liquid phase envelopes from temperature-scanned refractive index data

Abstract A novel method for estimating the upper critical solution temperature (UCST) of N,N-diethyl-m-toluamide (DEET)-polyethylene systems was developed. It was validated using data for the dimethylacetamide (DMA)-alkane systems which showed that refractive index mixing rules, linear in volume fraction, can accurately predict mixture composition for amide-alkane systems. Furthermore, rescaling the composition descriptor with a single adjustable parameter proved adequate to address any asymmetry when modeling the DMA-alkane phase envelopes. This allowed the translation of measured refractive index cooling trajectories of DEET-alkane systems into phase diagrams and facilitated the estimation of the UCST values by fitting the data with an adjusted composition descriptor model. For both the DEET- and DMA-alkane systems, linear behavior of UCST values in either the Flory–Huggins critical interaction parameter, or the alkane critical temperature, with increasing alkane molar mass is evident. The UCST values for polymer diluent systems were estimated by extrapolation using these two complimentary approaches. For the DEET-polyethylene system, values of 183.4 and 180.1 °C respectively were obtained. Both estimates are significantly higher than the melting temperature range of polyethylene. Initial liquid–liquid phase separation is therefore likely to be responsible for the previously reported microporous microstructure of materials formed from this binary system.

An Optimized Force Field for Vapor-Liquid Equilibria and Molecular Dynamics Simulations of Eco-Friendly Dielectric Fluid Perfluoronitriles.

A classical all-atom force field for perfluoronitriles (PFN-AA) is proposed for simulating the phase equilibria and dynamic transport properties of perfluoronitrile compounds that are a promising chemical family as a novel eco-friendly replacement for SF6 in various applications. The force-field parameters are developed primarily by fitting to molecular structures, vibrational frequencies, energetic profiles of the conformational rotation, and intermolecular interactions of the dimeric complexes from ab initio calculations. The performance of the PFN-AA force field is examined by simulating the vapor-liquid coexistence and physical properties of heptafluoro-iso-butyronitrile (C4) using the Gibbs ensemble simulation with the hybrid configurational-bias Monte Carlo technique and the molecular dynamics simulations. Theoretical vapor pressures and the boiling point of the pure C4 compound are in excellent agreement with available experimental data. The physical properties of C4 in the phase envelope including critical properties, self-diffusion coefficients, dielectric constants, shear viscosity, thermal conductivity, and thermodynamic properties are predicted computationally for the first time. In addition, the transferability of the PFN-AA force field with respect to other force fields, i.e., EPM2 for CO2, is validated by the successful description of the fluoronitrile/CO2 mixture. The current PFN-AA force field outperforms the generic potential models (e.g., COMPASS and CVFF) in the understanding of the fundamental properties of the novel perfluoronitrile dielectric fluids and their mixtures.

High-pressure phase equilibrium and volumetric properties of pseudo-binary mixtures of stock tank oil + methane up to 463K

High-pressure phase equilibrium and volumetric properties of highly asymmetric mixtures related to reservoir fluids are critical to the development of high-pressure and high-temperature (HPHT) reservoirs. However, there is a lack of the relevant data and accurate modeling tools. In this work, we prepared asymmetric pseudo-binary mixtures of methane (CH4) + stock tank oil (STO) and systematically measured their phase equilibrium and densities at temperatures from (298.15 to 463.15) K and pressures up to 140 MPa. The methane mole fraction in these mixtures range from 0.20 to 0.61 for the density measurement, and from 0.20 to 0.81 for the phase equilibrium measurement. From the experimental densities, the isothermal compressibility values, as well as the pseudo-excess volumes, were determined. Moreover, phase envelopes, relative volumes, and liquid volume fractions below the saturation point were also measured. These data are valuable for evaluating and improving thermodynamic models for HPHT reservoir fluids. The experimental results were modeled by the Soave-Redlich-Kwong (SRK) equation of state (EoS), the Peng-Robinson (PR) equation of state, their volume translated versions SRK-VT and PR-VT, and the Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT). For density, SRK and PR gave large deviations of ~18% and ~8%, respectively, as compared with ~3% for PC-SAFT. Inclusion of volume translation reduced their deviations to the same level as that for PC-SAFT. For isothermal compressibility, all the models gave deviations of 20-30%, with PC-SAFT, SRK-VT and PR-VT being slightly better. The excess volumes calculated by SRK, PR and PC-SAFT were similar and close to the experimental values. The deviations in the calculated excess volumes resulted in only ~1% deviations in the calculated densities if the experimentally determined STO densities were used. It was illustrated that the small deviations could be utilized in the excess volume method to accurately estimate the high-pressure live oil densities from the high-pressure STO densities. This excess volume method gave ~1% density deviation on average for all the models, with PC-SAFT giving the smallest maximum deviation. The deviations in calculated saturation pressures were ~5% for all the models with the overall deviation for PC-SAFT being slightly smaller.

Power Consumption Profiling of a Lightweight Development Board: Sensing with the INA219 and Teensy 4.0 Microcontroller

At the heart of most technological advancements is a network of processors executing code and consuming energy. Understanding those systems’ energy consumption profiles provides optimisation possibilities and thus contributes to strategies for reducing energy consumption in general. This paper assesses the power consumption characteristics of a highly competitive low cost, small form factor development board (the Raspberry Pi4 model B), powered with the minimal load associated with its bare-metal configuration and the related impact on baseline power consumption. We also consider the load associated with an out-of-box operating system, running at several underclocking frequency scaling levels and the associated impact on baseline power consumption. Our experimental set-up consists of integrating an INA219 high-side current sense amplifier for the capturing of power, current, and voltage measurements; and a Teensy 4.0 microcontroller for sampling. Overall, our results indicate statistically significant differences in overall power consumption distribution characteristics across all models. Our results also indicate the presence of three distinct power phase envelopes and statistically significant differences in mean and median power measurements between the different underclocking frequency test cases and the bare-metal cases. Our results also indicate that power consumption is an increasing monotonic function across test scenarios. Finally, our results have also shown that isolating power consumption composite distributions increases model predictability from 67% to 97%.

Speed of sound and phase equilibria for (CO2 + C3H8) mixtures

This work presents phase envelope and speed of sound data for the (0.60 CO2 + 0.40 C3H8) and (0.80 CO2 + 0.20 C3H8) binary mixtures. Phase equilibria was measured using a cylindrical resonator working in the microwave band whereas an acoustic resonator was used for speed of sound measurements. The experimental results were compared with GERG-2008 equation of state, obtaining average absolute deviations by 0.24% in pressure for phase equilibria data and 0.025% for speed of sound data. Speed of sound values were used to derive perfect-gas heat capacities, acoustic virial coefficients, and second density virial coefficients. In addition, AGA8-DC92 equation of state performance was checked for the results derived from speeds of sound.

Phase envelope calculations of synthetic gas systems with a crossover equation of state

We describe, in this work, a procedure for the calculation of the phase envelope of multi-component systems using a crossover Equation of State (EoS) based on the renormalization group theory and two different algorithms. The first algorithm utilizes pressure and temperature as natural variables, while the second uses volume and temperature. Our comparison shows that the second method is more suitable to a crossover EoS, as it avoids solving for the volume roots of the EoS, which is computationally intensive and potentially hampers the widespread use of such models in engineering applications. Moreover, we compare the simulated phase envelopes with the experimental data of 30 synthetic natural gas mixtures. The results indicate that the crossover SRK EoS has a similar performance to the classical model. Although larger deviations are observed for the representation of the bubble and dew-point curves, the crossover EoS yields a superior description of the critical points.

Validation of the Molar Flow Rates of Oil and Gas in Three-Phase Separators Using Aspen Hysys

A three-phase separator is the first vessel encountered by well fluids. The application of separators has been of great value to the oil and gas industry. In order to generate the gas phase envelope that is applicable to the study of reservoir fluid and the selection of optimum operating conditions of separators, this research utilizes a specified reservoir fluid stream to simulate a three-phase separator executed in Aspen HYSYS. Subsequently, a comparative study of the effects of specified inlet operating conditions on the output of gas and oil streams was carried out. The results show that changing the inlet pressure of the separator from 1000 to 8000 kPa reduces the gas outlet flow from 1213 to 908.6 kg mol/h, while it increases the liquid flow rate from 374 to 838.0 kg mole/h. By changing the temperature of the separator feed stream from 13 to 83 °C, the gas outlet stream was raised from 707.4 to 1111 kg mol/h, while the liquid flow rate dropped from 1037.0 to 646.1 kg mol/h. It was observed that the concentration of the outlet methane product is not affected by changing the flow rate of the feed stream at a specific pressure and temperature. Therefore, the thermodynamic property method is appropriate to simulate the separation of reservoir fluids which was achieved by selecting the Peng–Robinson (PR) model. The operating conditions of the separator were at 8000 kPa and 43 °C, which lies right on the dew point line. This is comparable to similar work on CHEMCAD which was in turn validated by plant data. Thus, the gas flow rate and the oil flow rate were dependent on pressure and temperature conditions of the plant.

Impact of Heavy Hydrocarbon Concentration on Natural Gas Flow through Transportation Pipelines

In this work, binary, ternary, quaternion, and quinary natural gas mixtures were evaluated including methane, ethane, propane, butane, and pentane to highlight their impact on pipeline performance and thermophysical properties of natural gas. The results presented that all the heavy hydrocarbons have a negative impact on natural gas phase envelope. For binary mixtures, methane/propane recorded the widest two-phase envelopes while the quinary mixtures generally formed the widest two-phase envelopes over the other mixtures. Besides, the heavy hydrocarbons content of different mixtures increased the critical pressures and critical temperatures in comparison to pure methane. The highest temperature drop of 6.495 °C was recorded by the binary mixture and the lowest temperature drop of 6.341 °C was by quinary mixture. The highest pressure drop of 4.964 bars was caused by the quinary mixture, while the lowest pressure drop of 4.1 bars was by the binary mixture. In addition, the results showed that natural gas density controlled by methane content caused increasing the methane content resulting in reducing the density of natural gas mixture. The viscosity of natural gas is a sensitive parameter to the content of the heavy hydrocarbon concentrations and all heavy hydrocarbons increased the viscosity of natural gas in comparison to pure methane.

Particle size and phase equilibria in classical logarithmic fluid

An interparticle interaction potential has been recently proposed in studies of condensate-like systems described by logarithmically nonlinear equations, such as the superfluid helium-4 and Korteweg-type melts. It has the shape of a Gaussian multiplied by a linear function and can switch between the attraction and repulsion regimes as the distance varies. We consider a classical fluid model with a discretized version of this potential in Monte Carlo molecular simulations in the Gibbs ensemble. We demonstrate a two-phase system consisting of a dense “liquid” phase in coexistence with a significantly less dense “vapour” phase. For computations, the particle size term in the potential was varied to determine its effect on both the phase envelope and the critical point of the system. It is found that the logarithm of the dimensionless critical temperature decreases in a sigmoid fashion with increasing particle size, while the critical density may be directly proportional to the particle size.

Process safety challenges of CO2 sequestration

Sequestration of carbon dioxide (CO2) is an increasingly popular method of reducing the environmental impact of natural gas and blue hydrogen development projects. While the hazards associated with natural gas processing are well understood, high pressure CO2 presents unique challenges which must be overcome by designers to make sequestration a safe and practical option. Many of these hazards are ultimately due to the CO2 phase envelope. Compression of CO2 for injection into a reservoir can involve the creation of a dense phase fluid, which shares some of the properties of both liquid and gas. Upset conditions can also create either liquid or solid CO2. These can create unforeseen consequences such as potential blockage and overpressure of vent piping, condensation and freezing of free water and inaccurate level transmitter readings. Further, the partial pressures of CO2 involved mean that corrosion rates for any carbon steel exposed in the presence of free water may be as high as 1mm per week. These safety challenges and potential solutions to them will be explored in this study.

Effect of the range of particle cohesion on the phase behavior and thermodynamic properties of fluids.

Molecular simulations are performed for the (m + 1, m) potential to systematically investigate the effect of changing the range of particle cohesion on both vapor-liquid equilibria and thermodynamic properties of fluids. The results are reported for m = 4-11, which represent a progressive narrowing of the potential energy well. The conventional Lennard-Jones potential is used as a reference point for normal fluid behavior. Small values of m result in a broadening of the phase envelope compared with the Lennard-Jones potential, whereas a contraction is observed in other cases. The critical properties are reported, and a relationship between the critical temperature and the Boyle temperature is determined. The low values of the critical compressibility factor when m < 6 reflect the behavior observed for real fluids such as n-alkanes. The results for supercritical thermodynamic properties are much more varied. Properties such as pressure, potential energy, isochoric thermal pressure coefficient, and thermal expansion coefficient vary consistently with m, whereas other properties such as the Joule-Thomson coefficient exhibit much more nuanced behavior. Maximum and minimum values are reported for both the isochoric heat capacity and isothermal compressibility. A minimum in the speed of sound is also observed.

Combining intermolecular potentials for the prediction of fluid properties: Two-body and three-body interactions.

The ability to combine intermolecular potentials without loss of information is investigated. Molecular simulation results for both vapor-liquid equilibria and supercritical isochoric heat capacities are reported for different combinations of n-m potentials. The role of both additional cohesion and repulsive terms is determined. The 12-8-6 potential obtained by adding an m = 6 contribution to the 12-8 potential significantly broadens the phase envelope, which remains inside of the 12-6 envelope. In contrast, the 12+9-6 potential that involves an additional n = 9 repulsive contribution lifts the phase envelope above the 12-6 values. The 12-8-6 potential significantly reduces the maximum and minimum observed for the isochoric heat capacity at supercritical conditions. In contrast, the additional repulsion of the 12+9-6 potential has a relatively small influence on the supercritical behavior of the isochoric heat capacity. Significantly, a comparison of vapor-liquid equilibria data for two-body only simulations for Ar, Kr, and Xe indicates that there is very good agreement with the 12-8-6 data. This means that the 12-8-6 potential may provide a useful description of two-body only interactions for the noble gases. The 12+9-8 potential at least partially reproduces vapor-liquid properties of noble gases interacting via two-body plus three-body interactions. In general, the combination of potentials provides a mechanism of simplifying the calculation of two-body and two-body plus three-body interactions.

Molecular engineering of sustainable phase-change solvents: From digital design to scaling-up for CO2 capture

• Digital design and experimental validation of phase-change CO 2 capture solvents. • Evaluation of thermodynamics, reactivity, process and sustainability properties. • SAFT-γ Mie predicts entire three-phase envelope for S 1 N/DMCA + H 2 O + CO 2 . • Low regeneration energy, viscosity and vapour losses, high cyclic capacity. • Favourable health and safety performance compared to other solvents. Phase-change solvents promise reduced energetic and environmental footprints for separation systems, including absorption-based CO 2 abatement technologies. The search for efficient phase-change solvents is limited by challenges in vapour-liquid–liquid equilibrium (VLLE) prediction and in sustainability assessment. We overcome these with a digital approach to screen billions of structures and design the novel phase-change solvent S 1 N (N1-cyclohexylpropane-1,3-diamine) and mixture S 1 N/DMCA (N,N-dimethylcyclohexylamine). Screening criteria include thermodynamic and process-related properties, reactivity and sustainability of solvent production and use. VLLE phase envelopes are predicted using the SAFT-γ Mie (Statistical Associating Fluid Theory) equation of state thanks to its transferability to any structure and the implicit modelling of ionic species. Experimental validation confirms the suitability of S 1 N/DMCA for scaling-up, with a cyclic capacity of 1.19 mol CO 2 / kg-solvent, a regeneration energy of 2.3 GJ/ton-CO 2 , and vapour losses and viscosity lower by 10% and 70% than those of other solvents. S 1 N is also safer for plant operation and working personnel.

Phase characteristics of hydrocarbons generated from different types of kerogen at different maturity levels in closed system

For studying phase characteristics of hydrocarbons generated from different types of kerogen at different maturity levels, pyrolysis data of MM type-I and II kerogen (Maoming oil shale) and Coal type-III (Turpan coal) were collected and used for building phase models by PVT simulation technology. Then, phase diagrams, as well as physical properties (GOR, density, and viscosity) related to different kerogen types and along with maturity history, were output and carried out for comparative studies. The results show that three different types of kerogen perform different hydrocarbon generation processes, which form various yields and hydrocarbon compositions, leading to different petroleum types and diverse phase characteristics. The GORwt and the relative proportion of light and heavy hydrocarbons are two critical factors to shape the phase envelopes. The nature of kerogen with different maturity processes controls the changes of hydrocarbon compositions to form diverse phase characteristics. Their phase diagrams and physical properties on the ground conditions confirmed the different maturity ranges of black oils, light oils, and gas condensates generated by kerogen, respectively. Our study clarified that all types of kerogen at early generations (relatively low maturities) extensively generate black oils even though phase characteristics are different. In contrast, at a relatively high maturity by considering yields and expulsions of hydrocarbons, the MM type-II kerogen prefers to generate light oils, while the MM type-I kerogen prefers to generate black oils and the Coal/type-III kerogen prefers to generate gas condensates.

High-pressure vapor + liquid equilibria for the binary system CO2 + (E)-2-hexenal

The isothermal vapor + liquid equilibria of carbon dioxide + (E)-2-hexenal (a key apple aroma) was measured using a visual equilibrium cell with an analytic methodology. The selected isotherms were (313.2, 323.2 and 333.2) K, and the pressures assessed ranged from (2.2–9.8) MPa. The thermodynamic consistency of the experimental data was verified, and the uncertainties of the molar fractions of the vapor and liquid phases were estimated. The density and dynamic viscosity of pure (E)-2-hexenal were measured at 101.13 kPa and temperatures from (292.2–353.2) K. Two equations of state were selected to model the vapor + liquid equilibria. The Peng-Robinson with two different mixing rules, and the Perturbed Chain - Statistical Associating Fluid Theory. The phase envelopes showed a critical pressure, detected at carbon dioxide molar fractions ≥ 95 % mol∙mol−1.

Evaluation of hydrogen concentration effect on the natural gas properties and flow performance

The natural gas flowing through transmission pipeline is impure and has a wide range of non-hydrocarbons components at different concentrations like hydrogen. The presence of hydrogen in the natural gas mixture influences its properties and flow performance. The effect of hydrogen concentration on the natural gas flowing through a transportation pipeline has not been adequately investigated and widely comprehended. In this paper, several mixtures flow through pipeline include typical natural gas and hydrogen at different concentrations up to 10% are evaluated to demonstrate their impact on the flow assurance and the natural gas properties. The string Ruswil – Griespass part from the Transitgas project with 94 km length is simulated applying Aspen Hysys Version 9 and validated using Aspen Plus. The simulation specifications were 1.228 ∗ 106 kg/h mass flowrate, 1200 mm and 1164 mm the outer and inner diameters, and 75 bar and 29.4 °C operating pressure, and temperature. The effect of different hydrogen concentrations has been examined and the differences from the typical mixture are estimated. The results show that the presence of hydrogen in the natural gas mixture reduces its density, 10% hydrogen content records 11.78% reduction in the density of typical natural gas. Interestingly, it has been found that up to 2% of hydrogen concentration turns in elevating the viscosity of the typical natural gas while the viscosity decreases at the point that hydrogen content increases above 2%. In addition, the pressure losses over the transmission pipeline increases due to the presence of hydrogen, 10% hydrogen concentration turns in 5.39% increase in the pressure drop of the natural gas mixture. Also, the temperature drop across the pipeline decreases as the hydrogen concentration increases; 10% hydrogen content can result in a 6.14% reduction in the temperature drop across the pipeline. As well as, the findings prove that the hydrogen strongly impacts the phase envelope by changing from size symmetric to size asymmetric diagram. The effect of pipeline elevations has been investigated by changing the elevation up to 25 m uphill and 25 m downhill. The results state that increase the pipeline elevation turns in increasing the pressure losses over the pipeline length. Along with this, the results illustrate that the presence of hydrogen in the mixture elevates the critical pressure and reduces the critical temperature.