Methane-ethane Mixtures Research Articles

Hydrate Formation from Joule Thomson Expansion Using a Single Pass Flowloop

Hydrate risk management is critically important for an energy industry that continues to see increasing demand. Hydrate formation in production lines is a potential threat under low temperature and high-pressure conditions where water and light gas molecules are present. Here, we introduce a 1-inch OD single-pass flow loop and demonstrate the Joule-Thomson (JT) expansion of a methane-ethane mixture. Initially, dry gas flowed through the apparatus at a variable pressure-differential. Larger pressure differentials resulted in more cooling, as predicted by standard thermodynamic models. A systematic deviation noted at higher pressure differentials was partially rectified through corrections incorporating heat transfer, thermal mass and kinetic energy effects. A wet gas system was then investigated with varying degrees of water injection. At the lowest rate, hydrate plugging occurred close to the expansion point and faster than for higher injection rates. This immediate and severe hydrate plugging has important implications for the design of safety relief systems in particular. Furthermore, this rate of plugging could not be predicted by existing software tools, suggesting that the atomization of liquids over an expansion valve is a critical missing component that must be incorporated for accurate predictions of hydrate plug formation severity.

MATHEMATICAL MODELLING OF THE DYNAMICS OF THERMAL CONVERSION OF METHANE-ETHANE MIXTURES IN A WIDE TEMPERATURE RANGE

A compact mechanism based on elementary radical reactions is proposed for the temperature conversion of methane-ethane mixtures. The kinetic model relying on this mechanism describes the literature data on the conversion of methane and ethane at millisecond time intervals in the temperature range 600-1400 °C. Within the kinetic model, the time dependences of the concentrations of hydrogen, ethylene, acetylene and benzene on the temperature and on the methane/ethane ratio in the initial mixture are determined in the isothermal approximation. Using the proposed mechanism for the calculations of axisymmetric gas-dynamic flows of reagents mixture, the yields of hydrogen and valuable unsaturated hydrocarbons in a non-isothermal tubular reactor are determined.

Natural Gas Pyrolysis in a Liquid Metal Bubble Column Reaction System—Part II: Pyrolysis Experiments and Discussion

This contribution presents the results of continued investigations on the production of hydrogen by means of pyrolysis in a liquid metal bubble column reactor, as developed at the Karlsruhe Institute of Technology in recent years. Part I of this contribution described the motivation and the methodology of this study, as well as a significant scale-up, and discussed its results for pure methane pyrolysis. Here in part II, two additional experimental campaigns with methane–ethane mixtures (MEMs) and high-calorific natural gas (nGH) will be presented and discussed for the first time, using the up-scaled liquid metal bubble column reactor. It could be proven that an MEM as the feed gas led to an increase in methane conversion at low temperatures, which is consistent with the literature data. The nGH pyrolysis confirms this trend and also results in a significant rise in methane conversion compared to pure methane pyrolysis. Furthermore, the nGH pyrolysis leads to an increased methane conversion even at higher temperatures compared to MEM pyrolysis. Additionally, both MEM and nGH pyrolysis also showed a shift in the formation of by-products toward lower temperatures.

Steam Conversion of Ethane and Methane–Ethane Mixtures in a Membrane Reactor with a Foil Made of a Pd–Ru Alloy

Steam Conversion of Ethane and Methane–Ethane Mixtures in a Membrane Reactor with a Foil Made of a Pd–Ru Alloy

Steam Conversion of Ethane and Methane–Ethane Mixtures in Membrane Reactor with a Foil from Pd–Ru Alloy

The features of steam conversion of ethane and methane-ethane mixtures containing 5, 10 and 15% ethane in a membrane reactor with a 30 μm thick Pd–Ru foil at temperatures of 1800 and 3600 h–1 and steam/feed rations of 3 and 5 have been investigated. Comparative experiments with “non-membrane” reaction have shown that in the membrane reactor the feedstock conversion to form H2 and CO2 increases and ethane hydrocracking decreases. Increasing the rate of H2 recovery through the membrane by permeate evacuation leads to an increase in the yield of H2 and CO2. With a decrease in the steam/feed ratio from 5 to 3, the ethane hydrocracking and the rate of carbon deposits formation increases. Optimal conditions for steam conversion of ethane and methane-ethane mixtures are T = 773 K, feed space velocity of 1800 h–1 and steam/feed ratio of 5. The established regularities are similar to those obtained earlier for other types of raw materials (mixtures of methane with propane, propane, n-butane, a mixture simulating the average composition of associated petroleum gas) in this membrane reactor.

Natural Gas Storage Filled with Peat-Derived Carbon Adsorbent: Influence of Nonisothermal Effects and Ethane Impurities on the Storage Cycle.

Adsorbed natural gas (ANG) is a promising solution for improving the safety and storage capacity of low-pressure gas storage systems. The structural-energetic and adsorption properties of active carbon ACPK, synthesized from cheap peat raw materials, are presented. Calculations of the methane-ethane mixture adsorption on ACPK were performed using the experimental adsorption isotherms of pure components. It is shown that the accumulation of ethane can significantly increase the energy capacity of the ANG storage. Numerical molecular modeling of the methane-ethane mixture adsorption in slit-like model micropores has been carried out. The molecular effects associated with the displacement of ethane by methane molecules and the formation of a molecule layered structure are shown. The integral molecular adsorption isotherm of the mixture according to the molecular modeling adequately corresponds to the ideal adsorbed solution theory (IAST). The cyclic processes of gas charging and discharging from the ANG storage based on the ACPK are simulated in three modes: adiabatic, isothermal, and thermocontrolled. The adiabatic mode leads to a loss of 27-33% of energy capacity at 3.5 MPa compared to the isothermal mode, which has a 9.4-19.5% lower energy capacity compared to the thermocontrolled mode, with more efficient desorption of both methane and ethane.

Numerical simulation on shell-side flow pattern transition and heat transfer of non-azeotropic refrigerant mixture

The non-azeotropic hydrocarbon refrigerant mixture flowing across shell-side of spiral wound heat exchanger is widely used in liquefied natural gas production industry. However, the phase-change heat transfer mechanism is still lack of thorough understanding. A numerical model is presented for simulating evaporation heat transfer of non-azeotropic hydrocarbon refrigerant mixture, CH4/C2H6, across multiple spiral wound tubes. Volume of Fluid model (VOF) was used to obtain liquid–vapor interface. The heat and mass transfer rates for each component were given as source terms. Thermophysical properties of the mixture were given using mixing laws in the literature. A flow pattern map was developed based on simulation results. The flow pattern transition and heat transfer were analyzed for the mixture with several component mixing ratios. With increasing vapor quality, pure ethane and methane-ethane mixture appear different flow patterns. The pure ethane has smoother liquid film on the tube wall than the methane-ethane mixture. The increasing of methane promotes the flow pattern transition. With vapor quality of 0.2–0.3, falling film flow transfers to shear flow. Shear flow transfers to spray flow for vapor quality of 0.7–0.8, where the heat transfer coefficient starts to decrease for methane-ethane mixture. For falling film flow, the heat transfer coefficient of pure ethane is higher than the methane-ethane mixture. The outcomes may help spiral wound heat exchanger design and evaluation for liquefied natural gas production.

Diffusion of fluids confined in carbonate minerals: A molecular dynamics simulation study for carbon dioxide and methane–ethane mixture within calcite

The ability to calculate how different compounds diffuse within mesoporous structures is paramount for a number of applications in the oil & gas sector, from oil exploration to separation, and even for the design of Carbon Capture, Utilization, and Storage (CCUS) processes. Molecular Dynamics simulations entail an excellent alternative to cases for which an experimental determination is unfeasible or extremely difficult, as it happens for fluids in mesopores. Nonetheless, being confined within a mineral mesopore makes the fluid spatial distribution inhomogeneous, requiring appropriate methods to compute the diffusion coefficients. Recently, some of us presented a new method for this purpose (Franco et al. 2016). In this work, we present a detailed study on how to apply such a method exploring fluids confined within calcite walls, which is a mineral representative of carbonate rocks found in several geological formations. From our results, we were able to map the evolution of the self-diffusion tensor components throughout the pore, showing the anisotropy among the components at different directions. We also show the influence of confinement and observe a significant effect at the center of the pore for small mesopores (< 7.5 nm), where the density distribution is constant. This is an unexpected result that shows how the confinement effect is manifested even at the so-called “bulk-like” region at the center of the pore.

Experimental measurement and model prediction of solid-liquid equilibrium for methane-ethane binary system

Solid-liquid equilibrium characteristics of light alkane mixtures are of great significance for their applications in chemical engineering and liquified natural gas industry. However, the related researches, especially on their eutectic characteristics and phase change behaviors, are insufficient. Therefore, in the present study, a test rig with a temperature preparing capacity below 70 K is built to measure the freezing point temperatures of different methane-ethane mixture samples. Fifteen experimental points are obtained from the tests in which the freezing temperature varies from 73.88 K to 90.65 K and the molar fraction of methane changes from 0 to 1. Three models are utilized to predict the solid–liquid equilibrium of methane-ethane binary system, and the comparison study shows that SRK model reaches the most accuracy with a relative standard deviation of 1.27%. Based on the data regression of experimental results, the binary interaction coefficient with k12 = -0.073 instead of k12 = 0 is recommended in the prediction of SLE of methane-ethane binary system. Furthermore, a cubic polynomial formula is proposed to corelate k12 variation with temperature, and the modified SRK model with temperature-dependent k12 gives a more accurate prediction on the SLE of methane-ethane binary system with the standard deviation of 0.99%. The predicted eutectic temperature of methane-ethane binary system by the modified model is about 72.71 K and the corresponding methane molar fraction is about 0.668, which are closer to the test data.

Diffusion of Fluids Confined in Carbonate Minerals: A Molecular Dynamics Simulation Study for Carbon Dioxide and Methane-Ethane Mixture within Calcite

Diffusion of Fluids Confined in Carbonate Minerals: A Molecular Dynamics Simulation Study for Carbon Dioxide and Methane-Ethane Mixture within Calcite

Numerical investigation on flow and heat transfer characteristics of supercritical methane–ethane mixture in a straight channel

Printed Circuit Heat Exchanger (PCHE) is considered as a promising heat exchanger for offshore Liquefied Natural Gas (LNG) production due to its compactness and high efficiency. To reveal the flow and heat transfer performance of real component nature gas mixture in PCHE, numerical study was conducted to obtain flow and heat transfer characteristics of supercritical methane–ethane mixture in a straight channel of PCHE. The influence of operating parameters including inlet temperature, mass flux and outlet pressure are investigated. The simulation results show that heat transfer coefficient and pressure drop increase with the increase of inlet temperature and mass flux, and decrease with the increase of outlet pressure. The overall variation tendency of heat transfer coefficient and pressure drop in supercritical methane–ethane mixture flow was similar to those in supercritical methane flow, but there still exists some difference due to their different physical properties. For the value of heat transfer coefficient, supercritical methane flow is about 7% larger than that of supercritical methane–ethane mixture flow. And for frictional pressure drop, supercritical methane flow is much larger by about 12%. Finally, new correlations were proposed for supercritical methane–ethane mixture flow, which are helpful for a more accurate flow and heat transfer calculation in PCHE designing for natural gas.

Understanding the Effect of Pore Size on the Separation Efficiency of Methane–Ethane Mixtures Using Kinetic Monte Carlo Simulation

Understanding the Effect of Pore Size on the Separation Efficiency of Methane–Ethane Mixtures Using Kinetic Monte Carlo Simulation

Calculation of thermodynamic properties of mixtures in two-phase equilibrium

Thermodynamic properties of mixtures in vapor-liquid equilibrium (VLE) were studied. Thermodynamic properties of the methane-ethane mixtures in VLE were calculated with highly accurate Helmholtz free energy equation of state GERG-2008, simplified GERG-2008 and common cubic PR equation of state (EOS). Results show that GERG-2008 has high accuracy in VLE calculations. However, simplified GERG-2008 and PR-EOS both work unsatisfactorily in VLE calculations.

Transformations of ethane and ethylene with methane on a resistive fechral catalyst in the presence of hydrogen

Transformations of methane-ethane, methane-ethylene, hydrogen-ethane and hydrogen-ethylene mixtures on an electrically heated resistive fechral catalyst were studied. During the transformations, the catalyst surface becomes covered with graphitic carbon deposits, which exertan additional catalytic action leading to the formation of C3 and C4 hydrocarbons. The formation of the indicated hydrocarbons proceeds most likely with the involvement of ethylene produced from ethane. The presence of hydrogen suppresses coking of the catalyst surface and decreases the yields of C3 and C4 hydrocarbons.

Pore-Scale Study of Oil Recovery by Gas and Foam in a Fractured Carbonate Rock at Different Gas–Oil Interfacial Tension

This work studies oil displacement by gas and foam in a fractured low-permeability oil-wet carbonate rock. In the three experiments conducted, gas is a methane–ethane mixture whose ethane mole frac...

Structural Transition of the Methane–Ethane Mixture Hydrate in a Hydrate/Water/Hydrocarbon Three-Phase Coexistence System: Effect of Gas Concentration

Hydrate formation of a natural gas mixture is fascinating. Whereas both pure methane and ethane form a structure I (sI) hydrate, their mixture may form a structure II (sII) hydrate at certain compo...

Surface and confinement effects on the self-diffusion coefficients for methane-ethane mixtures within calcite nanopores

The study of transport properties of unconventional oil reservoirs such as shale gas is crucial to optimize production, enhance oil extraction, and decrease costs and environmental hazards. One important dynamical property of fluids is diffusion, which is necessary to determine the oil mobility and rate of oil production from the reservoir, and can be obtained through the self-diffusion coefficient. To obtain the transport properties of fluids under confinement, one must take into account the surface and the confinement effects. Moreover, approaches that consider the position-dependency and the nonlinear particle distribution are required. Applying methods based on probability density function, the self-diffusion components of methane-ethane mixtures confined within calcite nanopores were calculated, using molecular dynamics simulations. The anisotropy between xx, yy, and zz components of the self-diffusion tensor has different effects depending on the position inside the nanopore. A surface effect causes an anisotropic behavior between parallel self-diffusion coefficients for this mixture close to the calcite walls. At the center of the pore, the confinement effect is manifested by lowering the value of the perpendicular self-diffusion coefficient when compared to the parallel ones. Mixture composition plays an important role, since a higher ethane content shows greater anisotropy between parallel components.

PHASE ENVELOPE CONSTRUCTION FOR MIXTURES USING HIGHLY ACCURATE HELMHOLTZ ENERGY EQUATION OF STATE

Phase envelope construction for mixtures is very important in the oil and gas industry. The most widely used model for phase envelope construction is Peng — Robinson equation of state (PR-EOS) due to its simplicity. In order to construct phase envelopes of natural gas, a highly accurate Helmholtz energy equation of state GERG-2008 was proposed. In this work, the accuracy of phase envelopes calculated by a highly accurate equation of state GERG-2008, simplified GERG-2008 and traditional cubic PR-EOS was analyzed. The pressure-based algorithm is used to calculate phase envelopes. Phase envelopes of the methane—ethane mixtures were constructed and compared with reference data. The results show that phase envelopes can be constructed with GERG-2008 in high accuracy. PR-EOS has good accuracy in phase envelope construction under low pressure. The simplified GERG-2008 also works well under low pressure; however, as pressure increases, it performs worse than the simpler PR-EOS, especially in the vicinity of critical point. Besides, a modified density solver for the complicated GERG-EOS was proposed. Calculations show that the proposed density solver can provide reliable results.

Phase equilibrium modelling for multi-component mixtures using highly accurate Helmholtz energy equation of state

Phase stability of a mixture at given conditions is studied. The modelling of equilibrium phase compositions is considered when the original phase of the mixture is unstable. The tangent plane distance criterion is used for stability analysis and the Gibbs energy minimisation is employed for phase equilibrium calculation when the successive substitution does not work well. With the Helmholtz free energy equation of state, thermodynamic properties in single phase and two-phase equilibrium were calculated for methane-ethane mixtures. Phase envelopes were also calculated.

Phase equilibrium modelling for multi-component mixtures using highly accurate Helmholtz energy equation of state

Phase stability of a mixture at given conditions is studied. The modelling of equilibrium phase compositions is considered when the original phase of the mixture is unstable. The tangent plane distance criterion is used for stability analysis and the Gibbs energy minimisation is employed for phase equilibrium calculation when the successive substitution does not work well. With the Helmholtz free energy equation of state, thermodynamic properties in single phase and two-phase equilibrium were calculated for methane-ethane mixtures. Phase envelopes were also calculated.