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There are many compressor stations along long-distance natural gas pipelines. Natural gas can be transported using different boot programs and import pressures, combined with temperature control parameters. Moreover, different transport methods have correspondingly different energy consumptions. At present, the operating parameters of many pipelines are determined empirically by dispatchers, resulting in high energy consumption. This practice does not abide by energy reduction policies. Therefore, based on a full understanding of the actual needs of pipeline companies, we introduce production unit consumption indicators to establish an objective function for achieving the goal of lowering energy consumption. By using a dynamic programming method for solving the model and preparing calculation software, we can ensure that the solution process is quick and efficient. Using established optimization methods, we analyzed the energy savings for the XQ gas pipeline. By optimizing the boot program, the import station pressure, and the temperature parameters, we achieved the optimal energy consumption. By comparison with the measured energy consumption, the pipeline now has the potential to reduce energy consumption by 11 to 16 percent.

The deposition of sulfur particles in gathering and transportation pipeline system can cause serious safety problems and economic losses. When the high sulfur content natural gas (HSCNG) flows through the throttle valve of the gathering and transportation system, it will cause the supersaturation of elemental sulfur in the gas phase, and then the sulfur crystal nuclei and sulfur particles will appear in the pipeline system. Studying the initial growth behavior of sulfur crystal nuclei and sulfur particles can lay a necessary prerequisite for the accurate prediction of sulfur particle deposition in high sulfur content natural gas gathering and transportation (HSCNGGT) pipelines. Based on the homogeneous nucleation theory in crystallization kinetics, a mathematical model of elemental sulfur nucleation was established. Taking the throttling condition in the process of HSCNGGT as an example, the effects of temperature, pressure and H2S concentration in HSCNG on the critical nucleation radius and nucleation rate of elemental sulfur were explored. The results show that: (1) after the supersaturation of elemental sulfur, sulfur crystal nuclei with nanoscale radius will be precipitated. The temperature and pressure after throttling have great influence on the nucleation radius, and the influence of H2S concentration on the nucleation radius is more complex. (2) The temperature, pressure and H2S concentration after throttling also have great influence on the nucleation rate. By solving the growth kinetics model of sulfur particles based on Brownian condensation, it is found that the nano-sized sulfur crystal nuclei can grow into micron-sized sulfur particles in a very short time. [ABSTRACT FROM AUTHOR]

The effect of gathering pipeline pressure, temperature, and key components on the solubility of monomeric sulfur in high-sulfur-content natural gas is directly related to the prediction and prevention of sulfur deposition in surface gathering pipelines. Based on our previous study on a prediction model of sulfur solubility in gas with a new formula for the binary interaction coefficient between sulfur and H2S, a new gas–solid thermodynamic phase equilibrium solubility prediction model for monomeric sulfur in high-sulfur-content natural gas was improved based on the gas–solid phase equilibrium principle considering both physical and chemical solution mechanisms. Two new expressions for binary interaction coefficients between sulfur and CO2 and CH4, considering both temperature and solvent density, are proposed in this new solubility prediction model. In this paper, the main factors, such as the gathering pipeline pressure, gathering pipeline temperature, H2S, and CO2, affecting the solubility law of elemental sulfur in high-sulfur-content natural gas are investigated. The results show that the total solubility of elemental sulfur in high-sulfur-bearing natural gas tends to decrease with an increase in the gathering temperature, in which the increase in temperature promotes physical solution, and the physical solution mechanism prevails. Conversely, chemical solution is promoted, and the chemical solution mechanism prevails. With an increase in the gathering pressure, the total solubility of elemental sulfur in high-sulfur-content gas tends to increase, where the physical solubility decreases slightly at first and then increases continuously, with a pressure inflection point of about 2.0 MPa, and the pressure increase has a significant promoting effect on the chemical solubility of elemental sulfur. The increase in the H2S concentration promotes the solution of elemental sulfur in the gas phase in general and significantly promotes the chemical solution of elemental sulfur. The effect on elemental sulfur solubility can be neglected when the molar concentration of CO2 in the gas phase does not exceed 10%. [ABSTRACT FROM AUTHOR]

Liquid and hydrate blockages often occur in natural gas pipelines, reducing pipeline transportation efficiency. When blockages completely occupy the pipeline, major production and safety accidents can occur, such as production shutdowns and overpressure damage. This study comprehensively describes in detail the technical principles and characteristics of 12 natural gas pipeline blockage detection methods and lists the challenges they face in practical applications. Moreover, common techniques for eliminating blockages in gas pipelines are presented. Then, whether the different detection techniques can realize the five functions of blockage quantity, blockage location, blockage length, blockage area, and continuous detection is theoretically discussed. Furthermore, the advantages, disadvantages, and limitations of different detection techniques are evaluated from six aspects: detection speed, accuracy, adaptability, anti-interference, impact on pipeline operation, need for historical information, and cost. Transient wave reflection and inverse transient analysis methods deserve more studies in this field. Finally, recommendations for future work are presented based on five aspects: morphology and number of blockages, acquisition of initial pipeline parameters, remote detection, signal processing, and blockage media. This study serves as a useful tool for gaining insights into recent advances in natural gas pipeline blockage detection methods. • The basic principle and research status of blockage detection technology are introduced. • The performance of different blockage detection techniques is discussed. • The detection speed, accuracy and applicability of different methods are compared. • The challenges and future work in this research field are discussed. [ABSTRACT FROM AUTHOR]

Ventilative drying is an essential drying method to protect natural gas pipeline from corrosion and prevent the formation of hydrate. A mathematical model describing the problem of pipelines drying with dehydrated air is developed based on the fundamental principle of mass, momentum, and species conservation in present work. To enhance the accuracy of the model, a new correlation of the evaporation rate of water in pipeline is introduced by taking interfacial resistance into account. Finite volume method (FVM) is employed to discretize the governing equations with first-order upwind scheme for mass and momentum equations and QUICK scheme for species equations. To reduce calculation load, a new solution strategy of semi-implicit method for Sm-linked equations is proposed to solve the nonlinear algebraic equations after the discretization of mathematical model. The results indicate that average absolute deviation between experimental data and the calculations are 8.8% and 8.2% for two cases, respectively. By analysis of dynamic process of the ventilative drying, it is found that the drying process takes place from the ends toward the center of the pipeline. In addition, the results also demonstrate that the nonuniform distribution of the liquid holdup may reduce the service efficiency of dehydrated air at the late period of drying process. Thus, we suggest that the drying process shifts to soak-test stage when the water vapor at the outlet reaches a minimum set value. Finally, a number of influential factors on the drying process are studied. [ABSTRACT FROM AUTHOR]

• This paper focuses on daily natural gas consumption forecasting. • A novel hybrid model is developed for daily natural gas consumption forecasting. • The most recent datasets of four cities in three climate zones are collected. • An improved singular spectrum analysis is first proposed. In daily natural gas consumption forecasting, the accuracy of forecasting models is vulnerably affected by the noise data in historical time series. Singular spectrum analysis (SSA) is often introduced into hybrid models for denoising. However, as a deterministic-based algorithm, SSA does not give good results when a time series is contaminated with a high noise level. Considering this fact, this paper proposes an improved SSA (ISSA) that modifies the determination method of subseries selection in the reconstruction stage of SSA. Combining ISSA with long short-term memory (LSTM), a novel hybrid model, ISSA-LSTM, is thus developed. Additionally, for validating the robustness and superiority of ISSA-LSTM, the historical datasets of four representative cities located in three climate zones are collected as the training and testing datasets, and a comparison of ISSA-LSTM with five advanced models is performed. The results reveal that SSA would generate negative values when time series close to zero and the contribution of SSA in improving the forecasting accuracy of LSTM is insignificant. In contrast, ISSA avoids generating negative values and reduces the mean absolute range normalized error (MARNE) of LSTM by a range of 0.86–11.86%. Among the models, ISSA-LSTM achieves the best performance and its MARNEs for London (temperate zone), Melbourne (subtropical zone), Karditsa (subtropical zone), and Hong Kong (tropical zone) are 4.68%, 5.72%, 5.76%, and 14.10%, respectively. The MARNE of the tropical city is higher than that of others, which is caused by the complex natural gas consumption pattern of itself. [ABSTRACT FROM AUTHOR]

Blending hydrogen into natural gas is a feasible way to transport hydrogen via natural gas pipelines. In hydrogen-blended natural gas (HBNG) pipelines, choking is an essential process that concerns safety issues like condensation and hydrate formation inside valves and the Joule-Thomson (J-T) characteristics like temperature drops, isenthalpic curve (IC), Joule-Thomson coefficient (JTC). However, these two aspects of HBNG differ from those of natural gas, and the differences in inside-valve flow remain unknown, and those in J-T characteristics remain less clear. Given the incapability of the isenthalpic model in obtaining inside-valve flow fields, we conduct a comprehensive study on the effects of hydrogen on inside-valve flow and J-T characteristics of HBNG by combining the computational fluid dynamics (CFD) model and the isenthalpic model. We develop a numerical model by coupling the isenthalpic equations, the conservation equations, the k - ω turbulence equations, and the species transport equations. For the first time, we discuss the effects of hydrogen on the temperature, pressure, and velocity fields of HBNG and evaluate the risks of p - T curves entering vapor-liquid equilibrium and hydrate formation regions. Then, we analyze the effects of hydrogen on ICs and JTCs. Results indicate that with increasing hydrogen mole fraction (HMF), the temperature along the center line rise, the minimum temperature increases roughly linearly, and the corresponding positions shift to the throat in a rough linear law. The JTCs of HBNG roughly linearly decrease with increasing HMF from 0% to 30%. • The inside-valve temperature profile of HBNG rises with increasing HMF. • The position with the lowest temperature shifts to the throat roughly linearly. • The inside-valve p - T curve shifts to the high-temperature side with increasing HMF. • The JTC of HBNG decreases with increasing HMF roughly linearly. • The JTC decreases by about 30% and 50% at HMFs of 15% and 30%, respectively. [ABSTRACT FROM AUTHOR]

Ferromagnetic pipelines provide a major means for the conveyance of oil and natural gas. The self-magnetic leakage field (SMLF) generated by ferromagnetic pipelines has therefore attracted considerable attention in the field of pipeline examination and defect detection. This paper has the objective of analysing the magnetomechanical effect, which can be observed in the geomagnetic field, by establishing a mathematical model of the SMLF based on the theory of magnetic dipoles and the magnetomechanical effect, and to discuss the influence of factors such as the outer diameter, the geomagnetic field intensity, the operating pressure, etc. The results show that the length of oil and gas pipelines can be considered as infinite for the calculation of the SMLF. In addition, both the total flux density and the gradient modulus of the SMLF are shown to reach their maximum values above the pipeline. The parameter analysis indicates that the pipeline diameter and the height of the covering soil are two crucial factors in determining the SMLF. Finally, in an experiment to test the model, the error between the theoretical calculation and the actual measurement was 4.6%. Therefore, the model proposed in this paper can provide technical support for the calculation of the SMLF induced by pipelines, which has significance for the inspection of pipeline locations and pipeline defects. [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]

The liquid-phase pipeline is the optimal choice for large-amount and long-distance ethane transportation. Selecting the optimal diameter is necessary for the economical design of the pipeline. However, the special critical temperature 32.2 °C and critical pressure 4.87 MPa of ethane makes it easy to become liquid-vapor phase change, which is not considered in the traditional natural gas or crude oil pipeline design. In this paper, a new mathematical model is built to calculate the optimal diameter of the ethane pipe by using the 'pump station + pipeline' unit as the research object. The model selects the lowest total pipeline construction and operation costs as the objective function, and the constraints include the ethane liquid-vapor phase change, the pipe maximum allowable stress, and pipe specifications. In particular, the liquid-vapor phase change constraint is added to the traditional model to avoid the ethane liquid-vapor phase change, which is obtained by quantitatively analyzing the variation of physical parameters of ethane close to the pressure-temperature phase boundary. The optimization model is solved by use of the genetic algorithm. Finally, optimal pipe diameters are calculated for the conditions of transmission capacity from 1000 t/d to 10,000 t/d. Comparisons of calculated pipe diameter with eight actual cases show that the results are feasible with the average and maximum deviations being less than 5% and 8%, respectively. The effects of pipe materials and electricity prices on the pipe diameter are analyzed. It is demonstrated that the pipe material has a negligible effect on the optimal diameter, whereas increasing the electricity price will lead to the increase of the optimal diameter in the case of large transmission volumes. • An optimal diameter model for the liquid-phase ethane pipeline is built. • The liquid-vapor phase change constraint ensures ethane pipeline safety. • The fitness function of the genetic algorithm is improved. • The optimal diameter is obtained and successfully applied to eight real cases. [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]

Due to the cooling effect of natural gas throttling, spontaneous condensation will occur in the throttle valve, which may affect pipeline system efficiency. However, the condensation characteristics (such as nucleation rate and condensation rate) remain unclear, and the traditional method based on the isenthalpic hypothesis can hardly solve this non-equilibrium issue. Based on the geometry differences between the throttle valve and the Laval nozzle, this paper explored the condensation parameters of the CH 4 –C 2 H 6 binary mixture in the throttle valve and the Laval nozzle using CFD techniques (solving non-equilibrium condensation at a lower cost). This paper discussed the influence of the inlet pressure and inlet temperature on the spontaneous condensation process in the throttle valve as well. The findings are that the nucleation and droplet growth regions in the throttle valve are closer to the throat but narrower than that of the Laval nozzle, and the liquid mass fraction decreases after reaching the peak value. The onset of droplet nucleation and droplet growth is closer to the throat when increases inlet pressure or decreases inlet temperature. The condensation rate of ethane in the throttle valve is lower than that in the Laval nozzle, and the sensitivity of the nucleation rate and the Wilson point to the inlet parameters is higher and lower than that in the Laval nozzle, respectively.. The main innovation of the paper lies in revealing the differences in the condensation between the throttle valve and the Laval nozzle using the non-equilibrium method. • A 2D transient CFD model of condensation of the CH 4 –C 2 H 6 mixture in the throttle valve was developed. • The condensation regions in the throttle valve are earlier than those in the Laval nozzle under the same conditions. • The condensation in the throttle valve occurs in a narrow region behind the throat unlike the Laval nozzle. • The condensation rate of C 2 H 6 positively and negatively correlates to the inlet pressure and temperature, respectively. [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]

The natural gas pressure-relieving system is essential to natural gas pipelines and equipment for their safe operations against overpressure. This paper divided the system into pipe and resistance elements (valve, bent, tee et al.). The pipe elements are simulated by the hydrodynamic and thermodynamic equations, and the resistance elements are simulated by their characteristic equations. Combined those two kinds of equations, as well as the composition-dependent physical property models of natural gas, a steady-state simulation model of pressure-relieving systems is proposed for pressure, flow rate and temperature predictions. The homogeneous assumption is introduced to handle two-phase flow. A velocity constraint is also integrated into the model, making it applicable for both critical and subcritical pressure relief situations. Besides, the proposed solution method is applicable for any pressure-relieving systems composed of any numbers of pipe and resistance elements, as long as there are no branches. Finally, the reliability of the model has been examined using experimental data from three real pressure-relieving systems in Sichuan Province, China. The experiments cover a wide pressure range from 2.23 MPa to 53.80 MPa, and a temperature range from 257.40 K to 335.70 K. The results show that the maximum temperature and flow rate relative errors between the simulation results and experimental data are 1.03% and 3.52%, while the minimum values are 0.22% and 0.31%. The average absolute errors of the temperature and flow rate are 1.83 K and 1.00 × 104 m3/d. The method is also successfully applied to a gas well under critical and subcritical conditions. [ABSTRACT FROM AUTHOR]

Forecasting daily natural gas load accurately is difficult because it is affected by various factors. A large number of redundant factors existing in the original dataset will increase computational complexity and decrease the accuracy of forecasting models. This study aims to provide accurate forecasting of natural gas load using a deep learning (DL)-based hybrid model, which combines principal component correlation analysis (PCCA) and (LSTM) network. PCCA is an improved principal component analysis (PCA) and is first proposed here in this paper. Considering the correlation between components in the eigenspace, PCCA can not only extract the components that affect natural gas load but also remove the redundant components. LSTM is a famous DL network, and it was used to predict daily natural gas load in our work. The proposed model was validated by using recent natural gas load data from Xi'an (China) and Athens (Greece). Additionally, 14 weather factors were introduced into the input dataset of the forecasting model. The results showed that PCCA–LSTM demonstrated better performance compared with LSTM, PCA–LSTM, back propagation neural network (BPNN), and support vector regression (SVR). The lowest mean absolute percentage errors of PCCA–LSTM were 3.22% and 7.29% for Xi'an and Athens, respectively. On these bases, the proposed model can be regarded as an accurate and robust model for daily natural gas load forecasting. [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 phenomenon of reverse condensation of natural gas was taken into account. • Empirical correction coefficients α and β were introduced into the condensation model under high pressure and temperature. • The flow pattern of the liquid phase in the STV and ATV is the annular flow and the stratified flow, respectively. • The maximum liquid mass fractions in STVs (type I, type II) and ATVs (type I, type II) are 3.12 %, 2.22 %, 3.42 %, and 3.24 %, respectively. The condensation of natural gas in the throttle valve may affect and even damage the downstream equipment, which threatens the safety and efficiency of the natural gas transport system. However, the mainly used method based on the isenthalpic hypothesis can hardly solve this problem. In this work, we developed a spontaneous condensation model of condensed natural gas with high temperature and pressure in the throttle valve using CFD modelling, which defined a hypothetical saturation line and introduced two empirical correction coefficients (α and β) into the nucleation and growth models. The scouring effect of natural gas on the valve was analysed, and the condensation characteristics and effect of latent heat of condensation on the flow were discussed in detail. The results show that the average absolute relative deviation (AARD) of the outlet temperature of the angle throttle valve (ATV) obtained by this model is 0.39% when α and β equal 10-10 and 10-2, respectively, while that without considering condensation is 1.13%. The inner wall near the throat of the straight-through throttle valve (STV) and ATV are susceptible to the scouring effect of natural gas. For STVs (type I, type II) and ATVs (type I, type II), after the droplet nucleation (1026 m−3·s−1) and growth (10-2 m/s) stage, the droplets are condensed and accumulated with a maximum liquid mass fractions of 3.12 %, 2.22 %, 3.42 %, and 3.24 %, respectively, then flow along the wall with a flow pattern of the annular flow and stratified flow. Compared to the case without condensation, the pressure and temperature at the condensation position increase slightly due to the latent heat of condensation, the condensation shock wave, while the velocity decreases slightly due to the momentum exchange between the natural gas and liquid phase. [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]

Natural gas pipeline aerial crossing (NGPAC), also called natural gas pipeline bridge, is an important structure for gas transmission pipelines crossing special areas that are not suitable for trenchless technologies. The typical types of large-scale NGPACs are suspension and cable-stayed pipeline bridges. During the pigging process, suspension and cable-stayed NGPACs prong to strong vibration and large displacement due to the dynamic loads generated by the moving pig and the liquid column running in front of the pig. This paper provides a review of the most relevant research progress related to the study of the dynamic response of NGPACs during the pigging process. The application history of the suspension and cable-stayed NGPACs is introduced. Also, the research progress regarding the experimental studies, pigging load simulation, and the dynamic response of the NGPAC during the pigging process are comprehensively reviewed. Besides, the research challenges of every research aspect are also discussed according to the review results. The overall research status is that there have been simulation findings of the dynamic response of NGPACs during the pigging process. But the two-phase flow-induced fluid–structure coupling vibration of a complex structure which is the core issue of the problem has not been well solved by both the theoretical and the numerical simulation research. This is jointly caused by the lack of experimental research, lack of simulation studies of the pigging load applicable to vibrated pipelines, and insufficient research of the two-phase flow fluid–structure interaction process. The systematical and joint research should be carried out based on the above three aspects to comprehensively simulate the fluid–structure interaction response and possible resonance of NGPACs during the pigging process. The findings are of great significance for reviewing the existing research findings, future research challenges and to improve the safety management of NGPACs. [ABSTRACT FROM AUTHOR]

• An improved multi-component diffusion model is proposed considering the CH 4 and H 2.interaction. • The main factor affecting the diffusion behavior of CH 4 /H 2 /air mixtures in the confined plant is expressed. • The potential explosion areas fall within the natural gas and H 2 components are figured out. • The additional high explosion risk area related to the mixed H 2 is close to the leakage hole. Mixing hydrogen into the natural gas pipeline network is the most effective and economical way to transport a large amount of hydrogen while resulting in more danger when gas mixtures leak in the confined compressor plant space. Existing studies on the diffusion behavior of CH 4 /H 2 /air mixtures ignore the physical property difference between the natural gas and hydrogen, resulting in a bias in evaluating the explosions regions in compressor plants. In this paper, an improved Fick diffusion matrix for CH 4 /H 2 /air mixtures is proposed which considers the interaction between CH 4 and H 2 components. After that, a 2D gas mixture diffusion model is built to research the effect of the gas pressures, leakage hole diameters, and ambient wind speeds on the diffusion range of the CH 4 /H 2 mixtures in air. The method is subsequently extended to a 3D confined compressor plant space with different leak positions, leakage lasting time, and H 2 volume concentrations. Results demonstrate that the leakage hole diameter is the main factor influencing the diffusion behavior of CH 4 /H 2 /air mixtures in the compressor plant among three factors (the H 2 mole fraction, leakage hole diameter, and leakage point). The CH 4 /H 2 /air mixtures easily accumulate both on the roof and at the corner of the confined plant. Particularly, the hydrogen concentration may fall within its explosion limit scope and induces an explosion at the position close to the leakage hole, where the natural gas does not easily cause the explosion because the natural gas concentration often exceeds its explosion up-limit. Finally, some suggestions for gas detector installation in compressor plants are proposed according to simulation results, which can give guidance for the safety management of compressor plants. [ABSTRACT FROM AUTHOR]