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[Objective] LNG has the obvious characteristics of high flammability, high explosiveness and ultra-low temperature. LNG terminals are generally built in coastal areas, and thus the pipeline elbows in an LNG terminal are easily located in the severe corrosive environment with high pressure difference due to the particularity of the process fow, facing a high risk of piercing failure. [Methods] Based on the general situation of piercing failure of pipeline elbows in an LNG terminal, the macroscopic morphology and the physical and chemical properties of the elbows, straight pipe sections and girth welds were analyzed through non-destructive testing and scanning electron microscopy. The macroscopic morphology analysis results show that the geometric size and wall thickness of the straight pipe section and the elbow meet the corresponding standards. However, obvious erosion wear is observed in the upstream straight pipe sections and the fange joint girth welds along the LNG fow direction, which is similar to the elbow defects. In the analysis of physical and chemical properties,it is found that the micro-morphology of the defective surfaces at the girth weld and the elbow are honeycomb-like, indicating that there is erosion wear. Besides, a numerical model was established with ANSYS Fluent software, and the fow state of LNG at elbows was simulated,showing that weld reinforcement affects the LNG fow in the pipeline, with throttling effect and vortex fow resulting. [Results] The failure mechanism of pipeline elbows in LNG terminal and the infuencing rules were revealed through the macroscopic morphology observation,physical and chemical properties analysis and numerical simulation in combination. Specifically, the fuid forms a high speed jet with liquid droplets in the gas phase behind the orifice plate, which erodes the wall surface of the elbow. Thereby, a low pressure area is formed on the inner side of the elbow, and a high pressure area is formed on the outer side. Then, the bubble burst produces shock waves and cavitation collapse, and finally causes the piercing of elbows. [Conclusion] The research results could provide theoretical reference for improving the fuid fow stability, optimizing the orifice design and developing elbow failure solutions in LNG terminals, which could reduce the risk of elbow piercing failure in LNG terminals, and improve the safety and reliability of pipeline system operation.

To design the two-dimensional structural parameters of the core throttling component, i.e., the perforated plate for a liquid nitrogen (LN2) balanced flowmeter, this paper presented an orthogonal experiment scheme with three parameters, three factors, and three interactions, combined with the three-dimensional CFD numerical simulation. The constructed mixture multi-phase flow numerical model considers the complex cavitation effect of LN2 with a thermal effect. A DN40 balanced flowmeter and an LN2 flowrate test setup based on a standard flowmeter were constructed, and the measured flowrate data were used to evaluate the CFD model. Based on the optimized two-dimensional structure and the validated numerical model, the influence of the three-dimensional thickness of the perforated plate on the flow and pressure drop coefficient was investigated. It was found that there are two throttling forms as the thickness increases, resulting in two pressure-changing characteristics. The formation mechanism was explained by analyzing the turbulence intensity distribution. Finally, the final flow coefficient, pressure drop coefficient, and upper limit of measurement due to the cavitation were analyzed and obtained. The results provide a feasible parameter design method for the cryogenic balanced flow meters. [ABSTRACT FROM AUTHOR]

Burning hydrogen-rich syngas fuels derived from various sources in combustion equipment is an effective pathway to enhance energy security and of significant practical implications. Emissions from the combustion of hydrogen-rich fuels have been a main concern in both academia and industry. In this study, the NO and CO emission characteristics of both laminar and turbulent counterflow premixed hydrogen-rich syngas/air flames were experimentally and numerically studied. The results showed that for both laminar and turbulent counterflow premixed flames, the peak NO mole fraction increased as the equivalence ratio increased from 0.6 to 1.0 and decreased as the strain rate increased. Compared with the laminar flames at the same bulk flow velocity, turbulent flames demonstrated a lower peak NO mole fraction but broader NO formation region. Using the analogy theorem, a one-dimensional turbulent counterflow flame model was established, and the numerical results indicated that the small-scale turbulence-induced heat and mass transport enhancements significantly affected NO emission. Considering NO formation at the same level of fuel consumption, the NO formation of the turbulent flame was significantly lower than that of the laminar flame at the same level of fuel consumption, implying that the turbulence-induced heat and mass transfer enhancement favored NOx suppression. [ABSTRACT FROM AUTHOR]

This study investigated the flame structure and dynamics of a bluff-body flame when numerically close to blow-off conditions. This includes the impact of the hydrogen ratio on lean CH4/H2/air flame stabilization and blow-off characteristics. In this study, we assessed the impacts of four different hydrogen ratios: 0%, 30%, 60%, and 90%. Large eddy simulation (LES) was coupled with a thickened flame (TF) model to determine the turbulent combustion using a 30-species skeletal mechanism. The numerical results were progressively validated using OH-PLIF and PIV techniques. The results obtained from the numerical simulations showed minor differences with the experimental data on the velocity field and flame structure for all conditions. The presented results reveal that the flame is stabilized in higher-strain-rate spots more easily in the presence of high hydrogen ratios. Moreover, the flame location moves away from the concentrated vortex area with an increasing hydrogen ratio. The results of our blow-off investigation indicate that the blow-off sequence of a premixed bluff-body flame can be separated into two stages. The entire blow-off process becomes shorter with an increase in the hydrogen ratio. The primary reason for global extinction is a reduction in the heat release rate, and enstrophy analysis implies that blending hydrogen can reduce the enstrophy values of flames at the downstream locations. The dilatation and baroclinic torque terms decrease close to blow-off, but their decline is not significant in high-hydrogen-ratio conditions. [ABSTRACT FROM AUTHOR]

In this paper, the characteristics of hydrogen-doped natural gas combustion in industrial boilers were investigated by means of numerical simulations. Initially, a jet flame test bench was constructed to conduct single-variable experiments at various hydrogen doping ratios and excess air coefficients, thus analyzing the impact on flame combustion patterns. Computational Fluid Dynamics (CFD) numerical simulations were performed using the Fluent software, focusing on the combustion zones within the burner and boiler chamber. Simulations were based on actual operating conditions to set parameters, employing the k-ε turbulence model. The SIMPLE algorithm facilitated examination of the effect of hydrogen doping ratios on the combustion temperature and concentration of pollutants, with a particular focus on the concentration of the flow field, temperature field, NOx generation rate, and the concentrations of O 2 and CO. The results show that: As the hydrogen doping percentage increases, the fuel flame propagation speed also increases, leading to a faster combustion process that yields a shorter, wider flame. Conversely, as the excess air coefficient rises, the flame becomes narrower, transitioning from a clearly-layered structure to a uniform one. Furthermore, an increase in the hydrogen doping ratio results in higher combustion temperatures and accelerated combustion reaction rates, accompanied by a decrease in CO concentration and an increase in NOx emission concentration. These results indicate that hydrogen doping enhances the combustion reaction and reduces pollutant emissions from gas combustion. This study provides a theoretical foundation for the practical application of hydrogen-doped natural gas in industrial boilers. • Experimental study of the effect of hydrogen doping ratio on flame morphology. • Effect of hydrogen doping ratio on combustion characteristics of natural gas. • Effect of excess air coefficient on combustion characteristics of natural gas. • Combining experimental and simulation to analyze combustion characteristics. • Analysis of combustion temperatures and pollutant generation characteristics. [ABSTRACT FROM AUTHOR]

During the transportation of hydrogen-blended natural gas (HBNG) through the natural gas pipeline network, the accuracy of the physical property model for real gas greatly influences the reliability of aerodynamic performance of compressor systems and the hydrothermal characteristics of pipeline networks. In this study, the adaptability of various equations of state (EOS) in predicting physical property parameters including compressibility factor, enthalpy difference, entropy difference, specific heat capacity, specific heat ratio and viscosity of natural gas (NG) and HBNG is evaluated based on the experimental data and NIST REFPROP firstly. The properties calculated using NIST REFPROP are compared with those from the EOSs, such as cubic EOSs (Redlich–Kwong EOS (RK), Soave–Redlich–Kwong EOS (SRK), Peng–Robinson EOS (PR)) and Soave-Benedict-Webb-Rubin (BWRS) EOS. After confirming the reliability of NIST REFPROP as the calculation benchmark, the accuracy of the four EOSs in calculating the physical properties of HBNG is assessed within the temperature range of 250∼350 K, pressure range of 1∼25 MPa, and hydrogen doping ratio of 0%–30%. Besides, the mixing rules of different equations of state (EOSs) are compared based on the NIST REFPROP calculation results. The results indicate that, except for specific heat capacity calculation, the mixing rule has little influence on the prediction accuracy of cubic EOS models, and the maximum calculation error between different mixing rules of the same EOS model does not exceed 0.5%. Under specific conditions, the traditional mixing rule exhibits better prediction accuracy and can be prioritized due to its simplicity. Furthermore, the pressure has a significant impact on the accuracy of EOS models, with the prediction accuracy decreasing as the pressure increased. The influence of temperature on the prediction accuracy is less significant than that of pressure. Generally, lower temperatures exhibit lower prediction accuracy, while higher temperatures show higher prediction accuracy. Among the cubic EOS models, the RK equation performs better than the SRK and PR EOS models. While the cubic EOSs show minimal differences in predicting specific heat ratio with an average relative error below 1%, the RK EOS shows significant advantages in predicting other physical parameters. The simple structure of RK EOS meets the calculation requirements for HBNG engineering. The comprehensive comparisons reveal that, the BWRS EOS has higher accuracy in predicting various physical properties parameters, with the maximum average relative error not exceeding 5% for each physical property parameter, and its stability is also better compared to the cubic EOSs. The further analysis shows that, the calculation of viscosity is influenced not only by the EOS but also by the viscosity model. When calculating viscosity using the LU-Model, the PR EOS provides the most accurate results. In contrast, when utilizing the LGE-Model or LBC-Model, the BWRS EOS demonstrates superior accuracy compared to other EOSs. • Mixing rules slightly effect state equations' accuracy across different x-H2, besides heat capacity calculations. • Unlike other parameters, the viscosity calculation depends on both the viscosity model and the equations. • Apart from viscosity calculations, Redlich-Kwong equation performs the best among the cubic state equations. • The Benedict-Webb-Rubin-Starling equation is more accurate than the cubic state equations overall. • The impact of pressure on equations' accuracy for hydrogen-blended natural gas is more obvious than that of temperature. [ABSTRACT FROM AUTHOR]

To reveal the deflagration hazard and propagation law of hydrogen-enriched natural gas (H 2 NG) in closed spaces, this paper studied the deflagration characteristic parameters under different H 2 blended ratio (λ) and inert gas dilution fraction (X dilution) in slender closed pipelines with steel circular hole obstacles. The results indicate that the positive feedback mechanism's sustained effect, failure, and re-action leads to a "three-zone" distribution of H 2 NG explosion overpressure along the pipeline, namely the acceleration, attenuation, and rebound zones. The maximum explosion overpressure (P max), maximum pressure rise rate ((dP/dt) max), and peak shock wave propagation velocity (V p) all increase with the increase of λ. The rise of λ has the most significant enhancement effect on (dP/dt) max , while the enhancement effect on V p is the smallest. This is because the main reasons affecting their increase are different. P max , (dP/dt) max , and V p exhibit exponential decay with increased N 2 and CO 2. However, CO 2 has a more significant inhibitory effect on the H 2 NG deflagration process. When X CO2 = 25% and X CO2 = 30%, the deflagration process of H 2 NG with λ = 20% and λ = 80% can be inhibited entirely, respectively, which has important guiding significance for the safe application of H 2 NG. • The evolution law of deflagration shock waves in slender closed pipelines by H 2 NG was researched. • Effects of H 2 blended ratio and N 2 /CO 2 dilution fraction on H 2 NG deflagration characteristics were revealed. • The effects of N 2 /CO 2 dilution fraction on the P max , (dP/dt) max , and V p were predicted by an exponential model. [ABSTRACT FROM AUTHOR]

To evaluate the explosion hazard of CH 4 /H 2 mixtures, experiments were conducted in a long and closed pipeline with a length-to-diameter ratio of 51 and built-in obstacles, and the characteristic parameters of deflagration shock waves were analyzed under different hydrogen blending ratios (0 ≤ λ ≤ 100%) and equivalence ratios (0.5 ≤ Φ ≤ 3). The results indicate that within the range of Φ = 0.8-1.2, the explosion overpressure ( P P ) exhibits a "two-zone" structure distribution. When 0 ≤ λ ≤ 80%, P P shows an initial increase and then a decrease in both regions, while deflagration to detonation transition (DDT) occurs in the second evolution region when λ = 100%, which is caused by the different strengths of the positive feedback mechanism coupled with flames and shock waves. The P max , (d P /d t ) max , and V a show a trend of first increasing and then decreasing and monotonically increasing with the increase of the equivalence ratio and hydrogen blending ratio, respectively, and reach their maximum values at Φ = 1.0 and λ = 100%. For CH 4 /H 2 mixtures with low hydrogen blending ratios (λ = 0 and 20%), the P max and (d P /d t ) max in the fuel-lean conditions (Φ = 0.9 and 0.8) are higher than those in the fuel-rich conditions (Φ = 1.1 and 1.2), while the CH 4 /H 2 mixtures under high hydrogen blending ratios (λ = 80 and 100%) are the opposite. Overall, the increase in H 2 at a high hydrogen blending ratio and the increase in the equivalence ratio at a fuel-lean condition significantly enhance the average V a . In addition, chemical kinetics analysis found that R38 and R52 elementary reactions are the dominant elementary reactions that promote and inhibit temperature increase, respectively. Their temperature sensitivity coefficients are negatively correlated with the hydrogen blending ratio and positively correlated with the equivalence ratio. The research results provide vital information for evaluating the explosion hazards of CH 4 /H 2 mixtures and developing safety protection measures., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)