Electrocoagulation (EC) is an eco-friendly technology that combines oil removal and hydrogen production. In this study, we investigate the impact of EC-induced foaming on simultaneous hydrogen production during EC treatment of oilfield-produced water and propose optimization strategies. Analyses of current intensity, electrode spacing, and initial pH reveal that currents >3A reduce foam stability and boost hydrogen yield, while 3 cm electrode spacing balances hydrogen production and oil removal. pH 7-9 enhances oil removal via polynuclear aluminum complexes. Then, the optimal antifoam agent was selected: polyether antifoam (7.5 mL, 46.35 % efficiency). Finally, response surface methodology was used to determine the ideal parameters: 4.24 A current, 2.70 cm spacing, and 6.14 mL antifoam agent, achieving 95.10 % oil removal and 172.90 mL hydrogen yield (H-2 concentration reached 90.14 %, bubble area as low as 3244 m(2)). Compared to traditional technology, H-2 increases by 17.69 %, and energy costs decrease by 5.29 %.

To address the insufficient pressure resistance of ferrofluid seals under the operating conditions involving large shaft diameter and wide gaps, which makes it difficult to meet vacuum sealing requirements, a ferrofluid seal with non-uniform opposing pole teeth (FFS-NOPT) structure was designed, along with a compatible kerosene-based ferrofluid. Based on the pressure resistance theory of ferrofluid seals, subsequently, simulations for static magnetic field were conducted to systematically analyze the effects of key structural parameters, including pole tooth height and width, sealing gap, and tooth groove width on the sealing performance. The results indicate that the oleic acid-modified Fe3O4 nanoparticles, exhibiting an average size of approximately 8.3 nm and a saturation magnetization of 57.4 emu/g, demonstrate superparamagnetic properties. Consequently, the ferrofluid prepared achieves a saturation magnetization of 35.67 kA/m. In addition, simulation results show that the pressure resistance of FFS-NOPT is significantly influenced by the height of pole tooth, and increases with the increasing tooth groove width. Compared to conventional structures with identical structural dimensions, the FFS-NOPT exhibits approximately 57% improvement in pressure resistance. These results demonstrate that this structure effectively enhances the pressure resistance of ferrofluid seals.

The efficient removal of tar and enhancement of hydrogen quality are crucial challenges during biomass targeted thermal conversion for hydrogen production. Biochar-based catalysts have emerged as a promising solution to address these issues. To elucidate the origin of biochar’s catalytic activity, the interactions between corn straw volatiles and biochars prepared under various thermal and activation conditions were investigated. The results demonstrate that surface active sites on biochars enhance hydrogen selectivity and yield. Specifically, biochar prepared at 600 °C in an inert atmosphere increased the hydrogen proportion to 58.4%(vol) and hydrogen yield of 29.58 mmol⋅g–1, primarily due to the promotion of the water-gas shift and steam reforming reactions by oxygen-containing functional groups. Furthermore, tar yield exhibited a strong inverse correlation with the total specific surface area. Using a CO2-activation biochar with a specific surface area of 734 m2⋅g–1, the tar yield was reduced to 0.50%(mass), as heavy polycyclic aromatic hydrocarbons (PAHs) were depolymerized into lighter species. This study emphasizes the catalytic properties of biochar in biomass steam reforming, revealing its practical potential as a sacrificial catalyst for efficient hydrogen production and laying a foundation for further development of biochar-based catalysts in biomass thermochemical conversion for hydrogen production.

Light non-aqueous phase liquids (LNAPLs) are the main components of petroleum hydrocarbons and pose severe challenges to global environmental regulation due to their concealment and persistence in the underground environments. This review systematically synthesized LNAPL behaviors across various scales and revealed that capillary trapping in micropores and wettability heterogeneity are the primary causes of the long-term persistence and recalcitrance of LNAPLs, which macro-scale models often underestimate by up to 35%. Furthermore, the review identified that dynamic hydrological conditions and soil heterogeneity synergistically control LNAPL redistribution, creating complex contamination plumes. Additionally, it was demonstrated how pore-scale processes dictate macroscopic fate by integrating advanced imaging techniques with multi-physics simulation. Finally, remediation technologies were critically evaluated, concluding that coupled strategies are essential to target the fraction of LNAPL trapped in low-permeability zones. This review presents the intrinsic connections among different scale studies, reveals the collaborative evolution of technological development and theoretical cognition, and provides a complete logical framework covering research background, status quo, methods, and trends for LNAPL migration and remediation in underground environments.

The growth characteristics of aggregates significantly affect the oil removal efficiency of electroflocculation. This study explored the aggregate growth process through experiments and simulation, proposing a new diffusion-limited cluster aggregation (DLCA) model that considers bubble and oil droplet size. The radius of gyration and fractal dimension were used to analyze the effects of three factor pairs: reaction time and total particle number, temperature and step size, and initial oil content and oil droplet concentration. The results showed that the total particle number (reaction time) most significantly affected aggregate growth, while the initial oil content had the least effect. With increasing reaction time, the radius of gyration and fractal dimension increased markedly. A temperature increase led to a smaller radius of gyration but a larger fractal dimension. In contrast, a higher initial oil content increased the radius of gyration but decreased the fractal dimension. Among the three parameters, reaction time was the most influential and initial oil content the least. Finally, the response trends and data fitting proved that the improved model has a better fit compared to the traditional model, providing a new idea for studying the growth mechanism of electroflocculated aggregates.

Direct contact condensation (DCC) of vapor bubbles in subcooled liquid is an efficient heat and mass transfer process, contributing significantly to industrial energy efficiency and sustainable energy utilization. This review synthesizes recent advances in the field. Beginning with fundamental theory, the physical nature of condensation is clarified, including bubble force balance and interfacial heat and mass transfer. Subsequently advanced experimental and numerical methods for capturing transient interfacial evolution and flow characteristics are critically assessed. On this basis, the dynamics and condensation mechanisms in both single-bubble and multibubble systems are analyzed. From an applied perspective, the influence of bubble interactions on interface distribution and flow structures is discussed, along with their implications for heat transfer efficiency and operational stability in practical devices. Although considerable progress has been made in elucidating macroscopic dynamics and average heat transfer behavior, clear gaps remain. They concern microscopic interfacial physics, high-resolution measurement of interfacial evolution, and predictive capability for multi-bubble and bubble-cluster dynamics under complex non-equilibrium conditions. Future efforts are suggested to prioritize elucidating microscopic interfacial evolution mechanisms and developing active control strategies for bubble clusters, thereby fostering innovation and performance enhancement of DCC technology in sustainable energy systems.

As oil field production progresses, the water content of the produced fluid increases and wax deposits form on the pipe wall as the crude oil is transported vertically through the pipeline. This causes the cross-sectional area of the pipeline to decrease, the flow resistance to increase and the pipeline pressure to decrease. As a result, production from oil wells declines and extraction costs rise. Therefore, in the current study, a vortex structure is utilized to generate a vertical core-annular flow for oil production and transportation in high-water-content oil wells. This study uses computational fluid dynamics (CFD) software to investigate the influence of various oil properties on the oil phase distribution and pressure drop in core-annular flow in vertical pipes. The findings demonstrate that the ring-forming effect of the core-annular flow increases with larger oil droplet sizes and lower oil phase densities, while it becomes weaker with higher inlet oil phase volume fraction and lower inlet velocities. As the size and density of the oil droplets grow and decrease, respectively, the pressure drop reduces. On the other hand, the pressure drop increases with higher inlet oil phase volume fraction and viscosity. When the oil droplet size is greater than 0.2 mm, the density is less than 850 kg/m3, the oil phase volume fraction is less than 30% and the inlet velocity is greater than 1 m/s, the annular flow works better. When the inlet oil phase volume fraction is above 30%, and the ring formation effect decreases significantly. The utilization of swirl core-annular fluid significantly mitigates the pressure drop in pipelines compared to pure oil transport downhole, rendering it highly suitable for conveying crude oil in high-water-content oil wells.

Air flotation separation technology has emerged as one of the core techniques for oily wastewater treatment in oilfields, owing to its advantages of high throughput, high separation efficiency, and short retention time. Originally applied in mineral processing, this technology was first introduced to oilfield produced water treatment by Shell in 1960. With the optimization of microbubble generators, advances in microbubble generation technology—characterized by small size, high stability, and uniformity—have further expanded its applications across various wastewater treatment scenarios. To optimize the separation performance of a horizontal compact closed-loop cyclonic air flotation unit, this study employs CFD numerical simulation to investigate two key aspects: First, for the flotation zone, the effects of structural parameters (deflector height, inclination angle) and operational parameters (gas–oil ratio, bubble size, inlet velocity) on flow patterns and gas distribution were systematically examined. Device performance was evaluated using metrics such as gas–oil ratio distribution curves and flow field characteristics, enabling the identification of operating conditions for stratified flow formation and the determination of optimal deflector structural parameters. Second, based on the Eulerian multiphase flow model and RSM turbulence model, a numerical simulation model for the oil–gas–water three-phase flow field was established. The influences of key parameters (bubble size, throughput, gas–oil ratio) on oil–water separation efficiency were investigated, and the optimal operating conditions for the unit were determined by integrating oil-phase/gas-phase distribution characteristics with oil removal rate data. This research provides theoretical support for the structural optimization and engineering application of horizontal compact closed-loop cyclonic flotation units.

Oilfield stations are major sources of volatile organic compound (VOC) emissions, with storage tanks and open oily sewage pools as the two primary contributors. While storage tank emissions have been widely studied, research on VOC volatilization and dispersion from open oily sewage pools is still limited. Therefore, a systematic investigation into the dispersion mechanisms of VOCs from open oily sewage pools is necessary. This study employs Computational Fluid Dynamics (CFD) to develop a three-dimensional numerical model based on the operational conditions of a typical oilfield joint station in North China. The model integrates field sampling data and simulations to analyze VOC diffusion under both non-obstacle factors (wind speed, environmental temperature, gas composition, and emission rate) and obstacle factors (storage tanks and buildings). Key findings reveal that wind speed significantly enhances downwind dispersion and dilution, while higher temperatures reduce near ground concentrations but extend diffusion distances. The main VOC components, C2H6 and C3H8, exhibit distinct diffusion behaviors, with C3 hydrocarbons playing a dominant role in the dispersion process. Obstacles such as storage tanks and buildings induce flow recirculation and local concentration accumulation, increasing explosion risks. This work provides a scientific basis for predicting the diffusion patterns of VOCs, optimizing the layout of monitoring points, and guiding risk mitigation strategies for open oily sewage pools in oilfields.

Supersonic separation technology is a natural gas treatment technology with easy processing, low investment, low energy consumption, no need to add chemicals, and environmental protection. However, supersonic separation technology is immature. Furthermore, the accuracy of existing nucleation theories for the droplet nucleation process in the supersonic nozzle remains unclear, because they do not consider the effect of swirling motion. The nucleation and condensation processes of water vapor were investigated via molecular dynamics (MD) simulations in this study, and the effects of cooling temperature, axial velocity, and tangential velocity on swirling flow condensation characteristics were analyzed kinetically and thermodynamically at the microscopic level. It is found that at lower cooling temperatures and higher axial velocities, the induction phase of the water vapor condensation process is shortened, the nucleation rate increases, and nucleation occurs more easily. When the axial velocity increases from 200 to 400 m/s, the nucleation rate increases about twice. When the cooling temperature increased from 313 to 353 K, the nucleation rate decreased by 57.7%. However, changes in tangentials have little effect on water vapor swirling flow condensation characteristics.

Supersonic separation technology enables efficient carbon capture, incorporating supersonic fluid dynamics, swirling flow, and enhanced gas-liquid heat and mass transfer processes. The nozzle is the key place to realize the above method, and its structure greatly affects the gas flow and condensation characteristics. To solve the problems of difficulty, accuracy, and high cost of traditional nozzle inner surface machining, a nozzle structure with centroid and straight pipe segment was proposed. Based on droplet growth and classical nucleation theory, a spontaneous condensation model of CH4-CO2mixture gas was established and the spontaneous condensation process of CO2 was analyzed. The findings indicated that the CO2 liquefaction efficiency in this structure can reach 42.5 %. A swirling condensation model is established, and the influences of swirling and inlet parameters on condensation parameters are considered. The findings indicate that: compared with the increase in inlet CO2 concentration and reduced inlet temperature, the increase in inlet pressure has a more obvious effect on improving the liquefaction effect. When the pressure is increased from 4 MPa to 7 MPa, the liquefaction efficiency is increased from 26.1 % to 60.1 %, which is increased by 1.30 times. The above research helps promote the application of supersonic swirl separation technology.

In order to study the thermal and flow properties of interstage coolers in the liquefaction of methane process, numerical analyses were carried out on methane flow within a printed circuit heat exchanger (PCHE) with airfoil fins. A geometry model was developed in this research to include staggered microchannels with airfoil fins. The SST k-omega turbulence model was utilized in the analysis of how various operating parameters, including inlet flux, outlet pressure and inlet temperature, impact flow and thermal characteristics. It was found that higher inlet temperatures result in improved thermal feature but are also associated with increased resistance. Conversely, higher outlet pressure conditions led to better overall flow and thermal feature. Furthermore, the impact of airfoil fins on flow characteristics was studied, considering factors such as secondary flow intensity and entropy generation. Correlations for Fanning frictional factor and Nusselt number were developed with a margin of error within +/- 3.5 %. These research findings are intended to benefit the design and optimization of PCHEs featuring airfoil fins microchannels for applications.

Efficient condensation of ammonia gas is a prerequisite for achieving ammonia-hydrogen separation in supersonic separators. However, the non-equilibrium condensation mechanism of ammonia under swirling conditions is not clear, and the energy conversion process affects the condensation efficiency. This paper develops a threedimensional mathematical model to study the characteristics of condensation flow and energy conversion of ammonia under backpressure conditions. The results indicate that ammonia experiences a centrifugal swirling motion inside the nozzle, with a notable increase in swirl velocity, under the impact of the central body and guiding vanes. Under backpressure conditions, aerodynamic shock waves form in nozzle divergent section. Local velocity differences create substantial shear forces, facilitating the exchange of momentum and energy. Viscous dissipation and aerodynamic losses are the primary contributors to the increase in entropy, accounting for 90% of the total entropy produced. The temperature and pressure distributions before the shock wave remain largely consistent, while increasing backpressure causes the shock wave to move progressively towards the nozzle throat. This movement affects not only the growth region but also the nucleation region, gradually disrupting the droplet nucleation process. As the pressure ratio increases from 0.25 to 0.6, condensation-related entropy generation decreases. At a pressure ratio of 0.6, the shock wave disrupts the nucleation process, reducing the condensation entropy generation to 0.

This study reviews the research and application advancements of pipeline robots in oil and gas pipelines. Oil and gas pipelines, as critical infrastructure for global energy transportation, have historically posed safety hazards such as corrosion and cracks, necessitating efficient and precise inspection and maintenance technologies. Traditional manual inspection methods and mechanical equipment are insufficient to address the modern demands for efficiency and accuracy in oil and gas pipeline systems. Pipeline robots, leveraging the integration of mechatronic technology, intelligent control systems, and advanced detection methods, are emerging as vital tools for pipeline inspection and maintenance. This paper categorizes and compares pipeline robots from multiple perspectives, analyzes the principles, tasks, and application scenarios of different robot types, and assesses their adaptability in oil and gas pipeline environments. It particularly summarizes the key technologies of pipeline robots, including defect detection technologies, pipeline adaptability technologies, navigation and localization technologies and energy supply technologies. The article concludes by outlining potential future directions for pipeline robot technology, highlighting that innovative robot design and intelligent technologies will provide more efficient solutions for the safe inspection and maintenance of oil and gas pipelines, thereby advancing pipeline integrity management technology.

The Soret effect is a significant factor in various scenarios, with thermodiffusion in binary systems serving as a common method for the study. Most research focuses rarely on the distribution characteristics of components in diffusion systems; and Soret coefficients in the porous media could not be obtained by typical methods based on the thermodiffusion column, which are particularly important in the field of oil and gas development. Moreover, experiments on ground conditions have struggled to determine the Soret coefficient accurately due to the convective effect caused by gravity differentiation. The thermodiffusion behavior of n-pentane (C5) and n-heptane (C7) binary mixtures in both bulk and porous media conditions have been investigated, aiming to provide corrected coefficients that mitigate the influence of gravity using theoretical derivation. A new method was proposed to calculate the Soret coefficients in this work by establishing a model based on gas chromatography technology. Dynamic variation of component concentration along the path was studied, and the corresponding Soret coefficients were calculated and analyzed in parallel. The results indicate that the concentration and temperature exhibit a logarithmic relationship with the distance from the heat source. The Soret coefficient values obtained from measurements in porous media are closer to the theoretically corrected values, which do not account for gravity effects. Additionally, as the permeability decreases, the counteracting effect of porous media on convection becomes more pronounced. Therefore, it presents a novel method for accurately measuring the Soret coefficient that ignores convection to some extent.

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