Search Results (135)

Supercritical CO₂ pipeline transportation is a crucial link in Carbon Capture, Utilization, and Storage (CCUS). Compared with traditional oil and gas pipelines, if a supercritical CO₂ pipeline is shut down for an excessively long time, the phase state of CO₂ may transform into a gas–liquid two-phase state. It is urgently necessary to conduct research on the phase change mechanism and safety control during the restart process of gas–liquid two-phase CO₂ pipelines. Based on a certain planned supercritical carbon dioxide pipeline demonstration project, this paper proposes a new pipeline safety restart scheme that actively seeks the liquefaction of gaseous CO₂ inside the pipeline by injecting liquid-phase CO₂ at the initial station. Through numerical simulation and experimental methods, the co-variation laws of parameters such as temperature, pressure, density, and phase state during the pipeline restart process were revealed. It was found that the pipeline shutdown and restart process could be subdivided into four stages: shutdown stage, liquefaction stage, pressurization stage, and displacement stage. The phase transition line would form a closed curve that is approximately trapezoidal. It is suggested to optimize the restart scheme from aspects such as reducing the restart time, controlling the pressure rise rate, and saving CO₂ consumption. It is proposed that the liquid holdup of CO₂ fluid in the pipe at the initial moment of restart and the mass flow rate of CO₂ injected at the initial station during the restart process are the main controlling factors affecting the evolution of the phase path of pipeline restart. For the demonstration project, the specific critical threshold values are given. The research results can provide a certain theoretical guidance and reference basis for the safe restart method of supercritical CO₂ pipelines. Full article

Although intensified flotation cells have been introduced as fast-kinetic and plug-flow-type flotation machines, there is limited empirical verification and information about their fluid flow patterns and dispersion regimes. The present communication paper investigates this for an Imhoflot^TM G-06 cell operated in an open-circuit mode using an impulse method to measure and model the residence time of a liquid–gas system. For experimental measurements, a concentrated KCl solution was employed, and water conductivity was monitored for 20 min. By fitting several relevant models, such as large and small tanks in series (LSTS), Weller, N-Mixer, and perfect mixer, to the experimental data, it was revealed that the N-Mixer represented the dispersion pattern the best (N = 1.3–1.6). Further, the obtained practical mean retention time (MRT) of 4.11 ± 0.16 min was somewhat aligned with the theoretical value, i.e., 5.0 min per pass, indicating a back-calculated gas hold-up magnitude of 18%–22% in the separator. These results provide an in-depth perception of scale-up procedures and requirements for cell modification. Full article

Computational fluid dynamics (CFD) was used to investigate influence of different gas sparger configurations and the presence of horizontal baffles on hydrodynamic characteristics in a flat bubble column. CFD results of time-averaged local and global gas holdup, liquid axial velocity, and Sauter mean diameter were experimentally validated. Subsequently, the validated CFD model was extended to investigate the effects of different gas sparger configurations, i.e., S₁, S₃, S₄, S₅, S₈, and S₇₂, and baffles arrangements, i.e., Config-A and Config-B on overall hydrodynamics at different superficial gas velocities (U_g = 0.0014 m/s and 0.0073 m/s). CFD results demonstrated significant influence of both sparger and U_g. Gas holdup and interfacial area increased with smaller, more numerous sparger openings, such that S₇₂ achieved ~1.55 times higher holdup and ~2 higher interfacial area than that of S₁. Spargers with fewer and larger openings induced stronger turbulence, which intensified early breakup and coalescence and broadened the bubble size distribution. Results revealed that spargers with many small openings (S₇₂) produced the narrowest distribution, retaining a high fraction of bubbles of initial size (5 mm), whereas spargers with fewer larger openings (S₁) generated broader distributions with significant coalescence, especially at higher U_g. The inclusion of baffles enhanced liquid circulation and gas–liquid mixing and contact. However, intensified turbulence below each baffle significantly increased coalescence, producing larger bubbles and resulting in only marginal changes in interfacial area despite increased gas holdup. Full article

Aeration is one of the most energy-intensive operations in wastewater treatment plants, with its efficiency strongly affected by the presence of surfactants. This study investigates the impact of Sodium Dodecyl Sulphate (SDS) on oxygen mass transfer using a commercial fine-bubble diffuser. Oxygen transfer experiments were performed under varying air flow rates and SDS concentrations. Key parameters, including the volumetric mass transfer coefficient ($k_{L}a$), gas holdup, bubble size, and interfacial area, were experimentally measured and analysed. SDS reduces the average bubble diameter by up to 50%; above 4 mg/L, further increases in concentration do not change the bubble size. Gas holdup increases by approximately 2% per mg L⁻¹ of SDS, and a new empirical correlation was proposed to predict gas holdup as a function of air flow rate and surfactant concentration, achieving an R² of 0.97 with deviations below 10%. Despite the increase in interfacial area, SDS strongly suppresses interfacial turbulence, reducing the liquid-side mass transfer coefficient ($k_L$) by up to 70%, which ultimately leads to a significant loss of overall oxygen transfer efficiency. The Sardeing model, originally developed for single bubbles, successfully predicted $k_L$ within ±15% of the experimental values, demonstrating its potential as a practical tool for estimating oxygen transfer in aeration systems. These findings highlight the substantial impact of surfactants on fine-bubble aeration performance and underscore the need to account for their effects in the design and operation of industrial aeration systems. Full article

The hydrodynamic and reaction characteristics of poly-alpha-olefin (PAO) polymerization in a continuous stirred tank reactor (CSTR) under Eulerian–Eulerian multiphase flow and a finite-rate chemical kinetics model were studied in this paper. A mathematical framework correlating 1-decene conversion with operational and structural parameters was established. Numerical simulations revealed an axial circulation flow pattern driven by combined impellers, with internal coils enhancing heat exchange and flow guidance. The gaseous catalyst, injected below the turbine impeller, achieved rapid dispersion and low gas holdup. The results demonstrated that 1-decene conversion exhibited insensitivity to impeller speed under fully turbulent mixing (mixing time <0.15% of space time), suggesting limited mass transfer benefits from further speed increases. Conversion positively correlated with temperature and space time, albeit with diminishing returns at prolonged durations. Series reactor configurations improved conversion efficiency, though incremental gains decreased with additional units. Optimal reactor design should balance conversion targets with economic factors, including energy consumption and capital investment. These findings provide critical insights into scaling PAO polymerization processes, emphasizing the interplay between reactor geometry, mixing dynamics, and reaction kinetics for industrial applications. Full article

Accurate dynamic characterization of wellbore multiphase flow is fundamental for production optimization and real-time control in oil and gas wells. Addressing technical constraints of existing dynamic fitting methods, this study proposes a novel dynamic fitting methodology integrating physical mechanisms with exponentially weighted parameter updating. The approach leverages multiphase flow theory to target the liquid holdup factor and friction factor as correction parameters for dynamic fitting. It incorporates Particle Swarm Optimization to achieve rapid and accurate fitting and introduces an Exponentially Weighted Moving Average mechanism to dynamically update parameters. By fusing historical data with real-time data, the Exponentially Weighted Moving Average method balances instantaneous responsiveness with long-term stability. Empirical validation using a dataset from Block XX of a Southern China oilfield demonstrates the superior accuracy of the fitting method under low-to-medium frequency data conditions. During data interruptions or anomalous disturbances, the method maintains high accuracy while exhibiting a low mean relative change percentage; it effectively suppressed the non-physical jumps of the fitting coefficients and maintained stable and accurate fitting. Full article

As a consequence of the gradual exhaustion of apatite ore reserves, intensive comminution has been implemented in mineral processing operations to enhance phosphorus liberation. Consequently, improving the flotation efficiency of fine particles has remained a persistent challenge within the phosphate industry. The performance of flotation columns is strongly affected by the interaction between gas (bubble) and particle. The present research was designed to evaluate how certain process variables and chemical dosages influence gas holdup and its correlation with the column flotation performance of fine particles derived from a low-grade apatite ore. Column flotation experiments were conducted employing a factorial experimental approach to evaluate the effects of air flow rate, surfactant concentration, collector dosage, and depressant dosage on gas holdup, P₂O₅ grade, and recovery. The results made it possible to identify the levels of gas holdup that lead to appropriate values of P₂O₅ grade and recovery simultaneously, and their relation with the operating variables and reagent dosage. Gas holdup values higher than 23.5% led to the desired values of P₂O₅ grade (>30%) and recovery (>60%) simultaneously. Statistical models were developed with high correlation coefficients (R² > 0.98) to predict P₂O₅ grade and recovery as functions of the operating variables. This research provides a comprehensive framework of the gas holdup effect on column flotation systems, offering significant potential for improving the economic viability of low-grade phosphate ore processing. Full article

The synergistic development of low-permeability reservoirs such as deep coalbed methane (CBM) and tight gas has emerged as a key technology to reduce development costs, enhance single-well productivity, and improve gas recovery. However, due to fundamental differences between coal seams and tight sandstones in their pore structure, permeability, water saturation, and pressure sensitivity, significant variations exist in their flow capacities and fluid production behaviors. To address the challenges of production allocation and main reservoir identification in the co-development of CBM and tight gas within deep gas-bearing basins, this study employs the transient multiphase flow simulation software OLGA to construct a representative dual-gas co-production well model. The regulatory mechanisms of the gas–liquid distribution, deliquification efficiency, and interlayer interference under two typical vertical stacking relationships—“coal over sand” and “sand over coal”—are systematically analyzed with respect to different tubing setting depths. A high-precision dynamic production allocation method is proposed, which couples the wellbore structure with real-time monitoring parameters. The results demonstrate that positioning the tubing near the bottom of both reservoirs significantly enhances the deliquification efficiency and bottomhole pressure differential, reduces the liquid holdup in the wellbore, and improves the synergistic productivity of the dual-reservoirs, achieving optimal drainage and production performance. Building upon this, a physically constrained model integrating real-time monitoring data—such as the gas and liquid production from tubing and casing, wellhead pressures, and other parameters—is established. Specifically, the model is built upon fundamental physical constraints, including mass conservation and the pressure equilibrium, to logically model the flow paths and phase distribution behaviors of the gas–liquid two-phase flow. This enables the accurate derivation of the respective contributions of each reservoir interval and dynamic production allocation without the need for downhole logging. Validation results show that the proposed method reliably reconstructs reservoir contribution rates under various operational conditions and wellbore configurations. Through a comparison of calculated and simulated results, the maximum relative error occurs during abrupt changes in the production capacity, approximately 6.37%, while for most time periods, the error remains within 1%, with an average error of 0.49% throughout the process. These results substantially improve the timeliness and accuracy of the reservoir identification. This study offers a novel approach for the co-optimization of complex multi-reservoir gas fields, enriching the theoretical framework of dual-gas co-production and providing technically adaptive solutions and engineering guidance for multilayer unconventional gas exploitation. Full article

Gas–water two-phase flow in horizontal and inclined wells is significantly influenced by gravitational forces and spatial asymmetry around the wellbore, resulting in complex and variable flow patterns. Accurate measurement of water holdup is essential for analyzing phase distribution and understanding multiphase flow behavior. Water holdup imaging provides a valuable means for visualizing the spatial distribution and proportion of gas and water phases within the wellbore. In this study, air and tap water were used to simulate downhole gas and formation water, respectively. An array capacitance arraay tool (CAT) was employed to measure water holdup under varying total flow rates and water cuts in a horizontal well experimental setup. A total of 228 datasets were collected, and the measurements were processed in MATLAB (2020 version) using three interpolation algorithms: simple linear interpolation, inverse distance interpolation, and Lagrangian nonlinear interpolation. Water holdup across the wellbore cross-section was also calculated using arithmetic averaging and integration methods. The results obtained from the three imaging algorithms were compared with these reference values to evaluate accuracy and visualize imaging performance. The CAT demonstrated reliable measurement capabilities under low- to medium-flow conditions, accurately capturing fluid distribution. For stratified flow regimes, the linear interpolation algorithm provided the clearest depiction of the gas–water interface. Under low- to medium-flow rates with high water content, both inverse distance and Lagrangian methods produced more refined images of phase distribution. In dispersed flow conditions, the Lagrangian nonlinear interpolation algorithm delivered the highest accuracy, effectively capturing subtle variations within the complex flow field. Full article

Industrial organic wastewater, with its complex composition, high biological toxicity, and recalcitrance, has become a major challenge in water pollution control. This is especially true for antibiotic-containing wastewater, such as ofloxacin wastewater, for which there is an urgent need to develop effective treatment technologies. Conventional treatment processes are insufficiently efficient, while individual advanced oxidation processes (AOPs) have drawbacks such as poor oxidation selectivity and catalyst deactivation. To address these issues, researchers have explored the coupling of different AOPs and found that such combinations can enhance the oxidation performance, achieve complementary advantages, reduce the equipment costs, and offer great development potential. An experiment was conducted to evaluate the performance of an Ozone-Electro-Fenton coupled process in treating ofloxacin industrial wastewater. The results demonstrated that under the same conditions, after four hours of treatment, the coupled process achieved a 70% reduction in the UV absorption peak of the wastewater, compared to less than 20% for individual processes, indicating a significant synergistic effect. Further optimization of the ozone aeration structure revealed that with a hole size of 0.5 mm, single-layer aeration holes, and six holes, the COD removal rate reached 96% after six hours, the ozone utilization improved to 85%, and the gas holdup stabilized at 4.6%. Under these conditions, the mixture of ozone and air bubbles formed mixed bubbles. Influenced by the electric field and electrode plate wall effects, the bubble residence time was prolonged. The bubble size was approximately 2.8 mm, the gas flow horizontal velocity was about 18.5 m/s, and after a horizontal displacement of 0.17 mm in the wastewater, the lateral velocity became zero. The ratio of the distance between the bubble center and the wall to the equivalent bubble diameter was approximately 3.45. The bubbles were subject to a strong wall effect, which extended their residence time. This not only facilitated the removal of small bubbles from the electrode plates but also enhanced the ion diffusion near the plates, thereby boosting pollutant degradation. This study shows that the Ozone-Electro-Fenton coupled process is highly effective in degrading ofloxacin industrial wastewater, offering an innovative solution for treating other antibiotic-containing wastewater. Future research will focus on further optimizing the process, improving its adaptability to complex matrix wastewater, and validating it at the pilot scale to promote its engineering application. Full article

During natural gas development, the gas–water two-phase flows in upward and horizontal wellbores are complex and variable. The accurate calculation of the water holdup in each production layer using appropriate methods based on the logging data collected by fluid identification instruments can enable the precise identification of primary oil-producing and water-producing layers and facilitate subsequent water shutoff operations. In this study, we first investigated the measurement techniques and calculation methods for gas–water two-phase holdups both in China and internationally. Second, we conducted gas–water two-phase simulation experiments in upward and horizontal large-diameter wellbores using a Triangular Arm Array Imager (TAAI) equipped with six fiber-optic probes in a multiphase flow simulation laboratory. We then categorized the flow patterns observed in the physical simulation experiments based on typical theoretical classifications of gas–water two-phase flow patterns. Subsequently, we calculated the spatial positions of the fiber-optic probes and the local water holdup in the wellbore cross-section from the data collected by TAAI and compared the results obtained by Gaussian radial basis function (GRBF) or inverse distance weighted (IDW) interpolation algorithms. We processed the experimental data and found significant discrepancies between the holdup calculated by the two algorithms and the actual wellbore holdup. Therefore, we applied the Levenberg–Marquardt (L-M) algorithm to optimize these interpolation algorithms and discovered that the holdup obtained from the optimized algorithms aligned more closely with the actual wellbore holdup with reduced errors. Finally, we applied the optimized algorithms to the processing of measured data from a gas–water two-phase horizontal well. The results indicate that the L-M algorithm can improve the accuracy of 4–5% of holdup calculations. In the actual production process, the output situation of each production layer can be more accurately judged to provide important opinions for the subsequent actual production by this study. Full article

The introduction of a gas phase into a liquid is used in a variety of technical applications. Based on the purpose of the application, different flow behaviors of the gas phase and specific gas phase parameters are preferred. In this study, the influence of the diameter and shape of a single-hole orifice sparger on the gas phase behavior was investigated. For this purpose, an experimental setup of a bubble column was built, and different orifice sizes and types were installed. The two different designs that were tested were direct flat orifices and single needle-type nozzles. The flat nozzle diameter was varied from 0.5 mm to 3 mm, whereas two different needle-type nozzles with diameters of 0.5 mm and 1 mm were also tested. Through high-speed imaging and digital image processing, a contour analysis of the bubbles was performed using a special technique for image segmentation and the identification of phase inhomogeneities. The gas holdup and surface area of the gas phase were calculated at different column heights and different flow rates. The results show that smaller nozzle diameters led to a higher gas holdup and a higher phase surface than larger-diameter orifices at the middle and upper sections of the column, implying a better mass and heat transfer performance. Full article

This study aimed to evaluate the effect of different concentrations of Tween 20 on various physical properties of agar gel as a model material. The effects of other sources of agar-agar powder on the gel properties were also evaluated. The pure gels were prepared with agar powders obtained from two suppliers. Also, agar gels with Tween 20 in the 0.10 to 0.70% range were produced. The measurement of density, water activity, maximal force at fracture and gelling temperature, and the agar gels’ rheological properties, showed that the gels prepared with different agar powders had similar properties. The syneresis and stability indexes, gas hold-up, mechanical and acoustic attributes, and structure of foamed gels with Tween 20 were measured. The addition of Tween 20 in amounts ranging from 0.10 to 0.35% contributed to a gradual decrease in the stability and mechanical parameters of the gels. Using a concentration of 0.7%, Tween was able to obtain foamed gels with a uniform structure and small pore size, but low hardness and gumminess. Application of a lower concentration of Tween of 0.1% produced more rigid gels with limited gel syneresis. Adding Tween 20 at the appropriate level can be a factor in obtaining gels with a tailored structure and texture. Full article

This study aims to contribute to the optimization of bio-methanation in bubble columns, making it a more viable alternative to stirred tank reactors. The primary challenge to be addressed is the enhancement of mass transfer, which strongly depends on parameters such as bubble size and gas hold-up. Various disperser designs were examined in a 0.14 mm diameter column, comparing their performance in terms of bubble diameter distribution and gas hold-up. The results indicate that an optimized plate disperser featuring a porous structure outperformed other designs by maintaining high gas retention without significant coalescence. Additionally, newly developed plug-in dispersers allowed for counter-current flow operation, enhancing process flexibility. Commercially available porous pin dispersers produced smaller bubbles compared to the other designs, yielding high gas hold-ups at lower gas velocities. Correlations between disperser type and column design parameters were established, laying the foundation for apparatus optimization. The findings contribute to the development of digital twin models, facilitating the refinement of bio-methanation processes within bubble columns for increased efficiency. Full article

In this study, in a three-phase reactor with a rectangular cross-section, the effects of liquid circulation rates and solid particle concentration on gas holdup and bubble size distribution (BSD) were investigated. Air, water, and glass beads were used as the gas, liquid, and solid phases, respectively. Different liquid circulation velocities and different solid loads were applied. The results demonstrate that increasing solid content from 0% to 6% can decrease gas holdup by 50% (due to increased slurry phase viscosity and promotion of bubble coalescence). Also, increasing the liquid circulation rate showed a weak effect on gas holdup, although a slight incremental effect was observed due to the promotion of bubble breakup and the extension of bubble residence time. The gas holdup in counter-current slurry bubble columns (CCSBCs) was predicted using a novel correlation that took into account the combined effects of solid concentration and liquid circulation rate. These findings are crucial for the design and optimization of the three-phase reactors used in industries such as mining and wastewater treatment. Full article