Gas-liquid Separation Process Research Articles

Numerical and experimental study of dynamic gas–liquid separator with various viscosities

The gas–liquid separation process is important in various industries, such as electric power, aerospace, and petroleum. This study introduces an innovative, dynamic gas–liquid separator (DGLS) in which a cyclonic flow pattern is induced by blade rotation. This cyclonic flow enhances the efficiency of gas and liquid phase separation while also imparting energy to facilitate the transport of the separated fluid. Numerical simulations are used to analyze the internal flow dynamics, power requirements, and separation efficiency of this DGLS. A comparison with experimental results is conducted to validate the reliability of the numerical model. The effects of liquid-phase viscosity on the internal energy consumption and separation performance of the DGLS are explored at various flow rates. The simulation results indicate that for a given viscosity, the degassing rate of the separator decreases while the liquid removal rate increases as the inlet flow rate rises. Furthermore, it is observed that higher viscosity leads to poorer separation performance, with a decrease in turbulent kinetic energy near the rotating axis and an increase in turbulence intensity near the wall. At lower flow rates, the effectiveness of liquid-phase outlet pressurization improves with increasing viscosity. However, at higher flow rates, increasing viscosity leads to a substantial decline in energy performance and a reduction in liquid-phase outlet pressurization. The increment in turbulent kinetic energy is greater than the square of the mean velocity, indicating a positive correlation between turbulence intensity and turbulent kinetic energy. These findings not only provide a theoretical basis for the prediction of flow losses within a DGLS and the efficient design of these separators, but also provide guidance for industrial applications involving high-viscosity fluids.

Process Intensification of Gas–Liquid Separations Using Packed Beds: A Review

The gas–liquid multiphase process plays a crucial role in the chemical industry, and the utilization of packed beds enhances separation efficiency by increasing the contact area and promoting effective gas–liquid interaction during the separation process. This paper primarily reviews the progress from fundamental research to practical application of gas–liquid multiphase processes in packed bed reactors, focusing on advancements in fluid mechanics (flow patterns, liquid holdup, and pressure drop) and the mechanisms governing gas–liquid interactions within these reactors. Firstly, we present an overview of recent developments in understanding gas–liquid flow patterns; subsequently we summarize liquid holdup and pressure drop characteristics within packed beds. Furthermore, we analyze the underlying mechanisms involved in bubble breakup and coalescence phenomena occurring during continuous flow of gas–liquid dispersions, providing insights for reactor design and operation strategies. Finally, we summarize applications of packed bed reactors in carbon dioxide absorption, chemical reactions, and wastewater treatment while offering future perspectives. These findings serve as valuable references for optimizing gas–liquid separation processes.

Kinetics and dynamics of Gas-liquid separation and bubble generation in surfactant solutions: Role of bulk/interfacial properties and hydrodynamic conditions

Understanding the kinetics and dynamics of gas–liquid separation and bubble generation in surfactant solutions is important for many industrial applications. To explore the potential mechanisms affecting the physical properties (expansion ratio, bubble size, and foam stability) of foams and bubbles, the surface tension of the solution, including the equilibrium and dynamic properties, was investigated. Then, the morphology of the surfactant aggregates was explored by cryo-transmission electron microscopy (cryo-TEM). Based on these experimental results, the effects of various physical and chemical factors (including the relative concentration of surfactant, dynamic surface tension, surface coverage, surface elasticity, surface mobility, aggregate morphology, etc.) on the expansion ratio and bubble size were analysed to identify which “universal” parameters can explain the phenomenon for all aqueous solutions in the gas–liquid separation process. Research has shown that the morphology of aggregates in a solution largely determines the surface properties of the solution at 1.5 ms (surface tension, surface coverage, surface elasticity, and so on). These surface properties significantly affect the expansion ratio. However, no good correlation was found between bubble size and these surface properties because surfactant vesicles can directly affect bubble size. In addition, the liquid flow rate and gas–liquid ratio have a significant impact on the expansion ratio and bubble size. Ultimately, we found that the foam stability, bubble size, and expansion ration can be described by a simple linear relationship. Our research provides new opinions for further understanding the effects of bulk/interfacial properties and hydrodynamic conditions on the physical properties of bubbles in the gas–liquid separation process.

Liquid carry-over control using three-phase horizontal smart separators in Khor Mor gas-condensate processing plant

Liquid carry-over phenomenon, where liquid droplets escape with gas, is a prevalent operational challenge in gas–liquid separators. Liquid carry-over leads to foaming issue and performance reduction within separator downstream absorption processes. In order to ascertain whether liquid carry-over is inducing foaming within the gas sweetening process’s absorption tower at Iraq’s Khor Mor gas-condensate processing plant, this study initiated an evaluation of the liquid droplet size distribution in the gas product and gas/liquid separation efficiency of upstream Alpha, Bravo #1, Bravo #2, and Charlee separators that feed into the aforementioned tower by using the Horizontal Vessel and ProSeparator correlations in Aspen HYSYS v.11 software. The study revealed that Alpha and Bravo #2 experienced liquid carry-over issues. In response to these challenges, an innovative smart separator design, referred to as an adjustable separator, was proposed, employing the Arnold-Stewart semi-empirical procedure. This design allows for easy adjustment to accommodate changes in feed composition and operational conditions, mitigating the liquid carry-over problem. The smart design demonstrated a significant increase in gas/liquid separation efficiency for Alpha separator, improving by 31.11% under current conditions and 77.65% under future conditions. Similarly, under both current and future conditions, the smart design of Bravo #2 separator yielded an enhancement of 21.31% and 28.23%, respectively. These results suggest that the smart design can be considered an optimal solution for controlling liquid carry-over. This innovation not only maintains high gas/liquid separation efficiency but also prevents foaming, offering a robust solution for ensuring sustained operational performance and productivity in gas–liquid separation processes.

Understanding the role of perforations on the local hydrodynamics of gas–liquid flows through structured packings

Structured packings are widely used to perform gas–liquid separation processes as they provide a large mass-transfer area and low-pressure drop. The overall performance of these packings is governed by the local liquid distribution/gas–liquid interfacial area. The local liquid distribution is substantially influenced by the arrangement and geometrical features of the structured packing. While the influence of arrangement and few geometrical features on the local liquid distribution has recently been investigated using the structure-resolved simulations, the perforations on the structured packings are usually ignored. In the present work, we have performed structure-resolved gas–liquid flow simulations, using the Volume-of-Fluid (VOF) method implemented in the open-source C++ library OpenFOAM, in a periodic domain of Mellapak.250 with and without resolving the perforations. We show that the presence of perforations results in flow separation as well as droplet formation leading to an increase in the liquid holdup, interfacial and wetted areas, irrespective of the fluid properties and wetting conditions (specified using static contact angle ‘θw’) considered in this work. We also show that at an inclination angle ‘β’ of 45° from horizontal, the location of the perforations governs the local liquid distribution and the resulting flow metrics. However, at a β of 90°, the number of perforations governs the local liquid distribution, irrespective of their location. Further, we also show that the predictions of structure-resolved VOF simulations, with perforations resolved, are in a relatively better agreement with the correlations in the literature at small values of θw in terms of liquid holdup and interfacial area.

Numerical simulation and an innovative design of the inlet gas distributor in an industrial adsorption tower

Gas distributor plays an important role in operation performance of gas-solid and gas-liquid reactions and separation processes. In this work, computational fluid dynamics method was used to simulate the gas distribution of the inlet gas distributor in an industrial pressure swing adsorption tower. The employed model has been validated with available empirical formula. The simulation results show that the industrial perforated plate gas distributor brings a strong flow along the elliptical head wall and large vortexes. It shows bad gas distribution performance. Therefore, a conical shell gas distributor is proposed. Its structural parameters, such as cone angle and hole distribution are optimized. The optimal cone angle is 166°. Furthermore, an imperforated area with a diameter of 290 mm is necessary to decrease the gas velocity at the center area. The optimal distributor can effectively weaken the large vortexes above the distributor and the high gas velocity at axial center. Compared with the industrial distributor, the inhomogeneity index M of the gas distribution is decreased from 5.61 to 2.48, and the pressure drop △P of the distributor is decreased from 59.3 Pa to 46.0 Pa. In addition, the designed distributor is also suitable for towers with larger diameters.

Gas-Liquid Separation Processes for Mud Logging Systems

Gas-Liquid Separation Processes for Mud Logging Systems

Effect of mechanical stirring on CO2 foaming in petroleum

CO2 flooding is an effective technology to improve oil recovery. However, because the foam layer produced in the actual production may affect the gas-liquid separation effect and cause damage to downstream devices. Therefore, it is necessary to study the defoaming technology in the separator. This paper mainly studies the influence of different stirring speeds on the death of the foam layer during the depressurization process and after the depressurization is stopped. The stirring blade can accelerate the formation and disappearance of foam, and the final result is to reduce the time required for defoaming. During the whole process, the survival time of large bubbles is short, but stirring has less influence on small bubbles. Stirring will increase the height of the foam layer, which will affect the gas-liquid separation efficiency in severe cases. Therefore, if the fluid entering the separator has good foam-ability, it is not recommended to directly use mechanical stirring to eliminate foam in the gas-liquid separation process.

Forming and stripping of the wall film and the influence on gas–liquid separation

AbstractThe paper aims to investigate re‐entrainment mechanisms of wall films. The computational fluid dynamics method was adopted to study the gas–liquid separation process considering the wall film model. The interaction between the droplets and gas was solved by Euler–Lagrange method, whereas the forming and stripping of the wall film was studied by Eulerian wall film model. The results reveal that superficial velocity affects the re‐entrainment significantly, and there is a critical superficial velocity determining the occurrence of wall film stripping. According to this work, the critical velocity for air continuous phase is 11.2 m/s. It is found that the discrete phase content and droplet size have no effect on film thickness but affect the separation efficiency. The molecular viscosity and the density of continuous phase affect the Eulerian wall film on two aspects. First, the critical stripping velocity decreases with the increase in molecular viscosity. Second, the film average thickness and separation efficiency decrease with the increase in the product of viscosity and density of the continuous phase. Because the high velocity causes some unsteady of the results, the bulk velocities lower than 20 m/s are recommended. The development of re‐entrainment mechanism provides a good understanding of inertia separation.

Experimental study and similarity analysis of separation efficiency of swirl-vane separator

Swirl-vane separator in nuclear steam generator is used as primary separator for separating more than 80% of the water from the steam-water mixture to feed the qualified steam to dryers and turbines. Laboratory tests are generally performed to seek alternatives for separator design and performance improvement. Though great efficiency is often obtainable in the reduced model, the performance of the full-sized prototype is not well predicted due to the lack of proven similarity analysis. In our previous study, a theoretical model for critical droplet diameter, grade efficiency and overall separation efficiency has been established to predict separator performance (Liu and Bai, 2016). Based on the model, the aim of this paper is to study the separation performance of downscaled separator and to identify important differences between small-scale and large-scale separators. Experiments are carried out on a small-sized swirl-vane separator using air and water as working fluids. Firstly, the characteristics of gas-liquid separation process are visually observed using high-speed camera to understand the operating principle of the separator. After that, the separation efficiency is measured over a wide range of flow conditions, and the gas and liquid velocities influencing the separator performance is analyzed in detail. The experimental data are then used with previous theoretical model to predict the performance of two larger separator prototypes. When model separator has a same shape but reduced size as that of prototypes, and their working pressure and gas-liquid superficial velocities are the same, the results indicate that the model separator has a significantly greater separation efficiency than the prototypes. Generally, the larger scale the prototypical separator is, the lower value the separation efficiency becomes.

Liquid Flow Morphology of Viscous Systems in Structured Packings: Investigations by X-ray Tomography

In the modeling of gas-liquid separation processes in structured packings, fluid dynamics is often reduced to a uniform liquid film flow over the packing surface. However, previous experiments with X-ray tomography indicate that this assumption is not valid when the liquid-phase viscosity is significantly higher than 1 mPa s. In order to improve existing modeling approaches for viscous systems, a better understanding of the influence of the liquid viscosity on the liquid flow inside the structured packing is necessary. In this work, X-ray tomography is used to investigate the flow morphology of liquid systems with low surface tension and a viscosity up to 50 mPa s. An empirical correlation that describes the hold-up fraction of the existing flow patterns is given and a modelling approach is proposed that allows to consider the influence of the different flow patterns on mass transfer.

Modeling and simulation of the gas-liquid separation process in an axial flow cyclone based on the Eulerian-Lagrangian approach and surface film model

Axial flow cyclones are a widely used gas-liquid separation equipment in the chemical industry, petroleum industry, nuclear industry, etc. The gas-liquid separation process inside an axial flow cyclone involves complex phenomena, including the deposition of droplets on the wall (forming a liquid film), the flow of this liquid film, and the entrainment of droplets in this film. Therefore, CFD simulations of the gas-liquid separation process in an axial flow cyclone are very challenging to perform. In the present study, the gas-liquid separation process inside an axial flow cyclone is successfully modeled using the Eulerian-Lagrangian approach and a surface film model. The gas core is described by the Eulerian-Lagrangian approach, and the liquid film flow is modeled based on a two-dimensional thin-film assumption. Then, the proposed model is implemented by using OpenFOAM and validated against various experimental data sources. Subsequently, the proposed model is employed to simulate the flow field in the cyclone, which directly affects the separation performance. Furthermore, the gas-liquid two-phase flow inside the cyclone with high operating pressure is investigated using the proposed model, and the relevant characteristics are analyzed. The research results are of great significance to the design, operation, and optimization of axial flow cyclones.

Antiwettability enhancement of PVDF-HFP membrane via superhydrophobic modification by SiO2 nanoparticles

Pore wetting is undesirable in the membrane gas–liquid separation process as it deteriorates the gas removal flux. To alleviate the affinity of a membrane surface toward a liquid solvent, its hydrophobicity needs to be enhanced. In this study, a superhydrophobic polyvinylidene fluoride-co-hexafluoropropylene membrane was synthesized via a simple and facile nonsolvent-induced phase inversion process. Hydrophobic nano-SiO2 particles were used as solvent additives to improve the wetting resistance of the membrane. The results revealed that blended nano-SiO2 membranes exhibited enhanced surface hydrophobicity in terms of water contact angle. Such improvement was attributed to the enhancement of surface roughness via the formation of hierarchical multilevel protrusions. Besides, the embedment of nanoparticles in polymer spherulitic globules also contributed to the reduction in surface energy of the membrane. As a result, the blended nano-SiO2 membrane achieved superhydrophobicity with a water contact angle of up to 151°.

Energy Consumption and Economic Analyses of a Supercritical Water Oxidation System with Oxygen Recovery

Oxygen consumption is one of the factors that contributes to the high treatment cost of a supercritical water oxidation (SCWO) system. In this work, we proposed an oxygen recovery (OR) process for an SCWO system based on the solubility difference between oxygen and CO2 in high-pressure water. A two-stage gas–liquid separation process was established using Aspen Plus software to obtain the optimized separation parameters. Accordingly, energy consumption and economic analyses were conducted for the SCWO process with and without OR. Electricity, depreciation, and oxygen costs contribute to the major cost of the SCWO system without OR, accounting for 46.18, 30.24, and 18.01 $·t−1, respectively. When OR was introduced, the total treatment cost decreased from 56.80 $·t−1 to 46.17 $·t−1, with a reduction of 18.82%. Operating cost can be significantly reduced at higher values of the stoichiometric oxygen excess for the SCWO system with OR. Moreover, the treatment cost for the SCWO system with OR decreases with increasing feed concentration for more reaction heat and oxygen recovery.

Air dehumidification by membrane with cold water for manned spacecraft environmental control

The traditional condensation dehumidification method requires additional gas-liquid separation and water recovery process in the manned spacecraft humidity control system, which would increase weight and complexity of systems. A new membrane dehumidification with cold water is proposed, which uses water vapor partial pressure difference to promote water vapor transmembrane mass transfer for dehumidification. The permeability of the membrane was measured and the experimental results agree well with the theoretical calculations. Based on the simulation of dehumidification process of cold water-membrane, the influence of module structure and working condition on dehumidification performance was analyzed, which provided reference for the design of membrane module construct. It can be seen from the simulation and experiments that the cold water-membrane dehumidification can effectively reduce the thermal load of the manned spacecraft.

Simple Continuous High‐Pressure Hydrogen Production and Separation System from Formic Acid under Mild Temperatures

AbstractA simple and continuous high‐pressure (>120 MPa) hydrogen production system was developed by the selective decomposition of formic acid at 80 °C using an iridium complex as a catalyst, with a view to its application in future hydrogen fuel filling stations. The system is devoid of any compressing system. The described method can provide high‐pressure H2 with 85 % purity after applying an effective gas–liquid separation process to separate the generated gas obtained from the decomposition of formic acid (H2/CO2=1:1). The efficiency of the catalyst lies with its high turnover frequency (1800 h−1 at 40 MPa) to produce high‐pressure H2 with a good lifetime of >40 h. Interestingly, only very low levels carbon monoxide (less than 6 vol ppm) were detected in the generated gas, even at 120 MPa.

Crystal growth of FeCO3 in mixed monoethylene glycol and water solvent

The transportation of natural gas in long subsea pipelines is a challenge when it comes to hydrate prevention, corrosion and mineral scaling. When monoethylene glycol (MEG) is injected into carbon steel pipelines to prevent formation of gas hydrates, the solubility of the corrosion products is altered. Understanding the kinetics of FeCO3 precipitation may make it possible to avoid deposition in the gas liquid separation process and improve solids removal in MEG recovery units. In this work, the growth kinetics of iron carbonate (siderite) has been studied in seeded batch experiments in MEG‐water solutions with 0 and 40 wt% MEG at 50 and 70 °C. Precautions were taken to keep anaerobic conditions and avoid oxidation of ferrous ions. The growth rate (G) was measured as function of supersaturation (S) and fitted to the equation: G = kr(S‐1)g. The growth order (g) was approximately 2 independent of the MEG concentration at the two temperatures. The growth rate constant (kr) was in the range of 6 × 10−11 to 1 × 10−10 m/s. Temperature increase from 50 to 70°C had no measurable effect on the growth rate while in the presence of 40 wt% MEG the growth rate constant decreased.

A Highly Efficient Deaerator Design and Application

In this paper, in view of the non-condensable gas in the process condensate can not effectively remove in industrial boiler, designed has developed a new type of high efficient deaerator. Three times the gas-liquid separation process can ensure the effective clutter the impurity gas discharge in this deaerator. When the condensation temperature is below 80 °C, standby mouth additional blower can be further improved degassing efficiency. The body of tank is designed by the liquid levels frequency conversion control and the upper tank provided with an overflow pipeline, to ensure the separation of the impurity gas, but also guarantee the safe operation of the system.

Gas–liquid separation processes based on physical solvents: opportunities for membranes

Membrane contactors have received increased attention since the 1980s and are already used for different industrial applications. A very large number of studies have been reported, more specifically to achieve intensified gas–liquid mass transfer, almost exclusively in water or aqueous solutions. In contrast, the potentialities of membrane contactors for gas–liquid processes based on non-aqueous physical solvents are essentially unexplored. This study intends to discuss the difficulties associated with the specific physical solvent context and explore the potentialities of membrane contactors for both absorption and regeneration steps. Theoretical arguments show that dense membranes based on superpermeable and mechanically resistant polymers could offer promising performances, owing to their capacity to simultaneously prevent wetting effects, sustain a high transmembrane pressure and offer process intensification possibilities. Moreover, a significant improvement in terms of energy efficiency is theoretically achievable for the regeneration step. A preliminary proof of concept study, which supports these potentialities, is presented and the research needs for this new approach in order to possibly achieve applications at industrial scale are discussed.

Characteristics of a rotating packed bed equipped with blade packings

This study examined pressure drop and mass transfer of a rotating packed bed (RPB) equipped with blade packings using stripping of oxygen from water and absorption of isopropyl alcohol from gas. As to pressure drop, the gas flow rate appeared to be a more important factor than the liquid flow rate due to less liquid holdup under centrifugal field. For stripping of oxygen from water, K L a increased with an increasing rotor speed and an increasing liquid flow rate. For absorption of isopropyl alcohol from gas, K G a increased with the rotor speed. Also, K G a increased with an increasing liquid flow rate and an increasing gas flow rate. The HTU values were about 2.2–2.4 cm for stripping of oxygen from water and about 1.1–3.3 cm for absorption of isopropyl alcohol from gas, respectively, implying that an RPB equipped with blade packings could provide an efficient mass transfer as compared to a conventional packed bed. Moreover, the obtained results indicated that the HTU values of an RPB equipped with blade packings were comparable to those of the RPB equipped with random and structure packings, suggesting a great potential of an RPB equipped with blade packings applied to the gas–liquid separation processes including stripping and absorption.