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

Reliable and long-term operation of gas compressors largely depends on the effective prevention of liquid phase ingress, particularly condensate, into the compressor flow path. Liquid carryover with the gas stream accelerates erosion processes, causes mechanical damage to internal compressor components, increases vibration levels, contaminates the lubrication system, and ultimately reduces the overall efficiency and reliability of the equipment. These issues are especially critical for high-speed and heavily loaded gas compressors operating under continuous service conditions. Separators installed at the inlet of gas compressors play a crucial role in the gas–liquid separation process. However, operational experience indicates that existing separator designs do not always provide the required separation efficiency under real operating conditions. High gas velocities, reduced condensate droplet sizes, non-uniform flow distribution, and insufficient performance of demister elements contribute to liquid carryover and subsequent condensate ingress into the compressor. This study investigates methods for reducing the amount of condensate entering a gas compressor by implementing design modifications to the inlet separator. The operating principle and structural features of the existing separator are analyzed, and key operational deficiencies are identified. The main hydrodynamic and design parameters influencing gas–liquid separation efficiency are determined. Based on the analysis, technical solutions are proposed, including optimization of the separator internals, improvement of inlet flow distribution, enhancement of demister elements, and upgrading of the condensate collection and drainage system. The implementation of the proposed design modifications resulted in a significant reduction in condensate carryover at the compressor inlet, stabilization of operating parameters, and an overall improvement in equipment reliability. The results confirm that optimizing separator design is an effective approach to enhancing the safety, efficiency, and service life of gas compressors and can be recommended for application in similar process systems. Keywords: Gas compressor, separator, condensate, gas–liquid separation, design modification, demister, operational reliability.

In this paper the Gradient Theory of inhomogeneous fluids interface will be discussed and applied to compute the interfacial tension of hydrocarbon mixtures. The two inputs of the Gradient Theory model are the Helmholtz free energy densities of homogeneous bulk phases and the influence parameters of inhomogeneous interface. The bulk phase properties are calculated by the Peng-Robinson Equation of State. The pure component influence parameters are obtained from a correlation based on pure component experimental surface tension data, and the mixture influence parameters are determined from the geometric mixing rule. Experimental interfacial tension data for binary hydrocarbon mixtures and real petroleum fluids from two gas condensate reservoirs are collected and used to evaluate the Gradient Theory and Parachor Method. It is found that the accuracy of the Gradient Theory is superior to the Parachor Method which is traditionally used in the oil industry for interfacial tension predictions. 1 Introduction It is well known that the interfacial tension is regarded as one of important thermophysical parameters in many industrial processes. For example, in gas liquid separation process, there are strong dependencies between liquid interfacial tensions and gas-liquid separation performance, because both droplet size distribution and re-entrainment are sensitive to interfacial tension in the scrubber. In addition surface tension also plays important role in oil recovery process, extraction process, refinery process, etc. In spite of the importance of interfacial tension in petroleum industry, there is still a considerable lack of reliable experimental data in the open literature, especially near the critical conditions. Therefore, the theoretical and semi empirical prediction of interfacial tensions are of particular significance. There are several approaches which have been proposed for the estimation of interfacial tensions. These approaches can be divided into two categories: empirical correlations and statistical thermodynamics-based method which takes into account the density gradient between the bulk phase interfaces. The simple estimation method includes the Parachor Method [1-2], the Corresponding State Correlation [3] and the Perturbation Theory [4], which are not satisfactory for estimating interfacial tension of mixtures that exhibit strong hydrogen bonding. The statistical thermodynamics based methods include the Density Function Theory [5-6] and the Gradient Theory [7-8]. The Gradient Theory is of particular importance for practical computations of surface and interfacial tensions. It was originated by Rayleigh and Van der Waals [7] and rediscovered by Cahn and Hilliard in 1958 [8]. In this work the Gradient Theory of inhomogeneous fluid interface will be applied to obtain the interfacial tension of the hydrocarbon mixtures. The short descriptions of the Gradient Theory can be found in section 2. The Peng-Robinson Equation of State will be recalled in the section 3 and is utilized to compute some thermodynamic properties of the vapor/liquid phases and the interface. Finally the predicted interfacial tensions will be compared to experimental tensions. The superiority of the Gradient Theory is that it simultaneously can simulate mixture compound density profiles over the interfaces which are hardly accessible in experimental observation and measurement. The density profiles are very useful for theoretical studies and characterization of the interfacial behaviors of the hydrocarbon mixtures.

Summary The major challenge in enhanced oil recovery (EOR) by gas injection is poor volumetric sweep efficiency, mainly due to the high gas mobility and reservoir heterogeneity. Injecting gas as a foam increases sweep efficiency, but maintaining foam stability within the reservoir remains a challenge. This research evaluates the synergistic interaction of one type of nanoparticle and a surfactant to increase foam stability, using the concentration ratio of the two components to tune the affinity of the nanoparticle for the gas/liquid interface. We test the capability of the synergistic two-component system to stabilize methane foam and compare it with foam stabilized by surfactants only. A key distinction is the foam stability upon contact with oil, and we explain the observations in static and dynamic conditions. Foam stability was measured in both static (bubble structure) and dynamic (flow through porous media) conditions. In the static test, foam is generated by the shaking method, and foam texture (bubble size and shape) and the decay of foam height with time are indicators of foam stability. To test static stability in the presence of oil, heavy oil is injected into the foam/liquid interface. In dynamic tests, foam is pregenerated before flowing at elevated pressures into sandpacks containing various oil saturations. Normalized pressure gradient and apparent viscosity are the indicators of foam stability and effectiveness for improving oil recovery. The extent to which nanoparticles are covered with surfactant governs the foam stability, in both static and dynamic conditions. Static foam is stable in the presence of oil only if the nanoparticles are partially covered by the surfactant. In the dynamic test, foam stabilized with only the surfactant collapses in the porous media when oil is present. Nanoparticles alone could not generate foam regardless of the presence of oil or salinity, but foam stabilized with nanoparticles partially covered by surfactant is stable in the presence of both residual and initial oil, and foam apparent viscosity could reach up to 400 cp at residual heavy oil condition. In both static and dynamic conditions, nanoparticles completely covered with a bilayer of surfactant do not stabilize foam in the presence of oil. Partially covered nanoparticle foam also demonstrated salt tolerance in both static and dynamic tests, and foam apparent viscosity can reach up to 200 cp with high salinity and residual heavy oil presented. Thus, at appropriate surface coverage, the combination of nanoparticles and surfactant is more effective than either stabilizer alone. The result shows that interaction of surfactant and nanoparticles is important in foam stability in the porous media with oil. In particular, this interaction is synergistic at certain coverage. This type of synergy can provide much more robust mobility control for EOR processes involving gas injection.

Various bubble generation methods have been developed to produce microbubbles, but current techniques are inadequate for meeting industrial demands for controlling the size of microbubbles accurately. This study aimed to investigate acoustic bubble generation as a potential solution to the demand. Initially, a capillary tube was exposed to a continuous standing wave to control the bubble generation, which resulted in a relatively large bubble size and number. However, the extent of bubble coalescence was high due to the attractive secondary acoustic radiation force (ARF) between vibrating bubbles. Alternatively, a pulsed wave could reduce attractive ARF, thereby simultaneously reducing bubble coalescence and controlling the bubble generation frequency and size. However, this approach compromised the quantity of bubbles generated. The research contributes to the mass production of microbubbles and the strategic control of bubble size to optimize process efficiency.

In this study, the effects of ten different food-grade particles on bubble quality and stabilization of particle-stabilized food foams in batch and continuous foaming with and without polyglycerol ester (PGE) as an emulsifier were investigated. Particle properties, such as contact angle and porosity, and varying process parameters, such as shear rate and gas fraction, were assessed with respect to their impact on bubble size x50,0, bubble size distribution width and drainage.The smallest bubble size x50,0 in foams without PGE could be achieved with banana powder (88 μm), calcium carbonate (89 μm) and microcrystalline cellulose (79 μm) particles. In comparison, the smallest size in the reference without particles were 105 μm. Combining the use of particles with PGE further reduced bubble size by up to 57% and drainage by up to 100%. Increasing the shear rate from 4922 s−1 (35 μm) to 9844 s−1 (14 μm) resulted in smaller mean bubble sizes and significantly narrower bubble size distributions whereas no distinct correlation between gas fraction and resulting bubble size was found.This study shows that using suitable particles in combination with an optimized foaming process promotes both bubble quality and the stability of foams.

Foamability of aqueous solutions: Role of surfactant type and concentration

The major challenge in enhanced oil recovery (EOR) by gas injection is poor volumetric sweep efficiency, mainly due to the high gas mobility and reservoir heterogeneity. Injecting gas as a foam increases sweep efficiency, but maintaining foam stability within the reservoir remains a challenge. This research evaluates the synergistic interaction of one type of nanoparticle and a surfactant to increase foam stability, using the concentration ratio of the two components to tune the affinity of the nanoparticle for the gas/liquid interface. We test the capability of the synergistic two-component system to stabilize methane foam and compare it with foam stabilized by surfactants only. A key distinction is the foam stability upon contact with oil, and we explain the observations in static and dynamic conditions. Foam stability was measured both in static (foam height) and dynamic (flow through porous media) conditions. In the static test, foam is generated by the shaking method, and foam texture (bubble size and shape) and the decay of foam height with time are indicators of foam stability. To test static stability in presence of oil, heavy oil is injected into the foam-liquid interface. In dynamic test, foam is pre-generated before flowing at elevated pressures into sandpacks containing various oil saturations. Normalized pressure gradient, and apparent viscosity are the indicators of foam stability and effectiveness for improving oil recovery. The extent to which nanoparticles are covered with surfactant governs the foam stability both in static and dynamic conditions. Static foam is stable in the presence of oil only if the nanoparticles are partially covered by the surfactant. In the dynamic test, foam stabilized with the only surfactant collapses in the porous media when oil is present. Nanoparticles alone could not generate foam regardless of the presence of oil, but foam stabilized with nanoparticles partially covered by surfactant is stable in the presence of both residual and initial oil. In both static and dynamic conditions, nanoparticles completely covered with a bilayer of surfactant do not stabilize foam in the presence of oil. Partially covered nanoparticles foam also demonstrated salt tolerance in both static and dynamic test. Thus at appropriate surface coverage, the combination of nanoparticles and surfactant is more effective than either stabilizer alone. The result shows that surfactant and nanoparticles interaction is important in foam stability in the porous media with oil. In particular, this interaction is synergistic at certain coverage. This type of synergy can provide much more robust mobility control for EOR processes involving gas injection.

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

Adsorption accumulation of proteins and dyes in foams of solutions and waste water

The objective of this study is to explore the interrelated mechanisms governing foam drainage and stability by modeling the foam column kinetics, measuring the interfacial properties of the air-water interface and conducting forced drainage experiments. Studies on foams are usually divided into four length scales: (i) a gas-liquid interface (molecular scale), (ii) a liquid film (nanometer scale), (iii) a bubble (millimeter scale), and (iv) a foam (meter scale). Although much progress has been made in each length scale, the correlation between the different length scales remains poorly understood and quantified. The present study seeks to address this problem. In many industrial processes, such as froth flotation and foam fractionation, careful control of the foam or froth stability is required to optimize the process performance. Therefore, an understanding of the correlation between the different length scales is of paramount interest for industrial applications. The present study can be divided into three different parts: (1) foam column kinetics, (2) mechanisms governing foamability and foam stability, and (3) foam drainage in the presence of solid particles. The first part models foam column kinetics to predict the evolution of foam growth, liquid fraction, the transport of liquid and gas in growing foams and foam collapse by analogy with chemical kinetics. First, a modeling framework was formulated to categorize the foam or froth growth models into zeroth, first and second order, according to the dependence of the foam collapse rate on the foam volume or height. Then, a novel kinetic model was developed based on the mass balance of gas and liquid in the foam column to simulate the foam column kinetics. Finally, the simulation results were compared with the reported experimental data. Good agreement between model predictions and published experimental results confirms the validity of the analogy between foam column kinetics and reaction kinetics. Mechanisms governing the foamability and foam stability are crucial to understanding foam behaviors. The foamability and foam stability of surfactant blend and surfactant solutions in different electrolyte concentrations were examined to elucidate the different mechanisms that collectively determine foamability and foam stability. The foam growth kinetic model developed in the previous section was also applied here. First, the foamability of sodium dodecyl sulfate (SDS)-dodecanol (DOH) solutions was investigated to test the conventional theories that apply to a single surfactant of pre-critical micelle concentration (CMC). The remarkable decrease in the foamability of SDS solutions caused by the addition of DOH could not be easily explained by the theories of surface tension and surface viscoelasticity. Instead, alternative mechanisms were proposed. Second, findings regarding the foamability of SDS-DOH solutions were extended to froth flotation, that is, the effect of a nonpolar collector (diesel oil) on the foamability of frother solutions (methyl isobutyl carbinol, MIBC). The results showed that the presence of diesel oil, even in trace amounts (e.g., 2 ppm), could effectively decrease the foam growth rate by accelerating the foam collapse process. Two mechanisms were proposed to explain the antifoam effect of diesel oil: (i) the spreading of the diesel oil droplets at the liquid film interface and (ii) the molecular interactions between the diesel oil and the frother molecules. Finally, the rupture of standing aqueous foams stabilized by SDS-DOH and SDS-NaCl mixtures was examined to obtain different values of the surface viscoelasticity and surface potential to elucidate the roles of surface rheology and intermolecular forces in foam stability. Foam drainage in the presence of solid particles is relevant to the field of froth flotation, where the wash water is commonly applied to the froth layer to improve the product’s grade. Forced drainage experiments were conducted to study the liquid flow within the foam stabilized by hexadecyltrimethylammonium bromide (CTAB) with glass beads. Two foam drainage models for aqueous foams were applied to simulate and interpret the experimental results. The simulation results showed that the presence of solid particles in foams increases the rigidity of the interfaces and the viscous losses in the channels (Plateau borders) of the foams, which consequently resulted in a decrease in the foam permeability. In summary, the present study focuses on modeling foam column kinetics, the effects of interfacial properties on the foamability and foam stability of surfactant solutions, and the effect of solid particles on foam drainage. To further understand the mechanisms governing foamability and foam stability, the interplay and magnitude of these mechanisms on the different stages of foam life should be addressed in future studies.

Effect of reagent interaction on froth stability of coal flotation

Micro-fabricated electrolytic micro-bubblers

One of the major issues in foam application for enhanced oil recovery (EOR) is the foam stability in presence and absence of oil. In this study, a systematic experimental study of the bulk and bubble scale stability of air and CO2 foams stabilised by sodium dodecyl sulphate (SDS) and nanoparticles were conducted. Foam-oil interactions were further study in etched glass micromodel in order to investigate and compare the foam performance at static and dynamic conditions. Influence of nanoparticles hydrophobicity and oil types on foam behaviors were assessed. Static bulk and bubble-scale experiments were conducted with KRÜSS dynamic foam analyser while the flow characteristics experiments were conducted in etched glass porous medium. Results show that the foam half-life increased while the size of generated bubbles decreased with the presence of nanoparticles in the surfactant solution. Successful propagation of nanoparticles-SDS foam through capillary snap-off and lamellae division was observed in presence of oil in the porous medium. Foam stability decreases with decreasing oil viscosity and density. Except for hydrophobic aluminum oxide nanoparticles with contact angle of 118.19°, the static and dynamic stability of the air and CO2 foams increased with increasing nanoparticles hydrophobicity. The addition of nanoparticles into the surfactant solution considerably improved foam stability due to the adsorption and aggregation of the nanoparticles at the thin lamellae and plateau border. This prevents liquid drainage and film thinning by increasing film elasticity and film strength from 23.2 µm to 136µm. It can be concluded from this study, that stable air and CO2 foams can be generated with nanoparticles- surfactant mixed systems in absence and presence of oil with favourable nanoparticles hydrophobicity.

Effect of bulk viscosity and surface tension kinetics on structure of foam generated at the pilot scale

Opposed bubbly jets at different impact angles: Jet structure and bubble properties