Slug Flow Conditions Research Articles

A novel synergistic intensification method for CO2 absorption by metal salt and task-specific ionic liquids hybrid solvent in microchannel reactor

A novel metal salt-promoting mass transfer intensification method for CO2 absorption into task-specific ionic liquids aqueous solution was proposed. The mass transfer intensification and intrinsic mechanisms of different concentrations of metal salts (NaBF4, KBF4, KCl, and CuCl2) with task-specific ionic liquids (1-aminopropyl-3-methylimidazolium tetrafluoroborate [Apmim] [BF4]) aqueous solutions for CO2 capture process were visually investigated using a microchannel reactor. The results showed that adding metal salts could remarkably enhance the interaction between metal cations and ionic liquid anions, thereby decreasing the interaction between anions and cations within the ionic liquid molecules and promoting the chemical reaction between ionic liquid cations and CO2. Under the condition of the same salt concentration, the addition of KBF4 has more obvious enhancement for mass transfer in CO2 absorption process. The mass transfer coefficient increases as the gas-liquid phase flow rate rise under slug flow condition. In addition, based on the effects of metal salt concentration, absorbent density, and gas-liquid phase flow rate on the CO2 volumetric mass transfer coefficient kLa, a new correlation for predicting the volumetric mass transfer coefficient of CO2 absorption into the hybrid solvent in microchannel reactor was proposed and validated.

Study of multiphase pump front homogenizer on the performance of fluctuating gas-liquid two-phase incoming flow reforming

As an important component of multiphase mixing technology in oilfield, the homogenizer plays the role of buffering the fluctuation of gas rate of incoming flow and gas-liquid homogenization, providing good inlet conditions for multiphase pumps. In this paper, the homogenizer designed and manufactured by ourselves is connected into the multiphase pump loop for experiment. The results show that the designed homogenizer can effectively improve the homogeneity of gas and liquid phases at the inlet of the multiphase pump, which in turn improves the pressurization capacity of the multiphase pump. The gas flow is buffered under slug flow condition, and the effective running time of multiphase pump is extended. The unsteady numerical simulation of the flow field in the homogenizer is carried out for three kinds of slug flow conditions. The results show that the homogenizer suppresses the fluctuation of gas content rate for the three blockage conditions. The gas content fluctuations of the outlet fluid were reduced by 71.3%, 64.7%, and 69.4%, respectively, compared with the incoming flow. In the homogenizer, the liquid phase entering the perforated pipe produced a significant jet phenomenon, which significantly enhanced the mixing with the gas phase. In the horizontal tube near the outlet, the gas phase floats due to gravity. The guide vane at the outlet effectively suppressed the gas-liquid stratification phenomenon that occurs here, which further improves the gas-liquid mixing at the outlet.

Study on transient flow behaviors in a three-stage helico-axial multiphase pump under slug flow condition from wellhead

Oilfield recovery often has extreme flow patterns of slug flow, and its gas volume fraction (GVF) still fluctuates strongly after being buffered by a homogenizer. After entering the multiphase pump, it causes transient fluctuations in pump performance, which challenges the stable operation of the multiphase pump. This paper simulates the flow field in a three-stage multiphase pump using the Euler–Euler two-fluid model and the shear stress transport k-omega (SST k−ω) turbulence model with the buffered slug flow as the boundary conditions. The results show that the differential pressure and torque of each impeller vary with the fluctuation of the inlet gas volume fraction (IGVF) and the maximum fluctuation rate reaches 36.48% and 32.97%, respectively; the maximum fluctuation rate of axial force and radial force is 1.02% and 51.18%, respectively, and the buffered slug flow has limited effect on the axial force. The main factor of pressure pulsation is the fluctuation of GVF flow and the interaction of static and dynamic. The main frequency in the impeller is the fluctuation frequency of the GVF or the diffuser blade frequency. The main frequency in the diffuser is the impeller blade frequency and its double frequency. The fluctuation frequency of the GVF is the secondary frequency, and the amplitude is relatively stable.

Influence of pressure disturbance wave on dynamic response characteristics of liquid film seal for multiphase pump

Slug flow or high GVF (Gas Volume Fraction) conditions can cause pressure disturbance waves and alternating loads at the boundary of mechanical seals for multiphase pumps, endangering the safety of multiphase pump units. The mechanical seal model is simplified by using periodic boundary conditions and numerical calculations are carried out based on the Zwart-Gerber-Belamri cavitation model. UDF (User Define Function) programs such as structural dynamics equations, alternating load equations, and pressure disturbance equations are embedded in numerical calculations, and the dynamic response characteristics of mechanical seal are studied using layered dynamic mesh technology. The results show that when the pressure disturbance occurs at the inlet, as the amplitude and period of the disturbance increase, the film thickness gradually decreases. And the fundamental reason for the hysteresis of the film thickness change is that the pressure in the high-pressure area cannot be restored in a timely manner. The maximum value of leakage and the minimum value of axial velocity are independent of the disturbance period and determined by the disturbance amplitude. The mutual interference between enhanced waves does not have a significant impact on the film thickness, while the front wave in the attenuated wave has a promoting effect on the subsequent film thickness changes, and the fluctuation of the liquid film cavitation rate and axial velocity under the attenuated wave condition deviates from the initial values. Compared with pressure disturbance conditions, alternating load conditions have a more significant impact on film thickness and leakage. During actual operation, it is necessary to avoid alternating load conditions in multiphase pump mechanical seals.

Continuous catalytic aerobic oxidation of o‑chlorotoluene to o-chlorobenzoic acid under slug flow conditions

Continuous catalytic aerobic oxidation of o‑chlorotoluene to o-chlorobenzoic acid under slug flow conditions

An experimental investigation of the stochastic nature of slug flow

Slug flow is widely encountered in oil and gas systems. It has an unsteady hydrodynamic behavior that motivated the development of mechanistic models to better understand and quantify the parameters of the flow. The present work investigated several slug flow conditions through an experimental campaign that was performed in a 2-in ID horizontal pipe facility. The experimental data were statistically analyzed and they indicated the suitability of a lognormal distribution to model the flow characteristics, such as slug length, film length, and frequency. Based on the mean results, slug and film lengths tend to increase as more gas is present in the flow. The mean frequency indicated that higher frequencies are obtained with lower gas fractions. All the slugs from each test were individually studied using different approaches to analyze the data. The results suggest the existence of a relationship between the slug and film lengths when the slug unit is identified starting from a film region followed by a slug region. The values of the coefficient of determination for the relation between slug length and film length indicate a possible influence of other flow parameters of stochastic nature, such as slug liquid holdup, that could affect the behavior of the slugs.

Void fraction measurement and calculation model of vertical upward co-current air–water slug flow

The focus of this paper is on the measurement and calculation model of void fraction for the vertical upward co-current air–water slug flow in a circular tube of 15 mm inner diameter. High-speed photography and optical probes were utilized, with water superficial velocity ranging from 0.089 to 0.65 m·s −1 and gas superficial velocity ranging from 0.049 to 0.65 m·s −1 . A new void fraction model based on the local parameters was proposed, disposing the slug flow as a combination of Taylor bubbles and liquid slugs. In the Taylor bubble region, correction factors of liquid film thickness C δ and nose shape C Z* were proposed to calculate α TB . In the liquid slug region, the radial void fraction distribution profiles were obtained to calculate α LS , by employing the image processing technique based on supervised machine learning. Results showed that the void fraction proportion in Taylor bubbles occupied crucial contribution to the overall void fraction. Multiple types of void fraction predictive correlations were assessed using the present data. The performance of the Schmidt model was optimal, while some models for slug flow performed not outstanding. Additionally, a predictive correlation was correlated between the central local void fraction and the cross-sectional averaged void fraction, as a straightforward form of the void fraction calculation model. The predictive correlation showed a good agreement with the present experimental data, as well as the data of Olerni et al. , indicating that the new model was effective and applicable under the slug flow conditions.

OPTIMIZATION OF RISERBASE GAS INJECTION FOR SLUG FLOW ATTENUATION

A new approach for the optimization of riserbase gas injection for slug flow attenuation has been proposed. Riserbase gas injection is an established method for slug flow mitigation, however it can be expensive due to the high volume of gas required and the cost of compression. In this study, optimum gas volumes required to stabilise a range of unstable slug flow conditions were obtained using bifurcation maps. The results showed that at the bifurcation point, minimum gas injection volume is required to achieve flow stability. This study established that the optimum gas volume required is dependent on the type of slug flow. For a very high frequency slug flow at high flow rate more volume of gas up to 100kg/s is required to achieve stability while slug flow at moderate flow rate could need up to 30kg/s and slug at low flow rate required about 6 kg/s to achieve stability. The developed approach in this work can help reduce the overall cost of gas injection for slug flow mitigation. Keywords: Slug attenuation; Bifurcation; Gas injection; slug flow; multiphase flow.

Investigation on the performance of a helico-axial multiphase pump under slug flow

The helico-axial multiphase pump is often used for gas-liquid mixture transportation in offshore oilfields, and slug flow is the main reason for the unstable operation of the pump. Aimed for slug flow condition, a self-designed three-stage multiphase pump is set to the object to perform unsteady simulations and fluid-structure interaction calculations, and the inlet gas void fraction (IGVF) is set from 20% to 80%. The results show that affected by the flow from the slug, the gas-liquid two-phase flow pattern in the multiphase pump changes sharply, resulting in severe fluctuations in the differential pressure, spindle torque and deformation of the multiphase pump. The gas-phase enters the first-impeller along the suction blade surface when affected by Taylor bubbles, while the second and third-stage impellers gas-phases are in the form of small air masses flow into the impeller along the pressure blade surface. The deformation trend of impeller torque, differential pressure and the main pump spindle is similar to that of trigonometric function, while the fluctuation of torque is more intense, and the shape variable of spindle increases with the inflow of liquid plug, and the maximum deformation amount increases by 10.9% at high GVF relative to IGVF.

A novel comprehensive model for predicting production of downhole choke wells

The mass-flow rate that flows through wellhead/downhole chokes is typically used to measure oil/gas production. Published mass-flow rate prediction models are proposed based on wellhead choke data; however, because of the different flow behavior between vertical and horizontal tubes, unacceptable errors may occur when used on downhole choke wells. These models can be improved by three additional factors; flow patterns, gravity, and gas expansion coefficient. In this study, 180 pressure, mass-flow rate, and flow pattern data points were measured with four different size chokes on a vertical tube. According to the flow behavior analysis, a new comprehensive model was proposed to improve the accuracy of multiphase mass-flow rate prediction for downhole chokes. The experimental results show that the downhole choke redistributes the gas and liquid phase, causing the flow patterns downstream of the choke to change. Additionally, pressure data analysis results show that the pressure difference between the Pu (pressure upstream of the chokes) and Pd (pressure downstream of the chokes) can be used to identify the flow pattern transitions upstream of the chokes. The statistical error results of the new model coupled with various slip models reveal that the Simpson (RMSE = 0.0018 Kg/s, R2 = 0.99) and Schuller (RMSE = 0.002 Kg/s, R2 = 0.97) models achieve the highest accuracy prediction for the intermittent and continuous flow, respectively. Furthermore, the critical pressure ratio measured on a vertical tube can be accurately predicted by the new comprehensive model. Compared to other models, the new comprehensive model is the most accurate, yielding the best mass-flow rate predictions for the dataset; slug (RMSE = 0.0018 Kg/s and R2 = 0.98), churn (RMSE = 0.0018 Kg/s and R2 = 0.99), and annular flow conditions (RMSE = 0.002 Kg/s and R2 = 0.97).

Numerical and Orthogonal Study on Optimization Analysis of Structure Parameters of Bubble Breaker for Electrical Submersible Pump System

Abstract Under slug flow conditions, electrical submersible pumps (ESPs) show a low efficiency due to Taylor bubbles, which cause pressure surging and gas pockets and the further deterioration of pressure boosting ability. In this study, a novel downhole bubble breaker is designed for mitigating the impact in ESP under slug flow conditions. The computational fluid dynamics-population balance model (CFD-PBM) coupled approach was used to calculate the bubble breaker's average bubble diameter to evaluate its efficiency. Meanwhile, experimental studies were conducted and compared with numerical results. Also, matlab and DIP-image technology was used to calculate the bubble diameter. Compared with experimental results, the simulation results agree well. Furthermore, the novel bubble breaker's performance was studied by orthogonal approach. The best result of range analysis is A2B3C4D1E4 (α = 30 deg, L = 300 mm, R = 2:1, vsg = 0.2 m/s, and vsl = 0.08 m/s), and sensitively analysis results present that the range of impact intensity are A (inlet angle) > E (superficial gas velocity) > B (total length) > D (superficial liquid velocity) > C (ratio of the gas–liquid channel). The optimal structure's bubble diameters are all less than that of the original structure, with a superficial gas velocity range of 0.2–0.6 m/s. The downstream bubble diameter of the optimal bubble is about 31.6% lower than the original structure at the maximum value point.

Effect of SDS surfactant on gas-liquid flow and slug characteristics in slightly upward pipeline

A new pigging approach with SDS (Sodium dodecyl sulfate) surfactant was proposed for foam drainage in the gathering pipelines with wet gas production, especially for the pipeline section with a great pigging risk. For this purpose, the loop of gas-liquid two-phase flow with a 3 ° slightly upward pipeline was designed. The flow pattern characteristics of gas-liquid two-phase flow were collected by a high-speed camera, and the flow patterns with typical morphological structure were classified. Ultrasonic Doppler velocimeter and ultrasonic transducer were used to measure the velocity signal of the liquid phase near the pipe, and the slug frequency was calculated accurately according to the change of velocity profile data. The slug length was measured by the signal collected by pressure and differential pressure transmitter. The results show that with the addition of SDS surfactant, the flow pattern of gas-liquid two-phase flow is obviously improved, and the working condition of slug flow is suppressed. Besides, in the specific slug flow condition, the slug frequency decreases significantly and the slug length increases. It indicates that the addition of SDS surfactant is favorable to liquid discharge, and provide a reference value for the application of SDS surfactant in foam drainage in wet-gas gathering pipelines.

Non-equilibrium solvent extraction in milliflow reactors: Precious and base metal separations with undiluted ionic liquids

Milliflow devices operating under slug flow (Taylor-flow) conditions provide an efficient mass transfer, a highly uniform droplet morphology and a narrow residence time distribution i.e. characteristics which are excellent for the performance of reactions under kinetic control. Milliflow devices have also been proposed in combination with ionic liquids, due to their ability to intensify the solvent use of these rather expensive and viscous liquids. In present research, the solvent extraction separation of a mixture of Au(III), Pd(II), Cu(II) and Fe(III) was studied using the chloride and bromide forms of the undiluted quaternary ammonium ionic liquid Aliquat 336 in a slug flow reactor channel with an internal diameter of 1.0 mm. The extraction of Au(III) and Pd(II) was found to be faster than that of Cu(II) and Fe(III), allowing the precious/base metal separation to be improved by modification of the contact time between both phases. An apparent correlation between the observed extraction rates and the equilibrium distribution ratio D was found. The most significant separation improvement was achieved at those conditions where the equilibrium separation was best i.e. low halide and metal concentrations and low organic-to-aqueous flow rate ratios. At a residence time of 25 s, quantitative Au(III) and Pd(II) recovery was achieved and decontamination factors increased by a factor up to 2, which corresponds to an increase in product purity of up to 14%. Upon substituting the chloride system for a bromide extraction medium, similar observations were made, except for a reversed Cu(II)/Fe(III) selectivity. Experiments were also conducted on the separation of Pt(IV), Pd(II) and Rh(III), where a reduced Rh(III) extraction rate was observed, allowing to suppress its co-extraction by up to 20%. A hydrodynamic analysis of the obtained flow regime of the ionic liquids revealed a stable and uniform slug flow characterized by a decreasing plug length and width with increasing flow rates. A comparison of the applied and observed phase ratio revealed a stagnant ionic liquid excess (i.e. hold-up) inside the reactor of up to 40% which effectively reduced the reactor diameter and consequently plug residence time.

Effect of Sand Fines Concentration on the Erosion-Corrosion Mechanism of Carbon Steel 90° Elbow Pipe in Slug Flow.

Erosion-corrosion of elbow configurations has recently been a momentous concern in hydrocarbon processing and transportation industries. The carbon steel 90° elbows are susceptible to the erosion-corrosion during the multiphase flow, peculiarly for erosive slug flows. This paper studies the erosion-corrosion performance of 90° elbows at slug flow conditions for impact with 2, 5, and 10 wt.% sand fines concentrations on AISI 1018 carbon steel exploiting quantitative and qualitative analyses. The worn surface analyses were effectuated by using laser confocal and scanning electron microscopy. The experiment was conducted under air and water slug flow containing sand fines of 50 µm average size circulated in the closed flow loop. The results manifest that with the increase of concentration level, the erosion-corrosion magnitude increases remarkably. Sand fines instigate the development of perforation sites in the form of circular, elongated, and coalescence pits at the elbow downstream and the corrosion attack is much more obvious with the increase of sand fines concentration. Another congruent finding is that cutting and pitting corrosion as the primitive causes of material degradation, the 10 wt.% sand fines concentration in carrier phase increases the erosion-corrosion rate of carbon steel up to 93% relative to the 2 wt.% sand fines concentration in slug flow.

Two-phase flow regime identification based on the liquid-phase velocity information and machine learning

Two-phase flow regime identification in a horizontal pipe was realized based on the liquid phase velocity information and the machine learning method. Ultrasound Doppler velocimetry was employed to measure the liquid velocity. Statistical features extracted from the velocity time series data, such as mean, root mean square, and power spectral density, were used to realize real-time flow regime identification. In addition, two novel parameters—maximum velocity ratio and maximum velocity difference ratio—were proposed to identify plug and decaying slug flow. Different classification algorithms were employed to achieve a high identification accuracy. Moreover, transient flow regime identification with a fast response was realized based on two classification algorithms—long–short term memory and convolutional neural network. The results show that the accuracy of real-time flow regime identification based on a flow regime map can reach up to 93.1% using support vector machine, the maximum velocity ratio and maximum velocity difference ratio are effective in identifying plug and decaying slug flow, and transient flow regime identification under slug flow condition can be realized with an accuracy of 94% based on a convolutional neural network (CNN). Decaying slugs with long lengths confuse the CNN and are responsible for the error in identification. The results presented herein are expected to expand the available knowledge on two-phase flow regime identification.

The extension of the one‐dimensional two‐fluid slug capturing method to simulate slug flow in vertical pipes

AbstractWhile many studies have been conducted on the application of the one‐dimensional (1D) two‐fluid model in horizontal and nearly horizontal pipes under slug flow condition, very few works have been carried out on the mechanistic simulation of the slug flow regime in vertical pipe configurations.This article presents the extension of a novel numerical scheme for slug capturing in pipes in vertical slug flows. The original numerical scheme includes an 1D transient, hyperbolic five‐equation two‐fluid model, and it has been embodied in a computer code called 5ESCARGOTS (5 Equations for Slug Capturing Analysis by a Roe solver in Gas and Oil Transient Simulation).This article demonstrates that the model is able to properly automatically capture and simulate the slug generation even in vertical flow. It shows that when appropriate closure relations are used for interfacial shear forces, the model is able to properly characterize the vertical slug flow.Numerous simulations have been carried out for different pipe configurations and flow conditions leading to slug flow. First, a qualitative discussion of the numerical results is proposed underlining that the model is able to properly simulate the evolution of the slug flow in vertical pipes. Experimental flow pattern maps have also been numerically computed and it has been demonstrated that the model correctly simulates slug conditions. Moreover, slug frequency, velocity, and average liquid holdup, computed numerically, have been compared with experimental data in order to quantitatively validate the model. It is shown that the numerical results agree fairly well with the experimental data. A sensitivity analysis on the mesh size and on the inlet boundary conditions has also been carried out.

Investigation of the Effect of Fluids Superficial Velocity on Initiation and Development of Slug Flow in a Horizontal Hydraulics Pipe

The aim of this study is to investigate the effect of fluids superficial velocity on the characteristics of two-phase slug flow in a horizontal hydraulics pipe covering slug flow initiation and development. Air and water were employed as the working fluids. Slug flow characteristics were visually observed at 25D and 200D in a 19 mm internal diameter of acrylic pipe for the initiation and fully developed slug flow conditions, respectively. Flow visualization was taken using high speed video cameras at 400 fps and then analyzed using image processing method. Based on the flow pattern characteristics, several slug flow initiation mechanisms were obtained. Under the investigated conditions, at low to medium air superficial velocity (JG) with low to high water superficial velocity (JL), slug flow initiation mechanisms consisted of wave growth, hydraulic jump, blockage, and slug decaying. While wave initiation, wave formation, disturbance, wave coalescence, and incompletely developed slug mechanisms were observed at medium to high JG with low to high JL. After slug flow was fully developed, it was found that the higher the water superficial velocity resulted in lower void fraction and higher slug frequency. In the meantime, pressure drop and liquid slug velocity increased considerably with the increase of both JG and JL. Maximum pressure drop of 8.35 kPa/m occurred at JL of 2.00 m/s and JG of 3.76 m/s. The highest slug frequency of 6.67 1/s was observed at JL of 2.00 m/s and JG of 2.12 m/s. This information is important for designing fluid flow in horizontal hydraulics pipes and for consideration in predicting the development of the slug flow in order to avoid the negative impact of slug flow in industrial applications.

Experiment and numerical simulation of sand particle erosion under slug flow condition in a horizontal pipe bend

Sand erosion is a common problem in oil and gas field development. An experimental facility was designed and used to study the sand erosion of pipe bend under slug flow. A detachable test pipe bend was designed to measure the weight loss at 36 discrete locations on the pipe bend before and after each experiment. A Computational Fluid Dynamics (CFD) based erosion prediction method was developed to get a further understanding of the erosion. The relationships among the gas and liquid distribution, the sand movement and the erosion profile were analyzed to explain the erosion mechanism. The most severe erosion area of the pipe bend occurs at the axial angle of the elbow between 67.5° and 90° and at the circumferential angle of the elbow between 45° and 90°. The erosion profiles of the pipe wall are dominated by three particle collision mechanisms, namely, micro-cutting, plowing and impact deformation.

An Experimental Study on the Erosion-Corrosion Performance of AISI 1018 Carbon Steel and AISI 304L Stainless Steel 90-Degree Elbow Pipe

Erosion-corrosion is an unavoidable material degradation process in flow pipelines transporting abrasive particles with carrier fluids. In this study, the multiphase flow loop apparatus is employed to assess the erosion-corrosion behavior and mechanism relative to AISI 1018 carbon steel (CS) and AISI 304L stainless steel (SS) 90° long radius elbows with the inner diameter of 50.8 mm. Fine silica sand of 50 µm average size was used as a dispersed phase and erosion-corrosion tests were conducted for slug flow conditions. The erosion-corrosion analysis of 90° elbows was determined from its surface morphologies before and after the experiment using confocal and scanning electron microscopy (SEM). The direct mass loss was measured to quantify the erosion-corrosion rate of the elbow configurations. Additionally, multilayer paint modeling experiments were performed to relate qualitative inferences on erosion distribution and location with the erosion-corrosion mechanism. It was observed that the erosion or corrosion pitting mechanism prevailed on the 1018 CS elbow surface, and the 304L SS displayed excellent erosion-corrosion resistance properties. Moreover, the erosion-corrosion rate was found to be 4.12 times more in the 1018 CS compared to the 304L SS with the maximum particle impaction identified at the exit of the horizontal-horizontal (H-H) 90° elbow for slug flow.

INFLUENCE OF SLUG FLOW ON LOCAL CORROSION OF PIPELINES

The influence of slug flow on local corrosion of pipeline was studied, and the protection measures for slug flow corrosion were well done to improve the safety of oil-gas-water-humidity mixed pipeline. An indoor loop test was designed to simulate the slug flow in real undulating pipelines. The surface microstructures of X70 hanging pieces were studied by scanning electron microscopy (SEM) under slug flow conditions at different test stages. At the beginning of the test, there was much pitting corrosion on the surface of the hanging pieces, but at the end of the test, only some pitting or pitting spots developed into serious local corrosion. The flow corrosion of slug in pipe had obvious characteristics of cavitation corrosion. Its occurrence was the result of synergistic action of various mechanisms. The strong impact force, high impact velocity and mechanical action of multi-frequency micro-jet produced by cavitation annihilation significantly affected the development process and characteristics of electrochemical corrosion, which resulted in that the cavitation corrosion was mostly pitting corrosion. The damage of corrosion product film caused by high-speed micro-jet impact caused by cavitation cracking was local, and the pitting tendency increased at the local damage of corrosion product film. However, with the formation of electrochemical corrosion products, the destroyed corrosion product film was repaired continuously, but did not develop into local corrosion. Local corrosion occurred only when the high-speed micro-jet with cavitation breakdown repeatedly impacted a point of pitting tendency, but this probability was smaller than that of pitting tendency.