Measurements of horizontal three‐phase solid‐liquid‐gas slug flow: Influence of hydrate‐like particles on hydrodynamics

Gas hydrate formation is a main flow assurance concern in oil and gas production. Understanding the effects of the introduction of solid particles in the slug flow is essential to improve the efficiency and safety of multiphase production. The purpose of the present work is the experimental characterization of solid‐liquid‐gas slug flow with the presence of dispersed hydrate‐like particles. Experimental tests were carried out with inert polyethylene particles of 0.5‐mm diameter with density similar to gas hydrates (938 kg/m³). The test section comprised a 26‐mm ID, 9‐m length horizontal duct of transparent Plexiglas. High Speed Imaging and resistivity sensors was used to analyze the slug flow unit cell behavior due to the introduction of the solid particles and to measure the unit cell translational velocity, the slug flow frequency, the bubble and slug lengths, and the phase fractions. Two distinct concentrations of solid particles were tested (6 and 8 g/dm³). © 2018 American Institute of Chemical Engineers AIChE J, 64: 2864–2880, 2018     

水平管段塞流特性及参数研究方法讨论

天然气于当前时代因其具有热值高、储量大而且污染小的能源而被广泛应用于各行业的生产中。油田伴生气是天然气的一项主要来源,为了提高经济性,用单条管道实行油气混输输至下游是一种常见的输送方式,这就有必要对复杂的多相流进行多方面的分析。在混输管路中,段塞流自身具有流动参数不稳定、流动形式复杂、给下游设施危害极大而又广泛存在于各种多相流的管路等不利因素,在设法减小甚至是消除段塞流之前,我们需要对段塞流的形成及流动特点等进行充分研究。当前对于多相流管路中流动的研究大体上以数值模拟和设计实验两方面入手。选取了水平管路中的段塞流流动特性及参数进行两方面的讲述。     

Liquid‐Liquid Stratified Flow through Horizontal Conduits

The stratified configuration is one of the basic and most important distributions during two phase flow through horizontal pipes. A number of studies have been carried out to understand gas‐liquid stratified flows. However, not much is known regarding the simultaneous flow of two immiscible liquids. There is no guarantee that the information available for gas‐liquid cases can be extended to liquid‐liquid flows. Therefore, the present work attempts a detailed investigation of liquid‐liquid stratified flow through horizontal conduits. Gas‐liquid flow exhibits either smooth or wavy stratified orientations, while liquid‐liquid flow exhibits other distinct stratified patterns like three layer flow, oil dispersed in water, and water flow, etc. Due to this, regime maps and transition equations available for predicting the regimes in gas‐liquid flow cannot be extended for liquid‐liquid cases by merely substituting phase physical properties in the equations. Further efforts have been made to estimate the in‐situ liquid holdup from experiments and theory. The analysis considers the pronounced effect of surface tension, and attempts to modify the Taitel‐Dukler model to account for the curved interface observed in these cases. The curved interface model of Brauner has been validated with experimental data from the present work and those reported in literature. It gives a better prediction of liquid holdup in oil‐water flows and reduces to the Taitel‐Dukler model for air‐water systems.     

基于段塞流捕捉的高黏油气两相流模型的建立与验证

随着传统油田的快速消耗,高黏稠油的开发逐渐引起了重视。有关高黏油的气液两相流研究主要集中在国外,国内的相关研究目前还较少。本文针对高黏油气混输管路,建立了一种捕捉段塞流的形成和发展过程,并进行两相流水力计算和液塞长度统计的组合模型。通过气液相间滑移速度和液相连续性方程的求解得到管路中不同时刻和位置的持液率,以持液率的变化反映段塞的形成和发展。建立气液动量守恒方程关联持液率和压力,得到管路中各位置的压力变化。闭合关系式中,通过液塞平移速度、壁面及气液相界面的剪切力关系式加入黏度的影响,最终建立适用于高黏油气两相流的段塞捕捉模型。使用不同来源的数据验证模型计算压降和液塞长度的准确性,数据分别来源于国外研究者的实验数据和大庆油田的现场数据。结果表明,模型具有较高的计算精度,大部分压降误差在±15%以内,大部分液塞长度误差在±20%以内。     

管式段塞流捕集器构造及其优化设计

天然气近年来由于技术的进步及其自身多项优势而被广泛利用,油气混输作为一种经济性良好的运输方式也开始服务于各大油气田。然而多相流的运动很复杂,加上一些其他因素而产生的段塞流则是危害较大,其主要危害体现在各项参数不稳,混输管路下游的处理设备会受到较大冲击,因此需要在混输管路末端设置段塞流捕集器来缓解这种冲击,保证下游的稳定供给。     

水平管内气液段塞流液塞长度发展规律的实验和模拟研究

In petroleum industry, the slug flow is a fre-quently encountered flow regime in multiphase flowpipeline. For pipeline designers, the liquid slug lengthdistribution is important for the proper design ofdownstream facilities, such as slug catcher and sepa-ration system. However, for its transient and unsteadynature, it is a great challenge for engineers to correctlypredict the flow parameters of slug flow, especiallythe maximum liquid slug length. The unit cell model for slug flow in horizontal…     

Ultrasonic Measurement for Two/Three‐Phase Flow Detection

Ultrasonic technique offers a good potential for phase holdup measurements in multiphase systems. Experiments were performed in an expanded fluidized bed consisting of water, air bubbles and/or glass beads. In this research note, the instantaneous signals of ultrasound were, for the first time, analyzed for the purpose of phase holdup determination. The results show that the fluctuations of the speed and attenuation of ultrasound are a well‐defined function of solid and gas holdups in a multiphase system.     

Hydrodynamics in an Internal Loop Airlift Reactor with a Convergence‐Divergence Draft Tube

Gas holdup and liquid circulation of one conventional draft tube and three different convergence‐divergence draft tubes in an internal loop airlift reactor were investigated. Experiments were carried out in two‐phase systems with air‐water and air‐CMC (carboxyl methyl cellulose) solution and three‐phase system with air‐water‐resin particles. The two‐phase drift‐flux model was used to estimate gas holdup for three‐phase Newtonian and two‐phase non‐Newtonian systems. It is shown that gas holdup in convergence‐divergence draft tubes is higher than that in a conventional draft tube and increases with superficial gas velocity. Variation of the structural parameters of convergence‐divergence draft tubes has little effect on gas holdup in the two‐phase and three‐phase system. The mathematical model, which is based on a drift‐flux model, was developed to describe the liquid circulation velocity in the reactor satisfactorily.     

Pressure Drop Models for Gas/Non‐Newtonian Power‐Law Fluids Flow in Horizontal Pipes

Models commonly used in literature are evaluated versus 696 data points to predict the pressure drop of gas/non‐Newtonian power‐law fluids flow in horizontal pipes. Suitable models are recommended. A new correlation is developed by ignoring the pressure drop across the gas slug and adopting the liquid slug holdup of gas/non‐Newtonian fluid flow into the homogeneous model. The theoretical curves can capture the test data trends and the overall agreement of predicted values with experimental data is sufficient to be practically applied in industry.     

Micromechanic modeling and analysis of the flow regimes in horizontal pneumatic conveying

Pneumatic conveying is an important technology for industries to transport bulk materials from one location to another. Different flow regimes have been observed in such transportation processes, but the underlying fundamentals are not clear. This article presents a three‐dimensional (3‐D) numerical study of horizontal pneumatic conveying by a combined approach of discrete element model for particles and computational fluid dynamics for gas. This particle scale, micromechanic approach is verified by comparing the calculated and measured results in terms of particle flow pattern and gas pressure drop. It is shown that flow regimes usually encountered in horizontal pneumatic conveying, including slug flow, stratified flow, dispersed flow and transition flow between slug flow and stratified flow, and the corresponding phase diagram can be reproduced. The forces governing the behavior of particles, such as the particle–particle, particle‐fluid and particle‐wall forces, are then analyzed in detail. It is shown that the roles of these forces vary with flow regimes. A general phase diagram in terms of these forces is proposed to describe the flow regimes in horizontal pneumatic conveying. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

水平管气液两相段塞流的波动特性

气液两相段塞流是液塞和长气泡在空间和时间上的交替,在流动过程中表现出间歇性和不稳定性。系统地研究了水平管中段塞流持液率、压力和压差的波动特性。结果表明,段塞流持液率的概率密度分布为双峰分布,高持液率峰对应于液塞区,低持液率峰对应于液膜区;在压力的概率密度分布中,当压力测试点到管道出口之间的段塞单元数目少时,压力分布出现双峰分布;当压力测试点到管道出口之间的段塞单元数目多时,压力分布出现单峰分布;压差信号分布呈单峰分布。这些特征为流型识别提供了可靠的段塞流标识。     

Studies on Liquid—Gas and Three‐Phase Fluidized Beds with Pulsating Air Flows

The effects of air‐flow pulsation and water and air flowrates on the hydrodynamics of liquid—gas and three‐phase fluidized beds containing 3‐mm glass beads have been studied in a 90‐mm i.d. column. Under steady‐flow conditions, both types of bed contained a relatively large number of small bubbles. With a pulsing air flow, however, a smaller number of much larger bubbles or slugs were formed. This was attributed to different mechanisms of bubble formation at the distributor. Variations in phase holdup were explained in terms of the effects of the operating parameters on the bubble characteristics.     

水平管段塞流持液率的波动特性

气液两相段塞流是液塞和长气泡在空间和时间上的交替,在流动过程中表现出间歇性和不稳定性.今对水平管中段塞流持液率的波动特性进行了分析.结果表明:在同一折算液速下,随着折算气速的增加,段塞单元的平均持液率和液膜持液率先快速下降再缓慢下降,而液塞持液率先缓慢下降再快速下降.段塞流持液率的概率密度分布为双峰分布,高持液率峰对应于液塞区,低持液率峰对应于液膜区;概率密度函数中较完好的峰所对应的持液率与光滑分层液膜区和液塞区的平均持液率相一致.     

Horizontal air–water flow in a square cross‐section channel: Pseudo‐slug flow regime

New experimental data for air–water flow in a horizontal square cross‐section channel (H = 24.25 mm) is presented, including data on liquid hold‐up, gas and liquid velocities, and wave velocities and frequencies. For the majority of gas and liquid flow rates studied, the regime observed was pseudo‐slug. Using visualization studies it was possible to identify wavy‐stratified and pseudo‐slug flows. For the pseudo‐slug regime new correlations were obtained for liquid hold‐up, for gas and liquid velocities as a function of the ratio between gas and liquid mass flow rates, and for the frequency of roll‐waves as a function of gas and liquid mass flow rates.     

垂直上升管内有水平柱体时气液两相局部流型转变的研究

1 INTRODUCTION Gas-liquid two-phase cross flow and heat transfer exists in oil production and chemical facilities. With the rapid development of the technology of modern industry, the gas-liquid two-phase flow across a rod and heat transfer characteristics are studied more ex- tensively, and its thorough understanding is of great importance to the design and operation of processing equipment. Flow pattern and its transition are important in the study of multiphase flow. Because of the com…     

The effect of gas injection on the flow of immiscible liquids in horizontal pipes

The flow of two immiscible liquids and the influence of an additional inserted gas phase in horizontal pipes is investigated. The experiments are carried out in a transparent horizontal pipe with an inner diameter of 59 mm and a total length of 48 m. Experimental results are presented for the flow regimes of the two phase and three phase flow of oil, water and gas mixtures. The effect of phase inversion on the pressure drop is measured. The experimental results obtained for the three phase flow of oil, water and air indicate that drag reduction is possible by injecting gas in laminar flowing mixtures of oil and water. In the aerated slug flow regime of oil, water and air a water dominated and an oil dominated flow system can be distinguished. The pressure drop of the three phase flow system is of the magnitude as the pressure drop of the two phase flow of gas and the dominating liquid phase.     

Ultrasonic Technique For Measuring Phase Holdups In Multiphase Systems

An ultrasonic technique is being developed to detect the dispersed phase holdups in multiphase systems. This technique is based on the fact that the transmission time and attenuation of ultrasound in suspensions differ from those in pure liquids. Experiments were carried out at three probe gap spacing, (2.04, 4.27, and 6.31 cm) in a fluidized bed of 7.6 cm diameter. Water was used as the continuous phase and air and 500 μm glass beads as the dispersed phases. The time-averaged amplitude ratio decays exponentially with gas and solid holdups, whereas the transmission time increases slightly with gas holdup but decreases with solid holdup. It is also observed, for the first time, that the fluctuations of the instantaneous ultrasonic signals can be correlated with the solid and gas holdups in a multiphase system. This correlation may provide a basis for the development of a new approach for phase holdup analysis in multiphase flow systems.     

天然气水合物的生成对浆液流动稳定性影响综述

目前在海底混输管道的水合物风险控制策略中,允许水合物在管道内的生成,以液固浆液流动的形式对海底油气产物进行输送。其中主要通过控制浆液中水合物的生成量和聚集程度,来实现对海底集输管线的流动安全保障。液固浆液流动具有相当复杂的流动特性,固相颗粒的引入对于流体的流动特性影响很大。本文分别综述了拟单相流动体系和气液多相流动体系中水合物颗粒对于管输体系流动稳定性的影响以及水合物对混输管道堵管特性的影响。着重讨论了水合物在管道壁面的生长和沉积特性、水合物与气液流型的耦合关系以及不同体系中水合物的堵管机理。此外,对软件模拟在水合物生成及浆液流动特性研究中的应用做了简单介绍。最后,根据对相关研究结果的总结,指出水合物在壁面生长沉积的微观特性和定量表述、颗粒不同分散形式的临界流速、不同气液流型条件下的水合物生成特性和颗粒行为等是今后水合物相关研究中需要进一步深入探究和明确的问题。     

Slug flow of air—water mixtures in a horizontal pipe: Determination of liquid holdup by γ-ray absorption

Two-phase pressure gradients and time-averaged values of liquid holdup have been measured for the co-current flow of air and water in a 42 mm bore horizontal pipeline. The majority of the data corresponded to the slug flow region, where rapid fluctuations in both wall pressure and holdup were observed. Instantaneous values of liquid holdup were also recorded by rapid scanning of a vertical cross-section of the pipe using the γ-ray absorption method, which enabled probability density functions (PDF) and power spectral densities (PSD) of holdup to be determined. From these functions, values of average film and slug holdups, average slug length and average slug frequency were estimated. These measurements facilitated the use of the Hubbard—Dukler slug flow model for two-phase pressure drop prediction which compared favourably with the Lockhart—Martinelli correlation over the X-parameter range 2–30.     

锥形鼓泡床内气含率特性的研究

本文分析了锥形鼓泡床内流型过渡、平均气含率及气含率轴向分布特性，考察了入口气体速度、静止液体（或淤浆）高度及淤浆浓度的影响，比较了与圆柱床的差异，结果表明对于鼓泡床内气体体积收缩的反应，用锥形床的冷态试验可以较精确地模拟其实际结果。