基于相场法模拟液滴在电场作用下的聚结特性

随着三元复合驱试验区的逐步扩大,联合站电脱水设备垮电场的问题日益凸显。为研究竖挂电极电脱水器中水滴的动力学行为及其影响因素,采用相场法模拟电场作用下分散液滴的变形和聚结过程,分析了电场强度、液滴距离、液滴直径和连续相粘度对液滴运动特性的影响。利用自制电脱装置和现场采出液开展了实验研究,实验结果与模拟结果相吻合。模拟研究结果表明,在竖挂电极中,随着电压的增大,聚结时间越短,但是存在最佳电场范围,当电场强度高于3000V/cm时,会发生电分散的现象。随着液滴直径变大,液滴聚结时间变短;随着液滴间距的变小,液滴聚结时间变短,但液滴开始作用的间距不能简单地用几倍直径来表示。实验研究结果表明电场强度越大脱水效果越好,作用时间越长脱水效果越好,所得结论可为现场电脱水器参数的选取提供参考。     

高频高压脉冲电场作用下水链形成与消散行为的实验研究

为深入探究原油乳状液静电聚结破乳过程中水链形成、消散行为机理,对高频高压脉冲电场作用下水链形成与消散行为进行显微实验研究,得到乳状液中水链形成与消散的方式。实验条件下,水链的形成方式有两种:单液滴在高电场强度下,由于较大的极化力引发的水滴中段扯裂成链,水链长度大于1000μm;液滴群在高频高压脉冲电场中发生接触时,液滴界面膜发生静电击穿引发聚结成链,链长为268μm。水链消散的方式也有两种:水链自身水滴在电场作用下发生极化,当液滴间的静电应力大于液滴表面张力时即发生聚并消散,链长51μm、平均粒径8.8μm的水链聚并消散为一个粒径16μm的液滴,而链长204μm、平均粒径20μm的水链聚并成链长68μm、平均粒径33μm的水链;外界液滴与水链端部液滴接触时,液滴和水链的部分电荷发生中和,电荷分布发生变化,水滴在电场极化力作用下发生聚并,粒径26μm的外界液滴与链长37μm、平均粒径9.3μm的小水链聚并成一个粒径30μm的大液滴,而粒径35μm的外界液滴与链长259μm、平均粒径39μm的水链聚并成链长210μm、平均粒径50μm的水链。     

高压高频动态脉冲电场参数对水滴聚并速率的影响

在室内动态实验研究基础上,全面考察高压高频脉冲电场的场强、频率、占空比对静电聚结器出口水滴粒度分布、中位粒径以及静电聚结器平均功率的影响规律,归纳了水滴聚并速率模型。研究结果表明,在乳状液初始分布一定的情况下,一定范围内增大电场强度、电场频率和脉宽比,有助于提升水滴的静电聚并速率。电场强度超过1.87k V?cm-1后发生电分散,聚并速率降低。连续相的黏度越小,水滴在迁移聚并过程中的阻力越小,聚并速率越大。脱水电流随各电场参数的增加而增大,电流过大时,部分电场能经水链发生泄漏,水滴聚并速率有所降低。所得到的水滴聚并速率表达式反映了高压高频脉冲电场参数对水滴聚并规律的影响,为脉冲静电聚结破乳机理的深入研究奠定基础。     

电场参数对高频脉冲水滴电聚结行为的影响

文章在高频高压脉冲电场条件下,研究了电场强度、电场频率、占空比等电场参数对水滴靠近过程中的变形及运动特性的影响。结果表明:在水滴靠近过程中,自开始施加电场到聚并时比为0.8时,平均变形度和靠近速率变化甚微,在此之后水滴由于偶极作用力和偶极极化变形效应的增强而发生大幅度变形和加速靠近,直至开始聚并。当E=1.071—1.813 kV/cm,f=2—6 kHz,n=12.8%—87.5%时,随电场参数的增大,水滴靠近时间呈现不同趋势的缩短,平均变形度明显加剧,靠近速率小幅增大,且后两者具有相近的变化规律,说明水滴间的极化力和本身的变形性具有一致性。本研究为高频脉冲电场下水滴电聚结和新型动态电聚结设备的优化提供理论基础。     

高频/高压静电聚结破乳评价方法及电场频率选择研究

为满足当前所处理原油劣质化的新挑战,实现设备紧凑高效、运行节能降耗等发展目标,采用高频/高压电场进行W/O型乳化液静电聚结破乳脱水已经成为国内外的研究热点。采用自主研制开发的全数字控制高频/高压脉冲方波交流电源,基于矩形流道连续流动实验装置,采用Turbiscan Lab分散稳定性分析仪评估静电聚结破乳特性,并系统研究了电场频率和乳化液含水率对分散相水液滴聚结长大的影响。研究结果表明,W/O型模拟乳化液含水率5%时,施加电压为5.4 kV、频率为1.1 kHz的电场,分散相水液滴的平均体积粒径增大39.75倍,稳定动力学参数增加3.12倍,破乳效果非常明显;W/O型模拟乳化液的含水率不同,分散相水液滴取得最佳聚结效果所对应的电场频率也不同,工程应用中应该根据不同油田原油乳化液的实际情况进行具体评估。     

非均匀电场下乳化油中液滴变形动力学行为

外加电场下液滴的变形动力学行为是乳化液电脱水机理研究的重要内容。基于Cahn-Hilliard方程的相场方法,建立了液滴在非均匀电场下的仿真模型,研究了电场作用下乳化液中液滴在形变、移动和聚结过程中电荷密度和电场力的分布规律,以及流场和电场的耦合作用。仿真分析了液滴粒径、电场强度以及电场非均匀系数对液滴运动行为的影响。利用实验室小型脱水系统开展了乳化液脱水实验,并通过高速摄像机对乳化液中液滴的运动行为进行了观测与分析。研究结果表明,在非均匀电场中液滴表面的极化电荷分布不均,由液滴中部向两端逐渐增大,在靠近电场集中方向处的电荷密度和Maxwell应力值最大;在一定范围内增大电场强度、电场非均匀系数或液滴粒径,可使液滴形变量增大,液滴向电场集中区域的移动速度以及液滴间的聚结速度增加。     

水滴间距对高压高频脉冲静电聚结特性的影响

为了深入探究W/O乳状液静电聚结过程中水滴间距对静电聚结特性的影响,本文在高压高频脉冲电场条件下,通过实验研究了水滴间距对水滴平均变形度及相互靠近速率的影响.结果表明:随着电场施加时间增加,水滴相互靠近,水滴的平均变形度随聚并时刻比的增大而增大;不同粒度条件下,随着水滴中心距比的增大,水滴的平均变形度呈现下降的趋势,水...     

非均匀高频电场下W/O型乳化液动态破乳聚结特性的实验研究

采用自主设计搭建的非均匀电场动态破乳聚结特性实验装置,首次在国内配套使用高频/高压脉冲交流电源和FBRM G600型聚焦光束反射仪,建立了W/O型乳化液中分散相水颗粒粒径分布的在线测试评价方法,进而系统研究了电场参数和流动参数对W/O型乳化液在非均匀电场作用下动态破乳聚结特性的影响规律。实验结果表明,对于所配制含水率为20%的W/O型乳化液,在电场强度为2.87 kV×cm~(-1)、电场频率为2 kHz、占空比为50%时,分散相水颗粒体积平均粒径(VMD)值较初始稳定状态的增长倍数达到最大值,为3.81倍;小粒径水颗粒(粒径小于10μm)数目较初始稳定状态减小至最小值,减少了62%;充分证明在非均匀电场下,合理电场参数的筛选对于乳化液破乳聚结具有重要意义。在实验流速范围内,VMD值增大倍数随着流速的增加先增大后减小,表明在确保足够停留时间的前提下,适度增加乳化液流速方能显著提升破乳聚结效率,因此合理流速的确定应当优先满足乳化液在电场中最短停留时间的要求。     

高频脉冲电场下无机盐及电场参数对水滴成链特性的影响研究

为了深入探究W/O乳状液静电聚结破乳过程中无机盐及电场参数对水滴成链特性的影响机理,分别改变无机盐浓度、种类及电场参数,对高频高压脉冲电场作用下水滴成链特性进行显微实验研究。结果表明,随NaCl浓度增加,电场作用前期,水链平均粒径先增大后减小,电场作用后期,顺序相反。电场作用前期,水链平均粒径从大到小的顺序为:Na_3PO_4、Na_2SO_4、NaNO_3、NaCl、Na_2CO_3和CaCl_2、MgCl_2、KCl、NaCl、NH_4Cl;电场作用后期,顺序相反。无机盐对水链链长的影响与其对水链平均粒径的影响相似。电场参数方面,随电场强度增加,水链链长先减小后增大,水链最大粒径和平均粒径先小幅增大后显著增大;随电场频率的增加,水链链长平缓减小,水链最大粒径和平均粒径先小幅增大后小幅减小;随占空比增大,水链链长先小幅减小后小幅增大再大幅减小,水链最大粒径和平均粒径先小幅增大后小幅下降。     

脉冲电场作用下水滴动态响应特性研究

通过利用comsol数值模拟软件,对脉冲电场作用下的液滴运动规律进行模拟,建立液滴在脉冲电场作用下的物理模型和乳状液界面动力学模型;研究脉冲电场中乳状液的电场强度、占空比、介电常数等参数对液滴的变形行为的影响;针对脉冲电场中乳状液的电场强度、分散相水滴的受力以及各电场参数对水滴变形的作用机理等进行深入探讨,最终得到的水滴变形速率方程,能够较为客观地反映出脉冲电场作用下水滴的变形规律,具有一定的指导意义。     

炼厂污油静电聚结脱水研究

针对目前炼油厂污油乳化严重、高含水、高含盐、性质复杂难处理的特点,在现有的静电聚结理论研究基础之上,采用绝缘复合电极装置,开展静电聚结污油脱水研究。通过静电聚结脱水试验考察了绝缘电极杆长度、电压、停留时间、温度、注水量等因素对污油脱水效率的影响。试验结果表明,对某炼厂含水率为15.36%的污油,进行一级电脱分离,即可满足污油脱后含水率小于0.5%的回炼指标,脱水效率可达97%以上。     

Electrostatic enhancement of coalescence of water droplets in oil: a review of the technology

The technology for electrostatic enhancement of coalescence of water droplets in oil emulsions is critically reviewed. Historically, the electrostatic coalescer was invented for the petroleum-related industries in California [US Patent 987 115 (1911)]. Nowadays, this technology is generally considered for the separation of an aqueous phase dispersed in a dielectric oil phase with a significantly lower dielectric constant than that of the dispersed phase. Various designs have been introduced, with most using alternating current (AC) electric fields with mains frequency (50 or 60 Hz). The direct current (DC) electric field has been less common in the past as compared to the AC. In 1981, the concept of pulsed DC electric fields was introduced, together with insulated electrodes [Trans. IChemE 59 (1981) 229–237; UK Patent 217 1031A (1986)]. Since then, this has become more common in the electrocoalescence technology. Pulsed DC and AC fields are especially useful, when the aqueous phase content of the emulsion is high, to prevent short-circuiting between the pair of electrodes. Processing of oil from old wells is a good example, where the volumetric water content could vary significantly. Reported work by some workers indicates the existence of an optimum frequency, which depends on the electrode coating material, its thickness and the liquid emulsion composition. This is however, a contentious issue which has not been completely resolved. The characteristics and geometry of the electrode system (generally cylindrical or plate) influence the performance of the electrostatic coalescer, and are closely related to the type of the applied electric field and the emulsion used. There are basically two types of electrode: uninsulated electrode and insulated electrode. Combination of electrocoalescence and mechanical separation (e.g., centrifugal force) has also been introduced. Heating and the addition of chemicals have been shown to further enhance the electrocoalescence of water droplets. Other methods that can be combined with the electrical treatment are filtration, methods employing high pressure and temperature, and mixing. This review paper also looks at some of the current specific industrial applications using the electrocoalescence technology. Besides the oil and petroleum industries, this technology has potential applications in the edible oil industries such as palm oil, sunflower oil and vegetable oil processing. Most of the currently available equipment is very big and bulky, having a large inventory of emulsion. Therefore, we see the future trend for new developments to be in the direction of inventing small portable devices, incorporating features such as optimum electric fields and combined electrical and centrifugal forces to further enhance the separation of water-in-oil emulsions. Furthermore, a better understanding of the fundamentals of electrocoalescence will enable a better design of the geometry of the electrodes, of the flow field with respect to the electric fields, the type of dispersion used and the type of the applied electric field.     

电场作用下基面液滴蒸发与内部流动数值模拟

为探究电场强化基面液滴蒸发的原理,本文采用有限元方法,对外加电场作用下的固体基面上液滴的蒸发过程进行了数值模拟,对比了不同电导率液滴的蒸发过程,分析了电场、液滴蒸发速率和内部流动的影响及其成因,以及液滴在电场作用下的内部流动与液滴传热传质的关系,结果表明,电场力的作用能够显著强化液滴内部的流动,对液滴的传热传质具有促进作用。此外,本文分析了温度对电场下基面液滴蒸发及内部流动的影响,发现温度对电场、液滴内部流动及蒸发的强化作用也有着较为明显的影响：对于电导率较低的纯水液滴,当电场强度低于和高于临界值6kV/cm时,温度对电场强化液滴内部流动和蒸发的影响有所不同;对于电导率较高的盐酸液滴,温度对电场强化液滴内部流动和蒸发的影响随电场强度升高均较大。本文为发展高效静电喷雾冷却技术提供了研究基础。     

高压静电场对海水蒸发和沸点的影响

研究了不同条件下高压静电场对海水蒸发速率和沸点的影响。实验结果表明:高压静电场下海水蒸发的速率是常态下的1.5~2.1倍;海水沸点随高压静电场强度的增大而降低。由实验现象和数据分析得出:水分子是极性分子,在高压静电场下易形成电偶极矩,电偶极矩使水分子之间的氢键断裂,从而水分更易蒸发;氢键断裂的能量来源于海水的内能,而不是电场能转化而来的能量。     

Electrocoalescence of binary water droplets falling in oil: Experimental study

The approaching movement and consequent coalescence of binary water droplets falling in stagnant oil and exposed to an external electric field are investigated using a high speed camera. Different situation of the droplets and electric field intensities are applied in the experiments. The qualitative results of the experimental observations are exhibited through the scaled images of the binary droplets snapshots in milliseconds. Furthermore, different approaching trends of the droplets are presented as quantitative plots and discussed based on the theoretical electrostatic and hydrodynamic models. The effect of the applied voltage amplitude, initial distance of the drop pair, and skew angle of the electric field are investigated. The experimental results prove the electrostatic theories; as acceleration in electrocoalescence demonstrated using a stronger electric field as well as closer distance between the droplets. It was also revealed that the skew angle of the electric field decelerates the electrocoalescence until alignment of the droplets.     

Enhanced Coalescence of Emulsion in an Electric Field

Abstract

The action of an electric field on an emulsion produced effects like drop disintegration and promoted coalescence. High and low field intensities modify droplet displacements due to electrostatic forces. In this investigation a water-in-oil type of emulsion was prepared using distilled water and soap as the surfactant. After mixing, these emulsions were separated under an applied direct current high voltage electric field at a fixed 2.09 kV applied output voltage across the system. The time of coalescence, upper plate position, mixing time, and dispersion/coalesced phase volume interface are the parameters considered to influence the coalescence parameter and dispersion band hold-up. The results show that the prepared emulsion can be separated back into its bulk phases by using electric fields. The degree of separation depends on the applied voltage.     

Movement of dispersed droplets of W/O emulsion in a uniform DC electrostatic field:Simulation on droplet coalescence☆

Considering the droplet coalescence, the motion of a group of dispersed droplets in W/O emulsion in a DC electric field is simulated. The simulation demonstrates the evolutions of droplet number, size as wel as its distribution, local concentration distribution and droplet size-velocity relation with the applied time of electric field. The sim-ulated average droplet size is roughly consistent with the experimental value. The simulated variation of droplet number with time under several applied voltages shows that increasing voltage is more effective for raising the rate of droplet coalescence than extending exerting time. However, with the further raise of applied voltage, the improvement in droplet coalescence rate becomes less significant. The evolution of simulated droplet size–velocity relationship with time shows that the inter-droplet electric repulsion force is very strong due to larger electric charge on the droplet under higher applied voltage, so that the magnitude and the direction of droplet velocity become more random, which looks helpful to droplet coalescence.     

直流脉冲电场下液滴-界面聚并行为

为了深入探究直流脉冲电场下液滴-界面聚并行为,针对去离子水作为分散相、葵花油作为连续相的体系,分别改变电场参数（电场强度、频率、波形）和物性参数（界面张力、电导率、液滴粒径、固体颗粒）进行显微实验研究,得到了液滴-界面聚并机制及各参数的影响规律。实验结果表明,液滴-界面存在完全聚并和不完全聚并两种机制,决定因素是泵吸和颈缩过程的相互作用。电场强度增大,不完全聚并程度增大,而电场频率的作用则相反,这与电场力大小和液滴稳定程度有关。随表面活性剂浓度增大,二次液滴急剧增大,超过临界胶束浓度后,小幅减小。随电导率和SiO₂浓度增大,不完全聚并程度均先增大后减小,而随液滴粒径增大,不完全聚并程度持续增大。大部分工况下,液滴在直流稳恒电场下不完全聚并程度高于直流脉冲电场。为脉冲静电破乳机理的深入探讨及高效紧凑脉冲电脱盐脱水设备的研发奠定了理论基础。     

高压静电破乳中离散液滴的动力学分析

考虑乳化液离散液滴的直径分布,对高压直流静电破乳过程中离散液滴的运动进行了理论模拟。模拟及实验结果表明,在高压静电作用下,离散滴液从一侧电极向另一侧电极运动。沿液滴运动方向,液滴浓度逐渐增大,并在电极附近达到最大。随着静电作用时间的延长,电极附近液滴浓度近似呈线性规律增大。在相同的作用时间内,高电压液滴浓度的增长幅度要更大。因此,尽可能提高施加电压要比单纯延长静电作用时间的破乳效果更好。此外,大的液滴运动速度更快,故对于离散相滴径较大的乳化液,破乳效率会更高。