电场作用下双液滴聚合特性

乳状液破乳分离是目前高含水期油田开采过程中难以解决的技术问题,电场破乳方法具有高效清洁等优点,是解决该问题的有效手段。采用数值模拟与试验验证相结合的方法研究电脱水过程中阶跃、斜坡电场诱导下双液滴的聚合与分离特性。结果表明,在斜坡电场作用下,界面张力引起的泵吸作用大于电场力引起的颈缩作用,有利于液滴聚并,且液滴发生二次乳化现象的概率降低。而施加阶跃电场时,一定范围内能够达到液滴破乳的目的,但液滴在聚并过程中易发生二次乳化现象。从电场对连续相影响的角度分析发现,阶跃电场不仅对液滴具有驱动作用,对连续相的影响也较为明显,阶跃电场会增大连续相内湍流作用,不利于电脱水过程。因此,采用斜坡信号诱导液滴聚合能够降低二次乳化现象发生的概率。     

Electro-coalescence of an aqueous droplet at an oil-water interface

The coalescence of an aqueous droplet at an oil-water interface under an electric field has been investigated, with a view to quantify conditions that give rise to secondary droplet formation. Two patterns of drop-interface coalescence may occur: complete coalescence and partial coalescence. The former is obviously the desirable pattern for industrial coalescers. However in practice, the process of coalescence could actually produce smaller droplets, which become more difficult to remove, and hence undesirable. This is caused by either necking, due to extensive elongation of the droplet, or reaction to a fast and energetic coalescence and is referred to as partial coalescence. The volume of the droplets formed in this way has been analyzed as a function of the initial droplet size, electric field strength and the distance between the droplet and the interface. The expansion speed of the neck connecting the droplet and interface at the beginning of the pumping process has also been quantified. These results are useful in optimizing the electro-coalescence process.     

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。     

Coalescence behaviour of water droplets in water‐oil interface under pulsatile electric fields

In this research, the deformation of water droplets in sunflower oil-interface under pulsatile electric field was studied experimentally. Three types of coalescence were observed:(i) complete coalescence, (ii) incomplete coalescence and (iii) no-coalescence. The first type is desirable because of leaving no secondary droplets. The second type that produced secondary droplets which caused by necking process, due to extreme elongation of droplets (mostly small droplets), was undesirable; because the small droplets were more difficult to coalesce and remove. The no-coalescence was caused by very fast coalescence and extensive pushing of droplet into the continuous phase. In this work the process was operated with the utilization of a batch cylindrical separator with high voltage system. The lower part of the cylinder was filled with the aqueous phase and its top part was filled with sunflower oil to form an interface between the two phases. The effects of electric field strength, frequency, and waveform types were investigated. It was found that, the ramp-ac waveform was the best waveform, avoiding the production of secondary droplets and in this case the frequency also played an important role.     

Coalescence of Water Droplets in Crude Oil Emulsions: Analytical Solution

In petroleum refineries, water is used in desalting units to remove the salt contained in crude oil. Typically, 7 % of the volume of hot crude oil is water, forming a water‐and‐oil emulsion. The emulsion flows between two electrodes and is subjected to an electric field. The electrical forces promote the coalescence of small droplets of water dispersed in crude oil, and these form bigger droplets. This paper calculates the forces acting on the droplets, highlighting particularly the mechanisms proposed for droplet–droplet coalescence under the influence of an applied electric field. Moreover, a model is developed in order to calculate the displacement speed of the droplets and the time between droplet collisions. Thus, it is possible to simulate and optimize the process by changing the operational variables (temperature, electrical field, and water quantity). The main advantage of this study is to show that it is feasible to increase the volume of water recycled in desalting processes, thus reducing the use of freshwater and the generation of liquid effluents in refineries.     

新型静电聚结器中水滴聚结特性研究

传统电脱水器采用裸电极,含水率较高时在高强电场作用下容易发生击穿现象,今设计了包覆绝缘层的高压电极并加工了新型静电聚结器,可有效避免击穿现象的发生。采用水/原油乳状液为实验介质,并利用显微高速摄像系统结合图像处理技术对水滴的聚结规律进行了观察和分析,探索了电场强度、流量、含水率等因素对水滴聚结特性的影响。结果表明:包覆绝缘层的高压电极可有效防止电击穿现象的发生,增加电场强度有助于油水分离,但高于临界场强后容易导致液滴破碎;含水率为10%、20%、30%时,最优电场强度不同,分别是372、320和204 kV m 1;含水率10%和30%乳化物液滴粒径增大倍数明显大于含水率20%的工况;电场作用时间影响液滴聚结效果,高强电场在低流量下具有很显著的作用;随着流量的增加电场作用降低,但高强电场在高流量下依然使液滴粒径明显增大。     

Functions of Demulsifiers in the Petroleum Industry

There are an increasing number of crude oil fields that are now producing both crude oil and water emulsions; such fields are both onshore and offshore. These emulsions are formed during oil exploitation due to the presence of natural surfactants, such as asphaltenes and resins. These molecules strongly stabilize the water/oil interface and prevent coalescence of water droplets. As water/oil phase separation is necessary before oil transportation and refining, demulsifiers are used to break water-in-oil emulsions. This review presents the crude oil emulsion formation, factors affecting demulsification of crude oil emulsion such as demulsifier chemical structure, water content, partition coefficient (K_P), and demulsifier concentration. This review also covers the kinetics and mechanism of the demulsification process.     

INVESTIGATION OF EMULSIFICATION AND COALESCENCE PHENOMENA IN CRUDE OIL/ALKALINE WATER SYSTEMS

Emulsihcation and coalescence processes in crude oil/alkaline water systems were examined and their influence on alkaline Hood enhanced oil recovery was assessed. Emulsification mechanisms were investigated under static and dynamic conditions using microvisual techniques. Coalescence rates were measured using the inclined spinning drop tensiometer. The relative impact of interfacial viscosity on coalescence processes was determined through measurements of interfacial shear viscosities. In addition, the influences of chemical composition on ease of emulsification, coalescence rate, and interfacial shear viscosity were examined.

Ease of emulsification was influenced by the composition of the crude oil, the electrolyte concentration, and the partitioning coefficient of surfactants. Coalescence was primarily affected by processes which disrupted the crude oil/water interface. Alkaline flood oil recovery efficiency was promoted by emulsification followed by rapid coalescence to form a stable oil bank.     

Electrically stressed water drops in oil

The deformation of water droplets in an electric field has been studied in hydrocarbon liquids. A water drop will elongate in an electric field due to the electrostatic pressure, and becomes unstable when a critical field limit is reached. By applying different voltage waveforms it is possible to measure both transient, time varying and static effects. An experimental method has been developed to study the rheological properties of the water droplet. The experimental results in surfactant-free model oil are in good agreement with classic Taylor theory. In diluted crude oil a correlation was found between the drop behavior in an electric field and the interface elasticity modulus, measured by dilational interfacial rheology. The static drop deformation was reduced with increasing elastic modulus due to adsorption of polar surfactants to the water/oil interface. Drop surface oscillations will be damped by the viscosity of the bulk liquid. The dynamic drop behavior was studied in viscosity standards prepared from different concentrations of polystyrene in toluene. The drop oscillations were modeled as damped oscillator, and the influence of viscosity on the eigen-frequency and damping coefficient was studied for different drop sizes. The oscillations can also explain the premature break-up of water droplets sometimes observed in the experiments.     

Influence of Oil Properties on Bed Coalescence Efficiency

Abstract

Bed coalescence efficiency of oil separation from formation water was studied on model systems involving 10 real samples of crude oil and its fractions of different characteristics. Oil components were varied and all other parameters were kept constant, and high mineralization water served as the continuous phase. All experiments were realized on a commercial WO/O4 two-stage bed coalescer. Temperature, oil content, and fluid velocity were kept constant for all samples. Model emulsion was dispersed by constant stirring during the experiment to obtain primarily droplets of 20 μm diameter. Correlations for predicting the coalescence efficiency as a function of some physical and chemical oil properties are presented. The investigated oil components ensured a wide span of viscosity, density, and interfacial tension. The influences of mean molecular weight, neutralization number, as well as the contents of n-alkenes, NSO, and aromatics on coalescence efficiency were analyzed. On the basis of the empirical dependences of coalescence efficiency on individual parameters obtained by regression analysis of the data, a general mathematical model was established.     

COALESCENCE OF SINGLE DROPS AT A LIQUID-LIQUID INTERFACE IN THE PRESENCE OF SURFACTANTS/POLYMERS

The stability of single oil droplets at a liquid-liquid interface in the presence of surfactants/polymers was investigated and the coalescence time of oil droplets at an oil-aqueous surfactant solution interface was measured in a specially constructed coalescence cell. A unique feature of the experimental set-up was that the drop size could be controlled quite accurately and was independent of the interfacial tension and the difference in the densities of the two phases used. The coalescence time of oil droplets correlated favorably with interfacial viscosity of the system. However, no correlation was found between interfacial tension and coalescence time or the rate of coalescence. Both the coalescence time and interfacial viscosity were found to be strong functions of the surfactant concentration.     

Effects of temperature and time on interfacial tension behavior between heavy oils and alkaline solutions

Heavy oils contain significantly more acidic components than conventional crude oils. Upon contact with aqueous alkaline solutions, water-soluble surfactants are formed in-situ at the interface. These surfactants have the ability to reduce the oil/water interfacial tension to ultra-low values. This work studies the significant effects of time and temperature on the interfacial tension between alkaline solutions and two Canadian heavy oils (Lloydminster and Cold Lake). The results obtained indicate that the time period during which interfacial tension remains ultra-low is just as important as the magnitude of the minimum attainable interfacial tension in determining the potential success of an alkaline flooding process in the field.     

Examination of the parameters governing oily soil removal from synthetic substrates

The rate of removal of mineral oil soils from model polyester sub-strates by the roll-up mechanism shows a marked dependence on nonionic surfactant concentration even above the critical micelle concentration (cmc). Similarly, although the solid/water interfacial tension is observed to be constant, the equilibrium oil/water inter-facial tension in these systems consistently decreases as the nonionic surfactant concentration is increased. The dependence of removal time and oil/water interfacial tension on surfactant concentration above the cmc is most pronounced for nonionic surfactants having relatively high cmc. At a given concentration, surfactants exhibiting the lowest equilibrium oil/water interfacial tension generally provide the most effective soil removal, suggesting that the reported depen-dence of removal time on surfactant concentration is related to the commensurate lowering of the oil/water interfacial tension. Nonyl phenol ethoxylates perform exceptionally well with mineral oil on polyester substrates because of the combination of a low oil/water interfacial tension and high solid/water adhesion tension. Regardless of surfactant structure, mineral oil on Teflon FEP maintains a high contact angle in the water because the solid/oil interfacial tension is less than the solid/water interfacial tension. Oil removal in such systems occurs only by an inefficient necking and drawing process. Oleyl alcohol displays a high contact angle in the water on both Teflon FEP and Mylar substrates for reasons similar to that of mineral oil on Teflon FEP. Partial oil removal occurs from both substrates in selected built systems, presumably because a low oil/ water interfacial tension promotes necking and drawing. Given sufficient time, unremoved oils develop a liquid crystalline phase which results in slow oil removal via dispersion. Triolein soils also possess a relatively low solid/oil interfacial tension and similarly exhibt a high contact angle (in water) on both Teflon FEP and Mylar substrates in unbuilt surfactant systems. Builder addition lowers the oil/water interfacial tension and thereby prompts necking and drawing action.     

The influence of NaOH on the stability of paraffinic crude oil emulsion

The alkaline–surfactant–polymer flooding using sodium hydroxide as the alkali component to enhance oil recovery at the on shore oil fields at Daqing in China has brought new problems for the oil industry. Even though, the reservoir contained paraffinic crude oil, the alkali added formed stable water-in-crude oil emulsion and de-emulsification process was necessary to separate oil and water.The problems related in the enhanced oil recovery process using the alkaline–surfactant–polymer flooding technique in the Daqing oil field have been investigated in the laboratory using fractions of Daqing crude oil. The oil was separated into asphaltene and aliphatic fractions and then used in an additive free jet oil to form model oils. The emulsion stability of each of the water-in-model oil emulsions formed between water or 0.6% sodium hydroxide solution and model oil was investigated. The interfacial properties such as interfacial tension and interfacial pressure of the systems were also measured. These in combination with the chemical nature of the fractions were used to get insight into the problem related to the ASP flooding technique using sodium hydroxide as the alkaline component.The study reveals that the sodium hydroxide solution reacts with fatty acids in the aliphatic fraction of the crude oil and/or with the fatty acids formed from the slow oxidation of long chain hydrocarbons, and form soap like interfacially active components. These accumulate at the crude oil–water interface and contribute to the stability of the oil/water emulsion.     

Application of magnetic nanoparticles as demulsifiers for surfactant-enhanced oil recovery

Nonionic surfactants are increasingly being applied in oil recovery processes due to their stability and low adsorption onto mineral surfaces. However, these surfactants lead to the production of emulsified oil that is extremely stable and difficult to separate by conventional methods. This research characterizes the stability of crude oil mixed with a nonionic surfactant, L24–22, in a brine solution. When subjected to gravity separation, a middle oil-rich and bottom water-rich emulsion are generated for various water–oil ratios. Thermal treatments can effectively break oil-rich emulsions, but the bottom water layer remains contaminated with micron-sized crude oil droplets. A magnetic nanoparticle treatment is shown to demulsify the crude oil emulsions, dropping the total organic carbon (TOC) in the water layer from 1470 to 30 ppm.     

Molecular dynamics simulation study on π-π stacking of Gemini surfactants in oil/water systems

Whereas the π-π stacking interactions at oil/water interfaces can affect interfacial structures hence the interfacial properties,the underlying microscopic mechanism remains largely unknown.We reported an all-atom molecular dynamics(MD) simulation study to demonstrate how the Gemini surfactants with pyrenyl groups affect the interracial properties,structural conformations,and the motion of molecules in the water/n-octane/surfactant ternary systems.It is found that the pyrenyl groups tend to be v...     

微通道内表面活性剂与界面传递现象研究进展

表面活性剂在微流体应用中具有重要作用,常伴随动态界面传递现象。综述了微通道内含表面活性剂的多相流研究进展,剖析了液滴尺寸、液体流变性、压力降与微流体中动态界面张力的关系。总结了表面活性剂作用下的界面传递现象,如气泡及液滴的生成、运动、形变、破裂和聚并动力学的研究进展。综述了微流体中表面活性剂的吸附动力学,对该领域的发展方向进行了展望。     

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.     

高分子生物表面活性剂Emulsan的研究进展

详细介绍了高分子生物表面活性剂Emulsan的生物合成、物化性质以及在稠油管道运输和油罐清洗中的应用。Emulsan是醋酸钙不动杆菌RAG-1代谢产生的胞外脂多糖,它不能显著降低油-水的界面张力,而是分布在油滴的表面,有效地阻止它们的聚并,使O/W型乳状液稳定,从而有助于它在石油工业中的应用。并对Emulsan研究方向及应用发展趋势进行了展望。     

驱油剂对三元复合驱含油污水中油滴稳定性的影响

三元复合驱技术已在大庆油田成功进行工业化应用。三元复合驱含油污水中由于含有残余的化学药剂，导致其很难处理，从而限制了三元复合驱技术的推广。本文首先采用室内实验制备模拟三元复合驱含油污水，然后通过沉降实验研究驱油剂对油滴稳定性的影响，最后结合驱油剂对油水界面张力、油滴Zeta电位、油滴粒径大小的影响来阐释驱油剂对油滴稳定性的作用机制。结果表明：油滴的稳定性随着NaOH浓度的增大先增大后减小，当NaOH浓度由0增大到400mg/L时，NaOH与原油中的酸性物质反应生成表面活性剂增强油滴的稳定性；当NaOH浓度大于400mg/L时，NaOH本身作为电解质压缩双电层，使油滴的稳定性减小。油滴的稳定性随着表面活性剂浓度的增大而增大，这是因为表面活性剂可以吸附在油滴表面，使油水界面张力减小，同时增大油滴表面的Zeta电位，从而使油滴的稳定性增强。油滴的稳定性随着聚合物浓度的增大先减小后增大，当聚合物的浓度小于300mg/L时，聚合物的桥接、絮凝作用起主导作用，聚合物分子可以吸附到油滴表面，将油滴连接到一起，同时聚合物分子可以压缩液滴表面的双电层，从而有利于油滴的聚结；当聚合物的浓度大于300mg/L时，体系的黏度增大，油滴的运动速度减小，此时聚合物分子占满油滴表面，表现出空间位阻作用，从而使油滴的稳定性增强，不利于油滴的聚结。