Mathematical modelling of a hydrocyclone for the down-hole oil–water separation (DOWS)

In this study, a mathematical model is developed to predict the efficiency of a down-hole oil–water separation hydrocyclone. In the proposed model, the separation efficiency is determined based on droplet trajectory of a single oil droplet through the continuous-phase. The droplet trajectory model is developed using a Lagrangian approach in which single droplets are traced in the continuous-phase. The droplet trajectory model uses the swirling flow of the continuous-phase to trace the oil droplets. By applying the droplet trajectory, a trial and error approach is used to determine the size of the oil droplet that reaches the reverse flow region, where they can be separated. The required input for the proposed model is hydrocyclone geometry, fluid properties, inlet droplet size distribution and operational conditions at the down hole. The model is capable of predicting the hydrocyclone hydrodynamic flow field, namely, the axial, tangential and radial velocity distributions of the continuous-phase. The model was then applied for some case studies from the field tested DOWS systems which exist in the literature. The results show that the proposed model can predict well the split ratio and separation efficiency of the hydrocyclone. Moreover, the results of the proposed model can be used as a preliminary evaluation for installing a down-hole oil–water separation hydrocyclone system in a producing well.     

Analysis of droplet expulsion in stagnant single water-in-oil-in-water double emulsion globules

Double emulsions created by phase inversion can be used for fast liquid–liquid separation; therefore, the coalescence behaviors of these types of multiple emulsions need to be predictable for different physical properties and drop size ratios. The aim of this study is to determine the influence of the effective overall drop diameter and the internal droplet size on the coalescence time and the coalescence behavior. Experimental investigations on the physical stability of single stagnant water-in-oil-in-water (W₁/O/W₂) double emulsion globules are performed. For this investigation, a formation device to inject one water droplet into an oil drop inside a water bulk phase is developed. The coalescence process of the sole internal water droplet floating on the O/W₂ interface with the water bulk phase, often termed droplet expulsion or external coalescence, is recorded with a high speed camera. Based on image analysis, the diameters of the effective overall drop D, containing the oil and entrapped water volume, and the internal water droplet d are determined. Additionally, the coalescence time τ, including the time from the first contact of the internal droplet and the drop-bulk interface to the film rupture is measured. A large increase in coalescence time with increasing water droplet diameters is found. For the investigated paraffin oil–water system and initial drop sizes, partial coalescence occurs. In this case, the diameter ratio of daughter-to-mother droplet ψ is determined.     

Multi-scale cross entropy analysis for inclined oil–water two-phase countercurrent flow patterns

The flow of an oil–water two-phase fluid in an inclined pipe exhibits fundamentally different behaviors to that of a vertical two-phase flow, especially the flow commonly presents complex countercurrent flow structure due to the influence of gravity. The understanding of inclined oil–water flow is of important significance for flow measurement and production optimization. We using multi-scale cross entropy (MSCE) analysis investigate the nonlinear dynamics of inclined water-dominated oil–water two-phase flow patterns which are Dispersion oil-in-water-Pseudoslugs (D O/W PS), Dispersion oil-in-water-Countercurrent (D O/W CT) and Transitional Flow (TF). We find that the rate of low-scale cross entropy can effectively identify flow patterns, and the high-scale cross entropy can represent their long-range dynamics. The research results show that the multi-scale cross entropy analysis can be a helpful tool for revealing nonlinear dynamics of inclined oil–water two-phase flow in terms of microscopic and macroscopic views.     

Experimental study of a vane-type pipe separator for oil–water separation

An experimental study of a new vane-type pipe separator (VTPS) was conducted for the possible application in the well-bore for oil–water separation and reinjection. Results by using particle image velocimetry (PIV) reveal a better flow field distribution for oil–water separation, which is formed in VTPS than that in hydrocyclone. The effects of split ratio, the oil content, guide vanes’ installation and number of guide vanes on oil–water separation performance have been investigated experimentally. Compared to a traditional single hydrocyclone, VTPS shows a good separation performance as the water content at the inlet of VTPS reaches 79.9%, the oil content at the water-rich outlet is about 400 ppm while the split is near 0.70. These results are helpful to provide a possibly new design for downhole oil–water separation.     

CFD analysis of microchannel emulsification: Droplet generation process and size effect of asymmetric straight flow-through microchannels

Asymmetric straight flow-through microchannel (MC) arrays are high-performance MC emulsification devices for stable mass production of uniform droplets. This paper presents computational fluid dynamics (CFD) simulation and analysis of the generation of soybean oil-in-water emulsion droplets via asymmetric straight flow-through MCs, each consisting of a microslot and a narrow MC. We also used CFD to investigate the effects of the channel size and the flow of the dispersed phase on MC emulsification using asymmetric straight flow-through MCs with a characteristic channel size of 5–400 μm. The overall shape of an oil–water interface and the time scale during droplet generation via a control asymmetric straight flow-through MC were appropriately simulated. Better insight was obtained on the flow profile of the two phases and the internal pressure balance of the dispersed phase during droplet generation. Comparison of the CFD and experiment results also provided insight into dynamic interfacial tension during droplet generation. Successful droplet generation was observed below a critical dispersed-phase velocity. In this case, the resultant droplet size was proportional to the channel size and was not sensitive to the dispersed-phase velocity applied. The maximum droplet generation rate per channel was inversely proportional to the channel size, unless the buoyancy force did not promote droplet detachment. The maximum droplet productivity per unit area of an asymmetric straight flow-through MC array was estimated to be constant, regardless of channel size.     

Effect of oil viscosity on the flow structure and pressure gradient in horizontal oil–water flow

The flow patterns and pressure gradient of immiscible liquids are still subject of immense research interest. This is partly because fluids with different properties exhibit different flow behaviours in different pipe's configurations under different operating conditions. In this study, a combination of oil–water properties (σ = 20.1 mN/m) not previously reported was used in a 25.4 mm acrylic pipe. Experimental data of flow patterns, pressure gradient and phase inversion in horizontal oil–water flow are presented and analyzed together with comprehensive comments. The effect of oil viscosity on flow structure was assessed by comparing the present work data with those of Angeli and Hewitt (2000) and Raj et al. (2005). The comparison revealed several important findings. For example, the water velocity required to initiate the transition to non-stratified flow at low oil velocities increased as the oil viscosity increased while it decreased at higher oil velocities. The formation of bubbly and annular flows and the extent of dual continuous region were found to increase as the oil–water viscosity ratio increased. Dispersed oil in water appeared earlier when oil viscosity decreased.     

Nonlinear characterization of oil–gas–water three-phase flow in complex networks

Understanding the dynamics of oil–gas–water three-phase flow has been a challenge in the fields of nonlinear dynamics and fluid mechanics. We systematically carried out oil–gas–water three-phase flow experiments for measuring the time series of flow signals, which is studied in terms of the mapping from time series to complex networks. Two network mapping methods are proposed for the analysis and identification of flow pattern dynamics, i.e. Flow Pattern Complex Network (FPCN) and Fluid Dynamic Complex Network (FDCN). Through detecting the community structure of FPCN based on K-means clustering, distinct flow patterns can be successfully distinguished and identified. A number of FDCN's under different flow conditions are constructed in order to reveal the dynamical characteristics of three-phase flows. The network information entropy of FDCN is sensitive to the transition among different flow patterns, which can be used to characterize nonlinear dynamics of the three-phase flow. These interesting and significant findings suggest that complex networks can be a potentially powerful tool for uncovering the nonlinear dynamics of oil–gas–water three-phase flows.     

Droplet coalescence model optimization using a detailed population balance model for RDC extraction column

Single droplet experiments in a small lab scale Rotating Disk Contactor (RDC) for two different liquid–liquid systems were used to evaluate the coalescence parameters necessary for column simulations. Five different coalescence models are studied; the models parameters were obtained by an inverse solution of the population balance model using the extended fixed-pivot technique for the discretization of the droplet internal coordinate. The estimated coalescence parameters by solving the inverse problem were found dependent on the chemical test system. The Coulaloglou and Tavlarides model was found to be the best model to predict the experimental data for both test systems. These parameters were used to study the hydrodynamics and mass transfer behavior of pilot plant RDC extraction column using the simulation tool LLECMOD. This is performed for two different liquid–liquid systems as recommended by the European Federation of Chemical Engineering (EFCE) (butylacetate–acetone–water (b–a–w) and toluene–acetone–water (t–a–w)). The simulated Sauter mean droplet diameter, hold-up values and concentration profiles for organic and aqueous phase were found to be well predicted compared to the experimental data.     

Non-coalescence behavior of neutral droplets suspended in oil under a direct current electric field

The excessive electric field gives rise to droplet non-coalescence and droplet chains in the electric dehydrator, which severely deteriorates oil–water separation efficiency and even leads to short circuit. To reveal the underlying mechanism of droplet non-coalescence, dynamic behavior of two neutral droplets in silicone oil under a direct current electric field is investigated by using high-speed photography. The experimental results show that there exists a critical electric field strength above which two droplets will bounce off after the contact. The critical electric field strength of droplet non-coalescence is affected by the initial separation distance between droplets, the radius of droplet, and the surfactant concentration. Whether the non-coalescence behavior occurs in the electric field is determined by the competition of electric force and capillary force, which dominates the evolution of tiny connection channel.     

Process analysis of the extract unit of vacuum residue through mixed C4 solvent for deasphalting

By employing the EXTRACT module in Aspen Plus Software with the aid of selected PSRK equation from our previous work [W. Li, P. Du, F. Cao, W. Ying, D. Fang, Simulation and optimization of the extract segment of solvent deasphalting plant, Computers and Applied Chemistry, 26 (2009) 455–460] [18], this work simulated a solvent deasphalting (SDA) process with mixed C4 solvent and the feedstock of vacuum residue (VR) obtained from a mixed crude oil (Zhongyuan oil:Tahe oil:Changqing oil:Oman crude oil:Zafiro crude oil = 35:5:2:40:18, wt/wt). The feed of VR was lumped as paraffinic, primitive and aromatic components according to their calculated K_UOP values. The relative errors not more than 3.94% illustrated the simulated results are comparable with the industrial data for both feedstock (VR and mixed C4 solvent) and products (deasphalted oil—DAO and deoiled asphalt—DOA). The DAO yield was predicted to reduce to 47.2% from 58.0% with increasing temperature of mixed C4 solvent from 100 to 120 °C under operating model-I, but increased from 51.6% to 56.1% with solvent–VR ratio up to 6.5 from 4.5. In addition, a heavier mixed C4 solvent would facilitate remarkable improvement of DAO yield but deteriorate its quality.     

DMI-44132型筛网沉降离心脱水机在选煤厂的应用

介绍了DMI44＊132型筛网沉降离心脱水机的用途、性能、工作原理、结构特点和脱水效果,阐明了该型离心脱水机在斜沟煤矿选煤厂的煤泥水系统中发挥的重要作用,达到了降低洗混煤水分的目的,取得了良好的经济效益,为类似情况选煤厂提供设备选择经验借鉴。     

A facile method to functionalize engineering solid membrane supports for rapid and efficient oil–water separation

A facile and low-cost method is developed to functionalize engineering metal membrane supports, such as stainless steel (SS), with epoxy-containing polymer poly(glycidyl methacrylate) (PGMA) to produce a versatile and universal platform for subsequent surface modification. With a PGMA anchoring layer, we have demonstrated that hydrogel particles, such as polyacrylamide-co-poly(acrylic acid) (PAM-co-PAA), can be subsequently grafted to form functional polymer membranes for rapid and efficient oil–water separation. By contact angle and AFM measurement, we have confirmed that PAM-co-PAA hydrogel particle layer grafted on a PGMA-modified SS surface exhibits excellent selectivity as required for liquid–liquid separation, showing high affinity to water but not to oils as an ideal membrane for oil–water separation. To evaluate the separation efficiency, a simple flow-through device is employed to separate free-floating oil from water in the mixture of varied initial oil volume fraction and oil composition. Under substantially high pump flow rate up to 1.3 L/min, PAM-co-PAA hydrogel treated SS mesh can achieve excellent separation efficiency with less than 5% oil or water in the respective filtrate at the flux of as high as 540 m³/(m²·h) and retentate at the flux of 1.95 m³/(m²·h). This separation efficiency is better than, or comparable to, the maximal performance achieved using conventional gravity methods at much lower flow rate. Similar approach could be also adapted to graft superhydrophobic and superoleophilic polymer membranes with PGMA-treated engineering support to separate water from oil.     

Driving liquid droplets on microstructured gradient surface by mechanical vibration

Dynamic transportation of water droplet on microstructured hydrophobic silicon substrate with a contact angle gradient is studied in this article. We propose a new type of substrate designed with microridges on a silicon wafer fabricated by photolithograph and subsequent coating with octadecyltrichlorosilane (OTS). When horizontal vibration is applied on the substrate, the water droplet can move to the direction with larger solid–liquid contact area fraction. It is found that the dynamic contact angle of the water droplet varied with the vibration direction and the speed of the substrate. The contact angle difference at the left and the right edge of the water droplet on the vibrated surface is obviously magnified compared to the contact angle difference of the droplet on the static surfaces, resulting in the increasing driving force. When the vibration amplitude of the exciter source (20 Hz) increases from 0.14 to 0.43 mm, the average velocity of 10 μL water droplet increases from 10 to 23 mm/s. The internal flow pattern of the water droplet moving on the microstructured hydrophobic surfaces is also obtained using particle image velocimetry (PIV) and particle tracking velocimetry (PTV) techniques. Both rolling and slipping motions are observed for the water droplet during its movement in the vibrated substrate.     

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。     

Analysis of energy dissipation in stirred suspension polymerisation reactors using computational fluid dynamics

This work evaluates the spatial distribution of normalised rates of droplet breakage and droplet coalescence in liquid–liquid dispersions maintained in agitated tanks at operation conditions normally used to perform suspension polymerisation reactions. Particularly, simulations are performed with multiphase computational fluid dynamics (CFD) models to represent the flow field in liquid–liquid styrene suspension polymerisation reactors for the first time. CFD tools are used first to compute the spatial distribution of the turbulent energy dissipation rates (ε) inside the reaction vessel; afterwards, normalised rates of droplet breakage and particle coalescence are computed as functions of ε. Surprisingly, multiphase simulations showed that the rates of energy dissipation can be very high near the free vortex surfaces, which has been completely neglected in previous works. The obtained results indicate the existence of extremely large energy dissipation gradients inside the vessel, so that particle breakage occurs primarily in very small regions that surround the impeller and the free vortex surface, while particle coalescence takes place in the liquid bulk. As a consequence, particle breakage should be regarded as an independent source term or a boundary phenomenon. Based on the obtained results, it can be very difficult to justify the use of isotropic assumptions to formulate particle population balances in similar systems, even when multiple compartment models are used to describe the fluid dynamic behaviour of the agitated vessel. © 2011 Canadian Society for Chemical Engineering     

Hydrodynamics of lube oil–water flow through 180° return bends

In the present work, the hydrodynamics of high viscous oil–water flow through return bends have been studied. Two bend geometries (U and rectangular) and three flow directions through the bend (up, down and horizontal flow) are considered. It is noted that the direction of flow of two-phase mixture through the bend has a significant influence on the downstream phase distribution while the bend geometry has a negligible influence on the same. The pressure drop is higher across the rectangular bend as expected and the loss coefficients are independent of flow patterns in all the cases.     

Surface modification of high calcium fly ash for its application in oil spill clean up

The present study aims at utilising an inorganic industrial by-product, high calcium fly ash (HCFA), in an environmental field: oil spill clean up. Properties, such as fine particle size, floating ability, hydrophobic character and porosity, make this material attractive for such a use. In order to investigate the oil sorption behaviour of HCFA an oil spill has been simulated, by using artificial ocean water and three types of oil (heating oil (HO), light cycle oil (LCO) and Iranian light crude oil (ILCO)). Two HCFA samples, a Ca-rich one (AD) and a Si-rich one (M), have been examined, so as to investigate the role of HCFA composition in its behaviour. The addition of HCFA to an oil spill results in the formation of a semi-solid oil–HCFA phase, allowing the quite total removal of oil from the water surface. HCFA’s oil sorption capacity in dry environment after 24 h is 0.7–0.9 g oil/g HCFA for AD and 0.5–0.6 g oil/g HCFA for M. HCFA’s behaviour, when added to an oil spill, necessitates the amelioration of its floating ability and affinity for oil and to this direction its hydrothermal treatment in an aqueous solution of sodium oleate (SO) under several conditions (time, temperature, HCFA:SO mass ratio, SO solution concentration, solution:HCFA ratio) has been applied. The treatment of the calcareous HCFA (AD) at 25 °C at a mass ratio HCFA:SO = 1:0.004 results in the formation of a cohesive semi-solid oil–HCFA phase, allowing the total removal of oil from the water surface, while the siliceous HCFA (M) requires a greater amount of SO (HCFA:SO = 1:0.5). The oil sorption behaviour of both HCFA and SO-modified HCFA seems to be related to the initial CaO content. During the treatment with SO, CaO is converted to calcite and calcium oleate, which contributes to the improvement of HCFA’s floating ability, due to its greater affinity for oil.     

Intensification of production of O/W emulsions using oscillatory woven metal micro-screen (WMMS)

Using high porosity woven metal micro-screen (WMMS), a novel design oscillatory emulsifier had been used for intensification of production of relatively narrow size distribution oil in water (O/W) emulsions. The average droplet size increased with increasing the dispersed phase flow and decreased with increasing both the oscillation frequency and amplitude. The emulsion polydispersity decreased with increasing both oscillation intensities as well as dispersed phase flux. Although the change in droplet size with oscillation was reasonably predicted using a simple torque balance model based on Stokes oscillatory flow, both the flow patterns and the surface phenomena are more complex, and the final droplet size is affected by interactions between different operating and physical parameters.     

Droplet breakage and coalescence models for the flow of water-in-oil emulsions through a valve-like element

An experimental and theoretical study was carried out regarding the evolution of droplet size distributions for the flow of water in oil emulsions through a valve-like element that simulates a mixing valve. The water droplets had diameters in the 0.1–100 μm range, which includes droplets that are either smaller or larger than the Kolmogorov length scale for the experimental conditions. Droplet breakage and coalescence models that can be used for this size range were proposed. A simplified population balance model was developed to interpret the experimental data and solved by the method of classes. The model parameters were estimated by the orthogonal distance regression method. The simplifying assumption of the model was verified by global optimization using a parallel implementation of the particle swarm optimization method. The agreement between simulated and experimental droplet volume size distributions was good. The predictions of the DeBroukere mean diameter, d₄₃, were unbiased with mean errors of 8%.     

聚酯装置酯化釜液位优化

利用反应动力学的原理 ,计算并调整第一酯化釜的停留时间 ,以达到合理控制酯化率。液位由 3 7 0 %降至 3 5 5 % ,停留时间减少 0 78h ,DEG含量由 0 74降至 0 70 ,耗热量明显降低 ,酯化脱水塔操作稳定性提高 ,馏出水中EG的质量分数由5 %降至 3 % ,为增容到 15 5t/d创造了条件。