原油组成对原油管道结蜡规律的影响

利用旋转式动态结蜡装置,对不同组成的人工油样(胶质和沥青质含量不同或蜡含量不同)进行了不同条件下的实验研究.通过对管壁沉积物取样并利用差式扫描量热法(DSC)和四组分法进行分析,探究了不同原油组成对结蜡的影响规律.结合胶质和沥青质在结蜡过程中的作用机理,发现胶质和沥青质的存在虽然总会削弱蜡分子的迁移动力,阻碍蜡分子的沉积,但在含量较小时会协同蜡分子的沉积作用,而当含量较大时会以粘壁的形式附着于管壁.对蜡含量不同原油的结蜡规律研究发现:原油所含蜡分子的碳数越高,结蜡层中的蜡含量就越少.但由于碳数较高的蜡分子具有相对较长的碳链,更容易与原油中的胶质和沥青质发生共晶作用,故更易与胶质和沥青质一起沉积于壁面.     

Study on wax precipitation characteristics of wax deposit in pipes

Wax deposit properties are a significant concern in pipeline pigging during waxy crude oil transportation. In the present work, the impacts of flow conditions and oil properties on the wax precipitation characteristics of wax deposits are investigated. A flow loop apparatus was developed to conduct wax deposition experiments using four crude oils collected from different field pipes. The differential scanning calorimetry (DSC) technique was employed to observe the wax precipitation characteristics of crude oil and wax deposit. The results show that the wax content and the wax appearance temperature (WAT) of the deposits increase with shear stress and radial temperature gradient, and decrease with radial wax molecule concentration gradient near the pipe wall. The DSC tests on the wax deposits revealed that the deposit wax content is strongly correlated to the oil wax content. Furthermore, an empirical correlation was developed to predict the wax content and the WAT of the wax deposit. Verification of the empirical correlation using the different oils indicated that the average relative error of the wax content prediction and average absolute error of WAT prediction were 13.2% and 3.6°C, respectively.     

Modelling wax deposition of diesel in sequential transportation of product oil pipeline using optimized back propagation neural network

Contamination of gasoline by wax deposit of diesel is a severe problem in sequential transportation of product oil pipelines in cold areas. However, most works on wax deposition are focused on crude oil. In response, this paper aims to investigate wax deposition from a unique perspective of diesel oil in sequential transportation. To this end, a cold finger apparatus was designed and constructed. It is found that the wax deposition rate of diesel oil increases with oil temperature and wax content, and decreases with cold finger temperature. A non-monotonic variation trend is observed against shear stress. To predict diesel wax deposition rate, a back propagation (BP) neural network optimized by bald eagle search (BES) algorithm is proposed. Grey relational analysis (GRA) is employed to get the highly relevant factors as input parameters of the developed model. Prediction accuracy and generalization ability of the BES-BP model is experimentally verified. This work will be helpful to schedule the transportation program of product oil to avoid contamination of gasoline by diesel wax deposit.     

沥青质引发的蜡油体系结蜡层分层现象及分层规律

利用自主研发的Couette结蜡装置,对蜡含量相同的油样1(不含沥青质)和油样2[含0.75%(质量分数)沥青质]进行结蜡实验,并研究其结蜡层的分层现象和分层规律。通过对油样1和油样2结蜡表层和底层的宏观形貌、DSC放热、析蜡量、蜡晶微观形貌的分析发现:油样1结蜡层无明显分层现象,而油样2结蜡层分层现象明显,沥青质的加入导致了结蜡层的分层。与结蜡表层相比,油样2结蜡底层的析蜡点、蜡含量与沥青质含量显著升高,蜡晶形貌发展为致密的类球状大蜡晶。油样2结蜡表层沉积量随壁温的升高、油壁温差和转速的增大而减小;结蜡底层沉积量随壁温升高而减小,随油壁温差和转速的增大而增大;总的蜡沉积量随壁温的升高和转速的增大而减小,随油壁温差的增大先增大后减小。     

Effect of polyethylene pipe on wax deposition under different temperature and flow rate conditions

Wax deposition is an important but troublesome boulder in petroleum industry that has always plagued pipeline engineering operators. In this study, wax deposition in the polyethylene pipes has different behaviors comparing wax deposition in stainless steel pipes such as smaller weight of wax deposits and lower wax content. After wax deposition experiments, some important parameters, including diffusivity and temperature gradient, were measured and calculated to explore the differences between two material pipes. Moreover, those factors can make a significant impact on radial mass flux. A series of results in polyethylene pipes suggests that higher diffusivity enhances diffusion flux of wax in the radial direction. But it was found that radial concentration gradient accounted for a larger proportion. These factors are the relationship of competition and cooperation and the combination of them results in different performances of wax deposition between polyethylene and stainless steel pipes.     

油水两相流蜡沉积研究进展

蜡沉积研究中,油水两相蜡沉积的研究已成为研究重点,但对此领域的研究还处于起步阶段。本文系统阐述了国内外蜡沉积研究的发展现况,对近些年蜡沉积机理研究的新进展--剪切剥离以及老化机理作了分析。介绍了冷板、冷指实验装置和环道实验装置,对国内外学者进行的蜡沉积实验情况作了概述。介绍了国内外单相原油与油水两相蜡沉积动力学模型的研究现状,在单相模型基础上对Couto油水两相模型和Bruno改进模型进行了描述。今后的研究应以蜡沉积机理与预测模型为重点,分析油水两相流蜡沉积的影响因素,这对于缓解输油管道蜡沉积问题,增强管道输送能力具有现实意义。     

蜡沉积厚度随时间变化规律的模型研究

在分析蜡沉积过程的基础上, 基于一定的假设条件, 建立了蜡沉积厚度随时间变化的模型。通过提取蜡沉积厚度随时间变化曲线的数据, 拟合了模型中的待求常数, 并对模型计算值和实验值的吻合程度进行了分析。结果表明:对数模型、指数模型及动平衡模型均能反映蜡沉积厚度随时间的变化趋势, 对数模型与实验值的吻合程度最好;指数模型和动平衡模型所得的结果与实验结果的吻合程度相当, 在沉积初期, 指数模型的吻合程度高于动平衡模型, 但当沉积时间接近实验规定时间时, 动平衡模型的吻合程度高于指数模型;所建立的模型简单实用, 能够反映沉积厚度随时间变化的增长快慢趋势, 不同实验数据应用时仍需对各模型的计算精度进一步验证, 从而使得选用模型能更好地符合实际。     

Influence of polymeric additives on paraffin wax crystallization in model oils

Wax deposition, precipitation, and gelation make the transport of crude oil in pipelines challenging. The effect of several ethylene copolymers, and small molecules with a long alkyl chain, on wax formation was investigated for n-C₃₂H₆₆ in decane and de-aromatized white oil. Addition of a small amount of EVA (ethylene-co-vinyl acetate) copolymers delayed nucleation by reducing the onset temperature and the wax appearance temperature. They modified the wax crystal-structure and morphology from large plates to tiny particles by adsorbing to the wax surfaces and inhibiting growth. Viscosity and the pour-point were improved by inhibiting the formation of large aggregates. It was demonstrated that the content of vinyl acetate groups in EVA copolymers affected wax crystallization. The small molecules, propylene copolymers, and ethylene copolymers with ethyl acrylate, maleic anhydride, and ethylene glycol showed a weak inhibiting effect. The effect of wax inhibitors was determined by the content and by the type of structure-disturbing groups in the copolymers.     

An experimentally validated heat and mass transfer model for wax deposition from flowing oil onto a cold surface

A transport model is proposed for wax deposition onto a cold finger from flowing wax-containing oils. The model solves transient energy and mass balances simultaneously for a reversible first-order kinetic rate for precipitation of pseudo-single-component wax, and the effects of yield stress using a critical solid wax concentration to withstand flow-induced stress at the deposit-fluid interface. The model can predict the time evolution of the deposit thickness, and the spatial and temporal evolution of temperature and wax concentration as validated using cold finger experiments. It was found that for high wax content oils, deposit thickness growth is dominated by heat transfer. For low wax content oils that are unable to gel, the thickness growth is slow and accompanied by occasional sloughing. Regardless of the mechanism controlling the growth, mass transfer cannot be neglected as wax diffusion into the deposit continues to take place after the deposit has stopped growing.     

A fundamental model of wax deposition in subsea oil pipelines

Wax deposition in subsea pipelines is a significant economic issue in the petroleum industry. A mathematical model has been developed to predict the increase in both the deposit thickness and the wax fraction of the deposit using a fundamental analysis of the heat and mass transfer for laminar and turbulent flow conditions. It was found that the precipitation of wax in the oil is a competing phenomenon with deposition. Two existing approaches consider either no precipitation (the independent heat and mass transfer model) or instantaneous precipitation (the solubility model) and result in either an overprediction or an underprediction of deposit thickness. By accounting for the kinetics of wax precipitation of wax in the oil (the kinetic model), accurate predictions for wax deposition for both lab‐scale and pilot‐scale flow‐loop experiments with three different oils were achieved. Furthermore, this kinetic model for wax precipitation in the oil was used to compare field‐scale deposition predictions for different oils. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

采用泰勒分散法测量蜡分子扩散系数

蜡分子扩散系数是蜡沉积预测模型中非常重要的物性参数。为测量蜡分子（高碳数正构烷烃）在液相体系中的分子扩散系数,建立了基于泰勒分散法的扩散系数测量装置,并对装置操作注意事项进行了详细探讨。采用该装置测量了丙酮水溶液、n-C₆+n-C₇溶液以及甲醇水溶液中溶质在溶剂中的分子扩散系数,以文献值对测量值进行校验,验证了装置的可靠性。分别以n-C₁₈、n-C₂₀、n-C₂₂、n-C₂₄、n-C₂₆为溶质,以n-C₇为溶剂,在不同温度、浓度下测量蜡分子在液相体系中的分子扩散系数,并将实验测量值与Hayduck-Minhas关系式计算值进行比较。结果表明：蜡分子扩散系数随温度升高而线性增大,随溶液中蜡分子摩尔分数的增大而以指数形式减小;在相同条件下,高碳数正构烷烃的分子扩散系数低于低碳数正构烷烃的分子扩散系数。采用Hayduck-Minhas关系式的计算结果比实验测量结果平均小50%,应用于蜡沉积预测时,将低估蜡分子扩散质量流。     

Composition and physicochemical properties of corn wax

Corn wax, as a kind of vegetable wax, is a by-product of the corn oil industry. In this study, the corn wax was obtained from the corn oil refineries and purified by solvent defatting and bleaching. The composition and physicochemical properties of corn wax were studied to provide theoretical guidance for the production and application of corn wax. The results showed that the purity of corn wax was higher than 95%, and the corn wax ester ranged from C42 to C58, with C46, C44, and C48 being predominant. The carbon number of fatty acids was in the range of 16–30, with a higher proportion of C20, C22, and C24. The fatty alcohols varied from C20 to C32 and were dominated by C22, C24, C30, and C23. The physicochemical properties of corn wax were also determined and compared with other vegetable and animal waxes to get a more comprehensive understanding of corn wax. The results showed that the water content, iodine number, saponification number, and melting point of corn wax were 0.03 ± 0.01%, 6.77 ± 0.85 g/100 g, 74.31 ± 3.49 mg/g and 77.28 ± 7.89°C respectively. Corn wax was a green and healthy natural resource, which has great application potential in food, health care, and medicine.     

Studies on the crystal growth of rice bran wax in a hexane medium

Rice bran oil (RBO) is well known for its high wax content (2–4%). A good separation of waxes must be ensured through the formation of crystals that can be removed with a minimal retention of oil to maintain high yields of refined oil. In the present study, the form and size distribution of RBO wax crystals were investigated using a laser diffraction technique. An attempt was made to study the effect of cooling on growth and size distribution of RBO wax crystals in hexane medium, and it showed that high cooling rate and low temperature induces the formation of a great number of small nuclei. In addition, experiments were performed to evaluate the effect on the growth of wax crystals of successive additions of gum and pure TG to the medium. The entire experiment was designed to optimize the temperature and incubation time of wax crystallization to facilitate the efficient separation of wax from crude RBO-hexane miscella using membrane technology.     

Storage of sunflower‐seeds: variation on the wax content of the oil

Storage conditions of oil seeds before industrial extraction might influence the quality of the crude oil. The objective of this work was to study the influence of sunflower seed storage conditions (temperature and time) on the quality of the resulting oil in terms of its wax content and composition. Sunflower seeds were stored under different conditions, 10, 21 and 37 °C, in sealed recipients. Extractions of the seeds with hexane were made to obtain the oil at different storage times. The amount of oil extracted (25–40%) showed no significant differences with storage conditions. Wax content of the samples was determined with two different methods (laser polarized turbidimetry and microscopy), and results showed that wax concentration increased with storage conditions (time and temperature). Composition of wax components, determined using capillary gas chromatography, during storage was approximately constant for C₃₅–C₃₉ and showed significant differences for C₄₀–C₄₈ components. Waxes with high carbon number cause more turbidity than waxes with low carbon number, due to their higher melting point, resulting in a low‐quality crude oil and therefore in variations in processing conditions during the oil refining. According to the data showed in this study, seed storage at low temperatures during short periods of time may be the more adequate conditions to obtain high‐quality oil.     

聚丙烯酸十八酯降凝剂对合成蜡油结蜡特性影响的研究

采用自主研发的Couette结蜡装置研究了聚丙烯酸十八酯（POA）降凝剂对合成蜡油体系结蜡特性的影响。通过对结蜡层表面样（远离结蜡筒）和底部样（靠近结蜡筒）的宏观观察、DSC放热、气相色谱及蜡晶微观结构的分析发现：POA的加入降低了蜡油体系的结蜡速率,加快了蜡油体系的老化速率,且在一定浓度范围内（50～200 μg·g^-1）导致了径向不均质蜡沉积结构的形成,从结蜡层表面到底部含蜡量逐渐升高,但在较高加剂浓度（400 μg·g^-1）时径向不均质蜡沉积结构消失;POA的加入使得结蜡层表面样和底部样的临界碳数（CCN）都由C₂₄升高到C₂₅,但结蜡层底部样与表面样相比低碳数正构烷烃（≤ C₂₅）有所减少,高碳数正构烷烃（≥ C₂₆）有所增加;随着油样中POA浓度的增大,结蜡层表面样与底部样的蜡晶形貌由针状蜡晶逐渐转变为片状蜡晶,且蜡晶尺寸逐渐变大,结构更为致密。     

A fundamental wax deposition model for water‐in‐oil dispersed flows in subsea pipelines

Water‐in‐oil dispersions frequently form in subsea oil pipeline transportation and their presence affects the wax deposition rate in subsea pipelines. A fundamental model for wax deposition on the wall of water‐in‐oil dispersed phase flow pipelines has not been developed. Dispersed water droplets can affect the heat and mass transfer characteristics of wax deposition and alter the deposit growth rate. In this study, wax deposition from water‐in‐oil dispersed flows is comprehensively modeled using first principles of heat and mass transfer. The role of the dispersed water phase on the heat and mass transfer aspects of wax deposition is analyzed. The developed model predicts different effects of the water volume fraction and droplet size on the wax deposition rates in laboratory flow loop experiments and in field scale wax deposition processes. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4201–4213, 2017     

基于最小二乘支持向量机的蜡沉积速率预测

考虑蜡沉积影响因素的复杂性和最小二乘支持向量机在小样本预测方面的优势,基于最小二乘支持向量机预测的原理,通过优化最小二乘支持向量机的参数,建立了蜡沉积速率的预测模型,并对蜡沉积速率进行了预测。结果表明：该方法在样本数量较小时仍具有较高的精度,蜡沉积速率的预测值和实验值的吻合程度较好;最小二乘支持向量机建模时可以得到直观的函数表达式,而神经网络方法却不能得到模型的显式表达式,因此该方法具有明显的优势;应用径向基核（RBF）作为核函数时,不同初值的正则化参数?和核函数宽度?对预测结果具有较大影响,使用时应合理选择。     

Investigation of thickness and wax content of wax deposits in polyethylene pipe using a flow loop

In this study, the thickness and wax content of wax deposits were found to be thinner and lower in the polyethylene (PE) pipe than in the stainless steel (SS) pipe using a flow loop apparatus. The diffusivity of wax, radial thermal gradient, and wax precipitation rate in the PE and SS pipes were calculated and compared. It was found the diffusivity of wax in the PE pipe was higher and tended to enhance the wax deposition in the PE pipe, while the radial thermal gradient and wax precipitation rate were lower in the PE pipe and had the opposite effects. These factors are shown to be comparable with each other and the effect of the thermal gradient dominates the mass flux of wax from bulk to the oil-deposit interface and into the deposits finally, thus causing differences in thickness and wax content of deposits between the PE and SS pipes.     

Settling and re‐entrainment of wax particles in near‐gelling systems

Under near‐gelling conditions, the precipitated wax particles can settle down due to gravity and form a bed at the bottom of the pipeline. During restart, the settled waxy bed can increase the pressure drop significantly, and the necessity for pigging and/or addition of chemicals has to be determined to re‐entrain settled wax particles. A laboratory‐scale flow loop, first of its kind, has been built and used to understand the settling and re‐entrainment behavior. The experimental results confirmed the settling of precipitated wax in a pipe under quiescent conditions when the oil temperature falls between wax appearance temperature and pour point. During restart, complete re‐entrainment was attained after reaching a critical flow rate. Solid transport models were able to predict reasonably good results in agreement with experiments. This work emphasizes the importance of understanding the behavior of waxy crude oil during production shutdown and design appropriate startup strategies. © 2017 American Institute of Chemical Engineers AIChE J, 64: 765–772, 2018     

原油中石蜡沉积的热力学模型

1 INTRODUCTION Crude oils are mixture of light and heavy hydro-carbons. The components in crude oils can be classi-fied into paraffin, naphthene and aromatic compo-nents[1]. Though the non-n-alkane components in crude oils are minor, it is essential to consider the in-fluence of non-alkane components in the model since their properties, such as fusion temperature and fusion enthalpy, are much different from paraffin. The solu-bility of each component of crude oils depends on the temperatu…