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轴向启旋式旋流器内油滴运动影响因素研究
Alternative TitleResearch on influencing factors of oil droplets motion in axial swirling hydrocyclone
顾成曦
Thesis Advisor许晶禹
2020-05
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype硕士
Degree Discipline工程力学
Keyword旋流场,离散相,实验测试,数值模拟
Abstract

随着我国油田资源开采进入中后期,油田采出液含水率不断升高,部分油田采出液含水率高达95%以上。高含水条件下,油相以液滴形式存在于采出液中,增加了采出液的处理成本和难度。目前,采出液处理主要分为预分离和含油污水处理两大环节,如果能够在上述环节中优化工艺,就能够有效降低油田的生产成本,提升经济效益。

离心分离法因其具体处理效率高、适用范围广等优势,在工业中应用较为广泛。根据来液进入方式的不同,液液旋流分离器可以分为切向入口式和轴向入口式两种,其中轴向入口式旋流器具有处理量大、重量轻、体积小等优点,适合在海上平台等一些特殊环境下使用。本文为提高轴向起旋式旋流器的分离性能,扩大其适用范围,对分离过程中存在的分散相颗的破碎、聚并和粒迁移等关键科学问题,采用实验测试和数值模拟相结合的方法进行了系统地研究。

实验研究中,搭建了应用于轴向启旋旋流分离器进行油水两相分离模拟的循环系统,分别采用压力传感器和马尔文在线粒度测量仪对旋流器各个关键位置上的压力和油滴粒径分布进行测量。然后,依据实验工况及测试结果对不同的湍流模型和多相流模型进行了对比分析,最终确定了以Eulerian模型、RNG k-ε模型和Luo模型的模拟方案。

通过研究得出,轴向入口旋流器在启旋装置前后的压降较大,压降大小与来液流量成正相关关系。经过启旋装置后,旋流器内的切向速度在距管道中心40mm处达到最大,最大切向速度约为混合来液流速的2.2倍。随着流量增加,分散相油滴的聚并效率先增加后下降,针对本文研究的结构尺寸,在来液流量为14~16m3/h时,聚并效率最高。这是由于流量的增加不仅提高了离心力,同时也增加了剪切力,造成大油滴破碎,在一定程度上降低聚并效率。增加来液中油相含率,可以提高油滴碰撞的概率,更易于形成大油滴;但同时增加油相含率也会使部分油滴在流动过程中发生乳化,增加分离难度。破乳剂有利于降低乳化现象,但效果受流速的影响,需要根据流速和含油率等参数对破乳剂进行筛选。油水界面张力以及油水间密度差的增大,有利于提高油滴碰撞效率以及碰撞概率,对油水分离有着积极作用。提高油相粘度会降低碰撞效率。这是因为粘性力会削弱离心力的作用,同时,提高来液中的油相粒度,可以显著提升旋流器内大油滴体积分数,提升油水分离效率。另一方面,通过改变导流片数目和锥段直径,开展了旋流器启旋装置结构参数对油滴聚并影响的研究,发现启旋装置导流叶片数为6片时,聚并率最大;启旋装置锥段直径为60mm时,旋流器内压降、切向速度幅值以及油滴聚结程度都最高。

上述研究成果可以为轴向启旋式旋流器的工业化应用和推广提供理论支持,有效提升原油开采中油水分离和污水处理的效率,实现经济化开采。

Other Abstract

With the development of oil field exploration in China, the water holdup of produced fluid in oil field keeps increasing, some may even exceed 95%. The oil exists in the produced fluid in the form of droplets, which increases the treatment cost and difficulty of production. At present, the treatment of produced liquid in crude oil exploitation is mainly divided into pre-process and oily sewage treatment. If the process can be optimized in procedures above, the production cost can be reduced and the economic benefit can be improved.

The centrifugal separation is widely used in industry due to its advantages of high specific treatment efficiency and wide application range, including a variety of liquid-liquid hydrocyclones. According to flow direction of the feeding fluid, the hydrocyclone can be divided into two types: tangential inlet type and axial inlet type. The axial inlet type hydrocyclone has the advantages of large capacity, light weight and small volume, which are suitable for application in some special environments such as offshore platforms. In order to improve the separation performance and scope of application of axial induced hydrocyclone, in view of the key scientific problems in the separation process of hydrocyclone, such as the crushing, coalescence and particle migration of dispersed phase particles, systematic analysis coupling experiment and CFD were conducted .

In the experimental study, a circulating system was built to simulate the oil-water two-phase separation of the axial induced hydrocyclone. The pressure and the droplet size distribution at each key position of the hydrocyclone were measured by the pressure sensor and the Marvin on-line particle size measuring instrument. Then, according to the experimental conditions and test results, different mathematic models of CFD were compared with tested data. Finally, in the numerical simulation study, method coupling Eulerian model, RNG –k-ε model and Luo model was used for simulation of the oil droplet coalescence and fragmentation.

The results showed that the pressure drop of the axial inlet hydrocyclone upstream and downstream the start-up device is large, and the pressure drop is positively related to the liquid flow. In downstream of the swirl generation device, the tangential velocity in the hydrocyclone reached the maximum at a distance of 40 mm from the center of the pipeline, and the maximum tangential velocity is about 2.2 times of the mixed flow velocity. With the increase of flow rate, the coalescence efficiency of dispersed phase oil drops increases first and then decreases. According to the structural parameter applied in this work, the coalescence efficiency is the highest when the flow rate is 14~16m3/h, which is mainly because the increase of flow rate not only improves the centrifugal force, but also increases the shear force, which will cause the large oil drops to break toreduce the coalescence efficiency. Increasing the oil concentration in the incoming liquid can increase the probability of oil drop collision and make it easier to form large oil droplets. However, increasing the oil content will also make some oil droplets emulsified in the flow process and thus make it difficult for separation. Adding the demulsifier is beneficial to reduce the emulsification of oil droplets. The effect of the demulsification is affected by the flow rate. In the specific application, the demulsifier should be selected according to the flow rate and oil content. The increase of oil-water interfacial tension and oil-water phase density difference are beneficial to the improvement of oil drop collision efficiency and collision probability, and has a positive effect on the oil-water separation. Increasing the viscosity of the oil phase will reduce the collision efficiencysince the viscosity will weaken the centrifugal force. At the same time, increasing the particle size of the oil phase in the liquid can significantly increase the volume fraction of large oil droplets in the hydrocyclone, and improve the oil-water separation efficiency.

Furthermore, by changing the number of guide vanes and the diameter of cone section, the influence of the structural paramters of hydrocyclone start-up device on oil droplet coalescence was carried out. The study showed that when the number of guide vanes was 6, the oil droplet coalescence rate is the largest; when the diameter of the cone section of the hydrocyclone is 60 mm, the pressure drop, tangential velocity amplitude and the degree of oil drop coalescence are the optimal.

The above research results of the oil droplet behavior in the hydrocyclone can provide theoretical support for the industrial application and development of the axial swing hydrocyclone. At the same time, above investigations can effectively improve the efficiency of oil-water separation and sewage treatment in crude oil production, and realize economic production.

Call NumberMas2020-015
Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/81919
Collection流固耦合系统力学重点实验室
Recommended Citation
GB/T 7714
顾成曦. 轴向启旋式旋流器内油滴运动影响因素研究[D]. 北京. 中国科学院大学,2020.
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