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IMECH-IR  > 流固耦合系统力学重点实验室(2012-)  > 学位论文
Title:
离散相油滴/气泡在旋流场中的行为特性研究
Alternative Title: Investigation on the Behavior Characteristics of Oil Droplets/ Bubbles in the Swirling Flow Field
Author: 刘硕
Abstract:

      油井产出液具有复杂的力学、物理和化学等性质,导致采出液分离成为非常复杂的工艺过程。自20世纪90年代起,国内很多油田生产进入中后期阶段。随着开采年限增长,油田含水率逐渐提高,部分油田含水率超过98%,让目前的采出液分离系统面临更大的压力,需要进行改进和优化。为了解决这些问题,一些油田在预分离工艺中采用管道式分离系统,通过旋流分离代替重力沉降。在这种背景下,研究含油率不低于0.1%的非稀疏相油滴/气泡在旋流器内的行为规律显得尤为重要。

        管道式分离技术根据启旋方式不同可以分为切向启旋和轴向启旋两种方式。切向启旋离心分离技术以水力旋流分离为主,目前已较为成熟。轴向启旋离心分离技术以导流片型分离为主,在结构复杂程度、压降和控制等方面优于切向启旋离心分离器。为了使导流片型分离技术应用于高含水率采出液预分离系统,本文通过理论分析、室内实验和数值模拟相结合的方式对旋流场中离散相(油滴或气泡)的行为特性进行了研究。

首先,系统地研究了油滴在导流片型旋流场中的行为特性。对旋流场中相含率在0.1%-6.0%的油水两相旋流场进行了实验研究。采用Malvern粒度仪在线测试了流场中油滴粒径分布,以导流片前后油滴粒径分布表征了油滴破碎聚并状况;采用电阻层析成像技术(ERT)获得旋流场截面相含率分布,表征了油滴在旋流场中的迁移规律。在数值模拟研究中,经过对比论证,采用欧拉-拉格朗日方法求解油水分散流,通过RNG k-ε湍流模型模拟连续相旋流场耦合离散相模型(DPM)模拟油滴在旋流场中的运动,同时通过Taylor相似模型(TAB)模型和O’rouke的聚并模型模拟油滴破碎与聚并过程。研究发现:旋流场中油滴在管道中心位置汇聚形成油核。油核中油相以离散相状态存在。油滴特征分布参数d50d32dmax间存在着线性关系,可以拟合出油滴分布参数aδ。不同尺寸的油滴在旋流场中破碎与聚并行为不同:小油滴在旋流场中聚并趋势明显;大油滴在15m3/h流量以下以聚并为主,在15m3/h-18m3/h入口流量区间受连续相剪切作用影响,出现破碎现象。旋流场中截面平均Sauter粒径沿下游逐渐增加,说明截面平均湍流能量耗散降低,湍流脉动更加有序。同时,油滴与旋流场之间存在着相互耦合作用,旋流场中的截面平均Sauter粒径与截面平均湍流能量耗散率在双对数坐标系下成线性关系。最后,通过无量纲旋流数和扩散数研究了旋流强度分布,确定了相收集装置的最佳区间。

        随后,通过理论、实验和数值模拟相结合的方式研究了气泡在导流片型旋流场中的行为特征。实验研究中,针对DN100管道内的气-液和气-CMC溶液在旋流场中气泡分布特征及气芯形状等展开了系统观察。采用Malvern粒度仪测试气泡粒径分布,采用ERT测试旋流场中截面相含率分布。基于旋流场气泡粒径分布测试结果,发展了Hinze的最大油滴粒径和Streiff的油滴d32粒径预测模型,使之适用于气泡特征分布参数的预测。在数值模拟研究中,基于前人研究成果,采用混合模型(Mixure)作为多相流模型,采用RNG k-ε湍流模型模拟连续相流场。研究发现:在入口流量低于20m3/h条件下,固定入口液相流量,由于相间滑移作用,气液两相旋流场中气芯宽度不随入口含气率增加而改变;入口流速高于2m/s时,入口含气率对气芯尺寸有影响;以增加表面活性剂的方式增加液相粘度、降低气液界面张力系数,在固定入口流量的条件下,气芯宽度受入口含气率影响。此外,通过研究气液两相旋流场的旋流强度分布发现,气芯的存在一定程度上降低了旋流场旋流强度。高入口流速(2m/s以上)旋流强度峰值高于实验工况(入口流量低于20m3/h),但衰减更快。

       最后,基于上述的研究结果,设计并加工了管道式导流片型气液分离器,并进行了相关实验验证。实验结果验证了数值模拟的计算,同时证实了导流片型气液分离设备在分离性能上的优越表现:除极端个别工况低于80%外,整体分离效率在95%以上。同时,通过实验测试发现,在入口液相流量较高、气相入口流量相对较低的工况下,分离设备表现更优,可以在较大的分流比范围内保持接近100%的分离效率。

English Abstract:

      Crude extractor has complex mechanical, physics and chemical properties, which makes it intricate technology for extractor separation. Since 1990s, as the extraction continuous in onshore and offshore fields, water content increases for years and even over 98%. It provides new challenges to crude process industry, which needs further optimization. In order to solve these problems, some oil field attempt pipe separation in produced liquid with high water content, which includes hydrocyclone instead of gravity settlers. Under this background, it becomes important to investigate behavior of none dilute drop/bubble (volume fraction larger than 0.1%) in the separation equipment.

      Pipe separation technology can be divided into axial swirling technique and tangential swirling technique according to swirling methods. The former one is widely applied as hydrocyclone separation with decades of evolution and modification. The later one is mainly vane type separation technology, with advantages of simple in structure, low pressure difference, and convenient in operation over hydrocyclone separation technique. In order to apply vane type separation technique to production liquid separation system with high water content, theoretical analysis, indoor experiment, together with numerical simulation were applied in this paper to investigate discrete phase (drop/bubble) behavior characteristics.

      At the beginning, drop behavior character in vane type swirling flow field is systematically investigated. Experimental research of oil-water multiphase flow in swirling flow field with inlet oil content ranging from 0.1% to 6.0% is conducted. Malvern particle size meter is applied to measure drop size distribution in the swirling flow field. The breakup and coalescence regularity are characterized through drop size distribution upstream and downstream vanes. Electrical resistance tomography is adopted to measure the phase concentration which characters drop transfer regularity in the swirling flow field. Through comparison and discussion, Eular-Lagrange method is applied to solve oil-water dispersion, with RNG k-ε model as continuous phase turbulent model coupling Discrete phase model (DPM) to simulate drop in swirling flow fields. Besides, Taylor analogy model (TAB) and O’rouke’s model are applied to simulate drop breakup and coalescence. Results show that: drops converge to be an oil core in the swirling flow field, with oil drop existing in the form of discrete droplet. Linear relationship exists among drop distribution character parameter d50d32 and dmax, from which drop distribution parameter a and δ can be fitted. Various sized drops have different breakup and coalescence regularity: small drops tend to coalescence; while large drops tend to coalescence in flow rate lower than 15m3/h, in flow rate between 15 to 18 m3/h, large drops tend to breakup instead due to shearing effect of continuous phase. Section Sauter diameter increases downstreamly, which means section average turbulent energy dissipation rate decrease, and the swirling flow field becomes more ordered. Meanwhile, coupling interaction exists between drops and continuous phase. Linear relationship exists in double logarithmic coordinate systems between section Sauter diameter and section average turbulent energy dissipation rate. At last, swirling intensity is characterized through swirling number and diffusion number, position for phase collection equipment was further elaborated.

      The next, theoretical analysis, experimental research and numerical simulation are conducted to investigate behavior character of bubble in swirling flow field. In experimental investigation, systematic observation is conducted to bubble size distribution and gas core shape in gas-water and gas-CMC solution of DN100 swirling flow field. Malvern particle size meter is applied for measurement of bubble size distribution and ERT for void fraction. On the basis of bubble size distribution measurement, Hinze’s model predicting maximal drop size and Streiff’s model predicting drop d32 are modified for prediction of bubble distribution characters. In the numerical simulation, on the basis of previous research work, the mixture model is applied as multiphase model, while RNG k-ε model as turbulent model. Results show that: for inlet flow rate lower than 20m3/h, when the liquid flow rate is fixed, gas core size has nothing to do with inlet gas concentration due to shearing between phases; when inlet velocity is higher than 2m/s, gas core size in the flowfield is influenced by inlet gas concentration under fixed inlet liquid flow rate; modifying liquid viscosity and surface tension coefficient through adding surface active agent, gas core size is sensitive to inlet gas concentration in fixed inlet flow rates. Besides, through research on the swirling intensity, gas core slashes swirling intensity. Under high inlet velocity (over 2m/s), swirling intensity is higher than that of experimental condition (inlet flow rate under 20m3/h) first and then attenuates faster.

      In the end, on the basis of research work above, vane type gas-liquid separator is fabricated and applied for experimental investigation. Experimental result confirms numerical simulation. Research validates excellent separation performance of vane-type equipment as well: except minor cases were under 80%, in most cases, the separation efficiency is over 95%. Meanwhile, through experimental investigation, it’s found that separator performs better (even nearly 100% separation efficiency) in high liquid flow rate-low gas flow rate conditions.

Degree Level: 博士
Issued Date: 2018-05-24
Degree Grantor: 中国科学院大学
Place of Degree Grantor: 北京
Supervisor: 许晶禹
Keyword: 油水分离 ; 气液分离 ; 导流片型旋流场 ; 非稀疏相 ; 行为特性
Major: 工程力学
Language: 英语
Other responsible: 中国科学院力学研究所
Content Type: 学位论文
URI: http://dspace.imech.ac.cn/handle/311007/73157
Appears in Collections:流固耦合系统力学重点实验室(2012-)_学位论文

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Recommended Citation:
刘硕. 离散相油滴/气泡在旋流场中的行为特性研究[D]. 北京. 中国科学院大学. 2018-05-24.
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