胶凝原油颗粒运动规律和变形特征的数值模拟研究

发布时间：2019-05-29 01:58

【摘要】：胶凝原油颗粒水力悬浮输送技术是不加热原油集输的新突破,此方法将胶凝原油通过流态化处理装置掺入温度在凝点附近或低于凝点的水中,凝成大小不同的胶凝颗粒,依靠低温水携带凝固原油颗粒进行水力悬浮输送,从而大大降低输送过程中的热量损失,达到节能目的。在此过程中,水-胶凝原油两相流是一个非常复杂的动力系统,包含着多种非线性非平衡特征。胶凝原油颗粒既像固体有其确定的界面,又有屈服-假塑性流体的特性,其运动规律和变形特征影响水力悬浮输送的效果,掌握胶凝原油颗粒在水力悬浮输送过程中的运动规律和变形特征对推动该技术的发展有重要意义。本文采用理论分析和数值模拟计算相结合的方法,对水力悬浮输送过程中胶凝原油颗粒的运动规律和变形特征进行研究。(1)胶凝原油颗粒在水力悬浮输送过程的运动规律研究。连续相采用k??湍流模型,离散相采用DPM模型,采用课题组建立的水-胶凝原油两相流中胶凝原油颗粒的曳力系数模型计算曳力,使用UDF定义管段入口速度分布,利用Fluent软件进行模拟,得到不同条件下胶凝原油颗粒的运动轨迹和y方向速度,并对颗粒粒径、颗粒密度、释放位置、颗粒初速度和水流速度等影响因素进行分析。结果表明:胶凝原油颗粒粒径越小、密度越大,颗粒在垂直方向上达到的终端上浮速度越小,越不容易发生碰壁;水流速度越大,在相同时间内胶凝原油颗粒沿管长方向的经过位移越大,越不容易发生碰壁;颗粒的水平速度同步于流场的速度变化,主要受释放位置的影响,与颗粒的初速度无关。根据两颗粒运动轨迹交叉原理,忽略颗粒的加速过程,建立了两颗粒的碰撞模型,利用Matlab软件对该模型进行理论计算,并将计算结果与Fluent软件模拟结果进行对比。(2)胶凝原油颗粒在水力悬浮输送过程的变形特征研究。通过原油流变特性测试给出了胶凝原油的流变方程,采用VOSET方法追踪胶凝原油颗粒的界面变化,借助Fluent软件模拟了单个胶凝原油颗粒在水力悬浮输送过程中的变形,分析了原油温度、颗粒粒径、界面张力、水流速度等因素对变形度的影响。结果表明,胶凝原油颗粒变形受流场的剪切作用、原油的屈服特性和剪切稀释性共同影响,在剪切速率较小的中心区域,作用于胶凝原油颗粒的剪切应力难以克服其屈服值,很难发生变形;当颗粒接近壁面时,剪切力大于屈服值,在剪切稀释性的影响下,粘度降低,变形迅速增大;温度越低,粘度越大,变形度越小;界面张力阻止颗粒的变形,界面张力越小,颗粒变形度越大;胶凝原油颗粒的粒径越小,变形度越小。最后分析了无量纲数We对变形度的影响,We越大,惯性力相对于界面张力效应越明显,颗粒的变形度越大。
[Abstract]:The hydraulic suspension transportation technology of cementitious crude oil particles is a new breakthrough in unheated crude oil gathering and transportation. In this method, the cementitious crude oil is mixed into water near or below the freezing point by fluidization treatment device to form cementitious particles of different sizes. Hydraulic suspension transportation is carried out by carrying solidified crude oil particles with low temperature water, so as to greatly reduce the heat loss in the transportation process and achieve the purpose of energy saving. In this process, water-cementitious crude oil two-phase flow is a very complex dynamic system, which contains a variety of nonlinear non-equilibrium characteristics. Cementitious crude oil particles have not only the definite interface of solid, but also the characteristics of yield-pseudoplastic fluid. The movement law and deformation characteristics of cementitious crude oil particles affect the effect of hydraulic suspension transportation. It is of great significance to master the movement law and deformation characteristics of cementitious crude oil particles in the process of hydraulic suspension transportation in order to promote the development of this technology. In this paper, the method of combining theoretical analysis with numerical simulation is adopted. The movement law and deformation characteristics of cementitious crude oil particles in the process of hydraulic suspension transportation are studied. (1) the movement law of cementitious crude oil particles in the process of hydraulic suspension transportation is studied. The continuous phase adopts k? In the turbulence model, the discrete phase adopts the DPM model, and the drag coefficient model of the cementitious crude oil particles in the water-cementitious crude oil two-phase flow established by the research group is used to calculate the drag force. The inlet velocity distribution of the pipe section is defined by UDF and simulated by Fluent software. The trajectory and y direction velocity of cementitious crude oil particles under different conditions were obtained, and the influencing factors such as particle size, particle density, release position, initial particle velocity and flow velocity were analyzed. The results show that the smaller the particle size and the higher the density of cementitious crude oil particles, the smaller the terminal floating speed reached by the particles in the vertical direction, and the less likely it is to collide with the wall. The larger the flow velocity is, the greater the displacement of cementitious crude oil particles along the length of the pipe is in the same time, and the less likely it is to collide with the wall. The horizontal velocity of particles synchronizes with the velocity change of flow field, which is mainly affected by the release position and independent of the initial velocity of particles. According to the intersection principle of the motion trajectory of the two particles and neglecting the acceleration process of the particles, the collision model of the two particles is established, and the theoretical calculation of the model is carried out by using Matlab software. The calculated results are compared with those simulated by Fluent software. (2) the deformation characteristics of cementitious crude oil particles during hydraulic suspension transportation are studied. The rheological equation of cementitious crude oil is given by testing the Rheological properties of crude oil. The interfacial changes of cementitious crude oil particles are traced by VOSET method, and the deformation of single cementitious crude oil particles in the process of hydraulic suspension transportation is simulated by Fluent software. The effects of crude oil temperature, particle size, interfacial tension and flow velocity on deformation were analyzed. The results show that the deformation of cementitious crude oil particles is affected by the shear action of flow field, the yield characteristics and shear dilution of crude oil. In the central region with low shear rate, the shear stress acting on cementitious crude oil particles is difficult to overcome its yield value. It is difficult to deform; When the particles are close to the wall, the shear force is greater than the yield value. Under the influence of shear dilution, the viscosity decreases and the deformation increases rapidly, and the lower the temperature is, the greater the viscosity is, the smaller the deformation degree is. The interfacial tension prevents the deformation of particles, the smaller the interfacial tension is, the greater the deformation degree of particles is, and the smaller the particle size of cementitious crude oil is, the smaller the deformation degree is. Finally, the influence of dimensionless number We on deformation is analyzed. The greater the We, the more obvious the inertia force relative to the interfacial tension effect, and the greater the deformation degree of particles.
【学位授予单位】：东北石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE81

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