天然气液烃输送管网仿真理论与技术研究

发布时间：2018-06-27 22:17

本文选题：天然气液烃 + 气液两相流　；参考：《西南石油大学》2014年博士论文

【摘要】：天然气液烃(Natural Gas Liquids, NGL)的主要成分是乙烷、丙烷、丁烷、凝析油及其混合物,是重要石油化工原料与燃料,具有较高经济价值和广阔应用前景。凝析气、页岩气和页岩油中含有非常丰富的NGL成分,脱除NGL不仅可以降低其烃露点,还可以提高气田的经济效益。管道是长距离、大量输送NGL最为经济的方式之一。然而,沿线温度、压力的变化,可能会使NGL汽化,导致管道中出现气液两相流动。在气液两相流状态下,气液相的比例和组成、黏度、密度等基础物性参数会不断的发生变化,并反过来影响管道的水力、热力参数分布规律。如果多条NGL管道相互连接,形成了复杂的NGL管网,将会使流动参数的预测和分析变得更加困难。针对上述问题,基于流体力学、热力学和传热传质学理论,采用实验、理论和数值模拟相结合的方法,研究了NGL的基础物性参数变化规律、汽化规律、气液两相流动规律,探索了复杂NGL管网系统仿真技术,开发了NGL气液两相流管网仿真软件,为NGL管网的设计、运行和管理提供了理论和技术支撑。具体的研究内容和取得的主要成果如下： (1)结合NGL气液两相输送管道中气液两相共存的特点,分析了SRK、PR、PRD、 PRSV2、PR-Twu、PRN、PRG、PPR78、VTPR共9种立方型状态方程,对于天然气露点及液烃密度预测的准确性；针对现有方法的局限性,提出了将基团贡献法(用于二元交互作用系数计算)和体积平移法相结合的PR状态方程改进新思路,建立了适用于NGL的VTPPR78状态方程,并验证了该方程的准确性。以此为基础,建立了NGL的泡点、露点、焓、熵、热容等基础物性参数计算模型。基于VTPRμ状态方程,建立了NGL气液两相黏度计算模型。考虑到化学位、逸度和表面张力之间的热力学关系,建立了NGL表面张力计算模型。 (2)基于气液两相流动的Navie-Stokes方程、RPI沸腾模型、VOF(Volume of Fluid)模型和CFD技术,开展了NGL汽化机理和气泡动力学的研究,并建立了气泡生成与发展过程的数值模拟模型；结合文献提供的实验数据,验证了数值模拟模型的可靠性。基于实验数据和数值模拟结果,研究了NGL气泡的脱离直径、起飞直径、脱离频率和活化核心密度等气泡动力学特征参数理论计算模型。 (3)以一维不稳定流动方程为基础,基于集中空穴假设,建立了低含气率NGL输送管道数学模型,并采用特征线法和有限差分法对模型进行了求解；基于NGL气泡起飞直径、脱离频率和活化核心密度,实现了对低含气率NGL输送管道中汽化速率的定量计算。 (4)以Navie-Stokes方程为基础,结合一维管道流动的特点,并针对NGL汽化过程中气液两相温度不相等的情况,建立了非平衡热力学状态下的NGL管道气液两相双流体模型。基于特征值理论,研究了NGL双流体模型的数学特征,指出在管输条件下：①当气液两相速度相等时,双流体模型的类型为双曲型；②当气液两相速度不相等时,双流体模型的类型为抛物型；③当气液两相流退化为单相流动时,相应的模型也退化为单相流动控制方程组,其类型为双曲型。采用Barne方法进行流型判别；建立了气泡流、分层流、段塞流和环状流下的剪切应力闭合关系式。针对模型的特点,研究了基于有限体积法的双流体模型离散方法。 (5)考虑到NGL管网多元件、多节点的特点和物理结构上的多样性,采用节点一元件关联矩阵法,实现了对任意管网物理结构的数学描述。在此基础上,结合管道元件,非管元件和节点的数学模型,建立了能够适用于任意结构管网的NGL气液两相流系统仿真模型。针对模型的高度非线性特点,研究了模型的线性化方法、以及基于LU分解法和阻尼Newton-Raphson法的模型求解方法。 (6)基于(1)～(5)的理论研究成果和西南石油大学“管网仿真系统PES”平台,开发了具有完全自主知识产权、能够适用于任意结构形式管网的“液烃输送管道仿真软件NGLPES"软件。NGLPES模拟的塔里木液化气管道的流量与实测值之间的平均绝对偏差为0.0845t/h,相对偏差为0.956%,温度的平均绝对偏差为1.29℃。仍基于塔里木液化气管道的基本参数,在动态工况下,NGLPES模拟的压力值与OLGA软件模拟值之间的平均绝对偏差为58.5kPa,持液率的平均绝对偏差为0.03。通过仿真实例,进一步验证了NGLPES对于复杂枝状、环状气液两相流管网仿真的适应性。 NGLPES已经获得了国家软件著作权,著作权登记号2014SR043986,并在中石油塔里木油田分公司油气运销部得到了实际应用。
[Abstract]:The main components of natural gas and liquid hydrocarbons (Natural Gas Liquids, NGL) are ethane, propane, butane, condensate, condensate oil and their mixtures. It is an important petrochemical raw material and fuel. It has high economic value and wide application prospect. Condensate gas, shale gas and shale oil contain very rich and rich NGL components. Removing NGL can not only reduce the dew point of hydrocarbon, but also can reduce its hydrocarbon dew point. In order to improve the economic benefit of the gas field, the pipeline is one of the most economical ways to transport NGL in a long distance. However, the change of temperature and pressure along the line may cause NGL vaporization and lead to gas-liquid two-phase flow in the pipeline. In the state of gas-liquid two-phase flow, the basic physical parameters, such as the proportion of gas-liquid phase, formation, viscosity, density and other basic physical parameters will continue to occur. Change and in turn affect the hydraulic and thermodynamic parameters distribution of the pipeline. If multiple NGL pipes are connected to each other, a complex NGL pipe network will be formed, which will make the prediction and analysis of the flow parameters more difficult.
In view of the above problems, based on the theory of fluid mechanics, thermodynamics and heat and mass transfer, the change law of the basic physical parameters of NGL, the law of vaporization and the law of gas-liquid two phase flow are studied by the method of experiment, theory and numerical simulation. The simulation technology of complex NGL pipe network system is explored, and the simulation software of NGL gas and liquid two phase flow network is developed. It provides theoretical and technical support for the design, operation and management of NGL pipe network.
The specific research contents and main achievements are as follows:
(1) combining the characteristics of gas-liquid two phase coexistence in NGL gas and liquid two phase transport pipeline, the 9 cubic equation of state, which are 9 kinds of cubic equation of state, for natural gas dew point and liquid hydrocarbon density, are analyzed for SRK, PR, PRD, PRSV2, PR-Twu, PRN, PRG, PPR78 and VTPR, and the group contribution method (used for the interaction coefficient meter of two yuan) is put forward in view of the local limit of the existing methods. A new idea to improve the PR equation of state combined with the volume translation method is proposed. The VTPPR78 equation of state suitable for NGL is established and the accuracy of the equation is verified. Based on this, a calculation model for the basic physical parameters of NGL is established, such as the bubble point, dew point, enthalpy, entropy, heat capacity and so on. Based on the VTPR Mu state equation, the calculation model of NGL gas and liquid two phase viscosity is established. Taking into account the thermodynamic relationship between degree of change, fugacity and surface tension, a NGL surface tension calculation model is established.
(2) based on the Navie-Stokes equation of gas-liquid two-phase flow, RPI boiling model, VOF (Volume of Fluid) model and CFD technology, the study of NGL vaporization mechanism and bubble dynamics is carried out, and the numerical simulation model of bubble generation and development process is established, and the reliability of the numerical simulation model is verified based on the experimental data provided by the literature. The experimental data and numerical simulation results are used to study the theoretical calculation model of the bubble dynamics, such as the diameter of the NGL bubble, the take-off diameter, the separation frequency and the density of the activation core.
(3) based on the one-dimensional unsteady flow equation and based on the centralized cavitation hypothesis, a mathematical model of the low gas bearing rate NGL pipeline is established. The model is solved by the characteristic line method and the finite difference method. Based on the NGL bubble take-off diameter, the vaporization rate of the low gas bearing rate NGL pipeline is realized by the separation of the frequency and the density of the activation core. The quantitative calculation.
(4) based on the Navie-Stokes equation, combined with the characteristics of one dimensional pipe flow, and aiming at the unequal gas and liquid two phase temperature in the NGL vaporization process, a two-phase two-phase fluid model of the NGL pipeline under the state of non equilibrium thermodynamics is established. Based on the eigenvalue theory, the mathematical characteristics of the NGL double fluid model are studied, and it is pointed out under the tube transport condition. When the velocity of gas-liquid two phases is equal, the type of two fluid model is hyperbolic type. When the velocity of gas-liquid two phases is not equal, the type of the two fluid model is parabolic. When the gas-liquid two phase flow is degraded into single phase flow, the corresponding model is also degenerated into a single phase flow control equation group, and its type is hyperbolic type. The Barne method is used. The flow pattern discrimination is used to establish the relationship between the bubble flow, the stratified flow, the slug flow and the shear stress closure under the annular flow. In view of the characteristics of the model, a two fluid model discrete method based on the finite volume method is studied.
(5) considering the characteristics of multi element and multi node in NGL pipe network and the diversity of physical structure, the mathematical description of physical structure of any pipe network is realized by using the node one element correlation matrix method. On this basis, the NGL gas liquid two, which can be applied to any structure pipe network, is established in combination with the mathematical model of pipe element, non tube element and node. In view of the highly nonlinear characteristics of the model, the linearization method of the model and the method of solving the model based on the LU decomposition method and the damping Newton-Raphson method are studied.
(6) based on the theoretical research results of (1) ~ (5) and the "PES" platform of the "network simulation system" of the Southwest Petroleum University, the average between the flow rate and the measured value of the Tarim liquefied gas pipeline, which has a complete independent intellectual property right and can be applied to a "liquid hydrocarbon conveying pipeline simulation software NGLPES", which can be applied to any structure pipe network, is developed. The absolute deviation is 0.0845t/h, the relative deviation is 0.956%, the average absolute deviation of the temperature is 1.29 C. It is still based on the basic parameters of the Tarim liquefied gas pipeline. Under the dynamic condition, the mean absolute deviation between the pressure value of the NGLPES simulation and the simulated value of the OLGA software is 58.5kPa, and the mean absolute deviation of the liquid holdup rate is 0.03. through the simulation example. One step verifies the adaptability of NGLPES to the simulation of complex branch and annular gas liquid two phase flow network.
NGLPES has obtained the national software copyright, the copyright registration number 2014SR043986, and has been applied in the oil and gas marketing department of PetroChina Tarim Oilfield Branch.
【学位授予单位】：西南石油大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TE832

【参考文献】