LNG真空多层绝热管道输送及安全性研究

发布时间：2018-06-04 12:03

本文选题：LNG + 管道输送　；参考：《中国石油大学(华东)》2015年博士论文

【摘要】：随着我国液化天然气(LNG)进口量的增加,卸载后LNG的输送研究也应运而生。与LNG气化后管输相比,在液态下直接管输不仅能够保有其冷量加以更合理的利用和在城市输气管网中更好的发挥调峰功能,而且在相同质量流量下,液态管输过程中所需要提供的动力要比气态管输小很多。然而,在LNG的管道输送中,采用可靠的绝热形式以及建立科学的管输模型是保证LNG液态输送平稳性和安全性的关键;本论文围绕这两方面,采用理论分析、数值模拟和实验研究相结合的方法对LNG的管道输及安全性输送进行了系统的深入研究,主要完成了以下研究内容:(1)进行了LNG热物性质的计算,在LNG的管道输送中要充分考虑到热力学和迁移性质的影响。采用LKP方程编制了LNG多组分系统相平衡的计算程序,分别分析了不同压力下的LNG密度、比热容、粘度和导热系数随温度的变化规律。结果表明在液相区LNG的密度、比热容、粘度和导热系数受压力的影响非常小,而随温度的响应比较敏感;在临界点附近相关的热物性质参数随压力和温度的变化较为剧烈;在气相区,天然气的相关热力学参数受压力变化的影响增大,而对温度响应有减弱的趋势。(2)对于LNG输送管道能够采用的堆积绝热、真空绝热、真空多层绝热形式进行传热过程分析和热阻构成的讨论,并进行了比选。在绝热性能上真空多层绝热略优于真空绝热,真空绝热优于堆积绝热;若选用单纯的真空绝热,一旦在LNG管道输送的过程中真空度丧失,则绝热性能将会大幅度下降,故在LNG的管输中采用了对真空度要求不高的、绝热性能好的真空多层绝热。在二维稳态假设前提基础上,对真空多层绝热管道进行了柱坐标系下的传热机理分析,包含有反射屏间的辐射换热、气体分子的导热和反射屏间固体的导热;通过编制程序计算得到了不同真空度量级下真空多层绝热管道各层的温度和径向上的热流密度值。(3)将给定组分下LNG进行了相态划分,分为过冷相态、密相和超临界相态;给出了LNG在管输送过程的数学模型,在真空多层绝热管道中LNG管输过程为径向和轴向上的二维稳态过程,给出了流场和温度场的边界条件;得到了LNG在轴向上的温度变化规律。由于采用绝热性能较好的真空多层绝热管道输送,在输送方向上LNG的温升并不迅速,故提出长距离管输条件是要满足在管输过程中任一截面上的温度要低于其截面压力所对应饱和温度,即过冷度以保证过冷态。在此基础上提出了液态最远输送距离的计算方法,通过编制程序得到了LNG在给定管道入口温度的条件下的最远输送距离,讨论了其影响因素入口压力、管内壁热流密度、管内径和输量对最远输送距离越的影响。(4)进行了管输过程绝热安全性的分析。在LNG管道的输送过程中内管破损和外管破损的出现会使得LNG输送过程中真空度逐渐丧失,使绝热性能下降、LNG的过冷态丧失。分别分析了内管破损、外管破损传热过程的变化。在基于假设的前提下分析了管道夹层环形空间的自然对流换热对整个换热的影响,建立了传热模型。通过编制程序分析得到了真空管道外壁温度、绝热材料的层数、绝热材料的导热系数和包扎密度对绝热丧失后热流密度的影响。结果表明,外管壁面温度越高,漏热量越大;绝热材料的层数越多,漏热量越小;包扎越紧实、密度越大,漏热量越大;间隔物热导率越小,漏热量越小。(5)对LNG真空多层绝热管道的真空丧失过程进行了实验研究,采用液氮代替LNG,在不同绝热材料层数下测得了真空丧失后的环形空间的压力、夹层材料壁面温度和漏热率,并在此基础上采用分子动力学的方法对内壁裂纹扩展进行了微观研究,将实验数据和模拟结果进行了分析比对,其结果变化趋势吻合较好,为LNG长距离管道输送的平稳和绝热安全性提供了有力保障。
[Abstract]:With the increase of the import of liquefied natural gas (LNG) in China, the transport research of LNG after unloading has come into being. Compared with the LNG after gasification, the direct pipe transport in liquid can not only protect its cooling capacity more rationally and better play the peak function in the urban gas pipeline network, but also the liquid pipe is transported under the same mass flow. However, in the pipeline transportation of LNG, the key to ensure the stability and safety of LNG liquid transport is to adopt reliable adiabatic form and establish a scientific pipe transport model. This paper uses theoretical analysis, numerical simulation and experimental research in these two aspects. The pipeline transportation and safe transport of LNG have been systematically studied. The following research contents are completed: (1) the calculation of the properties of LNG hot material is carried out. The influence of thermodynamics and migration properties should be fully taken into account in the pipeline transportation of LNG. The calculation program of phase equilibrium of LNG multi component system is compiled with LKP equation. The LNG density under the same pressure, the specific heat capacity, viscosity and thermal conductivity change with the temperature. The results show that the density of LNG in the liquid phase region is very little influenced by the heat capacity, viscosity and thermal conductivity, and is more sensitive to the response of the temperature; the properties of the related thermal properties near the critical point are more intense with the pressure and temperature. In gas phase, the relative thermodynamic parameters of natural gas are increased by pressure change, and the temperature response has a tendency to weaken. (2) the heat transfer process analysis and thermal resistance composition of the LNG pipeline can be analyzed and the thermal resistance composition is discussed. Adiabatic insulation is better than vacuum insulation, and vacuum insulation is superior to accumulation adiabatic. If the vacuum insulation is lost in the process of LNG pipeline transportation, the insulation performance will decrease greatly. Therefore, the vacuum multilayer insulation which is not high in vacuum and good in adiabatic performance is used in the pipeline transportation of LNG. On the basis of this, the heat transfer mechanism of the vacuum multi-layer insulation pipeline is analyzed, including the radiation heat transfer between the reflecting screens, the heat conduction of the gas molecules and the heat conduction between the solid in the reflecting screen, and the temperature and the radial flow density of the various layers of the vacuum multi-layer adiabatic pipelines under different vacuum measurements are calculated by programming. (3) (3) the phase state of the given component is divided into the supercooled phase state, the dense phase and the supercritical phase state. The mathematical model of the LNG in the pipeline transportation process is given. The LNG tube transmission process in the vacuum multilayer insulation pipe is a two-dimensional steady process in the radial and axial direction, and the boundary conditions of the flow field and the temperature field are given, and the LNG is obtained in the axial direction. The temperature change law. The temperature rise of LNG is not rapid in the direction of transportation because of the vacuum multilayer insulation pipeline with good insulation performance. Therefore, it is proposed that the long distance pipe transmission condition is to meet the saturation temperature of any section in the pipe transmission process below the pressure of its cross section, that is, supercooling to ensure the supercooling state. The calculation method for the farthest transportation distance of the liquid is put forward. Through the program, the farthest transportation distance of LNG at the inlet temperature of the given pipeline is obtained. The influence factors entrance pressure, the inner wall heat flux density, the inner diameter and the mass of the pipe on the farthest transportation distance are discussed. (4) the insulation safety of the pipe transmission process is divided. In the process of transportation of the LNG pipeline, the breakage of the inner tube and the breakage of the outer tube will cause the gradual loss of the vacuum degree in the process of LNG transportation, the decrease of the insulation performance and the loss of the supercooling state of the LNG. The changes in the internal pipe breakage and the damage of the outer tube are analyzed respectively. The natural pairs of the interlayer annular space in the pipeline are analyzed on the premise of the hypothesis. The effect of heat transfer on the heat transfer is established. Through the program analysis, the influence of the temperature of the outer wall of the vacuum pipe, the number of adiabatic materials, the thermal conductivity of the adiabatic material and the density of the coating on the heat flux after the adiabatic loss are obtained. The results show that the higher the temperature of the wall, the greater the temperature of the wall of the outer tube, the greater the heat leakage, and the more the layers of the adiabatic materials. The smaller the leakage heat, the smaller the density, the greater the density, the greater the density, the larger the density, the smaller the heat leakage of the spacer. (5) the vacuum loss process of the LNG vacuum multilayer insulation pipeline was experimentally studied. The pressure of the annular space after the vacuum loss was measured under the different layers of adiabatic materials, and the wall surface of the sandwich material was measured under the different layers of adiabatic materials. On the basis of the temperature and leakage heat rate, the crack propagation of the inner wall is studied by means of molecular dynamics. The experimental data and the simulation results are compared and compared. The change trend of the results is in good agreement, which provides a strong guarantee for the stability and adiabatic safety of the LNG long distance pipeline transportation.
【学位授予单位】：中国石油大学(华东)
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TE832

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