小尺度超临界二氧化碳泄漏过程物理机理研究

发布时间：2018-07-11 10:17

本文选题：超临界二氧化碳泄漏 + 二氧化碳运输安全　；参考：《中国科学技术大学》2016年博士论文

【摘要】：面对日益严峻的能源危机和环境安全形式,如何高效清洁利用化石燃料是当今世界广泛研究的一个科学技术问题。近些年来出现的碳捕捉与封存技术,由于其可观的工业化潜力,被公认为是各种节能减排技术中最有前景解决当前困扰的一种,也是向“低碳经济”过渡的重要节能减排手段。碳捕捉与封存技术主要分为碳捕捉、二氧化碳运输和碳封存三个部分。其中效率和安全是该技术中至关重要的两个指标,在其中二氧化碳运输环节中,这两个要点尤其重要,效率保证了运输的经济性,而安全则保证了运输的有效性。目前在英国、韩国等都开始了针对二氧化碳安全运输及其泄漏过程的研究,在我国这方面的研究也正处于起步阶段。本文的核心内容正是研究处于运输中的超临界二氧化碳在发生管道泄漏时,高压流体泄漏过程中的变化过程及其物理机理。管道运输是目前二氧化碳运输中的一种重要手段。而在管道运输中,为了保持运输的效率,通常会将管道中的流体保持在一定高压的状态。在管道运输过程中,一般会将二氧化碳加压到超临界状态运输。超临界状态的二氧化碳在流动时不仅具有类似气体的高扩散性、低粘性,还具有类似液体的高密度,比起在液态和气态运输,可以更为高效经济的运输二氧化碳。但是在管道发生泄漏时,超临界状态的二氧化碳对于管道和周围环境具有更高的危害性。由于其具有高压的特性,在泄漏发生时会在泄漏口内部出现壅塞流现象,对管内流动以及运输效率产生影响;在泄漏口附近,由于泄漏流体与环境压力的巨大压差形成的弓形激波、马赫盘和膨胀波等现象；在泄漏口外部由于焦汤效应,出现的干冰层现象,以及高压射流在管外形成的对流、空气卷吸等相关流体过程。本文选取了小尺度超临界二氧化碳泄漏这一主要研究对象,从气体动力学、传热学、流体力学以及安全学相关基础学科理论出发,结合实验研究,揭示了超临界二氧化碳泄漏过程中,在泄漏不同区域主要的的物理现象以及其对管道和周围环境安全产生的影响；并且通过数值模拟对比,进一步揭示了二氧化碳泄漏过程中出现的物理现象所产生的动力学机理：最终结合理论、实验和数值模拟的研究,为高压流体泄漏探测及分析工作提供了理论指导以及一定的技术意见。论文的具体工作主要为：在理论研究方面,首先介绍了前人一些有关快速高压射流的一些传统模型,并且结合超临界二氧化碳的特性加以改进,然后通过加入经典泄漏模型对比,建立了以泄漏口为分界的三段式超临界二氧化碳泄漏模型；在泄漏口内部研究高压泄漏对于管道内部流动影响时,鉴于小尺度管道泄漏内部流动参数难以测量的条件,提出了运用无量纲传热参数间接测量泄漏口内部壅塞流强度的方法;在泄漏口附近建立了近场高压泄漏模型,并且推导出了泄漏过程中速度和泄漏流量之间的关系,观测并解释了泄漏口附近干冰层以及弓形激波形成等物理现象；在泄漏口外部研究了气流温度以及速度分布的特点,以及其对高压气流流体特性的相互影响关系。在实验研究方面,自主设计并且搭建了“超临界态CO2管道运输及泄漏模拟实验平台”,并基于此平台开展了多种不同尺寸泄漏口径、不同泄漏流体状态的泄漏实验。第一系列是研究不同状态的二氧化碳在同一口径泄漏时,泄漏压力、泄漏质量流率、流速以及温度变化,对泄漏模型进行验证以及改进。第二系列是研究超临界二氧化碳在小尺度不同泄漏口径时,流体的状态变化,以及其与环境相互之间的影响关系,对超临界流体泄漏检测提供了详细的数据支持,并详细的分析了泄漏口径对于泄漏过程中物理现象及其影响其变化的物理参量的变化规律。在数值模拟研究方面,主要利用自主编写的两步L-W程序计算模拟超临界二氧化碳轴对称射流及其自由扩散过程。通过改变泄漏口径尺寸、泄漏口初始流体速度来模拟不同泄漏情况发生时超临界二氧化碳在泄漏口外部自由扩散。利用在程序中加入人工粘性,来模拟在实验中观测到的马赫盘,以及出现在流场近场中的弓形激波,并得到泄漏口附近温度、压力、速度等流动参量。最后结合理论和实验研究,,从物理上剖析了超临界二氧化碳泄漏发生时所发生物理现象及其机理,并通过数值模拟验证高压射流模型和其中各个参量之间耦合关系,将此前的研究工作完成了良好的串联。
[Abstract]:Facing the increasingly severe energy crisis and the form of environmental safety, how to effectively clean and use fossil fuels is a scientific and technical problem widely studied in the world today. In recent years, carbon capture and sequestration technology, due to its considerable industrialization potential, is recognized as the most promising solution to all kinds of energy saving and emission reduction technologies. One of them is also an important means of energy saving and emission reduction to the "low-carbon economy". Carbon capture and storage technology is mainly divided into three parts: carbon capture, carbon dioxide transport and carbon sequestration. Efficiency and safety are the two important indicators of the technology. In the process of transport of carbon dioxide, the two key points are especially important, and the efficiency is guaranteed. The economy of transportation is confirmed, and safety ensures the effectiveness of transportation. At present, in Britain, South Korea and other countries have begun to study the process of safe transportation and leakage of carbon dioxide. The research in this area is also in its infancy. The core content of this paper is that the supercritical carbon dioxide in transportation is occurring in the pipeline. The change process and physical mechanism during the leakage of high pressure fluid in the process of leakage, pipeline transportation is an important means of carbon dioxide transportation. In pipeline transportation, in order to maintain the efficiency of transportation, the fluid in the pipeline is usually maintained at a certain high pressure. In the pipeline transportation, carbon dioxide is generally added. The supercritical state transport of carbon dioxide in a supercritical state not only has high diffusivity similar to gas, low viscosity, but also has a high density of similar liquids, which can transport carbon dioxide more efficiently than in liquid and gaseous transport. Pipes and surrounding environment have higher hazards. Due to their high pressure characteristics, the choked flow occurs inside the leaks at the time of leakage, and affects the flow in the pipe and transport efficiency; the bow shock formed by the huge pressure difference between the leakage fluid and the environmental pressure near the leakage, Mahope and the expansion wave, etc. In this paper, the main object of small scale supercritical carbon dioxide leakage is selected, from gas dynamics, heat transfer, hydrodynamics and safety related basic subjects. Based on the theory and combined with experimental research, the main physical phenomena in different regions of the leakage of supercritical carbon dioxide and its influence on the safety of the pipeline and surrounding environment are revealed, and the dynamics of the physical phenomena occurring in the process of carbon dioxide leakage are further revealed by numerical simulation. Mechanism: the final combination of theory, experiment and numerical simulation provides theoretical guidance and some technical advice for the detection and analysis of high pressure fluid leakage. The main work of this paper is as follows: in the theoretical research, some traditional models of the high pressure jet are introduced first, and the supercritical fluid jet is combined with the supercritical fluid. The characteristics of carbon dioxide are improved, and then through the comparison of the classical leakage model, a three stage supercritical carbon dioxide leakage model with the leakage is established, and the condition that the internal flow parameters of the small scale pipeline are difficult to measure when the pressure leakage is affected to the internal flow in the pipe is studied. A method of indirect measurement of the intensity of the choked flow inside the leak with the dimensionless heat transfer parameters was used. A near field high pressure leakage model was established near the vent, and the relationship between the velocity and the leakage flow in the leakage process was deduced, and the physical phenomena such as the dry ice layer near the leakage and the formation of the bow shock wave were observed and explained, and the leakage of the leakage was explained. The characteristics of airflow temperature and velocity distribution and the interaction relationship between the flow characteristics of high pressure air flow are studied outside the mouth. In the experimental research, the "supercritical CO2 pipeline transportation and leakage simulation experiment platform" is designed and built independently. Based on this platform, many different sizes of leakage and different leakage flow are developed. The first series is to study the leakage pressure, leakage mass flow rate, flow velocity and temperature change in the same aperture leakage of different state carbon dioxide, to verify and improve the leakage model. The second series is to study the change of the state of the fluid when the supercritical carbon dioxide is leaked in a small scale. The relationship between the environment and the environment provides detailed data support for the detection of the leakage of the supercritical fluid, and the detailed analysis of the physical phenomena in the leakage process and the change rules of the physical parameters that affect the change of the leakage. In the numerical simulation study, the two step L-W program calculation model, which is written independently, is mainly used. The quasi supercritical carbon dioxide axisymmetric jet and its free diffusion process are simulated by changing the diameter of the leak aperture and the initial fluid velocity of the leakage to simulate the free diffusion of the supercritical carbon dioxide at the outside of the leakage. By adding the artificial viscosity in the program, the Maher disk observed in the experiment is simulated and the output is simulated. The current flow parameters such as temperature, pressure and velocity near the vent are obtained in the near field of the flow field. Finally, the physical phenomena and the mechanism of the supercritical carbon dioxide leakage are physically analyzed by the theoretical and experimental research, and the coupling between the high pressure jet model and the coupling parameters is verified by the numerical model. The partnership has completed a good series of previous research work.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TQ116.3;TQ022.115

【相似文献】