液化天然气泄漏扩散过程数值模拟

发布时间：2018-02-25 19:33

本文关键词： 液化天然气泄漏扩散浓度分布危险区域　出处：《大连理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：液化天然气(Liquefied Natural Gas,LNG)作为一种清洁、高效的能源,在工业生产与日常生活中受到广泛应用,由于LNG具有低温、可燃等特性,因而其安全问题一直备受关注。现有研究结果表明,液化天然气发生泄漏事故之后,泄漏出来的低温液体及其蒸发形成的低温蒸气云将会对周围的设备、人员造成危害；若遇到火源,将形成池火灾或蒸气云火灾,造成的危害更是不可估量,而外界环境因素则进一步影响了其危害程度。因此,有必要对液化天然气的泄漏扩散过程及其影响因素进行研究,预测事故造成的危害范围,以指导制定应急预案。鉴于此,本文进行的研究工作主要有：(1)以高斯扩散模型为基础,提出了非点源高斯烟羽混合模型,克服了高斯烟羽模型不能计算连续泄漏源的初期浓度分布及非点源的泄漏扩散问题。以MATLAB软件为计算工具,建立了LNG泄漏事故危害评估程序,可快速绘制出天然气的动态扩散过程,并自动进行危险区域划分,该过程可在数秒内完成,可及时为救援过程提供指导。(2)从流体动力学角度出发,利用CFD软件FLUENT,采用Realizable k-ε模型、组分输运模型、DPM模型,对液化天然气泄漏事故中涉及的流体流动、物质扩散以及蒸发相变问题进行了数值计算。选用了国外大型LNG泄漏实验-Burro系列实验的数据进行模型验证,结果表明：建立的预测模型可以很好地模拟气云的运动扩散过程；监测点及固定平面内浓度分布规律的计算结果与实验值比较吻合。(3)通过数值实验,研究了大气条件、地理环境等对气云扩散过程的影响,主要研究结果表明：大气风速对气云运动扩散的影响主要体现在顺风方向上,风速越大,对气云的平流输运及混合稀释作用越明显,导致气云的运动扩散越快；障碍物的存在增加了其附近流场的湍流程度,促进了气云与周围空气的混合,但阻碍了气云向下风方向的运动,减小了有害区域在下风方向的范围；上坡地面具有与障碍物类似的特性,增强了周围大气对气云的稀释作用,因而形成的危害区域消散较快,而下坡地面由于地势低洼,气云受重力作用堆积于下坡处,不利于扩散,因而形成的危害区域不容易消散。(4)以LNG泄漏扩散模型为基础,耦合泄漏源模型,对大型储罐的气相泄漏、液相泄漏及围堰作用进行了模拟分析,结果表明：液相泄漏事故造成的危害显著大于气相泄漏事故；围堰阻碍了液池的扩展和气云的扩散,降低了围堰外围区域的危险性,但增大了围堰内部区域的危险程度。最终,参照某LNG接收站的实际场景,建立了该接收站的LNG储罐泄漏扩散模型,对形成的危害区域进行了预测,为应急救援提供了建议。
[Abstract]:As a kind of clean and efficient energy, liquefied natural gas (LNG) has been widely used in industrial production and daily life. Because of its characteristics of low temperature and flammability, the safety problems of LNG have been paid much attention to. After the leakage of liquefied natural gas (LNG), the leaking low-temperature liquid and the low-temperature vapor cloud formed by evaporation will cause harm to the equipment and personnel around it; if the fire is encountered, it will form a pool fire or a steam cloud fire. The harm caused by the accident is even more incalculable, and the external environmental factors have further affected the harm degree. Therefore, it is necessary to study the leakage and diffusion process of liquefied natural gas and its influencing factors, and to predict the harm scope caused by the accident. In view of this, the main research work carried out in this paper is: 1) based on Gao Si's diffusion model, a mixed model of non-point Gao Si smoke plume is proposed. This paper overcomes the problem that Gao Si's smoke plume model can not calculate the initial concentration distribution of continuous leakage source and the leakage diffusion of non-point source. The MATLAB software is used as the calculation tool to establish the LNG leakage accident hazard assessment program. The dynamic diffusion process of natural gas can be drawn quickly and the dangerous area can be divided automatically. The process can be completed in a few seconds, and can provide guidance for the rescue process in time.) from the point of view of fluid dynamics, Realizable k- 蔚 model is adopted by using CFD software fluent. The component transport model and the DPM model are used to numerically calculate the fluid flow, material diffusion and evaporation phase transition in liquefied natural gas (LNG) leakage accident. The results show that the predicted model can well simulate the movement and diffusion process of the gas cloud, and the calculated results of the concentration distribution in the monitoring point and the fixed plane are in good agreement with the experimental values. (3) the atmospheric conditions are studied through numerical experiments. The main results show that the influence of atmospheric wind speed on the diffusion of gas cloud motion is mainly reflected in the direction of downwind, the greater the wind speed, the more obvious the advection transport and mixed dilution of gas cloud. The presence of obstacles increases the turbulence level of the flow field near the gas cloud and promotes the mixing of the gas cloud with the surrounding air, but hinders the movement of the downward wind direction of the gas cloud and reduces the range of the harmful area in the downwind direction. The upper slope surface has the characteristics similar to the obstacle, which enhances the dilution effect of the surrounding atmosphere on the gas cloud, and thus causes the dangerous area to dissipate more quickly, while the downward slope surface is accumulated in the downhill by gravity because of the low-lying terrain. Based on the LNG leakage diffusion model and coupling the leakage source model, the gas phase leakage, liquid phase leakage and cofferdam effect of large storage tanks are simulated and analyzed. The results show that the damage caused by the liquid phase leakage accident is significantly greater than that caused by the gas phase leakage accident, and the cofferdam hinders the expansion of the liquid pool and the diffusion of the gas cloud, reduces the danger of the surrounding region of the cofferdam, but increases the danger degree of the inner region of the cofferdam. According to the actual situation of a certain LNG receiving station, the leakage and diffusion model of the LNG storage tank of the receiving station is established, and the hazard area is predicted, which provides suggestions for emergency rescue.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE88;TQ021.4

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