应用FLUENT数值模拟天然气水合物开采过程

发布时间：2018-06-14 06:28

本文选题：天然气水合物 + 降压法　；参考：《吉林大学》2015年硕士论文

【摘要】：随着当今工业技术的不断发展，对能源的需求不断增加。能源问题陆续被提上世界各国的议事日程，成为亟待解决的重要问题。天然气水合物被认为是21世纪最具有开发前景的潜在新型洁净能源之一，具有高密度、高热值、洁净环保的优点。1m3的天然气水合物完全分解可以产生164m3标准状态下的甲烷气体。天然气水合物主要存在于陆地（基本为永久冻土层）和海洋中。目前在有关天然气水合物分布、储量以及运输等基础研究方面已取得重大进展，但是在开采方法上的研究相对滞后。本文对国内外天然气水合物的研究概况做了简单介绍。目前对于开采天然气水合物主要有四种开采方案：注热法、降压法、注化学试剂法和CO2置换法，在这四种不同的开采方案中，由于降压法在实际操作中只要开始就不需要连续的投入设备和材料，，在所有开采方案中成本最为低廉。本文数值模拟降压法开采天然气水合物的过程，在具体的数值模拟中，运用了商业软件FLUENT，建立降压法开采天然气水合物的数学模型，数值模拟了天然气水合物的分解。在FLUENT软件中加入自编的用户自定义函数（UDF），用于修改质量守恒方程、能量守恒方程和相对渗透率。采用二维轴对称的几何模型，数值模拟一个天然气水合物降压分解实验。模型中考虑气相、水相和天然气水合物相。天然气和水的流动符合达西定律。开始时，打开模型两端的阀门，使天然气水合物与外界的低压环境接触，天然气水合物开始分解，甲烷气体和水开始流动。数值模拟过程包括多孔介质中多相流动以及传热和化学反应。分别得到当天然气水合物分解过程进行至10分钟、40分钟、80分钟、160分钟和200分钟时的压力场、温度场，数值模拟的结果表明，水合物的分解速率受出口压力和周围环境温度等参数的影响，提高周围环境温度或者降低出口压力都有助于提高水合物分解速率。分解过程在0到80分钟内温度变化率和压力变化率最大，在80至120分钟内天然气水合物的温度变化率和压力变化率相对平缓，在120分钟至200分钟温度变化率和压力变化率逐渐减小。研究成果为进一步开展室内模拟实验以及工程应用研究提供了重要依据。
[Abstract]:With the development of industrial technology, the demand for energy is increasing. Energy issues have been put on the world's agenda one after another, becoming an important issue to be solved. Natural gas hydrate is considered as one of the most promising potential clean energy sources in the 21st century. The gas hydrate with high density, high calorific value and clean environmental protection can completely decompose methane gas under 164m3 standard state. Natural gas hydrate mainly exists on land (basically permafrost) and ocean. At present, great progress has been made in the basic research of gas hydrate distribution, reserves and transportation, but the research on exploitation methods is lagging behind. This paper briefly introduces the research situation of natural gas hydrate at home and abroad. At present, there are four kinds of exploitation schemes for exploiting natural gas hydrate: injection heat method, depressurization method, chemical reagent injection method and CO2 replacement method. In these four different mining schemes, Since the depressurization method does not require continuous input equipment and materials as long as it starts in practice, it is the cheapest in all mining schemes. In this paper, the process of exploiting natural gas hydrate by depressurization method is simulated. In the concrete numerical simulation, the mathematical model of natural gas hydrate extraction by pressure reduction method is established by using commercial software fluent, and the decomposition of natural gas hydrate is numerically simulated. The user defined function is added to fluent software, which is used to modify the mass conservation equation, energy conservation equation and relative permeability. A gas hydrate decomposing experiment is numerically simulated using a two-dimensional axisymmetric geometric model. Gas phase, water phase and gas hydrate phase are considered in the model. The flow of natural gas and water follows Darcy's law. At the beginning, the valve at both ends of the model is opened to make the gas hydrate contact with the external low pressure environment, the natural gas hydrate begins to decompose, and the methane gas and water begin to flow. The numerical simulation process includes multiphase flow, heat transfer and chemical reaction in porous media. The pressure field, temperature field and numerical simulation results are obtained when the gas hydrate decomposition process is carried out to 10 min / 40 min / 80 min / 160 min and 200 min, respectively. The decomposition rate of hydrate is affected by the parameters such as outlet pressure and ambient temperature. Increasing the ambient temperature or lowering the outlet pressure can help to increase the rate of hydrate decomposition. The temperature change rate and pressure change rate of natural gas hydrate is the largest in 0 to 80 minutes, and the temperature and pressure change rate of gas hydrate is relatively flat in 80 to 120 minutes. From 120 minutes to 200 minutes, the temperature change rate and pressure change rate gradually decreased. The research results provide an important basis for further indoor simulation experiments and engineering application research.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P744.4

【参考文献】