高海拔多年冻土区埋地式输气管道周围土体温度场及管—土热力耦合数值计算

发布时间：2018-06-17 08:58

本文选题：多年冻土区 + 埋地式输气管道　；参考：《兰州交通大学》2017年硕士论文

【摘要】：我国冻土区域分布较为广泛,作为世界第三大冻土国,冻土区面积约占国土面积的75%。在这些冻土区域中,尤其是多年冻土区,储藏着丰富的石油天然气资源。随着我国经济社会不断向前发展,因埋地式管道有着成本相对较低、运量大、占地少、建设周期短等优点,在多年冻土区敷设埋地式输气管道作为目前乃至今后长距离输送油气资源的主要方式仍将不可避免的要穿越这些区域。然而,在多年冻土区,尤其是在青藏高原这样平均海拔高、多年冻土面积分布广泛、多年冻土层厚度大、自然条件十分恶劣、地质条件十分复杂的多年冻土区敷设埋地式正温输气管道,国内尚无成熟的经验技术以供借鉴参考,同时对于多年冻土区埋地式管道与其周围多年冻土之间相互作用机理的研究仍处于逐步探索阶段,管道周围多年冻土的力学特征、热稳定性及管道的工程特性是研究多年冻土区埋地式正温输气管道工程的关键问题所在。本文以青藏高原多年冻土区正温埋地式输气管道某区段管道及周围土体为研究对象,针对该区段沿线多年冻土退化引起的病害,结合该区段多年冻土特征,考虑未来气候升温环境因素及传热学基本理论,利用大型有限元数值计算软件ANSYS对不同管道中心埋深、不同管内介质输送温度以及有无保温措施并考虑冰水相变过程条件下管道周围土体的非稳态温度场分布情况进行了数值求解,得到了不同条件下管道周围土体的温度场分布趋势,同时也利用ANSYS热力间接耦合方法计算了管道在不同条件下其内部等效应力的分布情形。本文的主要结论如下:(1)通过对不同条件下高海拔多年冻土区埋地式正温输气管道周围土体温度场的数值计算,分析发现该区段多年冻土热稳定性较差,埋设正温输气管道对管道周围多年冻土赖以保持稳定的冻土环境威胁极大;(2)管道中心埋深对管道周围多年冻土的温度场分布规律影响较大,一般来说,在管内介质管内介质输送温度一定时,管道中心埋深越大,在计算时间内管道底部的多年冻土融化深度也就越大:管道中心埋深分别为2.0m、2.5m、3.0m时,在管内介质输送温度为10℃和16℃条件下,计算第50年其管道底部的多年冻土融化深度分别为2.76m、3.21m、3.68m和2.84m、3.35m、3.76m,在正温输气管道设计、施工敷设时管道中心埋深要经济、合理;(3)随着管内介质管内介质输送温度的升高,管道底部下方土体最大融化厚度也就越大:管道中心埋深2.0m时,在管内介质输送温度为10℃和16℃条件下,管道底部下方土体最大融化厚度分别为43cm和50cm;管道中心埋深2.5m时,在管内介质输送温度为10℃和16℃条件下,管道底部下方土体最大融化厚度分别为38cm和47cm;管道中心埋深3.0m时,在管内介质输送温度为10℃和16℃条件下,管道底部下方土体最大融化厚度分别为35cm和43cm;在实际操作中应控制管内介质输送温度,尽量避免过高的管内介质输送温度;(4)使用45mm厚的聚氨酯泡沫作为管道外壁保温措施,可以有效减小正温输气管道热量对管道周围多年冻土的热扰动,直接表现为有保温措施时管道周围多年冻土的融化范围较无保温措施时极小:45mm厚的聚氨酯泡沫作为管道外壁保温措施,管道中心埋深2.0m时,在管内介质输送温度为10℃和16℃条件下,管道底部下方土体最大融化厚度分别为0mm和43.7mm;管道中心埋深2.5m时,在管内介质输送温度为10℃和16℃条件下,管道底部下方土体最大融化厚度分别为0mm和35.3mm;管道中心埋深3.0m时,在管内介质输送温度为10℃和16℃条件下,管道底部下方土体最大融化厚度分别为0mm和30.5mm;(5)在埋地式正温输气管道敷设、运营的前10~20年内,正温管道热量对管道周围多年冻土的热扰动最大,在此期间应注意加强管道周围土体的温度监测与管道维护;(6)不同条件下,由于管道内部压力、自重、上覆土体自重以及由于周围土体温度变化产生的荷载在管道中产生的等效应力最大值位于管道底部内侧;(7)不同管道中心埋深时其管道底部内侧等效应力随计算时间的增加逐渐增大,等效应力最大值在计算的第30年;(8)在管道管内介质输送温度为16℃、无保温措施情况下,管道中心埋深越大,由于管道内部压力、自重、上覆土体自重以及由于周围土体温度变化产生的荷载在管道中产生的等效应力也就越大;在计算的第30年,管道中心埋深3.0m情况下管道底部内侧等效应力为203MPa,管道中心埋深为2.5m、2.0m时其等效应力分别为172MPa、149MPa,分别是管道中心埋深为2.0m、2.5m时等效应力的1.36倍和1.18倍;(9)管道中心埋深相同、管道管内介质输送温度为16℃情况下,采取45mm聚氨酯泡沫作为保温措施可以有效减小由于管道内部压力、自重、上覆土体自重以及由于周围土体温度变化产生的荷载在管道中产生的等效应力,以管道中心埋深3.0m时管道底部内侧的等效应力值为135MPa最大,而管道中心埋深为2.0m、2.5m时其等效应力分别为78.3MPa和94.7MPa,分别是无保温措施时其管道底部内侧等效应力的两种管道中心埋深的52.6%、55.1%和58.7%。
[Abstract]:The permafrost region is widely distributed in China. As the third largest permafrost in the world, the 75%. of the permafrost area accounts for the land area. In these frozen soil areas, especially in the permafrost regions, the rich oil and natural gas resources are stored. With the continuous development of the economy and society in China, the buried pipeline has relatively low cost and a large amount of transportation. There are few advantages, such as short period of construction and short construction period. In permafrost area laying buried gas pipeline as the main way of transporting oil and gas in long distance will inevitably pass through these areas. However, in permafrost regions, especially in the Qinghai Tibet Plateau, the plateau is all above sea level, and permafrost area is widely distributed for many years. It is still in the stage of gradual exploration for the study of the interaction mechanism between buried pipelines and permafrost around permafrost regions, which have no mature experience technology for reference in the permafrost regions with large soil thickness, very bad natural conditions and complicated geological conditions. The mechanical characteristics of permafrost around the road, the thermal stability and the engineering characteristics of the pipeline are the key problems in the study of the buried pipeline project in the permafrost region. This paper takes the pipeline and the surrounding soil in a certain section of the pipeline and the surrounding soil in the permafrost region of the permafrost region of the Qinghai Tibet Plateau as the research object, aiming at the retreat of permafrost along the section. Combined with the characteristics of permafrost in this section, considering the future climate warming environmental factors and the basic theory of heat transfer, the large finite element numerical calculation software ANSYS is used for the buried depth of different pipeline centers, the temperature of the medium in different pipes, the insulation measures and the consideration of the soil around the pipeline under the condition of the phase change process of ice water. The distribution of the unsteady temperature field is numerically solved, and the temperature distribution trend of the soil around the pipe under different conditions is obtained. At the same time, the distribution of the internal equivalent stress of the pipeline under different conditions is calculated by using the ANSYS thermal indirect coupling method. The main conclusion of this paper is as follows: (1) through the high altitude under different conditions The numerical calculation of the soil temperature field around the buried positive temperature gas pipeline in permafrost region shows that the thermal stability of the permafrost in this section is poor, and the threat of the permafrost surrounding the permafrost around the pipeline is greatly threatened by the buried positive temperature pipeline. (2) the distribution of the temperature field around the permafrost around the pipeline center depth. In general, the deeper the buried depth of the pipe is, the greater the depth of the permafrost melting at the bottom of the pipe in the calculation time. When the buried depth of the pipe center is 2.0m, 2.5m, 3.0m, the pipeline bottom is calculated for fiftieth years under the conditions of the medium transport temperature of 10 and 16. The depth of permafrost melting in the Ministry is 2.76m, 3.21M, 3.68m and 2.84m, 3.35M, 3.76M. In the design of the positive temperature gas pipeline, the buried depth of the pipe center should be economical and reasonable. (3) the maximum melting thickness of the soil body below the bottom of the pipe is greater as the medium pipe inside the tube is transported. The pipe center buried depth 2.0m, in the pipe. The maximum melting thickness of the soil under the bottom of the pipeline is 43cm and 50cm under the conditions of the internal medium transport temperature of 10 and 16, and the maximum melting thickness of the soil below the bottom of the pipe is 38cm and 47cm under the buried depth of 2.5m in the pipe center, when the pipeline center is buried at the temperature of 10 and 16, and the medium is transported in the pipe center when the depth is 3.0m. Under the conditions of 10 C and 16 C, the maximum thicknesses of the soil under the bottom of the pipe are 35cm and 43cm, respectively. In the actual operation, the medium transport temperature should be controlled to avoid the high temperature in the tube, and (4) the use of 45mm thick polyurethane foam as the insulation of the outer wall of the pipeline can effectively reduce the heat of the positive temperature gas pipeline. When the thermal disturbance of permafrost around the pipe is measured, the melting range of permafrost around the pipe is less than that without heat preservation measures when there is heat preservation measures. The 45mm thick polyurethane foam is used as the insulation measure of the outer wall of the pipeline. When the pipeline center is buried deep for 2.0m, the medium bottom soil under the bottom of the pipe is under the condition of the medium transport temperature of 10 and 16. The maximum thicknesses of the body melt are 0mm and 43.7mm, and the maximum melting thickness of the soil below the bottom of the pipe is 0mm and 35.3mm under the condition of the medium transport temperature of 10 and 16 C in the pipe center, when the pipeline center is 10 and 16 C. The maximum melting of the soil below the bottom of the pipe under the buried depth of the pipeline is at the temperature of 10 and 16. The thickness is 0mm and 30.5mm, respectively. (5) during the first 10~20 years of buried positive temperature pipeline, the heat disturbance of the positive temperature pipeline is the greatest. During this period, the temperature monitoring and maintenance of the soil around the pipeline should be strengthened. (6) under different conditions, due to the internal pressure of the pipe, weight and overlying soil The maximum value of the equivalent stress generated by the weight and the change of the surrounding soil temperature is located inside the bottom of the pipe. (7) the equivalent stress at the bottom of the pipe gradually increases with the increase of the calculation time, and the maximum equivalent stress is thirtieth years in the calculation, and (8) the medium transport temperature in the pipe pipe. Under the condition of 16 degrees centigrade, the greater the depth of the pipe center is, the greater the buried depth of the pipe center, the greater the equivalent stress produced in the pipe due to the pressure inside the pipe, the weight of the self weight, the weight of the overlying soil and the load of the surrounding soil temperature. In the thirtieth year calculation, the equivalent stress at the bottom of the bottom of the pipe under the buried depth of 3.0m in the pipeline is 203MP. A, the buried depth of the pipe center is 2.5m, and the equivalent stress of 2.0m is 172MPa, 149MPa respectively, which is 1.36 times and 1.18 times the equivalent stress at the pipe center depth of 2.0m and 2.5m respectively. (9) the pipeline center buried depth is the same, the medium transport temperature in the pipe is 16 C, and the 45mm polyurethane foam can effectively reduce the pipe due to the pipeline. Internal pressure, self weight, weight of overlying soil mass and the equivalent stress produced by the load produced by the surrounding soil temperature change, the equivalent stress value at the bottom of the bottom of the pipe is 135MPa maximum when the pipe center is buried deep 3.0m, while the buried depth of the pipe center is 2.0m, and the equal effect force is 78.3MPa and 94.7MPa respectively, respectively, when 2.5m is no heat preservation. The equivalent stress of two pipes at the bottom of the pipeline is 52.6%, 55.1% and 58.7%. at the bottom of the pipeline.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE973

【参考文献】