摘要
建立了城市中压天然气管道小孔泄漏后在土壤中扩散的三维数值模型,采用CFD软件对泄漏天然气在壤土中的扩散过程进行了数值模拟,对比分析了不同土壤中天然气速度、质量分数的变化规律。研究结果表明:泄漏天然气在壤土中的流速场和压力场在极短的时间内(100 s内)达到稳定的分布状态。泄漏孔附近存在较大的速度梯度和压力梯度,远离泄漏孔处,天然气的扩散速度非常缓慢。在泄漏孔附近,天然气在压力差和体积分数差的作用下对流扩散,形成了一个垂直不对称高浓度区域,管道上方体积分数大于下方;在远离泄漏孔的壤土区域内,只有体积分数差引起的分子扩散,天然气呈同心扩散。随着泄漏时间的增加,危险半径和危险区域在逐渐扩大。在壤土中,当管道直径为100 mm,压力为0.4 MPa,泄漏孔直径为10 mm时,泄漏100 s时危险半径约为0.4 m,30 min时危险半径约为1.2 m,60 min时危险半径约为1.5 m。天然气体积分数变化沿管长方向呈高斯分布,泄漏孔上方体积分数最高。建议在直埋天然气管道定位泄漏点时,打孔位置为管道上方0.5 m高度。壤土中天然气报警时间与扩散距离之间成幂函数关系,根据该拟合公式可逆向预测天然气管道泄漏时间,从而为燃气事故风险评估提供理论依据。土壤种类对天然气泄漏扩散过程起着关键作用,天然气在不同类型的土壤中扩散速度由高到低为粉质沙土、壤土、黏土。
A three-dimensional mathematical model of the diffusion in soil after small-hole leakage in urban medium-pressure natural gas pipeline was established.The diffusion process of leaked natural gas in loam was simulated numerically by CFD software,and the variation laws of natural gas velocity and mass fraction in different soils were compared and analyzed.The study results show that the velocity field and pressure field of leaked natural gas in loam reach stable distribution state in a very short time(within 100 s).There are large velocity gradient and pressure gradient near the leakage hole,and the diffusion speed of natural gas is very slow at the place far away from the leakage hole.Near the leakage hole,the natural gas diffuses convectively under the action of the pressure difference and the volume fraction difference,forming a vertical asymmetric high concentration area,and the volume fraction above the pipeline is greater than that below the pipeline.In the loam area far away from the leakage hole,only molecular diffusion is caused by the difference in volume fraction,natural gas diffuses concentrically.With the increase of the leakage time,the danger radius and the danger area in the soil are gradually expanding.In loam,when the pipe diameter is 100 mm,the pressure is 0.4 MPa and the leakage hole diameter is 10 mm,the danger radius is about 0.4 m at 100 s,1.2 m at 30 min,and 1.5 m at 60 min.The change in the volume fraction of natural gas is Gaussian distribution along the direction of pipe length,and the volume fraction above the leakage hole is the highest.It is suggested that when locating the leakage point of directly buried natural gas pipeline,the drilling position should be 0.5 m above the pipeline.There is a power function relationship between the alarm time of natural gas in loam and the lateral diffusion distance.According to the fitting formula,the leakage time of natural gas pipeline can be predicted in reverse,which provides theoretical basis for risk assessment of gas accidents.Soil types play
作者
常欢
谭羽非
王雪梅
肖榕
张兴梅
CHANG Huan;TAN Yufei;WANG Xuemei;XIAO Rong;ZHANG Xingmei
出处
《煤气与热力》
2020年第11期28-34,I0042,I0043,共9页
Gas & Heat
基金
国家十三五重大专项课题“城市天然气管网相邻地下空间风险监测与韧性增强技术及系统”(2018YFC0809903)。
关键词
天然气
直埋管道
土壤
泄漏扩散
数值模拟
natural gas
directly buried pipeline
soil,leakage diffusion
numerical simulation
