城市管道天然气在土壤中扩散行为全尺度实验

为了及时发现管道天然气泄漏、快速准确判定泄漏点位置以及划定泄漏扩散影响范围，应用自主设计和构建的实验系统，开展了多组全尺度中低压埋地管道泄漏实验，揭示了管道天然气在土壤中的对流扩散基本特性，得到了其浓度场空间分布和变化规律。实验发现：①土壤中天然气浓度分布水平方向关于泄漏口基本对称，但泄漏前期其浓度分布垂直方向关于泄漏口不对称，即泄漏初始，天然气高浓度区等值线为椭圆（椭圆长轴为垂直方向），随着泄漏时间的推移，浓度等值线出现不规则变化（在泄漏口正上方有一个明显的凸起），且低压泄漏引起的高浓度区域凸起幅度比中压泄漏更大更明显，但随着管道天然气持续泄漏，其浓度等值线凸起也逐渐消失；②天然气浓度到达爆炸下限所需时间与距泄漏口距离呈现近似的幂指数关系；③随着管道压力、泄漏速率的增大，土壤中甲烷爆炸极限-泄漏时间特征曲线由凸形曲线变化为直线，且斜率越来越大。

Full-scale experiment of diffusion behaviors of city pipeline gas in soils

For discovering pipeline gas leakage in time, determining the leakage locations quickly and accurately and discriminating the influencing range of leakage and diffusion, multiple full-scale leak tests were performed on middle-low pressure buried pipelines by using an experiment system which was designed and built by ourselves. The basic characteristics of convective diffusion of pipeline gas in soils were revealed and spatial distribution and change rules of its concentration fields were presented. It is shown that gas concentration distribution in soils is basically symmetrical on leakage points along horizontal direction, but asymmetrical along vertical direction at the early stage of leakage. This means that the contour of high concentration zones is initially in the shape of ellipse (long axis along the vertical direction) at the early stage of leakage, but presents irregular change as leakage goes on, and an obvious convex occurs right above the leakage point. The convex amplitude of high concentration zones induced by low-pressure leakage is larger and more significant than that induced by medium-pressure leakage. And the convex will gradually disappears with the continuous leakage of pipeline gas. It is approximate power exponent relation between the time period needed by gas concentration to reach the low explosion limit and the distance to leakage points. And with the rise of pipeline pressure and leakage rate, the characteristic curve of explosion limit-leakage time of methane in sols varies from the convex curve to the straight line, with the slope larger and larger.