Purpose

Natural gas leak from underground pipelines could lead to serious damage and global warming, whose spreading in soil should be systematically investigated. This paper aims to propose a three-dimensional numerical model to analyze the methane–air transportation in soil. The results could help understand the diffusion process of natural gas in soil, which is essential for locating leak source and reducing damage after leak accident.

Design/methodology/approach

A numerical model using finite element method is proposed to simulate the methane spreading process in porous media after leaking from an underground pipe. Physical models, including fluids transportation in porous media, water evaporation and heat transfer, are taken into account. The numerical results are compared with experimental data to validate the reliability of the simulation model. The effects of methane leaking direction, non-uniform soil porosity, leaking pressure and convective mass transfer coefficient on ground surface are analyzed.

Findings

The methane mole fraction distribution in soil is significantly affected by the leaking direction. Horizontally and vertically non-uniform soil porosity has a stronger effect. Increasing leaking pressure causes increasing methane mole flux and flow rate on the ground surface.

Originality/value

Most existing gas diffusion models in porous media are for one- or two-dimensional simulation, which is not enough for predicting three-dimensional diffusion process after natural gas leak in soil. The heat transfer between gas and soil was also neglected by most researchers, which is very important for predicting the gas-spreading process affected by the soil moisture variation because of water evaporation. In this paper, a three-dimensional numerical model is proposed to further analyze the methane–air transportation in soil using finite element method, with the presence of water evaporation and heat transfer in soil.

中文翻译：

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地下管道泄漏后甲烷在多孔介质中扩散的数值模拟

目的

地下管道的天然气泄漏可能导致严重破坏和全球变暖，应系统调查其在土壤中的扩散。本文旨在提出一个三维数值模型来分析土壤中甲烷-空气的迁移。研究结果有助于了解天然气在土壤中的扩散过程，这对于确定泄漏源和减少泄漏事故后的破坏至关重要。

设计/方法/方法

提出了一种利用有限元方法建立的数值模型，模拟了地下管道泄漏后甲烷在多孔介质中的扩散过程。考虑了物理模型，包括在多孔介质中的流体传输，水蒸发和热传递。将数值结果与实验数据进行比较，以验证仿真模型的可靠性。分析了甲烷泄漏方向，不均匀的土壤孔隙度，泄漏压力和对流传质系数对地表的影响。

发现

土壤中甲烷摩尔分数的分布受泄漏方向的影响很大。水平和垂直方向上不均匀的土壤孔隙度影响更大。泄漏压力的增加导致地面上甲烷摩尔通量和流速的增加。

创意/价值

现有的大多数多孔介质中的气体扩散模型都是用于一维或二维模拟，这不足以预测天然气在土壤中泄漏后的三维扩散过程。大多数研究人员还忽略了气体与土壤之间的传热，这对于预测受水分蒸发影响的土壤水分变化影响的气体扩散过程非常重要。本文提出了一个三维数值模型，以利用土壤中水分蒸发和传热的有限元方法进一步分析甲烷-空气在土壤中的传输。