掺氢天然气管道的分层现象

Stratification in pipelines with hydrogen into natural gases

将氢气掺入现役天然气管道中混输是实现氢气大规模、长距离、低成本储运的有效方法,然而随着氢气的掺入,在氢气-天然气密度差的作用下掺氢天然气会呈现体积分数非均匀分布,造成管道局部氢分压和体积分数升高,进而导致管材失效引起泄漏。为降低掺氢天然气管道的安全风险,采用计算流体动力学方法,建立掺氢天然气混合模型,模拟储气瓶静置、管道停输和管道流动工况的氢气体积分数变化,研究掺氢天然气体积分数分布规律。结果表明:掺氢天然气在储气瓶存储和管道停输等静置过程中,氢气逐渐上浮到顶部,甲烷下沉到底部,出现明显的分层现象,且随着压力、掺氢比增大,温度和管径减小,管道重力方向的氢气体积分数梯度增大;掺氢天然气管道以非常小的流速运行时,氢气随着流动逐渐向管道顶部偏移,出现分层现象,且在低温、高压下更易分层;掺氢天然气管道适宜低压高速运行。

Blending hydrogen mixed into the existing natural gas pipelines is an effective way to achieve the large-scale,long-distance and low-cost storage and transportation of hydrogen.However,due to the density difference between hydrogen and natural gases,the addition of hydrogen in the natural gases will cause the non-uniform volume fraction distribution in the pipeline,resulting in the increase of local hydrogen partial pressure and volume fraction in the pipeline,and then leading to the pipe’s failure and leakage.In order to reduce the safety risk of hydrogen doped natural gas pipeline,the computational fluid dynamics(CFD) method was used to establish a hydrogen-natural gas mixture model,to simulate the hydrogen volume fraction changes under the conditions of gas cylinder standing,pipeline being shutdown and pipeline flowing,and then to explore the distribution law of the blended hydrogen-natural gas’ volume fraction.The results show that in the process of static storage,such as gas storage in cylinders and pipeline shutdown,hydrogen gradually floats to the top and methane sinks to the bottom,causing the obvious stratification phenomenon.With the increase of pressure and hydrogen mixing ratio,and also the decrease of temperature and pipe diameter,the hydrogen’s volume fraction gradient in the gravitational direction of the pipeline increases.When the blended hydrogen-natural gas pipeline is running at a very small flow rate,the hydrogen gradually shifts to the pipeline’s top with the flow,resulting in the stratification phenomenon,and it is easier to stratify at the low temperature and the high pressure.The blended hydrogen-natural gas pipeline is suitable in operation under the condition of low pressure and high speed.