长输油气管线动火作业过程的烟囱效应及控制

Stack effect and its control in long-distance oil and gas pipeline during hot operation

为分析长输油气管线动火作业过程中气体间的扩散特性,根据氮气置换后管道两端的能量变化得出影响管道烟囱效应的主要因素,以西三线某焊点换管作业为研究背景,采用组分输运模型,分析各因素对基坑内氮气扩散的影响。结果表明:管道内氮气向基坑扩散主要受管道沿程阻力、两端高差和环境风流的影响;且随着时间推移,氮气聚集区主要位于基坑的另一端。沿程阻力和高差主要影响氮气出口速度;沿程阻力系数是管道的一种特性,氮气出口速度会随沿程阻力系数的增大而下降;而动火点与下游阀室之间的落差越大,氮气出流速度越高。环境风流主要影响基坑内氮气的扩散形式,当风流与氮气流动方向相同时,会加快基坑内氮气的排出;但基坑工作区位置氧气质量分数仍低于19.5%,需进行强制通风。当基坑内风机采用“风机+风筒”的安装形式,安装位置与管道出口对齐、距地面0.8 m时,排污效果较好。

To analyze the gas diffusion characteristics during the hot operation of long-distance oil and gas pipelines,the main factors that affect the stack effect of the pipeline were obtained according to the energy changes at both ends of the pipeline after the nitrogen replacement.Taking the pipe changing operation of a welding spot on the west third line as the research background,the influence of various factors on the nitrogen diffusion in the foundation pit was simulated through a component transport model.The results show that the nitrogen diffusion from the pipeline to the foundation pit is mainly affected by the resistance along the pipeline,the height difference between the two ends,and the environmental wind flow.And as time goes by,the nitrogen accumulation area is mainly located at the other end of the foundation pit.The resistance along the way and the height difference between the two ends of the pipeline mainly affect the nitrogen s outlet velocity is.The nitrogen s outlet velocity will decrease with the increase of the drag coefficient along the way,which is a characteristic of the pipeline.The greater the height difference between the hot operation and the downstream valve chamber,the higher the nitrogen s outlet velocity is.The environmental wind flow mainly affects the form of nitrogen diffusion in the foundation pit.When the wind flow direction is the same as the nitrogen s flow direction,it will accelerate the discharge of nitrogen in the foundation pit.However,in this case,the oxygen concentration in the working area of the foundation pit is still below 19.5%,so forced ventilation is required.When the installation mode of"fan+air cylinder"is adopted in the fan inside the foundation pit,and then the installation position is aligned with the outlet of the pipe and is 0.8 m away from the ground,the sewage discharge effect is better.