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

Key words:  long-distance oil and gas pipeline  stack effect  height difference  gas diffusion  nitrogen mass fraction

Abstract:

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.