Study On Gas Leakage Diffusion And Control Method Of Underground Pipe Gallery

In this paper,for the underground gas pipeline leakage accident,the small hole leakage model with gas pipe pressure of 0.4MPa,pipe diameter of 600 mm and leakage hole of 20 mm is selected as the research object.Based on the CFD numerical simulation method,the natural gas concentration in the pipe gallery is controlled by accident ventilation.The changes of natural gas concentration at the leakage hole,the alarm point and the exhaust port,and the change of the natural gas leakage velocity at the leakage hole are analyzed.At the same time,the method of inerting nitrogen injection was adopted to study the control effect of different natural gas nozzles in the pipe gallery under different control intervals,different nitrogen injection rates and different exhaust system control.The transient process after the small hole leak in the section gas pipeline was simulated by Fluent software.Natural gas has a very high jet velocity at the beginning of the leak,exceeding 400m/s.The time periods of the natural gas concentration in the leakage hole,alarm point and exhaust port in the range of 5%~15% are 20~190s,27~168s and 85~269s respectively.It takes 249 seconds from the valve at both ends of the gas line of the accident ventilation opening and emergency shut-off section to the gas concentration in the entire section pipe gallery to be reduced to less than 5%.During the leakage process of natural gas,there have been two “sudden drops” in natural gas concentration.In the process of diffusion,the phenomenon of “ceiling jet” and “stratification” is significant,and the high natural gas concentration in the upper part of the pipe gallery is the longest in the explosion range,which is a dangerous concentrated area.Based on the position of the leakage hole under the accident ventilation control condition,the natural gas concentration in the pipe gallery is controlled by the method of nitrogen injection inerting.Six different nitrogen injection schemes were set up for a single nitrogen nozzle,and the maximum arrangement spacing of the nitrogen nozzles was 14 m when the natural gas concentration in the pipe gallery was effectively controlled under any leak hole position.Furthermore,under the control of nitrogen injection system,three scenarios of leakage holes from different positions of the exhaust port are simulated and analyzed.The research shows that the most economical nitrogen injection amount of a single nitrogen nozzle is 0.5m3/s,the more the leakage hole is from the exhaust port.Far,the better the control of natural gas concentration in the pipe gallery,the shorter the nitrogen injection time required to reduce the natural gas concentration in the pipe gallery to below 5%.At the same time,for the extremely uncontrollable situation when the leakage hole and the exhaust port are on the same side of the section gas pipeline,a control method for arranging a double exhaust system instead of a single exhaust system in the section pipe gallery is proposed,according to the location of the leak hole.The exhaust port at a position farther away from the leak hole is selected,and the most unfavorable situation when the leak hole is located in the middle of the gas pipe is studied,and the effectiveness of the dual exhaust port system control is verified.By comparing the two control methods,it can be seen that after the small hole leakage occurs at any position of the underground gas pipeline,the inertia of nitrogen injection is adopted,and the time required to control the natural gas concentration in the pipe gallery below 5% is much lower than that of the accident ventilation.The time required.When the nitrogen injection inerting method is adopted,the dangerous area in the pipe gallery is within 10 m,which greatly reduces the possibility of natural gas explosion in the pipe gallery and strives for valuable time for evacuation of people around the leakage area.