| In recent years, the leakage and explosion accidents of natural gas pipeline in gas transmission stations have caused great harm to the personal safety of the residents and significant losses to the state property. Currently, the study of the gas transmisson station is limited to a single risk evaluation or numerical simulation In this paper, taking the gas transmission initial station of Boai as the research object, the method of numerical simulation combining with the theoretical analysis was used to establish the leakage diffusion model and risk evaluation system of natural gas pipeline, which is of practical significance for the safe operation and management of gas transmission station.Based on fully investigating relevant research status of the leakage and diffusion of natural gas pipeline in gas transmission stations at home and abroad, the three-dimensional numerical simulation of upward, downward and lateral pipe leakage and diffusion in Boai first station was conducted by using FLUENT software, and the diffusion range after natural gas leakage and diffusion under different wind velocities, leakage hole diameters, leakage heights, different wind directions (windward and leeward side) were obtained. The results show that:When the leakage pressure is 1.89 MPa, the natural gas jet along the jet core, the initial maximum speed is 267 m/s, along the way it decrease slowly and the jet width increase gradually. When the leakage and diffusion of natural gas is stable, the time to reach the concentration boundary of 1% and 5% are 10 s and 5 s respectively, and the diffusion range is larger in the former case. The diffusion ranges of natural gas with the concentration boundary of 1% and 5% can come up to the largest at the maximum leak hole diameter of 0.2 m and the maximum wind velocity of 10 m/s. For the bottom leakage of a horizontal gas pipeline, and the lateral leakage of a vertical natural gas pipeline, the maximum diffusion range are larger, which is of great risk.Using Tecplot and CFD-post software, the change laws of natural gas concentration with time, leakage hole diameter and wind velocity under different operating conditions were discovered. The results show that:For the lateral leakage of a vertical natural gas pipeline, the natural gas concentration at the leakage port can be up to 0.85, and the concentration around the ground is above 0.15. When the contrary wind velocity is between 5 and 10 m/s, the gas concentration around the ground will reach 0.005～0.08, which is great harm to personal safety.Based on leakage accidents, the main hazard factors in the gas transmission station were analyzed, and leakage fault tree of Boai first station was established to determine the most dangerous event. Comprehensively considering the three aspects of pipeline leakage, environment factors and equipment leakage, an effective and complete safety index system for Boai station was built by using the analytic hierarchy process method. The security level was evaluated through fuzzy comprehensive evaluation and safety level fuzzy characteristic vector methods. The results show that:Analytic hierarchy process is applied to determine the three rule layers, including the pipeline leakage (U1), environmental factor (Ue) and equipment leakage (Us), and the corresponding index weight levels are 0.53,0.33,0.14 respectively. The safety fuzzy characteristic value scope is 2.29～3.03 and the middle value of safety fuzzy characteristic value scope is 2.66. This indicates that the safety level of Boai first station is excellent for the "General security" and is in accordance with the field conditions.Finally, the flow chart of accident emergency treatment was established, and meanwhile the emergency plan for leakage and fire accident were put forward for the three conditions of upward and downward leakage for horizontal overhead pipeline and lateral leakage for vertical overhead pipeline, which is a certain reference for the leakage safety pretection of the gas transmission station. |
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