Numerical Simulations Of Leak And Diffusion On Long Distance Nature Gas Pipelines

With the development of natural gas utilities, and the exploitation of remote gas field, the mileage and scale of long-distance natural gas pipeline are expanding. Therefore, the risk of accidents is also rising. As the most important part of long-distance gas transmission, the long-distance natural gas pipeline bears the responsibility of the connection between gas field and gas station or other facilities with the characteristics of large diameter, high pressure and large transportation. Hence once the long-distance natural gas pipeline leaks, it will not only affect businesses and residents daily production and life, but also cause significant economic losses and may cause explosion, fire or other accidents which seriously harm to people's lives and property. For these reasons, studies of the leak and diffusion process of long-distance natural gas pipeline have great significant to the development of emergency rescue scheme and reduce accident loss.On the basis of Chinese'Western Gas Transported to East'project backbone cable, through the establishment of the three-dimensional model of pipeline leak in the air, the computational fluid dynamics software was used in the study, and the Realizable k-epsilon model was chosen to simulate its process of leakage and diffusion in the air. In this paper, four factors were selected to study, such as the diameter of leak orifice, the velocity of wind, the initial velocity of leak and the leakage orifice shape. Besides, the influence strength of these four factors in the process of diffusion was analyzed.In the condition of constant velocity of wind, five processes of leakage were simulated which leakage aperture diameter was equal to 20mm,50mm,80mm,120mm, and 200mm respectively. The results show that, with the pore size increases, the decreasing trend of the jet velocity is slowing down with increasing altitude; the height and width of the jet core formed by leakage of the natural gas increases; the range of jet gradually increasing, which the growth on height direction is greater than the growth on the circumference direction.In the condition of constant diameter of leakage orifice, six processes of leakage are simulated which wind force ranges from 2 to 7 respectively. The studies show that as the wind speed increases, the angle between the jet formed by the natural gas and the X-axis continues to decrease; the height of the development of gas jet keeps on decreasing; and the direction of the development of gas jet gradually tilts to the wind down direction.Under the same conditions, the two initial velocity of the leakage were compared. With the initial leak rate increases, the jet extent increases along the direction of height, the decreasing trend of the velocity with the increasing altitude is slowing down, the range of spread of each component increases on the height direction, but decreases on the wind direction. The growth of jet on height direction is much greater than the change on the circumference direction.In the condition of constant velocity of wind and the same leakage orifice area, different shape of the leak orifice such as rectangle, square, triangle and round was simulated respectively. The results show that the shape of leakage orifice has great influence on the trend of that the velocity decreases with the height increasing. Under the same leakage orifice area, the range of leak is wider when the shape is rectangle or circle.