Numerical modeling for turbulent diffusion torch of flammable gas leak from damaged pipeline into atmosphere

Abstract

Assessment of pipeline safety is of paramount significance for safety of petrochemical plants. Any leakage of flammable gas from a pipeline poses a potential risk of an explosion followed by fire. Following a leak, a non-burning inert gaseous jet is first formed and, thereafter, ignition happens and an exothermal torch or flame occur. Safety assessments of such a scenario can be made by considering free-boundary-layer turbulent flows of fuel propagating in the surrounding atmosphere based on Prandtl’s mixing length theory. That implies modeling the fields of fuel/oxidizer concentrations, velocity, and temperature, and the overall shape of the axisymmetric inert jets and exothermal diffusion torches. Axisymmetric turbulent boundary layer equations have been solved numerically, and these solutions have been compared with self-similar solutions for inert jets. The comparison confirms that the difference between the numerical and self-similar solutions in the longitudinal velocity profile is within 1%. Furthermore, the numerical model predicts the fuel concentration within an uncertainty level of 15% when compared with the experimental data. In an exothermal torch, the combustion temperature keeps increasing until the fuel is depleted. Outside the fuel zone, the temperature of the torch cools abruptly in the radial direction. The longitudinal velocity of an exothermal torch is moderately higher than that of an inert jet because of the thermal expansion. In this work, results of parametric studies are presented for various values of the Reynolds number, which can be useful for petrochemical engineers who assess the risk level associated with potential fire hazards caused by pipeline leakages.