A hazard identification and parametric analysis of toxic pollutants dispersion from large liquid hydrocarbon fuel-tank fires

Modern petrochemical complexes, and especially refineries, comprise large storage facilities, which contain, among others, significant amounts of flammable hydrocarbon fuels and chemicals in large storage tanks. Despite the fact that the occurrence of a tank fire accident is a relatively rare phenomenon, its results may lead to unexpected consequences for the installation and also cause potential environmental and health damage that is difficult to assess apriori. The purpose of the present study is the hazard identification and parametric analysis of pollutants dispersion from large liquid hydrocarbon fuel tank fires, by using Computational Fluid Dynamics (CFD) techniques. Numerical simulations were performed for a physical domain of 34521 m length, 2400 m width and 3000 m height. Parametric analysis was performed for three different tank diameters, 85, 70 and 50 m, respectively. In addition a methodology was developed to calculate the ground-level concentration of the toxic contaminants and the height of the plume rise. Two types of fuel, namely crude and diesel oil, with different wind velocities were examined. The CFD code PHOENICS, along with an iterative algorithm for pressure-correction, namely SIMPLEST, was used for the numerical simulation. The code employs the finite volume method (FVM) for the discretization of partial differential equations governing the flow. The governing equations express the conservation of mass, momentum, chemical species, enthalpy and two turbulence variables in steady, threedimensional flow. The discretization of the above equations is obtained by using the hybrid scheme. The modified RNG k-ε model was employed in order to account for turbulent flow with strong buoyancy forces. In addition the Chen-Kim k-ε model was also examined for comparison purposes. A quantitative risk analysis was performed for the investigation of any potential human health risk (e.g. fire-fighters, personnel) and any repercussion to the environment. The identification of the risk zones was specified by comparing the pollutants ground-level concentration with the safety limits for each pollutant, such as IDLH, STEL and TWA. Finally, a dimensionless nomograph is derived for engineering purposes in order to prevent or avoid the bad effects from toxic pollutant dispersion and the results are presented and discussed.