Numerical simulation on gas dispersions and vapor cloud explosions induced by gas released from an ethylene storage tank

Abstract

Storage tanks may leak due to corrosion or human error, resulting in released gas dispersion and vapor cloud explosion accidents. The computational fluid dynamics software FLACS was employed to reveal the development processes of explosion accidents and estimate their influences on the environment, focusing on the effect of the leakage and environmental wind as two dominant factors on the ethylene gas dispersion and gas explosion. The results show that gas cloud dispersion distance and gas cloud volume increase with the increasing leak rate. When the leak rate is less than 6 kg/s, the gas cloud dispersion distance and gas cloud volume are similar in different leak directions. When the leak rate is greater than 6 kg/s, the dispersion of released gas and formation of gas cloud are influenced by the obstacles. The gas cloud dispersion distance decreases and the gas cloud volume increases as the blockage rate of the geometric obstacles increases. When the leak direction is perpendicular to the central axis of the storage tank group and the leak rate is 18 kg/s, the gas cloud attains its maximum dispersion distance of 81.5 m. When the leak direction is parallel to the central axis of the storage tank group and the leak rate is 24 kg/s, the gas cloud reaches its maximum volume of 9 604 m3. The impact pressure of the explosion wave increases with the increase in the leak rate. Under the influence of the environmental wind, the dilution of combustible gas is prominently accelerated and the combustible gas cloud volume is substantially lessened. Meanwhile, the probability of ignition of gas clouds and the intensity of the vapor cloud explosion are effectively reduced. Moreover, the time corresponding to achieve the peak explosion pressure is earlier and the decrease of the temperature is quicker than their counterparts under the condition without the environmental wind. When the leak rate is 24 kg/s, the explosion overpressure around the leakage location on the surface of the tank is only 6.88 kPa, but the temperature is 2 384 K. Therefore, when the explosion accident occurs, cooling the storage tanks is crucial in rescue in order to avoid the secondary disaster.