The effect of favorable conditions within chemical process units on vapour cloud explosion overpressures

Abstract

Accidents of flammable gas leaks and explosions are very likely to occur in process units of chemical plants due to various devices. Moreover, these facilities cause serious turbulence in the flow field, which may result in an explosion intensity that is difficult to be observed in previous conventional experiments. In this paper, we used the professional industrial disaster assessment software FLACS to reconstruct a real-size production unit, and obtained explosion overpressures under several cases by changing the size, concentration, location and ignition point of gas clouds. The experimental results demonstrate that the congestion of objects in an open environment can cause the explosion overpressure of cube-shaped gas clouds to reach a threshold sufficient to cause death or serious damage to facilities. However, this is not the case for pancake-shaped clouds. Furthermore, the explosion of confined spaces with large L/D ratios, as well as gas clouds covering multiple confined spaces, produce significantly greater blast overpressures than a single confined space, particularly if the ignition occurs in any one of these confined spaces. For a particular type of confined space, a reasonable method of characterizing the peak overpressure in terms of a degree of confinement parameter is proposed, and the two have a good linear correlation. There exist significant variations in the most sensitive concentrations during the overpressure rise phase corresponding to different operating conditions, whereas the range of most sensitive concentrations during the overpressure decline phase is concentrated within Φ = 1.3–1.4. Finally, the overpressure distribution patterns in the circumferential and elevational directions under a variety of cases are obtained for the most common cylindrical devices, and the determining factors affecting the results are discussed.