Dust explosions: Protection of silos by venting

Abstract

It is well established that dust explosions represent a serious hazard in many process industries and silo facilities. Many catastrophic cases have been reported, and statistics show that the number of incidents per year is still significant. Venting is the most common protective measure used in silos in order to prevent the appearance of unacceptably high internal pressures. However, the installation of venting devices is not always simple, and technical complications frequently arise. Furthermore, the cost of protection by venting must be taken into account. Vent areas in silos should be large enough to prevent damaging overpressures, but not so large that the use of venting becomes impracticable. Thus, vent area sizing is a critical issue. To calculate vent area size, standards EN 14491 (2006) and NFPA 68 (2007) are commonly used in Europe and North America, respectively, but in certain situations, they are contradictory.The aim of this study was to analyze dust explosion venting in silos by comparing the above venting standards and also conducting CFD simulations. The pressures and associated vent areas in these numerical simulations were compared to those contemplated in the standards. In addition, some calculations were carried out for venting devices with inertia. The simulated explosion pressures showed the expected trends for the associated vent areas and agreed reasonably well with the values contemplated in NFPA 68 (2007).For low overpressure values, the differences were significant compared to those vent areas predicted by standard EN 14491 (2006). Numerical simulations could serve as a powerful tool for helping engineers to design explosion protection and calculate the structure of vented silos. However, the results of numerical simulations should be extrapolated with caution since they are absolutely dependent on the flow characteristics and the dust concentration of the initial dust cloud. © 2012 by Nova Science Publishers, Inc. All Rights Reserved.