Validation of the DESC Code in Simulating the Effect of Vent Ducts on Dust Explosions

Abstract

The computational fluid dynamics (CFD) code DESC has been used to simulate a series of dust explosion experiments performed in an 18.5 m 3 vessel equipped with vent ducts of varying cross sections and lengths. The motivation behind the work is 3-fold: to validate the CFD code, to gain increased understanding of the parameters affecting dust explosion venting through ducts, and to investigate the validity of empirical correlations found in various standards and guidelines for design of explosion protection systems. Although the results from simulations agree reasonably well with experimental observations, DESC tends to underpredict the reduced explosion pressures for scenarios with vent ducts with diameters significantly larger than the vent openings. These discrepancies may be a result of inherent limitations in the model system, but poor repeatability and limited access to detailed experimental data complicates the analysis. Results from experiments and simulations are compared with predictions from various standards and guidelines for design of vent ducts in industry: EN 14491, VDI 3673, NFPA 68, and the methodology developed by FM Global. The correlations in NFPA 68, derived from the same set of experiments in the 18.5 m 3 vessel, yield the most accurate predictions. The FM Global method underestimates the reduced explosion pressure for the largest vent diameter and rear ignition and yields conservative results for smaller duct diameters. Neither experiments nor simulations support the concept of a critical duct length prescribed in EN 14491 and VDI 3673.

A Review of the Fire and Explosion Hazards of Particulates

“…In his 2010 lecture, Skjold presents a detailed and frank evaluation of the state of CFD for modeling dust explosions 100) , concluding that: "There remains much to be done before dust explosions are adequately understood". Meanwhile, Castellanos et al 101) have recently published an interesting application of DESC in a model calculation of a vented dust explosion with and without a duct and comparing it with experimental findings and calculation results based on guidelines and standards and empirical correlations.…”

Determination of upper flammability limits of C H O compounds in air at reference temperature and atmospheric pressure

“…Coward and Jones [4] stated that the flammability limits should be determined at constant pressure and such configuration has been applied by Mishra and Rahman [24] in their experiments. A constant pressure combustion process has been assumed in other works related to the determination of flammability limits [17,16,18,25] and this consideration is consistent with the experimental determination.…”

“…In other experimental configuration, described by Coward and Jones [4], the flame propagation is observed inside a cylindrical tube. The ignition source is located at one end of the cylindrical tube, and the flammability criterion establishes that a mixture is flammable if the flame propagates a certain distance towards the opposite end of the tube.…”

“…In another work, the flammability limits of ethanol were determined at different initial temperatures and pressures [2]. Earlier works by Zabetakis [3] and by Coward and Jones [4] describe a different apparatus used before the standardized tests were established. Experimental determination of the flammability limits of several compounds is being carried out since the first half of the 20th century.…”

“…The UFL is more sensitive to the flammability criterion than the LFL. It is also sensible to the direction of flame propagation [4]. This sensibility is an additional difficulty for the development of accurate methods for the determination of the UFLs of flammable compounds.…”