Comparing to CFD simulations, the VMEOC correlations provide a faster way to estimate the peak overpressure of a vented explosion. Parameters associated with burning velocity and turbulence generation, oscillatory combustion and flame instabilities in vented gas explosion are taken into account in the development of new correlations.
More than 350 simulations consisting of 16 enclosure scales, 12 vent area to enclosure roof area ratios, 8 gas equivalence ratios and 9 vent activation pressures are then carried out to develop the Vented Methane-air Explosion Overpressure Calculation (VMEOC) correlations. A series of experimental tests are carried out first and the results are used to validate the numerical models developed with the commercial CFD software FLACS. This paper presents new correlations developed through numerical simulations to estimate peak overpressures for vented methane-air explosions in cylindrical enclosures. This is an abstract of a paper presented at the 2013 AIChE Spring Meeting and 9th Global Congress on Process Safety (San Antonio, TX -).
However, the new methodology does not yet reproduce large-scale test data with repeated small obstacles simulating highly congested piping arrays and more work on this issue is necessary. Calculated vent areas using the new method also prevent under-sized vent areas for large enclosures with large equipment representative of many petrochemical process structures.
These equations compare favorably with the reference data sets for unobstructed and minimally obstructed enclosures. The 2013 equations are essentially a more transparent casting of the Swift-Epstein-Fauske derivations to provide a framework for including approaches to model flame accelerations and flame wrinkling/stretching in large enclosures with and without internal obstacles. The 2013 edition of NFPA 68 Standard on Explosion Protection by Deflagration Venting will replace vent area sizing equations containing the gas Deflagration Index, KG, for high-pressure applications with equations containing the laminar burning velocity.
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