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Eingeladener Vortrag
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Heavy gases in large quantities are used worldwide in various industries. Past incidents, such as the liquefied gas disaster in Viareggio (2009) have shown that these materials are difficult to handle in a safe manner. According to the German Hazardous Incident Ordinance (StörfallVO 2000 - 12. BIMSchV), plant operators with extended responsibilities must produce a report in which they verify that , in the event of an unintentional gas release, the surrounding area will not be aversely affected. Essential elements of this report are calculations of both the released mass flow and the gas dispersion. Using models such as the VDI guideline 3783 (state of the art in Germany) plant operators are able to predict the characteristics of likely gas dispersions. The presented experimental investigations were carried out at the BAM better understand heavy gas dispersion with high gas concentrations in the air (≥ 1 Vol.-%), as well as concentrations with approximately neutral density characteristics (≤ 3000ppm) in order to test the accuracy of the VDI guideline. The starting point for experimental trials was the heavy gas releases resulting from pipeline, vessel or standard gas bottle leaks, with mass flows of between 20 and 100 g s-1. Investigations on the gas-phase release process focused on the unsteady mass flow associated with releases from standard gas bottles. The experimental results will be used as comparative parameters for future simulations. The goal of these simulations is to develop a model with which calculation of the unsteady mass flow, based on the material characteristics for any gas, is possible.
COMSOL Multiphysics® was used as a tool for the better understanding of the evolution of flow patterns during the induced ignition of gases. A simplified model was developed for the scope, by coupling the weakly compressible Navier Stokes module and the convection and conduction module. The current paper presents the results of the performed simulations.
Zur Bemessung von Druckentlastungseinrichtungen bei Gasexplosionen in Umschließungen existieren derzeitig nur wenige wissenschaftlich fundierte Auslegungskriterien, die die konstruktiven Randbedingungen oder Prozessbedingungen der explosionsgefährdeten Anlagenteile ausreichend berücksichtigen. Aus diesem Grund werden in der Praxis häufig stark konservative Annahmen getroffen, die zu erheblichen Überdimensionierungen der Druckentlastungseinrichtungen führen können.
Aus sicherheitstechnischer Perspektive können gerade diese vermeintlichen Sicherheitsmargen zu einer erheblichen Beschleunigung des transienten Druckverlaufs und damit eher zu einer Unterdimensionierung führen oder sogar den Übergang von Deflagrationen zu Detonationen begünstigen.
Sowohl Messungen als auch erste Simulationen mit Hilfe von CFD-Modellen begründen die Notwendigkeit weiterer Untersuchungen mit
explosionsgefährdeten Gasanlagen.
Da insbesondere bei turbulenten Verbrennungsvorgängen in den Normen Verbesserungspotential herrscht, wird bei der BAM zukünftig verstärkt dieses Thema in Forschungsarbeiten berücksichtigt.
For the design of gas explosion venting systems for confinements only little guidance is given when considering the constructional boundary conditions or process conditions. For this reason conservative assumptions are prevalent in practice and in many cases the protective Systems become significantly oversized. Such safety margins in venting areas can lead to a critical acceleration of the pressure rise. Finally, a gas explosion at turbulent conditions caused by oversizing of the venting area rather leads to an under-sized system and supports the deflagration to detonation transition (DDT). The present investigation was focused especially on the influence of certain obstacles as well as the effect of the initial pressures on the explosion venting behavior of methane-air-mixtures and of hydrogen-air-mixtures.