Filtern
Dokumenttyp
Schlagworte
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.
There is a general lack of information on the effects of full-bore obstacles on combustion in the literature, these obstacles are prevalent in many applications and knowledge of their effects on phenomena including burning rate, flame acceleration and DDT is important for the correct placing of explosion safety devices such as flame arresters and venting devices. In this work methane, propane, ethylene and hydrogen-air explosions were investigated in an 18 m long DN150 closed pipe with a 90 degree bend and various baffle obstacles placed at a short distance from the ignition source. After carrying out multiple experiments with the same configuration it was found that a relatively large variance existed in the measured flame speeds and overpressures, this was attributed to a stochastic element in how flames evolved and also how they caused and interacted with turbulence to produce flame acceleration. This led to several experiments being carried out for one configuration in order to obtain a meaningful average. It was shown that a 90 degree bend in a long tube had the ability to enhance flame speeds and overpressures, and shorten the run-up distance to DDT to a varying degree for a number of gases. In terms of the qualitative effects on these parameters they were comparable to baffle type obstacles with a blockage ratios of between 10 and 20%.
The method described in this paper enabled reliable and accurate positioning of an overdriven detonation by calculation of shock wave velocities (detonation and retonation) for hydrogen explosions in a closed 18 m long horizontal DN150 pipe. This enabled an empirical correlation between the ignition position and the run-up distance to DDT to be determined. It was shown that the initial ability of the flame to expand unobstructed and the piston-like effect of burnt gas expanding against the closed end of the tube contributed to initial flame acceleration and hence were able to affect the run-up distance to overdriven detonation. Flame speeds and rates of initial pressure rise were also used to explain how these two competing effects were able to produce a minimum in the run-up distance to DDT. The shortest run-up distance to DDT, relative to the ignition position, for this pipe and gas configuration was found when the ignition position was placed 5.6 pipe diameters (or 0.9 m) from the closed pipe end. The shortest run-up distance to DDT relative to the end of the pipe was recorded when the ignition source was placed 4.4 pipe diameters or 0.7 m from the pipe end.