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- Explosionsdruckentlastung (4)
- Explosionsschutz (4)
- Turbulent combustion (4)
- Gas explosion venting (3)
- Obstacles (3)
- Turbulente Verbrennung (3)
- ANSYS CFX (1)
- Baffle (1)
- Bend (1)
- Deflagration to detonation transition (1)
Many industrial processes include a gas explosion hazard. If safety measures are not adequate to prevent a potentially explosive atmosphere or to avoid effective ignition sources in enclosures, at least the effects of an explosion can be limited e.g. by gas explosion venting systems.
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. From safety perspective such safety margins in venting areas can lead to a critical acceleration of the pressure rise. Moreover, a gas explosion venting at turbulent conditions caused by over sizing or by obstacles rather leads to an under-sized system. The present investigation was focused especially on the influence of certain obstacles as well as the influence of elevated initial pressures on explosion venting
behaviour of quiescent hydrogen, methane or ethylene in air.
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 (DDT) begünstigen [1-3].
Um die Gefahren bzw. die Einflussfaktoren dieser kritischen Zustände beurteilen zu
können, soll im Rahmen eines Forschungsprojektes das Explosionsverhalten in
Anwesenheit Turbulenz bildender Einbauten oder bei nicht atmosphärischen
Bedingungen speziell bei erhöhten Anfangsdrücken - systematisch untersucht
werden.
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 effects of a gas explosion in enclosures like vessels can be limited e.g. by gas explosion venting
systems. The major design step of this constructive explosion protection method is to determine the
required vent area, which depends significantly on whether turbulent combustion exists. However,
current standards like NFPA 68 or EN 14994 are applicable only to limited boundary conditions and
as far as possible only to laminar flame propagation. Difficulties arise in the assessment or predictability
of gas explosion hazard when turbulence occurs.
In this research especially venting at elevated initial pressure has been shown to accelerated
flame propagations and therefore, to a considerably higher reduced pressure. Therefore, it is essential
to provide a broader data base of turbulent combustion and explosion behaviour to verify the
existing rules or to determine their safety-relevant parameters.
For a better safety assessment or design of protective systems the turbulent combustion and
accelerated gas explosion behaviour of quiescent methane in air were investigated at initial pressures
up to 8 bar using vessels up to 100 litres. In particular a systematic study was performed to
investigate the influence of turbulence on the overpressure development during accelerated gas
explosion. Moreover, the present study consider the position of the spark igniters, the burning velocity
and the maximum pressure rise for different concentration of fuel as well as the size of orifice
and/or vent area.
A choice of experimental tests showed under the investigated conditions that not only turbulence
inducing obstacles but also over sized vent areas could lead to an increased pressure development
and therefore to an inacceptable safety state. Due to the numerous influencing variables of
explosion behaviour the presented experimental results help to judge whether another more sophisticated
method should be applied than the one described in standards.
The effects of a gas explosion in enclosures like vessels can be limited e.g. by gas explosion venting systems. The major design step of this constructive explosion protection method is to determine the required vent area, which depends significantly on whether turbulent combustion exists. However, current standards like NFPA 68 or EN 14994 are applicable only to limited boundary conditions and as far as possible only to laminar flame propagation. Difficulties arise in the assessment or predictability of gas explosion hazard when turbulence occurs. In this research especially venting at elevated initial pressure has been shown to accelerated flame propagations and therefore, to a considerably higher reduced pressure. Therefore, it is essential to provide a broader data base of turbulent combustion and explosion behavior to verify the existing rules or to determine their safety-relevant parameters. For a better safety assessment or design of protective systems the turbulent combustion and accelerated gas explosion behaviour of quiescent methane and hydrogen in air were investigated at initial pressures up to 8 bar using vessels up to 100 litres. In particular a systematic study was performed to investigate the influence of turbulence on the overpressure development during accelerated gas explosion. Moreover, the present study consider the position of the spark igniters, the burning velocity and the maximum pressure rise for different concentration of fuel as well as the size of orifice and/or vent area. A choice of experimental tests showed under the investigated conditions that not only turbulence inducing obstacles but also over sized vent areas could lead to an increased pressure development and therefore to an inacceptable safety state.
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.