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- Behälterversagen (4)
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- Fire (2)
Organisationseinheit der BAM
- 2 Prozess- und Anlagensicherheit (6)
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- 8 Zerstörungsfreie Prüfung (3)
- 8.1 Sensorik, mess- und prüftechnische Verfahren (3)
- 2.2 Prozesssimulation (2)
- 3 Gefahrgutumschließungen; Energiespeicher (2)
- 3.0 Abteilungsleitung und andere (2)
- 7 Bauwerkssicherheit (2)
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (2)
The Ignition Temperature (IT) of stoichiometric tetrafluoroethylene–air mixtures on hot walls was determined in a 3-dm³-reactor. Tests at elevated pressure conditions were performed, namely at 5, 15 and 25 bar(a), showing a decrease of the IT with the initial pressure. Furthermore, the measured ignition temperatures of stoichiometric tetrafluoroethylene–air mixtures were lower than the ignition temperatures required for the decomposition pure tetrafluoroethylene (Minimum Ignition Temperature of Decomposition, MITD) reported in previous works.
Equations from the Semenov thermal explosion theory on spontaneous ignition were used to identify approximate combustion kinetics of tetrafluoroethylene from the experimental results. The determined kinetics was used for the prediction of the IT of stoichiometric tetrafluoroethylene-air by simplified calculation methods. A very good agreement with the experimental results was observed.
Beim begehrten Kunststoff Teflon führt kein Weg an einem komplexen Herstellungsprozess vorbei, der aufgrund der besonderen Eigenschaften des Ausgangsstoffes spezieller sicherheitstechnischer Anforderungen bedarf.
Comsol Multiphysics unterstützte Wissenschaftler in der Auslegung der Produktionsanlagen bei der Identifizierung von Gefahrenquellen.
Preventing the explosion of acetylene cylinders involved in fire with help of numerical modeling
(2012)
The current paper describes a mathematical model, which was developed to simulate the heat transfer in acetylene cylinders during exposure to a fire. The cases of a direct engulfment of the cylinder in the flames and of exposure to a distant fire were considered. Furthermore, the model was also applied to the prediction of the heat transfer during the cooling with water of heated acetylene cylinders, in order to assess the effectiveness of this procedure as a measure to prevent the burst of the cylinder. To provide data for the definition and validation of the model a total of 13 bonfire tests with 8.9-, 10- and 50-dm³-cylinders were performed, where pressure and temperature measurements in the samples were performed. During 5 experiments the fire was extinguished before the expected cylinder burst and a cooling with water was applied. In the paper a short description of the experimental set-up and of the test results is given. Finally, a comparison with the model predictions is provided, showing reasonable agreement.
The Minimum Ignition Temperature of Decomposition (MITD) of tetrafluoroethylene in a partially heated pipe was analyzed for different initial pressures (5, 10 and 15 bara). The pipe used had an internal length of 1 m, an internal diameter of 30 mm with a volume of about 0.7 dm³ and was vertically oriented. Pressure at the pipe top and temperature at four different locations along the pipe axis were measured. Tetrafluoroethylene was found to decompose at lower temperatures for increasing initial pressures, in agreement with previous tests with reactors with fully heated walls. A complete passive quenching in the non-heated part of the pipe was observed only for an initial pressure of 5 bara, while for higher initial pressures, the decomposition propagated completely along the test pipe. Moreover, the test results on the MITD were compared with data from previous experiments in fully heated 0.2 and 3 dm³ cylindrical reactors and showed a decrease of the MITD with the heated volume through heated surface ratio of the vessel. Furthermore, the prediction of the MITD of tetrafluoroethylene by simplified calculation methods was attempted, showing a good agreement with the experimental results.
This work investigates the ignition of tetrafluoroethylene induced by the adiabatic compression that can arise by activating a high speed valve separating two portions of a pipeline with a high pressure difference. In the tests performed the high pressure zone contained tetrafluoroethylene at pressures between 15 and 30 bar. For the low pressure zone, experiments with nitrogen, air and tetrafluoroethylene were carried out. The pressure range in the low pressure zone was comprised between 0.05 and 1 bar. The pipe diameters analyzed were 15 and 20 mm. For the analyzed geometries, special conditions were required in order to reach reproducible ignitions, namely air at temperatures of at least 105 °C had to be present in the compression pipe. Furthermore, a minimum length of the compression pipe had to be used. The current work describes the experimental setup employed for the tests and discusses the achieved results. Numerical simulations were performed in order to clarify unexpected findings.
Acetylenflaschen im Feuer
(2012)
Acetylen ist eines der wichtigsten technischen Gase und findet insbesondere Anwendung beim Schweißen und Schneiden verschiedener Werkstoffe. Damit Acetylen in entsprechenden Mengen vor Ort zur Verfügung gestellt werden kann, wird es in Druckgasbehälter abgefüllt. Im Falle eines Brandes stehen Acetylenflaschen im Verdacht, jederzeit – auch nach Löschen des Feuers – aufgrund einer möglicherweise initiierten Zerfallsreaktion zu bersten. Um insbesondere Personenschäden zu vermeiden, evakuieren und sperren die Rettungskräfte einen Sicherheitsbereich mit einem Radius von mindestens 200 m um die verdächtige Flasche ab. Gleichzeitig wird umgehend mit der Kühlung der Flasche begonnen. Wie lange muss aber eine Acetylenflasche gekühlt werden, bis sie sicher abtransportiert werden kann, und wie lange muss der Sicherheitsbereich mit dem großen Radius aufrecht erhalten werden? Diesen Fragen ist die BAM in den vergangenen Jahren im Rahmen verschiedener Untersuchungen und Projekte nachgegangen.
In this paper two different approaches for predicting the heating-up of an acetylene cylinder involved in a fire and the afterward cooling with water are presented. In the simulations polynomial functions were used to describe the temperature dependency of the thermal properties of the cylinder interior, which is a complex system composed by a solid porous material, a solvent (typically acetone) and acetylene dissolved in it. Model equations covered heat conduction in the cylinder interior and at its walls. In the first approach the cylinder surroundings were simulated as a further domain constituted by CO2, during the fire exposure, and for water, during the cooling. In this domain the coupled heat transfer (convection and conduction) and the momentum equation (Navier-Stokes) were solved. In the second approach no further domain was considered but boundary conditions were set directly on the cylinder walls. Results of the calculations performed with both approaches are presented. This work could prove helpful in predicting to which extent the interior of an acetylene cylinder exposed to fire reaches temperatures capable of initiating the decomposition of acetylene and to determine how long a water cooling should be applied, so that the system is brought again under non-critical conditions.