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- Acetylene (4)
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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.
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.
Fire exposure tests of acetylene cylinders were performed. The purpose of the experiments was to gather information on the behavior in fire of such vessels, depending on the initial charge of acetylene. In fact "empty" acetylene cylinders still contain the solvent in which acetylene is dissolved plus the amount of acetylene to saturation at atmospheric pressure and ambient temperature and may still constitute a threat to safety. In the fire exposure tests performed the hazardousness of these vessels was demonstrated, since it was observed that not only fully charged acetylene cylinders but also cylinders with saturated solvent can explode, provided the heat transfer to the vessel is sufficient. The times to explosion were shorter for fully charged cylinders, due to the higher initial pressure and to the faster pressure increase. The effects of the explosions are comparable for both fully charged cylinders and for cylinders with saturated solvent, except for the smaller fireball which is produced in the second case, due to the smaller amount of fuel available. In both cases the cylinder walls or at least fragments can fly further than 100 m away from the burst location. Results of the experiments are presented in the paper. During the tests, temperature measurements at the cylinder walls and in the cylinder interior were performed. Furthermore, the pressure in the cylinder was recorded. The collected data will serve for the validation of a numerical model for the simulation of the heating of acetylene cylinders involved in fire and of the afterward cooling with water, which has been developed. The constitutive model equations and the results of some simulations are presented in the paper.
Prevention of the explosion of acetylene cylinders involved in fire: experiments and simulations
(2011)
In order to assess the effectiveness of water cooling of acetylene cylinders involved in fire, a total of 13 bonfire tests with 8.9-, 10
and 50-l-cylinders were performed. During the experiments the pressure
in the cylinder and the temperature at different locations within the porous material and on the Shell surface as well as the flame temperature were measured. Overall 8 burst tests were performed, in order to determine the times to explosion for the cylinders. Cylinders failed not later than 15 minutes from the ignition of the bonfire, often with generation of a fireball. During the other 5 tests, the fire was extinguished before the expected burst and the cylinder was cooled with water. In 2 of the 5 extinction experiments, the explosion of the cylinder could be prevented. Noticeably, in one case the on-set of the decomposition of acetylene had already been observed, before the cooling was started. In spite of that, the cooling was still effective. The interpretation of the current results and of the data from previous tests with 40-l-cylinder suggests that single acetylene cylinders involved in fire might be saved by cooling, if their pressure does not exceed a value of about 45 bara. The recorded values of pressure and temperature were used to develop and validate a mathematical model for the prediction of the heat transfer in acetylene cylinders during the exposure to fire and the afterward cooling. The predictions agreed well with the experimental results.
In this paper a mathematical model for predicting the heating-up of an acetylene cylinder involved in a fire is 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 and acetylene dissolved in it. Model equations covered heat conduction in the cylinder interior and at its walls, while the fire surrounding the cylinder was simulated by solving the coupled heat transfer and the momentum equation. Results of the calculations and the effects of some model parameters are discussed.
Ein entscheidendes Problem neuer Wasserstofftechnologien ist die leichte und sichere Lagerung ausreichender Mengen an Wasserstoff insbesondere für Nutzung bei tragbaren oder mobilen Anwendungen. Eine neue und innovative Technologie basierend auf gebündelte Kapillaren wurde entwickelt. Diese Systeme garantieren eine sichere Speicherung, Lagerung und kontrollierte Freisetzung von Wasserstoff, obgleich Speicherdrücke bis 1200 bar angewendet werden. Die neue Technologie ermöglicht die Lagerung einer erheblich größeren Menge Wasserstoff als andere Systeme und übertraf bereits die Zielsetzung des DOE 2010. Es wird erwartet, die DOE-Zielsetzung für das Jahr 2015 bereits in naher Zukunft zu erreichen. Hauptaspekt für die Speichertechnologie ist die Druckfestigkeit der Glaskapillaren. Es ist weithin bekannt, dass besonders Quarz eine dreimal höhere Festigkeit als Stahl hat. Gleichzeitig ist die Dichte ungefähr dreimal niedriger, was bedeutet, dass viel weniger Material notwendig ist, um die gleiche Druckfestigkeit zu erreichen. Die Druckfestigkeit einzelner Kapillare ist in der Abhängigkeit der Materialien, der Abmessungen, der Wandstärke etc. ermittelt worden, um optimale Parameter für die "finalen" Kapillaren herauszufinden.
Determination of deflagration venting requirements in chemical/process plants is usually carried out using well established standards employing an empirically based formula. However, this formula is shown to have severe shortcomings, especially in the range of low KG-values, where either negative or inconceivably large venting areas can be predicted. Due to these shortcomings a method has been developed using the efflux function for gases as a basis to predict the mass flow through a vent opening in a vessel during an internal explosion. The simulated rise in pressure due to the internal explosion is quantitatively determined from the KG-value, with the mass flow through the vent opening in the vessel resulting from the pressure difference between the vessel and its surroundings. This enables the maximum overpressure as a function of the pressure relief surface area to be predicted. The method takes into account the temperature of the efflux gases and turbulence enhancement brought about by the venting process. In the following paper explosion pressure relief experiments are described and the results from these experiments are compared to predictions from the efflux method. It is shown that by adjusting the assumed turbulence which evolves during the venting process, the reduced explosion pressure can be reasonably well reproduced.