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Dispersion of Heavy Gases
(2014)
Im Rahmen von Störfallauswirkungsbetrachtungen werden oft Szenarien betrachtet, in denen Gase freigesetzt werden, die schwerer als Luft sind. Für die Berechnung der Gefährdungsbereiche wird in Deutschland oft die Richtlinie VDI 3783 eingesetzt. Die Methodik zur Bestimmung der Konzentrationsverteilung bei der Freisetzung eines Schwergases ist im Blatt 2 der Richtlinie dargestellt und basiert auf Windkanaluntersuchungen mit verschiedenen Ausbreitungsgebieten. Unter der Zielsetzung, eine möglichst konservative Abschätzung des Gefährdungsbereichs zu erhalten, erfolgte die Gasfreisetzung am Boden. In der Praxis sind aber immer wieder Szenarien zu untersuchen, bei denen die Gasfreisetzung aus Anlagenteilen über Bodenniveau erfolgt. Durch Freilandversuche sollen Anhaltswerte für die Bestimmung einer kritischen Quellhöhe, ab der eine Schwergasausbreitung nicht mehr zu betrachten ist, ermittelt werden.
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. The essential elements of this report include calculations of both released
mass flow and 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.
Within the framework of the reported experimental trials, the release process of heavy gases
from standard gas cylinders was investigated. Using the results of this investigation a calculation
methodology has been developed which is able to predict the mass flow of a gas-phase release.
As input parameters only the geometry of the gas cylinder, the material properties of the
respective fluid as well as the environmental parameters such as velocity of approach and air
temperature are required. In the course of modeling various approaches for nucleate boiling have
been tested for their applicability. Both the calculation methodology and a comparison between
the calculated and experimental results will be presented.
Within the same framework of experimental trials, the dispersion process of the aforementioned
heavy gases was also investigated. The dispersed gas cloud in this case was considered as originating from a continuous point source under ambient conditions. For the various trials
concentrations both in the heavy gas (≥ 1 vol.-%) and in the neutral gas field (≤ 3000 ppm) were
measured. In the immediate area of the release the length, width and height of the heavy gas
cloud were evaluated. The experimental results, comparison calculations and the measurement
techniques will be presented.
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.