(104aq) Release and Dispersion of Heavy Gases - Experimental Results and Numerical Simulations

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 bottles was investigated with releases from both the gas and liquid phases. Using the results of this investigation a calculation methodology has been developed which is able to predict the mass flow of a single-phase as well as that of a two-phase release. As input parameters only the geometry of the gas bottle, 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 modelling various approaches for nucleate boiling have been tested for their applicability. Both the calculation methodology and a comparison of the calculated results with the experimental results will be presented.

Within the same framework of experimental trials, the dispersion process of heavy gases was also investigated. The starting point of the dispersion in this connection is an evaporating pool under ambient conditions. For different sized circular pools (1 m, 2 m, 3 m in diameter) 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 height and width of the heavy gas cloud were evaluated. The experimental results and measurement techniques will be presented.