Rainout Assessment after a Release of Hazardous Liquefied Gas: Effect of Physical and Storage Parameters

摘要

In process industry it is common practice to store and handle dangerous substances,rnwhich are gaseous at atmospheric temperature, as pressurized or refrigerated liquids. Inrncase of accidental release, a fluid in these conditions gives rise to a two-phase discharge.rnIn such conditions, the liquid breaks up in an aerosol cloud, whose behavior inrnatmosphere affects dispersion distances. The physical phenomena occurring after thernrelease to the atmosphere are mainly three: expansion to ambient pressure, liquidrnatomization (break-up) and rainout. In particular, the rainout fraction is a crucialrnparameter in quantitative risk analysis and therefore models capable of estimatingrnwhether it occurs or not are of paramount importance.rnThis study aims at emphasizing the influence of some physical parameters and storagernrelated parameters on the rainout fraction, taking into account continuous and stationaryrnreleases of ammonia and LNG (Liquefied Natural Gas). These represent two differentrnclasses of substances: gas liquefied by pressure (superheated) and gas liquefied byrnrefrigeration (subcooled), which undergo to different jet break-up mechanisms. Thernresults obtained for these two compounds can then be extended to the whole range ofrnpressurised liquids/liquefied gases.rnA simple model has been developed to evaluate rainout occurrence, the simple approachrnhere proposed (which has been validated comparing its results to those of otherrnsimulation models as well as to some available experimental data) allows to investigaternin a simple and effective way the importance of the different physical and storagernparameters involved during rainout.