Combustion of Fuel Droplet

Table fo Contents

Introduction3

Model for Combustion of Two-Phase Fuel Releases4

Governing Parameters6

Fuel Source6

Burning Cloud8

Results9

Fireballs from Flashing and Non-Flashing Releases14

BLEVE Modeling18

Other considerations for BLEVE21

Conclusion24

End Notes26

Literature Review

Introduction

Many chemical industry accidents are accompanied by fuel releases. Usually, a large quantity of fuel is stored at high pressure in a liquid state. Even a small rupture can cause a quick release of fuel from a tank [1]. For example, 100 tons of fuel are released in about 10 s. A failure of a tank with pressurised fuel is followed by abrupt decrease of pressure, explosive boiling and evaporation two-phase outflows of a liquid-vapour-air mixture. An ignition of such a fuel-droplet-vapour-air cloud can cause shock-free combustion with the formation of a fireball [1]. The powerful radiation flux emitted by the fireball is dangerous for people and the environment.

Several DOE standards and/or orders require the analysis of hypothetical releases of hazardous materials. For flammable materials such as liquefied petroleum gas (LPG) or propane stored as pressurized liquefied materials (i.e., stored as liquids in pressurized vessels), a boiling liquid expanding vapor explosion (BLEVE) event may prove to be a credible accident scenario [29]. A BLEVE occurs when a vessel containing a superheated liquid (e.g., propane) catastrophically fails, usually as a result of external fire exposure (i.e., a pool fire under the vessel or a jet- or torch-type fire impinging on the vessel walls). The fire pressurizes the vessel, causing the relief valve to open, which allows the pressurized vapor to escape. As the liquid level in the vessel decreases, the flames impinge on the vessel wall above the liquid level. The vessel wall rapidly heats up due to the poor heat transfer provided by the vapor on the inner side of the vessel wall. The wall weakens and then tears, resulting in a sudden catastrophic failure of the vessel [29].

This literature also analyses the BLEVE Model in detail. Boiling Liquid Expanding Vapour Explosions (or BLEVE's) occur when a container that is holding a liquid above its boiling point, fails catastrophically. There will be an explosive release as the liquid flash boils, as it instantly changes from a liquid into a vapour, in which the volume expands several hundred times[29]. The size of the container, and therefore the amount of liquid involved, can range from aerosol cans to bulk storage tanks in which a BLEVE can look like a small nuclear explosion. This is how a pilot reported one particular BLEVE incident while landing at Mexico City in 1984. The term BLEVE, and its explanation was first coined in 1957 by a group of engineers in the insurance industry.1 It wasn't until 1972, or some 15 years later, that the term filtered into the ranks of emergency services and acquired its fearsome reputation[2]. A BLEVE cannot occur in containers that are not sealed, or if the liquid inside the container is not above its boiling point. The containers must fail completely and instantaneously. Container failure may be due to metal fatigue from impact, corrosion, poor manufacture, or ...