The analysis on calculation model of heat-wave velocity during the process of crude oil storage tank fire
The formation mechanism of boilover fire in crude oil storage tank is very complex and harmful. Heat-wave velocity is an important research topic in the boilover fire. After introducing boilover mechanism, the models of heat transfer and heat-wave velocity was built by heat transfer analysis for oil layer. Comparing the calculation results of model with the experimental data, this heat-wave speed calculation model is reasonable. Through the research, several conclusions were found: the main factors that impact heat-wave rate are the viscosity and component of oil, heat of heat-wave comes mainly from thermal radiation of flame; Emulsified water in the oil will not trigger boilover fire normally. Only the heat-wave encountered bottom water cushion at the bottom of the tank, did boilover fire take place. In practice, the heat-wave moving speed can be valued 1m/h to estimate the occurrence time of boilover. The results of this study are important for control and security of boilover fire accident.
Burning of weathering and emulsified oil spills
Abstract In previous works, we described small-scale experiments that dealt with the combustion of fuel slicks on water and provided some features of the events that can lead to boilover. The experiments showed that the violent-eruptive vaporization may be due to boiling nucleation near the heating fuel/water interface that has been superheated, and the mechanisms causing this phenomenon to occur have been discussed. If an attempt is made to burn crude oils, which are multicomponent fuels, the problem becomes complicated with the “weathering” of slicks (progressive evaporation of lighter volatiles) and the possibility to have water-in-oil emulsions. The objective of the present work is to study how the combustion of crude oil-layers floating on water is influenced by the aging of oil (degree of oil evaporation) and the formation of emulsions. The experiments are dealing with burning rate, time to the start of boilover, burned mass ratio and boilover intensity. The results are discussed in relation to the main factors influencing the phenomenon: initial oil-layer thickness and pool diameter. The behavior of weathered crude oil agrees closely with the general behavior of single oils with increasing boiling point (the surface temperature will increase with weathering as the residual crude oil becomes less volatile). In contrast, the case of emulsions is more complex and somewhat difficult to model (thermal breakage of emulsified layers, boilover difficult to discern). Finally, the work is complemented by a study of smoke production during the pre-boilover phase. The procedure permits measurements of exhaust gas composition by means of a flow-through system. Results show that weathering increases both yield of soot and CO but that emulsification decreases these yields. The former effect is due to a residual liquid progressively less volatile, the later to vaporised water interacting chemically in the flame.
Experimental evidence for microexplosions in water/fuel oil emulsion flames inferred by laser light scattering
Water fuel-oil emulsion flames have been studied on an experimental apparatus, conceived and realised in order to offer optical access all along a semi-industrial confined flame. The main objective of the work was to provide experimental evidence and gather information on the secondary atomisation mechanism, which was previously observed only in single droplet experiments. Laser light scattering diagnostic was applied to confined 600 kW fuel-oil and water/fuel-oil emulsion flames. The coexistence of fuel droplets, soot and cenospheres required a proper interpretation of the experimental results. The analysis of the scattered light intensities, of the polarization ratios and light extinctions enabled to localise, in semi-industrial scale turbulent diffusion flames, microexplosion phenomena, through which the water emulsions reduce solid particulate emissions. Unburned solid conventional sampling confirmed the amount and size reduction of the cenospheres, due to the microexplosions. The beneficial effect of water on soot formation has also been detected, showing a different behaviour between soot and cenosphere emissions by increasing the emulsified water content.