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.
A study on large-scale boilover using crude oil containing emulsified water
In order to elucidate the effect of emulsified water on boilover, an experimental study on large scale boilover was conducted using Sarukawa crude oil, which is produced in Japan and contains about 0.3 vol.% water. A 1.9 m diameter pan was used in the experiments, and initial fuel depth was set at three different levels of 100, 200 and 400 mm. Radiation from the fires to outside targets, temperatures of fuel and flame, and fuel burning rate were measured, and direct and thermal images of flames were recorded. Boilover occurred after a period of long burning as expected, but the periods from ignition to boilover observed in the present study were shorter than those predicted on the basis of results of previous studies. This result was inferred to be due to emulsified water in the fuel.
Burning of water-in-oil emulsions
In a project entitled “Improved fuel oil combustion” several methods for reduction of the particulate (oil coke) emission resulting from the combustion of fuel oil were examined. By far the best method proved to be dispersion of water into the fuel oil. Four methods for carrying out this dispersion are described: 1. ultrasonic homogenizing. 2. mechanical (liquid whirling) homogenizing, 3. centrifugal pump as emulsifier and 4. atomization of water into the oil by means of pressure jet nozzles. Results are shown from trials with all four methods. It is claimed that the effect of the water is physical. When firing a water-in-oil emulsion, smaller oil droplets are produced by the sudden evaporation of the water droplets in the emulsion upon entering, the combustion chamber. A sort of secondary atomization is thereby achieved. A 2–5 μm (microns) water droplet should be aimed at, as much larger droplets will not be incorporated in the oil drops and will thus be ineffective, and the rather large amount of water they represent will be wasted. if the dispersion of water in the oil is not very efficient, reductions in oil coke emissions of about 90 percent can be obtained with 10–15 percent water. If, however, the dispersion is very fine so that no water is wasted in the form of large droplets, 2–3 percent water is sufficient. Examinations of the collected oil coke particles in a scanning electron microscope confirm the theory that the water breaks up the oil droplets as the particles that measure 30–50 μm when fired without water are reduced to a size of 2–5 μm when fired with water. Moreover fragments of broken particle are found, which seems to indicate that some of the droplets do not break up until after coking of the surface has taken place.