Experiment And Numerical Simulation On Characteristics Of Mixed Crude Oil Fires

Recently more and more mixed crude oil storage tank fire accidents occur. Compared to other fuels, boilover phenomenon always appears during the combustion process besides the steady burning due to the physical-chemical characteristics of the crude oil. A small-scale mixed crude oil fire experiment setup and numerical simulation model were developed to study the combustion process of the mixed crude oil tank. The main contents and conclusions are as follows:1. Four stages were discovered in the combustion process based on the variation of flame shape and medium temperature inside the tank.(1) Steady burning stage:The flame was stable and the temperature of the crude oil continued to rise with time.(2) Boilover precursor stage: The amount of smoke gradually increased. Accompanying by the drastic fluctuations of the temperature of the crude oil and the oil-water interface, boil phenomenon occurred.(3) Boilover stage:Flame brightness was intensified followed a "boom" sound. The flame height and width increased rapidly in a short time. Part of the combustible oil was ejected out of the tank. The temperature of the crude oil and the oil-water interface fluctuated drastically.(4) Ending stage:Flame brightness decreased significantly and the flame was gradually extinguished. The temperature of the crude oil and oil-water interface rapidly decreased.2. The burning characteristics during the boilover stage were specially investigated in the research. The temperature of the oil-water interface (110℃～145℃) was found to be the critical conditions for the occurrence of the boilover. Different influencing factors were examined by the small scale experiment. The conclusions achieved in this part are as follows:(1) Boilover was strongly affected by the tank diameter, the thickness of the oil and the thickness of the water cushion. Boilover was intensified with increasing the tank diameter and the thickness of the oil. For the thickness of the water cushion, when the oil was enough, the thicker the water cushion the greater the boilover intensity. On the contrary, the shortage of oil might lead to the weaken boilover even boilover never occurred.(2) As for as the flame height, the higher maximum height was achived for the smaller diameter tank after boilover. A high degree of flame height was consistent with the steady-state phase of Thomas formula.(3) The fireball diameter was affected by the tank diameter, the thickness of oil and the thickness of the water cushion. Testing results were similar with the boilover intensity for the small scale experiments.3. Steady burning stage was simulated by the developed FDS model, which was approved to be consistent with the experiments. On this basis, the flame temperature and heat radiation intensity of the large-scale mixed crude oil tank model of the were investigated by the developed model From the simulation, the safety distance of30m diameter tank was found to be10.1m.