Experimental study of the effect of storage tank boundary conditions on crude oil boilover fires

Water present at the bottom of crude oil storage tanks can lead to boilover phenomena during a fire, posing significant hazards. As the vessel containing crude oil, understanding the impact of tank boundary conditions on boilover provides theoretical support for tank design. This study investigates the effects of tank opening size, wall conditions, and dimensions through a series of experiments. The results show that reducing the tank opening size initially promotes, then inhibits combustion. When the opening is sufficiently small, the hot zone disappears, delaying the boilover onset time from 43.62 min to 130.35 min. The tank wall conditions significantly influence boilover behavior. When an interlayer is added to the tank wall and filled with air, it provides thermal insulation, reducing the boilover onset time to 40 % of that in an ordinary tank, while increasing the hot wave propagation rate by 1.5 times. When the interlayer is filled with static or flowing water, the formation of the hot zone is suppressed and no boilover occurs. The study shows that as tank diameter increases, boilover ejection intensity decreases, boilover onset time shortens ($t_b\propto \frac{1}{\sqrt{D}}$), and hot wave propagation rate increases before stabilizing. A theoretical model for hot wave propagation is derived from the energy conservation equation. A set of large-scale (D:1.5m) comparison experiments is conducted, and it is found that the hot zone temperature remains constant in the radial direction, but the hot zone temperature decreases instead of increasing compared to the small-scale experiments. For cases where smoke obscures the flame, a method for estimating the maximum flame height during the boiling period based on the solid flame radiation model is proposed. The results of the study help provide guidance for fire protection design and firefighting strategies in storage tanks.