CFD Study of Combustion Behavior of Single and 3x3 Arrayed Huge Oil Tanks in Free Burning and Whirling Conditions

摘要

Huge oil tanks filled with large amounts of flammable fuel have the potential to cause large fires and there have been many serious accidents due to huge oil tank fires. It is not only of great difficulty to suppress a fire occurring in one of these tanks, but also of extreme danger for firefighters if a fire whirl occurs, since the fire whirl will induce intense heat radiation and strong wind. In our previous study we numerically studied huge fire whirls in a large oil tank depot. This paper presents a further CFD simulation study to clarify the more detailed combustion behavior of fire whirls in single and multiple oil tanks. Detailed combustion characteristics such as heat release rates, velocities of whirling flames and radiative heat flux are examined for single and (3x3) arrayed oil tanks placed in a tall channel with four corner gaps. In a single oil tank fire, the fire whirl lengths are about 10 times the oil tank diameter, and in (3x3) oil tanks with a diameter of 40 m, a tall fire whirl more than 20 times the single oil tank diameter is generated. In single whirling fires, the radiative heat flux on the fuel surface reaches a maximum in the center of the tank, which induces a large amount of fuel evaporation therein. However, the fuel vapor moves upward without combustion due to insufficient oxygen. The critical merging distance in the (3×3) arrayed fire is inversely proportional to the square root of the tank diameter. The rotational cycles of whirling flames of single and (3x3) arrayed fires are found to be almost proportional to the inverse of the square root of the tank diameter or the array length. A method to prevent fire whirl generation is also preliminarily examined.