Abstract:

It is important to reveal the mechanism and law of oil vapor leakage and diffusion of external floating-roof tank (EFRT) to ensure the tank farm safety and reduce the environmental pollution. In present paper, numerical simulation and experimental verification were carried out for the oil vapor leakage and diffusion of large and small EFRT at different leak locations and pore sizes. The results were as follows. ① When the wind blows to the EFRT, a large scale eddy will form above the floating deck and form a symmetrical distribution of air flow from the downwind side to the upper wind side. ② When a pore leak occurs above the floating deck, oil vapor is closely attached to the floating deck and moves from the downwind to the upwind side. Oil vapor is easy to spread out when the leakage positions of the floating deck are located in the middle or the downwind side, but it is easy to accumulate when the positions are on upwind side or both sides of the floating deck, and there is a great potential safety hazard. The increase of wind speed is beneficial to the diffusion of oil vapor, but it will enlarge the scope of pollution. ③ when there was a rim leakage between the floating deck and tank wall, oil vapor diffuses along the tank wall to the upper space of the floating deck, and the extent of diffusion is: the sides of the floating deck > the upper wind side > the downwind side. ④ For the central leakage pore of the floating deck, when the pore diameter is 20 mm, the volume fraction of n-heptane is between 0.1% and 1.7%, which is within the corresponding explosion limit range; however, when the pore diameter is 6 mm, the volume fraction of n-heptane is between 0.02% and 0.26% and the volume fraction of gasoline vapor is between 0.05% and 0.65%, which all are not up to the explosion limit range. Thus, the possibility of explosion danger increases with the enlargement of the pore diameter. The research results will further reveal the migration law of the mixture gas of the vapor-air above the floating deck and the mass transfer mechanism of oil vapor diffusion, which can provide theoretical guidance for field practice and oil tank management and improve the theoretical system for evaluating the EFRT evaporation loss.

Key words: external floating-roof tank, oil vapor leakage, oil vapor diffusion, mass transfer mechanism, numerical simulation

摘要：

开展外浮顶罐油气泄漏扩散机理及规律的研究对于保障罐区安全、降低环境污染具有重要的意义。针对大、小外浮顶罐不同浮盘孔隙的油气泄漏扩散及其受风场的影响进行了数值模拟及实验验证。研究结果如下。①当风吹向外浮顶罐时，会在浮盘上方形成大尺度涡流，并在紧贴浮盘处形成从下风侧到上风侧的对称分布的气流运移。②泄漏位置在浮盘上时，油气均紧贴浮盘从下风侧向上风侧运移；泄漏位置位于浮盘中间及下风侧时，油气较容易扩散出去，而位于浮盘上风侧及两侧时，油气容易发生积聚，存在很大的安全隐患；风速增大有利于油气扩散，但会使污染范围扩大。③泄漏位置在浮盘与罐壁之间的边圈缝隙时，油气沿着罐壁向浮盘上方空间扩散，且扩散的程度为：浮盘两侧>上风侧>下风侧。④泄漏位置在浮盘中心、泄漏孔径为20mm时，正庚烷体积分数为0.1%~1.7%，处在对应的爆炸极限范围之内；而孔径为6mm时，正庚烷体积分数在0.02%~0.26%，汽油蒸气的体积分数在0.05%~0.65%，均未达到爆炸极限范围。因此，当泄漏孔隙较大时，出现爆炸危险的可能性增大。研究成果进一步揭示浮盘上方气流运移规律及油气扩散传质机理，可为生产实践和油罐管理提供理论指导，并进一步完善外浮顶罐蒸发损耗评价理论体系。

关键词: 外浮顶罐, 油气泄漏, 油气扩散, 传质机理, 数值模拟