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近年来,我国炼化产业不断发展,油品周转量稳步提升,储罐的使用也更频繁。在储罐生产作业中,设备工艺技术的限制及人为的疏忽均会造成溢油事故[1]。溢出油品在挥发扩散后遇火源极易产生火灾,甚至爆炸[2-3]。2005年,英国第五大油库邦斯菲尔德(Buncefield)油库的912罐在接收汽油时溢流,油气迅速扩散并造成多次爆炸[4-5]。2009年,波多黎加勒比石油公司一座储量2×104 m3的储罐发生溢流,油气在扩散时遇到火源发生爆炸[6-7]。此外,油品汽化后会形成挥发性有机物(volatile organic compounds,VOCs)[8],而VOCs的控制与治理是环境污染防治与管理中的重要内容[9]。2020年,生态环境部与国家市场监督管理总局联合颁布的《储油库大气污染物排放标准GB 20950-2020》中规定企业边界排放限值应小于4 g·m−3(非甲烷总烃)[10]。2020年10月,生态环境部与国家发展和改革委员会提出,2021年VOCs的治理重心将继续以石油化工行业为主[11]。因此,有关罐区油气扩散规律的研究对储油区大气污染控制及相关企业的环保与安全管理具有重要意义。
计算流体动力学(computational fluid dynamics,CFD)是数值数学和计算机科学相结合的学科,已发展为重要的研究手段。相对于实验研究,该研究手段具有成本低和耗时短等优点[12-15]。WANG等[16]采用CFD方法评估了分隔距离对储罐场中气体扩散和蒸气云爆炸的影响。SUN等[17]借助大涡模拟(large eddy simulation,LES)模型模拟了强风天气下储罐密封圈的风压变化及气体扩散情况。刘瑞等[18]结合CFD方法和ANSYS Fluent仿真软件求解了覆土油罐泄漏后的油气扩散轨迹。然而,数值模拟的结果通常具有不确定性,必要时需开展可信度的验证[19]。风洞实验因具有优越的可控性与稳定性,被广泛应用于气体流动的研究[20-23]。ZHANG等[24]借助风洞平台搭建内浮顶罐缩比模型研究了正己烷蒸气的扩散规律。徐川等[25]和辛保泉等[26]建立风洞模型对天然气扩散特征进行了研究。目前,关于油气泄漏的研究主要可分为3个方面:1)油气泄漏扩散规律的研究;2)油气爆炸的数值模拟;3)城市VOCs溯源系统的研发。
在储罐油气泄漏扩散规律方面的研究主要集中在单罐或多罐[27-29]形式的扩散研究,而对于大型罐区的油气扩散规律的研究较少。基于此,拟通过风洞实验平台与CFD数值模拟相结合,以获得溢油事故后大型罐区内油气泄漏扩散规律,为罐区设计、油库运行管理及城市VOCs溯源系统的研发提供参考。
基于风洞平台实验的大型罐区溢油事故后的油气扩散模拟
Numerical simulation of oil vapor diffusion after oil spill accident in large-scale tank farm based on wind tunnel platform
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摘要: 通过研究江苏省境内某实体罐区发生溢油事故后油气蒸发的扩散规律,掌握罐区空气浓度的变化,以达到保障罐区环保与安全的目的。基于风洞平台实验,测定油气蒸发速率并通过实验风场数据验证数值模型的准确性,建立与实际油库1∶1的大型罐区模型,使用UDF编译环境风方程导入。通过CFD数值模拟,重点分析了罐区发生溢油事故后油气扩散规律、储罐间的油气积聚现象、风速对油气扩散及油气质量分数的影响。结果表明:在风速影响下,罐间会形成涡流,导致油气的积聚,形成危险区域;防火堤对油气扩散存在阻滞作用,而背风侧会使油气聚集;风速越小,油气扩散越慢,油气质量分数越高;风速越大,油品的蒸发速率越大,油气扩散越快,油气质量分数越小。本研究成果可为罐区设计、油库运行及安全环保管理提供参考。Abstract: Study on the law of oil vapor evaporation and diffusion after oil spill accident in tank farm is of great significance for ensuring the safety and environmental protection of tank farm. Based on the wind tunnel test platform, the evaporation rate of oil vapor was measured, and the accuracy of the numerical model was verified by the experimental wind field data. A large-scale tank farm model was established with a ratio of 1∶1 to the actual oil depot, and the environmental wind equation was compiled by UDF to import the numerical simulation. Through CFD numerical simulation, the pattern of oil vapor diffusion after the oil spill accident in tank farm, the oil vapor accumulation between tanks, and the influence of wind speed on the diffusion and concentration of oil vapor, were emphatically analyzed. The results showed that with the influence of wind speed, the vortex between tanks would lead to the accumulation of oil vapor, which was prone to form a dangerous area. The fire dike had a blocking effect on oil vapor diffusion, while the leeward side would cause oil vapor accumulation. The lower the wind speed, the slower the oil vapor diffusion and the higher the oil vapor concentration would be; the higher the wind speed, the greater the evaporation rate of oil and the faster the diffusion of oil vapor would be. The research results are of reference value for tank farm design, oil depot operation and safety and environmental protection management.
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