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石油工业是我国的重要支柱产业之一,油田联合站是油田原油集输和处理的中枢[1]。在联合站中,各区块来油通过原油稳定系统将分离出的轻烃组分回收进入轻烃厂,处理后的原油组分通过联合站处理再进行外输[2-4]。在联合站的日常操作运行中,各种拱顶罐呼吸阀、干化池等存在油气逸散的风险。另外,储罐在运行过程中可能因腐蚀、雷击、油罐失效、人为损坏等意外因素导致油罐罐壁破损[5-6],从而泄漏和蒸发出大量易燃易爆、有毒的油气混合物。这些混合物即挥发性有机物 (volatile organic compounds,VOCs) 。VOCs的泄漏不仅会污染环境,还会严重威胁企业安全和人群健康、安全和环境 (Health、Safety、Environment,HSE) [7-10]。“十四五”规划提出,要强化多污染物协同控制和区域协同治理,加快VOCs排放综合整治,到2025年,VOCs排放总量下降10%以上[11-12]。经调研,油田联合站的多个环节 (如原油储罐及轻烃储罐、除油罐、净化罐、沉降罐、敞开液面) 存在VOCs排放问题,因此,有必要开展油田联合站VOCs排放的扩散规律研究。
目前,VOCs扩散规律分析方法主要有:现场测试[13-14]、风洞实验[15-16]和数值模拟[17-20]。其中,基于计算流体力学 (computational fluid dynamics,CFD) 及其Fluent软件的数值模拟方法的可操作性强,已在航天、汽车、能源、化工、材料、生物医药等诸多领域广泛应用[21]。KOUNTOURIOTIS等[22]通过数值模拟,在风速、风向、温度、油气扩散源位置等多种影响因素下,研究了不同成分的汽油挥发出的VOCs扩散规律,并发现在扩散源附近的VOCs浓度远远高于爆炸极限。基于风洞平台实验验证和Fluent数值模拟,建立了基于单膜传质理论的油气蒸发过程当量膜厚数值模拟计算方法,以及基于Stefan-Fuchs方程、Clausius-Clapeyron方程及若干准则数的非稳态蒸发单相传质的数值模拟方法,揭示了在各操作条件下油罐非稳态石油蒸发和油罐排放气在大气环境中的扩散行为及其内在机理,以及影响因素间的关联性[15,23-24]。
本课题组通过CFD 数值模拟和风洞实验平台研究了某石化企业的实体罐区发生溢油事故后油气蒸发的扩散规律,掌握了罐区VOCs浓度的变化特征[25]。然而,针对油田联合站内多排放源的VOCs扩散规律研究仍未出现。本研究以某油田大型联合站多点排放源为对象,通过CFD数值模拟和现场调研数据相结合,以探究正常工况下VOCs扩散机理及储罐裂缝处VOCs泄漏扩散的叠加效应。本研究结果可与前期针对大型罐区VOCs扩散数值模拟[25]成果相结合形成系列成果,为石油石化行业的运行管理及VOCs排放控制提供参考。
某油田大型联合站多排放源VOCs扩散的数值模拟
Numerical simulation of VOCs diffusion from multiple emission sources at a large combined station in an oilfield
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摘要: 油田联合站是油田的重要组成部分,存在油气 (VOCs) 排放的可能,有必要对其扩散规律进行研究,以制定相关污染防控及安全措施。以某典型联合站为例,建立1:1的实际模型,结合现场调研测试和数值模拟,重点分析了联合站正常工况下多排放源的VOCs扩散机理及储罐裂缝处VOCs泄漏扩散的叠加效应。结果表明:在风速影响下,罐间和背风侧由于出现绕流和回流,容易达到爆炸极限;在重力和涡流的作用下,联合站内的背风侧会出现VOCs聚集,但叠加效应不明显;当储罐发生罐壁破损时,在事故罐后方出现正压区,在涡流和强气流的影响下,叠加后的VOCs浓度会明显增强,并呈点射状向下风向扩散,油气爆炸危险区域加速扩展。本研究成果可为联合站设计、运行管理及制定安全环保措施提供参考。
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关键词:
- 油田联合站 /
- 油气(VOCs)扩散 /
- 储罐泄漏 /
- 数值模拟 /
- 叠加效应
Abstract: Oil field joint station is an important part of oil field, there is the possibility of oil and gas (VOCs) emission, it is necessary to carry out research on the oil vapor emission laws of oilfields. Therefore, taking a typical united station as an example, a 1:1 practical model was established. Combined with on-site investigation, testing and numerical simulation, an investigation of the oil vapor diffusion mechanism under normal conditions and the superposition effect of oil vapor leakage and diffusion at the crack of the storage tank was conducted emphatically. The results showed that: under the influence of wind speed, the oil vapor could easily reach the explosion limit due to the circumfluence and backflow between the tanks and the leeward side; under the action of gravity and eddy current, oil vapor would accumulate on the leeward side, but the superposition effect was not obvious; When the tank wall was damaged and leaked, a positive pressure area would appear behind the accident tank. Under the influence of eddy current and strong airflow, the superimposed oil vapor concentration would be significantly enhanced, and will spread to the downwind in a point-like manner, accelerating the extension of oil vapor explosion danger area. The results of this study can provide reference for the design, operation management and safety and environmental protection measures of the joint station. -
表 1 通用方程 (3) 中各参数的具体形式
Table 1. Detailed form of each parameter in general equation (3)
方程 广义变量Φ值 广义扩散系数Г值 广义源项S 质量守恒方程 1 0 0 动量守恒方程 ${u_i}$ $\mu $ $ - \partial p/\partial x+{S_i}$ 能量守恒方程 $T$ $ k/c $ ${S_T}$ 组分运输方程 ${C_S}$ ${D_S}\rho $ ${S_S}$ 表 2 G区储罐的尺寸
Table 2. Dimension of oil storage tank in area G
储罐
位号储罐
直径/m储罐
高度/m公称
容积/m3最大液体
高度/m平均液体
高度/mG1 17 13.15 3 000 12 10.68 G2 17 13.2 3 000 12 9 G3 17 13.14 3 000 12 9 表 3 数值模拟网格无关性检验结果
Table 3. Results of grid independence test for numerical simulation
网格数量 沿x方向的速度/ (m·s−1) 746 528 3.14 1 461 100 3.23 2 005 657 3.64 3 009 842 3.64 表 4 某油田联合站现场测试数据
Table 4. Data from field test of an united station
区域 采样点位 VOCs质量浓度/(mg·m−3) 采样时刻 风速/(m·s−1) I区 G3罐顶环境 11.40 14:45 2.0 G2罐顶环境 9.95 14:40 2.0 B环境 (停用) 24.50 15:15 0.5 I区厂门口 0.95 18:05 1.5 Ⅱ区 D5罐顶环境 20.00 11:51 3.2 Ⅱ区罐区环境 11.00 16:15 3.0 -
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