我国是液化石油气(LPG)消费大国，清洁高效的LPG作为燃料给工业生产和人民生活带来诸多便利的同时，在生产经营过程中存在泄漏、爆炸事故风险。现代大型石化厂区的气体泄漏、扩散及气云爆炸是一个复杂的过程，受制于诸多因素的影响，实际工作中难以通过真实环境对事故链灾害进行有效预测。为了防控石化厂区蒸气云爆炸事故，提高对混合气体“泄漏-扩散-爆炸”事故的预测能力，利用数值仿真技术针对石化厂区LPG“泄漏-扩散-爆炸”事故进行概率分析和后果推演，基于概率分析方法研究模块安全间距、防爆墙位置/高度/厚度对LPG蒸气云爆炸超压的影响。主要结论如下：

      (1) 对于开放空间中气体泄漏扩散过程，主要影响因素可归纳为四类：气体组成因素、泄漏条件因素、障碍物因素和环境因素，这四者相互作用决定了气体泄漏后的扩散过程及可燃气云形成，但这四类因素的影响程度有所差异。泄漏条件中的泄漏速率对Q9峰值的影响显著，LPG中丙烷和丁烷的不同气体比例对Q9峰值的影响较小。障碍物会影响气体扩散的初始动量和气体扩散过程，当气体射流遇到大型障碍物时，射流初始动量受到影响，气体的流动速率与流动方向受到干扰，进而影响气体泄漏扩散过程和气云形成。环境风速和风向会改变气体扩散过程中的局部通风情况和扩散路径，导致可燃气云体积大小和分布范围有所差异。

       (2) 气云性质、泄漏量、障碍物、点火源和环境因素共同决定了LPG蒸气云爆炸强度。气体组成中丙烷和丁烷体积分数的不同，主要影响可燃气云的爆炸浓度极限，且随着丙烷比重的增加，可燃气体爆炸浓度范围变宽。在一定泄漏量范围内，蒸气云爆炸超压随着泄漏量的增加明显增强。点火源相对于几何模型位置的不同，会导致火焰传播过程中障碍物的不同，随着障碍物阻塞程度的增加，蒸气云爆炸强度显著增强。环境温度的升高，导致爆炸极限浓度范围变宽，造成爆炸强度增加。

      (3) 采用多级爆炸风险分析方法，基于概率得到石化厂区高风险区域LPG“泄漏-扩散-爆炸”的爆炸超压峰值的超越概率曲线，有针对性低定量分析石化厂区复杂管网爆炸风险。开展复杂管网中泄漏速率为24~96 kg/s的LPG“泄漏-扩散”过程模拟，统计18组泄漏实验工况结果得到可燃气云体积在30,000~60,000 m³范围内，其中大于30,000 m³气云数量占比为88.89%。一旦上述气云被点燃发生爆炸事故，生活办公区的爆炸超压大小主要集中在0.2 barg以内，区域内最大爆炸超压不超过1.2 barg。

      (4) 增加模块安全间距和增设防爆墙的设计可以有效降低石化厂区LPG“泄漏-扩散-爆炸”事故风险。相比无防控措施的厂区模型，增加10 m模块安全间距和增设5 m高、0.3 m厚的防爆墙使得大于0.8 barg的概率值分别降低了10^-5和10^-6。防爆墙高度为11 m时，对应的越过防爆墙后形成的爆炸超压降幅达到70.33%。随着防爆墙高度的增加，防爆墙前承载的爆炸超压亦增大，故墙体的高度设计需要考量墙体自身的爆炸荷载，合理评估设计参数，才能使防爆墙有效降低爆炸事故危险性。

   China is a large consumer of liquefied petroleum gas (LPG). Clean and efficient LPG as a fuel brings many conveniences to industrial production and people's life. There are risks of leakage and explosion accidents in the production and operation. The gas leakage, diffusion, and gas cloud explosion in a modern large-scale petrochemical plant is a complicated process subject to many factors. It is challenging to predict accident chain disasters effectively through the actual environment in practical work. To prevent and control the vapor cloud explosion accident and improve the prediction ability of the mixed gas explosion accident, the probability analysis and consequence deduction of LPG "leakage-diffusion-explosion" accident in the petrochemical plant area is carried out using numerical simulation. Based on the probability method, the influence of module safety distance and blast wall position/height/thickness on LPG vapor cloud explosion overpressure is studied. The main conclusions are as follows:

   (1) For gas leakage and diffusion in open space, the main influencing factors can be summarized into four categories: gas composition factors, leakage condition factors, obstacle factors, and environmental factors. The interaction of these four factors determines the diffusion process and the formation of explosive gas clouds after gas leakage. Still, the influence degree of these four types of factors is different. The leakage rate in the leakage condition significantly impacts the Q9 peak, and the different gas ratios of propane and butane in LPG have little impact on the Q9 peak. Obstacles will affect the initial momentum of gas diffusion and the process of gas diffusion. When the gas jet encounters a significant obstacle, the initial momentum of the jet will be affected, and the flow rate and direction of the gas will be disturbed, thus affecting the process of gas leakage and diffusion and the formation of the gas cloud. The ambient wind speed and direction will change the local ventilation and diffusion path in gas diffusion, resulting in differences in combustible gas clouds' volume and distribution range.

    (2) The nature of the gas cloud, leakage, obstacles, ignition source, and environmental factors jointly determine the intensity of the LPG vapor cloud explosion. The gas composition mainly affects the explosion concentration limit of the combustible gas cloud. With the increase of propane-specific gravity, the explosion concentration range of combustible gas becomes wider. In a specific range of leakage, the overpressure of vapor cloud explosion increases obviously with the increase of leakage. The different positions of the ignition source relative to the geometric model will lead to different obstacles in flame propagation. With the increase in blockage degree of obstacles, the explosion intensity of the vapor cloud increases significantly. With the increase in ambient temperature, the range of explosion limit concentration becomes more expansive, and the explosion intensity increases.

    (3) The multi-level explosion risk analysis method is adopted to obtain the exceeding probability curve of the peak explosion overpressure of LPG "leakage-diffusion-explosion" in the high-risk area of the petrochemical plant are based on probability to analyze the explosion risk of the complex pipe network in the petrochemical plant area in a targeted and low quantitative way. The LPG "leakage-diffusion" process simulation with a leakage rate of 24~96 kg/s in the complicated pipeline network was carried out, and the results of 18 groups of leakage test conditions were counted. It was found that the volume of combustible gas clouds was in the range of 30,000~60,000 m³, of which the number of gas clouds greater than 30000 m³ accounted for 88.89%. Once the above gas cloud is ignited and an explosion accident occurs, the explosion overpressure in the living and office areas is mainly within 0.2 barg. The maximum explosion overpressure in the area is not more than 1.2 barg.

    (4) Increasing the safety distance between modules and adding blast walls can reduce the risk of LPG vapor cloud explosion accidents in petrochemical plants. Compared with the plant model without prevention and control measures, the increase of 10 m module safety distance and the addition of 5 m high and 0.3 m thick blast wall have reduced the probability values greater than 0.8 barg by 10^-5 and 10^-6 respectively. When the height of the blast wall is 11 m, the corresponding explosion overpressure drop after crossing the blast wall reaches 70.33%. With the increase in the height of the blast wall, the overpressure in front of the wall also increases. Therefore, the height design of the wall needs to consider the explosion load of the wall itself and reasonably evaluate the design parameters to reduce the risk of explosion accidents effectively.