Research On Large LNG Tank Area Leakage And Vapor Cloud Deflagration

LNG tank area is an important facility for connecting upstream and downstream industrial chains.Its capacity is constantly becoming larger,so its safety and reliability are crucial for society.It is easy to form a flammable and explosive gas cloud when LNG leaks out and diffuses.And there are so many factors which can affect leakage and diffusion processes and fire & explosion accidents.In this thesis,for tank area of LNG terminal,the LNG leakage and diffusion and vapor cloud deflagration simulations are completed.The main work consists of:1.In the LNG leakage and diffusion processes,different factors are considered and analyzed in the perspective of theory.2.For tank area of LNG terminal,FLACS is used to simulate the LNG leakage and diffusion processes in different conditions.It also can provide data support for vapor cloud deflagration accidents.The simulation shows that pool area increases linearly with time under different conditions;the wind speed and the ambient temperature are inversely proportional to the maximum pool area;but the leakage rate is directly proportional to the maximum pool area;furthermore,the evaporation rate per area of the pool is directly proportional to the wind speed,ambient temperature and leakage rate.Finally,The difference in LNG composition has less effect on the LNG leakage and diffusion,however,the leakage rate has a great influence on the LNG leakage and diffusion.3.Based on the simulation of leakage and diffusion,the equivalent stoichiometric cloud is extracted.The vapor cloud deflagration accidents are further simulated using FLACS software.The law of flash fire with obstacles and vapor cloud deflagration under different ignition positions are studied.The conclusion is that when there is an obstacle,the flash fire duration is shortened,the time when the overpressure reaches the maximum value is advanced,and the maximum diameter in the high temperature region is larger.When the vapor cloud is ignited in a confined space,the change in ignition location has a greater impact on the vapor cloud deflagration.The closer to the center of the gas cloud,the greater the overpressure and temperature maximum,the shorter the overpressure maximum time.