| In recent years,the Liquid Natural Gas（LNG）industry has developed rapidly due to the increasing penetration rate of natural gas in China.LNG is usually normal pressure and low temperature storage（boiling point-162℃）,once the liquid leakage accident,be a cryogenic liquid pool on the ground,under great temperature difference LNG liquid pool boiling evaporation occurs,when the evaporation gas mixed with air volume ratio is 5%～15%,meet fire after a fire accident,extremely easy with pool fire accident and among them,the most common accident upgrade disaster effect is most obvious.Therefore,LNG storage stations and other storage and transportation facilities are generally major hazard sources.Therefore,it is necessary to study the"domino"effect of fire caused by leakage and diffusion,pool fire accidents and fire accident escalation,as well as the reduction of accident influence scope and the reduction of accident escalation probability.After LNG liquid phase release,it is a complete process from the formation of cryogenic liquid pool,the formation of liquid evaporative combustion pool fire,and then to the domino effect of fire.However,the current understanding of this process is not enough,which makes the selection and optimization of corresponding safety measures lack of sufficient theoretical basis and data support.Therefore,this paper combines theoretical research,experimental research and numerical simulation research of ANSYS Fluent to study the LNG leakage and diffusion and the domino effect of pool fire.On this basis,the safety protection measures of LNG storage stations are proposed to reduce the impact range of pool fire accidents and the probability of pool fire domino accidents.The main research contents and achievements of this paper are as follows:1.The heat exchange process between LNG leakage and the environment and the low-temperature liquid pool diffusion process have an important impact on the domino effect of pool fire.Therefore,it is necessary to study the formation,diffusion and heat transfer process of the liquid pool after LNG leakage.In view of the problem that the traditional one-dimensional semi-infinite plate heat conduction formula can only predict the heat conduction between the low-temperature liquid pool（non-diffusive liquid pool）and the solid surface with a certain area,an improvement was made to make it suitable for predicting the heat conduction of low-temperature diffusive liquid pool.On this basis,the extended and improved Simplified Gasp1#model and Simplified Gasp2#model are established.The Simplified Gasp1#model and Simplified Gasp2#model were verified by building a small experimental platform for the diffusion and evaporation of cryogenic liquids on land surface.The results show that the errors of the Simplified Gasp1#model are 0.98%～12.4%,and the errors of the Simplified Gasp2#model are 4.39%～16.61%,both of which can be used to simulate the leakage and diffusion process of cryogenic liquid on the ground.2.The verified improved model was used to analyze and study the factors affecting the evaporation rate of the LNG liquid pool,and an optimized design scheme was proposed to reduce the evaporation rate of the LNG liquid pool.The results are as follows:（1）The influence of ambient temperature on evaporation rate is small.When the ambient temperature rises from-10℃to 30℃,the evaporation rate only increases by 0.003 kg/（m2·s）.（2）In the case of LNG liquid phase continuous leakage,when there is a fire dike to block the diffusion of the liquid pool,the liquid leakage is limited within a certain range.With the continuous cooling of the ground,the evaporation rate is reduced to 1/5 of the diffusion liquid pool.Therefore,the purpose of reducing the evaporation rate of the LNG liquid pool can be achieved by controlling the area of the fire dike.On this basis,the design scheme of fire embankment optimization is proposed,that is,the area of fire embankment should be as small as possible,or even made into the form of double-capacity tank or full-capacity tank,on the premise of meeting the design requirements to accommodate all the LNG liquid volume when the LNG storage tank is completely broken.（3）Wind speed has a great influence on the evaporation rate.The proportion of heat transfer and heat transfer decreases gradually with the passage of time and the ground cooling.The proportion of heat convection and heat transfer increases with the passage of time,and the proportion of heat radiation and heat transfer is small.When the ambient wind speed reaches 5 m/s,the convection heat transfer completely exceeds the conduction heat transfer.When the ambient wind speed reaches 8 m/s,the convection can increase the evaporation rate by more than 7 times.Therefore,it is necessary to set up a protective wall to prevent the convection heat transfer under windy conditions.Based on the simulation using ANSYS FLUENT software,the optimal setting scheme of the protective wall is proposed,that is,the protective wall should be set in the upwind direction of the dominant wind direction,with a height of 2 meters～5 meters,and the optimal height of 3 meters.3.Flammable and explosive methane gas will be formed after the evaporation of the leaking LNG,which is prone to fire accidents.Therefore,the fire accident of the LNG pool is studied.Based on the optimized pool fire physical model,this paper improves the model and establishes a multi-scale LNGpool fire physical model LNGPOOL to predict the flame height and inclination Angle of LNGpool fire.The experimental data were used to verify the established model.The results show that the LNGPOOL multi-scale LNGpool fire physical model can better predict the LNGpool fire.Under different fire scales（fire diameter 1.8m～35m）,the prediction error of flame height is less than 11%,and the prediction error of flame inclination Angle is less than 15%.4.The verified improved LNG pool fire model LNGPOOL is used to analyze and study the factors affecting the thermal radiation of LNGpool fire,and the optimized design scheme is proposed to reduce the thermal radiation range of LNGpool fire.The conclusions are as follows:（1）The distance between fire safety and fire safety increases with the increase of the radius of the fuel liquid pool.When the radius of the fuel liquid pool is 3 meters～8 meters,the distance between fire safety and fire safety increases by 1 times.Therefore,the distance between fire safety and fire safety can be reduced by controlling the radius of the fuel liquid pool.On this basis,an optimization scheme of fireproof embankment is proposed,that is,the radius of fireproof embankment should be as small as possible on the premise that the fireproof embankment meets the design requirements to accommodate all the LNG liquid volume when the LNG storage tank is completely broken.（2）there is wind environment environmental conditions（1 m/s～12 m/s）,the wind makes the combustion rate increases,when the wind speed of 12 m/s burning rate increased by 70%than the wind speed 0 m/s,in addition,the wind direction also makes under the thermal radiation to offset,shorter length of flame,tilting Angle change,leading to the next direction of thermal radiation,under the same distance as a result,you need to set up protective walls to reduce heat radiation.On the premise of full consideration of terrain conditions and construction difficulties,it is proposed that the height of upwind protective wall in a 200 m3vertical storage tank area should be 3meters,the height of downwind protective wall should be 5 meters,and the distance between the protective wall and the fire embankment should be 30 meters.5.Fire accident long time,thermal radiation intensity,easy to cause the escalation of the accident,called the fire accident"domino effect".Based on the accurate simulation of the thermal radiation of LNG pool fire,the Probit model is used to predict the probability upgrade of pool fire domino accident,and the Bayesian network method is used to predict the probability of pool fire domino accident.On this basis,the reduction degree of pool fire domino accident caused by safety protection measures is studied.The results show that:（1）The more safety protection measures,the lower the probability of domino accident escalation,and the better the safety protection;（2）Passive protection measures such as refractory coating have higher protection and reliability,which can reduce the probability of fire domino event from 5.934×10-6to 6.497×10-7without safety measures;（3）The fire partition can effectively reduce the fire heat radiation range,especially when the thermal conductivity of the fire partition is lower than 0.08W/（m·K）,the fire of a single storage tank will not cause domino accident. |
PDF Full Text Request