Research On Heat Radiation Characteristics Of LNG Multi-pool Fire Based On CFD

With the development of industry,the demand for energy has increased largely in China.Due to its advantages of non-polluting,high-efficiency,non-hazardous,high-storage rate,smaller area occupation,etc.LNG has attracted much attention.A series of serious accident hazards,such as fire,explosion,etc.may easily occur once LNG was released.The accident investigation and analysis show that the pool fire accidents occur frequently and more than 80%pool fires would trigger domino effect.In addition,it may cause catastrophic multi-pool fire accident in multi-tank stations.Currently,the fire safety distance between each tank and buildings or structures are an important basis for the design and layout of a LNG station according to Chinese codes.However,there is no specific regulations on which mathematical model must(or can)be used to pool fire accident consequence calculation.In recent years,with the rapid development of computer technique,many scholars have begun to use CFD to simulate the consequences of pool fire accidents.However,the numerical simulation of multi-pool fire mostly stays in the stage of experiments verification,and never application in engineering.Therefore,this paper investigate the status of the research of single and muti-pool fire experiments,empirical prediction model and CFD simulation to analyze the formation of the muti-pool fire and the applicable range,advantages and disadvantages for common pool fire radiation predicted model.According to the study of the fire interaction mechanism of multi-pool fire,the empirical and CFD mathematic models for the single and muti pool fire are established.Those models are used to analysis the characteristics of pool fire accidents,and then evaluate the accident consequences of a typical LNG station.Thus,the main contributions of this thesis are listed as follows:(1)According to the fundament concept of multi-pool fire and the comparative analysis of common thermal radiation models,the empirical prediction model of multi-pool fire was studied.By evaluating the applicability of the point source,LNGFIRE3 and PoFMISE models,the PoFMISE model was selected for the single pool fire radiation intensity prediction in this paper.It predicts that the average relative error of the single pool fire experiment data is 16.34%,while the multiple pool fire is 26.59%.It is necessary to modify this model,and the average relative error of the modified model is reduced to 19.72%.Therefore,combining the relevant semi-empirical correlation could improve the prediction accuracy of the empirical model,but the error is still relatively large.(2)Based on the CFD model foundation theory and FLUENT computing platrorm,the computational fluid dynamics(CFD)model has been built.The validate results show that,the average reliative error of the thermal radiation intensity distribution for the Montoir's single pool fire expertiments is 9.89%;for Fukuda multi-pool fire expertiments is 6.19%.Therefore,the CFD model has high prediction precision.Determination of flame surface shape in the CFD simulation is the key to analysis of flame characteristics,to compare the CFD and experiments results with different isothermal surface flame shape parameters found that,appropriate chooses 1200K isothermal surface for the single pool fire,and 1000K to the multi-pool fire.(3)The pool fire heat radiation intensity CFD model is used to discuss the flame merge condition of multi pool fire,and the principal feature of their combined blaze.The results show that the separation distance of the liquid pool is the critical factor affecting the merge of the flame.Thus,the multi pool fire in different merging states can be classified as complete merge,incomplete merge,complete non merger and independent single flame.Through the comparative analysis of the flame states of different merging states,it is found that the flame merging behavior has different degrees of enhancement to the flame height,temperature and heat radiation intensity.Further more,when the ratio of separation to tank diameter(S/D)is close to 0.50,the degree of fire hazard is the greatest.(4)To evaluate the safety distance in typical LNG stations,the standard specification,empirical prediction model and CFD model are used,respectively.The evaluation results of three methods indicate that the evaluation results of CFD model are most reasonable to compare with standard specification and empirical prediction model.Due to the wind and topography have some influence on thermal energy propagation and diffusion of pool fire,the C3+C4 double pool fire is the most serious fire scene.The most seriously damaged by radiation heat flux are gasifier and instrument control room,the comprehensive building and fire pump room are the second,and the other facilities in this stations are almost unaffected.(5)According to the above evaluation results,the optimization suggestions for the mitigation of the pool fire accidents are proposed,including 1)increase the distance between the gasifier and dike;2)Install the spraying water curtain or firewall between the instrument control room and dike.The optimal design results show that the radiation heat flux of the facilities within the station has decreased significantly,which is about 40%?95%lower than that before the optimization design.