Study On Prediction Model Of Fire Radiation In LNG Pool And Evaluation Of Fire Spacing

Liquefied natural gas has many advantages of non-polluting,high-efficiency,non-hazardous,non-corrosiveness,high-storage rate when compared to traditional power resource,which has been widely used in the fields of automobile,ship,refrigerating,chemical engineering,etc.With burgeoning demand for LNG in our country,the number of LNG stations increases daily.Also it has brought a series of security problems and has been arousing more and more attention.Due to the fact that the boiling point of LNG is-161.5 degrees centigrade under normal pressure,it will evaporate quickly once it is released,which renders the ambient air temperature drop suddenly.If it comes in contact with an open flame,the fire hazard will be sparked easily.When it comes to LNG station,the most common ones is the pool fire aroused by tank leakage.Currently,the fire separation distance between each tank and the fire separation distance between tank area and buildings or structures are clearly stipulated in correlative Chinese codes and specifications,but these specified values are mainly based on references of the location data of established LNG stations at home and abroad and empirical analysis.Moreover,there is no clear regulation on which calculation model must(or can)be used for LNG station in our country.In addition,the accident scenarios in national criteria are stipulated that the wind speed is at 0 level,the temperature is 21 degrees centigrade and the relative humidity is 50%.However,this stipulation may not consider the impacts of wind speed and dike size on the LNG pool fire radiation,which contributes to the conservative or insufficient determine of fire separation distance.Therefore,investigating the research status of LNG pool fire experiments and radiation prediction models,analyzing the scope of application of existing models and establishing LNG pool fire radiation prediction model for different fire hazard scenarios have important instruction significance for LNG station site selection,layout design,hazard scope evaluation and risk management.Thus,the main contributions of this thesis are listed as follows:(1)To predict the characteristics of LNG pool fire and the thermal radiation intensity received by surrounding accurately,the computational fluid dynamics(CFD)model of LNG pool fire has been built and the finite volume method(FVM)is adopted to solve it.The data of LNG pool fire experiments is also used to verify the accuracy of the CFD model.Moreover.the validated model is employed to analyze the main influence factors of LNG pool fire,including wind speed and dike diameter.The results indicate that the average relative error of prediction values of the LNG pool fire characteristics and the thermal radiation intensity received by monitoring points are 8.4%and 9.1%,respectively.Therefore,the CFD model has high prediction precision.(2)The data of LNG pool fire experiments has been concluded and reorganized through extensive literature research.These data is adopted to assess the application scope of calculation correlations of flame length,flame tilt,flame drag rate and thermal radiation intensity,which are widely used in LNG industry.Then,these correlations are combined to obtain a LNG pool fire radiation prediction model for multi-scenario.Furthermore,the prediction precision of this analytical model is compared with that of CFD model and other common models.The results indicate that the CFD model has the highest prediction precision,and the next are the multi-scenario analytical model and POOLFIRE3 model.The average relative error of them are 11%,17%,and 20%,respectively.Due to the relative error of the CFD model and the multi-scenario analytical model are both below 20%,the results of the models are reliable.(3)C language programming and the multi-scenario analytical model are adopted to carry out software design.Based on different pool fire hazard scenarios,the software can select the recommended calculation correlations automatically and combine them to establish the LNG pool fire prediction model for corresponding accident scenarios.In addition,the software can also realize the assessment of fire separation distances between tanks area and other facilities in LNG station,and judge whether the thermal radiation intensity of the location of facilities beyond the specified value in correlative codes and specifications.The accuracy of software is validated by comparing the results of software and the manual calculation results.(4)Take a LNG station in Sichuan province for an example,the developed software of LNG pool fire radiation influence sphere assessment is adopted to predict the thermal radiation intensity received by facilities in the LNG station for different pool fire hazard scenarios.Moreover,the fire separation distances between tanks area and other facilities are assessed according to domestic correlative codes and specifications.The results show that there exist the situations where the thermal radiation intensity of facility site beyond specified value.Then corresponding optimization schemes are proposed for these situations,including 1)Increase the distance between the dike and its surrounding facilities;2)Reduce the area of the dike and choose high dike or double capacity tank and full capacity tank;3)Install the spraying water curtain between the dike and surrounding facilities.