Experimental Investigation On The Vapor Mitigation In The Application Of Expansion Foam To The LNG Collection Pool

The natural gas is a promising energy owing to less pollution emitted per unit of energy.Liquefied natural gas(LNG)is believed to be an effective method to transport and store the natural gas under atmospheric pressure owing to its high energy ratio.However,an LNG spill can release 600 times natural gas of its own volume.Thus,the potential danger is tremendous,and this should be paid more attention to.High expansion foam can effectively mitigate the LNG vapor hazards.It can block the forced convection and radiation to the LNG pool,and thus effectively reduce the LNG vaporization and decrease the quantity of natural gas.Besides,it can heat the vapor and reduce the accumulation of natural gas around the ground.When the foam interacts with the LNG,an ice plate can form.But the influence of it on the mitigation was seldom reported.In addition,the water contained in the foam can cause the vaporization rate to increase.How to reduce this adverse effect and increase the favourable effect of foam requires deep investigation on the interaction between foam and LNG.By this the foam utilization and mitigation effect will be improved.Owing to the importance of the foam propertities and height on the mitigation,this work combined the theory analyses and experiment verification to investigate the expansion foam propertites and the mitigation mechanism in the application of foam to the LNG collection pool.It first analysed the variation of the foam height versus time in the process of foaming and foam collapse.Six parameters(function type,collapse trend,maximum and minimum collapse rate and their corresponding time)and the interrelationship between them were obtained.From this,the parameters to characterize the foam stability and submergence rate were proposed.And then Taguchi analyses were employed to investigate the effect of operation parameters,collection containers and time on the foam expansion ratio,stability and submergence rate.Owing to the proportional relationship between expansion ratio and submergence rate,only foam stability and expansion ratio were regulated.And then three foams were obtained to investigate the mitigation effect in the application of expansion foam to the LNG collection pool.According to the effect of expansion ratio,stability,LNG spill amount and foam submergence height on average LNG vaporization rate,the general and one-spot vapor-emit rate,the warming,boil-off and frozen layer(mainly natural gas hydrate layer)effect were quantitatively investigated as the foam interacted with the LNG pool.A modified model to explain the interaction between foam and LNG was developed by experiments.And then a novel process and method was proposed to improve the effectiveness.The main contents and conclusions are as follows:(1)Owing to the drawbacks of the industrial foam generators(hydraulic driver,the dependence among operating parameters,too high production rate and less precise data),a modified one applied in the lab was produced.It posseses many advantages,such as flexible regulation of the distance between the screen and nozzle,simple operation and ease to regulate,and so on.It is confirmed that this generator is capable to produce the foam with satisfactory expansion ratio,stability and production rate,and improves the customization,readability and accuracy.(2)Considering the field and lab research,this work constructed two platforms.The latter platform can research the effect of not only the foam but also the water curtain and barrier.A water tank was employed to realize the water block and simulation of different spill scenarios.The design conbined the universality,comprehensiveness,simplification and customization.A novel method was proposed to install the sensor in the wind tunnel.This method can be employed to various wind tunnel and conditions.And it can reduce the space occupied by the sensor in the wind tunnel,decrease the amount of sensor and realize the line measuring by point.(3)Copplase function and six parmaters to reflect the foam heigh variation were obtained by exploring the interrelationship between foam height and time.This helped deeply investigating and measuring the collapse process.In addition,it provides theoretical direction to the prediction of the foam height in the process of foaming and foam collapse.(4)Taguchi method was employed to quantitatively discuss the effect of the operating parameters,collection containers and time on the expansion ratio,stability and submergence rate.An equation related with foam stability was proposed.This provides theoretical direction to separately control the foam stability,expansion ratio and submergence rate.(5)Expansion ratio is proportional related with submergence rate,and weakly related with stability.According to the effect of the operation parameters,collection containers and time on the foam properties,a refined experiment was employed to obtain the foams who had the same expansion ratio but different stability and the opposite properties.The foams were employed to investigate the mitiation effect.(6)Novel indexes were proposed to visualization and quantification of vaporization,vapor-emit rate and warming effect at different stages.Diverse analyses help to discuss the effect of three factors(the expansion ratio and stability,the quantity of the LNG as well as the foam height)on the warming,boil-off and frozen layer(mainly natural gas hydrate layer)effects when the foam interacted with the LNG.It is discovered that foam properties affected the warming,boil-off and frozen layer(mainly natural gas hydrate layer)effects greater than LNG spill amount and foam submergence height.As the foam interacted with the LNG,this effect weakened,the mitigation effect by the foam also reduced,and the reducetion rate decreased.But the effect of foam properties on the mean vaporization was small.The spill amount affected the warming effect at later stages smally.Submergence height affected the intiatial boil-off effect smally but affected the warming effect greatly.(7)The hydrate layer indeed existes when the foam interactes with the LNG according to the measurement of density and gas ration of the frozen layer.The mass variation rate of the foam and LNG system does not equal LNG vaporization but the vapor-emit rate instead.According to discussion of the experiental phenomena and data,the positive effect of hydrate on the waming and blocking effects and its negative effect on the vaporization owing to the heat absored by the LNG pool were proposed by quatitatively investigation.A model to explain the interation between the foam and LNG was modified.(8)Stratified addition method was proposed.This method can improve the vapor hazard mitigation effect by 48% compared with the sole addition.At the beginning of foam addition,the foam with high expansion ratio and stability was expected to reduce the boil-off effect.And then the foam with the opposite property was applied to facilitate the formation of frozen layer(mainly the NGH).The foam at the top layer was supposed to be more stable and possess low expansion ratio to improve the warming effect.This work developed a modified mechanism model and proposed a novle method to improve the mitigation effectiveness.It quantified the effect degree and regularities of operation parameters on foam properties and provided the idea to improve the foam generator.Furthermore,it also quantified the effect degree and regularities of the foam properties,the LNG spill amount and the foam height on the warming,boil-off and frozen layer effects.This provides data and theoretical to support to the formulation of the standard,the simulation of the vapor behavior under expansion foam and the determination of the parameters in the application of the foam to the LNG collection pool.