Numerical Simulation Of Controlling Leakage And Diffusion Of Gas Tank Using Artificial Tornado

Gaseous hazardous chemicals are often stored in tanks using pressure or cooling means.However,medium corrosion,overpressure of storage tanks and operation errors are likely to cause leakage accidents.Due to the dangerous characteristics of tank media,leakage and diffusion may cause fire and explosion,personnel poisoning,environmental pollution and other domino effect accidents,which further expands the consequences of the accident.Therefore,this paper proposes that tornado wind field should be generated around the leaking gas storage tank by the way of jet tangent to control the leakage and diffusion process of the storage tank,so as to reduce the size of the area affected by harmful gas diffusion.Thus,secondary accidents caused by leakage can be avoided.Meanwhile,time for emergency evacuation and rescue can be saved,which is critical to reduce casualties.A mathematical model to calculate the artificial tornado is presented.The computational procedure was implemented by FLUENT program.The special feature of the model in this paper is the ability to calculate the artificial tornado wind field without the exhaust fans upper of gas tank.Radial distribution of the tangential velocity and pressure is presented,which is in line with the ideal Rankine vortex model.It can be verified that the result of numerical simulation was reasonable and it was proved that the artificial tornado wind field can be formed.By further study the influence of the artificial tornado wind field,a numerical analysis of the swirl ratio and intake’s influence on the characteristics of tornado wind field is carried out.The maximum tangential velocity at different heights was given and then different intensities artificial tornado wind field were obtained.Calculation results of different model were given.In the first model,the intake stayed constant while the swirl ratio was changed.As the swirl ratio increased,the maximum tangential velocity at the same height were decreased.That is to say,the greater of swirl ratio,the weaker ability to converge the air is.In the second model,the intake was changed while the swirl ratio stay constant.As the intake increased,the maximum tangential velocity at the same height were increased.Meanwhile,the height of the artificial tornado wind field was increased as well.It can be seen that,the greater intake the stronger ability to gathering the air.Ammonia is of great industrial importance.It is mainly used for fertilizers production and it is the basic product for the industrial synthesis of many chemicals.So this paper takes Ammonia as an example.Firstly,the model shows the time-dependent variation of the area influenced by the maximum permissible concentration of 30mg/m~3 and immediately dangerous to life or health concentration of 360mg/m~3.Numerical results show that,without wind field,the main leakage direction of ammonia diffusion gradually spread outward,which concentrated near the ground,while ammonia will flow up together with swirling jet produced by air inlet with wind field.The more time of gas diffusion,the greater the distance of dangerous area will be.When the diffusion time is 60s and the ammonia mass concentration is30 mg/m~3,the conditional diffusion distance without wind field is 82m,while 27.6m with wind field.Secondly,the concentration of ammonia at the height of exposure varies with the diffusion distance when the diffusion time is 60s.The concentration of ammonia with wind field is lower than that without wind field.While the concentration of ammonia with wind field is much lower than the maximum permissible concentration,the concentration of ammonia in the same diffusion distance without wind field is much higher than taht of immediately damgerous to life or health concentraction.It is proved that,wind field can effectively control the direction of airflow.Resorting to the suction effect of tornado field caused by tangent jet flow,we can reduce the harm of ammonia gas in the height of staff contact range by controlling the flow direction of tank leakage gas.Thirdly,a numerical analysis of the inlet angle,inlet radius,inlet velocity and leakage rate on the control effect of artificial tornado and the distance of leakage is carried out.With the increase of inlet angle,inflow radius and leakage rate,the range of ammonia diffusion increases gradually.With the increase of air inlet velocity,the convergence ability of the upper air flow of the tank is enhanced,thus the ammonia diffusion rate is increased,and then increased diffusion distance.In short,this paper discusses the control effect of artificial tornado wind field on gas diffusion under different conditions,which is of great significance.