Study On Numerical Stimulation Of Liquid Ammonia Leakage And Evacuation

With the development and implementation of the "12th Five-Year Plan",the chemical industry has become one of the hot industries of national economic development,and has an important status and role.In the vast majority of chemical companies,the liquid ammonia storage tank are set up,the ammonia inside the tank is sealed under high pressure in the form of liquid storage.After a long period of operation,together the storage medium of electrochemical corrosion,internal high pressure and the external operation of the destruction,the pressure storage tank easily prone to leaks,then leading to a large amounts of toxic gases in the tank released into the air,leakage of the gas tends to cause the acute poisoning or death of arounding people,and may even cause the disaster of fire and explosion.Aiming at this situation,a lot of experiments and numerical simulations have been carried out by the international and domestic academics.The main research directions are the size of the leak port,the shape of the leakage port,the pressure of the tank,the stability of the atmosphere,the obstacle and so on.But the study of phase transition in ammonia diffusion process has been the difficulty of the research domain.In addition,the emergency evacuation after the liquid ammonia tank leakage accident is one of the hot spots in the field.In this article a numerical simulation method was used to study the effect of different influence factors on the ammonia diffusion for liquid ammonia tank leakage accident.The main work and conclusions are as follows:By using FLUENT software to set up liquid ammonia tank 3D full size model and simulate the influence of the wind speed,wind direction and obstacle of ammonia diffusion.The ammonia in the vicinity of the leakage port is affected by the pressure in the tank,which makes it horizontal diffusion,and the distance of ammonia diffusing in the downwind is gradually increasing flowing time;when the ammonia is away from the leakage port,it is mainly affected by buoyancy and because the density of ammonia is less than the air,then there is the phenomenon of ammonia rise appears.At different wind speeds,first the diffusion distance of ammonia gas on the Y-axis increases and then decreases with the increasing of wind speed.Therefore,wind speed can aggravate the diffusion rate of ammonia gas toward downwind direction and increase the gas diffusion area,as well as exacerbate the dilution rate of the gas in the atmosphere preventing the concentration of ammonia in the diffusion process of accumulation.At different wind direction,when the wind direction is perpendicular to the tank leakage port,ammonia is most along with the leak down the wind direction to spread;the wind direction is parallel to the tank leakage port,and ammonia under the effect of its own dynamic action is perpendicular to the leakage port to diffuse;influenced by buoyancy and wind,ammonia changes the direction of diffusion,which is parallel to the tank leakage port to spread after it is away from the leakage port.That is along with the wind direction for diffusion.When there is an obstacle,the velocity in the downwind direction and area of the diffusion are obviously reduced.Ammonia in front of the obstruction is hindered.Part of the ammonia is along with the edge of the obstacle to spread to sides,and the rest in front of the obstruction reflows;The gas above the obstacle climbs over the obstruction and continues to spread to downwind with rising phenomenon.Based on FLUENT software development of the liquid ammonia evaporation phase trans formation model,this paper simulated the liquid ammonia evaporation phase transition proces s through the software user define functions(UDF)into the simulation and find out the law of ratio which made out from the spread of the liquid ammonia evaporation simulation results of the simulation results of diffusion and ammonia gas.Analysis under the condition of different volume ratio between liquid ammonia and ammonia,liquid ammonia evaporation phase have effect on ammonia diffusion.When ammonia gas diffusion along with liquid ammonia,the diffusion velocity and impact area of ammonia decrease obviously.This is because the droplets in the steam cloud make the quality of the steam cloud bigger,then suppress the diffusion speed and the influence area of the gas cloud.The GIS software was used to simulate and calculate the optimal path of emergency evacuation of surrounding people transfered to nearby resettlement site under the different wind effects when liquefied ammonia storage tank leaked.