The Mechanism Study Of Water Curtain Diluting Ammonia Release Dispersion

With the rising of the storage of ammonia in chemical and food industries, there is an upward trend of ammonia release accident. Water curtain has been widly used for gas dispersion accident, but the transfer mechanism between water curtain and ammonia is not clear, and the mass transfer has not been reported. So, the study of transfer mechanism between water curtain and ammonia, dillution effect under various water curtain parameters and building ammonia concentration prediction model are the hot spot issuses in the field of safety engineering.The paper firstly studied the mass transfer mechism between water curtain and ammonia cloud, and a function of ammonia absorption was built based on two-film theory. Then, the function was programmed using UDF and embedded into CFD to build a numerical model of ammonia forced dispersion and the model was validated by Dandrieux experiment. The results show that, compared with the standard k-? equation, RNG k-? equation can accurately simulate ammonia dispersion; the numerical model can accurately simulate the ammonia forced dispersion.The natural ammonia dispersion under various wind speed and the forced dispersion were studied. The results show that 2 sm is the dangerous wind speed. The momentum transfer effect is that a whirlpool reflux exicts on water curtain rear area, entrainment effect inhibited the movement of clouds to downwind to achieve the effectiveness of forced ammonia dispersion. The heat transfer effect is that the cloud temperature was improved by heater water droplets, the density of cloud is reduced and the trend of movement on up and either side of the clouds is increased. The mass transfer effect is that the ammonia concentrations are reduced through ammonia absorption on the first half of droplet trajectory. Ammonia absorption can provide about 25% contributions for dilution effectiveness.In addition, the key water curtain parameters, including droplet temperature, water flow and installation distance were studied. The results show that higher droplets temperature provides more heat to cloud and the density of cloud is descreased to strengthen promotion effect of the water curtain, and the spread of cloud downwind is inhibited. When the the momentum ratio is greater than 4, the dilution effectiveness achievied to a stable value. Water flow also affects the concentrations and total amount of ammonia absorption into droplets, with the increase of the water flow rate, concentrations and total amount of ammonia absorption into droplets quickly increase to the peak, and then descrease with the increase of water flows. When the install distance is increasing, the dilution effectiveness is generally descreasing, but the installation distance is not too small, otherwise the initial momentum of ammonia may cause the cloud goes through the water curtain clearance.A forced ammonia dispersion concentraion distribution model was built based on RED model and the calculated results were validated. The results show that the model can accurate calculate ammonia antural and forced concentrations, and provided a method for calculating ammonia release accident consequences and water dilution effectiveness. The disaster reduction under various water curtain parameters was calculated by the gas release probability function method. The results show that the increase of water flow rate is beneficial to reduce the ammonia concentrations, but when the water flow is too bigger, the increasing of dilution effectiveness is not obvious. The water curtain should be setted in the passive dispersion region.This research results developed the theory of ammonia forced dispersion, enriched effect law of key water curtain parameters and provided a reference for domestic and abroad security field. The ammonia forced dispersion concentration model can provide theoretical basis for design of water curtain system.