| It is important for steel industry to optimize production processes,improve energy conservation and environmental protection facilities,implementation of cleaner production due to the gradual enhancement limits of particulate emission and the increasing public awareness of environmental protection.The new oxygen converter gas recovery(OG)of primary dedusting system has the advantages of low smoke emission,high energy utilization,and low investment has a broad market prospect.The high efficiency spray tower is one of the core devices of the new OG system of primary dedusting system and its cooling and dust removal performance directly affects the operational performance of the system.Therefore,it is of important theoretical and practical significance to study the atomization characteristics and arrangement of the nozzles of high efficiency spray tower,for improving the cooling effect and energy saving of spray tower.In this work,an experimental system for the atomization characteristics of the nozzles was firstly set up.The image of the droplets in the atomization field was captured by the flash photography method,the photographed image was digitalized by the MATLAB image processing toolbox,and the parameters such as the particle size of the atomized droplets and the number of droplets were statistically calculated.The droplet size distribution and the Sauter Mean Diameter(SMD)of different working conditions were discussed,and the distribution and variation of droplets were studied.Secondly,the geometric model of pressure atomization nozzle atomization field was established.The discrete phase model in ANSYS FLUENT had been used to calculate the gas-liquid two-phase coupled flow,and the experimental results verified the credibility of the numerical calculation model.The influences of spray angle,injection pressure,the atomizer mass flow rate on the average diameter and evaporation efficiency of the atomization field were analyzed.The influence of the distance between the two nozzles on the droplet residence time and airflow distribution was studied.In this way,the optimum atomization parameters for the high efficiency spray tower in a new OG system were obtained.Finally,the geometric model of the high efficiency spray tower was established,and the different injection directions and spray layers of nozzles in the inlet section and the main section of the spray tower are numerically simulated respectively.The variations of velocity,temperature,turbulent kinetic energy and pressure loss between the gas-liquid two phases in the tower at different spray directions and spray levels were discussed.The results show that:(1)The atomization characteristics for the pressure swirl nozzle showed that farther distance from outlet of the nozzle,the droplets diameter gradually decreases,and the number of droplets increases,and the contact area between the gas and liquid phases increases during the experiment.The SMD value of the atomization field increases with the increase of the nozzle flow rate,but under the condition of the same nozzle flow,the smaller the aperture of the nozzle,the smaller the SMD value,the better the atomization effect.(2)In a certain range,with the increase of the spray angle of the pressure swirl nozzle in the atomization field,the coverage of the droplet in the atomization field is wider,the droplet residence time becomes longer,and the evaporation efficiency of the droplet increases,when the injection angle is greater than 60o,the SMD value decreases slowly.With the spray pressure increases,the evaporation efficiency of the droplets increases,and the atomization field SMD decreases,when the pressure is greater than 1 MPa,the influence of the spray pressure on SMD is small.With the increase of jet mass flow rate,the evaporation efficiency of the droplets decreases,and the SMD of the atomization field increases,when the flow rate is less than 0.15kg/s,the SMD value has not much increase.The larger horizontal distance between two nozzles,the wider the droplet distribution.When the nozzle distance is about 800 mm,the cross-sectional velocity distribution is more uniform.(3)When the injection direction of the nozzle is the downstream injection,the droplets residence time in the inlet section is the shortest,and using the counter flow injection is the longest time.The velocity distribution of the outlet section is relatively uniform and the cooling effect is better when the inlet section of the spray tower is the reverse flow.The velocity distribution of the exit section is uniform and the cooling is poor when the combined injection and the concurrent injection are used.Therefore,when it used for counter flow injection,the air distribution of the flue gas is the best and the heat exchange effect is better.(4)The number of spray layers in the main section has little effect on the residence time of the droplets.When the number of spray layers is three and four,the velocity of the flue gas near the wall in the tower is greater than the middle of the tower;when the number of spray layers is five,the velocity and flow of flue gas in the tower are relatively uniform,and the airflow velocity in the central position region is 2 m/s~4 m/s,when the airflow speed is small,it helps to increase the time between the gas and the droplet.With the increase of the number of spray layers,the average turbulent energy in the tower is gradually increased,and the spray layer has a greater effect on the air flow disturbance.Using different spraying layers has great influence on cooling effect inside the tower.When the number of spray layers is five,the temperature gradient changes rapidly.The distribution of water vapor mass fraction and temperature distribution correspond to each other.It is shown that the more the spray layer,the larger the liquid holding in the tower,and the larger air-liquid contact area in the tower,with the increase of the number of spray layers,the internal resistance of the tower increases,and the resistance in the towers under three working conditions does not exceed 500 Pa.According to the comprehensive analysis,the tower body section can be set to 5 spray layers during normal operation. |
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