Numerical Simulation Of Rotating Spray Evaporation Of Desulfurization Wastewater And Application Verification

In recent years,with the country’s emphasis on the zero-discharge process of desulfurization wastewater,more and more attention from coal-fired power plants has been attached on the rotating spray evaporation technology of desulfurization wastewater due to its low investment cost,good operation stability and strong applicability to wastewater.Meanwhile,with the wide application of computer technology and the enhancement of computing performance of CPU,numerical simulation has gradually become an important means to study desulfurization wastewater spray evaporation due to its low cost,intuitive and visual results.The existing evaporation models of desulfurization wastewater mostly replace the desulfurization wastewater droplets with pure water droplets,which makes the simulation results quite different from the actual ones.Evaporation model combined with practical evaporation process of desulfurization wastewater was applied to study the influence of key equipment structure and process parameters on evaporation characteristics,which was hoped to provide theoretical basis for the further optimization of rotating spray evaporation technology.A drying kinetic model of desulfurization wastewater was established based on the Reaction Engineering Approach(REA)and the single droplet drying(SDD)experiment.The results showed that the SDD experiments could quantitatively describe the changes of droplet morphology,temperature,particle size and quality during the evaporation process of desulfurization wastewater.The droplet evaporation process of desulfurization wastewater could be divided into four stages:evaporation preparation stage,constant speed evaporation stage,falling speed evaporation stage and evaporation end stage,which were obviously different from pure water.A REA-based standard activation energy characteristic curve of desulfurization wastewater fitted by mathematical statistics method and SDD experimental data could accurately reflect the evaporation process of the desulfurization wastewater droplet and the predicted value of the model was in good agreement with the experimental value.Combined with the computational fluid dynamics(CFD)method,the drying kinetic model of desulfurization wastewater was loaded into the numerical simulation,and the influences of key equipment structures such as the drying tower and the flue gas distributor on the evaporation characteristics of desulfurization wastewater were studied.The results showed that the distribution of gas-liquid flow field in the tower got more homogeneous with the increase of height-diameter ratio and diameter of drying tower;The cone angle of the inner cone,the deflection angle of the deflector and the length of the inner and outer flow channels had a great influence on the distribution of the gas-liquid phase flow field in the drying tower.In this simulation,when the height-diameter ratio was greater than 2:1,the diameter of the tower was greater than twice the atomization radius of the atomizing disc,and the cone angle of the inner cone was greater than 15°and less than 30°,the angle of the upper deflector was 15°,the angle of the lower deflector was 0°,and the length ratio of the inner and outer flow channels was 3:2,the gas flow field distribution in the tower and the droplet evaporation effect were better;In the shape deflector structure,the flue gas showed higher rotational fluidity,the distance for droplets to evaporate completely got shorter,the temperature and vapor were homogeneously distributed in the tower,and the evaporation effect was better.Numerical simulation was applied to study the influence of process parameters on the evaporation characteristics of the rotating spray evaporation of desulfurization wastewater.The results showed that the inlet flue gas temperature mainly affected the evaporation of droplets by the heat transfer process.With the increasing of the inlet flue gas temperature,the average temperature along the process got higher,which promoted the evaporation effect of the droplet group.When the inlet flue gas temperature increased from 300°C to 360°C,the average temperature at the bottom of the drying tower ranged from 161.3°C to 206.5°C;The evaporation gas-liquid ratio further affected the evaporation of the droplets by the mass transfer process.With the increasing of the evaporation gas-liquid ratio,the vapor concentration decreased in the tower and the evaporation effect of the droplets was promoted.When the evaporation gas-liquid ratio was greater than 12000 Nm~3/m~3,the droplet group could be evaporated completely in the drying tower;With the decreasing of the initial particle size of the droplet,the distance for the droplets to evaporate completely and the maximum evaporation time of the droplets decreased,which exhibited a better evaporation effect.When the droplet size of the desulfurization wastewater decreased from 150μm to 30μm,the distance for the droplets to evaporate completely was shortened from 9.10 m to 6.67 m.The numerical simulation of the rotating spray evaporation of desulfurization wastewater was applied to the coal-fired power plants.The results showed that the double-channel flue gas distributor with arc deflectors performed well under the design conditions,the desulfurization wastewater droplets could be evaporated completely in the drying tower,and the temperature and the vapor were homogeneously distributed in the drying tower.The temperature along the drying tower showed the tendency of being stable after decreasing.The vapor concentration along the drying tower showed the tendency of being stable after increasing.The temperature along the radius of the drying tower increased as the distance from the drying tower wall got closer;The simulated values of temperature,humidity and system resistance in the tower were basically consistent with the test values,which verified the effectiveness and accuracy of the evaporation model in practical industrial applications.The flue gas distributor with upper deflectors angle of 15°and lower deflectors angle of 0°had a reasonable distribution of the droplets that could be evaporated completely under the design conditions.