The Study On Fine Particles Pretreatment By Heterogeneous Condensation Combined With Turbulent Agglomeration

The frequent hazy weather in winter has become the primary problem of environmental pollution.The hazy weather has led to the decrease of atmospheric visibility and caused a series of respiratory diseases,which pose a serious threat to human health.The large amount of PM2.5 particles suspended in the air is considered as the main cause of hazy weather.The flue gas emitted from coal-fired power plant contains a large amount of PM2.5 paryicles,so the control for flue gas emission in coal-fired power plant is imperative.The traditional dust removal device is difficult to effectively remove fine particles.The most effective method for removing fine particles is to make the fine particles grow into larger particles by pretreatment technology so as to be removed by a traditional dust removal device.From the perspective of environmental protection and economic efficiency,heterogeneous condensation and turbulent agglomeration technology is the best pretreatment technology for application.First of all,combined with the mechanism of heterogeneous condensation and turbulent agglomeration,the interaction between particles and fluid in gas-solid two-phase flow is analyzed.The particles are subjected to the forces of gravity,buoyancy,inertia and Stokes resistance in the flow field.This paper mainly considers the influence of Stokes resistance on the agglomeration effect.According to the heterogeneous nucleation theory studied in previous studies,supersaturation is the most important parameter that influences the heterogeneous condensation process.According to the previous experimental results,the wall growth tube model was designed to simulate the growth of fine particles.The effects of initial supersaturation,residence time and growth tube wall temperature on the heterogeneous nucleation of water vapor were analyzed.The results show that adding the water vapor of the inlet,extending the residence time and reducing the wall temperature is favor to the fine particles growth.Adopted the k-ε turbulence model coupled with population balance model to simulate the turbulence agglomeration effect of particles behind the square column.The flow velocity and particle volume fraction were positively correlated with the particle agglomeration.The smaller the initial particle size,the better the agglomeration effect.Finally,based on the advantages of heterogeneous condensation and turbulent agglomeration,a new type of agglomeration chamber is designed according to the actual environmental conditions.The desired supersaturated environment was achieved by the high temperature flue gas contacting with the low temperature humid air.The combination of square columns and vanes forms vortex in the flow field.The results show that under the same other conditions,the pretreatment effect of fine particle in the new agglomeration chamber is optimal when the vanes array spacing is larger,the amount of humid air is more,the temperature difference is larger and the volume fraction of particles is large.