Numerical Simulation Of Nucleation And Growth Of Fine Particles Promoted By Heterogeneous Condensation Of Water Vapor

The fine particles in the flue gas of coal burning are small in size and large in quantity,which is difficult to be removed by the traditional dust removal equipment.Therefore,it is one of the important pretreatment measures to promote the efficient removal of the fine particles by using the heterogeneous condensation technology to grow larger particles.In this paper,the characteristics of heterogeneous nucleation and condensation growth of fine particles in supersaturated water vapor were studied by numerical simulation,which provides a theoretical reference for the emission control technology of fine particles in coal-fired power stations.Firstly,based on Fletcher’s classical nucleation theory and considering the linear tension and the diffusion of water vapor molecules on the surface of the droplets,the characteristics of heterogeneous nucleation of supersaturated water vapor on the smooth surface particles were numerically simulated.The results show that,compared with Fletcher’s classical nucleation theory,the prediction results of heterogeneous nucleation model considering water vapor molecular surface diffusion mechanism and linear tension are closer to the experimental results.The decrease of contact Angle,the increase of water vapor temperature or water vapor supersaturation can promote the occurrence of heterogeneous nucleation on the surface of fine particles.Secondly,a theoretical model for nucleation of supersaturated water vapor on rough surface particles was established,and the influence of roughness on nucleation characteristics was analyzed.The results show that the prediction results of the nucleation model considering the roughness are closer to the experimental results in the literature than the smooth surface particles.Heterogeneous nucleation condensation occurs more easily on rough surface than on fine particles on smooth surface.When the line tension is negative,the rougher the surface of fine particles,the smaller the nucleation free energy and critical supersaturation,and the higher the nucleation rate.Compared with the linear roughness factor,the surface roughness factor has a greater effect on the heterogeneous nucleation of water vapor on the surface of fine particles.Thirdly,based on the Heidenreich condensation growth kinetics model,the effects of particle size,water vapor supersaturation and water vapor temperature on the condensation growth of insoluble polydisperse particles were studied,considering the heat and mass transfer between particles and particles and the effects of particles on the competitive condensation of water vapor.The results show that the fine particles can complete the heterogeneous condensation growth within 50 ms.If the initial particle size is 0.3 μm,the final particle size is 3.39 μm after condensation.The peak value of particle size distribution increases and the range of particle size distribution narrows when the polydisperse particles are condensed.As the particle size,water vapor supersaturation and water vapor temperature increase,the particle size also increases when the particle grows up.Compared with the adiabatic system,the particle size in the isothermal system is larger after condensation.Finally,a theoretical model of the condensation growth of supersaturated water vapor on soluble particles was established,and the effects of the soluble components and operating conditions on the condensation growth of particles were studied.The results show that the soluble component on the surface of the particles is beneficial to increase the condensation growth rate,and the particle size of the soluble particles is larger than that of the insoluble particles after condensation.With the increase of water vapor supersaturation and water vapor temperature,the final particle size and the peak value of particle size distribution of soluble particles grow up.With the increase of water vapor supersaturation,the particle size difference between soluble and insoluble particles decreases gradually after condensation.