Study On The Agglomeration Of Fine Particles In Impinging Streams

At present,the traditional dust removal methods in coal-fired power plants mainly include electrostatic precipitator,bag filter and wet desulfurization and dust removal device,which can effectively remove coarse particles,but the removal efficiency of PM2.5 and other fine particles is not ideal.In order to remove such fine particles efficiently,pre-precipitation equipment is often used to agglomerate and grow microparticles through physical(such as electric field,turbulent flow field,etc.)and chemical(such as chemical agglomerator,etc.)methods.In this paper,the horizontal symmetrical gas-solid two-phase impinging stream is studied by numerical simulation.Firstly,the forces acting on particles in impinging stream are analyzed and the forces acting on particles are determined.A mathematical model for the trajectory of fly ash particles in a horizontal symmetrical impinging stream is established.The maximum flight distance and the required time of the particles in the reverse flow in the impinging stream are calculated.The total flight time and the flight distance of the particles in the impinging stream device are obtained.Then,the numerical simulation of gas-solid two-phase flow in horizontal symmetrical impinging stream is carried out by using computational fluid dynamics software FLUENT.The flow field distribution in the device is studied and the particle motion is obtained.The pressure and turbulence intensity in the impinging zone can be increased with the increase of the velocity of the impinging stream inlet,while the overall width of the impinging zone remains basically 0.2m.The pressure difference between inlet and outlet increases with the increase of gas velocity,and the gradient of pressure difference increases with the increase of gas velocity.The turbulence intensity is basically symmetrical distribution on the left and right sides of the impact surface in the axial direction.In the impact area,the turbulence intensity increases rapidly and reaches the maximum on the impact surface.With the increase of inlet gas velocity,the average flight time of particles in the impinging stream chamber decreases.Finally,Euler-Euler model is selected as the two-phase basic model in Fluent software,and Population Balance Model(PBM)is loaded to consider the agglomeration between particles(Brownian and turbulent agglomeration).Particle agglomeration kernel function is embedded by User Defined Function(UDF)to analyze the effects of inlet flue gas velocity,nozzle spacing,particle volume fraction of inlet flue gas and particle size range on particle agglomeration efficiency.For the impinging stream device studied in this paper,a suitable turbulent agglomeration operation parameter can be obtained,that is,the maximum agglomeration efficiency of the impinging stream device is obtained when the inlet velocity is 22m/s,the distance between the nozzles is 0.36 m and the particle volume fraction is 0.7% with wide particle size.